Enzymological studies on the biosynthesis of N-acylethanolamines

Plaat1l1 controls feeding induced NAPE biosynthesis and contributes to energy balance regulation in zebrafish

Dysregulation of energy balance leading to obesity is a significant risk factor for cardiometabolic diseases such as diabetes, non-alcoholic fatty liver disease and atherosclerosis. In rodents and several other vertebrates, feeding has been shown to induce a rapid rise in the intestinal levels of N-acyl-ethanolamines (NAEs) and the chronic consumption of a high fat diet abolishes this rise. Administering NAEs to rodents consuming a high fat diet reduces their adiposity, in part by reducing food intake and enhancing fat oxidation, so that feeding-induced intestinal NAE biosynthesis appears to be critical to appropriate regulation of energy balance. However, the contribution of feeding-induced intestinal NAE biosynthesis to appropriate energy balance remains poorly understood in part because there are multiple enzymes that can contribute to NAE biosynthesis and the specific enzyme(s) that are responsible for feeding-induced intestinal NAE biosynthesis have not been identified. The rate-limiting step in the intestinal biosynthesis of NAEs is formation of their immediate precursors, the N-acyl-phosphatidylethanolamines (NAPEs), by phosphatidylethanolamine N-acyltransferases (NATs). At least six NATs are found in humans and multiple homologs of these NATs are found in most vertebrate species. In recent years, the fecundity and small size of zebrafish (Danio rerio), as well as their similarities in feeding behavior and energy balance regulation with mammals, have led to their use to model key features of cardiometabolic disease. We therefore searched the Danio rerio genome to identify all NAT homologs and found two additional NAT homologs besides the previously reported plaat1, rarres3, and rarres3l, and used CRISPR/cas9 to delete these two NAT homologs (plaat1l1 and plaat1l2). While wild-type fish markedly increased their intestinal NAPE levels in response to a meal after fasting, this response was completely ablated in plaat1l1-/-fish. Furthermore, plaat1l1-/- fish fed a standard flake diet had increased weight gain and glucose intolerance compared to wild-type fish. The results support a critical role for feeding-induced NAPE and NAE biosynthesis in regulating energy balance and suggest that restoring this response in obese animals could potentially be used to treat obesity and cardiometabolic disease.

Strikingly High Activity of 15-Lipoxygenase Towards Di-Polyunsaturated Arachidonoyl/Adrenoyl-Phosphatidylethanolamines Generates Peroxidation Signals of Ferroptotic Cell Death

The vast majority of membrane phospholipids (PLs) include two asymmetrically positioned fatty acyls: oxidizable polyunsaturated fatty acids (PUFA) attached predominantly at the sn2 position, and non-oxidizable saturated/monounsaturated acids (SFA/MUFA) localized at the sn1 position. The peroxidation of PUFA-PLs, particularly sn2-arachidonoyl(AA)- and sn2-adrenoyl(AdA)-containing phosphatidylethanolamines (PE), has been associated with the execution of ferroptosis, a program of regulated cell death. There is a minor subpopulation (≈1-2 mol %) of doubly PUFA-acylated phospholipids (di-PUFA-PLs) whose role in ferroptosis remains enigmatic. Here we report that 15-lipoxygenase (15LOX) exhibits unexpectedly high pro-ferroptotic peroxidation activity towards di-PUFA-PEs. We revealed that peroxidation of several molecular species of di-PUFA-PEs occurred early in ferroptosis. Ferrostatin-1, a typical ferroptosis inhibitor, effectively prevented peroxidation of di-PUFA-PEs. Furthermore, co-incubation of cells with di-AA-PE and 15LOX produced PUFA-PE peroxidation and induced ferroptotic death. The decreased contents of di-PUFA-PEs in ACSL4 KO A375 cells was associated with lower levels of di-PUFA-PE peroxidation and enhanced resistance to ferroptosis. Thus, di-PUFA-PE species are newly identified phospholipid peroxidation substrates and regulators of ferroptosis, representing a promising therapeutic target for many diseases related to ferroptotic death.

Endocannabinoid System: Chemical Characteristics and Biological Activity

The endocannabinoid system (eCB) has been studied to identify the molecular structures present in Cannabis sativa. eCB consists of cannabinoid receptors, endogenous ligands, and the associated enzymatic apparatus responsible for maintaining energy homeostasis and cognitive processes. Several physiological effects of cannabinoids are exerted through interactions with various receptors, such as CB1 and CB2 receptors, vanilloid receptors, and the recently discovered G-protein-coupled receptors (GPR55, GPR3, GPR6, GPR12, and GPR19). Anandamide (AEA) and 2-arachidoylglycerol (2-AG), two small lipids derived from arachidonic acid, showed high-affinity binding to both CB1 and CB2 receptors. eCB plays a critical role in chronic pain and mood disorders and has been extensively studied because of its wide therapeutic potential and because it is a promising target for the development of new drugs. Phytocannabinoids and synthetic cannabinoids have shown varied affinities for eCB and are relevant to the treatment of several neurological diseases. This review provides a description of eCB components and discusses how phytocannabinoids and other exogenous compounds may regulate the eCB balance. Furthermore, we show the hypo- or hyperfunctionality of eCB in the body and how eCB is related to chronic pain and mood disorders, even with integrative and complementary health practices (ICHP) harmonizing the eCB.

Activation of cannabinoid type 1 receptor (CB1) modulates oligodendroglial process branching complexity in rat hippocampal cultures stimulated by olfactory ensheathing glia-conditioned medium

The endocannabinoid system (ECS) refers to a complex cell-signaling system highly conserved among species formed by numerous receptors, lipid mediators (endocannabinoids) and synthetic and degradative enzymes. It is widely distributed throughout the body including the CNS, where it participates in synaptic signaling, plasticity and neurodevelopment. Besides, the olfactory ensheathing glia (OEG) present in the olfactory system is also known to play an important role in the promotion of axonal growth and/or myelination. Therefore, both OEG and the ECS promote neurogenesis and oligodendrogenesis in the CNS. Here, we investigated if the ECS is expressed in cultured OEG, by assessing the main markers of the ECS through immunofluorescence, western blotting and qRT-PCR and quantifying the content of endocannabinoids in the conditioned medium of these cells. After that, we investigated whether the production and release of endocannabinoids regulate the differentiation of oligodendrocytes co-cultured with hippocampal neurons, through Sholl analysis in oligodendrocytes expressing O4 and MBP markers. Additionally, we evaluated through western blotting the modulation of downstream pathways such as PI3K/Akt/mTOR and ERK/MAPK, being known to be involved in the proliferation and differentiation of oligodendrocytes and activated by CB1, which is the major endocannabinoid responsive receptor in the brain. Our data show that OEG expresses key genes of the ECS, including the CB1 receptor, FAAH and MAGL. Besides, we were able to identify AEA, 2-AG and AEA related mediators palmitoylethanolamide (PEA) and oleoylethanolamide (OEA), in the conditioned medium of OEG cultures. These cultures were also treated with URB597 10-9 M, a FAAH selective inhibitor, or JZL184 10-9 M, a MAGL selective inhibitor, which led to the increase in the concentrations of OEA and 2-AG in the conditioned medium. Moreover, we found that the addition of OEG conditioned medium (OEGCM) enhanced the complexity of oligodendrocyte process branching in hippocampal mixed cell cultures and that this effect was inhibited by AM251 10-6 M, a CB1 receptor antagonist. However, treatment with the conditioned medium enriched with OEA or 2-AG did not alter the process branching complexity of premyelinating oligodendrocytes, while decreased the branching complexity in mature oligodendrocytes. We also observed no change in the phosphorylation of Akt and ERK 44/42 in any of the conditions used. In conclusion, our data show that the ECS modulates the number and maturation of oligodendrocytes in hippocampal mixed cell cultures.

