Metabolism of the endocannabinoids, 2-arachidonylglycerol and anandamide, into prostaglandin, thromboxane, and prostacyclin glycerol esters and ethanolamides

Combined inhibition of FAAH and COX produces enhanced anti-allodynic effects in mouse neuropathic and inflammatory pain models

Common pharmacological treatments of neuropathic and chronic inflammatory pain conditions generally lack efficacy and/or are associated with significant untoward side effects. However, recent preclinical data indicate that combined inhibition of cyclooxygenase (COX) and fatty acid amide hydrolase (FAAH), the primary catabolic enzyme of the endocannabinoid N-arachidonoylethanolamine (anandamide; AEA), produces enhanced antinociceptive effects in a variety of murine models of pain. Accordingly, the primary objective of the present study was to investigate the consequences of co-administration of the COX inhibitor diclofenac and the highly selective FAAH inhibitor PF-3845 in models of neuropathic pain (i.e., chronic constrictive injury of the sciatic nerve (CCI)) and inflammatory pain induced by an intraplantar injection of carrageenan. Here, we report that combined administration of subthreshold doses of these drugs produced enhanced antinociceptive effects in CCI and carrageenan pain models, the latter of which was demonstrated to require both CB1 and CB2 receptors. The combined administration of subthreshold doses of these drugs also increased AEA levels and decreased prostaglandin levels in whole brain. Together, these data add to the growing research that dual blockade of FAAH and COX represents a potential therapeutic strategy for the treatment of neuropathic and inflammatory pain states.

PERSPECTIVE

Tandem inhibition of FAAH and COX attenuates inflammatory and neuropathic pain states, which may avoid potentially harmful side effects of other therapeutic options, such as NSAIDs or opioids.

Inhibition of endocannabinoid metabolism by the metabolites of ibuprofen and flurbiprofen

Background

In addition to their effects upon prostaglandin synthesis, the non-steroidal anti-inflammatory drugs ibuprofen and flurbiprofen inhibit the metabolism of the endocannabinoids 2-arachidonoylglycerol (2-AG) and anandamide (AEA) by cyclooxygenase-2 (COX-2) and fatty acid amide hydrolase (FAAH), respectively. Here, we investigated whether these effects upon endocannabinoid metabolism are shared by the main metabolites of ibuprofen and flurbiprofen.

Methodology/Principal Findings

COX activities were measured via changes in oxygen consumption due to oxygenation of arachidonic acid (for COX-1) and arachidonic acid and 2-AG (for COX-2). FAAH activity was quantified by measuring hydrolysis of tritium labelled AEA in rat brain homogenates. The ability of ibuprofen and flurbiprofen to inhibit COX-2-catalysed oxygenation of 2-AG at lower concentrations than the oxygenation of arachidonic acid was seen with 4′-hydroxyflurbiprofen and possibly also 3′-hydroxyibuprofen, albeit at lower potencies than the parent compounds. All ibuprofen and flurbiprofen metabolites retained the ability to inhibit FAAH in a pH-dependent manner, although the potency was lower than seen with the parent compounds.

Conclusions/Significance

It is concluded that the primary metabolites of ibuprofen and flurbiprofen retain some of the properties of the parent compound with respect to inhibition of endocannabinoid metabolism. However, these effects are unlikely to contribute to the actions of the parent compounds in vivo.

Functionalization of β-caryophyllene generates novel polypharmacology in the endocannabinoid system

The widespread dietary plant sesquiterpene hydrocarbon β-caryophyllene (1) is a CB2 cannabinoid receptor-specific agonist showing anti-inflammatory and analgesic effects in vivo. Structural insights into the pharmacophore of this hydrocarbon, which lacks functional groups other than double bonds, are missing. A structure-activity study provided evidence for the existence of a well-defined sesquiterpene hydrocarbon binding site in CB2 receptors, highlighting its exquisite sensitivity to modifications of the strained endocyclic double bond of 1. While most changes on this element were detrimental for activity, ring-opening cross metathesis of 1 with ethyl acrylate followed by amide functionalization generated a series of new monocyclic amides (11a, 11b, 11c) that not only retained the CB2 receptor functional agonism of 1 but also reversibly inhibited fatty acid amide hydrolase (FAAH), the major endocannabinoid degrading enzyme, without affecting monoacylglycerol lipase (MAGL) and α,β hydrolases 6 and 12. Intriguingly, further modification of this monocyclic scaffold generated the FAAH- and endocannabinoid substrate-specific cyclooxygenase-2 (COX-2) dual inhibitors 11e and 11f, which are probes with a novel pharmacological profile. Our study shows that by removing the conformational constraints induced by the medium-sized ring and by introducing functional groups in the sesquiterpene hydrocarbon 1, a new scaffold with pronounced polypharmacological features within the endocannabinoid system could be generated. The structural and functional repertoire of cannabimimetics and their yet poorly understood intrinsic promiscuity may be exploited to generate novel probes and ultimately more effective drugs.

Substrate-selective COX-2 inhibition as a novel strategy for therapeutic endocannabinoid augmentation

Pharmacologic augmentation of endogenous cannabinoid (eCB) signaling is an emerging therapeutic approach for the treatment of a broad range of pathophysiological conditions. Thus far, pharmacological approaches have focused on inhibition of the canonical eCB inactivation pathways - fatty acid amide hydrolase (FAAH) for anandamide and monoacylglycerol lipase (MAGL) for 2-arachidonoylglycerol. We review here the experimental evidence that cyclooxygenase-2 (COX-2)-mediated eCB oxygenation represents a third mechanism for terminating eCB action at cannabinoid receptors. We describe the development, molecular mechanisms, and in vivo validation of 'substrate-selective' COX-2 inhibitors (SSCIs) that prevent eCB inactivation by COX-2 without affecting prostaglandin (PG) generation from arachidonic acid (AA). Lastly, we review recent data on the potential therapeutic applications of SSCIs with a focus on neuropsychiatric disorders.

