Lorcaserin improves glycemic control via a melanocortin neurocircuit

Gpr149 is involved in energy homeostasis in the male mouse

GPR149 is an orphan receptor about which little is known. Accordingly, in the present study, we mapped the tissue expression of Gpr149 in mice using three complementary approaches: quantitative PCR, in situ hybridization, and a newly generated Gpr149-Cre reporter mouse model. The strongest expressions of Gpr149 were observed in neurons of the islands of Calleja, the ventromedial hypothalamus, and the rostral interpeduncular nucleus. Moderate-to-low expression was also observed in the basal forebrain, striatum, hypothalamus, brainstem, and spinal cord. Some Gpr149 expression was also detected in the primary afferent neurons, enteric neurons, and pituitary endocrine cells. This expression pattern is consistent with the involvement of GPR149 signaling in the regulation of energy balance. To explore the physiological function of GPR149 in vivo, we used CRISPR-Cas9 to generate a global knockout allele with mice lacking Gpr149 exon 1. Preliminary metabolic findings indicated that Gpr149-/- mice partially resist weight gain when fed with a high-fat diet and have greater sensitivity to insulin than control mice. In summary, our data may serve as a resource for future in vivo studies on GPR149 in the context of diet-induced obesity.

Modulation of GABA release by 5-HT1B receptors: An interplay with AMPA-receptors and voltage-gated Ca2+ channels

Obesity has become a worldwide health challenge and commonly results from the intake of more calories than the body requires. The brain represents the master controller of food intake and as such has been the target of obesity medications. However, key mechanisms of druggable targets remain to be defined. Neurons within the arcuate nucleus of the hypothalamus co-expressing neuropeptide Y (NPY), agouti-related protein (AgRP) and GABA (NAG) are fundamental stimulators of hunger and food intake. NAG neurons also inhibit local satiety-promoting pro-opiomelanocortin (POMC) neurons. Agonists of the 1B subtype of metabotropic serotonin receptor (5-HT1BR) reduce food intake in part through the inhibition of hunger-promoting NAG neurons. We first confirmed that 5-HT1BR activation suppressed intake of a palatable Western diet in a mouse model of common dietary-induced obesity and genetically prone obesity. Next, we combined several electrophysiological approaches to analyse the effect of 5-HT1BRs in NAG neuron cell activity and GABA release. 5-HT1BR activation reduced NAG neuron action potential frequency and neurotransmitter release. We found that 5-HT1BR impact on GABA release from NAG neurons is mediated through voltage-gated Ca2+ channels with a critical input from glutamate receptors of AMPA subtype (AMPARs). As a fundamental outcome, this type of interplay provides an uncommon example of metabotropic action of AMPARs which regulates inhibitory signalling due to modulation of GABA release. As a translational outcome, our results provide a key mechanism through which 5-HT1BR drugs inhibit appetite-stimulating neurons within the brain to suppress food intake. This article is part of the Special Issue on "Ukrainian Neuroscience".

Sumatriptan, a serotonin 5HT1B receptor agonist, acutely reduces insulin secretion and sensitivity and glucose effectiveness in overweight humans: A double-blinded placebo-controlled cross-over trial

AIM

Evidence from mouse models suggests that brain serotonergic pathways control blood glucose. We hypothesized that sumatriptan (5HT1B -receptor agonist) would alter glucose homeostasis in humans.

MATERIALS AND METHODS

We conducted a two-visit random-order double-blinded placebo-controlled cross-over trial in 10 overweight adults that were otherwise healthy. Participants received sumatriptan (single dose, 100 mg) or placebo before undergoing a 60-min intravenous glucose tolerance test, followed by a 120-min hyperinsulinaemic euglycaemic clamp.

RESULTS

Glucose excursion was greater during intravenous glucose tolerance test with sumatriptan compared with placebo [iAUC0-60 min 316 (268-333) vs. 251 (197-319) min/mmol/L p = .047]. This was probably explained by a combination of reduced circulating insulin levels [iAUC0-10 min 1626 (1103-2733) vs. 2336 (1702-3269) min/pmol/L, p = .005], reduced insulin sensitivity [M/I-value 2.11 (1.15, 4.05) vs. 3.03 (1.14, 4.90) mg/kg/min per pmol/L, p = .010] and glucose effectiveness [SG 0.17 (0.12, 0.21) vs. 0.22 (0.18, 0.65)/min, p = .027].

CONCLUSIONS

5HT1B receptors have a glucoregulatory role in humans, probably acting on insulin secretion, insulin sensitivity and glucose effectiveness.

Defining Predictors of Weight Loss Response to Lorcaserin

CONTEXT

Individual responses to weight loss (WL) medications vary widely and prediction of response remains elusive.

OBJECTIVE

We investigated biomarkers associated with use of lorcaserin (LOR), a 5HT2cR agonist that targets proopiomelanocortin (POMC) neurons that regulate energy and glucose homeostasis, to identify predictors of clinical efficacy.

METHODS

Thirty individuals with obesity were treated with 7 days of placebo and LOR in a randomized crossover study. Nineteen participants continued on LOR for 6 months. Cerebrospinal fluid (CSF) POMC peptide measurements were used to identify potential biomarkers that predict WL. Insulin, leptin, and food intake during a meal were also studied.

