Hepatic dimethylarginine-dimethylaminohydrolase1 is reduced in cirrhosis and is a target for therapy in portal hypertension

Abstract

Background and Aims Portal hypertension is characterized by reduced hepatic eNOS activity. Asymmetric-dimethylarginine (ADMA), an eNOS inhibitor, is elevated in cirrhosis and correlates with severity of portal hypertension. Dimethylargininedimethylaminohydrolase-1 (DDAH-1) is the key enzyme metabolizing hepatic ADMA. This study characterized DDAH-1 in cirrhosis, and explored hepatic DDAH-1 reconstitution through 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 FXR agonist Obeticholic acid (OA, 5mg/kg) or vehicle for 5 days. Further animals underwent hydrodynamic injection with DDAH-1-expressing plasmid or saline control. 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 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). Conclusion 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.

Origins of Portal Hypertension in Nonalcoholic Fatty Liver Disease

“…FXR has recently become a major pharmacological target in NAFLD owing to its complex role in bile acid and lipid metabolism, inflammation, and fibrosis [101]. FXR increases the expression of dimethylarginine dimethylaminohydrolase (DDAH), which eliminates asymmetric dimethylarginine (ADMA), a competitive endogenous inhibitor of endothelial nitric oxide synthase (eNOS) abundant in cirrhosis [102]. Obeticholic acid (OCA), a synthetic bile acid ligand of FXR, reduces experimental PHT by reactivating FXR signaling pathways of vasorelaxation through DDAH and eNOS upregulation and Rho-kinase repression [103].…”

New cellular and molecular targets for the treatment of portal hypertension

“…Endothelial NO production can be improved by shortand long-term exogenous administration of the eNOS cofactor BH 4 , which improves eNOS activity and microsvascular dysfunction, and therefore reduces portal pressure [42,61]. In addition, a very recent paper described that the administration of obeticholic acid promotes the synthesis of the ADMA-metabolizer dimethylargininedimethylaminohydrolase-1 (DDAH-1), markedly improving eNOS activity in cirrhotic rats [62]. 4.…”

Farnesoid X Receptor Agonists and Other Bile Acid Signaling Strategies for Treatment of Liver Disease

“…The steroidal and non-steroidal FXR ligands have shown beneficial effects on portal hypertension in preclinical mouse models of pre- and intrahepatic portal hypertension [57,58,59]. These effects may be mediated by reducing intrahepatic resistance by promoting nitric oxide production, its anti-fibrotic effects but also potential impact on gut integrity reducing bacterial translocation.…”