Anandamide and 2-arachidonoylglycerol inhibit fatty acid amide hydrolase by activating the lipoxygenase pathway of the arachidonate cascade

Exploring the versatile roles of the endocannabinoid system and phytocannabinoids in modulating bacterial infections

The endocannabinoid system (ECS), initially identified for its role in maintaining homeostasis, particularly in regulating brain function, has evolved into a complex orchestrator influencing various physiological processes beyond its original association with the nervous system. Notably, an expanding body of evidence emphasizes the ECS's crucial involvement in regulating immune responses. While the specific role of the ECS in bacterial infections remains under ongoing investigation, compelling indications suggest its active participation in host-pathogen interactions. Incorporating the ECS into the framework of bacterial pathogen infections introduces a layer of complexity to our understanding of its functions. While some studies propose the potential of cannabinoids to modulate bacterial function and immune responses, the outcomes inherently hinge on the specific infection and cannabinoid under consideration. Moreover, the bidirectional relationship between the ECS and the gut microbiota underscores the intricate interplay among diverse physiological processes. The ECS extends its influence far beyond its initial discovery, emerging as a promising therapeutic target across a spectrum of medical conditions, encompassing bacterial infections, dysbiosis, and sepsis. This review comprehensively explores the complex roles of the ECS in the modulation of bacteria, the host's response to bacterial infections, and the dynamics of the microbiome. Special emphasis is placed on the roles of cannabinoid receptor types 1 and 2, whose signaling intricately influences immune cell function in microbe-host interactions.

Role of omega-3 and omega-6 endocannabinoids in cardiopulmonary pharmacology

Endocannabinoids are derived from dietary omega-3 and omega-6 fatty acids and play an important role in regulation of inflammation, development, neurodegenerative diseases, cancer, and cardiovascular diseases. They elicit this effect via interactions with cannabinoid receptors 1 and 2 which are also targeted by plant derived cannabinoid from cannabis. The evidence of the involvement of the endocannabinoid system in cardiopulmonary function comes from studies that show that cannabis consumption leads to cardiovascular effect such as arrythmia and is beneficial in lung cancer patients. Moreover, omega-3 and omega-6 endocannabinoids play several important roles in cardiopulmonary system such as causing airway relaxation, suppressing atherosclerosis and hypertension. These effects are mediated via the cannabinoids receptors that are abundant in the cardiopulmonary system. Overall, this chapter reviews the known role of phytocannabinoids and endocannabinoids in the cardiopulmonary context.

Activation of TRPV1 by Capsaicin or Heat Drives Changes in 2-Acyl Glycerols and N-Acyl Ethanolamines in a Time, Dose, and Temperature Dependent Manner

Endocannabinoids (eCBs) and transient receptor potential (TRP) channels are associated with thermoregulation; however, there are many gaps in the understanding of how these signaling systems work together in responding to changes in temperature. TRPV1, a calcium-permeable ion channel, is activated by capsaicin, elevated temperature, the eCB Anandamide, and over 15 additional endogenous lipids. There is also evidence for signaling crosstalk between TRPV1 and the eCB receptor, CB₁. We recently found that activation of TRPV1-HEK cells by capsaicin increases the production of the eCB, 2-arachidonoyl glycerol (2-AG), suggesting a molecular link between these receptors. Here, we tested the hypothesis that TRPV1 activation by capsaicin drives regulation of a wider-range of lipid signaling molecules and is time and dose-dependent. We also tested the hypothesis that changes in temperature that drive changes in calcium mobilization in TRPV1-HEK will likewise drive similar changes in lipid signaling molecule regulation. Lipid analysis was conducted by partial purification of methanolic extracts on C18 solid phase extraction columns followed by HPLC/MS/MS. Capsaicin increased the release of 2-acyl glycerols (2-AG, 2-linoleoyl glycerol, 2-oleoyl glycerol), in a concentration- and time-dependent manner, whereas levels of N-acyl ethanolamines (NAEs), including Anandamide, were significantly decreased. Analogous changes in 2-acyl glycerols and NAEs were measured upon ramping the temperature from 37 to 45°C. In contrast, opposite effects were measured when analyzing lipids after they were maintained at 27°C and then quickly ramped to 37°C, wherein 2-acyl glycerol levels decreased and NAEs increased. These results provide further evidence that the eCB system and TRPV1 have integrated signaling functions that are associated with the molecular response to temperature variation.

