Hydroxyeicosatetraenoic acids (HETEs)

Arachidonic acid metabolism in cultured adult myocardial cells under short-time hypoxic conditions

The present study utilized a cultured adult myocardial cell model to examine the arachidonic acid metabolism under different cell-damaging and normoxic conditions. Cell injury was caused by short-time hypoxia, calcium ionophore A 23187-triggered cell-damage under hypoxia and cell disruption by freezing and thawing. The current study demonstrates that under the cell-damaging conditions cultured adult heart myocytes resemble myocardial cells under normoxic conditions in metabolizing arachidonic acid into triacylglycerols and phospholipids as the major route (a), in formation of ETYA-inhibitable indomethacin-resistant lipid metabolites in minor amounts (b) and in being independent of calcium overload in the metabolic pathways of arachidonic acid metabolism (c). The ETYA-inhibitable components were resolved by HPLC. There was no evidence in formation of lipoxygenase products. The results were supported by negative hybridisation experiments of the total mRNA isolated from adult myocardial cells with a cDNA probe of a red-cell-specific lipoxygenase mRNA. We conclude from these observations that cell injury does not result in expression of lipoxygenase activities in heart myocytes.

Identification of prostaglandins and hydroxyeicosatetraenoic acids in kitten retina: comparison with other species

Conversion of arachidonic acid to eicosanoids by kitten retinae was investigated to evaluate whether the pattern of kitten retinal eicosanoids simulates that found in the human and other animal species. Freshly isolated kitten retinae were incubated with 20 microM radiolabeled arachidonic acid, and the metabolites were analysed by reverse phase-high pressure liquid chromatography, thin-layer chromatography and gas chromatography-mass spectroscopy. Kitten retinal tissues converted arachidonic acid into prostaglandins (PGs), thromboxane (Tx) and hydroxyeicosatetraenoic acids (HETEs). The major eicosanoid identified was 6kPGF1 alpha--the stable non-enzymatic hydrolysis product of prostacyclin. Other eicosanoids identified included TxB2, PGE2, PGF2 alpha, 12-hydroxy-heptadecatrienoic acid, 12-HETE, and 15-HETE. The spectrum of kitten retinal cyclooxygenase metabolites is similar to those obtained from bovine retina and human retinal vascular endothelium with prostacyclin being the major cyclooxygenase metabolite produced.

Distribution of tritium labeled 12(S) hydroxy-eicosatetraenoic acid (12-HETE) in the rat

The in vivo metabolism of 12-(S)-Hydroxy-eicosatetraenoic acid (12-HETE), the end-lipoxygenase product of arachidonic acid in platelets, has been investigated in the rat. Fifty microcuries of 5,6-[3H]-12-HETE (50 Ci/mmol) were injected to anesthetized rats and the radioactivity was followed in plasma. At the end of the experiment, various organs of the animal were removed and the radioactivity attached to them was determined. The label of the plasma plateaued to approximately one third of the initial radioactivity ten minutes after the injection. Among the various organs tested (brain, heart, intestine, kidney, liver, lungs, spleen, testis/uterus) the kidney was far the most active to accumulate 12-HETE and/or its labeled metabolites, and no radioactivity could be detected in urine during the course of the experiment. The analysis of lipid extracts from the various tissues revealed that 12-HETE was not accumulating in its unesterified form but was likely bound to phospholipids. We conclude that, although the label providing from the initial 12-HETE did not completely disappear from plasma, circulating 12-HETE cannot be considered as a circulating marker of cell activation.

Gas chromatographic-mass spectrometric analysis of lipoxygenase products in post-ischemic rabbit myocardium

Leukotriene B4 (LTB4) is a potent chemotactic compound for neutrophils and is thought to be an important mediator of myocardial ischemia-reflow injury. We have measured LTB4 in rabbit cardiac tissue following ischemia-reflow using a sensitive and specific gas chromatographic-mass spectrometric (GC-MS) assay. The concentration of LTB4 in rabbit myocardium following 45 min ischemia and 3 h reflow was 48.7 +/- 12.5 pg/g, significantly higher than in non-ischemic tissue from the same animal (17.5 +/- 3.9 pg/g). These concentrations were at least an order of magnitude lower than previously reported values assessed by radioimmunoassay (RIA). Compared with the GC-MS method, RIA greatly overestimated LTB4 concentrations in cardiac tissue. The capacity of post-ischemic myocardium to produce lipoxygenase products, LTB4, 5-, 12- and 15-HETEs was also assessed following incubation of myocardium ex vivo with calcium ionophore. In all animals ischemic cardiac tissue produced greater amounts of LTB4, 5-, and 12-HETEs than non-ischemic myocardium and 12-HETE was the major product. Neutrophils that have accumulated in the injured tissue may be a major source of these products. However, in contrast to cardiac tissue, isolated rabbit neutrophils stimulated with A23187 produced 5-HETE as the major product with very little 12-HETE formed. These latter findings suggest that cells other than neutrophils may contribute to the production of lipoxygenase products during myocardial ischemia-reflow injury.

