Discovery of an 11 (R)- and 12(S)-lipoxygenase activity in ovaries of the mussel Mytilus edulis

Stabilization and improved activity of arachidonate 11S-lipoxygenase from proteobacterium Myxococcus xanthus

Lipoxygenases (LOXs) catalyze the dioxygenation of PUFAs to produce regio- and stereospecific oxygenated fatty acids. The identification of regio- and stereospecific LOXs is important because their specific products are involved in different physiological activities in various organisms. Bacterial LOXs are found only in some proteobacteria and cyanobacteria, and they are not stable in vitro. Here, we used C20 and C22 PUFAs such as arachidonic acid (ARA), eicosapentaenoic acid, and docosahexaenoic acid to identify an 11S-specific LOX from the proteobacterium Myxococcus xanthus and explore its in vitro stability and activity. The activity and stability of M. xanthus ARA 11S-LOX as well as the production of 11S-hydroxyeicosatetraenoic acid from ARA were significantly increased by the addition of phosphatidylcholine, Ca²⁺, and coactosin-like protein (newly identified in the yeast Rhodosporidium toluroides) as stimulatory factors; in fact, LOX activity in the presence of all three factors increased approximately 3-fold. Our results indicate that these stimulatory factors can be used to increase the activity and stability of bacterial LOX and the production of bioactive hydroxy fatty acids, which can contribute to new academic research.

Differential regulation of the lipoxygenase pathway in shrimp hepatopancreases and ovaries during ovarian development in the black tiger shrimp Penaeus monodon

Dietary polyunsaturated fatty acids (PUFAs) are critical to the success of ovarian development in marine crustaceans, especially for domesticated species such as the black tiger shrimp Penaeus monodon. These fatty acids are stored in a midgut gland called the hepatopancreas and subsequently serve as an energy source or are incorporated in yolk during ovarian development. PUFAs are known precursors of hydroxy fatty acids, including hydroxyeicosatetraenoic acid and hydroxyeicosapentaenoic acid (HEPE), which are catalyzed by lipoxygenases (LOX). In previous studies, 8-HEPE has been shown to regulate female reproduction and adipogenesis in marine crustaceans. However, whether the biosynthesis of 8-HEPE in these species is the result of LOX activity has yet to be investigated. In this study, 8-HEPE was identified exclusively in P. monodon hepatopancreases using liquid chromatography-mass spectrometry. Treatment with nordihydroguaiaretic acid resulted in the reduction of 8-HEPE, suggesting the enzyme-dependent catalysis of 8-HEPE in hepatopancreases. Additionally, a full-length P. monodon LOX (PmLOX) was amplified from shrimp ovary cDNA. Sequence analysis revealed that the putative PmLOX contains domains and catalytic residues required for LOX catalytic function. Furthermore, PmLOX expression increased steadily as shrimp ovary maturation progressed, while PmLOX expression and the amount of 8-HEPE decreased in shrimp hepatopancreases. These findings not only suggest differential requirements for hydroxy fatty acid biosynthesis in shrimp ovaries and hepatopancreases during the P. monodon ovarian development, but also provide insights into the LOX pathway in marine crustaceans.

Structural and functional biology of arachidonic acid 15-lipoxygenase-1 (ALOX15)

Lipoxygenases (LOX) form a family of lipid peroxidizing enzymes, which have been implicated in a number of physiological processes and in the pathogenesis of inflammatory, hyperproliferative and neurodegenerative diseases. They occur in two of the three domains of terrestrial life (bacteria, eucarya) and the human genome involves six functional LOX genes, which encode for six different LOX isoforms. One of these isoforms is ALOX15, which has first been described in rabbits in 1974 as enzyme capable of oxidizing membrane phospholipids during the maturational breakdown of mitochondria in immature red blood cells. During the following decades ALOX15 has extensively been characterized and its biological functions have been studied in a number of cellular in vitro systems as well as in various whole animal disease models. This review is aimed at summarizing the current knowledge on the protein-chemical, molecular biological and enzymatic properties of ALOX15 in various species (human, mouse, rabbit, rat) as well as its implication in cellular physiology and in the pathogenesis of various diseases.

