Natalia Rudovich

Introduction: Insulin resistance (IR), a pathological state of low sensitivity to insulin in humans and animlas, is closely associated with type 2 diabetes mellitus, obesity and cardiovasculare dieseas. IR can be quantified using detailed protocols, such as the euglycemic-hyperinsulinemic clamp (EC) technique and the intravenous glucose tolerance test, or based on indices derived from the oral glucose tolerance test. Although these indices showed greater association with the incidence of diabetes, they allow no personalized estimation of the individual risk and cannot be used for monitoring of the individual changes in the insulin resistance. The modification of nutritional pattern is one of the first steps of prevention the IR and associated diseases. Diets with increased intake of branched chain amino acid lead to increase in IR in animals and human, possibly via disruption of insulin signaling in skeletal muscle. Here we aimed to investigate the changes in the plasma metabolome during constant insulin infusion. Additionally, the correlations between baseline concentrations of metabolites and changes of IR, which was measured in the EC-experiments, after high-protein and control diet were studied. Methods: In the first study (NCT00774488), middle-aged healthy obese subjects (n=14) underwent saline infusion and/or EC at a steady-state capillary plasma glucose concentration of 4.4 mmol/l. Plasma metabolites were measured using time-of-flight gas chromatography-mass spectrometry (GC-TOF/MS) technique. In the second study (NCT00579657), a randomized, controlled nutritional intervention (18-weeks) was conducted in 72 non-diabetic participants (overweight/obese: 29/43) with at least one further risk factor of metabolic syndrome. Participants were group-matched and allocated to 4 isoenergetic supplemented diets: control; high cereal-fiber; high-protein; or moderately increased cereal-fiber and protein (MIX). Whole-body IR was measured using EC. Plasma metabolome and IR were studied at 0, 6 and 18-weeks. Results: Eight metabolites: altrose, asparagine, glycerol-2-phosphate, gulose, heptadecanoic acid, phenylalanine, pyroglutamate and talose correlated with high-protein diet-induced changes in IR and significantly changed during EC. Conclusions: Multimarker strategy with use of plasma metabolic profiling appears to be a useful tool for both the assessment of IR and the ‘metabolic signature of insulin effects’ (i.e. doping control of elite athletes) in humans.

Acarbose, an alpha-glucosidase inhibitor, unexpectedly reduced the incidence of hypertension and cardiovascular endpoints in the STOP-NIDDM study. Based on the growing evidence of a link between vasoregulatory peptides and metabolic traits, we hypothesized that changes of the Glycemic Index by acarbose may modulate vasoregulatory peptide levels via regulation of postprandial metabolism. Subjects with type 2 diabetes and with metabolic syndrome were treated with acarbose (12 weeks, 300mg/d) in a double-blind, placebo-controlled, cross-over intervention. Changes in fasting and postprandial levels of midregional pro-atrial natriuretic peptide (MR-proANP), C-terminal pro-endothelin-1 (CT-proET-1) and midregional pro-adrenomedullin (MR-proADM), WNT1 Inducible Signaling Pathway Protein 1 (WISP1) as well as fasting and postprandial glucose/insulin levels in the liquid meal test were assessed. Acarbose strongly decreased postprandial insulin concentrations in subjects with metabolic syndrome (P=0.004), and postprandial glucose excursions in both groups. Postprandial MR-proANP and CT-proET-1 levels increased after acarbose treatment (P<0.01 and P<0.05, respectively) in subjects with metabolic syndrome only. No effect of acarbose treatment on MR-prADM was observed in both groups. All three peptides were correlated with each over, but neither with insulin sensitivity in euglycemic clamps, nor with adiponectin levels. WISP1 decreased after acarbose treatment in subjects with metabolic syndrome. Plasma MR- proANP and CT-proET-1 concentrations, but not MR-prADM concentrations, were affected by treatment with acarbose over 12 weeks. Our findings provide new possible mechanisms of acarbose action in diabetes and metabolic syndrome.

GLP-1 receptor agonists have antihypertensive properties, explained via release of atrial natriuretic peptide (ANP) as shown in mice (1). Whether GLP-1 directly interacts with the natriuretic peptide system in humans was studied in a single report (2). Here, we studied interaction of two major incretins, glucose-dependent insulinotropic peptide (GIP) and GLP-1, both administered exogenously, with ANP in patients with type 2 diabetes (nine men and three women, 61 ± 10 years, BMI 30.0 ± 3.7 kg/m2, HbA1c 7.3 ± 1.5%). Placebo (vehicle: 0.9% NaCl with 1% human serum albumin), GIP (4 pmol · kg−1 · min−1), GLP-1(7–36)-amide (1.2 pmol · kg−1 · min−1), or a combination of both hormones were infused over 360 min on different days in randomized order (3). Additionally, eight male overweight subjects with normal glucose tolerance (49.9 ± 3.2 years, BMI 32.9 ± 0.7 kg/m2) were given GIP infusion (2 pmol · kg−1 · min−1) and placebo (isotonic saline) infusion for 240 min (4). In cohort I, intact, biologically active GIP and GLP-1 were measured as described previously (3). In cohort II, total GIP was determined by commercial ELISA kit (Linco Research, St. Charles, MO). Midregional pro-ANP (MR-proANP) was measured with an immunoassay (MR-proANP LIA; B.R.A.H.M.S GmbH, Hennigsdorf, Germany). In subjects with type 2 diabetes, exogenous GIP elevated the total concentrations of GIP …

