Abstract: BACKGROUND: Acid-sensing ion channels can be involved in various physiological processes, such as synaptic plasticity, pain perception, and touch. Inflammation can trigger the activation and change of acidic microenvironment, which may be an important factor leading to persistence and high recurrence rate of related diseases.
OBJECTIVE: To investigate the effects of mecobalamin on neuropathic pain, c-Jun N-terminal kinase and chemokine (C-X-C motif) ligand 1 pathways and acid-sensing ion channels in rats with lumbar disc herniation.
METHODS: Forty healthy Sprague-Dawley rats were randomized into control group, model group, mecobalamin group, and drug control group (n=10 per group). The lumbar disc herniation model was established in the rats except for the control group. The model and groups were intraperitoneally injected with 0.8 mL/kg/d normal saline. The mecobalamin group was intraperitoneally injected with 104 μg/kg/d. The drug control group was intraperitoneally injected with celecoxib 0.5 mL/kg/d. Administration in each group was performed once a day for 14 days. Mechanical paw withdrawal thresholds were measured with an intelligent hot plate instrument 1 day before modeling, 1 day after modeling, and 7 and 14 days after treatment. PCR was used to detect the mRNA expression of acid-sensing ion channels 24 hours after administration. The levels of inflammatory factors, interleukin-6 and tumor necrosis factor α, were detected by ELISA at 7 and 14 days after treatment. Western blot assay was used to detect c-Jun N-terminal kinase and chemokine (C-X-C motif) ligand 1 protein levels.
RESULTS AND CONCLUSION: Compared with the control group, the mechanical paw withdrawal threshold of the hind limbs was significantly decreased in the model group (P < 0.05). The mechanical paw withdrawal threshold of the hind limbs was significantly higher in the mecobalamin group than the model group 
(P < 0.05) and the drug control group (P < 0.05). Compared with the control group, the levels of interleukin-6 and tumor necrosis factor α were increased in the model group (P < 0.05). While compared with the model and drug control groups, mecobalamin could significantly reduce the levels of interleukin-6 and tumor necrosis factor α (both P < 0.05). In the model group, neurons were vacuolated and irregular, with blurred and disordered nucleoli; in the mecobalamin group, a small number of neurons were pyknotic and presented with nuclear migration, the voiding area in the gray and white matter was reduced, the nucleoli were clear, and Nissl bodies in the cytoplasm were relatively uniform; in the drug control group, some neurons still presented with pyknosis, necrosis, and dissolution and the voiding area in the gray and white matter was reduced. Compared with the control group, the mRNA levels of acid-sensing ion channels 3 and 1a in the spinal dorsal horn of rats were significantly increased (P < 0.05) and the protein expressions of c-Jun N-terminal kinase and chemokine (C-X-C motif) ligand 1 were significantly upregulated in the model group (P < 0.05). The levels of the above-mentioned indicators were significantly lower in the mecobalamin group than the model and drug control groups (P < 0.05). To conclude, mecobalamin can alleviate neuropathic pain and inhibit the expression of inflammatory factors in serum and the activity of acid-sensing ion channels in rats with lumbar disc herniation. The mechanism may be related to the inhibition of c-Jun N-terminal kinase and chemokine (C-X-C motif) ligand 1 expression.

Key words: mecobalamin, lumbar disc herniation, neuropathic pain, c-Jun N-terminal kinase, chemokine (C-X-C motif) ligand 1, acid-sensing ion channels