Correction to: Identification of an intracellular metabolic signature impairing beta cell function in the rat beta cell line INS-1E and human islets

As part of an institutional investigation by University of Bremen, the work carried out by Kathrin Maedler's laboratory has been reviewed.

High-fat Diet and Physical Exercise Differentially Modulate Adult Neurogenesis in the Mouse Hypothalamus

The hypothalamus has emerged as a novel neurogenic niche in the adult brain during the past decade. However, little is known about its regulation and the role hypothalamic neurogenesis might play in body weight and appetite control. High-fat diet (HFD) has been demonstrated to induce an inflammatory response and to alter neurogenesis in the hypothalamus and functional outcome measures, e.g. body weight. Such modulation poses similarities to what is known from adult hippocampal neurogenesis, which is highly responsive to lifestyle factors, such as nutrition or physical exercise. With the rising question of a principle of neurogenic stimulation by lifestyle in the adult brain as a physiological regulatory mechanism of central and peripheral functions, exercise is interventionally applied in obesity and metabolic syndrome conditions, promoting weight loss and improving glucose tolerance and insulin sensitivity. To investigate the potential pro-neurogenic cellular processes underlying such beneficial peripheral outcomes, we exposed adult female mice to HFD together with physical exercise and evaluated neurogenesis and inflammatory markers in the arcuate nucleus (ArcN) of the hypothalamus. We found that HFD increased neurogenesis, whereas physical exercise stimulated cell proliferation. HFD also increased the amount of microglia, which was counteracted by physical exercise. Physiologically, exercise increased food and fat intake but reduced HFD-induced body weight gain. These findings support the hypothesis that hypothalamic neurogenesis may represent a counter-regulatory mechanism in response to environmental or physiological insults to maintain energy balance.

Circulating insulin-like growth factor binding protein-3 predicts one-year outcome after ischemic stroke

BACKGROUND

Insulin-like Growth Factor-1 (IGF-1) and Insulin-like Growth Factor Binding Protein-3 (IGFBP-3) have been ascribed neuroprotective effects. We sought to determine whether levels of IGF-1 and IGFBP-3 predict functional outcome after ischemic stroke.

METHODS

IGF-1 and IGFBP-3 levels were measured in the first week after stroke in patients with first ischemic stroke who were enrolled in the Berlin Cream&Sugar Study. National Institutes of Health Stroke Scale (NIHSS) was collected at admission. Lesion volume was determined from acute MRI if available. Functional outcome according to the modified Rankin Scale (mRS) was assessed after one year. In multivariate analyses we identified parameters associated with unfavourable functional outcome (mRS>2).

RESULTS

We included 100 patients. 21 patients had an unfavourable functional outcome. IGF-1 levels were<- 2 standard deviation score (SDS) in 7 patients, and>2 SDS in 12 patients. IGFBP-3 levels were<the 5(th) percentile in 13 patients, and no patient had IGFBP-3 levels>the 95(th) percentile. Low levels of IGFBP-3 (p=0.002), NIHSS at admission (p=0.043) and age (p=0.001) were associated with unfavourable functional outcome in the univariate analyses. In multivariate analysis including IGFBP-3, IGF-1, age, thrombolysis and NIHSS only low IGFBP-3 levels (OR 7.2, 95%CI 1.8-29.0, p=0.006) were associated with unfavourable functional outcome. If lesion volume was incuded (n=71), only IGFBP-3 levels (OR 7.2, 95%CI 1.5-35.5, p=0.015) were associated with unfavourable functional outcome.

CONCLUSION

IGFBP-3 levels after ischemic stroke may independently predict functional outcome after one year.

The impact of insulin-independent, glucagon-induced suppression of total ghrelin on satiety in obesity and type 1 diabetes mellitus

AIMS/HYPOTHESIS

The mechanisms underlying glucagon-induced satiety are incompletely understood. The glucagon-induced reduction in total ghrelin exerted at the hypothalamo-pituitary level might be responsible for this effect. Here we investigated glucagon-suppressive effects on circulating total and acyl-ghrelin, both in obesity and in type 1 diabetes mellitus (T1DM), with respect to the role of glucagon in appetite control. We further aimed to identify a possible mechanistic impact of changes in endogenous insulin.