Anandamide and other N-acylethanolamines: A class of signaling lipids with therapeutic opportunities

N-acylethanolamines (NAEs), including N-palmitoylethanolamine (PEA), N-oleoylethanolamine (OEA), N-arachidonoylethanolamine (AEA, anandamide), N-docosahexaenoylethanolamine (DHEA, synaptamide) and their oxygenated metabolites are a lipid messenger family with numerous functions in health and disease, including inflammation, anxiety and energy metabolism. The NAEs exert their signaling role through activation of various G protein-coupled receptors (cannabinoid CB₁ and CB₂ receptors, GPR55, GPR110, GPR119), ion channels (TRPV1) and nuclear receptors (PPAR-α and PPAR-γ) in the brain and periphery. The biological role of the oxygenated NAEs, such as prostamides, hydroxylated anandamide and DHEA derivatives, are less studied. Evidence is accumulating that NAEs and their oxidative metabolites may be aberrantly regulated or are associated with disease severity in obesity, metabolic syndrome, cancer, neuroinflammation and liver cirrhosis. Here, we comprehensively review NAE biosynthesis and degradation, their metabolism by lipoxygenases, cyclooxygenases and cytochrome P450s and the biological functions of these signaling lipids. We discuss the latest findings and therapeutic potential of modulating endogenous NAE levels by inhibition of their degradation, which is currently under clinical evaluation for neuropsychiatric disorders. We also highlight NAE biosynthesis inhibition as an emerging topic with therapeutic opportunities in endocannabinoid and NAE signaling.

The role of dopamine and endocannabinoid systems in prefrontal cortex development: Adolescence as a critical period

The prefrontal cortex plays a central role in the control of complex cognitive processes including action control and decision making. It also shows a specific pattern of delayed maturation related to unique behavioral changes during adolescence and allows the development of adult cognitive processes. The adolescent brain is extremely plastic and critically vulnerable to external insults. Related to this vulnerability, adolescence is also associated with the emergence of numerous neuropsychiatric disorders involving alterations of prefrontal functions. Within prefrontal microcircuits, the dopamine and the endocannabinoid systems have widespread effects on adolescent-specific ontogenetic processes. In this review, we highlight recent advances in our understanding of the maturation of the dopamine system and the endocannabinoid system in the prefrontal cortex during adolescence. We discuss how they interact with GABA and glutamate neurons to modulate prefrontal circuits and how they can be altered by different environmental events leading to long-term neurobiological and behavioral changes at adulthood. Finally, we aim to identify several future research directions to help highlight gaps in our current knowledge on the maturation of these microcircuits.

Roles of Endocannabinoids and Endocannabinoid-like Molecules in Energy Homeostasis and Metabolic Regulation: A Nutritional Perspective

The endocannabinoid system is involved in signal transduction in mammals. It comprises principally G protein-coupled cannabinoid receptors and their endogenous agonists, called endocannabinoids, as well as the enzymes and transporters responsible for the metabolism of endocannabinoids. Two arachidonic acid-containing lipid molecules, arachidonoylethanolamide (anandamide) and 2-arachidonoylglycerol, function as endocannabinoids. N-acylethanolamines and monoacylglycerols, in which the arachidonic acid chain is replaced with a saturated or monounsaturated fatty acid, are not directly involved in the endocannabinoid system but exhibit agonistic activities for other receptors. These endocannabinoid-like molecules include palmitoylethanolamide, oleoylethanolamide (OEA), and 2-oleoylglycerol. Endocannabinoids stimulate feeding behavior and the anabolism of lipids and glucose, while OEA suppresses appetite. Both central and peripheral systems are included in these nutritional and metabolic contexts. Therefore, they have potential in the treatment and prevention of obesity. We outline the structure, metabolism, and biological activities of endocannabinoids and related molecules, and focus on their involvement in energy homeostasis and metabolic regulation. Expected final online publication date for the Annual Review of Nutrition, Volume 41 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Synthesis, Quantification, and Characterization of Fatty Acid Amides from In Vitro and In Vivo Sources

Fatty acid amides are a diverse family of underappreciated, biologically occurring lipids. Herein, the methods for the chemical synthesis and subsequent characterization of specific members of the fatty acid amide family are described. The synthetically prepared fatty acid amides and those obtained commercially are used as standards for the characterization and quantification of the fatty acid amides produced by biological systems, a fatty acid amidome. The fatty acid amidomes from mouse N₁₈TG₂ cells, sheep choroid plexus cells, Drosophila melanogaster, Bombyx mori, Apis mellifera, and Tribolium castaneum are presented.

Application of Metabolomics in Pediatric Asthma: Prediction, Diagnosis and Personalized Treatment

Asthma in children remains a significant public health challenge affecting 5–20% of children in Europe and is associated with increased morbidity and societal healthcare costs. The high variation in asthma incidence among countries may be attributed to differences in genetic susceptibility and environmental factors. This respiratory disorder is described as a heterogeneous syndrome of multiple clinical manifestations (phenotypes) with varying degrees of severity and airway hyper-responsiveness, which is based on patient symptoms, lung function and response to pharmacotherapy. However, an accurate diagnosis is often difficult due to diversities in clinical presentation. Therefore, identifying early diagnostic biomarkers and improving the monitoring of airway dysfunction and inflammatory through non-invasive methods are key goals in successful pediatric asthma management. Given that asthma is caused by the interaction between genes and environmental factors, an emerging approach, metabolomics—the systematic analysis of small molecules—can provide more insight into asthma pathophysiological mechanisms, enable the identification of early biomarkers and targeted personalized therapies, thus reducing disease burden and societal cost. The purpose of this review is to present evidence on the utility of metabolomics in pediatric asthma through the analysis of intermediate metabolites of biochemical pathways that involve carbohydrates, amino acids, lipids, organic acids and nucleotides and discuss their potential application in clinical practice. Also, current challenges on the integration of metabolomics in pediatric asthma management and needed next steps are critically discussed.

A proposed modulatory role of the endocannabinoid system on adipose tissue metabolism and appetite in periparturient dairy cows

To sustain the nutrient demands of rapid fetal growth, parturition, and milk synthesis, periparturient dairy cows mobilize adipose tissue fatty acid stores through lipolysis. This process induces an inflammatory response within AT that is resolved as lactation progresses; however, excessive and protracted lipolysis compounds the risk for metabolic and inflammatory diseases. The suppression of lipolytic action and inflammation, along with amplification of adipogenesis and lipogenesis, serve as prospective therapeutic targets for improving the health of periparturient dairy cows. Generally, the activation of cannabinoid receptors by endocannabinoids enhances adipogenesis and lipogenesis, suppresses lipolysis, and increases appetite in mammals. These biological effects of activating the endocannabinoid system open the possibility of harnessing the endocannabinoid system through nutritional intervention in dairy herds as a potential tool to improve dairy cows' health, although much is still to be revealed in this context. This review summarizes the current knowledge surrounding the components of the endocannabinoid system, elaborates on the metabolic effects of its activation, and explores the potential to modulate its activity in periparturient dairy cows.

