Simultaneous determination of 2-arachidonoylglycerol, 1-arachidonoylglycerol and arachidonic acid in mouse brain tissue using liquid chromatography/tandem mass spectrometry

From Classical to Alternative Pathways of 2-Arachidonoylglycerol Synthesis: AlterAGs at the Crossroad of Endocannabinoid and Lysophospholipid Signaling

2-arachidonoylglycerol (2-AG) is the most abundant endocannabinoid (EC), acting as a full agonist at both CB1 and CB2 cannabinoid receptors. It is synthesized on demand in postsynaptic membranes through the sequential action of phosphoinositide-specific phospholipase Cβ1 (PLCβ1) and diacylglycerol lipase α (DAGLα), contributing to retrograde signaling upon interaction with presynaptic CB1. However, 2-AG production might also involve various combinations of PLC and DAGL isoforms, as well as additional intracellular pathways implying other enzymes and substrates. Three other alternative pathways of 2-AG synthesis rest on the extracellular cleavage of 2-arachidonoyl-lysophospholipids by three different hydrolases: glycerophosphodiesterase 3 (GDE3), lipid phosphate phosphatases (LPPs), and two members of ecto-nucleotide pyrophosphatase/phosphodiesterases (ENPP6-7). We propose the names of AlterAG-1, -2, and -3 for three pathways sharing an ectocellular localization, allowing them to convert extracellular lysophospholipid mediators into 2-AG, thus inducing typical signaling switches between various G-protein-coupled receptors (GPCRs). This implies the critical importance of the regioisomerism of both lysophospholipid (LPLs) and 2-AG, which is the object of deep analysis within this review. The precise functional roles of AlterAGs are still poorly understood and will require gene invalidation approaches, knowing that both 2-AG and its related lysophospholipids are involved in numerous aspects of physiology and pathology, including cancer, inflammation, immune defenses, obesity, bone development, neurodegeneration, or psychiatric disorders.

An Innovative Sandwich Type Biosensor towards Sensitive and Selective Monitoring of 2-Arachidonoylglycerol in Human Plasma Samples Using P(β-CD)-AuNPs-DDT as Amplificant Agent: A New Immuno-Platform for the Recognition of Endocannabinoids in Real Samples

In this work, 2-AG was successfully detected in human plasma samples using a new sandwich-type electrochemical immune device based on poly-β-cyclodextrin P(β-CD) functionalized with AuNPs-DDT and toluidine blue. The P(β-CD) ensured the bioactivity and stability of the immobilized 2-AG antibody by providing a broad surface for the efficient immobilization of the biotinylated antibody. To complete the top section of the immunosensor (reporter), an HRP-conjugated antibody of 2-AG (secondary antibody (Ab2)) was attached to the surface of a glassy carbon electrode (GCE) modified by P(β-CD), as well as a primarily biotinylated antibody (Ab1). The biosensor fabrication process was monitored using field-emission scanning electron microscope (FE-SEM) and EDS methods. Using the differential pulse voltammetry technique, the immunosensor was utilized for detection of 2-AG in real samples. The suggested interface increased the surface area, which allowed for the immobilization of a large quantity of anti-2-AG antibody while also improving biocompatibility, stability, and electrical conductivity. Finally, the suggested immunosensor’s limit of quantitation was determined to be 0.0078 ng/L, with a linear range of 0.0078 to 1.0 ng/L. The results showed that the suggested bioassay can be utilized for diagnosis of 2-AG in clinical samples as a unique and ultrasensitive electrochemical biodevice.

An innovative electrochemical immuno-platform towards ultra-sensitive monitoring of 2-arachidonoyl glycerol in samples from rats with sleep deprivation: bioanalysis of endogenous cannabinoids using biosensor technology

