To review existing publications using Household Consumption and Expenditure Survey (HCES) data to estimate household dietary nutrient supply to (1) describe scope of available literature, (2) identify the metrics reported and parameters used to construct these metrics, (3) summarise comparisons between estimates derived from HCES and individual dietary assessment data and (4) explore the demographic and socio-economic sub-groups used to characterise risks of nutrient inadequacy.This study is a systematic review of publications identified from online databases published between 2000 to 2019 that used HCES food consumption data to estimate household dietary nutrient supply. Further publications were identified by ‘snowballing’ the references of included database-identified publications.Publications using data from low- and lower-middle income countries.n 35), apparent nutrient intake per capita per day (n 24) and nutrient density (n 5). Nutrient intakes were generally overestimated using HCES food consumption data, with several studies finding sizeable discrepancies compared with intake estimates based on individual dietary assessment methods. Sub-group analyses predominantly focused on measuring variation in household dietary nutrient supply according to socio-economic position and geography.In total, fifty-eight publications were included. Three metrics were reported that characterised household dietary nutrient supply: apparent nutrient intake per adult-male equivalent per day (HCES data are increasingly being used to assess diets across populations. More research is needed to inform the development of a framework to guide the use of and qualified interpretation of dietary assessments based on these data. Micronutrient deficiencies continue to burden billions of people worldwide, disproportionately affecting the world’s poorest populations. Poor-quality diets, among other interconnected risk factors, are a main cause of micronutrient deficiencies because individuals do not consume adequate quantities of bioavailable nutrients to meet their physiological requirements. Diet-related risk factors are compounded by other systemic social issues common in poor populations, such as inadequate healthcare, high rates of infection and poor sanitation,5 and a lack of education–8. As highlighted in the 2020 Global Nutrition Report, reducing micronutrient deficiencies will require a coordinated effort between governments, businesses and civil society to address deep inequities that arise from unjust systems and processes, particularly for the world’s most nutritionally vulnerable groups.Vitamins and minerals, also known as micronutrients, are required in small quantities in the diet and are essential for human health,10, estimates of national micronutrient supply in food systems and individual micronutrient intake estimates from food consumption surveys. However, in many contexts, these data require significant time, capacity, expertise and specialist equipment to collect and analyse, meaning few countries routinely collect these data at scale. Household Consumption and Expenditure Surveys (HCESs) can contribute a unique source of nationally representative food acquisition data that are regularly collected in low- and lower-middle income countries. Questions about households’ food consumption and expenditures using a country-specific food item list are commonly integrated into HCESs, and these data can be used to estimate the acquisition and apparent consumption of foods by members of the household.Quantifying and characterising national burdens of micronutrient deficiencies require a combination of data types. These include biomarker assessment in micronutrient surveys–17. While HCES data in some countries have been publicly available since the 1980s, only more recently have data from the household food supply modules of these surveys been used to estimate individual-level micronutrient intake and to inform public health research and decision making. Alongside increased use of HCES food acquisition data have come an interest in assessing the how well these data can proxy for individual dietary assessment data.HCES is a term used to refer to a family of nationally and sub-nationally representative, multicomponent surveys , which are primarily designed to provide data to characterise an array of socio-economic conditions. National HCESs are implemented by national statistical agencies, often with technical assistance from the World Bank’s Living Standards Measurement Study group. In most countries, bar a few exceptions, these data are publicly accessible and can be used for a variety of rapid analyses, for instance, to monitor poverty, measure economic inequality, characterise vulnerability to economic shock, estimate agricultural production, calculate macroeconomic aggregate indicators (e.g. gross domestic product) and construct consumer price indices,20. Due to this, the use of the terms ‘nutrient supply’ at the household level and ‘apparent nutrient intake’ at the individual level are used to reflect the sources of error and imprecision when estimating nutrient intake from HCES compared with other more direct nutritional assessment methods  and food expenditures , some HCESs only collect food expenditure data, which require conversion of monetary units into units of food mass (e.g. grams) before calculating household nutrient supply. In addition, errors may be context specific, as HCES methods vary between countries, introducing a differential bias when making comparisons across populations. Recent reviews and guidelines have identified differences between HCES questionnaire designs from different countries, with the authors calling for analyses to evaluate the effect of these differences on dietary nutrient supply estimates. Subsequent analyses have reported potential effects due to the following: recall period length (7–30 d), measuring foods consumed away from home, food acquisition compared with consumption and length and composition of food item lists (50–300 items).HCES data are subject to error when used to estimate individual-level food consumption, which raises challenges for their use in estimating nutrient intakesds Table . SourcesWhat is the scope of the existing literature?What metrics have been used to estimate nutrient and energy supply/apparent intake and nutrient adequacy from HCES data and how do those estimates compare across metrics?How do HCES-derived estimates of apparent nutrient and energy intakes compare with those estimated using individual-level dietary assessment methods? Do results differ by age group ?What types of sub-group comparative analyses have been conducted using nutrient and energy supply/apparent intake estimates from HCES data?Despite these potential limitations, HCESs remain a source of information on what people eat and there is an expanding literature of studies that use HCES to estimate dietary micronutrient supplies and risks of deficiency. Studies have employed a variety of different metrics to report estimates of dietary nutrient supply/apparent nutrient intake and the prevalence of inadequacy, each requiring specific interpretation. This systematic review aims to identify and describe existing publications using HCES data to estimate nutrient supply/apparent nutrient intake in order to document current practices as they relate to the analysis of HCES food consumption data, summarise results of publications that aimed to validate the use of HCES consumption data to estimate nutrient supply/apparent nutrient intake and provide insights into how these estimates can identify sub-groups at heightened risk for micronutrient deficiencies from dietary inadequacy. This analysis addresses the following questions:. The study protocol is provided in Appendix 1 and was registered with the PROSPERO international database for systematic reviews (ref. 223 928).We conducted a systematic review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelineset al.. Where HCES search terms returned a large number of results (> 1000), secondary search terms were used to describe the food consumption module of the HCES questionnaire . The search terms for all databases used in this review are included in Appendix 2. Second, the reference list of all included publications identified through the database search were systematically searched to identify additional papers not identified by the database search. Titles and abstracts of all returned literature were screened to identify analyses using the food consumption module of the HCES, where positive screens were included for full-text review.A two-step procedure was used to identify and screen the available literature. First, fourteen public databases were systematically searched by one author in the domains of public health , agriculture and food systems , economics (e.g. EconLit) and general academia . The primary search terms were the different HCES name variations in both English and French as listed by Fiedler  and (2) estimated household nutrient supply or apparent intake of nutrients or energy using data from the HCES food consumption and/or expenditure module. Literature was excluded if it (1) was written in a language other than English or French or (2) was published before the year 2000. Any disagreements between the two co-authors about whether to include a publication were resolved through discussion. Data were managed using Mendeley Desktop .Literature selected by the identification and screening procedure underwent a full-text review for inclusion into this study independently by two authors. Literature was included if it: (1) used HCES data (or other household food consumption data using an HCES questionnaire format) from a low- or lower-middle-income country3. In brief, for Question 1, extracted data included the country/year the HCES was implemented, the nutrients analysed, recall period, methods of processing the HCES data and food composition data used. For Question 2, key information included the reported nutrient metric, parameters used for estimating energy requirements and reference values used to define inadequacy. For Question 3, key information included the individual dietary assessment method used if HCES-derived apparent intake estimates were compared with individual-level nutrient intake estimates, differences in nutrient intake and apparent nutrient intake estimates and disaggregation by age group if reported. For Question 4, we used the PROGRESS+ framework to guide extraction of information describing stratification by social determinants of diets. This framework, which captures place of residence, race/ethnicity/culture/language, occupation, gender/sex, religion, education, socioeconomic status and social capital, can be used to apply an equity lens when conducting public health research.Extraction of information from each publication was archived for comparison in Microsoft Excel  by one author. A complete list of all categories and extracted information is provided in Appendix n 48) or by snowballing (n 10) , Malawi (n 9 publications), India (n 6 publications) and Uganda (n 6 publications). Household dietary energy supply was reported by 83 % (n 48) of publications, where 33 % (n 19) reported only dietary energy supply without reporting nutrients. Of the publications that did report nutrient supply/apparent intake, estimates covered twenty different nutrients , vitamin A (n 32 publications) and Zn (n 27 publications). The number of publications per year increased substantially after 2012  of publications, whereas 41 % (n 24) used a number of other verbs to report the quantity of food in the survey questionnaire . More than half of the publications (n 36) used nationally specific food composition tables to estimate nutrient or energy content of foods. In countries where nationally specific food composition tables either did not exist or had missing values, data were drawn from food composition tables of neighbouring countries or for the broader region  or from food composition values of US food items compiled by the US Department of Agriculture or other