The endogenous cannabinoid system affects energy balance via central orexigenic drive and peripheral lipogenesis

Antipsychotics-induced metabolic alterations: Recounting the mechanistic insights, therapeutic targets and pharmacological alternatives

Atypical antipsychotics (AAPs) are the drug of choice in the management of mental illnesses by virtue of their advantage over typical antipsychotics i.e. least tendency of producing extrapyramidal motor symptoms (EPS) or pseudoparkinsonism. Despite the clinical efficacy, AAPs produces troublesome adverse effects, particularly hyperphagia, hyperglycemia, dyslipidemia weight gain, diabetes mellitus, insulin resistance and QT prolongation which further develops metabolic and cardiac complications with subsequent reduction in life expectancy, poor patient compliance, and sudden death. AAPs-induced weight gain and metabolic alterations are increasing at an alarming rate and became an utmost matter of concern for psychopharmacotherapy. Diverse underlying mechanisms have been explored such as the interaction of AAPs with neurotransmitter receptors, alteration in food reward anticipation behavior, altered expressions of hypothalamic orexigenic and anorexigenic neuropeptides, histamine H₁ receptor-mediated hypothalamic AMP-activated protein kinase (AMPK) activation, increased blood leptin, ghrelin, pro-inflammatory cytokines. Antipsychotics induced imbalance in energy homeostasis, reduction in energy expenditure which is linked to altered expression of uncoupling proteins (UCP-1) in brown adipose tissue and reduced hypothalamic orexin expressions are emerging insights. In addition, alteration in gut-microbiota and subsequent inflammation, dyslipidemia, obesity, and diabetes after AAPs treatment are also associated with weight gain and metabolic alterations. Oral hypoglycemics and lipid-lowering drugs are mainly prescribed in the clinical management of weight gain associated with AAPs while many other pharmacological and nonpharmacological interventions also have been explored in different clinical and preclinical studies. In this review, we critically discuss the current scenario, mechanistic insights, biomarkers, and therapeutic alternatives for metabolic alterations associated with antipsychotics.

Cocaine- and amphetamine-regulated transcript (CART): A multifaceted neuropeptide

Over the last 35 years, the continuous discovery of novel neuropeptides has been the key to the better understanding of how the central nervous system has integrated with neuronal signals and behavioral responses. Cocaine and amphetamine-regulated transcript (CART) was discovered in 1995 in the rat striatum but later was found to be highly expressed in the hypothalamus. The widespread distribution of CART peptide in the brain complicated the understanding of the role played by this neurotransmitter. The main objective of the current compact review is to piece together the fragments of available information about origin, expression, distribution, projection, and function of CART peptides. Accumulative evidence suggests CART as a neurotransmitter and neuroprotective agent that is mainly involved in regulation of feeding, addiction, stress, anxiety, innate fear, neurological disease, neuropathic pain, depression, osteoporosis, insulin secretion, learning, memory, reproduction, vision, sleep, thirst and body temperature. In spite of the vast number of studies about the CART, the overall pictures about the CART functions are sketchy. First, there is a lack of information about cloned receptor, specific agonist and antagonist. Second, CART peptides are detected in discrete sets of neurons that can modulate countless activities and third; CART peptides exist in several fragments due to post-translational processing. For these reasons the overall picture about the CART peptides are sketchy and confounding.

Adipocyte OGT governs diet-induced hyperphagia and obesity

Palatable foods (fat and sweet) induce hyperphagia, and facilitate the development of obesity. Whether and how overnutrition increases appetite through the adipose-to-brain axis is unclear. O-linked beta-D-N-acetylglucosamine (O-GlcNAc) transferase (OGT) couples nutrient cues to O-GlcNAcylation of intracellular proteins at serine/threonine residues. Chronic dysregulation of O-GlcNAc signaling contributes to metabolic diseases. Here we show that adipocyte OGT is essential for high fat diet-induced hyperphagia, but is dispensable for baseline food intake. Adipocyte OGT stimulates hyperphagia by transcriptional activation of de novo lipid desaturation and accumulation of N-arachidonyl ethanolamine (AEA), an endogenous appetite-inducing cannabinoid (CB). Pharmacological manipulation of peripheral CB1 signaling regulates hyperphagia in an adipocyte OGT-dependent manner. These findings define adipocyte OGT as a fat sensor that regulates peripheral lipid signals, and uncover an unexpected adipose-to-brain axis to induce hyperphagia and obesity.

An Analysis of Endocannabinoid Concentrations and Mood Following Singing and Exercise in Healthy Volunteers

The euphoric feeling described after running is, at least in part, due to increased circulating endocannabinoids (eCBs). eCBs are lipid signaling molecules involved in reward, appetite, mood, memory and neuroprotection. The aim of this study was to investigate whether activities other than running can increase circulating eCBs. Nine healthy female volunteers (mean 61 years) were recruited from a local choir. Circulating eCBs, haemodynamics, mood and hunger ratings were measured before and immediately after 30 min of dance, reading, singing or cycling in a fasted state. Singing increased plasma levels of anandamide (AEA) by 42% (P < 0.05), palmitoylethanolamine (PEA) by 53% (P < 0.01) and oleoylethanolamine (OEA) by 34% (P < 0.05) and improved positive mood and emotions (P < 0.01), without affecting hunger scores. Dancing did not affect eCB levels or hunger ratings, but decreased negative mood and emotions (P < 0.01). Cycling increased OEA levels by 26% (P < 0.05) and tended to decrease how hungry volunteers felt, without affecting mood. Reading increased OEA levels by 28% (P < 0.01) and increased the desire to eat. Plasma AEA levels were positively correlated with how full participants felt (P < 0.05). Plasma OEA levels were positively correlated with positive mood and emotions (P < 0.01). All three ethanolamines were positively correlated with heart rate (HR; P < 0.0001). These data suggest that activities other than running can increase plasma eCBs associated with changes in mood or appetite. Increases in eCBs may underlie the rewarding and pleasurable effects of singing and exercise and ultimately some of the long-term beneficial effects on mental health, cognition and memory.

Characterization of the endocannabinoid system in subcutaneous adipose tissue in periparturient dairy cows and its association to metabolic profiles

Adipose tissue (AT) plays a major role in metabolic adaptations in postpartum (PP) dairy cows. The endocannabinoid (eCB) system is a key regulator of metabolism and energy homeostasis; however, information about this system in ruminants is scarce. Therefore, this work aimed to assess the eCB system in subcutaneous AT, and to determine its relation to the metabolic profile in peripartum cows. Biopsies of AT were performed at 14 d prepartum, and 4 and 30 d PP from 18 multiparous peripartum cows. Cows were categorized retrospectively according to those with high body weight (BW) loss (HWL, 8.5 ± 1.7% BW loss) or low body weight loss (LWL, 2.9 ± 2.5% BW loss) during the first month PP. The HWL had higher plasma non-esterified fatty acids and a lower insulin/glucagon ratio PP than did LWL. Two-fold elevated AT levels of the main eCBs, N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG), were found 4 d PP compared with prepartum in HWL, but not in LWL cows. AT levels of the eCB-like molecules oleoylethanolamide, palmitoylethanolamide, and of arachidonic acid were elevated PP compared with prepartum in all cows. The abundance of monoglyceride lipase (MGLL), the 2-AG degrading enzyme, was lower in HWL vs. LWL AT PP. The relative gene expression of the cannabinoid receptors CNR1 and CNR2 in AT tended to be higher in HWL vs. LWL PP. Proteomic analysis of AT showed an enrichment of the inflammatory pathways’ acute phase signaling and complement system in HWL vs. LWL cows PP. In summary, eCB levels in AT were elevated at the onset of lactation as part of the metabolic adaptations in PP dairy cows. Furthermore, activating the eCB system in AT is most likely associated with a metabolic response of greater BW loss, lipolysis, and AT inflammation in PP dairy cows.

