Chemical probes of endocannabinoid metabolism

A Highly Selective and Versatile Probe Platform for Visualization of Monoacylglycerol Lipase

Monoacylglycerol lipase (MAGL) is a key enzyme for signal termination in the endocannabinoid system (ECS). MAGL inhibition results in indirect activation of the cannabinoid receptors, which offers unique advantages for the treatment of, e.g., multiple sclerosis, epilepsy, and other neurological disorders. Molecular imaging techniques are valuable tools to overcome the current poor understanding of MAGL's distribution and role in patho- and physiological processes within ECS signaling. Herein, we report the design, synthesis, and validation of highly selective versatile fluorescent and click-chemistry probes for MAGL. Structure-based design combined with a reverse-design approach allowed the development of a structural unit that selectively and effectively recognizes MAGL while offering a versatile platform to attach different fluorophores and further reporter units. In this way, labeled probes with sub-nanomolar potency carrying diverse fluorescent dyes were obtained. Probe affinity and selectivity remained invariant to changes in the fluorophore subunit, showing the remarkable robustness of this platform in delivering tailor-made probes. Highly consistent inhibition across species supports pharmacological model translatability. Extensive profiling and validation in various cellular systems shows the ability of these highly potent and selective probes to elucidate the complex role of MAGL in ECS cellular signaling, inflammatory processes, and disease progression.

Identification of a Possible Endocannabinoid-Mediated Mechanism of Action of Cetylated Fatty Acids

Some musculoskeletal disorders, including osteoarthritis; arthrosis; post-traumatic injuries; and other inflammatory tendon, joint and muscular afflictions, still represent unmet medical needs. Cetylated fatty acids (CFAs) are key components of widely distributed over-the-counter products, especially for topical use, which are intended to reduce symptoms associated with these conditions. Nevertheless, the mechanism of action of CFAs' analgesic and anti-inflammatory properties has not yet been clearly established. Endocannabinoids, such as 2-arachidonoylglycerol (2-AG) and anandamide (AEA), are known to produce analgesic and anti-inflammatory effects. These compounds undergo physiological inactivation operated by several enzymes, including monoacylglycerol lipase (MAGL). We herein demonstrate for the first time that the therapeutic effects of CFAs may be attributable, at least in part, to their MAGL inhibition activities, which induce a local increase in analgesic/anti-inflammatory endocannabinoids in close proximity to the site of administration. These findings pave the way for the development of new potent local analgesic agents, whose action is based on an indirect cannabinoid effect.

Acute and chronic cannabis vapor exposure influences basal and stress-induced release of glucocorticoids in male and female rats

Management of stress and anxiety is often listed as the primary motivation behind cannabis use. Human research has found that chronic cannabis use is associated with increased basal cortisol levels but blunted neuroendocrine responses to stress. Preclinical research has demonstrated mixed effects of Δ9-tetrahydrocannabinol (THC; the psychoactive constituent of cannabis), much of which is suggestive of dose-dependent effects; however, the predominance of this work has employed an injection method to deliver cannabis. As inhalation is the most common route of administration in humans, we employed a translationally relevant model of inhaled cannabis vapor exposure to help characterize the extent to which acute and chronic cannabis exposure modulates neuroendocrine responses to stress. Male and female Sprague-Dawley rats were acutely (single day) or chronically (10 days) exposed to cannabis or vehicle vapor, and the stress hormone, corticosterone, was analyzed prior to and following an acute 30-min restraint stress. Our results indicate that initial exposure to the vapor chambers, regardless of vehicle or cannabis exposure, is sufficient to elevate corticosterone levels in male and female rodents. Further, acute cannabis exposure was capable of increasing corticosterone levels in both male and female rats, however, this effect was modified by the habituation to the vapor chambers differentially in males and females. Regardless of sex, chronic cannabis exposure is sufficient to both elevate basal corticosterone levels and blunt stress-induced increases in corticosterone following a restraint stressor. Collectively, these data help characterize the impacts of cannabis vapor exposure on basal and stress-induced activation of the hypothalamic-pituitary-adrenal axis.

Chemical Probes for Investigating the Endocannabinoid System

Cannabis sativa has been used therapeutically since early civilizations, with key cannabinoids Δ9-tetrahydrocannabinol (THC) 3.1 and cannabidiol characterized in the 1960s, leading to the discovery of cannabinoid receptors type 1 (CB1R) and type 2 (CB2R) and the endocannabinoid system (ECS) in the 1990s. The ECS, involving endogenous ligands like 2-arachidonoylglycerol (2-AG) 1.1, anandamide (N-arachidonoylethanolamine (AEA)) 1.2, and various proteins, regulates vital processes such as sleep, appetite, and memory, and holds significant therapeutic potential, especially for neurological disorders. Small molecule-derived pharmacological tools, or chemical probes, target key components of the ECS and are crucial for target validation, mechanistic studies, pathway elucidation, phenotypic screening, and drug discovery. These probes selectively interact with specific proteins or pathways, enabling researchers to modulate target activity and observe biological effects. When they carry an additional reporter group, they are referred to as labeled chemical probes. Developed through medicinal chemistry, structural biology, and high-throughput screening, effective chemical probes must be selective, potent, and depending on their purpose meet additional criteria such as cell permeability and metabolic stability.This chapter describes high-quality labeled and unlabeled chemical probes targeting ECS constituents that have been successfully applied for various research purposes. CB1R and CB2R, class A G protein-coupled receptors, are activated by 2-AG 1.1, AEA 1.2, and THC 3.1, with numerous ligands developed for these receptors. Imaging techniques like single-photon emission computed tomography, positron emission tomography, and fluorescently labeled CB1R and CB2R probes have enhanced CB receptor studies. CB2R activation generally results in immunosuppressive effects, limiting tissue injury. AEA 1.2 is mainly degraded by fatty acid amide hydrolase (FAAH) or N-acylethanolamine acid amidase (NAAA) into ethanolamine and arachidonic acid (AA) 1.3. FAAH inhibitors increase endogenous fatty acid amides, providing analgesic effects without adverse effects. NAAA inhibitors reduce inflammation and pain in animal models. Diacylglycerol lipase (DAGL) is essential for 2-AG 1.1 biosynthesis, while monoacylglycerol lipase (MAGL) degrades 2-AG 1.1 into AA 1.3, thus regulating cannabinoid signaling. Multiple inhibitors targeting FAAH and MAGL have been generated, though NAAA and DAGL probe development lags behind. Similarly, advancements in inhibitors targeting endocannabinoid (eCB) cellular uptake or trafficking proteins like fatty acid-binding proteins have been slower. The endocannabinoidome (eCBome) includes the ECS and related molecules and receptors, offering therapeutic opportunities from non-THC cannabinoids and eCBome mediators. Ongoing research aims to refine chemical tools for ECS and eCBome study, addressing unmet medical needs in central nervous system disorders and beyond.

Endocannabinoid interference blocks post-global cerebral ischemia depression through prefrontal cortico-amygdala projections

Up to 45% of patients surviving from transient global cerebral ischemia (GCI) after cardiac arrest develop post-global cerebral ischemia depression (PGCID), but how to treat PGCID is clinically unknown. Here we find that cannabinoid type-1 receptor (CB1R) antagonists, CB1R knockout and endocannabinoid (eCB) synthesis inhibition block acute stress-induced PGCID. Application of acute stress to GCI mice increases CB1R activity from ventromedial prefrontal cortical (vmPFC) terminals synapsing with the basolateral amygdala (BLA) neurons, indicating the involvement of increased vmPFC-BLA synaptic eCB signaling in PGCID induction. This idea is supported by findings that optogenetic activation of CB1Rs in vmPFC-BLA projections mimics stress effects to induce PGCID, which is blocked by knock-down of eCB biosynthesis enzyme genes in vmPFC-BLA synapses. Interestingly, GCI mice show decreased mRNA expression of eCB degradation enzymes in vmPFCs without significant changes on mRNA expression of eCB biosynthesis and degradation enzymes in BLA cells. Thus, over-expression of eCB degradation enzymes in vmPFC cells innervating BLA neurons or activation of vmPFC-BLA projections blocks stress effects to induce PGCID. Our findings suggest that decreased eCB degradation and subsequent stress-increased eCB signaling in vmPFC-BLA circuits participate in the mechanism of PGCID, which can be treated clinically by eCB signaling interference systemically or in vmPFC-BLA circuits.