12-Hydroxyeicosatetraenoic acid (12-HETE) induces heat shock proteins in human leukocytes

12-Hydroxyeicosatetraenoic acid (12-HETE) induces the expression of individual heat shock proteins in human leukocytes (lymphocytes, monocytes, basophil granulocytes; LMBs). Metabolic radiolabeling of LMBs revealed that exogenous 12-HETE (20 ng) led to the expression of a 65- and 83kDa protein. Immunoreactivity towards the 65kDa protein was commonly detected. In contrast, after heat shock treatment and predominantly after incubation with 12-HETE significant immunoreactivity (anti-hsp72) was detected in the lower molecular weight range whereas immunoreactivity (anti-hsp90, AC88) was only observed after heat shock treatment of LMBs.

12-Lipoxygenase from rat basophilic leukemia cells: separation from 5-lipoxygenase and temperature-dependent inactivation by hydroperoxy fatty acid

12-Lipoxygenase and 5-lipoxygenase from rat basophilic leukemia cells were separated by protein-HPLC in a single step. Upon incubation in the presence of Ca2+, 12-lipoxygenase converted arachidonic acid into 12(S)-hydroxyeicosatetraenoic acid and linoleic acid into 13(S)-hydro(pero)xyoctadecadienoic acid. The reaction products were analyzed by reversed-phase and chiral straight-phase HPLC with ultraviolet-detection. Using the cytosolic fraction of rat basophilic leukemia cells, optimal 12-lipoxygenase activity was observed at 10 degrees C. At 37 degrees C 12-lipoxygenase was very rapidly inactivated by its own product, hydroperoxy fatty acid, at low concentrations (10-100 nM).

Stimulation of human airway epithelial cells by platelet activating factor (PAF) and arachidonic acid produces 15-hydroxyeicosatetraenoic acid (15-HETE) capable of contracting bronchial smooth muscle

Human airway epithelial cells grown to confluence were incubated with varying concentrations (10-100 microM) of arachidonic acid or platelet activating factor (PAF) for periods of 30 min to 24 h. Both stimuli caused the production of 15-hydroxyeicosatetraenoic acid (15-HETE) by epithelial cells as determined by HPLC. Neither stimulus caused the production of leukotrienes, thromboxane or prostaglandins aside from minimal amounts of PGE2. Maximal production of 15-HETE after arachidonic acid (10 microM; N = 9) occurred at 1 h (235 +/- 59 ng/mg protein), whereas maximum generation after PAF treatment (10 microM; N = 9) occurred at 6 h (153 +/- 48 ng/mg protein). Neither arachidonic acid nor PAF at concentrations up to 100 microM caused cell toxicity as determined by 51Cr release. 15-HETE at concentrations of greater than or equal to 0.1 microM contracted isolated human bronchus. An initial small amplitude, short-lasting (less than 15 min) contraction was followed by a much larger contraction beginning 30-60 min following 15-HETE challenge, reaching a maximum at approximately 2 hr. These results demonstrate that PAF may induce delayed airway smooth muscle contraction by the generation of 15-HETE from epithelial cells. The kinetics of 15-HETE generation and its contractile activity are compatible with it being a mediator of the late asthmatic reaction.

Stimulation by carrageenan of arachidonate 12-lipoxygenase activity in dog gingival tissue

At 4 h after injection of carrageenan into the gingiva, the 12-lipoxygenase activity of the gingival homogenate was markedly increased. Activity in the cytosol and microsomal fractions was markedly increased when assessed as the specific activity based on nmol/min/mg of protein, and in the cytosol fraction as the percentage distribution of total activity. The 12-lipoxygenase activity in the homogenate from carrageenan-treated gingiva was not affected by either EDTA or calcium ion, or a combination of the two. 12-lipoxygenase activity in both carrageenan-treated and untreated gingiva was inhibited dose-dependently by AA861, a striking difference from its effect on platelet 12-lipoxygenase. There was a marked increase of 12-lipoxygenase activity in experimentally inflamed gingiva compared to the non-inflamed gingiva.

