Discovery of an arachidonic acid C-8 lipoxygenase in the gorgonian coral Pseudoplexaura porosa

Promising Anti-Inflammatory Tools: Biomedical Efficacy of Lipoxins and Their Synthetic Pathways

Lipoxins (LXs) have attracted widespread attention as a class of anti-inflammatory lipid mediators that are produced endogenously by the organism. LXs are arachidonic acid (ARA) derivatives that include four different structures: lipoxin A4 (LXA4), lipoxin B4 (LXB4), and the aspirin-induced differential isomers 15-epi-LXA4 and 15-epi-LXB4. Because of their unique biological activity of reducing inflammation in the body, LXs have great potential for neuroprotection, anti-inflammatory treatment of COVID-19, and other related diseases. The synthesis of LXs in vivo is achieved through the action of lipoxygenase (LO). As a kind of important enzyme, LO plays a major role in the physiological processes of living organisms in mammals and functions in some bacteria and fungi. This suggests new options for the synthesis of LXs in vitro. Meanwhile, there are other chemical and biochemical methods to synthesize LXs. In this review, the recent progress on physiological activity and synthetic pathways of LXs is summarized, and new insights into the synthesis of LXs in vitro are provided.

Evolutionary aspects of lipoxygenases and genetic diversity of human leukotriene signaling

Leukotrienes are pro-inflammatory lipid mediators, which are biosynthesized via the lipoxygenase pathway of the arachidonic acid cascade. Lipoxygenases form a family of lipid peroxidizing enzymes and human lipoxygenase isoforms have been implicated in the pathogenesis of inflammatory, hyperproliferative (cancer) and neurodegenerative diseases. Lipoxygenases are not restricted to humans but also occur in a large number of pro- and eucaryotic organisms. Lipoxygenase-like sequences have been identified in the three domains of life (bacteria, archaea, eucarya) but because of lacking functional data the occurrence of catalytically active lipoxygenases in archaea still remains an open question. Although the physiological and/or pathophysiological functions of various lipoxygenase isoforms have been studied throughout the last three decades there is no unifying concept for the biological importance of these enzymes. In this review we are summarizing the current knowledge on the distribution of lipoxygenases in living single and multicellular organisms with particular emphasis to higher vertebrates and will also focus on the genetic diversity of enzymes and receptors involved in human leukotriene signaling.

Up-regulated expression of AOS-LOXa and increased eicosanoid synthesis in response to coral wounding

In octocorals, a catalase-like allene oxide synthase (AOS) and an 8R-lipoxygenase (LOX) gene are fused together encoding for a single AOS-LOX fusion protein. Although the AOS-LOX pathway is central to the arachidonate metabolism in corals, its biological function in coral homeostasis is unclear. Using an acute incision wound model in the soft coral Capnella imbricata, we here test whether LOX pathway, similar to its role in plants, can contribute to the coral damage response and regeneration. Analysis of metabolites formed from exogenous arachidonate before and after fixed time intervals following wounding indicated a significant increase in AOS-LOX activity in response to mechanical injury. Two AOS-LOX isoforms, AOS-LOXa and AOS-LOXb, were cloned and expressed in bacterial expression system as active fusion proteins. Transcription levels of corresponding genes were measured in normal and stressed coral by qPCR. After wounding, AOS-LOXa was markedly up-regulated in both, the tissue adjacent to the incision and distal parts of a coral colony (with the maximum reached at 1 h and 6 h post wounding, respectively), while AOS-LOXb was stable. According to mRNA expression analysis, combined with detection of eicosanoid product formation for the first time, the AOS-LOX was identified as an early stress response gene which is induced by mechanical injury in coral.

8R-Lipoxygenase-catalyzed synthesis of a prominent cis-epoxyalcohol from dihomo-γ-linolenic acid: a distinctive transformation compared with S-lipoxygenases