Cannabis, Endocannabinoids and Brain Development: From Embryogenesis to Adolescence

The endocannabinoid signalling system (ECS) plays a critical role from the very beginning of embryogenesis. Accordingly, the ECS is engaged early on in nervous system development, starting from neurulation, supported by the identification of ECS components-both receptors and enzymes controlling endocannabinoid metabolism-at these early stages. In particular, regarding the brain, the ECS is involved in the tightly regulated sequence of events that comprise brain development, from neurogenesis to neuronal migration, morphological guidance for neuronal connectivity, and synaptic circuitry refinement. The importance of this broad role of the ECS across various brain development processes is further underscored by the growing understanding of the consequences of cannabis exposure at different developmental stages. Despite the considerable knowledge we have on the role of the ECS in brain development, significant gaps in our understanding remain, particularly regarding the long-term impact and underlying mechanisms of cannabis exposure at different developmental stages. This review provides an overview of the current state of knowledge on the role of the ECS throughout brain development, from embryogenesis to adulthood, and discusses the impact of cannabis exposure, especially during adolescence-a critical period of circuitry maturation and refinement coinciding with an increased risk of cannabis use.

Cannabis constituents for chronic neuropathic pain; reconciling the clinical and animal evidence

Chronic neuropathic pain is a debilitating pain syndrome caused by damage to the nervous system that is poorly served by current medications. Given these problems, clinical studies have pursued extracts of the plant Cannabis sativa as alternative treatments for this condition. The vast majority of these studies have examined cannabinoids which contain the psychoactive constituent delta-9-tetrahydrocannabinol (THC). While there have been some positive findings, meta-analyses of this clinical work indicates that this effectiveness is limited and hampered by side-effects. This review focuses on how recent preclinical studies have predicted the clinical limitations of THC-containing cannabis extracts, and importantly, point to how they might be improved. This work highlights the importance of targeting channels and receptors other than cannabinoid CB1 receptors which mediate many of the side-effects of cannabis.

Disrupted stress-induced analgesia in a neuropathic pain state is rescued by the endocannabinoid degradation inhibitor JZL195

Acute stress normally engages descending brain pathways to produce an antinociceptive response, known as stress-induced analgesia. Paradoxically, these descending pain modulatory pathways are also involved in the maintenance of the abnormal pain associated with chronic neuropathic pain. It remains unclear how stress-induced analgesia is affected by neuropathic pain states. We therefore examined the impact of a chronic constriction nerve-injury (CCI) model of neuropathic pain on restraint stress-induced analgesia in C57BL/6 mice. Thirty minutes of restraint stress produced analgesia in the hotplate thermal nociceptive assay that was less in CCI compared to control mice who underwent a sham-surgery. In sham but not CCI mice, stress-induced analgesia was reduced by the opioid receptor antagonist naltrexone. The cannabinoid CB1 receptor antagonist AM281 did not affect stress-induced analgesia in either sham or CCI mice. Low-dose pre-treatment with the dual fatty acid amide hydrolase and monoacylglycerol lipase inhibitor JZL195 increased stress-induced analgesia in CCI but not sham mice. The JZL195 enhancement of stress-induced analgesia in CCI mice was abolished by AM281 but was unaffected by naltrexone. These findings indicate that the acute opioid-mediated analgesic response to a psychological stressor is disrupted in a nerve-injury model of neuropathic pain. Importantly, this impairment of stress-induced analgesia was rescued by blockade of endocannabinoid breakdown via a cannabinoid CB1 receptor dependent mechanism. These findings suggest that subthreshold treatment with endocannabinoid degradation blockers could be used to alleviate the disruption of endogenous pain control systems in a neuropathic pain state.

Protective effects of fatty acid amide hydrolase inhibition in UVB-activated microglia

Neuroinflammation is a hallmark of several neurodegenerative disorders that has been extensively studied in recent years. Microglia, the primary immune cells of the central nervous system (CNS), are key players in this physiological process, demonstrating a remarkable adaptability in responding to various stimuli in the eye and the brain. Within the complex network of neuroinflammatory signals, the fatty acid N-ethanolamines, in particular N-arachidonylethanolamine (anandamide, AEA), emerged as crucial regulators of microglial activity under both physiological and pathological states. In this study, we interrogated for the first time the impact of the signaling of these bioactive lipids on microglial cell responses to a sub-lethal acute UVB radiation, a physical stressor responsible of microglia reactivity in either the retina or the brain. To this end, we developed an in vitro model using mouse microglial BV-2 cells. Upon 24 h of UVB exposure, BV-2 cells showed elevated oxidative stress markers and, cyclooxygenase (COX-2) expression, enhanced phagocytic and chemotactic activities, along with an altered immune profiling. Notably, UVB exposure led to a selective increase in expression and activity of fatty acid amide hydrolase (FAAH), the main enzyme responsible for degradation of fatty acid ethanolamides. Pharmacological FAAH inhibition via URB597 counteracted the effects of UVB exposure, decreasing tumor necrosis factor α (TNF-α) and nitric oxide (NO) release and reverting reactive oxidative species (ROS), interleukin-1β (IL-1β), and interleukin-10 (IL-10) levels to the control levels. Our findings support the potential of enhanced fatty acid amide signaling in mitigating UVB-induced cellular damage, paving the way to further exploration of these lipids in light-induced immune responses.

Lysophosphatidylserine: A Signaling Lipid with Implications in Human Diseases

Lysophosphatidylserine (lyso-PS) has emerged as yet another important signaling lysophospholipid in mammals, and deregulation in its metabolism has been directly linked to an array of human autoimmune and neurological disorders. It has an indispensable role in several biological processes in humans, and therefore, cellular concentrations of lyso-PS are tightly regulated to ensure optimal signaling and functioning in physiological settings. Given its biological importance, the past two decades have seen an explosion in the available literature toward our understanding of diverse aspects of lyso-PS metabolism and signaling and its association with human diseases. In this Review, we aim to comprehensively summarize different aspects of lyso-PS, such as its structure, biodistribution, chemical synthesis, and SAR studies with some synthetic analogs. From a biochemical perspective, we provide an exhaustive coverage of the diverse biological activities modulated by lyso-PSs, such as its metabolism and the receptors that respond to them in humans. We also briefly discuss the human diseases associated with aberrant lyso-PS metabolism and signaling and posit some future directions that may advance our understanding of lyso-PS-mediated mammalian physiology.

Predator odor stress reactivity, alcohol drinking and the endocannabinoid system

Post-traumatic stress disorder (PTSD) and alcohol use disorder (AUD) are highly comorbid and individual differences in response to stress suggest resilient and susceptible populations. Using animal models to target neurobiological mechanisms associated with individual variability in stress coping responses and the relationship with subsequent increases in alcohol consumption has important implications for the field of traumatic stress and alcohol disorders. The current review discusses the unique advantages of utilizing predator odor stressor exposure models, specifically using 2,5-dihydro-2,4,5-trimethylthiazoline (TMT) on better understanding PTSD pathophysiology and neurobiological mechanisms associated with stress reactivity and subsequent increases in alcohol drinking. Furthermore, there has been increasing interest regarding the role of the endocannabinoid system in modulating behavioral responses to stress with an emphasis on stress coping and individual differences in stress-susceptibility. Therefore, the current review focuses on the topic of endocannabinoid modulation of stress reactive behaviors during and after exposure to a predator odor stressor, with implications on modulating distinctly different behavioral coping strategies.

Fatty Acid Amide Hydrolase and Cannabinoid Receptor Type 1 Genes Regulation is Modulated by Social Isolation in Rats

Social isolation is a state of lack of social connections, involving the modulation of different molecular signalling cascades and associated with high risk of mental health issues. To investigate if and how gene expression is modulated by social experience at the central level, we analyzed the effects of 5 weeks of social isolation in rats focusing on endocannabinoid system genes transcription in key brain regions involved in emotional control. We observed selective reduction in mRNA levels for fatty acid amide hydrolase (Faah) and cannabinoid receptor type 1 (Cnr1) genes in the amygdala complex and of Cnr1 in the prefrontal cortex of socially isolated rats when compared to controls, and these changes appear to be partially driven by trimethylation of Lysine 27 and acetylation of Lysine 9 at Histone 3. The alterations of Cnr1 transcriptional regulation result also directly correlated with those of oxytocin receptor gene. We here suggest that to counteract the effects of SI, it is of relevance to restore the endocannabinoid system homeostasis via the use of environmental triggers able to revert those epigenetic mechanisms accounting for the alterations observed.

