Differential Remodeling of the Oxylipin Pool After FLASH Versus Conventional Dose-Rate Irradiation In Vitro and In Vivo

PURPOSE

The products of lipid peroxidation have been implicated in human diseases and aging. This prompted us to investigate the response to conventional (CONV) versus FLASH irradiation of oxylipins, a family of bioactive lipid metabolites derived from omega-3 or omega-6 polyunsaturated fatty acids through oxygen-dependent non-enzymatic as well as dioxygenase-mediated free radical reactions.

METHODS AND MATERIALS

Ultrahigh performance liquid chromatography coupled to tandem mass spectrometry was used to quantify the expression of 37 oxylipins derived from eicosatetraenoic, eicosapentaenoic and docosahexaenoic acid in mouse lung and in normal or cancer cells exposed to either radiation modality under precise monitoring of the temperature and oxygenation. Among the 37 isomers assayed, 14-16 were present in high enough amount to enable quantitative analysis. The endpoints were the expression of oxylipins as a function of the dose of radiation, normoxia versus hypoxia, temperature and post-irradiation time.

RESULTS

In normal, normoxic cells at 37°C radiation elicited destruction and neosynthesis of oxylipins acting antagonistically on a background subject to rapid remodeling by oxygenases. Neosynthesis was observed in the CONV mode only, in such a way that the level of oxylipins at 5 minutes after FLASH irradiation was 20-50% lower than in non-irradiated and CONV-irradiated cells. Hypoxia mitigated the differential CONV versus FLASH response in some oxylipins. These patterns were not reproduced in tumor cells. Depression of specific oxylipins following FLASH irradiation was observed in mouse lung at 5 min following irradiation, with near complete recovery in 24 hours and further remodeling at one week and two months post-irradiation.

CONCLUSIONS

Down-regulation of oxylipins was a hallmark of FLASH irradiation specific of normal cells. Temperature effects suggest that this process occurs via diffusion-controlled, bimolecular recombination of a primary radical species upstream from peroxyl radical formation and evoke a major role of the membrane composition and fluidity in response to the FLASH modality.

Lipid Dys-Homeostasis Contributes to APOE4-Associated AD Pathology

The association of the APOE4 (vs. APOE3) isoform with an increased risk of Alzheimer's disease (AD) is unequivocal, but the underlying mechanisms remain incompletely elucidated. A prevailing hypothesis incriminates the impaired ability of APOE4 to clear neurotoxic amyloid-β peptides (Aβ) from the brain as the main mechanism linking the apolipoprotein isoform to disease etiology. The APOE protein mediates lipid transport both within the brain and from the brain to the periphery, suggesting that lipids may be potential co-factors in APOE4-associated physiopathology. The present study reveals several changes in the pathways of lipid homeostasis in the brains of mice expressing the human APOE4 vs. APOE3 isoform. Carriers of APOE4 had altered cholesterol turnover, an imbalance in the ratio of specific classes of phospholipids, lower levels of phosphatidylethanolamines bearing polyunsaturated fatty acids and an overall elevation in levels of monounsaturated fatty acids. These modifications in lipid homeostasis were related to increased production of Aβ peptides as well as augmented levels of tau and phosphorylated tau in primary neuronal cultures. This suite of APOE4-associated anomalies in lipid homeostasis and neurotoxic protein levels may be related to the accrued risk for AD in APOE4 carriers and provides novel insights into potential strategies for therapeutic intervention.

Esterification of Docosahexaenoic Acid Enhances Its Transport to the Brain and Its Potential Therapeutic Use in Brain Diseases

Docosahexaenoic acid-containing lysophosphatidylcholine (DHA-LysoPC) is presented as the main transporter of DHA from blood plasma to the brain. This is related to the major facilitator superfamily domain-containing protein 2A (Mfsd2a) symporter expression in the blood-brain barrier that recognizes the various lyso-phospholipids that have choline in their polar head. In order to stabilize the DHA moiety at the sn-2 position of LysoPC, the sn-1 position was esterified by the shortest acetyl chain, creating the structural phospholipid 1-acetyl,2-docosahexaenoyl-glycerophosphocholine (AceDoPC). This small structure modification allows the maintaining of the preferential brain uptake of DHA over non-esterified DHA. Additional properties were found for AceDoPC, such as antioxidant properties, especially due to the aspirin-like acetyl moiety, as well as the capacity to generate acetylcholine in response to the phospholipase D cleavage of the polar head. Esterification of DHA within DHA-LysoPC or AceDoPC could elicit more potent neuroprotective effects against neurological diseases.

Synovial Extracellular Vesicles: Structure and Role in Synovial Fluid Tribological Performances

The quality of the lubricant between cartilaginous joint surfaces impacts the joint’s mechanistic properties. In this study, we define the biochemical, ultrastructural, and tribological signatures of synovial fluids (SF) from patients with degenerative (osteoarthritis-OA) or inflammatory (rheumatoid arthritis-RA) joint pathologies in comparison with SF from healthy subjects. Phospholipid (PL) concentration in SF increased in pathological contexts, but the proportion PL relative to the overall lipids decreased. Subtle changes in PL chain composition were attributed to the inflammatory state. Transmission electron microscopy showed the occurrence of large multilamellar synovial extracellular vesicles (EV) filled with glycoprotein gel in healthy subjects. Synovial extracellular vesicle structure was altered in SF from OA and RA patients. RA samples systematically showed lower viscosity than healthy samples under a hydrodynamic lubricating regimen whereas OA samples showed higher viscosity. In turn, under a boundary regimen, cartilage surfaces in both pathological situations showed high wear and friction coefficients. Thus, we found a difference in the biochemical, tribological, and ultrastructural properties of synovial fluid in healthy people and patients with osteoarthritis and arthritis of the joints, and that large, multilamellar vesicles are essential for good boundary lubrication by ensuring a ball-bearing effect and limiting the destruction of lipid layers at the cartilage surface.

