Hydroxyeicosatetraenoic acids (HETEs)

Monohydroxy fatty acids esterified to phospholipids are decreased in lesional psoriatic skin

Because of the increasing number of reports of the important roles of monohydroxy derivatives of poly-unsaturated fatty acids in the regulation of cell function, we determined the pools of unesterified and esterified monohydroxy fatty acids (MHFAs) in keratomed epidermal slices, taken from lesional and non-lesional psoriatic skin. Extracted phospholipids were separated by thin-layer chromatography. The isolated fractions of phosphatidylcholine (PC), phosphatidylinositol (PI) and phosphatidyl-ethanolamine (PE) were treated with phospholipase A2 to release fatty acids in the sn-2 position. Released MHFAs were separated by reversed-phase and straight-phase high-performance liquid chromatography and identified as the linoleic acid derivatives 9-hydroxy-octadecadienoic acid (9-HODE) and 13-hydroxy-octadecadienoic acid (13-HODE) and as the arachidonic acid derivative 15-hydroxy-eicosatetraenoic acid (15-HETE). These findings are consistent with the presence of unesterified 9-HODE, 13-HODE and 15-HETE. In contrast, 12-hydroxy-eicosatetraenoic acid (12-HETE), although found to be present in high amounts as unesterified 12-HETE, was not detectable in the phospholipids. When compared with non-lesional psoriatic skin, the levels of 9-HODE, 13-HODE and 15-HETE esterified to the sn-2 position of PC, PI and PE in lesional psoriatic skin were significantly decreased (to 28-78% of those in non-lesional skin). This depletion of MHFAs in specific phospholipids may be due to an imbalance between phospholipase and acyltransferase activities. Because the levels of esterified MHFAs may influence signal transduction and eicosanoid metabolism the described changes may be relevant for the inflammatory processes occurring in psoriasis.

Biosynthesis, structure and biological activity of hydroxyeicosatetraenoic acids in Hydra vulgaris

Recent reports have suggested the involvement of arachidonic acid (AA) and its metabolites in the control of body pattern, head and tentacle regeneration and bud formation in Hydra spp. Here we describe for the first time the biosynthesis of hydroxyeicosatetraenoic acids (HETEs) in vitro by hydroid cytosolic extracts. Incubation of both unlabelled and tritiated AA with homogenates of Hydra vulgaris led to the conversion of up to 11% of the exogenous fatty acid into mainly two metabolites. These were characterized as 11-hydroperoxyeicosatetraenoic acid (11-HPETE) and 11-HETE by means of a combination of chromatographic, chemical, 1H-n.m.r. and electron-impact m.s. techniques. Trace amounts of 9-HETE and 12-HETE were also found. Analysis of 11-HETE by chiral-phase h.p.l.c. revealed that this metabolite was composed mainly of the R enantiomer. The production of 11-HPETE and 11-HETE was found to be: (1) associated with the cytosolic fraction of Hydra homogenates; (2) dependent on AA concentration, incubation time and protein amount in the homogenates; (3) unaffected by co-incubation with the 5- and 12-lipoxygenase inhibitors, 5,8,11-eicosatriynoic acid and nordihydroguaiaretic acid, the cyclo-oxygenase inhibitor, indomethacin, or the cytochrome P-450 inhibitors, proadifen and methoxalen. These results strongly suggest the presence of a very active (R)-11-lipoxygenase in H. vulgaris. The activity of both R and S enantiomers of synthetic 9-, 11- and 12-HETE and of 'endogenous' 11-HETE was studied on tentacle regeneration and bud formation in decapitated Hydra. Although almost all compounds tested inhibited budding, only endogenous 11-HETE and synthetic (R)-11-HETE significantly enhanced the average number of tentacles, thus suggesting that this eicosanoid might be one of the cellular regulators of regeneration in H. vulgaris.

Human alveolar macrophages have 15-lipoxygenase and generate 15(S)-hydroxy-5,8,11-cis-13-trans-eicosatetraenoic acid and lipoxins

Eicosanoids derived from lipoxygenase (LO)-catalyzed reactions play important roles in pulmonary inflammation. Here, we examined formation of LO-derived products by human alveolar macrophages (HAM). HAM converted [1-14C]-arachidonic acid to a product carrying 14C-radiolabel that was identified as 15(S)-hydroxy-5,8,11-cis-13-trans-eicosatetraenoic acid (15-HETE) by physical methods. 15-LO mRNA was demonstrated in HAM by reverse transcription-polymerase chain reaction. Incubation of HAM for 3 d with interleukin 4(IL-4) before exposure to [1-14C]arachidonic acid led to both increased mRNA for 15-LO and a 4-fold increase in 15-HETE formation. In contrast, 5(S)-hydroxy-6-trans-8,11,14-cis-eicosatetraenoic acid generation was not significantly altered by prior exposure to IL-4. Additionally, lipoxins (LXA4 and LXB4) were detected from endogenous substrate, albeit in lower levels than leukotriene B4 (LTB4), in electrochemical detection/high performance liquid chromatography profiles from HAM incubated in the presence and absence of the chemotactic peptide (FMLP) or the calcium ionophore (A23187). Exposure of HAM to leukotriene A4 (LTA4) resulted in a 2-fold increase in LXA4 and 10-fold increase in LXB4. These results demonstrate the presence of 15-LO mRNA and enzyme activity in HAM and the production of LXA4 and LXB4 by these cells. Along with 5-LO-derived products, the biosynthesis of 15-LO-derived eicosanoids by HAM may also be relevant in modulating inflammatory responses in the lung.

12-Lipoxygenase product as an inhibitor of the action of chemoattractant peptide fMet-Leu-Phe in rat neutrophils

1. 12-Hydroxyeicosatetraenoic acid (12-HETE) has been evaluated for its capacities to modulate neutrophil migration and cytosolic Ca2+ ([Ca2+]i) using compounds prepared by chemical synthesis and tissue extract from dog gingiva. 2. 12-HETE inhibited N-formyl-Met-Leu-Phe (fMLP)-stimulated neutrophil migration in a concentration-dependent fashion. 3. The tissue extract from dog gingiva mimicked the actions of 12-HETE. 4. Although 12-HETE failed to increase [Ca2+]i, preincubation of neutrophils with 12-HETE led to a suppression of [Ca2+]i when the cells were subsequently stimulated by fMLP. 5. Again tissue extract from dog gingiva mimicked the action of 12-HETE on [Ca2+]i. 6. These results suggest the possible correlation of the inhibitory activities of 12-HETE on the regulation of neutrophil migration and Ca2+ mobilization, and this may be important for the role of 12-HETE in pathogenesis in periodontal tissues.

