Bioactions of 5-hydroxyicosatetraenoate and its interaction with platelet-activating factor

Cross-talk between bioactive lipid mediators and the unfolded protein response in ischemic stroke

Ischemic cerebral stroke is a severe medical condition that affects about 15 million people every year and is the second leading cause of death and disability globally. Ischemic stroke results in neuronal cell death and neurological impairment. Current therapies may not adequately address the deleterious metabolic changes and may increase neurological damage. Oxygen and nutrient depletion along with the tissue damage result in endoplasmic reticulum (ER) stress, including the Unfolded Protein Response (UPR), and neuroinflammation in the affected area and cause cell death in the lesion core. The spatio-temporal production of lipid mediators, either pro-inflammatory or pro-resolving, decides the course and outcome of stroke. The modulation of the UPR as well as the resolution of inflammation promotes post-stroke cellular viability and neuroprotection. However, studies about the interplay between the UPR and bioactive lipid mediators remain elusive and this review gives insights about the crosstalk between lipid mediators and the UPR in ischemic stroke. Overall, the treatment of ischemic stroke is often inadequate due to lack of effective drugs, thus, this review will provide novel therapeutical strategies that could promote the functional recovery from ischemic stroke.

Evidence of Failed Resolution Mechanisms in Arrhythmogenic Inflammation, Fibrosis and Right Heart Disease

Inflammation is a complex program of active processes characterized by the well-orchestrated succession of an initiation and a resolution phase aiming to promote homeostasis. When the resolution of inflammation fails, the tissue undergoes an unresolved inflammatory status which, if it remains uncontrolled, can lead to chronic inflammatory disorders due to aggravation of structural damages, development of a fibrous area, and loss of function. Various human conditions show a typical unresolved inflammatory profile. Inflammatory diseases include cancer, neurodegenerative disease, asthma, right heart disease, atherosclerosis, myocardial infarction, or atrial fibrillation. New evidence has started to emerge on the role, including pro-resolution involvement of chemical mediators in the acute phase of inflammation. Although flourishing knowledge is available about the role of specialized pro-resolving mediators in neurodegenerative diseases, atherosclerosis, obesity, or hepatic fibrosis, little is known about their efficacy to combat inflammation-associated arrhythmogenic cardiac disorders. It has been shown that resolvins, including RvD1, RvE1, or Mar1, are bioactive mediators of resolution. Resolvins can stop neutrophil activation and infiltration, stimulate monocytes polarization into anti-inflammatory-M2-macrophages, and activate macrophage phagocytosis of inflammation-debris and neutrophils to promote efferocytosis and clearance. This review aims to discuss the paradigm of failed-resolution mechanisms (FRM) potentially promoting arrhythmogenicity in right heart disease-induced inflammatory status.

Analysis of differentially expressed genes and signaling pathways involved in atherosclerosis and chronic obstructive pulmonary disease

Atherosclerosis is an important medical and social problem, and the keys to solving this problem are still largely unknown. A common situation in real clinical practice is the comorbid course of atherosclerosis with chronic obstructive pulmonary disease (COPD). Diseases share some common risk factors and may be closely linked pathogenetically.

METHODS

Bioinformatics analysis of datasets from Gene Expression Omnibus (GEO) was performed to examine the gene ontology (GO) of common differentially expressed genes (DEGs) in COPD and peripheral arterial atherosclerosis. DEGs were identified using the limma R package with the settings p < 0.05, corrected using the Benjamini & Hochberg algorithm and ǀlog 2FCǀ > 1.0. The GO, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment, and the protein-protein interaction (PPI) network analysis were performed with the detected DEGs.

RESULTS

The biological processes and signaling pathways involving common DEGs from airway epithelial datasets in COPD and tissue in peripheral atherosclerosis were identified. A total of 15 DEGs were identified, comprising 12 upregulated and 3 downregulated DEGs. The GO enrichment analysis demonstrated that the upregulated hub genes were mainly involved in the inflammatory response, reactive oxygen species metabolic process, cell adhesion, lipid metabolic process, regulation of angiogenesis, icosanoid biosynthetic process, and cellular response to a chemical stimulus. The KEGG pathway enrichment analysis demonstrated that the common pathways were Toll-like receptor signaling pathway, NF-kappa B signaling pathway, lipid and atherosclerosis, and cytokine-cytokine receptor interaction.