Selective axonal and glial distribution of monoacylglycerol lipase immunoreactivity in the superficial spinal dorsal horn of rodents

The importance of 2-AG-mediated endogenous cannabinoid signaling in spinal pain control has recently been well substantiated. Although the degradation of 2-AG seems to be essential in cannabinoid-mediated spinal nociceptive information processing, no experimental data are available about the cellular distribution of monoacylglycerol lipase (MGL), the main degrading enzyme of 2-AG in the spinal dorsal horn. Thus, here we investigated the cellular distribution of MGL in laminae I-II of the spinal gray matter with immunocytochemical methods and revealed an abundant immunoreactivity for MGL in the rodent superficial spinal dorsal horn. We addressed the co-localization of MGL with markers of peptidergic and non-peptidergic primary afferents, axon terminals of putative glutamatergic and GABAergic spinal neurons, as well as astrocytic and microglial profiles, and we found that nearly 17 % of the peptidergic (immunoreactive for CGRP), a bit more than 10 % of the axon terminals of putative glutamatergic spinal neurons (immunoreactive for VGLUT2), and approximately 20 % of the astrocytic (immunoreactive for GFAP) profiles were immunolabeled for MGL. On the other hand, however, axon terminals of non-peptidergic (binding isolectin-B4) nociceptive primary afferents and putative inhibitory spinal neurons (immunoreactive for VGAT) as well as microglial (immunoreactive for CD11b) profiles showed negligible immunostaining for MGL. The results suggest that only nociceptive inputs arriving through a population of CGRP immunoreactive fibers are modulated by the spinal DGLα-MGL pathway. We also postulate that the DGLα-MGL signaling pathway may modulate spinal excitatory but not inhibitory neural circuits.

Increased angiotensin II contraction of the uterine artery at early gestation in a transgenic model of hypertensive pregnancy is reduced by inhibition of endocannabinoid hydrolysis

Increased vascular sensitivity to angiotensin II (Ang II) is a marker of a hypertensive human pregnancy. Recent evidence of interactions between the renin-angiotensin system and the endocannabinoid system suggests that anandamide and 2-arachidonoylglycerol may modulate Ang II contraction. We hypothesized that these interactions may contribute to the enhanced vascular responses in hypertensive pregnancy. We studied Ang II contraction in isolated uterine artery (UA) at early gestation in a rat model that mimics many features of preeclampsia, the transgenic human angiotensinogen×human renin (TgA), and control Sprague-Dawley rats. We determined the role of the cannabinoid receptor 1 by blockade with SR171416A, and the contribution of anandamide and 2-arachidonoylglycerol degradation to Ang II contraction by inhibiting their hydrolyzing enzyme fatty acid amide hydrolase (with URB597) or monoacylglycerol lipase (with JZL184), respectively. TgA UA showed increased maximal contraction and sensitivity to Ang II that was inhibited by indomethacin. Fatty acid amide hydrolase blockade decreased Ang IIMAX in Sprague-Dawley UA, and decreased both Ang IIMAX and sensitivity in TgA UA. Monoacylglycerol lipase blockade had no effect on Sprague-Dawley UA and decreased Ang IIMAX and sensitivity in TgA UA. Blockade of the cannabinoid receptor 1 in TgA UA had no effect. Immunolocalization of fatty acid amide hydrolase and monoacylglycerol lipase showed a similar pattern between groups; fatty acid amide hydrolase predominantly localized in endothelium and monoacylglycerol lipase in smooth muscle cells. We demonstrated an increased Ang II contraction in TgA UA before initiation of the hypertensive phenotype. Anandamide and 2-arachidonoylglycerol reduced Ang II contraction in a cannabinoid receptor 1-independent manner. These renin-angiotensin system-endocannabinoid system interactions may contribute to the enhanced vascular reactivity in early stages of hypertensive pregnancy.

What we know and do not know about the cannabinoid receptor 2 (CB2)

It has been well appreciated that the endocannabinoid system can regulate immune responses via the cannabinoid receptor 2 (CB2), which is primarily expressed by cells of the hematopoietic system. The endocannabinoid system is composed of receptors, ligands and enzymes controlling the synthesis and degradation of endocannabinoids. Along with endocannabinoids, both plant-derived and synthetic cannabinoids have been shown to bind to and signal through CB2 via G proteins leading to both inhibitory and stimulatory signals depending on the biological process. Because no cannabinoid ligand has been identified that only binds to CB2, the generation of mice deficient in CB2 has greatly expanded our knowledge of how CB2 contributes to immune cell development and function in health and disease. In regards to humans, genetic studies have associated CB2 with a variety of human diseases. Here, we review the endocannabinoid system with an emphasis on CB2 and its role in the immune system.

New players in the fatty acyl ethanolamide metabolism

Fatty acyl ethanolamides represent a class of endogenous bioactive lipid molecules and are generally referred to as N-acylethanolamines (NAEs). NAEs include palmitoylethanolamide (anti-inflammatory and analgesic substance), oleoylethanolamide (anorexic substance), and anandamide (endocannabinoid). The endogenous levels of NAEs are mainly regulated by enzymes responsible for their biosynthesis and degradation. In mammalian tissues, the major biosynthetic pathway starts from glycerophospholipids and is composed of two enzyme reactions. The first step is N-acylation of ethanolamine phospholipids catalyzed by Ca(2+)-dependent N-acyltransferase and the second step is the release of NAEs from N-acylated ethanolamine phospholipids by N-acylphosphatidylethanolamine (NAPE)-hydrolyzing phospholipase D (NAPE-PLD). As for the degradation of NAEs, fatty acid amide hydrolase plays the central role. However, recent studies strongly suggest the involvement of other enzymes in the NAE metabolism. These enzymes include members of the HRAS-like suppressor family (also called phospholipase A/acyltransferase family), which were originally discovered as tumor suppressors but can function as Ca(2+)-independent NAPE-forming N-acyltransferases; multiple enzymes involved in the NAPE-PLD-independent multi-step pathways to generate NAE from NAPE, which came to light by the analysis of NAPE-PLD-deficient mice; and a lysosomal NAE-hydrolyzing acid amidase as a second NAE hydrolase. These newly recognized enzymes may become the targets for the development of new therapeutic drugs. Here, we focus on recent enzymological findings in this area.

Changes in endocannabinoid and N-acylethanolamine levels in rat brain structures following cocaine self-administration and extinction training

Preclinical investigations have demonstrated that drugs of abuse alter the levels of lipid-based signalling molecules, including endocannabinoids (eCBs) and N-acylethanolamines (NAEs), in the rodent brain. In addition, several drugs targeting eCBs and/or NAEs are implicated in reward and/or seeking behaviours related to the stimulation of dopamine systems in the brain. In our study, the brain levels of eCBs (anandamide (AEA) and 2-arachidonoylglycerol (2-AG)) and NAEs (oleoylethanolamide (OEA) and palmitoylethanolamide (PEA)) were analyzed via an LC-MS/MS method in selected brain structures of rats during cocaine self-administration and after extinction training according to the "yoked" control procedure. Repeated (14days) cocaine (0.5mg/kg/infusion) self-administration and yoked drug delivery resulted in a significant decrease (ca. 52%) in AEA levels in the cerebellum, whereas levels of 2-AG increased in the frontal cortex, the hippocampus and the cerebellum and decreased in the hippocampus and the dorsal striatum. In addition, we detected increases (>150%) in the levels of OEA and PEA in the limbic areas in both cocaine treated groups, as well as an increase in the tissue levels of OEA in the dorsal striatum in only the yoked cocaine group and increases in the tissue levels of PEA in the dorsal striatum (both cocaine groups) and the nucleus accumbens (yoked cocaine group only). Compared to the yoked saline control group, extinction training (10days) resulted in a potent reduction in AEA levels in the frontal cortex, the hippocampus and the nucleus accumbens and in 2-AG levels in the hippocampus, the dorsal striatum and the cerebellum. The decreases in the limbic and subcortical areas were more apparent for rats that self-administered cocaine. Following extinction, there was a region-specific change in the levels of NAEs in rats previously injected with cocaine; a potent increase (ca. 100%) in the levels of OEA and PEA was detected in the prefrontal cortex and the hippocampus, whilst a drop was noted in the striatal areas versus yoked saline yoked animals. Our findings support the previous pharmacological evidence that the eCB system and NAEs are involved in reinforcement and extinction of positively reinforced behaviours and that these lipid-derived molecules may represent promising targets for the development of new treatments for drug addiction.

