Mitochondria-derived reactive oxygen species: Detection, involvement in mononuclear cell signal transduction and dysfunction

Studies over the last several decades have suggested a critical involvement of reactive oxygen species (ROS), including superoxide (O ₂.−) and hydrogen peroxide (H₂O ₂), in the pathogenesis of a diversity of human diseases and disorders. ROS can also act as potential cellular messengers involved in cell signal transduction, leading to physiological responses. Mitochondrial respiration usually consumes about 90% of the oxygen utilized by cells, and is generally considered the major source of cellular O₂.− and H₂O₂. Thus, we hypothesized that production of ROS from mitochondria could be an important mechanism involved in mononuclear cell signal transduction and dysfunction. To test this hypothesis, we have carried out the following studies, mainly using human myeloblastic ML-1 cells and the monocytes/macrophages derived from them as a model system.; We have shown that mitochondrial respiration is the major source of both cellular O₂.− and H₂O₂ in unstimulated monocytes/macrophages. We have also demonstrated that O ₂.− can exit mitochondria and be released extracellularly, being the major source of extracellular O₂.− with unstimulated monocytes/macrophages. We have shown that the O₂. − that exits from mitochondria can react with nitric oxide, forming peroxynitrite, and can cause the oxidation of low density lipoprotein.; To demonstrate a signaling role for mitochondrial ROS, we have determined the involvement of mitochondria-derived O₂.− and H₂O₂ in protein kinase C (PKC)-induced interleukin-1β (IL-1β) gene expression in monocytes/macrophages. We have observed that activation of the classical isoforms of PKC in monocytes/macrophages leads to translocation of these PKCs onto mitochondria and increased production of mitochondria-derived ROS, including both O₂.− and H₂O₂. We have demonstrated that the NADH dehydrogenase component of mitochondrial complex I appears to be the site of the ROS production following PKC activation. We have further demonstrated that following PKC activation the ROS, particularly O₂.− released from the mitochondria may be involved in the activation of the IL-1β gene, leading to the maturation and release of IL-1β molecules.; To determine the role of mitochondria-derived ROS in xenobiotic-induced mononuclear cell toxicity, we have investigated the interaction of the benzo(a)pyrene (BP)-derived quinones with mitochondria derived from monocytes/macrophages. With isolated mitochondria, we have observed that the BP-derived quinones can undergo redox cycling mediated by the mitochondrial electron transport chain (METC), resulting in production of O₂.− and H₂O₂. Both complexes I and III of the METC are able to catalyze the redox cycling of the BP-derived quinones. In intact myeloblastic ML-1 cells, BP-derived quinones also undergo METC-mediated redox cycling, producing ROS. We have further observed that the presence of submicromolar concentrations of BP-derived quinones does not affect the 12-O-tetradecanoylphorbol-13-acetate-induced differentiation of ML-1 cells to monocytes/macrophages. However, these differentiated monocytes/macrophages exhibit deficiency in mitochondrial functions and a decreased capacity to undergo phagocytosis and a respiratory burst, possibly resulting from BP quinone-mediated ROS production in mitochondria. (Abstract shortened by UMI.)...