A re-evaluation of 9-HODE activity at TRPV1 channels in comparison with anandamide: enantioselectivity and effects at other TRP channels and in sensory neurons

The endocannabinoid anandamide activates pro-resolving pathways in human primary macrophages by engaging both CB2 and GPR18 receptors

Resolution of inflammation is the cellular and molecular process that protects from widespread and uncontrolled inflammation and restores tissue function in the aftermath of acute immune events. This process is orchestrated by specialized pro-resolving mediators (SPM), a class of bioactive lipids able to reduce immune activation and promote removal of tissue debris and apoptotic cells by macrophages. Although SPMs are the lipid class that has been best studied for its role in facilitating the resolution of self-limited inflammation, a number of other lipid signals, including endocannabinoids, also exert protective immunomodulatory effects on immune cells, including macrophages. These observations suggest that endocannabinoids may also display pro-resolving actions. Interestingly, the endocannabinoid anandamide (AEA) is not only known to bind canonical type 1 and type 2 cannabinoid receptors (CB1 and CB2) but also to engage SPM-binding receptors such as GPR18. This suggests that AEA may also contribute to the governing of resolution processes. In order to interrogate this hypothesis, we investigated the ability of AEA to induce pro-resolving responses by classically-activated primary human monocyte-derived macrophages (MoDM). We found that AEA, at nanomolar concentration, enhances efferocytosis in MoDMs in a CB2- and GPR18-dependent manner. Using lipid mediator profiling, we also observed that AEA modulates SPM profiles in these cells, including levels of resolvin (Rv)D1, RvD6, maresin (MaR)2, and RvE1 in a CB2-dependent manner. AEA treatment also modulated the gene expression of SPM enzymes involved in both the formation and further metabolism of SPM such as 5-lipoxygenase and 15-Prostaglandin dehydrogenase. Our findings show, for the first time, a direct effect of AEA on the regulation of pro-resolving pathways in human macrophages. They also provide new insights into the complex interactions between different lipid pathways in activation of pro-resolving responses contributing to the reestablishment of homeostasis in the aftermath of acute inflammation.

A review of the direct targets of the cannabinoids cannabidiol, Δ9-tetrahydrocannabinol, N-arachidonoylethanolamine and 2-arachidonoylglycerol

Marijuana has been used by humans for thousands of years for both medicinal and recreational purposes. This included the treatment of pain, inflammation, seizures, and nausea. In the 1960s, the structure of the principal psychoactive ingredient Δ9-tetrahydrocannabinol was determined, and over the next few decades, two cannabinoid receptors were characterized along with the human endocannabinoid system and what it affects. This includes metabolism, the cardiovascular and reproductive systems, and it is involved in such conditions as inflammation, cancer, glaucoma, and liver and musculoskeletal disorders. In the central nervous system, the endocannabinoid system has been linked to appetite, learning, memory, and conditions such as depression, anxiety, schizophrenia, stroke, multiple sclerosis, neurodegeneration, addiction, and epilepsy. It was the profound effectiveness of cannabidiol, a non-psychoactive ingredient of marijuana, to relieve the symptoms of Dravet syndrome, a severe form of childhood epilepsy, that recently helped spur marijuana research. This has helped substantially to change society's attitude towards this potential source of useful drugs. However, research has also revealed that the actions of endocannabinoids, such as anandamide and 2-arachidonoylglycerol, and the phytocannabinoids, tetrahydrocannabinol and cannabidiol, were not just due to interactions with the two cannabinoid receptors but by acting directly on many other targets including various G-protein receptors and cation channels, such as the transient receptor potential channels for example. This mini-review attempts to survey the effects of these 4 important cannabinoids on these currently identified targets.

Investigating the alterations of endocannabinoidome signaling in the human small intestine in the context of obesity and type 2 diabetes

Background

Human studies have linked obesity-related diseases, such as type-2 diabetes (T2D), to the modulation of endocannabinoid signaling. Cannabinoid CB1 and CB2 receptor activation by the endocannabinoids (eCBs) 2-arachidonoylglycerol (2-AG) and N-arachidonoylethanolamine (AEA), both derived from arachidonic acid, play a role in homeostatic regulation. Other long chain fatty acid-derived endocannabinoid-like molecules have extended the metabolic role of this signaling system through other receptors. In this study, we aimed to assess in depth the interactions between the circulating and intestinal tone of this extended eCB system, or endocannabinoidome (eCBome), and their involvement in the pathogenesis of diabetes.

Methods

Plasma and ileum samples were collected from subjects with obesity and harboring diverse degrees of insulin resistance or T2D, who underwent bariatric surgery. The levels of eCBome mediators and their congeners were then assessed by liquid chromatography coupled to tandem mass spectrometry, while gene expression was screened with qPCR arrays.

Findings

Intestinal and circulating levels of eCBome mediators were higher in subjects with T2D. We found an inverse correlation between the intestinal and circulating levels of monoacylglycerols (MAGs). Additionally, we identified genes known to be implicated in both lipid metabolism and intestinal function that are altered by the context of obesity and glucose homeostasis.

Interpretation

Although the impact of glucose metabolism on the eCBome remains poorly understood in subjects with advanced obesity state, our results suggest a strong causative link between altered glucose homeostasis and eCBome signaling in the intestine and the circulation.

Interactions Between the Ubiquitin-Proteasome System, Nrf2, and the Cannabinoidome as Protective Strategies to Combat Neurodegeneration: Review on Experimental Evidence

Neurodegenerative disorders are chronic brain diseases that affect humans worldwide. Although many different factors are thought to be involved in the pathogenesis of these disorders, alterations in several key elements such as the ubiquitin-proteasome system (UPS), the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway, and the endocannabinoid system (ECS or endocannabinoidome) have been implicated in their etiology. Impairment of these elements has been linked to the origin and progression of neurodegenerative disorders, while their potentiation is thought to promote neuronal survival and overall neuroprotection, as proved with several experimental models. These key neuroprotective pathways can interact and indirectly activate each other. In this review, we summarize the neuroprotective potential of the UPS, ECS, and Nrf2 signaling, both separately and combined, pinpointing their role as a potential therapeutic approach against several hallmarks of neurodegeneration.

Binding interactions of fatty acyl lipid mediators within the vanilloid pocket of TRPV1: A molecular dynamics study

The transient receptor potential vanilloid 1 (TRPV1) channel is a ligand-gated, nonselective cation channel expressed in primary sensory neurons, which has a role in nociception. The channel is activated by noxious heat, pH, capsaicin and other endogenous vanilloids, including lipid mediators (LMs) enzymatically derived from polyunsaturated fatty acids (PUFA). Although capsaicin binding to TRPV1 has been well characterized, the molecular mechanism by which endogenous LM ligands bind the channel is not well understood. In this study, we characterized the binding interactions for 13 endogenous LM ligands, within the vanilloid pocket of TRPV1 using a molecular dynamics (MD) approach. We observed that LM ligands can be grouped based on their structure and affinity for the vanilloid pocket. Furthermore, the position as well as the number of the polar groups on the LM ligand directly impact binding stability through various polar interactions with the protein. As an additional control we performed docking experiments of the PUFA precursor molecules linoleic acid and arachidonic acid which failed to form stable interactions within the vanilloid pocket. While LM ligands with similar structures displayed similar binding interactions, there were notable exceptions in the case of 20-HETE, 9-HODE, and 9,10-DiHOME. Our study offers new insights into the mechanisms involved in TRPV1 activation by endogenous LM ligands. The observed binding interactions may assist in the interpretation of in vivo and in vitro pharmacodynamics studies.

