The anandamide membrane transporter and the therapeutic implications of its inhibition

The role of endocannabinoid pathway in the neuropathology of Alzheimer's disease: Can the inhibitors of MAGL and FAAH prove to be potential therapeutic targets against the cognitive impairment associated with Alzheimer's disease?

Alzheimer's disease is a neurodegenerative disease characterized by progressive decline of cognitive function in combination with neuronal death. Current approved treatment target single dysregulated pathway instead of multiple mechanism, resulting in lack of efficacy in slowing down disease progression. The proclivity of endocannabinoid system to exert neuroprotective action and mitigate symptoms of neurodegeneration condition has received substantial interest. Growing evidence suggest the endocannabinoids (eCB) system, viz. anadamide (AEA) and arachidonoyl glycerol (2-AG), as potential therapeutic targets with the ability to modify Alzheimer's pathology by targeting the inflammatory, neurodegenerative and cognitive aspects of the disease. In order to modulate endocannabinoid system, number of agents have been reported amongst which are inhibitors of the monoacylglycerol (MAGL) and fatty acid amide hydrolase (FAAH), the enzymes that hydrolyses 2-AG and AEA respectively. However, little is known regarding the exact mechanistic signalling and their effects on pathophysiology and cognitive decline associated with Alzheimer's disease. Both MAGL and FAAH inhibitors possess fascinating properties that may offer a multi-faceted approach for the treatment of Alzheimer's disease such as potential to protect neurons from deleterious effect of amyloid-β, reducing phosphorylation of tau, reducing amyloid-β induced oxidative stress, stimulating neurotrophin to support brain intrinsic repair mechanism etc. Based on empirical evidence, MAGL and FAAH inhibitors might have potential for therapeutic efficacy against cognitive impairment associated with Alzheimer's disease. The aim of this review is to summarize the experimental studies demonstrating the polyvalent properties of MAGL or FAAH inhibitor compounds for the treatment of Alzheimer's disease, and also effect of these on learning and types of memories, which together encourage to study these compounds over other therapeutics targets. Further research in this direction would enhance the molecular mechanisms and development of applicable interventions for the treatment of Alzheimer's disease, which nevertheless stay as the primary unmet need.

The endocannabinoid pathway and the female reproductive organs

Endocannabinoids are endogenous ligands of cannabinoid, vanilloid and peroxisome proliferator-activated receptors that activate multiple signal transduction pathways. Together with their receptor and the enzymes responsible for their synthesis and degradation, these compounds constitute the endocannabinoid system that has been recently shown to play, in humans, an important role in modulating several central and peripheral functions including reproduction. Given the relevance of the system, drugs that are able to interfere with the activity of endocannabinoids are currently considered as candidates for the treatment of various diseases. In this review, we will summarise the current knowledge regarding the effects of endocannabinoids in female reproductive organs. In particular, we will focus on some newly reported mechanisms that can affect endometrial plasticity both in physiological and in pathological conditions.

Pitfalls and solutions in assaying anandamide transport in cells

Nonspecific binding of anandamide to plastic exhibits many features that could be mistaken as biological processes, thereby representing an important source of conflicting data on the uptake and release of this lipophilic substance. Herein, we propose an improved method to assay anandamide transport, by using glass slides (i.e., coverslips) as physical support to grow cells. Although the results obtained using plastic do not differ significantly from those obtained using glass, the new procedure has the advantage of being faster, simpler, and more accurate. In fact, the lack of aspecific adsorption of anandamide to the glass surface yields a lower background and a higher precision and accuracy in determining transport kinetics, especially for the export process. Remarkably, the kinetic parameters of anandamide uptake obtained with the old and the new procedures may be similar or different depending on the cell type, thus demonstrating the complexity of the interference of plastic on the transport process. In addition, the novel procedure is particularly suitable for visualization and measurement of anandamide transport in intact cells by using a biotinylated derivative in confocal fluorescence microscopy.

Anandamide extends platelets survival through CB(1)-dependent Akt signaling

Platelets are stored at 22 degrees C, since incubation at 37 degrees C results in loss of viability. Nonetheless, in our body (37 degrees C), platelets survive for 8-10 days. This discrepancy has been explained in terms of deprivation of viability factors or accumulation of apoptotic factors during storage. We report that the endocannabinoid anandamide (AEA) may be one of the agents allowing platelet survival. In fact, at 37 degrees C, human platelets enhance the expression of pro-apoptotic proteins (caspases, Bax, Bak) and decrease the expression of Bcl-xL, thus changing the Bcl-xL/Bak ratio, a key platelet biological clock. AEA or its non-hydrolyzable analogue, methanandamide, extend platelet life span, without reversing the changes in Bcl-xL/Bak ratio induced by heat stress. Instead, AEA binding to type-1 cannabinoid receptor activates Akt, which regulates, through phosphorylation of Bad, the interactions among different Bcl-2 family members. These findings could have implications for platelet collection and, potentially, for their clinical use.

