Central administration of GLP-1 and GIP decreases feeding in mice

Glucose-dependent insulinotropic polypeptide (GIP)

BACKGROUND

Glucose-dependent insulinotropic polypeptide (GIP) was the first incretin identified and plays an essential role in the maintenance of glucose tolerance in healthy humans. Until recently GIP had not been developed as a therapeutic and thus has been overshadowed by the other incretin, glucagon-like peptide 1 (GLP-1), which is the basis for several successful drugs to treat diabetes and obesity. However, there has been a rekindling of interest in GIP biology in recent years, in great part due to pharmacology demonstrating that both GIPR agonism and antagonism may be beneficial in treating obesity and diabetes. This apparent paradox has reinvigorated the field, led to new lines of investigation, and deeper understanding of GIP.

SCOPE OF REVIEW

In this review, we provide a detailed overview on the multifaceted nature of GIP biology and discuss the therapeutic implications of GIPR signal modification on various diseases.

MAJOR CONCLUSIONS

Following its classification as an incretin hormone, GIP has emerged as a pleiotropic hormone with a variety of metabolic effects outside the endocrine pancreas. The numerous beneficial effects of GIPR signal modification render the peptide an interesting candidate for the development of pharmacotherapies to treat obesity, diabetes, drug-induced nausea and both bone and neurodegenerative disorders.

GIPR-Ab/GLP-1 peptide-antibody conjugate requires brain GIPR and GLP-1R for additive weight loss in obese mice

Glucose-dependent insulinotropic polypeptide receptor (GIPR) and glucagon-like peptide 1 receptor (GLP-1R) are expressed in the central nervous system (CNS) and regulate food intake. Here, we demonstrate that a peptide-antibody conjugate that blocks GIPR while simultaneously activating GLP-1R (GIPR-Ab/GLP-1) requires both CNS GIPR and CNS GLP-1R for maximal weight loss in obese, primarily male, mice. Moreover, dulaglutide produces greater weight loss in CNS GIPR knockout (KO) mice, and the weight loss achieved with dulaglutide + GIPR-Ab is attenuated in CNS GIPR KO mice. Wild-type mice treated with GIPR-Ab/GLP-1 and CNS GIPR KO mice exhibit similar changes in gene expression related to tissue remodelling, lipid metabolism and inflammation in white adipose tissue and liver. Moreover, GIPR-Ab/GLP-1 is detected in circumventricular organs in the brain and activates c-FOS in downstream neural substrates involved in appetite regulation. Hence, both CNS GIPR and GLP-1R signalling are required for the full weight loss effect of a GIPR-Ab/GLP-1 peptide-antibody conjugate.

Glucose-dependent insulinotropic peptide and beyond: co-agonist innovations in the treatment of metabolic diseases

Glucose-dependent insulinotropic peptide (GIP), a key incretin hormone, has emerged as a pivotal therapeutic target in metabolic disorders. Historically, its therapeutic potential in type 2 diabetes mellitus (T2DM) has been underestimated owing to GIP resistance and its limited acute effects on glycemic control and body weight regulation. However, emerging evidence has demonstrated that GIP resistance is reversible through sustained glycemic improvement, thereby restoring its physiological effectiveness. With the development of gut hormone co-agonists, the potential of GIP in the treatment of metabolic diseases has been reevaluated. The study of GIP and its co-agonists such as glucagon-like peptide-1 (GLP-1), revealed that its mechanism of action in regulating blood glucose, fat metabolism, and bone metabolism is complex and diverse. A better understanding of GIP evolution can help in designing more effective GIP-based treatment strategies. In this review, we summarize the physiological functions of GIP, systematically explores its diverse structural modifications, delves into the realm of unimolecular multi-agonists, and provides a nuanced portrayal of the developmental prospects of GIP analogs.

Dual and Triple Gut Peptide Agonists on the Horizon for the Treatment of Type 2 Diabetes and Obesity. An Overview of Preclinical and Clinical Data

PURPOSE OF REVIEW

The development of long-acting incretin receptor agonists represents a significant advance in the fight against the concurrent epidemics of type 2 diabetes mellitus (T2DM) and obesity. The aim of the present review is to examine the cellular processes underlying the actions of these new, highly significant classes of peptide receptor agonists. We further explore the potential actions of multi-agonist drugs as well as the mechanisms through which gut-brain communication can be used to achieve long-term weight loss without negative side effects.

RECENT FINDINGS

Several unimolecular dual-receptor agonists have shown promising clinical efficacy studies when used alone or in conjunction with approved glucose-lowering medications. We also describe the development of incretin-based pharmacotherapy, starting with exendin- 4 and ending with the identification of multi-incretin hormone receptor agonists, which appear to be the next major step in the fight against T2DM and obesity. We discuss the multi-agonists currently in clinical trials and how each new generation of these drugs improves their effectiveness. Since most glucose-dependent insulinotropic polypeptide (GIP) receptor: glucagon-like peptide- 1 receptor (GLP- 1) receptor: glucagon receptor triagonists compete in efficacy with bariatric surgery, the success of these agents in preclinical models and clinical trials suggests a bright future for multi-agonists in the treatment of metabolic diseases. To fully understand how these treatments affect body weight, further research is needed.

The unexpected role of GIP in transforming obesity treatment

Despite sharing incretin activity with glucagon-like peptide 1 (GLP-1), the development of gastric inhibitory polypeptide (GIP)-based drugs has been hindered by the minor effects of native GIP on appetite and body weight and genetic studies associating loss-of-function with reduced obesity. Yet, pharmacologically optimized GIP-based molecules have demonstrated profound weight lowering benefits of GIPR agonism when combined with GLP-1-based therapies, which has re-energized deeper exploration of the molecular mechanisms and downstream signaling of GIPR. Interestingly, both GIPR agonism and antagonism offer metabolic benefits, leading to differing viewpoints on how to target GIPR therapeutically. Here we summarize the emerging evidence about the tissue-specific mechanisms that positions GIP-based therapies as important targets for the next generation of anti-obesity and metabolic therapies.

Chronic GIPR agonism results in pancreatic islet GIPR functional desensitisation

OBJECTIVES

There is renewed interest in targeting the glucose-dependent insulinotropic polypeptide receptor (GIPR) for treatment of obesity and type 2 diabetes. G-protein coupled receptor desensitisation is suggested to reduce the long-term efficacy of glucagon-like-peptide 1 receptor (GLP-1R) agonists and may similarly affect the efficacy of GIPR agonists. We explored the extent of pancreatic GIPR functional desensitisation with sustained agonist exposure.

METHODS

A long-acting GIPR agonist, GIP108, was used to probe the effect of sustained agonist exposure on cAMP responses in dispersed pancreatic islets using live cell imaging, with rechallenge cAMP responses after prior agonist treatment used to quantify functional desensitisation. Receptor internalisation and β-arrestin-2 activation were investigated in vitro using imaging-based assays. Pancreatic mouse GIPR desensitisation was assessed in vivo via intraperitoneal glucose tolerance testing.

RESULTS

GIP108 treatment led to weight loss and improved glucose homeostasis in mice. Prolonged exposure to GIPR agonists produced homologous functional GIPR desensitisation in isolated islets. GIP108 pre-treatment in vivo also reduced the subsequent anti-hyperglycaemic response to GIP re-challenge. GIPR showed minimal agonist-induced internalisation or β-arrestin-2 activation.

CONCLUSIONS

Although GIP108 chronic treatment improved glucose tolerance, it also resulted in partial desensitisation of the pancreatic islet GIPR. This suggests that ligands with reduced desensitisation tendency might lead to improved in vivo efficacy. Understanding whether pancreatic GIPR desensitisation affects the long-term benefits of GIPR agonists in humans is vital to design effective metabolic pharmacotherapies.