RESULTS

LOR induced a significant decrease in CSF levels of the POMC prohormone and an increase in its processed peptide β-endorphin after 7 days; β-endorphin/POMC increased by 30% (P < .001). This was accompanied by a substantial decrease in insulin, glucose, and homeostasis model assessment of insulin resistance before WL. Changes in CSF POMC peptides persisted after WL (6.9%) at 6 months that were distinct from prior reports after diet alone. Changes in POMC, food intake, or other hormones did not predict WL. However, baseline CSF POMC correlated negatively with WL (P = .07) and a cutoff level of CSF POMC was identified that predicted more than 10% WL.

CONCLUSION

Our results provide evidence that LOR affects the brain melanocortin system in humans and that effectiveness is increased in individuals with lower melanocortin activity. Furthermore, early changes in CSF POMC parallel WL-independent improvements in glycemic indexes. Thus, assessment of melanocortin activity could provide a way to personalize pharmacotherapy of obesity with 5HT2cR agonists.

Unraveling the serotonin saga: from discovery to weight regulation and beyond - a comprehensive scientific review

The prevalence of obesity is rapidly increasing worldwide, while the development of effective obesity therapies lags behind. Although new therapeutic targets to alleviate obesity are identified every day, and drug efficacy is improving, adverse side effects and increased health risks remain serious issues facing the weight-loss industry. Serotonin, also known as 5-HT, has been extensively studied in relation to appetite reduction and weight loss. As a result, dozens of upstream and downstream neural targets of 5-HT have been identified, revealing a multitude of neural circuits involved in mediating the anorexigenic effect of 5-HT. Despite the rise and fall of several 5-HT therapeutics in recent decades, the future of 5-HT as a therapeutic target for weight-loss therapy looks promising. This review focuses on the history of serotonin, the state of current central serotonin research, previous serotonergic therapies, and the future of serotonin for treating individuals with obesity.

New Insight into Selective Serotonin Receptor Agonists in the Central Nervous System, Studied with WAY163909 in Obese and Diabetic Wistar Rats

Background and aims: We investigated the effect of WAY-163909, a novel 5-hydroxytryptamine selective 2C receptor agonist on body weight, blood glucose levels, and insulin resistance in obese and diabetic Wistar rats. Materials and methods: We used twenty male Wistar rats with obesity and obesity-induced diabetes and twenty healthy Wistar rats as a control group. Each of these groups was separated into two subgroups: one with a daily intraperitoneal application of WAY-163909 (1 mg/kg) and one without. During the study, body weight, blood glucose levels, and immunoreactive insulin were tracked. Results: A reduction of 5.5% (p < 0.05) in body weight was registered in the rat group with diabetes and obesity and 2.56% in the control group with a daily application of WAY-163909 (1 mg/kg) at the end of the study. Decreases of 35.4% in blood glucose levels at week four in the diabetic and obese rat group with a daily application of WAY-163909 (1 mg/kg) were registered. A reduction of insulin levels of 4.1% (p < 0.05) in the diabetic and obese rats group using WAY-163909 was also observed. Conclusion: In our study, using WAY-163909 (1 mg/kg) led to a reduction of blood glucose levels, immunoreactive insulin, and body weight.

5-HT2C Receptor Stimulation in Obesity Treatment: Orthosteric Agonists vs. Allosteric Modulators

Obesity is a substantial health and economic issue, and serotonin (5-hydroxytryptamine, 5-HT) is an important neurotransmitter system involved in the regulation of body weight. The 5-HT2C receptors (5-HT2CRs), one of 16 of the 5-HT receptor (5-HTRs) subtypes, play a significant role in food intake and body weight control. In this review, we focused on the 5-HTR agonists, such as fenfluramines, sibutramine, and lorcaserin, which act directly or indirectly at 5-HT2CRs and have been introduced into the clinic as antiobesity medications. Due to their unwanted effects, they were withdrawn from the market. The 5-HT2CR positive allosteric modulators (PAMs) can be potentially safer active drugs than 5-HT2CR agonists. However, more in vivo validation of PAMs is required to fully determine if these drugs will be effective in obesity prevention and antiobesity pharmacology treatment. Methodology strategy: This review focuses on the role of 5-HT2CR agonism in obesity treatment, such as food intake regulation and weight gain. The literature was reviewed according to the review topic. We searched the PubMed and Scopus databases and Multidisciplinary Digital Publishing Institute open-access scientific journals using the following keyword search strategy depending on the chapter phrases: (1) “5-HT2C receptor” AND “food intake”, and (2) “5-HT2C receptor” AND “obesity” AND “respective agonists”, and (3) “5-HT2C receptor” AND “PAM”. We included preclinical studies (only present the weight loss effects) and double-blind, placebo-controlled, randomized clinical trials published since the 1975s (mostly related to antiobesity treatment), and excluded the pay-walled articles. After the search process, the authors selected, carefully screened, and reviewed appropriate papers. In total, 136 articles were included in this review.

Obesity medication lorcaserin activates brainstem GLP-1 neurons to reduce food intake and augments GLP-1 receptor agonist induced appetite suppression

OBJECTIVE

Overweight and obesity are endemic in developed countries, with a substantial negative impact on human health. Medications developed to treat obesity include agonists for the G-protein coupled receptors glucagon-like peptide-1 (GLP-1R; e.g. liraglutide), serotonin 2C (5-HT2CR; e.g, lorcaserin), and melanocortin4 (MC4R) which reduce body weight primarily by suppressing food intake. However, the mechanisms underlying the therapeutic food intake suppressive effects are still being defined and were investigated here.

METHODS

We profiled PPG neurons in the nucleus of the solitary tract (PPGNTS) using single nucleus RNA sequencing (Nuc-Seq) and histochemistry. We next examined the requirement of PPGNTS neurons for obesity medication effects on food intake by virally ablating PPGNTS neurons. Finally, we assessed the effects on food intake of the combination of liraglutide and lorcaserin.

