It has been well established that a vegetarian and polyphenol-rich diet, including fruits, vegetables, teas, juices, wine, indigestible fiber and whole grains, provide health-promoting phytochemicals and phytonutrients that are beneficial for the heart and brain. What is not well-characterized is the affect these foods have when co-metabolized within our dynamic gut and its colonizing flora. The concept of a heart shunt within the microbiota-gut-brain axis underscores the close association between brain and heart health and the so-called “French paradox” offers clues for understanding neurodegenerative and cerebrovascular diseases. Moreover, oxidation-redox reactions and redox properties of so-called brain and heart-protective foods are underappreciated as to their enhanced or deleterious mechanisms of action. Focusing on prodromal stages, and common mechanisms underlying heart, cerebrovascular and neurodegenerative diseases, we may unmask and understanding the means to better treat these related diseases.  Part I, of a two-part series of concept papers, focuses on novel findings involving nutrition, biochemistry, microbiology and metabolism to suggest a heart shunt, as occurs when two organ systems are coupled and in this case within the microbiota-gut-brain axis. Here, we explore the bacterial species that contribute to disease and to health and suggest oxidative and inflammatory mechanism drive heart and brain disease and that wine polyphenols help protect us from bacterial-derived deleterious metabolites. Exploring aspects of co-metabolism within the microbiota-gut-brain axis and metabolites from prosaic foods could lead to a unifying hypothesis for age-related diseases and advance our understanding of vascular dementia, neurodegeneration and heart disease. When one considers ways to affect and modulate one’s own health, one must start with diet and lifestyle. After this, we then turn to the host resident microbial ecology. Findings from host digestion with gut microbiota and mycobiota co-metabolism suggest we can explore mechanisms of disease and new treatment approaches to modulate health. To simplify our understanding of the two most common and extremely complex diseases in the world today, namely coronary heart disease (CHD) and Alzheimer disease (AD), we describe a shunt between the heart and the brain, where commensal microorganisms though the microbiota-gut-brain (MGB) axis do affect both the heart and the brain, which are coupled through the vasculature. de novo synthesis by their hosts and the symbiont’s production of some metabolites demonstrate antagonistic pleiotropy [The gut microbiota has largely coevolved, in beneficial ways with their hosts, where they co-metabolize dietary foods in symbiosis. The relationship provides both a niche for the microbes, and extracts vitamins, vital nutrients and energy from diverse dietary sources for their hosts and themselves. In fact, it could well be that some microbe-provided nutrients have negated the need for eiotropy , which aWe know the microbiota are involved in the early development of the blood-brain barrier . In factIn search of beneficial dietary sources for health-promoting compounds led to fruits, vegetables, wine and grape juice, as their consumption was inversely correlated with coronary heart disease (CHD). Moreover, within populations who consumed a lot of red wine, it was observed that a paradox of sorts existed within one population in particular because they consumed foods known to be deleterious for heart health, yet had little heart disease. Thus, the cardio-protective effects of wine began to be enthusiastically studied and has come to be known as the “French paradox . This peAs the popularity of the French paradox increased, so did the need for evidence-based research. It is believed the French paradox is explained by the red wine constituents, which protect the French from heart attacks and have other health benefit. These foods are rich dietary sources of a class of compounds called flavonoids, which are small molecular weight polyphenols. To date, no less than 8000 phenolic structures having been identified in plants . PolypheThe topic of wine is frequently mentioned in nightly news reports. Often broadcasters cite the latest study to recommend the consumption of a glass of wine per day, or beer for that matter, will benefit human brain and heart health. Nevertheless, studies often have many limitations, but even fewer mention metabolism involving bacterial action or suggest redox properties of the constituents or metabolites of those prosaic foods. Redox potential, as in redox-paired compound activity, is an important environmental feature. The ability for redox pairs to find each other and have any activity is readily affected by host and bacterial metabolism and the microenvironment where the interaction occurs. When considering redox pairs for wine constituents, their potential when paired with deleterious reactive species is an important but under-appreciated feature of the gut environment. Both host and microbial enzymatic and non-enzymatic action, coupled with varying degrees and states of oxygen tension, are but a part of the dynamic involved in understanding protective mechanisms for polyphenols. Importantly, dietary polyphenols that are not taken up by bacteria for metabolism, pass through the small to the large intestine the gut lumen and are taken up by enterocytes or other intestinal cells enter the gut lumen and are subject to host and liver metabolism and modification, such as phase 1 and 2 conjugation.These phenolic compounds certainly become oxidized themselves to quinones and protect from oxidation-mediated damage but, quinones are potentially oxidizing as well. It would be a paucity of antioxidants or other mechanisms that would either contribute to or protect against disease pathogenesis. Few have considered whether microbial-host metabolism, or redox properties of bacterial-derived molecules, would interact with prosaic foods to either antagonize or synergize in disease pathogenesis. We suggest some of the action occurs either by directly possessing enzymatic or regulatory substrate interaction or by forming complexes, such as chelating redox metal-bound moieties, acting as glycation intermediates or via other oxidation-quenching mechanisms. Since polyphenols are powerful antioxidants and scavengers of ROS and RNS they protect extracellular lipids, proteins and nucleic acids from redox damage but questions remain as to whether some antioxidants or phytochemicals potentially could do more harm than good, as increases in glycation-mediated protein damage have been reported . Far lesin vivo. Oxidation reduction or redox potential (Eh) is measured in millivolts and represents the affinity of electron transfer to or from a chemical species in solution. The ability to either gain or lose electrons in that particular environment is concentration and temperature dependent. Chemical species with higher, more positive, reduction potentials than a particular species introduced into the system trend to gain electrons from the new species, become themselves reduced by the oxidizing species and solutions with lower, more negative, reduction potential tend to lose electrons to the new species and become themselves oxidized by reducing the new species [Since we cannot escape oxidative metabolism and oxidation is a common biochemical enzymatic mechanism, we must consider oxidation-reductions  species . 2 serve as inorganic oxidants, while reduced inorganic compounds, metals and organic substrates like hydrogen sulfide (H2S) serves as reductants [Within the gut, intestinal segments, the crypts lining it and other environmental niches within the gut continuum have changing redox states and differences in oxygen tension and the resident bacteria play a large role in maintain redox potential within these environmental segments. Moreover, it has been shown that imbalances between pro-oxidative and anti-oxidative mechanisms play a key role in the pathogenesis of irritable bowel disease and related intestinal damage ,13. For ductants  Probiotiductants .2) as dihydrogen and H2S, which have having antioxidant activity, such as reducing hydroxyl radicals and peroxynitrite from microbiota potentially generate up to 1 L per day during some fermentation processes [2S are produced by host metabolism, but it is mostly by hydrogen-producing bacteria, which include anaerobic cocci, certain strains of Clostridium and some Enterobacteriaceae, among others. H2S can inhibit Complex IV within the mitochondrial electron transport chain [2S is usually accompanied by symbiotic co-metabolizing species that consume H2S as in the case of sulfur and sulfate-reducing bacteria, methanogens, and acetogens bacteria [2 has intra- and inter-individual variability in relation to microbial composition and dietary choice. Since H2 is by far gut bacteria-derived and not of human origin [2 production for the CNS, vulnerable neurons and increases oxidative stress susceptibility in all ROS-related disorders. This is supported by Parkinson disease findings [Other central nervous system (CNS) antioxidants include diffusible bioactive gasses like molecular hydrogen  is considered to be a driver of gut dysbiosis [Molecular oxygen  and AD , which wVitis vinifera has inhibitory effects on HMG-Co A reductase through metabolites of the mevalonate pathway [The French paradox and polyphenol involvement could be further explained specifically by vitisin A and vitisin B, which have strong inhibitory activity against HMG-Co A reductase . Moreove pathway , which a pathway . When Ro pathway . Thus, pAlcohol maybe protective for CHD by increasing serum high density lipoprotein, decreasing cholesterol levels and by inhibiting platelet reactivity . Aside fFaecalibacterium prausnitzii on Clostridium difficile infection and damage [Ruminococcaceae or Firmicutes decreased in 24 h by half. In contrast, Bacteroidaceae, Lachnospiraceae and Veillonella members of the Firmicutes phyla and Coriobacteriaceae of the Actinobacteria phyla increased over 24 h. The Lachnospiraceae levels were sustained for up to 48 h and Coriobacteriaceae and Bifidobacteraceae Actinobacteria increased [Proteobacteria, Actinobacteria, Firmicutes and Bacteroidetes all compete for dietary carbohydrate in a closed system. Proteobacteria have a preference for host carbohydrates and mucin-derived and secondary metabolites.Many fruits and juices contain phenolic acids, polyphenols and indigestible carbohydrates, such as pectin, hemicellulose and various polysaccharides. It is this aspect of the diet that both supports select gut microbiota species and colonization through co-metabolism, whereby the gut microbiota can impart many beneficial effects on health through sustained co-metabolism of health-promoting foods. The microbial fermentation by-products are short chain fatty acids (SCFAs), particularly acetate, propionate, and butyrate . These pd damage . Others d damage . This grncreased . FurtherBacteroidetes fermentation and from Veillonella, members of the phyla Firmicutes. Butyrate, produced mainly by the Firmicutes subset, among others, features members of the Lachnospiraceae family [Lactobacillus rhamnosus to Caco-2 cells in vitro, but inhibited the adhesion of Salmonella enterica [When fermented kiwifruit was added, SCFAs increase, while lactate and after 24 h succinate concentrations declined and most of the genera observed produced acetic acid . Propione family . Additioe family . In the enterica  The diffOxidants are chemical species able to remove electrons from electronegative atoms or other molecule’s electrons and then accept those electrons the scavenged species then become oxidized . But theA reaction that is well-quenched by many polyphenols is the Fenton reaction, which involves hydroxyl radicals. This and other oxidative mechanisms affect redox signaling, activate survival pathways mediated by “redox sensors” and modulate the expression of certain anti-oxidant enzymes, which are kept under control by soluble and insoluble redox sinks, i.e., compounds able to quench oxidative stress or free radical species. The endothelium-derived Nitric oxide (NO), is a relaxing factor and free radical