METHODS

In our prospective, double-blinded, placebo-controlled study, we investigated the endocrine and metabolic responses to intramuscular glucagon administration in 13 patients with T1DM (6 males, 7 females; body mass index [BMI] 24.8 ± 0.95 kg/m(2)), 11 obese participants (OP; 5 males, 6 females; BMI 34.4 ± 1.7 kg/m(2)), and 13 healthy lean participants (LP; 6 males, 7 females; BMI 21.7 ± 0.6 kg/m(2)).

RESULTS

As compared with placebo, glucagon significantly increased satiety index in T1DM and in LP (P < .001) but failed to induce satiety in OP (P = .152). Total ghrelin significantly decreased after glucagon administration in all study groups (P < .01). Similarly, acyl-ghrelin significantly decreased in LP (P < .01). However, acyl-ghrelin concentrations showed no change in OP (P = .248) and even increased substantially in T1DM (P < .01). Changes in acyl-ghrelin correlated positively with changes in nonesterified fatty acid concentrations in all groups (r = 0.31-0.43; P < .01).

CONCLUSIONS/INTERPRETATION

Glucagon-induced satiety was preserved in T1DM but not in obesity. This effect was unrelated to changes in total or acylated ghrelin and was independent of endogenous insulin release. In contrast to the insulin-independent glucagon-induced suppression of total ghrelin, glucagon- and/or insulin-induced modification of lipolysis may determine changes in acylated ghrelin.

Leptin and endocrine parameters in marathon runners

Endurance training may lead to different hormonal alterations e. g., exercised induced hypothalamic ovarian/testicular dysfunction. The aim of this study was to reveal new connections between physical exercise, leptin and hormonal responses. 36 male participants of the Berlin-Marathon had their blood samples taken 2 days before the marathon. Hormones of the hypothalamic-pituitary axis and leptin were correlated with the training status and the achieved marathon time. Leptin correlated with the achieved marathon time after being adjusted for age and BMI (r=0.607, p<0.001) and was lowest in the best trained runners. Additionally, when the group was divided into quartiles of their achieved marathon time, significantly increased cortisol, fT4, cortisol/DHEAS ratio and decreased IGF-1 levels were observed in the slowest group. In the better trained group, a decrease of testosterone/DHT ratio and an increase of testosterone/cortisol ratio were observed. Our study supports the thesis of a linear relationship between physical fitness and leptin variations in the physiological range. We found an increased anabolic hormonal response in well trained marathon runners and hormonal reactions of increased stress in less trained runners. As the stress-induced neuroendocrine adaptations in our study group are associated with more higher leptin values, the pathophysiological role of decreased leptin values seems to be limited to overtrained athletes.

Identification of an intracellular metabolic signature impairing beta cell function in the rat beta cell line INS-1E and human islets

AIMS/HYPOTHESIS

Chronic hyperglycaemia promotes the progressive failure of pancreatic beta cells in patients with type 2 diabetes mellitus, a clinically highly relevant phenomenon known as glucotoxicity. The intracellular metabolic consequences of a chronically high availability of glucose in beta cells are, as yet, poorly understood in its full complexity.

METHODS

An unbiased metabolite profiling analysis (GC-time-of-flight-MS) was used to identify the time course of core metabolite patterns in rat beta cell line INS-1E during exposure to high glucose concentrations and its relation to insulin expression.

RESULTS

We report here that pentose phosphate pathway (PPP) metabolites accumulate remarkably during chronic but not acute glucose treatment, indicating altered processing of glucose through the pentose phosphate pathway. Subsequent functional studies in INS-1E cells and human islets revealed that a disturbance in this pathway contributes to decreases in insulin gene expression and a lack of glucose-stimulated insulin secretion. These effects were found to depend on the activation of extracellular-regulated-kinase (ERK1/2). Long-term inhibition of 6-phosphogluconic acid dehydrogenase resulted in accumulation of PPP metabolites, induced ERK1/2 activation independently of high glucose and impaired beta cell function. In turn, inhibition of ERK1/2 overstimulation during chronic glucose exposure partly inhibited metabolite accumulation and restored beta cell function.

CONCLUSIONS/INTERPRETATION

Based on unbiased metabolite analyses, the data presented here provide novel targets, namely the inhibition of PPP metabolite accumulation towards the therapeutic goal to preserve and potentially improve beta cell function in diabetes.

