Increased glucose effectiveness in normoglycemic but insulin-resistant relatives of patients with non-insulin-dependent diabetes mellitus. A novel compensatory mechanism

Short Sleep Duration Disrupts Glucose Metabolism: Can Exercise Turn Back the Clock?

Short sleep duration is prevalent in modern society and may be contributing to type 2 diabetes prevalence. This review will explore the effects of sleep restriction on glycemic control, the mechanisms causing insulin resistance, and whether exercise can offset changes in glycemic control. Chronic sleep restriction may also contribute to a decrease in physical activity leading to further health complications.

A novel splice-affecting HNF1A variant with large population impact on diabetes in Greenland

Background

The genetic disease architecture of Inuit includes a large number of common high-impact variants. Identification of such variants contributes to our understanding of the genetic aetiology of diseases and improves global equity in genomic personalised medicine. We aimed to identify and characterise novel variants in genes associated with Maturity Onset Diabetes of the Young (MODY) in the Greenlandic population.

Methods

Using combined data from Greenlandic population cohorts of 4497 individuals, including 448 whole genome sequenced individuals, we screened 14 known MODY genes for previously identified and novel variants. We functionally characterised an identified novel variant and assessed its association with diabetes prevalence and cardiometabolic traits and population impact.

Findings

We identified a novel variant in the known MODY gene HNF1A with an allele frequency of 1.9% in the Greenlandic Inuit and absent elsewhere. Functional assays indicate that it prevents normal splicing of the gene. The variant caused lower 30-min insulin (β = -232 pmol/L, β_SD = -0.695, P = 4.43 × 10^-4) and higher 30-min glucose (β = 1.20 mmol/L, β_SD = 0.441, P = 0.0271) during an oral glucose tolerance test. Furthermore, the variant was associated with type 2 diabetes (OR 4.35, P = 7.24 × 10^-6) and HbA1c (β = 0.113 HbA1c%, β_SD = 0.205, P = 7.84 × 10^-3). The variant explained 2.5% of diabetes variance in Greenland.

Interpretation

The reported variant has the largest population impact of any previously reported variant within a MODY gene. Together with the recessive TBC1D4 variant, we show that close to 1 in 5 cases of diabetes (18%) in Greenland are associated with high-impact genetic variants compared to 1-3% in large populations.

Funding

Novo Nordisk Foundation, Independent Research Fund Denmark, and Karen Elise Jensen's Foundation.

Application of kojic acid scaffold in the design of non-tyrosinase enzyme inhibitors

Kojic acid (KA) is a hydroxypyranone natural metabolite mainly known as tyrosinase inhibitor. Currently, this compound is used as a whitening agent in cosmetics and as an anti-browning agent in food industry. Given the easy-manipulation in different positions of the KA molecule, many investigations have been carried out to find new tyrosinase inhibitors derived from KA. Beside anti-tyrosinase activity, many KA-based compounds have been designed for targeting other enzymes including human neutrophil elastase, catechol-O-methyltransferase, matrix metalloproteinases, monoamine oxidase, human lactate dehydrogenase, endonucleases, D-amino acid oxidase, and receptors such as histamine H₃ and apelin (APJ) receptors. This review could help biochemists and medicinal chemists in designing diverse KA-derived enzyme inhibitors.

An Analysis of Glucose Effectiveness in Subjects With or Without Type 2 Diabetes via Hierarchical Modeling

Glucose effectiveness, defined as the ability of glucose itself to increase glucose utilization and inhibit hepatic glucose production, is an important mechanism maintaining normoglycemia. We conducted a minimal modeling analysis of glucose effectiveness at zero insulin (GEZI) using intravenous glucose tolerance test data from subjects with type 2 diabetes (T2D, n=154) and non-diabetic (ND) subjects (n=343). A hierarchical statistical analysis was performed, which provided a formal mechanism for pooling the data from all study subjects, to yield a single composite population model that quantifies the role of subject specific characteristics such as weight, height, age, sex, and glucose tolerance. Based on the resulting composite population model, GEZI was reduced from 0.021 min-1 (standard error - 0.00078 min-1) in the ND population to 0.011 min-1 (standard error - 0.00045 min-1) in T2D. The resulting model was also employed to calculate the proportion of the non-insulin-dependent net glucose uptake in each subject receiving an intravenous glucose load. Based on individual parameter estimates, the fraction of total glucose disposal independent of insulin was 72.8% ± 12.0% in the 238 ND subjects over the course of the experiment, indicating the major contribution to the whole-body glucose clearance under non-diabetic conditions. This fraction was significantly reduced to 48.8% ± 16.9% in the 30 T2D subjects, although still accounting for approximately half of the total in the T2D population based on our modeling analysis. Given the potential application of glucose effectiveness as a predictor of glucose intolerance and as a potential therapeutic target for treating diabetes, more investigations of glucose effectiveness in other disease conditions can be conducted using the hierarchical modeling framework reported herein.

Impact of prolonged fasting on insulin secretion, insulin action, and hepatic versus whole body insulin secretion disposition indices in healthy young males

The extent to which reduced insulin secretion during prolonged fasting reflects failure to compensate for whole body insulin resistance or a normal adjustment to potentially increased hepatic insulin action is unknown. We examined the effects of 36- versus 12-h fasting on insulin secretion and whole body versus hepatic insulin action in 13 healthy young males. Hepatic glucose production and insulin action were studied using stable isotopes, whereas whole body insulin action and insulin secretion were studied using an intravenous glucose tolerance test (IVGTT) and minimal modeling. Insulin, glucose, and lipid profiles were subsequently measured during a refeeding meal test. Prolonged fasting caused a minor reduction of first-phase insulin secretion in a context of improved hepatic insulin action, contrasting an increase in whole body insulin resistance. Accordingly, prolonged fasting was associated with opposite-directed effects on hepatic versus whole body insulin secretion disposition indices. Thirty-six-hour fasting compared with 12-h fasting was associated with increased serum insulin levels during the refeeding meal test. In conclusion, reduced insulin secretion during prolonged fasting may represent a healthy response to improved hepatic insulin action. Use of insulin secretion disposition indices without taking organ-specific insulin action into account may lead to erroneous conclusions.NEW & NOTEWORTHY Thirty-six-hour prolonged, compared with 12-h overnight fasting, is associated with slightly reduced first-phase insulin secretion in the face of opposite-directed changes in hepatic versus whole body insulin action in healthy young males. The paradoxical finding of increased hepatic versus decreased whole body insulin secretion disposition indices during prolonged fasting challenges the physiological understanding and validity of insulin secretion disposition indices not taking organ-specific insulin action into account.

Oxidative Stress, Intrauterine Growth Restriction, and Developmental Programming of Type 2 Diabetes

Intrauterine growth restriction (IUGR) leads to reduced birth weight and the development of metabolic diseases such as Type 2 diabetes in adulthood. Mitochondria dysfunction and oxidative stress are commonly found in key tissues (pancreatic islets, liver, and skeletal muscle) of IUGR individuals. In this review, we explore the role of oxidative stress in IUGR-associated diabetes etiology.

Glucose effectiveness is a critical pathogenic factor leading to glucose intolerance and type 2 diabetes: An ignored hypothesis

BACKGROUND

Although the ability of glucose to mediate its own in vivo metabolism is long documented, the quantitative measurement of whole body glucose-mediated glucose disposal at basal insulin levels (glucose effectiveness [GE]), followed the introduction of the Minimal Model intravenous glucose tolerance test technique.

METHODS

A literature review, combined with our own studies, of the role of GE in glucose metabolism in normal and "at risk" individuals, was undertaken to determine GE's contribution to glucose homeostasis.

RESULTS

GE accounts for ~45% to 65% of glucose disposal in man. A negative association between GE and insulin meditated glucose disposal (Si), is present in normal subjects without a family history of type 2 diabetes mellitus but is absent in normoglycaemic "at risk" relatives with a positive family history of diabetes mellitus. Intracellular GE disposal is mediated by mass action of glucose through the skeletal muscle membrane via facilitated Glut 4 transporters. However, GE is frequently forgotten as a significant contributor to the development of glucose intolerance in "at risk" individuals. Only limited studies have examined the role of a lower GE in such normoglycemic subjects with preexisting mild insulin resistance and β-cell dysfunction. These studies demonstrate that in "at risk" individuals, an initial low GE is a key contributor and predictor of future glucose intolerance, whereas an initial raised GE is protective against future glucose intolerance.

CONCLUSION

In "at risk" individuals, a low GE and genetically determined vulnerable β-cell function are more critical determinants of future glucose intolerance than their preexisting insulin-resistant state.

Insulin-stimulated glucose uptake in healthy and insulin-resistant skeletal muscle

Skeletal muscle is the largest tissues in the human body and is considered the primary target for insulin-stimulated glucose disposal. In skeletal muscle, binding of the insulin to insulin receptor (IR) initiates a signaling cascade that results in the translocation of the insulin-sensitive glucose transporter protein 4 (GLUT4) to the plasma membrane which leads to facilitated diffusion of glucose into the cell. Understanding the precise signaling events guiding insulin-stimulated glucose uptake is pivotal, because impairment in these signaling events leads to development of insulin resistance and type 2 diabetes. This review summarizes current understanding of insulin signaling pathways mediating glucose uptake in healthy and insulin-resistant skeletal muscle.

