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Rainer Lehmann,
Holger Franken,
Sascha Dammeier,
Lars Rosenbaum,
Konstantinos Kantartzis, Andreas Peter,
Andreas Zell,
Patrick Adam,
Jia Li,
Guowang Xu, [......],
Jürgen Machann,
Fritz Schick,
Martin Hrabé de Angelis,
Matthias Schwab,
Harald Staiger,
Erwin Schleicher,
Amalia Gastaldelli,
Andreas Fritsche,
Hans-Ulrich Häring,
Norbert Stefan
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ABSTRACT: OBJECTIVE
Nonalcoholic fatty liver (NAFL) is thought to contribute to insulin resistance and its metabolic complications. However, some individuals with NAFL remain insulin sensitive. Mechanisms involved in the susceptibility to develop insulin resistance in humans with NAFL are largely unknown. We investigated circulating markers and mechanisms of a metabolically benign and malignant NAFL by applying a metabolomic approach.RESEARCH DESIGN AND METHODSA total of 265 metabolites were analyzed before and after a 9-month lifestyle intervention in plasma from 20 insulin-sensitive and 20 insulin-resistant subjects with NAFL. The relevant plasma metabolites were then tested for relationships with insulin sensitivity in 17 subjects without NAFL and in plasma from 29 subjects with liver tissue samples.RESULTSThe best separation of the insulin-sensitive from the insulin-resistant NAFL group was achieved by a metabolite pattern including the branched-chain amino acids leucine and isoleucine, ornithine, the acylcarnitines C3:0-, C16:0-, and C18:0-carnitine, and lysophosphatidylcholine (lyso-PC) C16:0 (area under the ROC curve, 0.77 [P = 0.00023] at baseline and 0.80 [P = 0.000019] at follow-up). Among the individual metabolites, predominantly higher levels of lyso-PC C16:0, both at baseline (P = 0.0039) and at follow-up (P = 0.001), were found in the insulin-sensitive compared with the insulin-resistant subjects. In the non-NAFL groups, no differences in lyso-PC C16:0 levels were found between the insulin-sensitive and insulin-resistant subjects, and these relationships were replicated in plasma from subjects with liver tissue samples.CONCLUSIONS
From a plasma metabolomic pattern, particularly lyso-PCs are able to separate metabolically benign from malignant NAFL in humans and may highlight important pathways in the pathogenesis of fatty liver-induced insulin resistance.
Diabetes care 03/2013; · 8.09 Impact Factor
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Peiyuan Yin, Andreas Peter,
Holger Franken,
Xinjie Zhao,
Sabine S Neukamm,
Lars Rosenbaum,
Marianna Lucio,
Andreas Zell,
Hans-Ulrich Häring,
Guowang Xu,
Rainer Lehmann
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ABSTRACT: BACKGROUND: Metabolomics is a powerful tool that is increasingly used in clinical research. Although excellent sample quality is essential, it can easily be compromised by undetected preanalytical errors. We set out to identify critical preanalytical steps and biomarkers that reflect preanalytical inaccuracies.METHODS: We systematically investigated the effects of preanalytical variables (blood collection tubes, hemolysis, temperature and time before further processing, and number of freeze-thaw cycles) on metabolomics studies of clinical blood and plasma samples using a nontargeted LC-MS approach.RESULTS: Serum and heparinate blood collection tubes led to chemical noise in the mass spectra. Distinct, significant changes of 64 features in the EDTA-plasma metabolome were detected when blood was exposed to room temperature for 2, 4, 8, and 24 h. The resulting pattern was characterized by increases in hypoxanthine and sphingosine 1-phosphate (800% and 380%, respectively, at 2 h). In contrast, the plasma metabolome was stable for up to 4 h when EDTA blood samples were immediately placed in iced water. Hemolysis also caused numerous changes in the metabolic profile. Unexpectedly, up to 4 freeze-thaw cycles only slightly changed the EDTA-plasma metabolome, but increased the individual variability.CONCLUSIONS: Nontargeted metabolomics investigations led to the following recommendations for the preanalytical phase: test the blood collection tubes, avoid hemolysis, place whole blood immediately in ice water, use EDTA plasma, and preferably use nonrefrozen biobank samples. To exclude outliers due to preanalytical errors, inspect the biomarker signal intensities reflecting systematic as well as accidental and preanalytical inaccuracies before processing the bioinformatics data.
