P2X7R Regulates The Mechanism Of Hyperalgesia And Depression In Nicotine Withdrawal Rats With Bone Cancer Pain

Objectives: Patients with cancer,among which are smokers,often experience constant pain and psychological distress.In this study,we evaluate the effects of nicotine-withdrawal(NTW)on the comorbidities of bone cancer pain and depression,and further investigate the role of P2X7 receptor(P2X7R)related signaling pathways in hippocampal microglia.Methods: We have established nicotine-dependent bone cancer pain rat models in chronological order to simulate the development process of cancer pain in smoking addicted patients.By measuring the mechanical withdrawal threshold,the thermal withdrawal latency,the amount of sugar water preference,and the immobility time in the forced swimming test at different time points during the experiment,the changes in the behavior of rats during the nicotine withdrawal period were monitored.In addition,we used double immunofluorescence,western blotting and ELISA to detect the immunoreactivity of microglia-specific markers Iba-1 and P2X7 R in the hippocampus,and the expression of its downstream inflammasome NLRP3 and inflammatory cytokines in the hippocampus.Results: Our data suggested that NTW resulted in hyperalgesia and increased depressive-like behavior in rats with bone cancer pain.The microglia in the hippocampus was activated after NTW.In addition,we found that the expression of P2X7 R and NLRP3 in the hippocampus of NTW rats was up-regulated and the release of inflammatory cytokines interleukin 1β(IL-1β)and tumor necrosis factor α(TNF-α)was also increased.Nevertheless,microinfusion of P2X7 R selective pharmacological antagonist A-438079 in the hippocampus alleviated NTW-induced hyperalgesia and depression-like behaviors,and suppressed the reactivity of microglia and the expression of P2X7 R and downstream inflammatory cytokines.Conclusions: In conclusion,our research provided evidence that the hippocampal microglia P2X7R-NLRP3-inflammatory cytokine signaling pathway is involved in the negative development of comorbidity of cancer hyperalgesia and depression caused by NTW.Brain penetrating P2X7 R antagonists may be beneficial to alleviate the negative effects of NTW on bone cancer pain and depression-like behaviors.