Analysis of anandamide, an endogenous cannabinoid substance, and of other natural N-acylethanolamines

(Wh)olistic (E)ndocannabinoidome-Microbiome-Axis Modulation through (N)utrition (WHEN) to Curb Obesity and Related Disorders

The discovery of the endocannabinoidome (eCBome) is evolving gradually with yet to be elucidated functional lipid mediators and receptors. The diet modulates these bioactive lipids and the gut microbiome, both working in an entwined alliance. Mounting evidence suggests that, in different ways and with a certain specialisation, lipid signalling mediators such as N-acylethanolamines (NAEs), 2-monoacylglycerols (2-MAGs), and N-acyl-amino acids (NAAs), along with endocannabinoids (eCBs), can modulate physiological mechanisms underpinning appetite, food intake, macronutrient metabolism, pain sensation, blood pressure, mood, cognition, and immunity. This knowledge has been primarily utilised in pharmacology and medicine to develop many drugs targeting the fine and specific molecular pathways orchestrating eCB and eCBome activity. Conversely, the contribution of dietary NAEs, 2-MAGs and eCBs to the biological functions of these molecules has been little studied. In this review, we discuss the importance of (Wh) olistic (E)ndocannabinoidome-Microbiome-Axis Modulation through (N) utrition (WHEN), in the management of obesity and related disorders.

Advances in the discovery of fatty acid amide hydrolase inhibitors: what does the future hold?

INTRODUCTION

Fatty acid amide hydrolase (FAAH) is a membrane-bound enzyme, that inactivates endogenous signaling lipids of the fatty acid amide family, including the endocannabinoid anandamide (N-arachidonoylethanolamine, AEA). The latter compound has been shown to regulate a number of important pathophysiological conditions in humans, like feeding, obesity, immune response, reproductive events, motor coordination, and neurological disorders. Hence, direct manipulation of the endocannabinoid tone is thought to have therapeutic potential. A new opportunity to develop effective drugs may arise from multi-target directed ligand (MTDL) strategies, which brings the concept that a single compound can recognize different targets involved in the cascade of pathophysiological events.

AREAS COVERED

This review reports the latest advances in the development of new single targeted and dual-targeted FAAH inhibitors over the past 5 years.

EXPERT OPINION

In recent years, several FAAH inhibitors have been synthesized and investigated, yet to date none of them has reached the market as a systemic drug. Due to the diligence of inherent redundancy and robustness in many biological networks and pathways, multitarget inhibitors present a new prospect in the pharmaceutical industry for treatment of complex diseases.

An Atmospheric Pressure Chemical Ionization MS/MS Assay Using Online Extraction for the Analysis of 11 Cannabinoids and Metabolites in Human Plasma and Urine

BACKGROUND

Although, especially in the United States, there has been a recent surge of legalized cannabis for either recreational or medicinal purposes, surprisingly little is known about clinical dose-response relationships, pharmacodynamic and toxicodynamic effects of cannabinoids such as Δ9-tetrahydrocannabinol (THC). Even less is known about other active cannabinoids.

METHODS

To address this knowledge gap, an online extraction, high-performance liquid chromatography coupled with tandem mass spectrometry method for simultaneous quantification of 11 cannabinoids and metabolites including THC, 11-hydroxy-Δ9-tetrahydrocannabinol, 11-nor-Δ9-tetrahydrocannabinol-9-carboxylic acid, 11-nor-Δ9-tetrahydrocannabinol-9-carboxylic acid glucuronide (THC-C-gluc), cannabinol, cannabidiol, cannabigerol, cannabidivarin, Δ9-tetrahydrocannabivarin (THCV), and 11-nor-9-carboxy-Δ9-tetrahydrocannabivarin (THCV-COOH) was developed and validated in human urine and plasma.

RESULTS

In contrast to atmospheric pressure chemical ionization, electrospray ionization was associated with extensive ion suppression in plasma and urine samples. Thus, the atmospheric pressure chemical ionization assay was validated showing a lower limit of quantification ranging from 0.39 to 3.91 ng/mL depending on study compound and matrix. The upper limit of quantification was 400 ng/mL except for THC-C-gluc with an upper limit of quantification of 2000 ng/mL. The linearity was r > 0.99 for all analyzed calibration curves. Acceptance criteria for intrabatch and interbatch accuracy (85%-115%) and imprecision (<15%) were met for all compounds. In plasma, the only exceptions were THCV (75.3%-121.2% interbatch accuracy) and cannabidivarin (interbatch imprecision, 15.7%-17.2%). In urine, THCV did not meet predefined acceptance criteria for intrabatch accuracy.

CONCLUSIONS

This assay allows for monitoring not only THC and its major metabolites but also major cannabinoids that are of interest for marijuana research and clinical practice.

Endocannabinoid Analytical Methodologies: Techniques That Drive Discoveries That Drive Techniques

Identification of the two major endogenous cannabinoid ligands, known as endocannabinoids, N-arachidonoyl-ethanolamine (anandamide, AEA) and 2-arachidonoyl-glycerol (2-AG), opened the way for the identification and isolation of other lipid congeners, all derivatives of fatty acids and related to the Endocannabinoid System. The nomenclature of this anandamide-type class of lipids is evolving as new species are discovered all the time. However, they each fall under the larger umbrella of lipids that are a conjugation of a fatty acid with an amine through and amide bond, which we will refer to as lipoamines. Specific subspecies of lipoamines that have been discovered are the N-acyl-ethanolamides (including AEA), N-acyl-dopamines, N-acyl-serotonins, N-acyl-GABA, N-acyl-taurines, and a growing number of N-acyl amino acids. Emerging data from multiple labs also show that monoacylglycerols (including 2-AG), COX-2 metabolites, and fatty acid esters of hydroxyl fatty acids are interconnected with these lipoamines at both the biosynthetic and metabolic levels. Understanding the molecular relatedness of these lipids is important for studying how they act as signaling molecules; however, a first step in this process hinges on advances in being able to accurately measure them.

FABP1 in wonderland

Cannabinoid receptors hold a core position in the brain and control memory, cognition, movement, and pain sensitivity. sn-2 arachidonoylglycerol (2-AG) activates neuronal cannabinoid receptors as a full agonist. The brain may rely on circulating arachidonic acid to synthesize endogenous cannabinoids. This Editorial highlights a study by Martin and coworkers in the current issue of the Journal of Neurochemistry in which the authors describe, for the first time, that liver acts as a pool of arachidonic acid that under certain conditions feeds the brain to produce endocannabinoids. Therapeutics affecting liver FABP1 levels should take into account that FABP1 represents a fatty acid reservoirs for the brain. Read the highlighted article "FABP-1 gene ablation impacts brain endocannabinoid system in male mice" on page 407.

Lipidomic Analysis of Endocannabinoid Signaling: Targeted Metabolite Identification and Quantification

The endocannabinoids N-arachidonoylethanolamide (or anandamide, AEA) and 2-arachidonoylglycerol (2-AG) belong to the larger groups of N-acylethanolamines (NAEs) and monoacylglycerol (MAG) lipid classes, respectively. They are biologically active lipid molecules that activate G-protein-coupled cannabinoid receptors found in various organisms. After AEA and 2-AG were discovered in the 1990s, they have been extensively documented to have a broad range of physiological functions. Along with AEA, several NAEs, for example, N-palmitoylethanolamine (PEA), N-stearoylethanolamine (SEA), and N-oleoylethanolamine (OEA) are also present in tissues, usually at much larger concentrations than AEA. Any perturbation that involves the endocannabinoid pathway may subsequently alter basal level or metabolism of these lipid mediators. Further, the altered levels of these molecules often reflect pathological conditions associated with tissue damage. Robust and sensitive methodologies to analyze these lipid mediators are essential to understanding how they act as endocannabinoids. The recent advances in mass spectrometry allow researchers to develop lipidomics approaches and several methodologies have been proposed to quantify endocannabinoids in various biological systems.

