2-Arachidonoylglycerol: A signaling lipid with manifold actions in the brain

Cannabinoid signalling and effects of cannabis on the male reproductive system

Marijuana is the most widely consumed recreational drug worldwide, which raises concerns for its potential effects on fertility. Many aspects of human male reproduction can be modulated by cannabis-derived extracts (cannabinoids) and their endogenous counterparts, known as endocannabinoids (eCBs). These latter molecules act as critical signals in a variety of physiological processes through receptors, enzymes and transporters collectively termed the endocannabinoid system (ECS). Increasing evidence suggests a role for eCBs, as well as cannabinoids, in various aspects of male sexual and reproductive health. Although preclinical studies have clearly shown that ECS is involved in negative modulation of testosterone secretion by acting both at central and testicular levels in animal models, the effect of in vivo exposure to cannabinoids on spermatogenesis remains a matter of debate. Furthermore, inconclusive clinical evidence does not seem to support the notion that plant-derived cannabinoids have harmful effects on human sexual and reproductive health. An improved understanding of the complex crosstalk between cannabinoids and eCBs is required before targeting of ECS for modulation of human fertility becomes a reality.

Effect of Solvent on Acyl Migration of 2-Monoacylglycerols in Enzymatic Ethanolysis

Acyl migration occurs in many reactions and is the main obstacle for structured lipid synthesis. In this study, 2-monoacylglycerol (2-MAG) was prepared by enzymatic ethanolysis in three different media to evaluate the effect of environment on product composition. The contents of 2-MAG obtained in ethanol, hexane + ethanol, and t-butanol + ethanol systems were 30.6, 15.7, and 32.4%, respectively, after 3 h reaction. Afterward, the acyl migration kinetics of 2-MAG were studied in solvent and solventless systems without the use of lipase. Results indicate that 2-MAG in the solventless system had the highest acyl migration rate. The isomerization was efficiently prevented by the use of polar solvents, especially t-butanol. The rate constants were shown to be the highest and activation energy values were the lowest in solventless systems. The novel finding in this study was that solvent had inhibitory effect on 2-MAG isomerization, but the nonpolar hexane had the lowest inhibition of acyl migration compared to other solvents.

Phytocannabinoids and endocannabinoids: different in nature

Cannabis is one of the earliest cultivated plants, of which Cannabis sativa and Cannabis indica are the most widespread and best characterized species. Their extracts contain (phyto)cannabinoids (pCBs) of therapeutic interest, such as Δ9-tetrahydrocannabinol and cannabidiol, along with many other compounds, so that there is no “one cannabis” but several mixtures even from the same plant. This complexity is mirrored, or even exceeded, by the complexity of the molecular targets that pCBs find in our body, most of which belong to the so-called “endocannabinoid (eCB) system”. Here, we describe the major pCBs and the main components of the eCB system to appreciate their differences and mutual interactions, as well as the potential of using pCB/eCB-based drugs as novel therapeutics to treat human diseases, both in the central nervous system and at the periphery. Moreover, we address the question of the evolution of pCBs and eCBs, showing that the latter compounds were the first to appear in nature, and that the former substances took a few million years to mimic the three-dimensional structures of the latter, and hence their biological activity in our body.

Graphic abstract

Hippocampal 2-Arachidonoyl Glycerol Signaling Regulates Time-of-Day- and Stress-Dependent Effects on Rat Short-Term Memory

Background: Cannabinoids induce biphasic effects on memory depending on stress levels. We previously demonstrated that different stress intensities, experienced soon after encoding, impaired rat short-term recognition memory in a time-of-day-dependent manner, and that boosting endocannabinoid anandamide (AEA) levels restored memory performance. Here, we examined if two different stress intensities and time-of-day alter hippocampal endocannabinoid tone, and whether these changes modulate short-term memory. Methods: Male Sprague-Dawley rats were subjected to an object recognition task and exposed, at two different times of the day (i.e., morning or afternoon), to low or high stress conditions, immediately after encoding. Memory retention was assessed 1 hr later. Hippocampal AEA and 2-arachidonoyl glycerol (2-AG) content and the activity of their primary degrading enzymes, fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), were measured soon after testing. Results: Consistent with our previous findings, low stress impaired 1-hr memory performance only in the morning, whereas exposure to high stress impaired memory independently of testing time. Stress exposure decreased AEA levels independently of memory alterations. Interestingly, exposure to high stress decreased 2-AG content and, accordingly, increased MAGL activity, selectively in the afternoon. Thus, to further evaluate 2-AG’s role in the modulation of short-term recognition memory, rats were given bilateral intra-hippocampal injections of the 2-AG hydrolysis inhibitor KML29 immediately after training, then subjected to low or high stress conditions and tested 1 hr later. Conclusions: KML29 abolished the time-of-day-dependent impairing effects of stress on short-term memory, ameliorating short-term recognition memory performance.

