Selective blockade of 2-arachidonoylglycerol hydrolysis produces cannabinoid behavioral effects

Endocannabinoid Hydrolase Inhibitors: Potential Novel Anxiolytic Drugs

Over the past decade, the idea of targeting the endocannabinoid system to treat anxiety disorders has received increasing attention. Previous studies focused more on developing cannabinoid receptor agonists or supplementing exogenous cannabinoids, which are prone to various adverse effects due to their strong pharmacological activity and poor receptor selectivity, limiting their application in clinical research. Endocannabinoid hydrolase inhibitors are considered to be the most promising development strategies for the treatment of anxiety disorders. More recent efforts have emphasized that inhibition of two major endogenous cannabinoid hydrolases, monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), indirectly activates cannabinoid receptors by increasing endogenous cannabinoid levels in the synaptic gap, circumventing receptor desensitization resulting from direct enhancement of endogenous cannabinoid signaling. In this review, we comprehensively summarize the anxiolytic effects of MAGL and FAAH inhibitors and their potential pharmacological mechanisms, highlight reported novel inhibitors or natural products, and provide an outlook on future directions in this field.

A helping HAND: therapeutic potential of MAGL inhibition against HIV-1-associated neuroinflammation

Background

Human immunodeficiency virus (HIV) affects nearly 40 million people globally, with roughly 80% of all people living with HIV receiving antiretroviral therapy. Antiretroviral treatment suppresses viral load in peripheral tissues but does not effectively penetrate the blood-brain barrier. Thus, viral reservoirs persist in the central nervous system and continue to produce low levels of inflammatory factors and early viral proteins, including the transactivator of transcription (Tat). HIV Tat is known to contribute to chronic neuroinflammation and synaptodendritic damage, which is associated with the development of cognitive, motor, and/or mood problems, collectively known as HIV-associated neurocognitive disorders (HAND). Cannabinoid anti-inflammatory effects are well documented, but therapeutic utility of cannabis remains limited due to its psychotropic effects, including alterations within brain regions encoding reward processing and motivation, such as the nucleus accumbens. Alternatively, inhibiting monoacylglycerol lipase (MAGL) has demonstrated therapeutic potential through interactions with the endocannabinoid system.

Methods

The present study utilized a reward-related operant behavioral task to quantify motivated behavior in female Tat transgenic mice treated with vehicle or MAGL inhibitor MJN110 (1 mg/kg). Brain tissue was collected to assess dendritic injury and neuroinflammatory profiles, including dendritic microtubule-associated protein (MAP2ab) intensity, microglia density, microglia morphology, astrocyte density, astrocytic interleukin-1ß (IL-1ß) colocalization, and various lipid mediators.

Results

No significant behavioral differences were observed; however, MJN110 protected against Tat-induced dendritic injury by significantly upregulating MAP2ab intensity in the nucleus accumbens and in the infralimbic cortex of Tat(+) mice. No or only minor effects were noted for Iba-1+ microglia density and/or microglia morphology. Further, Tat increased GFAP+ astrocyte density in the infralimbic cortex and GFAP+ astrocytic IL-1ß colocalization in the nucleus accumbens, with MJN110 significantly reducing these measures in Tat(+) subjects. Lastly, selected HETE-related inflammatory lipid mediators in the striatum were downregulated by chronic MJN110 treatment.

Conclusions

These findings demonstrate anti-inflammatory and neuroprotective properties of MJN110 without cannabimimetic behavioral effects and suggest a promising alternative to cannabis for managing neuroinflammation.

Arachidonic acid in aging: New roles for old players

BACKGROUND

Arachidonic acid (AA), one of the most ubiquitous polyunsaturated fatty acids (PUFAs), provides fluidity to mammalian cell membranes. It is derived from linoleic acid (LA) and can be transformed into various bioactive metabolites, including prostaglandins (PGs), thromboxanes (TXs), lipoxins (LXs), hydroxy-eicosatetraenoic acids (HETEs), leukotrienes (LTs), and epoxyeicosatrienoic acids (EETs), by different pathways. All these processes are involved in AA metabolism. Currently, in the context of an increasingly visible aging world population, several scholars have revealed the essential role of AA metabolism in osteoporosis, chronic obstructive pulmonary disease, and many other aging diseases.

AIM OF REVIEW

Although there are some reviews describing the role of AA in some specific diseases, there seems to be no or little information on the role of AA metabolism in aging tissues or organs. This review scrutinizes and highlights the role of AA metabolism in aging and provides a new idea for strategies for treating aging-related diseases.

KEY SCIENTIFIC CONCEPTS OF REVIEW

As a member of lipid metabolism, AA metabolism regulates the important lipids that interfere with the aging in several ways. We present a comprehensivereviewofthe role ofAA metabolism in aging, with the aim of relieving the extreme suffering of families and the heavy economic burden on society caused by age-related diseases. We also collected and summarized data on anti-aging therapies associated with AA metabolism, with the expectation of identifying a novel and efficient way to protect against aging.

The role of the sensory input intervention in recovery of the motor function in hypoxic ischemic encephalopathy rat model

Motor disturbances predominantly characterize hypoxic-ischemic encephalopathy (HIE). Among its intervention methods, environmental enrichment (EE) is strictly considered a form of sensory intervention. However, limited research uses EE as a single sensory input intervention to validate outcomes postintervention. A Sprague-Dawley rat model subjected to left common carotid artery ligation and exposure to oxygen-hypoxic conditions is used in this study. EE was achieved by enhancing the recreational and stress-relief items within the cage, increasing the duration of sunlight, colorful items exposure, and introducing background music. JZL184 (JZL) was administered as neuroprotective drugs. EE was performed 21 days postoperatively and the rats were randomly assigned to the standard environment and EE groups, the two groups were redivided into control, JZL, and vehicle injection subgroups. The Western blotting and behavior test indicated that EE and JZL injections were efficacious in promoting cognitive function in rats following HIE. In addition, the motor function performance in the EE-alone intervention group and the JZL-alone group after HIE was significantly improved compared with the control group. The combined EE and JZL intervention group exhibited even more pronounced improvements in these performances. EE may enhance motor function through sensory input different from the direct neuroprotective effect of pharmacological treatment.NEW & NOTEWORTHY Rarely does literature assess motor function, even though it is common after hypoxia ischemic encephalopathy (HIE). Previously used environmental enrichment (EE) components have not been solely used as sensory inputs. Physical factors were minimized in our study to observe the effects of purely sensory inputs.

Binding of the monoacylglycerol lipase (MAGL) radiotracer [3H]T-401 in the rat brain after status epilepticus

OBJECTIVES

Monoacylglycerol lipase (MAGL) is a cytosolic serine hydrolase considered a potential novel drug target for the treatment of CNS disorders including epilepsy. Here we examined MAGL levels in a rat model of epilepsy.

METHODS

Autoradiography has been used to validate the binding properties of the MAGL radiotracer, [3H]T-401, in the rat brain, and to explore spatial and temporal changes in binding levels in a model of temporal lobe epilepsy model using unilateral intra-hippocampal injections of kainic acid (KA) in rats.

RESULTS

Specific and saturable binding of [3H]T-401 was detected in both cortical grey and subcortical white matter. Saturation experiments revealed a KD in the range between 15 nM and 17 nM, and full saturation was achieved at concentrations around 30 nM. The binding could be completely blocked with the cold ligand (Ki 44.2 nM) and at higher affinity (Ki 1.27 nM) with another structurally different MAGL inhibitor, ABD 1970. Bilateral reduction in [3H]T-401 binding was observed in the cerebral cortex and the hippocampus few days after status epilepticus that further declined to a level of around 30% compared to the control. No change in binding was observed in either the hypothalamus nor the white matter at any time point. Direct comparison to [3H]UCB-J binding to synaptic vesicle glycoprotein 2 A (SV2A), another protein localized in the pre-synapse, revealed that while binding to MAGL remained low in the chronic phase, SV2A was increased significantly in some cortical areas.

SIGNIFICANCE

These data show that MAGL is reduced in the cerebral cortex and hippocampus in a chronic epilepsy model and indicate that MAGL inhibitors may further reduce MAGL activity in the treatment resistant epilepsy patient.

