Dysregulation of the peripheral and adipose tissue endocannabinoid system in human abdominal obesity

Novel aspects of adipocyte-induced skeletal muscle insulin resistance

Insulin resistance in skeletal muscle is an early event in the development of diabetes with obesity being one of the major contributing factors. Conditioned medium (CM) from differentiated human adipocytes impairs insulin signalling in human skeletal muscle cells. Recent data on adipocyte-induced insulin resistance in skeletal muscle cells describes underlying mechanisms of this process. Skeletal muscle insulin resistance involves multiple pathways and irreversible changes in the expression level of critical proteins. Furthermore, the reversibility of insulin resistance could be demonstrated. Several strategies to combat insulin resistance have been developed. One recent approach to treat obesity and the metabolic syndrome is the use of endocannabinoid receptor antagonists such as rimonabant. These compounds might also reduce insulin resistance in type 2 diabetes with effects on adipose tissue and liver and possibly skeletal muscle.

Biological specificity of visceral adipose tissue and therapeutic intervention

With excess energy storage, obesity develops, leading to increased risk for type 2 diabetes and cardiovascular diseases. The distribution of body fat appears to be even more important than the total amount of fat. Abdominal and, in particular, visceral adiposity is strongly linked to insulin resistance, type 2 diabetes, hypertension, dyslipidaemia, sleep apnea, and other complications of obesity. Visceral adiposity, manifested as a high waist circumference, is now accepted as a major component of the metabolic syndrome. However, the biological mechanisms underlying the adverse impact of visceral fat accumulation remain to be established. This review will focus on the analysis of the biological specificity of adipose tissue located in the abdominal region, and will explore intervention strategies targeting the impaired function of the visceral adipocyte as potential therapies for the cardio-metabolic outcomes of patients with the metabolic syndrome.

Glycerolipid metabolism and signaling in health and disease

Maintenance of body temperature is achieved partly by modulating lipolysis by a network of complex regulatory mechanisms. Lipolysis is an integral part of the glycerolipid/free fatty acid (GL/FFA) cycle, which is the focus of this review, and we discuss the significance of this pathway in the regulation of many physiological processes besides thermogenesis. GL/FFA cycle is referred to as a "futile" cycle because it involves continuous formation and hydrolysis of GL with the release of heat, at the expense of ATP. However, we present evidence underscoring the "vital" cellular signaling roles of the GL/FFA cycle for many biological processes. Probably because of its importance in many cellular functions, GL/FFA cycling is under stringent control and is organized as several composite short substrate/product cycles where forward and backward reactions are catalyzed by separate enzymes. We believe that the renaissance of the GL/FFA cycle is timely, considering the emerging view that many of the neutral lipids are in fact key signaling molecules whose production is closely linked to GL/FFA cycling processes. The evidence supporting the view that alterations in GL/FFA cycling are involved in the pathogenesis of "fatal" conditions such as obesity, type 2 diabetes, and cancer is discussed. We also review the different enzymatic and transport steps that encompass the GL/FFA cycle leading to the generation of several metabolic signals possibly implicated in the regulation of biological processes ranging from energy homeostasis, insulin secretion and appetite control to aging and longevity. Finally, we present a perspective of the possible therapeutic implications of targeting this cycling.

Overactive endocannabinoid signaling impairs apolipoprotein E-mediated clearance of triglyceride-rich lipoproteins

The endocannabinoid (EC) system regulates food intake and energy metabolism. Cannabinoid receptor type 1 (CB1) antagonists show promise in the treatment of obesity and its metabolic consequences. Although the reduction in adiposity resulting from therapy with CB1 antagonists may not account fully for the concomitant improvements in dyslipidemia, direct effects of overactive EC signaling on plasma lipoprotein metabolism have not been documented. The present study used a chemical approach to evaluate the direct effects of increased EC signaling in mice by inducing acute elevations of endogenously produced cannabinoids through pharmacological inhibition of their enzymatic hydrolysis by isopropyl dodecylfluorophosphonate (IDFP). Acute IDFP treatment increased plasma levels of triglyceride (TG) (2.0- to 3.1-fold) and cholesterol (1.3- to 1.4-fold) in conjunction with an accumulation in plasma of apolipoprotein (apo)E-depleted TG-rich lipoproteins. These changes did not occur in either CB1-null or apoE-null mice, were prevented by pretreatment with CB1 antagonists, and were not associated with reduced hepatic apoE gene expression. Although IDFP treatment increased hepatic mRNA levels of lipogenic genes (Srebp1 and Fas), there was no effect on TG secretion into plasma. Instead, IDFP treatment impaired clearance of an intravenously administered TG emulsion, despite increased postheparin lipoprotein lipase activity. Therefore, overactive EC signaling elicits an increase in plasma triglyceride levels associated with reduced plasma TG clearance and an accumulation in plasma of apoE-depleted TG-rich lipoproteins. These findings suggest a role of CB1 activation in the pathogenesis of obesity-related hypertriglyceridemia and underscore the potential efficacy of CB1 antagonists in treating metabolic disease.

Adipose tissue dysfunction in obesity, diabetes, and vascular diseases

The classical perception of adipose tissue as a storage place of fatty acids has been replaced over the last years by the notion that adipose tissue has a central role in lipid and glucose metabolism and produces a large number of hormones and cytokines, e.g. tumour necrosis factor-alpha, interleukin-6, adiponectin, leptin, and plasminogen activator inhibitor-1. The increased prevalence of excessive visceral obesity and obesity-related cardiovascular risk factors is closely associated with the rising incidence of cardiovascular diseases and type 2 diabetes mellitus. This clustering of vascular risk factors in (visceral) obesity is often referred to as metabolic syndrome. The close relationship between an increased quantity of visceral fat, metabolic disturbances, including low-grade inflammation, and cardiovascular diseases and the unique anatomical relation to the hepatic portal circulation has led to an intense endeavour to unravel the specific endocrine functions of this visceral fat depot. The objective of this paper is to describe adipose tissue dysfunction, delineate the relation between adipose tissue dysfunction and obesity and to describe how adipose tissue dysfunction is involved in the development of diabetes mellitus type 2 and atherosclerotic vascular diseases. First, normal physiology of adipocytes and adipose tissue will be described.

