The CB1 antagonist rimonabant decreases insulin hypersecretion in rat pancreatic islets

The function of the endocannabinoid system in the pancreatic islet and its implications on metabolic syndrome and diabetes

The following review focuses on the scientific studies related to the role of endocannabinoid system (ECS) in pancreatic islet physiology and dysfunction. Different natural or synthetic agonists and antagonists have been suggested as an alternative treatment for diabetes, obesity and metabolic syndrome. Therapeutic use of Cannabis led to the discovery and characterization of the ECS, a signaling complex involved in regulation of various physiological processes, including food intake and metabolism. After the development of different agonists and antagonists, evidence have demonstrated the presence and activity of cannabinoid receptors in several organs and tissues, including pancreatic islets. Insulin and glucagon expression, stimulated secretion, and the development of diabetes and other metabolic disorders have been associated with the activity and modulation of ECS in pancreatic islets. However, according to the animal model and experimental design, either endogenous or pharmacological ligands of cannabinoid receptors have guided to contradictory and paradoxical results that suggest a complex physiological interaction. In consensus, ECS activity modulates insulin and glucagon secretions according to glucose in media; over-stimulation of cannabinoid receptors affects islets negatively, leading to glucose intolerance, meanwhile the treatment with antagonists in diabetic models and humans suggests an improvement in islets function.

Synthesis, molecular docking, and pharmacological evaluation of 5-(4-(2-(5-ethyl pyridine-2-yl) ethoxy) benzyl)-3-(phenylsulfonyl) thiazolidine-2, 4-dione against HFD-induced diabesity via interaction with the CB1 receptor

Objectives

CB1 antagonism arbitrates a dormant shape to the endocannabinoid system that alleviates diverse pathological incidents of diabesity. The present study pursued the synthesis and evaluation of thiazolidine derivative (BAC) having pleiotropic action on CB1R, with or without AM251 (selective antagonist of the CB1 receptor) against high-fat diet (HFD) induced diabesity in C57BL/6 mice.

Materials and Methods

A molecular docking study for CB1 antagonistic potential was conducted by Maestro 11.4 program (Schrodinger Inc., USA), and the thiazolidine derivative BAC was synthesized. The assessment of varied parameters including anthropometric, neurobehavioral, hyperglycemia, dyslipidemia, oxidative stress, and inflammatory cytokines was evaluated in HFD-fed animals as compared with individual and combined treatments of BAC and AM251.

Results

Incomparable to AM251, the treatment of BAC was reported for a significant reduction in food intake and obesity, diabetic biomarkers, lipid profile, oxidative stress, and proinflammatory cytokine release. Moreover, the BAC treatment showed no significant alteration in neurobehavioral activity, including anxiety and depression.

Conclusion

The preliminary in silico study suggests that BAC has a close interaction with CB1 antagonism but has no sign of neurobehavioral alteration. Simultaneously, this compound showed significant ability to ameliorate diversity by the underlying mechanisms of minimizing oxidative stress, regularizing the lipid profile, and reducing pro-inflammatory cytokines.

Obesity-induced changes in human islet G protein-coupled receptor expression: Implications for metabolic regulation

G protein-coupled receptors (GPCRs) are a large family of cell surface receptors that are the targets for many different classes of pharmacotherapy. The islets of Langerhans are central to appropriate glucose homeostasis through their secretion of insulin, and islet function can be modified by ligands acting at the large number of GPCRs that islets express. The human islet GPCRome is not a static entity, but one that is altered under pathophysiological conditions and, in this review, we have compared expression of GPCR mRNAs in human islets obtained from normal weight range donors, and those with a weight range classified as obese. We have also considered the likely outcomes on islet function that the altered GPCR expression status confers and the possible impact that adipokines, secreted from expanded fat depots, could have at those GPCRs showing altered expression in obesity.

The cannabinoid ligands SR141716A and AM251 enhance human and mouse islet function via GPR55-independent signalling

AIMS

Endocannabinoids are lipid mediators involved in the regulation of glucose homeostasis. They interact with the canonical cannabinoid receptors CB1 and CB2, and it is now apparent that some cannabinoid receptor ligands are also agonists at GPR55. Thus, CB1 antagonists such as SR141716A, also known as rimonabant, and AM251 act as GPR55 agonists in some cell types. The complex pharmacological properties of cannabinoids make it difficult to fully identify the relative importance of CB1 and GPR55 in the functional effects of SR141716A, and AM251. Here, we determine whether SR141716A and AM251 regulation of mouse and human islet function is through their action as GPR55 agonists.

METHODS

Islets isolated from Gpr55+/+ and Gpr55-/- mice and human donors were incubated in the absence or presence of 10 µM SR141716A or AM251, concentrations that are known to activate GPR55. Insulin secretion, cAMP, IP1, apoptosis and β-cell proliferation were quantified by standard techniques.

RESULTS

Our results provide the first evidence that SR141716A and AM251 are not GPR55 agonists in islets, as their effects are maintained in islets isolated from Gpr55-/- mice. Their signalling through Gq-coupled cascades to induce insulin secretion and human β-cell proliferation, and protect against apoptosis in vitro, indicate that they have direct beneficial effects on islet function.

CONCLUSION

These observations may be useful in directing development of peripherally restricted novel therapeutics that are structurally related to SR141716A and AM251, and which potentiate glucose-induced insulin secretion and stimulate β-cell proliferation.

Novel CB1 receptor antagonist BAR-1 modifies pancreatic islet function and clinical parameters in prediabetic and diabetic mice

BACKGROUDS

Cannabinoid receptor antagonists have been suggested as a novel treatment for obesity and diabetes. We have developed a synthetic cannabinoid receptor antagonist denominated BAR-1. As the function and integrity of a β-cell cellular structure are important keys for diabetes onset, we evaluated the effects of pharmacological administration of BAR-1 on prediabetic and diabetic rodents.