RESULTS

We found that 5-HT2CRs, but not GLP-1Rs or MC4Rs, were widespread in PPGNTS clusters and that lorcaserin significantly activated PPGNTS neurons. Accordingly, ablation of PPGNTS neurons prevented the reduction of food intake by lorcaserin but not MC4R agonist melanotan-II, demonstrating the functional significance of PPGNTS 5-HT2CR expression. Finally, the combination of lorcaserin with GLP-1R agonists liraglutide or exendin-4 produced greater food intake reduction as compared to either monotherapy.

CONCLUSIONS

These findings identify a necessary mechanism through which obesity medication lorcaserin produces its therapeutic benefit, namely brainstem PPGNTS neurons. Moreover, these data reveal a strategy to augment the therapeutic profile of the current frontline treatment for obesity, GLP-1R agonists, via coadministration with 5-HT2CR agonists.

A critical update on the leptin-melanocortin system

The discovery of leptin in 1994 was an "eureka moment" in the field of neurometabolism that provided new opportunities to better understand the central control of energy balance and glucose metabolism. Rapidly, a prevalent model in the field emerged that pro-opiomelanocortin (POMC) neurons were key in promoting leptin's anorexigenic effects and that the arcuate nucleus of the hypothalamus (ARC) was a key region for the regulation of energy homeostasis. While this model inspired many important discoveries, a growing body of literature indicates that this model is now outdated. In this review, we re-evaluate the hypothalamic leptin-melanocortin model in light of recent advances that directly tackle previous assumptions, with a particular focus on the ARC. We discuss how segregated and heterogeneous these neurons are, and examine how the development of modern approaches allowing spatiotemporal, intersectional, and chemogenetic manipulations of melanocortin neurons has allowed a better definition of the complexity of the leptin-melanocortin system. We review the importance of leptin in regulating glucose homeostasis, but not food intake, through direct actions on ARC POMC neurons. We further highlight how non-POMC, GABAergic neurons mediate leptin's direct effects on energy balance and influence POMC neurons.

The serotonergic system dysfunction in diabetes mellitus

Most peripheral serotonin (5-HT) is synthesized in enterochromaffin cells, and most circulating 5-HT is stored in platelets. As a monoamine, 5-HT has several functions in various non-neuronal and neuronal systems. In the central nervous system, it functions as a neurotransmitter to modulate feeding behavior and mood. Numerous clinical trials have focused on increasing 5-HT activation in the central nervous system, including those involving anti-obesity drugs currently in the market, although severe side effects on peripheral system can lead to the withdrawal of certain drugs. Recent studies have revealed that both the peripheral and central serotonergic systems play a vital role in diabetes and its complications. This review summarizes the roles of the serotonergic system in blood glucose regulation, diabetic macroangiopathy, diabetic peripheral neuropathy, and diabetic encephalopathy, indicating its potential clinical significance as a therapeutic target for the treatment of diabetes and its complications.

The Regulatory Role of the Central and Peripheral Serotonin Network on Feeding Signals in Metabolic Diseases

Central and peripheral serotonin (5-hydroxytryptamine, 5-HT) regulate feeding signals for energy metabolism. Disruption of central 5-HT signaling via 5-HT2C receptors (5-HT2CRs) induces leptin-independent hyperphagia in mice, leading to late-onset obesity, insulin resistance, and impaired glucose tolerance. 5-HT2CR mutant mice are more responsive than wild-type mice to a high-fat diet, exhibiting earlier-onset obesity and type 2 diabetes. High-fat and high-carbohydrate diets increase plasma 5-HT and fibroblast growth factor-21 (FGF21) levels. Plasma 5-HT and FGF21 levels are increased in rodents and humans with obesity, type 2 diabetes, and non-alcohol fatty liver diseases (NAFLD). The increases in plasma FGF21 and hepatic FGF21 expression precede hyperinsulinemia, insulin resistance, hyperglycemia, and weight gain in mice fed a high-fat diet. Nutritional, pharmacologic, or genetic inhibition of peripheral 5-HT synthesis via tryptophan hydroxylase 1 (Tph1) decreases hepatic FGF21 expression and plasma FGF21 levels in mice. Thus, perturbing central 5-HT signaling via 5-HT2CRs alters feeding behavior. Increased energy intake via a high-fat diet and/or high-carbohydrate diet can upregulate gut-derived 5-HT synthesis via Tph1. Peripheral 5-HT upregulates hepatic FGF21 expression and plasma FGF21 levels, leading to metabolic diseases such as obesity, insulin resistance, type 2 diabetes, and NAFLD. The 5-HT network in the brain–gut–liver axis regulates feeding signals and may be involved in the development and/or prevention of metabolic diseases.

Effects of the POMC System on Glucose Homeostasis and Potential Therapeutic Targets for Obesity and Diabetes

The hypothalamus is indispensable in energy regulation and glucose homeostasis. Previous studies have shown that pro-opiomelanocortin neurons receive both central neuronal signals, such as α-melanocyte-stimulating hormone, β-endorphin, and adrenocorticotropic hormone, as well as sense peripheral signals such as leptin, insulin, adiponectin, glucagon-like peptide-1, and glucagon-like peptide-2, affecting glucose metabolism through their corresponding receptors and related signaling pathways. Abnormalities in these processes can lead to obesity, type 2 diabetes, and other metabolic diseases. However, the mechanisms by which these signal molecules fulfill their role remain unclear. Consequently, in this review, we explored the mechanisms of these hormones and signals on obesity and diabetes to suggest potential therapeutic targets for obesity-related metabolic diseases. Multi-drug combination therapy for obesity and diabetes is becoming a trend and requires further research to help patients to better control their blood glucose and improve their prognosis.