Selective conversion and esterification of monohydroxyeicosatetraenoic acids by human vascular smooth muscle cells: relevance to smooth muscle cell proliferation

5-, 12-, and 15-hydroxyeicosatetraenoic acid (HETE), lipoxygenase metabolites of arachidonic acid that may modulate cell proliferation, were examined for their ability to affect the [3H]thymidine incorporation of human umbilical artery smooth muscle cells. We found that these hydroxy fatty acids inhibited the serum-induced [3H]thymidine incorporation of growth-arrested vascular smooth muscle cells in a similar dose-dependent manner. The inhibitory effect was dependent on the serum concentration used to stimulate cell growth. The higher the serum concentration, the lower the inhibitory effect of the HETE. In parallel experiments, the incorporation of HETEs into lipids of the smooth muscle cells was examined. After 20 h of incubation, we found that in the presence of 0.4% serum 70% of 3H-labeled 5-HETE was esterified into human vascular smooth muscle cell lipids. Twelve and eight percent, respectively, of 12- and 15-HETE were incorporated into smooth muscle cell lipids. Furthermore, we found that during the 20-h incubation of human umbilical artery smooth muscle cells with 12- and 15-HETE, these compounds were converted into metabolites with a chromatographic behavior on HPLC similar to that of diHETEs. 5-HETE was not converted into these polar metabolites. Increasing the serum concentration resulted in a decreased metabolism of all HETEs tested. Thus, the distinct differences between the metabolism of different HETEs by vascular smooth muscle cells does not reflect the proliferation inhibitory effect of these HETEs.

Lipoxygenase-mediated secretory effect of canatoxin the toxic protein from Canavalia ensiformis seeds

Canatoxin was shown to induce serotonin release from rabbit platelets and rat brain synaptosomes, as well as to release insulin from isolated pancreatic islets. All these effects were dose-dependent and were inhibited by lipoxygenase inhibitors, such as nordihydroguaiaretic acid and esculetin, but not by indomethacin, a cyclooxygenase inhibitor. The data suggest that canatoxin-induced secretory effect results from the activation of the lipoxygenase pathway which would elicit exocytosis. Thus, canatoxin might be a useful tool for the study of biological events that involve lipoxygenase mediation.

Smooth muscle cell growth factors

While the roles of the platelet-derived growth factors (PDGFs) in vascular smooth muscle cells (SMCs) continue to be elucidated, these cells, especially in their activated 'synthetic' state, have also been found to express, and proliferate in response to, many of the other families of polypeptide growth factors, such as the fibroblast growth factors. Other stimulators of DNA synthesis, and particularly of SMC hypertrophy, include the vasoconstrictor hormones such as angiotensin II, as well as physical forces, especially stretch or tension. For many of these ligands, multiple receptors have been identified and their means of signal transduction are being characterized rapidly. Regulatory regions of these genes are being identified as are transcription factors. Complex post-transcriptional regulation has also been shown by the findings that some growth factors are phosphorylated, or translocated to the nucleus or the extracellular matrix. Inhibitors have also been identified. These include some prostaglandins, calcium antagonists, agonists that activate guanylate and adenylate cyclases, inhibitors of angiotensin-converting enzyme, interferon gamma, and heparin. Future studies are likely to show that tyrosine phosphatases and recessive oncogenes also regulate growth. The existence of so many autocrine/paracrine mitogens--together with some experimental data--suggests some redundancy in the system as well as some additive effects. Redundancy may limit the efficacy of antibodies to a single growth factor to block cell proliferation. Their evolutionary conservation implies some unique roles for each growth factor but these have not been apparent from in vitro studies to date. Further insights are apt to come from the increasing recognition that growth factors have other effects--on cell attachment, migration, survival, production of extracellular matrix, thrombosis, vaso-constriction, regulation of cytokine synthesis, and inhibition of growth. Many of these effects may prove to be context-dependent, as with the case of growth inhibition by transforming growth factor-beta. Studies in monolayer cultures may not obtain the same results as studies using cocultures of endothelial and smooth muscle cells, or 3-dimensional matrix cultures, organ cultures, or in the intact animal. In vivo descriptive studies of growth factors expressed in vascular embryogenesis, hypertension, atherosclerosis, acute balloon injury and thrombosis are being supplemented by interventions such as infusions with growth factors, antibodies, and toxin conjugates. These studies, and studies using transgenic mice and homologous recombination, should yield information as to mechanisms and may also suggest new therapies.

