The Effect Of Spinal NF-kappa B/p65 Signaling Pathway On The Hyperalgesia In Knee Osteoarthritis

BackgroundKnee Osteoarthritis(KOA),a common disease in the elderly,causes patients physical or mental suffering and makes the government bearing a huge economic burden.The typical symptoms of KOA is physical inactivity and chronic pain,or even worse,the patients will be disability.Chronic pain is always the main reasons driving patients for medical help.Currently,there is not any safe and effective medicine for the long term therapy of KOA pain.In the end-stage of KOA,patients have no choice but to have total knee replacement(TKR)to improve joint function and relieve the unbearable pain.However,it's depressing that 16%-39%of the KOA patients still have chronic pain among six months since the surgery.KOA patients can't but bear the long-term chronic pain,bringing adverse influence on physical or mental health.Recently,one study revealed that knee pain is an independent predictor of mortality.Therefore,more and more researchers realize the importance of chronic pain and start to investigate the pathogenesis of KOA chronic pain for the effective target.Clinical and experimental studies have provided evidence that pain intensity is not consistent with the change in the joint and the change of pain-related central nervous system is main reason for chronic KOA pain.Clinicians have tried to use electrical stimulation for KOA pain relief.Therefore,we want to explore the ideal target for the treatment of KOA chronic pain in the central nervous system trough the further reveal of the central pathogenesis of chronic KOA pain.Nuclear factor-kappa B(NF-?B),a key transcription factor,is widely known for its ubiquitous roles in immune and inflammation responses,as well as cell division and apoptosis.In the nervous system,NF-?B pathway also can play important roles in learning,memory and pain except for the common function.A series of studies have found that the stimuli(inflammation and injury)and the products(inflammatory factors,neurotransmitters and neurotrophic factors)induced by these stimuli can active NF-?B pathway in central nervous system.The activation of NF-?B can increase inflammatory factors,neurotransmitters and ion channels in return,which can aggravate the pain degree.While the stimuli can't be removed,the long-term NF-?B activation will induce a chronic inflammatory state and increase the neurotransmitter receptors.What's worse,the structure of neurons and glial cells will change in the central nervous system,inducing refractory pain and neuropathic pain.NF-?B form a variety of homodimers,the most prevalent activated form is the heterodimer p65 and p50.p65,most common and important one,is chosen by us for research.We ha-ve found that knockdown of spinal NF-?B can relieve peripheral inflammation and hyperalgesia in rat adjuvant-induced arthritis.However,the typical pathological characteristics of KOA is degeneration rather than inflammation.We want to know whether NF-?B/p65 can relieve hyperalgesia in MIA(monosodium iodoacetate)-induced KOA model.ObjectiveTo establish the rat model of MIA-induced KOA and explore the effect and mechanisms of spinal NF-?B/p65 on KOA chronic pain.Methods1.The health female SD rats were divided into three groups:control group,KOA group and PDTC(pyrrolidine dithiocarbamate)+KOA group by random number method.Each group contains 50 rats.PDTC+KOA group rats were intrathecal administrated by PDTC 12?l(0.2mg/ml)per day after the intra-articular injection of MIA until death.2.50%paw withdrawal threshold(PWT)were assessed at 1 day before MIA intra-articular injection and 7,14,21,28days after.The pathological changes of knee were assessed by digital photograph and pathological section.The protein and mRNA level of NF-?B/p65 were detected by Western blot,immunofluorescence and real-time polymerase chain reaction(RT-PCR)· IL-1?(interleukin-1?)?IL-33 and TNF-a(tumor necrosis factor-a)transcription level were measured by RT-PCR.ResultsThe 50%PWT of KOA group rats increases during the 14 days since the intra-articular injection of MIA.On day 14,50%PWT reached the top and maintained at the higher level in the following days.The articular-cartilage degradation was becoming more severe and the joint space was becoming narrower since the injection of MIA.All the pathological changes of the knee joint are same as the clinic samples from the KOA patients.The change of spinal NF-?B/p65 protein and mRNA is same as the pain-related behavior.The transcription level of IL-1?,IL-33 and TNF-a also reach the peak at day 14,and then go down to a higher level.50%PWT of PDTC+KOA group is significantly lower than the KOA group since 21th days after injection of MIA.Spinal NF-KB/p65 protein and mRNA decrease since the injection of PDTC.On day 28,Spinal IL-1?,IL-33 and TNF-a mRNA is lower than the KOA group.ConclusionSpinal NF-?B/p65 increase and maintain a higher level in KOA model rats.Spinally delivered PDTC decrease NF-?B/p65 expression and significantly attenuated hyperalgesia.All the results prove that NF-KB/p65 is a key signaling pathway in the generation of chronic KOA pain.In addition,spinal delivery of PDTC reduced the over-expression of spinal IL-1?,IL-33 and TNF-?.Spinal NF-KB/p65 may increase the pain degree trough the inflammatory factors IL-1?,IL-33 and TNF-a at the late stage of KOA.