The Extracellular Surface of the GLP-1 Receptor Is a Molecular Trigger for Biased Agonism.

Ligand-directed signal bias offers opportunities for sculpting molecular events, with the promise of better, safer therapeutics. Critical to the exploitation of signal bias is an understanding of the molecular events coupling ligand binding to intracellular signaling. Activation of class B G protein-coupled receptors is driven by interaction of the peptide N terminus with the receptor core. To understand how this drives signaling, we have used advanced analytical methods that enable separation of effects on pathway-specific signaling from those that modify agonist affinity and mapped the functional consequence of receptor modification onto three-dimensional models of a receptor-ligand complex. This yields molecular insights into the initiation of receptor activation and the mechanistic basis for biased agonism. Our data reveal that peptide agonists can engage different elements of the receptor extracellular face to achieve effector coupling and biased signaling providing a foundation for rational design of biased agonists.

Metabolic cues impact non-oscillatory intergeniculate leaflet and ventral lateral geniculate nucleus: standard versus high-fat diet comparative study.

The intergeniculate leaflet and ventral lateral geniculate nucleus (IGL/VLG) are subcortical structures involved in entrainment of the brain's circadian system to photic and non-photic (e.g. metabolic and arousal) cues. Both receive information about environmental light from photoreceptors, exhibit infra-slow oscillations (ISO) in vivo, and connect to the master circadian clock. Although current evidence demonstrates that the IGL/VLG communicate metabolic information and are crucial for entrainment of circadian rhythms to time-restricted feeding, their sensitivity to food intake-related peptides has not been investigated yet. We examined the effect of metabolically relevant peptides on the spontaneous activity of IGL/VLG neurons. Using ex vivo and in vivo electrophysiological recordings as well as in situ hybridisation, we tested potential sensitivity of the IGL/VLG to anorexigenic and orexigenic peptides, such as cholecystokinin, glucagon-like peptide 1, oxyntomodulin, peptide YY, orexin A and ghrelin. We explored neuronal responses to these drugs during day and night, and in standard vs. high-fat diet conditions. We found that IGL/VLG neurons responded to all the substances tested, except peptide YY. Moreover, more neurons responded to anorexigenic drugs at night, while a high-fat diet affected the IGL/VLG sensitivity to orexigenic peptides. Interestingly, ISO neurons responded to light and orexin A, but did not respond to the other food intake-related peptides. In contrast, non-ISO cells were activated by metabolic peptides, with only some being responsive to light. Our results show for the first time that peptides involved in the body's energy homeostasis stimulate the thalamus and suggest functional separation of the IGL/VLG cells. KEY POINTS: The intergeniculate leaflet and ventral lateral geniculate nucleus (IGL/VLG) of the rodent thalamus process various signals and participate in circadian entrainment. In both structures, cells exhibiting infra-slow oscillatory activity as well as non-rhythmically firing neurons being observed. Here, we reveal that only one of these two groups of cells responds to anorexigenic (cholecystokinin, glucagon-like peptide 1 and oxyntomodulin) and orexigenic (ghrelin and orexin A) peptides. Neuronal responses vary depending on the time of day (day vs. night) and on the diet (standard vs. high-fat diet). Additionally, we visualised receptors to the tested peptides in the IGL/VLG using in situ hybridisation. Our results suggest that two electrophysiologically different subpopulations of IGL/VLG neurons are involved in two separate functions: one related to the body's energy homeostasis and one associated with the subcortical visual system.

The Mediterranean diet increases glucagon-like peptide 1 and oxyntomodulin compared with a vegetarian diet in patients with type 2 diabetes: A randomized controlled cross-over trial.