Proteomics of Skeletal Muscle: Focus on Insulin Resistance and Exercise Biology

Skeletal muscle is the largest tissue in the human body and plays an important role in locomotion and whole body metabolism. It accounts for ~80% of insulin stimulated glucose disposal. Skeletal muscle insulin resistance, a primary feature of Type 2 diabetes, is caused by a decreased ability of muscle to respond to circulating insulin. Physical exercise improves insulin sensitivity and whole body metabolism and remains one of the most promising interventions for the prevention of Type 2 diabetes. Insulin resistance and exercise adaptations in skeletal muscle might be a cause, or consequence, of altered protein expressions profiles and/or their posttranslational modifications (PTMs). Mass spectrometry (MS)-based proteomics offer enormous promise for investigating the molecular mechanisms underlying skeletal muscle insulin resistance and exercise-induced adaptation; however, skeletal muscle proteomics are challenging. This review describes the technical limitations of skeletal muscle proteomics as well as emerging developments in proteomics workflow with respect to samples preparation, liquid chromatography (LC), MS and computational analysis. These technologies have not yet been fully exploited in the field of skeletal muscle proteomics. Future studies that involve state-of-the-art proteomics technology will broaden our understanding of exercise-induced adaptations as well as molecular pathogenesis of insulin resistance. This could lead to the identification of new therapeutic targets.

Experimental hyperlipidemia induces insulin resistance in sheep

This study aimed to evaluate the effects of intravenous infusion of a soybean-based lipid emulsion on some blood energy-related metabolites and insulin sensitivity indexes in sheep. Four clinically healthy ewes were assigned into a 2-treatment, 2-period cross-over design. Either normal saline (NS) or lipid emulsion (LE) was intravenously introduced at a rate of 0.025 mL·kg(-1) min(-1) for 6 h. The concentrations of blood nonesterified fatty acid (NEFA), beta-hydroxybutyrate, triglyceride, cholesterol, urea, creatinine, cortisol, glucose, and insulin were measured at different time points. After 6 h, intravenous glucose tolerance test was performed. Lipid infusion elicited an increase (P < 0.05) in the NEFA, beta-hydroxybutyrate, and triglyceride concentrations compared with the baseline value and NS infusion. Infusion of NS did not influence blood glucose concentration; however, LE infusion increased plasma glucose concentration (P < 0.05). At time point 12 h, serum insulin concentrations were increased (P < 0.05) in NS treatment; however, such an increase was not observed in the LE treatment. Insulin sensitivity index for the LE infusion was lower (P < 0.05) than that for the NS treatment. The glucose effectiveness was not (P > 0.05) different among treatments. In the LE treatment, acute-phase insulin responses increased (P < 0.05) and disposition index decreased (P < 0.001) compared with NS treatment. The results showed that experimentally induced NEFA in blood could cause insulin resistance in sheep. The current model could be used to evaluate the pathogenesis of conditions associated with increased lipid mobilization and insulin resistance.

The forgotten role of glucose effectiveness in the regulation of glucose tolerance

Glucose effectiveness (SG) is the ability of glucose per se to stimulate its own uptake and to suppress its own production under basal/constant insulin concentrations. In an individual, glucose tolerance is a function of insulin secretion, insulin action and SG. Under conditions of declining insulin secretion and action (e.g. type 2 diabetes), the degree of SG assumes increasing significance in determining the level of glucose tolerance both in fasted and postprandial states. Although the importance of SG has been recognized for years, mechanisms that contribute to SG are poorly understood. Research data on modulation of SG and its impact in glucose intolerance is limited. In this review, we will focus on the role of SG in the regulation of glucose tolerance, its evaluation, and potential advantages of therapies that can enhance glucose-induced stimulation of glucose uptake and suppression of its own production in conditions of impaired insulin secretion and action.

Glycaemic regulation and insulin secretion are abnormal in cystic fibrosis pigs despite sparing of islet cell mass

Diabetes is a common and significant co-morbidity in cystic fibrosis (CF). The pathogenesis of cystic fibrosis related diabetes (CFRD) is incompletely understood. Because exocrine pancreatic disease is similar between humans and pigs with CF, the CF pig model has the potential to contribute significantly to the understanding of CFRD pathogenesis. We determined the structure of the endocrine pancreas in fetal, newborn and older CF and non-CF pigs and assessed endocrine pancreas function by intravenous glucose tolerance test (IV-GTT). In fetal pigs, pancreatic insulin and glucagon density was similar between CF and non-CF. In newborn and older pigs, the insulin and glucagon density was unchanged between CF and non-CF per total pancreatic area, but increased per remnant lobular tissue in CF reflecting exocrine pancreatic loss. Although fasting glucose levels were not different between CF and non-CF newborns, CF newborns demonstrated impaired glucose tolerance and increased glucose area under the curve during IV-GTT. Second phase insulin secretion responsiveness was impaired in CF newborn pigs and significantly lower than that observed in non-CF newborns. Older CF pigs had elevated random blood glucose levels compared with non-CF. In summary, glycaemic abnormalities and insulin secretion defects were present in newborn CF pigs and spontaneous hyperglycaemia developed over time. Functional changes in CF pig pancreas were not associated with a decline in islet cell mass. Our results suggest that functional islet abnormalities, independent of structural islet loss, contribute to the early pathogenesis of CFRD.

Effect of preeclampsia on insulin sensitivity

OBJECTIVE

The objective of this study is to investigate whether preeclampsia is associated with exacerbation of insulin resistance.

MATERIALS AND METHODS

The study was conducted over a period of 7 months from November 2011 to May 2012, in a tertiary care hospital attached to a medical college. A total of 14 pregnant women in the third trimester with preeclampsia were recruited for this study and 14 well-matched normotensive women in the third trimester were taken as control. 15 g, 50% dextrose load was given intravenously and blood sampling was carried out for glucose and insulin levels up to 3 h afterward. Minimal model analysis of glucose and insulin levels was performed to arrive at results.

RESULTS

No significant changes in mean age, body mass index, gestation, serum lipid and progesterone, cortisol and androgen concentrations were recognized. No significant difference was found between the glucose decay curves and between the glucose clearance rate K, in the two groups (preeclamptic vs. normotensive: 2.1 ± 0.2 vs. 2.2 ± 0.3; P = 0.48). Therefore, there was a small but prolonged decrease in the insulin response of women with preeclampsia compared with women in the normotensive group.

CONCLUSION

Preeclampsia per se is not a risk factor for development of insulin resistance.

Lean mass inversely predicts plasma glucose levels after oral glucose load independent of insulin secretion or insulin sensitivity in glucose intolerance subjects

Muscle mass inversely relates to 2 hours glucose levels after oral glucose load in non-diabetic subjects. A study in glucose intolerance subjects has never been performed. We conducted this study to determine the relationship between muscle mass and glucose level after oral glucose load in glucose intolerance subjects. Sixty Thai subjects, 44 drug-naïve, newly diagnosed type 2 diabetes mellitus and 16 impaired glucose tolerance were studied. The 180 min 75 g oral glucose tolerance test was performed. Total body fat and lean mass were measured by dual-energy x-ray absorptiometry. Insulin sensitivity was determined by insulin sensitivity index using model of Matsuda & DeFronzo. The 1st-phase and total insulin secretion were determined from glucose tolerance data. Pearson correlation and linear regression were used for the analysis. Lean mass was inversely correlated with area-under-curves of glucose 0-180 min (r =-0.320; p=0.013). The relationship was significant after adjustment with age and body-mass-index (r =-0.350; p=0.007). Area-under-curves of glucose 0-180 min was correlated with height (r =-0.282; p=0.029), fasting glucose (r =0.742; p<0.0001), log area-under-curves of insulin 0-180 min (r =-0.258; p=0.047) and log 1st-phase insulin secretion (r =-0.518; p<0.0001). By multivariate analysis, fasting glucose (standardized β=4.54; p<0.001), log 1st-phase insulin secretion (standardized β=-43.09; p=0.005) and lean mass (standardized β=-0.003; p=0.011) were the significant parameters predicting area-under-curves of glucose 0-180 min. In conclusion, lean mass inversely predicted glucose levels after oral glucose load independent of insulin secretion and insulin sensitivity in glucose intolerance subjects.

The metabolic responses induced by acute dexamethasone predict glucose tolerance and insulin secretion over 10 years in relatives of type 2 diabetic subjects

BACKGROUND

This study aimed to compare the metabolic and insulin secretory responses to dexamethasone with the metabolic responses observed at 10 years in normoglycaemic relatives of type 2 diabetic and healthy control subjects.

METHODS

Twenty relatives and 20 matched control subjects were studied twice at 0 year (pre- and post-dexamethasone) and at 10 years, employing a 75-g oral glucose tolerance test (OGTT), with serial measurements of glucose and insulin, for determination of glucose tolerance and calculations of acute insulin release (ΔI30 /ΔG30 ; insulinogenic index) and insulin sensitivity (SIHOMA ).

