- Dehydrogenase reductase 9 (SDR9C4) and related homologs recognize a broad spectrum of lipid mediator oxylipins as substrates
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Bioactive oxylipins play multiple roles during inflammation and in the immune response, with termination of their actions partly dependent on the activity of yet-to-be characterized dehydrogenases. Here, we report that human microsomal dehydrogenase reductase 9 (DHRS9, also known as SDR9C4 of the short-chain dehydrogenase/reductase (SDR) superfamily) exhibits a robust oxidative activity toward oxylipins with hydroxyl groups located at carbons C9 and C13 of octadecanoids, C12 and C15 carbons of eicosanoids, and C14 carbon of docosanoids. DHRS9/SDR9C4 is also active toward lipid inflammatory mediator dihydroxylated Leukotriene B4 and pro-resolving mediators such as tri-hydroxylated Resolvin D1 and Lipoxin A4, although notably, with lack of activity on the 15-hydroxyl of prostaglandins. We also found that the SDR enzymes phylogenetically related to DHRS9, i.e., human SDR9C8 (or retinol dehydrogenase 16), the rat SDR9C family member known as retinol dehydrogenase 7, and the mouse ortholog of human DHRS9 display similar activity toward oxylipin substrates. Mice deficient in DHRS9 protein are viable, fertile, and display no apparent phenotype under normal conditions. However, the oxidative activity of microsomal membranes from the skin, lung, and trachea of Dhrs9?/? mice toward 1 μM Leukotriene B4 is 1.7- to 6-fold lower than that of microsomes from wild-type littermates. In addition, the oxidative activity toward 1 μM Resolvin D1 is reduced by about 2.5-fold with DHRS9-null microsomes from the skin and trachea. These results strongly suggest that DHRS9 might play an important role in the metabolism of a wide range of bioactive oxylipins in vivo.
- Belyaeva, Olga V.,Boeglin, William E.,Brash, Alan R.,Goggans, Kelli R.,Karki, Suman,Kedishvili, Natalia Y.,Popov, Kirill M.,Wendell, Stacy G.,Wirth, Samuel E.
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- Inhibitory and mechanistic investigations of oxo-lipids with human lipoxygenase isozymes
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Oxo-lipids, a large family of oxidized human lipoxygenase (hLOX) products, are of increasing interest to researchers due to their involvement in different inflammatory responses in the cell. Oxo-lipids are unique because they contain electrophilic sites that can potentially form covalent bonds through a Michael addition mechanism with nucleophilic residues in protein active sites and thus increase inhibitor potency. Due to the resemblance of oxo-lipids to LOX substrates, the inhibitor potency of 4 different oxo-lipids; 5-oxo-6,8,11,14-(E,Z,Z,Z)-eicosatetraenoic acid (5-oxo-ETE), 15-oxo-5,8,11,13-(Z,Z,Z,E)-eicosatetraenoic acid (15-oxo-ETE), 12-oxo-5,8,10,14-(Z,Z,E,Z)-eicosatetraenoic acid (12-oxo-ETE), and 13-oxo-9,11-(Z,E)-octadecadienoic acid (13-oxo-ODE) were determined against a library of LOX isozymes; leukocyte 5-lipoxygenase (h5-LOX), human reticulocyte 15-lipoxygenase-1 (h15-LOX-1), human platelet 12-lipoxygenase (h12-LOX), human epithelial 15-lipoxygenase-2 (h15-LOX-2), soybean 15-lipoxygenase-1 (s15-LOX-1), and rabbit reticulocyte 15-LOX (r15-LOX). 15-Oxo-ETE exhibited the highest potency against h12-LOX, with an IC50 = 1 ± 0.1 μM and was highly selective. Steady state inhibition kinetic experiments determined 15-oxo-ETE to be a mixed inhibitor against h12-LOX, with a Kic value of 0.087 ± 0.008 μM and a Kiu value of 2.10 ± 0.8 μM. Time-dependent studies demonstrated irreversible inhibition with 12-oxo-ETE and h15-LOX-1, however, the concentration of 12-oxo-ETE required (Ki = 36.8 ± 13.2 μM) and the time frame (k2 = 0.0019 ± 0.00032 s-1) were not biologically relevant. These data are the first observations that oxo-lipids can inhibit LOX isozymes and may be another mechanism in which LOX products regulate LOX activity.
- Armstrong, Michelle M.,Diaz, Giovanni,Kenyon, Victor,Holman, Theodore R.
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p. 4293 - 4297
(2014/08/18)
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- Biosynthesis, isolation, and NMR analysis of leukotriene A epoxides: Substrate chirality as a determinant of the cis or trans epoxide confi guration
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Leukotriene (LT)A 4 and closely related allylic epoxides are pivotal intermediates in lipoxygenase (LOX) pathways to bioactive lipid mediators that include the leukotrienes, lipoxins, eoxins, resolvins, and protectins. Although the structure and stereochemistry of the 5-LOX product LTA 4 is established through comparison to synthetic standards, this is the exception, and none of these highly unstable epoxides has been analyzed in detail from enzymatic synthesis. Understanding of the mechanistic basis of the cis or trans epoxide confi guration is also limited. To address these issues, we developed methods involving biphasic reaction conditions for the LOX-catalyzed synthesis of LTA epoxides in quantities suffi cient for NMR analysis. As proof of concept, human 15-LOX-1 was shown to convert 15 S-hydroperoxy-eicosatetraenoic acid (15 S-HPETE) to the LTA analog 14 S ,15 S-trans-epoxy-eicosa-5 Z ,8 Z ,10 E ,12 E-tetraenoate, confi rming the proposed structure of eoxin A 4 . Using this methodology we then showed that recombinant Arabidopsis AtLOX1, an arachidonate 5-LOX, converts 5 S-HPETE to the trans epoxide LTA 4 and converts 5 R-HPETE to the cis epoxide 5-epi-LTA 4 , establishing substrate chirality as a determinant of the cis or trans epoxide confi guration. The results are reconciled with a mechanism based on a dual role of the LOX nonheme iron in LTA epoxide biosynthesis, providing a rational basis for understanding the stereochemistry of LTA epoxide intermediates in LOX-catalyzed transformations.Copyright
- Jin, Jing,Zheng, Yuxiang,Boeglin, William E.,Brash, Alan R.
