Cannabinoid receptor 1 (CB1) antagonism enhances glucose utilisation and activates brown adipose tissue in diet-induced obese mice

Characterization of the effects of cannabinoid receptor deletion on energy metabolism in female C57BL mice

Background

Despite the evidence that energy balance is regulated differently in females and that the endocannabinoid system is sexually dimorphic, previous studies on the endocannabinoid system and energy balance predominantly used male models. Here, we characterize the effects of cannabinoid receptor deletion on body weight gain and glucose metabolism in female C57BL mice.

Methods

Female mice lacking the cannabinoid-1 receptor (CB1R-/-), cannabinoid-2 receptor (CB2R-/-), or both receptors (CB1R-/-/CB2R-/-) and wild-type (WT) mice were fed with a low (LFD; 10% of calories from fat) or high-fat diet (HFD; 45% of calories from fat) for six weeks.

Results

Female WT mice fed with HFD gained significantly more weight than WT mice fed with LFD (p < 0.001). Similar pattern was observed for CB2/- mice fed with HFD compared to CB2R-/- mice fed with LFD (p < 0.001), but not for CB1R-/- fed with HFD vs. LFD (p = 0.22) or CB1R-/-/CB2R-/- fed with HFD vs. LFD (p = 0.96). Comparing the 4 groups on LFD, weight gain of CB1R-/- mice was greater than all other genotypes (p < 0.05). When fed with HFD, the deletion of CB1R alone in females did not attenuate weight gain compared to WT mice (p = 0.72). Female CB1R-/-/CB2R-/- mice gained less weight than WT mice when fed with HFD (p = 0.007) despite similar food intake and locomotor activity, potentially owing to enhanced thermogenesis in the white adipose tissue. No significant difference in weight gain was observed for female CB2R-/- and WT mice on LFD or HFD. Fasting glucose, however, was higher in CB2R-/- mice fed with LFD than all other groups (p < 0.05).

Conclusion

The effects of cannabinoid receptor deletion on glucose metabolism in female mice were similar to previously published findings on male mice, yet the effects on body weight gain and thermogenesis were attenuated in CB1R-/- mice.

Sympathetic innervation of interscapular brown adipose tissue is not a predominant mediator of oxytocin-elicited reductions of body weight and adiposity in male diet-induced obese mice

Previous studies indicate that CNS administration of oxytocin (OT) reduces body weight in high fat diet-induced obese (DIO) rodents by reducing food intake and increasing energy expenditure (EE). We recently demonstrated that hindbrain (fourth ventricular [4V]) administration of OT elicits weight loss and elevates interscapular brown adipose tissue temperature (T IBAT , a surrogate measure of increased EE) in DIO mice. What remains unclear is whether OT-elicited weight loss requires increased sympathetic nervous system (SNS) outflow to IBAT. We hypothesized that OT-induced stimulation of SNS outflow to IBAT contributes to its ability to activate BAT and elicit weight loss in DIO mice. To test this hypothesis, we determined the effect of disrupting SNS activation of IBAT on the ability of 4V OT administration to increase T IBAT and elicit weight loss in DIO mice. We first determined whether bilateral surgical SNS denervation to IBAT was successful as noted by ≥ 60% reduction in IBAT norepinephrine (NE) content in DIO mice. NE content was selectively reduced in IBAT at 1-, 6- and 7-weeks post-denervation by 95.9±2.0, 77.4±12.7 and 93.6±4.6% ( P <0.05), respectively and was unchanged in inguinal white adipose tissue, pancreas or liver. We subsequently measured the effects of acute 4V OT (1, 5 µg ≈ 0.99, 4.96 nmol) on T IBAT in DIO mice following sham or bilateral surgical SNS denervation to IBAT. We found that the high dose of 4V OT (5 µg ≈ 4.96 nmol) elevated T IBAT similarly in sham mice as in denervated mice. We subsequently measured the effects of chronic 4V OT (16 nmol/day over 29 days) or vehicle infusions on body weight, adiposity and food intake in DIO mice following sham or bilateral surgical denervation of IBAT. Chronic 4V OT reduced body weight by 5.7±2.23% and 6.6±1.4% in sham and denervated mice ( P <0.05), respectively, and this effect was similar between groups ( P =NS). OT produced corresponding reductions in whole body fat mass ( P <0.05). Together, these findings support the hypothesis that sympathetic innervation of IBAT is not necessary for OT-elicited increases in BAT thermogenesis and reductions of body weight and adiposity in male DIO mice.

Hemp Seed Oil Inhibits the Adipogenicity of the Differentiation-Induced Human Mesenchymal Stem Cells through Suppressing the Cannabinoid Type 1 (CB1)

Central and peripheral mechanisms of the endocannabinoid system (ECS) favor energy intake and storage. The ECS, especially cannabidiol (CBD) receptors, controls adipocyte differentiation (hyperplasia) and lipid accumulation (hypertrophy) in adipose tissue. In white adipose tissue, cannabidiol receptor 1 (CB1) stimulation increases lipogenesis and inhibits lipolysis; in brown adipose tissue, it decreases mitochondrial thermogenesis and biogenesis. This study compared the availability of phytocannabinoids [CBD and Δ9-tetrahydrocannabinol (THC)] and polyunsaturated fatty acids [omega 3 (ω3) and omega 6 (ω6)] in different hemp seed oils (HSO). The study also examined the effect of HSO on adipocyte lipid accumulation by suppressing cannabinoid receptors in adipogenesis-stimulated human mesenchymal stem cells (hMSCs). Most importantly, Oil-Red-O' and Nile red tests showed that HSO induced adipogenic hMSC differentiation without differentiation agents. Additionally, HSO-treated cells showed increased peroxisome proliferator-activated receptor gamma (PPARγ) mRNA expression compared to controls (hMSC). HSO reduced PPARγ mRNA expression after differentiation media (DM) treatment. After treatment with HSO, DM-hMSCs had significantly lower CB1 mRNA and protein expressions than normal hMSCs. HSO treatment also decreased transient receptor potential vanilloid 1 (TRPV1), fatty acid amide hydrolase (FAAH), and monoacylglycerol lipase (MGL) mRNAs in hMSC and DM-hMSCs. HSO treatment significantly decreased CB1, CB2, TRPV1, and G-protein-coupled receptor 55 (GPCR55) protein levels in DM-hMSC compared to hMSC in western blot analysis. In this study, HSO initiated adipogenic differentiation in hMSC without DM, but it suppressed CB1 gene and protein expression, potentially decreasing adipocyte lipid accumulation and lipogenic enzymes.

Pharmacological modulation of adaptive thermogenesis: new clues for obesity management?

BACKGROUND

Adaptive thermogenesis represents the main mechanism through which the body generates heat in response to external stimuli, a phenomenon that includes shivering and non-shivering thermogenesis. The non-shivering thermogenesis is mainly exploited by adipose tissue characterized by a brown aspect, which specializes in energy dissipation. A decreased amount of brown adipose tissue has been observed in ageing and chronic illnesses such as obesity, a worldwide health problem characterized by dysfunctional adipose tissue expansion and associated cardiometabolic complications. In the last decades, the discovery of a trans-differentiation mechanism ("browning") within white adipose tissue depots, leading to the generation of brown-like cells, allowed to explore new natural and synthetic compounds able to favour this process and thus enhance thermogenesis with the aim of counteracting obesity. Based on recent findings, brown adipose tissue-activating agents could represent another option in addition to appetite inhibitors and inhibitors of nutrient absorption for obesity treatment.

