Anandamide-Mediated Modulation of Nociceptive Transmission at the Spinal Cord Level

Three decades ago, the first endocannabinoid, anandamide (AEA), was identified, and its analgesic effect was recognized in humans and preclinical models. However, clinical trial failures pointed out the complexity of the AEA-induced analgesia. The first synapses in the superficial laminae of the spinal cord dorsal horn represent an important modulatory site in nociceptive transmission and subsequent pain perception. The glutamatergic synaptic transmission at these synapses is strongly modulated by two primary AEA-activated receptors, cannabinoid receptor 1 (CB1) and transient receptor potential vanilloid 1 (TRPV1), both highly expressed on the presynaptic side formed by the endings of primary nociceptive neurons. Activation of these receptors can have predominantly inhibitory (CB1) and excitatory (TRPV1) effects that are further modulated under pathological conditions. In addition, dual AEA-mediated signaling and action may occur in primary sensory neurons and dorsal horn synapses. AEA application causes balanced inhibition and excitation of primary afferent synaptic input on superficial dorsal horn neurons in normal conditions, whereas peripheral inflammation promotes AEA-mediated inhibition. This review focuses mainly on the modulation of synaptic transmission at the spinal cord level and signaling in primary nociceptive neurons by AEA via CB1 and TRPV1 receptors. Furthermore, the spinal analgesic effect in preclinical studies and clinical aspects of AEA-mediated analgesia are considered.

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.

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.

High-coverage lipidomics for functional lipid and pathway analyses

Rapid advances in front-end separation approaches and analytical technologies have accelerated the development of lipidomics, particularly in terms of increasing analytical coverage to encompass an expanding repertoire of lipids within a single analytical approach. Developments in lipid pathway analysis, however, have somewhat lingered behind, primarily due to (1) the lack of coherent alignment between lipid identifiers in common databases versus that generated from experiments, owing to the differing structural resolution of lipids at molecular level that is specific to the analytical approaches adopted by various laboratories; (2) the immense complexity of lipid metabolic relationships that may entail head group changes, fatty acyls modifications of various forms (e.g. elongation, desaturation, oxidation), as well as active remodeling that demands a multidimensional, panoramic view to take into account all possibilities in lipid pathway analyses. Herein, we discuss current efforts undertaken to address these challenges, as well as alternative form of "pathway analyses" that may be particularly useful for uncovering functional lipid interactions under different biological contexts. Consolidating lipid pathway analyses will be indispensable in facilitating the transition of lipidomics from its prior role of phenotype validation to a hypothesis-generating tool that uncovers novel molecular targets to drive downstream mechanistic pursuits under biomedical settings.

Regiochemical Assignment of N-Acylphosphatidylethanolamines (NAPE) by Liquid Chromatography/Electrospray Ionization with Multistage Mass Spectrometry and Its Application to Extracts of Lupin Seeds

1,2-Diacyl-sn-glycero-3-phospho-N-acyl-ethanolamines (NAPE) are low abundance phospholipids but important constituents of intracellular membranes of plant tissues, responsible for generating bioactive N-acylethanolamine (NAE), which participates in several physiological processes such as regulation of seed germination and protection against pathogenic attacks. From an analytical point of view, the critical aspect of these bioactive lipids lies in the determination of fatty acyl chains located in sn-1/sn-2 position on the glycerol backbone (O-linked), along with the amide-bound (N-linked) fatty acyl chain. Here, the identity and occurrence of NAPE in lipid extracts of lupin seeds (Lupinus luteus L.) was assessed by electrospray ionization in negative ion mode upon reversed-phase liquid chromatography (RPLC-ESI) coupled to mass spectrometry (MS) either at high- (i.e., Orbitrap FTMS) or low- (linear ion trap, LIT) resolution/accuracy. Collisional induced dissociation (CID)-tandem MS and MS³ acquisitions of chemically prepared NAPE allowed to unequivocally recognize the N-linked fatty acyl chain and to establish the diagnostic product ions that were successfully applied to identify NAPE in lipid extracts of yellow lupin seeds. The most abundant NAPE species were those containing N-acyl groups C18:1, C18:2; a minor prevalence was found for C16:0, C18:0, and C18:3, and almost the same acyl chains O-linked on the glycerol backbone in several sn-1/sn-2 combinations were observed. The positional isomers of NAPE species were identified as deprotonated molecules ([M-H]^-) at m/z 978.7541 (three isomers 52:3), m/z 980.7694 (two isomers 52:2), m/z 1002.7535 (four isomers 54:5), m/z 1004.7686 (two isomers 54:4), m/z 1006.7837 (two isomers 54:3), and m/z 1008.8026 (single isomer 54:2). The total amount of NAPE in lupin seeds ranged in the interval of 2.00 ± 0.13 mg/g dw, in agreement with other edible legumes. We anticipate our approach to be a robust assessment method potentially applicable to biological extracts containing NAPE species and can provide comprehensive profiles and contents.

Intracellular Ca2+-dependent formation of N-acyl-phosphatidylethanolamines by human cytosolic phospholipase A2ε

N-Acyl-phosphatidylethanolamines (NAPEs) are known to be precursors of bioactive N-acylethanolamines (NAEs), including the endocannabinoid arachidonoylethanolamide (anandamide) and anti-inflammatory palmitoylethanolamide. In mammals, NAPEs are produced by N-acyltransferases, which transfer an acyl chain from the sn-1 position of glycerophospholipid to the amino group of phosphatidylethanolamine (PE). Recently, the ɛ isoform of cytosolic phospholipase A₂ (cPLA₂ɛ) was found to be Ca²⁺-dependent N-acyltransferase. However, it was poorly understood which types of phospholipids serve as substrates in living cells. In the present study, we established a human embryonic kidney 293 cell line, in which doxycycline potently induces human cPLA₂ɛ, and used these cells to analyze endogenous substrates and products of cPLA₂ɛ with liquid chromatography-tandem mass spectrometry. When treated with doxycycline and Ca²⁺ ionophore, the cells produced various species of diacyl- and alkenylacyl-types of NAPEs as well as NAEs in large quantities. Moreover, the levels of diacyl- and alkenylacyl-types of PEs and diacyl-phosphatidylcholines (PCs) decreased, while those of lysophosphatidylethanolamines and lysophosphatidylcholines increased. These results suggested that cPLA₂ɛ Ca²⁺-dependently produces NAPEs by utilizing endogenous diacyl- and alkenylacyl-types of PEs as acyl acceptors and diacyl-type PCs and diacyl-type PEs as acyl donors.

Endocannabinoid System in Hepatic Glucose Metabolism, Fatty Liver Disease, and Cirrhosis

There is growing evidence that glucose metabolism in the liver is in part under the control of the endocannabinoid system (ECS) which is also supported by its presence in this organ. The ECS consists of its cannabinoid receptors (CBRs) and enzymes that are responsible for endocannabinoid production and metabolism. ECS is known to be differentially influenced by the hepatic glucose metabolism and insulin resistance, e.g., cannabinoid receptor type 1(CB₁) antagonist can improve the glucose tolerance and insulin resistance. Interestingly, our own study shows that expression patterns of CBRs are influenced by the light/dark cycle, which is of significant physiological and clinical interest. The ECS system is highly upregulated during chronic liver disease and a growing number of studies suggest a mechanistic and therapeutic impact of ECS on the development of liver fibrosis, especially putting its receptors into focus. An opposing effect of the CBRs was exerted via the CB₁ or CB₂ receptor stimulation. An activation of CB₁ promoted fibrogenesis, while CB₂ activation improved antifibrogenic responses. However, underlying mechanisms are not yet clear. In the context of liver diseases, the ECS is considered as a possible mediator, which seems to be involved in the synthesis of fibrotic tissue, increase of intrahepatic vascular resistance and subsequently development of portal hypertension. Portal hypertension is the main event that leads to complications of the disease. The main complication is the development of variceal bleeding and ascites, which have prognostic relevance for the patients. The present review summarizes the current understanding and impact of the ECS on glucose metabolism in the liver, in association with the development of liver cirrhosis and hemodynamics in cirrhosis and its complication, to give perspectives for development of new therapeutic strategies.

