Thrombin-activated human platelets acutely generate oxidized docosahexaenoic-acid-containing phospholipids via 12-lipoxygenase

Bioactive lipid regulation of platelet function, hemostasis, and thrombosis

Platelets are small, anucleate cells in the blood that play a crucial role in the hemostatic response but are also implicated in the pathophysiology of cardiovascular disease. It is widely appreciated that polyunsaturated fatty acids (PUFAs) play an integral role in the function and regulation of platelets. PUFAs are substrates for oxygenase enzymes cyclooxygenase-1 (COX-1), 5-lipoxygenase (5-LOX), 12-lipoxygenase (12-LOX) and 15-lipoxygenase (15-LOX). These enzymes generate oxidized lipids (oxylipins) that exhibit either pro- or anti-thrombotic effects. Although the effects of certain oxylipins, such as thromboxanes and prostaglandins, have been studied for decades, only one oxylipin has been therapeutically targeted to treat cardiovascular disease. In addition to the well-known oxylipins, newer oxylipins that demonstrate activity in the platelet have been discovered, further highlighting the expansive list of bioactive lipids that can be used to develop novel therapeutics. This review outlines the known oxylipins, their activity in the platelet, and current therapeutics that target oxylipin signaling.

Compartmentalized regulation of lipid signaling in oxidative stress and inflammation: Plasmalogens, oxidized lipids and ferroptosis as new paradigms of bioactive lipid research

Perturbations in lipid homeostasis combined with conditions favoring oxidative stress constitute a hallmark of the inflammatory response. In this review we focus on the most recent results concerning lipid signaling in various oxidative stress-mediated responses and inflammation. These include phagocytosis and ferroptosis. The best characterized event, common to these responses, is the synthesis of oxygenated metabolites of arachidonic acid and other polyunsaturated fatty acids. Major developments in this area have highlighted the importance of compartmentalization of the enzymes and lipid substrates in shaping the appropriate response. In parallel, other relevant lipid metabolic pathways are also activated and, until recently, there has been a general lack of knowledge on the enzyme regulation and molecular mechanisms operating in these pathways. Specifically, data accumulated in recent years on the regulation and biological significance of plasmalogens and oxidized phospholipids have expanded our knowledge on the involvement of lipid metabolism in the progression of disease and the return to homeostasis. These recent major developments have helped to establish the concept of membrane phospholipids as cellular repositories for the compartmentalized production of bioactive lipids involved in cellular regulation. Importantly, an enzyme classically described as being involved in regulating the homeostatic turnover of phospholipids, namely the group VIA Ca²⁺-independent phospholipase A₂ (iPLA₂β), has taken center stage in oxidative stress and inflammation research owing to its key involvement in regulating metabolic and ferroptotic signals arising from membrane phospholipids. Understanding the role of iPLA₂β in ferroptosis and metabolism not only broadens our knowledge of disease but also opens possible new horizons for this enzyme as a target for therapeutic intervention.

Bioactive lipids as biomarkers of adverse reactions associated with apheresis platelet concentrate transfusion

Platelet concentrate (PC) transfusion seeks to provide haemostasis in patients presenting severe central thrombocytopenia or severe bleeding. PCs may induce adverse reactions (AR) that can occasionally be severe (SAR). PCs contain active biomolecules such as cytokines and lipid mediators. The processing and storage of PCs creates so-called structural and biochemical storage lesions that accumulate when blood products reach their shelf life. We sought to investigate lipid mediators as bioactive molecules of interest during storage and review associations with adverse reactions post-transfusion. To facilitate understanding, we focused on single donor apheresis (SDA) PCs with approximately 31.8% of PCs being delivered in our setting. Indeed, pooled PCs are the most widely transfused products, but the study of a single donor lipid mediator is easier to interpret. We are investigating key lipid mediators involved in AR. Adverse reactions were closely monitored in accordance with current national and regional haemovigilance protocols. Residual PCs were analysed post-transfusion in a series of observations, both with and without severe reactions in recipients. A decrease in the lysophosphatidylcholine species to produce the lysophosphatidic acid species has been observed during storage and in the case of AR. Lysophosphatidic acid increased with primarily platelet-inhibitor lipids. Anti-inflammatory platelet-induced inhibition lipids were weakly expressed in cases of severe adverse reactions. We therefore propose that a decrease in lysophosphatidylcholine and an increase in lysophosphatidic acid can prospectively predict serious adverse transfusion reactions.

The role of procoagulant phospholipids on the surface of circulating blood cells in thrombosis and haemostasis

Phospholipids (PLs) are found in all cell types and are required for structural support and cell activation signalling pathways. In resting cells, PLs are asymmetrically distributed throughout the plasma membrane with native procoagulant aminophospholipids (aPLs) being actively maintained in the inner leaflet of the membrane. Upon platelet activation, aPLs rapidly externalize to the outer leaflet and are essential for supporting the coagulation cascade by providing binding sites for factors in the cell-based model. More recent work has uncovered a role for enzymatically oxidized PLs (eoxPLs) in facilitating coagulation, working in concert with native aPLs. Despite this, the role of aPLs and eoxPLs in thrombo-inflammatory conditions, such as arterial and venous thrombosis, has not been fully elucidated. In this review, we describe the biochemical structures, distribution and regulation of aPL externalization and summarize the literature on eoxPL generation in circulating blood cells. We focus on the currently understood role of these lipids in mediating coagulation reactions in vitro, in vivo and in human thrombotic disease. Finally, we highlight gaps in our understanding in how these lipids vary in health and disease, which may place them as future therapeutic targets for the management of thrombo-inflammatory conditions.

Characterization of the Structural Diversity and Structure-Specific Behavior of Oxidized Phospholipids by LC-MS/MS

Polyunsaturated fatty acids (PUFAs), esterified to phospholipids, are susceptible to oxidation. They form oxidized phospholipids (OxPLs) by oxygenases or reactive oxygen species (ROS), or both. These OxPLs are associated with various diseases, such as atherosclerosis, pulmonary injuries, neurodegenerative diseases, cancer, and diabetes. Since many types of OxPLs seem to be generated in vivo, precise determination of their structural diversity is required to understand their potential structure-specific functions. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is a powerful method to quantitatively measure the structural diversity of OxPLs present in biological samples. This review outlines recent advances in analytical methods for OxPLs and their physiological relevance in health and diseases.

