Endocannabinoids, hormone-cytokine networks and human fertility

(Endo)Cannabinoids and Gynaecological Cancers

Gynaecological cancers can be primary neoplasms, originating either from the reproductive tract or the products of conception, or secondary neoplasms, representative of metastatic disease. For some of these cancers, the exact causes are unknown; however, it is recognised that the precise aetiopathogeneses for most are multifactorial and include exogenous (such as diet) and endogenous factors (such as genetic predisposition), which mutually interact in a complex manner. One factor that has been recognised to be involved in the pathogenesis and progression of gynaecological cancers is the endocannabinoid system (ECS). The ECS consists of endocannabinoids (bioactive lipids), their receptors, and metabolic enzymes responsible for their synthesis and degradation. In this review, the impact of plant-derived (Cannabis species) cannabinoids and endocannabinoids on gynaecological cancers will be discussed within the context of the complexity of the proteins that bind, transport, and metabolise these compounds in reproductive and other tissues. In particular, the potential of endocannabinoids, their receptors, and metabolic enzymes as biomarkers of specific cancers, such as those of the endometrium, will be addressed. Additionally, the therapeutic potential of targeting selected elements of the ECS as new action points for the development of innovative drugs will be presented.

The Role of Endocannabinoid System Based on mRNA Expression During the Late Luteal Phase and Estrus in the Bovine Endometrium

There are several findings indicating that the endocannabinoid system (ECS) is an important factor, acting in multiple ways in regulating reproductive function but changes of this system in the bovine endometrium have rarely been investigated; therefore, this study was designed to consider an association between endometrial ECS expression and different stages of the estrous cycles. MRNA expressions of the ECS were investigated during the late luteal phase and estrus using real-time PCR. Following estrous synchronization of sixteen Holstein dairy cows (34±1.3 kg/day of milk production), using two PGF2α injections given 14 days apart, at 30 and 44 days in milk (DIM), blood samples and ultrasonography (US) were performed every other day from the day of second PGF2α injection (44 DIM) until the start of the next estrous cycle (67±2 DIM) to verify CL development and ovulation. Based on blood and US results endometrial tissue was collected on days 16 (late luteal phase) and 21 (estrus) of the synchronized estrous cycle (ovulation = d 0). Real-time PCR analysis of ECS mRNA expression revealed endocannabinoid receptor (CNR2), diacylglycerol lipase (DAGL), cyclooxygenase-2 (COX-2), fatty acid amide hydrolase (FAAH) and monoglyceride lipase (MGLL) had significant fold differences when comparing two different stages of the estrous cycle (late luteal phase vs. estrus). CNR2 and DAGL showed 2.01 and 2.57 fold increase, respectively (P=0.04 and P=0.02), in estrous cows. Among the analyzed genes FAAH (P=0.01) and MGLL (P=0.02) were significantly down-regulated in estrous cows, with a 5.01- and 2.44-fold difference in mRNA expression, respectively. Overall, this study highlights an association between the expression of the ECS in the bovine endometrium and stage of the estrous cycle.

The enigma of embryonic diapause

Embryonic diapause – a period of embryonic suspension at the blastocyst stage – is a fascinating phenomenon that occurs in over 130 species of mammals, ranging from bears and badgers to mice and marsupials. It might even occur in humans. During diapause, there is minimal cell division and greatly reduced metabolism, and development is put on hold. Yet there are no ill effects for the pregnancy when it eventually continues. Multiple factors can induce diapause, including seasonal supplies of food, temperature, photoperiod and lactation. The successful reactivation and continuation of pregnancy then requires a viable embryo, a receptive uterus and effective molecular communication between the two. But how do the blastocysts survive and remain viable during this period of time, which can be up to a year in some cases? And what are the signals that bring it out of suspended animation? Here, we provide an overview of the process of diapause and address these questions, focussing on recent molecular data.

[Influence of metanandamide on steroidogenesis in rat adrenocorticocytes in vitro]

It is known from literature about antioxidant, anti-inflammatory, membrane protective and adreniregulatory properties of N-acetylethanolamines, but data concerning their participation in regulation of steroidogenesis are insufficient. In order to study the influence of a synthetic analogue of endogenous canabinoid anandamide - metanandamide - on the intensity of steroidogenesis the influence of different concentrations of the drug on the contents of 11-hydroxicorticosteroides (11-HCS) in the culture medium after incubation of adrenal tissue in rats of both sexes was investigated. The quantitative determination of 11-HCS was conducted by fluorometric micromethod. It was shown that the incubation of tissue sections with metanandamide leads to a reduction of 11-HCS in males and an increase of their content in females. It was concluded that the inhibition of corticosteroid secretion and synthesis in males may be due to reduction of cAMP and inhibition of cAMP-dependent protein kinase A (PKA) under the effect of metanandamide. The opposite and dose-dependent effects of the preparation in females may be connected with the estrogen influence on the mechanisms of drug effect realization.

