Peripheral metabolic effects of endocannabinoids and cannabinoid receptor blockade

Δ9-Tetrahydrocannabinol Treatment Modifies Insulin Secretion in Pancreatic Islets from Prediabetic Mice Under Hypercaloric Diet

Background: The endocannabinoid system over-activation is associated with type-2 diabetes mellitus onset, involving physiological, metabolic, and genetic alterations in pancreatic islets. The use of Δ9-Tetrahydrocannabinol (THC) as treatment is still controversial since its effects and mechanisms on insulin secretion are unclear. The aim of this study was to evaluate the effects of THC treatment in pancreatic islets from prediabetic mice. Methods: Prediabetes was induced in mice by hypercaloric diet, and then treated with THC for 3 weeks. Blood glucose and body weight were determined, after behavior tests. Histological changes were evaluated in whole pancreas; in isolated islets we analyzed the effect of THC exposure in glucose-stimulated insulin secretion (GSIS), gene expression, intracellular cyclic adenosine monophosphate (cAMP), and cytosolic calcium changes. Results: THC treatment in prediabetic mice enhanced anxiety and antidepressive behavior without changes in food ingestion, decreased oral-glucose tolerance test, plasma insulin and weight, with small alterations on pancreatic histology. In isolated islets from healthy mice THC increased GSIS, cAMP, and CB1 receptor (CB1r) expression, meanwhile calcium release was diminished. Small changes were observed in islets from prediabetic mice. Conclusions: THC treatment improves some clinical parameters in prediabetic mice, however, in isolated islets, modifies GSIS, intracellular calcium and gene expression, suggesting specific effects related to diabetes evolution.

The endocannabinoid system in appetite regulation and treatment of obesity

The endocannabinoid system (ECS) is a complex cell-signaling system that is responsible for maintaining homeostasis by modulating various regulatory reactions in response to internal and environmental changes. The influence of ECS on appetite regulation has been a subject of much recent research, however, the full extent of its impact remains unknown. Current evidence links human obesity to ECS activation, increased endocannabinoid levels in both central and peripheral tissues, along with cannabinoid receptor type 1 (CBR1) up-regulation. These findings imply the potential pharmacological use of the ECS in the treatment of obesity. Here, we present various pathophysiological processes in obesity involving the ECS, highlighting different pharmacological options for modulating endocannabinoid activity to treat obesity. However, the potential of those pharmacological possibilities remains under investigation and requires further research.

Lipid endocannabinoids in energy metabolism, stress and developmental programming

The endocannabinoid system (ECS) regulates brain development and function, energy metabolism and stress in a sex-, age- and tissue-dependent manner. The ECS comprises mainly the bioactive lipid ligands anandamide (AEA) and 2-aracdonoylglycerol (2-AG), cannabinoid receptors 1 and 2 (CB1 and CB2), and several metabolizing enzymes. The endocannabinoid tonus is increased in obesity, stimulating food intake and a preference for fat, reward, and lipid accumulation in peripheral tissues, as well as favoring a positive energy balance. Energy balance and stress responses share adaptive mechanisms regulated by the ECS that seem to underlie the complex relationship between feeding and emotional behavior. The ECS is also a key regulator of development. Environmental insults (diet, toxicants, and stress) in critical periods of developmental plasticity, such as gestation, lactation and adolescence, alter the ECS and may predispose individuals to the development of chronic diseases and behavioral changes in the long term. This review is focused on the ECS and the developmental origins of health and disease (DOHaD).

Metabolic and inflammatory functions of cannabinoid receptor type 1 are differentially modulated by adiponectin

BACKGROUND

Antagonists of cannabinoid type 1 receptor (CB1) have been shown to promote body weight loss and improve insulin sensitivity. Cannabinoids decrease adiponectin, and CB1 blocker increase adiponectin. However, the mediators of CB1 actions are not well defined.

AIM

To investigate whether the beneficial effects of CB1 inhibition are, at least in part, mediated by adiponectin.

