ANTIOXIDATIVE ACTIVITY OF 5,6,7,8-TETRAHYDROBIOPTERIN AND ITS INHIBITORY EFFECT ON PARAQUAT-INDUCED CELL TOXICITY IN CULTURED RAT HEPATOCYTES

The in vitro antioxidative activity of 5,6,7,8-tetrahydrobiopterin (BP H4) was measured and the ability of BPH4 to prevent paraquat-induced c ell damage was examined in cultured hepatocytes. The scavenging activi ty of BPH4 against superoxide anion radicals was assayed in two system s, i.e., xanthine/xanthine oxidase (X/XOD) and rat macrophage/phorbol myristate acetate (M phi/PMA) radical-generating systems. BPH4 showed an extremely strong superoxide anion radical-scavenging activity in bo th assay systems. Biopterin (BP) itself did not show any activity in t he X/XOD system, but was effective in the M phi/PMA system. The antiox idative activities of BPH4 against both superoxide anion and hydroxyl radicals were confirmed by spin trapping-ESR spectrometry. BPH4 also p rotected rat brain homogenate against autooxidation. We further examin ed the effect of BPH4 on paraquat-induced cell toxicity in cultured ra t hepatocytes. The paraquat-induced elevation of the release of lactat e dehydrogenase (LDH), a marker enzyme for cytotoxicity from cultured hepatocytes was suppressed by BPH4 in a dose-dependent manner. The ele vation of lipid peroxides simultaneously induced by paraquat was also inhibited by BPH4 in the same manner. These results suggest that BPH4 might be useful in the treatment of various diseases whose pathogenesi s is active oxygen-related.