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

Evolutionary history of histamine receptors: Early vertebrate origin and expansion of the H3-H4 subtypes

Histamine receptors belonging to the superfamily of G protein-coupled receptors (GPCRs) mediate the diverse biological effects of biogenic histamine. They are classified into four phylogenetically distinct subtypes H₁-H₄, each with a different binding affinity for histamine and divergent downstream signaling pathways. Here we present the evolutionary history of the histamine receptors using a phylogenetic approach complemented with comparative genomics analyses of the sequences, gene structures, and synteny of gene neighborhoods. The data indicate the earliest emergence of histamine-mediated GPCR signaling by a H₂ in a prebilaterian ancestor. The analyses support a revised classification of the vertebrate H₃-H₄ receptor subtypes. We demonstrate the presence of the H₄ across vertebrates, contradicting the currently held notion that H₄ is restricted to mammals. These non-mammalian vertebrate H₄ orthologs have been mistaken for H₃. We also identify the presence of a new H₃ subtype (H₃B), distinct from the canonical H₃ (H₃A), and propose that the H₃A, H₃B, and H₄ likely emerged from a H₃ progenitor through the 1R/2R whole genome duplications in an ancestor of the vertebrates. It is apparent that the ability of the H₁, H₂, and H_3-4 to bind histamine was acquired convergently. We identified genomic signatures suggesting that the H₁ and H₃-H₄ shared a last common ancestor with the muscarinic receptor in a bilaterian predecessor whereas, the H₂ and the α-adrenoreceptor shared a progenitor in a prebilaterian ancestor. Furthermore, site-specific analysis of the vertebrate subtypes revealed potential residues that may account for the functional divergence between them.

Lipids, fatty acids and hydroxy-fatty acids of Euphausia pacifica

Euphausia pacifica is a good candidate for a resource of marine n-3 PUFA. However, few reports exist of the lipid and fatty acid composition of E. pacifica. To examine the potential of E. pacifica as a resource of marine n-3 PUFA, we analyzed E. pacifica oil. We extracted lipids from E. pacifica harvested from the Pacific Ocean near Sanriku, Japan. Lipid classes of E. pacifica oil were analyzed by TLC-FID and the fatty acid composition of the oil was analyzed by GC/MS. Free fatty acids and hydroxy-fatty acids were analyzed by LC/QTOFMS. The lipid content of E. pacifica ranged from 1.30% to 3.57%. The ratios of triacylglycerols, phosphatidylcholine, phosphatidylethanolamine and free fatty acids in E. pacifica lipids were 5.3-23.0%, 32.6-53.4%, 8.5-25.4% and 2.5-7.0%, respectively. The content of n-3 PUFA in E. pacifica lipids was 38.6-46.5%. We also showed that E. pacifica contains unusual fatty acids and derivatives: C16-PUFAs (9,12-hexadecadienoic acid, 6,9,12-hexadecatrienoic acid and 6,9,12,15-hexadecatetraenoic acid) and hydroxy-PUFAs (8-HETE and 10-HDoHE). E. pacifica is a good resource of marine n-3 PUFA. Moreover, E. pacifica can provide C16-PUFA and hydroxy-PUFAs.

Gemfibrozil inhibits Legionella pneumophila and Mycobacterium tuberculosis enoyl coenzyme A reductases and blocks intracellular growth of these bacteria in macrophages

We report here that gemfibrozil (GFZ) inhibits axenic and intracellular growth of Legionella pneumophila and of 27 strains of wild-type and multidrug-resistant Mycobacterium tuberculosis in bacteriological medium and in human and mouse macrophages, respectively. At a concentration of 0.4 mM, GFZ completely inhibited L. pneumophila fatty acid synthesis, while at 0.12 mM it promoted cytoplasmic accumulation of polyhydroxybutyrate. To assess the mechanism(s) of these effects, we cloned an L. pneumophila FabI enoyl reductase homolog that complemented for growth an Escherichia coli strain carrying a temperature-sensitive enoyl reductase and rendered the complemented E. coli strain sensitive to GFZ at the nonpermissive temperature. GFZ noncompetitively inhibited this L. pneumophila FabI homolog, as well as M. tuberculosis InhA and E. coli FabI.