Endocrine disruptors in the diet of male Sparus aurata: Modulation of the endocannabinoid system at the hepatic and central level by Di-isononyl phthalate and Bisphenol A

The increasing manufacture of plastics and their mismanagement has turned plastic into a ubiquitous waste in the marine environment. Among all the substances conforming the plastic items, the effects of a dietary Bisphenol A (BPA) and Di-isononyl phthalate (DiNP) have been evaluated in adult male gilthead sea bream, focusing on their effects in the modulation of the Endocannabinoid System (ECS). In zebrafish, the ECS has been recently chosen as a new target for the activity of some Endocrine Disrupting Chemicals (EDC), since it represents a complex lipid signaling network essential for the well-being of the organisms. The results obtained in gilthead seabream showed that BPA and DiNP altered the structure and the biochemical composition of liver, increasing the presence of lipids and triglycerides and decreasing the glycogen and phospholipids. Moreover, the addition of BPA or DiNP in the gilthead sea bream diet altered the levels of endocannabinoids (EC) and EC-like mediators in the liver. These alterations were also associated to changes at the transcriptomic level of genes involved in lipid biosynthesis and ECS metabolism. At the central level, both BPA and DiNP reduced the expression of the endocannabinoid receptor type I (cnr1) and the neuropeptide Y (npy) as well as the levels of the endocannabinoid Anandamide (AEA), suggesting a downregulation of appetite. The results herein reported highlighted the negative effects of chronic dietary exposure to DiNP or BPA on ECS functions and lipid metabolism of male gilthead sea bream liver, showing a similar disruptive activity of these contaminants at metabolic level. Moreover, the novelty of the biomarkers used evidenced possible innovative endpoints for the development of novel OEDCS test guidelines.

Lipidomic Study of Precursors of Endocannabinoids in Freshwater Bryozoan Pectinatella magnifica

Freshwater bryozoan Pectinatella magnifica was collected from a sand pit (South Bohemia). The total lipids after extraction from lyophilized bryozoans were analyzed using high-performance liquid chromatography/high-resolution negative tandem electrospray mass spectrometry. A total of 19 lipid classes were identified, including N-acyl-substituted phospholipids, that is, N-acylphosphatidylethanolamine and N-acylphosphatidylserine in their plasmenyl forms. Based on gas chromatography/mass spectrometry of 3-pyridylcarbonyl (picolinyl) esters, a very unusual fatty acid was identified, namely 24:7n-3 (all-cis-3,6,9,12,15,18,21-tetracosaheptaenoic acid). The presence of polyunsaturated fatty acids in individual classes is very specific: arachidonic and eicosapentaenoic acids being predominantly bound as amides in N-acyl phospholipids, that is, diacyl-N-acylphosphatidylethanolamines (NAPtdEtn), plasmenyl-N-acylphosphatidyl ethanolamines (PlsNAPtdEtn), diacyl-N-acylphosphatidylserines (NAPtdSer), and plasmenyl-N-acylphosphatidylserines (PlsNAPtdSer). While 24:6n-3 was identified in the sn-2 position of several phospholipids, 24:7n-3 was identified in only two plasmalogens, that is, PlsNAPtdEtn and PlsNAPtdSer. Thanks to the tandem mass spectrometry, we managed to identify the position of all acyl groups in both diacyl- and also in alkenyl-acyl-(plasmenyl) molecular species of N-acylphospholipids. The identification of the molecular species of N-acyl-substituted phosphatidylethanolamine and phosphatidylserine, including their plasmalogen forms, in the freshwater bryozoan P. magnifica has enabled the identification of endogenous cannabinoid precursors.

Peripheral tissue levels and molecular species compositions of N-acyl-phosphatidylethanolamine and its metabolites in mice lacking N-acyl-phosphatidylethanolamine-specific phospholipase D

N-acylethanolamines (NAEs), a class of lipid mediators, are produced from N-acyl-phosphatidylethanolamine (NAPE) by several pathways, including the direct release by NAPE-specific phospholipase D (NAPE-PLD) or the multistep pathway via sn-glycero-3-phospho-N-acylethanolamine (Gp-NAE). Using liquid chromatography-tandem mass spectrometry, we compared peripheral tissue levels of NAPE, Gp-NAE and NAE in NAPE-PLD-deficient (NAPE-PLD-/-) and wild type (WT) mice. NAPE-PLD was suggested to play a major role in the NAPE degradation in heart, kidney, and liver, but not in jejunum, because the NAPE levels except jejunum were significantly higher in NAPE-PLD-/- mice than in WT mice. The deletion of NAPE-PLD failed to alter the NAE levels of these tissues, suggesting its limited role in the NAE production. The enzyme assays with tissue homogenates confirmed the presence of NAPE-PLD-independent pathways in these peripheral tissues. Gp-NAE species having an acyl moiety with 22 carbons and 6 double bonds was enriched in these peripheral tissues. As for sn-2 acyl species of NAPE, 18:2-acyl-containing NAPE species were predominant over 18:1-containing species in heart, liver, and jejunum. Our results show that both molecular species composition of NAPE, NAE and Gp-NAE and their dependencies on Napepld are different among the peripheral tissues, suggesting that each tissue has distinct metabolic pathways and these NAE-containing lipids play tissue-specific roles.

Quantitative analysis of N-acylphosphatidylethanolamine molecular species in rat brain using solid-phase extraction combined with reversed-phase chromatography and tandem mass spectrometry

A novel method for the sensitive and selective identification and quantification of N‐acylphosphatidylethanolamine molecular species was developed. Samples were prepared using a combination of liquid–liquid and solid‐phase extraction, and intact N‐acylphosphatidylethanolamine species were determined by reversed‐phase high‐performance liquid chromatography coupled to positive electrospray tandem mass spectrometry. As a result of their biological functions as precursors for N‐acylethanolamines and as signaling molecules, tissue concentrations of N‐acylphosphatidylethanolamines are very low, and their analysis is additionally hindered by the vast excess of other sample components. Our sample preparation methods are able to selectively separate the analytes of interest from any expected biological interferences. Finally, the highest selectivity is achieved by coupling chromatographic separation and two N‐acyl chain specific selected reaction monitoring scans per analyte, enabling identification of both the N‐acyl chain and the phosphatidylethanolamine moiety. The validated method is suitable for the reliable quantification of N‐acylphosphatidylethanolamine species from rat brain with a lower limit of quantification of 10 pmol/g and a linear range up to 2300 pmol/g. In total, 41 N‐acylphosphatidylethanolamine molecular species with six different N‐acyl chains, amounting to a total concentration of 3 nmol/g, were quantified.