Differences in GIP Receptor Expression by Feeding Status in the Mouse Brain

Gastric inhibitory polypeptide (GIP) contributes to energy metabolism regulation. We investigated differences in GIP receptor expression in the brain by feeding status among lean and obese mice and the effect of acute central GIP administration on the expression of appetite-regulating hypothalamic neuropeptides. We divided the mice into four groups: fed/lean, fasted/lean, fed/obese, and fasted/obese. The arcuate nucleus (ARC), paraventricular nucleus of the hypothalamus, and nucleus of the solitary tract in the brainstem were harvested. GIP (6 nmol) or saline was injected for the acute intracerebroventricular administration test, followed by the collection of hypothalamic tissue after 2 h. Fed/obese mice had higher ARC GIP receptor mRNA levels than fasted/obese and lean mice. This difference was not observed among lean mice by feeding status. Obese mice had higher blood GIP levels than lean mice. Fed/obese mice had higher blood GIP levels than fasted/obese mice. This difference was not observed among lean mice by feeding status. GIP administration significantly increased proopiomelano-cortin (Pomc) mRNA levels (GIP: 7.59 ± 0.14; saline: 3.44 ± 1.38 arbitrary units; p = 0.030). Increased GIP receptor expression in the ARC in obese mice indicates its central nervous system involvement in energy balance regulation. GIP potentially regulates POMC-mediated appetite regulation in the hypothalamus. It is possible that POMC neurons are targets of GIP action in the brain.

The GIP receptor activates futile calcium cycling in white adipose tissue to increase energy expenditure and drive weight loss in mice

Obesity is a chronic disease that contributes to the development of insulin resistance, type 2 diabetes (T2D), and cardiovascular risk. Glucose-dependent insulinotropic polypeptide (GIP) receptor (GIPR) and glucagon-like peptide-1 (GLP-1) receptor (GLP-1R) co-agonism provide an improved therapeutic profile in individuals with T2D and obesity when compared with selective GLP-1R agonism. Although the metabolic benefits of GLP-1R agonism are established, whether GIPR activation impacts weight loss through peripheral mechanisms is yet to be fully defined. Here, we generated a mouse model of GIPR induction exclusively in the adipocyte. We show that GIPR induction in the fat cell protects mice from diet-induced obesity and triggers profound weight loss (∼35%) in an obese setting. Adipose GIPR further increases lipid oxidation, thermogenesis, and energy expenditure. Mechanistically, we demonstrate that GIPR induction activates SERCA-mediated futile calcium cycling in the adipocyte. GIPR activation further triggers a metabolic memory effect, which maintains weight loss after the transgene has been switched off, highlighting a unique aspect in adipocyte biology. Collectively, we present a mechanism of peripheral GIPR action in adipose tissue, which exerts beneficial metabolic effects on body weight and energy balance.

Research Progress on Peptide Drugs for Type 2 Diabetes and the Possibility of Oral Administration

Diabetes is a global disease that can lead to a range of complications. Currently, the treatment of type 2 diabetes focuses on oral hypoglycemic drugs and insulin analogues. Studies have shown that drugs such as oral metformin are useful in the treatment of diabetes but can limit the liver's ability to release sugar. The development of glucose-lowering peptides has provided new options for the treatment of type 2 diabetes. Peptide drugs have low oral utilization due to their easy degradation, short half-life, and difficulty passing through the intestinal mucosa. Therefore, improving the oral utilization of peptide drugs remains an urgent problem. This paper reviews the research progress of peptide drugs in the treatment of diabetes mellitus and proposes that different types of nano-formulation carriers, such as liposomes, self-emulsifying drug delivery systems, and polymer particles, should be combined with peptide drugs for oral administration to improve their absorption in the gastrointestinal tract.

GLP-1, GIP, and Glucagon Agonists for Obesity Treatment: A Hunger Perspective

For centuries, increasingly sophisticated methods and approaches have been brought to bear to promote weight loss. Second only to the Holy Grail of research on aging, the idea of finding a single and simple way to lose weight has long preoccupied the minds of laymen and scientists alike. The effects of obesity are far-reaching and not to be minimized; the need for more effective treatments is obvious. Is there a single silver bullet that addresses this issue without effort on the part of the individual? The answer to this question has been one of the most elusive and sought-after in modern history. Now and then, a miraculous discovery propagates the illusion that a simple solution is possible. Now there are designer drugs that seem to accomplish the task: we can lose weight without effort using mono, dual, and triple agonists of receptors for glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), and glucagon. There are, however, fundamental biological principles that raise intriguing questions about these therapies beyond the currently reported side-effects. This perspective reflects upon these issues from the angle of complex goal-oriented behaviors, and systemic and cellular metabolism associated with satiety and hunger.

Investigational and emerging gastric inhibitory polypeptide (GIP) receptor-based therapies for the treatment of obesity

INTRODUCTION

One billion people live with obesity. The most promising medications for its treatment are incretin-based therapies, based on enteroendocrine peptides released in response to oral nutrients, specifically glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP). The mechanisms by which GLP-1 receptor agonism cause weight reduction are becoming increasingly understood. However, the mechanisms by which GIP receptor-modulating medications cause weight loss remain to be clarified.

AREAS COVERED

This review describes GLP-1 and GIP physiology and explores the conflicting data regarding GIP and weight management. It details examples of how to reconcile the contradictory findings that both GIP receptor agonism and antagonism cause weight reduction. Specifically, it discusses the concept of 'biased agonism' wherein exogenous peptides cause different post-receptor signaling patterns than native ligands. It discusses how GIP effects in adipose tissue and the central nervous system may cause weight reduction. It describes GIP receptor-modulating compounds and their most current trials regarding weight reduction.

EXPERT OPINION

Effects of GIP receptor-modulating compounds on different tissues have implications for both weight reduction and other cardiometabolic diseases. Further study is needed to understand the implications of GIP agonism on not just weight reduction, but also cardiovascular disease, liver disease, bone health and fat storage.

Mechanisms of action and therapeutic applications of GLP-1 and dual GIP/GLP-1 receptor agonists

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are two incretins that bind to their respective receptors and activate the downstream signaling in various tissues and organs. Both GIP and GLP-1 play roles in regulating food intake by stimulating neurons in the brain's satiety center. They also stimulate insulin secretion in pancreatic β-cells, but their effects on glucagon production in pancreatic α-cells differ, with GIP having a glucagonotropic effect during hypoglycemia and GLP-1 exhibiting glucagonostatic effect during hyperglycemia. Additionally, GIP directly stimulates lipogenesis, while GLP-1 indirectly promotes lipolysis, collectively maintaining healthy adipocytes, reducing ectopic fat distribution, and increasing the production and secretion of adiponectin from adipocytes. Together, these two incretins contribute to metabolic homeostasis, preventing both hyperglycemia and hypoglycemia, mitigating dyslipidemia, and reducing the risk of cardiovascular diseases in individuals with type 2 diabetes and obesity. Several GLP-1 and dual GIP/GLP-1 receptor agonists have been developed to harness these pharmacological effects in the treatment of type 2 diabetes, with some demonstrating robust effectiveness in weight management and prevention of cardiovascular diseases. Elucidating the underlying cellular and molecular mechanisms could potentially usher in the development of new generations of incretin mimetics with enhanced efficacy and fewer adverse effects. The treatment guidelines are evolving based on clinical trial outcomes, shaping the management of metabolic and cardiovascular diseases.

Tirzepatide against obesity and insulin-resistance: pathophysiological aspects and clinical evidence

Obesity is a chronic, multifactorial disease in which accumulated excess body fat has a negative impact on health. Obesity continues to rise among the general population, resulting in an epidemic that shows no significant signs of decline. It is directly involved in development of cardiometabolic diseases, ischemic coronary heart disease peripheral arterial disease, heart failure, and arterial hypertension, producing global morbidity and mortality. Mainly, abdominal obesity represents a crucial factor for cardiovascular illness and also the most frequent component of metabolic syndrome. Recent evidence showed that Tirzepatide (TZP), a new drug including both Glucagon Like Peptide 1 (GLP-1) and Glucose-dependent Insulinotropic Polypeptide (GIP) receptor agonism, is effective in subjects with type 2 diabetes (T2D), lowering body weight, fat mass and glycated hemoglobin (HbA1c) also in obese or overweight adults without T2D. This review discusses the pathophysiological mechanisms and clinical aspects of TZP in treating obesity.