RESULTS

Following dexamethasone, the relatives group developed varying degrees of glucose intolerance, associated with reduced insulin sensitivity and insulinogenic index. By 10 years, fasting glucose and 2-h OGTT glucose were raised in the relatives group, especially in the relatives most metabolically affected by dexamethasone, including a reduced insulinogenic index. Multiple regression analysis of the data in relatives demonstrated that the 2-h OGTT glucose and fasting glucose values at 10 years depended on the 0-year post-dexamethasone 2-h OGTT glucose, post-dexamethasone fasting glucose and post-dexamethasone insulin sensitivity, r(2) adj = 56% (p < 0.001) and r(2) adj = 60% (p < 0.0001), respectively. No pre-dexamethasone metabolic or insulin secretory responses entered these models.

CONCLUSIONS

In relatives, fasting and 2-h OGTT glucose concentrations and β-cell responses to acute dexamethasone-induced insulin resistance are similar to those observed at 10 years, especially in relatives who develop the most disturbed dexamethasone-induced glucose intolerance and impaired acute insulin secretion. The combined 0-year, post-dexamethasone fasting and 2-h OGTT glucose concentrations and insulin resistance, measured as SIHOMA , are the best predictors in relatives of future dysglycaemia.

Cross-sectional and longitudinal changes of glucose effectiveness in relation to glucose tolerance: the insulin resistance atherosclerosis study

OBJECTIVE

Glucose effectiveness (S(G)), the capacity of glucose to enhance its own disposition, is an independent predictor of future diabetes. However, there are data on cross-sectional and longitudinal changes of S(G) and its components, basal insulin effect on S(G) (BIE) and S(G) at zero insulin (GEZI), but the natural course of S(G) has not been described in a large population.

RESEARCH DESIGN AND METHODS

S(G) was measured at baseline in 1,265 participants (aged 40-69 years) and at the 5-year examination in 827 participants in the Insulin Resistance Atherosclerosis Study (IRAS) using the frequently sampled intravenous glucose tolerance test. None of these participants were treated with glucose-lowering agents.

RESULTS

In cross-sectional analyses, S(G), BIE, and GEZI deteriorated with worsening of glucose tolerance (P < 0.001 for all three associations). In longitudinal analyses among subjects with normal glucose tolerance (NGT) at baseline, S(G), BIE, and GEZI declined in those who progressed to impaired glucose tolerance (IGT) or diabetes (P < 0.001 for all three measures). More modest longitudinal changes were demonstrated in individuals with IGT. The transition back to NGT (as opposed to no change) compared with the transition to diabetes was statistically significant for S(G) (P = 0.049) and BIE (P = 0.042) and was not a statistically significant trend for GEZI (P = 0.332). In individuals with diabetes, only BIE had a significant decline (P = 0.003).

CONCLUSIONS

S(G), BIE, and GEZI decline in subjects whose glycemic status worsens. S(G) and GEZI deteriorate more in the initial stages of the disease process.

Assessment of non-insulin-mediated glucose uptake: association with body fat and glycemic status

In the fasting state, approximately 83% of glucose uptake occurs via non-insulin-mediated mechanisms. A widely accepted static rate for NIMGU is 1.62 mg kg(-1)·min(-1). To investigate the variability of NIMGU, we examined differences by glucose tolerance, sex, age, race (American Indian/African American/Caucasian), and adiposity in 616 volunteers (including individuals with normal glucose regulation [NGR] and impaired glucose regulation [IGR] and diabetes mellitus [DM]) using data from euglycemic-hyperinsulinemic clamp experiments. NIMGU was determined by plotting basal glucose output and insulin action against fasting and steady-state clamp insulin. The intercept with the y-axis after extrapolation was interpreted as NIMGU at zero insulin. Body composition was determined by dual-energy x-ray absorptiometry; and glucose regulation, by a 75-g oral glucose tolerance test. Energy expenditure was measured by indirect calorimetry in a metabolic chamber. In individuals with NGR (n = 385), NIMGU was 1.63 mg kg(estimated metabolic body size (fat free mass + 17.7 kg))(-1) min(-1) (95% confidence interval, 1.59-1.66). NIMGU increased with IGR and DM (IGR: n = 189, 1.67 [1.62-1.72]; DM: n = 42, 2.39 [2.29-2.49]; P < .0001 across groups). NIMGU did not differ by sex (P = .13), age (P = .22), or race (P = .06); however, NIMGU was associated with percentage body fat (r(2) = 0.04, P < .0001). Furthermore, NIMGU was positively associated with 24-hour and sleep energy expenditure (r(2) = 0.002, P = .03; r(2) = 0.01, P < .01). Extrapolated NIMGU in individuals with NGR is remarkably consistent with previously published data. Our results indicate that NIMGU is associated with adiposity. NIMGU increases with declining glucose tolerance perhaps to preserve glucose uptake during increased insulin resistance.

Glucose effectiveness and insulin sensitivity measurements derived from the non-insulin-assisted minimal model and the clamp techniques are concordant

BACKGROUND

We investigated the concordance between glucose effectiveness (SG) and insulin sensitivity (SI), derived from the unmodified dynamic non-insulin-assisted intravenous glucose tolerance test (IVGTT) implemented by SG(MM) and SI(MM); simulation analysis and modelling/conversational interaction (SAAM/CONSAM) versus the eu/hyperglycaemic basal insulinaemic and the euglycaemic hyperinsulinaemic clamp (SG(CLAMP) and SI(CLAMP)).

METHODS

Twenty-seven of 30 normoglycaemic subjects completed a (1) euglycaemic hyperinsulinaemic clamp, (2) 6-h eu/hyperglycaemic near-normoinsulinaemic pancreatic clamp with hyperglycaemia present over the final 2 h of the clamp (Day 2 study), (3) identical clamp to (2) but with euglycaemia maintained over the entire 6 h (Day 3 study) and (4) IVGTT. SG(CLAMP) was calculated in two ways based on data from study (2) alone (Day 2 SG(CLAMP210-240')) or from data from study day (2) and (3) (Day 2-3 SG(CLAMP330-360')).

RESULTS

SG(MM) was unrelated to the magnitude of endogenous insulin release (AIR). The single-day (Day 2) and two-day (Day 2 and 3) SG(CLAMP) protocols correlated (r = 0.72, p = 0.003), but SG(CLAMP210-240') was significantly (p = 0.001) higher than SG(CLAMP330-360'). Employing the Day 2 and 3 SG(CLAMP) protocol, the whole body SG(CLAMP330-360') was similar to SG(MM) (1.80 ± 0.82 versus 1.73 ± 0.58 dL/min) and correlated (r = 0.45, p < 0.02). SG(CLAMP210-240') did not correlate with SG(MM) (r = 0.24). SI(MM) and SI(CLAMP) were similar (0.093 ± 0.060 versus 0.087 ± 0.029 dL/min per mU/L) and correlated (r = 0.76, p < 0.001).

CONCLUSIONS

The time-dependent increase in glucose disposal observed during a prolonged 6-h clamp significantly influences the estimation of SG(CLAMP), and significant concordance coefficients are observed between SG(MM), and SG(CLAMP330-360'), and SI(MM) and SI(CLAMP).

Effect of physical training on insulin secretion and action in skeletal muscle and adipose tissue of first-degree relatives of type 2 diabetic patients

Physical training affects insulin secretion and action, but there is a paucity of data on the direct effects in skeletal muscle and adipose tissue and on the effect of training in first-degree relatives (FDR) of patients with type 2 diabetes. We studied insulin action at the whole body level and peripherally in skeletal muscle and adipose tissue as well as insulin-secretory capacity in seven FDR and eight control (CON) subjects before and after 12 wk of endurance training. Training improved physical fitness. Insulin-mediated glucose uptake (GU) increased (whole body and leg; P < 0.05) after training in CON but not in FDR, whereas glucose-mediated GU increased (P < 0.05) in both groups. Adipose tissue GU was not affected by training, but it was higher (abdominal, P < 0.05; femoral, P = 0.09) in FDR compared with CON. Training increased skeletal muscle lipolysis (P < 0.05), and it was markedly higher (P < 0.05) in subcutaneous abdominal than in femoral adipose tissue and quadriceps muscle with no difference between FDR and CON. Glucose-stimulated insulin secretion was lower in FDR compared with CON, but no effect of training was seen. Glucagon-like peptide-1 stimulated insulin secretion five- to sevenfold. We conclude that insulin-secretory capacity is lower in FDR than in CON and that there is dissociation between training-induced changes in insulin secretion and insulin-mediated GU. Maximal GU rates are similar between groups and increases with physical training.

