Beta-cell Compensation For Insulin Resistance Research Articles

Glucocorticoid Receptor Is Instrumental for the Mechanism of Beta-Cell Compensation for Insulin Resistance in Dietary Obesity

The glucocorticoid receptor (GR) is known as a receptor of steroids - potent anti-inflammatory ligands that are commonly used for the medication of allergy or asthma in children and adults. However, chronic use of steroids is associated with a significant risk of developing visceral adiposity and insulin resistance, a medical condition that is known as the Cushing syndrome. We hypothesized that excessive GR activation is deleterious to beta-cells such that genetic GR depletion would preserve beta-cell mass and function in response to metabolic stress. To address this hypothesis, we generated beta-cell specific GR knockout (KO) mice, using an inducible Pdx1-CreERT2-loxP system. We then fed beta-cell GR-KO and WT littermates both regular chow and high-fat diet for up to 30 weeks, followed by determination of beta-cell mass and function. We found that GR-deficient mice, as opposed to WT littermates, developed high blood glucose levels and glucose intolerance. This effect was not secondary to alterations in weight gain or insulin sensitivity. Instead, we detected a significant reduction in glucose-stimulated insulin secretion, correlating with abnormal glucose metabolism in GR-KO mice. We reproduced these findings in both male and female GR-KO mice. Anti-insulin immunohistochemistry revealed that GR-KO mice had significantly reduced beta-cell mass, and decreased beta-cell replication, as visualized by in vivo BrdU-labeling assay. GR deficiency appears to impair the ability of beta-cells to compensate for fat-elicited obesity and insulin resistance, resulting in prediabetes in GR-KO mice. These results unveiled an unexpected role of the glucocorticoid-GR signaling in safeguarding beta-cell mass and function in response to metabolic stress. Disclosure J. Yamauchi: None. S. Lee: None. H. Dong: None.

Evolution of beta-cell dysfunction in impaired glucose tolerance and diabetes.

Patients with overt Type 2 diabetes consistently have alterations in insulin secretion, including reduced insulin secretory responses to glucose, delayed and blunted meal-induced insulin secretion, increased pro-insulin and abnormal insulin secretory oscillations. More recently, it has become evident that abnormal insulin secretion antedates the onset of overt hyperglycaemia and is present in people with impaired glucose tolerance, i.e. normal fasting glucose and glycohaemoglobin concentrations. These defects are subtle and include shifts to the right in the dose-response curves that relate to glucose and insulin secretion, reduced ability of the beta-cell to detect and respond to oscillatory changes in the plasma glucose concentration and impaired beta-cell compensation for insulin resistance. In order to define the factors responsible for these defects in secretion, we have infused human patients with a lipid emulsion and heparin to raise plasma free fatty acid concentrations. This is associated with reduced ability of the beta-cell to detect and respond to small changes in the plasma glucose concentration. In summary, defects in insulin secretion are consistently present in patients with impaired glucose tolerance and play a critical role in the progression from impaired glucose tolerance to diabetes.

Atypical Antipsychotics and Glucose Homeostasis

Persistent reports have linked atypical antipsychotics with diabetes, yet causative mechanisms responsible for this linkage are unclear. Goals of this review are to outline the pathogenesis of nonimmune diabetes and to survey the available literature related to why antipsychotics may lead to this disease. We accessed the literature regarding atypical antipsychotics and glucose homeostasis using PubMed. The search included English-language publications from 1990 through October 2004. Keywords used included atypical antipsychotics plus one of the following: glucose, insulin, glucose tolerance, obesity, or diabetes. In addition, we culled information from published abstracts from several national and international scientific meetings for the years 2001 through 2004, including the American Diabetes Association, the International Congress on Schizophrenia Research, and the American College of Neuropsychopharmacology. The latter search was necessary because of the paucity of well-controlled prospective studies. We examined publications with significant new data or publications that contributed to the overall comprehension of the impact of atypical antipsychotics on glucose metabolism. We favored original peer-reviewed articles and were less likely to cite single case studies and/or anecdotal information. Approximately 75% of the fewer than 150 identified articles were examined and included in this review. Validity of data was evaluated using the existence of peer-review status as well as our own experience with methodology described in the specific articles. The metabolic profile caused by atypical antipsychotic treatment resembles type 2 diabetes. These agents cause weight gain in treated subjects and may induce obesity in both visceral and subcutaneous depots, as occurs in diabetes. Insulin resistance, usually associated with obesity, occurs to varying degrees with different antipsychotics, although more comparative studies with direct assessment of resistance are needed. A major problem in assessing drug effects is that psychiatric disease itself can cause many of the manifestations leading to diabetes, including weight gain and sedentary lifestyle. While studies in healthy subjects are limited and inconclusive, studies in animal models are more revealing. In the conscious canine model, some atypical antipsychotics cause adiposity, including visceral obesity, a strong risk factor for the metabolic syndrome. Furthermore, while few studies have examined effects of antipsychotics on pancreatic beta-cell function, canine studies demonstrate that expected beta-cell compensation for insulin resistance may be reduced or even eliminated with these agents. Atypical antipsychotics have been shown to contribute to weight gain, which may well reflect increased body fat deposition. Such increased fat is known to cause resistance to insulin action, although more information regarding effect on insulin action is needed. The effect of these drugs on fat distribution has been clearly shown in animal models. It is known that the normal response to insulin resistance is compensatory hyperinsulinemia, which may prevent diabetes. In animals, there is evidence that the hyperinsulinemic compensation is inadequate in the face of atypical antipsychotic agents. It remains to be examined whether failure of adequate pancreatic beta-cell compensation for insulin resistance plays a central role in the pathogenesis of diabetes associated with this class of drugs.

