Daphnetin Ameliorates Neuropathic Pain in CCI Rats by Interfering With Microglia P2X4 - P38 MAPK (Daphnetin Improves Neuropathic Pain)

Background: Neuropathic pain is a common chronic pain caused by a lesion or diseases of somatosensory nervous system, which has a significant impact on the quality of life. It has been found that its underling pathological mechanism is related to inflammation. Daphnetin is a natural product with a variety of biological activities such as anti-inflammatory and analgesic. It has been shown to be effective in the treatment of chronic inflammatory pain, but its underlying mechanisms are not completely understood. We aimed to evaluate the effect and regulatory mechanism of daphnetin on neuropathic pain.Methods: The experimental animals were divided into 8 groups: control group, model group, sham group, positive group (0.0375mg/kg), DAPH group (0.0625mg/kg), DAPL group (0.025mg/kg), P2X4 blocker group (1mg/kg) and P38 blocker group (5mg/kg). After constructing the subdural drug delivery system in rats, the neuropathic pain model was established by chronic constrictive injury (CCI), and the pain sensitivity was evaluated by measuring mechanical withdrawal threshold (MWT) and thermal withdrawal threshold (TWT). The protein expression of inflammatory factors and related pathways was measured by Western Blot. The activation of microglia and neurons and the expression of target protein in spinal dorsal horn were measured by immunofluorescence staining.Results: Compared with the sham group, MWT and TWT decreased significantly in model group, and the expression of IL-1 β, IL-6 and TNF-α increased. After intrathecal injection of daphnetin, the MWT and TWT of rats were significantly increased, and the protein expression of IL-1 β, IL-6 and TNF- α was significantly decreased compared with the model group. Compared with sham group, the expression of P2X4, IRF8, IRF5, BDNF, p-P38 / P38, p-JNK / JNK and p-ERK1/2 / ERK1/2 in model group increased significantly. After intrathecal injection of daphnetin, the expression of the above proteins was significantly down-regulated compared with model group. Compared with sham group, microglia and neurons in the spinal dorsal horn of model group were activated, and the expression of P2X4 and P38 in microglia increased. After intrathecal injection of daphnetin, compared with the model group, the activation of microglia and neurons in the spinal dorsal horn decreased significantly, and the expression of P2X4 and P38 in microglia decreased. Importantly, daphnetin could not improve neuropathic pain in CCI rats under the action of P2X4 and P38 blocker.Conclusion: daphnetin can alleviate neuropathic pain in CCI model rats by interfering with P2X4-P38 MAPK pathway of microglia, suggesting that daphnetin is a potential drug for the treatment of neuropathic pain.