The endogenous cannabinoid system affects energy balance via central orexigenic drive and peripheral lipogenesis

Singing-driven gene expression in the developing songbird brain

Neural and behavioral development arises from an integration of genetic and environmental influences, yet specifying the nature of this interaction remains a primary problem in neuroscience. Here, we review molecular and behavioral studies that focus on the role of singing-driven gene expression during neural and vocal development in the male zebra finch (Taeniopygia guttata), a songbird that learns a species-typical vocal pattern during juvenile development by imitating an adult male tutor. A primary aim of our lab has been to identify naturally-occurring environmental influences that shape the propensity to sing. This ethological approach underlies our theoretical perspective, which is to integrate the significance of singing-driven gene expression into a broader ecological context.

The endocannabinoid system in the physiology and pathophysiology of the gastrointestinal tract

Numerous investigations have recently demonstrated the important roles of the endocannabinoid system in the gastrointestinal (GI) tract under physiological and pathophysiological conditions. In the GI tract, cannabinoid type 1 (CB1) receptors are present in neurons of the enteric nervous system and in sensory terminals of vagal and spinal neurons, while cannabinoid type 2 receptors are located in immune cells. Activation of CB1 receptors was shown to modulate several functions in the GI tract, including gastric secretion, gastric emptying and intestinal motility. Under pathophysiological conditions induced experimentally in rodents, the endocannabinoid system conveys protection to the GI tract (e.g. from inflammation and abnormally high gastric and enteric secretions). Such protective activities are largely in agreement with anecdotal reports from folk medicine on the use of Cannabis sativa extracts by subjects suffering from various GI disorders. Thus, the endocannabinoid system may serve as a potentially promising therapeutic target against different GI disorders, including frankly inflammatory bowel diseases (e.g. Crohn's disease), functional bowel diseases (e.g. irritable bowel syndrome) and secretion- and motility-related disorders. As stimulation of this modulatory system by CB1 receptor agonists can lead to unwanted psychotropic side effects, an alternative and promising avenue for therapeutic applications resides in the treatment with CB1 receptor agonists that are unable to cross the blood-brain barrier, or with compounds that inhibit the degradation of endogenous ligands (endocannabinoids) of CB1 receptors, hence prolonging the activity of the endocannabinoid system.

Food for thought: endocannabinoid modulation of lipogenesis

An emerging body of evidence implicates peripheral and central endocannabinoid pathways in the regulation of feeding behavior and body weight. A report in this issue of the JCI demonstrates the presence of a common endocannabinoid-regulated molecular pathway for peripheral lipogenic and central appetitive regulation. This pathway involves the activation of the transcription factor SREBP-1c and its associated enzymes, acetyl-CoA carboxylase-1 and fatty acid synthase, in the liver and hypothalamus. Activation of cannabinoid receptor 1 (CB(1)) in liver plays a key role in increased serum lipid production, fatty liver, and possibly diet-induced obesity. Conversely, stimulation of these receptors in the hypothalamus may lead to an increase in food consumption. Thus, targeting both of these pathways with CB(1) antagonists could promote sustained weight loss and favorable serum lipid profiles in obese patients.

Endocannabinoid activation at hepatic CB1 receptors stimulates fatty acid synthesis and contributes to diet-induced obesity

Endogenous cannabinoids acting at CB(1) receptors stimulate appetite, and CB(1) antagonists show promise in the treatment of obesity. CB(1) (-/-) mice are resistant to diet-induced obesity even though their caloric intake is similar to that of wild-type mice, suggesting that endocannabinoids also regulate fat metabolism. Here, we investigated the possible role of endocannabinoids in the regulation of hepatic lipogenesis. Activation of CB(1) in mice increases the hepatic gene expression of the lipogenic transcription factor SREBP-1c and its targets acetyl-CoA carboxylase-1 and fatty acid synthase (FAS). Treatment with a CB(1) agonist also increases de novo fatty acid synthesis in the liver or in isolated hepatocytes, which express CB(1). High-fat diet increases hepatic levels of the endocannabinoid anandamide (arachidonoyl ethanolamide), CB(1) density, and basal rates of fatty acid synthesis, and the latter is reduced by CB(1) blockade. In the hypothalamus, where FAS inhibitors elicit anorexia, SREBP-1c and FAS expression are similarly affected by CB(1) ligands. We conclude that anandamide acting at hepatic CB(1) contributes to diet-induced obesity and that the FAS pathway may be a common molecular target for central appetitive and peripheral metabolic regulation.