Association of Gly972Arg polymorphism of IRS1 gene with type 2 diabetes mellitus in lean participants of a national health survey in Mexico: a candidate gene study

Type 2 diabetes mellitus (T2D) is a main public health problem in the Mexican population. It is characterized by insulin resistance in peripheral tissues and a relative deficiency in the pancreatic beta-cell functions. Diverse single nucleotide polymorphisms (SNPs) of the IRS1 gene have been associated with insulin resistance and T2D risk. The aim of this study was to identify the association between known IRS1 polymorphisms (Pro512Ala, Asn1137Asp, Gly972Arg, and Arg158Pro) in a sample of diabetic patients compared with healthy controls selected from Mexico's 2000 National Health Survey, both with normal body mass index (BMI). We identified 444 diabetes cases that were age matched with the same number of controls. Genotypic and allelic frequencies were evaluated, and conditional logistic regression was used to evaluate the association between the SNPs and diabetes risk. Of the 4 SNPs studied, only Gly972Arg showed significant differences between cases and controls, with allele frequency of 2.6% in controls as compared with 7.9% in cases. Subjects with at least 1 copy of the Gly972Arg polymorphism of the IRS1 gene showed a greater risk for diabetes, with a crude odds ratio of 3.26 (95% confidence interval, 2.00-5.33); after adjusting for BMI, age, family history of T2D, and sex, the odds ratio was 2.91 (95% confidence interval, 1.73-4.90). Our results suggest the participation of Gly972Arg polymorphism of IRS1 in the genetic susceptibility to TD2 in Mexican population. The restriction of including only participants with normal BMI might increase the power to detect genetic determinants of T2D.

Exposure to recurrent sleep restriction in the setting of high caloric intake and physical inactivity results in increased insulin resistance and reduced glucose tolerance

CONTEXT

Epidemiological data indicate that reduced sleep duration is associated with increased incidence of type-2 diabetes.

OBJECTIVE

The aim of the study was to test the hypothesis that, when part of a Western-like lifestyle, recurrent bedtime restriction may result in decreased glucose tolerance and reduced insulin secretion and action.

DESIGN AND SETTING

We conducted a randomized crossover study at a university clinical research center and sleep research laboratory.

PARTICIPANTS

Eleven healthy volunteers (five females and six males) with a mean (+/-sd) age of 39 +/- 5 yr and body mass index of 26.5 +/- 1.5 kg/m(2) participated in the study.

INTERVENTION

The study included two 14-d periods of controlled exposure to sedentary living with ad libitum food intake and 5.5- or 8.5-h bedtimes.

MAIN OUTCOME MEASURES

Oral and iv glucose challenges were used to obtain measures of glucose tolerance, glucose effectiveness, insulin secretion, and insulin sensitivity at the end of each intervention. Secondary measures included circulating concentrations of the glucose counter-regulatory hormones, cortisol, GH, epinephrine, and norepinephrine.

RESULTS

Bedtime restriction reduced daily sleep by 122 +/- 25 min. Both study periods were associated with comparable weight gain; however, recurrent sleep restriction resulted in reduced oral glucose tolerance (2-h glucose value, 144 +/- 25 vs. 132 +/- 36 mg/dl; P < 0.01) and insulin sensitivity [3.3 +/- 1.1 vs. 4.0 +/- 1.6 (mU/liter)(-1) x min(-1); P < 0.03], and increased glucose effectiveness (0.023 +/- 0.005 vs. 0.020 +/- 0.005 min(-1); P < 0.04). Although 24-h cortisol and GH concentrations did not change, there was a modest increase in 24-h epinephrine and nighttime norepinephrine levels during the 5.5-h bedtime condition.

CONCLUSIONS

Experimental bedtime restriction, designed to approximate the short sleep times experienced by many individuals in Westernized societies, may facilitate the development of insulin resistance and reduced glucose tolerance.

Family history of diabetes impacts on interactions between minimal model estimates of insulin sensitivity and glucose effectiveness

AIMS/HYPOTHESIS

Insulin resistance and glucose effectiveness (S(G)) are major determinants of glucose tolerance and independently predict the development of type 2 diabetes in individuals with a family history of disease. We examined the inter-relationship between insulin sensitivity (S(I)) and S(G) in offspring of two parents with type 2 diabetes and in individuals with no family history of diabetes.

METHODS

Fifty non-diabetic individuals, including 26 offspring of two type 2 diabetic parents (family history, FH+) and 24 with no family history of diabetes (FH-) similar in gender, age, ethnicity and body mass index (BMI) were studied. Each subject underwent a 100-g oral glucose tolerance test (OGTT) and insulin modified frequently sampled intravenous glucose tolerance, analysed using the Bergman's minimal model (MINMOD).

RESULTS

Thirteen subjects of the FH+ group and nine of the FH- group had impaired glucose tolerance (IGT). S(I) and S(G) were independent variables in the FH+ group, while they correlated highly with each other in the FH- group (r = 0.69, p = 0.0002). The relationship between S(I) and S(G) persisted when analysing the IGT and normal glucose tolerance subgroups separately, demonstrating that these associations were not because of differences in glycaemia. Consistently, S(G) strongly correlated with additional measures of insulin resistance only in the FH- group, including fasting insulin (r = 0.56, p = 0.004), homeostasis model assessment of insulin resistance (r = 0.57 p = 0.003) and BMI (r = 0.66, p = 0.0004).

CONCLUSIONS

These results demonstrate that familial factors impart important physiological differences in the inter-relationship between insulin-dependent and insulin-independent glucose disposal, which may be important in modulating risk for development of disease.

The minimal model of glucose disposal in the analysis of glucose effectiveness: importance of early insulin data

BACKGROUND

Glucose effectiveness (S(g)) is an important component in glucose tolerance. Values of S(g) using "open loop" glucose kinetic computer programs are usually higher compared to closed loop method (CLM) programs that incorporate insulin secretion modeling. We aimed to test whether these differences are caused by (1) inclusion of insulin secretion modeling or (2) the method of representing plasma insulin values in the first few minutes of the frequently sampled intravenous glucose tolerance test (FSIGT).

METHODS

FSIGTs without insulin supplementation were performed in six healthy volunteers, and the Bergman minimal model was fitted to the data using the simulation and modeling program SAAM.

RESULTS

The CLM, which represents the insulin data in the first few minutes by a best-fit curve extrapolated to the y-axis, yielded a significantly lower S(g) than the approach similar to the computer program MINMOD, where the first few minutes of insulin data are represented by a line joining the basal to the peak values (1.55 +/- 0.28 vs. 1.97 +/- 0.27 [SE] x 10(-2)/min, P < 0.05). This second analysis was then repeated while forcing the program to represent the insulin data after the insulin peak in the same way as in the CLM, obtaining an almost identical result for S(g) (1.99 +/- 0.29). Insulin sensitivity was not significantly affected.

CONCLUSIONS

The higher S(g) estimates are caused by the method of representing the first few minutes of insulin data rather than by the incorporation of insulin secretion modeling. It is, therefore, important to know how the early insulin data are represented when comparing results from different computer modeling programs.

Application of the intravenous glucose tolerance test and the minimal model to patients with insulinoma: insulin sensitivity (Si) and glucose effectiveness (Sg) before and after surgical excision

BACKGROUND

The unmodified frequently sampled intravenous glucose tolerance test (FSIGT) has not previously been used to assess insulin/glucose kinetics in patients with insulinoma.

OBJECTIVE

To measure insulin sensitivity (Si) and glucose effectiveness (Sg) by means of the FSIGT in patients with insulinoma, before and after surgical removal of the tumour.

SUBJECTS AND METHODS

FSIGTs were performed in five patients, before and approximately 3 months post-surgery, and in 11 controls. Si and Sg were estimated using Minimal Model computer analysis of dynamic glucose and insulin data.

RESULTS

Si was lower in insulinoma patients before, compared with after surgery (3.37 +/- 0.62 vs. 6.24 +/- 1.09 SE [x10(-4)] min(-1)microU(-1) ml, P < 0.05). Sg was similar in patients pre- and post-surgery (3.0 +/- 0.67 vs. 2.4 +/- 0.6 [x10(-2)] min(-1), NS).

CONCLUSIONS

Insulin sensitivity improves after excision of an insulinoma. Glucose effectiveness is not influenced by chronic hyperinsulinaemia and hypoglycaemia.

Evidence for pancreatic beta-cell dysfunction in brothers of women with polycystic ovary syndrome

Hyperandrogenemia and insulin resistance are heritable traits in sisters of women with polycystic ovary syndrome (PCOS). Hyperandrogenemia also appears to be the male reproductive phenotype; however, it is less clear whether male relatives are at risk for the metabolic disorders associated with PCOS. In this study, we tested the hypothesis that brothers of women with PCOS have defects in insulin action and/or secretion. Twenty-three non-Hispanic white brothers of women with PCOS and 23 non-Hispanic white control men of comparable age matched for body mass index underwent a modified frequently sampled intravenous glucose tolerance test. Parameters of insulin sensitivity and secretion were determined using minimal-model Bergman protocol. Disposition index was significantly decreased (2540 [1080, 3172] vs 2901 [2096, 4487], P = .009) independent of a family history of diabetes mellitus, and glucose effectiveness was significantly increased (2.4 [1.9, 2.7] vs 2.0 [1.8, 2.2], P = .02) in brothers compared with control men. We conclude that brothers of women with PCOS have evidence for pancreatic beta-cell dysfunction and may be at increased risk for type 2 diabetes mellitus.

