Second generation CB1 receptor blockers and other inhibitors of peripheral endocannabinoid overactivity and the rationale of their use against metabolic disorders

Hemp seed significantly modulates the endocannabinoidome and produces beneficial metabolic effects with improved intestinal barrier function and decreased inflammation in mice under a high-fat, high-sucrose diet as compared with linseed

Omega-3 fatty acids support cardiometabolic health and reduce chronic low-grade inflammation. These fatty acids may impart their health benefits partly by modulating the endocannabinoidome and the gut microbiome, both of which are key regulators of metabolism and the inflammatory response. Whole hemp seeds (Cannabis sativa) are of exceptional nutritional value, being rich in omega-3 fatty acids. We assessed the effects of dietary substitution (equivalent to about 2 tablespoons of seeds a day for humans) of whole hemp seeds in comparison with whole linseeds in a diet-induced obesity mouse model and determined their effects on obesity and the gut microbiome-endocannabinoidome axis. We show that whole hemp seed substitution did not affect weigh gain, adiposity, or food intake, whereas linseed substitution did, in association with higher fasting glucose levels, greater insulin release during an oral glucose tolerance test, and higher levels of liver triglycerides than controls. Furthermore, hemp seed substitution mitigated diet-induced obesity-associated increases in intestinal permeability and circulating PAI-1 levels, while having no effects on markers of inflammation in epididymal adipose tissue, which were, however, increased in mice fed linseeds. Both hemp seeds and linseeds were able to modify the expression of several endocannabinoidome genes and markedly increased the levels of several omega-3 fatty acid–derived endocannabinoidome bioactive lipids with previously suggested anti-inflammatory actions in a tissue specific manner, despite the relatively low level of seed substitution. While neither diet markedly modified the gut microbiome, mice on the hemp seed diet had higher abundance of Clostridiaceae 1 and Rikenellaceae than mice fed linseed or control diet, respectively. Thus, hemp seed-containing foods might represent a source of healthy fats that are not likely to exacerbate the metabolic consequences of obesogenic diets while producing intestinal permeability protective effects and some anti-inflammatory actions.

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.

Functional Fine-Tuning of Metabolic Pathways by the Endocannabinoid System-Implications for Health and Disease

The endocannabinoid system (ECS) employs a huge network of molecules (receptors, ligands, and enzymatic machinery molecules) whose interactions with other cellular networks have still not been fully elucidated. Endogenous cannabinoids are molecules with the primary function of control of multiple metabolic pathways. Maintenance of tissue and cellular homeostasis by functional fine-tuning of essential metabolic pathways is one of the key characteristics of the ECS. It is implicated in a variety of physiological and pathological states and an attractive pharmacological target yet to reach its full potential. This review will focus on the involvement of ECS in glucose and lipid metabolism, food intake regulation, immune homeostasis, respiratory health, inflammation, cancer and other physiological and pathological states will be substantiated using freely available data from open-access databases, experimental data and literature review. Future directions should envision capturing its diversity and exploiting pharmacological options beyond the classical ECS suspects (exogenous cannabinoids and cannabinoid receptor monomers) as signaling through cannabinoid receptor heteromers offers new possibilities for different biochemical outcomes in the cell.

Emerging Roles of Cannabinoids and Synthetic Cannabinoids in Clinical Experimental Models

In recent years, an increasing number of investigations has demonstrated the therapeutic potential of molecules targeting the endocannabinoid system. Cannabinoids of endogenous, phytogenic, and synthetic nature have been assessed in a wide variety of disease models ranging from neurological to metabolic disorders. Even though very few compounds of this type have already reached the market, numerous preclinical and clinical studies suggest that cannabinoids are suitable drugs for the clinical management of diverse pathologies.In this chapter, we will provide an overview of the endocannabinoid system under certain physiopathological conditions, with a focus on neurological, oncologic, and metabolic disorders. Cannabinoids evaluated as potential therapeutic agents in experimental models with an emphasis in the most successful chemical entities and their perspectives towards the clinic will be discussed.

ABHD11, a new diacylglycerol lipase involved in weight gain regulation

Obesity epidemic continues to spread and obesity rates are increasing in the world. In addition to public health effort to reduce obesity, there is a need to better understand the underlying biology to enable more effective treatment and the discovery of new pharmacological agents. Abhydrolase domain-containing protein 11 (ABHD11) is a serine hydrolase enzyme, localized in mitochondria, that can synthesize the endocannabinoid 2-arachidonoyl glycerol (2AG) in vitro. In vivo preclinical studies demonstrated that knock-out ABHD11 mice have a similar 2AG level as WT mice and exhibit a lean metabolic phenotype. Such mice resist to weight gain in Diet Induced Obesity studies (DIO) and display normal biochemical plasma parameters. Metabolic and transcriptomic analyses on serum and tissues of ABHD11 KO mice from DIO studies show a modulation in bile salts associated with reduced fat intestinal absorption. These data suggest that modulating ABHD11 signaling pathway could be of therapeutic value for the treatment of metabolic disorders.

Joints for joints: cannabinoids in the treatment of rheumatoid arthritis

PURPOSE OF REVIEW

An increasing number of patients with rheumatoid arthritis (RA) are using cannabis to treat their symptoms, although systematic studies regarding efficacy in RA are lacking. Within this review we will give an overview on the overall effects of cannabinoids in inflammation and why they might be useful in the treatment of RA.

RECENT FINDINGS

Peripherally, cannabinoids show anti-inflammatory effects by activating cannabinoid type 2 receptors (CB2) which decrease cytokine production and immune cell mobilization. In contrast, cannabinoid type 1 receptor (CB1) activation on immune cells is proinflammatory while CB1 antagonism provides anti-inflammatory effects by increasing β2-adrenergic signaling in the joint and secondary lymphoid organs. In addition, the nonpsychotropic cannabinoid, cannabidiol (CBD) demonstrated antiarthritic effects independent of cannabinoid receptors. In addition to controlling inflammation, cannabinoids reduce pain by activating central and peripheral CB1, peripheral CB2 receptors and CBD-sensitive noncannabinoid receptor targets.

SUMMARY

Cannabinoids might be a suitable treatment for RA, but it is important to target the right receptors in the right place. For clinical studies, we propose a combination of a CB2 agonist to decrease cytokine production, a peripheral CB1 antagonist to prevent detrimental CB1 signaling and to support anti-inflammatory effects of CB2 via activation of β2-adrenergic receptors and CBD to induce cannabinoid-receptor-independent anti-inflammatory effects.

