The endocannabinoid system in obesity and type 2 diabetes

Targeting type 2 diabetes

The evolving concept of how nutrient excess and inflammation modulate metabolism provides new opportunities for strategies to correct the detrimental health consequences of obesity. In this review, we focus on the complex interplay among lipid overload, immune response, proinflammatory pathways and organelle dysfunction through which excess adiposity might lead to type 2 diabetes. We then consider evidence linking dysregulated CNS circuits to insulin resistance and results on nutrient-sensing pathways emerging from studies with calorie restriction. Subsequently, recent recommendations for the management of type 2 diabetes are discussed with emphasis on prevailing current therapeutic classes of biguanides, thiazolidinediones and incretin-based approaches.

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.

Expression of the cannabinoid system in muscle: effects of a high-fat diet and CB1 receptor blockade

The ECS (endocannabinoid system) plays an important role in the onset of obesity and metabolic disorders, implicating central and peripheral mechanisms predominantly via CB1 (cannabinoid type 1) receptors. CB1 receptor antagonist/inverse agonist treatment improves cardiometabolic risk factors and insulin resistance. However, the relative contribution of peripheral organs to the net beneficial metabolic effects remains unclear. In the present study, we have identified the presence of the endocannabinoid signalling machinery in skeletal muscle and also investigated the impact of an HFD (high-fat diet) on lipid-metabolism-related genes and endocannabinoid-related proteins. Finally, we tested whether administration of the CB1 inverse agonist AM251 restored the alterations induced by the HFD. Rats were fed on either an STD (standard/low-fat diet) or an HFD for 10 weeks and then treated with AM251 (3 mg/kg of body weight per day) for 14 days. The accumulated caloric intake was progressively higher in rats fed on the HFD than the STD, resulting in a divergence in body weight gain. AM251 treatment reduced accumulated food/caloric intake and body weight gain, being more marked in rats fed on the HFD. CB2 (cannabinoid type 2) receptor and PPARα (peroxisome-proliferator-activated receptor α) gene expression was decreased in HFD-fed rats, whereas MAGL (monoglyceride lipase) gene expression was up-regulated. These data suggest an altered endocannabinoid signalling as a result of the HFD. AM251 treatment reduced CB2 receptor, PPARγ and AdipoR1 (adiponectin receptor 1) gene expression in STD-fed rats, but only partially normalized the CB2 receptor in HFD-fed rats. Protein levels corroborated gene expression results, but also showed a decrease in DAGL (diacylglycerol) β and DAGLα after AM251 treatment in STD- and HFD-fed rats respectively. In conclusion, the results of the present study indicate a diet-sensitive ECS in skeletal muscle, suggesting that blockade of CB1 receptors could work towards restoration of the metabolic adaption imposed by diet.

Reversal of inflammation-induced impairment of glucose uptake in adipocytes by direct effect of CB1 antagonism on adipose tissue macrophages

Macrophage infiltration into adipose tissue (AT-MP) is thought to induce insulin resistance and diabetes in obesity. Here, we investigated the effect of the antiobesity drug SR141716 (a CB1 antagonist) on macrophage-mediated inhibition of insulin signaling in adipocytes. THP1 macrophages (THP1) were stimulated in vitro with lipopolysaccharide (LPS) and SR141716 or vehicle. The resulting conditioned medium (CM) was analyzed and incubated on human adipocytes. CM from LPS-stimulated THP1 inhibited insulin-induced AKT phosphorylation in adipocytes, in contrast to CM from nonactivated THP1. Moreover, it contained higher concentrations of tumor necrosis factor-α (TNFα) and lower levels of the anti-inflammatory cytokine IL-10. SR141716 reduced TNFα production and increased IL-10 secretion, resulting in a rescue of insulin signaling in adipocytes. To confirm these findings in vivo, AT-MP CM from cafeteria diet-fed or Zucker diabetic fatty (ZDF) rats that had received SR141716 for 3 weeks were isolated, analyzed, and incubated with adipocytes. Cafeteria diet induced macrophage-mediated inhibition of insulin signaling in adipocytes. Interestingly, SR141716 rescued insulin-induced glucose uptake in adipocytes. Finally, AT-MP CM from obese ZDF rats inhibited insulin-stimulated glucose uptake in adipocytes in contrast to AT-MP CM from lean ZDF rats. After treatment with SR141716, AT-MP CM rescued insulin-induced glucose uptake in adipocytes. In summary, our data indicate that CB1 receptor antagonism in macrophages modified their cytokine production and improved the insulin responsiveness of adipocytes that had been incubated with macrophage CM. Thus, SR141716 ameliorated adipose tissue insulin resistance by direct action on AT-MP demonstrating a novel peripheral mode of action of CB1 antagonism.

Splanchnic balance of free fatty acids, endocannabinoids, and lipids in subjects with nonalcoholic fatty liver disease

BACKGROUND & AIMS

Animal studies suggest that endocannabinoids could contribute to the development of nonalcoholic fatty liver disease (NAFLD). In addition, NAFLD has been shown to be associated with multiple changes in lipid concentrations in liver biopsies. There are no data on splanchnic free fatty acid (FFA), glycerol, ketone body, endocannabinoid, and lipid fluxes in vivo in subjects with NAFLD.

METHODS

We performed hepatic venous catheterization studies in combination with [(2)H(2)]palmitate infusion in the fasting state and during a low-dose insulin infusion in 9 subjects with various degrees of hepatic steatosis as determined using liver biopsy. Splanchnic balance of endocannabinoids and individual lipids was determined using ultra performance liquid chromatography coupled to mass spectrometry.

RESULTS

Concentrations of the endocannabinoid 2-arachidonoylglycerol were higher in arterialized (91 ± 33 μg/L basally) than in hepatic venous (51 ± 19 μg/L; P < .05) plasma. Fasting arterial (r = 0.72; P = .031) and hepatic venous (r = 0.70; P = .037) concentrations of 2-arachidonoylglycerol were related positively to liver fat content. Analysis of fluxes of 85 different triglycerides showed that the fatty liver overproduces saturated triglycerides. In the plasma FFA fraction in the basal state, the relative amounts of palmitoleate and linoleate were lower and those of stearate and oleate were higher in the hepatic vein than in the artery. Absolute concentrations of all nontriglyceride lipids were comparable in arterialized venous plasma and the hepatic vein both in the basal and insulin-stimulated states.

