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

12/15-Lipooxygenase Inhibition Reduces Microvessel Constriction and Microthrombi After Subarachnoid Hemorrhage in Mice

Impaired cerebral circulation, induced by blood vessel constrictions and microthrombi, leads to delayed cerebral ischemia after subarachnoid hemorrhage (SAH). 12/15-Lipooxygenase (12/15-LOX) overexpression has been implicated in worsening early brain injury outcomes following SAH. However, it is unknown if 12/15-LOX is important in delayed pathophysiological events after SAH. Since 12/15-LOX produces metabolites that induce inflammation and vasoconstriction, we hypothesized that 12/15-LOX leads to microvessel constriction and microthrombi formation after SAH, and thus, 12/15-LOX is an important target to prevent delayed cerebral ischemia. SAH was induced in C57BL/6 and 12/15-LOX-/- mice of both sexes by endovascular perforation. Expression of 12/15-LOX was assessed in brain tissue slices and in vitro. C57BL/6 mice were administered either ML351 (12/15-LOX inhibitor) or vehicle. Mice were evaluated for daily neuroscore and euthanized on day 5 to assess cerebral 12/15-LOX expression, vessel constrictions, platelet activation, microthrombi, neurodegeneration, infarction, cortical perfusion, and development of delayed deficits. Finally, the effect of 12/15-LOX inhibition on platelet activation was assessed in SAH patient samples using a platelet spreading assay. In SAH mice, 12/15-LOX was upregulated in brain vascular cells, and there was an increase in 12-S-HETE. Inhibition of 12/15-LOX improved brain perfusion on days 4-5 and attenuated delayed pathophysiological events, including microvessel constrictions, microthrombi, neuronal degeneration, and infarction. Additionally, 12/15-LOX inhibition reduced platelet activation in human and mouse blood samples. Cerebrovascular 12/15-LOX overexpression plays a major role in brain dysfunction after SAH by triggering microvessel constrictions and microthrombi formation, which reduces brain perfusion. Inhibiting 12/15-LOX may be a therapeutic target to improve outcomes after SAH.

12/15-Lipooxygenase Inhibition Reduces Microvessel Constriction and Microthrombi after Subarachnoid Hemorrhage in Mice

Background and Purpose

Impaired cerebral circulation, induced by blood vessel constrictions and microthrombi, leads to delayed cerebral ischemia after subarachnoid hemorrhage (SAH). 12/15-Lipooxygenase (12/15-LOX) overexpression has been implicated in worsening early brain injury outcomes following SAH. However, it is unknown if 12/15-LOX is important in delayed pathophysiological events after SAH. Since 12/15-LOX produces metabolites that induce inflammation and vasoconstriction, we hypothesized that 12/15-LOX leads to microvessel constriction and microthrombi formation after SAH, and thus 12/15-LOX is an important target to prevent delayed cerebral ischemia.

Methods

SAH was induced in C57BL/6 and 12/15-LOX-/- mice of both sexes by endovascular perforation. Expression of 12/15-LOX was assessed in brain tissue slices and in vitro. C57BL/6 mice were administered either ML351 (12/15-LOX inhibitor) or vehicle. Mice were evaluated for daily neuroscore and euthanized on day five to assess cerebral 12/15-LOX expression, vessel constrictions, platelet activation, microthrombi, neurodegeneration, infarction, cortical perfusion, and for development of delayed deficits. Finally, the effect of 12/15-LOX inhibition on platelet activation was assessed in SAH patient samples using a platelet spreading assay.

Results

In SAH mice, 12/15-LOX was upregulated in brain vascular cells and there was an increase in 12-S-HETE. Inhibition of 12/15-LOX improved brain perfusion on days 4-5 and attenuated delayed pathophysiological events, including microvessel constrictions, microthrombi, neuronal degeneration, and infarction. Additionally, 12/15-LOX inhibition reduced platelet activation in human and mouse blood samples.

Conclusions

Cerebrovascular 12/15-LOX overexpression plays a major role in brain dysfunction after SAH by triggering microvessel constrictions and microthrombi formation, which reduces brain perfusion. Inhibiting 12/15-LOX may be a therapeutic target to improve outcomes after SAH.

The oxylipin analog CS585 prevents platelet activation and thrombosis through activation of the prostacyclin receptor

Cardiovascular disease remains the primary cause of morbidity and mortality globally. Platelet activation is critical for maintaining hemostasis and preventing the leakage of blood cells from the vessel. There has been a paucity in the development of new drugs to target platelet reactivity. Recently, the oxylipin 12(S)-hydroxy-eicosatrienoic acid (12-HETrE), which is produced in platelets, was shown to limit platelet reactivity by activating the prostacyclin receptor. Here, we demonstrated the synthesis of a novel analog of 12-HETrE, known as CS585. Human blood and mouse models of hemostasis and thrombosis were assessed for the ability of CS585 to attenuate platelet activation and thrombosis without increasing the risk of bleeding. Human platelet activation was assessed using aggregometry, flow cytometry, western blot analysis, total thrombus formation analysis system, microfluidic perfusion chamber, and thromboelastography. Hemostasis, thrombosis, and bleeding assays were performed in mice. CS585 was shown to potently target the prostacyclin receptor on the human platelet, resulting in a highly selective and effective mechanism for the prevention of platelet activation. Furthermore, CS585 was shown to inhibit platelet function in human whole blood ex vivo, prevent thrombosis in both small and large vessels in mouse models, and exhibit long-lasting prevention of clot formation. Finally, CS585 was not observed to perturb coagulation or increase the risk of bleeding in the mouse model. Hence, CS585 represents a new validated target for the treatment of thrombotic diseases without the risk of bleeding or off-target activation observed with other prostaglandin receptor agonists.

Cryo-EM structures of human arachidonate 12S-lipoxygenase bound to endogenous and exogenous inhibitors

Human 12-lipoxygenase (12-LOX) is a key enzyme involved in platelet activation, and the regulation of its activity has been targeted for the treatment of heparin-induced thrombocytopenia. Despite the clinical importance of 12-LOX, the exact mechanisms by which it affects platelet activation are not fully understood, and the lack of structural information has limited drug discovery efforts. In this study, we used single-particle cryo-electron microscopy to determine high-resolution structures (1.7-2.8 Å) of human 12-LOX. Our results showed that 12-LOX can exist in multiple oligomeric states, from monomer to hexamer, which may affect its catalytic activity and membrane association. We also identified different conformations within the 12-LOX dimer, which likely represent different time points in its catalytic cycle. Furthermore, we identified small molecules bound to 12-LOX. The active site of the 12-LOX tetramer was occupied by an endogenous 12-LOX inhibitor, a long-chain acyl coenzyme A. In addition, we found that the 12-LOX hexamer can simultaneously bind to arachidonic acid and ML355, a selective 12-LOX inhibitor that has passed a phase 1 clinical trial for the treatment of heparin-induced thrombocytopenia and received a fast-track designation by the Food and Drug Administration. Overall, our findings provide novel insights into the assembly of 12-LOX oligomers, their catalytic mechanism, and small molecule binding, paving the way for further drug development targeting the 12-LOX enzyme.

Investigating the catalytic efficiency of C22-Fatty acids with LOX human isozymes and the platelet response of the C22-oxylipin products

Polyunsaturated fatty acids (PUFAs) have been extensively studied for their health benefits because they can be oxidized by lipoxygenases to form bioactive oxylipins. In this study, we investigated the impact of double bond placement on the kinetic properties and product profiles of human platelet 12-lipoxygenase (h12-LOX), human reticulocyte 15-lipoxygenase-1 (h15-LOX-1), and human endothelial 15-lipoxygenase-2 (h15-LOX-2) by using 22-carbon (C22) fatty acid substrates with differing double bond content. With respect to kcat/KM values, the loss of Δ4 and Δ19 led to an 18-fold loss of kinetic activity for h12-LOX, no change in kinetic capability for h15-LOX-1, but a 24-fold loss for h15-LOX-2 for both C22-FAs. With respect to the product profiles, h12-LOX produced mainly 14-oxylipins. For h15-LOX-1, the 14-oxylipin production increased with the loss of either Δ4 and Δ19, however, the 17-oxylipin became the major species upon loss of both Δ4 and Δ19. h15-LOX-2 produced mostly the 17-oxylipin products throughout the fatty acid series. This study also investigated the effects of various 17-oxylipins on platelet activation. The results revealed that both 17(S)-hydroxy-4Z,7Z,10Z,13Z,15E,19Z-DHA (17-HDHA) and 17-hydroxy-4Z,7Z,10Z,13Z,15E-DPAn6 (17-HDPAn6) demonstrated anti-aggregation properties with thrombin or collagen stimulation. 17-hydroxy-7Z,10Z,13Z,15E,19Z-DPAn3 (17-HDPAn3) exhibited agonistic properties, and 17-hydroxy-7Z,10Z,13Z,15E-DTA (17-HDTA) showed biphasic effects, inhibiting collagen-induced aggregation at lower concentrationsbut promoting aggregation at higher concentrations. Both 17-hydroxy-13Z,15E,19Z-DTrA (17-HDTrA), and 17-hydroxy-13Z,15E-DDiA (17-HDDiA) induced platelet aggregation. In summary, the number and placement of the double bonds affect platelet activation, with the general trend being that more double bonds generally inhibit aggregation, while less double bonds promote aggregation. These findings provide insights into the potential role of specific fatty acids and their metabolizing LOX isozymes with respect to cardiovascular health.

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.