The Expanded Endocannabinoid System/Endocannabinoidome as a Potential Target for Treating Diabetes Mellitus

PURPOSE OF REVIEW

The endocannabinoid (eCB) system, i.e. the receptors that respond to the psychoactive component of cannabis, their endogenous ligands and the ligand metabolic enzymes, is part of a larger family of lipid signals termed the endocannabinoidome (eCBome). We summarize recent discoveries of the roles that the eCBome plays within peripheral tissues in diabetes, and how it is being targeted, in an effort to develop novel therapeutics for the treatment of this increasingly prevalent disease.

RECENT FINDINGS

As with the eCB system, many eCBome members regulate several physiological processes, including energy intake and storage, glucose and lipid metabolism and pancreatic health, which contribute to the development of type 2 diabetes (T2D). Preclinical studies increasingly support the notion that targeting the eCBome may beneficially affect T2D. The eCBome is implicated in T2D at several levels and in a variety of tissues, making this complex lipid signaling system a potential source of many potential therapeutics for the treatments for T2D.

Functionalized 6-(piperidin-1-yl)-8,9-diphenyl purines as inverse agonists of the CB1 receptor - SAR efforts towards selectivity and peripheralization

Antagonists of type 1 cannabinoid receptors (CB1) may be useful in treating diabetes, hepatic disorders, and fibrosis. Otenabant (1) is a potent and selective CB1 inverse agonist that was under investigation as an anti-obesity agent, but its development was halted once adverse effects associated with another marketed inverse agonist rimonabant (2) became known. Non-tissue selective antagonists of CB1 that have high levels of brain penetration produce adverse effects in a small subset of patients including anxiety, depression and suicidal ideation. Currently, efforts are underway to produce compounds that have limited brain penetration. In this report, novel analogs of 1 are explored to develop and test strategies for peripheralization. The piperidine of 1 is studied as a linker, which is functionalized with alkyl, heteroalkyl, aryl and heteroaryl groups using a connector in the form of an amine, amide, sulfonamide, sulfamide, carbamate, oxime, amidine, or guanidine. We also report more polar replacements for the 4-chlorophenyl group in the 9-position of the purine core, which improve calculated physical properties of the molecules. These studies resulted in compounds such as 75 that are potent inverse agonists of hCB1 with exceptional selectivity for hCB1 over hCB2. SAR studies revealed ways to adjust physical properties to limit brain exposure.

Functionalized 6-(Piperidin-1-yl)-8,9-Diphenyl Purines as Peripherally Restricted Inverse Agonists of the CB1 Receptor

Peripherally restricted CB1 receptor antagonists may be useful in treating metabolic syndrome, diabetes, liver diseases, and gastrointestinal disorders. Clinical development of the centrally acting CB1 inverse agonist otenabant (1) was halted due to its potential of producing adverse effects. SAR studies of 1 are reported herein with the objective of producing peripherally restricted analogues. Crystal structures of hCB1 and docking studies with 1 indicate that the piperidine group could be functionalized at the 4-position to access a binding pocket that can accommodate both polar and nonpolar groups. The piperidine is studied as a linker, functionalized with alkyl, heteroalkyl, aryl, and heteroaryl groups using a urea connector. Orally bioavailable and peripherally selective compounds have been produced that are potent inverse agonists of hCB1 with exceptional selectivity for hCB1 over hCB2. Compound 38 blocked alcohol-induced liver steatosis in mice and has good ADME properties for further development.

A patent update on cannabinoid receptor 1 antagonists (2015-2018)

INTRODUCTION

The endocannabinoid system is an important regulator of various physiological processes. Preclinical and clinical studies indicate that attenuation of the endocannabinoid system via antagonism of the type 1 cannabinoid receptor (CB1) is an excellent strategy to treat obesity, metabolic syndrome and associated disorders. However, centrally acting antagonists of CB1 also produce adverse effects like depression and anxiety. Current efforts are geared towards discovery and optimization of antagonists and modulators of CB1 that have limited brain penetration.

AREAS COVERED

Several recent publications and patent applications support the development of peripherally acting CB1 receptor antagonists and modulators. In this review, recent patents and applications (2015-2018) are summarized and discussed.

EXPERT OPINION

Approximately 30 new inventions have been reported since 2015, along with 3 recent commercial deals, highlighting the importance of this class of therapeutics. Taken together, peripherally acting CB1 receptor antagonists and modulators are an emerging class of drugs for metabolic syndrome, non-alcoholic steatohepatitis (NASH) and other important disorders where this receptor has been implicated.

Role of the endocannabinoid system in drug addiction

Drug addiction is a chronic relapsing disorder that produces a dramaticglobal health burden worldwide. Not effective treatment of drug addiction is currently available probably due to the difficulties to find an appropriate target to manage this complex disease raising the needs for further identification of novel therapeutic approaches. The endocannabinoid system has been found to play a crucial role in the neurobiological substrate underlying drug addiction. Endocannabinoids and cannabinoid receptors are widely expressed in the main areas of the mesocorticolimbic system that participate in the initiation and maintenance of drug consumption and in the development of compulsion and loss of behavioral control occurring during drug addiction. The identification of the important role played by CB1 cannabinoid receptors in drug addiction encouraged the possible used of an early commercialized CB1 receptor antagonist for treating drug addiction. However, the incidence of serious psychiatric adverse events leaded to the sudden withdrawal from the market of this CB1 antagonist and all the research programs developed by pharmaceutical companies to obtain new CB1 antagonists were stopped. Currently, new research strategies are under development to target the endocannabinoid system for drug addiction avoiding these side effects, which include allosteric negative modulators of CB1 receptors and compounds targeting CB2 receptors. Recent studies showing the potential role of CB2 receptors in the addictive properties of different drugs of abuse have open a promising research opportunity to develop novel possible therapeutic approaches.

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.

Cannabinoids in health and disease: pharmacological potential in metabolic syndrome and neuroinflammation

The use of different natural and/or synthetic preparations of Cannabis sativa is associated with therapeutic strategies for many diseases. Indeed, thanks to the widespread diffusion of the cannabinoidergic system in the brain and in the peripheral districts, its stimulation, or inhibition, regulates many pathophysiological phenomena. In particular, central activation of the cannabinoidergic system modulates the limbic and mesolimbic response which leads to food craving. Moreover, cannabinoid agonists are able to reduce inflammatory response. In this review a brief history of cannabinoids and the protagonists of the endocannabinoidergic system, i.e. synthesis and degradation enzymes and main receptors, will be described. Furthermore, the pharmacological effects of cannabinoids will be outlined. An overview of the involvement of the endocannabinoidergic system in neuroinflammatory and metabolic pathologies will be made. Finally, particular attention will also be given to the new pharmacological entities acting on the two main receptors, cannabinoid receptor type 1 (CB1) and cannabinoid receptor type 2 (CB2), with particular focus on the neuroinflammatory and metabolic mechanisms involved.

