Identification of a high-affinity binding site involved in the transport of endocannabinoids

Antiproliferative effects of arvanil, olvanil and LY2183240 on human neuroblastoma and glioblastoma cell lines and their in vitro interactions with cisplatin and temozolomide: an isobolographic analysis

Glioblastoma is the most aggressive malignant brain tumor characterized by rapid development, poor prognosis and high mortality. The purpose of this in vitro study was to assess cytotoxic and anti-proliferative effects of arvanil, olvanil and LY2183240 (three cannabinoid receptor ligands), when used alone and in combination with cisplatin and temozolomide in various neuroblastoma (CHP-134 and KELLY) and glioblastoma (U87MG, C6, and T98G) cell lines in the MTT assay. Results indicate that arvanil, olvanil and LY2183240 considerably affected the viability of neuroblastoma and glioblastoma cell lines with selectivity index values ranging from 0.50 to 17.48 for arvanil; from 0.93 to 24.06 for olvanil; and from 1.68 to 14.52 for LY2183240. With isobolographic analysis we found that the combination of LY2183240 with cisplatin produced three different types of interactions: a synergy in CHP-134; an antagonism in T98G; and additivity in KELLY, C6 and U87MG cell lines in the MTT assay. The combinations of arvanil and olvanil with cisplatin exerted additive interaction in all the tested cell lines in the MTT assay. Similarly, the combinations of temozolomide with arvanil, olvanil and LY 2183240 produced the additive interaction in all the tested glioblastoma and neuroblastoma cell lines. In conclusion, the combinations of temozolomide with the three cannabinoids, due to their additive interactions, can be considered as a promising therapeutic direction in glioblastoma. Favorable combinations of cisplatin with arvanil, olvanil and LY2183240 can also be recommended, except for a combination of cisplatin with LY2183240 in glioblastoma T98G cell line in the MTT assay.

LY-2183240 enhances reward-seeking behavior with inducing neuronal excitation and early apoptosis in mouse

Cannabinoids interact with cannabinoid receptors, influencing diverse central nervous system (CNS) and peripheral functions, including anxiety, depression, and cognition. CB1 and CB2 receptors modulate signaling cascades via G-protein coupling, with anandamide acting as an endogenous ligand for CB1 receptors. LY-2183240, a putative endocannabinoid transport blocker, elevates brain anandamide levels, showing therapeutic potential in pain management and alcohol-related behaviors. LY-2183240 enhances neuronal excitability and is classified as a new psychoactive substance (NPS). However, its precise cellular mechanisms within the CNS remain poorly understood. In this study, the effect of LY-2183240 on cortical neurons and reward-seeking behavior is investigated. Our results indicate enhanced neuronal excitability and reward-seeking behavior induction by LY-2183240, shedding light on its pharmacological profile and NPS-associated risks. Our research underscores the importance of further understanding the cellular mechanisms of LY-2183240 to inform regulatory efforts and mitigate public health risks.

Antiproliferative effects of LY-2183240 combined with various chemotherapeutic drugs in an isobolographic in vitro model of malignant melanoma

Despite a great progress in identifying treatment options for patients with malignant melanoma, novel therapies tend to be costly and, in some cases, produce adverse effects forcing the melanoma patients to withdraw drugs. There is a strong need for less expensive drugs with a more favorable spectrum of anticancer actions. This study was designed to assess whether LY-2183240 (a potent inhibitor of both, anandamide cellular reuptake and fatty acid amide hydrolase (FAAH), an enzyme that degrades anandamide) has antiproliferative and cytotoxic effects on various human malignant melanoma cell lines (primary A375 and FM55P, metastatic SK-MEL28 and FM55M2) when administered alone or in combination with docetaxel, paclitaxel, mitoxantrone and cisplatin via the MTT assay. The MTT, LDH and BrdU assays were used to evaluate the potency and safety of LY-2183240, whereas isobolographic analysis of interactions was applied to characterize the interactions of LY-2183240 with the studied chemotherapeutics (docetaxel, paclitaxel, mitoxantrone and cisplatin). The isobolography confirmed that the combinations of LY-2183240 with docetaxel, paclitaxel and mitoxantrone produced additive interactions in all the tested melanoma cell lines. Only two antagonistic interactions for LY-2183240 combined with cisplatin in the A375 and FM55P cell lines were observed by the MTT assay. In conclusion, LY-2183240 can be considered an add-on drug for the treatment of melanoma, when combined with docetaxel, paclitaxel, or mitoxantrone, but not with cisplatin.

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.

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.

