褪黑素对糖尿病周围神经病变大鼠氧化应激及周围神经功能和形态的作用

Effect of melatonin on oxidative stress and peripheral nerve function in rats with diabetic peripheral neuropathy

背景:课题组前期针对糖尿病肾病的实验显示,褪黑素可以显著提高糖尿病大鼠血浆和肾脏内抗氧化酶的活性,改善肾脏的形态学变化。目的:在前期实验的基础上,进一步观察褪黑素对糖尿病周围神经病变大鼠氧化应激和周围神经功能和形态的作用。设计、时间及地点:随机对照动物试验,于2005-04/11在解放军第二军医大学动物实验中心完成。材料:2月龄健康雄性SD大鼠,单次腹腔注射链脲佐菌素60mg/kg诱导建立糖尿病大鼠模型。方法:将糖尿病模型大鼠维持饲养8周建立糖尿病周围神经病变大鼠模型,然后按体质量随机分为3组:模型组,褪黑素0.5,10mg/(kg·d)组,以未造模、鼠龄及体质量相匹配的8只大鼠为正常对照组。褪黑素0.5,10mg/(kg·d)组大鼠每日16:00灌胃给予相应剂量的褪黑素,其他2组大鼠予等量体积分数为0.02的乙醇溶液灌胃,持续8周。主要观察指标:检测各组大鼠坐骨神经内超氧化物歧化酶、谷胱甘肽过氧物酶活性和脂质过氧化产物丙二醛含量的变化,大鼠摆尾阈值、坐骨神经神经传导速度和超微结构的变化。结果:各组糖尿病大鼠坐骨神经传导速度显著低于正常对照组(P<0.01),褪黑素0.5,10mg/(kg·d)治疗后神经传导速度高于模型组(P<0.05,0.01)。褪黑素0.5,10mg/(kg·d)组丙二醛含量低于模型组(P<0.01),血清超氧化物歧化酶、谷胱甘肽过氧物酶活性高于模型组(P<0.01)。模型组大鼠坐骨神经多数有髓纤维髓鞘板结构破坏严重,出现裂隙、空泡等现象,轴突严重被挤压,轴突变性、萎缩。褪黑素治疗后坐骨神经纤维的髓鞘仍不正常,但较模型组明显减轻,褪黑素10mg/(kg·d)组改变要好于褪黑素0.5mg/(kg·d)组。结论:褪黑素能有效抑制糖尿病周围神经病变大鼠的氧化应激反应,改善神经功能和结构变化。糖尿病时自由基损伤和抗氧化能力的降低可能在糖尿病周围神经病变的发生发展中发挥重要作用。

BACKGROUND： Previous studies on diabetic nephropathy demonstrate that melatonin can accelerate the activity of antioxidase, and improve the renal morphology changes in diabetic rats. OBJECTIVE： To investigate the effects of melatonin on oxidative stress, sciatic nerve function and ultrastructure changes in rats with diabetic peripheral neuropathy. DESIGN, TIME AND SETTING： The randomized controlled experiment of animal was conducted in the Animal Experiment Center of The Second Military Medical University from April to November 2005. MATERIALS： Healthy, male, SD rats with 2-month-old were created diabetic rat＇s models by intraperitoneal injection 60 mg/kg streptozotocin. METHODS： Eight weeks later, diabetic peripheral neuropathy models were randomly assigned to the model, melatonin 0.5, 10 mg/（kg.d） and normal control groups according to different body weights. Rats in the melatonin group were performed intragastric administration of 0.5, 10 mg/（kg.d） melatonin, other groups were administrated with 0.02 alcohol solution for 8 weeks. MAIN OUTCOME MEASURES： The sciatic nerve superoxide dismutase, glutathione peroxidase, malonaldehyde, sciatic nerve ultrastructure changes and motor conduction velocity （MCV）, tailflick threshold were evaluated. RESULTS： MCV of the sciatic nerve in the control group were significantly lower than that of the normal control group （P 〈 0.01）, the melatonin group were obviously higher than the control group （P 〈 0.05, P 〈 0.01）. Superoxide dismutase and glutathione peroxidase activities were lower and malonaldehyde levels were higher in sciatic nerves of the melatonin group than those in the control group （P 〈 0.01）. Sciatic nerve showed significant demyelination changes and axon atrophy in the control group. Melatonin meliorated sciatic nerves nerve ultrastructure changes correlated with dosage. CONCLUSION： Melatonin can inhibit oxidative stress in sciatic nerve and improve sciatic nerve function and ultrastructure changes in diabetic rats. Overproduction of reactive oxygen free radicals and insufficiency in antioxidant enzymes may contribute to the development of diabetic peripheral neuropathy.