Drosophila melanogaster as a model system to study long-chain fatty acid amide metabolism

Long-chain fatty acid amides are cell-signaling lipids identified in mammals and, recently, in invertebrates, as well. Many details regarding fatty acid amide metabolism remain unclear. Herein, we demonstrate that Drosophila melanogaster is an excellent model system for the study long-chain fatty acid amide metabolism as we have quantified the endogenous levels of N-acylglycines, N-acyldopamines, N-acylethanolamines, and primary fatty acid amides by LC/QTOF-MS. Growth of D. melanogaster on media supplemented with [1-(13)C]-palmitate lead to a family of (13)C-palmitate-labeled fatty acid amides in the fly heads. The [1-(13)C]-palmitate feeding studies provide insight into the biosynthesis of the fatty acid amides.

Quantitative LC-MS/MS analysis of arachidonoyl amino acids in mouse brain with treatment of FAAH inhibitor

An additional class of endogenous lipid amides, N-arachidonoyl amino acids (Ara-AAs), is growing in significance in the field of endocannabinoids. The development, validation, and application of a sensitive and selective method to simultaneously monitor and quantify the level of Ara-AAs along with anandamide (AEA) and 2-arachidonoyl glycerol (2-AG) in mouse brain has been established. The linearity of the method over the concentration ranges of 0.2-120 pg/μl for the standards of N-arachidonoyl amino acids, N-arachidonoyl alanine (NAAla), serine (NASer), γ-aminobutyric acid (NAGABA), and glycine (NAGly); 0.7-90 pg/μl for AEA-d(0)/d(8); and 7.5-950 pg/μl for 2-AG was determined with R(2) values of 0.99. Also the effects of the FAAH inhibitor URB 597 on the endogenous levels of these analytes were investigated. AEA and NASer brain levels exhibit a dose-dependent increase after systemic administration of URB 597, whereas NAGly and NAGABA were significantly decreased after treatment. NAAla and 2-AG were not altered after URB 597 treatment. The potential benefit of establishing this assay extends beyond the quantification of the Ara-AAs along with AEA and 2-AG in mouse brain, to reveal a variety of pharmacological effects and physiological roles of these analytes.

Simultaneous UPLC-MS/MS quantification of the endocannabinoids 2-arachidonoyl glycerol (2AG), 1-arachidonoyl glycerol (1AG), and anandamide in human plasma: minimization of matrix-effects, 2AG/1AG isomerization and degradation by toluene solvent extraction

Analysis of the endocannabinoid (EC) system's key molecules 2-arachidonoyl glycerol (2AG) and arachidonoyl ethanolamide (anandamide, AEA) is challenging due to several peculiarities. 2AG isomerizes spontaneously to its biologically inactive analogue 1-arachidonoyl glycerol (1AG) by acyl migration and it is only chromatographically distinguishable from 1AG. Matrix-effects caused primarily by co-extracted phospholipids may further compromise analysis. In addition, 2AG and 1AG are unstable under certain conditions like solvent evaporation or reconstitution of dried extracts. We examined effects of different organic solvents and their mixtures, such as toluene, ethyl acetate, and chloroform-methanol, on 2AG/1AG isomerisation, 2AG/1AG stability, and matrix-effects in the UPLC-MS/MS analysis of 2AG and AEA in human plasma. Toluene prevented, both, 2AG isomerisation to 1AG and degradation of 2AG/1AG during evaporation. Toluene extracts contain only 2% of matrix-effect-causing plasma phospholipids compared to extracts from the traditionally used solvent mixture chloroform-methanol. Toluene and all other tested organic solvents provide comparable 2AG and AEA extraction yields (60-80%). Based on these favourable toluene properties, we developed and validated a UPLC-MS/MS method with positive electrospray ionization (ESI+) that allows for simultaneous accurate and precise measurement of 2AG and AEA in human plasma. The UPLC-MS/MS method was cross-validated with a previously described fully-validated GC-MS/MS method for AEA in human plasma. A close correlation (r(2)=0.821) was observed between the results obtained from UPLC-MS/MS (y) and GC-MS/MS (x) methods (y=0.01+0.85x). The UPLC-MS/MS method is suitable for routine measurement of 2AG and AEA in human plasma samples (1 mL) in clinical settings as shown by quality control plasma samples processed over a period of 100 days. The UPLC-MS/MS method was further extended to human urine. In urine, AEA was not detectable and 2AG was detected in only 3 out of 19 samples from healthy subjects at 160, 180 and 212 pM corresponding to 12.3, 14.5 and 9.9 pmol/mmol creatinine, respectively.

Inhibitor of fatty acid amide hydrolase normalizes cardiovascular function in hypertension without adverse metabolic effects

The enzyme fatty acid amide hydrolase (FAAH) catalyzes the in vivo degradation of the endocannabinoid anandamide, thus controlling its action at receptors. A novel FAAH inhibitor, AM3506, normalizes the elevated blood pressure and cardiac contractility of spontaneously hypertensive rats (SHR) without affecting these parameters in normotensive rats. These effects are due to blockade of FAAH and a corresponding rise in brain anandamide levels, resulting in CB₁ receptor-mediated decrease in sympathetic tone. The supersensitivity of SHR to CB₁ receptor-mediated cardiovascular depression is related to increased G protein coupling of CB₁ receptors. Importantly, AM3506 does not elicit hyperglycemia and insulin resistance seen with other FAAH inhibitors or in FAAH⁻/⁻ mice, which is related to its inability to inhibit FAAH in the liver due to rapid hepatic uptake and metabolism. This unique activity profile offers improved therapeutic value in hypertension.

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.

Pitfalls in the sample preparation and analysis of N-acylethanolamines

N-acylethanolamines (NAEs) are a group of lipid mediators synthesized in response to a number of physiological and pathological stimuli. Because of the low tissue concentrations of NAEs, analyses often include liquid extraction followed by solid-phase extraction and subsequent quantitation by LC/MS or GC/MS. Reported levels of NAEs vary considerably, however, and often no explanation is given for these discrepancies. Brought on by difficulties encountered during method development, the effects of using four different brands of silica-containing solid phase extraction (SPE) columns and five different brands of chloroform for sample preparation were investigated. Considerable variation in the retention and recoveries of seven NAEs and 2-arachidonoylglycerol existed between the SPE columns. Furthermore, it was found that some chloroforms contained quantifiable amounts of N-palmitoylethanolamine and N-stearoylethanolamine. Finally, it was found that use of one of the chloroforms resulted in a loss of N-oleoylethanolamine from solution due to addition of chlorine to the ω-9 bond. The identity of this reaction product was confirmed by LC-MS/MS and NMR. It is recommended that these aspects of sample preparation and analysis should be thoroughly validated during method development and the relevant information on specific brands used be reported in future communications in order to better estimate the validity of reported quantitative data.

An optimized GC-MS method detects nanomolar amounts of anandamide in mouse brain

The endocannabinoids anandamide and 2-arachidonoylglycerol, as well as several anandamide-related N-acylethanolamines, belong to a family of lipid transmitter that regulate fundamental physiological processes, including neurotransmission and neuroinflammation. Their precise quantification in biological matrices can be achieved by gas chromatography-mass spectrometry (GC-MS), but this method typically requires multiple time-consuming purification steps such as solid-phase extraction followed by HPLC. Here we report a novel solid-phase extraction procedure allowing for single-step, and thus higher throughput, purification of endocannabinoids and N-acylethanolamines before GC-MS quantification. We determined the minimal amount of mouse brain tissue required to reliably detect endocannabinoids and N-acylethanolamines when using this approach and provide direct evidence for quantification accuracy by using radioactive and deuterated standards spiked into mouse brain samples. Using this method, we found that mouse brain contains much higher levels of anandamide (>1 nmol/g tissue) than previously reported, whereas levels of 2-arachidonoylglycerol and other N-acylethanolamines are well within the range of previous reports. In addition, we show that mouse brain amounts of endocannabinoids and N-acylethanolamines differ depending on animal gender as well as on whether the tissue was fixed or not. Our study shows that endocannabinoid and N-acylethanolamine levels quantified in mouse brain by GC-MS depend closely on tissue amount and preparation as well as on animal gender and that, depending on such parameters, anandamide levels could be underestimated.