AIM: To compare a Mediterranean diet (MED) with a high-fibre vegetarian diet (HFV) in terms of hunger-satiety perception through post-prandial assessment of appetite-related hormones glucagon-like peptide 1 (GLP-1) and oxyntomodulin, as well as self-rated visual analogue scale (VAS) quantification, in overweight/obese subjects with type 2 diabetes (T2D). MATERIALS AND METHODS: Twelve T2D subjects (Male to female ratio = 7:5), mean age 63 ± 8.5 years, were enrolled in a randomized, controlled, crossover study. Participants consumed an MED meal as well as an isocaloric meal rich in complex carbohydrate as well as an isocaloric MED meal in two different visits with a 1-week washout period between the two visits. Appetite ratings, glucose/insulin, and gastrointestinal hormone concentrations were measured at fasting and every 30' until 210' following meal consumption. RESULTS: GLP-1 and oxyntomodulin levels were significantly higher following MED meal compared with HFV meals (210' area under the curve, p < 0.022 and p < 0.023, respectively). Both MED and HFV meal resulted in a biphasic pattern of GLP-1 and oxyntomodulin, although MED meal was related to a delayed, significantly higher second GLP-1 peak at 150' compared with that of HFV meal (p < 0.05). MED meal was related to lower glucose profile compared with HFV meal (p < 0.039), whereas we did not observe significant changes in terms of self-reported VAS scores and insulin trend. CONCLUSIONS: In T2D overweight/obese subjects, an MED meal is more effective than a HFV meal in terms of post-prandial plasma glucose homoeostasis and GLP-1 and oxyntomodulin release. These changes were not confirmed by VAS appetite self-assessment over a 210' period.

Fasting oxyntomodulin, glicentin, and gastric inhibitory polypeptide levels are associated with activation of reward- and attention-related brain centres in response to visual food cues in adults with obesity: A cross-sectional functional MRI study.

Postprandial increases in gastrointestinal hormones are associated with reduced energy intake, partially through direct effects on the brain. However, it remains unknown whether the fasting levels of gastrointestinal hormones are associated with altered brain activity in response to visual food stimuli. We therefore performed a whole-brain regression cross-sectional analysis to assess the association between fasting brain activations according to functional magnetic resonance imaging, performed during viewing of highly desirable versus less desirable food images, with fasting levels of five gastrointestinal hormones (glucagon-like peptide [GLP]-1, GLP-2, oxyntomodulin, glicentin and gastric inhibitory polypeptide [GIP]) in 36 subjects with obesity. We observed that fasting blood levels of GIP were inversely associated with the activation of attention-related areas (visual cortices of the occipital lobe, parietal lobe) and of oxyntomodulin and glicentin with reward-related areas (insula, putamen, caudate for both, and additionally orbitofrontal cortex for glicentin) and the hypothalamus when viewing highly desirable as compared to less desirable food images. Future studies are needed to confirm whether fasting levels of oxyntomodulin, glicentin and GIP are associated with the activation of brain areas involved in appetite regulation and with energy intake in people with obesity.

[Prognostic factors for the carbohydrate metabolism normalization in patients with type 2 diabetes mellitus and obesity using liraglutide 3.0 mg per day].

