Endogenous and new synthetic antioxidants for peroxynitrite: selective inhibitory effect of 5-methoxytryptamine and lipoic acid on tyrosine nitration by peroxynitrite.

The inhibitory effects of endogenous and synthetic compounds on the nitration and oxidation of L-tyrosine by peroxynitrite were examined. Nitration and oxidation activities of L-tyrosine by peroxynitrite were estimated by monitoring the formation of 3-nitrotyrosine and dityrosine with a high-performance liquid chromatography-ultraviolet (HPLC-UV)-fluorescence detector system. Glutathione and synthetic compounds ((2S,3R,4S)-N-ethylmercapto-3,4-dihydroxy-2-hydroxymethylpyrrolidine, L-N-dithiocarboxyproline) inhibited both the nitration and the oxidation reactions of L-tyrosine effectively. On the other hand, 5-methoxytryptamine and lipoic acid inhibited only the nitration reaction of L-tyrosine, and instead increased the oxidation reaction. It was assumed that 5-methoxytryptamine and lipoic acid reacted only with the nitrating species of peroxynitrite. This is the first report of a selective inhibitor for the nitrating reaction of peroxynitrite.