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p. 754 - 761
(2013/05/09)
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- Formation of a cyclopropyl epoxide via a leukotriene A synthase-related pathway in an anaerobic reaction of soybean lipoxygenase-1 with 15S-hydroperoxyeicosatetraenoic acid: Evidence that oxygen access is a determinant of secondary reactions with fatty acid hydroperoxides
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The further conversion of an arachidonic acid hydroperoxide to a leukotriene A (LTA) type epoxide by specific lipoxygenase (LOX) enzymes constitutes a key step in inflammatory mediator biosynthesis. Whereas mammalian 5-LOX transforms its primary product (5S-hydroperoxyeicosatetraenoic acid; 5S-HPETE) almost exclusively to LTA4, the model enzyme, soybean LOX-1, normally produces no detectable leukotrienes and instead further oxygenates its primary product 15S-HPETE to 5,15- and 8,15-dihydroperoxides. Mammalian 15-LOX-1 displays both types of activity. We reasoned that availability of molecular oxygen within the LOX active site favors oxygenation, whereas lack of O2 promotes LTA epoxide synthesis. To test this, we reacted 15S-HPETE with soybean LOX-1 under anaerobic conditions and identified the products by high pressure liquid chromatography, UV, mass spectrometry, and NMR. Among the products, we identified a pair of 8,15-dihydroxy diastereomers with all-trans-conjugated trienes that incorporated 18O from H 218O at C-8, indicative of the formation of 14,15-LTA4. A pair of 5,15-dihydroxy diastereomers containing two trans,trans-conjugated dienes (6E,8E,11E,13E) and that incorporated 18O from H 218O at C-5 was deduced to arise from hydrolysis of a novel epoxide containing a cyclopropyl ring, 14,15-epoxy-[9,10,11-cyclopropyl]- eicosa-5Z,7E,13E-trienoic acid. Also identified was the δ-lactone of the 5,15-diol, a derivative that exhibited no 18O incorporation due to its formation by intramolecular reaction of the carboxyl anion with the proposed epoxide intermediate. Our results support a model in which access to molecular oxygen within the active site directs the outcome from competing pathways in the secondary reactions of lipoxygenases.
- Zheng, Yuxiang,Brash, Alan R.
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experimental part
p. 13427 - 13436
(2011/03/22)
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- Physcomitrella patens has lipoxygenases for both eicosanoid and octadecanoid pathways
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Mosses have substantial amounts of long chain C20 polyunsaturated fatty acids, such as arachidonic and eicosapentaenoic acid, in addition to the shorter chain C18 α-linolenic and linoleic acids, which are typical substrates of lipoxygenases in flowering p
- Anterola, Aldwin,G?bel, Cornelia,Hornung, Ellen,Sellhorn, George,Feussner, Ivo,Grimes, Howard
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experimental part
p. 40 - 52
(2009/07/11)
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- Free radical oxidation of 15-(S)-hydroxyeicosatetraenoic acid with the Fenton reagent: characterization of an epoxy-alcohol and cytotoxic 4-hydroxy-2E-nonenal from the heptatrienyl radical pathway
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The oxidation of (5Z,8Z,11Z,13E,15S)-15-hydroxy-5,8,11,13-eicosatetraenoic acid (15-(S)-HETE, 1a) with the Fenton reagent (Fe2+/EDTA/H2O2) was investigated. In phosphate buffer, pH 7.4, the reaction proceeded with 75% substrate consumption after 1 h to give a mixture of products, one of which was identified as (2E,4S)-4-hydroxy-2-nonenal (3a, 18% yield). Methylation of the mixture with diazomethane allowed isolation of another main product which could be identified as methyl (5Z,8Z,13E)-11,12-trans-epoxy-15-hydroxy-5,8,13-eicosatrienoate (2a methyl ester, 8% yield). A similar oxidation carried out on (15-2H)-15-HETE (1b) indicated complete retention of the label in 2b methyl ester and 3b, consistent with an oxidation pathway involving as the primary event H-atom abstraction at C-10. Overall, these results support the recently proposed role of 1a as a potential precursor of the cytotoxic γ-hydroxyalkenal 3a and disclose a hitherto unrecognized interconnection between 1a and the epoxy-alcohol 2a, previously implicated only in the metabolic transformations of the 15-hydroperoxy derivative of arachidonic acid.
- Manini,Briganti,Fabbri,Picardo,Napolitano,d'Ischia
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- Synthesis of phospholipids bearing a conjugated oxo-polyunsaturated fatty acid residue
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2-(15'-Oxo-5',8',11',13'-eicosatetraenoyl)-1-stearoyl- sn- glycerol(3)phosphocholine (APC-CO) 1 and 2 and 2-(13'-oxo-9',11'- octadecadienoyl)-1-stearoyl-sn-glycero(3)phosphocholine (LPC-CO) 3 are synthesized and an analytical system established for the determination of geometrical isomers at the 13' position of APC-CO.
- Zhu, Changjin,Ohashi, Takaaki,Morimoto, Tatsuya,Onyango, Arnold N.,Takao, Kaneko,Shimizu, Sakayu,Nakajima, Shuhei,Baba, Naomichi
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p. 500 - 501
(2007/10/03)
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