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.

Identification of hydroxyeicosatetraenoic acid components of schistosomal hemozoin

During the late stages of Schistosoma mansoni infection, adult schistosomes catabolize host erythrocytic hemoglobin. In order to evade the toxic effects of free heme, the blood fluke biomineralizes dimeric heme into an inert crystalline pigment called hemozoin. In the present study, the chemical reactivity of schistosomal hemozoin (SmHz) toward lipid oxidation was examined, and the biological consequences of reactivity were investigated. Mass spectrometric analysis of polar lipid content associated with SmHz identified a variety of primary and secondary polyunsaturated fatty acid oxidation products, including hydroxyeicosatetraenoic acids. Furthermore, RAW 264.7 macrophage-like cells challenged with lipopolysaccharide prior to phagocytosis of SmHz experienced a decrease in nitric oxide production as compared to control experiments. The presence of these biologically active oxidation products suggests native SmHz is capable of modulating the innate immune response and may play a potential role in the pathogenesis of schistosomiasis.

Biosynthesis and functions of eicosanoids generated by the coelomocytes of the starfish, Asterias rubens

Eicosanoids are a group of oxygenated fatty acid derivatives formed from C20 polyunsaturated fatty acids, including arachidonic and eicosapentaenoic acids. The potential of the coelomocytes of the starfish, Asterias rubens, to generate eicosanoids through the cyclooxygenase (COX) and lipoxygenase (LOX) pathways was investigated using reverse-phase high performance liquid chromatography, enzyme immunoassay and gas chromatography-mass spectrometry. The principal LOX product was identified as 8-hydroxyeicosatetraenoic acid (8-HETE) with 8-hydroxyeicosapentaenoic acid (8-HEPE) synthesised at significantly lower levels. No classical prostaglandins (PG), such as PGE2 or PGD2, were found to be generated by ionophore-challenged coelomocytes. Incubation of coelomocytes with lipopolysaccharides from either Escherichia coli or Salmonella abortus failed to induce an increase in generation of LOX products and the presence of 8-HETE (0-25 microM) had no significant effect on the in vitro phagocytic activity of Asterias coelomocytes. Neither indomethacin (a COX inhibitor) or esculetin (a LOX inhibitor) had any effect on the clearance of the bacterium, Vibrio splendidus, from the coelomic cavity of starfish suggesting that products of these enzymes are not involved in such coelomocyte responses to foreign particles.

A novel beta-oxa polyunsaturated fatty acid downregulates the activation of the IkappaB kinase/nuclear factor kappaB pathway, inhibits expression of endothelial cell adhesion molecules, and depresses inflammation

Several novel polyunsaturated fatty acids (PUFAs) that contain either an oxygen or sulfur atom in the beta-position were found to exhibit more selective antiinflammatory properties than their natural PUFA counterparts. One of these, beta-oxa-23:4n-6, unlike natural PUFAs, lacked ability to stimulate oxygen radical production in neutrophils but caused marked inhibition of agonist-induced upregulation of leukocyte adhesion to cultured human umbilical vein endothelial cells (HUVEC) and E-selectin, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1 expression. In addition, beta-oxa-23:4n-6 inhibited acute and chronic inflammatory responses in mice as well as the upregulation of adhesion molecule expression in arterial endothelium. This action of beta-oxa-23:4n-6 required a functional 12- but not 5-lipoxygenase or cyclooxygenases, consistent with its metabolism via the 12-lipoxygenase pathway. Whereas beta-oxa-23:4n-6 did not affect the activation of mitogen-activated protein kinases by tumor necrosis factor, activation of the IkappaB kinase/nuclear factor kappaB pathway was selectively inhibited. These novel PUFAs could form the basis for a potential new class of pharmaceuticals for treating inflammatory diseases, including atherosclerosis.