Specific shifts in the endocannabinoid system in hibernating brown bears

In small hibernators, global downregulation of the endocannabinoid system (ECS), which is involved in modulating neuronal signaling, feeding behavior, energy metabolism, and circannual rhythms, has been reported to possibly drive physiological adaptation to the hibernating state. In hibernating brown bears (Ursus arctos), we hypothesized that beyond an overall suppression of the ECS, seasonal shift in endocannabinoids compounds could be linked to bear’s peculiar features that include hibernation without arousal episodes and capacity to react to external disturbance. We explored circulating lipids in serum and the ECS in plasma and metabolically active tissues in free-ranging subadult Scandinavian brown bears when both active and hibernating. In winter bear serum, in addition to a 2-fold increase in total fatty acid concentration, we found significant changes in relative proportions of circulating fatty acids, such as a 2-fold increase in docosahexaenoic acid C22:6 n-3 and a decrease in arachidonic acid C20:4 n-6. In adipose and muscle tissues of hibernating bears, we found significant lower concentrations of 2-arachidonoylglycerol (2-AG), a major ligand of cannabinoid receptors 1 (CB1) and 2 (CB2). Lower mRNA level for genes encoding CB1 and CB2 were also found in winter muscle and adipose tissue, respectively. The observed reduction in ECS tone may promote fatty acid mobilization from body fat stores, and favor carbohydrate metabolism in skeletal muscle of hibernating bears. Additionally, high circulating level of the endocannabinoid-like compound N-oleoylethanolamide (OEA) in winter could favor lipolysis and fatty acid oxidation in peripheral tissues. We also speculated on a role of OEA in the conservation of an anorexigenic signal and in the maintenance of torpor during hibernation, while sustaining the capacity of bears to sense stimuli from the environment.

Double lipoxygenation of polyunsaturated fatty acids of nutritional interest

Double lipoxygenation of polyunsaturated fatty acids having at least three methylene-interrupted double bonds can be made by two lipoxygenases, e.g. 5- and 12-LOX, or 15-LOX only, followed by reduction of the hydroperoxide products through the glutathione peroxidase action. Several biological activities have been reported for such a double 15-LOX product of docosahexaenoic acid, called protectin DX to differentiate it from protectin D1, a stereo and geometric isomer described for its potent anti-inflammatory potential. The geometric characteristic of the double lipoxygenase products is the conjugated triene E,Z,E (trans,cis,trans), which appears crucial in their biological activities. A focus is also done on single lipoxygenation of mono-hydroxylated products first made by aspirin-treated cyclooxygenase-2. The resulting (R,S)-diOH, E,Z,E conjugated trienes, instead of the (S,S)-diOH isomer in case of double lipoxygenation, seem to be even more active for some biological effects, making biologically relevant the single lipoxygenation in aspirin-treated situations.

Anti-inflammatory and anti-virus potential of poxytrins, especially protectin DX

Poxytrins (Pufa Oxygenated Trienes) are dihydroxy derivatives from polyunsaturated fatty acids (PUFA) with adjacent hydroxyl groups to a conjugated triene having the specific E,Z,E geometry. They are made by the double action of one lipoxygenase or the combined actions of two lipoxygenases, followed by reduction of the resulting hydroperoxides with glutathione peroxidase. Because of their E,Z,E conjugated triene, poxytrins may inhibit inflammation associated with cyclooxygenase (COX) activities, and reactive oxygen species (ROS) formation. In addition of inhibiting COX activities, at least one poxytrin, namely protectin DX (PDX) from docosahexaenoic acid (DHA), has also been reported as able to inhibit influenza virus replication by targeting its RNA metabolism.

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Poxytrins are double lipoxygenase end-products from natural polyunsaturated fatty acids having at least three double bond. Their characteristic is to own a cis,trans,cis / E,Z,E conjugated triene.

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Protectin DX / PDX is a poxytrin from double oxygenation of docosahexaenoic acid by 15/n-6-lipoxygenase.

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As other poxytrins, PDX inhibits cyclooxygenase-dependent inflammation. Also, PDX inhibits the RNA influenza virus replication.

Brain targeting with docosahexaenoic acid as a prospective therapy for neurodegenerative diseases and its passage across blood brain barrier

Docosahexaenoic acid (DHA, 22:6n-3) is the main omega-3 polyunsaturated fatty acid in brain tissues necessary for common brain growth and function. DHA can be provided to the body through two origins: an exogenous origin, from direct dietary intakes and an endogenous one, from the bioconversion of the essential α-linolenic acid (ALA, 18:3n-3) in the liver. In humans, the biosynthesis of DHA from its precursor ALA is very low. A reduction in the cerebral amount of DHA is detected in patients suffering from neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. Considering the vital functions of DHA for the brain, new methodologies to target the brain with DHA offers encouraging perceptions in the improvement of precautionary and therapeutic approaches for neurodegenerative diseases. The aim of the present review was to provide better understanding of the cerebral uptake of DHA in different form including free fatty acids, Lysophosphatidylcholines LysoPC-DHA as well as structured phospholipids. First, we explored the special structure of the blood-brain barrier BBB, BBB being a physical and metabolic barrier with restrictive properties. Then, we discussed the incorporation of DHA into the membrane phospholipids of the brain, the neuroprotective and therapeutic effect of DHA for neurological diseases.

