Diosmetin alleviates neuropathic pain by regulating the Keap1/Nrf2/NF-κB signaling pathway.

BACKGROUND: Neuropathic pain, a chronic condition with a high incidence, imposes psychological burdens on both patients and society. It is urgent to improve pain management and develop new analgesic drugs. Traditional Chinese medicine has gained popularity as a method for pain relief. Diosmetin (Dio) is mainly found in Chinese herbal medicines with effective antioxidant, anti-cancer, and anti-inflammatory properties. There are few known mechanisms underlying the effectiveness of Dio in treating neuropathic pain. However, the complete understanding of its therapeutic effect is missing. PURPOSE: This study aimed to evaluate Dio's therapeutic effects on neuropathic pain models and determine its possible mechanism of action. We hypothesized that Dio may activate antioxidants and reduce inflammation, inhibit the activation of Kelch-like epichlorohydrin-associated protein 1 (Keap1) and nuclear factor-k-gene binding (NF-κB), promote the metastasis of nuclear factor erythroid 2-related factor 2 (Nrf2) and the expression of heme oxygenase 1 (HO-1), thus alleviating the neuropathic pain caused by spinal nerve ligation. METHODS: Chronic nociceptive pain mouse models were established in vivo by L4 spinal nerve ligation (SNL). Different dosages of Dio (10, 50, 100 mg/kg) were intragastrically administered daily from the third day after the establishment of the SNL model. Allodynia, caused by mechanical stimuli, and hyperalgesia, caused by heat, were assessed using the paw withdrawal response frequency (PWF) and paw withdrawal latency (PWL), respectively. Cold allodynia were assessd by acetone test. RT-PCR was used to detect the content of interleukin-(IL)- 1ß, IL-6 and tumor necrosis factor (TNF)-a. Immunofluorescence and western blotting were employed to assess the expression levels of Glial fibrillary acidic protein (GFAP), ionized calcium-binding adapter molecule (Iba1), Keap1, Nrf2, HO-1, and NF-κB p-p65 protein. RESULTS: Dio administration relieved SNL-induced transient mechanical and thermal allodynia in mice. The protective effect of Dio in the SNL model was associated with its anti-inflammatory and anti-glial responses in the spinal cord. Dio inhibited both inflammatory factors and macrophage activation in the DRG. Furthermore, Dio regulated the Keap1/Nrf2/NF-κB signaling pathway. HO-1 and Nrf2 were upregulated following Dio administration, which also decreased the levels of Keap1 and NF-κB p65 protein. CONCLUSION: Mice with SNL-induced neuropathic pain were therapeutically treated with Dio. Dio may protect against pain by inhibiting inflammatory responses and improved Keap1/Nrf2/NF-κB pathway. These results highlight the potential therapeutic effect of Dio for the development of new analgesic drugs.

Astaxanthin alleviates inflammatory pain by regulating the p38 mitogen-activated protein kinase and nuclear factor-erythroid factor 2-related factor/heme oxygenase-1 pathways in mice.

Inflammatory pain is a complex process that has a substantial negative impact on post-injury quality of life. Astaxanthin (AST), which is a lipid-soluble red-orange carotenoid that is found in lobsters, inhibits the development and maintenance of inflammation in mice via its antioxidant and anti-inflammatory activities. However, the specific mechanisms underlying these effects remain unclear. In this study, we aimed to elucidate the mechanism by which astaxanthin alleviated inflammation using a mouse model with Complete Freund's adjuvant (CFA)-induced inflammatory pain. Mechanical allodynia and thermal hyperalgesia were observed on days 1-14 post CFA injection. Expression of p38 mitogen-activated protein kinase (MAPK) in the left paw and L4-6 dorsal root ganglia (DRG) were upregulated in the CFA-induced mice. Expression of the nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) pathways were also increased. Astaxanthin relieved mechanical allodynia and thermal hyperalgesia induced by CFA and inhibited the inflammatory response (e.g., infiltration of inflammatory cells and production of inflammatory factors) in the ipsilateral paw and DRG. Additionally, AST  inhibited p38 MAPK and enhanced Nrf2/HO-1 contents in the left paw and DRG, and reversed the pain induced by p38 MAPK agonist and Nrf2 inhibitors. These findings suggest that AST exerts anti-inflammatory effects and regulates p38 MAPK and Nrf2/HO-1 to alleviate inflammatory pain. AST may be a potential therapeutic agent for relieving inflammation.