Selective incorporation of (15S)-hydroxyeicosatetraenoic acid in phosphatidylinositol of human neutrophils: agonist-induced deacylation and transformation of stored hydroxyeicosanoids

The uptake and mobilization of (15S)-hydroxy-5,8,11-cis-13-trans-eicosatetraenoic acid (15-HETE), a major product of arachidonic acid metabolism, was examined with human neutrophils (polymorphonuclear leukocytes; PMNs). Upon exposure to labeled 15-HETE, PMNs rapidly (15 sec to 20 min) incorporated approximately 20% of the label into phosphatidylinositol, while less than 4% was associated with other phospholipid classes and neutral lipids. This pattern was distinct from that of either labeled arachidonate or labeled(5S)-hydroxy-8,11,14-cis-6-trans-eicosatetraenoic acid (5-HETE), which within 20 min were predominantly associated with triglycerides and phosphatidylcholine. After reversed-phase HPLC, greater than 98% of the label in phosphatidylinositol, isolated from PMNs, was released with phospholipase A2. Upon exposure to either chemotactic peptide (FMLP), phorbol 12-myristate 13-acetate, or an ionophore (A23187), 15-HETE-labeled PMNs released 15-HETE from phosphatidylinositol and displayed an impaired ability to generate leukotriene B4 (LTB4), 20-OH-LTB4, and 20-COOH-LTB4. Deacylated [3H]15-HETE was converted to (5S,15S)-dihydroxy-6,13-trans-8,11-cis-eicosatetraenoic acid (5,15-DHETE), lipoxin A4, and lipoxin B4, each carrying 3H label. PMNs labeled with 5-HETE also released and transformed this HETE when stimulated. However, the profile of labeled products differed between PMNs with either esterified 15-HETE or 5-HETE. When activated, 5-HETE-labeled PMNs generated both 5,20-DHETE and 5,15-DHETE but not labeled lipoxins. Threshold aggregation induced by FMLP with 15-HETE-labeled PMNs was inhibited (approximately 2 orders of magnitude), while the threshold response was relatively unimpaired with either A23187 or phorbol 12-myristate 13-acetate-induced aggregation. Results indicate that 15-HETE is rapidly esterified into phosphatidylinositol of PMNs, which can be mobilized and transformed upon exposure of the cells to a second signal. Moreover, they suggest that eicosanoid intermediates other than arachidonic acid can be stored by cells, released via signal transduction, and oxygenated to generate alternative profiles of eicosanoids.

Phospholipid fatty acid composition of various mouse tissues after feeding alpha-linolenate (18:3n-3) or eicosatrienoate (20:3n-3)

The selective incorporation of dietary alpha-linolenate (18:3n-3) and its elongation product, eicosatrienoate (20:3n-3), into various phospholipids (PL) of mouse liver, spleen, kidney, and heart, was examined in a two-week feeding trial by assessing mol % changes in associated fatty acids. Mice were fed fat-free AIN 76A diets modified with either 2 wt% safflower oil (control); 1% safflower and 1% linolenate; or 1% safflower and 1% eicosatrienoate. After linolenate or eicosatrienoate feeding, 20:4n-6 was reduced by 36-50% in liver phosphatidylcholine (PC) and in liver and spleen phosphatidylethanolamine (PE). Linolenate was minimally incorporated into PL, but was desaturated and elongated to 20:5n-3, 22:5n-3, and 22:6n-3, with notable differences in the quantity of these n-3 derivatives associated with different tissues and PL. Eicosatrienoate was uniquely incorporated into the cardiolipin (CL) pool of all organs. There was also considerable retroconversion of 20:3n-3 to 18:3n-3 (PC,PE). Dietary eicosatrienoate may therefore affect metabolism in diverse ways--20:3n-3, which is retroconverted to 18:3n-3, may provide substrate for 20:5n-3 and 22:6n-3 syntheses, whereas intact 20:3n-3 may be incorporated into the CL pool. Acyl modifications of CL are known to affect the activity of key innermitochondrial enzymes, such as cytochrome c oxidase.