CB1 receptors in the paraventricular nucleus of the hypothalamus modulate the release of 5-HT and GABA to stimulate food intake in rats

Endocannabinoids and their receptors not only contribute to the control of natural processes of appetite regulation and energy balance but also have an important role in the pathogenesis of obesity. CB1 receptors (CB1R) are expressed in several hypothalamic nuclei, including the paraventricular nucleus (PVN), where induce potent orexigenic responses. Activation of CB1R in the PVN induces hyperphagia by modulating directly or indirectly orexigenic and anorexigenic signals; however, interaction among these mediators has not been clearly defined. CB1R mRNA is expressed in serotonergic neurons that innervate the PVN, and activation of 5-HT receptors in the PVN constitutes an important satiety signal. Some GABAergic terminals are negatively influenced by 5-HT, suggesting that the hyperphagic effect of CB1R activation could involve changes in serotonergic and GABAergic signaling in the PVN. Accordingly, the present study was aimed to characterize the neurochemical mechanisms related to the hyperphagic effects induced by activation of CB1R in the PVN, studying in vitro and in vivo changes induced by direct activation these receptors. Here, we have found that the neurochemical mechanisms activated by stimulation of CB1 receptors in the PVN involve inhibition of 5-HT release, resulting in a decrease of serotonergic activity mediated by 5-HT_1A and 5-HT_1B receptors and inducing disinhibition of GABA release to stimulate food intake. In conclusion, these neurochemical changes in the PVN are determinant to the cannabinoid-induced stimulation of food intake. Our findings provide evidence of a functional connection among CB1R and serotonergic and GABAergic systems on the control of appetite regulation mediated by endocannabinoids.

An overview of the cannabinoid type 2 receptor system and its therapeutic potential

PURPOSE OF REVIEW

This narrative review summarizes recent insights into the role of the cannabinoid type 2 (CB2) receptor as potential therapeutic target in neuropathic pain and neurodegenerative conditions.

RECENT FINDINGS

The cannabinoid system continues to receive attention as a therapeutic target. The CB2 receptor is primarily expressed on glial cells only when there is active inflammation and appears to be devoid of undesired psychotropic effects or addiction liability. The CB2 receptor has been shown to have potential as a therapeutic target in models of diseases with limited or no currently approved therapies, such as neuropathic pain and neurodegenerative conditions such as Alzheimer's disease.

SUMMARY

The functional involvement of CB2 receptor in neuropathic pain and other neuroinflammatory diseases highlights the potential therapeutic role of drugs acting at the CB2 receptor.

Endocannabinoid and nitric oxide systems of the hypothalamic paraventricular nucleus mediate effects of NPY on energy expenditure

Objective

Neuropeptide Y (NPY) is one of the most potent orexigenic peptides. The hypothalamic paraventricular nucleus (PVN) is a major locus where NPY exerts its effects on energy homeostasis. We investigated how NPY exerts its effect within the PVN.

Methods

Patch clamp electrophysiology and Ca2+ imaging were used to understand the involvement of Ca2+ signaling and retrograde transmitter systems in the mediation of NPY induced effects in the PVN. Immuno-electron microscopy were performed to elucidate the subcellular localization of the elements of nitric oxide (NO) system in the parvocellular PVN. In vivo metabolic profiling was performed to understand the role of the endocannabinoid and NO systems of the PVN in the mediation of NPY induced changes of energy homeostasis.

Results

We demonstrated that NPY inhibits synaptic inputs of parvocellular neurons in the PVN by activating endocannabinoid and NO retrograde transmitter systems via mobilization of Ca2+ from the endoplasmic reticulum, suggesting that NPY gates the synaptic inputs of parvocellular neurons in the PVN to prevent the influence of non-feeding-related inputs. While intraPVN administered NPY regulates food intake and locomotor activity via NO signaling, the endocannabinoid system of the PVN selectively mediates NPY-induced decrease in energy expenditure.

Conclusion

Thus, within the PVN, NPY stimulates the release of endocannabinoids and NO via Ca²⁺-influx from the endoplasmic reticulum. Both transmitter systems appear to have unique roles in the mediation of the NPY-induced regulation of energy homeostasis, suggesting that NPY regulates food intake, energy expenditure, and locomotor activity through different neuronal networks of this nucleus.

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NPY increases the intracellular Ca²⁺ level of PVN neurons by mobilizing the Ca²⁺ from ER.

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NPY inhibits the input of these neurons by endocannabinoids and NO.

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IntraPVN administered NPY regulates food intake and locomotor activity via NO signaling.

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IntraPVN administered NPY regulates energy expenditure via the endocannabinoid system.

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NPY regulates the energy expenditure and food intake via different neuronal networks of the PVN.

Role of Cannabinoids in Obesity

Obesity is an increasing health problem worldwide. Its related comorbidities imply a high cost for the National Health System and diminish a patient's life quality. Adipose tissue is composed of three types of cells. White adipocytes are involved in fat storage and secretion of hormones. Brown adipocytes are involved in thermogenesis and caloric expenditure. Beige adipocytes are transitional adipocytes that in response to various stimuli can turn from white to brown and could be protective against the obesity, enhancing energy expenditure. The conversion of white in beige adipose tissue is a potential new therapeutic target for obesity. Cannabinoid receptors (CB) regulate thermogenesis, food intake and inflammation. CB1 ablation or inhibition helps reducing body weight and food intake. Stimulation of CB2 limits inflammation and promotes anti-obesity effects by reducing food intake and weight gain. Its genetic ablation results in adiposity development. CB receptors are also responsible for transforming white adipose tissue towards beige or brown adipocytes, therefore their modulation can be considered potential anti-obesity target. CB1 principal localization in central nervous system represents an important limit. Stimulation of CB2, principally localized on peripheral cells instead, should facilitate the anti-obesity effects without exerting remarkable psychotropic activity.