A large-scale genome-lipid association map guides lipid identification

Despite the crucial roles of lipids in metabolism, we are still at the early stages of comprehensively annotating lipid species and their genetic basis. Mass spectrometry-based discovery lipidomics offers the potential to globally survey lipids and their relative abundances in various biological samples. To discover the genetics of lipid features obtained through high-resolution liquid chromatography-tandem mass spectrometry, we analysed liver and plasma from 384 diversity outbred mice, and quantified 3,283 molecular features. These features were mapped to 5,622 lipid quantitative trait loci and compiled into a public web resource termed LipidGenie. The data are cross-referenced to the human genome and offer a bridge between genetic associations in humans and mice. Harnessing this resource, we used genome-lipid association data as an additional aid to identify a number of lipids, for example gangliosides through their association with B4galnt1, and found evidence for a group of sex-specific phosphatidylcholines through their shared locus. Finally, LipidGenie's ability to query either mass or gene-centric terms suggests acyl-chain-specific functions for proteins of the ABHD family.

Potential application of endocannabinoid system agents in neuropsychiatric and neurodegenerative diseases-focusing on FAAH/MAGL inhibitors

The endocannabinoid system (ECS) has received extensive attention for its neuroprotective effect on the brain. This system comprises endocannabinoids, endocannabinoid receptors, and the corresponding ligands and proteins. The molecular players involved in their regulation and metabolism are potential therapeutic targets for neuropsychiatric diseases including anxiety, depression and neurodegenerative diseases such as Alzheimer’s disease (AD) and Parkinson’s disease (PD). The inhibitors of two endocannabinoid hydrolases, i.e., fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), have the capacity to increase the level of endocannabinoids indirectly, causing fewer side effects than those associated with direct supplementation of cannabinoids. Their antidepressant and anxiolytic mechanisms are considered to modulate the hypothalamic-pituitary-adrenal axis and regulate synaptic and neural plasticity. In terms of AD/PD, treatment with FAAH/MAGL inhibitors leads to reduction in amyloid β-protein deposition and inhibition of the death of dopamine neurons, which are commonly accepted to underlie the pathogenesis of AD and PD, respectively. Inflammation as the cause of depression/anxiety and PD/AD is also the target of FAAH/MAGL inhibitors. In this review, we summarize the application and involvement of FAAH/MAGL inhibitors in related neurological diseases. Focus on the latest research progress using FAAH/MAGL inhibitors is expected to facilitate the development of novel approaches with therapeutic potential.

Glycerophosphodiesterase 3 (GDE3) is a lysophosphatidylinositol-specific ectophospholipase C acting as an endocannabinoid signaling switch

Endocannabinoid signaling plays a regulatory role in various (neuro)biological functions. 2-arachidonoylglycerol (2-AG) is the most abundant endocannabinoid, and although its canonical biosynthetic pathway involving phosphoinositide-specific phospholipase C and diacylglycerol lipase α is known, alternative pathways remain unsettled. Here, we characterize a noncanonical pathway implicating glycerophosphodiesterase 3 (GDE3, from GDPD2 gene). Human GDE3 expressed in HEK293T cell membranes catalyzed the conversion of lysophosphatidylinositol (LPI) into monoacylglycerol and inositol-1-phosphate. The enzyme was equally active against 1-acyl and 2-acyl LPI. When using 2-acyl LPI, where arachidonic acid is the predominant fatty acid, LC-MS analysis identified 2-AG as the main product of LPI hydrolysis by GDE3. Furthermore, inositol-1-phosphate release into the medium occurred upon addition of LPI to intact cells, suggesting that GDE3 is actually an ecto-lysophospholipase C. In cells expressing G-protein-coupled receptor GPR55, GDE3 abolished 1-acyl LPI-induced signaling. In contrast, upon simultaneous ex-pression of GDE3 and cannabinoid receptor CB2, 2-acyl LPI evoked the same signal as that induced by 2-AG. These data strongly suggest that, in addition to degrading the GPR55 LPI ligand, GDE3 can act as a switch between GPR55 and CB2 signaling. Coincident with a major expression of both GDE3 and CB2 in the spleen, spleens from transgenic mice lacking GDE3 displayed doubling of LPI content compared with WT mice. Decreased production of 2-AG in whole spleen was also observed, supporting the in vivo relevance of our findings. These data thus open a new research avenue in the field of endocannabinoid generation and reinforce the view of GPR55 and LPI being genuine actors of the endocannabinoid system.

Targeting Endocannabinoid Signaling: FAAH and MAG Lipase Inhibitors

Inspired by the medicinal properties of the plant Cannabis sativa and its principal component (-)-trans-Δ⁹-tetrahydrocannabinol (THC), researchers have developed a variety of compounds to modulate the endocannabinoid system in the human brain. Inhibitors of fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), which are the enzymes responsible for the inactivation of the endogenous cannabinoids anandamide and 2-arachidonoylglycerol, respectively, may exert therapeutic effects without inducing the adverse side effects associated with direct cannabinoid CB₁ receptor stimulation by THC. Here we review the FAAH and MAGL inhibitors that have reached clinical trials, discuss potential caveats, and provide an outlook on where the field is headed.