METHODS

We compared metabolic and inflammatory phenotypes of wild-type (WT) mice, CB1-null (CB1^-/-) and CB1/adiponectin double-knockout (DKO) mice. We assessed the insulin sensitivity using insulin tolerance test and glucose tolerance test, and inflammation using flow cytometry analysis of macrophages.

RESULTS

CB1^-/- mice exhibited significantly reduced body weight and fat mass when compared to WT mice. While no significance was found in total daily food intake and locomotor activity, CB1^-/- mice showed increased energy expenditure, enhanced thermogenesis in brown adipose tissue (BAT), and improved insulin sensitivity compared to WT mice. DKO showed no difference in body weight, adiposity, nor insulin sensitivity; only showed a modestly elevated thermogenesis in BAT compared to CB1^-/- mice. The metabolic phenotype of DKO is largely similar to CB1^-/- mice, suggesting that adiponectin is not a key mediator of the metabolic effects of CB1. Interestingly, CB1^-/- mice showed reduced pro-inflammatory macrophage polarization in both peritoneal macrophages and adipose tissue macrophages compared to WT mice; in contrast, DKO mice exhibited increased pro-inflammatory macrophage polarization in these macrophages compared to CB1^-/- mice, suggesting that adiponectin is an important mediator of the inflammatory effect of CB1.

CONCLUSION

Our findings reveal that CB1 functions through both adiponectin-dependent and adiponectin-independent mechanisms: CB1 regulates energy metabolism in an adiponectin-independent manner, and inflammation in an adiponectin-dependent manner. The differential effects of adiponectin on CB1-mediated metabolic and inflammatory functions should be taken into consideration in CB1 antagonist utilization.

What Role Does the Endocannabinoid System Play in the Pathogenesis of Obesity?

The endocannabinoid system (ECS) is an endogenous signaling system formed by specific receptors (cannabinoid type 1 and type 2 (CB₁ and CB₂)), their endogenous ligands (endocannabinoids), and enzymes involved in their synthesis and degradation. The ECS, centrally and peripherally, is involved in various physiological processes, including regulation of energy balance, promotion of metabolic process, food intake, weight gain, promotion of fat accumulation in adipocytes, and regulation of body homeostasis; thus, its overactivity may be related to obesity. In this review, we try to explain the role of the ECS and the impact of genetic factors on endocannabinoid system modulation in the pathogenesis of obesity, which is a global and civilizational problem affecting the entire world population regardless of age. We also emphasize that the search for potential new targets for health assessment, treatment, and the development of possible therapies in obesity is of great importance.

Meat Protein in High-Fat Diet Induces Adipogensis and Dyslipidemia by Altering Gut Microbiota and Endocannabinoid Dysregulation in the Adipose Tissue of Mice

Endocannabinoids modulate insulin and adipokine expression in adipocytes through cannabinoid receptors and their levels are elevated during hyperglycemia and obesity, but little is known about how diets affect them. We assessed the effects of dietary casein, chicken, beef, and pork proteins in a high-fat diet mode, on endocannabinoids, adipogenesis, and biomarkers associated with dyslipemdia. A high-fat beef or chicken diet upregulated cannabinoid 1 receptor, N-acyl phosphatidylethanolamine-selective phospholipase-D and diacylglycerol lipase α in adipose tissue and reduced the immunoreactivity of mitochondrial uncoupling protein 1 in brown adipose tissue. In addition, the high-fat diets with beef and chicken protein had a significant impact on adipocyte differentiation and mitochondrial biogenesis in obese mice. A 16S rRNA gene sequencing indicated that high-fat diets, regardless of the protein source, significantly enhanced the ratio of Firmicutes to Bacteroidetes in colon. Meat proteins in a high-fat diet significantly decreased the relative abundances of Akkermansia and Bifidobacteria but enhanced the lipopolysaccharides level in the serum, which promoted the adipogenesis process by causing dysregulation in the endocannabinoid receptors. Consumption of meat protein with high-fat-induced adiposity, visceral obesity, and dyslipidemia reduced the thermogenesis and had a distinctive effect on the mitochondrial biogenesis compared with casein protein.

