Cardioprotection of ginsenoside Rb1 against ischemia/reperfusion injury is associated with mitochondrial permeability transition pore opening inhibition.

Objective: To investigate the role of ginsenoside Rb1 (Gs-Rb1) in cardioprotection against ischemia/reperfusion (I/R) or hypoxia/reoxygenation (H/R) injury and to explore whether the cardioprotective action is mediated via attenuating the formation of mitochondrial permeability transition pore (mPTP).

Methods: A Langendorff-perfused model of rat heart was employed. I/R injury was induced by breaking off perfusion for 40 min then reperfusion for 60 min. Gs-Rb1 (100 μmol/L) were administrated for 10 min before I/R. Infarct size was estimated by the 2,3,5-triphenyl tetrazolium chloride (TTC) staining. Lactate dehydrogenase (LDH) and creatine kinase (CK) released from effluents were measured. Transmission electron microscopy was performed to assess morphological difference between cardiac mitochondrial isolated from I/R rats and Gs-Rb1 pretreated rats. Western blot analysis was used to determine phosphorylation of protein kinase B/Akt, and its downstream target glycogen synthase kinase 3β (GSK-3β). Incubation isolated cardiac mitochondria with Gs-Rb1, Ca-induced opening of the mPTP was assessed by the reduction of absorbance at 520 nm (A). Neonatal rat cardiomyocytes were subjected to hypoxia 9 h followed by reoxygenation 4 h to induce H/R injury. After pretreated with different concentration of Gs-Rb1 (6.25, 25, 100 μmol/L ), cell viability was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide (MTT) method. The membrane potential was estimated by Rh123 fluorescence. mPTP opening was measured using the probe calcein-AM.

Results: Gs-Rb1 100 μmol/L significantly reduced the infarct size of hearts (26.39%±11.67% vs. I/R group 56.68%±5.88%, P<0.01). Compared with the I/R group, Gs-Rb1 pretreatment decreased LDH and CK levels in the coronary effluent (P<0.05 or P<0.01) as well as attenuated destructive ultrastructure induced by I/R. The protective effect of Gs-Rb1 involved in phosphorylating protein kinase B/PKB (Akt) and GSK-3β. In mitochondria isolated from rat hearts, significant inhibition of Ca-induced swelling was observed in samples that were pretreated with Gs-Rb1 (6.25, 25, 100, 400 μmol/L) for 10 min. When cardiomyocytes were isolated from neonatal rat and subjected to H/R, cell viability was increased with treatment of Gs-Rb1 (6.25, 25, 100 μmol/L ). Gs-Rb1 inhibited mPTP opening and restored subsequent loss of mitochondrial membrane potential.

Conclusion: Gs-Rb1 presents cardioprotective effect against I/R or H/R injury which involves in activating Akt, phosphorylating GSK-3β and inhibiting mPTP opening.