CONCLUSIONS

Biological processes and signaling pathways associated with the immune response may link the development and progression of COPD and atherosclerosis.

Ensemble Analysis Identifies Nasal 15-Keto-PGE2 as a Predictor of Recovery in Experimental Rhinovirus Colds

BACKGROUND

Symptom intensity during a common cold is highly variable, particularly after the illness peaks, contributing to delay in recovery. Rhinoviruses frequently cause colds and, during acute infections, generate leukotriene B4 and prostaglandin E2 (PGE2). PGE2 is known to initiate oxylipin class switching and resolution of acute inflammation. Thus, we hypothesized that during acute rhinovirus colds, oxylipins with pro-resolving capabilities reduce symptom severity and speed recovery.

METHODS

Four groups of healthy volunteers were inoculated with placebo or 3 different doses of rhinovirus A16. Participants kept daily records of symptoms and contributed serial nasal lavage fluid samples. We collected semi-quantitative mass spectrometry data for 71 oxylipins in these acute samples from all participants. An ensemble analysis approach was used to further reduce this dataset.

RESULTS

Levels of 15-keto-PGE2 at day 3 of the cold were consistently among the top candidates in these models of recovery symptoms. 15-keto-PGE2 was the only oxylipin with an interaction between inoculum dose and time. Acute 15-keto-PGE2 levels were inversely associated with symptoms during cold recovery in a multivariable analysis (P = .0043).

CONCLUSIONS

These findings show that high 15-keto-PGE2 levels during the acute cold are associated with fewer symptoms during recovery.

Serum Metabolomic Profiling Based on Fourier Transform-Ion Cyclotron Resonance-Mass Spectrometry: Do the Dysfunctions of Metabolic Pathways Reveal a Universal Risk of Oxidative Stress in Schizophrenia?

Schizophrenia is a chronic, disabling, and complex mental illness, of which the pathogenesis remains elusive. To provide clues for the pathogenesis and etiology of schizophrenia, we performed serum metabolic profiling in 54 patients with schizophrenia and 54 matched healthy controls using Fourier transform-ion cyclotron resonance-mass spectrometry. Based on 94 differential metabolites identified, we discovered two dysregulated metabolic pathways in schizophrenia, including the upregulated arachidonic acid-related pathway and the downregulated aromatic amino acid-related pathway. Moreover, carnitine was identified as a promising diagnostic biomarker for schizophrenia with an area under the curve of 0.997. Given the antioxidant and pro-oxidant properties of these altered metabolites, these results pointed to an imbalance of the redox homeostasis in schizophrenia, which was further confirmed by a remarkable elevation of 8-hydroxydeoxyguanosine (8-OHdG), a reactive oxidative stress marker. Furthermore, correlation analyses demonstrated that 8-OHdG was negatively correlated with antioxidant biliverdin and positively related to oxidation products, 9-hydroxylinoleic acid and o-tyrosine, and that total antioxidant capacity was positively associated with antioxidant acetylcarnitine in schizophrenia. Our results lead to the hypothesis that the disturbed metabolic characteristics reveal enhanced oxidative stress, which in turn results in the damage of lipids, proteins, and DNA and ultimately promotes the development of schizophrenia.

The effect of inhibition of leukotriene synthesis on the activity of interleukin-8 and granulocyte-macrophage colony-stimulating factor

The cytokines interleukin-8 (IL-8) and granulocyte-macrophage colony-stimulating factor (GM-CSF) enhanced the extracellular release of arachidonate metabolites from ionophore-stimulated neutrophils by 145 ± 10% (mean ± S.E.M., n = 13) and 182 ± 11% (n = 16), respectively. To determine whether enhanced leukotriene production mediates the effects of these cytokines on neutrophil activity, two different specific arachidonate 5-lipoxygenase (5-LO) inhibitors, piriprost and MK-886, were used to inhibit leukotriene synthesis. Neither inhibitor affected the upregulation of CD11b β₂-integrin expression or priming of superoxide generation stimulated by IL-8 and GM-CSF. It is concluded that leukotrienes do not mediate either the direct or priming effects of these cytokines and that these classes of anti-inflammatory drugs are therefore unlikely to inhibit the effects of IL-8 and GM-CSF on neutrophil activation.