Modulation of the Primary Astrocyte-Enriched Cultures' Oxylipin Profiles Reduces Neurotoxicity

Recently, manipulations with reactive astrocytes have been viewed as a new therapeutic approach that will enable the development of treatments for acute brain injuries and neurodegenerative diseases. Astrocytes can release several substances, which may exert neurotoxic or neuroprotective effects, but the nature of these substances is still largely unknown. In the present work, we tested the hypothesis that these effects may be attributed to oxylipins, which are synthesized from n-3 or n-6 polyunsaturated fatty acids (PUFAs). We used astrocyte-enriched cultures and found that: (1) lipid fractions secreted by lipopolysaccharide (LPS)-stimulated rat primary astrocyte-enriched cultures-possessed neurotoxic activity in rat primary neuronal cultures; (2) both of the tested oxylipin synthesis inhibitors, ML355 and Zileuton, reduce the LPS-stimulated release of interleukin 6 (IL-6) by astrocyte cultures, but only ML355 can change lipid fractions from neurotoxic to non-toxic; and (3) oxylipin profiles, measured by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) from neurotoxic and non-toxic lipid fractions, reveal a group of n-3 docosahexaenoic acid derivatives, hydroxydocosahexaenoic acids (HdoHEs)-4-HdoHE, 8-HdoHE, and 17-HdoHE, which may reflect the neuroprotective features of lipid fractions. Regulating the composition of astrocyte oxylipin profiles may be suggested as an approach for regulation of neurotoxicity in inflammatory processes.

Lipid Receptor GPR31 (G-Protein-Coupled Receptor 31) Regulates Platelet Reactivity and Thrombosis Without Affecting Hemostasis

OBJECTIVE

12-LOX (12-lipoxygenase) produces a number of bioactive lipids including 12(S)-HETE that are involved in inflammation and platelet reactivity. The GPR31 (G-protein-coupled receptor 31) is the proposed receptor of 12(S)-HETE; however, it is not known whether the 12(S)-HETE-GPR31 signaling axis serves to enhance or inhibit platelet activity. Approach and Results: Using pepducin technology and biochemical approaches, we provide evidence that 12(S)-HETE-GPR31 signals through Gi to enhance PAR (protease-activated receptor)-4-mediated platelet activation and arterial thrombosis using both human platelets and mouse carotid artery injury models. 12(S)-HETE suppressed AC (adenylyl cyclase) activity through GPR31 and resulted in Rap1 (Ras-related protein 1) and p38 activation and low but detectable calcium flux but did not induce platelet aggregation. A GPR31 third intracellular (i3) loop-derived pepducin, GPR310 (G-protein-coupled receptor 310), significantly inhibited platelet aggregation in response to thrombin, collagen, and PAR4 agonist, AYPGKF, in human and mouse platelets but relative sparing of PAR1 agonist SFLLRN in human platelets. GPR310 treatment gave a highly significant 80% protection (P=0.0018) against ferric chloride-induced carotid artery injury in mice by extending occlusion time, without any effect on tail bleeding. PAR4-mediated dense granule secretion and calcium flux were both attenuated by GPR310. Consistent with these results, GPR310 inhibited 12(S)-HETE-mediated and PAR4-mediated Rap1-GTP and RASA3 translocation to the plasma membrane and attenuated PAR4-Akt and ERK activation. GPR310 caused a right shift in thrombin-mediated human platelet aggregation, comparable to the effects of inhibition of the Gi-coupled P2Y12 receptor. Co-immunoprecipitation studies revealed that GPR31 and PAR4 form a heterodimeric complex in recombinant systems.

CONCLUSIONS

The 12-LOX product 12(S)-HETE stimulates GPR31-Gi-signaling pathways, which enhance thrombin-PAR4 platelet activation and arterial thrombosis in human platelets and mouse models. Suppression of this bioactive lipid pathway, as exemplified by a GPR31 pepducin antagonist, may provide beneficial protective effects against platelet aggregation and arterial thrombosis with minimal effect on hemostasis.

The role of oxidized phospholipids in the development of disease

Oxidized phospholipids (OxPLs), complex mixtures of phospholipid oxidation products generated during normal or pathological processes, are increasingly recognized to show bioactive effects on many cellular signalling pathways. There is a growing body of evidence showing that OxPLs play an important role in many diseases, so it is essential to define the specific role of OxPLs in different diseases for the design of disease therapies. In vastly diverse pathological processes, OxPLs act as pro-inflammatory agents and contribute to the progression of many diseases; in addition, they play a role in anti-inflammatory processes, promoting the dissipation of inflammation and inhibiting the progression of some diseases. In addition to participating in the regulation of inflammatory responses, OxPLs affect the occurrence and development of diseases through other pathways, such as apoptosis promotion. In this review, the different and even opposite effects of different OxPL molecular species are discussed. Furthermore, the specific effects of OxPLs in various diseases, as well as the receptor and cellular mechanisms involved, are summarized.

Platelet lipidome: Dismantling the "Trojan horse" in the bloodstream

The platelet-lipid chapter in the story of atherothrombosis is an old one, recapitulated and revised in many contexts. For decades several stimulating facets have been added to it, both unraveling and increasing the perplexity of platelet-lipid interplay and its pathophysiological consequences. The recent paradigm shift in our perspective has evolved with lipidomic analysis of the intraplatelet compartment and platelet releasate. These investigations have disclosed that platelets are in constant interaction with circulatory lipids, often reflected in their lipid repertoire. In addition, they offer a shielded intracellular space for oxidative lipid metabolism generating "toxic" metabolites that escape degradation by plasma lipases and antioxidant defense, circulate undetected by conventional plasma lipid profile, and deposited at atherosclerotic lesions or thrombus. Lipidomics divulges this silent invader in platelet vehicles, thereby providing potential biomarkers of pathologic manifestations and therapeutic targets to be exploited, which is surmised in this review.

The Biosynthesis of Enzymatically Oxidized Lipids

Enzymatically oxidized lipids are a specific group of biomolecules that function as key signaling mediators and hormones, regulating various cellular and physiological processes from metabolism and cell death to inflammation and the immune response. They are broadly categorized as either polyunsaturated fatty acid (PUFA) containing (free acid oxygenated PUFA "oxylipins", endocannabinoids, oxidized phospholipids) or cholesterol derivatives (oxysterols, steroid hormones, and bile acids). Their biosynthesis is accomplished by families of enzymes that include lipoxygenases (LOX), cyclooxygenases (COX), cytochrome P450s (CYP), and aldo-keto reductases (AKR). In contrast, non-enzymatically oxidized lipids are produced by uncontrolled oxidation and are broadly considered to be harmful. Here, we provide an overview of the biochemistry and enzymology of LOXs, COXs, CYPs, and AKRs in humans. Next, we present biosynthetic pathways for oxylipins, oxidized phospholipids, oxysterols, bile acids and steroid hormones. Last, we address gaps in knowledge and suggest directions for future work.

