Preferential effects of the cannabinoid CB1 receptor antagonist, SR 141716, on food intake and body weight gain of obese (fa/fa) compared to lean Zucker rats

Hydroxytyrosol Linoleoyl Ether Ameliorates Metabolic-Associated Fatty Liver Disease Symptoms in Obese Zucker Rats

A main hepatic consequence of obesity is metabolic-associated fatty liver disease (MAFLD), currently treated by improving eating habits and administrating fibrates yet often yielding suboptimal outcomes. Searching for a new therapeutic approach, we aimed to evaluate the efficacy of hydroxytyrosol linoleoyl ether (HTLE), a dual Ppar-α agonist/Cb1 antagonist with inherent antioxidant properties, as an antisteatotic agent. Using lean and obese Zucker rats, they were administrated daily doses of HTLE (3 mg/kg) over a 15-day period, evaluating its safety profile, pharmacokinetics, impact on body weight, hepatic fat content, expression of key enzymes involved in lipogenesis/fatty acid oxidation, and antioxidant capacity. HTLE decreased the body weight and food intake in both rat genotypes. Biochemical analysis demonstrated a favorable safety profile for HTLE along with decreased concentrations of urea, total cholesterol, and aspartate aminotransferase AST transaminases in plasma. Notably, HTLE exhibited potent antisteatotic effects in obese rats, evidenced by a decrease in liver fat content and downregulation of lipogenesis-related enzymes, alongside increased expression of proteins controlling lipid oxidation. Moreover, HTLE successfully counteracted the redox imbalance associated with MAFLD in obese rats, attenuating lipid peroxidation and replenishing both glutathione levels and the overall antioxidant. Our findings highlight the effectiveness of triple-action strategies in managing MAFLD effectively. Based on our results in the Zucker rat model, HTLE emerges as a promising candidate with triple functionality as an anorexigenic, antisteatotic, and antioxidant agent, offering potential relief from MAFLD symptoms associated with obesity while exhibiting minimal side effects. In conclusion, our study positions HTLE as a highly promising compound for therapeutic intervention in MAFLD treatment, warranting further exploration in clinical trials.

Up-regulation of CB1 cannabinoid receptors located at glutamatergic terminals in the medial prefrontal cortex of the obese Zucker rat

The present study describes a detailed neuroanatomical distribution map of the cannabinoid type 1 (CB₁) receptor, along with the biochemical characterization of the expression and functional coupling to their cognate G_i/o proteins in the medial prefrontal cortex (mPCx) of the obese Zucker rats. The CB₁ receptor density was higher in the prelimbic (PL) and infralimbic (IL) subregions of the mPCx of obese Zucker rats relative to their lean littermates which was associated with a higher percentage of CB₁ receptor immunopositive excitatory presynaptic terminals in PL and IL. Also, a higher expression of CB₁ receptors and WIN55,212-2-stimulated [³⁵S]GTPγS binding was observed in the mPCx but not in the neocortex (NCx) and hippocampus of obese rats. Low-frequency stimulation in layers II/III of the mPCx induced CB₁ receptor-dependent long-term synaptic plasticity in IL of area obese Zucker but not lean rats. Overall, the elevated 2-AG levels, up-regulation of CB₁ receptors, and increased agonist-stimulated [³⁵S]GTPγS binding strongly suggest that hyperactivity of the endocannabinoid signaling takes place at the glutamatergic terminals of the mPCx in the obese Zucker rat. These findings could endorse the importance of the CB₁ receptors located in the mPCx in the development of obesity in Zucker rats.

Cannabinoids, Chemical Senses, and Regulation of Feeding Behavior

The herb Cannabis sativa has been traditionally used in many cultures and all over the world for thousands of years as medicine and recreation. However, because it was brought to the Western world in the late 19th century, its use has been a source of controversy with respect to its physiological effects as well as the generation of specific behaviors. In this regard, the CB1 receptor represents the most relevant target molecule of cannabinoid components on nervous system and whole-body energy homeostasis. Thus, the promotion of CB1 signaling can increase appetite and stimulate feeding, whereas blockade of CB1 suppresses hunger and induces hypophagia. Taste and flavor are sensory experiences involving the oral perception of food-derived chemicals and drive a primal sense of acceptable or unacceptable for what is sampled. Therefore, research within the last decades focused on deciphering the effect of cannabinoids on the chemical senses involved in food perception and consequently in the pattern of feeding. In this review, we summarize the data on the effect of cannabinoids on chemical senses and their influences on food intake control and feeding behavior.

Preclinical and Clinical Evidence for a Distinct Regulation of Mu Opioid and Type 1 Cannabinoid Receptor Genes Expression in Obesity

Among endogenous signaling networks involved in both rewarding and homeostatic mechanisms of obesity, a relevant role is played by the endocannabinoid (ECS) and the opioid (EOS) systems. We here studied the transcriptional regulation of ECS and EOS genes in the hypothalamus of Diet-induced obesity rats, a preclinical model of obesity, as well as in humans with obesity and healthy controls. A significant and selective increase in type 1 cannabinoid receptor gene (Cnr1) expression was observed at the beginning of obesity development (5 weeks on high fat diet) as well as after 21 weeks of high diet exposure. After 5 weeks on high fat diet, selective up-regulation of mu opioid receptor gene (Oprm1) expression was also observed. Consistently, epigenetic studies showed a selective and significant decrease in DNA methylation at specific CpG sites at both gene promoters in overweight rats, but only after 5 weeks on high fat diet. Moreover, significantly lower levels of DNA methylation were observed at selected CpG sites of both receptor gene promoters, analyzed in peripheral blood mononuclear cells from younger (<30 years old) humans with obesity, as well as in those with shorter time length from disease onset. Taken together, we here provide evidence of selective, synergistic and time-dependent transcriptional regulation of CNR1 and OPRM1 genes in overweight rats, as well as in human subjects. These alterations in genes regulation could contribute to the development of the obese phenotype, and we thus suggest CNR1 and OPRM1 epigenetic modulation as possible biomarkers of obesity development. Due to the reversible nature of the epigenetic hallmark, our data might also open new avenue to early environmental strategies of intervention.

Future Pharmacotherapy for Obesity: New Anti-obesity Drugs on the Horizon

PURPOSE OF REVIEW

Obesity is a global health crisis with detrimental effects on all organ systems leading to worsening disease state and rising costs of care. Persons with obesity failing lifestyle therapies need to be escalated to appropriate pharmacological treatment modalities, medical devices, and/or bariatric surgery if criteria are met and more aggressive intervention is needed. The progression of severe obesity in the patient population coupled with related co-morbidities necessitates the development of novel therapies for the treatment of obesity. This development is preceded by increased understanding of the underpinnings of energy regulation and neurohormonal pathways involved in energy homeostasis.

RECENT FINDINGS

Though there are approved anti-obesity drugs available in the USA, newer drugs are now in the pipeline for development given the urgent need. This review focuses on anti-obesity drugs in the pipeline including centrally acting agents (setmelanotide, neuropeptide Y antagonist [velneperit], zonisamide-bupropion [Empatic], cannabinoid type-1 receptor blockers), gut hormones and incretin targets (new glucagon-like-peptide-1 [GLP-1] analogues [semaglutide and oral equivalents], amylin mimetics [davalintide, dual amylin and calcitonin receptor agonists], dual action GLP-1/glucagon receptor agonists [oxyntomodulin], triple agonists [tri-agonist 1706], peptide YY, leptin analogues [combination pramlintide-metreleptin]), and other novel targets (methionine aminopeptidase 2 inhibitor [beloranib], lipase inhibitor [cetilistat], triple monoamine reuptake inhibitor [tesofensine], fibroblast growth factor 21), including anti-obesity vaccines (ghrelin, somatostatin, adenovirus36). With these new drugs in development, anti-obesity therapeutics have potential to vastly expand allowing better treatment options and personalized approach to obesity care.