Docosahexaenoic Acid (DHA) Bioavailability in Humans after Oral Intake of DHA-Containing Triacylglycerol or the Structured Phospholipid AceDoPC®

AceDoPC^® is a structured glycerophospholipid that targets the brain with docosahexaenoic acid (DHA) and is neuroprotective in the experimental ischemic stroke. AceDoPC^® is a stabilized form of the physiological 2-DHA-LysoPC with an acetyl group at the sn1 position; preventing the migration of DHA from the sn2 to sn1 position. In this study we aimed to know the bioavailability of ¹³C-labeled DHA after oral intake of a single dose of ¹³C-AceDoPC^®, in comparison with ¹³C-DHA in triglycerides (TAG), using gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) to assess the ¹³C enrichment of DHA-containing lipids. ¹³C-DHA enrichment in plasma phospholipids was significantly higher after intake of AceDoPC^® compared with TAG-DHA, peaking after 24 h in both cases. In red cells, ¹³C-DHA enrichment in choline phospholipids was comparable from both sources of DHA, with a maximum after 72 h, whereas the ¹³C-DHA enrichment in ethanolamine phospholipids was higher from AceDoPC^® compared to TAG-DHA, and continued to increase after 144 h. Overall, our study indicates that DHA from AceDoPC^® is more efficient than from TAG-DHA for a sustained accumulation in red cell ethanolamine phospholipids, which has been associated with increased brain accretion.

How the plasma lysophospholipid and unesterified fatty acid pools supply the brain with docosahexaenoic acid

The brain requires a constant supply of docosahexaenoic acid (DHA) from blood to maintain DHA levels within the brain. Several plasma pools have been proposed to supply the brain with DHA, including plasma lipoproteins, lysophosphatidylcholine and unesterified fatty acids. Here we briefly review the evidence for each plasma pool supplying the brain highlighting controversies and remaining questions. We conclude that circulating lysophosphatidylcholine has a higher brain/body partition coefficient than unesterified DHA while unesterified DHA entry into the brain is more rapid.

Physiological and pathological roles of FATP-mediated lipid droplets in Drosophila and mice retina

Increasing evidence suggests that dysregulation of lipid metabolism is associated with neurodegeneration in retinal diseases such as age-related macular degeneration and in brain disorders such as Alzheimer’s and Parkinson’s diseases. Lipid storage organelles (lipid droplets, LDs), accumulate in many cell types in response to stress, and it is now clear that LDs function not only as lipid stores but also as dynamic regulators of the stress response. However, whether these LDs are always protective or can also be deleterious to the cell is unknown. Here, we investigated the consequences of LD accumulation on retinal cell homeostasis under physiological and stress conditions in Drosophila and in mice. In wild-type Drosophila, we show that dFatp is required and sufficient for expansion of LD size in retinal pigment cells (RPCs) and that LDs in RPCs are required for photoreceptor survival during aging. Similarly, in mice, LD accumulation induced by RPC-specific expression of human FATP1 was non-toxic and promoted mitochondrial energy metabolism in RPCs and non-autonomously in photoreceptor cells. In contrast, the inhibition of LD accumulation by dFatp knockdown suppressed neurodegeneration in Aats-met^FBDrosophila mutants, which carry elevated levels of reactive oxygen species (ROS). This suggests that abnormal turnover of LD may be toxic for photoreceptors cells of the retina under oxidative stress. Collectively, these findings indicate that FATP-mediated LD formation in RPCs promotes RPC and neuronal homeostasis under physiological conditions but could be deleterious for the photoreceptors under pathological conditions.

Lipids are major cell constituents and are present in the membranes, as free lipids in the cytoplasm, or stored in vesicles called lipid droplets (LDs). Under conditions of stress, lipids stored in LDs can be released to serve as substrates for energy metabolism by mitochondria. However, lipid storage is dysregulated in many degenerative disorders such as age-related macular degeneration, Parkinson’s and Alzheimer’s diseases. Thus, it is unclear whether accumulation of LDs is protective or toxic for neuronal cells. To address this question, we examined the consequences of removal or enforced LD accumulation on the health of retinal cells in flies and mice. Like humans, fly and mouse retinas contain retinal pigment cells (RPC) that support the functions of neighboring photoreceptor cells. We found that overexpression of the fatty acid transport protein (FATP) in RPCs induced accumulation of LDs in both transgenic flies and mice. Moreover, LD accumulation in RPCs was not harmful for juxtaposed photoreceptors during aging, but was toxic under stress conditions. We propose that lipid storage promotes cellular communication that affects photoreceptor health.

Oxygenation of polyunsaturated fatty acids and oxidative stress within blood platelets

The oxygenation metabolism of arachidonic acid (ArA) has been early described in blood platelets, in particular with its conversion into the potent labile thromboxane A₂ that induces platelet aggregation and vascular smooth muscle cells contraction. In addition, the primary prostaglandins D₂ and E₂ have been mainly reported as inhibitors of platelet function. The platelet 12-lipoxygenase (12-LOX) product, i.e. the hydroperoxide 12-HpETE, appears to stimulate platelet ArA metabolism at the level of its release from membrane phospholipids through phospholipase A₂ (cPLA₂) and cyclooxygenase (COX-1) activities, the first enzymes in prostanoid production cascade. Also, 12-HpETE may regulate the oxygenation of other polyunsaturated fatty acids (PUFA) by platelets, especially that of eicosapentaenoic acid (EPA). On the other hand, the reduced product of 12-HpETE, 12-HETE, is able to antagonize TxA₂ action. This is even more obvious for the 12-LOX end-products from docosahexaenoic acid (DHA), 11- and 14-HDoHE. In addition, 12-HpETE plays a key role in platelet oxidative stress as observed in pathophysiological conditions, but may be regulated by DHA with a bimodal way according to its concentration. Other oxygenated products of PUFA, especially omega-3 PUFA, produced outside platelets may affect platelet functions as well.