and a neurotransmitter of the non-adrenergic non-cholinergic enteric nervous system is the of the autonomous nervous system . The sysAn important, but less concentrated constituent of red wine, is the phytoalexin resveratrol, which is a naturally occurring phenolic acid and effective lipid-soluble antioxidant. In the recent past, interest in resveratrol grew due not to its antioxidant properties but due to is activity as a histone deacetylase, which was expected to be a new AD therapy . AlthougHowever, we suggest alternative mechanisms may be favored and understanding examples from plants and fruits may provide insight. Since flavonoids are ubiquitously synthesized in all photosynthetic plants as an acute response phase compound under various stressors and during environmental attack. Similarly, these same compounds, when ingested, are likely to protect against the same environmental assaults and stressors common in human disease pathogenesis. One mechanism helpful to plants and humans likely involves the ability for flavonoids to sequester and chelate redox-active metals in response to heavy metal stressors . MoreoveOther putative factors in red wine that may be important to prevention cardiovascular disease and risk are folic acid and nitric oxide, which some suggest are involved in the French paradox . In boviImportant in the red wine debate is its ethanol content as alcohol participates in free radical reactions within biological systems though production of alkoxy-free and hydroxyl-free-radicals as the initial reaction products . HoweverHuman plasma contains many sulphur-containing proteins with intrinsic antioxidant properties, including glutathione peroxidase, thiols, some in their active site, as well as transition metal binding proteins, albumin and many oxidases and reductases that protect endogenous lipids proteins and nucleic acids from damage . InhibitLipid peroxidation and oxidative stress with platelet aggregation and LDL oxidation, has been inhibited by lipid soluble antioxidants, such as resveratrol and wine . FurtherThe French have perhaps the highest intake of total alcohol and wine for any developed country . PolypheSeveral classes of polyphenols are abundant in many foods, including tea, coffee, fruit, vegetables and chocolate ,73. ThosMore importantly, it was the Le Roy study that revealed grapes compared to other foods have a much richer concentration of polyphenols in their skin, specifically in red grapes versus white grapes and red wine had a higher polyphenol content compared to non-alcoholic grape juice . ResultsWhen considering the predominant red wine polyphenols studied, including the flavan-3-ol monomers and proanthocyanidins, we often find associated antimicrobial activity, which may be another reason why wine may be protective against heart disease as they affect the microbiota by exerting inhibitory effects through binding to certain bacterial membranes ,78. As sLachnospiraceae, Bacteroides, Alistipes, and Faecalibaculum and suggest novel insights into the mechanism of tea polyphenols on intestinal redox homeostasis [Polyphenols, such as those in tea, the theaflavins, are considered to have antimicrobial activity and underlie intestinal mechanisms that significantly ameliorated hyperlipidemia, improved the expression levels of hepatic lipid metabolism genes and modulate the gut microbiota in mice . The exaeostasis . Coccoides-Eubacterium rectale, Bifidobacterium, Eggerthella lenta, Bacteroides uniformis, Enterococcus, Bacteroides, and Prevotella groups and importantly a decrease in the Clostridium genera. These include Clostridium histolyticum, which produces collagenase that degrades animal tissue; Clostridium difficile, which causes severe diarrhea and death; Clostridium perfreingens, which causes gas gangrene; and other species responsible for disease in humans [Clostridium perfringens is closely related with progression of colonic cancer and the onset of inflammatory bowel disease [Eggerthella lenta and Bacteroides uniformis is associated with antiproliferative effects on human prostate cancer cells and proliferation was decreased after red wine consumption [Blautia, Coccides-Eubacterium rectale species was found important for the prevention of colon cancer [Studies show that regular moderate red wine consumption significantly modulates the growth of select gut microbiota in humans by inhibiting non beneficial bacteria from the human microbiota and potentiating the growth of probiotic bacteria. In a randomized, crossover and controlled intervention study, researchers evaluated the effect of moderate intake of red wine polyphenols on groups of human gut microbes . Resultsn humans . Clostri disease , which isumption . Blautian cancer  or ulcern cancer  due to tn cancer , which in cancer  and imprn cancer . Resultsn cancer .Diffusible polyphenols are oxidized by PPOs to quinonic compounds. Quinones and amino acids are usually compartmentally separated in vivo as they associate reversibly and irreversibly with proteins and amino acids . One junWine contains many anti-inflammatory molecules, such as betaine, phenolic acids, alcohol and all of which are able to lower inflammation. Folate contributes to the French paradox, since folate affects homocysteine levels and a cardio-protective role is suggested . BetaineS-methyltransferase (BHMT) re-methylates homocysteine to methionine producing dimethylglycine [Betaine See  is anothlglycine . This relglycine .Helobacter pylori bacteria, atrophic gastritis or acid-reducing drugs, such as proton (H2)-receptor agonists and proton-pump inhibitors or PPIs. Moreover, H. pylori is implicated in heart disease [When used as an FDA approved drug betaine is used to treat homocystinuria and liver disease but so is a combination of three vitamins folate, methylcobalamin and pyridoxine as well and offers an alternative to betaine BHMT pathway. Though it is not known whether betaine promotes cardiovascular disease through the action of select microbiota, any dichotomy that may exist between protective vs. deleterious effects is difficult to explain with current evidence. The truth may indeed be borne out from studying the microbiota of the French and co-culturing select prosaic foods with wine constituents under various incubation approaches. Human stool or fecal pools co-cultured with various compounds in a drug discovery approach should aid our understanding of microbial metabolism especially from wine constituents . Uses fo disease . If the explanation for the French paradox is that the French just eat more slowly than the rest of the world, then betaine proponents would argue that food breaks down in the stomach more slowly when stomach acid is inadequate. This means the inter-stomach transit time is longer due to slower stomach emptying, which could contribute to gastric reflux. Low stomach acidity has been linked to impaired absorption of vitamins B12 and C and minerals like iron, calcium and magnesium , all of While there is no know clinical study involving co-administration of Betaine HCl with pH-dependent drugs, PPIs or certain antibiotics , individCholine  is incluCholine helps maintain normal brain development and is derived largely from dietary phosphatidylcholine consumption. Foods high in choline include fish, eggs and peanuts. Choline, which occur in water soluble and lipid soluble forms, and the water-soluble B vitamins help maintain proper system function and energy metabolism. Choline, as well as betaine, a choline metabolite, play important roles in reducing inflammation and for our brain and cardiovascular health. Interestingly, both of these compounds reduce plasma homocysteine levels, which a modified amino acid mainly derived from meat consumption. High levels of homocysteine are linked to increased heart disease. The author has shown a relationship between thiamin(e) and Autistic Spectrum Disorder (ASD) . Moreover, the B vitamins thiamin(e), niacin, vitamin B6, riboflavin and pantothenic acid are required for transamination, decarboxylation, acylation, oxidation, and reduction of numerous substrates that eventually are involved in energy utilization and homeostasis. One or more of the B vitamins are important for cholesterol, steroid, amino acid, fatty acid and glucose synthesis. Several carboxylases require biotin for carbon dioxide fixation for respiration and the transmission of the energy pathway requires methylation and vitamin D, 5-MTHF (active folate), methylcobalamin (active vitamin B12), pyridoxal 5’-phosphate (active vitamin B6), betaine, choline, riboflavin 5’-phosphate (active vitamin B2) and magnesium are all needed for methyl-group transfer. Their metabolism intermingles at the pathway for conversion of homocysteine to methionine. Thiamine and pyridoxal sulfate are necessary for deoxyribonucleic acid (DNA) synthesis as is folate, which supplies single-carbon units in the pathway. There is growing evidence that some B vitamins, and choline may prevent the occurrence of developmental abnormalities and chronic degenerative or neoplastic diseases . HoweverHeart disease is the major cause of death in the United States and for many years, physicians and researchers have been emphasizing the importance of the Mediterranean diet. Consuming a Mediterranean diet can lower the risk for heart disease and stroke. However, this diet is rich in choline and betaine and it is choline metabolism that produces betaine. Many health bloggers have argued that most adults would benefit from choline and betaine HCl supplementation but few proper studies have ever supported those claims. More evidence is needed bout the health cost vs. benefit to choline consumption but new evidence suggests that betaine and choline supplementation may even be harmful. In that regard, the cholesterol theory of heart disease and its relationship to egg consumption is not well established as causing heart disease and our Cleveland Clinic Foundation (CCF) colleagues have identified a link between eggs and phosphatidylcholine (PC) with coronary heart disease that do not involve the cholesterol theory of CHD through production of trimethylamine-N-oxide (TMANO/TMAO) .Due to the metabolic enzymatic action of anaerobic bacteria, dietary choline, PC, betaine all produce TMANO . Prior tThe major precursor for TMANO in the human diet is choline, which increases urinary excretion of trimethylamine and its N-oxide . FollowiIn a study investigating TMANO formation from 46 different ingested foods, only fish and other sea-foods gave rise to significant increases in urinary trimethylamine and N-oxide , whereasOther foods have significantly more choline than eggs and a more significant impact on TMANO production. Nevertheless, this study appears to implicate meat consumption for the increased production. It appears that excessive intake of red meat in particular and foods high in choline readily increase plasma TMANO levels, which can cause blood clots and increases the risk of heart disease . For exaOne approach to preventing heart disease from this research group was to inhibit host enzymes that convert TMA to TMANO, but this caused the formation of pro-atherogenic intermediates  and the When choline is supplemented orally over two months, production of trimethylamine N-oxide increased ten-fold  The CCF in vivo, and if high TMANO causes heart disease, then one would expect greater rates of CHD among people who eat more fish, whole grains and choline rich foods, since these are a fair component of a Mediterranean diet and these foods produce more TMANO. Yet, this is the opposite of what cohort studies indicate, as eating more fish especially wild caught cold-water, fatty fish like salmon, rich in omega 3 fatty acids has consistently been shown in randomized controlled trials to reduce the risk of death from coronary heart disease, mortality and sudden death [However, flavonoids and lignans form wine have both antiplatelet and antithrombogenic activity, which is mediated through binding of cyclooxygenase . Their aen death . Recentlen death  and hearen death .TMANO is suspected of being many things from pharmacological therapeutic agent to evolutionary remnant of an osmolytes-regulation system among others. Among others, mutant protein chaperone  and