First phase release coefficient of insulin in subjects with normal glucose tolerance on glucose infusion analyzed by computer simulation

We report here a mathematical model using computer simulation to solve the phase fractionation coefficient (f) of instantaneous insulin release on glucose infusion. By extensive model testing with the cited parameters obtained from the literature, the values of the factor f were shown to lie in range of 0.93+/-0.02 (mean+/-2S.D., n=15), indicating that the high pulsatile bolus of glucose by i.v. infusion may trigger acute insulin release (AIR) corresponding to a fraction of more than 90% of the stored insulin release in the first phase from the secretory granules of pancreatic beta cells. In addition, the value of the factor f was shown to be independent of both the glucose infusion method and the non-insulin-dependent uptake of glucose.

The role of proinflammatory cytokine gene polymorphisms for development of insulin resistance after renal transplantation

BACKGROUND

Insulin resistance, a frequent prediabetic metabolic complication after renal transplantation, is generally linked to immunosuppressive drugs including corticosteroids, cyclosporine (CsA) or tacrolimus, as well as to age, cadaveric donors and ethnic factors. Cytokines are known to be inflammation modulatory substances that contribute to metabolic derangements after transplantation. The present study investigated the effects of cytokine gene polymorphisms on insulin resistance in renal transplant recipients.

PATIENTS AND METHODS

Sixty-one renal transplant recipients (37 men, 24 women; mean age: 39.3 +/- 10.8 years) who attended regular clinical visits without a known history of diabetes were enrolled in the study. All patients were on a regimen of steroid, CsA, and mycophenolate mofetil. Venous blood samples were collected for biochemical analyses after an overnight fast at 08:00 pm. CsA trough levels, C-reactive protein, and fibrinogen were also estimated. Additional 10 mL of blood was withdrawn into an ethylenediamine tetraacetic acid-containing tube to determine cytokine genotypes (tumor necrosis factor-alpha [TNF-alpha] -238 G/A, transforming growth factor-beta [TGF-beta] codon 10 -869 T/C). Insulin resistance was calculated by the homeostasis model assessment (HOMA) method using the values of fasting blood glucose (FBG) and insulin levels. Anthropometric indices as well as body height, weight, waist and hip circumferences were measured simultaneously to calculate body mass index (kg/m2) and waist-to-hip ratio. Impaired fasting glucose (IFG) was described as an FBG > or = 110 but < 126 mg/dL.

RESULTS

IFG was detected in 27.9% of this study group. The HOMA index was significantly higher among patients with IFG compared with normal FBG (NoGT) (6.3 +/- 4.5 vs 3.7 +/- 1.5; P = .01). Neither FBG and insulin nor HOMA values correlated with antrophometric, metabolic, or inflammatory parameters. Cytokine genotype allele frequencies, age, sex, immunosuppressive and antihypertensive drug type and doses, CsA trough levels, and donor source (cadaveric/living) were similar for patients with IFG and NoGT. Mutant allele carrier genotypes (AA + GA) for TNF-alpha -238 G/A showed higher fasting insulin (14.0 +/- 7.9 vs 34.1 +/- 17.7 microIU/mL; P = .04) and HOMA (4.01 +/- 2.01 vs 7.95 +/- 5.44; P = .002) levels than GG homozygote subjects. FBG, HOMA, and other metabolic and anthropometric indices were similar between TGF-beta codon 10 -869 T/C genotypes. The daily dose of steroid (mg/d) and A allele frequency for TNF-alpha -238 G/A genotype were significant predictors of HOMA index in linear regression analysis.

CONCLUSION

The present study revealed that beside the daily dose of steroids, TNF-alpha -238 G/A genotype may contribute to insulin resistance in renal transplant recipients. Further investigations may highlight the effects of cytokine gene heterogenity on insulin resistance in those patients.

Mathematical beta cell model for insulin secretion following IVGTT and OGTT

Evaluation of beta cell function is conducted by a variety of glucose tolerance tests and evaluated by a number of different models with less than perfect consistency among results obtained from different tests. We formulated a new approximation of the distributed threshold model for insulin secretion in order to approach a model for quantifying beta cell function, not only for one, but for several different experiments. Data was obtained from 40 subjects that had both an oral glucose tolerance test (OGTT) and an intravenous tolerance test (IVGTT) performed. Parameter estimates from the two experimental protocols demonstrate similarity, reproducibility, and indications of prognostic relevance. Useful first phase indexes comprise the steady state amount of ready releasable insulin A0 and the rate of redistribution krd, where both yield a considerable correlation (both r=0.67) between IVGTT and OGTT estimates. For the IVGTT, A0 correlates well (r=0.96) with the 10 min area under the curve of insulin above baseline, whereas krd represents a new and possibly more fundamental first phase index. For the useful second phase index gamma, a correlation of 0.75 was found between IVGTT and OGTT estimates.

Insulin signaling and glucose transport in skeletal muscle from first-degree relatives of type 2 diabetic patients

Aberrant insulin signaling and glucose metabolism in skeletal muscle from type 2 diabetic patients may arise from genetic defects and an altered metabolic milieu. We determined insulin action on signal transduction and glucose transport in isolated vastus lateralis skeletal muscle from normal glucose-tolerant first-degree relatives of type 2 diabetic patients (n = 8, 41 +/- 3 years, BMI 25.1 +/- 0.8 kg/m(2)) and healthy control subjects (n = 9, 40 +/- 2 years, BMI 23.4 +/- 0.7 kg/m(2)) with no family history of diabetes. Basal and submaximal insulin-stimulated (0.6 and 1.2 nmol/l) glucose transport was comparable between groups, whereas the maximal response (120 nmol/l) was 38% lower (P < 0.05) in the relatives. Insulin increased phosphorylation of Akt and Akt substrate of 160 kDa (AS160) in a dose-dependent manner, with comparable responses between groups. AS160 phosphorylation and glucose transport were positively correlated in control subjects (R(2) = 0.97, P = 0.01) but not relatives (R(2) = 0.46, P = 0.32). mRNA of key transcriptional factors and coregulators of mitochondrial biogenesis were also determined. Skeletal muscle mRNA expression of peroxisome proliferator-activated receptor (PPAR) gamma coactivator (PGC)-1alpha, PGC-1beta, PPARdelta, nuclear respiratory factor-1, and uncoupling protein-3 was comparable between first-degree relatives and control subjects. In conclusion, the uncoupling of insulin action on Akt/AS160 signaling and glucose transport implicates defective GLUT4 trafficking as an early event in the pathogenesis of type 2 diabetes.

Is non-insulin dependent glucose uptake a therapeutic alternative? Part 1: physiology, mechanisms and role of non insulin-dependent glucose uptake in type 2 diabetes

Several decades of research for treating type 2 diabetes have yielded new drugs but the actual experience with the available oral antidiabetic compounds clearly shows that therapeutic needs are not matched. This highlights the urgent need for exploring other pathways. All cell types have the capacity to take up glucose independently of insulin, whereby basal but also hyperglycaemia-promoted glucose supply is ensured. Although poorly explored, insulin-independent glucose uptake might nevertheless represent a therapeutic target, as an alternative to the clear limits of actual drug treatments. This review not only critically examines some major pathways not requiring insulin (although they may be influenced by the hormone) but importantly, this analysis extends to the clinical applicability of these potential therapeutic principles by also considering their predictable tolerability for long-term therapy. In particular vascular safety (the ultimate problem linked with diabetes) will be envisaged because of the ubiquitous distribution of glucose transporters and some linked mechanisms. Several mechanisms can be identified which do not require insulin for their functioning. The first part of this review deals with the description, the regulation and the limits of some mechanisms representing potential pharmacological targets capable of having a highly significant impact on glucose uptake. These selected topics are: a) unmasking and/or activation of glucose transporters in cell plasma membranes, b) insulin mimetics acting at postreceptor level, c) activation of AMPK, d) increasing nitric oxide and e) increasing glucose-6P and glycogen stores.

Genome-wide linkage scans for prediabetes phenotypes in response to 20 weeks of endurance exercise training in non-diabetic whites and blacks: the HERITAGE Family Study

AIMS/HYPOTHESIS

Impaired insulin secretion, insulin action, insulin-independent glucose effectiveness, glucose tolerance and the associated abnormalities in insulin and glucose metabolism phenotypes are precursors of type 2 diabetes. Genome-wide multipoint variance component linkage scans were carried out using 654 markers to identify quantitative trait loci for insulin sensitivity, acute insulin response to glucose, disposition index and glucose effectiveness training responses in whites and blacks in the HERITAGE Family Study.

METHODS

These phenotypes were obtained from an IVGTT with the minimal model. The distributions of insulin sensitivity, acute insulin response to glucose and disposition index training responses (post-training minus baseline) were approximately normalised using a square-root transformation. All phenotypes were adjusted for the effects of age, BMI and their respective baseline values within sex and generation by race prior to linkage scans.