Ion mobility mass spectrometry enhances low-abundance species detection in untargeted lipidomics

We describe a simple method for the detection of low intensity lipid signals in complex tissue samples, based on a combination of liquid chromatography/mass spectrometry and ion mobility mass spectrometry. The method relies on visual and software-assisted analysis of overlapped mobilograms (diagrams of mass-to-charge ratio, m/z, vs drift time, DT) and was successfully applied in untargeted lipidomics analyses of mouse brain tissue to detect relatively small variations in a scarce class of phospholipids (N-acyl phosphatidylethanolamines) generated during neural tissue damage, against a background of hundreds of lipid species. Standard analytical tools, including Principal Component Analysis, failed to detect such changes.

Effects of Fatty Acid Amide Hydrolase (FAAH) Inhibitors in Non-Human Primate Models of Nicotine Reward and Relapse

Inhibition of the enzyme fatty acid amide hydrolase (FAAH) counteracts reward-related effects of nicotine in rats, but it has not been tested for this purpose in non-human primates. Therefore, we studied the effects of the first- and second-generation O-arylcarbamate-based FAAH inhibitors, URB597 (cyclohexyl carbamic acid 3'-carbamoyl-3-yl ester) and URB694 (6-hydroxy-[1,1'-biphenyl]-3-yl-cyclohexylcarbamate), in squirrel monkeys. Both FAAH inhibitors: (1) blocked FAAH activity in brain and liver, increasing levels of endogenous ligands for cannabinoid and α-type peroxisome proliferator-activated (PPAR-α) receptors; (2) shifted nicotine self-administration dose-response functions in a manner consistent with reduced nicotine reward; (3) blocked reinstatement of nicotine seeking induced by reexposure to either nicotine priming or nicotine-associated cues; and (4) had no effect on cocaine or food self-administration. The effects of FAAH inhibition on nicotine self-administration and nicotine priming-induced reinstatement were reversed by the PPAR-α antagonist, MK886. Unlike URB597, which was not self-administered by monkeys in an earlier study, URB694 was self-administered at a moderate rate. URB694 self-administration was blocked by pretreatment with an antagonist for either PPAR-α (MK886) or cannabinoid CB1 receptors (rimonabant). In additional experiments in rats, URB694 was devoid of THC-like or nicotine-like interoceptive effects under drug-discrimination procedures, and neither of the FAAH inhibitors induced dopamine release in the nucleus accumbens shell--consistent with their lack of robust reinforcing effects in monkeys. Overall, both URB597 and URB694 show promise for the initialization and maintenance of smoking cessation because of their ability to block the rewarding effects of nicotine and prevent nicotine priming-induced and cue-induced reinstatement.

Identification of prostamides, fatty acyl ethanolamines, and their biosynthetic precursors in rabbit cornea

Arachidonoyl ethanolamine (anandamide) and pros-taglandin ethanolamines (prostamides) are biologically active derivatives of arachidonic acid. Although available through different precursor phospholipids, there is considerable overlap between the biosynthetic pathways of arachidonic acid-derived eicosanoids and anandamide-derived prostamides. Prostamides exhibit physiological actions and are involved in ocular hypotension, smooth muscle contraction, and inflammatory pain. Although topical application of bimatoprost, a structural analog of prostaglandin F2α ethanolamide (PGF2α-EA), is currently a first-line treatment for ocular hypertension, the endogenous production of prostamides and their biochemical precursors in corneal tissue has not yet been reported. In this study, we report the presence of anandamide, palmitoyl-, stearoyl-, α-linolenoyl docosahexaenoyl-, linoleoyl-, and oleoyl-ethanolamines in rabbit cornea, and following treatment with anandamide, the formation of PGF2α-EA, PGE2-EA, PGD2-EA by corneal extracts (all analyzed by LC/ESI-MS/MS). A number of N-acyl phosphatidylethanolamines, precursors of anandamide and other fatty acyl ethanolamines, were also identified in corneal lipid extracts using ESI-MS/MS. These findings suggest that the prostamide and fatty acid ethanolamine pathways are operational in the cornea and may provide valuable insight into corneal physiology and their potential influence on adjacent tissues and the aqueous humor.

A fatty gut feeling

The absorptive epithelium of the proximal small intestine converts oleic acid released during fat digestion into oleoylethanolamide (OEA), an endogenous high-affinity agonist of peroxisome proliferator-activated receptor-α (PPAR-α). OEA interacts with this receptor to cause a state of satiety characterized by prolonged inter-meal intervals and reduced feeding frequency. The two main branches of the autonomic nervous system, sympathetic and parasympathetic, contribute to this effect: the former by enabling OEA mobilization in the gut and the latter by relaying the OEA signal to brain structures, such as the hypothalamus, that are involved in feeding regulation. OEA signaling may be a key component of the physiological system devoted to the monitoring of dietary fat intake, and its dysfunction might contribute to overweight and obesity.

Pharmacological characterization of the peripheral FAAH inhibitor URB937 in female rodents: interaction with the Abcg2 transporter in the blood-placenta barrier

BACKGROUND AND PURPOSE

URB937 is a peripherally restricted inhibitor of the anandamide-deactivating enzyme fatty-acid amide hydrolase (FAAH). Despite its limited access to the CNS, URB937 produces marked antinociceptive effects in rodents. URB937 is actively extruded from the CNS by the ATP-binding cassette (ABC) membrane transporter, Abcg2. Tissue Abcg2 levels are markedly different between males and females, and this transporter is known to limit the access of xenobiotics to the fetoplacental unit in gestating female rodents. In the present study, we investigated the tissue distribution and antinociceptive properties of URB937 in female mice and rats.

EXPERIMENTAL APPROACH

We studied the systemic disposition of URB937 in female mice and the antinociceptive effects of this compound in models of visceral (acetic acid-induced writhing) and inflammatory nociception (carrageenan-induced hyperalgesia) in female mice and rats. Furthermore, we evaluated the interaction of URB937 with the blood-placenta barrier in gestating mice and rats.

KEY RESULTS

Abcg2 restricted the access of URB937 to the CNS of female mice and rats. Nevertheless, URB937 produced a high degree of antinociception in female mice and rats in models of visceral and inflammatory pain. Moreover, the compound displayed a restricted access to placental and fetal tissues in pregnant mice and rats.

CONCLUSIONS AND IMPLICATIONS

Peripheral FAAH blockade with URB937 reduces nociception in female mice and rats, as previously shown for males of the same species. In female mice and rats, Abcg2 limits the access of URB937, not only to the CNS, but also to the fetoplacental unit. LINKED ARTICLES This article is part of a themed section on Cannabinoids. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.167.issue-8.

PPARα regulates cholinergic-driven activity of midbrain dopamine neurons via a novel mechanism involving α7 nicotinic acetylcholine receptors

Ventral tegmental area dopamine neurons control reward-driven learning, and their dysregulation can lead to psychiatric disorders. Tonic and phasic activity of these dopaminergic neurons depends on cholinergic tone and activation of nicotinic acetylcholine receptors (nAChRs), particularly those containing the β2 subunit (β2*-nAChRs). Nuclear peroxisome proliferator-activated receptors type-α (PPARα) tonically regulate β2*-nAChRs and thereby control dopamine neuron firing activity. However, it is unknown how and when PPARα endogenous ligands are synthesized by dopamine cells. Using ex vivo and in vivo electrophysiological techniques combined with biochemical and behavioral analysis, we show that activation of α7-nAChRs increases in the rat VTA both the tyrosine phosphorylation of the β2 subunit of nAChRs and the levels of two PPARα endogenous ligands in a Ca(2+)-dependent manner. Accordingly, in vivo production of endogenous PPARα ligands, triggered by α7-nAChR activation, blocks in rats nicotine-induced increased firing activity of dopamine neurons and displays antidepressant-like properties. These data demonstrate that endogenous PPARα ligands are effectors of α7-nAChRs and that their neuromodulatory properties depend on phosphorylation of β2*-nAChRs on VTA dopamine cells. This reveals an autoinhibitory mechanism aimed at reducing dopamine cell overexcitation engaged during hypercholinergic drive. Our results unveil important physiological functions of nAChR/PPARα signaling in dopamine neurons and how behavioral output can change after modifications of this signaling pathway. Overall, the present study suggests PPARα as new therapeutic targets for disorders associated with unbalanced dopamine-acetylcholine systems.