Clinical Chemistry 02/2013; · 7.91 Impact Factor
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Robert Wagner,
Gabriele Kaiser,
Felicia Gerst,
Elisabeth Christiansen,
Maria Elisabeth Due-Hansen,
Manuel Grundmann,
Fausto Machicao, Andreas Peter,
Evi Kostenis,
Trond Ulven,
Andreas Fritsche,
Hans-Ulrich Häring,
Susanne Ullrich
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ABSTRACT: The role of free fatty acid receptor 1 (FFAR1/GPR40) in glucose homeostasis is still incompletely understood. Small receptor agonists stimulating insulin secretion are under investigation for the treatment of type 2 diabetes. Surprisingly, genome-wide association studies did not discover diabetes risk variants in FFAR1. We reevaluated the role of FFAR1 in insulin secretion using a specific agonist, FFAR1-knockout mice and human islets. Nondiabetic individuals were metabolically phenotyped and genotyped. In vitro experiments indicated that palmitate and a specific FFAR1-agonist, TUG-469, stimulate glucose-induced insulin secretion through FFAR1. The pro-apoptotic effect of chronic exposure of beta-cells to palmitate was independent of FFAR1. TUG-469 was protective, while inhibition of FFAR1 promoted apoptosis. In accordance with the pro-apoptotic effect of palmitate, in vivo crosssectional observations demonstrated a negative association between fasting free fatty acids (NEFA) and insulin secretion. As NEFA stimulate secretion through FFAR1, we examined the interaction of genetic variation in FFAR1 with NEFA and insulin secretion. The inverse association of NEFA and secretion was modulated by rs1573611 and became steeper for carriers of the minor allele. In conclusion, FFAR1 agonists support beta-cell function, but variation in FFAR1 influences NEFA effects on insulin secretion and could, therefore, affect therapeutic efficacy of FFAR1-agonists.
Diabetes 02/2013; · 8.29 Impact Factor
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Günther Silbernagel,
Marketa Kovarova,
Alexander Cegan,
Jürgen Machann,
Fritz Schick,
Rainer Lehmann,
Hans-Ulrich Häring,
Norbert Stefan,
Erwin Schleicher,
Andreas Fritsche, Andreas Peter
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ABSTRACT: Context:Increased hepatic de novo lipogenesis (DNL) in response to dietary sugar is implicated in the pathophysiology of fatty liver. Saturated fatty acids are the product of DNL and exert lipotoxic effects that promote liver fat accumulation. Desaturation of fatty acids by stearoyl-CoA desaturase 1 (SCD1) can prevent these deleterious effects. Here we investigated whether DNL and SCD1 are activated in parallel by dietary sugar and influence liver fat accumulation.Methods:In 20 healthy subjects (eight females and 12 males, aged 30.5 ± 2.0 yr, body mass index 25.9 ± 0.5 kg/m(2)) who received a 4-wk lipogenic diet supplemented with 150 g/d of monosaccharides, hepatic SCD1 activity and DNL were determined using validated fatty acid ratios (16:1n-7/16:0; 16:0/18:2n-6) in very low-density lipoprotein triglycerides. Liver fat content was measured by localized (1)H-magnetic resonance spectroscopy.Results:At baseline, liver fat content was positively associated with the DNL (r = 0.54, P = 0.01) but not the SCD1 activity index (r = 0.16, P = 0.49). Dietary sugar supplementation increased liver fat content and DNL and SCD1 activity indices (+33, +19, and +8%, respectively). The increase of the DNL index was strongly related to the changes in liver fat content during the sugar supplementation (r = 0.75, P = 0.0001) but showed no association with changes in the SCD1 activity (P > 0.35). After the monosaccharide supplementation, the DNL index was still positively associated with liver fat content (r = 0.52, P = 0.02), whereas SCD1 activity showed a strong negative correlation with liver fat content (r = -0.63, P = 0.002).Conclusions:DNL is closely linked with hepatic steatosis under dietary conditions rich in monosaccharides. Our data suggest that the individual hepatic SCD1 activity is a determinant of liver fat accumulation under lipogenic dietary conditions.