BACKGROUND: Glucagon-like peptide-1 receptor agonists (GLP-1 RA) are innovative drugs that effectively reduce glycemic levels and overweight in patients with type 2 diabetes mellitus (T2DM). However, the criteria for predicting the hypoglycemic effect of this group of drugs have not been practically defined. AIM: To assess the factors contributing to the achievement the glycemia normalization in patients with diabetes mellitus and obesity by adding to antihyperglycemic therapy (AT) a drug from the GLP-1 RA group liraglutide 3.0 mg per day. MATERIALS AND METHODS: A single-center, prospective, non-randomized study was provided. The objects of the study were patients with T2DM and obesity (n=22). Liraglutide 3.0 mg per day was added to the current AT of patients. Initially, the parameters of carbohydrate metabolism, hormones of the incretin system on an empty stomach and during the mixed-meal test, insulin resistance using the euglycemic hyperinsulinemic clamp test, and body composition were studied. After 9 months of therapy, all studies were repeated and a search for possible predictors of the carbohydrate metabolism normalization was made. RESULTS: The body mass index of patients decreased from 42.4 [37.7; 45.0] to 35.9 [33.0; 40.9] kg/m2. Fasting blood glucose and glycated hemoglobin levels decreased from 9.02 [7.40; 11.37] mmol/L and 7.85 [7.43; 8.65]% up to 5.90 [5.12; 6.18] mmol/L and 6.40 [5.90; 6.60]%, respectively. 14 (63.6%) patients reached normoglycemia. Insulin resistance according to the clamp test did not change over the study. Basal concentrations of oxyntomodulin, glycentin and the area under the GLP-1, oxyntomodulin, glycentin curve significantly decreased 9 months after liraglutide administration. The prognostic marker of the achievement of normoglycemia during therapy with liraglutide 3.0 mg/day is the level of endogenous GLP-15.5 pmol/L before the appointment of arGPP-1 therapy. CONCLUSION: The concentration of endogenous GLP-1 before the appointment of liraglutide therapy at a dose of 3.0 mg per day can be used for prediction the drug hypoglycemic effect and achieving normoglycemia possibility.

New Generation Oxyntomodulin Peptides with Improved Pharmacokinetic Profiles Exhibit Weight Reducing and Anti-Steatotic Properties in Mice.

Oxyntomodulin (OXM) is an intestinal peptide hormone that activates both glucagon-like peptide-1 (GLP-1) and glucagon (GCG) receptors. The natural peptide reduces body weight in obese subjects and exhibits direct acute glucoregulatory effects in patients with type II diabetes. However, the clinical utility of OXM is limited due to its lower in vitro potency and short in vivo half-life. To overcome these issues, we developed stapled, long-acting, and highly potent OXM analogs with balanced activities at both GLP-1 and GCG receptors. The lead molecule O14 exhibits potent and long-lasting effects on glucose control, body weight loss, and reduction of hepatic fat reduction in DIO mice. Importantly, O14 significantly reversed hepatic steatosis; reduced liver weight, total cholesterol, and hepatic triglycerides; and improved markers of liver function in a nonalcoholic steatohepatitis (NASH) mouse model. A symmetrical version of the peptide was also shown to be more efficacious and long-lasting in controlling glucose than semaglutide and the clinical candidate cotadutide in wild-type mice, highlighting the utility of our designs of the dual agonist as a potential new therapy for diabetes and liver diseases.

A dual GLP-1 and Gcg receptor agonist rescues spatial memory and synaptic plasticity in APP/PS1 transgenic mice.

Alzheimer's disease (AD) is a neurodegenerative disease that severely affects the health and lifespan of the elderly worldwide. Recently, the correlation between AD and type 2 diabetes mellitus (T2DM) has received intensive attention, and a promising new anti-AD strategy is the use of anti-diabetic drugs. Oxyntomodulin (Oxm) is a peptide hormone and growth factor that acts on neurons in the hypothalamus. OXM activates glucagon-like peptide 1 (GLP-1) and glucagon (Gcg) receptors, facilitates insulin signaling and has neuroprotective effects against Aß1-42-induced cytotoxicity in primary hippocampal neurons. Here, we tested the effects of the protease-resistant analogue (D-Ser2)Oxm on spatial memory and synaptic plasticity and the underlying molecular mechanisms in the APP/PS1 transgenic mouse model of AD. The results showed that (D-Ser2)Oxm not only alleviated the impairments of working memory and long-term spatial memory, but also reduced the number of Aß plaques in the hippocampus, and reversed the suppression of hippocampal synaptic long-term potentiation (LTP). Moreover, (D-Ser2)Oxm administration significantly increased p-PI3K/p-AKT1 expression and decreased p-GSK3ß levels in the hippocampus. These results are the first to show an in vivo neuroprotective role of (D-Ser2)Oxm in APP/PS1 mice, and this role involves the improvement of synaptic plasticity, clearance of Aß and normalization of PI3K/AKT/GSK3ß cell signaling in the hippocampus. This study suggests that (D-Ser2)Oxm holds promise for the prevention and treatment of AD.

