High yield enzymatic conversion of intravascular leukotriene A4 in blood-free perfused lungs

Abstract

Experiments to investigate the fate of intravascularly administered leukotriene (LT) A4, an unstable intermediate of LT generation, were performed in isolated, ventilated, and blood-free perfused rabbit lungs. LT extracted from the lung effluent were separated by different reverse phase and straight phase HPLC procedures as methylated and nonmethylated compounds. Identity of eluting LT was confirmed by UV spectrum analysis and immunoreactivity. Pulmonary artery injection of 75 to 300 nmol of LTA4 resulted in the rapid appearance of cysteinyl-LT as well as LTB4 in the recirculating perfusate. The yield of these enzymatically generated LTA4 metabolites vs non-enzymatic hydrolysis products (6-trans-LTB4, 5-trans-epi-LTB4, 5,6-dihydroxyeicosatetraenoic acids) ranged above 90%. Experiments with application of tritiated LTA4 showed exclusive origin of the detected LT from the exogenously applied precursor. The time course of cysteinyl-LT appearance in the perfusate suggested metabolism of LTC4 via LTD4 to LTE4, whereas there was no evidence for LTB4 omega-oxidation. In the dose range of LTA4 used, the enzymatic conversion of this LT precursor did not approach saturation. Collectively, these data indicate that the intact pulmonary vasculature contains a hitherto not described capacity for enzymatic conversion of intravascularly offered LTA4 to both cysteinyl-LT and LTB4. This may be of biological significance for a putative transcellular biosynthesis of LT in the pulmonary microcirculation upon contact with LTA4 feeder cells, such as activated granulocytes.