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

Expression and putative biological roles of lipoxygenases and leukotriene receptors in leukemia and lymphoma

This mini-review addresses lipoxygenases and receptors for leukotrienes in hematological malignancies. Potential novel biomarkers and drug targets in leukemia and B-cell lymphoma are discussed.

Lipidomics Reveals Myocardial Lipid Composition in a Murine Model of Insulin Resistance Induced by a High-Fat Diet

Ectopic fat accumulation in non-adipose tissues is closely related to diabetes-related myocardial dysfunction. Nevertheless, the complete picture of the lipid metabolites involved in the metabolic-related myocardial alterations is not fully characterized. The aim of this study was to characterize the specific lipid profile in hearts in an animal model of obesity/insulin resistance induced by a high-fat diet (HFD). The cardiac lipidome profiles were assessed via liquid chromatography-mass spectrometry (LC-MS)/MS-MS and laser desorption/ionization-mass spectrometry (LDI-MS) tissue imaging in hearts from C57BL/6J mice fed with an HFD or standard-diet (STD) for 12 weeks. Targeted lipidome analysis identified a total of 63 lipids (i.e., 48 triacylglycerols (TG), 5 diacylglycerols (DG), 1 sphingomyelin (SM), 3 phosphatidylcholines (PC), 1 DihydroPC, and 5 carnitines) modified in hearts from HFD-fed mice compared to animals fed with STD. Whereas most of the TG were up-regulated in hearts from animals fed with an HFD, most of the carnitines were down-regulated, thereby suggesting a reduction in the mitochondrial β-oxidation. Roughly 30% of the identified metabolites were oxidated, pointing to an increase in lipid peroxidation. Cardiac lipidome was associated with a specific biochemical profile and a specific liver TG pattern. Overall, our study reveals a specific cardiac lipid fingerprint associated with metabolic alterations induced by HFD.

Intrinsic 5-lipoxygenase activity regulates migration and adherence of mantle cell lymphoma cells

Human B-lymphocytes express 5-lipoxygenase (5-LOX) and 5-LOX activating protein (FLAP) and can convert arachidonic acid to leukotriene B4. Mantle cell lymphoma (MCL) cells contain similar amounts of 5-LOX as human neutrophils but the function and mechanism of activation of 5-LOX in MCL cells, and in normal B-lymphocytes, are unclear. Here we show that the intrinsic 5-LOX pathway in the MCL cell line JeKo-1 has an essential role in migration and adherence of the cells, which are important pathophysiological characteristics of B-cell lymphoma. Incubation of JeKo-1 with the FLAP inhibitor GSK2190915 or the 5-LOX inhibitor zileuton, at a concentration below 1 μM, prior to stimulation with the chemotactic agent CXCL12, led to a significant reduction of migration. CRISPR/Cas9 mediated deletion of ALOX5 gene in JeKo-1 cells also led to a significantly decreased migration of the cells. Furthermore, 5-LOX and FLAP inhibitors markedly decreased the adherence of JeKo-1 cells to stromal cells. In comparison, these drugs had a similar effect on adherence of JeKo-1 cells as the Bruton tyrosine kinase inhibitor ibrutinib, which has a proven anti-tumour effect. These results indicate that inhibition of 5-LOX may be a novel treatment for MCL and certain other B-cell lymphomas.

Phosphorylation of serine 523 on 5-lipoxygenase in human B lymphocytes

The key enzyme in leukotriene (LT) biosynthesis is 5-lipoxygenase (5-LO), which is expressed in myeloid cells and in B lymphocytes. There are three phosphorylation sites on 5-LO (Ser271, Ser523 and Ser663). Protein kinase A (PKA) phosphorylates 5-LO on Ser523. In this report, we demonstrate by immunoblotting that native 5-LO in mantle B cell lymphoma (MCL) cells (Granta519, JEKO1, and Rec1) and in primary chronic B lymphocytic leukemia cells (B-CLL) is phosphorylated on Ser523. In contrast, we could not detect phosphorylation of 5-LO on Ser523 in human granulocytes or monocytes. Phosphorylated 5-LO was purified from Rec1 cells, using an ATP-agarose column, and the partially purified enzyme could be dephosphorylated with alkaline phosphatase. Incubation of Rec1 cells with 8-Br-cAMP or prostaglandin E2 stimulated phosphorylation at Ser523. Furthermore, FLAG-5LO was expressed in Rec1 cells, and the cells were cultivated in the presence of 8-Br-cAMP. The 5-LO protein from these cells was immunoprecipitated, first with anti-FLAG, followed by anti-pSer523-5-LO. The presence of 5-LO protein in the final precipitate further supported the finding that the protein recognized by the pSer523 antibody was 5-LO. Taken together, this study shows that 5-LO in B cells is phosphorylated on Ser523 and demonstrates for the first time a chemical difference between 5-LO in myeloid cells and B cells.