Analysis of oxidised and glycated aminophospholipids: Complete structural characterisation by C30 liquid chromatography-high resolution tandem mass spectrometry

The aminophospholipids (APL), phosphatidylethanolamine (PE) and phosphatidylserine (PS) are widely present in cell membranes and lipoproteins. Glucose and reactive oxygen species (ROS), such as the hydroxyl radical (^•OH), can react with APL leading to an array of oxidised, glycated and glycoxidised derivatives. Modified APL have been implicated in inflammatory diseases and diabetes, and were identified as signalling molecules regulating cell death. However, the biological relevance of these molecules has not been completely established, since they are present in very low amounts, and new sensitive methodologies are needed to detect them in biological systems. Few studies have focused on the characterisation of APL modifications using liquid chromatography-tandem mass spectrometry (LC-MS/MS), mainly using C5 or C18 reversed phase (RP) columns. In the present study, we propose a new analytical approach for the characterisation of complex mixtures of oxidised, glycated and glycoxidised PE and PS. This LC approach was based on a reversed-phase C30 column combined with high-resolution MS, and higher energy C-trap dissociation (HCD) MS/MS. C30 RP-LC separated short and long fatty acyl oxidation products, along with glycoxidised APL bearing oxidative modifications on the glucose moiety and the fatty acyl chains. Functional isomers (e.g. hydroxy-hydroperoxy-APL and tri-hydroxy-APL) and positional isomers (e.g. 9-hydroxy-APL and 13-hydroxy-APL) were also discriminated by the method. HCD fragmentation patterns allowed unequivocal structural characterisation of the modified APL, and are translatable into targeted MS/MS fingerprinting of the modified derivatives in biological samples.

Reactive Oxygen Species-Induced Lipid Peroxidation in Apoptosis, Autophagy, and Ferroptosis

Reactive oxygen species- (ROS-) induced lipid peroxidation plays a critical role in cell death including apoptosis, autophagy, and ferroptosis. This fundamental and conserved mechanism is based on an excess of ROS which attacks biomembranes, propagates lipid peroxidation chain reactions, and subsequently induces different types of cell death. A highly evolved sophisticated antioxidant system exists that acts to protect the cells from oxidative damage. In this review, we discussed how ROS propagate lipid peroxidation chain reactions and how the products of lipid peroxidation initiate apoptosis and autophagy in current models. We also discussed the mechanism of lipid peroxidation during ferroptosis, and we summarized lipid peroxidation in pathological conditions of critical illness. We aim to bring a more global and integrative sight to know how different ROS-induced lipid peroxidation occurs among apoptosis, autophagy, and ferroptosis.

Mass spectrometry strategies to unveil modified aminophospholipids of biological interest

The biological functions of modified aminophospholipids (APL) have become a topic of interest during the last two decades, and distinct roles have been found for these biomolecules in both physiological and pathological contexts. Modifications of APL include oxidation, glycation, and adduction to electrophilic aldehydes, altogether contributing to a high structural variability of modified APL. An outstanding technique used in this challenging field is mass spectrometry (MS). MS has been widely used to unveil modified APL of biological interest, mainly when associated with soft ionization methods (electrospray and matrix-assisted laser desorption ionization) and coupled with separation techniques as liquid chromatography. This review summarizes the biological roles and the chemical mechanisms underlying APL modifications, and comprehensively reviews the current MS-based knowledge that has been gathered until now for their analysis. The interpretation of the MS data obtained by in vitro-identification studies is explained in detail. The perspective of an analytical detection of modified APL in clinical samples is explored, highlighting the fundamental role of MS in unveiling APL modifications and their relevance in pathophysiology.

A Comprehensive UHPLC Ion Mobility Quadrupole Time-of-Flight Method for Profiling and Quantification of Eicosanoids, Other Oxylipins, and Fatty Acids

Analysis of oxylipins by liquid chromatography mass spectrometry (LC/MS) is challenging because of the small mass range occupied by this diverse lipid class, the presence of numerous structural isomers, and their low abundance in biological samples. Although highly sensitive LC/MS/MS methods are commonly used, further separation is achievable by using drift tube ion mobility coupled with high-resolution mass spectrometry (DTIM-MS). Herein, we present a combined analytical and computational method for the identification of oxylipins and fatty acids. We use a reversed-phase LC/DTIM-MS workflow able to profile and quantify (based on chromatographic peak area) the oxylipin and fatty acid content of biological samples while simultaneously acquiring full scan and product ion spectra. The information regarding accurate mass, collision-cross-section values in nitrogen (^DTCCS_N2), and retention times of the species found are compared to an internal library of lipid standards as well as the LIPID MAPS Structure Database by using specifically developed processing tools. Features detected within the ^DTCCS_N2 and m/ z ranges of the analyzed standards are flagged as oxylipin-like species, which can be further characterized using drift-time alignment of product and precursor ions distinctive of DTIM-MS. This not only helps identification by reducing the number of annotations from LIPID MAPS but also guides discovery studies of potentially novel species. Testing the methodology on Salmonella enterica serovar Typhimurium-infected murine bone-marrow-derived macrophages and thrombin activated human platelets yields results in agreement with literature. This workflow has also annotated features as potentially novel oxylipins, confirming its ability in providing further insights into lipid analysis of biological samples.

Enzymatically oxidized phospholipids assume center stage as essential regulators of innate immunity and cell death

Enzymatically oxidized phospholipids (eoxPLs) are formed through regulated processes by which eicosanoids or prostaglandins are attached to phospholipids (PLs) in immune cells. These eoxPLs comprise structurally diverse families of biomolecules with potent bioactivities, and they have important immunoregulatory roles in both health and disease. The formation of oxPLs through enzymatic pathways and their signaling capabilities are emerging concepts. This paradigm is changing our understanding of eicosanoid, prostaglandin, and PL biology in health and disease. eoxPLs have roles in cellular events such as ferroptosis, apoptosis, and blood clotting and diseases such as arthritis, diabetes, and cardiovascular disease. They are increasingly recognized as endogenous bioactive mediators and potential targets for drug development. This review will describe recent evidence that places eoxPLs and their biosynthetic pathways center stage in immunoregulation.

