Amra C. Alibegovic

Insulin resistance induced by physical inactivity is associated with multiple transcriptional changes in skeletal muscle in young men

Physical inactivity is a risk factor for insulin resistance. We examined the effect of 9 days of bed rest on basal and insulin-stimulated expression of genes potentially involved in insulin action by applying hypothesis-generating microarray in parallel with candidate gene real-time PCR approaches in 20 healthy young men. Furthermore, we investigated whether bed rest affected DNA methylation in the promoter region of the peroxisome proliferator-activated receptor-γ coactivator-1α (PPARGC1A) gene. Subjects were reexamined after 4 wk of retraining. We found that bed rest induced insulin resistance and altered the expression of more than 4,500 genes. These changes were only partly normalized after 4 wk of retraining. Pathway analyses revealed significant downregulation of 34 pathways, predominantly those of genes associated with mitochondrial function, including PPARGC1A. Despite induction of insulin resistance, bed rest resulted in a paradoxically increased response to acute insulin stimulation in the general expression of genes, particularly those involved in inflammation and endoplasmatic reticulum (ER) stress. Furthermore, bed rest changed gene expressions of several insulin resistance and diabetes candidate genes. We also observed a trend toward increased PPARGC1A DNA methylation after bed rest. We conclude that impaired expression of PPARGC1A and other genes involved in mitochondrial function as well as a paradoxically increased response to insulin of genes involved in inflammation and ER stress may contribute to the development of insulin resistance induced by bed rest. Lack of complete normalization of changes after 4 wk of retraining underscores the importance of maintaining a minimum of daily physical activity.

Mitochondrial function in skeletal muscle is normal and unrelated to insulin action in young men born with low birth weight.

OBJECTIVE Low birth weight (LBW) is an independent risk factor of insulin resistance and type 2 diabetes. Recent studies suggest that mitochondrial dysfunction and impaired expression of genes involved in oxidative phosphorylation (OXPHOS) may play a key role in the pathogenesis of insulin resistance in aging and type 2 diabetes. The aim of this study was to determine whether LBW in humans is associated with mitochondrial dysfunction in skeletal muscle. METHODS Mitochondrial capacity for ATP synthesis was assessed by (31)phosphorus magnetic resonance spectroscopy in forearm and leg muscles in 20 young, lean men with LBW and 26 matched controls. On a separate day, a hyperinsulinemic euglycemic clamp with excision of muscle biopsies and dual-energy x-ray absorptiometry scanning was performed. Muscle gene expression of selected OXPHOS genes was determined by quantitative real-time PCR. RESULTS The LBW subjects displayed a variety of metabolic and prediabetic abnormalities, including elevated fasting blood glucose and plasma insulin levels, reduced insulin-stimulated glycolytic flux, and hepatic insulin resistance. Nevertheless, in vivo mitochondrial function was normal in LBW subjects, as was the expression of OXPHOS genes. CONCLUSIONS These data support and expand previous findings of abnormal glucose metabolism in young men with LBW. In addition, we found that the young, healthy men with LBW exhibited hepatic insulin resistance. However, the study does not support the hypothesis that muscle mitochondrial dysfunction per se is the underlying key metabolic defect that explains or precedes whole body insulin resistance in LBW subjects at risk for developing type 2 diabetes.

Metabolic aspects of insulin resistance in individuals born small for gestational age

