Oxidative metabolism of endocannabinoids

Therapeutic applicability of cannabidiol and other phytocannabinoids in epilepsy, multiple sclerosis and Parkinson's disease and in comorbidity with psychiatric disorders

Studies have demonstrated the neuroprotective effect of cannabidiol (CBD) and other Cannabis sativa L. derivatives on diseases of the central nervous system caused by their direct or indirect interaction with endocannabinoid system-related receptors and other molecular targets, such as the 5-HT1A receptor, which is a potential pharmacological target of CBD. Interestingly, CBD binding with the 5-HT1A receptor may be suitable for the treatment of epilepsies, parkinsonian syndromes and amyotrophic lateral sclerosis, in which the 5-HT1A serotonergic receptor plays a key role. The aim of this review was to provide an overview of cannabinoid effects on neurological disorders, such as epilepsy, multiple sclerosis and Parkinson's diseases, and discuss their possible mechanism of action, highlighting interactions with molecular targets and the potential neuroprotective effects of phytocannabinoids. CBD has been shown to have significant therapeutic effects on epilepsy and Parkinson's disease, while nabiximols contribute to a reduction in spasticity and are a frequent option for the treatment of multiple sclerosis. Although there are multiple theories on the therapeutic potential of cannabinoids for neurological disorders, substantially greater progress in the search for strong scientific evidence of their pharmacological effectiveness is needed.

Aerobic Exercise and Endocannabinoids: A Narrative Review of Stress Regulation and Brain Reward Systems

Aerobic exercise is a widely adopted practice, not solely for enhancing fitness and reducing the risk of various diseases but also for its ability to uplift mood and aid in addressing depression and anxiety disorders. Within the scope of this narrative review, we seek to consolidate current insights into the endocannabinoid-mediated regulation of stress and the brain's reward mechanism resulting from engaging in aerobic exercise. A comprehensive search was conducted across Medline, SPORTDiscus, Pubmed, and Scopus, encompassing data available until November 30, 2023. This review indicates that a bout of aerobic exercise, particularly of moderate intensity, markedly augments circulating levels of endocannabinoids - N-arachidonoyl-ethanolamine (AEA) and 2-acylglycerol (2-AG), that significantly contributes to mood elevation and reducing stress in healthy individuals.  The current understanding of how aerobic exercise impacts mental health and mood improvement is still unclear. Moderate and high-intensity aerobic exercise modulates stress through a negative feedback mechanism targeting both the hypothalamus-pituitary-adrenal (HPA) axis and the sympathetic nervous system, thereby facilitating stress regulation crucial role in endocannabinoid synthesis, ultimately culminating in the orchestration of negative feedback across multiple tiers of the HPA axis, coupled with its influence over cortical and subcortical brain structures. The endocannabinoid has been observed to govern the release of neurotransmitters from diverse neuronal populations, implying a universal mechanism that fine-tunes neuronal activity and consequently modulates both emotional and stress-related responses. Endocannabinoids further assume a pivotal function within brain reward mechanisms, primarily mediated by CB1 receptors distributed across diverse cerebral centers. Notably, these endocannabinoids partake in natural reward processes, as exemplified in aerobic exercise, by synergizing with the dopaminergic reward system. The genesis of this reward pathway can be traced to the ventral tegmental area, with dopamine neurons predominantly projecting to the nucleus accumbens, thereby inciting dopamine release in response to rewarding stimuli.

New role for the anandamide metabolite prostaglandin F2α ethanolamide: Rolling preadipocyte proliferation

White adipose tissue regulation is key to metabolic health, yet still perplexing. The chief endocannabinoid anandamide metabolite, prostaglandin F2α ethanolamide (PGF2αEA), inhibits adipogenesis, that is, the formation of mature adipocytes. We observed that adipocyte progenitor cells-preadipocytes-following treatment with PGF2αEA yielded larger pellet sizes. Thus, we hypothesized that PGF2αEA might augment preadipocyte proliferation. Cell viability MTT and crystal violet assays, cell counting, and 5-bromo-2'-deoxyuridine incorporation in cell proliferation ELISA analyses confirmed our prediction. Additionally, we discovered that PGF2αEA promotes cell cycle progression through suppression of the expression of cell cycle inhibitors, p21 and p27, as shown by flow cytometry and qPCR. Enticingly, concentrations of this compound that showed no visible effect on cell proliferation or basal transcriptional activity of peroxisome proliferator-activated receptor gamma could, in contrast, reverse the anti-proliferative and peroxisome proliferator-activated receptor gamma-transcription activating effects of rosiglitazone (Rosi). MTT and luciferase reporter examinations supported this finding. The PGF2αEA pharmaceutical analog, bimatoprost, was also investigated and showed very similar effects. Importantly, we suggest the implication of the mitogen-activated protein kinase pathway in these effects, as they were blocked by the selective mitogen-activated protein kinase kinase inhibitor, PD98059. We propose that PGF2αEA is a pivotal regulator of white adipose tissue plasticity, acting as a regulator of the preadipocyte pool in adipose tissue.

AEC and AFMSC Transplantation Preserves Fertility of Experimentally Induced Rat Varicocele by Expressing Differential Regenerative Mechanisms

Amniotic membrane and amniotic fluid derived cells are regarded as a promising stem cell source for developing regenerative medicine techniques, although they have never been tested on male infertility diseases such as varicocele (VAR). The current study aimed to examine the effects of two distinct cell sources, human Amniotic Fluid Mesenchymal Stromal Cells (hAFMSCs) and amniotic epithelial cells (hAECs), on male fertility outcomes in a rat induced VAR model. To explain cell-dependent enhancement of reproductive outcomes in rats transplanted with hAECs and hAFMSCs, insights on testis morphology, endocannabinoid system (ECS) expression and inflammatory tissue response have been carried out alongside cell homing assessment. Both cell types survived 120 days post-transplantation by modulating the ECS main components, promoting proregenerative M2 macrophages (Mφ) recruitment and a favorable anti-inflammatory IL10 expression pattern. Of note, hAECs resulted to be more effective in restoring rat fertility rate by enhancing both structural and immunoresponse mechanisms. Moreover, immunofluorescence analysis revealed that hAECs contributed to CYP11A1 expression after transplantation, whereas hAFMSCs moved towards the expression of Sertoli cell marker, SOX9, confirming a different contribution into the mechanisms leading to testis homeostasis. These findings highlight, for the first time, a distinct role of amniotic membrane and amniotic fluid derived cells in male reproduction, thus proposing innovative targeted stem-based regenerative medicine protocols for remedying high-prevalence male infertility conditions such as VAR.