METHODS

CD-1 mice fed a hypercaloric diet or treated with streptozotocin were treated with 10 mg/kg BAR-1 for 2, 4 or 8 weeks. Body weight, oral glucose tolerance test, HbA1c, triglycerides and insulin in serum were measured. In isolated islets, we evaluated stimulated secretion and mRNA expression, and relative area of islets in fixed pancreases. Docking analysis of BAR-1 was complemented.

RESULTS

BAR-1 treatment slowed down weight gain in prediabetic mice. Fasting glucose-insulin relation also decreased in BAR-1-treated mice and glucose-stimulated insulin secretion was increased in isolated islets, without effects in oral test. Diabetic mice treated with BAR-1 showed a reduced glucose and a partial recovery of islet integrity. Gene expression of insulin and glucagon showed biphasic behaviour, increasing after 4 weeks of BAR-1 administration; however, after 8 weeks, mRNA abundance decreased significantly. Administration of BAR-1 also prevents changes in endocannabinoid element expression observed in prediabetic mice. No changes were detected in other parameters studied, including the histological structure. A preliminary in-silico study suggests a close interaction with CB1 receptor.

CONCLUSIONS

BAR-1 induces improvement of islet function, isolated from both prediabetic and diabetic mice. Effects of BAR-1 suggest a possible interaction with other cannabinoid receptors.

LH-21 and abnormal cannabidiol improve β-cell function in isolated human and mouse islets through GPR55-dependent and -independent signalling

AIMS

To examine the effects of Abn-CBD (GPR55 agonist) and LH-21 (CB1 antagonist) on human and mouse islet function, and to determine signalling via GPR55 using islets from GPR55^-/- mice.

MATERIALS AND METHODS

Islets isolated from human organ donors and mice were incubated in the absence or presence of Abn-CBD or LH-21, and insulin secretion, [Ca²⁺ ]_i, cAMP_, apoptosis, β-cell proliferation and CREB and AKT phosphorylation were examined using standard techniques.

RESULTS

Abn-CBD potentiated glucose-stimulated insulin secretion and elevated [Ca²⁺ ]_i in human islets and islets from both GPR55^+/+ and GPR55^-/- mice. LH-21 also increased insulin secretion and [Ca²⁺ ]_i in human islets and GPR55^+/+ mouse islets, but concentrations of LH-21 up to 0.1 μM were ineffective in islets from GPR55^-/- mice. Neither ligand affected basal insulin secretion or islet cAMP levels. Abn-CBD and LH-21 reduced cytokine-induced apoptosis in human islets and GPR55^+/+ mouse islets, and these effects were suppressed after GPR55 deletion. They also increased β-cell proliferation: the effects of Abn-CBD were preserved in islets from GPR55^-/- mice, while those of LH-21 were abolished. Abn-CBD and LH-21 increased AKT phosphorylation in mouse and human islets.

CONCLUSIONS

This study showed that Abn-CBD and LH-21 improve human and mouse islet β-cell function and viability. Use of islets from GPR55^-/- mice suggests that designation of Abn-CBD and LH-21 as a GPR55 agonist and a CB1 antagonist, should be revised.

Peripheral modulation of the endocannabinoid system in metabolic disease

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

Endocannabinoid regulation of β-cell functions: implications for glycaemic control and diabetes

Visceral obesity is a major risk factor for the development of insulin resistance which can progress to overt type 2 diabetes (T2D) with loss of β-cell function and, ultimately, loss of β-cells. Insulin secretion by β-cells of the pancreatic islets is tightly coupled to blood glucose concentration and modulated by a large number of blood-borne or locally released mediators, including endocannabinoids. Obesity and its complications, including T2D, are associated with increased activity of the endocannabinoid/CB1 receptor (CB1 R) system, as indicated by the therapeutic effects of CB1 R antagonists. Similar beneficial effects of CB1 R antagonists with limited brain penetrance indicate the important role of CB1 R in peripheral tissues, including the endocrine pancreas. Pancreatic β-cells express all of the components of the endocannabinoid system, and endocannabinoids modulate their function via both autocrine and paracrine mechanisms, which influence basal and glucose-induced insulin secretion and also affect β-cell proliferation and survival. The present brief review will survey available information on the modulation of these processes by endocannabinoids and their receptors, with an attempt to assess the contribution of such effects to glycaemic control in T2D and insulin resistance.

Prolonged activation of human islet cannabinoid receptors in vitro induces adaptation but not dysfunction

BACKGROUND

Although in vivo studies have implicated endocannabinoids in metabolic dysfunction, little is known about direct, chronic activation of the endocannabinoid system (ECS) in human islets. Therefore, this study investigated the effects of prolonged exposure to cannabinoid agonists on human islet gene expression and function.

METHODS

Human islets were maintained for 2 and 5 days in the absence or presence of CB1r (ACEA) or CB2r (JWH015) agonists. Gene expression was quantified by RT-PCR, hormone levels by radioimmunoassay and apoptosis by caspase activities.

RESULTS

Human islets express an ECS, with mRNAs encoding the biosynthetic and degrading enzymes NAPE-PLD, FAAH and MAGL being considerably more abundant than DAGLα, an enzyme involved in 2-AG synthesis, or CB1 and CB2 receptor mRNAs. Prolonged activation of CB1r and CB2r altered expression of mRNAs encoding ECS components, but did not have major effects on islet hormone secretion. JWH015 enhanced insulin and glucagon content at 2 days, but had no effect after 5 days. Treatment with ACEA or JWH015 for up to 5 days did not have marked effects on islet viability, as assessed by morphology and caspase activities.

CONCLUSIONS

Maintenance of human islets for up to 5 days in the presence of CB1 and CB2 receptor agonists causes modifications in ECS element gene expression, but does not have any major impact on islet function or viability.