CONCLUSIONS

The human fatty liver takes up 2-arachidonoylglycerol and overproduces triacylglycerols containing saturated fatty acids, which might reflect increased de novo lipogenesis.

Modulation of adipocyte biology by δ(9)-tetrahydrocannabinol

It is recognized that the endocannabinoid system (ECS) plays a crucial role in the modulation of food intake and other aspects of energy metabolism. In this study, we aimed to investigate the effects of Δ(9)-tetrahydrocannabinol (THC) on adipocyte biology. 3T3-L1 cells were used to evaluate proliferation by sulforhodamine B (SRB) staining and methyl-(3)H-thymidine incorporation after 48 or 72 h of treatment with THC (1-500 nmol/l). Cells were differentiated in the presence or absence of the cannabinoid, and adipogenesis was determined by measuring lipid accumulation and peroxisome proliferator-activated receptor γ (PPARγ) transcription through reverse transcriptase-PCR (RT-PCR). Lipolysis was quantified under basal conditions or after isoproterenol (IP, 100 nmol/l) or insulin (INS, 100 nmol/l) treatment. Transforming growth factor β (TGFβ), diacylglycerol lipase α, and N-acylphosphatidylethanolamine-specific phospholipase D (NAPE-PLD) transcriptions were determined by RT-PCR in preadipocytes and adipocytes and adiponectin only in adipocytes. THC treatment increased culture protein content and reduced methyl-(3)H-thymidine incorporation. Cells treated with THC underwent adipogenesis shown by the expression of PPARγ and had increased lipid accumulation. Basal and IP-stimulated lipolyses were inhibited by THC and there was no effect on lipolysis of INS-treated adipocytes. The effects on methyl-(3)H-thymidine incorporation and lipolysis seem to be mediated through CB1- and CB2-dependent pathways. THC decreased NAPE-PLD in preadipocytes and increased adiponectin and TGFβ transcription in adipocytes. These results show that the ECS interferes with adipocyte biology and may contribute to adipose tissue (AT) remodeling. Although these observations point toward increased AT deposition, the stimulation of adiponectin production and inhibition of lipolysis may be in favor of improved INS sensitivity under cannabinoid influence.

Cannabinoid receptor stimulation impairs mitochondrial biogenesis in mouse white adipose tissue, muscle, and liver: the role of eNOS, p38 MAPK, and AMPK pathways

OBJECTIVE

Cannabinoid type 1 (CB1) receptor is involved in whole-body and cellular energy metabolism. We asked whether CB1 receptor stimulation was able to decrease mitochondrial biogenesis in different metabolically active tissues of obese high-fat diet (HFD)-fed mice.

RESEARCH DESIGN AND METHODS

The effects of selective CB1 agonist arachidonyl-2-chloroethanolamide (ACEA) and endocannabinoids anandamide and 2-arachidonoylglycerol on endothelial nitric oxide synthase (eNOS) expression were examined, as were mitochondrial DNA amount and mitochondrial biogenesis parameters in cultured mouse and human white adipocytes. These parameters were also investigated in white adipose tissue (WAT), muscle, and liver of mice chronically treated with ACEA. Moreover, p38 mitogen-activated protein kinase (MAPK) phosphorylation was investigated in WAT and isolated mature adipocytes from eNOS(-/-) and wild-type mice. eNOS, p38 MAPK, adenosine monophosphate-activated protein kinase (AMPK), and mitochondrial biogenesis were investigated in WAT, muscle, and liver of HFD mice chronically treated with ACEA.

RESULTS

ACEA decreased mitochondrial biogenesis and eNOS expression, activated p38 MAPK, and reduced AMPK phosphorylation in white adipocytes. The ACEA effects on mitochondria were antagonized by nitric oxide donors and by p38 MAPK silencing. White adipocytes from eNOS(-/-) mice displayed higher p38 MAPK phosphorylation than wild-type animals under basal conditions, and ACEA was ineffective in cells lacking eNOS. Moreover, mitochondrial biogenesis was downregulated, while p38 MAPK phosphorylation was increased and AMPK phosphorylation was decreased in WAT, muscle, and liver of ACEA-treated mice on a HFD.

CONCLUSIONS

CB1 receptor stimulation decreases mitochondrial biogenesis in white adipocytes, through eNOS downregulation and p38 MAPK activation, and impairs mitochondrial function in metabolically active tissues of dietary obese mice.

Cannabinoid receptor 1 mediates palmitic acid-induced apoptosis via endoplasmic reticulum stress in human renal proximal tubular cells

The endocannabinoid system (ECS) is activated at the onset of obesity and diverse metabolic diseases. Endocannabinoids mediate their physiological and behavioral effects by activating specific cannabinoid receptors, mainly cannabinoid receptor 1 (CB(1)R). Diabetic nephropathy (DN) is induced by hyperlipidemia, and renal proximal tubule cells are an important site for the onset of DN. However, the pathophysiology of CB(1)R, especially in the hyperlipidemia of DN, has not been elucidated. Therefore, we examined the effect of palmitic acid (PA) on CB(1)R expression and its related signal pathways in human renal proximal tubular cells (HK-2 cells). PA significantly increased CB(1)R mRNA and protein levels and induced CB(1)R internalization. PA-induced activation of CB(1)R is prevented by the treatment of AACOCF(3) (a cPLA(2) inhibitor), indomethacin and NS398 (a COX 2 inhibitors). Indeed, PA increased cPLA(2), and COX-2 but not COX-1. We also investigated whether the PA-induced activation of CB(1)R is linked to apoptosis. As a result, AM251 (a CB(1)R antagonist) attenuated PA-mediated apoptosis in a concentration-dependent manner. Furthermore, PA decreased GRP78 expression and induced increases in the endoplasmic reticulum (ER) stress signaling pathways p-PERK, p-eIF2α, p-ATF4, and CHOP, which were blocked by AM251 treatment. Moreover, PA increased the Bax/Bcl-2 ratio, cleaved PARP, and caspase-3 levels. The PA-induced apoptotic effects were decreased with CB(1)R-specific antagonist (AM251) treatment and CB1 si-RNA transfection. In conclusion, PA induced apoptosis through ER stress via CB(1)R expression in human proximal tubule cells. Our results provide evidence that CB(1)R blockade may be a potential anti-diabetic therapy for the treatment of DN.