Characterization of the endocannabinoid system in human spermatozoa and involvement of transient receptor potential vanilloid 1 receptor in their fertilizing ability

Human spermatozoa express type-1 cannabinoid receptor (CB1), whose activation by anandamide (AEA) affects motility and acrosome reaction (AR). In this study, we extended the characterization of the AEA-related endocannabinoid system in human spermatozoa, and we focused on the involvement of the AEA-binding vanilloid receptor (TRPV1) in their fertilizing ability. Protein expression was revealed for CB1 ( approximately 56 kDa), TRPV1 ( approximately 95 kDa), AEA-synthesizing phospholipase D (NAPE-PLD) ( approximately 46 kDa), and AEA-hydrolyzing enzyme [fatty acid amide hydrolase (FAAH), approximately 66 kDa]. Both AEA-binding receptors (CB1 and TRPV1) exhibited a functional binding activity; enzymatic activity was demonstrated for NAPE-PLD, FAAH, and the purported endocannabinoid membrane transporter (EMT). Immunoreactivity for CB1, NAPE-PLD, and FAAH was localized in the postacrosomal region and in the midpiece, whereas for TRPV1, it was restricted to the postacrosomal region. Capsazepine (CPZ), a selective antagonist of TRPV1, inhibited progesterone (P)-enhanced sperm/oocyte fusion, as evaluated by the hamster egg penetration test. This inhibition was due to a reduction of the P-induced AR rate above the spontaneous AR rate, which was instead increased. The sperm exposure to OMDM-1, a specific inhibitor of EMT, prevented the promoting effect of CPZ on spontaneous AR rate and restored the sperm responsiveness to P. No significant effects could be observed on sperm motility. In conclusion, this study provides unprecedented evidence that human spermatozoa exhibit a completely functional endocannabinoid system related to AEA and that the AEA-binding TRPV1 receptor could be involved in the sperm fertilizing ability.

Endocannabinoids: friends and foes of reproduction

Endocannabinoids are fatty acid amides like anandamide (AEA), and monoacylglycerols like 2-arachidonoylglycerol, that bind to cannabinoid, vanilloid and peroxisome proliferator-activated receptors. Their biological actions are controlled through not yet fully characterized cellular mechanisms. These compounds, together with their related enzymes, that include key proteins for the synthesis and degradation of endocannabinoids, cannabinoid and non-cannabinoid receptors, and purported membrane transporter(s), form the "endocannabinoid system (ECS)". In the past few years AEA and related ECS elements have emerged as essential players in various aspects of human reproduction, both for males and females. Here, the key features of the ECS and the potential of its components to direct human fertility towards a positive or negative end will be reviewed. In particular, the involvement of AEA and related ECS elements in regulating embryo oviductal transport, blastocyst implantation and placental development (in females), and sperm survival, motility, capacitation and acrosome reaction (in males) will be addressed, as well as the role of endocannabinoids in sperm-oviduct interactions. Additionally, the possibility that blood AEA and its hydrolase FAAH may represent reliable diagnostic markers of natural and assisted reproduction in humans will be discussed, along with the therapeutic exploitation of ECS-oriented drugs as useful fertility enhancers.

Expression of the endocannabinoid system in the bi-potential HEL cell line: commitment to the megakaryoblastic lineage by 2-arachidonoylglycerol

The role of the endocannabinoid system in haematopoietic cells is not completely understood. We investigated whether human erythroleukemia (HEL) cells were able to bind, metabolise and transport the main endocannabinoids, anandamide (AEA) and 2-arachidonoylglycerol (2-AG). We also investigated whether AEA or 2-AG could modulate HEL differentiation. Although able to internalise both endocannabinoids, HEL cells had the machinery to metabolise 2-AG only, since they were devoid of the enzymes needed to synthesise and degrade AEA. Nonetheless, the intracellular transport of exogenous AEA might be required to activate the vanilloid receptors, with yet unknown implications for vascular biology. On the contrary, 2-AG appeared to play a role in lineage determination. Indeed, 2-AG itself drove HEL cells towards megakaryocytic differentiation, as it enhanced expression of beta3 integrin subunit, a megakaryocyte/platelet surface antigen, and glycoprotein VI, a late marker of megakaryocytes; in parallel, it reduced the amount of messenger RNA encoding for glycophorin A, a marker of erythroid phenotype. All these effects were mediated by activation of CB(2) cannabinoid receptors that triggered an extracellular signal-regulated kinase-dependent signalling cascade. In addition, classical inducers of megakaryocyte differentiation reduced 2-AG synthesis (although they did not affect the binding efficiency of CB(2) receptors), suggesting that levels of this endocannabinoid may be critical for committing HEL cells towards the megakaryocytic lineage.