Conversion of fatty acid hydroperoxides to epoxyalcohols is a well known secondary reaction of lipoxygenases, described for S-specific lipoxygenases forming epoxyalcohols with a trans-epoxide configuration. Here we report on R-specific lipoxygenase synthesis of a cis-epoxyalcohol. Although arachidonic and dihomo-γ-linolenic acids are metabolized by extracts of the Caribbean coral Plexaura homomalla via 8R-lipoxygenase and allene oxide synthase activities, 20:3ω6 forms an additional prominent product, identified using UV, GC-MS, and NMR in comparison to synthetic standards as 8R,9S-cis-epoxy-10S-erythro-hydroxy-eicosa-11Z,14Z-dienoic acid. Both oxygens of (18)O-labeled 8R-hydroperoxide are retained in the product, indicating a hydroperoxide isomerase activity. Recombinant allene oxide synthase formed only allene epoxide from 8R-hydroperoxy-20:3ω6, whereas two different 8R-lipoxygenases selectively produced the epoxyalcohol.A biosynthetic scheme is proposed in which a partial rotation of the reacting intermediate is required to give the observed erythro epoxyalcohol product. This characteristic and the synthesis of cis-epoxy epoxyalcohol may be a feature of R-specific lipoxygenases.

Applications of stereospecifically-labeled Fatty acids in oxygenase and desaturase biochemistry

Oxygenation and desaturation reactions are inherently associated with the abstraction of a hydrogen from the fatty acid substrate. Since the first published application in 1965, stereospecific placement of a labeled hydrogen isotope (deuterium or tritium) at the reacting carbons has proven a highly effective strategy for investigating the chemical mechanisms catalyzed by lipoxygenases, hemoprotein fatty acid dioxygenases including cyclooxygenases, cytochromes P450, and also the desaturases and isomerases. This review presents a synopsis of all published studies through 2010 on the synthesis and use of stereospecifically labeled fatty acids (71 references), and highlights some of the mechanistic insights gained by application of stereospecifically labeled fatty acids.

The identification and role of a novel eicosanoid in the reproductive behaviour of barnacles (Balanus balanus)

Post-copulatory behaviour in barnacles involves a violent rocking movement of the opercular valves, which is thought to contribute to the expulsion of oocytes through the oviduct into the mantle cavity where they are fertilised. We demonstrate in this study that the seminal vesicles/testis of the subtidal barnacle Balanus balanus produce a biologically active factor,barnacle muscle stimulatory factor (BMSF), which causes a significant increase in cirral and body muscular activity. BMSF was identified using a combination of high performance liquid chromatography and mass spectrometry as a novel eicosanoid/oxylipin, 8,13-dihydroxyeicosapentaenoic acid. This is rapidly inactivated under mild acid conditions to form a complex range of triene and pentaene chromophore-containing products that have only been partially identified. Injection of purified BMSF into the mantle cavity of barnacles caused the rocking movements of the opercular valves as reported following fertilisation. In excised barnacles, it also caused muscular contractions of the whole body mass. The breakdown products of BMSF, however, were without such activities. The function of BMSF in facilitating fertilisation in barnacles is comparable to the role of other eicosanoids in human reproduction, reinforcing the view that these compounds have conserved activities in both invertebrates and vertebrates.

Synthesis of 8,9-leukotriene A4 by murine 8-lipoxygenase

Arachidonate 8-lipoxygenase was identified in phorbol ester induced mouse skin. We expressed the enzyme in an Escherichia coli system using pET-15b carrying an N-terminal histidine-tag sequence. The enzyme, purified by nickel-nitrilotriacetate affinity chromatography, showed specific activity of about 0.1 micromol/min/mg of protein with arachidonic acid as a substrate. When metabolites of arachidonic acid were reduced and analyzed by reverse-phase HPLC, 8-hydroxy derivative was a major product as measured by absorbance at 235 nm. In addition, three polar compounds (I, II, and III) were detected by measuring absorbance at 270 nm. These compounds were also produced when the enzyme was incubated with 8-hydroperoxyeicosa-5,9,11,14-tetraenoic acid. Neither heat-inactivated enzyme nor mutated enzyme produced these compounds, suggesting that they are enzymatically generated. Ultraviolet spectra of these compounds showed typical triplet peaks around 270 nm, indicating that they have a triene structure. Molecular weight of these compounds was determined to be 336 by liquid chromatography-mass spectrometry, indicating that they carry two hydroxyl groups. Compounds I and III were generated even under anaerobic condition, indicating that oxygenation reaction was not required for their generation from 8-hydroperoxyeicosa-5,9,11,14-tetraenoic acid. By analogy to the reactions of 5-lipoxygenase pathway where leukotriene A4 is generated, it is suggested that 8-hydroperoxyeicosa-5,9,11,14-tetraenoic acid is converted by the 8-lipoxygenase to 8,9-epoxyeicosa-5,10,12,14-tetraenoic acid which degrades to compounds I and III by non-enzymatic reaction. In contrast, compound II was not generated under anaerobic condition, indicating that it was produced by oxygenation reaction. Taken together, 8-lipoxygenase catalyzes both dehydration reaction to yield 8,9-epoxy derivative and oxygenation reaction presumably at 15-position of 8-hydroperoxyeicosa-5,9,11,14-tetraenoic acid.