Redox Signaling by Reactive Electrophiles and Oxidants

The concept of cell signaling in the context of nonenzyme-assisted protein modifications by reactive electrophilic and oxidative species, broadly known as redox signaling, is a uniquely complex topic that has been approached from numerous different and multidisciplinary angles. Our Review reflects on five aspects critical for understanding how nature harnesses these noncanonical post-translational modifications to coordinate distinct cellular activities: (1) specific players and their generation, (2) physicochemical properties, (3) mechanisms of action, (4) methods of interrogation, and (5) functional roles in health and disease. Emphasis is primarily placed on the latest progress in the field, but several aspects of classical work likely forgotten/lost are also recollected. For researchers with interests in getting into the field, our Review is anticipated to function as a primer. For the expert, we aim to stimulate thought and discussion about fundamentals of redox signaling mechanisms and nuances of specificity/selectivity and timing in this sophisticated yet fascinating arena at the crossroads of chemistry and biology.

Profile of Arachidonic Acid-Derived Inflammatory Markers and Its Modulation by Nitro-Oleic Acid in an Inherited Model of Amyotrophic Lateral Sclerosis

The lack of current treatments for amyotrophic lateral sclerosis (ALS) highlights the need of a comprehensive understanding of the biological mechanisms of the disease. A consistent neuropathological feature of ALS is the extensive inflammation around motor neurons and axonal degeneration, evidenced by accumulation of reactive astrocytes and activated microglia. Final products of inflammatory processes may be detected as a screening tool to identify treatment response. Herein, we focus on (a) detection of arachidonic acid (AA) metabolization products by lipoxygenase (LOX) and prostaglandin endoperoxide H synthase in SOD1^G93A mice and (b) evaluate its response to the electrophilic nitro-oleic acid (NO₂-OA). Regarding LOX-derived products, a significant increase in 12-hydroxyeicosatetraenoic acid (12-HETE) levels was detected in SOD1^G93A mice both in plasma and brain whereas no changes were observed in age-matched non-Tg mice at the onset of motor symptoms (90 days-old). In addition, 15-hydroxyeicosatetraenoic acid (15-HETE) levels were greater in SOD1^G93A brains compared to non-Tg. Prostaglandin levels were also increased at day 90 in plasma from SOD1^G93A compared to non-Tg being similar in both types of animals at later stages of the disease. Administration of NO₂-OA 16 mg/kg, subcutaneously (s/c) three times a week to SOD1^G93A female mice, lowered the observed increase in brain 12-HETE levels compared to the non-nitrated fatty acid condition, and modified many others inflammatory markers. In addition, NO₂-OA significantly improved grip strength and rotarod performance compared to vehicle or OA treated animals. These beneficial effects were associated with increased hemeoxygenase 1 (HO-1) expression in the spinal cord of treated mice co-localized with reactive astrocytes. Furthermore, significant levels of NO₂-OA were detected in brain and spinal cord from NO₂-OA -treated mice indicating that nitro-fatty acids (NFA) cross brain–blood barrier and reach the central nervous system to induce neuroprotective actions. In summary, we demonstrate that LOX-derived oxidation products correlate with disease progression. Overall, we are proposing that key inflammatory mediators of AA-derived pathways may be useful as novel footprints of ALS onset and progression as well as NO₂-OA as a promising therapeutic compound.

Phospholipid signaling in innate immune cells

Phospholipids comprise a large body of lipids that define cells and organelles by forming membrane structures. Importantly, their complex metabolism represents a highly controlled cellular signaling network that is essential for mounting an effective innate immune response. Phospholipids in innate cells are subject to dynamic regulation by enzymes, whose activities are highly responsive to activation status. Along with their metabolic products, they regulate multiple aspects of innate immune cell biology, including shape change, aggregation, blood clotting, and degranulation. Phospholipid hydrolysis provides substrates for cell-cell communication, enables regulation of hemostasis, immunity, thrombosis, and vascular inflammation, and is centrally important in cardiovascular disease and associated comorbidities. Phospholipids themselves are also recognized by innate-like T cells, which are considered essential for recognition of infection or cancer, as well as self-antigens. This Review describes the major phospholipid metabolic pathways present in innate immune cells and summarizes the formation and metabolism of phospholipids as well as their emerging roles in cell biology and disease.

Enzymatically oxidized phospholipids restore thrombin generation in coagulation factor deficiencies

Hemostatic defects are treated using coagulation factors; however, clot formation also requires a procoagulant phospholipid (PL) surface. Here, we show that innate immune cell–derived enzymatically oxidized phospholipids (eoxPL) termed hydroxyeicosatetraenoic acid–phospholipids (HETE-PLs) restore hemostasis in human and murine conditions of pathological bleeding. HETE-PLs abolished blood loss in murine hemophilia A and enhanced coagulation in factor VIII- (FVIII-), FIX-, and FX-deficient human plasma . HETE-PLs were decreased in platelets from patients after cardiopulmonary bypass (CPB). To explore molecular mechanisms, the ability of eoxPL to stimulate individual isolated coagulation factor/cofactor complexes was tested in vitro. Extrinsic tenase (FVIIa/tissue factor [TF]), intrinsic tenase (FVIIIa/FIXa), and prothrombinase (FVa/FXa) all were enhanced by both HETE-PEs and HETE-PCs, suggesting a common mechanism involving the fatty acid moiety. In plasma, 9-, 15-, and 12-HETE-PLs were more effective than 5-, 11-, or 8-HETE-PLs, indicating positional isomer specificity. Coagulation was enhanced at lower lipid/factor ratios, consistent with a more concentrated area for protein binding. Surface plasmon resonance confirmed binding of FII and FX to HETE-PEs. HETE-PEs increased membrane curvature and thickness, but not surface charge or homogeneity, possibly suggesting increased accessibility to cations/factors. In summary, innate immune-derived eoxPL enhance calcium-dependent coagulation factor function, and their potential utility in bleeding disorders is proposed.

Innate immune-derived enzymatically oxidized phospholipids enhance calcium-dependent coagulation factor function.

Ultra-Performance Liquid Chromatography-Mass Spectrometry Analysis of Free and Esterified Oxygenated Derivatives from Docosahexaenoic Acid in Rat Brain

Docosahexaenoic acid (DHA), a prominent long-chain fatty acid of the omega-3 family, is present at high amount in brain tissues, especially in membrane phospholipids. This polyunsaturated fatty acid is the precursor of various oxygenated lipid mediators involved in diverse physiological and pathophysiological processes. Characterization of DHA-oxygenated metabolites is therefore crucial for better understanding the biological roles of DHA. In this study, we identified and measured, by ultrahigh-performance liquid chromatography coupled with tandem mass spectrometry, a number of oxygenated products derived from DHA in exsanguinated and nonexsanguinated brains. These metabolites were found both in free form and esterified in phospholipids. Interestingly, both (R)- and (S)-monohydroxylated fatty acid stereoisomers were observed free and esterified in phospholipids. Monohydroxylated metabolites were the main derivatives; however, measurable amounts of dihydroxylated products such as protectin DX were detected. Moreover, exsanguination allowed discriminating brain oxygenated metabolites from those generated in blood. These results obtained in healthy rats allowed an overview on the brain oxygenated metabolism of DHA, which deserves further research in pathophysiological conditions, especially in neurodegenerative diseases.