Transmembrane signaling in human polymorphonuclear neutrophils: 15(S)-hydroxy-(5Z,8Z,11Z,13E)-eicosatetraenoic acid modulates receptor agonist-triggered cell activation

15(S)-Hydroxy-(5Z,8Z,11Z,13E)-eicosatetraenoic acid (15-HETE) exerted a time- and concentration-dependent inhibition of superoxide anion (O2-) production and exocytosis of both azurophil and specific granule constituents from human polymorphonuclear neutrophils (PMN) stimulated with the receptor-specific agonists, N-formylmethionylleucylphenylalanine (FMLP), platelet-activating factor, and leukotriene B4, but not that elicited by phorbol 12-myristate 13-acetate. 15-HETE did not alter the binding of FMLP to its specific receptors on PMN but, rather, appeared to interfere with a subsequent process in signal transduction. Receptor-coupled production of inositol 1,4,5-trisphosphate (InsP3) and increases in cytosolic free calcium elicited with FMLP, platelet-activating factor, and leukotriene B4 were suppressed by 15-HETE. 15-HETE did not, however, inhibit the mobilization of 45Ca from intracellular stores elicited by the addition of InsP3 to permeabilized PMN. 15-HETE suppressed O2- production and increases in intracellular [Ca2+] induced when cell-surface receptors were bypassed and the PMN were activated directly by the guanine nucleotide-binding protein (G protein) activators aluminum fluoride (AlF4-) and mastoparan. 15-HETE, however, did not perturb all G protein functions because cAMP production in FMLP-activated PMN was essentially unaffected by 15-HETE. These data support the proposition that 15-HETE modulates receptor-triggered activation of PMN either by uncoupling G protein stimulation of phospholipase C or by directly inhibiting phospholipase C, thus inhibiting the InsP3-dependent rise in intracellular [Ca2+] that is prerequisite for PMN responsiveness to receptor agonists.

Arachidonic acid and prostaglandin E2 in Malpighian tubules of female yellow fever mosquitoes

The fatty acid compositions of Malpighian tubules from adult females of the mosquito Aedes aegypti were determined for total lipids, phospholipids, triacylglycerols and three phospholipid fractions, namely phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol/phosphatidylserine (PI/PS). The prostaglandin precursor arachidonic acid (20:4n-6) occurred in total lipids and phospholipids, but not triacylglycerols. Within phospholipids, nearly all of the 20:4n-6 was detected in PC, with only traces in PE, and none was detected in PI/PS. Isolated Malpighian tubules incorporated exogenous radioactive 20:4n-6 into tissue phospholipids and diacylglycerols, with most of the radioactivity recovered in diacylglycerol. These data indicate selective incorporation of 20:4n-6 into tissue lipids. PGE2 was detected in Malpighian tubule whole mounts by immunohistochemical staining. These findings support the idea that prostaglandins are physiologically active in mosquito Malpighian tubules.

Protein kinase C-dependent effects of 12(S)-HETE on endothelial cell vitronectin receptor and fibronectin receptor

12(S)-HETE, a lipoxygenase metabolite of arachidonic acid induced a nondestructive and reversible endothelial cell (EC) retraction. 12(S)-HETE induced EC retraction was inhibited by protein kinase C inhibitors calphostin C and staurosporine but not by the protein kinase A inhibitor H8. The role of EC integrins alpha v beta 3 and alpha 5 beta 1 in 12(S)-HETE induced EC retraction was investigated. In confluent EC cultures, alpha v beta 3 is localized to focal adhesions at both the cell body and cell-cell borders and is colocalized with vinculin-containing focal adhesions. In contrast, alpha 5 beta 1 is primarily enriched at the cell-cell borders, demonstrating codistribution with cell cortical microfilaments and extracellular fibronectin. Both receptors were functional in mediating cell-cell or cell-matrix interactions based on the observations that specific antibodies inhibited EC adhesion to intact subendothelial matrix and disrupted the monolayer integrity. 12(S)-HETE induced a multistep, temporally defined redistribution of the alpha v beta 3-containing focal adhesions, leading to an eventual decrease in alpha v beta 3 plaques in the retracted ECs. This effect of 12(S)-HETE was inhibited by calphostin C but not by H8. The alterations of alpha v beta 3-containing focal adhesions preceded the development of EC retraction. 12(S)-HETE also enhanced EC alpha v beta 3 surface expression as revealed by immunofluorescence, flow cytometry, and digitized image analysis. 12(S)-HETE-induced alpha v beta 3 rearrangement (i.e., decreased focal adhesion localization and enhanced surface expression) did not result from altered mRNA transcription (as revealed by semi-quantitative RT-PCR analysis) or protein translation (as revealed by Western blotting). In contrast to its effect on alpha v beta 3, 12(S)-HETE did not demonstrate a temporally related, well-defined effect on the distribution pattern and the surface expression of alpha 5 beta 1, although the cell-cell border staining pattern of alpha 5 beta 1 was disrupted due to EC retraction. It is concluded that 12(S)-HETE-induced decrease of alpha v beta 3 localization to focal adhesions may contribute to the development of EC retraction and that 12(S)-HETE induced increase in alpha v beta 3 surface expression may promote adhesion of inflammatory leukocytes as well as tumor cells to endothelium.

12(S)-HETE promotes tumor-cell adhesion by increasing surface expression of alpha V beta 3 integrins on endothelial cells

The present work was undertaken to investigate the regulatory role of 12(S)-HETE, a lipoxygenase metabolite of arachidonic acid, in the surface expression of alpha v beta 3 integrin receptors in endothelial cells (rat aortic endothelial cells, or RAEC). Several monoclonal and polyclonal antibodies localized alpha v beta 3 in focal adhesions in both subconfluent and post-confluent RAEC. RAEC alpha v beta 3 integrins were further characterized by immunoblotting and immunoprecipitation. 12(S)-HETE, but not 12(R)-HETE or other lipoxygenase-derived hydroxy fatty acids, induced a dose-dependent increase in alpha v beta 3 surface expression in RAEC, which was antagonized by prostacyclin or its analog iloprost as well as by 13-HODE, a 15-lipoxygenase product of linoleic acid. 12(S)-HETE promoted RAEC adhesion to vitronectin, an effect inhibited by antibodies against alpha v beta 3. 12(S)-HETE also promoted tumor-cell (W256 carcinosarcoma) adhesion to vitronectin, which was inhibited by various antibodies against alpha IIb beta 3 but not by an antibody against alpha v. W256 adhesion to 12(S)-HETE-treated RAEC demonstrated a significant increase, which was inhibited by anti-alpha v, -beta 3, or -alpha v beta 3 antibodies and by 13-HODE. Western blotting, immunoprecipitation and reverse transcription-polymerase chain reaction indicated that W256 carcinosarcoma cells expressed alpha IIb beta 3 integrins but not alpha v beta 3. The results suggest that the lipoxygenase metabolites [i.e., 12(S)-HETE and 13-HODE] play a significant role in modulating tumor-cell interactions with endothelium by enhancing endothelial cell integrin (e.g., alpha v beta 3) expression.

Studies on the role of platelet eicosanoid metabolism and integrin alpha IIb beta 3 in tumor-cell-induced platelet aggregation

Platelet eicosanoid metabolism resulting from tumor-cell-induced platelet aggregation (TCIPA) was examined in a homologous in vitro system. Rat Walker 256 carcinosarcoma cells induced the aggregation of rat platelets via a thrombin-dependent mechanism with concomitant production of eicosanoid metabolites (e.g., 12-HETE, TXA2). TCIPA was dependent on the concentration of tumor cells inducing aggregation, as well as cyclooxygenase and lipoxygenase products. Cyclooxygenase inhibitors, but not lipoxygenase inhibitors, blocked platelet aggregation induced in vitro by a low concentration of agonist. At a high agonist concentration, neither cyclooxygenase nor lipoxygenase inhibitors alone affected platelet aggregation; however, the combined inhibition of both the cyclooxygenase and lipoxygenase pathways resulted in subsequent inhibition of platelet aggregation regardless of agonist concentration. The extent of platelet TXA2 and 12-HETE biosynthesis was likewise dependent on and correlated with agonist concentration. The inhibitors used in this study did not significantly inhibit protein kinase C activity at the doses tested. Platelet surface glycoprotein alpha IIb beta 3 play an important role in platelet aggregation. The effect of platelet cyclooxygenase and lipoxygenase inhibition in regulating alpha IIb beta 3 surface expression was examined by flow cytometric analysis. Thrombin stimulation of washed rat platelets resulted in significantly increased surface expression of platelet alpha IIb beta 3 integrin complex. The enhanced surface expression was not inhibited by a cyclooxygenase inhibitor (aspirin), a thromboxane synthase inhibitor (CGS-14854) or a thromboxane receptor antagonist (SQ 29,548), nor was it stimulated by a thromboxane A2 mimic (pinane-thromboxane A2). However, alpha IIb beta 3 expression was blocked by lipoxygenase inhibition and stereospecifically increased by the platelet lipoxygenase metabolite 12(S)-HETE. These results suggest that both the platelet lipoxygenase and cyclooxygenase pathways are important for TCIPA but that different mechanisms of action are involved.