Characterization and quantification of free and esterified 9- and 13-hydroxyoctadecadienoic acids (HODE) in barley, germinating barley, and finished malt

The analysis of (R)-9- and (S)-9-hydroxy-10E,12Z-octadecadienoic acid as well as (R)-13- and (S)-13-hydroxy-9Z,11E-octadecadienoic acid (HODE) as free acids, esterified in triacylglycerols (storage lipids), and esterified in polar lipids (phospholipids, glycolipids, etc.) in barley, germinating barley, and finished malt was performed using [13-(18)O(1)]-(S)-13-HODE isotope dilution assays with GC-MS and straight- and chiral-phase HPLC. 9- and 13- HODE occur approximately racemically in barley, indicating an autoxidation. The enantiomeric excesses increase to 78% S for free 9-HODE and to 58% S for free 13-HODE in germinating barley as a result of lipoxygenase-2 (LOX-2) catalysis, but free HODEs are at low concentration. More than 90% of HODEs in barley and malt are esterified. In the storage lipids of green malt 53 mg/kg 9-HODE and 147 mg/kg 13-HODE were detected. This ratio of 30:70 reflects the regioselectivity of the LOX-2 enzyme in malt. In the polar lipids 45 mg/kg 9-HODE and 44 mg/kg 13-HODE were characterized. The latter indicate a hitherto unknown 9-lipoxygenase activity with polar lipids as substrates. During kilning the contents of most HODEs decreased significantly due to chemical and enzymatic degradation, whereas polar-esterified (R)-13-HODE increased (43%) in the finished malt.

Eicosanoid generation in the intertidal barnacle,Balanus perforatus—effect of season and reproductive status

The nature and quantity of the principal lipoxygenase (LO) products generated by the intertidal barnacle Balanus perforatus were examined at monthly intervals and their potential involvement in reproductive events was investigated. The main mono-hydroxy products generated were found to be formed through the action of an 8-lipoxygenase (8-LO) activity and were the mono-hydroxy fatty acids, 8-hydroxyeicosapentaenoic acid (HEPE) and 8-hydroxyeicosatetraenoic acid. Generation of these products was found to be correlated with the environmental seawater temperature, although no change in either 8-LO activity or the precursor fatty acid levels in total phospholipids was found with the time of the year. Changes in fatty acid composition measured in animals collected from summer and winter conditions were found to follow the pattern expected by homeoviscous adaptation of a cold-acclimated animal. Oogenesis was found to occur in August and was linked to a significant reduction in 8-HEPE generation. Spermatozoa were found to be present year-round in the seminal vesicles although the testes became atrophic during the winter months.

Biological significance of essential fatty acids/prostanoids/lipoxygenase-derived monohydroxy fatty acids in the skin

The skin displays a highly active metabolism of polyunsaturated fatty acids (PUFA). Dietary deficiency of linoleic acid (LA), an 18-carbon (n-6) PUFA, results in characteristic scaly skin disorder and excessive epidermal water loss. Although arachidonic acid (AA), a 20-carbon (n-6) PUFA, is metabolized via cyclooxygenase pathway into predominantly prostaglandin E2 (PGE2) and PGF2alpha, the metabolism of AA via the 15-lipoxygenase (15-LOX) pathway, which is very active in skin epidermis and catalyzes the transformation of AA into predominantly 15S-hydroxyeicosatetraenoic acid (15S-HETE). Additionally, the 15-LOX also metabolizes the 18-carbon LA into 13S-hydroxyoctadecadienoic acid (13S-HODE), respectively. Interestingly, 15-LOX catalyzes the transformation of dihomo-gamma-linolenic acid (DGLA), derived from dietary gamma-linolenic acid, to 15S-hydroxyeicosatrienoic acid (15S-HETrE). These monohydroxy fatty acids are incorporated into the membrane inositol phospholipids which undergo hydrolytic cleavage to yield substituted-diacylglycerols such as 13S-HODE-DAG from 13S-HODE and 15S-HETrE-DAG from 15S-HETrE. These substituted-monohydroxy fatty acids seemingly exert anti-inflammatory/antiproliferative effects via the modulation of selective protein kinase C as well as on the upstream/down-stream nuclear MAP-kinase/AP-1/apoptotic signaling events.

