COMPLEX III AUGMENTS OXIDANTS DAMAGE IN ISCHEMIC AGED HEART

老年心脏缺血再灌流后心肌损伤加重。在24个月内，老化降低了氧化磷酸化的速率和电子传递链上的络合物HI和IV的活性。Fischer 344只大鼠心脏，而6个月。成人对照。衰老损伤对心肌线粒体纤维间质群具有选择性。 位于肌原纤维之间，而位于质膜下的肌膜下线粒体(SSM)没有改变。复合体III含有11个多肽亚基，包括3个催化中心：细胞色素b、细胞色素c1和Rieske铁硫蛋白(Isp)。在IFM中，衰老改变底物氧化部位的细胞色素b，即QO部位。IFM中复合体III的老化缺陷导致基线状态下活性氧物种(ROS)的产生增加。 成年和老年心脏在缺血过程中会发生线粒体损伤。在成人和老年心脏中，缺血损伤了复合体III的isp，降低了复合体III的活性。与成人心脏相比，老年心脏在缺血期间遭受额外的SSM和IFM氧化损伤。心磷脂是一种重要的线粒体膜磷脂，只有在老年心脏才能被修饰，从而产生一种新的心磷脂分子物种。同样，位于心磷脂附近的细胞色素c也只在老年心脏中被修饰。老年心脏缺血后细胞色素氧化酶活性降低，与成人心脏不同，外源性磷脂的加入不能恢复细胞色素氧化酶活性。在老年人心脏中的这种观察表明，缺血导致细胞色素氧化酶多肽亚单位的持续损害，而不是像成人心脏那样对复合体内膜环境的可逆性损害。因此，在缺血期间，电子传递链中的特定分子靶点，包括心磷脂，只有在 那颗衰老的心。 线粒体是心肌缺血时产生的ROS的主要来源。复合体III是成人心脏线粒体内产生ROS的主要部位，其在老年心脏缺血时的氧化损伤中的作用尚不清楚。我们发现，在缺血期间，通过在缺血前立即用鱼藤酮阻断络合物I来限制电子流入络合物III，可以保持老年心脏通过络合物III和IV进行的氧化磷酸化的速度。 我们认为，在缺血期间，复合体III是老年心脏氧化损伤增强的一个关键机制，我们假设复合体III的ROS损伤老年心脏的细胞色素氧化酶。复合体III的QO位的老化缺陷加速了IFM在缺血时的氧化损伤。我们假设，细胞色素氧化酶的损伤反过来导致细胞色素c和心磷脂的氧化修饰。我们假设，在老化的心肌线粒体受到缺血性损伤后，ROS的产生和释放增加，为再灌注期间的氧化损伤奠定了基础。 线粒体释放的ROS增加，进而放大再灌流期间的心脏损伤和功能障碍，这种损伤和功能障碍可以通过可逆地限制缺血期间流入复合体III的电子来减少。

Myocardial injury is increased following ischemia and reperfusion in the aged heart. Aging decreases the rate of oxidative phosphorylation and the activity of complexes HI and IV of the electron transport chain in the 24 mo. Fischer 344 rat heart, compared to 6 mo. adult controls. The aging impairment is selective to the interfibrillar population of cardiac mitochondria 0FM) that reside among the myofibrils, whereas subsarcolemmal mitochondria (SSM), located beneath the plasma membrane, are unaltered. Complex III contains 11 peptide subunits, including three catalytic centers: cytochrome b, cytochrome c1, and the Rieske iron-sulfur protein (ISP). Aging modifies cytochrome b at the site of substrate oxidation, the Qo site, in IFM. The aging defect in complex III in IFM leads to an increased production of reactive oxygen species (ROS) in the baseline state. Mitochondrial damage occurs during ischemia in the adult and aged heart. Ischemia damages the ISP of complex III and decreases complex III activity in both populations of mitochondria in adult and aged hearts. In contrast to the adult heart, the aged heart sustains additional oxidative damage to both SSM and IFM during ischemia. Cardiolipin, a key inner mitochondrial membrane phospholipid, is modified only in the aged heart, generating a new molecular species of cardiolipin. Cytochrome c, located in proximity to cardiolipin, is modified, again, only in the aged heart. Cytochrome oxidase activity decreases following ischemia in the aged heart, and, unlike in the adult heart, activity cannot be restored following the addition of exogenous phospholipid. This observation in the aged heart indicates that ischemia led to persistent damage to a peptide subunit of cytochrome oxidase, rather than reversible damage to the inner membrane environment of the complex as in the adult heart. Thus, during ischemia, specific molecular targets in the electron transport chain, including cardiolipin, sustain oxidative damage only in the aged heart. Mitochondria are the major source of the ROS generated during myocardial ischemia. Complex III is the major site of ROS production within mitochondria in the adult heart The role of complex III in the oxidative damage sustained by the aged heart during ischemia is unknown. We found that limitation of electron flow into complex III during ischemia achieved by blockade of complex I with rotenone immediately prior to ischemia preserves the rate of oxidative phosphorylation through complexes III and IV in the aged heart. We propose that during ischemia complex III is a key mechanism of the enhanced oxidative damage observed in the aged heart, We hypothesize that ROS from complex III damage cytochrome oxidase in the aged heart. Oxidative damage during ischemia is accelerated in IFM by the aging defect present at Qo site of complex III. We hypothesize that damage to cytochrome oxidase leads in turn to oxidative modification of cytochrome c and cardiolipin. We hypothesize that following ischemic damage to aged heart mitochondria, ROS production and release is increased, setting the stage for oxidative damage during reperfusion. Enhanced ROS release from mitochondria, in turn, amplifies cardiac damage and dysfunction during reperfusion that can be decreased by reversibly limiting electron flow into complex III during ischemia.