The 5-lipoxygenase/leukotriene pathway in preclinical models of cardiovascular disease

Leukotrienes (LTs) derived from 5-lipoxygenase (5-LO) activity are most widely known for their actions during acute inflammation and asthma. 5-LO/LT pathway involvement in cardiovascular disease (CVD) pathogenesis has come to the forefront based on provocative human genetic/population and animal studies leading to the hypothesis that this pathway promotes atherosclerosis, abdominal aortic aneurysm, and myocardial infarction/reperfusion injury via increased leucocyte chemotaxis, vascular inflammation and enhanced permeability, and subsequent tissue/matrix degeneration. A series of pre-clinical studies have tested this hypothesis by means of genetic or pharmacological inhibition of either the LT biosynthesis axis (5-LO, 5-LO-activating protein, LTA(4) hydrolase, LTC(4) synthase) or the cognate LT receptors. Here, we summarize, compare, and analyse these animal studies and relate their findings to human disease pathogenesis. We draw a complex picture of 5-LO/LT participation in cardiovascular disorders, which is further complicated by marked differences between species. Moreover, we discuss how the cytokine footprint of the respective pathological conditions determines the expression level and hence, the contribution of components of the pathway to the overall disease state. Current knowledge implies a role for 5-LO and LTs during the early/acute phase of CVD, but our understanding of a putative 5-LO/LT involvement in more advanced stages of CVD is limited, thereby preventing simple extrapolation of findings from animal studies to humans.

Lactonase and lactonizing activities of human serum paraoxonase (PON1) and rabbit serum PON3

Human paraoxonase (PON1) was previously shown to hydrolyze over 30 different lactones (cyclic esters). In the present study purified human PON1 was found to catalyze the reverse reaction (lactonization) of a broad range of hydroxy acids. Hydroxy acid lactonization or lactone hydrolysis is catalyzed until equilibrium between the open and closed forms is reached. Lactonization by PON1 was calcium-dependent, had a pH optimum of 5.5-6 and could be stimulated with dilauroylphosphatidylcholine. Rabbit serum PON3 and a serine esterase in mouse plasma, presumably a carboxylesterase, also catalyzed hydroxy acid lactonization. Two endogenous oxidized unsaturated fatty acids, (+/-)4-hydroxy-5E,7Z,10Z,13Z,16Z,19Z-docosahexaenoic acid (4-HDoHE) and (+/-)5-hydroxy-6E,8Z,11Z,14Z-eicosatetraenoic acid (5-HETE) lactone, were very efficiently lactonized and hydrolyzed, respectively, by PON1. Human and mouse plasma samples also catalyzed 4-HDoHE lactonization and 5-HETE lactone hydrolysis. Studies with the PON1 inhibitor EDTA and the serine esterase inhibitor phenylmethylsulfonylfluoride suggest that about 80-95% of both activities can be attributed to PON1 in the human samples. In the mouse sample, PON1 accounted for about 30% of the 4-HDoHE lactonizing activity and 72% of the 5-HETE lactonase activity. Our results demonstrate that PON1 can lactonize the hydroxy acid form of its lactone substrates and that reversible hydrolysis of lactones may be a property of lactonases that is not generally considered. Also, the high activity of PON1 towards 4-HDoHE and 5-HETE lactone suggests that oxidized eicosanoids and docosanoids may be important physiological substrates for PON1.

Eotaxin and RANTES enhance 5-oxo-6,8,11,14-eicosatetraenoic acid-induced eosinophil chemotaxis

BACKGROUND

The 5-lipoxygenase product 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is a potent activator of human eosinophils and, among lipid mediators, is the most active chemoattractant for these cells. Studies have demonstrated the importance of 5-lipoxygenase products in allergen-induced pulmonary eosinophilia. Because CC chemokines such as eotaxin and RANTES also play critical roles in this phenomenon, it would seem likely that members of both classes of mediators contribute to this response.

OBJECTIVE

The study was designed to directly compare the effects of 5-oxo-ETE on eosinophils with those of eotaxin and RANTES and to determine whether these chemokines could enhance the chemotactic response to 5-oxo-ETE.

METHODS

Eosinophil chemotaxis was measured with microchemotaxis chambers. CD11b, L-selectin, and actin polymerization were measured by flow cytometry. Calcium mobilization was measured by fluorescence.