Potential Benefits of Omega-3 Polyunsaturated Fatty Acids (N3PUFAs) on Cardiovascular Health Associated with COVID-19: An Update for 2023

The accumulating literature demonstrates that omega-3 polyunsaturated fatty acid (n-3 polyunsaturated fatty acid, N3PUFA) can be incorporated into the phospholipid bilayer of cell membranes in the human body to positively affect the cardiovascular system, including improving epithelial function, decreasing coagulopathy, and attenuating uncontrolled inflammatory responses and oxidative stress. Moreover, it has been proven that the N3PUFAs, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are precursors of some potent endogenous bioactive lipid mediators that mediate some favorable effects attributed to their parent substances. A dose-response relationship between increased EPA and DHA intake and reduced thrombotic outcomes has been reported. The excellent safety profile of dietary N3PUFAs makes them a prospective adjuvant treatment for people exposed to a higher risk of cardiovascular problems associated with COVID-19. This review presented the potential mechanisms that might contribute to the beneficial effects of N3PUFA and the optimal form and dose applied.

Hydroperoxidation of Docosahexaenoic Acid by Human ALOX12 and pigALOX15-mini-LOX

Human lipoxygenase 12 (hALOX12) catalyzes the conversion of docosahexaenoic acid (DHA) into mainly 14S-hydroperoxy-4Z,7Z,10Z,12E,16Z,19Z-docosahexaenoic acid (14S-H(p)DHA). This hydroperoxidation reaction is followed by an epoxidation and hydrolysis process that finally leads to maresin 1 (MaR1), a potent bioactive specialized pro-resolving mediator (SPM) in chronic inflammation resolution. By combining docking, molecular dynamics simulations, and quantum mechanics/molecular mechanics calculations, we have computed the potential energy profile of DHA hydroperoxidation in the active site of hALOX12. Our results describe the structural evolution of the molecular system at each step of this catalytic reaction pathway. Noteworthy, the required stereospecificity of the reaction leading to MaR1 is explained by the configurations adopted by DHA bound to hALOX12, along with the stereochemistry of the pentadienyl radical formed after the first step of the mechanism. In pig lipoxygenase 15 (pigALOX15-mini-LOX), our calculations suggest that 14S-H(p)DHA can be formed, but with a stereochemistry that is inadequate for MaR1 biosynthesis.

Synthesis and Significance of Arachidonic Acid, a Substrate for Cyclooxygenases, Lipoxygenases, and Cytochrome P450 Pathways in the Tumorigenesis of Glioblastoma Multiforme, Including a Pan-Cancer Comparative Analysis

Glioblastoma multiforme (GBM) is one of the most aggressive gliomas. New and more effective therapeutic approaches are being sought based on studies of the various mechanisms of GBM tumorigenesis, including the synthesis and metabolism of arachidonic acid (ARA), an omega-6 polyunsaturated fatty acid (PUFA). PubMed, GEPIA, and the transcriptomics analysis carried out by Seifert et al. were used in writing this paper. In this paper, we discuss in detail the biosynthesis of this acid in GBM tumors, with a special focus on certain enzymes: fatty acid desaturase (FADS)1, FADS2, and elongation of long-chain fatty acids family member 5 (ELOVL5). We also discuss ARA metabolism, particularly its release from cell membrane phospholipids by phospholipase A₂ (cPLA₂, iPLA₂, and sPLA₂) and its processing by cyclooxygenases (COX-1 and COX-2), lipoxygenases (5-LOX, 12-LOX, 15-LOX-1, and 15-LOX-2), and cytochrome P450. Next, we discuss the significance of lipid mediators synthesized from ARA in GBM cancer processes, including prostaglandins (PGE₂, PGD₂, and 15-deoxy-Δ^12,14-PGJ₂ (15d-PGJ₂)), thromboxane A₂ (TxA₂), oxo-eicosatetraenoic acids, leukotrienes (LTB₄, LTC₄, LTD₄, and LTE₄), lipoxins, and many others. These lipid mediators can increase the proliferation of GBM cancer cells, cause angiogenesis, inhibit the anti-tumor response of the immune system, and be responsible for resistance to treatment.

Fatty acids negatively regulate platelet function through formation of noncanonical 15-lipoxygenase-derived eicosanoids

The antiplatelet effect of polyunsaturated fatty acids is primarily attributed to its metabolism to bioactive metabolites by oxygenases, such as lipoxygenases (LOX). Platelets have demonstrated the ability to generate 15-LOX-derived metabolites (15-oxylipins); however, whether 15-LOX is in the platelet or is required for the formation of 15-oxylipins remains unclear. This study seeks to elucidate whether 15-LOX is required for the formation of 15-oxylipins in the platelet and determine their mechanistic effects on platelet reactivity. In this study, 15-HETrE, 15-HETE, and 15-HEPE attenuated collagen-induced platelet aggregation, and 15-HETrE inhibited platelet aggregation induced by different agonists. The observed anti-aggregatory effect was due to the inhibition of intracellular signaling including αIIbβ3 and protein kinase C activities, calcium mobilization, and granule secretion. While 15-HETrE inhibited platelets partially through activation of peroxisome proliferator-activated receptor β (PPARβ), 15-HETE also inhibited platelets partially through activation of PPARα. 15-HETrE, 15-HETE, or 15-HEPE inhibited 12-LOX in vitro, with arachidonic acid as the substrate. Additionally, a 15-oxylipin-dependent attenuation of 12-HETE level was observed in platelets following ex vivo treatment with 15-HETrE, 15-HETE, or 15-HEPE. Platelets treated with DGLA formed 15-HETrE and collagen-induced platelet aggregation was attenuated only in the presence of ML355 or aspirin, but not in the presence of 15-LOX-1 or 15-LOX-2 inhibitors. Expression of 15-LOX-1, but not 15-LOX-2, was decreased in leukocyte-depleted platelets compared to non-depleted platelets. Taken together, these findings suggest that 15-oxylipins regulate platelet reactivity; however, platelet expression of 15-LOX-1 is low, suggesting that 15-oxylipins may be formed in the platelet through a 15-LOX-independent pathway.

Oxylipin status, before and after LC n-3 PUFA supplementation, has little relationship with skeletal muscle biology in older adults at risk of sarcopenia

INTRODUCTION

Oxylipins form endogenously via the oxygenation of long-chain polyunsaturated fatty acids (LC PUFA). Several oxylipins are highly bioactive molecules and are believed to be key mediators of LC PUFA metabolism in the body. However, little is known in relation to whether oxylipins mediate alterations in skeletal muscle mass and function. The objective of this study was to determine if a relationship exists between the oxylipin profile and skeletal muscle biology in healthy older adults at risk of sarcopenia and determine if this changes in response to LC n-3 PUFA supplementation.

MATERIALS AND METHODS

This exploratory study investigated the baseline correlations between LC n-3, n-6 and n-9 PUFA-derived oxylipins and markers of muscle biology. For this, the concentration of 79 free (i.e., non-esterified) oxylipins was quantified in human plasma by liquid chromatography-mass spectrometry (LC-MS) and retrospectively correlated to phenotypic outcomes obtained pre-intervention from the NUTRIMAL study (n = 49). After examining the baseline relationship, the potential effect of supplementation (LC n-3 PUFA or an isoenergetic control made of high-oleic sunflower and corn oil) was evaluated by correlating the change in oxylipins concentration and the change in markers of skeletal muscle biology. The relationship between oxylipins pre- and post-intervention and their parent PUFA were also examined.

RESULTS

At baseline, the hydroxy product of mead acid (n-9 PUFA), 5-HETrE, was negatively correlated to the phenotypic parameters appendicular lean mass index (ALMI) (p = 0.003, r=-0.41), skeletal muscle mass index (SMMI) (p = 0.001, r=-0.46), handgrip strength (HGS) (p<0.001, r = 0.48) and isometric knee extension (p<0.001, r=-0.48). Likewise, LC n-6 PUFA hydroxy‑PUFA were negatively correlated to HGS (i.e., 12-HETrE, p = 0.002, r=-0.42, and 5- and 11-HETE, p = 0.006, r=-0.47 and p<0.001, r=-0.50 respectively), single leg stand time (i.e., 12-HETrE, p = 0.006, r=-0.39 and 16-HETE, p = 0.002, r=-0.43), and five-time-sit-to-stand test (FTST) performance (16-HETE, p = 0.006, r = 0.39), and positively correlated to gait speed (i.e., 12-HETrE, p = 0.007, r = 0.38 and 16-HETE, p = 0.006, r = 0.39). LC n-3 PUFA supplementation increased eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) derived oxylipins and reduced n-6 PUFA derived oxylipins. Parameters of skeletal muscle mass and strength were not significantly altered in either LC n-3 PUFA or placebo groups. Changes in plasma oxylipins concentrations were closely related to changes in their parent PUFA, assessed in the erythrocyte membrane, but were not associated with any changes in skeletal muscle parameters.

DISCUSSION AND CONCLUSION

At baseline, the status n-9 (5-HETrE) and n-6 PUFA derivates [12-HETrE, and 5-, 11- and 16-HETE], but not n-3 PUFA derived oxylipins, were associated with poor skeletal muscle health parameters (i.e., mass and strength). However, these correlations were no longer present when correlating relative changes from pre to post timepoints. An independent cohort validation is needed to explore baseline correlations further. Further research is warranted to assess other biological mechanisms by which LC n-3 PUFA might affect muscle biology.

