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.

Human OPRM1 and murine Oprm1 promoter driven viral constructs for genetic access to µ-opioidergic cell types.

With concurrent global epidemics of chronic pain and opioid use disorders, there is a critical need to identify, target and manipulate specific cell populations expressing the mu-opioid receptor (MOR). However, available tools and transgenic models for gaining long-term genetic access to MOR+ neural cell types and circuits involved in modulating pain, analgesia and addiction across species are limited. To address this, we developed a catalog of MOR promoter (MORp) based constructs packaged into adeno-associated viral vectors that drive transgene expression in MOR+ cells. MORp constructs designed from promoter regions upstream of the mouse Oprm1 gene (mMORp) were validated for transduction efficiency and selectivity in endogenous MOR+ neurons in the brain, spinal cord, and periphery of mice, with additional studies revealing robust expression in rats, shrews, and human induced pluripotent stem cell (iPSC)-derived nociceptors. The use of mMORp for in vivo fiber photometry, behavioral chemogenetics, and intersectional genetic strategies is also demonstrated. Lastly, a human designed MORp (hMORp) efficiently transduced macaque cortical OPRM1+ cells. Together, our MORp toolkit provides researchers cell type specific genetic access to target and functionally manipulate mu-opioidergic neurons across a range of vertebrate species and translational models for pain, addiction, and neuropsychiatric disorders.

Novel Insights into the Physiology of Nutrient Sensing and Gut-Brain Communication in Surgical and Experimental Obesity Therapy.

Despite standardized surgical technique and peri-operative care, metabolic outcomes of bariatric surgery are not uniform. Adaptive changes in brain function may play a crucial role in achieving optimal postbariatric weight loss. This review follows the anatomic-physiologic structure of the postbariatric nutrient-gut-brain communication chain through its key stations and provides a concise summary of recent findings in bariatric physiology, with a special focus on the composition of the intestinal milieu, intestinal nutrient sensing, vagal nerve-mediated gastrointestinal satiation signals, circulating hormones and nutrients, as well as descending neural signals from the forebrain. The results of interventional studies using brain or vagal nerve stimulation to induce weight loss are also summarized. Ultimately, suggestions are made for future diagnostic and therapeutic research for the treatment of obesity.

Creation of a Peptide Antagonist of the GFRAL-RET Receptor Complex for the Treatment of GDF15-Induced Malaise.

Growth differentiation factor 15 (GDF15) is a contributor to nausea, emesis, and anorexia following chemotherapy via binding to the GFRAL-RET receptor complex expressed in hindbrain neurons. Therefore, GDF15-mediated GFRAL-RET signaling is a promising target for improving treatment outcomes for chemotherapy patients. We developed peptide-based antagonists of GFRAL that block GDF15-mediated RET recruitment. Our initial library screen led to five novel peptides. Surface plasmon resonance and flow cytometric analyses of the most efficacious of this group, termed GRASP, revealed its capacity to bind to GFRAL. In vivo studies in rats revealed that GRASP could attenuate GDF15-induced nausea and anorexia resulting from cisplatin. Combined with Ondansetron, GRASP led to an even greater attenuation of the anorectic effects of cisplatin compared to either agent alone. Our results highlight the beneficial effects of GRASP as an agent to combat chemotherapy-induced malaise. GRASP may also be effective in other conditions associated with elevated levels of GDF15.

GPR-160 Receptor Signaling in the Dorsal Vagal Complex of Male Rats Modulates Meal Microstructure and CART-Mediated Hypophagia.

The g-protein coupled receptor GPR-160, recently identified as a putative receptor for the cocaine and amphetamine-regulated transcript (CART) peptide, shows abundant expression in the energy-balance control nuclei, including the dorsal vagal complex (DVC). However, its physiological role in the control of food intake has yet to be fully explored. Here, we performed a virally mediated, targeted knockdown (KD) of Gpr160 in the DVC of male rats to evaluate its physiological role in control of feeding. Our results indicate that DVC Gpr160 KD affects meal microstructure. Specifically, DVC Gpr160 KD animals consumed more frequent, but shorter meals during the dark phase and showed decreased caloric intake and duration of meals during the light phase. Cumulatively, however, these bidirectional effects on feeding resulted in no difference in body weight gain. We next tested the role of DVC GPR-160 in mediating the anorexigenic effects of exogenous CART. Our results show that DVC Gpr160 KD partially attenuates CART's anorexigenic effects. To further characterize Gpr160+ cells in the DVC, we utilized single-nucleus RNA sequencing data to uncover abundant GPR-160 expression in DVC microglia and only minimal expression in neurons. Altogether, our results suggest that DVC CART signaling may be mediated by Gpr160+ microglia, which in turn may be modulating DVC neuronal activity to control food intake.

