Human B and T lymphocytes convert leukotriene A4 into leukotriene B4

ACKR3 promotes CXCL12/CXCR4-mediated cell-to-cell-induced lymphoma migration through LTB4 production

Chemotaxis is an essential physiological process, often harnessed by tumors for metastasis. CXCR4, its ligand CXCL12 and the atypical receptor ACKR3 are overexpressed in many human cancers. Interfering with this axis by ACKR3 deletion impairs lymphoma cell migration towards CXCL12. Here, we propose a model of how ACKR3 controls the migration of the diffused large B-cell lymphoma VAL cells in vitro and in vivo in response to CXCL12. VAL cells expressing full-length ACKR3, but not a truncated version missing the C-terminus, can support the migration of VAL cells lacking ACKR3 (VAL-ko) when allowed to migrate together. This migration of VAL-ko cells is pertussis toxin-sensitive suggesting the involvement of a Gi-protein coupled receptor. RNAseq analysis indicate the expression of chemotaxis-mediating LTB4 receptors in VAL cells. We found that LTB4 acts synergistically with CXCL12 in stimulating the migration of VAL cells. Pharmacologic or genetic inhibition of BLT1R markedly reduces chemotaxis towards CXCL12 suggesting that LTB4 enhances in a contact-independent manner the migration of lymphoma cells. The results unveil a novel mechanism of cell-to-cell-induced migration of lymphoma.

HTLV-1-induced leukotriene B4 secretion by T cells promotes T cell recruitment and virus propagation

The human T-lymphotropic virus type 1 (HTLV-1) is efficiently transmitted through cellular contacts. While the molecular mechanisms of viral cell-to-cell propagation have been extensively studied in vitro, those facilitating the encounter between infected and target cells remain unknown. In this study, we demonstrate that HTLV-1-infected CD4 T cells secrete a potent chemoattractant, leukotriene B4 (LTB4). LTB4 secretion is dependent on Tax-induced transactivation of the pla2g4c gene, which encodes the cytosolic phospholipase A2 gamma. Inhibition of LTB4 secretion or LTB4 receptor knockdown on target cells reduces T-cell recruitment, cellular contact formation and virus propagation in vitro. Finally, blocking the synthesis of LTB4 in a humanized mouse model of HTLV-1 infection significantly reduces proviral load. This results from a decrease in the number of infected clones while their expansion is not impaired. This study shows the critical role of LTB4 secretion in HTLV-1 transmission both in vitro and in vivo.

Transcellular biosynthesis of eicosanoid lipid mediators

The synthesis of oxygenated eicosanoids is the result of the coordinated action of several enzymatic activities, from phospholipase A2 that releases the polyunsaturated fatty acids from membrane phospholipids, to primary oxidative enzymes, such as cyclooxygenases and lipoxygenases, to isomerases, synthases and hydrolases that carry out the final synthesis of the biologically active metabolites. Cells possessing the entire enzymatic machinery have been studied as sources of bioactive eicosanoids, but early on evidence proved that biosynthetic intermediates, albeit unstable, could move from one cell type to another. The biosynthesis of bioactive compounds could therefore be the result of a coordinated effort by multiple cell types that has been named transcellular biosynthesis of the eicosanoids. In several cases cells not capable of carrying out the complete biosynthetic process, due to the lack of key enzymes, have been shown to efficiently contribute to the final production of prostaglandins, leukotrienes and lipoxins. We will review in vitro studies, complex functional models, and in vivo evidences of the transcellular biosynthesis of eicosanoids and the biological relevance of the metabolites resulting from this unique biosynthetic pathway. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

Epoxide hydrolases: their roles and interactions with lipid metabolism

The epoxide hydrolases (EHs) are enzymes present in all living organisms, which transform epoxide containing lipids by the addition of water. In plants and animals, many of these lipid substrates have potent biologically activities, such as host defenses, control of development, regulation of inflammation and blood pressure. Thus the EHs have important and diverse biological roles with profound effects on the physiological state of the host organisms. Currently, seven distinct epoxide hydrolase sub-types are recognized in higher organisms. These include the plant soluble EHs, the mammalian soluble epoxide hydrolase, the hepoxilin hydrolase, leukotriene A4 hydrolase, the microsomal epoxide hydrolase, and the insect juvenile hormone epoxide hydrolase. While our understanding of these enzymes has progressed at different rates, here we discuss the current state of knowledge for each of these enzymes, along with a distillation of our current understanding of their endogenous roles. By reviewing the entire enzyme class together, both commonalities and discrepancies in our understanding are highlighted and important directions for future research pertaining to these enzymes are indicated.