Expression of 5-lipoxygenase and 15-lipoxygenase in rheumatoid arthritis synovium and effects of intraarticular glucocorticoids

Introduction

It was previously shown that lipoxygenase (LO) pathways are important in the rheumatoid arthritis (RA) inflammatory process and that synovial fluid from RA patients contains high amounts of leukotrienes. We therefore aimed to investigate the 5-LO and 15-LO-1 expression pattern in RA and ostheoarthritis (OA) synovial tissue and to study the effect of intraarticular glucocorticoid (GC) therapy on enzyme expression.

Methods

Expression of LOs was evaluated by immunohistochemistry in RA and OA synovial biopsies. Cellular localization of these enzymes was analyzed by double immunofluorescence. In synovial biopsies from 11 RA patients, 5-LO and 15-LO-1 expression was evaluated before and after triamcinolone hexacetonide knee injection and assessed by image analysis to quantify their expression. We also investigated the presence of 15-LO-1 by immunohistochemistry in synovial fluid (SF) cells as well as their ability to form 15-hydroxyeicosatetraenoic acid (15-HETE) following treatment with arachidonic acid (AA).

Results

5-LO and 15-LO-1 are present in RA and OA synovium, with 5-LO being mostly expressed in lining and sublining macrophages, neutrophils and mast cells and 15-LO-1 mainly in lining macrophages, fibroblasts and sublining endothelial cells. Intraarticular GC treatment resulted in a significant suppression of 5-LO expression, but did not influence the 15-LO-1 enzyme significantly. Also, SF cells express a functional 15-LO-1 and produce 15-HETE when challenged with AA.

Conclusions

These data demonstrate that local therapy with GC decreases 5-LO expression in RA synovium and offer an additional possible mechanism for the efficiency of intraarticular adjuvant therapy in RA.

High expression of 5-lipoxygenase in normal and malignant mantle zone B lymphocytes

Background

Human B lymphocytes can produce leukotriene B₄ but the biological function of the 5-lipoxygenase (5-LO) pathway in B cells is unclear. In order to better understand and define the role of 5-LO in B cells, we investigated the expression of 5-LO mRNA and protein in subsets of B cells from human tonsils and different types of B cell lymphoma.

Results

Based on RT-PCR and western blot/immunohistochemical staining, with a polyclonal antibody raised against 5-LO, high expression of 5-LO was found in mantle zone B cells from tonsils. By contrast, only a weak expression of 5-LO was detected in germinal centre cells and no expression in plasma cells from tonsils. This pattern of 5-LO expression was preserved in malignant lymphoma with high expression in mantle B cell lymphoma (MCL) and weak or no expression in follicular lymphoma. Primary leukemized MCL, so called B-prolymphocytic leukaemia cells, and MCL cell lines also expressed 5-LO and readily produced LTB₄ after activation.

Conclusion

The present report demonstrates the expression of 5-LO mainly in normal and malignant mantle zone B cells while the expression is low or absent in germinal centre B cells and plasma cells, indicating a role of the 5-LO pathway in B cells before the cells finally differentiate to plasma cells.

Involvement of 5-lipoxygenase in survival of Epstein–Barr virus (EBV)-converted B lymphoma cells

Epstein-Barr Virus (EBV) is involved in the progression of lymphomas through still unknown mechanism involving increased resistance to induced apoptosis. We show here that in a set of apoptosis-resistant EBV-converted Burkitt's lymphoma clones, 5- and 12-lipoxygenases (LOXs) are over-expressed. Further investigations on 5-LOX showed that resistance to apoptosis increases parallely with the expression of 5-lipoxygenase (5-LOX). Inhibitors of 5-LOX: (a) decrease peroxides level, indicating that this enzyme promotes the generation of oxidative stress in EBV+ cells, and (b) potently induce apoptosis in the EBV resistant cell line E2R. 5- and 15-HETE, the products of the 5 and 15-LOXs, respectively, counteract 5-LOX inhibitor induced apoptosis, indicating that products of arachidonate metabolism, rather than peroxides, trigger a signal transduction that is required for survival of the EBV-converted cells. These findings suggest that 5- and, to a lesser extent, other LOXs, that are involved in tumor progression of several cell types, may also participate in lymphomagenesis, especially that EBV-mediated.

