Mitochondrial damage mediated by reactive oxygen species : A study in corticosteroid myopathy and mitochondrial encephalomyopathies

皮质类固醇肌病是接受慢性皮质类固醇治疗的患者的主要临床问题，表现为四肢近端内侧进行性肌肉萎缩。虽然肌肉损伤的病理生理学机制已经被提出，但确切的发病机制仍然不清楚。我们评估了接受糖皮质激素治疗的患者与健康对照组或未接受糖皮质激素治疗的患者的线粒体功能。采用自行车测功机进行有氧运动试验，测定血清乳酸水平和总乳酸生成量。还研究了活组织骨骼肌中线粒体的呼吸活性和氧化损伤。有氧运动试验结果显示，接受皮质类固醇治疗的患者乳酸显著过剩(p&lt；0.005)，这与使用皮质类固醇的总剂量(p&lt；0.0001)呈正相关。在这些患者中，线粒体和核DNA中复合体I的线粒体酶活性显著降低(p&lt；0.001)，活组织骨骼肌的氧化损伤显著(p&lt；005)。RD细胞在含10^5~10^7M地塞米松的培养液中培养3h~7d。流式细胞术分别用DCFHDA和Annexin V/PI分析细胞内的活性氧和细胞凋亡率。从3h到7d，活性氧的产生逐渐增加，从2d到7d，细胞凋亡明显。结果提示，长期给予糖皮质激素可导致骨骼肌氧化损伤所致的线粒体功能障碍，这可能是糖皮质激素性肌病的至少部分发病机制。

Corticosteroid myopathy is a major clinical problem in patients undergoing chronic corticosteroid treatment and shows insideous and progressive muscle atrophy in proximal limbs. Although several mechanisms underlying the pathophysiology of muscle injury have been postulated, precise pathogenesis is still not clear.We evaluated the mitochondrial functions in patients administered with conticosteroids compared with those in healthy controls or patients not receiving corticosteroids. The serum levels and total production of lactate were investigated by an aerobic exercise test using a bicycle ergometer. Mitochondrial respiratory activities and oxidative damage in biopsied skeletal muscles were also studied. The results of aerobic exercise tests revealed a significant overproduction of lactate in patients treated with corticosteroids (p<0.005), which was positively correlated with total corticosteroid doses administered (p<0.0001). In these patients, mitochondrial enzyme activity in complex I was significantly decreased (p<0.05) and oxidative damage of biopsied skeletal muscle was remarkable both in mitochondrial and nuclear DNAs (p<0.001).The corticosteroid-induced mitochondrial damage was further studied in a cultured human muscle cell line, RD cell. RD cells were cultured in a medium containing 10^5-10^7M dexamethasone for 3 hours to 7 days. Reactive oxygen species and apoptosis were analyzed by flowcytometry using DCFHDA and Annexin V/PI, respectively. The production of reactive oxygen species was progressively increased form 3 hours to 7 days and apoptosis was prominent from 2 to 7 days. SOD (100 u/ml) decreased the production of reactive oxygen species and the apoptotic change.The results suggest that chronic corticosteroid administration induces oxidative damage-mediated mitochondrial dysfunction in skeletal muscles, which may be the pathogenesis, at least in part, of corticosteroid-induced myopathy.