Hypothalamic miR-219 regulates individual metabolic differences in response to diet-induced weight cycling

Consumption of a low calorie diet is the most common approach to lose weight. While generally effective at first, it is frequently followed by a relapse where the pre-diet weight is regained, and often exceeded. This pattern of repeated weight loss/regain is referred to as weight cycling and the resulting metabolic response varies greatly between individuals.

Objective

We attempted to address the issue of individual differences in the response to weight cycling in male mice.

Methods

We first exposed adult wild type mice to repeated cycles of high/low fat food. Next, using a lentiviral approach, we knocked-down or over-expressed miR-219 in the ventromedial hypothalamus (VMH) of an additional mouse cohort and performed a full metabolic assessment.

Results

Exposure of wild type males to weight cycling resulted in the division of the cohort into subsets of resistant versus metabolic-syndrome-prone (MS) animals, which differed in their metabolic profile and hypothalamic miR-219 levels. Lentiviral knock-down of miR-219 in the VMH led to exacerbation of metabolic syndrome. In contrast, over-expression of miR-219 resulted in moderation of the metabolic syndrome phenotype.

Conclusions

Our results suggest a role for miR-219 in the mediation of the metabolic phenotype resulting from repeated weight cycling.

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Repeated cycles of high fat diet induce different responses in adult males.

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Low miR-219 in ventromedial hypothalamus are linked to metabolic-syndrome proneness.

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Lentiviral knockdown of miR-219 induces metabolic-syndrome-prone phenotype.

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Lentiviral overexpression of miR-219 provides moderate protection from metabolic-syndrome.

LH-21, A Peripheral Cannabinoid Receptor 1 Antagonist, Exerts Favorable Metabolic Modulation Including Antihypertensive Effect in KKAy Mice by Regulating Inflammatory Cytokines and Adipokines on Adipose Tissue

Patients with obesity are susceptible to hypertension and diabetes. Over-activation of cannabinoid receptor 1 (CB₁R) in adipose tissue is proposed in the pathophysiology of metabolic disorders, which led to the metabolic dysfunction of adipose tissue and deregulated production and secretion of adipokines. In the current study, we determined the impact of LH-21, a representative peripheral CB₁R antagonist, on the obesity-accompanied hypertension and explored the modulatory action of LH-21 on the adipose tissue in genetically obese and diabetic KKAy mice. 3-week LH-21 treatment significantly decreased blood pressure with a concomitant reduction in body weight, white adipose tissue (WAT) mass, and a slight loss on food intake in KKAy mice. Meanwhile, glucose handling and dyslipidemia were also markedly ameliorated after treatment. Gene expression of pro-inflammatory cytokines in WAT and the aortae were both attenuated apparently by LH-21, as well the mRNA expression of adipokines (lipocalin-2, leptin) in WAT. Concomitant amelioration on the accumulation of lipocalin-2 was observed in both WAT and aortae. In corresponding with this, serum inflammatory related cytokines (tumor necrosis factor α, IL-6, and CXCL1), and lipocalin-2 and leptin were lowered notably. Thus according to current results, it can be concluded that the peripheral CB₁R antagonist LH-21 is effective in managing the obesity-accompanied hypertension in KKAy mice. These metabolic benefits are closely associated with the regulation on the production and secretion of inflammatory cytokines and adipokines in the WAT, particularly alleviated circulating lipocalin-2 and its accumulation in aortae.

Novel Peripherally Restricted Cannabinoid 1 Receptor Selective Antagonist TXX-522 with Prominent Weight-Loss Efficacy in Diet Induced Obese Mice

The clinical development of the first generation of globally active cannabinoid 1 receptor (CB1R) antagonists was suspended because of their adverse neuropsychiatric effects. Selective blockade of peripheral CB1Rs has the potential to provide a viable strategy for the treatment of severe obesity while avoiding these central nervous system side effects. In the current study, a novel compound (TXX-522) was rationally designed based on the parent nucleus of a classical CB1R-selective antagonist/inverse agonist, rimonabant (SR141716A). Docking assays indicate that TXX-522 was bound with the CB1R in a mode similar to that of SR141716A. TXX-522 showed good binding, CB1R-selectivity (over the CB2R), and functional antagonist activities in a range of in vitro molecular and cellular assays. In vivo analysis of the steady state distribution of TXX-522 in the rat brain and blood tissues and the assay of its functional effects on CB1R activity collectively showed that TXX-522 showed minimal brain penetration. Moreover, the in vivo pharmacodynamic study further revealed that TXX-522 had good oral bioavailability and a potent anti-obesity effect, and ameliorated insulin resistance in high-fat diet-induced obese mice. No impact on food intake was observed in this model, confirming the limited brain penetration of this compound. Thus, the current study indicates that TXX-522 is a novel and potent peripherally acting selective CB1R antagonist with the potential to control obesity and related metabolic disorders.

Developmental programming of somatic growth, behavior and endocannabinoid metabolism by variation of early postnatal nutrition in a cross-fostering mouse model

Background

Nutrient deprivation during early development has been associated with the predisposition to metabolic disorders in adulthood. Considering its interaction with metabolism, appetite and behavior, the endocannabinoid (eCB) system represents a promising target of developmental programming.

Methods

By cross-fostering and variation of litter size, early postnatal nutrition of CB6F1-hybrid mice was controlled during the lactation period (3, 6, or 10 pups/mother). After weaning and redistribution at P21, all pups received standard chow ad libitum. Gene expression analyses (liver, visceral fat, hypothalamus) were performed at P50, eCB concentrations were determined in liver and visceral fat. Locomotor activity and social behavior were analyzed by means of computer-assisted videotracking.

Results

Body growth was permanently altered, with differences for length, weight, body mass index and fat mass persisting beyond P100 (all 3>6>10,p<0.01). This was paralleled by differences in hepatic IGF-I expression (p<0.01). Distinct gene expression patterns for key enzymes of the eCB system were observed in fat (eCB-synthesis: 3>6>10 (DAGLα p<0.05; NAPE-PLD p = 0.05)) and liver (eCB-degradation: 3>6>10 (FAAH p<0.05; MGL p<0.01)). Concentrations of endocannabinoids AEA and 2-AG in liver and visceral fat were largely comparable, except for a borderline significance for higher AEA (liver, p = 0.049) in formerly overfed mice and, vice versa, tendencies (p<0.1) towards lower AEA (fat) and 2-AG (liver) in formerly underfed animals. In the arcuate nucleus, formerly underfed mice tended to express more eCB-receptor transcripts (CB1R p<0.05; CB2R p = 0.08) than their overfed fellows. Open-field social behavior testing revealed significant group differences, with formerly underfed mice turning out to be the most sociable animals (p<0.01). Locomotor activity did not differ.