Could Insulin Be a Better Regulator of Appetite/Satiety Balance and Body Weight Maintenance in Response to Glucose Exposure Compared to Sucrose Substitutes? Unraveling Current Knowledge and Searching for More Appropriate Choices

BACKGROUND

Insulin exerts a crucial impact on glucose control, cellular growing, function, and metabolism. It is partially modulated by nutrients, especially as a response to the intake of foods, including carbohydrates. Moreover, insulin can exert an anorexigenic effect when inserted into the hypothalamus of the brain, in which a complex network of an appetite/hunger control system occurs. The current literature review aims at thoroughly summarizing and scrutinizing whether insulin release in response to glucose exposure may be a better choice to control body weight gain and related diseases compared to the use of sucrose substitutes (SSs) in combination with a long-term, well-balanced diet.

METHODS

This is a comprehensive literature review, which was performed through searching in-depth for the most accurate scientific databases and applying effective and relevant keywords.

RESULTS

The insulin action can be inserted into the hypothalamic orexigenic/anorexigenic complex system, activating several anorexigenic peptides, increasing the hedonic aspect of food intake, and effectively controlling the human body weight. In contrast, SSs appear not to affect the orexigenic/anorexigenic complex system, resulting in more cases of uncontrolled body weight maintenance while also increasing the risk of developing related diseases.

CONCLUSIONS

Most evidence, mainly derived from in vitro and in vivo animal studies, has reinforced the insulin anorexigenic action in the hypothalamus of the brain. Simultaneously, most available clinical studies showed that SSs during a well-balanced diet either maintain or even increase body weight, which may indirectly be ascribed to the fact that they cannot cover the hedonic aspect of food intake. However, there is a strong demand for long-term longitudinal surveys to effectively specify the impact of SSs on human metabolic health.

Pharmacological Advances in Incretin-Based Polyagonism: What We Know and What We Don't

The prevalence of obesity continues to rise in both adolescents and adults, in parallel obesity is strongly associated with the increased incidence of type 2 diabetes, heart failure, certain types of cancer, and all-cause mortality. In relation to obesity, many pharmacological approaches of the past have tried and failed to combat the rising obesity epidemic, particularly due to insufficient efficacy or unacceptable side effects. However, while the history of antiobesity medication is plagued by failures and disappointments, we have witnessed over the last 10 years substantial progress, particularly in regard to biochemically optimized agonists at the receptor for glucagon-like peptide-1 (GLP-1R) and unimolecular coagonists at the receptors for GLP-1 and the glucose-dependent insulinotropic polypeptide (GIP). Although the GIP receptor:GLP-1R coagonists are being heralded as premier pharmacological tools for the treatment of obesity and diabetes, uncertainty remains as to why these drugs testify superiority over best-in-class GLP-1R monoagonists. Particularly with regard to GIP, there remains great uncertainty if and how GIP acts on systems metabolism and if the GIP system should be activated or inhibited to improve metabolic outcome in adjunct to GLP-1R agonism. In this review, we summarize recent advances in GLP-1- and GIP-based pharmacology and discuss recent findings and open questions related to how the GIP system affects systemic energy and glucose metabolism.

The preclinical discovery and clinical evaluation of tirzepatide for the treatment of type 2 diabetes

INTRODUCTION

Despite numerous antidiabetic medications available for the treatment of type 2 diabetes, a substantial percentage of patients fail to achieve optimal glycemic control. Furthermore, the escalating obesity pandemic underscores the urgent need for effective relevant pharmacotherapies. Tirzepatide, a novel dual GIP and GLP-1 receptor agonist, offers a promising therapeutic option.

AREAS COVERED

This review describes the discovery and clinical development of tirzepatide. Based on data from pivotal in vivo and in vitro studies, the authors present the pharmacodynamic profile of tirzepatide. Furthermore, they summarize data from the clinical trial programs that assessed the efficacy and safety of tirzepatide for the treatment of type 2 diabetes or obesity in a broad spectrum of patients, and discuss its therapeutic potential.

EXPERT OPINION

Tirzepatide effectively reduces glucose levels and body weight in patients with type 2 diabetes and/or obesity, with a generally safe profile. Based on data from phase 3 clinical trials, several agencies have approved its use for the treatment of type 2 diabetes and obesity. Clinicians should be aware of possible adverse events, mainly mild-to-moderate gastrointestinal side effects. Overall, tirzepatide represents a promising treatment option for the treatment of type 2 diabetes.

An imbalanced GLP-1R/GIPR co-agonist peptide with a site-specific N-terminal PEGylation to maximize metabolic benefits

Glycemic and body weight control gained from GLP-1R agonists remains an unmet need for diabetes and obesity treatment, leading to the development of GLP-1R/GIPR co-agonists. An imbalance in GLP-1R/GIPR agonism may extensively maximize the glucose- and weight-lowering effects. Hence, we prepared a potent and imbalanced GLP-1R/GIPR co-agonist, and refined its action time through a site-specific N-terminal PEGylation strategy. The pharmacological efficacy of these resulting long-acting co-agonists was interrogated both in vitro and in vivo. The results showed that peptide 1 possessed potent and imbalanced receptor-stimulating potency favoring GIP activity, but its hypoglycemic action was disrupted probably resulting from its short half-life. After PEGylation to improve the pharmacokinetics, the pharmacological effects were amplified compared to native peptide 1. Among the resulting derivatives, D-5K exhibited significant glycemic, HbA1c, body-weight, and food-intake control, outperforming GLP-1R mono-agonists. Based on its excellent pharmacological profiles, D-5K may hold the great therapeutic potential for diabetes and obesity treatment.

DR10627, a Novel Dual Glucagon‑like Peptide‑1 and Gastric Inhibitory Polypeptide Receptor Agonist for the Treatment of Obesity and Type 2 Diabetes Mellitus

Introduction

Diabetes and obesity are momentous risk factors threatening people's lives and health. Currently available incretin analogue glucagon-like peptide 1 (GLP-1) possesses huge hypoglycemic effect with the unsatisfactory effect of weight loss. Co-agonists targeting GLP-1R plus glucagon receptor (GCGR) or gastric inhibitory polypeptide receptor (GIPR) show synergistic benefits in glycaemic control and weight loss. Here, we describe a novel dual GIP and GLP-1 receptor agonist, DR10627, and performed a preclinical assessment of it.

Methods

The agonistic ability of DR10627 was indirectly assessed by inducing cAMP accumulation in Chinese hamster ovary (CHO) cells transfected with GLP-1R or GIPR in vitro. The plasma pharmacokinetics of DR10627 were analysed in cynomolgus monkeys. The OGTTs were performed in Sprague‑Dawley (SD) rats. The glucose lowering effects were evaluated by repeated administration of DR10627 in diabetic (db/db) mice for 4 weeks. The effects of anti-obesity and improving metabolism of DR10627 were evaluated by repeated administration of DR10627 in diet-induced obesity (DIO) mice for 57 days.

Results

DR10627 had the capacity to activate both GLP-1R and GIPR in vitro. The terminal half-life of DR10627 was found to be approximately 4.19-5.8 h in cynomolgus monkeys. DR10627 had a great improvement in oral glucose tolerance in SD rats. Moreover, DR10627 had a potent glucose-lowering effect in db/db mice, and the hypoglycemic effect of 18 nmol/kg DR10627 was better than that of 50 nmol/kg liraglutide. In addition, 10 and 30 nmol/kg DR10627 possessed the ability of potentiating the weight-loss, lipid-lowing efficacy and improving metabolism to a greater extent than 80 nmol/kg liraglutide.

Conclusion

Preclinical assessment demonstrated that administration of DR10627 resulted in glucose lowering in SD rats and db/db mice, and substantial body weight reduction and metabolism improvement in DIO mice. DR10627 is a promising agent deserving further investigation for the treatment of type 2 diabetes and obesity.

Hypothalamic control of body fat mass by food intake: The key to understanding why obesity should be treated as a disease

BACKGROUND

Hypothalamic centres have been recognized to play a central role in body weight regulation for nearly 70 years.

AIMS

In this review, we will explore the current undersanding of the role the hypothalamus plays in controlling food intake behaviours.

MATERIALS AND METHODS

Review of relevant literature from PubMed searches and review article citations.

RESULTS

Beginning with autopsy studies showing destructive hypothalamic lesions in patients manifesting hyperphagia and rapid weight gain, followed by animal lesioning studies pinpointing adjacent hypothalamic sites as the 'satiety' centre and the 'feeding' centre of the brain, the neurocircuitry that governs our body weight is now understood to consist of a complex, interconnected network, including the hypothalamus and extending to cortical sites, reward centres and brainstem. Neurons in these sites receive afferent signals from the gastrointestinal tract and adipose tissue indicating food availability, calorie content, as well as body fat mass.