Chronic Treatment With Psilocybin Decreases Changes in Body Weight in a Rodent Model of Obesity

BACKGROUND

There are currently relatively few effective pharmacological treatments for obesity, and existing ones may be associated with limiting side-effects. In the search for novel anti-obesity agents, drugs that modify central serotonergic systems have historically proven to be effective in promoting weight loss. Psilocin, which is rapidly metabolized from psilocybin, is an agonist at multiple serotonin receptors. In the present study we assessed the effects of psilocybin and a positive control (metformin) on changes in body weight in a rat model of obesity.

METHODS

Five groups of adult male rats were pre-conditioned with a cafeteria diet until obese (>600 g) and then treated with either psilocybin (0.1, 1, or 5 mg/kg, i.p.), metformin (300 mg/kg, p.o.) or vehicle control. Treatments were for 27 consecutive weekdays, and body weights and high calorie food intake were recorded daily. Fasting glucose levels were recorded after 11 days of treatment. At the end of treatment rats completed a glucose tolerance test, and multiple fat pads were dissected out to assess adiposity.

RESULTS

The medium dose psilocybin group had to be terminated from the study prematurely. Both the low and high dose psilocybin groups caused a significant decrease in changes in body weight compared to controls. The metformin group produced a greater decrease in change in body weight than either psilocybin groups or controls. Both high dose psilocybin and metformin decreased consumption of the high calorie diet, and exhibited decreased central adiposity.

CONCLUSION

Psilocybin demonstrated modest but significant effects on weight gain. Further study is recommended.

Lorcaserin Inhibit Glucose-Stimulated Insulin Secretion and Calcium Influx in Murine Pancreatic Islets

Lorcaserin is a serotonergic agonist specific to the 5-hydroxytryptamine 2c receptor (5-HT_2CR) that is FDA approved for the long-term management of obesity with or without at least one weight-related comorbidity. Lorcaserin can restrain patients' appetite and improve insulin sensitivity and hyperinsulinemia mainly through activating 5-HT_2CR in the hypothalamus. It is known that the mCPP, a kind of 5-HT_2CR agonist, decreases plasma insulin concentration in mice and previous research in our laboratory found that mCPP inhibited glucose-stimulated insulin secretion (GSIS) by activating 5-HT_2CR on the β cells. However, the effect of lorcaserin on GSIS of pancreatic β cell has not been studied so far. The present study found that 5-HT_2CR was expressed in both mouse pancreatic β cells and β-cell-derived MIN6 cells. Dose-dependent activation of 5-HT_2CR by lorcaserin suppressed GSIS and SB242084 or knockdown of 5-HT_2CR abolished lorcaserin's effect in vitro. Additionally, lorcaserin also suppressed GSIS in high-fat diet (HFD)-fed mice in dose-dependent manner. Lorcaserin did not change insulin synthesis ATP content, but lorcaserin decrease cytosolic free calcium level [(Ca²⁺)i] in MIN6 cells stimulated with glucose and also inhibit insulin secretion and (Ca²⁺)i in MIN6 treated with potassium chloride. Furthermore, stimulation with the L-type channel agonist, Bay K8644 did not restore GSIS in MIN6 exposed to lorcaserin. Lorcaserin inhibits the cAMP generation of MIN6 cells and pretreatment with the Gα i/o inhibitor pertussis toxin (PTX), abolished lorcaserin-induced suppression of GSIS in β cells, while membrane-permeable cAMP analogue db-cAMP had same effect as PTX. These date indicated lorcaserin coupled to PTX-sensitive Gα i/o proteins in β cells reduced intracellular cAMP level and Ca²⁺ influx, thereby causing GSIS dysfunction of β cell. These results highlight a novel signaling mechanism of lorcaserin and provide valuable insights into the further investigation of 5-HT_2CR functions in β-cell biology and it also provides guidance for the clinical application of lorcaserin.

Rolling out physical exercise and energy homeostasis: Focus on hypothalamic circuitries

Energy balance is the fine regulation of energy expenditure and energy intake. Negative energy balance causes body weight loss, while positive energy balance promotes weight gain. Modern societies offer a maladapted way of life, where easy access to palatable foods and the lack of opportunities to perform physical activity are considered the roots of the obesity pandemic. Physical exercise increases energy expenditure and, consequently, is supposed to promote weight loss. Paradoxically, physical exercise acutely drives anorexigenic-like effects, but the mechanisms are still poorly understood. Using an evolutionary background, this review aims to highlight the potential involvement of the melanocortin system and other hypothalamic neural circuitries regulating energy balance during and after physical exercise. The physiological significance of these changes will be explored, and possible signalling agents will be addressed. The knowledge discussed here might be important for clarifying obesity aetiology as well as new therapeutic approaches for body weight loss.

