Studies For The Analgesic Effect And Mechanism Of Intrathecal Injection Of Curcumin In Mouse Neuropathic Pain Model

Objective: Neuropathic pain is caused by injury or disease of the sensory system and often manifests as spontaneous pain,nociceptive hyperalgesia,and nociceptive hypersensitivity.Curcumin(Cur)is one of the many naturally occurring polyphenols that have been shown to play an active role in diseases such as cancer,metabolic diseases,liver diseases and neurological disorders.In addition,curcumin can produce analgesic effects in different animal models of pain.The objective of the present study was to evaluate the analgesic effect of intrathecal curcumin in a mouse model of neuropathic pain and to investigate its mechanism of action.Methods: This project firstly established an SNI(Spared Nerve Injury)induced neuropathic pain model in mice.1.Evaluation of the analgesic effect of intrathecal curcumin in SNI mice: 24 male mice with established neuropathic pain were selected and divided into four groups: vehicle(5 μl),25 μg Cur,50 μg Cur and 100 μg Cur.Mechanical pain thresholds before(0 h)and 7-time points(1,2,3,4,5 and 6 h)after administration were measured using Von Frey filaments.2.The effects of the nonselective opioid receptor antagonist naloxone and selective opioid receptor antagonist on the analgesic effects of curcumin were examined in the naloxone administration group: 18 mice with neuropathic pain were divided into three groups and were injected intrathecally with vehicle(5 μl),vehicle(5 μl)or naloxone(5 nmol,5 μl)10 min before administration or vehicle administration,respectively,and the eight-time points before(10 min and 0 h)and after(1,2,3,4,5 and 6 h)administration were examined using Von Frey filaments.3.Effect of curcumin on the release of endogenous opioid peptides:two groups of neuropathic pain mice,10 mice in each group,were injected intrathecally with vehicle or curcumin.The mice were executed 4 hours after drug administration and the lumbar dilated portion of the spinal cord was obtained,and the expression levels of IL-10,Pomc,Penk and Pdyn in the spinal cord tissues were measured by real-time fluorescence quantitative PCR.And the effects of curcumin on IL-10 and β-endorphin protein release in spinal cord tissues were detected by enzyme-linked immunofluorescence kits.4.Intrathecal injections of minocycline,IL-10 antibody andβ-endorphin antibody were used to determine the effects of antibodies on the analgesic effects of curcumin in each group before and 4 h after the administration of minocycline,respectively.18 mice that had completed neuropathic pain modeling were randomly divided into three groups of 6 mice each and injected intrathecally with vehicle(5 μl),vehicle(5 μl)or minocycline(50 μg)4 h prior to drug or vehicle administration,respectively.The eight-time points before(4 h and 0 h)and after(1,2,3,4,5 and 6 h)administration were examined using Von Frey fine filaments.Results: 1.Single intrathecal injections of curcumin(100 μg and 50 μg)produced a dose-dependent analgesic effect in a mouse model of neuropathic pain.2.The analgesic effect of curcumin in SNI mice was antagonized by naloxone and the μ-opioid receptor(MOR)antagonist β-FNA.3.Intrathecal administration of curcumin significantly increased the m RNA expression levels of IL-10 and Pdyn in the affected and healthy spinal cord.Also,it increased the m RNA expression of Pomc in the affected spinal cord.Expression levels of Pomc m RNA in the affected spinal cord.In addition,intrathecal administration of curcumin significantly increased the release of IL-10 andβ-endorphin proteins in the spinal cord.4.Intrathecal administration of minocycline,IL-10 antibody,and β-endorphin antibody alone did not alter the mechanical pain thresholds in the plantar aspect of the hind paw of mice bilaterally,but it completely reversed the analgesic effect of curcumin in the affected foot of mice with neuropathic pain at the 4h time point after administration.Conclusion: Intrathecal injection of curcumin produced a dose-dependent analgesic effect in a mouse model of neuropathic pain without significant effects on the basal values of mechanical pain thresholds.The mechanism of analgesic effect may be mediated through the IL-10/β-endorphin pathway in spinal microglia.