DISCUSSION

Integration of these complex signals leads to modulation of the two prime effector systems that defend a body fat mass set point: food intake and energy expenditure.

CONCLUSION

Understanding the hypothalamic control of food intake forms the foundation for understanding and managing obesity as a chronic disease.

The antiemetic actions of GIP receptor agonism

Nausea and vomiting are primitive aspects of mammalian physiology and behavior that ensure survival. Unfortunately, both are ubiquitously present side effects of drug treatments for many chronic diseases with negative consequences on pharmacotherapy tolerance, quality of life, and prognosis. One of the most critical clinical examples is the profound emesis and nausea that occur in patients undergoing chemotherapy, which continue to be among the most distressing side effects, even with the use of modern antiemetic medications. Similarly, antiobesity/diabetes medications that target the glucagon-like peptide-1 system, despite their remarkable metabolic success, also cause nausea and vomiting in a significant number of patients. These side effects hinder the ability to administer higher dosages for optimal glycemic and weight management and represent the major reasons for treatment discontinuation. Our inability to effectively control these side effects highlights the need to anatomically, molecularly, and functionally characterize novel neural substrates that drive and inhibit nausea and emesis. Here, we discuss clinical and preclinical evidence that highlights the glucose-dependent insulinotropic peptide receptor system as a novel therapeutic central target for the management of nausea and emesis.

Incretin hormones and pharmacomimetics rapidly inhibit AgRP neuron activity to suppress appetite

Analogs of the incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) have become mainstays of obesity and diabetes management. However, both the physiologic role of incretin hormones in the control of appetite and the pharmacologic mechanisms by which incretin-mimetic drugs suppress caloric intake remain incompletely understood. Hunger-promoting AgRP-expressing neurons are an important hypothalamic population that regulates food intake. Therefore, we set out to determine how incretins analogs affect their activity in vivo. Using fiber photometry, we observed that both GIP receptor (GIPR) and GLP-1 receptor (GLP-1R) agonism acutely inhibit AgRP neuron activity in fasted mice and reduce the response of AgRP neurons to food. Moreover, optogenetic stimulation of AgRP neurons partially attenuated incretin-induced feeding suppression, suggesting that AgRP neuron inhibition is necessary for the full appetite-suppressing effects of incretin-based therapeutics. Finally, we found that GIP but not GLP-1 is necessary for nutrient-mediated AgRP neuron inhibition, representing a novel physiologic role for GIP in maintaining energy balance. Taken together, these findings reveal neural mechanisms underlying the efficacy of incretin-mimetic obesity therapies. Understanding these drugs' mechanisms of action is crucial for the development of next-generation obesity pharmacotherapies with an improved therapeutic profile.

Recent clinical and pharmacological advancements of incretin-based therapy and the effects of incretin on physiology

A novel therapeutic target for diabetes mellitus is incretin-based therapies, glucagon-like peptide-1, and glucose-dependent insulinotropic polypeptides are released from the gastrointestinal (GI) tract and act on beta cells of pancreatic islets by increasing the secretion of insulin. The management and prevention of diabetes require habitual and pharmacological therapies along with quality and healthy lifestyle. This includes maintaining the body weight, blood glucose level, cardiovascular risk, complexity, and co-morbidities. The utilization of glucagon-like peptide-1 (GLP-1) agonists is an object of research with favorable hemoglobin A1C levels and weight loss in type 1 diabetic patients. However, cost-effectiveness and tolerability, remain significant barriers for patients to using these medications. The risk of suicidal tendencies and thoughts of self-harm have been increased in patients receiving GLP-1 receptor agonists. Tirzepatide treatment showed a potent glucose-lowering effect and promoted weight loss with minimum GI adverse effects in animal studies as well as phase I and II human trials, in comparison with established GLP-1 receptor agonists. The glucose-dependent insulinotropic polypeptide receptor (GIPR) peptide-antagonist effectively blocks the action of gastric-inhibitory-polypeptide (GIP) in vitro and ex vivo in human pancreas and in vivo in rodent models. However, incretin-based therapies have received enormous attention in the last few decades for the treatment of diabetes, obesity, and other repurposing including central nervous system disorders. Therefore, in this article, we demonstrate the overview, physiological, and pharmacological advances of incretin-based pharmacotherapies and their physiological roles. Furthermore, the recent updates of glucagon-like peptide-1 receptor agonist, Glucagon-like peptide-2 receptor agonist, GLP-1/GIP co-agonists, GIP/GLP-1/glucagon triple agonist and GIP-antagonist are also discussed.

Pharmacological modulation of adaptive thermogenesis: new clues for obesity management?

BACKGROUND

Adaptive thermogenesis represents the main mechanism through which the body generates heat in response to external stimuli, a phenomenon that includes shivering and non-shivering thermogenesis. The non-shivering thermogenesis is mainly exploited by adipose tissue characterized by a brown aspect, which specializes in energy dissipation. A decreased amount of brown adipose tissue has been observed in ageing and chronic illnesses such as obesity, a worldwide health problem characterized by dysfunctional adipose tissue expansion and associated cardiometabolic complications. In the last decades, the discovery of a trans-differentiation mechanism ("browning") within white adipose tissue depots, leading to the generation of brown-like cells, allowed to explore new natural and synthetic compounds able to favour this process and thus enhance thermogenesis with the aim of counteracting obesity. Based on recent findings, brown adipose tissue-activating agents could represent another option in addition to appetite inhibitors and inhibitors of nutrient absorption for obesity treatment.

PURPOSE

This review investigates the main molecules involved in the physiological (e.g. incretin hormones) and pharmacological (e.g. β3-adrenergic receptors agonists, thyroid receptor agonists, farnesoid X receptor agonists, glucagon-like peptide-1, and glucagon receptor agonists) modulation of adaptive thermogenesis and the signalling mechanisms involved.

Development of a novel Fc fusion protein dual glucagon-like peptide-1 and gastric inhibitory polypeptide receptor agonists

AIM

To develop and investigate an imbalanced dual gastric inhibitory polypeptide receptor (GIPR)/glucagon-like peptide-1 receptor (GLP-1 R) agonist with Fc fusion protein structure.

METHODS

We designed and constructed an Fc fusion protein that is a dual agonist (HEC-CG115) with an empirically optimized potency ratio for GLP-1R and GIPR. The long-term effects of HEC-CG115 on body weight and glycaemic control were evaluated in diet-induced obese mice and diabetic db/db mice. Repeat dose toxicity assays were performed to investigate the safety profile of HEC-CG115 in Sprague-Dawley rats.

RESULTS

HEC-CG115 displayed high potency for GIPR and relatively low potency for GLP-1R, and we labelled it 'imbalanced'. In animal models, HEC-CG115 (3 nmol/kg) led to more weight loss than semaglutide at a higher dose (10 nmol/kg) in diet-induced obese model mice. HEC-CG115 (one dose every 3 days) reduced fasting blood glucose and glycated haemoglobin levels similar to those after semaglutide (once daily) at the same dose. In a 4-week subcutaneous toxicity study conducted to assess the biosafety of HEC-CG115, the no observed adverse effect level was determined to be 3 mg/kg.

CONCLUSION

HEC-CG115 is a novel Fc fusion protein with imbalanced dual agonism that shows superior weight loss, glycaemic control and metabolic improvement in animal models, and has an optimal safety profile according to a repeat-dose toxicity study. Therefore, the use of HEC-CG115 appears to be safe and effective for the treatment of obesity and type 2 diabetes.

