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

Simultaneous Assessment of Serum Levels and Pharmacologic Effects of Cannabinoids on Endocannabinoids and N-Acylethanolamines by Liquid Chromatography-Tandem Mass Spectrometry

Introduction: The primary compounds of Cannabis sativa, delta-9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD), inflict a direct influence on the endocannabinoid system-a complex lipid signaling network with a central role in neurotransmission and control of inhibitory and excitatory synapses. These phytocannabinoids often interact with endogenously produced endocannabinoids (eCBs), as well as their structurally related N-acylethanolamines (NAEs), to drive neurobiological, nociceptive, and inflammatory responses. Identifying and quantifying changes in these lipid neuromodulators can be challenging owing to their low abundance in complex matrices. Materials and Methods: This article describes a robust liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the extraction and quantification of the eCBs anandamide and 2-arachidonoylglycerol, along with their congener NAEs oleoylethanolamine and palmitoylethanolamine, and phytocannabinoids CBD, Δ9-THC, and 11-Nor-9-carboxy-Δ9-tetrahydrocannabinol, a major metabolite of Δ9-THC. Our method was applied to explore pharmacokinetic and pharmacodynamic effects from intraperitoneal injections of Δ9-THC and CBD on circulating levels of eCBs and NAEs in rodent serum. Results: Detection limits ranged from low nanomolar to picomolar in concentration for eCBs (0.012-0.24 pmol/mL), NAEs (0.059 pmol/mL), and phytocannabinoids (0.24-0.73 pmol/mL). Our method displayed good linearity for calibration curves of all analytes (R2>0.99) as well as acceptable accuracy and precision, with quality controls not deviating >15% from their nominal value. Our LC-MS/MS method reliably identified changes to these endogenous lipid mediators that followed a causal relationship, which was dependent on both the type of phytocannabinoid administered and its pharmaceutical preparation. Conclusion: We present a rapid and reliable method for the simultaneous quantification of phytocannabinoids, eCBs, and NAEs in serum using LC-MS/MS. The accuracy and sensitivity of our assay infer it can routinely monitor endogenous levels of these lipid neuromodulators in serum and their response to external stimuli, including cannabimimetic agents.

Determination of endocannabinoids and their conjugated congeners in the brain by means of μSPE combined with UHPLC-MS/MS

The present study encompasses the development of a fast and reliable analytical method to quantify the main endocannabinoids and some of their conjugated congeners, particularly N-arachidonoyl amino acids, in brain tissue. Samples were homogenized and a micro solid phase extraction (μSPE) procedure was developed for brain homogenate clean-up. Miniaturized SPE was selected as it allowed to work with reduced sample amounts, while maintaining high sensitivity; this last feature was mandatory due to the low concentration of endocannabinoids in biological matrices that makes their determination a challenging analytical task. UHPLC-MS/MS was used for the analysis as it provided a great sensitivity, especially for conjugated forms that were detected by negative ionization. Polarity switching was applied during the run; low limits of quantification were between 0.003 ng g^-1 and 0.5 ng g^-1. This method provided also low matrix effect (lower than 30%) and good extraction recoveries in the brain. To the best of our knowledge, this is the first time that μSPE is applied on this matrix for this class of compounds. The method was validated according to international guidelines, and then tested on real cerebellum samples from mice, which were sub-chronically treated with URB597, a well-known inhibitor of the fatty acid amide hydrolase.

Development and validation of a sensitive assay for the quantification of arachidonoylcyclopropylamide (ACPA) in cell culture by LC–MS/MS

Synthetic and natural cannabinoid derivatives are highly investigated as drug candidates due to their antinociceptive, antiepileptic and anticancer potential. Arachidonoylcyclopropylamide (ACPA) is a synthetic cannabinoid with antiproliferative and apoptotic effects on non-small cell lung cancer and pancreatic and endometrial carcinoma. Thus, ACPA has a great potential for being used as an anticancer drug for epithelial cancers. Therefore, determining the levels of ACPA in biological fluids, cells, tissues and pharmaceutical dosage forms is crucial in monitoring the effects of various pharmacological, physiological and pathological stimuli on biological systems. However, the challenge in the quantification of ACPA is its short half-life and lack of UV signal. Therefore, we developed a liquid chromatography-tandem mass spectrometric (LC–MS/MS) method for sensitive and selective quantification of ACPA in cell culture medium and intracellular matrix. Multiple reaction monitoring in the positive ionization mode was used for detection with 344 → 203 m/z transitions. The separation of ACPA was performed on C18 column (50 × 3.0 mm, 2.1 μm) with the mobile phase run in the gradient mode with 0.1% formic acid (FA) in water and 0.1% FA in acetonitrile at a flow rate of 0.3 ml/min. The assay was linear in the concentration range of 1.8–1000 ng/mL (r = 0.999). The validation studies revealed that the method was linear, sensitive, accurate, precise, selective, repeatable, robust and rugged. Finally, the developed method was applied to quantify ACPA in cell culture medium and intracellular matrix.