The CB1 receptor antagonist rimonabant reverses the diet-induced obesity phenotype through the regulation of lipolysis and energy balance

We investigated the molecular events involved in the long-lasting reduction of adipose mass by the selective CB1 antagonist, SR141716. Its effects were assessed at the transcriptional level both in white (WAT) and brown (BAT) adipose tissues in a diet-induced obesity model in mice. Our data clearly indicated that SR141716 reversed the phenotype of obese adipocytes at both macroscopic and genomic levels. First, oral treatment with SR141716 at 10 mg/kg/d for 40 days induced a robust reduction of obesity, as shown by the 50% decrease in adipose mass together with a major restoration of white adipocyte morphology similar to lean animals. Second, we found that the major alterations in gene expression levels induced by obesity in WAT and BAT were mostly reversed in SR141716-treated obese mice. Importantly, the transcriptional patterns of treated obese mice were similar to those obtained in the CB1 receptor knockout mice fed a high-fat regimen and which are resistant to obesity, supporting a CB1 receptor-mediated process. Functional analysis of these modulations indicated that the reduction of adipose mass by the molecule resulted from an enhanced lipolysis through the induction of enzymes of the beta-oxidation and TCA cycle, increased energy expenditure, mainly through futile cycling (calcium and substrate), and a tight regulation of glucose homeostasis. These changes accompanied a significant cellular remodeling and contributed to a reduction of the obesity-related inflammatory status. In addition to a transient reduction of food consumption, increases of both fatty acid oxidation and energy expenditure induced by the molecule summate leading to a sustained weight loss. Altogether, these data strongly indicate that the endocannabinoid system has a major role in the regulation of energy metabolism.

Endocannabinoid control of food intake and energy balance

Marijuana and its major psychotropic component, Delta(9)-tetrahydrocannabinol, stimulate appetite and increase body weight in wasting syndromes, suggesting that the CB(1) cannabinoid receptor and its endogenous ligands, the endocannabinoids, are involved in controlling energy balance. The endocannabinoid system controls food intake via both central and peripheral mechanisms, and it may also stimulate lipogenesis and fat accumulation. Here we discuss the multifaceted regulation of energy homeostasis by endocannabinoids, together with its applications to the treatment of eating disorders and metabolic syndromes.

Cannabinoids and Ghrelin Have Both Central and Peripheral Metabolic and Cardiac Effects via AMP-activated Protein Kinase

Endocannabinoids and ghrelin are potent appetite stimulators and are known to interact at a hypothalamic level. However, both also have important peripheral actions, including beneficial effects on the ischemic heart and increasing adipose tissue deposition, while ghrelin has direct effects on carbohydrate metabolism. The AMP-activated protein kinase (AMPK) is a heterotrimeric enzyme that functions as a fuel sensor to regulate energy balance at both cellular and whole body levels, and it may mediate the action of anti-diabetic drugs such as metformin and peroxisome proliferator-activated receptor gamma agonists. Here we show that both cannabinoids and ghrelin stimulate AMPK activity in the hypothalamus and the heart, while inhibiting AMPK in liver and adipose tissue. These novel effects of cannabinoids on AMPK provide a mechanism for a number of their known actions, such as the reduction in infarct size in the myocardium, an increase in adipose tissue, and stimulation of appetite. The beneficial effects of ghrelin on heart function, including reduction of myocyte apoptosis, and its effects on lipogenesis and carbohydrate metabolism, can also be explained by its ability to activate AMPK. Our data demonstrate that AMPK not only links the orexigenic effects of endocannabinoids and ghrelin in the hypothalamus but also their effects on the metabolism of peripheral tissues.

Cannabinoid CB1 receptor is dispensable for memory extinction in an appetitively-motivated learning task

The interaction of the cannabinoid CB1 receptor with its endogenous ligands plays an essential role in extinction of aversive memories (Marsicano, G., Wotjak, C.T., Azad, S.C., Bisogno, T., Rammes, G., Cascio, M.G., Hermann, H., Tang, J., Hofmann, C., Zieglgansberger, W., Di, M., V, Lutz, B., 2002. The endogenous cannabinoid system controls extinction of aversive memories. Nature 418, 530-534). The present study tested the generality of this observation in respect to positively-reinforced memories. To this end, male cannabinoid CB1 receptor deficient mice (CB1R-/-) and their wild-type littermate controls (CB1R+/+) were trained in an appetitively-motivated operant conditioning task, in which food-deprived animals received a food reward on nose-poking into an illuminated hole. During training, CB1R-/- turned out to be less motivated to participate in the task. After further restriction of daily food consumption, however, CB1R-/- reached the same level of performance as CB1R+/+ as far as number of correct responses and errors of omission are concerned. The accuracy of performance served as a measure for the memory of the light-reward association and was stable at similarly high levels over a retention period of 9 days without additional training (97.6+/-0.5% vs. 97.0+/-0.9% correct responses). During subsequent extinction training, the positive reinforcement was omitted. As a consequence, both CB1R-/- and CB1R+/+ showed a similar decline in accuracy of performance and total number of correct responses, accompanied by an increase in errors of omission. These data demonstrate that the cannabinoid CB1 receptor is not essential for extinction of the stimulus-response association in an appetitively-motivated learning task.