RESULTS

5-Oxo-ETE stimulated eosinophil chemotaxis with a potency between those of eotaxin and RANTES and a maximal response about 50% higher than that of eotaxin. Threshold concentrations of eotaxin and RANTES increased the chemotactic potency of 5-oxo-ETE by more than 4-fold. 5-Oxo-ETE and eotaxin were approximately equipotent in mobilizing cytosolic calcium in eosinophils. Eotaxin was more potent in inducing CD11b expression and actin polymerization, but the maximal responses to 5-oxo-ETE were about 50% higher. 5-Oxo-ETE strongly induced L-selectin shedding, whereas eotaxin elicited only a weak and variable response.

CONCLUSION

5-Oxo-ETE is a strong activator of human eosinophils with a chemotactic potency comparable to those of eotaxin and RANTES, both of wwhich enhance 5-oxo-ETE-induced chemotaxis. 5-Oxo-ETE and CC chemokines may combine to induce pulmonary eosinophilia in asthma.

5-Oxo-eicosanoids and hematopoietic cytokines cooperate in stimulating neutrophil function and the mitogen-activated protein kinase pathway

The newly defined eicosatetraenoates (ETEs), 5-oxoETE and 5-oxo-15(OH)-ETE, share structural motifs, synthetic origins, and bioactions with leukotriene B4 (LTB4). All three eicosanoids stimulate Ca2+ transients and chemotaxis in human neutrophils (PMN). However, unlike LTB4, 5-oxoETE and 5-oxo-15(OH)-ETE alone cause little degranulation and no superoxide anion production. However, we show herein that, in PMN pretreated with granulocyte-macrophage or granulocyte colony-stimulating factor (GM-CSF or G-CSF), the oxoETEs become potent activators of the last responses. The oxoETEs also induce translocation of secretory vesicles from the cytosol to the plasmalemma, an effect not requiring cytokine priming. To study the mechanism of PMN activation in response to the eicosanoids, we examined the activation of mitogen-activated protein kinase (MAPK) and cytosolic phospholipase A2 (cPLA2). PMN expressed three proteins (40, 42, and 44 kDa) that reacted with anti-MAPK antibodies. The oxoETEs, LTB4, GM-CSF, and G-CSF all stimulated PMN to activate the MAPKs and cPLA2, as defined by shifts in these proteins' electrophoretic mobility and tyrosine phosphorylation of the MAPKs. However, the speed and duration of the MAPK response varied markedly depending on the stimulus. 5-OxoETE caused a very rapid and transient activation of MAPK. In contrast, the response to the cytokines was rather slow and persistent. PMN pretreated with GM-CSF demonstrated a dramatic increase in the extent of MAPK tyrosine phosphorylation and electrophoretic mobility shift in response to 5-oxoETE. Similarly, 5-oxoETE induced PMN to release some preincorporated [14C]arachidonic acid, while GM-CSF greatly enhanced the extent of this release. Thus, the synergism exhibited by these agents is prominent at the level of MAPK stimulation and phospholipid deacylation. Pertussis toxin, but not Ca2+ depletion, inhibited MAPK responses to 5-oxoETE and LTB4, indicating that responses to both agents are coupled through G proteins but not dependent upon Ca2+ transients. 15-OxoETE and 15(OH)-ETE were inactive while 5-oxo-15(OH)-ETE and 5(OH)-ETE had 3- and 10-fold less potency than 5-oxoETE, indicating a rather strict structural specificity for the 5-keto group. LY 255283, a LTB4 antagonist, blocked the responses to LTB4 but not to 5-oxoETE. Therefore, the oxoETEs do not appear to operate through the LTB4 receptor. In summary, the oxoETEs are potent activators of PMN that share some but not all activities with LTB4. The response to the oxoETEs is greatly enhanced by pretreatment with cytokines, indicating that combinations of these mediators may be very important in the pathogenesis of inflammation.