Closing the Gate to the Active Site

Fatty acid amide hydrolase (FAAH) is a dimeric, membranebound enzyme that degrades neuromodulatory fatty acid amides and esters and is expressed in mammalian brain and peripheral tissues. The cleavage of approximately 30 amino acids from each subunit creates an FAAH variant that is soluble and homogeneous in detergent-containing buffers, opening the avenue to the in vitro mechanistic and structural studies. Here we have studied the stability of FAAH as a function of guanidinium hydrochloride concentration and of hydrostatic pressure. The unfolding transition was observed to be complex and required a fitting procedure based on a three-state process with a monomeric intermediate. The first transition was characterized by dimer dissociation, with a free energy change of approximately 11 kcal/mol that accounted for approximately 80% of the total stabilization energy. This process was also paralleled by a large change in the solvent-accessible surface area, because of the hydration occurring both at the dimeric interface and within the monomers. As a consequence, the isolated subunits were found to be much less stable (DeltaG approximately 3 kcal/mol). The addition of methoxyarachidonyl fluorophosphonate, an irreversible inhibitor of FAAH activity, enhanced the stability of the dimer by approximately 2 kcal/mol, toward denaturant- and pressure-induced unfolding. FAAH inhibition by methoxyarachidonyl fluorophosphonate also reduced the ability of the protein to bind to the membranes. These findings suggest that local conformational changes at the level of the active site might induce a tighter interaction between the subunits of FAAH, affecting the enzymatic activity and the interaction with membranes.

Targeted lipidomics: discovery of new fatty acyl amides

The discovery of endogenous fatty acyl amides such as N-arachidonoyl ethanolamide (anandamide), N-oleoyl ethanolamide (OEA), and N-arachidonoyl dopamine (NADA) as important signaling molecules in the central and peripheral nervous system has led us to pursue other unidentified signaling molecules. Until recently, technical challenges, particularly those associated with lipid purification and chemical analysis, have hindered the identification of low abundance signaling lipids. Improvements in chromatography and mass spectrometry (MS) such as miniaturization of high-performance liquid chromatography components, hybridization of multistage mass spectrometers and time-of-flight technology, the development of electrospray ionization (ESI) and of information-dependent acquisition, now permit rapid identification of novel, low abundance, signaling lipids.

Determination of the endocannabinoid anandamide in human plasma by high-performance liquid chromatography

Anandamide (N-arachidonylethanolamine) is an endogenous cannabinoid receptor ligand that has been implicated in various physiological and pathophysiological functions. In the present study, a liquid-liquid extraction-based reversed-phase HPLC method with fluorometric detection was validated and applied for the analysis of anandamide in human plasma. Following derivatization with the fluorogenic reagent 4-(N,N-dimethylaminosulfonyl)-7-(N-chloroformylmethyl-N-methyl-amino)-2,1,3-benzoxadiazole (DBD-COCl), the analyte was separated using an acetonitrile-water gradient at a flow rate of 0.8 mL/min, and spectrophotometric detection at 560 nm with an excitation wavelength of 450 nm. The retention times for anandamide and R+-methanandamide (internal standard) were 27.1 and 30.7 min, respectively. The validated quantification range was 1-15 ng/mL. The developed procedure was applied to determine anandamide levels in human plasma following a 24 h incubation of human whole blood at 37 degrees C in the presence or absence of phenylmethylsulfonyl fluoride, an inhibitor of the anandamide-degrading enzyme fatty acid amide hydrolase. Anandamide levels determined under both conditions were within the validated concentration range with anandamide levels being 2.3-fold higher in plasma from PMSF-treated blood.

Design of on-target FAAH inhibitors

In this issue of Chemistry & Biology, Alexander and Cravatt propose a model for the binding of carbamate inhibitors to fatty acid amide hydrolase (FAAH), the enzyme that breaks down signaling lipids. Using competitive activity-based protein profiling and click chemistry, they designed potent and selective FAAH inhibitors and characterized their off-target reactions.

Decreased endocannabinoid levels in the brain and beneficial effects of agents activating cannabinoid and/or vanilloid receptors in a rat model of multiple sclerosis

Recent studies have addressed the changes in endocannabinoid ligands and receptors that occur in multiple sclerosis, as a way to explain the efficacy of cannabinoid compounds to alleviate spasticity, pain, tremor, and other signs of this autoimmune disease. Using Lewis rats with experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, we recently found a decrease in cannabinoid CB1 receptors mainly circumscribed to the basal ganglia, which could be related to the motor disturbances characteristic of these rats. In the present study, using the same model, we explored the potential changes in several neurotransmitters in the basal ganglia that might be associated with the motor disturbances described in these rats, but we only found a small increase in glutamate contents in the globus pallidus. We also examined whether the motor disturbances and the changes of CB1 receptors found in the basal ganglia of EAE rats disappear after the treatment with rolipram, an inhibitor of type IV phosphodiesterase able to supress EAE in different species. Rolipram attenuated clinical decline, reduced motor inhibition, and normalized CB1 receptor gene expression in the basal ganglia. As a third objective, we examined whether EAE rats also exhibited changes in endocannabinoid levels as shown for CB1 receptors. Anandamide and 2-arachidonoylglycerol levels decreased in motor related regions (striatum, midbrain) but also in other brain regions, although the pattern of changes for each endocannabinoid was different. Finally, we hypothesized that the elevation of the endocannabinoid activity, following inhibition of endocannabinoid uptake, might be beneficial in EAE rats. AM404, arvanil, and OMDM2 were effective to reduce the magnitude of the neurological impairment in EAE rats, whereas VDM11 did not produce any effect. The beneficial effects of AM404 were reversed by blocking TRPV1 receptors with capsazepine, but not by blocking CB1 receptors with SR141716, thus indicating the involvement of endovanilloid mechanisms in these effects. However, a role for CB1 receptors is supported by additional data showing that CP55,940 delayed EAE progression. In summary, our data suggest that reduction of endocannabinoid signaling is associated with the development of EAE in rats. We have also proved that the reduction of CB1 receptors observed in these rats is corrected following treatment with a compound used in EAE such as rolipram. In addition, the direct or indirect activation of vanilloid or cannabinoid receptors may reduce the neurological impairment experienced by EAE rats, although the efficacy of the different compounds examined seems to be determined by their particular pharmacodynamic and pharmacokinetic characteristics.

Regulation of gonadotropin-releasing hormone secretion by cannabinoids

Cannabinoids (CBs) exert untoward effects on reproduction by reducing LH secretion and suppressing gonadal function. Recent evidence suggests these effects are due primarily to hypothalamic dysfunction; however, the mechanism is obscure. Using immortalized hypothalamic GnRH neurons, we find these cells produce and secrete at least two different endocannabinoids. After release, 2-arachidonyl monoacylglycerol and anandamide are rapidly transported into GnRH neurons and are degraded to other lipids by fatty-acid amide hydrolase. The immortalized GnRH neurons also possess CB1 and CB2 receptors that are coupled to Gi/Go proteins whose activation leads to inhibition of GnRH secretion. In perifusion experiments, CBs block pulsatile release of GnRH. When a CB receptor agonist is delivered into the third ventricle of adult female mice, estrous cycles are prolonged by at least 2 d. Although in situ hybridization experiments suggest either that GnRH neurons in vivo do not possess CB1 receptors or that they are very low, transcripts are localized in close proximity to these neurons. Inasmuch as GnRH neurons in vivo possess G protein receptors that are coupled to phospholipase C and increased intracellular Ca2+, these same neurons should also be able to synthesize endocannabinoids. These lipids, in turn, could bind to CB receptors on neighboring cells, and perhaps GnRH neurons, to exert feedback control over GnRH function. This network could serve as a novel mechanism for regulating GnRH secretion where reproductive functions as diverse as the onset of puberty, timing of ovulation, duration of lactational infertility, and initiation/persistence of menopause may be affected.