Inhibition of Fatty Acid Amidohydrolase, the Enzyme Responsible for the Metabolism of the Endocannabinoid Anandamide, by Analogues of Arachidonoyl-serotonin

Arachidonoyl-serotonin inhibits in a mixed-type manner the metabolism of the endocannabinoid anandamide by the enzyme fatty acid amidohydrolase. In the present study, compounds related to arachidonoyl-serotonin have been synthesised and investigated for their ability to inhibit anandamide hydrolysis by this enzyme in rat brain homogenates. Removal of the 5-hydroxy from the serotonin head group of arachidonoyl-serotonin produced a compound (N-arachidonoyltryptamine) that was a 2.3-fold weaker inhibitor of anandamide hydrolysis, but which also produced its inhibition by a mixed-type manner (Ki(slope) 1.3 microM; Ki(intercept) 44 microM). Replacement of the amide linkage in this compound by an ester group further reduced the potency. In contrast, replacement of the arachidonoyl side chain by a linolenoyl side chain did not affect the observed potency. N-(Fur-3-ylmethyl) arachidonamide (UCM707), N-(fur-3-ylmethyl)linolenamide and N-(fur-3-ylmethyl)oleamide inhibited anandamide hydrolysis with pI50 values of 4.53, 5.36 and 5.25, respectively. The linolenamide derivative was also found to be a mixed-type inhibitor. It is concluded that the 5-hydroxy group of arachidonoyl-serotonin contributes to, but is not essential for, inhibitory potency at fatty acid amidohydrolase.

The endocannabinoid system and sex steroid hormone-dependent cancers

The "endocannabinoid system (ECS)" comprises the endocannabinoids, the enzymes that regulate their synthesis and degradation, the prototypical cannabinoid receptors (CB1 and CB2), some noncannabinoid receptors, and an, as yet, uncharacterised transport system. Recent evidence suggests that both cannabinoid receptors are present in sex steroid hormone-dependent cancer tissues and potentially play an important role in those malignancies. Sex steroid hormones regulate the endocannabinoid system and the endocannabinoids prevent tumour development through putative protective mechanisms that prevent cell growth and migration, suggesting an important role for endocannabinoids in the regulation of sex hormone-dependent tumours and metastasis. Here, the role of the endocannabinoid system in sex steroid hormone-dependent cancers is described and the potential for novel therapies assessed.

Differences in the endocannabinoid system of sperm from fertile and infertile men

Male infertility is a major cause of problems for many couples in conceiving a child. Recently, lifestyle pastimes such as alcohol, tobacco and marijuana have been shown to have further negative effects on male reproduction. The endocannabinoid system (ECS), mainly through the action of anandamide (AEA) and 2-arachidonoylglycerol (2-AG) at cannabinoid (CB₁, CB₂) and vanilloid (TRPV1) receptors, plays a crucial role in controlling functionality of sperm, with a clear impact on male reproductive potential. Here, sperm from fertile and infertile men were used to investigate content (through LC-ESI-MS), mRNA (through quantitative RT-PCR), protein (through Western Blotting and ELISA) expression, and functionality (through activity and binding assays) of the main metabolic enzymes of AEA and 2-AG (NAPE-PLD and FAAH, for AEA; DAGL and MAGL for 2-AG), as well as of their binding receptors CB₁, CB₂ and TRPV1. Our findings show a marked reduction of AEA and 2-AG content in infertile seminal plasma, paralleled by increased degradation: biosynthesis ratios of both substances in sperm from infertile versus fertile men. In addition, TRPV1 binding was detected in fertile sperm but was undetectable in infertile sperm, whereas that of CB₁ and CB₂ receptors was not statistically different in the two groups. In conclusion, this study identified unprecedented alterations of the ECS in infertile sperm, that might impact on capacitation and acrosome reaction, and hence fertilization outcomes. These alterations might also point to new biomarkers to determine male reproductive defects, and identify distinct ECS elements as novel targets for therapeutic exploitation of ECS-oriented drugs to treat male fertility problems.

The role of sex steroid hormones, cytokines and the endocannabinoid system in female fertility

BACKGROUND

Marijuana, the most used recreational drug, has been shown to have adverse effects on human reproduction. Endogenous cannabinoids (also called endocannabinoids) bind to the same receptors as those of Δ(9)-tetrahydrocannabinol (THC), the psychoactive component of Cannabis sativa. The most extensively studied endocannabinoids are anandamide (N-arachidonoylethanolamine, AEA) and 2-arachidonoylglycerol. The endocannabinoids, their congeners and the cannabinoid receptors, together with the metabolic enzymes and putative transporters form the endocannabinoid system (ECS). In this review, we summarize current knowledge about the relationships of ECS, sex steroid hormones and cytokines in female fertility, and underline the importance of this endocannabinoid-hormone-cytokine network.

METHODS

Pubmed and the Web of Science databases were searched for studies published since 1985, looking into the ECS, sex hormones, type-1/2 T-helper (Th1/Th2) cytokines, leukaemia inhibitory factor, leptin and reproduction.

RESULTS

The ECS plays a pivotal role in human reproduction. The enzymes involved in the synthesis and degradation of endocannabinoids normalize levels of AEA for successful implantation. The AEA degrading enzyme (fatty acid amide hydrolase) activity as well as AEA content in blood may potentially be used for the monitoring of early pregnancies. Progesterone and oestrogen are involved in the maintenance of endocannabinoid levels. The ECS plays an important role in the immune regulation of human fertility.