Lower brain fatty acid amide hydrolase in treatment-seeking patients with alcohol use disorder: a positron emission tomography study with [C-11]CURB

The endocannabinoid enzyme, fatty acid amide hydrolase (FAAH), has been proposed as a therapeutic target for alcohol use disorder (AUD) and co-morbid psychiatric illnesses. Investigating this target in the living human brain and its relationship to clinical outcome is a critical step of informed drug development. Our objective was to establish whether brain FAAH levels are low in individuals with AUD and related to drinking behavior. In this pilot study, treatment-seeking patients with AUD completed two PET scans with the FAAH radiotracer [C-11]CURB after 3-7 days (n = 14) and 2-4 weeks (n = 9) of monitored abstinence. Healthy controls (n = 25) completed one scan. FAAH genetic polymorphism (rs324420) and blood concentrations of anandamide and other N-acylethanolamines metabolized by FAAH were determined and AUD symptoms assessed. In AUD, brain FAAH levels were globally lower than controls during early abstinence (F(1,36) = 5.447; p = 0.025)) and FAAH substrates (anandamide, oleoylethanolamide, and N-docosahexaenoylethanolamide) were significantly elevated (30-67%). No significant differences in FAAH or FAAH substrates were noted after 2-4 weeks abstinence. FAAH levels negatively correlated with drinks per week (r = -0.57, p = 0.032) and plasma concentrations of the three FAAH substrates (r > 0.57; p < 0.04)). Our findings suggest that early abstinence from alcohol in AUD is associated with transiently low brain FAAH levels, which are inversely related to heavier alcohol use and elevated plasma levels of FAAH substrates. Whether low FAAH is an adaptive beneficial response to chronic alcohol is unknown. Therapeutic strategies focusing on FAAH inhibition should consider the possibility that low FAAH during early abstinence may be related to drinking.

Molecular Mechanism and Cannabinoid Pharmacology

Since antiquity, Cannabis has provoked enormous intrigue for its potential medicinal properties as well as for its unique pharmacological effects. The elucidation of its major cannabinoid constituents, Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD), led to the synthesis of new cannabinoids (termed synthetic cannabinoids) to understand the mechanisms underlying the pharmacology of Cannabis. These pharmacological tools were instrumental in the ultimate discovery of the endogenous cannabinoid system, which consists of CB1 and CB2 cannabinoid receptors and endogenously produced ligands (endocannabinoids), which bind and activate both cannabinoid receptors. CB1 receptors mediate the cannabimimetic effects of THC and are highly expressed on presynaptic neurons in the nervous system, where they modulate neurotransmitter release. In contrast, CB2 receptors are primarily expressed on immune cells. The endocannabinoids are tightly regulated by biosynthetic and hydrolytic enzymes. Accordingly, the endocannabinoid system plays a modulatory role in many physiological processes, thereby generating many promising therapeutic targets. An unintended consequence of this research was the emergence of synthetic cannabinoids sold for human consumption to circumvent federal laws banning Cannabis use. Here, we describe research that led to the discovery of the endogenous cannabinoid system and show how knowledge of this system benefitted as well as unintentionally harmed human health.

Ferrosenescence: The iron age of neurodegeneration?

Aging has been associated with iron retention in many cell types, including the neurons, promoting neurodegeneration by ferroptosis. Excess intracellular iron accelerates aging by damaging the DNA and blocking genomic repair systems, a process we define as ferrosenescence. Novel neuroimaging and proteomic techniques have pinpointed indicators of both iron retention and ferrosenescence, allowing for their early correction, potentially bringing prevention of neurodegenerative disorders within reach. In this review, we take a closer look at the early markers of iron dyshomeostasis in neurodegenerative disorders, focusing on preventive strategies based on nutritional and microbiome manipulations.