Mechanisms of endocannabinoid transport in the brain

The endocannabinoids 2-arachidonoylglycerol (2-AG) and anandamide are among the best studied lipid messengers in the brain. By activating cannabinoid receptors in the CNS, endocannabinoids tune synaptic function, thereby influencing a variety of physiological and behavioural processes. Extensive research conducted over the last few decades has considerably enhanced our understanding of the molecular mechanisms and physiological functions of the endocannabinoid system. It is now well-established that endocannabinoids are synthesized by postsynaptic neurons and serve as retrograde messengers that suppress neurotransmitter release at central synapses. While the detailed mechanisms by which endocannabinoids gate synaptic function and behavioural processes are relatively well characterized, the mechanisms governing endocannabinoid transport at central synapses remain ill defined. Recently, several studies have begun to unravel the mechanisms governing intracellular and intercellular endocannabinoid transport. In this review, we will focus on new advances in the mechanisms of intracellular and synaptic endocannabinoid transport in the CNS. LINKED ARTICLES: This article is part of a themed issue on New discoveries and perspectives in mental and pain disorders. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.17/issuetoc.

Untargeted metabolomics identifies the potential role of monocarboxylate transporter 6 (MCT6/SLC16A5) in lipid and amino acid metabolism pathways

Monocarboxylate transporter 6 (MCT6; SLC16A5) is an orphan transporter protein with expression in multiple tissues. The endogenous function of MCT6 related to human health and disease remains unknown. Our previous transcriptomic and proteomic analyses in Mct6 knockout (KO) mice suggested that MCT6 may play a role in lipid and glucose homeostasis, but additional evidence is required. Thus, the objective of this study was to further explore the impact of MCT6 on metabolic function using untargeted metabolomic analysis in Mct6 KO mice. The plasma from male and female mice and livers from male mice were submitted for global metabolomics analysis to assess the relative changes in endogenous small molecules across the liver and systemic circulation associated with absence of Mct6. More than 782 compounds were detected with 101 and 51 metabolites significantly changed in plasma of male and female mice, respectively, and 100 metabolites significantly changed in the livers of male mice (p < .05). Significant perturbations in lipid metabolism were annotated in the plasma and liver metabolome, with additional alterations in the amino acid metabolism pathway in plasma samples from male and female mice. Elevated lipid diacylglycerol and altered fatty acid metabolite concentrations were found in liver and plasma samples of male Mct6 KO mice. Significant reduction of N-terminal acetylated amino acids was found in plasma samples of male and female Mct6 KO mice. In summary, the present study confirmed the significant role of MCT6 in lipid and amino acid homeostasis, suggesting its contribution in metabolic diseases.

Endocannabinoid system contributions to sex-specific adolescent neurodevelopment

With an increasing number of countries and states adopting legislation permitting the use of cannabis for medical purposes, there is a growing interest among health and research professionals into the system through which cannabinoids principally act, the endocannabinoid system (ECS). Much of the seminal research into the ECS dates back only 30 years and, although there has been tremendous development within the field during this time, many questions remain. More recently, investigations have emerged examining the contributions of the ECS to normative development and the effect of altering this system during important critical periods. One such period is adolescence, a unique period during which brain and behaviours are maturing and reorganizing in preparation for adulthood, including shifts in endocannabinoid biology. The purpose of this review is to discuss findings to date regarding the maturation of the ECS during adolescence and the consequences of manipulations of the ECS during this period to normative neurodevelopmental processes, as well as highlight sex differences in ECS function, important technical considerations, and future directions. Because most of what we know is derived from preclinical studies on rodents, we provide relevant background of this model and some commentary on the translational relevance of the research in this area.

On the Biomedical Properties of Endocannabinoid Degradation and Reuptake Inhibitors: Pre-clinical and Clinical Evidence

The endocannabinoid system (ECS) is composed of endogenous cannabinoids; components involved in their synthesis, transport, and degradation; and an expansive variety of cannabinoid receptors. Hypofunction or deregulation of the ECS is related to pathological conditions. Consequently, endogenous enhancement of endocannabinoid levels and/or regulation of their metabolism represent promising therapeutic approaches. Several major strategies have been suggested for the modulation of the ECS: (1) blocking endocannabinoids degradation, (2) inhibition of endocannabinoid cellular uptake, and (3) pharmacological modulation of cannabinoid receptors as potential therapeutic targets. Here, we focused in this review on degradation/reuptake inhibitors over cannabinoid receptor modulators in order to provide an updated synopsis of contemporary evidence advancing mechanisms of endocannabinoids as pharmacological tools with therapeutic properties for the treatment of several disorders. For this purpose, we revisited the available literature and reported the latest advances regarding the biomedical properties of fatty acid amide hydrolase and monoacylglycerol lipase inhibitors in pre-clinical and clinical studies. We also highlighted anandamide and 2-arachidonoylglycerol reuptake inhibitors with promising results in pre-clinical studies using in vitro and animal models as an outlook for future research in clinical trials.