Peripheral CB1 cannabinoid receptor blockade improves cardiometabolic risk in mouse models of obesity

Obesity and its metabolic consequences are a major public health concern worldwide. Obesity is associated with overactivity of the endocannabinoid system, which is involved in the regulation of appetite, lipogenesis, and insulin resistance. Cannabinoid-1 receptor (CB1R) antagonists reduce body weight and improve cardiometabolic abnormalities in experimental and human obesity, but their therapeutic potential is limited by neuropsychiatric side effects. Here we have demonstrated that a CB1R neutral antagonist largely restricted to the periphery does not affect behavioral responses mediated by CB1R in the brains of mice with genetic or diet-induced obesity, but it does cause weight-independent improvements in glucose homeostasis, fatty liver, and plasma lipid profile. These effects were due to blockade of CB1R in peripheral tissues, including the liver, as verified through the use of CB1R-deficient mice with or without transgenic expression of CB1R in the liver. These results suggest that targeting peripheral CB1R has therapeutic potential for alleviating cardiometabolic risk in obese patients.

Intracellular trafficking of anandamide: new concepts for signaling

Endocannabinoids are key mediators of many aspects of human health and disease. The biological activity of anandamide, a prominent member of this group, depends on the metabolic control exerted by biosynthetic, catabolic and oxidative pathways working together. Cellular uptake and intracellular trafficking of anandamide are crucial steps in the process. Whereas the identity of anandamide transmembrane carriers remains undetermined, recent insights have been gained related to its intracellular stores (adiposomes) and intracellular binding proteins, particularly fatty acid binding proteins, albumin and heat shock protein 70. On this basis, we propose a reconsideration of the dogma that endocannabinoids are exclusively synthesized and released 'on demand', and suggest that their metabolic control is complemented by intracellular trafficking and storage in specific reservoirs.

The peptide hemopressin acts through CB1 cannabinoid receptors to reduce food intake in rats and mice

Hemopressin is a short, nine amino acid peptide (H-Pro-Val-Asn-Phe-Lys-Leu-Leu-Ser-His-OH) isolated from rat brain that behaves as an inverse agonist at the cannabinoid receptor CB(1), and is shown here to inhibit agonist-induced receptor internalization in a heterologous cell model. Since this peptide occurs naturally in the rodent brain, we determined its effect on appetite, an established central target of cannabinoid signaling. Hemopressin dose-dependently decreases night-time food intake in normal male rats and mice, as well as in obese ob/ob male mice, when administered centrally or systemically, without causing any obvious adverse side effects. The normal, behavioral satiety sequence is maintained in male mice fasted overnight, though refeeding is attenuated. The anorectic effect is absent in CB(1) receptor null mutant male mice, and hemopressin can block CB(1) agonist-induced hyperphagia in male rats, providing strong evidence for antagonism of the CB(1) receptor in vivo. We speculate that hemopressin may act as an endogenous functional antagonist at CB(1) receptors and modulate the activity of appetite pathways in the brain.

Cannabinoid CB1 receptor expression in relation to visceral adipose depots, endocannabinoid levels, microvascular damage, and the presence of the Cnr1 A3813G variant in humans

Dysregulation of the endocannabinoid system in the visceral adipose tissue (VAT) is associated with metabolic and cardiovascular complications of obesity. We studied perirenal VAT CB1 receptor expression in relation to anthropometry, VAT area and endocannabinoid levels, kidney microvascular damage (MVDa), and the presence of the CB1 gene A3813G variant, the frequency of which was also evaluated in a large population of obese-hypertensive (OH) patients with or without the metabolic syndrome (MetS). Perirenal VAT and kidney samples were obtained from 30 patients undergoing renal surgery. Total and perirenal VAT areas were determined by computed tomography. CB1 messenger RNA expression and endocannabinoid levels in perirenal VAT were determined by quantitative reverse transcriptase polymerase chain reaction and liquid chromatography-mass spectrometry, respectively. The MVDa was evaluated in healthy portions of kidney cortex. The A3813G alleles were identified by genotyping in these patients and in 280 nondiabetic OH patients (age <or=65 years). Metabolic syndrome was defined according to the Adult Treatment Panel III criteria. Perirenal VAT CB1 expression was 40% lower in patients with the A3813G polymorphism, and correlated positively with perirenal and total VAT area and with perirenal VAT levels of the endocannabinoid anandamide. A 2-fold higher CB1 expression was associated with MVDa. The OH patients with the A3813G allele had lower prevalence of MetS in both unadjusted and adjusted models. Genetics influence perirenal VAT CB1 expression and the prevalence of MetS in OH. Increased VAT is associated with increased perirenal VAT endocannabinoid tone, which in turn correlates with increased MVDa. Endocannabinoid overactivity might be involved in human visceral obesity and its renal complications.

Differential alterations of the concentrations of endocannabinoids and related lipids in the subcutaneous adipose tissue of obese diabetic patients

BACKGROUND

The endocannabinoids, anandamide and 2-AG, are produced by adipocytes, where they stimulate lipogenesis via cannabinoid CB1 receptors and are under the negative control of leptin and insulin. Endocannabinoid levels are elevated in the blood of obese individuals and nonobese type 2 diabetes patients. To date, no study has evaluated endocannabinoid levels in subcutaneous adipose tissue (SAT) of subjects with both obesity and type 2 diabetes (OBT2D), characterised by similar adiposity and whole body insulin resistance and lower plasma leptin levels as compared to non-diabetic obese subjects (OB).

DESIGN AND METHODS

The levels of anandamide and 2-AG, and of the anandamide-related PPARalpha ligands, oleoylethanolamide (OEA) and palmitoylethanolamide (PEA), in the SAT obtained by abdominal needle biopsy in 10 OBT2D, 11 OB, and 8 non-diabetic normal-weight (NW) subjects, were measured by liquid chromatography-mass spectrometry. All subjects underwent a hyperinsulinaemic euglycaemic clamp.

RESULTS

As compared to NW, anandamide, OEA and PEA levels in the SAT were 2-4.4-fold elevated (p < 0.05), and 2-AG levels 2.3-fold reduced (p < .05), in OBT2D but not in OB subjects. Anandamide, OEA and PEA correlated positively (p < .05) with SAT leptin mRNA and free fatty acid during hyperinsulinaemic clamp, and negatively with SAT LPL activity and plasma HDL-cholesterol, which were all specifically altered in OBT2D subjects.