Synthesis and Identification of AceDoxyPC, a Protectin-Containing Structured Phospholipid, Using Liquid Chromatography/Mass Spectrometry

Fatty acids have many health benefits in a great variety of diseases ranging from cardiovascular to cerebral diseases. For instance, docosahexaenoic acid (DHA), which is highly enriched in brain phospholipids, plays a major role in anti-inflammatory or neuroprotective pathways. Its effects are thought to be due, in part, to its conversion into derived mediators such as protectins. 1-Lyso,2-docosahexaenoyl-glycerophosphocholine (LysoPtdCho-DHA) is one of the physiological carrier of DHA to the brain. We previously synthesized a structured phosphatidylcholine to mimic 1-lyso,2-docosahexaenoyl-glycerophosphocholine, named AceDoPC® (1-acetyl,2-docosahexaenoyl-glycerophosphocholine), that is considered as a stabilized form of the physiological LysoPtdCho-DHA and that is neuroprotective in experimental ischemic stroke. Considering these, the current study aimed at enzymatically oxygenate DHA contained within AceDoPC® to synthesize a readily structured oxidized phospholipid containing protectin DX (PDX), thereafter named AceDoxyPC (1-acetyl,2-PDX-glycerophosphocholine). Identification of this product was performed using liquid chromatography/tandem mass spectrometry. Such molecule could be used as a bioactive mediator for therapy against neurodegenerative diseases and stroke.

Docosahexaenoic acid-containing choline phospholipid modulates LPS-induced neuroinflammation in vivo and in microglia in vitro

Background

Neuroinflammatory processes are considered a double-edged sword, having both protective and detrimental effects in the brain. Microglia, the brain’s resident innate immune cells, are a key component of neuroinflammatory response. There is a growing interest in developing drugs to target microglia and control neuroinflammatory processes. In this regard, docosahexaenoic acid (DHA), the brain’s n-3 polyunsaturated fatty acid, is a promising molecule to regulate pro-inflammatory microglia and cytokine production. Several works reported that the bioavailability of DHA to the brain is higher when DHA is acylated to phospholipid. In this work, we analyzed the anti-inflammatory activity of DHA-phospholipid, either acetylated at the sn-1 position (AceDoPC, a stable form thought to have superior access to the brain) or acylated with palmitic acid at the sn-1 position (PC-DHA) using a lipopolysaccharide (LPS)-induced neuroinflammation model both in vitro and in vivo.

Methods

In vivo, adult C57Bl6/J mice were injected intravenously (i.v.) with either AceDoPC or PC-DHA 24 h prior to LPS (i.p.). For in vitro studies, immortalized murine microglia cells BV-2 were co-incubated with DHA forms and LPS. AceDoPC and PC-DHA effect on brain or BV-2 PUFA content was assessed by gas chromatography. LPS-induced pro-inflammatory cytokines interleukin IL-1β, IL-6, and tumor necrosis factor (TNF) α production were measured by quantitative PCR (qPCR) or multiplex. IL-6 receptors and associated signaling pathway STAT3 were assessed by FACS analysis and western-blot in vitro.

Results

In vivo, a single injection of AceDoPC or PC-DHA decreased LPS-induced IL-6 production in the hippocampus of mice. This effect could be linked to their direct effect on microglia, as revealed in vitro. In addition, AceDoPC or PC-DHA reduced IL-6 receptor while only AceDoPC decreased IL-6-induced STAT3 phosphorylation.

Conclusions

These results highlight the potency of administered DHA—acetylated to phospholipids—to rapidly regulate LPS-induced neuroinflammatory processes through their effect on microglia. In particular, both IL-6 production and signaling are targeted by AceDoPC in microglia.

Mechanisms of DHA transport to the brain and potential therapy to neurodegenerative diseases

Docosahexaenoic acid (DHA; 22:6 ω-3) is highly enriched in the brain and is required for proper brain development and function. Its deficiency has been shown to be linked with the emergence of neurological diseases. Dietary ω-3 fatty acid supplements including DHA have been suggested to improve neuronal development and enhance cognitive functions. However, mechanisms of DHA incorporation in the brain remain to be fully understood. Findings suggested that DHA is better incorporated when esterified within lysophospholipid rather than under its non-esterified form. Furthermore, DHA has the potential to be converted into diverse oxylipins with potential neuroprotective effects. Since DHA is poorly synthesized de novo, targeting the brain with specific carriers of DHA might provide novel therapeutic approaches to neurodegenerative diseases.

The pleiotropic effects of omega-3 docosahexaenoic acid on the hallmarks of Alzheimer's disease

Among omega-3 polyunsaturated fatty acids (PUFAs), docosahexaenoic acid (DHA, 22:6n-3) is important for adequate brain development and cognition. DHA is highly concentrated in the brain and plays an essential role in brain functioning. DHA, one of the major constituents in fish fats, readily crosses the blood-brain barrier from blood to the brain. Its critical role was further supported by its reduced levels in the brain of Alzheimer's disease (AD) patients. This agrees with a potential role of DHA in memory, learning and cognitive processes. Since there is yet no cure for dementia such as AD, there is growing interest in the role of DHA-supplemented diet in the prevention of AD pathogenesis. Accordingly, animal, epidemiological, preclinical and clinical studies indicated that DHA has neuroprotective effects in a number of neurodegenerative conditions including AD. The beneficial effects of this key omega-3 fatty acid supplementation may depend on the stage of disease progression, other dietary mediators and the apolipoprotein ApoE genotype. Herein, our review investigates, from animal and cell culture studies, the molecular mechanisms involved in the neuroprotective potential of DHA with emphasis on AD.

Functional fluxolipidomics of polyunsaturated fatty acids and oxygenated metabolites in the blood vessel compartment

Synthesis of bioactive oxygenated metabolites of polyunsaturated fatty acids and their degradation or transformation products are made through multiple enzyme processes. The kinetics of the enzymes responsible for the different steps are known to be quite diverse, although not precisely determined. The location of the metabolites biosynthesis is diverse as well. Also, the biological effects of the primary and secondary products, and their biological life span are often completely different. Consequently, phenotypes of cells in response to these bioactive lipid mediators must then depend on their concentrations at a given time. This demands a fluxolipidomics approach that can be defined as a mediator lipidomics, with all measurements done as a function of time and biological compartments. This review points out what is known, even qualitatively, in the blood vascular compartment for arachidonic acid metabolites and number of other metabolites from polyunsaturated fatty acids of nutritional value. The functional consequences are especially taken into consideration.

