CYCLOSPORINE-A INHIBITS NITRIC-OXIDE SYNTHASE INDUCTION IN VASCULAR SMOOTH-MUSCLE CELLS

The effect of cyclosporin A on induction of nitric oxide synthase in r at aortic smooth muscle cells was examined. A combination of interleuk in-1 alpha (100 U/mL) and tumor necrosis factor-alpha (5000 U/mL) indu ced accumulation of nitrite/nitrate, the stable end products of nitric oxide, in culture media within 48 hours. Cyclosporin A inhibited this nitrite/nitrate accumulation in a concentration-dependent manner with an IC50 of 4 X 10(-7) mol/L when applied simultaneously with the cyto kines. The expression of inducible nitric oxide synthase messenger RNA (mRNA) induced by the combination of interleukin-1 alpha and tumor ne crosis factor-alpha was inhibited by the cyclosporin A cotreatment. Cy closporin A did not decrease inducible nitric oxide synthase mRNA stab ility in the presence of transcription inhibitor actinomycin D (5 mu g /mL). Induction of nitrite/nitrate production by the combination of tu mor necrosis factor-alpha and bacterial lipopolysaccharide or that of interleukin-1 alpha and interferon gamma (100 U/mL) was also inhibited by cyclosporin A cotreatment. Another inhibitor of calcineurin, FK506 (up to 10(-6) mol/L), had no effect on the induction of nitrite/nitra te production, suggesting the possibility that the inhibitory effect o f cyclosporin A may be exerted by means of a novel pathway other than inhibition of calcineurin. These results indicate that cyclosporin A i nhibits inducible nitric oxide synthase induction at the mRNA level an d that inducible nitric oxide synthase in vascular smooth muscle cells can be a target for cyclosporin A, providing a possible mechanism for the interference of the drug with the balance of vasoactive substance s.