Induction of apoptosis by a novel intestinal metabolite of ginseng saponinvia cytochrome c-mediated activation of caspase-3 protease

Ginseng saponins exert various important pharmacological effects with regar d to the control of many diseases including cancer. The novel intestinal ba cterial metabolites of ginseng protopanaxadiol saponins have recently been found and isolated after the oral administration of ginseng extract in huma n and rats. 20-O-(beta-D-Glucopyranosyl)-20(S)-protopanaxadiol (IH-901) for med from ginsenosides Rb1, Rb2, and Rc is of particular interest in cancer chemoprevention and treatment. We investigated the effects of IH-901 on the human myeloid leukemia cell line HL-60 in terms of inhibition of prolifera tion and induction of apoptosis. IH-901 showed a significant cytotoxic acti vity in HL-60 cells (IC50 = 24.3 mu M) following a 96-hr incubation. Treatm ent of HL-60 cells with IH-901 resulted in the formation of internucleosoma l DNA fragments. The dose- and time-dependent induction of apoptosis by IH- 901 was demonstrated in sandwich enzyme immunoassay and the results were co nfirmed by flow cytometric analysis. Morphological examination of IH-901-tr eated samples showed cells with chromatin condensation, cell shrinkage, and nuclear fragmentation, all typical characteristics of apoptotic cells. The treatment of HL-60 cells with IH-901 caused activation of caspase-3 protea se and subsequent proteolytic cleavage of poly(ADP-ribose) polymerase. IH-9 01 did not affect the expression of antiapoptotic protein Bcl-2 but did cau se a release of mitochondrial cytochrome c into cytosol. In conclusion, our results demonstrate that IH-901 dramatically suppresses HL-60 cell growth by inducing programed cell death through activation of caspase-3 protease, which occurs via mitochondrial cytochrome c release independently of Bcl-2 modulation. These results may provide a pivotal mechanism for the use of IH -901 in the prevention and treatment of leukemia. BIOCHEM PHARMACOL 60;5:67 7-685, 2000. (C) 2000 Elsevier Science Inc.