Imeglimin normalizes glucose tolerance and insulin sensitivity and improves mitochondrial function in liver of a high-fat, high-sucrose diet mice model

Imeglimin is the first in a new class of oral glucose-lowering agents currently in phase 2b development. Although imeglimin improves insulin sensitivity in humans, the molecular mechanisms are unknown. This study used a model of 16-week high-fat, high-sucrose diet (HFHSD) mice to characterize its antidiabetic effects. Six-week imeglimin treatment significantly decreased glycemia, restored normal glucose tolerance, and improved insulin sensitivity without modifying organs, body weights, and food intake. This was associated with an increase in insulin-stimulated protein kinase B phosphorylation in the liver and muscle. In liver mitochondria, imeglimin redirects substrate flows in favor of complex II, as illustrated by increased respiration with succinate and by the restoration of respiration with glutamate/malate back to control levels. In addition, imeglimin inhibits complex I and restores complex III activities, suggesting an increase in fatty acid oxidation, which is supported by an increase in hepatic 3-hydroxyacetyl-CoA dehydrogenase activity and acylcarnitine profile and the reduction of liver steatosis. Imeglimin also reduces reactive oxygen species production and increases mitochondrial DNA. Finally, imeglimin effects on mitochondrial phospholipid composition could participate in the benefit of imeglimin on mitochondrial function. In conclusion, imeglimin normalizes glucose tolerance and insulin sensitivity by preserving mitochondrial function from oxidative stress and favoring lipid oxidation in liver of HFHSD mice.

Human monocyte-derived dendritic cells turn into foamy dendritic cells with IL-17A

Interleukin 17A (IL-17A) is a proinflammatory cytokine involved in the pathogenesis of chronic inflammatory diseases. In the field of immunometabolism, we have studied the impact of IL-17A on the lipid metabolism of human in vitro-generated monocyte-derived dendritic cells (DCs). Microarrays and lipidomic analysis revealed an intense remodeling of lipid metabolism induced by IL-17A in DCs. IL-17A increased 2-12 times the amounts of phospholipids, cholesterol, triglycerides, and cholesteryl esters in DCs. Palmitic (16:0), stearic (18:0), and oleic (18:ln-9c) acid were the main fatty acid chains present in DCs. They were strongly increased in response to IL-17A while their relative proportion remained unchanged. Capture of extracellular lipids was the major mechanism of lipid droplet accumulation, visualized by electron microscopy and Oil Red O staining. Besides this foamy phenotype, IL-17A induced a mixed macrophage-DC phenotype and expression of the nuclear receptor NR1H3/liver X receptor-α, previously identified in the context of atherosclerosis as the master regulator of cholesterol homeostasis in macrophages. These IL-17A-treated DCs were as competent as untreated DCs to stimulate allogeneic naive T-cell proliferation. Following this first characterization of lipid-rich DCs, we propose to call these IL-17A-dependent cells "foamy DCs" and discuss the possible existence of foamy DCs in atherosclerosis, a metabolic and inflammatory disorder involving IL-17A.

Biological properties of a DHA-containing structured phospholipid (AceDoPC) to target the brain

1-acetyl,2-docosahexaenoyl-glycerophosphocholine (AceDoPC) has been made to prevent docosahexaenoyl (DHA) to move to the sn-1 position as it rapidly does when present in 1-lyso,2-docosahexaenoyl-GPC (lysoPC-DHA), an efficient DHA transporter to the brain. When incubated with human blood, AceDoPC behaves closer to lysoPC-DHA than PC-DHA in terms of binding to plasma albumin and lipoproteins, and DHA incorporation into platelets and red cells. In addition, AceDoPC prevents more efficiently the deleterious effects of the experimental stroke in rats than does unesterified DHA. Also, AceDoPC inhibits platelet-activating factor-induced human blood platelet aggregation. Overall, AceDoPC might act as an efficient DHA transporter to the brain, and as a neuro-protective agent by itself.

Omega-3 polyunsaturated fatty acids and oxygenated metabolism in atherothrombosis

Numerous epidemiological studies and clinical trials have reported the health benefits of omega-3 polyunsaturated fatty acids (PUFA), including a lower risk of coronary heart diseases. This review mainly focuses on the effects of alpha-linolenic (ALA), eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids on some risk factors associated with atherothrombosis, including platelet activation, plasma lipid concentrations and oxidative modification of low-density lipoproteins (LDL). Special focus is given to the effects of marine PUFA on the formation of eicosanoids and docosanoids, and to the bioactive properties of some oxygenated metabolites of omega-3 PUFA produced by cyclooxygenases and lipoxygenases. The antioxidant effects of marine omega-3 PUFA at low concentrations and the pro-oxidant effects of DHA at high concentrations on the redox status of platelets and LDL are highlighted. Non enzymatic peroxidation end-products deriving from omega-3 PUFA such as hydroxy-hexenals, neuroketals and EPA-derived isoprostanes are also considered in relation to atherosclerosis. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

Lipidomics of essential fatty acids and oxygenated metabolites

Polyunsaturated fatty acids in mammals may be oxygenated into a myriad of bioactive products through di- and monooxygenases, products that are rapidly degraded to control their action. To evaluate the phenotypes of biological systems regarding this wide family of compounds, a lipidomics approach in function of time and compartments would be relevant. The current review takes into consideration most of the diverse oxygenated metabolites of essential fatty acids at large and their immediate degradation products. Their biological function and life span are considered. Overall, this is a fluxolipidomics approach that is emerging.

Expanding the horizons of lipidomics. Towards fluxolipidomics

This short review takes into consideration the status of lipidomics as issued from almost a decade of development. Because of the huge number of molecular species analyzed, there is a trend in subdividing lipidomics according to subdomains, in particular relating to the function of molecules. It is also pointed out that lipid imaging without the use of exogenous probes will help making relationships between molecular structures and the topography of lipid assemblies, especially in cellular compartments. Finally, a fluxomics approach is proposed for lipid molecular species, both in terms of compartments and biochemical metabolism. The example of fluxolipidomics of essential fatty acids toward their enzyme-dependent oxygenated metabolites and further toward their degradation products is developed.