Acute and subacute antidiabetic studies of ENP-9, a new 1,5-diarylpyrazole derivative

OBJECTIVES

To explore the antihyperglycaemic and antidiabetic effects and to determine the acute toxicity of 5-(4-chlorophenyl)-1-(2,4-dichloro-phenyl)-4-methyl-N-(piperidin-1-yl)-1H-pyrazole-3-carboxamide (ENP-9).

METHODS

The antihyperglycaemic effect of ENP-9 (50 mg/kg) was determined by oral glucose tolerance test (OGTT). Also, the acute (16, 50 and 160 mg/kg) and subacute (50 mg/kg/day for 10 days) antidiabetic effects of ENP-9 were determined. After subacute treatment, blood samples were analysed to determine glucose and lipid profiles. Also, an acute toxicity determination of ENP-9 was conducted followed the OECD recommendation. Molecular docking was performed using AutoDock 4.2.6 at human cannabinoid receptor 1 (PDB code 5TGZ).

KEY FINDINGS

Acute Administration of ENP-9 showed significant antidiabetic effect and decreased the maximum OGTT peak, compared to the control group (P < 0.05). Moreover, the 10 days treatment induced a decrease in plasma glucose levels, being significant at the end of the experiments (P < 0.05); however, triacylglycerols and cholesterol were not modified. Finally, LD₅₀ of ENP-9 was estimated to be greater than 2000 mg/kg. Molecular docking suggests that ENP-9 may act as rimonabant does.

CONCLUSIONS

ENP-9 showed significant antihyperglycaemic and antidiabetic properties and also was demonstrated to be safety in the studied doses, which might allow future studies for its potential development as antidiabetic agent.

Regulation of Adipose Tissue Metabolism by the Endocannabinoid System

White adipose tissue (WAT) stores excess energy as triglycerides, and brown adipose tissue (BAT) is specialized in dissipating energy as heat. The endocannabinoid system (ECS) is involved in a broad range of physiological processes and is increasingly recognized as a key player in adipose tissue metabolism. High ECS tonus in the fed state is associated with a disadvantageous metabolic phenotype, and this has led to a search for pharmacological strategies to inhibit the ECS. In this review we present recent developments that cast light on the regulation of adipose tissue metabolism by the ECS, and we discuss novel treatment options including the modulation of endocannabinoid synthesis and breakdown enzymes.

Targeting the endocannabinoid/CB1 receptor system for treating obesity in Prader-Willi syndrome

Objective

Extreme obesity is a core phenotypic feature of Prader–Willi syndrome (PWS). Among numerous metabolic regulators, the endocannabinoid (eCB) system is critically involved in controlling feeding, body weight, and energy metabolism, and a globally acting cannabinoid-1 receptor (CB₁R) blockade reverses obesity both in animals and humans. The first-in-class CB₁R antagonist rimonabant proved effective in inducing weight loss in adults with PWS. However, it is no longer available for clinical use because of its centrally mediated, neuropsychiatric, adverse effects.

Methods

We studied eCB ‘tone’ in individuals with PWS and in the Magel2-null mouse model that recapitulates the major metabolic phenotypes of PWS and determined the efficacy of a peripherally restricted CB₁R antagonist, JD5037 in treating obesity in these mice.

Results

Individuals with PWS had elevated circulating levels of 2-arachidonoylglycerol and its endogenous precursor and breakdown ligand, arachidonic acid. Increased hypothalamic eCB ‘tone’, manifested by increased eCBs and upregulated CB₁R, was associated with increased fat mass, reduced energy expenditure, and decreased voluntary activity in Magel2-null mice. Daily chronic treatment of obese Magel2-null mice and their littermate wild-type controls with JD5037 (3 mg/kg/d for 28 days) reduced body weight, reversed hyperphagia, and improved metabolic parameters related to their obese phenotype.