Antepartum predictors of the development of type 2 diabetes in Latino women 11-26 months after pregnancies complicated by gestational diabetes.

In this study, we sought to identify antepartum characteristics that predict the de novo development of diabetes 11-26 months after the index pregnancy in a carefully characterized cohort of women with gestational diabetes mellitus (GDM). Oral and frequently sampled intravenous glucose tolerance tests (OGTTs and FSIGTs), hyperinsulinemic-euglycemic clamps with labeled glucose, and body composition studies were performed on 91 islet cell antibody-negative Latino women with GDM during the third trimester of pregnancy. The women were documented to be diabetes-free within 6 months postpartum. Their diabetes status was ascertained again between 11 and 26 months postpartum. Logistic regression analysis was used to identify independent predictors of the development of diabetes within that interval. Fourteen of the women developed diabetes by World Health Organization criteria 11-26 months after delivery of the index pregnancy. Three antepartum variables were independent predictors of diabetes: the 1-h postchallenge plasma glucose concentration from the 100-g OGTT at which GDM was diagnosed (higher = increased risk; P = 0.003); an index of pancreatic beta-cell compensation for insulin resistance, defined as the product of the 30-min incremental plasma insulin:glucose ratio on a 75-g OGTT and the insulin sensitivity index from a hyperinsulinemic-euglycemic clamp (lower = increased risk, P = 0.009); and the basal glucose production rate after an overnight fast (higher = increased risk; P = 0.04). We conclude that postchallenge hyperglycemia, poor pancreatic beta-cell compensation for insulin resistance, and elevated endogenous glucose production during pregnancy precede the development of type 2 diabetes in young Latino women by at least 1-2 years.

Multiple metabolic defects during late pregnancy in women at high risk for type 2 diabetes.

Detailed metabolic studies were carried out to compare major regulatory steps in glucose metabolism in vivo between 25 normal pregnant Latino women without and 150 pregnant Latino women with gestational diabetes mellitus (GDM). The two groups were frequency-matched for age, BMI, and gestational age at testing in the third trimester. After an overnight fast, women with GDM had higher fasting plasma glucose (P = 0.0001) and immunoreactive insulin (P = 0.0003) concentrations and higher glucose production rates (P = 0.01) but lower glucose clearance rates (P = 0.001) compared with normal pregnant women. During steady-state hyperinsulinemia (approximately 600 pmol/l) and euglycemia (approximately 4.9 mmol/l), women with GDM had lower glucose clearance rates (P = 0.0001) but higher glucose production rates (P = 0.0001) and plasma free fatty acid (FFA) concentrations (P = 0.0002) than the normal women. These intergroup differences persisted when a subgroup of 116 women with GDM who were not diabetic < or = 6 months after pregnancy were used in the analysis. When all subjects were considered, there was a very close correlation between glucose production rates and plasma FFA concentrations throughout the glucose clamps in control (r = 0.996) and GDM (r = 0.995) groups. Slopes and intercepts of the relationships were nearly identical, suggesting that blunted suppression of FFA concentrations contributed to blunted suppression of glucose production in the GDM group. In addition to these defects in insulin action, women with GDM had a 67% impairment of pancreatic beta-cell compensation for insulin resistance compared with normal pregnant women. These results demonstrate that women with GDM have multiple defects in insulin action together with impaired compensation for insulin resistance. Our findings suggest that defects in the regulation of glucose clearance, glucose production, and plasma FFA concentrations, together with defects in pancreatic beta-cell function, precede the development of type 2 diabetes in these high-risk women.