CONCLUSIONS

The observed alterations emphasize, for the first time in humans, the potential different role and regulation of adipose tissue anandamide (and its congeners) and 2-AG in obesity and type 2 diabetes.

Effect of rimonabant, the cannabinoid CB1 receptor antagonist, on peripheral nerve in streptozotocin-induced diabetic rat

The aim of this study is to investigate the effect of rimonabant, which has antiatherosclerotic and antiinflammatory properties, on peripheral neuropathy in a diabetic rat. Diabetic rat models were induced by treatment with streptozotocin and then either normal or diabetic rats were treated with an oral dose of 10mg/kg/day rimonabant or placebo for 24 weeks. We quantified the densities of intraepidermal (PGP9.5+) nerve fiber and total skin (RECA-1+) capillary length. We also measured the current perception threshold, as defined by the intensity of sine-wave stimulus, skin blood flow after treadmill running and TNF-alpha level in spinal cord tissue or plasma. After 24 weeks, rimonabant reduced the body weight and food intake in both diabetic and normal rats, but it had no effect on blood sugar levels. In addition, rimonabant treatment significantly improved the decreased intraepidermal nerve fiber density (5.53+/-0.12 vs. 4.36+/-0.27/mm, P<0.05) and alleviated the increased current perception threshold in rimonabant-treated versus control diabetic rats. These responses were closely associated with the attenuation of skin capillary loss (1.98+/-0.07 vs. 1.67+/-0.10 mm/mm(2), P<0.05), increase in skin blood flow (14.93+/-1.08 vs. 12.07+/-0.87 TPU, P<0.05) and reduction in TNF-alpha level in tissue (70.10+/-4.99 vs. 91.18+/-3.34 pg/mg, P<0.05) in rimonabant-treated diabetic rats compared with placebo. These findings suggest that rimonabant can be beneficial for treatment of diabetic peripheral neuropathy, possibly due to its potential role in micro- and macrovessel protection and its anti-inflammatory properties.

Effect of dietary fat on endocannabinoids and related mediators: consequences on energy homeostasis, inflammation and mood

Among the several known fatty acid-derived chemical signals, the endogenous ligands of cannabinoid receptors type-1 and -2, two G-protein-coupled receptors involved in several aspects of mammalian physiology and pathology, are perhaps those the levels of which have proven to be most sensitive to the fatty acid composition of the diet. The two most studied such ligands, known as endocannabinoids, are N-arachidonoyl-ethanolamine and 2-archidonoylglycerol, and are found in tissues together with other N-acyl-ethanolamines and 2-acylglycerols, not all of which activate the cannabinoid receptors, although several of them do exhibit important pharmacological effects. In this review article, we describe literature data indicating that the tissue concentrations of the endocannabinoids and related signalling molecules, and hence the activity of the respective receptors, can be modulated by modifying the fatty acid composition of the diet, and particularly its content in long chain PUFAs or in long chain PUFA precursors. We also discuss the potential impact of these diet-induced changes of endocannabinoid tone on three of the major pathological conditions in which cannabinoid receptors have been involved, that is metabolic dysfunctions, inflammation and affective disorders.

Receptor heteromerization and drug discovery

G-protein-coupled receptors (GPCRs) are membrane proteins that convert extracellular information into intracellular signals. They are involved in many biological processes and therefore represent powerful targets to modulate physiological and pathological states. Recent studies have demonstrated that GPCR activity is regulated by several mechanisms. Among these, protein-protein interactions (and in particular interactions with other receptors leading to heteromerization) has been shown to have an important role in modulating GPCR function. This has expanded their repertoire of signaling and added a new level of regulation to their physiological roles. Emerging studies provide evidence for tissue-specific and disease-specific receptor heteromerization. This suggests that heteromers represent novel drug targets for the identification of selective compounds with potentially fewer side-effects.

Regulation of MAP kinase-directed mitogenic and protein kinase B-mediated signaling by cannabinoid receptor type 1 in skeletal muscle cells

OBJECTIVE

The endogenous cannabinoid (or endocannabinoid) system (ECS) is part of a central neuromodulatory system thought to play a key role in the regulation of feeding behavior and energy balance. However, increasing evidence suggests that modulation of the ECS may also act to regulate peripheral mechanisms involved in these processes, including lipogenesis in adipose tissue and liver, insulin release from pancreatic beta-cells, and glucose uptake into skeletal muscle. It was recently shown that cannabinoid receptor type 1 (CB1) and type 2 (CB2), both key components of the ECS, are expressed in human and rodent skeletal muscle. However, their role in modulating insulin sensitivity in this metabolically active tissue has yet to be determined. Our aim was to establish the role, if any, of these receptors in modulating insulin sensitivity in skeletal muscle cells.

RESEARCH DESIGN AND METHODS

Cultured skeletal muscle cells were exposed to CB1 and/or CB2 pharmacological agonists/antagonists/inverse agonists, and the resulting effects on insulin-regulated phosphatidylinositol 3 kinase (PI 3-kinase)-protein kinase B (PKB) and extracellular signal-related kinases 1/2 (ERK1/2)-directed signaling were determined.

RESULTS

Here, we report that modulating the activity of the ECS in skeletal muscle regulates both insulin-dependent mitogen-activated protein (MAP) kinase (ERK1/2) and the canonical PI 3-kinase/PKB signaling pathways. We show that pharmacological activation or inhibition of CB1 receptor activity exerts a differential effect with regard to MAP kinase- and PKB-directed signaling.

CONCLUSIONS

Our study provides evidence that signaling via cannabinoid receptors can significantly modulate mitogenic and metabolic signaling in skeletal muscle with important implications for muscle growth and differentiation as well as the regulation of glucose and lipid metabolism.

Biomarkers of endocannabinoid system activation in severe obesity

BACKGROUND

Obesity is a worldwide epidemic, and severe obesity is a risk factor for many diseases, including diabetes, heart disease, stroke, and some cancers. Endocannabinoid system (ECS) signaling in the brain and peripheral tissues is activated in obesity and plays a role in the regulation of body weight. The main research question here was whether quantitative measurement of plasma endocannabinoids, anandamide, and related N-acylethanolamines (NAEs), combined with genotyping for mutations in fatty acid amide hydrolase (FAAH) would identify circulating biomarkers of ECS activation in severe obesity.