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.

Covalent modification of lipids and proteins in rat hepatocytes and in vitro by thioacetamide metabolites

Thioacetamide (TA) is a well-known hepatotoxin in rats. Acute doses cause centrilobular necrosis and hyperbilirubinemia while chronic administration leads to biliary hyperplasia and cholangiocarcinoma. Its acute toxicity requires its oxidation to a stable S-oxide (TASO) that is oxidized further to a highly reactive S,S-dioxide (TASO(2)). To explore possible parallels among the metabolism, covalent binding, and toxicity of TA and thiobenzamide (TB), we exposed freshly isolated rat hepatocytes to [(14)C]-TASO or [(13)C(2)D(3)]-TASO. TLC analysis of the cellular lipids showed a single major spot of radioactivity that mass spectral analysis showed to consist of N-acetimidoyl PE lipids having the same side chain composition as the PE fraction from untreated cells; no carbons or hydrogens from TASO were incorporated into the fatty acyl chains. Many cellular proteins contained N-acetyl- or N-acetimidoyl lysine residues in a 3:1 ratio (details to be reported separately). We also oxidized TASO with hydrogen peroxide in the presence of dipalmitoyl phosphatidylenthanolamine (DPPE) or lysozyme. Lysozyme was covalently modified at five of its six lysine side chains; only acetamide-type adducts were formed. DPPE in liposomes also gave only amide-type adducts, even when the reaction was carried out in tetrahydrofuran with only 10% water added. The exclusive formation of N-acetimidoyl PE in hepatocytes means that the concentration or activity of water must be extremely low in the region where TASO(2) is formed, whereas at least some of the TASO(2) can hydrolyze to acetylsulfinic acid before it reacts with cellular proteins. The requirement for two sequential oxidations to produce a reactive metabolite is unusual, but it is even more unusual that a reactive metabolite would react with water to form a new compound that retains a high degree of chemical reactivity toward biological nucleophiles. The possible contribution of lipid modification to the hepatotoxicity of TA/TASO remains to be determined.

Breast cancer cells adapt to metabolic stress by increasing ethanolamine phospholipid synthesis and CTP:ethanolaminephosphate cytidylyltransferase-Pcyt2 activity

The significance of phosphatidylethanolamine (PE) in breast cancer cell metabolism was investigated under stress conditions caused by serum deficiency. Serum deficient MCF-7 cells adapt to stress conditions by increasing synthesis and content of PE and diacylglycerol (DAG). The biosynthesis of PE from DAG and ethanolamine was regulated at the level of formation of CDP-ethanolamine, the metabolic step catalyzed by Pcyt2. The catalytic activity of Pcyt2 was elevated 2-3-fold, yet the enzyme remained rate-limiting in serum-deficient cells. Contributions to the elevated Pcyt2 activity included transcriptional and translational components. The mRNA levels of two splice variants, Pcyt2α and Pcyt2β, were 1.5-3-fold higher in deficient cells. The total amounts of Pcyt2 and Pcyt2α proteins were similarly elevated 1.5-2.5-fold. In vivo [γ(32)Pi] radiolabeling revealed that Pcyt2 was additionally regulated by phosphorylation. Under unfavorable metabolic conditions, both endogenous and His/Myc-tagged Pcyt2 were increasingly phosphorylated at Ser residues. The results established that elevated DAG formation and the increased activity of the rate-regulatory enzyme Pcyt2 were critical modulators of the PE Kennedy pathway, and total PE content in serum deprived breast cancer cells. Therefore, as an essential gene sensitive to nutritional microenvironment, Pcyt2 could represent a legitimate target in novel metabolic strategies for cancer.

Putative N-acylphosphatidylethanolamine synthase from Arabidopsis thaliana is a lysoglycerophospholipid acyltransferase

AT1G78690, a gene found in Arabidopsis thaliana, has been reported to encode a N-acyltransferase that transfers an acyl chain from acyl-CoA to the headgroup of phosphatidylethanolamine (PE) to form N-acylphosphatidylethanolamine (N-acyl-PE). Our investigation suggests that At1g78690p is not a PE-dependent N-acyltransferase but is instead a lysoglycerophospholipid O-acyltransferase. We overexpressed AT1G78690 in Escherichia coli, extracted the cellular lipids, and identified the accumulating glycerophospholipid as acylphosphatidylglycerol (acyl-PG). Electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-MS) analysis yielded [M - H](-) ions, corresponding by exact mass to acyl-PG rather than N-acyl-PE. Collision-induced dissociation mass spectrometry (MS/MS) yielded product ions consistent with acyl-PG. In addition, in vitro enzyme assays using both (32)P- and (14)C-radiolabeled substrates showed that AT1G78690 acylates 1-acyllysophosphatidylethanolamine (1-acyllyso-PE) and 1-acyllysophosphatidylglycerol (1-acyllyso-PG), but not PE or phosphatidylglycerol (PG), to form a diacylated product that co-migrates with PE and PG, respectively. We analyzed the diacylated product formed by AT1G78690 using a combination of base hydrolysis, phospholipase D treatment, ESI-MS, and MS/MS to show that AT1G78690 acylates the sn-2-position of 1-acyllyso-PE and 1-acyllyso-PG.

N-Docosahexaenoylethanolamide promotes development of hippocampal neurons

DHA (docosahexaenoic acid, C22:6,n-3) has been shown to promote neurite growth and synaptogenesis in embryonic hippocampal neurons, supporting the importance of DHA known for hippocampus-related learning and memory function. In the present study, we demonstrate that DHA metabolism to DEA (N-docosahexaenoylethanolamide) is a significant mechanism for hippocampal neuronal development, contributing to synaptic function. We found that a fatty acid amide hydrolase inhibitor URB597 potentiates DHA-induced neurite growth, synaptogenesis and synaptic protein expression. Active metabolism of DHA to DEA was observed in embryonic day 18 hippocampal neuronal cultures, which was increased further by URB597. Synthetic DEA promoted hippocampal neurite growth and synaptogenesis at substantially lower concentrations in comparison with DHA. DEA-treated neurons increased the expression of synapsins and glutamate receptor subunits and exhibited enhanced glutamatergic synaptic activity, as was the case for DHA. The DEA level in mouse fetal hippocampi was altered according to the maternal dietary supply of n-3 fatty acids, suggesting that DEA formation is a relevant in vivo process responding to the DHA status. In conclusion, DHA metabolism to DEA is a significant biochemical mechanism for neurite growth, synaptogenesis and synaptic protein expression, leading to enhanced glutamatergic synaptic function. The novel DEA-dependent mechanism offers a new molecular insight into hippocampal neurodevelopment and function.

