Sirolimus-induced vascular dysfunction -: Increased mitochondrial and nicotinamide adenosine dinucleotide phosphate oxidase-dependent superoxide production and decreased vascular nitric oxide formation

Objectives This study sought to analyze mechanisms that mediate vascular dysfunction induced by sirolimus. Background Despite excellent antirestenotic capacity, sirolimus-eluting stents have been found to trigger coronary endothelial dysfunction and impaired re-endothelialization. Methods To mimic the continuous sirolimus exposure of a stented vessel, Wistar rats underwent drug infusion with an osmotic pump for 7 days. Results Sirolimus treatment caused a marked degree of endothelial dysfunction as well as a desensitization of the vasculature to the endothelium-independent vasodilator nitroglycerin. Also, sirolimus stimulated intense transmural superoxide formation as detected by dihydroethidine fluorescence in aortae. Increased superoxide production was mediated in part by the vascular nicotinamide adenosine dinucleotide phosphate (NADPH) oxidase as indicated by a marked stimulation of p67(phox)/rac1 NADPH oxidase subunit expression and by increased rac1 membrane association. In addition, superoxide production in rat heart mitochondria was up-regulated by sirolimus, as measured by L012-enhanced chemiluminescence. As a consequence, electron spin resonance measurements showed a 40% reduction in vascular nitric oxide bioavailability, which was further supported by decreased serum nitrite levels. Conclusions Sirolimus causes marked vascular dysfunction and nitrate resistance after continuous treatment for 7 days. This impaired vasorelaxation may, in part, be induced by up-regulated mitochondrial superoxide release as well as by an up-regulation of NADPH oxidase-driven superoxide production. Both processes could contribute to endothelial dysfunction observed after coronary vascular interventions with sirolimus-coated stents.