Networks of enzymatically oxidized membrane lipids support calcium-dependent coagulation factor binding to maintain hemostasis

Blood coagulation functions as part of the innate immune system by preventing bacterial invasion, and it is critical to stopping blood loss (hemostasis). Coagulation involves the external membrane surface of activated platelets and leukocytes. Using lipidomic, genetic, biochemical, and mathematical modeling approaches, we found that enzymatically oxidized phospholipids (eoxPLs) generated by the activity of leukocyte or platelet lipoxygenases (LOXs) were required for normal hemostasis and promoted coagulation factor activities in a Ca²⁺- and phosphatidylserine (PS)-dependent manner. In wild-type mice, hydroxyeicosatetraenoic acid-phospholipids (HETE-PLs) enhanced coagulation and restored normal hemostasis in clotting-deficient animals genetically lacking p12-LOX or 12/15-LOX activity. Murine platelets generated 22 eoxPL species, all of which were missing in the absence of p12-LOX. Humans with the thrombotic disorder antiphospholipid syndrome (APS) had statistically significantly increased HETE-PLs in platelets and leukocytes, as well as greater HETE-PL immunoreactivity, than healthy controls. HETE-PLs enhanced membrane binding of the serum protein β2GP1 (β2-glycoprotein 1), an event considered central to the autoimmune reactivity responsible for APS symptoms. Correlation network analysis of 47 platelet eoxPL species in platelets from APS and control subjects identified their enzymatic origin and revealed a complex network of regulation, with the abundance of 31 p12-LOX-derived eoxPL molecules substantially increased in APS. In summary, circulating blood cells generate networks of eoxPL molecules, including HETE-PLs, which change membrane properties to enhance blood coagulation and contribute to the excessive clotting and immunoreactivity of patients with APS.

First Selective 12-LOX Inhibitor, ML355, Impairs Thrombus Formation and Vessel Occlusion In Vivo With Minimal Effects on Hemostasis

OBJECTIVE

Adequate platelet reactivity is required for maintaining hemostasis. However, excessive platelet reactivity can also lead to the formation of occlusive thrombi. Platelet 12(S)-lipoxygenase (12-LOX), an oxygenase highly expressed in the platelet, has been demonstrated to regulate platelet function and thrombosis ex vivo, supporting a key role for 12-LOX in the regulation of in vivo thrombosis. However, the ability to pharmacologically target 12-LOX in vivo has not been established to date. Here, we studied the effect of the first highly selective 12-LOX inhibitor, ML355, on in vivo thrombosis and hemostasis.

APPROACH AND RESULTS

ML355 dose-dependently inhibited human platelet aggregation and 12-LOX oxylipin production, as confirmed by mass spectrometry. Interestingly, the antiplatelet effects of ML355 were reversed after exposure to high concentrations of thrombin in vitro. Ex vivo flow chamber assays confirmed that human platelet adhesion and thrombus formation at arterial shear over collagen were attenuated in whole blood treated with ML355 comparable to aspirin. Oral administration of ML355 in mice showed reasonable plasma drug levels by pharmacokinetic assessment. ML355 treatment impaired thrombus growth and vessel occlusion in FeCl3-induced mesenteric and laser-induced cremaster arteriole thrombosis models in mice. Importantly, hemostatic plug formation and bleeding after treatment with ML355 was minimal in mice in response to laser ablation on the saphenous vein or in a cremaster microvasculature laser-induced rupture model.

CONCLUSIONS

Our data strongly support 12-LOX as a key determinant of platelet reactivity in vivo, and inhibition of platelet 12-LOX with ML355 may represent a new class of antiplatelet therapy.

Pleiotropic effects of oxidized phospholipids

Oxidized phospholipids (OxPLs) are increasingly recognized to play a role in a variety of normal and pathological states. OxPLs were implicated in regulation of inflammation, thrombosis, angiogenesis, endothelial barrier function, immune tolerance and other important processes. Rapidly accumulating evidence suggests that OxPLs are biomarkers of atherosclerosis and other pathologies. In addition, successful application of experimental drugs based on structural scaffold of OxPLs in animal models of inflammation was recently reported. This review briefly summarizes current knowledge on generation, methods of quantification and biological activities of OxPLs. Furthermore, receptor and cellular mechanisms of these effects are discussed. The goal of the review is to give a broad overview of this class of lipid mediators inducing pleiotropic biological effects.

Platelets as crucial partners for tumor metastasis: from mechanistic aspects to pharmacological targeting

Platelets are anucleated cells that circulate in the blood as sentinels of tissue integrity. In fact, they are rich in a plethora of proteins and other factors stored in different granules which they selectively release upon stimulation. Moreover, platelets synthesize a vast number of lipids and release various types of vesicles, including exosomes which are rich in genetic material. Platelets possess a central function to interact with other cell types, including inflammatory cells and cancer cells. Recent findings have enlightened the capacity of platelets to induce changes in the phenotype of cancer cells which acquire invasiveness thus enhancing their metastatic potential. Thus, it has been hypothesized that targeting the platelet may represent a novel strategy to prevent the development and progression of cancer. This is supported by the efficacy of the antiplatelet agent low-dose aspirin. Studies are ongoing to verify whether other antiplatelet agents share the anticancer effectiveness of aspirin.

Comprehensive analyses of oxidized phospholipids using a measured MS/MS spectra library

Oxidized phospholipids (OxPLs) are widely held to be associated with various diseases, such as arteriosclerosis, diabetes, and cancer. To characterize the structure-specific behavior of OxPLs and their physiological relevance, we developed a comprehensive analytical method by establishing a measured MS/MS spectra library of OxPLs. Biogenic OxPLs were prepared by the addition of specific oxidized fatty acids to cultured cells, where they were incorporated into cellular phospholipids, and untargeted lipidomics by LC-quadrupole/TOF-MS was applied to collect MS/MS spectra for the OxPLs. Based on the measured MS/MS spectra for about 400 molecular species of the biogenic OxPLs, we developed a broad-targeted lipidomics system using triple quadrupole MS. Separation precision of structural isomers was optimized by multiple reaction monitoring analysis and this system enabled us to detect OxPLs at levels as low as 10 fmol. When applied to biological samples, i.e., mouse peritoneal macrophages, this system enabled us to monitor a series of OxPLs endogenously produced in a 12/15-lipoxygenase-dependent manner. This advanced analytical method will be useful to elucidate the structure-specific behavior of OxPLs and their physiological relevance in vivo.