PURPOSE

This review investigates the main molecules involved in the physiological (e.g. incretin hormones) and pharmacological (e.g. β3-adrenergic receptors agonists, thyroid receptor agonists, farnesoid X receptor agonists, glucagon-like peptide-1, and glucagon receptor agonists) modulation of adaptive thermogenesis and the signalling mechanisms involved.

Changes in plasma endocannabinoids concentrations correlate with 18F-FDG PET/MR uptake in brown adipocytes in humans

Introduction: Recent data suggest a possible role of endocannabinoids in the regulation of brown adipose tissue (BAT) activity. Those findings indicate potential treatment options for obesity. The aim of this study was to evaluate the relationship between plasma endocannabinoids concentrations and the presence of BAT in humans. Methods: The study group consisted of 25 subjects divided into two groups: BAT positive BAT(+), (n = 17, median age = 25 years) and BAT negative BAT(-), (n = 8, median age = 28 years). BAT was estimated using 18F-FDG PET/MR after 2 h of cold exposure. The level of plasma endocannabinoids was assessed at baseline, 60 min and 120 min of cold exposure. Results: In both groups, BAT(+) and BAT(-), during the cooling, we observed a decrease of the same endocannabinoids: arachidonoylethanolamide (AEA), eicosapentaenoyl ethanolamide (EPEA) and oleoyl ethanolamide (OEA) with a much more profound decline in BAT(+) subjects. Statistically significant fall of PEA (palmitoylethanolamide) and SEA (stearoylethanolamide) concentrations after 60 min (FC = 0.7, p = 0.007 and FC = 0.8, p = 0.03, respectively) and 120 min (FC = 0.81, p = 0.004, and FC = 0.9, p = 0.01, respectively) of cooling was observed only in individuals with BAT. Conclusion: We noticed the profound decline of endocannabinoids concentrations in subjects with increased 18F-FDG PET/MR uptake in BAT. Identification of a new molecules related to BAT activity may create a new target for obesity treatment.

Remodeling of Adipose Tissues by Fatty Acids: Mechanistic Update on Browning and Thermogenesis by n-3 Polyunsaturated Fatty Acids

Enhancing thermogenesis by increasing the amount and activity of brown and brite adipocytes is a potential therapeutic target for obesity and its associated diseases. Diet plays important roles in energy metabolism and a myriad of dietary components including lipids are known to regulate thermogenesis through recruitment and activation of brown and brite adipocytes. Depending on types of fatty acids (FAs), the major constituent in lipids, their health benefits differ. Long-chain polyunsaturated FAs (PUFAs), especially n-3 PUFAs remodel adipose tissues in a healthier manner with reduced inflammation and enhanced thermogenesis, while saturated FAs exhibit contrasting effects. Lipid mediators derived from FAs act as autocrine/paracrine as well as endocrine factors to regulate thermogenesis. We discuss lipid mediators that may contribute to the differential effects of FAs on adipose tissue remodeling and hence, cardiometabolic diseases. We also discuss current understanding of molecular and cellular mechanisms through which n-3 PUFAs enhance thermogenesis. Elucidating molecular details of beneficial effects of n-3 PUFAs on thermogenesis is expected to provide information that can be used for development of novel therapeutics for obesity and its associated diseases.

CB1 Ligand AM251 Induces Weight Loss and Fat Reduction in Addition to Increased Systemic Inflammation in Diet-Induced Obesity

Diet-induced obesity (DIO) reduces fatty acid oxidation in skeletal muscle and decreases circulating levels of adiponectin. Endocannabinoid signaling is overactive in obesity, with some effects abated by antagonism of cannabinoid receptor 1 (CB₁). This research aimed to determine if treatment with the global CB₁ antagonist/inverse agonist, AM251, in high-fat diet (HFD) fed rats influenced adiponectin signaling in skeletal muscle and a “browning” of white adipose tissue (WAT) defined by UCP1 expression levels. Male Sprague Dawley rats consumed an HFD (21% fat) for 9 weeks before receiving daily intraperitoneal injections with vehicle or AM251 (3 mg/kg) for 6 weeks. mRNA expression of genes involved in metabolic functions were measured in skeletal muscle and adipose tissue, and blood was harvested for the measurement of hormones and cytokines. Muscle citrate synthase activity was also measured. AM251 treatment decreased fat pad weight (epididymal, peri-renal, brown), and plasma levels of leptin, glucagon, ghrelin, and GLP-1, and increased PAI-1 along with a range of pro-inflammatory and anti-inflammatory cytokines; however, AM251 did not alter plasma adiponectin levels, skeletal muscle citrate synthase activity or mRNA expression of the genes measured in muscle. AM251 treatment had no effect on white fat UCP1 expression levels. AM251 decreased fat pad mass, altered plasma hormone levels, but did not induce browning of WAT defined by UCP1 mRNA levels or alter gene expression in muscle treated acutely with adiponectin, demonstrating the complexity of the endocannabinoid system and metabolism. The CB₁ ligand AM251 increased systemic inflammation suggesting limitations on its use in metabolic disorders.

Yin and yang of cannabinoid CB1 receptor: CB1 deletion in immune cells causes exacerbation while deletion in non-immune cells attenuates obesity

While blockade of cannabinoid receptor 1 (CB1) has been shown to attenuate diet-induced obesity (DIO), its relative role in different cell types has not been tested. The current study investigated the role of CB1 in immune vs non-immune cells during DIO by generating radiation-induced bone marrow chimeric mice that expressed functional CB1 in all cells except the immune cells or expressed CB1 only in immune cells. CB1^−/− recipient hosts were resistant to DIO, indicating that CB1 in non-immune cells is necessary for induction of DIO. Interestingly, chimeras with CB1^−/− in immune cells showed exacerbation in DIO combined with infiltration of bone-marrow-derived macrophages to the brain and visceral adipose tissue, elevated food intake, and increased glucose intolerance. These results demonstrate the opposing role of CB1 in hematopoietic versus non-hematopoietic cells during DIO and suggests that targeting immune CB1 receptors provides a new pathway to ameliorate obesity and related metabolic disorders.

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Cannabinoid Receptor 1 (CB1), and not CB2, regulates diet-induced obesity (DIO)

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CB1 deficiency in non-immune cell types promotes DIO resistance

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CB1 deficiency in immune cells exacerbates DIO disease phenotype

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CB1 activation in immune cells is a potential therapeutic target for DIO attenuation

Expression of Functional Cannabinoid Type-1 (CB1) Receptor in Mitochondria of White Adipocytes

Via activation of the cannabinoid type-1 (CB₁) receptor, endogenous and exogenous cannabinoids modulate important biochemical and cellular processes in adipocytes. Several pieces of evidence suggest that alterations of mitochondrial physiology might be a possible mechanism underlying cannabinoids' effects on adipocyte biology. Many reports suggest the presence of CB₁ receptor mRNA in both white and brown adipose tissue, but the detailed subcellular localization of CB₁ protein in adipose cells has so far been scarcely addressed. In this study, we show the presence of the functional CB₁ receptor at different subcellular locations of adipocytes from epididymal white adipose tissue (eWAT) depots. We observed that CB₁ is located at different subcellular levels, including the plasma membrane and in close association with mitochondria (mtCB₁). Functional analysis in tissue homogenates and isolated mitochondria allowed us to reveal that cannabinoids negatively regulate complex-I-dependent oxygen consumption in eWAT. This effect requires mtCB₁ activation and consequent regulation of the intramitochondrial cAMP-PKA pathway. Thus, CB₁ receptors are functionally present at the mitochondrial level in eWAT adipocytes, adding another possible mechanism for peripheral regulation of energy metabolism.

