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

The pharmacology and therapeutic relevance of endocannabinoid derived cyclo-oxygenase (COX)-2 products

The discovery of anandamide and 2-arachidonyl glycerol (2-AG) as naturally occurring mammalian endocannabinoids has had important and wide-reaching therapeutic implications. This, to a large extent, ensues from the complexity of endocannabinoid biology. One facet of endocannabinoid biology now receiving increased attention is the cyclo-oxygenase-2 (COX-2) derived oxidation products. Anandamide and 2-AG are oxidized to a range of PG-ethanolamides and PG-glyceryl esters that closely approaches that of the prostaglandins (PGs) formed from arachidonic acid. The pharmacology of these electrochemically neutral PG-ethanolamides (prostamides) and PG-glyceryl esters appears to be unique. No meaningful interaction with natural or recombinant prostanoid receptors is apparent. Nevertheless, in certain cells and tissues, prostamides and PG-glyceryl esters exert potent effects. The recent discovery of selective antagonists for the putative prostamide receptor has been a major advance in further establishing prostamide pharmacology as an entity distinct from prostanoid receptors. Since discovery of the prototype prostamide antagonist (AGN 204396), rapid progress has been made. The latest prostamide antagonists (AGN 211334-6) are 100 times more potent than the prototype and are, therefore, sufficiently active to be used in living animal studies. These compounds will allow a full evaluation of the role of prostamides in health and disease. To date, the only therapeutic application for prostamides is in glaucoma. The prostamide analog, bimatoprost, being the most effective ocular hypotensive drug currently available. Interestingly, PGE(2)-glyceryl ester and its chemically stable analog PGE(2)-serinolamide also lower intraocular pressure in dogs. Nevertheless, the therapeutic future of PGE(2)-glyceryl ester is more likely to reside in inflammation.

Structural basis for induced formation of the inflammatory mediator prostaglandin E2

Prostaglandins (PG) are bioactive lipids produced from arachidonic acid via the action of cyclooxygenases and terminal PG synthases. Microsomal prostaglandin E synthase 1 (MPGES1) constitutes an inducible glutathione-dependent integral membrane protein that catalyzes the oxidoreduction of cyclooxygenase derived PGH(2) into PGE(2). MPGES1 has been implicated in a number of human diseases or pathological conditions, such as rheumatoid arthritis, fever, and pain, and is therefore regarded as a primary target for development of novel antiinflammatory drugs. To provide a structural basis for insight in the catalytic mechanism, we determined the structure of MPGES1 in complex with glutathione by electron crystallography from 2D crystals induced in the presence of phospholipids. Together with results from site-directed mutagenesis and activity measurements, we can thereby demonstrate the role of specific amino acid residues. Glutathione is found to bind in a U-shaped conformation at the interface between subunits in the protein trimer. It is exposed to a site facing the lipid bilayer, which forms the specific environment for the oxidoreduction of PGH(2) to PGE(2) after displacement of the cytoplasmic half of the N-terminal transmembrane helix. Hence, insight into the dynamic behavior of MPGES1 and homologous membrane proteins in inflammation and detoxification is provided.

Gastrointestinal endocannabinoid system: multifaceted roles in the healthy and inflamed intestine

1. The endogenous cannabinoid (endocannabinoid) system is emerging as a key modulator of intestinal physiology, influencing motility, secretion, epithelial integrity and immune function in the gut, in addition to influencing satiety and emesis. 2. Accumulating evidence suggests that the endocannabinoid system may play a pivotal role in the pathophysiology of gastrointestinal disease, particularly in the light of recent studies demonstrating an effect of endocannabinoids on the development of experimental inflammation and linkages with functional clinical disorders characterized by altered motility. 3. The predominant endocannabinoids, anandamide and 2-arachidonoylglycerol, not only mediate their effects via two recognized cannabinoid receptor subtypes, namely CB(1) and CB(2), but emerging evidence now shows they are also substrates for cyclo-oxygenase (COX)-2, generating a distinct and novel class of prostaglandin ethanolamides (prostamides) and prostaglandin glycerol esters. These compounds are bioactive and may mediate an array of biological effects distinct to those of conventional prostanoids. 4. The effects of prostamides on gastrointestinal motility, secretion, sensation and immune function have not been characterized extensively. Prostamides may play an important role in gastrointestinal inflammation, particularly given the enhanced expression of both COX-2 and endocannabinoids that occurs in the inflamed gut. 5. Further preclinical studies are needed to determine the therapeutic potential of drugs targeting the endocannabinoid system in functional and inflammatory gut disorders, to assist with the determination of feasibility for clinical translation.

Dual effect of anandamide on rat placenta nitric oxide synthesis

Anandamide (AEA) has been reported to have pleiotropic effects on reproduction, but the mechanism by which it exerts these effects is unclear. The aim of this study is to characterize rat placental endocannabinoid system and to analyze the possible functional role of AEA in the regulation of NO levels in rat placenta during pregnancy. We found that cannabinoids receptors (CB1 and CB2), FAAH and TRPV1 were expressed in chorio-allantoic placenta. NOS activity peaked at day 13 and decreased with progression of pregnancy. Both exogenous and endogenous AEA significantly decreased NOS activity. Although pre-incubation with AM251 (CB1 antagonist) or AM630 (CB2 antagonist) had no effect, co-incubation with both antagonists induced NOS activity. Furthermore, pre-incubation with exogenous AEA and both antagonists resulted in the induction of placental NOS activity and this effect was reverted with capsazepine (selective TRPV1 antagonist). Additionally, the enhanced NO synthesis caused by capsaicin was abrogated by co-treatment with capsazepine, illustrating that NOS activity could be modulated by TRPV1. Finally, the inhibition of TRPV1 receptor by capsazepine caused a significant fall in NOS activity. These data support the concept that AEA modulates NO levels by two independent pathways: (1) diminishing the NOS activity via CBs; and (2) stimulating NO synthesis via TRPV1. We hypothesized that AEA have an important implication in the normal function of placental tissues.

Cyclooxygenase-2 in synaptic signaling

Cyclooxygenase-2 (COX-2), a rate-limiting enzyme converting arachidonic acid to prostaglandins and a key player in neuroinflammation, has been implicated in the pathogenesis of neurodegenerative diseases such as multiple sclerosis, Parkinson's and Alzheimer's diseases, and in traumatic brain injury- and ischemia-induced neuronal damage, and epileptogenesis. Accumulated information suggests that the contribution of COX-2 to neuropathology is associated with its involvement in synaptic modification. Inhibition or elevation of COX-2 has been shown to suppress or enhance excitatory glutamatergic neurotransmission and long-term potentiation (LTP). These events are mainly mediated via PGE(2), the predominant reaction product of COX-2, and the PGE(2) subtype 2 receptor (EP(2))-protein kinase A pathway. Recent evidence shows that endogenous cannabinoids are substrates for COX-2 and can be oxygenated by COX-2 to form new classes of prostaglandins (prostaglandin glycerol esters and prostaglandin ethanolamides). These COX-2 oxidative metabolites of endocannabinoids, as novel signaling mediators, modulate synaptic transmission and plasticity and cause neurodegeneration. The actions of these COX-2 metabolites are likely mediated by mitogen-activated protein kinase (MAPK) and inositol 1,4,5-trisphosphate (IP(3)) signal transduction pathways. These discoveries suggest that the contributions of COX-2 to neurotransmission and brain malfunction result not only from its conversion of arachidonic acid to classic prostaglandins but also from its oxidative metabolism of endocannabinoids to novel prostaglandins. Thus, elucidation of COX-2 in synaptic signaling may provide a mechanistic basis for designing new drugs aimed at preventing, treating or alleviating neuroinflammation-associated neurological disorders.