COX-2-derived endocannabinoid metabolites as novel inflammatory mediators

Cyclooxygenase-2 (COX-2) is an enzyme that plays a key role in inflammatory processes. Classically, this enzyme is upregulated in inflammatory situations and is responsible for the generation of prostaglandins (PGs) from arachidonic acid (AA). One lesser-known property of COX-2 is its ability to metabolize the endocannabinoids, N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG). Endocannabinoid metabolism by COX-2 is not merely a means to terminate their actions. On the contrary, it generates PG analogs, namely PG-glycerol esters (PG-G) for 2-AG and PG-ethanolamides (PG-EA or prostamides) for AEA. Although the formation of these COX-2-derived metabolites of the endocannabinoids has been known for a while, their biological effects remain to be fully elucidated. Recently, several studies have focused on the role of these PG-G or PG-EA in vivo. In this review we take a closer look at the literature concerning these novel bioactive lipids and their role in inflammation.

Care and feeding of the endocannabinoid system: a systematic review of potential clinical interventions that upregulate the endocannabinoid system

Background

The “classic” endocannabinoid (eCB) system includes the cannabinoid receptors CB₁ and CB₂, the eCB ligands anandamide (AEA) and 2-arachidonoylglycerol (2-AG), and their metabolic enzymes. An emerging literature documents the “eCB deficiency syndrome” as an etiology in migraine, fibromyalgia, irritable bowel syndrome, psychological disorders, and other conditions. We performed a systematic review of clinical interventions that enhance the eCB system—ways to upregulate cannabinoid receptors, increase ligand synthesis, or inhibit ligand degradation.

Methodology/Principal Findings

We searched PubMed for clinical trials, observational studies, and preclinical research. Data synthesis was qualitative. Exclusion criteria limited the results to 184 in vitro studies, 102 in vivo animal studies, and 36 human studies. Evidence indicates that several classes of pharmaceuticals upregulate the eCB system, including analgesics (acetaminophen, non-steroidal anti-inflammatory drugs, opioids, glucocorticoids), antidepressants, antipsychotics, anxiolytics, and anticonvulsants. Clinical interventions characterized as “complementary and alternative medicine” also upregulate the eCB system: massage and manipulation, acupuncture, dietary supplements, and herbal medicines. Lifestyle modification (diet, weight control, exercise, and the use of psychoactive substances—alcohol, tobacco, coffee, cannabis) also modulate the eCB system.

Conclusions/Significance

Few clinical trials have assessed interventions that upregulate the eCB system. Many preclinical studies point to other potential approaches; human trials are needed to explore these promising interventions.

Endocannabinoids as biomarkers of human reproduction

BACKGROUND

Infertility is a condition of the reproductive system that affects ∼10-15% of couples attempting to conceive a baby. More than half of all cases of infertility are a result of female conditions, while the remaining cases can be attributed to male factors, or to a combination of both. The search for suitable biomarkers of pregnancy outcome is a challenging issue in human reproduction, aimed at identifying molecules with predictive significance of the reproductive potential of male and female gametes. Among the various candidates, endocannabinoids (eCBs), and in particular anandamide (AEA), represent potential biomarkers of human fertility disturbances. Any perturbation of the balance between synthesis and degradation of eCBs will result in local changes of their tone in human female and male reproductive tracts, which in turn regulates various pathophysiological processes, oocyte and sperm maturation included.

METHODS

PubMed and Web of Science databases were searched for papers using relevant keywords like 'biomarker', 'endocannabinoid', 'infertility', 'pregnancy' and 'reproduction'.

RESULTS

In this review, we discuss different studies on the measurements of AEA and related eCBs in human reproductive cells, tissues and fluids, where the local contribution of these bioactive lipids could be critical in ensuring normal sperm fertilizing ability and pregnancy.

CONCLUSION

Based on the available data, we suggest that the AEA tone has the potential to be exploited as a novel diagnostic biomarker of infertility, to be used in association with assays of conventional hormones (e.g. progesterone, β-chorionic gonadotrophin) and semen analysis. However further quantitative research of its predictive capacity is required.

Endogenous Bioactive Lipids and the Regulation of Conventional Outflow Facility

Perturbation of paracrine signaling within the human conventional outflow pathway influences tissue homeostasis and outflow function. For example, exogenous introduction of the bioactive lipids, sphingosine-1-phosphate, anandamide or prostaglandin F(2α), to conventional outflow tissues alters the rate of drainage of aqueous humor through the trabecular meshwork, and into Schlemm's canal. This review summarizes recent data that characterizes endogenous bioactive lipids, their receptors and associated signaling partners in the conventional outflow tract. We also discuss the potential of targeting such signaling pathways as a strategy for the development of therapeutics to treat ocular hypertension and glaucoma.

Impact of inflammation on neurotransmitter changes in major depression: an insight into the action of antidepressants

This review summarises the evidence that chronic low grade inflammation plays an important role in the pathology of depression. Evidence is provided that pro-inflammatory cytokines, together with dysfunctional endocrine and neurotransmitter systems, provide a network of changes that underlie depression and may ultimately contribute to the neurodegenerative changes that characterise depression in the elderly. Antidepressants attenuate the inflammatory changes and hypercortisolaemia by reducing the release of the pro-inflammatory cytokines from activated microglia, and by sensitizing the glucocorticoids receptors in the HPA axis. These effects correlate with an improvement in monoamine neurotransmitter function. The possible mechanisms whereby this cascade of changes occurs are outlined. In conclusion, the mechanisms whereby antidepressants act should now consider the involvement of the immune and endocrine systems in addition to the central neurotransmitters. This may open up possibilities for a new generation of antidepressants in the future.