PERK in POMC neurons connects celastrol with metabolism

ER stress and activation of the unfolded protein response in the periphery as well as the central nervous system have been linked to various metabolic abnormalities. Chemically lowering protein kinase R–like ER kinase (PERK) activity within the hypothalamus leads to decreased food intake and body weight. However, the cell populations required in this response remain undefined. In the current study, we investigated the effects of proopiomelanocortin-specific (POMC-specific) PERK deficiency on energy balance and glucose metabolism. Male mice deficient for PERK in POMC neurons exhibited improvements in energy balance on a high-fat diet, showing decreased food intake and body weight, independent of changes in glucose and insulin tolerances. The plant-based inhibitor of PERK, celastrol, increases leptin sensitivity, resulting in decreased food intake and body weight in a murine model of diet-induced obesity (DIO). Our data extend these observations by demonstrating that celastrol-induced improvements in leptin sensitivity and energy balance were attenuated in mice with PERK deficiency in POMC neurons. Altogether, these data suggest that POMC-specific PERK deficiency in male mice confers protection against DIO, possibly providing a new therapeutic target for the treatment of diabetes and metabolic syndrome.

Barbadin Potentiates Long-Term Effects of Lorcaserin on POMC Neurons and Weight Loss

Obesity is a serious global health problem because of its increasing prevalence and comorbidities, but its treatments are limited. The serotonin 2C receptor (5-HT2CR), a G-protein-coupled receptor, activates proopiomelanocortin (POMC) neurons in the arcuate nucleus of hypothalamus (ARH) to reduce appetite and weight gain. However, several 5-HT analogs targeting this receptor, e.g., lorcaserin (Lor), suffer from diminished efficacy to reduce weight after prolonged administration. Here, we show that barbadin (Bar), a novel β-arrestin/β2-adaptin inhibitor, can prevent 5-HT2CR internalization in cells and potentiate long-term effects of Lor to reduce appetite and body weight in male mice. Mechanistically, we demonstrate that Bar co-treatment can effectively maintain the sensitivity of the 5-HT2CR in POMCARH neurons, despite prolonged Lor exposure, thereby allowing these neurons to be activated through opening the transient receptor potential cation (TRPC) channels. Thus, our results prove the concept that inhibition of 5-HT2CR desensitization can be a valid strategy to improve the long-term weight loss effects of Lor or other 5-HT2CR agonists, and also provide an intellectual framework to develop effective long-term management of weight by targeting 5-HT2CR desensitization.SIGNIFICANCE STATEMENT By demonstrating that the combination of barbadin (Bar) with a G-protein-coupled receptor (GPCR) agonist can provide prolonged weight-lowering benefits in a preclinical setting, our work should call for additional efforts to validate Bar as a safe and effective medicine or to use Bar as a lead compound to develop more suitable compounds for obesity treatment. These results prove the concept that inhibition of serotonin 2C receptor (5-HT2CR) desensitization can be a valid strategy to improve the long-term weight loss effects of lorcaserin (Lor) or other 5-HT2CR agonists. Since GPCRs represent a major category as therapeutic targets for various human diseases and desensitization of GPCRs is a common issue, our work may provide a conceptual framework to enhance effects of a broad range of GPCR medicines.

Rap1 in the VMH regulates glucose homeostasis

The hypothalamus is a critical regulator of glucose metabolism and is capable of correcting diabetes conditions independently of an effect on energy balance. The small GTPase Rap1 in the forebrain is implicated in high-fat diet–induced (HFD-induced) obesity and glucose imbalance. Here, we report that increasing Rap1 activity selectively in the medial hypothalamus elevated blood glucose without increasing the body weight of HFD-fed mice. In contrast, decreasing hypothalamic Rap1 activity protected mice from diet-induced hyperglycemia but did not prevent weight gain. The remarkable glycemic effect of Rap1 was reproduced when Rap1 was specifically deleted in steroidogenic factor-1–positive (SF-1–positive) neurons in the ventromedial hypothalamic nucleus (VMH) known to regulate glucose metabolism. While having no effect on body weight regardless of sex, diet, and age, Rap1 deficiency in the VMH SF1 neurons markedly lowered blood glucose and insulin levels, improved glucose and insulin tolerance, and protected mice against HFD-induced neural leptin resistance and peripheral insulin resistance at the cellular and whole-body levels. Last, acute pharmacological inhibition of brain exchange protein directly activated by cAMP 2, a direct activator of Rap1, corrected glucose imbalance in obese mouse models. Our findings uncover the primary role of VMH Rap1 in glycemic control and implicate Rap1 signaling as a potential target for therapeutic intervention in diabetes.

Pharmacotherapy of obesity: An update

Several pharmacological approaches to controlling body weight have been developed over the last decades, albeit with limited success. Currently available agents include centrally acting appetite suppressants and peripherally acting compounds. Efficacy and safety of these agents in the clinical setting require a difficult balance. Further strategies including multiagonists able to simultaneously target multiple actors involved in obesity initiation and expansion such as the glucagon receptor family are under investigation. The results of recent clinical trials are encouraging and highlight emerging compounds as potential game changers. In view of the rising prevalence of obesity and the associated burden of comorbidities worldwide, and compared with other areas of pharmacological intervention, we feel that the field of obesity has been affected by therapeutic inertia. Of note, obesity may also affect the response to concomitant medications such as low-dose aspirin. Lessons from withdrawn agents such as the cannabinoid receptor antagonist rimonabant include developing compounds with a more targeted action profile (i.e., central vs peripheral, or antagonist versus inverse agonist) as well as careful selection of patients based on individual risk factors. We anticipate that the expanding knowledge base and clinical testing will result in improved outcomes for patients with obesity in the near future.