Pharmacological Evaluation of Signals of Disproportionality Reporting Related to Adverse Reactions to Antiepileptic Cannabidiol in VigiBase

Cannabidiol is the first cannabis-derived drug approved for the treatment of Lennox-Gastaut syndrome, Dravet syndrome, and Tuberous Sclerosis Complex. In the current study, we performed a descriptive analysis followed by a disproportionality analysis of potential adverse events caused by CBD extracted from the VigiBase® database. Furthermore, the biological plausibility of the association between CBD and the serotonin 5-HT1A receptor as a possible cause of adverse events was analyzed and discussed. Data were extracted from the VigiBase® database using the VigiLyze® signal detection and signal management tool. Adverse events in VigiBase® reports were coded using MedDRA, version 19 of Preferred Terms (PTs). Data were uploaded into SPSS software and analyzed via a disproportionality analysis. Statistically significant disproportionality signals for CBD were found for "weight decreased" (5.19 (95% CI: 4.54-5.70)), "hypophagia" (3.68 (95% CI: 3.22-5.27)), and "insomnia" (1.6 (95% CI: 1.40-1.83)). Positive IC025 values were found for "weight decreased" (2.2), "hypophagia" (1.3), and "insomnia" (0.5), indicating a surplus of reported cases. CBD's interactions with 5-HT1A serotonin receptors may offer a potential biological explanation for the occurrence of insomnia in patients. It is noteworthy that the risk profiles mentioned in the information for prescribing CBD as an antiepileptic agent by regulatory agencies showed disparities specifically related to the adverse event "insomnia".

NSC228155 alleviates septic cardiomyopathy via protecting mitochondria and inhibiting inflammation

Septic cardiomyopathy is a lethal symptom of sepsis. Discovery of effective therapy that prevents cardiac injury in sepsis is critical in the clinical management of sepsis. NSC228155 is a novel compound with therapeutic potential on acute kidney injury by preventing apoptosis and protecting mitochondria. Whether NSC228155 protects against septic cardiomyopathy is unclear. In the present study, adult C57BL/6J mice were i.p injected with 5 mg/kg/day NSC228155 for 2 days before 10 mg/kg lipopolysaccharide (LPS) injection. Cardiac functional testing and sampling for serum and tissue were performed 12 and 24 h post LPS injection, respectively. NSC228155 significantly improved cardiac function examined by echocardiography, decreased the serum lactate dehydrogenase (LDH) and creatine kinase-MB, and pathologically alleviated cardiac injury in LPS mice. Accordingly, NSC228155 attenuated cardiomyocytes' mitochondrial damage as shown by decreased damaged mitochondrial ratio and activated signals for mitochondrial biogenesis, dynamics and mitophagy in LPS mice model. Metabolomics analysis demonstrated that NSC228155 corrected the metabolic disturbance involved in oxidative stress and energy metabolism, and decreased tissue injury metabolites in LPS-stimulated cardiac tissue. In the LPS-stimulated cardiac cell culture derived from human induced pluripotent stem cells, NSC228155 effectively restored the beating frequency, decreased LDH release, and protected mitochondria. NSC228155 also inhibited inflammation shown by decreased pro-inflammatory mediators in both serum and cardiac tissue in LPS model. Taken together, NSC228155 significantly improved cardiac function by directly preventing against cardiac cell injury and inhibiting inflammation in LPS model, hence may be a potential novel therapy against septic cardiomyopathy.

Excessive dietary linoleic acid promotes plasma accumulation of pronociceptive fatty acyl lipid mediators

Various fatty acyl lipid mediators are derived from dietary polyunsaturated fatty acids (PUFAs) and modulate nociception. The modern diet is rich in linoleic acid, which is associated with nociceptive hypersensitivities and may present a risk factor for developing pain conditions. Although recommendations about fatty acid intake exist for some diseases (e.g. cardiovascular disease), the role of dietary fatty acids in promoting pain disorders is not completely understood. To determine how dietary linoleic acid content influences the accumulation of pro- and anti-nociceptive fatty acyl lipid mediators, we created novel rodent diets using custom triglyceride blends rich in either linoleic acid or oleic acid. We quantified the fatty acyl lipidome in plasma of male and female rats fed these custom diets from the time of weaning through nine weeks of age. Dietary fatty acid composition determined circulating plasma fatty acyl lipidome content. Exposure to a diet rich in linoleic acid was associated with accumulation of linoleic and arachidonic acid-derived pro-nociceptive lipid mediators and reduction of anti-nociceptive lipid mediators derived from the omega-3 PUFAs. Our findings provide mechanistic insights into exaggerated nociceptive hypersensitivity associated with excessive dietary linoleic acid intake and highlight potential biomarkers for pain risk stratification.

The neglected role of endocannabinoid actions at TRPC channels in ataxia

Transient receptor potential (TRP) channels are highly expressed in cells of the cerebellum including in the dendrites and somas of Purkinje cells (PCs). Their endogenous activation promotes influx of Ca²⁺ and Na⁺, resulting in depolarization. TRP channels can be activated by endogenous endocannabinoids (eCBs) and activity of TRP channels has been shown to modulate GABA and glutamate transmission. Ataxia is caused by disruption of multiple intracellular pathways which often involve changes in Ca²⁺ homeostasis that can result in neural cellular dysfunction and cell death. Based on available literature, alteration of transmission of eCBs would be expected to change activity of cerebellar TRP channels. Antagonists of the endocannabinoid system (ECS) including enzymes which break eCBs down have been shown to result in reductions in postsynaptic excitatory activity mediated by TRPC channels. Further, TRPC channel antagonists could modulate both pre and postsynaptically-mediated glutamatergic and GABAergic transmission, resulting in reductions in cell death due to excitotoxicity and dysfunctions caused by abnormal inhibitory signaling. Accordingly, TRP channels, and in particular the TRPC channel, represent a potential therapeutic target for management of ataxia.