Novel glucagon- and OXM-based peptides acting through glucagon and GLP-1 receptors with body weight reduction and anti-diabetic properties.

Oxyntomodulin (OXM) is an endogenous gastrointestinal hormone, which activates both the Glucagon-like peptide-1 receptor (GLP-1R) and the glucagon receptor (GCGR). However, OXM has shortcomings including poor GLP-1R agonism to control glycemia, short half-life and others. Inspired from the sequence relationship between OXM and glucagon, in this study, we introduced different C-terminus residues of GLP-1, exenatide and OXM to glucagon to get a series of hybrid peptides with enhanced GLP-1R activation. The formed glucagon-exenatide hybrid peptide shows higher GLP-1R activation properties than OXM. Then the peptides based on the glucagon-exenatide hybrid peptide were coupled with fatty acid side chains to prolong their half-lives. As a result, the most potent compound 16a could stimulate insulin secretion and maintain blood glucose in normal level for ~42.6 h in diabetic mice. 16a exhibited reduced HbA1c level in diabetic mice, lowered body weight significantly in obesity mice on chronic treatment assay. 16a, combined efficient GCGR/GLP-1R activity, is potential as novel treatment for obesity and diabetes. This finding provides new insights into balancing GLP-1/GCGR potency of glucagon-exenatide hybrid peptide and is helpful for discovery of novel anti-diabetic and bodyweight-reducing drugs.

Oxyntomodulin induces satiety and activates the arcuate nucleus of the hypothalamus in Japanese quail.

Oxyntomodulin (OXM) is a proglucagon-derived peptide that suppresses hunger in humans. There are some differences in its food intake-inhibitory effects among species. The central mechanisms are unclear and it is unknown if OXM is more efficacious in a gallinaceous species that has not undergone as much selection for growth as the chicken. The objective was thus to determine the effects of OXM on food and water intake and hypothalamic physiology in Japanese quail. At 7 days post-hatch, 6-h-fasted quail were injected intracerebroventricularly (ICV) or intraperitoneally (IP) with 0.32, 0.65, or 1.3 nmol of OXM. All doses decreased food intake for 180 min post-ICV injection. On a cumulative basis, water intake was not affected until 120 min, with the lowest and highest doses decreasing water intake after ICV injection. The two highest doses were anorexigenic when administered via the IP route, whereas all doses were anti-dipsogenic starting at 30 min post-injection. In hypothalamic samples collected at 1-h post-ICV injection, there was an increase in c-Fos immunoreactivity, an indicator of recent neuronal activation, in the arcuate nucleus (ARC) and dorsomedial nucleus (DMN) of the hypothalamus in OXM-injected individuals. Results suggest that quail are more sensitive than chickens to the satiety-inducing effects of OXM. The central mechanism is likely mediated through a pathway in the ARC that is conserved among species, and through activation of the DMN, an effect that is unique to quail. Such knowledge is critical for facilitating the development of novel, side effect-free anti-eating strategies to promote weight-loss in obesity.

Cellular and sub-cellular localisation of oxyntomodulin-like immunoreactivity in enteroendocrine cells of human, mouse, pig and rat.

