基于多聚唾液酸纳米递药系统的脊髓损伤靶向治疗与神经再生研究

Primary and Secondary neuronal apoptosis and limited nerve regeneration ability are the main difficulties for the therapy and neural restoration of spinal cord injury, which is a big challenge in the face of medical field. Polysialic acid, a unique carbohydrate polymer located on the cell surface, has the capacity of preventing close interactions between cell-cell and cell-extracellular matrix via binding to neural cell adhension molecule, thus promoting cell migration, synapse formation, remyelination and regeneration of neurons. Consequently, polysialic acid plays crucial roles in repair and regenation of lesioned central nervous system. Our previous study demonstrated that the hydrophobic modified polysialic acid conjugate could form micelles by self-aggregation, which could efficiently encapsulate the methylprednisolone and realize the sustained drug release. Furthermore, the conjugate micelles could highly distribute into the damaged tissue of spinal cord. In this project, we will further optimize this drug delivery system. After the drug delivery system distributed into the injured tissue, the released drug will reduce infiltration of inflammatory cells, the release of inflammatory factors, protect neurons, and significantly improve the secondary injury. Meanwhile, the remained polysialic acid conjugate can recruit endogenous progenitors to the lesioned area, and hence facilitate remyelination and regeneration of neurons and long distance growth of axon to realize the efficient therapy of primary injury. This double function of drug targeting therapy and nerve regeneration will provide novel idea and approach for the efficient therapy and nerve regeneration of spinal cord injury.

原发性和继发性神经元凋亡、神经再生能力低下是脊髓损伤治疗和康复的主要困境，是医学界面临的一大难题。多聚唾液酸是一种位于细胞表面的多聚碳水化合物，与神经细胞黏附因子结合后，促进细胞迁移、突触形成、神经元和髓鞘再生等，在中枢神经系统受损后的修复中起重要作用。我们前期的研究发现：多聚唾液酸经疏水改性后的嫁接物可自聚集形成胶束，有效包封肾上腺皮质激素甲基泼尼松龙，实现药物的缓释；并在脊髓损伤部位具有较强的靶向分布。本项目拟在此基础上，开展递药系统的优化研究；通过递药系统的脊髓损伤部位的药物靶向，减少炎性细胞的浸润和炎症因子的释放，保护神经元，显著改善继发性损伤；药物治疗后残留的多聚唾液酸嫁接物，吸引内源性神经干细胞至受损部位，促进神经元和髓鞘的再生及神经元轴突的长距离生长，实现针对原发性脊髓损伤的治疗。通过药物靶向治疗和神经再生的双重模式，为脊髓损伤的高效治疗和神经再生提供新思路、新手段。

脊髓损伤（spinal cord injury, SCI）是常见的致残致死性损伤，严重影响患者及其家庭的生活质量。盐酸米诺环素（MC.HCl）是一种四环素类抗生素，具有抗炎、抗氧化和抗凋亡活性，能够抑制继发性损伤并发挥神经保护作用，显著改善SCI模型动物的行为学功能，但需要长时间大剂量给药，易导致肝肾毒性。新型纳米给药系统是改善药物体内分布，降低药物毒副作用的有效手段，且可通过载体材料的功能化实现SCI的多靶点治疗。多聚唾液酸 (polysialic acid, PSA)是一种位于细胞表面的内源性碳水化合物，在细胞迁移、神经系统发育、突触形成、神经系统受损后的修复和神经再生中起重要作用，且有利于轴突的长距离生长。本研究以米诺环素为模型药物，以PSA为亲水性聚合物，构建纳米靶向给药系统，以实现药物的靶向递送和SCI的多靶点治疗。. 首先，采用硬脂胺（octadecylamine, ODA）对PSA进行疏水性修饰，成功合成了PSA-ODA（PSO）嫁接物；PSO可在水性介质中自组装形成胶束，并有效负载米诺环素，实现药物的缓释。PSA-ODA/MC嫁接物载药胶束（PSM）在体外能抑制小胶质细胞的激活，并在双氧水诱导的神经元受损模型中发挥神经保护作用。PSO嫁接物胶束经尾静脉给药后可通过被动靶向分布至SCI大鼠的脊髓受损部位；PSM经尾静脉注射给药24 h后，脊髓受损部位TNF-α、IL-6、IL-1β、MDA和NO的浓度显著降低，SOD酶的活力显著增强，iNOS蛋白表达有显著下降，细胞凋亡明显减少，继发性损伤得到有效抑制。PSM连续给药7 d后，脊髓受损部位的空洞面积减小，BDA阳性染色神经纤维数目增加，损伤所致的脱髓鞘病变有明显改善、胶质瘢痕形成减少，轴突能长距离生长并与尾侧组织重新建立连接；此外，在脊髓受损部位可观察到神经元的再生。因此，PSM组SCI大鼠后肢的运动学功能有明显改善，且优于MC.HCl和PSO治疗组。. 综上所述，本研究构建的功能性米诺环素递药系统可通过静脉给药，避免了原位给药、细胞移植、组织工程等治疗方法带来的二次损伤；可通过药物向脊髓受损部位的靶向递送，实现继发性损伤的有效抑制，同时残留的PSA可促进神经再生。通过药物和载体的协同作用，实现SCI的安全高效治疗。