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.

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.

The novel cannabinoid antagonist SM-11 reduces hedonic aspect of food intake through a dopamine-dependent mechanism

Cannabinoids, endogenous and exogenously administered, are known to positively regulate food intake and energy balance. Since CB1 receptor antagonists reduce food intake and antagonize overweight, we developed a new CB1 receptor antagonist in an attempt to identify a compound with potential application in overeating disorders. The newly developed SM-11 compound dose-dependently decreases food intake in rats by 15-20%. Moreover, SM-11 reduces self-administration of palatable food in both food restricted and ad libitum fed rats, suggesting an action on the hedonic component of food intake. Thus, we next tested the effect of SM-11 on the stimulating properties of the CB1 receptor agonist WIN55,212-2 (WIN) on the electrophysiological activity of Nucleus Accumbens-projecting dopaminergic neurons of the ventral tegmental area (VTA). SM-11 fully and readily antagonized the WIN-induced increments in single spiking and burst firing of antidromically-identified dopamine neurons. When administered to naïve (no WIN-pretreated) rats, SM-11 did not alter basal neuronal activity, thereby suggesting a pure antagonistic profile. SM-11 thus appears as a promising candidate in the search of potential anti-obesity medications.

Treatment with a novel oleic-acid-dihydroxyamphetamine conjugation ameliorates non-alcoholic fatty liver disease in obese Zucker rats

Fatty liver disease is one of the main hepatic complications associated with obesity. To date, there are no effective treatments for this pathology apart from the use of classical fibrates. In this study, we have characterized the in vivo effects of a novel conjugation of oleic acid with an amphetamine derivative (OLHHA) in an animal model of genetic obesity. Lean and obese Zucker rats received a daily intraperitoneal administration of OLHHA (5 mg kg⁻¹) for 15 days. Plasma and liver samples were collected for the biochemical and molecular biological analyses, including both immunohistochemical and histological studies. The expression of key enzymes and proteins that are involved in lipid metabolism and energy homeostasis was evaluated in the liver samples. The potential of OLHHA to produce adverse drug reactions or toxicity was also evaluated through the monitoring of interactions with hERG channel and liver cytochrome. We found that OLHHA is a drug with a safe pharmacological profile. Treatment for 15 days with OLHHA reduced the liver fat content and plasma triglyceride levels, and this was accompanied by a general improvement in the profile of plasma parameters related to liver damage in the obese rats. A decrease in fat accumulation in the liver was confirmed using histological staining. Additionally, OLHHA was observed to exert anti-apoptotic effects. This hepatoprotective activity in obese rats was associated with an increase in the mRNA and protein expression of the cannabinoid type 1 receptor and a decrease in the expression of the lipogenic enzymes FAS and HMGCR primarily. However, changes in the mRNA expression of certain proteins were not associated with changes in the protein expression (i.e. L-FABP and INSIG2). The present results demonstrate that OLHHA is a potential anti-steatotic drug that ameliorates the obesity-associated fatty liver and suggest the potential use of this new drug for the treatment of non-alcoholic fatty liver disease.

Drug Discovery Collection: OLHHA is a safe drug with hepatoprotective and anti-steatotic effects on non-alcoholic fatty liver disease in obese rats.

Dissociating the role of endocannabinoids in the pleasurable and motivational properties of social play behaviour in rats

Social play behaviour is a vigorous form of social interaction, abundant during the juvenile and adolescent phases of life in many mammalian species, including humans. Social play is highly rewarding and it is important for social and cognitive development. Being a rewarding activity, social play can be dissociated in its pleasurable and motivational components. We have previously shown that endocannabinoids modulate the expression of social play behaviour in rats. In the present study, we investigated whether endocannabinoids modulate the motivational and pleasurable properties of social play behaviour, using operant and place conditioning paradigms, respectively. Treatment with the anandamide hydrolysis inhibitor URB597 did not affect operant responding or social play-induced conditioned place preference (CPP) when administered at a dose (0.1mg/kg) known to increase the expression of social play behaviour, while it modestly reduced operant responding at a higher dose (0.2mg/kg). The cannabinoid-1 (CB1) receptor antagonist rimonabant reduced operant responding when administered at a dose (1mg/kg) known to decrease the expression of social play behaviour, although this effect may be secondary to concurrent drug-induced stereotypic behaviours (i.e., grooming and scratching). These data demonstrate that enhancing endocannabinoid levels does not differentially affect the motivational and pleasurable aspects of social play behaviour, whereas CB1 receptor blockade reduces the motivational aspects of social play behaviour, possibly due to response competition. Thus, endocannabinoids likely drive the expression of social play behaviour as a whole, without differentially affecting its motivational or pleasurable properties.

Behavioral Characterization of the Effects of Cannabis Smoke and Anandamide in Rats

Cannabis is the most widely used illicit drug in the world. Delta-9-tetrahydrocannabinol (Δ9-THC) is the main psychoactive component of cannabis and its effects have been well-studied. However, cannabis contains many other cannabinoids that affect brain function. Therefore, these studies investigated the effect of cannabis smoke exposure on locomotor activity, rearing, anxiety-like behavior, and the development of dependence in rats. It was also investigated if cannabis smoke exposure leads to tolerance to the locomotor-suppressant effects of the endogenous cannabinoid anandamide. Cannabis smoke was generated by burning 5.7% Δ9-THC cannabis cigarettes in a smoking machine. The effect of cannabis smoke on the behavior of rats in a small and large open field and an elevated plus maze was evaluated. Cannabis smoke exposure induced a brief increase in locomotor activity followed by a prolonged decrease in locomotor activity and rearing in the 30-min small open field test. The cannabinoid receptor type 1 (CB1) receptor antagonist rimonabant increased locomotor activity and prevented the smoke-induced decrease in rearing. Smoke exposure also increased locomotor activity in the 5-min large open field test and the elevated plus maze test. The smoke exposed rats spent more time in the center zone of the large open field, which is indicative of a decrease in anxiety-like behavior. A high dose of anandamide decreased locomotor activity and rearing in the small open field and this was not prevented by rimonabant or pre-exposure to cannabis smoke. Serum Δ9-THC levels were 225 ng/ml after smoke exposure, which is similar to levels in humans after smoking cannabis. Exposure to cannabis smoke led to dependence as indicated by more rimonabant-precipitated somatic withdrawal signs in the cannabis smoke exposed rats than in the air-control rats. In conclusion, chronic cannabis smoke exposure in rats leads to clinically relevant Δ9-THC levels, dependence, and has a biphasic effect on locomotor activity.

Baseline anandamide levels and body weight impact the weight loss effect of CB1 receptor antagonism in male rats

The individual weight loss response to obesity treatment is diverse. Here we test the hypothesis that the weight loss response to the CB1 receptor antagonist rimonabant is influenced by endogenous levels of receptor agonists. We show that baseline anandamide levels and body weight independently contribute to predict the treatment response to rimonabant in rodents, demonstrating that addition of biomarkers related to mode of action is relevant for a personalized health care approach to obesity treatment.

Glucocorticoid receptor antagonism disrupts the reconsolidation of social reward-related memories in rats

Reconsolidation is the process whereby consolidated memories are destabilized upon retrieval and restabilized to persist for later use. Although the neurobiology of the reconsolidation of both appetitive and aversive memories has been intensively investigated, reconsolidation of memories of physiologically relevant social rewards has received little attention. Social play, the most characteristic social behaviour displayed by young mammals, is highly rewarding, illustrated by the fact that it can induce conditioned place preference (CPP). Here, we investigated the role of signalling mechanisms implicated in memory processes, including reconsolidation, namely glucocorticoid, mineralocorticoid, NMDA glutamatergic and CB1 cannabinoid receptors, in the reconsolidation of social play-induced CPP in rats. Systemic treatment with the glucocorticoid receptor antagonist mifepristone before, but not immediately after, retrieval disrupted the reconsolidation of social play-induced CPP. Mifepristone did not affect social play-induced CPP in the absence of memory retrieval. Treatment with the NMDA receptor antagonist MK-801 modestly affected the reconsolidation of social play-induced CPP. However, the reconsolidation of social play-induced CPP was not affected by treatment with the mineralocorticoid and CB1 cannabinoid receptor antagonists spironolactone and rimonabant, respectively. We conclude that glucocorticoid neurotransmission mediates the reconsolidation of social reward-related memories in rats. These data indicate that the neural mechanisms of the reconsolidation of social reward-related memories only partially overlap with those underlying the reconsolidation of other reward-related memories.

