Cannabinoid-1 receptor antagonists in type-2 diabetes

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.

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.

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.

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.

Features, diagnosis, and treatment of nonalcoholic fatty liver disease

As the global incidence of obesity has increased, nonalcoholic fatty liver disease (NAFLD) has become a worldwide health concern. NAFLD occurs in children and adults of all ethnicities and includes isolated fatty liver and nonalcoholic steatohepatitis (NASH). Patients with NASH are at risk for developing cirrhosis, hepatic decompensation, and hepatocellular carcinoma and have increased all-cause mortality. NAFLD is associated with a variety of clinical conditions and is an independent risk factor for hepatocellular carcinoma. The pathogenesis of NAFLD and the specific steps that lead to NASH and advanced fibrosis are not fully understood, although researchers have found that a combination of environmental, genetic, and metabolic factors lead to advanced disease. There have been improvements in noninvasive radiographic methods to diagnose NAFLD, especially for advanced disease. However, liver biopsy is still the standard method of diagnosis for NASH. There are many challenges to treating patients with NASH, and no therapies have been approved by the U.S. Food and Drug Administration; multimodal approaches are being developed and becoming the standard of care. We review pathogenesis and treatment approaches for the West's largest liver-related public health concern.

Cannabinoid receptor agonists and antagonists stimulate insulin secretion from isolated human islets of Langerhans

AIMS

The role of cannabinoid receptors in human islets of Langerhans has not been investigated in any detail, so the current study examined CB1 and CB2 receptor expression by human islets and the effects of pharmacological cannabinoid receptor agonists and antagonists on insulin secretion.

METHODS

Human islets were isolated from pancreases retrieved from heart-beating organ donors. Messenger RNAs encoding human CB1 and CB2 receptors were amplified from human islet RNA by RT-PCR and receptor localization within islets was identified by immunohistochemistry. Dynamic insulin secretion from human islets perifused with buffers supplemented with CB1 and CB2 receptor agonists and antagonists was quantified by radioimmunoassay.

RESULTS

RT-PCR showed that both CB1 and CB2 receptors are expressed by human islets and immunohistochemistry indicated that receptor expression co-localized with insulin-expressing β-cells. Perifusion experiments using isolated human islets showed that insulin secretion was reversibly stimulated by both CB1 and CB2 receptor agonists, with CB1 receptor activation associated with increased basal secretion whereas CB2 receptors were coupled to initiation and potentiation of insulin secretion. Antagonists at CB1 (N-(Piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide) and CB2 (N-(1,3-Benzodioxol-5-ylmethyl)-1,2-dihydro-7-methoxy-2-oxo-8-(pentyloxy)-3-quinoline carboxamide) receptors failed to inhibit the stimulatory effects of the respective agonists and, unexpectedly, reversibly stimulated insulin secretion.

CONCLUSIONS

These data confirm the expression of CB1 and CB2 receptors by human islets and indicate that both receptor subtypes are coupled to the stimulation of insulin secretion. They also implicate involvement of CB1/2 receptor-independent pathways in the antagonist-induced stimulatory effects.

Impact of medical therapy on atheroma volume measured by different cardiovascular imaging modalities

Atherosclerosis is a systemic disease that affects most vascular beds. The gold standard of atherosclerosis imaging has been invasive intravascular ultrasound (IVUS). Newer noninvasive imaging modalities like B-mode ultrasound, cardiac computed tomography (CT), positron emission tomography (PET), and magnetic resonance imaging (MRI) have been used to assess these vascular territories with high accuracy and reproducibility. These imaging modalities have lately been used for the assessment of the atherosclerotic plaque and the response of its volume to several medical therapies used in the treatment of patients with cardiovascular disease. To study the impact of these medications on atheroma volume progression or regression, imaging modalities have been used on a serial basis providing a unique opportunity to monitor the effect these antiatherosclerotic strategies exert on plaque burden. As a result, studies incorporating serial IVUS imaging, quantitative coronary angiography (QCA), B-mode ultrasound, electron beam computed tomography (EBCT), and dynamic contrast-enhanced magnetic resonance imaging have all been used to evaluate the impact of therapeutic strategies that modify cholesterol and blood pressure on the progression/regression of atherosclerotic plaque. In this review, we intend to summarize the impact of different therapies aimed at halting the progression or even result in regression of atherosclerotic cardiovascular disease evaluated by different imaging modalities.

