Metabolism of 15-hydroxy-5,8,11,13-eicosatetraenoic acid by MOLT-4 cells and blood T-lymphocytes

MOLT-4 lymphocytes metabolize 15-hydroxy-5,8,11,13-eicosatetraenoic acid (15-HETE) via beta-oxidation with retention of the hydroxyl group at the omega 6-carbon atom. 15-HETE oxidation is accompanied by the time-dependent accumulation of both beta-hydroxy acids and metabolites produced by repetitive cycles of the beta-oxidation spiral. Detection of 7-hydroxy-5-dodecenoic acid shows that these cells continue to beta-oxidize the substrate when the conjugated diene is allylic to a hydroxyl group. When 15-HETE was the substrate, it was also possible to detect 12-hydroxy-5,8,10-heptadecatrien-1-al and 3,15-dihydroxy-8,11,13-eicosatrienoic acid. The former product may be produced by alpha-oxidation of 13-hydroxy-6,9,11-octadecatrienoic acid followed by its decarboxylation. Detection of a 20-carbon metabolite, lacking a double bond at position 5, suggests that an intermediate of beta-oxidation was used as a substrate for chain elongation. When 13-hydroxy-6,9,11-octadecatrienoic acid was used as a substrate, it was indeed possible to detect 3,15-dihydroxy-8,11,13-eicosatrienoic acid as well as 15-hydroxy-8,11,13-eicosatrienoic acid. In addition, 13-hydroxy-6,9,11-octadecatrienoic acid was a precursor for the biosynthesis of both 14-hydroxy-7,10,12-nonadecatrien-1-al and 1,14-dihydroxy-7,10,12-nonadecatriene. These studies with MOLT-4 cells as well as with T-lymphocytes isolated from blood show that products of the 15-lipoxygenase pathway are metabolized with the accumulation of a variety of compounds. Since 15-HETE has been implicated as a modulator of T-cell function, these findings raise the possibility that the newly described metabolites may be involved in regulating lymphocyte function.     

12-Hydroxyeicosatetraenoic acid is metabolized by beta-oxidation in mouse peritoneal macrophages. Identification of products and proposed pathway

The products derived from the metabolism of 12-hydroxyeicosatetraenoic acid (12-HETE) by mouse peritoneal macrophages were characterized by high performance liquid chromatography (HPLC) and GC-mass spectrometry. HPLC analysis demonstrated two predominant polar products and several minor ones. The proportion and amounts of these products were dependent on the concentration of 12-HETE, the number of macrophages incubated with the monohydroxy fatty acid, and the time of incubation. The products identified by GC-mass spectrometry suggested that 12-HETE had undergone beta-oxidation. The intermediates identified were: 3,12-dihydroxy-5,8,10,14, 20:4; 10-hydroxy-3,6,8,12, 18:4; 3,10-dihydroxy-6,8,12, 18:3; 8-hydroxy-4,6,10, 16:3; 6-hydroxy-4,8, 14:2; and 4-hydroxy, 12:1. The major products, as identified by HPLC and GC-mass spectrometry, were 8-hydroxy-4,6,10, 16:3 and 4-hydroxy, 12:1. A minor product, 10-hydroxy-6,8,12, 18:3 was postulated to arise from either the isomerization and reduction of 10-hydroxy-3,6,8,12, 18:4 or from chain elongation of 8-hydroxy-4,6,10, 16:3. Inhibiting cyclooxygenase and lipoxygenase activities by ibuprofen and nordihydroguaiaretic acid, respectively, did not inhibit the formation of these products. 82% to 98% of 12-HETE was converted and released into the medium as products of beta-oxidation. The remainder was taken up into cellular lipids. beta-Oxidation of 12-HETE was decreased by only 12 and 21% after inhibiting mitochondrial fatty acid oxidation by 89 and 93% by 5 and 100 microM concentrations of the mitochondrial fatty acid oxidation inhibitor, methyl palmoxirate, respectively. It is thus postulated that the beta-oxidation of 12-HETE by mouse peritoneal macrophages occurs in peroxisomes.     

