Molecular Identification of Albumin and Hsp70 as Cytosolic Anandamide-Binding Proteins

Chemical Probes for Investigating the Endocannabinoid System

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

Interplay between cannabinoids and the neuroimmune system in migraine

Migraine is a common and complex neurological disorder that has a high impact on quality of life. Recent advances with drugs that target the neuropeptide calcitonin gene-related peptide (CGRP) have helped, but treatment options remain insufficient. CGRP is released from trigeminal sensory fibers and contributes to peripheral sensitization, perhaps in part due to actions on immune cells in the trigeminovascular system. In this review, we will discuss the potential of cannabinoid targeting of immune cells as an innovative therapeutic target for migraine treatment. We will cover endogenous endocannabinoids, plant-derived phytocannabinoids and synthetically derived cannabinoids. The focus will be on six types of immune cells known to express multiple cannabinoid receptors: macrophages, monocytes, mast cells, dendritic cells, B cells, and T cells. These cells also contain receptors for CGRP and as such, cannabinoids might potentially modulate the efficacy of current CGRP-targeting drugs. Unfortunately, to date most studies on cannabinoids and immune cells have relied on cell cultures and only a single preclinical study has tested cannabinoid actions on immune cells in a migraine model. Encouragingly, in that study a synthetically created stable chiral analog of an endocannabinoid reduced meningeal mast cell degranulation. Likewise, clinical trials evaluating the safety and efficacy of cannabinoid-based therapies for migraine patients have been limited but are encouraging. Thus, the field is at its infancy and there are significant gaps in our understanding of the impact of cannabinoids on immune cells in migraine. Future research exploring the interactions between cannabinoids and immune cells could lead to more targeted and effective migraine treatments.

Lipolysis pathways modulate lipid mediator release and endocannabinoid system signaling in dairy cows' adipocytes

BACKGROUND

As cows transition from pregnancy to lactation, free fatty acids (FFA) are mobilized from adipose tissues (AT) through lipolysis to counter energy deficits. In clinically healthy cows, lipolysis intensity is reduced throughout lactation; however, if FFA release exceeds tissue demands or the liver's metabolic capacity, lipid byproducts accumulate, increasing cows' risk of metabolic and infectious disease. Endocannabinoids (eCBs) and their congeners, N-acylethanolamines (NAEs), are lipid-based compounds that modulate metabolism and inflammation. Their synthesis and release depend upon the availability of FFA precursors and the abundance of synthesizing and degrading enzymes and transporters. Therefore, we hypothesized that eCB production and transcription of endocannabinoid system components are modulated by lipolysis pathways in adipocytes. To test this hypothesis, we stimulated canonical (isoproterenol, 1 µmol/L; ISO) and inflammatory (lipopolysaccharide, 1 µg/mL; LPS) lipolysis pathways in adipocytes isolated from the AT of 5 Holstein dairy cows. Following, we assessed lipolysis intensity, adipocytes' release of eCBs, and transcription of endocannabinoid system components.

RESULTS

We found that ISO and LPS stimulated lipolysis at comparable intensities. Exposure to either treatment tended to elevate the release of eCBs and NAEs by cultured adipocytes; however, specific eCBs and NAEs and the transcriptional profiles differed by treatment. On one hand, ISO enhanced adipocytes' release of 2-arachidonoylglycerol (2-AG) but reduced NAE production. Notably, ISO enhanced the cells' expression of enzymes associated with 2-AG biosynthesis (INPP5F, GDPD5, GPAT4), transport (CD36), and adipogenesis (PPARG). Conversely, LPS enhanced adipocytes' synthesis and release of N-arachidonoylethanolamide (AEA). This change coincided with enhanced transcription of the NAE-biosynthesizing enzyme, PTPN22, and adipocytes' transcription of genes related to eCB degradation (PTGS2, MGLL, CYP27B1). Furthermore, LPS enhanced adipocytes' transcription of eCB and NAE transporters (HSPA1A, SCP2) and the expression of the anti-adipogenic ion channel, TRPV3.

CONCLUSIONS

Our data provide evidence for distinct modulatory roles of canonical and inflammatory lipolysis pathways over eCB release and transcriptional regulation of biosynthesis, degradation, transport, and ECS signaling in cows' adipocytes. Based on our findings, we conclude that, within adipocytes, eCB production and ECS component expression are, at least in part, mediated by lipolysis in a pathway-dependent manner. These findings contribute to a deeper understanding of the molecular mechanisms underlying metabolic regulation in dairy cows' AT, with potential implications for prevention and treatment of inflammatory and metabolic disorders.

Sperm proteostasis: Can-nabinoids be chaperone's partners?

The male gamete is a highly differentiated cell that aims to fuse with the oocyte in fertilization. Sperm have silenced the transcription and translational processes, maintaining proteostasis to guarantee male reproductive health. Despite the information about the implication of molecular chaperones as orchestrators of protein folding or aggregation, and the handling of body homeostasis by the endocannabinoid system, there is still a lack of basic investigation and random controlled clinical trials that deliver more evidence on the involvement of cannabinoids in reproductive function. Besides, we noticed that the information regarding whether recreational marijuana affects male fertility is controversial and requires further investigation. In other cell models, it has recently been evidenced that chaperones and cannabinoids are intimately intertwined. Through a literature review, we aim to explore the interaction between chaperones and cannabinoid signaling in sperm development and function. To untangle how or whether this dialogue happens within the sperm proteostasis. We discuss the action of chaperones, the endocannabinoid system and phytocannabinoids in sperm proteostasis. Reports of some heat shock and lipid proteins interacting with cannabinoid receptors prove that chaperones and the endocannabinoid system are in an intimate dialogue. Meanwhile, advancing the evidence to decipher these mechanisms for introducing innovative interventions into routine clinical settings becomes crucial. We highlight the potential interaction between chaperones and cannabinoid signaling in regulating proteostasis in male reproductive health.

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.

