Argininosuccinate synthase conditions the response to acute and chronic ethanol-induced liver injury in mice

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Background and Aim: Argininosuccinate synthase (ASS) is the rate-limiting enzyme in both the urea and the l-citrulline/nitric oxide (NO·) cycles regulating protein catabolism, ammonia levels and NO· generation (1-2). Since a proteomics analysis identified ASS and nitric oxide synthase-2 (NOS2) as co-induced in rat hepatocytes by chronic ethanol consumption, which also occurred in alcoholic liver disease (ALD) and in cirrhotic patients, we hypothesized that ASS could play a role in ethanol binge and chronic ethanol-induced liver damage.

Methods: To investigate the contribution of ASS to the pathophysiology of ALD, wild-type (WT) and Ass+/− mice (Ass−/− are lethal due to hyperammonemia) were exposed to an ethanol binge or to chronic ethanol drinking.

Results: Compared with WT, Ass+/− mice given an ethanol binge exhibited decreased steatosis, lower NOS2 induction and less 3-nitrotyrosine (3-NT) protein residues, indicating that reducing nitrosative stress via the l-citrulline/NO· pathway plays a significant role in preventing liver damage.

However, chronic ethanol treated Ass+/− mice displayed enhanced liver injury compared with WT mice. This was due to hyperammonemia, lower phosphorylated AMP-activated protein kinase (pAMPKα) to total AMPKα ratio, decreased sirtuin (Sirt-1) and peroxisomal proliferator-activated receptor coactivator-1α (Pgc1α) mRNAs, lower fatty acid β-oxidation due to down-regulation of carnitine palmitoyl transferase-II (CPT-II), decreased antioxidant defense and elevated lipid peroxidation end-products in spite of comparable nitrosative stress but likely reduced NOS3.

Conclusion: Partial Ass ablation protects only in acute ethanol-induced liver injury by decreasing nitrosative stress but not in a more chronic scenario where oxidative stress and impaired fatty acid β-oxidation are key events.


The version of record is available from the publisher at Copyright 2012 © American Association for the Study of Liver Diseases.