Gastrointestinal regulation of food intake: general aspects and focus on anandamide and oleoylethanolamide

Aged microbiota exacerbates cardiac failure by PPARα/PGC1α pathway

The dysbiosis of gut microbiota with aging has been extensively studied, revealing its substantial contribution to variety of diseases. However, the impact of aged microbiota in heart failure (HF) remains unclear. In this study, we employed the method of fecal microbiota transplantation (FMT) from aged donors to investigate its role in the context of HF. Our results demonstrate that FMT from aged donors alters the recipient's gut microbiota composition and abundance. Furthermore, FMT impairs cardiac function and physical activity in HF mice. Aged FMT induces metabolic alterations, leading to body weight gain, impaired glucose tolerance, increased respiratory exchange ratio (RER), and enhanced fat accumulation. The epicardium of aged FMT recipients shows fat accumulation, accompanied by cardiomyocyte hypertrophy, cardiac fibrosis and increased cellular apoptosis. Mechanistically, aged FMT suppresses the PPARα/PGC1α signaling pathway in HF. Notably, activation of PPARα effectively rescues the metabolic changes and myocardial injury caused by aged FMT. In conclusion, our study emphasizes the role of the PPARα/PGC1α signaling pathway in aged FMT-mediated HF.

Natural products targeting inflammation-related metabolic disorders: A comprehensive review

Currently, the incidence of metabolic disorders is increasing, setting a challenge to global health. With major advancement in the diagnostic tools and clinical procedures, much has been known in the etiology of metabolic disorders and their corresponding pathophysiologies. In addition, the use of in vitro and in vivo experimental models prior to clinical studies has promoted numerous biomedical breakthroughs, including in the discovery and development of drug candidates to treat metabolic disorders. Indeed, chemicals isolated from natural products have been extensively studied as prospective drug candidates to manage diabetes, obesity, heart-related diseases, and cancer, partly due to their antioxidant and anti-inflammatory properties. Continuous efforts have been made in parallel to improve their bioactivity and bioavailability using selected drug delivery approaches. Here, we provide insights on recent progress in the role of inflammatory-mediated responses on the initiation of metabolic disorders, with particular reference to diabetes mellitus, obesity, heart-related diseases, and cancer. In addition, we discussed the prospective role of natural products in the management of diabetes, obesity, heart-related diseases, and cancers and provide lists of potential biological targets for high throughput screening in drug discovery and development. Lastly, we discussed findings observed in the preclinical and clinical studies prior to identifying suitable approaches on the phytochemical drug delivery systems that are potential to be used in the treatment of metabolic disorders.

Intuitive eating is associated with elevated levels of circulating omega-3-polyunsaturated fatty acid-derived endocannabinoidome mediators

The regulation of food intake and eating behaviours involves interactions between different systems. The endocannabinoidome, comprising several fatty acid-derived mediators, plays a central role in the regulation of food intake. Alterations of this system have been suggested to intervene in the aetiology of eating disorders. This study aimed to examine the associations between non-pathological eating behaviours and circulating endocannabinoidome mediators in a heterogeneous human population. Plasma 2-monoacyl-glycerol and N-acyl-ethanolamine congeners were measured by LC-MS/MS in a sample of 190 men and women. Eating behaviours were assessed using the Three-Factor Eating Questionnaire (TFEQ) and the Intuitive Eating Scale-2 (IES-2). Following adjustment for body mass index and age, plasma levels of omega-3 polyunsaturated fatty acid-derived 2-monoacyl-glycerols, 2-eicosapentaenoyl-glycerol (2-EPG) and 2-docosapentaenoyl-glycerol (2-DPG), were associated with higher intuitive eating scores (0.15 ≤ rho ≤ 0.20; p < 0.05). These associations were independent of the dietary intake of the fatty acid precursors of these 2-monoacyl-glycerols. However, almost no association was found between plasma levels of N-acyl-ethanolamine congeners and the TFEQ or the IES-2 scores. The results of the present study suggest the association of 2-monoacyl-glycerols, especially 2-EPG and 2-DPG, in the regulation of intuitive eating and the potential implication therein of bioactive lipids.

Biphasic effects of methanandamide on murine gastric vagal afferent mechanosensitivity

KEY POINTS

The fine control of food intake is important for the maintenance of a healthy metabolic state. Gastric vagal afferents (GVAs) are involved in the peripheral regulation of food intake via signalling the degree of distension of the stomach which ultimately leads to feelings of fullness and satiety. This study provides evidence that endocannabinoids such as anandamide are capable of regulating GVA sensitivity in a concentration-dependent biphasic manner. This biphasic effect is dependent upon interactions between the CB1, TRPV1 and GHSR receptors. These data have important implications for the peripheral control of food intake.