Quantification of Endocannabinoids from Biological Samples Using Liquid Chromatography-Tandem Mass Spectrometry

Endocannabinoids (eCBs) are a family of lipid molecules with important regulatory function in the brain and immune system. The two well-studied eCBs are arachidonic acid derivatives, N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG). Currently one of the most important methods for quantitative analysis of eCBs and related lipids from biological matrices is liquid chromatographic separation coupled with tandem mass spectroscopy (LC-MS/MS) owing to its high sensitivity and selectivity, as well as no derivatization procedures needed. Here we describe pretreatment procedures using solid-phase extraction for tissue sampling and an in vivo brain microdialysis approach prior to LC-MS/MS analysis, followed by detailed steps of LC-MS/MS analytic method to demonstrate the potential and application of this method in quantification of eCBs and congeners from various biological matrices.

Distribution of an analgesic palmitoylethanolamide and other N-acylethanolamines in human placental membranes

BACKGROUND

Human amniotic and amniochorionic membranes (AM, ACM) represent the most often used grafts accelerating wound healing. Palmitoylethanolamide, oleoylethanolamide and anandamide are endogenous bioactive lipid molecules, generally referred as N-acylethanolamines. They express analgesic, nociceptive, neuroprotective and anti-inflammatory properties. We assessed the distribution of these lipid mediators in placental tissues, as they could participate on analgesic and wound healing effect of AM/ACM grafts.

METHODS

Seven placentas were collected after caesarean delivery and fresh samples of AM, ACM, placental disc, umbilical cord, umbilical serum and vernix caseosa, and decontaminated samples (antibiotic solution BASE 128) of AM and ACM have been prepared. Ultra-high-performance liquid chromatography-tandem mass spectrometry was used for N-acylethanolamines analysis.

RESULTS

N-acylethanolamines were present in all studied tissues, palmitoylethanolamide being the most abundant and the anandamide the least. For palmitoylethanolamide the maximum average concentration was detected in AM (350.33 ± 239.26 ng/g), while oleoylethanolamide and anandamide were most abundant in placenta (219.08 ± 79.42 ng/g and 30.06 ± 7.77 ng/g, respectively). Low levels of N-acylethanolamines were found in serum and vernix. A significant increase in the levels of N-acylethanolamines (3.1-3.6-fold, P < 0.001) was observed in AM when the tissues were decontaminated using antibiotic solution. The increase in decontaminated ACM was not statistically significant.

CONCLUSIONS

The presence of N-acylethanolamines, particularly palmitoylethanolamide in AM and ACM allows us to propose these lipid mediators as the likely factors responsible for the anti-hyperalgesic, but also anti-inflammatory and neuroprotective, effects of AM/ACM grafts in wound healing treatment. The increase of N-acylethanolamines levels in AM and ACM after tissue decontamination indicates that tissue processing is an important factor in maintaining the analgesic effect.

Combining Micropunch Histology and Multidimensional Lipidomic Measurements for In-Depth Tissue Mapping

While decades of technical and analytical advancements have been utilized to discover novel lipid species, increase speciation, and evaluate localized lipid dysregulation at subtissue, cellular, and subcellular levels, many challenges still exist. One limitation is that the acquisition of both in-depth spatial information and comprehensive lipid speciation is extremely difficult, especially when biological material is limited or lipids are at low abundance. In neuroscience, for example, it is often desired to focus on only one brain region or subregion, which can be well under a square millimeter for rodents. Herein, we evaluate a micropunch histology method where cortical brain tissue at 2.0, 1.25, 1.0, 0.75, 0.5, and 0.25 mm diameter sizes and 1 mm depth was collected and analyzed with multidimensional liquid chromatography, ion mobility spectrometry, collision induced dissociation, and mass spectrometry (LC-IMS-CID-MS) measurements. Lipid extraction was optimized for the small sample sizes, and assessment of lipidome coverage for the 2.0 to 0.25 mm diameter sizes showed a decline from 304 to 198 lipid identifications as validated by all 4 analysis dimensions (~35% loss in coverage for ~88% less tissue). While losses were observed, the ~200 lipids and estimated 4630 neurons contained within the 0.25 punch still provided in-depth characterization of the small tissue region. Furthermore, while localization routinely achieved by mass spectrometry imaging (MSI) and single cell analyses is greater, this diameter is sufficiently small to isolate subcortical, hypothalamic, and other brain regions in adult rats, thereby increasing the coverage of lipids within relevant spatial windows without sacrificing speciation. Therefore, micropunch histology enables in-depth, region-specific lipid evaluations, an approach that will prove beneficial to a variety of lipidomic applications.