Metabolism of 12(R)-hydroxy-5,8,10,14-eicosatetraenoic acid (12(R)-HETE) in corneal tissues: formation of novel metabolites

12(R)-Hydroxy-5,8,10,14-eicosatetraenoic acid [12(R)-HETE], a cytochrome P450 arachidonate metabolite, is metabolized by corneal tissues via three distinct metabolic pathways: beta-oxidation, omega-hydroxylation, and keto-reduction. The major metabolite released from the intact rabbit corneal epithelium or cultured cells was identified by mass spectrometric analysis as 8-hydroxy-4,6,10-hexadecatrienoic acid, the tetranor metabolite derived following two steps of beta-oxidation from the carboxy terminus. The beta-oxidation pathway was expressed in both microsomes and mitochondria isolated from bovine corneal epithelium and was dependent on the addition of oxidizing equivalents. The major metabolite of 12(R)-HETE in subcellular fractions of bovine corneal epithelial cells was a dihydro compound, 12-hydroxy-5,8,14-eicosatrienoic acid (12-HETrE). This derivative is presumably formed by an oxidation of the hydroxyl group followed by two keto-reduction steps, since its formation was accompanied by the appearance of a keto metabolite identified as 12-oxo-5,8,14-eicosatrienoic acid. The omega-hydroxylation, in contrast to other cell types, was a minor route for 12(R)-HETE metabolism in these tissues. Since 12(R)-HETE has been implicated as a modulator of Na(+)-K(+)-ATPase activity and its related functions in ocular tissues, these findings raise the possibility that the newly described metabolites may be involved in regulating corneal functions. In addition, the presence of a keto reductase in the cornea may be of great importance following injury since 12(R)-HETrE resulting from 12(R)-HETE by this activity is a potent ocular proinflammatory compound.     

Metabolism of 13-hydroxy-9,11-octadecadienoic acid by MOLT-4 lymphocytes

MOLT-4 lymphocytes metabolize 13-hydroxy-9,11-octadecadienoic acid, via the beta-oxidation pathway with retention of the omega 6 hydroxyl group and the conjugated diene system. The products which accumulate include 11-hydroxy-7,9-hexadecadienoic acid and 9-hydroxy-5,7-tetradecadienoic acid. In addition, it was possible to isolate two beta-hydroxy acids which were shown to be 3,13-dihydroxy-9,11-octadecadienoic acid and 3,11-dihydroxy-7,9-hexadecadienoic acid. The odd chain aldehyde, 12-hydroxy-8,10-heptadecadien-1-al, also was detected. However, neither the pathway nor the immediate precursor for the synthesis of this compound was established.     

Resolution by DEAE-cellulose chromatography of the enzymatic steps in the transformation of arachidonic acid into 8, 11, 12- and 10, 11, 12-trihydroxy-eicosatrienoic acid by the rat lung

The 30-50% ammonium sulfate fraction of the high speed supernatant (100,000 xg) of a rat lung homogenate is capable of catalysing the conversion of arachidonic acid into 8,11,12- and 10,11, 12-trihydroxyeicosatrienoic acids. This enzyme preparation was resolved through DEAE cellulose chromatography into three stages which were assayed with precursors specific for each stage. Thus in the first stage arachidonic acid is converted by 12-lipoxygenase into 12-hydroperoxy-5,8,10,14-eicosatetraenoic acid (12-HPETE) detected as the corresponding 12-hydroxy product (12-HETE). 12-HPETE in turn is converted into 8-hydroxy-11,12-epoxy-5,9,14-eicosatrienoic acid and 10-hydroxy-11,12-epoxy-5,8,14-eicosatrienoic acid. These epoxides are in turn selectively converted through an epoxide hydrase into the respective triols. While the first and third stages were carried out by distinct fractions from the DEAE columns, the second i.e. conversion of 12-HPETE into epoxides, was detected in all fractions as was the reduction of 12-HPETE into 12-HETE.     

