Synergistic metabolic benefits of an exenatide analogue and cholecystokinin in diet-induced obese and leptin-deficient rodents

Discovery of novel glucagon-like peptide 1/cholecystokinin 1 receptor dual agonists

The combined use of gastrointestinal hormones for treating metabolic diseases is gaining increasing attention. The potential of developing novel dual agonists targeting both cholecystokinin 1 (CCK-1) receptor and glucagon-like peptide 1 (GLP-1) receptor to improve the treatment of type 2 diabetes and obesity have not been fully explored. In this investigation, we reported a series of novel GLP-1/CCK-1 receptor co-agonists constructed by linking the C-terminus of a GLP-1 receptor agonist (bullfrog GLP-1) to the N-terminus of a CCK-1 receptor selective agonist NN9056. In comprehensive in vitro assays, these co-agonists exhibited complete agonistic potency on GLP-1 and CCK-1 receptor. Remarkably, 1f displayed superior hypoglycemic and insulinotropic effects when compared to NN9056 and semaglutide. Evaluation in Kunming and diet-induced obesity (DIO) mice unveiled significant acute and enduring hypoglycemic effects of 1f. Administration of 1f to DIO mice resulted in substantial weight loss, normalized lipid metabolism, and enhanced glucose regulation. These preclinical observations strongly advocate for the therapeutic potential CCK-1 and GLP-1 pathways could be harnessed in a single fusion peptide, yielding a promising combination therapy strategy for treating metabolic disorders.

Cholecystokinin (CCK): a neuromodulator with therapeutic potential in Alzheimer's and Parkinson's disease

Cholecystokinin (CCK) is a neuropeptide modulating digestion, glucose levels, neurotransmitters and memory. Recent studies suggest that CCK exhibits neuroprotective effects in Alzheimer's disease (AD) and Parkinson's disease (PD). Thus, we review the physiological function and therapeutic potential of CCK. The neuropeptide facilitates hippocampal glutamate release and gates GABAergic basket cell activity, which improves declarative memory acquisition, but inhibits consolidation. Cortical CCK alters recognition memory and enhances audio-visual processing. By stimulating CCK-1 receptors (CCK-1Rs), sulphated CCK-8 elicits dopamine release in the substantia nigra and striatum. In the mesolimbic pathway, CCK release is triggered by dopamine and terminates reward responses via CCK-2Rs. Importantly, activation of hippocampal and nigral CCK-2Rs is neuroprotective by evoking AMPK activation, expression of mitochondrial fusion modulators and autophagy. Other benefits include vagus nerve/CCK-1R-mediated expression of brain-derived neurotrophic factor, intestinal protection and suppression of inflammation. We also discuss caveats and the therapeutic combination of CCK with other peptide hormones.

Advances in obesity pharmacotherapy; learning from metabolic surgery and beyond

Currently, metabolic surgery (MS) constitutes the most effective means for durable weight loss of clinically meaningful magnitude, type 2 diabetes remission and resolution of non-alcoholic steatohepatitis, as well as other obesity-related comorbidities. Accumulating evidence on the mechanisms through which MS exerts its actions has highlighted the altered secretion of hormonally active peptides of intestinal origin with biological actions crucial to energy metabolism as key drivers of MS clinical effects. The initial success of glucagon-like peptide-1 (GLP-1) receptor agonists regarding weight loss and metabolic amelioration have been followed by the development of unimolecular dual and triple polyagonists, additionally exploiting the effects of glucagon and/or glucose-dependent insulinotropic polypeptide (GIP) which achieves a magnitude of weight loss approximating that of common MS operations. Through the implementation of such therapies, the feasibility of a "medical bypass", namely the replication of the clinical effects of MS through non-surgical interventions may be foreseeable in the near future. Apart from weight loss, this approach ought to be put to the test also regarding other clinical outcomes, such as liver steatosis and steatohepatitis, cardiovascular disease, and overall prognosis, on which MS has a robustly demonstrated impact. Besides, a medical bypass as an alternative, salvage, or combination strategy to MS may promote precision medicine in obesity therapeutics.

Poly-Agonist Pharmacotherapies for Metabolic Diseases: Hopes and New Challenges

The use of glucagon-like peptide-1 (GLP-1) receptor-based multi-agonists in the treatment of type 2 diabetes and obesity holds great promise for improving glycaemic control and weight management. Unimolecular dual and triple agonists targeting multiple gut hormone-related pathways are currently in clinical trials, with recent evidence supporting their efficacy. However, significant knowledge gaps remain regarding the biological mechanisms and potential adverse effects associated with these multi-target agents. The mechanisms underlying the therapeutic efficacy of GLP-1 receptor-based multi-agonists remain somewhat mysterious, and hidden threats may be associated with the use of gut hormone-based polyagonists. In this review, we provide a critical analysis of the benefits and risks associated with the use of these new drugs in the management of obesity and diabetes, while also exploring new potential applications of GLP-1-based pharmacology beyond the field of metabolic disease.

Sustained metabolic benefits of ΔTRTX-Ac1, a tarantula venom-derived peptide, when administered together with exenatide in high-fat fed mice

AIM

The aim of the present study was to assess the long-term therapeutic efficacy of a recently discovered 28 amino acid peptide, Δ-theraphotoxin-Ac1 (Δ-TRTX-Ac1), originally isolated from venom of the Aphonopelma chalcodes tarantula. Δ-TRTX-Ac has previously been shown to improve pancreatic beta-cell function and suppress appetite.

MATERIALS AND METHODS

Δ-TRTX-Ac1 was administered twice daily in high-fat fed (HFF) mice with streptozotocin (STZ)-induced insulin deficiency, namely HFF/STZ mice, for 28 days both alone and in combination with the venom-derived glucagon-like peptide-1 (GLP-1) mimetic, exenatide.

RESULTS

Initial pharmacokinetic profiling of ΔTRTX-Ac1 revealed a plasma half-life of 2 h in mice, with ΔTRTX-Ac1 also evidenced in the pancreas 12 h post-injection. Accordingly, HFF-STZ mice received twice-daily injections of Δ-TRTX-Ac1, exenatide or a combination of both peptides for 28 days. As anticipated, HFF/STZ mice presented with hyperglycaemia, impaired glucose tolerance, decreased plasma and pancreatic insulin and disturbed pancreatic islet morphology. Administration of ΔTRTX-Ac1 reduced body weight, improved glucose tolerance and augmented pancreatic insulin content while decreasing glucagon content. Exenatide had similar benefits on body weight and pancreatic hormone content while also reducing circulating glucose. ΔTRTX-Ac1 decreased energy expenditure on day 28 whereas exenatide had no impact. All treatment regimens restored pancreatic islet and beta-cell area towards lean control levels, which was linked to significantly elevated beta-cell proliferation rates. In terms of benefits of combined ΔTRTX-Ac1 and exenatide treatment over individual agents, there was augmentation of glucose tolerance and ambulatory activity with combination therapy, and these mice presented with increased pancreatic glucagon.

CONCLUSION

These data highlight the therapeutic promise of ΔTRTX-Ac1 for diabetes, with suggestion that benefits could be enhanced through combined administration with exenatide.

Obesity and its comorbidities, current treatment options and future perspectives: Challenging bariatric surgery?

