趨化因子CXCL7在周邊神經損傷引起神經病變性疼痛之探討

Abstract

神經病變性疼痛一直以來因為疾病本身非常複雜，在治療不易、預後不好的情況下，逐漸成為需要被重視的問題。在定義上，神經病變性疼痛是因為在周邊和中樞神經系統內的體感覺系統受到損傷或疾病的影響而產生的，一般可分類為中樞或周邊神經病變性疼痛。直到目前為止，既有的藥物治療效果都不甚明顯，因此，許多人仍致力於釐清神經病變性疼痛的致病機制，並期望於其中找出可作為藥物開發的標的對象。許多報導指出神經發炎參與神經病變性疼痛的病理過程，而且細胞激素/趨化激素的作用路徑也在神經發炎中扮演重要的角色，未來可能發展作為治療的標的，但是詳細的機制尚未釐清。本篇研究的主要目的即是藉由觀察動物疾病模式的腦脊髓液，尋找參與神經病變性疼痛病理過程相對重要的細胞激素/趨化激素。我們選用綁住單側L5 脊神經並剪斷的手術方式形成疾病模式，接著利用電子式疼痛測量儀和老鼠腳底熱刺激儀來做疼痛行為(對溫度和機械性刺激產生痛覺過敏)的評估。我們利用細胞激素/趨化激素微陣列觀察腦脊髓液，發現其中趨化激素CXCL7 在疾病模式比起控制組有顯著的表現量增強，另外，我們也觀察到在疾病模式單側的脊椎背角樣本中CXCL7 的蛋白質和mRNA 的表現量比起控制組都有增加的趨勢。接著，利用脊髓腔注射的方式直接給予CXCL7發現會引發老鼠產生痛覺敏感，也在組織切片中看到活化的神經膠細胞和神經胜肽CGRP 表現量增加。因為CXCL7 是藉由結合CXCR1 和CXCR2 產生下游的反應，所以進一步使用CXCR1/CXCR2的拮抗劑reparixin-L-lysine salt，當reparixin 和CXCL7 用脊髓腔注射的方式同時給予，可以觀察到reparixin 拮抗CXCL7 引發的痛覺過敏。因此，在疾病模式中給予reparixin 可以減少手術產生的痛覺敏感，在組織切片也看到活化的神經膠細胞比控制組少。最後，依據觀察到的現象和實驗結果，我們推測CXCL7 可能參與神經病變性疼痛的病理過程，而且CXCR1/CXCR2 的拮抗劑或許可以發展為治療神經病變性疼痛的藥物。

Neuropathic pain is a problem in general population because of the complexity of neuropathic symptoms, poor outcomes and difficult treatment decision. Neuropathic pain is defined as pain caused by a lesion or disease of the somatosensory system and can be subtyped as central and peripheral neuropathic pain. Until now, conventional pharmacological treatments for neuropathic pain are effective in <50% of patients. Therefore, clarifying actual mechanism in neuropathic pain and finding a new target remain important parts for developing new drugs. Neuroinflammation has been reported to be involved in the pathophysiology of neuropathic pain and is an emerging target of treatment. Although the cytokine/chemokine pathways play a major role in neuroinflammation, the exact mechanism in neuropathic pain remains unclear. To investigate the cytokines/chemokines changes, we used neuropathic pain animal model produced by unilateral L5 spinal nerve ligation-and-cut (SNL) and electronic von Frey test and plantar test for pain assessment (including mechanical and thermal hyperalgesia, respectively). We then screened cytokine expression in the cerebrospinal fluid using cytokine array, and it was found that CXCL7 increased markedly in SNL rats compared with control. The expression levels of both protein and messenger RNA of CXCL7 were up-regulated in spinal cord dorsal horn samples of SNL rats compared with control.Furthermore, intrathecal administration of recombinant chemokine CXCL7 induced mechanical and thermal hyperalgesia and increased glia activation and sensory neuropeptide CGRP expression level. To investigate the involvement of CXCR1/CXCR2, receptors of CXCL7, a CXCR1/CXCR2 antagonist reparixin-L-lysine salt (reparixin) was co-administered intrathecally with CXCL7 via osmotic pump. It was found that CXCR1/CXCR2 antagonist reversed CXCL7-induced hyperalgesia. We also evaluated the effect of CXCR1/CXCR2 in SNL rats. Right after SNL, intrathecal infusion of CXCR1/CXCR2 antagonist reparixin via osmotic pump for 7 days attenuated SNL-induced hyperalgesia and glia activation. These results indicate that CXCL7 might be involved in neuropathic pain and CXCR1/CXCR2 antagonist might be developed as drug for the treatment of neuropathic pain.