ABSTRACT

Gastric vagal afferents (GVAs) signal to the hindbrain resulting in satiety. Endocannabinoids are endogenous ligands of cannabinoid 1 receptor (CB1) and transient receptor potential vanilloid-1 (TRPV1) channels. The endocannabinoid anandamide (AEA) is expressed in the stomach, and its receptor CB1 is expressed in ghrelin-positive gastric mucosal cells. Further, TRPV1, CB1 and growth hormone secretagogue receptor (ghrelin receptor, GHSR) are expressed in subpopulations of GVA neurons. This study aimed to determine the interaction between TRPV1, CB1, GHSR and endocannabinoids in the modulation of GVA signalling. An in vitro electrophysiology preparation was used to assess GVA mechanosensitivity in male C57BL/6 mice. Effects of methanandamide (mAEA; 1-100 nm), on GVA responses to stretch were determined in the absence and presence of antagonists of CB1, TRPV1, GHSR, protein kinase-A (PKA), protein kinase-C (PKC) and G-protein subunits Gα_i/o , or Gα_q . Low doses (1-10 nm) of mAEA reduced GVA responses to 3 g stretch, whereas high doses (30-100 nm) increased the response. The inhibitory and excitatory effects of mAEA (1-100 nm) were reduced/lost in the presence of a CB1 and TRPV1 antagonist. PKA, Gα_i/o or GHSR antagonists prevented the inhibitory effect of mAEA on GVA mechanosensitivity. Conversely, in the presence of a PKC or Gα_q antagonist the excitatory effect of mAEA was reduced or lost, respectively. Activation of CB1, by mAEA, can activate or inhibit TRPV1 to increase or decrease GVA responses to stretch, depending on the pathway activated. These interactions could play an important role in the fine control of food intake.

Varied doses and chemical forms of selenium supplementation differentially affect mouse intestinal physiology

Varied doses and chemical forms of selenium supplementation differentially affect mouse intestinal physiology and perturbed the fecal metabolic profiles of and jejunal protein expression in mice.

Cannabinoid receptor type-1 partially mediates metabolic endotoxemia-induced inflammation and insulin resistance

Circulating levels of bacterial lipopolysaccharide (LPS) or endotoxin are chronically elevated in obesity (metabolic endotoxemia), resulting in low-grade inflammation. Metabolic endotoxemia has been identified as a triggering factor for obesity-associated metabolic complications such as insulin resistance. Furthermore, LPS has been shown to modulate endocannabinoid synthesis and notably to induce cannabinoid receptor type-1 (CB1) ligand synthesis. CB1 activation promotes inflammation, increases food intake and impairs insulin signaling. Therefore, we hypothesized that LPS acts through a CB1-dependent mechanism to aggravate inflammation and promote insulin resistance. Male Wistar rats fed a chow diet were implanted with mini-osmotic pumps delivering a low dose of LPS (n = 20; 12.5 μg/kg body weight (BW)/hr.) or saline (n = 10) continuously for six weeks. LPS-treated rats were injected daily with a CB1 antagonist (Rimonabant, SR141716A; 3 mg/kg, intraperitoneal (ip); LPS + CB1x; n = 10) or vehicle (1 mL/kg, LPS; n = 10). Control and LPS rats' food intake was matched to the LPS + CB1x group level. Despite no significant differences in body weight among groups, chronic exposure to low-level LPS altered hepatic endocannabinoid signaling, increased inflammation, and impaired insulin sensitivity and insulin clearance (P < 0.05). CB1 inhibition significantly attenuated LPS signaling (P < 0.05), which attenuated LPS-induced metabolic alterations. Therefore, we concluded that CB1 contributes to LPS-mediated inflammation and insulin resistance, suggesting that blocking CB1 signaling may have therapeutic benefits in reducing inflammation-induced metabolic abnormalities.

Effects of 6 vs 3 eucaloric meal patterns on glycaemic control and satiety in people with impaired glucose tolerance or overt type 2 diabetes: A randomized trial

BACKGROUND/OBJECTIVES

The study aimed to compare the effects of two eucaloric meal patterns (3 vs 6 meals/day) on glycaemic control and satiety in subjects with impaired glucose tolerance and plasma glucose (PG) levels 140-199mg/dL at 120min (IGT-A) or PG levels 140-199mg/dL at 120min and >200mg/dL at 30/60/90min post-oral glucose load on 75-g OGTT (IGT-B), or overt treatment-naïve type 2 diabetes (T2D).

SUBJECTS/METHODS

In this randomized crossover study, subjects with IGT-A (n=15, BMI: 32.4±5.2kg/m²), IGT-B (n=20, BMI: 32.5±5kg/m²) or T2D (n=12, BMI: 32.2±5.2kg/m²) followed a weight-maintenance diet (45% carbohydrates, 20% proteins, 35% fats) in 3 or 6 meals/day (each intervention lasting 12 weeks). Anthropometrics, diet compliance and subjective appetite were assessed every 2 weeks. OGTT and measurements of HbA1c and plasma lipids were performed at the beginning and end of each intervention period.

RESULTS

Body weight and physical activity levels remained stable throughout the study. In T2D, HbA1c and PG at 120min post-OGTT decreased with 6 vs 3 meals (P<0.001 vs P=0.02, respectively). The 6-meal intervention also improved post-OGTT hyperinsulinaemia in IGT-A subjects and hyperglycaemia in IGT-B subjects. In all three groups, subjective hunger and desire to eat were reduced with 6 vs 3 meals/day (P<0.05). There were no differences in HOMA-IR or plasma lipids between interventions.

CONCLUSION

Although weight loss remains the key strategy in hyperglycaemia management, dietary measures such as more frequent and smaller meals may be helpful for those not sufficiently motivated to adhere to calorie-restricted diets. Our study shows that 6 vs 3 meals a day can increase glycaemic control in obese patients with early-stage T2D, and may perhaps improve and/or stabilize postprandial glucose regulation in prediabetes subjects.