Endocannabinoids link feeding state and auditory perception-related gene expression

Singing by adult male zebra finches is a learned behavior important for courtship, kin recognition, and nest defense (Zann, 1996) and is inhibited by both brief periods of limited food availability and systemic injection of cannabinoids. These similar effects on singing, combined with increasing evidence for endocannabinoid involvement in feeding behavior, led us to evaluate a possible shared mechanism. We found that limited food availability both reduces singing in a cannabinoid antagonist-reversible manner and increases levels of the endocannabinoid 2-arachidonyl glycerol in various brain regions including the caudal telencephalon, an area that contains auditory telencephalon including the L2 subfield of L (L2) and caudal medial nidopallium (NCM). Development and use of an anti-zebra finch cannabinoid receptor type 1 (CB1) antibody demonstrates distinct, dense cannabinoid receptor expression within song regions including Area X, lMAN (lateral magnocellular nucleus of anterior nidopallium), HVC, RA (robust nucleus of arcopallium), and L2. NCM receives L2 projections and is implicated in integration of auditory information. Activity in this area, determined through expression of the transcription factor ZENK, is increased after exposure to unfamiliar song. Because previous work has shown that these novel song-stimulated increases in NCM activity are mitigated by cannabinoid exposure, we tested and found that similar effects on ZENK expression are produced by limiting food. Limited food-related reductions in the activity of NCM neurons were reversed by the cannabinoid antagonist SR141716A (N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methylpyrazole-3-carboxamide), implicating CB1 cannabinoid receptor involvement. Taken together, these experiments indicate a link between feeding state and gene expression related to auditory perception that is mediated by endocannabinoid signaling.

Keynote review: Medicinal chemistry strategies to CB1 cannabinoid receptor antagonists

The proven clinical efficacy of the CB(1) cannabinoid receptor antagonist rimonabant in both obesity and smoking cessation and its therapeutic potential in other disorders has given a tremendous impetus to the discovery of novel CB(1) antagonists. The number of disclosed patents wherein novel chemical entities having CB(1) antagonistic or inverse agonistic properties have been claimed has exploded. Besides novel compound classes that were identified in screening, rational medicinal chemistry approaches such as conformational constraint and scaffold hopping have been successfully applied. CB(1) receptor modelling has provided insight into crucial receptor-ligand interaction points thereby leading to a general CB(1) inverse agonist pharmacophore model.

Endocannabinoid activation at hepatic CB1 receptors stimulates fatty acid synthesis and contributes to diet-induced obesity

Endogenous cannabinoids acting at CB(1) receptors stimulate appetite, and CB(1) antagonists show promise in the treatment of obesity. CB(1) (-/-) mice are resistant to diet-induced obesity even though their caloric intake is similar to that of wild-type mice, suggesting that endocannabinoids also regulate fat metabolism. Here, we investigated the possible role of endocannabinoids in the regulation of hepatic lipogenesis. Activation of CB(1) in mice increases the hepatic gene expression of the lipogenic transcription factor SREBP-1c and its targets acetyl-CoA carboxylase-1 and fatty acid synthase (FAS). Treatment with a CB(1) agonist also increases de novo fatty acid synthesis in the liver or in isolated hepatocytes, which express CB(1). High-fat diet increases hepatic levels of the endocannabinoid anandamide (arachidonoyl ethanolamide), CB(1) density, and basal rates of fatty acid synthesis, and the latter is reduced by CB(1) blockade. In the hypothalamus, where FAS inhibitors elicit anorexia, SREBP-1c and FAS expression are similarly affected by CB(1) ligands. We conclude that anandamide acting at hepatic CB(1) contributes to diet-induced obesity and that the FAS pathway may be a common molecular target for central appetitive and peripheral metabolic regulation.

Effects of the cannabinoid-1 receptor blocker rimonabant on weight reduction and cardiovascular risk factors in overweight patients: 1-year experience from the RIO-Europe study

BACKGROUND

In animal models, cannabinoid-1 receptor (CB1) blockade produces a lean phenotype, with resistance to diet-induced obesity and associated dyslipidaemia. We assessed the effect of rimonabant, a selective CB1 blocker, on bodyweight and cardiovascular risk factors in overweight or obese patients.

METHODS

patients with body-mass index 30 kg/m2 or greater, or body-mass index greater than 27 kg/m2 with treated or untreated dyslipidaemia, hypertension, or both, were randomised to receive double-blind treatment with placebo, 5 mg rimonabant, or 20 mg rimonabant once daily in addition to a mild hypocaloric diet (600 kcal/day deficit). The primary efficacy endpoint was weight change from baseline after 1 year of treatment in the intention-to-treat population.

FINDINGS

Weight loss at 1 year was significantly greater in patients treated with rimonabant 5 mg (mean -3.4 kg [SD 5.7]; p=0.002 vs placebo) and 20 mg (-6.6 kg [7.2]; p<0.001 vs placebo) compared with placebo (-1.8 kg [6.4]). Significantly more patients treated with rimonabant 20 mg than placebo achieved weight loss of 5% or greater (p<0.001) and 10% or greater (p<0.001). Rimonabant 20 mg produced significantly greater improvements than placebo in waist circumference, HDL-cholesterol, triglycerides, and insulin resistance, and prevalence of the metabolic syndrome. The effects of rimonabant 5 mg were of less clinical significance. Rimonabant was generally well tolerated with mild and transient side effects.

INTERPRETATION

CB1 blockade with rimonabant 20 mg, combined with a hypocaloric diet over 1 year, promoted significant decrease of bodyweight and waist circumference, and improvement in cardiovascular risk factors.