Treatment with a γ-ketoaldehyde scavenger prevents working memory deficits in hApoE4 mice

Both inflammation and oxidative injury are features of Alzheimer's disease (AD), but the contribution of these intertwined phenomena to the loss of working memory in this disease is unclear. We tested the hypothesis that highly reactive γ-ketoaldehydes that are formed both by non-enzymatic free radical catalyzed lipid peroxidation and by cyclooxygenases may be causally linked to the development of memory impairment in AD. We found that levels of γ-ketoaldehyde protein adducts were increased in the hippocampus of brains obtained postmortem from patients with AD compared to age-matched controls, but that levels of γ-ketoaldehyde protein adducts in the cerebellum were not different in the two groups. Moreover, immunohistochemistry revealed that adducts localized to hippocampal pyramidal neurons. We tested the effect of an orally available γ-ketoaldehyde scavenger, salicylamine, on the development of spatial working memory deficits in hApoE4 targeted replacement mice, a mouse model of dementia. Long-term salicylamine supplementation did not significantly alter body weight or survival, but protected against the development of age-related deficits in spatial working memory in 12-14 month old ApoE4 mice. These findings suggest that γ-ketoaldehyde adduct formation is associated with damage to hippocampal neurons in patients with AD and can contribute to the pathogenesis of spatial working memory deficits in hApoE4 mice. These data provide a rational basis for future studies exploring whether γ-ketoaldehyde scavengers may mitigate the development of cognitive dysfunction in patients with AD.

Oil composition of high-fat diet affects metabolic inflammation differently in connection with endotoxin receptors in mice

Low-grade inflammation observed in obesity is a risk factor for cardiovascular disease. Recent studies revealed that this would be linked to gut-derived endotoxemia during fat digestion in high-fat diets, but nothing is known about the effect of lipid composition. The study was designed to test the impact of oil composition of high-fat diets on endotoxin metabolism and inflammation in mice. C57/Bl6 mice were fed for 8 wk with chow or isocaloric isolipidic diets enriched with oils differing in fatty acid composition: milk fat, palm oil, rapeseed oil, or sunflower oil. In vitro, adipocytes (3T3-L1) were stimulated or not with lipopolysaccharide (LPS; endotoxin) and incubated with different fatty acids. In mice, the palm group presented the highest level of IL-6 in plasma (P < 0.01) together with the highest expression in adipose tissue of IL-1β and of LPS-sensing TLR4 and CD14 (P < 0.05). The higher inflammation in the palm group was correlated with a greater ratio of LPS-binding protein (LBP)/sCD14 in plasma (P < 0.05). The rapeseed group resulted in higher sCD14 than the palm group, which was associated with lower inflammation in both plasma and adipose tissue despite higher plasma endotoxemia. Taken together, our results reveal that the palm oil-based diet resulted in the most active transport of LPS toward tissues via high LBP and low sCD14 and the greatest inflammatory outcomes. In contrast, a rapeseed oil-based diet seemed to result in an endotoxin metabolism driven toward less inflammatory pathways. This shows that dietary fat composition can contribute to modulate the onset of low-grade inflammation through the quality of endotoxin receptors.

Evidence for in situ ethanolamine phospholipid adducts with hydroxy-alkenals

Hydroxy-alkenals, such as 4-hydroxy-2(E)-nonenal (4-HNE; from n-6 fatty acids), are degradation products of fatty acid hydroperoxides, including those generated by free radical attack of membrane polyunsaturated fatty acyl moieties. The cytotoxic effects of hydroxy-alkenals are well known and are mainly attributable to their interaction with different molecules to form covalent adducts. Indeed, ethanolamine phospholipids (PEs) can be covalently modified in a cellular system by hydroxy-alkenals, such as 4-HNE, 4-hydroxy-2(E)-hexenal (4-HHE; from n-3 fatty acids), and 4-hydroxy-dodecadienal (4-HDDE; from the 12-lipoxygenase product of arachidonic acid), to form mainly Michael adducts. In this study, we describe the formation of PE Michael adducts in human blood platelets in response to oxidative stress and in retinas of streptozotocin-induced diabetic rats. We have successfully characterized and evaluated, for the first time, PEs coupled with 4-HHE, 4-HNE, and 4-HDDE by gas chromatography-mass spectrometry measurement of their ethanolamine moieties. We also report that aggregation of isolated human blood platelets enriched with PE-4-hydroxy-alkenal Michael adducts was altered. These data suggest that these adducts could be used as specific markers of membrane disorders occurring in pathophysiological states with associated oxidative stress and might affect cell function.

Effects of oxidative stress on adiponectin secretion and lactate production in 3T3-L1 adipocytes

Obesity is an increasing nutritional disorder in developed countries, and oxidative stress has been identified as a key factor in numerous pathologies such as diabetes, inflammation, and atherosclerosis, which are favored by obesity. The objective of the present study was to investigate the effects of oxidative stress in 3T3-L1 adipose cells on two parameters involved in metabolic complications associated with obesity, namely adiponectin secretion and lactate production. Differentiated 3T3-L1 adipose cells were exposed to increasing concentrations of glucose oxidase. 4-Hydroxynonenal (4-HNE), a relevant lipid peroxidation by-product which may affect several metabolic processes in making covalent adducts with various molecules; adiponectin secretion; and lactate production were measured in response to glucose oxidase exposure. Results show an inhibition of adiponectin mRNA expression by glucose oxidase and a significant inverse correlation between 4-HNE formation and adiponectin secretion. Furthermore, 4-HNE alone inhibits adiponectin production by 3T3-L1. On the other hand, glucose oxidase and 4-HNE significantly stimulated lactate production by 3T3-L1 adipocytes. These results demonstrate that adipose cells are highly sensitive to oxidative stress, with subsequent decreased adiponectin secretion and increased lactate production, two events involved in the development of insulin resistance.