Induction of heat-shock proteins by bacterial toxins, lipid mediators and cytokines in human leukocytes

We studied the influence of a lipid mediator (12-hydroxyeicosatetraenoic acid, 12-HETE), cytokines (IL-6 and TNF-alpha) and different bacterial toxins (alveolysin; exfoliative toxin; toxic shock syndrome toxin 1, TSST-1 and erythrogenic toxin A, ETA) on the expression of heat shock proteins (hsps) in isolated human leucocytes. 12-HETE induces the expression of individual heat shock proteins (65- and 83 kDa) protein in human leukocytes (lymphocytes, monocytes, basophilic granulocytes; LMBs). As was shown by Western blotting (anti-hsp72), IL-6 or TNF-alpha induced hsps preferentially in human LMBs and PMNs, respectively. Among the toxins, ETA and TSST-1 were potent inducers of hsps at low toxin concentrations (10 ng/ml). Alveolysin led to the expression of hsps at hemolytic concentrations (1 HU; 700 ng/ml) whereas at subhemolytic concentrations (7 ng/ml), no heat shock response was observed. The induction of heat shock proteins was also accompanied by increased mRNA levels for hsp70 as determined by PCR analysis. In contrast, exfoliative toxin led to a reduction of the hsp signal in PMNs as determined by Western blotting. Finally, it was demonstrated that PMNs which had been pretreated with TNF-alpha and therefore expressed intracellular hsps were more resistant to cytolytic attack by leukocidin than untreated cells.

Human tracheal epithelial cells selectively incorporate 15-hydroxyeicosatetraenoic acid into phosphatidylinositol

15-hydroxyeicosatetraenoic acid (15-HETE) is the major lipoxygenase metabolite of arachidonic acid produced by human airway epithelial cells. Because HETEs have been shown to be rapidly metabolized and/or incorporated into cellular lipids in other cell types, we investigated the uptake, metabolism, and intracellular distribution of exogenous 15-HETE by primary monolayer cultures of human tracheal epithelial (HTE) cells. At concentrations of 0.1 microM, [3H]15-HETE was rapidly incorporated by HTE cells and also metabolized primarily by beta-oxidation to several more polar products that were released extracellularly. The majority of cell-associated [3H]15-HETE radiolabel was distributed into phospholipids, with phosphatidylinositol (PI) accounting for approximately 75% of phospholipid radiolabel. Exogenous 5- and 12-HETE were also metabolized by HTE cells but were less extensively incorporated into phospholipids and were distributed primarily into phosphatidylcholine and phosphatidylethanolamine. Phospholipase A2 hydrolysis indicated selective esterification of unmodified 15-HETE to the sn-2 position of phospholipids. 15-HETE incorporation into total phospholipids and into PI was saturable (half maximal incorporation at 0.82 and 0.68 microM, respectively), while incorporation into neutral lipids continued to increase at concentrations of 15-HETE up to 5 microM. The incorporation of 15-HETE into PI was metabolically stable, with an intracellular half-life of 12 h, and was not subject to mobilization in response to 5 microM calcium ionophore A23187. HTE cells can incorporate and metabolize HETEs that the cells themselves produce as well as those that might be released by inflammatory cells recruited into the airway.(ABSTRACT TRUNCATED AT 250 WORDS)

12(S)-HETE-induced microvascular endothelial cell retraction results from PKC-dependent rearrangement of cytoskeletal elements and alpha V beta 3 integrins

12(S)-HETE, a lipoxygenase metabolite of arachidonic acid, has been demonstrated to induce a reversible retraction of vascular endothelial cells (EC). 12(S)-HETE-induced microvascular EC retraction was blocked by a selective protein kinase C inhibitor, calphostin C, but not by the protein kinase A inhibitor, H8. EC exposed to 12(S)-HETE demonstrated a gradual dissolution of actin microfilaments and a decrease of vinculin-containing focal adhesions. The intermediate filaments, vimentin, also underwent extensive reorganization (i.e., filament bundling and enrichment to the cell filapodia) following 12(S)-HETE treatment. In vivo phosphorylation studies revealed that 12(S)-HETE induced a hyperphosphorylation of several major cytoskeletal proteins including myosin light chain, actin, and vimentin. The increased phosphorylation of these cytoskeletal proteins following 12(S)-HETE stimulation was abolished by calphostin C but not by H8. Confluent EC express alpha v beta 3 in focal adhesions at both the cell body and the cell-cell borders. 12(S)-HETE induced a sequential rearrangement of the alpha v beta 3-containing focal adhesions, resulting in a general decrease in alpha v beta 3 integrin receptors, especially in those retracted EC. 12(S)-HETE-induced rearrangement of alpha v beta 3 was inhibited by calphostin C but not by H8. In contrast to alpha v beta 3, confluent EC enrich alpha 5 beta 1 integrin receptors primarily at the cell-cell borders, colocalizing with extracellular fibronectin and cell cortical microfilaments. 12(S)-HETE treatment also disrupted the cell-border distribution pattern of alpha 5 beta 1 as EC retracted, but no distinct alterations (such as time-related redistribution and quantitative differences) in alpha 5 beta 1 were observed.

Distribution of monohydroxy fatty acids in specific human epidermal phospholipids

Monohydroxy derivatives of polyunsaturated fatty acids such as arachidonic acid (AA) and linoleic acid (LA) can modulate inflammation and epidermal proliferation. The purpose of this study was to determine the in vivo distribution of the AA derivatives; 12- and 15-hydroxyeicosatetraenoic acid (12-HETE and 15-HETE) and the LA derivatives; 9- and 13-hydroxyotadecadienoic acid (9-HODE and 13-HODE) in specific phospholipids of normal human skin. Lipids were extracted from 6 normal keratome skin biopsies and phospholipids were separated into the major classes by two-dimensional thin layer chromatography. Monohydroxy fatty acids (MHFAs) released from specific phospholipids after treatment with phospholipase A2 were identified by reversed phase and straight phase high-performance liquid chromatography and UV-absorption spectra. Unesterified MHFAs were determined in a similar way. 9-HODE, 13-HODE and 15-HETE were detectable in phosphatidylcholine (PC), phosphatidylinositol (PI) and phosphatidylethanolamine (PE). Interestingly, 12-HETE was not detectable in these phospholipids, although the unesterified 12-HETE was detectable in amounts similar to unesterified 15-HETE. Esterified 15-HETE was equally distributed between PI and PC, in which 15-HETE was predominant, accounting for 60% and 69% of the total MHFAs, respectively (p < 0.05). These results demonstrate that the LA derivatives 9-HODE and 13-HODE, as well as the AA derivative 15-HETE, are esterified to PC, PI and PE of normal human epidermis in vivo. The possibility remains that 9-HODE, 13-HODE and 15-HETE, may mediate their biological effects by being incorporated into specific phospholipids.