Endocannabinoid System and Exogenous Cannabinoids in Depression and Anxiety: A Review

Background: There is a growing liberalization of cannabis-based preparations for medical and recreational use. In multiple instances, anxiety and depression are cited as either a primary or a secondary reason for the use of cannabinoids. Aim: The purpose of this review is to explore the association between depression or anxiety and the dysregulation of the endogenous endocannabinoid system (ECS), as well as the use of phytocannabinoids and synthetic cannabinoids in the remediation of depression/anxiety symptoms. After a brief description of the constituents of cannabis, cannabinoid receptors and the endocannabinoid system, the most important evidence is presented for the involvement of cannabinoids in depression and anxiety both in human and from animal models of depression and anxiety. Finally, evidence is presented for the clinical use of cannabinoids to treat depression and anxiety. Conclusions: Although the common belief that cannabinoids, including cannabis, its main studied components-tetrahydrocannabinol (THC) and cannabidiol (CBD)-or other synthetic derivatives have been suggested to have a therapeutic role for certain mental health conditions, all recent systematic reviews that we report have concluded that the evidence that cannabinoids improve depressive and anxiety disorders is weak, of very-low-quality, and offers no guidance on the use of cannabinoids for mental health conditions within a regulatory framework. There is an urgent need for high-quality studies examining the effects of cannabinoids on mental disorders in general and depression/anxiety in particular, as well as the consequences of long-term use of these preparations due to possible risks such as addiction and even reversal of improvement.

Roles of the Cannabinoid System in the Basal Ganglia in Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative disease usually caused by neuroinflammation, oxidative stress and other etiologies. Recent studies have found that the cannabinoid system present in the basal ganglia has a strong influence on the progression of PD. Altering the cannabinoid receptor activation status by modulating endogenous cannabinoid (eCB) levels can exert an anti-movement disorder effect. Therefore, the development of drugs that modulate the endocannabinoid system may be a novel strategy for the treatment of PD. However, eCB regulation is complex, with diverse cannabinoid receptor functions and the presence of dopaminergic, glutamatergic, and γ-aminobutyric signals interacting with cannabinoid signaling in the basal ganglia region. Therefore, the study of eCB is challenging. Here, we have described the function of the cannabinoid system in the basal ganglia and its association with PD in three parts (eCBs, cannabinoid receptors, and factors regulating the cannabinoid metabolism) and summarized the mechanisms of action related to the cannabinoid analogs currently aimed at treating PD. The shortcomings identified from previous studies and the directions that should be explored in the future will provide insights into new approaches and ideas for the future development of cannabinoid-based drugs and the treatment of PD.

Nitric oxide positively affects endometrial receptivity via FAAH and NAPE-PLD in vitro

Objective

To determine if models of human 'receptive' and 'non-receptive endometrium' differ in their responses to nitric oxide (NO) supplementation by measuring the levels of the enzymes of the endocannabinoid system (ECS) (fatty acid amide hydrolase (FAAH) and N-acylphosphatidylethanolamine-specific phospholipase D (NAPE-PLD)), which control the 'anandamide tone' essential for successful pregnancy.

Design

A study of FAAH and NAPE-PLD expression (using human endometrium) through the menstrual cycle and an in vitro using a model of 'receptive' (Ishikawa) and 'non-receptive' (HEC-1A) human endometrial cell lines treated with the NO-donating compound S-nitroso-N-acetylpenicillamine (SNAP).

Results

Immunoreactivity measured by optimised H-score for both FAAH and NAPE-PLD was reduced in secretory (receptive) endometrium compared to proliferative (non-receptive) endometrium (P = 0.0009 and <0.0001, respectively). FAAH and NAPE transcript levels were significantly higher in untreated Ishikawa cells than in HEC-1A cells (P = 0.0228 and 0.0001, respectively). Treatment of cultures with SNAP resulted in an increase in the amount of FAAH mRNA produced by Ishikawa cells and a decrease in NAPE-PLD mRNA. No effect of SNAP was observed in HEC-1A cells. Similarly, FAAH protein was significantly decreased in endometria representative of the receptive endometrium.

Conclusion

These data suggest that NO most likely affects the expression of ECS enzymes in the implantation site of a receptive endometrium; a phenomenon not seen in a non-receptive endometrium. These effects are most marked with FAAH expression, suggesting that FAAH may play the more critical role in ensuring the correct 'anandamide tone' for successful embryo implantation than NAPE-PLD.

Lay summary

Embryo implantation into the wall of the uterus is only successful when the inner wall of the uterus (the endometrium) is 'receptive', because if it is 'non-receptive', implantation will fail. Previous work showed that enzymes of the 'endocannabinoid system' are critical for implantation by maintaining the correct level of a fat called anandamide. This is by balancing its synthesis (by N-acylphosphatidylethanolamine specific phospholipase D, NAPE-PLD) and degradation (by fatty acid amide hydrolase, FAAH). Using immortalised cell lines as models of 'receptive' and 'non-receptive' human endometrium, we demonstrate a key stimulator of implantation, nitric oxide, has a positive effect on implantation by both increasing the mRNA levels of the degrading enzyme (FAAH) and decreasing the expression of the synthesising enzyme (NAPE-PLD). These effects are most marked with the degrading enzyme, suggesting that FAAH plays a more critical role than NAPE-PLD in ensuring the correct 'anandamide tone' for successful embryo implantation.

