Mitochondrial generation of reactive oxygen species is enhanced at the Q_o site of the complex III in the myocardium of Trypanosoma cruzi-infected mice: Beneficial effects of an antioxidant

In this study, we have characterized the cellular source and mechanism for the enhanced generation of reactive oxygen species (ROS) in the myocardium during Trypanosoma cruzi infection. Cardiac mitochondria of infected mice, as compared to normal controls, exhibited 63.3% and 30.8% increase in ROS-specific fluorescence of dihydroethidium (detects O₂ ^•-) and amplex red (detects H₂O₂), respectively. This increase in ROS level in cardiac mitochondria of infected mice was associated with a 59% and 114% increase in the rate of glutamate/malate- (complex I substrates) and succinate- (complex II substrate) supported ROS release, respectively, and up to a 74.9% increase in the rate of electron leakage from the respiratory chain when compared to normal controls. Inhibition studies with normal cardiac mitochondria showed that rotenone induced ROS generation at the Q _Nf-ubisemiquinone site in complex I. In complex III, myxothiazol induced ROS generation from a site located at the Q_o center that was different from the Q_i center of O₂ ^•- generation by antimycin. In cardiac mitochondria of infected mice, the rate of electron leakage at complex I during forward (complex I-to-complex III) and reverse (complex II-to-complex I) electron flow was not enhanced, and complex I was not the main site of increased ROS production in infected myocardium. Instead, defects of complex III proximal to the Q_o site resulted in enhanced electron leakage and ROS formation in cardiac mitochondria of infected mice. Treatment of infected mice with phenyl-α-tert-butyl-nitrone (PBN) improved the respiratory chain function, and, subsequently, decreased the extent of electron leakage and ROS release. In conclusion, we show that impairment of the Q_o site of complex III resulted in increased electron leakage and O₂ ^•- formation in infected myocardium, and was controlled by PBN.