Thora B. Bodvarsdottir

Inhibition of Insulin Secretion as a New Drug Target in the Treatment of Metabolic Disorders

The pattern of insulin release is crucial for regulation of glucose and lipid haemostasis. Deficient insulin release causes hyperglycemia and diabetes, whereas excessive insulin release can give rise to serious metabolic disorders, such as nesidioblastosis (Persistent Hyperinsulinemic Hypoglycemia of Infancy, PHHI) and might also be closely associated with development of type 2 diabetes and obesity. Type 2 diabetes is characterized by fasting hyperinsulinemia, insulin resistance and impaired insulin release, i.e. reduced first phase insulin release and decreased insulin pulse mass. The beta cell function of patients with type 2 diabetes slowly declines and will ultimately result in beta cell failure and increasing degrees of hyperglycemia. Type 2 diabetes, in combination with obesity and cardiovascular disorders, forms the metabolic syndrome. It has been possible to improve beta cell function and viability in preclinical models of type 1 and type 2 diabetes by reducing insulin secretion to induce beta cell rest. Clinical studies have furthermore indicated that inhibitors of insulin release will be of benefit in treatment or prevention of diabetes and obesity. Pancreatic beta cells secrete insulin in response to increased metabolism and by stimulation of different receptors. The energy status of the beta cell controls insulin release via regulation of open probability of the ATP sensitive potassium (K(ATP)) channels to affect membrane potential and the intracellular calcium concentration [Ca(2+)](i). Other membrane bound receptors and ion channels and intracellular targets that modulate [Ca(2+)](i)will affect insulin release. Thus, insulin release is regulated by e.g. somatostatin receptors, GLP-1 receptors, muscarinic receptors, cholecystokinin receptors and adrenergic receptors. Although the relationship between hyperinsulinemia and certain metabolic diseases has been known for decades, only a few inhibitors of insulin release have been characterized in vitro and in vivo. These include the K(ATP) channel openers diazoxide and NN414 and the somatostatin receptor agonist octreotide.

Effects of short-term therapy with glibenclamide and repaglinide on incretin hormones and oxidative damage associated with postprandial hyperglycaemia in people with type 2 diabetes mellitus

AIM To examine the effects of glibenclamide and repaglinide on glucose stimulated insulin release, incretins, oxidative stress and cell adhesion molecules in patients with type 2 diabetes suboptimally treated with metformin. METHODS A randomized clinical trial was performed recruiting 27 subjects (HbA(1c) between 7.5 and 10.5%) free from cardiovascular and renal disease. Glucose, insulin, C-peptide, glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), total antioxidant status, F(2)-isoprostane, interleukin-6 and cell adhesion molecules were measured during an oral glucose load at baseline and after eight weeks of treatment. The areas under the curve were analysed at 45, 60 and 120 min (AUC(45), AUC(60), AUC(120)). RESULTS Significant improvements in glucose were observed with repaglinide (HBA(1c): -1.5%, fasting glucose: -2.8 mmol/L, 2-h glucose: -3.7 mmol/L, AUC(120): -18.9%) and glibenclamide (-1.0%, -2.2 mmol/L, -2.5 mmol/L, -17.5%). Repaglinide was also associated with an increase in the AUC(60) and AUC(120) for insulin (+56%, +61%) and C-peptide (+41%, +36%). GLP-1, GIP, IL-6, ICAM-1 and E-selectin levels did not change in either group. No association was observed between GLP-1, GIP-1 and plasma markers of oxidative stress. CONCLUSION Repaglinide is associated with improved postprandial glycaemic control via insulin and C-peptide release. We observed no direct effects of glibenclamide or repaglinide on plasma levels of GLP-1 or GIP. We observed no associations of GLP-1 and GIP with plasma markers of oxidative stress.

Treatment with a proton pump inhibitor improves glycaemic control in type 2 diabetic patients - a retrospective analysis

We retrospectively studied whether treatment with esomeprazole improved HbA₁(c) levels in type 2 diabetic patients. We selected 21 patients who had been treated with esomeprazole for 11 ± 3 months and 21 controls. HbA₁(c) levels decreased in the esomeprazole-treated group. Our data indicate that proton pump inhibitors may improve glycaemic control in type 2 diabetic patients.

Liraglutide, but not vildagliptin, restores normoglycaemia and insulin content in the animal model of type 2 diabetes, Psammomys obesus

In order to investigate the effect and mechanism of liraglutide and vildagliptin in diabetic Psammomys obesus, we examined proliferation and apoptosis of beta-cells, beta-cell mass (BCM), and pancreatic insulin content after zero, six and fourteen days of treatment compared to control groups. One group of animals was kept on low-energy diet and seven groups were given high-energy diet (HED) that induced diabetes over a four week period. Non-fasting morning blood glucose, body weight, HbA(1C) and pancreatic insulin content were measured and beta cell mass (BCM), proliferation and apoptosis frequencies were determined using stereological point counting. Liraglutide significantly reduced blood glucose and even normalized it in all animals treated for six days and in 11 out of 17 animals treated for fourteen days. HED increased BCM and treatment with liraglutide did not change this. However, compared to the vehicle-treated animals pancreatic insulin content was normalized in animals treated for six and fourteen days with liraglutide. In contrast, vildagliptin, in doses causing full inhibition of plasma DPP-IV activity, neither reduced blood glucose nor altered HED-induced increases in BCM or pancreatic insulin content. These results suggest that liraglutide restores normoglycaemia and improves glycaemic control in P. obesus by increasing their insulin content and improving the function of the beta-cells. In contrast, vildagliptin does not improve glycaemic control in P. obesus nor affect beta-cell insulin content.

