Gingko biloba leaf extract induces oxidative stress in carcinoma HSC-2 cells

The antiproliferative effects of a Gingko biloba leaf extract to cells from tissues of the human oral cavity were studied. Toxicity to carcinoma HSC-2 cells was correlated with the prooxidative nature of the extract. G. biloba leaf extract generated reactive oxygen species (ROS) in cell culture medium and, albeit to a lesser extent, in buffer, with higher levels detected at alkaline pH. Lowered levels of ROS were detected in culture medium coamended with the extract and with either catalase or superoxide dismutase, indicating the generation of hydrogen peroxide and superoxide anion, respectively. Biological activity of the extract was through oxidative stress. Toxicity to the HSC-2 cells was lessened by the ROS scavengers, divalent cobalt and pyruvate, by catalase, and by the antioxidant, N-acetyl-L-cysteine, and was potentiated by the glutathione depleters, DL-buthionine-[S,R]-sulfoximine, 1-chloro-2,4-dinitrobenzene, and bis(2-chloroethyl)-N-nitrosourea. G. biloba reacted directly with authentic glutathione and lowered the intracellular glutathione content in HSC-2 cells. Induction of apoptosis upon exposure of HSC-2 cells to G. biloba extract was noted by apoptotic cell morphologies, by TUNEL staining, and by PARP cleavage. The data strongly suggest that the prooxidative nature of the G. biloba extract was the cause of apoptotic cell death.