Protection against endotoxemia in rats by a novel tetrahydrobiopterin analogue

We studied the effects of a novel pterin antagonist of NO synthase, the 4-a mino analogue of tetrahydrobiopterin (4-ABH(4)), in a rat model of endotoxi c shock and compared its properties with those of N-G-monomethyl L-arginine (L-NMMA). Treatment with a bolus dose of 4-ABH(4) at 2 h after LPS challen ge significantly improved the 6-day survival rate, compared with the contro ls treated with saline. L-NMMA treatment did not significantly influence th e survival rate. This bolus treatment, using either compound, had no effect on the plasma nitrite + nitrate or plasma IL-6 levels. The continuous infu sion of 4-ABH(4) efficiently suppressed the enhanced calcium-dependent/inde pendent NO synthase activities induced by endotoxin in lung homogenates and completely suppressed the increase in plasma nitrite + nitrate caused by e ndotoxin at 5 h, with no significant difference compared with the L-NMMA tr eatment. Treatment of RAW264.7 murine macrophages with 4-ABH(4) but not wit h L-NMMA suppressed endotoxin-induced tumor necrosis factor-alpha release b y the cells, whereas nitrite in the supernatant decreased in a dose-depende nt fashion in both assay systems. Our data show that 4-ABH(4), an inhibitor of inducible NO synthase, significantly improves survival in a rat model o f endotoxic shock when administered in a bolus dose that does not reduce pl asma total nitrite + nitrate levels. Because we observed no overt signs of toxicity and no influence on organ-specific tetrahydrobiopterin levels, we conclude that the novel compound 4-ABH(4) is a promising drug candidate for protection against endotoxin-related mortality.