Regulation of inflammation by cannabinoids, the endocannabinoids 2-arachidonoyl-glycerol and arachidonoyl-ethanolamide, and their metabolites

2-Arachidonoyl-glycerol (2-AG) and arachidonyl-ethanolamide (AEA) are endocannabinoids that have been implicated in many physiologic disorders, including obesity, metabolic syndromes, hepatic diseases, pain, neurologic disorders, and inflammation. Their immunomodulatory effects are numerous and are not always mediated by cannabinoid receptors, reflecting the presence of an arachidonic acid (AA) molecule in their structure, the latter being the precursor of numerous bioactive lipids that are pro- or anti-inflammatory. 2-AG and AEA can thus serve as a source of AA but can also be metabolized by most eicosanoid biosynthetic enzymes, yielding additional lipids. In this regard, enhancing endocannabinoid levels by using endocannabinoid hydrolysis inhibitors is likely to augment the levels of these lipids that could regulate inflammatory cell functions. This review summarizes the metabolic pathways involved in the biosynthesis and metabolism of AEA and 2-AG, as well as the biologic effects of the 2-AG and AEA lipidomes in the regulation of inflammation.

Endocannabinoids and their oxygenation by cyclo-oxygenases, lipoxygenases and other oxygenases

The naturally occurring mammalian endocannabinoids possess biological attributes that extend beyond interaction with cannabinoid receptors. These extended biological properties are the result of oxidative metabolism of the principal mammalian endocannabinoids arachidonoyl ethanolamide (anandamide; A-EA) and 2-arachidonoylglycerol (2-AG). Both endocannabinoids are oxidized by cyclo-oxygenase-2 (COX-2), but not by COX-1, to a series of prostaglandin derivatives (PGs) with quite different biological properties from those of the parent substrates. PG ethanolamides (prostamides, PG-EAs) and PG glyceryl esters (PG-Gs) are not only pharmacologically distinct from their parent endocannabinoids, they are distinct from the corresponding acidic PGs, and are differentiated from each other. Ethanolamides and glyceryl esters of the major prostanoids PGD2, PGE2, PGF2α, and PGI2 are formed by the various PG synthases, and thromboxane ethanolamides and glyceryl esters are not similarly produced. COX-2 is also of interest by virtue of its corollary central role in modulating endocannabinoid tone, providing a new therapeutic approach for treating pain and anxiety. Other major oxidative conversion pathways are provided for both A-EA and 2-AG by several lipoxygenases (LOXs), resulting in the formation of numerous hydroxyl metabolites. These do not necessarily represent inactivation pathways for endocannabinoids but may mimic or modulate the endocannabinoids or even display alternative pharmacology. Similarly, A-EA and 2-AG may be oxidized by P450 enzymes. Again a very diverse number of metabolites are formed, with either cannabinoid-like biological properties or an introduction of disparate pharmacology. The biological activity of epoxy and hydroxyl derivatives of the endocannabinoids remains to be fully elucidated. This review attempts to consolidate and compare the findings obtained to date in an increasingly important research area. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

Parsing the players: 2-arachidonoylglycerol synthesis and degradation in the CNS

The endogenous cannabinoid signalling system, composed of endogenous cannabinoids, cannabinoid receptors and the enzymes that synthesize and degrade the endogenous cannabinoids, is much more complex than initially conceptualized. 2-Arachidonoylglycerol (2-AG) is the most abundant endocannabinoid and plays a major role in CNS development and synaptic plasticity. Over the past decade, many key players in 2-AG synthesis and degradation have been identified and characterized. Most 2-AG is synthesized from membrane phospholipids via sequential activation of a phospholipase Cβ and a diacylglycerol lipase, although other pathways may contribute in specialized settings. 2-AG breakdown is more complicated with at least eight different enzymes participating. These enzymes can either degrade 2-AG into its components, arachidonic acid and glycerol, or transform 2-AG into highly bioactive signal molecules. The implications of the precise temporal and spatial control of the expression and function of these pleiotropic metabolizing enzymes have only recently come to be appreciated. In this review, we will focus on the primary organization of the synthetic and degradative pathways of 2-AG and then discuss more recent findings and their implications, with an eye towards the biological and therapeutic implications of manipulating 2-AG synthesis and metabolism.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-6.