Applications of Enteroendocrine Cells (EECs) Hormone: Applicability on Feed Intake and Nutrient Absorption in Chickens

This review focuses on the role of hormones derived from enteroendocrine cells (EECs) on appetite and nutrient absorption in chickens. In response to nutrient intake, EECs release hormones that act on many organs and body systems, including the brain, gallbladder, and pancreas. Gut hormones released from EECs play a critical role in the regulation of feed intake and the absorption of nutrients such as glucose, protein, and fat following feed ingestion. We could hypothesize that EECs are essential for the regulation of appetite and nutrient absorption because the malfunction of EECs causes severe diarrhea and digestion problems. The importance of EEC hormones has been recognized, and many studies have been carried out to elucidate their mechanisms for many years in other species. However, there is a lack of research on the regulation of appetite and nutrient absorption by EEC hormones in chickens. This review suggests the potential significance of EEC hormones on growth and health in chickens under stress conditions induced by diseases and high temperature, etc., by providing in-depth knowledge of EEC hormones and mechanisms on how these hormones regulate appetite and nutrient absorption in other species.

MC4R in Central and Peripheral Systems

Obesity has emerged as a critical and urgent health burden during the current global pandemic. Among multiple genetic causes, melanocortin receptor-4 (MC4R), involved in food intake and energy metabolism regulation through various signaling pathways, has been reported to be the lead genetic factor in severe and early onset obesity and hyperphagia disorders. Most previous studies have illustrated the roles of MC4R signaling in energy intake versus expenditure in the central system, while some evidence indicates that MC4R is also expressed in peripheral systems, such as the gut and endocrine organs. However, its physiopathological function remains poorly defined. This review aims to depict the central and peripheral roles of MC4R in energy metabolism and endocrine hormone homeostasis, the diversity of phenotypes, biased downstream signaling caused by distinct MC4R mutations, and current drug development targeting the receptor.

Neurochemical Basis of Inter-Organ Crosstalk in Health and Obesity: Focus on the Hypothalamus and the Brainstem

Precise neural regulation is required for maintenance of energy homeostasis. Essential to this are the hypothalamic and brainstem nuclei which are located adjacent and supra-adjacent to the circumventricular organs. They comprise multiple distinct neuronal populations which receive inputs not only from other brain regions, but also from circulating signals such as hormones, nutrients, metabolites and postprandial signals. Hence, they are ideally placed to exert a multi-tier control over metabolism. The neuronal sub-populations present in these key metabolically relevant nuclei regulate various facets of energy balance which includes appetite/satiety control, substrate utilization by peripheral organs and glucose homeostasis. In situations of heightened energy demand or excess, they maintain energy homeostasis by restoring the balance between energy intake and expenditure. While research on the metabolic role of the central nervous system has progressed rapidly, the neural circuitry and molecular mechanisms involved in regulating distinct metabolic functions have only gained traction in the last few decades. The focus of this review is to provide an updated summary of the mechanisms by which the various neuronal subpopulations, mainly located in the hypothalamus and the brainstem, regulate key metabolic functions.

Perspectives on weight control in diabetes - Tirzepatide

Tirzepatide, a once-weekly glucose-dependent insulinotropic polypeptide (GIP)/glucagon-like peptide-1 (GLP-1) receptor agonist (GIP/GLP-1 RA) improves glycemic control. Besides improvement of glycemic control, tirzepatide treatment is associated with significantly more weight loss as compared to potent selective GLP-1 receptor agonists as well as other beneficial changes in cardio-metabolic parameters, such as reduced fat mass, blood pressure, improved insulin sensitivity, lipoprotein concentrations, and circulating metabolic profile in individuals with type 2 diabetes (T2D). Some of these changes are partially associated with weight reduction. We review here the putative mechanisms of GIP receptor agonism contributing to GLP-1 receptor agonism-induced weight loss and respective findings with GIP/GLP-1 RAs, including tirzepatide in T2D preclinical models and clinical studies. Subsequently, we summarize the clinical data on weight loss and related non-glycemic metabolic changes of tirzepatide in T2D. These findings suggest that the robust weight loss and associated changes are important contributors to the clinical profile of tirzepatide for the treatment of T2D diabetes and serve as the basis for further investigations including clinical outcomes.

Multifaceted Roles of GLP-1 and Its Analogs: A Review on Molecular Mechanisms with a Cardiotherapeutic Perspective

Diabetes is one of the chronic metabolic disorders which poses a multitude of life-debilitating challenges, including cardiac muscle impairment, which eventually results in heart failure. The incretin hormone glucagon-like peptide-1 (GLP-1) has gained distinct recognition in reinstating glucose homeostasis in diabetes, while it is now largely accepted that it has an array of biological effects in the body. Several lines of evidence have revealed that GLP-1 and its analogs possess cardioprotective effects by various mechanisms related to cardiac contractility, myocardial glucose uptake, cardiac oxidative stress and ischemia/reperfusion injury, and mitochondrial homeostasis. Upon binding to GLP-1 receptor (GLP-1R), GLP-1 and its analogs exert their effects via adenylyl cyclase-mediated cAMP elevation and subsequent activation of cAMP-dependent protein kinase(s) which stimulates the insulin release in conjunction with enhanced Ca²⁺ and ATP levels. Recent findings have suggested additional downstream molecular pathways stirred by long-term exposure of GLP-1 analogs, which pave the way for the development of potential therapeutic molecules with longer lasting beneficial effects against diabetic cardiomyopathies. This review provides a comprehensive overview of the recent advances in the understanding of the GLP-1R-dependent and -independent actions of GLP-1 and its analogs in the protection against cardiomyopathies.

Elucidating the central anorexigenic mechanism of glucagon-like peptide 1 in Japanese quail (Coturnix japonica)

Glucagon-like peptide 1 (GLP-1) elicits a potent reduction in food intake, although the central mechanism mediating this appetite-suppressive effect is not fully understood in all species. To begin to elucidate the molecular mechanisms in quail, we administered GLP-1 via intracerebroventricular (ICV) injection to 7-day-old Japanese quail(Coturnix japonica) and determined effects on food and water intake, behavior, and brain nucleus activation. We observed a reduction in food and water intake, with the lowest effective dose being 0.01 nmol. Quail injected with GLP-1 displayed fewer steps, feeding pecks, exploratory pecks, and jumps, while time spent sitting increased. We quantified c-Fos immunoreactivity at 60 minutes post-injection in hypothalamic and brainstem nuclei that mediate food intake and determined that the hypothalamic paraventricular nucleus (PVN), and nucleus of the solitary tract and area postrema of the brainstem were activated in response to GLP-1.In conclusion, these results suggest that GLP-1 induces anorexigenic effects that are likely mediated at the level of the PVN and brainstem.

Study on the Hyperglycemic Effect of GLP-1 in Spinibarbus denticulatus by Oral Administration and Intraperitoneal Injection Methods

Glucagon-like peptide-1 (GLP-1), one of the expression products of the proglucagon (pg) gene, is an incretin mainly secreted by the gastrointestinal system. In mammals, GLP-1 has hypoglycemic and food-inhibiting effects; while in some fish species, it has been confirmed to increase blood glucose by promoting gluconeogenesis and stimulating glycogenolysis. In order to more deeply understand the role of GLP-1 in the process of glycometabolism in herbivorous fish, the pg gene was cloned from Spinibarbus denticulatus to obtain its sequence characteristics, and the changes in blood glucose level and pg gene expression in S. denticulatus were further explored by feeding with three kinds of carbohydrates and intraperitoneal injection of GLP-1. Basal and temporal blood glucose levels and pg gene expression of S. denticulatus (91.68 ± 10.79 g) were measured at 0, 1, 3, 5, 7, and 12 h after oral administration (n = 4). Then, the changes of blood glucose levels and pg and glucokinase (gk) gene expressions of S. denticulatus (94.29 ± 10.82 g) were determined at 0, 30, 60, and 120 min after intraperitoneal injection (n = 4). It was shown that polysaccharides could induce the upregulation of pg gene expression faster than monosaccharides and stimulate the secretion of GLP-1 in the intestine. Intraperitoneal injection of GLP-1 peptide rapidly raised blood glucose levels, and pg gene expression in the anterior intestine, whole brain, and hepatopancreas decreased continuously after 30 minutes. These results showed that S. denticulatus might inhibit the excessive accumulation of blood glucose by reducing the expression of the pg gene and increasing the expression of gk gene in a short time. It was speculated that GLP-1 of S. denticulatus might have a "gut-brain-liver" pathway similar to mammals in glycemia regulation. Therefore, this study provided a novel perspective for explaining the functional differences of GLP-1 in herbivorous fish and mammals.