Plasma fatty acid ethanolamides are associated with postprandial triglycerides, ApoCIII, and ApoE in humans consuming a high-fructose corn syrup-sweetened beverage

Epidemiological and clinical research studies have provided ample evidence demonstrating that consumption of sugar-sweetened beverages increases risk factors involved in the development of obesity, Type 2 diabetes, and cardiovascular disease (CVD). Our previous study demonstrated that when compared with aspartame (Asp), 2 wk of high-fructose corn syrup (HFCS)-sweetened beverages provided at 25% of daily energy requirement was associated with increased body weight, postprandial (pp) triglycerides (TG), and fasting and pp CVD risk factors in young adults. The fatty acid ethanolamide, anandamide (AEA), and the monoacylglycerol, 2-arachidonoyl- sn-glycerol (2-AG), are two primary endocannabinoids (ECs) that play a role in regulating food intake, increasing adipose storage, and regulating lipid metabolism. Therefore, we measured plasma concentrations of ECs and their analogs, oleoylethanolamide (OEA), docosahexaenoyl ethanolamide (DHEA), and docosahexaenoyl glycerol (DHG), in participants from our previous study who consumed HFCS- or Asp-sweetened beverages to determine associations with weight gain and CVD risk factors. Two-week exposure to either HFCS- or Asp-sweetened beverages resulted in significant differences in the changes in fasting levels of OEA and DHEA between groups after the testing period. Subjects who consumed Asp, but not HFCS, displayed a reduction in AEA, OEA, and DHEA after the testing period. In contrast, there were significant positive relationships between AEA, OEA, and DHEA vs. ppTG, ppApoCIII, and ppApoE in those consuming HFCS, but not in those consuming Asp. Our findings reveal previously unknown associations between circulating ECs and EC-related molecules with markers of lipid metabolism and CVD risk after HFCS consumption.

Monoacylglycerol lipase (MAGL) as a promising therapeutic target

Monoacylglycerol lipase (MAGL) has been characterized as the main enzyme responsible for the inactivation of the most abundant brain endocannabinoid, 2-arachidonoylglycerol (2-AG). Besides this role, MAGL has progressively acquired a growing importance as an integrative metabolic hub that controls not only the in vivo levels of 2-AG but also of other monoacylglycerides and, indirectly, the levels of free fatty acids derived from their hydrolysis as well as other lipids with pro-inflammatory or pro-tumorigenic effects, coming from the further metabolism of fatty acids. All these functions have only started to be elucidated in the last years due to the progress made in the knowledge of the structure of MAGL and in the development of genetic and chemical tools. In this review we report the advances made in the field with a special focus on the last decade and how MAGL has become a promising therapeutic target for the treatment of several diseases that currently lack appropriate therapies.

Inverse agonist of ERRγ reduces cannabinoid receptor type 1-mediated induction of fibrinogen synthesis in mice with a high-fat diet-intoxicated liver

Upon liver intoxication with malnutrition or high-fat diet feeding, fibrinogen is synthesized by hepatocytes and secreted into the blood in human and mouse. Its primary function is to occlude blood vessels upon damage and thereby stop excessive bleeding. High fibrinogen levels may contribute to the development of pathological thrombosis, which is one mechanism linking fatty liver disease with cardiovascular disease. Our previous results present ERRγ as key regulator of hepatocytic fibrinogen gene expression in human. In a therapeutic approach, we now tested ERRγ inverse agonist GSK5182 as regulator of fibrinogen levels in mouse hyperfibrinogenemia caused by diet-induced obesity and in mouse hepatocytes. ACEA, a CB1R agonist, up-regulated transcription of mouse fibrinogen via induction of ERRγ, whereas knockdown of ERRγ attenuated the effect of ACEA (10 µM) on fibrinogen expression in AML12 mouse hepatocytes. Deletion analyses of the mouse fibrinogen γ (FGG) gene promoter and ChIP assays revealed binding sites for ERRγ on the mouse FGG promoter. ACEA or adenovirus ERRγ injection induced FGA, FGB and FGG mRNA and protein expression in mouse liver, while ERRγ knockdown with Ad-shERRγ attenuated ACEA-mediated induction of fibrinogen gene expression. Moreover, mice maintained on a high-fat diet (HFD) expressed higher levels of fibrinogen, whereas cannabinoid receptor type 1 (CB1R)-KO mice fed an HFD had nearly normal fibrinogen levels. Finally, GSK5182 (40 mg/kg) strongly inhibits the ACEA (10 mg/kg) or HFD-mediated induction of fibrinogen level in mice. Taken together, targeting ERRγ with its inverse agonist GSK5182 represents a promising therapeutic strategy for ameliorating hyperfibrinogenemia.

Neuroprotection in Oxidative Stress-Related Neurodegenerative Diseases: Role of Endocannabinoid System Modulation

SIGNIFICANCE

Redox imbalance may lead to overproduction of reactive oxygen and nitrogen species (ROS/RNS) and subsequent oxidative tissue damage, which is a critical event in the course of neurodegenerative diseases. It is still not fully elucidated, however, whether oxidative stress is the primary trigger or a consequence in the process of neurodegeneration. Recent Advances: Increasing evidence suggests that oxidative stress is involved in the propagation of neuronal injury and consequent inflammatory response, which in concert promote development of pathological alterations characteristic of most common neurodegenerative diseases.

CRITICAL ISSUES

Accumulating recent evidence also suggests that there is an important interplay between the lipid endocannabinoid system [ECS; comprising the main cannabinoid 1 and 2 receptors (CB1 and CB2), endocannabinoids, and their synthetic and metabolizing enzymes] and various key inflammatory and redox-dependent processes.

FUTURE DIRECTIONS

Targeting the ECS to modulate redox state-dependent cell death and to decrease consequent or preceding inflammatory response holds therapeutic potential in a multitude of oxidative stress-related acute or chronic neurodegenerative disorders from stroke and traumatic brain injury to Alzheimer's and Parkinson's diseases and multiple sclerosis, just to name a few, which will be discussed in this overview. Antioxid. Redox Signal. 29, 75-108.

Endocannabinoids in Body Weight Control

Maintenance of body weight is fundamental to maintain one's health and to promote longevity. Nevertheless, it appears that the global obesity epidemic is still constantly increasing. Endocannabinoids (eCBs) are lipid messengers that are involved in overall body weight control by interfering with manifold central and peripheral regulatory circuits that orchestrate energy homeostasis. Initially, blocking of eCB signaling by first generation cannabinoid type 1 receptor (CB1) inverse agonists such as rimonabant revealed body weight-reducing effects in laboratory animals and men. Unfortunately, rimonabant also induced severe psychiatric side effects. At this point, it became clear that future cannabinoid research has to decipher more precisely the underlying central and peripheral mechanisms behind eCB-driven control of feeding behavior and whole body energy metabolism. Here, we will summarize the most recent advances in understanding how central eCBs interfere with circuits in the brain that control food intake and energy expenditure. Next, we will focus on how peripheral eCBs affect food digestion, nutrient transformation and energy expenditure by interfering with signaling cascades in the gastrointestinal tract, liver, pancreas, fat depots and endocrine glands. To finally outline the safe future potential of cannabinoids as medicines, our overall goal is to address the molecular, cellular and pharmacological logic behind central and peripheral eCB-mediated body weight control, and to figure out how these precise mechanistic insights are currently transferred into the development of next generation cannabinoid medicines displaying clearly improved safety profiles, such as significantly reduced side effects.