international food composition databases . Steps taken to clean and process HCES data varied by country due to differences in survey design, but conversion of food item quantities from local units  into standard units (e.g. kilograms), adjustments for edible portions of foods, adjustment for cooking yields and adjustment of outliers were most frequently reported. However, many studies did not provide sufficiently detailed descriptions of methods to make the study independently repeatable.Characteristics of food consumption data used in the included publications are provided in Supplemental Table . All studies using the AME approach assumed all household members had moderate or moderate-high physical activity levels when estimating individual energy requirements. Second, daily apparent nutrient intake per capita was used in 41 % (24/58) of publications. Per capita adjustment assumes that nutrient supplies are equally distributed among all members within the household . Third, the nutrient density of household diets, or nutrient supply per energy supply, was used in 9 % (5/58) of publications.Three nutrient supply metrics were identified in the included publications Fig. . First, per capita and AME metrics were used to estimate the population’s adequacy of dietary nutrient or energy supply by comparing apparent intake to a reference nutrient intake . Of these publications, twenty-seven focused on micronutrients, where apparent intake estimates were compared with the Estimated Average Requirement , the Recommended Nutrient Intake  and/or the Recommended Daily Allowance  for each micronutrient of interest. Among the twenty-three publications that focused on dietary energy, 57 % (13/23) compared household energy supply to the household’s total energy requirements calculated as the sum of the individual requirements of all household members, and 43 % (10/23) compared individual-level apparent energy intake to a pre-defined energy requirement threshold for an adult . No publications compared nutrient density estimates with nutrient density reference values, such as the critical nutrient density as defined by Vossenaar et al.. Of all the publications comparing nutrient or energy supply to a dietary requirement to estimate dietary inadequacy, 13 % (5/39) included additional nutrient or energy requirements necessary for a pregnancy in the household and 23 % (9/39) included additional requirements necessary for women during lactation.When evaluating inadequacy, –35, 24-h dietary recall of all household members estimated by the meal preparer,36 or observed-weighed food records of specific demographics within the household. Among these publications, four compared nutrient intake/apparent intake estimates from the same households or individuals within these households,33,36 and two compared nutrient intake/apparent intake estimates using different survey populations from the same country,35. Two publications used the same data from the Bangladesh Integrated Household Survey,36.For publications reporting apparent nutrient intake using the AME approach, six compared their results to individual-level estimates based on a variety of different types of individual-level dietary intake data. This included individual 24-h dietary recalls of specific demographics within the household ,33,36 or collected prospectively over 24 h . v. corresponding 24-h dietary recall data in Uganda and found no statistically significant difference in median nutrient density for the fourteen nutrients assessed with the exception of folate , vitamin B12 (10 % to 93 % difference) and vitamin C (19 % to 30 % difference). In this analysis, nutrient densities estimated from HCES data were consistently lower than nutrient densities estimated from corresponding 24-h dietary recall data for almost all nutrients.One publication compared differences in the nutrient density metric when applied to HCES data et al., included total household income, household expenditure, durable asset ownership, level of educational attainment and occupation. Geographic characteristics generally reflected HCES sampling methodology, where HCESs are designed to be representative of geopolitical administrative regions (n 30) and urban v. rural settings (n 29). A number of publications stratified nutrient supply estimates by individual-level characteristics of members within the household including sex (n 21) and age (n 21); however; the definition of age and sex of the household varied. For instance, analyses using only household-level data either used individual characteristics of the ‘head of household’ as a proxy for the entire household  or divided household nutrients according to energy requirements of individuals as a proxy for apparent individual intake of household members . Some HCES data included individual-level food consumption data of household members which enabled the calculation of nutrient intake specific to the sex (n 2) and age group (n 1).Most publications included in this review stratified nutrient supply estimates by one or more sub-groups of interest. The stratification of nutrient supply by sub-group characteristics was more frequent for indicators of socio-economic position and geography than for socio-cultural demographic or intra-household characteristics Fig. . Indicatper capita approach where household nutrient supply is divided evenly among constituent members and (3) nutrient density of household diets. Each of these metrics has strengths and limitations when estimating the adequacy of nutrient supply and identifying vulnerable populations at risk of deficiency. While other reviews have analysed applications of HCES data for broader food security indicators, this is the first review to summarise the use of HCES data to estimate nutrient supply and evaluate adequacy, an increasingly common practice accepted by the nutrition community.This systematic review found that the use of HCES data to quantify, characterise and evaluate the adequacy of household nutrient supply across populations is being increasingly represented in published literature. Three primary metrics have been used to report dietary nutrient supply. These are (1) apparent nutrient intake using the AME approach to allocate household nutrient supply among constituent members, (2) apparent nutrient intake using the  using one of two approaches: per capita or AME. While the use of the per capita approach is simpler, it does not account for any difference in nutrient intakes between household members, which will skew estimates between households of different composition, especially those with large families. Following the publication of a paper series in 2012,31 that described the methods to distribute nutrients according to AME energy requirement and its application to household micronutrient supply, an increasing number of publications have estimated dietary supply using the AME approach. The major assumption underlying this approach is that foods consumed by the household are distributed among all household members in proportion to each member’s energy requirements, but the method requires data describing individual household members’ age, sex, weight, physical activity level, pregnancy status and lactation status. HCESs often collect data on individual household members’ age and sex, but data on other parameters affecting individual energy requirements are often not available and require simplifying assumptions to calculate the AME factors . With 57 % of publications identified in this review estimating apparent nutrient intake using the AME approach, despite a dependency on these assumptions, the AME approach is becoming standard practice.Households differ in size and composition across and within countries and regions, so the majority of publications attempted to convert nutrient supply estimated at the household level to estimates of individual-level apparent intake. Poor agreement for young children was likely influenced by the inability of HCES to capture the nutrient contributions of breastmilk and the distribution of nutrients from foods consumed only by young children to the entire household ; none of the publications identified by this review made adjustments for these nutrient contributions for young children. Both household- and individual-level recalls are subject to measurement error, but the size of the difference for young children compared with other age groups suggests that HCES food consumption data are often not particularly accurate for young children. Using HCES may lead to systematic overestimation of nutrient intakes for infants and young children when adjustments are not made for breastmilk intakes and subsequent estimates of apparent micronutrient intake and inadequacy should be interpreted with caution. These differences, coupled with the increasing availability and use of HCES data for describing and assessing the micronutrient adequacy of diets across populations, suggest that more research is necessary to inform the development of a structured framework to guide the use and nuanced interpretation of HCES nutrient supply data that reflect its limitations.Differences between estimates of apparent nutrient intake (using HCES data with the AME approach) and nutrient intakes  reported in the literature ranged between 12 % and 72 % and were greater for young children based on results by Karageorgou et al.. HCESs are conducted regularly, and data are typically made publicly available. HCESs are typically based on 7- to 30-d recall periods that pose some advantages compared with a single 24-h dietary recall estimates when examining associations between food consumption and determinants affecting diets as HCESs account for day-to-day variation that may attenuate associations. In addition, large-scale individual-level dietary intake data are not routinely collected or available in many settings, meaning that the alternative to HCES are national-level Food Balance Sheets, which, among other limitations, lack sub-national resolution.The use of HCESs for nutrient analysis has a number of strengths. The HCES food consumption module is considerably less laborious and less expensive to conduct than national scale individual-level dietary surveysv. HCES with the AME approach, potentially driven by numerous factors including food consumption patterns,33,35 and differences in diet between sex and age groups,44. This presents challenges when conducting individual-level sub-group analyses using HCES data and isolating certain sub-groups for analysis may pose problems when using HCES data, considering food consumption is reported at the household level by one member, generally the head female. Foods regularly consumed away from home by other family members may be systematically under-reported, although the collection of household food supply data is evolving to adjust for foods consumed away from home, especially in urban contexts,24. Second, it is unknown how individual model parameters used in the AME approach, such as physical activity level and body weights, might affect apparent nutrient intake estimates, as few publications reported sensitivity analyses evaluating this. Additional research exploring the sensitivity of AME factors to individual parameter assumptions would improve general understanding of how much these broad population assumptions impact inadequacy estimates. Third, HCES data quality can vary between countries due to differences in HCES questionnaire design, leading to varying availability of important demographic variables, such as pregnancy status. These data are important to characterise household member’s nutrient requirements, and the lack of these data increases uncertainty in estimates of apparent intake and inadequacy.While HCES data can be used to estimate household-level nutrient supply, HCES data do not provide information about the distribution of foods consumed among household members. A majority of studies used the AME approach to convert from household-level to individual-level estimates; however, the following points are important to consider. First, the literature demonstrated