Effect of dietary krill oil supplementation on the endocannabinoidome of metabolically relevant tissues from high-fat-fed mice

Background

Omega-3 polyunsaturated fatty acids (ω-3-PUFA) are known to ameliorate several metabolic risk factors for cardiovascular disease, and an association between elevated peripheral levels of endogenous ligands of cannabinoid receptors (endocannabinoids) and the metabolic syndrome has been reported. We investigated the dose-dependent effects of dietary ω-3-PUFA supplementation, given as krill oil (KO), on metabolic parameters in high fat diet (HFD)-fed mice and, in parallel, on the levels, in inguinal and epididymal adipose tissue (AT), liver, gastrocnemius muscle, kidneys and heart, of: 1) the endocannabinoids, anandamide and 2-arachidonoylglycerol (2-AG), 2) two anandamide congeners which activate PPARα but not cannabinoid receptors, N-oleoylethanolamine and N-palmitoylethanolamine, and 3) the direct biosynthetic precursors of these compounds.

Methods

Lipids were identified and quantified using liquid chromatography coupled to atmospheric pressure chemical ionization single quadrupole mass spectrometry (LC-APCI-MS) or high resolution ion trap-time of flight mass spectrometry (LC-IT-ToF-MS).

Results

Eight-week HFD increased endocannabinoid levels in all tissues except the liver and epididymal AT, and KO reduced anandamide and/or 2-AG levels in all tissues but not in the liver, usually in a dose-dependent manner. Levels of endocannabinoid precursors were also generally down-regulated, indicating that KO affects levels of endocannabinoids in part by reducing the availability of their biosynthetic precursors. Usually smaller effects were found of KO on OEA and PEA levels.

Conclusions

Our data suggest that KO may promote therapeutic benefit by reducing endocannabinoid precursor availability and hence endocannabinoid biosynthesis.

An amyloid β42-dependent deficit in anandamide mobilization is associated with cognitive dysfunction in Alzheimer's disease

The endocannabinoids and their attending cannabinoid (CB)(1) receptors have been implicated in the control of cognition, but their possible roles in dementias are still unclear. In the present study, we used liquid chromatography/mass spectrometry to conduct an endocannabinoid-targeted lipidomic analysis of postmortem brain samples from 38 Alzheimer's disease (AD) patients and 17 control subjects, matched for age and postmortem interval. The analysis revealed that midfrontal and temporal cortex tissue from AD patients contains, relative to control subjects, significantly lower levels of the endocannabinoid anandamide and its precursor 1-stearoyl, 2-docosahexaenoyl-sn-glycero-phosphoethanolamine-N-arachidonoyl (NArPE). No such difference was observed with the endocannabinoid 2-arachidonoyl-sn-glycerol or 15 additional lipid species. In AD patients, but not in control subjects, statistically detectable positive correlations were found between (1) anandamide content in midfrontal cortex and scores of the Kendrick's Digit Copy test (p = 0.004, r = 0.81; n = 10), which measures speed of information processing; and (2) anandamide content in temporal cortex and scores of the Boston Naming test (p = 0.027, r = 0.52; n = 18), which assesses language facility. Furthermore, anandamide and NArPE levels in midfrontal cortex of the study subjects inversely correlated with levels of the neurotoxic amyloid peptide, amyloid β-protein (Aβ)(42), while showing no association with Aβ(40) levels, amyloid plaque load or tau protein phosphorylation. Finally, high endogenous levels of Aβ(42) in Swedish mutant form of amyloid precursor protein (APP(SWE))/Neuro-2a cells directly reduced anandamide and NArPE concentrations in cells lysates. The results suggest that an Aβ(42)-dependent impairment in brain anandamide mobilization contributes to cognitive dysfunction in AD.

Diacylglycerol lipase-alpha and -beta control neurite outgrowth in neuro-2a cells through distinct molecular mechanisms

The endocannabinoid 2-arachidonoyl-sn-glycerol (2-AG) is produced through hydrolysis of 1,2-diacyl-sn-glycerol (DAG), which is catalyzed by DAG lipase (DGL). Two DGL isoforms have been molecularly cloned, but their respective roles in endocannabinoid signaling have not been fully elucidated. Here, we report that DGL-α and DGL-β may contribute to all-trans-retinoic acid (RA)-induced neurite outgrowth in neuroblastoma Neuro-2a cells through distinct mechanisms. RA-induced differentiation of Neuro-2a cells was associated with elevations of cellular 2-AG levels and DGL activity, which were accompanied by temporally separated transcription of DGL-α and DGL-β mRNA. Knockdown of either DGL-α or DGL-β expression attenuated neurite outgrowth, which indicates that both isoforms contribute to neuritogenesis. Immunostaining experiments showed that DGL-β is localized to perinuclear lipid droplets, whereas DGL-α is found on plasma membranes. After RA-induced differentiation, both DGL-α- and DGL-β-green fluorescent protein were distributed also in neurites but in distinguishable patterns. Overexpression of either DGL-α or DGL-β increased the number of neurite-bearing cells, but DGL-β caused substantially larger morphological changes than DGL-α did. Finally, the cannabinoid-1 antagonist rimonabant (1 μM) inhibited DGL-α-induced neuritogenesis, whereas it had no such effect on DGL-β-induced morphological differentiation. The results indicate that RA-induced DGL expression is required for neurite outgrowth of Neuro-2a cells. The findings further suggest that DGL-α and -β may regulate neurite outgrowth by engaging temporally and spatially distinct molecular pathways.

Plasma lipidomics reveals potential prognostic signatures within a cohort of cystic fibrosis patients

Cystic fibrosis (CF) is associated with abnormal lipid metabolism. We have recently shown variations in plasma levels of several phosphatidylcholine (PC) and lysophopshatidylcholine (LPC) species related to disease severity in CF patients. Here our goal was to search for blood plasma lipid signatures characteristic of CF patients bearing the same mutation (F508del) and different phenotypes, and to study their correlation with forced expiratory volume in 1 s (FEV1) and Pseudomonas aeruginosa chronic infection, evaluated at the time of testing (t = 0) and three years later (t = 3). Samples from 44 F508del homozygotes were subjected to a lipidomic approach based on LC-ESI-MS. Twelve free fatty acids were positively correlated with FEV1 at t = 0 (n = 29). Four of them (C20:3n-9, C20:5n-3, C22:5n-3, and C22:6n-3) were also positively correlated with FEV1 three years later, along with PC(32:2) and PC(36:4) (n = 31). Oleoylethanolamide (OEA) was negatively correlated with FEV1 progression (n = 17). Chronically infected patients at t = 0 showed lower PC(32:2), PC(38:5), and C18:3n-3 and higher cholesterol, cholesterol esters, and triacylglycerols (TAG). Chronically infected patients at t = 3 showed significantly lower levels of LPC(18:0). These results suggest a potential prognostic value for some lipid signatures in, to our knowledge, the first longitudinal study aimed at identifying lipid biomarkers for CF.

New lipidomic approaches in cystic fibrosis

Lipid analysis has been a crucial source of information in cystic fibrosis (CF). New methodologies for qualitative and quantitative lipidomics allow evaluation of a large number of samples, of special interest in patient screening for diagnostic and prognostic biological markers, as well as in cell physiology. In this chapter, two new complementary approaches are described: matrix-assisted laser desorption coupled to time of flight (MALDI-TOF-ClinProTools™) and liquid chromatography coupled to ion trap mass spectrometry (LC-MS( n )). MALDI-TOF-ClinProTools™ offers a large unbiased screening for the discovery of potential lipid alterations in diseased patients. LC-MS( n ) represents a state-of-the-art lipidomic tool for the identification and quantification of such alterations. The combination of both may open new perspectives in the quest for lipids participating in CF pathogenesis, therapy targets, and biomarkers.