The Endocannabinoid System: A Potential Target for the Treatment of Various Diseases

The Endocannabinoid System (ECS) is primarily responsible for maintaining homeostasis, a balance in internal environment (temperature, mood, and immune system) and energy input and output in living, biological systems. In addition to regulating physiological processes, the ECS directly influences anxiety, feeding behaviour/appetite, emotional behaviour, depression, nervous functions, neurogenesis, neuroprotection, reward, cognition, learning, memory, pain sensation, fertility, pregnancy, and pre-and post-natal development. The ECS is also involved in several pathophysiological diseases such as cancer, cardiovascular diseases, and neurodegenerative diseases. In recent years, genetic and pharmacological manipulation of the ECS has gained significant interest in medicine, research, and drug discovery and development. The distribution of the components of the ECS system throughout the body, and the physiological/pathophysiological role of the ECS-signalling pathways in many diseases, all offer promising opportunities for the development of novel cannabinergic, cannabimimetic, and cannabinoid-based therapeutic drugs that genetically or pharmacologically modulate the ECS via inhibition of metabolic pathways and/or agonism or antagonism of the receptors of the ECS. This modulation results in the differential expression/activity of the components of the ECS that may be beneficial in the treatment of a number of diseases. This manuscript in-depth review will investigate the potential of the ECS in the treatment of various diseases, and to put forth the suggestion that many of these secondary metabolites of Cannabis sativa L. (hereafter referred to as "C. sativa L." or "medical cannabis"), may also have potential as lead compounds in the development of cannabinoid-based pharmaceuticals for a variety of diseases.

Mechanisms of endocannabinoid control of synaptic plasticity

The endogenous cannabinoid transmitter system regulates synaptic transmission throughout the nervous system. Unlike conventional transmitters, specific stimuli induce synthesis of endocannabinoids (eCBs) in the postsynaptic neuron, and these travel backwards to modulate presynaptic inputs. In doing so, eCBs can induce short-term changes in synaptic strength and longer-term plasticity. While this eCB regulation is near ubiquitous, it displays major regional and synapse specific variations with different synapse specific forms of short-versus long-term plasticity throughout the brain. These differences are due to the plethora of pre- and postsynaptic mechanisms which have been implicated in eCB signalling, the intricacies of which are only just being realised. In this review, we shall describe the current understanding and highlight new advances in this area, with a focus on the retrograde action of eCBs at CB1 receptors (CB₁Rs).

Human cell receptors: potential drug targets to combat COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes the coronavirus disease 2019 (COVID-19). The World Health Organization (WHO) has announced that COVID-19 is a pandemic having a higher spread rate rather than the mortality. Identification of a potential approach or therapy against COVID-19 is still under consideration. Therefore, it is essential to have an insight into SARS-CoV-2, its interacting partner, and domains for an effective treatment. The present study is divided into three main categories, including SARS-CoV-2 prominent receptor and its expression levels, other interacting partners, and their binding domains. The first section focuses primarily on coronaviruses' general aspects (SARS-CoV-2, SARS-CoV, and the Middle East Respiratory Syndrome Coronaviruses (MERS-CoV)) their structures, similarities, and mode of infections. The second section discusses the host receptors which includes the human targets of coronaviruses like dipeptidyl peptidase 4 (DPP4), CD147, CD209L, Angiotensin-Converting Enzyme 2 (ACE2), and other miscellaneous targets (type-II transmembrane serine proteases (TTSPs), furin, trypsin, cathepsins, thermolysin, elastase, phosphatidylinositol 3-phosphate 5-kinase, two-pore segment channel, and epithelium sodium channel C-α subunit). The human cell receptor, ACE2 plays an essential role in the Renin-Angiotensin system (RAS) pathway and COVID-19. Thus, this section also discusses the ACE2 expression and risk of COVID-19 infectivity in various organs and tissues such as the liver, lungs, intestine, heart, and reproductive system in the human body. Absence of ACE2 protein expression in immune cells could be used for limiting the SARS-CoV-2 infection. The third section covers the current available approaches for COVID-19 treatment. Overall, this review focuses on the critical role of human cell receptors involved in coronavirus pathogenesis, which would likely be used in designing target-specific drugs to combat COVID-19.

N-Acyl pyrazoles: Effective and tunable inhibitors of serine hydrolases

A series of N-acyl pyrazoles was examined as candidate serine hydrolase inhibitors in which the active site acylating reactivity and the leaving group ability of the pyrazole could be tuned not only through the nature of the acyl group (reactivity: amide > carbamate > urea), but also through pyrazole C4 substitution with electron-withdrawing or electron-donating substituents. Their impact on enzyme inhibitory activity displayed pronounced effects with the activity improving substantially as one alters both the nature of the reacting carbonyl group (urea > carbamate > amide) and the pyrazole C4 substituent (CN > H > Me). It was further demonstrated that the acyl chain of the N-acyl pyrazole ureas can be used to tailor the potency and selectivity of the inhibitor class to a targeted serine hydrolase. Thus, elaboration of the acyl chain of pyrazole-based ureas provided remarkably potent, irreversible inhibitors of fatty acid amide hydrolase (FAAH, apparent K_i = 100-200 pM), dual inhibitors of FAAH and monoacylglycerol hydrolase (MGLL), or selective inhibitors of MGLL (IC₅₀ = 10-20 nM) while simultaneously minimizing off-target activity (e.g., ABHD6 and KIAA1363).

