Hydroxyeicosatetraenoic acids (HETEs)

Sickle red blood cells stimulate endothelial cell production of eicosanoids and diacylglycerol

The effects of sickle red cell-endothelial cell interaction on endothelial cell arachidonic: acid (AA) mobilization, eicosanoid release, and diacylglycerol (DAG) production were evaluated by using bovine aortic endothelial cells. We have shown that coincubation of washed red blood cells (RBCs) from patients with sickle cell disease with endothelial cells stimulate AA release (90% increase as compared with buffer controls, n = 8, p < 0.002). Released AA was mobilized from membrane phosphatidylcholine and phosphatidylserine and was converted to eicosanoids via the cyclooxygenase and lipoxygenase pathways in increased amounts in the presence of sickle erythrocytes. The production of prostacyclin and 15-hydroxyeicosatetraenoic acid (15-HETE) were increased by 78% (p < 0.01) and 103% (p < 0.025), respectively, as shown by both chromatographic and immunoassay procedures. Sickle erythrocytes also stimulated the hydrolysis of endothelial cell phosphoinositides, including phosphatidylinositol-mono-phosphate (p < 0.03) and phosphatidylinositol-bis-phosphate (p < 0.006). This response was accompanied by a significant increase in the production of DAG (50% increase as compared with buffer control, n = 8, p < 0.025). In contrast, coincubation of washed erythrocytes from normal healthy donors with endothelial cells had no significant effect on endothelial cell phospholipid turnover. When the sickle RBC-induced biochemical changes in endothelial cells were contrasted with those observed with normal RBCs, the ability of sickle RBCs to induce AA mobilization and the production of mono-HETEs and DAG was markedly increased (p = 0.05 to p < 0.025). Because 15-HETE is a pro-adhesinogenic eicosanoid and DAG is an endogamous activator of protein kinase C, an enzyme involved in modulating cell surface adhesive properties, both 15-HETE and DAG could potentially play a role in the vascular pathophysiology of sickle cell disease.

Role of Pseudomonas aeruginosa lipase in inflammatory mediator release from human inflammatory effector cells (platelets, granulocytes, and monocytes

Previously, we have shown that Pseudomonas aeruginosa lipase and phospholipase C (PLC), two extracellular lipolytic enzymes, interact with each other during 12-hydroxyeicosatetraenoic acid (HETE) generation from human platelets. In this regard. the addition of purified P. aeruginosa lipase to PLC-containing crude P. aeruginosa culture supernatants enhances the generation of the chemotactically active 12-HETE from human platelets. Therefore, we analyzed the interaction of purified P. aeruginosa lipase and purified hemolytic P. aeruginosa PLC with regard to inflammatory mediator release from human platelets, neutrophilic and basophilic granulocytes, and monocytes. Purified P. aeruginosa PLC, but not purified lipase by itself, induced 12-HETE generation from human platelets, the generation of leukotriene B4 (LTB4) and oxygen metabolites, enzyme release from human neutrophils, and histamine release from basophils but diminished interleukin-8 (IL-8) release from human monocytes in a dose-dependent manner. The addition of purified lipase enhanced PLC-induced 12-HETE and LTB4 generation, did not influence enzyme, histamine, or IL-8 release, but diminished the PLC-induced chemiluminescent response. Similar results were obtained when the hemolytic PLC from Clostridium perfringens was used instead of P. aeruginosa PLC. For further comparison, we used the well-defined calcium ionophore A23187 and phorbol-12-myristate-13-acetate (PMA) as stimuli. Lipase enhanced calcium ionophore-induced LTB4 generation and beta-glucuronidase release but reduced calcium ionophore-induced and PMA-induced chemiluminescence. In parallel, we analyzed the role of lipase in a crude P. aeruginosa culture supernatant containing PLC and lipase. Lipase activity in the P. aeruginosa culture supernatant was inhibited by treatment with the lipase-specific inhibitor hexadecylsulfonyl fluoride, leaving the activity of PLC unaffected. The capacity of "lipase-inactivated culture supernatant" to induce 12-HETE and LTB4 generation was diminished by 50 to 100%. Our results suggest that the simultaneous secretion of lipase and PLC by P. aeruginosa residing in an infected host may result in severe pathological effects which cannot be explained by the sole action of the individual virulence factor on inflammatory effector cells.

Arachidonic acid diols produced by cytochrome P-450 monooxygenases are incorporated into phospholipids of vascular endothelial cells

Epoxyeicosatrienoic acids (EETs) are synthesized by cytochrome P-450 monooxygenases and released into the blood. When taken up by vascular endothelial and smooth muscle cells, the EETs are primarily esterified to phospholipids or converted to dihydroxyeicosatetraenoic acids (DHETs) and released. In the present studies, radiolabeled 8,9-, 11,12-, and 14,15-DHETs released into the medium from vascular smooth muscle cells were isolated and incubated for 4-16 h with cultured bovine aortic endothelial cells. The uptake ranged from 2 to 50% for the three regioisomers. Hydrolysis of the endothelial lipids and gas chromatographic-mass spectral analyses of the products indicated that all three DHET regioisomers were incorporated intact into phosphatidylcholine and phosphatidylinositol. Similar incubations with EETs confirmed that small amounts of DHETs were also esterified to endothelial phospholipids. These studies indicate that DHETs are incorporated into phospholipids either at the time of EET conversion to DHET or upon release and re-uptake of DHETs. Beside demonstrating for the first time that fatty acid diols are incorporated intact into endothelial lipids, these studies raise the possibility that both EETs and DHETs remain long enough in the vascular wall to produce chronic vasoactive effects.

Lipoxygenase metabolites induced expression of adhesion molecules and transendothelial migration of monocyte-like HL-60 cells is linked to protein kinase C activation

Studies have shown that, among lipoxygenase metabolites examined, 15(S)-hydroperoxy-5,8,11,13-eicosa-tetraenoic acid (15[S]-HPETE), at micromolar concentrations, selectively causes injury to cultured endothelial cells. We investigated whether physiologically relevant concentrations of lipoxygenase metabolites affected the expression of cell adhesion molecules (CAMs) involved in the adhesion of leukocytes and/or the accumulation of leukocytes in the vascular endothelium, these being the initial events in endothelial cell injury. Among lipoxygenase metabolites, 15(S)-HPETE and 12(S)-HETE, at nanomolar concentrations, induced surface expression of a subset of cell adhesion molecules (CAM), ICAM-1, ELAM-1, and VCAM-1, in human umbilical vein endothelial cells (HUVEC), which is associated with an increased binding activity of the transcription factor, NF-kappa B, to the consensus motif common to the CAM genes in the HUVEC nuclear extracts. Furthermore, 15(S)-HPETE (1 nM) caused a threefold increase in the rate of transendothelial migration of vitamin D3-differentiated HL-60 monocyte-like cells and showed a thirtyfold increase in the phosphorylation of PECAM-1, an adhesion molecule involved in endothelial cell-cell adhesion. Both an antibody to PECAM-1 and the protein kinase C inhibitor, GF 109203X, reduced 15(S)-HPETE-induced transmigration of monocyte-like HL-60 cells by approximately 75% and 85%, respectively. Treatment of HUVEC with a phosphatase inhibitor, calyculin A, augmented both the phosphorylation of PECAM-1 and transmigration of monocyte-like HL-60 cells induced by 15(S)-HPETE. Our results show that 15(S)-HPETE, at physiological concentrations, induced activation of protein kinase C in HUVEC and leads to the phosphorylation of PECAM-1, thus facilitating the migration of monocyte-like HL-60 cells across the endothelial cell monolayer. It is suggested that phosphorylation/dephosphorylation events in PECAM-1 are important in regulating the trafficking of monocytes across the endothelial cell monolayer.