Leukotriene receptor antagonists and synthesis inhibitors reverse survival in eosinophils of asthmatic individuals

Eosinophilia is a feature of airway inflammation associated with asthma. Leukotriene antagonists provide therapeutic benefit in asthma, but their potential antiinflammatory actions have not been fully explored. We have examined the role of eosinophil-derived cysteinyl leukotrienes in the maintenance of eosinophil survival, and the involvement of leukotrienes in the paracrine stimulation of eosinophil survival by mast cells and lymphocytes. We obtained eosinophils and autologous lymphocytes from peripheral blood of asthmatic subjects. Leukotriene (LT)-B(4), LTC(4) and LTD(4), granulocyte-macrophage colony-stimulating factor (GM-CSF), and fibronectin promoted eosinophil survival. LTD(4) (10(-)(6) M) was as effective as GM-CSF (5 ng/ml) and fibronectin (400 ng/ml) in promoting survival. Lymphocytes and conditioned medium from a human mast cell line (HMC-1) induced eosinophil survival. Blockade of cysteinyl leukotriene receptors with SKF 104353 (pobilukast, 3 nM), and inhibition of 5-lipoxygenase (5-LO) with BW A4C (1 microM) and of 5-LO activating protein with MK 886 (1 microM), all increased basal rates of eosinophil apoptosis and reversed GM-CSF-induced eosinophil survival. Fifty percent reversal of GM-CSF- induced survival was achieved with SKF 104353 at 0.3 nM. The potency of SKF 104353 was two orders of magnitude greater than that of the LTB(4) receptor antagonist SB 201146. Mast cell- and lymphocyte-induced eosinophil survival were completely reversed by SB 201146, SKF 104353, BW A4C, and MK 886. These findings provide evidence for the involvement of an autocrine cysteinyl leukotriene pathway that supports eosinophil survival in response to a range of survival stimuli. They also suggest that LTB(4) could act as a paracrine stimulus of eosinophil survival.

Characteristics of leukotriene biosynthesis by human granulocytes in presence of plasma

The formation of leukotriene B4 (LTB4) by neutrophils stimulated with the ionophore A23187 or physiological stimuli in heparinized plasma was investigated. In comparison with neutrophils stimulated (A23187) in a protein-free buffered salt solution, neutrophils stimulated in plasma produced only trace amounts of LTB4. The addition of human recombinant LTA4-hydrolase or erythrocytes to plasma prior to A23187 stimulation strongly and selectively stimulated (> 4-fold) the formation of LTB4 supporting that neutrophils activated in plasma with A23187 release in the extracellular milieu most of LTA4 formed by the cells, and indicating that plasma proteins drastically slow down the further metabolism of LTA4 released by neutrophils. The formation of LTB4 was then investigated in GM-CSF-primed neutrophils stimulated with fMLP in plasma; levels of synthesis were very low and the addition of erythrocytes prior to stimulation strongly enhanced LTB4 synthesis, demonstrating that agonist-stimulated neutrophils also release most of LTA4 generated in the extracellular milieu. Investigations on the fate of LTA4 in plasma revealed that LTA4 was slowly degraded through an unknown process, i.e. not through the previously described non-enzymic hydrolysis resulting in the formation of dihydroxy derivatives of LTA4. Using neutrophils labeled with tritiated arachidonate, we also demonstrated that neutrophils stimulated in plasma with fMLP or A23187, almost exclusively use endogenous arachidonate, as opposed to plasma arachidonate, to generate 5-lipoxygenase products. Finally, experiments performed with purified eosinophils indicated that contrary to neutrophils, the eosinophils do not release LTA4, but directly release LTC4.

LTA4 hydrolase in human skin: decreased activity, but normal concentration in lesional psoriatic skin. Evidence for different LTA4 hydrolase activity in human lymphocytes and human skin