Conclusion

Our data indicate a developmental plasticity of somatic growth, behavior and parameters of the eCB system, with long-lasting impact of early postnatal nutrition. Developmental programming of the eCB system in metabolically active tissues, as shown here for liver and fat, may play a role in the formation of the adult cardiometabolic risk profile following perinatal malnutrition in humans.

Metabolic Profiling of CB1 Neutral Antagonists

PIMSR is among the first neutral antagonists for the CB1R and was demonstrated pharmacologically to bind to the CB1R, yet not alter calcium flux. It was further shown computationally to be able to stabilize both the active and inactive states of CB1R revealing the molecular interactions that mechanistically afford the property of neutral antagonism. PIMSR shows dramatic positive effects in reducing weight, food intake, and adiposity as well as in improving glycemic control and lipid homeostasis in high-fat diet-induced obese mice, but also shows increased ALT and liver weight as markers of liver injury with chronic administration. Further, in a separate study, 3-day administration of PIMSR in C57BL/6J mice, hepatic steatosis from an acute administration of high of ethanol was significantly reduced. Also, it partially prevented alcohol-induced increases in ALT, AST, and LDH. The differences in ALT levels in obese and nonobese mice under different test paradigms are unlikely to be due to neutral antagonism itself since other neutral antagonists (AM6545) do not exhibit liver injury. The brain levels of low micromolar would support significant brain CB1 receptor occupancy (re: Ki=17nM), thus potentially including both CNS and peripheral influences on the observed weight loss. Overall, these studies suggest that marked improvements in aspects of metabolic disease and alcoholic steatosis can be realized with CB1R neutral antagonists and hence warrants the exploration of further members of this class of cannabinoid ligands.

Pharmacological comparison of traditional and non-traditional cannabinoid receptor 1 blockers in rodent models in vivo

Cannabinoid receptor 1 (CB1R) antagonists have been proven to be effective anti-obesity drugs; however, psychiatric side effects have halted their pharmaceutical development worldwide. Despite the emergence of next generation CB1R blockers, a preclinical head to head comparison of the anti-obesity and psychiatric side effect profiles of the key compounds has not been performed. Here, we compared classical CB1R antagonists (rimonabant, taranabant, otenabant, ibipinabant, and surinabant) and non-traditional CB1R blockers (the partial agonist O-1269, the neutral antagonists VCHSR and LH-21 and the peripherally acting inverse agonist JD-5037) using an in vivo screening cascade. First, the potencies of these compounds to reduce CB1R agonist-induced hypothermia and decrease fasting-induced food intake were determined. Then, equipotent doses of the non-toxic compounds were compared in a diet-induced obesity (DIO) test, which includes measurements of metabolic syndrome markers. Psychiatric side effects were assessed by measuring anxiogenicity in an ultrasonic vocalization test. All classical CB1R blockers were centrally acting appetite suppressants and decreased body weight and food intake in an obesity-dependent manner, with only slight effects on metabolic syndrome markers. In addition, all classical CB1R blockers increased ultrasonic vocalization. Surprisingly, none of the non-classical CB1R blockers was eligible for the DIO comparison and side effect profiling. O-1269 and LH-21 induced convulsive behavior, whereas VCHSR and JD-5037 were devoid of any in vivo activity. The classical CB1R blockers displayed similar therapeutic and side effect profiles in vivo, whereas the available non-traditional CB1R blockers were not appropriate tools for testing the therapeutic potential of alternative CB1R inhibitors.

MECHANISMS IN ENDOCRINOLOGY: Endocannabinoids and metabolism: past, present and future

The endocannabinoid system (ECS), including cannabinoid type 1 and type 2 receptors (CB₁R and CB₂R), endogenous ligands called endocannabinoids and their related enzymatic machinery, is known to have a role in the regulation of energy balance. Past information generated on the ECS, mainly focused on the involvement of this system in the central nervous system regulation of food intake, while at the same time clinical studies pointed out the therapeutic efficacy of brain penetrant CB₁R antagonists like rimonabant for obesity and metabolic disorders. Rimonabant was removed from the market in 2009 and its obituary written due to its psychiatric side effects. However, in the meanwhile a number of investigations had started to highlight the roles of the peripheral ECS in the regulation of metabolism, bringing up new hope that the ECS might still represent target for treatment. Accordingly, peripherally restricted CB₁R antagonists or inverse agonists have shown to effectively reduce body weight, adiposity, insulin resistance and dyslipidemia in obese animal models. Very recent investigations have further expanded the possible toolbox for the modulation of the ECS, by demonstrating the existence of endogenous allosteric inhibitors of CB₁R, the characterization of the structure of the human CB₁R, and the likely involvement of CB₂R in metabolic disorders. Here we give an overview of these findings, discussing what the future may hold in the context of strategies targeting the ECS in metabolic disease.

Rimonabant improves metabolic parameters partially attributed to restoration of high voltage-activated Ca2+ channels in skeletal muscle in HFD-fed mice

Cannabinoid type 1 receptor (CB1R) inhibition tends to be one of the promising strategies for the treatment of obesity and other related metabolic disorders. Although CB1R inhibition may cause adverse psychiatric effects including depression and anxiety, the investigation of the role of peripheral CB1R on weight loss and related metabolic parameters are urgently needed. We first explored the effect of rimonabant, a selective CB1R antagonist/inverse agonist, on some metabolic parameters in high fat-diet (HFD)-induced obesity in mice. Then, real-time PCR and electrophysiology were used to explore the contribution of high voltage-activated Ca²⁺ channels (HVACCs), especially Ca_v1.1, on rimonabant's effect in skeletal muscle (SM) in HFD-induced obesity. Five-week HFD feeding caused body weight gain, and decreased glucose/insulin tolerance in mice compared to those in the regular diet group (P<0.05), which was restored by rimonabant treatment compared to the HFD group (P<0.05). Interestingly, HVACCs and Ca_v1.1 were decreased in soleus muscle cells in the HFD group compared to the control group. Daily treatment with rimonabant for 5 weeks was shown to counter such decrease (P<0.05). Collectively, our findings provided a novel understanding for peripheral CB1R's role in the modulation of body weight and glucose homeostasis and highlight peripheral CB1R as well as Cav1.1 in the SM as potential targets for obesity treatment.