Endocannabinoids and the control of energy homeostasis

Endocannabinoids (ECBs) are ubiquitous lipid mediators that act through the same G protein-coupled receptors (CB1 and CB2) that recognize plant-derived cannabinoids. As regulators of metabolism, ECBs are anabolic: they increase the intake, promote the storage, and decrease the expenditure of energy. Recent work indicates that activation of peripheral CB1 receptors by ECBs plays a key role in the hormonal/metabolic changes associated with obesity/metabolic syndrome and may be targeted for its pharmacotherapy.

Dyslipidemia and glucose dysregulation in overweight and obese patients

Inactivity and a sedentary lifestyle contribute to overweight, obesity, and cardiometabolic risk. Overweight and obesity can lead to metabolic abnormalities, insulin resistance, type 2 diabetes mellitus (DM), lipid disorders, and cardiovascular disease. Diet and exercise can effectively reverse overweight and obesity and their related comorbidities. Modest weight loss (5%-10%) and modest physical activity (30 minutes a day) are first-line recommendations for the prevention of type 2 DM. Clinical trials have demonstrated that insulin sensitivity can be improved and type 2 DM can be prevented through lifestyle modification and pharmacologic therapy, including antiobesity drugs, antidiabetic drugs, statins, and antihypertensive drugs. The endocannabinoid system plays an important role in regulating metabolism through its effects on food intake at the level of the hypothalamus and on body composition through peripheral effects on adipose tissue.

A human fatty acid amide hydrolase (FAAH) functional gene variant is associated with lower blood pressure in young males

BACKGROUND

Fatty acid amide hydrolase (FAAH) inhibitors, preventing endocannabinoid (EC) degradation, reduce blood pressure (BP) and heart rate in young male (YM) hypertensive rodents. The functional human FAAH 129T gene variant results in reduced protein level and enzymatic activity but its relationship with BP is unknown. This study investigates the relationship among FAAH P129T alleles and cardiovascular features in YMs at baseline and after 9-year follow-up, and in older male obese hypertensive (OH) patients, in whom the EC system (ECS) is overactive.

METHODS

Genotype analysis was performed in 215 Caucasian male students (24 (0.2) years old) and in 185 older OH patients (50 (0.2) years old). YMs were also followed up for 9 years. Clinical and anthropometric variables, BP, cardiac and carotid artery echographic measurements were evaluated.

RESULTS

YMs with the FAAH 129T allele had lower systolic (P = 0.042) and mean BP (P = 0.022), and a trend toward lower diastolic BP (P = 0.06). Such significant association was maintained at follow-up. In contrast, the same allele was not associated with BP in older OH. No association was found with other cardiac and vascular variables.

CONCLUSION

An FAAH defective gene variant results in lower BP in YMs, similar to the findings in young rodents. This effect is lost in older OH patients. Because cannabinoid CB1 receptor blockade is associated with BP reduction in OH patients, EC effects and the use of ECS-interfering drugs is likely to be age and clinical-condition dependent.

The CB1 endocannabinoid system modulates adipocyte insulin sensitivity

Mounting evidence suggests that the endocannabinoid system regulates energy metabolism through direct effects on peripheral tissues as well as central effects that regulate appetite. Here we examined the effect of cannabinoid receptor 1 (CB1) signaling on insulin action in fat cells. We examined effects of the natural CB1 agonist, 2-Arachidonoylglycerol (2-AG), and the synthetic CB1 antagonist, SR141716, on insulin action in cultured adipocytes. We used translocation of glucose transporter GLUT4 to plasma membrane (PM) as a measure of insulin action. 2-AG activation of the CB1 receptor promoted insulin sensitivity whereas antagonism by SR141716 reduced insulin sensitivity. Neither drug affected GLUT4 translocation in the absence of insulin or with high doses of insulin. Consistent with these results we found that insulin-stimulated phosphorylation of the protein kinase Akt was increased by 2-AG, attenuated by SR141716, and unaffected in the absence of insulin or by addition of high-dose insulin. These data provide a functional and molecular link between the CB1 receptor and insulin sensitivity, because insulin-stimulated phosphorylation of Akt is required for GLUT4 translocation to the PM. The sensitizing effects of 2-AG were abrogated by SR141716 and Pertussis toxin, indicating that the effects are mediated by CB1 receptor. Importantly, neither 2-AG nor SR141716 alone or in combination with maximal dose of insulin had effects on GLUT4 translocation and Akt phosphorylation. These data are consistent with a model in which the endocannabinoid system sets the sensitivity of the insulin response in adipocytes rather than directly regulating the redistribution of GLUT4 or Akt phosphorylation.

Endocannabinoid system in food intake and metabolic regulation

PURPOSE OF REVIEW

As the incidence of obesity and the metabolic syndrome has increased, research has focused on the importance of the endocannabinoid system in the brain and peripheral tissues. Rimonabant, an inverse agonist of the CB1 receptor is being used therapeutically. This review presents recent advances in endocannabinoid physiology.

RECENT FINDINGS

The endocannabinoid system interacts with other anorexigenic and orexigenic pathways to regulate food intake in the hypothalamus, and the hedonistic value of food in the mesolimbic system. Endocannabinoid system overactivity contributes to hepatic steatosis, increased adipose tissue inflammation, dysregulated insulin signalling in the pancreas and disturbed oxidative pathways in skeletal muscle. The breakdown pathways for anandamide and 2-arachidonoylglycerol, the endocannabinoid receptor ligands, are reviewed, and the recent discoveries of endocannabinoid receptor polymorphisms and their relationship to obesity and metabolic disease noted. The favourable effect of rimonabant on fat mass glycaemic control, lipid metabolism and overall cardiovascular risk must be tempered by adverse effects on mood.