GIP receptor agonism blocks chemotherapy-induced nausea and vomiting.

OBJECTIVE: Nausea and vomiting remain life-threatening obstacles to successful treatment of chronic diseases, despite a cadre of available antiemetic medications. Our inability to effectively control chemotherapy-induced nausea and vomiting (CINV) highlights the need to anatomically, molecularly, and functionally characterize novel neural substrates that block CINV. METHODS: Behavioral pharmacology assays of nausea and emesis in 3 different mammalian species were combined with histological and unbiased transcriptomic analyses to investigate the beneficial effects of glucose-dependent insulinotropic polypeptide receptor (GIPR) agonism on CINV. RESULTS: Single-nuclei transcriptomics and histological approaches in rats revealed a topographical, molecularly distinct, GABA-ergic neuronal population in the dorsal vagal complex (DVC) that is modulated by chemotherapy but rescued by GIPR agonism. Activation of DVCGIPR neurons substantially decreased behaviors indicative of malaise in cisplatin-treated rats. Strikingly, GIPR agonism blocks cisplatin-induced emesis in both ferrets and shrews. CONCLUSION: Our multispecies study defines a peptidergic system that represents a novel therapeutic target for the management of CINV, and potentially other drivers of nausea/emesis.

Screening study of anti-emetics to improve GDF15-induced malaise and anorexia: Implications for emesis control.

Considerable preclinical and clinical attention has focused on the food intake and body weight suppressive effects of growth differentiation factor 15 (GDF15) and its elevated blood levels as a consequence of disease states and disease treatment therapeutics. We have previously reported that exogenous administration of GDF15 induces anorexia through nausea and emesis in multiple species. Importantly, GDF15 signaling as a meditator of chemotherapy-induced anorexia and emesis has recently been demonstrated in both murine and nonhuman primate models. The mechanism, however, by which GDF15 induces malaise and the utility of existing therapeutic targets to counteract its effects remain largely unknown. Using a dose of GDF15 that mimics stimulated levels following chemotherapy administration and reliably induces malaise, we sought to screen anti-emetics that represent distinct pharmacotherapeutic classes hypothesized to reduce GDF15-induced effects in rats. Strikingly, our results showed that none of the tested compounds were effective at preventing GDF15-induced malaise. These results illustrate the complexity of GDF15 signaling mechanism and may have important implications for medical conditions characterized by elevated GDF15 levels and incomplete symptom control, such as chemotherapy-induced nausea and vomiting.

Peripherally restricted oxytocin is sufficient to reduce food intake and motivation, while CNS entry is required for locomotor and taste avoidance effects.

OBJECTIVES: Oxytocin (OT) has a well-established role in reproductive behaviours; however, it recently emerged as an important regulator of energy homeostasis. In addition to central nervous system (CNS), OT is found in the plasma and OT receptors (OT-R) are found in peripheral tissues relevant to energy balance regulation. Here, we aim to determine whether peripheral OT-R activation is sufficient to alter energy intake and expenditure. METHODS AND RESULTS: We first show that systemic OT potently reduced food intake and food-motivated behaviour for a high-fat reward in male and female rats. As it is plausible that peripherally, intraperitoneally (IP) injected OT crosses the blood-brain barrier (BBB) to produce some of the metabolic effects within the CNS, we screened, with a novel fluorescently labelled-OT (fAF546-OT, Roxy), for the presence of IP-injected Roxy in CNS tissue relevant to feeding control and compared such with BBB-impermeable fluorescent OT-B12 (fCy5-OT-B12; BRoxy). While Roxy did penetrate the CNS, BRoxy did not. To evaluate the behavioural and thermoregulatory impact of exclusive activation of peripheral OT-R, we generated a novel BBB-impermeable OT (OT-B12 ), with equipotent binding at OT-R in vitro. In vivo, IP-injected OT and OT-B12 were equipotent at food intake suppression in rats of both sexes, suggesting that peripheral OT acts on peripheral OT-R to reduce feeding behaviour. Importantly, OT induced a potent conditioned taste avoidance, indistinguishable from that induced by LiCl, when applied peripherally. Remarkably, and in contrast to OT, OT-B12 did not induce any conditioned taste avoidance. Limiting the CNS entry of OT also resulted in a dose-dependent reduction of emesis in male shrews. While both OT and OT-B12 proved to have similar effects on body temperature, only OT resulted in home-cage locomotor depression. CONCLUSIONS: Together our data indicate that limiting systemic OT CNS penetrance preserves the anorexic effects of the peptide and reduces the clinically undesired side effects of OT: emesis, taste avoidance and locomotor depression. Thus, therapeutic targeting of peripheral OT-R may be a viable strategy to achieve appetite suppression with better patient outcomes.

