Epicatechin-3-gallate signaling and protection against cardiac ischemia/reperfusion injury.

At concentrations found in human after ingestion of 1-2 cups of green tea, Epicatechin-3-gallate (ECG) modulates Na/K-ATPase conformation and activity. Akin to ouabain, an archetypal Na/K-ATPase ligand of the cardiotonic steroids (CTS) family, ECG also activates PKCɛ translocation and increases the force of contraction of the rat heart. This study evaluated whether, like ouabain, ECG also modulates Na/K-ATPase/Src receptor function and triggers pre- and post-conditioning against ischemia/reperfusion (I/R) injury. In vitro, ECG activated the purified Na/K-ATPase/Src complex. In Langendorff-perfused rat hearts, sub-micromolar concentrations of ECG administered either before or after ischemia reduced infarct size by more than 40%, decreased lactate dehydrogenase release, and improved the recovery of cardiac function. ECG protection was blocked by PKCɛ inhibition and attenuated by mitochondrial KATP channel inhibition. In a unique mammalian cell system with depleted Na/K-ATPase α1 expression, ECG-induced PKCɛ activation persisted but protection against I/R was blunted. Taken together, these results reveal a Na/K-ATPase- and PKCɛ-dependent mechanism of protection by ECG that is also distinct from the mechanism of action of ouabain. These ECG properties likely contribute to the positive impact of green tea consumption on cardiovascular health and warrant further investigation into the role of cardiac Na/K-ATPase signaling in the cardioprotective effect of green tea consumption. SIGNIFICANCE STATEMENT: Consumption of green tea, the richest dietary source of ECG, is associated with a reduced risk of cardiac mortality. Anti-oxidant effects of ECG and other tea polyphenols are well known, but reported for concentrations well above dietary levels. Therefore, the mechanism underlying the cardioprotective effect of green tea remains incompletely understood. This study provides experimental evidence that ECG concentrations commonly detected in human after consumption of a cup of tea trigger Na/K-ATPase/Src receptor in a cell-free system, activate a CTS-like signaling pathway, and provide PKCε-dependent protection against ischemia/reperfusion injury in rat hearts. Mechanistic studies in mammalian cells with targeted Na/K-ATPase depletion revealed that although Na/K-ATPase does not mediate ECG-induced PKCɛ activation, it is required for ECG-induced protection against ischemia/reperfusion injury.