Relationship Between Circulating Fatty Acids and Fatty Acid Ethanolamide Levels After a Single 2-h Dietary Fat Feeding in Male Sprague-Dawley Rats : Elevated levels of oleoylethanolamide, palmitoylethanolamide, linoleoylethanolamide, arachidonoylethanolamide and docosahexanoylethanolamide after a single 2 h dietary fat feeding in male Sprague Dawley rats

Previous studies show that long term variations in dietary fat consumption impact circulating fatty acid ethanolamide (FAE) concentrations, however, few studies have investigated short term effects of dietary fat feeding on FAE levels. The trial's objective was to explore the effect of acute feeding of varying amounts of dietary n-9 and n-3 fatty acids on plasma and organ levels of FAE. Sixty-four rats were assigned to four groups fed meals containing 40% of energy as either safflower oil (control), canola oil (CO), or DHA rich oil (DRO), each consumed as a bolus within a 2-h window. Plasma and tissue FAE levels were measured at 3, 6, 12 and 24 h following the bolus. FAE profiles over time exhibited patterns that were specific both to FAE and to dietary fat type provided. At 3 h, plasma and liver OEA levels were higher (p < 0.05) in the 95% CO:5% DRO compared with other groups. At 12 h, plasma PEA levels were lower (p < 0.05) in the 50% CO:50% DRO group compared to the 95% CO group. Plasma DEA levels showed an increase (p < 0.05) only after 24 h of feeding. All four dietary groups manifested increased DEA levels in a dose-dependent manner. Data demonstrate that a single meal feeding of diets with different ratios of fat types impacts tissue levels of FAE within a short time frame, which could further influence the physiological roles of FAE on appetite regulation and energy expenditure.

The Role of the Autonomic Nervous System in the Pathophysiology of Obesity

Obesity is reaching epidemic proportions globally and represents a major cause of comorbidities, mostly related to cardiovascular disease. The autonomic nervous system (ANS) dysfunction has a two-way relationship with obesity. Indeed, alterations of the ANS might be involved in the pathogenesis of obesity, acting on different pathways. On the other hand, the excess weight induces ANS dysfunction, which may be involved in the haemodynamic and metabolic alterations that increase the cardiovascular risk of obese individuals, i.e., hypertension, insulin resistance and dyslipidemia. This article will review current evidence about the role of the ANS in short-term and long-term regulation of energy homeostasis. Furthermore, an increased sympathetic activity has been demonstrated in obese patients, particularly in the muscle vasculature and in the kidneys, possibily contributing to increased cardiovascular risk. Selective leptin resistance, obstructive sleep apnea syndrome, hyperinsulinemia and low ghrelin levels are possible mechanisms underlying sympathetic activation in obesity. Weight loss is able to reverse metabolic and autonomic alterations associated with obesity. Given the crucial role of autonomic dysfunction in the pathophysiology of obesity and its cardiovascular complications, vagal nerve modulation and sympathetic inhibition may serve as therapeutic targets in this condition.

The role of alginates in regulation of food intake and glycemia: a gastroenterological perspective

Regulation of food intake through modulation of gastrointestinal responses to ingested foods is an ever-growing component of the therapeutic approaches targeting the obesity epidemic. Alginates, viscous and gel-forming soluble fibers isolated from the cell wall of brown seaweeds and some bacteria, are recently receiving considerable attention because of their potential role in satiation, satiety, and food intake regulation in the short term. Enhancement of gastric distension, delay of gastric emptying, and attenuation of postprandial glucose responses may constitute the basis of their physiological benefits. Offering physical, chemical, sensorial, and physiological advantages over other viscous and gel-forming fibers, alginates constitute promising functional food ingredients for the food industry. Therefore, the current review explores the role of alginates in food intake and glycemic regulation, their underlying modes of action and their potential in food applications.

Effect of meal frequency on glucose and insulin levels in women with polycystic ovary syndrome: a randomised trial

BACKGROUND/OBJECTIVES

The aim of the study was to compare the effect of two-meal patterns (three vs six meals per day) on glucose and insulin levels in women with polycystic ovary syndrome (PCOS).

SUBJECTS/METHODS

In a randomised, crossover, 24-week study, 40 women with PCOS, aged 27±6 years, body mass index 27±6 kg/m(2), followed a weight maintenance diet (% carbohydrates:protein:fat, 40:25:35), consumed either as a three- or a six-meal pattern, with each intervention lasting for 12 weeks. Anthropometric measurements, diet compliance and subjective hunger, satiety and desire to eat were assessed biweekly. All women underwent an oral glucose tolerance test (OGTT) with 75 g glucose for measurement of plasma glucose and insulin at the beginning and end of each intervention. HaemoglobinA1c (HbA1c), blood lipids and hepatic enzymes were measured at the beginning and end of each intervention.

RESULTS

Body weight remained stable throughout the study. Six meals decreased significantly fasting insulin (P=0.014) and post-OGTT insulin sensitivity (Matsuda index, P=0.039) vs three meals. After incorporation of individual changes over time, with adjustment for potential confounders, the only variable that remained significant was the Matsuda index, which was then used in multivariate analysis and general linear models. Six meals improved post-OGTT insulin sensitivity independently of age and body weight vs three meals (P=0.012). No significant differences were found between six and three meals for glucose, HbA1c, blood lipids, hepatic enzymes, subjective desire to eat and satiety.

CONCLUSIONS

Six meals had a more favourable effect on post-OGTT insulin sensitivity in women with PCOS compared with isocaloric three meals.