We use a monoclonal antibody against the C-terminal of oxyntomodulin (OXM) to investigate enteroendocrine cells (EEC) in mouse, rat, human and pig. This antibody has cross-reactivity with the OXM precursor, glicentin (Gli) but does not recognise glucagon. The antibody stained EEC in the jejunum and colon of each species. We compared OXM/Gli immunoreactivity with that revealed by antibodies against structurally related peptides, GLP-1 and glucagon and against GIP and PYY that are predicted to be in some EEC that express OXM/Gli. We used super-resolution to locate immunoreactive vesicles. In the pancreas, OXM/Gli was in glucagon cells but was located in separate storage vesicles to glucagon. In jejunal EEC, OXM/Gli and GIP were in many of the same cells but often in separate vesicles, whereas PYY and OXM/Gli were commonly colocalised in the same storage vesicles of colonic EEC. When binding of anti-GLP-1 to the structurally related GIP was removed by absorption with GIP peptide, GLP-1 and OXM/Gli immunoreactivities were contained in the same population of EEC in the intestine. We conclude that anti-OXM/Gli is a more reliable marker than anti-GLP-1 for EEC expressing preproglucagon products. Storage vesicles that were immunoreactive for OXM/Gli were almost always immunoreactive for GLP-1. OXM concentrations, measured by ELISA, were highest in the distal ileum and colon. Lesser concentrations were found in more proximal parts of small intestine and pancreas. Very little was in the stomach. In EEC containing GIP and OXM/Gli, these hormones are packaged in different secretory vesicles. Separate packaging also occurred for OXM and glucagon, whereas OXM/Gli and PYY and OXM/Gli and GLP-1 were commonly contained together in secretory vesicles.

Gut Hormone Responses to Mixed Meal Test in New-Onset Prediabetes/Diabetes After Acute Pancreatitis.

The study was aimed to investigate gut hormone responses to mixed meal test in individuals with new-onset prediabetes or diabetes after acute pancreatitis (cases) compared with healthy controls, and the effect of body fat parameters. A total of 29 cases and 29 age- and sex-matched healthy controls were recruited. All participants were given standard mixed meal drink and blood samples were collected to measure dipeptidyl peptidase IV, gastric inhibitory peptide, glucagon like peptide-1, insulin, oxyntomodulin, and peptide YY. Body fat parameters were measured using magnetic resonance imaging. Repeated measures and linear regression analyses were conducted in unadjusted and adjusted models. Gastric inhibitory peptide levels were significantly higher whereas oxyntomodulin levels were significantly lower in cases compared with controls in both the unadjusted (p<0.001 and p<0.001, respectively) and adjusted (p<0.001 and p<0.001, respectively) models. In cases, liver fat % contributed up to 13.4% (vs. 2.9% in controls) to variance in circulating levels of gastric inhibitory peptide whereas body mass index - up to 20.8% (vs. 9.9% in controls) in circulating levels of oxyntomodulin. New-onset prediabetes/diabetes after acute pancreatitis is characterised by increased levels of gastric inhibitory peptide and decreased levels of oxyntomodulin. Further, liver fat % and body mass index appear to be the body fat parameters that contribute most significantly to gastric inhibitory peptide and oxyntomodulin levels, respectively.

Design, screening and biological evaluation of novel fatty acid chain-modified oxyntomodulin-based derivatives with prolonged glucose-lowering ability and potent anti-obesity effects.

Recently, oxyntomodulin (OXM) has emerged as a treatment option for type 2 diabetes mellitus and obesity. In order to develop more promising novel OXM derivatives combining glycemic effects of glucagon-like peptide-1 (GLP-1) and lipolytic properties of glucagon, six 12-mer GLP-1 receptor agonists (PP01-PP06) were screened using a phage display method and then fused to OXM (3-37) to generate hybrid OXM derivatives (PP07-PP12). PP11, as a selected starting point, was further site-specifically modified with three lengths of fatty acid chains to provide long-acting conjugates PP13-PP24, among which PP18 was found not only to retain almost the entire balanced activation potency of PP11 in GLP-1/glucagon receptors but also to enhance plasma stability and prolong hypoglycemic activity. PP18 was further confirmed as an insulin secretagogue and glycemic agent in gene knockout mice. The protracted antidiabetic effects and in vivo half-life of PP18 were further proved by hypoglycemic efficacies in diet-induced obesity (DIO) mice and pharmacokinetics tests in Sprague Dawley (SD) rats, respectively. Nevertheless, administration of PP18 once per day normalized food intake, body weight, blood biochemical indexes, insulin resistance and islet function of DIO mice. These preclinical results suggested that PP18, as a novel OXM-based dual GLP-1 and glucagon receptor agonist, may serve as a novel therapeutic approach to treat T2DM and obesity.

