Potent inhibition of inducible nitric oxide synthase by geldanamycin, a tyrosine kinase inhibitor, in endothelial, smooth muscle cells, and in rat aorta.

We have examined whether specific protein tyrosine kinase (PTK) inhibitors (genistein, tyrphostin, or geldanamycin) prevent nitric oxide (NO.) production in rat smooth muscle cells (SMC), in murine brain endothelial cells (MBE), and in isolated rat aortas treated with endotoxin (LPS) and/or cytokines. Tyrphostin failed to inhibit either the release of nitrite in both endothelial and smooth muscle cells or vascular hyporeactivity in rat aorta, caused by immunostimulants. Genistein decreased nitrite production in MBE only at high concentration but had no effect on nitrite production in SMC and on the hypocontractility in aortic rings. In contrast, low concentrations of geldanamycin abolished the release of nitrite in MBE and in SMC treated with endotoxin and/or cytokines. Geldanamycin inhibited also the hypocontractility to phenylephrine in aortic rings treated with LPS or interleukin-1. This inhibitor failed to inhibit the release of nitrite and the vascular hyporeactivity once nitric oxide synthase (NOS) was induced by immunostimulants whereas methyl-L-arginine, an inhibitor of NOS, had significant effects. These data suggest that LPS- and cytokines-induced NO. production initiate a common signaling pathway involving a PTK that is inhibited by geldanamycin but not or slightly by tyrphostin or genistein at a point that precedes the induction of NOS.