Characterization of certain inflammatory variables in the peripheral blood of clinically healthy dogs

Many laboratory techniques have been developed to study and quantify the inflammatory response, including the release of acid hydrolase enzymes, leukotriene B(4) (LTB(4)) production, reactive oxygen species (ROS) production and complement conversion studies. Although extensively studied in human health and disease, the relevance of such tests in the dog is largely unknown. After isolation of the peripheral blood mononuclear cell (PBMC) and polymorphonuclear cell (PMN) fractions from the peripheral blood of 38 clinically healthy dogs, values for ROS production were similar for both cell fractions when measured by luminol-enhanced chemiluminescence (17,853+/-9,695 U/10(6) cells versus 19,138+/-14,569 U/10(6) cells for the PBMC (n=38) and PMN (n=18) fractions, respectively). However, the mean time taken to reach maximum chemiluminescence was noticeably shorter in the PBMC fraction (5.1+/-3.3 versus 10.7+/-2.5 min for PBMCs (n=36) and PMNs (n=18), respectively). Intracellular concentrations of beta-glucuronidase, beta-galactosidase and N-acetyl-beta-glucosaminidase were assayed by spectrofluorometry. Mean values for all three enzymes were higher in PBMCs (n=31-35) than in PMNs (n=10-14). Both cell fractions released 20% of the intracellular enzyme concentration when stimulated with opsonized zymosan. Following incubation with A23187 (1 microM), mean LTB(4) production was higher in PBMCs (4.45+/-2.92 ng/10(6) cells; n=27) than in PMNs (0.96+/-2.22 ng/10(6) cells; n=13) using a validated high performance liquid chromatography (HPLC) assay. Immunoprecipitation studies revealed that the mean percentage conversion of C3 to C3b following stimulation with opsonized zymosan was 57.3+/-13.4% (n=36). The results provide normal values for clinically healthy dogs that may subsequently be used in future studies investigating dogs with various inflammatory disorders.

Leukotriene B4 plays a pivotal role in CD40-dependent activation of chronic B lymphocytic leukemia cells

Biosynthesis of leukotrienes (LTs) occurs in human myeloid cells and B lymphocytes. However, the function of leukotrienes in B lymphocytes is unclear. Here, we report that B-cell chronic lymphocytic leukemia (B-CLL) cells produce leukotriene B4, and that specific leukotriene biosynthesis inhibitors counteracted CD40-dependent activation of B-CLL cells. Studies on the expression of the high-affinity receptor for LTB4 (BLT1) by flow cytometry analysis showed that the receptor was expressed, to a varying degree, in all investigated B-CLL clones. At a concentration of 100 nM, the drugs BWA4C (a specific 5-lipoxygenase inhibitor) and MK-886 (a specific 5-lipoxygenase activating protein inhibitor) markedly inhibited CD40-induced DNA synthesis (45% and 38%, respectively) and CD40-induced expression of CD23, CD54, and CD150. Addition of exogenous LTB4 (150 nM) almost completely reversed the effect of the inhibitors on DNA synthesis and antigen expression. Taken together, the results of the present study suggest that leukotriene biosynthesis inhibitors may have a therapeutic role in B-CLL.

Reactive oxygen species released from granulocytes stimulate 5-lipoxygenase activity in a B-lymphocytic cell line

B-lymphocytes express 5-lipoxygenase (5-LO) protein but cellular leukotriene production is suppressed by selenium-dependent peroxidases. Thus it was of interest to check whether reactive oxygen species (ROS) which are released under inflammatory conditions can stimulate B-lymphocyte 5-LO and counteract peroxidase-mediated suppression of cellular 5-LO activity. It was found that 5-LO in the Epstein-Barr virus-transformed B-lymphocytic cell line BL41-E95-A is activated by addition of hydrogen peroxide or xanthine/xanthine oxidase and after increasing the oxidative state of the cell by azodicarboxylic acid bis(dimethylamide). Generation of endogenous ROS from mitochondria by antimycin A also lead to a threefold upregulation of 5-LO activity in B-cells. There was almost no detectable endogenous superoxide formation in BL41-E95-A cells after stimulation with 4beta-phorbol 12-myristate 13-acetate. Co-incubation experiments with BL41-E95-A cells and granulocytes demonstrated that granulocyte-derived ROS can activate B-lymphocyte 5-LO. Addition of superoxide dismutase and/or catalase to the B-lymphocyte/granulocyte co-incubations and to B-lymphocyte homogenates revealed that the 5-LO activation is due to the superoxide-derived release of hydroperoxides or hydrogen peroxide from granulocytes. The data suggest that ROS formation plays an important role in the regulation of cellular 5-LO activity in B-lymphocytes. As leukotrienes affect B-cell functions like cell proliferation, activation and maturation, this finding provides a new link between the formation of ROS and the regulation of immune responses.