GIPR Agonism Inhibits PYY-Induced Nausea-Like Behavior.

The induction of nausea and emesis is a major barrier to maximizing the weight loss profile of obesity medications, and therefore, identifying mechanisms that improve tolerability could result in added therapeutic benefit. The development of peptide YY (PYY)-based approaches to treat obesity are no exception, as PYY receptor agonism is often accompanied by nausea and vomiting. Here, we sought to determine whether glucose-dependent insulinotropic polypeptide (GIP) receptor (GIPR) agonism reduces PYY-induced nausea-like behavior in mice. We found that central and peripheral administration of a GIPR agonist reduced conditioned taste avoidance (CTA) without affecting hypophagia mediated by a PYY analog. The receptors for GIP and PYY (Gipr and Npy2r) were found to be expressed by the same neurons in the area postrema (AP), a brainstem nucleus involved in detecting aversive stimuli. Peripheral administration of a GIPR agonist induced neuronal activation (cFos) in the AP. Further, whole-brain cFos analyses indicated that PYY-induced CTA was associated with augmented neuronal activity in the parabrachial nucleus (PBN), a brainstem nucleus that relays aversive/emetic signals to brain regions that control feeding behavior. Importantly, GIPR agonism reduced PYY-mediated neuronal activity in the PBN, providing a potential mechanistic explanation for how GIPR agonist treatment reduces PYY-induced nausea-like behavior. Together, the results of our study indicate a novel mechanism by which GIP-based therapeutics may have benefit in improving the tolerability of weight loss agents.

Hypophagia induced by salmon calcitonin, but not by amylin, is partially driven by malaise and is mediated by CGRP neurons.

OBJECTIVE: The behavioral mechanisms and the neuronal pathways mediated by amylin and its long-acting analog sCT (salmon calcitonin) are not fully understood and it is unclear to what extent sCT and amylin engage overlapping or distinct neuronal subpopulations to reduce food intake. We here hypothesize that amylin and sCT recruit different neuronal population to mediate their anorectic effects. METHODS: Viral approaches were used to inhibit calcitonin gene-related peptide (CGRP) lateral parabrachial nucleus (LPBN) neurons and assess their role in amylin's and sCT's ability to decrease food intake in mice. In addition, to test the involvement of LPBN CGRP neuropeptidergic signaling in the mediation of amylin and sCT's effects, a LPBN site-specific knockdown was performed in rats. To deeper investigate whether the greater anorectic effect of sCT compared to amylin is due do the recruitment of additional neuronal pathways related to malaise multiple and distinct animal models tested whether amylin and sCT induce conditioned avoidance, nausea, emesis, and conditioned affective taste aversion. RESULTS: Our results indicate that permanent or transient inhibition of CGRP neurons in LPBN blunts sCT-, but not amylin-induced anorexia and neuronal activation. Importantly, sCT but not amylin induces behaviors indicative of malaise including conditioned affective aversion, nausea, emesis, and conditioned avoidance; the latter mediated by CGRPLPBN neurons. CONCLUSIONS: Together, the present study highlights that although amylin and sCT comparably decrease food intake, sCT is distinctive from amylin in the activation of anorectic neuronal pathways associated with malaise.

Glucagon-like peptide-1 in diabetes care: Can glycaemic control be achieved without nausea and vomiting?

Introduced less than two decades ago, glucagon-like peptide-1 receptor agonists rapidly reshaped the field of Type 2 diabetes mellitus (T2DM) care by providing glycaemic control in tandem with weight loss. However, FDA-approved GLP-1 receptor agonists are often accompanied by nausea and emesis and, in some lean T2DM patients, by undesired anorexia. Importantly, the hypophagic and emetic effects of GLP-1 receptor agonists are caused by activation of central GLP-1 receptors. This review summarizes two different approaches to mitigate the incidence and severity of nausea and emesis related to GLP-1 receptor agonists: conjugation with vitamin B12 , or related corrin ring-containing compounds ('corrination'), and development of dual agonists of GLP-1 receptors with glucose-dependent insulinotropic polypeptide (GIP). Such approaches could lead to the generation of GLP-1 receptor agonists with improved therapeutic efficacy, thus decreasing treatment attrition, increasing patient compliance and extending treatment to a broader population of T2DM patients. The data reviewed show that it is possible to pharmacologically separate the emetic effects of GLP-1 receptor agonists from their glucoregulatory action. LINKED ARTICLES: This article is part of a themed issue on GLP1 receptor ligands (BJP 75th Anniversary). To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.4/issuetoc.