Effect of repeated systemic administration of selective inhibitors of endocannabinoid inactivation on rat brain endocannabinoid levels

Several selective inhibitors of endocannabinoid inactivation via either the fatty acid amide hydrolase (FAAH) or the putative endocannabinoid transporter have been developed so far. Here, we have studied the effect in rats of a subchronic intraperitoneal treatment with three recently developed selective inhibitors of endocannabinoid uptake (VDM-11, UCM-707 and OMDM-2) or with a selective FAAH inhibitor (N-arachidonoyl-serotonin, AA-5-HT), on the brain levels of anandamide and 2-arachidonoylglycerol (2-AG) measured by means of isotope dilution LC-MS 1, 5 and 12 h after the last treatment. OMDM-2 was the most efficacious compound at enhancing the levels of anandamide at all time points, with a maximal effect (1.9-fold enhancement) after 5h. This compound also enhanced 2-AG levels by approximately 1.3-fold, but only 5 and 12h from administration. VDM-11 slightly, albeit significantly, enhanced anandamide levels (1.3-fold) only at 1h from administration and 2-AG levels (1.3-fold) only after 5h. Finally, UCM-707 only affected 2-AG levels (by two-fold) at only 1h from administration. FAAH inhibition by AA-5-HT significantly enhanced the levels of both anandamide (between 1.3- and 1.5-fold, maximal effect after 1 h) and 2-AG (between 1.3- and 1.6-fold, maximal effect after 12 h) at all time points. Brains from rats treated with AA-5-HT did never exhibit enhanced levels of serotonin, thus pointing to the metabolic stability of this FAAH inhibitor. These data indicate that: (1) the pharmacological effects reported so far for the four compounds under study in animal models of diseases may be due to enhancement of both anandamide and 2-AG levels; (2) 2-AG seems to need a longer time after the last administration in order to be augmented; (3) OMDM-2 and AA-5-HT should be regarded as enhancers of endocannabinoid levels suitable for use in vivo.

Occurrence and possible biological role of the endocannabinoid system in the sea squirt Ciona intestinalis

A cannabinoid receptor orthologue (CiCBR) has been described in the sea squirt Ciona intestinalis. Here we report that CiCBR mRNA expression is highest in cerebral ganglion, branchial pharynx, heart and testis of C. intestinalis, and that this organism also contains cannabinoid receptor ligands and some of the enzymes for ligand biosynthesis and inactivation. Using liquid chromatography-mass spectrometry, the endocannabinoid anandamide was found in all tissues analysed (0.063-5.423 pmol/mg of lipid extract), with the highest concentrations being found in brain and heart. The endocannabinoid 2-arachidonoylglycerol (2-AG) was fivefold more abundant than anandamide, and was most abundant in stomach and intestine and least abundant in heart and ovaries (2.677-50.607 pmol/mg of lipid extract). Using phylogenomic analysis, we identified orthologues of several endocannabinoid synthesizing and degrading enzymes. In particular, we identified and partly sequenced a fatty acid amide hydrolase (FAAH) orthologue, showing 44% identity with human FAAH and containing nearly all the amino acids necessary for a functional FAAH enzyme. Ciona intestinalis also contained specific binding sites for cannabinoid receptor ligands, and an amidase enzyme with pH-dependency and subcellular/tissue distribution similar to mammalian FAAHs. Finally, a typical C. intestinalis behavioural response, siphon reopening after closure induced by mechanical stimulation, was inhibited by the cannabinoid receptor agonist HU-210, and this effect was significantly attenuated by mammalian cannabinoid receptor antagonists.

Use of reversed phase HP liquid chromatography to assay conversion of N-acylglycines to primary fatty acid amides by peptidylglycine-alpha-amidating monooxygenase

Primary fatty acid amides (R-CO-NH2) and N-acylglycines (R-CO-NH-CH2-COOH) are classes of compounds that have only recently been isolated and characterized from biological sources. Key questions remain regarding how these lipid amides are produced and degraded in biological systems. Relative to the fatty acids, little has been done to develop methods to separate and quantify the fatty acid amides and N-acylglycines. We describe reversed phase HPLC methods for the separation of C2-C12 primary fatty acid amides and N-acylglycines and also C12-C22 fatty acid amides. Separation within each class occurs primarily on the basis of simple interactions between the acyl chain and the chromatographic stationary phase, but the polar headgroups on these and related fatty acids and N-acylethanolamides modulate the absolute retention in reversed phase mode. We use these methods to measure the enzyme-mediated, two-step conversion of N-octanoylglycine to octanoamide.

Pharmacological modulation of the endocannabinoid system in a viral model of multiple sclerosis

Theiler's virus infection of the central nervous system (CNS) induces an immune-mediated demyelinating disease in susceptible mouse strains and serves as a relevant infection model for human multiple sclerosis (MS). Cannabinoids have been shown to exert beneficial effects on animal models of MS and evidence suggests that the endocannabinoid system plays a role in the tonic control of spasticity. In this study we show that OMDM1 [(R)-N-oleoyl-(1'-hydroxybenzyl)-2'-ethanolamine] and OMDM2 [(S)-N-oleoyl-(1'-hydroxybenzyl)-2'-ethanolamine], two selective inhibitors of the putative endocannabinoid transporter and hence of endocannabinoid inactivation, provide an effective therapy for Theiler murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD). Treatment of TMEV-infected mice with OMDM1 and OMDM2 enhanced anandamide levels in the spinal cord and ameliorated motor symptoms. This was associated with a down-regulation of inflammatory responses in the spinal cord. In addition we show that OMDM1 and OMDM2 down-regulate macrophage function by (i) decreasing the surface expression of major histocompatibility complex (MHC) class II molecules, (ii) inhibiting nitric oxide synthase-2 (NOS-2) expression and (iii) reducing the production of the pro-inflammatory cytokines interleukin-1beta (IL-1beta) and interleukin-12 (IL-12p40). Taken together, these results point to the manipulation of the endocannabinoid system as a possible strategy to develop future MS therapeutic drugs.

Changes in endocannabinoid contents in reward-related brain regions of alcohol-exposed rats, and their possible relevance to alcohol relapse

1. Chronic alcohol exposure modifies endocannabinoid levels in different brain regions, while pharmacological targeting of the endocannabinoid system has been reported to influence ethanol intake in laboratory animals. 2. The present study was aimed at evaluating the pattern of changes of endocannabinoids and their receptors, with emphasis on reward-related brain areas, in Wistar rats subjected to consecutive phases of alcoholization, alcohol deprivation (abstinence), and voluntary consumption of alcohol (relapse). 3. We observed that, in the limbic forebrain, anandamide (AEA) and 2-arachidonoylglycerol (2-AG) contents increased after 7 days of alcoholization, then to dramatically decrease after 48 h of alcohol deprivation and, in the case of 2-AG, to further decrease when rats were allowed to relapse to alcohol consumption. By contrast, in the midbrain, there was a marked reduction in AEA, but not 2-AG, content, after alcoholization. This decrease was not affected during alcohol abstinence, but both AEA and 2-AG contents were then significantly reduced when rats were allowed to relapse to alcohol consumption. 4. Based on these data, we examined whether pharmacological activation/blockade of endocannabinoid transmission might influence ethanol intake in rats allowed to relapse to alcohol consumption after subsequent periods of alcoholization and alcohol deprivation. 5. Treatment with either Delta(9)-tetrahydrocannabinol or CP55,940, two cannabinoid agonists, reduced both total liquid and ethanol intake but did not affect ethanol preference. Treatment with SR141716, a selective cannabinoid CB(1) receptor antagonist, also produced a significant reduction in both total liquid and ethanol intake without affecting ethanol preference. Accordingly, none of these effects on ethanol intake were accompanied by changes in dopamine and GABA in limbic structures. 6. In summary, the levels of endocannabinoids underwent significant changes in reward-related areas during alcoholization, alcohol deprivation, and relapse, showing the lowest values in this latter phase. Treatment with cannabinoid agonists or a selective CB(1) receptor antagonist resulted in a reduction of ethanol intake by rats allowed to relapse to alcohol consumption after periods of alcoholization and alcohol deprivation, but these effects did not appear to be due to changes in neurobiological substrates currently involved in alcohol reinforcement/relapse.

