Prostaglandin D 2 Inhibits Inducible Nitric Oxide Synthase Expression in Rat Vascular Smooth Muscle Cells

Abstract

Abstract —Vascular smooth muscle cells (VSMCs) as well as macrophages have been shown to generate a substantial amount of NO in inflammatory vascular lesions. Prostaglandin (PG) D 2 (PGD 2 ) is produced by inflammatory cells, including mast cells and macrophages. We investigated whether PGD 2 modulates NO metabolism in rat VSMCs. PGD 2 at a concentration of 10 –7 mol/L or greater dose-dependently inhibited nitrite accumulation in the medium of cultured VSMCs stimulated with interleukin 1β (IL-1β). In a dose-response analysis of IL-1β and nitrite accumulation, PGD 2 was seen to decrease the maximal ability of VSMCs to generate NO, arguing against competition by PGD 2 at cytokine receptors. Northern analysis showed that PGD 2 suppresses induction of inducible NO synthase (iNOS) mRNA in IL-1β–stimulated VSMCs, with consequent inhibition of iNOS protein expression in Western analysis. A thromboxane A 2 (TXA 2 ) analogue, U46619 (10 –5 mol/L), produced less inhibition of NO generation than did PGD 2 . Neither the PGI 2 analog carbaprostacyclin nor PGE 1 showed any inhibition. PGD 2 dose-dependently inhibited NO generation despite the addition of the TXA 2 antagonist SQ29548. PGJ 2 , Δ 12 -PGJ 2 , and 15-deoxy-Δ 12,14 -PGJ 2 , all metabolites of PGD 2 , were as potent as or slightly stronger than PGD 2 in the inhibition of NO generation. These data suggest that PGD 2 suppresses NO generation in VSMCs by inhibiting iNOS mRNA expression, most likely through the cascade of the PGJ 2 series rather than through the TX receptor or cAMP upregulation. Such action makes it likely that PGD 2 regulates NO metabolism in vascular lesions.