Effect of glycyrrhizin on traumatic brain injury in rats and its mechanism

Objective: To investigate the neuroprotective effects of glycyrrhizin (Gly) as well as its effect on expression of high-mobility group box 1 (HMGB1) in rats after traumatic brain injury (TBI). Methods: Male Sprague-Dawley rats were randomly divided into three groups: sham group, TBI group, and TBI+Gly group (n=36 per group). Rat TBI model was made by using the modified Feeney's method. In TBI+Gly group, Gly was administered intravenously at a dosage of 10 mg/kg 30 min after TBI. At 24 h after TBI, motor function and brain water content were evaluated. Meanwhile, HMGB1/HMGB1 receptors including toll-like receptor 4 (TLR4) and receptor for advanced glycation end products (RAGE)/nuclear factor - kappa B(NF - kappa B) signaling pathway and inflammatory cytokines in the injured brain tissues were detected using quantitative real-time polymerase chain reaction, western blot, electrophoretic mobility shift assay and enzyme-linked immunosorbent assay. Furthermore, HMGB1, RAGE and TLR4 immunohistochemistry and apoptosis were analyzed. Results: Beam walking performance impairment and brain edema were significantly reduced in TBI+Gly group compared with TBI group; meanwhile, the over-expressions of HMGB1/HMGB1 receptors (TLR4 and RAGE)/NF - kappa B DNA-binding activity and inflammatory cytokines were inhibited. The percentages of HMGB1, RAGE and TLR4-positive cells and apoptotic cells were respectively 58.37%+/- 5.06%, 54.15%+/- 4.65%, 65.50%+/- 4.83%, 52.02%+/- 4.63% in TBI group and 39.99%+/- 4.99%, 34.87%+/- 5.02%, 43.33%+/- 4.54%, 37.84%+/- 5.16% in TBI+Gly group (all P<0.01 compared with TBI group). Conclusion: Gly can reduce secondary brain injury and improve outcomes in rat following TBI by down-regulation of HMGB1/HMGB1 receptors (TLR4 and RAGE)/NF - kappa B - mediated inflammatory responses in the injured rat brain.