Macrophage Migration Inhibitory Factor In Complex Regional Pain Syndrome Type 1 Expression In Rat And Significance

Background: Although the first description of CRPS was probably inJohn Hunter's historical lectures published in1786, pathophysiology ofCRPS1remains unclear for decades. Many CRPS patients haveexperienced chronic pain and disability. After rat models of CRPS1werereported in2004, researches on pathology of CRPS1have achieved bigprogress. Two types of rat models were reported in15articles fromPubmed searching with key words (CRPS; model). They are rat model ofpost-fracture chronic pain(PFCP) and model of chronic post-ischemiapain(CPIP). We compared different feature between these two models andaim to find some guidance for choosing appropriate model for furtherexperiments.Objective:To investigate differences between the two rat models ofcomplex regional pain syndrome type1.Method:32adult health SD rats were randomly assigned to normalcontrol group, sham-operated group, PFCP group and CPIP grouprespectively, with8rats in each group. Pain behaviors and skinmicrocirculation were observed. Serum level of Substance P and tumor necrosis factor alpha were detected by ELISA. Skin and sciatic nervestructure were observed by HE staining under light-microscope.Results:3rats in tibia fracture group lost the broken leg. Painthreshold of rats in PFCP group and CPIP group decreased obviously aftermodeling. The expression of serum SP and TNF-αin two model groupswere significantly higher than that of control group and sham-operatedgroup (P<0.05-0.01). Changes on skin microcirculation are more severe inPFCP group than that in CPIP group. No noted change was found in skinand sciatic nerve sections under light-microscope. Ulcer-like lesion in theskin section of one rat and slight edema in the sciatic nerve was observed inPFCP group.Conclusions:Both rat models can effectively create CRPS-1-likesymptomatology. But PFCP model has more permanent symptoms andpathologic changes than CPIP model. Background:Complex regional pain syndrome-type1(CRPS-I) is adisease causing chronic pain and even disability. Because skin, bloodvessels, bones and joints are involved in the disease, it is categorized as arheumatic disease. The pathology of complex regional pain syndrome-type1is still unclear. Patients with CRPS always suffer from severe pain anddisability but no specific effective treatment is available. In the last fewdecades, being Considered as neuropathologic disorder, treatment ofCRPS-1is just aim to control symptom of pain, including pain medication,physical therapy, nerve block and surgery. Recently, pathology in CRPS-I isknown as a possible mechanism of inflammation participated by immunecells and inflammatory factors. Previous studies reported the increasedexpressions of some inflammatory factors (such as (TNF)-α, IL-2,6,sTNF-R1, NFκB) and some neuroinflammatory factors (including SP,CGRP and NGF) in CRPS1rat model. The positive results are encouraging,but some data were controversial and the key inflammatory factor in CRPShas not been found yet.MIF is initially described as a T cell-derived factor that inhibits therandom migration of macrophages. It plays a critical role in the host controlof inflammation and immunity. Studies demonstrated that MIF can be released from a variety of cells, such as lymphocytes, macrophages andneutrophils, endothelial cell, neuron and peripheral nerve. As amultifunctional modulator, MIF is increasingly recognized as afundamental constituent of many pathologic conditions, includingtraumatic inflammation, autoimmunopathies, cardiopathies andangiogenesis. Considering pathology in CRPS-I is known as a possiblemechanism for neurogenic inflammation and vasculatic neuropathy, wehypothesize that MIF is an important unique inflammatory factor involvedin neuropathy, vascular abnormality and immune response in the majorpathogenesis of CRPS-I. To our knowledge, this is the first time that theexpression of MIF in CRPS has been studied.Objective: To study the expression of MIF in rat tibia fracture modelof CRPS-1.Methods: We used the rat model of tibia fracture with limbimmobilization in our experiments. The expression of MIF in serum, CSF,skin, sciatic nerve and spinal cord were determined by ELISA,immunohistochemistry and western blot analysis, respectively. Before andafter modeling, hindpaw nociceptive behaviors were also tested.Results: Comparing to normal group and sham-operated group, theexpression of MIF determined by ELISA was up-regulated significantly inserum, CSF, hindpaw