RESULTS

In blacks, a promising linkage with a maximum lod score of 3.1 on 19q (54-62 Mb) for glucose effectiveness training response was found. Six interesting linkages with lod scores of at least 1.0 were found for disposition index training response in whites. They included 1p (30 Mb), 3q (152 Mb), 6p (23-42 Mb), 7q (95-96 Mb), 10p (15 Mb) and 12q (119-126 Mb).

CONCLUSIONS/INTERPRETATION

Quantitative trait loci for 20 weeks of endurance exercise training responses in insulin action and glucose metabolism phenotypes were found on chromosome 19q as well as 6p and 7q, with nominal (6p, 7q) but consistent (6p) linkages across the races.

Sending the signal: molecular mechanisms regulating glucose uptake

The molecular signaling mechanisms by which insulin leads to increased glucose transport and metabolism and gene expression are not completely elucidated. We have characterized the nature of insulin signaling defects in skeletal muscle from Type 2 diabetic patients. Insulin receptor substrate (IRS-1) phosphorylation, phosphatidylinositol (PI) 3-kinase activity, and glucose transport activity are impaired as a consequence of functional defects, whereas insulin receptor tyrosine phosphorylation, mitogen-activated protein kinase (MAPK) phosphorylation, and glycogen synthase activity are normal. Using biotinylated photoaffinity labeling, we have shown that reduced cell surface GLUT4 levels can explain glucose transport defects in skeletal muscle from Type 2 diabetic patients under insulin-stimulated conditions. Current work is focused on mechanisms behind insulin-dependent and insulin-independent regulation of glucose uptake. We have recently determined the independent effects of insulin and hypoxia/AICAR exposure on glucose transport and cell surface GLUT4 content in skeletal muscle from nondiabetic and Type 2 diabetic subjects. Hypoxia and AICAR increase glucose transport via an insulin-independent mechanism involving activation of 5'-AMP-activated kinase (AMPK). AMPK signaling is intact, because 5-aminoimidazole-4-carboxamide 1-beta-D-ribonucleoside (AICAR) increased AMPK and acetyl-CoA carboxylase (ACC) phosphorylation to a similar extent in Type 2 diabetic and nondiabetic subjects. However, AICAR responses on glucose uptake were impaired. Our studies highlight important AMPK-dependent and independent pathways in the regulation of GLUT4 and glucose transport activity in insulin resistant skeletal muscle. Understanding signaling mechanisms to downstream metabolic responses may provide valuable clues to a future therapy for Type 2 diabetes.

Impaired insulin sensitivity, insulin secretion, and glucose effectiveness predict future development of impaired glucose tolerance and type 2 diabetes in pre-diabetic African Americans: implications for primary diabetes prevention

OBJECTIVE

We examined the determinants of impaired glucose tolerance (IGT) and type 2 diabetes in first-degree relatives of African-American type 2 diabetic patients over 5-8 years (median 6).

RESEARCH DESIGN AND METHODS

A total of 81 healthy subjects (age 41.5 +/- 4.8 years; BMI 31.3 +/- 3.6 kg/m(2)) participated in the study. Each subject underwent an oral glucose tolerance test (OGTT) and a frequently sampled intravenous glucose tolerance test at baseline. Insulin sensitivity index (S(i)) and glucose effectiveness index (S(g)) were determined by the minimal model method. Homeostasis model assessment (HOMA) was used to estimate insulin resistance (HOMA-IR) and beta-cell function (HOMA-%B). A total of 18 subjects progressed to either IGT or type 2 diabetes (progressors), whereas 19 subjects maintained normal glucose tolerance (nonprogressors).

RESULTS

Comparing the progressors and nonprogressors, mean fasting serum glucose levels (95 +/- 8 vs. 80 +/- 14 mg/dl, P < 0.01) and 2-h serum glucose levels (149 +/- 27 vs. 100 +/- 60 mg/dl, P < 0.01) as well as 2-h serum insulin levels (117 +/- 81 vs. 72 +/- 87 microU/ml, P < 0.01) during OGTT were higher at baseline. Mean acute first-phase insulin secretion (205 +/- 217 vs. 305 +/- 230 microU/ml), HOMA-%B (148 +/- 60 vs. 346 +/- 372, P < 01), S(i) (1.61 +/- 1.13 vs. 2.48 +/- 1.25 x 10(-4). min(-1) [microU/ml](-1)), and S(g) (1.48 +/- 0.61 vs. 2.30 +/- 0.97 x 10(-2). min(-1)) were lower in the progressors than in the nonprogressors at baseline. Mean HOMA-IR (3.31 +/- 1.64 vs. 2.36 +/- 1.64) was significantly greater in the progressors than the nonprogressors. At the time of diagnosis of glucose intolerance (IGT + diabetes), HOMA-%B (101 +/- 48 vs. 148 +/- 60, P < 0.001) and HOMA-IR (5.44 +/- 2.55 vs. 3.31 +/- 1.64, P < 0.003) deteriorated in the progressors versus baseline.

CONCLUSIONS

We conclude that nondiabetic, first-degree relatives of African-American type 2 diabetic patients who progressed to IGT and type 2 diabetes manifest triple defects (decreased insulin secretion, insulin action, and glucose effectiveness) that antecede the disease.

Whole body insulin resistance in rat offspring of mothers consuming alcohol during pregnancy or lactation: comparing prenatal and postnatal exposure

This study examined the effects of maternal ethanol (EtOH) consumption during pregnancy or lactation on glucose homeostasis in the adult rat offspring. Glucose disposal was determined by minimal model during an intravenous glucose tolerance test in rats that had a small or normal birth weight after EtOH exposure in utero and in rats whose mothers were given EtOH during lactation only. All three EtOH groups had decreased glucose tolerance index and insulin sensitivity index, but their glucose effectiveness was not different from that of controls. In addition, EtOH rat offspring that were small at birth had elevated plasma, liver, and muscle triglyceride levels. The data show that EtOH exposure during pregnancy programs the body to insulin resistance later in life, regardless of birth weight, but that this effect also results in dyslipidemia in growth-restricted rats. In addition, insulin resistance is also evident after EtOH exposure during lactation.

Metabolic effects of chronic glipizide gastrointestinal therapeutic system on serum glucose, insulin secretion, insulin sensitivity, and hepatic insulin extraction in glucose-tolerant, first-degree relatives of African American patients with type 2 diabetes: new insights on mechanisms of action

We examined the long-term metabolic effects of a potent sulfonylurea (SU), glipizide gastrointestinal therapeutic system (glipizide GITS) in normal glucose-tolerant (NGT), first-degree relatives of African American patients with type 2 diabetes in a randomized, placebo-controlled, double-blind manner for 24 months and 6 months after discontinuation of glipizide GITS. Fifty NGT African American first-degree relatives (n = 50)) were randomized to receive either glipizide GITS (GITS, 5 mg/d) or identical placebo (PLAC). The NGT consisted of NGT/GITS (n = 16; mean age, 43.1 +/- 8.7years; body mass index [BMI], 34.8 +/- 10) and NGT/PLAC (n = 34; 45.5 +/- 9.7 years; BMI, 31.3 +/- 3.1years). Each of the subjects underwent an oral glucose tolerance test (OGTT) and frequently sampled intravenous glucose tolerance test (FSIGT) at baseline and at yearly intervals for 2 years. Insulin sensitivity (Si) and glucose effectiveness (Sg) were determined by Bergman's minimal model method. Hepatic insulin extraction (HIE) was calculated as the molar ratio of C-peptide and insulin. The mean fasting serum glucose, insulin, and C-peptide levels in the NGT/GITS were not different from that of the NGT/PLAC. After oral glucose challenge, mean serum glucose responses slightly increased (P = not significant [NS]) at 12 and 24 months in the NGT/GITS group when compared with the baseline, 0 month, but remained unchanged in the NGT/PLAC group. In addition, serum insulin and C-peptide responses significantly increased in the NGT/GITS group, but were unchanged in the NGT/PLAC group at 12 and 24 months versus 0 month. The HIE, during OGTT, decreased by 30% from the baseline (0 month) values in the NGT/ GITS, but remained unchanged in the NGT/PLAC group at 12 and 24 months. Mean Si decreased by 30% from the baseline in the NGT/GITS group by 12 and 24 months, but remained unchanged in the NGT/PLAC group. However, the disposition index (DI) remained normal in the NGT/GITS and the NGT/PLAC groups. The DI data in the NGT/GITS group suggested that beta cells maintained the ability to compensate for the lower Si during the chronic GITS administration in our high risk African Americans. Chronic GITS was well tolerated without any symptoms of either hypoglycemia or weight gain in the NGT/IGTS group. After discontinuation of GITS, the altered metabolic parameters significantly improved, returning to baseline values in the NGT/IGTS group in 6 months. In summary, chronic glipizide GITS administration (5 mg/d) was associated with increased beta-cell secretion, peripheral hyperinsulinemia, reduced Si, and reduced HIE in glucose-tolerant, first-degree relatives of African American patients with type 2 diabetes. These metabolic changes were reversible within 6 months after discontinuation of glipizide GITS. Our study defines a unique mode of action of glipizide GITS in African Americans at high risk for type 2 diabetes. We conclude that the use of glipizide GITS in the primary prevention of type 2 diabetes in nondiabetic first-degree relatives of patients with type 2 diabetes impaired glucose homeostasis.