Annual change in insulin sensitivity

The incidence of both type 2 diabetes and cardiac events is reported to be higher during winter, indicating a putative annual periodic change in insulin sensitivity (IS). Annual differences in IS - quantified as HOMA-%S and Matsuda-Sensitivity Index - were analyzed using a cosine wave-fitting algorithm in a cross-sectional study group including 2 385 participants. Additionally, semi-annual differences in IS were compared. We found periodicity for HOMA-%S and Matsuda-Sensitivity Index (p=0.02 or 0.006), which was strengthened after restriction to participants without diabetes (p=0.009 or 0.004). The rhythm amplitude of 0.08 indicated moderate changes in IS throughout the year. IS was significantly higher when participants were enrolled during the second vs. the first half of the year (HOMA-%S 112.0±3.0% vs. 97.4±2.4%, p<0.001). The impact of the half-year on IS, which remained significant after adjustment for confounders, was again moderate and explained only 0.5% of the variation. IS showed a significant moderate annual periodicity, which may affect the interpretation of studies reporting small changes in IS.

Design and cohort description of the InterAct Project: an examination of the interaction of genetic and lifestyle factors on the incidence of type 2 diabetes in the EPIC Study

AIMS/HYPOTHESIS

Studying gene-lifestyle interaction may help to identify lifestyle factors that modify genetic susceptibility and uncover genetic loci exerting important subgroup effects. Adequately powered studies with prospective, unbiased, standardised assessment of key behavioural factors for gene-lifestyle studies are lacking. This case-cohort study aims to investigate how genetic and potentially modifiable lifestyle and behavioural factors, particularly diet and physical activity, interact in their influence on the risk of developing type 2 diabetes.

METHODS

Incident cases of type 2 diabetes occurring in European Prospective Investigation into Cancer and Nutrition (EPIC) cohorts between 1991 and 2007 from eight of the ten EPIC countries were ascertained and verified. Prentice-weighted Cox regression and random-effects meta-analyses were used to investigate differences in diabetes incidence by age and sex.

RESULTS

A total of 12,403 verified incident cases of type 2 diabetes occurred during 3.99 million person-years of follow-up of 340,234 EPIC participants eligible for InterAct. We defined a centre-stratified subcohort of 16,154 individuals for comparative analyses. Individuals with incident diabetes who were randomly selected into the subcohort (n = 778) were included as cases in the analyses. All prevalent diabetes cases were excluded from the study. InterAct cases were followed-up for an average of 6.9 years; 49.7% were men. Mean baseline age and age at diagnosis were 55.6 and 62.5 years, mean BMI and waist circumference values were 29.4 kg/m(2) and 102.7 cm in men, and 30.1 kg/m(2) and 92.8 cm in women, respectively. Risk of type 2 diabetes increased linearly with age, with an overall HR of 1.56 (95% CI 1.48-1.64) for a 10 year age difference, adjusted for sex. A male excess in the risk of incident diabetes was consistently observed across all countries, with a pooled HR of 1.51 (95% CI 1.39-1.64), adjusted for age.

CONCLUSIONS/INTERPRETATION

InterAct is a large, well-powered, prospective study that will inform our understanding of the interplay between genes and lifestyle factors on the risk of type 2 diabetes development.

Effects of hyperlipidaemia on glucocorticoid metabolism: results of a randomized controlled trial in healthy young women

OBJECTIVE

It is well established that the hypothalamic-pituitary-adrenal (HPA) axis is altered in obese individuals. Hyperlipidaemia with elevated levels of free fatty acids (FFAs) is also frequently seen in obesity and in the metabolic syndrome. We hypothesized, therefore, that hyperlipidaemia may alter the activity of the HPA axis.

PATIENTS AND METHODS

The effects of hyperlipidaemia, including increased circulating FFAs, on ACTH secretion and cortisol metabolism were analysed in 13 healthy young women during the early follicular phase of two subsequent cycles. We administered a 20% lipid/heparin (LHI) or a saline/heparin infusion (SHI) using a crossover design in random order for 330 min. A detailed characterization of glucocorticoid metabolism was performed by measurement of plasma ACTH, cortisol and urinary excretion rates of adrenal glucocorticoids and the glucocorticoid metabolites.

