| Objective: Neuropathic pain(NeP)is a kind of chronic pain and one of the serious problems that plague human health.It can be caused by inflammation,trauma,surgery,cancer,metabolic diseases(such as diabetes),immune diseases(such as AIDS)and many other factors.It manifests as spontaneous and tactile pain,which is pain and hyperalgesia caused by non-noxious stimuli under normal conditions.Studies have shown that obesity is already a known risk factor for postoperative acute pain.Obesity increases the body’s sensitivity to pain and is more sensitive to noxious thermal and mechanical stimulation than normal rats.The movement and sensory nerve action potential of obese people are significantly impaired,the thermal pain threshold of neuropathic pain is increased,the nerve damage may be more serious,and the pain may be more sensitive.Obesity may enhance neuropathic paroxysmal pain and risk factors,but its specific mechanism of action and signaling pathways are not fully understood.Peroxisome proliferators-activated receptors(PPARs)are expressed in dorsal root ganglia and the central nervous system including brain and spinal cord and play an important role in the regulation of inflammatory responses.Studies have shown that PPARα is involved in peripheral inflammation inflammatory model of obese animals,the expression of central PPARα has been significantly reduced,and exogenously increased PPARα activity can improve inflammatory pain.These results suggest that obesity may lead to central levels.Abnormal expression of PPARα affects peripheral inflammatory response and inflammatory hyperalgesia.In this study,we established a neuropathic pain model of obese rats to detect the pain threshold(PWT)in rats,and confirmed that obesity increase the body’s sensitivity to pain;further detect the expression of PPARα in rat spinal cord,and explore the neuropathic pain of PPARα in obese rats.The possible role and its molecular mechanism provide a new target for the treatment of neuropathic pain.Methods: 1.Establish a rat model of neuropathic pain,respectively,and give low-fat and high-fat diets,and establish 4 groups,randomly:(1)low-fat diet rat group(LF),(2)low-fat diet rat + Neuropathic pain group(LF+SNI),(3)high-fat diet rat group(HF),(4)high-fat diet rat + neuropathic pain group(HF+SNI).The body weight and pain thresholdwere detected in each group.Enzyme-linked immunosorbent assay(ELISA)was used to detect the concentration of CGRP,TNF-α,IL-1β,IL6,IL-10 in spinal cord(SC)and dorsal root ganglion(DRG).The activity of superoxide dismutase(SOD)was detected by xanthine oxidase method(hydroxylamine hydrochloride method),and the content of malondialdehyde(MDA)was detected by thiobarbital(TBA)method.Real-time PCR and Western Blot were used to detect the expression of PPARα.Western Blot was used to detect the expression of Bax,Bcl-2.2.PPARα agonist(PEA)and PPARα antagonist(GW 6471)were administered to the rats with high-fat diet neuropathic pain,and a total of 4 groups were established,randomly:(1)high-fat diet rat group(HF),(2)High-fat diet rats + neuropathic pain group(HF+SNI),(3)high-fat diet rats + neuropathic pain + PPARα agonist group(HF+SNI+PEA),(4)high-fat diet Rat + neuropathic pain + PPAR alpha antagonist group(HF + SNI + GW 6471).The pain threshold in each group were detected.The concentrations of TNF-α,IL-1β,IL-6 and IL-10 in the spinal cord and dorsal root ganglia of each group were detected by ELISA.The activity of SOD was detected by hydroxylamine hydrochloride and the content of MDA by TBA.The expression of Bax,Bcl-2,p-AMPK,PPARα and NF-kB p65 protein were detected by Western Blot.3.PPARα agonist,PPARα antagonist,CGRP antagonist and AMPK inhibitor were administered to the rats with neuropathic pain in high-fat diet,rats were divided into six groups randomly:(1)High-fat diet rat group(HF),(2)high-fat diet rat + neuropathic pain group(HF+SNI),(3)high-fat diet rat + neuropathic pain + PPARα agonist group(HF+SNI+PEA),(4)Rats with high-fat diet + neuropathic pain + PPARα agonist +AMPK inhibitor group(HF+SNI+PEA+DOR),(5)High-fat diet rats + neuropathic pain+ CGRP antagonist group(HF+SNI+ CGRP8-37),(6)high fat diet rats + neuropathic pain + CGRP antagonist + PPARα antagonist group(HF+SNI+ CGRP8-37 + GW 6471).The pain threshold of rats was detected.The concentrations of CGRP,TNF-α,IL-1β,IL-6and IL-10 were detected by ELISA.The SOD activity was detected by hydroxylamine hydrochloride and the MDA content was detected by TBA.Bax was detected by Western Blot.Expression of Bcl-2,p-AMPK,PPARα,CGRP,NF-kB p65 protein.Results:1.The rat model of neuropathic pain was prepared by selecting the injury of the sciaticnerve branch.After 6 weeks of feeding,the weight of the high-fat diet group was significantly increased,compared with the low-fat diet group,and the body weight change was more obvious at 12 weeks(P<0.05).Compared with the low-fat diet group,the pain threshold of the rats in the high-fat diet group was significantly lower(P<0.05).At the 12 th week,the expression of CGRP in the spinal cord and dorsal root ganglia of the high-fat group was significantly increased(P< 0.05);the LF+SNI group,the PWT of the HF+SNI group was significantly lower(P<0.05);and the expression of TNF-α,IL-1β,IL-6 