CONCLUSIONS

The available studies suggest that tight control of the endocannabinoid-hormone-cytokine network is required for successful implantation and early pregnancy maintenance. This hormone-cytokine network is a key element at the maternal-foetal interface, and any defect in such a network may result in foetal loss.

Effects of endocannabinoid 1 and 2 (CB1; CB2) receptor agonists on luteal weight, circulating progesterone, luteal mRNA for luteinizing hormone (LH) receptors, and luteal unoccupied and occupied receptors for LH in vivo in ewes

Thirty to forty percent of ruminant pregnancies are lost during the first third of gestation due to inadequate progesterone secretion. During the estrous cycle, luteinizing hormone (LH) regulates progesterone secretion by small luteal cells (SLC). Loss of luteal progesterone secretion during the estrous cycle is increased via uterine secretion of prostaglandin F(2α) (PGF(2α)) starting on days 12-13 post-estrus in ewes with up to 4-6 pulses per day. Prostaglandin F(2α) is synthesized from arachidonic acid, which is released from phospholipids by phospholipase A2. Endocannabinoids are also derived from phospholipids and are associated with infertility. Endocannabinoid-induced infertility has been postulated to occur primarily via negative effects on implantation. Cannabinoid (CB) type 1 (CB1) or type 2 (CB2) receptor agonists and an inhibitor of the enzyme fatty acid amide hydrolase, which catabolizes endocannabinoids, decreased luteal progesterone, prostaglandin E (PGE), and prostaglandin F(2α) (PGF(2α)) secretion by the bovine corpus luteum in vitro by 30 percent. The objective of the experiment described herein was to determine whether CB1 or CB2 receptor agonists given in vivo affect circulating progesterone, luteal weights, luteal mRNA for LH receptors, and luteal occupied and unoccupied LH receptors during the estrous cycle of ewes. Treatments were: Vehicle, Methanandamide (CB1 agonist; METH), or 1-(4-chlorobenzoyl)-5-methoxy-1H-indole-3-acetic acid morpholineamide (CB2 agonist; IMMA). Ewes received randomized treatments on day 10 post-estrus. A single treatment (500 μg; N=5/treatment group) in a volume of 1 ml was given into the interstitial tissue of the ovarian vascular pedicle adjacent to the luteal-containing ovary. Jugular venous blood was collected at 0 h and every 6-48 h for the analysis of progesterone by radioimmunoassay (RIA). Corpora lutea were collected at 48 h, weighed, bisected, and frozen in liquid nitrogen until analysis of unoccupied and occupied LH receptors and mRNA for LH receptors. Profiles of jugular venous progesterone, luteal weights, luteal mRNA for LH receptors, and luteal occupied and unoccupied LH receptors were decreased (P≤0.05) by CB1 or CB2 receptor agonists when compared to Vehicle controls. Progesterone in 80 percent of CB1 or CB2 receptor agonist-treated ewes was decreased (P≤0.05) below 1 ng/ml by 48 h post-treatment. It is concluded that the stimulation of either CB1 or CB2 receptors in vivo affected negatively luteal progesterone secretion by decreasing luteal mRNA for LH receptors and also decreasing occupied and unoccupied receptors for LH on luteal membranes. The corpus luteum may be an important site for endocannabinoids to decrease fertility as well as negatively affect implantation, since progesterone is required for implantation.

Cannabinoids, endocannabinoids, and related analogs in inflammation

This review covers reports published in the last 5 years on the anti-inflammatory activities of all classes of cannabinoids, including phytocannabinoids such as tetrahydrocannabinol and cannabidiol, synthetic analogs such as ajulemic acid and nabilone, the endogenous cannabinoids anandamide and related compounds, namely, the elmiric acids, and finally, noncannabinoid components of Cannabis that show anti-inflammatory action. It is intended to be an update on the topic of the involvement of cannabinoids in the process of inflammation. A possible mechanism for these actions is suggested involving increased production of eicosanoids that promote the resolution of inflammation. This differentiates these cannabinoids from cyclooxygenase-2 inhibitors that suppress the synthesis of eicosanoids that promote the induction of the inflammatory process.

Nuclear localisation of the endocannabinoid metabolizing enzyme fatty acid amide hydrolase (FAAH) in invasive trophoblasts and an association with recurrent miscarriage