SUMMARY

The ubiquitous role of the endocannabinoid system in food intake and energy metabolism is now established. Drugs that manipulate different aspects of this system may benefit subjects with the metabolic and cachectic syndromes.

The endocannabinoid system in obesity and type 2 diabetes

Endocannabinoids (ECs) are defined as endogenous agonists of cannabinoid receptors type 1 and 2 (CB1 and CB2). ECs, EC anabolic and catabolic enzymes and cannabinoid receptors constitute the EC signalling system. This system participates in the control of lipid and glucose metabolism at several levels, with the possible endpoint of the accumulation of energy as fat. Following unbalanced energy intake, however, the EC system becomes dysregulated, and in most cases overactive, in several organs participating in energy homeostasis, particularly, in intra-abdominal adipose tissue. This dysregulation might contribute to excessive visceral fat accumulation and reduced adiponectin release from this tissue, and to the onset of several cardiometabolic risk factors that are associated with obesity and type 2 diabetes. This phenomenon might form the basis of the mechanism of action of CB1 antagonists/inverse agonists, recently developed by several pharmaceutical companies as adjuvants to lifestyle modification for weight reduction, glycaemic control and dyslipidaemia in obese and type 2 diabetes patients. It also helps to explain why some of the beneficial actions of these new therapeutics appear to be partly independent from weight loss.

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.

Leptin controls adipose tissue lipogenesis via central, STAT3-independent mechanisms

Leptin (encoded by Lep) controls body weight by regulating food intake and fuel partitioning. Obesity is characterized by leptin resistance and increased endocannabinoid tone. Here we show that leptin infused into the mediobasal hypothalamus (MBH) of rats inhibits white adipose tissue (WAT) lipogenesis, which occurs independently of signal transducer and activator of transcription-3 (STAT3) signaling. Correspondingly, transgenic inactivation of STAT3 signaling by mutation of the leptin receptor (s/s mice) leads to reduced adipose mass compared to db/db mice (complete abrogation of leptin receptor signaling). Conversely, the ability of hypothalamic leptin to suppress WAT lipogenesis in rats is lost when hypothalamic phosphoinositide 3-kinase signaling is prevented or when sympathetic denervation of adipose tissue is performed. MBH leptin suppresses the endocannabinoid anandamide in WAT, and, when this suppression of endocannabinoid tone is prevented by systemic CB1 receptor activation, MBH leptin fails to suppress WAT lipogenesis. These data suggest that the increased endocannabinoid tone observed in obesity is linked to a failure of central leptin signaling to restrain peripheral endocannabinoids.

The cannabinoid CB1 receptor is expressed in pancreatic delta-cells

Antagonists of cannabinoid CB1 receptor (CB1, CNR1) promote weight loss and decrease hyperglycemia in patients with type 2 diabetes. While the endocannabinoid system may modulate islet hormone secretion, the cell-type expressing CB1 receptor in islets has not been fully resolved. In this study, we verified receptor gene expression in rodent islets and cell lines and examined the distribution of CB1 receptor in mouse, rat, and human islets by confocal immunofluorescence (IF) microscopy. IF demonstrated CB1 receptor was present in beta-cell lines, but co-localized solely with somatostatin in the islet delta-cells of Zucker rats, C57BL/6 mice, and humans; no CB1 receptor expression was observed in alpha-, beta-, or pp-cells. Similarly, a rat somatostatinoma cell line, MSL-G2-Tu6, was found to express CB1 receptor. We also found monoacylglycerol lipase (MAGL) to be expressed in delta-cells and fatty acid amide hydrolase (FAAH) to be expressed in alpha-cells. The specific expression of CB1 in delta-cells suggests that the ECS may play a role in modulating islet hormone secretion. As there are some differences between our findings and previous reports, further studies, including detailed physiological studies of the effects of the ECS on islet function, are warranted.

Endocannabinoids, adipose tissue and lipid metabolism

Endocannabinoids regulate energy balance by modulating hypothalamic circuits controlling food intake and energy expenditure. However, convincing evidence has accumulated indicating that the endocannabinoid system is present also in peripheral tissues, in particular in adipose tissue. Fat cells produce (and are targets of) endocannabinoids. Adipogenesis, lipogenesis and glucose uptake are stimulated by endocannabinoids through CB(1) receptors and these effects are blocked by the CB(1) receptor antagonist rimonabant, suggesting that the weight-lowering effect of CB(1) receptor blockade is partly due to peripheral mechanisms. This review will focus on the role of endocannabinoids in adipose tissue metabolism, adipokine production and interactions between endocannabinoids and peroxisome proliferator activated receptors during adipogenesis.

Endocannabinoids, blood pressure and the human heart

The effects of exogenous and endogenous cannabinoids on the cardiovascular system have been the focus of extensive research. The direct and indirect effects of cannabinoids on heart and blood vessels depend upon experimental conditions, animal species, and, in humans, clinical background. Cannabinoids decrease blood pressure in hypertensive rodents primarily because of decrease cardiac contractility, leading researchers to postulate a role in the treatment of hypertension and cardiac hypertrophy. Rimonabant, the CB(1) receptor blocker in clinical use in many countries, induced a marked and sustained increase in cardiac contractility and blood pressure in hypertensive rats but, on the contrary, contributed to decrease blood pressure in weight-loss clinical trials especially in obese patients with hypertension. In the midst of the obesity pandemic and from the cardiometabolic point of view, the overactivation of the endocannabinoid system present in intra-abdominal obesity appears to be very harmful. Moreover, novel human findings suggest a relationship between CB(1)-mediated overactive endocannabinoid system and nephrovascular damage. Overall, it appears that CB(1) blockade in obese patients behaves as a 'multiplier' of the many beneficial effects of body weight loss induced by a hypocaloric diet and increased physical activity (the 'lifestyle changes' that are so difficult to start and maintain). Thus, the concept - based mostly on experimental results using in vitro or animal models - that CB(1)-mediated endocannabinoid effects are beneficial for the cardiovascular system should be revised at least in obese patients. The results of long-term clinical trials such as the STRADIVARIUS and the CRESCENDO trials will tell whether the improvement in the cardiometabolic risk profile induced by Rimonabant translates into vascular changes, reducing the risk of myocardial infarction, stroke and cardiovascular death in patients with abdominal obesity. Time (and much more work) will tell us much more about cannabinoids and the human heart.

