Influence of seawater immersion on expression of proinflammatory cytokines and intervention effect of methylprednisolone for sciatic nerve injury in rats

Objective　To explore the mechanism of aggravation of sciatic nerve injury after seawater immersion and the protective effect of methylprednisolone against injury so as to provide an experimental basis for clinical treatment of seawater immersion complicated sciatic nerve injury. Methods 　A total of 192 Sprague-Dawley rats were randomly divided into group A (sham injury group), group B (injury control group), group C (seawater immersion + injury group), group D (methylprednisolone treatment group). The model of rat sciatic nerve injury was reproduced by crush injury in groups B, C and D. The sciatic nerves were crushed followed by seawater immersion for 1 hour in groups C and D. Methylprednisolone (20mg/(kg.d)) was injected viathe tail vein in group D for 2 days. The Sciatic Functional Index (SFI) was used to assess the nerve function on 3rd day and 1, 2 and 4 weeks after injury, and IL-1β, IL-6, TNF-α mRNA and protein expression were determined with RT-PCR or immunohistochemistry. Results　The SFI of group A showed no significant change on 3rd day up to 4 weeks after injury. The SFIs in groups B, C and D were gradually increased from 3rd day to 4 weeks after injury. SFI was lower in group C compared with groups B and D (P<0.05). The expressions of IL -1β, IL -6 and TNF-α mRNA in group A were lower on 3rd day and 1, 2 and 4 weeks after injury. The expressions of IL-1β and IL-6 mRNA in groups B, C and D were gradually decreased from 3 days to 4 weeks after injury, and the expression in group C was significantly higher than that of groups B and D on 3rd day and 1 and 2 weeks (P<0.05). No statistical difference was found in the 4th week among groups B, C and D. The expressions of TNF-α mRNA in groups B, C and D were gradually decreased from 3 days to 2 weeks after injury. The expression of TNF-α mRNA in group C was significantly higher than that of groups B and D on the 3rd day and 1st week (P<0.05). No statistical significant difference was found among groups B, C and D at the 2nd and 4th week. The expression levels of IL-1β, IL-6 and TNF-α protein in group A were from (-) to (+) on 3rd day and 1, 2 and 4 weeks after injury. The expression levels of IL-1β, IL-6 and TNF-α protein in groups B, C and D were (+++) on 3rd days and 1 week after injury, while those of IL-1β and IL-6 protein were (++), and TNF-α protein (-) to (+) at 2 weeks. The expression levels of IL-1β, IL-6 and TNF-α protein in groups B, C and D were (-) to (+) 4 weeks after injury. Conclusions　Seawater immersion would upregulate the expressions of IL-1β, IL-6 and TNF-α after sciatic nerve injury in rats, and it would cause inflammation and hinder the recovery of nerve function. Methylprednisolone could promote the regeneration of sciatic nerve after seawater immersion in rats, probably by inhibiting the inflammatory reaction. DOI: 10.11855/j.issn.0577-7402.2015.10.04