This study is to investigate the mechanism underlying the anti-apoptotic effects of freeze-dried grape
powder (FDGP) and identify the polyphenolic compounds involved. We examined apoptotic signaling pathways affected by FDGP and by its active components, including
epicatechin,
cyanidin,
quercetin, and
resveratrol, in human Huh7
hepatoma cells by assaying cell viability assays, the activities of
caspase 3 and
caspase 7, and the expression of endoplasmic reticulum stress-associated
proteins. FDGP dramatically decreased
taurodeoxycholic acid (TDCA)-induced production of
reactive oxygen species (ROS). Assessment of individual active components revealed that at concentrations corresponding to 300 μg/mL FDGP, only
quercetin demonstrated cytoprotective effects against mitochondrial-mediated apoptosis. In contrast, increased concentrations of other individual polyphenolic compounds were required to produce measurable cytoprotective effect. Only combinations of all four polyphenolic compounds (
epicatechin,
cyanidin,
quercetin, and
resveratrol) restored a degree of the anti-apoptotic effects seen with FDGP. The pretreatment of FDGP at 30 μg/mL concentration could reverse the
thapsigargin-induced effects on the expression of endoplasmic reticulum stress-associated
proteins. In conclusion, FDGP reduced oxidative stress, endoplasmic reticulum stress, and apoptosis. The mechanisms involved in the anti-apoptotic effects of FDGP included reduced generation of ROS, and reduced processing of certain
caspases. We demonstrated that
quercetin,
epicatechin, and
cyanidin are active compounds within FDGP that attenuate apoptosis. These findings contribute to our understanding of the molecular mechanisms of anti-apoptotic and
anti-oxidant effects of grape and are expected to assist in developing clinical protocols to treat a variety of stress-mediated conditions.