Endocannabinoids and liver disease. IV. Endocannabinoid involvement in obesity and hepatic steatosis

Endocannabinoids are endogenous lipid mediators that interact with the same receptors as plant-derived cannabinoids to produce similar biological effects. The well-known appetitive effect of smoking marijuana has prompted inquiries into the possible role of endocannabinoids in the control of food intake and body weight. This brief review surveys recent evidence that endocannabinoids and their receptors are involved at multiple levels in the control of energy homeostasis. Endocannabinoids are orexigenic mediators and are part of the leptin-regulated central neural circuitry that controls energy intake. In addition, they act at multiple peripheral sites including adipose tissue, liver, and skeletal muscle to promote lipogenesis and limit fat elimination. Their complex actions could be viewed as anabolic, increasing energy intake and storage and decreasing energy expenditure, as components of an evolutionarily conserved system that has insured survival under conditions of starvation. In the era of plentiful food and limited physical activity, pharmacological inhibition of endocannabinoid activity offers benefits in the treatment of obesity and its hormonal/metabolic consequences.

The endocannabinoid system and the control of glucose homeostasis

Blockade of the CB(1) receptor is one of the promising strategies for the treatment of obesity. The first selective CB(1) receptor antagonist, rimonabant, which has already successfully completed phase III clinical trials, led to sustained weight loss and a reduction in waist circumference. Patients treated with rimonabant also demonstrated statistically significant improvement in high-density lipoprotein cholesterol levels, triglyceride levels and insulin resistance, as well as a reduced overall prevalence of metabolic syndrome. Currently, one of the most discussed aspects of endocannabinoid system function is to what extent the endocannabinoid system might affect metabolism independently of its control over body weight and food intake. Specifically, a food-intake- and body-weight-independent role in the regulation of glucose homeostasis and insulin sensitivity could have major impact on the potential of drug candidates targeting the endocannabinoid system for the prevention and treatment of metabolic syndrome. This review summarises the effects of the endocannabinoid system on glucose homeostasis and insulin sensitivity.

Dysregulation of the endocannabinoid system in obesity

An activation of the endocannabinoid system (ECS) in obesity with increased concentrations of endocannabinoids in several tissues and in the circulation is described in this review. This increased availability of endocannabinoids might stimulate cannabinoid receptors in a pathophysiological manner. The successful use of the cannabinoid receptor CB(1) inverse agonists rimonabant and taranabant for weight loss and the treatment of obesity-associated metabolic disorders might well be through blocking this overstimulation of cannabinoid receptors. At present, no single mechanism has been identified that explains the increased bioavailability of endocannabinoids in obesity. Both increased synthesis and decreased degradation appear to operate in a species- and tissue-dependent manner, but many pieces of the puzzle still need to be collected. For example, most data show decreased fatty acid amide hydrolase (FAAH) expression and/or activity as a result of obesity or high-fat intake, but the endocannabinoid predominantly increased in tissues is 2-arachidonoylglycerol (2-AG), which is not degraded by FAAH in vivo. Furthermore, the influence of dietary fatty acids on the synthesis of endocannabinoids needs to be studied in much more detail. Although weight loss does not seem to influence activation of the endocannabinoid system (ECS) in human obesity, suggesting an underlying mechanisms independent of body weight, no such mechanism at the genetic level has yet been identified either. Thus, activation of the ECS is a hallmark of abdominal obesity, and explains the success of pharmacological CB(1) blockade, but serious attempts have to be made to clarify the underlying mechanisms of this activation.

Peripheral endocannabinoid system activity in patients treated with sibutramine

OBJECTIVE

The endocannabinoid system (ECS) promotes weight gain and obesity-associated metabolic changes. Weight loss interventions may influence obesity-associated risk indirectly through modulation of the peripheral ECS. We investigated the effect of acute and chronic treatment with sibutramine on components of the peripheral ECS.

METHODS AND PROCEDURES

Twenty obese otherwise healthy patients received randomized, double-blind, crossover treatment with placebo and 15 mg/day sibutramine for 5 days each, followed by 12 weeks open-label sibutramine treatment. We determined circulating anandamide and 2-arachidonoylglycerol and expression levels of endocannabinoid genes in subcutaneous abdominal adipose tissue biopsies.

RESULTS

Body weight was stable during the acute treatment period and decreased by 6.0+/-0.8 kg in those patients completing 3 months of sibutramine treatment (P<0.05). Circulating endocannabinoids and the expression of ECS genes did not change with acute or chronic sibutramine treatment.

DISCUSSION

The ECS is activated in obesity. We did not find any influence of 5% body weight loss induced by sibutramine on circulating levels of endocannabinoids and adipose-tissue expression of endocannabinoid genes in obese subjects. These data confirm our previous findings on dietary weight loss and suggest that the dysregulation of the ECS may be a cause rather than a consequence of obesity.

The role of adipocyte insulin resistance in the pathogenesis of obesity-related elevations in endocannabinoids

OBJECTIVE

Obesity is associated with an overactive endocannabinoid (EC) system. The mechanisms responsible for increased ECs in obese individuals are poorly understood. Therefore, we examined the role of adipocyte insulin resistance in intracellular EC metabolism.

METHODS

We used 3T3-L1 adipocytes and diet-induced obese (DIO) mice to examine the role of obesity and insulin resistance in the regulation and/or dysregulation of intracellular ECs.