GENERAL SIGNIFICANCE

These data suggest that the metabolic dysfunction associated with over-activation of the ECS in obesity and diabetes in humans is unlikely to be secondary to impaired islet function.

Blockade of cannabinoid 1 receptor improves GLP-1R mediated insulin secretion in mice

The cannabinoid 1 receptor (CB1) is an important regulator of energy metabolism. Reports of in vivo and in vitro studies give conflicting results regarding its role in insulin secretion, possibly due to circulatory factors, such as incretins. We hypothesized that this receptor may be a regulator of the entero-insular axis. We found that despite lower food consumption and lower body weight postprandial GLP-1 plasma concentrations were increased in CB1(-/-) mice compared to CB1(+/+) mice administered a standard diet or high fat/sugar diet. Upon exogenous GLP-1 treatment, CB1(-/-) mice had increased glucose-stimulated insulin secretion. In mouse insulinoma cells, cannabinoids reduced GLP-1R-mediated intracellular cAMP accumulation and subsequent insulin secretion. Importantly, such effects were also evident in human islets, and were prevented by pharmacologic blockade of CB1. Collectively, these findings suggest a novel mechanism in which endocannabinoids are negative modulators of incretin-mediated insulin secretion.

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 cannabinoid CB1 receptor and mTORC1 signalling pathways interact to modulate glucose homeostasis in mice

The endocannabinoid system (ECS) is an intercellular signalling mechanism that is present in the islets of Langerhans and plays a role in the modulation of insulin secretion and expansion of the β-cell mass. The downstream signalling pathways mediating these effects are poorly understood. Mammalian target of rapamycin complex 1 (mTORC1) signalling is a key intracellular pathway involved in energy homeostasis and is known to importantly affect the physiology of pancreatic islets. We investigated the possible relationship between cannabinoid type 1 (CB₁) receptor signalling and the mTORC1 pathway in the endocrine pancreas of mice by using pharmacological analysis as well as mice genetically lacking the CB₁ receptor or the downstream target of mTORC1, the kinase p70S6K1. In vitro static secretion experiments on islets, western blotting, and in vivo glucose and insulin tolerance tests were performed. The CB₁ receptor antagonist rimonabant decreased glucose-stimulated insulin secretion (GSIS) at 0.1 µM while increasing phosphorylation of p70S6K1 and ribosomal protein S6 (rpS6) within the islets. Specific pharmacological blockade of mTORC1 by 3 nM rapamycin, as well as genetic deletion of p70S6K1, impaired the CB₁-antagonist-mediated decrease in GSIS. In vivo experiments showed that 3 mg/kg body weight rimonabant decreased insulin levels and induced glucose intolerance in lean mice without altering peripheral insulin sensitivity; this effect was prevented by peripheral administration of low doses of rapamycin (0.1 mg/kg body weight), which increased insulin sensitivity. These findings suggest a functional interaction between the ECS and the mTORC1 pathway within the endocrine pancreas and at the whole-organism level, which could have implications for the development of new therapeutic approaches for pancreatic β-cell diseases.

Summary: Evidence supporting a functional interaction between the endocannabinoid system and the mTORC1 pathway within the endocrine pancreas, which could have implications for the development of new therapeutic approaches for diabetes.

Fetal endocannabinoids orchestrate the organization of pancreatic islet microarchitecture

Endocannabinoids are implicated in the control of glucose utilization and energy homeostasis by orchestrating pancreatic hormone release. Moreover, in some cell niches, endocannabinoids regulate cell proliferation, fate determination, and migration. Nevertheless, endocannabinoid contributions to the development of the endocrine pancreas remain unknown. Here, we show that α cells produce the endocannabinoid 2-arachidonoylglycerol (2-AG) in mouse fetuses and human pancreatic islets, which primes the recruitment of β cells by CB1 cannabinoid receptor (CB1R) engagement. Using subtractive pharmacology, we extend these findings to anandamide, a promiscuous endocannabinoid/endovanilloid ligand, which impacts both the determination of islet size by cell proliferation and α/β cell sorting by differential activation of transient receptor potential cation channel subfamily V member 1 (TRPV1) and CB1Rs. Accordingly, genetic disruption of TRPV1 channels increases islet size whereas CB1R knockout augments cellular heterogeneity and favors insulin over glucagon release. Dietary enrichment in ω-3 fatty acids during pregnancy and lactation in mice, which permanently reduces endocannabinoid levels in the offspring, phenocopies CB1R(-/-) islet microstructure and improves coordinated hormone secretion. Overall, our data mechanistically link endocannabinoids to cell proliferation and sorting during pancreatic islet formation, as well as to life-long programming of hormonal determinants of glucose homeostasis.

Decreased 11β-Hydroxysteroid Dehydrogenase 1 Level and Activity in Murine Pancreatic Islets Caused by Insulin-Like Growth Factor I Overexpression

We have reported a high expression of IGF-I in pancreatic islet β-cells of transgenic mice under the metallothionein promoter. cDNA microarray analysis of the islets revealed that the expression of 82 genes was significantly altered compared to wild-type mice. Of these, 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1), which is responsible for the conversion of inert cortisone (11-dehydrocorticosterone, DHC in rodents) to active cortisol (corticosterone) in the liver and adipose tissues, has not been identified previously as an IGF-I target in pancreatic islets. We characterized the changes in its protein level, enzyme activity and glucose-stimulated insulin secretion. In freshly isolated islets, the level of 11β-HSD1 protein was significantly lower in MT-IGF mice. Using dual-labeled immunofluorescence, 11β-HSD1 was observed exclusively in glucagon-producing, islet α-cells but at a lower level in transgenic vs. wild-type animals. MT-IGF islets also exhibited reduced enzymatic activities. Dexamethasone (DEX) and DHC inhibited glucose-stimulated insulin secretion from freshly isolated islets of wild-type mice. In the islets of MT-IGF mice, 48-h pre-incubation of DEX caused a significant decrease in insulin release, while the effect of DHC was largely blunted consistent with diminished 11β-HSD1 activity. In order to establish the function of intracrine glucocorticoids, we overexpressed 11β-HSD1 cDNA in MIN6 insulinoma cells, which together with DHC caused apoptosis and a significant decrease in proliferation. Both effects were abolished with the treatment of an 11β-HSD1 inhibitor. Our results demonstrate an inhibitory effect of IGF-I on 11β-HSD1 expression and activity within the pancreatic islets, which may mediate part of the IGF-I effects on cell proliferation, survival and insulin secretion.