Insulin secretion without the participation of arachidonic acid

In order to study the role of arachidonic acid (AA) in depolarization-induced insulin secretion rat insulinoma cells (RINm5F) were depleted of AA by cultivation in essential fatty acid-free medium. Within 2 weeks AA content of these cells was decreased to a non-detectable level as assessed by gas chromatography (GC). Different cell lines were obtained by supplementation of the defatted medium with oleic acid or the AA precursor linoleic acid (7 and 70 microM, each). The AA content varied in dependence from the precursor availability from 0 to about 14% of long chain fatty acids. Variation in AA content or the depletion of AA to a non-detectable level did not modulate insulin synthesis, basal and potassium-induced insulin release, cell growth (cell number and protein), membrane depolarization and increases in cytosolic Ca2+. In AA containing cells no eicosanoids was produced in the course of stimulated hormone release. The data suggest that in RINm5F cells release of AA and/or formation of oxidized metabolites from AA are not essential for functional integrity.

Interactions between the monocyte/macrophage and the vascular smooth muscle cell. Stimulation of mitogenesis by a soluble factor and of prostanoid synthesis by cell-cell contact

The effect of soluble factors from the monocyte/macrophage (M phi) on cell proliferation and the functional effects of cell-cell contact on the arachidonic acid (AA) cascade were studied with vascular smooth muscle cells (SMCs). Peripheral blood M phi s were isolated by adherence or in a Percoll gradient, and alveolar M phi s were obtained by lavage. Conditioned medium (CM) was prepared by preincubating M phi s with medium alone or by separating SMC and M phi cocultures by a membrane insert. Cell proliferation (image analysis) and 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha, radioimmunoassay) were measured in SMCs. Labeled prostanoids and other eicosanoid metabolites were isolated by high-performance liquid chromatography from SMCs prelabeled with 14C-AA. M phi s did not synthesize 6-keto-PGF1 alpha. The CM enhanced proliferation but did not stimulate 6-keto-PGF1 alpha synthesis in SMCs. However, cell-cell contact in cocultures of SMCs with the same concentration of M phi s used to generate CM resulted in increased 6-keto-PGF1 alpha synthesis by SMCs. Since the stimulatory effect of cell contact was not blocked by butylated hydroxytoluene, it could not be attributed to an oxidative burst from M phi s. Functional studies showed that the stimulatory effect of cell contact was enhanced by exogenous free AA and by endogenous AA release through A23187. Release of total radioactivity from prelabeled SMCs was enhanced by cell contact, and this effect was blocked by indomethacin (IM). Cell contact did not increase the release of free AA from prelabeled SMCs, even in the presence of IM. Finally, cell contact only stimulated the formation of prostanoids (IM-sensitive eicosanoid metabolites) from prelabeled SMCs. Lipoxygenase and other products of AA were not formed through cell-cell contact. These data showed that M phi s express a soluble factor that enhances SMC proliferation without affecting prostanoid synthesis. Subsequent cell contact between SMCs and M phi s stimulates prostanoid synthesis, which may possibly serve as a local and focal homeostatic mechanism for the regulation of uncontrolled SMC proliferation in atherogenesis.

PKC mediates 12(S)-HETE-induced cytoskeletal rearrangement in B16a melanoma cells

The fatty acid 12(S)-HETE may be a new second messenger capable of activating PKC. In tumor cells 12(S)-HETE stimulates cytoskeleton-dependent cellular responses such as adhesion and spreading. Analysis of 12(S)-HETE effects on B16a melanoma cell cytoskeleton revealed reversible rearrangement of microtubules, microfilaments, the actin-binding proteins, vinculin, myosin heavy (MHC) and light chains (MLC), as well as bundling of vimentin intermediate filaments. The alterations in microfilaments and intermediate filaments occurred very rapidly, i.e., 5 min after exposure of tumor cells to 12(S)-HETE. The 12(S)-HETE-induced cytoskeletal alterations were accompanied by centrifugal organelle-translocation. Interestingly, MLC exhibited clear association with the cytoplasmic organelles. Biochemical analysis of the 12(S)-HETE effect indicated a PKC-mediated reversible hyperphosphorylation of MLC, vimentin, and a 130 kD cytoskeletal-associated protein. Optimal effects were obtained after 5 min treatment with 12(S)-HETE at 0.1 microM concentration. 12(S)-HETE pretreatment induced tumor cell spreading on a fibronectin matrix which required the intactness of all three major cytoskeletal components. The spreading process was dependent upon the activity of PKC. Our data suggest that 12(S)-HETE is a physiological stimulant of PKC. Further, it induces rearrangement of the cytoskeleton of tumor cells in interphase resulting in the stimulation of cytoskeleton-dependent cell activity such as spreading.

Fatty acid modulation of tumor cell-platelet-vessel wall interaction

Prostaglandins and other eicosanoids have been studied extensively in their physical, biochemical, biophysical and pharmacological aspects. However, studies on their role in tumor progression, especially metastases are relatively recent. Following a brief overview of the history of discovery and metabolism of eicosanoids and other fatty acids, we discuss the functions of these fatty acids (with emphasis on prostacyclin, thromboxane A2, 12-hydroxyeicosatetraenoic acid and 13-hydroxyoctadecadienoic acid) in cell transformation, tumor promotion and particularly in tumor cell metastasis. The relation between these monohydroxy fatty acids and tumor cell metastasis is discussed from three different perspectives, i.e., their effects on tumor cells, on platelets and on endothelial cells. The mechanism of these effects are then addressed at cell adhesion molecule, motility, protease, cell cytoskeleton, protein kinase and eicosanoid receptor levels. Finally, regulation of three key enzymes which generate eicosanoids (phospholipase, prostaglandin endoperoxide synthase and lipoxygenase) is explored.

Fatty acid modulation of tumor cell adhesion to microvessel endothelium and experimental metastasis

Tumor cell interaction with the endothelium of the vessel wall is a rate limiting step in metastasis. The fatty acid modulation of this interaction was investigated in low (LM) and high (HM) metastatic B16 amelanotic melanoma (B16a) cells. 12(S)-HETE increased the adhesion of LM cells to endothelium derived from pulmonary microvessels. All other monohydroxy and dihydroxy fatty acids were ineffective. LTB4 induced a modest stimulation but LTC4, LTD4, LTE4 as well as LXA4 and LXB4 were ineffective. The 12(S)-HETE enhanced adhesion of B16a cells was inhibited by pretreatment with 13(S)-HODE but not by 13(R)-, 9(S)-HODE or 13-OXO-ODE. 13(S)-HODE decreased adhesion of HM B16a cells to endothelium. 12(S)-HETE enhanced surface expression of integrin alpha IIb beta 3 and monoclonal antibodies against this integrin but not against alpha 5 beta 1, blocked enhanced but not basal adhesion to endothelium. Intravenous injection of 12(S)-HETE treated LM cells resulted in increased lung colonization (experimental metastasis). This effect was specific for 12(S)-HETE and was inhibited by 13(S)-HODE but not by other HODE's. 12(S)-HETE also enhanced lung colonization by HM cells and 13(S)-HODE decreased lung colonization by HM cells. Our results suggest a highly specific bidirectional modulation of metastatic phenotype and lung colonization by 12(S)-HETE and 13(S)-HODE.

