Mechanisms Of Sciatica:Modulation Of Sodium Activated Potassium Channels(KNA) By P38 MAP Kinase

Part 1:A cohort study comparing the serum levels of pro-or anti-inflammatory cytokines in patients with lumbar radicular pain and healthy subjectsPurpose:The factors influencing the presence or absence of pain in sciatica secondary to disc herniation remain incompletely understood.We hypothesized that the imbalance in inflammatory cytokines is implicated in the generation of pain.In our study,serum levels of pro-inflammatory and anti-inflammatory cytokines were investigated among patients with severe sciatica;the serum levels were compared with those of patients with mild sciatica and healthy subjects.Methods:In this prospective study,blood protein levels of the pro-inflammatory cytokines,namely,interleukin-6(IL-6),interleukin-8(IL-8),and tumor necrosis factor-a(TNF-?),and the anti-inflammatory cytokines,namely,interleukin-4(IL-4)and interleukin-10(IL-10),of 58 patients with severe sciatica,50 patients with mild sciatica,and 30 healthy control subjects were analyzed through ELISA.Physical and mental health symptoms were determined using the Oswestry Disability Index(ODI)and short form-36(SF-36)questionnaire.Spearman rank correlation coefficient was also determined to calculate the correlation between the scores obtained from the questionnaires and the serum levels of cytokines.Results-IL-6 protein was detected in the three groups and median levels were about 1.5 times higher in patients with severe sciatica than the mild sciatica group(p = 0.02)and the controls(P= 0.03).Median levels of IL-8 in sciatica patients were higher than those of the healthy controls(P= 0.001 for severe sciatica,P= 0.02 for mild sciatica).The TNF-? protein values were approximately twofold higher in the severe sciatica group than in the mild sciatica group(P<0.01)and in the healthy control group(P<0.01).Median levels of IL-4 were about 2.5-fold higher in mild sciatica(P<0.01)and about twofold higher in patients with severe sciatica(P= 0.012)when compared with controls.Median protein levels of IL-10 showed a trend to be higher in patients with mild sciatica compared with severe sciatica(P<0.01)and with healthy controls(P<0.01).ODI was significantly correlated with IL-6(r = 0.394,P= 0.013),TNF-a(r = 0.629,P<0.001),and IL-10(r =-0.415,P= 0.009).ODI was not significantly correlated with IL-4(r =-0.174,P= 0.29)and IL-8(r =-0.133,P= 0.418).Conclusion:These findings support our hypothesis that sciatica pain is accompanied by the imbalance in inflammatory cytokines.Part 2:Tumor necrosis factor a modulates sodium-activated potassium channel SLICK in rat dorsal horn neurons via p38 MAPK activation pathwayPurpose:The dorsal horn(DH)of the spinal cord is the integrative center that processes and transmits pain sensation.Abnormal changes in ion channel expression can enhance the excitability of pain-related DH neurons.Sodium-activated potassium(KNa)channels are highly expressed particularly in the central nervous system;however,information about whether rat DH neurons express the SLICK channel protein is lacking,and the direct effects on SLICK in response to inflammation and the potential signaling pathway mediating such effects are yet to be elucidated.Methods:In this study,tumor necrosis factor-? was applied on dorsal horn neurons of neonatal rat to explore the current voltage,protein and gene changes of sodium-activatedpotassium channel.Then,observe whether the p38 inhibitor SB202190 is resistant to these changes.Results:Here,we have shown that tumor necrosis factor-a inhibits the total outward potassium current IK and the KNa current predominantly as well as induces a progressive loss of firing accommodation.However,we found that this change in channel activity is offset by the p38 inhibitor SB202190,thereby suggesting the modulation of SLICK channel activity via the p38 MAPK pathway.Conclusion:Tumor necrosis factor-a modulation of KNachannels does not occur at the level of SLICK channel gating but arises from possible posttranslational modification.Part 3:p3 8 MAPK mediated sodium-activated potassium channel involved in the mechanism of sciatica:a vivo studyPurpose:To evaluate the contributionof the p38 MPK pathway to neuropathic pain and the potentiality of this pathway as anovel therapeutic target.Methods:SD rats were randomly divided into normal group,sham operation group and autologous nucleus pulposus transplantation group.In the autologous nucleus pulposus transplantation group,three concentrations of p3 8 MAPK inhibitor SB202190(0.3 mg/kg,1.0 mg/kg,3.2 mg/kg)were intrathecally administered,saline as control.To expression of sodium-activated potassium channel,located in dorsal root ganglion and spinal dorsal horn of rats,were measured by westernblot and RT-PCR.The mechanical and thermal pain thresholds of rats were recorded-The data were analyzed statistically.Results:The mechanical and thermal pain thresholds of the rats in the autologous nucleus pulposus group were significantly lower than those in the normal and sham operation groups at each postoperative point(P<0.05).SLICK mRNA and SLACK mRNA were significantly decreased in autologous nucleus pulposus(P<0.05),and the trend was opposite to that of p3 8 mRNA.Protein immunoblot analysis showed in a consistent manner with gene.At the time of intrathecal injection,the mechanical and thermal hyperalgesia of rats were significantly improved on the second day after operation(P<0.01).SB202190 also significantly increased the level of sodium-activated potassium channel protein expression,but did not play a role in transcriptional activity.Conclusion:Inhibition of p38 MAPK pathway activation in the spinal cord,and increased sodium-activated potassium channel expression can relieve the painful state of sciatica.