Endocannabinoid modulation of allergic responses: Focus on the control of FcεRI-mediated mast cell activation

Allergic reactions are highly prevalent pathologies initiated by the production of IgE antibodies against harmless antigens (allergens) and the activation of the high-affinity IgE receptor (FcεRI) expressed in the surface of basophils and mast cells (MCs). Research on the mechanisms of negative control of those exacerbated inflammatory reactions has been intense in recent years. Endocannabinoids (eCBs) show important regulatory effects on MC-mediated immune responses, mainly inhibiting the production of pro-inflammatory mediators. However, the description of the molecular mechanisms involved in eCB control of MC activation is far from complete. In this review, we aim to summarize the available information regarding the role of eCBs in the modulation of FcεRI-dependent activation of that cell type, emphasizing the description of the eCB system and the existence of some of its elements in MCs. Unique characteristics of the eCB system and cannabinoid receptors (CBRs) localization and signaling in MCs are mentioned. The described and putative points of cross-talk between CBRs and FcεRI signaling cascades are also presented. Finally, we discuss some important considerations in the study of the effects of eCBs in MCs and the perspectives in the field.

The conserved endocannabinoid anandamide modulates olfactory sensitivity to induce hedonic feeding in C. elegans

The ability of cannabis to increase food consumption has been known for centuries. In addition to producing hyperphagia, cannabinoids can amplify existing preferences for calorically dense, palatable food sources, a phenomenon called hedonic amplification of feeding. These effects result from the action of plant-derived cannabinoids that mimic endogenous ligands called endocannabinoids. The high degree of conservation of cannabinoid signaling at the molecular level across the animal kingdom suggests hedonic feeding may also be widely conserved. Here, we show that exposure of Caenorhabditis elegans to anandamide, an endocannabinoid common to nematodes and mammals, shifts both appetitive and consummatory responses toward nutritionally superior food, an effect analogous to hedonic feeding. We find that anandamide's effect on feeding requires the C. elegans cannabinoid receptor NPR-19 but can also be mediated by the human CB1 cannabinoid receptor, indicating functional conservation between the nematode and mammalian endocannabinoid systems for the regulation of food preferences. Furthermore, anandamide has reciprocal effects on appetitive and consummatory responses to food, increasing and decreasing responses to inferior and superior foods, respectively. Anandamide's behavioral effects require the AWC chemosensory neurons, and anandamide renders these neurons more sensitive to superior foods and less sensitive to inferior foods, mirroring the reciprocal effects seen at the behavioral level. Our findings reveal a surprising degree of functional conservation in the effects of endocannabinoids on hedonic feeding across species and establish a new system to investigate the cellular and molecular basis of endocannabinoid system function in the regulation of food choice.

Deciphering Complex Interactions in Bioactive Lipid Signaling

Lipids are usually viewed as metabolic fuel and structural membrane components. Yet, in recent years, different families of lipids able to act as authentic messengers between cells and/or intracellularly have been discovered. Such lipid signals have been shown to exert their biological activity via specific receptors that, by triggering distinct signal transduction pathways, regulate manifold pathophysiological processes in our body. Here, endogenous bioactive lipids produced from arachidonic acid (AA) and other poly-unsaturated fatty acids will be presented, in order to put into better perspective the relevance of their mutual interactions for health and disease conditions. To this end, metabolism and signal transduction pathways of classical eicosanoids, endocannabinoids and specialized pro-resolving mediators will be described, and the intersections and commonalities of their metabolic enzymes and binding receptors will be discussed. Moreover, the interactions of AA-derived signals with other bioactive lipids such as shingosine-1-phosphate and steroid hormones will be addressed.

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.

Endocannabinoid Metabolism and Transport as Drug Targets

The wide distribution of the endocannabinoid system (ECS) throughout the body and its pivotal pathophysiological role offer promising opportunities for the development of novel therapeutic drugs for treating several diseases. However, the need for strategies to circumvent the unwanted psychotropic and immunosuppressive effects associated with cannabinoid receptor agonism/antagonism has led to considerable research in the field of molecular alternatives, other than type-1 and type-2 (CB_1/2) receptors, as therapeutic targets to indirectly manipulate this pro-homeostatic system. In this context, the use of selective inhibitors of proteins involved in endocannabinoid (eCB) transport and metabolism allows for an increase or decrease of the levels of N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG) in the sites where these major eCBs are indeed needed. This chapter will briefly review some preclinical and clinical evidence for the therapeutic potential of ECS pharmacological manipulation.

Visualization of Endocannabinoids in the Cell

A still unsolved, although critical, issue in endocannabinoid research is the mechanism by which the lipophilic anandamide (AEA) moves from its site of synthesis, crosses the aqueous milieu, and reaches the different intracellular membrane compartments, where its metabolic and signaling pathways take place. The difficulty of studying intracellular AEA transport and distribution results from the lack of specific probes and techniques to track and visualize this bioactive lipid within the cells. Herein, we describe the use of a biotinylated, non-hydrolyzable derivative of AEA (biotin-AEA, b-AEA) for visualizing the subcellular distribution of this endocannabinoid by means of confocal fluorescence microscopy.

Assay of Endocannabinoid Uptake

Endocannabinoids at nanomolar physiological concentrations cross cellular membranes by facilitated diffusion, a process that can be studied by measuring transport kinetics and endocannabinoid trafficking employing radioligands and mass spectrometry. Here, we describe radiosubstrate-based assays using arachidonoyl[1-³H]ethanolamine and 2-arachidonoyl[1,2,3-³H]glycerol to measure cellular endocannabinoid uptake in a three-phase assay with human U937 cells. Liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS/MS)-based lipidomics was used to interrogate the roles of serum and albumin for endocannabinoid trafficking in U937 cells.

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.

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.

Cannabidiol Promotes Neuronal Differentiation Using Akt and Erk Pathways Triggered by Cb1 Signaling

Recently, the scientific community has started to focus on the neurogenic potential of cannabinoids. The phytocompound cannabidiol (CBD) shows different mechanism of signaling on cannabinoid receptor 1 (CB1), depending on its concentration. In this study, we investigated if CBD may induce in vitro neuronal differentiation after treatment at 5 µM and 10 µM. For this purpose, we decided to use the spinal cord × neuroblastoma hybrid cell line (NSC-34) because of its proliferative and undifferentiated state. The messenger RNAs (mRNAs) expression profiles were tested using high-throughput sequencing technology and Western blot assay was used to determine the number of main proteins in different pathways. Interestingly, the treatment shows different genes associated with neurodifferentiation statistically significant, such as Rbfox3, Tubb3, Pax6 and Eno2. The CB1 signaling pathway is responsible for neuronal differentiation at 10 µM, as suggested by the presence of p-ERK and p-AKT, but not at 5 µM. A new correlation between CBD, neurodifferentiation and retinoic acid receptor-related orphan receptors (RORs) has been observed.

