3-methylindole-induced toxicity to human bronchial epithelial cell lines

Transfected BEAS-2B cells that express different cytochrome P450 enzymes were used to assess whether human bronchial epithelial cell lines are target cells for 3-methylindole (3MI)-induced damage. Four different transfected BEAS-2B lines overexpressing P450s 2A6, 3A4, 2F1, and 2E1 (B-CMV2A6, B-CMV3A4, B-CMV2F1, and B-CMV2E1), respectively, were compared. The B-CMV2F1 and B-CMV3A4 cells were the most susceptible to 3MI-mediated cytotoxicity, measured by leakage of lactate dehydrogenase into the medium after a 48-h incubation. The toxicity was ameliorated by pretreatment with 1-aminobenzotriazole (ABT). Depletion of glutathione with diethylmaleate decreased the onset and increased the extent of cell death with 3MI. Thus, 3MI is cytotoxic to immortalized bronchial epithelial cells overexpressing 2F1 without concomitant depletion of GSH, but depletion of GSH modestly enhances the cytotoxicity of 3MI to human lung cells. Additional studies clearly demonstrated that a low concentration of 3MI (10 μM) induced apoptosis in BEAS-2B cells that was measured by DNA fragmentation, and apoptosis was inhibited by the presence of ABT. The B-CMV2F1 cells overexpressing 2F1 demonstrated increased apoptosis (measured by Annexin-V binding) at 24 h with 100 μM 3MI. Therefore, CYP2F1 in human bronchial epithelial lung cells may bioactivate 3MI to 3-methyleneindolenine, which induces programmed cell death at relatively low concentrations. Human lung cells may be susceptible to this prototypical pneumotoxicant.