Genetic variants in a haplotype block spanning IDE are significantly associated with plasma Abeta42 levels and risk for Alzheimer disease

Risk for late onset Alzheimer disease (LOAD) and plasma amyloid beta levels (Abeta42; encoded by APP), an intermediate phenotype for LOAD, show linkage to chromosome 10q. Several strong candidate genes (VR22, PLAU, IDE) lie within the 1-lod support interval for linkage. Others have independently identified haplotypes in the chromosome 10q region harboring IDE that show highly significant association with intermediate AD phenotypes and with risk for AD. To pursue these associations, we analyzed the same haplotypes for association with plasma Abeta42 in 24 extended LOAD families and for association with LOAD in two independent case-control series. One series (MCR, 188 age-matched case-control pairs) did not show association (p=0.64) with the six haplotypes in the 276-kb region spanning three genes (IDE, KNSL1, and HHEX) previously shown to associate with LOAD. The other series (MCJ, 109 age-matched case-control pairs) showed significant (p=0.003) association with these haplotypes. In the MCJ series, the H4 (odds ratio [OR]=5.1, p=0.003) and H2(H7) haplotypes (OR=0.60, p=0.04) had the same effects previously reported. In this series, the H8 haplotype (OR=2.7, p=0.098) also had an effect similar as in one previous case control series but not in others. In the extended families, the H8 haplotype was associated with significantly elevated plasma Abeta42 (p=0.02). In addition, the H5(H10) haplotype, which is associated with reduced risk for AD in the other study is associated with reduced plasma Abeta42 (p=0.007) in our family series. These results provide strong evidence for pathogenic variant(s) in the 276-kb region harboring IDE that influence intermediate AD phenotypes and risk for AD.     

Effect of C-peptide administration on whole body glucose utilization in STZ-induced diabetic rats

Recent studies suggest that C-peptide stimulates glucose transport in isolated skeletal muscle. In order to determine the effect of C-peptide on whole body glucose utilization, streptozotocin (60 mg kg^-1) (STZ)-induced diabetic and normal rats were studied using the euglycaemic clamp procedure and continuous infusion of somatostatin (1.0 μg kg^-1 min^-1) in pentobarbital-anaesthetized rats. Plasma insulin levels during the 6.0- and 30.0-mU kg^-1 min^-1 insulin infusions rose to 70–90 μU mL^-1 and 500–700 μU mL^-1, respectively. Blood glucose concentrations were clamped at 7.5–7.9 mmol L^-1 in the diabetic rats and at basal levels or 7.7 mmol L^-1 in the non-diabetic (normal) rats. Biosynthetic human C-peptide (0.5 nmol kg^-1 min^-1) was infused in 12 diabetic and 11 normal rats, resulting in concentrations of 26–41 nmol L^-1. The metabolic clearance rate of glucose (MCR) for the diabetic rats receiving C-peptide (12.0±1.0 mL kg^-1 min^-1) was significantly (P<0.01) higher than that in the diabetic rats given saline (6.3±0.7 mL kg^-1 min^-1) or a randomly scrambled C-peptide (7.8±1.3 mL kg^-1 min^-1) at low-dose insulin infusion but not at the high-dose insulin infusion. In normal rats C-peptide did not significantly increase the MCR for glucose. These results thus demonstrate that C-peptide has the capacity to increase glucose utilization in STZ-induced diabetic rats.     

Prediction models for insulin resistance in the polycystic ovary syndrome

Women with the polycystic ovary syndrome (PCOS) have a high prevalence of insulin resistance, with consequent increased risk of metabolic diseases later in life. An early metabolic screening would therefore be of clinical relevance. By using stepwise regression analysis on several variables obtained in 72 women with PCOS, we constructed simple and reliable mathematical models predicting insulin sensitivity, as measured by the euglycaemic hyperinsulinaemic clamp. The normal ranges of insulin sensitivity were calculated from 81 non-hirsute, normally menstruating women with normal ovaries, and similar body mass index (BMI) and age as the women with PCOS. Measured variables included BMI, waist and hip circumferences, truncal-abdominal skin folds, circulating concentrations of gonadotrophins, androgens, sex hormone-binding globulin (SHBG), triglycerides, total cholesterol and cholesterol subfractions, fasting insulin, C-peptide and free fatty acids. The three best prediction models included waist circumference, together with insulin (model I: R(2) = 0.77), serum triglycerides (model II: R(2) = 0.65), and the subscapularis skin fold (model III: R(2) = 0. 64). Using reference limits for insulin sensitivity obtained in the 81 normal pre-menopausal women, the models identify insulin resistant women with PCOS. These simple and inexpensive models are potentially useful in clinical practice as an early screening in women with PCOS.     

