Anti-inflammatory and cyclooxygenase (COX)-2 inhibitory activities of Rumex nepalensis Spreng

Rumex nepalensis Spreng (Polygonaceae) is an annual or perennial herbaceous plant found in the temperate Himalayas between 1200–2700m altitudes [1]. The root extract was reported to block prostaglandin production in the skin of rabbits [2]. Based on this preliminary experimental evidence and as a part of our ongoing search for COX inhibitors from Indian medicinal plants [3], we have aimed the present study to evaluate anti-inflammatory, COX-2 inhibitory activity of roots of R. nepalensis and to isolate and characterize the bioactive compounds.

The air dried powdered roots (2kg) were extracted successively with n-hexane, chloroform, ethyl acetate and methanol in Soxhlet apparatus. The ethyl acetate extract was evaluated for COX-2 inhbitory activity in vitro using EIA-kit (Cayman Chemical Company, USA) and found to exhibit 78.9% inhibition at 50µg/ml concentration. The bioassay-directed fractionation of ethyl acetate extract resulted in the isolation of physcion, nepodin and emodin as COX-2 inhibitory compounds. Of these, emodin was the most active and showed 78.1% COX-2 inhibition at 25µM concentration whereas celecoxib, a positive control showed 88.6% COX-2 inhibition at the same concentration. As the ethyl acetate extract and isolated compounds showed COX-2 inhibition, they were evaluated for anti-inflammatory activity using 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced ear edema in mice. The ethyl acetate extract showed dose-dependent inhibition of ear edema with 78.46 and 66.9% inhibition at 1 and 0.5mg/ear respectively. Emodin and nepodin showed 63.8 and 43.2% inhibition of ear edema at 0.5mg/ear concentration respectively whereas indomethancin, a positive control exhibited 81.4% inhibition at the same concentration. In conclusion, the anti-inflammatory activity of ethyl acetate extract of R. nepalensis roots could be explained in part due to its COX-2 inhibitory mechanism and contributed significantly by emodin and nepodin.

References: 1. Kirtikar, K.R., Basu, B.D. (1987) Indian Medicinal Plants. Lalit Mohan Basu. Allahabad, India. Vol. III, pp. 2113–2114.

2. Aggarwal, P.K. et al. (1986) Ann. Allergy 56: 177–182. 3. Jachak, S.M. (2006) Curr Med Chem 13: 659–678.