CB2 Receptors and Neuron-Glia Interactions Modulate Neurotoxicity Generated by MAGL Inhibition

Monoacylglycerol lipase inhibition (MAGL) has emerged as an interesting therapeutic target for neurodegenerative disease treatment due to its ability to modulate the endocannabinoid system and to prevent the production of proinflammatory mediators. To obtain a beneficial response, it is necessary to understand how this inhibition affects the neuron-glia crosstalk and neuron viability. In this study, the effect of MAGL inhibition by KML29 was evaluated in two types of rat cortical primary cultures; mixed cultures, including neuron and glial cells, and neuron-enriched cultures. The risk of neuronal death was estimated by longitudinal survival analysis. The spontaneous neuronal risk of death in culture was higher in the absence of glial cells, a process that was enhanced by KML29 addition. In contrast, neuronal survival was not compromised by MAGL inhibition in the presence of glial cells. Blockade of cannabinoid type 2 (CB2) receptors expressed mainly by microglial cells did not affect the spontaneous neuronal death risk but decreased neuronal survival when KML29 was added. Modulation of cannabinoid type 1 (CB1) receptors did not affect neuronal survival. Our results show that neuron-glia interactions are essential for neuronal survival. CB2 receptors play a key role in these protective interactions when neurons are exposed to toxic conditions.

Endocannabinoid levels in patients with Parkinson's disease with and without levodopa-induced dyskinesias

Levodopa-induced dyskinesias (LID) in Parkinson's disease (PD) are frequent complications, and the endocannabinoid system has a role on its pathophysiology. To test the hypothesis that the functioning of the endocannabinoid system would be altered in PD and in LID by measuring plasma and CSF levels of α-N-arachidonoylethanolamine (AEA) and 2-arachidonoyl-glycerol (2-AG) in patients with PD with and without LID and in healthy controls. Blood and CSF samples were collected from 20 healthy controls, 23 patients with PD without LID, and 24 patients with PD with LID. The levels of AEA and 2-AG were measured using a highly sensitive column switching ultrahigh-performance liquid chromatography-tandem mass spectrometry method. When pooled together, patients with PD had lower plasma and CSF levels of 2-AG and higher CSF levels of AEA compared to healthy controls (Mann-Whitney statistics = 303.0, p = 0.02). Patients with PD without LID had lower CSF levels of 2-AG (Kruskal-Wallis statistics = 7.76, p = 0.02) and higher CSF levels of AEA levels than healthy controls (Kruskal-Wallis statistics = 8.81, p = 0.01). The findings suggest that the endocannabinoid system participates in the pathophysiology of PD symptoms, but its role in the pathophysiology of LID is still unclear.

Anandamide prevents the adhesion of filamentous Candida albicans to cervical epithelial cells

Candidiasis is a fungal infection caused by Candida species that have formed a biofilm on epithelial linings of the body. The most frequently affected areas include the vagina, oral cavity and the intestine. In severe cases, the fungi penetrate the epithelium and cause systemic infections. One approach to combat candidiasis is to prevent the adhesion of the fungal hyphae to the epithelium. Here we demonstrate that the endocannabinoid anandamide (AEA) and the endocannabinoid-like N-arachidonoyl serine (AraS) strongly prevent the adherence of C. albicans hyphae to cervical epithelial cells, while the endocannabinoid 2-arachidonoylglycerol (2-AG) has only a minor inhibitory effect. In addition, we observed that both AEA and AraS prevent the yeast-hypha transition and perturb hyphal growth. Real-time PCR analysis showed that AEA represses the expression of the HWP1 and ALS3 adhesins involved in Candida adhesion to epithelial cells and the HGC1, RAS1, EFG1 and ZAP1 regulators of hyphal morphogenesis and cell adherence. On the other hand, AEA increased the expression of NRG1, a transcriptional repressor of filamentous growth. Altogether, our data show that AEA and AraS have potential anti-fungal activities by inhibiting hyphal growth and preventing hyphal adherence to epithelial cells.

Role of the Endocannabinoidome in Human and Mouse Atherosclerosis

The Endocannabinoid (eCB) system and its role in many physiological and pathological conditions is well described and accepted, and includes cardiovascular disorders. However, the eCB system has been expanded to an "-ome"; the endocannabinoidome (eCBome) that includes endocannabinoid-related mediators, their protein targets and metabolic enzymes, many of which significantly impact upon cardiometabolic health. These recent discoveries are here summarized with a special focus on their potential involvement in atherosclerosis. We described the role of classical components of the eCB system (eCBs, CB1 and CB2 receptors) and eCB-related lipids, their regulatory enzymes and molecular targets in atherosclerosis. Furthermore, since increasing evidence points to significant cross-talk between the eCBome and the gut microbiome and the gut microbiome and atherosclerosis, we explore the possibility that a gut microbiome - eCBome axis has potential implications in atherosclerosis.

