The lipoxygenase pathway and chemiluminescence in horse eosinophilic leukocytes

It was shown in several cell types that the dual lipoxygenase and cyclooxygenase inhibitor eicosatetraynoic acid but not the cyclooxygenase inhibitor acetylsalicylic acid suppressed luminol-dependent chemiluminescence. Since lipoxygenase is known to generate chemiluminescence in vitro, these observations were interpreted as evidence for a direct contribution of the lipoxygenase pathway to light emission in intact cells. We have investigated a possible contribution of the lipoxygenase to the chemiluminescence of horse eosinophils by directly comparing the formation of the byproduct chemiluminescence with the formation of stable end-products of the lipoxygenase pathway, leukotrienes and HETEs. Azide as well as eicosatetraynoic acid almost completely inhibited chemiluminescence stimulated by the calcium ionophore A23187 but had less effect on the formation of leukotrienes. The tumour-promoting ester, phorbol myristate acetate, stimulated chemiluminescence in an azide- and eicosatetraynoic acid-sensitive manner and failed to evoke the production of leukotrienes. Azide, but also eicosatetraynoic acid inhibited the luminol-dependent chemiluminescence generated by isolated eosinophil peroxidase in the presence of H2O2. Our results argue against a direct role of the lipoxygenase pathway in the generation of light in horse eosinophilic leukocytes but do not exclude that product(s) of this pathway may be involved in stimulus-response coupling.