The Journal of clinical endocrinology and metabolism 09/2012; · 6.50 Impact Factor
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ABSTRACT: Impaired insulin action in the brain represents an early step in the progression toward type 2 diabetes, and elevated levels of saturated free fatty acids are known to impair insulin action in prediabetic subjects. One potential mediator that links fatty acids to inflammation and insulin resistance is the Toll-like receptor (TLR) family. Therefore, C3H/HeJ/TLR2-KO (TLR2/4-deficient) mice were fed a high-fat diet (HFD), and insulin action in the brain as well as cortical and locomotor activity was analyzed by using telemetric implants. TLR2/4-deficient mice were protected from HFD-induced glucose intolerance and insulin resistance in the brain and displayed an improvement in cortical and locomotor activity that was not observed in C3H/HeJ mice. Sleep recordings revealed a 42% increase in rapid eye movement sleep in the deficient mice during daytime, and these mice spent 41% more time awake during the night period. Treatment of control mice with a neutralizing IL-6 antibody improved insulin action in the brain as well as cortical activity and diminished osteopontin protein to levels of the TLR2/4-deficient mice. Together, our data suggest that the lack of functional TLR2/4 protects mice from a fat-mediated impairment in insulin action, brain activity, locomotion, and sleep architecture by an IL-6/osteopontin-dependent mechanism.
The FASEB Journal 01/2012; 26(5):1799-809. · 5.71 Impact Factor
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Clinical Chemistry 05/2011; 57(5):670-3. · 7.91 Impact Factor
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Andreas Peter,
Norbert Stefan,
Alexander Cegan,
Mareike Walenta,
Silvia Wagner,
Alfred Königsrainer,
Ingmar Königsrainer,
Fausto Machicao,
Fritz Schick,
Hans-Ulrich Häring,
Erwin Schleicher
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ABSTRACT: Glucokinase (GCK) phosphorylates glucose to form glucose 6-phosphate and thereby regulates hepatic glucose disposal and activates hepatic lipogenesis. Hepatic GCK activity is regulated on the level of GCK mRNA expression and by the inhibitory glucokinase regulatory protein. In this study, we aimed to investigate the relation between GCK mRNA expression and markers of lipogenesis as well as liver fat content in human liver biopsies. Additionally, we investigated whether genetic variation in the liver specific GCK promoter determines liver fat content in humans.
Hepatic mRNA expression and liver triglyceride content was analyzed in 50 human liver biopsies. In a second cohort of 330 individuals, liver fat was precisely measured by 1H magnetic resonance spectroscopy.
Hepatic GCK mRNA expression is associated with triglyceride content in human liver biopsies (r = 0.50, P = 0.0002). Furthermore, hepatic GCK mRNA expression is associated with lipogenic gene expression (fatty acid synthase, r = 0.49, P = 0.0003; acetyl-coenzyme A carboxylase-α, r = 0.44, P = 0.0015, and acetyl-coenzyme A carboxylase-β, r = 0.48, P = 0.0004) and the de novo lipogenesis index (r = 0.36, P = 0.01). In support of these findings, the single-nucleotide polymorphism rs2041547 in the liver-specific GCK promoter is associated with liver fat content in prediabetic individuals (P = 0.047).
In this study, we demonstrate for the first time that GCK mRNA expression is associated with markers of de novo lipogenesis and liver triglyceride content in humans. This suggests that increased GCK activity may induce fatty liver and its metabolic and hepatic consequences in humans. Thus, the widely used approach to nonspecifically activate β-cell and hepatic GCK to treat diabetes mellitus is therefore questionable and may cause serious side effects.
The Journal of clinical endocrinology and metabolism 04/2011; 96(7):E1126-30. · 6.50 Impact Factor
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Stefan Z Lutz,
Anita M Hennige,
Susanne Feil, Andreas Peter,
Andrea Gerling,
Jürgen Machann,
Stefan M Kröber,
Michaela Rath,
Annette Schürmann,
Cora Weigert,
Hans-Ulrich Häring,
Robert Feil
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ABSTRACT: The nitric oxide/cGMP/cGMP-dependent protein kinase type I (cGKI) signaling pathway regulates cell functions that play a pivotal role in the pathogenesis of type 2 diabetes. However, the impact of a dysfunction of this pathway for glucose metabolism in vivo is unknown.
The expression of cGKI in tissues relevant to insulin action was analyzed by immunohistochemistry. The metabolic consequences of a genetic deletion of cGKI were studied in mice that express cGKI selectively in smooth muscle but not in other cell types (cGKI-SM mice).