Obesity and its comorbidities, including type 2 diabetes mellitus, cardiovascular disease, heart failure and non-alcoholic liver disease are a major health and economic burden with steadily increasing numbers worldwide. The need for effective pharmacological treatment options is strong, but, until recently, only few drugs have proven sufficient efficacy and safety. This article provides a comprehensive overview of obesity and its comorbidities, with a special focus on organ-specific pathomechanisms. Bariatric surgery as the so far most-effective therapeutic strategy, current pharmacological treatment options and future treatment strategies will be discussed. An increasing knowledge about the gut-brain axis and especially the identification and physiology of incretins unfolds a high number of potential drug candidates with impressive weight-reducing potential. Future multi-modal therapeutic concepts in obesity treatment may surpass the effectivity of bariatric surgery not only with regard to weight loss, but also to associated comorbidities.

Designer GLP1 poly-agonist peptides in the management of diabesity

INTRODUCTION

To date, the 21^st Century has witnessed key developments in the management of diabesity (a conflation of obesity and Type 2 Diabetes Mellitus [T2D]), including Glucagon Like Peptide 1 (GLP1) receptor agonist therapies, and recently the 'designer' GLP1 Poly-agonist Peptides (GLP1PPs).

AREAS COVERED

A PubMed search of published data on the GLP1PP class of therapies was conducted. The gut-brain axis forms complex multi-directional interlinks that include autonomic nervous signaling, components of the gut microbiota (including metabolic by-products and gram-negative cell wall components [e.g. endotoxinaemia]), and incretin hormones that are secreted from the gut in response to the ingestion of nutrients. The development of dual-incretin agonist therapies includes combinations of the GLP1 peptide with Glucose-dependent Insulinotropic Polypeptide (GIP), Glucagon (Gcg), Cholecystokinin (CCK), Peptide YY (PYY), and Glucagon-Like Peptide 2 (GLP2). Triple incretin agonist therapies are also under development.

EXPERT OPINION

At the dawn of a new era in the therapeutic management of diabesity, the designer GLP1PP class holds great promise, with each novel combination building on a preexisting palimpsest of clinical data and insights. Future innovations of the GLP1PP class will likely enable medically induced weight loss and glycemic control in diabesity to rival or even out-perform those resulting from bariatric surgery.

The administration of Exendin-4 and CCK affects food intake differentially in female and male rats tested on an alternate day fasting paradigm

Alternate day fasting (ADF) which involves the repetition of a 2-day cycle of a day of free access to food followed by a day of limited or no access to food, is an effective dietary intervention for weight loss in both humans and rats. We have previously reported that when presented with a high energy (HE) and standard chow diet, rats maintained on an ADF schedule displayed decreased HE diet preference compared to controls. Both male and female ADF rats increased overall intake of chow. However, this increase was driven by both meal size and meal number for males and only number of meals for females. Administration of cholecystokinin (CCK) or the glucagon-like peptide 1 (GLP-1) receptor agonist Exendin-4 (Ex-4) reduces food intake. It appears that CCK decreases food intake primarily through satiety signals whereas GLP-1 signaling may reduce intake by satiety and reward cues. Here, female and male rats were administered (i.p.) saline, 3.0 µg/kg Ex-4 (3 h before test), 3.0 µg/kg CCK (15 min before test) or a combination of both. Next, all rats were presented 23-h access to both HE diet and chow following food-restriction (ADF) or free access to chow (CON). Compared to saline-control sessions, administration of the combination of Ex-4 and CCK, but not Ex-4 or CCK alone, resulted in a decrease in both HE and chow intake early in the session for male ADF rats but the combination primarily decreased chow diet intake early in the session for female ADF rats. Thus, it appears that under these energy homeostatic conditions, administration of Ex-4 or CCK alone does not affect intake in ADF rats, but the combination produces decreases in feeding that are more than the sum of their individual effects. These findings support a role for the combination of GLP-1 and CCK signaling in the changes in diet preference induced by an alternate day fasting paradigm differentially in female and male rats.

A GLP-1/glucagon/CCK-2 receptors tri-agonist provides new therapy for obesity and diabetes

BACKGROUND AND PURPOSE

Glucagon-like peptide-1 receptor (GLP-1R) and glucagon receptor (GCGR) dual agonists have exerted promising therapeutic effects for the treatment of obesity and diabetes in clinical development. Moreover, GLP-1R and cholecystokinin 2 receptor (CCK-2R) dual agonists have been shown to restore pancreas function and improve glycemic control in many preclinical studies. In the present study, we describe for the first time that the beneficial effects of GLP-1R/GCGR and GLP-1R/CCK-2R dual agonists can be integrated into one peptide, resulting in significant anti-diabetes and anti-obesity effectiveness.

EXPERIMENTAL APPROACH

The in vitro potency of a novel GLP-1R/GCGR/CCK-2R tri-agonist (xGLP/GCG/gastrin) against GLP-1R, GCGR, CCK-1R and CCK-2R was determined on cells expressing the corresponding receptors by cAMP accumulation or ERK1/2 phosphorylation assays. The in vivo anti-diabetes and anti-obesity effects of xGLP/GCG/gastrin were studied in both db/db and diet induced obesity (DIO) mice.

KEY RESULTS

xGLP/GCG/gastrin was a potent and selective GLP-1R, GCGR, and CCK-2R tri-agonist. In DIO mice, the metabolic benefits of xGLP-1/GCG/gastrin such as reduction of body weight and hepatic lipid contents were significantly better than those of ZP3022 (GLP-1R/CCK-2R dual agonist) and liraglutide. In the short term study in db/db mice, xGLP/GCG/gastrin treatment exerted considerable effects on increasing islet numbers, islet areas, and insulin content. In the long-term treatment study in db/db mice, xGLP-1/GCG/gastrin displayed a significantly sustained improvement in glucose tolerance and glucose control compared with those of liraglutide, ZP3022, cotadutide (GLP-1R/GCGR dual agonist), and xGLP/GCG-15.

CONCLUSIONS AND IMPLICATIONS

These results demonstrate the therapeutic promise of xGLP-1/GCG/gastrin for obesity and diabetes.

Vagal afferent cholecystokinin receptor activation is required for glucagon-like peptide-1-induced satiation

Peripheral glucagon-like peptide-1 (GLP-1) and cholecystokinin (CCK) are secreted from enteroendocrine cells, and their plasma concentrations increase in response to eating. While the satiating effect of gut-derived CCK on food-intake control is well documented, the effect of peripheral GLP-1 is less clear. There is evidence that native GLP-1 can inhibit food intake only in the fed state but not in the fasting state. We therefore hypothesized that other gut peptides released during a meal might influence the subsequent effect of endogenous GLP-1 and investigated whether CCK could do so. We found that intraperitoneal injection of CCK in food-restricted mice inhibited food intake during the first 30-minute segment of a 1-hour session of ad libitum chow intake and that mice compensated by increasing their intake during the second half of the session. Importantly, this compensatory behaviour was abolished by an intraperitoneal injection of GLP-1 administered following an intraperitoneal injection of CCK and prior to the 1-hour session. In vivo activation of the free fatty acid 1 (FFA1) receptor with orally administered TAK875 increased plasma CCK concentration and, consistent with the effect of exogenous CCK, we found that prior oral administration of TAK875 increased the eating inhibitory effect of peripherally administered GLP-1. To examine the role of the vagus nerve in this effect, we utilized a saporin-based lesioning procedure to selectively ablate the CCK receptor-expressing gastrointestinal vagal afferent neurones (VANs). We found that the combined anorectic effect of TAK875 and GLP-1 was significantly attenuated in the absence of CCK receptor expressing VANs. Taken together, our results indicate that endogenous CCK interacts with GLP-1 to promote satiation and that activation of the FFA1 receptor can initiate this interaction by stimulating the release of CCK.