12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid is a more potent neutrophil chemoattractant than the 12(R) epimer in the rat cornea

12(R)-hydroxy-5,8,10,14-eicosatetraenoic acid [12(R)-HETE] is reported to be more potent than its epimer 12(S)-HETE as a chemoattractant for human neutrophils in vitro and following topical application to the skin. To assess the in vivo neutrophil chemoattractant potencies of 12(S)-HETE and 12(R)-HETE in the rat, we injected 1 microgram, 5 micrograms, or 10 micrograms of these eicosanoids into the corneal stroma. Rats were killed 12-15 hours after injection, and the number of neutrophils in the stroma was counted in a histological section of the cornea including the injection site. The number of neutrophils was significantly increased in corneas injected with 5 micrograms (+103% of control) or 10 micrograms (+456% of control) of 12(S)-HETE and in those injected with 10 micrograms of 12(R)-HETE (+111% of control). The neutrophilic infiltrate in corneas injected with 1 microgram or 5 micrograms of 12(S)-HETE was not significantly different from that in corneas injected with 1 microgram of leukotriene B4. The data for the 10 micrograms injections indicate that 12(S)-HETE is a more potent neutrophil chemoattractant than 12(R)-HETE in the rat cornea. Our results suggest that species or tissue specificity may determine the relative potencies of 12-HETE epimers as chemoattractants for neutrophils, and that 12(S)-HETE may be an important inflammatory mediator in the rat cornea.

Production of arachidonic and linoleic acid metabolites by guinea pig tracheal epithelial cells

Pulmonary epithelial cells may be responsible for regulating airway smooth muscle function, in part by release of fatty acid-derived mediators. Incubation of isolated guinea pig tracheal epithelial cells with radiolabeled arachidonic acid (AA) leads to the production of 5- and 15-hydroxyeicosatetraenoic acid (5- and 15-HETE) and smaller amounts of leukotriene (LT) B4 and C4 and 12-hydroxyheptadecatrienoic acid (HHT). Epithelial cells also are able to release linoleic acid (LA) metabolites. Incubation with radiolabeled linoleic acid leads to the formation of 9- and 13-hydroxyoctadecadienoic acid (9- and 13-HODE). The biological significance of these mediators produced by epithelial cells is discussed.

Origin, pattern, and mechanism of bile duct proliferation following biliary obstruction in the rat

Proliferation of bile duct-like structures is a hepatic cellular reaction observed in most forms of human liver disease and in a variety of experimental conditions associated with liver injury. Yet the origin, means of initiation, and significance of this hyperplasia are unknown. To clarify these issues we induced bile duct proliferation in rats by ligating the common bile duct and studied (a) hepatic incorporation of [3H]thymidine by histoautoradiography, (b) hepatic morphometry, (c) biliary tree volume using [3H]taurocholate as a marker of biliary transit time, (d) immunohistochemical expression of cytokeratin no. 19, (e) the effect of indomethacin, and (f) the role of increased biliary pressure, in the absence of physiological and biochemical evidence of cholestasis, on [3H]thymidine incorporation by the bile-duct cells. The results have demonstrated that (a) the proliferating bile duct-like cells are products of the extant biliary epithelium and retain its characteristics; (b) bile duct cells divide irrespective of the size of the duct in which they are located and form a system with a lumen continuous with the preexisting one; (c) bile duct proliferation results mainly in elongation, not in circumferential enlargement or sprouting of side branches; (d) portal macrophage infiltration does not play a role in the hyperplastic reaction, and (e) increased biliary pressure is the initiating factor in bile duct cell division. Our results provide evidence that under the present conditions, ductular metaplasia of hepatocytes does not occur and there is no functioning stem cell for biliary epithelial growth segregated in any particular duct size or within the portal connective tissue.

