Effect of cations on leukotriene release: requirements for the metabolism of peptido-leukotrienes (leukotrienes C4, D4) by human polymorphonuclear granulocytes.

Stimulation of human polymorphonuclear granulocytes with opsonized zymosan leads to a time-dependent release of the leukotrienes LTB4, 6-trans-LTB4, 12-epi-6-trans-LTB4 and LTC4 measured by HPLC analysis and LTC4 radioimmunoassay. The amounts of leukotrienes released on stimulation with opsonized zymosan are lower than those obtained with the calcium ionophore A23187. Opsonized zymosan as stimulus required higher calcium concentrations to obtain optimal leukotriene release as compared with the calcium ionophore. Magnesium in the presence of calcium increased the leukotriene formation with opsonized zymosan. Addition of the peptido-leukotrienes LTC4, LTD4 to the unseparated, opsonized zymosan-prestimulated cell suspension leads to the generation of 6-trans-LTB4, 12-epi-6-trans-LTB4 and a metabolite which is more polar than LTC4. The rate of LTC4 metabolism is strongly dependent on the time of prestimulation as well as on the stimuli used for cell triggering, e.g. opsonized zymosan, phorbol-12-myristate-13-acetate, calcium ionophore A23187 or formyl-methionyl-leucyl-phenylalanine. Inhibitors of the oxidative burst decreased LTC4 metabolism. Thus, the peptido-leukotriene LTC4 is metabolized by two pathways: the enzymes gamma-glutamyl-transpeptidase and dipeptidase transform LTC4 into LTD4 and LTE4; these enzymes are present within the supernatants of stimulated cells; transformation of LTC4 into LTB4-isomers occurs in the presence of stimulated cells.