Aims/hypothesisCarbohydrate-free diet prevents hyperglycaemia and beta cell destruction in the New Zealand Obese (NZO) mouse model. Here we have used a sequential dietary regimen to dissociate the effects of obesity and hyperglycaemia on beta cell function and integrity, and to study glucose-induced alterations of key transcription factors over 16 days.MethodsMice were rendered obese by feeding a carbohydrate-free diet for 18 weeks. Thereafter, a carbohydrate-containing diet was given. Plasma glucose, plasma insulin and total pancreatic insulin were determined, and forkhead box O1 protein (FOXO1) phosphorylation and the transcription factors pancreatic and duodenal homeobox 1 (PDX1), NK6 homeobox 1 protein (NKX6.1) and v-maf musculoaponeurotic fibrosarcoma oncogene family, protein A (avian) (MAFA) were monitored by immunohistochemistry for 16 days.ResultsDietary carbohydrates produced a rapid and continuous increase in plasma glucose in NZO mice between day 2 and 16 after the dietary challenge. Hyperglycaemia caused a dramatic dephosphorylation of FOXO1 at day 2, followed by a progressive depletion of insulin stores. The loss of beta cells was triggered by apoptosis (detectable at day 8), associated with reduction of crucial transcription factors (PDX1, NKX6.1 and MAFA). Incubation of isolated islets from carbohydrate-restricted NZO mice or MIN6 cells with palmitate and glucose for 48 h resulted in a dephosphorylation of FOXO1 and thymoma viral proto-oncogene 1 (AKT) without changing the protein levels of both proteins.Conclusions/interpretationThe dietary regimen dissociates the effects of obesity (lipotoxicity) from those of hyperglycaemia (glucotoxicity) in NZO mice. Obese NZO mice are unable to compensate for the carbohydrate challenge by increasing insulin secretion or synthesising adequate amounts of insulin. In response to the hyperglycaemia, FOXO1 is dephosphorylated, leading to reduced levels of beta cell-specific transcription factors and to apoptosis of the cells.Electronic supplementary materialThe online version of this article (doi:10.1007/s00125-010-1973-8) contains supplementary material, which is available to authorised users.

Uncoupling of oxidative phosphorylation represents a potential target for the treatment of hyperglycemia and insulin resistance in obesity and type 2 diabetes. The present study investigated whether the expression of uncoupling protein 1 in skeletal muscles of transgenic (mUCP1 TG) mice modulates insulin action in major insulin target tissues in vivo. Euglycemic-hyperinsulinemic clamps (17 pM x kg lean body mass(-1) x min(-1)) were performed in 9-mo-old hemizygous male mUCP1 TG mice and wild-type (WT) littermates matched for body composition. mUCP1 TG mice exhibited fasting hypoglycemia and hypoinsulinemia compared with WT mice, whereas fasting hepatic glucose production rates were comparable in both genotypes. mUCP1 TG mice were markedly more sensitive to insulin action compared with WT mice and displayed threefold higher glucose infusion rates, enhanced skeletal muscle and white adipose tissue glucose uptake, and whole body glycolysis rates. In the absence of alterations in plasma adiponectin concentrations, acceleration of insulin-stimulated glucose turnover in skeletal muscle of mUCP1 TG mice was accompanied by increased phosphorylated Akt-to-Akt and phosphorylated AMP-activated protein kinase (AMPK)-to-AMPK ratios compared with WT mice. UCP1-mediated uncoupling of oxidative phosphorylation in skeletal muscle was paralleled by AMPK activation and thereby stimulated insulin-mediated glucose uptake in skeletal muscle.

hepatic glucose production, to stimulate fatty acid oxidation in liver, and to enhance glucose transport in skeletal muscle. Estrogen also protects pancreatic β-cell function and survival in conditions of oxidative stress (reviewed in [ 11 ]).

Obesity in NZO mice develops independent of the dietary sucrose or fat content, and of the fat quality. However, the dietary fat content accelerates the onset of diabetes without enhancing adiposity. In contrast, chow diet exerts an anti-adipogenic/anti-diabetogenic effect that appears to be due to its lower caloric density and/or its higher fibre content.

Objective: We have previously reported that a high-fat, carbohydrate-free diet prevents diabetes and β-cell destruction in the New Zealand Obese (NZO) mouse strain. Here we investigated the effect of diets with and without carbohydrates on obesity and development of β-cell failure in a second mouse model of type 2 diabetes, the db/db mouse. Results: When kept on a carbohydratecontaining standard (SD; with (w/w) 5.1, 58.3, and 17.6% fat, carbohydrates and protein, respectively) or high-fat diet (HFD; 14.6, 46.7 and 17.1%), db/db mice developed severe diabetes (blood glucose >20 mmol/l, weight loss, polydipsia and polyurea) associated with a selective loss of pancreatic β-cells, reduced GLUT2 expression in the remaining β-cells, and reduced plasma insulin levels. In contrast, db/db mice kept on a high-fat, carbohydrate-free diet (CFD; with 30.2 and 26.4% (w/w) fat or protein) did not develop diabetes and exhibited near-normal, hyperplastic islets in spite of a morbid obesity (fat content >60%) associated with hyperinsulinaemia. Conclusion: These data indicate that in genetically different mouse models of obesity-associated diabetes, obesity and dietary fat are not sufficient, and dietary carbohydrates are required, for β-cell destruction.