helpIn regard to kidney function and renal insufficiency, TMANO’s effect on increased atherosclerosis and heart disease risk in humans and rats may involve its interaction with angiotensin II  which, iIn regard to leaky gut, leaky brain and other barrier permeability states, it is suggested that TMANO might cause BBB or other barrier disruption by reducing the expression of tight junction protein-1 ZO-1 and claudin-5 . MoreoveInflammation in the body may lead to direct and even disruptive effects on the brain via the blood–brain barrier and blood-gut barrier. This may be perhaps why we find TMANO in the brain. During systemic inflammation, whether from infection or LPS translocation, the BBB may undergo changes in patients with neurological disease to become abnormally sensitive to the effects of systemic inflammation . ConversIn addition to heart disease, Alzheimer disease, schizophrenia, ASD and autism are increasingly expected to be influenced by the gut microbiota. In that regard, it is well established that bacteria can directly cause human blood and plasma to clot. Moreover, these coagulation states can be acquired from systemic diseases or sequalae associated with an increased risk of thrombosis. For instance, hyperlipidemia, malignancy, myeloproliferative disorders, use of oral contraceptives, pregnancy, and even diabetes all are known to cause hyper-coagulation . PreviouEnterobacteriaceae [Enterobacteriaceae, which is a common bacteria in mammals. In the Colon, anaerobic respiration with TMANO was at the same time able to inhibit the facultative pathogen Staphylococcus aureus and other bacterial growth [Bacillus, Staphylococcus, Corynebacterium, Fusobacterium and many members of the phylum Proteobacteria are opportunistic species, especially Enterobacteriaceae, thrive in an inflamed environment [It is important to revisit redox mechanisms in regard to TMANO as it potentially affects oxidation-reduction mechanisms, impair fatty acid oxidation in cardiac mitochondria  and serveriaceae . These rl growth . Facultaironment . Substanironment  and we sPrevotella bacteria is known to produce higher levels of TMANO. Intestinal microbiota metabolism of L-carnitine, which promote atherosclerosis [Prevotella bacteria [Clostridia difficlie may be another culprit and find that Clostridia difficlie is lower in vegetarians vs. carnivores (unpublished observations). Yet, carnitine supplementation coupled with alpha lipoic acid, is able to protect the heart and brain from oxidative stress, aging and possibly bacterial action and may be one solution to the problem. Moreover, polyphenols help prevent inflammation and oxidation and thus help prevent downstream effects from these processes, which are implicated in almost every disease [Further, carnitine, abundant in meat and high energy drinks may responsible for increasing production of smaller amounts of TMANO from bacterial metabolism. What we don’t know is which specific bacteria, are involved, although clerosis , is founbacteria . The aut disease .So, while it cannot be concluded that choline, betaine and carnitine are responsible for strokes or heart disease, we should not eliminate them from the diet. The Cleveland Clinic Foundation researchers demonstrated that a Mediterranean diet altered the activity of gut microbes, which may be the very node that modifies bacterial risk in humans. Nevertheless, scientists should explore bacteria-host co-metabolism with phenolic acids, antioxidants and polyphenol administration and sequence the microbiota of the heart healthy for genetic associations or polymorphisms to gain a better understanding. Regardless, it may be best to consume TMANO-promoting foods in moderation, or focus on eating more vegetation or drink a glass of red wine per day and so on or at least until all the facts are made clear. Other foods in the aforementioned dietary challenge like fish, whole grain etc. may increase Prevotella colonization .sakei and Lactobacillus arabinose isomerase to isomerize of D-galactose to D-tagatose. They overcame low catalytic efficiency and low thermal stability by encapsulating the enzyme in a gram-positive Lactobacillus plantarum, which was chemically permeable and enabled high reaction rates at high temperatures [Polyphenols help lower systemic inflammation, improve metabolic syndrome and favorably affect the microbiota as a prebiotic. They also induce the microbiota to release prebiotics, such as SCFAs . In addieratures . What thSince polyphenols and antioxidants are able to counteract many deleterious bacteria-driven mechanisms, it follows that unwanted co-metabolism could be inhibited by prosaic foods rather than with inhibitors or drugs. Natural compounds are preferred over synthetic ones since they are readily available, inexpensive, and comparatively less toxic. However, they are very difficult to synthesize commercially. Nevertheless, support for this notion comes from the Cleveland Clinic Foundation researchers, themselves, who found that prosaic foods like cold-pressed extra virgin olive oil, balsamic vinegar and grape seed oils could also inhibit microbes from transforming meat, choline, betaine and carnitine into metabolic by-products of TMANO in animal studies, but they did not explore antioxidants or redox mechanisms directly. There is considerable conjecture about vitamin supplementation and choline is not exempt. High levels of TMANO are associated with a greater risk of heart attack and stroke. However, according to a large Finnish study, adequate intake of choline reduced the risk of dementia , cardiovTechnical aspects typical with human studies like the TMANO studies make our determination difficult such as those from confounding factors like diet and the constitution of the study subjects. For example, kidney function is important in toxin clearance and we see filtration rate and kidney function from some study participants but any impaired urinary clearance of TMANO or impaired kidney function would diminish the results. The conjecture is supported in the New England Journal of Medicine paper, where the highest levels of TMANO had an average glomerular filtration rate (GFR) of 69 mL/min, which is indicative of a reduced filtration determined as a GFR between 60–89 mL/min. In their defense, however, a healthy volunteer study was conducted where the results appeared to hold. Further, the microbial milieu should be determined throughout these studies as some gut microbiota, i.e., Prevotella species are known to predispose one to increases in TMANO production .In summation, we cannot say that choline and betaine are protective or deleterious as food consumption goes, but they do affect many aspects of our health, especially when considering potential transformation by enteric bacteria in the colon. Nevertheless, consuming excess choline-rich foods or when supplements are added, may increase TMANO levels and could increase the risk of heart disease. Yet, the betaine, when consumed in red wine, however, may be protective and red wine with a choline-rich meal may impart similar protection from choline formation via a microbial route. As yet, no one has established a clear mechanism for how the French enjoy their food or any heart disease-sparing mechanism and more work is necessary to address these aspects, which we elucidate here both for the microbiota gut brain heart shunt and in neurodegenerative disease. This work calls for reexamining many experimental approaches and couple them with exploring the microbiota of the French. Taken together, we argue that oxidative stress, through microbial action and metabolism, could contribute to TMANO formation but other factors may be more important in modulating heart and cerebrovascular disease and related forms of AD, VaD and dementia (See


Despite considerable progress for the regenerative medicine, repair of full-thickness articular cartilage defects and osteochondral interface remains challenging. This low efficiency is largely due to the difficulties in recapitulating the stratified zonal architecture of articular cartilage and engineering complex gradients for bone-soft tissue interface. This has led to increased interest in three-dimensional (3D) printing technologies in the field of musculoskeletal tissue engineering. Printable and biocompatible hydrogels are attractive materials for 3D printing applications because they not only own high tunability and complexity, but also offer favorable biomimetic environments for live cells, such as porous structure, high water content, and bioactive molecule incorporation. However, conventional hydrogels are usually mechanically weak and brittle, which cannot reach the mechanical requirements for repair of articular cartilage defects and osteochondral interface. Therefore, the development of elastic and high-strength hydrogels for 3D printing in the repairment of cartilage defects and osteochondral interface is crucial. In this review, we summarized the recent progress in elastic and high-strength hydrogels for 3D printing and categorized them into six groups, namely ion bonds interactions, nanocomposites integrated in hydrogels, supramolecular guest–host interactions, hydrogen bonds interactions, dynamic covalent bonds interactions, and hydrophobic interactions. These 3D printed elastic and high-strength hydrogels may provide new insights for the treatment of osteochondral and cartilage diseases. Damage of cartilage and osteochondral tissue is one of the most common health problems worldwide, which occurred due to various reasons such as disease, injuries, and trauma. Traumatic injuries to the joint, osteochondritis dissecans, and osteoarthritis are the most common reasons for osteochondral and cartilage diseases. Investigations by arthroscopy have reported the prevalence of cartilage and osteochondral damage was 60% in the general population . As lifeUnlike the majority of other tissues, cartilage is low in cellularity and basically avascular in nature . TherefoAlthough they are often used clinically, significant drawbacks and limitations still exist. The microfractures drills small holes through the subchondral bone to allow the bone marrow to flow into the defect area. By introducing biomolecules and stem cells into the defect, it is expected to promote cartilage and osteochondral regeneration. However, it usually causes the fibrocartilage formation that has inferior properties compared with the hyaline cartilage . AutologTo solve these problems, cartilage and osteochondral tissue engineering have been recommended to promote more effective treatments. One of the promise methods is to make artificial constructs to imitate the mechanical properties, biological functions, and architectural features of native cartilage and osteochondral tissue. Via combining advanced three-dimensional (3D) printing technology and specially designed biopolymers, it becomes possible to develop materials with sufficient mechanical properties to articular cartilage . The priUnlike the traditional hydrogels formed by covalent networks, which is hard to cause huge changes for the properties of hydrogels due to an unchanging covalent framework, hydrogels formed by non-covalent networks exhibit reversible crosslinking with a kinetic rate that can change with the environment. Non-covalent bonds can be broken to dissipate energy under stress, and self-healed to reform the hydrogels. The hydrogels can also significantly change over time without permanent changes to the hydrogel network . Due to In this review, we focus on recent progress in the development of high-strength and elastic hydrogels for cartilage and osteochondral tissue engineering. We review various classes of high-strength and elastic hydrogel systems including: (1) physical associations to assemble hydrogels , (2) physical associations to assemble particle-based hydrogels (nanocomposites integrated in hydrogels), and (3) dynamic covalent chemistry to form hydrogels . The various mechanisms of hydrogel formation, mechanical properties, and applications in cartilage and osteochondral regeneration are summarized for each subgroup. Additionally, recent advances in 3D bioprinting for cartilage and osteochondral tissue engineering are also discussed.The hydrogen bonds are