Protective effects of total flavonoids from Clinopodium chinense (Benth.) O. Ktze on myocardial injury in vivo and in vitro via regulation of Akt/Nrf2/HO-1 pathway

Background: Clinopodium chinense (Benth.) O. Ktze is a traditional Chinese herbal medicine, which comprises the plant's total flavonoids. TFCC plays an important role in the treatment of cardiovascular disease.

Purpose: The aim of the study was to study the protective effects and possible mechanism of TFCC against isoproterenol (ISO)-mediated myocardial injury in vivo and anoxia/reoxygenation (A/R)-induced H9c2 cell injury in vitro.

Methods: Male Sprague-Dawley (SD) rats were intragastrically pretreated with TFCC for 15 days. After 2 h of TFCC administration on days 14 and 15, a myocardial injury model was established with intragastric administration of 120 mg/kg of ISO daily for 2 days. The experiment was stopped 12 h after the last administration of the drugs. ECG recordings were taken after the treatment. Serum samples were assayed to determine the serum cardiac enzymes (e.g., creatine kinase, aspartate aminotransferase, and lactate dehydrogenase). The left ventricle was excised for histopathological examination, and myocardial homogenates were prepared to detection catalase, glutathione peroxidase, and superoxide dismutase. Reactive oxygen species (ROS), heme oxygenase-1(HO-1),and peroxidase were detected by the corresponding ELISA kits. H9c2 cells were pretreated with different concentrations of TFCC for 12 h before A/R exposure. Afterward, cell viability, LDH release, hoechst 33,342, and peromide iodine (PI) double staining, JC-1 staining, and ROS examination were determined. Western blot analyses of B-cell lymphoma-2, Bcl-2associated X protein, cleaved cysteinylaspartate specific protease-3 and-9, nuclear factor 2(Nrf2), HO-1 and serine/threonine protein kinase (AKT), and P-AKT were conducted.

Results: The pretreatment of TFCC (10, 20, and 40 mg/kg) daily for 15 days prevented ISO-induced myocardial damage, including the decrease in serum cardiac enzymes and cardiomyocyte apoptotic index and improvement in the heart rate and vacuolation. TFCC also improved the free radical scavenging and antioxidant potential, thereby suggesting that one possible mechanism of TFCC-induced cardio protection is mediated by blocking the oxidative stress. To clarify these mechanisms, we performed the in vitro study by A/R-induced cytotoxicity model in H9c2 cells. TFCC pretreatment prevented apoptosis, increased the expression of HO-1, and enhanced the nuclear translocation of Nrf2. TFCC also activated phosphorylation of AKT, whereas the addition of LY294002, which is the pharmacologic inhibitor of PI3K, blocked the TFCC-induced Nrf2/HO-1 activation and cytoprotective effect.

Conclusions: TFCC protects against myocardial injury and enhances cellular antioxidant defense capacity by inducing the phosphorylation of AKT, which subsequently activated the Nrf2/HO-1 signaling pathway.