RESULTS

For the first time, we provide evidence that insulin is a major regulator of EC metabolism. Insulin treatment reduced intracellular ECs (2-arachidonylglycerol [2-AG] and anandamide [AEA]) in 3T3-L1 adipocytes. This corresponded with insulin-sensitive expression changes in enzymes of EC metabolism. In insulin-resistant adipocytes, patterns of insulin-induced enzyme expression were disturbed in a manner consistent with elevated EC synthesis and reduced EC degradation. Expression profiling of adipocytes from DIO mice largely recapitulated in vitro changes, suggesting that insulin resistance affects the EC system in vivo. In mice, expression changes of EC synthesis and degradation enzymes were accompanied by increased plasma EC concentrations (2-AG and AEA) and elevated adipose tissue 2-AG.

CONCLUSIONS

Our findings suggest that insulin-resistant adipocytes fail to regulate EC metabolism and decrease intracellular EC levels in response to insulin stimulation. These novel observations offer a mechanism whereby obese insulin-resistant individuals exhibit increased concentrations of ECs.

Dysregulation of peripheral endocannabinoid levels in hyperglycemia and obesity: Effect of high fat diets

Increasing evidence indicates that endocannabinoid (EC) signalling is dysregulated during hyperglycemia and obesity, particularly at the level of anandamide (AEA) and/or 2-arachidonoylglycerol (2-AG) concentrations in tissues involved in the control of energy intake and processing, such as the liver, white adipose tissue and pancreas. Here we review this previous evidence and provide new data on the possible dysregulation of EC levels in organs with endocrine function (adrenal glands and thyroid), involved in energy expenditure (brown adipose tissue and skeletal muscle), or affected by the consequences of metabolic disorders (heart and kidney), obtained from mice fed for 3, 8 and 14 weeks with two different high fat diets (HFDs), with different fatty acid compositions and impact on fasting glucose levels. Statistically significant elevations (in the skeletal muscle, heart and kidney) or reductions (in the thyroid) of the levels of either AEA or 2-AG, or both, were found. Depending on the diet, these changes preceded or accompanied the development of overt obesity and/or hyperglycemia. In the adrenal gland, first a reduction and then an elevation of EC levels were observed. In the brown fat, a very early elevation of both AEA and 2-AG normalized levels was observed with one of the diets, whereas delayed decreases were explained by an increase of the amount of fat tissue weight induced by the HFDs. The potential implications of these and previous findings in the general framework of the proposed roles of the EC system in the control of metabolic, endocrine and cardiovascular and renal functions are discussed.

Paracrine activation of hepatic CB1 receptors by stellate cell-derived endocannabinoids mediates alcoholic fatty liver

Alcohol-induced fatty liver, a major cause of morbidity, has been attributed to enhanced hepatic lipogenesis and decreased fat clearance of unknown mechanism. Here we report that the steatosis induced in mice by a low-fat, liquid ethanol diet is attenuated by concurrent blockade of cannabinoid CB1 receptors. Global or hepatocyte-specific CB1 knockout mice are resistant to ethanol-induced steatosis and increases in lipogenic gene expression and have increased carnitine palmitoyltransferase 1 activity, which, unlike in controls, is not reduced by ethanol treatment. Ethanol feeding increases the hepatic expression of CB1 receptors and upregulates the endocannabinoid 2-arachidonoylglycerol (2-AG) and its biosynthetic enzyme diacylglycerol lipase beta selectively in hepatic stellate cells. In control but not CB1 receptor-deficient hepatocytes, coculture with stellate cells from ethanol-fed mice results in upregulation of CB1 receptors and lipogenic gene expression. We conclude that paracrine activation of hepatic CB1 receptors by stellate cell-derived 2-AG mediates ethanol-induced steatosis through increasing lipogenesis and decreasing fatty acid oxidation.

Endocannabinoid dysregulation in the pancreas and adipose tissue of mice fed with a high-fat diet

OBJECTIVE

In mice, endocannabinoids (ECs) modulate insulin release from pancreatic beta-cells and adipokine expression in adipocytes through cannabinoid receptors. Their pancreatic and adipose tissue levels are elevated during hyperglycemia and obesity, but the mechanisms underlying these alterations are not understood.

METHODS AND PROCEDURES

We assessed in mice fed for up to 14 weeks with a standard or high-fat diet (HFD): (i) the expression of cannabinoid receptors and EC biosynthesizing enzymes (N-acyl-phosphatidyl-ethanolamine-selective phospholipase D (NAPE-PLD) and DAGLalpha) and degrading enzymes (fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL)) in pancreatic and adipose tissue sections by immunohistochemical staining; (ii) the amounts, measured by liquid chromatography-mass spectrometry, of the ECs, 2-AG, and anandamide (AEA).

RESULTS

Although CB(1) receptors and biosynthetic enzymes were found mostly in alpha-cells, degrading enzymes were identified in beta-cells. Following HFD, staining for biosynthetic enzymes in beta-cells and lower staining for FAAH were observed together with an increase of EC pancreatic levels. While we observed no diet-induced change in the intensity of the staining of EC metabolic enzymes in the mesenteric visceral fat, a decrease in EC concentrations was accompanied by lower and higher staining of biosynthesizing enzymes and FAAH, respectively, in the subcutaneous fat. No change in cannabinoid receptor staining was observed following HFD in any of the analyzed tissues.

DISCUSSION

We provide unprecedented information on the distribution of EC metabolic enzymes in the pancreas and adipose organ, where their aberrant expression during hyperglycemia and obesity contribute to dysregulated EC levels.

Efficacy and safety of rimonabant for improvement of multiple cardiometabolic risk factors in overweight/obese patients: pooled 1-year data from the Rimonabant in Obesity (RIO) program

OBJECTIVE

To better define the efficacy and safety of rimonabant, the first selective cannabinoid type 1 (CB(1)) receptor antagonist, in a large population of overweight and obese patients using pooled efficacy data from three Phase III nondiabetes Rimonabant in Obesity and Related Metabolic Disorders (RIO) studies, selected efficacy data from the RIO-Diabetes study, and pooled safety data for all four RIO studies.