usually used to strengthen hydrogels due to its relative stability in aqueous condition. In addition, the dissociation energy of hydrogen bonds is relatively low. Moreover, the strength of multiple hydrogen bonds could be equivalent to a covalent bond . The hydThe use of polymer chains with a series of hydrogen bonding sites can also generate strong hydrogen bond interactions in the hydrogel. Compared with simple amide hydrogen bond, dual amide hydrogen bonds are relatively more stable. Thus, study has designed a hydrogel based on N-acryloyl glycinamide (NAGA), a glycinamide-conjugated polymerizable monomer that consists of two amides . By photThe strength of hydrogen bonds can also be significantly influenced by incorporating hydrophobic groups, which can further affect the mechanical properties of the hydrogels contain donor comonomer units and hydrogen bond acceptor. Study has reported introduction of methyl motif to acrylic acid (MAAc) can obviously increase the mechanical property of hydrogen-bonded hydrogels . The hydBy adding hydrogen bonds interactions to the networks of hydrogels, studies have developed hydrogels with high strength for cartilage regeneration. In the study by Different from other non-covalent interactions that rely on direct intermolecular attraction, hydrophobic interactions are driven by the tendency of water molecules to maintain their hydrogen-bonded network intact around non-polar solutes. It can be altered by the presence of cosolutes, increased temperature, as well as size of species . PolymerElastic and self-healing networks of hydrophobically cross-linked materials can be developed by micellar copolymerization of (1) hydrophilic comonomers, such as N-alkylacrylamides , acrylamide (AAm) or acrylic acid (AAc); with (2) large hydrophobic monomers, such as dococyl acrylate (C22) , stearylC22- and C18-acrylamide copolymer hydrogels with a SDS-NaCl system could reach an elastic modulus at 1 kPa. Study has demonstrated that after copolymerization, the hydrogel becomes mechanically stronger after the surfactant micelles are swollen and extracted, as the hydrophobic interaction is enhanced in the absence of surfactant . After rBy introducing hydrophobic interactions into the networks of hydrogels, studies have attempted to replicate the unique characteristics of cartilage in hydrogels. In the study by In a supramolecular guest–host interaction, a guest moiety is physically inserted into another host moiety, and is held together by non-covalent bonds. Harada’s pioneering research proved that polyethylene oxide (PEO) can insert multiple α-cyclodextrin (CD) groups, which is the driving force for the research and development of supramolecular guest–host assembly hydrogels . Since tSelf-healing and shear-thinning properties of supramolecular hydrogels have been demonstrated in different types of polymeric entities . Studies4 M–1. Hydrogel cross-linked only by the above host–guest interaction is relatively weak and deforms under stress  and acryloylated tetra-ethylene glycol-modified adamantane (A-TEG-Ad). Then, a host–guest supramolecular hydrogel (HGGelMA) was obtained via copolymerization between the arms of the guest–host interaction and GelMA to form a covalently crosslinked network  (PEG) to constitute an IPN , study hr models .The tunable stress relaxation properties of these ionic hydrogels made them applicable to tissue engineering. Study has revealed that compared with the hydrogel with the same gel modulus, cells are more widely distributed on the stress-relaxed soft viscoelastic hydrogels . This phHydrogels integrated with nanocomposite are defined as hydrated networks which are chemically or physically cross-linked by nanoparticles . Differein vitro. In the study by Some nanoparticles-reinforced hydrogels can be also used for 3D printing . Comparein vitro. Notably, an external magnet could be used to direct this hydrogel remotely to the cartilage defect site  and diols can develop a reversible boronate ester in aqueous environment, and can be brought into polymer network to form elastic materials. For instance, study has reported an elastic material using the reversible boronate ester complexation between salicylhydroxamic acid (SHA) and PBA. This material is able to exhibit various mechanical properties in a wide range of pH . Study hAnother major approach for developing dynamic covalent elastic and self-healing hydrogels is through imine bonds interactions, sometimes also called Schiff bases. For example, a self-healing hydrogel was made at room temperature by synthesizing telechelic dibenzaldehyde-terminated PEG and mixing it with an amine-containing biomacromolecule solution, such as peptides, chitosan, and gelatin . CompareStudy has also reported a shear-thinning and self-healing hydrogel crosslinked through dynamic covalent chemistry for 3D printing . SpecifiHydrogels crosslinked by dynamic covalent interactions have also used to enhance osteochondral tissue regeneration. In the study by Since bio-inks are usually based on hydrogels, they are usually weak and therefore cannot mimic the mechanical properties of cartilage tissue, which has high strength, and is elastic and shock-absorbent. By co-printing with artificial thermoplastic polymers, significant enhancement of mechanical property can be obtained . Howeverin vitro, and not lead to the immune response in vivo. Several elastic and high-strength hydrogels have been reported with good cytocompatibility  and recombinant human bone morphogenic protein 2 (BMP) can lead to localized chondrogenic and osteogenic differentiation of MSCs in hydrogels . MoreoveIncreasing studies have highlighted the advantages of adding physical and biochemical gradients in osteochondral and cartilage tissue engineering. With combinations of biochemical and physical gradients, it could be possible to develop more native like cartilage and osteochondral tissues. In the study by An alternative approach to construct stratified cartilage and osteochondral tissues is to bioprint gradients of different cells. The cell sources most widely used for cartilage and osteochondral tissue engineering are chondrocytes and MSCs . Co-cultOsteochondral damage is a very common clinical disease. Although there are several clinical treatment strategies for this disease, such as microfracture, osteochondral autografts and allografts, as well as autologous chondrocyte implantation, significant drawbacks and limitations still exist. As current surgical techniques for cartilage pathologies are insufficient to cure the cartilage injuries, and halt the development and progression of osteoarthritis, which has accelerated the development of alternative tissue engineering strategies. However, although cartilage is perceived as a simple tissue, developing biomaterials that can reach the mechanical properties of native cartilage remains a challenge.Traditionally, the covalently bonded hydrogels are stiff and brittle, and cannot simulate mechanical properties of natural cartilage and osteochondral tissue, which has high strength, and is elastic and shock-absorbent . Unlike Despite the obvious advantages and significant progress, the ultimate aim of cartilage and osteochondral tissue engineering is to translate a promising therapeutic strategy to the clinics to regenerate and restore the articular cartilage for patients. Non-covalently formed hydrogels have a promising place among the biomaterials evaluated for clinical regeneration of cartilage and osteochondral tissues for patients with osteoarthritis due to their tunable mechanical strength and self-healing property. Moreover, because of their shear-thinning property, these hydrogels are promising inks for 3D bioprinting, which could potentially contribute to the next generation personalized strategy that addresses each patients’ requirement as it is a automated, computerized, and rapid technology to develop constructs that mimic native cartilage and osteochondral tissues. However, before translating to clinics, meticulous choice of these hydrogels with robust features such as regenerative potential, biocompatibility, and degradability assessed in pre-clinical trials is required.WD and MS drafted the manuscript. XL, XH, and WD collected and sorted the information. YA and XH designed the conception and revised the manuscript. All authors contributed to the article and approved the submitted version.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Pharmaceutical and personal care products (PPCPs) are commonly used chemicals that are increasingly detected in urban-impacted environments, particularly those receiving treated wastewater. PPCPs may have toxicological effects on the macrofauna that are exposed through contaminated water; thus, there is interest in microbially mediated transformations that may degrade PPCPs. This review discusses specific examples of PPCP transformations that may occur in anoxic environments, including O-methylation and O-demethylation. Pharmaceuticals enter wastewater treatment plants through ingestion and subsequent excretion3, through improper disposal down a household drain4, or from pharmaceutical manufacturing plant discharge5. Wastewater treatment plants are not designed to remove these complex organic contaminants, which can result in incomplete PPCP removal. A major concern is, therefore, that treated effluent may contain low concentrations of PPCPs that can enter receiving waters or soils when biosolids are used as fertilizer8.Pharmaceutical and personal care products (PPCPs) contain chemicals that are widely distributed in surface waters, sediment, and soil9 or can cause unwanted physiological responses to non-target organisms, including endocrine disruption (e.g. feminization of fish), altered development of aquatic organisms including fish and frogs, and changes to behavior13. In addition, bioaccumulation in aquatic organisms is a concern, particularly in fish intended for human consumption14. Not only are these findings a potential public health problem, but they also raise concerns about the health of the ecosystem and overall water quality. While the concentrations of an individual chemical may be in the ng L-1 range , and antimicrobial compounds (e.g. triclosan and triclocarban). Others may have unexpected inhibitory effects. Ibuprofen, for example, has been shown to inhibit the growth of a variety of microorganisms28. In freshwater systems, nitrate, iron, or carbonate are predominant electron acceptors available for respiration, whereas coastal marine waters would additionally have sulfate as a respiratory electron acceptor. These different conditions, therefore, support diverse microbial communities that may also be capable of divergent biochemical mechanisms for biodegradation in surface waters and anoxic sediments. This must all be taken into account when modeling the environmental fate of PPCPs, as degradation might be more likely to occur, proceed to a greater extent, or produce different intermediates depending on the location. Naproxen transformation, for example, has been shown to occur under sulfate-reducing and methanogenic conditions in constructed wetlands, estuarine sediment, and anaerobic digester sludge, yet nitrate-reducing conditions in constructed wetlands yielded little transformation activity29. Oxybenzone, in contrast, was transformed under aerobic, nitrate-reducing, iron-reducing, sulfate-reducing, and methanogenic conditions31. PPCPs have diverse chemical structures that underscore the need for a broader understanding of how microbes in different environments will metabolize the different classes of compounds. This is valuable for predicting potential activity in the environment, as partial microbial transformations may make the original PPCP undetectable by standard methods, yet the new transformation product may have ecotoxicological effects.PPCPs enter changing environmental conditions and encounter diverse microbial communities as they pass from households through the wastewater treatment process and ultimately into the environment. The initial stages of wastewater treatment are designed to first use well-oxygenated units to support aerobic degradation. Later in the process, further degradation of the sludge solids takes place in anaerobic