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

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

Inhibition of fatty acid amide hydrolase and cyclooxygenase-2 increases levels of endocannabinoid related molecules and produces analgesia via peroxisome proliferator-activated receptor-alpha in a model of inflammatory pain

The antinociceptive effects of the endocannabinoids (ECs) are enhanced by inhibiting catabolic enzymes such as fatty acid amide hydrolase (FAAH). The physiological relevance of the metabolism of ECs by other pathways, such as cyclooxygenase-2 (COX2) is less clear. To address this question we compared the effects of local inhibition of FAAH versus COX2 (URB597 and nimesulide, respectively) on inflammatory hyperalgesia and levels of endocannabinoids and related molecules in the hindpaw. Inflammatory hyperalgesia was measured following intraplantar injection of carrageenan. Effects of intraplantar injection of URB597 (25 microg and 100 microg) or nimesulide (50 microg) on hyperalgesia and hindpaw levels of anandamide (AEA), 2-arachidonoylglycerol (2AG) and N-palmitoylethanolamine (PEA) were determined. Although both doses of URB597 increased levels of AEA and 2AG in the carrageenan inflamed hindpaw, only the lower dose of URB597 attenuated hyperalgesia (P<0.05). Nimesulide attenuated both hyperalgesia and hindpaw oedema (P<0.001, P<0.01, respectively) and increased levels of PEA (P<0.05) in the hindpaw. Since both AEA and PEA are ligands for peroxisome proliferator-activated receptor-alpha (PPARalpha), the effects of the PPARalpha antagonist GW6471 on nimesulide- and URB597-mediated effects were studied. GW6471, but not a PPARgamma antagonist, blocked the inhibitory effects of nimesulide and URB597 on hyperalgesia. Our data suggest that both COX2 and FAAH play a role in the metabolism of endocannabinoids and related molecules. The finding that PPARalpha antagonism blocked the inhibitory effects of nimesulide and URB597 suggests that PPARalpha contributes to their antinociceptive effects in the carrageenan model of inflammatory hyperalgesia.

Non-redundant functions of cyclooxygenases: oxygenation of endocannabinoids

The two cyclooxygenase (COX) enzymes catalyze the oxygenation of arachidonic acid to prostaglandin endoperoxides, which are the common intermediates in the biosynthesis of the bioactive lipids prostaglandins and thromboxane. COX-1 and COX-2 are approximately 60% identical in amino acid sequence, exhibit highly homologous three-dimensional structures, and appear functionally similar at the biochemical level. Recent work has uncovered a subtle functional difference between the two enzymes, namely the ability of COX-2 to efficiently utilize neutral derivatives (esters and amides) of arachidonic acid as substrates. Foremost among these neutral substrates are the endocannabinoids 2-arachidonoylglycerol and arachidonoylethanolamide. This raises the possibility that COX-2 oxygenation plays a role in a novel signaling pathway dependent on agonist-induced release of endocannabinoids and their selective oxygenation by COX-2. Among the products of COX-2 oxygenation of endocannabinoids are glyceryl prostaglandins, some of which (e.g. glyceryl prostaglandin E(2) and glyceryl prostaglandin I(2)) exhibit interesting biological activities in inflammatory, neurological, and vascular systems. These compounds are produced in intact cells stimulated with physiological agonists and have been isolated from in vivo sources. Important concepts relevant to the hypothesis of a COX-2-selective signaling pathway are presented.

Glucocorticoids shift arachidonic acid metabolism toward endocannabinoid synthesis: a non-genomic anti-inflammatory switch

Glucocorticoids are capable of exerting both genomic and non-genomic actions in target cells of multiple tissues, including the brain, which trigger an array of electrophysiological, metabolic, secretory and inflammatory regulatory responses. Here, we have attempted to show how glucocorticoids may generate a rapid anti-inflammatory response by promoting arachidonic acid-containing endocannabinoids biosynthesis. According to our hypothesized model, non-genomic action of glucocorticoids results in the global shift of membrane lipid metabolism, subverting metabolic pathways toward the synthesis of the anti-inflammatory endocannabinoids, anandamide (AEA) and 2-arachidonoyl-glycerol (2-AG), and away from arachidonic acid production. Post-transcriptional inhibition of cyclooxygenase-2 (COX(2)) synthesis by glucocorticoids assists this mechanism by suppressing the synthesis of pro-inflammatory prostaglandins as well as endocannabinoid-derived prostanoids. In the central nervous system (CNS) this may represent a major neuroprotective system, which may cross-talk with leptin signaling in the hypothalamus allowing for the coordination between energy homeostasis and the inflammatory response.

COX-2 oxidative metabolism of endocannabinoids augments hippocampal synaptic plasticity

Endocannabinoids (eCBs) are important endogenous lipid mediators in synaptic transmission and plasticity and are oxygenated by cyclooxygenase-2 (COX-2) to form new types of prostaglandins. However, little is known about whether COX-2 oxidative metabolism of eCBs and their metabolites alter synaptic signaling. Here we demonstrate that increased COX-2 expression significantly enhances basal synaptic transmission and augments long-term potentiation (LTP) in the mouse hippocampus. This augmentation was inhibited in the presence of a selective COX-2 inhibitor or with deletion of the COX-2 gene. The CB(1) receptor-mediated depolarization-induced suppression of inhibition (DSI) was diminished when COX-2 expression was increased either with lipopolysaccharide (LPS) stimulation or transgenic neuronal over-expression of COX-2. Conversely, DSI was potentiated when COX-2 activity was pharmacologically or genetically inhibited. Interestingly, COX-2 oxidative metabolites of eCBs elevated LTP, an effect opposite to that of their parent molecules 2-arachidonoylglycerol (2-AG) and arachidonoyl ethanolamide (AEA). In addition, the ERK/MAPK and IP(3) pathways were found to mediate PGE(2)-G-induced enhancement of LTP. Our results indicate that COX-2 oxidative metabolism of eCBs is an important signaling pathway in modulation of synaptic transmission and plasticity.

Presynaptic modulation by endocannabinoids

Modulation of neurotransmitter release by G-protein-coupled receptors (GPCRs) is a prominent presynaptic mechanism for regulation of synaptic transmission. Activation of GPCRs located at the presynaptic terminal can decrease the probability of neurotransmitter release. This presynaptic depression involves activation of Gi/o-type G-proteins that mediate different inhibitory mechanisms, including inhibition of voltage-gated calcium channels, activation of potassium channels, and direct inhibition of the vesicle fusion process. A variety of neurotransmitters and modulatory agents can activate GPCRs that produce presynaptic depression. Among these are lipid metabolites that serve as agonists for GPCRs. The discovery of endocannabinoids and their cognate receptors, including the CB1 receptor, has stimulated intense investigation into the neurophysiological roles of these lipid metabolites. It is now clear that presynaptic depression is the major physiological role for the CB1 receptor. Endocannabinoids activate this receptor mainly via a retrograde signaling process in which these compounds are synthesized in and released from postsynaptic neuronal elements, and travel back to the presynaptic terminal to act on the CB1 receptor. This retrograde endocannabinoid modulation has been implicated in short-term synaptic depression, including suppression of excitatory or inhibitory transmission induced by postsynaptic depolarization and transient synaptic depression induced by activation of postsynaptic GPCRs during agonist treatment or synaptic activation. Endocannabinoids and the CB1 receptor also play a key role in one form of long-term synaptic depression (LTD) that involves a longlasting decrease in neurotransmitter release.

Molecular characterization of a novel type of prostamide/prostaglandin F synthase, belonging to the thioredoxin-like superfamily

Prostaglandin F (PGF) ethanolamide (prostamide F) synthase, which catalyzed the reduction of prostamide H(2) to prostamide F(2alpha), was found in mouse and swine brain. The enzyme was purified from swine brain, and its amino acid sequence was defined. The mouse enzyme consisted of a 603-bp open reading frame coding for a 201-amino acid polypeptide with a molecular weight of 21,669. The amino acid sequence placed the enzyme in the thioredoxin-like superfamily with Cys(44) being the active site. The enzyme expressed in Escherichia coli as well as the native enzyme catalyzed not only the reduction of prostamide H(2) to prostamide F(2alpha) but also that of PGH(2) to PGF(2alpha). The V(max) and K(m) values for prostamide H(2) were about 0.25 micromol/min.mg of protein and 7.6 microm, respectively, and those for PGH(2) were about 0.69 micromol/min.mg of protein and 6.9 microm, respectively. Neither PGE(2) nor PGD(2) served as a substrate for this synthase. Based on these data, we named the enzyme prostamide/PGF synthase. Although the enzyme showed a broad specificity for reductants, reduced thioredoxin preferentially served as a reducing equivalent donor for this enzyme. Moreover, Northern and Western blot analyses in addition to the prostamide F synthase activity showed that the enzyme was mainly distributed in the brain and spinal cord, and the immunohistochemical study in the spinal cord showed that the enzyme was found mainly in the cytosol. These results suggest that prostamide/PGF synthase may play an important functional role in the central nervous system.

