Human endothelial cells stimulate leukotriene synthesis and convert granulocyte released leukotriene A₄ into leukotrienes B₄, C₄, D₄ and E₄

Abstract

Incubation of human endothelial cells with leukotriene A4 resulted in the formation of leukotrienes B4, C4, D4 and E4. Endothelial cells did not produce leukotrienes after stimulation with the ionophore A23187 and/or exogenously added arachidonic acid. However, incubation of polymorphonuclear leukocytes with ionophore A231 87 together with endothelial cells led to an increased synthesis of cysteinyl-containing leukotrienes (364%, mean, n = 11) and leukotriene B4 (52%) as compared to leukocytes alone. Thus, the major part of leukotriene C4 recovered in mixed cultures was attributable to the presence of endothelial cells. Similar incubations of leukocytes with fibroblasts or smooth muscle cells did not cause an increased formation of leukotriene C4 or leukotriene B4.The increased biosynthesis of cysteinyl-containing leukotrienes and leukotriene B4 in coincubations of leukocytes and endothelial cells appeared to be caused by two independent mechanisms. First, cell interactions resulted in an increased production of the total amount of leukotrienes, suggesting a stimulation of the leukocyte 5-lipoxygenase pathway, induced by a factor contributed by endothelial cells.Secondly, when endothelial cells prelabeled with [35S]cysteine were incubated with either polymorphonuclear leukocytes and A23187, or synthetic leukotriene A4, the specific activity of the isolated cysteinyl-containing leukotrienes were similar. Thus, transfer of leukotriene A4 from stimulated leukocytes to endothelial cells appeared to be an important mechanism causing an increased formation of cysteinyl-containing leukotrienes in mixed cultures of leukocytes and endothelial cells.In conclusion, the present study indicates that the vascular endothelium, when interacting with activated leukocytes, modulates both the quantity and profile of liberated leukotrienes.

Novel transcellular interaction: conversion of granulocyte‐derived leukotriene A4 to cysteinyl‐containing leukotrienes by human platelets

“…In the presence of platelets, LTA4 was also converted to a compound co-chromatographing with LTB4 on reversedphase HPLC, and giving an ultraviolet spectrum with maximal absorbance at 270 nm, indicating a leukotriene structure. This peak was also observed in control incubations of LTA4 in buffer as described [24]. The levels of this material were significantly higher in platelet incubations [41 5 pmol/ml (mean SEM, n = 11) compared to 19 f 2 pmol/ml (n = 4) in controls; P < 0.0251, suggesting minor LTA4 hydrolase activity in platelets.…”

Transcellular biosynthesis of eicosanoids

“…At the same time, LTC 4 formation by transcellular biosynthesis was reported by Feinmark and Cannon [16] 4 . Several groups also reported similar results, providing unequivocal evidence that the activation of neutrophils in the presence of endothelial cells could lead to the unexpected formation of cysteinyl leukotrienes [8,26]. Early on, the neutrophil leukocyte appeared to be a cell type specifically suited to participate in transcellular metabolic processes.…”

Human fibroblasts show expression of the leukotriene‐A4‐hydrolase gene, which is increased after simian‐virus‐40 transformation

“…Thus, the observed activities could not be explained by the presence of invading or tissue-bound leukocytes, since these cells would be expected to contribute both LTA, hydrolase and 5-lipoxygenase. However, fibroblasts and endothelial cells (which also have LTA4 hydrolase but lack 5-lipoxygenase [24]) are present in most tissues and could account for the widespread LTA,-hydrolase activity. These cells might produce LTB4 in vivo only if LTA4 is provided by cells with 5-lipoxygenase (for example leukocytes or macrophages) via transcellular processes, as has been observed in several cell systems in vitro [ l l , 12, 24 -261.…”