RESULTS

We observed that LHI-induced hyperlipidaemia elevated serum cortisol levels compared to SHI. No changes in plasma ACTH levels, daily urinary excretion rates of adrenal glucocorticoids, glucocorticoid precursors/metabolites and the calculated activities of the 5α-reductase, 3β-hydroxysteroid dehydrogenase (HSD), 11-, 17-, 21-hydroxylase and 11β-HSD 1 or 2 were found.

CONCLUSION

Our randomized controlled trial suggests that the adrenal sensitivity to ACTH may be enhanced by LHI-induced hyperlipidaemia in normal-weight healthy young women. This effect might contribute to the disturbances of the HPA axis described in women with abdominal obesity and impaired lipid metabolism.

T3/rT3-ratio is associated with insulin resistance independent of TSH

Thyroid dysfunction has been shown to be associated with insulin resistance (IR). This may involve peripheral thyroid hormone metabolism, which is assumed to be reflected by the ratio triiodothyronine/reverse triiodothyronine (T3/rT3-ratio). To explore a potential association between the T3/rT3-ratio and IR we investigated pairs which differed in IR, but were matched by sex, age, body mass index (BMI), and thyroid stimulating hormone (TSH). For this purpose, matched pair analyses were embedded into a cross sectional study group. 22 pairs were matched from either the first or the third tertile of HOMA%S of a cohort of 353 euthyroid subjects with normal glucose metabolism who did not take any medication. The T3/rT3-ratio was compared in the matched pairs. The T3/rT3-ratio was significantly increased in the insulin resistant subjects compared to their insulin sensitive partners (8.78 ± 0.47 vs. 7.33 ± 0.33, p=0.019). Furthermore the T3/rT3-ratio was lower in men compared to women (p for the within-subject effect=0.046) both in the insulin sensitive and the insulin resistant subjects. Here we show that the T3/rT3-ratio, which is supposed to reflect the tissue thyroid hormone metabolism, is significantly increased in insulin resistant subjects. This further supports a link between thyroid function and IR.

Improved insulin sensitivity, preserved beta cell function and improved whole-body glucose metabolism after low-dose growth hormone replacement therapy in adults with severe growth hormone deficiency: a pilot study

AIMS/HYPOTHESIS

Growth hormone-deficient patients show deterioration of insulin sensitivity and beta cell function. High-dose growth hormone treatment often induces further impairment of insulin sensitivity, leading to an increase in insulin and glucose levels or even, in cases of preexisting beta cell defect, to overt diabetes. However, low-dose treatment may improve insulin sensitivity, although data in humans with detailed metabolic phenotyping are as yet not available. We postulated that long-term low-dose growth hormone replacement, restoring IGF-1 to the low-normal range, might beneficially affect glucose metabolism.

METHODS

We studied prospectively the metabolic responses to 24 and 48 weeks of growth hormone treatment in a small group of six adults with severe growth hormone deficiency (four men, two women; age 40-59 years; BMI 30.2 +/- 1 kg/m(2); mean growth hormone dose 0.3 +/- 0.04 mg/day). All participants underwent an oral glucose tolerance test, euglycaemic-hyperinsulinaemic clamp and hyperglycaemic-hyperinsulinaemic clamp plus i.v. L: -arginine on three occasions. Insulin sensitivity was measured by calculating the M value during the steady state of the euglycaemic-hyperinsulinaemic clamp. Insulin secretion and clearance were estimated from AUC(C-peptide), AUC(insulin) and their ratio at each phase of the hyperglycaemic-hyperinsulinaemic clamp.

RESULTS

Growth hormone significantly improved insulin sensitivity (M value 13.8 +/- 2.6 [baseline] vs 19.6 +/- 2.6 [24 weeks] and 23.7 +/- 1.9 [48 weeks] micromol kg(-1) min(-1); p < 0.01). Although the insulin response to glucose and arginine decreased slightly, the disposition index, integrating insulin sensitivity and secretion, significantly increased (p < 0.01), indicating an improvement in whole-body glucose metabolism. Insulin clearance was not affected during treatment (p > 0.05).

CONCLUSIONS/INTERPRETATION

Our data indicate that long-term low-dose growth hormone treatment may improve insulin sensitivity and whole-body glucose metabolism in adults with severe growth hormone-deficiency.