Obesity and Type 2 Diabetes: Adiposopathy as a Triggering Factor and Therapeutic Options

Obesity and type 2 diabetes (T2DM) are major public health concerns associated with serious morbidity and increased mortality. Both obesity and T2DM are strongly associated with adiposopathy, a term that describes the pathophysiological changes of the adipose tissue. In this review, we have highlighted adipose tissue dysfunction as a major factor in the etiology of these conditions since it promotes chronic inflammation, dysregulated glucose homeostasis, and impaired adipogenesis, leading to the accumulation of ectopic fat and insulin resistance. This dysfunctional state can be effectively ameliorated by the loss of at least 15% of body weight, that is correlated with better glycemic control, decreased likelihood of cardiometabolic disease, and an improvement in overall quality of life. Weight loss can be achieved through lifestyle modifications (healthy diet, regular physical activity) and pharmacotherapy. In this review, we summarized different effective management strategies to address weight loss, such as bariatric surgery and several classes of drugs, namely metformin, GLP-1 receptor agonists, amylin analogs, and SGLT2 inhibitors. These drugs act by targeting various mechanisms involved in the pathophysiology of obesity and T2DM, and they have been shown to induce significant weight loss and improve glycemic control in obese individuals with T2DM.

Glucose-dependent insulinotropic polypeptide counteracts diet-induced obesity along with reduced feeding, elevated plasma leptin and activation of leptin-responsive and proopiomelanocortin neurons in the arcuate nucleus

AIM

To clarify the effects of glucose-dependent insulinotropic polypeptide (GIP) receptor agonists (GIPRAs) on feeding and body weight.

MATERIALS AND METHODS

Acute and subchronic effects of subcutaneous GIPFA-085, a long-acting GIPRA, on blood glucose, food intake, body weight, respiratory exchange ratio and plasma leptin levels were measured in diet-induced obese (DIO) mice and/or functional leptin-deficient ob/ob mice. The effects of GIPFA-085 on the hypothalamic arcuate nucleus (ARC) neurons from lean and DIO mice were studied by measuring cytosolic Ca²⁺ concentration ([Ca²⁺ ]_i ).

RESULTS

Single bolus GIPFA-085 (30, 300 nmol/kg) dose-dependently reduced blood glucose in glucose tolerance tests, elevated plasma leptin levels at 0.5-6 hours and inhibited food intake at 2-24 hours after injection in DIO mice. Daily GIPFA-085 (300 nmol/kg) inhibited food intake and increased fat utilization on day 1, and reduced body weight gain on days 3-12 of treatment in DIO, but not ob/ob, mice. GIPFA-085 increased [Ca²⁺ ]_i in the ARC leptin-responsive and proopiomelanocortin (POMC) neurons. GIPFA-085 and leptin cooperated to increase [Ca²⁺ ]_i in ARC neurons and inhibit food intake.

CONCLUSIONS

GIPFA-085 acutely inhibits feeding and increases lipid utilization, and sustainedly lowers body weight in DIO mice via mechanisms involving rises in leptin and activation of ARC leptin-responsive and POMC neurons. This study highlights the therapeutic potential of GIPRAs for treating obesity and diabetes.

Effects of site-directed mutagenesis of GLP-1 and glucagon receptors on signal transduction activated by dual and triple agonists

The paradigm of one drug against multiple targets, known as unimolecular polypharmacology, offers the potential to improve efficacy while overcoming some adverse events associated with the treatment. This approach is best exemplified by targeting two or three class B1 G protein-coupled receptors, namely, glucagon-like peptide-1 receptor (GLP-1R), glucagon receptor (GCGR) and glucose-dependent insulinotropic polypeptide receptor for treatment of type 2 diabetes and obesity. Some of the dual and triple agonists have already shown initial successes in clinical trials, although the molecular mechanisms underlying their multiplexed pharmacology remain elusive. In this study we employed structure-based site-directed mutagenesis together with pharmacological assays to compare agonist efficacy across two key signaling pathways, cAMP accumulation and ERK1/2 phosphorylation (pERK1/2). Three dual agonists (peptide 15, MEDI0382 and SAR425899) and one triple agonist (peptide 20) were evaluated at GLP-1R and GCGR, relative to the native peptidic ligands (GLP-1 and glucagon). Our results reveal the existence of residue networks crucial for unimolecular agonist-mediated receptor activation and their distinct signaling patterns, which might be useful to the rational design of biased drug leads.

How dietary amino acids and high protein diets influence insulin secretion

Glucose homeostasis is the maintenance and regulation of blood glucose concentration within a tight physiological range, essential for the functioning of most tissues and organs. This is primarily achieved by pancreatic secretion of insulin and glucagon. Deficient pancreatic endocrine function, coupled with or without peripheral insulin resistance leads to prolonged hyperglycemia with chronic impairment of glucose homeostasis, most commonly seen in diabetes mellitus. High protein diets (HPDs) are thought to modulate glucose homeostasis through various metabolic pathways. Insulin secretion can be directly modulated by the amino acid products of protein digestion, which activate nutrient receptors and nutrient transporters expressed by the endocrine pancreas. Insulin secretion can also be modulated indirectly, through incretin release from enteroendocrine cells, and via vagal neuronal pathways. Additionally, glucose homeostasis can be promoted by the satiating effects of anorectic hormones released following HPD consumption. This review summarizes the insulinotropic mechanisms by which amino acids and HPDs may influence glucose homeostasis, with a particular focus on their applicability in the management of Type 2 diabetes mellitus.

Tirzepatide suppresses palatable food intake by selectively reducing preference for fat in rodents

AIM

To investigate the role of glucose-dependent insulinotropic polypeptide receptor (GIPR) agonists alone or combined with glucagon-like peptide-1 receptor (GLP-1R) agonists to regulate palatable food intake and the role of specific macronutrients in these preferences.

METHODS

To understand this regulation, we treated mice and rats on several choice diet paradigms of chow and a palatable food option with individual or dual GIPR and GLP-1R agonists.

RESULTS

In mice, the dual agonist tirzepatide suppressed total caloric intake, while promoting the intake of chow over a high fat/sucrose diet. Surprisingly, GIPR agonism alone did not alter food choice. The food intake shift observed with tirzepatide in wild-type mice was completely absent in GLP-1R knockout mice, suggesting that GIPR signalling does not regulate food preference. Tirzepatide also selectively suppressed the intake of palatable food but not chow in a rat two-diet choice model. This suppression was specific to lipids, as GLP-1R agonist and dual agonist treatment in rats on a choice paradigm assessing individual palatable macronutrients robustly inhibited the intake of Crisco (lipid) without decreasing the intake of a sucrose (carbohydrate) solution.

CONCLUSIONS

Decreasing preference for high-caloric, high-fat foods is a powerful action of GLP-1R and dual GIPR/GLP-1R agonist therapeutics, which may contribute to the weight loss success of these drugs.

Obesity pharmacotherapy: incretin action in the central nervous system

The prevalence of obesity is rising, creating an urgent need for efficacious therapies. Recent clinical trials show that tirzepatide, a dual agonist of receptors for the incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), yields more weight loss than selective GLP-1 receptor (GLP-1R) agonists. Incretin receptors in the central nervous system (CNS) may contribute to these effects. Yet exactly how each receptor regulates body weight from within the CNS is not clearly understood. It remains especially unclear how GIP receptor (GIPR) signalling contributes to the effects of tirzepatide because both stimulation and inhibition of CNS GIPRs yield weight loss in preclinical models. We summarise current knowledge on CNS incretin receptor pharmacology to provide insight into the potential mechanisms of action of dual GIPR/GLP-1R agonists, with tirzepatide as the exemplar. In addition, we discuss recent developments in incretin-based dual- and tri-agonism for inducing weight loss in obese individuals.