Arachidonic acid 15-lipoxygenase from rabbit peritoneal polymorphonuclear leukocytes. Partial purification and properties

Arachidonic acid 15-lipoxygenase was purified from rabbit peritoneal polymorphonuclear leukocytes. The enzyme was recovered in the cytosol fraction after sonication and purified about 250-fold by acetone precipitation, column chromatography on CM52, Sephadex G-150, and hydroxyapatite. The enzyme catalyzed the conversion of arachidonic acid to 15-hydroperoxy-5,8,11,13-eicosatetraenoic acid (15-HPETE), which then decomposed to a mixture of 15-hydroxy-5,8,11,13-eicosatetraenoic acid (15-HETE), 15-keto-5,8,11,13-eicosatetraenoic acid, 13-hydroxy-14,15-epoxy-5,8,11-eicosatrienoic acid, and 11,14,15-trihydroxy-5,8,12-eicosatrienoic acid. The enzyme was specific for oxygenation at carbon 15 of arachidonic acid. The apparent molecular weight of the enzyme was about 61,000 as measured by Sephadex G-150 gel filtration chromatography. The enzyme was sensitive to sulfhydryl-blocking reagents such as p-chloromercuribenzoic acid. The enzyme activity was inhibited by eicosatetraynoic acid (ETYA) or 3-amino-1-(m-(trifluoromethyl)-phenyl)2-pyrazoline (BW755C), but not by indomethacin up to 200 micrograms/ml.     

Rabbit renal cortical microsomes metabolize arachidonic acid to trihydroxyeicosatrienoic acids

(1-¹⁴C) Eicosatetraenoic (Arachidonic) acid was incubated wiht microsomes from rabbit renal cortex and NADPH (1 mM) for 15 min at 37°C. The products were extracted and purified by high pressure liquid chromatography. Some of the most polar metabolites were identified by gas chromatography mass spectrometry. They were 11, 12, 19- and 11, 12,20-trihydroxy-5,8-14-eicosatrienoic acid, 14,15,19- and 14,15,20- trihydroxy-5,8,11-eicosatrienoic acid, and 11,12-dihydroxy-19-oxo- 5,8,14-eicosatrienoic acid. These products were likely formed by ω- and (ω−1)-hydroxylation of 11,12-dihydroxy-5,8,14-eicosatrienoic aic and 14,15-dihydroxy-5,8,11-eicosatrienoic acid, two recently identified metabolites of arachidonic acid in fortified rabbit kidney microsomes.     

Biosynthesis and metabolism of 15-hydroperoxy-5,8,11,13-eicosatetraenoic acid by human umbilical vein endothelial cells

Incubation of cultured human umbilical vein endothelial cells with [1-14C]arachidonic acid, followed by reverse-phase high-pressure liquid chromatography analysis, results in the appearance of two principal radioactive products besides 6-keto-prostaglandin F1 alpha. The first peak is 12-L-hydroxy-5,8,10-heptadecatrienoic acid, a hydrolysis product of the prostaglandin endoperoxide. The second peak was esterified, converted to the trimethylsilyl ether derivative, and analyzed by gas chromatography-mass spectrometry and shown to be the lipoxygenase product 15(S)-hydroxy-5,8,11,13-eicosatetraenoic acid (15-HETE). Incubation of the 15-HETE precursor 15(S)-hydroperoxy-5,8,11,13-eicosatetraenoic acid (15-HPETE) with endothelial cells results in the formation of four distinct UV absorbing peaks. UV and gas chromatography-mass spectrometry analysis showed these peaks to be 8,15(S)-dihydroxy-5,8,11,13-eicosatetraenoic acids (8,15-diHETE) differing only in their hydroxyl configuration and cis trans double-bond geometry. Formation of 8,15-diHETE molecules suggests the prior formation of the unstable epoxide molecule 14(S),15(S)-trans-oxido-5,8-Z-14,15-leukotriene A4 or an attack at C-10 of 15-HPETE by an enzyme with mechanistic features in common with a 12-lipoxygenase. The observation that endothelial cells can synthesize both 15-HETE and 8,15-diHETE molecules suggests that this cell type contains both a 15-lipoxygenase and a system that can synthesize 14,15-leukotriene A4.     

