Spinal cord regeneration by immunosuppressive drugs and their derivatives

据报道，除了众所周知的免疫抑制作用外，亲免疫素配体还具有神经营养活性，包括促进神经突的活性，但其神经营养作用的机制尚不清楚。我们推测亲免疫素配体通过调节神经营养因子的合成而表现出神经营养作用，并通过体外和体内实验验证了这一可能性。免疫亲素配体环孢素A和FK506已被证明可以刺激培养的神经元和星形胶质细胞或成年大鼠脑中的脑源性神经营养因子（BDNF）和/或胶质细胞系源性神经营养因子（GDNF）的合成，这表明免疫亲素配体可能用作某些神经系统疾病的神经保护剂。然而，其免疫抑制活性不利于一般疾病的治疗。因此，我们试图通过聚焦FK506和环孢素A与亲免疫蛋白结合的活性结构，寻找一种无免疫抑制活性的活性亲免疫素配体。由疏水氨基酸组成的二肽，如Leu-Ile、Pro-Leu或Pro-Ile，类似于免疫抑制药物的活性结构，可以结合亲免疫蛋白。我们检测了这些物质及其衍生物，发现亮氨酸二肽及其类似物[A]是具有神经营养因子合成刺激活性而无免疫抑制活性的活性物质。由于这两种物质都被认为是理想的神经再生药物，我们将[A]物质每天1次，连续30天应用于脊髓半横断大鼠。运动活动在给药后3天开始恢复，恢复到脊髓损伤前的水平。这些结果表明，没有免疫抑制活性的亲免疫素配体可以刺激脊髓再生，并可能导致未来临床使用更有效的物质。

Immunophilin ligands have been reported to possess neurotrophic activities including neurite-promoting activity in addition to well-known immunosuppressive actions, but the mechanisms under the neurotrophic effects remain unknown. We presumed that immunophilin ligands show the neurotrophic actions by the regulation of synthesis ot neurotrophic factors, and examined this possibility by in vitro and in vivo experiments. Immunophilin ligands, cyclosporin A and FK506, have been proved to stimulate synthesis of brain-derived neurotrophic factor (BDNF) and/or glial cell line-derived neurotrophic factor (GDNF) in cultured neurons and astrocytes or in adult rat brain, suggesting a possible use of immunophilin ligands as neuroprotective agents in some neurological disorders However, the immunosuppressive activity is disadvantageous for therapeutic use for general disorders. Therefore, we tried to find an active immunophilin ligand without immunosuppressive activity by focusing the active structure of FK506 and cyclosporin A for binding to immunophilin proteins. Dipeptides composed of hydrophobic amino acid such as Leu-Ile Pro-Leu or Pro-Ile resemble to the active structure of immunosuppressive drugs, and can bind immunophilins. We examined these and their derivatives, and found the Leu-Ile dipeptide and its analogue [A] as active substances with neurotrophic factor synthesis stimulatory activity and without immunosuppressive activity. As both substances were considered to be ideal agents for neuroregeneration, we applied [A] substance once a day for 30 days to the rats with spinal cord semi-transection. Motor activity was started to restore 3 days after the administration, and attained to the level before spinal cord injury. These results suggest that an immunophilin ligand without immunosuppressive activity can stimulate spinal cord regeneration, and may lead to more potent substances valid for clinical use in future.