In wild-type mice, cGKI protein was detected in hepatic stellate cells, but not in hepatocytes, skeletal muscle, fat cells, or pancreatic β-cells. Compared with control animals, cGKI-SM mice had higher energy expenditure in the light phase associated with lower body weight and fat mass and increased insulin sensitivity. Mutant mice also showed higher fasting glucose levels, whereas insulin levels and intraperitoneal glucose tolerance test results were similar to those in control animals. Interleukin (IL)-6 signaling was strongly activated in the liver of cGKI-SM mice as demonstrated by increased levels of IL-6, phospho-signal transducer and activator of transcription 3 (Tyr 705), suppressor of cytokine signaling-3, and serum amyloid A2. Insulin-stimulated tyrosine phosphorylation of the insulin receptor in the liver was impaired in cGKI-SM mice. The fraction of Mac-2-positive macrophages in the liver was significantly higher in cGKI-SM mice than in control mice. In contrast with cGKI-SM mice, conditional knockout mice lacking cGKI only in the nervous system were normal with respect to body weight, energy expenditure, fasting glucose, IL-6, and insulin action in the liver.
Genetic deletion of cGKI in non-neuronal cells results in a complex metabolic phenotype, including liver inflammation and fasting hyperglycemia. Loss of cGKI in hepatic stellate cells may affect liver metabolism via a paracrine mechanism that involves enhanced macrophage infiltration and IL-6 signaling.
Diabetes 04/2011; 60(5):1566-76. · 8.29 Impact Factor
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ABSTRACT: Saturated long-chain fatty acids (SFAs) exert unfavourable metabolic effects (lipotoxicity) and induce apoptotic cell death (lipoapoptosis) in certain cell-types. Their contribution to inflammatory cell responses is unclear. We studied the expression of 113 inflammatory genes in human coronary artery endothelial cells (hCAECs) and their regulation by SFAs and unsaturated long-chain fatty acids (UFAs). Gene regulation in hCAECs was assessed with macroarrays, real-time RT-PCR and immunoblotting. Participation of the transcription factor NFκB and the stress kinases JNK and p38 MAPK in gene-regulatory events was examined with pharmacological inhibitors. Based on macroarray data, 59 inflammatory genes were expressed in hCAECs, 14 were regulated by the SFA palmitate. SFA-triggered induction of IL1A, IL6, IL8, CXCL2, CXCL3, CCL20, SPP1 and CEBPB was confirmed by RT-PCR or immunoblotting. All gene inductions were SFA-specific. Using inhibitor SN50, palmitate-induced expression of IL8, CXCL3 and CCL20 was NFκB-dependent (all p<0.05). Furthermore, JNK was involved in palmitate-induced expression of IL1A, IL8, CXCL3, SPP1 and CEBPB as determined with inhibitor SP600125 (all p<0.05). Finally, the effectiveness of the tested fatty acids to induce inflammatory genes was closely reflected by their effectiveness to trigger endoplasmic reticulum stress. In conclusion, hCAECs express a large panel of inflammatory genes with a series of genes being regulated by palmitate and stearate, but not by UFAs. Thus, SFAs represent potential contributors to vascular inflammation.
Microvascular Research 01/2011; 81(1):52-9. · 2.83 Impact Factor
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ABSTRACT: In the human brain, there are at least as many astrocytes as neurons. Astrocytes are known to modulate neuronal function in several ways. Thus, they may also contribute to cerebral insulin actions. Therefore, we examined whether primary human astrocytes are insulin-responsive and whether their metabolic functions are affected by the hormone.
Commercially available Normal Human Astrocytes were grown in the recommended medium. Major players in the insulin signaling pathway were detected by real-time RT-PCR and Western blotting. Phosphorylation events were detected by phospho-specific antibodies. Glucose uptake and glycogen synthesis were assessed using radio-labeled glucose. Glycogen content was assessed by histochemistry. Lactate levels were measured enzymatically. Cell proliferation was assessed by WST-1 assay.
We detected expression of key proteins for insulin signaling, such as insulin receptor β-subunit, insulin receptor substrat-1, Akt/protein kinase B and glycogen synthase kinase 3, in human astrocytes. Akt was phosphorylated and PI-3 kinase activity increased following insulin stimulation in a dose-dependent manner. Neither increased glucose uptake nor lactate secretion after insulin stimulation could be evidenced in this cell type. However, we found increased insulin-dependent glucose incorporation into glycogen. Furthermore, cell numbers increased dose-dependently upon insulin treatment.
This study demonstrated that human astrocytes are insulin-responsive at the molecular level. We identified glycogen synthesis and cell proliferation as biological responses of insulin signaling in these brain cells. Hence, this cell type may contribute to the effects of insulin in the human brain.