The endocannabinoid system (ECS) is a complex of neurotransmitters in the central nervous system and plays a key role in regulating cognitive and physiological processes. 2-Arachidonoylglycerol (2-AG) is one of the imperative endocannabinoids that play key roles in the central nervous system. It acts as a signaling lipid and activates the cannabinoid CB1 receptor. In addition, 2-AG is involved in a variety of physiological functions such as energy balance, emotion, pain sensation, cognition, and neuroinflammation. So, rapid and specific diagnosis of 2-AG is of great importance in medical neuroscience. The development of new methods in this area has been one of the most important research areas in recent years. Herein, an innovative immunosensor is developed for quantification of 2-AG. For this means, gold nanostars (GNS) were synthesized and conjugated with a specific biotinylated antibody against 2-AG. The resultant bioconjugate, a bioreceptor with GNS, was immobilized on the surface of a gold electrode and used for the detection of the antigen based on the immunocomplex formation followed by analysis using different electrochemical techniques. For the first time, 2-AG protein was measured with an excellent linear range of 0.48–1 ng mL⁻¹ and lower limit of quantification of 0.48 ng L⁻¹ by the electroanalysis method. The engineered immunosensor showed high sensitivity and specificity in the presence of interfering antigens, proving its utility in neurological disorder detection. This immunosensor is the first sandwich type immunoassay for the detection of 2-AG in real samples and the first innovation of designing a novel sandwich type immunosensor for this analyte. Also, excellent analytical results are other advantages of this biosensor for the detection of 2-AG in human plasma samples and serum samples of rats under sleep deprivation. So, this is the first report of an immunosensor of 2-AG using a sandwich type immunosensor.

A novel electrochemical immunosensor based gold nanoparticles for the sensitive recognition of 2-AG was introduced.

Bioconjugation of 2-arachidonoyl glycerol (2-AG) biotinylated antibody with gold nano-flowers toward immunosensing of 2-AG in human plasma samples: A novel immuno-platform for the screening of immunomodulation and neuroprotection using biosensing

Human 2-arachidonoylglycerol (2-AG) is an agonist of endocannabinoid system and acts as an important modulator of many physiological processes such as emotional state and pain sensation. Identification and quantification of 2-AG is vital for medical and pathological processes. There are no reports on the measurement of 2-AG in human biofluids using modern methods such as biosensors. This study reports an ultra-sensitive and selective immunosensor to determine endocannabinoids 2-AG in human plasma samples. In this study, gold nano-flowers (AuNFs) were synthesized and conjugated with a specific biotinylated antibody of 2-AG. Bioconjugated composite (bioreceptor with AuNFs) was immobilized on the surface of a gold electrode and used for the monitoring of the antigen (target molecules) based on the immunoreaction process. Moreover, a constructed interface was characterized by field-emission scanning electron microscopy (FE-SEM), dynamic light scattering (DLS), transmission electron microscopy (TEM) and zeta potential methods. Using the proposed immuno-platform, 2-AG was determined in two dynamic ranges of 0.00024-0.0078 ng L-1 and 2-16 ng L-1 with a lower limit of quantitation (LLOQ) of 0.00024 ng L-1. These results suggest that our immunosensor might be appropriate for an early diagnosis of 2-AG towards the screening of immunomodulatory activity and neuroprotection.

Compensatory Activation of Cannabinoid CB2 Receptor Inhibition of GABA Release in the Rostral Ventromedial Medulla in Inflammatory Pain

The rostral ventromedial medulla (RVM) is a relay in the descending pain modulatory system and an important site of endocannabinoid modulation of pain. Endocannabinoids inhibit GABA release in the RVM, but it is not known whether this effect persists in chronic pain states. In the present studies, persistent inflammation induced by complete Freund's adjuvant (CFA) increased GABAergic miniature IPSCs (mIPSCs). Endocannabinoid activation of cannabinoid (CB1) receptors known to inhibit presynaptic GABA release was significantly reduced in the RVM of CFA-treated rats compared with naive rats. The reduction in CFA-treated rats correlated with decreased CB1 receptor protein expression and function in the RVM. Paradoxically, the nonselective CB1/CB2 receptor agonist WIN55212 inhibited GABAergic mIPSCs in both naive and CFA-treated rats. However, WIN55212 inhibition was reversed by the CB1 receptor antagonist rimonabant in naive rats but not in CFA-treated rats. WIN55212-mediated inhibition in CFA-treated rats was blocked by the CB2 receptor-selective antagonist SR144528, indicating that CB2 receptor function in the RVM is increased during persistent inflammation. Consistent with these results, CB2 receptor agonists AM1241 and GW405833 inhibited GABAergic mIPSC frequency only in CFA-treated rats, and the inhibition was reversed with SR144528. When administered alone, SR144528 and another CB2 receptor-selective antagonist AM630 increased mIPSC frequency in the RVM of CFA-treated rats, indicating that CB2 receptors are tonically activated by endocannabinoids. Our data provide evidence that CB2 receptor function emerges in the RVM in persistent inflammation and that selective CB2 receptor agonists may be useful for treatment of persistent inflammatory pain.

