Longitudinal Analyses among Overweight,Insulin Resistance,and Cardiovascular Risk Factors in Children

Objective: It has been questioned whether insulin resistance or obesity is the central abnormality contributing to the cardiovascular risk factors dyslipidemia and hypertension in obesity. Research Methods and Procedures: We studied weight status [SD score (SDS)‐BMI], lipids (triglycerides, low‐density lipoprotein‐ and high‐density lipoprotein‐cholesterol), blood pressure, and insulin resistance index [as homeostasis model assessment (HOMA) model] over a 1‐year period in 229 obese white children (median age 12 years). Results: Any degree of decrease in HOMA was associated with significant decreases in triglycerides (p < 0.001), systolic blood pressure (p < 0.001), and diastolic blood pressure (p < 0.001), whereas the children with different changes in HOMA did not differ significantly in their weight changes. Only the children in the highest quartile of weight reduction (decrease in SDS‐BMI > 0.5) demonstrated a significant decrease in systolic blood pressure (p < 0.001), diastolic blood pressure (p < 0.001), and triglycerides (p = 0.012), and an increase in high‐density lipoprotein‐cholesterol (p = 0.023), whereas with a lower degree of weight loss, there were no significant changes in cardiovascular risk factors. In contrast with a lower degree of weight loss, a reduction of >0.5 SDS‐BMI was associated with a significant decrease in HOMA (p < 0.001). Discussion: Because blood pressure and triglycerides decreased with any degree of decrease in HOMA, independently of changes in weight status, these findings support the hypothesis that insulin resistance is the central abnormality contributing to these cardiovascular risk factors. Therefore, improving insulin resistance seems more important than reducing overweight to prevent or treat hypertension and dyslipidemia in obese children.     

Pollen Typhae total flavone improves insulin resistance in high-fat diet and low-dose streptozotocin-induced type 2 diabetic rats

Pollen Typhae total flavone (PTF), the extract from Pollen Typhae, is reported to enhance glucose uptake in C2C12 myotubes in vitro, but the convincing evidence is lacking in vivo. In this study, PTF ameliorated insulin resistance and dyslipidemia, but failed to significantly increase body weight in type 2 diabetic rats induced by high-fat diet and low-dose streptozotocin.     

Effects of oral glucosamine and chondroitin sulfate alone and in combination on the metabolism of SHR and SD rats

Glucosamine (G), often combined with chondroitin sulfate (CS), is a popular natural supplement used widely to treat osteoarthritis. However, use of glucosamine has been linked to development of insulin resistance. To assess the association between glucosamine and insulin resistance more closely, we challenged two rat strains highly sensitive to sugarinduced insulin resistance – SpragueDawley (SD) and Spontaneously Hypertensive (SHR) rats. Since elevations of systolic blood pressure (SBP) have been found to be an early and highly sensitive sign of insulin resistance in these two rat strains, we used this parameter as our primary endpoint. Four groups of both rat strains received either no agent (control), G, CS, or a combination of both for 9 weeks. The intake of each agent was calculated to be approximately 3–7 times comparable to human dose. Throughout the study, SBP of both strains consuming the two ingredients alone and in combination were not elevated. Rather, they were significantly lower than control, contrary to what is found in glucoseinduced insulin resistance in rats. Over the study period, body weights of the four groups of SD and SHR did not vary significantly. Furthermore, no consistent trends in circulating glucose concentrations were found among the four different groups in the two strains after oral challenge with glucose. Finally, no significant histological differences were found in hearts, kidneys, and livers among the various groups of SHR and SD. From the above result, we conclude that glucosamine and chondroitin sulfate given alone or together do not produce insulin resistance or other related perturbations in two rat strains highly sensitive to sugarinduced insulin resistance.     

Cellular responses elicited by insulin mimickers in cells lacking detectable plasma membrane insulin receptors

Madin-Darby canine kidney (MDCK) cells were previously shown to have few or no plasma membrane insulin binding sites (Hofmann et al: J Biol Chem 258:11774, 1983]. Accordingly, neither insulin-stimulated incorporation of [14C]glucose into glycogen, nor insulin-induced uptake of radiolabeled alpha-aminoisobutyrate ([3H]AIB) could be demonstrated. To probe for receptors, MDCK cultures were surface-labeled with Na125I or were labeled with [35S]methionine. When solubilized cells were immunoprecipitated with sera containing antibodies to the insulin receptor, and immunoprecipitates were analyzed on SDS-gel electrophoresis, no evidence for insulin receptor components was found. Also, when intact MDCK cells wee incubated first with serum containing antibodies to the insulin receptor and then with 125I-protein A, no radiolabeling of insulin receptors occurred. Various agents reported to have insulin-like activity were tested on MDCK cells. The insulinomimetic lectins concanavalin A and wheat germ agglutinin as well as hydrogen peroxide enhanced incorporation of [14C]glucose into glycogen and induced stimulated [3H]AIB uptake, whereas trypsin, vanadate, and serum containing antibodies to the insulin receptor were without effects. Altogether, these results showed that MDCK cells had few or no insulin receptors and were correspondingly insulin-insensitive. However, since insulin-associated responses could be elicited by some insulin mimickers, the post-receptor limb of response in MDCK cells was apparently intact.     