PLoS ONE 01/2011; 6(6):e21594. · 4.09 Impact Factor
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ABSTRACT: Recent data suggested that sex hormone-binding globulin (SHBG) levels decrease when fat accumulates in the liver and that circulating SHBG may be causally involved in the pathogenesis of type 2 diabetes in humans. In the present study, we investigated mechanisms by which high SHBG may prevent development to diabetes.
Before and during a 9-month lifestyle intervention, total body and visceral fat were precisely measured by magnetic resonance (MR) tomography and liver fat was measured by (1)H-MR spectroscopy in 225 subjects. Insulin sensitivity was estimated from a 75-g oral glucose tolerance test (IS(OGTT)) and measured by a euglycemic hyperinsulinemic clamp (IS(clamp), n = 172). Insulin secretion was measured during the OGTT and an ivGTT (n = 172).
SHBG levels correlated positively with insulin sensitivity (IS(OGTT), P = 0.037; IS(clamp), P = 0.057), independently of age, sex, and total body fat. In a multivariate model, these relationships were also significant after additional adjustment for levels of the adipokine adiponectin and the hepatokine fetuin-A (IS(OGTT), P = 0.0096; IS(clamp), P = 0.029). Adjustment of circulating SHBG for liver fat abolished the relationships of SHBG with insulin sensitivity. In contrast, circulating SHBG correlated negatively with fasting glycemia, before (r = -0.17, P = 0.009) and after (r = -0.14, P = 0.04) adjustment for liver fat. No correlation of circulating SHBG with adjusted insulin secretion was observed (OGTT, P = 0.16; ivGTT, P = 0.35). The SNP rs1799941 in SHBG was associated with circulating SHBG (P ≤ 0.025) but not with metabolic characteristics (all P > 0.18).
Possible mechanisms by which high circulating SHBG prevents the development of type 2 diabetes involve regulation of fasting glycemia but not alteration of insulin secretory function.
Diabetes 12/2010; 59(12):3167-73. · 8.29 Impact Factor
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ABSTRACT: Stearoyl-CoA desaturase-1 (SCD1) has gained much interest as a future drug target to treat fatty liver and its consequences. However, there are few and inconsistent human data about expression and activity of this important enzyme. We investigated activity and expression of SCD1 and their relationships with liver fat (LF) content in human liver samples. Fifty subjects undergoing liver surgery were studied. SCD1 activity was estimated from the ratio of oleate (C18:1) to stearate (C18:0) within lipid subfractions. Furthermore, SCD1 mRNA expression and LF content were measured. Similarly to previous studies, we observed a strong positive correlation between LF content and the C18:1/C18:0 ratio in the combined fatty acid (FA) fractions (r = 0.96, P < 0.0001), which could be interpreted as higher SCD1 activity with increasing LF. However, hepatic SCD1 mRNA expression did not correlate with LF (r = 0.16, P = 0.13). To solve these conflicting data, we analyzed the FA composition of hepatic lipid subfractions. With increasing LF content the amount of FAs from the triglyceride (TG) fraction increased (r = 0.96, P < 0.0001), whereas the FAs from the phospholipid (PL) fraction remained unchanged (r = -0.17, P = 0.19). Of these two major lipid fractions, the C18:1/C18:0 ratio in TG was 16-fold higher than in PL. Supporting the SCD1 mRNA expression data, the C18:1/C18:0 ratio of the TG or PL fraction did not correlate with LF (r = 0.26, P = 0.12 and r = 0.08, P = 0.29). We provide novel information that SCD1 activity and mRNA expression appear not to be elevated in subjects with high LF content. We suggest that the FA composition of lipid subclasses, rather than of mixed lipids, should be analyzed to estimate SCD1 activity.