Qualitative and quantitative analysis of lipoxygenase products in bovine corneal epithelium by liquid chromatography-mass spectrometry with an ion trap

Electrospray ionization ion trap mass spectra of 5-, 12-, and 15-hydroperoxyeicosatetraenoic (HPETE), hydroxyeicosatetraenoic (HETE), and ketoeicosatetraenoic (KETE) acids were recorded. The HPETE were partly dehydrated to the corresponding KETE in the heated capillary of the mass spectrometer. 12-HPETE and 15-HPETE were also converted to KETE by collision-induced dissociation (CID) in the ion trap, whereas CID of 5-HPETE yielded little formation of 5-KETE. Subcellular fractions of bovine corneal epithelium were incubated with arachidonic acid (AA) and the metabolites were analyzed. 15-HETE and 12-HETE were consistently formed, whereas significant accumulation of HPETE and KETE was not detected. Biosynthesis of 12- and 15-HETE was quantified with octadeuterated 12-HETE and 15-HETE as internal standards. The average biosynthesis of 15-HETE and 12-HETE from 30 microM AA by the cytosol was 38 +/- 8 and below 3 ng/mg protein/30 min, respectively, which increased to 78 +/- 21 and 10 +/- 4 ng/mg protein/30 min in the presence of 1 mM free Ca2+. The microsomal biosynthesis was unaffected by Ca2+. The microsomes metabolized AA to 15-HETE as the main metabolite at a low protein concentration (0.3 mg/mL), whereas 12-HETE and 15-HETE were formed in a 2:1 ratio at a combined rate of 0.7 +/- 0.2 microg/mg protein/30 min at a high protein concentration (1.8 mg/mL). The level of 12-HETE in corneal epithelial cells was 50 +/- 13 pg/mg tissue, whereas the endogenous amount of 15-HETE was low or undetectable (<3 pg/mg tissue). Incubation of corneas for 20 min at 37 degrees C before processing selectively increased the amounts of 12-HETE in the epithelium fourfold to approximately 0.2 ng/mg tissue. We conclude that 12-HETE is the main endogenously formed lipoxygenase product of bovine corneal epithelium.

Gene expression of 5-lipoxygenase and LTA4 hydrolase in renal tissue of nephrotic syndrome patients

Leukotrienes (LT) of the 5-lipoxygenase pathway constitute a class of potent biological lipid mediators of inflammation implicated in the pathogenesis of different models of experimental glomerulonephritis. The key enzyme, 5-lipoxygenase (5-LO), catalyses oxygenation of arachidonic acid to generate the primary leukotriene LTA4. This LT, in turn, serves as a substrate for either LTA4 hydrolase, to form the potent chemoattractant LTB4, or LTC4 synthase, to produce the powerful vasoconstrictor LTC4. To investigate the potential role of LT in the pathogenesis of human glomerulonephritis with nephrotic syndrome, we examined the gene expression of 5-LO and LTA4 hydrolase in renal tissue of 21 adult patients with nephrotic syndrome and 11 controls. The patients consisted of 11 cases of membranous nephropathy (MN), seven focal and segmental glomerulosclerosis (FSGS), two non-IgA mesangial glomerulonephritis and one minimal change disease. Total RNA purified from renal tissue was reverse transcribed into cDNA and amplified with specific primers in a polymerase chain reaction (RT-PCR). Eight patients' renal tissue, four MN and four FSGS, co-expressed 5-LO and LTA4 hydrolase. In situ hybridization analysis revealed 5-LO expression and distribution limited to the interstitial cells surrounding the peritubular capillaries. Comparative clinical and immunohistological data showed that these eight patients had impaired renal function and interstitial changes that significantly correlated with 5-LO expression. These findings suggest that leukotrienes may play an important role in the pathogenesis of MN and FSGS. These results are also relevant to elucidating the pathophysiologic mechanisms which underlie progression to renal failure in these diseases.