Altered GABAergic neurotransmission is associated with increased kainate-induced seizure in prostaglandin-endoperoxide synthase-2 deficient mice

Excitotoxicity involves over activation of brain excitatory glutamate receptors and has been implicated in neurological, neurodegenerative and neuropsychiatric diseases. Metabolism of arachidonic acid (AA) through the phospholipase A(2) (PLA(2))/prostaglandin-endoperoxide synthase (PTGS) pathway is increased after excitotoxic stimulation. However, the individual roles of the PTGS isoforms in this process are not well established. We assessed the role of the PTGS isoforms in the process of excitotoxicity by exposing mice deficient in either PTGS-1 (PTGS-1(-/-)) or PTGS-2 (PTGS-2(-/-)) to the prototypic excitotoxin, kainic acid (KA). Seizure intensity and neuronal damage were significantly elevated in KA-exposed PTGS-2(-/-), but not in PTGS-1(-/-), mice. The increased susceptibility was not associated with an alteration in KA receptor binding activity or mediated through the CB1 endocannabinoid receptor. The frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) was decreased in the CA1 pyramidal neurons of PTGS-2(-/-) mice, suggesting an alteration of GABAergic function. In wild-type mice, six weeks treatment with the PTGS-2 selective inhibitor celecoxib recapitulated the increased susceptibility to KA-induced excitotoxicity observed in PTGS-2(-/-) mice, further supporting the role of PTGS-2 in the excitotoxic process. The increased susceptibility to KA was also associated with decreased brain levels of PGE(2), a biomarker of PTGS-2 activity. Our results suggest that PTGS-2 activity and its specific products may modulate neuronal excitability by affecting GABAergic neurotransmission. Further, inhibition of PTGS-2, but not PTGS-1, may increase the susceptibility to seizures.

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

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

The contribution of cyclooxygenase-2 to endocannabinoid metabolism and action

The development of sensitive analytical methods for measurement of endocannabinoids, their metabolites, and related lipids, has underlined the complexity of the endocannabinoid system. A case can be made for an 'endocannabinoid soup' (akin to the inflammatory soup) whereby the net effect of a pathological state and/or a pharmacological intervention on this system is the result not only of changes in endocannabinoid levels but also of their metabolites and related compounds that affect their function. With respect to the metabolism of anandamide and 2-arachidonoylglycerol, the main hydrolytic enzymes involved are fatty acid amide hydrolase and monoacylglycerol lipase. However, other pathways can come into play when these are blocked. Cyclooxygenase-2 derived metabolites of anandamide and 2-arachidonoylglycerol have a number of properties, including effects upon cell viability, contraction of the cat iris sphincter (an effect mediated by a novel receptor), mobilization of calcium and modulation of synaptic transmission. Nonsteroidal anti-inflammatory agents, whose primary mode of action is the inhibition of cyclooxygenase, can also interact with the endocannabinoid system both in vitro and in vivo. Other enzymes, such as the lipoxygenase and cytochrome P450 oxidative enzymes, can also metabolize endocannabinoids and produce biologically active compounds. It is concluded that sensitive analytical methods, which allow for measurement of endocannabinoids and related lipids, should provide vital information as to the importance of these alternative metabolic pathways when the primary hydrolytic endocannabinoid metabolizing enzymes are inhibited.

Prostamides (prostaglandin-ethanolamides) and their pharmacology

The prostamides are part of a large and continually expanding series of pharmacologically unique neutral lipids. They are COX-2 derived oxidation products of the endocannabinoid/endovanniloid anandamide. Prostamide pharmacology is unique and, as in the case of the endocannabinoids anandamide and 2-arachidonylglycerol, bears little resemblance to that of the corresponding free acids. By virtue of its close relationship to the anti-glaucoma drug bimatoprost, prostamide F(2alpha) has received the greatest research attention. Prostamide F(2alpha) and bimatoprost effects appear independent of prostanoid FP receptor activation, according to a litany of agonist studies. Studies involving freshly isolated and separate feline iridial smooth muscle cells revealed that bimatoprost and FP receptor agonists stimulated different cells, without exception. This suggests the existence of receptors that preferentially recognize prostamide F(2alpha). The recent discovery of prostamide antagonists has provided further support for prostamide receptors as discrete entities. The prototypical prostamide antagonists, AGN 204396 and 7, blocked the effects of prostamide F(2alpha) and bimatoprost but not those of PGF(2alpha) and FP receptor agonists in the feline iris. Second generation more potent prostamide antagonists, such as AGN 211334, should allow the role of prostamides in health and disease to be elucidated. From the therapeutics standpoint, the prostamide F(2alpha) analogue bimatoprost is the most efficacious ocular hypotensive agent currently available for the treatment of glaucoma.

Conformationally constrained analogues of 2-arachidonoylglycerol

Novel monocyclic analogues of 2-arachidonoylglycerol (2-AG) were designed in order to explore the pharmacophoric conformations of this endocannabinoid ligand at the key cannabinergic proteins. All 2-arachidonoyl esters of 1,2,3-cyclohexanetriol [meso-7 (AM5504), (+/-)-8 (AM5503), and meso-9 (AM5505)] were synthesized by regioselective acylation of 2,3-dihydroxycyclohexanone followed by selective reductions. The optically active isomers (+)-8 (AM4434) and (-)-8 (AM4435) were synthesized from (2S,3S)- and (2R,3R)-2,3-dihydroxycyclohexanone, respectively, via a chemoenzymatic route. These head group constrained and conformationally restricted analogues of 2-AG as well as the 1-keto precursors were evaluated as substrates for the endocannabinoid deactivating hydrolytic enzymes monoacylglycerol lipase (MGL) and fatty acid amide hydrolase (FAAH), and also were tested for their affinities for CB1 and CB2 cannabinoid receptors. The observed biochemical differences between these ligands can help define the conformational requirements for 2-AG activity at each of the above endocannabinoid protein targets.

Tempo and mode in the endocannaboinoid system

The best-known endocannabinoid ligands, anandamide and 2-AG, signal at least seven receptors and involve ten metabolic enzymes. Genes for the receptors and enzymes were examined for heterogeneities in tempo (relative rate of evolution, RRE) and mode (selection pressure, Ka/Ks) in six organisms with sequenced genomes. BLAST identified orthologs as reciprocal best hits, and nucleotide alignments were performed with ClustalX and MacClade. Two bioinformatics platforms, LiKaKs (a distance-based LWL85 model) and SNAP (a parsimony-based NG86 model) made pairwise comparisons of orthologs in murids (rat and mouse) and primates (human and macaque). Mean RRE of the 18 endocannabinoid genes was significantly greater in murids than primates, whereas mean Ka/Ks did not differ significantly. Next we used FUGE (tree-based maximum-likelihood model) to compute human lineage-specific Ka/Ks calculations for 18 genes, which ranged from 1.11 to 0.00, in rank order from highest to lowest: PTPN22, NAAA, TRPV1, TRPA1, NAPE-PLD, MAGL, PPARgamma, FAAH1, COX2, FAAH2, ABDH4, CB2, GPR55, DAGLbeta, PPARalpha, TRPV4, CB1, DAGLalpha; differences were significant (p < 0.0001). Rat and mouse presented different rank orders (e.g., GPR55 generated the greatest Ka/Ks ratio). The 18 genes were then tested for recent positive selection (within 10,000 yr) using an extended haplotype homozygosity analysis of SNP data from the HapMap database. Significant evidence (p < 0.05) of a positive "selective sweep" was exhibited by PTPN22, TRPV1, NAPE-PLD, and DAGLalpha. In conclusion, the endocannabinoid system is collectively under strong purifying selection, although some genes show evidence of adaptive evolution.