Endocannabinoid contributions to alcohol habits and motivation: Relevance to treatment

Individuals with alcohol use disorder exhibit compulsive habitual behaviors that are thought to be, in part, a consequence of chronic and persistent use of alcohol. The endocannabinoid system plays a critical role in habit learning and in ethanol self-administration, but the role of this neuromodulatory system in the expression of habitual alcohol seeking is unknown. Here, we investigated the role of the endocannabinoid system in established alcohol habits using contingency degradation in male C57BL/6 mice. We found that administration of the novel diacyl glycerol lipase inhibitor DO34, which decreases the biosynthesis of the endocannabinoid 2-arachidonoyl glycerol (2-AG), reduced habitual responding for ethanol and ethanol approach behaviors. Moreover, administration of the endocannabinoid transport inhibitor AM404 or the cannabinoid receptor type 1 antagonist AM251 produced similar reductions in habitual responding for ethanol and ethanol approach behaviors. Notably, AM404 was also able to reduce ethanol seeking and consumption in mice that were insensitive to lithium chloride-induced devaluation of ethanol. Conversely, administration of JZL184, a monoacyl glycerol lipase inhibitor that increases levels of 2-AG, increased motivation to respond for ethanol on a progressive ratio schedule of reinforcement. These results demonstrate an important role for endocannabinoid signaling in the motivation to seek ethanol, in ethanol-motivated habits, and suggest that pharmacological manipulations of endocannabinoid signaling could be effective therapeutics for treating alcohol use disorder.

Blockade of the Lysophosphatidylserine Lipase ABHD12 Potentiates Ferroptosis in Cancer Cells

Ferroptosis is a type of cell death caused by the pathogenic accumulation of lipid hydroperoxides. Pharmacological mechanisms to induce ferroptosis may provide a way to kill cancer cells that are resistant to other forms of cell death like apoptosis. Nonetheless, the proteins that regulate ferroptotic sensitivity in cancer cells remain incompletely understood. Here, we screened a panel of inhibitors of serine hydrolases-an enzyme class important for regulating lipid metabolism-for potentiation of ferroptosis in HT1080 fibrosarcoma cells. We found that DO264, a selective inhibitor of the lyso- and ox-phosphatidylserine (PS) lipase ABHD12, enhances ferroptotic death caused by RSL3, an inhibitor of the lipid peroxidase GPX4. RSL3-induced ferroptosis was also potentiated by genetic disruption of ABHD12. Metabolomic experiments revealed that, in addition to elevated lyso-PS, ABHD12-inactivated cells show higher quantities of arachidonate (C20:4)-containing PS and 2-arachidonoyl glycerol, pointing to potential oxidation-sensitive lipid mediators of ferroptosis regulated by ABHD12.

Protective Effects of N-Oleoylglycine in a Mouse Model of Mild Traumatic Brain Injury

Traumatic brain injury (TBI) is one of the main causes of death in young people for which currently no efficacious treatment exists. Recently, we have reported that mice with mild-TBI with a specific injury in the insula showed elevated levels of a little investigated N-acyl amino acid, N-oleoylglycine (OlGly). N-acyl amino acids have recently experienced an increased interest because of their important biological activities. They belong to the endocannabinoidome family of lipids with structural similarities with the endocannabinoids (eCBs). The aim of this study was to test the neuroprotective and antihyperalgesic actions of OlGly in a model of mouse mild-TBI (mTBI) and its effect on levels of eCBs and N-acylethanolamines at the end of treatment. Following mTBI, mice were administered a daily injection of OlGly (10-50-100 mg/kg i.p.) for 14 days. Treatment with OlGly normalized motor impairment and behavior in the light/dark box test, ameliorated TBI-induced thermal hyperalgesia and mechanical allodynia, and normalized aggressiveness and depression. Moreover, levels of eCBs and some N-acylethanolamines underwent significant changes 60 days after TBI, especially in the prefrontal cortex and hypothalamus, and OlGly reversed some of these changes. In conclusion, our findings reveal that OlGly ameliorates the behavioral alterations associated with mTBI in mice, while concomitantly modulating eCB and eCB-like mediator tone.