Leukotriene A4 (LTA4) hydrolase which transforms LTA4 into the proinflammatory compound LTB4 has been identified in human epidermis. The purpose of this study was to investigate the potential role of this enzyme in psoriasis, in which LTB4 is present in biologically active concentrations. The concentration and activity of LTA4 hydrolase was determined in normal skin and in matched samples of involved and uninvolved psoriatic skin. The enzyme content was determined using an affinity-purified antibody. This antibody was also used for immunohistochemical staining of skin biopsies. Immunohistochemically LTA4 hydrolase was localized predominantly in the basal and spinous layers in normal skin and in involved and uninvolved psoriatic skin. The LTA4 hydrolase content varied between 2.8 and 3.1 micrograms enzyme/mg protein and was found to be similar in normal and psoriatic skin, involved as well as uninvolved. In contrast, the activity of the enzyme was decreased significantly in involved psoriatic skin (9.9 +/- 2.1 micrograms LTB4/mg enzyme per min) compared with matched uninvolved psoriatic skin (16.4 +/- 3.5 micrograms LTB4/mg enzyme per min), but was decreased only insignificantly compared with normal skin (12.4 +/- 1.8 micrograms LTB4/mg enzyme per min). It was found that the conversion of LTA4 to LTB4 results in inactivation of LTA4 hydrolase activity. This finding is compatible with the idea that the decreased LTA4 hydrolase activity in involved psoriatic skin reflects transcellular LTB4 formation in vivo. In peripheral lymphocytes the enzyme content was 1.3 +/- 0.3 microgram enzyme/mg protein in normal lymphocytes and 1.4 +/- 0.3 microgram enzyme/mg protein in psoriatic lymphocytes, which was significantly lower than in the skin. In contrast, the specific LTA4 hydrolase activities in normal and psoriatic lymphocytes (23.4 +/- 1.3 and 21.3 +/- 1.7 micrograms LTB4/mg enzyme per min) were significantly higher than in normal skin. These findings may indicate the existence of LTA4 hydrolase isoforms in human lymphocytes and human skin.

Leukotrienes and lipoxins--new potential performers in the regulation of human myelopoiesis

Leukotrienes and lipoxins are bioactive lipoxygenase products formed by leukocytes alone or in collaboration with other cells. While the physiological role of lipoxins remains to be clarified, accumulating evidence shows that leukotrienes are important mediators in asthma and inflammation. Consequently, recent clinical trials with leukotriene D4 receptor antagonists and 5-lipoxygenase inhibitors have demonstrated marked reduction of airway symptoms in asthmatic patients. In addition, both leukotrienes and lipoxins have been indicated as modulators of cell proliferation. This article reviews recent findings suggesting that these compounds may also participate in the regulation of human myelopoiesis. Such a role is conceivable since leukotrienes and lipoxins can be produced by bone marrow cells and potently modulate GM-CSF-induced myeloid stem cell proliferation.

Stimulated human gastric tumor cells (HGT) fail to synthesize eicosanoids

HGT cells are a human gastric tumor cell line. Preliminary data have shown that HGT cells incorporate exogenous arachidonic acid (AA) in their membrane lipids. However, we found that HGT cells are unable to produce significant amounts of AA metabolites after stimulation with calcium ionophore A23187. Furthermore, no lipoxygenase activity was detected in crude HGT cell extracts by employing an assay monitoring the in vitro utilization of linoleic acid. The meaning of these results is discussed in respect of the role of eicosanoids during cell proliferation.

5-Lipoxygenase: enzyme expression and regulation of activity

5-Lipoxygenase catalyzes the transformation of arachidonic acid to leukotriene A4. This unstable intermediate can be converted to leukotriene B4 by LTA4-hydrolase or to leukotriene C4 by LTC4-synthase. Leukotrienes are involved in host defense reactions and play an important role in inflammatory diseases like asthma, inflammatory bowel disease and arthritis. The capability to release leukotrienes is restricted to a few cell types. Under pathophysiological conditions, leukotrienes are released from granulocytes, mast cells or macrophages. During hematopoiesis the competence of these cells for leukotriene biosynthesis is supposed to be upregulated. In mature cells, 5-lipoxygenase activity is tightly regulated and seems to be under the control of additional cellular components. One cellular component, a membrane-bound peptide termed FLAP, which is necessary for 5-LO activity in intact cells has been recently identified. Inhibitors of FLAP function prevent translocation of 5-lipoxygenase from cytosol to the membrane and inhibit 5-LO activation. Thus, the understanding of the regulatory mechanisms of cellular leukotriene biosynthesis provides new concepts for the development of antiinflammatory drugs. This review focuses on the regulation of gene expression and activity of 5-lipoxygenase.

