15-Hydroxyeicosatetraenoic acid dehydrogenase activity in microsomal fraction of mouse liver homogenate

Simulation and Reconstruction of Metabolite-Metabolite Association Networks Using a Metabolic Dynamic Model and Correlation Based Algorithms

Biological networks play a paramount role in our understanding of complex biological phenomena, and metabolite-metabolite association networks are now commonly used in metabolomics applications. In this study we evaluate the performance of several network inference algorithms (PCLRC, MRNET, GENIE3, TIGRESS, and modifications of the MRNET algorithm, together with standard Pearson's and Spearman's correlation) using as a test case data generated using a dynamic metabolic model describing the metabolism of arachidonic acid (consisting of 83 metabolites and 131 reactions) and simulation individual metabolic profiles of 550 subjects. The quality of the reconstructed metabolite-metabolite association networks was assessed against the original metabolic network taking into account different degrees of association among the metabolites and different sample sizes and noise levels. We found that inference algorithms based on resampling and bootstrapping perform better when correlations are used as indexes to measure the strength of metabolite-metabolite associations. We also advocate for the use of data generated using dynamic models to test the performance of algorithms for network inference since they produce correlation patterns that are more similar to those observed in real metabolomics data.

Mechanisms for anti-inflammatory effects of 1-[15(S)-hydroxyeicosapentaenoyl] lysophosphatidylcholine, administered intraperitoneally, in zymosan A-induced peritonitis

BACKGROUND AND PURPOSE

Lysophosphatidylcholines (lysoPCs) with polyunsaturated acyl chains are known to exert anti-inflammatory actions. 15-Lipoxygeanation is crucial for anti-inflammatory action of polyunsaturated acylated lysoPCs. Here, the anti-inflammatory actions of 1-(15-hydroxyeicosapentaenoyl)-lysoPC (15-HEPE-lysoPC) and its derivatives were examined in a mechanistic analysis.

EXPERIMENTAL APPROACH

Anti-inflammatory actions of 15-HEPE-lysoPC in zymosan A-induced peritonitis of mice were examined by measuring plasma leakage and leucocyte infiltration, and determining levels of lipid mediators or cytokines.

KEY RESULTS

When each lysoPC, administered i.v., was assessed for its ability to suppress zymosan A-induced plasma leakage, 15-HEPE-lysoPC was found to be more potent than 1-(15-hydroperoxyeicosapentaenoyl)-lysoPC or 1-eicosapentaenoyl-lysoPC. Separately, i.p. administration of 15-HEPE-lysoPC markedly inhibited plasma leakage, in contrast to 15-HEPE, which had only a small effect. 15-HEPE-lysoPC also decreased leucocyte infiltration. Moreover, it reduced the formation of LTC₄ and LTB₄, 5-lipoxygenation products, as well as the levels of pro-inflammatory cytokines. The time-course study indicated that 15-HEPE-lysoPC might participate in both the early inflammatory phase and resolution phase. Additionally, 15-HEPE-lysoPC administration caused a partial suppression of LTC₄-induced plasma leakage and LTB₄-induced leucocyte infiltration. In the metabolism study, peritoneal exudate was shown to contain lysoPC-hydrolysing activity, crucial for anti-inflammatory activity, and a system capable of generating lipoxin A from 15-hydroxy eicosanoid precursor.

CONCLUSIONS AND IMPLICATIONS

15-HEPE-lysoPC, a precursor for 15-HEPE in target cells, induced anti-inflammatory actions by inhibiting the formation of pro-inflammatory leukotrienes and cytokines, and by enhancing the formation of lipoxin A. 15-HEPE-lysoPC might be one of many potent anti-inflammatory lipids in vivo.