Single nuclei RNA sequencing of the rat AP and NTS following GDF15 treatment.

OBJECTIVE: Growth differentiation factor 15 (GDF15) is known to play a role in feeding, nausea, and body weight, with action through the GFRAL-RET receptor complex in the area postrema (AP) and nucleus tractus solitarius (NTS). To further elucidate the underlying cell type-specific molecular mechanisms downstream of GDF15 signaling, we used a single nuclei RNA sequencing (snRNAseq) approach to profile AP and NTS cellular subtype-specific transcriptomes after systemic GDF15 treatment. METHODS: AP and NTS micropunches were used for snRNAseq from Sprague Dawley rats 6 h following GDF15 or saline injection, and Seurat was used to identify cellular subtypes and cell type-specific alterations in gene expression that were due to the direct and secondary effects of systemic GDF15 treatment. RESULTS: Using the transcriptome profile of ∼35,000 individual AP/NTS nuclei, we identified 19 transcriptomically distinct cellular subtypes, including a single population Gfral and Ret positive excitatory neurons, representing the primary site of action for GDF15. A total of ∼600 cell type-specific differential expression events were identified in neurons and glia, including the identification of transcriptome alterations specific to the direct effects of GDF15 in the Gfral-Ret positive excitatory neurons and shared transcriptome alterations across neuronal and glial cell types. Downstream analyses identified shared and cell type-specific alterations in signaling pathways and upstream regulatory mechanisms of the observed transcriptome alterations. CONCLUSIONS: These data provide a considerable advance in our understanding of AP and NTS cell type-specific molecular mechanisms associated with GDF15 signaling. The identified cellular subtype-specific regulatory mechanism and signaling pathways likely represent important targets for future pharmacotherapies.

GIP Receptor Agonism Attenuates GLP-1 Receptor Agonist-Induced Nausea and Emesis in Preclinical Models.

Glucagon-like peptide 1 receptor (GLP-1R) agonists decrease body weight and improve glycemic control in obesity and diabetes. Patient compliance and maximal efficacy of GLP-1 therapeutics are limited by adverse side effects, including nausea and emesis. In three different species (i.e., mice, rats, and musk shrews), we show that glucose-dependent insulinotropic polypeptide receptor (GIPR) signaling blocks emesis and attenuates illness behaviors elicited by GLP-1R activation, while maintaining reduced food intake, body weight loss, and improved glucose tolerance. The area postrema and nucleus tractus solitarius (AP/NTS) of the hindbrain are required for food intake and body weight suppression by GLP-1R ligands and processing of emetic stimuli. Using single-nuclei RNA sequencing, we identified the cellular phenotypes of AP/NTS cells expressing GIPR and GLP-1R on distinct populations of inhibitory and excitatory neurons, with the greatest expression of GIPR in γ-aminobutyric acid-ergic neurons. This work suggests that combinatorial pharmaceutical targeting of GLP-1R and GIPR will increase efficacy in treating obesity and diabetes by reducing nausea and vomiting.

The Role of GIP in the Regulation of GLP-1 Satiety and Nausea.

Gastric inhibitory peptide (GIP) is best known for its role as an incretin hormone in control of blood glucose concentrations. As a classic satiation signal, however, the literature illustrates a mixed picture of GIP involvement with an at best weak anorectic response profile being reported for GIP receptor (GIPR) signaling. Not surprisingly, the pursuit of exploiting the GIP system as a therapeutic target for diabetes and obesity has fallen behind that of the other gastrointestinal-derived incretin, glucagon-like peptide 1 (GLP-1). However, recent discoveries highlighted here support potential therapeutic advantages of combinatorial therapies targeting GIP and GLP-1 systems together, with perhaps the most surprising finding that GIPR agonism may have antiemetic properties. As nausea and vomiting are the most common side effects of all existing GLP-1 pharmacotherapies, the ability for GIP agonism to reduce GLP-1-induced illness behaviors but retain (if not enhance) weight loss and glycemic control may offer a new era in the treatment of obesity and diabetes.