Brain region-specific changes in N-acylethanolamine contents with time of day

The N-acylethanolamines (NAEs) exert important behavioral, physiological, and immunological effects through actions at cannabinoid and other receptors. We measured concentrations of three NAEs, the Km and Vmax for fatty acid amide hydrolysis (FAAH), FAAH protein and FAAH mRNA in prefrontal cortex, hippocampus, hypothalamus, amygdala, striatum, and cerebellum at 4 h intervals, starting at 03:00. Significant differences in N-arachidonylethanolamine contents among the times examined occur in the prefrontal cortex (PFC), hippocampus, hypothalamus, and striatum. N-Oleoylethanolamine concentrations exhibit large fluctuations over the day in the cerebellum, including a threefold decrease between 19:00 and 23:00. N-Palmitoylethanolamine and N-oleoylethanolamine were significantly, positively correlated in all regions examined except the hypothalamus. FAAH Km values are significantly affected by time of day in PFC, hippocampus and amygdala and FAAH Vmax values are significantly affected in PFC, hippocampus and cerebellum. However, correlational data indicate that FAAH does not play a primary role in the circadian regulation of the NAE concentrations. FAAH protein expression is not significantly different among the harvest times in any brain region examined. Concentrations of 2-arachidonoylglycerol are significantly affected by time of harvest in the striatum and cerebellum, but not in other brain regions. Together, these data indicate that the NAEs exhibit diverse patterns of change with time of day that are likely the result of alterations in biosynthesis, and support the hypothesis that N-arachidonylethanolamine is a tonic activator of cannabinoid receptor signaling.

Endocannabinoid system and pain: an introduction

The endocannabinoid (EC) system consists of two main receptors: cannabinoid type 1 receptor cannabinoid receptors are found in both the central nervous system (CNS) and periphery, whereas the cannabinoid type 2 receptor cannabinoid receptor is found principally in the immune system and to a lesser extent in the CNS. The EC family consists of two classes of well characterised ligands; the N-acyl ethanolamines, such as N-arachidonoyl ethanolamide or anandamide (AEA), and the monoacylglycerols, such as 2-arachidonoyl glycerol. The various synthetic and catabolic pathways for these enzymes have been (with the exception of AEA synthesis) elucidated. To date, much work has examined the role of EC in nociceptive processing and the potential of targeting the EC system to produce analgesia. Cannabinoid receptors and ligands are found at almost every level of the pain pathway from peripheral sites, such as peripheral nerves and immune cells, to central integration sites such as the spinal cord, and higher brain regions such as the periaqueductal grey and the rostral ventrolateral medulla associated with descending control of pain. EC have been shown to induce analgesia in preclinical models of acute nociception and chronic pain states. The purpose of this review is to critically evaluate the evidence for the role of EC in the pain pathway and the therapeutic potential of EC to produce analgesia. We also review the present clinical work conducted with EC, and examine whether targeting the EC system might offer a novel target for analgesics, and also potentially disease-modifying interventions for pathophysiological pain states.

Ethanolamide oxylipins of linolenic acid can negatively regulate Arabidopsis seedling development

N-Acylethanolamines (NAEs) are fatty-acid derivatives with potent biological activities in a wide range of eukaryotic organisms. Polyunsaturated NAEs are among the most abundant NAE types in seeds of Arabidopsis thaliana, and they can be metabolized by either fatty acid amide hydrolase (FAAH) or by lipoxygenase (LOX) to low levels during seedling establishment. Here, we identify and quantify endogenous oxylipin metabolites of N-linolenoylethanolamine (NAE 18:3) in Arabidopsis seedlings and show that their levels were higher in faah knockout seedlings. Quantification of oxylipin metabolites in lox mutants demonstrated altered partitioning of NAE 18:3 into 9- or 13-LOX pathways, and this was especially exaggerated when exogenous NAE was added to seedlings. When maintained at micromolar concentrations, NAE 18:3 specifically induced cotyledon bleaching of light-grown seedlings within a restricted stage of development. Comprehensive oxylipin profiling together with genetic and pharmacological interference with LOX activity suggested that both 9-hydroxy and 13-hydroxy linolenoylethanolamides, but not corresponding free fatty-acid metabolites, contributed to the reversible disruption of thylakoid membranes in chloroplasts of seedling cotyledons. We suggest that NAE oxylipins of linolenic acid represent a newly identified, endogenous set of bioactive compounds that may act in opposition to progression of normal seedling development and must be depleted for successful establishment.

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.

2-arachidonoylglycerol interferes with lithium-induced vomiting in the house musk shrew, Suncus murinus

The role of the endocannabinoid system in vomiting has been previously studied using several animal species. These investigations have clearly demonstrated an anti-emetic role for the eCB, anandamide, in these animal models; however, research concerning the role of 2-arhachidonoylglycerol (2AG) has been less clear. The aim of the present study was to assess the effects of exogenous 2AG administration in the house musk shrew, Suncus murinus. In Experiment 1, shrews were injected with vehicle or 2AG (1, 2, 5, 10 mg/kg) 15 min prior to behavioral testing in which the frequency of vomiting episodes was observed. In Experiment 2, shrews were pre-treated with 2AG (2, 5 mg/kg) prior to being administered the emetic drug, lithium chloride (LiCl). It was found that 2AG alone did not induce emesis, but interfered with vomiting in response to LiCl administration. The anti-emetic effects of 2AG in Suncus murinus do not appear to be mediated by CB1 receptors, as concomitant pretreatment with the CB1 receptor antagonist, SR141716, did not reverse the suppressive effects of 2AG. These results confirm that manipulations that increase levels of 2AG exert anti-emetic effects in the house musk shrew.

Recent progress in prostaglandin F2α ethanolamide (prostamide F2α) research and therapeutics

Prostamide (prostaglandin ethanolamide) research emerged from two distinct lines of research: 1) the unique pharmacology of the antiglaucoma drug bimatoprost and 2) the discovery that endocannabinoid anandamide was converted by COX-2 to a series of electrochemically neutral prostaglandin (PG) ethanolamides. Bimatoprost pharmacology was found to be virtually identical to that of prostamide F2α. The earliest studies relied on comparison of agonist potencies compared with PGF2α and synthetic prostaglandin F2α (FP) receptor agonists. The subsequent discovery of selective and potent prostamide receptor antagonists (AGN 211334-6, as shown in Fig. 3) was critical for distinguishing between prostamide and FP receptor-mediated effects. The prostamide F2α receptor was then modeled by cotransfecting the wild-type FP receptor with an mRNA splicing variant (altFP4).Bimatoprost is now used therapeutically for treating both glaucoma and eyelash hypotrichosis. Bimatoprost also stimulates hair growth in isolated human scalp hair follicles. A strong effect is also seen in mouse pelage hair, where bimatoprost essentially halves the onset of hair regrowth and the time to achieve full hair regrowth in shaved mice. Beyond glaucoma and hair growth, bimatoprost has potential for reducing fat deposition. Studies to date suggest that preadipocytes are the cellular target for bimatoprost. The discovery of the enzyme prostamide/PGF synthase was invaluable in elucidating the anatomic distribution of prostamide F2α. High expression in the central nervous system provided the impetus for later studies that described prostamide F2α as a nociceptive mediator in the spinal cord. At the translational level, bimatoprost has already provided therapeutics in two distinct areas and the use of both prostamide agonists and antagonists may provide other useful medicaments.

