Abstract: BACKGROUND: The imbalance of inflammatory microenvironment after spinal cord injury can aggravate secondary spinal cord injury and hinder the repair of nerve function. Tetramethylpyrazine can inhibit inflammatory responses and protect nerve cells; however, its research in the field of spinal cord injury is less.
OBJECTIVE: To observe whether tetramethylpyrazine can improve inflammatory responses and recover nerve function after spinal cord injury in rats and to explore its potential mechanism.
METHODS: Thirty-six Sprague-Dawley rats were randomly divided into sham operation group, model group, and tetramethylpyrazine group, with 12 rats in each group. The sham operation group received T10 laminectomy; the model and tetramethylpyrazine groups received T10 spinal cord complete transection by self-made double-edge microshear. After modeling, the tetramethylpyrazine group was given tetramethylpyrazine hydrochloride injection via intraperitoneal injection (200 mg/kg/d) for consecutive 5 days. Basso, Beattie and Bresnahan score and modified Rivlin oblique plate test were used to evaluate the recovery of motor function at 1, 3, 7, and 14 days after surgery. Tissue samples were stained with hematoxylin-eosin and Nissl staining to observe the morphological changes at 14 days after surgery. Changes in C-reactive protein were detected by enzyme-linked immunosorbent assay. The expression of inflammatory factors, including nuclear factor-кB, tumor necrosis factor-α, interleukin-10, was analyzed by immunohistochemical staining.
RESULTS AND CONCLUSION: At each time point after spinal cord injury, Basso, Beattie and Bresnahan score and modified Rivlin slant angle in the sham operation group were significantly higher than those in the other groups (P < 0.05), while there were no significant differences between the model and tetramethylpyrazine groups (P > 0.05). Hematoxylin-eosin staining results showed that the number of inflammatory cells in the tetramethylpyrazine group was significantly lower than that in the model group. Nissl staining results revealed that the number of neurons at both broken ends of the spinal cord was significantly higher in the tetramethylpyrazine group than the model group. After spinal cord injury, C-reactive protein expression increased firstly and then decreased, and tetramethylpyrazine could significantly reduce the expression of C-reactive protein (P < 0.05). At 7 days after modeling, the expression of nuclear factor-кB and tumor necrosis factor-α in the model group was significantly higher than that in the sham operation group (P < 0.05), while the expression of interleukin-10 was lower than that in the sham operation group. Compared with the model group, tetramethylpyrazine could significantly decrease the expression of nuclear factor-кB and increase the expression of interleukin-10 (P < 0.05). At 14 days after modeling, the expression levels of nuclear factor-кB and tumor necrosis factor-α increased significantly in the model group compared with the sham operation group, while the expression level of interleukin-10 was significantly lower than the sham operation group (P < 0.05). Compared with the model group, tetramethylpyrazine could significantly increase the expression of interleukin-10 (P < 0.05). All these findings suggest that after spinal cord injury, the expression of pro-inflammatory factors is significantly increased and the inflammatory microenvironment becomes unbalanced. Tetramethylpyrazine can regulate the immune inflammatory response after spinal cord injury, improve the inflammatory microenvironment, and promote the repair of spinal cord injury. 

Key words: spinal cord injury, tetramethylpyrazine, inflammation, inflammatory factor, nuclear factor-кB, tumor necrosis factor-α, interleukin-10