Abstract: BACKGROUND: Previous studies found that treatment with awn needles can improve the inflammatory response after spinal cord injury, reduce the expression of high-mobility group protein 1 (HMGB-1) and pro-inflammatory factors, and inhibit the activity of nuclear transcription factors and the occurrence of neuronal apoptosis.
OBJECTIVE: To analyze the relationship between the mechanism of inflammatory response and the HMGB-1/Toll-like receptor 4 (TLR4)/nuclear factor-κB (NF-κB) signaling pathway after spinal cord injury. 
METHODS: The T9-10 spinal cord injury model was made according to the internationally recognized modified Allen’s modeling method. The blood samples of the spinal cord and tail artery were obtained for Basso, Beattie and Bresnahan scoring at 6, 24 hours, 3 and 7 days after modeling. The HMGB-1 content in the spinal cord and tail artery serum was measured by ELISA to determine the highest point of HMGB-1 in the spinal cord and the change rule of HMGB-1 content in serum and spinal cord. Taking the highest HMGB-1 content as the research point and using glycyrrhizic acid as the HMGB-1 inhibitor, the rats were divided into four groups: model group, glycyrrhizic acid group (intragastric administration of glycyrrhizic acid, 200 mg/kg), blank group and sham operation group. The highest HMGB-1 expression was determined by ELISA. The spinal cord was obtained at the highest point of HMGB1 expression. The correlation between HMGB-1/TLR4/NF-κB signaling pathway and inflammation after spinal cord injury was explored by immunoblotting and RT-PCR detection, and the pathological changes of spinal cord in rats were observed. Approval for this study was obtained by the Animal Experimental Ethics Committee of Zhejiang Chinese Medical University .
RESULTS AND CONCLUSION: The expression of HMGB-1 in the spinal cord and blood at 3 days after spinal cord injury was significantly higher than that at 6 hours, 24 hours, and 7 days (P < 0.05). At 3 days after spinal cord injury, the expressions of HMGB-1, TLR4, NF-κB, interleukin-6, and tumor necrosis factor-α in the glycyrrhizic acid group were lower than those in the model group, but higher than those in the blank group and sham operation group (P < 0.05). The expressions of HMGB-1, TLR4 and NF-κB at gene and protein levels in the glycyrrhizic acid group were lower than those in the model group, but higher than those in the blank group and the sham operation group (P < 0.05). To conclude, after spinal cord injury, HMGB-1 in blood and spinal cord increased significantly and reached the highest value at 3 days. After inhibiting HMGB-1, it was found that the HMGB-1/TLR4/NF-κB pathway is one of the important pathways to induce inflammation after spinal cord injury.

Key words: spinal cord, injury, protein, nuclear factor, pathway, inflammatory response, model, rat