The lipoxygenase metabolite 12(S)-HETE promotes alpha IIb beta 3 integrin-mediated tumor-cell spreading on fibronectin

Tumor-cell interaction with the vessel wall during metastasis involves adhesion, induction of endothelial-cell retraction and spreading on the exposed sub-endothelial matrix. The signals for initiation of tumor-cell spreading and the receptors involved are unknown. A protocol was developed to distinguish between initial tumor-cell (B16 amelanotic melanoma; B16a) adhesion to and spreading on fibronectin. The time for maximum spreading was 50 min. Treatment with a lipoxygenase metabolite of arachidonic acid [12(S)-HETE] resulted in maximum spreading in 15 min (max. effect approx. 0.1 microM). Other lipoxygenase metabolites were ineffective. 12(S)-HETE treatment induced a rearrangement of F-actin, vinculin, vimentin intermediate filaments and integrin alpha IIb beta 3, but not integrin alpha 5 beta 1. Antibodies to alpha IIb beta 3 but not alpha 5 beta 1 blocked the 12(S)-HETE effect on B16a spreading. B16a-cell attachment to fibronectin resulted in increased metabolism of arachidonic acid to 12(S)-HETE, which was inhibited by lipoxygenase but not by cyclo-oxygenase inhibitors. Accordingly, lipoxygenase inhibitors but not cyclo-oxygenase inhibitors blocked spontaneous B16a-cell spreading. The protein-kinase-C inhibitors calphostin C, H7 and staurosporine also inhibited spreading, while the protein-kinase-A inhibitor H8 was ineffective. These data suggest that B16a-cell spreading on fibronectin is initiated by a lipoxygenase metabolite [12(S)-HETE] of arachidonic acid and is mediated by protein kinase C.

Induction of inflammatory mediator release (serotonin and 12-hydroxyeicosatetraenoic acid) from human platelets by Pseudomonas aeruginosa glycolipid

Purified glycolipid from Pseudomonas aeruginosa induced the generation of significant amounts of 12-hydroxyeicosatetraenoic acid (12-HETE) and serotonin release from human platelets. The release of serotonin was first observed 2 min after addition of the glycolipid and increased with time. Significant serotonin release was obtained at glycolipid concentrations above 5 micrograms/ml and increased dose-dependently up to 100% at glycolipid concentrations above 40 micrograms/ml. Glycolipid induced 12-HETE in a time- and dose-dependent manner. 12-HETE formation was first measured after 10 min of incubation and increased with time. Optimal 12-HETE formation was obtained at a glycolipid concentration of 50 micrograms/ml; higher concentrations of glycolipid led to a decrease in 12-HETE formation, indicating a cytotoxic effect. Stimulation of platelets with glycolipid (12-HETE formation and serotonin release) was accompanied by calcium influx, translocation of protein kinase C, activation of guanylylimidodiphosphate binding, and increased GTPase activity in platelet membranes within the same concentration range.

New isoflavonoids as inhibitors of porcine 5-lipoxygenase

The inhibitory activity of new isoflavonoids on 5-lipoxygenase of porcine leukocytes was investigated. Isoflavans (I) proved to be stronger inhibitors than isoflavones (II). The isoflavans containing ortho-hydroxy groups in ring A showed the lowest Ki values (0.8-50 microM). In comparison, isoflavans with meta-dihydroxy groups exhibited Ki values higher than 150 microM. The effect of commercial antioxidants was tested also on porcine 5-lipoxygenase. Butylated hydroxyanisole (Ki: 25 microM) and butylated hydroxytoluene (Ki: 55 microM) revealed moderate inhibitory activity, whereas L-ascorbic acid, L-ascorbyl palmitate, dl-alpha-tocopherol and n-propyl gallate showed weak inhibitory activities (Ki: 100-260 microM).

Profiling assay for lipoxygenase products of linoleic and arachidonic acid by gas chromatography-mass spectrometry

A method for determination of the lipoxygenase products of linoleic acid (9- and 13-hydroxyoctadecadienoic acid; 9-HODE, 13-HODE) and of arachidonic acid (5-, 8-, 9-, 11-, 12-, and 15-hydroxyeicosatetraenoic acid; 5-, 8-, 9-, 11-, 12-, and 15-HETE) is described. The method combines solid-phase extraction, derivatization to the corresponding fully hydrogenated methylester/trimethylsilylether derivatives and capillary gas chromatography coupled with electron impact mass spectrometry. Each regioisomeric HODE and HETE shows a unique pair of mass spectrometric fragment ions originating from fission of the fatty acid carbon chain at the hydroxylated position. The carboxyl-terminal fragment is used for quantification relative to a carboxyl-18O2-labeled analogue added as internal standard and the methyl-terminal fragment is monitored for confirmation. The assay can be extended for quantification of the complete hydroxylation profile of linoleic and arachidonic acid. Applications of this assay are demonstrated for the quantification of HODEs and HETEs in normal, hyperplastic, and neoplastic mouse epidermis. In mouse epidermis papilloma, the tissue levels of 8- and 12-HETE were found to be increased by one to two orders of magnitude compared to levels in normal epidermis.

Fifteen-S-hydroxyeicosatetraenoic acid (15-S-HETE) specifically antagonizes the chemotactic action and glomerular synthesis of leukotriene B4 in the rat

In models of experimental glomerulonephritis, there is temporal concordance between the shift in the glomerular cellular infiltrate from neutrophils (PMN) to macrophages/monocytes and the suppression of glomerular leukotriene B4 (LTB4) generation. Since macrophages are a rich source of 15-lipoxygenase (15-LO) products, we investigated whether the principal product of arachidonate 15-lipoxygenation, 15-S-hydroxyeicosatetraenoic acid (15-S-HETE), was capable of antagonizing the proinflammatory actions of LTB4 in the rat. PMN exhibited chemotaxis to LTB4 in a dose dependent manner with an LC50 of 10(-8) M. When rat neutrophils were pre-treated with 15-S-HETE, chemotaxis to LTB4 was inhibited in a dose dependent manner (maximal at 30 microM 15-S-HETE) but, the same concentration did not inhibit chemotaxis to n-formyl-1-methionyl-1-phenylalanine (FMP). 12-S-HETE (30 microM) did not inhibit chemotaxis to LTB4. Glomeruli from rats injected with nephrotoxic serum three hours earlier generated increased levels of LTB4; prior exposure of such glomeruli to 15-S-HETE totally normalized LTB4 production. The glomerular production of 15-S-HETE and LTB4 was also determined 3 hours, 72 hours and 2 weeks after administration of nephrotoxic serum. Whereas there was an early, short-lived, burst of LTB4 followed by a return to baseline levels, the production of 15-S-HETE increased steadily over the two week period and was present in amounts fivefold greater than LTB4. Thus, these studies assign a role for locally generated 15-LO derivatives in arresting LTB4-promoted PMN infiltration and suppressing LTB4 synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute hypoxia alters eicosanoid production of perfused pulmonary artery endothelial cells in culture