AJP Endocrinology and Metabolism 11/2010; 300(2):E321-6. · 4.75 Impact Factor
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Anita M Hennige,
Martin Heni,
Jürgen Machann,
Harald Staiger,
Tina Sartorius,
Miriam Hoene,
Rainer Lehmann,
Cora Weigert, Andreas Peter,
Antje Bornemann,
Stefan Kroeber,
Anna Pujol,
Sylvie Franckhauser,
Fatima Bosch,
Fritz Schick,
Reiner Lammers,
Hans-Ulrich Häring
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ABSTRACT: Among the multitude of dysregulated signalling mechanisms that comprise insulin resistance in divergent organs, the primary events in the development of type 2 diabetes are not well established. As protein kinase C (PKC) activation is consistently present in skeletal muscle of obese and insulin resistant subjects, we generated a transgenic mouse model that overexpresses constitutively active PKC-beta(2) in skeletal muscle to test whether activation of PKC is sufficient to cause an aversive whole-body phenotype. Upon this genetic modification, increased serine phosphorylation in Irs1 was observed and followed by impaired (3)H-deoxy-glucose uptake and muscle glycogen content, and transgenic mice exhibited insulin and glucose intolerance as they age. Muscle histochemistry revealed an increase in lipid deposition (intramyocellular lipids), and transgenic mice displayed impaired expression of transcriptional regulators of genes involved in fatty acid oxidation (peroxisome proliferator-activated receptor-gamma, PGC-1beta, acyl-CoA oxidase) and lipolysis (hormone-sensitive lipase). In this regard, muscle of transgenic mice exhibited a reduced capacity to oxidize palmitate and contained less mitochondria as determined by citrate synthase activity. Moreover, the phenotype included a profound decrease in the daily running distance, intra-abdominal and hepatic fat accumulation and impaired insulin action in the brain. Together, our data suggest that activation of a classical PKC in skeletal muscle as present in the pre-diabetic state is sufficient to cause disturbances in whole-body glucose and lipid metabolism followed by profound alterations in oxidative capacity, ectopic fat deposition and physical activity.
Journal of Cellular and Molecular Medicine 04/2010; 14(4):903-13. · 4.13 Impact Factor
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ABSTRACT: The pathogenesis of type 2 diabetes is characterized by insulin resistance and beta-cell dysfunction. Pancreatic fat load may add to the development of beta-cell dysfunction. The aim was to thoroughly quantify the fat content of pancreas sections (caput, corpus, and cauda) and to compare the impact of pancreatic, intrahepatic, and visceral fat on insulin secretion in humans.
Fifty-one subjects were subjected to an oral glucose tolerance test (OGTT) with glucose, insulin, and C-peptide measurements [28 subjects displayed normal glucose tolerance, 23 impaired fasting glycemia (IFG)] and/or impaired glucose tolerance (IGT)], and also to whole-body magnetic resonance imaging (MRI), pancreas MRI, and liver magnetic resonance spectroscopy (MRS).
After adjustment for gender and age, the mean pancreatic fat content was positively associated with body mass index (BMI), visceral adipose tissue (VAT), and waist circumference (all p < or = 0.0013). The mean pancreatic fat content was negatively associated with OGTT-based measures of insulin secretion (all p < or = 0.03). Analysis of the subgroups of glucose tolerance showed that this was restricted to subjects with IGT and/or IFG. Visceral fat also represented a determinant of beta-cell function in individuals with IGT and/or IFG (all p < or = 0.02), whereas intrahepatic fat did not. In a stepwise multivariate regression analysis, pancreatic fat turned out to be a stronger determinant of impaired insulin secretion than visceral fat.
Pancreatic fat is negatively associated with insulin secretion in subjects with IGT/IFG and, therefore, might represent an additional pathogenetic factor leading to beta-cell dysfunction.
Diabetes/Metabolism Research and Reviews 03/2010; 26(3):200-5. · 3.37 Impact Factor
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ABSTRACT: Stearoyl-coenzyme A desaturase 1 (SCD1) catalyzes the limiting step of monounsaturated fatty acid synthesis in humans and is an important player in triglyceride generation. SCD1 has been repeatedly implicated in the pathogenesis of metabolic and inflammatory diseases. Therefore it is of great importance to determine SCD1 activity in human samples. In this study we aimed to evaluate a hepatic SCD1 activity index derived from plasma VLDL triglyceride composition as a tool to estimate hepatic SCD1 expression in humans. Additionally, we further evaluated commonly used fatty acid ratios [elongase, de novo lipogenesis, and Delta5 and Delta6 desaturase] in plasma VLDL and hepatic lipid fractions.
Liver biopsies and plasma samples were simultaneously collected from 15 individuals. Plasma VLDL was obtained by ultracentrifugation. Hepatic and plasma VLDL lipids were fractionated by thin-layer chromatography, and the fatty acid composition of each fraction was analyzed by gas chromatography. Hepatic SCD1 expression was determined by real-time PCR.