Endocannabinoids are lipid signalling molecules that are related to the major psychoactive component in marijuana, delta-9-tetrahydrocannabinol and are increasingly recognized as being important in implantation and development of early embryos. The endocannabinoid anandamide, is metabolized by the enzyme fatty acid amide hydrolase (FAAH), and insufficient levels of this enzyme have been implicated in spontaneous miscarriage in women and implantation failure in mice. We screened placental bed biopsies and placental tissue from 45 women with recurrent miscarriage and 17 gestation-matched women with normal pregnancies for the expression of FAAH by immunohistochemistry. Unexpectedly, the enzyme appeared to be localised to the nucleus of trophoblasts and this was confirmed by western blotting of sub-cellular fractions and confocal microscopy. FAAH was expressed in the cytoplasm of large decidual stromal cells and significantly more women with recurrent miscarriage (73%) expressed FAAH in these cells than women with normal pregnancy (31%). FAAH was also expressed in the nucleus of extravillous trophoblasts that had invaded the decidua from 67% of women with recurrent miscarriage but was not expressed by these cells in any women with normal pregnancies. In contrast, FAAH was expressed in extravillous trophoblasts that had migrated out of the villi but that had not yet invaded the decidua in both normal pregnancies and in cases of recurrent miscarriage. FAAH was also present in the nucleus of a small number of villous trophoblasts in some specimens. FAAH appears to be over expressed in trophoblasts that have invaded the decidua, as well as in large decidual stromal cells in many cases of recurrent miscarriage. This may reflect inadequate control of the cannabinoid system in the uterus of women who experience recurrent miscarriages. The functional significance of the unexpected nuclear localisation of FAAH in trophoblasts is not yet clear.

A COX-2 metabolite of the endogenous cannabinoid, 2-arachidonyl glycerol, mediates suppression of IL-2 secretion in activated Jurkat T cells

Previous studies from this laboratory have demonstrated that a COX-2 metabolite of the endogenous cannabinoid, 2-arachidonyl glycerol (2-AG), inhibits IL-2 secretion in activated T cells through PPARgamma activation independent of the cannabinoid receptors, CB1/CB2. Because numerous cyclooxygenase (COX) products have been shown to activate PPARgamma, the primary purpose of the present studies was to determine the role of COX metabolism in the inhibition of IL-2 secretion by 2-AG. Pretreatment with nonselective and COX-2-specific inhibitors completely abrogated 2-AG-mediated suppression of IL-2 secretion. In contrast, pretreatment with COX-1-specific inhibitors had no effect upon 2-AG-mediated inhibition of IL-2 secretion. Interestingly, the current studies also demonstrate that while the potency of 2-AG is comparable between human Jurkat T cells and murine splenocytes, anandamide (AEA) is markedly more potent in suppressing IL-2 production in Jurkat T cells compared to murine splenocytes. Additionally, the present studies also demonstrate that COX-2 protein is readily detectable in resting Jurkat T cells, which is in contrast to resting murine splenocytes in which COX-2 protein is virtually undetectable. Furthermore, COX-2 protein and mRNA levels are significantly increased over basal levels by 2h following activation of Jurkat cells, whereas increases in COX-2 protein in murine splenocytes are not observed until 4h after cellular activation. These studies suggest that the potency of AEA in the suppression of IL-2 secretion may correlate with COX-2 protein levels in different T cell models. The present studies are also significant in that they demonstrate 2-AG-mediated inhibition of IL-2 secretion is dependent upon COX-2 metabolism.

The cannabinoid system and male reproductive functions

Cannabinoids, the main active components of marijuana, have been shown to exert different adverse effects on male reproduction both in vertebrates and invertebrates. In vivo, cannabinoids exert negative effects on hypothalamic-hypophyseal reproductive hormone secretion and testicular endocrine and exocrine functions. Furthermore, a large amount of experimental data obtained in vitro have clearly shown that cannabinoids negatively influence important sperm functions, including motility and acrosome reaction, two fundamental processes necessary for oocyte fertilisation. These inhibitory effects are mediated by the direct action of cannabinoids on sperm through the activation of the cannabinoid receptor subtype CNR1 that has been shown to be expressed in mature sperm. In the present paper, we briefly review the effects of cannabinoids and endocannabinoids, a particular group of endogenously produced cannabinoids, on male reproductive function.

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.

The endocannabinoid system in vertebrate male reproduction: a comparative overview

Prevailing studies emphasize on endocannabinoid activity in brain. However, sporadic evidences hint that endocannabinoid system controls male reproduction ranging from invertebrates to vertebrates. Although N-arachidonoylethanolamine is described in rat testis, its activity is still poorly known. Type-1 cannabinoid receptor and fatty acid amide hydrolase are particularly expressed in elongating spermatids and spermatozoa suggesting that endocannabinoids affect spermiogenesis and sperm physiology. Aim of this paper is to provide an analysis of the information available in vertebrates on male germ cell progression and sperm maturation mediated by the endocannabinoid system.

Augmentation of endogenous cannabinoid tone modulates lipopolysaccharide-induced alterations in circulating cytokine levels in rats

