A Chinese Herbal Decoction, Shaoyao-Gancao Tang, Exerts Analgesic Effect by Down-Regulating the TRPV1 Channel in a Rat Model of Arthritic Pain

Shaoyao-Gancao Tang (SGT) is one of the most frequently used compound formulas in the treatment of pain-related diseases in the medical practice of traditional Chinese medicine (TCM). To investigate the anti-inflammatory and antinociceptive effects, as well as to uncover the molecular mechanism of SGT, the rat pain model of arthritis was experimentally induced by single unilateral injection of rats' left hind paw with Freund's complete adjuvant (FCA). SGT was orally administered to the rats daily at three doses individually for a period of 16 days post-model induction. Swollen degrees and pain thresholds of the rats in different groups were measured for evaluation of the anti-inflammatory and anti-nociceptive effects of SGT. Furthermore, the mRNA and protein expression levels of transient receptor potential ion channel protein vanilloid receptor 1 (TRPV1) channel as well as its calcium-mediating function in the isolated DRG neurons were further detected to provide indexes for exploration of the molecular mechanisms mediating anti-arthritic activities of SGT. As a result, FCA injection induced significant allodynia, inflammation and edema, accompanied by a significant increase in both expression and calcium-mediating function of the TRPV1 channel. Pharmacologically, oral administration of SGT at a high or middle dose demonstrated a significant relief from the above-mentioned pathological conditions in a dose-dependent manner. Simultaneously the mRNA and protein expressional levels of TRPV1 channel, as well as its calcium-mediating function, were down-regulated greatly. These findings suggest that SGT possesses a significant analgesic and anti-inflammatory effect on arthritis rats; its therapeutic activities might be achieved through reversing the elevated expression and function of TRPV1 channel evoked by FCA.