Numerous studies have shown an association between low weight at birth and being born small for gestational age (SGA) on the one hand and risk of developing insulin resistance and type 2 diabetes on the other. Our studies in twins have indicated a non-genetic age-dependent origin of insulin resistance and type 2 diabetes associated with being born SGA. In order to gain insight into the molecular metabolic defects and mechanisms linking SGA with insulin resistance and type 2 diabetes, we performed a series of experiments in young and elderly twins, and, in particular, in young men (aged 19–23 years) with a weight at birth at term in the lowest 10th percentile with no family history of diabetes. The control group included age-matched men with birth weights at term in the upper normal range. While body mass index and waist-to-hip ratios were similar in the individuals born SGA and controls, dual-energy X-ray absorptiometry studies documented a higher degree of abdominal obesity in the men who had a low weight at birth. Using the gold standard hyperinsulinaemic-euglycaemic clamp technique combined with glucose tracers and studies of forearm glucose uptake, we found an impairment of insulin-stimulated glycolytic flux and reduced forearm (muscle) glucose uptake in the face of normal whole-body glucose uptake. In addition, we found a significantly decreased insulin secretion rate during oral glucose ingestion after correction for insulin action (disposition index), a paradoxical enhanced insulin suppression of hepatic glucose production and lower fasting plasma glycerol levels, suggesting impaired lipolysis. Finally, analysis of skeletal muscle biopsies showed reduced muscle expression of several key proteins involved in insulin signalling and glucose transport, including protein kinase C-ζ, the two subunits of phosphoinositol 3-kinase (i.e., p85α and p110β) and the insulin-sensitive glucose transporter, Glut-4, in individuals of low birth weight. In conclusion, being born SGA and of low birth weight is associated with type 2 diabetes in a non-genetic manner, and programming of muscle insulin action and signalling represents an early mechanism responsible for this association.

Impact of 9 Days of Bed Rest on Hepatic and Peripheral Insulin Action, Insulin Secretion, and Whole-Body Lipolysis in Healthy Young Male Offspring of Patients With Type 2 Diabetes

OBJECTIVE The aim of this study was to investigate the impact of 9 days of bed rest on insulin secretion, insulin action, and whole-body glucose and fat metabolism in first-degree relative (FDR) and matched control (CON) subjects. RESEARCH DESIGN AND METHODS A total of 13 FDR and 20 CON subjects participated in the study. All were studied before and after 9 days of bed rest using the clamp technique combined with indirect calorimetry preceded by an intravenous glucose tolerance test. Glucose and glycerol turnover rates were studied using stable isotope kinetics. RESULTS Bed rest caused a significant decrease in whole-body insulin sensitivity in both groups. Hepatic insulin resistance was elevated in FDR subjects prior to bed rest and was significantly augmented by bed rest in FDR (P < 0.01) but not in CON (P = NS) subjects. The rate of whole-body lipolysis decreased during bed rest in both FDR and CON subjects, with no significant differences between the groups. Insulin resistance induced by bed rest was fully accounted for by the impairment of nonoxidative glucose metabolism in both groups (overall P < 0.001). CONCLUSIONS Whole-body insulin action in both insulin-resistant FDR and healthy CON subjects deteriorates with 9 days of bed rest, converging toward similar degrees of whole-body insulin resistance. FDR subjects exhibit hepatic insulin resistance (HIR), which, in contrast to CON subjects, deteriorates in response to physical inactivity. FDR subjects exhibit reduced insulin secretion when seen in relation to their degree of HIR but not peripheral insulin resistance.

Increased Risk of Type 2 Diabetes in Elderly Twins

OBJECTIVE Genetic susceptibility, low birth weight (LBW), and aging are key etiological factors in the development of type 2 diabetes. LBW is common among twins. It is unknown whether twin status per se is associated with risk of type 2 diabetes, and valid concordance rates of type 2 diabetes in twins on a lifetime perspective are lacking. RESEARCH DESIGN AND METHODS A clinical study was done on a population-based cohort of same-sex elderly monozygotic (MZ) and dizygotic (DZ) twins (n = 297) and singleton control subjects (C) (n = 71) including measures of anthropometry and glucose tolerance. In addition, type 2 diabetes incidence cases in twins (n = 626) and singletons (n = 553) were identified through the National Diabetes Register. RESULTS Twins were more abdominally obese, insulin resistant, and glucose intolerant, as evidenced by a higher A1C (%) (means ± SD) (MZ: 6.0 ± 1.0, DZ: 5.8 ± 0.7, C: 5.6 ± 0.3, P = 0.004) and 120-min post–oral glucose tolerance test plasma glucose levels (in mmol/l) (MZ: 8.6 ± 4.6, DZ: 8.4 ± 3.9, C: 6.8 ± 2.4, P = 0.003) compared with singletons. Importantly, twins had a higher prevalence of type 2 diabetes (MZ: 17.5% [95% CI 14.4–20.6], DZ: 15.7% [13.1–18.3], C: 5.6% [3.0–8.2], P = 0.03) together with a 60% higher incidence rate of type 2 diabetes compared with singletons. Cumulative concordance rates of type 2 diabetes to the age of 84 years were similar among elderly MZ (0.76 [0.68–0.84]) and DZ (0.71 [0.63–0.78]) twins. CONCLUSIONS Twin status per se is associated with abdominal obesity, insulin resistance, and increased prevalence of type 2 diabetes in elderly twins. The data support a quantitatively significant impact of the fetal environment as opposed to genetics on risk of type 2 diabetes.