Covalent binding of isoketals to ethanolamine phospholipids

Free radicals have been strongly implicated in the pathogenesis of many human diseases. We previously identified the formation of highly reactive gamma-ketoaldehydes, isoketals, in vivo as products of free radical-induced peroxidation of arachidonic acid. Isoketals react with lysine residues on proteins at a rate that far exceeds that of 4-hydroxynonenal and demonstrate a unique proclivity to crosslink proteins. Hydroxynonenal has been shown to react with aminophospholipids, particularly phosphatidylethanolamine. We explored whether isoketals also react with phosphatidylethanolamine. Using liquid chromatography/electrospray mass spectrometry, we found that isoketals form pyrrole and Schiff base adducts with phosphatidylethanolamine. In addition, the ability of isoketals to covalently modify phosphatidylethanolamine is greater than that of 4-hydroxynonenal. These studies identify in vitro novel isoketal adducts. This provides the basis to explore the formation of isoketal-aminophospholipid adducts in vivo and the biological consequences of the formation of these adducts.

Characterization of bis(levuglandinyl) urea derivatives as products of the reaction between prostaglandin H2 and arginine

Levuglandins are gamma-keto aldehydes formed by rearrangement of prostaglandin (PG) H(2) in aqueous solution. Levuglandins are highly reactive with primary amines. We had previously characterized adducts formed after reaction of levuglandin E(2) (LGE(2)) or PGH(2) with lysine. In this study, we assessed whether reaction of PGH(2) with arginine yielded covalent adducts. Using N(alpha)-acetylarginine and both PGH(2) and synthetic LGE(2), we discovered a novel series of levuglandinyl adducts derived from reaction of two levuglandin moieties with the guanidino group of arginine. Subsequent spontaneous hydrolysis of the adducted amino acid yields bis(levuglandinyl) urea and the corresponding ornithine residue. Using liquid chromatography tandem mass spectrometry, we characterized the molecular structure of these novel adducts and demonstrated their formation after coincubation of PGH(2) with synthetic peptides and proteins. The soluble characteristic of these molecules provides a potential strategy for development of biological markers of lipid modification of proteins following cyclooxygenase activity or lipid peroxidation.

Covalent binding of hydroxy-alkenals 4-HDDE, 4-HHE, and 4-HNE to ethanolamine phospholipid subclasses

Lipid oxidation is implicated in a wide range of pathophysiogical disorders, and leads to reactive compounds such as fatty aldehydes, of which the most well known is 4-hydroxy-2E-nonenal (4-HNE) issued from 15-hydroperoxyeicosatetraenoic acid (15-HpETE), an arachidonic acid (AA) product. In addition to 15-HpETE, 12(S)-HpETE is synthesized by 12-lipoxygenation of platelet AA. We first show that 12-HpETE can be degraded in vitro into 4-hydroxydodeca-(2E,6Z)-dienal (4-HDDE), a specific aldehyde homologous to 4-HNE. Moreover, 4-HDDE can be detected in human plasma. Second, we compare the ability of 4-HNE, 4-HDDE, and 4-hydroxy-2E-hexenal (4-HHE) from n-3 fatty acids to covalently modify different ethanolamine phospholipids (PEs) chosen for their biological relevance, namely AA- (20: 4n-6) or docosahexaenoic acid- (22:6n-3) containing diacyl-glycerophosphoethanolamine (diacyl-GPE) and alkenylacyl-glycerophosphoethanolamine (alkenylacyl-GPE) molecular species. The most hydrophobic aldehyde used, 4-HDDE, generates more adducts with the PE subclasses than does 4-HNE, which itself appears more reactive than 4-HHE. Moreover, the aldehydes show higher reactivity toward alkenylacyl-GPE compared with diacyl-GPE, because the docosahexaenoyl-containing species are more reactive than those containing arachidonoyl. We conclude that the different PE species are differently targeted by fatty aldehydes: the higher their hydrophobicity, the higher the amount of adducts made. In addition to their antioxidant potential, alkenylacyl-GPEs may efficiently scavenge fatty aldehydes.

Identification of oxidized derivatives of neuroketals

Oxidative stress and protein aggregation have been implicated in the pathogenesis of neurodegenerative diseases. The formation of neuroprostanes, isoprostane-like compounds formed from oxidation of docosahexaenoic acid, which is uniquely enriched in the brain, is increased in Alzheimer's disease. We recently identified the formation of a new class of highly reactive gamma-keto aldehydes, neuroketals, in vivo as products of the neuroprostane pathway. Neuroketals adduct to lysine residues of proteins with remarkable rapidity and induce cross-linking. Because neuroketals have either a 1,4-pentadiene or 1,4,7-octatriene side chain structure, we hypothesized that they could undergo further oxidation to form neuroketals with an additional hydroxyl group. Oxidation of docosahexaenoic acid in vitro yielded a series of compounds that were confirmed to be oxidized neuroketals by mass spectrometric analyses. Analysis of oxidized neuroketal adducts during oxidation of docosahexaenoic acid in the presence of lysine revealed the formation of oxidized Schiff base and hydroxylactam adducts. Oxidized hydroxylactam neuroketal-lysyl protein adducts, analyzed after digestion of proteins to individual amino acids, were not detected in nonoxidized rat brain synaptosomes but were readily detected following oxidation of synaptosomes. These studies indicate that neuroketals can undergo further oxidation, which in turn suggests that measurement of only unoxidized neuroketal adducts likely underestimates the amount of neuroketal adducts present in the brain in disorders of oxidant stress.