digester units that promote a fermenting and methanogenic community operating under low oxidation-reduction potential (<–350 mV). Treated wastewater effluent is released into oxic surface water; however, some PPCPs will eventually migrate into anoxic sediments34. Treated wastewater effluents are one of the main pathways by which PPCPs enter watersheds. While some removal during wastewater treatment can be attributed to the biological activity of microorganisms, there are few simplified consortia or pure cultures available to demonstrate the biochemistry involved in PPCP transformation. Without biochemical evidence, it is difficult to determine if the PPCP in question has been mineralized35, lost due to abiotic processes such as sorption to solids38, or transformed into unknown metabolites39.There have been many reports of PPCP removal during the biological stages of wastewater treatment , a metabolite formerly known to be generated only by mammals and fungi50. While the parent compound, diphenhydramine, suppressed both fermentative and methanogenic activity in the anaerobic digester community, the metabolite suppressed only methanogenic activity. In contrast, there was negligible toxicity of naproxen and 6-O-desmethylnaproxen to the same community20. These differences highlight how chemically different PPCPs and their transformation products may have different effects on the same microbial community, further underscoring the complexity of the fate and effect of the PPCPs.Similarly, diphenhydramine can be transformed by anaerobic digester sludge microbes via N-demethylation to N-desmethyl diphenhydramine see;18, a m31. Microbial communities enriched under both methanogenic and sulfate-rich conditions showed this capability when provided with naproxen, guaifenesin, methylparaben, or oxybenzone31. The sulfate-rich cultures formed O-demethylated metabolites, shown in31.While anaerobic O-demethylation of aromatic compounds has been well established see, less is45, resulting in metabolites with increased toxicity as shown from differences in survival and occurrence of developmental lesions in developing zebrafish embryos exposed to BPA, BPA MME, and BPA DME. The monomethyl and dimethyl ether derivatives were more toxic than BPA, resulting in increased mortality. Furthermore, exposure to either of the O-methylated metabolites resulted in an increase in the incidence of developmental lesions as compared to BPA exposure45. These data illustrate a new mechanism for the microbial transformation of BPA, producing metabolites warranting further study to understand their prevalence and effects in the environment. In addition, the O-methylated transformation products could serve as potential substrates for O-demethylation by the organisms described above51. The interconversion between O-methylated and O-demethylated forms thus presents a mechanism by which a PPCP compound can be transformed in one environment and the original parent compound regenerated by microbes that are active in another environment. This is similar to reports of flame-retardant and antimicrobial compound transformations that have been described in plants54.In contrast, many phenolic compounds can be transformed by microbial O-methylation see. For exaet al.55 used a systematic approach to identify potential metabolites of PPCPs that contain an amine group, applying this method to predicting reactions in aerobic activated sludge. Alternatively, we used a culture-based approach to examine the range of O-demethylation substrates in anoxic sediments and anaerobic wastewater digestion31. Gonzalez-Gilet al.56 used enzyme assays to examine co-metabolic transformations of diverse PPCPs, including naproxen, nonylphenol, octylphenol, triclosan, and BPA, that were mediated by acetate kinase. The extent to which transformation occurred varied with the substrate from 10–90% and suggested the involvement of additional transformation pathways56, which could lead to a mixture of different transformation products existing from the same parent compound. Laboratory-based assays, such as those conducted by Gonzalez-Gilet al.56 and Wolfsonet al.31, represent a starting point for the identification of potential metabolites, although it may not be representative of the dominant transformation mechanism that occurs in the environment. Likewise, the microbial community composition may have an effect on PPCP transformations, especially under methanogenic conditions57. Additionally, the effects that mixtures of PPCPs and associated transformation products will have on microbial community function cannot be overlooked.Identifying common functional groups may serve as a basis for predicting transformation products. Gulde62. These new technologies have shown promise with higher removal rates in pilot treatment plants than with conventional treatment63. In combination with increased removal efficiencies, re-designing PPCPs to promote biodegradability could lead to a reduction in the environmental load in the future65. Understanding transformation products is important not only to the health of impacted aquatic ecosystems and humans but also for monitoring the safety of reclaimed wastewater reuse (for review, see70.Recognition of the expanding extent of PPCP contamination has stimulated the search for solutions that remove pharmaceuticals from wastewater before they can reach the environment, including technologies like advanced oxidation processes and membrane bioreactors71, thus providing a steady stream of diverse chemical structures that may be entering wastewater treatment and the environment. Given that pharmaceuticals are used daily throughout the world, their release into the environment is both a public and an environmental health concern. Understanding not only the microbial transformation processes but also the metabolites that are formed is essential for comprehensive accounting of pharmaceuticals and potential pharmaceutically active compounds in the environment. The environmental context, be it the engineered anaerobic digester or freshwater or estuarine sediments that are impacted by treated wastewater, is critical for understanding potential microbial activities and biodegradation mechanisms to determine if biodegradation will occur or if potential metabolites may form and accumulate under the given redox conditions. This knowledge may provide solutions to remove these pharmaceuticals during wastewater treatment and prevent environmental deposition as well as to understand environmental processes that may occur to remove pharmaceuticals that have already entered the environment.An Organization for Economic Cooperation and Development report projects that sales of chemicals worldwide will increase by 3% annually between now and 2050


Magnetoencephalography (MEG) is a functional brain imaging technique with high temporal resolution compared with techniques that rely on metabolic coupling. MEG has an important role in traumatic brain injury (TBI) research, especially in mild TBI, which may not have detectable features in conventional, anatomical imaging techniques. This review addresses the original research articles to date that have reported on the use of MEG in TBI. Specifically, the included studies have demonstrated the utility of MEG in the detection of TBI, characterization of brain connectivity abnormalities associated with TBI, correlation of brain signals with post-concussive symptoms, differentiation of TBI from post-traumatic stress disorder, and monitoring the response to TBI treatments. Although presently the utility of MEG is mostly limited to research in TBI, a clinical role for MEG in TBI may become evident with further investigation. Traumatic brain injury (TBI) occurs an estimated 27 million to 69 million times per year throughout the world ,2. The pFunctional imaging techniques can be useful for diagnosis and prognosis in mild TBI and for monitoring the effects of therapeutic interventions ,5. FunctMost functional imaging techniques measure neuronal activity indirectly through neurovascular or metabolic coupling, that is, to provide energy for increased neuronal activity, local cerebral blood flow, and glucose uptake increase. Neurovascular coupling is the basis for functional MRI (fMRI) with blood-oxygen-level-dependent (BOLD) imaging or arterial spin labeling (ASL) MRI. Neurovascular coupling is also the basis for single-photon emission computed tomography (SPECT), which measures gamma emissions from Technetium tc 99 m exametazime. Finally, neurovascular coupling is the basis for functional near infrared spectroscopy (fNIRS), which compares light absorbance in the wavelengths absorbed by oxyhemoglobin with the wavelengths absorbed by deoxyhemoglobin. Alternatively, metabolism coupling to neuronal activity is the basis for positron emission tomography (PET), which detects emissions from a radiotracer linked to a biologically active molecule such as fluorodeoxyglucose (FDG). Byrnes et al. have comprehensively reviewed the use of FDG-PET in TBI . AlthougMEG measures magnetic flux on the surface of the head associated with underlying neuronal electrical currents. Magnetic signals from the brain were first recorded by the physicist David Cohen in 1968 . Since tGiven the high incidence and prevalence of TBI and the need for new technologies for the diagnosis, prognosis, and monitoring response to treatments in TBI, this review examines the current evidence for the use of MEG in TBI.The authors conducted a PubMed search using the Medical Subject Headings (MeSH) “traumatic brain injury” and “magnetoencephalography” and the filter for human studies. The articles were screened by reviewing their abstracts for relevance to clinical and research applications of MEG in adults with TBI. Articles were included in the review only if the full text was available in English.There were 22 articles in PubMed fitting the search criteria. Screening the abstracts yielded 18 articles relevant to clinical and research applications of MEG in people with TBI. One of these articles was excluded because the full text was not available in English. From the reference lists of the articles found in the PubMed search, we identified 11 additional original research articles on the use of MEG in TBI. Together, the articles described the use of MEG for detecting TBI, differentiating TBI from conditions with similar features, characterizing changes in brain rhythm or connectivity from TBI, correlating imaging findings with clinical features, and monitoring the response to treatments. These applications are described in detail herein. Participant demographics for each study are shown in Whereas most patients with severe TBI have hemorrhage, edema, and/or ischemia detectable via CT or anatomical MRI, many mild and sometimes moderate injuries do not have features visible with these conventional techniques. As with other functional imaging techniques, MEG has been shown to detect TBI that is otherwise silent in conventional imaging. MEG features indicating mild TBI include abnormal resting state neural oscillations and altered connectivity between brain regions, as described in detail in this section.Among the first to investigate MEG in TBI, Lewine et al. in 1999 compared conventional MRI, EEG, and resting-state MEG findings in 20 normal participants, 20 symptomatic post-concussion patients, and 10 asymptomatic post-concussion patients . The posFurther studies have confirmed that resting-state MEG is sensitive for detecting mild TBI. Huang et al. (2009) analyzed MEG integration with diffusion tensor imaging (DTI) for detection of mild TBI in a case–control series of 10 patients with subacute to chronic mild TBI and persistent post-concussive symptoms for an average of 17 months and 14 matched controls ,44. LateBeyond comparing MEG rhythm abnormalities among specific brain regions, the connectivity between brain regions has also been used to detect TBI. Studies by Zouridakis et al. and Vakorin et al. used resting-state MEG network connectivity and machine learning to detect mild TBI ,21. PatiIn another study of brain region connectivity with resting-state MEG, Kaltiainen et al. included data from the same participants at multiple points in time. The authors analyzed