Dysfunction of antioxidative enzymes in the trinitrobenzenesulfonic acid-induced colitis rat

Abstract

Reactive oxygen and nitrogen species are thought to be involved in various inflammatory bowel diseases. We have previously shown a marked decrease in the levels of manganese superoxide dismutase (MnSOD) in the early stages of colitis in model rats after administration of unbuffered 2,4,6-trinitrobenzensulfonic acid (TNBS). Here we have extended the work in order to understand the relationship between colitis and the reactive nitrogen and oxygen species. Immunoblot analysis with an anti-nitrotyrosine antibody identified tyrosine nitration in TNBS-induced colitis tissues in rats. In addition, immunoprecipitation with an anti-MnSOD antibody followed by detection with the anti-nitrotyrosine antibody confirmed the nitration of the tyrosine residues of MnSOD. Then TNBS was administrated to rat aortic smooth muscle cells (RASMC) in culture to see if the same phenomenon occurred in vitro. RASMC exposed to TNBS neither produced NO nor induced tyrosine nitration in MnSOD. However, when activity of glutathione peroxidase (GPx), which is inactivated by various oxidants including NO, was measured, a significant decrease was observed in the early stage of experimental colitis as well as RASMC exposed to TNBS in culture. When direct effects of TNBS on these antioxidative enzymes were examined, GPx but neither MnSOD nor CuZnSOD was inactivated by TNBS and the effect was enhanced by the presence of ascorbate. Taken these data together, dysfunction of antioxidative enzymes are caused by both reactive nitrogen and oxygen species produced by activated inflammatory cells under pathological conditions and by TNBS and/or its metabolites under experimental conditions, and may be responsible for developing colitis through accumulation of such potentially harmful molecules.