Fetal Syndrome of Endocannabinoid Deficiency (FSECD) In Maternal Obesity

The theory of a fetal origin of adult diseases links many pathological conditions to very early life events and is known as a "developmental programming" phenomenon. The mechanisms of this phenomenon are not quite understood and have been explained by inflammation, stress, etc. In particular the epidemic of obesity, with more than 64% of women being overweight or obese, has been associated with conditions in later life such as mental disorders, diabetes, asthma, and irritable bowel syndrome. Interestingly, these diseases were classified a decade ago as Clinical Syndrome of Endocannabinoid Deficiency (CECD), which was first described by Russo in 2004. Cannabinoids have been used for the treatment of chronic pain for millenniums and act through the mechanism of "kick-starting" the components of the endogenous cannabinoid system (ECS). ECS is a pharmacological target for the treatment of obesity, inflammation, cardiovascular and neuronal damage, and pain. We hypothesize that the deteriorating effect of maternal obesity on offspring health is explained by the mechanism of Fetal Syndrome of Endocannabinoid Deficiency (FSECD), which accompanies maternal obesity. Here we provide support for this hypothesis.

Tetrahydroindazole derivatives as potent and peripherally selective cannabinoid-1 (CB1) receptor inverse agonists

A series of potent and receptor-selective cannabinoid-1 (CB1) receptor inverse agonists has been discovered. Peripheral selectivity of the compounds was assessed by a mouse tissue distribution study, in which the concentrations of a test compound in both plasma and brain were measured. A number of peripherally selective compounds have been identified through this process. Compound 2p was further evaluated in a 3-week efficacy study in the diet-induced obesity (DIO) mouse model. Beneficial effects on plasma glucose were observed from the compound-treated mice.

Possible Therapeutic Doses of Cannabinoid Type 1 Receptor Antagonist Reverses Key Alterations in Fragile X Syndrome Mouse Model

Fragile X syndrome (FXS) is the most common monogenetic cause of intellectual disability. The cognitive deficits in the mouse model for this disorder, the Fragile X Mental Retardation 1 (Fmr1) knockout (KO) mouse, have been restored by different pharmacological approaches, among those the blockade of cannabinoid type 1 (CB1) receptor. In this regard, our previous study showed that the CB1 receptor antagonist/inverse agonist rimonabant normalized a number of core features in the Fmr1 knockout mouse. Rimonabant was commercialized at high doses for its anti-obesity properties, and withdrawn from the market on the bases of mood-related adverse effects. In this study we show, by using electrophysiological approaches, that low dosages of rimonabant (0.1 mg/kg) manage to normalize metabotropic glutamate receptor dependent long-term depression (mGluR-LTD). In addition, low doses of rimonabant (from 0.01 mg/kg) equally normalized the cognitive deficit in the mouse model of FXS. These doses of rimonabant were from 30 to 300 times lower than those required to reduce body weight in rodents and to presumably produce adverse effects in humans. Furthermore, NESS0327, a CB1 receptor neutral antagonist, was also effective in preventing the novel object-recognition memory deficit in Fmr1 KO mice. These data further support targeting CB1 receptors as a relevant therapy for FXS.

Metabolic effects of smoking cessation

Smoking continues to be the leading cause of preventable death in the USA, despite the vast and widely publicized knowledge about the negative health effects of tobacco smoking. Data show that smoking cessation is often accompanied by weight gain and an improvement in insulin sensitivity over time. However, paradoxically, post-cessation-related obesity might contribute to insulin resistance. Furthermore, post-cessation weight gain is reportedly the number one reason why smokers, especially women, fail to initiate smoking cessation or relapse after initiating smoking cessation. In this Review, we discuss the metabolic effects of stopping smoking and highlight future considerations for smoking cessation programs and therapies to be designed with an emphasis on reducing post-cessation weight gain.

A novel live cell assay to measure diacylglycerol lipase α activity

Diacylglycerol lipase α (DAGLα) hydrolyses DAG to generate the principal endocannabinoid (eCB) 2-arachidonoylglycerol (2-AG) in the central nervous system. DAGLα dependent cannabinoid (CB) signalling has been implicated in numerous processes including axonal growth and guidance, adult neurogenesis and retrograde signalling at the synapse. Recent studies have implicated DAGLα as an emerging drug target for several conditions including pain and obesity. Activity assays are critical to the drug discovery process; however, measurement of diacylglycerol lipase (DAGL) activity using its native substrate generally involves low-throughput MS techniques. Some relatively high-throughput membrane based assays utilizing surrogate substrates have been reported, but these do not take into account the rate-limiting effects often associated with the ability of a drug to cross the cell membrane. In the present study, we report the development of a live cell assay to measure DAGLα activity. Two previously reported DAGLα surrogate substrates, p-nitrophenyl butyrate (PNPB) and 6,8-difluoro-4-methylumbelliferyl octanoate (DiFMUO), were evaluated for their ability to detect DAGLα activity in live cell assays using a human cell line stably expressing the human DAGLα transgene. Following optimization, the small molecule chromogenic substrate PNPB proved to be superior by providing lower background activity along with a larger signal window between transfected and parental cells when compared with the fluorogenic substrate DiFMUO. The assay was further validated using established DAGL inhibitors. In summary, the live cell DAGLα assay reported here offers an economical and convenient format to screen for novel inhibitors as part of drug discovery programmes and compliments previously reported high-throughput membrane based DAGL assays.

Controlled downregulation of the cannabinoid CB1 receptor provides a promising approach for the treatment of obesity and obesity-derived type 2 diabetes

Increased activity of the endocannabinoid system has emerged as a pathogenic factor in visceral obesity, which is a risk factor for type 2 diabetes mellitus (T2DM). The endocannabinoid system is composed of at least two Gprotein-coupled receptors (GPCRs), the cannabinoid receptor type 1 (CB1), and the cannabinoid receptor type 2 (CB2). Downregulation of CB1 activity in rodents and humans has proven efficacious to reduce food intake, abdominal adiposity, fasting glucose levels, and cardiometabolic risk factors. Unfortunately, downregulation of CB1 activity by universally active CB1 inverse agonists has been found to elicit psychiatric side effects, which led to the termination of using globally active CB1 inverse agonists to treat diet-induced obesity. Interestingly, preclinical studies have shown that downregulation of CB1 activity by CB1 neutral antagonists or peripherally restricted CB1 inverse agonists provided similar anorectic effects and metabolic benefits without psychiatric side effects seen in globally active CB1 inverse agonists. Furthermore, downregulation of CB1 activity may ease endoplasmic reticulum and mitochondrial stress which are contributors to obesity-induced insulin resistance and type 2 diabetes. This suggests new approaches for cannabinoid-based therapy in the management of obesity and obesity-related metabolic disorders including type 2 diabetes.

