Glutathione oxidation and mitochondrial depolarization as mechanisms of nordihydroguaiaretic acid-induced apoptosis in lipoxygenase-deficient FL5.12 cells

Nordihydroguaiaretic acid (NDGA) induces apoptosis in a variety of cell lines. The mechanism(s) of this effect is not known, although the focus has been on the ability of NDGA to inhibit lipoxygenase (LOX) activities. In the present study, NDGA-induced apoptosis was studied in a murine hematopoietic cell line, FL5.12. Although this cell line lacks detectable LOX protein or activities, NDGA(10 mu M) was able to induce apoptosis, There was a massive loss of mitochondrial membrane potential by 4 h after the addition of NDGA, suggesting that this organelle might be targeted by NDGA. A pro-oxidant NDGA effect has been suggested as playing a role in apoptosis. This was supported by the findings that glutathione disulfide levels were increased by 4 h following treatment with 10 mu M NDGA, that pretreatment with N-acetylcysteine completely blocked the NDGA-induced loss of membrane potential and apoptosis, and that lipid peroxidation was enhanced in cells treated with NDGA. However, no evidence of increased levels of reactive oxygen could be seen in NDGA-treated cells loaded with dichlorofluorescin diacetate or dihydrorhodamine and analyzed by flow cytometry. Bcl-x(L) protein levels were unaffected by NDGA treatment. Caspase-3 was rapidly activated with a peak at 8 h after FL5.12 cells were treated with NDGA, Ac-DEVD-CHO (25 mu M) and boc-asp-FMK (20 mu M) both inhibited caspase-3 enzyme activity by 97% 8 h after NDGA treatment. Boc-asp-FMK, a more general caspase inhibitor, delayed NDGA-induced apoptosis while Ac-DEVD-CHO, a more specific inhibitor of caspase-3, had no effect. These results suggest that NDGA-induced apoptosis happens through reactions that depolarize mitochondria, oxidize glutathione and lipids, but do not generate significant amounts of free reactive oxygen species.