Effect of CoQ homologues on reactive oxygen generation by mitochondria.

Effect of CoQ compounds (Qs) on reactive oxygen (ROS) generation by mitochondrial complex I was studied using rat liver mitochondria and chemiluminescence probe L012. Kinetic analysis revealed that short chain Qs, such as Q2 and idebenone enhanced ROS generation by mitochondrial NADH oxidase system by a succinate-inhibitable mechanism. Lipid peroxidation in mitochondrial membranes induced by NADH and iron was inhibited by short chain Qs. The inhibitory activity was enhanced by co-oxidation of succinate as determined by chemiluminescence method and by electron spin resonance spectroscopy. These results suggested that the reduced form of short chain Qs inhibited mitochondrial ROS generation and lipid peroxidation.

Mechanism and characteristics of stimuli-dependent ROS generation in undifferentiated HL-60 cells.

It has been widely believed that undifferentiated human promyelocytic leukemia cells (HL-60) have no ability to generate reactive oxygen species (ROS) responding to stimuli. We report here that undifferentiated HL-60 cells possess NADPH oxidase and that generation of superoxide can be measured using a highly sensitive chemiluminescence dye, L-012. Five subunits of NADPH oxidase, namely, gp91(phox), p22(phox), p67(phox), p47(phox), and Rac 2, were detected in undifferentiated HL-60 cells by immunoblotting analysis. The contents of these NADPH oxidase components in the cells were increased with the differentiation induced by phorbol myristate acetate (PMA), except for p22(phox). Messenger RNAs of these subunits were also detected by the RT-PCR method, and their expressions increased except that of p22(phox) with the differentiation induced by PMA. Kinetic analysis using L-012 revealed that HL-60 cells generated substantial amounts of ROS by various stimulants, including formylmethionyl-leucyl-phenylalanine, PMA, myristic acid, and a Ca2+ ionophore, A23187. Both diphenyleneiodonium (an inhibitor of FAD-dependent oxidase) and apocynin (a specific inhibitor of NADPH oxidase) suppressed this stimuli-dependent ROS generation. Genistein, staurosporine, uric acid, and sodium azide inhibited the ROS generation in undifferentiated HL-60 cells in a similar way to that in undifferentiated neutrophils. These results suggested that the mechanism of ROS generation in undifferentiated HL-60 cells is the same as that in primed neutrophils.

Cross talk of nitric oxide, oxygen radicals, and superoxide dismutase regulates the energy metabolism and cell death and determines the fates of aerobic life.

Although oxygen is required for the energy metabolism in aerobic organisms, it generates reactive oxygen and nitrogen species that impair a wide variety of biological molecules, including lipids, proteins, and DNA, thereby causing various diseases. Because mitochondria are the major site of free radical generation, they are highly enriched with enzymes, such as Mn-type superoxide dismutase in matrix, and antioxidants including GSH on both sides of inner membranes, thus minimizing oxidative stress in and around this organelle. We recently showed that a cross talk of nitric oxide and oxygen radicals regulates the circulation, energy metabolism, reproduction, and remodeling of cells during embryonic development, and functions as a major defense system against pathogens. The present work shows that Cu/Zn-type superoxide dismutase, which has been postulated for a long time to be a cytosolic enzyme, also localizes bound to inner membranes of mitochondria, thereby minimizing oxidative stress in and around this organelle, while mitochondrial association decreases markedly with the variant types of the enzyme found in patients with familial amyotrophic lateral sclerosis. We also report that a cross talk of nitric oxide, superoxide, and molecular oxygen cooperatively regulates the fates of pathogens and their hosts and that oxidative stress in and around mitochondria also determines cell death in the development of animals and tissue injury caused by anticancer agents by some carnitine-inhibitable mechanism.

Mitochondrial generation of reactive oxygen species and its role in aerobic life.

Mitochondria are the major site for the generation of ATP at the expense of molecular oxygen. Significant fractions (approximately 2%) of oxygen are converted to the superoxide radical and its reactive metabolites (ROS) in and around mitochondria. Although ROS have been known to impair a wide variety of biological molecules including lipids, proteins and DNA, thereby causing various diseases, they also play critical roles in the maintenance of aerobic life. Because mitochondria are the major site of free radical generation, they are highly enriched with antioxidants including GSH and enzymes, such as superoxide dismutase (SOD) and glutathione peroxidase, on both sides of their membranes to minimize oxidative stress in and around this organelle. The present work reviews the sites and mechanism of ROS generation by mitochondria, mitochondrial localization of Mn-SOD and Cu,Zn-SOD which has been postulated for a long time to be a cytosolic enzyme. The present work also describes that a cross-talk of molecular oxygen, nitric oxide (NO) and superoxide radicals regulates the circulation, energy metabolism, apoptosis, and functions as a major defense system against pathogens. Pathophysiological significance of ROS generation by mitochondria in the etiology of aging, cancer and degenerative neuronal diseases is also described.

Effect of permethrin insecticide on rat polymorphonuclear neutrophils.

Polymorphonuclear neutrophils are professional phagocytes whose efficacy depends on a multicomponent NADPH oxidase for generating superoxide anions and bacterial killing. They can be primed and activated by different agents that can impair oxidative burst and phagocytosis with opposite effects: reduced capability to destroy bacteria or hyperactivation that induces the generation of large quantities of toxic reactive oxygen species, which can damage surrounding tissue and participate in inflammation. The present study was designed to evaluate the effect of sub-chronic (60 days) permethrin treatment (1/10 DL(50)) on rat polymorphonuclear neutrophils respiratory burst. The results show that permethrin treatment increases superoxide anion production (33 times) and the activity of hydrogen peroxide-myeloperoxidase system (67 times). In vitro experiments suggest that this effect can be related to permethrin priming and to physico-chemical changes at the plasma membrane level of neutrophils. The antioxidant supplementation with Vitamin E and coenzyme Q(10) can protect against the abnormal respiratory burst in rat treated with permethrin. The in vitro studies show that neutrophil apoptosis begins soon after 1h of incubation with permethrin (0.725% of total cells) or its metabolites (3-phenoxybenzyl alcohol, 3-phenoxybenzaldehyde and 3-phenoxybenzoic acid 1.36, 2.26 and 1.3 of total cells, respectively) and that the level of apoptotic cells is very low. In conclusion, immunotoxicity of permethrin measured in rats could prompt future studies on the consequences of chronic insecticide exposure.