Andrabi Shaida A, Sayeed Iqbal, Siemen Detlef, Wolf Gerald, Horn Thomas F W
Institute for Medical Neurobiology, Otto-von-Guericke University, Magdeburg, Germany.
FASEB J. 2004 May;18(7):869-71. doi: 10.1096/fj.03-1031fje. Epub 2004 Mar 19.
Melatonin, the secretory product of the pineal gland, is known to be neuroprotective in cerebral ischemia, which is so far mostly attributed to its antioxidant properties. Here we show that melatonin directly inhibits the mitochondrial permeability transition pore (mtPTP). mtPTP contributes to the pathology of ischemia by releasing calcium and cytochrome c (cyt c) from mitochondria. Consistently, NMDA-induced calcium rises were diminished by melatonin in cultured mouse striatal neurons, similar to the pattern seen with cyclosporine A (CsA). When the mouse striatal neurons were subjected to oxygen-glucose deprivation (OGD), melatonin strongly prevented the OGD-induced loss of the mitochondrial membrane potential. To assess the direct effect of melatonin on the mtPTP activity at the single channel level, recordings from the inner mitochondrial membrane were obtained by a patch-clamp approach using rat liver mitoplasts. Melatonin strongly inhibited mtPTP currents in a dose-dependent manner with an IC50 of 0.8 microM. If melatonin is an inhibitor of the mtPTP, it should prevent mitochondrial cyt c release as seen in stroke models. Rats underwent middle cerebral artery occlusion (MCAO) for 2 h followed by reperfusion. Melatonin (10 mg/kg ip) or vehicle was given at the time of occlusion and at the time of reperfusion. Indeed, infarct area in the brain sections of melatonin-treated animals displayed a considerably decreased cyt c release along with less activation of caspase-3 and apoptotic DNA fragmentation. Melatonin treatment diminished the loss of neurons and decreased the infarct volume as compared with untreated MCAO rats. Our findings suggest that the direct inhibition of the mtPTP by melatonin may essentially contribute to its anti-apoptotic effects in transient brain ischemia.
褪黑素是松果体分泌的产物，已知其在脑缺血中具有神经保护作用，目前这主要归因于其抗氧化特性。在此我们表明，褪黑素可直接抑制线粒体通透性转换孔（mtPTP）。mtPTP通过从线粒体释放钙和细胞色素c（cyt c）而导致缺血病理过程。同样，在培养的小鼠纹状体神经元中，褪黑素可减少N-甲基-D-天冬氨酸（NMDA）诱导的钙升高，其模式与环孢素A（CsA）所见相似。当小鼠纹状体神经元遭受氧糖剥夺（OGD）时，褪黑素可强烈阻止OGD诱导的线粒体膜电位丧失。为了在单通道水平评估褪黑素对mtPTP活性的直接影响，使用大鼠肝线粒体膜片钳记录线粒体内膜电流。褪黑素以剂量依赖性方式强烈抑制mtPTP电流，半数抑制浓度（IC50）为0.8微摩尔。如果褪黑素是mtPTP的抑制剂，那么在中风模型中它应能阻止线粒体cyt c释放。大鼠进行大脑中动脉闭塞（MCAO）2小时后再灌注。在闭塞时和再灌注时给予褪黑素（10毫克/千克腹腔注射）或溶剂。实际上，褪黑素处理动物的脑切片梗死面积显示cyt c释放明显减少，同时半胱天冬酶-3激活减少和凋亡性DNA片段化减少。与未处理的MCAO大鼠相比，褪黑素处理减少了神经元损失并减小了梗死体积。我们的研究结果表明，褪黑素对mtPTP的直接抑制可能在短暂性脑缺血中对其抗凋亡作用起重要作用。