WISP1 (Wnt1-inducible signaling pathway protein-1, also known as CCN4) is a member of the secreted extracellular matrix–associated proteins of the CCN family and a target gene of the Wingless-type (WNT) signaling pathway. Growing evidence links the WNT signaling pathway to the regulation of adipogenesis and low-grade inflammation in obesity. We aimed to validate WISP1 as a novel adipokine. Human adipocyte differentiation was associated with increased WISP1 expression and secretion. Stimulation of human macrophages with WISP1 led to a proinflammatory response. Circulating WISP1 and WISP1 subcutaneous adipose tissue expression were regulated by weight changes in humans and mice. WISP1 expression in visceral and subcutaneous fat tissue was associated with markers of insulin resistance and inflammation in glucose-tolerant subjects. In patients with nonalcoholic fatty liver disease, we found no correlation among disease activity score, liver fat content, and WISP1 expression. Insulin regulated WISP1 expression in adipocytes in vitro but had no acute effect on WISP1 gene expression in subcutaneous fat tissue in overweight subjects who had undergone hyperinsulinemic clamp experiments. The data suggest that WISP1 may play a role in linking obesity to inflammation and insulin resistance and could be a novel therapeutic target for obesity.

OBJECTIVE Insulin clearance is decreased in type 2 diabetes mellitus (T2DM) for unknown reasons. Subjects with metabolic syndrome are hyperinsulinemic and have an increased risk of T2DM. We aimed to investigate the relationship between hepatic insulin clearance (HIC) and different components of metabolic syndrome and tested the hypothesis that HIC may predict the risk of metabolic syndrome. RESEARCH DESIGN AND METHODS Individuals without diabetes from the Metabolic Syndrome Berlin Brandenburg (MeSyBePo) study (800 subjects with the baseline examination and 189 subjects from the MeSyBePo recall study) underwent an oral glucose tolerance test (OGTT) with assessment of insulin secretion (insulin secretion rate [ISR]) and insulin sensitivity. Two indices of HIC were calculated. RESULTS Both HIC indices showed lower values in subjects with metabolic syndrome (P < 0.001) at baseline. HIC indices correlate inversely with waist circumference, diastolic blood pressure, fasting glucose, triglycerides, and OGTT-derived insulin secretion index. During a mean follow-up of 5.1 ± 0.9 years, 47 individuals developed metabolic syndrome and 33 subjects progressed to impaired glucose metabolism. Both indices of HIC showed a trend of an association with increased risk of metabolic syndrome (HIC_C-peptide odds ratio 1.13 [95% CI 0.97–1.31], P = 0.12, and HIC_ISR 1.38 [0.88–2.17], P = 0.16) and impaired glucose metabolism (HIC_C-peptide 1.12 [0.92–1.36], P = 0.26, and HIC_ISR 1.31 [0.74–2.33] P = 0.36), although point estimates reached no statistical significance. CONCLUSIONS HIC was associated with different components of metabolic syndrome and markers of insulin secretion and insulin sensitivity. Decreased HIC may represent a novel pathophysiological mechanism of the metabolic syndrome, which may be used additionally for early identification of high-risk subjects.

The gastric peptide ghrelin promotes energy storage, appetite, and food intake. Nutrient intake strongly suppresses circulating ghrelin via molecular mechanisms possibly involving insulin and gastrointestinal hormones. On the basis of the growing evidence that glucose-dependent insulinotropic polypeptide (GIP) is involved in the control of fuel metabolism, we hypothesized that GIP and/or insulin, directly or via changes in plasma metabolites, might affect circulating ghrelin. Fourteen obese subjects were infused with GIP (2.0 pmol·kg⁻¹·min⁻¹) or placebo in the fasting state during either euglycemic hyperinsulinemic (EC) or hyperglycemic hyperinsulinemic clamps (HC). Apart from analysis of plasma ghrelin and insulin levels, GC-TOF/MS analysis was applied to create a hormone-metabolite network for each experiment. The GIP and insulin effects on circulating ghrelin were analyzed within the framework of those networks. In the HC, ghrelin levels decreased in the absence (19.2% vs. baseline, P = 0.028) as well as in the presence of GIP (33.8%, P = 0.018). Ghrelin levels were significantly lower during HC with GIP than with placebo, despite insulin levels not differing significantly. In the GIP network combining data on GIP-infusion, EC+GIP and HC+GIP experiments, ghrelin was integrated into hormone-metabolite networks through a connection to a group of long-chain fatty acids. In contrast, ghrelin was excluded from the network of experiments without GIP. GIP decreased circulating ghrelin and might have affected the ghrelin system via modification of long-chain fatty acid pools. These observations were independent of insulin and offer potential mechanistic underpinnings for the involvement of GIP in systemic control of energy metabolism.

