Anti-Allergic Activities of Smilax glabra Rhizome Extracts and Its Isolated Compounds

The rhizomes of Smilax glabra (SG) has long been used in Traditional Chinese and Thai herbal medicine to treat a variety of infectious diseases and immunological disorders.

To investigate the in vitro anti-allergic activities of crude extracts andpure isolated flavonoid compounds from SG by determination of inhibitory effect on antigen-induced release of β-hexosaminidasefrom RBL-2H3 cells.

The in vitro inhibitory effects ofcrude aqueous and organic extracts on β-hexosaminidase release in RBL-2H3 cells were evaluated as an in vitro indication ofpossible anti-allergic activity. Bioassay-guided fractionation of extracts was used to isolate flavonoid compounds from the ethanolic extracts.

The 95% and 50% ethanolic extracts of SG showed remarkably high anti-allergic activity, with IC50 values of 5.74 ± 2.44 and 23.54 ± 4.75 µg/ml, much higher activity than that for Ketotifen (IC50 58.90 µM). The water extract had negligible activity (IC50 > 100 µg/ml). The two isolated flavonols, Engeletin and Astilbin, showed weak anti-allergic activity, IC50 values 97.46 ± 2.04 and >100 µg/ml, respectively.

The 95% and 50% ethanolic extracts of SG showed strong anti-allergic activity, but two flavonol constituents did not show any significant anti-allergic activity. These findings suggest that a combination of effects of various phytochemicals in crude extracts used in traditional medicine, are responsible for the purported anti-allergic activity of SG herbal preparations. The plethora of constituents in crude extracts, as yet unidentified, are likely to be acting synergistically to account for the strong observed anti-allergic in vitro activity.