3-Hydroxy-3-methylglutaryl-CoA Reductase Inhibitors Enhance Cytokine-mediated Induction of Nitric Oxide Synthesis in Vascular Smooth Muscle Cells

Abstract

We investigated the effects of by 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors, cerivastatin and fluvastatin, on the induction of nitric oxide (NO) production in vascular smooth muscle cells ( VSMC) stimulated by interleukin-1β (1L-1) or in combination with interferon-γ (IFN). IL-1 activated VSMC to synthesize and release NO, which was significantly potentiated by IFN. NO production induced by IL-1 or IL-1/lFN was dosedependently enhanced by both HMG-CoA reductase inhibitors. Incubating VSMC with IL-1/IFN stimulated inducible NO synthase (iNOS) mRNA expression. Both HMG-CoA reductase inhibitors significantly upreguiated IL/IFN-stimulated iNOS mRNA expression, and enhanced iNOS gene transcription as shown by nuclear run-on assays. Both IIMG-CoA reductase inhibitors slightly modulated IL-1/IFN-induced NF-kB activation, which was not associated with their effect on NO production. Cytokines induce the de novo synthesis of tetrahydrobiopterin (BH4) in VSMC. This event is essential for the induction of NO synthesis, which requires transcriptional induction of the genes that encode not only iNOS but also guanosine triphosphate cyclohydrolase I (GTPCH), the first and rate-limiting enzyme in de novo BH4 synthesis. The synthesis of BH4 and GFPCH mRNA induced by IL-1/IFΝ were enhanced by both HMG-CoA reductase inhibitors. Exogenous mevalonate significantly prevented and geranylgeranylpyrophosphate reversed the stimulatory effect of HMG-CoA reductase inhibitors. Thus, the effect of HMG-CoA reductase inhibitors on NO production is due at least partly through blocking the biosynthesis of mevalonate, which prevents isoprenoid biosynthesis. Our data demonstrated that HMG-CoA reductase inhibitors enhance immunostimulants-induced NO production by increasing iNOS gene expression at the transcriptional level via an NF-kB-independent pathway. In addition to augmenting iNOS expression, HMG-CoA reductase inhibitors potentiate GTPCH gene expression and BH4 synthesis, thereby prevents a relative shortage of BH4 which may shift in the balance between NOS-catalyzed generation of protective NO and deletorious reactive oxygen species.

Keywords

• statin
• nitric oxide
• tetrahydrobiopterin
• vascular smooth muscle cell