A new strategy to block tumor growth by inhibiting endocannabinoid inactivation

Endocannabinoid signaling has been shown to be enhanced in several cancer tissues and malignant cells, and studies in cell lines have shown that this up-regulation might serve the purpose of providing transformed cells with a further means to inhibit their proliferation. Here we investigated the effect of inhibitors of endocannabinoid degradation on the growth of rat thyroid tumor xenografts induced in athymic mice. VDM-11, a selective inhibitor of endocannabinoid cellular re-uptake, and arachidonoyl-serotonin (AA-5-HT), a selective blocker of endocannabinoid enzymatic hydrolysis, both inhibited the growth in vivo of tumor xenografts induced by the subcutaneous injection of rat thyroid transformed (KiMol) cells. This effect was accompanied by significantly enhanced endocannabinoid concentrations in the tumors excised at the end of the in vivo experiments. Endocannabinoids, as well as VDM-11 and AA-5-HT, inhibited the growth in vitro of the transformed rat thyroid cells used to induce the tumors in vivo, and their effect was reversed at least in part by the cannabinoid CB1 receptor antagonist SR141716A. This compound, however, when administered alone, did not enhance, but instead slightly inhibited, the growth of rat thyroid transformed cells both in vitro and in tumor xenografts induced in vivo. These findings indicate that endocannabinoids tonically control tumor growth in vivo by both CB1-mediated and non-CB1-mediated mechanisms and that, irrespective of the molecular mechanism of their anti-proliferative action, inhibitors of their inactivation might be used for the development of novel anti-cancer drugs.

Endocannabinoid signalling in the blood of patients with schizophrenia

AIM

To test the hypothesis that schizophrenia might be associated with alterations of the endogenous cannabinoid system in human blood.

RESULTS

Blood from 20 healthy volunteers and 12 patients with schizophrenia, 5 of which both before and after a successful antipsychotic treatment, was analysed for: 1) the amounts of the endocannabinoid anandamide; 2) the levels of cannabinoid CB1 and CB2 receptor mRNAs, and 3) the levels of the mRNA encoding the enzyme fatty acid amide hydrolase (FAAH), responsible for anandamide degradation. The amounts of anandamide were significantly higher in the blood of patients with acute schizophrenia than in healthy volunteers (7.79 +/- 0.50 vs. 2.58 +/- 0.28 pmol/ml). Clinical remission was accompanied by a significant decrease of the levels of anandamide (3.88 +/- 0.72 pmol/ml) and of the mRNA transcripts for CB2 receptors and FAAH.

CONCLUSION

These findings indicate that endocannabinoid signalling might be altered during the acute phase of schizophrenia not only in the central nervous system but also in the blood. These changes might be related to the several immunological alterations described in schizophrenia.

Chronic morphine modulates the contents of the endocannabinoid, 2-arachidonoyl glycerol, in rat brain

Opioids and cannabinoids are among the most widely consumed drugs of abuse in humans and the phenomena of cross-tolerance or mutual potentiation have been demonstrated between the two drugs. Several authors have suggested that both drugs share common links in their molecular mechanisms of action, although this has been a matter of controversy. Furthermore, no data exist on the possible adaptive changes in the contents of arachidonoylethanolamide (anandamide, AEA) and 2-arachidonoylglycerol (2-AG), the two major endogenous ligands for cannabinoid receptors, in morphine-tolerant rats. In the present work, we investigated the alterations in cannabinoid receptor functionality and endocannabinoid levels in rats chronically treated with morphine (5 mg/kg, s.c., twice a day for 5 days). Autoradiographic-binding studies using [(3)H]CP-55 940 revealed a slight but significant reduction in cannabinoid receptor level in the cerebellum and hippocampus of morphine-tolerant rats, while CP-55 940-stimulated [(35)S]GTPgammaS binding showed a strong decrease (40%) in receptor/G protein coupling in the limbic area of these animals. Moreover, in the same brain regions we measured, by isotope-dilution gas chromatography/mass spectrometry, the contents of AEA and 2-AG. Chronic morphine exposure produced a strong reduction in 2-AG contents without changes in AEA levels in several brain regions (ie striatum, cortex, hippocampus, limbic area, and hypothalamus). These findings clearly demonstrate that prolonged activation of opioid receptors could alter the cannabinoid system, in terms of both receptor functionality and endocannabinoid levels, and suggest the involvement of this system, alone or in combination with other mediators, in the phenomenon of morphine tolerance.

Changes in endocannabinoid contents in the brain of rats chronically exposed to nicotine, ethanol or cocaine

Despite recent data suggesting that the endocannabinoid transmission is a component of the brain reward system and plays a role in dependence/withdrawal to different habit-forming drugs, only a few studies have examined changes in endocannabinoid ligands and/or receptors in brain regions related to reinforcement processes after a chronic exposure to these drugs. Recently, we carried out a comparative analysis of the changes in cannabinoid CB(1) receptor density in several rat brain regions caused by chronic exposure to some of the most powerful habit-forming drugs. In the present study, we have extended this objective by examining changes in the brain contents of arachidonoylethanolamide (AEA) and 2-arachidonoyl-glycerol (2-AG), the endogenous ligands for cannabinoid receptors, in animals chronically exposed to cocaine, nicotine or ethanol. Results were as follows. Cocaine was the drug exhibiting the minor number of effects, with only a small, but significant, decrease in the content of 2-AG in the limbic forebrain. In contrast, chronic alcohol exposure caused a decrease in the contents of both AEA and 2-AG in the midbrain, while it increased AEA content in the limbic forebrain. This latter effect was also observed after chronic nicotine exposure together with an increase in AEA and 2-AG contents in the brainstem. In contrast, the hippocampus, the striatum and the cerebral cortex exhibited a decrease in AEA and/or 2-AG contents after chronic nicotine exposure. We also tested the effect of chronic nicotine on brain CB(1) receptors, which had not been investigated before, and found an almost complete lack of changes in mRNA levels or binding capacity for these receptors. In summary, our results, in concordance with previous data on CB(1) receptors, indicate that the three drugs tested here produce different changes in endocannabinoid transmission. Only in the case of alcohol and nicotine, we observed a common increase in AEA contents in the limbic forebrain. This observation is important considering that this region is a key area for the reinforcing properties of habit-forming drugs, which might support the involvement of endocannabinoid transmission in some specific events of the reward system activated by these drugs.

Endocannabinoid levels in rat limbic forebrain and hypothalamus in relation to fasting, feeding and satiation: stimulation of eating by 2-arachidonoyl glycerol

Endocannabinoids are implicated in appetite and body weight regulation. In rodents, anandamide stimulates eating by actions at central CB1 receptors, and hypothalamic endocannabinoids may be under the negative control of leptin. However, changes to brain endocannabinoid levels in direct relation to feeding or changing nutritional status have not been investigated. We measured anandamide and 2-arachidonoyl glycerol (2-AG) levels in feeding-associated brain regions of rats, during fasting, feeding of a palatable food, or after satiation. Endocannabinoid levels were compared to those in rats fed ad libitum, at a point in their daily cycle when motivation to eat was absent. Fasting increased levels of anandamide and 2-AG in the limbic forebrain and, to a lesser extent, of 2-AG in the hypothalamus. By contrast, hypothalamic 2-AG declined as animals ate. No changes were detected in satiated rats. Endocannabinoid levels in the cerebellum, a control region not directly involved in the control of food intake, were unaffected by any manipulation. As 2-AG was most sensitive to variation during feeding, and to leptin regulation in a previous study, we examined the behavioural effects of 2-AG when injected into the nucleus accumbens shell, a limbic forebrain area strongly linked to eating motivation. 2-AG potently, and dose-dependently, stimulated feeding. This effect was attenuated by the CB1 receptor antagonist SR141716. These findings provide the first direct evidence of altered brain levels of endocannabinoids, and of 2-AG in particular, during fasting and feeding. The nature of these effects supports a role for endocannabinoids in the control of appetitive motivation.

