Background: 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.
Objective: To investigate the in vitro anti-allergic activities of crude extracts and pure isolated flavonoid compounds from SG
by determination of inhibitory effect on antigen-induced release of β-hexosaminidase from RBL-2H3 cells.
Material and Method: The in vitro inhibitory effects of crude aqueous and organic extracts on β-hexosaminidase release in
RBL-2H3 cells were evaluated as an in vitro indication of possible anti-allergic activity. Bioassay-guided fractionation of extracts was used to isolate flavonoid compounds from the ethanolic extracts.
Results: 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.
Conclusion: 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.

Keywords: Smilax glabra, Anti-allergic activity, RBL-2H3 cells, Astilbin, Engeletin