钙蛋白酶抑制剂3对新生鼠缺氧缺血性脑损伤的保护作用

目的探讨钙蛋白酶抑制剂3（MDL 28170）对新生大鼠缺氧缺血性脑损伤（HIBD）的保护作用及机制。方法将新生7dSD大鼠随机分为对照组、HIBD组及钙蛋白酶抑制剂．3治疗组（MDL组）,分别于HI后6、24、72h取材,采用实时荧光定量PCR技术检测μ-calpain mRNA变化,免疫印迹法检测μ-calpain及caspase-3活性蛋白表达,TUNEL法观察大脑皮质凋亡细胞数;并计数HI后24h海马CA1区神经元死亡数。结果脑缺氧缺血后μ-calpain mRNA在6h即增高,24h达到高峰（P〈0．05）;μ-calpain蛋白质的活化片段76000与总片段80000比值6h即高于对照组（P〈0．05）,24h达到高峰（P〈0．01）,72h仍处于较高水平（P〈0．05）;caspase-3活性蛋白质在HI后24h达到高峰（P〈0．01）,72h降至对照组水平（P〉0．05）;损伤侧大脑皮质凋亡细胞随着时间延长逐渐增多,24h达到高峰,72h与对照组差异仍有统计学意义（P〈0．01）;24h时HIBD组CA1区神经元死亡数显著高于对照组（P〈0．01）。予MDL 28170干预后,MDL6h及24h组μ-calpain及caspase-3活性蛋白质表达、凋亡细胞数均较同时间点HIBD组减少（P〈0．05）,同时24h CA1区神经元死亡数明显减少（P〈0．05）;MDL28170虽然能降低μ-calpain mRNA的表达量,但与HIBD组相比差异不明显（P〉0．05）。结论HI后μ-calpain基因及蛋白质表达增加,参与了HIBD的发生;钙蛋白酶抑制剂-3可通过抑制μ-calpain及caspase-3蛋白质表达,对抗细胞坏死和凋亡,发挥脑保护作用。

Protective effect of calpain inhibitor-3 on hypoxic-ischemic brain damage of neonatal rats

OBJECTIVE: The mechanisms of hypoxic-ischemic brain damage (HIBD) are still largely unknown. Elevation of intracellular calcium concentration and subsequent calcium-dependent proteases activation such as calpains seem to play an important role in the process of neuronal death. Calpain inhibitors showed neuroprotective effects in adult rat cerebral ischemia models. This study aimed to investigate the protective effect and associated mechanisms of calpain inhibitor-3 (MDL28170) on HIBD of neonatal rats. METHODS: Seven-day old Sprague-Dawley rats were randomly divided into three groups: the control group (n = 18), HIBD group (n = 48) and calpain inhibitor-3 treated group (MDL group, n = 48). The mice in the latter two groups were subjected to hypoxia-ischemia (HI) insult. The puppies in MDL group were intraperitoneally injected with MDL28170 (25 mg/kg) at 0, 2 and 4 h after HI, while those in the other two groups were intraperitoneally injected with normal saline instead. All the pupies were sacrificed at 6 h, 24 h and 72 h after HI. Quantitative real-time fluorescent polymerase chain reaction was employed to detect micro-calpain gene expression, immunoblotting technique was used to measure mu-calpain and caspase-3 protein activation, apoptosis of ipsilateral cortex was detected by terminal deoxynucleotidyl transferase mediated d-UTP nick end labeling staining (TUNEL). CA1 neuronal loss was counted 24 h after HI by light microscopy. RESULTS: After HI mu-calpain mRNA began to increase at 6 h and reached peak at 24 h compared to the control (1.805 and 4.83 vs. 1, P < 0.05); mu-calpain was activated through autolysis, the ratio of its activated fragment (76 000) vs. whole fragment (80 000) was significantly higher at 6 h (0.547 +/- 0.095) compared to the control (0.095 +/- 0.016, P < 0.05), it reached peak at 24 h (0.921 +/- 0.058, P < 0.01) and was still at a high level at 72 h (0.708 +/- 0.025, P < 0.05). Expression of activated caspase-3 protein reached peak at 24 h (3.78 +/- 0.30, P < 0.01), decreased to the same level as the control (1.56 +/- 0.07) at 72 h (1.82 +/- 0.11, P > 0.05). Apoptotic cells in the cortex ipsilateral to HI insult increased after HIBD, reached peak at 24 h (135.46 +/- 17.52/visual field) and was still markedly higher at 72 h (79.32 +/- 17.79/visual field) compared with the control (5.33 +/- 1.53/visual field, P < 0.01). At 24 h after HI CA1 neuronal loss (30.0 +/- 6.2/oil immersion lens field) in the HIBD group was significantly higher than that of the control (2.4 +/- 0.3/oil immersion lens field, P < 0.01). However, in the MDL group the expressions of mu-calpain and caspase-3 proteins were diminished, TUNEL positive cells at 6 h and 24 h were decreased and CA1 neuronal loss (18.2 +/- 2.4/oil immersion lens field, P < 0.05) was alleviated. The amount of micro-calpain mRNA was decreased in the MDL group, but there was no significant difference compared with the HIBD group. CONCLUSION: mu-calpain gene and protein expressions increased after HI, which may contribute to the pathogenensis of HIBD. Calpain inhibitor-3 may intervene neural necrosis and apoptosis by diminishing expressions of mu-calpain and caspase-3 to play a protective role after HI insult of neonatal brain.