A UPLC-MS/MS method for simultaneous determination of arachidonic acid, stearic acid, and related endocannabinoids in human plasma

Endocannabinoids (eCBs) exert considerable influence over energy metabolism, lipid metabolism, and glucose metabolism within the human body. Among the most biologically active cannabinoids identified thus far are 2-arachidonoylglycerol (2-AG), arachidonoyl ethanolamide (AEA), 1-stearoylglycerol (1-SRG), and stearoyl ethanolamide (SEA), which are derived from arachidonic acid (AA) and stearic acid (SA). However, despite the unique in bioactivities exhibited by eCBs, their determination in plasma has been hindered by the lack of sensitive analytical methods. The aim of this study was to develop and validate a highly sensitive and rapid method using ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) for accurate measurement of AEA, SEA, 2-AG, 1-SRG, AA, and SA levels in human plasma samples. Sample preparation involved a protein precipitation method and a methyl tert-butyl ether liquid-liquid extraction method. Chromatographic separation was accomplished by utilizing an ACQUITY UPLC BEH C8 column with a mobile phase of acetonitrile containing 0.1% formic acid and water containing 0.1% formic acid, flowing at a rate of 0.35 mL/min. AA-d8, 2-AG-d5, and AEA-d8 were selected as deuterated internal standards. The analytes were determined with MRM in both positive and negative ion mode. The lower limit of quantification ranged from 0.1 to 400 ng/mL, and the correlation coefficient (R2) was >0.99. Inter-day and intra-day precision exhibited values of 0.55-13.29% and 0.62%-13.90%, respectively. Recovery and matrix effect were within the range of 77.7%-109.7%, and 90.0%-113.5%, respectively. Stability tests confirmed the acceptability of all analytes. To demonstrate the effectiveness of the approach, it was implemented to assess and compare plasma samples from healthy volunteers (n = 49) and individuals with non-alcoholic fatty liver disease (NAFLD) (n = 62). The study revealed significant differences in AEA, SEA, AA, and SA levels between the two groups.

Recent advances in bioluminescent probes for neurobiology

Bioluminescence is a popular modality for imaging in living organisms. The platform relies on enzymatically (luciferase) generated light via the oxidation of small molecule luciferins. Since no external light is needed for photon production, there are no concerns with background autofluorescence or photobleaching over time-features that have historically limited other optical readouts. Bioluminescence is thus routinely used for longitudinal tracking across whole animals. Applications in the brain, though, have been more challenging due to a lack of sufficiently bioavailable, bright, and easily multiplexed probes. Recent years have seen the development of designer luciferase and luciferin pairs that address these issues, providing more sensitive and real-time readouts of biochemical features relevant to neurobiology. This review highlights many of the advances in bioluminescent probe design, with a focus on the small molecule light emitter, the luciferin. Specific efforts to improve luciferin pharmacokinetics and tissue-penetrant emission are covered, in addition to applications that such probes have enabled. The continued development of improved bioluminescent probes will aid in illuminating critical neurochemical processes in the brain.

Design, synthesis, ADME and biological evaluation of benzylpiperidine and benzylpiperazine derivatives as novel reversible monoacylglycerol lipase (MAGL) inhibitors

The degradation of the endocannabinoid 2-arachidonoylglycerol is mediated by the enzyme monoacylglycerol lipase (MAGL), thus generating arachidonic acid, the precursor of prostaglandins and other pro-inflammatory mediators. MAGL also contributes to the hydrolysis of monoacylglycerols into glycerol and fatty acids in peripheral body districts, which may act as pro-tumorigenic signals. For this reason, MAGL inhibitors have been considered as interesting therapeutic agents for their anti-nociceptive, anti-inflammatory, antioxidant and anti-cancer properties. So far, only a limited series of reversible MAGL inhibitors, which are devoid of side effects shown by irreversible inhibitors in animal models, have been reported. Here we optimized a class of benzylpiperidine and benzylpiperazine-based compounds for a reversible MAGL inhibition. The best MAGL inhibitors of this class, compounds 28 and 29, showed a very good inhibition potency, both on the isolated enzyme and in U937 cells, as confirmed by molecular modeling studies that predicted their binding mode into the MAGL active site. Both compounds are characterized by a high selectivity for MAGL versus other serine hydrolases including enzymes of the endocannabinoid system, as confirmed by ABPP experiments in mouse brain membranes. Moreover, very good properties concerning ADME parameters and low in vivo toxicity have been observed for both compounds.

A monoacylglycerol lipase inhibitor showing therapeutic efficacy in mice without central side effects or dependence

Monoacylglycerol lipase (MAGL) regulates endocannabinoid 2-arachidonoylglycerol (2-AG) and eicosanoid signalling. MAGL inhibition provides therapeutic opportunities but clinical potential is limited by central nervous system (CNS)-mediated side effects. Here, we report the discovery of LEI-515, a peripherally restricted, reversible MAGL inhibitor, using high throughput screening and a medicinal chemistry programme. LEI-515 increased 2-AG levels in peripheral organs, but not mouse brain. LEI-515 attenuated liver necrosis, oxidative stress and inflammation in a CCl4-induced acute liver injury model. LEI-515 suppressed chemotherapy-induced neuropathic nociception in mice without inducing cardinal signs of CB1 activation. Antinociceptive efficacy of LEI-515 was blocked by CB2, but not CB1, antagonists. The CB1 antagonist rimonabant precipitated signs of physical dependence in mice treated chronically with a global MAGL inhibitor (JZL184), and an orthosteric cannabinoid agonist (WIN55,212-2), but not with LEI-515. Our data support targeting peripheral MAGL as a promising therapeutic strategy for developing safe and effective anti-inflammatory and analgesic agents.

Sexually dimorphic effects of monoacylglycerol lipase inhibitor MJN110 on stress-related behaviour and drinking in Marchigian Sardinian alcohol-preferring rats

BACKGROUND AND PURPOSE

The endocannabinoid (eCB) system plays an important homeostatic role in the regulation of stress circuits and has emerged as a therapeutic target to treat stress disorders and alcohol use disorder (AUD). Extensive research has elucidated a role for the eCB anandamide (AEA), but less is known about 2-arachidonoylglycerol (2-AG) mediated signalling.

EXPERIMENTAL APPROACH

We pharmacologically enhanced eCB signalling by inhibiting the 2-AG metabolizing enzyme, monoacylglycerol lipase (MAGL), in male and female Marchigian Sardinian alcohol-preferring (msP) rats, a model of innate alcohol preference and stress hypersensitivity, and in control Wistar rats. We tested the acute effect of the selective MAGL inhibitor MJN110 in alleviating symptoms of alcohol drinking, anxiety, irritability and fear.

KEY RESULTS

A single systemic administration of MJN110 increased 2-AG levels in the central amygdala, prelimbic and infralimbic cortex but did not acutely alter alcohol drinking. MAGL inhibition reduced aggressive behaviours in female msPs, and increased defensive behaviours in male msPs, during the irritability test. Moreover, in the novelty-induced hypophagia test, MJN110 selectively enhanced palatable food consumption in females, mitigating stress-induced food suppression. Lastly, msP rats showed increased conditioned fear behaviour compared with Wistar rats, and MJN110 reduced context-associated conditioned fear responses, but not cue-probed fear expression, in male msPs.

CONCLUSIONS AND IMPLICATIONS

Acute inhibition of MAGL attenuated some stress-related responses in msP rats but not voluntary alcohol drinking. Our results provide new insights into the sex dimorphism documented in stress-induced responses. Sex-specific eCB-based approaches should be considered in the clinical development of therapeutics.