Targeting the Enteroendocrine System for Treatment of Obesity

Mimetics of the anorexigenic gut hormone glucagon-like peptide 1 (GLP-1) were originally developed as insulinotropic anti-diabetic drugs but also evoke significant weight loss, leading to their recent approval as obesity therapeutics. Co-activation of receptors for GLP-1 and other gut hormones which reduce food intake - peptide YY (PYY_3-36), cholecystokinin (CCK) and glucose-dependent insulinotropic peptide (GIP) - is now being explored clinically to enhance efficacy. An alternative approach involves pharmacologically stimulating endogenous secretion of these hormones from enteroendocrine cells (EECs) to recapitulate the metabolic consequences of bariatric surgery, where highly elevated postprandial levels of GLP-1 and PYY_3-36 are thought to contribute to improved glycaemia and weight loss.

Anti-obesity drug discovery: advances and challenges

Enormous progress has been made in the last half-century in the management of diseases closely integrated with excess body weight, such as hypertension, adult-onset diabetes and elevated cholesterol. However, the treatment of obesity itself has proven largely resistant to therapy, with anti-obesity medications (AOMs) often delivering insufficient efficacy and dubious safety. Here, we provide an overview of the history of AOM development, focusing on lessons learned and ongoing obstacles. Recent advances, including increased understanding of the molecular gut-brain communication, are inspiring the pursuit of next-generation AOMs that appear capable of safely achieving sizeable and sustained body weight loss.

Structures of the human cholecystokinin receptors bound to agonists and antagonists

Cholecystokinin receptors, CCK_AR and CCK_BR, are important neurointestinal peptide hormone receptors and play a vital role in food intake and appetite regulation. Here, we report three crystal structures of the human CCK_AR in complex with different ligands, including one peptide agonist and two small-molecule antagonists, as well as two cryo-electron microscopy structures of CCK_BR-gastrin in complex with G_i2 and G_q, respectively. These structures reveal the recognition pattern of different ligand types and the molecular basis of peptide selectivity in the cholecystokinin receptor family. By comparing receptor structures in different conformational states, a stepwise activation process of cholecystokinin receptors is proposed. Combined with pharmacological data, our results provide atomic details for differential ligand recognition and receptor activation mechanisms. These insights will facilitate the discovery of potential therapeutics targeting cholecystokinin receptors.

The critical role of CCK in the regulation of food intake and diet-induced obesity

In 1973, Gibbs, Young, and Smith showed that exogenous cholecystokinin (CCK) administration reduces food intake in rats. This initial report has led to thousands of studies investigating the physiological role of CCK in regulating feeding behavior. CCK is released from enteroendocrine I cells present along the gastrointestinal (GI) tract. CCK binding to its receptor CCK1R leads to vagal afferent activation providing post-ingestive feedback to the hindbrain. Vagal afferent neurons' (VAN) sensitivity to CCK is modulated by energy status while CCK signaling regulates gene expression of other feeding related signals and receptors expressed by VAN. In addition to its satiation effects, CCK acts all along the GI tract to optimize digestion and nutrient absorption. Diet-induced obesity (DIO) is characterized by reduced sensitivity to CCK and every part of the CCK system is negatively affected by chronic intake of energy-dense foods. EEC have recently been shown to adapt to diet, CCK1R is affected by dietary fats consumption, and the VAN phenotypic flexibility is lost in DIO. Altered endocannabinoid tone, changes in gut microbiota composition, and chronic inflammation are currently being explored as potential mechanisms for diet driven loss in CCK signaling. This review discusses our current understanding of how CCK controls food intake in conditions of leanness and how control is lost in chronic energy excess and obesity, potentially perpetuating excessive intake.

Synergistic Treatment of Obesity via Locally Promoting Beige Adipogenesis and Antioxidative Defense in Adipose Tissues

Obesity is a primary risk factor for type 2 diabetes, cardiovascular diseases, cancer, and other chronic diseases. Current antiobesity medications need frequent administration and show limited efficacy with severe side effects. Herein, browning agent rosiglitazone (Rsg) and antioxidant manganese tetroxide nanoparticles (MnNPs, around 250 nm) are integrated into electrospun short fibers (SF@Rsg-Mn) with a 1.5 μm width and a 20 μm length. Upon injection into inguinal adipose tissues, SF@Rsg-Mn are well retained in the local depots to sustainably release Rsg in 30 days for adipose tissue browning, while MnNPs on the fiber surface continuously scavenge adipose reactive oxygen species (ROS) for an extended period of time. Synergistic inhibition of fat accumulation through ROS scavenging and white adipocyte browning has been demonstrated for the first time, and the optimal synergistic ratio of Rsg and MnNPs is determined to be 1/14 via combination index examination. SF@Rsg-Mn inhibit lipid accumulation through downregulation of adipogenic gene PPARγ while promoting energy expenditure through upregulation of brown-specific gene UCP1 and mitochondrial function gene COX7A1. In a diet-induced obesity mouse model, a single injection of SF@Rsg-Mn into inguinal adipose tissues has accomplished a synergistic effect on body weight loss, fat reduction, glucose, and lipid metabolic improvement while minimizing adverse effects on other tissues, thereby paving the way to efficacious, safe, and practical treatment of obesity.

Behavioural and neurochemical mechanisms underpinning the feeding-suppressive effect of GLP-1/CCK combinatorial therapy

OBJECTIVES

Combinatorial therapies are under intense investigation to develop more efficient anti-obesity drugs; however, little is known about how they act in the brain to produce enhanced anorexia and weight loss. The goal of this study was to identify the brain sites and neuronal populations engaged during the co-administration of GLP-1R and CCK1R agonists, an efficient combination therapy in obese rodents.

METHODS

We measured acute and long-term feeding and body weight responses and neuronal activation patterns throughout the neuraxis and in specific neuronal subsets in response to GLP-1R and CCK1R agonists administered alone or in combination in lean and high-fat diet fed mice. We used PhosphoTRAP to obtain unbiased molecular markers for neuronal populations selectively activated by the combination of the two agonists.

RESULTS

The initial anorectic response to GLP-1R and CCK1R co-agonism was mediated by a reduction in meal size, but over a few hours, a reduction in meal number accounted for the sustained feeding suppressive effects. The nucleus of the solitary tract (NTS) is one of the few brain sites where GLP-1R and CCK1R signalling interact to produce enhanced neuronal activation. None of the previously categorised NTS neuronal subpopulations relevant to feeding behaviour were implicated in this increased activation. However, we identified NTS/AP Calcrl+ neurons as treatment targets.

CONCLUSIONS

Collectively, these studies indicated that circuit-level integration of GLP-1R and CCK1R co-agonism in discrete brain nuclei including the NTS produces enhanced rapid and sustained appetite suppression and weight loss.