Potential Therapeutic Targets to Modulate the Endocannabinoid System in Alzheimer's Disease

Alzheimer's disease (AD), the most common neurodegenerative disease (NDD), is characterized by chronic neuronal cell death through progressive loss of cognitive function. Amyloid beta (Aβ) deposition, neuroinflammation, oxidative stress, and hyperphosphorylated tau proteins are considered the hallmarks of AD pathology. Different therapeutic approaches approved by the Food and Drug Administration can only target a single altered pathway instead of various mechanisms that are involved in AD pathology, resulting in limited symptomatic relief and almost no effect in slowing down the disease progression. Growing evidence on modulating the components of the endocannabinoid system (ECS) proclaimed their neuroprotective effects by reducing neurochemical alterations and preventing cellular dysfunction. Recent studies on AD mouse models have reported that the inhibitors of the fatty acid amide hydrolase (FAAH) and monoacylglycerol (MAGL), hydrolytic enzymes for N-arachidonoyl ethanolamine (AEA) and 2-arachidonoylglycerol (2-AG), respectively, might be promising candidates as therapeutical intervention. The FAAH and MAGL inhibitors alone or in combination seem to produce neuroprotection by reversing cognitive deficits along with Aβ-induced neuroinflammation, oxidative responses, and neuronal death, delaying AD progression. Their exact signaling mechanisms need to be elucidated for understanding the brain intrinsic repair mechanism. The aim of this review was to shed light on physiology and pathophysiology of AD and to summarize the experimental data on neuroprotective roles of FAAH and MAGL inhibitors. In this review, we have also included CB1R and CB2R modulators with their diverse roles to modulate ECS mediated responses such as anti-nociceptive, anxiolytic, and anti-inflammatory actions in AD. Future research would provide the directions in understanding the molecular mechanisms and development of new therapeutic interventions for the treatment of AD.

Elevating levels of the endocannabinoid 2-arachidonoylglycerol blunts opioid reward but not analgesia

Converging findings have established that the endocannabinoid (eCB) system serves as a possible target for the development of new treatments for pain as a complement to opioid-based treatments. Here we show in male and female mice that enhancing levels of the eCB, 2-arachidonoylglycerol (2-AG), through pharmacological inhibition of its catabolic enzyme, monoacylglycerol lipase (MAGL), either systemically or in the ventral tegmental area (VTA) with JZL184, leads to a substantial attenuation of the rewarding effects of opioids in male and female mice using conditioned place preference and self-administration paradigms, without altering their analgesic properties. These effects are driven by CB1 receptors (CB1Rs) within the VTA as VTA CB1R conditional knockout, counteracts JZL184's effects. Conversely, pharmacologically enhancing the levels of the other eCB, anandamide (AEA), by inhibition of fatty acid amide hydrolase (FAAH) has no effect on opioid reward or analgesia. Using fiber photometry with fluorescent sensors for calcium and dopamine (DA), we find that enhancing 2-AG levels diminishes opioid reward-related nucleus accumbens (NAc) activity and DA neurotransmission. Together these findings reveal that 2-AG counteracts the rewarding properties of opioids and provides a potential adjunctive therapeutic strategy for opioid-related analgesic treatments.

ABHD6 suppresses colorectal cancer progression via AKT signaling pathway

Colorectal cancer (CRC) continues to be a prevalent malignancy, posing a significant risk to human health. The involvement of alpha/beta hydrolase domain 6 (ABHD6), a serine hydrolase family member, in CRC development was suggested by our analysis of clinical data. However, the role of ABHD6 in CRC remains unclear. This study seeks to elucidate the clinical relevance, biological function, and potential molecular mechanisms of ABHD6 in CRC. We investigated the role of ABHD6 in clinical settings, conducting proliferation, migration, and cell cycle assays. To determine the influence of ABHD6 expression levels on Oxaliplatin sensitivity, we also performed apoptosis assays. RNA sequencing and KEGG analysis were utilized to uncover the potential molecular mechanisms of ABHD6. Furthermore, we validated its expression levels using Western blot and reactive oxygen species (ROS) detection assays. Our results demonstrated that ABHD6 expression in CRC tissues was notably lower compared to adjacent normal tissues. This low expression correlated with a poorer prognosis for CRC patients. Moreover, ABHD6 overexpression impeded CRC cell proliferation and migration while inducing G0/G1 cell cycle arrest. In vivo experiments revealed that downregulation of ABHD6 resulted in an increase in tumor weight and volume. Mechanistically, ABHD6 overexpression inhibited the activation of the AKT signaling pathway and decreased ROS levels in CRC cells, suggesting the role of ABHD6 in CRC progression via the AKT signaling pathway. Our findings demonstrate that ABHD6 functions as a tumor suppressor, primarily by inhibiting the AKT signaling pathway. This role establishes ABHD6 as a promising prognostic biomarker and a potential therapeutic target for CRC patients.

Chemical proteomics to study metabolism, a reductionist approach applied at the systems level

Cellular metabolism encompasses a complex array of interconnected biochemical pathways that are required for cellular homeostasis. When dysregulated, metabolism underlies multiple human pathologies. At the heart of metabolic networks are enzymes that have been historically studied through a reductionist lens, and more recently, using high throughput approaches including genomics and proteomics. Merging these two divergent viewpoints are chemical proteomic technologies, including activity-based protein profiling, which combines chemical probes specific to distinct enzyme families or amino acid residues with proteomic analysis. This enables the study of metabolism at the network level with the precision of powerful biochemical approaches. Herein, we provide a primer on how chemical proteomic technologies custom-built for studying metabolism have unearthed fundamental principles in metabolic control. In parallel, these technologies have leap-frogged drug discovery through identification of novel targets and drug specificity. Collectively, chemical proteomics technologies appear to do the impossible: uniting systematic analysis with a reductionist approach.

Discovery of a novel class of reversible monoacylglycerol lipase inhibitors for potential treatment of depression

Biological studies on the endocannabinoid system (ECS) have suggested that monoacylglycerol lipase (MAGL), an essential enzyme responsible for the hydrolysis of 2-arachidonoylglycerol (2-AG), is a novel target for developing antidepressants. A decrease of 2-AG levels in the hippocampus of the brain has been observed in depressive-like models induced by chronic stress. Herein, employing a structure-based approach, we designed and synthesized a new class of (piperazine-1-carbonyl) quinolin-2(1H)-one derivatives as potent, reversible and selective MAGL inhibitors. And detailed structure-activity relationships (SAR) studies were discussed. Compound 27 (IC50 = 10.3 nM) exhibited high bioavailability (92.7%) and 2-AG elevation effect in vivo. Additionally, compound 27 exerted rapid antidepressant effects caused by chronic restraint stress (CRS) and didn't show signs of addictive properties in the conditioned place preference (CPP) assays. Our study is the first to report that reversible MAGL inhibitors can treat chronic stress-induced depression effectively, which may provide a new potential therapeutic strategy for the discovery of an original class of safe, rapid antidepressant drugs.

ENDOCANNABINOID SYSTEM IN THE PARAVENTRICULAR NUCLEUS OF THE HYPOTHALAMUS MODULATES AUTONOMIC AND CARDIOVASCULAR CHANGES BUT NOT VASOPRESSIN RESPONSE IN A RAT HEMORRHAGIC SHOCK MODEL

ABSTRACT

We evaluated the participation of the endocannabinoid system in the paraventricular nucleus of the hypothalamus (PVN) on the cardiovascular, autonomic, and plasma vasopressin (AVP) responses evoked by hemorrhagic shock in rats. For this, the PVN was bilaterally treated with either vehicle, the selective cannabinoid receptor type 1 antagonist AM251, the selective fatty acid amide hydrolase amide enzyme inhibitor URB597, the selective monoacylglycerol-lipase enzyme inhibitor JZL184, or the selective transient receptor potential vanilloid type 1 antagonist capsazepine. We evaluated changes on arterial pressure, heart rate, tail skin temperature (ST), and plasma AVP responses induced by bleeding, which started 10 min after PVN treatment. We observed that bilateral microinjection of AM251 into the PVN reduced the hypotension during the hemorrhage and prevented the return of blood pressure to baseline values in the posthemorrhagic period. Inhibition of local 2-arachidonoylglycerol metabolism by PVN treatment with JZL184 induced similar effects in relation to those observed in AM251-treated animals. Inhibition of local anandamide metabolism via PVN treatment with URB597 decreased the depressor effect and ST drop induced by the hemorrhagic stimulus. Bilateral microinjection of capsazepine mitigated the fall in blood pressure and ST. None of the PVN treatments altered the increased plasma concentration of AVP and tachycardia induced by hemorrhage. Taken together, present results suggest that endocannabinoid neurotransmission within the PVN plays a prominent role in cardiovascular and autonomic, but not neuroendocrine, responses evoked by hemorrhage.