Incorporation of 12(S)-hydroxyeicosatetraenoic acid into the phosphatidylcholine signaling pathway

The incorporation of 12-lipoxygenase metabolites into phospholipids (PLs) could modify second messengers such as diacylglycerols (DAG) and phosphatidic acids. Incubation of [(14)C]12(S)-HETE (1 microM) with bovine pulmonary artery endothelial cells (BPAEC), resulted in its incorporation in PLs with concentration-dependent kinetics. After a 4 h incubation, the proportion of radioactive phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS) + phosphatidylinositol (PI) isolated by TLC, was 77.9%, 16.4% and 5.7%, respectively. In PC, [(14)C]12(S)-HETE was incorporated at the position 2 of the glycerol. Three major peaks of radioactive PC were isolated on RP-HPLC which were hydrolysed by phospholipase C (PLC). The resulting diacylglycerols were derivatized and identified by GC/MS as 1-oleyl-, 1-stearoyl- and 1-palmitoyl-2-[12-HETE] PC. BPAEC were incubated with [(14)C]12(S)-HETE (1 microM) before stimulation with bradykinin (1 microM). (A) 1-acyl-2-[12-HETE] diacylglycerols were isolated, derivatized and analysed by MS. We identified a major ion with m/z = 926 that corresponds to the molecular ion of authentic 1-stearoyl-2-12(S)-HETE DAG, and 2 other ions with m/z = 924 and 898 that correspond to the molecular ions of 1-oleyl- and 1-palmitoyl-2-12(S)-HETE DAG, respectively. (B) Radioactive PA was isolated and hydrolysed by alkaline phosphatase. The MS of resulting diacylglycerols identified 1-stearoyl-, 1-oleyl-, and 1-palmitoyl-2-12(S)-HETE phosphatidic acids. The quantities of 12-HETE PA and the 3 major 12-HETE diacylglycerols were shown to increase following bradykinin stimulation. Thus, the incorporation of 12(S)-HETE into PLs results in the production of altered phosphatidic acids and diacylglycerols. The time-course of increases in 1-acyl-2-(12-HETE) phosphatidic acids and 1-acyl-2-(12-HETE) diacylglycerols showed maximal concentrations 1 and 2 min after bradykinin stimulation, respectively, followed by the decrease of both compounds. Propranolol, an inhibitor of PA phosphohydrolase, totally abolished the bradykinin-induced increase in 12-HETE DAG while increasing the magnitude and duration of 12-HETE PA release. The inhibiting effect of propranolol on bradykinin-induced increase of 12-HETE DAG demonstrates that 12-HETE PA is the principal precursor for 12-HETE DAG. This affords a novel method for confirming the major role of phospholipase D in PC metabolic pathways triggered during cell signaling.

Incorporation of 12(S)-hydroxyeicosatetraenoic acid into phospholipids and active diacylglycerols in rat liver epithelial cells: effects on DNA synthesis

12(S)-Hydroxyeicosatetraenoic acid (12-HETE), the 12-lipoxygenase-derived metabolite of arachidonic acid, was incorporated into membrane phospholipids (PL) in various cells. PL are precursors of diacylglycerol (DAG), a protein kinase C (PKC) activator involved in cell-growth signaling. We studied 12-HETE incorporation into PL in non-transformed (NT-) and spontaneously transformed (T-) rat liver epithelial cells (RLEC), and its consequence on DNA synthesis. NT- and T-RLEC incorporated 12-HETE predominantly into phosphatidylcholine (PC). 12-HETE was incorporated at a greater rate, and with a higher phosphatidylethanolamine (PE)/PC ratio in T-cells. Preincubation of RLEC with 12-HETE at > or = 0.5 microM partially inhibited basal DNA synthesis in NT- and T-RLEC. Preincubation of NT-RLEC with 12-HETE (2.5 microM) also decreased bradykinin-stimulated DNA synthesis. Unstimulated RLEC produced 1-acyl-2-(12-HETE)DAG which was increased in NT-RLEC by bradykinin stimulation. Finally, 1-stearoyl-2-(12-HETE)DAG was as potent an in vitro PKC activator as 1-stearoyl-2-arachidonyl-DAG. These data demonstrate that 12-HETE incorporation into PL resulted in the production of active 12-HETE-containing DAG, together with reduced DNA synthesis.

Uptake of 12-HETE by human bronchial epithelial cells (HBEC): effects on HBEC cytokine production

12-HETE, the major lipoxygenase end-product of platelets and macrophages, may be released in contact of bronchial epithelium in inflammatory diseases of the lung. We have studied the outcome of 12-HETE in presence of human bronchial epithelial cells (HBEC). When HBEC were incubated with [3H]12-HETE for 30 minutes, 27.5% of total radioactivity was found in HBEC and 72.5% in supernatants. Unesterified 12-HETE accounted for 22.4% of total radioactivity, 4.5% being recovered in phospholipids, preferentially in phosphatidylcholine and phosphatidylethanolamine. No incorporation in neutral lipids was detected. 72.9% of the incubated radioactivity was recovered in un identified metabolites. As 12-HETE has been shown to modulate the expression and production of various proteins, the consequence of the 12-HETE uptake on the release of GM-CSF and IL8 by HBEC was assessed. HBEC from control subjects were cultured for 24 hours with 12-HETE (10(-9) to 10(-7)M) in the presence or absence of TNF alpha. Detectable amounts of both cytokines were released in the supernatant in basal conditions at 24hr, and TNF alpha increased significantly the release of GM-CSF. 12-HETE at 10(-7)M weakly but significantly decreased the TNF-induced release of GM-CSF from HBEC. Thus the uptake of 12-HETE could affect the epithelial cell function in some situations.

What can we learn from prostaglandins and related eicosanoids in insects?

Eicosanoids are oxygenated metabolites of three C20 polyunsaturated fatty acids (20:3n-6, 20:4n-6, and 20:5n-3). While eicosanoids are very well known in mammalian systems, mostly due to their pharmaceutical interest, there is increasing recognition of the significance of these compounds in insects and other invertebrates. In this paper we consider four major concepts emerging from work on eicosanoids in invertebrates. First, the biological significance of eicosanoids extends far beyond their physiological and pathophysiological actions in human and veterinary medicine. Second, we can greatly improve our understanding of eicosanoids in insects by integrating our work on insects into ongoing studies of other invertebrates. Third, some eicosanoid actions may be fundamental to animals. Fourth, the biochemistry of eicosanoids in insects and other invertebrates can differ from expectations based on the mammalian background. Finally, we point to an uncharted frontier in insect studies--the biochemical mechanisms of eicosanoid action--by drawing attention to some of the work on eicosanoid receptors in mammalian systems.

