Cyclosporin A Inhibits Nitric Oxide Synthase Induction in Vascular Smooth Muscle Cells

Abstract

Abstract The effect of cyclosporin A on induction of nitric oxide synthase in rat aortic smooth muscle cells was examined. A combination of interleukin-1α (100 U/mL) and tumor necrosis factor−α (5000 U/mL) induced 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 IC ₅₀ of 4×10 ⁻⁷ mol/L when applied simultaneously with the cytokines. The expression of inducible nitric oxide synthase messenger RNA (mRNA) induced by the combination of interleukin-1α and tumor necrosis factor–α was inhibited by the cyclosporin A cotreatment. Cyclosporin A did not decrease inducible nitric oxide synthase mRNA stability in the presence of transcription inhibitor actinomycin D (5 μg/mL). Induction of nitrite/nitrate production by the combination of tumor necrosis factor–α and bacterial lipopolysaccharide or that of interleukin-1α 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/nitrate production, suggesting the possibility that the inhibitory effect of cyclosporin A may be exerted by means of a novel pathway other than inhibition of calcineurin. These results indicate that cyclosporin A inhibits inducible nitric oxide synthase induction at the mRNA level and 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 substances.