Potential for endocannabinoid system modulation in ocular pain and inflammation: filling the gaps in current pharmacological options

Challenges in the management of ocular pain are an underappreciated topic. Currently available therapeutics lack both efficacy and clear guidelines for their use, with many also possessing unacceptable side effects. Promising novel agents would offer analgesic, anti-inflammatory, and possibly neuroprotective actions; have favorable ocular safety profiles; and show potential in managing neuropathic pain. Growing evidence supports a link between the endocannabinoid system (ECS) and a range of physiological and disease processes, notably those involving inflammation and pain. Both preclinical and clinical data suggest analgesic and anti-inflammatory actions of cannabinoids and ECS-modifying drugs in chronic pain conditions, including those of neuropathic origin. This review will examine existing evidence for the anatomical and physiological basis of ocular pain, specifically, ocular surface disease and the development of chronic ocular pain. The mechanism of action, efficacy, and limitations of currently available treatments will be discussed, and current knowledge related to ECS-modulation of ocular pain and inflammatory disease will be summarized. A perspective will be provided on the future directions of ECS research in terms of developing cannabinoid therapeutics for ocular pain.

Monoacylglycerol lipase (MAGL) as a promising therapeutic target

Monoacylglycerol lipase (MAGL) has been characterized as the main enzyme responsible for the inactivation of the most abundant brain endocannabinoid, 2-arachidonoylglycerol (2-AG). Besides this role, MAGL has progressively acquired a growing importance as an integrative metabolic hub that controls not only the in vivo levels of 2-AG but also of other monoacylglycerides and, indirectly, the levels of free fatty acids derived from their hydrolysis as well as other lipids with pro-inflammatory or pro-tumorigenic effects, coming from the further metabolism of fatty acids. All these functions have only started to be elucidated in the last years due to the progress made in the knowledge of the structure of MAGL and in the development of genetic and chemical tools. In this review we report the advances made in the field with a special focus on the last decade and how MAGL has become a promising therapeutic target for the treatment of several diseases that currently lack appropriate therapies.

Therapeutic applications of cannabinoids

The psychoactive property of cannabinoids is well known and there has been a continuous controversy regarding the usage of these compounds for therapeutic purposes all over the world. Their use for medical and research purposes are restricted in various countries. However, their utility as medications should not be overshadowed by its negative physiological activities. This review article is focused on the therapeutic potential and applications of phytocannabinoids and endocannabinoids. We further highlights their mode of action, overall effects on physiology, various in vitro and in vivo studies that have been done so far and the extent to which these compounds can be useful in different disease conditions such as cancer, Alzheimer's disease, multiple sclerosis, pain, inflammation, glaucoma and many others. Thus, this work is an attempt to make the readers understand the positive implications of these compounds and indicates the significant developments of utilizing cannabinoids as therapeutic agents.

Neuroprotection in Oxidative Stress-Related Neurodegenerative Diseases: Role of Endocannabinoid System Modulation

SIGNIFICANCE

Redox imbalance may lead to overproduction of reactive oxygen and nitrogen species (ROS/RNS) and subsequent oxidative tissue damage, which is a critical event in the course of neurodegenerative diseases. It is still not fully elucidated, however, whether oxidative stress is the primary trigger or a consequence in the process of neurodegeneration. Recent Advances: Increasing evidence suggests that oxidative stress is involved in the propagation of neuronal injury and consequent inflammatory response, which in concert promote development of pathological alterations characteristic of most common neurodegenerative diseases.

CRITICAL ISSUES

Accumulating recent evidence also suggests that there is an important interplay between the lipid endocannabinoid system [ECS; comprising the main cannabinoid 1 and 2 receptors (CB1 and CB2), endocannabinoids, and their synthetic and metabolizing enzymes] and various key inflammatory and redox-dependent processes.

FUTURE DIRECTIONS

Targeting the ECS to modulate redox state-dependent cell death and to decrease consequent or preceding inflammatory response holds therapeutic potential in a multitude of oxidative stress-related acute or chronic neurodegenerative disorders from stroke and traumatic brain injury to Alzheimer's and Parkinson's diseases and multiple sclerosis, just to name a few, which will be discussed in this overview. Antioxid. Redox Signal. 29, 75-108.