RESEARCH DESIGN AND METHODS

The RIO studies enrolled patients who were either overweight (BMI >27 kg/m(2)) with at least one comorbidity (i.e., hypertension, dyslipidemia, or, for RIO-Diabetes, type 2 diabetes) or obese. All patients received daily treatment with rimonabant (5 or 20 mg) or placebo for 1 year plus a hypocaloric diet (600 kcal/day deficit) and advice on increased physical activity. RIO-Europe (n = 1,508), RIO-North America (n = 3,045), and RIO-Lipids (n = 1,036) excluded patients with type 2 diabetes; untreated dyslipidemia was an entry requirement for RIO-Lipids. RIO-Diabetes (n = 1,047) required the presence of type 2 diabetes inadequately controlled by sulfonylurea or metformin monotherapy.

RESULTS

The pooled intention-to-treat population comprised 5,580 patients without diabetes (3,165 completed treatment) and 1,047 patients with diabetes (692 completed treatment). Most efficacy measures improved during the 4-week placebo run-in period, except that HDL cholesterol decreased as expected in the early phase of a hypocaloric diet. After 1 year of randomized treatment, changes from baseline with 20 mg rimonabant in the nondiabetic population were as follows: body weight -6.5 kg, waist circumference -6.4 cm, HDL cholesterol +16.4%, triglycerides -6.9%, fasting insulin -0.6 muU/ml, and homeostasis model assessment for insulin resistance (HOMA-IR) -0.2 (all P < 0.001 vs. placebo). In the diabetic population, 20 mg rimonabant reduced A1C levels by 0.6% (P < 0.001 vs. placebo). Regression analysis of change in HDL cholesterol, triglycerides, adiponectin (in RIO-Lipids), and A1C (in RIO-Diabetes) versus body weight at 1 year by ANCOVA suggested that 45-57% of the effect of rimonabant could not be explained by the observed weight loss. At 1 year, adverse events more frequently reported with rimonabant were gastrointestinal, neurological, and psychiatric in nature. Serious adverse events were infrequent and almost equivalent to placebo. Overall discontinuation rates were similar across treatment groups, except discontinuation from adverse events, which occurred more frequently with 20 mg rimonabant versus placebo (most commonly, depressive disorders [1.9 vs. 0.8%], nausea [1.4 vs. 0.1%], mood alterations with depressive symptoms [1.0 vs. 0.6%], and anxiety [1.0 vs. 0.3%]). A thorough review of psychiatric and neurological adverse events was performed.

CONCLUSIONS

In overweight/obese patients, 20 mg/day rimonabant produced weight loss and significant improvements in multiple cardiometabolic risk factors such as waist circumference, A1C, HDL cholesterol, and triglycerides. Rimonabant was generally well tolerated, with more frequently reported adverse events being gastrointestinal, neurological, and psychiatric in nature.

Endocannabinoid system overactivity and the metabolic syndrome: prospects for treatment

The endocannabinoid system (ECS) plays a physiologic role in modulating energy balance, feeding behavior, lipoprotein metabolism, insulin sensitivity, and glucose homeostasis, which when dysregulated can all contribute to cardiometabolic risk. Evidence has suggested that the ECS is overactive in human obesity and in animal models of genetic and diet-induced obesity. ECS stimulation centrally and peripherally drives metabolic processes that mimic the metabolic syndrome. These findings have led to the development of potential novel therapeutic targets, including the drug rimonabant, a selective CB1 receptor antagonist, which has been shown to promote weight loss, reduce inflammation, improve dyslipidemia, and improve glucose homeostasis.

Pitfalls in measuring the endocannabinoid 2-arachidonoyl glycerol in biological samples

BACKGROUND

The endocannabinoid 2-arachidonoyl glycerol (2-AG) undergoes spontaneous isomerization to biologically inactive 1-AG. This effect has not been adequately addressed in previous studies that reported 2-AG concentrations in biological samples.

METHODS

Liquid chromatography tandem-mass spectrometry (LC-MS/MS) was used for 1-AG and 2-AG analyses.

RESULTS

Identical collision-induced disintegration spectra were found for 1-AG and 2-AG. For specific detection of both compounds, which share a common mass transition, baseline chromatographic separation is mandatory, even when applying MS/MS technology with its generally high detection specificity. When using standard chromatographic conditions with the very short run times typically used in LC-MS/MS methods, co-elution of 2-AG with 1-AG, which is present in human serum, causes false 2-AG results.

CONCLUSIONS

Our data highlight that the analytical specificity of MS/MS can be limited by interference from isobaric isomers with identical disintegration patterns. The specificity of this technology must be carefully evaluated for each individual application.

Evaluating the association of FAAH common gene variation with childhood, adult severe obesity and type 2 diabetes in the French population

OBJECTIVE

The endocannabinoid pathway is involved in eating behavior and body weight regulation in both animals and humans. The association of a missense polymorphism (Pro129Thr) in FAAH gene with overweight/obesity has been recently questioned.

SUBJECTS AND METHODS

To evaluate the contribution of the FAAH gene variation in polygenic obesity and type 2 diabetes mellitus (T2DM) in the French population, we investigated the entire FAAH locus. We selected and genotyped ten tagged single nucleotide polymorphisms (SNPs) in 635 obese children, 896 morbidly obese adults, 2,238 T2DM subjects and 1,340 control subjects, all of French European origin. Case control association tests were performed using logistic regression models.

RESULTS

Nominal evidences of association were observed for rs6429600, rs324419, rs324418, rs2295633, rs7520850 and risk for class III adult obesity (0,001 < p < 0.04). The rs324420 (Pro129Thr) was nominally associated with class III adult obesity (ORadditive = 0.79 (95% CI 0.67-0.93), p = 0.005; ORdominant = 0.76 (95% CI 0.63-0.92), p = 0.005), Pro129 being the obesity risk allele. These associations did not remain significant after Bonferroni correction for multiple testing. There was no significant association between FAAH SNPs and risk for childhood obesity or T2DM.