Human platelets generate phospholipid-esterified prostaglandins via cyclooxygenase-1 that are inhibited by low dose aspirin supplementation

Oxidized phospholipids (oxPLs) generated nonenzymatically display pleiotropic biological actions in inflammation. Their generation by cellular cyclooxygenases (COXs) is currently unknown. To determine whether platelets generate prostaglandin (PG)-containing oxPLs, then characterize their structures and mechanisms of formation, we applied precursor scanning-tandem mass spectrometry to lipid extracts of agonist-activated human platelets. Thrombin, collagen, or ionophore activation stimulated generation of families of PGs comprising PGE₂ and D₂ attached to four phosphatidylethanolamine (PE) phospholipids (16:0p/, 18:1p/, 18:0p/, and 18:0a/). They formed within 2 to 5 min of activation in a calcium, phospholipase C, p38 MAP kinases, MEK1, cPLA₂, and src tyrosine kinase-dependent manner (28.1 ± 2.3 pg/2 × 10⁸ platelets). Unlike free PGs, they remained cell associated, suggesting an autocrine mode of action. Their generation was inhibited by in vivo aspirin supplementation (75 mg/day) or in vitro COX-1 blockade. Inhibitors of fatty acyl reesterification blocked generation significantly, while purified COX-1 was unable to directly oxidize PE in vitro. This indicates that they form in platelets via rapid esterification of COX-1 derived PGE₂/D₂ into PE. In summary, COX-1 in human platelets acutely mediates membrane phospholipid oxidation via formation of PG-esterified PLs in response to pathophysiological agonists.

Cyclooxygenase-2, prostaglandin E2 glycerol ester and nitric oxide are involved in muscarine-induced presynaptic enhancement at the vertebrate neuromuscular junction

Previous work has demonstrated that activation of muscarinic acetylcholine receptors at the lizard neuromuscular junction (NMJ) induces a biphasic modulation of evoked neurotransmitter release: an initial depression followed by a delayed enhancement. The depression is mediated by the release of the endocannabinoid 2-arachidonylglycerol (2-AG) from the muscle and its binding to cannabinoid type 1 receptors on the motor nerve terminal. The work presented here suggests that the delayed enhancement of neurotransmitter release is mediated by cyclooxygenase-2 (COX-2) as it converts 2-AG to the glycerol ester of prostaglandin E2 (PGE2-G). Using immunofluorescence, COX-2 was detected in the perisynaptic Schwann cells (PSCs) surrounding the NMJ. Pretreatment with either of the selective COX-2 inhibitors, nimesulide or DuP 697, prevents the delayed increase in endplate potential (EPP) amplitude normally produced by muscarine. In keeping with its putative role as a mediator of the delayed muscarinic effect, PGE2-G enhances evoked neurotransmitter release. Specifically, PGE2-G increases the amplitude of EPPs without altering that of spontaneous miniature EPPs. As shown previously for the muscarinic effect, the enhancement of evoked neurotransmitter release by PGE2-G depends on nitric oxide (NO) as the response is abolished by application of either N(G)-nitro-l-arginine methyl ester (l-NAME), an inhibitor of NO synthesis, or carboxy-PTIO, a chelator of NO. Intriguingly, the enhancement is not prevented by AH6809, a prostaglandin receptor antagonist, but is blocked by capsazepine, a TRPV1 and TRPM8 receptor antagonist. Taken together, these results suggest that the conversion of 2-AG to PGE2-G by COX-2 underlies the muscarine-induced enhancement of neurotransmitter release at the vertebrate NMJ.

Dynamic changes to the endocannabinoid system in models of chronic pain

The analgesic effects of cannabinoid ligands, mediated by CB1 receptors are well established. However, the side-effect profile of CB1 receptor ligands has necessitated the search for alternative cannabinoid-based approaches to analgesia. Herein, we review the current literature describing the impact of chronic pain states on the key components of the endocannabinoid receptor system, in terms of regionally restricted changes in receptor expression and levels of key metabolic enzymes that influence the local levels of the endocannabinoids. The evidence that spinal CB2 receptors have a novel role in the modulation of nociceptive processing in models of neuropathic pain, as well as in models of cancer pain and arthritis is discussed. Recent advances in our understanding of the spinal location of the key enzymes that regulate the levels of the endocannabinoid 2-AG are discussed alongside the outcomes of recent studies of the effects of inhibiting the catabolism of 2-AG in models of pain. The complexities of the enzymes capable of metabolizing both anandamide (AEA) and 2-AG have become increasingly apparent. More recently, it has come to light that some of the metabolites of AEA and 2-AG generated by cyclooxygenase-2, lipoxygenases and cytochrome P450 are biologically active and can either exacerbate or inhibit nociceptive signalling.

The endocannabinoid system in energy homeostasis and the etiopathology of metabolic disorders

Endocannabinoids and cannabinoid CB1 receptors are known to play a generalized role in energy homeostasis. However, clinical trials with the first generation of CB1 blockers, now discontinued due to psychiatric side effects, were originally designed to reduce food intake and body weight rather than the metabolic risk factors associated with obesity. In this review, we discuss how, in addition to promoting energy intake, endocannabinoids control lipid and glucose metabolism in several peripheral organs, particularly the liver and adipose tissue. Direct actions in skeletal muscle and pancreas are also emerging. This knowledge may help in the design of future therapies for the metabolic syndrome.

Characterisation of the prostaglandin E2-ethanolamide suppression of tumour necrosis factor-α production in human monocytic cells

BACKGROUND AND PURPOSE

Prostaglandin ethanolamides or prostamides are naturally occurring neutral lipid derivatives of prostaglandins that have been shown to be synthesised in vivo following COX-facilitated oxygenation of arachidonoyl ethanolamine (anandamide). Although the actions of prostaglandins have been extensively studied, little is known about the physiological or pathophysiological effects of prostamides. Since prostaglandin E2 has potent immunosuppressive/immunomodulating actions, the aim of the present study was to determine whether the derivative, prostaglandin E2 ethanolamide (PGE2-EA), could modulate the production of the pro-inflammatory cytokine tumour necrosis factor-α in human blood and human monocytic cells and indicate whether this action involved the same receptor systems/signals as PGE2.

