The effect of obesity on plasma triglycerides and fasting plasma IRI levels. Significance of insulinogenic index and glucose tolerance

Effects of leptin and adiponectin on pancreatic β-cell function

Leptin and adiponectin are hormones secreted from adipocytes that have important roles in metabolism and energy homeostasis. This review evaluates the effects of leptin and adiponectin on β-cell function by analyzing and compiling results from human clinical trials and epidemiologic studies as well as in vitro and in vivo experiments. Leptin has been shown to inhibit ectopic fat accumulation and thereby prevent β-cell dysfunction and protect the β-cell from cytokine- and fatty acid-induced apoptosis. However, leptin suppresses insulin gene expression and secretion as well as glucose transport into the β-cell. Adiponectin stimulates insulin secretion by enhancing exocytosis of insulin granules and upregulating the expression of the insulin gene; however, this effect depends on the prevailing glucose concentration and status of insulin resistance. In addition, adiponectin has antiapoptotic properties in β-cells. Available evidence concerning the role of these adipokines on insulin secretion, insulin gene expression, and apoptosis is not always entirely consistent; and many fundamental questions remain to be answered by future studies.

Preferable effect of pravastatin compared to atorvastatin on beta cell function in Japanese early-state type 2 diabetes with hypercholesterolemia

While a large numbers of clinical trials using various kinds of statins has been reported, a possible preventive effect on new onset of type 2 diabetes mellitus was shown only by the subanalysis of The West of Scotland Coronary Prevention Study (WOSCOPS) using pravastatin. The aim of this study was to investigate whether pravastatin has a preferable effect on glucose tolerance among statins. An open-label prospective cross-over trial was performed to compare the effect of pravastatin (10 mg/day) or atorvastatin (10 mg/day) in Japanese early-state type 2 diabetes mellitus with hypercholesterolemia. The analyzed study subjects were treated with pravastatin (10 mg/day, n = 12) or atorvastatin (10 mg/day, n = 12) for 12 weeks. After a 4-week-washout period, the drugs were switched and treatment was continued for another 12 weeks. Oral glucose tolerance test (OGTT) was performed to evaluate several parameters including the appropriateness of beta cell function for the individual insulin sensitivity (disposition index: product of a validated secretion parameter and sensitivity) at the end of each therapy. HbA(1c) and 2 h-glucose levels during OGTT in the pravastatin treatment were significantly lower than atorvastatin treatment. Disposition index after pravastatin treatment was significantly higher than after atorvastatin treatment. In conclusion, our study suggests that pravastatin has a favorable effect on pancreatic beta cell function compared with atorvastatin.

ATP-sensitive K+ channel-mediated glucose uptake is independent of IRS-1/phosphatidylinositol 3-kinase signaling

We previously found that disruption of Kir6.2-containing ATP-sensitive K+ (KATP) channels increases glucose uptake in skeletal muscle, but the mechanism is not clear. In the present study, we generated knockout mice lacking both Kir6.2 and insulin receptor substrate-1 (IRS-1). Because IRS-1 is the major substrate of insulin receptor kinase, we expected disruption of the IRS-1 gene to reduce glucose uptake in Kir6.2 knockout mice. However, the double-knockout mice do not develop insulin resistance or glucose intolerance. An insulin tolerance test reveals the glucose-lowering effect of exogenous insulin in double-knockout mice and in Kir6.2 knockout mice to be similarly enhanced compared with wild-type mice. The basal 2-deoxyglucose uptake rate in skeletal muscle of double-knockout mice is increased similarly to the rate in Kir6.2 knockout mice. Accordingly, disruption of the IRS-1 gene affects neither systemic insulin sensitivity nor glucose uptake in skeletal muscles of Kir6.2-deficient mice. In addition, no significant changes were observed in phosphatidylinositol 3-kinase (PI3K) activity and its downstream signal in skeletal muscle due to lack of the Kir6.2 gene. Disruption of Kir6.2-containing Katp channels clearly protects against IRS-1-associated insulin resistance by increasing glucose uptake in skeletal muscles by a mechanism separate from the IRS-1/PI3K pathway.

