Pharmacological characterization of hydrolysis-resistant analogs of oleoylethanolamide with potent anorexiant properties

Oleoylethanolamide facilitates PPARα and TFEB signaling and attenuates Aβ pathology in a mouse model of Alzheimer's disease

BACKGROUND

Age is the strongest risk factor for the development of Alzheimer's disease (AD). Besides the pathological hallmarks of β-amyloid (Aβ) plaques and neurofibrillary tangles, emerging evidence demonstrates a critical role of microglia and neuroinflammation in AD pathogenesis. Oleoylethanolamide (OEA) is an endogenous lipid amide that has been shown to promote lifespan and healthspan in C. elegans through regulation of lysosome-to-nucleus signaling and cellular metabolism. The goal of our study was to determine the role of OEA in the mediation of microglial activity and AD pathology using its stable analog, KDS-5104.

METHODS

We used primary microglial cultures and genetic and pharmacological approaches to examine the signaling mechanisms and functional roles of OEA in mediating Aβ phagocytosis and clearance, lipid metabolism and inflammasome formation. Further, we tested the effect of OEA in vivo in acute LPS-induced neuroinflammation and by chronic treatment of 5xFAD mice.

RESULTS

We found that OEA activates PPARα signaling and its downstream cell-surface receptor CD36 activity. In addition, OEA promotes TFEB lysosomal function in a PPARα-dependent but mTORC1-independent manner, the combination of which leads to enhanced microglial Aβ uptake and clearance. These are associated with the suppression of LPS-induced lipid droplet accumulation and inflammasome activation. Chronic treatment of 5xFAD mice with KDS-5104 restored dysregulated lipid profiles, reduced reactive gliosis and Aβ pathology and rescued cognitive impairments.

CONCLUSION

Together, our study provides support that augmenting OEA-mediated lipid signaling may offer therapeutic benefit against aging and AD through modulating lipid metabolism and microglia phagocytosis and clearance.

Oleoylethanolamide facilitates PPARa and TFEB signaling and attenuates Ab pathology in a mouse model of Alzheimer's disease

Emerging evidence implicates impaired microglia function and dysregulation of lipid metabolism in Alzheimer's disease (AD). Oleoylethanolamide (OEA), an endogenous lipid and PPARα agonist, has been shown to promote longevity in C. elegans through regulation of lysosome-to-nucleus signaling and cellular metabolism. Using a stable OEA analog, KDS-5104, we found that OEA-PPARα signaling promotes TFEB lysosomal activity independent of mTORC1 and upregulates cell-surface receptor CD36, leading to enhanced microglial Aβ uptake and clearance. These are associated with the suppression of LPS-induced lipid droplet accumulation and inflammasome activation. Chronic treatment of the 5xFAD mice with KDS-5104 restored dysregulated profiles, reduced reactive gliosis and Aβ pathology and rescued cognitive impairments. Together, our study provides support that augmenting OEA-mediated lipid signaling may offer therapeutic benefit against aging and AD through modulating lipid metabolism and microglia phagocytosis and clearance.

OLHA (Nα-oleoylhistamine) modulates activity of mouse brain histaminergic neurons

Histaminergic (HA) neurons are located in the tuberomamillary nucleus (TMN) of the posterior hypothalamus, from where they project throughout the whole brain to control wakefulness. We examined the effects of N^α-oleoylhistamine (OLHA), a non-enzymatic condensation product of oleic acid (OLA) and histamine, on activity of mouse HA neurons in brain slices. OLHA bidirectionally modulated the firing of HA neurons. At 10 nM OLHA inhibited or had no action, whereas at 1 μM it evoked excitatory and inhibitory responses. Inhibition was not seen in presence of the histamine receptor H3 (H₃R) antagonist clobenpropit and in calcium-free medium. Pre-incubation with a histamine-reuptake blocker prevented the decrease in firing by OLHA. OLHA-evoked increase in firing (EC₅₀ ∼44 nM) was insensitive to blockers of cannabinoid 1 and 2 receptors and of the capsaicin receptor, but was significantly impaired by the peroxisome proliferator-activated receptor-alpha (PPAR-alpha) antagonist MK886, which suppressed also the rise in intracellular calcium level caused by OLHA. The OLHA-evoked excitation was mimicked by synthetic PPAR-alpha agonists (gemfibrozil and GW7647) and was abolished by the PKA inhibitor H-89. The H₃R affinity (Ki) for histamine, measured in HEK293 cells with stable expression of human H₃R, was higher than for OLHA (Ki: 42 vs 310 nM, respectively). Expression of PPAR-alpha was not different between TMN regions of males and females, responses to OLHA did not differ. Molecular modelling of PPAR-alpha bound to either OLHA or OEA showed similar binding energies. These findings shed light on a novel biotransformation product of histamine which may play a role in health and disease.

Tranilast: a potential anti-Inflammatory and NLRP3 inflammasome inhibitor drug for COVID-19

SARS-CoV-2 is a type of beta-CoV that develops acute pneumonia, which is an inflammatory condition. A cytokine storm has been recognized as one of the leading causes of death in patients with COVID-19. ALI and ARDS along with multiple organ failure have also been presented as the consequences of acute inflammation and cytokine storm. It has been previously confirmed that SARS-CoV, as another member of the beta-CoV family, activates NLRP3 inflammasome and consequently develops acute inflammation in a variety of ways through having complex interactions with the host immune system using structural and nonstructural proteins. Numerous studies conducted on Tranilast have further demonstrated that the given drug can act as an effective anti-chemotactic factor on controlling inflammation, and thus, it can possibly help the improvement of the acute form of COVID-19 by inhibiting some key inflammation-associated transcription factors such as NF-κB and impeding NLRP3 inflammasome. Several studies have comparably revealed the direct effect of this drug on the prevention of inappropriate tissue's remodeling; inhibition of neutrophils, IL-5, and eosinophils; repression of inflammatory cell infiltration into inflammation site; restriction of factors involved in acute airway inflammation like IL-33; and suppression of cytokine IL-13, which increase mucosal secretions. Therefore, Tranilast may be considered as a potential treatment for patients with the acute form of COVID-19 along with other drugs.