Biochemical and hydrogen-deuterium exchange studies of the single nucleotide polymorphism Y649C in human platelet 12-lipoxygenase linked to a bleeding disorder

Human platelet 12-lipoxygenase (h12-LOX) is responsible for the formation of oxylipin products that play an important role in platelet aggregation. Single nucleotide polymorphisms (SNPs) of h12-LOX have been implicated in several diseases. In this study, we investigate the structural, dynamical, and functional impact of a h12-LOX SNP that generates a tyrosine-to-cysteine mutation at a buried site (Y649C h12-LOX) and was previously ascribed with reduced levels of 12(S)-hydroxyeicosatetraenoic acid (12S-HETE) production in isolated platelets. Herein, in vitro Michaelis-Menten kinetics show reduced catalytic rates for Y649C compared to WT h12-LOX at physiological or lower temperatures. Both proteins exhibited similar melting temperatures, metal content, and oligomerization state. Liposome binding for both proteins was also dependent upon the presence of calcium, temperature, and liposome composition; however, the Y649C variant was found to have lowered binding capacity to liposomes compared to WT at physiological temperatures. Further, hydrogen-deuterium exchange mass spectrometry (HDX-MS) experiments revealed a regional defined enhancement in the peptide mobility caused by the mutation. This increased instability for the mutation stemmed from a change in an interaction with an arched helix that lines the substrate binding site, located ≥15 Å from the mutation site. Finally, differential scanning calorimetry demonstrated a reduced protein (un)folding enthalpy, consistent with the HDX results. Taken together, these results demonstrate remarkable similarity between the mutant and WT h12-LOX, and yet, subtle changes in activity, membrane affinity and protein stability may be responsible for the significant physiological changes that the Y649C SNP manifests in platelet biology.

The Plasma Oxylipin Signature Provides a Deep Phenotyping of Metabolic Syndrome Complementary to the Clinical Criteria

Metabolic syndrome (MetS) is a complex condition encompassing a constellation of cardiometabolic abnormalities. Oxylipins are a superfamily of lipid mediators regulating many cardiometabolic functions. Plasma oxylipin signature could provide a new clinical tool to enhance the phenotyping of MetS pathophysiology. A high-throughput validated mass spectrometry method, allowing for the quantitative profiling of over 130 oxylipins, was applied to identify and validate the oxylipin signature of MetS in two independent nested case/control studies involving 476 participants. We identified an oxylipin signature of MetS (coined OxyScore), including 23 oxylipins and having high performances in classification and replicability (cross-validated AUC_ROC of 89%, 95% CI: 85–93% and 78%, 95% CI: 72–85% in the Discovery and Replication studies, respectively). Correlation analysis and comparison with a classification model incorporating the MetS criteria showed that the oxylipin signature brings consistent and complementary information to the clinical criteria. Being linked with the regulation of various biological processes, the candidate oxylipins provide an integrative phenotyping of MetS regarding the activation and/or negative feedback regulation of crucial molecular pathways. This may help identify patients at higher risk of cardiometabolic diseases. The oxylipin signature of patients with metabolic syndrome enhances MetS phenotyping and may ultimately help to better stratify the risk of cardiometabolic diseases.

Supplementation with omega-3 or omega-6 fatty acids attenuates platelet reactivity in postmenopausal women

Postmenopausal women are at increased risk for a cardiovascular event due to platelet hyperactivity. There is evidence suggesting that ω-3 polyunsaturated fatty acids (PUFAs) and ω-6 PUFAs have cardioprotective effects in these women. However, a mechanistic understanding of how these fatty acids regulate platelet function is unknown. In this study, we supplemented postmenopausal women with fish oil (ω-3 fatty acids) or evening primrose oil (ω-6 fatty acids) and investigated the effects on their platelet activity. The effects of fatty acid supplementation on platelet aggregation, dense granule secretion, and activation of integrin αIIbβ3 at basal levels and in response to agonist were tested in postmenopausal women following a supplementation and washout period. Supplementation with fish oil or primrose oil attenuated the thrombin receptor PAR4-induced platelet aggregation. Supplementation with ω-3 or ω-6 fatty acids decreased platelet dense granule secretion and attenuated basal levels of integrin αIIbβ3 activation. Interestingly, after the washout period following supplementation with primrose oil, platelet aggregation was similarly attenuated. Additionally, for either treatment, the observed protective effects post-supplementation on platelet dense granule secretion and basal levels of integrin activation were sustained after the washout period, suggesting a long-term shift in platelet reactivity due to fatty acid supplementation. These findings begin to elucidate the underlying mechanistic effects of ω-3 and ω-6 fatty acids on platelet reactivity in postmenopausal women. Hence, this study supports the beneficial effects of fish oil or primrose oil supplementation as a therapeutic intervention to reduce the risk of thrombotic events in postmenopausal women. https://clinicaltrials.gov/ct2/show/NCT02629497.

Eicosanoids in inflammation in the blood and the vessel

Polyunsaturated fatty acids (PUFAs) are structural components of membrane phospholipids in cells. PUFAs regulate cellular function through the formation of derived lipid mediators termed eicosanoids. The oxygenation of 20-carbon PUFAs via the oxygenases cyclooxygenases, lipoxygenases, or cytochrome P450, generates a class of classical eicosanoids including prostaglandins, thromboxanes and leukotrienes, and also the more recently identified hydroxy-, hydroperoxy-, epoxy- and oxo-eicosanoids, and the specialized pro-resolving (lipid) mediators. These eicosanoids play a critical role in the regulation of inflammation in the blood and the vessel. While arachidonic acid-derived eicosanoids are extensively studied due to their pro-inflammatory effects and therefore involvement in the pathogenesis of inflammatory diseases such as atherosclerosis, diabetes mellitus, hypertension, and the coronavirus disease 2019; in recent years, several eicosanoids have been reported to attenuate exacerbated inflammatory responses and participate in the resolution of inflammation. This review focused on elucidating the biosynthesis and the mechanistic signaling of eicosanoids in inflammation, as well as the pro-inflammatory and anti-inflammatory effects of these eicosanoids in the blood and the vascular wall.

Biochemical Characterization of 13-Lipoxygenases of Arabidopsis thaliana

13-lipoxygenases (13-LOX) catalyze the dioxygenation of various polyunsaturated fatty acids (PUFAs), of which α-linolenic acid (LeA) is converted to 13-S-hydroperoxyoctadeca-9, 11, 15-trienoic acid (13-HPOT), the precursor for the prostaglandin-like plant hormones cis-(+)-12-oxophytodienoic acid (12-OPDA) and methyl jasmonate (MJ). This study aimed for characterizing the four annotated A. thaliana 13-LOX enzymes (LOX2, LOX3, LOX4, and LOX6) focusing on synthesis of 12-OPDA and 4Z,7Z,10Z)-12-[[-(1S,5S)-4-oxo-5-(2Z)-pent-2-en-1yl] cyclopent-2-en-1yl] dodeca-4,7,10-trienoic acid (OCPD). In addition, we performed interaction studies of 13-LOXs with ions and molecules to advance our understanding of 13-LOX. Cell imaging indicated plastid targeting of fluorescent proteins fused to 13-LOXs-N-terminal extensions, supporting the prediction of 13-LOX localization to plastids. The apparent maximal velocity (V_max app) values for LOX-catalyzed LeA oxidation were highest for LOX4 (128 nmol·s⁻¹·mg protein⁻¹), with a K_m value of 5.8 µM. A. thaliana 13-LOXs, in cascade with 12-OPDA pathway enzymes, synthesized 12-OPDA and OCPD from LeA and docosahexaenoic acid, previously shown only for LOX6. The activities of the four isoforms were differently affected by physiologically relevant chemicals, such as Mg²⁺, Ca²⁺, Cu²⁺ and Cd²⁺, and by 12-OPDA and MJ. As demonstrated for LOX4, 12-OPDA inhibited enzymatic LeA hydroperoxidation, with half-maximal enzyme inhibition at 48 µM. Biochemical interactions, such as the sensitivity of LOX toward thiol-reactive agents belonging to cyclopentenone prostaglandins, are suggested to occur in human LOX homologs. Furthermore, we conclude that 13-LOXs are isoforms with rather specific functional and regulatory enzymatic features.

ANXA7 Regulates Platelet Lipid Metabolism and Ca2+ Release in Arterial Thrombosis

[Figure: see text].

Antisense overlapping long non-coding RNA regulates coding arachidonate 12-lipoxygenase gene by translational interference

The arachidonate 12-lipoxygenase (ALOX12) enzyme catalyzes polyunsaturated fatty acids and facilitates generation of bioactive lipid mediators associated with various biological processes and disease pathologies. The human genome assembly revealed that the ALOX12 gene overlaps an antisense non-coding gene designated as ALOX12-antisense 1 (ALOX12-AS1). This arrangement indicates that the uncharacterized ALOX12-AS1 long non-coding RNA (lncRNA) may bind to the sense coding ALOX12 mRNA to form an antisense-sense duplex providing the basis of a novel ALOX12 regulatory mechanism. Therefore, this study was designed to determine whether the interaction of ALOX12-AS1 with ALOX12 mRNA functions as an anti-sense/sense duplex-mediated regulatory mechanism controlling the cellular content of ALOX12. Our findings indicate that two major isoforms of ALOX12-AS1 lncRNA are ubiquitously expressed in a variety of primary adult human tissues and different transformed cell types. RNA-FISH revealed cell-type-specific cytosolic as well as nuclear and nucleolar localization of the lncRNA. Interestingly, phorbol ester-induced nucleo-cytoplasmic translocation of the lncRNA in monocytic THP-1 cells resulted in a reduction of ALOX12 protein without a concomitant change in its mRNA level. This indicated ALOX12-AS1 operates via an antisense-sense duplex-mediated translational downregulation mechanism. This deduction was validated by demonstrating sense/antisense duplex formation and an association of the duplex with ribosomal proteins in HEK293 cells. Overall, this study revealed a hitherto unknown mechanism of antisense lncRNA-mediated translational downregulation of ALOX12 that adds to the existing regulatory mechanisms for the modulation of potent bioactive lipid mediators that contribute to both health and disease.