Plasma endocannabinoids in cocaine dependence and their relation to cerebral metabotropic glutamate receptor 5 density

Animal models indicate that the endocannabinoid system (ECS) plays a modulatory role in stress and reward processing, both crucially impaired in addictive disorders. Preclinical findings showed endocannabinoid-modulated synaptic plasticity in reward brain networks linked to the metabotropic-glutamate-5 receptor (mGluR5), contributing to drug-reinforcing effects and drug-seeking behavior. Although animal models postulate a link between ECS and cocaine addiction, human translational studies are lacking. Here, we tested previous preclinical findings by investigating plasma endocannabinoids (eCBs) anandamide (AEA), 2-arachidonoylglycerol (2-AG), and the related N-acylethanolamines (NAEs) palmitoylethanolamide (PEA) and oleoylethanolamide (OEA), including their interaction with cerebral mGluR5, in chronic cocaine users (CU). We compared basal plasma concentrations between chronic CU (N = 103; 69 recreational CU and 34 dependent CU) and stimulant-naïve healthy controls (N = 92). Follow-up basal eCB/NAE plasma levels after 12 months were used for reliability and stability check (CU: N = 33; controls: N = 43). In an additional analysis using 11C-ABP688 positron emission tomography (PET) in a male subsample (CU: N = 18; controls: N = 16), we investigated the relationships between eCBs/NAEs and mGluR5 density in the brain. We found higher 2-AG plasma levels in dependent CU compared to controls and recreational CU. 2-AG levels were stable over time across all groups. In the PET-subsample, a positive association between 2-AG and mGluR5 brain density only in CU was found. Our results corroborate animal findings suggesting an alteration of the ECS in cocaine dependence and an association between peripheral 2-AG levels and cerebral mGluR5 in humans. Therefore, the ECS might be a promising pharmaco-therapeutic target for novel treatments of cocaine dependence.

Goods and Bads of the Endocannabinoid System as a Therapeutic Target: Lessons Learned after 30 Years

The cannabis derivative marijuana is the most widely used recreational drug in the Western world and is consumed by an estimated 83 million individuals (∼3% of the world population). In recent years, there has been a marked transformation in society regarding the risk perception of cannabis, driven by its legalization and medical use in many states in the United States and worldwide. Compelling research evidence and the Food and Drug Administration cannabis-derived cannabidiol approval for severe childhood epilepsy have confirmed the large therapeutic potential of cannabidiol itself, Δ9-tetrahydrocannabinol and other plant-derived cannabinoids (phytocannabinoids). Of note, our body has a complex endocannabinoid system (ECS)-made of receptors, metabolic enzymes, and transporters-that is also regulated by phytocannabinoids. The first endocannabinoid to be discovered 30 years ago was anandamide (N-arachidonoyl-ethanolamine); since then, distinct elements of the ECS have been the target of drug design programs aimed at curing (or at least slowing down) a number of human diseases, both in the central nervous system and at the periphery. Here a critical review of our knowledge of the goods and bads of the ECS as a therapeutic target is presented to define the benefits of ECS-active phytocannabinoids and ECS-oriented synthetic drugs for human health. SIGNIFICANCE STATEMENT: The endocannabinoid system plays important roles virtually everywhere in our body and is either involved in mediating key processes of central and peripheral diseases or represents a therapeutic target for treatment. Therefore, understanding the structure, function, and pharmacology of the components of this complex system, and in particular of key receptors (like cannabinoid receptors 1 and 2) and metabolic enzymes (like fatty acid amide hydrolase and monoacylglycerol lipase), will advance our understanding of endocannabinoid signaling and activity at molecular, cellular, and system levels, providing new opportunities to treat patients.

Synaptic and cellular endocannabinoid signaling mechanisms regulate stress-induced plasticity of nucleus accumbens somatostatin neurons

Interneuron populations within the nucleus accumbens (NAc) orchestrate excitatory-inhibitory balance, undergo experience-dependent plasticity, and gate-motivated behavior, all biobehavioral processes heavily modulated by endogenous cannabinoid (eCB) signaling. While eCBs are well known to regulate synaptic plasticity onto NAc medium spiny neurons and modulate NAc function at the behavioral level, how eCBs regulate NAc interneuron function is less well understood. Here, we show that eCB signaling differentially regulates glutamatergic and feedforward GABAergic transmission onto NAc somatostatin-expressing interneurons (NAcSOM+) in an input-specific manner, while simultaneously increasing postsynaptic excitability of NAcSOM+ neurons, ultimately biasing toward vHPC (ventral hippocampal), and away from BLA (basolateral amygdalalar), activation of NAcSOM+ neurons. We further demonstrate that NAcSOM+ are activated by stress in vivo and undergo stress-dependent plasticity, evident as a global increase in intrinsic excitability and an increase in excitation-inhibition balance specifically at vHPC, but not BLA, inputs onto NAcSOM+ neurons. Importantly, both forms of stress-induced plasticity are dependent on eCB signaling at cannabinoid type 1 receptors. These findings reveal eCB-dependent mechanisms that sculpt afferent input and excitability of NAcSOM+ neurons and demonstrate a key role for eCB signaling in stress-induced plasticity of NAcSOM+-associated circuits.

Plants and Small Molecules: An Up-and-Coming Synergy

The emergence of Arabidopsis thaliana as a model system has led to a rapid and wide improvement in molecular genetics techniques for studying gene function and regulation. However, there are still several drawbacks that cannot be easily solved with molecular genetic approaches, such as the study of unfriendly species, which are of increasing agronomic interest but are not easily transformed, thus are not prone to many molecular techniques. Chemical genetics represents a methodology able to fill this gap. Chemical genetics lies between chemistry and biology and relies on small molecules to phenocopy genetic mutations addressing specific targets. Advances in recent decades have greatly improved both target specificity and activity, expanding the application of this approach to any biological process. As for classical genetics, chemical genetics also proceeds with a forward or reverse approach depending on the nature of the study. In this review, we addressed this topic in the study of plant photomorphogenesis, stress responses and epigenetic processes. We have dealt with some cases of repurposing compounds whose activity has been previously proven in human cells and, conversely, studies where plants have been a tool for the characterization of small molecules. In addition, we delved into the chemical synthesis and improvement of some of the compounds described.

Identification of a novel fatty acid binding protein-5-CB2 receptor-dependent mechanism regulating anxiety behaviors in the prefrontal cortex

The endocannabinoid (eCB) system represents a promising neurobiological target for novel anxiolytic pharmacotherapies. Previous clinical and preclinical evidence has revealed that genetic and/or pharmacological manipulations altering eCB signaling modulate fear and anxiety behaviors. Water-insoluble eCB lipid anandamide requires chaperone proteins for its intracellular transport to degradation, a process that requires fatty acid-binding proteins (FABPs). Here, we investigated the effects of a novel FABP-5 inhibitor, SBFI-103, on fear and anxiety-related behaviors using rats. Acute intra-prelimbic cortex administration of SBFI-103 induced a dose-dependent anxiolytic response and reduced contextual fear expression. Surprisingly, both effects were reversed when a cannabinoid-2 receptor (CB2R) antagonist, AM630, was co-infused with SBFI-103. Co-infusion of the cannabinoid-1 receptor antagonist Rimonabant with SBFI-103 reversed the contextual fear response yet showed no reversal effect on anxiety. Furthermore, in vivo neuronal recordings revealed that intra-prelimbic region SBFI-103 infusion altered the activity of putative pyramidal neurons in the basolateral amygdala and ventral hippocampus, as well as oscillatory patterns within these regions in a CB2R-dependent fashion. Our findings identify a promising role for FABP5 inhibition as a potential target for anxiolytic pharmacotherapy. Furthermore, we identify a novel, CB2R-dependent FABP-5 signaling pathway in the PFC capable of strongly modulating anxiety-related behaviors and anxiety-related neuronal transmission patterns.

Activity-based protein profiling - finding general solutions to specific problems

In this retrospective/perspective, I will share thoughts on developing and applying the activity-based protein profiling (ABPP) technology, an endeavor that has consumed much of our lab's attention over our 25+ year existence. Before doing so, I first wish to thank the colleagues who so kindly contributed to this Special Issue. I am appreciative and humbled that they were willing to share their innovative and impactful science in this format.

The Anti-Tumorigenic Role of Cannabinoid Receptor 2 in Colon Cancer: A Study in Mice and Humans

The endocannabinoid system, particularly cannabinoid receptor 2 (CB2 in mice and CNR2 in humans), has controversial pathophysiological implications in colon cancer. Here, we investigate the role of CB2 in potentiating the immune response in colon cancer in mice and determine the influence of CNR2 variants in humans. Comparing wild-type (WT) mice to CB2 knockout (CB2^-/-) mice, we performed a spontaneous cancer study in aging mice and subsequently used the AOM/DSS model of colitis-associated colorectal cancer and a model for hereditary colon cancer (Apc^Min/+). Additionally, we analyzed genomic data in a large human population to determine the relationship between CNR2 variants and colon cancer incidence. Aging CB2^-/- mice exhibited a higher incidence of spontaneous precancerous lesions in the colon compared to WT controls. The AOM/DSS-treated CB2^-/- and Apc^Min/+CB2^-/- mice experienced aggravated tumorigenesis and enhanced splenic populations of immunosuppressive myeloid-derived suppressor cells along with abated anti-tumor CD8+ T cells. Importantly, corroborative genomic data reveal a significant association between non-synonymous variants of CNR2 and the incidence of colon cancer in humans. Taken together, the results suggest that endogenous CB2 activation suppresses colon tumorigenesis by shifting the balance towards anti-tumor immune cells in mice and thus portray the prognostic value of CNR2 variants for colon cancer patients.