Mechanisms of platelet-activating factor-induced lipid body formation: requisite roles for 5-lipoxygenase and de novo protein synthesis in the compartmentalization of neutrophil lipids

Lipid bodies, lipid rich cytoplasmic inclusions, are characteristically abundant in vivo in leukocytes associated with inflammation. Because lipid bodies are potential reservoirs of esterified arachidonate and sites at which eicosanoid-forming enzymes may localize, we evaluated mechanisms of lipid body formation in neutrophils (PMN). Among receptor-mediated agonists, platelet activating factor (PAF), but not C5a, formyl-methyl-phenylalanine, interleukin 8, or leukotriene (LT) B4, induced the rapid formation of lipid bodies in PMN. This action of PAF was receptor mediated, as it was dose dependently inhibited by the PAF receptor antagonist WEB 2086 and blocked by pertussis toxin. Lipid body induction by PAF required 5-lipoxygenase (LO) activity and was inhibited by the 5-lipoxygenase-activating protein antagonist MK 886 and the 5-LO inhibitor zileuton, but not by cyclooxygenase inhibitors. Corroborating the dependency of PAF-induced lipid body formation on 5-LO, PMN and macrophages from wild-type mice, but not from 5-LO genetically deficient mice, formed lipid bodies on exposure to PAF both in vitro and in vivo within the pleural cavity. The 5-LO product inducing lipid body formation was not LTB4 but was 5(S)-hydroxyeicosatetraenoic acid [5(S)-HETE], which was active at 10-fold lower concentrations than PAF and was also inhibited by pertussis toxin but not by zileuton or WEB 2086. Furthermore, 5-HETE was equally effective in inducing lipid body formation in both wild-type and 5-LO genetically deficient mice. Both PAF- and 5(S)-HETE-induced lipid body formation were inhibited by protein kinase C (PKC) inhibitors staurosporine and chelerythrine, the phospholipase C (PLC) inhibitors D609 and U-73122, and by actinomycin D and cycloheximide. Prior stimulation of human PMN with PAF to form lipid bodies enhanced eicosanoid production in response to submaximal stimulation with the calcium ionophore A23187; and the levels of both prostaglandin (PG) E2 and LTB4 correlated with the number of lipid bodies. Furthermore, pretreatment of cells with actinomycin D or cycloheximide inhibited not only the induction of lipid body formation by PAF, but also the PAF-induced "priming" for enhanced PGE2 and LTB4 in PMN. Thus, the compartmentalization of lipids to form lipid bodies in PMN is dependent on specific cellular responses that can be PAF receptor mediated, involves signaling through 5-LO to form 5-HETE and then through PKC and PLC, and requires new protein synthesis. Since increases in lipid body numbers correlated with priming for enhanced PGE2 and LTB4 production in PMN, the induction of lipid bodies may have a role in the formation of eicosanoid mediators by leukocytes involved in inflammation.

Eicosanoid production by parasites:

In this review, Adam Belley and Kris Chadee discuss eicosanoid production by various parasites and propose roles they may play in pathogenesis and immunomodulation. The commonality between parasites is prostaglandin production and, therefore, special attention is given to the cyclooxygenase pathway, highlighting the enzymes and functions of prostaglandins.

Phospholipases and activation of the NADPH oxidase

The signal transductional mechanisms regulating the activation of NADPH oxidase, the respiratory burst enzyme in phagocytic cells, are not completely understood. Receptors for most physiologic stimuli trigger the activation of various phospholipases, including phospholipases A2, C, and D. The lipid mediators formed (arachidonic acid, 1,2-diacylglycerol, and phosphatidic acid) have been implicated as second messengers in the induction of the respiratory burst. In intact cells, we have correlated phospholipase D activation and the production of phosphatidic acid with the activation of NADPH oxidase, using the drug propranolol. Phosphatidic acid activated NADPH oxidase in a cell-free system, but the level of activation was low. 1,2-Diacylglycerol markedly enhanced NADPH oxidase activation by phosphatidic acid. The synergistic effect required the diacyl species, since mono- or tri-acylglycerols were ineffective. Phosphatidic acid could be replaced by either lysophosphatidic acid or phosphatidylserine, but not by phosphatidylcholine, phosphatidylethanolamine, or phosphatidylinositol, suggesting specificity for an anionic phospholipid. Since other cell-free activators of NADPH oxidase (arachidonic acid, sodium dodecyl sulfate) are also anionic amphiphiles, phosphatidic acid may directly interact with an enzyme component(s). The targets for phosphatidic acid and diacylglycerol in the cell-free system are currently under investigation. These results emphasize the critical importance of phospholipases, particularly phospholipase D, in the regulation of the respiratory burst.