Hepatic SCD1 mRNA expression was associated with the product/precursor ratios (16:1/16:0 and 18:1/18:0) of hepatic lipid fractions. The 16:1/16:0 ratio in hepatic and VLDL triglycerides as well as the 18:1/18:0 ratio in plasma VLDL were closely associated with hepatic SCD1 expression. The hepatic de novo lipogenesis index from triglycerides was associated with expression of lipogenic genes [fatty acid synthase (FASN), acetyl-Coenzyme A carboxylase alpha (ACACA), and sterol regulatory element binding transcription factor 1 (SREBP-1)] and is closely reflected by the de novo lipogenesis index in VLDL triglycerides.
We demonstrated for the first time that hepatic SCD1 expression can be estimated noninvasively from routine blood samples by measuring the SCD1 activity index in fasting plasma VLDL.
Clinical Chemistry 10/2009; 55(12):2113-20. · 7.91 Impact Factor
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Konstantinos Kantartzis, Andreas Peter,
Fausto Machicao,
Jürgen Machann,
Silvia Wagner,
Ingmar Königsrainer,
Alfred Königsrainer,
Fritz Schick,
Andreas Fritsche,
Hans-Ulrich Häring,
Norbert Stefan
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ABSTRACT: In a genome-wide association scan, the rs738409 C>G single nucleotide polymorphism (SNP) in the patatin-like phospholipase 3 gene (PNPLA3) was strongly associated with increased liver fat but not with insulin resistance estimated from fasting values. We investigated whether the SNP determines liver fat independently of visceral adiposity and whether it may even play a role in protecting from insulin resistance.
Liver fat was measured by (1)H magnetic resonance spectroscopy and total and visceral fat by magnetic resonance tomography in 330 subjects. Insulin sensitivity was estimated during an oral glucose tolerance test and the euglycemic-hyperinsulinemic clamp (n = 222). PNPLA3 and tumor necrosis factor-alpha mRNA and triglyceride content were measured in liver biopsies from 16 subjects.
Liver fat correlated strongly with insulin sensitivity (P < 0.0001) independently of age, sex, total fat, and visceral fat. G allele carriers of the SNP rs738409 had higher liver fat (P < 0.0001) and an odds ratio of 2.38 (95% CI 1.37-4.20) for having fatty liver compared to C allele homozygotes. Interestingly, insulin sensitivity (oral glucose tolerance test: P = 0.99; clamp: P = 0.32), serum C-reactive protein levels, lipids, or liver enzymes (all P > 0.14) were not different among the genotypes. Additional adjustment for liver fat actually revealed increased insulin sensitivity in more obese carriers of the G allele (P = 0.01). In liver biopsies triglyceride content correlated positively with expression of the proinflammatory gene tumor necrosis factor-alpha in C allele homozygotes (n = 6, P = 0.027) but not in G allele carriers (n = 10, P = 0.149).
PNPLA3 may be an important key to understand the mechanisms discriminating fatty liver with and without metabolic consequences.
Diabetes 09/2009; 58(11):2616-23. · 8.29 Impact Factor
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ABSTRACT: Increased plasma levels of free fatty acids occur in obesity and type 2 diabetes and contribute to the development of insulin resistance. Saturated fatty acids (SFAs) such as palmitate especially have lipotoxic effects leading to endoplasmatic reticulum (ER) stress, inflammation, and insulin resistance. Stearoyl-CoA desaturase 1 (SCD1) plays a key role in preventing lipotoxic effects, as it converts SFAs to less harmful monounsaturated fatty acids. Here, we tested the hypothesis that individual differences in the regulation of SCD1 expression by palmitate exist and influence insulin sensitivity and the cellular response to palmitate.
Palmitate-induced gene expression was studied in primary human myotubes of 39 metabolically characterized individuals, as well as in an SCD1-overexpressing cell culture model.
SCD1 mRNA expression and inducibility by palmitate in cultured myotubes showed a broad interindividual variation, presumably due to inheritable characteristics of the donors. Overexpression of SCD1 prevented the inflammatory and ER stress response to palmitate exposure. In primary human myotubes, high SCD1 inducibility was associated with a low inflammatory (interleukin [IL]-6, IL-8, and chemokine [CXC motif] ligand 3 [CXCL3]) and ER stress (CCAAT/enhancer binding protein [C/EBP] homologous protein, activating transcription factor 3 [ATF3], and X-box binding protein 1 [XBP1]) response to palmitate exposure. Finally, palmitate-stimulated SCD1 mRNA expression, positively correlated with intramyocellular lipid (IMCL) content of the donors, was measured by (1)H-magnetic resonance spectroscopy. After adjustment for IMCL, SCD1 expression and inducibility were positively correlated with insulin sensitivity.