EXPERIMENTAL APPROACH

Whole human blood, monocytes isolated from the blood or the human monocytic cell line THP-1 was incubated with LPS and the level of TNF-α produced was measured by ELISA assay. The actions of PGE2-EA were assessed on the LPS-induced TNF-α release. In addition, in order to ascertain the receptors involved, the levels of cyclic AMP in cells were measured in monocytes and THP-1 cells in response to PGE2-EA and directly compared to those of PGE2. The effect of PGE2-EA on the binding of radiolabelled PGE2 to cells was also measured. Cells were incubated with radiolabelled arachidonic acid and ethanolamine to estimate the production of PGE2-EA.

KEY RESULTS

PGE2-EA potently suppressed TNF-α production in blood, monocytes and the cell line THP-1 in a concentration-dependent manner. This occurred via cyclic AMP pathways as indicated by agents which interfere with these pathways and also direct ligand binding experiments. It was also shown that the cells were able to endogenously produce PGE2-EA.

CONCLUSIONS AND IMPLICATIONS

This study reports that PGE2-EA can downregulate the production of TNF-α by human mononuclear cells in response to an immune stimulus, i.e. LPS-activated TLR4, and that this appears to occur via a cAMP-dependent mechanism that most likely involves binding to the EP2 receptor.

Lipids and addiction: how sex steroids, prostaglandins, and cannabinoids interact with drugs of abuse

Lipidomics aims to identify and characterize all endogenous species of lipids and understand their roles in cellular signaling and, ultimately, the functioning of the organism. We are on the cusp of fully understanding the functions of many of the lipid signaling systems that have been identified for decades (e.g., steroids, prostaglandins), whereas our understanding of newer lipid signaling systems (e.g., endocannabinoids, N-acyl amides) still lags considerably behind. With an emphasis on their roles in the neurophysiology of addiction, we will examine three classes of lipids--sex steroids, prostaglandins, and cannabinoids--and how they work synergistically in the neurocircuitry of motivation. We will first give a brief overview of the biosynthesis for each class of lipid and its receptors, and then summarize what is known about the collective roles of the lipids in cocaine and alcohol abuse. This approach provides a novel view of lipid signaling as a class of molecules and their synergistic roles in addiction.

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.

2-Arachidonoyl-glycerol- and arachidonic acid-stimulated neutrophils release antimicrobial effectors against E. coli, S. aureus, HSV-1, and RSV

The endocannabinoid 2-AG is highly susceptible to its hydrolysis into AA, which activates neutrophils through de novo LTB(4) biosynthesis, independently of CB activation. In this study, we show that 2-AG and AA stimulate neutrophils to release antimicrobial effectors. Supernatants of neutrophils activated with nanomolar concentrations of 2-AG and AA indeed inhibited the infectivity of HSV-1 and RSV. Additionally, the supernatants of 2-AG- and AA-stimulated neutrophils strongly impaired the growth of Escherichia coli and Staphylococcus aureus. This correlated with the release of a large amount (micrograms) of α-defensins, as well as a limited amount (nanograms) of LL-37. All the effects of AA and 2-AG mentioned above were prevented by inhibiting LTB(4) biosynthesis or by blocking BLT(1). Importantly, neither CB(2) receptor agonists nor antagonists could mimic nor prevent the effects of 2-AG, respectively. In fact, qPCR data show that contaminating eosinophils express ∼100-fold more CB(2) receptor mRNA than purified neutrophils, suggesting that CB(2) receptor expression by human neutrophils is limited and that contaminating eosinophils are likely responsible for the previously documented CB(2) expression by freshly isolated human neutrophils. The rapid conversion of 2-AG to AA and their subsequent metabolism into LTB(4) promote 2-AG and AA as multifunctional activators of neutrophils, mainly exerting their effects by activating the BLT(1). Considering that nanomolar concentrations of AA or 2-AG were sufficient to impair viral infectivity, this suggests potential physiological roles for 2-AG and AA as regulators of host defense in vivo.

Bioactive lipid mediators in skin inflammation and immunity

The skin is the primary barrier from the outside environment, protecting the host from injury, infectious pathogens, water loss and solar ultraviolet radiation. In this role, it is supported by a highly organized system comprising elements of innate and adaptive immunity, responsive to inflammatory stimuli. The cutaneous immune system is regulated by mediators such as cytokines and bioactive lipids that can initiate rapid immune responses with controlled inflammation, followed by efficient resolution. However, when immune responses are inadequate or mounted against non-infectious agents, these mediators contribute to skin pathologies involving unresolved or chronic inflammation. Skin is characterized by active lipid metabolism and fatty acids play crucial roles both in terms of structural integrity and functionality, in particular when transformed to bioactive mediators. Eicosanoids, endocannabinoids and sphingolipids are such key bioactive lipids, intimately involved in skin biology, inflammation and immunity. We discuss their origins, role and influence over various cells of the epidermis, dermis and cutaneous immune system and examine their function in examples of inflammatory skin conditions. We focus on psoriasis, atopic and contact dermatitis, acne vulgaris, wound healing and photodermatology that demonstrate dysregulation of bioactive lipid metabolism and examine ways of using this insight to inform novel therapeutics.

Monoacylglycerol lipase - a target for drug development?

The endocannabinoid (eCB) system is involved in processes as diverse as control of appetite, perception of pain and the limitation of cancer cell growth and invasion. The enzymes responsible for eCB breakdown are attractive pharmacological targets, and fatty acid amide hydrolase inhibitors, which potentiate the levels of the eCB anandamide, are now undergoing pharmaceutical development. 'Drugable' selective inhibitors of monoacylglycerol lipase, a key enzyme regulating the levels of the other main eCB, 2-arachidonoylglycerol, were however not identified until very recently. Their availability has resulted in a large expansion of our knowledge concerning the pharmacological consequences of monoacylglycerol lipase inhibition and hence the role(s) played by the enzyme in the body. In this review, the pharmacology of monoacylglycerol lipase will be discussed, together with an analysis of the therapeutic potential of monoacylglycerol lipase inhibitors as analgesics and anticancer agents.

Receptor-dependent and receptor-independent endocannabinoid signaling: a therapeutic target for regulation of cancer growth

The endocannabinoid system comprises the G-protein coupled CB1 cannabinoid receptor (CB1R) and CB2 cannabinoid receptor (CB2R), their endogenous ligands (endocannabinoids), and the enzymes responsible for their synthesis and catabolism. Recent works have revealed several important interactions between the endocannabinoid system and cancer. Moreover, it is now well established that synthetic small molecule cannabinoid receptor agonist acting on either CB1R or CB2R or both exerts anti-cancer effects on a variety of tumor cells. Recent results from many laboratories reported that the expression of CB1R and CB2R in prostate cancer, breast cancer, and many other cancer cells is higher than that in corresponding non-malignant tissues. The mechanisms by which cannabinoids acting on CB1R or CB2R exert their effects on cancer cells are quite diverse and complex. Further, several studies demonstrated that some of the anti-proliferative and apoptotic effects of cannabinoids are mediated by receptor-independent mechanisms. In this minireview we provide an overview of the major findings on the effects of endogenous and/or synthetic cannabinoids on breast and prostate cancers. We also provide insight into receptor independent mechanisms of the anti-cancer effects of cannabinoids under in vitro and in vivo conditions.