Photoreactive bioorthogonal lipid probes and their applications in mammalian biology

Lipids are an important class of biological molecules that possess many critical physiological functions, which enable the optimal survival of all organisms, including humans. While the role of lipids in the formation of biological cellular membranes and as a source of energy is fairly well understood, the cellular signalling pathways that lipids modulate in mammals are, in comparison, poorly characterized mechanistically and/or largely unknown. In an effort to dissect these mammalian cellular pathways regulated by signalling lipids and map hitherto unknown protein-lipid interactions, the last two decades have seen tremendous progress in the development of multifunctional lipid probes that, in conjunction with well-established bioorthogonal chemistries and chemoproteomics platforms, has almost exponentially expanded our knowledge in this field. In this review, we focus on the various photoreactive bioorthogonal lipid probes described in the literature, and briefly summarize the different photo-crosslinking groups and bioorthogonal chemistries used by them. Furthermore, we report specific case examples of such photoreactive bioorthogonal lipid probes, and discuss the new biological pathways and insights that have emerged from their use through chemoproteomics in mammalian cells. Finally, we highlight the challenges associated with the use of lipid probes in biological systems, and highlight their importance in the discovery and mechanistic understanding of lipid signalling pathways in the years to come.

Targeting the endocannabinoid system for the treatment of abdominal pain in irritable bowel syndrome

The management of visceral pain in patients with disorders of gut-brain interaction, notably irritable bowel syndrome, presents a considerable clinical challenge, with few available treatment options. Patients are increasingly using cannabis and cannabinoids to control abdominal pain. Cannabis acts on receptors of the endocannabinoid system, an endogenous system of lipid mediators that regulates gastrointestinal function and pain processing pathways in health and disease. The endocannabinoid system represents a logical molecular therapeutic target for the treatment of pain in irritable bowel syndrome. Here, we review the physiological and pathophysiological functions of the endocannabinoid system with a focus on the peripheral and central regulation of gastrointestinal function and visceral nociception. We address the use of cannabinoids in pain management, comparing them to other treatment modalities, including opioids and neuromodulators. Finally, we discuss emerging therapeutic candidates targeting the endocannabinoid system for the treatment of pain in irritable bowel syndrome.

Endocannabinoids at the synapse and beyond: implications for neuropsychiatric disease pathophysiology and treatment

Endocannabinoids (eCBs) are lipid neuromodulators that suppress neurotransmitter release, reduce postsynaptic excitability, activate astrocyte signaling, and control cellular respiration. Here, we describe canonical and emerging eCB signaling modes and aim to link adaptations in these signaling systems to pathological states. Adaptations in eCB signaling systems have been identified in a variety of biobehavioral and physiological process relevant to neuropsychiatric disease states including stress-related disorders, epilepsy, developmental disorders, obesity, and substance use disorders. These insights have enhanced our understanding of the pathophysiology of neurological and psychiatric disorders and are contributing to the ongoing development of eCB-targeting therapeutics. We suggest future studies aimed at illuminating how adaptations in canonical as well as emerging cellular and synaptic modes of eCB signaling contribute to disease pathophysiology or resilience could further advance these novel treatment approaches.

Anandamide and other N-acylethanolamines: A class of signaling lipids with therapeutic opportunities

N-acylethanolamines (NAEs), including N-palmitoylethanolamine (PEA), N-oleoylethanolamine (OEA), N-arachidonoylethanolamine (AEA, anandamide), N-docosahexaenoylethanolamine (DHEA, synaptamide) and their oxygenated metabolites are a lipid messenger family with numerous functions in health and disease, including inflammation, anxiety and energy metabolism. The NAEs exert their signaling role through activation of various G protein-coupled receptors (cannabinoid CB₁ and CB₂ receptors, GPR55, GPR110, GPR119), ion channels (TRPV1) and nuclear receptors (PPAR-α and PPAR-γ) in the brain and periphery. The biological role of the oxygenated NAEs, such as prostamides, hydroxylated anandamide and DHEA derivatives, are less studied. Evidence is accumulating that NAEs and their oxidative metabolites may be aberrantly regulated or are associated with disease severity in obesity, metabolic syndrome, cancer, neuroinflammation and liver cirrhosis. Here, we comprehensively review NAE biosynthesis and degradation, their metabolism by lipoxygenases, cyclooxygenases and cytochrome P450s and the biological functions of these signaling lipids. We discuss the latest findings and therapeutic potential of modulating endogenous NAE levels by inhibition of their degradation, which is currently under clinical evaluation for neuropsychiatric disorders. We also highlight NAE biosynthesis inhibition as an emerging topic with therapeutic opportunities in endocannabinoid and NAE signaling.

The Endocannabinoid 2-Arachidonoylglycerol Bidirectionally Modulates Acute and Protracted Effects of Predator Odor Exposure

BACKGROUND

Stress-related disorders are among the most prevalent psychiatric disorders, characterized by excess fear and enhanced avoidance of trauma triggers. Elucidating the mechanisms regulating temporally distinct aspects of innate and conditioned fear responses could facilitate novel therapeutic development for stress-related disorders. One potential target that has recently emerged is the endocannabinoid system, which has been reported to mediate the physiological response to stress and represents an important substrate underlying individual differences in stress susceptibility.

METHODS

Here, we exposed male and female CD-1 mice to an innate predator stressor, 2MT (2-methyl-2-thiazoline), to investigate the ability of endocannabinoid signaling to modulate temporally distinct innate and conditioned fear behaviors.

RESULTS

We found that 2MT exposure increased amygdala 2-AG (2-arachidonoylglycerol) content and selectively increased excitability in central, but not basolateral, amygdala neurons. We also found that pharmacological 2-AG augmentation during stress exposure exacerbated both acute freezing responses and central amygdala hyperexcitability via cannabinoid receptor type 1- and type 2-dependent mechanisms. Finally, 2-AG augmentation during stress exposure reduced long-term contextual conditioned freezing, and 2-AG augmentation 24 hours after stress exposure reduced conditioned avoidance behavior.

CONCLUSIONS

Our findings demonstrate a bidirectional effect of 2-AG augmentation on innate and conditioned fear behavior, with enhancement of 2-AG levels during stress promoting innate fear responses but ultimately resulting in long-term conditioned fear reduction. These data could reconcile contradictory data on the role of 2-AG in the regulation of innate and conditioned fear-related behavioral responses.

Cannabidiol treatment prevents drug reinstatement and the molecular alterations evoked by amphetamine on receptors and enzymes from dopaminergic and endocannabinoid systems in rats

In psychostimulant drug addiction, relapse is the most concerning outcome to be managed, considering there is no approved treatment for this neuropsychiatric condition. Here, we investigated the effects of the CBD treatment on the relapse behavior triggered by stress, after being submitted to the amphetamine (AMPH)-induced conditioned place preference (CPP) in rats. To elucidate the mechanisms of action underlying the CBD treatment, we evaluated the neuroadaptations on dopaminergic and endocannabinoid targets in the ventral striatum (VS) and ventral tegmental area (VTA) of the brain. Animals received d,l-AMPH (4 mg/kg, i.p.) or vehicle in the CPP paradigm for 8 days. Following the first CPP test, animals were treated with CBD (10 mg/kg, i.p.) or its vehicle for 5 days and subsequently submitted to forced swim stress protocol to induce AMPH-CPP relapse. Behavioral findings showed that CBD treatment prevented AMPH-reinstatement, also exerting anxiolytic activity. At the molecular level, in the VTA, CBD restored the CB1R levels decreased by AMPH-exposure, increased NAPE-PLD, and decreased FAAH levels. In the VS, the increase of D1R and D2R, as well as the decrease of DAT levels induced by AMPH were restored by CBD treatment. The current outcomes evidence a substantial preventive action of the CBD on the AMPH-reinstatement evoked by stress, also involving neuroadaptations in both dopaminergic and endocannabinoid systems in brain areas closely involved in the addiction. Although further studies are needed, these findings support the therapeutic potential of CBD in AMPH-relapse prevention.