Cannabinoids-A New Perspective in Adjuvant Therapy for Pulmonary Hypertension

Currently, no treatment can completely cure pulmonary hypertension (PH), which can lead to right ventricular failure and, consequently, death. Therefore, searching for new therapies remains important. Increased resistance in pulmonary circulation is mainly caused by the excessive contraction and proliferation of small pulmonary arteries. Cannabinoids, a group of lipophilic compounds that all interact with cannabinoid receptors, exert a pulmonary vasodilatory effect through several different mechanisms, including mechanisms that depend on vascular endothelium and/or receptor-based mechanisms, and may also have anti-proliferative and anti-inflammatory properties. The vasodilatory effect is important in regulating pulmonary resistance, which can improve patients’ quality of life. Moreover, experimental studies on the effects of cannabidiol (plant-derived, non-psychoactive cannabinoid) in animal PH models have shown that cannabidiol reduces right ventricular systolic pressure and excessive remodelling and decreases pulmonary vascular hypertrophy and pulmonary vascular resistance. Due to the potentially beneficial effects of cannabinoids on pulmonary circulation and PH, in this work, we review whether cannabinoids can be used as an adjunctive therapy for PH. However, clinical trials are still needed to recommend the use of cannabinoids in the treatment of PH.

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

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

Neuroprotective and Immunomodulatory Action of the Endocannabinoid System under Neuroinflammation

Endocannabinoids (eCBs) are lipid-based retrograde messengers with a relatively short half-life that are produced endogenously and, upon binding to the primary cannabinoid receptors CB_1/2, mediate multiple mechanisms of intercellular communication within the body. Endocannabinoid signaling is implicated in brain development, memory formation, learning, mood, anxiety, depression, feeding behavior, analgesia, and drug addiction. It is now recognized that the endocannabinoid system mediates not only neuronal communications but also governs the crosstalk between neurons, glia, and immune cells, and thus represents an important player within the neuroimmune interface. Generation of primary endocannabinoids is accompanied by the production of their congeners, the N-acylethanolamines (NAEs), which together with N-acylneurotransmitters, lipoamino acids and primary fatty acid amides comprise expanded endocannabinoid/endovanilloid signaling systems. Most of these compounds do not bind CB_1/2, but signal via several other pathways involving the transient receptor potential cation channel subfamily V member 1 (TRPV1), peroxisome proliferator-activated receptor (PPAR)-α and non-cannabinoid G-protein coupled receptors (GPRs) to mediate anti-inflammatory, immunomodulatory and neuroprotective activities. In vivo generation of the cannabinoid compounds is triggered by physiological and pathological stimuli and, specifically in the brain, mediates fine regulation of synaptic strength, neuroprotection, and resolution of neuroinflammation. Here, we review the role of the endocannabinoid system in intrinsic neuroprotective mechanisms and its therapeutic potential for the treatment of neuroinflammation and associated synaptopathy.

In it together? The case for endocannabinoid-noradrenergic interactions in fear extinction

Anxiety and trauma-related disorders, such as post-traumatic stress disorder (PTSD), are debilitating mental illnesses with great personal and socioeconomic costs. Examining memory formation and relevant behavioural responding associated with aversive stimuli may improve our understanding of the neurobiology underlying fear memory processing and PTSD treatment. The neurocircuitry underpinning learned fear and its inhibition through extinction is complex, involving synergistic interactions between different neurotransmitter systems in inter-connected brain areas. Endocannabinoid and noradrenergic transmission have both been implicated separately in fear memory processing and PTSD, but potential interactions between these systems in relation to fear extinction have received little attention to date. Their receptors are expressed together in brain areas crucial for fear extinction, which is enhanced by both cannabinoid and noradrenergic receptor activation in these areas. Moreover, cannabinoid signalling modulates the activity of locus coeruleus noradrenaline (NA) neurons and the release of NA in the medial prefrontal cortex, a brain area that is crucial for fear extinction. Interestingly, endocannabinoid-noradrenergic system interactions have been shown to regulate the encoding and retrieval of fear memory. Thus, noradrenergic regulation of fear extinction may also be driven indirectly in part via cannabinoid receptor signalling. In this perspective paper, we collate the available relevant literature and propose a synergistic role for the endocannabinoid and noradrenergic systems in regulating fear extinction, the study of which may further our understanding of the neurobiological substrates of PTSD and its treatment.

The rise and fall of anandamide: processes that control synthesis, degradation, and storage

Anandamide is an endocannabinoid derived from arachidonic acid-containing membrane lipids and has numerous biological functions. Its effects are primarily mediated by the cannabinoid receptors CB1 and CB2, and the vanilloid TRPV1 receptor. Anandamide is known to be involved in sleeping and eating patterns as well as pleasure enhancement and pain relief. This manuscript provides a review of anandamide synthesis, degradation, and storage and hence the homeostasis of the anandamide signaling system.

Non-opioid Analgesics and the Endocannabinoid System

Non-steroidal anti-inflammatory drugs produce antinociceptive effects mainly through peripheral cyclooxygenase inhibition. In opposition to the classical non-steroidal anti-inflammatory drugs, paracetamol and dipyrone exert weak anti-inflammatory activity, their antinociceptive effects appearing to be mostly due to mechanisms other than peripheral cyclooxygenase inhibition. In this review, we classify classical non-steroidal anti-inflammatory drugs, paracetamol and dipyrone as “non-opioid analgesics” and discuss the mechanisms mediating participation of the endocannabinoid system in their antinociceptive effects. Non-opioid analgesics and their metabolites may activate cannabinoid receptors, as well as elevate endocannabinoid levels through different mechanisms: reduction of endocannabinoid degradation via fatty acid amide hydrolase and/or cyclooxygenase-2 inhibition, mobilization of arachidonic acid for the biosynthesis of endocannabinoids due to cyclooxygenase inhibition, inhibition of endocannabinoid cellular uptake directly or through the inhibition of nitric oxide synthase production, and induction of endocannabinoid release.