Lipoxygenase-catalyzed formation of R-configuration hydroperoxides

Prototypical lipoxygenases (LOXs) of animals and plants synthesize hydroperoxy fatty acids of the S stereoconfiguration, yet enzymes forming R-configuration products are found in both the animal and plant kingdoms. R-LOX are widespread in aquatic invertebrates, in some of which their R-HETE products have a defined role in reproductive function. A 12R-LOX has been found recently in humans and mice. The human 12R-LOX product, 12R-HETE, appears to be involved in the pathophysiology of psoriasis and other proliferative skin diseases; a role in normal skin development is implied from the spatial and temporal expression patterns of the 12R-LOX in the mouse embryo. In plants, there are few reports of R-LOX activity and in higher plants this is limited to enzymes that catalyze a significant degree of non-specific oxygenation. There are no obvious amino acid sequence motifs characterizing R-LOXs; and in the phylogenetic tree of the LOX superfamily, the R-LOXs do not group into a specific branch of genes. The mechanistic basis of stereocontrol over the oxygenation reaction performed by LOXs may relate to a changed binding orientation of the fatty acid substrate or to the direction of attack by molecular oxygen. A potentially relevant precedent for switching of R- and S-oxygenation specificity was described recently in studies of prostaglandin C-15 oxygenation during cycloxygenase catalysis; single amino acid changes can invert the oxygenation stereospecificity at C-15. In this case, the evidence suggests that R/S switching can occur with the substrate binding in the normal conformation.

Evidence of a cyclooxygenase-related prostaglandin synthesis in coral. The allene oxide pathway is not involved in prostaglandin biosynthesis

Certain corals are rich natural sources of prostaglandins, the metabolic origin of which has remained undefined. By analogy with the lipoxygenase/allene oxide synthase pathway to jasmonic acid in plants, the presence of (8R)-lipoxygenase and allene oxide synthase in the coral Plexaura homomalla suggested a potential metabolic route to prostaglandins (Brash, A. R., Baertshi, S. W., Ingram, C.D., and Harris, T. M. (1987) J. Biol. Chem. 262, 15829-15839). Other evidence, from the Arctic coral Gersemia fruticosa, has indicated a cyclooxygenase intermediate in the biosynthesis (Varvas, K., Koljak, R., Järving, I., Pehk, T., and Samel, N. (1994) Tetrahedron Lett. 35, 8267-8270). In the present study, active preparations of G. fruticosa have been used to identify both types of arachidonic acid metabolism and specific inhibitors were used to establish the enzyme type involved in the prostaglandin biosynthesis. The synthesis of prostaglandins and (11R)-hydroxyeicosatetraenoic acid was inhibited by mammalian cyclooxygenase inhibitors (indomethacin, aspirin, and tolfenamic acid), while the formation of the products of the 8-lipoxygenase/allene oxide pathway was not affected or was increased. The specific cyclooxygenase-2 inhibitor, nimesulide, did not inhibit the synthesis of prostaglandins in coral. We conclude that coral uses two parallel routes for the initial oxidation of polyenoic acids: the cyclooxygenase route, which leads to optically active prostaglandins, and the lipoxygenase/allene oxide synthase metabolism, the role of which remains to be established. An enzyme related to mammalian cyclooxygenases is the key to prostaglandin synthesis in coral. Based on our inhibitor data, the catalytic site of this evolutionary early cyclooxygenase appears to differ significantly from both known mammalian cyclooxygenases.