Hydroxyeicosatetraenoic acid oxidation in Chinese hamster ovary cells: a peroxisomal metabolic pathway

To evaluate the peroxisomal requirement for beta-oxidation of hydroxyeicosatetraenoic acids (HETES), we tested 5-, 12- and 15-HETE oxidation in wild-type and mutant Chinese hamster ovary (CHO) cells. Mutant CHO cells contain peroxisomal ghosts, have random cytosolic localization of catalase and lack two of the enzymes necessary for peroxisomal beta-oxidation. Reverse-phase HPLC indicated that 33% of 12-HETE radioactivity was converted by wild-type CHO cells during a 2 h incubation to one major and several minor polar metabolites. Wild-type CHO cells also converted 15-HETE to one major and several minor polar metabolites. Neither 12- nor 15-HETE were converted to any metabolites by the mutant CHO cell lines, despite appreciable cellular uptake of these hydroxyeicosanoids. 5-HETE was not converted to any metabolic products by either the wild-type or the mutant CHO cells. Docosahexaenoic acid beta-oxidation was substantially reduced in the mutants as compared to the wild-type cells, palmitic acid beta-oxidation was reduced to an intermediate extent in the mutants, but octanoate beta-oxidation and citrate synthase activity were not impaired. Protein immunoblotting for mitochondrial manganese superoxide dismutase indicated a single band of identity at 20 kDa in both wild-type and mutant CHO cells. Since mutant CHO cells fail to convert 12- and 15-HETE to oxidative metabolites but contain normal mitochondrial enzymatic activities, intact peroxisomes appear to be the organelle responsible for HETE oxidation.     

Diterpenes from Croton salutaris

The twigs of Croton salutaris afforded three new acyclic diterpenes and a new tricyclic diterpene as well as a known compound, sonderianol. The structures of three acyclic diterpenes [(10E)-3,12-dihydroxy-3,7,11,15-tetramethyl-1,10,14-hexadecatrien-5,13-dione, (6E,10E)-3,12-dihydroxy-3,7,11,15-tetramethyl-1,6,10,14-hexadecatetraen-5,13-dione and (6Z,10E)-3,12-dihydroxy-3,7,11,15-tetramethyl-1,6,10,14-hexadecatetraen-5,13-dione] and a tricyclic diterpene [12-hydroxy-13-methylpodocarpa-9,11,13-trien-3-one] were determined by spectral methods.     

Occurrence of free and esterified lipoxygenase products in leaves of Glechoma hederacea L. and other Labiatae

Leaves of Glechoma hederacea L. and other Labiatae contain (9S,10E,12Z,15Z)-9-hydroxy-10,12,15-octadecatrienoic acid, (10E,12Z,15Z)-9-oxo-10,12,15-octadecatrienoic acid, (9S,10E,12Z)-9-hydroxy-10,12-octadecadienoic acid and (10E,12Z)-9-oxo-10,12-octadecadienoic acid in a ratio of 71/14/12/3 (by mass), predominantly esterified in the membrane ester lipids. The leaves contain the highest level of these products, whereas only small amounts were found in the stalk and the roots. The chemical structures of these compounds were established by ultraviolet and infrared spectroscopy, by co-chromatography with authentic standards on various types of HPLC columns including chiral-phase HPLC and gas chromatography/mass spectrometry. The stereochemical specificity indicates the enzymatic origin of the products, most probably via a lipoxygenase reaction. Freshly harvested specimens of G. hederacea L. contain only small amounts of hydroxy-polyenoic fatty acids. Air-drying causes a strong increase in the content of free and esterified (9S,10E,12Z,15Z)-9-hydroxy-10,12,15-octadecatrienoic acid. Up to 80% of the hydroxy fatty acids of the total lipid extracts were esterified in the cellular lipids. The data presented indicate that lipoxygenase products occur in the cellular ester lipids of G. hederacea L. and other Labiatae. The results are discussed in the light of a possible involvement of the lipoxygenase pathway in the natural senescence of leaves.     

Transformation of arachidonic acid by 5- and 15-lipoxygenase pathways in bovine adrenal fasciculata cells

[1-14C]Arachidonic acid was incubated with isolated bovine adrenal fasciculata cells for 15 min at 37gC. The metabolites were separated and purified by reverse- and straight-phase high performance liquid chromatography, and identified by gas chromatography-mass spectrometry or radioimmunoassay. Identified metabolites were 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE), 15-hydroxy-5,8,11,13-eicosatetraenoic acid (15-HETE), leukotriene B4 and 11,14,15-trihydroxy-5,8,12-eicosatrienoic acid (11,14,15-THET). Addition of 15-hydroperoxy-5,8,11,13-eicosatetraenoic acid (15-HPETE), an intermediate metabolite of 15-lipoxygenase pathway to microsomes of bovine adrenal fasciculata cells resulted in the formation of 11,14,15-THET. The formation of 11,14,15-THET by microsomes was not dependent on the presence of NADPH, while it was dose-dependently suppressed by ketoconazole, a potent inhibitor of cytochrome P-450 dependent enzymes. These results indicate that 5- and 15-lipoxygenase pathways of arachidonic acid may exist in bovine adrenal fasciculata cells and that 15-HPETE is further metabolized to 11,14,15-THET by adrenal microsomal cytochrome P-450.     