CONCLUSION

Our results in 5,109 subjects suggest that FAAH Pro129Thr polymorphism may modestly contribute to class III adult obesity in the French population. Further validation is needed to precise the role of this gene variant in obesity susceptibility background.

Peripheral metabolic effects of endocannabinoids and cannabinoid receptor blockade

The endocannabinoid system consists of endogenous arachidonic acid derivates that activate cannabinoid receptors. The two most prominent endocannabinoids are anandamide and 2-arachidonoyl glycerol. In obesity, increased concentrations of circulating and tissue endocannabinoid levels have been described, suggesting increased activity of the endocannabinoid system. Increased availability of endocannabinoids in obesity may over-stimulate cannabinoid receptors. Blockade of cannabinoid type 1 (CB1) receptors was the only successful clinical development of an anti-obesity drug during the last decade. Whereas blockade of CB1 receptors acutely reduces food intake, the long-term effects on metabolic regulation are more likely mediated by peripheral actions in liver, skeletal muscle, adipose tissue, and the pancreas. Lipogenic effects of CB1 receptor signalling in liver and adipose tissue may contribute to regional adipose tissue expansion and insulin resistance in the fatty liver. The association of circulating 2-arachidonoyl glycerol levels with decreased insulin sensitivity strongly suggests further exploration of the role of endocannabinoid signalling for insulin sensitivity in skeletal muscle, liver, and adipose tissue. A few studies have suggested a specific role for the regulation of adiponectin secretion from adipocytes by endocannabinoids, but that has to be confirmed by more experiments. Also, the potential role of CB1 receptor blockade for the stimulation of energy expenditure needs to be studied in the future. Despite the current discussion of safety issues of cannabinoid receptor blockade, these findings open a new and exciting perspective on endocannabinoids as regulators of body weight and metabolism.

The concept of cardiometabolic risk: Bridging the fields of diabetology and cardiology

The lack of physical activity and the adoption of poor nutritional habits is the major cause of the obesity epidemic that is currently sweeping the world. The expansion of adipose tissue mass, especially of the visceral adipose tissue depot, is observed in the vast majority of individuals carrying the clinical features of the metabolic syndrome, an important (and reversible) risk factor of type 2 diabetes and cardiovascular disease. As waist circumference can be used as a crude estimate of visceral fat accumulation, its measurement provides further information on cardiovascular and type 2 diabetes risk, at any given body mass index value. However, an elevated waist circumference might also be the result of an increased 'cardioprotective' subcutaneous adipose tissue mass. We have proposed that the measurement of plasma triglycerides along with waist circumference, the so-called 'hypertriglyceridemic waist' might better quantify visceral obesity and its health hazards than waist circumference alone. "Hypertriglyceridemic waist" is thought to represent an altered, dysfunctional, and highly lipolytic adipose tissue that is a major culprit abnormality behind the metabolic syndrome and associated cardiometabolic risk, independently from classical cardiovascular disease risk factors such as age, sex, and plasma low density lipoprotein (LDL) cholesterol levels.

The endocannabinoid system in the regulation of cardiometabolic risk factors

Obesity has increased at a striking rate over the last 3 decades in the Western world. This negative trend dramatically affects physical health and, ultimately, cardiovascular risks. In fact, particularly at the visceral level, obesity is strongly associated with an increased risk for life-threatening conditions, such as type 2 diabetes mellitus, hypertension, dyslipidemia, and cardiovascular disease. Although nutritional changes and physical activity are commonly thought of as the core treatments for obesity, it is necessary to further support obese patients with a pharmacologic approach for 2 reasons: to reduce the metabolic risk profile, and to avoid the regaining of weight. Among the various pharmacologic targets explored in recent years, the endocannabinoid (EC) system now constitutes the most promising proposal so far. In this review, after focusing on the central and peripheral signaling pathways that preserve energy homeostasis, we review the role of the EC system in regulating food's rewarding properties, controlling caloric intake by acting in hypothalamic pathways, and in modulating metabolic functions of several peripheral organs. In addition, we provide evidence that supports the recently proposed hypothesis that a close association exists between obesity and overactivation of the EC system.

Adrenocortical dysregulation as a major player in insulin resistance and onset of obesity

The aim of this review is to explore the dysregulation of adrenocortical secretions as a major contributor in the development of obesity and insulin resistance. Disturbance of adipose tissue physiology is one of the primary events in the development of pathologies associated with the metabolic syndrome, such as obesity and type 2 diabetes. Several studies indicate that alterations in metabolism of glucocorticoids (GC) and androgens, as well as aldosterone in excess, are involved in the emergence of metabolic syndrome. Cross talk among adipose tissue, the hypothalamo-pituitary complex, and adrenal gland activity plays a major role in the control of food intake, glucose metabolism, lipid storage, and energy balance. Perturbation of this cross talk induces alterations in the regulatory mechanisms of adrenocortical steroid synthesis, secretion, degradation, and/or recycling, at the level of the zonae glomerulosa (aldosterone), fasciculata (GC and GC metabolites), and reticularis (androgens and androgen precursors DHEA and DHEAS). As a whole, these adrenocortical perturbations contribute to the development of metabolic syndrome at both the paracrine and systemic level by favoring the physiological dysregulation of organs responsive to aldosterone, GC, and/or androgens, including adipose tissue.

Gene expression of adiponectin receptors in human visceral and subcutaneous adipose tissue is related to insulin resistance and metabolic parameters and is altered in response to physical training

OBJECTIVE

Adiponectin receptors 1 and 2 (AdipoR1 and AdipoR2, respectively) mediate the effects of adiponectin on glucose and lipid metabolism in vivo. We examined whether AdipoR1 and/or AdipoR2 mRNA expression in human adipose tissue is fat-depot specific. We also studied whether their expression in visceral and subcutaneous fat depots is associated with metabolic parameters and whether their expression is regulated by intensive physical exercise.