Leukotriene B4 induces interleukin 5 generation from human T lymphocytes

Leukotriene B4 (LTB4) has been shown to affect several interleukin (IL)-linked functions of human lymphocytes. In this study, we investigated whether LTB4 regulates IL-5 generation from human T cells and subsequently modulates eosinophil functions. Preincubation of T cells with very low concentrations (10(-12) to 10(-8) M) of LTB4 induced concentration-dependent IL-5 production, the event occurring after the first 24 h of cultivation. However, direct action of LTB4 to IL-5 generation is strictly dependent on a preincubation with appropriate concentration of LTB4. In contrast, the stereoisomer of LTB4, 5S,12S-dihydroxy-6,8,10,14-eicosatetraenoic acid showed no enhancement of IL-5 production. IL-5 released from LTB4-primed T cells elicited sustained viability of mature eosinophils and reduced the content of eosinophil cationic protein in their crystalloid matrix by degranulation. These data suggest that LTB4 induces bioactive IL-5 production from T cells and that the released IL-5 modulates eosinophil functions which might play a crucial role in eosinophil-linked allergic inflammatory process.

Leukotriene B4 formation during human neutrophil keratinocyte interactions: evidence for transformation of leukotriene A4 by putative keratinocyte leukotriene A4 hydrolase

In the present study, keratinocytes were coincubated with human neutrophils to determine whether or not an increase in leukotriene B4 formation can occur. Human keratinocytes used were cultured in serum-free, low-calcium medium, whereas neutrophils were purified from heparinized venous blood. After coincubations, formation of leukotriene B4 was determined by reversed-phase high-performance liquid chromatography, coupled with its characteristic UV scan. Confirmation and quantification was by radioimmunoassay. Our data revealed that incubations of keratinocytes (1.5 x 10(6)) alone stimulated with calcium ionophore resulted in no detectable amounts of leukotriene B4. In contrast, incubations of neutrophils (5 x 10(6)) alone resulted in the generation of 62.2 +/- 8.5 ng of LTB4. Coincubations of the neutrophils with keratinocytes (ratio 3:1) resulted in a 56-163% increase in leukotriene B4 formation. To delineate the source of the newly formed leukotriene B4, incubations of keratinocytes with leukotriene A4 revealed that keratinocytes can transform leukotriene A4 into leukotriene B4. These latter findings indicate that although keratinocytes cannot directly metabolize arachidonic acid into leukotriene B4 via the 5-lipoxygenase enzyme, they can transform neutrophil-derived leukotriene A4 into leukotriene B4, thus indicating the possible existence of a putative keratinocyte-leukotriene A4 hydrolase. It is therefore reasonable to speculate that the keratinocytes possess the capacity to generate leukotriene B4 in the epidermis when provided leukotriene A4 and thereby can amplify the inflammatory processes occurring during neutrophil exocytosis. These findings indicate that transcellular metabolism of arachidonic acid metabolites in the epidermis by keratinocytes and neutrophils may contribute to the high levels of leukotriene B4 in lesional skin of inflammatory skin diseases.

On the expression and regulation of 5-lipoxygenase in human lymphocytes

The expression of arachidonate 5-lipoxygenase (arachidonate:oxygen 5-oxidoreductase, EC 1.13.11.34) and the 5-lipoxygenase-activating protein (FLAP) genes in human tonsillar B cells and lymphoblastoid B-cell lines was demonstrated at the transcriptional level by reverse transcription-PCR analysis. Also, five lymphoblastoid T-cell lines were investigated and found to express the FLAP gene but not the 5-lipoxygenase gene, suggesting that the transcriptional regulation of these two genes is different. Western blot analysis of the cytosolic proteins from a lymphoblastoid B-cell line with an antiserum raised against purified human leukocyte 5-lipoxygenase revealed an immunoreactive band that comigrated with recombinant human 5-lipoxygenase. Intact B cells produced very low amounts of leukotriene B4 and 5-hydroxyeicosatetraenoic acid upon stimulation with the calcium ionophore A23187 and arachidonic acid, in comparison to the amounts formed by sonicates of these cells. However, preincubation of intact lymphoblastoid B cells with the glutathione-depleting agents azodicarboxylic acid bis(dimethylamide) or 1-chloro-2,4-dinitrobenzene prior to the addition of the calcium ionophore A23187 and arachidonic acid led to similar amounts of leukotriene B4 as were formed by sonicated cells. In contrast, the glutathione synthesis inhibitor buthionine sulfoximine diminished the cellular level of glutathione by greater than 90% but did not influence the production of leukotriene B4 or 5-hydroxyeicosatetraenoic acid in intact cells. These results demonstrate that certain drugs affecting the redox status can stimulate the cryptic 5-lipoxygenase activity in intact lymphoblastoid B cells but that the mechanism of this activation is unclear and appears not to be directly related to intracellular glutathione levels.