Arachidonic acid and 15(S)-hydroxy-5,8,11-cis-13-trans-eicosatetraenoic acid modulate human polymorphonuclear neutrophil activation by monocyte derived neutrophil activating factor

Exposure of human polymorphonuclear neutrophils (PMN) to human monocyte derived neutrophil activating factor(s) (NAF) resulted in a concentration-dependent extracellular release of granule constituents. NAF also induced the generation of 5(S),12(R)-dihydroxy-6,14-cis-8,10-trans-eicosatetraenoic acid [Leukotriene B4 (LTB4)] by PMNs which was enhanced in the presence of exogenous arachidonic acid (AA). In contrast to its enhancing effect on LTB4 production, AA inhibited NAF-stimulated PMN degranulation. 15(S)-hydroxy-5,8,11-cis-13-trans-eicosatetraenoic acid (15-HETE), a product of the 15-lipoxy-genation of AA in PMNS, caused a concentration-dependent suppression of degranulation and LTB4 generation by PMNs in contact with NAF. 15-HETE also inhibited the rise in cytosolic-free calcium [( Ca2+]i) observed in NAF activated PMNs. These data suggest that AA and a 15-lipoxygenase product modulate the NAF-associated activation pathway in human PMNs.     

Measurement of icosanoids. Report of the Group for Standardization of Methods in Icosanoid Research

This statement from laboratories highly qualified in icosanoid analysis identifies the urgent need for the availability of the following compounds in labeled (deuterium and tritium) and unlabeled form: PGE2 PGF2 alpha PGD2 6-keto-PGF1 alpha Thromboxane B2 9 alpha,20-dihydroxy-11,15-dioxo-2,3- dinorprost -5-enoic acid 9 alpha-hydroxy-11,15-dioxo-2,3,18,19- tetranorprost -5-ene-1,20-dioic acid 15-keto-13,14-dihydro-PGE2 15-keto-13,14-dihydro-PGF2 alpha 5 alpha-7 alpha-dihydroxy-11- ketotetranorprosta -1,16-dioic acid 7 alpha-hydroxy-5,11-diketo- tetranorprosta -1,16-dioic acid 2,3 dinor-thromboxane B2 2,3 dinor-6-keto-PGF1 alpha 2,3 dinor-6,15-diketo 13,14 dihydro-20-carboxyl-PGF1 alpha 2,3 dinor-13,14-dihydro-6,15-diketo-PGF1 alpha LTB4 LTC4 LTD4 LTE4 LTF4 20-OH-LTB4 20-COOH-LTB4 5-HETE 12-HETE 15-HETE omega-OH-12-HETE 5S, 12S-di HETE 5S, 15S-di HETE HHT other hydroxylated polyunsaturated fatty acids and their epoxides.     

Modulation of insulin secretion by lipoxygenase products of arachidonic acid. Relation to lipoxygenase activity of pancreatic islets