In Vitro Biosynthetic Pathway Investigations of Neuroprotectin D1 (NPD1) and Protectin DX (PDX) by Human 12-Lipoxygenase, 15-Lipoxygenase-1, and 15-Lipoxygenase-2

In this paper, human platelet 12-lipoxygenase [h12-LOX (ALOX12)], human reticulocyte 15-lipoxygenase-1 [h15-LOX-1 (ALOX15)], and human epithelial 15-lipoxygenase-2 [h15-LOX-2 (ALOX15B)] were observed to react with docosahexaenoic acid (DHA) and produce 17S-hydroperoxy-4Z,7Z,10Z,13Z,15E,19Z-docosahexaenoic acid (17S-HpDHA). The kcat/KM values with DHA for h12-LOX, h15-LOX-1, and h15-LOX-2 were 12, 0.35, and 0.43 s-1 μM-1, respectively, which demonstrate h12-LOX as the most efficient of the three. These values are comparable to their counterpart kcat/KM values with arachidonic acid (AA), 14, 0.98, and 0.24 s-1 μM-1, respectively. Comparison of their product profiles with DHA demonstrates that the three LOX isozymes produce 11S-HpDHA, 14S-HpDHA, and 17S-HpDHA, to varying degrees, with 17S-HpDHA being the majority product only for the 15-LOX isozymes. The effective kcat/KM values (kcat/KM × percent product formation) for 17S-HpDHA of the three isozymes indicate that the in vitro value of h12-LOX was 2.8-fold greater than that of h15-LOX-1 and 1.3-fold greater than that of h15-LOX-2. 17S-HpDHA was an effective substrate for h12-LOX and h15-LOX-1, with four products being observed under reducing conditions: protectin DX (PDX), 16S,17S-epoxy-4Z,7Z,10Z,12E,14E,19Z-docosahexaenoic acid (16S,17S-epoxyDHA), the key intermediate in neuroprotection D1 biosynthesis [NPD1, also known as protectin D1 (PD1)], 11,17S-diHDHA, and 16,17S-diHDHA. However, h15-LOX-2 did not react with 17-HpDHA. With respect to their effective kcat/KM values, h12-LOX was markedly less effective than h15-LOX-1 in reacting with 17S-HpDHA, with a 55-fold lower effective kcat/KM in producing 16S,17S-epoxyDHA and a 27-fold lower effective kcat/KM in generating PDX. This is the first direct demonstration of h15-LOX-1 catalyzing this reaction and reveals an in vitro pathway for PDX and NPD1 intermediate biosynthesis. In addition, epoxide formation from 17S-HpDHA and h15-LOX-1 was negatively affected via allosteric regulation by 17S-HpDHA (Kd = 5.9 μM), 12S-hydroxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (12S-HETE) (Kd = 2.5 μM), and 17S-hydroxy-13Z,15E,19Z-docosatrienoic acid (17S-HDTA) (Kd = 1.4 μM), suggesting a possible regulatory pathway in reducing epoxide formation. Finally, 17S-HpDHA and PDX inhibited platelet aggregation, with EC50 values of approximately 1 and 3 μM, respectively. The in vitro results presented here may help advise in vivo PDX and NPD1 intermediate (i.e., 16S,17S-epoxyDHA) biosynthetic investigations and support the benefits of DHA rich diets.

Omega-6 DPA and its 12-lipoxygenase-oxidized lipids regulate platelet reactivity in a nongenomic PPARα-dependent manner

Arterial thrombosis is the underlying cause for a number of cardiovascular-related events. Although dietary supplementation that includes polyunsaturated fatty acids (PUFAs) has been proposed to elicit cardiovascular protection, a mechanism for antithrombotic protection has not been well established. The current study sought to investigate whether an omega-6 essential fatty acid, docosapentaenoic acid (DPAn-6), and its oxidized lipid metabolites (oxylipins) provide direct cardiovascular protection through inhibition of platelet reactivity. Human and mouse blood and isolated platelets were treated with DPAn-6 and its 12-lipoxygenase (12-LOX)-derived oxylipins, 11-hydroxy-docosapentaenoic acid and 14-hydroxy-docosapentaenoic acid, to assess their ability to inhibit platelet activation. Pharmacological and genetic approaches were used to elucidate a role for DPA and its oxylipins in preventing platelet activation. DPAn-6 was found to be significantly increased in platelets following fatty acid supplementation, and it potently inhibited platelet activation through its 12-LOX-derived oxylipins. The inhibitory effects were selectively reversed through inhibition of the nuclear receptor peroxisome proliferator activator receptor-α (PPARα). PPARα binding was confirmed using a PPARα transcription reporter assay, as well as PPARα-/- mice. These approaches confirmed that selectivity of platelet inhibition was due to effects of DPA oxylipins acting through PPARα. Mice administered DPAn-6 or its oxylipins exhibited reduced thrombus formation following vessel injury, which was prevented in PPARα-/- mice. Hence, the current study demonstrates that DPAn-6 and its oxylipins potently and effectively inhibit platelet activation and thrombosis following a vascular injury. Platelet function is regulated, in part, through an oxylipin-induced PPARα-dependent manner, suggesting that targeting PPARα may represent an alternative strategy to treat thrombotic-related diseases.

Regulation of Tissue Inflammation by 12-Lipoxygenases

Lipoxygenases (LOXs) are lipid metabolizing enzymes that catalyze the di-oxygenation of polyunsaturated fatty acids to generate active eicosanoid products. 12-lipoxygenases (12-LOXs) primarily oxygenate the 12th carbon of its substrates. Many studies have demonstrated that 12-LOXs and their eicosanoid metabolite 12-hydroxyeicosatetraenoate (12-HETE), have significant pathological implications in inflammatory diseases. Increased level of 12-LOX activity promotes stress (both oxidative and endoplasmic reticulum)-mediated inflammation, leading to damage in these tissues. 12-LOXs are also associated with enhanced cellular migration of immune cells-a characteristic of several metabolic and autoimmune disorders. Genetic depletion or pharmacological inhibition of the enzyme in animal models of various diseases has shown to be protective against disease development and/or progression in animal models in the setting of diabetes, pulmonary, cardiovascular, and metabolic disease, suggesting a translational potential of targeting the enzyme for the treatment of several disorders. In this article, we review the role of 12-LOXs in the pathogenesis of several diseases in which chronic inflammation plays an underlying role.

DHA 12-LOX-derived oxylipins regulate platelet activation and thrombus formation through a PKA-dependent signaling pathway

BACKGROUND

The effects of docosahexaenoic acid (DHA) on cardiovascular disease are controversial and a mechanistic understanding of how this omega-3 polyunsaturated fatty acid (ω-3 PUFA) regulates platelet reactivity and the subsequent risk of a thrombotic event is warranted. In platelets, DHA is oxidized by 12-lipoxygenase (12-LOX) producing the oxidized lipids (oxylipins) 11-HDHA and 14-HDHA. We hypothesized that 12-LOX DHA-oxylipins may be involved in the beneficial effects observed in dietary supplemental treatment with ω-3 PUFAs or DHA itself.

OBJECTIVES

To determine the effects of DHA, 11-HDHA, and 14-HDHA on platelet function and thrombus formation, and to elucidate the mechanism by which these ω-3 PUFAs regulate platelet activation.

METHODS AND RESULTS

DHA, 11-HDHA, and 14-HDHA attenuated collagen-induced human platelet aggregation, but only the oxylipins inhibited ⍺IIbβ3 activation and decreased ⍺-granule secretion. Furthermore, treatment of whole blood with DHA and its oxylipins impaired platelet adhesion and accumulation to a collagen-coated surface. Interestingly, thrombus formation was only diminished in mice treated with 11-HDHA or 14-HDHA, and mouse platelet activation was inhibited following acute treatment with these oxylipins or chronic treatment with DHA, suggesting that under physiologic conditions, the effects of DHA are mediated through its oxylipins. Finally, the protective mechanism of DHA oxylipins was shown to be mediated via activation of protein kinase A.

CONCLUSIONS

This study provides the first mechanistic evidence of how DHA and its 12-LOX oxylipins inhibit platelet activity and thrombus formation. These findings support the beneficial effects of DHA as therapeutic intervention in atherothrombotic diseases.

Distinctive Under-Expression Profile of Inflammatory and Redox Genes in the Blood of Elderly Patients with Cardiovascular Disease

Purpose

Chronic low-grade inflammation and oxidative stress are present in most of the pathologic mechanisms underlying non-communicable diseases. Inflammation and redox biomarkers might therefore have a value in disease prognosis and therapy response. In this context, we performed a case–control study for assessing in whole blood the expression profile of inflammation and redox-related genes in elderly subjects with various comorbidities.

Patients and Methods

In the blood of 130 elderly subjects with various pathologies (cardiovascular disease, hypertension, dyslipidemia including hypercholesterolemia, type 2 diabetes mellitus), kept under control by polyvalent disease-specific medication, we investigated by pathway-focused qRT-PCR a panel comprising 84 inflammation-related and 84 redox-related genes.

Results

The study highlights a distinctive expression profile of genes critically involved in NF-κB-mediated inflammation and redox signaling in the blood of patients with cardiovascular disease, characterized by significant down-regulation of the genes NFKB2, NFKBIA, RELA, RELB, AKT1, IRF1, STAT1, CD40, LTA, TRAF2, PTGS1, ALOX12, DUOX1, DUOX2, MPO, GSR, TXNRD2, HSPA1A, MSRA, and PDLIM1. This gene expression profile defines the transcriptional status of blood leukocytes in stable disease under medication control, without discriminating between disease- and therapy-related changes.

Conclusion

The study brings preliminary proof on a minimally invasive strategy for monitoring disease in patients with cardiovascular pathology, from the point of view of inflammation or redox dysregulation in whole blood.