Steric stabilisers govern the colloidal and chemical stability but not in vitro cellular toxicity of linoleoylethanolamide cubosomes

Linoleoylethanolamide (LEA) is an endogenous lipid with remarkable neuromodulatory properties. However, its therapeutic potential is limited by rapid clearance in vivo, targetability and solubility. This study aimed to formulate LEA into liquid crystalline nanoparticles (cubosomes) as a strategy to address the aforementioned challenges. The influence of three different steric stabilisers: Tween 80 and Pluronic F68, both of which have the potential to interact with receptors expressed at the blood-brain barrier and Pluronic F127 as a control, on colloidal stability, internal structure, chemical stability and cytotoxicity of the dispersions were investigated. We found that for effective stabilization of LEA dispersions, a higher concentration of Tween 80 was required compared to Pluronics. Freshly prepared dispersions showed mean particle size of <250 nm and low PDIs (<0.2), with an Im3m type cubic structure but with different lattice parameters. Upon storage at ambient temperature for a week, increased mean particle size and PDI, with a significant reduction in the concentration of LEA was observed in Tween 80-stabilised dispersions. Greater than 80% cell viability was observed at concentrations of up to 20 μg/mL LEA in the presence of all three stabilisers. Collectively, our results suggest that the stabiliser type influences colloidal and chemical stability but not cytotoxicity of LEA cubosomes. This study highlights the potential of endogenous bioactive lipids to be utilized as core cubosome forming lipids with the view to improving their solubility, rapid clearance and targetability to enable delivery of these bioactive molecules to the brain.

A systematic review of the effects of oleoylethanolamide, a high-affinity endogenous ligand of PPAR-α, on the management and prevention of obesity

Along with an increase in overweight and obesity among all age groups, the development of efficacious and safe anti-obesity strategies for patients, as well as health systems, is critical. Oleoylethanolamide (OEA), a high-affinity endogenous ligand of nuclear receptor peroxisome proliferator-activated receptor alpha (PPAR-α), plays important physiological and metabolic actions. OEA is derived from oleic acid, a monounsaturated fatty acid, which has beneficial effects on body composition and regional fat distribution. The role of OEA in the modulation of food consumption and weight management makes it an attractive molecule requiring further exploration in obesogenic environments. This systematic review was conducted to assess the effects of OEA on the obesity management, with emphasizing on its physiological roles and possible mechanisms of action in energy homeostasis. We searched PubMed/Medline, Google Scholar, ScienceDirect, Scopus, ProQuest, and EMBASE up until September 2019. Out of 712 records screened, 30 articles met the study criteria. The evidence reviewed here indicates that OEA, an endocannabinoid-like compound, leads to satiation or meal termination through PPAR-α activation and fatty acid translocase (FAT)/CD36. Additionally, the lipid-amide OEA stimulates fatty acid uptake, lipolysis, and beta-oxidation, and also promotes food intake control. OEA also exerts satiety-inducing effects by activating the hedonic dopamine pathways and increasing homeostatic oxytocin and brain histamine. In conclusion, OEA may be a key component of the physiological system involved in the regulation of dietary fat consumption and energy homeostasis; therefore, it is suggested as a possible therapeutic agent for the management of obesity.

Mast Cell-Derived Histamine Regulates Liver Ketogenesis via Oleoylethanolamide Signaling

The conversion of lipolysis-derived fatty acids into ketone bodies (ketogenesis) is a crucial metabolic adaptation to prolonged periods of food scarcity. The process occurs primarily in liver mitochondria and is initiated by fatty-acid-mediated stimulation of the ligand-operated transcription factor, peroxisome proliferator-activated receptor-α (PPAR-α). Here, we present evidence that mast cells contribute to the control of fasting-induced ketogenesis via a paracrine mechanism that involves secretion of histamine into the hepatic portal circulation, stimulation of liver H₁ receptors, and local biosynthesis of the high-affinity PPAR-α agonist, oleoylethanolamide (OEA). Genetic or pharmacological interventions that disable any one of these events, including mast cell elimination, deletion of histamine- or OEA-synthesizing enzymes, and H₁ blockade, blunt ketogenesis without affecting lipolysis. The results reveal an unexpected role for mast cells in the regulation of systemic fatty-acid homeostasis, and suggest that OEA may act in concert with lipolysis-derived fatty acids to activate liver PPAR-α and promote ketogenesis.

Oleoylethanolamide: The role of a bioactive lipid amide in modulating eating behaviour

Fatty acid ethanolamides are lipid mediators that regulate a plethora of physiological functions. One such bioactive lipid mediator, oleoylethanolamide (OEA), is a potent agonist of the peroxisome proliferator-activated receptor-alpha (PPAR-α), which modulates increased expression of the fatty acid translocase CD36 that enables the regulation of feeding behaviour. Consumption of dietary fat rich in oleic acid activates taste receptors in the gut activating specific enzymes that lead to the formation of OEA. OEA further combines with PPAR-α to enable fat oxidation in the liver, resulting in enhanced energy production. Evidence suggests that sustained ingestion of a high-fat diet abolishes the anorexic signal of OEA. Additionally, malfunction of the enterocyte that transforms oleic acid produced during fat digestion into OEA might be responsible for reduced satiety and hyperphagia, resulting in overweight and obesity. Thus, OEA anorectic signalling may be an essential element of the physiology and metabolic system regulating dietary fat intake and obesity. The evidence reviewed in this article indicates that intake of oleic acid, and thereby the resulting OEA imparting anorexic properties, is dependent on CD36, PPAR-α, enterocyte fat sensory receptors, histamine, oxytocin and dopamine; leading to increased fat oxidation and enhanced energy expenditure to induce satiety and increase feeding latency; and that a disruption in any of these systems will cease/curb fat-induced satiety.