A sensitive LC-MS/MS method for the study of exogenously administered 13 C-oleoylethanolamide in rat plasma and brain tissue

Oleoylethanolamide is an endogenous molecule with neuroprotective effects. It has been reported that exogenous oleoylethanolamide can be administered therapeutically, but the confounding presence of the endogenous molecule has led to conflicting reports regarding the mechanisms of the effects and highlights a need for an adequate methodology to differentiate them. We have developed a liquid chromatography-tandem mass spectrometry method to study oleoylethanolamide in rat plasma and brain using a ¹³ C-labeled isotope, ¹³ C-oleoylethanolamide. ¹³ C-oleoylethanolamide was extracted using a liquid-liquid extraction employing acetonitrile and tert-butyl methyl ether (1:4). Analysis was performed using a gradient with a total run time of 12 min. ¹³ C-oleoylethanolamide, d₄ -oleoylethanolamide (internal standard), and ¹² C-oleoylethanolamide (endogenous background) eluted simultaneously at 1.64 min. The method was validated for specificity, sensitivity, accuracy, and precision and found to be capable of quantification within acceptable limits of ±15% over the calibration range of 0.39-25 ng/mL for the plasma and 1.17-75 ng/g for the brain. It was then applied to quantify ¹³ C-oleoylethanolamide over 90 min after intravenous administration of a solution (1 mg/kg) in rats. Results suggest that ¹³ C-oleoylethanolamide does not reach therapeutic concentrations in the brain, despite a relatively prolonged plasma circulation, suggesting that rapid degradation in the brain remains an obstacle to its clinical application to neurological disease.

Chronic Oral Palmitoylethanolamide Administration Rescues Cognitive Deficit and Reduces Neuroinflammation, Oxidative Stress, and Glutamate Levels in A Transgenic Murine Model of Alzheimer's Disease

N-palmitoylethanolamide (PEA) is a lipid mediator belonging to the class of the N-acylethanolamine. Products containing PEA, also in ultramicronized formulation (um-PEA), are already licensed for use in humans for its analgesic and anti-inflammatory properties, and demonstrated high safety and tolerability. Preclinical studies indicate that PEA, especially in the ultramicronized form, could be a potential therapeutic agent for Alzheimer's disease (AD). In this study, we evaluated the neuroprotective and antioxidant effects of chronic (three months) um-PEA administration in an animal model of AD (3×Tg-AD mice). For translation purposes, the compound has been orally administered. Cognitive performance as well as biochemical markers [(interleukin-16 (IL-16) and tumor necrosis factor- (TNF-)] levels, reactive oxygen species (ROS) production, synaptophysin and glutamate levels) have been evaluated at the end of um-PEA treatment. The results indicate that orally administered um-PEA was adsorbed and distributed in the mice brain. The chronic treatment with um-PEA (100 mg/kg/day for three months) rescued cognitive deficit, restrained neuroinflammation and oxidative stress, and reduced the increase in hippocampal glutamate levels observed in 3×Tg-AD mice. Overall, these data reinforce the concept that um-PEA exerts beneficial effects in 3×Tg-AD mice. The fact that PEA is already licensed for the use in humans strongly supports its rapid translation in clinical practice.