Palmitoylethanolamide and Related ALIAmides for Small Animal Health: State of the Art

ALIAmides are a family of fatty acid amides whose name comes from their mechanism of action, i.e., the Autacoid Local Injury Antagonism (ALIA). Actually, the ALIAmide parent molecule, palmitoylethanolamide (PEA), is locally produced on demand from a cell membrane precursor in order to control immune-inflammatory cell responses, avert chronic non-resolving inflammation, and limit the resulting clinical signs. ALIAmide sister compounds, such as Adelmidrol and palmitoylglucosamine, share mechanisms of action with PEA and may also increase endogenous levels of PEA. Provided that their respective bioavailability is properly addressed (e.g., through decreasing the particle size through micronization), exogenously administered ALIAmides thus mimic or sustain the prohomeostatic functions of endogenous PEA. The aim of the present paper is to review the main findings on the use of ALIAmides in small animals as a tribute to the man of vision who first believed in this “according-to-nature” approach, namely Francesco della Valle. After briefly presenting some key issues on the molecular targets, metabolism, and pharmacokinetics of PEA and related ALIAmides, here we will focus on the preclinical and clinical studies performed in dogs and cats. Although more data are still needed, ALIAmides may represent a novel and promising approach to small animal health.

Role of the Endocannabinoid System in the Regulation of Intestinal Homeostasis

The maintenance of intestinal homeostasis is fundamentally important to health. Intestinal barrier function and immune regulation are key determinants of intestinal homeostasis and are therefore tightly regulated by a variety of signaling mechanisms. The endocannabinoid system is a lipid mediator signaling system widely expressed in the gastrointestinal tract. Accumulating evidence suggests the endocannabinoid system is a critical nexus involved in the physiological processes that underlie the control of intestinal homeostasis. In this review we will illustrate how the endocannabinoid system is involved in regulation of intestinal permeability, fluid secretion, and immune regulation. We will also demonstrate a reciprocal regulation between the endocannabinoid system and the gut microbiome. The role of the endocannabinoid system is complex and multifaceted, responding to both internal and external factors while also serving as an effector system for the maintenance of intestinal homeostasis.

Chemical Proteomics Reveals Off-Targets of the Anandamide Reuptake Inhibitor WOBE437

Anandamide or N-arachidonoylethanolamine (AEA) is a signaling lipid that modulates neurotransmitter release via activation of the type 1 cannabinoid receptor (CB₁R) in the brain. Termination of anandamide signaling is thought to be mediated via a facilitated cellular reuptake process that utilizes a purported transporter protein. Recently, WOBE437 has been reported as a novel, natural product-based inhibitor of AEA reuptake that is active in cellular and in vivo models. To profile its target interaction landscape, we synthesized pac-WOBE, a photoactivatable probe derivative of WOBE437, and performed chemical proteomics in mouse neuroblastoma Neuro-2a cells. Surprisingly WOBE437, unlike the widely used selective inhibitor of AEA uptake OMDM-1, was found to increase AEA uptake in Neuro-2a cells. In line with this, WOBE437 reduced the cellular levels of AEA and related N-acylethanolamines (NAEs). Using pac-WOBE, we identified saccharopine dehydrogenase-like oxidoreductase (SCCPDH), vesicle amine transport 1 (VAT1), and ferrochelatase (FECH) as WOBE437-interacting proteins in Neuro-2a cells. Further genetic studies indicated that SCCPDH and VAT1 were not responsible for the WOBE437-induced reduction in NAE levels. Regardless of the precise mechanism of action of WOB437 in AEA transport, we have identified SSCPHD, VAT1, and FECH as unprecedented off-targets of this molecule which should be taken into account when interpreting its cellular and in vivo effects.

Inhibiting Endocannabinoid Hydrolysis as Emerging Analgesic Strategy Targeting a Spectrum of Ion Channels Implicated in Migraine Pain

Migraine is a disabling neurovascular disorder characterized by severe pain with still limited efficient treatments. Endocannabinoids, the endogenous painkillers, emerged, alternative to plant cannabis, as promising analgesics against migraine pain. In this thematic review, we discuss how inhibition of the main endocannabinoid-degrading enzymes, monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), could raise the level of endocannabinoids (endoCBs) such as 2-AG and anandamide in order to alleviate migraine pain. We describe here: (i) migraine pain signaling pathways, which could serve as specific targets for antinociception; (ii) a divergent distribution of MAGL and FAAH activities in the key regions of the PNS and CNS implicated in migraine pain signaling; (iii) a complexity of anti-nociceptive effects of endoCBs mediated by cannabinoid receptors and through a direct modulation of ion channels in nociceptive neurons; and (iv) the spectrum of emerging potent MAGL and FAAH inhibitors which efficiently increase endoCBs levels. The specific distribution and homeostasis of endoCBs in the main regions of the nociceptive system and their generation ‘on demand’, along with recent availability of MAGL and FAAH inhibitors suggest new perspectives for endoCBs-mediated analgesia in migraine pain.

Hypothalamic endocannabinoids in obesity: an old story with new challenges

The crucial role of the hypothalamus in the pathogenesis of obesity is widely recognized, while the precise molecular and cellular mechanisms involved are the focus of intense research. A disrupted endocannabinoid system, which critically modulates feeding and metabolic functions, through central and peripheral mechanisms, is a landmark indicator of obesity, as corroborated by investigations centered on the cannabinoid receptor CB1, considered to offer promise in terms of pharmacologically targeted treatment for obesity. In recent years, novel insights have been obtained, not only into relation to the mode of action of CB receptors, but also CB ligands, non-CB receptors, and metabolizing enzymes considered to be part of the endocannabinoid system (particularly the hypothalamus). The outcome has been a substantial expansion in knowledge of this complex signaling system and in drug development. Here we review recent literature, providing further evidence on the role of hypothalamic endocannabinoids in regulating energy balance and the implication for the pathophysiology of obesity. We discuss how these lipids are dynamically regulated in obesity onset, by diet and metabolic hormones in specific hypothalamic neurons, the impact of gender, and the role of endocannabinoid metabolizing enzymes as promising targets for tackling obesity and related diseases.

