The Mechanism of Emodin Negatively Regulating HMGB1 via the SIRT1 Pathway to Alleviate Pain Hypersensitivity in Rats With Neuropathic Pain

Background: Neuropathic pain (NP) is chronic pain caused by damage to or disease of the somatosensory nervous system. Emodin is known to protect nerves from injury and inflammation, but its underlying mechanisms remain unclear. This study aims to investigate whether emodin negatively regulates the effect of high mobility group box 1 (HMGB1) on hyperalgesia in NP via the sirtuin 1 (SIRT1) pathway. Methods: We established in vivo and in vitro models of NP to investigate emodin's specific mechanisms of action. A chronic constriction injury (CCI) model was created in adult rats. Paw withdrawal mechanical threshold and paw withdrawal thermal latency were used to assess hyperalgesia in the rats. Next, hematoxylin and eosin (H&E) staining was performed on the sciatic nerve and immunohistochemistry was used to assess changes in glial fibrillary acidic protein (GFAP) and ionized calcium-binding adapter molecule 1 (Iba-1) levels in spinal cord tissues. Then, enzyme-linked immunosorbent assay (ELISA) kits were used to measure the concentrations of tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), and interleukin-6 (IL-6) in the serum of CCI rats. Western blotting and co-immunoprecipitation were used to examine the interaction between SIRT1 and HMGB1, as well as the expression of HMGB1-related pathways. Cell Counting Kit-8 (CCK-8) assay was used to evaluate the cytotoxicity of emodin at different concentrations on mouse microglial cell line (BV2) cells. RT-qPCR was used to analyze the transfection efficiency of si-SIRT1. A neuroinflammatory cell model induced by lipopolysaccharide (LPS) was established for the BV2. Transwell assay was used to evaluate cell migration. Western blotting and immunofluorescence were used to detect the expression of microglial markers and of pathways related to SIRT1 and HMGB1. Results: Emodin reduced CCI-induced hyperalgesia and inflammation, upregulated SIRT1 expression, and inhibited the expression of HMGB1/Toll like receptors4 (TLR4)/nuclear factor kappa-B (NF-κB). SIRT1 inhibitor abolished the ameliorative effect of emodin on CCI-induced spinal cord inflammation. In the LPS-induced cell model, emodin reversed LPS-induced migration, activation, and inflammation of BV2 cells. Furthermore, in LPS-treated BV2 microglial cells, emodin inactivated the HMGB1/TLR4/NF-κB pathway. Emodin also significantly inhibited the translocation of HMGB1 from the nucleus to the cytoplasm by upregulating SIRT1. Knockdown of SIRT1 abolished the protective effects of emodin against LPS-induced BV2 microglial cell migration, activation, and inflammation. Conclusion: Emodin negatively regulates HMGB1 via the SIRT1 pathway to alleviate hyperalgesia in neuropathic pain both in vivo and in vitro. This research provides a new direction for clinical pharmacological treatment of NP and offers new insights into the mechanisms underlying NP.