Effects of hydrogen-rich saline on chronic inflammatory pain in rats

Abstract

Objective To evaluate the effects of hydrogen-rich saline on chronic inflammatory pain in rats. Methods Thirty-two male Sprague-Dawley rats, aged 8-10 weeks, weighing 200-250 g, were randomly divided into 4 groups(n=8 each)using a random number table: control group(group C); complete Freund's adjuvant(CFA)group; hydrogen-rich saline group(group H2); CFA + hydrogen-rich saline group(CFA+ H2 group). Chronic inflammatory pain was induced by injecting CFA 100 μl into the plantar surface of the left hindpaw in CFA and CFA+ H2 groups.In H2 and CFA+ H2 groups, 0.6 mmol/L hydrogen-rich saline 5 ml/kg was injected intraperitoneally once a day for 7 consecutive days starting from 1 day after injection of CFA, while the equal volume of normal saline was given instead of hydrogen-rich saline in C and CFA groups.The mechanical paw withdrawal threshold(MWT)and thermal paw withdrawal latency(TWL)were measured at 1 day before CFA injection and 1, 3 and 7 days after CFA injection.The rats were sacrificed after the last measurement of pain threshold on day 7 after CFA injection.The left lumbar segments(L4-5)of the spinal cord were removed for determination of nuclear factor E2-related factor 2(Nrf2)and heme oxygenase-1(HO-1)expression by Western blot. Results Compared with C group, no significant change was found in the MWT, TWL and expression of Nrf2 and HO-1 in H2 group, and the MWT was significantly decreased, the TWL was shortened, and the expression of Nrf2 and HO-1 was up-regulated in CFA and CFA+ H2 groups.Compared with CFA group, the MWT was significantly increased, the TWL was prolonged, and the expression of Nrf2 and HO-1 was up-regulated in CFA+ H2 group. Conclusion Hydrogen-rich saline can alleviate chronic inflammatory pain in rats, and activation of Nrf2/ARE signaling pathway in the spinal cord is involved in the mechanism. Key words: Hydrogen; Pain; Inflammation