Peer CJ, Callery PS, Hollander JM. Diabetic cardiomyopathy-associated dysfunction in spatially distinct mitochondrial subpopulations. Am J Physiol Heart Circ Physiol 296: H359 -H369, 2009. First published December 5, 2008 doi:10.1152/ajpheart.00467.2008.-Diabetic cardiomyopathy is the leading cause of heart failure among diabetic patients, and mitochondrial dysfunction has been implicated as an underlying cause in the pathogenesis. Cardiac mitochondria consist of two spatially, functionally, and morphologically distinct subpopulations, termed subsarcolemmal mitochondria (SSM) and interfibrillar mitochondria (IFM). SSM are situated beneath the plasma membrane, whereas IFM are embedded between myofibrils. The goal of this study was to determine whether spatially distinct cardiac mitochondrial subpopulations respond differently to a diabetic phenotype. Swiss-Webster mice were subjected to intraperitoneal injections of streptozotocin or citrate saline vehicle. Five weeks after injections, diabetic hearts displayed decreased rates of contraction, relaxation, and left ventricular developed pressures (P Ͻ 0.05 for all three). Both mitochondrial size (forward scatter, P Ͻ 0.01) and complexity (side scatter, P Ͻ 0.01) were decreased in diabetic IFM but not diabetic SSM. Electron transport chain complex II respiration was decreased in diabetic SSM (P Ͻ 0.05) and diabetic IFM (P Ͻ 0.01), with the decrease being greater in IFM. Furthermore, IFM complex I respiration and complex III activity were decreased with diabetes (P Ͻ 0.01) but were unchanged in SSM. Superoxide production was increased only in diabetic IFM (P Ͻ 0.01). Oxidative damage to proteins and lipids, indexed through nitrotyrosine residues and lipid peroxidation, were higher in diabetic IFM (P Ͻ 0.05 and P Ͻ 0.01, respectively). The mitochondria-specific phospholipid cardiolipin was decreased in diabetic IFM (P Ͻ 0.01) but not SSM. These results indicate that diabetes mellitus imposes a greater stress on the IFM subpopulation, which is associated, in part, with increased superoxide generation and oxidative damage, resulting in morphological and functional abnormalities that may contribute to the pathogenesis of diabetic cardiomyopathy. diabetes; free radical; mitochondria
The antioxidant ␣-lipoic acid (LA) is a naturally occurring compound that has been shown to possess promising anticancer activity because of its ability to preferentially induce apoptosis and inhibit proliferation of cancer cells relative to normal cells. However, the molecular mechanisms underlying the apoptotic effect of LA are not well understood. We report here that LA induced reactive oxygen species (ROS) generation and a concomitant increase in apoptosis of human lung epithelial cancer H460 cells. Inhibition of ROS generation by ROS scavengers or by overexpression of antioxidant enzymes glutathione peroxidase and superoxide dismutase effectively inhibited LA-induced apoptosis, indicating the role of ROS, especially hydroperoxide and superoxide anion, in the apoptotic process. Apoptosis induced by LA was found to be mediated through the mitochondrial death pathway, which requires caspase-9 activation. Inhibition of caspase activity by the pan-caspase inhibitor (z-VAD-FMK) or caspase-9-specific inhibitor (z-LEHD-FMK) completely inhibited the apoptotic effect of LA. Likewise, the mitochondrial respiratory chain inhibitor rotenone potently inhibited the apoptotic and ROS-inducing effects of LA, supporting the role of mitochondrial ROS in LA-induced cell death. LA induced down-regulation of mitochondrial Bcl-2 protein through peroxide-dependent proteasomal degradation, and overexpression of the Bcl-2 protein prevented the apoptotic effect of LA. Together, our findings indicate a novel pro-oxidant role of LA in apoptosis induction and its regulation by Bcl-2, which may be exploited for the treatment of cancer and related apoptosis disorders.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.