Endocannabinoid-Like Lipid Neuromodulators in the Regulation of Dopamine Signaling: Relevance for Drug Addiction

The family of lipid neuromodulators has been rapidly growing, as the use of different -omics techniques led to the discovery of a large number of naturally occurring N-acylethanolamines (NAEs) and N-acyl amino acids belonging to the complex lipid signaling system termed endocannabinoidome. These molecules exert a variety of biological activities in the central nervous system, as they modulate physiological processes in neurons and glial cells and are involved in the pathophysiology of neurological and psychiatric disorders. Their effects on dopamine cells have attracted attention, as dysfunctions of dopamine systems characterize a range of psychiatric disorders, i.e., schizophrenia and substance use disorders (SUD). While canonical endocannabinoids are known to regulate excitatory and inhibitory synaptic inputs impinging on dopamine cells and modulate several dopamine-mediated behaviors, such as reward and addiction, the effects of other lipid neuromodulators are far less clear. Here, we review the emerging role of endocannabinoid-like neuromodulators in dopamine signaling, with a focus on non-cannabinoid N-acylethanolamines and their receptors. Mounting evidence suggests that these neuromodulators contribute to modulate synaptic transmission in dopamine regions and might represent a target for novel medications in alcohol and nicotine use disorder.

Synergic Therapeutic Potential of PEA-Um Treatment and NAAA Enzyme Silencing In the Management of Neuroinflammation

Inflammation is a key element in the pathobiology of neurodegenerative diseases and sees the involvement of different neuronal and non-neuronal cells as players able to respond to inflammatory signals of immune origin. Palmitoylethanolamide (PEA) is an endogenous potent anti-inflammatory agent, in which activity is regulated by N-acylethanolamine acid amidase (NAAA), that hydrolyzes saturated or monounsaturated fatty acid ethanolamides, such as PEA. In this research, an in vitro study was performed on different neuronal (SH-SY5Y) and non-neuronal cell lines (C6, BV-2, and Mo3.13) subjected to NAAA enzyme silencing and treated with PEA ultra-micronized (PEA-um) (1, 3, and 10 μM) to increase the amount of endogenous PEA available for counteract neuroinflammation provoked by stimulation with lipopolysaccharide (LPS) (1 μg/mL) and interferon gamma (INF-γ )(100 U/mL). Cell viability was performed by MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide) staining, suggesting a protective effect of PEA-um (3 and 10 μM) on all cell lines studied. Western Blot analysis for inflammatory markers (Inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX-2)) was carried out in control and NAAA-silenced cells, highlighting how the concomitant treatment of the neuronal and non-neuronal cells with PEA-um after NAAA genic downregulation is satisfactory to counteract neuroinflammation. These in vitro findings support the protective role of endogenous PEA availability in the neuronal field, bringing interesting information for a translational point of view.

ALIAmides Update: Palmitoylethanolamide and Its Formulations on Management of Peripheral Neuropathic Pain

Neuropathic pain results from lesions or diseases of the somatosensory nervous system and it remains largely difficult to treat. Peripheral neuropathic pain originates from injury to the peripheral nervous system (PNS) and manifests as a series of symptoms and complications, including allodynia and hyperalgesia. The aim of this review is to discuss a novel approach on neuropathic pain management, which is based on the knowledge of processes that underlie the development of peripheral neuropathic pain; in particular highlights the role of glia and mast cells in pain and neuroinflammation. ALIAmides (autacoid local injury antagonist amides) represent a group of endogenous bioactive lipids, including palmitoylethanolamide (PEA), which play a central role in numerous biological processes, including pain, inflammation, and lipid metabolism. These compounds are emerging thanks to their anti-inflammatory and anti-hyperalgesic effects, due to the down-regulation of activation of mast cells. Collectively, preclinical and clinical studies support the idea that ALIAmides merit further consideration as therapeutic approach for controlling inflammatory responses, pain, and related peripheral neuropathic pain.

Steric stabilisers govern the colloidal and chemical stability but not in vitro cellular toxicity of linoleoylethanolamide cubosomes

Linoleoylethanolamide (LEA) is an endogenous lipid with remarkable neuromodulatory properties. However, its therapeutic potential is limited by rapid clearance in vivo, targetability and solubility. This study aimed to formulate LEA into liquid crystalline nanoparticles (cubosomes) as a strategy to address the aforementioned challenges. The influence of three different steric stabilisers: Tween 80 and Pluronic F68, both of which have the potential to interact with receptors expressed at the blood-brain barrier and Pluronic F127 as a control, on colloidal stability, internal structure, chemical stability and cytotoxicity of the dispersions were investigated. We found that for effective stabilization of LEA dispersions, a higher concentration of Tween 80 was required compared to Pluronics. Freshly prepared dispersions showed mean particle size of <250 nm and low PDIs (<0.2), with an Im3m type cubic structure but with different lattice parameters. Upon storage at ambient temperature for a week, increased mean particle size and PDI, with a significant reduction in the concentration of LEA was observed in Tween 80-stabilised dispersions. Greater than 80% cell viability was observed at concentrations of up to 20 μg/mL LEA in the presence of all three stabilisers. Collectively, our results suggest that the stabiliser type influences colloidal and chemical stability but not cytotoxicity of LEA cubosomes. This study highlights the potential of endogenous bioactive lipids to be utilized as core cubosome forming lipids with the view to improving their solubility, rapid clearance and targetability to enable delivery of these bioactive molecules to the brain.

Engineering yeast phospholipid metabolism for de novo oleoylethanolamide production

Phospholipids, the most abundant membrane lipid components, are crucial in maintaining membrane structures and homeostasis for biofunctions. As a structurally diverse and tightly regulated system involved in multiple organelles, phospholipid metabolism is complicated to manipulate. Thus, repurposing phospholipids for lipid-derived chemical production remains unexplored. Herein, we develop a Saccharomyces cerevisiae platform for de novo production of oleoylethanolamide, a phospholipid derivative with promising pharmacological applications in ameliorating lipid dysfunction and neurobehavioral symptoms. Through deregulation of phospholipid metabolism, screening of biosynthetic enzymes, engineering of subcellular trafficking and process optimization, we could produce oleoylethanolamide at a titer of 8,115.7 µg l^-1 and a yield on glucose of 405.8 µg g^-1. Our work provides a proof-of-concept study for systemically repurposing phospholipid metabolism for conversion towards value-added biological chemicals, and this multi-faceted framework may shed light on tailoring phospholipid metabolism in other microbial hosts.

