Anti-apoptotic effect and the mechanism of orientin on ischaemic/reperfused myocardium.

We investigated the anti-apoptotic effect of orientin, from bamboo leaves (Phyllostachys nigra), on rat heart after treatment with ischemia/reperfusion (I/R), and on rat cardiomyocytes injured by hypoxia/reoxygenation (H/R). I/R injury was induced by occluding the left anterior descending coronary artery for 45 min and restoring perfusion for 240 min. Orientin (0.5, 1.0 and 2.0 mg kg(-1)) or its vehicle was injected i.v. 10 min prior to ischemia. Cultured cardiomyocytes were subjected to hypoxia for 120 min, then reoxygenated for 60 min to induce H/R. Vehicle or orientin (3, 10, 30 micromol l(-1) was added 10 min before hypoxia and reoxygenated. TUNEL assay and DNA fragmentation assay demonstrated that myocardium apoptosis was attenuated by pretreatment with orientin (0.5, 1.0 and 2.0 mg kg(-1). Flow cytometric analysis also showed that apoptosis of cardiomyocytes was reduced by pretreatment with orientin (3, 10 and 30 micromol l(-1)). In addition, results of immunohistochemistry and Western blot analysis showed that orientin increased the expression of bcl-2 and reduced Bax expression, resulting in up-regulation of the bcl-2/Bax ratio. Cytochrome c (Cyt-c) and caspase-3 expression was also reduced in myocardium and cardiomyocytes injured by I/R and H/R. These observations indicate that orientin exerts a potent cardioprotective effect on I/R- and H/R-treated myocardium and cardiomyocytes, and inhibits apoptosis by preventing activation of the mitochondrial apoptotic pathway (cytochrome c-caspase-3).