differences between nutrient intake/apparent intake estimated using individual-level dietary data . Yet contrasting results were found in Ethiopia, where groups hypothesised to be more ‘vulnerable’ (i.e. women and children) were found using 24-h dietary recall data to consume a greater share of energy and protein in relation to their dietary requirements than their male and adult counterparts . While differences in these results may be due to cultural differences between countries, understanding general uncertainty in intrahousehold allocation of food is important for sub-groups who are often the focus of nutrition policy, such as pregnant or lactating women, women of reproductive age, infants and children. Due to this, individual-level surveys  will remain important when characterising the micronutrient status of these sub-groups. HCES data do, however, serve as a potential resource to identify dietary nutrient shortfalls putting populations at risk of deficiency, and this information may guide the design of individual-level surveys. For example, HCES data can be used to highlight regional and socio-economic variation and seasonal fluctuations in dietary nutrient supply, which can be useful when developing sampling units for future individual-level surveys.Uncertainty in how food is allocated within households and if intrahousehold allocation factors can be generalised across different contexts remains a key limitation in the use of HCES data to estimate individual-level apparent nutrient intake. Evidence from Bangladesh suggests that household heads  received proportionally more dietary energy compared with their spouses and children than equitable intra-household food allocation using the AME approach would suggest, which must be addressed by policies intended to improve equity in the broader food system. This review demonstrates that estimating nutrient supply from HCES data may help identify populations at risk of nutrient deficiencies due to poor diets. The literature identified in this review used HCES data to disaggregate nutrient supply results by well-documented social factors affecting diets, such as wealth,48,49, education,51, geography,52 and ruralness,53,54. HCESs collect microdata describing a wide range of socio-economic and geographic determinants of diets, which provides the opportunity to explore the mechanisms driving these associations in great depth. Considering the original intention of HCESs was to provide microdata to characterise poverty and social welfare in low- and lower-middle income countries, there exist a number of potential opportunities to combine other variables already collected in these surveys with nutrition metrics to identify vulnerable populations and integrate this information into the development of nutrition policies that promote equity. Additionally, characterising these high-risk groups from information provided by HCESs can help guide nutrition interventions (e.g. do high-risk populations routinely purchase staple foods or food vehicles suitable for fortification?). To better address equity in nutrition policy, there lies potential opportunities for using HCES data to identify and target vulnerable populations disproportionally affected by key socio-economic and geographic determinants affecting diets. Further research is required to identify indicators of social determinants of poor-quality diets from HCESs and their relation to the specific mechanisms that affect nutrient supply, to inform consistent applications to designing and monitoring nutrition programmes and policy.Diets in low- and lower-middle income countries are affected by a myriad of social determinantsThe growing evidence base guiding the use of HCES data to estimate nutrient supply has highlighted the potential opportunities HCES data have in informing food systems interventions. As this practice becomes more common, consistency in processing HCES data and reporting results will be important for comparability between findings. While estimating nutrient supply from HCES data will always require time and effort, detailed standard operating procedures, repositories for processed data and descriptive methods, access to standard weight/measure conversions and open-sourced data processing scripts could encourage further analyses, improve consistency between studies and facilitate research collaboration. In addition, to further understand what insights and to what degree of certainty HCES dietary analyses can contribute to understanding the adequacy of diets across populations, more research is needed to compare HCES estimates of nutrient adequacy derived from nutrient density compared with the AME approach, as well as to adequacy estimates from individual 24-h dietary recall data in various country contexts.This systematic review had a number of strengths. The screening procedure was exhaustive, including a broad database search and snowballing. This resulted in a wide range of publications from peer-reviewed journals, working papers from multi-national institutions and other grey literature. Our study also extracted data describing the process of transforming HCES data to estimate nutrient supply and social determinants that may affect diets. The current study, however, had limitations. There were very few publications that applied the nutrient density approach, making it difficult to draw conclusions regarding potential variation in assumptions and applications of the metric. In addition, while the screening of results from the database search was independently undertaken by two individuals, the review of identified publications during screening was only conducted by one.Estimates of nutrient supply and dietary quality using HCES data can play an important role in micronutrient surveillance and the design of interventions to tackle micronutrient deficiencies. However, HCES remain under-exploited for the identification of vulnerable populations at greatest risk of micronutrient deficiencies and for the design of effective and equitable micronutrient interventions. Further research is required to understand the implications of key methodological decisions when building models using HCES data in an effort to inform national nutrition policy.


This Special Issue, entitled “Personalized Medicine for Liver Disease: From Molecular Mechanisms to Potential Targeted Therapies”, includes 11 publications from colleagues working on various liver diseases including non-alcoholic fatty liver disease (NAFLD), alcoholic liver disease (ALD), hepatocellular carcinoma (HCC), primary biliary cholangitis (PBC), as well as various treatment modalities including pharmacotherapies and liver transplantation. Fatty liver disease (FLD) has been traditionally classified as either non-alcoholic fatty liver disease (NAFLD) or alcoholic liver disease (ALD). As critical inducers of hepatic steatosis, both high-fat diets and chronic alcohol consumption are profoundly associated with the recent burden of metabolic syndromes. In Fact, Kim et al. show that concomitant intake of dietary fat and alcohol can work synergistically to worsen liver injury . With thGiven the prevalence of NAFLD today, its heterogeneous presentation with multiple possible comorbidities, and the variety of therapeutic treatment options, it is critical to stratify patients and tailor treatments to each case. In this Special Issue, Finotti et al. provide a concise but detailed review of NAFLD pathogenesis and the pharmacological and surgical treatment options .The importance of stratifying and tailoring treatments is further strengthened in a retrospective study looking at clinical lab parameters before and during ursodeoxycholic acid (UCDA) treatment of patients with primary biliary cholangitis (PBC) . UDCA isHepatocellular carcinoma (HCC) remains a major health problem worldwide with a continuously increasing prevalence. Despite the introduction of targeted therapies such as the multi-kinase inhibitor sorafenib, treatment outcomes are not encouraging. The prognosis of advanced HCC is still dismal, emphasizing the need for novel effective treatments. Apart from the various risk factors that predispose to the development of HCC, epigenetic factors also play functional roles in tumorigenesis. Histone deacetylases (HDAC) are enzymes that regulate critical cellular functions via acetylation of histone and non-histone protein targets. Considering that HDAC activity is elevated in HCC, treatment strategies with HDAC inhibitors showed some promise. Nevertheless, HCC is a prominent multifactorial disease with numerous etiologies making broad-spectrum chemotherapies and treatments unreliable, thereby necessitating precision therapies. Bioinformatics and multi-omic approaches that identify biomarkers and therapeutic targets such as stathmin-1, HGF, and miR-29a may be the key to realizing true therapeutic results with precision therapies in specific subclasses of HCC ,6,7. WanmicroRNAs (miRNA) are known to widely participate in the regulation of expression of oncogenes and tumor suppressor genes, directly and epigenetically, and play a major role in cancer progression. Regarding HCC, miR-29a is believed to be hepatoprotective, and Yang et al. give a detailed review of its molecular mechanisms and the diagnostic and prognostic value of its expression and activity . Liver transplantation has become much more commonplace as a treatment option for a variety of liver diseases including non-alcoholic fatty liver disease and hepatocellular carcinoma, but the procedure is fraught with difficulties due to a shortage of transplantable organs, the need for immunosuppressive drugs, and post-surgical complications within the liver and other organ systems, all of which necessitate identifying the best patients to transplant. The high demand for liver transplantation has led to the development of living-donor partial liver transplants, as well as the transplantation of isolated liver cells (hepatocytes). Cell transplantation requires the isolation of hepatocytes from an intact organ and subsequent purification steps, which are subject to the risk of contamination and increased damage due to ischemia. Chen et al. evaluate the use of a semi-automated closed-circuit system “Cell Saver Elite” in isolation of transplantable cells . AlthougNevertheless, the shortage of transplantable organs makes identifying the patients most in need of a life-saving transplant critical. Acute chronic liver failure can arise from a variety of confounding insults in patients with underlying cirrhosis. The heterogeneity in etiology leads to variable disease courses and has hampered accurate diagnosis and prognosis. Lu et al. investigate dynamic changes in clinical markers, especially within the first 2 weeks of clinical admission, that aid in predicting poor prognosis and indicate the necessitation of fast-tracking therapeutic interventions or transplant prioritization .Immunosuppression is required post-liver transplantation to ensure patient and graft survival, and tacrolimus is the most widely used immunosuppressant drug post-transplant. However, blood concentrations post-transplant must be closely monitored to minimize toxic effects and infections. Hsiao et al. reveal that long-term survival post-transplant was optimum when tacrolimus levels were at or above 4.6 ng/mL . Post-liver transplant acute kidney injury is a prevalent complication that can lead to chronic kidney injury and even death. Several risk factors have been associated including high BMI, low albumin levels, poor graft quality, prior kidney dysfunction, and inflammation. Antithrombin III has anticoagulation and anti-inflammatory properties and in a retrospective study, Kim et al. identify ATIII levels as a predictive factor in the incidence of post-transplant acute kidney injury . Liver diseases such as NAFLD, ALD, HCC, and PBC may be lumped into a classification of a particular disease, but each individual case is in and of itself unique and therefore must be treated as such. The future of medicine is tailored, targeted, precision therapeutics personalized for each patient.