Aldehydes from n-6 fatty acid peroxidation. Effects on aminophospholipids

4-Hydroxy-nonenal (4-HNE) is a major by-product of n-6 fatty acid peroxidation. It has been described to covalently bind biomolecules expressing primary amine, especially the Lys residues in proteins. Low-density lipoproteins (LDL) are well-described macromolecules to be modified by 4-HNE, making them available to scavenger receptors on macrophages. Those macrophages then become foam cells and play an active role in atherogenesis. This paper reports on the covalent binding of 4-HNE to phosphatidylethanolamine (PE), a major aminophospholipid in biological membranes. In contrast, phosphatidylserine (PS) is virtually not modified by 4-HNE. One stable adduct, the Michael adduct PE/4-HNE is a poor substrate of secreted phospholipase A(2) and is not cleaved by phospholipase D. Plasmalogen PE, an important subclass of PE, is covalently modified by 4-HNE as well, but appears to be further degraded on its sn-1 position, the alkenyl chain, which might alter the antioxidant potential of the molecule. An aldehyde homologous to 4-HNE has been characterized as a breakdown product of 12-hydroperoxyeicosatetraenoic acid (12-HpETE) and named 4-hydroxy-2E,6Z-dodecadienal (4-HDDE). This compound as well as 4-HNE was detected in human plasma. Finally, 4-HDDE appears almost 3-fold more active than 4-HNE to make covalent adducts with PE. We conclude that 4-HNE and 4-HDDE are two biologically relevant markers of n-6 fatty acid peroxidation that may alter the phospholipid-dependent cell signaling.

Effects of reactive gamma-ketoaldehydes formed by the isoprostane pathway (isoketals) and cyclooxygenase pathway (levuglandins) on proteasome function

Oxidative stress can impair proteasome function, both of which are features of neurodegenerative diseases. Inhibition of proteasome function leads to protein accumulation and cell death. We discovered recently the formation of highly reactive g-ketoaldehydes, isoketals (IsoKs), and neuroketals (NeuroKs) as products of the isoprostane and neuroprostane pathways of free radical-induced lipid peroxidation that are analogous to cyclooxygenase-derived levuglandins (LGs). Because aldehydes that are much less reactive than IsoKs have been shown to inhibit proteasome function, we explored the ability of the proteasome to degrade IsoK-adducted proteins/peptides and the effect of IsoK and IsoK-adducted proteins/peptides on proteasome function. Adduction of IsoK to model proteasome substrates significantly reduced their rate of degradation by the 20S proteasome. The ability of IsoK to inhibit proteasome function directly was observed only at very high concentrations. However, at much lower concentrations, an IsoK-adducted protein (ovalbumin) and peptide (Ab1-40) significantly inhibited chymotrypsin-like activity of the 20S proteasome. Moreover, incubation of IsoK with P19 neuroglial cultures dose-dependently inhibited proteasome activity (IC50 = 330 nM) and induced cell death (LC50 = 670 nM). These findings suggest that IsoKs/NeuroKs/LGs can inhibit proteasome activity and, if overproduced, may have relevance to the pathogenesis of neurodegenerative diseases.

Formation of highly reactive gamma-ketoaldehydes (neuroketals) as products of the neuroprostane pathway

Neuroprostanes are prostaglandin-like compounds produced by free radical-induced peroxidation of docosahexaenoic acid, which is highly enriched in the brain. We previously described the formation of highly reactive gamma-ketoaldehydes (isoketals) as products of the isoprostane pathway of free radical-induced peroxidation of arachidonic acid. We therefore explored whether isoketal-like compounds (neuroketals) are also formed via the neuroprostane pathway. Utilizing mass spectrometric analyses, neuroketals were found to be formed in abundance in vitro during oxidation of docosahexaenoic acid and were formed in greater abundance than isoketals during co-oxidation of docosahexaenoic and arachidonic acid. Neuroketals were shown to rapidly adduct to lysine, forming lactam and Schiff base adducts. Neuroketal lysyl-lactam protein adducts were detected in nonoxidized rat brain synaptosomes at a level of 0.09 ng/mg of protein, which increased 19-fold following oxidation in vitro. Neuroketal lysyl-lactam protein adducts were also detected in vivo in normal human brain at a level of 9.9 +/- 3.7 ng/g of brain tissue. These studies identify a new class of highly reactive molecules that may participate in the formation of protein adducts and protein-protein cross-links in neurodegenerative diseases and contribute to the injurious effects of other oxidative pathologies in the brain.

The retinitis pigmentosa GTPase regulator (RPGR) interacts with novel transport-like proteins in the outer segments of rod photoreceptors

Mutations in the retinitis pigmentosa GTPase regulator (RPGR) gene cause X-linked retinitis pigmentosa type 3 (RP3), a severe, progressive and degenerative retinal dystrophy eventually leading to complete blindness. RPGR is ubiquitously expressed, yet mutations in the RPGR gene lead to a retina-restricted phenotype. To date, all RP3 associated missense mutations that have been identified are located in the RCC1-homologous domain (RHD) of RPGR. To investigate the molecular pathogenesis of RP3, we screened retinal yeast two-hybrid libraries with the RHD of RPGR. We identified several alternatively spliced gene products, some with retina-restricted expression, that interact specifically with RPGR in vivo and in vitro. Thus, these proteins were named RPGR-interacting protein 1 (RPGRIP1) isoforms. They contain a C-terminal RPGR-interacting domain and stretches of variable coiled-coil domains homologous to proteins involved in vesicular trafficking. The interaction between RPGR and RPGRIP1 isoforms was impaired in vivo by RP3-associated mutations in RPGR. Moreover, RPGR and RPGRIP1 co-localize in the outer segment of rod photoreceptors, which is in full agreement with the retinitis pigmentosa phenotype observed in RP3 patients. The localization of RPGRIP1 at 14q11 makes it a strong candidate gene for RP16. These results provide a clue for the retina-specific pathogenesis in RP3, and hint towards the involvement of RPGR and RPGRIP1 in mediating vesicular transport-associated processes.