Coordinated Regulation of Murine Cardiomyocyte Contractility by Nanomolar (−)-Epigallocatechin-3-Gallate, the Major Green Tea Catechin

Abstract

Green tea polyphenolic catechins exhibit biological activity in a wide variety of cell types. Although reports in the lay and scientific literature suggest therapeutic potential for improving cardiovascular health, the underlying molecular mechanisms of action remain unclear. Previous studies have implicated a wide range of molecular targets in cardiac muscle for the major green tea catechin, (Ϫ)-epigallocatechin-3-gallate (EGCG), but effects were observed only at micromolar concentrations of unclear clinical relevance. Here, we report that nanomolar concentrations of EGCG significantly enhance contractility of intact murine myocytes by increasing electrically evoked Ca 2ϩ transients, sarcoplasmic reticulum (SR) Ca 2ϩ content, and ryanodine receptor type 2 (RyR2) channel open probability. Voltageclamp experiments demonstrate that 10 nM EGCG significantly inhibits the Na ϩ -Ca 2ϩ exchanger. Of importance, other Na ϩ and Ca 2ϩ handling proteins such as Ca 2ϩ -ATPase, Na ϩ -H ϩ exchanger, and Na ϩ -K ϩ -ATPase were not affected by EGCG Յ1 M. Thus, nanomolar EGCG increases contractility in intact myocytes by coordinately modulating SR Ca 2ϩ loading, RyR2-mediated Ca 2ϩ release, and Na ϩ -Ca 2ϩ exchange. Inhibition of Na ϩ -K ϩ -ATPase activity probably contributes to the positive inotropic effects observed at EGCG concentrations Ͼ1 M. These newly recognized actions of nanomolar and micromolar EGCG should be considered when the therapeutic and toxicological potential of green tea supplementation is evaluated and may provide a novel therapeutic strategy for improving contractile function in heart failure.

Epigallocatechin-3-Gallate Accelerates Relaxation and Ca2+ Transient Decay and Desensitizes Myofilaments in Healthy and Mybpc3-Targeted Knock-in Cardiomyopathic Mice

“…Nevertheless, 1.8 μM EGCg reduced relaxation time, and this effect was more prominent in KI cells, whereas the effects on diastolic Ca 2+ and Ca 2+ kinetics did not differ between the genotypes. The increase in diastolic Ca 2+ could be explained by an inhibiting effect on the Na + /Ca 2+ exchanger (NCX), as reported with 10 nM (Feng et al, 2012) and 2.5 μM (Lorenz et al, 2008). The faster time to peak Ca 2+ is probably due to EGCg effects on the ryanodine receptor.…”

Isolation and Physiological Analysis of Mouse Cardiomyocytes

“…In both genetic and environmental models of heart disease, utilizing this protocol provides key information about cell contractility, sarcomeric contractility and relaxation, calcium transients, and cytoskeletal disruption. This system is often used to test the effect of drugs on isolated cardiomyocytes 6,7 . We employ the system to compare contractility and calcium transients of cardiomyocytes between wild type mice and mice with a mutation leading to dilated cardiomyopathy.…”

“…Isolation and physiological analysis of myocytes have been used by countless labs for a variety of experiments including studying the effect of drugs 6,7 [15][16][17] . With the application of any of these stressors, changes in heart function could be due to any combination of changes in the cardiomyocytes themselves and changes in the surrounding environment of the heart, such as scarring, changes in conductivity, or changes to the extracellular matrix.…”

Design, development, and characterization of lipid nanocarriers-based epigallocatechin gallate delivery system for preventive and therapeutic supplementation

“…This permits the conclusion that both lipid NPs are highly stable systems and can be considered suitable carriers for the oral administration of EGCG, avoiding the premature release of EGCG in simulated gastric and intestinal conditions and allowing a controlled release after the absorbance into the bloodstream. Finally, the in vitro viability and cytotoxicity studies revealed that the formulations were biocompatible, and the obtained IC 50 is far superior to the reported therapeutic concentrations 20–22…”