Olanzapine Administration Reduces Chemotherapy-Induced Nausea Behavior in Rats.

Nausea and vomiting are consistently identified among the most distressing side effects of chemotherapy. In recent years, Olanzapine (OLZ) treatment was added to anti-emetic guidelines as a treatment for chemotherapy-induced nausea and vomiting (CINV), despite little available data supporting a mechanism behind the positive benefits of the drug. Here, we examine whether OLZ reduces cisplatin chemotherapy-induced side effects on food intake and pica behavior in rats (i.e., kaolin intake, a proxy for nausea/emesis). Behavioral experiments tested whether systemic or hindbrain administration of OLZ ameliorated cisplatin-induced pica, anorexia, and body weight loss in rats. We also tested whether systemic OLZ reduces cisplatin-induced neuronal activation in the dorsal vagal complex (DVC), a hindbrain region controlling emesis. Lastly, given their role in regulating feeding and emesis, circulating ghrelin levels and central mRNA expression levels of serotonin (HT) receptor subunits, including 5-HT2C, were measured in brain regions that regulate CINV and energy balance in an exploratory analysis to investigate potential mediators of OLZ action. Our results show that both systemic and hindbrain administration of OLZ attenuated cisplatin-induced kaolin intake and body weight loss, but not anorexia. Systemic OLZ decreased cisplatin-induced c-Fos immunofluorescence in the DVC and prevented cisplatin-induced reductions in circulating ghrelin levels. IP OLZ also blocked cisplatin-induced increases in Htr2c expression in DVC and hypothalamic micropunches. These data suggest hindbrain exposure to OLZ is sufficient to induce reductions in cisplatin-induced pica and that central serotonergic signaling, via 5-HT2C, and changes in circulating ghrelin may be potential mediators of olanzapine anti-emetic action.

Synthesis, Optimization, and Biological Evaluation of Corrinated Conjugates of the GLP-1R Agonist Exendin-4.

Corrination is the conjugation of a corrin ring containing molecule, such as vitamin B12 (B12) or B12 biosynthetic precursor dicyanocobinamide (Cbi), to small molecules, peptides, or proteins with the goal of modifying pharmacology. Recently, a corrinated GLP-1R agonist (GLP-1RA) exendin-4 (Ex4) has been shown in vivo to have reduced penetration into the central nervous system relative to Ex4 alone, producing a glucoregulatory GLP-1RA devoid of anorexia and emesis. The study herein was designed to optimize the lead conjugate for GLP-1R agonism and binding. Two specific conjugation sites were introduced in Ex4, while also utilizing various linkers, so that it was possible to identify Cbi conjugates of Ex4 that exhibit improved binding and agonist activity at the GLP-1R. An optimized conjugate (22), comparable with Ex4, was successfully screened and subsequently assayed for insulin secretion in rat islets and in vivo in shrews for glucoregulatory and emetic behavior, relative to Ex4.

Activation of PPG neurons following acute stressors differentially involves hindbrain serotonin in male rats.

Within the hindbrain, serotonin (5-HT) functions as a modulator of the central glucagon-like peptide-1 (GLP-1) system. This interaction between 5-HT and GLP-1 is achieved via 5-HT2C and 5-HT3 receptors and is relevant for GLP-1-mediated feeding behavior. The central GLP-1 system is activated by various stressors, activates the hypothalamic pituitary adrenocortical (HPA) axis, and contributes to stress-related behaviors. Whether 5-HT modulates GLP-1's role in the stress response in unknown. We hypothesized that the serotonergic modulation of GLP-1-producing neurons (i.e., PPG neurons) is stimuli-specific and that stressed-induced PPG activity is one of the modalities in which 5-HT plays a role. In this study, we investigated the roles of 5-HT2C and 5-HT3 receptors in mediating the activation of PPG neurons in the nucleus tractus solitarius (NTS) following exposure to three different acute stressors: lithium chloride (LiCl), noncontingent cocaine (Coc), and novel restraint stress (RES). Results showed that increased c-Fos expression in PPG neurons following LiCl and RES-but not Coc-is dependent on hindbrain 5-HT2C and 5-HT3 receptor signaling. Additionally, stressors that depend on 5-HT signaling to activate PPG neurons (i.e., LiCl and RES) increased c-Fos expression in 5-HT-expressing neurons within the caudal raphe (CR), specifically in the raphe magnus (RMg). Finally, we showed that RMg neurons innervate NTS PPG neurons and that some of these PPG neurons lie in close proximity to 5-HT axons, suggesting RMg 5-HT-expressing neurons are the source of 5-HT input responsible for engaging NTS PPG neurons. Together, these findings identify a direct RMg to NTS pathway responsible for the modulatory effect of 5-HT on the central GLP-1 system-specifically via activation of 5-HT2C and 5-HT3 receptors-in the facilitation of acute stress responses.