Adverse endocrine and metabolic effects of psychotropic drugs: selective clinical review

The article critically reviews selected, clinically significant, adverse endocrine and metabolic effects associated with psychotropic drug treatments, including hyperprolactinaemia, hyponatraemia, diabetes insipidus, hypothyroidism, hyperparathyroidism, sexual dysfunction and virilization, weight loss, weight gain and metabolic syndrome (type 2 diabetes mellitus, dyslipidaemia and hypertension). Such effects are prevalent and complex, but can be managed clinically when recognized. They encourage continued critical assessment of benefits versus risks of psychotropic drugs and underscore the importance of close coordination of psychiatric and general medical care to improve long-term health of psychiatric patients. Options for management of hyperprolactinaemia include lowering doses, switching to agents such as aripiprazole, clozapine or quetiapine, managing associated osteoporosis, carefully considering the use of dopamine receptor agonists and ruling out stress, oral contraceptive use and hypothyroidism as contributing factors. Disorders of water homeostasis may include syndrome of inappropriate antidiuretic hormone (SIADH), managed by water restriction or slow replacement by hypertonic saline along with drug discontinuation. Safe management of diabetes insipidus, commonly associated with lithium, involves switching mood stabilizer and consideration of potassium-sparing diuretics. Clinical hypothyroidism may be a more useful marker than absolute cut-offs of hormone values, and may be associated with quetiapine, antidepressant and lithium use, and managed by thyroxine replacement. Hyper-parathyroidism requires comprehensive medical evaluation for occult tumours. Hypocalcaemia, along with multiple other psychiatric and medical causes, may result in decreased bone density and require evaluation and management. Strategies for reducing sexual dysfunction with psychotropics remain largely unsatisfactory. Finally, management strategies for obesity and metabolic syndrome are reviewed in light of the recent expert guidelines, including risk assessment and treatments, such as monoamine transport inhibitors, anticonvulsants and cannabinoid receptor antagonists, as well as lifestyle changes.

Effect of antiobesity medications in patients with type 2 diabetes mellitus

Obesity is considered as a major health problem, as its prevalence continuously rises worldwide. One of the common health consequences of obesity is type 2 diabetes mellitus. Therefore, antiobesity management is a prerequisite in treating diabetic patients. Lifestyle modifications combined with pharmacological agents appear to be an effective approach. Sibutramine is a serotonin-noradrenaline reuptake inhibitor, which acts centrally by promoting the feeling of satiety and decreasing caloric intake, thus resulting in weight loss. A potential association with cardiovascular side effects has been noted. Orlistat, a gastric and pancreatic lipase inhibitor, also achieves significant weight loss and improves glycaemic status, but it has gastrointestinal side effects. Rimonabant, the first endocannabinoid CB1 antagonist, is associated with weight reduction and it improves diabetic parameters; nevertheless, it is associated with psychiatric disorders; indeed, a recently conducted safety review led to the temporal suspension of its commercialization. The above-mentioned medications seem to be currently useful agents for treating obesity in patients with type 2 diabetes mellitus. Other medications used for diabetes management, such as exenatide, liraglutide and pramlintide, have also shown body weight reduction. Ongoing research is needed to scrutinize the precise impact of these agents in the daily clinical practice of management of obesity in patients with type 2 diabetes mellitus.

Use of cannabinoid CB1 receptor antagonists for the treatment of metabolic disorders

Abdominal obesity is associated with numerous metabolic abnormalities, including insulin resistance, impaired glucose tolerance/type-2 diabetes, and atherogenic dyslipidaemia with low high-density lipoprotein (HDL) cholesterol, high triglycerides, and increased small dense low-density lipoprotein (LDL) cholesterol. A proportion of these metabolic disorders may be attributed to increased endocannabinoid activity. The selective cannabinoid 1 (CB1) receptor antagonist rimonabant has been shown to reduce body weight, waist circumference, insulin resistance, triglycerides, dense LDL, C-reactive protein (CRP), and blood pressure, and to increase HDL and adiponectin concentrations in both non-diabetic and diabetic overweight/obese patients. Besides an improvement in glucose tolerance in non-diabetic subjects, a reduction of 0.5-0.7% in haemoglobin A1C (HbA(1c)) levels was consistently observed in various groups of patients with type-2 diabetes. Almost half the metabolic changes could not be explained by weight loss, supporting direct peripheral effects of rimonabant. Ongoing studies should demonstrate whether improved metabolic disorders with CB1 receptor antagonists (rimonabant, taranabant, etc.) would translate into fewer cardiovascular complications among high-risk individuals.

Safety of ephedra and related anorexic medications

BACKGROUND

The increasing incidence of obesity, anorexia and bulimia has resulted in an increased interest in anorexic medications that can modify human eating behaviors. History and medical research is replete with consequences of addressing behavioral disorders with pharmacologic approaches to intervention in the absence of cognitive therapies such as self-efficacy counseling, which we and others have shown to be extremely effective at modifying behaviors previously thought to be resistant to such treatment. This paper looks at some of the ramifications of using anorexic medications, including ephedra, in modern society's efforts to address weight-related health problems.

METHODS

A review of the medical literature about ephedra and related anorexic medications was undertaken as they are linked to eating disorders. The findings included limited evidence of clinical benefit from such medications with concerns over side effects such as cardiovascular, gastrointestinal, CNS and other potential problems. We provide information about current recommendations for using these medications along with concerns for their use.