Leukotriene B4 in the immune system

Leukotriene (LT) B4 is a biologically active molecule derived from arachidonic acid via the 5-lipoxygenase pathway. It mediates certain inflammatory and immunological reactions. The role of LTB4 in the immune system has been questioned since lymphocytes have been regarded to lack the enzymes involved in LTB4 formation. This review focuses on the recently described biosynthesis of LTB4 in B-lymphocytes and the effects of this compound on lymphocyte functions.

Epithelial strips: an alternative technique for examining arachidonate metabolism in equine tracheal epithelium

We have developed an alternative method for examining equine tracheal epithelial arachidonic acid (AA) metabolism that utilizes strips of pseudostratified columnar epithelium attached to a layer of elastic tissue 80 to 130 microns thick. We compared the responses of this preparation with those of enzymatically dispersed suspensions of tracheal epithelium obtained from the same animal. Strips incubated with [3H]AA incorporated 40.8 +/- 3.6% of added radioactivity and released 2.55 +/- 0.23% of incorporated radioactivity when stimulated with 5 microM A23187. Values for the cell suspension were 59.6 +/- 1.6% and 1.90 +/- 0.08%, respectively. Stimulation with 50 microM histamine or bradykinin resulted in significant release of free [3H]AA only from the strips. High-performance liquid chromatography radioactivity profiles of eicosanoids released following stimulation with 5 microM A23187 demonstrated peaks that coeluted with free AA, prostaglandin (PG) E2, and PGF2 alpha for the strips, and free AA, leukotriene B4, and 5-HETE for the cell suspensions. The absence of PGE2 production by cell suspensions was confirmed by assaying immunoreactive PGE2 in supernatants from unlabeled strips and suspensions stimulated with 5 microM A23187. Epithelial strips produced 10.3 +/- 1.3 ng PGE2/ml supernatant, whereas 5 x 10(6) cells in suspension produced less than 100 pg/ml. Despite the lack of PG production by the cell suspensions, immunocytochemical staining with an anti-PGH synthase antibody demonstrated the presence of PGH synthase in epithelial cells of both preparations. These data indicate that, in contrast to epithelial cell suspensions, epithelial strips synthesize cyclooxygenase metabolites and respond to peptide agonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Human B lymphocytes possess 5-lipoxygenase activity and convert arachidonic acid to leukotriene B4

Incubation of cell sonicates from monoclonal B cells with arachidonic acid led to the formation of leukotriene (LT) B4 and 5-hydroxy-eicosatetraenoic acid (5-HETE). In contrast, stimulation of intact B cells with the calcium ionophore A23187 +/- arachidonic acid did not, under similar conditions, lead to formation of LTB4. The identification of these products was based on reverse phase- and straight phase-HPLC analysis, UV-spectroscopy and gas chromatography-mass spectrometry. Cell sonicates of highly enriched human tonsillar B lymphocytes also converted arachidonic acid to LTB4 and 5-HETE. Activation of these cells with B cell mitogen and cytokines for three days led to an upregulation of 5-lipoxygenase activity. This study provides evidence for the biosynthesis of LTB4 from arachidonic acid in B cell lines and in normal human tonsillar B lymphocytes.

Leukotriene A4 hydrolase in the human B-lymphocytic cell line Raji: indications of catalytically divergent forms of the enzyme

Leukotriene A4 hydrolase was purified 1400-fold, with an approximate yield of 25%, to apparent homogeneity from the human B-lymphocytic cell line Raji. The purification included ammonium sulfate precipitations followed by anion exchange, hydrophobic interaction, and molecular exclusion fast protein liquid chromatography. Kinetic properties at 2 degrees C varied between different enzyme preparations. Two patterns were observed, one with a Km of about 12 microM and Vmax of about 1.1 mumol LTB4/mg protein/min which correlated well with the properties of the human leukocytic LTA4 hydrolase. In other enzyme preparations a higher catalytic activity was observed. These enzyme batches did not obey Michaelis-Menten kinetics but were compatible with a mixture of enzymatic species. Heat treatment (60 degrees C) led to a time-dependent decline in catalytic activity. However, certain enzyme preparations contained a subfraction of enzymatic activity which was more resistant to heat treatment, yielding a biphasic inactivation pattern. It is thus suggested, on the basis of the kinetic properties and the heat-inactivation pattern, that these enzyme preparations contained an addition form of LTA4 hydrolase.