Pathophysiology of anorexia in the cancer cachexia syndrome

Anorexia is commonly present in persons with cancer and a major component of cancer cachexia. There are multiple causes of anorexia in cancer. Peripherally, these can be due to (i) substances released from or by the tumour, e.g. pro-inflammatory cytokines, lactate, and parathormone-related peptide; (ii) tumours causing dysphagia or altering gut function; (iii) tumours altering nutrients, e.g. zinc deficiency; (iv) tumours causing hypoxia; (v) increased peripheral tryptophan leading to increased central serotonin; or (vi) alterations of release of peripheral hormones that alter feeding, e.g. peptide tyrosine tyrosine and ghrelin. Central effects include depression and pain, decreasing the desire to eat. Within the central nervous system, tumours create multiple alterations in neurotransmitters, neuropeptides, and prostaglandins that modulate feeding. Many of these neurotransmitters appear to produce their anorectic effects through the adenosine monophosphate kinase/methylmalonyl coenzyme A/fatty acid system in the hypothalamus. Dynamin is a guanosine triphosphatase that is responsible for internalization of melanocortin 4 receptors and prostaglandin receptors. Dynamin is up-regulated in a mouse model of cancer anorexia. A number of drugs, e.g. megestrol acetate, cannabinoids, and ghrelin agonists, have been shown to have some ability to be orexigenic in cancer patients.

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.

Acute activation of cannabinoid receptors by anandamide reduces gastrointestinal motility and improves postprandial glycemia in mice

The endocannabinoid system (ECS) is associated with an alteration of glucose homeostasis dependent on cannabinoid receptor-1 (CB1R) activation. However, very little information is available concerning the consequences of ECS activation on intestinal glucose absorption. Mice were injected intraperitoneally with anandamide, an endocannabinoid binding both CB1R and CB2R. We measured plasma glucose and xylose appearance after oral loading, gastrointestinal motility, and glucose transepithelial transport using the everted sac method. Anandamide improved hyperglycemia after oral glucose charge whereas glucose clearance and insulin sensitivity were impaired, pointing out some gastrointestinal events. Plasma xylose appearance was delayed in association with a strong decrease in gastrointestinal transit, while anandamide did not alter transporter-mediated glucose absorption. Interestingly, transit was nearly normalized by coinjection of SR141716 and AM630 (CB1R and CB2R antagonist, respectively), and AM630 also reduced the delay of plasma glucose appearance induced by anandamide. When gastric emptying was bypassed by direct glucose administration in the duodenum, anandamide still reduced plasma glucose appearance in wild-type but not in CB1R(-/-) mice. In conclusion, our findings demonstrated that acute activation of intestinal ECS reduced postprandial glycemia independently on intestinal glucose transport but rather inhibiting gastric emptying and small intestine motility and strongly suggest the involvement of both CB1R and CB2R.

Distinct signatures of host-microbial meta-metabolome and gut microbiome in two C57BL/6 strains under high-fat diet

A combinatory approach using metabolomics and gut microbiome analysis techniques was performed to unravel the nature and specificity of metabolic profiles related to gut ecology in obesity. This study focused on gut and liver metabolomics of two different mouse strains, the C57BL/6J (C57J) and the C57BL/6N (C57N) fed with high-fat diet (HFD) for 3 weeks, causing diet-induced obesity in C57N, but not in C57J mice. Furthermore, a 16S-ribosomal RNA comparative sequence analysis using 454 pyrosequencing detected significant differences between the microbiome of the two strains on phylum level for Firmicutes, Deferribacteres and Proteobacteria that propose an essential role of the microbiome in obesity susceptibility. Gut microbial and liver metabolomics were followed by a combinatory approach using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and ultra performance liquid chromatography time of tlight MS/MS with subsequent multivariate statistical analysis, revealing distinctive host and microbial metabolome patterns between the C57J and the C57N strain. Many taurine-conjugated bile acids (TBAs) were significantly elevated in the cecum and decreased in liver samples from the C57J phenotype likely displaying different energy utilization behavior by the bacterial community and the host. Furthermore, several metabolite groups could specifically be associated with the C57N phenotype involving fatty acids, eicosanoids and urobilinoids. The mass differences based metabolite network approach enabled to extend the range of known metabolites to important bile acids (BAs) and novel taurine conjugates specific for both strains. In summary, our study showed clear alterations of the metabolome in the gastrointestinal tract and liver within a HFD-induced obesity mouse model in relation to the host-microbial nutritional adaptation.

Effect of charge density of polysaccharides on self-assembled intragastric gelation of whey protein/polysaccharide under simulated gastric conditions

Charge density of polysaccharides and biopolymer ratio are the major factors affecting their intragastric gelation and their digestion properties.

The role of cholecystokinin 1 receptor in prolactin inhibited gastric emptying of male rat

Background/Aims

Prolactin (PRL) is essential for the lactating mammals, while cholecystokinin (CCK) does inhibit gastric emptying (GE). Present study attempted to determine whether both peptides interacted on the male rat GE, particularly the role of putative CCK1 receptor.

Methods

Acute hyperprolactinemia of male rats was induced by the intraperitoneal injection of ovine PRL (oPRL) in several divided doses 15 minutes before motility study. Rat chronic hyperprolactinemia was induced by the graft of 2 pituitary glands into the capsule of left kidney, while control rats received cerebral cortex graft only. Motility study was conducted 6 weeks later after graft surgery. Fifteen minutes after the intragastric feeding of radiochromium, rat was sacrificed to measure GE via the distribution of radioactivities within stomach and intestine. Among the CCK1 receptor blocking study using lorglumide, rats were divided to receive the regimens in terms of oPRL-vehicle plus lorglumide-vehicle, oPRL plus lorglumide-vehicle, oPRL-vehicle plus lorglumide and oPRL plus lorglumide. Plasma CCK level was measured using a homemade radioimmunoassay kit.