SIGNIFICANCE STATEMENT

These studies demonstrate that endocannabinoid signaling to CB1 and CB2 receptors in adult rostral ventromedial medulla is altered in persistent inflammation. The emergence of CB2 receptor function in the rostral ventromedial medulla provides additional rationale for the development of CB2 receptor-selective agonists as useful therapeutics for chronic inflammatory pain.

The Ratio of 2-AG to Its Isomer 1-AG as an Intrinsic Fine Tuning Mechanism of CB1 Receptor Activation

Endocannabinoids are pleiotropic lipid messengers that play pro-homeostatic role in cellular physiology by strongly influencing intracellular Ca²⁺ concentration through the activation of cannabinoid receptors. One of the best-known endocannabinoid ‘2-AG’ is chemically unstable in aqueous solutions, thus its molecular rearrangement, resulting in the formation of 1-AG, may influence 2-AG-mediated signaling depending on the relative concentration and potency of the two isomers. To predict whether this molecular rearrangement may be relevant in physiological processes and in experiments with 2-AG, here we studied if isomerization of 2-AG has an impact on 2-AG-induced, CB1-mediated Ca²⁺ signaling in vitro. We found that the isomerization-dependent drop in effective 2-AG concentration caused only a weak diminution of Ca²⁺ signaling in CB1 transfected COS7 cells. We also found that 1-AG induces Ca²⁺ transients through the activation of CB1, but its working concentration is threefold higher than that of 2-AG. Decreasing the concentration of 2-AG in parallel to the prevention of 1-AG formation by rapid preparation of 2-AG solutions, caused a significant diminution of Ca²⁺ signals. However, various mixtures of the two isomers in a fix total concentration – mimicking the process of isomerization over time – attenuated the drop in 2-AG potency, resulting in a minor decrease in CB1 mediated Ca²⁺ transients. Our results indicate that release of 2-AG into aqueous medium is accompanied by its isomerization, resulting in a drop of 2-AG concentration and simultaneous formation of the similarly bioactive isomer 1-AG. Thus, the relative concentration of the two isomers with different potency and efficacy may influence CB1 activation and the consequent biological responses. In addition, our results suggest that 1-AG may play role in stabilizing the strength of cannabinoid signal in case of prolonged 2-AG dependent cannabinoid mechanisms.

WWL70 attenuates PGE2 production derived from 2-arachidonoylglycerol in microglia by ABHD6-independent mechanism

BACKGROUND

α/β-Hydrolase domain 6 (ABHD6) is one of the major enzymes for endocannabinoid 2-arachidonoylglycerol (2-AG) hydrolysis in microglia cells. Our recent studies have shown that a selective ABHD6 inhibitor WWL70 has anti-inflammatory and neuroprotective effects in animal models of traumatic brain injury and multiple sclerosis. However, the role of ABHD6 in the neuroinflammatory response and the mechanisms by which WWL70 suppresses inflammation has not yet been elucidated in reactive microglia.

METHODS

The hydrolytic activity and the levels of 2-AG in BV2 cells were measured by radioactivity assay and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). The expression of cyclooxygenase-2 (COX-2) and prostaglandin E₂ (PGE₂) synthases in microglia treated with lipopolysaccharide (LPS) with/without WWL70 was determined by western blot and quantitative RT-PCR. The conversion of 2-AG to PGE₂ or PGE₂-glyceryl ester (PGE₂-G) was assessed by enzyme-linked immunoassay (EIA) or LC-MS/MS. The involvement of ABHD6 in PGE₂ production was assessed using pharmacological inhibitors and small interfering RNA (siRNA). The effect of WWL70 on PGE₂ biosynthesis activity in the microsome fraction from BV2 cells and experimental autoimmune encephalopathy (EAE) mouse brain was also examined.