Simultaneous measurement of anandamide and 2-arachidonoylglycerol by polymyxin B-selective adsorption and subsequent high-performance liquid chromatography analysis: increase in endogenous cannabinoids in the sera of patients with endotoxic shock

Anandamide (ANA) and 2-arachidonoylglycerol (2-AG), two endogenous cannabinoids, can be generated by activated macrophages and platelets, respectively, in the context of endotoxic shock, and are proposed to play a crucial role in the induction of the shock-related hypotension. Taking advantage of our recently discovered function of polymyxin B (PMB) binding to ANA and 2-AG, we developed a new method for measuring ANA and 2-AG by applying PMB-immobilized beads to selectively adsorb them in biological fluids, instead of organic solvent extraction. The eluate from beads can be directly fractionated by reverse-phase high-performance liquid chromatography (HPLC), and the fractionations corresponding to authentic ANA and 2-AG are collected and derivatized with fluorogenic reagent and subsequently quantified by HPLC with fluorometric detection. The calibration graphs of ANA and 2-AG were linear over a range of 1 to 500 pmol/ml. The limits of detection for ANA and 2-AG were 20 and 50 fmol, respectively. Intraassay precision was 2.24-4.25 and 3.47-5.44%, and interassay was 4.05-6.14 and 4.92-7.28% for ANA and 2-AG, respectively. Using this method, we first determined a 4-fold and 3-fold higher level of ANA and 2-AG, respectively, in the sera of patients with endotoxic shock than in normal serum. This finding should help in elucidating the role of the endogenous cannabinoids in the hypotension of human endotoxic shock. This method is rapid, sensitive, and reliable for simultaneously quantifying ANA and 2-AG in biological fluids, and has potential for clinical usage.

Evidence for an endocannabinoid system in the central nervous system of the leech Hirudo medicinalis

In invertebrates, like Hydra and sea urchins, evidence for a functional cannabinoid system was described. The partial characterization of a putative CB1 cannabinoid receptor in the leech Hirudo medicinalis led us to investigate the presence of a complete endogenous cannabinoid system in this organism. By using gas chromatography-mass spectrometry, we demonstrate the presence of the endocannabinoids anandamide (N-arachidonoylethanolamine, 21.5+/-0.7 pmol/g) and 2-arachidonoyl-glycerol (147.4+/-42.7 pmol/g), and of the biosynthetic precursor of anandamide, N-arachidonylphosphatidyl-ethanolamine (16.5+/-3.3 pmol/g), in the leech central nervous system (CNS). Anandamide-related molecules such as N-palmitoylethanolamine (32.4+/-1.6 pmol/g) and N-linolenoylethanolamine (5.8 pmol/g) were also detected. We also found an anandamide amidase activity in the leech CNS cytosolic fraction with a maximal activity at pH 7 and little sensitivity to typical fatty acid amide hydrolase (FAAH) inhibitors. Using an antiserum directed against the amidase signature sequence, we focused on the identification and the localization of the leech amidase. Firstly, leech nervous system protein extract was subjected to Western blot analysis, which showed three immunoreactive bands at ca. approximately 42, approximately 46 and approximately 66 kDa. The former and latter bands were very faint and were also detected in whole homogenates from the coelenterate Hydra vulgaris, where the presence of CB1-like receptors, endocannabinoids and a FAAH-like activity was reported previously. Secondly, amidase immunocytochemical detection revealed numerous immunoreactive neurons in the CNS of three species of leeches. In addition, we observed that leech amidase-like immunoreactivity matches to a certain extent with CB1-like immunoreactivity. Finally, we also found that stimulation by anandamide of this receptor leads, as in mammals, to inhibition of cAMP formation, although this effect appeared to be occurring through the previously described anandamide-induced and CB1-mediated activation of nitric oxide release. Taken together, these results suggest the existence of a complete and functional cannabinoid system in leeches.

Gas chromatography-mass spectrometry analysis of endogenous cannabinoids in healthy and tumoral human brain and human cells in culture

Endocannabinoids are lipid mediators thought to modulate central and peripheral neural functions. We report here gas chromatography-electron impact mass spectrometry analysis of human brain, showing that lipid extracts contain anandamide and 2-arachidonoylglycerol (2-AG), the most active endocannabinoids known to date. Human brain also contained the endocannabinoid-like compounds N-oleoylethanolamine, N-palmitoylethanolamine and N-stearoylethanolamine. Anandamide and 2-AG (0.16 +/- 0.05 and 0.10 +/- 0.05 nmol/mg protein, respectively) represented 7.7% and 4.8% of total endocannabinoid-like compounds, respectively. N-Palmitoyethanolamine was the most abundant (50%), followed by N-oleoyl (23.6%) and N-stearoyl (13.9%) ethanolamines. A similar composition in endocannabinoid-like compounds was found in human neuroblastoma CHP100 and lymphoma U937 cells, and also in rat brain. Remarkably, human meningioma specimens showed an approximately six-fold smaller content of all N-acylethanolamines, but not of 2-AG, and a similar decrease was observed in a human glioblastoma. These ex vivo results fully support the purported roles of endocannabinoids in the nervous system.

Determination of the phospholipid precursor of anandamide and other N-acylethanolamine phospholipids before and after sodium azide-induced toxicity in cultured neocortical neurons

Phospholipase D-mediated hydrolysis of N-acylethanolamine phospholipids (NAPEs) releases anandamide and other N-acylethanolamines, resulting in different actions at cellular targets in the CNS. Recently, we have demonstrated that these N-acyl lipids accumulate in cultured neocortical neurons subjected to sodium azide-induced cell injury. We here extend the information on the NAPE response, reporting on the composition of N-acylspecies of NAPE, employing a new methodological approach of HPLC-coupled electrospray ionization mass spectrometry. Exposure to sodium azide (5 mM) increased the total amount of NAPE threefold over control levels; however, no alteration of the relative composition of NAPE species was detected. The anandamide precursor (20 : 4-NAPE) constituted only 0.1% of all NAPEs detected in the neurons. Total NAPE species in control cells amounted to 956-1,060 pmol/10(7) cells. Moreover, we detected the presence of an unknown NAPE species with molecular weight identical to 20 : 4-NAPE. This may suggest the presence of a putative stereoisomer of the anandamide precursor with at least one trans-configured double bond in the N-arachidonoyl moiety. These results show that with the present method, neuronal NAPE species can be identified and quantified with respect to N-acyl composition, including a trans-isomer of the anandamide precursor. The anandamide precursor is up-regulated to the same extent as other NAPEs upon neuronal injury.

Quantification of bioactive acylethanolamides in rat plasma by electrospray mass spectrometry

We developed a high-performance liquid chromatography/mass spectrometry (HPLC/MS) method for the identification and quantification of anandamide, an endogenous cannabinoid substance, and other fatty acid ethanolamides (AEs) in biological samples. Using a mobile-phase system of methanol/water and gradient elution, we achieved satisfactory resolution of all major AEs, including anandamide, palmitylethanolamide (PEA), and oleylethanolamide (OEA). Electrospray-generated quasi-molecular species were used as diagnostic ions and detected by selected ion monitoring (SIM). Synthetic deuterium-labeled AEs were used as internal standards, and quantification was carried out by isotope dilution. A linear correlation (r2 = 0.99) was observed in the calibration curves for standard AEs over the range 0-0.5 nmol. Detection limits between 0.1 and 0.3 pmol per sample and quantification limits between 0.5 and 1.2 pmol per sample were obtained. The method was applied to the quantification of anandamide, PEA, and OEA in plasma prepared from rat blood collected either by cardiac puncture or by decapitation. After cardiac puncture, AE levels were in the low-nanomolar range: anandamide, 3.1 +/- 0.6 pmol/ml; PEA, 9.4 +/- 1.6 pmol/ml; OEA, 9.2 +/- 1.8 pmol/ml (mean +/- SE, n = 9). By contrast, after decapitation AEs were dramatically elevated (anandamide, 144 +/- 13 pmol/ml; PEA, 255 +/- 55 pmol/ml; OEA, 175 +/- 48 pmol/ml). Thus, disruptive procedures of blood collection may result in gross overestimates in the concentrations of circulating AEs.