Cannabinoid receptor 1 antagonist treatment induces glucagon release and shows an additive therapeutic effect with GLP-1 agonist in diet-induced obese mice

Cannabinoid 1 (CB1) receptor antagonists reduce body weight and improve insulin sensitivity. Preclinical data indicates that an acute dose of CB1 antagonist rimonabant causes an increase in blood glucose. A stable analog of glucagon-like peptide 1 (GLP-1), exendin-4 improves glucose-stimulated insulin secretion in pancreas, and reduces appetite through activation of GLP-1 receptors in the central nervous system and liver. We hypothesized that the insulin secretagogue effect of GLP-1 agonist exendin-4 may synergize with the insulin-sensitizing action of rimonabant. Intraperitoneal as well as intracerebroventricular administration of rimonabant increased serum glucose upon glucose challenge in overnight fasted, diet-induced obese C57 mice, with concomitant rise in serum glucagon levels. Exendin-4 reversed the acute hyperglycemia induced by rimonabant. The combination of exendin-4 and rimonabant showed an additive effect in the food intake, and sustained body weight reduction upon repeated dosing. The acute efficacy of both the compounds was additive for inducing nausea-like symptoms in conditioned aversion test in mice, whereas exendin-4 treatment antagonized the effect of rimonabant on forced swim test upon chronic dosing. Thus, the addition of exendin-4 to rimonabant produces greater reduction in food intake owing to increased aversion, but reduces the other central nervous system side effects of rimonabant. The hyperglucagonemia induced by rimonabant is partially responsible for enhancing the antiobesity effect of exendin-4.

Acute and chronic systemic CB1 cannabinoid receptor blockade improves blood pressure regulation and metabolic profile in hypertensive (mRen2)27 rats

We investigated acute and chronic effects of CB₁ cannabinoid receptor blockade in renin‐angiotensin system‐dependent hypertension using rimonabant (SR141716A), an orally active antagonist with central and peripheral actions. In transgenic (mRen2)27 rats, a model of angiotensin II‐dependent hypertension with increased body mass and insulin resistance, acute systemic blockade of CB₁ receptors significantly reduced blood pressure within 90 min but had no effect in Sprague‐Dawley rats. No changes in metabolic hormones occurred with the acute treatment. During chronic CB₁ receptor blockade, (mRen2)27 rats received daily oral administration of SR141716A (10 mg/kg/day) for 28 days. Systolic blood pressure was significantly reduced within 24 h, and at Day 21 of treatment values were 173 mmHg in vehicle versus 149 mmHg in drug‐treated rats (P < 0.01). This accompanied lower cumulative weight gain (22 vs. 42 g vehicle; P < 0.001), fat mass (2.0 vs. 2.9% of body weight; P < 0.05), and serum leptin (2.8 vs. 6.0 ng/mL; P < 0.05) and insulin (1.0 vs. 1.9 ng/mL; P < 0.01), following an initial transient decrease in food consumption. Conscious hemodynamic recordings indicate twofold increases occurred in spontaneous baroreflex sensitivity (P < 0.05) and heart rate variability (P < 0.01), measures of cardiac vagal tone. The beneficial actions of CB₁ receptor blockade in (mRen2)27 rats support the interpretation that an upregulated endocannabinoid system contributes to hypertension and impaired autonomic function in this angiotensin II‐dependent model. We conclude that systemic CB₁ receptor blockade may be an effective therapy for angiotensin II‐dependent hypertension and associated metabolic syndrome.

Acute and chronic systemic CB₁ cannabinoid receptor blockade significantly lowers blood pressure in Angiotensin II‐dependent hypertensive (mRen2)27 rats, with a concomitant positive influence over conscious autonomic blood pressure regulation and metabolic profile. Results from our study indicate novel mechanisms for maintenance of hypertension, metabolic syndrome, and impaired autonomic control of blood pressure associated with upregulation of Angiotensin II signaling.

Behavioral effects of the cannabinoid CB1 receptor allosteric modulator ORG27569 in rats

The cannabinoid CB₁ receptor system is involved in feeding behaviors and the CB₁ receptor antagonist SR141716A is an effective antiobesity drug. However, SR141716A also has serious side effects, which prompted the exploration of alternative strategies to modulate this important drug target. Recently a CB₁ receptor allosteric modulating site has been discovered and the allosteric modulating activity of several modulators including ORG27569 has been characterized in vitro. Yet, little is known of the in vivo pharmacological effects of ORG27569. This study examined the behavioral pharmacology of ORG27569 in rats. ORG27569 (3.2–10 mg/kg, i.p.) selectively attenuated the hypothermic effects of CB₁ receptor agonists CP55940 (0.1–1 mg/kg) and anandamide (3.2–32 mg/kg). In contrast, SR141716A only attenuated the hypothermic effects of CP55940 but not anandamide. SR141716A but not ORG27569 blocked CP55940-induced catalepsy and antinociception. In addition, ORG27569 did not modify SR141716A-elicited grooming and scratching behaviors. In feeding studies, ORG27569 decreased palatable and plain food intake which was partially blocked by CP55940. The hypophagic effect of ORG27569 developed tolerance after 4 days of daily 5.6 mg/kg treatment; however, the effect on body weight gain outlasted the drug treatment for 10 days. These data suggest that ORG27569 may not function as a CB₁ receptor allosteric modulator in vivo, although its hypophagic activity still has potential therapeutic utility.

Rimonabant's reductive effects on high densities of food reinforcement, but not palatability, in lean and obese Zucker rats

RATIONALE

Cannabinoid antagonists purportedly have greater effects in reducing the intake of highly palatable food compared to less palatable food. However, this assertion is based on free-feeding studies in which the amount of palatable food eaten under baseline conditions is often confounded with other variables, such as unequal access to both food options and differences in qualitative features of the foods.

OBJECTIVE

We attempted to reduce these confounds by using a model of choice that programmed the delivery rates of sucrose and carrot-flavored pellets.

METHODS

Lever pressing of ten lean (Fa/Fa or Fa/fa) and ten obese (fa/fa) Zucker rats was placed under three conditions in which programmed ratios for food pellets on two levers were 5:1, 1:1, and 1:5. In phase 1, responses on the two levers produced one type of pellet (sucrose or carrot); in phase 2, responses on one lever produced sucrose pellets and on the other lever produced carrot pellets. After responses stabilized under each food ratio, acute doses of rimonabant (0, 3, and 10 mg/kg) were administered before experimental sessions. The number of reinforcers and responses earned per session under each ratio and from each lever was compared.

RESULTS AND CONCLUSIONS

Rimonabant reduced reinforcers in 1:5 and 5:1 food ratios in phase 1, and across all ratios in phase 2. Rimonabant reduced sucrose and carrot-flavored pellet consumption similarly; rimonabant did not affect bias toward sucrose, but increased sensitivity to amount differences in lean rats. This suggests that relative amount of food, not palatability, may be an important behavioral mechanism in the effects of rimonabant.

