Role of oleoylethanolamide as a feeding regulator in goldfish

Dietary oleic acid contributes to the regulation of food intake through the synthesis of intestinal oleoylethanolamide

INTRODUCTION

Among the fatty acid ethanolamides (FAEs), oleoylethanolamide (OEA), linoleoylethanolamide (LEA), and palmitoylethanolamide (PEA) are reported to be involved in feeding regulation. In particular, OEA is well characterized as a satiety signal. Following food consumption, OEA is synthesized from oleic acid (OA) via an N-acyl phosphatidylethanolamine-specific phospholipase D-dependent pathway in the gastroenterocytes, and OEA induces satiety by recruiting sensory fibers. Thus, we hypothesized that dietary OA is an important satiety-inducing molecule. However, there has been no direct demonstration of the effect of dietary OA on satiety induction without the influence of the endogenous biosynthesis of OA from stearic acid (SA) or other FAEs.

METHODS

In this study, we used two experimental diets to test our hypothesis: (i) an OA diet (OAD; 38.4 mg of OA/g and 7.2 mg of SA/g) and (ii) a low OA diet (LOAD; 3.1 mg of OA/g and 42.4 mg of SA/g).

RESULTS

Relative to mice fed the OAD, mice fed the LOAD for two weeks exhibited reduced levels of jejunal OEA but not jejunal LEA and PEA. The LOAD-fed mice showed an increase in food intake and body weight gain. Moreover, LOAD-induced increase in food intake was immediately observed after the switch from the OAD, whereas these effects were diminished by the switch back to the OAD. Furthermore, treatment with OA and OEA diminished the effects of LOAD on food intake.

CONCLUSION

Collectively, these results show that dietary OA is a key factor in the reduction of food intake and increase in satiety mediated by OEA signaling.

Cannabinoids modulate food preference and consumption in Drosophila melanogaster

Cannabinoids have an important role in regulating feeding behaviors via cannabinoid receptors in mammals. Cannabinoids also exhibit potential therapeutic functions in Drosophila melanogaster, or fruit fly that lacks cannabinoid receptors. However, it remains unclear whether cannabinoids affect food consumption and metabolism in a cannabinoid receptors-independent manner in flies. In this study, we systematically investigated pharmacological functions of various cannabinoids in modulating food preference and consumption in flies. We show that flies display preferences for consuming cannabinoids, independent of two important sensory regulators Poxn and Orco. Interestingly, phyto- and endo- cannabinoids exhibit an inhibitory effect on food intake. Unexpectedly, the non-selective CB1 receptor antagonist AM251 attenuates the suppression of food intake by endocannabinoids. Moreover, the endocannabinoid anandamide (AEA) and its metabolite inhibit food intake and promote resistance to starvation, possibly through reduced lipid metabolism. Thus, this study has provided insights into a pharmacological role of cannabinoids in feeding behaviors using an adult Drosophila model.

Feeding regulation by oleoylethanolamide synthesized from dietary oleic acid

Oleoylethanolamide (OEA), a well-known satiety factor, is produced during feeding in the proximal intestine. Enterocytes sense oleic acid in dietary fat via CD36 and convert it to OEA through NAPE-PLD dependent or independent pathways. The satiety function of OEA is known to involve peroxisome proliferator-activated receptor type-α (PPAR-α). OEA stimulates afferent sensory fibers (possibly those of the vagus nerve) and provoke the recruitment of feeding-controlling circuits in the brain that use oxytocin and histamine as neurotransmitters for regulating satiety. Dysfunction of OEA synthesis by high-fat feeding might contribute to increased weight and obesity. Here, we describe the roles played by OEA in the regulation of energy metabolism and food intake by introducing our preliminary data regarding this lipid mediator, and we briefly outline the biosynthesis and deactivation of OEA.