Level of Potassium Is Associated with Saturated Fatty Acids in Cell Membranes and Influences the Activation of the 9 and 13 HODE and 5 HETE Synthesis Pathways in PCOS

Potassium helps to maintain the water–electrolyte and acid–base balance. There is little research on the relationship between plasma fatty acids (FAs), inflammatory mediators and red blood cell potassium levels in women with polycystic ovary syndrome (PCOS). This study included 38 Caucasian women with PCOS. Potassium in the erythrocytes was determined by inductively coupled atomic plasma emission spectrometry. The FAs were analysed with gas chromatography, and liquid chromatography was used to separate the eicosanoids. The relationships between the potassium content and the amounts of fatty acids, as well as potassium and arachidonic acid (AAs) derivatives, were analysed. Significant negative correlations were found with, among others, pentadecanoic acid, palmitic acid, stearic acid and arachidic acid, whereas a positive correlation was found with neuronic acid. Positive correlations were observed with 9, 13 HODE (derivatives synthetized from linolenic acid) and 5 oxo ETE and 5 HETE (from 5 LOX pathway). Saturated fatty acids reduce the influx of potassium into the cell by destabilizing the pH of the cytosol, and thus exacerbating the inflammatory response through the activation of the AA cascade. Therefore, improving the flow of potassium inside the cell is important in the treatment of patients.

Anti-Microbial Activity of Phytocannabinoids and Endocannabinoids in the Light of Their Physiological and Pathophysiological Roles

Antibiotic resistance has become an increasing challenge in the treatment of various infectious diseases, especially those associated with biofilm formation on biotic and abiotic materials. There is an urgent need for new treatment protocols that can also target biofilm-embedded bacteria. Many secondary metabolites of plants possess anti-bacterial activities, and especially the phytocannabinoids of the Cannabis sativa L. varieties have reached a renaissance and attracted much attention for their anti-microbial and anti-biofilm activities at concentrations below the cytotoxic threshold on normal mammalian cells. Accordingly, many synthetic cannabinoids have been designed with the intention to increase the specificity and selectivity of the compounds. The structurally unrelated endocannabinoids have also been found to have anti-microbial and anti-biofilm activities. Recent data suggest for a mutual communication between the endocannabinoid system and the gut microbiota. The present review focuses on the anti-microbial activities of phytocannabinoids and endocannabinoids integrated with some selected issues of their many physiological and pharmacological activities.

Spinal Reflex Control of Arterial Blood Pressure: The Role of TRP Channels and Their Endogenous Eicosanoid Modulators

The spinal cord is an important integrative center for blood pressure control. Spinal sensory fibers send projections to sympathetic preganglionic neurons of the thoracic spinal cord and drive sympathetically-mediated increases in blood pressure. While these reflexes responses occur in able-bodied individuals, they are exaggerated following interruption of descending control - such as occurs following spinal cord injury. Similar reflex control of blood pressure may exist in disease states, other than spinal cord injury, where there is altered input to sympathetic preganglionic neurons. This review primarily focuses on mechanisms wherein visceral afferent information traveling via spinal nerves influences sympathetic nerve activity and blood pressure. There is an abundance of evidence for the widespread presence of this spinal reflex arch originating from virtually every visceral organ and thus having a substantial role in blood pressure control. Additionally, this review highlights specific endogenous eicosanoid species, which modulate the activity of afferent fibers involved in this reflex, through their interactions with transient receptor potential (TRP) cation channels.

Minor Cannabinoids: Biosynthesis, Molecular Pharmacology and Potential Therapeutic Uses

The medicinal use of Cannabis sativa L. can be traced back thousands of years to ancient China and Egypt. While marijuana has recently shown promise in managing chronic pain and nausea, scientific investigation of cannabis has been restricted due its classification as a schedule 1 controlled substance. A major breakthrough in understanding the pharmacology of cannabis came with the isolation and characterization of the phytocannabinoids trans-Δ⁹-tetrahydrocannabinol (Δ⁹-THC) and cannabidiol (CBD). This was followed by the cloning of the cannabinoid CB1 and CB2 receptors in the 1990s and the subsequent discovery of the endocannabinoid system. In addition to the major phytocannabinoids, Δ⁹-THC and CBD, cannabis produces over 120 other cannabinoids that are referred to as minor and/or rare cannabinoids. These cannabinoids are produced in smaller amounts in the plant and are derived along with Δ⁹-THC and CBD from the parent cannabinoid cannabigerolic acid (CBGA). While our current knowledge of minor cannabinoid pharmacology is incomplete, studies demonstrate that they act as agonists and antagonists at multiple targets including CB1 and CB2 receptors, transient receptor potential (TRP) channels, peroxisome proliferator-activated receptors (PPARs), serotonin 5-HT_1a receptors and others. The resulting activation of multiple cell signaling pathways, combined with their putative synergistic activity, provides a mechanistic basis for their therapeutic actions. Initial clinical reports suggest that these cannabinoids may have potential benefits in the treatment of neuropathic pain, neurodegenerative diseases, epilepsy, cancer and skin disorders. This review focuses on the molecular pharmacology of the minor cannabinoids and highlights some important therapeutic uses of the compounds.

Synthesis and molecular targets of N-13-hydroxy-octadienoyl-ethanolamine, a novel endogenous bioactive 15-lipoxygenase-derived metabolite of N-linoleoyl-ethanolamine found in the skin and saliva

N-Arachidonoyl-ethanolamine (AEA) is an endocannabinoid (eCB) and endogenous lipid mimicking many of the effects of Δ9-tetrahydrocannabinol, notably on brain functions, appetite, pain and inflammation. The eCBs and eCB-like compounds contain fatty acids, the main classes being the monoacylglycerols and the N-acyl-ethanolamines (NAEs). Thus, each long chain fatty acid likely exists under the form of a monoacylglycerol and NAE, as it is the case for arachidonic acid (AA) and linoleic acid (LA). Following their biosynthesis, AA and AEA can be further metabolized into additional eicosanoids, notably by the 15-lipoxygenase pathway. Thus, we postulated that NAEs possessing a 1Z,4Z-pentadiene motif, near their omega end, would be transformed into their 15-lipoxygenase metabolites. As a proof of concept, we investigated N-linoleoyl-ethanolamine (LAE). We successfully synthesized LEA and LEA-d4 as well as their 15-lipoxygenase-derived derivatives, namely 13-hydroxy-9Z,11E-octadecadienoyl-N-ethanolamine (13-HODE-EA) and 13-HODE-EA-d4, using Novozyme 435 immobilized on acrylic resin and soybean lipoxygenase respectively. We also show that both human 15-lipoxygenase-1 and -2 can biosynthesize 13-HODE-EA. Co-incubation of LEA and LA with either human 15-lipoxygenase led to the biosynthesis of 13-HODE-EA and 13-HODE in a ratio equal to or greater than 3:1, indicating that LEA is preferred to LA by these enzymes. Finally, we show that 13-HODE-EA is found in human saliva and skin and is a weak although selective TRPV1 agonist. The full biological importance of 13-HODE-EA remains to be explored.