Molecular networks underlying cannabinoid signaling in skeletal muscle plasticity

The cannabinoid system is ubiquitously present and is classically considered to engage in neural and immunity processes. Yet, the role of the cannabinoid system in the whole body and tissue metabolism via central and peripheral mechanisms is increasingly recognized. The present review provides insights in (i) how cannabinoid signaling is regulated via receptor-independent and -dependent mechanisms and (ii) how these signaling cascades (might) affect skeletal muscle plasticity and physiology. Receptor-independent mechanisms include endocannabinoid metabolism to eicosanoids and the regulation of ion channels. Alternatively, endocannabinoids can act as ligands for different classic (cannabinoid receptor 1 [CB₁ ], CB₂ ) and/or alternative (e.g., TRPV1, GPR55) cannabinoid receptors with a unique affinity, specificity, and intracellular signaling cascade (often tissue-specific). Antagonism of CB₁ might hold clues to improve oxidative (mitochondrial) metabolism, insulin sensitivity, satellite cell growth, and muscle anabolism, whereas CB₂ agonism might be a promising way to stimulate muscle metabolism and muscle cell growth. Besides, CB₂ ameliorates muscle regeneration via macrophage polarization toward an anti-inflammatory phenotype, induction of MyoD and myogenin expression and antifibrotic mechanisms. Also TRPV1 and GPR55 contribute to the regulation of muscle growth and metabolism. Future studies should reveal how the cannabinoid system can be targeted to improve muscle quantity and/or quality in conditions such as ageing, disease, disuse, and metabolic dysregulation, taking into account challenges that are inherent to modulation of the cannabinoid system, such as central and peripheral side effects.

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).

Cross-Talk Between Gut Microbiota and Adipose Tissues in Obesity and Related Metabolic Diseases

The rapid increase of obesity and associated diseases has become a major global health problem. Adipose tissues are critical for whole-body homeostasis. The gut microbiota has been recognized as a significant environmental factor in the maintenance of energy homeostasis and host immunity. A growing body of evidence suggests that the gut microbiota regulates host metabolism through a close cross-talk with adipose tissues. It modulates energy expenditure and alleviates obesity by promoting energy expenditure, but it also produces specific metabolites and structural components that may act as the central factors in the pathogenesis of inflammation, insulin resistance, and obesity. Understanding the relationship between gut microbiota and adipose tissues may provide potential intervention strategies to treat obesity and associated diseases. In this review, we focus on recent advances in the gut microbiota and its actions on adipose tissues and highlight the joint actions of the gut microbiota and adipose tissue with each other in the regulation of energy metabolism.

The Peripheral Cannabinoid Receptor Type 1 (CB1) as a Molecular Target for Modulating Body Weight in Man

The cannabinoid 1 (CB₁) receptor regulates appetite and body weight; however, unwanted central side effects of both agonists (in wasting disorders) or antagonists (in obesity and diabetes) have limited their therapeutic utility. At the peripheral level, CB₁ receptor activation impacts the energy balance of mammals in a number of different ways: inhibiting satiety and emesis, increasing food intake, altering adipokine and satiety hormone levels, altering taste sensation, decreasing lipolysis (fat break down), and increasing lipogenesis (fat generation). The CB₁ receptor also plays an important role in the gut–brain axis control of appetite and satiety. The combined effect of peripheral CB₁ activation is to promote appetite, energy storage, and energy preservation (and the opposite is true for CB₁ antagonists). Therefore, the next generation of CB₁ receptor medicines (agonists and antagonists, and indirect modulators of the endocannabinoid system) have been peripherally restricted to mitigate these issues, and some of these are already in clinical stage development. These compounds also have demonstrated potential in other conditions such as alcoholic steatohepatitis and diabetic nephropathy (peripherally restricted CB₁ antagonists) and pain conditions (peripherally restricted CB₁ agonists and FAAH inhibitors). This review will discuss the mechanisms by which peripheral CB₁ receptors regulate body weight, and the therapeutic utility of peripherally restricted drugs in the management of body weight and beyond.

Roles of Endocannabinoids and Endocannabinoid-like Molecules in Energy Homeostasis and Metabolic Regulation: A Nutritional Perspective

The endocannabinoid system is involved in signal transduction in mammals. It comprises principally G protein-coupled cannabinoid receptors and their endogenous agonists, called endocannabinoids, as well as the enzymes and transporters responsible for the metabolism of endocannabinoids. Two arachidonic acid-containing lipid molecules, arachidonoylethanolamide (anandamide) and 2-arachidonoylglycerol, function as endocannabinoids. N-acylethanolamines and monoacylglycerols, in which the arachidonic acid chain is replaced with a saturated or monounsaturated fatty acid, are not directly involved in the endocannabinoid system but exhibit agonistic activities for other receptors. These endocannabinoid-like molecules include palmitoylethanolamide, oleoylethanolamide (OEA), and 2-oleoylglycerol. Endocannabinoids stimulate feeding behavior and the anabolism of lipids and glucose, while OEA suppresses appetite. Both central and peripheral systems are included in these nutritional and metabolic contexts. Therefore, they have potential in the treatment and prevention of obesity. We outline the structure, metabolism, and biological activities of endocannabinoids and related molecules, and focus on their involvement in energy homeostasis and metabolic regulation. Expected final online publication date for the Annual Review of Nutrition, Volume 41 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Metabolic roles of G protein-coupled receptor signaling in obesity and type 2 diabetes

The incidence of obesity and type 2 diabetes (T2D) has been increasing steadily worldwide. It is estimated that by 2045 more than 800 million people will be suffering from diabetes. Despite the advancements in modern medicine, more effective therapies for treating obesity and T2D are needed. G protein-coupled receptors (GPCRs) have emerged as important drug targets for various chronic diseases, including obesity, T2D, and liver diseases. During the past two decades, many laboratories worldwide focused on understanding the role of GPCR signaling in regulating glucose metabolism and energy homeostasis. The information gained from these studies can guide the development of novel therapeutic agents. In this review, we summarize recent studies providing insights into the role of GPCR signaling in peripheral, metabolically important tissues such as pancreas, liver, skeletal muscle, and adipose tissue, focusing primarily on the use of mutant animal models and human data.

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.

A Peripheral CB1R Antagonist Increases Lipolysis, Oxygen Consumption Rate, and Markers of Beiging in 3T3-L1 Adipocytes Similar to RIM, Suggesting that Central Effects Can Be Avoided

With the increased prevalence of obesity and related co-morbidities, such as type 2 diabetes (T2D), worldwide, improvements in pharmacological treatments are necessary. The brain- and peripheral-cannabinoid receptor 1 (CB1R) antagonist rimonabant (RIM) has been shown to induce weight loss and improve glucose homeostasis. We have previously demonstrated that RIM promotes adipose tissue beiging and decreased adipocyte cell size, even during maintenance on a high-fat diet. Given the adverse side-effects of brain-penetrance with RIM, in this study we aimed to determine the site of action for a non-brain-penetrating CB1R antagonist AM6545. By using in vitro assays, we demonstrated the direct effects of this non-brain-penetrating CB1R antagonist on cultured adipocytes. Specifically, we showed, for the first time, that AM6545 significantly increases markers of adipose tissue beiging, mitochondrial biogenesis, and lipolysis in 3T3-L1 adipocytes. In addition, the oxygen consumption rate (OCR), consisting of baseline respiratory rate, proton leak, maximal respiratory capacity, and ATP synthase activity, was greater for cells exposed to AM6545, demonstrating greater mitochondrial uncoupling. Using a lipolysis inhibitor during real-time OCR measurements, we determined that the impact of CB1R antagonism on adipocytes is driven by increased lipolysis. Thus, our data suggest the direct role of CB1R antagonism on adipocytes does not require brain penetrance, supporting the importance of focus on peripheral CB1R antagonism pharmacology for reducing the incidence of obesity and T2D.