resting-state MEG in 26 patients with mild TBI that occurred 6 days to 6 months prior to the study . In 12 oBeyond resting-state MEG, task-based MEG has also proven useful in detecting TBI. Tormenti et al. published data from MEG recordings during a language and spatial task in five patients with a history of concussion within the past 4 months and five controls . The parDa Costa et al. (2015) also used task-based MEG in 16 patients with mild TBI within 2 months of the study . PatientIn conclusion, both resting-state and task-based MEG have proven sensitive for detecting TBI even when conventional CT or MRI is normal. MEG may even be more sensitive than other advanced imaging modalities such as SPECT. In the resting state, abnormal low-frequency MEG signals are associated with TBI, and the brain regions with the low-frequency signals correlate with the injury locations and symptoms. Moreover, MEG may be used as an adjunctive study for determining recovery from brain injury.Whereas abnormal low-frequency MEG activity may be sensitive for detecting TBI, it is not specific to TBI. Other neurologic and psychiatric conditions also feature abnormal low-frequency activity, including brain tumors, infarcts, epilepsy, Alzheimer disease, and schizophrenia . ClinicaContrasting brain abnormalities between post-traumatic stress disorder (PTSD) and TBI is especially relevant because these conditions are frequently comorbid, and mild TBI may exacerbate PTSD symptoms ,47,48. PBuilding on this theory, Popescu et al. published a study in 2016 in which they analyzed resting-state MEG recordings in 32 active-duty service-member patients with mild TBI and persistent post-concussive symptoms . Each paIn another study investigating MEG activity in veterans with mild TBI and PTSD, Rowland et al. examined six veteran patients with both PTSD and chronic mild TBI, six patients with only chronic mild TBI, six patients with only PTSD, and 10 controls . The parIn a step closer to using MEG clinically to diagnose PTSD, Zhang et al. (2020) developed a machine learning classifier to identify military service members with PTSD . They coAlthough detecting mild TBI and differentiating it from other conditions with similar features can be clinically important for tailoring existing treatment regimens, understanding the pathophysiology of persistent symptoms after TBI is important to developing and testing new treatment modalities. Previous studies have used both resting-state and task-based EEG to study the effect of TBI on brain rhythm and connectivity, and MEG has also become useful for this ,53,54,55Luo et al. (2013) were among the first to show a correlation between MEG signal and specific cognitive symptoms in patients with TBI . Using rAs described in the section on TBI detection, Dimitriadis et al. (2015) analyzed MEG connectivity based on PLVs with machine learning to detect mild TBI with high accuracy, but they also used graph theory to better characterize the different regional brain network connectivity between patients with mild TBI and age-matched controls . The conIn 2020, Antonakakis et al. studied spontaneous network microstates in patients with TBI . Using rA study by Alhourani et al. (2017) also used PLVs from resting-state MEG data to characterize functional connectivity in patients with chronic, mild TBI (3–96 months after injury) and persistent post-concussive symptoms . Using gAnother study correlating post-concussion symptoms with brain connectivity findings was published by Popescu et al. in 2017 . Rather Finally, MEG can also be combined with EEG to characterize activity in the brain associated with TBI. In 2015, Li et al. published a study in which they analyzed resting-state MEG and EEG activity at 68 brain regions of interest . CompariMultiple studies have shown that MEG abnormalities in TBI dissipate with time since the injury and/or with recovery from the injury ,24,56, aIn early studies on response to TBI treatment, Castellanos et al. (2010) compared resting-state MEG recordings in patients with chronic TBI (range 2–6 months after injury) before and after a neuropsychological rehabilitation program ,40. The MEG has also been used to evaluate a more specific therapeutic intervention, perception attention therapy (PATH), which is a visual timing training task involving movement discrimination. Lawton and Huang (2019) studied four patients with cognitive deficits attributed to TBI who underwent working memory task-based MEG before and after 8 weeks of PATH neurotraining . After tBesides rehabilitation programs requiring active participation, a passive TBI treatment intervention has also been tested with MEG. Huang et al. (2017) recorded MEG data in patients with chronic TBI and persistent post-concussive symptoms (average duration 48 ± 25 months) before and after a 6-week passive neurofeedback intervention using low-intensity pulse transcranial electrical stimulation with EEG monitoring . They reAlthough the temporal resolution of MEG is very good, its spatial resolution is inferior to that of MRI. For functional brain activity maps, MEG data are often co-registered with anatomical MRI for MEG source imaging, requiring patients/participants to undergo an MRI scan in addition to the MEG data acquisition session. However, even with MRI-aided source modelling, Kaltiainen et al. (2018) demonstrated limited sensitivity of MEG to traumatic lesions deep in the brain (>3 cm from the cortex) . TherefoMEG machines are also very expensive and require a magnetically shielded room. Specialized expertise is also required for analysis and interpretation. Thus, it is not available in many institutions. The benefit of MEG as an adjunct in choosing depth electrode sites for epilepsy surgery planning may be worth the additional cost . HoweverMEG is a functional brain imaging technique with high temporal resolution and reasonable spatial resolution when co-registered with anatomical MRI. TBI researchers have demonstrated a variety of uses for MEG, especially in the detection of mild TBI and the characterization of functional network connectivity changes from TBI that cannot be seen with conventional anatomical imaging techniques. Combining MEG with other techniques, such as EEG or DTI, can support efforts to understand connectivity changes from TBI. MEG research has also been directed toward differentiating TBI from other conditions with similar clinical features, such as PTSD, as well as toward assessing responses to TBI treatment interventions. Although presently the utility of MEG is mostly limited to research in TBI, future research may eventually identify a clinical role for it in TBI as it has in epilepsy.


Mitochondria are essential organelles important for energy production, proliferation, and cell death. Biogenesis, homeostasis, and degradation of this organelle are tightly controlled to match cellular needs and counteract chronic stress conditions. Despite providing their own DNA, the vast majority of mitochondrial proteins are encoded in the nucleus, synthesized by cytosolic ribosomes, and subsequently imported into different mitochondrial compartments. The integrity of the mitochondrial proteome is permanently challenged by defects in folding, transport, and turnover of mitochondrial proteins. Therefore, damaged proteins are constantly sequestered from the outer mitochondrial membrane and targeted for proteasomal degradation in the cytosol via mitochondrial-associated degradation (MAD). Recent studies identified specialized quality control mechanisms important to decrease mislocalized proteins, which affect the mitochondrial import machinery. Interestingly, central factors of these ubiquitin-dependent pathways are shared with the ER-associated degradation (ERAD) machinery, indicating close collaboration between both tubular organelles. Here, we summarize recently described cellular stress response mechanisms, which are triggered by defects in mitochondrial protein import and quality control. Moreover, we discuss how ubiquitin-dependent degradation is integrated with cytosolic stress responses, particularly focused on the crosstalk between MAD and ERAD. Mitochondrial integrity relies on a sophisticated network of quality control machineries, which have been evolved to counteract challenges associated with the endosymbiotic integration of this organelle into eukaryotic cells . Along wBesides the important role in ATP production and synthesis of amino acids, nucleotides, and iron-sulfur clusters , mitochoIn this review we focus on quality control pathways that maintain mitochondrial functionality, involving cross-communication with the ER and other cellular compartments. We discuss recent discoveries on the role of the ubiquitin/proteasome-system (UPS) in mitochondrial quality control, including pathways that are constitutively active or triggered by metabolic stress to ensure mitochondrial integrity.Protein quality control is required at all steps originating from protein synthesis and involves a series of mechanisms dedicated to the surveillance of protein translation, transport, and turnover . CentralThe turnover of soluble ubiquitylated proteins is mainly conducted by the 26S proteasome . It consIn contrast to soluble substrates, proteins organized in multimeric complexes or membrane bound, require an additional extraction step prior to proteasomal degradation. This function is mainly executed by Cdc48 (p97 or VCP in vertebrates), which belongs to the family of AAA-ATPases associated with diverse cellular activities (AAA+), commonly using ATP to perform mechanochemical reactions . In collLarger structures such as aggregated proteins or organelles are targeted for degradation inside lysosomes (vacuole in yeast and plants), which contain promiscuous proteolytic enzymes for degradation of engulfed cargoes. In this process termed macroautophagy (hereafter autophagy), substrates are recognized by autophagy receptors bound to autophagosomal membranes, which triggers substrate engulfment by the autophagosomal membrane and subsequent lysosomal fusion . SimilarThe degradation of ER-resident or mitochondrial proteins is regulated by two mechanistically similar ubiquitin-dependent pathways termed ER-associated degradation (ERAD) and mitochondria-associated degradation (MAD) . For botThe mitochondrial mass is efficiently regulated by the balanced coordination between biogenesis and degradation. In addition to the degradation of damaged mitochondrial proteins the UPS also contributes to remodeling of the mitochondrial proteome in response to metabolic changes  Bragosz. MitochoNotably, the first identified MAD substrate was in fact the yeast mitofusin Fzo1 , which iDepending on the physiological conditions, Cdc48 also appears to be required for Fzo1 regulation . Under oin vitro system of reconstituted proteoliposomes  supports extraction and degradation of mitochondrial proteins . Despiteiposomes .