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.

Unravelling the brain metabolome: A review of liquid chromatography - mass spectrometry strategies for extracellular brain metabolomics

The analysis of the brain extracellular metabolome is of interest for numerous subdomains within neuroscience. Not only does it provide information about normal physiological functions, it is even more of interest for biomarker discovery and target discovery in disease. The extracellular analysis of the brain is particularly interesting as it provides information about the release of mediators in the brain extracellular fluid to look at cellular signaling and metabolic pathways through the release, diffusion and re-uptake of neurochemicals. In vivo samples are obtained through microdialysis, cerebral open-flow microperfusion or solid-phase microextraction. The analytes of potential interest are typically low in concentration and can have a wide range of physicochemical properties. Liquid chromatography coupled to mass spectrometry has proven its usefulness in brain metabolomics. It allows sensitive and specific analysis of low sample volumes, obtained through different approaches. Several strategies for the analysis of the extracellular fluid have been proposed. The most widely used approaches apply sample derivatization, specific stationary phases and/or hydrophilic interaction liquid chromatography. Miniaturization of these methods allows an even higher sensitivity. The development of chiral metabolomics is indispensable, as it allows to compare the enantiomeric ratio of compounds and provides even more challenges. Some limitations continue to exist for the previously developed methods and the development of new, more sensitive methods remains needed. This review provides an overview of the methods developed for sampling and liquid chromatography-mass spectrometry analysis of the extracellular metabolome.

Monoacylglycerol Lipase Inhibition Prevents Short-Term Mitochondrial Dysfunction and Oxidative Damage in Rat Brain Synaptosomal/Mitochondrial Fractions and Cortical Slices: Role of Cannabinoid Receptors

Inhibition of enzymes responsible for endocannabinoid hydrolysis represents an invaluable emerging tool for the potential treatment of neurodegenerative disorders. Monoacylglycerol lipase (MAGL) is the enzyme responsible for degrading 2-arachydonoylglycerol (2-AG), the most abundant endocannabinoid in the central nervous system (CNS). Here, we tested the effects of the selective MAGL inhibitor JZL184 on the 3-nitropropinic acid (3-NP)-induced short-term loss of mitochondrial reductive capacity/viability and oxidative damage in rat brain synaptosomal/mitochondrial fractions and cortical slices. In synaptosomes, while 3-NP decreased mitochondrial function and increased lipid peroxidation, JZL184 attenuated both markers. The protective effects evoked by JZL184 on the 3-NP-induced mitochondrial dysfunction were primarily mediated by activation of cannabinoid receptor 2 (CB2R), as evidenced by their inhibition by the selective CB2R inverse agonist JTE907. The cannabinoid receptor 1 (CB1R) also participated in this effect in a lesser extent, as evidenced by the CB1R antagonist/inverse agonist AM281. In contrast, activation of CB1R, but not CB2R, was responsible for the protective effects of JZL184 on the 3-NP-iduced lipid peroxidation. Protective effects of JZL184 were confirmed in other toxic models involving excitotoxicity and oxidative damage as internal controls. In cortical slices, JZL184 ameliorated the 3-NP-induced loss of mitochondrial function, the increase in lipid peroxidation, and the inhibition of succinate dehydrogenase (mitochondrial complex II) activity, and these effects were independent on CB1R and CB2R, as evidenced by the lack of effects of AM281 and JTE907, respectively. Our novel results provide experimental evidence that the differential protective effects exerted by JZL184 on the early toxic effects induced by 3-NP in brain synaptosomes and cortical slices involve MAGL inhibition, and possibly the subsequent accumulation of 2-AG. These effects involve pro-energetic and redox modulatory mechanisms that may be either dependent or independent of cannabinoid receptors' activation.

Repeated Mild Traumatic Brain Injury and JZL184 Produce Sex-Specific Increases in Anxiety-Like Behavior and Alcohol Consumption in Wistar Rats

Alcohol use disorder (AUD) is highly comorbid with traumatic brain injury (TBI). Previously, using a lateral fluid percussion model (LFP) (an open-head injury model) to generate a single mild to moderate traumatic brain injury (TBI) we showed that TBI produces escalation in alcohol drinking, that alcohol exposure negatively impacts TBI outcomes, and that the endocannabinoid degradation inhibitor (JZL184) confers significant protection from behavioral and neuropathological outcomes in male rodents. In the present study, we used a weight drop model (a closed-head injury model) to produce repeated mild TBI (rmTBI; three TBIs separated by 24 hours) in male and female rats to examine the sex-specific effects on anxiety-like behavior and alcohol consumption, and whether systemic treatment with JZL184 would reverse TBI effects on those behaviors. In two separate studies, adult male and female Wistar rats were subjected to rmTBI or sham procedure using the weight drop model. Physiological measures of injury severity were collected from all animals. Animals in both studies were allowed to consume alcohol using an intermittent 2-bottle choice procedure (12 pre-TBI sessions and 12 post-TBI sessions). Neurological severity and neurobehavioral scores (NSS and NBS, respectively) were tested 24 hours after the final injury. Anxiety-like behavior was tested at 37-38 days post-injury in Study 1-, and 6-8-days post-injury in Study 2. Our results show that females exhibited reduced respiratory rates relative to males with no significant differences between Sham and rmTBI, no effect of rmTBI or sex on righting reflex, and increased neurological deficits in rmTBI groups in both studies. In Study 1, rmTBI increased alcohol consumption in female but not male rats. Male rats consistently exhibited higher levels of anxiety-like behavior than females. The rmTBI did not affect anxiety-like behavior 37-38 days post-injury. In Study 2, rmTBI once again increased alcohol consumption in female but not male rats, and repeated systemic treatment with JZL184 did not affect alcohol consumption. Also in Study 2, rmTBI increased anxiety-like behavior in males but not females and repeated systemic treatment with JZL184 produced an unexpected increase in anxiety-like behavior 6-8 days post-injury. In summary, rmTBI increased alcohol consumption in female rats, systemic JZL184 treatment did not alter alcohol consumption, and both rmTBI and systemic JZL184 treatment increased anxiety-like behavior 6-8 days post-injury in males but not females, highlighting robust sex differences in rmTBI effects.

The endocannabinoid system as a putative target for the development of novel drugs for the treatment of psychiatric illnesses

Cannabis is well established to impact affective states, emotion and perceptual processing, primarily through its interactions with the endocannabinoid system. While cannabis use is quite prevalent in many individuals afflicted with psychiatric illnesses, there is considerable controversy as to whether cannabis may worsen these conditions or provide some form of therapeutic benefit. The development of pharmacological agents which interact with components of the endocannabinoid system in more localized and discrete ways then via phytocannabinoids found in cannabis, has allowed the investigation if direct targeting of the endocannabinoid system itself may represent a novel approach to treat psychiatric illness without the potential untoward side effects associated with cannabis. Herein we review the current body of literature regarding the various pharmacological tools that have been developed to target the endocannabinoid system, their impact in preclinical models of psychiatric illness and the recent data emerging of their utilization in clinical trials for psychiatric illnesses, with a specific focus on substance use disorders, trauma-related disorders, and autism. We highlight several candidate drugs which target endocannabinoid function, particularly inhibitors of endocannabinoid metabolism or modulators of cannabinoid receptor signaling, which have emerged as potential candidates for the treatment of psychiatric conditions, particularly substance use disorder, anxiety and trauma-related disorders and autism spectrum disorders. Although there needs to be ongoing clinical work to establish the potential utility of endocannabinoid-based drugs for the treatment of psychiatric illnesses, the current data available is quite promising and shows indications of several potential candidate diseases which may benefit from this approach.

Anxiety Modulation by Cannabinoids-The Role of Stress Responses and Coping

Endocannabinoids were implicated in a variety of pathological conditions including anxiety and are considered promising new targets for anxiolytic drug development. The optimism concerning the potentials of this system for anxiolysis is probably justified. However, the complexity of the mechanisms affected by endocannabinoids, and discrepant findings obtained with various experimental approaches makes the interpretation of research results difficult. Here, we review the anxiety-related effects of the three main interventions used to study the endocannabinoid system: pharmacological agents active at endocannabinoid-binding sites present on both the cell membrane and in the cytoplasm, genetic manipulations targeting cannabinoid receptors, and function-enhancers represented by inhibitors of endocannabinoid degradation and transport. Binding-site ligands provide inconsistent findings probably because they activate a multitude of mechanisms concomitantly. More robust findings were obtained with genetic manipulations and particularly with function enhancers, which heighten ongoing endocannabinoid activation rather than affecting all mechanisms indiscriminately. The enhancement of ongoing activity appears to ameliorate stress-induced anxiety without consistent effects on anxiety in general. Limited evidence suggests that this effect is achieved by promoting active coping styles in critical situations. These findings suggest that the functional enhancement of endocannabinoid signaling is a promising drug development target for stress-related anxiety disorders.