We hypothesize that myocellular SCD1 inducibility by palmitate is an individual characteristic that modulates lipid storage, palmitate-induced inflammation, ER stress, and insulin resistance. This may describe individuals with increased capability of innoxious free fatty acid handling and benign triglyceride storage.
Diabetes 06/2009; 58(8):1757-65. · 8.29 Impact Factor
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Atherosclerosis 06/2009; 207(2):341-2. · 3.79 Impact Factor
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Anita M Hennige,
Martin Heni,
Jürgen Machann,
Harald Staiger,
Tina Sartorius,
Miriam Hoene,
Rainer Lehmann,
Cora Weigert, Andreas Peter,
Antje Bornemann,
Stefan Kroeber,
Anna Pujol,
Sylvie Franckhauser,
Fatima Bosch,
Fritz Schick,
Reiner Lammers,
Hans-Ulrich Håring
[show abstract]
[hide abstract]
ABSTRACT: Among the multitude of dysregulated signaling mechanisms that comprise insulin resistance in divergent organs, the primary events in the development of type 2 diabetes are not well established. As protein kinase C (PKC) activation is consistently present in skeletal muscle of obese and insulin resistant subjects, we generated a transgenic mouse model that overexpresses constitutively active PKC beta 2 in skeletal muscle to test whether activation of PKC is sufficient to cause an aversive whole-body phenotype. Upon this genetic modification, increased serine phosphorylation in Irs1 was observed and followed by impaired (3)H-deoxy-glucose uptake and muscle glycogen content, and transgenic mice exhibited insulin and glucose intolerance as they age. Muscle histochemistry revealed an increase in lipid deposition (IMCL), and transgenic mice displayed impaired expression of transcriptional regulators of genes involved in fatty acid oxidation (PPARdelta, PGC-1beta, ACO) and lipolysis (HSL). In this regard, muscle of transgenic mice exhibited a reduced capacity to oxidize palmitate and contained less mitochondria as determined by citrate synthase activity. Moreover, the phenotype included a profound decrease in the daily running distance, intraabdominal and hepatic fat accumulation and impaired insulin action in the brain. Together, our data suggest that activation of a classical PKC in skeletal muscle as present in the pre-diabetic state is sufficient to cause disturbances in whole-body glucose and lipid metabolism followed by profound alterations in oxidative capacity, ectopic fat deposition, and physical activity.
Journal of Cellular and Molecular Medicine 01/2009; · 4.13 Impact Factor
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ABSTRACT: The oral glucose tolerance test (oGTT) is a common tool to provoke a metabolic challenge for scientific purposes, as well as for diagnostic reasons, to monitor the kinetics of glucose and insulin. Here, we aimed to follow the variety of physiological changes of the whole metabolic pattern in plasma during an oGTT in healthy subjects in a nontargeted reversed-phase ultra performance liquid chromatography coupled to electrospray ionization quadrupole time of flight mass spectrometric metabolomics approach. We detected 11,500 metabolite ion masses/individual. Applying multivariate data analysis, four major groups of metabolites have been detected as the most discriminating oGTT biomarkers: free fatty acids (FFA), acylcarnitines, bile acids, and lysophosphatidylcholines. We found in detail 1) a strong decrease of all saturated and monounsaturated FFA studied during the oGTT; 2) a significant faster decline of palmitoleate (C16:1) and oleate (C18:1) FFA levels than their saturated counterparts; 3) a strong relative increase of polyunsaturated fatty acids in the fatty acid pattern at 120 min; and 4) a clear decrease in plasma C10:0, C12:0, and C14:1 acylcarnitine levels. These data reflect the switch from beta-oxidation to glycolysis and fat storage during the oGTT. Moreover, the bile acids glycocholic acid, glycochenodeoxycholic acid, and glycodeoxycholic acid were highly discriminative, showing a biphasic kinetic with a maximum of a 4.5- to 6-fold increase at 30 min after glucose ingestion, a significant decrease over the next 60 min followed by an increase until the end of the oGTT. Lysophosphatidylcholines were also increased significantly. The findings of our metabolomics study reveal detailed insights in the complex physiological regulation of the metabolism during an oGTT offering novel perspectives of this widely used procedure.
AJP Endocrinology and Metabolism 01/2009; 296(2):E384-93. · 4.75 Impact Factor