First evidence on the role of palmitoylethanolamide in energy homeostasis in fish

The objective of this study was to investigate the role of palmitoylethanolamide (PEA) in the regulation of energy homeostasis in goldfish (Carassius auratus). We examined the effects of acute or chronic intraperitoneal treatment with PEA (20 μg·g^-1 body weight) on parameters related to food intake and its regulatory mechanisms, locomotor activity, glucose and lipid metabolism, and the possible involvement of transcription factors and clock genes on metabolic changes in the liver. Acute PEA treatment induced a decrease in food intake at 6 and 8 h post-injection, comparable to that observed in mammals. This PEA anorectic effect in goldfish could be mediated through interactions with leptin and NPY, as PEA increased hepatic expression of leptin aI and reduced hypothalamic expression of npy. The PEA chronic treatment reduced weight gain, growth rate, and locomotor activity. The rise in glycolytic potential together with the increased potential of glucose to be transported into liver suggests an enhanced use of glucose in the liver after PEA treatment. In addition, part of glucose may be exported to be used in other tissues. The activity of fatty acid synthase (FAS) increased after chronic PEA treatment, suggesting an increase in the hepatic lipogenic capacity, in contrast with the mammalian model. Such lipogenic increment could be linked with the PEA-induction of REV-ERBα and BMAL1 found after the chronic treatment. As a whole, the present study shows the actions of PEA in several compartments related to energy homeostasis and feeding behavior, supporting a regulatory role for this N-acylethanolamine in fish.

The effects of oleoylethanolamide, an endogenous PPAR-α agonist, on risk factors for NAFLD: A systematic review

Non-alcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease. Recently, some novel compounds have been investigated for the prevention and treatment of NAFLD. Oleoylethanolamide (OEA), an endogenous PPAR-α agonist, has exhibited a plethora of pharmacological properties for the treatment of obesity and other obesity-associated metabolic complications. This systematic review was performed with a focus on the effects of OEA on the risk factors for NAFLD. PubMed, Scopus, Embase, ProQuest, and Google Scholar databases were searched up to December 2018 using relevant keywords. All articles written in English evaluating the effects of OEA on the risk factors for NAFLD were eligible for the review. The evidence reviewed in this article illustrates that OEA regulates multiple biological processes associated with NAFLD, including lipid metabolism, inflammation, oxidative stress, and energy homeostasis through different mechanisms. In summary, many beneficial effects of OEA have led to the understanding that OEA may be an effective therapeutic strategy for the management of NAFLD. Although a wide range of studies have demonstrated the most useful effects of OEA on NAFLD and the associated risk factors, further clinical trials, from both in vivo studies and in vitro experiments, are warranted to verify these outcomes.

Diurnal Profiles of N-Acylethanolamines in Goldfish Brain and Gastrointestinal Tract: Possible Role of Feeding

N-acylethanolamines (NAEs) are a family of endogenous lipid signaling molecules that are involved in regulation of energy homeostasis in vertebrates with a putative role on circadian system. The aim of this work was to study the existence of daily fluctuations in components of NAEs system and their possible dependence on food intake. Specifically, we analyzed the content of oleoylethanolamide (OEA), palmitoylethanolamide (PEA), stearoylethanolamide (SEA), their precursors (NAPEs), as well as the expression of nape-pld (NAEs synthesis enzyme), faah (NAEs degradation enzyme), and pparα (NAEs receptor) in gastrointestinal and brain tissues of goldfish (Carassius auratus) throughout a 24-h cycle. Daily profiles of bmal1a and rev-erbα expression in gastrointestinal tissues were also quantified because these clock genes are also involved in lipid metabolism, are PPAR-targets in mammals, and could be a link between NAEs and circadian system in fish. Gastrointestinal levels of NAEs exhibited daily fluctuations, with a pronounced and rapid postprandial increase, the increment being likely caused by food intake as it is not present in fasted animals. Such periprandial differences were not found in brain, supporting that NAEs mobilization occurs in a tissue-specific manner and suggesting that these three NAEs could be acting as peripheral satiety signals. The abundance of pparα mRNA displayed a daily rhythm in the intestine and the liver, suggesting a possible rhythmicity in the NAEs functionality. The increment of pparα expression during the rest phase can be related with its role stimulating lipid catabolism to obtain energy during the fasting state of the animals. In addition, the clock genes bmal1a and rev-erbα also showed daily rhythms, with a bmal1a increment after feeding, supporting its role as a lipogenic factor. In summary, our data show the existence of all components of NAEs system in fish (OEA, PEA, SEA, precursors, synthesis and degradation enzymes, and the receptor PPARα), supporting the involvement of NAEs as peripheral satiety signals.