Hypoxia alters vascular tone which regulates regional blood flow in the pulmonary circulation. Endothelial derived eicosanoids alter vascular tone and blood flow and have been implicated as modulators of hypoxic pulmonary vasoconstriction. Eicosanoid production was measured in cultured bovine pulmonary endothelial cells during constant flow and pressure perfusion at two oxygen tensions (hypoxia: 4% O2, 5% CO2, 91% N2; normoxia: 21% O2, 5% CO2, 74% N2). Endothelial cells were grown to confluence on microcarrier beads. Cell cartridges (N = 8) containing 2 ml of microcarrier beads (congruent to 5 x 10(6) cells) were constantly perfused (3 ml/min) with Krebs' solutions (pH 7.4, T 37 degrees C) equilibrated with each gas mixture. After a ten minute equilibration period, lipids were extracted (C18 Sep Pak) from twenty minute aliquots of perfusate over three hours (nine aliquots per cartridge). Eicosanoids (6-keto PGF1 alpha; TXB2; and total leukotriene [LT - LTC4, LTD4, LTE4, LTF4]) were assayed by radioimmunoassay. Eicosanoid production did not vary over time. 6-keto PGF1 alpha production was increased during hypoxia (normoxia 291 +/- 27 vs hypoxia 395 +/- 35 ng/min/gm protein; p less than 0.01). Thromboxane production (normoxia 19 +/- 2 vs hypoxia 20 +/- 2 ng/min/gm protein) and total leukotriene production (normoxia 363 +/- 35 vs hypoxia 329 +/- 29 ng/min/gm protein) did not change with hypoxia. These data demonstrated that oxygen increased endothelial prostacyclin production but did not effect thromboxane or leukotriene production.

Atherosclerosis: the eicosanoid connection

This bird's eye view presents connections between the metabolically short-lived local hormones (collectively known as eicosanoids) and atherosclerotic cardiovascular disease. The discussion will be centered around an overview of coronary atherosclerosis with an emphasis on the sequences involved in the formation of atherosclerotic lesions; structure and historical background of oxygenated fatty acids cyclooxygenase and lipoxygenase products--eicosanoids; the generation of free radicals during the formation of endoperoxides by cyclooxygenase; the involvement of eicosanoids in the atherosclerotic inflammatory process, and finally, the effects of non-steroidal and steroidal anti-inflammatory drugs on the synthesis of eicosanoids and experimental atherosclerosis. Little is known about the exact role of eicosanoids in the genesis of atherosclerosis.

Role of resident macrophages in canatoxin-induced in vivo neutrophil migration

Canatoxin (Cntx), a toxic protein purified from Canavalia ensiformis seeds, was shown to have lipoxygenase-mediated effects either in vivo or in vitro. Data here show that Cntx induced a dose-dependent migration of neutrophils and mononuclear cells when injected into rat peritoneal cavities. Furthermore, Cntx was able to induce neutrophil migration into pleural cavities and into air pouches. These effects were inhibited by dexamethasone but not by inhibitors of arachidonic acid metabolism (indomethacin, NDGA, and BW-755c) or by a PAF antagonist (BN 52021). In the peritoneal cavity Cntx caused an increase in vascular permeability inhibited by dexamethasone and BW-755c. Neutrophil migration induced by this toxin was dependent on the number of resident macrophages, since the migratory effect was enhanced by increasing the peritoneal macrophage population with thioglycollate pretreatment and was diminished when this population was reduced by peritoneal wash. It was also observed that Cntx induced release of a chemotactic factor from macrophage monolayers in vitro. Dexamethasone blocked this release but did not affect in vivo neutrophil recruitment induced by that factor. These data suggest that Cntx-induced neutrophil migration may be mediated by the same macrophage-derived neutrophil chemotactic factor released by other stimuli such as LPS, IL-1, and INF-gamma.

Metabolism of 12(R)-hydroxyeicosatetraenoic acid by rat liver microsomes

The in vitro metabolism of 12(R)-hydroxyeicosatetraenoic acid was studied using freshly isolated rat liver microsomes. Ten metabolites were isolated and identified by a combination of ultraviolet spectroscopy and gas chromatography/mass spectrometry. The two major metabolites were dihydroxyeicosatetraenoic acids generated by omega/omega-1 hydroxylation. Oxidation at C-5 resulted in the formation of four leukotriene-like compounds, two of which differed from leukotriene B4 in double-bond geometry alone. The other two differed from leukotriene B4 in olefin geometry and C-5 configuration. Epoxidation at the 14,15-olefin resulted in the formation of two diastereomeric epoxy alcohols, while C-16 hydroxylation gave two diastereomeric dihydroxyeicosatetraenoic acids.

Differential metabolism of hydroxyeicosatetraenoic acid isomers by mouse cerebromicrovascular endothelium

Hydroxyeicosatetraenoic acid (HETE) derivatives of arachidonic acid are produced in the brain and have been implicated as pathologic mediators in various types of brain injury. To understand better their fate in the brain, particularly in cerebral microvessels, several HETEs were incubated with cultured mouse cerebromicrovascular endothelium for 1, 2, and 4 h, followed by HPLC analysis of medium and cellular lipids. 5(S)-, 8(RS)-, and 9(RS)-HETE were not metabolized by the cells, but were extensively incorporated, unmodified, into cell lipids. On the other hand, 11(RS)-, 12(S)-, and 15(S)-HETE were extensively metabolized and only minimally incorporated into cell lipids. Previously, the major 12-HETE metabolite was identified as 8-hydroxyhexadecatrienoic acid. In the present study, we identified the major 11-HETE metabolite as 7-hydroxyhexadecatrienoic acid and the major 15-HETE metabolite as 11-hydroxyhexadecatrienoic acid. omega-3 compounds, 15(S)- and 12(S)-hydroxyeicosapentaenoic acids (HEPE), were also metabolized to more polar compounds, but to a lesser extent than their tetraenoic acid, omega-6 counterparts. Comparison of 5-, 12-, and 15-HETE enantiomers revealed no differences in metabolism or incorporation between the R and S stereoisomers. These data suggest that many isomers of HETE and HEPE can be incorporated into cell lipids or metabolized by pathways that do not distinguish between enantiomers. These pathways, however, are sensitive to the position or number of double bonds and are selective based on the position of the hydroxyl group.

Type II alveolar epithelial eicosanoid metabolism: predominance of cyclooxygenase pathways and transcellular lipoxygenase metabolism in co-culture with neutrophils

Arachidonic acid (AA) metabolism was studied in freshly isolated type II alveolar epithelial cells of rabbits. Substantial basal secretion of prostanoids with predominance of prostaglandin (PG) I2 was noted. Challenge with the calcium ionophore A23187 resulted in a time- and dose-dependent increase in the generation of all AA cyclooxygenase products to severalfold values following the rank order of 12-heptadecatrienoic acid (12-HHT) greater than PGI2 greater than PGE2 greater than or equal to thromboxane A2 greater than PGF2 alpha approximately PGD2. Even larger augmentation of prostanoid generation was evoked by challenge with free exogenous AA. Generation of the different AA cyclooxygenase products was inhibited by acetylsalicylic acid with IC50 in the range between 250 and 500 microM. In addition to the prostanoid release, ionophore-challenged type II pneumocytes liberated substantial amounts of AA lipoxygenase products with leukotriene (LT) B4 greater than 15-hydroxyeicosatetraenoic acid (HETE) greater than 12-HETE greater than 5-HETE. Generation of LTs and HETEs was markedly increased upon simultaneous disposal of free exogenous AA. No omega-oxidation of LTB4 was noted, and no evidence for secretion of intact LTA4 was obtained. The epithelial cells displayed avid uptake of exogenously offered LTA4 with subsequent enzymatic conversion to LTB4. Co-stimulation of pneumocytes with neutrophils (PMN) resulted in an amplification of LTB4 generation, paralleled by a decrease in nonenzymatic decay products of PMN-derived LTA4; both phenomena were dose dependent on the pneumocyte-PMN ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular oxidative modification of low density lipoprotein does not require lipoxygenases

