L-methionine reduces oxidant stress in endothelial cells: role of heme oxygenase-1, ferritin, and nitric oxide.

The amino acid L-methionine is known to exert antioxidant effects by as yet unidentified mechanisms. In the present study, L-methionine led to a concentration-dependent induction of the antioxidant proteins heme oxygenase-1 (HO-1) and ferritin in cultured endothelial cells (ECV 304). HO-1 protein expression was accompanied by an increased catalytic activity of the enzyme. Long-term pre-incubation of endothelial cells with L-methionine reduced NADPH-mediated radical formation by up to 60%. The antioxidant effect of L-methionine was mimicked by the HO-1 product bilirubin, which suppressed free radical formation almost completely. Reduction of superoxide generation by L-methionine was inhibited in the presence of the nitric oxide (NO) synthase inhibitor L-NMMA, suggesting the involvement of endogenous NO in L-methionine-dependent cytoprotection. These findings demonstrate that L-methionine reduces free radical formation in endothelial cells, possibly through induction of heme oxygenase-1 and ferritin. This novel, indirect antioxidant action might be relevant for the preventive potential of methionine and methionine rich diets under conditions of inflammation and oxidative stress.