title: Ammonia reduction with ornithine phenylacetate restores brain eNOS activity via the DDAH-ADMA pathway in bile duct-ligated cirrhotic rats.
abstract: Ammonia is central in the pathogenesis of hepatic encephalopathy, which is associated with dysfunction of the nitric oxide (NO) signaling pathway. Ornithine phenylacetate (OP) reduces hyperammonemia and brain water in cirrhotic animals. This study aimed to determine whether endothelial NO synthase activity is altered in the brain of cirrhotic animals, whether this is associated with changes in the endogenous inhibitor, asymmetric-dimethylarginine (ADMA) and its regulating enzyme, dimethylarginine-dimethylaminohydrolase (DDAH-1), and whether these abnormalities are restored by ammonia reduction using OP. Sprague-Dawley rats were studied 4-wk after bile duct ligation (BDL) (n = 16) or sham operation (n = 8) and treated with placebo or OP (0.6 g/kg). Arterial ammonia, brain water, TNF-α, plasma, and brain ADMA were measured using standard techniques. NOS activity was measured radiometrically, and protein expression for NOS enzymes, ADMA, DDAH-1, 4-hydroxynonenol ((4)HNE), and NADPH oxidase (NOX)-1 were measured by Western blotting. BDL significantly increased arterial ammonia (P < 0.0001), brain water (P < 0.05), and brain TNF-α (P < 0.01). These were reduced significantly by OP treatment. The estimated eNOS component of constitutive NOS activity was significantly lower (P < 0.05) in BDL rat, and this was significantly attenuated in OP-treated animals. Brain ADMA levels were significantly higher and brain DDAH-1 significantly lower in BDL compared with sham (P < 0.01) and restored toward normal following treatment with OP. Brain (4)HNE and NOX-1 protein expression were significantly increased in BDL rat brain, which were significantly decreased following OP administration. We show a marked abnormality of NO regulation in cirrhotic rat brains, which can be restored by reduction in ammonia concentration using OP.
authors: Liver Failure Group, UCL Institute of Hepatology, Royal Free Hospital, London, United Kingdom.
authors: Vairappan
authors: V
authors: Balasubramaniyan
authors: Gavin
authors: G
authors: Wright
authors: Vikram
authors: V
authors: Sharma
authors: Nathan A
authors: NA
authors: Davies
authors: Yalda
authors: Y
authors: Sharifi
authors: Abeba
authors: A
authors: Habtesion
authors: Rajeshwar P
authors: RP
authors: Mookerjee
authors: Rajiv
authors: R
authors: Jalan
mesh_terms: D000581:Amidohydrolases / Q000378:metabolism*; D000641:Ammonia / Q000097:blood / Q000378:metabolism*; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives* / Q000378:metabolism; D001652:Bile Ducts / Q000601:surgery; D001921:Brain / Q000187:drug effects* / Q000378:metabolism*; D008026:Ligation; D008103:Liver Cirrhosis / Q000209:etiology / Q000378:metabolism*; D008297:Male; D019255:NADPH Oxidases / Q000032:analysis; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D009952:Ornithine / Q000494:pharmacology*; D010648:Phenylacetates / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014409:Tumor Necrosis Factor-alpha / Q000097:blood
chemical_list: D010648:Phenylacetates; D014409:Tumor Necrosis Factor-alpha; C487735:dimethylarginine; D000641:Ammonia; D001120:Arginine; D009952:Ornithine; D052250:Nitric Oxide Synthase Type III; C496316:Nos3 protein, rat; D019255:NADPH Oxidases; D000581:Amidohydrolases; C059999:dimethylargininase; C025136:phenylacetic acid