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.

Endocannabinoids and energy homeostasis: an update

The endocannabinoid system (ECS) is a widespread intercellular signaling system that plays a critical role in energy homeostasis, meant as the precise matching of caloric intake with energy expenditure which normally keeps body weight stable over time. Complex interactions between environmental and neurohormonal systems directly contribute to the balance of energy homeostasis. This review highlights established and more recent data on the brain circuits in which the ECS plays an important regulatory role, with focus on the hypothalamus, a region where numerous interacting systems regulating feeding, satiety, stress, and other motivational states coexist. Although not meant as an exhaustive review of the field, this article will discuss how endocannabinoid tone, in addition to reinforcing reward circuitries and modulating food intake and the salience of food, controls lipid and glucose metabolism in several peripheral organs, particularly the liver and adipose tissue. Direct actions in the skeletal muscle and pancreas are also emerging and are briefly discussed. This review provides new perspectives into endocannabinoid control of the neurochemical causes and consequences of energy homeostasis imbalance, a knowledge that might lead to new potential treatments for obesity and related morbidities.

The cannabinoid receptor 1 and its role in influencing peripheral metabolism

Evidence from in vitro and in vivo studies has demonstrated the deleterious pathological effects of a dysregulated endocannabinoid system. Increased stimulation of the cannabinoid receptor 1 (CB1 ) and subsequent downstream cellular signalling are both causative in the deleterious pathological effects observed in a number of diseases. When the CB1 cell signalling cascade is blocked, this results in whole body weight-loss, leading to a reduction in obesity and associated co-morbidities. In the central nervous system; however, CB1 antagonism results in adverse psychological side effects. Blockade of CB1 via peripheral acting compounds that do not cross the blood-brain barrier have been determined to have beneficial effects in metabolic tissues such as the liver and skeletal muscle. These results support the notion that peripheral blockade of CB1 using pharmacological antagonists is a viable target for the treatment of the current epidemic of obesity and its associated co-morbidities.

Biochemical and immunohistochemical changes in delta-9-tetrahydrocannabinol-treated type 2 diabetic rats

The regulation of glucose, lipid metabolism and immunoreactivities of insulin and glucagon peptides by delta-9-tetrahydrocannabinol (Δ(9)-THC) in diabetes were examined in an experimental rat model. Male Sprague-Dawley rats were divided into four groups: (1) control, (2) Δ(9)-THC treated, (3) diabetic, and (4) diabetic+Δ(9)-THC. The type 2 diabetic rat model was established by intraperitoneal (i.p.) injection of nicotinamide (85 mg/kg body weight) followed after 15 min by i.p. injection of streptozotocin (STZ) at 65 mg/kg of body weight. Δ(9)-THC and Δ(9)-THC treated diabetic groups received 3mg/kg/day of Δ(9)-THC for 7 days. The immunolocalization of insulin and glucagon peptides was investigated in the pancreas using a streptavidin-biotin-peroxidase technique. High density lipoprotein cholesterol (HDL), low density lipoprotein cholesterol (LDL), very low density lipoprotein cholesterol (VLDL), triglycerides (TG), total cholesterol (TC) and total protein (TP) levels were measured in serum. Total islet area percent of insulin immunoreactive cells slightly changed in diabetic+Δ(9)-THC rats compared to diabetic animals. However, the area percent of glucagon immunoreactive cells showed a decrease in diabetic+Δ(9)-THC rats compared to that of diabetic animals alone. Serum TC, HDL and LDL levels of diabetes+Δ(9)-THC group showed a decrease compared to the diabetic group. These results indicate that Δ(9)-THC may serve a protective role against hyperlipidemia and hyperglycemia in diabetic rats.

CB1 cannabinoid receptors couple to focal adhesion kinase to control insulin release

Endocannabinoid signaling has been implicated in modulating insulin release from β cells of the endocrine pancreas. β Cells express CB1 cannabinoid receptors (CB1Rs), and the enzymatic machinery regulating anandamide and 2-arachidonoylglycerol bioavailability. However, the molecular cascade coupling agonist-induced cannabinoid receptor activation to insulin release remains unknown. By combining molecular pharmacology and genetic tools in INS-1E cells and in vivo, we show that CB1R activation by endocannabinoids (anandamide and 2-arachidonoylglycerol) or synthetic agonists acutely or after prolonged exposure induces insulin hypersecretion. In doing so, CB1Rs recruit Akt/PKB and extracellular signal-regulated kinases 1/2 to phosphorylate focal adhesion kinase (FAK). FAK activation induces the formation of focal adhesion plaques, multimolecular platforms for second-phase insulin release. Inhibition of endocannabinoid synthesis or FAK activity precluded insulin release. We conclude that FAK downstream from CB1Rs mediates endocannabinoid-induced insulin release by allowing cytoskeletal reorganization that is required for the exocytosis of secretory vesicles. These findings suggest a mechanistic link between increased circulating and tissue endocannabinoid levels and hyperinsulinemia in type 2 diabetes.