High levels of anandamide, an endogenous cannabinoid, block the growth of sheep preimplantation embryos by inducing apoptosis and reversible arrest of cell proliferation

BACKGROUND

The process of implantation is mediated by various molecules, one of which is anandamide (AEA), a lipid signalling ligand belonging to the family of endocannabinoids. AEA exerts its effects on implantation by binding to the Type 1 Cannabinoid Receptor (CB1-R), expressed in both blastocysts and uterus. We wanted to know whether the endocannabinoid signalling system was present also in the sheep reproductive tract and which kind of effect(s) AEA had on the development of sheep blastocysts in vitro.

METHODS

We analysed the expression and activity of the endocannabinoid system in sheep reproductive tracts and blastocysts. Hatched sheep blastocysts were then exposed to AEA and its effect(s) were determined by TUNEL assay and by measuring the rate of necrosis and 5-bromo-deoxyuridine incorporation.

RESULTS

We show that the AEA signalling system is present in sheep and that high concentrations of AEA induce apoptosis and inhibit cell proliferation via a CB1-R-dependent mechanism. Indeed, AEA effects were blocked when sheep blastocysts were cultured in the presence of the CB1-R antagonist SR161417A. Moreover, AEA inhibition of cell proliferation was reversible, as arrested embryos resumed a normal growth rate upon AEA removal from the medium.

CONCLUSIONS

Our results suggest that disturbed regulation of AEA signalling via CB1-R may be associated with pregnancy failure. AEA could lower the quality of blastocysts by inducing apoptosis and inhibiting cell proliferation, thus making them incompetent for implantation.

Characterization of biotin-anandamide, a novel tool for the visualization of anandamide accumulation

Anandamide (N-arachidonoylethanolamide; AEA) acts as an endogenous agonist of both cannabinoid and vanilloid receptors. During the last two decades, its metabolic pathways and biological activity have been investigated extensively and relatively well characterized. In contrast, at present, the effective nature and mechanism of AEA transport remain controversial and still unsolved issues. Here, we report the characterization of a biotinylated analog of AEA (b-AEA) that has the same lipophilicity of the parent compound. In addition, by means of biochemical assays and fluorescence microscopy, we show that b-AEA is accumulated inside the cells in a way superimposable on that of AEA. Conversely, b-AEA does not interact or interfere with the other components of the endocannabinoid system, such as type-1 and type-2 cannabinoid receptors, vanilloid receptor, AEA synthetase (N-acylphosphatidylethanolamine-hydrolyzing phospholipase D), or AEA hydrolase (fatty acid amide hydrolase). Together, our data suggest that b-AEA could be a very useful probe for visualizing the accumulation and intracellular distribution of this endocannabinoid.

Anandamide regulates keratinocyte differentiation by inducing DNA methylation in a CB1 receptor-dependent manner

Anandamide (arachidonoylethanolamide, AEA) belongs to an important class of endogenous lipids including amides and esters of long chain polyunsaturated fatty acids, collectively termed "endocannabinoids." Recently we have shown that AEA inhibits differentiation of human keratinocytes, by binding to type-1 cannabinoid receptors (CB1R). To further characterize the molecular mechanisms responsible for this effect, we investigated the expression of epidermal differentiation-related genes after AEA treatment. We observed that keratin 1 and 10, transglutaminase 5 and involucrin are transcriptionally down-regulated by AEA. Most importantly, we found that AEA is able to decrease differentiating gene expression by increasing DNA methylation in human keratinocytes, through a p38, and to a lesser extent p42/44, mitogen-activated protein kinase-dependent pathway triggered by CB1R. An effect of AEA on DNA methylation because of CB1R-mediated increase of methyltransferase activity is described here for the first time, and we believe that the importance of this effect clearly extends beyond the regulation of skin differentiation. In fact, the modulation of DNA methylation by endocannabinoids may affect the expression of a number of genes that regulate many cell functions in response to these substances.