2型糖尿病患者垂体-肾上腺轴的变化与胰岛素抵抗

目的探讨2型糖尿病患者早期垂体-肾上腺轴的改变与胰岛素抵抗(IR)的关系。方法采用化学发光等方法测定67例新诊断的2型糖尿病患者和33名志愿者(对照组)的血皮质醇(F)和促肾上腺皮质激素(ACTH)(8Am、4Pm和地米抑制后次8Am)以及血清胰岛素(INS)、C肽(C-P)和血糖水平;按HOMA模型计算胰岛素抵抗指数HOM-IR=FINS×FBG/22.5,以此反映2型糖尿病患者IR的情况。结果①2型糖尿病患者8Am血浆F和ACTH、4Pm和地米抑制后次8Am血浆F、血糖、INS、C-P水平以及HOMA-IR均明显高于对照组(P<0.01);②4Pm和地米抑制后次8Am血浆ACTH水平显著低于对照组;③直线相关统计分析显示,皮质醇浓度的升高与空腹血糖升高呈正相关(r=0.48,P<0.01)。与HOMA-IR的升高无直线相关性。结论2型糖尿病患者早期呈现ACTH、皮质醇过度分泌和慢性垂体-肾上腺轴功能紊乱,诱发并加重了糖代谢紊乱和胰岛素抵抗。     

Metformin during pregnancy reduces insulin, insulin resistance, insulin secretion, weight, testosterone and development of gestational diabetes: prospective longitudinal assessment of women with polycystic ovary syndrome from preconception throughout pregnancy

BACKGROUND: In a prospective observational study of 42 pregnancies in 39 Caucasian women (age 30 +/- 4 years) with polycystic ovary syndrome (PCOS), we examined effects of metformin on maternal insulin, insulin resistance (IR), insulin secretion (IS), weight gain, development of gestational diabetes (GD), testosterone and plasminogen activator inhibitor activity. We assessed the hypothesis that diet-metformin (MET) lessens the physiological gestational increase in IR and reduces gestational weight gain, thus reducing GD. METHODS: Preconception, in an out-patient clinical research centre, MET 1.5 (eight pregnancies) to 2.55 g/day (34 pregnancies) was started. Women with body mass index <25 or >or=25 kg/m(2) were given a 2000 or 1500 calorie/day, high-protein (26% of calories), low-carbohydrate (44%) diet. Calorie restrictions were dropped after conception. RESULTS: On MET, GD developed in three out of 42 pregnancies (7.1%). Median entry weight (94.5 kg) fell to 82.7 on MET at the last preconception visit (P = 0.0001), fell further to 81.6 during the first trimester, was 83.6 in the second trimester, and 89.1 kg in the third trimester. Median weight gain during pregnancy was 3.5 kg. The median percentage reduction in serum insulin was 40% on MET at the last preconception visit; insulin did not increase in the first or second trimesters (P > 0.05), and rose 10% in the third trimester. The median percentage reduction in HOMA IR was 46% on MET at the last preconception visit; IR did not increase (P > 0.05) in the first, second or third trimesters. HOMA insulin secretion fell 45% on MET at the last preconception visit, did not increase in the first trimester, rose 24% in the second trimester, and rose 109% in the third trimester. Testosterone fell 30% on MET at the last preconception visit (P = 0.01) and then rose 74, 61 and 95% during trimesters 1, 2 and 3; median testosterone during the third trimester did not differ from pre-treatment levels. CONCLUSIONS: By reducing preconception weight, insulin, IR, insulin secretion and testosterone, and by maintaining these insulin-sensitizing effects throughout pregnancy, MET-diet reduces the likelihood of developing GD, and prevents androgen excess for the fetus.     