Plasma and serum oxylipin, endocannabinoid, bile acid, steroid, fatty acid and nonsteroidal anti-inflammatory drug quantification in a 96-well plate format

The goal of this research was to develop a high-throughput, cost-effective method for metabolic profiling of lipid mediators and hormones involved in the regulation of inflammation and energy metabolism, along with polyunsaturated fatty acids and common over-the-counter non-steroidal anti-inflammatory drugs (NSAIDs). We describe a 96-well plate protein precipitation and filtration procedure for 50 μL of plasma or serum in the presence of 37 deuterated analogs and 2 instrument internal standards. Data is acquired in two back-to-back UPLC-MS/MS analyses using electrospray ionization with positive/negative switching and scheduled multiple reaction monitoring for the determination of 145 compounds, including oxylipins, endocannabinoids and like compounds, bile acids, glucocorticoids, sex steroids, polyunsaturated fatty acids, and 3 NSAIDs. Intra- and inter-batch variability was <25% for >70% of metabolites above the LOQ in both matrices, but higher inter-batch variability was observed for serum oxylipins and some bile acids. Results for NIST Standard Reference Material 1950, compared favorably with the 20 certified metabolite values covered by this assay, and we provide new data for oxylipins, N-acylethanolamides, glucocorticoids, and 17-hydroxy-progesterone in this material. Application to two independent cohorts of elderly men and women showed the routine detection of 86 metabolites, identified fasting state influences on essential fatty acid-derived oxylipins, N-acylethanolamides and conjugated bile acids, identified rare presence of high and low testosterone levels and the presence of NSAIDs in ∼10% of these populations. The described method appears valuable for investigations in large cohort studies to provide insight into metabolic cross-talk between the array of mediators assessed here.

Exploiting oxidized lipids and the lipid-binding GPCRs against cardiometabolic diseases

Lipids govern vital cellular processes and drive physiological changes in response to different pathological or environmental cues. Lipid species can be roughly divided into structural and signalling lipids. The former is essential for membrane composition, while the latter are usually oxidized lipids. These mediators provide beneficial effects against cardiometabolic diseases (CMDs), including fatty-liver diseases, atherosclerosis, thrombosis, obesity, and Type 2 diabetes. For instance, several oxylipins were recently found to improve glucose homeostasis, increase insulin secretion, and inhibit platelet aggregation, while specialized pro-resolving mediators (SPMs) are able to ameliorate CMD by shaping the immune system. These lipids act mainly by stimulating GPCRs. In this review, we provide an updated and comprehensive overview of the current state of the literature on signalling lipids in the context of CMD. We also highlight the network encompassing the lipid-modifying enzymes and the lipid-binding GPCRs, as well as their interactions in health and disease.

Could Arachidonic Acid-Derived Pro-Resolving Mediators Be a New Therapeutic Strategy for Asthma Therapy?

Asthma represents one of the leading chronic diseases worldwide and causes a high global burden of death and disability. In asthmatic patients, the exacerbation and chronification of the inflammatory response are often related to a failure in the resolution phase of inflammation. We reviewed the role of the main arachidonic acid (AA) specialized pro-resolving mediators (SPMs) in the resolution of chronic lung inflammation of asthmatics. AA is metabolized by two classes of enzymes, cyclooxygenases (COX), which produce prostaglandins (PGs) and thromboxanes, and lypoxygenases (LOX), which form leukotrienes and lipoxins (LXs). In asthma, two primary pro-resolving derived mediators from COXs are PGE₂ and the cyclopentenone prostaglandin15-Deoxy-Delta-12,14-PGJ₂ (15d-PGJ₂) while from LOXs are the LXA₄ and LXB₄. In different models of asthma, PGE₂, 15d-PGJ₂, and LXs reduced lung inflammation and remodeling. Furthermore, these SPMs inhibited chemotaxis and function of several inflammatory cells involved in asthma pathogenesis, such as eosinophils, and presented an antiremodeling effect in airway epithelial, smooth muscle cells and fibroblasts in vitro. In addition, PGE₂, 15d-PGJ₂, and LXs are all able to induce macrophage reprogramming to an alternative M2 pro-resolving phenotype in vitro and in vivo. Although PGE₂ and LXA₄ showed some beneficial effects in asthmatic patients, there are limitations to their clinical use, since PGE₂ caused side effects, while LXA₄ presented low stability. Therefore, despite the strong evidence that these AA-derived SPMs induce resolution of both inflammatory response and tissue remodeling in asthma, safer and more stable analogs must be developed for further clinical investigation of their application in asthma treatment.

Role of Human 15-Lipoxygenase-2 in the Biosynthesis of the Lipoxin Intermediate, 5S,15S-diHpETE, Implicated with the Altered Positional Specificity of Human 15-Lipoxygenase-1

The oxylipins, 5S,12S-dihydroxy-6E,8Z,10E,14Z-eicosatetraenoic acid (5S,12S-diHETE) and 5S,15S-dihydroxy-6E,8Z,11Z,13E-eicosatetraenoic acid (5S,15S-diHETE), have been identified in cell exudates and have chemotactic activity toward eosinophils and neutrophils. Their biosynthesis has been proposed to occur by sequential oxidations of arachidonic acid (AA) by lipoxygenase enzymes, specifically through oxidation of AA by h5-LOX followed by h12-LOX, h15-LOX-1, or h15-LOX-2. In this work, h15-LOX-1 demonstrates altered positional specificity when reacting with 5S-HETE, producing 90% 5S,12S-diHETE, instead of 5S,15S-diHETE, with kinetics 5-fold greater than that of h12-LOX. This is consistent with previous work in which h15-LOX-1 reacts with 7S-HDHA, producing the noncanonical, DHA-derived, specialized pro-resolving mediator, 7S,14S-diHDHA. It is also determined that oxygenation of 5S-HETE by h15-LOX-2 produces 5S,15S-diHETE and its biosynthetic kcat/KM flux is 2-fold greater than that of h15-LOX-1, suggesting that h15-LOX-2 may have a greater role in lipoxin biosynthesis than previously thought. In addition, it is shown that oxygenation of 12S-HETE and 15S-HETE by h5-LOX is kinetically slow, suggesting that the first step in the in vitro biosynthesis of both 5S,12S-diHETE and 5S,15S-diHETE is the production of 5S-HETE.

Bitis arietans Snake Venom Induces an Inflammatory Response Which Is Partially Dependent on Lipid Mediators

Bitis arietans is a snake of medical importance, as it is responsible for more accidents in humans and domestic animals than all other African snakes put together. The accidents are characterized by local and systemic alterations, such as inflammation, cardiovascular and hemostatic disturbances, which can lead victims to death or permanent disability. However, little is known about the envenomation mechanism, especially regarding the inflammatory response, which is related to severe clinical conditions triggered by the venom. Therefore, the aim of the present study was to evaluate the inflammatory response related to the B. arietans envenomation using a peritonitis mice model. By pharmacological interventions and use of mice genetically deficient of the 5-lipoxygenase enzyme (5-LO^-/-) or platelet-activating factor (PAF) receptor (PAFR^-/- the participation of eicosanoids and PAF in this response was also investigated. The obtained results demonstrated that the venom induces an in vivo inflammatory response, characterized by an early increased vascular permeability, followed by an accumulation of polymorphonuclear (PMN) cells in the peritoneal cavity, accompanied by the production of the eicosanoids LTB₄, LTC₄, TXB₂ and PGE₂, as well as the local and systemic production of IL-6 and MCP-1. These inflammatory events were attenuated by the pre-treatment with anti-inflammatory drugs that interfere in lipid mediators' functions. However, 5-LO^-/- mice did not show a reduction of inflammatory response induced by the venom, while PAFR^-/- mice showed a reduction in both the PMN leukocytes number and the local and systemic production of IL-6 and MCP-1. This study demonstrated that the Bitis arietans venom contains toxins that trigger an inflammatory process, which is partially dependent on lipid mediators, and may contribute to the envenomation pathology.

Measurement of Enzymatic and Nonenzymatic Polyunsaturated Fatty Acid Oxidation Products in Plasma and Urine of Macular Degeneration Using LC-QTOF-MS/MS

Oxidized polyunsaturated fatty acids (PUFA) are associated to pathogenesis of diseases including cardiovascular and neurodegeneration. The novel products are not only biomarkers but also lipid mediators in gene regulation and signaling pathways. Herein, simultaneous quantitation of 28 products derived from nonenzymatic and enzymatic oxidation of PUFA i.e. 5-, 15-F_2t -isoprostanes, 7-, 17-F_2t -dihomo-isoprostanes, 7-, 17-F_2t -dihomo-isofurans, 5-, 8-, 18-F_3t -isoprostanes, 4-, 10-, 13-, 14-, 20-F_4t -neuroprostanes, 5-, 8-, 9-, 11-,12-, 15-, 20-HETE, 4-, 7-, 11-, 14-, 17-HDHA, RvE1, and NPD1 using LC-(ESI)-QTOF-MS/MS was developed. These products were measurable in a single sample and the analytical time was relative short (~15 min). Furthermore, we showed that the use of internal standards is a requisite to normalize matrix effects and preparation loss for the quantitation. Validation assays indicated the method to be robust for plasma and mid-stream urine sample analysis in particular from those of age-related macular degeneration subjects, where the accuracy of quantitation displayed good repeatability.