Manganese lipoxygenase. Purification and characterization

A linoleic acid (13R)-lipoxygenase was purified to homogeneity from the culture medium of Gäumannomyces graminis, the take-all fungus, by hydrophobic interaction, cation exchange, lectin affinity, and size-exclusion chromatography. The purified dioxygenase lacked light absorption between 300 and 700 nm. Gel filtration indicated an apparent molecular mass of approximately 135 kDa in 6 M urea and approximately 160 kDa in buffer. SDS-polyacrylamide gel electrophoresis (PAGE) showed that the enzyme was heterogeneous in size and consisted of diffuse protein bands of 100-140 kDa. Treatment with glycosidases for N- and O-linked oligosaccharides yielded a distinct protein of approximately 73 kDa on SDS-PAGE. Atomic emission spectroscopy indicated 0.5-1.0 manganese atom/enzyme molecule. The isoelectric point was approximately 9.7, and the enzyme was active between pH 5 and 11 with optimum activity at pH 7. 0. For molecular oxygen, Km was 30 microM and Vmax 10 micromol mg-1min-1; for linoleic acid, Km was 4.4 micromol, Vmax 8.2 micromol mg-1min-1, and the turnover number 1100 min-1. The enzyme oxidized linolenic acid twice as fast as linoleic acid. The main products were identified by mass spectrometry as 13-hydroperoxy-(9Z,11E, 15Z)-octadecatrienoic and 13-hydroperoxy-(9Z,11E)-octadecadienoic acids, respectively. After reduction of the hydroperoxide, steric analysis of methyl 13-hydroxyoctadecadienoate by chiral high performance liquid chromatography yielded one enantiomer (>95%), which co-eluted with the R-stereoisomer of methyl (13R, 13S)-hydroxyoctadecadienoate. Arachidonic and dihomogammalinolenic acids were not substrates, while oxygen consumption, UV analysis, and mass spectrometric analysis indicated that gamma-linolenic acid was oxygenated both at C-11 and C-13. The enzyme was active at 60 degreesC and after treatment with 6 M urea. It was strongly inhibited by 10-50 microM concentrations of eicosatetraynoic acid and a lipoxygenase inhibitor (N-(3-phenoxycinnamyl)acetohydroxamic acid), but many other lipoxygenase inhibitors (100 microM) were without effect. We conclude that, after deglycosylation, the enzyme has the same size on SDS-PAGE as mammalian and marine lipoxygenases, but it differs from all previously described lipoxygenases in three ways. It is secreted, it forms (13R)-hydroperoxy-(9Z, 11E)-octadecadienoic acid, and it contains manganese.

Identification of an 8-lipoxygenase pathway in nervous tissue of Aplysia californica

Arachidonic acid is converted to (8R)-hydroperoxyeicosa-5,9,11, 14-tetraenoic acid (8-HPETE) during incubations with homogenates of the central nervous system of the marine mollusc, Aplysia californica. 8-HPETE can be reduced to the corresponding hydroxy acid or be enzymatically converted to a newly identified metabolite, 8-ketoeicosa-5,9,11,14-tetraenoic acid (8-KETE). These metabolites were identified by high performance liquid chromatography, UV absorbance, and gas chromatography/mass spectrometry. Stereochemical analysis of the products demonstrate that the neuronal enzyme is an (8R)-lipoxygenase. Previously we have shown that the neurotransmitters, histamine and Phe-Met-Arg-Phe-amide, activate 12-lipoxygenase metabolism in isolated identified Aplysia neurons. We now show that acetylcholine activates the (8R)-lipoxygenase pathway within intact nerve cells. Thus, both (12S)- and (8R)-lipoxygenase co-exist in intact Aplysia nervous tissue but are differentially activated by several neurotransmitters. The precise physiological role of the 8-lipoxygenase products is currently under investigation, but by analogy to the well-described 12-lipoxygenase pathway, we suggest that (8R)-HPETE and 8-KETE may serve as second messengers in Aplysia cholinoceptive neurons.

Identification and hatching factor activity of monohydroxyeicosapentaenoic acid in homogenates of the barnacle Elminius modestus

A crude eicosanoid extract of the barnacle Elminius modestus caused hatching of isolated egg masses from both E. modestus and Balanus balanoides . On thin-layer chromatography (TLC) two bands containing hatching factor activity were identified, a monohydroxy fatty acid (MHFA) band with potent hatching factor activity and a less active trihydroxy fatty acid (THFA) band. Gas chromatography-mass spectrometry (GC-MS) of the MHFA band showed that it consisted mainly of positional isomers of monohydroxyeicosapentaenoic acid, predominantly 8-hydroxyeicosapentaenoic acid (8-HEPE). A range of positional isomers of monohydroxyeicosapent­aenoic acid was produced by autoxidation of the methyl ester and this mixture was highly active in hatching E. modestus eggs. The commer­cially available stereoisomer 8( S )-HEPE hatched E. modestus eggs at concentrations as low as 10 -8 M. The saturated derivative 8-hydroxyeicosanoic acid did not show hatching factor activity.