Glucose (16.7 mM)-induced insulin secretion from isolated pancreatic islets of rats was inhibited by nordihydroguaiaretic acid (NDGA), 1-phenyl-3-pyrazolidinone (phenidone), 3-amino-1-(3-trifluoromethylphenyl)-2-pyrazoline (BW755C), 2,3,5-trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinone (AA861), and 2,6-di-tert-butyl-4-methylphenol (BHT). Indomethacin and aspirin, however, failed to inhibit the glucose-induced insulin secretion but rather tended to enhance it. The glucose-induced insulin secretion was inhibited by 15-hydroxy-5,8,11,13-eicosatetraenoic acid (15-HETE) (50 microM), 15-hydroperoxy-5,8,11,13-eicosatetraenoic acid (15-HPETE) (100 microM), and 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) (100 microM), but not by 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) (100 microM). Exogenous 5-HETE (10 microM) induced significant insulin secretion in a low glucose (3.3 mM) medium. Racemic 5-HETE also showed insulinotropic effect in a concentration-dependent manner with the concentrations 20 microM or above, whereas 12-HETE, 15-HETE, 15-HPETE, 5,12-dihydroxy-6,8,10,14-eicosatetraenoic acid, 5-hydroxy-6-glutathionyl-7,9,11,14-eicosatetraenoic acid, 5-hydroxy-6-cysteinylglycinyl-7,9,11,14-eicosatetraenoic acid, prostaglandin E2, and prostaglandin F2 alpha failed to induce insulin secretion. Although significant insulin release was observed with arachidonic acid (greater than or equal to 100 microM), reduce cell viability was evident at 200 microM. When the 10,000 X g supernatant of isolated pancreatic islet homogenate was incubated with [3H]arachidonic acid at 37 degrees C in the presence of GSH and Ca2+, and the labeled metabolites then extracted with ethyl acetate and subjected to reverse phase high pressure liquid chromatography, several radioactive peaks, coeluted with authentic 15-, 12-, and 5-HETE, were observed. The radioactive peaks were completely suppressed by the addition of either NDGA, BW755C, or phenidone into the medium. The results support our contention i.e. the involvement of lipoxygenase product(s) in the secretory mechanism of insulin, and further suggest that 5-lipoxygenase system may play a role.     

Dual metabolic pathways of 12-HETE in rat aortic smooth muscle cells.

12(S)-HETE, a major lipoxygenase-derived compound from arachidonic acid is incorporated and metabolized by vascular smooth muscle cells via beta-oxidation. We have now identified for the first time in this cell type 12(S)-HETE metabolites formed by a combination of reductase and oxidation pathways. HPLC and GC-MS analysis of time-course experiments allow us to characterize two different metabolic pathways: a direct peroxisomal beta-oxidation of 12(S)-HETE leading to the formation of 16:3 (8-OH) which accumulates first and a reduction of one of the conjugated double bonds of 12(S)-HETE giving the dihydro-intermediate 20:3(12-OH) that transiently accumulates before being converted itself by peroxisomal beta-oxidation to 16:2(8-OH). Taken together these results may suggest that the transient accumulation of 20:3(12-OH) through transcellular metabolism of 12(S)-HETE may represent a part of the modulatory effect of 12(S)-HETE on vascular function.     

Characterization and biological effects of di-hydroxylated compounds deriving from the lipoxygenation of ALA

We have recently described a di-hydroxylated compound called protectin DX (PDX) which derives from docosahexaenoic acid (DHA) by double lipoxygenation. PDX exhibits anti-aggregatory and anti-inflammatory properties, that are also exhibited by similar molecules, called poxytrins, which possess the same E,Z,E conjugated triene geometry, and are synthesized from other polyunsaturated fatty acids with 22 or 20 carbons. Here we present new biological activities of di-hydroxylated metabolites deriving from α-linolenic acid (18:3n-3) treated by soybean 15-lipoxygenase (sLOX). We show that 18:3n-3 is converted by sLOX into mainly 13(S)-OH-18:3 after reduction of the hydroperoxide product. But surprisingly, and in contrast to DHA which is metabolized into only one di-hydroxylated compound, 18:3n-3 leads to four di-hydroxylated fatty acid isomers. We report here the complete characterization of these compounds using high field NMR and GC-MS techniques, and some of their biological activities. These compounds are: 9(R),16(S)-dihydroxy-10E,12E,14E-octadecatrienoic acid, 9(S),16(S)-dihydroxy-10E,12E,14E-octadecatrienoic acid, 9(S),16(S)-dihydroxy-10E,12Z,14E-octadecatrienoic acid, and 9(R),16(S)-dihydroxy-10E,12Z,14E-octadecatrienoic acid. They can also be synthesized by the human recombinant 15-lipoxygenase (type 2). Their inhibitory effect on blood platelet and anti-inflammatory properties were compared with those already reported for PDX.     