In the development of therapeutic proteins, analytical assessment of structural stability and integrity constitutes an important activity, as protein stability and integrity influence drug efficacy, and ultimately patient safety. Existing analytical methodologies solely rely on relative changes in optical properties such as fluorescence or scattering upon thermal or chemical perturbation. Here, we present an absolute analytical method for assessing protein stability, structure, and unfolding utilizing Taylor dispersion analysis (TDA) and LED-UV fluorescence detection. The developed TDA method measures the change in size (hydrodynamic radius) and intrinsic fluorescence of a protein during in-line denaturation with guanidinium hydrochloride (GuHCl). The conformational stability of the therapeutic antibody adalimumab and human serum albumin were characterized as a function of pH. The simple workflow and low sample consumption (40 ng protein per data point) of the methodology make it ideal for assessing protein characteristics related to stability in early drug development or when having a scarce amount of sample available. Tm) or concentration (Cm), leading to equal fractions of native and denatured protein  is the denaturant concentration. The resulting unfolding curves were fitted to the unfolding model (derived in the Cm) was determined from:Subsequently, the denaturation midpoint (Rh), intrinsic fluorescence, and stability . We envision that the developed method can find applications within the early drug-development phase, or when only scarce amounts of material are available for analysis. This work presented an optimized protocol for assessing protein stability towards unfolding, utilizing TDA employing UV-LED fluorescence detection. The TDA method only requires 40 ng of protein per data point, takes 6 min per measurement (corresponding to ~80 min for a full titration curve), has a simple workflow, is fully automated, and is conducted under native conditions in-solution. Furthermore, in contrast to existing methodologies, multiple readouts are obtained in a single-assay format, including structural features (


Neurodegenerative disorders have been extremely challenging to treat with traditional drug-based approaches and curative therapies are lacking. Given continued progress in stem cell technologies, cell replacement strategies have emerged as concrete and potentially viable therapeutic options. In this review, we cover advances in methods used to differentiate human pluripotent stem cells into several highly specialized types of neurons, including cholinergic, dopaminergic, and motor neurons, and the potential clinical applications of stem cell-derived neurons for common neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, ataxia, and amyotrophic lateral sclerosis. Additionally, we summarize cellular differentiation techniques for generating glial cell populations, including oligodendrocytes and microglia, and their conceivable translational roles in supporting neural function. Clinical trials of specific cell replacement therapies in the nervous system are already underway, and several attractive avenues in regenerative medicine warrant further investigation. Age—it’s the one mountain you can’t overcome, and as the average life expectancy extends into the eighth decade, neurodegenerative diseases are becoming increasingly prevalent. Despite their increasing incidence, preventative or disease-modifying strategies for these emotionally and financially draining disorders are lacking. Due to the fundamental lack of regeneration within the central nervous system (CNS), neurodegenerative diseases relentlessly attacking discrete populations of neurons are excellent candidates for cell replacement therapies. Here, we review the current prospects on the application of pluripotent stem cell-derived cell types for the treatment of neurodegenerative disease.Pluripotent stem cells provide a uniquely scalable source of functional somatic cells, including cells of the CNS, that can potentially replace damaged or diseased tissues. Although prospects for using stem cell derivatives seemed fanciful at the start of the millennium, approximately two decades later several clinical trials using cellular products of pluripotent stem cells are underway or about to reach the clinic . This prin vitro stem cell-derived cells of the neural  is characterized by the degeneration of several neuronal subtypes, most notably the dopaminergic neurons of the substantia nigra pars compacta (SNpc), located in the ventral midbrain. These neurons project to the dorsal striatum of the basal ganglia and function in motor control, and the loss of these neurons contributes to the movement symptoms observed in the initial stages of PD. Fetal-derived dopamine neurons have had promising clinical benefits for PD patients . To avoiFrom the initial basic science studies that furnished the directed differentiation strategies of dopaminergic neurons to their large-scale production in GMP-facilities for transplantation studies, the research program for midbrain dopamine neurons has made excellent progress. Several groups developed methods to produce FOXA2/LMX1A-positive midbrain neurons capable of releasing dopamine . For exaNeurological conditions involving both memory loss and impaired judgment are classified as dementia . AlzheimOne of the earliest cell types perturbed by AD is the basal forebrain cholinergic neuron (BFCN). These neurons, which arise from the median ganglionic eminence (MGE) during development, are responsible for various aspects of cognition including learning, memory, and attention. At the molecular level, BFCNs are primary cholinergic neurons and innervate the cerebral cortex, hippocampus, and amygdala, and play critical roles in processing information related to cognitive function . TransplSeveral methods to differentiate pluripotent stem cells into BFCNs have been described . TypicalCerebral cortex development consists of three major processes: cell proliferation, neuronal migration, and cortical organization into multiple well-defined layers. The cerebral cortex contains two major classes of neurons; a majority population of excitatory glutamatergic projections neurons that arise during development from the dorsal telencephalon, which is the developmental precursor to the cerebral cortex, and a minor population of inhibitory interneurons. Through successive waves of neurogenesis, these neurons generate the six layers of the neocortex, which can be further functionally divided based on specific patterns of axonal output and dendritic input. Due to their abundance and ability to project long distances, cortical pyramidal neurons, named for their shape, are able to integrate and send information across the entire nervous system .The production of pyramidal neurons from pluripotent stem cells is considered to be a default differentiation fate because it occurs in the absence of exogenous signaling factors . InhibitIn both the brain and spinal cord, gamma-aminobutyric acid (GABA)-releasing interneurons are the major class of inhibitory neurons and play crucial roles in modulating neural circuits. There are many distinct subtypes of interneurons that differ in their synaptic connections, expression of neuropeptides, neurotransmitter machinery, and developmental origin with some immature interneurons having the remarkable ability to migrate and disperse long distances to integrate throughout the CNS . This inSeveral groups have developed directed differentiation approaches for producing interneurons from human pluripotent stem cells . These aComposed of granule and pyramidal neurons, the hippocampus plays a critical role in learning and memory. It is also an area of the brain that deteriorates in AD, additional forms of dementia, and other age-related cognitive declines of distinct etiologies. Interestingly, in addition to the subventricular zone, the dentate gyrus of the hippocampus is a unique site of adult neurogenesis . Therefore, incorporation of immature stem cell-derived neurons into existing neural circuity beyond embryonic development is a hopeful prospect.To generate hippocampal neurons, stem cells are patterned to dorsal forebrain progenitors by inhibiting both branches of the SMAD signaling as well as factors to promote WNT and SHH signaling. Subsequently, WNT3a is applied along with BDNF to drive the neurogenesis of hippocampal granule neurons . InitialHTT gene, resulting in an extended polyglutamine (polyQ) tract within the Huntingtin protein. The progressive loss of neurons and gross atrophy in the neostriatum (caudate nucleus and putamen) disrupts neuronal circuits involving the basal ganglia and leads to gradually worsening motor impairment and, as additional brain regions are affected, significant cognitive and psychiatric symptoms.Huntington’s disease (HD) is caused by a CAG trinucleotide repeat expansion within the coding region of the Medium spiny neurons that reside in the striatum, contribute to the complex circuits that control movement and are particularly vulnerable in HD. During development, these inhibitory neurons arise from the lateral ganglionic eminence (LGE) and are marked by the expression of DARPP32 (dopamine- and cAMP-regulated phosphoprotein Mr∼32 kDa) . The relNumerous groups have validated directed differentiation approaches for producing medium spiny neurons from stem cells . Like