15-Lipoxygenase-1 biosynthesis of 7S,14S-diHDHA implicates 15-lipoxygenase-2 in biosynthesis of resolvin D5

The two oxylipins 7S,14S-dihydroxydocosahexaenoic acid (diHDHA) and 7S,17S-diHDHA [resolvin D5 (RvD5)] have been found in macrophages and infectious inflammatory exudates and are believed to function as specialized pro-resolving mediators (SPMs). Their biosynthesis is thought to proceed through sequential oxidations of DHA by lipoxygenase (LOX) enzymes, specifically, by human 5-LOX (h5-LOX) first to 7(S)-hydroxy-4Z,8E,10Z,13Z,16Z,19Z-DHA (7S-HDHA), followed by human platelet 12-LOX (h12-LOX) to form 7(S),14(S)-dihydroxy-4Z,8E,10Z,12E,16Z,19Z-DHA (7S,14S-diHDHA) or human reticulocyte 15-LOX-1 (h15-LOX-1) to form RvD5. In this work, we determined that oxidation of 7(S)-hydroperoxy-4Z,8E,10Z,13Z,16Z,19Z-DHA to 7S,14S-diHDHA is performed with similar kinetics by either h12-LOX or h15-LOX-1. The oxidation at C14 of DHA by h12-LOX was expected, but the noncanonical reaction of h15-LOX-1 to make over 80% 7S,14S-diHDHA was larger than expected. Results of computer modeling suggested that the alcohol on C7 of 7S-HDHA hydrogen bonds with the backbone carbonyl of Ile399, forcing the hydrogen abstraction from C12 to oxygenate on C14 but not C17. This result raised questions regarding the synthesis of RvD5. Strikingly, we found that h15-LOX-2 oxygenates 7S-HDHA almost exclusively at C17, forming RvD5 with faster kinetics than does h15-LOX-1. The presence of h15-LOX-2 in neutrophils and macrophages suggests that it may have a greater role in biosynthesizing SPMs than previously thought. We also determined that the reactions of h5-LOX with 14(S)-hydroperoxy-4Z,7Z,10Z,12E,16Z,19Z-DHA and 17(S)-hydroperoxy-4Z,7Z,10Z,13Z,15E,19Z-DHA are kinetically slow compared with DHA, suggesting that these reactions may be minor biosynthetic routes in vivo. Additionally, we show that 7S,14S-diHDHA and RvD5 have anti-aggregation properties with platelets at low micromolar potencies, which could directly regulate clot resolution.

Dietary n-6 and n-3 PUFA alter the free oxylipin profile differently in male and female rat hearts

Oxylipins are bioactive lipid mediators synthesised from PUFA. The most well-known oxylipins are the eicosanoids derived from arachidonic acid (ARA), and many of them influence cardiac physiology in health and disease. Oxylipins are also formed from other n-3 and n-6 PUFA such as α-linolenic acid (ALA), EPA, DHA and linoleic acid (LA), but fundamental data on the heart oxylipin profile, and the effect of diet and sex on this profile, are lacking. Therefore, weanling female and male Sprague-Dawley rats were given American Institute of Nutrition (AIN)-93G-based diets modified in oil composition to provide higher levels of ALA, EPA, DHA, LA and LA + ALA, compared with control diets. After 6 weeks, free oxylipins in rat hearts were increased primarily by their precursor PUFA, except for EPA oxylipins, which were increased not only by dietary EPA but also by dietary ALA or DHA. Dietary DHA had a greater effect than ALA or EPA on reducing ARA oxylipins. An exception to the dietary n-3 PUFA-lowering effects on ARA oxylipins was observed for several ARA-derived PG metabolites that were higher in rats given EPA diets. Higher dietary LA increased LA oxylipins, but it had no effect on ARA oxylipins. Overall, heart oxylipins were higher in female rats, but this depended on dietary treatment: the female oxylipin:male oxylipin ratio was higher in rats provided the ALA compared with the DHA diet, with other diet groups having ratios in between. In conclusion, individual PUFA and sex have unique and interactive effects on the rat heart free oxylipin profile.

Biosynthesis of the Maresin Intermediate, 13S,14S-Epoxy-DHA, by Human 15-Lipoxygenase and 12-Lipoxygenase and Its Regulation through Negative Allosteric Modulators

Human reticulocyte 15-lipoxygenase-1 (h15-LOX-1 or ALOX15) and platelet 12-lipoxygenase (h12-LOX or ALOX12) catalysis of docosahexaenoic acid (DHA) and the maresin precursor, 14S-hydroperoxy-4Z,7Z,10Z,12E,16Z,19Z-docosahexaenoic acid (14S-HpDHA), were investigated to determine their product profiles and relative rates in the biosynthesis of the key maresin intermediate, 13S,14S-epoxy-4Z,7Z,9E,11E,16Z,19Z-docosahexaenoic acid (13S,14S-epoxy-DHA). Both enzymes converted DHA to 14S-HpDHA, with h12-LOX having a 39-fold greater kcat/KM value (14.0 ± 0.8 s-1 μM-1) than that of h15-LOX-1 (0.36 ± 0.08 s-1 μM-1) and a 1.8-fold greater 14S-HpDHA product selectivity, 81 and 46%, respectively. However, h12-LOX was markedly less effective at producing 13S,14S-epoxy-DHA from 14S-HpDHA than h15-LOX-1, with a 4.6-fold smaller kcat/KM value, 0.0024 ± 0.0002 and 0.11 ± 0.006 s-1 μM-1, respectively. This is the first evidence of h15-LOX-1 to catalyze this reaction and reveals a novel in vitro pathway for maresin biosynthesis. In addition, epoxidation of 14S-HpDHA is negatively regulated through allosteric oxylipin binding to h15-LOX-1 and h12-LOX. For h15-LOX-1, 14S-HpDHA (Kd = 6.0 μM), 12S-hydroxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (12S-HETE) (Kd = 3.5 μM), and 14S-hydroxy-7Z,10Z,12E,16Z,19Z-docosapentaenoic acid (14S-HDPAω-3) (Kd = 4.0 μM) were shown to decrease 13S,14S-epoxy-DHA production. h12-LOX was also shown to be allosterically regulated by 14S-HpDHA (Kd = 3.5 μM) and 14S-HDPAω-3 (Kd = 4.0 μM); however, 12S-HETE showed no effect, indicating for the first time an allosteric response by h12-LOX. Finally, 14S-HpDHA inhibited platelet aggregation at a submicrololar concentration, which may have implications in the benefits of diets rich in DHA. These in vitro biosynthetic pathways may help guide in vivo maresin biosynthetic investigations and possibly direct therapeutic interventions.

12-LOX catalyzes the oxidation of 2-arachidonoyl-lysolipids in platelets generating eicosanoid-lysolipids that are attenuated by iPLA2γ knockout

The canonical pathway of eicosanoid production in most mammalian cells is initiated by phospholipase A2-mediated release of arachidonic acid, followed by its enzymatic oxidation resulting in a vast array of eicosanoid products. However, recent work has demonstrated that the major phospholipase in mitochondria, iPLA2γ (patatin-like phospholipase domain containing 8 (PNPLA8)), possesses sn-1 specificity, with polyunsaturated fatty acids at the sn-2 position generating polyunsaturated sn-2-acyl lysophospholipids. Through strategic chemical derivatization, chiral chromatographic separation, and multistage tandem MS, here we first demonstrate that human platelet-type 12-lipoxygenase (12-LOX) can directly catalyze the regioselective and stereospecific oxidation of 2-arachidonoyl-lysophosphatidylcholine (2-AA-LPC) and 2-arachidonoyl-lysophosphatidylethanolamine (2-AA-LPE). Next, we identified these two eicosanoid-lysophospholipids in murine myocardium and in isolated platelets. Moreover, we observed robust increases in 2-AA-LPC, 2-AA-LPE, and their downstream 12-LOX oxidation products, 12(S)-HETE-LPC and 12(S)-HETE-LPE, in calcium ionophore (A23187)-stimulated murine platelets. Mechanistically, genetic ablation of iPLA2γ markedly decreased the calcium-stimulated production of 2-AA-LPC, 2-AA-LPE, and 12-HETE-lysophospholipids in mouse platelets. Importantly, a potent and selective 12-LOX inhibitor, ML355, significantly inhibited the production of 12-HETE-LPC and 12-HETE-LPE in activated platelets. Furthermore, we found that aging is accompanied by significant changes in 12-HETE-LPC in murine serum that were also markedly attenuated by iPLA2γ genetic ablation. Collectively, these results identify previously unknown iPLA2γ-initiated signaling pathways mediated by direct 12-LOX oxidation of 2-AA-LPC and 2-AA-LPE. This oxidation generates previously unrecognized eicosanoid-lysophospholipids that may serve as biomarkers for age-related diseases and could potentially be used as targets in therapeutic interventions.

Therapeutic strategies for thrombosis: new targets and approaches

Antiplatelet agents and anticoagulants are a mainstay for the prevention and treatment of thrombosis. However, despite advances in antithrombotic therapy, a fundamental challenge is the side effect of bleeding. Improved understanding of the mechanisms of haemostasis and thrombosis has revealed new targets for attenuating thrombosis with the potential for less bleeding, including glycoprotein VI on platelets and factor XIa of the coagulation system. The efficacy and safety of new agents are currently being evaluated in phase III trials. This Review provides an overview of haemostasis and thrombosis, details the current landscape of antithrombotic agents, addresses challenges with preventing thromboembolic events in patients at high risk and describes the emerging therapeutic strategies that may break the inexorable link between antithrombotic therapy and bleeding risk.

Muscle Loss Associated Changes of Oxylipin Signatures During Biological Aging: An Exploratory Study From the PROOF Cohort

Characterizations of the multiple mechanisms determining biological aging are required to better understand the etiology and identify early biomarkers of sarcopenia. Oxylipins refer to a large family of signaling lipids involved in the regulation of various biological processes that become dysregulated during aging. To investigate whether comprehensive oxylipin profiling could provide an integrated and fine characterization of the early phases of sarcopenia, we performed a quantitative targeted metabolomics of oxylipins in plasma of 81-year-old subjects from the PROOF cohort with decreased (n = 12), stable (n = 16), or increased appendicular muscle mass (n = 14). Multivariate and univariate analyses identified significant and concordant changes of oxylipin profiles according to the muscle status. Of note, 90% of the most discriminant oxylipins were derived from EPA and DHA and were increased in the sarcopenic subjects. The oxylipins signatures of sarcopenic subjects revealed subtle activation of inflammatory resolution pathways, coagulation processes, and oxidative stress as well as the inhibition of angiogenesis. Heat maps highlighted relationships between oxylipins and the cardiometabolic health parameters which were mainly lost in sarcopenic subjects. This exploratory study supports that targeted metabolomics of oxylipins could provide relevant and subtle characterization of early disturbances associated with muscle loss during aging.