Role of serotonin in body weight, insulin secretion and glycaemic control

Obesity and type 2 diabetes are key healthcare challenges of the 21st century. Subsequent to its discovery in 1948, serotonin (5-hydroxytryptamine; 5-HT) has emerged as a principal modulator of energy homeostasis and body weight, prompting it to be a target of weight loss medications (eg, fenfluramine, D-fenfluramine, fenfluramine-phentermine and sibutramine). The potential risk of off-target effects led to these medications being withdrawn from clinical use and spurred drug discovery into 5-HT receptor selective ligands. The serotonin 2C receptor (5-HT_2C R) is the primary receptor through which 5-HT impacts feeding and body weight and 5-HT_2C R agonist lorcaserin was released for obesity treatment in 2012. Obese patients with type 2 diabetes prescribed medications that produce weight loss commonly observe improvements in type 2 diabetes. However, recent research has provided compelling evidence that 5-HT_2C R agonists produce effects on blood glucose and insulin sensitivity independent of weight loss. As such, neuroactive 5-HT_2C R agonists are a potential new category of type 2 diabetes medications. 5-HT is also expressed within pancreatic β cells, is co-released with insulin and may have a role in modulating insulin secretion. This review highlights the latest advances in the function of 5-HT in body weight, insulin release and glycaemic control.

Whole-brain activation signatures of weight-lowering drugs

OBJECTIVE

The development of effective anti-obesity therapeutics relies heavily on the ability to target specific brain homeostatic and hedonic mechanisms controlling body weight. To obtain further insight into neurocircuits recruited by anti-obesity drug treatment, the present study aimed to determine whole-brain activation signatures of six different weight-lowering drug classes.

METHODS

Chow-fed C57BL/6J mice (n = 8 per group) received acute treatment with lorcaserin (7 mg/kg; i.p.), rimonabant (10 mg/kg; i.p.), bromocriptine (10 mg/kg; i.p.), sibutramine (10 mg/kg; p.o.), semaglutide (0.04 mg/kg; s.c.) or setmelanotide (4 mg/kg; s.c.). Brains were sampled two hours post-dosing and whole-brain neuronal activation patterns were analysed at single-cell resolution using c-Fos immunohistochemistry and automated quantitative three-dimensional (3D) imaging.

RESULTS

The whole-brain analysis comprised 308 atlas-defined mouse brain areas. To enable fast and efficient data mining, a web-based 3D imaging data viewer was developed. All weight-lowering drugs demonstrated brain-wide responses with notable similarities in c-Fos expression signatures. Overlapping c-Fos responses were detected in discrete homeostatic and non-homeostatic feeding centres located in the dorsal vagal complex and hypothalamus with concurrent activation of several limbic structures as well as the dopaminergic system.

CONCLUSIONS

Whole-brain c-Fos expression signatures of various weight-lowering drug classes point to a discrete set of brain regions and neurocircuits which could represent key neuroanatomical targets for future anti-obesity therapeutics.

Central 5-HTR2C in the Control of Metabolic Homeostasis

The 5-hydroxytryptamine 2C receptor (5-HTR2C) is a class G protein-coupled receptor (GPCR) enriched in the hypothalamus and the brain stem, where it has been shown to regulate energy homeostasis, including feeding and glucose metabolism. Accordingly, 5-HTR2C has been the target of several anti-obesity drugs, though the associated side effects greatly curbed their clinical applications. Dissecting the specific neural circuits of 5-HTR2C-expressing neurons and the detailed molecular pathways of 5-HTR2C signaling in metabolic regulation will help to develop better therapeutic strategies towards metabolic disorders. In this review, we introduced the regulatory role of 5-HTR2C in feeding behavior and glucose metabolism, with particular focus on the molecular pathways, neural network, and its interaction with other metabolic hormones, such as leptin, ghrelin, insulin, and estrogens. Moreover, the latest progress in the clinical research on 5-HTR2C agonists was also discussed.

Higher HbA1c levels associate with lower hippocampal serotonin transporter availability in non-diabetic adults with obesity

The current study aimed to investigate whether the in vivo availability of central serotonin reuptake transporters (5-HTT) is associated with plasma levels of glycosylated hemoglobin (HbA1c) in non-diabetic humans with obesity. 5-HTT availability was measured by using positron emission tomography (PET) imaging with the 5-HTT selective radiotracer [¹¹C]DASB in 23 non-diabetic individuals with obesity and 14 healthy, non-obesity controls. Parametric images of binding potential BP_ND were generated from the PET data and analyzed together with HbA1c levels by using volume of interest analysis for brain areas relevant to appetite control. Voxel-based morphometry (VBM) of individual magnetic resonance imaging data was further performed to correlate grey matter density (GMD) maps with HbA1c. We found significant negative correlations between HbA1c levels and BP_ND in right and left hippocampus in obesity (r = − 0.717, p < 0.001, and r = − 0.557, p = 0.006, respectively). VBM analyses revealed that higher HbA1c levels were associated with GMD in the right para-hippocampal area. Our results indicate that chronically high blood glucose levels may evoke changes in hippocampal 5-HTT levels that are in part tied to local microstructure.

The Role of Descending Pain Modulation in Chronic Primary Pain: Potential Application of Drugs Targeting Serotonergic System

Chronic primary pain (CPP) is a group of diseases with long-term pain and functional disorders but without structural or specific tissue pathologies. CPP is becoming a serious health problem in clinical practice due to the unknown cause of intractable pain and high cost of health care yet has not been satisfactorily addressed. During the past decades, a significant role for the descending pain modulation and alterations due to specific diseases of CPP has been emphasized. It has been widely established that central sensitization and alterations in neuroplasticity induced by the enhancement of descending pain facilitation and/or the impairment of descending pain inhibition can explain many chronic pain states including CPP. The descending serotonergic neurons in the raphe nuclei target receptors along the descending pain circuits and exert either pro- or antinociceptive effects in different pain conditions. In this review, we summarize the possible underlying descending pain regulation mechanisms in CPP and the role of serotonin, thus providing evidence for potential application of analgesic medications based on the serotonergic system in CPP patients.