Endothelial TRP channels and cannabinoid receptors are involved in affinin-induced vasodilation

Affinin is mainly recognized by its antinociceptive effect. Recently, our research group demonstrated that this compound produces vasodilation via activation of the gasotransmitters signaling pathways. However, the molecular targets of affinin were not identified. Considering the structural similarity of this alkamide with anandamide, we hypothesized that affinin-induced vasodilation could involve participation of TRP channels and cannabinoid receptors. In this work, by using the isolated rat aorta assay, we assessed involvement of TRP channels, the cannabinoid system, and the HNO-CGRP-TRPA₁ pathway on the mechanism of action of affinin. Additionally, we measured NO and H₂S levels elicited by affinin on rat aorta homogenates and carried out computer simulations of molecular interactions between affinin and the TRPA₁ and TRPV₁ channels and the CB₁ receptor. Our results indicated that affinin induces an increase in aortic NO and H₂S levels. We found evidence that the vasodilator effect induced by affinin involves activation of TRPA₁ and TRPV₁ channels and the CB₁ and eCB receptors. In silico analyses showed that affinin is able to bind with high affinity to these molecular targets. Moreover, we also proved that affinin-induced vasodilation is partly mediated via activation of the HNO-TRPA₁-CGRP pathway. Based on these results we propose a novel mechanism of action to explain the vasodilatory effect of affinin, which could be developed as an alternative drug to treat cardiovascular diseases.

The endocannabinoid system

Thirty years ago, the discovery of a cannabinoid (CB) receptor that interacts with the psychoactive compound in Cannabis led to the identification of anandamide, an endogenous receptor ligand or endocannabinoid. Research on endocannabinoids has since exploded, and additional receptors along with their lipid mediators and signaling pathways continue to be revealed. Specifically, in humans, the release of endocannabinoids from membrane lipids occurs on demand and the signaling process is rapidly attenuated by the breakdown of the ligand suggesting a tight regulation of the endocannabinoid system (ECS). Additionally, the varying distribution of CB receptors between the central nervous system and other tissues allows for the ECS to participate in a wide range of cognitive and physiological processes. Select plant-derived 'phyto'cannabinoids such as Δ-9-tetrahydrocannabinol (Δ9-THC) bind to the CB receptors and trigger the ECS, and in the case of Δ9-THC, while it has therapeutic value, can also produce detrimental effects. Current research is aimed at the identification of additional phytocannabinoids with minimal psychotropic effects with potential for therapeutic development. Although decades of research on the ECS and its components have expanded our understanding of the mechanisms and implications of endocannabinoid signaling in mammals, it continues to evolve. Here, we provide a brief overview of the ECS and its overlap with other related lipid-mediated signaling pathways.

Soluble Epoxide Hydrolase Regulation of Lipid Mediators Limits Pain

The role of lipids in pain signaling is well established and built on decades of knowledge about the pain and inflammation produced by prostaglandin and leukotriene metabolites of cyclooxygenase and lipoxygenase metabolism, respectively. The analgesic properties of other lipid metabolites are more recently coming to light. Lipid metabolites have been observed to act directly at ion channels and G protein-coupled receptors on nociceptive neurons as well as act indirectly at cellular membranes. Cytochrome P450 metabolism of specifically long-chain fatty acids forms epoxide metabolites, the epoxy-fatty acids (EpFA). The biological role of these metabolites has been found to mediate analgesia in several types of pain pathology. EpFA act through a variety of direct and indirect mechanisms to limit pain and inflammation including nuclear receptor agonism, limiting endoplasmic reticulum stress and blocking mitochondrial dysfunction. Small molecule inhibitors of the soluble epoxide hydrolase can stabilize the EpFA in vivo, and this approach has demonstrated relief in preclinical modeled pain pathology. Moreover, the ability to block neuroinflammation extends the potential benefit of targeting soluble epoxide hydrolase to maintain EpFA for neuroprotection in neurodegenerative disease.

N-Palmitoylglycine and other N-acylamides activate the lipid receptor G2A/GPR132

The G-protein-coupled receptor GPR132, also known as G2A, is activated by 9-hydroxyoctadecadienoic acid (9-HODE) and other oxidized fatty acids. Other suggested GPR132 agonists including lysophosphatidylcholine (LPC) have not been readily reproduced. Here, we identify N-acylamides in particular N-acylglycines, as lipid activators of GPR132 with comparable activity to 9-HODE. The order-of-potency is N-palmitoylglycine > 9-HODE ≈ N-linoleoylglycine > linoleamide > N-oleoylglycine ≈ N-stereoylglycine > N-arachidonoylglycine > N-docosehexanoylglycine. Physiological concentrations of N-acylglycines in tissue are sufficient to activate GPR132. N-linoleoylglycine and 9-HODE also activate rat and mouse GPR132, despite limited sequence conservation to human. We describe pharmacological tools for GPR132, identified through drug screening. SKF-95667 is a novel GPR132 agonist. SB-583831 and SB-583355 are peptidomimetic molecules containing core amino acids (glycine and phenylalanine, respectively), and structurally related to previously described ligands. A telmisartan analog, GSK1820795A, antagonizes the actions of N-acylamides at GPR132. The synthetic cannabinoid CP-55 940 also activates GPR132. Molecular docking to a homology model suggested a site for lipid binding, predicting the acyl side-chain to extend into the membrane bilayer between TM4 and TM5 of GPR132. Small-molecule ligands are envisaged to occupy a "classical" site encapsulated in the 7TM bundle. Structure-directed mutagenesis indicates a critical role for arginine at position 203 in transmembrane domain 5 to mediate GPR132 activation by N-acylamides. Our data suggest distinct modes of binding for small-molecule and lipid agonists to the GPR132 receptor. Antagonists, such as those described here, will be vital to understand the physiological role of this long-studied target.

Mammalian Transient Receptor Potential TRPA1 Channels: From Structure to Disease

The transient receptor potential ankyrin (TRPA) channels are Ca²⁺-permeable nonselective cation channels remarkably conserved through the animal kingdom. Mammals have only one member, TRPA1, which is widely expressed in sensory neurons and in non-neuronal cells (such as epithelial cells and hair cells). TRPA1 owes its name to the presence of 14 ankyrin repeats located in the NH₂ terminus of the channel, an unusual structural feature that may be relevant to its interactions with intracellular components. TRPA1 is primarily involved in the detection of an extremely wide variety of exogenous stimuli that may produce cellular damage. This includes a plethora of electrophilic compounds that interact with nucleophilic amino acid residues in the channel and many other chemically unrelated compounds whose only common feature seems to be their ability to partition in the plasma membrane. TRPA1 has been reported to be activated by cold, heat, and mechanical stimuli, and its function is modulated by multiple factors, including Ca²⁺, trace metals, pH, and reactive oxygen, nitrogen, and carbonyl species. TRPA1 is involved in acute and chronic pain as well as inflammation, plays key roles in the pathophysiology of nearly all organ systems, and is an attractive target for the treatment of related diseases. Here we review the current knowledge about the mammalian TRPA1 channel, linking its unique structure, widely tuned sensory properties, and complex regulation to its roles in multiple pathophysiological conditions.