Oleoylethanolamide: a novel potential pharmacological alternative to cannabinoid antagonists for the control of appetite

The initial pharmaceutical interest for the endocannabinoid system as a target for antiobesity therapies has been restricted by the severe adverse effects of the CB1 antagonist rimonabant. This study points at oleoylethanolamide (OEA), a monounsaturated analogue, and functional antagonist of anandamide, as a potential and safer antiobesity alternative to CB1 antagonism. Mice treated with equal doses (5 or 10 mg/kg, i.p.) of OEA or rimonabant were analyzed for the progressive expression of spontaneous behaviors (eating, grooming, rearing, locomotion, and resting) occurring during the development of satiety, according to the paradigm called behavioral satiety sequence (BSS). Both drugs reduced food (wet mash) intake to a similar extent. OEA treatment decreased eating activity within the first 30 min and caused a temporary increase of resting time that was not accompanied by any decline of horizontal, vertical and total motor activity. Besides decreasing eating activity, rimonabant caused a marked increase of the time spent grooming and decreased horizontal motor activity, alterations that might be indicative of aversive nonmotivational effects on feeding. These results support the idea that OEA suppresses appetite by stimulating satiety and that its profile of action might be predictive of safer effects in humans as a novel antiobesity treatment.

Cannabinoid control of brain bioenergetics: Exploring the subcellular localization of the CB1 receptor

Brain mitochondrial activity is centrally involved in the central control of energy balance. When studying mitochondrial functions in the brain, however, discrepant results might be obtained, depending on the experimental approaches. For instance, immunostaining experiments and biochemical isolation of organelles expose investigators to risks of false positive and/or false negative results. As an example, the functional presence of cannabinoid type 1 (CB₁) receptors on brain mitochondrial membranes (mtCB₁) was recently reported and rapidly challenged, claiming that the original observation was likely due to artifact results. Here, we addressed this issue by directly comparing the procedures used in the two studies. Our results show that the use of appropriate controls and quantifications allows detecting mtCB₁ receptor with CB₁ receptor antibodies, and that, if mitochondrial fractions are enriched and purified, CB₁ receptor agonists reliably decrease respiration in brain mitochondria. These data further underline the importance of adapted experimental procedures to study brain mitochondrial functions.

Novel effects of the cannabinoid inverse agonist AM 251 on parameters related to metabolic syndrome in obese Zucker rats

BACKGROUND AND OBJECTIVE

Recent research suggests that cannabinoid receptor CB1 antagonists can affect appetite and body weight gain, although their influence on other parameters related to metabolic syndrome is not well documented. The present study was designed to assess the effects of chronic treatment with the CB1 receptor inverse agonist AM 251 (3 mg/kg for 3 weeks) in obese and lean Zucker rats on parameters related to metabolic syndrome.

MATERIALS AND METHODS

Four groups of rats were used: lean Zucker rats, untreated obese Zucker rats, AM 251-treated obese Zucker rats and a pair-fed obese Zucker rat experimental group which received the same amount of food as that consumed by the animals treated with AM251. Food intake, body weight gain, energy expenditure, plasma biochemical parameters, leptin, insulin and hepatic status markers were analysed.

RESULTS

Daily injection of AM 251 in obese Zucker rats produced a marked and sustained decrease in daily food intake and body weight and a considerable increase in energy expenditure in comparison with untreated obese Zucker rats. AM 251 administration to obese rats significantly reduced plasma levels of glucose, leptin, AST, ALT, Gamma GT, total bilirubin and LDL cholesterol whereas HDL cholesterol plasma levels increased. The results also showed a decrease in liver/weight body ratio and total fat content in the liver. The main effects of AM251 (3 mg/kg) found in this study were not observed in pair-fed obese animals, highlighting the additional beneficial effects of treatment with AM 251. The results obtained in obese rats can be interpreted as a decrease in leptin and insulin resistance, thereby improving glucose and lipid metabolism, alleviating the steatosis present in the metabolic syndrome and thus favourably modifying plasma levels of hepatic biomarkers.

CONCLUSION

Our results indicate that the cannabinoid CB1 inverse agonist AM 251 represents a promising therapeutic strategy for the treatment of obesity and metabolic syndrome.

PUFA-derived endocannabinoids: an overview

Following on from the discovery of cannabinoid receptors, of their endogenous agonists (endocannabinoids) and of the biosynthetic and metabolic enzymes of the endocannabinoids, significant progress has been made towards the understanding of the role of the endocannabinoid system in both physiological and pathological conditions. Endocannabinoids are mainly n-6 long-chain PUFA (LCPUFA) derivatives that are synthesised by neuronal cells and inactivated via a two-step process that begins with their transport from the extracellular to the intracellular space and culminates in their intracellular degradation by hydrolysis or oxidation. Although the enzymes responsible for the biosynthesis and metabolism of endocannabinoids have been well characterised, the processes involved in their cellular uptake are still a subject of debate. Moreover, little is yet known about the roles of endocannabinoids derived from n-3 LCPUFA such as EPA and DHA. Here, I provide an overview of what is currently known about the mechanisms for the biosynthesis and inactivation of endocannabinoids, together with a brief analysis of the involvement of the endocannabinoids in both food intake and obesity. Owing to limited space, recent reviews will be often cited instead of original papers.

Addition of a low dose of rimonabant to orlistat therapy decreases weight gain and reduces adiposity in dietary obese rats

1. The aim of the present study was to determine whether the addition of a subeffective dose of rimonabant (1 mg/kg) to orlistat would be beneficial in the treatment of diet-induced obesity in rats compared with orlistat monotherapy. 2. Male rats were divided into five groups: (i) rats fed a low-fat diet for 4 months; (ii) rats fed a high-fat diet (HFD) for 4 months and treated daily with vehicle (0.2% Tween-80 solution); (iii) orlistat (10 mg/kg per day)-treated HFD-fed rats; (iv) rimonabant (1 mg/kg per day)-treated HFD-fed rats; and (v) HFD-fed rats treated with a combination of orlistat plus rimonabant. Fasting blood glucose, serum insulin, leptin and adiponectin levels were measured. Liver and adiposity indices were calculated and liver and adipose tissues were processed for histological examination. 3. Over the 4 months of the study, vehicle-treated HFD-fed rats exhibited increased cumulative food intake, bodyweight and liver and adiposity indices. Moreover, vehicle-treated HFD-fed rats exhibited a deterioration in liver function and an abnormal lipid profile. Insulin resistance and serum leptin were increased in this group, whereas serum adiponectin levels were decreased. Orlistat monotherapy or combination therapy with orlistat plus rimonabant improved all these parameters. 4. The addition of the low subeffective dose of rimonabant to orlistat therapy ameliorated HFD-induced obesity to a much greater extent than orlistat monotherapy. This combination showed better weight control and metabolic profile compared with orlistat alone. Therefore, the results of the present study encourage reassessment of the use of a low dose of rimonabant to potentiate the effect of orlistat in the clinical management of obesity if proper clinical safety data are available.

Low dose naloxone attenuates the pruritic but not anorectic response to rimonabant in male rats

RATIONALE

Previous research suggests that the acute anorectic effect of cannabinoid CB1 receptor antagonist/inverse agonists may be secondary to response competition from the compulsive scratching and grooming syndrome characteristic of these agents.

OBJECTIVES

As the pruritic effect of rimonabant can be attenuated by the opioid receptor antagonist naloxone, these studies test the prediction that naloxone co-treatment should prevent acute rimonabant anorexia.

METHODS

Two experiments comprehensively profiled the behavioural effects of an anorectic dose of rimonabant (1.5 mg/kg) in the absence or presence of naloxone (experiment 1: 0.01 or 0.1 mg/kg; experiment 2: 0.05 mg/kg).