RESEARCH DESIGN AND METHODS

We determined metabolic parameters and assessed AdipoR1 and AdipoR2 mRNA expression using quantitative real-time PCR in adipose tissue in an observational study of 153 subjects and an interventional study of 60 subjects (20 each with normal glucose tolerance, impaired glucose tolerance, and type 2 diabetes) before and after intensive physical training for 4 weeks.

RESULTS

AdipoR1 and AdipoR2 mRNA expression is not significantly different between omental and subcutaneous fat, but their expression is several-fold lower in adipose tissue than in muscle. AdipoR2 mRNA expression in visceral fat is highly correlated with its expression in subcutaneous fat. AdipoR2 mRNA expression in both visceral and subcutaneous fat is positively associated with circulating adiponectin and HDL levels but negatively associated with obesity as well as parameters of insulin resistance, glycemia, and other lipid levels before and after adjustment for fat mass. Physical training for 4 weeks resulted in increased AdipoR1 and AdipoR2 mRNA expression in subcutaneous fat.

CONCLUSIONS

AdipoR2 mRNA expression in fat is negatively associated with insulin resistance and metabolic parameters independently of obesity and may mediate the improvement of insulin resistance in response to exercise.

Cannabinoid-1 receptor antagonists in type-2 diabetes

Type-2 diabetes is closely related to abdominal obesity and is generally associated with other cardiometabolic risk factors, resulting in a risk of major cardiovascular disease. Several animal and human observations suggest that the endocannabinoid system is over-active in the presence of abdominal obesity and/or diabetes. Both central and peripheral endocannabinoid actions, via the activation of CB1 receptors, promote weight gain and associated metabolic changes. Rimonabant, the first selective CB(1) receptor blocker in clinical use, has been shown to reduce body weight, waist circumference, triglycerides, blood pressure, insulin resistance index and C-reactive protein levels, and to increase high-density lipoprotein (HDL) cholesterol and adiponectin concentrations in both non-diabetic and diabetic overweight/obese patients. In addition, a 0.5-0.7% reduction in HbA1c levels was observed in metformin- or sulphonylurea-treated patients with type-2 diabetes and in drug-naïve diabetic patients. Almost half of the metabolic changes, including HbA1c reduction, could not be explained by weight loss, suggesting that there are direct peripheral effects. Rimonabant was generally well-tolerated, and the safety profile was similar in diabetic and non-diabetic patients, with a higher incidence of depressed mood disorders, nausea and dizziness. In conclusion, the potential role of rimonabant in overweight/obese patients with type-2 diabetes and at high risk of cardiovascular disease deserves much consideration.

The endogenous cannabinoid system stimulates glucose uptake in human fat cells via phosphatidylinositol 3-kinase and calcium-dependent mechanisms

BACKGROUND

The endogenous cannabinoid system participates in the regulation of energy balance, and its dysregulation may be implicated in the pathogenesis of obesity. Adipose tissue endocannabinoids may produce metabolic and endocrine effects, but very few data are available in human adipose tissue and in primary human fat cells.

EXPERIMENTAL DESIGN

We measured expression of type 1 and type 2 cannabinoid receptors (CNR), enzymes of cannabinoids synthesis and degradation in human omental, sc abdominal, and gluteal adipose tissue from lean and obese subjects. Furthermore, we assessed the effect of CNR1 stimulation on glucose uptake and intracellular transduction mechanisms in primary human adipocytes. Then we assessed the reciprocal regulation between CNR1 and peroxisome proliferator-activated receptor-gamma (PPARgamma). Finally, we tested whether leptin and adiponectin are regulated by CNR1 in human adipocytes.

RESULTS

We found that most genes of the endocannabinoid system are down-regulated in gluteal fat and up-regulated in visceral and sc abdominal adipose tissue of obese patients. Treatment of adipocytes with rosiglitazone markedly down-regulated CNR1 expression, whereas Win 55,212 up-regulated PPARgamma. Win 55,212 increased (+50%) glucose uptake, the translocation of glucose transporter 4, and intracellular calcium in fat cells. All these effects were inhibited by SR141716 and wortmannin and by removing extracellular calcium. Win 55,212 and SR141716 had no effect on expression of adiponectin and leptin.

CONCLUSIONS

These results indicate a role for the local endocannabinoids in the regulation of glucose metabolism in human adipocytes and suggest a role in channeling excess energy fuels to adipose tissue in obese humans.

Endocannabinoids and related N-acylethanolamines in the control of appetite and energy metabolism: emergence of new molecular players

PURPOSE OF REVIEW

Endocannabinoids (anandamide and 2-arachidonoylgycerol) and related N-acylethanolamines (N-oleoylethanolamine) exhibit opposite effects in the control of appetite. The purpose of this review is to highlight the similarities and differences of three major lipid-signaling molecules by focusing on their mode of action and the proteins involved in the control of food intake and energy metabolism.

RECENT FINDINGS

Anandamide and 2-arachidonoylglycerol promote food intake and are the main endogenous ligands of the cannabinoid receptors. One of them, the cannabinoid receptor 1, is responsible for the control of food intake and energy expenditure both at a central and a peripheral level, affecting numerous anorexigenic and orexigenic mediators (leptin, neuropeptide Y, ghrelin, orexin, endogenous opioids, corticotropin-releasing hormone, alpha-melanocyte stimulating hormone, cocaine and amphetamine-related transcript). In the gut, N-oleoylethanolamine plays an opposite role in food regulation, by interacting with two molecular targets different from the cannabinoid receptors: the nuclear receptor peroxisome proliferator-activated receptor alpha and a G-protein coupled receptor GPR119.

SUMMARY

Recent findings on the molecular mechanisms underlying the promotion of food intake or, in contrast, the suppression of food intake by anandamide and N-oleoylethanolamine, are summarized. Potential strategies for treating overweight, metabolic syndrome, and type II diabetes are briefly outlined.