Long-term exposure to histamine induces the expression of an embryonic-like motor pattern in an adult nervous system

Neuromodulatory inputs play important roles in shaping the outputs of neural networks. While the actions of neuromodulatory substances over the short term (seconds, minutes) have been examined in detail, far less is known about the possible longer-term (hours) effects of these substances. To investigate this issue, we used the stomatogastric nervous system (STNS) of the lobster to examine the short- and long-term effects of histamine on rhythmic network activity. The application of histamine to the entire STNS had strong inhibitory effects on all three of the STNS networks, observable within minutes. In contrast, longer-term (> 1 h) application of histamine induced the expression of a single, unified rhythm involving neurons from all three networks. Selective application of histamine to different regions of the STNS demonstrated that a unified rhythm arises following the long-term application of histamine to the commissural ganglia (CoGs; modulatory centres), but not the stomatogastric ganglion (site of neural networks). Strikingly, the single rhythm observed following the long-term application of histamine to the CoGs exhibits many similarities with the single rhythm expressed by the embryonic STNS. Together, these results demonstrate that histamine has markedly different short- and long-term effects on network activity; short-term effects arising through direct actions on the networks and long-term effects mediated by actions on modulatory neurons. Furthermore, they indicate that histamine is able to induce the expression of an embryonic-like rhythm in an adult system, suggesting that long-term actions of histamine may play key roles in the development of the STNS networks.

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.

Platelet particle formation by anti GPIIIa49-66 Ab, Ca2+ ionophore A23187, and phorbol myristate acetate is induced by reactive oxygen species and inhibited by dexamethasone blockade of platelet phospholipase A2, 12-lipoxygenase, and NADPH oxidase

An HIV antibody (Ab) against platelet integrin GPIIIa49-66 induces complement-independent platelet particle formation by the elaboration of reactive oxygen species (ROS) downstream of the activation of the platelet NADPH oxidase by the 12-lipoxygenase (12-LO) product 12(S)-HETE. To determine whether other inducers of platelet particle formation also function via the induction of ROS, we examined the effects of the Ca(2+) ionophore A23187 and phorbol myristate acetate (PMA). Both agents induced oxidative platelet particle formation in an identical fashion as Ab, requiring Ca(2+) flux and 12(S)-HETE production as well as intact NADPH oxidase and 12-LO pathways. Since HIV-ITP patients with this Ab correct their platelet counts with dexamethasone (Dex), we examined the role of this steroid in this unique autoimmune disorder. Dex at therapeutic concentrations inhibited Ab-, A23187-, or PMA-induced platelet particle formation by inhibiting platelet PLA(2), 12-LO, and NADPH oxidase. The operational requirement of translocation of PLA(2), 12-LO, and NADPH oxidase components (p67 phox) from cytosol to membrane for induction of ROS was both inhibited and partially reversed by Dex in platelets. We conclude that (1) platelet particle formation can be induced by the generation of ROS; and (2) platelet PLA(2), 12-LO, NADPH oxidase, and cytosol membrane translocation, requirements for ROS production, are inhibited by Dex.

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.

Complement-independent Ab-induced peroxide lysis of platelets requires 12-lipoxygenase and a platelet NADPH oxidase pathway

Antiplatelet GPIIIa49-66 Ab of HIV-related thrombocytopenic patients induces thrombocytopenia and platelet fragmentation by the generation of peroxide and other reactive oxygen species (ROS). Here we report the presence of a functional platelet NADPH oxidase pathway that requires activation by the platelet 12-lipoxygenase (12-LO) pathway to fragment platelets. A new Ab-mediated mechanism is described in which the platelet 12-LO product, 12(S)-HETE activates the NADPH oxidase pathway to generate ROS.