Sex steroid influence on cannabinoid CB(1) receptor mRNA and endocannabinoid levels in the anterior pituitary gland

Recent studies have demonstrated the occurrence of endocannabinoid synthesis and of gene expression and immunoreactivity for the cannabinoid CB(1) receptor in the anterior pituitary gland. Since the activity of this gland is under the influence of circulating sex steroids, the present study was designed to elucidate whether expression of the CB(1) receptor gene in the anterior pituitary gland is also under the influence of these steroids. To this aim, we first examined the possible changes in the levels of CB(1) receptor-mRNA transcripts in the anterior pituitary gland of intact male rats and normal cycling female rats at the different stages of the ovarian cycle. We observed that males had higher levels of CB(1) receptor-mRNA transcripts than females. In addition, these transcripts fluctuated in females during the different phases of the ovarian cycle, with the highest values observed on the second day of diestrus and the lowest on estrus. In these animals, we also measured the content of endocannabinoids in the anterior pituitary gland and the hypothalamus. We observed that females had higher contents of anandamide than males in both cases. The content of anandamide in females also fluctuated during the ovarian cycle in both the anterior pituitary gland and the hypothalamus. The highest values in the anterior pituitary gland were found in the estrus and the lowest on the first day of diestrus and proestrus, whereas the inverse tendency was found in the hypothalamus. No changes were observed in the other major endocannabinoid, 2-arachidonoyl-glycerol, between males and females and during the ovarian cycle. To further explore the potential influence of circulating sex steroids on CB(1) receptor gene expression in the anterior pituitary gland, as a second objective, we examined the possible changes in the amount of transcripts for this receptor in gonadectomized and sex steroid-replaced gonadectomized rats of both sexes. We observed that orchidectomy (ORCHX) in males reduced CB(1) receptor-mRNA levels, whereas replacement with dihydrotestosterone also maintained low levels of this messenger. In females, estradiol-replaced ovariectomized (OVX) rats exhibited significantly lower CB(1) receptor-mRNA levels than OVX animals that had not been replaced with this estrogen. In this experiment, we also examined if the previously reported response of the CB(1) receptor gene in the anterior pituitary lobe to chronic administration of Delta(9)-tetrahydrocannabinol (Delta(9)-THC) is under sex steroid influence. We observed that chronic Delta(9)-THC treatment decreased CB(1) receptor-mRNA levels in intact and ORCHX males, but not in dihydrotestosterone-replaced ORCHX males. In females, Delta(9)-THC treatment produced no effect in both OVX- and estradiol-replaced OVX rats. In summary, these data collectively support that expression of the CB(1) receptor gene in the anterior pituitary gland is regulated by sex steroids in both males and females. Furthermore, gonadal steroids appear to affect the response of this gene to chronic cannabinoid administration. We have also observed that anandamide contents in the anterior pituitary gland and the hypothalamus might be controlled by circulating sex steroids. The functional implications of these data are discussed.

Sensitive determination of anandamide in rat brain utilizing a coupled-column HPLC with fluorimetric detection

A fluorimetric determination method for N-arachidonoylethanolamine (anandamide) was developed using a precolumn fluorescence derivatization followed by coupled-column high-performance liquid chromatography (HPLC). Anandamide extracted from the rat brain tissue was derivatized with 4-N-chloroformylmethyl-N-methylamino-7-N, N-dimethylaminosulfonyl-2,1,3-benzoxadiazole (DBD-COCl), purified by a solid-phase extraction (Emporetrade mark), and assayed by the coupled-column HPLC. The HPLC consisted of phenyl (100 x 4.6 mm i.d. ) and octadecylsilica columns (250 x 4.6 mm i.d.), both connected by a six-port valve. The concentration of anandamide in rat brain was 3. 37 +/- 0.73 pmol/g with 6.47 and 3.57% of intra- and inter-day precisions, respectively. Using this method, we investigated the alteration of anandamide concentration in rat brain 30 min after administration of anandamide (2 mg/kg, i.p.) to rats pretreated with or without phenylmethylsulfonyl fluoride (PMSF; 30 mg/kg, i.p.), an inhibitor of amidohydrolase. In rats pretreated with PMSF, the brain concentration of anandamide was approx. 16-fold higher than that of rats without PMSF (p < 0.01).

Enhancement of anandamide formation in the limbic forebrain and reduction of endocannabinoid contents in the striatum of delta9-tetrahydrocannabinol-tolerant rats

Recent studies have shown that the pharmacological tolerance observed after prolonged exposure to synthetic or plant-derived cannabinoids in adult rats is accompanied by down-regulation/desensitization of brain cannabinoid receptors. However, no evidence exists on possible changes in the contents of the endogenous ligands of cannabinoid receptors in the brain of cannabinoid-tolerant rats. The present study was designed to elucidate this possibility by measuring, by means of isotope dilution gas chromatography/mass spectrometry, the contents of both anandamide (arachidonoylethanolamide; AEA) and its biosynthetic precursor, N-arachidonoylphosphatidylethanolamine (NArPE), and 2-arachidonoylglycerol (2-AG) in several brain regions of adult male rats treated daily with delta9-tetrahydrocannabinol (delta9-THC) for a period of 8 days. The areas analyzed included cerebellum, striatum, limbic forebrain, hippocampus, cerebral cortex, and brainstem. The same regions were also analyzed for cannabinoid receptor binding and WIN-55,212-2-stimulated guanylyl-5'-O-(gamma-[35S]thio)-triphosphate ([35S]GTPgammaS) binding to test the development of the well known down-regulation/desensitization phenomenon. Results were as follows: As expected, cannabinoid receptor binding and WIN-55,212-2-stimulated [35S]GTPgammaS binding decreased in most of the brain areas of delta9-THC-tolerant rats. The only region exhibiting no changes in both parameters was the limbic forebrain. This same region exhibited a marked (almost fourfold) increase in the content of AEA after 8 days of delta9-THC treatment. By contrast, the striatum exhibited a decrease in AEA contents, whereas no changes were found in the brainstem, hippocampus, cerebellum, or cerebral cortex. The increase in AEA contents observed in the limbic forebrain was accompanied by a tendency of NArPE levels to decrease, whereas in the striatum, no significant change in NArPE contents was found. The contents of 2-AG were unchanged in brain regions from delta9-THC-tolerant rats, except for the striatum where they dropped significantly. In summary, the present results show that prolonged activation of cannabinoid receptors leads to decreased endocannabinoid contents and signaling in the striatum and to increased AEA formation in the limbic forebrain. The pathophysiological implications of these findings are discussed in view of the proposed roles of endocannabinoids in the control of motor behavior and emotional states.

Novel and sensitive method for the detection of anandamide by the use of its dansyl derivative

The dansyl ester of anandamide was prepared and showed intense fluorescence on silica gel thin-layer chromatography when viewed under long-wavelength ultraviolet light (detection limit, 15 fmol). A high-performance liquid chromatography method for the quantitation of anandamide was developed using a C18 column (250 x 4.6 mm) with gradient elution (1% acetic acid-methanol) and detection at 255 nm. The method was applied to the measurement of anandamide in media from cultured hepatocytes. Sample preparation involved extraction with a C18 cartridge, derivatization with dansyl chloride, thin-layer chromatography, and quantitation. The detection limit in hepatocyte media is 4.3 nmol at a signal-to-noise ratio of three.