Biosynthesis of arachiodonic acid metabolites in Limulus polyphemus amebocytes: analysis by liquid chromatography-electrospray ionization mass spectrometry

Eicosanoid metabolites were generated by isolated granular amebocytes of the primitive arthropod, Limulus polyphemus, when stimulated by the calcium ionophore A23187 and/or exogenous arachidonic acid. The metabolites were isolated, identified, and the major metabolite was quantified using reverse-phase high pressure liquid chromatography (RP-HPLC) coupled to electrospray ionization mass spectrometry (ESI-MS). Qualitative examination revealed putative metabolites and the major product, 8-hydroxyeicosatetraenoic acid (8-HETE), which was quantified using standard curves generated from extracted ion profiles of the molecular ion. Electrospray ionization of the HETEs in negative ion mode produces a base peak for all isomers which corresponded to the molecular ion [(M-H)-: m/z 319]. The molecular ion was accompanied by the neutral loss of water and carbon dioxide [(M-H -H2O)-: m/z 301; (M-H -H2O -CO2)-: m/z 257], as well as daughter ions which were dependent upon the position of hydroxy substitution. Standard curves were generated in full scan mode for standards ranging from 6.25 to 100 ng, whereas selected ion recording was used for the lower levels of 0.8 to 6.25 ng.

Purification and molecular cloning of an 8R-lipoxygenase from the coral Plexaura homomalla reveal the related primary structures of R- and S-lipoxygenases

Lipoxygenases that form S configuration fatty acid hydroperoxides have been purified or cloned from plant and mammalian sources. Our objectives were to characterize one of the lipoxygenases with R stereospecificity, many of which are described in marine and freshwater invertebrates. Characterization of the primary structure of an R-specific enzyme should help provide a new perspective to consider the enzyme-substrate interactions that are the basis of the specificity of all lipoxygenases. We purified an 8R-lipoxygenase of the prostaglandin-containing coral Plexaura homomalla by cation and anion exchange chromatography. This yielded a colorless enzyme preparation, a band of approximately 100 kDa on SDS-polyacrylamide gel electrophoresis, and turnover numbers of 4000 min-1 of 8R-lipoxygenase activity in peak chromatographic fractions. The full-length cDNA was cloned by PCR using peptide sequence from the purified protein and by 5'- and 3'-rapid amplification of cDNA ends. The cDNA encodes a polypeptide of 715 amino acids, including over 70 amino acids identified by peptide microsequencing. A peptide presequence of 52 amino acids is cleaved to give the mature protein of 76 kDa; the difference from the estimated size by SDS-PAGE implies a post-translational modification of the P. homomalla enzyme. All of the iron-binding histidines of S-lipoxygenases are conserved in the 8R-lipoxygenase. However, the C-terminal amino acid is a threonine, as opposed to the isoleucine that provides the carboxylate ligand to the iron in all known S-lipoxygenases. These results establish that the 8R-lipoxygenase is related in primary structure to the S-lipoxygenases. A model of the basis of R and S stereospecificity is described.

Clavulones and related tert-hydroxycyclopentenone fatty acids: occurrence, physiological activity and problem of biogenetic origin

The present review is concerned with a group of prostanoids from soft corals, namely, clavulones and their congeners, as well as with related octadecanoids found in plants of the genus Chromolaena (Compositae). Known physiological properties of these prostaglandin-like fatty acids are discussed. Special attention is paid to published hypotheses on the biogenetic origin of clavulones and related fatty acids. According to a newly proposed biosynthetic route, acyclic alpha-ketols are metabolic precursors of cyclopentenolones.

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

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

Biosynthesis of eicosanoids by blood cells of the crab, Carcinus maenas

Blood cells from the crab, Carcinus maenas, stimulated with calcium ionophore A23187, in the presence of exogenous fatty acid, produced cyclooxygenase, lipoxygenase and monooxygenase derivatives of eicosatetraenoic (20:4(n - 6)) and eicosapentaenoic (20:5(n - 3)) acids. Isolation, identification and quantification of these products was achieved using chiral and reverse phase-high performance liquid chromatography, gas-chromatography, radioimmunoassay and gas chromatography-mass spectrometry. The principle metabolites observed were 8-hydroxy fatty acids and 'E' series prostaglandins. Smaller amounts of thromboxane B2, 6-keto-prostaglandin F1 alpha and 5-, 9-, 11-, 12- and 15-hydroxy-eicosatetraenoic acids were also synthesised. Lipoxygenase, cyclooxygenase and cytochrome P-450 inhibitors were used to investigate the mode of product formation. Mixtures of hydroxy-fatty acid enantiomers were produced and the dominant chiral form varied with the position of the hydroxyl group. No leukotrienes or lipoxins were detected.