Endocannabinoid release at ventral hippocampal-amygdala synapses regulates stress-induced behavioral adaptation

The endocannabinoid (eCB) system is a key modulator of glutamate release within limbic neurocircuitry and thus heavily modulates stress responsivity and adaptation. The ventral hippocampus (vHPC)-basolateral amygdala (BLA) circuit has been implicated in the expression of negative affective states following stress exposure and is modulated by retrograde eCB signaling. However, the mechanisms governing eCB release and the causal relationship between vHPC-BLA eCB signaling and stress-induced behavioral adaptations are not known. Here, we utilized in vivo optogenetic- and biosensor-based approaches to determine the temporal dynamics of activity-dependent and stress-induced eCB release at vHPC-BLA synapses. Furthermore, we demonstrate that genetic deletion of cannabinoid type-1 receptors selectively at vHPC-BLA synapses decreases active stress coping and exacerbates stress-induced avoidance and anhedonia phenotypes. These data establish the in vivo determinants of eCB release at limbic synapses and demonstrate that eCB signaling within vHPC-BLA circuitry serves to counteract adverse behavioral consequences of stress.

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.

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.

Mechanisms of cannabinoid tolerance

Cannabis has been used recreationally and medically for centuries, yet research into understanding the mechanisms of its therapeutic effects has only recently garnered more attention. There is evidence to support the use of cannabinoids for the treatment of chronic pain, muscle spasticity, nausea and vomiting due to chemotherapy, improving weight gain in HIV-related cachexia, emesis, sleep disorders, managing symptoms in Tourette syndrome, and patient-reported muscle spasticity from multiple sclerosis. However, tolerance and the risk for cannabis use disorder are two significant disadvantages for cannabinoid-based therapies in humans. Recent work has revealed prominent sex differences in the acute response and tolerance to cannabinoids in both humans and animal models. This review will discuss evidence demonstrating cannabinoid tolerance in rodents, non-human primates, and humans and our current understanding of the neuroadaptations occurring at the cannabinoid type 1 receptor (CB1R) that are responsible tolerance. CB1R expression is downregulated in tolerant animals and humans while there is strong evidence of CB1R desensitization in cannabinoid tolerant rodent models. Throughout the review, critical knowledge gaps are indicated and discussed, such as the lack of a neuroimaging probe to assess CB1R desensitization in humans. The review discusses the intracellular signaling pathways that are responsible for mediating CB1R desensitization and downregulation including the action of G protein-coupled receptor kinases, β-arrestin2 recruitment, c-Jun N-terminal kinases, protein kinase A, and the intracellular trafficking of CB1R. Finally, the review discusses approaches to reduce cannabinoid tolerance in humans based on our current understanding of the neuroadaptations and mechanisms responsible for this process.

Monoacylglycerol Lipase Protects the Presynaptic Cannabinoid 1 Receptor from Desensitization by Endocannabinoids after Persistent Inflammation

Cannabinoid-targeted pain therapies are increasing with the expansion of cannabis legalization, however, their efficacy may be limited by pain-induced adaptations in the cannabinoid system. Cannabinoid receptor subtype 1 (CB1R) inhibition of spontaneous, GABAergic miniature IPSCs (mIPSCs) and evoked IPSCs (eIPSCs) in the ventrolateral periaqueductal gray (vlPAG) were compared in slices from naive and inflamed male and female Sprague Dawley rats. Complete Freund's Adjuvant (CFA) injections into the hindpaw induced persistent inflammation. In naive rats, exogenous cannabinoid agonists robustly reduce both eIPSCs and mIPSCs. After 5-7 d of inflammation, the effects of exogenous cannabinoids are significantly reduced because of CB1R desensitization via GRK2/3, as function is recovered in the presence of the GRK2/3 inhibitor, Compound 101 (Cmp101). Inhibition of GABA release by presynaptic μ-opioid receptors in the vlPAG does not desensitize with persistent inflammation. Unexpectedly, while CB1R desensitization significantly reduces the inhibition produced by exogenous agonists, depolarization-induced suppression of inhibition protocols that promote 2-arachidonoylglycerol (2-AG) synthesis exhibit prolonged CB1R activation after inflammation. 2-AG tone is detected in slices from CFA-treated rats when GRK2/3 is blocked, suggesting an increase in 2-AG synthesis after persistent inflammation. Inhibiting 2-AG degradation with the monoacylglycerol lipase (MAGL) inhibitor JZL184 during inflammation results in the desensitization of CB1Rs by endocannabinoids that is reversed with Cmp101. Collectively, these data indicate that persistent inflammation primes CB1Rs for desensitization, and MAGL degradation of 2-AG protects CB1Rs from desensitization in inflamed rats. These adaptations with inflammation have important implications for the development of cannabinoid-based pain therapeutics targeting MAGL and CB1Rs.SIGNIFICANCE STATEMENT Presynaptic G-protein-coupled receptors are resistant to desensitization. Here we find that persistent inflammation increases endocannabinoid levels, priming presynaptic cannabinoid 1 receptors for desensitization on subsequent addition of exogenous agonists. Despite the reduced efficacy of exogenous agonists, endocannabinoids have prolonged efficacy after persistent inflammation. Endocannabinoids readily induce cannabinoid 1 receptor desensitization if their degradation is blocked, indicating that endocannabinoid concentrations are maintained at subdesensitizing levels and that degradation is critical for maintaining endocannabinoid regulation of presynaptic GABA release in the ventrolateral periaqueductal gray during inflammatory states. These adaptations with inflammation have important implications for the development of cannabinoid-based pain therapies.

JZL184 increases anxiety-like behavior and does not reduce alcohol consumption in female rats after repeated mild traumatic brain injury

Alcohol use disorder (AUD) is highly comorbid with traumatic brain injury (TBI). Previously, using a lateral fluid percussion model (LFP) (an open model of head injury) to generate a single mild to moderate traumatic brain injury (TBI), we showed that TBI produces escalation in alcohol drinking, that alcohol exposure negatively impacts TBI outcomes, and that the endocannabinoid degradation inhibitor (JZL184) confers significant protection from behavioral and neuropathological outcomes in male rodents. In the present study, we used a weight drop model (a closed model of head injury) to produce a repeated mild TBI (rmTBI, 3 TBIs, spaced by 24 hours) to examine the sex-specific effects on alcohol consumption and anxiety-like behavior in rats, and whether systemic treatment with JZL184 would reverse TBI effects on those behaviors in both sexes. In two separate studies, adult male and female Wistar rats were subjected to rmTBI or sham using the weight drop model. Physiological measures of injury severity were collected from all animals. Animals in both studies were allowed to consume alcohol using an intermittent 2-bottle choice procedure (12 pre-TBI sessions and 12 post-TBI sessions). Neurological severity and neurobehavioral scores (NSS and NBS, respectively) were tested 24 hours after the final injury. Anxiety-like behavior was tested at 37-38 days post-injury in Study 1, and 6-8 days post-injury in Study 2. Our results show that females exhibited reduced respiratory rates relative to males with no significant differences between Sham and rmTBI, no effect of rmTBI or sex on righting reflex, and increased neurological deficits in rmTBI groups in both studies. In Study 1, rmTBI increased alcohol consumption in female but not male rats. Male rats consistently exhibited higher levels of anxiety-like behavior than females. rmTBI did not affect anxiety-like behavior 37-38 days post-injury. In Study 2, rmTBI once again increased alcohol consumption in female but not male rats, and repeated systemic treatment with JZL184 did not affect alcohol consumption. Also in Study 2, rmTBI increased anxiety-like behavior in males but not females and repeated systemic treatment with JZL184 produced an unexpected increase in anxiety-like behavior 6-8 days post-injury. In summary, rmTBI increased alcohol consumption in female rats, systemic JZL184 treatment did not alter alcohol consumption, and both rmTBI and sub-chronic systemic JZL184 treatment increased anxiety-like behavior 6-8 days post-injury in males but not females, highlighting robust sex differences in rmTBI effects.