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.

Mitochondrial ADP/ATP exchange inhibition: a novel off-target mechanism underlying ibipinabant-induced myotoxicity

Cannabinoid receptor 1 (CB1R) antagonists appear to be promising drugs for the treatment of obesity, however, serious side effects have hampered their clinical application. Rimonabant, the first in class CB1R antagonist, was withdrawn from the market because of psychiatric side effects. This has led to the search for more peripherally restricted CB1R antagonists, one of which is ibipinabant. However, this 3,4-diarylpyrazoline derivative showed muscle toxicity in a pre-clinical dog study with mitochondrial dysfunction. Here, we studied the molecular mechanism by which ibipinabant induces mitochondrial toxicity. We observed a strong cytotoxic potency of ibipinabant in C2C12 myoblasts. Functional characterization of mitochondria revealed increased cellular reactive oxygen species generation and a decreased ATP production capacity, without effects on the catalytic activities of mitochondrial enzyme complexes I-V or the complex specific-driven oxygen consumption. Using in silico off-target prediction modelling, combined with in vitro validation in isolated mitochondria and mitoplasts, we identified adenine nucleotide translocase (ANT)-dependent mitochondrial ADP/ATP exchange as a novel molecular mechanism underlying ibipinabant-induced toxicity. Minor structural modification of ibipinabant could abolish ANT inhibition leading to a decreased cytotoxic potency, as observed with the ibipinabant derivative CB23. Our results will be instrumental in the development of new types of safer CB1R antagonists.

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.

Cannabinoid-based drugs targeting CB1 and TRPV1, the sympathetic nervous system, and arthritis

Chronic inflammation in rheumatoid arthritis (RA) is accompanied by activation of the sympathetic nervous system, which can support the immune system to perpetuate inflammation. Several animal models of arthritis already demonstrated a profound influence of adrenergic signaling on the course of RA. Peripheral norepinephrine release from sympathetic terminals is controlled by cannabinoid receptor type 1 (CB1), which is activated by two major endocannabinoids (ECs), arachidonylethanolamine (anandamide) and 2-arachidonylglycerol. These ECs also modulate function of transient receptor potential channels (TRPs) located on sensory nerve fibers, which are abundant in arthritic synovial tissue. TRPs not only induce the sensation of pain but also support inflammation via secretion of pro-inflammatory neuropeptides. In addition, many cell types in synovial tissue express CB1 and TRPs. In this review, we focus on CB1 and transient receptor potential vanilloid 1 (TRPV1)-mediated effects on RA since most anti-inflammatory mechanisms induced by cannabinoids are attributed to cannabinoid receptor type 2 (CB2) activation. We demonstrate how CB1 agonism or antagonism can modulate arthritic disease. The concept of functional antagonism with continuous CB1 activation is discussed. Since fatty acid amide hydrolase (FAAH) is a major EC-degrading enzyme, the therapeutic possibility of FAAH inhibition is studied. Finally, the therapeutic potential of ECs is examined since they interact with cannabinoid receptors and TRPs but do not produce central side effects.

Two non-psychoactive cannabinoids reduce intracellular lipid levels and inhibit hepatosteatosis

BACKGROUND & AIMS

Obesity and associated metabolic syndrome have quickly become a pandemic and a major detriment to global human health. The presence of non-alcoholic fatty liver disease (NAFLD; hepatosteatosis) in obesity has been linked to the worsening of the metabolic syndrome, including the development of insulin resistance and cardiovascular disease. Currently, there are few options to treat NAFLD, including life style changes and insulin sensitizers. Recent evidence suggests that the cannabinoids Δ(9)-tetrahydrocannabivarin (THCV) and cannabidiol (CBD) improve insulin sensitivity; we aimed at studying their effects on lipid levels.

METHODS

The effects of THCV and CBD on lipid levels were examined in a variety of in vitro and in vivo systems, with special emphasis on models of hepatosteatosis. Transcriptional, post-translational and metabolomic changes were assayed.

RESULTS

THCV and CBD directly reduce accumulated lipid levels in vitro in a hepatosteatosis model and adipocytes. Nuclear magnetic resonance- (NMR) based metabolomics confirmed these results and further identified specific metabolic changes in THCV and CBD-treated hepatocytes. Treatment also induced post-translational changes in a variety of proteins such as CREB, PRAS40, AMPKa2 and several STATs indicating increased lipid metabolism and, possibly, mitochondrial activity. These results are supported by in vivo data from zebrafish and obese mice indicating that these cannabinoids are able to increase yolk lipid mobilization and inhibit the development of hepatosteatosis respectively.

CONCLUSIONS

Our results suggest that THCV and CBD might be used as new therapeutic agents for the pharmacological treatment of obesity- and metabolic syndrome-related NAFLD/hepatosteatosis.

Role of the endocannabinoid system in obesity induced by neuropeptide Y overexpression in noradrenergic neurons

Objective:

Endocannabinoids and neuropeptide Y (NPY) promote energy storage via central and peripheral mechanisms. In the hypothalamus, the two systems were suggested to interact. To investigate such interplay also in non-hypothalamic tissues, we evaluated endocannabinoid levels in obese OE-NPY^DβH mice, which overexpress NPY in the noradrenergic neurons in the sympathetic nervous system and the brain.

Methods:

The levels of the endocannabinoids anandamide and 2-arachidonoylglycerol (2-AG) were measured in key regulatory tissues, that is, hypothalamus, pancreas, epididymal white adipose tissue (WAT), liver and soleus muscle, over the development of metabolic dysfunctions in OE-NPY^DβH mice. The effects of a 5-week treatment with the CB1 receptor inverse agonist AM251 on adiposity and glucose metabolism were studied.

Results:

2-AG levels were increased in the hypothalamus and epididymal WAT of pre-obese and obese OE-NPY^DβH mice. Anandamide levels in adipose tissue and pancreas were increased at 4 months concomitantly with higher fat mass and impaired glucose tolerance. CB1 receptor blockage reduced body weight gain and glucose intolerance in OE-NPY^DβH to the level of vehicle-treated wild-type mice.

Conclusions:

Altered endocannabinoid tone may underlie some of the metabolic dysfunctions in OE-NPY^DβH mice, which can be attenuated with CB1 inverse agonism suggesting interactions between endocannabinoids and NPY also in the periphery. CB1 receptors may offer a target for the pharmacological treatment of the metabolic syndrome with altered NPY levels.

