Local Injection Of Metformin Relieves Neuropathic Pain

Background The neuropathic pain(NPP)is a syndrome caused by injury or dysfunction in somatosensory system and its treatment remains a huge clinical challenge.Currently,clinical drugs for NPP include antidepressants,antiepileptics,local anesthetics,opioid analgesics and nonsteroidal anti-inflammatory drugs but their effects are far from satisfactory.The hypothesis of neuroinflammation has been well established to explain the syndrome.However,clinical trails showed that both gliocyte inhibitors and CCR2 receptor inhibitors failed to make a significant analgesic effect.So inhibiting neuroinflammation is possiblely not working for NPP treatment.We are supposed to look for a new way to solve the problem.Macrophages are reported to have potential to promote tissue repair and release ?-endorphin under certain situation.Our previous study showed AMPK activation relieved neuropathic pain significantly and it is suggested to promote P-endorphin release in macrophages.We hypothesized that using AMPK as a molecular switch to domesticate macrophages to release ?-endorphin and treat neuropathic pain.Objective This study aims to decide whether AMPK activation is able to facilitate macrophages p-endorphin release to reduce neuropathic pain,and to explore the underlying signal mechanisms.Methods(1)SD rats were used for Von-fray test to evaluate the degree of pain.(2)?-endorphin concentration in supernatant of BMDMs was measured by commercial Elisa kits.(3)Cell signaling was measured by western blot assay and(4)immunofluorescence assay.(5)The method of co-immunoprecipitation was applied to test the formation of AMPK-TAB1-p38 complex.Results(1)AMPK activation with metformin relieved CCI-induced neuropathic pain in vivo significantly and(2)meanwhile stimulated ?-endorphin release in vitro in BMDM;(3)AMPK and p38 MAPK were activated by metforming in BMDMs.(4)?-endorphin was possibly localized in primary granules in BMDMs and got released after metformin treatment in a p38 dependent way.(5)AMPK-TAB1-p38 complex chould be the mechanism underlying metformin induced p38 activation.Conclusion AMPK activation with metformin local treatmentattenuated neuropathic pain in CCI rats via promoting macrophage ?-endorphin release locally.AMPK-TAB1-p38MAPK-primary granule pathway was found to be responsible for the phenomeanon mentioned above.objective To explore the involvement of JNK-Gap junction regulation in bone cancer pain rat model and figure out whether AMPK activator metformin could attenuate bone cancer pain through this mechanism.Methods Tumor cell implantation(TCI)induced bone cancer pain model in rats were prepared and the Von Frey Assay was used to test the mechanical pain threshold.The activity of GFAP,IBA-1 and p-Cx43 in spinal cord was evaluated by Immunohistochemistry.Changes of p-JNK expression were detected by western blotting method.Results JNK inhibitor SP600125 relieved TCI-induced bone cancer pain significantly in rats,while this analgesic effect was almost canceled by the blocker of gap junctions CBX(carbenoxolone).Various concentrations of metformin(50,100?g/20ul,i.t.)significantly inhibited TCI-induced mechanical allodynia and the changes of p-JNK,p-Cx43 expression were also reversed in spinal cord in rats.Conclusion Activation of AMPK with metformin attenuated TCI-induced bone cancer pain via regulating the function of JNK-Gap junction in rats.