Targeting the Endocannabinoid CB1 Receptor to Treat Body Weight Disorders: A Preclinical and Clinical Review of the Therapeutic Potential of Past and Present CB1 Drugs

Obesity rates are increasing worldwide and there is a need for novel therapeutic treatment options. The endocannabinoid system has been linked to homeostatic processes, including metabolism, food intake, and the regulation of body weight. Rimonabant, an inverse agonist for the cannabinoid CB1 receptor, was effective at producing weight loss in obese subjects. However, due to adverse psychiatric side effects, rimonabant was removed from the market. More recently, we reported an inverse relationship between cannabis use and BMI, which has now been duplicated by several groups. As those results may appear contradictory, we review here preclinical and clinical studies that have studied the impact on body weight of various cannabinoid CB1 drugs. Notably, we will review the impact of CB1 inverse agonists, agonists, partial agonists, and neutral antagonists. Those findings clearly point out the cannabinoid CB1 as a potential effective target for the treatment of obesity. Recent preclinical studies suggest that ligands targeting the CB1 may retain the therapeutic potential of rimonabant without the negative side effect profile. Such approaches should be tested in clinical trials for validation.

Peptides from Natural or Rationally Designed Sources Can Be Used in Overweight, Obesity, and Type 2 Diabetes Therapies

Overweight and obesity are among the most prominent health problems in the modern world, mostly because they are either associated with or increase the risk of other diseases such as type 2 diabetes, hypertension, and/or cancer. Most professional organizations define overweight and obesity according to individual body-mass index (BMI, weight in kilograms divided by height squared in meters). Overweight is defined as individuals with BMI from 25 to 29, and obesity as individuals with BMI ≥30. Obesity is the result of genetic, behavioral, environmental, physiological, social, and cultural factors that result in energy imbalance and promote excessive fat deposition. Despite all the knowledge concerning the pathophysiology of obesity, which is considered a disease, none of the existing treatments alone or in combination can normalize blood glucose concentration and prevent debilitating complications from obesity. This review discusses some new perspectives for overweight and obesity treatments, including the use of the new orally active cannabinoid peptide Pep19, the advantage of which is the absence of undesired central nervous system effects usually experienced with other cannabinoids.

Brown Adipose Tissue Response to Cold Stimulation Is Reduced in Girls With Autoimmune Hypothyroidism

Objective

The interaction between thyroid status and brown adipose tissue (BAT) activation is complex. We assessed the effect of autoimmune hypothyroidism (ATD) in female children on BAT activation, measured using infrared thermography.

Design

Twenty-six female participants (14 with ATD and 12 healthy controls) between 5 and 17 years of age attended a single study session. Thermal images were taken of the supraclavicular region before, and after, the introduction of a cool stimulus.

Results

Participants with ATD had lower resting (hypothyroid, 34.9 ± 0.7°C; control, 35.4 ± 0.5°C; P = 0.03) and stimulated (hypothyroid, 35.0 ± 0.6°C; control, 35.5 ± 0.5°C; P = 0.04) supraclavicular temperatures compared with controls, but there was no difference between groups in the temperature increase with stimulation. BAT activation, calculated as the relative temperature change comparing the supraclavicular temperature to a sternal reference region, was reduced in participants with ATD (hypothyroid, 0.1 ± 0.1°C; control, 0.2 ± 0.2°C; P = 0.04). Children with ATD were frequently biochemically euthyroid due to replacement therapy, but, despite this, increased relative supraclavicular temperature was closely associated with increased TSH (r = 0.7, P = 0.01) concentrations.

Conclusions

Girls with ATD had an attenuated thermogenic response to cold stimulation compared with healthy controls, but, contrary to expectation, those with suboptimal biochemical control (with higher TSH) showed increased BAT activation. This suggests that the underlying disease process may have a negative effect on BAT response, but high levels of TSH can mitigate, and even stimulate, BAT activity. In summary, thyroid status is a complex determinant of BAT activity in girls with ATD.

Beyond adiponectin and leptin: adipose tissue-derived mediators of inter-organ communication

The breakthrough discoveries of leptin and adiponectin more than two decades ago led to a widespread recognition of adipose tissue as an endocrine organ. Many more adipose tissue-secreted signaling mediators (adipokines) have been identified since then, and much has been learned about how adipose tissue communicates with other organs of the body to maintain systemic homeostasis. Beyond proteins, additional factors, such as lipids, metabolites, noncoding RNAs, and extracellular vesicles (EVs), released by adipose tissue participate in this process. Here, we review the diverse signaling mediators and mechanisms adipose tissue utilizes to relay information to other organs. We discuss recently identified adipokines (proteins, lipids, and metabolites) and briefly outline the contributions of noncoding RNAs and EVs to the ever-increasing complexities of adipose tissue inter-organ communication. We conclude by reflecting on central aspects of adipokine biology, namely, the contribution of distinct adipose tissue depots and cell types to adipokine secretion, the phenomenon of adipokine resistance, and the capacity of adipose tissue to act both as a source and sink of signaling mediators.

Activation of NPRs and UCP1-independent pathway following CB1R antagonist treatment is associated with adipose tissue beiging in fat-fed male dogs

CB1 receptor (CB1R) antagonism improves the deleterious effects of a high-fat diet (HFD) by reducing body fat mass and adipocyte cell size. Previous studies demonstrated that the beneficial effects of the CB1R antagonist rimonabant (RIM) in white adipose tissue (WAT) are partially due to an increase of mitochondria numbers and upregulation thermogenesis markers, suggesting an induction of WAT beiging. However, the molecular mechanism by which CB1R antagonism induces weight loss and WAT beiging is unclear. In this study, we probed for genes associated with beiging and explored longitudinal molecular mechanisms by which the beiging process occurs. HFD dogs received either RIM (HFD+RIM) or placebo (PL) (HFD+PL) for 16 wk. Several genes involved in beiging were increased in HFD+RIM compared with pre-fat, HFD, and HFD+PL. We evaluated lipolysis and its regulators including natriuretic peptide (NP) and its receptors (NPRs), β-1 and β-3 adrenergic receptor (β1R, β3R) genes. These genes were increased in WAT depots, accompanied by an increase in lipolysis in HFD+RIM. In addition, RIM decreased markers of inflammation and increased adiponectin receptors in WAT. We observed a small but significant increase in UCP1; therefore, we evaluated the newly discovered UCP1-independent thermogenesis pathway. We confirmed that SERCA2b and RYR2, the two key genes involved in this pathway, were upregulated in the WAT. Our data suggest that the upregulation of NPRs, β-1R and β-3R, lipolysis, and SERCA2b and RYR2 may be one of the mechanisms by which RIM promotes beiging and overall the improvement of metabolic homeostasis induced by RIM.

