Effect of hyperbaric oxygen therapy on neuropathic pain and its mechanism
Objective To explore the mechanism of hyperbaric oxygen(HBO)therapy for alleviating neuropathic pain.Methods A total of 96 adult healthy male C57BU6J mice were divided into three groups,according to the random number table method:sham group(group S),model of chronic compression injury group(group C),and HBO group(group H),with 32 mice in each group.The neuropathic pain model in the group C and group H was established by chronic compression injury(CCI)of sciatic nerve,and sham operation was performed only in the group S.The mice in the group H were treated with HBO on the first day after operation,once a day for five consecutive days.The mice in the group S and group C were simply placed in oxygen chamber without HBO treatment.After modeling,the mechanical withdrawal threshold(MWT)and thermal withdrawal latency(TWL)were measured on postoperative days 1,3,5,7,14,21,and 28,respectively.On postoperative days 7,14,21,and 28,eight mice were euthanized in each group and the right dorsal root ganglia were harvested.The mRNA expression levels of HIF-1α,iNOS,Arg-1,TNF-α,IL-6,and IL-10 in the dorsal root ganglia of each group were determined by RT-qPCR.Results Compared with the group S,at each postoperative time point,the group C had lower MWT and shorter TWL(P<0.001),higher mRNA expression levels of HIF-1α,iNOS,TNF-α,and IL-6,and lower mRNA expression levels of IL-10 and Arg-1(P<0.05,P<0.01,or P<0.001).Compared with the group C,the mice in the group H showed significant increases in MWT and TWL on postoperative days 1,3,7,and 14(P<0.001),and on postoperative days 7 and 14,the mRNA expression levels of HIF-1α,TNF-α,IL-6,and iNOS were significantly decreased,while the mRNA expression levels of Arg-1 and IL-10 were significantly increased(P<0.01 or P<0.001).Conclusion HBO therapy is effective for short-term relief of neuropathic pain in mice,and its mechanism may be related to the regulation of macrophage polarization mediated by HIF-1α and its anti-inflammatory effects.