A Novel Peroxisome Proliferator-activated Receptor (PPAR)α Agonist and PPARγ Antagonist,Z-551, Ameliorates High-fat Diet-induced Obesity and Metabolic Disorders in Mice

A novel peroxisome proliferator-activated receptor (PPAR) modulator, Z-551, having both PPARα agonistic and PPARγ antagonistic activities, has been developed for the treatment of obesity and obesity-related metabolic disorders. We examined the effects of Z-551 on obesity and the metabolic disorders in wild-type mice on the high-fat diet (HFD). In mice on the HFD, Z-551 significantly suppressed body weight gain and ameliorated insulin resistance and abnormal glucose and lipid metabolisms. Z-551 inhibited visceral fat mass gain and adipocyte hypertrophy, and reduced molecules involved in fatty acid uptake and synthesis, macrophage infiltration, and inflammation in adipose tissue. Z-551 increased molecules involved in fatty acid combustion, while reduced molecules associated with gluconeogenesis in the liver. Furthermore, Z-551 significantly reduced fasting plasma levels of glucose, triglyceride, free fatty acid, insulin, and leptin. To elucidate the significance of the PPAR combination, we examined the effects of Z-551 in PPARα-deficient mice and those of a synthetic PPARγ antagonist in wild-type mice on the HFD. Both drugs showed similar, but weaker effects on body weight, insulin resistance and specific events provoked in adipose tissue compared with those of Z-551 as described above, except for lack of effects on fasting plasma triglyceride and free fatty acid levels. These findings suggest that Z-551 ameliorates HFD-induced obesity, insulin resistance, and impairment of glucose and lipid metabolisms by PPARα agonistic and PPARγ antagonistic activities, and therefore, might be clinically useful for preventing or treating obesity and obesity-related metabolic disorders such as insulin resistance, type 2 diabetes, and dyslipidemia.     

Resistance to trophic neurite outgrowth of sensory neurons exposed to insulin

Insulin offers trophic support through receptors expressed widely on peripheral neurons. In this work, we studied whether peripheral sensory neurons demonstrate resistance to its trophic properties, a property relevant during type 2 diabetes mellitus or following supraphysiological therapy. Insulin receptors were not only localized to neuronal membranes and cytoplasm but also had a unique, previously unrecognized localization to neuronal nuclei. We confirmed that nanomolar doses increased neurite outgrowth of adult sensory neurons, but in response to micromolar doses of insulin, even following a brief 2-h exposure, survival and outgrowth of neurites were blunted. Neurons exposed to picomolar insulin concentrations in their media for 5 days had resistance to the impact of later nanomolar doses of insulin. Using a stripe assay seeded with insulin, neurites were more likely to reject higher doses of insulin. Insulin down-regulated mRNAs of the insulin receptor β subunit and up-regulated levels of GSK-3β, both potential mechanisms of insulin resistance, while down-regulating the protein expression of pAkt and pGSK-3β. Overall, these studies identify neuronal nuclear targeting of insulin and evidence for insulin-induced resistance to its trophic properties. The findings have implications for the understanding of the actions of insulin in the treatment of diabetes and neurological disorders.     

高糖高胰岛素对去甲肾上腺素诱导的心肌细胞肥大的影响

目的:利用体外培养的乳鼠心肌细胞,观测高浓度胰岛素和高浓度葡萄糖作用下对去甲肾上腺素诱导的心肌细胞肥大的影响,并探讨其可能作用机制.方法:以培养的乳鼠心肌细胞为模型分组给药后,用显微镜目镜计数心肌细胞搏动的频率;用Lowrys法测心肌细胞的蛋白质含量;用消化分离法,利用计算机图象分析系统测心肌细胞的体积;用[3H]leucine标记法测定心肌细胞蛋白的合成.结果:与对照组相比,去甲肾上腺素(NE)组、高糖组、高胰岛素组心肌细胞蛋白含量、体积、蛋白合成均有明显增加,而与高糖加NE组和高糖高胰岛素组相比较,高糖高胰岛素加NE组心肌细胞蛋白含量、体积、蛋白合成增加则更为显著.结论:单纯高浓度胰岛素培养可促进心肌细胞肥大,同时用高糖高胰岛素联合培养,可使去甲肾上腺素诱导的心肌细胞肥大作用进一步增强.     

BIG3 inhibits insulin granule biogenesis and insulin secretion

While molecular regulation of insulin granule exocytosis is relatively well understood, insulin granule biogenesis and maturation and its influence on glucose homeostasis are relatively unclear. Here, we identify a novel protein highly expressed in insulin-secreting cells and name it BIG3 due to its similarity to BIG/GBF of the Arf-GTP exchange factor (GEF) family. BIG3 is predominantly localized to insulin- and clathrin-positive trans-Golgi network (TGN) compartments. BIG3-deficient insulin-secreting cells display increased insulin content and granule number and elevated insulin secretion upon stimulation. Moreover, BIG3 deficiency results in faster processing of proinsulin to insulin and chromogranin A to β-granin in β-cells. BIG3-knockout mice exhibit postprandial hyperinsulinemia, hyperglycemia, impaired glucose tolerance, and insulin resistance. Collectively, these results demonstrate that BIG3 negatively modulates insulin granule biogenesis and insulin secretion and participates in the regulation of systemic glucose homeostasis.     

Approaches to the molecular cloning of protein-tyrosine phosphatases in insulin-sensitive tissues

The intrinsic tyrosyl kinase activity of the insulin receptor is regulated by a balance between insulin-induced receptor autophosphorylation, which stimulates the receptor kinase, and enzymatic dephosphorylation of the receptor, which deactivates its kinase activity. The cellular protein-tyrosine phosphatase (PTPase) enzymes responsible for reversing the activated state of the insulin receptor have not been characterized. Our laboratory is interested in identifying and cloning the specific PTPase(s) that regulate the phosphorylation state of the insulin receptor. This chapter will summarize the design and results of our initial molecular cloning studies to identify specific PTPases in insulin-sensitive tissues that may have a potential physiological role in insulin action and clinical insulin resistance.