4-Methylesculetin attenuates inflammatory pain via inhibition of Sp1-TRPV1 and inflammation related signaling pathways

Abstract

Background

Discovering lead compounds with anti-inflammatory and analgesic activities from natural products with minimal toxic side effects has been a long-term goal for researchers. 4-Methylesculetin (4-ME), a natural coumarin derivative, has been reported to have anti-inflammatory and antioxidant properties, but its analgesic effect has not yet been studied. This research investigates the analgesic effect and underlying mechanism of 4-ME in peripheral inflammatory pain.

Methods

Acute or chronic inflammatory pain model was established by injecting formalin or Complete Freund's Adjuvant (CFA) into the right hindpaw of rat, respectively. The mechanical and thermal thresholds were detected by using Von Frey and thermal radiation instrument. Patch-clamp recording was performed to study the electrophysiological properties of ion channel. RT-qPCR, western blot, and immunofluorescence were used to analyze mRNA and protein expressions of relevant signaling pathway molecules.

Results

Intraperitoneal injection of 4-ME could significantly alleviate mechanical and thermal hyperalgesia induced by CFA injection, as well as spontaneous pain induced by formalin injection. In the CFA-induced chronic pain model, 4-ME reduced the levels of IL-6, TNF-α, IL-1β, and inhibited ERK, NF-κB, NLRP3 pathways in dorsal root ganglia (DRG). It downregulated abnormally high expression of TRPV1 caused by CFA injection in DRG, without altering the electrophysiological properties of TRPV1 channel. Further mechanistic studies demonstrated that 4-ME regulated the expression of TRPV1 by inhibiting the transcription factor Sp1. Compared to other coumarin derivatives, 4-ME exhibited a better analgesic effect at low dosage.

Conclusion

Our study reveals for the first time that 4-ME could alleviate peripheral inflammatory pain by inhibiting Sp1-TRPV1 pathway, suggests 4-ME as a potential analgesic, and provides a theoretical basis for 4-ME translation into clinical application.