The endogenous cannabinoid system plays an important role in regulating the immune system. Modulation of endogenous cannabinoids represents an attractive alternative for the treatment of inflammatory disorders. This study investigated the effects of URB597, a selective inhibitor of fatty acid amide hydrolase (FAAH), the enzyme catalysing degradation of the endogenous cannabinoid anandamide, and AM404, an inhibitor of anandamide transport, on lipopolysaccharide (LPS)-induced increases in plasma cytokine levels in rats. Both URB597 and AM404 potentiated the LPS-induced increase in plasma tumour necrosis factor-alpha (TNF-alpha) levels. The peroxisome proliferator-activated receptor gamma (PPARgamma) antagonist, GW9662, attenuated the AM404-induced augmentation of TNF-alpha levels. Furthermore, the selective cannabinoid CB1 and CB2 receptor antagonists, AM251 and AM630 respectively, and the transient receptor potential vanilloid receptor-1 (TRPV1) antagonist, SB366791, reduced LPS-induced TNF-alpha plasma levels both alone and in combination with AM404. In contrast, AM404 inhibited LPS-induced increases in circulating interleukin-1beta (IL-1beta) and IL-6. AM251 attenuated the immunosuppressive effect of AM404 on IL-1beta. None of the antagonists altered the effect of AM404 on LPS-induced IL-6. Moreover, AM251, AM630 and SB366791, administered alone, inhibited LPS-induced increases in plasma IL-1beta and IL-6 levels. In conclusion, inhibition of endocannabinoid degradation or transport in vivo potentiates LPS-induced increases in circulating TNF-alpha levels, an effect which may be mediated by PPARgamma and is also reduced by pharmacological blockade of CB1, CB2 and TRPV1. The immunosuppressive effect of AM404 on IL-1beta levels is mediated by the cannabinoid CB1 receptor. Improved understanding of endocannabinoid-mediated regulation of immune function has fundamental physiological and potential therapeutic significance.

Effect of anandamide on erythrocyte survival

The endocannabinoid anandamide (Arachidonylethanolamide, AEA) is known to induce apoptosis in a wide variety of nucleated cells. The present study explored whether anandamide induces suicidal death of erythrocytes or eryptosis, which is characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine exposure at the erythrocyte surface. Eryptotic cells are phagocytosed and thus cleared from circulating blood. Triggers of eryptosis include increase of cytosolic Ca2+ activity, formation of PGE(2), oxidative stress and excessive cell shrinkage. Erythrocyte Ca2+ activity was estimated from Fluo3 fluorescence, phosphatidylserine exposure from annexin V binding, and erythrocyte volume from forward scatter in FACS analysis. Exposure of erythrocytes to anandamide (= 2.5 microM) increased cytosolic Ca2+ activity, enhanced the percentage of annexin V binding erythrocytes and decreased erythrocyte forward scatter, effects significantly blunted in the presence of cycloxygenase inhibitors acetylsalicylic acid (50 microM) or ibuprofen (100 microM) and in the nominal absence of extracellular Ca2+. Anandamide further enhanced the stimulating effects of hypertonic (addition of 550 mM sucrose) or isotonic (isosmotic replacement of Cl- with gluconate) cell shrinkage on annexin V binding. The present observations demonstrate that anandamide increases cytosolic Ca2+ activity, thus leading to cell shrinkage and cell membrane scrambling of mature erythrocytes.

The orphan receptor GPR55 is a novel cannabinoid receptor

BACKGROUND

The endocannabinoid system functions through two well characterized receptor systems, the CB1 and CB2 receptors. Work by a number of groups in recent years has provided evidence that the system is more complicated and additional receptor types should exist to explain ligand activity in a number of physiological processes.

EXPERIMENTAL APPROACH

Cells transfected with the human cDNA for GPR55 were tested for their ability to bind and to mediate GTPgammaS binding by cannabinoid ligands. Using an antibody and peptide blocking approach, the nature of the G-protein coupling was determined and further demonstrated by measuring activity of downstream signalling pathways.

KEY RESULTS

We demonstrate that GPR55 binds to and is activated by the cannabinoid ligand CP55940. In addition endocannabinoids including anandamide and virodhamine activate GTPgammaS binding via GPR55 with nM potencies. Ligands such as cannabidiol and abnormal cannabidiol which exhibit no CB1 or CB2 activity and are believed to function at a novel cannabinoid receptor, also showed activity at GPR55. GPR55 couples to Galpha13 and can mediate activation of rhoA, cdc42 and rac1.

CONCLUSIONS

These data suggest that GPR55 is a novel cannabinoid receptor, and its ligand profile with respect to CB1 and CB2 described here will permit delineation of its physiological function(s).

Endocannabinoid control of sperm motility: the role of epididymus

Endocannabinoids are endogenous ligands for plasma membrane receptors (CB1 and CB2), belonging to the superfamily of G-protein-coupled receptors. They mimic some of the effects played by D9-tetrahydrocannabinol (THC), the active principle isolated from Cannabis sativa. N-arachidonoylethanolamine (anandamide, AEA) is the main endocannabinoid described to date in the testis and in human seminal plasma. However, the activity of AEA in controlling male reproduction is still poorly understood. In this study we report on physiological activity of endocannabinoids in the male reproductive tract. Using wild type (WT) and CB1 knock out mice (CB1KO) we show that endocannabinoids act in the epididymus. Here, through CB1, they inhibit sperm motility measured as the percentage of motile spermatozoa (SPZ). In particular, while in WT mice, as expected, the percentage of motile SPZ (measured in caput and cauda of epididymus) was significantly lower in the caput as compared with the cauda, in CB1KO mice a strong increase of motile SPZ in the caput was measured.