Cannabinoids as Glial Cell Modulators in Ischemic Stroke: Implications for Neuroprotection

Stroke is the second leading cause of death worldwide following coronary heart disease. Despite significant efforts to find effective treatments to reduce neurological damage, many patients suffer from sequelae that impair their quality of life. For this reason, the search for new therapeutic options for the treatment of these patients is a priority. Glial cells, including microglia, astrocytes and oligodendrocytes, participate in crucial processes that allow the correct functioning of the neural tissue, being actively involved in the pathophysiological mechanisms of ischemic stroke. Although the exact mechanisms by which glial cells contribute in the pathophysiological context of stroke are not yet completely understood, they have emerged as potentially therapeutic targets to improve brain recovery. The endocannabinoid system has interesting immunomodulatory and protective effects in glial cells, and the pharmacological modulation of this signaling pathway has revealed potential neuroprotective effects in different neurological diseases. Therefore, here we recapitulate current findings on the potential promising contribution of the endocannabinoid system pharmacological manipulation in glial cells for the treatment of ischemic stroke.

Reversible Monoacylglycerol Lipase Inhibitors: Discovery of a New Class of Benzylpiperidine Derivatives

Monoacylglycerol lipase (MAGL) is the enzyme responsible for the metabolism of 2-arachidonoylglycerol in the brain and the hydrolysis of peripheral monoacylglycerols. Many studies demonstrated beneficial effects deriving from MAGL inhibition for neurodegenerative diseases, inflammatory pathologies, and cancer. MAGL expression is increased in invasive tumors, furnishing free fatty acids as pro-tumorigenic signals and for tumor cell growth. Here, a new class of benzylpiperidine-based MAGL inhibitors was synthesized, leading to the identification of 13, which showed potent reversible and selective MAGL inhibition. Associated with MAGL overexpression and the prognostic role in pancreatic cancer, derivative 13 showed antiproliferative activity and apoptosis induction, as well as the ability to reduce cell migration in primary pancreatic cancer cultures, and displayed a synergistic interaction with the chemotherapeutic drug gemcitabine. These results suggest that the class of benzylpiperidine-based MAGL inhibitors have potential as a new class of therapeutic agents and MAGL could play a role in pancreatic cancer.

Genes Responsible for H2S Production and Metabolism Are Involved in Learning and Memory in Drosophila melanogaster

The gasotransmitter hydrogen sulfide (H2S) produced by the transsulfuration pathway (TSP) is an important biological mediator, involved in many physiological and pathological processes in multiple higher organisms, including humans. Cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) enzymes play a central role in H2S production and metabolism. Here, we investigated the role of H2S in learning and memory processes by exploring several Drosophila melanogaster strains with single and double deletions of CBS and CSE developed by the CRISPR/Cas9 technique. We monitored the learning and memory parameters of these strains using the mating rejection courtship paradigm and demonstrated that the deletion of the CBS gene, which is expressed predominantly in the central nervous system, and double deletions completely block short- and long-term memory formation in fruit flies. On the other hand, the flies with CSE deletion preserve short- and long-term memory but fail to exhibit long-term memory retention. Transcriptome profiling of the heads of the males from the strains with deletions in Gene Ontology terms revealed a strong down-regulation of many genes involved in learning and memory, reproductive behavior, cognition, and the oxidation-reduction process in all strains with CBS deletion, indicating an important role of the hydrogen sulfide production in these vital processes.

Osteogenic growth peptide is a potent anti-inflammatory and bone preserving hormone via cannabinoid receptor type 2

The endocannabinoid system consists mainly of 2-arachidonoylglycerol and anandamide, as well as cannabinoid receptor type 1 (CB1) and type 2 (CB2). Based on previous studies, we hypothesized that a circulating peptide previously identified as Osteogenic Growth Peptide (OGP) maintains a bone-protective CB2 tone. We tested OGP activity in mouse models and cells, and in human osteoblasts. We show that the OGP effects on osteoblast proliferation, osteoclastogenesis, and macrophage inflammation in vitro, as well as rescue of ovariectomy-induced bone loss and prevention of ear edema in vivo are all abrogated by genetic or pharmacological ablation of CB2. We also demonstrate that OGP binds at CB2 and may act as both an agonist and positive allosteric modulator in the presence of other lipophilic agonists. In premenopausal women, OGP circulating levels significantly decline with age. In adult mice, exogenous administration of OGP completely prevented age-related bone loss. Our findings suggest that OGP attenuates age-related bone loss by maintaining a skeletal CB2 tone. Importantly, they also indicate the occurrence of an endogenous peptide that signals via CB2 receptor in health and disease.

The Role of Nutritional Status, Gastrointestinal Peptides, and Endocannabinoids in the Prognosis and Treatment of Children with Cancer

Neoplastic diseases in children are the second most frequent cause of death among the young. It is estimated that 400,000 children worldwide will be diagnosed with cancer each year. The nutritional status at diagnosis is a prognostic indicator and influences the treatment tolerance. Both malnutrition and obesity increase the risk of mortality and complications during treatment. It is necessary to constantly search for new factors that impair the nutritional status. The endocannabinoid system (ECS) is a signaling system whose best-known function is regulating energy balance and food intake, but it also plays a role in pain control, embryogenesis, neurogenesis, learning, and the regulation of lipid and glucose metabolism. Its action is multidirectional, and its role is being discovered in an increasing number of diseases. In adults, cannabinoids have been shown to have anti-cancer properties against breast and pancreatic cancer, melanoma, lymphoma, and brain tumors. Data on the importance of both the endocannabinoid system and synthetic cannabinoids are lacking in children with cancer. This review highlights the role of nutritional status in the oncological treatment process, and describes the role of ECS and gastrointestinal peptides in regulating appetite. We also point to the need for research to evaluate the role of the endocannabinoid system in children with cancer, together with a prospective assessment of nutritional status during oncological treatment.

Endocannabinoid Modulation Using Monoacylglycerol Lipase Inhibition in Tourette Syndrome: A Phase 1 Randomized, Placebo-Controlled Study

INTRODUCTION

Tourette syndrome (TS) is a complex neurodevelopmental disorder characterized by chronic motor and vocal tics. While consistently effective treatment is lacking, evidence indicates that the modulation of endocannabinoid system is potentially beneficial. Lu AG06466 (previously ABX-1431) is a highly selective inhibitor of monoacylglycerol lipase, the primary enzyme responsible for the degradation of the endocannabinoid ligand 2-arachidonoylglycerol. This exploratory study aimed to determine the effect of Lu AG06466 versus placebo on tics and other symptoms in patients with TS.

METHODS

In this phase 1b cross-over study, 20 adult patients with TS on standard-of-care medications were randomized to a single fasted dose of Lu AG06466 (40 mg) or placebo in period 1, followed by the other treatment in period 2. The effects on tics, premonitory urges, and psychiatric comorbidities were evaluated using a variety of scaled approaches at different time points before and after treatment.

RESULTS

All scales showed an overall trend of tic reduction, with two out of three tic scales (including the Total Tic Score of the Yale Global Tic Severity Score) showing a significant effect of a single dose of Lu AG06466 versus placebo at various timepoints. Treatment with Lu AG06466 resulted in a significant reduction in premonitory urges versus placebo. Single doses of Lu AG06466 were generally well-tolerated, and the most common adverse events were headache, somnolence, and fatigue.

CONCLUSION

In this exploratory trial, a single dose of Lu AG06466 showed statistically significant positive effects on key measures of TS symptoms.