Endocannabinoid-Based Therapies

The endocannabinoids are lipid-derived messengers that play a diversity of regulatory roles in mammalian physiology. Dysfunctions in their activity have been implicated in various disease conditions, attracting attention to the endocannabinoid system as a possible source of therapeutic drugs. This signaling complex has three components: the endogenous ligands, anandamide and 2-arachidonoyl-sn-glycerol (2-AG); a set of enzymes and transporters that generate, eliminate, or modify such ligands; and selective cell surface receptors that mediate their biological actions. We provide an overview of endocannabinoid formation, deactivation, and biotransformation and outline the properties and therapeutic potential of pharmacological agents that interfere with those processes. We describe small-molecule inhibitors that target endocannabinoid-producing enzymes, carrier proteins that transport the endocannabinoids into cells, and intracellular endocannabinoid-metabolizing enzymes. We briefly discuss selected agents that simultaneously interfere with components of the endocannabinoid system and with other functionally related signaling pathways. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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.

Roles of Endocannabinoids and Endocannabinoid-like Molecules in Energy Homeostasis and Metabolic Regulation: A Nutritional Perspective

The endocannabinoid system is involved in signal transduction in mammals. It comprises principally G protein-coupled cannabinoid receptors and their endogenous agonists, called endocannabinoids, as well as the enzymes and transporters responsible for the metabolism of endocannabinoids. Two arachidonic acid-containing lipid molecules, arachidonoylethanolamide (anandamide) and 2-arachidonoylglycerol, function as endocannabinoids. N-acylethanolamines and monoacylglycerols, in which the arachidonic acid chain is replaced with a saturated or monounsaturated fatty acid, are not directly involved in the endocannabinoid system but exhibit agonistic activities for other receptors. These endocannabinoid-like molecules include palmitoylethanolamide, oleoylethanolamide (OEA), and 2-oleoylglycerol. Endocannabinoids stimulate feeding behavior and the anabolism of lipids and glucose, while OEA suppresses appetite. Both central and peripheral systems are included in these nutritional and metabolic contexts. Therefore, they have potential in the treatment and prevention of obesity. We outline the structure, metabolism, and biological activities of endocannabinoids and related molecules, and focus on their involvement in energy homeostasis and metabolic regulation. Expected final online publication date for the Annual Review of Nutrition, Volume 41 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

BIONOTE as an Innovative Biosensor for Measuring Endocannabinoid Levels

In this study, a novel approach was developed to quantify endocannabinoids (eCBs), and was based on the liquid biosensor BIONOTE. This device is composed of a probe that can be immersed in a solution, and an electronic interface that can record a current related to the oxy-reductive reactions occurring in the sample. The two most representative members of eCBs have been analysed in vitro by BIONOTE: anandamide (N-arachidonoylethanolamine, AEA) and 2-arachidonoylglycerol (2-AG). Bovine serum albumin was used to functionalize the probe and improve the sensibility of the whole analytical system. We show that BIONOTE is able to detect both AEA and 2-AG at concentrations in the low nanomolar range, and to discriminate between these eCBs and their moieties arachidonic acid, ethanolamine and glycerol. Notably, BIONOTE distinguished these five different molecules, and it was also able to quantify AEA in human plasma. Although this is just a proof-of-concept study, we suggest BIONOTE as a cheap and user-friendly prototype sensor for high throughput quantitation of eCB content in biological matrices, with an apparent diagnostic potential for tomorrow’s medicine.

Missing Pieces to the Endocannabinoid Puzzle

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

Potential of Cannabinoid Receptor Ligands as Treatment for Substance Use Disorders

Substance use disorder (SUD) is a major public health crisis worldwide, and effective treatment options are limited. During the past 2 decades, researchers have investigated the impact of a variety of pharmacological approaches to treat SUD, one of which is the use of medical cannabis or cannabinoids. Significant progress was made with the discovery of rimonabant, a selective CB1 receptor (CB1R) antagonist (also an inverse agonist), as a promising therapeutic for SUDs and obesity. However, serious adverse effects such as depression and suicidality led to the withdrawal of rimonabant (and almost all other CB1R antagonists/inverse agonists) from clinical trials worldwide in 2008. Since then, much research interest has shifted to other cannabinoid-based strategies, such as peripheral CB1R antagonists/inverse agonists, neutral CB1R antagonists, allosteric CB1R modulators, CB2R agonists, fatty acid amide hydrolase (FAAH) inhibitors, monoacylglycerol lipase (MAGL) inhibitors, fatty acid binding protein (FABP) inhibitors, or nonaddictive phytocannabinoids with CB1R or CB2R-binding profiles, as new therapeutics for SUDs. In this article, we first review recent progress in research regarding the endocannabinoid systems, cannabis reward versus aversion, and the underlying receptor mechanisms. We then review recent progress in cannabinoid-based medication development for the treatment of SUDs. As evidence continues to accumulate, neutral CB1R antagonists (such as AM4113), CB2R agonists (JWH133, Xie2-64), and nonselective phytocannabinoids (cannabidiol, β-caryophyllene, ∆9-tetrahydrocannabivarin) have shown great therapeutic potential for SUDs, as shown in experimental animals. Several cannabinoid-based medications (e.g., dronabinol, nabilone, PF-04457845) that entered clinical trials have shown promising results in reducing withdrawal symptoms in cannabis and opioid users.

The endocannabinoid system is affected by cholesterol dyshomeostasis: Insights from a murine model of Niemann Pick type C disease

The dyshomeostasis of intracellular cholesterol trafficking is typical of the Niemann-Pick type C (NPC) disease, a fatal inherited lysosomal storage disorder presenting with progressive neurodegeneration and visceral organ involvement. In light of the well-established relevance of cholesterol in regulating the endocannabinoid (eCB) system expression and activity, this study was aimed at elucidating whether NPC disease-related cholesterol dyshomeostasis affects the functional status of the brain eCB system. To this end, we exploited a murine model of NPC deficiency for determining changes in the expression and activity of the major molecular components of the eCB signaling, including cannabinoid type-1 and type-2 (CB₁ and CB₂) receptors, their ligands, N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG), along with their main synthesizing/inactivating enzymes. We found a robust alteration of distinct components of the eCB system in various brain regions, including the cortex, hippocampus, striatum and cerebellum, of Npc1-deficient compared to wild-type pre-symptomatic mice. Changes of the eCB component expression and activity differ from one brain structure to another, although 2-AG and AEA are consistently found to decrease and increase in each structure, respectively. The thorough biochemical characterization of the eCB system was accompanied by a behavioral characterization of Npc1-deficient mice using a number of paradigms evaluating anxiety, locomotor activity, spatial learning/memory abilities, and coping response to stressful experience. Our findings provide the first description of an early and region-specific alteration of the brain eCB system in NPC and suggest that defective eCB signaling could contribute at producing and/or worsening the neurological symptoms of this disorder.