Benefits of Sustained Upregulated Unimolecular GLP-1 and CCK Receptor Signalling in Obesity-Diabetes

Combined activation of GLP-1 and CCK1 receptors has potential to synergistically augment the appetite-suppressive and glucose homeostatic actions of the individual parent peptides. In the current study, pancreatic beta-cell benefits of combined GLP-1 and CCK1 receptor upregulation were established, before characterising bioactivity and antidiabetic efficacy of an acylated dual-acting GLP-1/CCK hybrid peptide, namely [Lys¹²Pal]Ex-4/CCK. Both exendin-4 and CCK exhibited (p<0.001) proliferative and anti-apoptotic effects in BRIN BD11 beta-cells. Proliferative benefits were significantly (p<0.01) augmented by combined peptide treatment when compared to either parent peptide alone. These effects were linked to increases (p<0.001) in GLUT2 and glucokinase beta-cell gene expression, with decreased (p<0.05-p<0.001) expression of NFκB and BAX. [Lys¹²Pal]Ex-4/CCK exhibited prominent insulinotropic actions in vitro, coupled with beneficial (p<0.001) satiety and glucose homeostatic effects in the mice, with bioactivity evident 24 h after administration. Following twice daily injection of [Lys¹²Pal]Ex-4/CCK for 28 days in diabetic high fat fed (HFF) mice with streptozotocin (STZ)-induced compromised beta-cells, there were clear reductions (p<0.05-p<0.001) in energy intake and body weight. Circulating glucose was returned to lean control concentrations, with associated increases (p<0.001) in plasma and pancreatic insulin levels. Glucose tolerance and insulin secretory responsiveness were significantly (p<0.05-p<0.001) improved by hybrid peptide therapy. In keeping with this, evaluation of pancreatic histology revealed restoration of normal islet alpha- to beta-cell ratios and reduction (p<0.01) in centralised islet glucagon staining. Improvements in pancreatic islet morphology were associated with increased (p<0.05) proliferation and reduced (p<0.001) apoptosis of beta-cells. Together, these data highlight the effectiveness of sustained dual GLP-1 and CCK1 receptor activation by [Lys¹²Pal]Ex-4/CCK for the treatment of obesity-related diabetes.

Roles of Cholecystokinin in the Nutritional Continuum. Physiology and Potential Therapeutics

Cholecystokinin is a gastrointestinal peptide hormone with important roles in metabolic physiology and the maintenance of normal nutritional status, as well as potential roles in the prevention and management of obesity, currently one of the dominant causes of direct or indirect morbidity and mortality. In this review, we discuss the roles of this hormone and its receptors in maintaining nutritional homeostasis, with a particular focus on appetite control. Targeting this action led to the development of full agonists of the type 1 cholecystokinin receptor that have so far failed in clinical trials for obesity. The possible reasons for clinical failure are discussed, along with alternative pharmacologic strategies to target this receptor for prevention and management of obesity, including development of biased agonists and allosteric modulators. Cellular cholesterol is a natural modulator of the type 1 cholecystokinin receptor, with elevated levels disrupting normal stimulus-activity coupling. The molecular basis for this is discussed, along with strategies to overcome this challenge with a corrective positive allosteric modulator. There remains substantial scope for development of drugs to target the type 1 cholecystokinin receptor with these new pharmacologic strategies and such drugs may provide new approaches for treatment of obesity.

Stapled and Xenopus Glucagon-Like Peptide 1 (GLP-1)-Based Dual GLP-1/Gastrin Receptor Agonists with Improved Metabolic Benefits in Rodent Models of Obesity and Diabetes

Diabetes is characterized by pancreas dysfunction and is commonly associated with obesity. Hypoglycemic agents capable of improving β-cell function and reducing body weight therefore are gaining increasing interest. Though glucagon-like peptide 1 receptor (GLP-1R)/cholecystokinin 2 receptor (CCK-2R) dual agonist ZP3022 potently increases β-cell mass and improves glycemic control in diabetic db/db mice, the in vivo half-life (t_1/2) is short, and its body weight reducing activity is limited. Here, we report the discovery of a series of novel GLP-1R/CCK-2R dual agonists. Starting from Xenopus GLP-1, dual cysteine mutation was conducted followed by covalent side chain stapling and albumin binder incorporation, resulting in a stabilized secondary structure, increased agonist potency, and improved stability. Further C-terminal conjugation of gastrin-6 generated GLP-1R/CCK-2R dual agonists, among which 6a and 6b showed higher stability and hypoglycemic activity than liraglutide and ZP3022. Desirably, 6a and 6b exhibited prominent metabolic benefits in diet-induced obesity mice without causing nausea responses and exerted considerable effects on β-cell restoration in db/db mice. These preclinical studies suggest the potential role of GLP-1R/CCK-2R dual agonists as effective agents for treating diabetes and related metabolic disorders.

Glucagon-like peptide-1 receptor co-agonists for treating metabolic disease

Background

Glucagon-like peptide-1 receptor (GLP-1R) agonists are approved to treat type 2 diabetes and obesity. They elicit robust improvements in glycemic control and weight loss, combined with cardioprotection in individuals at risk of or with pre-existing cardiovascular disease. These attributes make GLP-1 a preferred partner for next-generation therapies exhibiting improved efficacy yet retaining safety to treat diabetes, obesity, non-alcoholic steatohepatitis, and related cardiometabolic disorders. The available clinical data demonstrate that the best GLP-1R agonists are not yet competitive with bariatric surgery, emphasizing the need to further improve the efficacy of current medical therapy.

Scope of review

In this article, we discuss data highlighting the physiological and pharmacological attributes of potential peptide and non-peptide partners, exemplified by amylin, glucose-dependent insulinotropic polypeptide (GIP), and steroid hormones. We review the progress, limitations, and future considerations for translating findings from preclinical experiments to competitive efficacy and safety in humans with type 2 diabetes and obesity.

Major conclusions

Multiple co-agonist combinations exhibit promising clinical efficacy, notably tirzepatide and investigational amylin combinations. Simultaneously, increasing doses of GLP-1R agonists such as semaglutide produces substantial weight loss, raising the bar for the development of new unimolecular co-agonists. Collectively, the available data suggest that new co-agonists with robust efficacy should prove superior to GLP-1R agonists alone to treat metabolic disorders.

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GLP-1 is a preferred partner for co-agonist development.

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Co-agonist combinations must exhibit improved weight loss beyond GLP-1 alone.

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Unimolecular coagonists must exhibit retained or improved cardioprotection.

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Obesity represents an optimal condition for the development of new GLP-1 co-agonists.

Hindbrain melanocortin 3/4 receptors modulate the food intake and body weight suppressive effects of the GLP-1 receptor agonist, liraglutide

Simultaneously targeting multiple energy balance control systems is a promising direction for the development of obesity pharmacotherapies. Here, we explore the interaction between the GLP-1 and melanocortin system within the dorsal vagal complex (DVC) of the caudal brainstem. Using a pharmacological approach, we demonstrate that the full anorectic potential of liraglutide, an FDA-approved GLP-1 analog for the treatment of obesity, requires DVC melanocortin 3/4 receptor (MC3/4R) signaling. Specifically, the food intake and body weight suppressive effects of liraglutide were attenuated by DVC administration of the MC3/4R antagonist SHU9119. In contrast, the anorectic effects of liraglutide were enhanced by combined activation of DVC MC3/4Rs using the agonist MTII. Our findings highlight the modulation of liraglutide-induced anorexia by DVC MC3/4R signaling, thereby suggesting a site of action at which two important energy balance control systems interact.

Multiagonist Unimolecular Peptides for Obesity and Type 2 Diabetes: Current Advances and Future Directions

The ever-increasing prevalence of obesity and Type 2 diabetes has necessitated the development of newer and more effective approaches for achieving efficient glycemic control and weight loss. Conventional treatment methods often result in weight gain, further deteriorating the already impaired metabolic control in people with obesity/Type 2 diabetes. Alleviation of obesity and diabetes achieved after bariatric surgeries highlight the therapeutic importance of gut-brain axis and entails development of more patient-friendly approaches replicating the positive metabolic effects of bariatric surgery. Given the potential involvement of several gut hormones in the success of bariatric surgery, the therapeutic importance of synergistic interaction between these hormones for improved metabolism cannot be ignored. Many unimolecular multiagonist peptides are in preclinical and clinical trials as they maximize the combinatorial metabolic efficacy by concurrent activation of multiple gut hormone receptors. This review summarizes the ongoing developments of multiagonist peptides as novel therapeutic approaches against obesity-diabetes.