Results

Compared to vehicle treatment, acute hyperprolactinemic rats under highest dose (2.0 mg/kg) of oPRL treatment showed delayed GE (70.6% ± 3.0% vs 42.1% ± 6.6%, P < 0.05). Chronic hyperprolactinemic rats under graft surgery also showed inhibited GE (70.5% ± 1.7% vs 54.5% ± 4.7%, P < 0.05). Both models finally obtained elevated plasma CCK levels (P < 0.05). Lorglumide itself did not influence GE, however, delayed GE under oPRL treatment was restored following the concomitant lorglumide treatment.

Conclusions

Our study suggests that PRL may delay male rat GE via a mechanism of endogenous CCK activation involving the peripheral CCK1 receptor.

Effects of manipulating eating frequency during a behavioral weight loss intervention: a pilot randomized controlled trial

Eating frequency has been inversely related to BMI but the impact of eating frequency on weight loss is unclear. This randomized controlled trial pilot study examined the effect of eating frequency on hunger, energy intake, and weight loss during a 6-month behavioral weight loss intervention. Participants (age: 51.0 ± 9.9 years, BMI: 35.5 ± 4.8 kg/m(2), 57.8% female, 94.1% white) were randomized to one of two eating frequency prescriptions: Three meal (n = 25): three eating bouts/day; or grazing (n = 26): eat at least 100 kcals every 2-3 h. Both groups attended 20 sessions and had identical dietary (1,200-1,500 kcals/day, <30% kcals from fat) and physical activity goals (200 min/week). Assessments were conducted at 0, 3, and 6 months. Using intent-to-treat analyses, grazing reported a greater eating frequency than three meal at 6 months (5.8 ± 1.1 eating bouts/day vs. 3.2 ± 0.6 eating bouts/day, P < 0.001). Grazing reported a significant reduction in hunger from 0 to 6 months (56.3 ± 15.7 mm vs. 47.9 ± 18.5 mm, P < 0.05). Energy intake and BMI were significantly (P < 0.001) reduced from 0 to 6 months (energy intake: 2,198 ± 692 kcals/day vs. 1,266 ± 353 kcals/day; BMI: 35.5 ± 4.8 kg/m(2) vs. 30.6 ± 4.9 kg/m(2)). There were no significant differences in energy intake or BMI between the groups. While eating more frequently reduced hunger, it may not be related to greater reductions in energy intake or BMI during a behavioral weight loss intervention.

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.

Gastrointestinal targets to modulate satiety and food intake

This review discusses the role of enteroendocrine cells in the gastrointestinal tract as chemoreceptors that sense intraluminal contents and induce changes in food intake through the release of signalling substances, such as satiety hormones. Recent evidence supports the concept that chemosensing in the gut involves G protein-coupled receptors (GPCRs) that are known to mediate gustatory signals in the oral cavity. GPCRs can be grouped into several families, depending on the stimuli to which they respond, e.g. proteins, amino acids, carbohydrates, fatty acids, or tastants. Sensing of these stimuli by GPCRs results in hormone secretions of enteroendocrine cells, which participate in the control of food intake. A better understanding of the stimuli that induce the strongest binding with these receptors, and thus induce a strong release of hormones, can be a very useful strategy for the development of novel foods in the treatment of obesity.

Effects of protein quality on appetite and energy metabolism in normal weight subjects

OBJECTIVE

The purpose of this study was to compare the effects of consumption of different protein sources on food intake and energy expenditure in normal weight subjects.

SUBJECTS AND METHODS

Breakfast preparations (casein, soy protein, whey protein or control) were ingested during seven consecutive days. Appetite, food intake, and energy expenditure were assessed.

RESULTS

Casein consumption led to a lower energy intake than whey protein. There was lower energy intake on day 7 than on day 1 of the casein session. Soy protein preparations resulted in higher diet induced thermogenesis (DIT) than in control preparations. The respiratory quotient (RQ) obtained in the whey protein session was lower than the control and soy protein sessions.

CONCLUSION

These results suggest that the consumption of different protein types leads to distinct effects on satiety (casein), DIT (soy protein), and/or RQ (whey protein).

Recent advances in the discovery and evaluation of fatty acid amide hydrolase inhibitors

IMPORTANCE OF THE FIELD

Cannabis has been used for both medicinal and recreational purposes since ancient times. Although cannabinoid-based medicines hold great promise in several challenging therapeutic areas such as pain management and mode control, their development has been hampered by psychoactive and other CNS-related side effects. The identification of fatty acid amide hydrolase (FAAH), a key enzyme responsible for the degradation of endocannabinoids, has brought in tremendous opportunities in that inhibition of FAAH leads to local elevation of endocannabinoids under certain stimuli, thus, avoiding the side effects from global activation of cannabinoid receptors by exogenous cannabimimetic compounds. The search for selective FAAH inhibitors has thus become a strong focus in current drug discovery.

AREAS COVERED IN THIS REVIEW

This review summarizes our current understanding of FAAH including its structure, catalytic mechanism and biological functions with emphases on its role in the regulation of endocannabinoids and other signaling lipids. The review then highlights the most recent discovery and biological activities of different classes of FAAH inhibitors. Last, the review discusses challenges and potential drawbacks in the development of FAAH inhibitor-based therapy.

