Berbamine Protects the Heart From Ischemia/Reperfusion Injury by Maintaining Cytosolic Ca<sup>2+</sup> Homeostasis and Preventing Calpain Activation

Abstract

Berbamine, a natural compound from Barberry, was reported to protect myocardium from ischemia/reperfusion (I/R) injury, but the underlying mechanisms are largely unknown. Berbamine pretreatment from 10 to 100nmol/L concentration-dependently improved post-ischemic myocardial function. Similar protection was confirmed in isolated cardiomyocytes characterized by the attenuation of I/R-induced intracellular free Ca(2+) concentration ([Ca(2+)](i)) overloading and the depression of cell shortening and Ca(2+) transients, which were partially mimicked but not augmented by calpain inhibitor calpeptin and abolished by mitochondrial ATP-sensitive potassium (mitoK(ATP) channel inhibitor 5-hydroxydecanoate (5-HD) and phosphoinositide 3-kinase (PI3K) inhibitor wortmannin. Consistently, I/R-induced increase of calpain activity and decrease of sarcoplasmic reticulum Ca(2+) ATPase (SERCA2) activity; and protein expression of SERCA2a, desmin, calpastatin and Akt was significantly attenuated by berbamine. In addition, I/R-decreased Akt protein was reversed by calpeptin. Moreover, berbamine further increased I/R-enhanced phosphorylation of Akt and glycogen synthase kinase-3β (GSK3β). These protections were abolished by wortmannin. Furthermore, berbamine significantly attenuated I/R-induced lactate dehydrogenase release, infarct size and contractile dysfunction, and such cardioprotective actions were abolished by wortmannin and 5-HD or mimicked by glycogen synthase kinase-3β (GSK3β) inhibitor SB216763 but without additive effect. These findings suggest that berbamine confers cardioprotection against I/R injury by attenuating [Ca(2+)inf(i) overloading and preventing calpain activation through the activation of the PI3K-Akt-GSK3β pathway and, subsequently, opening of the mitoK(ATP) channel.