The role of the endocannabinoid system in gametogenesis, implantation and early pregnancy

Maternal use of marijuana, in which the exocannabinoid Delta(9)-tetrahydrocannabinol is the most active psychoactive ingredient, is known to have adverse effects on various aspects of reproduction including ovulation, spermatogenesis, implantation and pregnancy duration. Endogenous cannabinoids of which Anandamide is the prototype are widely distributed in the body especially in the reproductive tract and pregnancy tissues and act through the same receptors as the receptor as Delta(9)-tetrahydrocannabinol. Anandamide, has been reported to have pleiotropic effects on human reproduction and in experimental animal models. It appears to be the important neuro-cytokine mediator synchronizing the embryo-endometrial development for timed implantation, the development of the embryo into the blastocyst and transport of the embryo across the fallopian tubes. The mechanisms by which it exerts these effects are unclear but could be via direct actions on the various sites within the reproductive system or its differential actions on vascular tone dependent. In this review article we bring together the current knowledge on the role of endoccanabinoids in reproduction and postulate on the potential mechanisms on how these affect reproduction. In addition, we examine its role on the endothelium and vascular smooth muscle as a potential mechanism for adverse pregnancy outcome.

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.

Endocannabinoid System in Frog and Rodent Testis: Type-1 Cannabinoid Receptor and Fatty Acid Amide Hydrolase Activity in Male Germ Cells1

N-arachidonoylethanolamide (anandamide [AEA]) is the main endocannabinoid described to date in the testis. It exerts its effects through the activation of G-protein coupled cannabinoid receptors (CNR). However, the activity of AEA in controlling male reproduction is still poorly known. Here we provide direct evidence on the presence of the "endocannabinoid system," constituted by type-1 cannabinoid receptor (CNR1) and fatty acid amide hydrolase (FAAH), in the frog Rana esculenta testis demonstrating its expression in tubular compartment. In fact, during the annual reproductive cycle, both proteins increase in September, when the appearance of spermatids (SPT) occurs. Immunocytochemistry confirms their localization in germ cells and, in particular, in elongated SPT. Signals are still present in spermatozoa (SPZ), as demonstrated by Western blot analysis. Furthermore, the activation of CNR1 reduces sperm motility. Comparative research, carried out using mouse and rat SPZ, definitely indicates that the endocannabinoid system operates in SPZ of phylogenetically distant species. A conserved physiological role of endocannabinoid system in controlling the inhibition of sperm motility is suggested.

The emerging role of the endocannabinoid system in endocrine regulation and energy balance

During the last few years, the endocannabinoid system has emerged as a highly relevant topic in the scientific community. Many different regulatory actions have been attributed to endocannabinoids, and their involvement in several pathophysiological conditions is under intense scrutiny. Cannabinoid receptors, named CB1 receptor and CB2 receptor, first discovered as the molecular targets of the psychotropic component of the plant Cannabis sativa, participate in the physiological modulation of many central and peripheral functions. CB2 receptor is mainly expressed in immune cells, whereas CB1 receptor is the most abundant G protein-coupled receptor expressed in the brain. CB1 receptor is expressed in the hypothalamus and the pituitary gland, and its activation is known to modulate all the endocrine hypothalamic-peripheral endocrine axes. An increasing amount of data highlights the role of the system in the stress response by influencing the hypothalamic-pituitary-adrenal axis and in the control of reproduction by modifying gonadotropin release, fertility, and sexual behavior. The ability of the endocannabinoid system to control appetite, food intake, and energy balance has recently received great attention, particularly in the light of the different modes of action underlying these functions. The endocannabinoid system modulates rewarding properties of food by acting at specific mesolimbic areas in the brain. In the hypothalamus, CB1 receptor and endocannabinoids are integrated components of the networks controlling appetite and food intake. Interestingly, the endocannabinoid system was recently shown to control metabolic functions by acting on peripheral tissues, such as adipocytes, hepatocytes, the gastrointestinal tract, and, possibly, skeletal muscle. The relevance of the system is further strenghtened by the notion that drugs interfering with the activity of the endocannabinoid system are considered as promising candidates for the treatment of various diseases, including obesity.

Effects of cannabinoids on hypothalamic and reproductive function

Marijuana and cannabinoids have been shown to exert profound effects on hypothalamic regulatory functions and reproduction in both experimental animals and humans. Here we review the role of (endo)cannabinoids in the regulation of appetite and food intake. There is converging evidence that the hypothalamic endocannabinoid system changes after leptin treatment. Cannabinoid administration decreases heat production by altering hypothalamic neurotransmitter production. Experimental and human data have also shown that the endocannabinoid system is involved in the regulation of reproductive function at both central and peripheral levels. We discuss also the role of fatty acid amide hydrolase (FAAH) in gestation, and in particular the regulation of the activity of FAAH by progesterone and leptin. We show that endocannabinoids inhibit the release of leukaemia inhibitory factor (LIF) from peripheral T lymphocytes. Taken together, endocannabinoids not only help to maintain neuroendocrine homeostasis, but also take part in immunological changes occurring during early pregnancy.

