Ketotifen inhibits paf-acether biosynthesis and beta-hexosaminidase release in mouse mast cells stimulated with antigen.

Acetyl-CoA acetyltransferase (1-O-alkyl-sn-glycero-3-phosphocholine) is a key enzyme in paf-acether biosynthesis. Its immunological activation as related to paf-acether formation was investigated in mast cells derived from mouse bone marrow. The action of ketotifen, a prophylactic anti-asthma drug, on the antigen-induced activation of acetyltransferase and on the release of paf-acether and beta-hexosaminidase was studied in mast cells. Mast cells were sensitized with dinitrophenyl-specific monoclonal IgE and preincubated for 15 min at 37 degrees C with various concentrations of ketotifen or vehicle prior to challenge with dinitrophenyl coupled to bovine serum albumin (40 ng/ml). Acetyltransferase activity and mediator formation and release were measured. Ketotifen inhibited dose dependently the antigen-induced paf-acether formation and release, beta-hexosaminidase release and acetyltransferase stimulation. The IC50 values were 20.0 +/- 4.4, 11.8 +/- 6.2, 8.8 +/- 3.8 and 20.5 +/- 3.4 microM (mean +/- S.E.M., n = 3) respectively. Mast cells were preincubated with 50 microM ketotifen for 15 min at 37 degrees C then washed prior to antigen challenge. The release of paf-acether and beta-hexosaminidase and the stimulation of acetyltransferase were inhibited by 90.0 +/- 15.0, 91.0 +/- 15.0 and 88.0 +/- 11.0% (n = 3) respectively. In addition, Ca2+ entry was inhibited by 100% as assessed from Quin-2 fluorescence. Thus, the release of a preformed granular enzyme beta-hexosaminidase is inhibited by ketotifen together with the enzymatic formation of a newly formed mediator.(ABSTRACT TRUNCATED AT 250 WORDS)