Glycolipid RC-552 induces delayed preconditioning-like effect via iNOS-dependent pathway in mice

We recently demonstrated that monophosphoryl lipid A (MLA)-induced delayed cardioprotection is mediated by inducible nitric oxide synthase (iNOS) in mice. In the present study, we determined whether RC-552, a novel synthetic glycolipid related in chemical structure to MLA, could afford similar protection. Adult mice were pretreated with vehicle or RC-552 (350 microg/kg IP, n = 7 mice/group) 24 h before global ischemia and reperfusion in a Langendorff isolated, perfused heart model. A group of RC-552-treated mice received S-methylisothiourea (SMT), a selective inhibitor of iNOS (3 mg/kg IP), 30 min before heart perfusion. Myocardial infarct size was significantly reduced from 19.2 +/- 2.0% in vehicle to 8.2 +/- 2.9% in RC-552 group (P < 0.05). Treatment with SMT abolished RC-552-induced reduction in infarct size (20.0 +/- 3.9%). In addition, RC-552 failed to reduce infarct size in isolated hearts from iNOS knockout mice (27.1 +/- 2.8%) compared with that in hearts from control knockout mice without drug treatment (22.9 +/- 5.4%). Acute buffer perfusion with RC-552 (0.1, 1.0, or 2.5 microg/ml) for 8 min immediately before ischemia-reperfusion did not reduce infarct size significantly. We concluded that RC-552 induces delayed cardioprotection via an iNOS-dependent pathway.