Partial deletion of argininosuccinate synthase protects from pyrazole plus lipopolysaccharide-induced liver injury by decreasing nitrosative stress

Lu Y, Leung TM, Ward SC, Nieto N. Partial deletion of argininosuccinate synthase protects from pyrazole plus lipopolysaccharide-induced liver injury by decreasing nitrosative stress. Am J Physiol Gastrointest Liver Physiol 302: G287-G295, 2012. First published November 3, 2011; doi:10.1152/ajpgi.00375.2011.-Argininosuccinate synthase (ASS) is the rate-limiting enzyme in the urea cycle. Along with nitric oxide synthase (NOS)-2, ASS endows cells with the L-citrulline/nitric oxide (NO center dot) salvage pathway to continually supply L-arginine from L-citrulline for sustained NO center dot generation. Because of the relevant role of NOS in liver injury, we hypothesized that downregulation of ASS could decrease the availability of intracellular substrate for NO center dot synthesis by NOS-2 and, hence, decrease liver damage. Previous work demonstrated that pyrazole plus LPS caused significant liver injury involving NO center dot generation and formation of 3-nitrotyrosine protein adducts; thus, wild-type (WT) and Ass(+/-) mice (Ass(+/-) mice are lethal) were treated with pyrazole plus LPS, and markers of nitrosative stress, as well as liver injury, were analyzed. Partial ablation of Ass protected from pyrazole plus LPS-induced liver injury by decreasing nitrosative stress and hepatic and circulating TNF alpha. Moreover, apoptosis was prevented, since pyrazole plus LPS-treated Ass(+/-) mice showed decreased phosphorylation of JNK; increased MAPK phosphatase-1, which is known to deactivate JNK signaling; and lower cleaved caspase-3 than treated WT mice, and this was accompanied by less TdT-mediated dUTP nick end labeling-positive staining. Lastly, hepatic neutrophil accumulation was almost absent in pyrazole plus LPS-treated Ass(+/-) compared with WT mice. Partial Ass ablation prevents pyrazole plus LPS-mediated liver injury by reducing nitrosative stress, TNF alpha, apoptosis, and neutrophil infiltration.