Endocannabinoid-dependent decrease of GABAergic transmission on dopaminergic neurons is associated with susceptibility to cocaine stimulant effects in pre-adolescent male MAOA hypomorphic mice exposed to early life stress

Vulnerability to cocaine use disorder depends upon a combination of genetic and environmental risk factors. While early life adversity is a critical environmental vulnerability factor for drug misuse, allelic variants of the monoamine oxidase A (MAOA) gene have been shown to moderate its influence on the risk of drug-related problems. However, data on the interactions between MAOA variants and early life stress (ES) with respect to predisposition to cocaine abuse are limited. Here, we show that a mouse model capturing the interaction of genetic (low-activity alleles of the Maoa gene; MAOA^Neo) and environmental (i.e., ES) vulnerability factors displays an increased sensitivity to repeated in vivo cocaine psychomotor stimulant actions associated with a reduction of GABAA receptor-mediated inhibition of dopamine neurons of the ventral tegmental area (VTA). Depolarization-induced suppression of inhibition (DSI), a 2-arachidonoylglycerol (2AG)-dependent form of short-term plasticity, also becomes readily expressed by dopamine neurons from male MAOA^Neo ES mice repeatedly treated with cocaine. The activation of either dopamine D2 or CB1 receptors contributes to cocaine-induced DSI expression, decreased GABA synaptic efficacy, and hyperlocomotion. Next, in vivo pharmacological enhancement of 2AG signaling during repeated cocaine exposure occludes its actions both in vivo and ex vivo. This data extends our knowledge of the multifaceted sequelae imposed by this gene-environment interaction in VTA dopamine neurons of male pre-adolescent mice and contributes to our understanding of neural mechanisms of vulnerability for early onset cocaine use.

Inhibiting degradation of 2-arachidonoylglycerol as a therapeutic strategy for neurodegenerative diseases

Endocannabinoids are endogenous lipid signaling mediators that participate in a variety of physiological and pathological processes. 2-Arachidonoylglycerol (2-AG) is the most abundant endocannabinoid and is a full agonist of G-protein-coupled cannabinoid receptors (CB1R and CB2R), which are targets of Δ⁹-tetrahydrocannabinol (Δ⁹-THC), the main psychoactive ingredient in cannabis. While 2-AG has been well recognized as a retrograde messenger modulating synaptic transmission and plasticity at both inhibitory GABAergic and excitatory glutamatergic synapses in the brain, growing evidence suggests that 2-AG also functions as an endogenous terminator of neuroinflammation in response to harmful insults, thus maintaining brain homeostasis. Monoacylglycerol lipase (MAGL) is the key enzyme that degrades 2-AG in the brain. The immediate metabolite of 2-AG is arachidonic acid (AA), a precursor of prostaglandins (PGs) and leukotrienes. Several lines of evidence indicate that pharmacological or genetic inactivation of MAGL, which boosts 2-AG levels and reduces its hydrolytic metabolites, resolves neuroinflammation, mitigates neuropathology, and improves synaptic and cognitive functions in animal models of neurodegenerative diseases, including Alzheimer's disease (AD), multiple sclerosis (MS), Parkinson's disease (PD), and traumatic brain injury (TBI)-induced neurodegenerative disease. Thus, it has been proposed that MAGL is a potential therapeutic target for treatment of neurodegenerative diseases. As the main enzyme hydrolyzing 2-AG, several MAGL inhibitors have been identified and developed. However, our understanding of the mechanisms by which inactivation of MAGL produces neuroprotective effects in neurodegenerative diseases remains limited. A recent finding that inhibition of 2-AG metabolism in astrocytes, but not in neurons, protects the brain from TBI-induced neuropathology might shed some light on this unsolved issue. This review provides an overview of MAGL as a potential therapeutic target for neurodegenerative diseases and discusses possible mechanisms underlying the neuroprotective effects of restraining degradation of 2-AG in the brain.

The role of the endocannabinoid 2-arachidonoylglycerol in the in vivo spinal oxytocin-induced antinociception in male rats

Oxytocin receptor (OTR) activation at the spinal level produces antinociception. Some data suggest that central OTR activation enhances social interaction via an increase of endocannabinoids (eCB), but we do not know if this could occur at the spinal level, modulating pain transmission. Considering that oxytocin via OTR stimulates diacylglycerol formation, a key intermediate in synthesizing 2-arachidonylglycerol (2-AG), an eCB molecule, we sought to test the role of the eCB system on the spinal oxytocin-induced antinociception. Behavioral and electrophysiological experiments were conducted in naïve and formalin-treated (to induce long-term mechanical hypersensitivity) male Wistar rats. Intrathecal RHC 80267 injections, an inhibitor of the enzyme diacylglycerol lipase (thus, decreasing 2-AG formation), produces transient mechanical hypersensitivity, an effect unaltered by oxytocin but reversed by gabapentin. Similarly, in in vivo extracellular recordings of naïve spinal wide dynamic range cells, juxtacellular picoinjection of RHC 80267 increases the firing of nociceptive Aδ-, C-fibers, and post-discharge, an effect unaltered by oxytocin. Interestingly, in sensitized rats, oxytocin picoinjection reverses the RHC 80627-induced hyperactivity of Aδ-fibers (but not C- or post-discharge activity). In contrast, a sub-effective dose of JZL184 (a monoacylglycerol lipase inhibitor, thus favoring 2-AG levels), which does not have per se an antinociceptive effect in the formalin-induced hypernociception, the oxytocin-induced antinociception is boosted. Similarly, electrophysiological experiments suggest that juxtacellular JZL184 diminishes the neuronal firing of nociceptive fibers, and co-injection with oxytocin prolongs and enhances the antinociceptive effect. These data may imply that 2-AG formation may play a role in the spinal antinociception induced by oxytocin.

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.

In vivo quantitative high-throughput screening for drug discovery and comparative toxicology

Quantitative high-throughput screening (qHTS) pharmacologically evaluates chemical libraries for therapeutic uses, toxicological risk and, increasingly, for academic probe discovery. Phenotypic high-throughput screening assays interrogate molecular pathways, often relying on cell culture systems, historically less focused on multicellular organisms. Caenorhabditis elegans has served as a eukaryotic model organism for human biology by virtue of genetic conservation and experimental tractability. Here, a paradigm enabling C. elegans qHTS using 384-well microtiter plate laser-scanning cytometry is described, in which GFP-expressing organisms revealing phenotype-modifying structure-activity relationships guide subsequent life-stage and proteomic analyses, and Escherichia coli bacterial ghosts, a non-replicating nutrient source, allow compound exposures over two life cycles, mitigating bacterial overgrowth complications. We demonstrate the method with libraries of anti-infective agents, or substances of toxicological concern. Each was tested in seven-point titration to assess the feasibility of nematode-based in vivo qHTS, and examples of follow-up strategies were provided to study organism-based chemotype selectivity and subsequent network perturbations with a physiological impact. We anticipate that this qHTS approach will enable analysis of C. elegans orthologous phenotypes of human pathologies to facilitate drug library profiling for a range of therapeutic indications.

Augmentation of 2-arachidonoylglycerol signaling in astrocytes maintains synaptic functionality by regulation of miRNA-30b

2-Arachidonoylglycerol (2-AG), the most abundant endocannabinoid, displays anti-inflammatory and neuroprotective properties. Inhibition of 2-AG degradation by inactivation of monoacylglycerol lipase (MAGL), a key enzyme degrading 2-AG in the brain, alleviates neuropathology and improves synaptic and cognitive functions in animal models of neurodegenerative diseases. In particular, global inactivation of MAGL by genetic deletion of mgll enhances hippocampal long-term potentiation (LTP) and hippocampus-dependent learning and memory. However, our understanding of the molecular mechanisms by which chronic inactivation of MAGL enhances synaptic activity is still limited. Here, we provide evidence that pharmacological inactivation of MAGL suppresses hippocampal expression of miR-30b, a small non-coding microRNA, and upregulates expression of its targets, including ephrin type-B receptor 2 (ephB2), sirtuin1 (sirt1), and glutamate ionotropic receptor AMPA type subunit 2 (GluA2). Importantly, suppression of miR-30b and increase of its targets by inactivation of MAGL result primarily from inhibition of 2-AG metabolism in astrocytes, rather than in neurons. Inactivation of MAGL in astrocytes prevents miR-30b overexpression-induced impairments in synaptic transmission and long-term potentiation (LTP) in the hippocampus. Suppression of miR-30b expression by inactivation of MAGL is apparently associated with augmentation of 2-AG signaling, as 2-AG induces a dose-dependent decrease in expression of miR-30b. 2-AG- or MAGL inactivation-suppressed expression of miR-30b is not mediated via CB1R, but by peroxisome proliferator-activated receptor γ (PPARγ). This is further supported by the results showing that MAGL inactivation-induced downregulation of miR-30b and upregulation of its targets are attenuated by antagonism of PPARγ, but mimicked by PPARγ agonists. In addition, we observed that 2-AG-induced reduction of miR-30b expression is mediated via NF-kB signaling. Our study provides evidence that 2-AG signaling in astrocytes plays an important role in maintaining the functional integrity of synapses in the hippocampus by regulation of miR-30b expression.

