Heyneanol A induces apoptosis via cytochrome c release and caspase activation in human leukemic U937 cells

Abstract

Heyneanol A, a tetramer of resveratrol, is isolated from the roots of Vitis amurensis by cytotoxicity based fractionation. In this study, the mechanism of apoptosis by heyneanol A was evaluated in human leukemic U937 cells. Heyneanol A (IC50 = 6.6 μM at 24 h) exhibited stronger cytotoxic effect than resveratrol (IC50 = 100 μM at 24 h) by 15-fold on human leukemic U937 cells by XTT assay. Apoptotic bodies were observed in U937 cells treated with 6 μM of heyneanol A by TUNEL assay. Heyneanol A effectively increased the portion of sub-G1 DNA content in a time- and concentration-dependent manner by flow cytometric analysis. Heyneanol A also induced cytochrome c release from mitochondria into the cytosol and subsequent caspase activation involving caspase 9 and 3 to cleave PARP. However, it did not affect the expressions of Bax and Bcl-2 by western blotting. It was confirmed that the activation of caspase 8, 9 and 3 and the cleavage of PARP by heyneanol A were completely blocked by adding Z-VAD-FMK, a caspase inhibitor. These findings suggest that heyneanol A has anti-tumor activity, which may be mediated by apoptosis caused by cytochrome c release and caspase activation in human leukemic U937 cells.