Effect of dual glucose-dependent insulinotropic peptide/glucagon-like peptide-1 receptor agonist on weight loss in subjects with obesity

The occurrence of obesity is an increasing issue worldwide, especially in industrialized countries. Weight loss is important both to treat obesity and to prevent the development of complications. Currently, several drugs are used to treat obesity, but their efficacy is modest. Thus, new anti-obesity treatments are needed. Recently, there has been increased interest in the development of incretins that combine body-weight-lowering and glucose-lowering effects. Therefore, a new drug that simultaneously coactivates both the glucose-dependent insulinotropic polypeptide (GIP) receptor (GIPR) and the glucagon-like peptide-1 receptor (GLP-1R) has been developed. Tirzepatide, the first in this class, improves glycemic control by increasing insulin sensitivity and lipid metabolism as well as by reducing body weight. Combining the activation of the two receptors, greater improvement of β-cell function offers more effective treatment of diabetes and obesity with fewer adverse effects than selective GLP-1R agonists. In the present review, we discuss the progress in the use of GIPR and GLP-1R coagonists and review literature from in vitro studies, animal studies, and human trials, highlighting the synergistic mechanisms of tirzepatide.

Mucosal and hormonal adaptations after Roux-en-Y gastric bypass

The aim of this study was to perform a comprehensive literature review regarding the relevant hormonal and histologic changes observed after Roux-en-Y gastric bypass (RYGB). We aimed to describe the relevant hormonal (glucagon-like peptides 1 and 2 [GLP-1 and GLP-2], peptide YY [PYY], oxyntomodulin [OXM], bile acids [BA], cholecystokinin [CCK], ghrelin, glucagon, gastric inhibitory polypeptide [GIP], and amylin) profiles, as well as the histologic (mucosal cellular) adaptations happening after patients undergo RYGB. Our review compiles the current evidence and furthers the understanding of the rationale behind the food intake regulatory adaptations occurring after RYGB surgery. We identify gaps in the literature where the potential for future investigations and therapeutics may lie. We performed a comprehensive database search without language restrictions looking for RYGB bariatric surgery outcomes in patients with pre- and postoperative blood work hormonal profiling and/or gut mucosal biopsies. We gathered the relevant study results and describe them in this review. Where human findings were lacking, we included animal model studies. The amalgamation of physiologic, metabolic, and cellular adaptations following RYGB is yet to be fully characterized. This constitutes a fundamental aspiration for enhancing and individualizing obesity therapy.

Tremella fuciformis polysaccharide reduces obesity in high-fat diet-fed mice by modulation of gut microbiota

Obesity is a metabolic disease associated with gut microbiota and low-grade chronic inflammation. Tremella fuciformis is a medicinal and edible fungus; polysaccharide (TP) is the main active component, which has a variety of biological activities, such as hypoglycemic and hypolipidemic. However, the anti-obesity effects and potential mechanisms of TP have never been reported. This study was conducted to elucidate the inhibitory effect of TP on high-fat diet (HFD)-induced obesity in mice. Mice were split into five groups: normal chow diet (NCD) group, NCD_TP_H group, HFD group, HFD_TP_L group and HFD_TP_H group. Our study showed that TP inhibited high-fat diet-induced weight gain and fat accumulation in mice and reduced blood glucose, hyperlipidemia and inflammation. TP also improved gut microbiota disorders by reducing the Firmicutes/Bacteroidetes ratio and modulating the relative abundance of specific gut microbiota. We also found that the anti-obesity and gut microbiota-modulating effects of TP could be transferred to HFD-fed mice via faecal microbiota transplantation (FMT), confirming that the gut microbiota was one of the targets of TP for obesity inhibition. Further studies showed that TP increased the production of short-chain fatty acids and the secretion of intestinal hormones. Our studies showed that TP inhibited obesity by modulating inflammation and the microbe-gut-brain axis, providing a rationale for developing TP to treat obesity and its complications.

Tirzepatide, the Newest Medication for Type 2 Diabetes: A Review of the Literature and Implications for Clinical Practice

Objective:

The objective of this article was to review pharmacology, efficacy, safety, and place in therapy of tirzepatide, a dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist.

Data Sources:

PubMed/MEDLINE and ClinicalTrials.gov were searched through September 7, 2022, using the keyword “tirzepatide.”

Study Selection and Data Extraction:

Clinical trials with available results were included.

Data Synthesis:

Seven published phase 3, multicenter, randomized, parallel-group trials investigated efficacy and safety of tirzepatide versus placebo, semaglutide, insulin degludec, and insulin glargine for type 2 diabetes mellitus (T2DM) treatment. Studies included adults with uncontrolled T2DM and body mass index above 23 or 25 kg/m2. Hemoglobin A1c reduction from baseline was greater with tirzepatide across all studies with absolute reductions up to 3.02% and relative reductions ranging 0.44% (vs semaglutide) to 2.11% (vs placebo). Weight loss was significant. Incidence of gastrointestinal adverse effects (AE) was similar to semaglutide, and major cardiovascular events was similar to insulin glargine.

Relevance to Patient Care and Clinical Practice:

Studies demonstrated greater A1c lowering and weight reduction versus placebo and active comparators with AE similar to semaglutide, suggesting tirzepatide will be a valuable addition to the growing list of antidiabetic medications. Although tirzepatide’s effects on major cardiovascular events was not increased when compared with insulin glargine, further evidence is needed to assess long-term implications on cardiovascular outcomes compared with agents with proven cardiovascular benefits.

Conclusions:

Tirzepatide has the potential to significantly impact the clinical management of T2DM, and results of ongoing clinical trials will help to fully determine its place in therapy.

Tirzepatide, a dual GIP/GLP-1 receptor co-agonist for the treatment of type 2 diabetes with unmatched effectiveness regrading glycaemic control and body weight reduction

Tirzepatide is the first dual GIP/GLP-1 receptor co-agonist approved for the treatment of type 2 diabetes in the USA, Europe, and the UAE. Tirzepatide is an acylated peptide engineered to activate the GIP and GLP-1 receptors, key mediators of insulin secretion that are also expressed in regions of the brain that regulate food intake. Five clinical trials in type 2-diabetic subjects (SURPASS 1-5) have shown that tirzepatide at 5-15 mg per week reduces both HbA1c (1.24 to 2.58%) and body weight (5.4-11.7 kg) by amounts unprecedented for a single agent. A sizable proportion of patients (23.0 to 62.4%) reached an HbA1c of < 5.7% (which is the upper limit of the normal range indicating normoglycaemia), and 20.7 to 68.4% lost more than 10% of their baseline body weight. Tirzepatide was significantly more effective in reducing HbA1c and body weight than the selective GLP-1 RA semaglutide (1.0 mg per week), and titrated basal insulin. Adverse events related to tirzepatide were similar to what has been reported for selective GLP-1RA, mainly nausea, vomiting, diarrhoea, and constipation, that were more common at higher doses. Cardiovascular events have been adjudicated across the whole study program, and MACE-4 (nonfatal myocardial infarction, non-fatal stroke, cardiovascular death and hospital admission for angina) events tended to be reduced over up to a 2 year-period, albeit with low numbers of events. For none of the cardiovascular events analysed (MACE-4, or its components) was a hazard ratio > 1.0 vs. pooled comparators found in a meta-analysis covering the whole clinical trial program, and the upper bounds of the confidence intervals for MACE were < 1.3, fulfilling conventional definitions of cardiovascular safety. Tirzepatide was found to improve insulin sensitivity and insulin secretory responses to a greater extent than semaglutide, and this was associated with lower prandial insulin and glucagon concentrations. Both drugs caused similar reductions in appetite, although tirzepatide caused greater weight loss. While the clinical effects of tirzepatide have been very encouraging, important questions remain as to the mechanism of action. While GIP reduces food intake and body weight in rodents, these effects have not been demonstrated in humans. Moreover, it remains to be shown that GIPR agonism can improve insulin secretion in type 2 diabetic patients who have been noted in previous studies to be unresponsive to GIP. Certainly, the apparent advantage of tirzepatide, a dual incretin agonist, over GLP-1RA will spark renewed interest in the therapeutic potential of GIP in type 2 diabetes, obesity and related co-morbidities.