in the HF+SNI group was significantly increased,while the IL-10 expression was significantly decreased(P<0.05),and there was no significant increased in the HF group compared with the LF group(P > 0.05).In the HF+SNI group,the MDA level in the spinal cord and dorsal root ganglia increased significantly,while the SOD activity decreased significantly.Compared with the HF group,the difference was obvious(P<0.05),the activity of MDA levels was statistically significant in HF group(P<0.05),compared with the LF group;The expression of Bax in the spinal cord and dorsal root ganglia of the HF+SNI group was significantly increased,but the level of Bcl-2 protein has dropped significantly.Compared with the LF+SNI group,the distinct was apparent(P<0.05),compared with LF group,the expression of Bax and Bcl-2protein in HF group was statistically significant(P<0.05).Compared with LF+SNI group,the expression of PPARα mRNA and protein in the spinal cord and dorsal root ganglia of HF+SNI group was significantly decreased(P<0.05).2.In the HF+SNI group,the pain threshold was significantly decreased.The pain threshold was significantly increased in rats after PPARα agonist administration,while the pain threshold was significantly decreased in rats after PPARα antagonist administration(P<0.05).The expressions of CGRP,TNF-α,IL-1β,IL-6 and MDA in the spinal cord and dorsal root ganglia of the HF+SNI group were significantly increased,while the levels of IL-10 and SOD were significantly decreased(P<0.05).The expression of CGRP,TNF-α,IL-1β,IL-6 and MDA was significantly decreased after administration of PPARα agonist,while the levels of IL-10 and SOD were significantly increased(P<0.05),and the expression of CGRP,TNF-α,IL-1β,IL-6,MDA was significantly increased after PPARα antagonist administration,while the levels of IL-10 and SOD were significantly decreased(P<0.05).Western Blot showed that the expression of Baxof HF+SNI group was significantly increased,and the expression of Bcl-2 was apparently reduced,PPARα and p-AMPK were significantly decreased,AMPK was not significantly changed,and NF-k B p65 was significantly increased(P<0.05),when PPARα agonist was administered,the expression of Bax was significantly decreased,and the expression of Bcl-2 and p-AMPK was significantly increased,while that of NF-kB p65 was significantly decreased(P<0.05),after administration of PPARα antagonist,Bax expression was significantly increased,Bcl-2 expression was obviously downgraded,PPARα was significantly decreased,p-AMPK was significantly decreased,and NF-kB p65 was significantly increased(P<0.05).3.The pain threshold was significantly decreased in the HF+SNI group,and the pain threshold was significantly increased in rats after PPARα agonist or CGRP antagonist(P<0.05).Compared with the HF+SNI group,the expression of CGRP,TNF-α,IL-1β,IL-6 and MDA in the spinal cord and dorsal root ganglia of rats was significantly decreased after administration of PPARα agonist or CGRP antagonist,while IL-10 and SOD levels increased significantly(P<0.05).Western Blot showed that the expression of Bax was significantly decreased of rats after administration of PPARα agonist or CGRP antagonist,but there was obvious decrease of Bcl-2 protein,PPARα and p-AMPK were significantly increased,and AMPK expression was not observed,while NF-kB p65 was significantly reduced(P <0.05);However,when the AMPK inhibitor was administered,the above-described regulatory effects of the PPARα agonist on HF+SNI rats were inhibited,and the modulation of CGRP antagonists in HF+SNI rats was also blocked by PPARα antagonists.Conclusion:1.Obesity increases neuropathic pain sensitivity;obesity neuropathic pain increased inflammation sensitivity,promoted oxidative stress response and cell apoptosis process in the central and peripheral nervous system;obese neuropathic pain reduced PPARα but increased central CGRP expression in the central.2.After administration of PPARα agonist in obese neuropathic pain rats,the agonist can relieve pain and inhibit inflammation,oxidative stress and cell apoptosis process;increased PPARα,p-AMPK expression,reduced CGRP,NF-Bp65 expression;But after giving PPARα antagonist,the above results were reversed.It suggested that PPARαagonists can regulate AMPK/CGRP pathway to improve obese neuropathic pain by reducing oxidative stress-inflammatory response.3.After administration of PPARα agonist and AMPK inhibitorin obese neuropathic pain rats,the effect of PPARα agonist was blocked,and the pain was enhanced;inflammation,oxidative stress and apoptosis were promoted;The expression of PPARα and p-AMPK decreased,but that of CGRP and NF-Bp65 increased.After administration of CGRP antagonist,it can also relieve pain;inhibited inflammation,oxidative stress and apoptosis;increased PPARα,p-AMPK expression,decreased CGRP,NF-Bp65 expression;If PPARα antagonist is administered simultaneously,it reversed the threshold of pain;promoted inflammation,oxidative stress and apoptosis;decreased PPARα,p-AMPK expression,increased CGRP,NF-Bp65 expression.It further suggested that the AMPK/PPARα/CGRP pathway improves obese neuropathic pain by reducing oxidative stress-inflammatory responses. |
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