Gut Peptide Agonism in the Treatment of Obesity and Diabetes

Obesity is a global healthcare challenge that gives rise to devastating diseases such as the metabolic syndrome, type-2 diabetes (T2D), and a variety of cardiovascular diseases. The escalating prevalence of obesity has led to an increased interest in pharmacological options to counteract excess weight gain. Gastrointestinal hormones such as glucagon, amylin, and glucagon-like peptide-1 (GLP-1) are well recognized for influencing food intake and satiety, but the therapeutic potential of these native peptides is overall limited by a short half-life and an often dose-dependent appearance of unwanted effects. Recent clinical success of chemically optimized GLP-1 mimetics with improved pharmacokinetics and sustained action has propelled pharmacological interest in using bioengineered gut hormones to treat obesity and diabetes. In this article, we summarize the basic biology and signaling mechanisms of selected gut peptides and discuss how they regulate systemic energy and glucose metabolism. Subsequently, we focus on the design and evaluation of unimolecular drugs that combine the beneficial effects of selected gut hormones into a single entity to optimize the beneficial impact on systems metabolism. © 2020 American Physiological Society. Compr Physiol 10:99-124, 2020.

Premises for Cholecystokinin and Gastrin Peptides in Diabetes Therapy

Gastrin and cholecystokinin (CCK) are classical gastrointestinal peptide hormones. Their biogenesis, structures, and intestinal secretory patterns are well-known with the striking feature that their receptor-bound 'active sites' are highly homologous and that this structure is conserved for more than 500 million years during evolution. Consequently, gastrin and CCK are agonists for the same receptor (the CCK2 receptor). But in addition, tyrosyl O-sulphated CCK are also bound to the specific CCK1 receptor. The receptors are widely expressed in the body, including pancreatic islet-cell membranes. Moreover, CCK and gastrin peptides are at various developmental stages and diseases expressed in pancreatic islets; also in human islets. Accordingly, bioactive gastrin and CCK peptides stimulate islet-cell growth as well as insulin and glucagon secretion. In view of their insulinotropic effects, gastrin and CCK peptides have come into focus as drug targets, either alone or in combination with other insulinotropic gut hormones or growth factors. So far, modified CCK and gastrin peptides are being examined as potential drugs for therapy of type 1 as well as type 2 diabetes mellitus.

Simultaneous angiotensin receptor blockade and glucagon-like peptide-1 receptor activation ameliorate albuminuria in obese insulin-resistant rats

Insulin resistance increases renal oxidant production by upregulating NADPH oxidase 4 (Nox4) expression contributing to oxidative damage and ultimately albuminuria. Inhibition of the renin-angiotensin system (RAS) and activation of glucagon-like peptide-1 (GLP-1) receptor signalling may reverse this effect. However, whether angiotensin receptor type 1 (AT1) blockade and GLP-1 receptor activation improve oxidative damage and albuminuria through different mechanisms is not known. Using insulin-resistant Otsuka Long-Evans Tokushima Fatty (OLETF) rats, we tested the hypothesis that simultaneous blockade of AT1 and activation of GLP-1r additively decrease oxidative damage and urinary albumin excretion (U_alb V) in the following groups: (a) untreated, lean LETO (n = 7), (b) untreated, obese OLETF (n = 9), (c) OLETF + angiotensin receptor blocker (ARB; 10 mg olmesartan/kg/d; n = 9), (d) OLETF + GLP-1 mimetic (EXE; 10 µg exenatide/kg/d; n = 7) and (e) OLETF + ARB +exenatide (Combo; n = 6). Mean kidney Nox4 protein expression and nitrotyrosine (NT) levels were 30% and 46% greater, respectively, in OLETF compared with LETO. Conversely, Nox4 protein expression and NT were reduced to LETO levels in ARB and EXE, and Combo reduced Nox4, NT and 4-hydroxy-2-nonenal levels by 21%, 27% and 27%, respectively. At baseline, U_alb V was nearly double in OLETF compared with LETO and increased to nearly 10-fold greater levels by the end of the study. Whereas ARB (45%) and EXE (55%) individually reduced U_alb V, the combination completely ameliorated the albuminuria. Collectively, these data suggest that AT1 blockade and GLP-1 receptor activation reduce renal oxidative damage similarly during insulin resistance, whereas targeting both signalling pathways provides added benefit in restoring and/or further ameliorating albuminuria in a model of diet-induced obesity.

Glucagon-like peptide 1 (GLP-1)

BACKGROUND

The glucagon-like peptide-1 (GLP-1) is a multifaceted hormone with broad pharmacological potential. Among the numerous metabolic effects of GLP-1 are the glucose-dependent stimulation of insulin secretion, decrease of gastric emptying, inhibition of food intake, increase of natriuresis and diuresis, and modulation of rodent β-cell proliferation. GLP-1 also has cardio- and neuroprotective effects, decreases inflammation and apoptosis, and has implications for learning and memory, reward behavior, and palatability. Biochemically modified for enhanced potency and sustained action, GLP-1 receptor agonists are successfully in clinical use for the treatment of type-2 diabetes, and several GLP-1-based pharmacotherapies are in clinical evaluation for the treatment of obesity.

SCOPE OF REVIEW

In this review, we provide a detailed overview on the multifaceted nature of GLP-1 and its pharmacology and discuss its therapeutic implications on various diseases.

MAJOR CONCLUSIONS

Since its discovery, GLP-1 has emerged as a pleiotropic hormone with a myriad of metabolic functions that go well beyond its classical identification as an incretin hormone. The numerous beneficial effects of GLP-1 render this hormone an interesting candidate for the development of pharmacotherapies to treat obesity, diabetes, and neurodegenerative disorders.

Direct and indirect effects of liraglutide on hypothalamic POMC and NPY/AgRP neurons - Implications for energy balance and glucose control

Objective

The long-acting glucagon-like peptide-1 receptor (GLP-1R) agonist, liraglutide, stimulates insulin secretion and efficiently suppresses food intake to reduce body weight. As such, liraglutide is growing in popularity in the treatment of diabetes and chronic weight management. Within the brain, liraglutide has been shown to alter the activity of hypothalamic proopiomelanocortin (POMC) and Neuropeptide Y/Agouti-related peptide (NPY/AgRP) neurons. Moreover, the acute activities of POMC and NPY neurons have been directly linked to feeding behavior, body weight, and glucose metabolism. Despite the increased usage of liraglutide and other GLP-1 analogues as diabetic and obesity interventions, the cellular mechanisms by which liraglutide alters the activity of metabolically relevant neuronal populations are poorly understood.

Methods

In order to resolve this issue, we utilized neuron-specific transgenic mouse models to identify POMC and NPY neurons for patch-clamp electrophysiology experiments.

Results

We found that liraglutide directly activated arcuate POMC neurons via TrpC5 channels, sharing a similar mechanistic pathway to the adipose-derived peptide leptin. Liraglutide also indirectly increases excitatory tone to POMC neurons. In contrast, liraglutide inhibited NPY/AgRP neurons through post-synaptic GABA_A receptors and enhanced activity of pre-synaptic GABAergic neurons, which required both TrpC5 subunits and K-ATP channels. In support of an additive role of leptin and liraglutide in suppressing food intake, leptin potentiated the acute effects of liraglutide to activate POMC neurons. TrpC5 subunits in POMC neurons were also required for the intact pharmacological effects of liraglutide on food intake and body weight. Thus, the current study adds to recent work from our group and others, which highlight potential mechanisms to amplify the effects of GLP-1 agonists in vivo. Moreover, these data highlight multiple sites of action (both pre- and post-synaptic) for GLP-1 agonists on this circuit.