Effect of the PAF-receptor antagonist SM-12502 on human platelets

We analyzed the effect of the PAF receptor antagonist (+)-cis-3,5-dimethyl-2-(3-pyridyl)thiazolidin-4-one hydrochloride (SM-12502) on human platelet aggregation as well as mediator release. After incubation of human platelet with different concentrations of SM-12502 the cells were subsequently stimulated with either the Ca ionophore A23187, with human thrombin, or with an activator of heterotrimeric G-proteins, sodium fluoride (NaF, in the presence of Al3+). Preincubation of platelets with the PAF receptor antagonist led to an inhibition of 12-lipoxygenase derived 12(S)-HETE and cyclooxygenase derived 12(S)-HHT. Pretreatment of platelets with the PAF receptor antagonist SM-12502 prior to activation with the Ca ionophore A23187 or PAF also inhibited platelet aggregation. Our data clearly indicate an inhibitory effect of the new PAF receptor antagonist SM-12502 on the formation of platelet derived inflammatory mediators of the lipoxygenase pathway as well as of the cyclooxygenase pathway, and furtherone, treatment with the PAF receptor antagonist diminished platelet aggregation after subsequent specific and unspecific activation.

12- and 15-hydroxyeicosatetraenoic acid are excreted in the urine of peroxisome-deficient patients: evidence for peroxisomal metabolism in vivo

To determine the importance of peroxisomes and mitochondria in hydroxyeicosatetraenoic acid (HETE) oxidation in vivo, urinary excretion of 12- and 15-HETE was measured in eight patients with a peroxisome deficiency disorder (Zellweger syndrome) showing normal mitochondrial beta-oxidation capacity, in three patients with a defect of mitochondrial long-chain fatty acid oxidation (long-chain acyl-CoA dehydrogenase deficiency), and in eight healthy subjects. 12- and 15-HETE were identified and quantified by gas chromatography/negative ion chemical ionization-mass spectrometry and specific RIA. The free compounds were found exclusively in the urine of peroxisome-deficient subjects (12-HETE: median 26 pg/mL, range 17-36 pg/mL; 15-HETE: median 40 pg/mL, range 29-61 pg/mL), whereas both compounds were below the detection limit (< 0.5 pg/mL) in the urine of patients with defective mitochondrial long-chain fatty acid oxidation and normal subjects (p < 0.002). These results implicate that peroxisomes are the main cellular organelle responsible for HETE oxidation in vivo. Analysis of HETE excretion in urine represents an additional new specific diagnostic tool in patients with Zellweger syndrome.

Anandamide hydroxylation by brain lipoxygenase:metabolite structures and potencies at the cannabinoid receptor

Anandamide (arachidonyl ethanolamide) is a compound that was identified from porcine brain lipids by its ability to bind to the brain cannabinoid receptor. This study assessed anandamide as a substrate for a brain lipoxygenase and characterised the brain metabolite 12-hydroxyanandamide. Anandamide was also compared with arachidonic acid as a lipoxygenase substrate by examining enzyme kinetics in the presence of either of the two compounds. In addition, a non-mammalian enzyme was used to generate 11- and 15-hydroxy-anandamide in order to compare the cannabinomimetic properties of a range of anandamide derivatives. A ligand displacement assay indicated a large variation in the affinity of anandamide metabolites for the brain cannabinoid receptor. The brain metabolite, 12-hydroxyanandamide had an affinity twice that of anandamide, although the 11- and 15- hydroxy-metabolites were considerably poorer ligands of this receptor. Consistent with the receptor binding data, 12-hydroxyanandamide (unlike 15-hydroxyanandamide) inhibited forskolin-stimulated cAMP synthesis, indicating it to be a functional agonist at the brain cannabinoid receptor. Pharmacological studies of the capacity of anandamide and its metabolites to inhibit the murine vas deferens twitch response indicated the 12-hydroxy-metabolite to be less active than the parent compound, but a better cannabinomimetic than 15-hydroxyanandamide.

Triggering of a phospholipase D pathway upon mitogenic stimulation of human peripheral blood mononuclear cells enriched with 12(S)-hydroxyicosatetraenoic acid

The influence of 12(S)-hydroxyicosatetraenoic acid (12-HETE), that we have previously shown to decrease the proliferative response of human lymphocytes to mitogens, on diacylglycerol and phosphatidic acid (PtdOH) formation was investigated in stimulated human peripheral blood mononuclear cells (PBMC). When human PBMC were first enriched with 12-HETE, then stimulated by the mitogenic lectin concanavalin A (Con A), the production of PtdOH normally associated with Con A stimulation was markedly increased as compared with non-enriched cells. The Con-A-induced rise in the PtdOH mass was markedly decreased by 1% ethanol in 12-HETE-enriched cells, whereas it was unaffected in control cells stimulated by Con A alone. Furthermore, in [3H]arachidonic-acid-labelled cells previously enriched with 12-HETE, the formation of [3H]arachidonic-acid-labelled phosphatidylalcohol was significantly increased upon Con A stimulation, no phosphatidylalcohol being synthesized in non-enriched cells. Collectively, these results suggest that, in the presence of 12-HETE, Con A stimulates a phospholipase D activity which was not triggered by Con A alone. These data are consistent with the lack of effect of suramin, reported as a phospholipase D inhibitor, which we observed in cells stimulated by Con A alone and with the suramin-induced decrease of PtdOH mass in 12-HETE-plus-Con-A-treated cells. Moreover, 12-[3H]HETE-enriched PBMC produced a significant amount of 12-[3H]HETE-containing PtdOH (0.4% of the total PtdOH) in resting conditions. Upon mitogenic stimulation by Con A, the phorbol ester tetradecanoylphorbol acetate or the anti-CD3 mAb OKT3, this proportion was decreased to 0.1-0.2%, since the total PtdOH mass was more drastically increased than the 12-HETE-containing PtdOH species. Although present in relatively low amount in stimulated cells, 12-HETE-containing PtdOH species might have been generated in strategic compartments of the membrane bilayer so that the following events involved in the transduction of the mitogenic signal could be impaired. GC analyses have pointed out drastic variations in the fatty acid composition of PtdOH in non-enriched and in 12-HETE-enriched stimulated cells. Especially PtdOH synthesized in 12-HETE-enriched cells upon Con A stimulation contained a higher amount of saturated fatty acids and a lower amount of arachidonic acid than that formed in control cells stimulated with Con A alone. Such saturated PtdOH species with a low arachidonic acid content are very likely to have a low mitogenic potential.