Age‐ and site‐specific decline in insulin‐like growth factor‐I receptor expression is correlated with differential growth plate activity in the mouse hindlimb

The proximal and distal growth plates of the principal long bones do not contribute equally to longitudinal growth. Most forelimb elongation occurs at the shoulder and wrist, while most hindlimb growth occurs at the knee. This study examined whether insulin‐like growth factor‐I (IGF‐I), a potent growth regulator, could underlie this variation via differential receptor expression. The spatiotemporal distribution of the IGF‐I receptor (IGF‐IR) was mapped in hindlimb growth plates (overall and within regional zones) from immature mice using immunohistochemistry. Growth activity was assessed by size/morphology of the growth plate and proliferating cell nuclear antigen (PCNA) expression. Both IGF‐IR and PCNA staining declined considerably with age in the proximal femur and distal tibia (hip and ankle), but expression remained high in the more active distal femur and proximal tibia (knee) throughout growth. Growth plate size decreased with age in all sites, but the absolute and relative decline in IGF‐IR in the hips and ankles of older mice indicated a site‐specific loss of IGF‐I sensitivity in these less active regions. These results suggest that regulation of the IGF‐IR may at least partially mediate differential long bone growth, thereby providing a local mechanism for altering skeletal proportions absent modification of systemic hormone levels. Anat Rec, 2007. © 2007 Wiley‐Liss, Inc.     

Epidermal growth factor and insulin short‐term increase hPepT1‐mediated glycylsarcosine uptake in Caco‐2 cells

Aims: Little is known about the physiological regulation of the human intestinal di/tri‐peptide transporter, hPepT1. In the present study we evaluated the effects of epidermal growth factor (EGF) and insulin on hPepT1‐mediated dipeptide uptake in the intestinal cell line Caco‐2. Methods: Caco‐2 cells were grown on filters for 23–27 days. Apical dipeptide uptake was measured using [¹⁴C]glycylsarcosine([¹⁴C]Gly‐Sar). HPepT1 mRNA levels were investigated using RT‐PCR, cytosolic pH was determined using the pH‐sensitive fluorescent probe BCECF. Results: Basolateral application of EGF increased [¹⁴C]Gly‐Sar uptake with an ED₅₀ value of 0.77 ± 0.25 ng mL^?1 (n = 3?6) and a maximal stimulation of 33 ± 2% (n = 3?6). Insulin stimulated [¹⁴C]Gly‐Sar uptake with an ED₅₀ value of 3.5 ± 2.0 ng mL^?1 (n = 3?6) and a maximal stimulation of approximately 18% (n = 3?6). Gly‐Sar uptake followed simple Michaelis‐Menten kinetics. K_m in control cells was 0.98 ± 0.11 mM (n = 8) and V_max was 1.86 ± 0.07 nmol cm^?2 min^?1 (n = 8). In monolayers treated with 200 ng mL^?1 of EGF, K_m was 1.11 ± 0.05 mM (n = 5) and V_max was 2.79 ± 0.05 nmol cm^?2 min^?1 (n = 5). In monolayers treated with 50 ng mL^?1 insulin, K_m was 1.03 ± 0.08 mM and V_max was 2.19 ± 0.06 nmol cm^?2 min^?1 (n = 5). Kinetic data thus indicates an increase in the number of active transporters, following stimulation. The incrased Gly‐Sar uptake was not accompanied by changes in hPepT1 mRNA, nor by measurable changes in cytosolic pH. Conclusions: Short‐term stimulation with EGF and insulin caused an increase in hPepT1‐mediated uptake of Gly‐Sar in Caco‐2 cell monolayers, which could not be accounted for by changes in hPepT1 mRNA or proton‐motive driving force.     

mTOR signaling contributes to chondrocyte differentiation.

The mammalian Target Of Rapamycin (mTOR) is a nutrient-sensing protein kinase that regulates numerous cellular processes. Fetal rat metatarsal explants were used as a physiological model to study the effect of mTOR inhibition on chondrogenesis. Insulin significantly enhanced their growth. Rapamycin significantly diminished this response to insulin through a selective effect on the hypertrophic zone. Cell proliferation (bromodeoxyuridine incorporation) was unaffected by rapamycin. Similar observations were made when rapamycin was injected to embryonic day (E) 19 fetal rats in situ. In the ATDC5 chondrogenic cell line, rapamycin inhibited proteoglycan accumulation and collagen X expression. Rapamycin decreased content of Indian Hedgehog (Ihh), a regulator of chondrocyte differentiation. Addition of Ihh to culture medium reversed the effect of rapamycin. We conclude that modulation of mTOR signaling contributes to chondrocyte differentiation, perhaps through its ability to regulate Ihh. Our findings support the hypothesis that nutrients, acting through mTOR, directly influence chondrocyte differentiation and long bone growth.     