Oxidized Lipids in Persistent Pain States

Chemotherapy, nerve injuries, or diseases like multiple sclerosis can cause pathophysiological processes of persistent and neuropathic pain. Thereby, the activation threshold of ion channels is reduced in peripheral sensory neurons to normally noxious stimuli like heat, cold, acid, or mechanical due to sensitization processes. This leads to enhanced neuronal activity, which can result in mechanical allodynia, cold allodynia, thermal hyperalgesia, spontaneous pain, and may initiate persistent and neuropathic pain. The treatment options for persistent and neuropathic pain patients are limited; for about 50% of them, current medication is not efficient due to severe side effects or low response to the treatment. Therefore, it is of special interest to find additional treatment strategies. One approach is the control of neuronal sensitization processes. Herein, signaling lipids are crucial mediators and play an important role during the onset and maintenance of pain. As preclinical studies demonstrate, lipids may act as endogenous ligands or may sensitize transient receptor potential (TRP)-channels. Likewise, they can cause enhanced activity of sensory neurons by mechanisms involving G-protein coupled receptors and activation of intracellular protein kinases. In this regard, oxidized metabolites of the essential fatty acid linoleic acid, 9- and 13-hydroxyoctadecadienoic acid (HODE), their dihydroxy-metabolites (DiHOMEs), as well as epoxides of linoleic acid (EpOMEs) and of arachidonic acid (EETs), as well as lysophospholipids, sphingolipids, and specialized pro-resolving mediators (SPMs) have been reported to play distinct roles in pain transmission or inhibition. Here, we discuss the underlying molecular mechanisms of the oxidized linoleic acid metabolites and eicosanoids. Furthermore, we critically evaluate their role as potential targets for the development of novel analgesics and for the treatment of persistent or neuropathic pain.

Cannabinoid Ligands Targeting TRP Channels

Transient receptor potential (TRP) channels are a group of membrane proteins involved in the transduction of a plethora of chemical and physical stimuli. These channels modulate ion entry, mediating a variety of neural signaling processes implicated in the sensation of temperature, pressure, and pH, as well as smell, taste, vision, and pain perception. Many diseases involve TRP channel dysfunction, including neuropathic pain, inflammation, and respiratory disorders. In the pursuit of new treatments for these disorders, it was discovered that cannabinoids can modulate a certain subset of TRP channels. The TRP vanilloid (TRPV), TRP ankyrin (TRPA), and TRP melastatin (TRPM) subfamilies were all found to contain channels that can be modulated by several endogenous, phytogenic, and synthetic cannabinoids. To date, six TRP channels from the three subfamilies mentioned above have been reported to mediate cannabinoid activity: TRPV1, TRPV2, TRPV3, TRPV4, TRPA1, and TRPM8. The increasing data regarding cannabinoid interactions with these receptors has prompted some researchers to consider these TRP channels to be “ionotropic cannabinoid receptors.” Although CB1 and CB2 are considered to be the canonical cannabinoid receptors, there is significant overlap between cannabinoids and ligands of TRP receptors. The first endogenous agonist of TRPV1 to be discovered was the endocannabinoid, anandamide (AEA). Similarly, N-arachidonyl dopamine (NADA) and AEA were the first endogenous TRPM8 antagonists discovered. Additionally, Δ⁹-tetrahydrocannabinol (Δ⁹-THC), the most abundant psychotropic compound in cannabis, acts most potently at TRPV2, moderately modulates TRPV3, TRPV4, TRPA1, and TRPM8, though Δ⁹-THC is not reported to modulate TRPV1. Moreover, TRP receptors may modulate effects of synthetic cannabinoids used in research. One common research tool is WIN55,212-2, a CB1 agonist that also exerts analgesic effects by desensitizing TRPA1 and TRPV1. In this review article, we aim to provide an overview and classification of the cannabinoid ligands that have been reported to modulate TRP channels and their therapeutic potential.

Emerging role of 12/15-Lipoxygenase (ALOX15) in human pathologies

12/15-lipoxygenase (12/15-LOX) is an enzyme, which oxidizes polyunsaturated fatty acids, particularly omega-6 and -3 fatty acids, to generate a number of bioactive lipid metabolites. A large number of studies have revealed the importance of 12/15-LOX role in oxidative and inflammatory responses. The in vitro studies have demonstrated the ability of 12/15-LOX metabolites in the expression of various genes and production of cytokine related to inflammation and resolution of inflammation. The studies with the use of knockout and transgenic animals for 12/15-LOX have further shown its involvement in the pathogenesis of a variety of human diseases, including cardiovascular, renal, neurological and metabolic disorders. This review summarizes our current knowledge on the role of 12/15-LOX in inflammation and various human diseases.

n-3 polyunsaturated N-acylethanolamines are CB2 cannabinoid receptor-preferring endocannabinoids

Anandamide, the first identified endogenous cannabinoid and TRPV1 agonist, is one of a series of endogenous N-acylethanolamines, NAEs. We have generated novel assays to quantify the levels of multiple NAEs in biological tissues and their rates of hydrolysis through fatty acid amide hydrolase. This range of NAEs was also tested in rapid response assays of CB₁, CB₂ cannabinoid and TRPV1 receptors. The data indicate that PEA, SEA and OEA are not endocannabinoids or endovanilloids, and that the higher endogenous levels of these metabolites compared to polyunsaturated analogues are a correlate of their slow rates of hydrolysis. The n-6 NAEs (AEA, docosatetraenoyl and docosapentaenoyl derivatives) activated both CB₁ and CB₂ receptors, as well as TRPV1 channels, suggesting them to be 'genuine' endocannabinoids and 'endovanilloids'. The n-3 NAEs (eicosapentaenoyl, docosapentaenoyl and docosahexaenoyl derivatives) activated CB₂ receptors and some n-3 NAEs (docosapentaenoyl and docosahexaenoyl derivatives) also activated TRPV1 channels, but failed to activate the CB₁ receptor. We hypothesise that the preferential activation of CB₂ receptors by n-3 PUFA NAEs contributes, at least in some part, to their broad anti-inflammatory profile.