Impaired repression at a vasopressin promoter polymorphism underlies overexpression of vasopressin in a rat model of trait anxiety

Two inbred rat lines have been developed that show either high (HAB) or low (LAB) anxiety-related behavior. The behavioral phenotype correlates with arginine vasopressin (AVP) expression at the level of the hypothalamic paraventricular nucleus (PVN), but not supraoptic nucleus, with HAB animals overexpressing the neuropeptide in both magnocellular and parvocellular subdivisions of the PVN. We detected a number of single nucleotide polymorphisms (SNPs) in the AVP locus that differ between the HAB and LAB animals, two of which were embedded in cis-regulatory elements. The HAB-specific allele of the AVP gene promoter occurs in 1.5% of outbred Wistar rats and is more transcriptionally active in vivo, as revealed by allele-specific transcription studies in cross-mated HAB/LAB F1 animals. Interestingly, one specific SNP [A(-1276)G] conferred reduced binding of the transcriptional repressor CArG binding factor A (CBF-A) in the HAB allele, the consequent differential regulation of the AVP promoter resulting in an overexpression of AVP in vitro and in vivo. Furthermore, CBF-A is highly coexpressed in AVP-containing neurons of the PVN supporting an important role for regulation of AVP gene expression in vivo. Taken together, our results demonstrate a role for an AVP gene polymorphism and CBF-A in elevated AVP expression in the PVN of HAB rats likely to contribute to their behavioral and neuroendocrine phenotype.

Central and peripheral signaling mechanisms involved in endocannabinoid regulation of feeding: a perspective on the munchies

The endocannabinoid system is a critical regulator of energy homeostasis and food intake. Through cannabinoid (CB)(1) receptors in the brain and periphery, endocannabinoids exert powerful effects on the systems of the body that coordinate the balance between food intake, metabolism, and energy expenditure. These integrative systems control food intake both by modulating the inputs to various brain areas that monitor energy balance and by increasing the hedonic or reward value of the food consumed. Cannabinoids also alter metabolism, acting through both centrally located CB(1) receptors that drive neuronal pathways controlling metabolism and peripheral CB(1) receptors located in tissues throughout the body.

Effects of the endocannabinoid noladin ether on body weight, food consumption, locomotor activity, and cognitive index in mice

We have investigated the effect of 2-arachidonylglyceryl-ether (Noladin) on food consumption, weight, activity, and cognitive function in mice during diet restriction for 17 days and subsequent ad libitum feeding for 32 days. Female Sabra mice were given food for 2.5 h/day (equal to 60% diet restriction), received Noladin (0.001, 0.01, 0.1 mg/(kg day) intraperitonially (i.p.)) with or without the CB1 antagonist SR141716A (1 mg/kg i.p.) during days 3-17. Noladin (0.001 mg/kg) significantly increased food consumption without a change in body weight, probably due to increased activity and there was no change in cognitive function. A higher dose (0.1 mg/kg) did not affect food consumption, but increased activity and slightly decreased weight 32 days after termination of Noladin administration; however, cognitive deterioration was observed. At all doses tested, Noladin did not affect weight during the diet-restriction period, whereas the CB1 antagonist (with or without Noladin) caused a very significant decline in weight in this phase. Weight catch-up was observed 1 month after administration of Noladin was discontinued. Weight at day 32 after the termination of Noladin (0.1 mg/(kg day)) treatment was 5% less than control. Female C57BL/6 mice (same protocol, with 0.001 mg/(kg day) Noladin) gave similar results to 0.1 mg/kg in Sabra mice as regards weight. CB1 antagonist treatment caused very significant decline in both weight and food consumption; cognition and activity were unchanged. These results indicate that Noladin has a significant dose-dependent effect on food consumption, cognition and weight maintenance after weight loss. Low doses of Noladin may possibly allow an increase in food intake without a gain in weight after dieting. Thus, Noladin could be of potential clinical benefit in treating disorders of body weight. Noladin seems to signal food consumption and weight through CB1 receptors based on effects observed with the CB1 antagonist, while the cognition and activity are probably mediated by non-cannabinoid receptors.

Coexpression of the cannabinoid receptor type 1 with the corticotropin-releasing hormone receptor type 1 in distinct regions of the adult mouse forebrain

The high abundance of the cannabinoid receptor type 1 (CB1) in the brain and the discovery of its endogenous ligands possessing neuromodulatory activities suggest an important potential of the endocannabinoid system to influence the functions of other receptor systems in the brain, including the corticotropin releasing hormone (CRH) system. Several studies evidenced a cross-talk between these two receptor systems. In trying to detail functional interactions between CB1 and the CRH receptor type 1 (CRHR1), we performed double-label-in situ hybridisation on mouse forebrain sections to localise the transcripts encoding the two receptors at a cellular level. Colocalisation of both receptor mRNAs was only detected in low CB1-expressing cells, which are mainly principal projecting neurons, whereas high CB1-expressing cells, which are considered to be mostly GABAergic did not contain mRNA encoding CRHR1. CB1 is differentially coexpressed with CRHR1 in olfactory regions, in several cortical and limbic structures, and in some hypothalamic and thalamic nuclei. These observations suggest a complex mechanism underlying the mutual interrelation and modulation of the two receptor systems. In particular, high levels of coexpressing cells in cortical and limbic areas may relate to cognitive functions, such as working memory, emotional and declarative learning. Colocalisation of CB1 and CRHR1 in hypothalamic regions strongly suggests functional interactions regarding the neuroendocrine homeostasis, including feeding behaviour.