Regulation of Adipose Tissue Metabolism by the Endocannabinoid System

White adipose tissue (WAT) stores excess energy as triglycerides, and brown adipose tissue (BAT) is specialized in dissipating energy as heat. The endocannabinoid system (ECS) is involved in a broad range of physiological processes and is increasingly recognized as a key player in adipose tissue metabolism. High ECS tonus in the fed state is associated with a disadvantageous metabolic phenotype, and this has led to a search for pharmacological strategies to inhibit the ECS. In this review we present recent developments that cast light on the regulation of adipose tissue metabolism by the ECS, and we discuss novel treatment options including the modulation of endocannabinoid synthesis and breakdown enzymes.

Effect of maternal high-fat diet on key components of the placental and hepatic endocannabinoid system

Maternal obesity in pregnancy has been linked to a spectrum of adverse developmental changes. Involvement of eCBs in obesity is well characterized. However, information regarding eCB physiology in obesity associated with pregnancy is sparse. This study evaluated fetomaternal hepatic, systemic, and placental eCB molecular changes in response to maternal consumption of a HFD. From ≥9 mo before conception, nonpregnant baboons ( Papio spp.) were fed a diet of either 45 (HFD; n = 11) or 12% fat or a control diet (CTR; n = 11), and dietary intervention continued through pregnancy. Maternal and fetal venous plasma samples were evaluated using liquid chromatography-mass spectrometry to quantify AEA and 2-AG. Placental, maternal and fetal hepatic tissues were analyzed using RT-PCR, Western blot, and immunohistochemistry. mRNA and protein expression of endocannabinoid receptors (CB1R and CB2R), FAAH, DAGL, MAGL, and COX-2 were determined. Statistical analyses were performed with the nonparametric Scheirer-Ray-Hare extension of the Kruskal-Wallis test to analyze the effects of diet (HFD vs. CTR), fetal sex (male vs. female), and the diet × sex interaction. Fetal weight was influenced by fetal sex but not by maternal diet. The increase in maternal weight in animals fed the HFD vs. the CTR diet approached significance ( P = 0.055). Maternal circulating 2-AG concentrations increased, and fetal circulating concentrations decreased in the HFD group, independently of fetal sex. CB1R receptor expression was detected in syncytiotrophoblasts (HFD) and the fetal endothelium (CTR and HFD). Placental CB2R protein expression was higher in males and lower in female fetuses in the HFD group. Fetal hepatic CB2R, FAAH, COX-2 (for both fetal sexes), and DAGLα (in male fetuses) protein expression decreased in the HFD group compared with the CTR group. We conclude that consumption of a HFD during pregnancy results in fetal systemic 2-AG and hepatic eCB deficiency.

Cannabinoids for the treatment of neuropsychiatric symptoms, pain and weight loss in dementia

PURPOSE OF REVIEW

Efficacious treatment for neuropsychiatric symptoms (NPS), pain and weight loss for dementia patients is desperately needed. This review presents an up-to-date look at the literature investigating the use of cannabinoid for these symptoms in dementia.

RECENT FINDINGS

We searched electronically for publications regarding cannabinoid use in dementia, with a focus on Alzheimer's disease. Seven studies and one case report have been conducted to examine the use of cannabinoids for the treatment of NPS of dementia, and three of these trials reported on the effect of cannabinoids on weight. Five studies reported decreased agitation or improvements in sleep with cannabinoid use. One crossover trial found that cannabinoids positively impacted weight, whereas a chart review study found no impact on weight with cannabinoids, but an increase in food intake. There were no trials examining the use of cannabinoids for pain in dementia.

SUMMARY

Findings from trials with small sample sizes and various clinical populations suggest that cannabinoid use may be well tolerated and effective for treatment of NPS such as agitation as well as weight and pain management in patients with dementia. Additional studies are necessary to further elucidate the relative risks and benefits of this treatment.

The therapeutic potential of targeting the peripheral endocannabinoid/CB1 receptor system

Endocannabinoids (eCBs) are internal lipid mediators recognized by the cannabinoid-1 and -2 receptors (CB₁R and CB₂R, respectively), which also mediate the different physiological effects of marijuana. The endocannabinoid system, consisting of eCBs, their receptors, and the enzymes involved in their biosynthesis and degradation, is present in a vast number of peripheral organs. In this review we describe the role of the eCB/CB₁R system in modulating the metabolism in several peripheral organs. We assess how eCBs, via activating the CB₁R, contribute to obesity and regulate food intake. In addition, we describe their roles in modulating liver and kidney functions, as well as bone remodeling and mass. Special importance is given to emphasizing the efficacy of the recently developed peripherally restricted CB₁R antagonists, which were pre-clinically tested in the management of energy homeostasis, and in ameliorating both obesity- and diabetes-induced metabolic complications.

Cannabinoid Receptors in Diabetic Kidney Disease

PURPOSE OF REVIEW

The purpose of this review is to examine and summarize studies assessing the relevance of the endocannabinoid system (ECS) in diabetic kidney disease (DKD).

RECENT FINDINGS

Endocannabinoids and endocannabinoid receptors of type 1 (CB1R) and of type 2 (CB2R) are present in the normal kidney. Expression of CB1R and CB2R is altered in experimental DKD. Studies in experimental animals and cultured kidney cells show a beneficial effect of peripheral CB1R blockade and CB2R activation in DKD and an even greater efficacy of a combined treatment. Preclinical studies confirm that both CB1R and CB2R are implicated in the pathogenesis of DKD and may represent novel targets for treatment. However, we need to gain a better understanding of the ECS prior to move to human clinical trial.

New role of phenothiazine derivatives as peripherally acting CB1 receptor antagonizing anti-obesity agents

Developing peripherally active cannabinoid 1 (CB1) receptor antagonists is a novel therapeutic approach for the management of obesity. An unusual phenothiazine scaffold containing CB1R antagonizing hit was identified by adopting virtual screening work flow. The hit so identified was further modified by introducing polar functional groups into it to enhance the polar surface area and decrease the hydrophobicity of the resulting molecules. CB1 receptor antagonistic activity for the designed compounds was computed by the previously established pharmacophore and three dimensional quantitative structure-activity relationship models. Docking studies of these designed compounds confirmed the existence of favourable interactions within the active site of the CB1 receptor. The designed compounds were synthesized and evaluated for their CB1 receptor antagonistic activity. Parallel artificial membrane permeability assay was performed to evaluate their potential to permeate into the central nervous system wherein it was observed that the compounds did not possess the propensity to cross the blood brain barrier and would be devoid of central nervous system side effects. In pharmacological evaluation, the synthesized compounds (23, 25, 27 and 34) showed significant decrease in food intake suggesting their potential application in the management of obesity through CB1 receptor antagonist activity.

Peripheral modulation of the endocannabinoid system in metabolic disease

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

Effects of a Weight Loss Program on Metabolic Syndrome, Eating Disorders and Psychological Outcomes: Mediation by Endocannabinoids?

OBJECTIVE

To evaluate the effects of weight loss on endocannabinoids, cardiometabolic and psychological parameters, eating disorders (ED) as well as quality of life (QoL) and to elucidate the role of endocannabinoids in metabolic syndrome (MS).