Molecular pathways linking adipose innervation to insulin action in obesity and diabetes mellitus

Adipose tissue comprises adipocytes and many other cell types that engage in dynamic crosstalk in a highly innervated and vascularized tissue matrix. Although adipose tissue has been studied for decades, it has been appreciated only in the past 5 years that extensive arborization of nerve fibres has a dominant role in regulating the function of adipose tissue. This Review summarizes the latest literature, which suggests that adipocytes signal to local sensory nerve fibres in response to perturbations in lipolysis and lipogenesis. Such adipocyte signalling to the central nervous system causes sympathetic output to distant adipose depots and potentially other metabolic tissues to regulate systemic glucose homeostasis. Paracrine factors identified in the past few years that mediate such adipocyte-neuron crosstalk are also reviewed. Similarly, immune cells and endothelial cells within adipose tissue communicate with local nerve fibres to modulate neurotransmitter tone, blood flow, adipocyte differentiation and energy expenditure, including adipose browning to produce heat. This understudied field of neurometabolism related to adipose tissue biology has great potential to reveal new mechanistic insights and potential therapeutic strategies for obesity and type 2 diabetes mellitus.

Atypical cannabinoid ligands O-1602 and O-1918 administered chronically in diet-induced obesity

Atypical cannabinoid compounds O-1602 and O-1918 are ligands for the putative cannabinoid receptors G protein-coupled receptor 55 and G protein-coupled receptor 18. The role of O-1602 and O-1918 in attenuating obesity and obesity-related pathologies is unknown. Therefore, we aimed to determine the role that either compound had on body weight and body composition, renal and hepatic function in diet-induced obesity. Male Sprague-Dawley rats were fed a high-fat diet (40% digestible energy from lipids) or a standard chow diet for 10 weeks. In a separate cohort, male Sprague-Dawley rats were fed a high-fat diet for 9 weeks and then injected daily with 5 mg/kg O-1602, 1 mg/kg O-1918 or vehicle (0.9% saline/0.75% Tween 80) for a further 6 weeks. Our data demonstrated that high-fat feeding upregulates whole kidney G protein receptor 55 expression. In diet-induced obesity, we also demonstrated O-1602 reduces body weight, body fat and improves albuminuria. Despite this, treatment with O-1602 resulted in gross morphological changes in the liver and kidney. Treatment with O-1918 improved albuminuria, but did not alter body weight or fat composition. In addition, treatment with O-1918 also upregulated circulation of pro-inflammatory cytokines including IL-1α, IL-2, IL-17α, IL-18 and RANTES as well as plasma AST. Thus O-1602 and O-1918 appear not to be suitable treatments for obesity and related comorbidities, due to their effects on organ morphology and pro-inflammatory signaling in obesity.

Germinated soy germ extract ameliorates obesity through beige fat activation

Obesity is a worldwide public health concern requiring safe and effective strategies. Recent studies suggest that bioactive compounds from soybeans have beneficial effects on weight loss and reducing fat accumulation. However, despite the biochemical and nutritional changes during germination, the biological effects of germinated soy germ have not been fully investigated. In this article, germinated soy germ extract (GSGE) was evaluated as a potential treatment option for obesity using 3T3-L1 pre-adipocyte and high-fat diet (HFD)-induced obese mice. In vitro studies demonstrated that GSGE suppressed the differentiation of 3T3-L1 cells into mature adipocytes, along with reductions in lipid accumulation and lipid droplet formation. In vivo studies also showed that a daily dose of 1 mg kg-1 of GSGE reduced weight gain, adipocyte area, serum triglyceride, and LDL-cholesterol in HFD-fed mice. The GSGE treatment promoted browning, which was associated with increased UCP1 expression in vitro and in vivo. In addition, GSGE treatment induced beige fat activation by upregulation of lipolysis and beta-oxidation. Furthermore, gene and protein expression levels of endocannabinoid system-related factors such as NAPE-PLD, FAAH, DAGL-α, and CB2 were altered along with browning and beige fat activation by GSGE. The present study indicates that GSGE effectively inhibits lipid accumulation and promotes beige fat transition and activation. Therefore, we suggest that GSGE treatment could be a promising strategy for the prevention of obesity by promoting weight loss, reducing fat accumulation, and improving obesity-related metabolic disorders.

Fatty Acid Metabolites as Novel Regulators of Non-shivering Thermogenesis

Fatty acids are essential contributors to adipocyte-based non-shivering thermogenesis by acting as activators of uncoupling protein 1 and serving as fuel for mitochondrial heat production. Novel evidence suggests a contribution to this thermogenic mechanism by their conversion to bioactive compounds. Mammalian cells produce a plethora of oxylipins and endocannabinoids, some of which have been identified to affect the abundance or thermogenic activity of brown and brite adipocytes. These effectors are produced locally or at distant sites and signal toward thermogenic adipocytes via a direct interaction with these cells or indirectly via secondary mechanisms. These interactions are evoked by the activation of receptor-mediated pathways. The endogenous production of these compounds is prone to modulation by the dietary intake of the respective precursor fatty acids. The effect of nutritional interventions on uncoupling protein 1-derived thermogenesis may thus at least in part be conferred by the production of a supportive oxylipin and endocannabinoid profile. The manipulation of this system in future studies will help to elucidate the physiological potential of these compounds as novel, endogenous regulators of non-shivering thermogenesis.

GPR55 deficiency is associated with increased adiposity and impaired insulin signaling in peripheral metabolic tissues

Emerging evidence indicates that G-protein coupled receptor 55 (GPR55), a nonclassic receptor of the endocannabinoid system that is activated by L-α-lysophosphatidylinositol and various cannabinoid ligands, may regulate endocrine function and energy metabolism. We examined how GPR55 deficiency and modulation affects insulin signaling in skeletal muscle, adipose tissue, and liver alongside expression analysis of proteins implicated in insulin action and energy metabolism. We show that GPR55-null mice display decreased insulin sensitivity in these tissues, as evidenced by reduced phosphorylation of PKB/Akt and its downstream targets, concomitant with increased adiposity and reduced physical activity relative to wild-type counterparts. Impaired tissue insulin sensitivity coincided with reduced insulin receptor substrate-1 abundance in skeletal muscle, whereas in liver and epididymal fat it was associated with increased expression of the 3-phosphoinoistide lipid phosphatase, phosphatase and tensin homolog. In contrast, GPR55 activation enhanced insulin signaling in cultured skeletal muscle cells, adipocytes, and hepatocytes; this response was negated by receptor antagonists and GPR55 gene silencing in L6 myotubes. Sustained GPR55 antagonism in 3T3-L1 adipocytes enhanced expression of proteins implicated in lipogenesis and promoted triglyceride accumulation. Our findings identify GPR55 as a positive regulator of insulin action and adipogenesis and as a potential therapeutic target for countering obesity-induced metabolic dysfunction and insulin resistance.-Lipina, C., Walsh, S. K., Mitchell, S. E., Speakman, J. R., Wainwright, C. L., Hundal, H. S. GPR55 deficiency is associated with increased adiposity and impaired insulin signaling in peripheral metabolic tissues.

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.