Synthesis and biological evaluation of ferrocene-based cannabinoid receptor 2 ligands

Ferrocene analogs of known fatty acid amide hydrolase inhibitors and CB2 ligands have been synthesized and characterized spectroscopically and crystallographically. The resulting bio-organometallic isoxazoles were assayed for their effects on CB1 and CB2 receptors as well as on fatty acid amide hydrolase. None had any fatty acid amide hydrolase activity but compound 3, 5-(2-(pentyloxy)phenyl)-N-ferrocenylisoxazole-3-carboxamide, was found to be a potent CB2 ligand (Ki = 32.5 nM).

From Phytocannabinoids to Cannabinoid Receptors and Endocannabinoids: Pleiotropic Physiological and Pathological Roles Through Complex Pharmacology

Apart from having been used and misused for at least four millennia for, among others, recreational and medicinal purposes, the cannabis plant and its most peculiar chemical components, the plant cannabinoids (phytocannabinoids), have the merit to have led humanity to discover one of the most intriguing and pleiotropic endogenous signaling systems, the endocannabinoid system (ECS). This review article aims to describe and critically discuss, in the most comprehensive possible manner, the multifaceted aspects of 1) the pharmacology and potential impact on mammalian physiology of all major phytocannabinoids, and not only of the most famous one Δ9-tetrahydrocannabinol, and 2) the adaptive pro-homeostatic physiological, or maladaptive pathological, roles of the ECS in mammalian cells, tissues, and organs. In doing so, we have respected the chronological order of the milestones of the millennial route from medicinal/recreational cannabis to the ECS and beyond, as it is now clear that some of the early steps in this long path, which were originally neglected, are becoming important again. The emerging picture is rather complex, but still supports the belief that more important discoveries on human physiology, and new therapies, might come in the future from new knowledge in this field.

Intracellular Self-Assembly of Cyclic d-Luciferin Nanoparticles for Persistent Bioluminescence Imaging of Fatty Acid Amide Hydrolase

Fatty acid amide hydrolase (FAAH) overexpression induces several disorder symptoms in nerve systems, and therefore long-term tracing of FAAH activity in vivo is of high importance but remains challenging. Current bioluminescence (BL) methods are limited in detecting FAAH activity within 5 h. Herein, by rational design of a latent BL probe (d-Cys-Lys-CBT)2 (1), we developed a "smart" method of intracellular reduction-controlled self-assembly and FAAH-directed disassembly of its cyclic d-luciferin-based nanoparticles (i.e., 1-NPs) for persistent BL imaging of FAAH activity in vitro, in cells, and in vivo. Using aminoluciferin methyl amide (AMA), Lys-amino-d-luciferin (Lys-Luc), and amino-d-luciferin (NH2-Luc) as control BL probes, we validated that the persistent BL of 1 from luciferase-expressing cells or tumors was controlled by the activity of intracellular FAAH. With the property of long-term tracing of FAAH activity in vivo of 1, we envision that our BL precursor 1 could probably be applied for in vivo screening of FAAH inhibitors and the diagnosis of their related diseases (or disorders) in the future.

Endocannabinoid transport revisited

Endocannabinoids are arachidonic acid-derived endogenous lipids that activate the endocannabinoid system which plays a major role in health and disease. The primary endocannabinoids are anandamide (AEA, N-arachidonoylethanolamine) and 2-arachidonoyl glycerol. While their biosynthesis and metabolism have been studied in detail, it remains unclear how endocannabinoids are transported across the cell membrane. In this review, we critically discuss the different models of endocannabinoid trafficking, focusing on AEA cellular uptake which is best studied. The evolution of the current knowledge obtained with different AEA transport inhibitors is reviewed and the confusions caused by the lack of their specificity discussed. A comparative summary of the most important AEA uptake inhibitors and the studies involving their use is provided. Based on a comprehensive literature analysis, we propose a model of facilitated AEA membrane transport followed by intracellular shuttling and sequestration. We conclude that novel and more specific probes will be essential to identify the missing targets involved in endocannabinoid membrane transport.

Inhibitors of Fatty Acid Amide Hydrolase and Monoacylglycerol Lipase: New Targets for Future Antidepressants

Cannabis and analogs of Δ⁹-tetrahydrocannabinol have been used for therapeutic purposes, but their therapeutic use remains limited because of various adverse effects. Endogenous cannabinoids have been discovered, and dysregulation of endocannabinoid signaling is implicated in the pathophysiology of major depressive disorder (MDD). Recently, endocannabinoid hydrolytic enzymes such as fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) have become new therapeutic targets in the treatment of MDD. Several FAAH or MAGL inhibitors are reported to have no cannabimimetic side effects and, therefore, are new potential therapeutic options for patients with MDD who are resistant to first-line antidepressants (selective serotonin and serotonin-norepinephrine reuptake inhibitors). In this review, we focus on the possible relationships between MDD and the endocannabinoid system as well as the inhibitors' therapeutic potential. MAGL inhibitors may reduce inflammatory responses through activation of cannabinoid receptor type 2. In the hypothalamic-pituitary-adrenal axis, repeated FAAH inhibitor administration may be beneficial for reducing circulating glucocorticoid levels. Both FAAH and MAGL inhibitors may contribute to dopaminergic system regulation. Recently, several new inhibitors have been developed with strong potency and selectivity. FAAH inhibitor, MAGL inhibitor, or dual blocker use would be promising new treatments for MDD. Further pre-clinical studies and clinical trials using these inhibitors are warranted.