The melanocortin pathway and control of appetite-progress and therapeutic implications

The initial discovery that ob/ob mice become obese because of a recessive mutation of the leptin gene has been crucial to discover the melanocortin pathway to control appetite. In the melanocortin pathway, the fed state is signaled by abundance of circulating hormones such as leptin and insulin, which bind to receptors expressed at the surface of pro-opiomelanocortin (POMC) neurons to promote processing of POMC to the mature hormone α-melanocyte-stimulating hormone (α-MSH). The α-MSH released by POMC neurons then signals to decrease energy intake by binding to melanocortin-4 receptor (MC4R) expressed by MC4R neurons to the paraventricular nucleus (PVN). Conversely, in the 'starved state' activity of agouti-related neuropeptide (AgRP) and of neuropeptide Y (NPY)-expressing neurons is increased by decreased levels of circulating leptin and insulin and by the orexigenic hormone ghrelin to promote food intake. This initial understanding of the melanocortin pathway has recently been implemented by the description of the complex neuronal circuit that controls the activity of POMC, AgRP/NPY and MC4R neurons and downstream signaling by these neurons. This review summarizes the progress done on the melanocortin pathway and describes how obesity alters this pathway to disrupt energy homeostasis. We also describe progress on how leptin and insulin receptors signal in POMC neurons, how MC4R signals and how altered expression and traffic of MC4R change the acute signaling and desensitization properties of the receptor. We also describe how the discovery of the melanocortin pathway has led to the use of melanocortin agonists to treat obesity derived from genetic disorders.

The Role of Anti-Obesity Medication in Prevention of Diabetes and Its Complications

Diabetes is prevalent in obese population, and obesity management is the first step in preventing diabetes. Traditionally, lifestyle modification including reduced-calorie diet, physical activity, and behavior intervention is the core of obesity management. However, pharmacotherapy is frequently required in addition to the lifestyle modification for effective reduction of body weight. There are five classes of anti-obesity medications approved by the U.S. Food and Drug Administration for chronic treatment used in obesity management. As the goal of obesity management is to prevent obesity-related comorbidities, clinical trials were conducted to evaluate the effect of anti-obesity medications on cardiovascular risk factors including hyperglycemia. Orlistat and liraglutide have been tested for their effect on diabetes prevention as a primary outcome. Cardiovascular safety studies were conducted for lorcaserin and liraglutide (as an anti-diabetic medication). In addition, there are many indirect evidences of the role of anti-obesity medications on diabetes prevention and its microvascular and macrovascular complications. This review focused on current evidences of anti-obesity medications related with diabetes, which is a major complication of obesity.

Lorcaserin and metabolic disease: weight-loss dependent and independent effects

OBJECTIVE

Weight management pharmacotherapies can improve metabolic diseases through weight-dependent and weight-independent effects. Lorcaserin is a selective 5-hydroxytryptamine 2C receptor agonist. The objective of this analysis is to quantify the relative contribution of weight loss to the treatment effects of lorcaserin 10 mg twice a day on key metabolic parameters.

METHODS

This retrospective analysis evaluated 6,897 patients with overweight or obesity (with or without diabetes mellitus) across three randomized, placebo-controlled, double-blind, 52-week clinical trials that evaluated lorcaserin 10 mg twice daily (BID; NCT00395135, NCT00603902, and NCT00603291); 509 patients from only one of the studies had type 2 diabetes mellitus. A mediation analysis was applied to help rank the relative contribution of weight loss to metabolic study outcomes.

RESULTS

According to this mediation analysis, lorcaserin 10 mg BID improved a spectrum of adiposopathic metabolic abnormalities with varying contributions attributable to weight loss. Improvements in waist circumference and blood pressure were almost exclusively attributable to weight loss. Less than 50% of the improvement in glucose parameters (fasting blood glucose and haemoglobin A1c) were attributable to weight loss.

CONCLUSIONS

Across Phase III clinical trials, lorcaserin 10 mg BID improved multiple cardiometabolic parameters through both weight-loss dependent and independent mechanisms.

Effect of lorcaserin on prevention and remission of type 2 diabetes in overweight and obese patients (CAMELLIA-TIMI 61): a randomised, placebo-controlled trial

BACKGROUND

There is a direct relationship between bodyweight and risk of diabetes. Lorcaserin, a selective serotonin 2C receptor agonist that suppresses appetite, has been shown to facilitate sustained weight loss in obese or overweight patients. We aimed to evaluate the long-term effects of lorcaserin on diabetes prevention and remission.

METHODS

In this randomised, double-blind, placebo-controlled trial done in eight countries, we recruited overweight or obese patients (body-mass index ≥27 kg/m²) with or at high risk for atherosclerotic vascular disease. Eligible patients were aged 40 years or older; patients at high risk for atherosclerotic vascular disease had to be aged 50 years or older with diabetes and at least one other risk factor. Patients were randomly assigned to receive either lorcaserin (10 mg twice daily) or matching placebo. Additionally, all patients had access to a standardised weight management programme based on lifestyle modification. The prespecified primary metabolic efficacy endpoint of time to incident diabetes was assessed in patients with prediabetes at baseline. The prespecified secondary outcomes for efficacy were incident diabetes in all patients without diabetes, achievement of normoglycaemia in patients with prediabetes, and change in glycated haemoglobin (HbA_1c) in patients with diabetes. Hypoglycaemia was a prespecified safety outcome. Analysis was by intention to treat, using Cox proportional hazard models for time-to-event analyses. This trial is registered with ClinicalTrials.gov, number NCT02019264.