Conclusions

Dysregulation of the eCB/CB₁R system may contribute to hyperphagia and obesity in Magel2-null mice and in individuals with PWS. Our results demonstrate that treatment with peripherally restricted CB₁R antagonists may be an effective strategy for the management of severe obesity in PWS.

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Circulating levels of endocannabinoids are increased in individuals with PWS.

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Magel2 is a negative regulator of hypothalamic endocannabinoid ‘tone’.

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Peripherally-restricted CB1 receptor blockade reverses obesity in Magel2-null mice.

Deletion of G-protein-coupled receptor 55 promotes obesity by reducing physical activity

BACKGROUND/OBJECTIVES

Cannabinoid receptor 1 (CB1) is the best-characterized cannabinoid receptor, and CB1 antagonists are used in clinical trials to treat obesity. Because of the wide range of CB1 functions, the side effects of CB1 antagonists pose serious concerns. G-protein-coupled receptor 55 (GPR55) is an atypical cannabinoid receptor, and its pharmacology and functions are distinct from CB1. GPR55 regulates neuropathic pain, gut, bone, immune functions and motor coordination. GPR55 is expressed in various brain regions and peripheral tissues. However, the roles of GPR55 in energy and glucose homeostasis are unknown. Here we have investigated the roles of GPR55 in energy balance and insulin sensitivity using GPR55-null mice (GPR55(-/-)).

METHODS

Body composition of the mice was measured by EchoMRI. Food intake, feeding behavior, energy expenditure and physical activity of GPR55(-/-) mice were determined by indirect calorimetry. Muscle function was assessed by forced treadmill running test. Insulin sensitivity was evaluated by glucose and insulin tolerance tests. Adipose inflammation was assessed by flow cytometry analysis of adipose tissue macrophages. The expression of inflammatory markers in adipose tissues and orexigenic/anorexigenic peptides in the hypothalamus was also analyzed by real-time PCR.

RESULTS

GPR55(-/-) mice had normal total energy intake and feeding pattern (i.e., no changes in meal size, meal number or feeding frequency). Intriguingly, whereas adult GPR55(-/-) mice only showed a modest increase in overall body weight, they exhibited significantly increased fat mass and insulin resistance. The spontaneous locomotor activity of GPR55(-/-) mice was dramatically decreased, whereas resting metabolic rate and non-shivering thermogenesis were unchanged. Moreover, GPR55(-/-) mice exhibited significantly decreased voluntary physical activity, showing reduced running distance on the running wheels, whereas muscle function appeared to be normal.

CONCLUSIONS

GPR55 has an important role in energy homeostasis. GPR55 ablation increases adiposity and insulin resistance by selectively decreasing physical activity, but not by altering feeding behavior as CB1.

Influence of dietary fat intake on the endocannabinoid system in lean and obese subjects

OBJECTIVE

Endocannabinoid system (ECS) activation promotes obesity-associated metabolic disease. Increased dietary fat intake increases blood endocannabinoids and alters adipose and skeletal muscle ECS gene expression in human.

METHODS

Two weeks isocaloric low- (LFD) and high-fat diets (HFD) in obese (n = 12) and normal-weight (n = 17) subjects in a randomized cross-over study were compared. Blood endocannabinoids were measured in the fasting condition and after food intake using mass spectrometry. Adipose and skeletal muscle gene expression was determined using real-time RT-PCR.

RESULTS

Baseline fasting plasma endocannabinoids were similar with both diets. Anandamide decreased similarly with high- or low-fat test meals in both groups. Baseline arachidonoylglycerol plasma concentrations were similar between groups and diets, and unresponsive to eating. In subcutaneous adipose tissue, DAGL-α mRNA was upregulated and fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) mRNAs were down-regulated in obese subjects, but the diets had no influence. In contrast, the HFD produced pronounced reductions in skeletal muscle CB1-R and MAGL mRNA expression, whereas obesity did not affect muscular gene expression.

CONCLUSIONS

Weight-neutral changes in dietary fat intake cannot explain excessive endocannabinoid availability in human obesity. Obesity and dietary fat intake affect ECS gene expression in a tissue-specific manner.