Cannabinoids and Reproduction: A Lasting and Intriguing History

Starting from an historical overview of lasting Cannabis use over the centuries, we will focus on a description of the cannabinergic system, with a comprehensive analysis of chemical and pharmacological properties of endogenous and synthetic cannabimimetic analogues. The metabolic pathways and the signal transduction mechanisms, activated by cannabinoid receptors stimulation, will also be discussed. In particular, we will point out the action of cannabinoids and endocannabinoids on the different neuronal networks involved in reproductive axis, and locally, on male and female reproductive tracts, by emphasizing the pivotal role played by this system in the control of fertility.

Interplay between endocannabinoids, steroids and cytokines in the control of human reproduction

The use of marijuana, which today is the most used recreational drug, has been demonstrated to affect adversely reproduction. Marijuana smokers, both men and women, show impaired fertility, owing to defective signalling pathways, aberrant hormonal regulation, or wrong timing during embryo implantation. Anandamide (N-arachidonoylethanolamine, AEA) and 2-arachidonoylglycerol (2-AG) mimic Delta(9)-tetrahydrocannabinol (THC), the psychoactive principle of Cannabis sativa, by binding to both the brain-type (CB(1)) and the spleen-type (CB(2)) cannabinoid receptors. These 'endocannabinoids' exert several actions either in the central nervous system or in peripheral tissues, and are metabolised by specific enzymes that synthesise or hydrolyse them. In this review, we shall describe the elements that constitute the endocannabinoid system (ECS), in order to put in a better perspective the role of this system in the control of human fertility, both in females and males. In addition, we shall discuss the interplay between ECS, sex hormones and cytokines, which generates an endocannabinoid-hormone-cytokine array critically involved in the control of human reproduction.

Effects of cocaine in 5-lipoxygenase-deficient mice

5-Lipoxygenase (5-LOX), along with 12-lipoxygenase and cyclooxygenases, metabolizes arachidonic acid into eicosanoids. In rodents, 12-lipoxygenase deficiency alters behavioral responses to cocaine. We used 5-LOX-deficient mice and their controls to investigate cocaine's actions. After repeated cocaine injections, the increase in locomotor activity was greater in 5-LOX-deficient mice. Since the 5-LOX pathway may regulate the levels/metabolism of arachidonoylethanolamide (AEA) we assayed the AEA levels in the striatum, the binding of the endogenous AEA to the cannabinoid receptor CB1R, and anandamide hydrolase (FAAH) activity in the striatum, hippocampus, and cortex. Striatal AEA levels decreased after repeated cocaine injections. Cocaine also decreased CB1R binding in all brain regions studied and the only significant differences between 5-LOX-deficient and control mice was the greater hippocampal FAAH activity in 5-LOX-deficient mice. Our results demonstrated that a 5-LOX deficiency alters sensitivity to repeated cocaine. It should be investigated whether a human 5-LOX gene polymorphism affects cocaine's actions.

The complications of promiscuity: endocannabinoid action and metabolism

In this review, we present our understanding of the action and metabolism of endocannabinoids and related endogenous molecules. It is clear that the interactions between the multiple endocannabinoid-like molecules (ECLs) are highly complex, both at the level of signal transduction and metabolism. Thus, ECLs are a group of ligands active at 7-transmembrane and nuclear receptors, as well as transmitter-gated and ion channels. ECLs and their metabolites can converge on common endpoints (either metabolic or signalling) through contradictory or reinforcing pathways. We highlight the complexity of the endocannabinoid system, based on the promiscuous nature of ECLs and their metabolites, as well as the synthetic modulators of the endocannabinoid system.

Endocannabinoid metabolism and uptake: novel targets for neuropathic and inflammatory pain

Cannabinoid CB1 and CB2 receptors are located at key sites involved in the relaying and processing of noxious inputs. Both CB1 and CB2 receptor agonists have analgesic effects in a range of models of inflammatory and neuropathic pain. Importantly, clinical trials of cannabis-based medicines indicate that the pre-clinical effects of cannabinoid agonists may translate into therapeutic potential in humans. One of the areas of concern with this pharmacological approach is that CB1 receptors have a widespread distribution in the brain and that global activation of CB1 receptors is associated with adverse side effects. Studies of the endogenous cannabinoids (endocannabinoids) have demonstrated that they are present in most tissues and that in some pain states, such as neuropathic pain, levels of endocannabinoids are elevated at key sites involved in pain processing. An alternative approach that can be used to harness the potential therapeutic effects of cannabinoids is to maximise the effects of the endocannabinoids, the actions of which are terminated by re-uptake and metabolism by various enzymes, including fatty acid amide hydrolase (FAAH), monoacylglycerol lipase (MAGL) and cyclooxygenase type 2 (COX2). Preventing the metabolism, or uptake, of endocannabinoids elevates levels of these lipid compounds in tissue and produces behavioural analgesia in models of acute pain. Herein we review recent studies of the effects of inhibition of metabolism of endocannabinoids versus uptake of endocannabinoids on nociceptive processing in models of inflammatory and neuropathic pain.