METHODOLOGY/PRINCIPAL FINDINGS

Plasma samples were obtained from 96 severely obese subjects with body mass index (BMI) of > or = 40 kg/m(2), and 48 normal weight subjects with BMI of < or = 26 kg/m(2). Triple-quadrupole mass spectroscopy methods were used to measure plasma ECS analogs. Subjects were genotyped for human FAAH gene mutations. The principal analysis focused on the FAAH 385 C-->A (P129T) mutation by comparing plasma ECS metabolite levels in the FAAH 385 minor A allele carriers versus wild-type C/C carriers in both groups. The main finding was significantly elevated mean plasma levels of anandamide (15.1+/-1.4 pmol/ml) and related NAEs in study subjects that carried the FAAH 385 A mutant alleles versus normal subjects (13.3+/-1.0 pmol/ml) with wild-type FAAH genotype (p = 0.04), and significance was maintained after controlling for BMI.

CONCLUSIONS/SIGNIFICANCE

Significantly increased levels of the endocannabinoid anandamide and related NAEs were found in carriers of the FAAH 385 A mutant alleles compared with wild-type FAAH controls. This evidence supports endocannabinoid system activation due to the effect of FAAH 385 mutant A genotype on plasma AEA and related NAE analogs. This is the first study to document that FAAH 385 A mutant alleles have a direct effect on elevated plasma levels of anandamide and related NAEs in humans. These biomarkers may indicate risk for severe obesity and may suggest novel ECS obesity treatment strategies.

Obesity: genes, brain, gut, and environment

Obesity, which is assuming alarming proportions, has been attributed to genetic factors, hypothalamic dysfunction, and intestinal gut bacteria and an increase in the consumption of energy-dense food. Obesity predisposes to the development of type 2 diabetes mellitus, hypertension, coronary heart disease, and certain forms of cancer. Recent studies have shown that the intestinal bacteria in obese humans and mice differ from those in lean that could trigger a low-grade systemic inflammation. Consumption of a calorie-dense diet that initiates and perpetuates obesity could be due to failure of homeostatic mechanisms that regulate appetite, food consumption, and energy balance. Hypothalamic factors that regulate energy needs of the body, control appetite and satiety, and gut bacteria that participate in food digestion play a critical role in the onset of obesity. Incretins, cholecystokinin, brain-derived neurotrophic factor, leptin, long-chain fatty acid coenzyme A, endocannabinoids and vagal neurotransmitter acetylcholine play a role in the regulation of energy intake, glucose homeostasis, insulin secretion, and pathobiology of obesity and type 2 diabetes mellitus. Thus, there is a cross-talk among the gut, liver, pancreas, adipose tissue, and hypothalamus. Based on these evidences, it is clear that management of obesity needs a multifactorial approach.

Conversion of 4-cyanomethyl-pyrazole-3-carboxamides into CB1 antagonists with lowered propensity to pass the blood-brain-barrier

A series of amides, amidines and amidoximes have been made from the corresponding nitrile compounds, to provide potent antagonists and inverse agonists for the CB1 receptor with considerably lower lipophiliciy, higher polar surface area and improved plasma/brain ratios compared to the centrally acting rimonabant. Extensive investigations of ADME and in vivo pharmacological properties led to selection of the amide series and specifically the 4-(4-fluorophenyl)piperidin-4-ol derivative D4. A clear improvement in the peripheral profile over rimonabant was seen, although some contribution of central effect on the pronounced weight reduction in obese mice cannot be ruled out.

CB1 cannabinoid receptors promote oxidative stress and cell death in murine models of doxorubicin-induced cardiomyopathy and in human cardiomyocytes

AIMS

Here we investigated the mechanisms by which cardiovascular CB1 cannabinoid receptors may modulate the cardiac dysfunction, oxidative stress, and interrelated cell death pathways associated with acute/chronic cardiomyopathy induced by the widely used anti-tumour compound doxorubicin (DOX).

METHODS AND RESULTS

Both load-dependent and -independent indices of left-ventricular function were measured by the Millar pressure-volume conductance system. Mitogen-activated protein kinase (MAPK) activation, cell-death markers, and oxidative/nitrosative stress were measured by molecular biology/biochemical methods and flow cytometry. DOX induced left-ventricular dysfunction, oxidative/nitrosative stress coupled with impaired antioxidant defense, activation of MAPK (p38 and JNK), and cell death and/or fibrosis in hearts of wide-type mice (CB1(+/+)), and these effects were markedly attenuated in CB1 knockouts (CB1(-/-)). In human primary cardiomyocytes expressing CB1 receptors (demonstrated by RT-PCR, western immunoblot, and flow cytometry) DOX, likewise the CB1 receptor agonist HU210 and the endocannabinoid anandamide (AEA), induced MAPK activation and cell death. The DOX-induced MAPK activation and cell death were significantly enhanced when DOX was co-administered with CB1 agonists AEA or HU210. Remarkably, cell death and MAPK activation induced by AEA, HU210, and DOX +/- AEA/HU210 were largely attenuated by either CB1 antagonists (rimonabant and AM281) or by inhibitors of p38 and JNK MAPKs. Furthermore, AEA or HU210 in primary human cardiomyocytes triggered increased reactive oxygen species generation.

CONCLUSION

CB1 activation in cardiomyocytes may amplify the reactive oxygen/nitrogen species-MAPK activation-cell death pathway in pathological conditions when the endocannabinoid synthetic or metabolic pathways are dysregulated by excessive inflammation and/or oxidative/nitrosative stress, which may contribute to the pathophysiology of various cardiovascular diseases.

Exploring SAR features in diverse library of 4-cyanomethyl-pyrazole-3-carboxamides suitable for further elaborations as CB1 antagonists

A chemically diverse library of secondary and tertiary 4-cyanomethyl-1,5-diphenyl-1H-pyrazole-3-carboxamides was synthesized to enable mapping of the SAR, in the eastern amide region, with regard to CB1 antagonist activity, This study was initiated as a prelude to the design and synthesis of possible CB1 antagonists that do not readily pass the blood-brain-barrier. In general a range of modifications were found to be tolerated in this part of the molecule, although polar and especially charged groups did to a degree reduce the CB1 antagonistic activity. Several compounds with single-digit or even sub-nanomolar potency, suitable for further elaboration of the nitrile moiety, were identified.

