Inhibition of leukotriene C 4 and B 4 generation by human eosinophils and neutrophils with the lipoxygenase pathway inhibitors U60257 and BW755C

Abstract

Human eosinophils and neutrophils have the capacity to generate leukotriene C 4 (LTC 4) and leukotriene B 4 (LTB 4) respectively when stimulated by calcium ionophore A23187. Leukotriene production by mixtures of these cell types was measured by radioimmunoassay for LTC 4 and LTB 4, and the specificities of the assays determined by assessing cross-reactivities with a number of other arachidonic acid metabolites. The IC 50s for LTC 4 and LTB 4 in their respective assays were 1.76 ± 0.04 nmol and 3.00 ± 0.08 nmol. Cross-reactivity for anti-LTC 4 was shown by leukotriene D 4 (LTD 4) (70%) and leukotriene E 4 (LTE 4) (8%), when compared to LTC 4, whereas in the radioimmunoassay for LTB 4, only the 5(S), 12(R) 6-trans isomer of LTB 4 showed appreciable interaction (12%). LTC 4 production by eosinophil enriched cell fractions obtained from metrizamide gradients was inhibited in a dose-dependent fashion by the prostacyclin analogue, 6,9-deepoxy-6,9-phenylimino-Δ 6,8-prostaglandin I, (U60257) and by 3-amino-1-(3-trifluoromethyl phenyl)-2-pyrazole (BW755C). The ID 50 values for U60257 and BW755C were 2 × 10 −6 and 5 × 10 −6 M respectively. This demonstration of LTC 4 production by human eosinophils, which are known to be important cells in clinical asthma, provides an in vitro model to assess 5-lipoxygenase inhibitors in human tissue.