Hepatic dimethylarginine-dimethylaminohydrolase1 is reduced in cirrhosis and is a target for therapy in portal hypertension.
BACKGROUND & AIMS
Portal hypertension is characterized by reduced hepatic eNOS activity. Asymmetric-dimethylarginine (ADMA), an eNOS inhibitor, is elevated in cirrhosis and correlates with the severity of portal hypertension. Dimethylarginine dimethylaminohydrolase-1 (DDAH-1) is the key enzyme metabolizing hepatic ADMA. This study characterized DDAH-1 in cirrhosis, and explored hepatic DDAH-1 reconstitution through farnesoid X receptor (FXR) agonism and DDAH-1 gene therapy.


METHODS
DDAH-1 immunohistochemistry was conducted on human cirrhosis and healthy liver tissue. Subsequently, sham-operated or bile-duct-ligated (BDL) cirrhosis rats were treated with the FXR agonist obeticholic acid (OA, 5 mg/kg) or vehicle for 5 days. Further, animals underwent hydrodynamic injection with DDAH-1-expressing plasmid or saline control, which resulted in the following groups: sham+saline, BDL+saline, BDL+DDAH-1-plasmid. Portal pressure (PP) measurements were performed. Plasma ALT was measured by COBAS INTEGRA, DDAH-1 expression by qPCR and Western blot, eNOS activity by radiometric assay.


RESULTS
Immunohistochemistry and Western-blotting confirmed hepatic DDAH-1 was restricted to hepatocytes, and expression decreased significantly in cirrhosis. In BDL rats, reduced DDAH-1 expression was associated with elevated hepatic ADMA, reduced eNOS activity and high PP. OA treatment significantly increased DDAH-1 expression, reduced hepatic tissue ADMA, and increased liver NO generation. PP was significantly reduced in BDL+OA vs. BDL+vehicle (8±1 vs. 13.5±0.6 mmHg; p<0.01) with no change in the mean arterial pressure (MAP). Similarly, DDAH-1 hydrodynamic injection significantly increased hepatic DDAH-1 gene and protein expression, and significantly reduced PP in BDL+DDAH-1 vs. BDL+saline (p<0.01).


CONCLUSIONS
This study demonstrates DDAH-1 is a specific molecular target for portal pressure reduction, through actions on ADMA-mediated regulation of eNOS activity. Our data support translational studies, targeting DDAH-1 in cirrhosis and portal hypertension.
['Mookerjee|Rajeshwar P|RP|', 'Mehta|Gautam|G|', 'Balasubramaniyan|Vairappan|V|', 'Mohamed|Fatma El Zahraa|Fel Z|', 'Davies|Nathan|N|', 'Sharma|Vikram|V|', 'Iwakiri|Yasuko|Y|', 'Jalan|Rajiv|R|']
D000581:Amidohydrolases D000818:Animals D015415:Biomarkers D001706:Biopsy D015153:Blotting, Western D002478:Cells, Cultured D004195:Disease Models, Animal D005786:Gene Expression Regulation D015316:Genetic Therapy D006801:Humans D006975:Hypertension, Portal D007150:Immunohistochemistry D008099:Liver D008103:Liver Cirrhosis D008297:Male D016133:Polymerase Chain Reaction D012313:RNA D051381:Rats D017207:Rats, Sprague-Dawley
Portal hypertension ADMA DDAH-1 Nitric oxide