CB1 antagonists for obesity--what lessons have we learned from rimonabant?

When compared with other modifiable cardiovascular risk factors, such as hypertension, dyslipidemia and smoking, obesity remains a surprisingly puzzling condition to prevent and treat. The history of the development of anti-obesity drugs has known more defeats than even partial victories. With very few drugs on the market, and bad publicity related to adverse events, obesity remains an almost completely unmet challenge for the pharmaceutical industry. In light of past experience with endocannabinoid-system antagonists, such as rimonabant, we propose that a major paradigm shift in clinical practice might be necessary to justify the use of pharmacotherapy for obesity. Furthermore, we suggest that the criteria currently used by regulatory authorities to evaluate and approve anti-obesity drugs should be rigorously re-examined. Finally, we discuss how pharmacological approaches that aim to counteract overactivity of the endocannabinoid system should be revisited in the future to treat visceral (intra-abdominal) obesity and its metabolic consequences.

New therapies for diabesity

Many patients with type 2 diabetes are obese (diabesity), and the two conditions together impose a particularly complex therapeutic challenge. Several differently acting agents are often required at the same time, encouraging development of more single-tablet combinations. Longer-acting (once daily and once weekly) injected agonists of glucagon-like peptide-1 are due to provide additional options to stimulate insulin secretion with weight loss and minimal risk of hypoglycemia. Further, dipeptidyl peptidase-4 inhibitors ("weight-neutral" insulinotropic agents) are also expected. Sodium-glucose cotransporter 2 inhibitors offer a new option to reduce hyperglycemia and facilitate weight loss by increasing the elimination of glucose in the urine. Selective peroxisome proliferator-activated receptor modulators are being studied to produce compounds with desired effects. Many other agents with antidiabetic and antiobesity activity are progressing in clinical development.

The CB1 antagonist rimonabant decreases insulin hypersecretion in rat pancreatic islets

Type 2 diabetes and obesity are characterized by elevated nocturnal circulating free fatty acids, elevated basal insulin secretion, and blunted glucose-stimulated insulin secretion (GSIS). The CB1 receptor antagonist, Rimonabant, has been shown to improve glucose tolerance and insulin sensitivity in vivo but its direct effect on islets has been unclear. Islets from lean littermates and obese Zucker (ZF) and Zucker Diabetic Fatty (ZDF) rats were incubated for 24 h in vitro and exposed to 11 mmol/l glucose and 0.3 mmol/l palmitate (GL) with or without Rimonabant. Insulin secretion was determined at basal (3 mmol/l) or stimulatory (15 mmol/l) glucose concentrations. As expected, basal secretion was significantly elevated in islets from obese or GL-treated lean rats whereas the fold increase in GSIS was diminished. Rimonabant decreased basal hypersecretion in islets from obese rats and GL-treated lean rats without decreasing the fold increase in GSIS. However, it decreased GSIS in islets from lean rats without affecting basal secretion. These findings indicate that Rimonabant has direct effects on islets to reduce insulin secretion when secretion is elevated above normal levels by diet or in obesity. In contrast, it appears to decrease stimulated secretion in islets from lean animals but not in obese or GL-exposed islets.

Endocannabinoids may mediate the ability of (n-3) fatty acids to reduce ectopic fat and inflammatory mediators in obese Zucker rats

Dietary (n-3) long-chain PUFA [(n-3) LCPUFA] ameliorate several metabolic risk factors for cardiovascular diseases, although the mechanisms of these beneficial effects are not fully understood. In this study, we compared the effects of dietary (n-3) LCPUFA, in the form of either fish oil (FO) or krill oil (KO) balanced for eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) content, with a control (C) diet containing no EPA and DHA and similar contents of oleic, linoleic, and alpha-linolenic acids, on ectopic fat and inflammation in Zucker rats, a model of obesity and related metabolic dysfunction. Diets were fed for 4 wk. Given the emerging evidence for an association between elevated endocannabinoid concentrations and metabolic syndrome, we also measured tissue endocannabinoid concentrations. In (n-3) LCPUFA-supplemented rats, liver triglycerides and the peritoneal macrophage response to an inflammatory stimulus were significantly lower than in rats fed the control diet, and heart triglycerides were lower, but only in KO-fed rats. These effects were associated with a lower concentration of the endocannabinoids, anandamide and 2-arachidonoylglycerol, in the visceral adipose tissue and of anandamide in the liver and heart, which, in turn, was associated with lower levels of arachidonic acid in membrane phospholipids, but not with higher activity of endocannabinoid-degrading enzymes. Our data suggest that the beneficial effects of a diet enriched with (n-3) LCPUFA are the result of changes in membrane fatty acid composition. The reduction of substrates for inflammatory molecules and endocannabinoids may account for the dampened inflammatory response and the physiological reequilibration of body fat deposition in obese rats.

The endocannabinoid system of the skin in health and disease: novel perspectives and therapeutic opportunities

The newly discovered endocannabinoid system (ECS; comprising the endogenous lipid mediators endocannabinoids present in virtually all tissues, their G-protein-coupled cannabinoid receptors, biosynthetic pathways and metabolizing enzymes) has been implicated in multiple regulatory functions both in health and disease. Recent studies have intriguingly suggested the existence of a functional ECS in the skin and implicated it in various biological processes (e.g. proliferation, growth, differentiation, apoptosis and cytokine, mediator or hormone production of various cell types of the skin and appendages, such as the hair follicle and sebaceous gland). It seems that the main physiological function of the cutaneous ECS is to constitutively control the proper and well-balanced proliferation, differentiation and survival, as well as immune competence and/or tolerance, of skin cells. The disruption of this delicate balance might facilitate the development of multiple pathological conditions and diseases of the skin (e.g. acne, seborrhea, allergic dermatitis, itch and pain, psoriasis, hair growth disorders, systemic sclerosis and cancer).

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.