Biosynthetic intermediates and stereochemical aspects of aldehyde biosynthesis in the marine diatom Thalassiosira rotula

Intermediates of the aldehyde biosynthesis in Thalassiosira rotula are investigated. Use of labeled precursors and cell preparations proves production of 2E,4Z-octadienal from 6Z,9Z,12Z-hexadecatrienoic acid (C16:3 omega-4) through the lipoxygenase-dependent intermediate (9S)-9-hydroperoxyhexadeca-6,10,12-trienoic acid. On the contrary, synthesis of 2E,4Z,7Z-decatrienal involves mainly EPA (C20:5 omega-3) by a 11R-lipoxygenase, as suggested by identification of chiral 11R-HEPE (12% e.e.) in the diatom extracts. Consistently with the necessity to have a rapid transport and metabolization of the intermediate hydroperoxides, we show that lipoxygenase and lyase activities are both found in the same subcellular fraction of the microalga.

Identification and characterization of an arachidonate 11R-lipoxygenase

11R-Lipoxygenase (11R-LOX) activity has been detected in several marine invertebrates, and here we report the first cloning and expression of the enzyme. The cDNA encoding a protein of 77kDa was isolated by RT-PCR from the soft coral Gersemia fruticosa and expressed in Escherichia coli. Incubations of recombinant enzyme with arachidonic acid yielded a single product, identified by RP-HPLC, GC-MS, and chiral phase-HPLC as 11R-hydroperoxyeicosatetraenoic acid. Other C18, C20, and C22 substrates are also oxygenated, preferentially at the omega10 position. Significantly, both Ca(2+)-ions and a membrane fraction are required for catalytic activity. Calcium effects translocation of the soluble 11R-LOX to the membrane and this association is reversible by Ca(2+) chelation. The enzyme sequence contains some conserved amino acids implicated in calcium activation of mammalian 5-LOX, and with its obligate requirement for membrane interaction the 11R-LOX may thus provide a new model for further analysis of this aspect of lipoxygenase activation.

A comprehensive model of positional and stereo control in lipoxygenases

The lipoxygenase gene family can synthesize an array of chiral hydroperoxy derivatives from polyunsaturated fatty acids. An individual enzyme, however, reacts molecular oxygen on a single position on the carbon chain and in a single stereo configuration. Regiospecificity is regulated by the orientation and depth of substrate entry into the active site. Stereospecificity is a different issue and only recently has experimental support emerged to explain the conceptual basis of stereo control. A key determinant is a single active site residue conserved as an Ala in S lipoxygenases and a Gly in R lipoxygenases; this residue controls R or S stereochemistry by switching the position of oxygenation on the reacting pentadiene of the substrate. In this review, we meld together the factors that control product regio- and stereochemistry into a general model that can account for the specificity of individual lipoxygenase reactions.

Effect of nordihydroguaiaretic acid on intracellular Ca(2+) concentrations in hepatocytes

The effect of nordihydroguaiaretic acid (NDGA) on Ca(2+) signaling in human hepatoma cells (HA22/VGH) has been investigated. NDGA (5-50 microM) increased [Ca(2+)](i) concentration-dependently. The [Ca(2+)](i) increase comprised an initial rise and an elevated phase over a time period of 4 min. Removal of extracellular Ca(2+) reduced 10-50 microM NDGA induced [Ca(2+)](i) signals by 45+/-5%. Consistently, the 50 microM NDGA-induced [Ca(2+)](i) increase in Ca(2+)-containing medium was reduced by 41+/-2% by 10 microM of La(3+), nifedipine or verapamil. In Ca(2+)-free medium, pretreatment with 20 microM NDGA for 6 min abolished the [Ca(2+)](i) increase induced by the endoplasmic reticulum Ca(2+) pump inhibitor thapsigargin (1 microM). Conversely, 20 microM NDGA failed to increase [Ca(2+)](i) after 1 microM thapsigargin had depleted the endoplasmic reticulum Ca(2+) store. Inhibition of phospholipase C with 2 microM U73122 had little effect on 20 microM NDGA-induced Ca(2+) release. Several other lipoxygenase inhibitors had no effect on basal [Ca(2+)](i). Together, the data suggest that NDGA increased [Ca(2+)](i) in hepatocytes in a lipoxygenase-independent manner, by releasing Ca(2+) from the endoplasmic reticulum and causing Ca(2+) influx.

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.