RESULTS

In both experiments, rimonabant not only significantly suppressed food intake and time spent eating but also induced compulsive scratching and grooming. In experiment 1, although the lower dose of naloxone seemed to weakly attenuate the effects of rimonabant both on ingestive and compulsive behaviours, the higher dose more strongly suppressed the compulsive elements but did not significantly affect the anorectic response. The results of experiment 2 showed that naloxone at a dose which markedly attenuated rimonabant-induced grooming and scratching did not alter the effects of the compound on food intake or time spent feeding. The apparent independence of the ingestive and compulsive effects of rimonabant was confirmed by the observation that despite a 'normalising' effect of naloxone co-treatment on behavioural structure (BSS), the opioid antagonist did not impact the suppressant effect of rimonabant on peak feeding.

CONCLUSION

The acute anorectic response to rimonabant would not appear to be secondary to compulsive scratching and grooming.

Endocannabinoids and obesity

A safe and effective antiobesity drug is needed to combat the global obesity epidemic. The discovery of cannabinoids from medicinal herbs has revealed the endocannabinoid system (ECS) in animals and humans, which regulates various physiological activities such as feeding, thermogenesis, and body weight (BW). Although cannabinoid receptors 1 (CB1) antagonists have shown antiobesity efficacies in animal models and in the clinic, they failed to establish as a treatment due to their psychological side effects. Recent studies indicate that CB1 in various peripheral tissues may mediate some of the therapeutic effects of CB1 antagonists, such as improved lipid and glucose homeostasis. It rationalizes the development of compounds with limited brain penetration, for minimizing the side effects while retaining the therapeutic efficacies. A survey of the literature has revealed some controversies about how the ECS affects obesity. This review summarizes the research progresses and discusses some future perspectives.

Impulsive-choice patterns for food in genetically lean and obese Zucker rats

Behavioral-economic studies have shown that differences between lean and obese Zuckers in food consumption depend on the response requirement for food. Since a response requirement inherently increases the delay to reinforcement, differences in sensitivity to delay may also be a relevant mechanism of food consumption in the obese Zucker rat. Furthermore, the endocannabinoid neurotransmitter system has been implicated in impulsivity, but studies that attempt to characterize the effects of cannabinoid drugs (e.g., rimonabant) on impulsive choice may be limited by floor effects. The present study aimed to characterize impulsive-choice patterns for sucrose using an adjusting-delay procedure in genetically lean and obese Zuckers. Ten lean and ten obese Zucker rats chose between one lever that resulted in one pellet after a standard delay (either 1 s or 5 s) and a second lever that resulted in two or three pellets after an adjusting delay. After behavior stabilized under baseline, rimonabant (0-10 mg/kg) was administered prior to some choice sessions in the two-pellet condition. Under baseline, obese Zuckers made more impulsive choices than leans in three of the four standard-delay/pellet conditions. Additionally, in the 2-pellet condition, rimonabant increased impulsive choice in lean rats in the 1-s standard-delay condition; however, rimonabant decreased impulsive choice in obese rats in the 1-s and 5-s standard-delay conditions. These data suggest that genetic factors that influence impulsive choice are stronger in some choice conditions than others, and that the endocannabinoid system may be a relevant neuromechanism.

Possible involvement of endocannabinoids in the increase of morphine consumption in maternally deprived rat

Whether adolescent exposure to chronic delta-9-tetrahydrocannabinol (THC) facilitates progression to opioid consumption is still controversial. In a maternal deprivation model (3 h daily from postnatal day 1-14), we previously reported that adolescent exposure to chronic THC blocks morphine dependence in maternally deprived (D) rats. Owing to the existence of a functional cross-interaction between the opioid and cannabinoid systems in reward, we evaluated if the vulnerability to opiate reward in D rats, may involve an alteration of the endocannabinoid system. Anandamide and 2-arachidonoylglycerol (2-AG), were quantified in the striatum and mesencephalon of adolescent and adult D and non-deprived (animal facility rearing, AFR) rats by isotope dilution liquid chromatography-mass spectrometry. Oral morphine self-administration behavior was analyzed for 14 weeks, 24 days after chronic injection of the cannabinoid CB1 receptor antagonist/inverse agonist, SR141716A (3 mg/kg) for 2 weeks during adolescence (PND 35-48). Adolescent D rats exhibited higher basal levels of anandamide than adolescent AFR rats in the nucleus accumbens (38%), the caudate-putamen nucleus (62%) and the mesencephalon (320%), whereas adult D rats showed an increase of anandamide and 2-AG levels in the nucleus accumbens (50% and 24%, respectively) and of 2-AG in the caudate-putamen nucleus (48%), compared to adult AFR rats. Chronic administration of SR141716A to adolescent D rats blocked the escalation behavior in the morphine consumption test. Our data suggest that altered brain endocannabinoid levels may contribute to the escalation behavior in the morphine consumption test in a maternal deprivation model.

Obese and lean Zucker rats demonstrate differential sensitivity to rates of food reinforcement in a choice procedure

The obese Zucker rat carries two recessive fa alleles that result in the expression of an obese phenotype. Obese Zuckers have higher food intake than lean controls in free-feed studies in which rats have ready access to a large amount of one type of food. The present study examined differences in obese and lean Zucker rats using concurrent schedules of reinforcement, which more ecologically models food selection using two food choices that have limited, but generally predictable availability. Lever-pressing of ten lean (Fa/Fa or Fa/fa) and ten obese (fa/fa) Zucker rats was placed under three concurrent variable interval variable interval (conc VI VI) schedules of sucrose and carrot reinforcement, in which the programmed reinforcer ratios for 45-mg food pellets were 5:1, 1:1, and 1:5. Allocation of responses to the two food alternatives was characterized using the generalized matching equation, which allows sensitivity to reinforcer rates (a) and bias toward one alternative (log k) to be quantified. All rats showed a bias toward sucrose, though there were no differences between lean and obese Zucker rats. In addition, obese Zucker rats exhibited higher sensitivity to reinforcement rates than lean rats. This efficient pattern of responding was related to overall higher deliveries of food pellets. Effective matching for food, then, may be another behavioral pattern that contributes to an obese phenotype.

Structural analogs of pyrazole and sulfonamide cannabinoids: effects on acute food intake in mice

Obesity contributes to a multitude of serious health problems. Given the demonstrated role of the endogenous cannabinoid system in appetite regulation, the purpose of the present study was to evaluate structural analogs of two cannabinoids, rimonabant (cannabinoid CB(1) receptor antagonist) and O-2050 (sulfonamide analog of Δ(8)-tetrahydrocannabinol), that showed appetite suppressant effects in previous studies. Structure-activity relationships of these two lead compounds were examined in several assays, including cannabinoid CB(1) and CB(2) receptor binding, food intake, and an in vivo test battery (locomotor activity, antinociception, ring immobility, and body temperature) in mice. Rimonabant and O-2050 reliably decreased feeding in mice; however, their analogs decreased feeding only at higher doses, even though some compounds had quite good cannabinoid CB(1) binding affinity. Results of the in vivo test battery were inconsistent, with some of the compounds producing effects characteristic of cannabinoid agonists while other compounds were inactive or were antagonists against an active dose of Δ(9)-tetrahydrocannabinol. These results demonstrate that reduction of food intake is not a characteristic effect of pyrazole and sulfonamide cannabinoid analogs with favorable cannabinoid CB(1) binding affinity, suggesting that development of these classes of cannabinoids for the treatment of obesity will require evaluation of their effects in a broad spectrum of pharmacological assays.

Anti-obesity efficacy of LH-21, a cannabinoid CB(1) receptor antagonist with poor brain penetration, in diet-induced obese rats

BACKGROUND AND PURPOSE

Peripheral blockade of cannabinoid CB(1) receptors has been proposed as a safe and effective therapy against obesity, putatively devoid of the adverse psychiatric side effects of centrally acting CB(1) receptor antagonists. In this study we analysed the effects of LH-21, a peripherally acting neutral cannabinoid receptor antagonist with poor brain penetration, in an animal model of diet-induced obesity.