Polymorphisms in the insulin receptor substrate-1 (IRS-1) gene and the insulin receptor substrate-2 (IRS-2) gene influence glucose homeostasis and body mass index in women with polycystic ovary syndrome and non-hyperandrogenic controls

BACKGROUND: We aimed to evaluate the influence of the Gly972Arg variant of the insulin receptor substrate-1 gene (IRS-1) and the Gly1057Asp variant in IRS-2 on insulin resistance and glucose tolerance in women with polycystic ovary syndrome (PCOS) and healthy controls. METHODS: Genotypes, allelic frequencies, indexes of insulin resistance, glucose tolerance and hormone profiles were studied in a large sample of Spanish PCOS (n = 103) women compared with a control group (n = 48) of healthy women matched for body mass index. RESULTS: No differences in genotype or allelic frequencies were found between PCOS patients and healthy controls. When considering control subjects and PCOS patients as a whole, IRS-1 Arg972 carriers also presented with increased fasting insulin (133 +/- 60 versus 95 +/- 67 pmol/l, P = 0.008) and insulin resistance measured by homeostasis model assessment (4.3 +/- 2.1 versus 3.1 +/- 2.4, P = 0.009) compared with subjects homozygous for Gly972 alleles. These differences were even higher when restricting the analysis to PCOS patients. Subjects homozygous for the Gly1057 allele of IRS-2 presented with increased 60 and 90 min oral glucose tolerance test (OGTT) glucose levels compared with carriers of one or two Asp1057 alleles (7.9 +/- 2.1 versus 7.1 +/- 2.1 mmol/l, P = 0.042 and 7.0 +/- 2.1 versus 6.0 +/- 1.8 mmol/l, P = 0.014), and a similar tendency was observed for 120 min OGTT glucose levels. CONCLUSIONS: The Gly972Arg in IRS-1 and Gly1057Asp in IRS-2 polymorphisms influence glucose homeostasis in premenopausal women, but are not associated with PCOS.     

The acute effects of insulin on the cardiorespiratory responses to hypoxia in streptozotocin‐induced diabetic rats

Aims: We examined whether or not streptozotocin (STZ)‐induced diabetic rats, which have a lower heart rate (HR, beats min^?1) than control rats, could maintain hypoxic ventilatory response. Methods: Twenty‐six Wistar rats, which had been injected with STZ (60 mg kg^?1, EXP) or vehicle (0.1 m citrate buffer, CONT) intraperitoneally at 9 weeks of age, had their cardiorespiratory responses to normoxia and 12%O₂ examined after 5 weeks. Results: Compared with CONT rats, EXP rats had a higher blood glucose [24 ± 3 vs. 5 ± 1 (mean ± SD) mmol L^?1], a lower body weight (320 ± 23 vs. 432 ± 24 g), lower HR (303 ± 49 vs. 380 ± 44 in normoxia, and 343 ± 56 vs. 443 ± 60 in hypoxia) and a lower mean arterial blood pressure (MAP) (89 ± 6 vs. 102 ± 10 mmHg in hypoxia). In contrast, both groups had similar values in ventilation (), –metabolic rate (MR) ratio and arterial blood gases (ABGs). In EXP rats, with an acute insulin supplement (i.v., 0.75 U h^?1 for 1.5–2 h), not only blood glucose, but also HR, and MAP were normalized as those obtained in CONT rats, and in hypoxia further increased without affecting –MR ratio and ABGs. Such acute cardiorespiratory stimulating effects of insulin could not be obtained in non‐diabetic rats (n = 7, 355 ± 24 g), in which euglycaemia (mean 6.4 mmol L^?1) was maintained during the measurements. Conclusions: Our results suggest that, in STZ‐induced diabetic rats: (1) ventilation is hardly suppressed by hyperglycaemia, (2) cardiorespiratory responses can be acutely stimulated by short insulin injection, and (3) the effects, including those through acute blood glucose normalization, are possibly specific for the diabetic impairments.