Discovery libraries targeting the major enzyme classes: the serine hydrolases

Two libraries of modestly reactive ureas containing either electron-deficient acyl anilines or acyl pyrazoles were prepared and are reported as screening libraries for candidate serine hydrolase inhibitors. Within each library is a small but powerful subset of compounds that serve as a chemotype fragment screening library capable of subsequent structural diversification. Elaboration of the pyrazole-based ureas provided remarkably potent irreversible inhibitors of fatty acid amide hydrolase (FAAH, apparent Ki=100-200 pM) complementary to those previously disclosed enlisting electron-deficient aniline-based ureas.

α-Ketoheterocycle inhibitors of fatty acid amide hydrolase: exploration of conformational constraints in the acyl side chain

A series of α-ketooxazoles containing heteroatoms embedded within conformational constraints in the C2 acyl side chain of 2 (OL-135) were synthesized and evaluated as inhibitors of fatty acid amide hydrolase (FAAH). The studies reveal that the installation of a heteroatom (O) in the conformational constraint is achievable, although the potency of these novel derivatives is reduced slightly relative to 2 and the analogous 1,2,3,4-tetrahydronaphthalene series. Interestingly, both enantiomers (R and S) of the candidate inhibitors bearing a chiral center adjacent to the electrophilic carbonyl were found to effectively inhibit FAAH.

Characterization of four new designer drugs, 5-chloro-NNEI, NNEI indazole analog, α-PHPP and α-POP, with 11 newly distributed designer drugs in illegal products

Our continuous survey of illegal products in Japan revealed the new distribution of 15 designer drugs. We identified four synthetic cannabinoids, i.e., NNEI (1), 5-fluoro-NNEI (2), 5-chloro-NNEI (3) and NNEI indazole analog (4), and seven cathinone derivatives, i.e., MPHP (5), α-PHPP (6), α-POP (7), 3,4-dimethoxy-α-PVP (8), 4-fluoro-α-PVP (9), α-ethylaminopentiophenone (10) and N-ethyl-4-methylpentedrone (11). We also determined LY-2183240 (12) and its 2'-isomer (13), which were reported to inhibit endocannabinoid uptake, a methylphenidate analog, 3,4-dichloromethylphenidate (14), and an MDA analog, 5-APDB (15). No chemical and pharmaceutical data for compounds 3, 4, 6 and 7 had been reported, making this the first report on these compounds.

Design, synthesis, and characterization of α-ketoheterocycles that additionally target the cytosolic port Cys269 of fatty acid amide hydrolase

A series of α-ketooxazoles incorporating electrophiles at the C5 position of the pyridyl ring of 2 (OL-135) and related compounds were prepared and examined as inhibitors of fatty acid amide hydrolase (FAAH) that additionally target the cytosolic port Cys269. From this series, a subset of the candidate inhibitors exhibited time-dependent FAAH inhibition and noncompetitive irreversible inactivation of the enzyme, consistent with the targeted Cys269 covalent alkylation or addition, and maintained or enhanced the intrinsic selectivity for FAAH versus other serine hydrolases. A preliminary in vivo assessment demonstrates that these inhibitors raise endogenous brain levels of anandamide and other FAAH substrates upon intraperitoneal (i.p.) administration to mice, with peak levels achieved within 1.5–3 h, and that the elevations of the signaling lipids were maintained >6 h, indicating that the inhibitors effectively reach and remain active in the brain, inhibiting FAAH for a sustained period.