12(S)-hydroxyeicosatetraenoic acid and 13(S)-hydroxyoctadecadienoic acid regulation of protein kinase C-alpha in melanoma cells: role of receptor-mediated hydrolysis of inositol phospholipids

Protein kinase C (PKC) isoenzymes are essential components of cell signaling. In this study, we investigated the regulation of PKC-alpha in murine B16 amelanotic melanoma (B16a) cells by the monohydroxy fatty acids 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE] and 13(S)-hydroxyoctadecadienoic acid [13(S)-HODE]. 12(S)-HETE induced a translocation of PKC-alpha to the plasma membrane and focal adhesion plaques, leading to enhanced adhesion of B16a cells to the matrix protein fibronectin. However, 13(S)-HODE inhibited these 12(S)-HETE effects on PKC-alpha. A receptor-mediated mechanism of action for 12(S)-HETE and 13(S)-HODE is supported by the following findings. First, 12(S)-HETE triggered a rapid increase in cellular levels of diacylglycerol and inositol trisphosphate in B16a cells. 13(S)-HODE blocked the 12(S)-HETE-induced bursts of both second messengers. Second, the 12(S)-HETE-increased adhesion of B16a cells to fibronectin was sensitive to inhibition by a phospholipase C inhibitor and pertussis toxin. Finally, a high-affinity binding site (Kd = 1 nM) for 12(S)-HETE was detected in B16a cells, and binding of 12(S)-HETE to B16a cells was effectively inhibited by 13(S)-HODE (IC50 = 4 nM). In summary, our data provide evidence that regulation of PKC-alpha by 12(S)-HETE and 13(S)-HODE may be through a guanine nucleotide-binding protein-linked receptor-mediated hydrolysis of inositol phospholipids.

The linoleic acid metabolite 13-HODE modulates degranulation of human polymorphonuclear leukocytes

The effect of the linoleic acid metabolite 13-hydroxyoctadecadienoic acid human polymorphonuclear leukocytes (PMNs) was investigated by measuring the expression of CD11b and CD67 on the plasma membrane. 13-HODE (5 microM) by itself induced degranulation of PMNs, but to a lesser extent as compared to PAF and fMLP. In addition, 13-HODE was found to inhibit the PAF-induced degranulation whereas an additive effect on the fMLP-induced PMNs degranulation was observed. These results indicate that 13-HODE can play a modulatory role in degranulation of PMNs.

Esterification of 12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid into the phospholipids of human peripheral blood mononuclear cells: inhibition of the proliferative response

12-hydroxy-eicosatetraenoic acid (12-HETE), the lipoxygenase metabolite of arachidonic acid produced by activated platelets, has been shown to accumulate in peripheral blood mononuclear cells (PBMC) of elderly people. 12-HETE being antimitogenic for lymphocytes, its accumulation in blood cells might be involved in the well-known decline in immune function which accompanies aging. Because HETEs have been shown to be rapidly metabolized and/or incorporated into cellular lipids in a variety of cell types, we have investigated the uptake, metabolism, and intracellular distribution of exogenous 12-HETE by human PBMC. [3H]-12-HETE was dose and time dependently incorporated by PBMC and also metabolized to more polar products. These polar metabolites were mainly released extracellularly and only marginally esterfied in phospholipids. Although [3H]-12-HETE radiolabel was preferentially associated with phosphatidylcholine, especially after prolonged labeling incubations or following successive short labeling pulses, a substantial amount of radiolabel was also found associated with phosphatidylinositol (20-50% of the labeled phospholipids). The stability of 12-HETE in the phospholipid pool was comparable to that reported for most other cell types, with 50% of the initial radiolabel being still present after 18 hr. Upon exposure to mitogenic activation, 12-HETE-labeled PBMC released unmodified 12-HETE from phosphatidylinositol. In addition, 12-HETE dose dependently inhibited the proliferative response of PBMC to Con A stimulation. These results suggest that 12-HETE esterification in phospholipids might lead to the generation of unusual lipid second messengers with impaired capacity to transduce activation signals, thus decreasing lymphocyte function.

Characterization of specific subcellular 15-hydroxyeicosatetraenoic acid (15-HETE) binding sites on rat basophilic leukemia cells

15-Hydroxyeicosatetraenoic acid [15-(S)-HETE], a major arachidonic acid metabolite produced from the 15-lipoxygenase pathway, has been characterized as an antiinflammatory cellular mediator since it can inhibit the in vivo and in vitro formation of the proinflammatory leukotrienes via the 5-lipoxygenase pathway in various cells. 15-HETE has been confirmed to inhibit the 5-lipoxygenase in rat basophilic leukemia cell (RBL-1) homogenates with an I50 = 7.7 microM. The I50 of the 12-HETE isomer was 6 microM whereas prostaglandin F2 alpha was ineffective. In order to examine the mechanistic basis underlying the inhibitory action of 15-HETE, association assays of [3H]-15-HETE with RBL-1 subcellular fractions were carried out. The presence of the zwitterionic detergent CHAPS enhanced specific [3H]-15-HETE binding in the membrane fractions three-fold and specific 15-HETE binding was distributed among the nuclear (32%)-, granule (19%)-, plasma membrane (35%)-, and cytosol (14%)-enriched fractions. Studies using combined granule and plasma membrane enriched-, CHAPS treated-fractions showed that [3H]-15-HETE binding was time-dependent, specific and reversible, sensitive to pertussis toxin treatment, and indicated a single class of binding sites with a Kd = 460 +/- 160 nM and Bmax = 5.0 +/- 1.1 nM. Competition experiments showed that the order of 15-HETE or analogs in inhibiting the binding of [3H]-15-HETE was: 15(S)-HETE > or = 12-(S)-HETE = 5-(S)-HETE > 15-(R)-HETE > arachidonic acid. Prostaglandin F2 alpha and lipoxin B4 were ineffective as competitors. The similar profiles of the binding assays and inhibition of the 5-lipoxygenase suggest that 15-HETE binding sites may mediate this inhibitory action of 15-HETE.

Eicosanoid biosynthesis by hemocytes from the tobacco hornworm, Manduca sexta

We describe eicosanoid biosynthesis by microsomal-enriched preparations of hemocytes from larvae of the tobacco hornworm Manduca sexta. Four major prostaglandins, PGA2, PGE2, PGD2, and PGF2 alpha, and a lipoxygenase product that co-chromatographed with 15-hydroxyeicosatetraenoic acid (HETE) were synthesized under most conditions. The HETE's fraction was the predominant product. Eicosanoid biosynthesis was sensitive to experimental conditions, including incubation time, temperature, and protein concentration. Optimal biosynthesis was observed with 1.5 mg of microsomal-enriched protein, incubated at 30 degrees C for 2 min. The hemocyte preparation is sensitive to low dosages of naproxin and esculetin. As in mammals, most lipoxygenase activity (87%) was localized in the cytosolic fraction of hemocytes. Unlike mammals, in which PGH synthase is associated with intracellular membranes, the hemocytic activity was detected in microsomal (59%), cytosolic (35%) and mitochondrial fractions (5%).