The role of n-3 PUFA-derived fatty acid derivatives and their oxygenated metabolites in the modulation of inflammation

Notwithstanding the ongoing debate on their full potential in health and disease, there is general consensus that n-3 PUFAs play important physiological roles. Increasing dietary n-3 PUFA intake results in increased DHA and EPA content in cell membranes as well as an increase in n-3 derived oxylipin and -endocannabinoid concentrations, like fatty acid amides and glycerol-esters. These shifts are believed to (partly) explain the pharmacological and anti-inflammatory effects of n-3 PUFAs. Recent studies discovered that n-3 PUFA-derived endocannabinoids can be further metabolized by the oxidative enzymes CYP-450, LOX and COX, similar to the n-6 derived endocannabinoids. Interestingly, these oxidized n-3 PUFA derived endocannabinoids of eicosapentaenoyl ethanolamide (EPEA) and docosahexaenoyl ethanolamide (DHEA) have higher anti-inflammatory and anti-proliferative potential than their precursors. In this review, an overview of recently discovered n-3 PUFA derived endocannabinoids and their metabolites is provided. In addition, the use of chemical probes will be presented as a promising technique to study the n-3 PUFA and n-3 PUFA metabolism within the field of lipid biochemistry.

Metabolic studies of synaptamide in an immortalized dopaminergic cell line

INTRODUCTION

Synaptamide, the N-acylethanolamine of docosahexaenoic acid (DHA), is structurally similar to the endocannabinoid N-arachidonoylethanolamine, anandamide. It is an endogenous ligand at the orphan G-protein coupled receptor 110 (GPR110; ADGRF1), and induces neuritogenesis and synaptogenesis in hippocampal and cortical neurons, as well as neuronal differentiation in neural stem cells.

PURPOSE

Our goal was to characterize the metabolic fate (synthesis and metabolism) of synaptamide in a dopaminergic cell line using immortalized fetal mesencephalic cells (N27 cells). Both undifferentiated and differentiating N27 cells were used in this study in an effort to understand synaptamide synthesis and metabolism in developing and adult cells.

METHODS

Radiotracer uptake and hydrolysis assays were conducted in N27 cells incubated with [1-¹⁴C]DHA or with one of two radioisotopomers of synaptamide: [α,β-¹⁴C₂]synaptamide and [1-¹⁴C-DHA]synaptamide.

RESULTS

Neither differentiated nor undifferentiated N27 cells synthesized synaptamide from radioactive DHA, but both rapidly incorporated radioactivity from exogenous synaptamide into membrane phospholipids, regardless of which isotopomer was used. Pharmacological inhibition of fatty acid amide hydrolase (FAAH) reduced formation of labeled phospholipids in undifferentiated but not differentiated cells.

CONCLUSIONS

In undifferentiated cells, synaptamide uptake and metabolism is driven by its enzymatic hydrolysis (fatty acid amide hydrolase; FAAH), but in differentiating cells, the process seems to be FAAH independent. We conclude that differentiated and undifferentiated N27 cells utilize synaptamide via different mechanisms. This observation could be extrapolated to how different mechanisms may be in place for synaptamide uptake and metabolism in developing and adult dopaminergic cells.

Varied doses and chemical forms of selenium supplementation differentially affect mouse intestinal physiology

Varied doses and chemical forms of selenium supplementation differentially affect mouse intestinal physiology and perturbed the fecal metabolic profiles of and jejunal protein expression in mice.

Hedonic Eating and the "Delicious Circle": From Lipid-Derived Mediators to Brain Dopamine and Back

Palatable food can be seductive and hedonic eating can become irresistible beyond hunger and negative consequences. This is witnessed by the subtle equilibrium between eating to provide energy intake for homeostatic functions, and reward-induced overeating. In recent years, considerable efforts have been devoted to study neural circuits, and to identify potential factors responsible for the derangement of homeostatic eating toward hedonic eating and addiction-like feeding behavior. Here, we examined recent literature on “old” and “new” players accountable for reward-induced overeating and possible liability to eating addiction. Thus, the role of midbrain dopamine is positioned at the intersection between selected hormonal signals involved in food reward information processing (namely, leptin, ghrelin, and insulin), and lipid-derived neural mediators such as endocannabinoids. The impact of high fat palatable food and dietary lipids on endocannabinoid formation is reviewed in its pathogenetic potential for the derangement of feeding homeostasis. Next, endocannabinoid signaling that regulates synaptic plasticity is discussed as a key mechanism acting both at hypothalamic and mesolimbic circuits, and affecting both dopamine function and interplay between leptin and ghrelin signaling. Outside the canonical hypothalamic feeding circuits involved in energy homeostasis and the notion of “feeding center,” we focused on lateral hypothalamus as neural substrate able to confront food-associated homeostatic information with food salience, motivation to eat, reward-seeking, and development of compulsive eating. Thus, the lateral hypothalamus-ventral tegmental area-nucleus accumbens neural circuitry is reexamined in order to interrogate the functional interplay between ghrelin, dopamine, orexin, and endocannabinoid signaling. We suggested a pivotal role for endocannabinoids in food reward processing within the lateral hypothalamus, and for orexin neurons to integrate endocrine signals with food reinforcement and hedonic eating. In addition, the role played by different stressors in the reinstatement of preference for palatable food and food-seeking behavior is also considered in the light of endocannabinoid production, activation of orexin receptors and disinhibition of dopamine neurons. Finally, type-1 cannabinoid receptor-dependent inhibition of GABA-ergic release and relapse to reward-associated stimuli is linked to ghrelin and orexin signaling in the lateral hypothalamus-ventral tegmental area-nucleus accumbens network to highlight its pathological potential for food addiction-like behavior.

Metabolomics of postprandial plasma alterations: a comprehensive Japanese study

While endogenous metabolites in plasma can be used as clinical biomarkers, intra-day variations should be carefully considered. The postprandial effect is a large contributing factor and is dependent on regional features (e.g. meals, ethnicity). Thus, for clinical application, regional-specific postprandial baseline data are required. In this study, 10 healthy Japanese volunteers of different ages and genders ate the same meal, and blood samples were taken 30 min before and 1 h after the meal challenge. Plasma metabolomics was conducted and metabolites that significantly changed with the meal challenge were extracted. Principal component analysis of the data from 1101 metabolites showed a postprandial shift with a common direction despite marked individual variation. Pathway enrichment analysis demonstrated known postprandial effects, including the energy utilization shift from lipolysis to glycolysis and the elevation of bile acids for lipid absorption. Other postprandial metabolic changes were observed, including decreases in orexigenic signals and increases of food-derived components. The postprandial alteration accumulated in this study will be used for the understanding of Japanese clinical metabolomics for health promotion in Japan.