Role of the Endocannabinoidome in Human and Mouse Atherosclerosis

The Endocannabinoid (eCB) system and its role in many physiological and pathological conditions is well described and accepted, and includes cardiovascular disorders. However, the eCB system has been expanded to an "-ome"; the endocannabinoidome (eCBome) that includes endocannabinoid-related mediators, their protein targets and metabolic enzymes, many of which significantly impact upon cardiometabolic health. These recent discoveries are here summarized with a special focus on their potential involvement in atherosclerosis. We described the role of classical components of the eCB system (eCBs, CB1 and CB2 receptors) and eCB-related lipids, their regulatory enzymes and molecular targets in atherosclerosis. Furthermore, since increasing evidence points to significant cross-talk between the eCBome and the gut microbiome and the gut microbiome and atherosclerosis, we explore the possibility that a gut microbiome - eCBome axis has potential implications in atherosclerosis.

Redox (phospho)lipidomics of signaling in inflammation and programmed cell death

In addition to the known prominent role of polyunsaturated (phospho)lipids as structural blocks of biomembranes, there is an emerging understanding of another important function of these molecules as a highly diversified signaling language utilized for intra- and extracellular communications. Technological developments in high-resolution mass spectrometry facilitated the development of a new branch of metabolomics, redox lipidomics. Analysis of lipid peroxidation reactions has already identified specific enzymatic mechanisms responsible for the biosynthesis of several unique signals in response to inflammation and regulated cell death programs. Obtaining comprehensive information about millions of signals encoded by oxidized phospholipids, represented by thousands of interactive reactions and pleiotropic (patho)physiological effects, is a daunting task. However, there is still reasonable hope that significant discoveries, of at least some of the important contributors to the overall overwhelmingly complex network of interactions triggered by inflammation, will lead to the discovery of new small molecule regulators and therapeutic modalities. For example, suppression of the production of AA-derived pro-inflammatory mediators, HXA3 and LTB4, by an iPLA2 γ inhibitor, R-BEL, mitigated injury associated with the activation of pro-inflammatory processes in animals exposed to whole-body irradiation. Further, technological developments promise to make redox lipidomics a powerful approach in the arsenal of diagnostic and therapeutic instruments for personalized medicine of inflammatory diseases and conditions.

Endocannabinoid Analytical Methodologies: Techniques That Drive Discoveries That Drive Techniques

Identification of the two major endogenous cannabinoid ligands, known as endocannabinoids, N-arachidonoyl-ethanolamine (anandamide, AEA) and 2-arachidonoyl-glycerol (2-AG), opened the way for the identification and isolation of other lipid congeners, all derivatives of fatty acids and related to the Endocannabinoid System. The nomenclature of this anandamide-type class of lipids is evolving as new species are discovered all the time. However, they each fall under the larger umbrella of lipids that are a conjugation of a fatty acid with an amine through and amide bond, which we will refer to as lipoamines. Specific subspecies of lipoamines that have been discovered are the N-acyl-ethanolamides (including AEA), N-acyl-dopamines, N-acyl-serotonins, N-acyl-GABA, N-acyl-taurines, and a growing number of N-acyl amino acids. Emerging data from multiple labs also show that monoacylglycerols (including 2-AG), COX-2 metabolites, and fatty acid esters of hydroxyl fatty acids are interconnected with these lipoamines at both the biosynthetic and metabolic levels. Understanding the molecular relatedness of these lipids is important for studying how they act as signaling molecules; however, a first step in this process hinges on advances in being able to accurately measure them.

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

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

Promising cannabinoid-based therapies for Parkinson's disease: motor symptoms to neuroprotection

Parkinson’s disease (PD) is a slow insidious neurological disorder characterized by a loss of dopaminergic neurons in the midbrain. Although several recent preclinical advances have proposed to treat PD, there is hardly any clinically proved new therapeutic for its cure. Increasing evidence suggests a prominent modulatory function of the cannabinoid signaling system in the basal ganglia. Hence, use of cannabinoids as a new therapeutic target has been recommended as a promising therapy for PD. The elements of the endocannabinoid system are highly expressed in the neural circuit of basal ganglia wherein they bidirectionally interact with dopaminergic, glutamatergic, and GABAergic signaling systems. As the cannabinoid signaling system undergoes a biphasic pattern of change during progression of PD, it explains the motor inhibition typically observed in patients with PD. Cannabinoid agonists such as WIN-55,212-2 have been demonstrated experimentally as neuroprotective agents in PD, with respect to their ability to suppress excitotoxicity, glial activation, and oxidative injury that causes degeneration of dopaminergic neurons. Additional benefits provided by cannabinoid related compounds including CE-178253, oleoylethanolamide, nabilone and HU-210 have been reported to possess efficacy against bradykinesia and levodopa-induced dyskinesia in PD. Despite promising preclinical studies for PD, use of cannabinoids has not been studied extensively at the clinical level. In this review, we reassess the existing evidence suggesting involvement of the endocannabinoid system in the cause, symptomatology, and treatment of PD. We will try to identify future threads of research that will help in the understanding of the potential therapeutic benefits of the cannabinoid system for treating PD.

Design and synthesis of novel prostaglandin E2 ethanolamide and glycerol ester probes for the putative prostamide receptor(s)

Novel prostaglandin-ethanolamide (PGE₂-EA) and glycerol ester (2-PGE₂-G) analogs were designed and synthesized to aid in the characterization of a putative prostamide receptor. Our design incorporates the electrophilic isothiocyanato and the photoactivatable azido groups at the terminal tail position of the prototype. Stereoselective Wittig and Horner-Wadsworth-Emmons reactions install the head and the tail moieties of the PGE₂ skeleton. The synthesis is completed using Mitsunobu azidation and peptide coupling as the key steps. A chemoenzymatic synthesis for the 2-PGE₂-G is described for first time.