Modulation of the endocannabinoid system by focal brain ischemia in the rat is involved in neuroprotection afforded by 17beta-estradiol

Endogenous levels of the endocannabinoid anandamide, and the activities of the synthesizing and hydrolyzing enzymes, i.e. N-acylphosphatidylethanolamine-hydrolyzing phospholipase D and fatty acid amide hydrolase, respectively, were determined in the cortex and the striatum of rats subjected to transient middle cerebral artery occlusion. Anandamide content was markedly increased ( approximately 3-fold over controls; P < 0.01) in the ischemic striatum after 2 h of middle cerebral artery occlusion, but not in the cortex, and this elevation was paralleled by increased activity of N-acylphosphatidylethanolamine-hydrolyzing phospholipase D ( approximately 1.7-fold; P < 0.01), and reduced activity ( approximately 0.6-fold; P < 0.01) and expression ( approximately 0.7-fold; P < 0.05) of fatty acid amide hydrolase. These effects of middle cerebral artery occlusion were further potentiated by 1 h of reperfusion, whereas anandamide binding to type 1 cannabinoid and type 1 vanilloid receptors was not affected significantly by the ischemic insult. Additionally, the cannabinoid type 1 receptor antagonist SR141716, but not the receptor agonist R-(+)-WIN55,212-2, significantly reduced (33%; P < 0.05) cerebral infarct volume detected 22 h after the beginning of reperfusion. A neuroprotective intraperitoneal dose of 17beta-estradiol (0.20 mg x kg(-1)) that reduced infarct size by 43% also minimized the effect of brain ischemia on the endocannabinoid system, in an estrogen receptor-dependent manner. In conclusion, we show that the endocannabinoid system is implicated in the pathophysiology of transient middle cerebral artery occlusion-induced brain damage, and that neuroprotection afforded by estrogen is coincident with a re-establishment of anandamide levels in the ischemic striatum through a mechanism that needs to be investigated further.

Differential modulation of type 1 and type 2 cannabinoid receptors along the neuroimmune axis

Endocannabinoid-signaling chains have been implicated in a variety of pathophysiological functions, including memory, coordination, vasoregulation, reproduction, neurodegeneration, and inflammation. These activities were thought to be mediated by the activation of two G-protein-coupled receptors (GPCRs), type 1 and type 2 cannabinoid receptors (CB(1)R and CB(2)R). These two CBR subtypes share common agonists and trigger similar signaling pathways, yet they present several important differences in structure and cell distribution. In particular, recent research has shown that the CB(1)R and CB(2)R are differentially linked to lipid rafts, specialized microdomains of the plasma membrane involved in the signaling of many other GPCRs. We present an overview of the current literature on the effects that lipid raft perturbation have on CBRs activities, and provide a mechanistic model to interpret these data in terms of structural and functional aspects. These findings may also have important implications for the development of new therapeutic approaches, including lipid raft perturbing drugs, aimed to selectively modulate CB(1)R signaling in a variety of pathological conditions.

Human adipose tissue binds and metabolizes the endocannabinoids anandamide and 2-arachidonoylglycerol

Endocannabinoids are a group of biologically active endogenous lipids that have recently emerged as important mediators in energy balance control. The two best studied endocannabinoids, anandamide (N-arachidonoylethanolamine, AEA) and 2-arachidonoylglycerol (2-AG) are the endogenous ligands of the central and peripheral cannabinoid receptors. Furthermore, AEA binds to the transient receptor potential vanilloid type-1 (TRPV1), a capsaicin-sensitive, non-selective cation channel. The synthesis of these endocannabinoids is catalyzed by the N-acylphosphatidylethanolamine-selective phospholipase D (NAPE-PLD) and the sn-1-selective diacylglycerol lipase (DAGL), whereas their degradation is accomplished by the fatty acid amide hydrolase (FAAH) and the monoglyceride lipase (MGL), respectively. We investigated the presence of a functional endocannabinoid system in human adipose tissue from seven healthy subjects. Subcutaneous abdominal adipose tissue underwent biochemical and molecular biology analyses, aimed at testing the expression of this system and its functional activity. AEA and 2-AG levels were detected and quantified by HPLC. Real time PCR analyzed the expression of the endocannabinoid system and immunofluorescence assays showed the distribution of its components in the adipose tissue. Furthermore, binding assay for the cannabinoid and vanilloid receptors and activity assay for each metabolic enzyme of the endocannabinoid system gave clear evidence of a fully operating system. The data presented herein show for the first time that the human adipose tissue is able to bind AEA and 2-AG and that it is endowed with the biochemical machinery to metabolize endocannabinoids.

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.