Objective Brain edema is one of the main pathological manifestations after cerebral ischemia. Although some studies have demonstrated that aquaporin-4(AQP4)plays an important role in the formation and development of brain edema after cerebral infarction, little is known about the correlation between parameters of magnetic resonance diffusion weighted imaging(MRI-DWI)and AQP4 expression in the early stage of the reperfusion following acute cerebral ischemia. The present study aimed to observe the dynamic changes of rat brain in the early stage of the reperfusion following acute cerebral ischemia with MRI-DWI, to analysis the relationship among DWI signal intensity(SI), apparent diffusion coefficient(ADC)and the expression of AQP4 in the brain damage zone, and to investigate the relationship between the expression of AQP4 and ischemic brain edema. Method Forty SD male rats were randomly divided into 4 groups: MCAO/R groups(cerebral ischemia reperfusion 12h group, 1d group, 3d group)and sham group, respectively. n=10 for each group. The right middle cerebral artery occlusion and reperfusion (MCAO/R)model in the rats was induced with the intraluminal suture method. The Zea Longa score was used to assess the neurological function of the rats in the MCAO/R groups and sham group. All rats underwent DWI scanning. The ADC map was reconstructed on the workstation, and the DWI-SI, ADC and the relative ADC(rADC)values of each rat were calculated. All rats were sacrificed and the cerebral ischemic tissues were examined for histopathology. The infarct volumes at each time point were assessed by 2,3,5-Triphenyltetrazolium chloride(TTC)staining. The expression of AQP4 protein in ischemic brain tissue at different reperfusion time points(12h, 1d, 3d, sham)was determined by immunohistochemistry method, and the mean optical density(MOD)was measured to evaluate the degree of staining. The correlation between rADC values and AQP4 expression was analyzed with Pearson correlation test. Results There were no neurological deficits in sham group. Compared to the sham-operated group, all the ischemic groups have significantly neurological deficits indicated by higher Longa score(P<0.05). The white dying area was not found in sham group and whole brain was stained red. The model groups rats showed white staining area in the right striatum and the surrounding cortex and staining area gradually expanded from 12h to 3d, including the right basal ganglia and frontotemporal cortex. The highest infarct volume was found in the 3d group. The ischemic brain edema volume showed a similar change at the same time points. The expression of AQP4 in the hippocampus and cortical area was very little in sham group. AQP4 positive staining cells were found in cortex and hippocampus on the side of ischemia at 12h group. The AQP4 mean optical density value increased gradually over time, reached the peak at 3d group. The AQP4 expression levels of three groups were significantly higher than those in the sham group(P<0.05). No abnormal signal was detected on DWI and ADC maps in the sham group. The high signal area in DWI and the signal intensity increased gradually from 12h to 3d. The cerebral edema volume of rats and AQP4 expression level of cortex in the side of ischemic showed a positive correlation at 12h, 1d and 3d groups(r=0.642,P<0.05), and also positively related to the MOD value of the AQP4 expression level of hippocampus(r=0.605,P<0.05). The rADC value of basal ganglia and AQP4 expression levels of cortex and hippocampus in the side of ischemia showed a positive correlation at three groups(r=0.542,P=0.037,r=0.655,P=0.008). Conclusion There were significantly correlation among ischemic brain edema, rADC value and the expression level of AQP4 in brain damage zone in early stage of reperfusion following acute cerebral ischemia. Thus combining DWI with histological examination may provide a new diagnostic idea and treatment method for the treatment of brain edema.%目的脑水肿是脑缺血后主要的病理表现之一，研究表明水通道蛋白4（AQP4）在脑梗死后脑水肿的形成和发展中起着重要作用，目前尚缺乏磁共振弥散加权成像（DWS）与 AQP4表达在急性脑缺血-再灌注早期相关性的研究。本文旨在评估大鼠脑缺血—再灌注早期脑损伤区水通道蛋白4表达、DWI信号强度（SI）及表观扩散系数（ADC）之间的相关性以及 AQP4表达与缺血性脑水肿之间的关系。方法健康成年 SD 雄性大鼠（n=40），随机分成4组，分别为脑缺血—再灌注12h、1d、3d 组和假手术组，采用线栓法制作大鼠右侧大脑中动脉缺血—再灌注（MCAO/R）模型，Zea Longa 评分评价神经功能损伤程度，Philips Achieva 3.0T MRI 扫描仪对假手术组和缺血—再灌注后不同时间点大鼠脑部行冠状位 DWI 扫描，在工作站上重建 ADC 图，测量基底核层面梗死灶 DWI-SI 和 ADC 值，计算相对 ADC 值（rADC）和相对 DWI—SI（rDWI—SI）值。2,3,5-氯化三苯基四氮唑（TTC）染色评价梗死体积的变化。免疫组化染色测定 AQP4蛋白表达，用平均吸光度（MOD）值评价染色程度。结果假手术组动物麻醉苏醒后未见神经功能缺损，脑缺血—再灌注后12h、1d 和3d 组大鼠出现不同程度神经功能损伤，1d 组最重。假手术组 TTC 染色未见梗死体积，脑缺血—再灌注后12h、1d 和3d 梗死体积逐渐增加，3d 时最大。水肿变化规律同梗死体积相仿。假手术组海马区及皮质区 AQP4免疫组化染色较浅淡，MCAO/R 后12h 缺血侧海马区及皮质均可见 AQP4阳性细胞，12h-3d AQP4的 MOD 值随时间延长逐渐增高，3d 时达到高峰。12h、1d 和3d 组大鼠脑水肿体积与相应时间点缺血侧皮质区和海马区 AQP4表达均呈正相关（r=0.642，r=0.605，均 P<0.05）；三组大鼠基底核区梗死灶 rADC 值与缺血侧皮质区、海马区 AQP4表达均呈正相关（r=0.542，P=0.037；r=0.655，P=0.008）。结论大鼠脑缺血—再灌注早期脑水肿体积、rADC 值与 AQP4的表达水平存在时间上的相关性。因此结合 DWI 检查对脑缺血后 AQP4表达部位、作用及调节机制进行更深入系统的研究，可能为临床早期治疗缺血性脑水肿提供新的思路。
展开▼