EXPERIMENTAL APPROACH

To induce obesity, male Wistar rats were fed a high-fat diet (HFD; 60 kcal% fat) whereas controls received a standard diet (SD; 10 kcal% fat). Following 10 weeks of feeding, animals received a daily i.p. injection of vehicle or 3 mg·kg(-1) LH-21 for 10 days. Plasma and liver samples were used for biochemical analyses whereas visceral fat-pad samples were analysed for lipid metabolism gene expression using real-time RT-PCR. In addition, the potential of LH-21 to interact with hepatic cytochrome P450 isoforms and cardiac human Ether-à-go-go Related Gene (hERG) channels was evaluated.

KEY RESULTS

LH-21 reduced feeding and body weight gain in HFD-fed animals compared with the control group fed SD. In adipose tissue, this effect was associated with decreased gene expression of: (i) leptin; (ii) lipogenic enzymes, including SCD-1; (iii) CB(1) receptors; and (iv) both PPARα and PPARγ. Although there were no significant differences in plasma parameters between HFD- and SD-fed rats, LH-21 did not seem to induce hepatic, cardiac or renal toxicity.

CONCLUSIONS AND IMPLICATIONS

These results support the hypothesis that treatment with the peripherally neutral acting CB(1) receptor antagonist, LH-21, may promote weight loss through modulation of visceral adipose tissue.

Excess of the endocannabinoid anandamide during lactation induces overweight, fat accumulation and insulin resistance in adult mice

BACKGROUND

Environmental conditions in early life can induce permanent physiological changes, sometimes increasing the risk of chronic diseases during adulthood. Neural and peripheral circuits controlling energy balance may be modulated during such a critical period. Since type 1 cannabinoid receptors (CB1R) have recently emerged as targets for modulating energy balance, their premature chronic activation during early life may result in long-term metabolic consequences associated to overweight/obesity. Endogenous activation of CB1R mainly occurs after binding to the endocannabinoid Anandamide (AEA).

OBJECTIVE

To evaluate long-term effects of AEA treatment during lactation on body weight, epididymal fat accumulation and related metabolic parameters during adulthood.

DESIGN

Male mice pups were orally treated with a solution of AEA (20 μg/g body weight in soy oil) or vehicle during the whole lactation period. After weaning, food intake and body weight were recorded every 10 days. Adult animals were subjected to glucose and insulin tolerance tests. Subsequently, animals were sacrificed and epididymal fat pads were extracted. Circulating levels of plasma insulin, leptin, non-sterified fatty acids (NEFA), triglyceride and cholesterol were also evaluated.

RESULTS

AEA-treated mice during lactation showed a significant increase in accumulated food intake, body weight and epididymal fat during adulthood when compared to control mice. When evaluating CB1R protein expression in epididymal fat, the AEA-treated group showed a 150 % increase in expression compared to the control mice. This group also displayed significantly higher levels of circulating glucose, insulin, leptin, triglycerides, cholesterol and NEFA. Moreover, a marked state of insulin resistance was an important finding in the AEA-treated group.

CONCLUSION

This study showed that overweight, accumulation of visceral fat and associated metabolic disturbances, such as a higher lipid profile and insulin resistance, can be programmed by a treatment with the endocannabinoid AEA during lactation in adult mice.

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

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

Ibipinabant attenuates β-cell loss in male Zucker diabetic fatty rats independently of its effects on body weight

AIM

To test the antidiabetic efficacy of ibipinabant, this new cannabinoid receptor 1 (CB1) antagonist was compared with food-restriction-induced weight loss, rosiglitazone (4 mg/kg) and rimonabant (3 and 10 mg/kg), using parameters of glycaemic control in male Zucker diabetic fatty (ZDF) rats.

METHODS

Body weight, food and water intake, fasted and non-fasted glucose and insulin, glucose tolerance and glycosylated haemoglobin (HbA1c) were all assessed over the course of the 9-week study. Pancreatic insulin content and islet area were also evaluated.

RESULTS

At the end of the study, vehicle-treated ZDF rats were severely hyperglycaemic and showed signs of β-cell decline, including dramatic reductions in unfasted insulin levels. Ibipinanbant (10 mg/kg) reduced the following relative to vehicle controls: fasting glucose (-61%), glucose excursion area under the curve (AUC) in an oral glucose tolerance test (OGTT, -44%) and HbA1c (-50%). Furthermore, non-fasting insulin, islet area and islet insulin content were all increased (71, 40 and 76%, respectively) relative to vehicle controls by the end of the study. All of these effects were similar to those of rimonabant and rosiglitazone, where ibipinabant was slightly more effective than rimonabant at the lowest dose and somewhat less effective than rosiglitazone at all doses. These antidiabetic effects appear independent of weight loss because none of the parameters above were consistently improved by the comparable weight loss induced by food restriction.

CONCLUSIONS

Ibipinabant may have weight loss-independent antidiabetic effects and may have the potential to attenuate β-cell loss in a model of progressive β-cell dysfunction.

Animal models to explore the effects of CNS drugs on food intake and energy expenditure

Obesity has reached epidemic proportions globally with an increasing incidence not just in Western cultures but also Mexico, Brazil, China and parts of Africa. In terms of pharmacological intervention, the track record of drug treatments for obesity is poor, especially in the case of centrally acting medicines, and there remains an unmet need for the development of safer compounds delivering superior efficacy. Animal models are of importance not only in detecting changes in food intake, energy expenditure and body weight but also providing confidence that these changes are behaviourally specific and not a result of drug-induced side effects. We review animal models of feeding behaviour that are used to aid our understanding of the control of body weight and energy regulation with special reference to CNS-acting drugs. The use of such models in the discovery of new drugs for the treatment of obesity is given particular emphasis. This article is part of a Special Issue entitled 'Central Control of Food Intake'.

The utility of animal models to evaluate novel anti-obesity agents

The global incidence of obesity continues to rise and is a major driver of morbidity and mortality through cardiovascular and cerebrovascular diseases. Animal models used in the discovery of novel treatments for obesity range from straightforward measures of food intake in lean rodents to long-term studies in animals exhibiting obesity due to the continuous access to diets high in fat. The utility of these animal models can be extended to determine, for example, that weight loss is due to fat loss and/or assess whether beneficial changes in key plasma parameters (e.g. insulin) are evident. In addition, behavioural models such as the behavioural satiety sequence can be used to confirm that a drug treatment has a selective effect on food intake. Typically, animal models have excellent predictive validity whereby drug-induced weight loss in rodents subsequently translates to weight loss in man. However, despite this, at the time of writing orlistat (Europe; USA) remains the only drug currently marketed for the treatment of obesity, with sibutramine having recently been withdrawn from sale globally due to the increased incidence of serious, non-fatal cardiovascular events. While the utility of rodent models in predicting clinical weight loss is detailed, the review also discusses whether animals can be used to predict adverse events such as those seen with recent anti-obesity drugs in the clinic.