Determination of anandamide in cerebrospinal fluid samples by disposable pipette extraction and ultra-high performance liquid chromatography tandem mass spectrometry

This work describes the development and validation of an ultra-high performance liquid chromatography tandem mass spectrometry method that uses disposable pipette extraction (DPX-UHPLC-MS/MS) to determine the endocannabinoid anandamide (AEA) in cerebrospinal fluid samples (CSF). The DPX parameters sorption equilibrium time, sample volume, number of draw-eject cycles, washing solvent volume, and elution solvent volume were optimized by design of experiments (DOE) techniques. The simple DPX protocol proposed herein required a reduced amount of CSF sample and organic solvent. The DPX-UHPLC-MS/MS method presented linear range from 0.10 ng mL^-1 (LLOQ) to 3.0 ng mL^-1, inter- and intra-assay accuracy with EPR values varying from -8.2% to 9.6%, inter- and intra-assay precision with CV values ranging from 1.3% to 14.8% (except for the LLOQ), and no significant matrix effect. The innovative DPX-UHPLC-MS/MS method was successfully applied to determine AEA in CSF samples from Parkinson's disease (PD) patients and should therefore be used in clinical studies.

Analysis of endocannabinoids in plasma samples by biocompatible solid-phase microextraction devices coupled to mass spectrometry

Anandamide (AEA) and 2-arachidonoyl glycerol (2-AG) represent two of the most important endocannabinoids (ECs) investigated in neurobiology as therapeutic targets for several mental disorders. However, the determination of these ECs in biological matrices remains a challenging task because of the low concentrations, low stability and high protein-bound (LogP ∼ 6). This work describes innovative analytical methods based on biocompatible SPME (Bio-SPME), SPME-UHPLC-MS/MS and Bio-SPME-Nano-ESI-MS/MS, to determine AEA and 2-AG in human plasma samples. The direct coupling of Bio-SPME with nano-ESI-MS/MS can be considered an alternative tool for faster analysis. Different Bio-SPME fibers based on silica and polymeric coating (i.e. C₁₈, C₃₀, and HLB) were evaluated. Different desorption solvents based on combinations of methanol, acetonitrile, and isopropanol were also evaluated for efficient elution with minimum carry-over. Given the high protein binding analytes and the fact that SPME extracts the free-concentration of the analytes, the plasma samples were modified with additives such as guanidine hydrochloride (Gu-HCl), trifluoroacetic acid, and acetonitrile. This study was carried out by experimental design to achieve complete protein denaturation and the release of target analytes. The maximum extraction efficiency was obtained under the following conditions: HLB coated fibers (10 mm length, 20 μm coating thickness), matrix modified (300 μL of plasma) with 50 μL of Gu-HCL 1 mol L^-1, 75 μL of ACN and 75 μL of water, and desorption with methanol/isopropanol solution (50:50, v/v). Both methods were validated based on current international guidelines and can be applied for monitoring of concentrations of endocannabinoids in plasma samples. SPME-UHPLC-MS/MS method presented lower LOQ values than SPME-nanoESI-MS/MS. The additional separation (chromatographic column) favored the detectability of LC-MS/MS method. However, the SPME-nano-ESI-MS/MS decrease the total analysis time, due to significant reductions in desorption and detection times.

In vivo monitoring of rat brain endocannabinoids using solid-phase microextraction

Aim: Solid-phase microextraction is proposed to measure concentrations of anandamide and 2-arachidonoyl glycerol in live rat brains in response to stress. Materials & methods: Solid-phase microextraction fibers were prepared from steel with 1.5 mm extraction coating. 24 male rats were divided into groups based on brain region, stria terminalis or posterior hypothalamus and loud noise or control groups. The fibers were desorbed in acetonitrile-water (75:25) and analyzed by ultraperformance LC-MS/MS. The linear range of the method was 0.05-50 ng/ml and the in vivo concentrations were found to be between 0.3 and 40 ng/ml. Conclusion: The new approach was successfully used to determine the concentrations of anandamide and 2-arachidonoyl glycerol in vivo and could be used in the future to measure other endogenous compounds.

Its complicated: The relationship between alcohol and microglia in the search for novel pharmacotherapeutic targets for alcohol use disorders

Alcohol use disorder (AUD) is a chronic relapsing disorder with wide-ranging health consequences. Alcohol targets the central nervous system producing neurodegeneration and subsequent cognitive and behavioral deficits, but the mechanisms behind these effects remain unclear. Recently, evidence has been mounting for the role of neuroimmune activation in the pathogenesis of AUDs, but our nascent state of knowledge about the interaction of alcohol with the neuroimmune system supports that the relationship is complicated. As the resident macrophage of the central nervous system, microglia are a central focus. Human and animal research on the interplay between microglia and alcohol in AUDs has proven to be complex, and though early research focused on a pro-inflammatory phenotype of microglia, the anti-inflammatory and homeostatic roles of microglia must be considered. How these new roles for microglia should be incorporated into our thinking about the neuroimmune system in AUDs is discussed in the context of developing novel pharmacotherapies for AUDs.