Oral Palmitoylethanolamide Treatment Is Associated with Reduced Cutaneous Adverse Effects of Interferon-β1a and Circulating Proinflammatory Cytokines in Relapsing-Remitting Multiple Sclerosis

Palmitoylethanolamide (PEA) is an endogenous lipid mediator known to reduce pain and inflammation. However, only limited clinical studies have evaluated the effects of PEA in neuroinflammatory and neurodegenerative diseases. Multiple sclerosis (MS) is a chronic autoimmune and inflammatory disease of the central nervous system. Although subcutaneous administration of interferon (IFN)-β1a is approved as first-line therapy for the treatment of relapsing-remitting MS (RR-MS), its commonly reported adverse events (AEs) such as pain, myalgia, and erythema at the injection site, deeply affect the quality of life (QoL) of patients with MS. In this randomized, double-blind, placebo-controlled study, we tested the effect of ultramicronized PEA (um-PEA) added to IFN-β1a in the treatment of clinically defined RR-MS. The primary objectives were to estimate whether, with um-PEA treatment, patients with MS perceived an improvement in pain and a decrease of the erythema width at the IFN-β1a injection site in addition to an improvement in their QoL. The secondary objectives were to evaluate the effects of um-PEA on circulating interferon-γ, tumor necrosis factor-α, and interleukin-17 serum levels, N-acylethanolamine plasma levels, Expanded Disability Status Scale (EDSS) progression, and safety and tolerability after 1 year of treatment. Patients with MS receiving um-PEA perceived an improvement in pain sensation without a reduction of the erythema at the injection site. A significant improvement in QoL was observed. No significant difference was reported in EDSS score, and um-PEA was well tolerated. We found a significant increase of palmitoylethanolamide, anandamide and oleoylethanolamide plasma levels, and a significant reduction of interferon-γ, tumor necrosis factor-α, and interleukin-17 serum profile compared with the placebo group. Our results suggest that um-PEA may be considered as an appropriate add-on therapy for the treatment of IFN-β1a-related adverse effects in RR-MS.

The Endocannabinoid Signaling System in the CNS: A Primer

The purpose of this chapter is to provide an introduction to the mechanisms for the regulation of endocannabinoid signaling through CB1 cannabinoid receptors in the central nervous system. The processes involved in the synthesis and degradation of the two most well-studied endocannabinoids, 2-arachidonoylglycerol and N-arachidonylethanolamine are outlined along with information regarding the regulation of the proteins involved. Signaling mechanisms and pharmacology of the CB1 cannabinoid receptor are outlined, as is the paradigm of endocannabinoid/CB1 receptor regulation of neurotransmitter release. The reader is encouraged to appreciate the importance of the endocannabinoid/CB1 receptor signaling system in the regulation of synaptic activity in the brain.

Fatty acid amide hydrolase inhibitors: a patent review (2009-2014)

INTRODUCTION

Fatty acid amide hydrolase (FAAH) is a key enzyme responsible for the degradation of the endocannabinoid anandamide. FAAH inactivation is emerging as a strategy to treat several CNS and peripheral diseases, including inflammation and pain. The search for effective FAAH inhibitors has thus become a key focus in present drug discovery.

AREAS COVERED

Patents and patent applications published from 2009 to 2014 in which novel chemical classes are claimed to inhibit FAAH.

EXPERT OPINION

FAAH is a promising target for treating many disease conditions including pain, inflammation and mood disorders. In the last few years, remarkable efforts have been made to develop new FAAH inhibitors (either reversible and irreversible) characterized by excellent potency and selectivity, to complete the arsenal of tools for modulating FAAH activity. The failure of PF-04457845 in a Phase II study on osteoarthritis pain has not flattened the interest in FAAH inhibitors. New clinical trials on 'classical' FAAH inhibitors are now ongoing, and new strategies based on compounds with peculiar in vivo distribution (e.g., peripheral) or with multiple pharmacological activities (e.g., FAAH and COX) are under investigation and could boost the therapeutic potential of this class in the next future.

Fatty acids, endocannabinoids and inflammation

From their phylogenetic and pharmacological classification it might be inferred that cannabinoid receptors and their endogenous ligands constitute a rather specialised and biologically distinct signalling system. However, the opposite is true and accumulating data underline how much the endocannabinoid system is intertwined with other lipid and non-lipid signalling systems. Endocannabinoids per se have many structural congeners, and these molecules exist in dynamic equilibria with different other lipid-derived mediators, including eicosanoids and prostamides. With multiple crossroads and shared targets, this creates a versatile system involved in fine-tuning different physiological and metabolic processes, including inflammation. A key feature of this 'expanded' endocannabinoid system, or 'endocannabinoidome', is its subtle orchestration based on interactions between a relatively small number of receptors and multiple ligands with different but partly overlapping activities. Following an update on the role of the 'endocannabinoidome' in inflammatory processes, this review continues with possible targets for intervention at the level of receptors or enzymes involved in formation or breakdown of endocannabinoids and their congeners. Although its pleiotropic character poses scientific challenges, the 'expanded' endocannabinoid system offers several opportunities for prevention and therapy of chronic diseases. In this respect, successes are more likely to come from 'multiple-target' than from 'single-target' strategies.

Inhibiting endocannabinoid biosynthesis: a novel approach to the treatment of constipation

BACKGROUND AND PURPOSE

Endocannabinoids are a family of lipid mediators involved in the regulation of gastrointestinal (GI) motility. The expression, localization and function of their biosynthetic enzymes in the GI tract are not well understood. Here, we examined the expression, localization and function of the enzyme diacylglycerol lipase-α (DAGLα), which is involved in biosynthesis of the endocannabinoid 2-arachidonoylglycerol (2-AG).

EXPERIMENTAL APPROACH

Cannabinoid CB1 receptor-deficient, wild-type control and C3H/HeJ mice, a genetically constipated strain, were used. The distribution of DAGLα in the enteric nervous system was examined by immunohistochemistry. Effects of the DAGL inhibitors, orlistat and OMDM-188 on pharmacologically induced GI hypomotility were assessed by measuring intestinal contractility in vitro and whole gut transit or faecal output in vivo. Endocannabinoid levels were measured by mass spectrometry.

KEY RESULTS

DAGLα was expressed throughout the GI tract. In the intestine, unlike DAGLβ, DAGLα immunoreactivity was prominently expressed in the enteric nervous system. In the myenteric plexus, it was colocalized with the vesicular acetylcholine transporter in cholinergic nerves. In normal mice, inhibiting DAGL reversed both pharmacologically reduced intestinal contractility and pharmacologically prolonged whole gut transit. Moreover, inhibiting DAGL normalized faecal output in constipated C3H/HeJ mice. In colons incubated with scopolamine, 2-AG was elevated while inhibiting DAGL normalized 2-AG levels.

CONCLUSIONS AND IMPLICATIONS

DAGLα was expressed in the enteric nervous system of mice and its inhibition reversed slowed GI motility, intestinal contractility and constipation through 2-AG and CB1 receptor-mediated mechanisms. Our data suggest that DAGLα inhibitors may be promising candidates for the treatment of constipation.

ABHD4 regulates multiple classes of N-acyl phospholipids in the mammalian central nervous system

N-Acyl phospholipids are atypical components of cell membranes that bear three acyl chains and serve as potential biosynthetic precursors for lipid mediators such as endocannabinoids. Biochemical studies have implicated ABHD4 as a brain N-acyl phosphatidylethanolamine (NAPE) lipase, but in vivo evidence for this functional assignment is lacking. Here, we describe ABHD4(-/-) mice and their characterization using untargeted lipidomics to discover that ABHD4 regulates multiple classes of brain N-acyl phospholipids. In addition to showing reductions in brain glycerophospho-NAEs (GP-NAEs) and plasmalogen-based lyso-NAPEs (lyso-pNAPEs), ABHD4(-/-) mice exhibited decreases in a distinct set of brain lipids that were structurally characterized as N-acyl lysophosphatidylserines (lyso-NAPSs). Biochemical assays confirmed that NAPS lipids are direct substrates of ABHD4. These findings, taken together, designate ABHD4 as a principal regulator of N-acyl phospholipid metabolism in the mammalian nervous system.