A Cross Talk between the Endocannabinoid System and Different Systems Involved in the Pathogenesis of Hypertensive Retinopathy

The prognosis of hypertension leads to organ damage by causing nephropathy, stroke, retinopathy, and cardiomegaly. Retinopathy and blood pressure have been extensively discussed in relation to catecholamines of the autonomic nervous system (ANS) and angiotensin II of the renin–angiotensin aldosterone system (RAAS) but very little research has been conducted on the role of the ECS in the regulation of retinopathy and blood pressure. The endocannabinoid system (ECS) is a unique system in the body that can be considered as a master regulator of body functions. It encompasses the endogenous production of its cannabinoids, its degrading enzymes, and functional receptors which innervate and perform various functions in different organs of the body. Hypertensive retinopathy pathologies arise normally due to oxidative stress, ischemia, endothelium dysfunction, inflammation, and an activated renin–angiotensin system (RAS) and catecholamine which are vasoconstrictors in their biological nature. The question arises of which system or agent counterbalances the vasoconstrictors effect of noradrenaline and angiotensin II (Ang II) in normal individuals? In this review article, we discuss the role of the ECS and its contribution to the pathogenesis of hypertensive retinopathy. This review article will also examine the involvement of the RAS and the ANS in the pathogenesis of hypertensive retinopathy and the crosstalk between these three systems in hypertensive retinopathy. This review will also explain that the ECS, which is a vasodilator in its action, either independently counteracts the effect produced with the vasoconstriction of the ANS and Ang II or blocks some of the common pathways shared by the ECS, ANS, and Ang II in the regulation of eye functions and blood pressure. This article concludes that persistent control of blood pressure and normal functions of the eye are maintained either by decreasing systemic catecholamine, ang II, or by upregulation of the ECS which results in the regression of retinopathy induced by hypertension.

Endocannabinoid System and Exogenous Cannabinoids in Depression and Anxiety: A Review

Background: There is a growing liberalization of cannabis-based preparations for medical and recreational use. In multiple instances, anxiety and depression are cited as either a primary or a secondary reason for the use of cannabinoids. Aim: The purpose of this review is to explore the association between depression or anxiety and the dysregulation of the endogenous endocannabinoid system (ECS), as well as the use of phytocannabinoids and synthetic cannabinoids in the remediation of depression/anxiety symptoms. After a brief description of the constituents of cannabis, cannabinoid receptors and the endocannabinoid system, the most important evidence is presented for the involvement of cannabinoids in depression and anxiety both in human and from animal models of depression and anxiety. Finally, evidence is presented for the clinical use of cannabinoids to treat depression and anxiety. Conclusions: Although the common belief that cannabinoids, including cannabis, its main studied components-tetrahydrocannabinol (THC) and cannabidiol (CBD)-or other synthetic derivatives have been suggested to have a therapeutic role for certain mental health conditions, all recent systematic reviews that we report have concluded that the evidence that cannabinoids improve depressive and anxiety disorders is weak, of very-low-quality, and offers no guidance on the use of cannabinoids for mental health conditions within a regulatory framework. There is an urgent need for high-quality studies examining the effects of cannabinoids on mental disorders in general and depression/anxiety in particular, as well as the consequences of long-term use of these preparations due to possible risks such as addiction and even reversal of improvement.

Endocannabinoid Degradation Enzyme Inhibitors as Potential Antipsychotics: A Medicinal Chemistry Perspective

The endocannabinoid system (ECS) plays a very important role in numerous physiological and pharmacological processes, such as those related to the central nervous system (CNS), including learning, memory, emotional processing, as well pain control, inflammatory and immune response, and as a biomarker in certain psychiatric disorders. Unfortunately, the half-life of the natural ligands responsible for these effects is very short. This perspective describes the potential role of the inhibitors of the enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MGL), which are mainly responsible for the degradation of endogenous ligands in psychic disorders and related pathologies. The examination was carried out considering both the impact that the classical exogenous ligands such as Δ⁹-tetrahydrocannabinol (THC) and (-)-trans-cannabidiol (CBD) have on the ECS and through an analysis focused on the possibility of predicting the potential toxicity of the inhibitors before they are subjected to clinical studies. In particular, cardiotoxicity (hERG liability), probably the worst early adverse reaction studied during clinical studies focused on acute toxicity, was predicted, and some of the most used and robust metrics available were considered to select which of the analyzed compounds could be repositioned as possible oral antipsychotics.

Developmental treatments with Δ9- tetrahydrocannabinol and the MAGL inhibitor JZL184 persistently alter adult cocaine conditioning in contrasting ways

Using a songbird, zebra finches, as a developmental drug abuse model we found previously that cannabinoid agonists administered during the sensorimotor period of vocal learning (50-75 days of age) persistently alter song patterns and cocaine responsiveness in adulthood. However, these effects were not produced in adults exposed to similar treatment regimens. Currently, we have used the MAGL inhibitor, JZL184, to test whether enhanced endocannabinoid signaling may similarly alter cocaine responsiveness. We found that, as expected and consistent with prior results, repeated developmental (but not adult) treatments with Δ⁹-tetrahydrocannabinol (THC, 3 mg/kg QD IM) resulted in increased time spent in cocaine-paired chambers. Unexpectedly and in contrast, repeated developmental JZL184 (4 mg/kg QD IM) treatments decreased time spent in cocaine-conditioned chambers. That is, young finches repeatedly treated with JZL184 avoided cocaine-paired chambers later in adulthood, while similar development treatments with THC had the opposite effect. To begin to identify brain regions that may underly this differential responsiveness we used c-Fos expression as a marker of neuronal activity. Differences in c-Fos expression patterns following placement of cocaine-conditioned finches into vehicle- vs. cocaine-paired chambers suggest distinct involvement of circuits through striatal and amygdaloid regions in respective effects of THC and JZL184. Results demonstrate that, like exogenous cannabinoid exposure, inhibition of MAGL activity during late post-natal development persistently alters behavior in adulthood. Contrasting effects of THC vs. MAGL inhibition with JZL184 suggests the latter alters development of brain regions to favor promotion of aversive rather than appetitive cocaine responsiveness later in adulthood.

Endocannabinoid hydrolases differentially distribute in platelets and red blood cells and are differentially released by thrombin

BACKGROUND

Plasma levels of the major endocannabinoids 2-arachidonoylgycerol (2AG) and anandamide (N-arachidonoylethanolamine, AEA) have been identified to vary independently with particular pathological conditions. The levels of these endocannabinoids are tightly regulated by two hydrolytic enzymes, monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), respectively.

OBJECTIVES

In this study, we have quantified these enzyme activities in the major blood fractions.

PATIENTS/METHODS

In blood fractions from human volunteers, radiometric assays were used to quantify monoacylglycerol lipase and fatty acid amide hydrolase. Tagging with fluorophosphonate-rhodamine allowed quantification of platelet serine hydrolase activities.

RESULTS

Fatty acid amide hydrolase activity was highest in platelets, while MAGL activity was most abundant in erythrocytes. Sampling the blood of donors on two further occasions 15 days apart showed no significant change in platelet FAAH or erythrocyte MAGL activities. Activities were not different when comparing female donors with males. Storage of these blood fractions at - 80 °C was associated with a rapid loss in enzyme activities, which could largely by avoided by storage in liquid nitrogen. Incubation of platelets and erythrocytes in the presence of thrombin lead to release of measurable FAAH, but not MAGL, activity. Tagging of serine hydrolase activities with fluorophosphonate-rhodamine allowed confirmation of MAGL activity in platelet preparations, as well as multiple other enzymes.