Effects of adhesins from mannose-resistant Escherichia coli on mediator release from human lymphocytes, monocytes, and basophils and from polymorphonuclear granulocytes

We investigated the role of Escherichia coli expressing mannose-resistant hemagglutination and adhesins with regard to the induction of leukotrienes from a suspension of human lymphocytes, monocytes, and basophils (LMBs) compared with human polymorphonuclear granulocytes (PMNs). Genetically cloned E. coli strains expressing various types of mannose-resistant hemagglutination (MRH+) were phagocytosed to a higher degree by monocytes than the nonadherent E. coli strain. The various strains differed in their capacity to induce a chemiluminescence response, which showed the same pattern for LMBs and PMNs. Stimulation of LMBs with bacteria alone, unlike granulocytes, did not activate the cells for the release of leukotrienes. However, preincubation of LMBs with bacteria decreased subsequent leukotriene formation when the cells were stimulated with calcium ionophore. The inhibitory effect was dependent on the concentration of bacteria used for preincubation as well as on the preincubation temperature. The various bacterial strains differed in inhibitory potency for mediator release. Preincubation of LMBs with zymosan, opsonized zymosan, the bacterial peptide FMLP, and peptidoglycan had no inhibitory effect or even increased subsequent leukotriene formation. Opsonized bacteria were far less inhibitory than nonopsonized bacteria. In contrast to human LMBs, preincubation of human PMNs with mannose-resistant bacteria led to increased leukotriene B4 generation and reduced w-oxidation of leukotriene B4. Our data suggest that phagocytes (neutrophils, monocytes) respond in a different way for leukotriene formation after interaction with mannose-resistant E. coli.

Hydroxyeicosatetraenoic acid metabolism in cultured human skin fibroblasts. Evidence for peroxisomal beta-oxidation

To determine whether the peroxisome is responsible for hydroxyeicosatetraenoic acid (HETE) oxidation, 12- and 15-HETE oxidation was measured in normal and peroxisomal deficient skin fibroblasts from patients with Zellweger's (cerebrohepatorenal) syndrome. When incubated for 1 h with normal fibroblasts, reverse phase HPLC indicated that 24% of the 12-HETE radioactivity was converted to one major polar metabolite. Chemical derivatization followed by reverse phase HPLC and TLC indicated that this metabolite is 8-hydroxyhexadecatrienoic acid [16:3(8-OH)]. Similarly, 33% of the added 15-HETE was also converted to a more polar metabolite. Neither 12- nor 15-HETE were converted to any metabolites by the peroxisomal deficient (Zellweger) cells. No defect in HETE oxidation was found in other human fibroblast cell lines with diverse metabolic abnormalities. Zellweger fibroblasts accumulated increased amounts of 12-HETE, compared with normal fibroblasts. As in the normal cells, most of the 12-HETE incorporated into Zellweger fibroblasts was present in the choline and ethanolamine phosphoglycerides. Protein synthesis, lysosomal acid lipase activity, and mitochondrial butyrate oxidation were not impaired in the Zellweger fibroblasts. Since the Zellweger cells do not convert 12- and 15-HETE to oxidative metabolites, peroxisomes appear to be the cellular organelle responsible for HETE oxidation.

Formation of 12-lipoxygenase metabolites in rat cerebral cortical slices: stimulation by calcium ionophore, glutamate and N-methyl-D-aspartate

The 12-lipoxygenase pathway of arachidonic acid metabolism in rat cerebral cortex slices is stimulated by exogenous arachidonic acid, Ca2+ ionophore A23187, phorbol ester, glutamate, N-methyl-D-aspartate (NMDA) but not by kainate and other neurotransmitters except norepinephrine. The 12-hydroxyeicosatetraenoic acid formed is the (S)-enantiomer. A specific role for 12-lipoxygenase metabolites in NMDA receptor activation and long term potentiation is proposed.

Oxidative metabolism of linoleic acid by human leukocytes

Upon incubation with human leukocytes, [1-14C] linoleic acid is almost exclusively transformed into 13-hydroxy-9Z, 11E-octadecadienoic acid (13-HODE) if the linoleic acid concentration is lower than 50 microM. Identification of 13-HODE was done by GLC-MS at the level of its methyl ester, trimethylsilyl ether and by comparison with authentic 13-HODE in two different HPLC systems. Analysis of the products by chiral phase HPLC shows that 13(S)-hydroxy-9Z, 11E-octadecadienoic acid is by far the major metabolite formed by human leukocytes. Comparison of reactions performed with intact or lyzed cells suggests that the formation of 13(S)-HODE by human leukocytes occurs in two steps, a dioxygenation catalyzed by a 15-lipoxygenase and a reduction of intermediate 13-HPODE by a glutathione-dependent peroxidase.