Journal
JOURNAL OF HEPATOLOGY
Volume 60, Issue 3, Pages 545-553Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.jhep.2013.10.012
Keywords
Glutamine synthetase; Glutaminase; Hepatic encephalopathy; Amino acids; Ammonia; Cirrhosis; Chronic liver failure; Ornithine phenylacetate
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Funding
- Intra-European Fellowship Marie Curie in the Seventh Framework Programme [PIEF-GA-2010-272485]
- EPSRC through the UCL CoMPLEX doctoral training centre
- Centro de Investigacion Biomedica en Red de Enfermedades Hepaticas y Digestivas del Institut de Salud Carlos III of the Ministry of Spanish Health
- Medical Research Council [G0701742] Funding Source: researchfish
- MRC [G0701742] Funding Source: UKRI
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Background & Aims: In liver failure, ammonia homeostasis is dependent upon the function of the ammonia metabolising enzymes, glutamine synthetase (GS) and glutaminase (GA) but data about their protein expression and activity are lacking. The aims of this study were to determine the protein expression and activity of GS and GA in individual organs in a rat model of chronic liver disease and to test whether the treatment with the ammonia-lowering agent ornithine phenylacetate (OP) modulates their activities. Methods: 49 SD rats were studied 35 days after sham-operation or bile duct ligation (BDL). The BDL group received: L-ornithine (0.6 mg/kg/day), Phenylacetate (0.6 mg/kg/day), OP (0.6 mg/kg/day) or placebo (saline) for 5 days prior to sacrifice. Arterial ammonia, amino acids and liver biochemistry were measured. Expressions of GS and GA were determined by Western-blotting and activities by end-point methods in liver, muscle, gut, kidney, lung, and frontal cortex. Results: In BDL rats, hepatic GS enzyme activity was reduced by more than 80% compared to sham rats. Further, in BDL rats GA activity was reduced in liver but increased in the gut, muscle and frontal cortex compared to sham rats. OP treatment resulted in a reduction in hyperammonemia in BDL rats, associated with increased GS activity in the muscle and reduced gut GA activity. Conclusions: In a rat model of chronic liver failure, hyperammonemia is associated with inadequate compensation by liver and muscle GS activity and increased gut GA activity. OP reduces plasma ammonia by increasing GS in the muscle and reducing GA activity in the gut providing additional insights into its mechanism of its action. GS and GA may serve as important future therapeutic targets for hyperammonemia in liver failure. (C) 2013 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.
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