Monoacylglycerol lipase inhibitors: modulators for lipid metabolism in cancer malignancy, neurological and metabolic disorders

Monoacylglycerol lipase (MAGL) is a serine hydrolase that plays a crucial role catalysing the hydrolysis of monoglycerides into glycerol and fatty acids. It links the endocannabinoid and eicosanoid systems together by degradation of the abundant endocannabinoid 2-arachidaoylglycerol into arachidonic acid, the precursor of prostaglandins and other inflammatory mediators. MAGL inhibitors have been considered as important agents in many therapeutic fields, including anti-nociceptive, anxiolytic, anti-inflammatory, and even anti-cancer. Currently, ABX-1431, a first-in-class inhibitor of MAGL, is entering clinical phase 2 studies for neurological disorders and other diseases. This review summarizes the diverse (patho)physiological roles of MAGL and will provide an overview on the development of MAGL inhibitors. Although a large number of MAGL inhibitors have been reported, novel inhibitors are still required, particularly reversible ones.

Dopamine D1 receptor signaling and endocannabinoid cooperate to fuel striatal plasticity: An Editorial Highlight for "Cyclic AMP-dependent protein kinase and D1 dopamine receptors regulate diacylglycerol lipase-α and synaptic 2-arachidonoyl glycerol signaling" on page 334

Endocannabinoids (eCBs) play key roles in short-term and long-term synaptic plasticity in the corticostriatal circuit. By activating cannabinoid receptors expressed in the central nervous system, eCBs regulate several neural functions and behaviors. The major eCB 2-arachidonoyl-glycerol (2-AG) is particularly important for triggering a short-term form of synaptic plasticity (depolarization-induced suppression of excitatory transmission or DSE) on cortical glutamatergic afferents inputting the striatum. The neurotransmitter dopamine, through the action of D1 and D2 receptors, is also critically involved in corticostriatal plasticity. This Editorial highlights the study by Shonesy et al., which presents evidence that activation of dopamine D1 receptor and its classical downstream target cAMP-dependent protein kinase (PKA) are involved in increasing the synthesis of 2-AG in striatal medium spiny neurons (MSN) to drive DSE in the corticostriatal circuit, as schematically outlined in Figure 1. The authors used a set of complementary approaches and identified a putative serine (Ser) residue phosphorylated by PKA in diacylglycerol lipase (DGL) alpha that is required for generating 2-AG, providing a mechanistic clue into how the canonical D1 pathway in MSN might fine-tune short-term plasticity in the corticostriatal circuit. Besides, the work by Shonesy et al. may pave the way for further studies exploring the signaling interplay between canonical dopamine D1 receptor pathway and eCBs to control other forms of synaptic plasticity in different brain circuits with possible pathological relevance.

CDP-Diacylglycerol Synthases (CDS): Gateway to Phosphatidylinositol and Cardiolipin Synthesis

Cytidine diphosphate diacylglycerol (CDP-DAG) is a key intermediate in the synthesis of phosphatidylinositol (PI) and cardiolipin (CL). Both PI and CL have highly specialized roles in cells. PI can be phosphorylated and these phosphorylated derivatives play major roles in signal transduction, membrane traffic, and maintenance of the actin cytoskeletal network. CL is the signature lipid of mitochondria and has a plethora of functions including maintenance of cristae morphology, mitochondrial fission, and fusion and for electron transport chain super complex formation. Both lipids are synthesized in different organelles although they share the common intermediate, CDP-DAG. CDP-DAG is synthesized from phosphatidic acid (PA) and CTP by enzymes that display CDP-DAG synthase activities. Two families of enzymes, CDS and TAMM41, which bear no sequence or structural relationship, have now been identified. TAMM41 is a peripheral membrane protein localized in the inner mitochondrial membrane required for CL synthesis. CDS enzymes are ancient integral membrane proteins found in all three domains of life. In mammals, they provide CDP-DAG for PI synthesis and for phosphatidylglycerol (PG) and CL synthesis in prokaryotes. CDS enzymes are critical for maintaining phosphoinositide levels during phospholipase C (PLC) signaling. Hydrolysis of PI (4,5) bisphosphate by PLC requires the resynthesis of PI and CDS enzymes catalyze the rate-limiting step in the process. In mammals, the protein products of two CDS genes (CDS1 and CDS2) localize to the ER and it is suggested that CDS2 is the major CDS for this process. Expression of CDS enzymes are regulated by transcription factors and CDS enzymes may also contribute to CL synthesis in mitochondria. Studies of CDS enzymes in protozoa reveal spatial segregation of CDS enzymes from the rest of the machinery required for both PI and CL synthesis identifying a key gap in our understanding of how CDP-DAG can cross the different membrane compartments in protozoa and in mammals.

The (endo)cannabinoid signaling in female reproduction: What are the latest advances?

