Desloratadine prevents compound 48/80-induced mast cell degranulation: visualization using a vital fluorescent dye technique

Background: Desloratadine is a selective H-1-antihistamine used in the treatment of allergic rhinitis and chronic idiopathic urticaria. Desloratadine inhibits the release of allergic inflammatory mediators in vitro. We studied the impact of desloratadine on mast cell degranulation due to activation and re-activation by the secretagogue, compound 48/80. Methods: Rat peritoneal eluate containing 5-6% mast cells were activated by a low concentration of compound 48/80 in a medium containing the vital fluorescent dye, Sulforhodamine-B (SFRM-B, 200 mug/ml), which is engulfed by activated mast cells. The fluorescent image of activated mast cells was captured digitally and the total fluorescent area was analyzed when desloratadine was applied before or after compound 48/80. Results: Mast cells were not activated by desloratadine (10(-4) M), SFRM-B (200 mug/ml), or diluent alone. A low concentration of compound 48/80 (0.125 mug/ml) induced fluorescence, while mast cells lost fluorescent images due to further degranulation on re-exposure to compound 48/80. Desloratadine (10(-8)-10(-4) M), inhibited compound 48/80-induced mast cell degranulation in a concentration-dependent manner. Desloratadine also reduced the loss of fluorescent images due to re-exposure to compound 48/80. Conclusions: Desloratadine may have a mast cell stabilizing effect at low concentrations in response to repeated mast cell activation in vitro.