Effect of Adjunct Metformin Treatment in Patients with Type-1 Diabetes and Persistent Inadequate Glycaemic Control. A Randomized Study

Background Despite intensive insulin treatment, many patients with type-1 diabetes (T1DM) have longstanding inadequate glycaemic control. Metformin is an oral hypoglycaemic agent that improves insulin action in patients with type-2 diabetes. We investigated the effect of a one-year treatment with metformin versus placebo in patients with T1DM and persistent poor glycaemic control. Methodology/Principal Findings One hundred patients with T1DM, preserved hypoglycaemic awareness and HaemoglobinA1c (HbA1c) ≥8.5% during the year before enrolment entered a one-month run-in on placebo treatment. Thereafter, patients were randomized (baseline) to treatment with either metformin (1 g twice daily) or placebo for 12 months (double-masked). Patients continued ongoing insulin therapy and their usual outpatient clinical care. The primary outcome measure was change in HbA1c after one year of treatment. At enrolment, mean (standard deviation) HbA1c was 9.48% (0.99) for the metformin group (n = 49) and 9.60% (0.86) for the placebo group (n = 51). Mean (95% confidence interval) baseline-adjusted differences after 12 months with metformin (n = 48) versus placebo (n = 50) were: HbA1c, 0.13% (−0.19; 0.44), p = 0.422; Total daily insulin dose, −5.7 U/day (−8.6; −2.9), p<0.001; body weight, −1.74 kg (−3.32; −0.17), p = 0.030. Minor and overall major hypoglycaemia was not significantly different between treatments. Treatments were well tolerated. Conclusions/Significance In patients with poorly controlled T1DM, adjunct metformin therapy did not provide any improvement of glycaemic control after one year. Nevertheless, adjunct metformin treatment was associated with sustained reductions of insulin dose and body weight. Further investigations into the potential cardiovascular-protective effects of metformin therapy in patients with T1DM are warranted. Trial Registration ClinicalTrials.gov NCT00118937

Effect of 10 days of bedrest on metabolic and vascular insulin action: a study in individuals at risk for type 2 diabetes

Physical inactivity is a known risk factor for type 2 diabetes. We studied whole body and forearm insulin sensitivity in subjects at increased risk for type 2 diabetes [persons with low birth weight (LBW group; n = 20) and first-degree relatives to type 2 diabetic patients (FDR group; n = 13)] as well as a control (CON) group (n = 20) matched for body mass index, age, and physical activity levels before and after 10 days of bedrest. Subjects were studied by hyperinsulinemic isoglycemic clamp combined with arterial and deep venous catheterization of the forearm. Forearm blood flow (FBF) was measured by venous occlusion plethysmography. All groups responded with a decrease in whole body insulin sensitivity in response to bedrest [CON group: 6.8 +/- 0.5 to 4.3 +/- 0.3 mg x min(-1) x kg(-1) (P < 0.0001), LBW group: 6.2 +/- 0.5 to 4.3 +/- 0.3 mg x min(-1) x kg(-1) (P < 0.0001), and FDR group: 4.3 +/- 0.7 to 3.1 +/- 0.3 mg x min(-1) x kg(-1) (P = 0.068)]. The percent decrease was significantly greater in the CON group compared with the FDR group (CON group: 34 +/- 4%, LBW group: 27 +/- 4%, and FDR group: 10 +/- 13%). Forearm insulin-stimulated glucose clearance decreased significantly in the CON and LBW groups in response to bedrest; in the FDR group, clearance was very low before bedrest and no change was observed. Before bedrest, the CON and LBW groups demonstrated a significant increase in FBF during hyperinsulinemia; after bedrest, an increase in FBF was observed only in the CON group. In conclusion, bedrest induced a pronounced reduction in whole body, skeletal muscle, and vascular insulin sensitivity in the CON and LBW groups. The changes were most pronounced in the CON group. In the FDR group, insulin resistance was already present before bedrest, but even this group displayed a high sensitivity to changes in daily physical activity.