Rapid screening for potentially relevant polymorphisms in the human fatty acid amide hydrolase gene using Pyrosequencing

INTRODUCTION

Fatty acid amides such as the endocannabinoid anandamide serve as mammalian lipid transmitters in various physiological and pathophysiological processes including inflammation. They are rapidly degraded by the fatty acid amide hydrolase (FAAH). Non-functional FAAH resulted in reduced inflammatory and nociceptive responses. Evidence suggests that human genetic FAAH variants modulate pain and addiction but their clinical role is still poorly known. We therefore developed reliable high-throughput screening assays for FAAH polymorphisms to facilitate research of their clinical role.

MATERIALS AND METHODS

Six simplex Pyrosequencing assays were developed for FAAH polymorphisms dbSNP rs932816, rs4141964, rs324420, rs324419, rs2295633 and rs12029329 spanning the whole FAAH gene. They are frequent or have been functionally associated. Assays were established and validated in DNA samples from 350 healthy unrelated Caucasians.

RESULTS

In all 350 DNA samples the six FAAH polymorphisms were identified correctly as verified by control samples obtained by conventional sequencing. The observed frequencies of homozygous, heterozygous and non-carriers of the minor alleles were in agreement with the Hardy-Weinberg equilibrium. Minor allelic frequencies were: rs932816G>A=0.26, rs4141964C>T=0.37, rs324420C>A=0.20, rs324419C>T=0.15, rs2295633G>A=0.35 and rs12029329G>C=0.25. SNPs were in high linkage except between rs324419 and rs12029329. One single haploblock was identified, spanning either the whole gene range or excluding rs12029329 in the 3' region, depending on the statistical procedure of haloblock assignment.

CONCLUSION

The presently developed Pyrosequencing assays allow for quick and reliable detection of FAAH genotypes and may facilitate investigations of FAAH genetic functional associations.

COX-2 oxidative metabolite of endocannabinoid 2-AG enhances excitatory glutamatergic synaptic transmission and induces neurotoxicity

Neuroinflammation has been implicated in the pathogenesis of neurodegenerative diseases. Cyclooxygenase-2 (COX-2), an inducible enzyme converting arachidonic acid (AA) to prostaglandins, is the key player in neuroinflammation. It has been long thought that the COX-2-mediated neuronal injury/degeneration is attributed to the increased production of AA-derived prostaglandins. Recent studies show that endogenous cannabinoid 2-arachidonoylglycerol (2-AG) is a natural substrate for COX-2, and it can be oxygenated by COX-2 to form prostaglandin glyceryl esters. In this study, we demonstrate that prostaglandin E(2) glyceryl ester (PGE(2)-G), a major COX-2 oxidative metabolite of 2-arachidonoylglycerol, enhanced hippocampal glutamatergic synaptic transmission indicated by the increased frequency of miniature excitatory post-synaptic currents, and induced neuronal injury/death revealed by the terminal transferase dUTP nick end labeling staining and caspase 3 activation. The actions of PGE(2)-G are not mediated via a cannabinoid receptor 1, but mediated through ERK, p38 mitogen-activated protein kinase, IP(3), and NF-kappaB signal transduction pathways. In addition, the PGE(2)-G-induced neurotoxicity is attenuated by blockade of the NMDA receptors. Our results suggest that the COX-2 oxidative metabolism of endocannabinoids is an important mechanism contributing to the inflammation-induced neurodegeneration.

Effect of chronic CB1 cannabinoid receptor antagonism on livers of rats with biliary cirrhosis

Recent studies have shown that the activated endocannabinoid system participates in the increase in IHR (intrahepatic resistance) in cirrhosis. The increased hepatic production of vasoconstrictive eicosanoids is involved in the effect of endocannabinoids on the hepatic microcirculation in cirrhosis; however, the mechanisms of these effects are still unknown. The aim of the present study was to investigate the effects of chronic CB(1) (cannabinoid 1) receptor blockade in the hepatic microcirculation of CBL (common bile-duct-ligated) cirrhotic rats. After 1 week of treatment with AM251, a specific CB(1) receptor antagonist, IHR, SMA (superior mesenteric artery) blood flow and hepatic production of eicosanoids [TXB(2) (thromboxane B(2)), 6-keto PGF(1alpha) (prostaglandin F(1alpha)) and Cys-LTs (cysteinyl leukotrienes)] were measured. Additionally, the protein levels of hepatic COX (cyclo-oxygenase) isoforms, 5-LOX (5-lipoxygenase), CB(1) receptor, TGF-beta(1) (transforming growth factor beta(1)), cPLA(2) [cytosolic PLA(2) (phospholipase A(2))], sPLA(2) (secreted PLA(2)) and collagen deposition were also measured. In AM251-treated cirrhotic rats, a decrease in portal venous pressure was associated with the decrease in IHR and SMA blood flow. Additionally, the protein levels of hepatic CB(1) receptor, TGF-beta(1), cPLA(2) and hepatic collagen deposition, and the hepatic levels of 5-LOX and COX-2 and the corresponding production of TXB(2) and Cys-LTs in perfusates, were significantly decreased after 1 week of AM251 treatment in cirrhotic rats. Furthermore, acute infusion of AM251 resulted in a decrease in SMA blood flow and an increase in SMA resistance in CBL rats. In conclusion, the chronic effects of AM251 treatment on the intrahepatic microcirculation were, at least partly, mediated by the inhibition of hepatic TGF-beta(1) activity, which was associated with decreased hepatic collagen deposition and the activated PLA(2)/eicosanoid cascade in cirrhotic livers.

Participation of CGRP and prostanoids in the sex-linked differences of vascular anandamide effects in mesenteric beds of Sprague-Dawley rats

The in vitro exposure to anandamide elicits greater relaxations in mesenteric beds isolated from female compared to male rats. The present work shows that in mesenteric beds precontracted with noradrenaline the removal of endothelium increased the relaxation caused by anandamide in male and ovariectomized female but not in sham-operated female rats. The nitric oxide synthase inhibition with 100 microM N(omega)-nitro-L-arginine methyl ester hydrochloride (L-NAME) and the sensory in vivo denervation through neonatal administration of capsaicin also reduced anandamide-induced relaxations but these effects had the same extent in male and in female mesenteries. The content of calcitonin gene related peptide (CGRP) in mesenteric beds, that was higher in intact female than in male rats, was reduced by ovariectomy and restored to control values 21 days after a 3 weekly i.m. administration of 450 microg/kg 17beta-oestradiol. This latter treatment also increased CGRP content in mesenteries from males up to the same levels observed in females. The basal release of CGRP in mesenteric beds was equivalent in either sex, but the exposure to anandamide increased CGRP release solely in female mesenteries. The ratio prostacyclin/thromboxane A(2) was selectively reduced in mesenteries from male rats after exposure to anandamide, due to the decrease of the tissue levels of prostacyclin. Moreover, the cyclooxygenase-2 inhibitor 0.1 microM N-[2-(cyclohexyloxy)-4-nitrophenyl]-methanesulphonamide (NS-398) diminished the relaxations caused by anandamide solely in female rats. It is proposed that relaxing factors such as CGRP and prostacyclin contribute to the higher relaxations caused by anandamide in the vasculature of female rats.