Effect of Fatty Acid Amide Hydrolase Inhibitor URB597 on Orofacial Pain Perception in Rats

Endocannabinoids act as analgesic agents in a number of headache models. However, their effectiveness varies with the route of administration and the type of pain. In this study, we assessed the role of the fatty acid amide hydrolase inhibitor URB597 in an animal model of orofacial pain based on tooth pulp stimulation. More specifically, we assessed the effects of intracerbroventricular (i.c.v.) and intraperitoneal (i.p.) administration of URB597 on the amplitude of evoked tongue jerks (ETJ) in rats. The levels of the investigated mediators anandamide (AEA), 2-arachidonyl glycerol (2-AG), Substance P (SP), calcitonin-gene-related peptide (CGRP), endomorphin-2 (EM-2) and fatty acid amide hydrolase (FAAH) inhibitor by URB597 and receptors cannabinoid type-1 receptors (CB1R), cannabinoid type-2 receptors (CB2R) and µ-opioid receptors (MOR) were determined in the mesencephalon, thalamus and hypothalamus tissues. We have shown that increasing endocannabinoid AEA levels by both central and peripheral inhibition of FAAH inhibitor by URB597 has an antinociceptive effect on the trigemino-hypoglossal reflex mediated by CB1R and influences the activation of the brain areas studied. On the other hand, URB597 had no effect on the concentration of 2-AG in the examined brain structures and caused a significant decrease in CB2R mRNA expression in the hypothalamus only. Tooth pulp stimulation caused in a significant increase in SP, CGRP and EM-2 gene expression in the midbrain, thalamus and hypothalamus. In contrast, URB597 administered peripherally one hour before stimulation decreased the mRNA level of these endogenous neuropeptides in comparison with the control and stimulation in all examined brain structures. Our results show that centrally and peripherally administered URB597 is effective at preventing orofacial pain by inhibiting AEA catabolism and reducing the level of CGRP, SP and EM-2 gene expression and that AEA and 2-AG have different species and model-specific regulatory mechanisms. The data presented in this study may represent a new promising therapeutic target in the treatment of orofacial pain.

The endocannabinoid system in borderline personality disorder and antisocial personality disorder: A scoping review

Individuals with borderline personality disorder (BPD) or antisocial personality disorder (ASPD) are overrepresented in forensic settings. Yet, despite the burden these disorders place on healthcare and criminal justice systems, there remains a lack of evidence-based pharmacological treatments. Epidemiological data have shown that comorbid cannabis use disorders are common in BPD and ASPD. ∆9 -Tetrahydrocannabinol, the primary psychoactive constituent of cannabis, is an exogenous cannabinoid that stimulates the endocannabinoid system (ECS). Hence, an investigation of the ECS in these conditions is warranted. This scoping review screened 105 records and summarized the extant research on the ECS in ASPD (n = 69) and BPD (n = 61) participants. Preliminary results suggest that alterations of the ECS may be present in these disorders. Although research examining the ECS in personality disorders is still in its infancy, more research is warranted given initial positive findings.

Reactive chemistry for covalent probe and therapeutic development

Bioactive small molecules that form covalent bonds with a target protein are important tools for basic research and can be highly effective drugs. This review highlights reactive groups found in a collection of thiophilic and oxophilic drugs that mediate pharmacological activity through a covalent mechanism of action (MOA). We describe the application of advanced proteomic and bioanalytical methodologies for assessing selectivity of these covalent agents to guide and inspire the search for additional electrophiles suitable for covalent probe and therapeutic development. While the emphasis is on chemistry for modifying catalytic serine, threonine or cysteine residues, we devote a substantial fraction of the review to a collection of exploratory reactive groups of understudied residues on proteins.

Catalytic Activation of Bioorthogonal Chemistry with Light (CABL) Enables Rapid, Spatiotemporally Controlled Labeling and No-Wash, Subcellular 3D-Patterning in Live Cells Using Long Wavelength Light

Described is the spatiotemporally controlled labeling and patterning of biomolecules in live cells through the catalytic activation of bioorthogonal chemistry with light, referred to as "CABL". Here, an unreactive dihydrotetrazine (DHTz) is photocatalytically oxidized in the intracellular environment by ambient O2 to produce a tetrazine that immediately reacts with a trans-cyclooctene (TCO) dienophile. 6-(2-Pyridyl)dihydrotetrazine-3-carboxamides were developed as stable, cell permeable DHTz reagents that upon oxidation produce the most reactive tetrazines ever used in live cells with Diels-Alder kinetics exceeding k2 of 106 M-1 s-1. CABL photocatalysts are based on fluorescein or silarhodamine dyes with activation at 470 or 660 nm. Strategies for limiting extracellular production of singlet oxygen are described that increase the cytocompatibility of photocatalysis. The HaloTag self-labeling platform was used to introduce DHTz tags to proteins localized in the nucleus, mitochondria, actin, or cytoplasm, and high-yielding subcellular activation and labeling with a TCO-fluorophore were demonstrated. CABL is light-dose dependent, and two-photon excitation promotes CABL at the suborganelle level to selectively pattern live cells under no-wash conditions. CABL was also applied to spatially resolved live-cell labeling of an endogenous protein target by using TIRF microscopy to selectively activate intracellular monoacylglycerol lipase tagged with DHTz-labeled small molecule covalent inhibitor. Beyond spatiotemporally controlled labeling, CABL also improves the efficiency of "ordinary" tetrazine ligations by rescuing the reactivity of commonly used 3-aryl-6-methyltetrazine reporters that become partially reduced to DHTzs inside cells. The spatiotemporal control and fast rates of photoactivation and labeling of CABL should enable a range of biomolecular labeling applications in living systems.

Targeting the Endocannabinoid System in the Treatment of Posttraumatic Stress Disorder: A Promising Case of Preclinical-Clinical Translation?

The endocannabinoid (eCB) system is one the most ubiquitous signaling systems of the brain and offers a rich pharmacology including multiple druggable targets. Preclinical research shows that eCB activity influences functional connectivity between the prefrontal cortex and amygdala and thereby influences an organism's ability to cope with threats and stressful experiences. Animal studies show that CB1 receptor activation within the amygdala is essential for extinction of fear memories. Failure to extinguish traumatic memories is a core symptom of posttraumatic stress disorder, suggesting that potentiating eCB signaling may have a therapeutic potential in this condition. However, it has been unknown whether animal findings in this domain translate to humans. Data to inform this critical question are now emerging and are the focus of this review. We first briefly summarize the biology of the eCB system and the animal studies that support its role in fear extinction and stress responding. We then discuss the pharmacological eCB-targeting strategies that may be exploited for therapeutic purposes: direct CB1 receptor activation, using Δ9-tetrahydrocannabinol or its synthetic analogs; or indirect potentiation, through inhibition of eCB-degrading enzymes, the anandamide-degrading enzyme fatty acid amide hydrolase; or the 2-AG (2-arachidonoyl glycerol)-degrading enzyme monoacylglycerol lipase. We then review recent human data on direct CB1 receptor activation via Δ9-tetrahydrocannabinol and anandamide potentiation through fatty acid amide hydrolase blockade. The available human data consistently support a translation of animal findings on fear memories and stress reactivity and suggest a potential therapeutic utility in humans.

Hexafluoroisopropyl carbamates as selective MAGL and dual MAGL/FAAH inhibitors: biochemical and physicochemical properties

A series of hexafluoroisopropyl carbamates with indolylalkyl‐ and azaindolylalkyl‐substituents at the carbamate nitrogen was synthesized and evaluated for inhibition of the endocannabinoid degrading enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL). The synthesized derivatives with butyl to heptyl spacers between the heteroaryl and the carbamate moiety were inhibitors of both enzymes. For investigated compounds in which the alkyl chain was partially incorporated into a piperidine ring, different results were obtained. Compounds with a methylene spacer between the piperidine ring and the heteroaromatic system were found to be selective MAGL inhibitors, while an extension of the alkyl spacer to two to four atoms resulted in dual inhibition of FAAH/MAGL. The only small change in enzyme inhibitory activity with variation of the heteroaromatic system indicates that the reactive hexafluoroisopropyl carbamate group is mainly responsible for the strength of the inhibitory effect of the compounds. Selected derivatives were also tested for hydrolytic stability in aqueous solution, liver homogenate and blood plasma as well as for aqueous solubility and for permeability in a Caco‐2 cell model. Some compounds showed a slightly higher MAGL inhibitory effect than the known selective MAGL inhibitor ABX‐1431 and also partly surpassed this substance with regard to certain physicochemical and biochemical properties such as water solubility and cell permeability.