thATXN-2 results in SCA2 that can manifest with ataxia, loss of neurological reflexes, and Parkinsonian symptoms. Ataxias can be associated with other inherited disorders. For examples, an autosomal recessively-inherited GAA trinucleotide repeat expansions in FXN, encoding frataxin, cause Friedrich’s ataxia, which is characterized by progressive ataxia, impaired speech, loss of vibratory and proprioceptive sensation due to degeneration of spinal cord neurons and nerve fiber tracts connecting to the cerebellum. There are no effective treatments for these debilitating and often fatal diseases.Spinocerebellar ataxias (SCAs) are a clinically and genetically heterogenous group of neurological disorders associated with impairments in motor coordination due to degeneration of the cerebellum and connected neuronal pathways. Many SCAs are caused by CAG nucleotide repeat expansions within certain genes leading to the production of polyglutamine (polyQ)-containing proteins with putative toxic gain-of-function effects. For instance, an autosomal dominantly-inherited, abnormally long (>33 CAG repeats) trinucleotide repeat expansion within CACNA1A associated with SCA6  and spinal muscular atrophy (SMA). Both diseases involve the progressive loss of motor function, eventually progressing to fatal paralysis. In nearly all (∼97%) of cases of ALS, motor neurons in both the brain and spinal exhibit pathological changes in the cellular localization of the RNA binding protein TDP-43, which include loss of the normal nuclear localization and the formation of cytoplasmic inclusions .Motor neurons represent a diverse group of neuronal subtypes and provide the pivotal link between mind and the animation of the body. Generally, there are two types of motor neurons; upper motor neurons that reside in the frontal cortex and project to lower motor neurons, found in the ventral brainstem and spinal cord, which in turn form synapses with the musculature. Decades of developmental studies and genetic analyses have illuminated the molecular underpinnings of lower motor neuron specification during embryo development  with theLeveraging this knowledge, stem cell scientists developed methods to generate motor neurons from mouse embryonic stem cells by applying retinoic acid (RA) to caudalize the cells toward a spinal cord  identity and activating SHH to ventralize them toward a motor, rather than sensory, identity . SeveralSo far, motor neuron transplant results have been encouraging. For example pioneering transplant studies demonstrate that mES-derived motor neurons injected into tibial nerve of adult mice can form functional NMJs and ameliorate muscle atrophy . Anotherin vitro for cell replacement approaches. Three main types of glia exist in the CNS: astrocytes, oligodendrocytes (OLs), and microglia. In brief, astrocytes are responsible for forming and modulating the blood–brain barrier (BBB) and modifying the chemical microenvironment governing synaptic function. Microglia are the resident immune cells of the CNS that function in synaptic pruning during development, immune surveillance, debris clearance and defense from pathogens. Oligodendrocytes are responsible for myelinating axons in the CNS, thereby maintaining strong electrical connectivity of brain circuitry. Glia have been implicated in almost all neurodegenerative diseases, and their dysfunction in this context are more extensively reviewed elsewhere  while a small subset of them are maintained in a progenitor state. Their great migratory abilities, plasticity and pivotal role in neuronal support render these cells ideal for transplantation studies and replacement therapies.Similar to astrocytes, oligodendrocytes are derived in development after neurogenesis. In both the forebrain and the spinal cord, oligodendroglial progenitor cells (OPCs) are generated from Nkx2.1in vivo  identity by the addition of PDGF-AA. These OPCs can be matured into OLs by various cocktails of small molecules, often containing IGF-1 and T3 . Severalin vivo  or by diin vivo . Protocoin vivo . García-Stem cell-derived OLs hold promise for both demyelinating diseases and spinal cord injury. Multiple sclerosis (MS) is a chronic, autoimmune disease characterized by the loss of myelin and associated oligodendrocytes, often in a remitting and relapsing clinical course that results in gradual neurological decline. MS-iPSC-derived OPCs can myelinate the corpus callosum of immunocompromised hypomyelinated (shiver) mice , offerinUnlike other glial cells, microglia are immune cells not derived from the neuroectoderm but originate from the embryonic yolk sac in early stages of development and then migrate to the neural tube . ChemicaLong term engraftment studies have been rendered difficult by the lack of homology between murine and human CSF1, which is pivotal for long term microglial survival. However, initial studies have shown the feasibility of transplantation of hiPSC-derived iMGLs in humanized mouse models .in vitro (Directed differentiation approaches have evolved considerably since the initial derivation of neurons from human embryonic stem cells . Althougin vitro , openingin vitro . Whetherin vitro disease modeling studies, we have found that co-culture of human neurons with murine glial cells effectively increased neuronal activity, but co-culture with non-human cells is not an ideal strategy for cell replacement therapies. Instead, Gage and colleagues have developed a defined neuronal medium, BrainPhys, which better mimics the environment present in healthy human brains and enhances both spontaneous electrical and synaptic activity of human neurons (It is unclear whether nascent, immature neurons or elaborate, mature neurons will integrate more successfully into a degenerating brain to provide therapeutic benefit. Either way, the ability to control the functional maturation of stem cell-derived neurons would benefit many applications. For  neurons . WhetherThe process of reprogramming adult cells back to the pluripotent state erases many aspects of aging that put vulnerable cells at risk in the first place . AlthougInduced pluripotent stem cell technology marshaled in the possibility of personalized regenerative medicine using therapies based on an individual’s own cells. To this end, investigators in Japan started a clinical trial to treat age-related macular degeneration using autologous transplants, however, the trial was eventually suspended after treating one patient . SeveralDespite recent advances, the overall time to move from the collection of fibroblasts via skin biopsy in the clinic, the reprogramming of fibroblasts into PSCs with completion of appropriate quality controls, to the differentiation of individualized stem cells into a personal population of a specific cell type, such as mature motor neurons, remains extensive, and hence possibly beyond the therapeutic window for rapidly progressive neurodegenerative diseases like ALS. To meet the demands of future clinical applications, state-of-the-art technologies for the cryopreservation of differentiated cell types are being tested to provide a ready to go off-the-shelf product . Indeed,For cell replacement therapies, even rare proliferating cells are especially worrisome because they could ultimately lead to the growth of tumors. Moreover, genomic instability of pluripotent stem cells has long been a concern for the field as aneuploid cells have readily been observed . To idenTo overcome the laborious nature of converting somatic cells into pluripotent stem cells, the New York Stem Cell Foundation has developed an automated platform for the high throughput conversion of skin biopsies into iPS cells . This hiFinally, widely applicable and efficient cell banking methods are needed to meet the demand of cell transplantation therapies. There are ongoing efforts in both Japan and the United States to screen and bank cells for allogeneic transplantations. Estimates from Cellular Dynamics International suggest that top 183 haplotypes could cover 95% of the US population. To gain maximum population coverage and provide social justice , a univeIt’s an incredibly exciting time for stem cell-based regenerative medicine with a number of clinical trials started and more just on the horizon for neurodegenerative diseases, including one for PD . The IntThe demand for neurodegenerative disease therapeutics continues to grow as populations around the globe age. Currently, no pharmacological strategies exist that can significantly alter disease course for neurodegenerative diseases, thus cell replacement therapies remain an attractive avenue of exploration. Although the prospect of using stem cell-derived neurons to treat many of the diseases discussed above remains abstract, the PD clinical trials, grounded on years of fetal transplant studies and animal models with high fidelity, will provide important guideposts as others venture into these uncharted territories. In this review, we highlighted current methodologies for generating therapeutically relevant neuronal and glial cell types. Although directed differentiation strategies for some of these CNS cell types are in their nascent stage, they represent important first steps toward heralding in a new era of cellular therapeutics.JK conceived of the review and drafted the figures. DM drafted the table. All authors drafted the original manuscript and read, edited, and approved the submitted version.