Modulation of Mast Cell Reactivity by Lipids: The Neglected Side of Allergic Diseases

Mast cells (MCs) have long been mainly regarded as effector cells in IgE-associated allergic disorders with potential immunoregulatory roles. Located close to the allergen entry sites in the skin and mucosa, MCs can capture foreign substances such as allergens, toxins, or noxious substances and are exposed to the danger signals produced by epithelial cells. MC reactivity shaped by tissue-specific factors is crucial for allergic responses ranging from local skin reactions to anaphylactic shock. Development of Th2 response leading to allergen-specific IgE production is a prerequisite for MC sensitization and induction of FcεRI-mediated MC degranulation. Up to now, IgE production has been mainly associated with proteins, whereas lipids present in plant pollen grains, mite fecal particles, insect venoms, or food have been largely overlooked regarding their immunostimulatory and immunomodulatory properties. Recent studies, however, have now demonstrated that lipids affect the sensitization process by modulating innate immune responses of epithelial cells, dendritic cells, and NK-T cells and thus crucially contribute to the outcome of sensitization. Whether and how lipids affect also MC effector functions in allergic reactions has not yet been fully clarified. Here, we discuss how lipids can affect MC responses in the context of allergic inflammation. Direct effects of immunomodulatory lipids on MC degranulation, changes in local lipid composition induced by allergens themselves and changes in lipid transport affecting MC reactivity are possible mechanisms by which the function of MC might be modulated.

Role of pannexin-1 in the cellular uptake, release and hydrolysis of anandamide by T84 colon cancer cells

The large pore ion channel pannexin-1 (Panx1) has been reported to play a role in the cellular uptake and release of anandamide (AEA) in the hippocampus. It is not known whether this is a general mechanism or limited to the hippocampus. We have investigated this pharmacologically using T84 colon cancer cells. The cells expressed Panx1 at the mRNA level, and released ATP in a manner that could be reduced by treatment with the Panx1 inhibitors carbenoxolone and mefloquine and the Panx1 substrate SR101. However, no significant effects of these compounds upon the uptake or hydrolysis of exogenously applied AEA was seen. Uptake by T84 cells of the other main endocannabinoid 2-arachidonoylglycerol and the AEA homologue palmitoylethanolamide was similarly not affected by carbenoxolone or mefloquine. Total release of tritium from [³H]AEA-prelabelled T84 cells over 10 min was increased, rather than inhibited by carbenoxolone and mefloquine. Finally, AEA uptake by PC3 prostate cancer and SH-SY5Y neuroblastoma cells, which express functional Panx1 channels, was not inhibited by carbenoxolone. Thus, in contrast to the hippocampus, Panx1 does not appear to play a role in AEA uptake and release from the cells studied under the conditions used.

FABP1 controls hepatic transport and biotransformation of Δ9-THC

The increasing use of medical marijuana highlights the importance of developing a better understanding of cannabinoid metabolism. Phytocannabinoids, including ∆⁹-tetrahydrocannabinol (THC), are metabolized and inactivated by cytochrome P450 enzymes primarily within the liver. The lipophilic nature of cannabinoids necessitates mechanism(s) to facilitate their intracellular transport to metabolic enzymes. Here, we test the central hypothesis that liver-type fatty acid binding protein (FABP1) mediates phytocannabinoid transport and subsequent inactivation. Using X-ray crystallography, molecular modeling, and in vitro binding approaches we demonstrate that FABP1 accommodates one molecule of THC within its ligand binding pocket. Consistent with its role as a THC carrier, biotransformation of THC was reduced in primary hepatocytes obtained from FABP1-knockout (FABP1-KO) mice. Compared to their wild-type littermates, administration of THC to male and female FABP1-KO mice potentiated the physiological and behavioral effects of THC. The stark pharmacodynamic differences were confirmed upon pharmacokinetic analyses which revealed that FABP1-KO mice exhibit reduced rates of THC biotransformation. Collectively, these data position FABP1 as a hepatic THC transport protein and a critical mediator of cannabinoid inactivation. Since commonly used medications bind to FABP1 with comparable affinities to THC, our results further suggest that FABP1 could serve a previously unrecognized site of drug-drug interactions.

Multiple endocannabinoid-mediated mechanisms in the regulation of energy homeostasis in brain and peripheral tissues

The endocannabinoid (eCB) system is widely expressed in many central and peripheral tissues, and is involved in a plethora of physiological processes. Among these, activity of the eCB system promotes energy intake and storage, which, however, under pathophysiological conditions, can favour the development of obesity and obesity-related disorders. It is proposed that eCB signalling is evolutionary beneficial for survival under periods of scarce food resources. Remarkably, eCB signalling is increased both in hunger and in overnutrition conditions, such as obesity and type-2 diabetes. This apparent paradox suggests a role of the eCB system both at initiation and at clinical endpoint of obesity. This review will focus on recent findings about the role of the eCB system controlling whole-body metabolism in mice that are genetically modified selectively in different cell types. The current data in fact support the notion that eCB signalling is not only engaged in the development but also in the maintenance of obesity, whereby specific cell types in central and peripheral tissues are key sites in regulating the entire body's energy homeostasis.