Endocannabinoid metabolism by cytochrome P450 monooxygenases

The endogenous cannabinoid system was first uncovered following studies of the recreational drug Cannabis sativa. It is now recognized as a vital network of signaling pathways that regulate several physiological processes. Following the initial discovery of the cannabinoid receptors 1 (CB1) and 2 (CB2), activated by Cannabis-derived analogs, many endogenous fatty acids termed "endocannabinoids" are now known to be partial agonists of the CB receptors. At present, the most thoroughly studied endocannabinoid signaling molecules are anandamide (AEA) and 2-arachidonylglycerol (2-AG), which are both derived from arachidonic acid. Both AEA and 2-AG are also substrates for the eicosanoid-synthesizing pathways, namely, certain cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP) enzymes. In the past, research in the endocannabinoid field focused on the interaction of AEA and 2-AG with the COX and LOX enzymes, but accumulating evidence also points to the involvement of CYPs in modulating endocannabinoid signaling. The focus of this review is to explore the current understanding of CYP-mediated metabolism of endocannabinoids.

Endocannabinoids, related compounds and their metabolic routes

Endocannabinoids are lipid mediators able to bind to and activate cannabinoid receptors, the primary molecular targets responsible for the pharmacological effects of the Δ⁹-tetrahydrocannabinol. These bioactive lipids belong mainly to two classes of compounds: N-acylethanolamines and acylesters, being N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG), respectively, their main representatives. During the last twenty years, an ever growing number of fatty acid derivatives (endocannabinoids and endocannabinoid-like compounds) have been discovered and their activities biological is the subject of intense investigations. Here, the most recent advances, from a therapeutic point of view, on endocannabinoids, related compounds, and their metabolic routes will be reviewed.

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.

Endocannabinoid signaling in the etiology and treatment of major depressive illness

The purpose of this review is to examine human and preclinical data that are relevant to the following hypotheses. The first hypothesis is that deficient CB1R-mediated signaling results in symptoms that mimic those seen in depression. The second hypothesis is that activation of CB1R-mediated signaling results in behavioral, endocrine and other effects that are similar to those produced by currently used antidepressants. The third hypothesis is that conventional antidepressant therapies act through enhanced CB1R mediated signaling. Together the available data indicate that activators of CB1R signaling, particularly inhibitors of fatty acid amide hydrolase, should be considered for clinical trials for the treatment of depression.

Oxidized PLs and vascular inflammation

Oxidized PLs (OxPLs) generated in health and disease are now recognized as important mediators of cellular signalling. There is an increasing body of evidence showing that PL peroxidation is not only increased in vascular disorders, but is also a physiological event of relevance to coagulation, innate immunity, and self-tolerance. Nonenzymatically formed OxPLs generated during chronic inflammation is an uncontrolled event, generating hundreds of diverse structures, and prone to more deleterious bioactivities. In contrast, enzymatic formation of OxPLs is tightly regulated, involving receptors and intracellular signaling, acting as part of the normal physiological response to injury in order to restore homeostasis. In the present review, the major nonenzymatic OxPLs structures found during vascular inflammation are summarized, along with a brief description of their known biological activities. Also, we review what is currently known about enzymatic formation of OxPLs by acutely activated immune cells and their signaling actions under homeostatic and pathological conditions.

Chemical probes of endocannabinoid metabolism

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

Latest advances in the discovery of fatty acid amide hydrolase inhibitors

INTRODUCTION

Fatty acid amide hydrolase (FAAH) is the major catabolic enzyme of the endocannabinoid N-arachidonoylethanolamine (anandamide) that, with different degrees of efficiency, also hydrolyzes other endogenous fatty acid ethanolamides. FAAH is increasingly being considered a relevant therapeutic target, especially in models of inflammatory pain. The opportunity to selectively increase the endocannabinoid tone only in those tissues where such an enhancement can be beneficial might result in a therapeutic benefit with more limited side effects, compared to the use of direct agonists of anandamide-binding receptors. Thus the research for selective FAAH inhibitors has become a hot topic in current drug discovery.

AREAS COVERED

This review highlights the advances in the development of different compounds belonging to different chemical families that have been proposed as FAAH inhibitors. Several classes of inhibitors have been reported so far, and they may be classified into two major classes: reversible and irreversible compounds. These inhibitors are reviewed herein with an emphasis on their potency and selectivity.

EXPERT OPINION

In recent years, tremendous efforts have been made to develop the FAAH inhibitors, and consequently many novel chemical templates have been discovered. It is still a major challenge to identify the first inhibitor of FAAH suitable for clinical exploitation that satisfies the requirements of potency, selectivity versus proteins related to anandamide activity as well as other potential off-targets, reversibility versus irreversibility, and efficacy toward rat versus human FAAH.

Metabolism of endocannabinoids and related N-acylethanolamines: canonical and alternative pathways

Endocannabinoids are endogenous ligands of the cannabinoid receptors CB1 and CB2. Two arachidonic acid derivatives, arachidonoylethanolamide (anandamide) and 2-arachidonoylglycerol, are considered to be physiologically important endocannabinoids. In the known metabolic pathway in mammals, anandamide and other bioactive N-acylethanolamines, such as palmitoylethanolamide and oleoylethanolamide, are biosynthesized from glycerophospholipids by a combination of Ca(2+)-dependent N-acyltransferase and N-acyl-phosphatidylethanolamine-hydrolyzing phospholipase D, and are degraded by fatty acid amide hydrolase. However, recent studies have shown the involvement of other enzymes and pathways, which include the members of the tumor suppressor HRASLS family (the phospholipase A/acyltransferase family) functioning as Ca(2+)-independent N-acyltransferases, N-acyl-phosphatidylethanolamine-hydrolyzing phospholipaseD-independent multistep pathways via N-acylated lysophospholipid, and N-acylethanolamine-hydrolyzing acid amidase, a lysosomal enzyme that preferentially hydrolyzes palmitoylethanolamide. Although their physiological significance is poorly understood, these new enzymes/pathways may serve as novel targets for the development of therapeutic drugs. For example, selective N-acylethanolamine-hydrolyzing acid amidase inhibitors are expected to be new anti-inflammatory and analgesic drugs. In this minireview, we focus on advances in the understanding of these enzymes/pathways. In addition, recent findings on 2-arachidonoylglycerol metabolism are described.

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.