12-lipoxygenase metabolites of arachidonic acid mediate metabotropic glutamate receptor-dependent long-term depression at hippocampal CA3-CA1 synapses

Arachidonic acid metabolites have been proposed as signaling molecules in hippocampal long-term potentiation (LTP) and long-term depression (LTD) for >15 years. However, the functional role of these molecules remains controversial. Here we used a multidisciplinary biochemical, electrophysiological, and genetic approach to examine the function of the 12-lipoxygenase metabolites of arachidonic acid in long-term synaptic plasticity at CA3-CA1 synapses. We found that the 12-lipoxygenase pathway is required for the induction of metabotropic glutamate receptor-dependent LTD (mGluR-LTD), but is not required for LTP: (1) Hippocampal homogenates were capable of synthesizing the 12-lipoxygenase metabolite of arachidonic acid, 12(S)-hydroxyeicosa-5Z,8Z,10E,14Z-tetraenoic acid (HETE). (2) Stimulation protocols that induce mGluR-LTD lead to a release of 12-(S)-HETE from acute hippocampal slices. (3) A mouse in which the leukocyte-type 12-lipoxygenase (the neuronal isoform) was deleted through homologous recombination was deficient in mGluR-LTD, but showed normal LTP. (4) Pharmacological inhibition of 12-lipoxygenase also blocked induction of mGluR-LTD. (5) Finally, direct application of 12(S)-HPETE, but not 15(S)-HPETE, to hippocampal slices induced a long-term depression of synaptic transmission that mimicked and occluded mGluR-LTD induced by synaptic stimulation. Thus, 12(S)-hydroperoxyeicosa-5Z, 8Z, 10E, 14Z-tetraenoic acid (12(S)-HPETE), a 12-lipoxygenase metabolite of arachidonic acid, satisfies all of the criteria of a messenger molecule that is actively recruited for the induction of mGluR-LTD.

Role of monocytes in atherogenesis

This review focuses on the role of monocytes in the early phase of atherogenesis, before foam cell formation. An emerging consensus underscores the importance of the cellular inflammatory system in atherogenesis. Initiation of the process apparently hinges on accumulating low-density lipoproteins (LDL) undergoing oxidation and glycation, providing stimuli for the release of monocyte attracting chemokines and for the upregulation of endothelial adhesive molecules. These conditions favor monocyte transmigration to the intima, where chemically modified, aggregated, or proteoglycan- or antibody-complexed LDL may be endocytotically internalized via scavenger receptors present on the emergent macrophage surface. The differentiating monocytes in concert with T lymphocytes exert a modulating effect on lipoproteins. These events propagate a series of reactions entailing generation of lipid peroxides and expression of chemokines, adhesion molecules, cytokines, and growth factors, thereby sustaining an ongoing inflammatory process leading ultimately to lesion formation. New data emerging from studies using transgenic animals, notably mice, have provided novel insights into many of the cellular interactions and signaling mechanisms involving monocytes/macrophages in the atherogenic processes. A number of these studies, focusing on mechanisms for monocyte activation and the roles of adhesive molecules, chemokines, cytokines and growth factors, are addressed in this review.

Loading and recycling of synaptic vesicles in the Torpedo electric organ and the vertebrate neuromuscular junction

In vertebrate motor nerve terminals and in the electromotor nerve terminals of Torpedo there are two major pools of synaptic vesicles: readily releasable and reserve. The electromotor terminals differ in that the reserve vesicles are twice the diameter of the readily releasable vesicles. The vesicles contain high concentrations of ACh and ATP. Part of the ACh is brought into the vesicle by the vesicular ACh transporter, VAChT, which exchanges two protons for each ACh, but a fraction of the ACh seems to be accumulated by different, unexplored mechanisms. Most of the vesicles in the terminals do not exchange ACh or ATP with the axoplasm, although ACh and ATP are free in the vesicle interior. The VAChT is controlled by a multifaceted regulatory complex, which includes the proteoglycans that characterize the cholinergic vesicles. The drug (-)-vesamicol binds to a site on the complex and blocks ACh exchange. Only 10-20% of the vesicles are in the readily releasable pool, which therefore is turned over fairly rapidly by spontaneous quantal release. The turnover can be followed by the incorporation of false transmitters into the recycling vesicles, and by the rate of uptake of FM dyes, which have some selectivity for the two recycling pathways. The amount of ACh loaded into recycling vesicles in the readily releasable pool decreases during stimulation. The ACh content of the vesicles can be varied over eight-fold range without changing vesicle size.

Metabotropic histamine receptors--nothing for invertebrates?

