The role of a mitochondrial pathway in the induction of apoptosis by chemicals extracted from diesel exhaust particles

We are interested in the cytotoxic and proinflammatory effects of particula te pollutants in the respiratory tract. We demonstrate that methanol extrac ts made from diesel exhaust particles (DEP) induce apoptosis and reactive o xygen species (ROS) in pulmonary alveolar macrophages and RAW 264.7 cells. The toxicity of these organic extracts mimics the cytotoxicity of the intac t particles and could be suppressed by the synthetic sulfhydryl compounds, N-acetylcysteine and bucillamine. Because DEP-induced apoptosis follows cyt ochrome c release, we studied the effect of DEP chemicals on mitochondriall y regulated death mechanisms. Crude DEP extracts induced ROS production and perturbed mitochondrial function before and at the onset of apoptosis, Thi s mitochondrial perturbation follows an orderly sequence of events, which c ommence with a change in mitochondrial membrane potential, followed by cyto chrome c release, development of membrane asymmetry (annexin V staining), a nd propidium iodide uptake. Structural damage to the mitochondrial inner me mbrane, evidenced by a decrease in cardiolipin mass, leads to O-2(.-) gener ation and uncoupling of oxidative phosphorylation (decreased intracellular ATP levels). N-Acetylcysteine reversed these mitochondrial effects and ROS production. Overexpression of the mitochondrial apoptosis regulator, Bcl-2, delayed but did not suppress apoptosis, Taken together, these results sugg est that DEP chemicals induce apoptosis in macrophages via a toxic effect o n mitochondria.