The Importance of the Gastrointestinal Tract in Controlling Food Intake and Regulating Energy Balance.

The gastrointestinal tract, the key interface between ingested nutrients and the body, plays a critical role in regulating energy homeostasis. Gut-derived signals convey information regarding incoming nutrients to the brain, initiating changes in eating behavior and energy expenditure, to maintain energy balance. Here we review hormonal, neural, and nutrient signals emanating from the gastrointestinal tract and evidence for their role in controlling feeding behavior. Mechanistic studies that have utilized pharmacologic and/or transgenic approaches targeting an individual hormone/mediator have yielded somewhat disappointing body weight changes, often leading to the hormone/mediator in question being dismissed as a potential obesity therapy. However, the recent finding of sustained weight reduction in response to systemic administration of a long-acting analog of the gut-hormone glucagon-like peptide-1 highlights the therapeutic potential of gut-derived signals acting via nonphysiologic mechanisms. Thus, we also review therapeutics strategies being utilized or developed to leverage gastrointestinal signals in order to treat obesity.

Enteroendocrine, Musashi 1 and neurogenin 3 cells in the large intestine of Thai and Norwegian patients with irritable bowel syndrome.

OBJECTIVES: The prevalence, gender distribution and clinical presentation of IBS differ between Asian and Western countries. This study aimed at studying and comparing enteroendocrine, Musashi 1 (Msi 1) and neurogenin 3 (neurog 3) cells in Thai and Norwegian IBS patients. MATERIAL AND METHODS: Thirty Thai and 61 Norwegian IBS patients as well as 20 Thai and 24 Norwegian controls were included. Biopsy samples were taken from each of the sigmoid colon and the rectum during a standard colonoscopy. The samples were immunostained for serotonin, peptide YY, oxyntomodulin, pancreatic polypeptide, somatostatin, Msi 1 and neurog 3. The densities of immunoreactive cells were determined with computerized image analysis. RESULTS: The densities of several enteroendocrine cell types were altered in both the colon and rectum of both Thai and Norwegian IBS patients. Some of these changes were similar in Thai and Norwegian IBS patients, while others differed. CONCLUSIONS: The findings of abnormal densities of the enteroendocrine cells in Thai patients support the notion that enteroendocrine cells are involved in the pathophysiology of IBS. The present observations highlight that IBS differs in Asian and Western countries, and show that the changes in large-intestine enteroendocrine cells in Thai and Norwegian IBS patients might be caused by different mechanisms.

Abnormalities in ileal stem, neurogenin 3, and enteroendocrine cells in patients with irritable bowel syndrome.

BACKGROUND: This study examined whether the densities of stem- and enteroendocrine cell progenitors are abnormal in the ileum of patients with irritable bowel syndrome (IBS), and whether any abnormalities in ileal enteroendocrine cells are correlated with abnormalities in stem cells and enteroendocrine cell progenitors. METHODS: One hundred and one IBS patients covering all IBS subtypes were recruited, and 39 non-IBS subjects were included as a control group. The patients and controls underwent standard colonoscopies, during which biopsy specimens were obtained from the ileum. The biopsy specimens were stained with hematoxylin-eosin and immunostained for Musashi-1 (Msi-1), neurogenin 3 (NEUROG3), chromogranin A (CgA), serotonin, peptide YY (PYY), oxyntomodulin (enteroglucagon), pancreatic polypeptide, and somatostatin. The immunoreactive cells were quantified by computerized image analysis. RESULTS: The densities of Msi-1, NEUROG3, CgA, and serotonin cells were reduced in all IBS patients and in patients with diarrhea-predominant IBS (IBS-D), mixed-diarrhea-and-constipation IBS (IBS-M), and constipation-predominant (IBS-C) relative to the control subjects. While the PYY cell density was increased in IBS-C relative to controls, it did not differ between control subjects and IBS-D and IBS-M patients. The densities of Msi-1 and NEUROG3 cells were strongly correlated with that of CgA cells. CONCLUSIONS: The abnormalities in the ileal enteroendocrine cells appear to be caused by two mechanisms: (1) decreases in the clonogenic activity of the stem cells and in the endocrine-cell progenitors differentiating into enteroendocrine cells, and (2) switching on the expression of PYY and switching off the expression of certain other hormones in other types of the enteroendocrine cells.

