Effects of a specific inhibitor of the 5-lipoxygenase pathway on mediator release from human basophils and mast cells

We have characterized the effect of a specific inhibitor of the 5-lipoxygenase pathway on mediator release from human basophils and lung mast cells. In four experiments with purified basophils the phenothiazine derivative, L651-392, proved to be an effective inhibitor of leukotriene (LT) C₄ release in the range 1-10 μM (P < .005) although the release of histamine was unaffected by the highest doses of the drug. The release of 5-hydroxyeico-satetraenoic acid (5-HETE) from purified basophils (n = 2) was also reduced from 8.6 ng/10⁶ basophils to below the limit of detection (1.2 ng/10⁶ basophils). Intermediate concentrations of L651-392 (0.5 μM) reduced both the rate at which LTC₄ was produced and the final concentration. The release of LTC₄ was complete within 20-30 min and was unaffected by increased incubation periods (up to 90 min). HPLC analysis revealed that the drug was not promoting the metabolism of LTC₄ to LTD₄ or LTE₄. Basophils (average purity = 78 ± 3, n = 3) labeled with ³H-arachidonic acid (AA) were challenged with anti-IgE (0.1 μg/ml) and the lipid mediators analyzed by HPLC. Control cells released ³H-LTC₄, ³H-HETE, unmetabolized ³H-AA, and an unidentified metabolite, whereas those pretreated with L651-392 released only ³H-AA and the unknown metabolite with no detectable ³H-LTC₄ or ³H-HETE. The specificity of the drug for the 5-lipoxygenase pathway was confirmed in three experiments with human lung mast cells. L651-392 completely inhibited the release of LTC₄ (P < .02) in the range 1-10 μM with minimal effects on the release of PGD₂ (P < .1); histamine release was unaffected by even the highest concentrations of the drug (P < .75). The use of this drug indicates that the release of 5-lipoxygenase products from mast cells and basophils can be reduced to values below the limit of detection without any adverse effects on the release of histamine.