Effects of monocyte-lymphocyte interaction on the synthesis of leukotriene B4

Human monocytes in monolayers were challenged with the calcium ionophore A23187. Methanol trapping of the products in the cell-free supernatants, followed by analysis on HPLC and by ultraviolet spectroscopy, revealed the presence of two compounds, which exhibited a conjugated-triene spectrum and chromatographed with the compounds formed when synthetic leukotriene (LT) A4 was added to warm acidified methanol. Furthermore, addition of purified LTA4 hydrolase to the cell-free supernatant of monocytes, stimulated with the ionophore A23187, resulted in increased levels of LTB4. These results indicate that monocytes release LTA4 extracellularly after activation with the calcium ionophore. Incubation of monocytes together with monoclonal lymphocytic cells, of both B and T cell lineage, yielded increased levels of LTB4 whereas the non-enzymatic isomers of this compound, i.e. delta 6-trans-LTB4 and 12-epi-delta 6-trans-LTB4, declined. In addition, the sum of LTB4 and its non-enzymatically formed isomers increased in mixed cultures of monocytes and monoclonal lymphocytic cells as compared to monocytes alone. The present study indicates that activated monocytes release LTA4, which is converted into LTB4 by monoclonal lymphocytic cells. Furthermore, the increase of the total amounts of leukotrienes on incubation of monocytes with lymphocytic cells, suggests the presence of an additional mechanism leading to activation of the 5-lipoxygenase pathway in monocytes.

Biosynthesis and biological activity of leukotriene B4

The leukotrienes are a family of biologically active molecules derived from arachidonic acid. While prostaglandins and thromboxanes are products of the cyclooxygenase pathway of arachidonic acid metabolism, the leukotrienes are formed by arachidonate 5-lipoxygenase, an enzyme present in phagocytes, mast cells, and basophils. Inflammatory stimuli, such as chemotactic peptides, platelet-activating factor, phagocytic particles, and immunological stimuli, which activate phagocytes and mast cells, stimulate leukotriene synthesis. Leukotriene B4, a dihydroxy derivative of arachidonic acid, has a unique stimulatory activity on important functional responses of phagocytes; leukotriene B4 exerts chemotactic and chemokinetic activity towards phagocytes in vitro and in vivo, and it is a putative mediator of inflammation.

B-lymphocytic cell line Raji expresses the leukotriene A4 hydrolase gene but not the 5-lipoxygenase gene

The expression of LTA hydrolase and 5-lipoxygenase genes was studied in Raji cells, a Burkitt lymphoma derived B-cell line. Northern and Western blot analyses clearly showed the expression, both at the transcriptional and translational level, of the LTA4 hydrolase gene in these cells. However, expression of the 5-lipoxygenase gene was undetectable. Thus, the genes coding for the two enzymes required for biosynthesis of leukotriene B4 from arachidonic acid, 5-lipoxygenase and LTA4 hydrolase, were differentially expressed in the Raji cells.

Clotting of whole human blood induces cysteinyl-leukotriene formation

Using radioimmunoassay techniques we studied the formation of the 5-lipoxygenase-derived cysteinyl-leukotrienes (LT) in comparison to the cyclooxygenase product thromboxane (TX) B2 in whole human blood allowed to clot at 37 degrees C in vitro. Spontaneous clotting resulted in a time-dependent release of smaller amounts of cysteinyl-LT as well as release of large amounts of TXB2 into the serum. Cysteinyl-LT were characterized by their immunoreactive behaviour and their biological activity in the guinea pig ileum bioassay, an effect which could be antagonized by the SRS-A antagonist FPL 55712 (0.38 microM). By reversed phase HPLC cysteinyl-LT in the serum were identified as a mixture of LTC4, LTD4 and LTE4. At 90 and 120 min part of the immunoreactive material consisted of the omega-oxidized metabolite 20-OH-LTE4. Almost complete inhibition of cyclooxygenase activity by indomethacin (2.8 microM) did not affect cysteinyl-LT formation by clotting whole human blood in vitro nor did activation of platelets by compounds such as the TX mimetic U 46619 (10 microM), platelet-activating factor (PAF, 1 microM) or thrombin (3 IU/ml). In contrast, the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA, 10 microM), the Ca2+-chelating anticoagulants trisodium citrate (10 microM) and edetate disodium (EDTA, 5.4 mM) as well as the functionally unrelated heparin (20 IU/ml) significantly inhibited the formation of cysteinyl-LT as well as of TXB2. Thus, an event related to the process of clotting of whole human blood appears to be able to induce cysteinyl-LT formation in amounts which might be functionally relevant during thromboembolic events.