The purpose of this study was to characterize the protective effect of tetrahydrobiopterin ( BH4L one of the cofactors of nitric oxide (NO) synthase, against NO-induced endothelial cell injury. The addition of S-nitroso-N-acetyl-D,L-penicillamine (SNAP), a NO donor, to endothelial cells induced the release of lactate dehydrogenase (LDH), a marker for cell injury. The SNAP-induced endothelial cell injury was markedly reduced by pretreatment with sepiapterin, a precursor of BH4 synthesis. On the

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... ther hand, exogenous BH4 had little effect on the SNAP-induced endothelial cell injury. We recently found that NO-induced endothelial cell injury involves a part of H 2 0 2 production, since the injury was blocked by the treatment with catalase. Although BH4 released reactive oxygen species (ROS) in cell-free conditions, the increase in intracellular BH4 by pretreatment with sepiapterin strongly reduced H 2 0 2 -induced intracellular oxidative stress. These findings suggest that the increase in intracellular BH4 content but not extracellular BH 4 , strongly attenuates NO-induced endothelial cell injury by at least one of the mechanisms by which BH4 reduces H 2 0 2 -induced oxidative stress. Intracellular BH4 seems mainly to playa role as an antioxidant or as a ROS-scavenger. induces cell injury in vascular endothelial cells (4-6). Although the mechanisms of NO-induced cell injury are not clear, the cytotoxicity of NO is likely to involve the production of hydrogen peroxide (H 2 0 2 ) in the cells, since the toxic effect of NO is reduced by catalase (5,6). Recently, we showed that BH 4 , an essential cofactor for NO synthase, has a protective effect against H 2 0 2 -induced endothelial cell injury (7) . The protective effect of BH4 seems to involve ROS scavenging activity. Moreover, BH4 has a protective effect against NO donor-induced endo-Unauthenticated Download Date | 2/25/20 11:05 AM