Kirsten Raun

The arcuate nucleus mediates GLP-1 receptor agonist liraglutide-dependent weight loss

Liraglutide is a glucagon-like peptide-1 (GLP-1) analog marketed for the treatment of type 2 diabetes. Besides lowering blood glucose, liraglutide also reduces body weight. It is not fully understood how liraglutide induces weight loss or to what degree liraglutide acts directly in the brain. Here, we determined that liraglutide does not activate GLP-1-producing neurons in the hindbrain, and liraglutide-dependent body weight reduction in rats was independent of GLP-1 receptors (GLP-1Rs) in the vagus nerve, area postrema, and paraventricular nucleus. Peripheral injection of fluorescently labeled liraglutide in mice revealed the presence of the drug in the circumventricular organs. Moreover, labeled liraglutide bound neurons within the arcuate nucleus (ARC) and other discrete sites in the hypothalamus. GLP-1R was necessary for liraglutide uptake in the brain, as liraglutide binding was not seen in Glp1r(-/-) mice. In the ARC, liraglutide was internalized in neurons expressing proopiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART). Electrophysiological measurements of murine brain slices revealed that GLP-1 directly stimulates POMC/CART neurons and indirectly inhibits neurotransmission in neurons expressing neuropeptide Y (NPY) and agouti-related peptide (AgRP) via GABA-dependent signaling. Collectively, our findings indicate that the GLP-1R on POMC/CART-expressing ARC neurons likely mediates liraglutide-induced weight loss.

Liraglutide, a Long-Acting Glucagon-Like Peptide-1 Analog, Reduces Body Weight and Food Intake in Obese Candy-Fed Rats, Whereas a Dipeptidyl Peptidase-IV Inhibitor, Vildagliptin, Does Not

Metabolic effects of the glucagon-like peptide-1 analog liraglutide and the dipeptidyl peptidase-IV inhibitor vildagliptin were compared in rats made obese by supplementary candy feeding. Female Sprague-Dawley rats were randomized to 12-week diets of chow or chow plus candy. The latter were randomized for 12 further weeks to continue their diet while receiving 0.2 mg/kg liraglutide twice daily subcutaneously, 10 mg/kg vildagliptin twice daily orally, or vehicle or to revert to chow-only diet. Energy expenditure was measured, and oral glucose tolerance tests (OGTTs) were performed. Body composition was determined by dual-energy X-ray absorptiometry scanning, and pancreatic β-cell mass was determined by histology. Candy feeding increased weight, fat mass, and feeding-associated energy expenditure. Liraglutide or reversal to chow diet fully reversed weight and fat gains. Liraglutide was associated with decreased calorie intake and shifted food preference (increased chow/decreased candy consumption). Despite weight loss, liraglutide-treated rats did not decrease energy expenditure compared with candy-fed controls. Vildagliptin affected neither weight, food intake, nor energy expenditure. OGTTs, histology, and blood analyses indirectly suggested that both drugs increased insulin sensitivity. Liraglutide and vildagliptin inhibited obesity-associated increases in β-cell mass. This was associated with weight and fat mass normalization with liraglutide, but not vildagliptin, where the ratio of β-cell to body mass was low.

Liraglutide: short-lived effect on gastric emptying—long lasting effects on body weight

Aim: Previous studies with the novel once daily glucagon‐like peptide‐1 (GLP‐1) analogue liraglutide and the GLP‐1 receptor agonist exenatide have revealed profound insulinotrophic and antidiabetic effects, but also potent effects on gastric emptying (GE) and long‐term and lasting reductions in body weight. In this study, we examined the acute and chronic effects of two different GLP‐1 analogues with different pharmacokinetic profiles on GE, food intake and body weight.

Laboratory animals as surrogate models of human obesity.

Obesity and obesity-related metabolic diseases represent a growing socioeconomic problem throughout the world. Great emphasis has been put on establishing treatments for this condition, including pharmacological intervention. However, there are many obstacles and pitfalls in the development process from pre-clinical research to the pharmacy counter, and there is no certainty that what has been observed pre-clinically will translate into an improvement in human health. Hence, it is important to test potential new drugs in a valid translational model early in their development. In the current mini-review, a number of monogenetic and polygenic models of obesity will be discussed in view of their translational character.