Vanilloid receptor 1 (TRPV1/VR1) co-localizes with fatty acid amide hydrolase (FAAH) in retinal amacrine cells

Fatty acid amide hydrolase (FAAH) is the degradative enzyme for anandamide (AEA), an endogenous ligand for the vanilloid receptor (TRPV1) and cannabinoid receptor 1. As FAAH and TRPV1 are integral membrane proteins, FAAH activity could modulate the availability of AEA for TRPV1 activation. Previous studies in this laboratory reported an extensive endocannabinoid system in goldfish retina. Immunocytochemistry was used to determine the relative distributions of FAAH-immunoreactivity (IR) and TRPV1-IR in goldfish retina. Here, we show the first example in an intact neural system in which TRPV1-IR co-localizes in subpopulations of FAAH-immunoreactive neurons, in this case amacrine cells. These cells are rare and consist of three subtypes: 1. ovoid cell with granular-type dendrites restricted to sublamina a, 2. pyriform cell with smooth processes in sublamina b, and 3. fusiform cell with smooth processes that project to sublaminae a and b. The varied appearances of reaction product in the dendrites suggest different subcellular localization of TRPV1, and hence function of FAAH activity regarding TRPV1 stimulation among the cell types. Ovoid and pyriform amacrine cells, but not fusiform cells, labeled with GAD-IR and constituted subsets of GABAergic amacrine cells. TRPV1 amacrine cells, though rare, are represented in the ON, OFF and ON/OFF pathways of the retina. As TRPV1 stimulation increases intracellular calcium with numerous downstream effects, co-localization of TRPV1 and FAAH suggests an autoregulatory function for anandamide. Due to the rarity of these cells, the three vanilloid amacrine cell types may be involved in global effects rather than feature extraction, for example: sampling of ambient light or maintaining homeostasis.

Jekyll and hyde: two faces of cannabinoid signaling in male and female fertility

Mammalian reproduction is a complicated process designed to diversify and strengthen the genetic complement of the offspring and to safeguard regulatory systems at various steps for propagating procreation. An emerging concept in mammalian reproduction is the role of endocannabinoids, a group of endogenously produced lipid mediators, that bind to and activate cannabinoid receptors. Although adverse effects of cannabinoids on fertility have been implicated for years, the mechanisms by which they exert these effects were not clearly understood. With the identification of cannabinoid receptors, endocannabinoid ligands, their key synthetic and hydrolytic pathways, and the generation of mouse models missing cannabinoid receptors, a wealth of information on the significance of cannabinoid/endocannabinoid signaling in spermatogenesis, fertilization, preimplantation embryo development, implantation, and postimplantation embryonic growth has been generated. This review focuses on various aspects of the endocannabinoid system in male and female fertility. It is hoped that a deeper insight would lead to potential clinical applications of the endocannabinoid signaling as a target for correcting infertility and improving reproductive health in humans.

Anandamide Uptake Is Consistent with Rate-limited Diffusion and Is Regulated by the Degree of Its Hydrolysis by Fatty Acid Amide Hydrolase