FINDINGS

Between Feb 7, 2014, and Nov 20, 2015, 12 000 patients were randomly assigned to lorcaserin or placebo (6000 patients in each group) and followed up for a median of 3·3 years (IQR 3·0-3·5). At baseline, 6816 patients (56·8%) had diabetes, 3991 (33·3%) prediabetes, and 1193 (9·9%) normoglycaemia. At 1 year, patients treated with lorcaserin had a net weight loss beyond placebo of 2·6 kg (95% CI 2·3-2·9) for those with diabetes, 2·8 kg (2·5-3·2) for those with prediabetes, and 3·3 kg (2·6-4·0) for those with normoglycaemia (p<0·0001 for all analyses). Lorcaserin reduced the risk of incident diabetes by 19% in patients with prediabetes (172 [8·5%] of 2015 vs 204 [10·3%] of 1976; hazard ratio 0·81, 95% CI 0·66-0·99; p=0·038) and by 23% in patients without diabetes (174 [6·7%] of 2615 vs 215 [8·4%] of 2569; 0·77, 0·63-0·94; p=0·012). Lorcaserin resulted in a non-significant increase in the rate of achievement of normoglycaemia in patients with prediabetes (185 [9·2%] vs 151 [7·6%]; 1·20, 0·97-1·49; p=0·093). In patients with diabetes, lorcaserin resulted in a reduction of 0·33% (95% CI 0·29-0·38; p<0·0001) in HbA_1c compared with placebo at 1 year from a mean baseline of 53 mmol/mol (7·0%). In patients with diabetes at baseline, severe hypoglycaemia with serious complications was rare, but more common with lorcaserin (12 [0·4%] vs four [0·1%] events; p=0·054).

INTERPRETATION

Lorcaserin decreases risk for incident diabetes, induces remission of hyperglycaemia, and reduces the risk of microvascular complications in obese and overweight patients, supporting the role of lorcaserin as an adjunct to lifestyle modification for chronic management of weight and metabolic health.

FUNDING

Eisai.

Nucleus of the Solitary Tract Serotonin 5-HT2C Receptors Modulate Food Intake

To meet the challenge to human health posed by obesity, a better understanding of the regulation of feeding is essential. Medications targeting 5-hydroxytryptamine (5-HT; serotonin) 2C receptors (htr2c; 5-HT_2CR) improve obesity. Here we probed the functional significance of 5-HT_2CRs specifically within the brainstem nucleus of the solitary tract (5-HT_2CR^NTS) in feeding behavior. Selective activation of 5-HT_2CR^NTS decreased feeding and was sufficient to mediate acute food intake reductions elicited by the 5-HT_2CR agonist obesity medication lorcaserin. Similar to pro-opiomelanocortin neurons expressed within the hypothalamic arcuate nucleus (POMC^ARC), a subset of POMC^NTS neurons co-expressed 5-HT_2CRs and were activated by 5-HT_2CR agonists. Knockdown of POMC^NTS prevented the acute appetite-suppressive effect of lorcaserin, whereas POMC^ARC knockdown prevented the full anorectic effect. These data identify 5-HT_2CR^NTS as a sufficient subpopulation of 5-HT_2CRs in reducing food intake when activated and reveal that 5-HT_2CR agonist obesity medications require POMC within the NTS and ARC to reduce food intake.

Design and rationale for the Cardiovascular and Metabolic Effects of Lorcaserin in Overweight and Obese Patients-Thrombolysis in Myocardial Infarction 61 (CAMELLIA-TIMI 61) trial

OBJECTIVES

Lorcaserin, a selective serotonin 2C receptor agonist, is an effective pharmacologic weight-loss therapy that improves several cardiovascular risk factors. The long-term clinical cardiovascular and metabolic safety and efficacy in patients with elevated cardiovascular risk are unknown.

RESEARCH DESIGN AND METHODS

CAMELLIA-TIMI 61 (NCT02019264) is a randomized, double-blind, placebo-controlled, multinational clinical trial designed to evaluate the safety and efficacy of lorcaserin with regard to major adverse cardiovascular events and progression to diabetes in overweight or obese patients at high cardiovascular risk. Overweight or obese patients either with established cardiovascular disease or with diabetes and at least 1 other cardiovascular risk factor were randomized in a 1:1 ratio to lorcaserin 10 mg twice daily or matching placebo. The primary safety objective is to assess for noninferiority of lorcaserin for the composite end point of cardiovascular death, myocardial infarction, or stroke (major adverse cardiovascular event [MACE]) (with noninferiority defined as the upper bound of a 1-sided 97.5% CI excluding a hazard ratio of 1.4) compared with placebo assessed at an interim analysis with 460 adjudicated events. The efficacy objectives, assessed at study completion, will evaluate the superiority of lorcaserin for the primary composite end point of cardiovascular death, myocardial infarction, stroke, hospitalization for unstable angina, heart failure, or any coronary revascularization (MACE+) and the key secondary end point of conversion to diabetes. Recruitment began in January 2014 and was completed in November 2015 resulting in a total population of 12,000 patients. The trial is planned to continue until at least 1,401 adjudicated MACE+ events are accrued and the median treatment duration exceeds 2.5 years.

CONCLUSION

CAMELLIA-TIMI 61 is investigating the safety and efficacy of lorcaserin for MACEs and conversion to diabetes in overweight or obese patients with established cardiovascular disease or multiple cardiovascular risk factors.