Anandamide Metabolism by Human Liver and Kidney Microsomal Cytochrome P450 Enzymes to Form Hydroxyeicosatetraenoic and Epoxyeicosatrienoic Acid Ethanolamides

The endocannabinoid anandamide is an arachidonic acid derivative that is found in most tissues where it acts as an important signaling mediator in neurological, immune, cardiovascular, and other functions. Cytochromes P450 (P450s) are known to oxidize arachidonic acid to the physiologically active molecules hydroxyeicosatetraenoic acids (HETEs) and epoxyeicosatrienoic acids (EETs), which play important roles in blood pressure regulation and inflammation. To determine whether anandamide can also be oxidized by P450s, its metabolism by human liver and kidney microsomes was investigated. The kidney microsomes metabolized anandamide to a single mono-oxygenated product, which was identified as 20-HETE-ethanolamide (EA). Human liver microsomal incubations with anandamide also produced 20-HETE-EA in addition to 5,6-, 8,9-, 11-12, and 14,15-EET-EA. The EET-EAs produced by the liver microsomal P450s were converted to their corresponding dihydroxy derivatives by microsomal epoxide hydrolase. P450 4F2 was identified as the isoform that is most probably responsible for the formation of 20-HETE-EA in both human kidney and human liver, with an apparent Km of 0.7 microM. The apparent Km values of the human liver microsomes for the formation of the EET-EAs were between 4 and 5 microM, and P450 3A4 was identified as the primary P450 in the liver responsible for epoxidation of anandamide. The in vivo formation and biological relevance of the P450-derived HETE and EET ethanolamides remains to be determined.

A shifted repertoire of endocannabinoid genes in the zebrafish (Danio rerio)

The zebrafish has served as a model organism for developmental biology. Sequencing its genome has expanded zebrafish research into physiology and drug-development testing. Several cannabinoid pharmaceuticals are in development, but expression of endocannabinoid receptors and enzymes remains unknown in this species. We conducted a bioinformatics analysis of the zebrafish genome using 17 human endocannabinoid genes as a reference set. Putative zebrafish orthologs were identified in filtered BLAST searches as reciprocal best hits. Orthology was confirmed by three in silico methods: phylogenetic testing, synteny analysis, and functional mapping. Zebrafish expressed orthologs of cannabinoid receptor 1, transient receptor potential channel vanilloid receptor 4, GPR55 receptor, fatty acid amide hydrolase 1, monoacylglycerol lipase, NAPE-selective phospholipase D, abhydrolase domain-containing protein 4, and diacylglycerol lipase alpha and beta; and paired paralogs of cannabinoid receptor 2, fatty acid amide hydrolase 2, peroxisome proliferator-activated receptor alpha, prostaglandin-endoperoxide synthase 2, and transient receptor potential cation channel subtype A1. Functional mapping suggested the orthologs of transient receptor potential vanilloid receptor 1 and peroxisome proliferator-activated receptor gamma lack specific amino acids critical for cannabinoid ligand binding. No orthologs of N-acylethanolamine acid amidase or protein tyrosine phosphatase, non-receptor type 22 were identified. In conclusion, the zebrafish genome expresses a shifted repertoire of endocannabinoid genes. In vitro analyses are warranted before using zebrafish for cannabinoid development testing.

Neuropharmacology of the endocannabinoid signaling system-molecular mechanisms, biological actions and synaptic plasticity

The endocannabinoid signaling system is composed of the cannabinoid receptors; their endogenous ligands, the endocannabinoids; the enzymes that produce and inactivate the endocannabinoids; and the endocannabinoid transporters. The endocannabinoids are a new family of lipidic signal mediators, which includes amides, esters, and ethers of long-chain polyunsaturated fatty acids. Endocannabinoids signal through the same cell surface receptors that are targeted by Delta(9)-tetrahydrocannabinol (Delta(9)THC), the active principles of cannabis sativa preparations like hashish and marijuana. The biosynthetic pathways for the synthesis and release of endocannabinoids are still rather uncertain. Unlike neurotransmitter molecules that are typically held in vesicles before synaptic release, endocannabinoids are synthesized on demand within the plasma membrane. Once released, they travel in a retrograde direction and transiently suppress presynaptic neurotransmitter release through activation of cannabinoid receptors. The endocannabinoid signaling system is being found to be involved in an increasing number of pathological conditions. In the brain, endocannabinoid signaling is mostly inhibitory and suggests a role for cannabinoids as therapeutic agents in central nervous system (CNS) disease. Their ability to modulate synaptic efficacy has a wide range of functional consequences and provides unique therapeutic possibilities. The present review is focused on new information regarding the endocannabinoid signaling system in the brain. First, the structure, anatomical distribution, and signal transduction mechanisms of cannabinoid receptors are described. Second, the synthetic pathways of endocannabinoids are discussed, along with the putative mechanisms of their release, uptake, and degradation. Finally, the role of the endocannabinoid signaling system in the CNS and its potential as a therapeutic target in various CNS disease conditions, including alcoholism, are discussed.

Identification of an antagonist that selectively blocks the activity of prostamides (prostaglandin-ethanolamides) in the feline iris

BACKGROUND AND PURPOSE

The prostamides (prostaglandin-ethanolamides) and prostaglandin (PG) glyceryl esters are biosynthesized by COX-2 from the respective endocannabinoids anandamide and 2-arachidonyl glycerol. Agonist studies suggest that their pharmacologies are unique and unrelated to prostanoid receptors. This concept was further investigated using antagonists.

EXPERIMENTAL APPROACH

The isolated feline iris was used as a key preparation, where prostanoid FP receptors and prostamide activity co-exist. Activity at human recombinant FP and other prostanoid receptors was determined using stable transfectants.

KEY RESULTS

In the feline iris, AGN 204396 produced a rightward shift of the dose-response curves for prostamide F2alpha and the prostamide F2alpha analog bimatoprost but did not block the effects of PGF2alpha and synthetic FP receptor agonists. Studies on human recombinant prostanoid receptors confirmed that AGN 204396 did not behave as a prostanoid FP receptor antagonist. AGN 204396 exhibited no antagonism at DP and EP1-4, but was a highly effective TP receptor antagonist. Contrary to expectation, the FP receptor antagonist AL-8810 efficaciously contracted the cat iris. AGN 204396 did not affect AL-8810 induced contractions, demonstrating that AL-8810 and AGN 204396 are pharmacologically distinct. Unlike AL-8810, the ethylamide derivate of AL-8810 was not an agonist. Al-8810 did not block prostamide F2alpha activity. Finally, AGN 204396 did not block PGE2-glyceryl ester activity.

CONCLUSIONS AND IMPLICATIONS

The ability of AGN 204396 to selectively block prostamide responses suggests the existence of prostamide sensitive receptors as entities distinct from receptors recognizing PGF2alpha and PGE2-glyceryl ester.

The PGH-synthase system and isozyme-selective inhibition

Virtually all human cell types can express both cyclooxygenase (COX)-1 and COX-2 under appropriate circumstances. Both isoforms can subserve physiologic and pathophysiologic roles when coupled with the appropriate stimuli and downstream prostaglandin (PG)H2-isomerases and prostanoid receptors. Although the ratio of maximal biosynthetic capacity of human platelets to the basal rate of production of thromboxane A2 is approximately 5000, this ratio is much lower in the case of PGI2, thus dictating quite different requirements for the extent and duration of COX inhibition in human platelets and vascular endothelial cells to detect functional and clinical effects. The development of low-dose aspirin as an antiplatelet agent has been instrumental in characterizing the role of platelet COX-1 in atherothrombosis. Similarly, though quite unexpectedly, the development of coxibs as anti-inflammatory agents has been instrumental in elucidating the role of endothelial COX-2 in vascular occlusion. Because of differential requirements for the inhibition of thromboxane A2 versus PGI2 biosynthesis in vivo, most traditional nonsteroidal anti-inflammatory drugs tend to mimic the effects of coxibs, rather than aspirin, on prostanoid-dependent cardiovascular homeostasis.