Islet cannabinoid receptors: cellular distribution and biological function

OBJECTIVES

This study aimed to determine the cellular distribution of islet cannabinoid receptors (CBs) and their involvement in the development of metabolic and hormonal changes in rats fed a fructose-rich diet (F).

METHODS

In normal rat islets, we determined CBs (immunofluorescence and retrotranscription-polymerase chain reaction) and glucose-stimulated insulin secretion (GSIS) of isolated islets incubated with the CB1 antagonist rimonabant (R) and/or different CBs agonists. In 3-week F-fed rats, we determined the in vivo effect of R on serum glucose, triglyceride, and insulin levels; homeostasis model assessment for insulin resistance, GSIS, and CBs and insulin receptor substrate gene expression levels (real-time polymerase chain reaction).

RESULTS

Cannabinoid receptors appeared exclusively in islet α cells. Whereas different CB agonists enhanced GSIS in normal rat islets, R did not affect it. F rats had higher serum triglyceride and insulin levels and homeostasis model assessment for insulin resistance than control rats; these alterations were prevented by R coadministration. Although R did not correct the increased GSIS observed in F islets, it modulated CBs and insulin receptor substrate gene expression.

CONCLUSIONS

Islet CBs would exert an important modulatory role in metabolic homeostasis. Administration of R and F affected islet CB expression and prevented the development of F-induced metabolic impairment. Selective islet CB1 blockers could be useful to prevent/treat the alterations induced by the intake of unbalanced/unhealthy diets.

Reduced food intake is the major contributor to the protective effect of rimonabant on islet in established obesity-associated type 2 diabetes

PURPOSE

Although the presence of cannabinoid type 1 (CB1) receptor in islets has been reported, the major contributor to the protective effect of rimonabant on islet morphology is unknown. We determined whether the protective effect of rimonabant on pancreatic islet morphology is valid in established diabetes and also whether any effect was independent of decreased food intake.

MATERIALS AND METHODS

After diabetes was confirmed, Otsuka Long-Evans Tokushima Fatty rats, aged 32 weeks, were treated with rimonabant (30 mg/kg/d, rimonabant group) for 6 weeks. Metabolic profiles and islet morphology of rats treated with rimonabant were compared with those of controls without treatment (control group), a pair-fed control group, and rats treated with rosiglitazone (4 mg/kg/d, rosiglitazone group).

RESULTS

Compared to the control group, rats treated with rimonabant exhibited reduced glycated albumin levels (p<0.001), islet fibrosis (p<0.01), and improved glucose tolerance (p< 0.05), with no differences from the pair-fed control group. The retroperitoneal adipose tissue mass was lower in the rimonabant group than those of the pair-fed control and rosiglitazone groups (p<0.05). Rimonabant, pair-fed control, and rosiglitazone groups showed decreased insulin resistance and increased adiponectin, with no differences between the rimonabant and pair-fed control groups.

CONCLUSION

Rimonabant had a protective effect on islet morphology in vivo even in established diabetes. However, the protective effect was also reproduced by pair-feeding. Thus, the results of this study did not support the significance of islet CB1 receptors in islet protection with rimonabant in established obesity-associated type 2 diabetes.

The endocannabinoid system in energy homeostasis and the etiopathology of metabolic disorders

Endocannabinoids and cannabinoid CB1 receptors are known to play a generalized role in energy homeostasis. However, clinical trials with the first generation of CB1 blockers, now discontinued due to psychiatric side effects, were originally designed to reduce food intake and body weight rather than the metabolic risk factors associated with obesity. In this review, we discuss how, in addition to promoting energy intake, endocannabinoids control lipid and glucose metabolism in several peripheral organs, particularly the liver and adipose tissue. Direct actions in skeletal muscle and pancreas are also emerging. This knowledge may help in the design of future therapies for the metabolic syndrome.

The complex effects of cannabinoids on insulin secretion from rat isolated islets of Langerhans

Recent interest in the endocrine pancreas has revealed the presence of a functional endocannabinoid system in pancreatic islets, however, the effects of endocannabinoids and cannabinoid CB receptor activation on downstream signalling and on insulin release still remains unclear. In the current study, a variety of purported cannabinoid CB receptor agonists and antagonists were evaluated for their effects on insulin secretion. In fresh rat isolated islets, the endocannabinoid anandamide caused a glucose-dependent, concentration-dependent inhibition of insulin release, with two populations of islets being identified based on their sensitivity to anandamide. Methanandamide (a non-hydrolysable analogue of anandamide) elicited similar inhibition of insulin secretion, comparable to the responses obtained with anandamide-sensitive islets, suggesting that the islet responsiveness may be due to differences in local metabolism of anandamide. The antagonists O-2050 (CB1) and AM630 (CB2) failed to reveal the involvement of cannabinoid receptors in the inhibitory activity of anandamide on insulin release. Inhibition of fatty acid amide hydrolase (FAAH) with URB597 did not alter basal or glucose-induced insulin secretion, suggesting that endogenous islet endocannabinoids do not affect insulin release, or that islet FAAH content is low. URB597 also failed to affect the inhibitory actions of anandamide on insulin release in fresh isolated islets. However, in islets following overnight culture, anandamide caused augmentation of basal and glucose-mediated insulin release. The effects of cannabinoid agents on insulin secretion described in this study does not identify a precise mode of action but points to important modulation which may be dependent on local metabolism and prevailing cellular conditions.