Up-regulation of the endocannabinoid system in the uterus of leptin knockout (ob/ob) mice and implications for fertility

The levels of the endocannabinoids anandamide and 2-arachidonoylglycerol (2-AG) are under the negative control of leptin in the rodent hypothalamus. As leptin and endocannabinoids play opposite roles in the control of reproduction, we have investigated whether the impaired fertility typical of leptin-defective ob/ob mice is due, in part, to enhanced uterine endocannabinoid levels. We found that levels of both anandamide and 2-AG in the uterus of ob/ob mice are significantly elevated with respect to wild-type littermates, due to reduced hydrolase activity in the case of anandamide, and to reduced monoacylglycerol lipase and enhanced diacylglycerol lipase activity in the case of 2-AG. Furthermore, the process mediating endocannabinoid cellular uptake was also impaired in ob/ob mice, whereas the levels of cannabinoid and anandamide receptors were not modified. Although ineffective in wild-type mice, treatment of ob/ob mice with leptin re-established endocannabinoid levels and enzyme activities back to the values observed in wild-type littermates. Finally, treatment of ob/ob females with the CB1 receptor antagonist SR141716A did not improve their fertility, and inhibition of endocannabinoid inactivation with the endocannabinoid uptake inhibitor OMDM-1 in wild-type females did not result in impaired fertility.

Characterization of the endocannabinoid system in early human pregnancy

In recent years, it has been demonstrated that high circulating levels of the endogenous cannabinoid anandamide, resulting from low expression of its metabolizing enzyme fatty acid amide hydrolase (FAAH), may contribute to spontaneous miscarriage and poor outcome in women undergoing in vitro fertilization. The site of action of this compound, however, has not been determined. In this study, we examined the distribution of the cannabinoid receptors, CB1 and CB2, and the endocannabinoid-metabolizing enzyme FAAH in first trimester human placenta. Here, we show that FAAH is expressed throughout the human first trimester placenta, in extravillous trophoblast columns, villous cytotrophoblasts, syncytiotrophoblasts, and macrophages. Furthermore, FAAH mRNA levels appear to be regulated during gestation, with levels peaking at 11 wk before declining again. The immune system-associated cannabinoid CB2 receptors were localized only to placental macrophages. Interestingly, the cannabinoid receptor CB1 was not identified in first trimester placenta despite having previously been shown to be present in placental tissues at term. These findings suggest that the placenta may form a barrier preventing maternal-fetal transfer of anandamide and/or modulate local levels of anandamide by regulation of FAAH expression with gestation.

The endocannabinoid-CB1 receptor system in pre- and postnatal life

Recent research suggests that the endogenous cannabinoids ("endocannabinoids") and their cannabinoid receptors have a major influence during pre- and postnatal development. First, high levels of the endocannaboid anandamide and cannabinoid receptors are present in the preimplantation embryo and in the uterus, while a temporary reduction of anandamide levels is essential for embryonal implantation. In women accordingly, an inverse association has been reported between fatty acid amide hydrolase (the anandamide degrading enzyme) in human lymphocytes and miscarriage. Second, CB(1) receptors display a transient presence in white matter areas of the pre- and postnatal nervous system, suggesting a role for CB(1) receptors in brain development. Third, endocannabinoids have been detected in maternal milk and activation of CB(1) receptors appears to be critical for milk sucking by newborn mice, apparently activating oral-motor musculature. Fourth, anandamide has neuroprotectant properties in the developing postnatal brain. Finally, prenatal exposure to the active constituent of marihuana (Delta(9)-tetrahydrocannabinol) or to anandamide affects prefrontal cortical functions, memory and motor and addictive behaviors, suggesting a role for the endocannabinoid CB(1) receptor system in the brain structures which control these functions. Further observations suggest that children may be less prone to psychoactive side effects of Delta(9)-tetrahydrocannabinol or endocannabinoids than adults. The medical implications of these novel developments are far reaching and suggest a promising future for cannabinoids in pediatric medicine for conditions including "non-organic failure-to-thrive" and cystic fibrosis.

Identification of the CB1 Cannabinoid Receptor and Fatty Acid Amide Hydrolase (FAAH) in the Human Placenta

Synthetic cannabinoids, the psychoactive components of the Cannabis sativa (marijuana) plant and their endogenous counterparts, act through two G protein-coupled receptors, CB1 and CB2. The endocannabinoids are metabolized by fatty acid amide hydrolase (FAAH). Previous research has described the impact of cannabis consumption on pregnancy, potential roles of endocannabinoids and abnormalities of FAAH expression in recurrent miscarriage and pregnancy. However, the cellular localization of the CB1 cannabinoid receptor and FAAH in the human placenta has not been determined. We have examined CB1 receptor and FAAH expression in human term placenta by immunohistochemistry. CB1 receptor was found to be present in all layers of the membrane, with particularly strong expression in the amniotic epithelium and reticular cells and cells of the maternal decidua layer. Moderate expression was observed in the chorionic cytotrophoblasts. The expression of FAAH was highest in the amniotic epithelial cells, chorionic cytotrophoblast and maternal decidua layer. Our results suggest that the human placenta is a likely target for cannabinoid action and metabolism. This is consistent with a placental site of action of endocannabinoids and cannabis being responsible, at least in part, for the poor outcomes associated with cannabis consumption and pathology in the endocannabinoid system during pregnancy.