Binge Alcohol Exposure Transiently Changes the Endocannabinoid System: A Potential Target to Prevent Alcohol-Induced Neurodegeneration

Excessive alcohol consumption leads to neurodegeneration, which contributes to cognitive decline that is associated with alcohol use disorders (AUDs). The endocannabinoid system has been implicated in the development of AUDs, but little is known about how the neurotoxic effects of alcohol impact the endocannabinoid system. Therefore, the current study investigated the effects of neurotoxic, binge-like alcohol exposure on components of the endocannabinoid system and related N-acylethanolamines (NAEs), and then evaluated the efficacy of fatty acid amide hydrolase (FAAH) inhibition on attenuating alcohol-induced neurodegeneration. Male rats were administered alcohol according to a binge model, which resulted in a transient decrease in [³H]-CP-55,940 binding in the entorhinal cortex and hippocampus following two days, but not four days, of treatment. Furthermore, binge alcohol treatment did not change the tissue content of the three NAEs quantified, including the endocannabinoid and anandamide. In a separate study, the FAAH inhibitor, URB597 was administered to rats during alcohol treatment and neuroprotection was assessed by FluoroJade B (FJB) staining. The administration of URB597 during binge treatment did not significantly reduce FJB+ cells in the entorhinal cortex or hippocampus, however, a follow up "target engagement" study found that NAE augmentation by URB597 was impaired in alcohol intoxicated rats. Thus, potential alcohol induced alterations in URB597 pharmacodynamics may have contributed to the lack of neuroprotection by FAAH inhibition.

Anandamide and 2-AG are endogenously present within the laterodorsal tegmental nucleus: Functional implications for a role of eCBs in arousal

Previously, we presented electrophysiological evidence for presence in mice brain slices of functional cannabinoid type I receptors (CB1Rs) within the laterodorsal tegmentum (LDT), a brain stem nucleus critical in control of arousal and rapid eye movement (REM) sleep. Further, using pharmacological agents, we provided data suggestive of the endogenous presence of cannabinoids (CBs) acting at LDT CB1Rs. However, in those studies, identification of the type(s) of CB ligands endogenously present in the LDT remained outstanding, and this information has not been provided elsewhere. Accordingly, we used the highly-sensitive liquid chromatography/mass spectrometry (LC-MS) method to determine whether N-arachidonoylethanolamide (Anandamide or AEA) and 2-arachidonyl glycerol (2-AG), which are both endogenous CB ligands acting at CB1Rs, are present in the LDT. Mice brain tissue samples of the LDT were assayed using ion trap LC-MS in selected ion monitoring mode. Chromatographic analysis and product-ion MS scans identified presence of the CBs, AEA and 2-AG, from LDT mouse tissue. Data using the LC-MS method show that AEA and 2-AG are endogenously present within the LDT and when coupled with our electrophysiological findings, lead to the suggestion that AEA and 2-AG act at electropharmacologically-demonstrated CB1Rs in this nucleus. Accordingly, AEA and 2-AG likely play a role in processes governed by the LDT, including control of states of cortical gamma band activity seen in alert, aroused states, as well as cortical and motor activity characteristic of REM sleep.

A column switching ultrahigh-performance liquid chromatography-tandem mass spectrometry method to determine anandamide and 2-arachidonoylglycerol in plasma samples

This study reports a fast, sensitive, and selective column switching ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method to determine the endocannabinoids (eCBs), anandamide (AEA), and 2-arachidonoylglycerol (2-AG) in plasma samples. This bidimensional system used a restricted access media column (RP-8 ADS, 25 mm × 4 mm × 25 μM) in the first dimension and a core-shell Kinetex C18 (100 mm × 2, 1.7 mm × 1 μM) column in the second dimension, followed by detection in a mass spectrometer triple quadrupole (multiple reactions monitoring mode) operating in the positive mode. RP-8 ADS was used for trace enrichment of eCBs (reverse phase partitioning) and macromolecular matrix size exclusion; the core-shell column was used for the chromatographic separation. The column switching UHPLC-MS/MS method presented a linear range spanning from 0.1 ng mL^-1 (LOQ) to 6 ng mL^-1 for AEA and from 0.04 ng mL^-1 (LOQ) to 10 ng mL^-1 for 2-AG. Excluding the LLOQ values, the precision assays provided coefficients of variation lower than 8% and accuracy with relative standard error values lower than 14%. Neither carryover nor matrix effects were detected. This high-throughput column switching method compared to conventional methods is time saving as it involves fewer steps, consumes less solvent, and presents lower LLOQ. The column switching UHPLC-MS/MS method was successfully applied to determine AEA and 2-AG in plasma samples obtained from Alzheimer's disease patients. Graphical abstract A column switching ultra high-performance liquid chromatography-tandem mass spectrometry method using RP-8 ADS column and core shell column to determine endocannabinoids in plasma samples.