Combination of Lutein and Zeaxanthin, and DHA Regulated Polyunsaturated Fatty Acid Oxidation in H2O2-Stressed Retinal Cells

Photochemical and oxidative damages in retinal pigment epithelial (RPE) cells are key events in the pathogenesis of age-related macular degeneration. Polyunsaturated fatty acids (PUFA) and carotenoids are rich in retinal cells, and under oxidative stress leads to oxidation and release lipid mediators. We evaluated the impact of carotenoids (lutein, zeaxanthin) and docosahexaenoic acid (DHA) supplementation on RPE cells under oxidative stress. ARPE-19 cells were exposed to H₂O₂ after pre-treatment with lutein, zeaxanthin, DHA, lutein + zeaxanthin or lutein + zeaxanthin with DHA. The data showed H₂O₂ reduced cell viability and DHA content, while promoted catalase activity and certain oxidized PUFA products. Treatment with DHA enhanced omega-3 PUFA enzymatic oxidation namely, anti-inflammatory mediators such as hydroxy-DHA, resolvins and neuroprotection compared to control; the effects were not influenced by the carotenoids. Omega-6 PUFA oxidation, namely pro-inflammatory HETE (5-, 9-, 12 and 20-HETE), and isoprostanes (5- and 15-F_2t-IsoP and 4-F_3t-IsoP) were reduced by lutein + zeaxanthin while the addition of DHA did not further reduce these effects. We observed transcriptional regulation of 5-lipoxygenase by DHA and GPx1 and NEFEL2 by the carotenoids that potentially resulted in decreased HETEs and glutathione respectively. 4-HNE was not affected by the treatments but 4-HHE was reduced by lutein + zeaxanthin with and without DHA. To conclude, carotenoids and DHA appeared to regulate inflammatory lipid mediators while the carotenoids also showed benefits in reducing non-enzymatic oxidation of omega-6 PUFA.

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.

A joint analysis of metabolomic profiles associated with muscle mass and strength in Caucasian women

Both loss of muscle mass and strength are important sarcopenia-related traits. In this study, we investigated both specific and shared serum metabolites associated with these two traits in 136 Caucasian women using a liquid chromatography-mass spectrometry method. A joint analysis of multivariate traits was used to examine the associations of individual metabolites with muscle mass measured by the body mass index-adjusted appendicular lean mass (ALM/BMI) and muscle strength measured by hand grip strength (HGS). After adjusting for multiple testing, nine metabolites including two amino acids (aspartic acid and glutamic acid) and an amino acid derive (pipecolic acid), one peptide (phenylalanyl-threonine), one carbohydrate (methyl beta-D-glucopyranoside), and four lipids (12S-HETRE, arachidonic acid, 12S-HETE, and glycerophosphocholine) were significant in the joint analysis. Of them, the two amino acids (aspartic acid and glutamic acid) and two lipids (12S-HETRE and 12S-HETE) were associated with both ALM/BMI and HGS, and the other five were only associated with ALM/BMI. The pathway analysis showed the amino acid metabolism pathways (aspartic acid and glutamic acid) might play important roles in the regulation of muscle mass and strength. In conclusion, our study identified novel metabolites associated with sarcopenia-related traits, suggesting novel metabolic pathways for muscle regulation.

Increase in omega-6 and decrease in omega-3 polyunsaturated fatty acid oxidation elevates the risk of exudative AMD development in adults with Chinese diet

Appropriate diet is essential for the regulation of age-related macular degeneration (AMD). In particular the type of dietary polyunsaturated fatty acids (PUFA) and poor antioxidant status including carotenoid levels concomitantly contribute to AMD risk. Build-up of oxidative stress in AMD induces PUFA oxidation, and a mix of lipid oxidation products (LOPs) are generated. However, LOPs are not comprehensively evaluated in AMD. LOPs are considered biomarkers of oxidative stress but also contributes to inflammatory response. In this cross-sectional case-control study, plasma omega-6/omega-3 PUFA ratios and antioxidant status (glutathione, superoxide dismutase and catalase), and plasma and urinary LOPs (41 types) were determined to evaluate its odds-ratio in the risk of developing exudative AMD (n = 99) compared to age-gender-matched healthy controls (n = 198) in adults with Chinese diet. The odds ratio of developing exudative AMD increased with LOPs from omega-6 PUFA and decreased from those of omega-3 PUFA. These observations were associated with a high plasma omega-6/omega-3 PUFA ratio and low carotenoid levels. In short, poor PUFA and antioxidant status increased the production of omega-6 PUFA LOPs such as dihomo-isoprostane and dihomo-isofuran, and lowered omega-3 PUFA LOPs such as neuroprostanes due to the high omega-6/omega-3 PUFA ratios; they were also correlated to the risk of AMD development. These findings indicate the generation of specific LOPs is associated with the development of exudative AMD.

Oxidative pathways of arachidonic acid as targets for regulation of platelet activation

Platelet activation plays an important role in acute and chronic cardiovascular disease states. Multiple pathways contribute to platelet activation including those dependent upon arachidonic acid. Arachidonic acid is released from the platelet membrane by phospholipase A2 action and is then metabolized in the cytosol by specific arachidonic acid oxidation enzymes including prostaglandin H synthase, 12-lipoxygenase, and cytochrome P450 to produce pro- and anti-inflammatory eicosanoids. This review aims to analyze the role of arachidonic acid oxidation on platelet activation, the enzymes that use it as a substrate associated as novel therapeutics target for antiplatelet drugs.

12-Lipoxygenase is a Critical Mediator of Type II Pneumocyte Senescence, Macrophage Polarization and Pulmonary Fibrosis after Irradiation

Radiation-induced pulmonary fibrosis (RIPF) is a chronic, progressive complication of therapeutic irradiation of the thorax. It has been suggested that senescence of type II pneumocytes (AECIIs), an alveolar stem cell, plays a role in the development of RIPF through loss of replicative reserve and via senescent AECII-driven release of proinflammatory and profibrotic cytokines. Within this context, we hypothesized that arachidonate 12-lipoxygenase (12-LOX) is a critical mediator of AECII senescence and RIPF. Treatment of wild-type AECIIs with 12S-hydroxyeicosateraenoic acid (12S-HETE), a downstream product of 12-LOX, was sufficient to induce senescence in a NADPH oxidase 4 (NOX4)-dependent manner. Mice deficient in 12-LOX exhibited reduced AECII senescence, pulmonary collagen accumulation and accumulation of alternatively activated (M2) macrophages after thoracic irradiation (5 × 6 Gy) compared to wild-type mice. Conditioned media from irradiated or 12S-HETE-treated primary pneumocytes contained elevated levels of IL-4 and IL-13 compared to untreated pneumocytes. Primary macrophages treated with conditioned media from irradiated AECII demonstrated preferential M2 type polarization when AECIIs were derived from wild-type mice compared to 12-LOX-deficient mice. Together, these data identified 12-LOX as a critical component of RIPF and a therapeutic target for radiation-induced lung injury.

Metabolomics Profiling before, during, and after the Beijing Olympics: A Panel Study of Within-Individual Differences during Periods of High and Low Air Pollution

BACKGROUND

The metabolome is a collection of exogenous chemicals and metabolites from cellular processes that may reflect the body's response to environmental exposures. Studies of air pollution and metabolomics are limited.

OBJECTIVES

To explore changes in the human metabolome before, during, and after the 2008 Beijing Olympics Games, when air pollution was high, low, and high, respectively.

METHODS

Serum samples were collected before, during, and after the Olympics from 26 participants in an existing panel study. Gas and ultra-high performance liquid chromatography/mass spectrometry were used in metabolomics analysis. Repeated measures ANOVA, network analysis, and enrichment analysis methods were employed to identify metabolites and classes associated with air pollution changes.

RESULTS

A total of 886 molecules were measured in our metabolomics analysis. Network partitioning identified four modules with 65 known metabolites that significantly changed across the three time points. All known molecules in the first module ([Formula: see text]) were lipids (e.g., eicosapentaenoic acid, stearic acid). The second module consisted primarily of dipeptides ([Formula: see text], e.g., isoleucylglycine) plus 8 metabolites from four other classes (e.g., hypoxanthine, 12-hydroxyeicosatetraenoic acid). Most of the metabolites in Modules 3 (19 of 23) and 4 (5 of 5) were unknown. Enrichment analysis of module-identified metabolites indicted significantly overrepresented pathways, including long- and medium-chain fatty acids, polyunsaturated fatty acids (n3 and n6), eicosanoids, lysolipid, dipeptides, fatty acid metabolism, and purine metabolism [(hypo) xanthine/inosine-containing pathways].

CONCLUSIONS

We identified two major metabolic signatures: one consisting of lipids, and a second that included dipeptides, polyunsaturated fatty acids, taurine, and xanthine. Metabolites in both groups decreased during the 2008 Beijing Olympics, when air pollution was low, and increased after the Olympics, when air pollution returned to normal (high) levels. https://doi.org/10.1289/EHP3705.