Differential regulation of endocannabinoid synthesis and degradation in the uterus during embryo implantation

Preimplantation embryo development to the blastocyst stage and uterine differentiation to the receptive state are prerequisites for embryo implantation. Burgeoning evidence suggests that endocannabinoid signaling is critical to early pregnancy events. Anandamide (N-arachidonoylethanolamine) and 2-AG (2-arachidonoylglycerol) are two major endocannabinoids that bind to and activate G-protein coupled cannabinoid receptors CB1 and CB2. We have previously shown that a physiological tone of anandamide is critical to preimplantation events in mice, since either silencing or amplification of anandamide signaling causes retarded development and oviductal retention of embryos via CB1, leading to deferred implantation and compromised pregnancy outcome. Whether 2-AG, which also influences many biological functions, has any effects on early pregnancy remains unknown. Furthermore, mechanisms by which differential uterine endocannabinoid gradients are established under changing pregnancy state is not clearly understood. We show here that 2-AG is present at levels one order of magnitude higher than those of anandamide in the mouse uterus, but with similar patterns as anandamide, i.e. lower levels at implantation sites and higher at interimplantation sites. We also provide evidence that region- and stage-specific uterine expression of N-acylphosphatidylethanolamine-specific phospholipase D (NAPE-PLD) and fatty acid amide hydrolase (FAAH), and sn-1-diacylglycerol (DAG) lipase alpha (DAGLalpha) and monoacylglycerol lipase (MAGL) for synthesis and hydrolysis of anandamide and 2-AG, respectively, creates endocannabinoid gradients conducive to implantation. Our genetic evidence suggests that FAAH is the major degrading enzyme for anandamide, whereas COX-2, MAGL and to some extent COX-1 participate in metabolizing 2-AG in the pregnant uterus. The results suggest that aberrant functioning of these pathways impacting uterine anandamide and/or 2-AG levels would compromise pregnancy outcome.

Contributions of cyclooxygenase-2 to neuroplasticity and neuropathology of the central nervous system

Cyclooxygenase (COX) enzymes, or prostaglandin-endoperoxide synthases (PTGS), are heme-containing bis-oxygenases that catalyze the first committed reaction in metabolism of arachidonic acid (AA) to the potent lipid mediators, prostanoids and thromboxanes. Two isozymes of COX enzymes (COX-1 and COX-2) have been identified to date. This review will focus specifically on the neurobiological and neuropathological consequences of AA metabolism via the COX-2 pathway and discuss the potential therapeutic benefit of COX-2 inhibition in the setting of neurological disease. However, given the controversy surrounding the use of COX-2 selective inhibitors with respect to cardiovascular health, it will be important to move beyond COX to identify which down-stream effectors are responsible for the deleterious and/or potentially protective effects of COX-2 activation in the setting of neurological disease. Important advances toward this goal are highlighted herein. Identification of unique effectors in AA metabolism could direct the development of new therapeutics holding significant promise for the prevention and treatment of neurological disorders.

Lipid signaling and synaptic plasticity

Lipids are essential components of plasma- and organelle-membranes, not only providing a frame for embedded proteins (e.g., receptors and ion channels) but also functioning as reservoirs for lipid mediators. Increasing evidence indicates that bioactive lipids such as eicosanoids, endocannabinoids, and lysophospholipids serve as intercellular and intracellular signaling molecules participating in physiological and pathological functions in the brain. The discovery of some of these lipid receptors and novel lipid signaling mediators has sparked an intense interest in lipidomic neurobiology research. Classic prostaglandins (PGD(2), PGE(2), PGF(2alpha), PGI(2), and TXA(2)), catalyzed by cyclooxygenases (COX), are synthesized from arachidonic acid (AA). Experimental studies demonstrate that prostaglandin E(2) (PGE(2)), mainly derived from the COX-2 reaction, is an important mediator, acting as a retrograde messenger via a presynaptic PGE(2) subtype 2 receptor (EP(2)) in modulation of synaptic events. Novel prostaglandins (prostaglandin glycerol esters and prostaglandin ethanolamides) are COX-2 oxidative metabolites of endogenous cannabinoids (2-arachidonyl glycerol and arachidonyl ethanolamide). Recent evidence suggests that these new types of prostaglandins are likely novel signaling mediators involved in synaptic transmission and plasticity. This means that COX- 2 plays a central role in metabolisms of AA and endocannabinoids (eCBs) and productions of AA- and eCB- derived prostaglandins. Thus, in the present review article, the authors will mainly discuss COX-2 regulation of prostaglandin signaling in modulation of hippocampal synaptic transmission and plasticity.

Zymosan-induced glycerylprostaglandin and prostaglandin synthesis in resident peritoneal macrophages: roles of cyclo-oxygenase-1 and -2

COX [cyclo-oxygenase; PG (prostaglandin) G/H synthase] oxygenates AA (arachidonic acid) and 2-AG (2-arachidonylglycerol) to endoperoxides that are converted into PGs and PG-Gs (glycerylprostaglandins) respectively. In vitro, 2-AG is a selective substrate for COX-2, but in zymosan-stimulated peritoneal macrophages, PG-G synthesis is not sensitive to selective COX-2 inhibition. This suggests that COX-1 oxygenates 2-AG, so studies were carried out to identify enzymes involved in zymosan-dependent PG-G and PG synthesis. When macrophages from COX-1-/- or COX-2-/- mice were treated with zymosan, 20-25% and 10-15% of the PG and PG-G synthesis observed in wild-type cells respectively was COX-2 dependent. When exogenous AA and 2-AG were supplied to COX-2-/- macrophages, PG and PG-G synthesis was reduced as compared with wild-type cells. In contrast, when exogenous substrates were provided to COX-1-/- macrophages, PG-G but not PG synthesis was reduced. Product synthesis also was evaluated in macrophages from cPLA(2alpha) (cytosolic phospholipase A2alpha)-/- mice, in which zymosan-induced PG synthesis was markedly reduced, and PG-G synthesis was increased approx. 2-fold. These studies confirm that peritoneal macrophages synthesize PG-Gs in response to zymosan, but that this process is primarily COX-1-dependent, as is the synthesis of PGs. They also indicate that the 2-AG and AA used for PG-G and PG synthesis respectively are derived from independent pathways.

Evaluation of the role of the arachidonic acid cascade in anandamide's in vivo effects in mice

The pharmacological profiles of the endocannabinoid anandamide and exogenous cannabinoids (e.g., Delta9-tetrahydrocannabinol) are similar, but not exactly the same. One notable difference is that anandamide's in vivo effects in mice are not blocked by the brain cannabinoid (CB1) receptor antagonist SR141716A. The degree to which the rapid metabolism of anandamide to arachidonic acid might be involved in this unexpected lack of effect was the focus of this study. Mice were tested in a tetrad of tests sensitive to cannabinoids, consisting of spontaneous locomotion, ring immobility, rectal temperature and tail flick nociception. Anandamide and arachidonic acid produced a similar profile of effects, but neither drug was blocked by SR141716A. When hydrolysis of anandamide was inhibited by an amidase inhibitor (phenylmethyl sulfonyl fluoride; PMSF), however, SR141716A significantly attenuated anandamide's effects but did not completely block them. Similarly, the effects of the metabolically stable anandamide analog O-1812 were attenuated by SR141716A. The role of oxidative metabolism in anandamide's effects in the tetrad was also investigated through pharmacological modulation of cyclooxygenase and lipoxygenase, two major classes of enzymes that degrade arachidonic acid. Whereas the non-selective cyclooxygenase inhibitor ibuprofen blocked the in vivo effects of arachidonic acid, it did not alter anandamide's effects. Other modulators of the cyclooxygenase and lipoxygenase pathways also failed to block anandamide's effects. Together, these results offer partial support for a pharmacokinetic explanation of the failure of SR141716A to antagonize the effects of anandamide; however, they also suggest that non-CB1, non-CB2 receptors may be involved in mediation of anandamide's in vivo actions, particularly at higher doses.