CB1 blockade potentiates down-regulation of lipogenic gene expression in perirenal adipose tissue in high carbohydrate diet-induced obesity

De novo lipogenesis and hypercaloric diets are thought to contribute to increased fat mass, particularly in abdominal fat depots. CB₁ is highly expressed in adipose tissue, and CB₁-mediated signalling is associated with stimulation of lipogenesis and diet-induced obesity, though its contribution to increasing fat deposition in adipose tissue is controversial. Lipogenesis is regulated by transcription factors such as liver X receptor (LXR), sterol-response element binding protein (SREBP) and carbohydrate-responsive-element-binding protein (ChREBP). We evaluated the role of CB₁ in the gene expression of these factors and their target genes in relation to lipogenesis in the perirenal adipose tissue (PrAT) of rats fed a high-carbohydrate diet (HCHD) or a high-fat diet (HFD). Both obesity models showed an up-regulated gene expression of CB₁ and Lxrα in this adipose pad. The Srebf-1 and ChREBP gene expressions were down-regulated in HFD but not in HCHD. The expression of their target genes encoding for lipogenic enzymes showed a decrease in diet-induced obesity and was particularly dramatic in HFD. In HCHD, CB₁ blockade by AM251 reduced the Srebf-1 and ChREBP expression and totally abrogated the remnant gene expression of their target lipogenic enzymes. The phosphorylated form of the extracellular signal-regulated kinase (ERK-p), which participates in the CB₁-mediated signalling pathway, was markedly present in the PrAT of obese rats. ERK-p was drastically repressed by AM251 indicating that CB₁ is actually functional in PrAT of obese animals, though its activation loses the ability to stimulate lipogenesis in PrAT of obese rats. Even so, the remnant expression levels of lipogenic transcription factors found in HCHD-fed rats are still dependent on CB₁ activity. Hence, in HCHD-induced obesity, CB₁ blockade may help to further potentiate the reduction of lipogenesis in PrAT by means of inducing down-regulation of the ChREBP and Srebf-1 gene expression, and consequently in the expression of lipogenic enzymes.

NESS038C6, a novel selective CB1 antagonist agent with anti-obesity activity and improved molecular profile

The present work aims to study the effects induced by a chronic treatment with a novel CB1 antagonist (NESS038C6) in C57BL/6N diet-induced obesity (DIO) mice. Mice treated with NESS038C6 and fed with a fat diet (NESS038C6 FD) were compared with the following three reference experimental groups: DIO mice fed with the same fat diet used for NESS038C6 and treated with vehicle or the reference CB1 antagonist/inverse agonist rimonabant, "VH FD" and "SR141716 FD", respectively; DIO mice treated with vehicle and switched to a normal diet (VH ND). NESS038C6 chronic treatment (30 mg/kg/day for 31 days) determined a significant reduction in DIO mice weight relative to that of VH FD. The entity of the effect was comparable to that detected in both SR141716 FD and VH ND groups. Moreover, if compared to VH FD, NESS038C6 FD evidenced: (i) improvement of cardiovascular risk factors; (ii) significant decrease in adipose tissue leptin expression; (iii) increase in mRNA expression of hypothalamic orexigenic peptides and a decrease of anorexigenic peptides; (iv) expression increase of metabolic enzymes and peroxisome proliferator-activated receptor-α in the liver; (v) normalization of monoaminergic transporters and neurotrophic expression in mesolimbic area. However, in contrast to the case of rimonabant, the novel CB1 antagonist improved the disrupted expression profile of genes linked to the hunger-satiety circuit, without altering monoaminergic transmission. In conclusion, the novel CB1 antagonist compound NESS038C6 may represent a useful candidate agent for the treatment of obesity and its metabolic complications, without or with reduced side effects relative to those instead observed with rimonabant.

