Diesel exhaust particle-induced cell death of cultured normal human bronchial epithelial cells

We investigated the effect of diesel exhaust particles (DEPs) on normal human bronchial epithelial (NHBE) cells. Inclusion of DEPs in culture media was lethal to NHBE cells. NHBE cells are more susceptible to DEPs than other normal human lung cells, normal human pulmonary artery endothelial cells and normal human embryonic lung fibroblasts. DEP-induced cell death was mainly due to necrosis. Using the fluorescence probes diacetoxymethyl 6-carboxy-3',6'-diacetoxy-2',7'-dichloro-3',6'-dideoxydihydrofluorescinate and 4,5-diaminofluorescein diacetate, it was observed that hydrogen peroxide and nitrogen monoxide, respectively, were generated within DEP-exposed NHBE cells. DEP cytotoxicity increased or decreased with an increase or decrease in the cellular level of reduced glutathione (GSH) by treatment with L-buthionine-(R,S)-sulfoximine or ethyl reduced glutathionate, respectively. In addition, DEPs themselves decreased the cellular level of GSH in a dose-dependent manner. Upon exposure of NHBE cells to high concentrations of DEPs, their cellular GSH was depleted almost throughout. Further, the following agents decreased DEP cytotoxicity: 1) antioxidants 2,2,5,7,8-pentamethylchroman-6-ol, ebselen, and N,N'-bis(salicylidene)ethylenediaminomanganese(II) dihydrate (EUK-8); 2) iron ion-chelating agents disodium bathophenanthrolinedisulfonate and desferrioxamine mesylate; 3) nitrogen monoxide synthase inhibitors N-G-nitro-L-arginine methyl ester hydrochloride and N-G-methyl-L-arginine acetate salt; and 4) an endocytosis inhibitor quinacrine. On the basis of these observations, the mechanism of DEP cytotoxicity toward NHBE cells is discussed.