AM404 attenuates reinstatement of nicotine seeking induced by nicotine-associated cues and nicotine priming but does not affect nicotine- and food-taking

Multiple studies suggest a pivotal role of the endocannabinoid system in the regulation of the reinforcing effects of various substances of abuse. Different approaches have been used to modulate endocannabinoid neurotransmission including the use of endogenous cannabinoid anandamide reuptake inhibitors. Previously, the effects of one of them, N-(4-hydroxyphenyl)-arachidonamide (AM404), have been explored in rodents trained to self-administer ethanol and heroin, producing some promising results. Moreover, AM404 attenuated the development and reinstatement of nicotine-induced conditioned place preference (CPP). In this study, we used the nicotine intravenous self-administration procedure to assess the effects of intraperitoneal administration of 0, 1, 3 and 10 mg/kg AM404 on nicotine-taking and food-taking behaviors under fixed-ratio and progressive-ratio schedules of reinforcement, as well as on reinstatement of nicotine-seeking induced by nicotine priming and by presentation of nicotine-associated cues. The ability of AM404 to produce place preference was also evaluated. AM404 did not produce CPP and did not modify nicotine-taking and food-taking behaviors. In contrast, AM404 dose-dependently attenuated reinstatement of nicotine-seeking behavior induced by both nicotine-associated cues and nicotine priming. Our results indicate that AM404 could be a potential promising therapeutic option for the prevention of relapse to nicotine-seeking in abstinent smokers.

Chemical probes of endocannabinoid metabolism

The endocannabinoid signaling system regulates diverse physiologic processes and has attracted considerable attention as a potential pharmaceutical target for treating diseases, such as pain, anxiety/depression, and metabolic disorders. The principal ligands of the endocannabinoid system are the lipid transmitters N-arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol (2-AG), which activate the two major cannabinoid receptors, CB1 and CB2. Anandamide and 2-AG signaling pathways in the nervous system are terminated by enzymatic hydrolysis mediated primarily by the serine hydrolases fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), respectively. In this review, we will discuss the development of FAAH and MAGL inhibitors and their pharmacological application to investigate the function of anandamide and 2-AG signaling pathways in preclinical models of neurobehavioral processes, such as pain, anxiety, and addiction. We will place emphasis on how these studies are beginning to discern the different roles played by anandamide and 2-AG in the nervous system and the resulting implications for advancing endocannabinoid hydrolase inhibitors as next-generation therapeutics.

Marijuana, Spice 'herbal high', and early neural development: implications for rescheduling and legalization

Marijuana is the most widely used illicit drug by pregnant women in the world. In utero exposure to Δ⁹-tetrahydrocannabinol (Δ⁹-THC), a major psychoactive component of marijuana, is associated with an increased risk for anencephaly and neurobehavioural deficiencies in the offspring, including attention deficit hyperactivity disorder (ADHD), learning disabilities, and memory impairment. Recent studies demonstrate that the developing central nervous system (CNS) is susceptible to the effects of Δ⁹-THC and other cannabimimetics, including the psychoactive ingredients of the branded product 'Spice' branded products. These exocannabinoids interfere with the function of an endocannabinoid (eCB) system, present in the developing CNS from E12.5 (week 5 of gestation in humans), and required for proliferation, migration, and differentiation of neurons. Until recently, it was not known whether the eCB system is also present in the developing CNS during the initial stages of its ontogeny, i.e. from E7.0 onwards (week 2 of gestation in humans), and if so, whether this system is also susceptible to the action of exocannabinoids. Here, we review current data, in which the presence of an eCB system during the initial stage of development of the CNS is demonstrated. Furthermore, we focus on recent advances on the effect of canabimimetics on early gestation. The relevance of these findings and potential adverse developmental consequences of in utero exposure to 'high potency' marijuana, Spice branded products and/or cannabinoid research chemicals during this period is discussed. Finally, we address the implication of these findings in terms of the potential dangers of synthetic cannabinoid use during pregnancy, and the ongoing debate over legalization of marijuana.

Evidence for bidirectional endocannabinoid transport across cell membranes

Despite extensive research on the trafficking of anandamide (AEA) across cell membranes, little is known about the membrane transport of other endocannabinoids, such as 2-arachidonoylglycerol (2-AG). Previous studies have provided data both in favor and against a cell membrane carrier-mediated transport of endocannabinoids, using different methodological approaches. Because AEA and 2-AG undergo rapid and almost complete intracellular hydrolysis, we employed a combination of radioligand assays and absolute quantification of cellular and extracellular endocannabinoid levels. In human U937 leukemia cells, 100 nm AEA and 1 μm 2-AG were taken up through a fast and saturable process, reaching a plateau after 5 min. Employing differential pharmacological blockage of endocannabinoid uptake, breakdown, and interaction with intracellular binding proteins, we show that eicosanoid endocannabinoids harboring an arachidonoyl chain compete for a common membrane target that regulates their transport, whereas other N-acylethanolamines did not interfere with AEA and 2-AG uptake. By combining fatty acid amide hydrolase or monoacyl glycerol lipase inhibitors with hydrolase-inactive concentrations of the AEA transport inhibitors UCM707 (1 μm) and OMDM-2 (5 μm), a functional synergism on cellular AEA and 2-AG uptake was observed. Intriguingly, structurally unrelated AEA uptake inhibitors also blocked the cellular release of AEA and 2-AG. We show, for the first time, that UCM707 and OMDM-2 inhibit the bidirectional movement of AEA and 2-AG across cell membranes. Our findings suggest that a putative endocannabinoid cell membrane transporter controls the cellular AEA and 2-AG trafficking and metabolism.