Progesterone activates fatty acid amide hydrolase (FAAH) promoter in human T lymphocytes through the transcription factor Ikaros. Evidence for a synergistic effect of leptin

Physiological concentrations of progesterone stimulate the activity of the endocannabinoid-degrading enzyme fatty acid amide hydrolase (FAAH) in human T lymphocytes, up to a approximately 270% over the untreated controls. Stimulation of FAAH occurred through up-regulation of gene expression at transcriptional and translational level and was specific. Indeed, neither the activity of the anandamide-synthesizing N-acyltransferase and phospholipase D, nor the activity of the anandamide transporter, nor the binding to cannabinoid receptors were affected by progesterone under the same experimental conditions. The activation of FAAH by progesterone was paralleled by a decrease (down to 60%) of the cellular levels of anandamide and involved increased nuclear levels of the transcription factor Ikaros. Analysis of the FAAH promoter showed an Ikaros binding site, and mutation of this site prevented FAAH activation by progesterone in transient expression assays. Electrophoretic mobility shift and supershift assays further corroborated the promoter activity data. Furthermore, the effect of progesterone on FAAH promoter was additive to that of physiological amounts of leptin, which binds to a cAMP response element-like site in the promoter region. Taken together, these results suggest that progesterone and leptin, by up-regulating the FAAH promoter at different sites, enhance FAAH expression, thus tuning the immunomodulatory effects of anandamide. These findings might also have critical implications for human fertility.

Identification of the CB1 cannabinoid receptor and fatty acid amide hydrolase (FAAH) in the human placenta

Synthetic cannabinoids, the psychoactive components of the Cannabis sativa (marijuana) and their endogenous counterparts, act through two G protein-coupled receptors, CB1 and CB2. The endocannabinoids are metabolized by fatty acid amide hydrolase (FAAH). Previous research has described the impact of cannabis consumption on pregnancy, potential roles of endocannabinoids and abnormalities of FAAH expression in recurrent miscarriage and pregnancy. However, the cellular localization of the CB1 cannabinoid receptor and FAAH in the human placenta has not been determined. We have examined CB1 receptor and FAAH expression in human term placenta by immunohistochemistry. CB1 receptor was found to be present in all layers of the membrane, with particularly strong expression in the amniotic epithelium and reticular cells and cells of the maternal decidua layer. Moderate expression was observed in the chorionic cytotrophoblasts. The expression of FAAH was the highest in amniotic epithelial cells, chorionic cytotrophoblast and maternal decidua layer. Our results suggest that the human placenta is a likely target for cannabinoid action and metabolism. This is consistent with a placental site of action of endocannabinoids and cannabis being responsible, at least in part, for the poor outcomes associated with cannabis consumption and pathology in the endocannabinoid system during pregnancy.

Leptin activates the anandamide hydrolase promoter in human T lymphocytes through STAT3

Physiological concentrations of leptin stimulate the activity of the endocannabinoid-degrading enzyme anandamide hydrolase (fatty acid amide hydrolase, FAAH) in human T lymphocytes up to approximately 300% over the untreated controls. Stimulation of FAAH occurred through up-regulation of gene expression at transcriptional and translational levels and involved binding of leptin to its receptor with an apparent dissociation constant (K(d)) of 1.95 +/- 0.14 nm and maximum binding (B(max)) of 392 +/- 8 fmol x mg protein(-1). Leptin binding to the receptor triggered activation of STAT3 but not STAT1 or STAT5 or the mitogen-activated protein kinases p38, p42, and p44. Peripheral lymphocytes of leptin knock-out (ob/ob) mice showed decreased FAAH activity and expression (approximately 25% of the wild-type littermates), which were reversed to control levels by exogenous leptin. Analysis of the FAAH promoter showed a cAMP-response element-like site, which is a transcriptional target of STAT3. Consistently, mutation of this site prevented FAAH activation by leptin in transient expression assays. Electrophoretic mobility shift and supershift assays further corroborated the promoter activity data. Taken together, these results suggest that leptin, by up-regulating the FAAH promoter through STAT3, enhances FAAH expression, thus tuning the immunomodulatory effects of anandamide. These findings might also have critical implications for human fertility.

The enzymatic inactivation of the fatty acid amide class of signaling lipids

The fatty acid amide (FAA) class of signaling lipids modulates a number of neurobehavioral processes in mammals, including pain, sleep, feeding, and locomotor activity. Representative FAAs include the endogenous cannabinoid anandamide and the sleep-inducing lipid oleamide. Despite activating several neuroreceptor systems in vitro, most FAAs produce only weak and transient behavioral effects in vivo, presumably due to their expeditious catabolism. This review focuses on one enzyme, fatty acid amide hydrolase (FAAH) that appears to play a major role in regulating the amplitude and duration of FAA signals in vivo. In particular, we will highlight a series of recent papers that have investigated the physiological functions of the mouse and human FAAH enzymes. Collectively, these studies promote FAAH as a central component of FAA signaling pathways, especially those mediated by the endocannabinoid anandamide, and suggest that this enzyme may represent an attractive pharmaceutical target for the treatment of pain and related neurophysiological disorders.