Asthma and leukotrienes: antileukotrienes as novel anti-asthmatic drugs

Antileukotriene drugs inhibit the formation or action of leukotrienes, which are potent lipid mediators generated from arachidonic acid in lung tissue and inflammatory cells. The leukotrienes were discovered in basic studies of arachidonic acid metabolism in leucocytes 20 years ago and were found to display a number of biological activities which may contribute to airway obstruction. Clinical studies with antileukotriene drugs have indeed demonstrated that leukotrienes are significant mediators of airway obstruction evoked by many common trigger factors in asthma. Moreover, treatment trials have established that this new class of drugs has beneficial anti-asthmatic properties, and several antileukotrienes have recently been introduced as new therapy of asthma. This communication presents an overview of the biosynthesis of leukotrienes, their biological effects and clinical effects of antileukotrienes in the treatment of asthama.

DMSO induction of the leukotriene LTC4 by Lewis rat Schwann cells

Schwann cells are capable of producing many immunomodulatory molecules, which indicates that they may play an active role in autoimmune diseases of the peripheral nervous system. We have previously reported production of the prostanoids prostaglandin E2 and thromboxane A2, products of arachidonic acid metabolism, by Schwann cells. This study reports that Schwann cells are capable of producing leukotriene C4, also a product of arachidonic acid metabolism. Production of leukotriene C4 was in response to pre-incubation of the Schwann cells with the cytokines interferon-gamma and tumour necrosis factor-alpha followed by incubation with dimethylsulfoxide. The cytokines alone did not elicit a response nor did stimulation with calcium ionophore, phorbol ester or lipopolysaccharide.

Multiple splice variants of the human calcium-independent phospholipase A2 and their effect on enzyme activity

Recently, the cloning of a novel Ca2+-independent phospholipase A2 (iPLA2) from Chinese hamster ovary cells as well as from mouse and rat sources containing a C-terminal lipase motif and eight N-terminal ankyrin repeats has been described. In this report we describe the cloning of the human iPLA2 cDNA and its expression in B-cells and show that the iPLA2 gene undergoes extensive alternative splicing generating multiple isoforms that contribute to a novel mechanism to control iPLA2 activity. The full-length cDNA clone encodes a 806-amino acid protein with a calculated molecular mass of 88 kDa. The protein contains a lipase motif, GXSXG, and ankyrin repeats, as described for the hamster and rodent forms of the enzyme but has an additional 54-amino acid proline-rich insertion in the last of the eight ankyrin repeats (residues 395-449). Furthermore, at least three additional isoforms most likely due to alternative splicing were identified. One that is present as a partial cDNA in the expressed sequence tag data base is similar to iPLA2 but terminates just after the lipase active site, and two other isoforms contain only the iPLA2 ankyrin repeat sequence (ankyrin-iPLA2-1 and -2). Ankyrin repeats are involved in protein-protein interactions and because the purified iPLA2 enzyme exists as a multimeric complex of 270-350 kDa, the expression of just the ankyrin-iPLA2 sequence suggested that these may also interact with the iPLA2 oligomeric complexes and perhaps modulate PLA2 activity. Transfection of the human iPLA2 cDNA into COS cells resulted in a substantial increase in calcium-independent PLA2 activity in cell lysate. No activity above background was observed following ankyrin-iPLA2-1 cDNA transfection. However, co-transfection of the ankyrin-iPLA2-1 and the iPLA2 cDNAs resulted in a 2-fold reduction in activity compared with iPLA2 alone. A similar co-transfection of ankyrin-iPLA2-1 cDNA with the cPLA2 cDNA had no effect on PLA2 activity. These results suggest that the ankyrin-iPLA2 sequence can function as a negative regulator of iPLA2 activity and that the alternative splicing of the iPLA2 gene can have a direct effect on the attenuation of enzyme activity.