Synthesis and SAR of 5,6-diarylpyridines as human CB1 inverse agonists

Structure-activity relationship studies for two series of 2-benzyloxy-5-(4-chlorophenyl)-6-(2,4-dichlorophenyl)pyridines having either a 3-cyano or 3-carboxamide moiety resulted in the preparation of the 2-(3,4-difluorobenzyloxy)-3-nitrile analog 10d and the 2-(3,4-difluorobenzyloxy)-3-(N-propylcarboxamide) analog 16c, (hCB1 IC(50)=1.3 and 1.7 nM, respectively) as potent and selective hCB1 inverse agonists. Their synthesis and biological activities are described herein.

The endocannabinoid system:A new approach to control cardiovascular disease

The endocannabinoid (EC) system consists of 2 types of G-protein-coupled cannabinoid receptors--cannabinoid type 1 (CB1) and cannabinoid type 2 (CB2)--and their natural ligands. The EC system plays a key role in the regulation of food intake and fat accumulation, as well as glucose and lipid metabolism. When overactivated, the EC system triggers dyslipidemia, thrombotic and inflammatory states, and insulin resistance. Blocking CB1 receptors centrally and peripherally in adipose tissue can help normalize an overactivated EC system. CB1 blockade helps regulate food intake and adipose tissue metabolism, contributing to improved insulin sensitivity and other features of the metabolic syndrome. Visceral adipose tissue is most closely associated with the metabolic syndrome, which is a constellation of conditions that place people at high risk for coronary artery disease. Targeting the EC system represents a new approach to treating visceral obesity and reducing cardiovascular risk factors.

The endocannabinoid system and the treatment of obesity

The endocannabinoids are endogenous lipids capable of binding to both cannabinoid receptors (CB) CB1 and CB2. These receptors belong to the G protein-coupled family receptors and they were discovered while investigating the mode of action of ?(9)-tetrahydrocannabinol, a component of Cannabis sativa, to which they bind with high affinity. Among many other brain sites, CB1 is present in the hypothalamic nuclei involved in the control of energy balance and body weight, as well as in neurons of the mesolimbic system which is believed to mediate the incentive value of food. At central nervous system level, CB1 activation is necessary to induce food intake after a short period of food deprivation, and when CB1 is activated by endocannabinoids produced in situ, a stimulation of the ingestion of palatable food has been described. CB1 stimulation leads to modulation of the release of some hypothalamic anorexigenic and orexigenic mediators, as well as of dopamine in the nucleus accumbens shell. Recent evidence has proved that CB1 is also present in the peripheral organs, such as the adipose tissue and gastrointestinal system, key organs in the regulation of energy metabolism. Animal models have provided solid evidence that genetically induced obesity leads to long-lasting overstimulation of endocannabinoid system synthesis resulting in permanent overactivation of CB1, which may then contribute to the maintenance of this disease. Importantly, at peripheral level, CB1 activation has been shown to stimulate lipogenesis in adipocytes. CB1 blockers increase adiponectin production in adipocytes, which leads to increased fatty acid oxidation and free fatty acid clearance. Moreover, CB1 has been shown to be up-regulated in adipocytes derived from obese rodents. These results support the role of endocannabinoids in the development and maintenance of obesity, paving the way for the development of a new class of drugs such as the CB1 blockers as a therapy for tackling obesity and the associated major cardiovascular risk factors.

Potential modulation of plasma ghrelin and glucagon-like peptide-1 by anorexigenic cannabinoid compounds, SR141716A (rimonabant) and oleoylethanolamide

The CB1 cannabinoid receptor antagonist, N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methylpyrazole-3-carboxamide (rimonabant; SR141716A), and oleoylethanolamide (OEA) are known to reduce food consumption, by, at least partially, a peripheral regulation of feeding. The effects of systemic SR141716A or OEA (5 mg/kg) administrations on food consumption in 24 h food-deprived and fed rats were investigated. In fasted rats, SR141716A and OEA produced an inhibition in food intake measurable the first 20 min following injection. The increase in ghrelin levels observed in the vehicle-injected rats was abolished in animals receiving OEA and significantly reduced with SR141716A. Neither OEA nor SR141716A modified glucagon-like peptide-1 (7-36) amide portal levels 20 min after the administration. In fed rats, plasma ghrelin levels of SR141716A- and OEA-treated rats were 35% lower as compared with those of the vehicle-injected rats. These results show an influence of cannabinoid agents on circulating ghrelin levels and suggest that their short-term action on appetite seems to be in accordance with the control of secretion of gastrointestinal orexigenic peptides, mainly expressed in the upper part of the gastrointestinal tract.

CART in feeding and obesity

CART (cocaine- and amphetamine-regulated transcript) peptides are neurotransmitters that have received much attention as mediators of feeding behavior and body-weight regulation in mammals. CART peptides and their mRNAs are found in many brain regions and in peripheral tissues that are involved in feeding, and many animal studies implicate CART as an inhibitor of feeding. Animal studies also demonstrate that CART expression is regulated by both leptin and glucocorticoids, two hormones known to be associated with the regulation of body weight. A recent study also links a mutation in the CART gene to obesity in humans. These peptides might become targets for drug development in the area of obesity.