β-Amyloid exacerbates inflammation in astrocytes lacking fatty acid amide hydrolase through a mechanism involving PPAR-α, PPAR-γ and TRPV1, but not CB₁ or CB₂ receptors

BACKGROUND AND PURPOSE

The endocannabinoid system may regulate glial cell functions and their responses to pathological stimuli, specifically, Alzheimer's disease. One experimental approach is the enhancement of endocannabinoid tone by blocking the activity of degradative enzymes, such as fatty acid amide hydrolase (FAAH).

EXPERIMENTAL APPROACH

We examined the role of FAAH in the response of astrocytes to the pathologic form of β-amyloid (Aβ). Astrocytes from wild-type mice (WT) and from mice lacking FAAH (FAAH-KO) were incubated with Aβ for 8, 24 and 48 h, and their inflammatory responses were quantified by elisa, western-blotting and real-time quantitative-PCR.

KEY RESULTS

FAAH-KO astrocytes were significantly more responsive to Aβ than WT astrocytes, as shown by the higher production of pro-inflammatory cytokines. Expression of COX-2, inducible NOS and TNF-α was also increased in Aβ-exposed KO astrocytes compared with that in WTs. These effects were accompanied by a differential pattern of activation of signalling cascades involved in mediating inflammatory responses, such as ERK1/2, p38MAPK and NFκB. PPAR-α and PPAR-γ as well as transient receptor potential vanilloid-1 (TRPV1), but not cannabinoid CB₁ or CB₂ receptors, mediate some of the differential changes observed in Aβ-exposed FAAH-KO astrocytes. The pharmacological blockade of FAAH did not render astrocytes more sensitive to Aβ. In contrast, exogenous addition of several acylethanolamides (anandamide, palmitoylethanolamide and oleoylethanolamide) induced an antiinflammatory response.

CONCLUSIONS

The genetic deletion of FAAH in astrocytes exacerbated their inflammatory phenotype against Aβ in a process involving PPAR-α, PPAR-γ and TRPV1 receptors.

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.

Defining the COX inhibitor selectivity of NSAIDs: implications for understanding toxicity

The hypothesis that the anti-inflammatory activity of NSAIDs derives from COX inhibition is well established. It also underpins the accepted mechanism of the gastrointestinal and renal toxicity of NSAIDs. However, in terms of NSAID-induced cardiovascular toxicity, is COX inhibition then guilty by association? Multiple experimental models of COX-1/COX-2 inhibition have enabled ranking of the relative inhibitory activity of NSAIDs. Inhibition is expressed as an IC(50) value and the index of COX selectivity as the ratio of the IC(50) value for COX-2 and COX-1. These data informed the 'imbalance hypothesis' that the cardiovascular risk of NSAIDs results from an imbalance in the detrimental actions of COX-1-derived thromboxane A(2) and the beneficial actions of COX-2-derived prostacyclin (PGI(2)). Data derived from in vitro models used to generate NSAID IC(50) values are discussed in the context of the difficulties in defining COX selectivity and hence understanding the toxicity of NSAIDs in current clinical use.

Lack of effect of chronic pre-treatment with the FAAH inhibitor URB597 on inflammatory pain behaviour: evidence for plastic changes in the endocannabinoid system

BACKGROUND AND PURPOSE

Elevating levels of endocannabinoids with inhibitors of fatty acid amide hydrolase (FAAH) is a major focus of pain research, purported to be a safer approach devoid of cannabinoid receptor-mediated side effects. Here, we have determined the effects of sustained pharmacological inhibition of FAAH on inflammatory pain behaviour and if pharmacological inhibition of FAAH was as effective as genetic deletion of FAAH on pain behaviour.

EXPERIMENTAL APPROACH

Effects of pre-treatment with a single dose, versus 4 day repeated dosing with the selective FAAH inhibitor, URB597 (i.p. 0.3 mg·kg⁻¹), on carrageenan-induced inflammatory pain behaviour and spinal pro-inflammatory gene induction were determined in rats. Effects of pain induction and of the drug treatments on levels of arachidonoyl ethanolamide (AEA), palmitoyl ethanolamide (PEA) and oleolyl ethanolamide (OEA) in the spinal cord were determined.

KEY RESULTS

Single, but not repeated, URB597 treatment significantly attenuated the development of inflammatory hyperalgesia (P < 0.001, vs. vehicle-treated animals). Neither mode of URB597 treatment altered levels of AEA, PEA and OEA in the hind paw, or carrageenan-induced paw oedema. Single URB597 treatment produced larger increases in AEA, PEA and OEA in the spinal cord, compared with those after repeated administration. Single and repeated URB597 treatment decreased levels of immunoreactive N-acylphosphatidylethanolamine phospholipase D (NAPE-PLD) in the spinal cord and attenuated carrageenan-induced spinal pro-inflammatory gene induction.

CONCLUSION AND IMPLICATIONS

Changes in the endocannabinoid system may contribute to the loss of analgesic effects following repeated administration of low dose URB597 in this model of inflammatory pain.

Prostaglandin H synthase-2-catalyzed oxygenation of 2-arachidonoylglycerol is more sensitive to peroxide tone than oxygenation of arachidonic acid

The endocannabinoid, 2-arachidonoylglycerol (2-AG), is a selective substrate for the inducible isoform of prostaglandin H synthase (PGHS), PGHS-2. Its turnover leads to the formation of glyceryl esters of prostaglandins (PG-Gs), a subset of which elicits agonism at unique, as yet unidentified, receptors. The k(cat)/K(m) values for oxygenation of arachidonic acid (AA) and 2-AG by PGHS-2 are very similar, but the sensitivities of the two substrates to peroxide-dependent activation have not been compared. 15-Hydroperoxy derivatives of AA and 2-AG were found to be comparable in their ability to serve as substrates for the peroxidase activities of PGHS-2, PGHS-1, and glutathione peroxidase (GPx). They also were comparable in the activation of AA oxygenation by cyanide-inhibited PGHS-2. However, oxygenation of 2-AG was significantly suppressed relative to AA by the presence of GPx and GSH. Furthermore, 2-AG oxygenation by peroxidase-deficient H388YmPGHS-2 was much less efficient than AA oxygenation. Wild-type rates of 2-AG oxygenation were restored by treatment of H388YmPGHS-2 with hydroperoxide derivatives of AA or 2-AG. RNAi silencing of phospholipid hydroperoxide-specific GPx (GPx4) in NIH/3T3 cells led to increases in cellular peroxidation and in the levels of the isoprostane product, 8-epi-PGF(2α). GPx4 silencing led to 2-4-fold increases in PG-G formation but no change in PG formation. Thus, cellular peroxide tone may be an important determinant of the extent of endocannabinoid oxygenation by PGHS-2.