Conclusions

Taken together, our results identify critical molecular mechanisms linking GLP-1 analogues in arcuate POMC and NPY/AgRP neurons with metabolism.

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Liraglutide directly activates arcuate POMC neurons, while also increasing pre-synaptic excitatory inputs to POMC neurons.

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Leptin potentiates the acute effects of liraglutide to activate POMC neurons.

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Liraglutide indirectly inhibits arcuate NPY/AgRP neurons via presynaptic TrpC 5 subunits and K_ATP channels.

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TrpC5 subunits in POMC neurons are required for the intact pharmacological effects of liraglutide.

Cannabinoid CB1 Receptors Inhibit Gut-Brain Satiation Signaling in Diet-Induced Obesity

Gut-brain signaling controls feeding behavior and energy homeostasis; however, the underlying molecular mechanisms and impact of diet-induced obesity (DIO) on these pathways are poorly defined. We tested the hypothesis that elevated endocannabinoid activity at cannabinoid CB₁ receptor (CB₁Rs) in the gut of mice rendered DIO by chronic access to a high fat and sucrose diet for 60 days inhibits nutrient-induced release of satiation peptides and promotes overeating. Immunoreactivity for CB₁Rs was present in enteroendocrine cells in the mouse’s upper small-intestinal epithelium that produce and secrete the satiation peptide, cholecystokinin (CCK), and expression of mRNA for CB₁Rs was greater in these cells when compared to non-CCK producing cells. Oral gavage of corn oil increased levels of bioactive CCK (CCK-8) in plasma from mice fed a low fat no-sucrose diet. Pretreatment with the cannabinoid receptor agonist, WIN55,212-2, blocked this response, which was reversed by co-administration with the peripherally-restricted CB₁R neutral antagonist, AM6545. Furthermore, monoacylglycerol metabolic enzyme function was dysregulated in the upper small-intestinal epithelium from DIO mice, which was met with increased levels of a variety of monoacylglycerols including the endocannabinoid, 2-arachidonoyl-sn-glycerol. Corn oil failed to affect levels of CCK in DIO mouse plasma; however, pretreatment with AM6545 restored the ability for corn oil to stimulate increases in levels of CCK, which suggests that elevated endocannabinoid signaling at small intestinal CB₁Rs in DIO mice inhibits nutrient-induced CCK release. Moreover, the hypophagic effect of AM6545 in DIO mice was reversed by co-administration with the CCK_A receptor antagonist, devazepide. Collectively, these results provide evidence that hyperphagia associated with DIO is driven by a mechanism that includes CB₁R-mediated inhibition of gut-brain satiation signaling.

Long-Acting Neurotensin Synergizes With Liraglutide to Reverse Obesity Through a Melanocortin-Dependent Pathway

Neurotensin (NT), a gut hormone and neuropeptide, increases in circulation after bariatric surgery in rodents and humans and inhibits food intake in mice. However, its potential to treat obesity and the subsequent metabolic dysfunctions have been difficult to assess owing to its short half-life in vivo. Here, we demonstrate that a long-acting, pegylated analog of the NT peptide (P-NT) reduces food intake, body weight, and adiposity in diet-induced obese mice when administered once daily for 6 days. Strikingly, when P-NT was combined with the glucagon-like peptide 1 mimetic liraglutide, the two peptides synergized to reduce food intake and body weight relative to each monotherapy, without inducing a taste aversion. Further, P-NT and liraglutide coadministration improved glycemia and reduced steatohepatitis. Finally, we show that the melanocortin pathway is central for P-NT-induced anorexia and necessary for the full synergistic effect of P-NT and liraglutide combination therapy. Overall, our data suggest that P-NT and liraglutide combination therapy could be an enhanced treatment for obesity with improved tolerability compared with liraglutide monotherapy.

Anti-Obesity Therapy: from Rainbow Pills to Polyagonists

With their ever-growing prevalence, obesity and diabetes represent major health threats of our society. Based on estimations by the World Health Organization, approximately 300 million people will be obese in 2035. In 2015 alone there were more than 1.6 million fatalities attributable to hyperglycemia and diabetes. In addition, treatment of these diseases places an enormous burden on our health care system. As a result, the development of pharmacotherapies to tackle this life-threatening pandemic is of utmost importance. Since the beginning of the 19th century, a variety of drugs have been evaluated for their ability to decrease body weight and/or to improve deranged glycemic control. The list of evaluated drugs includes, among many others, sheep-derived thyroid extracts, mitochondrial uncouplers, amphetamines, serotonergics, lipase inhibitors, and a variety of hormones produced and secreted by the gastrointestinal tract or adipose tissue. Unfortunately, when used as a single hormone therapy, most of these drugs are underwhelming in their efficacy or safety, and placebo-subtracted weight loss attributed to such therapy is typically not more than 10%. In 2009, the generation of a single molecule with agonism at the receptors for glucagon and the glucagon-like peptide 1 broke new ground in obesity pharmacology. This molecule combined the beneficial anorectic and glycemic effects of glucagon-like peptide 1 with the thermogenic effect of glucagon into a single molecule with enhanced potency and sustained action. Several other unimolecular dual agonists have subsequently been developed, and, based on their preclinical success, these molecules illuminate the path to a new and more fruitful era in obesity pharmacology. In this review, we focus on the historical pharmacological approaches to treat obesity and glucose intolerance and describe how the knowledge obtained by these studies led to the discovery of unimolecular polypharmacology.

Peptide-based multi-agonists: a new paradigm in metabolic pharmacology

Obesity and its comorbidities, such as type 2 diabetes, are pressing worldwide health concerns. Available anti-obesity treatments include weight loss pharmacotherapies and bariatric surgery. Whilst surgical interventions typically result in significant and sustained weight loss, available pharmacotherapies are far less effective, typically decreasing body weight by no more than 5-10%. An emerging class of multi-agonist drugs may eventually bridge this gap. This new class of specially tailored drugs hybridizes the amino acid sequences of key metabolic hormones into one single entity with enhanced potency and sustained action. Successful examples of this strategy include multi-agonist drugs targeting the receptors for glucagon-like peptide-1 (GLP-1), glucagon and the glucose-dependent insulinotropic polypeptide (GIP). Due to the simultaneous activity at several metabolically relevant receptors, these multi-agonists offer improved body weight loss and glucose tolerance relative to their constituent monotherapies. Further advancing this concept, chimeras were generated that covalently link nuclear acting hormones such as oestrogen, thyroid hormone (T₃ ) or dexamethasone to peptide hormones such as GLP-1 or glucagon. The benefit of this strategy is to restrict the nuclear hormone action exclusively to cells expressing the peptide hormone receptor, thereby maximizing combinatorial metabolic efficacy of both drug constituents in the target cells whilst preventing the nuclear hormone cargo from entering and acting on cells devoid of the peptide hormone receptor, in which the nuclear hormone might have unwanted effects. Many of these multi-agonists are in preclinical and clinical development and may represent new and effective tools in the fight against obesity and its comorbidities.

The Origin and Understanding of the Incretin Concept

Gastrointestinal hormones that stimulate insulin secretion at physiological concentrations are incretins. This concept has recently attracted considerable attention in the wake of drugs developed from the gut hormone GLP-1 (glucagon-like peptide-1) for diabetes therapy. But the renewed enthusiasm has also restricted the concept to just two hormones, GLP-1 and GIP (glucose-dependent insulinotropic polypeptide). The purpose of the present overview is two-fold: First to tell that the incretin concept is far from new. It has a more than a century long history full of ups and downs. Second, that the incretin concept may now have become too narrow. Thus, it is likely that incretin comprises additional gastrointestinal hormones, which interact with GIP and GLP-1 during normal meals containing protein, fat and complex carbohydrates (and not just pure glucose). Such broader incretin concept may stimulate development of novel gut hormone-derived drugs.