Simultaneous HPLC-APCI-MS/MS quantification of endogenous cannabinoids and glucocorticoids in hair

Hair matrix could retrospectively record association of endogenous cannabinoids (e.g. 2-arachidonoyl glycerol, 2-AG and N-arachidonoyl-ethanolamine, AEA) and glucocorticoids (e.g. cortisol and cortisone) in a myriad of physiological functions. However, depending on the extraction conditions, the spontaneous isomerization of 2-AG to 1-arachidonoylglycerol (1-AG) and the possible rearrangement of O-arachidonoyl ethanolamine (OAEA) to AEA in various sample matrices could be major obstacles encountered in the detection of both 2-AG and AEA. This study aimed to develop a novel method for simultaneous quantification of 2-AG, AEA, cortisol and cortisone in hair. Methanol was used as the incubation solution and an acidic mixture of deionized water and methanol were utilized as mobile phase in order to avert possible rearrangements of both OAEA and 2-AG. The analyses were performed on a high-performance liquid chromatography tandem mass spectrometer with atmosphere pressure chemical ionization in positive mode. The method showed good linearity in the range of 3.0-250pg/mg for AEA, 15.0-1250pg/mg for 2-AG and 1-250pg/mg for cortisol and cortisone. Limit of detection was 1.5pg/mg for AEA, 6.0pg/mg for 2-AG and 0.5pg/mg for cortisol and cortisone. For all four analytes, intra and inter-day coefficients of variation were less than 20% and recovery above 90%. Population analyses in 473 hair samples established that 2-AG was significantly correlated with AEA. 2-AG was significantly and positively correlated with cortisol and cortisone. There was a significant positive correlation of AEA with cortisol, but not with cortisone. Obese participants showed a significantly higher concentration of cortisone and 2-AG. Males showed significantly higher 2-AG and cortisone levels but significantly lower AEA levels than females.

Glial Modulation by N-acylethanolamides in Brain Injury and Neurodegeneration

Neuroinflammation involves the activation of glial cells and represents a key element in normal aging and pathophysiology of brain damage. N-acylethanolamides (NAEs), naturally occurring amides, are known for their pro-homeostatic effects. An increase in NAEs has been reported in vivo and in vitro in the aging brain and in brain injury. Treatment with NAEs may promote neuroprotection and exert anti-inflammatory actions via PPARα activation and/or by counteracting gliosis. This review aims to provide an overview of endogenous and exogenous properties of NAEs in neuroinflammation and to discuss their interaction with glial cells.

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.

Validation of a tandem mass spectrometry method using combined extraction of 37 oxylipins and 14 endocannabinoid-related compounds including prostamides from biological matrices

There is a clinical need for more relevant coverage of bioactive lipids using smaller sample volumes. Therefore, we have validated a tandem mass spectrometry method for combined solid phase extraction of 37 compounds in the oxylipin (OxL) and 14 in the endocannabinoid (eCB) metabolome, as well as prostamides. The limits of quantification (LOQ) for compounds in the eCB metabolome were in the range 0.5-1000 fg on column, intraday accuracy and precision ranges (%) were 83-125 and 0.3-17, respectively, and interday accuracy and precision ranges (%) were 80-119 and 1.2-20, respectively, dependent upon the compound and the concentration studied. Corresponding values for OxL were 0.5 fg-4.2 pg on column (LOQ), 85-115% (inter- and intraday accuracy) and <5% (precision). The combined extraction method was successfully applied to tissues, cell extracts, human plasma and milk samples. A deeper study of levels in elk, pig and cow brain, as well as cow heart and liver revealed tissue and species-specific elevation of eicosanoids: arachidonate diols, 20-HETE and 12(S)-HEPE (cow liver), LTB4 (cow brain), and monohydroxy metabolites (HETEs), epoxides and 5-oxo-ETE in elk brain, which might be caused by factors of stress and/or post-mortem reactions in the tissues.