Administration of N-Acyl-Phosphatidylethanolamine Expressing Bacteria to Low Density Lipoprotein Receptor-/- Mice Improves Indices of Cardiometabolic Disease

Obesity increases the risk for cardiometabolic diseases. N-acyl phosphatidylethanolamines (NAPEs) are precursors of N-acylethanolamides, which are endogenous lipid satiety factors. Incorporating engineered bacteria expressing NAPEs into the gut microbiota retards development of diet induced obesity in wild-type mice. Because NAPEs can also exert anti-inflammatory effects, we hypothesized that administering NAPE-expressing bacteria to low-density lipoprotein receptor (Ldlr)^-/- mice fed a Western diet would improve various indices of cardiometabolic disease manifested by these mice. NAPE-expressing E. coli Nissle 1917 (pNAPE-EcN), control Nissle 1917 (pEcN), or vehicle (veh) were given via drinking water to Ldlr^-/- mice for 12 weeks. Compared to pEcN or veh treatment, pNAPE-EcN significantly reduced body weight and adiposity, hepatic triglycerides, fatty acid synthesis genes, and increased expression of fatty acid oxidation genes. pNAPE-EcN also significantly reduced markers for hepatic inflammation and early signs of fibrotic development. Serum cholesterol was reduced with pNAPE-EcN, but atherosclerotic lesion size showed only a non-significant trend for reduction. However, pNAPE-EcN treatment reduced lesion necrosis by 69% indicating an effect on preventing macrophage inflammatory death. Our results suggest that incorporation of NAPE expressing bacteria into the gut microbiota can potentially serve as an adjuvant therapy to retard development of cardiometabolic disease.

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.

Central regulation of food intake in fish: an evolutionary perspective

Evidence indicates that central regulation of food intake is well conserved along the vertebrate lineage, at least between teleost fish and mammals. However, several differences arise in the comparison between both groups. In this review, we describe similarities and differences between teleost fish and mammals on an evolutionary perspective. We focussed on the existing knowledge of specific fish features conditioning food intake, anatomical homologies and analogies between both groups as well as the main signalling pathways of neuroendocrine and metabolic nature involved in the homeostatic and hedonic central regulation of food intake.

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.

Dissecting the Physiology and Pathophysiology of Glucagon-Like Peptide-1

An aging world population exposed to a sedentary life style is currently plagued by chronic metabolic diseases, such as type-2 diabetes, that are spreading worldwide at an unprecedented rate. One of the most promising pharmacological approaches for the management of type 2 diabetes takes advantage of the peptide hormone glucagon-like peptide-1 (GLP-1) under the form of protease resistant mimetics, and DPP-IV inhibitors. Despite the improved quality of life, long-term treatments with these new classes of drugs are riddled with serious and life-threatening side-effects, with no overall cure of the disease. New evidence is shedding more light over the complex physiology of GLP-1 in health and metabolic diseases. Herein, we discuss the most recent advancements in the biology of gut receptors known to induce the secretion of GLP-1, to bridge the multiple gaps into our understanding of its physiology and pathology.

