RELEASE OF LEUKOTRIENE A(4) VERSUS LEUKOTRIENE B-4 FROM HUMAN POLYMORPHONUCLEAR LEUKOCYTES

The reactive intermediate formed by 5-lipoxygenase metabolism of arach idonic acid, leukotriene A(4), is known to be released from cells and subsequently taken up by other cells for biochemical processing, The o bjective of this study was to determine the relative amount of leukotr iene A(4) synthesized by human polymorphonuclear leukocytes (PMNL) tha t is available for transcellular biosynthetic processes, This was acco mplished by diluting cell suspensions and measuring the relative amoun ts of enzymatic versus nonenzymatic leukotriene A(4)-derived metabolit es after challenge with the Ca2+ ionophore A23187, Nonenzymatic leukot riene A(4)-derived metabolites were used as a quantitative index of th e amount of leukotriene A(4) released into the extracellular milieu, T he results obtained demonstrated that in human PMNL, the relative amou nts of nonenzymatic versus enzymatic leukotriene A(4)-derived metaboli tes increased with decreasing cell concentrations, After a 20-fold dil ution of PMNL in cell preparations, a doubling in the amount of nonenz ymatic leukotriene A(4)-derived metabolites was observed following cha llenge (from 53.9 +/- 1.3 to 110.4 +/- 8.9 pmol/10(6) PMNL, p < 0.01). Reduction of possible cell-cell interactions by dilution suggested th at over 50% of leukotriene A(4) synthesized is released from the PMNL, These data provide evidence that, in human PMNL preparations, transfe r of leukotriene A(4) to neighboring PMNL is taking place, resulting i n additional formation of leukotriene B-4 and its omega-oxidized metab olites 20-hydroxy- and 20 carboxy-leukotriene B-4. Neutrophil reuptake of extracellular leukotriene A(4) leads to an underestimation of the fraction of leukotriene A(4) that is in fact available for transcellul ar metabolism when tight cell-cell interactions occur, such as during PMNL adhesion to the microvascular endothelium and diapedesis.