Anandamide suppresses pain initiation through a peripheral endocannabinoid mechanism

Peripheral cannabinoid receptors exert a powerful inhibitory control over pain initiation, but the endocannabinoid signal that normally engages this intrinsic analgesic mechanism is unknown. To address this question, we developed a peripherally restricted inhibitor (URB937) of fatty acid amide hydrolase (FAAH), the enzyme responsible for the degradation of the endocannabinoid anandamide. URB937 suppressed FAAH activity and increased anandamide levels outside the rodent CNS. Despite its inability to access brain and spinal cord, URB937 attenuated behavioral responses indicative of persistent pain in rodent models of peripheral nerve injury and inflammation and prevented noxious stimulus-evoked neuronal activation in spinal cord regions implicated in nociceptive processing. CB₁ cannabinoid receptor blockade prevented these effects. These results suggest that anandamide-mediated signaling at peripheral CB₁ receptors controls the access of pain-related inputs to the CNS. Brain-impenetrant FAAH inhibitors, which strengthen this gating mechanism, might offer a new approach to pain therapy.

Enzymological studies on the biosynthesis of N-acylethanolamines

Ethanolamides of different long-chain fatty acids constitute a class of endogenous lipid molecules generally called N-acylethanolamines (NAEs). They contain N-arachidonoylethanolamine (anandamide), N-palmitoylethanolamine, and N-oleoylethanolamine, which receive considerable attention because of their actions as an endogenous cannabinoid receptor ligand (endocannabinoid), an anti-inflammatory substance, and an appetite-suppressing substance, respectively. Identification of their biosynthetic routes in animal tissues and molecular characterization of the enzymes involved are essential for better understanding of physiological importance of NAEs as well as development of enzyme inhibitors as possible therapeutic drugs. In the classical "transacylation-phosphodiesterase pathway", NAEs are formed from glycerophospholipids via N-acylphosphatidylethanolamine (NAPE), an unusual derivative of phosphatidylethanolamine with a third acyl chain attached to the amino group, by sequential catalyses by Ca(2+)-dependent N-acyltransferase and NAPE-hydrolyzing phospholipase D. However, recent studies reveal that NAE-generating pathways are more complex than presumed before. In this review article, we will focus on recent findings regarding mammalian enzymes that are involved or might be involved in the biosynthesis of NAEs.

Lipid profiling reveals tissue-specific differences for ethanolamide lipids in mice lacking fatty acid amide hydrolase

N-Acylethanolamines (NAE) are fatty acid derivatives, some of which function as endocannabinoids in mammals. NAE metabolism involves common (phosphatidylethanolamines, PEs) and uncommon (N-acylphosphatidylethanolamines, NAPEs) membrane phospholipids. Here we have identified and quantified more than a hundred metabolites in the NAE/endocannabinoid pathway in mouse brain and heart tissues, including many previously unreported molecular species of NAPE. We found that brain tissue of mice lacking fatty acid amide hydrolase (FAAH (-/-)) had elevated PE and NAPE molecular species in addition to elevated NAEs, suggesting that FAAH activity participates in the overall regulation of this pathway. This perturbation of the NAE pathway in brain was not observed in heart tissue of FAAH (-/-) mice, indicating that metabolic regulation of the NAE pathway differs in these two organs and the metabolic enzymes that catabolize NAEs are most likely differentially distributed and/or regulated. Targeted lipidomics analysis, like that presented here, will continue to provide important insights into cellular lipid signaling networks.

A liquid chromatography-tandem mass spectrometry method for measurement of N-modified phosphatidylethanolamines

N-Acyl phosphatidylethanolamines (NAPEs) are synthesised in response to stress in a variety of organisms from bacteria to humans. More recently, nonenzymatic modification of the ethanolamine headgroup of phosphatidylethanolamine (PE) by various aldehydes, including levuglandins/isoketals (which are gamma-ketoaldehydes [gammaKAs] derived from arachidonic acid), has also been demonstrated. The levels of these various N-modified PEs formed during stress and their biological significance remain to be fully characterized. Such studies require an accurate, facile, and cost-effective method for quantifying N-modified PEs. Previously, NAPE and some of the nonenzymatically N-modified PE species have been quantified by mass spectrometry after hydrolysis to their constituent N-acylethanolamine by enzymatic hydrolysis, most typically with Streptomyces chromofuscus phospholipase D. However, enzymatic hydrolysis is not cost-effective for routine analysis of a large number of samples, and hydrolytic efficiency may vary for different N-modified PEs, making quantitation more difficult. Therefore, we sought a robust and inexpensive chemical hydrolysis approach. Methylamine (CH(3)NH(2))-mediated deacylation has previously been used in headgroup analysis of phosphatidylinositol phosphates. Therefore, we developed an accurate assay for NAPEs and gammaKA-PEs using CH(3)NH(2)-mediated deacylation and quantitation of the resulting glycerophospho-N-modified ethanolamines by liquid chromatography-tandem mass spectrometry.

Evidence for a role of endocannabinoids, astrocytes and p38 phosphorylation in the resolution of postoperative pain

BACKGROUND

An alarming portion of patients develop persistent or chronic pain following surgical procedures, but the mechanisms underlying the transition from acute to chronic pain states are not fully understood. In general, endocannabinoids (ECBs) inhibit nociceptive processing by stimulating cannabinoid receptors type 1 (CB(1)) and type 2 (CB(2)). We have previously shown that intrathecal administration of a CB(2) receptor agonist reverses both surgical incision-induced behavioral hypersensitivity and associated over-expression of spinal glial markers. We therefore hypothesized that endocannabinoid signaling promotes the resolution of acute postoperative pain by modulating pro-inflammatory signaling in spinal cord glial cells.

METHODOLOGY/PRINCIPAL FINDINGS

To test this hypothesis, rats receiving paw incision surgery were used as a model of acute postoperative pain that spontaneously resolves. We first characterized the concentration of ECBs and localization of CB(1) and CB(2) receptors in the spinal cord following paw incision. We then administered concomitant CB(1) and CB(2) receptor antagonists/inverse agonists (AM281 and AM630, 1 mg x kg(-1) each, i.p.) during the acute phase of paw incision-induced mechanical allodynia and evaluated the expression of glial cell markers and phosphorylated p38 (a MAPK associated with inflammation) in the lumbar dorsal horn. Dual blockade of CB(1) and CB(2) receptor signaling prevented the resolution of postoperative allodynia and resulted in persistent over-expression of spinal Glial Fibrillary Acidic Protein (GFAP, an astrocytic marker) and phospho-p38 in astrocytes. We provide evidence for the functional significance of these astrocytic changes by demonstrating that intrathecal administration of propentofylline (50 microg, i.t.) attenuated both persistent behavioral hypersensitivity and over-expression of GFAP and phospho-p38 in antagonist-treated animals.

CONCLUSIONS/SIGNIFICANCE

Our results demonstrate that endocannabinoid signaling via CB(1) and CB(2) receptors is necessary for the resolution of paw incision-induced behavioral hypersensitivity and for the limitation of pro-inflammatory signaling in astrocytes following surgical insult. Our findings suggest that therapeutic strategies designed to enhance endocannabinoid signaling may prevent patients from developing persistent or chronic pain states following surgery.