The infiltrative character of supratentorial lower grade glioma makes it possible for eloquent neural pathways to remain within tumoural tissue, which renders complete surgical resection challenging. Neuromodulation-Induced Cortical Prehabilitation (NICP) is intended to reduce the likelihood of premeditated neurologic sequelae that otherwise would have resulted in extensive rehabilitation or permanent injury following surgery. This review aims to conceptualise current approaches involving Repetitive Transcranial Magnetic Stimulation (rTMS-NICP) and extraoperative Direct Cortical Stimulation (eDCS-NICP) for the purposes of inducing cortical reorganisation prior to surgery, with considerations derived from psychiatric, rehabilitative and electrophysiologic findings related to previous reports of prehabilitation. Despite the promise of reduced risk and incidence of neurologic injury in glioma surgery, the current data indicates a broad but compelling possibility of effective cortical prehabilitation relating to perisylvian cortex, though it remains an under-explored investigational tool. Preliminary findings may prove sufficient for the continued investigation of prehabilitation in small-volume lower-grade tumour or epilepsy patients. However, considering the very low number of peer-reviewed case reports, optimal stimulation parameters and duration of therapy necessary to catalyse functional reorganisation remain equivocal. The non-invasive nature and low risk profile of rTMS-NICP may permit larger sample sizes and control groups until such time that eDCS-NICP protocols can be further elucidated. Cerebral plasticity is considered an intrinsic property of the human nervous system, one that is continuously changing as a consequence of all neural activity. In the instance of pathophysiologic processes, intra- and inter-hemispheric interactions may shift over time to promote the establishment of new structural or functional changes . The braHistorically, focal cortical diaschisis is only partially correlated with behavioural changes , contrarIn contemporary clinical practice, it is presumed that cerebral function is organised hodotopically via a series of interconnected meta-networks involving both hemispheres responsible for various cognition, speech, motor, and sensory faculties . Broca’sAdvances in functional neuro-imaging technologies such as task-based and resting-state functional Magnetic Resonance Imaging (rs-fMRI), MEG, nTMS, Diffusion Tensor Imaging Fiber Tracking (DTI-FT) and techniques relating to DCS have contributed to a greater comprehension of this connectomic theory during surgery for intra-axial brain tumours, which inadvertently provides an investigational landscape to uncover how the brain might be capable of reorganising eloquent functional networks with regard to iatrogenic mechanical or ischaemic injury, rehabilitation, disease progression and recently, concepts of cortical “prehabilitation”, which attempts to simulate a virtual lesion involving tumoural or peri-tumoural tissue to induce diaschisis and subsequent cerebral plasticity to avoid or reduce severity of premeditated post-operative deficits.Task-based fMRI has become the dominant modality for functional brain imaging in both the clinical and the research community as a safe and painless clinical investigation tool. It allows for whole-brain coverage, including the ability to examine activity in deep brain structures. Assessment of neural function depends upon the Blood Oxygen Level Dependent (BOLD) signal, which is a surrogate marker of the changing ratios of oxyhemoglobin and deoxyhemoglobin in metabolically active brain regions. fMRI protocols for language assessment are not always reliable in comparison with DCS data , though MEG measures diminutive magnetic fields created by bioelectric currents outside of the head that are generated by neural activity. In contrast to fMRI, MEG does not depend upon surrogate markers and offers excellent temporal resolution (<1 ms) because it directly measures these fields. MEG can be limited by its relative preference for specifically oriented field sources, as it primarily senses the tangential currents in the brain closer to the surface. Studies comparing pre-operative MEG with intraoperative DCS are compelling for motor regions ,21 as weTMS applies a brief pulse of high-strength magnetic field over the scalp which passes through the skull and induces an electrical current in the underlying brain region , based oDTI-FT uses the direction of water diffusion parallel to white matter tracts as a surrogate marker for visualisation, which is able to graphically distinguish fiber bundles originating from a defined cortical or subcortical Region of Interest (ROI) often relating to the corticospinal tract or subcortical white matter pathways relating to speech and language relative to the tumour . ROIs cThis review aims to conceptualise the current state of invasive and non-invasive neuromodulation for the purposes of inducing cortical reorganisation, referred to as Neuromodulation-Induced Cortical Prehabilitation (NICP), to reduce the risk of premeditated post-operative neurologic sequelae following eloquent brain tumour surgery. We will first describe current surgical approaches and outcomes relating to lower grade glioma surgery. In section two, we explore electrophysiologic mechanisms and techniques relating to invasive and non-invasive brain mapping in glioma surgery. Section three details current applications of non-invasive neuromodulation in psychiatric and rehabilitation settings. Section four then relates previous sections to current case studies attempting to catalyse NICP in brain tumour patients harbouring perisylvian tumours. Section five then considers several neuroethical implications of prehabilitation relating to clinical decision making in lower grade glioma surgery, and whether or not current data supports the notion that current applications of NICP may permit future indications of reduced risk and improved post-operative course without transient injury and subsequent exhaustive rehabilitative therapy.Focused, non-systematic literature searches were conducted to identify studies relating to sections one, two and three in consideration of section four and as a conceptual basis for section five. The authors nominated this approach in consideration of the vast undertaking required for systematic reviews for each section, however, a systematic literature search was reserved for studies relating to neuromodulation-induced cortical prehabilitation, of which no existing review protocol exists. The authors searched PubMed, Scopus and MEDLINE databases for articles published until December 2021 with the following MESH terms for section four: “cortical prehabilitation”, “functional reorganisation”, “neural plasticity”, “cerebral plasticity”, “eloquent brain tumour”. Inclusion criteria were studies investigating invasive or non-invasive neuromodulation to induce functional cortical reorganisation to reduce the risk of neurologic sequelae.The dilemma of brain tumour surgery involving the eloquent cortex is maximizing the extent of resection whilst minimizing neurologic morbidity, referred to as the onco-functional balance. Clinical approaches and philosophies are widely heterogeneous with regard to glioma surgery; however, it is universally accepted that safe and maximal resection with avoidance of significant ischaemic or neurologic sequelae is desirable. Part of the risk analyses to determine patient eligibility of brain tumour surgery often considers anatomical landmarks associated with eloquent function as indicated by proximity to classical  anatomic regions, or presumed functional cortex indicated by neuroimaging. Manipulation or resection near-to or within functional areas during surgery can result in transient or permanent neurologic injury, which can be severely debilitating in addition to leading to a poor prognosis. As such, careful consideration is made during surgery to reduce risk to these areas often with the integration of neuroimaging data and stereotactic navigation, with guidance from DCS.Gliomas in particular can be located within close proximity or attached to these functionally important cortical areas and can also infiltrate subcortical white matter tracts. In a review by Krishna et al. , it has Lower grade gliomas  grow slowly over time and are believed to induce cortical plasticity, with some recommendations that tumour resection be staged to preserve eloquence after observing functional reorganization between procedures . The infGlioma surgery involving presumed functional cortex or subcortical white matter tracts is performed with the patient awake or asleep, though the criteria for either approach differs among neurosurgical centres. Asleep craniotomy under general anaesthesia is typically indicated for perirolandic regions unlikely to involve speech and language function. Awake craniotomy involves either conscious sedation or “asleep-awake-asleep” sedation and is classically reserved for perisylvian regions with the patient sedated but aware and responsive so that they can adequately perform neuropsychological speech assessment tasks during surgery aided with DCS.Awake craniotomy with brain mapping is often clinically effective but technically demanding for both the patient and the surgeon. Considerations for surgery include medical comorbidities, neurological status, seizure frequency, body habitus and psychological status . In prepDuring surgery, awake brain mapping tasks are individually tailored to assess suspected speech and language pathways affected or within proximity to the tumour or subcortical tracts, often including counting, comprehension, picture naming and semantic association, among others. DCS applied during these tasks attempts to disrupt neural pathways to confirm or disprove eloquent cortical or subcortical involvement subject to site of stimulation as indicated by the induction of aphasia, dysarthria, semantic paraphasia, amongst others, interpreted by neuropsychology or speech therapy teams and reported to the surgeon. Neuropsychological analysis during awake surgery is also heterogenous, with reports of high interrater variability, variability of selection and interpretation of intraoperative tasks, and subsequent indication of surgical termination points .Awake craniotomy even without brain mapping is often still regarded as the ‘gold standard’ of functional assuredness during surgery as it provides ‘online’ feedback in real time without being affected by brain shift or anaesthesia. Outcome data also demonstrates that classically inoperable lesions involving eloquent cortex can be safely resected if aided by DCS, with most post-operative deficits reported to be mild , or transient in nature ,48. SurvPoor surgical outcomes have been independently predicted by advanced age, poor performance, pre-existing motor, language deficits  and tumoOncological outcome is typically measured as overall progression free survival or time to malignant transformation, whereas functional outcomes relate to the patient’s ability to communicate and move, though these assessments are not standardised and widely subjective . Rates oOverall, transient neurologic injury following attempts of maximal resection in awake or asleep brain surgery is tolerated by multidisciplinary neurosurgical teams with the expertise and experience to conduct comprehensive brain mapping, integrate neuro-imaging data, and facilitate effective neurorehabilitation . CurrentIntraoperative brain mapping strategies are widely heterogeneous in practice. Various DCS configurations exist that are described in greater detail elsewhere ,63,64,65From an electrophysiologic perspective, bipolar LF-DCS provides a 50–60 Hz biphasic pulse with 1 ms pulse width and interstimulus interval of ~16 Hz, with intensity ranging typically between 0.5–20 mA. This is typically regarded as the Penfield technique , popularAlthough LF-DCS is also useful for mapping of motor regions, HF-DCS is preferred as it permits objective measurement during general anaesthesia and is often associated with a lower incidence of intraoperative seizure activity ,77,78,79Glioma surgery with brain mapping is associated with fewer late and severe neurologic deficits and a more extensive tumour resection, with recommendations to instate mapping as a standard of care . There aFundamental principles of neurophysiological excitation and inhibition derived from DCS are similar in single-pulse nTMS and repetitive nTMS (rTMS), where low frequency (≤1 Hz) stimulation decreases cortical excitability and high frequency (≤5 Hz) stimulation increases cortical excitability. Pulses can be monophasic or biphasic in nature. Similarly, intermittent theta-burst rTMS (50 Hz) increases cortical excitability, whereas continuous theta-burst rTMS decreases cortical excitability. For greater detail, refer to position statements by Lefaucheuer et al.  and OlivnTMS is considered to be an emerging neuroimaging tool in glioma surgery. It has been reported to permit greater resection ,115,116,There are various reports of a close correlation between nTMS and DCS data. Jeltema et al.  performeSimilarly, Raffa et al.  conducteThere is also recent data to suggest that a lesion to tract distance of <16 mm for the arcuate fasciculus and <25 mm for other close-by language tracts increases the risk of speech injuries post-operatively . SimilarThese findings have important implications for surgical planning and pre-surgical risk stratification. It is generally accepted that lesions involving classical or topologic primary motor (periorolandic) and language (perisylvian) regions may necessitate either (a) an awake functional resection with DCS, (b) an awake functional