Human Liver Fatty Acid Binding Protein-1 T94A Variant, Nonalcohol Fatty Liver Disease, and Hepatic Endocannabinoid System

Hepatic endocannabinoids (EC) and their major binding/"chaperone" protein (i.e., liver fatty acid binding protein-1 [FABP1]) are associated with development of nonalcoholic fatty liver (NAFLD) in animal models and humans. Since expression of the highly prevalent human FABP1 T94A variant induces serum lipid accumulation, it is important to determine its impact on hepatic lipid accumulation and the EC system. This issue was addressed in livers from human subjects expressing only wild-type (WT) FABP1 T94T (TT genotype) or T94A variant (TC or CC genotype). WT FABP1 males had lower total lipids (both neutral cholesteryl esters, triacylglycerols) and phospholipids than females. WT FABP1 males' lower lipids correlated with lower levels of the N-acylethanolamide DHEA and 2-monoacylglycerols (2-MAG) (2-OG, 2-PG). T94A expression in males increased the hepatic total lipids (triacylglycerol, cholesteryl ester), which is consistent with their higher level of CB1-potentiating 2-OG and lower antagonistic EPEA. In contrast, in females, T94A expression did not alter the total lipids, neutral lipids, or phospholipids, which is attributable to the higher cannabinoid receptor-1 (CB1) agonist arachidonoylethanolamide (AEA) and its CB1-potentiator OEA being largely offset by reduced potentiating 2-OG and increased antagonistic EPEA. Taken together, these findings indicate that T94A-induced alterations in the hepatic EC system contribute at least in part to the hepatic accumulation of lipids associated with NAFLD, especially in males.

Structural properties and role of the endocannabinoid lipases ABHD6 and ABHD12 in lipid signalling and disease

The endocannabinoid (eCB) system is an important part of both the human central nervous system (CNS) and peripheral tissues. It is involved in the regulation of various physiological and neuronal processes and has been associated with various diseases. The eCB system is a complex network composed of receptor molecules, their cannabinoid ligands, and enzymes regulating the synthesis, release, uptake, and degradation of the signalling molecules. Although the eCB system and the molecular processes of eCB signalling have been studied extensively over the past decades, the involved molecules and underlying signalling mechanisms have not been described in full detail. An example pose the two poorly characterised eCB-degrading enzymes α/β-hydrolase domain protein six (ABHD6) and ABHD12, which have been shown to hydrolyse 2-arachidonoyl glycerol-the main eCB in the CNS. We review the current knowledge about the eCB system and the role of ABHD6 and ABHD12 within this important signalling system and associated diseases. Homology modelling and multiple sequence alignments highlight the structural features of the studied enzymes and their similarities, as well as the structural basis of disease-related ABHD12 mutations. However, homologies within the ABHD family are very low, and even the closest homologues have widely varying substrate preferences. Detailed experimental analyses at the molecular level will be necessary to understand these important enzymes in full detail.

Anandamide Effects in a Streptozotocin-Induced Alzheimer's Disease-Like Sporadic Dementia in Rats

Alzheimer's disease (AD) is characterized by multiple cognitive deficits including memory and sensorimotor gating impairments as a result of neuronal and synaptic loss. The endocannabinoid system plays an important role in these deficits but little is known about its influence on the molecular mechanism regarding phosphorylated tau (p-tau) protein accumulation - one of the hallmarks of AD -, and on the density of synaptic proteins. Thus, the aim of this study was to investigate the preventive effects of anandamide (N-arachidonoylethanolamine, AEA) on multiple cognitive deficits and on the levels of synaptic proteins (syntaxin 1, synaptophysin and synaptosomal-associated protein, SNAP-25), cannabinoid receptor type 1 (CB₁) and molecules related to p-tau degradation machinery (heat shock protein 70, HSP70), and Bcl2-associated athanogene (BAG2) in an AD-like sporadic dementia model in rats using intracerebroventricular (icv) injection of streptozotocin (STZ). Our hypothesis is that AEA could interact with HSP70, modulating the level of p-tau and synaptic proteins, preventing STZ-induced cognitive impairments. Thirty days after receiving bilateral icv injections of AEA or STZ or both, the cognitive performance of adult male Wistar rats was evaluated in the object recognition test, by the escape latency in the elevated plus maze (EPM), by the tone and context fear conditioning as well as in prepulse inhibition tests. Subsequently, the animals were euthanized and their brains were removed for histological analysis or for protein quantification by Western Blotting. The behavioral results showed that STZ impaired recognition, plus maze and tone fear memories but did not affect contextual fear memory and prepulse inhibition. Moreover, AEA prevented recognition and non-associative emotional memory impairments induced by STZ, but did not influence tone fear conditioning. STZ increased the brain ventricular area and this enlargement was prevented by AEA. Additionally, STZ reduced the levels of p-tau (Ser199/202) and increased p-tau (Ser396), although AEA did not affect these alterations. HSP70 was found diminished only by STZ, while BAG2 levels were decreased by STZ and AEA. Synaptophysin, syntaxin and CB₁ receptor levels were reduced by STZ, but only syntaxin was recovered by AEA. Altogether, albeit AEA failed to modify some AD-like neurochemical alterations, it partially prevented STZ-induced cognitive impairments, changes in synaptic markers and ventricle enlargement. This study showed, for the first time, that the administration of an endocannabinoid can prevent AD-like effects induced by STZ, boosting further investigations about the modulation of endocannabinoid levels as a therapeutic approach for AD.

Impact of Fabp1 Gene Ablation on Uptake and Degradation of Endocannabinoids in Mouse Hepatocytes

Liver fatty-acid-binding protein (FABP1, L-FABP) is the major cytosolic binding/chaperone protein for both precursor arachidonic acid (ARA) and the endocannabinoid (EC) products N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG). Although FABP1 regulates hepatic uptake and metabolism of ARA, almost nothing is known regarding FABP1's impact on AEA and 2-AG uptake, intracellular distribution, and targeting of AEA and 2-AG to degradative hepatic enzymes. In vitro assays revealed that FABP1 considerably enhanced monoacylglycerol lipase hydrolysis of 2-AG but only modestly enhanced AEA hydrolysis by fatty-acid amide hydrolase. Conversely, liquid chromatography-mass spectrometry of lipids from Fabp1 gene-ablated (LKO) hepatocytes confirmed that loss of FABP1 markedly diminished hydrolysis of 2-AG. Furthermore, the real-time imaging of novel fluorescent NBD-labeled probes (NBD-AEA, NBD-2-AG, and NBD-ARA) resolved FABP1's impact on uptake vs intracellular targeting/hydrolysis. FABP1 bound NBD-ARA with 2:1 stoichiometry analogous to ARA, but bound NBD-2-AG and NBD-AEA with 1:1 stoichiometry-apparently at different sites in FABP1's binding cavity. All three probes were taken up, but NBD-2-AG and NBD-AEA were targeted to lipid droplets. LKO reduced the uptake of NBD-ARA as expected, significantly enhanced that of NBD-AEA, but had little effect on NBD-2-AG. These data indicated that FABP1 impacts hepatocyte EC levels by binding EC and differentially impacts their intracellular hydrolysis (2-AG) and uptake (AEA).