Transcellular biosynthesis of lipoxin A4 during adhesion of platelets and neutrophils in experimental immune complex glomerulonephritis

Polymorphonuclear neutrophils are important effectors of injury in host defense and inflammation. Many inflammatory diseases are self-limiting, raising the possibility that compounds are generated in vivo during the course of inflammation that inhibit neutrophil recruitment and tissue destruction. Lipoxins, a more recent addition to the families of bioactive eicosanoids, are potential candidates in this regard. Lipoxins are generated via pathways that initially involve the dual lipoxygenation of arachidonic acid and are potent inhibitors of several neutrophil trafficking events in vitro. Here, we present evidence that lipoxin A4 is generated in rat kidneys during experimental immune complex-mediated glomerulonephritis in vivo. Renal lipoxin A4 levels were markedly reduced by prior depletion of animals of either neutrophils or platelets, suggesting that most lipoxin A4 generated in vivo was derived from transcellular biosynthetic pathways during platelet-neutrophil interactions. Electron microscopic examination of glomerulonephritic kidneys revealed areas of intimate contact between neutrophils and platelets within the lumen of glomerular capillaries. P-selectin on platelets is an important mediator of platelet-neutrophil adhesion in vitro and in vivo. Prior treatment of animals with a blocking monoclonal antibody (mAb) against P-selectin (mAb CY1747), but not an isotype-matched non-blocking control mAb (mAb PNB1.6), caused striking inhibition of lipoxin A4 generation without attenuating neutrophil recruitment. Anti-P-selectin mAb also blunted transcellular lipoxin A4 generation during coincubations of activated neutrophils and platelets in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of hydroxy fatty acids as pentafluorobenzyl ester, trimethylsilyl ether derivatives by electron ionization gas chromatography/mass spectrometry

Electron ionization (EI) gas chromatography/mass spectrometry (GC/MS) analysis of pentafluorobenzyl ester-trimethyl sllyl ether (PFB-TMS) derivatives of hydroxy-subshtuted fatty acids provides structural information comparable to that obtained in analysis of methyl ester-trimethyl silyl ether (Me-TMS) derivatives. Use of this derivative eliminates the need to prepare two separate derivatives, the PFB-TMS derivative for molecular weight determination by electron capture ionization (negative ions) analysis and the Me-TMS derivative for structural determination by EI GC/MS analysis. The relative abundance of fragment ions observed during EI GC/MS analysis of these derivatized unsaturated fatty acids indicates the location of the -OTMS substituents relative to double bond positions in those cases studied. The most abundant fragment ions are observed when the compound contains an unsaturation two carbon atoms removed from the -OTMS ether carbon (the β-OTMS position). The "saddle effect" observed in the GC/MS analyses of some derivatized monohy- droxy unsaturated fatty acids is suggested to be due to a thermally allowed pericyclic double bond rearrangement and indicates the presence of a conjugated diene one carbon atom removed from the -OTMS ether carbon (the α-OTMS position). The saddle effect is most prominent for fatty acids that contain additional unsaturation separated by a single methylene unit from the conjugated diene moiety.

Characterization of integrin expression and regulation on SW-480 human colon adenocarcinoma cells and the effect of rhodostomin on basal and upregulated tumor cell adhesion

Integrins are a superfamily of cell surface glycoproteins that mediate cell-extracellular matrix (ECM) and cell-cell adhesion. Immunofluorescence microscopy and flow cytometric analysis using anti-integrin mAbs as the primary binding ligands demonstrated that the platelet integrin receptor alpha IIb beta 3, as well as alpha v beta 3, alpha 5 beta 1 and alpha 6 beta 1, are present on the surface of SW-480 human colon adenocarcinoma cells. Monoclonal antibodies (mAbs) against alpha IIb beta 3 and alpha 5 beta 1 inhibited unstimulated basal adhesion to fibronectin by approximately 30% and 40%, respectively. The surface immunoreactivity of tumor cells for alpha IIb beta 3 was enhanced by pretreatment (5 min) with a phorbol ester (12-O-tetradecanoylphorbol-13-acetate (TPA)) or a lipoxygenase metabolite of arachidonic acid, 12-hydroxyeicosatetraenoic acid (12-HETE) in a dose- and time-dependent manner. SW-480 cells possess a large intracellular pool of alpha IIb beta 3, from which the receptor complex translocates to the cell surface following pretreatment with TPA or 12(S)-HETE. This pretreatment enhances adhesion to fibronectin, which is mediated exclusively by alpha IIb beta 3 integrins. Staurosporine was found to block alpha IIb beta 3 up-regulation and enhanced-adhesion. TPA and 12(S)-HETE also facilitated the redistribution of alpha IIb beta 3 during the enhanced-spreading process. Rhodostomin, an Arg-Gly-Asp- (RGD) containing antiplatelet snake venom peptide, was about 400-times more potent than RGDS at inhibiting control, TPA- or 12(S)-HETE-enhanced adhesion of SW-480 cells to fibronectin. The binding of mAbs against alpha IIb beta 3, alpha v beta 3 and alpha 5 beta 1 was inhibited by pretreatment with rhodostomin, suggesting that rhodostomin binds via its RGD sequence to multiple integrin receptors (i.e., alpha IIb beta 3, alpha v beta 3, alpha 5 beta 1) expressed on the SW-480 cell surface, inhibiting cell adhesion to ECM.

12-lipoxygenases and 12(S)-HETE: role in cancer metastasis

Arachidonic acid metabolites have been implicated in multiple steps of carcinogenesis. Their role in tumor cell metastasis, the ultimate challenge for the treatment of cancer patients, are however not well-documented. Arachidonic acid is primarily metabolized through three pathways, i.e., cyclooxygenase, lipoxygenase, and P450-dependent monooxygenase. In this review we focus our attention on one specific lipoxygenase, i.e., 12-lipoxygenase, and its potential role in modulating the metastatic process. In mammalian cells there exist three types of 12-lipoxygenases which differ in tissue distribution, preferential substrates, and profile of their metabolites. Most of these 12-lipoxygenases have been cloned and sequenced, and the molecular and biochemical determinants responsible for catalysis of specific substrates characterized. Solid tumor cells express 12-lipoxygenase mRNA, possess 12-lipoxygenase protein, and biosynthesize 12(S)-HETE [12(S)-hydroxyeicosatetraenoic acid], as revealed by numerous experimental approaches. The ability of tumor cells to generate 12(S)-HETE is positively correlated to their metastatic potential. A large collection of experimental data suggest that 12(S)-HETE is a crucial intracellular signaling molecule that activates protein kinase C and mediates the biological functions of many growth factors and cytokines such as bFGF, PDGF, EGF, and AMF. 12(S)-HETE plays a pivotal role in multiple steps of the metastatic 'cascade' encompassing tumor cell-vasculature interactions, tumor cell motility, proteolysis, invasion, and angiogenesis. The fact that 12-lipoxygenase is expressed in a wide diversity of tumor cell lines and 12(S)-HETE is a key modulatory molecule in metastasis provides the rationale for targeting these molecules in anti-cancer and anti-metastasis therapeutic protocols.