Effect of adjunct metformin treatment on levels of plasma lipids in patients with type 1 diabetes

Background: In addition to its glucose‐lowering effect, metformin treatment has been suggested to improve lipidaemia in patients with type 2 diabetes. In contrast, in patients with type 1 diabetes (T1DM), information about the effect of metformin treatment on lipidaemia is limited. In this study, we report the effect of a 1‐year treatment with metformin vs. placebo on plasma lipids in T1DM patients and persistent poor glycaemic control.

The T-Allele of TCF7L2 rs7903146 Associates With a Reduced Compensation of Insulin Secretion for Insulin Resistance Induced by 9 Days of Bed Rest

OBJECTIVE The aim of this study was to determine whether the type 2 diabetes–associated T-allele of transcription factor 7-like 2 (TCF7L2) rs7903146 associates with impaired insulin secretion to compensate for insulin resistance induced by bed rest. RESEARCH DESIGN AND METHODS A total of 38 healthy young Caucasian men were studied before and after bed rest using the hyperinsulinemic-euglycemic clamp technique combined with indirect calorimetry preceded by an intravenous glucose tolerance test. The TCF7L2 rs7903146 was genotyped using allelic discrimination performed with an ABI 7900 system. The genetic analyses were done assuming a dominant model of inheritance. RESULTS The first-phase insulin response (FPIR) was significantly lower in carriers of the T-allele compared with carriers of the CC genotype before bed rest, with and without correction for insulin resistance. The incremental rise of FPIR in response to insulin resistance induced by bed rest was lower in carriers of the T-allele (P < 0.001). Fasting plasma glucagon levels were significantly lower in carriers of the T-allele before and after bed rest. While carriers of the CC genotype developed increased hepatic insulin resistance, the TCF7L2 rs7903146 did not influence peripheral insulin action or the rate of lipolysis before or after bed rest. CONCLUSIONS Healthy carriers of the T-allele of TCF7L2 rs7903146 exhibit a diminished increase of insulin secretion in response to intravenous glucose to compensate for insulin resistance as induced by bed rest. Reduced paracrine glucagon stimulation may contribute to the impairment of β-cell function in the carriers TCF7L2 rs7903146 T-allele associated with increased risk of type 2 diabetes.

Impact of Physical Inactivity on Subcutaneous Adipose Tissue Metabolism in Healthy Young Male Offspring of Patients With Type 2 Diabetes

OBJECTIVE Physical inactivity is a risk factor for type 2 diabetes and may be more detrimental in first-degree relative (FDR) subjects, unmasking underlying defects of metabolism. Using a positive family history of type 2 diabetes as a marker of increased genetic risk, the aim of this study was to investigate the impact of physical inactivity on adipose tissue (AT) metabolism in FDR subjects. RESEARCH DESIGN AND METHODS A total of 13 FDR and 20 control (CON) subjects participated in the study. All were studied before and after 10 days of bed rest using the glucose clamp technique combined with measurements of glucose uptake, lipolysis, and lactate release from subcutaneous abdominal (SCAAT) and femoral (SCFAT) adipose tissue by the microdialysis technique. Additionally, mRNA expression of lipases was determined in biopsies from SCAAT. RESULTS Before bed rest, the FDR subjects revealed significantly increased glucose uptake in SCAAT. Furthermore, mRNA expression of lipases was significantly decreased in the SCAAT of FDR subjects. Bed rest significantly decreased lipolysis and tended to increase glucose uptake in the SCFAT of both CON and FDR subjects. In response to bed rest, SCAAT glucose uptake significantly increased in CON subjects but not in FDR subjects. CONCLUSIONS FDR subjects exhibit an abnormal AT metabolism including increased glucose uptake prior to bed rest. However, the differences between FDR and CON subjects in AT metabolism were attenuated during bed rest due to relatively more adverse changes in CON subjects compared with FDR subjects. Physical inactivity per se is not more deleterious in FDR subjects as compared with CON subjects with respect to derangements in AT metabolism.