Role of the area postrema in the hypophagic effects of oleoylethanolamide

The satiety-promoting action of oleoylethanolamide (OEA) has been associated to the indirect activation of selected brain areas, such as the nucleus of the solitary tract (NST) in the brainstem and the tuberomammillary (TMN) and paraventricular (PVN) nuclei in the hypothalamus, where noradrenergic, histaminergic and oxytocinergic neurons play a necessary role. Visceral ascending fibers were hypothesized to mediate such effects. However, our previous findings demonstrated that the hypophagic action of peripherally administered OEA does not require intact vagal afferents and is associated to a strong activation of the area postrema (AP). Therefore, we hypothesized that OEA may exert its central effects through the direct activation of this circumventricular organ. To test this hypothesis, we subjected rats to the surgical ablation of the AP (APX rats) and evaluated the effects of OEA (10mgkg^-1 i.p.) on food intake, Fos expression, hypothalamic oxytocin (OXY) immunoreactivity and on the expression of dopamine beta hydroxylase (DBH) in the brainstem and hypothalamus. We found that the AP lesion completely prevented OEA's behavioral and neurochemical effects in the brainstem and the hypothalamus. Moreover OEA increased DBH expression in AP and NST neurons of SHAM rats while the effect in the NST was absent in APX rats, thus suggesting the possible involvement of noradrenergic AP neurons. These results support the hypothesis of a necessary role of the AP in mediating OEA's central effects that sustain its pro-satiety action.

Incorporation of an Endogenous Neuromodulatory Lipid, Oleoylethanolamide, into Cubosomes: Nanostructural Characterization

Oleoylethanolamide (OEA) is an endogenous lipid with neuroprotective properties and the fortification of its concentration in the brain can be beneficial in the treatment of many neurodegenerative disorders. However, OEA is rapidly eliminated by hydrolysis in vivo, limiting its therapeutic potential. We hypothesize that packing OEA within a nanoparticulate system such as cubosomes, which can be used to target the blood-brain barrier (BBB), will protect it against hydrolysis and enable therapeutic concentrations to reach the brain. Cubosomes are lipid-based nanoparticles with a unique bicontinuous cubic phase internal structure. In the present study, the incorporation and chemical stability of OEA in cubosomes was investigated. Cubosomes containing OEA had a mean particle size of less than 200 nm with low polydispersity (polydispersity index <0.25). Infrared spectroscopy and high-performance liquid chromatography showed chemical stability and the encapsulation of OEA within cubosomes. Cryo-TEM and SAXS measurements were used to probe the influence of the addition of OEA on the internal structure of the cubosomes. Up to 30% w/w OEA (relative to phytantriol) could be incorporated into phytantriol cubosomes without any significant disruption of the nanostructure of the cubosomes. Combined, the results indicate that OEA-loaded cubosomes have the potential for application as a colloidal carrier for OEA, potentially preventing hydrolysis in vivo.

An update on PPAR activation by cannabinoids

Some cannabinoids activate the different isoforms of PPARs (α, β and γ), as shown through the use of reporter gene assays, binding studies, selective antagonists and knockout studies. Activation of all isoforms, but primarily PPARα and γ, mediates some (but not all) of the analgesic, neuroprotective, neuronal function modulation, anti-inflammatory, metabolic, anti-tumour, gastrointestinal and cardiovascular effects of some cannabinoids, often in conjunction with activation of the more traditional target sites of action such as the cannabinoid CB1 and CB2 receptors and the TRPV1 ion channel. PPARs also mediate some of the effects of inhibitors of endocannabinoid degradation or transport. Cannabinoids may be chaperoned to the PPARs by fatty acid binding proteins. The aims of this review are to update the evidence supporting PPAR activation by cannabinoids and to review the physiological responses to cannabinoids that are mediated, and not mediated, by PPAR activation.

Expanding the chemical space of hydrophobic pharmacophores: the role of hydrophobic substructures in the development of novel transcription modulators

Interactions between biologically active compounds and their targets often involve hydrophobic interactions, and hydrophobicity also influences the pharmacokinetic profile.

Central mechanisms mediating the hypophagic effects of oleoylethanolamide and N-acylphosphatidylethanolamines: different lipid signals?

The spread of “obesity epidemic” and the poor efficacy of many anti-obesity therapies in the long-term highlight the need to develop novel efficacious therapy. This necessity stimulates a large research effort to find novel mechanisms controlling feeding and energy balance. Among these mechanisms a great deal of attention has been attracted by a family of phospholipid-derived signaling molecules that play an important role in the regulation of food-intake. They include N-acylethanolamines (NAEs) and N-acylphosphatidylethanolamines (NAPEs). NAPEs have been considered for a long time simply as phospholipid precursors of the lipid mediator NAEs, but increasing body of evidence suggest a role in many physiological processes including the regulation of feeding behavior. Several observations demonstrated that among NAEs, oleoylethanolamide (OEA) acts as a satiety signal, which is generated in the intestine, upon the ingestion of fat, and signals to the central nervous system. At this level different neuronal pathways, including oxytocinergic, noradrenergic, and histaminergic neurons, seem to mediate its hypophagic action. Similarly to NAEs, NAPE (with particular reference to the N16:0 species) levels were shown to be regulated by the fed state and this finding was initially interpreted as fluctuations of NAE precursors. However, the observation that exogenously administered NAPEs are able to inhibit food intake, not only in normal rats and mice but also in mice lacking the enzyme that converts NAPEs into NAEs, supported the hypothesis of a role of NAPE in the regulation of feeding behavior. Indirect observations suggest that the hypophagic action of NAPEs might involve central mechanisms, although the molecular target remains unknown. The present paper reviews the role that OEA and NAPEs play in the mechanisms that control food intake, further supporting this group of phospholipids as optimal candidate for the development of novel anti-obesity treatments.