WHAT THE READER WILL GAIN

Readers will have an overview of FAAH and obtain a rationale on FAAH as an attractive therapeutic target for the development of medicines for treating pain, inflammation, anxiety and other diseases. More importantly, readers will gain knowledge on various newly established FAAH inhibitor scaffolds and their development potentials, and such information will hopefully stimulate ideas for the designing of new inhibitors with superior activity profiles. The discussions on the potential challenges in developing FAAH inhibitors will impose more caution in the decision-making process, thus, lowering the possibility of late stage failure.

TAKE HOME MESSAGE

FAAH is an attractive target for modulating the endocannabinoid system, thus, treating many disease conditions including pain and mode control without the CNS side effects associated with cannabis usage. In recent years, tremendous effort has been focused in the FAAH inhibitor research field, and consequently many novel chemical templates have been discovered. FAAH hydrolyzes several important signaling lipids, but the long-term effects of FAAH inhibition in humans remain to be seen. While it is challenging to identify the right molecule with the right level of intervention of the FAAH function for treating a disease condition, it is possible to avoid mechanism-related undesired effects. With the entry of several compounds into clinical trials, FAAH inhibitor-based medicines are on the horizon.

Expression of cannabinoid CB1 receptors by vagal afferent neurons: kinetics and role in influencing neurochemical phenotype

The intestinal hormone cholecystokinin (CCK) inhibits food intake via stimulation of vagal afferent neurons (VAN). Recent studies suggest that CCK also regulates the expression of some G protein-coupled receptors and neuropeptide transmitters in these neurons. The aim of the present study was to characterize the expression of cannabinoid (CB)1 receptors in VAN and to determine whether stimulation of these receptors plays a role in regulating neurochemical phenotype. Expression of CB1 in rat VAN was detectable by in situ hybridization or immunohistochemistry after 6 h of fasting and increased to a maximum after 24 h when approximately 50% of neurons in the mid and caudal regions expressed the receptor. Melanin-concentrating hormone (MCH)1 receptors also increased with fasting, but the changes were delayed compared with CB1; in contrast Y2 receptors (Y2R) exhibited reciprocal changes in expression to CB1. Administration of CCK8s (10 nmol ip) to fasted rats decreased expression of CB1 with a t(1/2) of approximately 1 h compared with 3 h for MCH1. The action of CCK8s was inhibited by ghrelin and orexin-A. The CB1 agonist anandamide (intraperitoneally) reversed the effect of CCK8s on CB1, MCH1, and Y2 receptor expression. In contrast, in rats fasted for 18 h, administration of a CB1 antagonist/inverse agonist (AM281 ip) downregulated CB1 expression and increased Y2 receptor expression. Activation of vagal CB1 receptors therefore influences the neurochemical phenotype of these neurons, indicating a new and hitherto unrecognized role for endocannabinoids in gut-brain signaling.

The endocannabinoid system: its roles in energy balance and potential as a target for obesity treatment

Obesity and cardiometabolic risk continue to be major public health concerns. A better understanding of the physiopathological mechanisms leading to obesity may help to identify novel therapeutic targets. The endocannabinoid system discovered in the early 1990s is believed to influence body weight regulation and cardiometabolic risk factors. This article aims to review the literature on the endocannabinoid system including the biological roles of its major components, namely, the cannabinoid receptors, their endogenous ligands the endocannabinoids and the ligand-metabolising enzymes. The review also discusses evidence that the endocannabinoid system constitutes a new physiological pathway occurring in the central nervous system and peripheral tissues that has a key role in the control of food intake and energy expenditure, insulin sensitivity, as well as glucose and lipid metabolism. Based on the important finding that there is a close association between obesity and the hyperactivity of the endocannabinoid system, interest in blocking stimulation of this pathway to aid weight loss and reduce cardiometabolic risk factor development has become an important area of research. Among the pharmacological strategies proposed, the antagonism of the cannabinoid receptors has been particularly investigated and several clinical trials have been conducted. One challenging pharmacological task will be to target the endocannabinoid system in a more selective, and hence, safe way. As the management of obesity also requires lifestyle modifications in terms of healthy eating and physical activity, the targeting of the endocannabinoid system may represent a novel approach for a multifactorial therapeutic strategy.

Pitfalls in the sample preparation and analysis of N-acylethanolamines

N-acylethanolamines (NAEs) are a group of lipid mediators synthesized in response to a number of physiological and pathological stimuli. Because of the low tissue concentrations of NAEs, analyses often include liquid extraction followed by solid-phase extraction and subsequent quantitation by LC/MS or GC/MS. Reported levels of NAEs vary considerably, however, and often no explanation is given for these discrepancies. Brought on by difficulties encountered during method development, the effects of using four different brands of silica-containing solid phase extraction (SPE) columns and five different brands of chloroform for sample preparation were investigated. Considerable variation in the retention and recoveries of seven NAEs and 2-arachidonoylglycerol existed between the SPE columns. Furthermore, it was found that some chloroforms contained quantifiable amounts of N-palmitoylethanolamine and N-stearoylethanolamine. Finally, it was found that use of one of the chloroforms resulted in a loss of N-oleoylethanolamine from solution due to addition of chlorine to the ω-9 bond. The identity of this reaction product was confirmed by LC-MS/MS and NMR. It is recommended that these aspects of sample preparation and analysis should be thoroughly validated during method development and the relevant information on specific brands used be reported in future communications in order to better estimate the validity of reported quantitative data.