METHODS

In total, 114 patients with obesity were prospectively included in a 12-month weight loss program. Plasma endocannabinoids were measured by mass spectrometry; ED, psychological and QoL-related parameters were evaluated by self-reported questionnaires; physical activity was measured by accelerometer. Nutritional assessment was done by a 3-day food diary.

RESULTS

Among completers (n = 87), body weight decreased in 35 patients (-9.1 ± 8.6 kg), remained stable in 39 patients, and increased in 13 patients (+5.8 ± 3.4 kg). 75% of patients with MS at baseline were free of MS at follow-up, and their baseline plasma N-palmitoylethanolamide (PEA) values were significantly lower when compared to patients with persisting MS. At baseline, there was a positive relationship between PEA and waist circumference (p = 0.005, R2 = 0.08), fasting glucose (p < 0.0001, R2 = 0.12), total cholesterol (p = 0.001, R2 = 0.11), triglycerides (p = 0.001, R2 = 0.11), LDL-cholesterol (p = 0.03, R2 = 0.05) as well as depression score (p = 0.002, R2 = 0.29).

CONCLUSION

Plasma PEA might play a role in metabolic improvement after weight loss. Even in subjects without weight loss, a multidisciplinary intervention improves psychological outcomes, ED, and QoL.

Adipocyte cannabinoid receptor CB1 regulates energy homeostasis and alternatively activated macrophages

Dysregulated adipocyte physiology leads to imbalanced energy storage, obesity, and associated diseases, imposing a costly burden on current health care. Cannabinoid receptor type-1 (CB1) plays a crucial role in controlling energy metabolism through central and peripheral mechanisms. In this work, adipocyte-specific inducible deletion of the CB1 gene (Ati-CB1-KO) was sufficient to protect adult mice from diet-induced obesity and associated metabolic alterations and to reverse the phenotype in already obese mice. Compared with controls, Ati-CB1-KO mice showed decreased body weight, reduced total adiposity, improved insulin sensitivity, enhanced energy expenditure, and fat depot-specific cellular remodeling toward lowered energy storage capacity and browning of white adipocytes. These changes were associated with an increase in alternatively activated macrophages concomitant with enhanced sympathetic tone in adipose tissue. Remarkably, these alterations preceded the appearance of differences in body weight, highlighting the causal relation between the loss of CB1 and the triggering of metabolic reprogramming in adipose tissues. Finally, the lean phenotype of Ati-CB1-KO mice and the increase in alternatively activated macrophages in adipose tissue were also present at thermoneutral conditions. Our data provide compelling evidence for a crosstalk among adipocytes, immune cells, and the sympathetic nervous system (SNS), wherein CB1 plays a key regulatory role.

Endocannabinoids: Effectors of glucocorticoid signaling

For decades, there has been speculation regarding the interaction of cannabinoids with glucocorticoid systems. Given the functional redundancy between many of the physiological effects of glucocorticoids and cannabinoids, it was originally speculated that the biological mechanisms of cannabinoids were mediated by direct interactions with glucocorticoid systems. With the discovery of the endocannabinoid system, additional research demonstrated that it was actually the opposite; glucocorticoids recruit endocannabinoid signaling, and that the engagement of endocannabinoid signaling mediated many of the neurobiological and physiological effects of glucocorticoids. With the development of advances in pharmacology and genetics, significant advances in this area have been made, and it is now clear that functional interactions between these systems are critical for a wide array of physiological processes. The current review acts a comprehensive summary of the contemporary state of knowledge regarding the biological interactions between glucocorticoids and endocannabinoids, and their potential role in health and disease.

Effects of nicotine on homeostatic and hedonic components of food intake

Chronic tobacco use leads to nicotine addiction that is characterized by exaggerated urges to use the drug despite the accompanying negative health and socioeconomic burdens. Interestingly, nicotine users are found to be leaner than the general population. Review of the existing literature revealed that nicotine affects energy homeostasis and food consumption via altering the activity of neurons containing orexigenic and anorexigenic peptides in the brain. Hypothalamus is one of the critical brain areas that regulates energy balance via the action of these neuropeptides. The equilibrium between these two groups of peptides can be shifted by nicotine leading to decreased food intake and weight loss. The aim of this article is to review the existing literature on the effect of nicotine on food intake and energy homeostasis and report on the changes that nicotine brings about in the level of these peptides and their receptors that may explain changes in food intake and body weight induced by nicotine. Furthermore, we review the effect of nicotine on the hedonic aspect of food intake. Finally, we discuss the involvement of different subtypes of nicotinic acetylcholine receptors in the regulatory action of nicotine on food intake and energy homeostasis.

The CB1 Receptor as the Cornerstone of Exostasis

The type-1 cannabinoid receptor (CB1) is the main effector of the endocannabinoid system (ECS), which is involved in most brain and body functions. In this Perspective, we provide evidence indicating that CB1 receptor functions are key determinants of bodily coordinated exostatic processes. First, we will introduce the concepts of endostasis and exostasis as compensation or accumulation for immediate or future energy needs and discuss how exostasis has been necessary for the survival of species during evolution. Then, we will argue how different specific biological functions of the CB1 receptor in the body converge to provide physiological exostatic processes. Finally, we will introduce the concept of proactive evolution-induced diseases (PEIDs), which helps explain the seeming paradox that an evolutionary-selected physiological function can become the cause of epidemic pathological conditions, such as obesity. We propose here a possible unifying theory of CB1 receptor functions that can be tested by future experimental studies.

Re-visiting the Endocannabinoid System and Its Therapeutic Potential in Obesity and Associated Diseases

PURPOSE OF REVIEW

The purpose of the review was to revisit the possibility of the endocannabinoid system being a therapeutic target for the treatment of obesity by focusing on the peripheral roles in regulating appetite and energy metabolism.

RECENT FINDINGS

Previous studies with the global cannabinoid receptor blocker rimonabant, which has both central and peripheral properties, showed that this drug has beneficial effects on cardiometabolic function but severe adverse psychiatric side effects. Consequently, focus has shifted to peripherally restricted cannabinoid 1 (CB1) receptor blockers as possible therapeutic agents that mitigate or eliminate the untoward effects in the central nervous system. Targeting the endocannabinoid system using novel peripheral CB1 receptor blockers with negligible penetrance across the blood-brain barrier may prove to be effective therapy for obesity and its co-morbidities. Perhaps the future of blockers targeting CB1 receptors will be tissue-specific neutral antagonists (e.g., skeletal muscle specific to treat peripheral insulin resistance, adipocyte-specific to treat fat excess, liver-specific to treat fatty liver and hepatic insulin resistance).

