The immune-modulating cytokine interleukin-6 (IL-6) is expressed both in adipose tissue and centrally in hypothalamic nuclei that regulate body composition. We investigated the impact of loss of IL-6 on body composition in mice lacking the gene encoding IL-6 (Il6-/- mice) and found that they developed mature-onset obesity that was partly reversed by IL-6 replacement. The obese Il6-/- mice had disturbed carbohydrate and lipid metabolism, increased leptin levels and decreased responsiveness to leptin treatment. To investigate the possible mechanism and site of action of the anti-obesity effect of IL-6, we injected rats centrally and peripherally with IL-6 at low doses. Intracerebroventricular, but not intraperitoneal IL-6 treatment increased energy expenditure. In conclusion, centrally acting IL-6 exerts anti-obesity effects in rodents.
This study characterizes the high-fat diet-fed mouse as a model for impaired glucose tolerance (IGT) and type 2 diabetes. Female C57BL/6J mice were fed a high-fat diet (58% energy by fat) or a normal diet (11% fat). Body weight was higher in mice fed the high-fat diet already after the first week, due to higher dietary intake in combination with lower metabolic efficiency. Circulating glucose increased after 1 week on high-fat diet and remained elevated at a level of ϳ1 mmol/l throughout the 12-month study period. In contrast, circulating insulin increased progressively by time. Intravenous glucose challenge revealed a severely compromised insulin response in association with marked glucose intolerance already after 1 week. To illustrate the usefulness of this model for the development of new treatment, mice were fed an orally active inhibitor of dipeptidyl peptidase-IV (LAF237) in the drinking water (0.3 mg/ ml) for 4 weeks. This normalized glucose tolerance, as judged by an oral glucose tolerance test, in association with augmented insulin secretion. We conclude that the high-fat diet-fed C57BL/6J mouse model is a robust model for IGT and early type 2 diabetes, which may be used for studies on pathophysiology and development of new treatment. Diabetes 53 (Suppl. 3):S215-S219, 2004 T here is a need for new treatment modalities of type 2 diabetes in view of the progressive deterioration of metabolic control that occurs in spite of intense treatment with existing modalities (1). New treatment should aim at normalizing the basic defects in the disease, which are islet dysfunction in combination with insulin resistance (2). There is, however, also a need for more knowledge of the molecular mechanisms underlying these basic defects. These two needs require reliable and clinically relevant experimental models. Most animal models do not, however, fulfill such requirements, since they are based on monogenic disorders of little relevance for human diabetes (3-5) or on chemical destruction of ␤-cells, which is also of less clinical relevance (6,7). An important and relevant model, however, is the high-fat diet-fed C57BL/6J mouse model. This model was originally introduced by Surwit et al. in 1988 (8). The model has shown to be accompanied by insulin resistance, as determined by intravenous glucose tolerance tests, and of insufficient islet compensation to the insulin resistance (9). The model has, accordingly, been used in studies on pathophysiology of impaired glucose tolerance (IGT) and type 2 diabetes (10 -12) and for development of new treatments (13-16). Here we report the characteristics of this model and illustrate its relevance in studies on developing new treatment modes by showing beneficial influences of a novel and efficient orally active inhibitor of dipeptidyl peptidase-IV (DPP-IV), which is a new mode for treating type 2 diabetes by preventing the degradation of glucagon-like peptide-1 (GLP-1) (17-19).
RESEARCH DESIGN AND METHODSFemale C57BL/6J mice were purchased from Taconic (Skensved, Denmark). The ani...
The stimulation of insulin vs. inhibition of glucagon secretion in relation to the antidiabetic action of glucagon-like peptide-1 (GLP-1) is not established. Here, the influence of a 4-wk increase in circulating GLP-1 by inhibition of dipeptidyl peptidase-4 (DPP-4) on 24-h glucose and insulin and glucagon responses to breakfast was studied in subjects with dietary controlled diabetes [age: 65 +/- 8 yr (SD), body mass index: 27.3 +/- 3.3 kg/m(2), fasting plasma glucose: 9.0 +/- 1.3 mmol/liter]. Compared with placebo (n = 19), a specific DPP-4 inhibitor [(1-[[(3-hydroxy-1-adamantyl) amino] acetyl]-2-cyano-(S)-pyrrolidine) (LAF237); 100 mg daily, n = 18] reduced fasting glucose by 0.70 mmol/liter (P = 0.037), 4-h prandial glucose excursion by 1.45 mmol/liter (P < 0.001), and mean 24-h glucose by 0.93 mmol/liter (P < 0.001). Baseline and postprandial active GLP-1 were increased by LAF237. The glucagon response to breakfast was reduced by LAF237 (glucagon levels at 60 min were 88 +/- 8 pg/ml before treatment vs. 77 +/- 5 pg/ml after; P = 0.001). In contrast, the overall insulin levels were not altered. The 4-wk reduction in glucagon correlated with the reduction in 2-h glucose (r = 0.61; P = 0.008). No such association was observed for insulin. Thus, improved metabolic control by DPP-4 inhibition in type 2 diabetes is seen in association with reduced glucagon levels and, despite the lower glycemia, unaltered insulin levels.
Obesity, hyperlipidemia, and insulin resistance are common forerunners of type 2 diabetes mellitus. We have identified the human winged helix/forkhead transcription factor gene FOXC2 as a key regulator of adipocyte metabolism. Increased FOXC2 expression, in adipocytes, has a pleiotropic effect on gene expression, which leads to a lean and insulin sensitive phenotype. FOXC2 affects adipocyte metabolism by increasing the sensitivity of the beta-adrenergic-cAMP-protein kinase A (PKA) signaling pathway through alteration of adipocyte PKA holoenzyme composition. Increased FOXC2 levels, induced by high fat diet, seem to counteract most of the symptoms associated with obesity, including hypertriglyceridemia and diet-induced insulin resistance--a likely consequence hereof would be protection against type 2 diabetes.
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