Inhibition of Macrophage Activation by Minocycline Attenuates CCI-Induced Neuropathic Pain

Neuropathic pain is characterized by a high prevalence and associated with a variety of disorders of the peripheral and central nervous systems. It remains a major challenge for clinical management due to lack effective treatments. Our previous studies have demonstrated that nerve injury-induced neuroinflammation plays a critical role in regulating the development and maintenance of neuropathic pain. In the present study, we found that chronic constriction injury (CCI) led to a significant increase in the number of macrophages at the site of injured nerves. To elucidate the role of macrophage activation in CCI-induced neuropathic pain, we employed chemical agents, including clodronate liposomes, which is known for their ability to deplete macrophages, and minocycline, an inhibitor of macrophage function. Both intravenous injection of liposome-encapsulated clodronate and intrasciatic delivery of minocycline effectively attenuated CCI-induced mechanical and heat hyperalgesia. Furthermore, transfer of polarized M2 macrophages significantly alleviated CCI-induced neuropathic pain, but not under the condition of M1 macrophage transfer. Mechanistically, our findings indicated that pretreatment with minocycline increased the expression level of CD206 but decreased that of IL-1β, while post-polarization treatment markedly decreased the expression level of both. Additionally, an in vitro migration assay revealed that minocycline exerts an inhibitory effect on macrophage migration. In brief, our study elucidates the effect of CCI-induced macrophage activation on neuropathic pain and provides new insights into the potential clinical application of minocycline for managing neuropathic pain.