Central and peripheral control of food intake

The maintenance of the body weight at a stable level is a major determinant in keeping the higher animals and mammals survive. Th e body weight depends on the balance between the energy intake and energy expenditure. Increased food intake over the energy expenditure of prolonged time period results in an obesity. Th e obesity has become an important worldwide health problem, even at low levels. The obesity has an evil effect on the health and is associated with a shorter life expectancy. A complex of central and peripheral physiological signals is involved in the control of the food intake. Centrally, the food intake is controlled by the hypothalamus, the brainstem, and endocannabinoids and peripherally by the satiety and adiposity signals. Comprehension of the signals that control food intake and energy balance may open a new therapeutic approaches directed against the obesity and its associated complications, as is the insulin resistance and others. In conclusion, the present review summarizes the current knowledge about the complex system of the peripheral and central regulatory mechanisms of food intake and their potential therapeutic implications in the treatment of obesity.

Developmental programming of somatic growth, behavior and endocannabinoid metabolism by variation of early postnatal nutrition in a cross-fostering mouse model

Background

Nutrient deprivation during early development has been associated with the predisposition to metabolic disorders in adulthood. Considering its interaction with metabolism, appetite and behavior, the endocannabinoid (eCB) system represents a promising target of developmental programming.

Methods

By cross-fostering and variation of litter size, early postnatal nutrition of CB6F1-hybrid mice was controlled during the lactation period (3, 6, or 10 pups/mother). After weaning and redistribution at P21, all pups received standard chow ad libitum. Gene expression analyses (liver, visceral fat, hypothalamus) were performed at P50, eCB concentrations were determined in liver and visceral fat. Locomotor activity and social behavior were analyzed by means of computer-assisted videotracking.

Results

Body growth was permanently altered, with differences for length, weight, body mass index and fat mass persisting beyond P100 (all 3>6>10,p<0.01). This was paralleled by differences in hepatic IGF-I expression (p<0.01). Distinct gene expression patterns for key enzymes of the eCB system were observed in fat (eCB-synthesis: 3>6>10 (DAGLα p<0.05; NAPE-PLD p = 0.05)) and liver (eCB-degradation: 3>6>10 (FAAH p<0.05; MGL p<0.01)). Concentrations of endocannabinoids AEA and 2-AG in liver and visceral fat were largely comparable, except for a borderline significance for higher AEA (liver, p = 0.049) in formerly overfed mice and, vice versa, tendencies (p<0.1) towards lower AEA (fat) and 2-AG (liver) in formerly underfed animals. In the arcuate nucleus, formerly underfed mice tended to express more eCB-receptor transcripts (CB1R p<0.05; CB2R p = 0.08) than their overfed fellows. Open-field social behavior testing revealed significant group differences, with formerly underfed mice turning out to be the most sociable animals (p<0.01). Locomotor activity did not differ.

Conclusion

Our data indicate a developmental plasticity of somatic growth, behavior and parameters of the eCB system, with long-lasting impact of early postnatal nutrition. Developmental programming of the eCB system in metabolically active tissues, as shown here for liver and fat, may play a role in the formation of the adult cardiometabolic risk profile following perinatal malnutrition in humans.

Inhibition of Endocannabinoid-Metabolizing Enzymes in Peripheral Tissues Following Developmental Chlorpyrifos Exposure in Rats

Repeated developmental exposure to the organophosphate (OP) insecticide chlorpyrifos (CPF) inhibits brain fatty acid amide hydrolase (FAAH) activity at low levels, whereas at higher levels, it inhibits brain monoacylglycerol lipase (MAGL) activity. FAAH and MAGL hydrolyze the endocannabinoids anandamide (AEA) and 2-arachidonylglycerol (2-AG), respectively. Peripherally, AEA and 2-AG have physiological roles in the regulation of lipid metabolism and immune function, and altering the normal levels of these lipid mediators can negatively affect these processes. Exposure to CPF alters brain endocannabinoid hydrolysis activity, but it is unclear whether low-level exposure alters this activity in peripheral tissues important in metabolic and immune function. Therefore, rat pups were exposed orally from day 10 to 16 to 0.5, 0.75, or 1.0 mg/kg CPF or 0.02 mg/kg PF-04457845 (a specific FAAH inhibitor). At 12 hours postexposure, FAAH, MAGL, and cholinesterase (ChE) activities were determined. All treatments inhibited FAAH activity in brain, spleen, and liver. CPF inhibited ChE activity in spleen and liver (all dosages) and in brain (highest dosage only). CPF inhibited total 2-AG hydrolysis and MAGL-specific activity in brain and spleen (high dosage only). In liver, total 2-AG hydrolysis was inhibited by all treatments and could be attributed to inhibition of non-MAGL-mediated 2-AG hydrolysis, indicating involvement of other enzymes. MAGL-specific activity in liver was inhibited only by the high CPF dosage, whereas PF-04457845 slightly increased this activity. Overall, exposure to low levels of CPF and to PF-04457845 can alter endocannabinoid metabolism in peripheral tissues, thus potentially affecting physiological processes.

Oral Administration of the Endocannabinoid Anandamide during Lactation: Effects on Hypothalamic Cannabinoid Type 1 Receptor and Food Intake in Adult Mice

We have previously shown that administration of the endocannabinoid anandamide (AEA) during lactation leads to overweight, increased body fat accumulation, and insulin resistance in adult mice. This study was designed to elucidate if these effects are due to increased food intake, stimulated by an augmented abundance and binding ability of the hypothalamic cannabinoid type 1 receptor (CB1R). With this aim, male mice pups were treated with a daily oral dose of AEA during lactation. Adult mice were also treated with a single oral dose of AEA, to evaluate acute food intake during 4 h. At 21 and 160 days, CB1R protein abundance was calculated by western blot analysis. Capacity of hypothalamic membranes to specifically bind the radioligand ³[H]-CP55.940 was also measured. Western blots showed a 72% increase in CB1R abundance in AEA-treated 21-day-old mice, without differences in adult mice. Additionally, specific binding of ³[H]-CP55.940 to hypothalamic membranes from adult mice was significantly lower in those mice treated with AEA during lactation. Moreover, AEA did not stimulate acute food intake in both, AEA-treated and control mice. Results suggest that metabolic alterations found in adult mice because of AEA treatment during lactation are not associated with hypothalamic CB1R.

Metabolic Profiling of CB1 Neutral Antagonists

PIMSR is among the first neutral antagonists for the CB1R and was demonstrated pharmacologically to bind to the CB1R, yet not alter calcium flux. It was further shown computationally to be able to stabilize both the active and inactive states of CB1R revealing the molecular interactions that mechanistically afford the property of neutral antagonism. PIMSR shows dramatic positive effects in reducing weight, food intake, and adiposity as well as in improving glycemic control and lipid homeostasis in high-fat diet-induced obese mice, but also shows increased ALT and liver weight as markers of liver injury with chronic administration. Further, in a separate study, 3-day administration of PIMSR in C57BL/6J mice, hepatic steatosis from an acute administration of high of ethanol was significantly reduced. Also, it partially prevented alcohol-induced increases in ALT, AST, and LDH. The differences in ALT levels in obese and nonobese mice under different test paradigms are unlikely to be due to neutral antagonism itself since other neutral antagonists (AM6545) do not exhibit liver injury. The brain levels of low micromolar would support significant brain CB1 receptor occupancy (re: Ki=17nM), thus potentially including both CNS and peripheral influences on the observed weight loss. Overall, these studies suggest that marked improvements in aspects of metabolic disease and alcoholic steatosis can be realized with CB1R neutral antagonists and hence warrants the exploration of further members of this class of cannabinoid ligands.