Liraglutide, a once-daily human glucagon-like peptide-1 analog, minimizes food intake in severely obese minipigs.

Objectives: To evaluate the efficacy of liraglutide, a new, stable, once‐daily human analog of glucagon‐like peptide‐1, in a new animal model of obesity.

Fibroblast Growth Factor 21 (FGF21) and Glucagon-Like Peptide 1 Contribute to Diabetes Resistance in Glucagon Receptor–Deficient Mice

Mice genetically deficient in the glucagon receptor (Gcgr−/−) show improved glucose tolerance, insulin sensitivity, and α-cell hyperplasia. In addition, Gcgr−/− mice do not develop diabetes after chemical destruction of β-cells. Since fibroblast growth factor 21 (FGF21) has insulin-independent glucose-lowering properties, we investigated whether FGF21 was contributing to diabetes resistance in insulin-deficient Gcgr−/− mice. Plasma FGF21 was 25-fold higher in Gcgr−/− mice than in wild-type mice. FGF21 was found to be expressed in pancreatic β- and α-cells, with high expression in the hyperplastic α-cells of Gcgr−/− mice. FGF21 expression was also significantly increased in liver and adipose tissue of Gcgr−/− mice. To investigate the potential antidiabetic actions of FGF21 in insulin-deficient Gcgr−/− mice, an FGF21-neutralizing antibody was administered prior to oral glucose tolerance tests (OGTTs). FGF21 neutralization caused a decline in glucose tolerance in insulin-deficient Gcgr−/− mice during the OGTT. Despite this decline, insulin-deficient Gcgr−/− mice did not develop hyperglycemia. Glucagon-like peptide 1 (GLP-1) also has insulin-independent glucose-lowering properties, and an elevated circulating level of GLP-1 is a known characteristic of Gcgr−/− mice. Neutralization of FGF21, while concurrently blocking the GLP-1 receptor with the antagonist Exendin 9-39 (Ex9-39), resulted in significant hyperglycemia in insulin-deficient Gcgr−/− mice, while blocking with Ex9-39 alone did not. In conclusion, FGF21 acts additively with GLP-1 to prevent insulinopenic diabetes in mice lacking glucagon action.

Chronic Administration of the Glucagon-Like Peptide-1 Analog, Liraglutide, Delays the Onset of Diabetes and Lowers Triglycerides in UCD-T2DM Rats

OBJECTIVE The efficacy of liraglutide, a human glucagon-like peptide-1 (GLP-1) analog, to prevent or delay diabetes in UCD-T2DM rats, a model of polygenic obese type 2 diabetes, was investigated. RESEARCH DESIGN AND METHODS At 2 months of age, male rats were divided into three groups: control, food-restricted, and liraglutide. Animals received liraglutide (0.2 mg/kg s.c.) or vehicle injections twice daily. Restricted rats were food restricted to equalize body weights to liraglutide-treated rats. Half of the animals were followed until diabetes onset, whereas the other half of the animals were killed at 6.5 months of age for tissue collection. RESULTS Before diabetes onset energy intake, body weight, adiposity, and liver triglyceride content were higher in control animals compared with restricted and liraglutide-treated rats. Energy-restricted animals had lower food intake than liraglutide-treated animals to maintain the same body weights, suggesting that liraglutide increases energy expenditure. Liraglutide treatment delayed diabetes onset by 4.1 ± 0.8 months compared with control (P < 0.0001) and by 1.3 ± 0.8 months compared with restricted animals (P < 0.05). Up to 6 months of age, energy restriction and liraglutide treatment lowered fasting plasma glucose and A1C concentrations compared with control animals. In contrast, liraglutide-treated animals exhibited lower fasting plasma insulin, glucagon, and triglycerides compared with both control and restricted animals. Furthermore, energy-restricted and liraglutide-treated animals exhibited more normal islet morphology. CONCLUSIONS Liraglutide treatment delays the development of diabetes in UCD-T2DM rats by reducing energy intake and body weight, and by improving insulin sensitivity, improving lipid profiles, and maintaining islet morphology.

