NEOPTERIN INDUCES NITRIC OXIDE-DEPENDENT APOPTOSIS IN RAT VASCULAR SMOOTH-MUSCLE CELLS

Numerous studies indicate that proinflammatory substances like tumor n ecrosis factor alpha (TNF-alpha) and interferon gamma (IFN-gamma) as w ell as macrophage-derived neopterin are increased in atherosclerotic t issue and thus are potentially involved in the process of atherogenesi s. Since apoptotic death of vascular smooth muscle cells (VSMC) is rep orted to occur in atherosclerotic lesions, we investigated the effects of neopterin, TNF-alpha, and IFN-gamma on apoptosis in cultured VSMC. Mor phological changes characteristic of apoptosis as well as DNA fra gmentation were detected in cells treated with neopterin, TNF-alpha/IF N-gamma, and neopterin + TNF-alpha/IFN-gamma. Simultaneously, neopteri n, TNF-alpha/IFN-gamma, and neopterin + TNF-alpha/IFN-gamma led to ind ucible nitric oxide synthase (iNOS) gene expression and nitric oxide ( NO) synthesis. NO generation was significantly reduced when cells were cotreated with the competitive iNOS inhibitor aminoguanidine. This wa s accompanied by decreased percentual apoptosis as detected by FAGS an alysis using all kinds of stimuli. We conclude that neopterin as well as TNF-alpha/IFN-gamma are potent mediators of apoptotic death in VSMC which is at least in part triggered by NO synthesis induced by these proinflammatory mediators.