Reduced sensitivity to reward in CB1 knockout mice

RATIONALE

Previous studies have demonstrated that the activation and blockade of the cannabinoid type 1 receptor (CB1) leads to an enhancement and decrease of the consumption of food and other orally ingested reinforcers, respectively.

OBJECTIVE

To gain further knowledge about the role of CB1 in sucrose/saccharin reinforcing efficacy and intake, we tested CB1 knockout (CB1-KO) and littermate wild-type (WT) control mice in several self-administration experimental protocols.

METHODS

Operant (fixed or progressive ratio schedule) and non-operant conditioning procedures were used. In addition, a choice analysis based on the "matching law" as well as a microstructural analysis of the intra-session pattern of self-administration was performed.

RESULTS

CB1-KO mice consume less sucrose under operant conditions or when using a two-bottle free choice procedure. Moreover, as revealed by additional behavioural analysis, CB1-KO mice exhibit a decreased sensitivity to the rewarding properties of sucrose. In agreement with this finding, the differences between WT and CB1-KO mice faded away when the palatability of sucrose was devaluated by adding quinine, but not when a non-caloric sweetener, saccharin, was available.

CONCLUSIONS

These results demonstrate a modulatory role of CB1 in the determination of the rewarding properties of sucrose and probably, as suggested by previous studies, other reinforcers.

Emerging aspects of pharmacotherapy for obesity and metabolic syndrome

Obesity is a multifactorial, chronic disorder that has reached epidemic proportions in most industrialized countries and is threatening to become a global epidemic. Obese patients are at higher risk from coronary artery disease, hypertension, hyperlipidemia, diabetes mellitus, cancers, cerebrovascular accidents, osteoarthritis, restrictive pulmonary disease, and sleep apnoea. In particular, visceral fat accumulation is usually accompanied by insulin resistance or type 2 diabetes mellitus, hypertension, hypertriglyceridemia, high uremic acid levels, low high density lipoprotein (HDL) cholesterol to define a variously named syndrome or metabolic syndrome. Metabolic syndrome is now considered a major cardiovascular risk factor in a large percentage of population in worldwide. Both obesity and metabolic syndrome are particularly challenging clinical conditions to treat because of their complex pathophysiological basis. Indeed, body weight represents the integration of many biological and environmental components and relationships among fat and glucose tolerance or blood pressure are not completely understood. Efforts to develop innovative anti-obesity drugs, with benefits for metabolic syndrome, have been recently intensified. In general two distinct strategies can be adopted: first, to reduce energy intake; second, to increase energy expenditure. Here we review some among the most promising avenues in these two fields of drug therapy of obesity and, consequently, of metabolic syndrome.

Mice with deficiency of G protein gamma3 are lean and have seizures

Emerging evidence suggests that the gamma subunit composition of an individual G protein contributes to the specificity of the hundreds of known receptor signaling pathways. Among the twelve gamma subtypes, gamma3 is abundantly and widely expressed in the brain. To identify specific functions and associations for gamma3, a gene-targeting approach was used to produce mice lacking the Gng3 gene (Gng3-/-). Confirming the efficacy and specificity of gene targeting, Gng3-/- mice show no detectable expression of the Gng3 gene, but expression of the divergently transcribed Bscl2 gene is not affected. Suggesting unique roles for gamma3 in the brain, Gng3-/- mice display increased susceptibility to seizures, reduced body weights, and decreased adiposity compared to their wild-type littermates. Predicting possible associations for gamma3, these phenotypic changes are associated with significant reductions in beta2 and alphai3 subunit levels in certain regions of the brain. The finding that the Gng3-/- mice and the previously reported Gng7-/- mice display distinct phenotypes and different alphabetagamma subunit associations supports the notion that even closely related gamma subtypes, such as gamma3 and gamma7, perform unique functions in the context of the organism.

The endocannabinoid system and its therapeutic exploitation

The term 'endocannabinoid' - originally coined in the mid-1990s after the discovery of membrane receptors for the psychoactive principle in Cannabis, Delta9-tetrahydrocannabinol and their endogenous ligands - now indicates a whole signalling system that comprises cannabinoid receptors, endogenous ligands and enzymes for ligand biosynthesis and inactivation. This system seems to be involved in an ever-increasing number of pathological conditions. With novel products already being aimed at the pharmaceutical market little more than a decade since the discovery of cannabinoid receptors, the endocannabinoid system seems to hold even more promise for the future development of therapeutic drugs. We explore the conditions under which the potential of targeting the endocannabinoid system might be realized in the years to come.