Actions and Regulation of Ionotropic Cannabinoid Receptors

Almost three decades have passed since the identification of the two specific metabotropic receptors mediating cannabinoid pharmacology. Thereafter, many cannabinoid effects, both at central and peripheral levels, have been well documented and characterized. However, numerous evidences demonstrated that these pharmacological actions could not be attributable solely to the activation of CB1 and CB2 receptors since several important cannabimimetic actions have been found in biological systems lacking CB1 or CB2 gene such as in specific cell lines or transgenic mice. It is now well accepted that, beyond their receptor-mediated effects, these molecules can act also via CB1/CB2-receptor-independent mechanism. Cannabinoids have been demonstrated to modulate several voltage-gated channels (including Ca²⁺, Na⁺, and various type of K⁺ channels), ligand-gated ion channels (i.e., GABA, glycine), and ion-transporting membranes proteins such as transient potential receptor class (TRP) channels. The first direct, cannabinoid receptor-independent interaction was reported on the function of serotonin 5-HT₃ receptor-ion channel complex. Similar effects were reported also on the other above mentioned ion channels. In the early ninety, studies searching for endogenous modulators of L-type Ca²⁺ channels identified anandamide as ligand for L-type Ca²⁺ channel. Later investigations indicated that other types of Ca²⁺ currents are also affected by endocannabinoids, and, in the late ninety, it was discovered that endocannabinoids activate the vanilloid receptor subtype 1 (TRPV1), and nowadays, it is known that (endo)cannabinoids gate at least five distinct TRP channels. This chapter focuses on cannabinoid regulation of ion channels and lays special emphasis on their action at transient receptor channels.

Plasma levels of the endocannabinoid anandamide, related N-acylethanolamines and linoleic acid-derived oxylipins in patients with migraine

There is evidence that patients with migraine have deficient levels of the endogenous cannabinoid receptor ligand anandamide (AEA). It is not known, however, if this is a localised or generalised phenomenon. In the present study, levels of AEA, related N-acylethanolamines (NAEs) and linoleic acid-derived oxylipins have been measured in the blood of 26 healthy women and 38 women with migraine (26 with aura, 12 without aura) who were matched for age and body-mass index. Blood samples were taken on two occasions: the first sample near the start of the menstrual cycle (when present) and the second approximately fourteen days later. For a subset of migraine patients, two additional blood samples were taken, one during a migraine attack and one approximately 1 month later (to be at the same stage in the menstrual cycle, when present). NAEs and oxylipins were measured by liquid chromatography coupled to mass spectrometry. Twenty-nine lipids were quantified, of which 16 were found to have a high reproducibility of measurement. There were no significant differences in the levels of AEA, the related NAEs stearoylethanolamide and oleoylethanolamide or any of the nine linoleic acid-derived oxylipins measured either between migraine patients with vs. without aura, or between controls and migraine patients (after stratification to take into account whether or not the individuals had regular menstruation cycles) in either of the first two samples. Levels of linoleoylethanolamide were lower in the patients with vs. without aura on the second sample but not in the first sample, but the biological importance of this finding is unclear. Due to time-dependent increases in their concentrations ex vivo prior to centrifugation, AEA and oleoylethanolamide levels in the samples collected during migraine attacks were not analysed, but for the other fourteen lipids, there were no significant differences in plasma concentrations during migraine vs. one month later. It is concluded that migraine is not associated with a generalised (as opposed to localised) deficiency in these lipids.

The G2A receptor (GPR132) contributes to oxaliplatin-induced mechanical pain hypersensitivity

Chemotherapy-induced peripheral neuropathic pain (CIPN) is a common and severe debilitating side effect of many widely used cytostatics. However, there is no approved pharmacological treatment for CIPN available. Among other substances, oxaliplatin causes CIPN in up to 80% of treated patients. Here, we report the involvement of the G-protein coupled receptor G2A (GPR132) in oxaliplatin-induced neuropathic pain in mice. We found that mice deficient in the G2A-receptor show decreased mechanical hypersensitivity after oxaliplatin treatment. Lipid ligands of G2A were found in increased concentrations in the sciatic nerve and dorsal root ganglia of oxaliplatin treated mice. Calcium imaging and patch-clamp experiments show that G2A activation sensitizes the ligand-gated ion channel TRPV1 in sensory neurons via activation of PKC. Based on these findings, we conclude that targeting G2A may be a promising approach to reduce oxaliplatin-induced TRPV1-sensitization and the hyperexcitability of sensory neurons and thereby to reduce pain in patients treated with this chemotherapeutic agent.

Transient Receptor Potential Melastatin 8 Channel (TRPM8) Modulation: Cool Entryway for Treating Pain and Cancer

TRPM8 ion channels, the primary cold sensors in humans, are activated by innocuous cooling (<28 °C) and cooling compounds (menthol, icilin) and are implicated in sensing unpleasant cold stimuli as well as in mammalian thermoregulation. Overexpression of these thermoregulators in prostate cancer and in other life-threatening tumors, along with their contribution to an increasing number of pathological conditions, opens a plethora of medicinal chemistry opportunities to develop receptor modulators. This Perspective seeks to describe current known modulators for this ion channel because both agonists and antagonists may be useful for the treatment of most TRPM8-mediated pathologies. We primarily focus on SAR data for the different families of compounds and the pharmacological properties of the most promising ligands. Furthermore, we also address the knowledge about the channel structure, although still in its infancy, and the role of the TRPM8 protein signalplex to channel function and dysfunction. We finally outline the potential future prospects of the challenging TRPM8 drug discovery field.

Beyond the classic eicosanoids: Peripherally-acting oxygenated metabolites of polyunsaturated fatty acids mediate pain associated with tissue injury and inflammation

Pain is a complex sensation that may be protective or cause undue suffering and loss of function, depending on the circumstances. Peripheral nociceptor neurons (PNs) innervate most tissues, and express ion channels, nocisensors, which depolarize the cell in response to intense stimuli and numerous substances. Inflamed tissues manifest inflammatory hyperalgesia in which the threshold for pain and the response to painful stimuli are decreased and increased, respectively. Constituents of the inflammatory milieu sensitize PNs, thereby contributing to hyperalgesia. Polyunsaturated fatty acids undergo enzymatic and free radical-mediated oxygenation into an array of bioactive metabolites, oxygenated polyunsaturated fatty acids (oxy-PUFAs), including the classic eicosanoids. Oxy-PUFA production is enhanced during inflammation. Pioneering studies by Vane and colleagues from the early 1970s first implicated classic eicosanoids in the pain associated with inflammation. Here, we review the production and action of oxy-PUFAs that are not classic eicosanoids, but nevertheless are produced in injured/ inflamed tissues and activate or sensitize PNs. In general, oxy-PUFAs that sensitize PNs may do so directly, by activation of nocisensors, ion channels or GPCRs expressed on the surface of PNs, or indirectly, by increasing the production of inflammatory mediators that activate or sensitize PNs. We focus on oxy-PUFAs that act directly on PNs. Specifically, we discuss the role of arachidonic acid-derived 12S-HpETE, HNE, ONE, PGA2, iso-PGA2 and 15d-PGJ2, 5,6-and 8,9-EET, PGE2-G and 8R,15S-diHETE, as well as the linoleic acid-derived 9-and 13-HODE in inducing acute nocifensive behavior and/or inflammatory hyperalgesia in rodents. The nocisensors TRPV1, TRPV4 and TRPA1, and putative Gαs-type GPCRs are the PN targets of these oxy-PUFAs.