Background: This study assessed the effect of postprandial glucose reduction by acarbose on insulin sensitivity and biomarkers of systemic inflammation. Methods: This was a single-center, double-blind, randomized, placebo-controlled, crossover study n = 24). Conclusions: Reduction of the glycemic load by acarbose decreased fasting levels of proinsulin but had no effect on adiponectin and whole-body insulin sensitivity as well as biomarkers reflecting inflammation. The preventive effects of acarbose on type 2 diabetes mellitus and cardiovascular risk need further investigation and cannot be explained by changes of insulin resistance and inflammatory biomarkers.

Diets high in cereal-fiber (HCF) have been shown to improve whole-body insulin sensitivity. In search for potential mechanisms we hypothesized that a supplemented HCF-diet influences the composition of the human gut microbiota and/or biomarkers of colonic carbohydrate fermentation. We performed a randomized controlled 18-week intervention in group-matched overweight participants. Fecal samples of 69 participants receiving isoenergetic HCF (cereal-fiber 43 g/day), or control (cereal-fiber 14 g/day), or high-protein (HP, 28% of energy-intake, cereal-fiber 14 g/day), or moderately high cereal fiber/protein diets (MIX; protein 23% of energy-intake, cereal-fiber 26 g/day) with comparable fat contents were investigated for diet-induced changes of dominant groups of the gut microbiota, and of fecal short-chain fatty-acids (SCFA) including several of their proposed targets, after 0, 6, and 18-weeks of dietary intervention. In vitro fermentation of the cereal fiber extracts as used in the HCF and MIX diets was analyzed using gas chromatography. Diet-induced effects on whole-body insulin-sensitivity were measured using euglycaemic-hyperinsulinemic clamps and re-calculated in the here investigated subset of n = 69 participants that provided sufficient fecal samples on all study days. Gut microbiota groups and biomarkers of colonic fermentation were comparable between groups at baseline (week 0). No diet-induced differences were detected between groups during this isoenergetic intervention, neither in the full model nor in uncorrected subgroup-analyses. The cereal-fiber extract as used for preparation of the supplements in the HCF and MIX groups did not support in vitro fermentation. Fecal acetate, propionate, and butyrate concentrations remained unchanged, as well as potential targets of increased SCFA, whereas valerate increased after 6-weeks in the HP-group only (p = 0.037). Insulin-sensitivity significantly increased in the HCF-group from week-6 (baseline M-value 3.8 ± 0.4 vs 4.3 ± 0.4 mg·kg^-1·min^-1, p = 0.015; full model 0-18-weeks, treatment-x-time interaction, p = 0.046). Changes in the composition of the gut microbiota and/or markers of colonic carbohydrate fermentation did not contribute explaining the observed early onset and significant improvement of whole-body insulin sensitivity with the here investigated HCF-diet. This trial was registered at http://www.clinicaltrials.gov as NCT00579657

Background: A progressive weight gain is associated with various pharmacological options improving glycemic control in type 2 diabetes mellitus (T2DM). Ghrelin has been implicated in the regulation of feeding behavior and energy balance in humans. Based on evidence that functional ATP-sensitive channels are present in ghrelin-producing cells, we hypothesized that meglitinides may affect circulating ghrelin levels in subjects with type 2 diabetes. Methods: In a single-blinded randomized three-period crossover study (n = 20), repaglinide or nateglinide was given in combination with metformin for two treatment periods over a 1-week period, respectively, separated by a 1-week treatment with placebo. Liquid meal challenge tests (LMCTs) with single preprandial doses of repaglinide (2 mg), nateglinide (120 mg), or placebo were performed at the end of each treatment period. Ten control subjects without diabetes underwent a single LMCT without any medication. Results: Fasting ghrelin concentrations were not different between all treatments and between patients with diabetes and control subjects. Subjects with T2DM treated with placebo showed no suppression of ghrelin in the LMCT. After administration of meglitinides a nadir of serum ghrelin was observed at 60 min (8.6% of baseline [P = 0.038] for repaglinide and 7.5% of baseline [P = 0.081] for nateglinide), which was similar to the secretion pattern seen in control subjects. No correlations between postprandial insulin or glucose levels and circulating ghrelin concentrations were observed. Conclusions: Treatment with meglitinides reconstructed postprandial ghrelin secretion patterns to those of controls without diabetes. This observation may help to improve the control of feeding behavior in patients with T2DM.