Stearoylethanolamide exerts anorexic effects in mice via downregulation of liver stearoyl‐coenzyme A desaturase‐1 mRNA expression

Given the recent demonstration that oleoylethanolamide (OEA), a cannabinoid receptor-inactive N-acylethanolamine, decreases food intake by activating the nuclear receptor PPARalpha (peroxisome proliferator-activated receptor alpha) in the periphery, we here evaluated the effects of both saturated and unsaturated C18 N-acylethanolamides (C18:0; C18:1; C18:2) in mice feeding behavior after overnight starvation. Our results show stearoylethanolamide (SEA, C18:0) exerts, unlike other unsaturated C18 homologs, a marked dose-dependent anorexic effect evident already at 2 h after its intraperitoneal administration. In addition, oral administration of SEA (25 mg/kg) was also effective in reducing food consumption, an effect ascribed to the molecule itself and not to its catabolites. Moreover, although the anorexic response to oral administered SEA was not associated with changes in the levels of various hematochemical parameters (e.g., glucose, cholesterol, triglycerides, leptin) nor in liver mRNA expression of peroxisome proliferator-activated receptors (PPARs) including PPARalpha, the anorexic effect of SEA was interestingly accompanied by a reduction in liver stearoyl-CoA desaturase-1 (SCD-1) mRNA expression. As SCD-1 has been recently proposed as a molecular target for the treatment of obesity, the novel observation provided here that SEA reduces food intake in mice in a structurally selective manner, in turn, correlated with downregulation of liver SCD-1 mRNA expression, has the potential of providing new insights on a class of lipid mediators with suitable properties for the pharmacological treatment of over-eating dysfunctions.

CB1 cannabinoid receptor knockout in mice leads to leanness, resistance to diet-induced obesity and enhanced leptin sensitivity

OBJECTIVE

There is growing evidence for an implication of the CB1 receptor subtype of the endocannabinoid system in the regulation of eating and fat deposition. To further define the physiological role of these receptors in the control of energy balance, we characterized the phenotype of CB1 receptor knockout (CB1(-/-)) mice maintained on an obesity-prone regimen or on a standard chow.

DESIGN

CB1(-/-) male mice were compared to wild-type animals (CB1(+/+) male mice) in two feeding paradigms: (1) with a standard laboratory regimen (3.5 kcal/g, 14.5% of energy as fat) and (2) on a free-choice paradigm consisting of offering both the standard laboratory chow and a high-fat diet (HFD) (4.9 kcal/g, 49% of energy as fat).

RESULTS

When maintained on the standard diet, CB1(-/-) mice are lean. At the age of 20 weeks, their body weight and adiposity are, respectively, 24 and 60% lower than that of CB1(+/+) mice. They are slightly hypophagic, but when expressed as percent of body weight, their relative energy intake is similar to that of the wild-type animals. Furthermore, inactivation of CB1 receptors reduces plasma insulin and leptin levels, and enhances the response to intracerebroventricular leptin injection. The free-choice paradigm shows that the preference for a high-fat highly palatable chow is slightly delayed in onset but maintained in CB1(-/-) mice. However, loading CB1(-/-) mice with this obesity-prone diet does not result in development of obesity. Knockout mice do not display hyperphagia or reduction of their relative energy intake in contrast to CB1(+/+) mice, and their feeding efficiency remains low. These data suggest an improved energetic metabolism with the high-fat regimen. Furthermore, the insulin resistance normally occurring in HFD-fed mice is not present in CB1(-/-) mice.

CONCLUSION

These results provide evidence that the stimulation of CB1 receptors is a key component in the development of diet-induced obesity, and that these receptors and their endogenous ligands are implicated not only in feeding control but also in peripheral metabolic regulations. The lack of effect of SR141716, a selective CB1 receptor antagonist, in CB1(-/-) mice further supports this hypothesis, as this compound was previously shown to display potent anti-obesity properties in diet-induced obese C57BL/6 mice.

Expression of cannabinoid CB1 receptors by vagal afferent neurons is inhibited by cholecystokinin

Both inhibitory (satiety) and stimulatory (orexigenic) factors from the gastrointestinal tract regulate food intake. In the case of the satiety hormone cholecystokinin (CCK), these effects are mediated via vagal afferent neurons. We now report that vagal afferent neurons expressing the CCK-1 receptor also express cannabinoid CB1 receptors. Retrograde tracing established that these neurons project to the stomach and duodenum. The expression of CB1 receptors determined by RT-PCR, immunohistochemistry and in situ hybridization in rat nodose ganglia was increased by withdrawal of food for > or =12 hr. After refeeding of fasted rats there was a rapid loss of CB1 receptor expression identified by immunohistochemistry and in situ hybridization. These effects were blocked by administration of the CCK-1 receptor antagonist lorglumide and mimicked by administration of CCK to fasted rats. Because CCK is a satiety factor that acts via the vagus nerve and CB1 agonists stimulate food intake, the data suggest a new mechanism modulating the effect on food intake of satiety signals from the gastrointestinal tract.

Obesity wars: molecular progress confronts an expanding epidemic

The worldwide prevalence of obesity is increasing at an alarming rate, with major adverse consequences for human health. This "obesity epidemic" is paralleled by a rapid and substantive increase in our understanding of molecular pathways and physiologic systems underlying the regulation of energy balance. While efforts to address the environmental factors that are responsible for the recent "epidemic" must continue, new molecular and physiologic insights into this system offer exciting possibilities for future development of successful therapies.

