三七总皂苷抑制大鼠全脑缺血后海马CA1区神经元凋亡及其机制研究

Inhibition and machanisms of total saponins from Panax notoginseng on apoptosis of hippocampal CA1 subfield neurons of rats following global cerebral ischemia

目的探讨三七总皂苷(TSPN)抑制大鼠全脑缺血后海马CA1区神经元的凋亡作用及其相关机制。方法采用四血管阻断法制备大鼠全脑缺血模型,缺血后30 min再灌注;大鼠分成假手术组、模型组和TSPN组。TSPN组ip不同剂量(25、50、75、100 mg/kg)TSPN。再灌注第14天,通过海马CA1区尼氏染色和大鼠的生存率确定TSPN发挥神经保护作用的最佳剂量。对模型组和最佳剂量TSPN组大鼠在不同再灌注时间点(1、3、7、14 d)进行神经功能评分,采用免疫组化法观察CA1区Caspase-3、Bcl-2、Bax的阳性细胞密度,并采用免疫印迹技术检测Caspase-3、Bcl-2、Bax蛋白在海马的表达水平。结果 75 mg/kg TSPN组大鼠生存率为100%,CA1区神经元密度显著高于模型组和其他剂量TSPN组(P<0.05);TSPN(75 mg/kg)组神经功能评分显著少于模型组(P<0.01);TSPN(75 mg/kg)组CA1区Caspase-3阳性细胞密度在全脑缺血第7、14天显著低于模型组(P<0.001);20 000的Caspase-3第3、7、14天的蛋白水平及17 000的Caspase-3在第7、14天蛋白水平均显著低于模型组(P<0.001);TSPN(75 mg/kg)组CA1区Bcl-2阳性细胞密度及蛋白水平在第7、14天高于模型组(P<0.001),而Bax阳性细胞密度第7、14天低于模型组(P<0.001),TSPN组第3、7、14天海马Bax蛋白水平显著低于模型组(P<0.001);TSPN组Bcl-2和Bax阳性细胞及蛋白水平的比值在第7、14天显著高于模型组(P<0.001)。结论 TSPN可通过上调Bcl-2和Bax阳性细胞和蛋白水平的比值,减少Caspase-3的活化而抑制全脑缺血后大鼠海马CA1区神经元的凋亡。

Objective To explore whether total saponins of Panax notoginseng（TSPN） can protect hippocampal CA1 subfield neurons against apoptosis following global cerebral ischemia via up-regulating the Bcl-2/Bax ratio and preventing Caspase-3 activation. Methods Using four-vessel occlusion method to build the global cerebral ischemia model and the ischemia time was 30 min. All rats were divided into Sham group, vehicle group, and different doses（25, 50, 75, and 100 mg/kg） of TSPN groups. The rats in TSPN groups were ip administered with TSPN. The dose of TSPN was suspended in 0.9% saline（10 g/L）, while rats in vehicle group were treated with equal volume of 0.9% saline, one injection per day. Compared the survival rate and hippocampal CA1 subfield neuronal density by Nissl staining after reperfusion of 14 d to make sure the best dose of TSPN for neuroprotection. Then to evaluate the neurological score and investigate the expression level of the Caspase-3, Bcl-2, and Bax in the hippocampus CA1 region at days 1, 3, 7, and 14 post-ischemia by immunohistochemistry; In addition, the Western-blotting was adopted to test the protein level of these three proteins. Results The survival rate of the rats in 75 mg/kg TSPN groups was 100%, and its neuronal density was significantly higher than that in vehicle group and other doses of TSPN groups（P 〈0.05）; The neurological score in TSPN group was significantly less than that in vehicle group（P 〈0.01）; The Caspase-3 neuronal density in the CA1 subfield of TSPN group on days 7 and 14 was significantly less than that in vehicle group（P 〈0.001）; The statistical meaning existed about the protein level of Caspase-3 with molecular weight of 20 000 on days 3, 7, and 14 and 17 000 on days 7 and 14 in two groups（P 〈0.001）. The neuronal density of Bcl-2 cells in the CA1 subfield and Bcl-2 protein level in the hippocampus of TSPN group at days 7 and 14 was significantly higher than that in vehicle group（P〈 0.001）; Besides, the Bax neuronal density at days 7 and 14 was significantly lower than that in vehicle group（P 〈0.001）; And its protein level of the hippocampus was less than that in vehicle group at days 3, 7 and 14（P〈 0.001）. The results of ratio of Bcl-2/Bax from not only the neuronal density but also the protein expression demonstrated that the Bcl-2/Bax ratio in TSPN group was significantly higher than that in vehicle groups on days 7 and 14（P 〈0.001）. Conclusion TSPN can protect the hippocampal CA1 subfield neurons against apoptosis following global cerebral ischemia in adult rats via up-regulating the Bcl-2/Bax ratio and preventing Caspase-3 activation.