Chronic activation of cannabinoid receptors in vitro does not compromise mouse islet function

We have demonstrated previously that mouse and human islets express ECS (endocannabinoid system) elements, and that short-term activation of islet cannabinoid CB1r and CB2r (cannabinoid type 1 and 2 receptors respectively) stimulates insulin secretion in vitro. There is evidence that the ECS is overactive in Type 2 diabetes, impairing glucose homoeostasis, but little is known about whether it is implicated in islet dysfunction. Therefore the aim of the present study was to investigate the effect of chronic exposure of isolated mouse islets to cannabinoid receptor agonists on islet gene expression and function. Quantitative RT-PCR (reverse transcription-PCR) indicated that mRNAs encoding synthesis [NAPE-PLD (N-acyl-phosphatidyl ethanolamide-hydrolysing phospholipase D)] and degradation [FAAH (fatty acid amide hydrolase)] of the endocannabinoid AEA (anandamide) were the most abundant ECS elements in mouse islets, with much lower levels of CB1r, CB2r, DAGL (diacylglycerol lipase) and MAGL (monoacylglycerol lipase) mRNAs. Maintenance of islets for up to 7 days in the presence of the CB1r agonist ACEA [N-(2-chloroethyl)-5Z,8Z,11Z,14Z-eiscosatetraenamide] or the CB2r agonist JWH015 [(2-methyl-1propyl-1H-indol3-yl)-1-napthalenylmethanone] did not compromise islet viability, as assessed by islet morphology and caspase activities, but there were some changes in mRNAs encoding ECS components. Neither glucose-stimulated insulin secretion nor acute insulin secretory responses to ACEA or JWH015 at 16 mM glucose were substantially modified by a 48 h or 7 day pre-exposure to these cannabinoid receptor agonists, but the stimulation of secretion at 3 mM glucose by 100 nM ACEA was significantly reduced after prolonged treatment with ACEA. Despite JWH015-induced reductions in islet glucagon content at 48 h and 7 days, there were no reductions in arginine-induced glucagon secretion from islets pre-exposed to JWH015 or ACEA. These data indicate that treatment of islets with agonists of CB1r and CB2r for up to 7 days does not have any major impact on islet function, suggesting that the impairments in glucose homoeostasis observed following overactivation of the ECS should be sought in relation to insulin resistance rather than β-cell dysfunction.

Beneficial metabolic effects of CB1R anti-sense oligonucleotide treatment in diet-induced obese AKR/J mice

An increasing amount of evidence supports pleiotropic metabolic roles of the cannibinoid-1 receptor (CB1R) in peripheral tissues such as adipose, liver, skeletal muscle and pancreas. To further understand the metabolic consequences of specific blockade of CB1R function in peripheral tissues, we performed a 10-week-study with an anti-sense oligonucleotide directed against the CB1R in diet-induced obese (DIO) AKR/J mice. DIO AKR/J mice were treated with CB1R ASO Isis-414930 (6.25, 12.5 and 25 mg/kg/week) or control ASO Isis-141923 (25 mg/kg/week) via intraperitoneal injection for 10 weeks. At the end of the treatment, CB1R mRNA from the 25 mg/kg/week CB1R ASO group in the epididymal fat and kidney was decreased by 81% and 63%, respectively. Body weight gain was decreased in a dose-dependent fashion, significantly different in the 25 mg/kg/week CB1R ASO group (46.1±1.0 g vs veh, 51.2±0.9 g, p<0.05). Body fat mass was reduced in parallel with attenuated body weight gain. CB1R ASO treatment led to decreased fed glucose level (at week 8, 25 mg/kg/week group, 145±4 mg/dL vs veh, 195±10 mg/dL, p<0.05). Moreover, CB1R ASO treatment dose-dependently improved glucose excursion during an oral glucose tolerance test, whereas control ASO exerted no effect. Liver steatosis was also decreased upon CB1R ASO treatment. At the end of the study, plasma insulin and leptin levels were significantly reduced by 25 mg/kg/week CB1R ASO treatment. SREBP1 mRNA expression was decreased in both epididymal fat and liver. G6PC and fatty acid translocase/CD36 mRNA levels were also reduced in the liver. In summary, CB1R ASO treatment in DIO AKR/J mice led to improved insulin sensitivity and glucose homeostasis. The beneficial effects of CB1R ASO treatment strongly support the notion that selective inhibition of the peripheral CB1R, without blockade of central CB1R, may serve as an effective approach for treating type II diabetes, obesity and the metabolic syndrome.

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.

Some cannabinoid receptor ligands and their distomers are direct-acting openers of SUR1 K(ATP) channels

Here, we examined the chronic effects of two cannabinoid receptor-1 (CB1) inverse agonists, rimonabant and ibipinabant, in hyperinsulinemic Zucker rats to determine their chronic effects on insulinemia. Rimonabant and ibipinabant (10 mg·kg⁻¹·day⁻¹) elicited body weight-independent improvements in insulinemia and glycemia during 10 wk of chronic treatment. To elucidate the mechanism of insulin lowering, acute in vivo and in vitro studies were then performed. Surprisingly, chronic treatment was not required for insulin lowering. In acute in vivo and in vitro studies, the CB1 inverse agonists exhibited acute K channel opener (KCO; e.g., diazoxide and NN414)-like effects on glucose tolerance and glucose-stimulated insulin secretion (GSIS) with approximately fivefold better potency than diazoxide. Followup studies implied that these effects were inconsistent with a CB1-mediated mechanism. Thus effects of several CB1 agonists, inverse agonists, and distomers during GTTs or GSIS studies using perifused rat islets were unpredictable from their known CB1 activities. In vivo rimonabant and ibipinabant caused glucose intolerance in CB1 but not SUR1-KO mice. Electrophysiological studies indicated that, compared with diazoxide, 3 μM rimonabant and ibipinabant are partial agonists for K channel opening. Partial agonism was consistent with data from radioligand binding assays designed to detect SUR1 K(ATP) KCOs where rimonabant and ibipinabant allosterically regulated ³H-glibenclamide-specific binding in the presence of MgATP, as did diazoxide and NN414. Our findings indicate that some CB1 ligands may directly bind and allosterically regulate Kir6.2/SUR1 K(ATP) channels like other KCOs. This mechanism appears to be compatible with and may contribute to their acute and chronic effects on GSIS and insulinemia.