The oxidative modification of low density lipoprotein (LDL) may play an important role in the pathogenesis of atherosclerosis. LDL can be oxidatively modified in vitro by endothelial cells, mouse peritoneal macrophages, or copper ions. Studies using lipoxygenase inhibitors have suggested that lipoxygenase(s) is required for the cellular modification of LDL [Rankin, S. M., Parthasarathy, S. & Steinberg, D. (1991) J. Lipid Res. 32, 449-456]. We have reexamined the effect of lipoxygenase inhibitors on cellular modification and found that (i) inhibitors specific for 5-lipoxygenase do not block LDL modification; (ii) inhibitors that block lipoxygenase by donating one electron to the enzyme (reductive inactivation) prevent LDL modification by cells and also modification mediated by copper ions, implying that they act as general antioxidants; (iii) the lipoxygenase inhibitor 5,8,11,14-eicosatetraynoic acid blocks 15-lipoxygenase activity in intact macrophages at concentrations 100 times less than those required to block LDL modification by macrophages; and (iv) 5,8,11,14-eicosatetraynoic acid is cytotoxic at concentrations about twice those required to prevent modification. Furthermore, macrophages and the RECB4 line of endothelial cells modify LDL with similar efficiencies despite dramatic differences in 15-lipoxygenase activity. Thus we conclude that neither 5-lipoxygenase nor 15-lipoxygenase is required for modification of LDL by cultured cells.

Lipoxygenase metabolites of arachidonic and linoleic acids modulate the adhesion of tumor cells to endothelium via regulation of protein kinase C

12(S)-hydroxyeicosatetraenoic acid (12[S]-HETE) and 13(S)-hydroxyoctadecadienoic acid (13[S]-HODE), lipoxygenase metabolites of arachidonic acid and linoleic acid, respectively, previously have been suggested to regulate tumor cell adhesion to endothelium during metastasis. Adhesion of rat Walker carcinosarcoma (W256) cells to a rat endothelial cell monolayer was enhanced after treatment with 12(S)-HETE and this 12(S)-HETE enhanced adhesion was blocked by 13(S)-HODE. Protein kinase inhibitors, staurosporine, calphostin C, and 1-(5-isoquinoline-sulfonyl)-2-methylpiperazine, inhibited the 12(S)-HETE enhanced W256 cell adhesion. Depleting W256 cells of protein kinase C (PKC) with phorbol 12-myristate-13-acetate abolished their ability to respond to 12(S)-HETE. Treatment of W256 cells with 12(S)-HETE induced a 100% increase in membrane-associated PKC activity whereas 13(S)-HODE inhibited the effect of 12(S)-HETE on PKC translocation. High-performance liquid chromatographic analysis revealed that in W256 cells 12-HETE and 13-HODE were two of the major lipoxygenase metabilites of arachidonic acid and linoleic acid, respectively. Therefore, these two metabolites may provide an alternative signaling pathway for the regulation of PKC. Further, these findings suggest that the regulation of tumor cell adhesion to endothelium by 12(S)-HETE and 13(S)-HODE may be a PKC-dependent process.

Bioactions of 5-hydroxyicosatetraenoate and its interaction with platelet-activating factor

In a variety of stimulated cells, platelet-activating factor (PAF) and numerous arachidonate derivatives are co-products that form as a consequence of receptor-mediated phospholipid mobilization. These lipid co-products produce a plethora of biological effects in a wide variety of cell systems. Furthermore, they often have a fascinating although less widely appreciated, interaction. 5-HETE, at submicromolar concentrations, exerts relatively few direct bioactions. It does, however, potently (16-160 nM) raise cytosolic free calcium [Ca2+]i and augment PAF-induced responses in human polymorphonuclear neutrophils (PMN) by as much as 100- to 1000-fold. 5-HETE acts on PMN by a structurally specific, stereospecific and pertussis toxin-inhibitable mechanism. In addition, PMN exposed to 5-HETE exhibit homologous but not heterologous desensitization. These findings suggest that 5-HETE, like PAF, may bind to its own specific plasmalemmal receptors to exert its unique set of bioactions. However, further investigation is required to demonstrate any putative 5-HETE receptors. Other potential mechanisms of 5-HETE-induced bioactions together with the possible effects of 5-HETE on PAF transduction mechanisms are also discussed.

The lipoxygenase metabolite 12(S)-HETE induces a cytoskeleton-dependent increase in surface expression of integrin alpha IIb beta 3 on melanoma cells

Integrin receptors are mediators of cell-extracellular matrix and cell-cell interactions. Biochemical and immunocytochemical evidence shows that the platelet integrin receptor alpha IIb beta 3 is present on the cell surface, at focal adhesion plaques and in the perinuclear region of metastatic B16a murine melanoma cells. Antibody to the fibronectin receptor alpha 5 beta i, inhibits basal adhesion by approx. 30%, whereas antibodies to alpha IIb beta 3 are ineffective. The surface immunoreactivity of tumor cells for alpha IIb beta 3 can be enhanced by pre-treatment (5 min) with a lipoxygenase metabolite of arachidonic acid [i.e. 12-(S)-HETE] in a dose-dependent manner (max. effect approx. 0.1 microM). Other lipoxygenase metabolites are ineffective. B16a cells possess a large intracellular pool of alpha IIb beta 3, from which the receptor complex translocates to the cell surface following 12-(S)-HETE pretreatment. This pre-treatment of tumor cells enhances their adhesion to fibronectin, which is mediated exclusively by alpha IIb beta 3 receptors. 12-(S)-HETE also facilitates the redistribution of alpha IIb beta 3 in the plasma membrane with localization at the focal adhesion plaques. The cytoskeleton of the B16a cell is characterized by an absence of distinct microtubules in interphase cells and the presence of prominent microfilaments and vimentin intermediate filaments. In B16a cells, the disruption of intermediate filaments and/or microfilaments prevents the 12-(S)-HETE-induced increase in plasma membrane alpha IIb beta 3 and enhanced tumor-cell adhesion to fibronectin. The microtubule-disrupting agent, colchicine, is ineffective in both respects. We conclude that the lipoxygenase metabolite of arachidonic acid, 12-(S)-HETE, regulates the surface expression and function of the alpha IIb beta 3 integrin in B16a cells. Further, these data support the hypothesis that microfilaments and intermediate filaments have a profound role in regulating the expression of a multifunctional integrin in B16a tumor cells.

Extensive incorporation of dietary delta-5,11,14 eicosatrienoate into the phosphatidylinositol pool

The acyl composition of phosphatidylinositol (PI) is remarkably resistant to dietary fatty acid modification. To investigate the basis of this selectivity, we have probed fatty acids lacking the usual methylene interrupted double bonds. When mice were fed delta-5,11,14 20:3 as 3% of total lipid, this fatty acid, lacking the delta-8 double bond essential for eicosanoid synthesis, replaced a significant quantity of 20:4 (n-6) in PI, but not PC and PE. By altering the acyl composition of PI, novel second messengers may be formed. This fatty acid structure thus provides a unique nutritional tool for investigating the basis of PI acyl specificity, and for determining the metabolic consequences of acyl alteration, in vivo.

