Role of nitric oxide and peroxynitrite in the cytokine-induced sustained myocardial dysfunction in dogs in vivo.

Studies in vitro suggested that inflammatory cytokines could cause myocardial dysfunction. However, the detailed mechanism for the cytokine-induced myocardial dysfunction in vivo remains to be examined. We thus examined this point in our new canine model in vivo, in which microspheres with and without IL-1beta were injected into the left main coronary artery. Left ventricular ejection fraction (LVEF) was evaluated by echocardiography for 1 wk. Immediately after the microsphere injection, LVEF decreased to approximately 30% in both groups. While LVEF rapidly normalized in 2 d in the control group, it was markedly impaired in the IL-1beta group even at day 7. Pretreatment with dexamethasone or with aminoguanidine, an inhibitor of inducible nitric oxide synthase, prevented the IL-1beta-induced myocardial dysfunction. Nitrotyrosine concentration, an in vivo marker of the peroxynitrite production by nitric oxide and superoxide anion, was significantly higher in the myocardium of the IL-1beta group than in that of the control group or the group cotreated with dexamethasone or aminoguanidine. There was an inverse linear relationship between myocardial nitrotyrosine concentrations and LVEF. These results indicate that IL-1beta induces sustained myocardial dysfunction in vivo and that nitric oxide produced by inducible nitric oxide synthase and the resultant formation of peroxynitrite are substantially involved in the pathogenesis of the cytokine-induced sustained myocardial dysfunction in vivo.

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 microns in diameter) with and without interleukin-1 beta (IL-1 beta) were injected into the left main coronary artery (control and IL-1 beta group). Left ventricular ejection fraction (LVEF) was evaluated by echocardiography for 1 week. RESULTS: Immediately after the intracoronary injection of MS (10(6)/kg), LVEF equally decreased to approximately 30% in both the control and IL-1 beta group. While LVEF rapidly recovered within 2 days in the control group, it remained depressed in the IL-1 beta group until day 7 (p < 0.0001 vs. control group). Pretreatment with OPC-6535 (an inhibitor of superoxide production) before (2 mg/kg i.v.) and 1 and 2 days after IL-1 beta MS application (1 mg/kg i.v.) prevented the IL-1 beta-induced myocardial dysfunction. Superoxide production in the myocardium was significantly higher in the IL-1 beta group than in the control group at day 2 (p < 0.01), and OPC-6535 significantly suppressed the IL-1 beta-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-1 beta but not in that with control MS. OPC-6535 abolished the IL-1 beta-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.

Inhibition of adhesion molecules markedly ameliorates cytokine-induced sustained myocardial dysfunction in dogs in vivo.

Adhesion molecules are key molecules for inflammatory cardiovascular diseases and are known to be up-regulated by inflammatory cytokines. However, the role of adhesion molecules in the cytokine-induced myocardial dysfunction in vivo remains unclear. This role was examined in our novel canine model, in which chronic treatment of the heart with IL-1 beta-bound microspheres (MS), but not control MS, causes sustained myocardial dysfunction in vivo. The expression of P-selectin (mRNA and immunoreactivity) was more prominent in the IL-1 beta group than in the control group (treated with control MS alone) after MS injection. The extent of neutrophil infiltration and myocardial myeloperoxidase (MPO) activity were significantly increased in the IL-1 beta group (P < 0.01). Pre-treatment with SLeX-OS (a novel oligosaccharide analog of sialyl LewisX) or PB1.3 (a monoclonal antibody to P-selectin) prevented the myocardial dysfunction and significantly suppressed the neutrophil infiltration and the increase in myocardial MPO activity induced by IL-1 beta (P < 0.01 each). These results indicate that adhesion molecules play an important role in the pathogenesis of the cytokine-induced sustained myocardial dysfunction in dogs in vivo.