CONCLUSIONS

These investigations suggest a potential role for FAAH in regulation of coagulation, while the role of MAGL in blood requires further investigation.

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

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

Endocannabinoid signaling in brain diseases: Emerging relevance of glial cells

The discovery of cannabinoid receptors as the primary molecular targets of psychotropic cannabinoid Δ⁹ -tetrahydrocannabinol (Δ⁹ -THC) in late 1980s paved the way for investigations on the effects of cannabis-based therapeutics in brain pathology. Ever since, a wealth of results obtained from studies on human tissue samples and animal models have highlighted a promising therapeutic potential of cannabinoids and endocannabinoids in a variety of neurological disorders. However, clinical success has been limited and major questions concerning endocannabinoid signaling need to be satisfactorily addressed, particularly with regard to their role as modulators of glial cells in neurodegenerative diseases. Indeed, recent studies have brought into the limelight diverse, often unexpected functions of astrocytes, oligodendrocytes, and microglia in brain injury and disease, thus providing scientific basis for targeting glial cells to treat brain disorders. This Review summarizes the current knowledge on the molecular and cellular hallmarks of endocannabinoid signaling in glial cells and its clinical relevance in neurodegenerative and chronic inflammatory disorders.

Endocannabinoid signaling in the central nervous system

It is hard to overestimate the influence of the endocannabinoid signaling (ECS) system on central nervous system (CNS) function. In the 40 years since cannabinoids were found to trigger specific cell signaling cascades, studies of the ECS system continue to cause amazement, surprise, and confusion! CB1 cannabinoid receptors are expressed widely in the CNS and regulate cell-cell communication via effects on the release of both neurotransmitters and gliotransmitters. CB2 cannabinoid receptors are difficult to detect in the CNS but seem to "punch above their weight" as compounds targeting these receptors have significant effects on inflammatory state and behavior. Positive and negative allosteric modulators for both receptors have been identified and examined in preclinical studies. Concentrations of the endocannabinoid ligands, N-arachidonoylethanolamine and 2-arachidonoylglycerol (2-AG), are regulated by a combination of enzymatic synthesis and degradation and inhibitors of these processes are available and making their way into clinical trials. Importantly, ECS regulates many essential brain functions, including regulation of reward, anxiety, inflammation, motor control, and cellular development. While the field is on the cusp of preclinical discoveries providing impactful clinical and therapeutic insights into many CNS disorders, there is still much to be learned about this remarkable and versatile modulatory system.

The endocannabinoid system's involvement in motor development relies on cannabinoid receptors, TRP channels, and Sonic Hedgehog signaling

The endocannabinoid system (eCS) plays critical roles in locomotor function and motor development; however, the roles of non-canonical cannabinoid receptor systems such as transient receptor potential (TRP) channels and the Sonic Hedgehog (SHH) signaling pathway in conjunction with the eCS in sensorimotor development remains enigmatic. To investigate the involvement of canonical and non-canonical cannabinoid receptors, TRP channels, and the SHH pathway in the development of sensorimotor function in zebrafish, we treated developing animals with pharmacological inhibitors of the CB1R, CB2R, TRPA1/TRPV1/TRPM8, and a smoothened (SMO) agonist, along with inhibitors of the eCS catabolic enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) during the first ~24 h of zebrafish embryogenesis. Locomotor function was examined by assessing touch-evoked escape swimming at 2 days post-fertilization. We report that FAAH inhibition had no effect on swimming while MAGL inhibition using JZL 184 reduced swimming distance and the dual FAAH/MAGL inhibitor JZL 195 impaired swimming distance and mean swimming velocity. The CB1R antagonist AM 251 prevented locomotor deficits caused by eCS perturbation but the CB2R antagonist AM 630 did not. Inhibition of TRPA1/TRPV1/TRPM8 using AMG 9090 rescued the locomotor reductions caused by FAAH/MAGL inhibition, but not by MAGL inhibition alone. The SMO agonist purmorphamine attenuated the effects of JZL 184 and JZL 195 on swimming distance, but not mean velocity. Together, these findings provide one of the first investigations examining the interactions between the eCS and its non-canonical receptor systems in vertebrate motor development.

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.

The Endocannabinoid System as a Target for Neuroprotection/Neuroregeneration in Perinatal Hypoxic-Ischemic Brain Injury

The endocannabinoid (EC) system is a complex cell-signaling system that participates in a vast number of biological processes since the prenatal period, including the development of the nervous system, brain plasticity, and circuit repair. This neuromodulatory system is also involved in the response to endogenous and environmental insults, being of special relevance in the prevention and/or treatment of vascular disorders, such as stroke and neuroprotection after neonatal brain injury. Perinatal hypoxia-ischemia leading to neonatal encephalopathy is a devastating condition with no therapeutic approach apart from moderate hypothermia, which is effective only in some cases. This overview, therefore, gives a current description of the main components of the EC system (including cannabinoid receptors, ligands, and related enzymes), to later analyze the EC system as a target for neonatal neuroprotection with a special focus on its neurogenic potential after hypoxic-ischemic brain injury.

Chemical Probes to Control and Visualize Lipid Metabolism in the Brain

Signaling lipids, such as the endocannabinoids, play an important role in the brain. They regulate synaptic transmission and control various neurophysiological processes, including pain sensation, appetite, memory formation, stress, and anxiety. Unlike classical neurotransmitters, lipid messengers are produced on demand and degraded by metabolic enzymes to control their lifespan and signaling actions. Chemical biology approaches have become one of the main driving forces to study and unravel the physiological role of lipid messengers in the brain. Here, we review how the development and use of chemical probes has allowed one to study endocannabinoid signaling by (i) inhibiting the biosynthetic and metabolic enzymes; (ii) visualizing the activity of these enzymes; and (iii) controlling the release and transport of the endocannabinoids. Activity-based probes were instrumental to guide the discovery of highly selective and in vivo active inhibitors of the biosynthetic (DAGL, NAPE-PLD) and metabolic (MAGL, FAAH) enzymes of endocannabinoids. These inhibitors allowed one to study the role of these enzymes in animal models of disease. For instance, the DAGL-MAGL axis was shown to control neuroinflammation and the NAPE-PLD-FAAH axis to regulate emotional behavior. Activity-based protein profiling and chemical proteomics were essential to guide the drug discovery and development of compounds targeting MAGL and FAAH, such as ABX-1431 (Lu AG06466) and PF-04457845, respectively. These experimental drugs are now in clinical trials for multiple indications, including multiple sclerosis and post-traumatic stress disorders. Activity-based probes have also been used to visualize the activity of these lipid metabolizing enzymes with high spatial resolution in brain slices, thereby showing the cell type-specific activity of these lipid metabolizing enzymes. The transport, release, and uptake of signaling lipids themselves cannot, however, be captured by activity-based probes in a spatiotemporal controlled manner. Therefore, bio-orthogonal lipids equipped with photoreactive, photoswitchable groups or photocages have been developed. These chemical probes were employed to investigate the protein interaction partners of the endocannabinoids, such as putative membrane transporters, as well as to study the functional cellular responses within milliseconds upon irradiation. Finally, genetically encoded sensors have recently been developed to monitor the real-time release of endocannabinoids with high spatiotemporal resolution in cultured neurons, acute brain slices, and in vivo mouse models. It is anticipated that the combination of chemical probes, highly selective inhibitors, and sensors with advanced (super resolution) imaging modalities, such as PharmacoSTORM and correlative light-electron microscopy, will uncover the fundamental basis of lipid signaling at nanoscale resolution in the brain. Furthermore, chemical biology approaches enable the translation of these fundamental discoveries into clinical solutions for brain diseases with aberrant lipid signaling.