The uptake of arachidonoyl ethanolamide (anandamide, AEA) in rat basophilic leukemia cells (RBL-2H3) has been proposed to occur via a saturable transporter that is blocked by specific inhibitors. Measuring uptake at 25 s, when fatty acid amide hydrolase (FAAH) does not appreciably affect uptake, AEA accumulated via a nonsaturable mechanism at 37 degrees C. Interestingly, saturation was observed when uptake was plotted using unbound AEA at 37 degrees C. Such apparent saturation can be explained by rate-limited delivery of AEA through an unstirred water layer surrounding the cells (1). In support of this, we observed kinetics consistent with rate-limited diffusion at 0 degrees C. Novel transport inhibitors have been synthesized that are either weak FAAH inhibitors or do not inhibit FAAH in vitro (e.g. UCM707, OMDM2, and AM1172). In the current study, none of these purported AEA transporter inhibitors affected uptake at 25 s. Longer incubation times illuminate downstream events that drive AEA uptake. Unlike the situation at 25 s, the efficacy of these inhibitors was unmasked at 5 min with appreciable inhibition of AEA accumulation correlating with partial inhibition of AEA hydrolysis. The uptake and hydrolysis profiles observed with UCM707, VDM11, OMDM2, and AM1172 mirrored two selective and potent FAAH inhibitors CAY10400 and URB597 (at low concentrations), indicating that weak inhibition of FAAH can have a pronounced effect upon AEA uptake. At 5 min, the putative transport inhibitors did not reduce AEA uptake in FAAH chemical knock-out cells. This strongly suggests that the target of UCM707, VDM11, OMDM2, and AM1172 is not a transporter at the plasma membrane but rather FAAH, or an uncharacterized intracellular component that delivers AEA to FAAH. This system is therefore unique among neuro/immune modulators because AEA, an uncharged hydrophobic molecule, diffuses into cells and partial inhibition of FAAH has a pronounced effect upon its uptake.

Modulators of endocannabinoid enzymic hydrolysis and membrane transport

Tissue concentrations of the endocannabinoids N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG) are regulated by both synthesis and inactivation. The purpose of this review is to compile available data regarding three inactivation processes: fatty acid amide hydrolase, monoacylglycerol lipase, and cellular membrane transport. In particular, we have focused on mechanisms by which these processes are modulated. We describe the in vitro and in vivo effects of inhibitors of these processes as well as available evidence regarding their modulation by other factors.

The biosynthesis, fate and pharmacological properties of endocannabinoids

The finding of endogenous ligands for cannabinoid receptors, the endocannabinoids, opened a new era in cannabinoid research. It meant that the biological role of cannabinoid signalling could be finally studied by investigating not only the pharmacological actions subsequent to stimulation of cannabinoid receptors by their agonists, but also how the activity of these receptors was regulated under physiological and pathological conditions by varying levels of the endocannabinoids. This in turn meant that the enzymes catalysing endocannabinoid biosynthesis and inactivation had to be identified and characterized, and that selective inhibitors of these enzymes had to be developed to be used as (1) probes to confirm endocannabinoid involvement in health and disease, and (2) templates for the design of new therapeutic drugs. This chapter summarizes the progress achieved in this direction during the 12 years following the discovery of the first endocannabinoid.

Inhibition of monoacylglycerol lipase and fatty acid amide hydrolase by analogues of 2-arachidonoylglycerol

The pharmacology of monoacylglycerol lipase (MAGL) is not well understood. In consequence, the abilities of a series of analogues of 2-arachidonoylglycerol (2-AG) to inhibit cytosolic 2-oleoylglycerol and membrane-bound anandamide hydolysis by MAGL and fatty acid amide hydrolase (FAAH), respectively, have been investigated. 2-AG and its 1-regioisomer (1-AG) interacted with MAGL with similar affinities (IC(50) values 13 and 17 mum, respectively). Shorter homologues of 2-AG (2-linoleoylglycerol and 2-oleoylglycerol) had affinities for MAGL similar to 2-AG. This pattern was also seen when the arachidonoyl side chain of arachidonoyl trifluoromethylketone was replaced by an oleoyl side chain. Arachidonoyl serinol (IC(50) value 73 microM) was a weaker inhibitor of MAGL than 2-AG. The IC(50) values of noladin ether towards MAGL and FAAH were 36 and 3 microM, respectively. Arachidonoyl glycine interacted with FAAH (IC(50) value 4.9 microM) but only weakly interacted with MAGL (IC(50) value >100 microM). alpha-Methyl-1-AG had similar potencies towards MAGL and FAAH (IC(50) values of 11 and 33 microM, respectively). O-2203 (1-(20-cyano-16,16-dimethyl-eicosa-5,8,11,14-tetraenoyl) glycerol) and O-2204 (2-(20-hydroxy-16,16-dimethyl-eicosa-5,8,11,14-tetraenoyl) glycerol) were slightly less potent, but again affected both enzymes equally. alpha-Methyl-1-AG, O-2203 and O-2204 interacted only weakly with cannabinoid CB(1) receptors expressed in CHO cells (K(i) values 1.8, 3.7 and 3.2 microM, respectively, compared with 0.24 microM for 1-AG) and showed no evidence of central cannabinoid receptor activation in vivo at doses up to 30 mg kg(-1) i.v. It is concluded that compounds like alpha-Methyl-1-AG, O-2203 and O-2204 may be useful as leads for the discovery of selective MAGL inhibitors that lack direct effects upon cannabinoid receptors.