A GLP-1:CCK fusion peptide harnesses the synergistic effects on metabolism of CCK-1 and GLP-1 receptor agonism in mice

Combination approaches for the treatment of metabolic diseases such as obesity and diabetes are becoming increasingly relevant. Co-administration of a glucagon-like peptide-1 receptor (GLP-1R) agonist with a cholecystokinin receptor-1 (CCKR1) agonist exert synergistic effects on weight loss in obese rodents. Here, we report on the effects of a novel fusion peptide (C2816) comprised of a stabilized GLP-1R agonist, AC3174, and a CCKR1-selective agonist, AC170222. C2816 was constructed such that AC3174 was linked to the N-terminus of AC170222, thus preserving the C-terminal amide of the CCK moiety. In functional in vitro assays C2816 retained full agonism at GLP-1R and CCKR1 at lower potency compared to parent molecules, whereas a previously reported fusion peptide in the opposite orientation, (pGlu-Gln)-CCK-8/exendin-4, exhibited no activity at either receptor. Acutely, in vivo, C2816 increased cFos in key central nuclei relevant to feeding behavior, and reduced food intake in wildtype (WT), but less so in GLP-1R-deficient (GLP-1RKO), mice. In sub-chronic studies in diet-induced obese (DIO) mice, C2816 exerted superior reduction in body weight compared to co-administration of AC3174 and AC170222 albeit at a higher molar dose. These data suggest that the synergistic pharmacological effects of GLP-1 and CCK pathways can be harnessed in a single therapeutic peptide.

Combined gastrin releasing peptide-29 and glucagon like peptide-1 reduce body weight more than each individual peptide in diet-induced obese male rats

To test the hypothesis that gastrin releasing peptide-29 (GRP-29) combined with glucagon like peptide-1 (7-36) (GLP-1 (7-36)) reduce body weight (BW) more than each of the peptides given individually, we infused the two peptides (0.5nmol/kg each) in the aorta of free feeding, diet-induced obese (DIO) male Sprague Dawley rats once daily for 25days and measured BW. We found that GRP-29 and GLP-1 reduce BW, GRP-29 reduced it more than GLP-1 and GRP-29+GLP-1 reduce BW more than each peptide given alone. This reduction was accompanied by decrease 24-hour food intake (normal rat chow), meal size (MS), duration of first meal and number of meals, and increase latency to the first meal, intermeal interval (IMI) and satiety ratio (IMI/MS, amount of food consumed per a unit of time). Furthermore, the peptides and their combination decreased 24-hour glucose levels. In conclusion, GRP-29+GLP-1 reduce BW more than each of the peptides given individually.

Cholecystokinin (CCK) and related adjunct peptide therapies for the treatment of obesity and type 2 diabetes

Cholecystokinin (CCK) is a hormone secreted from I-cells of the gut, as well as neurons in the enteric and central nervous system, that binds and activates CCK-1 and CCK-2 receptors to mediate its biological actions. To date knowledge relating to the physiological significance of CCK has predominantly focused around induction of short-term satiety. However, CCK has also been highlighted to possess important actions in relation to the regulation of insulin secretion, as well as overall beta-cell function and survival. Consequently, this has led to the development of enzymatically stable, biologically active, CCK peptide analogues with proposed therapeutic promise for both obesity and type 2 diabetes. In addition, several studies have demonstrated metabolic, and therapeutically relevant, complementary biological actions of CCK with those of the incretin hormones GIP and GLP-1, as well as with amylin and leptin. Thus, stable CCK derivatives not only offer promise as potential independent weight-reducing and glucose-lowering drugs, but also as effective adjunctive therapies. This review focuses on the recent and ongoing developments of CCK in the context of new therapies for obesity and type 2 diabetes.

Beneficial metabolic effects of dietary epigallocatechin gallate alone and in combination with exendin-4 in high fat diabetic mice

OBJECTIVE

Significant attempts are being made to generate multifunctional, hybrid or peptide combinations as novel therapeutic strategies for type 2 diabetes, however this presents key challenges including design and pharmaceutical development. In this study, we evaluated metabolic properties of oral nutritional supplement epigallocatechin gallate (EGCG) in combination with GLP-1 agonist exendin-4 in a mouse model of dietary-induced diabetes and obesity.

METHODS

EGCG, exendin-4 or combination of both were administered twice-daily over 28 days to high fat (HF) mice on background of low-dose streptozotocin. Energy intake, body weight, fat mass, glucose tolerance, insulin sensitivity, lipid profile, biochemical and hormone markers, and islet histology were examined.

RESULTS

All treatment groups exhibited significantly reduced body weight, fat mass, circulating glucose and insulin concentrations, and HbA1c levels which were independent of changes in energy intake. Similarly, there was marked improvement in glycaemic control, glucose-stimulated insulin release, insulin sensitivity, total cholesterol and triglycerides, with most prominent effects observed following combination therapy. Circulating corticosterone concentrations and 11beta-hydroxysteroid dehydrogenase type1 (11β-HSD1) staining (in pancreas) were beneficially decreased without changes in circulating interleukin 6 (IL-6), alanine transaminase (ALT) and glutathione reductase. Combination therapy resulted in increased islet area and number, beta cell area, and pancreatic insulin content. Generally, metabolic effects were much more pronounced in mice which received combination therapy.

CONCLUSIONS

EGCG alone and particularly in combination with exendin-4 exerts positive metabolic properties in HF mice. EGCG may be useful dietary adjunct alongside GLP-1 mimetics in treatment of diabetes and related disorders.

Gut check on diabesity: leveraging gut mechanisms for the treatment of type 2 diabetes and obesity

Gut hormones have long been understood to regulate food intake and metabolism. Bariatric surgery significantly elevates circulating gut hormone levels and is proven to affect acute remission of type 2 diabetes before any weight loss is observed. Subsequent weight loss is accrued over weeks to months but is sustained into the long term. Hence, there exists great enthusiasm to recapitulate these changes in gut hormones in the form of novel combination drugs for type 2 diabetes and obesity.

Ghrelin, CCK, GLP-1, and PYY(3-36): Secretory Controls and Physiological Roles in Eating and Glycemia in Health, Obesity, and After RYGB

The efficacy of Roux-en-Y gastric-bypass (RYGB) and other bariatric surgeries in the management of obesity and type 2 diabetes mellitus and novel developments in gastrointestinal (GI) endocrinology have renewed interest in the roles of GI hormones in the control of eating, meal-related glycemia, and obesity. Here we review the nutrient-sensing mechanisms that control the secretion of four of these hormones, ghrelin, cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), and peptide tyrosine tyrosine [PYY(3-36)], and their contributions to the controls of GI motor function, food intake, and meal-related increases in glycemia in healthy-weight and obese persons, as well as in RYGB patients. Their physiological roles as classical endocrine and as locally acting signals are discussed. Gastric emptying, the detection of specific digestive products by small intestinal enteroendocrine cells, and synergistic interactions among different GI loci all contribute to the secretion of ghrelin, CCK, GLP-1, and PYY(3-36). While CCK has been fully established as an endogenous endocrine control of eating in healthy-weight persons, the roles of all four hormones in eating in obese persons and following RYGB are uncertain. Similarly, only GLP-1 clearly contributes to the endocrine control of meal-related glycemia. It is likely that local signaling is involved in these hormones' actions, but methods to determine the physiological status of local signaling effects are lacking. Further research and fresh approaches are required to better understand ghrelin, CCK, GLP-1, and PYY(3-36) physiology; their roles in obesity and bariatric surgery; and their therapeutic potentials.