HETEs and coronary artery endothelial cells: metabolic and functional interactions

Porcine coronary artery endothelial cells have been established in culture. These cells produce prostaglandin (PG) I2, PGF2 alpha, and PGE2 when exposed to either arachidonic acid or ionophore A23187. PG formation was reduced when the cells were exposed to monohydroxy and dihydroxy unsaturated fatty acids. Although all of the hydroxyeicosatetraenoic acids (HETEs) produced reductions, 5-HETE caused the largest decrease in PGI2 formation. Therefore, these lipoxygenase products, especially 5-HETE, may impair the nonthrombogenic surface and some vasodilator responses of coronary endothelium. The cells took up each of the HETEs and incorporated them into phospholipids. Uptake was not affected by equimolar amounts of oleic or linoleic acids; even arachidonic acid reduced 12- and 15-HETE uptake by only 50-60%. Like other cells, the coronary endothelium converted 12- and 15-HETE to polar metabolites. As opposed to other cells, however, these cultures also converted 5-HETE to a more polar metabolite. Thus coronary artery endothelium can take up and metabolize all of the major HETEs, including 5-HETE, and thereby reduce their potentially injurious effects in the coronary circulation.

Brain microvessel 12-hydroxyeicosatetraenoic acid is the (S) enantiomer and is lipoxygenase derived

12-Hydroxyeicosatetraenoic acid (12-HETE) production from arachidonic acid by cerebral microvessels isolated from perfused adult murine brain was reduced by the lipoxygenase inhibitors baicalein, esculetin, gossypol, nordihydroguaiaretic acid, and quercetin. Except for quercetin and gossypol, the IC50 did not exceed 10 microM. Each inhibitor, except baicalein, also decreased microvessel prostaglandin production when present in concentrations above their IC50 value for 12-HETE. In contrast, inhibitors of the cytochrome P450 monooxygenase system, clotrimazole, metyrapone, and proadifen (SKF-525A), had little effect on microvessel 12-HETE production. Chiral phase HPLC analysis revealed that only the (S) enantiomer of 12-HETE was formed. The major microvessel metabolite of eicosapentaenoic acid co-eluted with 12-hydroxyeicosapentaenoic acid (12-HEPE) on reverse-phase HPLC and the (S) enantiomer of 12-HEPE on chiral phase HPLC. Furthermore, like 12-HETE, 12-HEPE production was blocked by lipoxygenase inhibitors. These studies demonstrate that brain microvessels produce only the (S) enantiomeric 12-hydroxy derivatives of both arachidonic acid and eicosapentaenoic acid by the action of a lipoxygenase that can be selectively inhibited by baicalein. Since arachidonic acid and eicosapentaenoic acid are available to cerebral blood vessels in certain pathological settings, these 12-hydroxy acid lipoxygenase products may mediate some of the cerebrovascular dysfunction that occurs following stroke, brain trauma, or seizures.

Hepoxilin A3 induces heat shock protein (HSP72) expression in human neutrophils

In this paper we show that hepoxilin A3 induces the expression of heat shock protein expression in human neutrophils at a concentration of 100 nM using Western blotting techniques employing the use of a commercial monoclonal antibody to HSP72. No regiospecificity was observed as the 8S enantiomer of HxA3 was as active as the 8R enantiomer of HxA3. Comparison of the effects of HxA3 with 12S-HETE and PGA1 indicated that HxA3 was as effective as 12S-HETE although PGA1 was essentially inactive at the same concentration used for these 12-lipoxygenase products.

Improved purification of 12-lipoxygenase from rat basophilic leukemia cells and conditions for optimal enzyme activity

12-Lipoxygenase from rat basophilic leukemia cells was purified about 300-fold by protein-HPLC in a single run. Maximal 12-lipoxygenase activity was observed at pH 7.5, while the enzyme became almost inactive at pH 6 and 9. Although Ca2+ was not essential for 12-lipoxygenase activity, the partially purified enzyme was stimulated approx. 2-fold in the presence of 0.1-5.0 mM Ca2+. Contrary to 5-lipoxygenase from RBL-1 cells, 12-lipoxygenase was not inactivated by preincubation with Ca2+ for 1-10 min, nor was it stimulated by 0.1-10 mM ATP.

Saturability of esterification pathways of major monohydroxyeicosatetraenoic acids in rat basophilic leukemia cells

The principal monohydroxyeicosatetraenoic acids (HETEs), 5-, 12-, and 15-HETE, which can be produced by rat basophilic leukemia (RBL-1) cells, are also esterified by these cells. Exogenously added 5-, 12-, and 15-HETE were rapidly incorporated as esters in RBL cells, reaching plateau levels within 25 min. In incubations in culture medium with protein added, all three HETEs were essentially completely metabolized within 24 h. 5-HETE was esterified more rapidly and to a greater extent than 12-HETE or 15-HETE when these were incubated together with RBL cells, indicating some degree of selectivity in the esterification pathways. When arachidonic acid (AA) was incubated in increasing concentrations with constant concentrations of 15-HETE and RBL cells, the free 15-HETE concentration increased and esterified 15-HETE concentration decreased markedly at AA: 15-HETE molar ratios above 9. 15-HETE esterification in RBL cells was also markedly inhibited by the polyunsaturated fatty acids, eicosatetraynoic and eicosapentanoic acids, but not by oleic or linoleic acids. In separate experiments with unlabeled and radiolabeled substrates, the extent of incorporation of esterified HETE in RBL cells decreased at higher concentrations of 15-HETE and AA, which showed that the pathway was saturable. The shapes of the curves for these fatty acid inhibitors suggest a concentration-dependent two-compartment pathway of esterification. These data indicate that the HETEs and other 20 carbon fatty acid substrates probably compete for activity of a specific arachidonyl-CoA synthetase, which is the first and rate-limiting step for esterification of arachidonic acid by many human cells. Esterified 15-HETE was found to be predominantly in the phosphatidylethanolamine fraction of RBL cell lipids.

Metabolism of arachidonic acid by human epidermal cells depends upon maturational stage

Synthesis of 12- and/or 15-HETE by human epidermal cells was investigated after separating basal cells from suprabasal epidermal cell layers. We found that the main metabolite of 3H-arachidonic acid (3H-AA), formed by freshly prepared upper epidermal layers (stratum granulosum and spinosum), upon RP-HPLC co-eluted with authentic 3H-12-HETE. A 3H-15-HETE co-eluting peak selectively occurred in chromatograms obtained from supernatants of fractions containing basal cells. Supernatants of freshly prepared suspensions rich in basal keratinocytes appeared to contain 3H-15-HETE as their main 3H-AA metabolite, by far exceeding the recovered amounts of 3H-12-HETE. Moreover, keratinocytes cultured for 1 week or longer were found to produce predominantly a 3H-AA metabolite co-eluting with 3H-15-HETE. In supernatants of cultured cells, little if any 3H-12-HETE was detectable. Cultured human skin fibroblasts were not found to produce relevant amounts of HETE. Genuine tissue rich in basal cells, i.e., cells of hair follicles, were found to form twice as much 3H-15-HETE as 3H-12-HETE (3H-15-HETE/3H-12-HETE-ratio = 1.9 +/- 0.8; n = 7). Apparently, different epidermal layers are able to produce a characteristic pattern of 3H-AA metabolites. 3H-15-HETE generation seems to be a marker for proliferating keratinocytes, whereas 3H-12-HETE formation appears to be typical for differentiating suprabasal epidermal cells. Our results may explain the heretofore varying patterns of AA-metabolites by keratinocytes reported in the literature.