Anandamide and vanilloid TRPV1 receptors

A large body of evidence now exists to substantiate that the endocannabinoid, anandamide, activates TRPV1 receptors. It is a low intrinsic efficacy TRPV1 agonist that behaves as a partial agonist in tissues with a low receptor reserve, while in tissues with high receptor reserve and in circumstances associated with certain disease states, it behaves as a full agonist. The efficacy of anandamide as a TRPV1 agonist is influenced by a succession of factors including receptor reserve, phosphorylation, metabolism and uptake, CB1 receptor activation, voltage, temperature, pH and bovine serum albumin. There are indications that the endocannabinoid system may play a role in the modulation of TRPV1 receptor activation. The activation of TRPV1 receptors by anandamide has potential implications in the treatment of inflammatory, respiratory and cardiovascular disorders. The relative importance of anandamide as a physiological and/or pathophysiological TRPV1 receptor agonist in comparison to other potential candidates has yet to be revealed.

Mitochondrial energy dissipation by fatty acids. Mechanisms and implications for cell death

For most cell types, fatty acids are excellent respiratory substrates. After being transported across the outer and inner mitochondrial membranes they undergo beta-oxidation in the matrix and feed electrons into the mitochondrial energy-conserving respiratory chain. On the other hand, fatty acids also physically interact with mitochondrial membranes, and possess the potential to alter their permeability. This occurs according to two mechanisms: an increase in proton conductance of the inner mitochondrial membrane and the opening of the permeability transition pore, an inner membrane high-conductance channel that may be involved in the release of apoptogenic proteins into the cytosol. This article addresses in some detail the mechanisms through which fatty acids exert their protonophoric action and how they modulate the permeability transition pore and discusses the cellular effects of fatty acids, with specific emphasis on their role as potential mitochondrial mediators of apoptotic signaling.

Endocannabinoids and their actions

Endocannabinoids are a new class of lipid mediators, which includes amides and esters of long-chain polyunsaturated fatty acids. Anandamide (I) and 2-arachidonoylglycerol (II) are the main endogenous agonists of cannabinoid receptors, able to mimic several pharmacological effects of delta 9-tetrahydrocannabinol (III), the active principle of Cannabis sativa preparations such as hashish and marijuana. The pathways leading to the synthesis and release of anandamide and 2-arachidonoylglycerol from neuronal and nonneuronal cells are rather uncertain. Instead, evidence has accumulated showing that the activity of these compounds at their specific receptors is limited by cellular uptake through a specific membrane transporter, followed by intracellular degradation by a fatty acid amide hydrolase. Here, the endocannabinoids and the endocannabinoid-like compounds most relevant for human physiology will be discussed, along with the synthetic and degradative pathways of anandamide and 2-arachidonoylglycerol and their molecular targets on the cell surface. The main actions of the endocannabinoids in human cells and tissues will also be reviewed, focusing on the activities most recently discovered in the central nervous system and in the periphery.

Block of erg current by linoleoylamide, a sleep-inducing agent, in pituitary GH3 cells

