Stevens, T; Cheng, W; Jaspers, I; Madden, M
Rationale: Diesel exhaust has been shown to induce adverse pulmonary health effects; however, the underlying mechanisms for these effects are still unclear. Previous studies have implicated mitochondrial dysfunction in the toxicity of diesel exhaust particles (DEP). DEP contain a complex and highly variable mixture of organic compounds that includes carboxylic acids (CA) of varying chain length. In order to determine whether the total organic and CA content are relevant determinants of DEP cytotoxicity, we examined the effect of exposure to DEP of varying organic content and DEP-associated CA on mitochondrial membrane potential in the human airway epithelial cell line BEAS 2B.
Methods: Human bronchial epithelial cells (BEAS-2B) were exposed to various DE particles (NDEP, CDEP, and ADEP containing 1.5%, 18.9%, and 67% of extractable organic mass, respectively) at concentrations ranging from 1-200 μg/ml for 1 hr. We also exposed cells to CAs of various carbon (C) lengths at concentrations ranging from 25-400 μM also for 1 hr. Cell viability and mitochondrial membrane potential (MMP) were measured in BEAS with the fluorescein-based indicators calcein and 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide (JC-1), respectively.
Results: Viability was unaffected at DEP concentrations < 200 ug/ml. Compared to control, exposure to 1 ug/ml NDEP, CDEP, and ADEP decreased MMP by 22.1± 7.1%, 38.8 ± 6.7 %, and 49.6 ± 2.5 %, respectively. Hexanoic (C6), palmitic (C16), erucic (C22), and tetracosanoic (C24) acids decreased membrane potential by 16.9 ±2.7%, 14.4 ± 4.0%, 31.3 ± 9.1%, and 61.3 ± 4.6%, respectively, at concentrations as low as 25 μM. In contrast, glyoxylic (C2) and myristic (C14) acids showed no effects on MMP at concentrations below 400 μM.
Conclusion: Concentration dependent decreases in MMP were seen with all DEP exposures. The potency of the reductions in MMP correlated with the amount of organic content in DE. There appeared to be no relationship between CA carbon length and the magnitude of the MMP effect. Overall, CAs associated with DE have the potential to disrupt MMP and may play a role in DE-induced lung injury. [This abstract does not reflect US EPA policy.]