Pore formation by the Escherichia coli alpha-hemolysin: role for mediator release from human inflammatory cells

The Escherichia coli alpha-hemolysin represents a potent stimulus for inflammatory mediator release (O2-, beta-glucuronidase release, and leukotriene generation) from human polymorphonuclear granulocytes, for histamine release from a suspension of human lymphocyte/monocyte basophil cells (LMB), and for serotonin release and 12-hydroxyeicosatetraenoic acid generation from human platelets. In contrast, the E. coli alpha-hemolysin leads to a downregulation of cytokine release (interleukin-1 beta [IL-1 beta], IL-6, and tumor necrosis factor alpha) from human LMB. Recently, it became apparent that the E. coli alpha-hemolysin is composed of several functional structures. We analyzed the role of pore formation, pore stability, and calcium-dependent membrane binding for inflammatory mediator release by using washed bacteria as well as culture supernatants of isogenic recombinant E. coli strains expressing no hemolysin (Hly-), the wild-type hemolysin (Hly+), or hemolysin molecules deficient or modulated in defined functions (pore formation, calcium-dependent membrane binding, or pore stability). In human granulocytes and platelets, mutant hemolysin with enhanced pore stability did not lead to a further increase in induction; mutant hemolysin deficient in pore-forming activity or calcium-dependent membrane binding no longer induced leukotriene B4 generation or beta-glucuronidase release compared with the wild-type hemolysin. Similar results were obtained with regard to histamine release from human LMB. The induction of cytokine release from human LMB differed depending on the type of mutant E. coli alpha-hemolysin. The wild-type hemolysin, the mutant hemolysin with enhanced pore-forming activity, and, to a lesser degree, the mutant hemolysin deficient in pore-forming activity decreased cytokine release (IL-1 beta, IL-6, IL-8, and tumor necrosis factor) compared with untreated cells. In contrast, the mutant hemolysin deficient in calcium-dependent membrane binding led to an increase of up to 50% in cytokine release compared with that by unstimulated cells. Our results indicate that simultaneous expression of the pore-forming and calcium-dependent membrane-binding activities of the hemolysin molecule was necessary to obtain the full cellular inflammatory response pattern observed with the wild-type hemolysin.

Modulation of the transcellular metabolism of 12(S)HETE by 10-11 reductase activity in cultured rat aortic smooth muscle cells

Cultured rat aortic smooth muscle cells (SMC) metabolize 12(S)hydroxyeicosatetraenoic acid (12(S)HETE) by two different pathways; beta-oxidation leading to 16:3(8-OH), and 10-11 reductase activity producing 20:3(12-OH) which is beta-oxidized to 16:2(8-OH). In this work, we demonstrate that 10-11 reductase activity is modulated in cultured rat aortic SMC as a function of cell state (proliferating vs quiescent) and stimulated by serum. Most of the 20:3(12-OH) is recovered in the incubation medium but a significant part is esterified into phospholipids. By comparison with its parent compound, 12(S)HETE, 20:3 (12-OH) is mainly incorporated into phosphatidyl-choline and phosphatidyl-ethanolamine, suggesting that it may affect cellular functions. Taken together, these findings may be relevant to the effects of 12(S)HETE on vascular SMC functions related to atherosclerotic development.

Incorporation of polyunsaturated fatty acids into phospholipids of hemocytes from the tobacco hornworm, Manduca sexta

We examined the incorporation of four radioactive fatty acids, 18:1n-9, 18:2n-6, 20:4n-6 and 20:5n-3, into cellular lipids of hemocytes from tobacco hornworms, Manduca sexta. Most of the radioactivity associated with 18:1n-9 was recovered from triacylglycerols (TGs), and the radioactivity associated with 18:2n-6 was heavily incorporated into phospholipids (PLs) and TGs. Most of the radioactivity associated with the two eicosanoid-precursor polyunsaturated fatty acids (PUFAs), 20:4n-6 and 20:5n-3, was incorporated into PLs. The incorporated fatty acids were redistributed among the lipid classes during 2 h incubations. The two C20 PUFAs were moved from PLs to TGs. While 18:2n-6 underwent little change, 18:1n-9 was redistributed from TGs to PLs. Within PLs, each of the fatty acids were incorporated into phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PtG) and phosphatidylserine/inositol (PS/PI). The incorporation patterns changed over time, indicating that the incorporated fatty acids were redistributed among the four PL fractions. The radioactivity associated with 18:1n-9 was mostly recovered from the sn-1 position of PC (59%) and PE (83%). Most of the radioactivity associated with 18:2n-6 was found in the sn-2 position of PC (88%) and PE (67%). Over 90% of the radioactivity associated with 20:5n-3 was recovered from the sn-2 position of PC and PE. Incorporation of 20:4n-6 differed from 20:5n-3 because more radioactivity was recovered from the sn-2 position of PC (93%) than PE (69%). These findings are in line with the general background of lipid biochemistry, from which incorporation of 20:4n-6 into PE marks a notable departure: 31% of the radioactivity associated with this acid was recovered from the sn-1 position of PE. These findings indicate that hemocytes from the tobacco hornworm elaborate a fatty acid incorporation system, which exhibits specificity with respect to fatty acid structure and lipid class.

Differences in the metabolism of eicosatetraenoic (20:4(n - 6)), tetracosatetraenoic (24:4(n - 6)) and triacontatetraenoic (30:4(n - 6)) acids in human neutrophils

The metabolism of [1-14C]eicosatetraenoic (arachidonic, 20:4(n - 6)), [1-14C]tetracosatetraenoic (24:4(n - 6)) and [1-14C]triacontatetraenoic (30:4(n - 6)) acids was studied in intact human neutrophils. [1-14C]20:4(n - 6) and [1-14C]24:4(n - 6) were efficiently taken up by the neutrophils, esterified into neutral lipids and phospholipids, and elongated by up to four carbon units. In contrast, [1-14C]30:4(n - 6) was poorly incorporated into the cells and remained predominantly in the original unesterified form. The [1-14C]tetraenoic fatty acids were mainly esterified into triacylglycerol, suggesting that this lipid class is important in the intracellular trafficking of polyunsaturated fatty acids. The leukocytes demonstrated a low capacity to beta-oxidize and desaturate the fatty acid substrates. In the presence of calcium ionophore A23187 the neutrophils converted [1-14C]20:4(n - 6) to a variety of radiolabelled oxygenated fatty acid derivatives including prostaglandins, thromboxanes, mono- and dihydroxylated fatty acids and leukotrienes. The major eicosanoid products were 5-monohydroxy-20:4(n - 6) and leukotriene B4. In contrast, [1-14C]24:4(n - 6) was metabolized to radiolabelled monohydroxylated fatty acids (predominantly the 9-hydroxy positional isomer) but not to other lipoxygenase or cyclooxygenase products by the calcium ionophore-stimulated cells. Negligible oxygenated fatty acid compounds were formed from [1-14C]30:4(n - 6), indicating that it is a poor substrate for the neutrophil cyclooxygenase and lipoxygenase enzymes.

Possible involvement of arachidonic acid and eicosanoids in metamorphic events in Hydractinia echinata (Coelenterata; Hydrozoa)

Upon induction of metamorphosis, larvae of the marine hydroid Hydractinia echinata release [14C]-arachidonic acid from previously labeled endogenous sources. The lipoxygenase inhibitors nordihydroguaiaretic acid and 5,8,11,14-eicosatetraynoic acid inhibited metamorphosis induced by Cs+ and 1,2-sn-dioctanoylglycerol, whereas the inhibitors of cyclooxygenase, indomethacin, and acetylsalicylic acid were ineffective, suggesting a role for lipoxygenase metabolites of arachidonic acid in induction of metamorphosis. Lipoxygenase products in Hydractinia echinata were isolated and identified by gas chromatography/mass spectrometry. 8- and 12-HETE were the most abundant metabolites. In cytosolic fractions from larvae activity of an arachidonic acid metabolizing enzyme, presumably a lipoxygenase, was found. The metabolic product was identified by 1H-NMR and chiral phase HPLC as 8(R)-HETE. Its production was strongly inhibited by NDGA, but not by indomethacin.