Amino Acid Derivatives as Palmitoylethanolamide Prodrugs: Synthesis, In Vitro Metabolism and In Vivo Plasma Profile in Rats

Palmitoylethanolamide (PEA) has antinflammatory and antinociceptive properties widely exploited in veterinary and human medicine, despite its poor pharmacokinetics. Looking for prodrugs that could progressively release PEA to maintain effective plasma concentrations, we prepared carbonates, esters and carbamates at the hydroxyl group of PEA. Chemical stability (pH 7.4) and stability in rat plasma and liver homogenate were evaluated by in vitro assays. Carbonates and carbamates resulted too labile and too resistant in plasma, respectively. Ester derivatives, prepared by conjugating PEA with various amino acids, allowed to modulate the kinetics of PEA release in plasma and stability in liver homogenate. L-Val-PEA, with suitable PEA release in plasma, and D-Val-PEA, with high resistance to hepatic degradation, were orally administered to rats and plasma levels of prodrugs and PEA were measured at different time points. Both prodrugs showed significant release of PEA, but provided lower plasma concentrations than those obtained with equimolar doses of PEA. Amino-acid esters of PEA are a promising class to develop prodrugs, even if they need further chemical optimization.

Design and synthesis of silicon-containing fatty acid amide derivatives as novel peroxisome proliferator-activated receptor (PPAR) agonists

We recently reported that diphenylsilane structure can function as a cis-stilbene mimetic. Here, we investigate whether silyl functionality can also serve as a mimetic of aliphatic cis-olefin. We designed and synthesized various silyl derivatives of oleoylethanolamide (OEA: 8), an endogenous cis-olefin-containing PPARα agonist, and evaluated their PPARα/δ/γ agonistic activity. We found that diethylsilyl derivative 20 exhibited PPARα/δ agonistic activity, and we also obtained a PPARδ-selective agonist, 32. Our results suggest that incorporation of silyl functionality is a useful option for structural development of biologically active compounds.

Intestinal lipid-derived signals that sense dietary fat

Fat is a vital macronutrient, and its intake is closely monitored by an array of molecular sensors distributed throughout the alimentary canal. In the mouth, dietary fat constituents such as mono- and diunsaturated fatty acids give rise to taste signals that stimulate food intake, in part by enhancing the production of lipid-derived endocannabinoid messengers in the gut. As fat-containing chyme enters the small intestine, it causes the formation of anorexic lipid mediators, such as oleoylethanolamide, which promote satiety. These anatomically and functionally distinct responses may contribute to the homeostatic control and, possibly, the pathological dysregulation of food intake.

Aging. Lysosomal signaling molecules regulate longevity in Caenorhabditis elegans

Lysosomes are crucial cellular organelles for human health that function in digestion and recycling of extracellular and intracellular macromolecules. We describe a signaling role for lysosomes that affects aging. In the worm Caenorhabditis elegans, the lysosomal acid lipase LIPL-4 triggered nuclear translocalization of a lysosomal lipid chaperone LBP-8, which promoted longevity by activating the nuclear hormone receptors NHR-49 and NHR-80. We used high-throughput metabolomic analysis to identify several lipids in which abundance was increased in worms constitutively overexpressing LIPL-4. Among them, oleoylethanolamide directly bound to LBP-8 and NHR-80 proteins, activated transcription of target genes of NHR-49 and NHR-80, and promoted longevity in C. elegans. These findings reveal a lysosome-to-nucleus signaling pathway that promotes longevity and suggest a function of lysosomes as signaling organelles in metazoans.

Oleic acid content of a meal promotes oleoylethanolamide response and reduces subsequent energy intake in humans

Animal data suggest that dietary fat composition may influence endocannabinoid (EC) response and dietary behavior. This study tested the hypothesis that fatty acid composition of a meal can influence the short-term response of ECs and subsequent energy intake in humans. Fifteen volunteers on three occasions were randomly offered a meal containing 30 g of bread and 30 mL of one of three selected oils: sunflower oil (SO), high oleic sunflower oil (HOSO) and virgin olive oil (VOO). Plasma EC concentrations and appetite ratings over 2 h and energy intake over 24 h following the experimental meal were measured. Results showed that after HOSO and VOO consumption the circulating oleoylethanolamide (OEA) was significantly higher than after SO consumption; a concomitantly significant reduction of energy intake was found. For the first time the oleic acid content of a meal was demonstrated to increase the post-prandial response of circulating OEA and to reduce energy intake at subsequent meals in humans.

