Research On The Analgesic Effects Of Sinomenine On Different Inflammatory Pain Models

Objective: To study the analgesic effect and its mechanism of sinomenine(SIN)on chronic inflammatory pain induced by complete Freund's adjuvant(CFA)and acute inflammatory pain induced by formalin,in order to provide new targets and ideas for the treatment of inflammatory pain and the development and utilization of SIN.Methods:(1)The CFA-induced inflammatory pain model was established to investigate the analgesic effect and mechanism of SIN.Healthy male SD rats were randomly divided into five groups,namely control group,CFA model group,CFA+SIN 10 mg/kg group,CFA+SIN 20 mg/kg group,CFA+SIN 40 mg/kg group.The animal model of inflammatory pain was prepared by subcutaneously injecting 50% CFA 150 ?L into the left hindfoot of the rat.SIN rats in each dose group were intraperitoneally injected with SIN 10,20,and 40 mg/kg for 7 days(twice a day).During the experiment,the morphological changes of the injected foot of the rats were observed,and the indexes such as body weight,foot thickness,mechanical withdrawal threshold(MWT)and thermal withdrawal latency(TWL)were measured.After the behavioral experiment,the L4–L6 dorsal root ganglion(DRG)and spinal cord tissues of rats were taken,and the protein expression changes of NLRP3,ASIC3,CaMK2? were detected by Western blot.(2)The formalin-induced inflammatory pain model was established to investigate the analgesic effect and mechanism of SIN.Healthy male mice were randomly divided into 4 groups,namely control group,formalin model group,formalin plus SIN 40 mg/kg group,formalin plus SIN 80 mg/kg group.SIN rats in each dose group were injected intraperitoneally with SIN 40 and 80 mg/kg,and the control group and model group were given the same volume of 0.9% saline.Thirty minutes later,the formalin model group and the SIN dose groups were injected with 5% formalin(20 ?L/20 g)subcutaneously in the left hindfoot of the mice.After modeling,the mice were immediately placed in the observation room for 1 hour,and the time of licking/rubbing the injection site or raising the paw(pain response index)was recorded.Then,the L4–L6 DRG and spinal cord of the mice were taken,and the protein expression of NLRP3,ASIC3,CaMK2? were measured by Western blot.Results:(1)The results of SIN on CFA-induced chronic inflammatory pain were showed as follows: Compared with the control group,the model group rats showed redness and swelling on the sole of the foot,and the thickness of the heel and palm were significantly thickened(p?0.01),the MWT and TWL were significantly reduced(p?0.01),the expression of NLRP3,ASIC3,CaMK2? in spinal cord were significantly increased(p?0.01).Compared with the model group,After treatment with SIN 10,20,or 40 mg/kg,the redness of the sole was reduced in SIN-treated rats,the thickness of the heel and palm were significantly reduced(p?0.05),MWT and TWL were significantly increased(p?0.05 or 0.01).The expression of NLRP3,ASIC3 and CaMK2? in the spinal cord of rats in SIN 20 and 40 mg/kg groups were significantly reduced(p?0.05 or 0.01),and the expression of ASIC3 in spinal cord of SIN 10 mg/kg group was significantly reduced(p? 0.01),while the expression of NLRP3 and CaMK2? did not change significantly.(2)The results of SIN on formalin-induced inflammatory pain were showed as follows: Compared with the control group,the pain response of the model group mice was significantly increased(p?0.01),showing the characteristics of biphasic pain response,the expressions of NLRP3,ASIC3 and CaMK2? in mouse spinal cord were significantly increased(p?0.05 or 0.01),and the expressions of ASIC3 and CaMK2? in DRG were also significantly increased(p?0.05 or 0.01).Compared with the model group,the first-phase and two-phase pain responses were significantly reduced in the SIN 80 mg/kg group(p?0.05 or 0.01),but only one-phase pain response was significantly reduced in the SIN 40 mg/kg group(p?0.01).The expressions of ASIC3 and CaMK2? in DRG and spinal cord of mice were all significantly reduced in each dose group of SIN(p?0.05 or 0.01),and the expression of NLRP3 in spinal cord were also significantly reduced in each dose group of SIN(p?0.05 or 0.01).Conclusion:SIN can effectively alleviate chronic inflammatory pain induced by CFA and acute inflammatory pain induced by formalin in a dose-dependent manner,and its analgesic mechanism may be related to the regulation of CaMK2?-ASIC3-NLRP3 signaling pathway.