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 families of bioactive oxidized phospholipids generated by immune cells: identification and signaling actions

Phospholipids are of critical importance in mammalian cell biology, both through providing a permeability barrier and acting as substrates for synthesis of lipid mediators. Recently, several new families of bioactive lipids were identified that form through the enzymatic oxidation of membrane phospholipids in circulating innate immune cells and platelets. These comprise eicosanoids attached to phosphatidylethanolamine and phosphatidylcholine and form within 2-5 minutes of cell activation by pathophysiologic agonists, via the coordinated action of receptors and enzymes. In this review, we summarize what is currently known regarding their structures, mechanisms of formation, cell biology, and signaling actions. We show that phospholipid oxidation by acutely activated immune cells is a controlled event, and we propose a central role in regulating membrane biology and innate immune function during health and disease. We also review the mass spectrometry methods used for identification of the lipids and describe how these approaches can be used for discovery of new lipid mediators in complex biologic samples.

Metabolism of anandamide into eoxamides by 15-lipoxygenase-1 and glutathione transferases

Human 15-lipoxygenase-1 (15-LO-1) can metabolize arachidonic acid (ARA) into pro-inflammatory mediators such as the eoxins, 15-hydroperoxyeicosatetraenoic acid (HPETE), and 15-hydroxyeicosatetraenoyl-phosphatidylethanolamine. We have in this study investigated the formation of various lipid hydroperoxide by either purified 15-LO-1 or in the Hodgkin lymphoma cell line L1236, which contain abundant amount of 15-LO-1. Both purified 15-LO-1 and L1236 cells produced lipid hydroperoxides more efficiently when anandamide (AEA) or 2-arachidonoyl-glycerol ester was used as substrate than with ARA. Furthermore, L1236 cells converted AEA to a novel class of cysteinyl-containing metabolites. Based on RP-HPLC, mass spectrometry and comparison to synthetic products, these metabolites were identified as the ethanolamide of the eoxin (EX) C(4) and EXD(4). By using the epoxide EXA(4)-ethanol amide, it was also found that platelets have the capacity to produce the ethanolamide of EXC(4) and EXD(4). We suggest that the ethanolamides of the eoxins should be referred to as eoxamides, in analogy to the ethanolamides of prostaglandins which are named prostamides. The metabolism of AEA into eoxamides might engender molecules with novel biological effects. Alternatively, it might represent a new mechanism for the termination of AEA signalling.

Production and actions of the anandamide metabolite prostamide E2 in the renal medulla

Medullipin has been proposed to be an antihypertensive lipid hormone released from the renal medulla in response to increased arterial pressure and renal medullary blood flow. Because anandamide (AEA) possesses characteristics of this purported hormone, the present study tested the hypothesis that AEA or one of its metabolites represents medullipin. AEA was demonstrated to be enriched in the kidney medulla compared with cortex. Western blotting and enzymatic analyses of renal cortical and medullary microsomes revealed opposite patterns of enrichment of two AEA-metabolizing enzymes, with fatty acid amide hydrolase higher in the renal cortex and cyclooxygenase-2 (COX-2) higher in the renal medulla. In COX-2 reactions with renal medullary microsomes, prostamide E2, the ethanolamide of prostaglandin E₂, was the major product detected. Intramedullarily infused AEA dose-dependently increased urine volume and sodium and potassium excretion (15-60 nmol/kg/min) but had little effect on mean arterial pressure (MAP). The renal excretory effects of AEA were blocked by intravenous infusion of celecoxib (0.1 μg/kg/min), a selective COX-2 inhibitor, suggesting the involvement of a prostamide intermediate. Plasma kinetic analysis revealed longer elimination half-lives for AEA and prostamide E2 compared with prostaglandin E₂. Intravenous prostamide E2 reduced MAP and increased renal blood flow (RBF), actions opposite to those of angiotensin II. Coinfusion of prostamide E2 inhibited angiotensin II effects on MAP and RBF. These results suggest that AEA and/or its prostamide metabolites in the renal medulla may represent medullipin and function as a regulator of body fluid and MAP.

"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.

The endocannabinoid system: an overview

Upon the identification of anandamide (AEA) in the porcine brain, numerous studies contributed to the current state of knowledge regarding all elements that form the “endocannabinoid system (ECS).”How this complex system of receptors, ligands, and enzymes is integrated in helping to regulate fundamental processes at level of central nervous and peripheral systems and how its regulation and dysregulation might counteract disturbances of such functions, is nowadays still under investigation. However, the most recent advances on the physiological distribution and functional role of ECS allowed the progress of various research tools aimed at the therapeutic exploitation of endocannabinoid (eCB) signaling, as well as the development of novel drugs with pharmacological advantages. Here, we shall briefly overview the metabolic and signal transduction pathways of the main eCBs representatives, AEA, and 2-arachidonoylglycerol (2-AG), and we will discuss the therapeutic potential of new ECS-oriented drugs.

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.

Metamizol, a non-opioid analgesic, acts via endocannabinoids in the PAG-RVM axis during inflammation in rats

The most commonly used drugs against pain act by inhibiting the cyclooxygenases (COXs). Metamizol (dipyrone) inhibits the COXs and is widely used in Europe and Latin America as a non-opioid analgesic. One target of metamizol and other non-opioid analgesics is the periaqueductal grey matter (PAG), where they trigger descending inhibition of spinal nociceptive transmission. Also, cannabinoids exert an analgesic action at several structures in the peripheral and central nervous system, including the PAG. The present study investigates whether the antinociceptive action of metamizol in the lateral-ventrolateral (LVL) PAG during inflammation is related to endocannabinoids. In anaesthetized rats, unitary action potentials were recorded from spinal nociceptive neurons with receptive fields in the ipsilateral hind paw. Inflammation of the paw induced neuronal hyperexcitability, which was attenuated by intra-LVL-PAG microinjection of metamizol either at the beginning of inflammation or when hyperexcitability was fully established. In both cases, the antinociceptive effect of metamizol was reduced by a microinjection of AM251, an antagonist at the CB1 cannabinoid receptor, either into the LVL-PAG or into the rostral ventromedial medulla (RVM). The RVM is a downstream structure that funnels PAG-derived descending inhibition into the spinal cord. These results show that endocannabinoids and their CB1 receptor (1) contribute at the LVL-PAG to the antinociceptive effects of metamizol, and possibly other non-opioid analgesics; and (2) participate in the PAG-derived activation of RVM descending antinociceptive influences.