Investigation of the mechanism of biosynthesis of 8-hydroxyeicosatetraenoic acid in mouse skin

One of the many changes induced by topical application of phorbol ester or calcium ionophore A23187 to mouse skin is the appearance of an enzymic activity which will convert arachidonic acid to its 8-hydroxyeicosatetraenoic acid metabolite (8-HETE) (Gschwendt, M., et al (1986) Carcinogenesis 7, 449-455). Induction of this activity is lower in strains of mice with a weak inflammatory response to TPA, and the 8-HETE may be involved in the inflammation or hyperplasia. To further characterize the activity, we first measured the chirality of the product; it is almost exclusively the 8DS)-hydroxy enantiomer (8S-HETE). The 8(S)-HETE is formed from octadeuterated arachidonic acid with complete retention of deuterium labels, indicating that a keto intermediate is not involved in the biosynthesis. Using arachidonic acids labeled with a prochiral tritium in either the 10DR or 10LS positions, we found that the biosynthesis of 8S-HETE is associated with the stereoselective abstraction of the 10DR hydrogen from the 10-carbon of the substrate. This stereoselective hydrogen removal conforms to the properties of an 8S-lipoxygenase. This is the only lipoxygenase known to catalyze solely 8S-oxygenation of arachidonic acid. The recent characterization of stereoselective biological effects for other HETEs serve as strong precedents to suggest that 8S-HETE has a specific role in the cellular tissue response to TPA.

"Enzymatic" lipid peroxidation: reactions of mammalian lipoxygenases

Lipoxygenase is a dioxygenase which incorporates one molecule of oxygen at a certain position of unsaturated fatty acids such as arachidonic and linolenic acids. The enzymatic oxygenation of unsaturated fatty acids is stereospecific concomitant with a stereoselective abstraction of hydrogen atom. Fatty acid cyclooxygenase is an atypical lipoxygenase incorporating two molecules of oxygen, and initiates the biosynthesis of prostaglandins and thromboxanes. Arachidonate 5-lipoxygenase is responsible for the leukotriene synthesis. No such bioactive compound has been found as a metabolite of the 12- and 15-lipoxygenase pathways, and their physiological roles are still unclarified. These enzymes have been purified, and their molecular and catalytic properties have been investigated. Their cDNA clones have been isolated, and their nucleotide sequences have been determined deducing the primary structures of the enzymes.

Characterization and behaviour of 15-lipoxygenase during peanut cotyledonary senescence

Lipoxygenase (EC 1.13.11.12) (LOX), a ubiquitous plant enzyme which catalyzes the hydroperoxidation of unsaturated fatty acids (PUFA), plays an important role during the course of leaf and cotyledonary senescence. In the present study, senescence related changes in chlorophyll and protein content and lipoxygenase activity have been examined in peanut cotyledons. The chlorophyll content of the cotyledons increased from the 2nd to 8th day followed by a steady decline. In contrast, protein content of peanut cotyledons decreased continuously during senescence. Lipoxygenase activity, on the other hand, increased in early stages of germination followed by a decrease in the later course of senescing peanut cotyledons. Analysis of the product profile, the lipoxygenase with arachidonic acid as the substrate on HPLC, has shown a single peak comigrating with standard 15-Hydroperoxyeicosatetraenoic acid. The results on peanut cotyledonary 15-lipoxygenase activity in relation to abscisic acid and kinetin are discussed.

Activation of leukocyte movement and displacement of [3H]leukotriene B4 from leukocyte membrane preparations by (12R)- and (12S)-hydroxyeicosatetraenoic acid

Both (12R)- and (12S)-hydroxyeicosatetraenoic acid were demonstrated to produce aggregation of rat leukocytes and enhance human leukocyte chemokinesis. (12R)-Hydroxyeicosatetraenoic acid was 10-20-fold more potent than (12S)-hydroxyeicosatetraenoic acid but at least 500-fold less potent than leukotriene B4 in these assays. These relative potencies are correlated with the potencies of (12R)- and (12S)-hydroxyeicosatetraenoic acid for competition of [3H]leukotriene B4 binding to rat and human leukocyte membrane preparations.