RESULTS

We found that WWL70 suppressed PGE₂ production in LPS-activated microglia via cannabinoid receptor-independent mechanisms, although intracellular levels of 2-AG were elevated by WWL70 treatment. This reduction was not attributable to WWL70 inhibition of ABHD6, given the fact that downregulation of ABHD6 by siRNA or use of KT182, an alternative ABHD6 inhibitor failed to suppress PGE₂ production. WWL70 attenuated the expression of COX-2 and PGES-1/2 leading to the downregulation of the biosynthetic pathways of PGE₂ and PGE₂-G. Moreover, PGE₂ production from arachidonic acid was reduced in the microsome fraction, indicating that WWL70 also targets PGE₂ biosynthetic enzymes, which are likely to contribute to the therapeutic mechanisms of WWL70 in the EAE mouse model.

CONCLUSIONS

WWL70 is an anti-inflammatory therapeutic agent capable of inhibiting PGE₂ and PGE₂-G production, primarily due to its reduction of COX-2 and microsomal PGES-1/2 expression and their PGE₂ biosynthesis activity in microglia cells, as well as in the EAE mouse brain.

Shotgun Lipidomics Approach to Stabilize the Regiospecificity of Monoglycerides Using a Facile Low-Temperature Derivatization Enabling Their Definitive Identification and Quantitation

Monoglycerides play a central role in lipid metabolism and are important signaling metabolites. Quantitative analysis of monoglyceride molecular species has remained challenging due to rapid isomerization via α-hydroxy acyl migration. Herein, we describe a shotgun lipidomics approach that utilizes a single-phase methyl tert-butyl ether extraction to minimize acyl migration, a facile low temperature diacetyl derivatization to stabilize regiospecificity, and tandem mass spectrometric analysis to identify and quantify regioisomers of monoglycerides in biological samples. The rapid and robust diacetyl derivatization at low temperatures (e.g., -20 °C, 30 min) prevents postextraction acyl migration and preserves regiospecificity of monoglyceride structural isomers. Furthermore, ionization of ammonium adducts of diacetyl monoglyceride derivatives in positive-ion mode markedly increases analytic sensitivity (low fmol/μL). Critically, diacetyl derivatization enables the differentiation of discrete monoglyceride regioisomers without chromatography through their distinct signature fragmentation patterns during collision induced dissociation. The application of this approach in the analysis of monoglycerides in multiple biologic tissues demonstrated diverse profiles of molecular species. Remarkably, the regiospecificity of individual monoglyceride molecular species is also diverse from tissue to tissue. Collectively, this developed approach enables the profiling, identification and quantitation of monoglyceride regioisomers directly from tissue extracts.

Modulation of Long-Term Potentiation of Cortico-Amygdala Synaptic Responses and Auditory Fear Memory by Dietary Polyunsaturated Fatty Acid

Converging evidence suggests that an imbalance of ω3 to ω6 polyunsaturated fatty acid (PUFA) in the brain is involved in mental illnesses such as anxiety disorders. However, the underlying mechanism is unknown. We previously reported that the dietary ratio of ω3 to ω6 PUFA alters this ratio in the brain, and influences contextual fear memory. In addition to behavioral change, enhancement of cannabinoid CB1 receptor-mediated short-term synaptic plasticity and facilitation of the agonist sensitivity of CB1 receptors have been observed in excitatory synaptic responses in the basolateral nucleus of the amygdala (BLA). However, it is not known whether long-term synaptic plasticity in the amygdala is influenced by the dietary ratio of ω3 to ω6 PUFA. In the present study, we examined long-term potentiation (LTP) of optogenetically-evoked excitatory synaptic responses in synapses between the terminal of the projection from the auditory cortex (ACx) and the pyramidal cells in the lateral nucleus of the amygdala. We found that LTP in this pathway was attenuated in mice fed with a high ω3 to ω6 PUFA ratio diet (0.97), compared with mice fed with a low ω3 to ω6 PUFA ratio diet (0.14). Furthermore, mice in the former condition showed reduced fear responses in an auditory fear conditioning test, compared with mice in the latter condition. In both electrophysiological and behavioral experiments, the effect of a diet with a high ω3 to ω6 PUFA diet ratio was completely blocked by treatment with a CB1 receptor antagonist. Furthermore, a significant reduction was observed in cholesterol content, but not in the level of an endogenous CB1 receptor agonist, 2-arachidonoylglycerol (2-AG), in brain samples containing the amygdala. These results suggest that the balance of ω3 to ω6 PUFA has an impact on fear memory and cortico-amygdala synaptic plasticity, both in a CB1 receptor-dependent manner.