Vagal afferents are not necessary for the satiety effect of the gut lipid messenger oleoylethanolamide

The endogenous lipid messenger oleoylethanolamide (OEA) inhibits eating and modulates fat metabolism supposedly through the activation of peroxisome proliferator-activated receptor-α (PPARα) and vagal sensory fibers. We tested in adult male rats whether OEA stimulates fatty acid oxidation (FAO) and ketogenesis and whether it increases plasma levels of the satiating gut peptides glucagon-like peptide-1 (GLP-1) and peptide YY (PYY). We also explored whether OEA still inhibits eating after subdiaphragmatic vagal deafferentation (SDA). We found that intraperitoneally injected OEA (10 mg/kg body wt) reduced ( P < 0.05) food intake mainly by increasing meal latency and that this effect was stronger in rats fed a 60% high-fat diet (HFD) than in chow-fed rats. OEA increased ( P < 0.05) postprandial plasma nonesterified fatty acids and β-hydroxybutyrate (BHB) in the hepatic portal vein (HPV) and vena cava (VC) 30 min after injection, which was more pronounced in HFD- than in chow-fed rats. OEA also increased the protein expression of the key ketogenetic enzyme, mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase, in the jejunum of HFD-fed rats, but not in the liver or duodenum of either diet group. Furthermore, OEA decreased GLP-1 and PYY concentrations ( P < 0.05) in the HPV and VC 30 min after administration. Finally, OEA reduced food intake in SDA and sham-operated rats similarly. Our findings indicate that neither intact abdominal vagal afferents nor prandial increases in GLP-1 or PYY are necessary for the satiety effect of OEA. The enhanced FAO and ketogenesis raise the possibility of an involvement of intestine-derived BHB in OEA's satiety effect under certain conditions.

Role of oleoylethanolamide as a feeding regulator in goldfish

Oleoylethanolamide (OEA) is a bioactive lipid mediator, produced in the intestine and other tissues, which is involved in energy balance regulation in mammals, modulating feeding and lipid metabolism. The purpose of the present study was to investigate the presence and possible role of OEA in feeding regulation in goldfish (Carassius auratus). We assessed whether goldfish peripheral tissues and brain contain OEA and their regulation by nutritional status. OEA was detected in all studied tissues (liver, intestinal bulb, proximal intestine, muscle, hypothalamus, telencephalon and brainstem). Food deprivation (48 h) reduced intestinal OEA levels and levels increased upon re-feeding, suggesting that this compound may be involved in the short-term regulation of food intake in goldfish, as a satiety factor. Next, the effects of acute intraperitoneal administration of OEA on feeding, swimming and plasma levels of glucose and triglycerides were analysed. Food intake, swimming activity and circulating triglyceride levels were reduced by OEA 2 h post-injection. Finally, the possible interplay among OEA and other feeding regulators (leptin, cholecystokinin, ghrelin, neuropeptide Y, orexin and monoamines) was investigated. OEA actions on energy homeostasis in goldfish could be mediated, at least in part, through interactions with ghrelin and the serotonergic system, as OEA treatment reduced ghrelin expression in the intestinal bulb, and increased serotonergic activity in the telencephalon. In summary, our results indicate for the first time in fish that OEA could be involved in the regulation of feeding, swimming and lipid metabolism, suggesting a high conservation of OEA actions in energy balance throughout vertebrate evolution.

Galactosyl prodrug of palmitoylethanolamide: synthesis, stability, cell permeation and cytoprotective activity

N-Palmitoylethanolamide (PEA) is emerging as a novel therapeutic agent in the treatment of neuropathic pain and neurodegenerative diseases. Unfortunately, PEA poorly reaches the central nervous system (CNS), after peripheral administration, since it is inactivated through intracellular hydrolysis by lipid amidases. Since prodrug approach is one of the most popular methods used to increase cell permeability, the aim of this paper consists in the synthesis of a new galactosyl prodrug of PEA, the palmitoylethanolamide-succinamyl-D-galactos-6'-yl ester (PEAGAL). Biological experiments both in neuroblastoma and in C6 glioma cells, together with quantitative analyses performed through a LC-MS-MS technique, demonstrate the better efficacy of PEAGAL compared to PEA and its higher cell permeation. Our results encourage further experiments in animal models of neuropathic pain and of neurological disorders and/or neurodegenerative diseases, in order to promote a more effective peripherally administrated derivative of PEA.

Oleoylethanolamide: a novel potential pharmacological alternative to cannabinoid antagonists for the control of appetite

The initial pharmaceutical interest for the endocannabinoid system as a target for antiobesity therapies has been restricted by the severe adverse effects of the CB1 antagonist rimonabant. This study points at oleoylethanolamide (OEA), a monounsaturated analogue, and functional antagonist of anandamide, as a potential and safer antiobesity alternative to CB1 antagonism. Mice treated with equal doses (5 or 10 mg/kg, i.p.) of OEA or rimonabant were analyzed for the progressive expression of spontaneous behaviors (eating, grooming, rearing, locomotion, and resting) occurring during the development of satiety, according to the paradigm called behavioral satiety sequence (BSS). Both drugs reduced food (wet mash) intake to a similar extent. OEA treatment decreased eating activity within the first 30 min and caused a temporary increase of resting time that was not accompanied by any decline of horizontal, vertical and total motor activity. Besides decreasing eating activity, rimonabant caused a marked increase of the time spent grooming and decreased horizontal motor activity, alterations that might be indicative of aversive nonmotivational effects on feeding. These results support the idea that OEA suppresses appetite by stimulating satiety and that its profile of action might be predictive of safer effects in humans as a novel antiobesity treatment.