Evaluation of different methods for assessment of insulin sensitivity in Gottingen minipigs: introduction of a new, simpler method

The use of animal models in diabetes research requires reliable tests for evaluation of insulin sensitivity and beta-cell function. Minipigs are being increasingly used in metabolic research, and the aim of this study was to compare different tests and indexes for evaluation of insulin sensitivity and beta-cell function in Göttingen minipigs. Hyperinsulinemic, isoglycemic clamp, intravenous (IVGTT) and oral glucose tolerance tests (OGTT), and a modified insulin tolerance test were performed in minipigs fed either low- or high-energy diet. Furthermore, the reproducibility of IVGTT-derived parameters was assessed. Previously described insulin sensitivity indexes [steady-state glucose infusion rate/glucose concentration/insulin concentration from clamp (M/G/I); oral glucose insulin sensitivity (OGIS) and ISI(comp) from OGTT; S(I) from minimal model analysis of IVGTT; and quantitative insulin sensitivity check index from fasting values] were calculated together with an insulin sensitivity index from the modified insulin tolerance test (ISI(ITT)) and a new simple index (S2) derived from the first 30 min of the IVGTT. beta-Cell function was assessed from the IVGTT and the OGTT. Reproducibility of the IVGTT-derived parameters was calculated as median intraindividual coefficient of variation (CV%).M/G/I correlated significantly only with S2 (P < 0.05, r = 0.54). S2 furthermore correlated with S(I) (P < 0.001, r = 0.81), ISI(ITT) (P < 0.001, r = 0.57), and the two indexes from OGTT, ISI(comp) (P < 0.001, r = 0.78) and OGIS (p < 0.05, r = 0.48). No correlation was found between beta-cell function indexes from OGTT and IVGTT. The median CV% of the new S2 index was 13. In conclusion, the new simple index of insulin sensitivity, S2, was revealed to be useful for evaluation of insulin sensitivity in pigs.

Evalution of the castrated male Sprague–Dawley rat as a model of the metabolic syndrome and type 2 diabetes

Objective:Low testosterone levels have been shown to be predictive for the development of the metabolic syndrome in men. The aim of this study was to describe effects of testosterone deficiency on metabolic syndrome-related parameters in male rats in order to evaluate the rat as a model for the human metabolic syndrome related to low testosterone levels.Methods:Male Sprague–Dawley rats were castrated or sham operated at 16 weeks of age and fed either a standard or a high energy diet. Measured parameters were: food intake, body weight, fat distribution, energy expenditure, physical activity and blood/plasma parameters related to glucose and lipid metabolism.Results:Castration led to an increase in the amount of subcutaneous fat, but did not result in any changes in the visceral fat. Fasting blood glucose levels were increased and free fatty acids concentration decreased in the castrated rats from 2 weeks after castration and throughout the study, whereas no significant differences between the groups were found in any of the other parameters measured. A high-energy diet did not change the response to castration in male Sprague–Dawley rats.Conclusion:Compared to humans rats respond differently to testosterone deficiency. Only few of the features typical for the human metabolic syndrome were observed in castrated male Sprague–Dawley rats. Therefore, we conclude that with the present experimental setup the castrated rat is not an optimal model for studies on the influence of testosterone deficiency on body fat distribution and the development of other central components of the metabolic syndrome.

Analytic framework for peptidomics applied to large-scale neuropeptide identification

Large-scale mass spectrometry-based peptidomics for drug discovery is relatively unexplored because of challenges in peptide degradation and identification following tissue extraction. Here we present a streamlined analytical pipeline for large-scale peptidomics. We developed an optimized sample preparation protocol to achieve fast, reproducible and effective extraction of endogenous peptides from sub-dissected organs such as the brain, while diminishing unspecific protease activity. Each peptidome sample was analysed by high-resolution tandem mass spectrometry and the resulting data set was integrated with publically available databases. We developed and applied an algorithm that reduces the peptide complexity for identification of biologically relevant peptides. The developed pipeline was applied to rat hypothalamus and identifies thousands of neuropeptides and their post-translational modifications, which is combined in a resource format for visualization, qualitative and quantitative analyses.