Cannabis extracts like marijuana have the highest consumption rate worldwide. Yet, their societal acceptance as recreational and therapeutic drugs could represent a serious hazard to female human reproduction, because cannabis ingredients [termed (phyto)cannabinoids] can perturb an endogenous system of lipid signals known as endocannabinoids. Accumulated evidence on animal models and humans has demonstrated a crucial role of these endogenous signals on different aspects of female reproduction, where they act through an ensamble of proteins that synthesize, transport, degrade and traffic them. Several reports have recently evidenced the potential role of endocannabinoids as biomarkers of female infertility for disease treatment and prevention, as well as their possible epigenetic effects on pregnancy. The purpose of this review is to provide an update of data collected in the last decade on the effects of cannabinoids and endocannabinoids on female reproductive events, from development and maturation of follicles and oocytes, to fertilization, oviductal transport, implantation and labor. In this context, a particular attention has been devoted to the ovary and the production of fertilizable oocytes, because recent studies have addressed this hot topic with conflicting results among species.

Missing Pieces to the Endocannabinoid Puzzle

The most bioactive ingredient of cannabis (Cannabis sativa or indica) extracts, Δ⁹-tetrahydrocannabinol (THC), was identified in the 1960s as one of more than 110 phytocannabinoids. It activates receptors of chemically different endogenous ligands (endocannabinoids) that, unlike THC, are metabolized by several enzymes of the endocannabinoid system. Here, the complexity of the plant-derived and endogenous cannabinoids (eCBs) is discussed, to better appreciate the challenge of: (i) dissecting their mutual interactions; (ii) understanding their impact on human pathophysiology; and (iii) exploiting them for human disease. To this aim, missing pieces to the eCB puzzle must be urgently found, by solving the 3D structures of key components, and interrogating noncanonical modes of regulation and trafficking of these lipid signals.

ABHD2 Inhibitor Identified by Activity-Based Protein Profiling Reduces Acrosome Reaction

ABHD2 is a serine hydrolase that belongs to the subgroup of the α,β-hydrolase fold-containing proteins, which is involved in virus propagation, immune response, and fertilization. Chemical tools to selectively modulate the activity of ABHD2 in an acute setting are highly desired to investigate its biological role, but are currently lacking. Here, we report a library-versus-library screening using activity-based protein profiling (ABPP) to evaluate in parallel the selectivity and activity of a focused lipase inhibitor library against ABHD2 and a panel of closely related ABHD proteins. This screen resulted in the rapid identification of novel inhibitors for ABHD2. The selectivity of the inhibitor was further investigated in native mouse testis proteome by competitive ABPP, revealing a highly restricted off-target profile. The progesterone-induced acrosome reaction was reduced in a dose-dependent manner by the newly identified inhibitor, which provides further support for the key-role of ABHD2 in the P4-stimulated acrosome reaction. On this basis, the ABHD2 inhibitor is an excellent starting point for further optimization of ABHD2 inhibitors that can modulate sperm fertility and may lead to novel contraceptives.

Regulating membrane lipid levels at the synapse by small-molecule inhibitors of monoacylglycerol lipase: new developments in therapeutic and PET imaging applications

Monoacylglycerol lipase (MAGL) is a major endocannabinoid hydrolyzing enzyme and can be regulated to control endogenous lipid levels in the brain. This review highlights the pharmacological roles and in vivo PET imaging of MAGL in brain.

Different Routes to Inhibit Fatty Acid Amide Hydrolase: Do All Roads Lead to the Same Place?

There is robust evidence indicating that enhancing the endocannabinoid (eCB) tone has therapeutic potential in several brain disorders. The inhibition of eCBs degradation by fatty acid amide hydrolase (FAAH) blockade, is the best-known option to increase N-acyl-ethanolamines-(NAEs)-mediated signaling. Here, we investigated the hypothesis that intranasal delivery is an effective route for different FAAH inhibitors, such as URB597 and PF-04457845. URB597 and PF-04457845 were subchronically administered in C57BL/6 male mice every other day for 20 days for overall 10 drug treatment, and compared for their ability to inhibit FAAH activity by the way of three different routes of administration: intranasal (i.n.), intraperitoneal (i.p.) and oral (p.o.). Lastly, we compared the efficacy of the three routes in terms of URB597-induced increase of NAEs levels in liver and in different brain areas. Results: We show that PF-04457845 potently inhibits FAAH regardless the route selected, and that URB597 was less effective in the brain after p.o. administration while reached similar effects by i.n. and i.p. routes. Intranasal URB597 delivery always increased NAEs levels in brain areas, whereas a parallel increase was not observed in the liver. By showing the efficacy of intranasal FAAH inhibition, we provide evidence that nose-to-brain delivery is a suitable alternative to enhance brain eCB tone for the treatment of neurodegenerative disorders and improve patients’ compliance.