Metabolism of arachidonic acid by isolated rat hepatocytes,renal cells and by some rabbit tissues: Detection of vicinal diols by mass fragmentography

Purified cytochromes P-450 (LM₂ and PB-B₂) in a reconstituted system and epoxide hydrolase were recently found to metabolize arachidonic (eicosatetraenoic) acid to four vicinal dihydroxyeicosatrienoic acids. These metabolites were chemically synthetized from octadeuterated arachidonic acid and employed as internal standards for mass fragmentography. Isolated rat hepatocytes and renal cells were incubated with arachidonic acid (0.1 mM; 37°C, 15 min) and, following extractive isolation and reversed-phase HPLC, formation of 11,12-dihydroxy-5,8,14-eicosatrienoic acid and 14,15-dihydroxy-5,8,11-eicosatrienoic acid was demonstrated by mass fragmentography using a capillary GC column. Furthermore, these diols were also detected in rabbit liver and renal cortex and they therefore appear to be formed endogenously. Formation of vicinal diols was also studied in cell free systems. Rabbit liver and renal cortical microsomes were incubated with NADPH (1 mM) and arachidonic acid (0.15 mM) for 15 min at 37°C and, besides 11,12-dihydroxy- and 14,15-dihydroxyeicosatrienoic acid, small amounts of 8,9-dihydroxy- and 5,6-dihydroxyeicosatrienoic acid could be detected by mass fragmentography. Renal as well as hepatic monooxygenases can thus epoxidize each of the four double bonds of arachidonic acid. In contrast, rabbit lung microsomes and NADPH metabolize arachidonic acid mainly to prostaglandins and 19-hydroxy- and 20-hydroxyarachidonic acid, while only small amounts of 11,12-dihydroxyeicosatrienoic acid could be found. Monooxygenase metabolism of arachidonic acid by epoxidation might therefore be a significant pathway for the metabolism of this essential fatty acid in isolated rat renal cells and hepatocytes but presumably not in the lung.     

The 650-kDa 12(S)-hydroxyeicosatetraenoic acid binding complex: occurrence in human platelets, identification of hsp90 as a constituent, and binding properties of its 50-kDa subunit.

A cytosolic 650-kDa complex which binds 12(S)-hydroxy-5,8,10, 14-eicosatetraenoic acid (12(S)-HETE) with high affinity and specificity has been found in various cell lines but not until now in platelet cytosol. After incubation of human platelets with 12(S)-[3H]HETE, a labeled cytosolic 650-kDa complex was isolated. As previously shown for the binding complex in Lewis lung carcinoma (LLC) cells, ATP treatment transformed the platelet complex into a 50-kDa ligand-binding subunit. These results are of interest for two reasons: (a) 12(S)-HETE is a major arachidonic acid metabolite in platelets, and (b) platelets contain large amounts of the cell adhesion molecule GpIIb/IIIa, the activation of which is regulated by 12(S)-HETE. Hsp90 was found to be a component of the 12(S)-HETE binding complex in Lewis lung carcinoma cells, and the 50-kDa ligand-binding subunit itself bound 12(S)-HETE with high affinity. Competition experiments showed that 12(R)-HETE, 15-deoxy-Delta12, 14-prostaglandin J2, and 5(S)-HETE had lower affinity for the 50-kDa subunit than 12(S)-HETE. The 12(S)-HETE binding protein appears to be distinct from known members of the steroid hormone receptor superfamily of nuclear receptors.     

Lipoxygenase Metabolism of Arachidonic Acid in Brain

When blood-free mouse brain slices were incubated with exogenous radiolabeled arachidonic acid, gas chromatography/mass spectrometry confirmed that the major radioactive lipoxygenase enzyme product of arachidonic acid was 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE), with lesser amounts of 5-hydroxy-5,6,8,11,14-eicosatetraenoic acid and 15-hydroxy-5,8,11,13-eicosatetraenoic acid. When 12-[2H]HETE was used to measure endogenous 12-HETE in brain tissue frozen with liquid nitrogen, the level of 12-HETE was 41 +/- 6 ng/g of wet weight tissue. This frozen tissue level was not due to the presence of blood. When brain slices were incubated in vitro for 20 min, the 12-HETE level increased to 964 +/- 35 ng/g of wet weight tissue. Elimination of residual intravascular blood before tissue incubation reduced the brain slice 12-HETE concentration by one-half.