Cannabinoid Type 1 Receptors Are Upregulated During Acute Activation of Brown Adipose Tissue

Activating brown adipose tissue (BAT) could provide a potential approach for the treatment of obesity and metabolic disease in humans. Obesity is associated with upregulation of the endocannabinoid system, and blocking the cannabinoid type 1 receptor (CB1R) has been shown to cause weight loss and to decrease cardiometabolic risk factors. These effects may be mediated partly via increased BAT metabolism, since there is evidence that CB1R antagonism activates BAT in rodents. To investigate the significance of CB1R in BAT function, we quantified the density of CB1R in human and rodent BAT using the positron emission tomography radioligand [¹⁸F]FMPEP-d₂ and measured BAT activation in parallel with the glucose analog [¹⁸F]fluorodeoxyglucose. Activation by cold exposure markedly increased CB1R density and glucose uptake in the BAT of lean men. Similarly, β3-receptor agonism increased CB1R density in the BAT of rats. In contrast, overweight men with reduced BAT activity exhibited decreased CB1R in BAT, reflecting impaired endocannabinoid regulation. Image-guided biopsies confirmed CB1R mRNA expression in human BAT. Furthermore, CB1R blockade increased glucose uptake and lipolysis of brown adipocytes. Our results highlight that CB1Rs are significant for human BAT activity, and the CB1Rs provide a novel therapeutic target for BAT activation in humans.

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.

Peripheral modulation of the endocannabinoid system in metabolic disease

Dysfunction of the endocannabinoid system (ECS) has been identified in metabolic disease. Cannabinoid receptor 1 (CB₁) is abundantly expressed in the brain but also expressed in the periphery. Cannabinoid receptor 2 (CB₂) is more abundant in the periphery, including the immune cells. In obesity, global antagonism of overexpressed CB₁ reduces bodyweight but leads to centrally mediated adverse psychological outcomes. Emerging research in isolated cultured cells or tissues has demonstrated that targeting the endocannabinoid system in the periphery alleviates the pathologies associated with metabolic disease. Further, peripheral specific cannabinoid ligands can reverse aspects of the metabolic phenotype. This Keynote review will focus on current research on the functionality of peripheral modulation of the ECS for the treatment of obesity.

Efferent neural pathways for the control of brown adipose tissue thermogenesis and shivering

The fundamental central neural circuits for thermoregulation orchestrate behavioral and autonomic repertoires that maintain body core temperature during thermal challenges that arise from either the ambient or the internal environment. This review summarizes our understanding of the neural pathways within the fundamental thermoregulatory reflex circuitry that comprise the efferent (i.e., beyond thermosensory) control of brown adipose tissue (BAT) and shivering thermogenesis: the motor neuron systems consisting of the BAT sympathetic preganglionic neurons and BAT sympathetic ganglion cells, and the alpha- and gamma-motoneurons; the premotor neurons in the region of the rostral raphe pallidus, and the thermogenesis-promoting neurons in the dorsomedial hypothalamus/dorsal hypothalamic area. Also included are inputs to, and neurochemical modulators of, these efferent neuronal populations that could influence their activity during thermoregulatory responses. Signals of metabolic status can be particularly significant for the energy-hungry thermoeffectors for heat production.

Neural circuits of eating behaviour: Opportunities for therapeutic development

Understanding of the neural and physiological substrates of hunger and satiety has increased rapidly over the last three decades, and pharmacological targets have already been identified for the treatment of obesity that has moved from pre-clinical screening to therapies approved by regulatory authorities. Initially, this review describes the way in which physiological signals of energy availability interact with hedonic and rewarding properties of food to modulate the neural circuitry that supports eating behaviour. This is followed by a brief account of current and promising targets for drug development and a review of the wide range of preclinical paradigms that model important influences on human eating behaviour, and can be used to guide early stages of the drug development process.

Adipocyte cannabinoid receptor CB1 regulates energy homeostasis and alternatively activated macrophages

Dysregulated adipocyte physiology leads to imbalanced energy storage, obesity, and associated diseases, imposing a costly burden on current health care. Cannabinoid receptor type-1 (CB1) plays a crucial role in controlling energy metabolism through central and peripheral mechanisms. In this work, adipocyte-specific inducible deletion of the CB1 gene (Ati-CB1-KO) was sufficient to protect adult mice from diet-induced obesity and associated metabolic alterations and to reverse the phenotype in already obese mice. Compared with controls, Ati-CB1-KO mice showed decreased body weight, reduced total adiposity, improved insulin sensitivity, enhanced energy expenditure, and fat depot-specific cellular remodeling toward lowered energy storage capacity and browning of white adipocytes. These changes were associated with an increase in alternatively activated macrophages concomitant with enhanced sympathetic tone in adipose tissue. Remarkably, these alterations preceded the appearance of differences in body weight, highlighting the causal relation between the loss of CB1 and the triggering of metabolic reprogramming in adipose tissues. Finally, the lean phenotype of Ati-CB1-KO mice and the increase in alternatively activated macrophages in adipose tissue were also present at thermoneutral conditions. Our data provide compelling evidence for a crosstalk among adipocytes, immune cells, and the sympathetic nervous system (SNS), wherein CB1 plays a key regulatory role.

The CB1 Receptor as the Cornerstone of Exostasis

The type-1 cannabinoid receptor (CB1) is the main effector of the endocannabinoid system (ECS), which is involved in most brain and body functions. In this Perspective, we provide evidence indicating that CB1 receptor functions are key determinants of bodily coordinated exostatic processes. First, we will introduce the concepts of endostasis and exostasis as compensation or accumulation for immediate or future energy needs and discuss how exostasis has been necessary for the survival of species during evolution. Then, we will argue how different specific biological functions of the CB1 receptor in the body converge to provide physiological exostatic processes. Finally, we will introduce the concept of proactive evolution-induced diseases (PEIDs), which helps explain the seeming paradox that an evolutionary-selected physiological function can become the cause of epidemic pathological conditions, such as obesity. We propose here a possible unifying theory of CB1 receptor functions that can be tested by future experimental studies.

Radiosynthesis and evaluation of new PET ligands for peripheral cannabinoid receptor type 1 imaging

Cannabinoid receptor type 1 (CB1) is mainly expressed in the brain, as well as being expressed in functional relevant concentrations in various peripheral tissues. 1-(4-Chlorophenyl)-3-(3-(6-(pyrrolidin-1-yl)pyridin-2-yl)phenyl)urea (PSNCBAM-1, 1) was developed as a potent allosteric antagonist for CB1 and its oral administration led to reductions in the appetite and body weight of rats. Several analogs of 1 (compounds 2 and 3) were recently identified through a series of structure-activity relationship studies. Herein, we report the synthesis of radiolabeled analogs of these compounds using [¹¹C]COCl₂ and an evaluation of their potential as PET ligands for CB1 imaging using in vitro and in vivo techniques. [¹¹C]2 and [¹¹C]3 were successfully synthesized in two steps using [¹¹C]COCl₂. The radiochemical yields of [¹¹C]2 and [¹¹C]3 were 17±8% and 20±9% (decay-corrected to the end of bombardment, based on [¹¹C]CO₂). The specific activities of [¹¹C]2 and [¹¹C]3 were 42±36 and 37±13GBq/μmol, respectively. The results of an in vitro binding assay using brown adipose tissue (BAT) homogenate showed that the binding affinity of 2 for CB1 (K_D=15.3µM) was much higher than that of 3 (K_D=26.0µM). PET studies with [¹¹C]2 showed a high uptake of radioactivity in BAT, which decreased in animals pretreated with AM281 (a selective antagonist for CB1). In conclusion, [¹¹C]2 may be a useful PET ligand for imaging peripheral CB1 in BAT.