Voluntary running exercise prevents β-cell failure in susceptible islets of the Zucker diabetic fatty rat

Physical activity improves glycemic control in type 2 diabetes (T2D), but its contribution to preserving β-cell function is uncertain. We evaluated the role of physical activity on β-cell secretory function and glycerolipid/fatty acid (GL/FA) cycling in male Zucker diabetic fatty (ZDF) rats. Six-week-old ZDF rats engaged in voluntary running for 6 wk (ZDF-A). Inactive Zucker lean and ZDF (ZDF-I) rats served as controls. ZDF-I rats displayed progressive hyperglycemia with β-cell failure evidenced by falling insulinemia and reduced insulin secretion to oral glucose. Isolated ZDF-I rat islets showed reduced glucose-stimulated insulin secretion expressed per islet and per islet protein. They were also characterized by loss of the glucose regulation of fatty acid oxidation and GL/FA cycling, reduced mRNA expression of key β-cell genes, and severe reduction of insulin stores. Physical activity prevented diabetes in ZDF rats through sustaining β-cell compensation to insulin resistance shown in vivo and in vitro. Surprisingly, ZDF-A islets had persistent defects in fatty acid oxidation, GL/FA cycling, and β-cell gene expression. ZDF-A islets, however, had preserved islet insulin mRNA and insulin stores compared with ZDF-I rats. Physical activity did not prevent hyperphagia, dyslipidemia, or obesity in ZDF rats. In conclusion, islets of ZDF rats have a susceptibility to failure that is possibly due to altered β-cell fatty acid metabolism. Depletion of pancreatic islet insulin stores is a major contributor to islet failure in this T2D model, preventable by physical activity.

Cannabinoids inhibit insulin receptor signaling in pancreatic β-cells

OBJECTIVE

Optimal glucose homeostasis requires exquisitely precise adaptation of the number of insulin-secreting β-cells in the islets of Langerhans. Insulin itself positively regulates β-cell proliferation in an autocrine manner through the insulin receptor (IR) signaling pathway. It is now coming to light that cannabinoid 1 receptor (CB1R) agonism/antagonism influences insulin action in insulin-sensitive tissues. However, the cells on which the CB1Rs are expressed and their function in islets have not been firmly established. We undertook the current study to investigate if intraislet endogenous cannabinoids (ECs) regulate β-cell proliferation and if they influence insulin action.

RESEARCH DESIGN AND METHODS

We measured EC production in isolated human and mouse islets and β-cell line in response to glucose and KCl. We evaluated human and mouse islets, several β-cell lines, and CB1R-null (CB1R(-/-)) mice for the presence of a fully functioning EC system. We investigated if ECs influence β-cell physiology through regulating insulin action and demonstrated the therapeutic potential of manipulation of the EC system in diabetic (db/db) mice.

RESULTS

ECs are generated within β-cells, which also express CB1Rs that are fully functioning when activated by ligands. Genetic and pharmacologic blockade of CB1R results in enhanced IR signaling through the insulin receptor substrate 2-AKT pathway in β-cells and leads to increased β-cell proliferation and mass. CB1R antagonism in db/db mice results in reduced blood glucose and increased β-cell proliferation and mass, coupled with enhanced IR signaling in β-cells. Furthermore, CB1R activation impedes insulin-stimulated IR autophosphorylation on β-cells in a Gα(i)-dependent manner.

CONCLUSIONS

These findings provide direct evidence for a functional interaction between CB1R and IR signaling involved in the regulation of β-cell proliferation and will serve as a basis for developing new therapeutic interventions to enhance β-cell function and proliferation in diabetes.

Effect of the cannabinoid receptor-1 antagonist rimonabant on inflammation in mice with diet-induced obesity

We studied whether cannabinoid receptor (CB1) blockade with rimonabant has an anti-inflammatory effect in obese mice, and whether this effect depends on weight loss and/or diet consumption. High-fat diet (HFD)-induced obese mice were treated orally with rimonabant (HFD-R) or vehicle (HFD-V) for 4 weeks. Paired-feeding was conducted in two additional groups of obese mice to achieve either the same body weight (HFD-BW) or the same HFD intake (HFD DI) as HFD-R. All these groups of mice were maintained on HFD throughout, with mice on normal diet (ND) throughout as lean controls. Rimonabant treatment of obese mice induced marked diet-intake reduction and weight loss during the first week, which was followed by maintenance of low body weight but not diet-intake reduction. Lower HFD intake was required to reach the same degree of weight loss in HFD-BW. HFD-DI had similar weight loss initially, but then started to gain weight, reaching a higher body weight than HFD-R. Despite the same degree of weight loss, HFD-R had less fat mass and lower adipogenic gene expression than HFD-BW. Compared to HFD-V or HFD-DI, HFD-R had reduced inflammation in adipose tissue (AT) and/or liver indicated primarily by lower monocyte chemoattractant protein-1 (MCP-1) levels. However, MCP-1 levels were not significantly different between HFD-R and HFD-BW. In vitro incubation of rimonabant with AT explants did not change MCP-1 levels. Thus, rimonabant induced weight loss in obese mice by diet-intake-dependent and -independent fashions. Rimonabant decreased inflammation in obese mice, possibly through a primary effect on weight reduction.