Identification and characterization of a novel human microsomal glutathione S-transferase with leukotriene C4 synthase activity and significant sequence identity to 5-lipoxygenase-activating protein and leukotriene C4 synthase

5-Lipoxygenase-activating protein (FLAP) and leukotriene C4 (LTC4) synthase, two proteins involved in leukotriene biosynthesis, have been demonstrated to be 31% identical at the amino acid level. We have recently identified and characterized a novel member of the FLAP/LTC4 synthase gene family termed microsomal glutathione S-transferase II (microsomal GST-II). The open reading frame encodes a 16.6-kDa protein with a calculated pI of 10.4. Microsomal GST-II has 33% amino acid identity to FLAP, 44% amino acid identity to LTC4 synthase, and 11% amino acid identity to the previously characterized human microsomal GST (microsomal GST-I). Microsomal GST-II also has a similar hydrophobicity pattern to FLAP, LTC4 synthase, and microsomal GST-I. Fluorescent in situ hybridization mapped microsomal GST-II to chromosomal localization 4q28-31. Microsomal GST-II has a wide tissue distribution (at the mRNA level) and was specifically expressed in human liver, spleen, skeletal muscle, heart, adrenals, pancreas, prostate, testis, fetal liver, and fetal spleen. In contrast, microsomal GST-II mRNA expression was very low (when present) in lung, brain, placenta, and bone marrow. This differs from FLAP mRNA, which was detected in lung, various organs of the immune system, and peripheral blood leukocytes, and LTC4 synthase mRNA, which could not be detected in any tissues by Northern blot analysis. Microsomal GST-II and LTC4 synthase were expressed in a baculovirus insect cell system, and microsomes from Sf9 cells containing microsomal GST-II or LTC4 synthase were both found to catalyze the production of LTC4 from LTA4 and reduced glutathione. Microsomal GST-II also catalyzed the formation of another product, displaying a conjugated triene UV absorption spectra with a maximum at 283 nm, suggesting less catalytic stereospecificity compared with LTC4 synthase. Also, the apparent Km for LTA4 was higher for microsomal GST-II (41 microM) than LTC4 synthase (7 microM). In addition, unlike LTC4 synthase, microsomal GST-II was able to catalyze the conjugation of 1-chloro-2, 4-dinitrobenzene with reduced glutathione. Therefore, it is proposed that this novel membrane protein is a member of the microsomal glutathione S-transferase family, also including LTC4 synthase, with significant sequence identities to both LTC4 synthase and FLAP.

The effect of leukotrienes B and selected HETEs on the proliferation of colon cancer cells

Eicosanoids have been implicated in colon carcinogenesis, but very little is known on the potential role of leukotrienes (LTs) and hydroxyeicosatetraenoic acids (HETEs) in this process; such compounds are produced by colonocytes and tumor infiltrating leukocytes. We studied the effect of LTB4, LTB4 methyl ester, LTB5, 12(R)-HETE, 12(S)-HETE and 15(S)-HETE (10(-10), 10(-8), 10(-6) M) on the proliferation rate, the cell cycle distribution, and the rate of apoptosis in HT-29 and HCT-15 human colon carcinoma cells. Our data show that LTB4, a lipoxygenase product, increased the proliferation rate of both cell lines in a time- and concentration-dependent manner. In HT-29 cells the concentration-response curve was bell-shaped (maximal effect at 10(-8) M). The proliferative effects of LTB4 in HT-29 cells were inhibited by SC-41930, a competitive antagonist of LTB4, suggesting the existence of an LTB4 receptor in epithelial cells. The methyl ester of LTB4 stimulated the proliferation of these cells, but LTB5, an isomer of LTB4 derived from eicosapentaenoic acid, did not. Of the HETEs, only 12(R)-HETE, a P-450 product, stimulated the proliferation of both cell lines; the other HETEs, all lipoxygenase products, failed to affect the proliferation of these cells. None of these eicosanoids had any effect on cell cycle distribution or apoptosis in either cell line. Taken together with our previous data showing that PGs stimulate colon cancer cell proliferation (Qiao et al. (1995) Biochim. Biophys. Acta 1258, 215-223), these findings indicate that arachidonic acid products synthesized via at least three different pathways (cyclooxygenase, lipoxygenase, P-450) may not be able to modulate the growth of colon cancer, and suggest a potential role in human colon carcinogenesis for LTB4 and 12(R)-HETE.