Anti-inflammatory lipoxin A4 is an endogenous allosteric enhancer of CB1 cannabinoid receptor

Allosteric modulation of G-protein-coupled receptors represents a key goal of current pharmacology. In particular, endogenous allosteric modulators might represent important targets of interventions aimed at maximizing therapeutic efficacy and reducing side effects of drugs. Here we show that the anti-inflammatory lipid lipoxin A(4) is an endogenous allosteric enhancer of the CB(1) cannabinoid receptor. Lipoxin A(4) was detected in brain tissues, did not compete for the orthosteric binding site of the CB(1) receptor (vs. (3)H-SR141716A), and did not alter endocannabinoid metabolism (as opposed to URB597 and MAFP), but it enhanced affinity of anandamide at the CB1 receptor, thereby potentiating the effects of this endocannabinoid both in vitro and in vivo. In addition, lipoxin A(4) displayed a CB(1) receptor-dependent protective effect against β-amyloid (1-40)-induced spatial memory impairment in mice. The discovery of lipoxins as a class of endogenous allosteric modulators of CB(1) receptors may foster the therapeutic exploitation of the endocannabinoid system, in particular for the treatment of neurodegenerative disorders.

Alterations in endocannabinoid tone following chemotherapy-induced peripheral neuropathy: effects of endocannabinoid deactivation inhibitors targeting fatty-acid amide hydrolase and monoacylglycerol lipase in comparison to reference analgesics following cisplatin treatment

Cisplatin, a platinum-derived chemotherapeutic agent, produces mechanical and coldallodynia reminiscent of chemotherapy-induced neuropathy in humans. The endocannabinoid system represents a novel target for analgesic drug development. The endocannabinoid signaling system consists of endocannabinoids (e.g. anandamide (AEA) and 2-arachidonoylglycerol (2-AG)), cannabinoid receptors (e.g. CB(1) and CB(2)) and the enzymes controlling endocannabinoid synthesis and degradation. AEA is hydrolyzed by fatty-acid amide hydrolase (FAAH) whereas 2-AG is hydrolyzed primarily by monoacylglycerol lipase (MGL). We compared effects of brain permeant (URB597) and impermeant (URB937) inhibitors of FAAH with an irreversible inhibitor of MGL (JZL184) on cisplatin-evoked behavioral hypersensitivities. Endocannabinoid modulators were compared with agents used clinically to treat neuropathy (i.e. the opioid analgesic morphine, the anticonvulsant gabapentin and the tricyclic antidepressant amitriptyline). Cisplatin produced robust mechanical and cold allodynia but did not alter responsiveness to heat. After neuropathy was fully established, groups received acute intraperitoneal (i.p.) injections of vehicle, amitriptyline (30 mg/kg), gabapentin (100 mg/kg), morphine (6 mg/kg), URB597 (0.1 or 1 mg/kg), URB937 (0.1 or 1 mg/kg) or JZL184 (1, 3 or 8 mg/kg). Pharmacological specificity was assessed by coadministering each endocannabinoid modulator with either a CB(1) (AM251 3 mg/kg), CB(2) (AM630 3 mg/kg), TRPV1 (AMG9810 3 mg/kg) or TRPA1 (HC030031 8 mg/kg) antagonist. Effects of cisplatin on endocannabinoid levels and transcription of receptors (CB(1), CB(2), TRPV1, TRPA1) and enzymes (FAAH, MGL) linked to the endocannabinoid system were also assessed. URB597, URB937, JZL184 and morphine reversed cisplatin-evoked mechanical and cold allodynia to pre-cisplatin levels. By contrast, gabapentin only partially reversed the observed allodynia while amitriptyline, administered acutely, was ineffective. CB(1) or CB(2) antagonists completely blocked the anti-allodynic effects of both FAAH (URB597, URB937) and MGL (JZL184) inhibitors to mechanical and cold stimulation. By contrast, the TRPV1 antagonist AMG9810 blocked the anti-allodynic efficacy of both FAAH inhibitors, but not the MGL inhibitor. By contrast, the TRPA1 antagonist HC30031 did not attenuate anti-allodynic efficacy of any endocannabinoid modulator. When the levels of endocannabinoids were examined, cisplatin increased both anandamide (AEA) and 2-arachidonoylglycerol (2-AG) levels in the lumbar spinal cord and decreased 2-AG levels (but not AEA) in dorsal hind paw skin. RT-PCR showed that mRNA for FAAH, but not other markers, was upregulated by cisplatin treatment in lumbar spinal cord. The present studies demonstrate that cisplatin alters endocannabinoid tone and that inhibition of endocannabinoid hydrolysis alleviates chemotherapy-induced mechanical and cold allodynia. The anti-allodynic effects of FAAH and MGL inhibitors are mediated by CB(1) and CB(2) cannabinoid receptors, whereas TRPV1, but not TRPA1, -dependent mechanisms contribute to the anti-allodynic efficacy of FAAH (but not MGL) inhibitors. Strikingly, endocannabinoid modulators potently suppressed cisplatin-evoked allodynia with a rapid onset and showed efficacy that equaled or exceeded that of major classes of anti-neuropathic pain medications used clinically. Thus, inhibition of endocannabinoid hydrolysis, via FAAH or MGL inhibitors, represents an efficacious pharmacological approach for suppressing chemotherapy-induced neuropathic pain.

Quantitative LC-MS/MS analysis of arachidonoyl amino acids in mouse brain with treatment of FAAH inhibitor

An additional class of endogenous lipid amides, N-arachidonoyl amino acids (Ara-AAs), is growing in significance in the field of endocannabinoids. The development, validation, and application of a sensitive and selective method to simultaneously monitor and quantify the level of Ara-AAs along with anandamide (AEA) and 2-arachidonoyl glycerol (2-AG) in mouse brain has been established. The linearity of the method over the concentration ranges of 0.2-120 pg/μl for the standards of N-arachidonoyl amino acids, N-arachidonoyl alanine (NAAla), serine (NASer), γ-aminobutyric acid (NAGABA), and glycine (NAGly); 0.7-90 pg/μl for AEA-d(0)/d(8); and 7.5-950 pg/μl for 2-AG was determined with R(2) values of 0.99. Also the effects of the FAAH inhibitor URB 597 on the endogenous levels of these analytes were investigated. AEA and NASer brain levels exhibit a dose-dependent increase after systemic administration of URB 597, whereas NAGly and NAGABA were significantly decreased after treatment. NAAla and 2-AG were not altered after URB 597 treatment. The potential benefit of establishing this assay extends beyond the quantification of the Ara-AAs along with AEA and 2-AG in mouse brain, to reveal a variety of pharmacological effects and physiological roles of these analytes.