Effects of alterations in cannabinoid signaling, alone and in combination with morphine, on pain-elicited and pain-suppressed behavior in mice

Inhibitors of fatty acid amide hydrolase (FAAH) and anandamide (AEA) uptake, which limit the degradation of endogenous cannabinoids, have received interest as potential therapeutics for pain. There is also evidence that endogenous cannabinoids mediate the antinociceptive effects of opioids. Assays of pain-elicited and pain-suppressed behavior have been used to differentiate the effects of drugs that specifically alter nociception from drugs that alter nociception caused by nonspecific effects such as catalepsy or a general suppression of activity. Using such procedures, this study examines the effects of the direct cannabinoid type 1 (CB1) agonist (-)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-trans-4-(3-hydroxypropyl)cyclohexanol (CP55940), the FAAH inhibitor cyclohexylcarbamic acid 3'-carbamoylbiphenyl-3-yl ester (URB597), and the AEA uptake inhibitor N-(4-hydroxyphenyl) arachidonylamide (AM404). Additional experiments examined these compounds in combination with morphine. CP55940 produced antinociception in assays of pain-elicited, but not pain-suppressed, behavior and disrupted responding in an assay of schedule-controlled behavior. URB597 and AM404 produced antinociception in assays of pain-elicited and pain-suppressed behavior in which acetic acid was the noxious stimulus, but had no effect on the hotplate and schedule-controlled responding. CP55940 in combination with morphine resulted in effects greater than those of morphine alone in assays of pain-elicited and scheduled-controlled behavior but not pain-suppressed behavior. URB597 in combination with morphine resulted in enhanced morphine effects in assays of pain-elicited and pain-suppressed behavior in which diluted acetic acid was the noxious stimulus, but did not alter morphine's effects on the hotplate or schedule-controlled responding. These studies suggest that, compared with direct CB1 agonists, manipulations of endogenous cannabinoid signaling have enhanced clinical potential; however, their effects depend on the type of noxious stimulus.

Cannabinoid-related agents in the treatment of anxiety disorders: current knowledge and future perspectives

Rich evidence has shown that cannabis products exert a broad gamut of effects on emotional regulation. The main psychoactive ingredient of hemp, Δ9-tetrahydrocannabinol (THC), and its synthetic cannabinoid analogs have been reported to either attenuate or exacerbate anxiety and fear-related behaviors in humans and experimental animals. The heterogeneity of cannabis-induced psychological outcomes reflects a complex network of molecular interactions between the key neurobiological substrates of anxiety and fear and the endogenous cannabinoid system, mainly consisting of the arachidonic acid derivatives anandamide and 2-arachidonoylglycerol (2-AG) and two receptors, respectively termed CB1 and CB2. The high degree of interindividual variability in the responses to cannabis is contributed by a wide spectrum of factors, including genetic and environmental determinants, as well as differences in the relative concentrations of THC and other alkaloids (such as cannabidiol) within the plant itself. The present article reviews the currently available knowledge on the herbal, synthetic and endogenous cannabinoids with respect to the modulation of anxiety responses, and highlights the challenges that should be overcome to harness the therapeutic potential of some of these compounds, all the while limiting the side effects associated with cannabis consumption. In addition the article presents some promising patents on cannabinoid-related agents.

The endocannabinoid system as a key mediator during liver diseases: new insights and therapeutic openings

Chronic liver diseases represent a major health problem due to cirrhosis and its complications. During the last decade, endocannabinoids and their receptors have emerged as major regulators of several pathophysiological aspects associated with chronic liver disease progression. Hence, hepatic cannabinoid receptor 2 (CB(2)) receptors display beneficial effects on alcoholic fatty liver, hepatic inflammation, liver injury, regeneration and fibrosis. Cannabinoid receptor 1 (CB(1)) receptors have been implicated in the pathogenesis of several lesions such as alcoholic and metabolic steatosis, liver fibrogenesis, or circulatory failure associated with cirrhosis. Although the development of CB(1) antagonists has recently been suspended due to the high incidence of central side effects, preliminary preclinical data obtained with peripherally restricted CB(1) antagonists give real hopes in the development of active CB(1) molecules devoid of central adverse effects. CB(2) -selective molecules may also offer novel perspectives for the treatment of liver diseases, and their clinical development is clearly awaited. Whether combined treatment with a peripherally restricted CB(1) antagonist and a CB(2) agonist might result in an increased therapeutic potential will warrant further investigation.

The discovery and development of inhibitors of fatty acid amide hydrolase (FAAH)

A summary of the discovery and advancement of inhibitors of fatty acid amide hydrolase (FAAH) is presented.