Enantiospecific synthesis of bioactive hydroxyeicosatetraenoic acids (HETEs) in Hydra magnipapillata

Recent reports have shown the occurrence of regiospecific and enantioselective lipoxygenase-mediated metabolism of arachidonic acid (AA) in cytosolic extracts of marine and freshwater hydroids. Here we report that cytosolic extracts of Hydra magnipapillata are unique among hydrozoans for their capability of converting AA into two major metabolites which showed chromatographic, mass spectrometric and nuclear magnetic resonance properties identical to those of 11-R- and 12-S-hydroxyeicosatetraenoic acid (11-R-HETE and 12-S-HETE). The production of neither compound was affected by co-incubation of H. magnipapillata extracts with the cytochrome P-450 inhibitor proadifen. The 5- and 12-lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA), while inhibiting 12-S-HETE formation at high concentrations, did not influence 11-R-HETE production, thus suggesting the co-localisation, unprecedented in hydroids, of two separate enantioselective lipoxygenase-like activities. The possible role of the two metabolites in the control of hydroid body pattern was investigated. At low micromolar concentrations, both enantiomers of 11-HETE inhibited diacylglycerol-induced ectopic head formation (EHF), while 12-S-HETE, and its likely precursor 12-S-hydroperoxy-eicosatetraenoic acid (12-S-HPETE), enhanced bud formation, thus providing the first example of endogenous metabolites controlling, respectively, hydroid 'head activation potential' and asexual reproduction.

Decreased arachidonic acid metabolism in human platelets by autologous neutrophils: possible role of cell adhesion

The amount of the 12-lipoxygenase and cyclo-oxygenase products, 12(S)-hydroxy-(Z,Z,E,Z)-5,8,10,14-eicosatetraenoic acid (12-HETE) and 12(S)-hydroxy-(E,E,Z)-5,8,10-heptadecatrienoic acid (HHT), in human platelets stimulated by thrombin (0.1 and 2.5 units/ml), was studied in the presence of autologous neutrophils. A decreased formation of both products was induced by unstimulated neutrophils or neutrophils challenged with N-formylmethionyl- leucyl-phenylalanine (0.1 microM) or Ca2+ ionophore A23187 (0.15 microM). The effect of neutrophils was observed only in the presence of Ca2+. 12-HETE and HHT were also produced in platelets stimulated with thrombin in the absence of Ca2+ and/or Mg2+, but their level was not altered by neutrophils. 12(S),20-Dihydroxy-(Z,Z,E,Z)-5,8,10,14-eicosatetraenoic acid (12,20-DHETE), the cytochrome P-450 product from 12-HETE in neutrophils, was hardly detected, and its level did not compensate for the decrease in 12-HETE observed after platelet and neutrophil co-incubation. 5(S),12(S)-Dihydroxy-(E,Z,E,Z)- 6,8,10,14-eicosatetraenoic acid (5(S),12(S)-DHETE), the 5-lipoxygenase product of 12-HETE in neutrophils, was never detectable. In addition, the inhibition of 12-HETE and HHT formations appeared not to be due to degradation or thrombin uptake by neutrophils, nor was the decrease observed when the two cell populations were physically separated. A monoclonal antibody against the human platelet glycoprotein GMP140 (CD62), mediating Ca(2+)-dependent platelet-neutrophil adhesion, mimicked the inhibitory effect of neutrophils in a dose-dependent fashion. Furthermore, the 12-HETE and HHT productions were not affected when platelets were stimulated in the presence of neutrophils previously incubated with sialidase, which removes the sialic acid from a sialyl Lewis(x) structure assumed to be the neutrophil receptor for platelet GMP140. We conclude that the decrease in thrombin-stimulated 12-HETE and HHT formation observed when platelets were co-incubated with autologous neutrophils might be the consequence of platelet-neutrophil adherence, presumably through platelet GMP140.

Polyunsaturated-fatty-acid oxidation in Hydra: regioselectivity, substrate-dependent enantioselectivity and possible biological role

A novel and abundant lipoxygenase-like activity converting cis-eicosa-5,8,11,14-tetraenoic acid (arachidonic acid) into (11R)-hydroxyeicosatetraenoic acid has been recently described in homogenates of the freshwater hydrozoan Hydra vulgaris. In this study, other substrates for this enzyme were selected from the polyunsaturated fatty acids (PUFAs) present in H. vulgaris, and the chemical natures of the hydroperoxy and hydroxy derivatives produced, as well as the activity of some of the latter on hydroid tentacle regeneration, were investigated. The highest conversion among C20 fatty acids was observed for arachidonic acid, and among C18 fatty acids for cis-octadeca-9,12,15- and cis-octadeca-6,9,12-trienoic (alpha- and gamma-linolenic) acids. Cis double bonds on the 10th carbon atom from the aliphatic end of the substrate (e.g. C-9, C-11 and C-13 respectively in C18, C20 and C22 PUFAs) were regiospecifically peroxidized. Conversely, trans-octadeca-9,12-dienoic (linoelaidic) acid was not a substrate for lipoxygenase activity. Enantioselectivity of lipoxygenation depended on the degree of unsaturation of the substrate, with the amount of the R enantiomer increasing when passing, for example, from cis-eicosa-11,14-dienoic to cis-eicosa-5,8,11,14,17-pentaenoic acid. Regiospecific formation of keto acids was observed only when incubating C18 PUFAs. Commercially available hydroxyacids corresponding to the reaction products of some of the most abundant H. vulgaris PUFAs were tested for effects on Hydra tentacle regeneration. An enhancement of average tentacle number, in a fashion depending on the stereochemistry and on the number of double bonds, was found for two compounds, thus suggesting for the 11-lipoxygenase-like enzyme a role in the production of metabolites potentially active in the control of hydroid regenerative processes.

Prostaglandin biosynthesis by fat body from the tobacco hornworm, Manduca sexta

We describe prostaglandin (PG) biosynthesis by microsomal-enriched preparations of fat body from larvae of the tobacco hornworm Manduca sexta. Four major PGs were synthesized under most experimental conditions, PGA2, PGE2, PGD2 and PGF2 alpha. PGA2, was the predominant product under most conditions. Unlike mammals, in which PGA2, is generally thought to arise from non-enzymatic rearrangements of PGE2, the fat body preparations did not convert exogenous PGE2 into PGA2. These findings suggest that PGA2 is an important fat body product that is synthesized by a route that does not involve PGE2. The PG synthase activity and the overall profile of PG synthesis were sensitive to experimental conditions, including incubation time, temperature, and protein concentration. Optimal PG biosynthesis was observed with 1 mg of microsomal-rich protein, incubated at 30 degrees C for 1-2 min. The fat body preparations is sensitive to two non-steroidal anti-inflammatory drugs, indomethacin and naproxen, both of which inhibited PG synthesis at low dosages.