Enantioselective synthesis of (10S)- and (10R)-methyl-anandamides

For the development of novel endocannabinoid templates with potential resistance to hydrolytic and oxidative metabolism, we are targeting the bis-allylic carbons of the arachidonoyl skeleton. Toward this end, we recently disclosed the synthesis and preliminary biological data for the (13S)-methyl-anandamide. We report now the total synthesis of the (10S)- and (10R)-methyl-counterparts. Our synthetic approach is stereospecific, efficient, and provides the analogs without the need for resolution. Peptide coupling, P-2 nickel partial hydrogenation, and cis-selective Wittig olefination are the key steps.

New insights on endocannabinoid transmission in psychomotor disorders

The endocannabinoids are lipid signaling molecules that bind to cannabinoid CB(1) and CB(2) receptors and other metabotropic and ionotropic receptors. Anandamide and 2-arachidonoyl glycerol, the two best-characterized examples, are released on demand in a stimulus-dependent manner by cleavage of membrane phospholipid precursors. Together with their receptors and metabolic enzymes, the endocannabinoids play a key role in modulating neurotransmission and synaptic plasticity in the basal ganglia and other brain areas involved in the control of motor functions and motivational aspects of behavior. This mini-review provides an update on the contribution of the endocannabinoid system to the regulation of psychomotor behaviors and its possible involvement in the pathophysiology of Parkinson's disease and schizophrenia.

"Redundancy" of endocannabinoid inactivation: new challenges and opportunities for pain control

Redundancy of metabolic pathways and molecular targets is a typical feature of all lipid mediators, and endocannabinoids, which were originally defined as endogenous agonists at cannabinoid CB(1) and CB(2) receptors, are no exception. In particular, the two most studied endocannabinoids, anandamide and 2-arachidonoylglycerol, are inactivated through alternative biochemical routes, including hydrolysis and oxidation, and more than one enzyme might be used even for the same type of inactivating reaction. These enzymes also recognize as substrates other concurrent lipid mediators, whereas, in turn, endocannabinoids might interact with noncannabinoid receptors with subcellular distribution and ultimate biological actions either similar to or completely different from those of cannabinoid receptors. Even splicing variants of endocannabinoid hydrolyzing enzymes, such as FAAH-1, might play distinct roles in endocannabinoid inactivation. Finally, the products of endocannabinoid catabolism may have their own targets, with biological roles different from those of cannabinoid receptors. These peculiarities of endocannabinoid signaling have complicated the use of inhibitors of its inactivation mechanisms as a safer and more efficacious alternative to the direct targeting of cannabinoid receptors for the treatment of several pathological conditions, including pain. However, new strategies, including the rediscovery of "dirty drugs", and the use of certain natural products (including non-THC cannabis constituents), are emerging that might allow us to make a virtue of necessity and exploit endocannabinoid redundancy to develop new analgesics.

Psychopharmacology of the endocannabinoids: far beyond anandamide

The study of endocannabinoid pharmacology has proceeded from the discovery of Δ9-tetrahydrocannabinol, the main psychoactive compound in Cannabis sativa, to the identification of an endogenous endocannabinoid system that is essential for physiological modulation of neuronal functions. We have not yet achieved a complete understanding of the various roles of the endocannabinoids, but this is one of the fastest-growing fields in psychopharmacology. This review starts with a brief historical description of the discovery of the endocannabinoids and then focuses on recent pharmacological advances and recently discovered endocannabinoid mechanisms of action (e.g. functional selectivity, allosterism, and receptor trafficking). Finally, we will discuss the contention that the existence of evidence-based therapeutic applications for cannabinoids and the wide range of physiological functions affected by endocannabinoids suggests that the careful study of the endocannabinoid system may lead to the development of novel therapeutic drugs with higher societal acceptability and lower side effects profiles.

Esterified eicosanoids: generation, characterization and function

Eicosanoids are oxidation products of C20 polyunsaturated fatty acids (e.g. arachidonic acid) that include prostaglandins, thromboxanes, leukotrienes and hydroperoxy fatty acids. They have important biological roles in vivo, including regulation of renal, cardiovascular and gastrointestinal function. Historically, eicosanoids were thought to mediate their signaling actions exclusively as free acids, however evidence is now emerging that they may also be generated attached to other functional groups including phospholipids and glycerol, and that these more complex forms are pathophysiological signaling mediators in their own right. Early studies showed that exogenously added eicosanoids could become esterified into membrane phospholipids of cells, while more recently, it was uncovered that esterified eicosanoids are formed endogenously. This review summarizes our current knowledge of this area, starting with the early discoveries documenting what is known about eicosanoid generation and their esterification, and moving on to discuss the discovery that esterified eicosanoids are generated endogenously by a number of different cell types. Recent research that is highlighting new structures and functions of these important lipid mediators will be presented. This article is part of a Special Issue entitled: Oxidized phospholipids-their properties and interactions with proteins.

Cannabinoid as a neuroprotective strategy in perinatal hypoxic-ischemic injury

Perinatal hypoxia-ischemia remains the single most important cause of brain injury in the newborn, leading to death or lifelong sequelae. Because of the fact that there is still no specific treatment for perinatal brain lesions due to the complexity of neonatal hypoxic-ischemic pathophysiology, the search of new neuroprotective therapies is of great interest. In this regard, therapeutic possibilities of the endocannabinoid system have grown lately. The endocannabinoid system modulates a wide range of physiological processes in mammals and has demonstrated neuroprotective effects in different paradigms of acute brain injury, acting as a natural neuroprotectant. Concerning perinatal asphyxia, the neuroprotective role of this endogenous system is emerging these years. The present review mainly focused on the current knowledge of the cannabinoids as a new neuroprotective strategy against perinatal hypoxic-ischemic brain injury.