Lipid-metabolizing serine hydrolases in the mammalian central nervous system: endocannabinoids and beyond

The metabolic serine hydrolases hydrolyze ester, amide, or thioester bonds found in broad small molecule substrates using a conserved activated serine nucleophile. The mammalian central nervous system (CNS) express a diverse repertoire of serine hydrolases that act as (phospho)lipases or lipid amidases to regulate lipid metabolism and signaling vital for normal neurocognitive function and CNS integrity. Advances in genomic DNA sequencing have provided evidence for the role of these lipid-metabolizing serine hydrolases in neurologic, psychiatric, and neurodegenerative disorders. This review briefly summarizes recent progress in understanding the biochemical and (patho)physiological roles of these lipid-metabolizing serine hydrolases in the mammalian CNS with a focus on serine hydrolases involved in the endocannabinoid system. The development and application of specific inhibitors for an individual serine hydrolase, if available, are also described. This article is part of a Special Issue entitled Novel functions of phospholipase A2 Guest Editors: Makoto Murakami and Gerard Lambeau.

Scp-2/Scp-x ablation in Fabp1 null mice differentially impacts hepatic endocannabinoid level depending on dietary fat

Dysregulation of the hepatic endocannabinoid (EC) system and high fat diet (HFD) are associated with non-alcoholic fatty liver disease. Liver cytosol contains high levels of two novel endocannabinoid binding proteins-liver fatty acid binding protein (FABP1) and sterol carrier protein-2 (SCP-2). While Fabp1 gene ablation significantly increases hepatic levels of arachidonic acid (ARA)-containing EC and sex-dependent response to pair-fed high fat diet (HFD), the presence of SCP-2 complicates interpretation. These issues were addressed by ablating Scp-2/Scp-x in Fabp1 null mice (TKO). In control-fed mice, TKO increased hepatic levels of arachidonoylethanolamide (AEA) in both sexes. HFD impacted hepatic EC levels by decreasing AEA in TKO females and decreasing 2-arachidonoyl glycerol (2-AG) in WT of both sexes. Only TKO males on HFD had increased hepatic 2-AG levels. Hepatic ARA levels were decreased in control-fed TKO of both sexes. Changes in hepatic AEA/2-AG levels were not associated with altered amounts of hepatic proteins involved in AEA/2-AG synthesis or degradation. These findings suggested that ablation of the Scp-2/Scp-x gene in Fabp1 null mice exacerbated hepatic EC accumulation and antagonized the impact of HFD on hepatic EC levels-suggesting both proteins play important roles in regulating the hepatic EC system.

Δ9-Tetrahydrocannabinol induces endocannabinoid accumulation in mouse hepatocytes: antagonism by Fabp1 gene ablation

Phytocannabinoids, such as Δ9-tetrahydrocannabinol (THC), bind and activate cannabinoid (CB) receptors, thereby "piggy-backing" on the same pathway's endogenous endocannabinoids (ECs). The recent discovery that liver fatty acid binding protein-1 (FABP1) is the major cytosolic "chaperone" protein with high affinity for both Δ9-THC and ECs suggests that Δ9-THC may alter hepatic EC levels. Therefore, the impact of Δ9-THC or EC treatment on the levels of endogenous ECs, such as N-arachidonoylethanolamide (AEA) and 2-arachidonoylglycerol (2-AG), was examined in cultured primary mouse hepatocytes from WT and Fabp1 gene-ablated (LKO) mice. Δ9-THC alone or 2-AG alone significantly increased AEA and especially 2-AG levels in WT hepatocytes. LKO alone markedly increased AEA and 2-AG levels. However, LKO blocked/diminished the ability of Δ9-THC to further increase both AEA and 2-AG. In contrast, LKO potentiated the ability of exogenous 2-AG to increase the hepatocyte level of AEA and 2-AG. These and other data suggest that Δ9-THC increases hepatocyte EC levels, at least in part, by upregulating endogenous AEA and 2-AG levels. This may arise from Δ9-THC competing with AEA and 2-AG binding to FABP1, thereby decreasing targeting of bound AEA and 2-AG to the degradative enzymes, fatty acid amide hydrolase and monoacylglyceride lipase, to decrease hydrolysis within hepatocytes.

Involvement of TRPV1 Channels in Energy Homeostasis

The ion channel TRPV1 is involved in a wide range of processes including nociception, thermosensation and, more recently discovered, energy homeostasis. Tightly controlling energy homeostasis is important to maintain a healthy body weight, or to aid in weight loss by expending more energy than energy intake. TRPV1 may be involved in energy homeostasis, both in the control of food intake and energy expenditure. In the periphery, it is possible that TRPV1 can impact on appetite through control of appetite hormone levels or via modulation of gastrointestinal vagal afferent signaling. Further, TRPV1 may increase energy expenditure via heat production. Dietary supplementation with TRPV1 agonists, such as capsaicin, has yielded conflicting results with some studies indicating a reduction in food intake and increase in energy expenditure, and other studies indicating the converse. Nonetheless, it is increasingly apparent that TRPV1 may be dysregulated in obesity and contributing to the development of this disease. The mechanisms behind this dysregulation are currently unknown but interactions with other systems, such as the endocannabinoid systems, could be altered and therefore play a role in this dysregulation. Further, TRPV1 channels appear to be involved in pancreatic insulin secretion. Therefore, given its plausible involvement in regulation of energy and glucose homeostasis and its dysregulation in obesity, TRPV1 may be a target for weight loss therapy and diabetes. However, further research is required too fully elucidate TRPV1s role in these processes. The review provides an overview of current knowledge in this field and potential areas for development.

Visualization of Endocannabinoids in the Cell

A still unsolved, although critical, issue in endocannabinoid research is the mechanism by which the lipophilic compound anandamide (AEA) moves from its site of synthesis, crosses the aqueous milieu, and reaches the different intracellular compartments, where its metabolic and signaling pathways take place. The difficulty of studying intracellular AEA transport and distribution results from the lack of specific probes and techniques to track and visualize this bioactive lipid within the cell. Here, we describe the use of a biotinylated, non-hydrolyzable derivative of AEA (biotin-AEA, b-AEA) for visualizing the subcellular distribution of this endocannabinoid by means of confocal fluorescence microscopy.