Structure Kinetics Relationships and Molecular Dynamics Show Crucial Role for Heterocycle Leaving Group in Irreversible Diacylglycerol Lipase Inhibitors

Drug discovery programs of covalent irreversible, mechanism-based enzyme inhibitors often focus on optimization of potency as determined by IC₅₀-values in biochemical assays. These assays do not allow the characterization of the binding activity (K_i) and reactivity (k_inact) as individual kinetic parameters of the covalent inhibitors. Here, we report the development of a kinetic substrate assay to study the influence of the acidity (pK_a) of heterocyclic leaving group of triazole urea derivatives as diacylglycerol lipase (DAGL)-α inhibitors. Surprisingly, we found that the reactivity of the inhibitors did not correlate with the pK_a of the leaving group, whereas the position of the nitrogen atoms in the heterocyclic core determined to a large extent the binding activity of the inhibitor. This finding was confirmed and clarified by molecular dynamics simulations on the covalently bound Michaelis–Menten complex. A deeper understanding of the binding properties of covalent serine hydrolase inhibitors is expected to aid in the discovery and development of more selective covalent inhibitors.

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

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

Cannabimimetic plants: are they new cannabinoidergic modulators?

Phytochemicals and secondary metabolites able to interact with the endocannabinoid system (Cannabimimetics) have been recently described in a broad range of plants and fruits. These findings can open new alternative avenues to explore for the development of novel therapeutic compounds. The cannabinoids regulate many physiological and pathological functions in both animals and plants. Cannabis sativa is the main plant that produces phytocannabinoids inside resins capable to defend the plant from the aggression of parasites and herbivores. Animals produce anandamide and 2-arachidonoyl glycerol, which thanks to binding with main receptors such as type-1 cannabinoid receptor (CB1R) and the type-2 cannabinoid receptor (CB2R) are involved in inflammation processes and several brain functions. Endogenous cannabinoids, enzymes for synthesis and degradation of cannabinoids, and CB1R and CB2R constitute the endocannabinoid system (ECS). Other plants can produce cannabinoid-like molecules such as perrottetinene extracted from Radula perrottetii, or anandamide and 2-arachidonoyl glycerol extracted from some bryophytes. Moreover, several other secondary metabolites can also interact with the ECS of animals and take the name of cannabimimetics. These phytoextracts not derived from Cannabis sativa can act as receptor agonists or antagonist, or enzyme inhibitors of ECS and can be involved in the inflammation, oxidative stress, cancer, and neuroprotection. Finally, given the evolutionary heterogeneity of the cannabimimetic plants, some authors speculated on the fascinating thesis of the evolutionary convergence between plants and animals regarding biological functions of ECS. The review aims to provide a critical and complete assessment of the botanical, chemical and therapeutic aspects of cannabimimetic plants to evaluate their spread in the world and medicinal potentiality.

Endocannabinoid and Prostanoid Crosstalk in Pain

Interfering with endocannabinoid (eCB) metabolism to increase their levels is a proven anti-nociception strategy. However, because the eCB and prostanoid systems are intertwined, interfering with eCB metabolism will affect the prostanoid system and inversely. Key to this connection is the production of the cyclooxygenase (COX) substrate arachidonic acid upon eCB hydrolysis as well as the ability of COX to metabolize the eCBs anandamide (AEA) and 2-arachidonoylglycerol (2-AG) into prostaglandin-ethanolamides (PG-EA) and prostaglandin-glycerol esters (PG-G), respectively. Recent studies shed light on the role of PG-Gs and PG-EAs in nociception and inflammation. Here, we discuss the role of these complex systems in nociception and new opportunities to alleviate pain by interacting with them.

Intake of arachidonic acid-containing lipids in adult humans: dietary surveys and clinical trials

Long-chain polyunsaturated fatty acids (LCPUFAs) have important roles in physiological homeostasis. Numerous studies have provided extensive information about the roles of n-3 LCPUFA, such as docosahexaenoic acid and eicosapentaenoic acid. Arachidonic acid (ARA) is one of the major n-6 LCPUFAs and its biological aspects have been well studied. However, nutritional information for ARA is limited, especially in adult humans. This review presents a framework of dietary ARA intake and the effects of ARA supplementation on LCPUFA metabolism in adult humans, and the nutritional significance of ARA and LCPUFA is discussed.

Astroglial monoacylglycerol lipase controls mutant huntingtin-induced damage of striatal neurons