Cocaine- and amphetamine-regulated transcript mediates the actions of cholecystokinin on rat vagal afferent neurons

BACKGROUND & AIMS

Cholecystokinin (CCK) acts on vagal afferent neurons to inhibit food intake and gastric emptying; it also increases expression of the neuropeptide cocaine- and amphetamine-regulated transcript (CART), but the significance of this is unknown. We investigated the role of CARTp in vagal afferent neurons.

METHODS

Release of CART peptide (CARTp) from cultured vagal afferent neurons was determined by enzyme-linked immunosorbent assay. Expression of receptors and neuropeptides in rat vagal afferent neurons in response to CARTp was studied using immunohistochemistry and luciferase promoter reporter constructs. Effects of CARTp and CCK were studied on food intake.

RESULTS

CCK stimulated CARTp release from cultured nodose neurons. CARTp replicated the effect of CCK in stimulating expression of Y2R and of CART itself in these neurons in vivo and in vitro, but not in inhibiting cannabinoid-1, melanin-concentrating hormone, and melanin-concentrating hormone-1 receptor expression. Effects of CCK on Y2R and CART expression were reduced by CART small interfering RNA or brefeldin A. Exposure of rats to CARTp increased the inhibitory action of CCK on food intake after short-, but not long-duration, fasting.

CONCLUSIONS

The actions of CCK in stimulating CART and Y2R expression in vagal afferent neurons and in inhibiting food intake are augmented by CARTp; CARTp is released by CCK from these neurons, indicating that it acts as an autocrine excitatory mediator.

Cannabinoids and the gut: new developments and emerging concepts

Cannabis has been used to treat gastrointestinal (GI) conditions that range from enteric infections and inflammatory conditions to disorders of motility, emesis and abdominal pain. The mechanistic basis of these treatments emerged after the discovery of Delta(9)-tetrahydrocannabinol as the major constituent of Cannabis. Further progress was made when the receptors for Delta(9)-tetrahydrocannabinol were identified as part of an endocannabinoid system, that consists of specific cannabinoid receptors, endogenous ligands and their biosynthetic and degradative enzymes. Anatomical, physiological and pharmacological studies have shown that the endocannabinoid system is widely distributed throughout the gut, with regional variation and organ-specific actions. It is involved in the regulation of food intake, nausea and emesis, gastric secretion and gastroprotection, GI motility, ion transport, visceral sensation, intestinal inflammation and cell proliferation in the gut. Cellular targets have been defined that include the enteric nervous system, epithelial and immune cells. Molecular targets of the endocannabinoid system include, in addition to the cannabinoid receptors, transient receptor potential vanilloid 1 receptors, peroxisome proliferator-activated receptor alpha receptors and the orphan G-protein coupled receptors, GPR55 and GPR119. Pharmacological agents that act on these targets have been shown in preclinical models to have therapeutic potential. Here, we discuss cannabinoid receptors and their localization in the gut, the proteins involved in endocannabinoid synthesis and degradation and the presence of endocannabinoids in the gut in health and disease. We focus on the pharmacological actions of cannabinoids in relation to GI disorders, highlighting recent data on genetic mutations in the endocannabinoid system in GI disease.

Pain and beyond: fatty acid amides and fatty acid amide hydrolase inhibitors in cardiovascular and metabolic diseases

Fatty acid amide hydrolase (FAAH) is responsible for the hydrolysis of several important endogenous fatty acid amides (FAAs), including anandamide, oleoylethanolamide and palmitoylethanolamide. Because specific FAAs interact with cannabinoid and vanilloid receptors, they are often referred to as 'endocannabinoids' or 'endovanilloids'. Initial interest in this area, therefore, has focused on developing FAAH inhibitors to augment the actions of FAAs and reduce pain. However, recent literature has shown that these FAAs - through interactions with unique receptors (extracellular and intracellular) - can induce a diverse array of effects that include appetite suppression, modulation of lipid and glucose metabolism, vasodilation, cardiac function and inflammation. This review gives an overview of FAAs and diverse FAAH inhibitors and their potential therapeutic utility in pain and non-pain indications.

N-acylethanolamines, anandamide and food intake

Anandamide and the other N-acylethanolamines, e.g. oleoylethanolamide (OEA), palmitoylethanolamide (PEA), and linoleoylethanolamide (LEA), may be formed by several enzymatic pathways from their precursors, which are the N-acylated ethanolamine phospholipids. The exact enzymatic pathways involved in their biosynthesis in specific tissues are not clarified. It has been suggested that endogenous anandamide could stimulate food intake by activation of cannabinoid receptors in the brain and/or in the intestinal tissue. On the other hand, endogenous OEA and PEA have been suggested to inhibit food intake by acting on receptors in the intestine. At present, there is no clear role for endogenous anandamide in controlling food intake via cannabinoid receptors, neither centrally nor in the gastrointestinal tract. However, OEA, PEA and perhaps also LEA may be involved in regulation of food intake by selective prolongation of feeding latency and post-meal interval. These N-acylethanolamines seem to be formed locally in the intestine, where they can activate PPARalpha located in close proximity to their site of synthesis. The rapid onset of OEA response and its reliance on an intact vagus nerve suggests that activation of PPARalpha does not result in formation of a transcription-dependent signal but must rely on an unidentified non-genomic signal that translates to activation of vagal afferents. Whether GPR119, TRPV1 and/or intestinal ceramide levels also contribute to the anorectic and weight-reducing effect of exogenous OEA is less clear. Prolonged intake of dietary fat (45 energy%) may promote over-consumption of food by decreasing the endogenous levels of OEA, PEA and LEA in the intestine.

