选择性Cox-2 抑制剂在放射性脑损伤中的保护作用及机制研究

The radiation induced brain injury seriously affect the patient's survival quality. Improving the radiation tolerance of normal brain tissue and alleviating radiation induced brain injury are key strategies to ameliorate the efficacy of radiotherapy for patients with intracranial tumors or head and neck tumor. Cyclooxygenase-2 (COX-2) is a key inflammation mediator in the brain tissue, plays an important role in radiation induced brain injury. Our previous studies indicated that COX-2 expressed in malignant glioma at a higher level than the normal brain tissue, inhibitors of COX-2 enhanced the radio-sensitivity of the malignant glioma, and alleviated brain edema and glial cell hyperplasia in the normal brain tissue, which laid the foundation for the study of finding new radiation protection agent targeted COX-2. This project intends to establish a radiation-induced brain injury model in rats, using COX-2 as a target, focus on the protective role and mechanism of the specific COX-2 inhibitors to nerve cell and vascular endothelial injury during radiation therapy. The brain neural stem cells, glial cells and vascular endothelial cells and inflammatory cytokines involved in the process will be study thoroughly. At the same time, both the role of the antioxidant and reducing cerebrovascular vascular injury will be studied too. In summary, the purpose of the study is to confirm the protective effect of COX-2 inhibitors on radiation induced brain injury and to elucidate its possible mechanism; to provide new ideas and solutions using COX-2 inhibitors to improve the radiation tolerance of normal brain tissue and alleviate radiation induced brain injury in clinical.

放射性脑损伤严重影响患者的生存质量，加强对正常脑组织的辐射防护，减轻放射性脑损伤，是提高颅内和头颈部肿瘤放疗疗效和改善患者生存质量的关键。COX-2是脑中重要的炎症介质，在脑损伤中发挥重要作用。我们前期研究表明COX-2在胶质瘤中的表达明显高于正常脑组织，COX-2抑制剂可增强胶质瘤放射敏感性，同时能减轻正常脑组织水肿和胶质细胞增生等早期放射损伤，为研究以COX-2为靶点的放射保护剂奠定了基础。本课题将建立放射性脑损伤动物模型，以COX-2为靶点，研究选择性COX-2抑制剂对放射造成的脑组织损伤的保护作用及机制，重点关注对脑神经干细胞、胶质细胞和血管内皮细胞的影响，以及参与调控炎症因子、抗氧化和减轻脑血管损伤的作用。确认选择性COX-2抑制剂对放射性脑损伤的保护作用并阐明其可能的机制，为临床选用选择性COX-2抑制剂，加强对正常脑组织的的辐射防护，减轻放射性脑损伤提供新的思路和解决办法。

放射性脑损伤在肿瘤放射治疗临床实践中比较普遍,严重影响治疗进展及患者生存预后。本课题通过动物及细胞学实验，探究了塞来昔布脑保护的相关可能机制。首先选取了正常胶质细胞(oln193)和胶质瘤细胞(u373)作为实验细胞，发现在40μmol/L浓度塞来昔布条件下，脑胶质瘤细胞的增敏作用比周围正常脑组织显著，且塞来昔布对正常脑胶质细胞没有放射增敏效应。动物实验选取SD大鼠，探究VEGF蛋白在大鼠放射性脑损伤模型中的动态变化。结果发现在放射性脑损伤模型中，脑血管内皮细胞、胶质及神经细胞表达的VEGF蛋白在观察期内持续上调，并参与了急性期内诱导脑水肿，形成血栓相关事件等。后通过Agilent芯片检测大鼠放射性脑损伤的全基因表达变化，选取VEGF和NF-kB两个经典的靶基因，从血管损伤与修复和自身免疫性炎症反应两个方面对放射性脑损伤进行深入探究，发现了COX-2 mRNA及蛋白质在放射性脑损伤模型中动态变化的趋势，结果显示各时间点照射给药组各组织结构、血栓形成程度、水肿等对比单纯照射组明显减轻，且NF-kB、VEGF的蛋白及mRNA表达明显下降，发现塞来昔布可以减轻大鼠受照后的血脑屏障损伤。后选取人脑微血管内皮细胞(HBMECs)进行实验，发现在30μmol/L塞来昔布实验浓度下，未观察到塞来昔布放射增敏效果；对比单纯照射组，照射给药组TXB2释放减少，TXB2/6-keto-PGF1α比值下降，COX-2及各凋亡相关蛋白表达下降，提示塞来昔布可降低放射后人脑微血管内皮细胞凋亡所致血管重塑，以及减少血栓形成相关因子的释放，减小血栓形成的几率，通过HBMEC方面解释了动物实验观察到的一些现象。总之，本课题发现了塞来昔布具有放射性脑保护作用，且解释了选择性COX-2抑制剂塞来昔布放射性脑保护的可能机制，为后期实验研究提供了一定的指导意义。