Inhibitory effects of steroidal timosaponins isolated from the rhizomes of Anemarrhena asphodeloides against passive cutaneous anaphylaxis reaction and pruritus

To investigate the antiallergic effect of the rhizome of Anemarrhena asphodeloides (AA, family Liliaceae), which was found to inhibit the mouse passive cutaneous anaphylaxis (PCA) reaction induced by the antigen-immunoglobulin E (IgE) complex in preliminary experiments, main steroidal saponins, timosaponins AIII, BIII, and D, were isolated and their inhibitory effects against PCA reaction and scratching behaviors investigated in mice. Oral administration of three main steroidal sapogenins blocked the PCA reaction and scratching behaviors, timosaponin AIII was the most potent. However, intraperitoneal administration of timosaponin AIII showed weak inhibition. To understand its metabolism and antiallergic mechanism, timosaponin AIII was anaerobically incubated with human intestinal microflora to afford a main metabolite, sarsasapogenin. Intraperitoneal administration of sarsasapogenin inhibited allergic reaction more potently than timosaponin AIII. In addition, sarsasapogenin more potently inhibited degranulation and IL-4 protein expression of RBL-2H3 cells induced by IgE-antigen complex than timosaponin AIII. On the basis of these findings, antiallergic effect of AA may be due to those of its steroidal constituents, and that of timosaponin AIII may be activated by using intestinal microflora.