PGE2 glycerol ester, a COX-2 oxidative metabolite of 2-arachidonoyl glycerol, modulates inhibitory synaptic transmission in mouse hippocampal neurons

The oxygenation of endogenous cannabinoids (eCBs) 2-arachidonoyl glycerol (2-AG) and arachidonoyl ethanolamide by cyclooxygenase-2 (COX-2) produces novel types of prostanoids: prostaglandin glycerol esters (PG-Gs) and prostaglandin ethanolamides (PG-EAs). However, the physiological function of COX-2 oxidative metabolites of eCBs is still unclear. Here we demonstrate that PGE2-G, a COX-2 oxidative metabolite of 2-AG, induced a concentration-dependent increase in the frequency ofminiature inhibitory postsynaptic currents (mIPSCs) in primary cultured hippocampal neurons, an effect opposite to that of 2-AG. This increase was not inhibited by SR141716, a CB1 receptor antagonist, but was attenuated by an IP3 or MAPK inhibitor. In addition, we also examined the effects of other prostanoids derived from COX-2 oxygenation of eCBs on mIPSCs. PGD2-G, PGF2alpha-G and PGD2-EA, but not PGE2-EA or PGF2alpha-EA, also increased the frequency of mIPSCs. The eCB-derived prostanoid-induced responses appeared to be different from those of corresponding arachidonic acid-derived prostanoids, implying that these effects are not mediated via known prostanoid receptors. We further discovered that the inhibition of COX-2 activity reduced inhibitory synaptic activity and augmented depolarization-induced suppression of inhibition (DSI), whereas the enhancement of COX-2 augmented the synaptic transmission and abolished DSI. Our results, which show that COX-2 oxidative metabolites of eCBs exert opposite effects to their parent molecules on inhibitory synaptic transmission, suggest that alterations in COX-2 activity will have significant impact on endocannabinoid signalling in hippocampal synaptic activity.

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

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

Bimatoprost: A Novel Antiglaucoma Agent

The aim of glaucoma therapy is to preserve vision by reducing intraocular pressure (IOP). Following recent National Eye Institute sponsored studies, it is becoming increasingly apparent that every mmHg of extra IOP lowering counts. Bimatoprost is the newest and most effective addition to the physician's armamentarium of ocular hypotensive drugs. Direct clinical comparisons have demonstrated that it is more efficacious than the prostaglandin (PG) FP receptor agonist prodrugs, latanoprost and travoprost, as well as a beta-adrenoceptor antagonist, timolol, alone or in fixed combination with the carbonic anhydrase inhibitor, dorzolamide. Moreover, patients that are refractory to latanoprost therapy may be successfully treated with bimatoprost. Such evidence provides support, at the clinical level, for the contention that bimatoprost is pharmacologically distinct from PG FP receptor agonist prodrugs. Bimatoprost is a structural analog of PGF2alpha-ethanolamide (prostamide F2alpha), which is formed from the endocannabinoid anandamide by a biosynthetic pathway involving cyclooxygenase-2 (COX-2). Their pharmacology is remarkably similar, such that bimatoprost may be regarded as a prostamide mimetic. The target receptor for bimatoprost and the prostamides appears unique and unrelated to PG- and endocannabinoid-sensitive receptors. Extensive ocular distribution/metabolism studies in non-human primates demonstrate that bimatoprost is not a prodrug, it remains essentially intact. Its profound ocular hypotensive effects may, therefore, be attributed to its prostamide-mimetic properties.

Mediator mechanisms involved in TRPV1 and P2X receptor-mediated, ROS-evoked bradypneic reflex in anesthetized rats

Inhalation of H2O2 is known to evoke bradypnea followed by tachypnea, which are reflexes resulting from stimulation by reactive oxygen species of vagal lung capsaicin-sensitive and myelinated afferents, respectively. This study investigated the pharmacological receptors and chemical mediators involved in triggering these responses. The ventilatory responses to 0.2% aerosolized H2O2 were studied before and after various pharmacological pretreatments in anesthetized rats. The initial bradypneic response was reduced by a transient receptor potential vanilloid 1 (TRPV1) receptor antagonist [capsazepine; change (Delta) = -53%] or a P2X purinoceptor antagonist [iso-pyridoxalphosphate-6-azophenyl-2',5'-disulphonate (PPADS); Delta = -47%] and was further reduced by capsazepine and iso-PPADS in combination (Delta = -78%). The initial bradypneic response was reduced by a cyclooxygenase inhibitor (indomethacin; Delta = -48%), ATP scavengers (apyrase and adenosine deaminase in combination; Delta = -50%), or capsazepine and indomethacin in combination (Delta = -47%), was further reduced by iso-PPADS and indomethacin in combination (Delta = -75%) or capsazepine and ATP scavengers in combination (Delta = -83%), but was not affected by a lipoxygenase inhibitor (nordihydroguaiaretic acid) or by any of the various vehicles. No pretreatment influenced delayed tachypnea. We concluded that 1) the initial bradypneic response to H2O2 results from activation of both TRPV1 and P2X receptors, possibly located at terminals of vagal lung capsaicin-sensitive afferent fibers; 2) the functioning of the TRPV1 and P2X receptors in triggering the initial bradypnea is, in part, mediated through the actions of cyclooxygenase metabolites and ATP, respectively; and 3) these mechanisms do not contribute to the H2O2-evoked delayed tachypnea.

Interleukin-2 suppression by 2-arachidonyl glycerol is mediated through peroxisome proliferator-activated receptor gamma independently of cannabinoid receptors 1 and 2

2-Arachidonyl glycerol (2-AG) is an endogenous arachidonic acid derivative that binds cannabinoid receptors CB1 and CB2 and is hence termed an endocannabinoid. 2-AG also modulates a variety of immunological responses, including expression of the autocrine/paracrine T cell growth factor interleukin (IL)-2. The objective of the present studies was to determine the mechanism responsible for IL-2 suppression by 2-AG. Because of the labile properties of 2-AG, 2-AG ether, a nonhydrolyzable analog of 2-AG, was also used. Both 2-AG and 2-AG ether suppressed IL-2 expression independently of CB1 and CB2, as demonstrated in leukocytes derived from CB1/CB2-null mice. Moreover, we demonstrated that both 2-AG and 2-AG ether treatment activated peroxisome proliferator-activated receptor gamma (PPARgamma), as evidenced by forced differentiation of 3T3-L1 cells into adipocytes, induction of aP2 mRNA levels, and activation of a PPARgamma-specific luciferase reporter in transiently transfected 3T3-L1 cells. Consequently, the putative role of PPARgamma in IL-2 suppression by 2-AG and 2-AG ether was examined in Jurkat T cells. Concordant with PPARgamma involvement, the PPARgamma-specific antagonist 2-chloro-5-nitro-N-(4-pyridyl)-benzamide (T0070907) blocked 2-AG- and 2-AG ether-mediated IL-2 suppression. Likewise, 2-AG suppressed the transcriptional activity of two transcription factors crucial for IL-2 expression, nuclear factor of activated T cells and nuclear factor kappaB, in the absence but not in the presence of T0070907. 2-AG treatment also induced PPARgamma binding to a PPAR response element in activated Jurkat T cells. Together, the aforementioned studies identify PPARgamma as a novel intracellular target of 2-AG, which mediates the suppression of IL-2 by 2-AG in a manner that is independent of CB1 and/or CB2.

Effect of Anandamide on Cytosolic Ca2+ Levels and Proliferation in Canine Renal Tubular Cells

The effect of the endogenous cannabinoid anandamide on cytosolic free Ca(2+) concentration ([Ca(2+)](i)) and proliferation is largely unknown. This study examined whether anandamide altered Ca(2+) levels and caused Ca(2+)-dependent cell death in Madin-Darby canine kidney (MDCK) cells. [Ca(2+)](i) and cell death were measured using the fluorescent dyes fura-2 and WST-1 respectively. Anandamide at concentrations above 5 muM increased [Ca(2+)](i) in a concentration-dependent manner. The Ca(2+) signal was reduced by 78% by removing extracellular Ca(2+). The anandamide-induced Ca(2+) influx was insensitive to L-type Ca(2+) channel blockers and the cannabinoid receptor antagonist AM 251, but was inhibited differently by aristolochic acid, WIN 55,212-2 (a cannabinoid receptor agonist), phorbol ester, GF 109203X and forskolin. After pretreatment with thapsigargin (an endoplasmic reticulum Ca(2+) pump inhibitor), anandamide-induced Ca(2+) release was inhibited. Inhibition of phospholipase C with U73122 did not change anandamide-induced Ca(2+) release. At concentrations of 100 muM and 200 muM, anandamide killed 50% and 95% cells, respectively. The cytotoxic effect of 100 muM anandamide was completely reversed by pre-chelating cytosolic Ca(2+) with BAPTA. Collectively, in MDCK cells, anandamide induced [Ca(2+)](i) rises by causing Ca(2+) release from endoplasmic reticulum and Ca(2+) influx from extracellular space. Furthermore, anandamide can cause Ca(2+)-dependent cytotoxicity in a concentration-dependent manner.