Chemical and biological characterization of oxo-eicosatetraenoic acids

Eicosatetraenoates (ETEs) with 5-oxo residues are known to induce human neutrophil (PMN) Ca2+ transients and chemotaxis. We find that 5-oxoETE, 5-oxo-8-trans-ETE, 5-oxo-15-hydroxy-ETE, 5-hydroxy-ETE, 5-hydroxy-15-oxoETE, 5,15-dioxoETE, and 5,15-dihydroxy-ETE have respective relative potencies of 10, 5, 3, 1, 0.2, 0.1, and 0.02 in: a) causing PMN to mobilize Ca2+, aggregate, and release small amounts of granule enzymes and b) promoting large degranulation and oxidative burst responses in PMN co-challenged with platelet-activating factor, tumor necrosis factor-alpha, or ATP. Contrastingly, 12(R)-hydroxy-ETE, 12(S)-hydroxy-ETE, and 12-oxoETE induced PMN Ca2+ transients and aggregation [respective potencies (5-hydroxy-ETE = 1) of 0.1, 0.01, and 0.003] but did not effect degranulation, and 15-hydroxy-ETE, 15-oxoETE, and 15-oxo-11-trans-ETE were inactive in all assays. Finally, 5-oxo/hydroxy-ETEs desensitized PMN to themselves but not to 12-oxo/hydroxy-ETEs or leukotriene (LT)B4; 12-oxo/hydroxy-ETEs and LTB4 desensitized PMN to themselves and each other but not to 5-oxo/hydroxy-ETEs; 15-oxo/hydroxy-ETEs did not desensitize PMN; and a LTB4 receptor antagonist blocked responses to LTB4 and 12-oxo/hydroxy-ETEs but not to 5-oxo/hydroxy-ETEs. Thus, 5-oxo/hydroxy-ETEs act by a common, LTB4 receptor-independent mechanism that recognizes 5- but not 12- or 15-oxo/hydroxy-ETEs and prefers oxo over hydroxy residues at C5 whereas 12-oxo/hydroxy-ETEs act via a LTB4 receptor mechanism that recognizes 12- but not 5- or 15-oxo/hydroxy-ETEs and prefers hydroxy over oxo residues at C12.

Lipoxin A4 metabolism by differentiated HL-60 cells and human monocytes: conversion to novel 15-oxo and dihydro products

Lipoxins are tetraene-containing eicosanoids that possess biological activity in several organ systems. To determine their route of further metabolism, [11,12-3H]lipoxin A4 was prepared and incubated with human neutrophils, promyelocytic leukemia (HL-60) cells, and adherent monocytes. Intact neutrophils and undifferentiated HL-60 cells did not significantly metabolize [11,12-3H]LXA4, while HL-60 cells differentiated with PMA to monocyte/macrophage lineage rapidly (< 15 s) transformed this eicosanoid. The major radiolabeled LXA4-derived metabolites were characterized by physical methods and were shown to be 15-oxo-LXA4, 13,14-dihydro-15-oxo-LXA4, and 13,14-dihydro-LXA4. Substrate competition with cell-free supernatants from differentiated HL-60 cells suggests that lipoxins compete for 15-hydroxyprostaglandin dehydrogenase activity or an equivalent enzyme system. In addition, adherent monocytes exposed to [11,12-3H]LXA4 rapidly metabolized (> 60% within 30 s) the label to its oxo and dihydro derivatives. These results indicate that, unlike leukotrienes, LXA4 is subject to dehydrogenation and reduction of its conjugated tetraene to form triene-containing products. Moreover, they suggest that monocytes participate in lipoxin metabolism in their local milieu.

Occurrence of 9- and 13-keto-octadecadienoic acid in biological membranes oxygenated by the reticulocyte lipoxygenase

Membranes of intact rabbit reticulocytes and rat liver mitochondrial membranes oxygenated by the pure reticulocyte lipoxygenase contain 13-keto-9Z,11E-octadecadienoic acid and 9-keto-10E,12Z-octadecadienoic acid. In mitochondrial membranes not treated with lipoxygenase and in rabbit erythrocyte membranes these products were not detected. The chemical structure of the compounds has been identified by cochromatography with authentic standards on various types of HPLC columns, by uv and ir spectroscopy and GC/MS. In the membranes of rabbit reticulocytes up to 2% of the linoleate residues are present as its 9- and 13-keto derivatives. Most of the keto compounds (up to 90%) are esterified in the membrane ester lipids, only about 10% were found in the free fatty acid fraction. It is proposed that the keto dienoic fatty acids are formed via decomposition of hydroperoxy polyenoic fatty acids originating from the oxygenation of the membrane lipids by the reticulocyte lipoxygenase.