–Ufd1–Npl4 complex  are degraded by the UPS before their import . HoweverIn mammalian cells, quality control of membrane proteins recruited to mitochondria is provided by ubiquilins , which aMitochondrial targeting and protein import are governed at the mitochondrial import channel by a newly proposed MAD pathway. A subpopulation of Ubx2 binds to the TOM complex, which recruits Cdc48 to initiate degradation of partially imported proteins similarly to ERAD  Figure . This meThe first contact of mitochondrial proteins with the cytosolic proteostasis network occurs already during translation at cytosolic ribosomes. It was recently shown that stalling of ribosomes, which indicates aberrant mRNA, defective ribosome assembly, or an accumulation of nascent protein, triggers ribosome-associated quality control (RQC) . StalledSince the targeting sequence of many mitochondrial proteins is at the N-terminus, import can occur either post-translationally or co-translationally . If impoC. elegans, mitochondrial impairment was linked to defective turnover of cytosolic UPS model substrates despite no increase in ROS, suggesting the existence of a distinct response mechanisms regulating UPS activity  has been thoroughly investigated   . Thus, dRmt (am) .The use of deep transcriptome sequencing, combined with proteomics allowed to monitor transcriptional and translational changes over time after ‘clogging’ of the TOM complex in yeast. Under these conditions the heat shock responsive transcription factor Hsf1 is activated and triggers the expression of molecular chaperones. Interestingly, one Hsf1-dependent target gene encodes the transcription factor Rpn4, which specifically upregulates proteasomal subunits, constituting a second layer of response that is activated upon prolonged stress . In addiam (Although a general transcriptional program has not been identified yet, an intricate cooperation of the different quality control pathways becomes evident. For example, Rpn4 is not only initiated upon TOM “clogging,” but also in import-defective yeast mutants related to UPRam . Howeveram , import-am . These dam  (Boos etam .mt (An additional cellular strategy to avoid UPS overload under prolonged mitochondrial stress conditions is based on suppression of protein translation both inside and outside of the organelle . The premt .Even though a common mechanism has not been identified yet, it is obvious that diverse, overlapping mitochondrial signaling pathways are activated to support proteostasis and cellular survival. These pathways influence gene expression to adapt mitochondrial and cytosolic protein degradation pathways under mitochondrial stress conditions.Each cellular sub-compartment is equipped with specialized quality control machineries, which are intricately connected and cross-communicate. The reported studies support the idea that ubiquitin-dependent mitochondrial quality control pathways efficiently adapt in response to environmental and metabolic changes. However, in case of acute stress conditions, specialized response programs are induced to adjust the UPS capacity and thereby restore organellar proteostasis . BesidesRegulation of mitochondrial quality control by the UPS emerged to be conserved in all eukaryotes, involving Cdc48/p97 and the 26S proteasome. However, mechanistic details on substrate selection and ubiquitin ligases remain largely unclear. In contrast to proteasomal degradation of OMM proteins, little is known about the turnover of intra-mitochondrial proteins. Especially how mitochondrial substrates are retro-translocated from the different inner mitochondrial compartments into the cytosol is of central importance for understanding the regulation of MAD. Conversely, a novel functional role of the mitochondrial translocation machinery has been identified, which seems to import cytosolic aggregation-prone proteins into mitochondria for efficient degradation . A more Besides the high degree of mechanistic similarities between the MAD and ERAD pathways, mitochondrial quality control is further defined by functional mitochondria-ER interactions. For example, substrates extracted from the OMM by Msp1 are targeted to the ER for subsequent proteasomal degradation . MoreoveMitochondrial impairments have been associated to several pathologies not only limited to metabolic diseases or myopathies, but including cancer , pulmonaAll authors conceived, wrote the manuscript, and critically revised the manuscript. SR designed the figures.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Heart failure (HF) after myocardial infarction (MI) due to blockage of coronary arteries is a major public health issue. MI results in massive loss of cardiac muscle due to ischemia. Unfortunately, the adult mammalian myocardium presents a low regenerative potential, leading to two main responses to injury: fibrotic scar formation and hypertrophic remodeling. To date, complete heart transplantation remains the only clinical option to restore heart function. In the last two decades, tissue engineering has emerged as a promising approach to promote cardiac regeneration. Tissue engineering aims to target processes associated with MI, including cardiomyogenesis, modulation of extracellular matrix (ECM) remodeling, and fibrosis. Tissue engineering dogmas suggest the utilization and combination of two key components: bioactive molecules and biomaterials. This chapter will present current therapeutic applications of biomaterials in cardiac regeneration and the challenges still faced ahead. The following biomaterial-based approaches will be discussed: Nano-carriers for cardiac regeneration-inducing biomolecules; corresponding matrices for their controlled release; injectable hydrogels for cell delivery and cardiac patches. The concept of combining cardiac patches with controlled release matrices will be introduced, presenting a promising strategy to promote endogenous cardiac regeneration. Heart failure (HF) is a leading, growing public health problem, affecting millions of people worldwide . Most caThe human heart has only a modest capability to replace the damaged tissue and restore functionality after MI. Conversely, in the case of lower vertebrates, including some fish and amphibian species, regenerative capacity is retained throughout adult life without evidence of scarring . It was Currently, the most common clinical intervention after MI resulting from blood vessel occlusion includes rapid re-perfusion to minimize CM death . PrimaryIn this review, the intrinsic restraints behind endogenous cardiac regeneration following cardiac injury will be presented, defining five main target processes for therapeutic interventions. Next, cardiac regeneration strategies and limitations, namely cell-based therapies and exogenous administration of bioactive molecules will be discussed. Finally, the biomaterial-based tissue engineering approach will be introduced, focusing on current therapeutic applications of endogenous cardiac regeneration, remaining challenges and future perspectives.The main obstacle on the way to recovery from myocardial injury is the poor endogenous regenerative capacity of the adult mammalian heart. Cardiac regeneration is limited mainly since the majority of adult CMs do not proliferate. Shortly after birth, the cardiac tissue mechanism of growth shifts from hyperplasia to hypertrophy, meaning cell enlargement . A majorConsequently, the adult myocardium responds to MI by two main mechanisms: (a) The formation of a fibrotic scar through a wound healing process and (b) hypertrophic remodeling of the surviving myocardium . These sConsidering the poor intrinsic capability of the adult heart to properly regenerate, key hallmarks of adult heart post-MI must be overcome. Achieving effective cardiac regeneration should include tissue recovery following injury , overturn or attenuation of tissue remodeling and fibrosis, and myocardium renewal via formation of new myocardium and blood vessels. Therefore, the therapeutic strategy could target each or all the following five major processes associated with MI:(a)Cardioprotection – prevention of resident CMs massive death (up to 1 billion cells) post-MI, by inhibition of apoptotic signaling pathways and/or induction of pro-survival signals .(b)Inflammation – in response to ischemia, necrotic CM signaling initiates a pro-inflammatory response, in order to remove remaining cell debris. The second phase includes an anti-inflammatory response, the purpose of which is to allow wound healing and scar formation. The shift between each of these responses is tightly regulated by multiple interactions between cellular myocardium components and the immune system. Manipulation of the time frames of the pro-/anti-inflammatory response after MI by changing the chemokine/cytokine profile or cellular responses may allow proper tissue repair to occur rather than the undesired results of an excessive inflammation, including cell death and scarring .(c)Extracellular matrix (ECM) remodeling and cardiac fibrosis – attenuation of the fibrotic response, meaning ECM composition changes and scar formation, by altering pro-fibrotic signaling pathways. This includes inhibition of matrix metalloproteinases (MMPs) or changes in balance between MMPs and tissue residing inhibitors, in order to slow down scarring in favor of desired tissue healing .(d)Angiogenesis and vascularization – formation of new blood vessels to allow appropriate nutrient supply to the ischemic regions. This could be achieved by induction of pro- angiogenesis signals, including proteins, endothelial cell (EC) recruitment, and altering inflammation and scarring .(e)Cardiomyogenesis – To fully restore cardiac function, it is essential that the infarct zone will be replaced by regenerated myocardium, which could involve proliferation of CPCs/CSCs, proliferation of adult CMs via induction of cell-cycle re-entry, and/or exogenous transplantation of CMs/CPCs .Several approaches to repair or replace injured cardiac tissue were suggested over the last two decades. One of them is the cell-based therapy, namely injection of a cell suspension. The concept is to use an engraftment of cardiac cells to reconstruct the lost muscle tissue. Injection of these suspended cells directly into the myocardium could attenuate myocardial deterioration and dysfunction.This application requires the use of cell sources capable of yielding mature and functional CMs. Furthermore, the transplanted cells should be of autologous origin or immunotolerated by the host. Several cell sources were suggested for this purpose. CPCs/CSCs, assumed to naturally occupy the adult myocardium, are one subpopulation capable of self-renewal and differentiation. Yet, harvesting these cells requires their isolation from a myocardial biopsy, followed by cell expansion, thus limiting their availability for transplantation when treating acute MI .de novo, mature CM production. Both cell types can be differentiated into CMs in vitro  and induced pluripotent stem cells (iPSCs) have been considered the most attractive stem cell types as a source for in vitro , while ain vitro . iPSCs ain vitro .in situ  (i.e. cytokines/chemokines), non-coding RNA (i.e. microRNAs (miRNAs) and small interference RNA), and extracellular vesicles (EVs) (i.e. microvesicles and exosomes).Growth factors are signaling molecules, mostly proteins, which were identified to participate in various cellular processes. For example, insulin-like GF 1 (IGF-1) was previously shown to delay cellular aging and promote cell survival, while also benefit angiogenesis . VasculaNevertheless, the effect of systemic/local administration of GFs was inconsistent in clinical trials, showing no beneficial effects . This coMicroRNAs are short (∼22 nucleotides long), non-coding, single stranded RNAs. Most commonly, these RNA molecules are inhibitors of protein expression, by interacting with specific mRNA in the cytoplasm, subsequently leading to mRNA cleavage or repression of translation . NumerouBesides CM proliferation, miRNAs were shown to affect other target processes associated with MI, including miR-21, which could modulate inflammation processes and reduce CM apoptosis . InhibitEven though miRNAs are normally detected outside the cell in body fluids, circulating miRNAs are at risk to be cleaved by RNases in these biofluids. Moreover, the strong negative charge of soluble nucleic acids results in inadequate cellular uptake . Hence, Extracellular vesicles are emerging, natural carriers that could potentially deliver miRNA. These are small, membrane-enclosed vesicles that are generated and secreted by living cells. One class of EVs are exosomes, classified as double-membraned vesicles that range between 30 and 150 nm in diameter . ExosomeIt has been well documented that exosomes are used for communication between cells ; prominein vitro and in vivo . In general, TE strategies suggest using biomaterials, mostly in combination with bioactive molecules and/or a cell source for regeneration . The ricex vivo cell cultivation, reviewed in The traditional applications of TE destinate biomaterials the role of a three-dimensional scaffold for cell retention . Biomatein situ  by thickening the scar . MechaniBiomaterials are also commonly used for the purpose of drug delivery vehicles . VariousDrug delivery platforms could also be fabricated from biomaterials, as a standalone application or incorporated with delivery vehicles. Biomaterial mechanical properties could be designed and tailored using different fabrication methods and by chemical formulation and modifications . TherefoAll these advantages are already implemented in biomaterial-based strategies meant to improve cardiac regeneration and restore functionality post cardiac injuries. In the following section, four main classes of biomaterial-based approaches will be reviewed: (a) bioactive nano-carriers; (b) hydrogel-assisted cell delivery, (c) cardiac patches, and (d) drug delivery platforms .Many efforts were invested to improve the delivery of regeneration inducing agents, mainly in the means of treatment safety, efficacy, and specificity. Nano-carriers can be generally divided into two classes: nanoparticles (NPs) and natural or bio-inspired biomolecule carriers.Polymer-based NPs could come in many forms, including polymeric chains enveloping therapeutic drugs, polymer–macromolecule conjugates or drugs encapsulated in polymeric micelles . These mNanoparticles were also shown to improve protein bioavailability and decrease their toxicity due to supraphysiological dosage . For exaNucleic acids delivered systemically  are subjected to fast elimination and/or degradation, while also facing difficulties to enter their target cells . Even thThe second class of nano-carriers utilizes natural existing delivery vehicles. One example for such carriers are liposomes, closed bilayer phospholipid systems, inspired by the cellular membrane. Liposomes have been investigated for over half a century, and have been applied in very sophisticated drug delivery systems for proteins and nucleic acids, reviewed in details by Liposomes can be targeted to the infarcted region by conjugation of specific ligands overexpressed in infarcted hearts. Such strategy was demonstrated by Improvement of cell retention is one of the key requirements in cell-based therapies . BiomateHydrogel design criteria for cardiac cell delivery should include three key parameters: (a) mechanical stiffness of injected hydrogel; (b) physical and biochemical microenvironment suitable for encapsulated cells; and (c) duration of cell retention post transplantation. For hydrogels to withstand the mechanical demands required for myocardial applications, their stiffness modulus should be between 20 and 0.1 kPa . On the Nevertheless, the microenvironment provided by the encapsulating matrix is also important in directing cell fate. Biochemical cues, including matrix-anchoring features, have a beneficial effect on cell survival and maturation. In a study aimed at enhancing engraftment of hESC-derived CMs, researchers developed a hydrogel system composed of self-assembling peptides, incorporated with RGD residue. This hydrogel not only increased cell retention in the infarcted heart, it also induced transplanted cells’ maturation and integration with the host, evident by expression of mature phenotype and formation of gap junctions with host CMs .The duration of cell survival post transplantation depends on the mechanism by which the delivered cells promote regeneration. If cell transplantation aims to replace damaged tissue , the degradation profile should allow cell integration into host myocardium (>10 days). However, if transplanted cells act by a paracrine effect (e.g. stem cells), the biomaterial should support cell survival for enough time to be effective . For exaex vivo and ready for transplant. In the context of cardiac malfunction, such patches could be used to replace large portions of the injured heart  functioning heart tissue, developed ed heart . Many caed heart . Others ed heart . Similared heart .Besides biochemical cues, anisotropic features were also shown to promote better tissue organization . Since bThe advances in cardiac patch research are not limited to the microenvironment scale. Cardiac patch designs have demonstrated improved cellular delivery rates and feasibility to achieve a clinically relevant cardiac graft in means of size and function . 3D bio-ex vivo. After application of mechanical and electrical stimuli, iPSC-derived CMs were successfully forced to maturation and increased tissue contractility (Other studies offer the use of exogenous stimuli to improve cardiac maturation and tissue organization actility . Anotheractility .®) , the benefits of a cardiac patch are not limited to cellular components. To date, the most investigated biomaterial used for acellular patches is decellularized ECM. Studies conducted in small  and larg®) . CorMatrribution . Anotherribution . Using aribution , the auxribution . FurtherThe successful implementation of cardiac patches as a therapeutic strategy still faces several hurdles. In order to truly restore cardiac function, the cardiac patches must assimilate with the surrounding myocardium at three levels: physical and biochemical continuity, electrophysiological communication, and nutrient supply .Even though cardiac patches improve cell viability and retention, cells engrafted through such constructs or through intracardiac injection could still provoke an immunogenic response, which ultimately will lead to allograft rejection . In addiIt is also mandatory that designed scaffolds would be accessible for cell migration from areas close to the infarcted zones and allow the formation of blood vessels and nerves . Later, To date, grafts still present inferior functionality, mainly in action potential conductivity . Moreovein vivo -stimulated gold nanowires incorporated within the scaffold, engineered tissue was positioned on the myocardium and successfully attached . AnotherPlatforms of controlled, sustained release are required for applications demanding local, time adjusted, and temporary delivery of bioactive molecules. Polymeric materials, capable of forming 2D and 3D matrices, have been superior candidates for this purpose for several decades . Since ein situ. They developed an injectable hydrogel, based on high-affinity interactions between two oligosaccharides, modified with HA. This hydrogel system was capable of binding cholesterol with high affinity. For the application, miR-302 mimic, an identified CM proliferating inducer, was conjugated to cholesterol and mixed within the hydrogel. The resulting hydrogel exhibited a slow, sustained release profile over 3 weeks, thus demonstrating the potential to induce cardiac proliferation in the relatively long term. Indeed, they were able to show significant clonal expansion of CMs, following miR-302 releasing hydrogel injection into infarcted hearts of Confetti mice . This trial was conducted in a randomized, double-blind, controlled setup, treating 303 patients worldwide. The interventional procedure included the injection of BCM into the infarct-related artery, 2–5 days after primary PCI. Safety endpoints for this research show no significant difference from saline injections; however, the BCM treatment did not reduce LV remodeling or major cardiovascular events after a 6-month follow-up. Among the reasons for this observation, the researchers specified the large infarct sizes selected (around 30% of LV area), in which remodeling could not possibly be prevented ], was tested for its safety and effectiveness for prevention of left ventricular remodeling . Algisyl-LVRTM was tested for its safety and efficacy in two separate clinical trials: One aimed to quantify its effect when combined with coronary artery bypass grafting  and the second its employment as a method of left ventricular augmentation and restoration to treat patients with advanced chronic HF . In both trials the treatment included an open-heart procedure, followed by 10–15 implant injections into the left ventricular heart muscle. The first clinical trial showed remarkable improvement in cardiac function, including elevated ejection fraction (from 32 ± 8 to 47 ± 17% after 3 months), decreased end-systolic and diastolic volumes, and an increase in average wall thickness compared with control saline injections  compared to control. However, these results should be considered with caution, as this trial was subjected to bias due to lack of blinding for the assignment of patients to the surgical procedure , an acellular, porcine-cardiac ECM hydrogel, was also examined in a recently published phase I clinical trial . In this study, researchers evaluated the safety and feasibility of VentriGelTM. The hydrogel was delivered trans-endocardially within a time window between 60 days to 3 years since the first, large ST elevation MI. The outcomes of this first-in-man trial highlighted the safety and feasibility of this treatment, while also showing improvement in exercise capacity examined by a 6-min walk test, even though this study was not designed to test effectiveness of treatment , claimed to promote endogenous cardiac regeneration. Pre-clinical studies with CorMatrix® patches for epicardial infarct repair in a pig model supported this claim, presenting neovascularization in the interface between the infarct and the patch . The fibrin cardiac patch, 20 cm2 in size seeded with ex vivo differentiated cells, was inserted inside a “pocket” under the pericardium. The results of this trial mostly demonstrated the capability to produce highly purified hESC-derived cardiac progenitor cells, without evidence of tumor formation or arrhythmias , and perform as a platform for sustained drug delivery, achieving cardiac regeneration based on the paracrine effect hypothesis. The common principle behind the use of biomaterials is their ability to function as potential mediators between the therapeutic agents and their target, while also having beneficial influence on their own.Biomaterial-based strategies offer a wide range of solutions and additives to various cardiac regeneration therapeutic approaches, making them more and more effective and clinically relevant. Biomaterials may be utilized as a vehicle for efficient delivery of regeneration-inducing small molecules and/or cells, to act as matrix guiding cell maturation (Even though biomaterials were already tested in clinical trials for their safety, showing encouraging results and implying improvement in cardiac function, there are still some findings in pre-clinical and clinical trials that should not be overlooked. The most important issue regards foreign body response of the host to biomaterials used as medical devices. An adverse immunogenic response is common to all the biomaterial applications discussed in this review. In general, when a biomaterial, either natural or synthetic, is in contact with host tissue, it induces a response of the innate immune system, and later the adaptive immune system. Degradation products of implanted biomaterials also activate immune system components. The development of an excessive inflammatory response might severely impair the efficacy of biomaterial applications, since the endpoint of this process is fibrotic encapsulation of the device, thus minimizing its surface interplay with the host tissue and if the device is a drug delivery system, the encapsulation would affect the release profile of the drug from the device . TherefoEven though biomaterials are already established members in many therapeutic approaches for cardiovascular diseases, such applications have not yet reached their full potential, as there is still more room for improvements in means of mechanical stability, tolerance to immunogenic host responses, and proper integration and functional improvement with biomaterial applications. For example, the greatest challenge cardiac patches are still facing is associated with their assimilation with host myocardium. Based on the success of biomaterials to perform as drug delivery platforms and construct a highly sophisticated cardiac patch design, it is also possible that biomaterials could be the answer for that issue as well, by combining the two. For instance, incorporation of a biomaterial-based drug delivery system within a fully developed cardiac patch, acting simultaneously to treat the harmful consequences of MI while also having the potential to restore cardiac function by improving integration with the remaining, healthy cardiac tissue. Since none of the applications can fully regenerate an entire new muscle by itself, this combination could have a synergistic effect on cardiac regeneration.AB wrote the manuscript with inputs from SC.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.