15-HETE: selective incorporation into inositol phospholipids of MDCK cells

The interaction of 15-hydroxyeicosatetraenoic acid (15-HETE) and cultured MDCK renal tubular epithelial cells was investigated to determine whether incorporation of this lipoxygenase product will affect polyphosphoinositide formation. MDCK cells were incubated with 1 microM [3H]-15-HETE for 15 to 120 minutes. Maximum uptake occurred between 15 and 30 minutes, and after 60 minutes, 70% of the incorporated 15-HETE was present in the phosphatidylinositol (PI) fraction. Some 15-HETE was also incorporated into phosphatidylinositol-4-monophosphate (PIP) and phosphatidylinositol-4,5-bisphosphate (PIP2). However, even though more 15-HETE than arachidonic acid was incorporated into PI, the fractional amount of 15-HETE present in the polyphosphoinositides was smaller than arachidonic acid. Therefore, although 15-HETE is selectively channeled into PI, conversion of PI species containing 15-HETE to PIP and PIP2 is relatively impaired. This suggests that either PI containing 15-HETE is a less effective substrate for phosphorylation, or PI containing arachidonic acid is a preferred substrate. MDCK cells converted 15-HETE to polar metabolites that were released into the extracellular fluid. This process may constitute a renal tubular mechanism for the clearance of 15-HETE and related lipoxygenase products.

Fatty acid compositions of phospholipids and triacylglycerols from selected terrestrial arthropods

The fatty acid compositions of phospholipids and triacylglycerols from selected orthognath spider tissues, scorpion body segments, whole millipedes, and whole labidognath spiders were determined. The major components were C16 and C18 saturated and unsaturated fatty acids as well as C20 polyunsaturated fatty acids. The eicosanoid precursor polyunsaturated fatty acids 20:4n-6 and 20:5n-3 were present in substantial proportions of phospholipids in all tissues examined. The fatty acid profiles of these terrestrial arthropods differ markedly from corresponding profiles of terrestrial insects in that substantially greater proportions of C20 polyunsaturated fatty acids are present in the organisms in this study. This finding supports the idea that maintaining low proportions of C20 polyunsaturated fatty acids is a special condition of terrestrial insects.

Remodeling of neutrophil phospholipids with 15(S)-hydroxyeicosatetraenoic acid inhibits leukotriene B4-induced neutrophil migration across endothelium

5-Lipoxygenase products, such as leukotrienes, are important stimuli for leukocyte-mediated tissue injury in acute inflammation. 15-Hydroxyeicosatetraenoic acid (15-HETE) is an eicosanoid generated by a variety of cell types via the actions of 15-lipoxygenases and, in addition, cyclooxygenases and epoxygenases. 15-HETE levels are frequently elevated at sites of inflammation, and extracellular 15(S)-HETE is esterified rapidly into neutrophil (PMN) phospholipids in vitro to levels that are comparable with arachidonic acid. We present evidence that remodeling of PMN phospholipids with 15(S)-HETE stereoselectively inhibits PMN migration across endothelium in response to leukotriene B4 (LTB4) and other chemoattractants. Esterified 15(S)-HETE causes a striking reduction in the affinity of LTB4 cell-surface receptors for their ligand and inhibition of LTB4-triggered stimulus-response coupling. As a result of these actions, esterified 15(S)-HETE attenuates the cytoskeletal rearrangements and CD11/CD18-mediated adhesive events that subserve directed locomotion of PMN across endothelium. These observations indicate that products of the 5-lipoxygenase and 15-lipoxygenase pathways can exert counterbalancing influences on PMN trafficking across endothelium. They suggest that 15(S)-HETE may be a potent endogenous inhibitor of PMN-endothelial interactions in vivo and serve to limit or reverse acute inflammation.

Expression of prostaglandin H2-mediated mechanism of vascular contraction in hypertensive rats. Relation to lipoxygenase and prostacyclin synthase activities

We tested the hypothesis that a prostanoid-mediated mechanism of vascular contraction is expressed in rats with aortic coarctation-induced hypertension. Rings of descending thoracic aorta taken from normotensive and hypertensive rats were contrasted in terms of constrictor responsiveness to arachidonic acid (AA), AA-induced release of eicosanoids, and ability to convert exogenous prostaglandin (PG) H2 to PGI2. AA (10(-8) to 10(-5) mol/L) increased isometric tension in aortic rings (bathed in Krebs' bicarbonate buffer) of hypertensive but not normotensive rats. AA (10(-5) mol/L) also elicited the release of PGI2, PGE2, thromboxane (TX) A2, and monohydroxyeicosatetraenoic acids (HETEs); this release from the aortic rings of hypertensive rats exceeded the corresponding release from the aortic rings of normotensive rats. However, the rate of conversion of exogenous PGH2 to PGI2 by aortic rings of hypertensive rats was < 50% the rate of conversion by aortic rings of normotensive rats. The constrictor effect of AA in aortic rings of hypertensive rats was abolished by an inhibitor of cyclooxygenase (indomethacin, 10 mumol/L) and a blocker of TXA2-PGH2 receptors (SQ29548, 1 mumol/L) but was not affected by an inhibitor of TXA2 synthesis (CGS13080, 10 mumol/L), suggesting mediation by PGH2. The lipoxygenase inhibitor baicalein (75 mumol/L) also attenuated the constrictor effect of AA in aortic rings of hypertensive rats while decreasing the associated release of HETEs and correcting the impairment in the conversion of PGH2 to PGI2.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitation of monohydroxy fatty acids by high-performance liquid chromatography with fluorescence detection

A high-performance liquid chromatographic (HPLC) procedure for the separation of hydroxyeicosatetraenoic acids (HETEs) and hydroxyoctadecanoic acids (HODEs) after derivatization of the hydroxy group with 1-anthroylnitrile is described. Anthroyl esters of HETEs were separated from those of HODEs by reversed-phase HPLC. The positional isomers of the HETEs and HODEs were well separated by normal-phase HPLC. The fluorimetric HPLC method has a high sensitivity and naturally occurring HETEs can be quantitatively analyzed at the picomolar level. The amount of 5-HETE in A23187-stimulated polymorphonuclear leukocytes (PMNLs) was determined by the present method. PMNLs produced approximately 150 ng of 5-HETE per 10(7) cells at 5 min stimulation. The amount of 5-HETE determined by fluorimetric detection was consistent with that determined by ultraviolet detection (235 nm).

Regulation of melanoma-cell motility by the lipoxygenase metabolite 12-(S)-HETE

Cellular motility, a prerequisite for metastasis of tumor cells, is affected by a 55-kDa tumor-cell-secreted cytokine which influences the migration of the producing cells and is called autocrine motility factor (AMF). Previous studies indicated that AMF stimulates motility by binding to its receptor, a cell-surface glycoprotein of 78 kDa (gp78), inducing its phosphorylation, activating a pertussis toxin (PT)-sensitive G-protein, and stimulating inositol metabolism. However, the intracellular signaling mechanisms which transduce and regulate the AMF motility response remain largely unknown. 12-(S)-HETE, a lipoxygenase metabolite of arachidonic acid which affects the cytoskeletal architecture of murine melanoma cells, also stimulates cell motility independently of PT-sensitive G-proteins and up-regulates gp78 surface expression. 12-(S)-HETE induces the phosphorylation of gp78 in a manner analogous to AMF and the motility response of these murine melanoma cells to both AMF and 12-(S)-HETE is inhibited by protein kinase C inhibitors. Furthermore, perturbation of the AMF receptor stimulated endogenous biosynthesis of 12(S)HETE. These results suggest the existence of an "autocrine motility cycle" which influences melanoma cell motility by gp78 activation, and production of second messengers which affect the cytoskeletal architecture and expression of the AMF receptor itself.