Mechanism Study on Liquiritin Alleviating Nociceptive Sensitization in Knee Osteoarthritis via Promoting M2 Macrophage Polarization Through Regulation of the Rap1/PI3K/Akt Signaling Pathway.

Knee osteoarthritis (KOA) is a widespread chronic osteoarticular condition, with pain constituting a critical clinical symptom necessitating prompt intervention. Persistent pain substantially diminishes patients' quality of life. Glycyrrhiza, a component of traditional Chinese medicine, has shown effectiveness in the treatment of KOA. Liquiritin (LQ), a principal active compound in licorice, demonstrates therapeutic potential; however, its mechanisms of action have yet to be comprehensively understood. This study aims to investigate the underlying pharmacological mechanisms by which LQ alleviates KOA nociceptive sensitization by establishing in vivo and in vitro KOA models and integrating transcriptomic analyses. In vivo, a KOA mice model was established via destabilization of the medial meniscus (DMM) surgery. The ameliorative effects of LQ on mechanical allodynia were assessed. We established an in vitro coculture model of bone marrow-derived macrophages (BMDM) and dorsal root ganglion (DRG) to investigate the effects of various treatments on TRP channels in mouse DRG neurons and further elucidated the mechanism of LQ action on BMDM through transcriptomic analysis. In vivo findings demonstrated that inflammatory conditions reduced M2 macrophage infiltration in DRG tissues while concurrently elevating transcriptional and protein expression levels of TRPA1, TRPV1, TRPM8, NGF, and Substance P. LQ intervention significantly increased M2 macrophage infiltration in DRG tissues and simultaneously suppressed transcriptional and protein expression of TRPA1, TRPV1, TRPM8, NGF, and Substance P. This result is consistent with the findings from mice behavioral assessments, indicating that LQ effectively alleviates KOA-induced nociceptive sensitization. In vitro experiments revealed that LQ alleviates KOA nociceptive sensitization by promoting M2 macrophage activation. Integrated transcriptomic analysis further demonstrated that LQ likely facilitates M2 macrophage polarization by suppressing the Rap1/PI3K/Akt signaling pathway in BMDMs. LQ alleviates nociceptive sensitization in KOA mice by modulating the Rap1/PI3K/Akt signaling pathway to promote M2 macrophage polarization in DRG tissues.