Histamine, a major neurotransmitter both in vertebrates and invertebrates, transmits its actions through a set of well-known receptors. In vertebrates, these receptors belong to the family of G-protein-coupled receptors. In invertebrates, the few well-characterized actions of histamine are transmitted through ionotropic histamine receptors. To evaluate if metabotropic histamine receptors are part of the invertebrate histaminergic signaling cascade, I identified the complete set of metabotropic bioamine receptors from two invertebrates, whose entire genome has been sequenced: the fruitfly Drosophila melanogaster and the soil nematode Caenorhabditis elegans. A comparison with representatives of all groups of metabotropic bioamine receptors from vertebrates and invertebrates showed that none of these receptors clusters together with any of the four groups of vertebrate histamine receptors. This implies that no direct homologues to vertebrate metabotropic histamine receptor are present in invertebrates. Therefore, it is reasonable to account that the histaminergic neurotransmission in invertebrates is exclusively transmitted through ionotropic histamine receptors and that metabotropic histamine receptors evolved after the split between vertebrates and invertebrates.

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.

The heart ofCiona intestinalis: eicosanoid-generating capacity and the effects of precursor fatty acids and eicosanoids on heart rate

Eicosanoids are a group of oxygenated fatty-acid derivatives formed from C20 polyunsaturated fatty acids including arachidonic and eicosapentaenoic acids. In mammals, these compounds have been shown to be key molecules in several physiological processes including regulation of the vascular system. This study determined whether eicosanoids or their precursors are involved in the regulation of heart rate in the sea squirt Ciona intestinalis. Eicosanoid generation by both heart and blood cells was measured. The major lipoxygenase products formed were both derivatives of eicosapentaenoic acid,namely 8- and 12-hydroxyeicosapentaenoic acids (8-HEPE and 12-HEPE). Smaller amounts of 8,15-dihydroxyeicosapentaenoic acid (8,15-diHEPE) were also formed. The cyclo-oxygenase product prostaglandin E was also found in small amounts in the heart. Isolated hearts were exposed either to these fatty acid precursors or to 8-HEPE, 12-HEPE or prostaglandin E3, and the effect on heart rate was recorded. Both eicosapentaenoic and arachidonic acids stimulated the heart rate at concentrations between 50 and 200 μmoll-1. 12-HEPE(5 μmoll-1) and prostaglandin E3 (50μmoll-1) caused a modest increase in heart rate, while 8-HEPE had no significant effects at any of the time periods studied (≤180 min). Overall, the results show that arachidonic and eicosapentaenoic acids have limited effects on heart rate and only at concentrations unlikely to be routinely liberated in vivo. Similarly, the eicosanoids tested had a minor stimulatory activity on heart rate. The potential mechanisms for this stimulation are discussed. Overall, these results suggest that such compounds are of limited importance in regulating the heart and vascular system of sea squirts.

A Pertussis Toxin-Sensitive 8-Lipoxygenase Pathway Is Activated by a Nicotinic Acetylcholine Receptor inAplysia Neurons

Acetylcholine (ACh) activates two types of chloride conductances in Aplysia neurons that can be distinguished by their kinetics and pharmacology. One is a rapidly desensitizing current that is blocked by α-conotoxin-ImI and the other is a sustained current that is insensitive to the toxin. These currents are differentially expressed in Aplysia neurons. We report here that neurons that respond to ACh with a sustained chloride conductance also generate 8-lipoxygenase metabolites. The sustained chloride conductance and the activation of 8-lipoxygenase have similar pharmacological profiles. Both are stimulated by suberyldicholine and nicotine, and both are inhibited by α-bungarotoxin. Like the sustained chloride conductance, the activation of 8-lipoxygenase is not blocked by α-conotoxin-ImI. In spite of the similarities between the metabolic and electrophysiological responses, the generation of 8-lipoxygenase metabolites does not appear to depend on the ion current since an influx of chloride ions is neither necessary nor sufficient for the formation of the lipid metabolites. In addition, the application of pertussis toxin blocked the ACh-activated release of arachidonic acid and the subsequent production of 8-lipoxygenase metabolites, yet the ACh-induced activation of the chloride conductance is not dependent on a G protein. Our results are consistent with the idea that the nicotinic ACh receptor that activates the sustained chloride conductance can, independent of the chloride ion influx, initiate lipid messenger synthesis.

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.