Pharmacological blockade of the fatty acid amide hydrolase (FAAH) alters neural proliferation, apoptosis and gliosis in the rat hippocampus, hypothalamus and striatum in a negative energy context

Endocannabinoids participate in the control of neurogenesis, neural cell death and gliosis. The pharmacological effect of the fatty acid amide hydrolase (FAAH) inhibitor URB597, which limits the endocannabinoid degradation, was investigated in the present study. Cell proliferation (phospho-H3⁺ or BrdU⁺ cells) of the main adult neurogenic zones as well as apoptosis (cleaved caspase-3⁺), astroglia (GFAP⁺), and microglia (Iba1⁺ cells) were analyzed in the hippocampus, hypothalamus and striatum of rats intraperitoneally treated with URB597 (0.3 mg/kg/day) at one dose/4-days resting or 5 doses (1 dose/day). Repeated URB597 treatment increased the plasma levels of the N-acylethanolamines oleoylethanolamide, palmitoylethanolamide and arachidonoylethanolamine, reduced the plasma levels of glucose, triglycerides and cholesterol, and induced a transitory body weight decrease. The hippocampi of repeated URB597-treated rats showed a reduced number of phospho-H3⁺ and BrdU⁺ subgranular cells as well as GFAP⁺, Iba1⁺ and cleaved caspase-3⁺ cells, which was accompanied with decreased hippocampal expression of the cannabinoid CB1 receptor gene Cnr1 and Faah. In the hypothalami of these rats, the number of phospho-H3⁺, GFAP⁺ and 3-weeks-old BrdU⁺ cells was specifically decreased. The reduced striatal expression of CB1 receptor in repeated URB597-treated rats was only associated with a reduced apoptosis. In contrast, the striatum of acute URB597-treated rats showed an increased number of subventricular proliferative, astroglial and apoptotic cells, which was accompanied with increased Faah expression. Main results indicated that FAAH inhibitor URB597 decreased neural proliferation, glia and apoptosis in a brain region-dependent manner, which were coupled to local changes in Faah and/or Cnr1 expression and a negative energy context.

N-Acyl amines of docosahexaenoic acid and other n-3 polyunsatured fatty acids - from fishy endocannabinoids to potential leads

N-3 Long-chain polyunsaturated fatty acids (n-3 LC-PUFAs), in particular α-linolenic acid (18:3n-3), eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3) are receiving much attention because of their presumed beneficial health effects. To explain these, a variety of mechanisms have been proposed, but their interactions with the endocannabinoid system have received relatively little attention so far. However, it has already been shown some time ago that consumption of n-3 LC-PUFAs not only affects the synthesis of prototypic endocannabinoids like anandamide but also stimulates the formation of specific n-3 LC-PUFA-derived conjugates with ethanolamine, dopamine, serotonin or other amines. Some of these fatty amides show overlapping biological activities with those of typical endocannabinoids, whereas others possess distinct and sometimes largely unknown receptor affinities and other properties. The ethanolamine and dopamine conjugates of DHA have been the most investigated thus far. These mediators may provide promising new leads to the field of inflammatory and neurological disorders and for other pharmacological applications, including their use as carrier molecules for neurotransmitters to target the brain. Furthermore, combinations of n-3 LC-PUFA-derived fatty acid amides, their precursors and FAAH inhibitors offer possibilities to optimise their effects in health and disease.

The endocannabinoid system and appetite: relevance for food reward

Mounting evidence substantiates the central role of the endocannabinoid system (ECS) in the modulation of both homeostatic and hedonic elements of appetite and food intake. Conversely, feeding status and dietary patterns directly influence activity of the ECS. Following a general introduction on the functioning of the ECS, the present review specifically addresses its role in the modulation of hedonic eating. Humans possess strong motivational systems triggered by rewarding aspects of food. Food reward is comprised of two components: one appetitive (orienting towards food); the other consummatory (hedonic evaluation), also referred to as 'wanting' and 'liking', respectively. Endocannabinoid tone seems to influence both the motivation to feed and the hedonic value of foods, probably by modifying palatability. Human physiology underlying hedonic eating is still not fully understood. A better understanding of the role of the ECS in the rewarding value of specific foods or diets could offer new possibilities to optimise the balance between energy and nutrient intake for different target groups. These groups include the obese and overweight, and potentially individuals suffering from malnutrition. Examples for the latter group are patients with disease-related anorexia, as well as the growing population of frail elderly suffering from persistent loss of food enjoyment and appetite resulting in malnutrition and involuntary weight loss. It has become clear that the psychobiology of food hedonics is extremely complex and the clinical failure of CB1 inverse agonists including rimonabant (Accomplia®) has shown that 'quick wins' in this field are unlikely.

New players in the fatty acyl ethanolamide metabolism

Fatty acyl ethanolamides represent a class of endogenous bioactive lipid molecules and are generally referred to as N-acylethanolamines (NAEs). NAEs include palmitoylethanolamide (anti-inflammatory and analgesic substance), oleoylethanolamide (anorexic substance), and anandamide (endocannabinoid). The endogenous levels of NAEs are mainly regulated by enzymes responsible for their biosynthesis and degradation. In mammalian tissues, the major biosynthetic pathway starts from glycerophospholipids and is composed of two enzyme reactions. The first step is N-acylation of ethanolamine phospholipids catalyzed by Ca(2+)-dependent N-acyltransferase and the second step is the release of NAEs from N-acylated ethanolamine phospholipids by N-acylphosphatidylethanolamine (NAPE)-hydrolyzing phospholipase D (NAPE-PLD). As for the degradation of NAEs, fatty acid amide hydrolase plays the central role. However, recent studies strongly suggest the involvement of other enzymes in the NAE metabolism. These enzymes include members of the HRAS-like suppressor family (also called phospholipase A/acyltransferase family), which were originally discovered as tumor suppressors but can function as Ca(2+)-independent NAPE-forming N-acyltransferases; multiple enzymes involved in the NAPE-PLD-independent multi-step pathways to generate NAE from NAPE, which came to light by the analysis of NAPE-PLD-deficient mice; and a lysosomal NAE-hydrolyzing acid amidase as a second NAE hydrolase. These newly recognized enzymes may become the targets for the development of new therapeutic drugs. Here, we focus on recent enzymological findings in this area.

Role of anorectic N-acylethanolamines in intestinal physiology and satiety control with respect to dietary fat

Anandamide is a well-known agonist for the cannabinoid receptors. Along with endogenous anandamide other non-endocannabinoid N-acylethanolamines are also formed, apparently in higher amounts. These include mainly oleoylethanolamide (OEA), palmitoyelethanolamide (PEA) and linoleoylethanolamide (LEA), and they have biological activity by themselves being anorectic and anti-inflammatory. It appears that the major effect of dietary fat on the level of these molecules is in the gastrointestinal system, where OEA, PEA and LEA in the enterocytes may function as homeostatic signals, which are decreased by prolonged consumption of a high-fat diet. These lipid amides appear to mediate their signaling activity via activation of PPARα in the enterocyte followed by activation of afferent vagal fibers leading to the brain. Through this mechanism OEA, PEA and LEA may both reduce the consumption of a meal as well as increase the reward value of the food. Thus, they may function as homeostatic intestinal signals involving hedonic aspects that contribute to the regulation of the amounts of dietary fat to be ingested.

