Analgesic Effect And Mechanism Of BTX-A For Rats’ Knee Osteoarthritis In Rats

Objectives:Knee osteoarthritis was a degenerative joint disease that was characterized by degeneration of articular cartilage,loss,bone hyperplasia and osteophytes formation at joint marginal, secondary hyperplasia and hypertrophy of joint capsule and synovial, the main clinical manifestations was joint pain, deformity and limited activity.Joint pain influenced the patient’s quality of life seriously due to its refractory, so it need a new treatment urgently. The one of the main mechanisms was that pain transmission like Nav l.8 sodium channel bring excessive expression in the spinal cord,made the pain sensitivity of patients higher.Studies had shown that,botulinum toxin type A for neuropathic pain had better analgesic effect, but for knee osteoarthritis pain’s analgesic effect and mechanisms,especially analgesic mechanisms of the spinal cord’s level were still lack of appropriate reports.This study in rats’ model of osteoarthritis, analgesia were observed in rats’ knee osteoarthritis after intra-articular BTX-A injection,and analgesic mechanism was clarified from the spinal cord by expression changes of Nav l.8 sodium channel were observed in the spinal dorsal horn.Its aim was to explore a new safe and effective method for the treatment of knee osteoarthritis.It bring important meaning for reducing the morbidity of the population and improving patients’ quality of life.Methods:20 male SD healthy rats, the weight was between 150~180 g, knee osteoarthritis animal models were builded by giving injection of 4% papain solution 0.3ml in right knee articular. 1.By building a successful knee arthritis model,they were randomly divided into two groups:BTX-A group(n=10):intra-articular BTX-A injection 0.1IU/5μl;WFI group(n=10):intra-articular sterile water injection 5μl;Sham group(n=10):non-arthritis model group. At different time(1d,3d,5d) after the injection, doing the spontaneous pain gaitanalysis, thermal pain threshold testing and comparing changes between three groups.2.The rats’ osteoarthritis pain model were given BTX-A or sterile water injection. After five days perfused the rats,and immunofluorescence to observe Nav1.8 expression in spinal ganglion. 3. We analyzed data by using SPSS 20.0 statistical software.Behavior test results were analyzed by using nonparametric rank and inspection. The data which was the same group rats at different test time was analyzed by using Friedman test.Taking mean±standard deviation shows categorical data, it was analyzed by using t test and variance analysis, P<0.05 had statistical significance.Results:1.Knee osteoarthritis model building: the rats’ right knee joints were injected with 4%papain solution 0.3ml, at the fifth day 80% rats had showed different degrees joint swelling and limited activity, reached the top in 7 day.2.Spontaneous pain test :20 knee osteoarthritis model rats were divided into two groups, the right knee osteoarthritis model were separately injected BTX-A or WFI. In the Fifth day after treatment,compared with WFI group,BTX-A group improved obviously on spontaneous pain behavior, the difference was statistically significant.Rats’ knee osteoarthritis had been injected botulinum toxin type A after 1、3 and 5 day, they carried on spontaneous pain gait analysis separately. Time was different after BTX-A injection,improvement was also different on spontaneous pain behaviors, the difference was statistically significance. Afterr 1、3 and 5 day of BTX-A injection,difference were statistically significant by comparing two samples repeatedly, and longer time after injection(less than 5 days), the more obvious improvement on spontaneous pain gait.3.Paw withdrawal latency test:Three groups of rats:Sham group,arthritis+WFI group,arthritis+BTX-A group.After 1、3 and 5 day of BTX-A or sterilized water injection, testing the rats right foot’s paw withdrawal latency separately.At the time of experimental observation,the model intervention group compared with Sham group, PWTL decreased.The results showed that after 1 day when the model group’s rats were given BTX-A injection,thermal pain threshold increased significantly in the next day,and relieved the pain effect gradually obvious with extension of time,continued till the 5th day afterinjection.Compared with WFI group, the BTX-A group was significantly higher than the control group. The experimental results show that BTX-A injection could relieve pain and increase thermal pain threshold.4.Expression of Nav1.8 in the spinal ganglia:Immunohistochemistry results showed that it was that the expression of Nav1.8 protein which is on DRG neurons in model group,compared with Sham group,it had statistical significance.After 5 day of BTX-A injection, phenomenon which was the expression of Nav1.8 on rat DRG neurons was inhibited obviously, compared with WFI group, it had statistical significance.Conclusion:In the rats’ knee osteoarthritis model,BTX-A could improve the spontaneous pain gait,increase thermal pain threshold,and decrease expression of sodium channels Nav1.8 on spinal ganglia by intra-articular injection of BTX-A.It may down regulate expression of Nav1.8 protein,reduce the central sensitization,relieve joint pain, raise the pain threshold, thus it produced analgesic effect.