Blockade of cannabinoid receptor 1 improves insulin resistance, lipid metabolism, and diabetic nephropathy in db/db mice

The endocannabinoid system is important in the pathogenesis of obesity-related metabolic disorders. However, the effect of inhibiting the endocannabinoid system in type 2 diabetic nephropathy is unclear. Therefore, we examined the effect of the cannabinoid (CB)1 receptor antagonist, SR141716, on insulin resistance and diabetic nephropathy in db/db mice. Six-week-old db/db mice were treated with the CB1-specific antagonist SR141716 (10 mg/kg · d) for 3 months. Treatment with SR141716 significantly improved insulin resistance and lipid abnormalities. Concomitantly, CB1 antagonism improved cardiac functional and morphological abnormality, hepatic steatosis, and phenotypic changes of adipocytes into small differentiated forms, associated with increased adiponectin expression and decreased lipid hydroperoxide levels. CB1 receptor was overexpressed in diabetic kidneys, especially in podocytes. Treatment with the SR141716 markedly decreased urinary albumin excretion and mesangial expansion and suppressed profibrotic and proinflammatory cytokine synthesis. Furthermore, SR141716 improved renal lipid metabolism and decreased urinary 8-isoprostane levels, renal lipid hydroperoxide content, and renal lipid content. In cultured podocytes, high-glucose stimulation increased CB1 receptor expression, and SR141716 treatment abolished high-glucose-induced up-regulation of collagen and plasminogen activator inhibitor-1 synthesis. Additionally, knockdown of CB1 receptor expression by stealth small interfering RNA abolished high-glucose-induced sterol-regulatory element-binding protein-1 expression in podocytes. These findings suggest that CB1 blockade improves insulin resistance and protect against renal injury through both metabolic and antifibrotic effects in type 2 diabetic nephropathy. Targeting CB1 blockade could therefore provide a new therapeutic target to prevent type 2 diabetic nephropathy.

The effect of vertical sleeve gastrectomy on food choice in rats

Objective

Diets high in fat are implicated in the development and maintenance of obesity, and obese individuals display greater preferences for high-fat foods than do their lean counterparts. Weight-reduction bariatric surgery is associated with changes in food choice. In particular, after Roux-en-Y Gastric Bypass (RYGB), humans and rodents select or prefer foods which are lower in fat content. We asked whether a bariatric surgical procedure limited to the stomach, Vertical Sleeve Gastrectomy (VSG), causes a similar reduction of fat intake/preference.

Research Design and Methods

Rats received VSG or Sham surgery or remained surgically naïve, and were assessed for food preference using three diet-choice paradigms. Using progressive-ratio and conditioned taste aversion paradigms, we further asked whether surgically-induced changes in food choice are secondary to changes in the reward value of food and/or to the formation of a food aversion. Finally, food choice was compared between VSG and RYGB-operated rats.

Results

VSG rats decreased their intake of dietary fat, and shifted their preference toward lower caloric-density foods. This change in food choice was not associated with changes in motivated responding on a progressive-ratio schedule for either a fat or a carbohydrate food reinforcer. When VSG and RYGB were compared directly, both procedures caused comparable changes in food choice. The conditioned taste aversion paradigm revealed that VSG rats form an aversion to an intra-gastric oil administration whereas RYGB rats do not.

Conclusions

VSG and RYGB, two anatomically-distinct bariatric procedures, produce similar changes in food choice.

Excretion, metabolism, and pharmacokinetics of 1-(8-(2-chlorophenyl)-9-(4-chlorophenyl)-9H-purin-6-yl)-4-(ethylamino)piperidine-4-carboxamide, a selective cannabinoid receptor antagonist, in healthy male volunteers

The disposition of 1-(8-(2-chlorophenyl)-9-(4-chlorophenyl)-9H- purin-6-yl)-4-(ethylamino)-piperidine-4-carboxamide (CP-945,598), an orally active antagonist of the cannabinoid CB1 receptor, was studied after a single 25-mg oral dose of [(14)C]CP-945,598 to healthy human subjects. Serial blood samples and complete urine and feces were collected up to 672 h after dose. The mean total recovery of radioactivity was 60.1 ± 12.8 from the urine and feces, with the majority of the dose excreted in the feces. The absorption of CP-945,598 in humans was slow with T(max) at 6 h. Less than 2% of the dose was recovered as unchanged drug in the combined excreta, suggesting that CP-945,598 is extensively metabolized. The primary metabolic pathway of CP-945,598 involved N-de-ethylation to form an N-desethyl metabolite (M1), which was then subsequently metabolized by amide hydrolysis (M2), N-hydroxylation (M3), piperidine ring hydroxylation (M6), and ribose conjugation (M9). M3 was further metabolized to oxime (M4) and keto (M5) metabolites. M1, M4, and M5 were the major circulating metabolites, with AUC((0-48)) values 4.7-, 1.5-, and 1.1-fold greater than that of CP-945,598. M1, M2, and M9 accounted for 5.6, 33.6, and 6.30% of the dose, respectively, in excreta. The results from in vitro experiments with recombinant isoforms suggested that the oxidative metabolism of CP-945,598 to M1 is catalyzed primarily by CYP3A4/3A5. The molecular docking study showed that the N-ethyl moiety of CP-945,598 can access to the heme iron-oxo of CYP3A4 in an energetically favored orientation. Together, these data suggest that CP-945,598 is well absorbed and eliminated largely by CYP3A4/3A5-catalyzed metabolism.

Rimonabant reduces the essential value of food in the genetically obese Zucker rat: an exponential demand analysis

Research on free-food intake suggests that cannabinoids are implicated in the regulation of feeding. Few studies, however, have characterized how environmental factors that affect food procurement interact with cannabinoid drugs that reduce food intake. Demand analysis provides a framework to understand how cannabinoid blockers, such as rimonabant, interact with effort in reducing demand for food. The present study examined the effects rimonabant had on demand for sucrose in obese Zucker rats when effort to obtain food varied and characterized the data using the exponential ("essential value") model of demand. Twenty-nine male (15 lean, 14 obese) Zucker rats lever-pressed under eight fixed ratio (FR) schedules of sucrose reinforcement, in which the number of lever-presses to gain access to a single sucrose pellet varied between 1 and 300. After behavior stabilized under each FR schedule, acute doses of rimonabant (1-10mg/kg) were administered prior to some sessions. The number of food reinforcers and responses in each condition was averaged and the exponential and linear demand equations were fit to the data. These demand equations quantify the value of a reinforcer by its sensitivity to price (FR) increases. Under vehicle conditions, obese Zucker rats consumed more sucrose pellets than leans at smaller fixed ratios; however, they were equally sensitive to price increases with both models of demand. Rimonabant dose-dependently reduced reinforcers and responses for lean and obese rats across all FR schedules. Data from the exponential analysis suggest that rimonabant dose-dependently increased elasticity, i.e., reduced the essential value of sucrose, a finding that is consistent with graphical depictions of normalized demand curves.

Excretion, metabolism, and pharmacokinetics of CP-945,598, a selective cannabinoid receptor antagonist, in rats, mice, and dogs

1-(8-(2-Chlorophenyl)-9-(4-chlorophenyl)-9H-purin-6-yl)-4-(ethylamino)piperidine-4-carboxamide (CP-945,598) is an orally active antagonist of the cannabinoid CB-1 receptor that progressed into phase 3 human clinical trials for the treatment of obesity. In this study, we investigated the metabolic fate and disposition of CP-945,598 in rats, Tg-RasH2 mice, and dogs after oral administration of a single dose of [(14)C]CP-945,598. Total mean recoveries of the radioactive dose were 97.7, 97.8, and 99.3% from mice, rats, and dogs, respectively. The major route of excretion in all three species was via the feces, but on the basis of separate studies in bile duct-cannulated rats and dogs, this probably reflects excretion in bile rather than incomplete absorption. CP-945,598 underwent extensive metabolism in all three species, because no unchanged parent compound was detected in the urine across species. The primary metabolic pathway of CP-945,598 involved N-deethylation to form an N-desethyl metabolite (M1). M1 was subsequently metabolized by amide hydrolysis, oxidation, and ribose conjugation to numerous novel and unusual metabolites. The major circulating and excretory metabolites were species-dependent; however, several common metabolites were observed in more than one species. In addition to parent compound, M1, M3, M4, and M5 in rats, M1, M3, and M4 in mice, and M1 and M2 in dogs were identified as the major circulating metabolites. Gender-related differences were also apparent in the quantitative and qualitative nature of the metabolites in rats. An unprecedented metabolite, M4, formed by deamidation of M1 or M3 (N-hydroxy-M1), but not by decarboxylation of M2, was identified in all species. M4 was nonenzymatically converted to M5.