Studies on the regulation and localization of 5-lipoxygenase in human B-lymphocytes

Stimulated B-lymphocytes, isolated from patients with chronic lymphocytic leukemia of B-cell type (B-CLL cells) or from human tonsils, produced similar amounts of leukotriene (LT) B4 and 5-hydroxyeicosatetraenoic acid (5-HETE) as polymorphonuclear granulocytes. Unlike intact granulocytes or monocytes, human B-lymphocytes require calcium ionophore, exogenous arachidonic acid and an oxidative environment in order to produce 5-lipoxygenase products. Several thiol-reactive compounds such as N-ethylmaleimide, methyl methanethiosulfonate, azodicarboxylic acid bis[dimethylamide] (diamide) as well as hydrogen peroxide were all found to stimulate cellular leukotriene biosynthesis. Reverse transcriptase (RT)-PCR analysis demonstrated the expression of 5-lipoxygenase, 5-lipoxygenase-activating protein (FLAP) and LTA4 hydrolase mRNA in B-CLL cells. Western blot analysis demonstrated a band corresponding to the molecular size of FLAP in the B-CLL cell membrane. Furthermore, MK886, the FLAP-binding cellular leukotriene biosynthesis inhibitor, reduced both LTB4 and 5-HETE formation. Immunocytochemistry showed that 5-lipoxygenase was mainly localized in the nuclei of non-activated B-CLL cells, tonsillar B-lymphocytes and monoclonal B-cells. In contrast, neither human peripheral T-lymphocytes nor Jurkat cells were stained. These results suggest that 5-lipoxygenase and its products function in the nucleus of B-lymphocytes.

Diverse expression of cytosolic phospholipase A2, 5-lipoxygenase and prostaglandin H synthase 2 in acute pre-B-lymphocytic leukaemia cells

Several lines of evidence suggest that phospholipases A2, leukotrienes and prostaglandins play a role in the proliferation of haemopoietic cells. The expression of genes involved in the biosynthesis of leukotrienes and prostaglandins was investigated in peripheral B lymphoblasts, isolated from eight patients with acute pre-B-lymphocytic leukaemia (pre B-ALL). RT-PCR analysis demonstrated that four of the investigated pre-B-ALL clones expressed the gene coding for cytosolic phospholipase A2 (cPLA2), but not the gene coding for 5-lipoxygenase. In contrast, the remaining four pre-B-ALL clones expressed 5-lipoxygenase but not cPLA2, suggesting that the transcriptional regulation of these two genes are different and that their cellular functions are not linked to each other. The capacity of pre B-ALL cells to produce LTB4 and to express the 5-lipoxygenase protein, correlated with the expression of 5-lipoxygenase mRNA. All pre-B-ALL clones expressed genes coding for 5-lipoxygenase activating protein (FLAP), leukotriene A4 hydrolase and prostaglandin (PG)H synthase 1. Seven of the eight pre B-ALL clones expressed PGH synthase 2. In comparison, normal tonsillar B cells did not express cPLA2 or PGH synthase 2.

The 5-lipoxygenase pathway in cultured human intestinal epithelial cells

Leukotrienes (LTs), the 5-lipoxygenase (5-LOX) metabolites of arachidonic acid, have roles in many biological processes relevant to the gastrointestinal tract, including intestinal inflammation. We screened two well-known human intestinal epithelial cell lines, HT29 and Caco-2, for evidence of LT-associated enzyme transcripts and LT synthesis. Northern blot analysis of total RNA from both intestinal lines demonstrated high levels of transcripts for LTA4 hydrolase, a multisubstrate enzyme that converts the 5-LOX metabolite, LTA4, to LTB4. With total RNA, the 5-LOX transcript was detected only in HT29. Caco-2 failed to show 5-LOX message even with poly A-containing RNA, although the transcript could be amplified with the polymerase chain reaction. Messenger RNA for FLAP, the 5-lipoxygenase-activating protein, was detectable in both cell lines, but only with poly A-containing RNA. In a sonicated cell preparation, HT29, but not Caco-2, revealed detectable levels of 5-HETE and LTB4. These results suggest that certain intestinal epithelial cells possess a limited capacity to synthesize LTs.

Eicosanoid generation and effects on the aggregation of thrombocytes from the rainbow trout, Oncorhynchus mykiss

