Leukotriene A₄, and not leukotriene B₄, is the main 5‐lipoxygenase metabolite released by bovine leukocytes

Abstract

The production of leukotriene A4 (LTA4)-derived metabolites, analysed by RP-HPLC, was studied in purified bovine polymorphonuclear leukocyte (PMNL) preparations and in PMNL-platelet coincubations after challenge with the calcium ionophore A23187. The results obtained show that in bovine PMNL LTB4 represents the main LTA4 metabolite. When washed platelets were added to PMNL, LTC4 was the main enzymatic metabolite observed, indicating a substantial transfer of PMNL-derived LTA4 to platelets. The synthesis of LTC4 was accompanied by a significant decrease in LTB4, suggesting that a quota of the LTB4 synthesized in PMNL preparations is the result of transcellular metabolism of released LTA4 by neighbouring PMNL. Reduction of PMNL-PMNL interactions through dilution of cell incubates allowed us to estimate that most of the leukotriene A4 synthesized by PMNL is indeed released from the cell. LTA4, and not LTB4, represents the main 5-1ipoxygenase metabolite released by bovine PMNL.

Cysteinyl leukotriene 2 receptor and protease-activated receptor 1 activate strongly correlated early genes in human endothelial cells

“…L eukotrienes (LTs), i.e., LTB 4 and the cysteinyl LTs (cysLT) LTC 4 , LTD 4 , and LTE 4 constitute a group of lipid mediators derived from the 5-lipoxygenase (5-LO) pathway (1,2). LTs are either produced by leukocytes at sites of inflammation or formed through transcellular metabolism after uptake and metabolism of leukocyte-derived LTA 4 by downstream enzymes of the 5-LO pathway (LTA 4 hydrolase and LTC 4 synthase) in cells that normally do not express 5-LO, such as endothelial cells (ECs) (3,4).…”

“…LTs are either produced by leukocytes at sites of inflammation or formed through transcellular metabolism after uptake and metabolism of leukocyte-derived LTA 4 by downstream enzymes of the 5-LO pathway (LTA 4 hydrolase and LTC 4 synthase) in cells that normally do not express 5-LO, such as endothelial cells (ECs) (3,4). LTs act through G protein-coupled surface receptors (GPCRs), i.e., the LTB 4 receptors and the cysLT receptors (LT-Rs) (cysLT 1 -R and cysLT 2 -R) (5)(6)(7)(8)(9)(10).…”

“…Considerable information is available on cysLT 1 -R, whereas little is known about cysLT 2 -R. We have used human umibilical vein (HUV)ECs as a model of vascular cells to study cysLT 2 -R activation by demonstrating that cysLTs exclusively signal through cysLT 2 -R in this cell type (18): In fact, HUVECs are the first primary cell type that selectively expresses cysLT 2 -R. In the study detailed below, we determined HUVEC gene signatures in response to LTD 4 and characterized the resulting phenotypes. LTD 4 responses were compared with those of the prototype vasoactive agonist thrombin, which, in HUVEC, acts through protease-activated receptor (PAR)-1 (19).…”

“…LTD 4 responses were compared with those of the prototype vasoactive agonist thrombin, which, in HUVEC, acts through protease-activated receptor (PAR)-1 (19). Thrombin was used as a positive control for LTD 4 because it shares many acute effects with LTD 4 on ECs, both act through GPCRs, and thrombin and LTD 4 may be formed concomitantly during vascular injury (see below). Our data show that cysLT 2 -R activation induces early gene signatures that resemble those after PAR-1 activation and that the combined actions of LTD 4 and thrombin further stimulate gene expression.…”

“…Thrombin was used as a positive control for LTD 4 because it shares many acute effects with LTD 4 on ECs, both act through GPCRs, and thrombin and LTD 4 may be formed concomitantly during vascular injury (see below). Our data show that cysLT 2 -R activation induces early gene signatures that resemble those after PAR-1 activation and that the combined actions of LTD 4 and thrombin further stimulate gene expression. Thus, if LTD 4 and thrombin are produced at the same time and site, they may cooperate in EC activation during states of vascular perturbation in vivo.…”