Structure-activity relationship studies of novel pyrazole and imidazole carboxamides as cannabinoid-1 (CB1) antagonists

The synthesis and biological evaluation of novel pyrazole and imidazole carboxamides as CB1 antagonists are described. As a part of eastern amide SAR, various chemically diverse motifs were introduced on rimonabant template. The central pyrazole core was also replaced with its conformationally constrained motif and imidazole moieties. In general, a range of modifications were well tolerated. Several molecules with low- and sub-nanomolar potencies were identified as potent CB1 receptor antagonists. The in vivo proof of principle for weight loss is demonstrated with a lead compound in DIO mice model.

CB1 receptors mediate rimonabant-induced pruritic responses in mice: investigation of locus of action

RATIONALE

Cannabinoids have recently been identified as potential neuronal modulators of pruritic response, representing a potential target in the treatment of itch associated with a variety of pathophysiologic conditions. While the selective CB(1) receptor antagonist rimonabant is an established pruritic agent in both animal and clinical testing, its receptor mechanism of action and anatomical loci remain unclear.

OBJECTIVE

The purpose of this study was to determine whether CB(1) receptor blockade is critical to rimonabant-induced scratching and to identify differences in scratching response based on different routes of administration. Furthermore, experiments were designed to elucidate any evidence as to whether rimonabant elicits scratching behavior through common immunologic hypersensitivity mechanisms.

RESULTS

Rimonabant was equally effective at producing scratching via intraperitoneal and local subcutaneous injection. This compound also produced an intense scratching response when administered intrathecally, but had no effects after intracerebroventricular administration. Repeated administration of rimonabant led to a decreased magnitude of scratching. While rimonabant-induced scratching was not attenuated either by pretreatment with the H(1) receptor antagonist loratadine or in mast cell-deficient mice, it lacked efficacy in CB(1) (-/-) mice.

CONCLUSIONS

Rimonabant is a potent and fully effective pruritogen when administered spinally or systemically and requires CB(1) receptors to induce scratching, suggesting an important spinal CB(1) receptor component of action. The lack of responsiveness to H(1) antagonism or mast cell deficiency supports previous findings that cannabinoids modulate itch through neuronal mechanisms, and not by traditional hypersensitivity activation.

The highs and lows of cannabinoid receptor expression in disease: mechanisms and their therapeutic implications

Alterations in the endogenous cannabinoid system have been described in almost every category of disease. These changes can alternatively be protective or maladaptive, such as producing antinociception in neuropathic pain or fibrogenesis in liver disease, making the system an attractive therapeutic target. However, the challenge remains to selectively target the site of disease while sparing other areas, particularly mood and cognitive centers of the brain. Identifying regional changes in cannabinoid receptor-1 and -2 (CB(1)R and CB(2)R) expression is particularly important when considering endocannabinoid system-based therapies, because regional increases in cannabinoid receptor expression have been shown to increase potency and efficacy of exogenous agonists at sites of disease. Although there have been extensive descriptive studies of cannabinoid receptor expression changes in disease, the underlying mechanisms are only just beginning to unfold. Understanding these mechanisms is important and potentially relevant to therapeutics. In diseases for which cannabinoid receptors are protective, knowledge of the mechanisms of receptor up-regulation could be used to design therapies to regionally increase receptor expression and thus increase efficacy of an agonist. Alternatively, inhibition of harmful cannabinoid up-regulation could be an attractive alternative to global antagonism of the system. Here we review current findings on the mechanisms of cannabinoid receptor regulation in disease and discuss their therapeutic implications.

Leptin potentiates the anti-obesity effects of rimonabant

We hypothesized that a combination of low doses of rimonabant and leptin would markedly reduce body weight through the modulation of neuronal activity within the hypothalamus. To this end, high fat diet-induced obese rats were randomized to receive either leptin (0.5mg/kg subcutaneously), rimonabant (3mg/kg), the combination of both, or vehicle, daily for a duration of 2 weeks. A subset of rats was pair-fed to the combination-treated animals and received either vehicle or leptin. At the end of the weight loss phase, leptin treatment was maintained for 7 days while rimonabant was discontinued to assess changes in body weight during the rebound phase. The combination of rimonabant and leptin resulted in a marked inhibition of food intake and a profound reduction in body weight that was greater than achieved with either leptin or rimonabant alone. Treatment with leptin during the rebound phase inhibited compensatory increases in body weight associated with restitution of ad libitum feeding in previously pair-fed rats. Moreover, leptin partially blunted the rebound in food intake and body weight associated with cessation of rimonabant therapy.To investigate the effect of the combination on neuronal firing in the rat hypothalamus, single unit activity was recorded from brain slices containing the ventromedial and arcuate nuclei. The combination of rimonabant and leptin synergistically increased and decreased neuronal firing in the ventromedial and arcuate nuclei, respectively. Overall, these data demonstrate profound anti-obesity effects of combining cannabinoid type 1 receptor antagonists and leptin.

Safety evaluation and treatment affect of LY2190416, a CB-1 antagonist/inverse agonist in growing beagle dogs

The objective of this study was to assess the safe use of LY2190416, a cannabinoid receptor 1 receptor antagonist/inverse agonist, for obesity management in dogs. Twenty-four clinically normal young beagle dogs were administered LY2190416 at doses of 3, 9, or 18 mg/kg or placebo, orally, once daily for 13 weeks. Food consumption and body weight were determined, and dogs were evaluated for changes in hematology, clinical chemistry, urinalysis, and serum cortisol. LY2190416 had no significant effect on hematology, clinical chemistry, urinalysis, and serum cortisol. All dogs consumed 100% of their entire daily allowance throughout the study. All dogs gained weight during the study, but treated dogs gained less than control dogs by the end of the study. During the first month, dogs exhibited a dose-dependent decrease in rate of weight gain (19.7 g/day for control dogs vs. 10.6 g/day for the 18 mg/kg dose group). LY2190416 was found to be safe at doses up to 18 mg/kg administered daily for 3 months. Results suggest that LY2190416 decreases rate of weight gain without affecting appetite or causing significant adverse health effects in normal growing dogs. Possible mechanisms for a proposed metabolic effect are discussed.

A novel peripherally restricted cannabinoid receptor antagonist, AM6545, reduces food intake and body weight, but does not cause malaise, in rodents

BACKGROUND AND PURPOSE

Cannabinoid CB(1) receptor antagonists reduce food intake and body weight, but clinical use in humans is limited by effects on the CNS. We have evaluated a novel cannabinoid antagonist (AM6545) designed to have limited CNS penetration, to see if it would inhibit food intake in rodents, without aversive effects.

EXPERIMENTAL APPROACH

Cannabinoid receptor binding studies, cAMP assays, brain penetration studies and gastrointestinal motility studies were carried out to assess the activity profile of AM6545. The potential for AM6545 to induce malaise in rats and the actions of AM6545 on food intake and body weight were also investigated.

KEY RESULTS

AM6545 binds to CB(1) receptors with a K(i) of 1.7 nM and CB(2) receptors with a K(i) of 523 nM. AM6545 is a neutral antagonist, having no effect on cAMP levels in transfected cells and was less centrally penetrant than AM4113, a comparable CB(1) receptor antagonist. AM6545 reversed the effects of WIN55212-2 in an assay of colonic motility. In contrast to AM251, AM6545 did not produce conditioned gaping or conditioned taste avoidance in rats. In rats and mice, AM6545 dose-dependently reduced food intake and induced a sustained reduction in body weight. The effect on food intake was maintained in rats with a complete subdiaphragmatic vagotomy. AM6545 inhibited food intake in CB(1) receptor gene-deficient mice, but not in CB(1)/CB(2) receptor double knockout mice.

CONCLUSIONS AND IMPLICATIONS

Peripherally active, cannabinoid receptor antagonists with limited brain penetration may be useful agents for the treatment of obesity and its complications.