Oleic acid-derived oleoylethanolamide: A nutritional science perspective

The fatty acid ethanolamide oleoylethanolamide (OEA) is an endogenous lipid mediator derived from the monounsaturated fatty acid, oleic acid. OEA is synthesized from membrane glycerophospholipids and is a high-affinity agonist of the nuclear transcription factor peroxisome proliferator-activated receptor α (PPAR-α). Dietary intake of oleic acid elevates circulating levels of OEA in humans by increasing substrate availability for OEA biosynthesis. Numerous clinical studies demonstrate a beneficial relationship between high-oleic acid diets and body composition, with emerging evidence to suggest OEA may mediate this response through modulation of lipid metabolism and energy intake. OEA exposure has been shown to stimulate fatty acid uptake, lipolysis, and β-oxidation, and also promote food intake control. Future research on high-oleic acid diets and body composition is warranted to confirm these outcomes and elucidate the underlying mechanisms by which oleic acid exerts its biological effects. These findings have significant practical implications, as the oleic acid-derived OEA molecule may be a promising therapeutic agent for weight management and obesity treatment.

Stimulatory effect of the secretogranin-ll derived peptide secretoneurin on food intake and locomotion in female goldfish (Carassius auratus)

Secretoneurin (SN) is a conserved peptide derived by proteolytic processing from the middle domain of the ∼600 amino acid precursor secretogranin-II (SgII). Secretoneurin is widely distributed in secretory granules of endocrine cells and neurons and has important roles in reproduction as it stimulates luteinizing hormone release from the pituitary. A potential new role of SN in goldfish feeding is the subject of this study. Firstly, we established that acute (26 h; p<0.0001) and short-term (72 h; p=0.016) fasting increased SgIIa precursor mRNA levels 1.25-fold in the telencephalon, implicating SN in the control of feeding. Secondly, we determined that intracerebroventricular injections of the type A SN (SNa; 0.2 and 1 ng/g BW) increased food intake and locomotor behavior by 60 min. Fish injected with the lower and higher doses of SNa (0.2 and 1 ng/g) respectively exhibited significant 1.77- and 2.58-fold higher food intake (p<0.0001) than the saline-injected control fish. Locomotor behavior was increased by 1.35- and 2.26-fold for 0.2 ng/g SNa (p=0.0001) and 1 ng/g SNa (p<0.0001), respectively. Injection of 1 ng/g SNa increased mRNA levels of hypothalamic neuropeptide Y 1.36-fold (p=0.038) and decreased hypothalamic cocaine-and amphetamine-regulated transcript by 33% (p=0.01) at 2h and 5h post-injection, respectively. These data suggest interactions of SNa with stimulatory and inhibitory pathways of food intake control in fish.

Dietary fatty acid composition affects food intake and gut-brain satiety signaling in Senegalese sole (Solea senegalensis, Kaup 1858) larvae and post-larvae

Little is known how dietary lipids affect food intake during larval development of fish, especially with regard to fatty acid (FA) composition. In fact, very little work has been done on appetite regulation and food intake in fish larvae in general, due to biological and technical difficulties associated with this type of studies. A new method using fluorescent microspheres as markers was developed in this study to evaluate food intake and prey selectivity of Senegalese sole larvae and post-larvae. Food intake was quantified in fish fed Artemia metanauplii enriched with oils differing in FA profile: cod liver oil (CLO), linseed oil (LSO), soybean oil (SBO) or olive oil (OO). The fish did not preferentially ingest a specific diet when presented with a choice. However, pre-metamorphic larvae from the CLO treatment ingested more metanauplii per g body weight, while differences in post-larvae were not significant. These findings were developed further by analyzing mRNA levels of a range of putative anorexigenic (pyya, pyyb, glp1, cckl, cart1a, cart1b, cart2a, cart4, pomca, pomcb, crf) and orexigenic (gal, npy, agrp2) genes, to identify those which are significantly affected by feeding and/or dietary FA composition. The variety of expression patterns observed highlighted the complexity of appetite regulatory mechanisms. In general, fish fed the CLO diet tended to show gene expression patterns most dissimilar to the remaining treatments. Expression in pre-metamorphic larvae was generally less in accordance with the putative function of the genes than in post-larvae, which could suggest a yet underdeveloped regulatory system.

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.