The endocannabinoid system: an emerging key player in inflammation

PURPOSE OF REVIEW

The purpose of this review is to illustrate the expanding view of the endocannabinoid system (ECS) in relation to its roles in inflammation.

RECENT FINDINGS

According to the formal classification, the ECS consists of two cannabinoid receptors, their endogenous fatty acid-derived ligands, and a number of enzymes involved in their synthesis and breakdown. However, many endogenous congeners of classical endocannabinoids have now been discovered, together with a set of receptors structurally or functionally related to the cannabinoid receptors. Endocannabinoids per se behave 'promiscuously' with regard to their receptor interactions. It is increasingly recognized how tightly this expanded ECS is intertwined with key processes involved in inflammation. A continuous dynamic exchange of substrates and metabolites exists between ECS and eicosanoid pathways. Endocannabinoids can also be oxygenated by cyclooxygenase and other enzymes to biologically active 'hybrid' structures. Diet is among the main factors determining synthesis and release of endocannabinoids and related mediators.

SUMMARY

The complexity of what may be called the 'endocannabinoidome' requires approaches that take into account its dynamics and interconnections with other regulatory systems. This endocannabinoidome continues to offer possibilities for prevention and intervention, but multiple target approaches will probably provide the only keys to success.

Regulation of nausea and vomiting by cannabinoids and the endocannabinoid system

Nausea and vomiting (emesis) are important elements in defensive or protective responses that animals use to avoid ingestion or digestion of potentially harmful substances. However, these neurally-mediated responses are at times manifested as symptoms of disease and they are frequently observed as side-effects of a variety of medications, notably those used to treat cancer. Cannabis has long been known to limit or prevent nausea and vomiting from a variety of causes. This has led to extensive investigations that have revealed an important role for cannabinoids and their receptors in the regulation of nausea and emesis. With the discovery of the endocannabinoid system, novel ways to regulate both nausea and vomiting have been discovered that involve the production of endogenous cannabinoids acting centrally. Here we review recent progress in understanding the regulation of nausea and vomiting by cannabinoids and the endocannabinoid system, and we discuss the potential to utilize the endocannabinoid system in the treatment of these frequently debilitating conditions.

Brain region-specific changes in N-acylethanolamine contents with time of day

The N-acylethanolamines (NAEs) exert important behavioral, physiological, and immunological effects through actions at cannabinoid and other receptors. We measured concentrations of three NAEs, the Km and Vmax for fatty acid amide hydrolysis (FAAH), FAAH protein and FAAH mRNA in prefrontal cortex, hippocampus, hypothalamus, amygdala, striatum, and cerebellum at 4 h intervals, starting at 03:00. Significant differences in N-arachidonylethanolamine contents among the times examined occur in the prefrontal cortex (PFC), hippocampus, hypothalamus, and striatum. N-Oleoylethanolamine concentrations exhibit large fluctuations over the day in the cerebellum, including a threefold decrease between 19:00 and 23:00. N-Palmitoylethanolamine and N-oleoylethanolamine were significantly, positively correlated in all regions examined except the hypothalamus. FAAH Km values are significantly affected by time of day in PFC, hippocampus and amygdala and FAAH Vmax values are significantly affected in PFC, hippocampus and cerebellum. However, correlational data indicate that FAAH does not play a primary role in the circadian regulation of the NAE concentrations. FAAH protein expression is not significantly different among the harvest times in any brain region examined. Concentrations of 2-arachidonoylglycerol are significantly affected by time of harvest in the striatum and cerebellum, but not in other brain regions. Together, these data indicate that the NAEs exhibit diverse patterns of change with time of day that are likely the result of alterations in biosynthesis, and support the hypothesis that N-arachidonylethanolamine is a tonic activator of cannabinoid receptor signaling.

Evaluation of plasma-free endocannabinoids and their congeners in abstinent cocaine addicts seeking outpatient treatment: impact of psychiatric co-morbidity

Cocaine is associated with serious health problems including psychiatric co-morbidity. There is a need for the identification of biomarkers for the stratification of cocaine-addicted subjects. Several studies have evaluated circulating endocannabinoid-related lipids as biomarkers of inflammatory, metabolic and mental disorders. However, little is known in substance use disorders. This study characterizes both free N-acyl-ethanolamines (NAEs) and 2-acyl-glycerols in abstinent cocaine addicts from outpatient treatment programs who were diagnosed with cocaine use disorder (CUD; n = 88), and age-/gender-/body mass-matched healthy control volunteers (n = 46). Substance and mental disorders that commonly occur with substance abuse were assessed by the semi-structured interview 'Psychiatric Research Interview for Substance and Mental Diseases' according to the 'Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, Text Revision' (DSM-IV-TR) and plasma-free acyl derivatives were quantified by a liquid chromatography-tandem mass spectrometry system. The results indicate that plasma acyl derivatives are altered in abstinent cocaine-addicted subjects with CUD (CUD subjects). While NAEs were found to be increased, 2-acyl-glycerols were decreased in CUD subjects compared with controls. Multivariate predictive models based on these lipids as explanatory variables were developed to distinguish CUD subjects from controls providing high discriminatory power. However, these alterations were not influenced by the DSM-IV-TR criteria for cocaine abuse and dependence as cocaine trait severity measure. In contrast, we observed that some free acyl derivatives in CUD subjects were found to be affected by the diagnosis of some co-morbid psychiatric disorders. Thus, we found that the monounsaturated NAEs were significantly elevated in CUD subjects diagnosed with mood [N-oleoyl-ethanolamine and N-palmitoleoyl-ethanolamine (POEA)] and anxiety (POEA) disorders compared with non-co-morbid CUD subjects. Interestingly, the coexistence of alcohol use disorders did not influence the circulating levels of these free acyl derivatives. In summary, we have identified plasma-free acyl derivatives that might serve as reliable biomarkers for CUD. Furthermore, we found that monounsaturated NAE levels are also enhanced by co-morbid mood and anxiety disorders in cocaine addicts. These findings open the way for the development of new strategies for cocaine addiction diagnosis and treatment.

PUFA-derived endocannabinoids: an overview

Following on from the discovery of cannabinoid receptors, of their endogenous agonists (endocannabinoids) and of the biosynthetic and metabolic enzymes of the endocannabinoids, significant progress has been made towards the understanding of the role of the endocannabinoid system in both physiological and pathological conditions. Endocannabinoids are mainly n-6 long-chain PUFA (LCPUFA) derivatives that are synthesised by neuronal cells and inactivated via a two-step process that begins with their transport from the extracellular to the intracellular space and culminates in their intracellular degradation by hydrolysis or oxidation. Although the enzymes responsible for the biosynthesis and metabolism of endocannabinoids have been well characterised, the processes involved in their cellular uptake are still a subject of debate. Moreover, little is yet known about the roles of endocannabinoids derived from n-3 LCPUFA such as EPA and DHA. Here, I provide an overview of what is currently known about the mechanisms for the biosynthesis and inactivation of endocannabinoids, together with a brief analysis of the involvement of the endocannabinoids in both food intake and obesity. Owing to limited space, recent reviews will be often cited instead of original papers.

