Ishikawa Tetsuhiro, Miyagi Masayuki, Yamashita Masaomi, Kamoda Hiroto, Eguchi Yawara, Arai Gen, Suzuki Miyako, Sakuma Yoshihiro, Oikawa Yasuhiro, Orita Sumihisa, Inoue Gen, Ozawa Tomoyuki, Aoki Yasuchika, Toyone Tomoaki, Takahashi Kazuhisa, Yamaguchi Atsushi, Ohtori Seiji
Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan.
J Orthop Sci. 2013 Jul;18(4):636-45. doi: 10.1007/s00776-013-0397-y. Epub 2013 Apr 27.
Neuropathic pain is difficult to control and patient response to current treatment is often inadequate. Opioids have been widely used to treat a variety of pain states, but have several side effects. Endogenous opioids are clinically safe, but are not used for treatment because of rapid metabolism. However, in-vivo transfection of endogenous opioid genes could have a powerful and safe analgesic effect. The purpose of this study was to investigate the efficacy of proopiomelanocortin (POMC, a precursor of the endogenous opioid peptide β-endorphin) gene transfer by use of radial shock waves (RSWs) in a rat neuropathic pain model.
As a neuropathic pain model, we used the Bennett chronic constriction injury (CCI) method. Immediately after CCI induction, POMC plasmid was injected into the rats' gastrocnemius muscle followed by exposure to RSW. Mechanical allodynia was measured for 4 weeks and dorsal root ganglion (DRG) neurons were sectioned and immunostained.
β-Endorphin blood levels and the number of β-endorphin-immunoreactive (IR) muscle fibers increased over 28 days. β-Endorphin overexpression caused a decrease in the number of calcitonin gene-related peptide (CGRP)-IR DRG neurons and suppressed neuropathic pain induced by CCI without causing adverse side effects. The size-distribution pattern of CGRP-IR DRG neurons shifted from small to large cells in the CCI group; however, the number of both small and large CGRP-IR cells decreased in the POMC group.
POMC gene transfection alleviated allodynia and reduced CGRP expression in DRG neurons without adverse effects. CGRP is not produced in large neurons under physiologic conditions; however, in this study CGRP expression was shifted to large neurons after nerve injury. This change in cell-size distribution suggests that CGRP expression in large neurons is related to neuropathic pain. These findings suggest that POMC gene transfection using RSWs is a safe and effective treatment for neuropathic pain.
神经性疼痛难以控制，患者对当前治疗的反应往往不足。阿片类药物已被广泛用于治疗各种疼痛状态，但有多种副作用。内源性阿片类物质在临床上是安全的，但由于代谢迅速而未用于治疗。然而，内源性阿片类基因的体内转染可能具有强大且安全的镇痛作用。本研究的目的是在大鼠神经性疼痛模型中研究使用径向冲击波（RSW）进行阿黑皮素原（POMC，内源性阿片肽β-内啡肽的前体）基因转移的疗效。
作为神经性疼痛模型，我们采用了贝内特慢性压迫损伤（CCI）方法。在诱导CCI后立即将POMC质粒注射到大鼠的腓肠肌中，随后进行RSW照射。测量4周的机械性异常性疼痛，并对背根神经节（DRG）神经元进行切片和免疫染色。
β-内啡肽的血液水平和β-内啡肽免疫反应性（IR）肌纤维的数量在28天内增加。β-内啡肽的过表达导致降钙素基因相关肽（CGRP）-IR DRG神经元数量减少，并抑制了CCI诱导的神经性疼痛，且未引起不良副作用。在CCI组中，CGRP-IR DRG神经元的大小分布模式从小细胞转变为大细胞；然而，在POMC组中，小和大的CGRP-IR细胞数量均减少。
POMC基因转染减轻了异常性疼痛，并降低了DRG神经元中CGRP的表达，且无不良影响。在生理条件下，大神经元不产生CGRP；然而，在本研究中，神经损伤后CGRP的表达转移到了大神经元。这种细胞大小分布的变化表明，大神经元中CGRP的表达与神经性疼痛有关。这些发现表明，使用RSW进行POMC基因转染是一种治疗神经性疼痛的安全有效的方法。