Role of anorectic N-acylethanolamines in intestinal physiology and satiety control with respect to dietary fat

Anandamide is a well-known agonist for the cannabinoid receptors. Along with endogenous anandamide other non-endocannabinoid N-acylethanolamines are also formed, apparently in higher amounts. These include mainly oleoylethanolamide (OEA), palmitoyelethanolamide (PEA) and linoleoylethanolamide (LEA), and they have biological activity by themselves being anorectic and anti-inflammatory. It appears that the major effect of dietary fat on the level of these molecules is in the gastrointestinal system, where OEA, PEA and LEA in the enterocytes may function as homeostatic signals, which are decreased by prolonged consumption of a high-fat diet. These lipid amides appear to mediate their signaling activity via activation of PPARα in the enterocyte followed by activation of afferent vagal fibers leading to the brain. Through this mechanism OEA, PEA and LEA may both reduce the consumption of a meal as well as increase the reward value of the food. Thus, they may function as homeostatic intestinal signals involving hedonic aspects that contribute to the regulation of the amounts of dietary fat to be ingested.

Atheroprotective effect of oleoylethanolamide (OEA) targeting oxidized LDL

Dietary fat-derived lipid oleoylethanolamide (OEA) has shown to modulate lipid metabolism through a peroxisome proliferator-activated receptor-alpha (PPAR-α)-mediated mechanism. In our study, we further demonstrated that OEA, as an atheroprotective agent, modulated the atherosclerotic plaques development. In vitro studies showed that OEA antagonized oxidized LDL (ox-LDL)-induced vascular endothelial cell proliferation and vascular smooth muscle cell migration, and suppressed lipopolysaccharide (LPS)-induced LDL modification and inflammation. In vivo studies, atherosclerosis animals were established using balloon-aortic denudation (BAD) rats and ApoE(-/-) mice fed with high-caloric diet (HCD) for 17 or 14 weeks respectively, and atherosclerotic plaques were evaluated by oil red staining. The administration of OEA (5 mg/kg/day, intraperitoneal injection, i.p.) prevented or attenuated the formation of atherosclerotic plaques in HCD-BAD rats or HCD-ApoE(-/-) mice. Gene expression analysis of vessel tissues from these animals showed that OEA induced the mRNA expressions of PPAR-α and downregulated the expression of M-CFS, an atherosclerotic marker, and genes involved in oxidation and inflammation, including iNOS, COX-2, TNF-α and IL-6. Collectively, our results suggested that OEA exerted a pharmacological effect on modulating atherosclerotic plaque formation through the inhibition of LDL modification in vascular system and therefore be a potential candidate for anti-atherosclerosis drug.

A fatty gut feeling

The absorptive epithelium of the proximal small intestine converts oleic acid released during fat digestion into oleoylethanolamide (OEA), an endogenous high-affinity agonist of peroxisome proliferator-activated receptor-α (PPAR-α). OEA interacts with this receptor to cause a state of satiety characterized by prolonged inter-meal intervals and reduced feeding frequency. The two main branches of the autonomic nervous system, sympathetic and parasympathetic, contribute to this effect: the former by enabling OEA mobilization in the gut and the latter by relaying the OEA signal to brain structures, such as the hypothalamus, that are involved in feeding regulation. OEA signaling may be a key component of the physiological system devoted to the monitoring of dietary fat intake, and its dysfunction might contribute to overweight and obesity.

AM404 attenuates reinstatement of nicotine seeking induced by nicotine-associated cues and nicotine priming but does not affect nicotine- and food-taking

Multiple studies suggest a pivotal role of the endocannabinoid system in the regulation of the reinforcing effects of various substances of abuse. Different approaches have been used to modulate endocannabinoid neurotransmission including the use of endogenous cannabinoid anandamide reuptake inhibitors. Previously, the effects of one of them, N-(4-hydroxyphenyl)-arachidonamide (AM404), have been explored in rodents trained to self-administer ethanol and heroin, producing some promising results. Moreover, AM404 attenuated the development and reinstatement of nicotine-induced conditioned place preference (CPP). In this study, we used the nicotine intravenous self-administration procedure to assess the effects of intraperitoneal administration of 0, 1, 3 and 10 mg/kg AM404 on nicotine-taking and food-taking behaviors under fixed-ratio and progressive-ratio schedules of reinforcement, as well as on reinstatement of nicotine-seeking induced by nicotine priming and by presentation of nicotine-associated cues. The ability of AM404 to produce place preference was also evaluated. AM404 did not produce CPP and did not modify nicotine-taking and food-taking behaviors. In contrast, AM404 dose-dependently attenuated reinstatement of nicotine-seeking behavior induced by both nicotine-associated cues and nicotine priming. Our results indicate that AM404 could be a potential promising therapeutic option for the prevention of relapse to nicotine-seeking in abstinent smokers.

The anandamide transport inhibitor AM404 reduces the rewarding effects of nicotine and nicotine-induced dopamine elevations in the nucleus accumbens shell in rats

BACKGROUND AND PURPOSE

The fatty acid amide hydrolase inhibitor URB597 can reverse the abuse-related behavioural and neurochemical effects of nicotine in rats. Fatty acid amide hydrolase inhibitors block the degradation (and thereby magnify and prolong the actions) of the endocannabinoid anandamide (AEA), and also the non-cannabinoid fatty acid ethanolamides oleoylethanolamide (OEA) and palmitoylethanolamide (PEA). OEA and PEA are endogenous ligands for peroxisome proliferator-activated receptors alpha (PPAR-α). Since recent evidence indicates that PPAR-α can modulate nicotine reward, it is unclear whether AEA plays a role in the effects of URB597 on nicotine reward.

EXPERIMENTAL APPROACH

A way to selectively increase endogenous levels of AEA without altering OEA or PEA levels is to inhibit AEA uptake into cells by administering the AEA transport inhibitor N-(4-hydroxyphenyl)-arachidonamide (AM404). To clarify AEA's role in nicotine reward, we investigated the effect of AM404 on conditioned place preference (CPP), reinstatement of abolished CPP, locomotor suppression and anxiolysis in an open field, and dopamine elevations in the nucleus accumbens shell induced by nicotine in Sprague-Dawley rats.