resection without DCS, (c) an asleep anatomic resection with DCS. or (d) an asleep anatomic resection without DCS. nTMS is capable of identifying any risks to eloquent cortex prior to surgery to determine individually tailored surgical approaches, and there are also preliminary findings to suggest that this data may permit asleep surgery for patients that are ineligible for awake surgery .With compelling spatial resolution for the accurate localisation of eloquent cortical topography, nTMS has also been used to map facial recognition , visuospThe wide heterogeneity of tumour progression patterns in addition to inter-individual variability of eloquent cortex and subsequent description of ‘meta-networks’ relating to cognitive function renders the standardisation of brain mapping and brain imaging challenging, which renders each procedure investigational and as such should be individually tailored. With the ultimate goal of preserving neurologic function with safe and maximal tumour resection, the information gathered during brain tumour surgery can also contribute to a comprehensive and potentially mechanistic understanding of network level activation relating to the hodotopic organisation of human brain function. As the wider literature continues to increase reports of brain mapping techniques used in the treatment of lower grade glioma, combined with improved neuro-imaging methodologies relating to the assessment of neural function, there has been increasing interest in commandeering the potential neuromodulatory effects of emerging clinical technologies to induce functional organization under circumstances where eloquent regions infiltrated by tumour are considered ‘inoperable’.In contrast to nTMS as a pre-surgical neuroimaging modality for functional localisation, rTMS is capable of modulating neural activity beyond the stimulation period. This is often related to notions of long-term potentiation (LTP), which enhances synaptic strength between regions, or long-term depression (LTD), which depresses synaptic activity. This has been comprehensively described  and has Therapeutic applications of non-invasive neuromodulation target neurologic biomarkers often indicated by fMRI and related to clinical diagnoses to ameliorate symptoms associated with the disorder under investigation. Thus far, rTMS applications are considered an investigational but effective therapeutic tool for medication-resistant depression ,130, bipCommonly targeted regions for psychiatric applications of rTMS include the anterior and lateral aspects of the dorsolateral prefrontal cortex (DLPFC) and associative networks, however, the frontopolar cortex, ventromedial prefrontal cortex and ventrolateral prefrontal cortex have also been associated with depression pathophysiology. In a systematic review exploring targeted biomarkers for rTMS therapy , depressTMS is considered non-invasive thanks in part to its safety profile. When the parameters of stimulation are maintained within established ranges, the rates of complications associated with TMS protocols are low. Minor adverse effects include headache , temporaBeyond psychiatric applications, rTMS findings in stroke studies have contributed to a wider understanding of mechanisms involved in neuroplasticity, whereby the sudden loss of specialized neural tissue initiates a reorganisation of functional architecture. During the acute phase, damage in critical areas relating to motor or language function can contribute to global network dysfunction made worse if involving white matter tract disconnection . In the Positive clinical outcomes in lower grade glioma surgery are frequently reported, though the risk of transient or permanent neurologic injury persists. It is evident that the integration of neuroimaging and brain mapping data is capable of investigating processes related to adaptive neural plasticity, however, data derived from psychiatric and rehabilitation studies indicate that cerebral function and related neural networks might well be harnessed for therapeutic benefit ,182. RecSimilarly to neurophysiological mechanisms of deep brain stimulation, cortical reorganization initiated by neuromodulation-induced prehabilitation is still are matter of debate and has been far less investigated in comparison. The rationale is to regularly electrically modulate targeted functional regions or networks involving the tumour partnered with relevant neuropsychological or motor function tasks in order to catalyse cortical plasticity . To compBarcia et al.  reportedIn a separate case study, Barcia and colleagues  attempten = 4) and pre-central gyrus (n = 1), with a mean extraoperative mapping time of 18.8 days , and subsequent re-operation mean 33.6 days later. Extraoperative stimulation continued until it no longer resulted in functional deficits at maximal stimulation intensity. In contrast to Barcia et al.’s non-invasive approach [In a similar exploration of eDCS-NICP, Rivera-Rivera et al.  reportedapproach , complicRecently, Serrano-Castro et al.  investigBy definition, neuromodulation-induced cortical prehabilitation (NICP) is designed to prevent premeditated neurologic sequelae that otherwise would have resulted in extensive rehabilitation or permanent injury following surgery. The possibility of inducing functional reorganization by means of NICP in lower grade glioma or epilepsy patients may be feasible given the slow-growing nature of WHO grade I and II lesions. However, neuro-oncological strategies for the management of lower grade glioma favours early surgical intervention as the primary treatment option to facilitate opportunities of progression-free survival. Indeed, under circumstances where eloquent pathways are detected intraoperatively, it has been reported that surgical procedures can be staged and accompanied with speech and physiotherapy to initiate natural functional reorganisation . PrelimiThere are inherent ethical considerations relating to the time necessary to catalyse cortical prehabilitation versus the earliest opportunity for surgical intervention to increase opportunities of progression-free survival. On average, WHO II tumour growth is reported to be approximately 4 mm per year . DuratioFuture prehabilitation studies may require longer periods of therapy than currently reported, however, if they prove to be fruitful, there are also resource and economic considerations relating to pre-operative prehabilitation pathways in comparison to the possibility of post-operative rehabilitation pathways. The aforementioned preliminary findings may prove sufficient for the continued investigation of prehabilitation in small-volume lower-grade tumour or epilepsy  patients. However, in consideration of the very low number of peer-reviewed case reports it remains equivocal as to the stimulation ‘dosage’ parameters and duration necessary to facilitate NICP therapy.It is understood that brain stimulation of any description can induce differential effects. Andoh et al.  noted thInterestingly, there are no further reports of rTMS-NICP following Barcia et al.’s description , which wIn comparison to Barcia et al.’s  non-invaWith preliminary findings suggesting that invasive or non-invasive neuromodulation may be achievable for inducing functional reorganization of perisylvian cortex or speech related networks, clinicians and tumour boards must consider the feasibility of inducing plasticity prior to surgery, delaying surgery after intraoperative detection of eloquent cortical pathways , or acceFunctional reorganization must also be objectively measured and validated, ideally with predictive markers indicative of a clinical response, or lack thereof. Prospective research protocols would likely need to incorporate intrasubject evaluations of plasticity at various time points, ideally in comparison with healthy controls to highlight true signal variation reflective of functional changes that could be attributed to neuromodulation. With regard to fMRI, rs-fMRI and MEG, this would likely become a resource burden. However, for less-invasive modalities such as nTMS and Electroencephalography (EEG), or indeed an integrated nTMS-EEG platform, may prove more feasible for detection and progressive activation of homologous regions or modulation of GABAergic processes during therapy. Further, progressive nTMS or fMRI imaging during eDCS-NICP attempts may be marred by the influence of artifact associated with platinum iridium electrode coil arrays, which may be contraindicated or result in significant signal distortion. This may render rTMS-NICP as preferential during subsequent investigations, as nTMS has been reported to reliably measure cortical plasticity ,196,197 Overall, a number of methodological considerations can be made from these studies to promote further investigation into the possibility of neuromodulation-induced prehabilitation. For one, a general consensus on the definition of cortical plasticity is yet to be considered uniform relative to lower grade glioma. This often refers to the complex and multifaceted mechanisms of the brain to compensate for impaired function and substantiated by the clinical investigation of stroke, epilepsy, and brain tumours, in addition to neuroimaging and psychiatric studies. Concepts of NICP should refer to the measurable induction or precipitation of functional reorganization, either invasively or non-invasively, that attempts to catalyse impaired function resulting in diaschisis and thus inducing plasticity. This can only be accomplished with a multidisciplinary clinical team.Secondly, there are divergent methods of analysing functional changes from neuroimaging data and neurocognitive assessment. Despite the compelling and often sophisticated data provided by DCS, nTMS, rTMS, MEG, and fMRI, there are methodological limitations and significant variability not only in the application of these technologies, but also among patients. Future protocol design might consider a systematic approach to their investigations that could include homogenous subgroups relating to invasive versus non-invasive neuromodulation, suspected histopathology of tumour, anatomic location etc to ensure that data can be reliably associated with the successful or unsuccessful induction of diaschisis. Similarly, as a novel investigational protocol, it is important to maintain the ethical requirements that patients are provided informed consent, the benefit of the research outweighs the risks, and if applicable, there is an equal distribution of burdens and benefits across patients. Whilst evidence-based medicine calls for randomized controlled trials, in the current instance this remains a significant challenge given the significant heterogeneity of disease progression, neurologic status, neuropsychological status, psychosocial faculties, in addition to variable surgical strategies employed across neurosurgical centres globally. Until such trials can be responsibly designed and executed, prospective case series such as those aforementioned remain a valuable clinical and research opportunity.The possibility of inducing cortical functional reorganization is definitely promising for lower grade gliomas in order to ensure a reduced likelihood of iatrogenic insult, which results in debilitating compromise of quality of life in addition to a poor prognosis. At the time of writing, early stage invasive or non-invasive prehabilitation findings are at best an experimental indication of utility that warrants continued and systematic investigation. The small series of reported case studies should be taken into consideration for larger cohorts and where possible compared with healthy controls. Despite the promise of such science fiction-like clinical intervention, there are inherent technical and neuroethical considerations to be made. It is evident that future studies exploring invasive or non-invasive neuromodulation in lower grade glioma or epilepsy patients will demand careful and highly selective patient recruitment, in order to avoid increased risks associated with disease progression. Given the non-invasive nature and low risk profile of rTMS-NICP, larger sample sizes are likely more achievable using this modality until such time that eDCS-NICP protocols are further elucidated.It is unmistakeable that brain tumour patients have inadvertently provided a circumstance permissible to the wider understanding of neurocognitive function, often at the expense of an unfortunate prognosis. As doctors, surgeons, and scientists are gradually beginning to understand how the brain might be organised, and under which circumstances it is capable of reorganising itself, treatment paradigms in neuro-oncological surgery are evolving with the information gathered in its wake. Recent advances in functional neuro-imaging technology are capable of characterising the mechanisms of neural redistribution initiated by lower grade gliomas, and ultimately how the brain is capable of functional reorganisation during disease progression and following surgical resection. Whilst the current findings indicate a broad possibility of successful cortical prehabilitation relating to perisylvian cortex, invasive and non-invasive brain stimulation paradigms remain a compelling but under-explored investigational tool for the modulation of the eloquent brain to permit greater resection and reduce neurologic sequelae in lower grade glioma patients. Future studies should define patient selection criteria, optimal stimulation ‘dosage’ parameters, and duration of treatment, in addition to functional biomarkers for therapy discontinuation beyond the measurement of focal diaschisis, to establish whether cortical prehabilitation may represent a viable therapeutic pathway in contrast to the possibility of rehabilitation following surgery.


