Topical anti-inflammatory and analgesic activity of kirenol isolated from Siegesbeckia orientalis

Ethnopharmacological relevance: Siegesbeckia orientalis has been traditionally used as a topical anti-inflammatory and analgesic agent.

Aims of the study: Current study was designed to explore the topical anti-inflammatory and analgesic effects of a constituent isolated from Siegesbeckia orientalis (Compositae), in order to validate its folk use.

Materials and methods: Kirenol was isolated from ethanolic extract of Siegesbeckia orientalis. Several topical formulations containing kirenol were investigated for anti-inflammatory and analgesic activities in rat. The effects were studied using carrageenan-induced rat acute inflammation model, complete Freund's adjuvant (CFA)-induced chronic inflammation and formalin test in rats. Piroxicam gel and methyl salicylate ointment were studied as positive control for anti-inflammatory and analgesic activity, respectively.

Results: The anti-inflammatory effect of kirenol 0.4-0.5% (w/w) was similar to the effect of piroxicam gel 4h after carrageenan injection. The analgesic activity of topical preparation with more than 0.4% (w/w) was observed in the late phase. These effects may be due, at least in part, to the pro-inflammatory cytokine production of IL-1β and TNF-α. The administration of kirenol cream at the dose of 0.3, 0.4 and 0.5% (w/w) significantly inhibited the development of joint swelling induced by CFA, which was auxiliary supported by histopathological studies.

Conclusion: Kirenol has demonstrated its significant potential to be further investigated for its discovery as a new lead compound for management of topical pain and inflammation, although further pharmacological research is necessary to fully understand its mechanism of action. It also supports the potential beneficial effect of topically administered Siegesbeckia orientalis in inflammatory diseases.