Aim: To investigate whether R-848 (resiquimod, toll-like receptor 7/8 agonist) can induce late preconditioning in neonatal cardiacmyocytes.Methods: The protective effects of R-848 on neonatal myocytes against anoxia-reoxygenation-induced injury were tested, and intra- cellular reactive oxygen species (ROS) were determined. The protein synthesis inhibitor cyclohexamide (CH) and the ROS scavenger N-acetylcysteine (NAC) were used in this model to test if new protein synthesis and oxidative stress were necessary for their cardiopro- tective effects. The activation of nuclear factor kappa B (NFKB) and hypoxia inducible factor 1 (HIF1) was investigated by electropho-retic mobility shift assays (EMSA), and inducible nitric oxide synthase (iNOS) was assessed by immunoblotting. After iNOS was down-regulated by small interfering RNA (siRNA) transfection, the cardioprotective effect was reassessed.Results: ROS were triggered soon after R-848 (0.01-1.0 μg/L) administration, however, the cardioprotective effect of which was induced 24 h later. This protection was abolished by CH or NAC pretreatment. NFKB and HIF1 activation and iNOS up-regulation were involved in this protective mechanism. The cardioprotective effect was also attenuated after iNOS was knocked down. Conclusion: R-848 provided a cardioprotective effect through a late preconditioning mechanism via a ROS/NFKB-HIF1/iNOS-dependent pathway.
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