Targeting the gastrointestinal tract to treat type 2 diabetes

The rising global rates of type 2 diabetes and obesity present a significant economic and social burden, underscoring the importance for effective and safe therapeutic options. The success of glucagon-like-peptide-1 receptor agonists in the treatment of type 2 diabetes, along with the potent glucose-lowering effects of bariatric surgery, highlight the gastrointestinal tract as a potential target for diabetes treatment. Furthermore, recent evidence suggests that the gut plays a prominent role in the ability of metformin to lower glucose levels. As such, the current review highlights some of the current and potential pathways in the gut that could be targeted to improve glucose homeostasis, such as changes in nutrient sensing, gut peptides, gut microbiota and bile acids. A better understanding of these pathways will lay the groundwork for novel gut-targeted antidiabetic therapies, some of which have already shown initial promise.

Pharmacological Approaches in the Treatment and Maintenance of Weight Loss

Obesity is a growing global health concern, associated with a number of important comorbid conditions. It increases the risk of diabetes and contributes to development of cardiovascular disease. While the benefits of weight loss are well established, weight reduction remains a difficult-to-reach goal in overweight and obese individuals due to several metabolic and psychological factors. For many patients, lifestyle intervention is insufficient to achieve long-term weight loss, and additional options, such as pharmacotherapy, need to be considered. Besides the challenging enterprise of weight reduction, weight maintenance remains an even more crucial and outcome-determining aspect of weight management. This article focuses on the potential of currently available pharmacological strategies to support weight loss and maintenance goals in individuals at risk. Two pharmacotherapy types are considered: those developed primarily to induce weight loss and those developed primarily for blood glucose control that have a favorable effect on body weight. Finally, the potential of very low- and low-calorie diets combined with pharmacotherapy and pharmacological combination therapies are discussed, as well as emerging approaches in development.

Use of CRISPR/Cas9-engineered INS-1 pancreatic β cells to define the pharmacology of dual GIPR/GLP-1R agonists

Dual-agonist molecules combining glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) activity represent an exciting therapeutic strategy for diabetes treatment. Although challenging due to shared downstream signalling pathways, determining the relative activity of dual agonists at each receptor is essential when developing potential novel therapeutics. The challenge is exacerbated in physiologically relevant cell systems expressing both receptors. To this end, either GIP receptors (GIPR) or GLP-1 receptors (GLP-1R) were ablated via RNA-guided clustered regularly interspaced short palindromic repeat (CRISPR)/Cas9 endonucleases in the INS-1 pancreatic β-cell line. Multiple clonal cell lines harbouring gene disruptions for each receptor were isolated and assayed for receptor activity to identify functional knockouts (KOs). cAMP production in response to GIPR or GLP-1R activation was abolished and GIP- or GLP-1-induced potentiation of glucose-stimulated insulin secretion (GSIS) was attenuated in the cognate KO cell lines. The contributions of individual receptors derived from cAMP and GSIS assays were confirmed in vivo using GLP-1R KO mice in combination with a monoclonal antibody antagonist of GIPR. We have successfully applied CRISPR/Cas9-engineered cell lines to determining selectivity and relative potency contributions of dual-agonist molecules targeting receptors with overlapping native expression profiles and downstream signalling pathways. Specifically, we have characterised molecules as biased towards GIPR or GLP-1R, or with relatively balanced potency in a physiologically relevant β-cell system. This demonstrates the broad utility of CRISPR/Cas9 when applied to native expression systems for the development of drugs that target multiple receptors, particularly where the balance of receptor activity is critical.

Glucagon-like peptide-1 and cholecystokinin production and signaling in the pancreatic islet as an adaptive response to obesity

Precise control of blood glucose is dependent on adequate β‐cell mass and function. Thus, reductions in β‐cell mass and function lead to insufficient insulin production to meet demand, and result in diabetes. Recent evidence suggests that paracrine signaling in the islet might be important in obesity, and disruption of this signaling could play a role in the pathogenesis of diabetes. For example, we recently discovered a novel islet incretin axis where glucagon‐like peptide‐1 regulates β‐cell production of another classic gut hormone, cholecystokinin. This axis is stimulated by obesity, and plays a role in enhancing β‐cell survival. In the present review, we place our observations in the wider context of the literature on incretin regulation in the islet, and discuss the potential for therapeutic targeting of these pathways.

Emerging opportunities for the treatment of metabolic diseases: Glucagon-like peptide-1 based multi-agonists

Obesity is a pathogenic gateway to the metabolic syndrome and the complications thereof, thus interventions aimed at preventing or reversing the metabolic derangements underlying obesity hold great therapeutic promise. However, the complexity of energy balance regulation, combined with the heterologous pathophysiology of human obesity, renders effective medicinal intervention very difficult. Indeed, the search for the silver bullet in anti-obesity medicines has been laden with drugs of underwhelming efficacy and unacceptable side effects. This can partly be the consequence that many of these drug interventions have been historically directed at single molecular targets. New multi-molecular combination therapies have shown promising clinical outcomes in terms of weight loss, yet multi-functional single molecules may offer even more advantages than adjunctive co-treatments. Single molecules with integrated activities derived from multiple hormones involved in the physiological control of metabolism have emerged as one of the more promising candidates for reversing obesity. The inclusion of glucagon-like peptide-1 (GLP-1) as one of the constituents is a unifying factor amongst the majority of these unimolecular multi-agonists. The scope of this review is to summarize the current preclinical and clinical landscape of GLP-1-based therapies, focusing on combinatorial therapies with a particular emphasis on single molecule compounds displaying multi-agonist properties.

New perspectives on exploitation of incretin peptides for the treatment of diabetes and related disorders

The applicability of stable gut hormones for the treatment of obesity-related diabetes is now undisputable. This is based predominantly on prominent and sustained glucose-lowering actions, plus evidence that these peptides can augment insulin secretion and pancreatic islet function over time. This review highlights the therapeutic potential of glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), oxyntomodulin (OXM) and cholecystokinin (CCK) for obesity-related diabetes. Stable GLP-1 mimetics have already been successfully adopted into the diabetic clinic, whereas GIP, CCK and OXM molecules offer promise as potential new classes of antidiabetic drugs. Moreover, recent studies have shown improved therapeutic effects following simultaneous modulation of multiple receptor signalling pathways by combination therapy or use of dual/triple agonist peptides. However, timing and composition of injections may be important to permit interludes of beta-cell rest. The review also addresses the possible perils of incretin based drugs for treatment of prediabetes. Finally, the unanticipated utility of stable gut peptides as effective treatments for complications of diabetes, bone disorders, cognitive impairment and cardiovascular dysfunction is considered.

Brain signaling systems in the Type 2 diabetes and metabolic syndrome: promising target to treat and prevent these diseases

The changes in the brain signaling systems play an important role in etiology and pathogenesis of Type 2 diabetes mellitus (T2DM) and metabolic syndrome (MS), being a possible cause of these diseases. Therefore, their restoration at the early stages of T2DM and MS can be regarded as a promising way to treat and prevent these diseases and their complications. The data on the functional state of the brain signaling systems regulated by insulin, IGF-1, leptin, dopamine, serotonin, melanocortins and glucagon-like peptide-1, in T2DM and MS, are analyzed. The pharmacological approaches to restoration of these systems and improvement of insulin sensitivity, energy expenditure, lipid metabolism, and to prevent diabetic complications are discussed.