CONCLUSION

This paper is a review of ephedra and similar anorexic medications and nonprescription substances used in the treatment of obesity and other eating disorders along with some of the potential and proven consequences of such treatment.

Inhibitors of cannabinoid receptors and glucose metabolism

PURPOSE OF REVIEW

Abdominal obesity is closely related to type 2 diabetes and overactivity of the endocannabinoid system. The present review aims at evaluating the role of endocannabinoid system in glucose dysregulation and the effects of cannabinoid 1 receptor blockade on glucose metabolism in both animal models and overweight/obese humans, especially with type 2 diabetes.

RECENT FINDINGS

Cannabinoid 1 receptors have been identified not only in the brain, but also in the adipose tissue, the gut, the liver, the skeletal muscle and even the pancreas, all organs playing a key role in glucose metabolism and type 2 diabetes. Rimonabant, the first selective cannabinoid 1 receptor blocker in clinical use, has been shown to reduce body weight, waist circumference, glycated haemoglobin, triglycerides, insulin resistance index, and to increase HDL cholesterol and adiponectin concentrations in patients with type 2 diabetes, confirming data on nondiabetic overweight/obese patients. Almost half of the metabolic changes, including glycated haemoglobin reduction, could not be explained by weight loss, in agreement with direct peripheral effects.

SUMMARY

Cannabinoid 1 blockade reduces food intake and body weight and improves metabolic regulation beyond just weight loss. Because of its positive effect on glucose metabolism, rimonabant deserves consideration in the treatment of overweight/obese patients with type 2 diabetes.

Diagnosis and therapy of nonalcoholic steatohepatitis

The increasing prevalence of obesity, insulin resistance, and the metabolic syndrome has significant implications for the future of chronic liver disease. The resultant increase in the number of patients with nonalcoholic fatty liver disease (NAFLD) is expected to translate into increased numbers of patients with end-stage liver disease (cirrhosis), liver failure, and hepatocellular carcinoma. It is particularly important to identify the patients who are at greatest risk of these aforementioned complications of chronic liver disease, those nonalcoholic fatty liver disease patients with nonalcoholic steatohepatitis. Currently liver biopsy is the gold standard for diagnosis, but less invasive, highly accurate, and affordable screening tools are required. These tools may include radiologic or laboratory studies to identify patients noninvasively who may benefit from therapeutic interventions. Clinical scoring systems that may be used in general practice as initial screening tools also may prove useful. Most therapeutic modalities available or under development target the major pathways thought essential in the pathogenesis of nonalcoholic steatohepatitis and often are directed at reducing body mass index and improving insulin resistance via pharmacologic, surgical, dietary, or exercise regimens. Other potential therapeutic agents directed at cytoprotection or reduction of fibrosis are under investigation. This article focuses on diagnosis and therapy available and under development for this chronic liver disease.

CB1 receptor blockade and its impact on cardiometabolic risk factors: overview of the RIO programme with rimonabant

Rimonabant, the first selective CB(1) receptor antagonist in clinical use, has been extensively investigated in the Rimonabant in Obesity (RIO) programme, comprising four 1-2 year placebo-controlled randomised clinical trials recruiting more than 6600 overweight/obese patients with or without co-morbidities. Rimonabant 20 mg daily consistently reduced body weight, waist circumference, triglycerides, blood pressure, insulin resistance and C-reactive protein levels, and increased HDL cholesterol concentrations in both non-diabetic and type-2 diabetic overweight/obese patients. Adiponectin levels were increased, an effect that correlated with HDL cholesterol augmentation, while small dense LDL cholesterol levels were decreased in patients receiving rimonabant 20 mg compared with those receiving placebo in RIO Lipids. Furthermore, in RIO Diabetes, a 0.7% reduction in glycated haemoglobin (HbA1c) levels was observed in metformin- or sulphonylurea-treated patients with type-2 diabetes, an effect recently confirmed in the 6-month SERENADE (Study Evaluating Rimonabant Efficacy in drug-NAive DiabEtic patients) trial in drug-naive diabetic patients. Almost half of metabolic changes occurred beyond weight loss, in agreement with direct peripheral effects. The positive effects observed after 1 year were maintained after 2 years. Rimonabant was generally well-tolerated, but with a slightly higher incidence of depressed mood disorders, anxiety, nausea and dizziness compared with placebo. In clinical practice, rimonabant has to be prescribed to the right patient, i.e. overweight/obese subjects with cardiometabolic risk factors and with no major depressive illness and/or ongoing antidepressive treatment, in order to both maximise efficacy and minimise safety issues. New trials are supposed to confirm the potential role of rimonabant in patients with abdominal adiposity, atherogenic dyslipidaemia and/or type-2 diabetes, i.e. at high cardiometabolic risk.