Cannabinoids exert neuroprotection in a wide array of preclinical models. A number of these studies has focused on cannabinoid CB₁ receptors in striatal medium spiny neurons (MSNs) and the most characteristic MSN-degenerative disease, Huntington's disease (HD). Accruing evidence supports that astrocytes contribute to drive HD progression, and that they express CB₁ receptors, degrade endocannabinoids, and modulate endocannabinergic transmission. However, the possible role of the astroglial endocannabinoid system in controlling MSN integrity remains unknown. Here, we show that JZL-184, a selective inhibitor of monoacylglycerol lipase (MGL), the key enzyme that deactivates the endocannabinoid 2-arachidonoylglycerol, prevented the mutant huntingtin-induced up-regulation of the pro-inflammatory cytokine tumor necrosis factor-α in primary mouse striatal astrocytes via CB₁ receptors. To study the role of astroglial MGL in vivo, we injected stereotactically into the mouse dorsal striatum viral vectors that encode mutant or normal huntingtin under the control of the glial fibrillary acidic protein promoter. We observed that, in wild-type mice, pharmacological blockade of MGL with JZL-184 (8 mg/kg/day, i.p.) conferred neuroprotection against mutant huntingtin-induced striatal damage, as evidenced by the prevention of MSN loss, astrogliosis, and motor coordination impairment. We next found that conditional mutant mice bearing a genetic deletion of MGL selectively in astroglial cells (MGL^{floxed/floxed;GFAP-Cre/+} mice) were resistant to mutant huntingtin-induced MSN loss, astrogliosis, and motor coordination impairment. Taken together, these data support that astroglial MGL controls the availability of a 2-arachidonoylglycerol pool that ensues protection of MSNs in the mouse striatum in vivo, thus providing a potential druggable target for reducing striatal neurodegeneration.

High Fat Diet Increases Circulating Endocannabinoids Accompanied by Increased Synthesis Enzymes in Adipose Tissue

The endocannabinoid system (ECS) controls energy balance by regulating both energy intake and energy expenditure. Endocannabinoid levels are elevated in obesity suggesting a potential causal relationship. This study aimed to elucidate the rate of dysregulation of the ECS, and the metabolic organs involved, in diet-induced obesity. Eight groups of age-matched male C57Bl/6J mice were randomized to receive a chow diet (control) or receive a high fat diet (HFD, 45% of calories derived from fat) ranging from 1 day up to 18 weeks before euthanasia. Plasma levels of the endocannabinoids 2-arachidonoylglycerol (2-AG) and anandamide (N-arachidonoylethanolamine, AEA), and related N-acylethanolamines, were quantified by UPLC-MS/MS and gene expression of components of the ECS was determined in liver, muscle, white adipose tissue (WAT) and brown adipose tissue (BAT) during the course of diet-induced obesity development. HFD feeding gradually increased 2-AG (+132% within 4 weeks, P < 0.05), accompanied by upregulated expression of its synthesizing enzymes Daglα and β in WAT and BAT. HFD also rapidly increased AEA (+81% within 1 week, P < 0.01), accompanied by increased expression of its synthesizing enzyme Nape-pld, specifically in BAT. Interestingly, Nape-pld expression in BAT correlated with plasma AEA levels (R ² = 0.171, β = 0.276, P < 0.001). We conclude that a HFD rapidly activates adipose tissue depots to increase the synthesis pathways of endocannabinoids that may aggravate the development of HFD-induced obesity.

Transcriptional regulation of the endocannabinoid system in a rat model of binge-eating behavior reveals a selective modulation of the hypothalamic fatty acid amide hydrolase gene

OBJECTIVE

Binge-eating episodes are recurrent and are defining features of several eating disorders. Thus binge-eating episodes might influence eating disorder development of which exact underlying mechanisms are still largely unknown.

METHODS

Here we focused on the transcriptional regulation of the endocannabinoid system, a potent regulator of feeding behavior, in relevant rat brain regions, using a rat model in which a history of intermittent food restriction and a frustration stress induce binge-like palatable food consumption.

RESULTS

We observed a selective down-regulation of fatty acid amide hydrolase (faah) gene expression in the hypothalamus of rats showing the binge-eating behavior with a consistent reduction in histone 3 acetylation at lysine 4 of the gene promoter. No relevant changes were detected for any other endocannabinoid system components in any brain regions under study, as well as for the other epigenetic mechanisms investigated (DNA methylation and histone 3 lysine 27 methylation) at the faah gene promoter.

DISCUSSION

Our findings suggest that faah transcriptional regulation is a potential biomarker of binge-eating episodes, with a relevant role in the homeostatic regulation of food intake.

Activity-Based Protein Profiling Delivers Selective Drug Candidate ABX-1431, a Monoacylglycerol Lipase Inhibitor, To Control Lipid Metabolism in Neurological Disorders

Monoacylglycerol lipase (MGLL or MAGL) is a critical point of regulation of both endocannabinoid and eicosanoid signaling pathways in the brain, thereby providing novel therapeutic opportunities for neurological and neurodegenerative diseases. In this issue Cisar et al. disclose the discovery, optimization, and initial preclinical profiling of ABX-1431, a covalent, irreversible MGLL inhibitor. Activity-based protein profiling was key to the discovery of ABX-1431. ABX-1431 is a first-in-class experimental drug that was well-tolerated and safe in phase 1 clinical studies. Data from an exploratory phase 1b study indicate that it has the potential to treat symptoms of adult patients with syndrome of Gilles de la Tourette. ABX-1431 is currently entering clinical phase 2 studies for this neurological disorder as well as for other indications, such as neuromyeltis optica and multiple sclerosis.