Linoleoylamide is physiological constituent of neurons. The effects of this agent, also a sleep-inducing agent, on ion currents in pituitary GH(3) cells were investigated. Hyperpolarization-elicited K(+) currents in GH(3) cells bathed in a high-K(+), Ca(2+)-free solution were studied to determine the effects of linoleoylamide and other related compounds on the I(K(IR)) that was sensitive to inhibition by E-4031 and identified as an erg (ether-à-go-go-related-gene) current. Linoleoylamide suppressed the amplitude of I(K(IR)) in a concentration-dependent manner with an IC(50) value of 5 microM. Oleamide (20 microM) inhibited the amplitude of I(K(IR)), while neither arachidonic acid (20 microM) nor 14,15-epoxyeicosatrienoic acid (20 microM) had an effect on it. In GH(3) cells incubated with anandamide (20 microM) or arachidonic acid (20 microM), the linoleoylamide-induced inhibition of I(K(IR)) remained unaltered. In inside-out patches, arachidonic acid (20 microM) and 14,15-epoxyeicosatrienoic acid (20 microM) stimulated large-conductance Ca(2+)-activated K(+) channels; however, linoleoylamide (20 microM) had little or no effect on them. Under current-clamp mode, linoleoylamide (20 microM) increased the firing rate. In IMR-32 neuroblastoma cells, linoleoylamide also suppressed I(K(IR)). This study provides the evidence that linoleoylamide has a depressant effect on the erg current, and suggests that this effect may affect hormonal secretion.

Anandamide activity and degradation are regulated by early postnatal aging and follicle-stimulating hormone in mouse Sertoli cells

Anandamide (AEA), a prominent member of the endogenous ligands of cannabinoid receptors (endocannabinoids), is known to adversely affect female fertility. However, a potential role of AEA in male reproductive functions is unknown. Here we report evidence that immature mouse Sertoli cells have the biochemical tools to bind and inactivate AEA, i.e. a functional type-2 cannabinoid receptor (CB2R), a selective AEA membrane transporter, and an AEA-degrading enzyme fatty acid amide hydrolase. We show that, unlike CB2R, the activity of AEA membrane transporter and the activity and expression of FAAH decrease, whereas the apoptosis-inducing activity of AEA increases with age during the neonatal period. We also show that FSH reduces the apoptotic potential of AEA, but not that of its nonhydrolyzable analog methanandamide. Concomitantly, FSH enhances FAAH activity in a manner dependent on mRNA transcription and protein synthesis and apparently involving cAMP. These data demonstrate that Sertoli cells partake in the peripheral endocannabinoid system, and that FSH reduces the apoptotic potential of AEA by activating FAAH. Taken together, it can be suggested that the endocannabinoid network plays a role in the hormonal regulation of male fertility.

Palmitoylethanolamide inhibits the expression of fatty acid amide hydrolase and enhances the anti-proliferative effect of anandamide in human breast cancer cells

Palmitoylethanolamide (PEA) has been shown to act in synergy with anandamide (arachidonoylethanolamide; AEA), an endogenous agonist of cannabinoid receptor type 1 (CB(1)). This synergistic effect was reduced by the CB(2) cannabinoid receptor antagonist SR144528, although PEA does not activate either CB(1) or CB(2) receptors. Here we show that PEA potently enhances the anti-proliferative effects of AEA on human breast cancer cells (HBCCs), in part by inhibiting the expression of fatty acid amide hydrolase (FAAH), the major enzyme catalysing AEA degradation. PEA (1-10 microM) enhanced in a dose-related manner the inhibitory effect of AEA on both basal and nerve growth factor (NGF)-induced HBCC proliferation, without inducing any cytostatic effect by itself. PEA (5 microM) decreased the IC(50) values for AEA inhibitory effects by 3-6-fold. This effect was not blocked by the CB(2) receptor antagonist SR144528, and was not mimicked by a selective agonist of CB(2) receptors. PEA enhanced AEA-evoked inhibition of the expression of NGF Trk receptors, which underlies the anti-proliferative effect of the endocannabinoid on NGF-stimulated MCF-7 cells. The effect of PEA was due in part to inhibition of AEA degradation, since treatment of MCF-7 cells with 5 microM PEA caused a approximately 30-40% down-regulation of FAAH expression and activity. However, PEA also enhanced the cytostatic effect of the cannabinoid receptor agonist HU-210, although less potently than with AEA. PEA did not modify the affinity of ligands for CB(1) or CB(2) receptors, and neither did it alter the CB(1)/CB(2)-mediated inhibitory effect of AEA on adenylate cyclase type V, nor the expression of CB(1) and CB(2) receptors in MCF-7 cells. We suggest that long-term PEA treatment of cells may positively affect the pharmacological activity of AEA, in part by inhibiting FAAH expression.