KEY RESULTS

AM404 prevented the development of nicotine-induced CPP and impeded nicotine-induced reinstatement of the abolished CPP. Furthermore, AM404 reduced nicotine-induced increases in dopamine levels in the nucleus accumbens shell, the terminal area of the brain's mesolimbic reward system. AM404 did not alter the locomotor suppressive or anxiolytic effect of nicotine.

CONCLUSIONS AND IMPLICATIONS

These findings suggest that AEA transport inhibition can counteract the addictive effects of nicotine and that AEA transport may serve as a new target for development of medications for treatment of tobacco dependence.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids in Biology and Medicine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-8. To view Part I of Cannabinoids in Biology and Medicine visit http://dx.doi.org/10.1111/bph.2011.163.issue-7.

The cytoprotective effects of oleoylethanolamide in insulin-secreting cells do not require activation of GPR119

BACKGROUND AND PURPOSE

β-cells express a range of fatty acid-responsive G protein-coupled receptors, including GPR119, which regulates insulin secretion and is seen as a potential therapeutic target in type 2 diabetes. The long-chain unsaturated fatty acid derivative oleoylethanolamide (OEA) is an endogenous agonist of GPR119 and, under certain conditions, some long-chain unsaturated fatty acids can promote β-cell cytoprotection. It is not known, however, if OEA is cytoprotective in β-cells. The present study has examined this and determined whether GPR119 is involved.

METHODS

Clonal rat insulin-secreting cell lines, BRIN-BD11 or INS-1E, were exposed to fatty acids complexed with BSA. cAMP levels, insulin release and cell viability were measured. Protein expression was studied by Western blotting and receptor expression by RT-PCR.

KEY RESULTS

GPR119 was expressed in both BRIN-BD11 and INS-1E cells and OEA was cytoprotective in these cells. However, cytoprotection was not reproduced by any of a range of selective, synthetic ligands of GPR119. The cytoprotective response to OEA was lost during exposure to inhibitors of fatty acid amide hydrolase (FAAH) suggesting that OEA per se is not the cytoprotective species but that release of free oleate is required. Similar data were obtained with anandamide, which was cytoprotective only under conditions favouring release of free arachidonate.

CONCLUSIONS AND IMPLICATIONS

Activation of GPR119 is not required to mediate the cytoprotective actions of OEA in BRIN-BD11 or INS-1E cells. Rather, OEA is internalised and subjected to hydrolysis by FAAH to release free oleate, which then mediates the cytoprotection.

The selective anandamide transport inhibitor VDM11 attenuates reinstatement of nicotine seeking behaviour, but does not affect nicotine intake

BACKGROUND AND PURPOSE

The endocannabinoid system appears to play a pivotal role in mediating the rewarding and reinforcing effects of nicotine. Recent studies have shown that the inhibition of fatty acid amide hydrolase (FAAH) attenuates reinstatement of nicotine-seeking induced by nicotine priming and nicotine-associated cues. FAAH hydrolyses the endogenous endocannabinoid anandamide, as well as other non-cannabinoid ligands such as oleoylethanolamide (OEA) and palmitoylethanolamide (PEA). As OEA and PEA can attenuate both nicotine-taking and nicotine-seeking behaviour, the specific role of anandamide remains unclear. In this study, we have tested the selective anadamide uptake inhibitor, VDM11, which elevates anandamide levels without affecting levels of OEA/PEA, on nicotine-taking and nicotine-seeking behaviour.

EXPERIMENTAL APPROACH

We used a nicotine intravenous self-administration model in rats to assess the effect of VDM11, given i.p., on nicotine taking using fixed and progressive ratio schedules of reinforcement as well as on reinstatement of nicotine-seeking induced by nicotine priming and nicotine-associated cues.

KEY RESULTS

VDM11 did not affect levels of responding for nicotine under fixed-ratio and progressive-ratio schedules of reinforcement. In contrast, VDM11 dose-dependently attenuated reinstatement of nicotine-seeking behaviour induced by nicotine-associated cues and nicotine priming.

CONCLUSIONS AND IMPLICATIONS

These results indicate that ligands elevating anandamide levels could have therapeutic value for preventing relapse into nicotine-seeking behaviour and should be tested in humans trying to quit smoking.

Decreased body weight and hepatic steatosis with altered fatty acid ethanolamide metabolism in aged L-Fabp -/- mice

The tissue-specific sources and regulated production of physiological signals that modulate food intake are incompletely understood. Previous work showed that L-Fabp(-/-) mice are protected against obesity and hepatic steatosis induced by a high-fat diet, findings at odds with an apparent obesity phenotype in a distinct line of aged L-Fabp(-/-) mice. Here we show that the lean phenotype in L-Fabp(-/-) mice is recapitulated in aged, chow-fed mice and correlates with alterations in hepatic, but not intestinal, fatty acid amide metabolism. L-Fabp(-/-) mice exhibited short-term changes in feeding behavior with decreased food intake, which was associated with reduced abundance of key signaling fatty acid ethanolamides, including oleoylethanolamide (OEA, an agonist of PPARα) and anandamide (AEA, an agonist of cannabinoid receptors), in the liver. These reductions were associated with increased expression and activity of hepatic fatty acid amide hydrolase-1, the enzyme that degrades both OEA and AEA. Moreover, L-Fabp(-/-) mice demonstrated attenuated responses to OEA administration, which was completely reversed with an enhanced response after administration of a nonhydrolyzable OEA analog. These findings demonstrate a role for L-Fabp in attenuating obesity and hepatic steatosis, and they suggest that hepatic fatty acid amide metabolism is altered in L-Fabp(-/-) mice.