Platelets: much more than bricks in a breached wall

Platelets have various roles in vascular biology and homeostasis. They are the first actor in primary haemostasis and play important roles in thrombosis pathogenesis, but they are also part of innate immunity, which initiates and accelerate many inflammatory conditions. In some contexts, their immune functions are protective, while in others they contribute to adverse inflammatory outcomes. Platelets express numerous receptors and contain hundreds of secretory molecules that are crucial for platelet functional responses. The capacity of platelets to produce and secrete cytokines, chemokines and related molecules, under the control of specific intracellular pathways, is intimately related to their key role in inflammation. They are also able to intervene in tissue regeneration and repair because they produce pro-angiogenic mediators. Due to this characteristic platelets are involved in cancer progression and spreading. In this review we discuss the complex role of platelets, which bridges haemostasis, inflammation and immune response both in physiological and pathological conditions.

Iron and ferroptosis: A still ill-defined liaison

Ferroptosis is a recently described form of regulated necrotic cell death, which appears to contribute to a number of diseases, such as tissue ischemia/reperfusion injury, acute renal failure, and neurodegeneration. A hallmark of ferroptosis is iron-dependent lipid peroxidation, which can be inhibited by the key ferroptosis regulator glutathione peroxidase 4(Gpx4), radical trapping antioxidants and ferroptosis-specific inhibitors, such as ferrostatins and liproxstatins, as well as iron chelation. Although great strides have been made towards a better understanding of the proximate signals of distinctive lipid peroxides in ferroptosis, still little is known about the mechanistic implication of iron in the ferroptotic process. Hence, this review aims at summarizing recent advances in our understanding to what is known about enzymatic and nonenzymatic routes of lipid peroxidation, the involvement of iron in this process and the identification of novel players in ferroptotic cell death. Additionally, we review early works carried out long time before the term "ferroptosis" was actually introduced but which were instrumental in a better understanding of the role of ferroptosis in physiological and pathophysiological contexts. © 2017 IUBMB Life, 69(6):423-434, 2017.

DioxolaneA3-phosphatidylethanolamines are generated by human platelets and stimulate neutrophil integrin expression

Activated platelets generate an eicosanoid proposed to be 8-hydroxy-9,10-dioxolane A3 (DXA₃). Herein, we demonstrate that significant amounts of DXA₃ are rapidly attached to phosphatidylethanolamine (PE) forming four esterified eicosanoids, 16:0p, 18:0p, 18:1p and 18:0a/DXA₃-PEs that can activate neutrophil integrin expression. These lipids comprise the majority of DXA₃ generated by platelets, are formed in ng amounts (24.3±6.1ng/2×10⁸) and remain membrane bound. Pharmacological studies revealed DXA₃-PE formation involves cyclooxygenase-1 (COX), protease-activated receptors (PAR) 1 and 4, cytosolic phospholipase A₂ (cPLA₂), phospholipase C and intracellular calcium. They are generated primarily via esterification of newly formed DXA_3, but can also be formed in vitro via co-oxidation of PE during COX-1 co-oxidation of arachidonate. All four DXA₃-PEs were detected in human clots. Purified platelet DXA₃-PE activated neutrophil Mac-1 expression, independently of its hydrolysis to the free eicosanoid. This study demonstrates the structures and cellular synthetic pathway for a family of leukocyte-activating platelet phospholipids generated on acute activation, adding to the growing evidence that enzymatic PE oxidation is a physiological event in innate immune cells.

Mapping the Human Platelet Lipidome Reveals Cytosolic Phospholipase A2 as a Regulator of Mitochondrial Bioenergetics during Activation

Human platelets acutely increase mitochondrial energy generation following stimulation. Herein, a lipidomic circuit was uncovered whereby the substrates for this are exclusively provided by cPLA2, including multiple fatty acids and oxidized species that support energy generation via β-oxidation. This indicates that acute lipid membrane remodeling is required to support energetic demands during platelet activation. Phospholipase activity is linked to energy metabolism, revealing cPLA2 as a central regulator of both lipidomics and energy flux. Using a lipidomic approach (LipidArrays), we also estimated the total number of lipids in resting, thrombin-activated, and aspirinized platelets. Significant diversity between genetically unrelated individuals and a wealth of species was revealed. Resting platelets demonstrated ∼5,600 unique species, with only ∼50% being putatively identified. Thrombin elevated ∼900 lipids >2-fold with 86% newly appearing and 45% inhibited by aspirin supplementation, indicating COX-1 is required for major activation-dependent lipidomic fluxes. Many lipids were structurally identified. With ∼50% of the lipids being absent from databases, a major opportunity for mining lipids relevant to human health and disease is presented.

Lysophospholipid acyltransferases and eicosanoid biosynthesis in zebrafish myeloid cells

Eicosanoids derived from the enzymatic oxidation of arachidonic acid play important roles in a large number of physiological and pathological processes in humans. Many animal and cellular models have been used to investigate the intricate mechanisms regulating their biosynthesis and actions. Zebrafish is a widely used model to study the embryonic development of vertebrates. It expresses homologs of the key enzymes involved in eicosanoid production, and eicosanoids have been detected in extracts from adult or embryonic fish. In this study we prepared cell suspensions from kidney marrow, the main hematopoietic organ in fish. Upon stimulation with calcium ionophore, these cells produced eicosanoids including PGE2, LTB4, 5-HETE and, most abundantly, 12-HETE. They also produced small amounts of LTB5 derived from eicosapentaenoic acid. These eicosanoids were also produced in kidney marrow cells stimulated with ATP, and this production was greatly enhanced by preincubation with thimerosal, an inhibitor of arachidonate reacylation into phospholipids. Microsomes from these cells exhibited acyltransferase activities consistent with expression of MBOAT5/LPCAT3 and MBOAT7/LPIAT1, the main arachidonoyl-CoA:lysophospholipid acyltransferases. In summary, this work introduces a new cellular model to study the regulation of eicosanoid production through a phospholipid deacylation-reacylation cycle from a well-established, versatile vertebrate model species.