Decoding functional metabolomics with docosahexaenoyl ethanolamide (DHEA) identifies novel bioactive signals

Neuroinflammation and traumatic brain injury involve activation of inflammatory cells and production of local pro-inflammatory mediators that can amplify tissue damage. Using LC-UV-MS-MS-based lipidomics in tandem with functional screening at the single-cell level in microfluidic chambers, we identified a series of novel bioactive oxygenated docosahexaenoyl ethanolamide- (DHEA) derived products that regulated leukocyte motility. These included 10,17-dihydroxydocosahexaenoyl ethanolamide (10,17-diHDHEA) and 15-hydroxy-16(17)-epoxy-docosapentaenoyl ethanolamide (15-HEDPEA), each of which was an agonist of recombinant CB2 receptors with EC(50) 3.9 × 10(-10) and 1.0 × 10(-10) M. In human whole blood, 10,17-diHDHEA and 15-HEDPEA at concentrations as low as 10 pM each prevented formation of platelet-leukocyte aggregates involving either platelet-monocyte or platelet-polymorphonuclear leukocyte. In vivo, 15-HEDPEA was organ-protective in mouse reperfusion second organ injury. Together these results indicate that DHEA oxidative metabolism produces potent novel molecules with anti-inflammatory and organ-protective properties.

Soluble epoxide hydrolase inhibition, epoxygenated fatty acids and nociception

The soluble epoxide hydrolase (sEH) enzyme regulates the levels of endogenous epoxygenated fatty acid (EFA) lipid metabolites by rapidly degrading these molecules. The EFAs have pleiotropic biological activities including the modulation of nociceptive signaling. Recent findings indicate that the EFAs, in particular the arachidonic acid (AA) derived epoxyeicosatrienoic acids (EETs), the docosahexaenoic acid (DHA) derived epoxydocosapentaenoic acids (EpDPEs) and eicosapentaenoic acid (EPA) derived epoxyeicosatetraenoic acids (EpETEs) are natural signaling molecules. The tight regulation of these metabolites speaks to their importance in regulating biological functions. In the past several years work on EFAs in regard to their activities in the nervous system evolved to demonstrate that these molecules are anti-inflammatory and anti-nociceptive. Here we focus on the recent advances in understanding the effects of sEH inhibition and increased EFAs on the nociceptive system and their ability to reduce pain. Evidence of their role in modulating pain signaling is given by their direct application and by inhibiting their degradation in various models of pain. Moreover, there is mounting evidence of EFAs role in the crosstalk between major nociceptive and anti-nociceptive systems which is reviewed herein. Overall the fundamental knowledge generated within the past decade indicates that orally bioavailable small molecule inhibitors of sEH may find a place in the treatment of a number of diverse painful conditions including inflammatory and neuropathic pain.

Lipoxygenase-mediated oxidation of polyunsaturated N-acylethanolamines in Arabidopsis

N-acylethanolamines (NAEs) are bioactive fatty acid derivatives that occur in all eukaryotes. In plants, NAEs have potent negative growth-regulating properties, and fatty acid amide hydrolase (FAAH)-mediated hydrolysis is a primary catabolic pathway that operates during seedling establishment to deplete these compounds. Alternatively, polyunsaturated (PU)-NAEs may serve as substrates for lipid oxidation. In Arabidopsis, PU-NAEs (NAE 18:2 and NAE 18:3) were the most abundant NAE species in seeds, and their levels were depleted during seedling growth even in FAAH tDNA knock-out plants. Therefore, we hypothesized that lipoxygenase (LOX) participated in the metabolism of PU-NAEs through the formation of NAE-oxylipins. Comprehensive chromatographic and mass spectrometric methods were developed to identify NAE hydroperoxides and -hydroxides. Recombinant Arabidopsis LOX enzymes expressed in Escherichia coli utilized NAE 18:2 and NAE 18:3 as substrates with AtLOX1 and AtLOX5 exhibiting 9-LOX activity and AtLOX2, AtLOX3, AtLOX4, and AtLOX6 showing predominantly 13-LOX activity. Feeding experiments with exogenous PU-NAEs showed they were converted to hydroxide metabolites indicating that indeed Arabidopsis seedlings had the capacity for LOX-mediated metabolism of PU-NAEs in planta. Detectable levels of endogenous NAE-oxylipin metabolites were identified in FAAH fatty acid amide hydrolase seedlings but not in wild-type or FAAH overexpressors, suggesting that NAE hydroxide pools normally do not accumulate unless flux through hydrolysis is substantially reduced. These data suggest that Arabidopsis LOXs indeed compete with FAAH to metabolize PU-NAEs during seedling establishment. Identification of endogenous amide-conjugated oxylipins suggests potential significance of these metabolites in vivo, and FAAH mutants may offer opportunities to address this in the future.

Biosynthesis and degradation of the endocannabinoid 2-arachidonoylglycerol

2-Arachidonoylglycerol (2-AG) is a monoacylglycerol (MAG) molecule containing an esterified arachidonic acid chain at sn-2 position of the glycerol backbone. Together with structurally similar N-arachidonoylethanolamine (anandamide), 2-AG has been extensively studied as an endogenous ligand of cannabinoid receptors (an endocannabinoid) in brain and other mammalian tissues. Accumulating evidence demonstrates that the endocannabinoid system, including the central-type cannabinoid receptor CB1 and 2-AG, is responsible for synaptic retrograde signaling in the central nervous system. As 2-AG is rapidly formed from membrane phospholipids on cellular stimuli and degraded to arachidonic acid and glycerol, the enzymes catalyzing its biosynthesis and degradation are believed to play crucial roles in the regulation of its tissue levels. The major biosynthetic pathway appears to consist of sequential hydrolyses of inositol phospholipids via diacylglycerol (DAG) by β-type phospholipase C and DAG lipase, while MAG lipase is a principal enzyme in the degradation. In this short review, we will briefly outline rapid advances in enzymological research on the biosynthetic and degradative pathways of 2-AG.

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.