Fish blood lacks anucleate platelets but contains a nucleated cell type termed the thrombocyte that is thought to be functionally analogous. Thrombocytes were purified from the peripheral blood of the rainbow trout, Oncorhynchus mykiss, by a two step gradient centrifugation method. Following this procedure, the recovered thrombocytes were 78-86% pure as defined by immunoreactivity to a panel of monoclonal antibodies and were of variable morphology from round to spindle-shaped. Incubation of thrombocyte suspensions with either calcium ionophore, A23187, platelet-activating factor or a thromboxane (TX) mimetic, U-46619, generated a range of eicosanoids derived from arachidonic acid including 12-hydroxyeicosatetraenoic acid (12-HETE), TXB2, prostaglandin (PG) E2, leukotriene (LT) B4 and lipoxin (LX) A4. The equivalent products derived from eicosapentaenoic acid were also formed. Co-incubation of thrombocytes with either erythrocytes or granulocytes/monocytes in the presence of calcium ionophore did not result in the formation of any further new lipoxygenase products. Incubation of isolated thrombocytes in plasma-free conditions with U-46619 (0.03-10 microM) resulted in a rapid, dose-dependent aggregatory response. This effect was markedly augmented in the presence of mammalian fibrinogen (400 micrograms ml-1). Thrombin (0.1-1.3 units ml-1), like U-46619, was also a potent proaggregatory compound for trout thrombocytes. LXA4 and LTB4 had limited aggregatory potential and then only at high concentrations (10 microM), while 12-HETE and PAD had no significant effect at all concentrations tested. These results demonstrate that some of the eicosanoids released during the activation of trout thrombocytes are involved in the aggregatory behaviour of this cell type.

The effect of eicosanoids on rainbow trout, Oncorhynchus mykiss, leucocyte proliferation

Proliferation of rainbow trout head kidney leucocytes in response to the mitogen phytohaemagglutinin-P (PHA-P) was modulated in the presence of inhibitors of eicosanoid synthesis and by exogenous eicosanoids. The presence of indomethacin, a cyclooxygenase inhibitor, resulted in a stimulatory effect, whereas the presence of nordihydroguiaretic acid, a lipoxygenase inhibitor, resulted in an inhibitory effect on mitogenicity. The addition of prostaglandins and lipoxins was also found to be inhibitory, whilst the addition of leukotrienes was stimulatory. Some class/series effects of the eicosanoids were also apparent. Prostaglandin E2 was a more potent inhibitor than prostaglandin E3, and proliferation was more sensitive to the effects of leukotriene B4 than to leukotriene B5. Whilst PHA-P was able to directly induce the release of prostaglandins from head kidney leucocytes, it did not induce the release of lipoxygenase products.

Leukotriene formation by peripheral monocytes in contact-activated human blood

Contact activation of the intrinsic coagulation cascade in whole human blood in vitro has previously been demonstrated to trigger release of leukotrienes (LT) into serum samples. In our present study we intended to identify the cellular origin of the activated 5-lipoxygenase pathway leading to LT formation under these experimental conditions. Therefore, whole human blood samples incubated for 60 min in vitro were supplemented with Percoll-isolated, 5-lipoxygenase-carrying, autologous blood cells. Surprisingly, exogenously added polymorphonuclear neutrophils (PMN, 5 x 10(6) or 15 x 10(6)/ml) capable of producing cysteinyl-LT in response to ionophore A23187 (1 microM) stimulation, had no effect neither on immunoreactive cysteinyl-LT nor on thromboxane (TX) B2 formation. However, exogenously added mononuclear cells (MNC, 5 x 10(6) or 15 x 10(6)/ml) led to a cell number-dependent increase in cysteinyl-LT generation as did supplementation with peripheral monocytes (PM, 5 x 10(5) or 15 x 10(5)/ml). While MNC enhanced the TXB2 production, PM had no such effect. Incubation of PM (5 x 10(5) or 15 x 10(5)/ml) in recalcified platelet-rich plasma (PRP) induced a cysteinyl-LT formation comparable to that in whole human blood. In contrast to the TXB2 generation, the cysteinyl-LT formation appears to be largely independent from thrombin, since recombinant hirudin (HBW 023, 2 microM), a specific thrombin inhibitor, had no significant effect on the cysteinyl-LT production but nearly completely abolished the TXB2 formation. By reverse phase HPLC the immunoreactive cysteinyl-LT were shown to consist of a mixture of LTC4, LTD4 and LTE4, with LTC4 being the predominant metabolite in all samples studied.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Thromboxane A2 synthesis in human erythroleukemia cells

Human erythroleukemia cells transformed arachidonic acid and prostaglandin endoperoxide H2 into thromboxane A2. Stimulation of these cells with A23187 or thrombin, however, produced no thromboxane. Similarly, cells labeled with [3H]-arachidonic acid released no detectable label upon stimulation. Data suggest that human erythroleukemia cells contain the enzymatic capacity for thromboxane formation from exogenous precursors, but lack the endogenous mechanisms for arachidonate release. The presence of thromboxane synthase messenger RNA was verified using the polymerase chain reaction. Amplification and sequence analysis of a 528 bp cDNA demonstrated virtually 100% identity to a published thromboxane synthase cDNA fragment.