Anandamide reduces infarct size in rat isolated hearts subjected to ischaemia-reperfusion by a novel cannabinoid mechanism

Although the endocannabinoids 2-arachidonoylglycerol (2-AG) and anandamide share a similar pharmacology, 2-AG reportedly limits myocardial ischaemia-reperfusion injury whereas anandamide does not. We therefore investigated whether or not anandamide reduces infarct size and which, if any, of the known cannabinoid-signalling pathways are involved. Rat isolated perfused hearts were subjected to global, no-flow ischaemia (30 min) and reperfusion (1 h). Agonists were present from 5 min before ischaemia until the end of reperfusion. Antagonists, where used, were present throughout the protocol. Recovery of left ventricular developed pressure and coronary flow was incomplete in control hearts and not significantly affected by any drug treatment. In vehicle-treated hearts, 26+/-3% (n=13) of the left ventricle was infarcted at the end of reperfusion. Infarction of the left ventricle was significantly reduced after 1 microM anandamide (10+/-1%, n=7) or 1 microM methanandamide (12+/-4%, n=6) but not 1 microM HU210. Neither ACPA (1 microM; CB1 receptor agonist) nor JWH133 (1 microM; CB2 receptor agonist), individually or combined significantly affected infarct size. Anandamide (1 microM) did not reduce infarct size in the presence of the CB1 receptor antagonist rimonabant (SR141716A, 1 microM) or the CB2 receptor antagonist, SR144528 (1 microM). Despite sensitivity to CB1 and CB2 receptor antagonists, the infarct-limiting action of anandamide was not mimicked by agonists selective for CB1 or CB2 receptors suggesting the involvement of a novel cannabinoid site of action.

Roles of anandamide in the hepatic microcirculation in cirrhotic rats

Cannabinoids have been reported to participate in the pathogenesis of peripheral vasodilatation in cirrhosis. However, their roles in increased intrahepatic resistance (IHR) in cirrhotic livers are unknown. We aimed to investigate the effects of cannabinoids in the hepatic microcirculation of cirrhotic rats produced by bile duct ligation. In isolated liver perfusion, portal perfusion pressure (PPP) and the production of eicosanoids in the perfusate were measured. In addition, various hepatic protein levels [cyclooxygenase (COX) isoform and 5-lipoxygenase (5-LOX)] were also determined. Finally, concentration-response curves for PPP and the corresponding production of eicosanoids in response to anandamide (1.44 x 10(-10)-1.44 x 10(-3) M) after indomethacin (COX inhibitor), piriprost (5-LOX inhibitor), or furegrelate (thromboxane A(2) synthase inhibitor) preincubation were obtained. The study showed that cirrhotic livers had significantly higher levels of PPP, COX-2 and 5-LOX protein expression, and production of thromboxane B(2) (TXB(2)) and cysteinyl leukotrienes (Cys-LTs) than normal livers. Anandamide induced a dose-dependent increase in PPP in both normal and cirrhotic livers. The anandamide-induced increase in PPP was found concomitantly with a significant increase in TXB(2) and Cys-LT production in the perfusate. In response to anandamide administration, cirrhotic livers exhibited a significantly greater increase in IHR and production of TXB(2) and Cys-LTs than normal livers. Indomethacin and furegrelate, but not piriprost, significantly ameliorated the anandamide-induced increase in IHR in cirrhotic livers. In conclusion, anandamide plays, in part, an important role in increased IHR of cirrhotic livers. The anandamide-induced increase in IHR in cirrhotic livers may be mediated by increased COX-derived eicosanoid (mainly thromboxane A(2)) production.

Differentiation-dependent regulation of the cyclooxygenase cascade during adipogenesis suggests a complex role for prostaglandins

AIM

A thorough understanding of the mechanisms of adipocyte differentiation and metabolism is important for the prevention and/or treatment of obesity and its complications, including type 2 diabetes mellitus. A complex role for prostaglandins (PGs) in adipogenesis is suggested. We examined the expression and cellular localization of enzymes in the cyclooxygenase (COX) cascade that synthesize PGs as well as the PG profile as a function of differentiation status in 3T3-L1 cells.

METHODS

Murine 3T3-L1 preadipocytes were used as a model for studies of adipocyte differentiation induced by a hormone cocktail and compared with the parental fibroblastic line NIH 3T3. Both cell lines were incubated in maintenance medium or differentiation medium. Nine days after differentiation, the expression of enzymes in the COX cascade was evaluated by immunoblot analysis, reverse transcriptase-polymerase chain reaction (RT-PCR) and immunocytochemistry, and PG formation was examined using enzyme immunoassay.

RESULTS

A differentiation-dependent diminution of COX-1 and COX-2 mRNA and cognate proteins in 3T3-L1 cells was observed. PG release, including PGE(2), 6-keto PGF(1alpha), PGD(2) and 15d-PGJ(2), significantly decreased following differentiation in 3T3-L1 cells (anova/Tukey, p < 0.05). However, microsomal PGE synthase (mPGES) and lipocalin-type PGD synthase (L-PGDS) were selectively upregulated. Immunocytochemistry revealed that COX-1 and COX-2 became intracellularly more diffuse upon differentiation, whereas mPGES was redistributed to the nuclear compartment.

CONCLUSIONS

Regulation of PG formation and COX-2 expression in 3T3-L1 cells is differentiation-dependent and involves changes in the levels of gene expression of the individual isoforms as well as redistribution of the enzymes within cellular compartments.

Cannabinoid mechanisms of pain suppression

A large body of literature indicates that cannabinoids suppress behavioral responses to acute and persistent noxious stimulation in animals. This review examines neuroanatomical, behavioral, and neurophysiological evidence supporting a role for cannabinoids in suppressing pain at spinal, supraspinal, and peripheral levels. Localization studies employing receptor binding and quantitative autoradiography, immunocytochemistry, and in situ hybridization are reviewed to examine the distribution of cannabinoid receptors at these levels and provide a neuroanatomical framework with which to understand the roles of endogenous cannabinoids in sensory processing. Pharmacological and transgenic approaches that have been used to study cannabinoid antinociceptive mechanisms are described. These studies provide insight into the functional roles of cannabinoid CB1 (CB1R) and CB2 (CB2R) receptor subtypes in cannabinoid antinociceptive mechanisms, as revealed in animal models of acute and persistent pain. The role of endocannabinoids and related fatty acid amides that are implicated in endogenous mechanisms for pain suppression are discussed. Human studies evaluating therapeutic potential of cannabinoid pharmacotherapies in experimental and clinical pain syndromes are evaluated. The potential of exploiting cannabinoid antinociceptive mechanisms in novel pharmacotherapies for pain is discussed.

Lipid signaling in embryo implantation

A reciprocal interaction between the implantation-competent blastocyst and the receptive uterus is required for successful implantation. Although various molecular pathways are known to participate in this cross-talk, a comprehensive understanding of the implantation process is still missing. Gene expression studies and genetically engineered mouse models have provided evidence that lipid mediators serve as important signaling molecules in coordinating the series of events during early pregnancy including preimplantation embryo formation and development, implantation and postimplantation growth. This review focuses on the roles of two groups of lipid mediators, prostaglandins (PGs) and endocannabinoids, during early pregnancy. Our laboratory has shown that while PGs generated by the cPLA2-cyclooxygenase (COX) system are essential to ovulation, fertilization, and implantation, endocannabinoids are important for synchronizing preimplantation embryo development with uterine receptivity for implantation. A better understanding of these molecular signaling pathways is hoped to generate new strategies to correct implantation failure and improve pregnancy rates in women.