Polyunsaturated fatty acids and endocannabinoids in health and disease

Polyunsaturated fatty acids (PUFAs) are lipid derivatives of omega-3 (docosahexaenoic acid, DHA, and eicosapentaenoic acid, EPA) or of omega-6 (arachidonic acid, ARA) synthesized from membrane phospholipids and used as a precursor for endocannabinoids (ECs). They mediate significant effects in the fine-tune adjustment of body homeostasis. Phyto- and synthetic cannabinoids also rule the daily life of billions worldwide, as they are involved in obesity, depression and drug addiction. Consequently, there is growing interest to reveal novel active compounds in this field. Cloning of cannabinoid receptors in the 90s and the identification of the endogenous mediators arachidonylethanolamide (anandamide, AEA) and 2-arachidonyglycerol (2-AG), led to the characterization of the endocannabinoid system (ECS), together with their metabolizing enzymes and membrane transporters. Today, the ECS is known to be involved in diverse functions such as appetite control, food intake, energy balance, neuroprotection, neurodegenerative diseases, stroke, mood disorders, emesis, modulation of pain, inflammatory responses, as well as in cancer therapy. Western diet as well as restriction of micronutrients and fatty acids, such as DHA, could be related to altered production of pro-inflammatory mediators (e.g. eicosanoids) and ECs, contributing to the progression of cardiovascular diseases, diabetes, obesity, depression or impairing conditions, such as Alzheimer' s disease. Here we review how diets based in PUFAs might be linked to ECS and to the maintenance of central and peripheral metabolism, brain plasticity, memory and learning, blood flow, and genesis of neural cells.

Increase in hypothalamic AMPK phosphorylation induced by prolonged exposure to LPS involves ghrelin and CB1R signaling

Acute administration of lipopolysaccharide (LPS) from Gram-negative bacteria induces hypophagia. However, the repeated administration of LPS leads to desensitization of hypophagia, which is associated with increased hypothalamic p-AMPK expression. Because ghrelin and endocannabinoids modulate AMPK activity in the hypothalamus, we hypothesized that these neuromodulators play a role in the reversal of tolerance to hypophagia in rats under long-term exposure to LPS. Male Wistar rats were treated with single (1 LPS, 100μg/kg body weight, ip) or repeated injections of LPS over 6days (6 LPS). Food intake was reduced in the 1 LPS, but not in the 6 LPS group. 6 LPS rats showed an increased serum concentration of acylated ghrelin and reduced ghrelin receptor mRNA expression in the hypothalamus. Ghrelin injection (40μg/kg body weight, ip) increased food intake, body weight gain, p-AMPK hypothalamic expression, neuropeptide Y (NPY) and Agouti related peptide (AgRP) mRNA expression in control animals (Saline). However, in 6 LPS rats, ghrelin did not alter these parameters. Central administration of a CB1R antagonist (AM251, 200ng/μl in 5μl/rat) induced hypophagia in 6 LPS animals, suggesting that the endocannabinoid system contributes to preserved food intake during LPS tolerance. In the presence of AM251, the ability of ghrelin to phosphorylate AMPK in the hypothalamus of 6 LPS group was restored, but not its orexigenic effect. Our data highlight that the orexigenic effects of ghrelin require CB1R signaling downstream of AMPK activation. Moreover, CB1R-mediated pathways contribute to the absence of hypophagia during repeated exposure to endotoxin.

Overactivation of the endocannabinoid system alters the antilipolytic action of insulin in mouse adipose tissue

Evidence has accumulated that obesity-related metabolic dysregulation is associated with overactivation of the endocannabinoid system (ECS), which involves cannabinoid receptor 1 (CB1R), in peripheral tissues, including adipose tissue (AT). The functional consequences of CB1R activation on AT metabolism remain unclear. Since excess fat mobilization is considered an important primary event contributing to the onset of insulin resistance, we combined in vivo and in vitro experiments to investigate whether activation of ECS could alter the lipolytic rate. For this purpose, the appearance of plasma glycerol was measured in wild-type and CB1R^-/- mice after acute anandamide administration or inhibition of endocannabinoid degradation by JZL195. Additional experiments were conducted on rat AT explants to evaluate the direct consequences of ECS activation on glycerol release and signaling pathways. Treatments stimulated glycerol release in mice fasted for 6 h and injected with glucose but not in 24-h fasted mice or in CB1R^-/-, suggesting that the effect was dependent on plasma insulin levels and mediated by CB1R. We concomitantly observed that Akt cascade activity was decreased, indicating an alteration of the antilipolytic action of insulin. Similar results were obtained with tissue explants exposed to anandamide, thus identifying CB1R of AT as a major target. This study indicates the existence of a functional interaction between CB1R and lipolysis regulation in AT. Further investigation is needed to test if the elevation of ECS tone encountered in obesity is associated with excess fat mobilization contributing to ectopic fat deposition and related metabolic disorders.

Sugars, Sweet Taste Receptors, and Brain Responses

Sweet taste receptors are composed of a heterodimer of taste 1 receptor member 2 (T1R2) and taste 1 receptor member 3 (T1R3). Accumulating evidence shows that sweet taste receptors are ubiquitous throughout the body, including in the gastrointestinal tract as well as the hypothalamus. These sweet taste receptors are heavily involved in nutrient sensing, monitoring changes in energy stores, and triggering metabolic and behavioral responses to maintain energy balance. Not surprisingly, these pathways are heavily regulated by external and internal factors. Dysfunction in one or more of these pathways may be important in the pathogenesis of common diseases, such as obesity and type 2 diabetes mellitus.

Peripheral cannabinoid-1 receptor blockade restores hypothalamic leptin signaling

Objective

In visceral obesity, an overactive endocannabinoid/CB₁ receptor (CB₁R) system promotes increased caloric intake and decreases energy expenditure, which are mitigated by global or peripheral CB₁R blockade. In mice with diet-induced obesity (DIO), inhibition of food intake by the peripherally restricted CB₁R antagonist JD5037 could be attributed to endogenous leptin due to the rapid reversal of hyperleptinemia that maintains leptin resistance, but the signaling pathway engaged by leptin has remained to be determined.

Methods

We analyzed the hypothalamic circuitry targeted by leptin following chronic treatment of DIO mice with JD5037.

Results

Leptin treatment or an increase in endogenous leptin following fasting/refeeding induced STAT3 phosphorylation in neurons in the arcuate nucleus (ARC) in lean and JD5037-treated DIO mice, but not in vehicle-treated DIO animals. Co-localization of pSTAT3 in leptin-treated mice was significantly less common with NPY⁺ than with POMC⁺ ARC neurons. The hypophagic effect of JD5037 was absent in melanocortin-4 receptor (MC4R) deficient obese mice or DIO mice treated with a MC4R antagonist, but was maintained in NPY^−/− mice kept on a high-fat diet.

Conclusions

Peripheral CB₁R blockade in DIO restores sensitivity to endogenous leptin, which elicits hypophagia via the re-activation of melanocortin signaling in the ARC.