Activity-based Photoacoustic Probes Reveal Elevated Intestinal MGL and FAAH Activity in a Murine Model of Obesity

Obesity is a chronic health condition characterized by the accumulation of excessive body fat which can lead to and exacerbate cardiovascular disease, type-II diabetes, high blood pressure, and cancer through systemic inflammation. Unfortunately, visualizing key mediators of the inflammatory response, such as monoacylglycerol lipase (MGL) and fatty acid amide hydrolase (FAAH), in a selective manner is a profound challenge owing to an overlapping substrate scope that involves arachidonic acid (AA). Specifically, these enzymes work in concert to generate AA, which in the context of obesity, has been implicated to control appetite and energy metabolism. In this study, we developed the first selective activity-based sensing probes to detect MGL (PA-HD-MGL) and FAAH (PA-HD-FAAH) activity via photoacoustic imaging. Activation of PA-HD-MGL and PA-HD-FAAH by their target enzymes resulted in 1.74-fold and 1.59-fold signal enhancements, respectively. Due to their exceptional selectivity profiles and deep-tissue photoacoustic imaging capabilities, these probes were employed to measure MGL and FAAH activity in a murine model of obesity. Contrary to conflicting reports suggesting levels of MGL can be attenuated or elevated, our results support the latter. Indeed, we discovered a marked increase of both targets in the gastrointestinal tract. These key findings set the stage to uncover the role of the endocannabinoid pathway in obesity-mediated inflammation.

2-Arachidonoylglycerol-mediated endocannabinoid signaling modulates mechanical hypersensitivity associated with alcohol withdrawal in mice

BACKGROUND

Alcohol use disorder (AUD) commonly occurs in patients with chronic pain, and a major barrier to achieving abstinence and preventing relapse is the emergence of hyperalgesia during alcohol withdrawal. Elucidating novel therapeutic approaches to target hyperalgesia associated with alcohol withdrawal could have important implications for treating AUD. Here, we examined the role of 2-arachidonoylglycerol (2-AG)-mediated endocannabinoid (eCB) signaling in the regulation of hyperalgesia associated with alcohol withdrawal in mice. We tested the hypothesis that pharmacological augmentation of 2-AG signaling could reduce hyperalgesia during withdrawal.

METHODS

Male and female C57BL/6J mice were tested during withdrawal from a continuous access two-bottle choice (2BC) paradigm to investigate how eCB signaling modulates mechanical and thermal sensitivity during withdrawal. Mice were pretreated with the monoacylglycerol lipase (MAGL) inhibitor JZL184 to elevate levels of 2-AG. Rimonabant or AM630 were given to block CB1 and CB2 receptor activity, respectively. DO34 was given to reduce 2-AG by inhibiting the 2-AG synthetic enzyme diacylglycerol lipase (DAGL).

RESULTS

After 72 h of withdrawal, male and female mice exhibited increased mechanical, but not thermal, hypersensitivity, which normalized by 7 days. This effect was reversed by pretreatment with JZL184. The effects of JZL184 were prevented by coadministration of either the CB1 or the CB2 antagonist. DO34, Rimonabant, and AM630 exacerbated mechanical hypersensitivity during alcohol withdrawal, causing an earlier onset and persistent hypersensitivity even 1 week into withdrawal.

CONCLUSIONS

Our findings demonstrate the critical role of 2-AG signaling in the bidirectional regulation of mechanical sensitivity during alcohol withdrawal, with enhancement of 2-AG levels reducing sensitivity, and inhibition of 2-AG signaling exacerbating sensitivity. These data suggest that 2-AG augmentation represents a novel approach to the treatment of alcohol withdrawal-associated hyperalgesia and AUD in patients with comorbid pain disorders.

Assessment of dependence potential and abuse liability of Δ8-tetrahydrocannabinol in mice

Delta-8-tetrahydrocannabinol (Δ8-THC) is a psychotropic cannabinoid produced in low quantities in the cannabis plant. Refinements in production techniques, paired with the availability of inexpensive cannabidiol substrate, have resulted in Δ8-THC being widely marketed as a quasi-legal, purportedly milder alternative to Δ9-THC. Yet, little research has probed the behavioral and physiological effects of repeated Δ8-THC use. The present study aimed to evaluate the effects of acute and repeated exposure to Δ8-THC. We hypothesized that Δ8-THC produces effects similar to Δ9-THC, including signs of drug tolerance and dependence. Adult male and female C57BL/6J mice were treated acutely with Δ8-THC (6.25-100 mg/kg, i.p.) or vehicle and tested in the tetrad battery to quantify cannabimimetic effects (i.e., catalepsy, antinociception, hypothermia, immobility) as compared with a non-selective synthetic cannabinoid (WIN 55,212-2) and Δ9-THC. As previously reported, Δ8-THC (≥12.5 mg/kg) induced cannabimimetic effects. Pretreatment with the CB1 receptor-selective antagonist rimonabant (3 mg/kg, i.p.) blocked each of these effects. In addition, repeated administration of Δ8-THC (50 mg/kg, s.c.) produced tolerance, as well as cross-tolerance to WIN 55,212-2 (10 mg/kg, s.c.) in tetrad, consistent with downregulated CB1 receptor function. Behavioral signs of physical dependence in the somatic signs, tail suspension, and marble burying assays were also observed following rimonabant-precipitated withdrawal from Δ8-THC (≥10 mg/kg BID for 6 days). Lastly, Δ8-THC produced Δ9-THC-like discriminative stimulus effects in both male and female mice. Together, these findings demonstrate that Δ8-THC produces qualitatively similar effects to Δ9-THC, including risk of drug dependence and abuse liability.

The impact of phyto- and endo-cannabinoids on central nervous system diseases：A review

Background and aim

Cannabis sativa L. is a medicinal plant with a long history. Phyto-cannabinoids are a class of compounds from C. sativa L. with varieties of structures. Endocannabinoids exist in the human body. This article provides an overview of natural cannabinoids (phyto-cannabinoids and endocannabinoids) with an emphasis on their pharmacology activities.

Experimental procedure

The keywords "Cannabis sativa L″, "cannabinoids", and "central nervous system (CNS) diseases" were used for searching and collecting pieces of literature from PubMed, ScienceDirect, Web of Science, and Google Scholar. The data were extracted and analyzed to explore the effects of cannabinoids on CNS diseases.

Result and conclusion

In this paper, schematic diagrams are used to intuitively show the phyto-cannabinoids skeletons' mutual conversion and pharmacological activities, with special emphasis on their relevant pharmacological activities on central nervous system (CNS) diseases. It was found that the endocannabinoid system and microglia play a crucial role in the treatment of CNS diseases. In the past few years, pharmacological studies focused on Δ⁹-THC, CBD, and the endocannabinoids system. It is expected to encourage new studies on a more deep exploration of other types of cannabinoids and the mechanism of their pharmacological activities in the future.

Endocannabinoids produced in photoreceptor cells in response to light activate Drosophila TRP channels

Drosophila phototransduction is a model for signaling cascades that culminate in the activation of transient receptor potential (TRP) cation channels. TRP and TRPL are the canonical TRP (TRPC) channels that are regulated by light stimulation of rhodopsin and engagement of Gαq and phospholipase Cβ (PLC). Lipid metabolite(s) generated downstream of PLC are essential for the activation of the TRPC channels in photoreceptor cells. We sought to identify the key lipids produced subsequent to PLC stimulation that contribute to channel activation. Here, using genetics, lipid analysis, and Ca2+ imaging, we found that light increased the amount of an abundant endocannabinoid, 2-linoleoyl glycerol (2-LG), in vivo. The increase in 2-LG amounts depended on the PLC and diacylglycerol lipase encoded by norpA and inaE, respectively. This endocannabinoid facilitated TRPC-dependent Ca2+ influx in a heterologous expression system and in dissociated ommatidia from compound eyes. Moreover, 2-LG and mechanical stimulation cooperatively activated TRPC channels in ommatidia. We propose that 2-LG is a physiologically relevant endocannabinoid that activates TRPC channels in photoreceptor cells.

Endocannabinoid System of the Blood-Brain Barrier: Current Understandings and Therapeutic Potentials

The endocannabinoid system (ECS) has been found at the blood-brain barrier (BBB), as Cannabinoid receptors were characterized in human brain microvascular endothelial cells and astrocytes. In several in vitro and in vivo studies, cannabinoids decreased BBB permeability and enhanced membrane integrity, which may be achieved through endothelial tight junctions and other mechanisms. These permeability regulation effects of cannabinoids suggested that the ECS may protect the brain by enhancing barrier integrity. Related questions about cannabinoid-drug interaction and drug distribution across the BBB are also raised. Specifically, can cannabinoids significantly reduce drug bioavailability to the brain? More in-depth and systematic investigations are needed to characterize and quantify these effects of cannabinoids on brain microvasculature physiopathology. Therefore, this review summarizes literatures from different disciplines to promote more research on assessing the therapeutic benefits and risks of using cannabinoids to protect BBB from dysfunctions or breakdown, and to avoid consequent brain damages due to inflammation, neurodegenerations, hemorrhage, ischemia, or other causes.