5-amino-imidazole carboxamide riboside increases glucose transport and cell-surface GLUT4 content in skeletal muscle from subjects with type 2 diabetes

AMP-activated protein kinase (AMPK) activation by AICAR (5-amino-imidazole carboxamide riboside) is correlated with increased glucose transport in rodent skeletal muscle via an insulin-independent pathway. We determined in vitro effects of insulin and/or AICAR exposure on glucose transport and cell-surface GLUT4 content in skeletal muscle from nondiabetic men and men with type 2 diabetes. AICAR increased glucose transport in a dose-dependent manner in healthy subjects. Insulin and AICAR increased glucose transport and cell-surface GLUT4 content to a similar extent in control subjects. In contrast, insulin- and AICAR-stimulated responses on glucose transport and cell-surface GLUT4 content were impaired in subjects with type 2 diabetes. Importantly, exposure of type 2 diabetic skeletal muscle to a combination of insulin and AICAR increased glucose transport and cell-surface GLUT4 content to levels achieved in control subjects. AICAR increased AMPK and acetyl-CoA carboxylase phosphorylation to a similar extent in skeletal muscle from subjects with type 2 diabetes and nondiabetic subjects. Our studies highlight the potential importance of AMPK-dependent pathways in the regulation of GLUT4 and glucose transport activity in insulin-resistant skeletal muscle. Activation of AMPK is an attractive strategy to enhance glucose transport through increased cell surface GLUT4 content in insulin-resistant skeletal muscle.

Central fat predicts deterioration of insulin secretion index and fasting glycaemia: 6-year follow-up of subjects at varying risk of Type 2 diabetes mellitus

AIMS

To examine the relationships between body composition and changes in fasting glycaemia, and in indices of insulin secretion and insulin action over 6 years in females with a family history of Type 2 diabetes with or without prior gestational diabetes ('at risk' group, AR) and control females (control group, C).

METHODS

At baseline and at follow-up, an oral glucose tolerance test and dual energy X-ray absorptiometry assessment of body composition were performed. Indices of insulin resistance (HOMA R') and insulin secretion (HOMA beta') were obtained from fasting insulin and glucose concentrations.

RESULTS

At baseline, the groups were similar for age, body mass index, fasting levels of plasma glucose and insulin, HOMA R' and HOMA beta'. Despite similar total body fatness, AR had significantly greater waist circumference and central fat (both P < 0.02) compared with C. At follow-up there was a significant increase in central adiposity only in AR, and the fasting plasma glucose (FPG) level was higher in AR compared with C (5.0 +/- 0.2 vs. 4.3 +/- 0.2 mmol/l, P = 0.02). This rise in plasma glucose in AR was related to a decline in HOMA beta' (r = 0.45, P = 0.0065). Both the baseline and the increments in total and central abdominal fat mass were associated with the time-related decline in HOMA beta'.

CONCLUSIONS

Six years after initial assessment, AR showed deterioration in FPG levels due predominantly to a decline in insulin secretion index without major change in insulin resistance index. Importantly, baseline body fatness (especially central adiposity), as well as increases in fatness with time, were the major predictors of the subsequent decline of insulin secretion index and the consequent rise in FPG.

Altered homeostatic adaptation of first- and second-phase beta-cell secretion in the offspring of patients with type 2 diabetes: studies with a minimal model to assess beta-cell function

We adapted a minimal model to assess beta-cell function during a hyperglycemic glucose clamp and to uncover peculiar aspects of the relationship among beta-cell function, plasma glucose, and insulin sensitivity (IS) in offspring of Caucasian patients with type 2 diabetes (OfT2D). We pooled two data sets of OfT2D (n = 69) and control subjects (n = 45) with normal glucose regulation. Plasma C-peptide was measured during a hyperglycemic clamp ( approximately 10 mmol/l) to quantify model-based first-phase secretion and glucose sensitivity of second-phase secretion (beta). IS was quantified during the hyperglycemic clamp. In the pooled data, first-phase secretion was linearly and negatively related to fasting plasma glucose, but not IS; OfT2D lay on a distinct line shifted to the left of the control subjects. In contrast, beta was negatively related to IS, and OfT2D lay on a distinct line shifted more and more to the left of the control subjects, as IS was worse. Thus, in OfT2D lower beta-cell adaptive responses exist between ambient glycemia and first-phase insulin secretion and between IS and second-phase secretion. Under conditions leading to decreased insulin sensitivity, these disturbed relationships may lead to progression to diabetes in OfT2D.

Regulation of glucose transport in human skeletal muscle

Glucose transport, the rate limiting step in glucose metabolism in skeletal muscle, is mediated by insulin-sensitive glucose transporter 4 (GLUT4) and can be activated in skeletal muscle by two separate and distinct signalling pathways: one stimulated by insulin and the second by muscle contractions. Skeletal muscle is the principal tissue responsible for insulin-stimulated glucose disposal and thus the major site of peripheral insulin resistance. Impaired glucose transport in skeletal muscle leads to impaired whole body glucose uptake, and contributes to the pathogenesis of Type 2 diabetes mellitus. A combination of genetic and environmental factors is likely to contribute to the pathogenesis of Type 2 diabetes mellitus; however, the primary defect is still unknown. Intense efforts are underway to define the molecular mechanisms that regulate glucose metabolism in insulin sensitive tissues. This review will present our current understanding of mechanisms regulating glucose transport in skeletal muscle in humans. Elucidation of the pathways involved in the regulation of glucose homeostasis will offer insight into the pathogenesis of insulin resistance and Type 2 diabetes mellitus and may lead to the identification of biochemical entry points for drug intervention to improve glucose homeostasis.

Non-diabetic relatives of Type 2 diabetic families: dietary intake contributes to the increased risk of diabetes

AIMS

Non-diabetic first degree relatives of Type 2 diabetic patients are at increased risk of developing diabetes and cardiovascular disease. This is assumed to reflect a shared genetic predisposition. The aim of this study was to test the hypothesis that lifestyle factors, specifically dietary factors, are also important to the increased risk in non-diabetic relatives.

METHODS

Dietary intake was assessed using a validated food frequency questionnaire in 149 non-diabetic first degree relatives (age 20-65 years) from families of North European extraction with two or more living Type 2 diabetic family members, and 143 age- and sex-matched control subjects from the background population with no family history of diabetes.

RESULTS

Relatives reported higher absolute intakes of total fat (mean (95% confidence intervals) 83 (76-91) vs. 71 (66-76) g/day, P = 0.01), saturated fat (SFA; 39 (36-43) vs. 33 (30-36) g/day, P < 0.01) and cholesterol (391 (354-427) vs. 318 (287-349) mg/day, P < 0.01), and a lower intake of non-starch polysaccharide (P < 0.05). Considered as percentage of total daily energy intake, relatives had higher intakes of total fat (P < 0.01) and SFA (P < 0.02), and a lower intake of carbohydrate (P < 0.02). These differences remained after exclusion of suspected under- and over-reporters of dietary intake.

CONCLUSIONS

Non-diabetic relatives of Type 2 diabetic patients were found to consume diets that will promote rather than prevent the development of diabetes and cardiovascular disease. This suggests that the increased risk to non-diabetic relatives is therefore not entirely genetic, and there is scope for decreasing the risk through lifestyle modification.

Predictors of target organ damage in hypertensive blacks and whites

The purpose of this study was to evaluate the association of the insulin resistance syndrome with both blood pressure and target organ damage in blacks and whites with essential hypertension. Eighty-two black and 63 white French Canadian patients were studied. None had diabetes, and antihypertensive medications had been discontinued for >/=1 week. Measurements included 24-hour blood pressure monitoring, fasting plasma lipids, insulin sensitivity determined with the Bergman minimal model, echocardiogram, microalbumin excretion, and inulin and lithium clearances. Compared with the white French Canadians, black patients had an attenuated nighttime reduction in blood pressure (P<0.02), increased cardiac dimensions (P<0.001), greater microalbumin excretion (P<0.05), increased inulin clearance (indicative of glomerular hyperfiltration; P<0.001), and decreased lithium clearance (indicative of increased sodium reabsorption in the proximal tubule; P<0.001). Blood pressure levels were not related to insulin resistance; although in blacks, the nighttime reduction in systolic blood pressure was inversely related to fasting plasma insulin (r=-0.18, P<0.04). In a stepwise multivariate analysis (including blood pressure levels and components of the insulin resistance syndrome as independent variables), race was the strongest predictor of left ventricular mass (r=0.53, P<0.000), relative wall thickness (r=0.49, P<0.000), and both inulin (r=0.53, P<0.000) and lithium (r=0.41, P<0.000) clearances. Nighttime systolic blood pressure was also a significant determinant of concentric left ventricular hypertrophy (r=0.37, P<0.000). In blacks, microalbumin excretion was related to insulin resistance. These observations are consistent with the hypothesis that there is a genetic contribution to cardiac hypertrophy, glomerular hyperfiltration, and sodium retention in blacks with essential hypertension.

