Spinal cord regeneration by immunosuppressive drugs and their derivatives

据报道，免疫亲和素配体除了具有众所周知的免疫抑制作用外，还具有神经营养活性，包括促进轴突生长的活性，但其神经营养作用的机制尚不清楚。我们推测免疫亲和素配体通过调节神经营养因子的合成而发挥神经营养作用，并通过体外和体内实验验证了这一可能性。免疫亲和素配体环孢素A和FK506已被证明能刺激培养的神经元和星形胶质细胞或成年大鼠脑内脑源性神经营养因子(BDNF)和/或胶质细胞源性神经营养因子(GDNF)的合成，提示免疫亲和素配体可能作为神经保护剂用于某些神经疾病的治疗，但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FK506和环孢菌素A的活性结构与免疫亲和素结合，寻找一种不具有免疫抑制活性的亲免疫配体。由Leu-Ile、Pro-Ile或Pro-Ile等疏水氨基酸组成的二肽类似于免疫抑制药物的活性结构，能与免疫亲和素结合。我们检测了这些及其衍生物，发现亮氨酸二肽及其类似物[A]是具有神经营养因子合成促进活性的活性物质，而不具有免疫抑制活性。由于这两种物质都被认为是理想的神经再生剂，我们在脊髓半横断大鼠身上应用了[A]物质，每天一次，连续30天。给药后3d运动活动开始恢复，达到脊髓损伤前水平。这些结果表明，没有免疫抑制活性的免疫亲和素配体可以刺激脊髓再生，并可能导致更有效的物质在未来的临床应用。

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.