title: Hepatic dimethylarginine-dimethylaminohydrolase1 is reduced in cirrhosis and is a target for therapy in portal hypertension.
abstract: OBJECTIVE
  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.
authors.affiliation: Liver Failure Group, Institute for Liver and Digestive Health, University College London, UK. Electronic address: r.mookerjee@ucl.ac.uk.
authors.forename: Rajeshwar P
authors.initials: RP
authors.lastname: Mookerjee
authors.affiliation: Liver Failure Group, Institute for Liver and Digestive Health, University College London, UK.
authors.forename: Gautam
authors.initials: G
authors.lastname: Mehta
authors.affiliation: Liver Failure Group, Institute for Liver and Digestive Health, University College London, UK.
authors.forename: Vairappan
authors.initials: V
authors.lastname: Balasubramaniyan
authors.affiliation: Liver Failure Group, Institute for Liver and Digestive Health, University College London, UK.
authors.forename: Fatma El Zahraa
authors.initials: Fel Z
authors.lastname: Mohamed
authors.affiliation: Liver Failure Group, Institute for Liver and Digestive Health, University College London, UK.
authors.forename: Nathan
authors.initials: N
authors.lastname: Davies
authors.affiliation: Liver Failure Group, Institute for Liver and Digestive Health, University College London, UK.
authors.forename: Vikram
authors.initials: V
authors.lastname: Sharma
authors.affiliation: Sections of Digestive Diseases, Department of Medicine, Yale University School of Medicine, New Haven, CT, USA.
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Iwakiri
authors.affiliation: Liver Failure Group, Institute for Liver and Digestive Health, University College London, UK.
authors.forename: Rajiv
authors.initials: R
authors.lastname: Jalan
mesh_terms: D000581:Amidohydrolases / Q000096:biosynthesis / Q000235:genetics*; D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D001706:Biopsy; D015153:Blotting, Western; D002478:Cells, Cultured; D004195:Disease Models, Animal; D005786:Gene Expression Regulation; D015316:Genetic Therapy / Q000379:methods*; D006801:Humans; D006975:Hypertension, Portal / Q000188:drug therapy* / Q000201:enzymology / Q000209:etiology; D007150:Immunohistochemistry; D008099:Liver / Q000201:enzymology* / Q000473:pathology; D008103:Liver Cirrhosis / Q000150:complications / Q000201:enzymology / Q000235:genetics*; D008297:Male; D016133:Polymerase Chain Reaction; D012313:RNA / Q000235:genetics*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D015415:Biomarkers; D012313:RNA; D000581:Amidohydrolases; C059999:dimethylargininase
keywords: ADMA; DDAH-1; Nitric oxide; Portal hypertension