Effect of dietary fat on endocannabinoids and related mediators: consequences on energy homeostasis, inflammation and mood

Among the several known fatty acid-derived chemical signals, the endogenous ligands of cannabinoid receptors type-1 and -2, two G-protein-coupled receptors involved in several aspects of mammalian physiology and pathology, are perhaps those the levels of which have proven to be most sensitive to the fatty acid composition of the diet. The two most studied such ligands, known as endocannabinoids, are N-arachidonoyl-ethanolamine and 2-archidonoylglycerol, and are found in tissues together with other N-acyl-ethanolamines and 2-acylglycerols, not all of which activate the cannabinoid receptors, although several of them do exhibit important pharmacological effects. In this review article, we describe literature data indicating that the tissue concentrations of the endocannabinoids and related signalling molecules, and hence the activity of the respective receptors, can be modulated by modifying the fatty acid composition of the diet, and particularly its content in long chain PUFAs or in long chain PUFA precursors. We also discuss the potential impact of these diet-induced changes of endocannabinoid tone on three of the major pathological conditions in which cannabinoid receptors have been involved, that is metabolic dysfunctions, inflammation and affective disorders.

N-acylethanolamine metabolism with special reference to N-acylethanolamine-hydrolyzing acid amidase (NAAA)

N-acylethanolamines (NAEs) constitute a class of bioactive lipid molecules present in animal and plant tissues. Among the NAEs, N-arachidonoylethanolamine (anandamide), N-palmitoylethanolamine, and N-oleoylethanolamine attract much attention due to cannabimimetic activity as an endocannabinoid, anti-inflammatory and analgesic activities, and anorexic activity, respectively. In mammalian tissues, NAEs are formed from glycerophospholipids through the phosphodiesterase-transacylation pathway consisting of Ca(2+)-dependent N-acyltransferase and N-acylphosphatidylethanolamine-hydrolyzing phospholipase D. Recent studies revealed the presence of alternative pathways and enzymes responsible for the NAE formation. As for the degradation of NAEs, fatty acid amide hydrolase (FAAH), which hydrolyzes NAEs to fatty acids and ethanolamine, plays a central role. However, a lysosomal enzyme referred to as NAE-hydrolyzing acid amidase (NAAA) also catalyzes the same reaction and may be a new target for the development of therapeutic drugs. In this article we discuss recent progress in the studies on the enzymes involved in the biosynthesis and degradation of NAEs with special reference to NAAA.

Dietary docosahexaenoic acid supplementation alters select physiological endocannabinoid-system metabolites in brain and plasma

The endocannabinoid metabolome consists of a growing, (patho)physiologically important family of fatty-acid derived signaling lipids. Diet is a major source of fatty acid substrate for mammalian endocannabinoid biosynthesis. The principal long-chain PUFA found in mammalian brain, docosahexaenoic acid (DHA), supports neurological function, retinal development, and overall health. The extent to which dietary DHA supplementation influences endocannabinoid-related metabolites in brain, within the context of the circulating endocannabinoid profile, is currently unknown. We report the first lipidomic analysis of acute 2-week DHA dietary supplementation effects on the physiological state of 15 fatty-acid, N-acylethanolamine, and glycerol-ester endocannabinoid metabolome constituents in murine plasma and brain. The DHA-rich diet markedly elevated DHA, eicosapentaenoic acid, 2-eicosapentanoylglycerol (EPG), and docosahexanoylethanolamine in both compartments. Dietary DHA enhancement generally affected the synthesis of the N-acyl-ethanolamine and glycerol-ester metabolites to favor the docosahexaenoic and eicosapentaenoic vs. arachidonoyl and oleoyl homologs in both brain and plasma. The greater overall responsiveness of the endocannabinoid metabolome in plasma versus brain may reflect a more circumscribed homeostatic response range of brain lipids to dietary DHA supplementation. The ability of short-term DHA enhancement to modulate select constituents of the physiological brain and plasma endocannabinoid metabolomes carries metabolic and therapeutic implications.

A second generation of carbamate-based fatty acid amide hydrolase inhibitors with improved activity in vivo

The fatty acid ethanolamides are a class of signaling lipids that include agonists at cannabinoid and alpha type peroxisome proliferator-activated receptors (PPARalpha). In the brain, these compounds are primarily hydrolyzed by the intracellular serine enzyme fatty acid amide hydrolase (FAAH). O-aryl carbamate FAAH inhibitors such as URB597 are being evaluated clinically for the treatment of pain and anxiety, but interactions with carboxylesterases in liver might limit their usefulness. Here we explore two strategies aimed at overcoming this limitation. Lipophilic N-terminal substitutions, which enhance FAAH recognition, yield potent inhibitors but render such compounds susceptible to attack by broad-spectrum hydrolases and inactive in vivo. By contrast, polar electron-donating O-aryl substituents, which decrease carbamate reactivity, yield compounds, such as URB694, that are highly potent FAAH inhibitors in vivo and less reactive with off-target carboxylesterases. The results suggest that an approach balancing inhibitor reactivity with target recognition produces FAAH inhibitors that display significantly improved drug-likeness.

A novel lipidomic strategy reveals plasma phospholipid signatures associated with respiratory disease severity in cystic fibrosis patients

The aim of this study was to search for lipid signatures in blood plasma from cystic fibrosis (CF) patients using a novel MALDI-TOF-ClinProTools strategy, initially developed for protein analysis, and thin layer chromatography coupled to MALDI-TOF (TLC-MALDI). Samples from 33 CF patients and 18 healthy children were subjected to organic extraction and column chromatography separation of lipid classes. Extracts were analyzed by MALDI-TOF, ion signatures were compared by the ClinProTools software and by parallel statistical analyses. Relevant peaks were identified by LC-MSn. The ensemble of analyses provided 11 and 4 peaks differentially displayed in CF vs healthy and in mild vs severe patients respectively. Ten ions were significantly decreased in all patients, corresponding to 4 lysophosphatidylcholine (18:0, 18:2, 20:3, and 20:5) and 6 phosphatidylcholine (36:5, O-38:0, 38:4, 38:5, 38:6, and P-40:1) species. One sphingolipid, SM(d18:0), was significantly increased in all patients. Four PC forms (36:3, 36:5, 38:5, and 38:6) were consistently downregulated in severe vs mild patients. These observations were confirmed by TLC-MALDI. These results suggest that plasma phospholipid signatures may be able to discriminate mild and severe forms of CF, and show for the first time MALDI-TOF-ClinProTools as a suitable methodology for the search of lipid markers in CF.

Lipidomic analysis of endocannabinoid metabolism in biological samples

The endocannabinoids are signaling lipids present in many living organisms. They activate G protein-coupled cannabinoid receptors to modulate a broad range of biological processes that include emotion, cognition, inflammation and reproduction. The endocannabinoids are embedded in an interconnected network of cellular lipid pathways, the regulation of which is likely to control the strength and duration of endocannabinoid signals. Therefore, physiopathological or pharmacological perturbations of these pathways may indirectly affect endocannabinoid activity and, vice versa, endocannabinoid activity may influence lipid pathways involved in other metabolic and signaling events. Recent progress in liquid chromatography and mass spectrometry has fueled the development of targeted lipidomic approaches, which allow researchers to examine complex lipid interactions in cells and gain a broader view of the endocannabinoid system. Here, we review these new developments from the perspective of our laboratory's experience in the field.

