SYNTHESIS OF 4-SERIES AND 5-SERIES LEUKOTRIENES IN THE LUNG MICROVASCULATURE CHALLENGED WITH ESCHERICHIA-COLI HEMOLYSIN - CRITICAL DEPENDENCE ON EXOGENOUS FREE FATTY-ACID SUPPLY

Escherichia coli hemolysin (HlyA) has been identified as a potent indu ctor of phosphoinositide hydrolysis and related metabolic responses in neutrophils (Grimminger and colleagues, 1991, J. Clin. Invest. 88:153 1-1539). In isolated perfused rabbit lungs, which harbor a large numbe r of entrapped microvascular leukocytes, we investigated the effect of a low dose of HlyA on lipoxygenase product formation in the presence of exogenous free arachidonic acid (AA), eicosapentaenoic acid (EPA), or both precursor fatty acids. Leukotrienes (LT) and hydroxyeicosatetr a(penta)enoic acids (HET[P]E) in the recirculating perfusate were quan tified using high-performance liquid chromatography techniques. In the absence of exogenous precursor fatty acid supply, 0.02 hemolytic unit s/ml HlyA elicited only minor amounts of LTs and 5-HETE. AA, 10 mu M, provoked the generation of limited quantities of LTB(4), LTE(4), and 5 -HETE. Combined application of HlyA and AA caused a manifold amplifica tion of 4-series LT and 5-HETE generation, with predominance of cystei nyl-LTs. EPA, 10 mu M, elicited the synthesis of 5-series LTs accompan ied by marked quantities of 5-HEPE. Dual stimulation with HlyA and EPA provoked exclusive generation of excessive quantities of all 5-series 5-lipoxygenase products. When HlyA was administered in the presence o f both AA (10 mu M) and EPA (10 mu M), the n-3 fatty acid clearly turn ed out to be the preferred substrate, with ratios of the various 5-ser ies to 4-series products ranging between 1.8 and 14.5. Moreover, the a bsolute quantities of AA-derived metabolites and the total sum of all 5-lipoxygenase products was markedly reduced under these conditions. W e conclude that the HlyA-evoked 5-lipoxygenase product formation in th e pulmonary vasculature of the rabbit is critically dependent on the p resence of free precursor fatty acids. The profile of LTs suggests neu trophil (PMN)-related transcellular eicosanoid synthesis as a major un derlying metabolic pathway. EPA represents the preferred substrate as compared with AA, resulting in a marked suppression of AA metabolite f ormation. Therapeutic attempts to provide n-3 fatty acids via the intr avenous route may have a major impact on lipid mediator profiles in PM N-related inflammatory events.