skin, sciatic nerve and spinal cord in rat model ofCRPS-I(P<0.05-0.01). The expression of MIF in skin, sciatic nerve and spinal cord in model group were higher than those in normal group andsham-operated group by western blot analysis (P<0.05). It is shown byimmunohistochemistry analysis that rat skin and sciatic nerve in modelgroup expressed high quantities of MIF.Conclusion: The results suggest that MIF may wildly participate inpathogenesis of CRPS-I. Background:Complex regional pain syndrome type1(CRPS1) is acomplication characterized by pain, swelling, limited range of motion,vasomotor instability, skin changes, and patchy bone demineralizationwithout evidence of nervous damage after minor surgery or injury. It wasknown as a neuropathic disorder in the past decades and most studiesfocused on the neurogenic dysregulation of nervous system. But so far,there has been no consensus on either pathophysiology or the treatment forthe disease. Recently, studies show several particular inflammatory factorsparticipated in pathogenesis of CRPS1and glucocorticoids are effective inpatients with CRPS1(Grade1A). However, considering its side effects,glucocorticoid has not been listed in the first line treatment for CRPS yet.Since targeted anti-cytokine therapies is considered as a valuable tool fortreatment of immunoinflammatory disorders, inhibition of inflammatoryfactors might be a promising target for novel therapeutic strategies inCRPS-1.MIF is an important pro-inflammatory factor in inflammatoryresponse which plays a pivotal role in the pathogenesis of numerousinflammatory and autoimmune disorders. Therefore, MIF is an attractivetherapeutic target for these disorders. Recently, it was demonstrated that an inhibitor of the catalytically active tautomerase site of MIF,ISO-1[(S,R)-3-(4-hydroxyphenyl)-4,5-dihydro-5-isoxazole acetic acid,methyl ester] can suppress inflammation by blocking MIF bioactivity asdetermined by the inhibition of MIF-mediated stimulation of ERK1/2MAPkinase. In the last chapter, the results showed that the expression of MIFwas up-regulated significantly in serum, CSF, hindpaw skin, sciatic nerveand spinal cord in rat model of CRPS-I. It suggests that MIF mayparticipate wildly in pathogenesis of CRPS-I hence the inhibition of MIFmight be a novel therapeutic strategy in CRPS-1.Objective: To investigate efficacy of inhibition of MIF in CRPS-I ratmodel and its influence on efficacy of glucocoticoid in CRPS-1.Methods:59adult health SD rats were randomized into normalcontrol group(n=5), sham-operated group(n=5), model control group(n=7),GC-treated group-1(n=7) with Methylprednisolone(MP) at1mg/(kg·d),GC-treated group-2(n=7) with MP at10mg/(kg·d), ISO-1-treatedgroup-1(n=7) with ISO-1dissolved in10ul5%DMSO at0.1mg/(kg·d),ISO-1-treated group-2(n=7) with ISO-1at1mg/(kg·d), Combinationgroup-1(n=7) with ISO-1at0.1mg/(kg·d)and MP at1mg/(kg·d),combination group-2(n=7) with ISO-1at0.1mg/(kg·d)and MP at10mg/(kg·d). Pain behaviors were tested after2-week-treatment. Serum MIFand SP were measured using ELISA at the8th hour,1st week,2nd weekafter the whole treatment. Skin microcirculation was observed at the2nd week after treatment.Results:(1)Hindpaw edema and Pain threshold were significantly improvedafter2-week-treatment in all treated groups(P<0.05). Serum level of SPwere lower in all treated groups than model control group(P<0.01-0.05).(2)At the8thhour and1stweek after treatment,except GC-treatedgroup-1,pain threshold of rats in other treated groups were significantlyhigher than model control group(P<0.05). Pain threshold of rats inGC-treated group-2and combination treated group-2were higher than inother treated groups during2weeks after treatment(P<0.05).(3)Except GC-treated group-1and ISO-1treated group-1,serumlevel of MIF in other treated groups were decreased significantly than inmodel treated group(P<0.05-0.01).(4)microcirculation scores in combination treated groups were lowerthan other treated groups(P<0.05).Conclusions:(1) Inhibitor of MIF, ISO-1, can release edema and pain in CRPS-I ratmodel depending on the dose. It suggests that MIF may play an importantrole in pathology of edema and pain in rats of CRPS1. Targeted MIFtherapy might be a novel treatment in CRPS-1.(2) low-dose glucocorticoid can't inhibit the expression of MIF andhad no effect on pain in rats of CRPS-1. (3) ISO-1is better than glucocorticoid in improving microcirculationdisorders.(4) ISO-1can act as a 'steroid-sparing agent' to increase efficacy oflow dose GC in CRPS-1by inhibiting the expression of MIF.