Beta-arrestin-based Bret2 screening assay for the "non"-beta-arrestin binding CB1 receptor

CB1 receptor (CB1R) antagonists have been demonstrated to be effective in treating obesity and related disorders. This study has been focused on establishing a beta-arrestin 2-based screening assay for the CB1R using BRET2 technology. When the existing BRET2 screening platform was applied to the CB1R, the authors discovered that the receptor interacted weakly with beta-arrestin 2, resulting in unsatisfactory assay performance. To enhance the beta-arrestin binding capacity, they replaced the C-terminal tail of the CB1R with tails from either the V2 or BRS3 receptors, both of which interact strongly with beta-arrestin 2. Using this chimeric approach, the authors screened a small compound library and identified 21 antagonist and inverse agonist hits with IC50 and EC50 values ranging from 0.3 nM to 7.5 microM. Both primary and secondary screening were performed with Z'>0.5, suggesting that the assay is a robust and cost-effective alternative to existing cell-based assays.

Cannabinoid receptor antagonists: pharmacological opportunities, clinical experience, and translational prognosis

The endogenous cannabinoid (CB) (endocannabinoid) signaling system is involved in a variety of (patho)physiological processes, primarily by virtue of natural, arachidonic acid-derived lipids (endocannabinoids) that activate G protein-coupled CB1 and CB2 receptors. A hyperactive endocannabinoid system appears to contribute to the etiology of several disease states that constitute significant global threats to human health. Consequently, mounting interest surrounds the design and profiling of receptor-targeted CB antagonists as pharmacotherapeutics that attenuate endocannabinoid transmission for salutary gain. Experimental and clinical evidence supports the therapeutic potential of CB1 receptor antagonists to treat overweight/obesity, obesity-related cardiometabolic disorders, and substance abuse. Laboratory data suggest that CB2 receptor antagonists might be effective immunomodulatory and, perhaps, anti-inflammatory drugs. One CB1 receptor antagonist/inverse agonist, rimonabant, has emerged as the first-in-class drug approved outside the United States for weight control. Select follow-on agents (taranabant, otenabant, surinabant, rosonabant, SLV-319, AVE1625, V24343) have also been studied in the clinic. However, rimonabant's market withdrawal in the European Union and suspension of rimonabant's, taranabant's, and otenabant's ongoing development programs have highlighted some adverse clinical side effects (especially nausea and psychiatric disturbances) of CB1 receptor antagonists/inverse agonists. Novel CB1 receptor ligands that are peripherally directed and/or exhibit neutral antagonism (the latter not affecting constitutive CB1 receptor signaling) may optimize the benefits of CB1 receptor antagonists while minimizing any risk. Indeed, CB1 receptor-neutral antagonists appear from preclinical data to offer efficacy comparable to or better than that of prototype CB1 receptor antagonists/inverse agonists, with less propensity to induce nausea. Continued pharmacological profiling, as the prelude to first-in-man testing of CB1 receptor antagonists with unique modes of targeting/pharmacological action, represents an exciting translational frontier in the critical path to CB receptor blockers as medicines.

Islet G protein-coupled receptors as potential targets for treatment of type 2 diabetes

Islet dysfunction - characterized by a combination of defective insulin secretion, inappropriately high glucagon secretion and reduced beta-cell mass - has a central role in the pathophysiology of type 2 diabetes. Several G protein-coupled receptors (GPCRs) expressed in islet beta-cells are known to be involved in the regulation of islet function, and therefore are potential therapeutic targets. This is evident from the recent success of glucagon-like peptide 1 (GLP1) mimetics and dipeptidyl peptidase 4 (DPP4) inhibitors, which promote activation of the GLP1 receptor to stimulate insulin secretion and inhibit glucagon secretion, and also have the potential to increase beta-cell mass. Other islet beta-cell GPCRs that are involved in the regulation of islet function include the glucose-dependent insulinotropic peptide (GIP) receptor, lipid GPCRs, pleiotropic peptide GPCRs and islet biogenic amine GPCRs. This Review summarizes islet GPCR expression, signalling and function, and highlights their potential as targets for the treatment of type 2 diabetes.

Peripheral endocannabinoid dysregulation in obesity: relation to intestinal motility and energy processing induced by food deprivation and re-feeding

BACKGROUND AND PURPOSE

Endocannabinoids in tissues controlling energy homeostasis are altered in obesity, thus contributing to metabolic disorders. Here we evaluate endocannabinoid dysregulation in the small intestine of mice with diet-induced obesity (DIO) and in peripheral tissues of Zucker and lean rats following food deprivation and re-feeding.

EXPERIMENTAL APPROACH

Intestinal transit, evaluated using rhodamine-B-labelled dextran, and small intestinal endocannabinoid levels, measured by liquid chromatography mass spectrometry, were measured in mice fed normal or high-fat diets (HFDs). Endocannabinoid levels were measured also in various tissues of lean and Zucker rats fed ad libitum or following overnight food deprivation with and without subsequent re-feeding.

KEY RESULTS

After 8 weeks of HFD, baseline intestinal transit was increased in DIO mice and enhanced by cannabinoid CB(1) receptor antagonism less efficaciously than in lean mice. Small intestinal anandamide and 2-arachidonoylglycerol levels were reduced and increased respectively. In Zucker rats, endocannabinoids levels were higher in the pancreas, liver and duodenum, and lower in the subcutaneous adipose tissue. Food deprivation increased endocannabinoid levels in the duodenum and liver of both rat strains, in the pancreas of lean rats and in adipose tissues of Zucker rats.

CONCLUSIONS AND IMPLICATIONS

Reduced anandamide levels might account for increased intestinal motility in DIO mice. Regulation of endocannabinoid levels in rat peripheral tissues, induced by food deprivation and re-feeding, might participate in food intake and energy processing and was altered in Zucker rats. These data, together with previous observations, provide further evidence for dysregulation of peripheral endocannabinoids in obesity.

Cannabinoids and appetite: food craving and food pleasure

The ability of Cannabis sativa to promote eating has been documented for many centuries, with the drug reported by its users to promote strong cravings for, and an intensification of the sensory and hedonic properties of food. These effects are now known to result from the actions of cannabinoid molecules at specific cannabinoid receptor sites within the brain, and to reflect the physiological role of their natural ligands, the endocannabinoids, in the control of appetite. Recent developments in the biochemistry and pharmacology of endocannabinoid systems have generated convincing evidence from animal models for a normal role of endocannabinoids in the control of eating motivation. The availability of specific cannabinoid receptor agonists and antagonists raises the possibility of improved therapies for disorders of eating and body weight: not only in the suppression of appetite to counter our susceptibility to the over-consumption of highly pleasurable and energy-dense foods; but also in the treatment of conditions that involve reduced appetite and weight loss. Here, we outline some of the findings of the past decade that link endocannabinoid function appetite control, and the possible clinical applications of that knowledge.