Palmitic Acid: Physiological Role, Metabolism and Nutritional Implications

Palmitic acid (PA) has been for long time negatively depicted for its putative detrimental health effects, shadowing its multiple crucial physiological activities. PA is the most common saturated fatty acid accounting for 20–30% of total fatty acids in the human body and can be provided in the diet or synthesized endogenously via de novo lipogenesis (DNL). PA tissue content seems to be controlled around a well-defined concentration, and changes in its intake do not influence significantly its tissue concentration because the exogenous source is counterbalanced by PA endogenous biosynthesis. Particular physiopathological conditions and nutritional factors may strongly induce DNL, resulting in increased tissue content of PA and disrupted homeostatic control of its tissue concentration. The tight homeostatic control of PA tissue concentration is likely related to its fundamental physiological role to guarantee membrane physical properties but also to consent protein palmitoylation, palmitoylethanolamide (PEA) biosynthesis, and in the lung an efficient surfactant activity. In order to maintain membrane phospholipids (PL) balance may be crucial an optimal intake of PA in a certain ratio with unsaturated fatty acids, especially PUFAs of both n-6 and n-3 families. However, in presence of other factors such as positive energy balance, excessive intake of carbohydrates (in particular mono and disaccharides), and a sedentary lifestyle, the mechanisms to maintain a steady state of PA concentration may be disrupted leading to an over accumulation of tissue PA resulting in dyslipidemia, hyperglycemia, increased ectopic fat accumulation and increased inflammatory tone via toll-like receptor 4. It is therefore likely that the controversial data on the association of dietary PA with detrimental health effects, may be related to an excessive imbalance of dietary PA/PUFA ratio which, in certain physiopathological conditions, and in presence of an enhanced DNL, may further accelerate these deleterious effects.

Human serum albumin: A modulator of cannabinoid drugs

The endocannabinoid system is a unique neuromodulatory system that affects a wide range of biological processes and maintains the homeostasis in all mammal body systems. In recent years, several pharmacological tools to target endocannabinoid neurotransmission have been developed, including direct and indirect cannabinoid agonists and cannabinoid antagonists. Due to their hydrophobic nature, cannabinoid agonists and antagonists need to bind specific transporters to allow their distribution in body fluids. Human serum albumin (HSA), the most abundant plasma protein, is a key determinant of drug pharmacokinetics. As HSA binds both the endocannabinoid anandamide and the active ingredient of Cannabis sativa, Δ-9-tetrahydrocannabinol, we hypothesize that HSA can be the most important carrier of cannabinoid drugs. In silico docking observations strongly indicate that HSA avidly binds the indirect cannabinoid agonists URB597, AM5206, JZL184, JZL195, and AM404, the direct cannabinoid agonists WIN55,212-2 and CP55,940, and the prototypical cannabinoid antagonist/inverse agonist SR141716. Values of the free energy for cannabinoid drugs binding to HSA range between -5.4 kcal mol^-1 and -10.9 kcal mol^-1 . Accounting for the HSA concentration in vivo (∼ 7.5 × 10^-4 M), values of the free energy here determined suggest that the formation of the HSA:cannabinoid drug complexes may occur in vivo. Therefore, HSA appears to be an important determinant for cannabinoid efficacy and may guide the choice of the drug dose regimen to optimize drug efficacy and to avoid drug-related toxicity. © 2017 IUBMB Life, 69(11):834-840, 2017.

Loss of fatty acid binding protein-1 alters the hepatic endocannabinoid system response to a high-fat diet

Upregulation of the hepatic endocannabinoid (EC) receptor [cannabinoid receptor-1 (CB1)] and arachidonoylethanolamide (AEA) is associated with nonalcoholic fatty liver disease (NAFLD). Male mice fed high-fat diet (HFD) ad libitum also exhibit NAFLD, increased hepatic AEA, and obesity. But, preference for HFD complicates interpretation and almost nothing is known about these effects in females. These issues were addressed by pair-feeding HFD. Similarly to ad libitum-fed HFD, pair-fed HFD also increased WT male and female mouse fat tissue mass (FTM), but preferentially at the expense of lean tissue mass. In contrast, pair-fed HFD did not elicit NAFLD in WT mice regardless of sex. Concomitantly, pair-fed HFD oppositely impacted hepatic AEA, 2-arachidonoyl glycerol, and/or CB1 in WT males versus females. In pair-fed HFD mice, liver FA binding protein-1 (Fabp1) gene ablation (LKO): i) exacerbated FTM in both sexes; ii) did not elicit liver neutral lipid accumulation in males and only slightly in females; iii) increased liver AEA in males, but decreased it in females; and iv) decreased CB1 only in males. Thus, pair-fed HFD selectively impacted hepatic ECs more in females, but did not elicit NAFLD in either sex. These effects were modified by LKO consistent with FABP1's ability to impact EC and FA metabolism.

Endocannabinoid Transport Proteins: Discovery of Tools to Study Sterol Carrier Protein-2

The endocannabinoid (eCB) neurotransmitter system regulates diverse neurological functions including stress and anxiety, pain, mood, and reward. Understanding the mechanisms underlying eCB regulation is critical for developing targeted pharmacotherapies to treat these and other neurologic disorders. Cellular studies suggest that the arachidonate eCBs, N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG), are substrates for intracellular binding and transport proteins, and several candidate proteins have been identified. Initial evidence from our laboratory indicates that the lipid transport protein, sterol carrier protein 2 (SCP-2), binds to the eCBs and can regulate their cellular concentrations. Here, we present methods for evaluating SCP-2 binding of eCBs and their application to the discovery of the first inhibitor lead molecules. Using a fluorescent probe displacement assay, we found SCP-2 binds the eCBs, AEA (Ki=0.68±0.05μM) and 2-AG (Ki=0.37±0.02μM), with moderate affinity. A series of structurally diverse arachidonate analogues also bind SCP-2 with Ki values between 0.82 and 2.95μM, suggesting a high degree of tolerance for arachidonic acid head group modifications in this region of the protein. We also report initial structure-activity relationships surrounding previously reported inhibitors of Aedis aegypti SCP-2, and the results of an in silico high-throughput screen that identified structurally novel SCP-2 inhibitor leads. The methods and results reported here provide the basis for a robust probe discovery effort to fully elucidate the role of facilitated transport mediated by SCP-2 in eCB regulation and function.