Forbes R A, Steenbergen C, Murphy E
Laboratory of Signal Transduction, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC, USA.
Circ Res. 2001 Apr 27;88(8):802-9. doi: 10.1161/hh0801.089342.
Diazoxide, a selective opener of the mitochondrial ATP-sensitive potassium channel, has been shown to elicit tolerance to ischemia in cardiac myocytes and in perfused heart. However, the mechanism of this cardioprotection is poorly understood. Because reactive oxygen species (ROS) are recognized as important intracellular signaling molecules and have been implicated in ischemic preconditioning, we examined diazoxide-induced ROS production in adult cardiomyocytes. Cells treated with 50 micromol/L diazoxide showed a 173% increase in ROS production relative to baseline. 5-Hydroxydecanoate was found to attenuate the diazoxide-induced increase in ROS generation. The diazoxide-induced increase in ROS also was abrogated by the addition of either the antioxidant N-acetylcysteine (NAC) or N-mercaptopropionylglycine. We also examined the ability of NAC to block the protective effects of diazoxide in the perfused rat heart. After 20 minutes of global ischemia and 20 minutes of reflow, hearts perfused with 100 micromol/L diazoxide before ischemia showed significantly improved postischemic contractile function relative to untreated hearts (84% versus 29% of initial left ventricular developed pressure, respectively). Hearts treated with diazoxide in the presence of 4 mmol/L NAC recovered 53% of initial left ventricular developed pressure, whereas hearts treated with NAC alone recovered 46% of preischemic function. Using (31)P NMR spectroscopy, we found that, similar to preconditioning, diazoxide significantly attenuated ischemia-induced intracellular acidification and enhanced post- ischemic recovery of phosphocreatine levels, both of which were blocked by cotreatment with NAC. These data suggest that the cardioprotective actions of diazoxide are mediated by generation of a pro-oxidant environment.
二氮嗪是一种线粒体ATP敏感性钾通道的选择性开放剂，已被证明可使心肌细胞和灌注心脏对缺血产生耐受性。然而，这种心脏保护作用的机制尚不清楚。由于活性氧（ROS）被认为是重要的细胞内信号分子，并与缺血预处理有关，我们研究了二氮嗪在成年心肌细胞中诱导的ROS产生。用50 μmol/L二氮嗪处理的细胞显示ROS产生相对于基线增加了173%。发现5-羟基癸酸可减弱二氮嗪诱导的ROS生成增加。添加抗氧化剂N-乙酰半胱氨酸（NAC）或N-巯基丙酰甘氨酸也可消除二氮嗪诱导的ROS增加。我们还研究了NAC阻断二氮嗪对灌注大鼠心脏保护作用的能力。在进行20分钟全心缺血和20分钟再灌注后，缺血前用100 μmol/L二氮嗪灌注的心脏与未处理的心脏相比，缺血后收缩功能有显著改善（分别为初始左心室舒张末压的84%和29%）。在4 mmol/L NAC存在下用二氮嗪处理的心脏恢复了初始左心室舒张末压的53%，而单独用NAC处理的心脏恢复了缺血前功能的46%。使用磷-31核磁共振波谱法，我们发现，与预处理相似，二氮嗪显著减弱了缺血诱导的细胞内酸化，并增强了缺血后磷酸肌酸水平的恢复，而这两者均被与NAC联合处理所阻断。这些数据表明，二氮嗪的心脏保护作用是由促氧化环境的产生介导的。