URB597 induces subtle changes to aggression in adult Lister Hooded rats

The endocannabinoid system has been implicated in both social and cognitive processing. The endocannabinoid metabolism inhibitor, URB597, dose-dependently improves non-social memory in adult Wistar and Sprague Dawley rats, whereas its effect on social interaction (SI) is affected by both rat strain and drug dose. Lister Hooded rats consistently respond differently to drug treatment in general compared with albino strains. This study sought to investigate the effects of different doses of URB597 on social and non-social memory in Lister Hooded rats, as well as analyzing the behavioral composition of the SI. Males were tested for novel object recognition (NOR), social preference (between an object and an unfamiliar rat), social novelty recognition (for a familiar vs. unfamiliar rat) and SI with an unfamiliar rat. URB597 (0.1 or 0.3 mg/kg) or vehicle was given 30 min before testing. During SI testing, total interaction time was assessed along with time spent on aggressive and explorative behaviors. Lister Hooded rats displayed expected non-social and social memory and social preference, which was not affected by URB597. During SI, URB597 did not affect total interaction time. However, the high dose increased aggression, compared to vehicle, and decreased anogenital sniffing, compared to the low dose of URB597. In summary, URB597 did not affect NOR, social preference or social recognition memory but did have subtle behavioral effects during SI in Lister hooded rats. Based on our findings we argue for the importance of considering strain as well as the detailed composition of behavior when investigating drug effects on social behavior.

Cannabinoids and Cancer Chemotherapy-Associated Adverse Effects

The use of cannabis is not unfamiliar to many cancer patients, as there is a long history of its use for cancer pain and/or pain, nausea, and cachexia induced by cancer treatment. To date, the US Food and Drug Administration has approved 2 cannabis-based pharmacotherapies for the treatment of cancer chemotherapy-associated adverse effects: dronabinol and nabilone. Over the proceeding decades, both research investigating and societal attitudes toward the potential utility of cannabinoids for a range of indications have progressed dramatically. The following monograph highlights recent preclinical research focusing on promising cannabinoid-based approaches for the treatment of the 2 most common adverse effects of cancer chemotherapy: chemotherapy-induced peripheral neuropathy and chemotherapy-induced nausea and vomiting. Both plant-derived and synthetic approaches are discussed, as is the potential relative safety and effectiveness of these approaches in relation to current treatment options, including opioid analgesics.

Modulation of Neurolipid Signaling and Specific Lipid Species in the Triple Transgenic Mouse Model of Alzheimer's Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and the most common cause of dementia in aging populations. Recently, the regulation of neurolipid-mediated signaling and cerebral lipid species was shown in AD patients. The triple transgenic mouse model (3xTg-AD), harboring βAPP_Swe, PS1_M146V, and tau_P301L transgenes, mimics many critical aspects of AD neuropathology and progressively develops neuropathological markers. Thus, in the present study, 3xTg-AD mice have been used to test the involvement of the neurolipid-based signaling by endocannabinoids (eCB), lysophosphatidic acid (LPA), and sphingosine 1-phosphate (S1P) in relation to the lipid deregulation. [³⁵S]GTPγS autoradiography was used in the presence of specific agonists WIN55,212-2, LPA and CYM5442, to measure the activity mediated by CB₁, LPA₁, and S1P₁ G_i/0 coupled receptors, respectively. Consecutive slides were used to analyze the relative intensities of multiple lipid species by MALDI Mass spectrometry imaging (MSI) with microscopic anatomical resolution. The quantitative analysis of the astrocyte population was performed by immunohistochemistry. CB₁ receptor activity was decreased in the amygdala and motor cortex of 3xTg-AD mice, but LPA₁ activity was increased in the corpus callosum, motor cortex, hippocampal CA1 area, and striatum. Conversely, S1P₁ activity was reduced in hippocampal areas. Moreover, the observed modifications on PC, PA, SM, and PI intensities in different brain areas depend on their fatty acid composition, including decrease of polyunsaturated fatty acid (PUFA) phospholipids and increase of species containing saturated fatty acids (SFA). The regulation of some lipid species in specific brain regions together with the modulation of the eCB, LPA, and S1P signaling in 3xTg-AD mice indicate a neuroprotective adaptation to improve neurotransmission, relieve the myelination dysfunction, and to attenuate astrocyte-mediated neuroinflammation. These results could contribute to identify new therapeutic strategies based on the regulation of the lipid signaling in familial AD patients.

Amygdalar endocannabinoids are affected by predator odor stress in a sex-specific manner and modulate acoustic startle reactivity in female rats

Understanding sex differences in behavioral and molecular effects of stress has important implications for understanding the vulnerability to chronic psychiatric disorders associated with stress response circuitry. The amygdala is critical for emotional learning and generating behavioral responses to stressful stimuli, and preclinical studies indicate that amygdalar endocannabinoid (eCB) signaling regulates emotional states. This study measured eCB contents in the basolateral (BLA) and central (CeA) amygdala of male and female rats exposed to predator odor stress (bobcat urine) and tested for contextual avoidance 24 h later. Stressed females had lower levels of 2-arachidonoyl glycerol (2-AG) in the BLA and higher levels of anandamide (AEA) in the CeA, while exposure to bobcat urine did not affect amygdalar eCB contents in males. We previously reported that female rats exposed to bobcat urine exhibit blunted acoustic startle reactivity (ASR) 48 h after predator odor stress. Therefore, we tested the hypothesis that intra-BLA injection of a diacylglycerol lipase (DAGL) inhibitor (which would be expected to reduce 2-AG levels in BLA) and intra-CeA injection of a fatty acid amide hydrolase (FAAH) inhibitor (which would be expected to increase AEA levels in CeA) would mimic previously observed predator odor stress-induced reductions in ASR. Contrary to our hypothesis, microinjections of either the DAGL inhibitor DO34 into the BLA or the FAAH inhibitor URB597 into the CeA significantly increased ASR in females compared to vehicle-treated rats. These findings describe sex-specific effects of predator odor stress on amygdalar eCBs, and new roles for amygdalar eCBs in regulating behavior in females.

Behavioral aspects and neurobiological properties underlying medical cannabis treatment in Shank3 mouse model of autism spectrum disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disease with a wide spectrum of manifestation. The core symptoms of ASD are persistent deficits in social communication, and restricted and repetitive patterns of behavior, interests, or activities. These are often accompanied by intellectual disabilities. At present, there is no designated effective treatment for the core symptoms and co-morbidities of ASD. Recently, interest is rising in medical cannabis as a treatment for ASD, with promising clinical data. However, there is a notable absence of basic pre-clinical research in this field. In this study, we investigate the behavioral and biochemical effects of long-term oral treatment with CBD-enriched medical cannabis oil in a human mutation-based Shank3 mouse model of ASD. Our findings show that this treatment alleviates anxiety and decreases repetitive grooming behavior by over 70% in treated mutant mice compared to non-treated mutant mice. Furthermore, we were able to uncover the involvement of CB1 receptor (CB1R) signaling in the Avidekel oil mechanism, alongside a mitigation of cerebrospinal fluid (CSF) glutamate concentrations. Subsequently, RNA sequencing (RNA seq) of cerebellar brain samples revealed changes in mRNA expression of several neurotransmission-related genes post-treatment. Finally, our results question the relevancy of CBD enrichment of medical cannabis for treating the core symptoms of ASD, and emphasize the importance of the THC component for alleviating deficits in repetitive and social behaviors in ASD.

Early suppression of the endocannabinoid degrading enzymes FAAH and MAGL alters locomotor development in zebrafish

The fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) enzymes are the predominant catabolic regulators of the major endocannabinoids (eCBs) anadamide (AEA) and 2-arachidonoylglycerol (2-AG), respectively. The expression and roles of eCBs during early embryogenesis remain to be fully investigated. Here, we inhibited FAAH and MAGL in zebrafish embryos during the first 24 h of life and examined motor neuron and locomotor development at 2 and 5 days post fertilization (dpf). Application of the dual FAAH/MAGL inhibitor, JZL195 (2 µmol l−1), resulted in a reduction in primary and secondary motor neuron axonal branching. JZL195 also reduced nicotinic acetylcholine receptor (nAChR) expression at neuromuscular junctions. Application of URB597 (5 µmol l−1), a specific inhibitor of the FAAH enzyme, also decreased primary motor neuron branching but did not affect secondary motor neuron branching and nAChR expression. Interestingly, JZL184 (5 µmol l−1), a specific inhibitor of MAGL, showed no effects on motor neuron branching or nAChR expression. Co-treatment of the enzyme inhibitors with the CB1R inhibitor AM251 confirmed the involvement of CB1R in motor neuron branching. Disruption of FAAH or MAGL reduced larval swimming activity, and AM251 attenuated the JZL195- and URB597-induced locomotor changes, but not the effects of JZL184. Together, these findings indicate that inhibition of FAAH, or augmentation of AEA acting through CB1R during early development, may be responsible for locomotor deficiencies.