Developmental Biology of the Psammomys obesus Pancreas: Cloning and Expression of the Neurogenin-3 Gene

The desert gerbil Psammomys obesus, an established model of type 2 diabetes (T2D), has previously been shown to lack pancreatic and duodenal homeobox gene 1 (Pdx-1) expression. Pdx-1 deficiency leads to pancreas agenesis in both mice and humans. We have therefore further examined the pancreas of P. obesus during embryonic development. Using Pdx-1 antisera raised against evolutionary conserved epitopes, we failed to detect Pdx-1 immunoreactivity at any time points. However, at E14.5, Nkx6.1 immunoreactivity marks the nuclei of all epithelial cells of the ventral and dorsal pancreatic buds and the only endocrine cell types found at this time point are glucagon and PYY. At E18.5 the pancreas is well branched and both glucagon- and ghrelin-positive cells are scattered or found in clusters, whereas insulin-positive cells are not found. At E22.5, the acini of the exocrine pancreas are starting to mature, and amylase and carboxypeptidase A immunoreactivity is found scattered and not in all acini. Ghrelin-, glucagon-, PYY-, gastrin-, somatostatin (SS)-, pancreatic polypeptide (PP)-, and insulin-immunoreactive cells are found scattered or in small groups within or lining the developing ductal epithelium as marked by cytokeratin 19. Using degenerate PCR, the P. obesus Neurogenin-3 (Ngn-3) gene was cloned. Nucleotide and amino acid sequences show high homology with known Ngn-3 sequences. Using specific antiserum, we can observe that Ngn-3-immunoreactive cells are rare at E14.5 but readily detectable at E18.5 and E22.5. In conclusion, despite the lack of detection of Pdx-1, the P. obesus pancreas develops similarly to Muridae species, and the Ngn-3 sequence and expression pattern is highly conserved in P. obesus.

Inhibition of the nuclear factor-κB pathway prevents beta cell failure and diet induced diabetes in Psammomys obesus.

BACKGROUND High doses of anti-inflammatory drugs, such as aspirin and salicylates, improve glucose metabolism in insulin resistant and type 2 diabetic patients. It has also been shown that the glucose lowering effect is related to the unspecific ability of these drugs to inhibit inhibitor kinaseβ (IKKβ). In this study we have investigated the effect of a selective IKKβ-inhibitor on beta cell survival and the prevention of diet induced type 2 diabetes in the gerbil Psammomys obesus (P. obesus). METHODOLOGY/PRINCIPAL FINDINGS P. obesus were fed a diabetes inducing high energy diet for one month in the absence or presence of the IKKβ-inhibitor. Body mass, blood glucose, HbA(1C), insulin production and pancreatic insulin stores were measured. The effects on beta cell survival were also studied in INS-1 cells and primary islets. The cells were exposed to IL-1β and subsequently reactive oxygen species, insulin release and cell death were measured in the absence or presence of the IKKβ-inhibitor. In primary islets and beta cells, IL-1β induced the production of reactive oxygen species, reduced insulin production and increased beta cell death, which were all reversed by pre-treatment with the IKKβ-inhibitor. In P. obesus the IKKβ-inhibitor prevented the development of hyperglycaemia and hyperinsulinaemia, and maintained pancreatic insulin stores with no effect on body weight. CONCLUSIONS/SIGNIFICANCE Inhibition of IKKβ activity prevents diet-induced diabetes in P. obesus and inhibits IL-1β induced reactive oxygen species, loss of insulin production and beta cell death in vitro.

FGF21 decreases body weight without reducing food intake or bone mineral density in high-fat fed obese rhesus macaque monkeys

ObjectiveAdministration of FGF21 and FGF21 analogues reduce body weight; improve insulin sensitivity and dyslipidemia in animal models of obesity and in short term clinical trials. However potential adverse effects identified in mice have raised concerns for the development of FGF21 therapeutics. Therefore, this study was designed to address the actions of FGF21 on body weight, glucose and lipid metabolism and importantly its effects on bone mineral density (BMD), bone markers, and plasma cortisol in high-fat fed obese rhesus macaque monkeys.MethodsObese non-diabetic rhesus macaque monkeys (five males and five ovariectomized (OVX) females) were maintained on a high-fat diet and treated for 12 weeks with escalating doses of FGF21. Food intake was assessed daily and body weight weekly. Bone mineral content (BMC) and BMD were measured by DEXA scanning prior to the study and on several occasions throughout the treatment period as well as during washout. Plasma glucose, glucose tolerance, insulin, lipids, cortisol, and bone markers were likewise measured throughout the study.ResultsOn average, FGF21 decreased body weight by 17.6 ± 1.6% after 12 weeks of treatment. No significant effect on food intake was observed. No change in BMC or BMD was observed, while a 2-fold increase in CTX-1, a marker of bone resorption, was seen. Overall glucose tolerance was improved with a small but significant decrease in HbA1C. Furthermore, FGF21 reduced concentrations of plasma triglycerides and very low density lipoprotein cholesterol. No adverse changes in clinical chemistry markers were demonstrated, and no alterations in plasma cortisol were observed during the study.ConclusionIn conclusion, FGF21 reduced body weight in obese rhesus macaque monkeys without reducing food intake. Furthermore, FGF21 had beneficial effects on body composition, insulin sensitivity, and plasma triglycerides. No adverse effects on bone density or plasma cortisol were observed after 12 weeks of treatment.