Synthesis of oleoylethanolamide using lipase

An effective process for the enzymatic synthesis of oleoylethanolamide is described in this study. The process included purification of a commercial oleic acid product and then optimization of the reaction between the purified oleic acid and ethanolamine in the presence of hexane and a lipase. Under the optimal amidation reaction conditions identified, oleoylethanolamide was obtained with 96.6% purity. The synthesis was also conducted on a large scale (50 mmol of each of the reactants), and oleoylethanolamide purity and yield after crystallization purification were 96.1 and 73.5%, respectively. Compared to the previous studies, the current method of preparing high-purity oleoylethanolamide is more effective and economically feasible. The scalability and ease for such synthesis make it possible to study the biological and nutritional functions of the cannabinoid-like oleoylethanolamide in animal or human subjects.

Lipid transport function is the main target of oral oleoylethanolamide to reduce adiposity in high-fat-fed mice

We evaluated the biological basis of reduced fat gain by oleoylethanolamide (OEA) in high-fat-fed mice and sought to determine how degradation of OEA affected its efficiency by comparing its effects to those of KDS-5104, a nonhydrolyzable lipid OEA analog. Mice were given OEA or KDS-5104 by the oral route (100 mg/kg body weight). Sixty-eight variables per mouse, describing six biological processes (lipid transport, lipogenesis, energy intake, energy expenditure, endocannabinoid signaling, and glucose metabolism), spanning gene expression of biochemical and physiological parameters were examined to determine the primary target whereby OEA reduces fat gain. Although KDS-5104 but not OEA was resistant to fatty acid amide hydrolase hydrolysis, OEA was degraded by an unidentified hydrolysis system in the liver. Nevertheless, both compounds equally decreased body fat pads after 5 weeks (20%; P < 0.05). The six biological functions constructed from the 68 initial variables predicted up to 58% of adipose fat variations. Lipid transport appeared central to the explanation for body fat deposition (16%; P < 0.0001), in which decreased expression of the FAT/CD36 gene was the component most related to adipose depots. Lipid transport appears to be a determinant player in the OEA fat-lowering response, with adipose tissue FAT/CD36 expression being the most relevant bioindicator of OEA action.

Blockade of nicotine reward and reinstatement by activation of alpha-type peroxisome proliferator-activated receptors

BACKGROUND

Recent findings indicate that inhibitors of fatty acid amide hydrolase (FAAH) counteract the rewarding effects of nicotine in rats. Inhibition of FAAH increases levels of several endogenous substances in the brain, including the endocannabinoid anandamide and the noncannabinoid fatty acid ethanolamides oleoylethanolamide (OEA) and palmitoylethanolamide, which are ligands for alpha-type peroxisome proliferator-activated nuclear receptors (PPAR-α). Here, we evaluated whether directly acting PPAR-α agonists can modulate reward-related effects of nicotine.

METHODS

We combined behavioral, neurochemical, and electrophysiological approaches to evaluate effects of the PPAR-α agonists [[4-Chloro-6-[(2,3-dimethylphenyl)amino]-2-pyrimidinyl]thio]acetic acid (WY14643) and methyl oleoylethanolamide (methOEA; a long-lasting form of OEA) on 1) nicotine self-administration in rats and squirrel monkeys; 2) reinstatement of nicotine-seeking behavior in rats and monkeys; 3) nicotine discrimination in rats; 4) nicotine-induced electrophysiological activity of ventral tegmental area dopamine neurons in anesthetized rats; and 5) nicotine-induced elevation of dopamine levels in the nucleus accumbens shell of freely moving rats.

RESULTS

The PPAR-α agonists dose-dependently decreased nicotine self-administration and nicotine-induced reinstatement in rats and monkeys but did not alter food- or cocaine-reinforced operant behavior or the interoceptive effects of nicotine. The PPAR-α agonists also dose-dependently decreased nicotine-induced excitation of dopamine neurons in the ventral tegmental area and nicotine-induced elevations of dopamine levels in the nucleus accumbens shell of rats. The ability of WY14643 and methOEA to counteract the behavioral, electrophysiological, and neurochemical effects of nicotine was reversed by the PPAR-α antagonist 1-[(4-Chlorophenyl)methyl]-3-[(1,1-dimethylethyl)thio]-a,a-dimethyl-5-(1-methylethyl)-1H-Indole-2-propanoic acid (MK886).

CONCLUSIONS

These findings indicate that PPAR-α might provide a valuable new target for antismoking medications.

N-acylethanolamine metabolism with special reference to N-acylethanolamine-hydrolyzing acid amidase (NAAA)

N-acylethanolamines (NAEs) constitute a class of bioactive lipid molecules present in animal and plant tissues. Among the NAEs, N-arachidonoylethanolamine (anandamide), N-palmitoylethanolamine, and N-oleoylethanolamine attract much attention due to cannabimimetic activity as an endocannabinoid, anti-inflammatory and analgesic activities, and anorexic activity, respectively. In mammalian tissues, NAEs are formed from glycerophospholipids through the phosphodiesterase-transacylation pathway consisting of Ca(2+)-dependent N-acyltransferase and N-acylphosphatidylethanolamine-hydrolyzing phospholipase D. Recent studies revealed the presence of alternative pathways and enzymes responsible for the NAE formation. As for the degradation of NAEs, fatty acid amide hydrolase (FAAH), which hydrolyzes NAEs to fatty acids and ethanolamine, plays a central role. However, a lysosomal enzyme referred to as NAE-hydrolyzing acid amidase (NAAA) also catalyzes the same reaction and may be a new target for the development of therapeutic drugs. In this article we discuss recent progress in the studies on the enzymes involved in the biosynthesis and degradation of NAEs with special reference to NAAA.