Central and peripheral cannabinoid receptors as therapeutic targets in the control of food intake and body weight

The endocannabinoid system consists of lipid-derived agonists that activate cannabinoid (CB) receptors. CB receptor agonists, namely, the phytocannabinoid Δ(9)-THC and the endocannabinoid anandamide, increase hunger sensation and food intake. These discoveries led to the clinical use of Δ(9)-THC derivatives for the treatment of cancer and HIV-related nausea and cachexia. Animal studies clarified the important role of CB1 receptors in the hypothalamus and in the limbic system in mediating orexigenic effects. In parallel, data on CB1-specific blockade either by drugs or by genetic ablation further demonstrated that CB1 inhibition protects against weight gain induced by high-fat feeding and reduces body weight in obese animals and humans. The mechanisms of weight reduction by CB1 blockade are complex: they comprise interactions with several orexigenic and anorexigenic neuropeptides and hormones, regulation of sympathetic activity, influences on mitochondrial function, and on lipogenesis. Although these mechanisms appear to be mainly mediated by the CNS, weight loss also occurs when drugs that do not reach CNS concentrations sufficient to inhibit CB1 signaling are used. The development of peripherally restricted CB1 inverse agonists and antagonists opened new routes in CB1 pharmacology because centrally acting CB1 inverse agonists, e.g., rimonabant and taranabant, exerted unacceptable side effects that precluded their further development and application as weight loss drugs. Tissue and circulating endocannabinoid concentrations are often increased in animal models of obesity and in obese humans, especially those with visceral fat accumulation. Thus, further research on CB1 inhibition is still promising to treat human obesity.

Role of genetic variation in the cannabinoid type 1 receptor gene (CNR1) in the pathophysiology of human obesity

AIMS

The endocannabinoid system may contribute to the association of visceral fat accumulation with metabolic diseases. Here we investigated the effects of genetic variation in the cannabinoid type 1 receptor gene (CNR1) on its mRNA expression in adipose tissue from visceral and subcutaneous depots and on the development of obesity.

MATERIALS & METHODS

CNR1 was sequenced in 48 nonrelated German Caucasians to detect genetic variation. Five representative variants including HapMap tagging SNPs (rs12720071, rs806368, rs806370, rs1049353 and rs806369) were genotyped for subsequent association studies in two independent cohorts (total n = 2774) with detailed metabolic testing: subjects from the Leipzig Study (n = 1857) and a self-contained population of Sorbs from Germany (n = 917).

RESULTS

In a case-control study of lean (BMI <25 kg/m(2)) versus obese (BMI >30 kg/m(2)) subjects, rs806368 was found to be nominally associated with obesity in the Sorbian cohort (adjusted p < 0.05), but not in the Leipzig cohort. Also, several SNPs (rs806368, rs806370 and rs12720071) were nominally associated with serum leptin levels (p < 0.05 after adjusting for age, sex and BMI). However, none of these associations remained significant after accounting for multiple testing. Furthermore, none of the SNPs were related to CNR1 mRNA expression in visceral and subcutaneous fat.

CONCLUSION

The data suggest that common genetic variation in the CNR1 gene does not influence mRNA expression in adipose tissue nor does it play a significant role in the pathophysiology of obesity in German and Sorbian populations.

Psychosis following anti-obesity treatment with rimonabant

BACKGROUND

In this report, we present the case of a patient with a relapse of schizophrenia following an episode of depression and increased anxiety after antiobesity treatment with rimonabant, a cannabinoid type 1 receptor antagonist.

CASE REPORT

After 4 weeks of treatment the patient developed psychiatric symptoms, i.e. depressed mood and elevated anxiety. Four months after the discontinuation of rimonabant, the patient presented with psychotic symptoms fulfilling ICD-10 criteria of paranoid schizophrenia. Antipsychotic treatment with quetiapine was initialized. A stable recovery took further 4 weeks in which combined treatment with quetiapine and ziprasidone was given.

CONCLUSION

The course of the illness suggests that the continuous affective symptoms, which were most likely a side effect of rimonabant, may have triggered the psychosis analogous to the stress-diathesis model of schizophrenia. As a consequence, rimonabant may not be the first choice in obese patients with a history of schizophrenia due to a potentially increased risk of a relapse via an indirect mechanism.