Ischemic postconditioning (IPO) reduces lethal reperfusion injury under normal conditions, but its effectiveness in hypercholesterolemia (HC) is disputed. We measured the cardioprotection of IPO in hypercholesterolemic rats and determined the roles of glycogen synthase kinase-3β (GSK-3β) and the mitochondrial permeability transition pore (mPTP). Isolated rat hearts underwent 30-min global ischemia and 120-min reperfusion. Postconditioning protocol induced six cycles of 10s ischemia and 10s reperfusion at the onset of the reperfusion. Myocardial infarct size was estimated by triphenyltetrazolium chloride staining and cardiomyocyte apoptosis was assessed by TUNEL staining. GSK-3β phosphorylation was measured by immunoblotting. The opening of mPTP was measured by NAD(+) content in myocardium. In normocholesterolemia (NC) groups, infarct size and cardiomyocyte apoptosis were significantly reduced after IPO. These reductions were completely abolished by HC, as evidenced by a similar infarct size and cardiomyocyte apoptosis observed between the IPO-HC and IR (ischemia-reperfusion)-HC groups. GSK-3β phosphorylation was significantly higher in the IPO-NC than the IPO-HC group. In addition, NAD(+) content in myocardium, a marker of mPTP opening, was higher in the IPO-NC group than the IPO-HC group. In conclusion, cardioprotection of IPO is blocked by hypercholesterolemia. This might be due to the impairment of phosphorylation of GSK-3β and attenuation of mPTP opening.

Abstract. Pharmacological preconditioning and postconditioning may reduce myocardial necrosis and apoptosis during ischemia/reperfusion (I/R), however, hypercholesterolemia interferes with the associated cardioprotective mechanisms. The present study investigated whether pharmacological preconditioning and postconditioning with nicorandil could attenuate myocardial necrosis and apoptosis induced by I/R in hypercholesterolemic rats, and explored the possible mechanisms involved. Male Wistar rats (n=160) were fed normal (normocholesterolemic group, n=10) or high-cholesterol (hypercholesterolemic group, n=150) diets for 8 weeks. Hearts harvested from the normal and hypercholesterolemic rats were subsequently placed on modified Langendorff perfusion apparatus and 30-min global ischemia was performed, followed by 120-min reperfusion. Nicorandil (1, 3, 10, 30, 100 µmol/l), and mitochondrial adenosine triphosphate-sensitive potassium (mitoKATP) channel blocker 5-hydroxydecanoic acid sodium salt (5-HD) (100 µmol/l) or soluble guanylyl cyclase (sGC) blocker 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (10 µmol/l) were perfused for 10 min, prior to ischemia or at the onset of reperfusion. The myocardial infarct size was determined by triphenyltetrazolium chloride staining, and cardiomyocyte apoptosis was detected by terminal deoxynucleotidyl transferase dUTP nick-end labeling staining. In order to investigate the potential mechanisms, the expression levels of caspase-3, B-cell lymphoma-2 (Bcl-2) proteins and Bcl-2-associated X protein (Bax) were measured using western blot analysis. The present study demonstrated that, in hypercholesterolemic rats, pharmacological preconditioning and postconditioning with nicorandil decreased I/R-induced myocardial necrosis and apoptosis in a concentration-dependent manner. The optimal preconditioning and postconditioning concentration of nicorandil determined to have anti-infarct and anti-apoptosis effects was 30 µmol/l, which significantly (P<0.05) reduced the infarct size to 14.88±3.25% and 15.96±3.29%, and attenuated the percentage of cardiomyocyte apoptosis to 25.20±3.93% and 26.18±4.82%, respectively, compared with the I/R group. However, the cardioprotective effects of nicorandil were partially suppressed by cotreatment with 5-HD or ODQ. Western blot analysis demonstrated that pharmacological preconditioning and postconditioning with nicorandil significantly downregulated caspase-3 and Bax expression, and upregulated Bcl-2 expression compared with the I/R group (P<0.05). The results of the present study suggest that pharmacological preconditioning and postconditioning with nicorandil may protect hypercholesterolemic hearts against I/R-induced necrosis and apoptosis; and the cardioprotective effects of nicorandil may be due to the dual pharmacological mechanisms of opening the mitoKATP channels and a nitric oxide/sGC-dependent mechanism, and regulation of the expression of caspase-3, Bax and Bcl-2.

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Ischemic postconditioning (IPoC) reduces lethal reperfusion injury under normal conditions, but its effectiveness is blocked by hypercholesterolemia. The present study aimed to determine whether the inhibition of Rho‑kinase by fasudil restores the cardioprotection of IPoC in the hypercholesterolemic rat heart, and to elucidate the potential mechanisms underlying this process. The isolated rat hearts underwent 30 min global ischemia and 120 min reperfusion. IPoC was induced by six cycles of 10 sec ischemia and 10 sec reperfusion at the onset of the reperfusion. Fasudil was administered 15 min prior to ischemia, and wortmannin and L‑NAME were administered following IPoC. The myocardial infarct size, apoptosis, myocardial nitric oxide (NO) content and Rho‑kinase activity, as well as the activation of the phosphatidylinositol 3‑kinase/Akt/endothelial nitric oxide synthase (PI3K/Akt/eNOS) pathway, were examined. The results revealed that IPoC and 1 µM fasudil treatment alone failed to reduce the infarct size and apoptosis rate. However, IPoC combined with 1 µM fasudil treatment or 10 µM fasudil treatment alone restored the cardioprotection as evidenced by the decreasing in infarct size and apoptosis rate, whereas it was blocked by the administration of wortmannin or L‑NAME. Furthermore, IPoC combined with 1 µM fasudil treatment also enhanced the phosphorylation of Akt and eNOS and conferred a significant increase in the content of NO. By contrast, no significant improvements were demonstrated in the phosphorylation of Akt and eNOS, as well as myocardial NO content when treated with 1 µM fasudil and IPoC alone. The inhibition of Rho‑kinase by fasudil was able to restore the cardioprotection of IPoC in the hypercholesterolemic rat heart. The underlying mechanisms involved in this process appear to be mediated by the activation of the PI3K/Akt/eNOS signal pathway and an increase in the myocardial NO content.