Polyunsaturated fatty acids and endocannabinoids in health and disease

Polyunsaturated fatty acids (PUFAs) are lipid derivatives of omega-3 (docosahexaenoic acid, DHA, and eicosapentaenoic acid, EPA) or of omega-6 (arachidonic acid, ARA) synthesized from membrane phospholipids and used as a precursor for endocannabinoids (ECs). They mediate significant effects in the fine-tune adjustment of body homeostasis. Phyto- and synthetic cannabinoids also rule the daily life of billions worldwide, as they are involved in obesity, depression and drug addiction. Consequently, there is growing interest to reveal novel active compounds in this field. Cloning of cannabinoid receptors in the 90s and the identification of the endogenous mediators arachidonylethanolamide (anandamide, AEA) and 2-arachidonyglycerol (2-AG), led to the characterization of the endocannabinoid system (ECS), together with their metabolizing enzymes and membrane transporters. Today, the ECS is known to be involved in diverse functions such as appetite control, food intake, energy balance, neuroprotection, neurodegenerative diseases, stroke, mood disorders, emesis, modulation of pain, inflammatory responses, as well as in cancer therapy. Western diet as well as restriction of micronutrients and fatty acids, such as DHA, could be related to altered production of pro-inflammatory mediators (e.g. eicosanoids) and ECs, contributing to the progression of cardiovascular diseases, diabetes, obesity, depression or impairing conditions, such as Alzheimer' s disease. Here we review how diets based in PUFAs might be linked to ECS and to the maintenance of central and peripheral metabolism, brain plasticity, memory and learning, blood flow, and genesis of neural cells.

Endocannabinoids--at the crossroads between the gut microbiota and host metabolism

Various metabolic disorders are associated with changes in inflammatory tone. Among the latest advances in the metabolism field, the discovery that gut microorganisms have a major role in host metabolism has revealed the possibility of a plethora of associations between gut bacteria and numerous diseases. However, to date, few mechanisms have been clearly established. Accumulating evidence indicates that the endocannabinoid system and related bioactive lipids strongly contribute to several physiological processes and are a characteristic of obesity, type 2 diabetes mellitus and inflammation. In this Review, we briefly define the gut microbiota as well as the endocannabinoid system and associated bioactive lipids. We discuss existing literature regarding interactions between gut microorganisms and the endocannabinoid system, focusing specifically on the triad of adipose tissue, gut bacteria and the endocannabinoid system in the context of obesity and the development of fat mass. We highlight gut-barrier function by discussing the role of specific factors considered to be putative 'gate keepers' or 'gate openers', and their role in the gut microbiota-endocannabinoid system axis. Finally, we briefly discuss data related to the different pharmacological strategies currently used to target the endocannabinoid system, in the context of cardiometabolic disorders and intestinal inflammation.

Endocannabinoid regulation in white and brown adipose tissue following thermogenic activation

The endocannabinoids and their main receptor, cannabinoid type-1 (CB1), suppress intracellular cyclic AMP levels and have emerged as key players in the control of energy metabolism. CB1 agonists and blockers have been reported to influence the thermogenic function of white and brown adipose tissue (WAT and BAT), affecting body weight through the inhibition and stimulation of energy expenditure, respectively. The purpose of the current study was to investigate the regulation of the endocannabinoid system in WAT and BAT following exposure to either cold or specific agonism of β3-adrenoceptors using CL316,243 (CL), conditions known to cause BAT activation and WAT browning. To address this question, we performed quantitative PCR-based mRNA profiling of genes important for endocannabinoid synthesis, degradation, and signaling, and determined endocannabinoid levels by LC-MS in WAT and BAT of control, cold-exposed, and CL-treated wild-type mice as well as primary brown adipocytes. Treatment with CL and exposure to cold caused an upregulation of endocannabinoid levels and biosynthetic enzymes in WAT. Acute β3-adrenoceptor activation increased endocannabinoids and a subset of genes of biosynthesis in BAT and primary brown adipocytes. We suggest that the cold-mediated increase in endocannabinoid tone is part of autocrine negative feed-back mechanisms controlling β3-adrenoceptor-induced BAT activation and WAT browning.

Combination cannabinoid and opioid receptor antagonists improves metabolic outcomes in obese mice

The CB1 receptor antagonist, rimonabant, causes weight loss but also produces undesirable psychiatric side effects. We investigated using a combination of rimonabant with the opioid receptor antagonists naloxone and norBNI to treat the metabolic sequelae of long-term high fat diet feeding in mice. This combination has previously been shown to have positive effects on both weight loss and mood related behaviour. Diet-induced obese mice were treated chronically with either low dose rimonabant (1 mg/kg) or the combination of rimonabant, naloxone and norBNI (rim nal BNI). After 6 days of treatment, glucose and insulin tolerance tests were performed and body composition analysed using DEXA. Changes in BAT thermogenesis were assessed using implantable radio telemetry probes. Behavioural responses to acute rimonabant or rim nal BNI were examined in the forced swim test and elevated plus maze. Separately, we assessed shifts in Fos immunoreactivity in response to rimonabant or rim nal BNI. Rim nal BNI was significantly better than rimonabant treatment alone at reducing body weight and food intake. In addition, it improved fasting blood glucose and fat mass. Acute low dose rimonabant did not alter behaviour in either the forced swim test or elevated plus maze. Combination rim nal BNI reversed the behavioural effects of high dose (10 mg/kg) rimonabant in obese mice. Rim nal BNI altered Rimonabant-induced Fos in a number of nuclei, with particular shifts in expression in the central and basolateral amygdala, and insular cortex. This study demonstrates that the combination of rimonabant, naloxone and norBNI is effective at producing weight loss over a sustained period of time without altering performance in standardised mouse behaviour tests. Fos expression patterns offer insight into the neuroanatomical substrates subserving these physiological and behavioural changes. These results indicate that CB1-targeted drugs for weight loss may still be feasible.

Hypothalamic control of brown adipose tissue thermogenesis

It has long been known, in large part from animal studies, that the control of brown adipose tissue (BAT) thermogenesis is insured by the central nervous system (CNS), which integrates several stimuli in order to control BAT activation through the sympathetic nervous system (SNS). SNS-mediated BAT activity is governed by diverse neurons found in brain structures involved in homeostatic regulations and whose activity is modulated by various factors including oscillations of energy fluxes. The characterization of these neurons has always represented a challenging issue. The available literature suggests that the neuronal circuits controlling BAT thermogenesis are largely part of an autonomic circuitry involving the hypothalamus, brainstem and the SNS efferent neurons. In the present review, we recapitulate the latest progresses in regards to the hypothalamic regulation of BAT metabolism. We briefly addressed the role of the thermoregulatory pathway and its interactions with the energy balance systems in the control of thermogenesis. We also reviewed the involvement of the brain melanocortin and endocannabinoid systems as well as the emerging role of steroidogenic factor 1 (SF1) neurons in BAT thermogenesis. Finally, we examined the link existing between these systems and the homeostatic factors that modulate their activities.

The Endocannabinoid System: Pivotal Orchestrator of Obesity and Metabolic Disease

The endocannabinoid system (ECS) functions to adjust behavior and metabolism according to environmental changes in food availability. Its actions range from the regulation of sensory responses to the development of preference for the consumption of calorically-rich food and control of its metabolic handling. ECS activity is beneficial when access to food is scarce or unpredictable. However, when food is plentiful, the ECS favors obesity and metabolic disease. We review recent advances in understanding the roles of the ECS in energy balance, and discuss newly identified mechanisms of action that, after the withdrawal of first generation cannabinoid type 1 (CB1) receptor antagonists for the treatment of obesity, have made the ECS once again an attractive target for therapy.