Legal highs: staying on top of the flood of novel psychoactive substances

There has been growing clinical, public, and media awareness and concern about the availability and potential harmfulness of so-called 'legal highs', which are more appropriately called new or novel psychoactive substances (NPS). A cat-and-mouse process has emerged wherein unknown chemists and laboratories are producing new, and as yet nonproscribed, compounds for human consumption; and as soon as they are banned, which they inevitably are, slightly modified analogues are produced to circumvent new laws. This rapidly changing environment, 81 new substances were identified in 2013 alone, has led to confusion for clinicians, psychopharmacologists, and the public at large. Our difficulties in keeping up with the process has had a two-fold negative effect: the danger of ignoring what is confusing; and the problem that some of the newer synthesized compounds appear ever more potent. This review aims to circumscribe a quick moving and growing field, and to categorize NPS into five major groups based upon their 'parent' compounds: stimulants similar to cocaine, amphetamines and ecstasy; cannabinoids; benzodiazepine based drugs; dissociatives similar to ketamine and phencyclidine (PCP); and those modelled after classic hallucinogens such as LSD and psilocybin. Pharmacodynamic actions, subjective and physical effects, harmfulness, risk of dependency and, where appropriate, putative clinical potentials are described for each class. Clinicians might encounter NPS in various ways: anecdotal reportage; acute intoxication; as part of a substance misuse profile; and as a precipitant or perpetuating factor for longer-term physical and psychological ill health. Current data are overall limited, and much of our knowledge and treatment strategies are based upon those of the 'parent' compound. There is a critical need for more research in this field, and for professionals to make themselves more aware of this growing issue and how it might affect those we see clinically and try to help: a brave new world of so-called 'psychonauts' consuming NPS will also need informed 'psychotherapeutonauts'. The paper should serve as a primer for clinicians and interested readers, as well as provide a framework into which to place the new substances that will inevitably be synthesized in the future.

New perspectives on the development of antiobesity drugs

After many years of research, obesity is still a disease with an unmet medical need. Very few compounds have been approved, acting mainly on neuromediators; researches, in recent years, pointed toward compounds potentially safer than first-generation antiobesity drugs, able to interact with one or more (multitarget therapy) receptors for substances produced by the gut, adipose tissue and other targets outside CNS. Other holistic approaches, such as those involving gut microbiota and plant extracts, appeared recently in the literature, and undoubtedly will contribute to the discovery of a valuable therapy for this disease. This review deals with the positive results and the pitfalls obtained following these approaches, with a view on their clinical trial studies.

(4-(Bis(4-fluorophenyl)methyl)piperazin-1-yl)(cyclohexyl)methanone hydrochloride (LDK1229): a new cannabinoid CB1 receptor inverse agonist from the class of benzhydryl piperazine analogs

Some inverse agonists of cannabinoid receptor type 1 (CB1) have been demonstrated to be anorectic antiobesity drug candidates. However, the first generation of CB1 inverse agonists, represented by rimonabant (SR141716A), otenabant, and taranabant, are centrally active, with a high level of psychiatric side effects. Hence, the discovery of CB1 inverse agonists with a chemical scaffold distinct from these holds promise for developing peripherally active CB1 inverse agonists with fewer side effects. We generated a new CB1 inverse agonist, (4-(bis(4-fluorophenyl)methyl)piperazin-1-yl)(cyclohexyl)methanone hydrochloride (LDK1229), from the class of benzhydryl piperazine analogs. This compound binds to CB1 more selectively than cannabinoid receptor type 2, with a Ki value of 220 nM. Comparable CB1 binding was also observed by analogs 1-[bis(4-fluorophenyl)methyl]-4-cinnamylpiperazine dihydrochloride (LDK1203) and 1-[bis(4-fluorophenyl)methyl]-4-tosylpiperazine hydrochloride (LDK1222), which differed by the substitution on the piperazine ring where the piperazine of LDK1203 and LDK1222 are substituted by an alkyl group and a tosyl group, respectively. LDK1229 exhibits efficacy comparable with SR141716A in antagonizing the basal G protein coupling activity of CB1, as indicated by a reduction in guanosine 5'-O-(3-thio)triphosphate binding. Consistent with inverse agonist behavior, increased cell surface localization of CB1 upon treatment with LDK1229 was also observed. Although docking and mutational analysis showed that LDK1229 forms similar interactions with the receptor as SR141716A does, the benzhydryl piperazine scaffold is structurally distinct from the first-generation CB1 inverse agonists. It offers new opportunities for developing novel CB1 inverse agonists through the optimization of molecular properties, such as the polar surface area and hydrophilicity, to reduce the central activity observed with SR141716A.

Is there a "metabolic-mood syndrome"? A review of the relationship between obesity and mood disorders

Obesity and mood disorders are highly prevalent and co-morbid. Epidemiological studies have highlighted the public health relevance of this association, insofar as both conditions and its co-occurrence are associated with a staggering illness-associated burden. Accumulating evidence indicates that obesity and mood disorders are intrinsically linked and share a series of clinical, neurobiological, genetic and environmental factors. The relationship of these conditions has been described as convergent and bidirectional; and some authors have attempted to describe a specific subtype of mood disorders characterized by a higher incidence of obesity and metabolic problems. However, the nature of this association remains poorly understood. There are significant inconsistencies in the studies evaluating metabolic and mood disorders; and, as a result, several questions persist about the validity and the generalizability of the findings. An important limitation in this area of research is the noteworthy phenotypic and pathophysiological heterogeneity of metabolic and mood disorders. Although clinically useful, categorical classifications in both conditions have limited heuristic value and its use hinders a more comprehensive understanding of the association between metabolic and mood disorders. A recent trend in psychiatry is to move toward a domain specific approach, wherein psychopathology constructs are agnostic to DSM-defined diagnostic categories and, instead, there is an effort to categorize domains based on pathogenic substrates, as proposed by the National Institute of Mental Health (NIMH) Research Domain Criteria Project (RDoC). Moreover, the substrates subserving psychopathology seems to be unspecific and extend into other medical illnesses that share in common brain consequences, which includes metabolic disorders. Overall, accumulating evidence indicates that there is a consistent association of multiple abnormalities in neuropsychological constructs, as well as correspondent brain abnormalities, with broad-based metabolic dysfunction, suggesting, therefore, that the existence of a "metabolic-mood syndrome" is possible. Nonetheless, empirical evidence is necessary to support and develop this concept. Future research should focus on dimensional constructs and employ integrative, multidisciplinary and multimodal approaches.

