Role of superoxide anion in the pathogenesis of cytokine-induced myocardial dysfunction in dogs in vivo

Objective: Although studies in vitro have implicated oxygen-derived free radicals as possible mediators of inflammatory cytokine-induced cell injury, the role of the radicals in the cytokine-induced myocardial dysfunction in vivo remains unclear. The present study was designed to address this point in our novel canine model of cytokine-induced myocardial dysfunction in vivo. Methods: Studies were performed in mongrel dogs, in which microspheres (MS, 15 μm in diameter) with and without interleukin-1β (IL-1β) were injected into the left main coronary artery (control and IL-1β group). Left ventricular ejection fraction (LVEF) was evaluated by echocardiography for 1 week. Results: Immediately after the intracoronary injection of MS (10⁶/kg), LVEF equally decreased to approximately 30% in both the control and IL-1β group. While LVEF rapidly recovered within 2 days in the control group, it remained depressed in the IL-1β group until day 7 (p<0.0001 vs. control group). Pretreatment with OPC-6535 (an inhibitor of superoxide production) before (2 mg/kg IV) and 1 and 2 days after IL-1β MS application (1 mg/kg IV) prevented the IL-1β-induced myocardial dysfunction. Superoxide production in the myocardium was significantly higher in the IL-1β group than in the control group at day 2 (p<0.01), and OPC-6535 significantly suppressed the IL-1β-induced superoxide production (p<0.01). An HPLC assay showed that nitrotyrosine, a marker of the formation of peroxynitrite by superoxide anion and nitric oxide, was present in the myocardium treated with IL-1β but not in that with control MS. OPC-6535 abolished the IL-1β-induced formation of myocardial nitrotyrosine. Conclusion: These results indicate that superoxide anion and the resultant formation of peroxynitrite may substantially be involved in the pathogenesis of the cytokine-induced myocardial dysfunction in dogs in vivo.