Effects of activating and deactivating cytokines on the functionally linked tetrahydrobiopterin No pathways in vascular smooth muscle cells

Abstract

The functional relationship of nitric oxide (NO) production and synthesis of tetrahydrobiopterin (BH 4), the requisite cofactor for NO synthase, was investigated in rat aortic smooth muscle cells (SMC). Inflammatory cytokines induced BH 4 and NO synthesis in different ratios, IL-1β induced mainly NO synthesis with concomitant but limiting amounts of BH 4 for maximal NO production. TNFα did not induce NO synthesis but induced BH 4 synthesis. IFNγ was ineffective on both the induction of NO and BH 4 synthesis. TGFβ downregulated NO production but did not affect BH 4 biosynthesis. IL-4 and IL-10 had no effect on both BH 4 and NO synthesis. Activating cytokines strongly synergized in induction of NO production, whereas endogenous BH 4 production became insufficient for maximal NO synthesis. Exogenous cofactor in the form of sepiapterin or authentic BH 4, but not the natural isomer 7-BH 4, enhanced NO production twofold. Inhibition of BH 4 synthesis with dicumarol abolished NO production that could be restored in the presence of BH 4.