Endocannabinoids and Metabolic Disorders

The endocannabinoid system (ECS) is known to exert regulatory control on essentially every aspect related to the search for, and the intake, metabolism and storage of calories, and consequently it represents a potential pharmacotherapeutic target for obesity, diabetes and eating disorders. While the clinical use of the first generation of cannabinoid type 1 (CB(1)) receptor blockers has been halted due to the psychiatric side effects that their use occasioned, recent research in animals and humans has provided new knowledge on the mechanisms of actions of the ECS in the regulation of eating behavior, energy balance, and metabolism. In this review, we discuss these recent advances and how they may allow targeting the ECS in a more specific and selective manner for the future development of therapies against obesity, metabolic syndrome, and eating disorders.

Concurrent pharmacological modification of cannabinoid-1 and glucagon-like peptide-1 receptor activity affects feeding behavior and body weight in rats fed a free-choice, high-carbohydrate diet

To extend preliminary studies on the effects on food intake of the combined use of cannabinoid (CB) 1 and glucagon-like peptide-1 (GLP-1) receptor agonists and antagonists, the effect of these drugs on the feeding behavior in rats maintained on a free-choice, high-carbohydrate diet was investigated over a longer period of time. Rats were fed a standard diet for 3 days and then fed with both the standard and the high-sucrose chow. After 4 days of the high-calorie diet, the following combination treatments were administered daily by an intraperitoneal injection for the next 3 days: 1 mg/kg AM 251 (a CB1 receptor antagonist) or 1 mg/kg WIN 55,212-2 (a CB1 receptor agonist) together with 3 µg/kg exendin-4 (Ex-4, a GLP-1 receptor agonist) or 160 µg/kg exendin (9-39) [Ex (9-39), a GLP-1 receptor antagonist]. The total daily caloric intake and body weight were significantly reduced in rats treated with Ex-4 and AM 251 or WIN 55,212-2 compared with either of the drugs injected alone and the saline-injected controls. Both drug combinations selectively inhibited ingestion of the high-sucrose chow. Although Ex (9-39) administration did not significantly affect food consumption, it resulted in a marked body weight gain, indicating that the GLP-1 receptor antagonist caused a positive energy balance. It is concluded that AM 251 or WIN 55,212-2 and Ex-4, injected together, exert additive, inhibitory effects on the consumption of high-sugar food.

The endocannabinoid system and appetite: relevance for food reward

Mounting evidence substantiates the central role of the endocannabinoid system (ECS) in the modulation of both homeostatic and hedonic elements of appetite and food intake. Conversely, feeding status and dietary patterns directly influence activity of the ECS. Following a general introduction on the functioning of the ECS, the present review specifically addresses its role in the modulation of hedonic eating. Humans possess strong motivational systems triggered by rewarding aspects of food. Food reward is comprised of two components: one appetitive (orienting towards food); the other consummatory (hedonic evaluation), also referred to as 'wanting' and 'liking', respectively. Endocannabinoid tone seems to influence both the motivation to feed and the hedonic value of foods, probably by modifying palatability. Human physiology underlying hedonic eating is still not fully understood. A better understanding of the role of the ECS in the rewarding value of specific foods or diets could offer new possibilities to optimise the balance between energy and nutrient intake for different target groups. These groups include the obese and overweight, and potentially individuals suffering from malnutrition. Examples for the latter group are patients with disease-related anorexia, as well as the growing population of frail elderly suffering from persistent loss of food enjoyment and appetite resulting in malnutrition and involuntary weight loss. It has become clear that the psychobiology of food hedonics is extremely complex and the clinical failure of CB1 inverse agonists including rimonabant (Accomplia®) has shown that 'quick wins' in this field are unlikely.

Peripheral targets in obesity treatment: a comprehensive update

Obesity is a major epidemic of our time and is associated with diseases such as metabolic syndrome, type 2 diabetes mellitus and atherosclerotic cardiovascular disease. Although weight loss drugs, when accompanied by diet and exercise, could be a very helpful medical tool in treating obese or overweight patients, their usefulness has been questioned due to the complexity of this type of medication, which regards a plethora of issues such as efficacy and safety of the drug and also risks and benefits among different patients. In general, obesity drugs that target peripheral pathophysiological mechanisms can be divided into two main categories. The first category includes anti-obesity agents able to reduce or limit energy absorption, such as pancreatic lipase and microsomal triglyceride transfer protein inhibitors. The second category consists of a heterogeneous group of compounds aiming to decrease fat mass by increasing energy expenditure or by redistributing adipose tissue. Angiogenesis inhibitors, beta-3 receptor agonists, sirtuin-I activators, diazoxide and other molecules belong to this group. The glucagon-like peptide-1 receptor agonists consist the third category of peripheral anti-obesity agents discussed therein. This review aims to provide a general overview of the molecules and substances that are already or could potentially be used as peripheral anti-obesity drugs, the molecular mechanisms by which they act, as well as their current stage of development, production and/or availability.

Characterization of the intrinsic activity for a novel class of cannabinoid receptor ligands: Indole quinuclidine analogs

Our laboratory recently reported that a group of novel indole quinuclidine analogs bind with nanomolar affinity to cannabinoid type-1 and type-2 receptors. This study characterized the intrinsic activity of these compounds by determining whether they exhibit agonist, antagonist, or inverse agonist activity at cannabinoid type-1 and/or type-2 receptors. Cannabinoid receptors activate Gi/Go-proteins that then proceed to inhibit activity of the downstream intracellular effector adenylyl cyclase. Therefore, intrinsic activity was quantified by measuring the ability of compounds to modulate levels of intracellular cAMP in intact cells. Concerning cannabinoid type-1 receptors endogenously expressed in Neuro2A cells, a single analog exhibited agonist activity, while eight acted as neutral antagonists and two possessed inverse agonist activity. For cannabinoid type-2 receptors stably expressed in CHO cells, all but two analogs acted as agonists; these two exceptions exhibited inverse agonist activity. Confirming specificity at cannabinoid type-1 receptors, modulation of adenylyl cyclase activity by all proposed agonists and inverse agonists was blocked by co-incubation with the neutral cannabinoid type-1 antagonist O-2050. All proposed cannabinoid type-1 receptor antagonists attenuated adenylyl cyclase modulation by cannabinoid agonist CP-55,940. Specificity at cannabinoid type-2 receptors was confirmed by failure of all compounds to modulate adenylyl cyclase activity in CHO cells devoid of cannabinoid type-2 receptors. Further characterization of select analogs demonstrated concentration-dependent modulation of adenylyl cyclase activity with potencies similar to their respective affinities for cannabinoid receptors. Therefore, indole quinuclidines are a novel structural class of compounds exhibiting high affinity and a range of intrinsic activity at cannabinoid type-1 and type-2 receptors.

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.