Atypical sensors for direct and rapid neuronal detection of bacterial pathogens

Bacterial infection can threaten the normal biological functions of a host, often leading to a disease. Hosts have developed complex immune systems to cope with the danger. Preceding the elimination of pathogens, selective recognition of the non-self invaders is necessary. At the forefront of the body’s defenses are the innate immune cells, which are equipped with particular sensor molecules that can detect common exterior patterns of invading pathogens and their secreting toxins as well as with phagocytic machinery. Inflammatory mediators and cytokines released from these innate immune cells and infected tissues can boost the inflammatory cascade and further recruit adaptive immune cells to maximize the elimination and resolution. The nervous system also seems to interact with this process, mostly known to be affected by the inflammatory mediators through the binding of neuronal receptors, consequently activating neural circuits that tune the local and systemic inflammatory states. Recent research has suggested new contact points: direct interactions of sensory neurons with pathogens. Latest findings demonstrated that the sensory neurons not only share pattern recognition mechanisms with innate immune cells, but also utilize endogenous and exogenous electrogenic components for bacterial pathogen detection, by which the electrical firing prompts faster information flow than what could be achieved when the immune system is solely involved. As a result, rapid pain generation and active accommodation of the immune status occur. Here we introduced the sensory neuron-specific detector molecules for directly responding to bacterial pathogens and their signaling mechanisms. We also discussed extended issues that need to be explored in the future.

Diet-induced changes in n-3- and n-6-derived endocannabinoids and reductions in headache pain and psychological distress

Omega-3 and omega-6 fatty acids are biosynthetic precursors of endocannabinoids with antinociceptive, anxiolytic, and neurogenic properties. We recently reported that targeted dietary manipulation-increasing omega-3 fatty acids while reducing omega-6 linoleic acid (the H3-L6 intervention)-reduced headache pain and psychological distress among chronic headache patients. It is not yet known whether these clinical improvements were due to changes in endocannabinoids and related mediators derived from omega-3 and omega-6 fatty acids. We therefore used data from this trial (N = 55) to investigate 1) whether the H3-L6 intervention altered omega-3- and omega-6-derived endocannabinoids in plasma and 2) whether diet-induced changes in these bioactive lipids were associated with clinical improvements. The H3-L6 intervention significantly increased the omega-3 docosahexaenoic acid derivatives 2-docosahexaenoylglycerol (+65%, P < .001) and docosahexaenoylethanolamine (+99%, P < .001) and reduced the omega-6 arachidonic acid derivative 2-arachidonoylglycerol (-25%, P = .001). Diet-induced changes in these endocannabinoid derivatives of omega-3 docosahexaenoic acid, but not omega-6 arachidonic acid, correlated with reductions in physical pain and psychological distress. These findings demonstrate that targeted dietary manipulation can alter endocannabinoids derived from omega-3 and omega-6 fatty acids in humans and suggest that 2-docosahexaenoylglycerol and docosahexaenoylethanolamine could have physical and/or psychological pain modulating properties.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT01157208) PERSPECTIVE: This article demonstrates that targeted dietary manipulation can alter endocannabinoids derived from omega-3 and omega-6 fatty acids and that these changes are related to reductions in headache pain and psychological distress. These findings suggest that dietary interventions could provide an effective, complementary approach for managing chronic pain and related conditions.

The contribution of the endogenous TRPV1 ligands 9-HODE and 13-HODE to nociceptive processing and their role in peripheral inflammatory pain mechanisms

BACKGROUND AND PURPOSE

The transient receptor potential vanilloid type 1 (TRPV1) plays a fundamental role in the detection of heat and inflammatory pain responses. Here we investigated the contribution of two potential endogenous ligands [9- and 13- hydroxyoctadecadienoic acid (HODE)] to TRPV1-mediated noxious responses and inflammatory pain responses.

EXPERIMENTAL APPROACH

9- and 13-HODE, and their precursor, linoleic acid, were measured in dorsal root ganglion (DRG) neurons and in the hindpaws of control and carrageenan-inflamed rats by liquid chromatography/tandem electrospray mass spectrometry. Calcium imaging studies of DRG neurons were employed to determine the role of TRPV1 in mediating linoleic acid, 9-HODE- and 13-HODE-evoked responses, and the contribution of 15-lipoxygenase to the generation of the HODEs. Behavioural studies investigated the contribution of 9- and 13-HODE and 15-lipoxygenase to inflammatory pain behaviour.

KEY RESULTS

9-HODE (35 ± 7 pmol g(-1)) and 13-HODE (32 ± 6 pmol g(-1)) were detected in hindpaw tissue, but were below the limits of detection in DRGs. Following exposure to linoleic acid, 9- and 13-HODE were detected in DRGs and TRPV1 antagonist-sensitive calcium responses evoked, which were blocked by the 15-lipoxygenase inhibitor PD146176 and an anti-13-HODE antibody. Levels of linoleic acid were significantly increased in the carrageenan-inflamed hindpaw (P < 0.05), whereas levels of 9- and 13-HODE were, however, decreased. Intraplantar co-administration of anti-9- and 13-HODE antibodies and treatment with PD146176 significantly (P < 0.01) attenuated carrageenan-induced hyperalgesia.

CONCLUSIONS AND IMPLICATIONS

This study demonstrates that, although 9- and 13-HODE can activate TRPV1 in DRG cell bodies, the evidence for a role of these lipids as endogenous peripheral TRPV1 ligands in a model of inflammatory pain is at best equivocal.

Are sensory TRP channels biological alarms for lipid peroxidation?

Oxidative stress induces numerous biological problems. Lipid oxidation and peroxidation appear to be important steps by which exposure to oxidative stress leads the body to a disease state. For its protection, the body has evolved to respond to and eliminate peroxidation products through the acquisition of binding proteins, reducing and conjugating enzymes, and excretion systems. During the past decade, researchers have identified a group of ion channel molecules that are activated by oxidized lipids: transient receptor potential (TRP) channels expressed in sensory neurons. These ion channels are fundamentally detectors and signal converters for body-damaging environments such as heat and cold temperatures, mechanical attacks, and potentially toxic substances. When messages initiated by TRP activation arrive at the brain, we perceive pain, which results in our preparing defensive responses. Excessive activation of the sensory neuronal TRP channels upon prolonged stimulations sometimes deteriorates the inflammatory state of damaged tissues by promoting neuropeptide release from expresser neurons. These same paradigms may also work for pathologic changes in the internal lipid environment upon exposure to oxidative stress. Here, we provide an overview of the role of TRP channels and oxidized lipid connections during abnormally increased oxidative signaling, and consider the sensory mechanism of TRP detection as an alert system.