Design and Evaluation of Peptide Dual-Agonists of GLP-1 and NPY2 Receptors for Glucoregulation and Weight Loss with Mitigated Nausea and Emesis.

There is a critical unmet need for therapeutics to treat the epidemic of comorbidities associated with obesity and type 2 diabetes, ideally devoid of nausea/emesis. This study developed monomeric peptide agonists of glucagon-like peptide 1 receptor (GLP-1R) and neuropeptide Y2 receptor (Y2-R) based on exendin-4 (Ex-4) and PYY3-36. A novel peptide, GEP44, was obtained via in vitro receptor screens, insulin secretion in islets, stability assays, and in vivo rat and shrew studies of glucoregulation, weight loss, nausea, and emesis. GEP44 in lean and diet-induced obese rats produced greater reduction in body weight compared to Ex-4 without triggering nausea associated behavior. Studies in the shrew demonstrated a near absence of emesis for GEP44 in contrast to Ex-4. Collectively, these data demonstrate that targeting GLP-1R and Y2-R with chimeric single peptides offers a route to new glucoregulatory treatments that are well-tolerated and have improved weight loss when compared directly to Ex-4.

Corrination of a GLP-1 Receptor Agonist for Glycemic Control without Emesis.

Glucagon-like peptide-1 receptor (GLP-1R) agonists used to treat type 2 diabetes mellitus often produce nausea, vomiting, and in some patients, undesired anorexia. Notably, these behavioral effects are caused by direct central GLP-1R activation. Herein, we describe the creation of a GLP-1R agonist conjugate with modified brain penetrance that enhances GLP-1R-mediated glycemic control without inducing vomiting. Covalent attachment of the GLP-1R agonist exendin-4 (Ex4) to dicyanocobinamide (Cbi), a corrin ring containing precursor of vitamin B12, produces a "corrinated" Ex4 construct (Cbi-Ex4). Data collected in the musk shrew (Suncus murinus), an emetic mammal, reveal beneficial effects of Cbi-Ex4 relative to Ex4, as evidenced by improvements in glycemic responses in glucose tolerance tests and a profound reduction of emetic events. Our findings highlight the potential for clinical use of Cbi-Ex4 for millions of patients seeking improved glycemic control without common side effects (e.g., emesis) characteristic of current GLP-1 therapeutics.

A second-generation glucagon-like peptide-1 receptor agonist mitigates vomiting and anorexia while retaining glucoregulatory potency in lean diabetic and emetic mammalian models.

AIM: To develop a conjugate of vitamin B12 bound to the glucagon-like peptide-1 receptor (GLP-1R) agonist exendin-4 (Ex4) that shows reduced penetrance into the central nervous system while maintaining peripheral glucoregulatory function. METHODS: We evaluated whether a vitamin B12 conjugate of Ex4 (B12-Ex4) improves glucose tolerance without inducing anorexia in Goto-Kakizaki (GK) rats, a lean type 2 diabetes model of an understudied but medically compromised population of patients requiring the glucoregulatory effects of GLP-1R agonists without anorexia. We also utilized the musk shrew (Suncus murinus), a mammalian model capable of emesis, to test B12-Ex4 on glycaemic profile, feeding and emesis. RESULTS: In both models, native Ex4 and B12-Ex4 equivalently blunted the rise in blood glucose levels during a glucose tolerance test. In both GK rats and shrews, acute Ex4 administration decreased food intake, leading to weight loss; by contrast, equimolar administration of B12-Ex4 had no effect on feeding and body weight. There was a near absence of emesis in shrews given systemic B12-Ex4, in contrast to reliable emesis produced by Ex4. When administered centrally, both B12-Ex4 and Ex4 induced similar potency of emesis, suggesting that brain penetrance of B12-Ex4 is required for induction of emesis. CONCLUSIONS: These findings highlight the potential therapeutic value of B12-Ex4 as a novel treatment for type 2 diabetes devoid of weight loss and with reduced adverse effects and better tolerance, but similar glucoregulation to current GLP-1R agonists.