Multiplexed Quantification of Proglucagon-Derived Peptides by Immunoaffinity Enrichment and Tandem Mass Spectrometry after a Meal Tolerance Test.

BACKGROUND: Proglucagon-derived peptides (PGDPs), which include glucagon-like peptide (GLP)-1, glucagon, and oxyntomodulin, are key regulators of glucose homeostasis and satiety. These peptide hormones are typically measured with immuno-based assays (e.g., ELISA, RIA), which often suffer from issues of selectivity. METHODS: We developed a multiplexed assay for measuring PGDPs including GLP-1 (7-36) amide, GLP-1 (9-36) amide, glucagon, and oxyntomodulin by mass spectrometry and used this assay to examine the effect of a meal tolerance test on circulating concentrations of these hormones. Participants fasted overnight and were either given a meal (n = 8) or continued to fast (n = 4), with multiple blood collections over the course of 3 h. Plasma samples were analyzed by microflow immunoaffinity (IA)-LC-MS/MS with an isotope dilution strategy. RESULTS: Assay performance characteristics were examined and established during analytical validation for all peptides. Intra- and interassay imprecision were found to be 2.2%-10.7% and 6.8%-22.5%, respectively. Spike recovery was >76%, and dilution linearity was established up to a 16-fold dilution. Immediately after the meal tolerance test, GLP-1 and oxyntomodulin concentrations increased and had an almost identical temporal relationship, and glucagon concentrations increased with a slight delay. CONCLUSIONS: IA-LC-MS/MS was used for the simultaneous and selective measurement of PGDPs. This work includes the first indication of the physiological concentrations and modulation of oxyntomodulin after a meal.

Polar transmembrane interactions drive formation of ligand-specific and signal pathway-biased family B G protein-coupled receptor conformations.

Recently, the concept of ligand-directed signaling--the ability of different ligands of an individual receptor to promote distinct patterns of cellular response--has gained much traction in the field of drug discovery, with the potential to sculpt biological response to favor therapeutically beneficial signaling pathways over those leading to harmful effects. However, there is limited understanding of the mechanistic basis underlying biased signaling. The glucagon-like peptide-1 receptor is a major target for treatment of type-2 diabetes and is subject to ligand-directed signaling. Here, we demonstrate the importance of polar transmembrane residues conserved within family B G protein-coupled receptors, not only for protein folding and expression, but also in controlling activation transition, ligand-biased, and pathway-biased signaling. Distinct clusters of polar residues were important for receptor activation and signal preference, globally changing the profile of receptor response to distinct peptide ligands, including endogenous ligands glucagon-like peptide-1, oxyntomodulin, and the clinically used mimetic exendin-4.

Sustained treatment with a stable long-acting oxyntomodulin analogue improves metabolic control and islet morphology in an experimental model of type 1 diabetes.