TRPV1 and Endocannabinoids: Emerging Molecular Signals that Modulate Mammalian Vision

Transient Receptor Potential Vanilloid 1 (TRPV1) subunits form a polymodal cation channel responsive to capsaicin, heat, acidity and endogenous metabolites of polyunsaturated fatty acids. While originally reported to serve as a pain and heat detector in the peripheral nervous system, TRPV1 has been implicated in the modulation of blood flow and osmoregulation but also neurotransmission, postsynaptic neuronal excitability and synaptic plasticity within the central nervous system. In addition to its central role in nociception, evidence is accumulating that TRPV1 contributes to stimulus transduction and/or processing in other sensory modalities, including thermosensation, mechanotransduction and vision. For example, TRPV1, in conjunction with intrinsic cannabinoid signaling, might contribute to retinal ganglion cell (RGC) axonal transport and excitability, cytokine release from microglial cells and regulation of retinal vasculature. While excessive TRPV1 activity was proposed to induce RGC excitotoxicity, physiological TRPV1 activity might serve a neuroprotective function within the complex context of retinal endocannabinoid signaling. In this review we evaluate the current evidence for localization and function of TRPV1 channels within the mammalian retina and explore the potential interaction of this intriguing nociceptor with endogenous agonists and modulators.

Simultaneous tissue profiling of eicosanoid and endocannabinoid lipid families in a rat model of osteoarthritis

We describe a novel LC method for the simultaneous and quantitative profiling of 43 oxylipins including eicosanoids, endocannabinoids, and structurally related bioactive lipids with modified acyl groups. The LC-MS/MS method uses switching at a defined time between negative and positive electrospray ionization modes to achieve optimal detection sensitivity for all the lipids. The validated method is linear over a range of 0.01–5 nmol/g (0.1–50 nmol/g for 2-arachidonoyl glycerol) with intra- and interday precision and accuracy between 1.38 and 26.76% and 85.22 and 114.3%, respectively. The method successfully quantified bioactive lipids in different tissue types in the rat, including spinal cord, dorsal root ganglia (DRGs), knee joint, brain, and plasma. Distinct regional differences in the pattern of lipid measured between tissue types were observed using principle component analysis. The method was applied to analyze tissue samples from an established preclinical rat model of osteoarthritis (OA) pain and showed that levels of 12-hydroxyeicosatetraenoic acid were significantly increased in the OA rat knee joint compared with controls, and that 15-hydroxyeicosatetraenoic acid was significantly increased in the DRGs in the model of OA compared with controls. The developed LC-MS/MS method has the potential to provide detailed pathway profiling in tissues and biofluids where the disruption of bioactive oxylipins may be involved in disease states.

Effect of chirality and lipophilicity in the functional activity of evodiamine and its analogues at TRPV1 channels

BACKGROUND AND PURPOSE

Evodiamine, a racemic quinazolinocarboline alkaloid isolated from the traditional Chinese medicine Evodiae fructus, has been reported to act as an agonist of the transient receptor potential vanilloid type-1 (TRPV1) cation channel both in vitro and in vivo. Evodiamine is structurally different from all known TRPV1 activators, and has significant clinical potential as a thermogenic agent. Nevertheless, the molecular bases for its actions are still poorly understood.

EXPERIMENTAL APPROACH

To investigate the structure-activity relationships of evodiamine, the natural racemate was resolved, and a series of 23 synthetic analogues was prepared, using as the end point the intracellular Ca(2+) elevation in HEK-293 cells stably overexpressing either the human or the rat recombinant TRPV1.

KEY RESULTS

S-(+) evodiamine was more efficacious and potent than R-(-) evodiamine, and a new potent lead (Evo30) was identified, more potent than the reference TRPV1 agonist, capsaicin. In general, potency and efficacy correlated with the lipophilicity of the analogues. Like other TRPV1 agonists, several synthetic analogues could efficiently desensitize TRPV1 to activation by capsaicin.

CONCLUSIONS AND IMPLICATIONS

Evodiamine qualifies as structurally unique lead structure to develop new potent TRPV1 agonists/desensitizers.

The endocannabinoid system: an emerging key player in inflammation

PURPOSE OF REVIEW

The purpose of this review is to illustrate the expanding view of the endocannabinoid system (ECS) in relation to its roles in inflammation.

RECENT FINDINGS

According to the formal classification, the ECS consists of two cannabinoid receptors, their endogenous fatty acid-derived ligands, and a number of enzymes involved in their synthesis and breakdown. However, many endogenous congeners of classical endocannabinoids have now been discovered, together with a set of receptors structurally or functionally related to the cannabinoid receptors. Endocannabinoids per se behave 'promiscuously' with regard to their receptor interactions. It is increasingly recognized how tightly this expanded ECS is intertwined with key processes involved in inflammation. A continuous dynamic exchange of substrates and metabolites exists between ECS and eicosanoid pathways. Endocannabinoids can also be oxygenated by cyclooxygenase and other enzymes to biologically active 'hybrid' structures. Diet is among the main factors determining synthesis and release of endocannabinoids and related mediators.

SUMMARY

The complexity of what may be called the 'endocannabinoidome' requires approaches that take into account its dynamics and interconnections with other regulatory systems. This endocannabinoidome continues to offer possibilities for prevention and intervention, but multiple target approaches will probably provide the only keys to success.

The role of endogenous molecules in modulating pain through transient receptor potential vanilloid 1 (TRPV1)

Pain is a physiological response to a noxious stimulus that decreases the quality of life of those sufferring from it. Research aimed at finding new therapeutic targets for the treatment of several maladies, including pain, has led to the discovery of numerous molecular regulators of ion channels in primary afferent nociceptive neurons. Among these receptors is TRPV1 (transient receptor potential vanilloid 1), a member of the TRP family of ion channels. TRPV1 is a calcium-permeable channel, which is activated or modulated by diverse exogenous noxious stimuli such as high temperatures, changes in pH, and irritant and pungent compounds, and by selected molecules released during tissue damage and inflammatory processes. During the last decade the number of endogenous regulators of TRPV1's activity has increased to include lipids that can negatively regulate TRPV1, as is the case for cholesterol and PIP2 (phosphatidylinositol 4,5-biphosphate) while, in contrast, other lipids produced in response to tissue injury and ischaemic processes are known to positively regulate TRPV1. Among the latter, lysophosphatidic acid activates TRPV1 while amines such as N-acyl-ethanolamines and N-acyl-dopamines can sensitize or directly activate TRPV1. It has also been found that nucleotides such as ATP act as mediators of chemically induced nociception and pain and gases, such as hydrogen sulphide and nitric oxide, lead to TRPV1 activation. Finally, the products of lipoxygenases and omega-3 fatty acids among other molecules, such as divalent cations, have also been shown to endogenously regulate TRPV1 activity. Here we provide a comprehensive review of endogenous small molecules that regulate the function of TRPV1. Acting through mechanisms that lead to sensitization and desensitization of TRPV1, these molecules regulate pathways involved in pain and nociception. Understanding how these compounds modify TRPV1 activity will allow us to comprehend how some pathologies are associated with its deregulation.