Department of Internal Medicine/Endocrinology, University of Iowa and Iowa City Veterans Affairs Medical Center, Iowa City, Iowa, USA.
Am J Physiol Regul Integr Comp Physiol. 2011 Dec;301(6):R1616-24. doi: 10.1152/ajpregu.00395.2011. Epub 2011 Sep 21.
Mitochondrial superoxide is important in the pathogeneses of diabetes and its complications. However, there is uncertainty regarding the intrinsic propensity of mitochondria to generate this radical. Studies to date suggest that superoxide production by mitochondria of insulin-sensitive target tissues of insulin-deficient rodents is reduced or unchanged. Moreover, little is known of the role of the Coenzyme Q (CoQ), whose semiquinone form reacts with molecular oxygen to generate superoxide. We measured reactive oxygen species (ROS) production, respiratory parameters, and CoQ content in mitochondria from gastrocnemius muscle of control and streptozotocin (STZ)-diabetic rats. CoQ content did not differ between mitochondria isolated from vehicle- or STZ-treated animals. CoQ also was unaffected by weight loss in the absence of diabetes (induced by caloric restriction). Under state 4 or state 3 conditions, both respiration and ROS release were reduced in diabetic mitochondria fueled with succinate, glutamate plus malate, or with all three substrates (continuous TCA cycle). However, H(2)O(2) and directly measured superoxide production were substantially increased in gastrocnemius mitochondria of diabetic rats when expressed per unit oxygen consumed. On the basis of substrate and inhibitor effects, the mechanism involved multiple electron transport sites. More limited results using heart mitochondria were similar. ROS per unit respiration was greater in muscle mitochondria from diabetic compared with control rats during state 3, as well as state 4, while the reduction in ROS per unit respiration on transition to state 3 was less for diabetic mitochondria. In summary, ROS production is, in fact, increased in mitochondria from insulin-deficient muscle when considered relative to electron transport. This is evident on multiple energy substrates and in different respiratory states. CoQ is not reduced in diabetic mitochondria or with weight loss due to food restriction. The implications of these findings are discussed.
线粒体超氧物在糖尿病及其并发症的发病机制中很重要。然而，对于线粒体产生这种自由基的内在倾向仍存在不确定性。迄今为止的研究表明，胰岛素缺乏啮齿动物胰岛素敏感靶组织的线粒体产生超氧物的能力降低或不变。此外，对于辅酶 Q（CoQ）的作用知之甚少，其半醌形式与分子氧反应生成超氧物。我们测量了来自对照和链脲佐菌素（STZ）糖尿病大鼠腓肠肌线粒体的活性氧（ROS）产生、呼吸参数和 CoQ 含量。从载体或 STZ 处理的动物中分离的线粒体中 CoQ 含量没有差异。CoQ 也不受糖尿病（由热量限制引起）时体重减轻的影响。在琥珀酸、谷氨酸加苹果酸或所有三种底物（连续 TCA 循环）为燃料的情况下，糖尿病线粒体的呼吸和 ROS 释放均在状态 4 或状态 3 下降低。然而，当以单位耗氧量表示时，糖尿病大鼠腓肠肌线粒体中的 H2O2 和直接测量的超氧物产生大大增加。基于底物和抑制剂的作用，所涉及的机制涉及多个电子传递位点。使用心脏线粒体的更有限的结果相似。与对照组相比，在状态 3 以及状态 4 下，糖尿病大鼠肌肉线粒体的单位呼吸 ROS 更大，而糖尿病线粒体向状态 3 过渡时单位呼吸 ROS 的减少幅度较小。总之，当考虑到电子传递时，胰岛素缺乏的肌肉线粒体中的 ROS 产生实际上增加了。这在多种能量底物和不同的呼吸状态下都是如此。CoQ 在糖尿病线粒体中或由于食物限制引起的体重减轻时没有减少。讨论了这些发现的意义。