A quantitiative LC-MS/MS method for the measurement of arachidonic acid, prostanoids, endocannabinoids, N-acylethanolamines and steroids in human plasma

Free arachidonic acid is functionally interlinked with different lipid signaling networks including those involving prostanoid pathways, the endocannabinoid system, N-acylethanolamines, as well as steroids. A sensitive and specific LC-MS/MS method for the quantification of arachidonic acid, prostaglandin E2, thromboxane B2, anandamide, 2-arachidonoylglycerol, noladin ether, lineoyl ethanolamide, oleoyl ethanolamide, palmitoyl ethanolamide, steroyl ethanolamide, aldosterone, cortisol, dehydroepiandrosterone, progesterone, and testosterone in human plasma was developed and validated. Analytes were extracted using acetonitrile precipitation followed by solid phase extraction. Separations were performed by UFLC using a C18 column and analyzed on a triple quadrupole MS with electron spray ionization. Analytes were run first in negative mode and, subsequently, in positive mode in two independent LC-MS/MS runs. For each analyte, two MRM transitions were collected in order to confirm identity. All analytes showed good linearity over the investigated concentration range (r>0.98). Validated LLOQs ranged from 0.1 to 190ng/mL and LODs ranged from 0.04 to 12.3ng/mL. Our data show that this LC-MS/MS method is suitable for the quantification of a diverse set of bioactive lipids in plasma from human donors (n=32). The determined plasma levels are in agreement with the literature, thus providing a versatile method to explore pathophysiological processes in which changes of these lipids are implicated.

Quantification of anandamide, oleoylethanolamide and palmitoylethanolamide in rodent brain tissue using high performance liquid chromatography-electrospray mass spectroscopy

Reported concentrations for endocannabinoids and related lipids in biological tissues can vary greatly; therefore, methods used to quantify these compounds need to be validated. This report describes a method to quantify anandamide (AEA), oleoylethanolamide (OEA) and palmitoylethanolamide (PEA) from rodent brain tissue. Analytes were extracted using acetonitrile without further sample clean up, resolved on a C18 reverse-phase column using a gradient mobile phase and detected using electrospray ionization in positive selected ion monitoring mode on a single quadrupole mass spectrometer. The method produced high recovery rates for AEA, OEA and PEA, ranging from 98.1% to 106.2%, 98.5% to 102.2% and 85.4% to 89.5%, respectively. The method resulted in adequate sensitivity with a lower limit of quantification for AEA, OEA and PEA of 1.4 ng/mL, 0.6 ng/mL and 0.5 ng/mL, respectively. The method was reproducible as intraday and interday accuracies and precisions were under 15%. This method was suitable for quantifying AEA, OEA and PEA from rat brain following pharmacological inhibition of fatty acid amide hydrolase.

Synaptic Zn2+ inhibits neurotransmitter release by promoting endocannabinoid synthesis

Although it is well established that many glutamatergic neurons sequester Zn(2+) within their synaptic vesicles, the physiological significance of synaptic Zn(2+) remains poorly understood. In experiments performed in a Zn(2+)-enriched auditory brainstem nucleus--the dorsal cochlear nucleus--we discovered that synaptic Zn(2+) and GPR39, a putative metabotropic Zn(2+)-sensing receptor (mZnR), are necessary for triggering the synthesis of the endocannabinoid 2-arachidonoylglycerol (2-AG). The postsynaptic production of 2-AG, in turn, inhibits presynaptic probability of neurotransmitter release, thus shaping synaptic strength and short-term synaptic plasticity. Zn(2+)-induced inhibition of transmitter release is absent in mutant mice that lack either vesicular Zn(2+) or the mZnR. Moreover, mass spectrometry measurements of 2-AG levels reveal that Zn(2+)-mediated initiation of 2-AG synthesis is absent in mice lacking the mZnR. We reveal a previously unknown action of synaptic Zn(2+): synaptic Zn(2+) inhibits glutamate release by promoting 2-AG synthesis.

