Antiallergic activity of Tylophora sylvatica

Tylophora sylvatica is a medicinal plant successfully used in African folk medicine for the management of various allergic conditions. This plant was investigated using screening methods suitable for the isolation of the active constituents which inhibit the release of chemical mediators of allergic reactions. Chromatographic studies led to the characterization of two classes of active principles: known fatty acids (oleic, linoleic and linolenic acids) with 0.064% yield; two novel glycosides, tylophoroside and acetyltylophoroside, having 0.008% and 0.0113% yields, respectively. Mild acidic hydrolysis of these glycosides generated an aglycone termed tylogenin which appears to be a biodegraded steroid. The antiallergic activity of these compounds was further assessed for inhibition of antigen-induced mediator release by the rabbit basophil-dependent serotonin release(B08R) and human leukocyte-dependent histamine release(LDHR) assay systems. The activity of tylogenin was found to increase with the incubation time. In the B08R assay, at optimal incubation time, tylogenin with a geom mean IC₅₀ of 38.9 μM, (geom SD=1.3, n=5), exhibited an activity similar to that of the fatty acids. This activity differed significantly (p<0.05) from that of the standard corticosteroids, dexamethasone (geom mean IC50=912 μM, geom 80=2.8, n=5) and prednisolone (geom mean IC₅₀=1071.5 μM, geom 80=3.2, n=4). In the LOHR assay, the activity of tylogenin (geom mean IC₅₀=49.0 μM, geom 80=1.6, n=5) significantly exceeded that of dexamethasone (geom mean IC₅₀=257 μM geom 80=8.1), (p