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.

Upregulation of alpha cell glucagon-like peptide 1 (GLP-1) in Psammomys obesus--an adaptive response to hyperglycaemia?

AIMS/HYPOTHESIS: The hormone glucagon-like peptide 1 (GLP-1) is released in response to a meal from the intestinal L-cells, where it is processed from proglucagon by the proconvertase (PC)1/3. In contrast, in the adult islets proglucagon is processed to glucagon by the PC2 enzyme. The aim of the study was to evaluate if, during the development of diabetes, alpha cells produce GLP-1 that, in turn, might trigger beta cell growth. METHODS: Beta cell mass, GLP-1 and insulin levels were measured in the gerbil Psammomys obesus (P. obesus), a rodent model of nutritionally induced diabetes. Furthermore, the presence of biologically active forms of GLP-1 and PC1/3 in alpha cells was demonstrated by immunofluorescence, and the release of GLP-1 from isolated P. obesus, mouse and human islets was investigated. RESULTS: During the development of diabetes in P. obesus, a significant increase in GLP-1 was detected in the portal vein (9.8 ± 1.5 vs 4.3 ± 0.7 pmol/l, p < 0.05), and in pancreas extracts (11.4 ± 2.2 vs 5.1 ± 1.3 pmol/g tissue, p < 0.05). Freshly isolated islets from hyperglycaemic animals released more GLP-1 following 24 h culture than islets from control animals (28.2 ± 4.4 pmol/l vs 5.8 ± 2.4, p < 0.01). GLP-1 release was increased from healthy P. obesus islets following culture in high glucose for 6 days (91 ± 9.1 pmol/l vs 28.8 ± 6.6, p < 0.01). High levels of GLP-1 were also found to be released from human islets. PC1/3 colocalised weakly with alpha cells. CONCLUSIONS/INTERPRETATION: GLP-1 release from alpha cells is upregulated in P. obesus during the development of diabetes. A similar response is seen in islets exposed to high glucose, which supports the hypothesis that GLP-1 released from alpha cells promotes an increase in beta cell mass and function during metabolic challenge such as diabetes.

Treatment with a proton pump inhibitor improves glycaemic control in Psammomys obesus, a model of type 2 diabetes.

AIMS/HYPOTHESIS: Gastrin has been implicated in islet growth/neogenesis, and proton pump inhibitors (PPIs) have been shown to increase endogenous gastrin levels in animals and humans. Therefore, we investigated the effect of PPIs in a model of type 2 diabetes, Psammomys obesus. METHODS: P. obesus (morning blood glucose [mBG] 16.9 +/- 0.6 mmol/l) were treated with vehicle or different doses (1-15 mg/kg) of lansoprazole for 17 days. RESULTS: Treatment with lansoprazole resulted in up to ninefold dose-dependent increases in endogenous gastrin levels (p < 0.05 for 10 mg/kg lansoprazole vs vehicle). There was a significant reduction in mBG levels in all animals in the high-dose lansoprazole groups during the 17 day treatment period, whereas there was no significant improvement in mBG in animals in the vehicle groups. The mBG at end of study was 18.2 +/- 2.1, 8.7 +/- 2.2 (p < 0.01), and 6.1 +/- 2.3 (p < 0.001) mmol/l for vehicle and lansoprazole 10 and 15 mg/kg, respectively. The animals treated with 15 mg/kg lansoprazole, compared with vehicle, had a 2.3-fold increase in the intensity of insulin staining in beta cells (p=0.0002) and 50% higher beta cell mass (p=0.04). CONCLUSIONS/INTERPRETATIONS: The PPI lansoprazole had significant glucose-lowering effects in an animal model of type 2 diabetes, an effect that is most likely mediated through an increase in endogenous gastrin levels.

Quality of plasma sampled by different methods for multiple blood sampling in mice.

For oral glucose tolerance test (OGTT) in mice, multiple blood samples need to be taken within a few hours from conscious mice. Today, a number of essential parameters may be analysed on very small amounts of plasma, thus reducing the number of animals to be used. It is, however, crucial to obtain high-quality plasma or serum in order to avoid increased data variation and thereby increased group sizes. The aim of this study was to find the most valid and reproducible method for withdrawal of blood samples when performing OGTT. Four methods, i.e. amputation of the tail tip, lateral tail incision, puncture of the tail tip and periorbital puncture, were selected for testing at 21 degrees C and 30 degrees C after a pilot study. For each method, four blood samples were drawn from C57BL/6 mice at 30 min intervals. The presence of clots was registered, haemolysis was monitored spectrophotometrically at 430 nm, and it was noted whether it was possible to achieve 30-50 microL blood. Furthermore, a small amount of extra blood was sampled before and after the four samplings for testing of whether the sampling induced a blood glucose change over the 90 min test period. All methods resulted in acceptable amounts of plasma. Clots were observed in a sparse number of samples with no significant differences between the methods. Periorbital puncture did not lead to any haemolysed samples at all, and lateral tail incision resulted in only a few haemolysed samples, while puncture or amputation of the tail tip induced haemolysis in a significant number of samples. All methods, except for puncture of the tail tip, influenced blood glucose. Periorbital puncture resulted in a dramatic increase in blood glucose of up to 3.5 mmol/L indicating that it is stressful. Although lateral tail incision also had some impact on blood glucose, it seems to be the method of choice for OGTT, as it is likely to produce a clot-free non-haemolysed sample, while periorbital sampling, although producing a high quality of sample, induces such a dramatic change in blood glucose that it should not be applied for OGTT in mice.