The role of the endocannabinoid system in lipogenesis and fatty acid metabolism

Endocannabinoids (ECs) regulate energy balance by modulating hypothalamic circuits controlling food intake and energy expenditure. However, convincing evidence has accumulated indicating that the EC system is present also in peripheral tissues, in particular in adipose tissue. Fat cells produce and are targets of ECs. Glucose uptake and lipoprotein lipase (LPL) activity, lipogenesis and adipogenesis are stimulated by ECs through cannabinoid 1 (CB1) receptors. Moreover, CB1 activation leads to a decreased mitochondrial biogenesis and function through inhibition of endothelial nitric oxide synthase (eNOS). All these effects are blocked by the CB1 antagonist rimonabant, suggesting that the weight-reducing effect of CB1 blockade is due not only to the transient suppression of food intake and reduction of lipogenesis but also to an increased mitochondrial biogenesis and oxidative metabolism which counteracts the inhibitory effects of ECs, levels of which are increased in fat tissues of obese rodents and humans. This review focuses on the role of ECs in adipose tissue metabolism, adipokine production, and interactions between ECs and peroxisome proliferator-activated receptors (PPARs) during adipogenesis.

An introduction to the endocannabinoid system: from the early to the latest concepts

A rather complex and pleiotropic endogenous signalling system was discovered in the late 1990s, starting from studies on the mechanism of action of Delta(9)-tetrahydrocannabinol, the major psychoactive principle of the hemp plant Cannabis sativa. This system includes: (1) at least two G-protein-coupled receptors, known as the cannabinoid CB(1) and CB(2) receptors; (2) the endogenous agonists at these receptors, known as endocannabinoids, of which anandamide and 2-arachidonoylglycerol are the best known; and (3) proteins and enzymes for the regulation of endocannabinoid levels and action at receptors. The number of the members of this endocannabinoid signalling system seems to be ever increasing as new non-CB(1) non-CB(2) receptors for endocannabinoids, endocannabinoid-related molecules with little activity at CB(1) and CB(2) receptors, and new enzymes for endocannabinoid biosynthesis and degradation are being identified every year. The complexity of the endocannabinoid system and of its physiological and pathological function is outlined in this introductory chapter, for a better understanding of the subsequent chapters in this special issue.

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.

Central side-effects of therapies based on CB1 cannabinoid receptor agonists and antagonists: focus on anxiety and depression

Both agonists (e.g. Delta(9)-tetrahydrocannabinol, nabilone) and antagonists (e.g. rimonabant, taranabant) of the cannabinoid type-1 (CB(1)) receptor have been explored as therapeutic agents in diverse fields of medicine such as pain management and obesity with associated metabolic dysregulation, respectively. CB(1) receptors are widely distributed in the central nervous system and are involved in the modulation of emotion, stress and habituation responses, behaviours that are thought to be dysregulated in human psychiatric disorders. Accordingly, CB(1) receptor activation may, in some cases, precipitate episodes of psychosis and panic, while its inhibition may lead to behaviours reminiscent of depression and anxiety-related disorders. The present review discusses these side-effects, which have to be taken into account in the therapeutic exploitation of the endocannabinoid system.

Changes in plasma endocannabinoid levels in viscerally obese men following a 1 year lifestyle modification programme and waist circumference reduction: associations with changes in metabolic risk factors

AIMS/HYPOTHESIS

We previously reported that the plasma levels of the endocannabinoid, 2-arachidonoylglycerol (2-AG), in a cohort of viscerally obese men are directly correlated with visceral adipose tissue (VAT) accumulation and metabolic risk factors including low HDL-cholesterol and high triacylglycerol. It is not known, however, if such correlations persist after vigorous lifestyle interventions that reduce metabolic risk factors. We analysed the changes in endocannabinoid levels in a subsample from the same cohort following a 1 year lifestyle modification programme, and correlated them with changes in VAT and metabolic risk factors.

METHODS

Forty-nine viscerally obese men (average age 49 years, BMI 30.9 kg/m(2), waist 107.3 cm) underwent a 1 year lifestyle modification programme including healthy eating and physical activity. Plasma levels of 2-AG and the other most studied endocannabinoid, anandamide, were measured by liquid chromatography-mass spectrometry. Anthropometric and metabolic risk factors, including VAT, insulin resistance and glucose intolerance, HDL-cholesterol and triacylglycerol, were measured.

RESULTS

Most risk factors were improved by the intervention, which led to a significant decrease in body weight (-6.4 kg, p < 0.0001), waist circumference (-8.0 cm, p < 0.0001) and VAT (-30%, p < 0.0001), and in plasma 2-AG (-62.3%, p < 0.0001) and anandamide (-7.1%, p = 0.005) levels. The decrease in levels of 2-AG but not those of anandamide correlated with decreases in VAT and triacylglycerol levels, and with the increase in HDL(3)-cholesterol levels. Multivariate analyses suggested that decreases in 2-AG and VAT were both independently associated with decreases in triacylglycerol.

CONCLUSIONS/INTERPRETATION

This study shows that a strong correlation exists between 2-AG levels and high plasma triacylglycerol and low HDL(3)-cholesterol in viscerally obese men.

Should peripheral CB(1) cannabinoid receptors be selectively targeted for therapeutic gain?

Endocannabinoids, endogenous lipid ligands of cannabinoid receptors, mediate a variety of effects similar to those of marijuana. Cannabinoid CB(1) receptors are highly abundant in the brain and mediate psychotropic effects, which limits their value as a potential therapeutic target. There is growing evidence for CB(1) receptors in peripheral tissues that modulate a variety of functions, including pain sensitivity and obesity-related hormonal and metabolic abnormalities. In this review we propose that selective targeting of peripheral CB(1) receptors has potential therapeutic value because it would help to minimize addictive, psychoactive effects in the case of CB(1) agonists used as analgesics, or depression and anxiety in the case of CB(1) antagonists used in the management of cardiometabolic risk factors associated with the metabolic syndrome.