AIM: To assess the therapeutic benefits of regulatory peptides other than insulin, which have to date received limited consideration in the context of type 1 diabetes. METHODS: We assessed the effects of subchronic administration of the stable, oxyntomodulin (Oxm) analogue, (d-Ser(2) )Oxm[Lys(38) -γ-glu-PAL], for 28 days in streptozotocin (STZ)-induced insulin-deficient diabetic mice. RESULTS: Twice-daily injection with (d-Ser(2) )Oxm[Lys(38) -γ-glu-PAL] significantly countered the excessive food and fluid intake in STZ-induced diabetic mice, and maintained normal body weight. Lean body mass was normalized, whilst fat mass was significantly increased compared with control STZ-induced diabetic mice. In addition, circulating glucose was significantly reduced by the Oxm analogue, whilst plasma and pancreatic insulin concentrations were increased and glucagon decreased by day 28. Plasma lipid profile was normalized by (d-Ser(2) )Oxm[Lys(38) -γ-glu-PAL] administration and circulating amylase was not significantly altered by induction of diabetes or Oxm analogue therapy. This was associated with significantly improved glucose tolerance and insulin secretion. Peripheral insulin sensitivity was also significantly improved by Oxm analogue treatment. Histological examination of pancreata showed beneficial elevations of total islet and ß-cell area, associated with an increase in the number of smaller-sized islets. Further analysis revealed enhanced islet cell proliferation relative to apoptosis in Oxm analogue-treated mice. CONCLUSION: These studies emphasize the potential of stable Oxm-based peptides, such as (d-Ser(2) )Oxm[Lys(38) -γ-glu-PAL], as therapeutic agents for insulin-deficient type 1 diabetes.

Models and strategies in the development of antiobesity drugs.

Obesity is a leading cause of morbidity and mortality worldwide. There is still a wide disparity between the necessity and availability of safe and effective antiobesity pharmacotherapies. Current drugs are associated with adverse effects and are limited in their efficacy. There is thus an urgent need for new antiobesity agents. Animal models are critical to the study of the biological mechanisms underpinning energy homeostasis and obesity and provide useful tools for the development of novel antiobesity agents. Our understanding of the complex neuronal and hormonal systems that regulate appetite and body weight has largely been based on studies in animals. This review describes the physiological basis of appetite, rodent models used in the development of antiobesity drugs, and potential future targets for novel antiobesity agents.

Response to lowering plasma glucose is characterised by decreased oxyntomodulin: Results from a randomised controlled trial.

BACKGROUND: With the prevalence of diabetes reaching an epidemic level, there is a growing interest in the investigation of its remission. Proglucagon-derived peptides (PGDP) have been shown to have a glucose-regulating effect. However, whether they play a role in diabetes remission remains poorly understood. AIM: To investigate changes in plasma levels of PGDP in glycaemic responders versus non-responders. METHODS: The study was a randomised placebo-controlled trial comprising 18 adults with prediabetes (registered at www. CLINICALTRIALS: gov as NCT03889210). Following an overnight fast, participants consumed ketone ß-hydroxybutyrate (KEßHB)-supplemented beverage and placebo beverage in crossover manner. Serial blood samples were collected from baseline to 150 min at 30-min intervals. The endpoints were changes in glucagon-like peptide-1 (GLP-1), glicentin, oxyntomodulin, glucagon, and major proglucagon fragment (MPGF). Participants were stratified into the 'responders' and 'non-responders' subgroups based on their glycaemic changes following the ingestion of KEßHB. The area under the curve (AUC) was calculated to estimate the accumulated changes in the studied PGDP and compared using paired-t test between the KEßHB and placebo beverages. RESULTS: Responders had a significantly greater reduction in plasma glucose compared with non-responders following acute ketosis (p < 0.001). The AUC0-150 for oxyntomodulin was significantly lower following the KEßHB beverage compared with the placebo (p = 0.045) in responders, but not in non-responders (p = 0.512). No significant differences in AUCs0-150 were found for GLP-1, glicentin, glucagon, and MPGF in either responders or non-responders. CONCLUSION: Oxyntomodulin is involved in lowering plasma glucose and may play an important role in diabetes remission.