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High-fat diet-induced leptin resistance is reversed by peripheral CB1 blockade.

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Restored leptin signaling by peripheral CB1 blockade occurs via POMC/MC4R pathway.

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AgRP/NPY neurons are not required for peripheral CB1 blockade-induced hypophagia in mice with diet-induced obesity.

Lipid signaling and fat storage in the dark-eyed junco

Seasonal hyperphagia and fattening promote survivorship in migratory and wintering birds, but reduced adiposity may be more advantageous during the breeding season. Factors such as photoperiod, temperature, and food predictability are known environmental determinants of fat storage, but the underlying neuroendocrine mechanisms are less clear. Endocannabinoids and other lipid signaling molecules regulate multiple aspects of energy balance including appetite and lipid metabolism. However, these functions have been established primarily in mammals; thus the role of lipid signals in avian fat storage remains largely undefined. Here we examined relationships between endocannabinoid signaling and individual variation in fat storage in captive white-winged juncos (Junco hyemalis aikeni) following a transition to long-day photoperiods. We report that levels of the endocannabinoid 2-arachidonoylglycerol (2-AG), but not anandamide (AEA), in furcular and abdominal fat depots correlate negatively with fat mass. Hindbrain mRNA expression of CB₁ endocannabinoid receptors also correlates negatively with levels of fat, demonstrating that fatter animals experience less central and peripheral endocannabinoid signaling when in breeding condition. Concentrations of the anorexigenic lipid, oleoylethanolamide (OEA), also inversely relate to adiposity. These findings demonstrate unique and significant relationships between adiposity and lipid signaling molecules in the brain and periphery, thereby suggesting a potential role for lipid signals in mediating adaptive levels of fat storage.

Cannabinoid Receptor Signaling in Central Regulation of Feeding Behavior: A Mini-Review

Cannabinoids are lipid messengers that modulate a variety of physiological processes and modify the generation of specific behaviors. In this regard, the cannabinoid receptor type 1 (CB₁) represents the most relevant target molecule of cannabinoids so far. One main function of central CB₁ signaling is to maintain whole body energy homeostasis. Thus, cannabinoids functionally interact with classical neurotransmitters in neural networks that control energy metabolism and feeding behavior. The promotion of CB₁ signaling can increase appetite and stimulate feeding, while blockade of CB₁ suppresses hunger and induces hypophagia. However, in order to treat overeating, pharmacological blockade of CB₁ by the inverse agonist rimonabant not only suppressed feeding but also resulted in psychiatric side effects. Therefore, research within the last decade focused on deciphering the underlying cellular and molecular mechanisms of central cannabinoid signaling that control feeding and other behaviors, with the overall aim still being the identification of specific targets to develop safe pharmacological interventions for the treatment of obesity. Today, many studies unraveled the subcellular localization of CB₁ and the function of cannabinoids in neurons and glial cells within circumscribed brain regions that represent integral parts of neural circuitries controlling feeding behavior. Here, these novel experimental findings will be summarized and recent advances in understanding the mechanisms of CB₁-dependent cannabinoid signaling being relevant for central regulation of feeding behavior will be highlighted. Finally, presumed alternative pathways of cannabinoids that are not driven by CB₁ activation but also contributing to control of feeding behavior will be introduced.

Monoglyceride lipase deficiency affects hepatic cholesterol metabolism and lipid-dependent gut transit in ApoE-/- mice

Monoglyceride lipase (MGL) hydrolyzes monoglycerides (MGs) to glycerol and fatty acids. Among various MG species MGL also degrades 2-arachidonoylglycerol (2-AG), the most abundant endocannabinoid and potent activator of cannabinoid receptors (CBR) 1 and 2. MGL-knockout (-/-) mice exhibit pronounced 2-AG accumulation, but lack central cannabimimetic effects due to CB1R desensitization. We have previously shown that MGL affects plaque stability in apolipoprotein E (ApoE)-/- mice, an established animal model for dyslipidemia and atherosclerosis. In the current study, we investigated functional consequences of MGL deficiency on lipid and energy metabolism in ApoE/MGL double knockout (DKO) mice. MGL deficiency affected hepatic cholesterol metabolism by causing increased cholesterol elimination via the biliary pathway. Moreover, DKO mice exhibit lipid-triggered delay in gastric emptying without major effects on overall triglyceride and cholesterol absorption. The observed phenotype of DKO mice is likely not a consequence of potentiated CB1R signaling but rather dependent on the activation of alternative signaling pathways. We conclude that MGL deficiency causes complex metabolic changes including cholesterol metabolism and regulation of gut transit independent of the endocannabinoid system.

Metabolite profiling identifies anandamide as a biomarker of nonalcoholic steatohepatitis

The discovery of metabolite-phenotype associations may highlight candidate biomarkers and metabolic pathways altered in disease states. We sought to identify novel metabolites associated with obesity and one of its major complications, nonalcoholic fatty liver disease (NAFLD), using a liquid chromatography-tandem mass spectrometry method. In 997 individuals in Framingham Heart Study Generation 3 (FHS Gen 3), we identified an association between anandamide (AEA) and BMI. Further examination revealed that AEA was associated with radiographic hepatic steatosis. In a histologically defined NAFLD cohort, AEA was associated with NAFLD severity, the presence of nonalcoholic steatohepatitis, and fibrosis. These data highlight AEA as a marker linking cardiometabolic disease and NAFLD severity.

Genetic interaction of DGAT2 and FAAH in the development of human obesity

PURPOSE

DGAT2 is the critical catalyzing enzyme for triglyceride biosynthesis, and excess triglyceride accumulation in fat tissues is a fundamental process for obesity. Mutations in DGAT2 or other genes interacting with DGAT2 associated with adiposity have not been reported in human to date.

METHODS

DGAT2 mutation was identified based on our in-home database-exome sequencing 227 young obese subjects (body-mass index (BMI), 35.1-61.7 kg/m²) and 219 lean controls (BMI, 17.5-23.0 kg/m²), further validated in 1190 lean subjects and the pedigree of the proband. The trios of the proband were further subjected to whole-exome sequencing to explore the candidate genes for obesity. The mutations in DGAT2 and FAAH were functionally evaluated in vitro.

RESULTS

We detected two rare variants in DGAT2 with no significant difference between obese and lean individuals. One novel heterozygous nonsense variant c.382C > T (p.R128*) was identified in one obese subject but not in 219 lean subjects and another 1190 lean subjects. Notably, in vitro study showed that R128* mutation severely damaged the TG-biosynthesis ability of DGAT2, and all other R128* carriers in the pedigree were lean. Thus, we further identified a loss-of-function variant c. 944G > T (p.R315I) in FAAH in the proband inheriting from his obese father. Importantly, FAAH overexpression inhibited DGAT2 expression and TG synthesis, while R315I mutant largely eliminated this inhibitory effect. We first report loss-of-function mutations in DGAT2 and FAAH in one obese subject, which may interact with each other to affect the adiposity penetrance, providing a model of genetic interaction associated with human obesity.