Platelet-type 12-lipoxygenase deletion provokes a compensatory 12/15-lipoxygenase increase that exacerbates oxidative stress in mouse islet β cells

In type 1 diabetes, an autoimmune event increases oxidative stress in islet β cells, giving rise to cellular dysfunction and apoptosis. Lipoxygenases are enzymes that catalyze the oxygenation of polyunsaturated fatty acids that can form lipid metabolites involved in several biological functions, including oxidative stress. 12-Lipoxygenase and 12/15-lipoxygenase are related but distinct enzymes that are expressed in pancreatic islets, but their relative contributions to oxidative stress in these regions are still being elucidated. In this study, we used mice with global genetic deletion of the genes encoding 12-lipoxygenase (arachidonate 12-lipoxygenase, 12S type [Alox12]) or 12/15-lipoxygenase (Alox15) to compare the influence of each gene deletion on β cell function and survival in response to the β cell toxin streptozotocin. Alox12 ^-/- mice exhibited greater impairment in glucose tolerance following streptozotocin exposure than WT mice, whereas Alox15 ^-/- mice were protected against dysglycemia. These changes were accompanied by evidence of islet oxidative stress in Alox12 ^-/- mice and reduced oxidative stress in Alox15 ^-/- mice, consistent with alterations in the expression of the antioxidant response enzymes in islets from these mice. Additionally, islets from Alox12 ^-/- mice displayed a compensatory increase in Alox15 gene expression, and treatment of these mice with the 12/15-lipoxygenase inhibitor ML-351 rescued the dysglycemic phenotype. Collectively, these results indicate that Alox12 loss activates a compensatory increase in Alox15 that sensitizes mouse β cells to oxidative stress.

Probing the Electrostatic and Steric Requirements for Substrate Binding in Human Platelet-Type 12-Lipoxygenase

Human platelet ALOX12 (hALOX12 or h12-LOX) has been implicated in a variety of human diseases. The present study investigates the active site of hALOX12 to more thoroughly understand how it positions the substrate and achieves nearly perfect regio- and stereospecificities (i.e., 100 ± 5% of the 12(S)-hydroperoxide product), utilizing site-directed mutagenesis. Specifically, we have determined that Arg402 is not as important in substrate binding as previously seen for hALOX15 but that His596 may play a role in anchoring the carboxy terminal of the arachidonic acid during catalysis. In addition, Phe414 creates a π-stacking interaction with a double bond of arachidonic acid (Δ¹¹), and Ala417/Val418 define the bottom of the cavity. However, the influence of Ala417/Val418 on the profile is markedly less for hALOX12 than that seen in hALOX15. Mutating these two residues to larger amino acids (Ala417Ile/Val418Met) only increased the generation of 15-HpETE by 24 ± 2%, but conversely, smaller residues at these positions converted hALOX15 to almost 100% hALOX12 reactivity [Gan et al. (1996) J. Biol. Chem. 271, 25412-25418]. However, we were able to increase 15-HpETE to 46 ± 3% by restricting the width of the active site with the Ala417Ile/Val418Met/Ser594Thr mutation, indicating both depth and width of the active site are important. Finally, residue Leu407 is shown to play a critical role in positioning the substrate correctly, as seen by the increase of 15-HpETE to 21 ± 1% for the single Leu407Gly mutant. These results outline critical differences between the active site requirements of hALOX12 relative to hALOX15 and explain both their product specificity and inhibitory differences.

Inflammatory response to dietary linoleic acid depends on FADS1 genotype

Background

The health benefits of substituting dietary polyunsaturated fatty acids (PUFAs) for saturated fatty acids are well known. However, limited information exists on how the response to dietary intake of linoleic acid (LA; 18:2n-6) is modified by polymorphisms in the fatty acid desaturase (FADS) gene cluster.

Objectives

The aim of the current study was to test the hypothesis that the FADS1 rs174550 genotype modifies the effect of dietary LA intake on the fatty acid composition of plasma lipids, fasting glucose, and high-sensitivity C-reactive protein (hsCRP).

Methods

Associations were investigated between genotype, plasma PUFAs, fasting glucose, and hsCRP concentrations in the cross-sectional, population-based Metabolic Syndrome in Men cohort (n = 1337). In addition, 62 healthy men from the cohort who were homozygotes for the TT or CC genotype of the FADS1 rs174550 were recruited to a 4-wk intervention (FADSDIET) with an LA-enriched diet. The fatty acid composition of plasma PUFAs and concentrations of plasma fasting glucose, serum hsCRP, and plasma lipid mediators (eicosanoids and related analogs) were measured at the beginning and end of the 4-wk intervention period.

Results

In the FADSDIET trial, the plasma LA proportion increased in both genotype groups in response to an LA-enriched diet. Responses in concentrations of serum hsCRP and plasma fasting glucose and the proportion of arachidonic acid (20:4n-6) in plasma phospholipids and cholesteryl esters differed between genotype groups (interaction of diet × genotype, P < 0.05). In TT homozygous subjects, plasma eicosanoid concentrations correlated with the arachidonic acid proportion in plasma and with hsCRP (r = 0.4-0.7, P < 0.05), whereas in the CC genotype there were no correlations.

Conclusions

Our findings show that the FADS1 genotype modifies metabolic responses to dietary LA. The emerging concept that personalized dietary counseling should be modified by the FADS1 genotype needs to be tested in larger randomized trials. The study was registered at clinicaltrials.gov as NCT02543216.

Lipid Metabolism and Signaling in Platelet Function

Modern society has changed its diet composition, transitioning to a higher intake of saturated fat with a 50% increase of cardiovascular risk (CVD). Within the context of increased CVD, there is an induction of a prothrombotic phenotype mainly due to increased platelet reactivity as well as decreased platelet response to inhibitors. Platelets maintain haemostasis through both blood components and endothelial cells that secrete inhibitory or stimulatory molecules to regulate thrombus formation. There exist a correlation between platelets' polyunsaturated fatty acid (PUFA) and the increase in platelet reactivity. The aim of this chapter is to review the metabolism of the main PUFAs involved in platelet function associated with the role that their enzyme-derived oxidized metabolites exert in platelet function and fate. Finally, how lipid metabolism in the organism affect platelet aggregation and activation and the pharmacological modulation of these processes will also be discussed.

Emerging role of 12/15-Lipoxygenase (ALOX15) in human pathologies

12/15-lipoxygenase (12/15-LOX) is an enzyme, which oxidizes polyunsaturated fatty acids, particularly omega-6 and -3 fatty acids, to generate a number of bioactive lipid metabolites. A large number of studies have revealed the importance of 12/15-LOX role in oxidative and inflammatory responses. The in vitro studies have demonstrated the ability of 12/15-LOX metabolites in the expression of various genes and production of cytokine related to inflammation and resolution of inflammation. The studies with the use of knockout and transgenic animals for 12/15-LOX have further shown its involvement in the pathogenesis of a variety of human diseases, including cardiovascular, renal, neurological and metabolic disorders. This review summarizes our current knowledge on the role of 12/15-LOX in inflammation and various human diseases.

5 S,15 S-Dihydroperoxyeicosatetraenoic Acid (5,15-diHpETE) as a Lipoxin Intermediate: Reactivity and Kinetics with Human Leukocyte 5-Lipoxygenase, Platelet 12-Lipoxygenase, and Reticulocyte 15-Lipoxygenase-1

The reaction of 5 S,15 S-dihydroperoxyeicosatetraenoic acid (5,15-diHpETE) with human 5-lipoxygenase (LOX), human platelet 12-LOX, and human reticulocyte 15-LOX-1 was investigated to determine the reactivity and relative rates of producing lipoxins (LXs). 5-LOX does not react with 5,15-diHpETE, although it can produce LXA₄ when 15-HpETE is the substrate. In contrast, both 12-LOX and 15-LOX-1 react with 5,15-diHpETE, forming specifically LXB₄. For 12-LOX and 5,15-diHpETE, the kinetic parameters are k_cat = 0.17 s^-1 and k_cat/ K_M = 0.011 μM^-1 s^-1 [106- and 1600-fold lower than those for 12-LOX oxygenation of arachidonic acid (AA), respectively]. On the other hand, for 15-LOX-1 the equivalent parameters are k_cat = 4.6 s^-1 and k_cat/ K_M = 0.21 μM^-1 s^-1 (3-fold higher and similar to those for 12-HpETE formation by 15-LOX-1 from AA, respectively). This contrasts with the complete lack of reaction of 15-LOX-2 with 5,15-diHpETE [Green, A. R., et al. (2016) Biochemistry 55, 2832-2840]. Our data indicate that 12-LOX is markedly inferior to 15-LOX-1 in catalyzing the production of LXB₄ from 5,15-diHpETE. Platelet aggregation was inhibited by the addition of 5,15-diHpETE, with an IC₅₀ of 1.3 μM; however, LXB₄ did not significantly inhibit collagen-mediated platelet activation up to 10 μM. In summary, LXB₄ is the primary product of 12-LOX and 15-LOX-1 catalysis, if 5,15-diHpETE is the substrate, with 15-LOX-1 being 20-fold more efficient than 12-LOX. LXA₄ is the primary product with 5-LOX but only if 15-HpETE is the substrate. Approximately equal proportions of LXA₄ and LXB₄ are produced by 12-LOX but only if LTA₄ is the substrate, as described previously [Sheppard, K. A., et al. (1992) Biochim. Biophys. Acta 1133, 223-234].

Role of the 12-lipoxygenase pathway in diabetes pathogenesis and complications

12-lipoxygenase (12-LOX) is one of several enzyme isoforms responsible for the metabolism of arachidonic acid and other poly-unsaturated fatty acids to both pro- and anti-inflammatory lipid mediators. Mounting evidence has shown that 12-LOX plays a critical role in the modulation of inflammation at multiple checkpoints during diabetes development. Due to this, interventions to limit pro-inflammatory 12-LOX metabolites either by isoform-specific 12-LOX inhibition, or by providing specific fatty acid substrates via dietary intervention, has the potential to significantly and positively impact health outcomes of patients living with both type 1 and type 2 diabetes. To date, the development of truly specific and efficacious inhibitors has been hampered by homology of LOX family members; however, improvements in high throughput screening have improved the inhibitor landscape. Here, we describe the function and role of human 12-LOX, and mouse 12-LOX and 12/15-LOX, in the development of diabetes and diabetes-related complications, and describe promise in the development of strategies to limit pro-inflammatory metabolites, primarily via new small molecule 12-LOX inhibitors.