N-ALPHA-TOSYL-L-LYSINE CHLOROMETHYLKETONE PREVENTS EXPRESSION OF INOSIN VASCULAR SMOOTH-MUSCLE BY BLOCKING ACTIVATION OF NF-KAPPA-B

Certain cytokines and lipopolysaccharide stimulate expression of induc ible nitric oxide synthase (iNOS) in vascular smooth muscle, an event that is regulated at the transcriptional level and appears to involve several transcription factors, including nuclear factor kappa B (NF-ka ppa B). Since proteases play an essential role in NF-kappa B activatio n, experiments were designed to clarify, in both cultured rat aortic s mooth muscle cells (SMCs) and isolated rat aortas, whether protease in hibitors affect the interleukin-1 beta (IL-1 beta)-elicited expression of iNOS. The formation of NO was assessed by nitrite release in cultu red SMCs and the attenuation of phenylephrine-induced contraction in a ortic rings, the expression of iNOS by Western blot analysis and rever se transcription-polymerase chain reaction, and NF-kappa B activity in nuclear extracts by gel electrophoretic mobility shift assay. Exposur e of cultured SMCs to IL-1 beta increased NF-kappa B binding activity within 30 minutes and was associated with nitrite accumulation and the appearance of iNOS protein 24 hours later. These responses were aboli shed in cells that had been exposed to the cytokine in the presence of the protease inhibitor N-alpha-tosyl-L-lysine chloromethylketone. Apr otinin and p-toluenesulfonyl-L-arginine methyl ester, two other protea se inhibitors, also reduced the cytokine-stimulated release of nitrite and the level of iNOS protein. Exposure of rat aortic segments withou t endothelium to IL-1 beta activated NF-kappa B within 30 minutes and was associated with the appearance of iNOS mRNA and an attenuation of phenylephrine-induced contraction 6 hours later. These responses were blunted when the segments were incubated with the cytokine and N-alpha -tosyl-L-lysine chloromethyl ketone. The present observations indicate that protease inhibitors prevent iNOS expression in both cultured and native vascular SMCs by blocking the activation of NF-kappa B.