Platelet 12-LOX is essential for FcγRIIa-mediated platelet activation

Platelets are essential in maintaining hemostasis following inflammation or injury to the vasculature. Dysregulated platelet activity often results in thrombotic complications leading to myocardial infarction and stroke. Activation of the FcγRIIa receptor leads to immune-mediated thrombosis, which is often life threatening in patients undergoing heparin-induced thrombocytopenia or sepsis. Inhibiting FcγRIIa-mediated activation in platelets has been shown to limit thrombosis and is the principal target for prevention of immune-mediated platelet activation. In this study, we show for the first time that platelet 12(S)-lipoxygenase (12-LOX), a highly expressed oxylipin-producing enzyme in the human platelet, is an essential component of FcγRIIa-mediated thrombosis. Pharmacologic inhibition of 12-LOX in human platelets resulted in significant attenuation of FcγRIIa-mediated aggregation. Platelet 12-LOX was shown to be essential for FcγRIIa-induced phospholipase Cγ2 activity leading to activation of calcium mobilization, Rap1 and protein kinase C activation, and subsequent activation of the integrin αIIbβ3. Additionally, platelets from transgenic mice expressing human FcγRIIa but deficient in platelet 12-LOX, failed to form normal platelet aggregates and exhibited deficiencies in Rap1 and αIIbβ3 activation. These results support an essential role for 12-LOX in regulating FcγRIIa-mediated platelet function and identifies 12-LOX as a potential therapeutic target to limit immune-mediated thrombosis.

Platelet lipidomics: modern day perspective on lipid discovery and characterization in platelets

Lipids are diverse families of biomolecules that perform essential structural and signaling roles in platelets. Their formation and metabolism are tightly controlled by enzymes and signal transduction pathways, and their dysregulation leads to significant defects in platelet function and disease. Platelet activation is associated with significant changes to membrane lipids, and formation of diverse bioactive lipids plays essential roles in hemostasis. In recent years, new generation mass spectrometry analysis of lipids (termed lipidomics) has begun to alter our understanding of how these molecules participate in key cellular processes. Although the application of lipidomics to platelet biology is still in its infancy, seminal earlier studies have shaped our knowledge of how lipids regulate key aspects of platelet biology, including aggregation, shape change, coagulation, and degranulation, as well as how lipids generated by platelets influence other cells, such as leukocytes and the vascular wall, and thus how they regulate hemostasis, vascular integrity, and inflammation, as well as contribute to pathologies, including arterial/deep vein thrombosis and atherosclerosis. This review will provide a brief historical perspective on the characterization of lipids in platelets, then an overview of the new generation lipidomic approaches, their recent application to platelet biology, and future perspectives for research in this area. The major platelet-regulatory lipid families, their formation, metabolism, and their role in health and disease, will be summarized.

Platelets and cancer: a casual or causal relationship: revisited

Human platelets arise as subcellular fragments of megakaryocytes in bone marrow. The physiologic demand, presence of disease such as cancer, or drug effects can regulate the production circulating platelets. Platelet biology is essential to hemostasis, vascular integrity, angiogenesis, inflammation, innate immunity, wound healing, and cancer biology. The most critical biological platelet response is serving as "First Responders" during the wounding process. The exposure of extracellular matrix proteins and intracellular components occurs after wounding. Numerous platelet receptors recognize matrix proteins that trigger platelet activation, adhesion, aggregation, and stabilization. Once activated, platelets change shape and degranulate to release growth factors and bioactive lipids into the blood stream. This cyclic process recruits and aggregates platelets along with thrombogenesis. This process facilitates wound closure or can recognize circulating pathologic bodies. Cancer cell entry into the blood stream triggers platelet-mediated recognition and is amplified by cell surface receptors, cellular products, extracellular factors, and immune cells. In some cases, these interactions suppress immune recognition and elimination of cancer cells or promote arrest at the endothelium, or entrapment in the microvasculature, and survival. This supports survival and spread of cancer cells and the establishment of secondary lesions to serve as important targets for prevention and therapy.

Lipidomic profiling of influenza infection identifies mediators that induce and resolve inflammation

Bioactive lipid mediators play a crucial role in the induction and resolution of inflammation. To elucidate their involvement during influenza infection, liquid chromatography/mass spectrometry lipidomic profiling of 141 lipid species was performed on a mouse influenza model using two viruses of significantly different pathogenicity. Infection by the low-pathogenicity strain X31/H3N2 induced a proinflammatory response followed by a distinct anti-inflammatory response; infection by the high-pathogenicity strain PR8/H1N1 resulted in overlapping pro- and anti-inflammatory states. Integration of the large-scale lipid measurements with targeted gene expression data demonstrated that 5-lipoxygenase metabolites correlated with the pathogenic phase of the infection, whereas 12/15-lipoxygenase metabolites were associated with the resolution phase. Hydroxylated linoleic acid, specifically the ratio of 13- to 9-hydroxyoctadecadienoic acid, was identified as a potential biomarker for immune status during an active infection. Importantly, some of the findings from the animal model were recapitulated in studies of human nasopharyngeal lavages obtained during the 2009-2011 influenza seasons.

Oxidized PLs and vascular inflammation

Oxidized PLs (OxPLs) generated in health and disease are now recognized as important mediators of cellular signalling. There is an increasing body of evidence showing that PL peroxidation is not only increased in vascular disorders, but is also a physiological event of relevance to coagulation, innate immunity, and self-tolerance. Nonenzymatically formed OxPLs generated during chronic inflammation is an uncontrolled event, generating hundreds of diverse structures, and prone to more deleterious bioactivities. In contrast, enzymatic formation of OxPLs is tightly regulated, involving receptors and intracellular signaling, acting as part of the normal physiological response to injury in order to restore homeostasis. In the present review, the major nonenzymatic OxPLs structures found during vascular inflammation are summarized, along with a brief description of their known biological activities. Also, we review what is currently known about enzymatic formation of OxPLs by acutely activated immune cells and their signaling actions under homeostatic and pathological conditions.

Emerging importance of omega-3 fatty acids in the innate immune response: molecular mechanisms and lipidomic strategies for their analysis

The beneficial health properties of dietary omega-3 polyunsaturated fatty acids, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have long been known and their metabolic dysfunction has been linked to a range of diseases including various inflammatory disorders, cardiovascular diseases, and cancer. However, the molecular mechanisms underlying their health benefits have remained unclear. Recent technological advances in lipidomic analytical strategies have resulted in the discovery of a range of bioactive mediators derived from EPA and DHA that possess potent anti-inflammatory and pro-resolving properties and that may be responsible, at least in part, for the beneficial effects observed. These mediators include resolvins, protectins and maresins, as well as EPA derivatives of classical arachidonic acid derived eicosanoids, such as prostaglandin E3 . The aim of this review is to provide an overview of the biosynthetic pathways and biological properties of these omega-3 mediators, with a particular focus on the emerging importance of the counter-regulatory role of omega-3 and -6 fatty acids in the spatial and temporal regulation of the inflammatory response. It will also provide an insight into a range of lipidomic approaches, which are currently available to analyse these fatty acids and their metabolites in biological matrices.