Enzymatic formation of anandamide

In animal tissues anandamide and other bioactive N-acylethanolamines are principally produced from glycerophospholipids through the transacylation-phosphodiesterase pathway consisting of two enzymatic reactions. The first reaction is the generation of N-acylphosphatidylethanolamine (NAPE) by transferring an acyl group esterified at sn-1 position of glycerophospholipid to the amino group of phosphatidylethanolamine. This reaction is catalyzed by Ca(2+)-dependent N-acyltransferase. The discovery of Ca(2+)-independent N-acyltransferase revealed the existence of plural enzymes which are capable of catalyzing this reaction. The second reaction is the release of N-acylethanolamine from NAPE catalyzed by NAPE-hydrolyzing phospholipase D (NAPE-PLD). The enzyme belongs to the metallo-beta-lactamase family and specifically hydrolyzes NAPEs. Recent studies, including analysis of NAPE-PLD-deficient mice, led to the discovery of NAPE-PLD-independent pathways for the anandamide biosynthesis.

N-acylethanolamines, anandamide and food intake

Anandamide and the other N-acylethanolamines, e.g. oleoylethanolamide (OEA), palmitoylethanolamide (PEA), and linoleoylethanolamide (LEA), may be formed by several enzymatic pathways from their precursors, which are the N-acylated ethanolamine phospholipids. The exact enzymatic pathways involved in their biosynthesis in specific tissues are not clarified. It has been suggested that endogenous anandamide could stimulate food intake by activation of cannabinoid receptors in the brain and/or in the intestinal tissue. On the other hand, endogenous OEA and PEA have been suggested to inhibit food intake by acting on receptors in the intestine. At present, there is no clear role for endogenous anandamide in controlling food intake via cannabinoid receptors, neither centrally nor in the gastrointestinal tract. However, OEA, PEA and perhaps also LEA may be involved in regulation of food intake by selective prolongation of feeding latency and post-meal interval. These N-acylethanolamines seem to be formed locally in the intestine, where they can activate PPARalpha located in close proximity to their site of synthesis. The rapid onset of OEA response and its reliance on an intact vagus nerve suggests that activation of PPARalpha does not result in formation of a transcription-dependent signal but must rely on an unidentified non-genomic signal that translates to activation of vagal afferents. Whether GPR119, TRPV1 and/or intestinal ceramide levels also contribute to the anorectic and weight-reducing effect of exogenous OEA is less clear. Prolonged intake of dietary fat (45 energy%) may promote over-consumption of food by decreasing the endogenous levels of OEA, PEA and LEA in the intestine.

Pharmacological and therapeutic secrets of plant and brain (endo)cannabinoids

Research on the chemistry and pharmacology of cannabinoids and endocannabinoids has reached enormous proportions, with approximately 15,000 articles on Cannabis sativa L. and cannabinoids and over 2,000 articles on endocannabinoids. The present review deals with the history of the Cannabis sativa L. plant, its uses, constituent compounds and their biogeneses, and similarity to compounds from Radula spp. In addition, details of the pharmacology of natural cannabinoids, as well as synthetic agonists and antagonists are presented. Finally, details regarding the pioneering isolation of the endocannabinoid anandamide, as well as the pharmacology and potential therapeutic uses of endocannabinoid congeners are presented.

Lipidomic analysis of biological samples by liquid chromatography coupled to mass spectrometry

Lipidomics studies the large-scale changes in nonwater-soluble metabolites (lipids) accompanying perturbations of biological systems. Because lipids are involved in crucial biological mechanisms, there is a growing scientific interest in using lipidomic approaches to understand the regulation of the lipid metabolism in all eukaryotic and prokaryotic organisms. Lipidomics is a powerful tool in system biology that can be used together with genomics, transcriptomics, and proteomics to answer biological questions arising from various scientific areas such as environmental sciences, pharmacology, nutrition, biophysics, cell biology, physiology, pathology, and disease diagnostics. One of the main challenges for lipidomic analysis is the range of concentrations and chemical complexity of different lipid species. In this chapter, we present a lipidomic approach that combines sample preparation, chromatographic, and intrasource ionization separation coupled to mass spectrometry for analyzing a broad-range of lipid molecules in biological samples.

Targeted lipidomics as a tool to investigate endocannabinoid function

Endocannabinoids are a family of lipid messengers present in a wide range of living organisms. They bind and activate the membrane receptors that are targeted by Delta(9)-tetrahydrocannabinol, the main psychoactive principle in marijuana (Cannabis). In the brain, they regulate ion-channel activity and neurotransmitter release critical to biological processes such as synaptic plasticity and learning and memory. Endocannabinoids are embedded within an intricate network of lipid pathways, the regulation of which controls the strength and duration of their signaling. Therefore, physiological, pathological, or pharmacological perturbations of these interconnected lipid pathways have a profound effect on the regulation of endocannabinoid signaling. The recent development of high-sensitivity and high-throughput analytical tools affords a broader view of the endocannabinoid system, allowing researchers to place individual endocannabinoid molecules in the context of the interconnected network of their precursors and derivatives. Targeted lipidomics provides new opportunities for understanding endocannabinoid metabolism.

Fatty acid amide hydrolase inhibition heightens anandamide signaling without producing reinforcing effects in primates

BACKGROUND

CB(1) cannabinoid receptors in the brain are known to participate in the regulation of reward-based behaviors. However, the contribution of each of the endocannabinoid transmitters, anandamide and 2-arachidonoylglycerol (2-AG), to these behaviors remains undefined. To address this question, we assessed the effects of URB597, a selective anandamide deactivation inhibitor, as a reinforcer of drug-seeking and drug-taking behavior in squirrel monkeys.

METHODS

We investigated the reinforcing effects of the fatty acid amide hydrolase (FAAH) inhibitor URB597 in monkeys trained to intravenously self-administer Delta(9)-tetrahydrocannabinol (THC), anandamide, or cocaine and quantified brain endocannabinoid levels using liquid chromatography/mass spectrometry. We measured brain FAAH activity using an ex vivo enzyme assay.

RESULTS

URB597 (.3 mg/kg, intravenous) blocked FAAH activity and increased anandamide levels throughout the monkey brain. This effect was accompanied by a marked compensatory decrease in 2-AG levels. Monkeys did not self-administer URB597, and the drug did not promote reinstatement of extinguished drug-seeking behavior previously maintained by THC, anandamide, or cocaine. Pretreatment with URB597 did not modify self-administration of THC or cocaine, even though, as expected, it significantly potentiated anandamide self-administration.

CONCLUSIONS

In the monkey brain, the FAAH inhibitor URB597 increases anandamide levels while causing a compensatory down-regulation in 2-AG levels. These effects are accompanied by a striking lack of reinforcing properties, which distinguishes URB597 from direct-acting cannabinoid agonists such as THC. Our results reveal an unexpected functional heterogeneity within the endocannabinoid signaling system and suggest that FAAH inhibitors might be used therapeutically without risk of abuse or triggering of relapse to drug abuse.

Role of cannabinoids and endocannabinoids in cerebral ischemia

The human costs of stroke are very large and growing; it is the third largest cause of death in the United States and survivors are often faced with loss of ability to function independently. There is a large need for therapeutic approaches that act to protect neurons from the injury produced by ischemia and reperfusion. The goal of this review is to introduce and discuss the available data that endogenous cannabinoid signaling is altered during ischemia and that it contributes to the consequences of ischemia-induced injury. Overall, the available data suggest that inhibition of CB1 receptor activation together with increased CB2 receptor activation produces beneficial effects.