Alterations in cerebrospinal fluid glycerophospholipids and phospholipase A2 activity in Alzheimer's disease

Our aim is to study selected cerebrospinal fluid (CSF) glycerophospholipids (GP) that are important in brain pathophysiology. We recruited cognitively healthy (CH), minimally cognitively impaired (MCI), and late onset Alzheimer's disease (LOAD) study participants and collected their CSF. After fractionation into nanometer particles (NP) and supernatant fluids (SF), we studied the lipid composition of these compartments. LC-MS/MS studies reveal that both CSF fractions from CH subjects have N-acyl phosphatidylethanolamine, 1-radyl-2-acyl-sn-glycerophosphoethanolamine (PE), 1-radyl-2-acyl-sn-glycerophosphocholine (PC), 1,2-diacyl-sn-glycerophosphoserine (PS), platelet-activating factor-like lipids, and lysophosphatidylcholine (LPC). In the NP fraction, GPs are enriched with a mixture of saturated, monounsaturated, and polyunsaturated fatty acid species, while PE and PS in the SF fractions are enriched with PUFA-containing molecular species. PC, PE, and PS levels in CSF fractions decrease progressively in participants from CH to MCI, and then to LOAD. Whereas most PC species decrease equally in LOAD, plasmalogen species account for most of the decrease in PE. A significant increase in the LPC-to-PC ratio and PLA2 activity accompanies the GP decrease in LOAD. These studies reveal that CSF supernatant fluid and nanometer particles have different GP composition, and that PLA2 activity accounts for altered GPs in these fractions as neurodegeneration progresses.

Quantitative metabolic profiling of lipid mediators

Lipids are heterogeneous biological molecules that possess multiple physiological roles including cell structure, homeostasis, and restoration of tissue functionality during and after inflammation. Lipid metabolism constitutes a network of pathways that are related at multiple biosynthetic hubs. Disregulation of lipid metabolism can lead to pathophysiological effects and multiple lipid mediators have been described to be involved in physiological processes, (e.g. inflammation). Accordingly, a thorough description of these pathways may shed light on putative relations in multiple complex diseases, including chronic obstructive pulmonary disease, asthma, Alzheimer's disease, multiple sclerosis, obesity, and cancer. Due to the structural complexity of lipids and the low abundance of many lipid mediators, mass spectrometry is the most commonly employed method for analysis. However, multiple challenges remain in the efforts to analyze every lipid subfamily. In this review, the biological role of sphingolipids, glycerolipids, oxylipins (e.g. eicosanoids), endocannabinoids, and N-acylethanolamines in relation to health and disease and the state-of-the-art analyses are summarized. The characterization and understanding of these pathways will increase our ability to examine for interrelations among lipid pathways and improve the knowledge of biological mechanisms in health and disease.

Retinol and retinyl esters: biochemistry and physiology

By definition, a vitamin is a substance that must be obtained regularly from the diet. Vitamin A must be acquired from the diet, but unlike most vitamins, it can also be stored within the body in relatively high levels. For humans living in developed nations or animals living in present-day vivariums, stored vitamin A concentrations can become relatively high, reaching levels that can protect against the adverse effects of insufficient vitamin A dietary intake for six months, or even much longer. The ability to accumulate vitamin A stores lessens the need for routinely consuming vitamin A in the diet, and this provides a selective advantage to the organism. The molecular processes that underlie this selective advantage include efficient mechanisms to acquire vitamin A from the diet, efficient and overlapping mechanisms for the transport of vitamin A in the circulation, a specific mechanism allowing for vitamin A storage, and a mechanism for mobilizing vitamin A from these stores in response to tissue needs. These processes are considered in this review.

Palmitoylethanolamide and stearoylethanolamide levels in the interstitium of the trapezius muscle of women with chronic widespread pain and chronic neck-shoulder pain correlate with pain intensity and sensitivity

Chronic widespread pain (CWP) is a complex condition characterized by central hyperexcitability and altered descending control of nociception. However, nociceptive input from deep tissues is suggested to be an important drive. N-Acylethanolamines (NAEs) are endogenous lipid mediators involved in regulation of inflammation and pain. Previously we have reported elevated levels of the 2 NAEs, the peroxisome proliferator-activated receptor type-α ligand N-palmitoylethanolamine (PEA) and N-stearoylethanolamine (SEA) in chronic neck/shoulder pain (CNSP). In the present study, the levels of PEA and SEA in women with CWP (n=18), CNSP (n=34) and healthy controls (CON, n=24) were investigated. All subjects went through clinical examination, pressure pain threshold measurements and induction of experimental pain in the tibialis anterior muscle. Microdialysis dialysate of the trapezius was collected before and after subjects performed a repetitive low-force exercise and analyzed by mass spectrometry. The levels of PEA and SEA in CNSP were significantly higher post exercise compared with CWP, and both pre and post exercise compared with CON. Levels of both NAEs decreased significantly pre to post exercise in CWP. Intercorrelations existed between aspects of pain intensity and sensitivity and the level of the 2 NAEs in CWP and CNSP. This is the first study demonstrating that CNSP and CWP differ in levels of NAEs in response to a low-force exercise which induces pain. Increases in pain intensity as a consequence of low-force exercise were associated with low levels of PEA and SEA in CNSP and CWP. These results indicate that PEA and SEA have antinociceptive roles in humans.

Metabolism of endocannabinoids and related N-acylethanolamines: canonical and alternative pathways

Endocannabinoids are endogenous ligands of the cannabinoid receptors CB1 and CB2. Two arachidonic acid derivatives, arachidonoylethanolamide (anandamide) and 2-arachidonoylglycerol, are considered to be physiologically important endocannabinoids. In the known metabolic pathway in mammals, anandamide and other bioactive N-acylethanolamines, such as palmitoylethanolamide and oleoylethanolamide, are biosynthesized from glycerophospholipids by a combination of Ca(2+)-dependent N-acyltransferase and N-acyl-phosphatidylethanolamine-hydrolyzing phospholipase D, and are degraded by fatty acid amide hydrolase. However, recent studies have shown the involvement of other enzymes and pathways, which include the members of the tumor suppressor HRASLS family (the phospholipase A/acyltransferase family) functioning as Ca(2+)-independent N-acyltransferases, N-acyl-phosphatidylethanolamine-hydrolyzing phospholipaseD-independent multistep pathways via N-acylated lysophospholipid, and N-acylethanolamine-hydrolyzing acid amidase, a lysosomal enzyme that preferentially hydrolyzes palmitoylethanolamide. Although their physiological significance is poorly understood, these new enzymes/pathways may serve as novel targets for the development of therapeutic drugs. For example, selective N-acylethanolamine-hydrolyzing acid amidase inhibitors are expected to be new anti-inflammatory and analgesic drugs. In this minireview, we focus on advances in the understanding of these enzymes/pathways. In addition, recent findings on 2-arachidonoylglycerol metabolism are described.