Determination of the two major endocannabinoids in human plasma by μ-SPE followed by HPLC-MS/MS

Endocannabinoids (ECs) are endogenous compounds that interact with type-1 and type-2 cannabinoid receptors (CB(1) and CB(2)), as well as non-cannabinoid receptors. The multitude of roles attributed to ECs makes them an emerging target of pharmacotherapy for a number of disparate diseases. Here a high-throughput bioanalytical method based on micro SPE (μ-SPE) followed by LC-MS/MS analysis for the simultaneous determination of the two major endocannabinoids 2-arachidonoylglycerol (2-AG) and N-arachidonoylethanolamine (anandamide, AEA) in human plasma is presented. The chromatographic conditions obtained with the fused-core column allowed a good separation in 10 min also of the AG isomers. A very simple and reliable extraction has been optimised by means of C18-modified tips: it requires only 100 μL of plasma and allows the use of minimal volumes of organic solvent. The present method allows a rapid and effective clean-up, which also minimises the isomerisation of 2-AG. The whole procedure has been validated following the FDA guidelines for bioanalytical methods validation: the satisfactory recovery values, the negligible matrix effect and the good values of accuracy and reproducibility make it a simple and high-throughput analytical tool for clinical and biochemical studies on endocannabinoid signaling in humans.

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.

A methodology for radiolabeling of the endocannabinoid 2-arachidonoylglycerol (2-AG)

The metabolic intermediate and endocannabinoid signaling lipid 2-arachidonoylglycerol (2-AG) has not been readily labeled, primarily because of its instability toward rearrangement. We now detail a synthetic method that easily gives tritiated 2-AG from [5,6,8,9,11,12,14,15-(3)H(N)]arachidonic acid in two steps. We utilized a short chain 1,3-diacylglycerol and proceeded through the "structured lipid" [5'',6'',8'',9'',11'',12'',14'',15''-(3)H(N)]2-arachidonoyl-1,3-dibutyrylglycerol, a triacylglycerol that was conveniently deprotected in ethanol with acrylic beads containing Candida antarctica lipase B to give [5'',6'',8'',9'',11'',12'',14'',15''-(3)H(N)]2-arachidonoylglycerol ([(3)H]2-AG). The flash chromatographic separation necessary to isolate the labeled 2-acylglycerol [(3)H]2-AG resulted in only 4% of the rearrangement byproducts that have been a particular problem with previous methodologies. This reliable "kit" method to prepare the radiolabeled endocannabinoid as needed gave tritiated 2-arachidonoylglycerol [(3)H]2-AG with a specific activity of 200 Ci/mmol for enzyme assays, metabolic studies, and tissue imaging. It has been run on unlabeled materials on over 10 mg scales and should be generally applicable to other 2-acylglycerols.

Monoacylglycerol lipase activity is a critical modulator of the tone and integrity of the endocannabinoid system

Endocannabinoids are lipid molecules that serve as natural ligands for the cannabinoid receptors CB1 and CB2. They modulate a diverse set of physiological processes such as pain, cognition, appetite, and emotional states, and their levels and functions are tightly regulated by enzymatic biosynthesis and degradation. 2-Arachidonoylglycerol (2-AG) is the most abundant endocannabinoid in the brain and is believed to be hydrolyzed primarily by the serine hydrolase monoacylglycerol lipase (MAGL). Although 2-AG binds and activates cannabinoid receptors in vitro, when administered in vivo, it induces only transient cannabimimetic effects as a result of its rapid catabolism. Here we show using a mouse model with a targeted disruption of the MAGL gene that MAGL is the major modulator of 2-AG hydrolysis in vivo. Mice lacking MAGL exhibit dramatically reduced 2-AG hydrolase activity and highly elevated 2-AG levels in the nervous system. A lack of MAGL activity and subsequent long-term elevation of 2-AG levels lead to desensitization of brain CB1 receptors with a significant reduction of cannabimimetic effects of CB1 agonists. Also consistent with CB1 desensitization, MAGL-deficient mice do not show alterations in neuropathic and inflammatory pain sensitivity. These findings provide the first genetic in vivo evidence that MAGL is the major regulator of 2-AG levels and signaling and reveal a pivotal role for 2-AG in modulating CB1 receptor sensitization and endocannabinoid tone.