Human platelets generate phospholipid-esterified prostaglandins via cyclooxygenase-1 that are inhibited by low dose aspirin supplementation

Oxidized phospholipids (oxPLs) generated nonenzymatically display pleiotropic biological actions in inflammation. Their generation by cellular cyclooxygenases (COXs) is currently unknown. To determine whether platelets generate prostaglandin (PG)-containing oxPLs, then characterize their structures and mechanisms of formation, we applied precursor scanning-tandem mass spectrometry to lipid extracts of agonist-activated human platelets. Thrombin, collagen, or ionophore activation stimulated generation of families of PGs comprising PGE₂ and D₂ attached to four phosphatidylethanolamine (PE) phospholipids (16:0p/, 18:1p/, 18:0p/, and 18:0a/). They formed within 2 to 5 min of activation in a calcium, phospholipase C, p38 MAP kinases, MEK1, cPLA₂, and src tyrosine kinase-dependent manner (28.1 ± 2.3 pg/2 × 10⁸ platelets). Unlike free PGs, they remained cell associated, suggesting an autocrine mode of action. Their generation was inhibited by in vivo aspirin supplementation (75 mg/day) or in vitro COX-1 blockade. Inhibitors of fatty acyl reesterification blocked generation significantly, while purified COX-1 was unable to directly oxidize PE in vitro. This indicates that they form in platelets via rapid esterification of COX-1 derived PGE₂/D₂ into PE. In summary, COX-1 in human platelets acutely mediates membrane phospholipid oxidation via formation of PG-esterified PLs in response to pathophysiological agonists.

15-Lipoxygenase-1-mediated metabolism of docosahexaenoic acid is required for syndecan-1 signaling and apoptosis in prostate cancer cells

Fatty acid metabolism impacts multiple intracellular signaling pathways in many cell types, but its role in prostate cancer cells is still unclear. Our previous studies have shown that the n-3 polyunsaturated fatty acid docosahexaenoic acid (DHA) induces apoptosis in human prostate cancer cells by a syndecan-1 (SDC-1)-dependent mechanism. Here, we examined the contribution of lipoxygenase (LOX)- and cyclooxygenase (COX)-mediated DHA metabolism to this effect. Pan-LOX inhibitor (nordihydroguaiaretic acid), 15-LOX inhibitor (luteolin) or 15/12-LOX inhibitor (baicalein) blocked the induced effect of DHA on SDC-1 expression and apoptosis in human prostate cancer cells, whereas 5-LOX inhibitor, AA861, was ineffective. Human prostate cancer cells lines (PC3, LNCaP and DU145 cells) expressed two 15-LOX isoforms, 15-LOX-1 and 15-LOX-2, with higher 15-LOX-1 and lower 15-LOX-2 expressions compared with human epithelial prostate cells. Knockdown of 15-LOX-1 blocked the effect of DHA on SDC-1 expression and caspase-3 activity, whereas silencing 15-LOX-2, 5-LOX, COX-1, COX-2 or 12-LOX had no effect. Moreover, the ability of DHA to inhibit the activity of the PDK/Akt (T308) signaling pathway was abrogated by silencing 15-LOX-1. These findings demonstrate that 15-LOX-1-mediated metabolism of DHA is required for it to upregulate SDC-1 and trigger the signaling pathway that elicits apoptosis in prostate cancer cells.

Novel keto-phospholipids are generated by monocytes and macrophages, detected in cystic fibrosis, and activate peroxisome proliferator-activated receptor-γ

12/15-Lipoxygenases (LOXs) in monocytes and macrophages generate novel phospholipid-esterified eicosanoids. Here, we report the generation of two additional families of related lipids comprising 15-ketoeicosatetraenoic acid (KETE) attached to four phosphatidylethanolamines (PEs). The lipids are generated basally by 15-LOX in IL-4-stimulated monocytes, are elevated on calcium mobilization, and are detected at increased levels in bronchoalveolar lavage fluid from cystic fibrosis patients (3.6 ng/ml of lavage). Murine peritoneal macrophages generate 12-KETE-PEs, which are absent in 12/15-LOX-deficient mice. Inhibition of 15-prostaglandin dehydrogenase prevents their formation from exogenous 15-hydroxyeicosatetraenoic acid-PE in human monocytes. Both human and murine cells also generated analogous hydroperoxyeicosatetraenoic acid-PEs. The electrophilic reactivity of KETE-PEs is shown by their Michael addition to glutathione and cysteine. Lastly, both 15-hydroxyeicosatetraenoic acid-PE and 15-KETE-PE activated peroxisome proliferator-activated receptor-γ reporter activity in macrophages in a dose-dependent manner. In summary, we demonstrate novel peroxisome proliferator-activated receptor-γ-activating oxidized phospholipids generated enzymatically by LOX and 15-prostaglandin dehydrogenase in primary monocytic cells and in a human Th2-related lung disease. The lipids are a new family of bioactive mediators from the 12/15-LOX pathway that may contribute to its known anti-inflammatory actions in vivo.

Investigations of human platelet-type 12-lipoxygenase: role of lipoxygenase products in platelet activation

Human platelet-type 12-lipoxygenase (12-LOX) has recently been shown to play an important role in regulation of human platelet function by reacting with arachidonic acid (AA). However, a number of other fatty acids are present on the platelet surface that, when cleaved from the phospholipid, can be oxidized by 12-LOX. We sought to characterize the substrate specificity of 12-LOX against six essential fatty acids: AA, dihomo-γ-linolenic acid (DGLA), eicosapentaenoic acid (EPA), α-linolenic acid (ALA), eicosadienoic acid (EDA), and linoleic acid (LA). Three fatty acids were comparable substrates (AA, DGLA, and EPA), one was 5-fold slower (ALA), and two showed no reactivity with 12-LOX (EDA and LA). The bioactive lipid products resulting from 12-LOX oxidation of DGLA, 12-(S)-hydroperoxy-8Z,10E,14Z-eicosatrienoic acid [12(S)-HPETrE], and its reduced product, 12(S)-HETrE, resulted in significant attenuation of agonist-mediated platelet aggregation, granule secretion, αIIbβ3 activation, Rap1 activation, and clot retraction. Treatment with DGLA similarly inhibited PAR1-mediated platelet activation as well as platelet clot retraction. These observations are in surprising contrast to our recent work showing 12(S)-HETE is a prothrombotic bioactive lipid and support our hypothesis that the overall effect of 12-LOX oxidation of fatty acids in the platelet is dependent on the fatty acid substrates available at the platelet membrane.