E-coli hemolysin-induced lipid mediator metabolism in alveolar macrophages: impact of eicosapentaenoic acid

Escherichia coli hemolysin (HlyA) is a prototype of a large family of pore- forming proteinaceous exotoxins that have been implicated in the pathogenet ic sequelae of severe infection and sepsis, including development of acute lung injury. In the present study in rabbit alveolar macrophages (AMs), sub cytolytic concentrations of purified HlyA evoked rapid synthesis of platele t-activating factor, with quantities approaching those in response to maxim um calcium ionophore challenge. In parallel, large quantities of leukotrien e (LT) B-4 and 5-, 8-, 9-, 12-, and 15-hydroxyeicosatetraenoic acid (HETE) were liberated from HlyA-exposed AMs depending on exogenous arachidonic aci d (AA) supply. Coadministration of eicosapentaenoic acid (EPA) dose depende ntly suppressed generation of the proinflammatory lipoxygenase products LTB 4 and 5-, 8-, 9-, and 12- HETE in parallel with the appearance of the corre sponding EPA-derived metabolites LTB5 and 5-, 8-, 9-, and 12-hydroxyeicosap entaenoic acid (HEPE). At equimolar concentrations, EPA turned out to be th e preferred substrate over AA for these AM lipoxygenase pathways, with the sum of LTB5 and 5-, 8-, 9-, and 12- HEPE surpassing the sum of LTB4 and 5-, 8-, 9-, and 12- HETE by >80-fold. In contrast, coadminstration of EPA did not significantly reduce HlyA-elicited generation of the anti-inflammatory AA lipoxygenase product 15-HETE. We conclude that AMs are sensitive target cells for HlyA attack, resulting in marked proinflammatory lipid mediator s ynthesis. In the presence of EPA, lipoxygenase product formation is shifted from a pro- to an antiinflammatory profile.