New insights on the role of the endocannabinoid system in the regulation of energy balance

Within the past 15 years, the endocannabinoid system (ECS) has emerged as a lipid signaling system critically involved in the regulation of energy balance, as it exerts a regulatory control on every aspect related to the search, the intake, the metabolism and the storage of calories. An overactive endocannabinoid cannabinoid type 1 (CB1) receptor signaling promotes the development of obesity, insulin resistance and dyslipidemia, representing a valuable pharmacotherapeutic target for obesity and metabolic disorders. However, because of the psychiatric side effects, the first generation of brain-penetrant CB1 receptor blockers developed as antiobesity treatment were removed from the European market in late 2008. Since then, recent studies have identified new mechanisms of action of the ECS in energy balance and metabolism, as well as novel ways of targeting the system that may be efficacious for the treatment of obesity and metabolic disorders. These aspects will be especially highlighted in this review.

The Cannabinoid Receptor-1 Is an Imaging Biomarker of Brown Adipose Tissue

Recently, the existence of significant deposits of brown adipose tissue (BAT) in human adults was confirmed. Its role in the human metabolism is unknown but could be substantial. Inhibition of the cannabinoid receptor-1 (CB1) by the antagonist rimonabant (SR141716) has been associated with activation of BAT thermogenesis and weight loss in mice and rats. The role of peripheral and central CB1 in the activation of BAT merits further investigation. Here we developed a technique for quantifying CB1 in BAT by PET.

METHODS

Sections of rat BAT and subcutaneous white adipose tissue (WAT) were stained for CB1 and uncoupling protein-1 by immunofluorescent staining. Binding of the radiolabeled CB1 antagonist (3R,5R)-5-(3-(18F-fluoromethoxy)phenyl)-3-(((R)-1-phenylethyl)amino)-1-(4-(trifluoromethyl)-phenyl)pyrrolidin-2-one ((18)F-FMPEP-d2) to BAT in vivo and in vitro was assessed in rats by PET.

RESULTS

We found that CB1 was colocalized with uncoupling protein-1 in BAT, but neither protein was found in WAT. Binding of the radiotracer to BAT sections (but not WAT) in vitro was high and displaceable by pretreatment with rimonabant. Deposits of BAT in rats had significant binding of (18)F-FMPEP-d2 in vivo, indicating high CB1 density. WAT deposits were negative for (18)F-FMPEP-d2, consistent with the immunofluorescent staining and in vitro results.

CONCLUSION

(18)F-FMPEP-d2 PET can quantify CB1 density noninvasively in vivo in rats. CB1 is therefore a promising surrogate imaging biomarker for assessing the presence of BAT deposits as well as for elucidating the mechanism of CB1 antagonist-mediated weight loss.

Central nervous system regulation of brown adipose tissue

Thermogenesis, the production of heat energy, in brown adipose tissue is a significant component of the homeostatic repertoire to maintain body temperature during the challenge of low environmental temperature in many species from mouse to man and plays a key role in elevating body temperature during the febrile response to infection. The sympathetic neural outflow determining brown adipose tissue (BAT) thermogenesis is regulated by neural networks in the CNS which increase BAT sympathetic nerve activity in response to cutaneous and deep body thermoreceptor signals. Many behavioral states, including wakefulness, immunologic responses, and stress, are characterized by elevations in core body temperature to which central command-driven BAT activation makes a significant contribution. Since energy consumption during BAT thermogenesis involves oxidation of lipid and glucose fuel molecules, the CNS network driving cold-defensive and behavioral state-related BAT activation is strongly influenced by signals reflecting the short- and long-term availability of the fuel molecules essential for BAT metabolism and, in turn, the regulation of BAT thermogenesis in response to metabolic signals can contribute to energy balance, regulation of body adipose stores and glucose utilization. This review summarizes our understanding of the functional organization and neurochemical influences within the CNS networks that modulate the level of BAT sympathetic nerve activity to produce the thermoregulatory and metabolic alterations in BAT thermogenesis and BAT energy expenditure that contribute to overall energy homeostasis and the autonomic support of behavior.

A cannabinoid receptor agonist N-arachidonoyl dopamine inhibits adipocyte differentiation in human mesenchymal stem cells

Endocannabinoids can affect multiple cellular targets, such as cannabinoid (CB) receptors, transient receptor potential cation channel, subfamily V, member 1 (TRPV1) and peroxisome proliferator-activated receptor γ (PPARγ). The stimuli to induce adipocyte differentiation in hBM-MSCs increase the gene transcription of the CB₁ receptor, TRPV1 and PPARγ. In this study, the effects of three endocannabinoids, N-arachidonoyl ethanolamine (AEA), N-arachidonoyl dopamine (NADA) and 2-arachidonoyl glycerol (2-AG), on adipogenesis in hBM-MSCs were evaluated. The adipocyte differentiation was promoted by AEA whereas inhibited by NADA. No change was observed by the treatment of non-cytotoxic concentrations of 2-AG. The difference between AEA and NADA in the regulation of adipogenesis is associated with their effects on PPARγ transactivation. AEA can directly activate PPARγ. The effect of AEA on PPARγ in hBM-MSCs may prevail over that on the CB₁ receptor mediated signal transduction, giving rise to the AEA-induced promotion of adipogenesis. In contrast, NADA had no effect on the PPARγ activity in the PPARγ transactivation assay. The inhibitory effect of NADA on adipogenesis in hBM-MSCs was reversed not by capsazepine, a TRPV1 antagonist, but by rimonabant, a CB₁ antagonist/inverse agonist. Rimonabant by itself promoted adipogenesis in hBM-MSCs, which may be interpreted as the result of the inverse agonism of the CB₁ receptor. This result suggests that the constantly active CB₁ receptor may contribute to suppress the adipocyte differentiation of hBM-MSCs. Therefore, the selective CB₁ agonists that are unable to affect cellular PPARγ activity inhibit adipogenesis in hBM-MSCs.

Adipose tissue NAPE-PLD controls fat mass development by altering the browning process and gut microbiota

Obesity is a pandemic disease associated with many metabolic alterations and involves several organs and systems. The endocannabinoid system (ECS) appears to be a key regulator of energy homeostasis and metabolism. Here we show that specific deletion of the ECS synthesizing enzyme, NAPE-PLD, in adipocytes induces obesity, glucose intolerance, adipose tissue inflammation and altered lipid metabolism. We report that Napepld-deleted mice present an altered browning programme and are less responsive to cold-induced browning, highlighting the essential role of NAPE-PLD in regulating energy homeostasis and metabolism in the physiological state. Our results indicate that these alterations are mediated by a shift in gut microbiota composition that can partially transfer the phenotype to germ-free mice. Together, our findings uncover a role of adipose tissue NAPE-PLD on whole-body metabolism and provide support for targeting NAPE-PLD-derived bioactive lipids to treat obesity and related metabolic disorders.

Endocannabinoids are bioactive lipid molecules produced in the body. Here, Geurts et al. create mice lacking the endocannabinoid-producing enzyme NAPE-PLD in adipocytes and report defects in adipose-induced browning, which are mediated by alterations in the gut microbiome.

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.