Analysis of cannabinoid receptor binding and mRNA expression and endogenous cannabinoid contents in the developing rat brain during late gestation and early postnatal period

Cannabinoid CB(1) receptors emerge early in the rat brain during prenatal development, supporting their potential participation in events related to neural development. In the present investigation, we completed earlier studies, analyzing CB(1) receptor binding and mRNA expression by using autoradiography and in situ hybridization, respectively, in the brain of rat fetuses at gestational day (GD) 21 and of newborns at postnatal days (PND) 1 and 5, in comparison with the adult brain. These analyses were paralleled by quantitation of levels of anandamide and its precursor, N-arachidonoyl-phosphatidylethanolamine (NAPE), and of 2-arachidonoyl-glycerol (2-AG), carried out by using gas chromatography / mass spectrometry of the tri-methyl-sylyl-ether derivatives. As expected, CB(1) receptor binding was detected at GD21 in a variety of brain structures. In most of them, such as the hippocampus, cerebral cortex, cerebellum, basal ganglia, and limbic nuclei, there were no marked differences in the density of CB(1) receptors in animals at GD21 as compared to early newborns (PND1 and 5), although it markedly increased in these regions in adulthood. However, with the exception of the cerebellum and, in part, the caudate-putamen, the pattern observed for binding in these regions was clearly different from that observed for mRNA expression of the CB(1) receptor, which currently exhibited the highest levels at PND1 and the lowest in the adult brain. This was also seen in the basolateral amygdaloid nucleus, ventromedial hypothalamic nucleus, medial habenula, and other structures. In the caudate-putamen and, particularly, in the cerebellum, mRNA expression was higher in the adult brain as compared with other ages. As previously reported, specific binding for CB(1) receptors was also detected at GD21 in white matter areas, such as the corpus callosum, anterior commissure, fornix, fimbria, stria medullaris, stria terminalis, and fasciculus retroflexum. With the exception of the anterior commissure and the fimbria, specific binding progressively decreased at PND1 and PND5 until disappearing in the adult brain. In the fimbria, the highest values of binding were seen at PND1, but binding also completely disappeared in the adult brain, whereas in the anterior commissure, specific binding at PND1 and PND5 was lesser than that observed at GD21 and, particularly, in adulthood. CB(1) receptor mRNA expression was not detected in these white matter areas, thus dismissing the possible presence of these receptors in glial cells rather than in neuronal axons. However, mRNA expression was detected in the brainstem, an area also rich in white matter, and it mostly correlated with receptor binding, exhibiting a progressive decrease from GD21 up to adulthood. CB(1) receptor mRNA expression was also detected at GD21 in atypical areas where binding was not detected. These areas are proliferative regions, such as the subventricular zones of the neocortex, striatum, and nucleus accumbens. This atypical location only persisted at PND1 and PND5 in the striatal subventricular zone, but disappeared in the adult brain. We also found measurable levels of different endogenous cannabinoids in the developing brain. High levels of 2-AG, comparable to those found in the adult brain, were measured at GD21, whereas significantly lower levels were measured for anandamide and NAPE at this fetal age compared with the levels found in the adult brain. Levels of anandamide and NAPE increased during the early postnatal period until reaching the maximum in the adult brain. By contrast, 2-AG levels peaked at PND1, with values approximately twofold higher than those found at the other ages. In summary, all these data demonstrate that the endogenous cannabinoid system, constituted by endogenous ligands and receptor signaling pathways, is present in the developing brain, which suggests a possible specific role of this system in key processes of neural development. (c) 1999 Wiley-Liss, Inc.

Finding of the endocannabinoid signalling system in Hydra, a very primitive organism: possible role in the feeding response

Hydra (Cnidaria) is the first animal organism to have developed a neural network, which has been proposed to control, inter alia, the "feeding response", i.e. a mechanism through which the coelenterate opens and then closes its mouth in the presence of prey and/or glutathione. Here, we report that Hydra contains: (i) selective cannabinoid binding sites; (ii) the endogenous cannabinoid receptor ligand, anandamide (arachidonoylethanolamide); (iii) a fatty acid amide hydrolase-like activity catalysing anandamide hydrolysis; and (iv) the putative biosynthetic precursor of anandamide, N-arachidonoylphosphatidylethanolamine. We suggest that this "endogenous cannabinoid system" is involved in the modulation of the "feeding response". Anandamide (1 nM-1 microM) potently inhibited (up to 45%) the glutathione-induced "feeding response" by accelerating Hydra vulgaris mouth closure. The effect was maximal at 100 nM anandamide and was reversed by the selective antagonist of the CB1 subtype of mammalian cannabinoid receptors, SR 141716A (50-100 nM). Specific cannabinoid binding sites were detected in membranes from Hydra polyps by using [3H]SR 141716A (Kd= 1.87 nM, Bmax = 26.7 fmol/mg protein), and increasing anandamide concentrations were found to displace the binding of [3H]SR 141716A to these membranes (Ki = .505 nM). Hydra polyps were also found to contain amounts of anandamide (15.6 pmol/g) and N-arachidonoylphosphatidylethanolamine (32.4 pmol/g), as well as the other "endocannabinoid" 2-arachidonoylglycerol (11.2 nmol/g), comparable to those described previously for mammalian brain. Finally, a fatty acid amide hydrolase activity (Vmax = 3.4 nmol/min/mg protein), with subcellular distribution, pH dependency and sensitivity to inhibitors similar to those reported for the mammalian enzyme, but with a lower affinity for anandamide (Km = 400 microM), was also detected in Hydra polyps. These data suggest that the endocannabinoid signalling system plays a physiological role in Hydra that is to control the feeding response. Hydra is the simplest living organism described so far to use this recently discovered regulatory system.

GC/MS analysis of anandamide and quantification of N-arachidonoylphosphatidylethanolamides in various brain regions, spinal cord, testis, and spleen of the rat

Anandamide [N-arachidonoylethanolamide (NAE)] was initially isolated from porcine brain and proposed as an endogenous ligand for cannabinoid receptors in 1992. Accumulating evidence has now suggested that, in the tissue, NAE is generated from N-arachidonoylphosphatidylethanolamides (N-ArPEs) by phosphodiesterase. In this study a sensitive and specific procedure was developed to quantify NAE and N-ArPE, including organic solvent extraction, reverse-phase C-18 cartridge separation, derivatization, and gas chromatography/mass spectrometry (GC/MS) analysis. NAE is converted by a two-step derivatization procedure to a pentafluorobenzoyl ester followed by pentafluoropropionyl acylation. Quantification was performed by isotope dilution GC/MS using deuterium-labeled NAE (NAE-2H8) as an internal standard. The same chemical derivatization was applicable to N-ArPE quantification. The separated N-ArPE fractions were converted by a two-step cleavage/derivatization procedure into the pentafluorobenzoyl ester of NAE and then to its pentafluoropropionyl amide. The derivative was quantified by GC/MS using deuterium-labeled 1,2-[2H8]dioleoyl-sn-glycero-3-phospho(arachidonoyl)ethanolamid e as an internal standard. Using these methods, we have found that endogenous NAE levels in rat brain, spleen, testis, liver, lung, and heart were below the level of quantification achievable (0.1 pmol/mg of protein) but that N-ArPE is readily quantifiable and is widely distributed in the rat CNS with the highest level in the spinal cord. The striatum, hippocampus, and accumbens contain intermediate concentrations of N-ArPE, whereas the value is lowest in the cerebellum.

Biochemistry of the endogenous ligands of cannabinoid receptors

In 1992 the discovery of the first endogenous ligand of cannabinoid receptors, anandamide, provided conclusive support to the hypothesis that an "endogenous cannabinoid regulatory system" exists in mammalian nervous tissue. Anandamide (N-arachidonoyl-ethanolamine) was the first of a series of long-chain fatty acid derivatives, including two other polyunsaturated N-acylethanolamines and 2-arachidonoyl-glycerol, found to exert cannabimimetic properties in either central or peripheral tissues. Here we review the current knowledge on the biochemical bases of the formation and inactivation of endogenous cannabinoid ligands as well as of their interaction with cannabinoid receptor subtypes.

Endocannabinoids

The background knowledge leading to the isolation and identification of anandamide and 2-arachidonoyl glycerol, the principal endocannabinoids is described. The structure-activity relationships of these lipid derivatives are summarized. Selected biochemical and pharmacological topics in this field are discussed, the main ones being levels of endocannabinoids in unstimulated tissue and cells, biosynthesis, release and inactivation of endocannabinoids, the effects of 'entourage' compounds on the activities of anandamide and 2-arachidonoyl glycerol, their signaling mechanisms and effects in animals.

'Endocannabinoids' and other fatty acid derivatives with cannabimimetic properties: biochemistry and possible physiopathological relevance

The only endogenous substances isolated and characterised so far that are capable of mimicking the pharmacological actions of the active principle of marijuana, (-)-Delta9-tetrahydrocannabinol, are amides and esters of fatty acids. Some of these compounds, like anandamide (N-arachidonoylethanolamine) and 2-arachidonoylglycerol, act as true 'endogenous cannabinoids' by binding and functionally activating one or both cannabinoid receptor subtypes present on nervous and peripheral cell membranes. The metabolic pathways and molecular mode of actions of these metabolites, as well as their possible implication in physiopathological responses, are reviewed here.