Signaling pathways in obesity: mechanisms and therapeutic interventions

Obesity is a complex, chronic disease and global public health challenge. Characterized by excessive fat accumulation in the body, obesity sharply increases the risk of several diseases, such as type 2 diabetes, cardiovascular disease, and nonalcoholic fatty liver disease, and is linked to lower life expectancy. Although lifestyle intervention (diet and exercise) has remarkable effects on weight management, achieving long-term success at weight loss is extremely challenging, and the prevalence of obesity continues to rise worldwide. Over the past decades, the pathophysiology of obesity has been extensively investigated, and an increasing number of signal transduction pathways have been implicated in obesity, making it possible to fight obesity in a more effective and precise way. In this review, we summarize recent advances in the pathogenesis of obesity from both experimental and clinical studies, focusing on signaling pathways and their roles in the regulation of food intake, glucose homeostasis, adipogenesis, thermogenesis, and chronic inflammation. We also discuss the current anti-obesity drugs, as well as weight loss compounds in clinical trials, that target these signals. The evolving knowledge of signaling transduction may shed light on the future direction of obesity research, as we move into a new era of precision medicine.

Glucose-Dependent Insulinotropic Polypeptide-A Postprandial Hormone with Unharnessed Metabolic Potential

Glucose-dependent insulinotropic polypeptide (GIP) is released from the upper small intestine in response to food intake and contributes to the postprandial control of nutrient disposition, including of sugars and fats. Long neglected as a potential therapeutic target, the GIPR axis has received increasing interest recently, with the emerging data demonstrating the metabolically favorable outcomes of adding GIPR agonism to GLP-1 receptor agonists in people with type 2 diabetes and obesity. This review examines the physiology of the GIP axis, from the mechanisms underlying GIP secretion from the intestine to its action on target tissues and therapeutic development. Expected final online publication date for the Annual Review of Nutrition, Volume 42 is August 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Potential Therapeutic Targeting Neurotransmitter Receptors in Diabetes

Neurotransmitters are signaling molecules secreted by neurons to coordinate communication and proper function among different sections in the central neural system (CNS) by binding with different receptors. Some neurotransmitters as well as their receptors are found in pancreatic islets and are involved in the regulation of glucose homeostasis. Neurotransmitters can act with their receptors in pancreatic islets to stimulate or inhibit the secretion of insulin (β cell), glucagon (α cell) or somatostatin (δ cell). Neurotransmitter receptors are either G-protein coupled receptors or ligand-gated channels, their effects on blood glucose are mainly decided by the number and location of them in islets. Dysfunction of neurotransmitters receptors in islets is involved in the development of β cell dysfunction and type 2 diabetes (T2D).Therapies targeting different transmitter systems have great potential in the prevention and treatment of T2D and other metabolic diseases.

ANGT_HUMAN[448–462], an Anorexigenic Peptide Identified using Plasma Peptidomics

The discovery of bioactive peptides is an important research target that enables the elucidation of the pathophysiology of human diseases and provides seeds for drug discovery. Using a large number of native peptides previously identified using plasma peptidomics technology, we sequentially synthesized selected sequences and subjected them to functional screening using human cultured cells. A 15-amino-acid residue proangiotensinogen-derived peptide, designated ANGT_HUMAN[448–462], elicited cellular responses and bound to cultured human cells. Synthetic fluorescent-labeled and biotinylated ANGT_HUMAN[448–462] peptides were rendered to bind to cell- and tissue-derived proteins and peptide-cell protein complexes were retrieved and analyzed using liquid chromatography-tandem mass spectrometry, revealing the β-subunit of ATP synthase as its cell-surface binding protein. Because ATP synthase mediates the effects of anorexigenic peptides, the ability of ANGT_HUMAN[448–462] to modulate eating behavior in mice was investigated. Both intraperitoneal and intracerebroventricular injections of low doses of ANGT_HUMAN[448–462] suppressed spontaneous food and water intake throughout the dark phase of the diurnal cycle without affecting locomotor activity. Immunoreactive ANGT_HUMAN[448–462], distributed throughout human tissues and in human-derived cells, is mostly co-localized with angiotensin II and is occasionally present separately from angiotensin II. In this study, an anorexigenic peptide, ANGT_HUMAN[448–462], was identified by exploring cell surface target proteins of the human native peptides identified using plasma peptidomics.

Large-scale GWAS of food liking reveals genetic determinants and genetic correlations with distinct neurophysiological traits

We present the results of a GWAS of food liking conducted on 161,625 participants from the UK-Biobank. Liking was assessed over 139 specific foods using a 9-point scale. Genetic correlations coupled with structural equation modelling identified a multi-level hierarchical map of food-liking with three main dimensions: "Highly-palatable", "Acquired" and "Low-caloric". The Highly-palatable dimension is genetically uncorrelated from the other two, suggesting that independent processes underlie liking high reward foods. This is confirmed by genetic correlations with MRI brain traits which show with distinct associations. Comparison with the corresponding food consumption traits shows a high genetic correlation, while liking exhibits twice the heritability. GWAS analysis identified 1,401 significant food-liking associations which showed substantial agreement in the direction of effects with 11 independent cohorts. In conclusion, we created a comprehensive map of the genetic determinants and associated neurophysiological factors of food-liking.

Gut peptide regulation of food intake - evidence for the modulation of hedonic feeding

The number of people living with obesity has tripled worldwide since 1975 with serious implications for public health, as obesity is linked to a significantly higher chance of early death from associated comorbidities (metabolic syndrome, type 2 diabetes, cardiovascular disease and cancer). As obesity is a consequence of food intake exceeding the demands of energy expenditure, efforts are being made to better understand the homeostatic and hedonic mechanisms governing food intake. Gastrointestinal peptides are secreted from enteroendocrine cells in response to nutrient and energy intake, and modulate food intake either via afferent nerves, including the vagus nerve, or directly within the central nervous system, predominantly gaining access at circumventricular organs. Enteroendocrine hormones modulate homeostatic control centres at hypothalamic nuclei and the dorso-vagal complex. Additional roles of these peptides in modulating hedonic food intake and/or preference via the neural systems of reward are starting to be elucidated, with both peripheral and central peptide sources potentially contributing to central receptor activation. Pharmacological interventions and gastric bypass surgery for the treatment of type 2 diabetes and obesity elevate enteroendocrine hormone levels and also alter food preference. Hence, understanding of the hedonic mechanisms mediated by gut peptide action could advance development of potential therapeutic strategies for the treatment of obesity and its comorbidities.

The incretin/glucagon system as a target for pharmacotherapy of obesity

Obesity is a chronic, multifactorial, relapsing disease. Despite multicomponent lifestyle interventions, including pharmacotherapy, maintaining bodyweight loss is challenging for many people. The pathophysiology of obesity is complex, and currently approved pharmacotherapies only target a few of the many pathways involved; thus, single-targeting agents have limited efficacy. Proglucagon-derived peptides, glucagon, and the incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), represent attractive targets for managing obesity and metabolic disorders because they may have direct roles in multiple mechanisms including satiety, energy homeostasis, and lipolytic activity. Unimolecular dual and triple agonists targeting glucagon and incretin hormone receptors have been shown to promote bodyweight loss, lower glucose levels, and reduce food intake in animal models of obesity. Multiple dual receptor agonists are in clinical development for the treatment of obesity, including GLP-1/GIP and GLP-1/glucagon receptor agonists. The extent to which glucagon contributes to treatment effects remains to be understood, but it may promote bodyweight loss by reducing food intake, while concomitant GLP-1 receptor agonism ensures normal glucose control. Further research is required to fully understand the molecular mechanisms of action and metabolic effects of both dual and triple receptor agonists.

The Emerging Role of Dual GLP-1 and GIP Receptor Agonists in Glycemic Management and Cardiovascular Risk Reduction

The incretin pathway is a self-regulating feedback system connecting the gut with the brain, pancreas, and liver. Its predominant action is on the postprandial glucose levels, with extraglycemic effects on fat metabolism and endovascular function. Of the two main incretin hormones released with food ingestion, the actions of glucagon-like peptide-1 (GLP-1) have been exploited for therapeutic benefit. However, little attention has been paid to glucose-dependent insulinotropic polypeptide (GIP) until the recent experimental introduction of dual agonists, or "twincretins". Interestingly, simultaneous activation of both receptors is not only replicative of normal physiology, it seems to be an innovative way to enhance their mutual salubrious actions. In patients with type 2 diabetes, dual agonists can have powerful benefits for glucose control and weight reduction. Additionally, there is mounting evidence of their favorable cardiovascular impact, making them potentially appealing pharmacologic agents of choice in the future. Although we seem to be poised on the horizons of exciting new breakthroughs, much knowledge has yet to be gained before these novel agents are ready for prime time.