Inhibitory effects of aloe extracts on antigen- and compound 48/80-induced histamine release from rat peritoneal mast cells

Abstract

The inhibitory effects of water extracts of five genera of aloe (Aloe arborescens MILLER, A. ferox M., A. barbadensis M., A. africana M., A. saponaria HAWAII) and aloe powder of Japanese Pharmacopoeia (JP Aloe powder) on histamine release from rat peritoneal mast cells induced by antigen and compound 48/80 were investigated in vitro. All the aloe extracts tested inhibited histamine release from mast cells induced by antigen and compound 48/80 in a concentration-dependent manner. The extract of A. ferox M. and JP Aloe powder paticularly strongly inhibited release by either antigen or compound 48/80 at medium inhibitory concentration (IC50) of 0.16 and 0.07 mg/ml, respectively, for antigen and of 0.41 and 0.29 mg/ml for compound 48/80. These results suggest that aloes may be useful in the treatment of type I immediate allergic disorders. Barbaloin, a major constituent of aloes, also exhibited concentration-dependent inhibitory effects on histamine release induced by these two substances, with IC50 being 0.02 and 0.06 mg/ml, respectively. From its yield and inhibitory effects, barbaloin is considered to account for the inhibitory action of the water extracts of A. arborescens M., A. africana M. and JP Aloe powder. Although tranilast, a current antiallergic agent, strongly inhibited antigeninduced histamine release (IC50=0.07 mg/ml), it showed a weak inhibitory effect on compound 48/80-induced histamine release (IC50=0.84 mg/ml). These results suggest that the mechanism of inhibitory action of barbaloin on histamine release differs from that of tranilast.