Voluntary exercise augments acute effects of CB1-receptor inverse agonist on body weight loss in obese and lean mice

Cannabinoid CB1 receptor (CB1R) inverse agonists reduce appetite and body weight (BW) gain in various species. Exercise is thought to be a natural reward process and the cannabinoid system is also believed to influence reward. We tested the hypothesis that voluntary exercise would augment the effects of AM251, a CB1R inverse agonist, on food intake (FI) and BW loss in murine genetic models of obesity. ob/ob, agouti yellow (A(y)), and lean C57BL/6J mice were treated via oral gavage with vehicle or AM251 (1, 3, or 10 mg/kg) 1 h before the dark cycle. The suppressive effects of 3 and 10 mg/kg AM251 on overnight FI, BW gain, and water intake (WI) were significant in ob/ob mice. In contrast, in A(y) mice, 10 mg/kg AM251 decreased FI and BW gain while it did not influence WI. Food consumption of ob/ob and A(y) mice, as evidenced by feeding frequency (FF) and feeding duration (FD), was reduced by AM251 for 4-6 h. AM251 at these doses had no impact on the appetitive behavior or BW gain of lean mice. After a 1-week wash-out period, mice were given running wheels in their home cages. With running wheel exercise, lean and obese mice exhibited increased sensitivity to AM251. Low voluntary wheel running activity of ob/ob mice precluded detection of combined effects of AM251 and exercise in this genetic model of obesity. Lean and agouti mice given AM251 combined with exercise lost a greater amount of BW than with AM251 alone. Our data suggest that voluntary exercise can enhance CB1R inverse agonist effects on appetite and BW loss in both lean and agouti obese mice.

Endocannabinoid Receptor Antagonists

Obesity has been described as a global epidemic. Its increasing prevalence is matched by growing costs, not only to the health of the individual, but also to the medical services required to treat a range of obesity-related diseases. In most instances, obesity is a product of progressively less energetic lifestyles and the over-consumption of readily available, palatable, and highly caloric foods. Past decades have seen massive investment in the search for effective anti-obesity therapies, so far with limited success. An important part of the process of developing new pharmacologic treatments for obesity lies in improving our understanding of the psychologic and physiologic processes that govern appetite and bodyweight regulation. Recent discoveries concerning the endogenous cannabinoids are beginning to give greater insight into these processes. Current research indicates that endocannabinoids may be key to the appetitive and consummatory aspects of eating motivation, possibly mediating the craving for and enjoyment of the most desired, most fattening foods. Additionally, endocannabinoids appear to modulate central and peripheral processes associated with fat and glucose metabolism. Selective cannabinoid receptor antagonists have been shown to suppress the motivation to eat, and preferentially reduce the consumption of palatable, energy-dense foods. Additionally, these agents act to reduce adiposity through metabolic mechanisms that are independent of changes in food intake. Given the current state of evidence, we conclude that the endocannabinoids represent an exciting target for new anti-obesity therapies.

Antidepressant-like and anorectic effects of the cannabinoid CB1 receptor inverse agonist AM251 in mice

Psychopathological disorders, and depression in particular, are strongly linked to eating attitude in obese patients. The identification of cannabinoid CB1 receptors (CB1Rs) in areas of the central nervous system (CNS) that have been implicated in regulation of mood and food intake suggests that these receptors may mediate such a behavioral link. The goal of this study was to evaluate CB1R modulation of antidepressant-like effects and food intake. For this purpose, 129/SVE and C57BL/6 male mice were acutely dosed intraperitoneally (i.p.) with the CB1R inverse agonist AM251 (3-30 mg/kg) and tested, respectively, in the tail-suspension test (TST) and in the forced-swim test (FST), which have been used widely as tests sensitive to antidepressant compounds. Like the antidepressant desipramine (DMI, 16 mg/kg), AM251 significantly reduced immobility at 10 mg/kg in the TST and at 1 and 10 mg/kg in the FST. Such a decrease of immobility was not accompanied by an increase in motor activity in the open field, suggesting that occupancy of CB1R by AM251 induced antidepressant-like effects. This was supported by two additional experiments. First, the co-administration of the CB1R agonist CP55940, at a dose that did not induce motor impairment or profound hypothermia (0.01 mg/kg), reversed effects of AM251 in the TST. Secondly, effects of AM251 in the FST were absent in CB1R knockout (KO) mice. In addition to an antidepressant-like effect, AM251 reduced fasting-induced hyperphagia over a comparable dose range. Taken together, these data suggest that regulation of mood and food intake might be obtained through inverse agonism of CB1R.

Cannabinoids: potential anticancer agents

Cannabinoids - the active components of Cannabis sativa and their derivatives - exert palliative effects in cancer patients by preventing nausea, vomiting and pain and by stimulating appetite. In addition, these compounds have been shown to inhibit the growth of tumour cells in culture and animal models by modulating key cell-signalling pathways. Cannabinoids are usually well tolerated, and do not produce the generalized toxic effects of conventional chemotherapies. So, could cannabinoids be used to develop new anticancer therapies?

Endocannabinoids and the regulation of body fat: the smoke is clearing

Endocannabinoids, endogenous ligands of cannabinoid receptor type 1 (CB1), have emerged as novel and important regulators of energy homeostasis. A report in this issue demonstrates reduced body weight, fat mass, and appetite in CB1-/- mice. Examination of the underlying mechanisms reveals a dual role for endocannabinoids as they affect both appetite and peripheral lipolysis.