Bioactive compound emodin from clinical formula Zhi-Lou-Xun-Xi decoction exerts rapid analgesic effects by targeting TRPV1

Background: Effective postoperative pain management after hemorrhoidectomy remains a significant clinical challenge, largely due to the scarcity of safe and effective non-opioid analgesics. Zhi-Lou-Xun-Xi decoction (J5) is a traditional Chinese formula that has been used clinically for decades, yet its active components and mechanism of action remain unclear.

Purpose: This study aimed to systematically identify the active analgesic components in J5 and elucidate their molecular mechanism of action.

Methods: We employed an integrated pharmacological approach, beginning with a retrospective clinical analysis to confirm the analgesic and wound-healing effects of J5. Pharmacodynamic assays were conducted to evaluate its interaction with TRPV1. High-resolution mass spectrometry and structure-based virtual screening were used to identify candidate compounds. The mechanism of emodin, the primary active constituent, was further investigated through SPR assays, patch-clamp recording, molecular dynamics simulations, and extensive in vivo pain models using TRPV1 knockout (KO) mice.

Results: Emodin was identified as the key TRPV1-antagonizing component in J5. In multiple pain models, emodin produced dose-dependent analgesia without inducing common TRPV1 antagonist-related side effects, particularly altered thermal sensitivity or hyperthermia. These findings not only clarify the mechanistic basis of J5's clinical efficacy but also position emodin as a promising topical analgesic candidate that acts via local TRPV1 inhibition.