Relationship of body fat distribution to metabolic complications in obese prepubertal boys: gender related differences

Our purpose was to assess the relationship of obesity and body fat distribution to serum glucose values, insulin concentration and insulin resistance in obese prepubertal boys. Thirteen obese and 15 control prepubertal boys were studied. Biceps, triceps, subscapular and suprailiac skin fold thicknesses were measured. Percentage of body fat and total body fat were calculated. Body fat distribution was assessed by analyzing the central (supra-iliac, subscapular)/peripheral (biceps, triceps) ratios. During an oral glucose tolerance test, serum glucose and insulin were measured and insulin/glucose was calculated. Body fat data and body fat distribution indices were significantly higher in the obese group. The obese population presented significantly elevated values of insulin and insulin/glucose. In the obese group insulin showed significant correlations with percentage of body fat, total body fat and subscapular skin fold thickness, whereas insulin/glucose had significant positive correlations with percentage of body fat, total body fat and supra-iliac skin fold thickness. In obese boys significant positive correlations were also shown by subscapular/supra-iliac with insulin and insulin/glucose, and by subscapular/triceps with insulin. In prepubertal boys obesity is centripetal and an upper central body fat distribution seems to be first associated with an abnormal glucose-insulin homeostasis.

Relationship of body fat distribution to metabolic complications in obese prepubertal girls

The purpose of this study is to assess the relative effects of body fat distribution and obesity "per se" on serum glucose, insulin, and insulin resistance. Seventeen obese and nine nonobese control prepubertal girls were studied. Biceps, triceps, subscapular, and suprailiac skinfold thickness were measured. Percentage of body fat (% BF) and total body fat (TBF) were calculated. Body fat distribution was assessed by analyzing the central (suprailiac, subscapular)/peripheral (biceps, triceps) ratios. Oral glucose tolerance test was performed. Serum glucose and insulin were measured and insulinogenic index (insulin/glucose) was calculated. Body fat anthropometric data and body fat distribution indexes were significantly higher (p less than 0.001) in the obese group. The obese population presented significantly elevated values of glucose, insulin, and insulinogenic indexes (p less than 0.01-p less than 0.001). In the obese group, insulin showed significant positive correlations (p less than 0.05-p less than 0.001) with biceps, subscapular, and suprailiac skinfolds, % BF and TBF, whereas the insulinogenic index had positive correlations with suprailiac skinfold and TBF (p less than 0.05). Obese girls showed positive correlations between the body fat distribution indexes and insulin or insulinogenic indexes (p less than 0.05-p less than 0.001). In prepubertal girls obesity is of the centripetal (central) type. This pattern has an important role in determining the alterations in the glucose-insulin homeostasis that characterize the childhood nutritional obesity.

In vitro pancreatic B-cell response of hyperinsulinemic rats. Differences between pregnancy and VMH-lesions

We investigated in vitro the pancreatic B-cell response of hyperinsulinemic animals compared to that of controls with the aim of clarifying if the hyperinsulinemia is related to an alteration of the islet insulin secretion. Hyperinsulinemia was induced by pregnancy (observation at 19.5 days) and electrolytic lesions of the hypothalamic nucleus ventromedialis (2 days after lesion). The kinetics of the glucose dose/response curves (measured during a 60 min incubation period) differed markedly in the two hyperinsulinemic conditions. Whereas the islets from pregnant rats were characterized by a lowered glucose threshold, an enhanced half-maximal and maximal secretion rate, those of lesioned rats showed only an increased half-maximal and maximal secretion response in spite of a comparable islet insulin content. When culturing islets of hyperinsulinemic animals up to 6 days, the insulin secretion of those prepared from VMH-lesioned rats behaved identically to controls, whereas the islets of pregnant rats maintained their enhanced sensitivity at a glucose concentration of 5 mmol/l. These results confirm that the pancreatic B-cell response contributed significantly to the hyperinsulinemia, but different mechanisms are likely to be responsible for the altered B-cell secretion.