Even in the era of effective antiretroviral therapies, people living with Human Immunodeficiency Virus (HIV) are burdened with debilitating neurological dysfunction, such as HIV-associated neurocognitive disorders (HAND) and HIV-associated pain, for which there are no FDA approved treatments. Disruption to the neural circuits of cognition and pain in the form of synaptic degeneration is implicated in developing these dysfunctions. Glia-mediated synaptic pruning is a mechanism of structural plasticity in the healthy central nervous system (CNS), but recently, it has been discovered that dysregulated glia-mediated synaptic pruning is the cause of synaptic degeneration, leading to maladaptive plasticity and cognitive deficits in multiple diseases of the CNS. Considering the essential contribution of activated glial cells during the development of HAND and HIV-associated pain, it is possible that glia-mediated synaptic pruning is the causative mechanism of synaptic degeneration induced by HIV. This review will analyze the known examples of synaptic pruning during disease in order to better understand how this mechanism could contribute to the progression of HAND and HIV-associated pain. As HIV has transitioned to a chronic disease with the implementation of effective antiretroviral therapies, people living with HIV (PLWH) are living longer, healthier lives. However, PLWH can still be affected by the often-debilitating neurological dysfunction associated with HIV. HIV-associated neurocognitive disorders (HAND) and HIV-associated chronic pain affect ~42.6%  and 55–6HAND and HIV-associated pain are characterized by multiple different pathologies in the CNS, some of which are common to both forms of dysfunction. Neuronal loss and HIVE are both associated with HAD and higher viral load, but not with the less severe forms of HAND, which have become more prevalent in the cART era ,12. BBB Several of the pathologies associated with HAND were present in the most severe form, HAD, and not ANI and MNI, which now comprise 96% of the HAND impairment seen in HIV patients. A comparison of cortical synaptic density in HIV patients with a range of neuropsychological impairments found a correlation between decreasing excitatory synaptic density and increasing impairment at all levels, not just in HAD . SynaptiA study investigating the lumbar spinal dorsal horn tissue of HIV patients found that pain expression was associated with a decrease in synaptic markers, indicating synaptic degeneration. Moreover, the pain-positive patients also increased HIV glycoprotein gp120, glial activation, and inflammation . All syn2+ homeostasis, are disrupted, this can lead to synapse loss and neurodegeneration [While HAND and HIV-associated pain are two separate sequelae of HIV infection of the CNS, synapse degeneration has been implicated in the development of both syndromes, suggesting that they could share this causative mechanism. Loss of synapses in the CNS can be attributed to neuronal loss, disruption to synapse maintenance, neuron-autonomous homeostatic scaling, and non-autonomous glia-mediated pruning. As previously mentioned, synapse degeneration precludes neuronal loss during the development of HAND , and as neration ,27. Neurneration . Scalingneration . Glia-meneration ,31, and neration . While tThe removal of synaptic connections in a controlled manner is an important aspect of structural plasticity in the healthy CNS ,33 and pSynaptic pruning by glial cells is not limited to the dLGN or only limited to the developmental period. It has also been seen in multiple locations that we currently know of in the developing CNS, such as the hippocampus, cortex, and thalamus . Beyond There are multiple known molecular mechanisms of microglia-mediated synapse pruning that have been identified See . These iIn astrocytes, confirmed mechanisms See  include Recent studies have demonstrated that astrocytes and microglia communicate with and influence the activity of each other , and thiAlzheimer’s disease is one of the most common neurodegenerative diseases, leading to memory loss and cognitive decline. AD is characterized by two types of misfolded protein aggregates: hyperphosphorylated tau neurofibrillary tangles and amyloid-beta plaques. Synaptic degeneration is a prominent pathology in AD  and is tThe importance of microglia is highlighted by the role of TREM2, rare variants of which, most notably the R47H mutation, increase the risk of developing AD by 2–4-fold . As prevAnother gene linked to increased risk of AD development is APOE, with APOE2 decreasing risk 2-fold  and APOEWest Nile Virus (WNV) is a neurotropic virus that causes encephalitis and meningitis in the CNS and long-lasting cognitive deficits. More than half of those infected with WNV experienced cognitive deficits up to a year after infection . WNV canSynaptic engulfment analysis of glial cells in this model revealed that microglia, and not astrocytes, engulfed synapses in the CA3 hippocampus. Knockdown of C3 and C3aR rescued synapse levels and decreased microglial pruning activity, indicating that the classical complement pathway is integral to this process . C3aR isZika virus (ZIKV) infection causes neurological issues in adults as well as severe neurodevelopmental deficits, including, most notably, microcephaly in infants. Similar to WNV infection, ZIKV infects all three cell types but appears to target neurons over microglia and astrocytes  preferenMicroglial synapse pruning has been observed during ZIKV infection. In an intracranial ventricular injection mouse model of ZIKV infection, presynaptic degeneration and synaptic dysfunction were detected in the CA3 hippocampus alongside memory deficits assessed using a novel object recognition (NOR) test . MeanwhiThe blocking of microglial activation using minocycline prevented ZIKV-induced memory deficits and did not lead to increased brain viral replication . This suAn increase in astrocyte phagocytosis of ZIKV viral particles marked with nanogold was demonstrated via ultra-structural analysis after pharmacological microglia depletion in a mouse model, in which mice deficient in type 1 interferon signaling were injected intravenously with ZIKV . This fiThe most common mechanism reported in disease-induced microglial and astrocytic synaptic pruning is the complement pathway , which hGlial cells are the primary cells infected by HIV in the CNS, while neurons are not ,84. The Increased levels of complement proteins, including C1q and C3, have been reported in the CNS of patients with HIV . The potLittle is known about the potential involvement of astrocytes in synapse pruning in the context of HIV-associated synapse loss. Astrocytes are reported to contribute to synaptic pruning during development and normal brain function, but dysregulated synaptic pruning by astrocytes leading to synaptic degeneration has not yet been seen. Yuan, et al., reported pain-associated synapse degeneration and astrocyte activation in the SDH of HIV patients . These oGlia-mediated synaptic pruning is vital for developing neuronal circuits and the plasticity of developed circuits. Disruption to this mechanism of structural plasticity may lead to circuit dysfunction  and synapse degeneration . Increas