Cannabinoids and endocannabinoids in metabolic disorders with focus on diabetes

The cannabinoid receptors for Δ(9)-THC, and particularly, the CB(1) receptor, as well as its endogenous ligands, the endocannabinoids anandamide and 2-arachidonoylglycerol, are deeply involved in all aspects of the control of energy balance in mammals. While initially it was believed that this endocannabinoid signaling system would only facilitate energy intake, we now know that perhaps even more important functions of endocannabinoids and CB(1) receptors in this context are to enhance energy storage into the adipose tissue and reduce energy expenditure by influencing both lipid and glucose metabolism. Although normally well controlled by hormones and neuropeptides, both central and peripheral aspects of endocannabinoid regulation of energy balance can become dysregulated and contribute to obesity, dyslipidemia, and type 2 diabetes, thus raising the possibility that CB(1) antagonists might be used for the treatment of these metabolic disorders. On the other hand, evidence is emerging that some nonpsychotropic plant cannabinoids, such as cannabidiol, can be employed to retard β-cell damage in type 1 diabetes. These novel aspects of endocannabinoid research are reviewed in this chapter, with emphasis on the biological effects of plant cannabinoids and endocannabinoid receptor antagonists in diabetes.

Rimonabant-mediated changes in intestinal lipid metabolism and improved renal vascular dysfunction in the JCR:LA-cp rat model of prediabetic metabolic syndrome

Rimonabant (SR141716) is a specific antagonist of the cannabinoid-1 receptor. Activation of the receptor initiates multiple effects on central nervous system function, metabolism, and body weight. The hypothesis that rimonabant has protective effects against vascular disease associated with the metabolic syndrome was tested using JCR:LA-cp rats. JCR:LA-cp rats are obese if they are cp/cp, insulin resistant, and exhibit associated micro- and macrovascular disease with end-stage myocardial and renal disease. Treatment of obese rats with rimonabant (10 mg.kg(-1).day(-1), 12-24 wk of age) caused transient reduction in food intake for 2 wk, without reduction in body weight. However, by 4 wk, there was a modest, sustained reduction in weight gain. Glycemic control improved marginally compared with controls, but at the expense of increased insulin concentration. In contrast, rimonabant normalized fasting plasma triglyceride and reduced plasma plasminogen activator inhibitor-1 and acute phase protein haptoglobin in cp/cp rats. Furthermore, these changes were accompanied by reduced postprandial intestinal lymphatic secretion of apolipoprotein B48, cholesterol, and haptoglobin. While macrovascular dysfunction and ischemic myocardial lesion frequency were unaffected by rimonabant treatment, both microalbuminuria and glomerular sclerosis were substantially reduced. In summary, rimonabant has a modest effect on body weight in freely eating obese rats and markedly reduces plasma triglyceride levels and microvascular disease, in part due to changes in intestinal metabolism, including lymphatic secretion of apolipoprotein B48 and haptoglobin. We conclude that rimonabant improves renal disease and intestinal lipid oversecretion associated with an animal model of the metabolic syndrome that appears to be independent of hyperinsulinemia or macrovascular dysfunction.

CB1 cannabinoid receptor expression is regulated by glucose and feeding in rat pancreatic islets

Endocannabinoid system is involved in food intake and energy balance. Beside the hypothalamus, pancreatic islet also expresses CB1 cannabinoid receptor, however little is known about its physiological role and regulation. Since gene expression of many specific proteins of the islet depends on the concentration of glucose, we studied CB1 receptor expression in response to fasting and feeding. Whole pancreas or islets were isolated from food-deprived adult Wistar rats, with or without a previous 1.5 g/kg glucose oral-intake. CB1, insulin and glucagon expressions were analyzed by confocal immunofluorescence and PCR. In vitro, rat islets were cultured at different glucose concentrations, in the presence of anandamide, or with Rimonabant analog BAR-1. CB1, insulin, glucagon, glucokinase, and PDX-1 expression were determined by real-time RT-PCR, and insulin secretion and islet content by ELISA. CB1 expression in pancreatic islets is upregulated during food restriction, and decreases in response to glucose intake or feeding. In cultured islets, 16 mmol/l glucose, BAR-1, and anandamide at low glucose reduced CB1 mRNA. Insulin, glucagon, glucokinase and PDX-1 expression increased in islets treated with anandamide at low glucose, while BAR-1 modified PDX-1 and glucagon mRNA at high glucose. Basal insulin secretion and insulin content in islets increased with anandamide, but not the glucose-stimulated response. Our results suggest that the endocannabinoid system has an important role in gene expression on islets and its close relationship with glucose response.

CB1 antagonism exerts specific molecular effects on visceral and subcutaneous fat and reverses liver steatosis in diet-induced obese mice

OBJECTIVE

The beneficial effects of the inactivation of endocannabinoid system (ECS) by administration of antagonists of the cannabinoid receptor (CB) 1 on several pathological features associated with obesity is well demonstrated, but the relative contribution of central versus peripheral mechanisms is unclear. We examined the impact of CB1 antagonism on liver and adipose tissue lipid metabolism in a mouse model of diet-induced obesity.

RESEARCH DESIGN AND METHODS

Mice were fed either with a standard diet or a high-sucrose high-fat (HSHF) diet for 19 weeks and then treated with the CB1-specific antagonist SR141716 (10 mg x kg(-1) x day(-1)) for 6 weeks.

RESULTS

Treatment with SR141716 reduced fat mass, insulin levels, and liver triglycerides primarily increased by HSHF feeding. Serum adiponectin levels were restored after being reduced in HSHF mice. Gene expression of scavenger receptor class B type I and hepatic lipase was induced by CB1 blockade and associated with an increase in HDL-cholesteryl ether uptake. Concomitantly, the expression of CB1, which was strongly increased in the liver and adipose tissue of HSHF mice, was totally normalized by the treatment. Interestingly, in visceral but not subcutaneous fat, genes involved in transport, synthesis, oxidation, and release of fatty acids were upregulated by HSHF feeding, while this effect was counteracted by CB1 antagonism.

CONCLUSIONS

A reduction in the CB1-mediated ECS activity in visceral fat is associated with a normalization of adipocyte metabolism, which may be a determining factor in the reversion of liver steatosis induced by treatment with SR141716.