Peripheral endocannabinoid dysregulation in obesity: relation to intestinal motility and energy processing induced by food deprivation and re-feeding

BACKGROUND AND PURPOSE

Endocannabinoids in tissues controlling energy homeostasis are altered in obesity, thus contributing to metabolic disorders. Here we evaluate endocannabinoid dysregulation in the small intestine of mice with diet-induced obesity (DIO) and in peripheral tissues of Zucker and lean rats following food deprivation and re-feeding.

EXPERIMENTAL APPROACH

Intestinal transit, evaluated using rhodamine-B-labelled dextran, and small intestinal endocannabinoid levels, measured by liquid chromatography mass spectrometry, were measured in mice fed normal or high-fat diets (HFDs). Endocannabinoid levels were measured also in various tissues of lean and Zucker rats fed ad libitum or following overnight food deprivation with and without subsequent re-feeding.

KEY RESULTS

After 8 weeks of HFD, baseline intestinal transit was increased in DIO mice and enhanced by cannabinoid CB(1) receptor antagonism less efficaciously than in lean mice. Small intestinal anandamide and 2-arachidonoylglycerol levels were reduced and increased respectively. In Zucker rats, endocannabinoids levels were higher in the pancreas, liver and duodenum, and lower in the subcutaneous adipose tissue. Food deprivation increased endocannabinoid levels in the duodenum and liver of both rat strains, in the pancreas of lean rats and in adipose tissues of Zucker rats.

CONCLUSIONS AND IMPLICATIONS

Reduced anandamide levels might account for increased intestinal motility in DIO mice. Regulation of endocannabinoid levels in rat peripheral tissues, induced by food deprivation and re-feeding, might participate in food intake and energy processing and was altered in Zucker rats. These data, together with previous observations, provide further evidence for dysregulation of peripheral endocannabinoids in obesity.

Role of acylethanolamides in the gastrointestinal tract with special reference to food intake and energy balance

Acylethanolamides (AEs) are a group of lipids occurring in both plants and animals. The best-studied AEs are the endocannabinoid anandamide (AEA), the anti-inflammatory compound palmitoylethanolamide (PEA), and the potent anorexigenic molecule oleoylethanolamide (OEA). AEs are biosynthesized in the gastrointestinal tract, and their levels may change in response to noxious stimuli, food deprivation or diet-induced obesity. The biological actions of AEs within the gut are not limited to the modulation of food intake and energy balance. For example, AEs exert potential beneficial effects in the regulation of intestinal motility, secretion, inflammation and cellular proliferation. Molecular targets of AEs, which have been identified in the gastrointestinal tract, include cannabinoid CB(1) and CB(2) receptors (activated by AEA), transient receptor potential vanilloid type 1 (TRPV1, activated by AEA and OEA), the nuclear receptor peroxisome proliferators-activated receptor-alpha (PPAR-alpha, activated by OEA and, to a less extent, by PEA), and the orphan G-coupled receptors GPR119 (activated by OEA) and GPR55 (activated by PEA and, with lower potency, by AEA and OEA). Modulation of AE levels in the gut may provide new pharmacological strategies not only for the treatment of feeding disorders but also for the prevention or cure of widespread intestinal diseases such as inflammatory bowel disease and colon cancer.

The versatility of the vagus

The gut is one of several organs contributing to the peripheral signalling network that controls food intake. Afferent neurons of the vagus nerve provide an important pathway for gut signals that act by triggering ascending pathways from the brain stem to hypothalamus. Recent work indicates the existence of mechanisms operating at the level of vagal afferent neurons to modulate the effect of gastrointestinal satiety signals. Thus, the well known satiety hormone cholecystokinin (CCK) not only stimulates the discharge of these neurons but also controls their expression of both G-protein coupled receptors and peptide neurotransmitters known to influence food intake. When plasma CCK concentrations are low e.g. in fasting, the expression by vagal afferent neurons of cannabinoid (CB)-1 and melanin concentrating hormone (MCH)-1 receptors is increased. Release of CCK by feeding leads to a rapid down-regulation of expression of both receptors and to increased expression of Y2 receptors. In fasting, there is also increased expression in these neurons of the appetite-stimulating neuropeptide transmitter MCH, and depressed expression of the satiety-peptide cocaine and amphetamine regulated transcript (CARTp); endogenous CCK decreases MCH expression and stimulates CART expression. The gastric orexigenic hormone ghrelin blocks these actions of CCK at least in part by excluding phosphoCREB from the nucleus. The data suggest that CCK acts as a gatekeeper to determine the capacity of other neuroendocrine signals to act via vagal afferent neurons to influence food intake.

Alcohol dehydrogenase-catalyzed in vitro oxidation of anandamide to N-arachidonoyl glycine, a lipid mediator: synthesis of N-acyl glycinals

N-Arachidonoyl ethanolamide or anandamide is an endocannabinoid found in most tissues where it acts as an important signaling mediator in a number of physiological and pathophysiological processes. Consequently, intense effort has been focused on understanding all its biosynthetic and metabolic pathways. Herein we report human alcohol dehydrogenase-catalyzed sequential oxidation of anandamide to N-arachidonoyl glycine, a prototypical member of the class of long chain fatty acyl glycines, a new group of lipid mediators with a wide array of physiological effects. We also present a straightforward synthesis for a series of N-acyl glycinals including N-arachidonoyl glycinal, an intermediate in the alcohol dehydrogenase-catalyzed oxidation of anandamide.