Metabolic impact of a family history of Type 2 diabetes. Results from a European multicentre study (EGIR)

BACKGROUND

Insulin resistance was found in some but not in all previous studies of non-diabetic first degree relatives of Type 2 diabetic patients. Small study groups, ethnic differences and/or non-optimal techniques may explain the conflicting results.

AIM

To study the impact of a family history of Type 2 diabetes on insulin action in a large group of non-diabetic Europeans using the 'gold standard' euglycaemic hyperinsulinaemic clamp technique.

METHODS

Non-diabetic subjects (n = 235) with a positive family history of Type 2 diabetes (FH+) and 564 subjects with no family history of diabetes (FH-) were recruited from The European Group of Insulin Resistance (EGIR) database. This database includes measurements of insulin action using the insulin clamp technique (1 mU/kg per min) in normal glucose-tolerant individuals from 20 different European centres. In a subset of subjects the measurements were performed in combination with indirect calorimetry (n = 80 vs. 213 with and without family history of Type 2 diabetes).

RESULTS

The body mass index (BMI) was slightly higher in FH+ compared with FH- (26.7 +/- 4.6 vs. 25.1 +/- 4.7 kg/m(2); P < 0.02). After correction for covariates according to differences between investigators and subject characteristics including BMI (multiple regression analysis), insulin-stimulated glucose disposal was lower in FH+ compared with FH- (P < 0.00001). Insulin-stimulated glucose oxidation was slightly increased in FH+ compared with FH-, and insulin-stimulated non-oxidative glucose metabolism was consequently markedly reduced in FH+ compared with FH- (P < 0.0005).

CONCLUSION

Insulin resistance is present in European non-diabetic relatives of Type 2 diabetic patients. The insulin resistance is independent of degree of obesity and is restricted solely to the pathway of non-oxidative glucose metabolism. Diabet. Med. 18, 533-540 (2001)

Insulin secretion and insulin sensitivity are normal in non-diabetic subjects from maternal inheritance diabetes and deafness families

BACKGROUND

The pathophysiological mechanism of diabetes mellitus in the presence of the 3243 A-G tRNALEU(UR) mitochondrial DNA mutation is thought to result from deficient insulin secretion. However, few subjects with normal glucose tolerance have been studied to determine the sequence of events resulting in the development of diabetes mellitus.

AIM

To determine whether abnormalities of insulin sensitivity, insulin secretion or glucose effectiveness are present in non-diabetic subjects with the 3243 A-G tRNALEU(UUR) mitochondrial DNA mutation.

METHODS

Twelve non-diabetic subjects with the mutation were compared with 12 controls, matched for age and anthropometric parameters, using both oral and intravenous glucose tolerance tests, the latter with Minimal Model analysis.

RESULTS

Following an oral glucose load we found significantly higher blood glucose levels at 90 min and 120 min and significantly higher insulin levels at 120 min and 180 min in non-diabetic subjects with the mutation but no difference in the insulinogenic indices at 30 min and 180 min. From the intravenous glucose tolerance test there was no difference in overall glucose tolerance, insulin sensitivity, first- or second-phase insulin secretion, proinsulin secretion or glucose effectiveness. Insulin-independent glucose disposal was increased in subjects with lower insulin sensitivity and declined with increasing age in subjects with the mutation but not in controls.

CONCLUSIONS

While there appear to be subtle defects of glucose handling in non-diabetic subjects with the 3243 mutation, these could not be explained by differences in insulin sensitivity or secretion.

Fetal growth and the physiological control of glucose tolerance in adults: a minimal model analysis

Although there is now substantial evidence linking low birthweight with impaired glucose tolerance and type 2 diabetes in adult life, the extent to which reduced fetal growth is associated with impaired insulin sensitivity, defective insulin secretion, or a combination of both factors is not clear. We have therefore examined the relationships between birth size and both insulin sensitivity and insulin secretion as assessed by an intravenous glucose tolerance test with minimal model analysis in 163 men and women, aged 20 yr, born at term in Adelaide, South Australia. Birth size did not correlate with body mass index or fat distribution in men or women. Men who were lighter or shorter as babies were less insulin sensitive (P = 0.03 and P = 0.01, respectively), independently of their body mass index or body fat distribution. They also had higher insulin secretion (P = 0.007 and P = 0.006) and increased glucose effectiveness (P = 0.003 and P = 0.003). Overall glucose tolerance, however, did not correlate with birth size, suggesting that the reduced insulin sensitivity was being compensated for by an increase in insulin secretion and insulin-independent glucose disposal. There were no relationships between birth size and insulin sensitivity or insulin secretion in women. These results show that small size at birth is associated with increased insulin resistance and hyperinsulinemia in young adult life but that these relationships are restricted to the male gender in this age group.

Evidence for impaired glucose effectiveness in cirrhotic patients after liver transplantation

To evaluate the impact of acute and chronic liver disease and single immunosuppression (cyclosporine A [CSA] or FK506) on insulin sensitivity and glucose effectiveness in liver-grafted patients, we performed a frequently sampled intravenous glucose tolerance test (FSIGTT) in nondiabetic patients after orthotopic liver transplantation (OLT) with acute liver failure ([ALF] group, n = 9, with CSA therapy), in patients after OLT with chronic liver disease (CSA group, n = 8; FK506 group, n = 8), and in 9 healthy control subjects. Insulin sensitivity and glucose effectiveness were determined by analyzing glucose and insulin data from the FSIGTT with Bergman's minimal model technique for glucose. The intravenous glucose tolerance index ([KG] ie, the slope of the regression of the logarithm of blood glucose concentration) was not different between the ALF group (2.17 +/- 0.16 min(-1)) and controls (2.29 +/- 0.13 min(-1)), but was lower (P < .05) in both groups with chronic liver disease (CSA group, 1.46 +/- 0.1; FK506 group, 1.61 +/- 0.11 min(-1)) compared with the ALF group (P < .05). A positive relation for the KG and glucose effectiveness was found in all liver-grafted patients and controls. Insulin sensitivity was not different between all liver-grafted patients and controls. The body mass index (BMI) was the overall determinant of insulin sensitivity in all groups. Single immunosuppressive therapy does not impair insulin sensitivity in liver-grafted patients. The lower glucose effectiveness in liver-grafted patients with chronic liver disease but not in patients after ALF points to a defect in the regulation of glucose-mediated glucose uptake in peripheral tissue.

Insulin secretion in growth hormone-deficient adults: effects of 24 months' therapy and five days' acute withdrawal of recombinant human growth hormone

Beta-cell function in growth hormone (GH)-deficient (GHD) adults is poorly documented. Beta-cell function was therefore studied in 10 GHD adults (age, 40+/-3 years; weight, 79.3+/-4.8 kg; body mass index [BMI], 27.5+/-1.3 kg x m(-2)) before and after 6- and 24-month recombinant human GH (rhGH) therapy (0.24 IU x kg(-1) x wk(-1)) compared with 10 age-, sex-, weight-, and BMI-matched control subjects. With rhGH therapy, fat-free mass (FFM) increased (48.2+/-4.9, 52.5+/-4.8, and 59+/-6.8 kg, respectively) and fat mass (FM) decreased (33.8%+/-2.8%, 28.0%+/-3.0%, and 29.4%+/-2.5%, respectively), as did serum cholesterol. Oral glucose tolerance initially deteriorated at 6 months, but improved toward the control value by 24 months. Fasting insulin (FI) increased significantly, as did the acute insulin response to oral glucose (deltaAIR(OGTT)/deltaG) at 30 minutes (FI: pretreatment 9.8+/-0.8, 6 months, 14.0+/-1.8, 24 months 12.5+/-1.6 v control 11.4+/-1.9 mU x L(-1); deltaAIR(OGTT)/deltaG: pretreatment 201+/-24, 6 months 356+/-41, 24 months 382+/-86 v control 280+/-47 mU x mmol(-1)). However, the acute insulin response to intravenous (IV) glucose (AIR(G)) and IV glucagon at euglycemia and hyperglycemia did not change with rhGH therapy and were similar to the control group values. Importantly, the expected reciprocal relationships (as observed for the control group) between the various insulin secretory parameters and insulin sensitivity (SI) either were not present or were statistically weak in GHD subjects, despite the 35% decrease in SI by 24 months of rhGH therapy. In particular, over time, there was an attenuation of insulin secretion with respect to the ongoing insulin resistance with rhGH therapy, particularly for AIR(G) at 24 months. After 5 days of rhGH withdrawal, insulin secretion decreased and SI improved in GHD subjects. It is concluded that the current long-term rhGH treatment regimens appear to impact on insulin secretion such that the normal relationships between insulin secretion and SI are altered despite the favorable impact on body composition and serum lipid profiles.