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Paglialunga S.,Maastricht University | Van Bree B.,Maastricht University | Bosma M.,Maastricht University | Valdecantos M.P.,University of Navarra | And 8 more authors.
Diabetologia | Year: 2012

Aims/hypothesis: High-fat, high-sucrose diet (HF)-induced reactive oxygen species (ROS) levels are implicated in skeletal muscle insulin resistance and mitochondrial dysfunction. Here we investigated whether mitochondrial ROS sequestering can circumvent HF-induced oxidative stress; we also determined the impact of any reduced oxidative stress on muscle insulin sensitivity and mitochondrial function. Methods: The Skulachev ion (plastoquinonyl decyltriphenylphosphonium) (SkQ), a mitochondria-specific antioxidant, was used to target ROS production in C2C12 muscle cells as well as in HF-fed (16 weeks old) male C57Bl/6 mice, compared with mice on low-fat chow diet (LF) or HF alone. Oxidative stress was measured as protein carbonylation levels. Glucose tolerance tests, glucose uptake assays and insulin-stimulated signalling were determined to assess muscle insulin sensitivity. Mitochondrial function was determined by high-resolution respirometry. Results: SkQ treatment reduced oxidative stress in muscle cells (-23% p∈<∈0.05), but did not improve insulin sensitivity and glucose uptake under insulin-resistant conditions. In HF mice, oxidative stress was elevated (56% vs LF p∈<∈0.05), an effect completely blunted by SkQ. However, HF and HF+SkQ mice displayed impaired glucose tolerance (AUC HF up 33%, p∈<∈0.001; HF+SkQ up 22%; p∈<∈0.01 vs LF) and disrupted skeletal muscle insulin signalling. ROS sequestering did not improve mitochondrial function. Conclusions/interpretation: SkQ treatment reduced muscle mitochondrial ROS production and prevented HF-induced oxidative stress. Nonetheless, whole-body glucose tolerance, insulin-stimulated glucose uptake, muscle insulin signalling and mitochondrial function were not improved. These results suggest that HF-induced oxidative stress is not a prerequisite for the development of muscle insulin resistance. © 2012 Springer-Verlag.

Corpe C.P.,U.S. National Institutes of Health | Eck P.,U.S. National Institutes of Health | Eck P.,University of Manitoba | Wang J.,U.S. National Institutes of Health | And 4 more authors.
Journal of Biological Chemistry | Year: 2013

Intestinal vitamin C (Asc) absorption was believed to be mediated by the Na+-dependent ascorbic acid transporter SVCT1. However, Asc transport across the intestines of SVCT1 knockout mice is normal indicating that alternative ascorbic acid transport mechanisms exist. To investigate these mechanisms, rodents were gavaged with Asc or its oxidized form dehydroascorbic acid (DHA), and plasma Asc concentrations were measured. Asc concentrations doubled following DHA but not Asc gavage. We hypothesized that the transporters responsible were facilitated glucose transporters (GLUTs). Using Xenopus oocyte expression, we investigated whether facilitative glucose transporters GLUT2 and GLUT5-12 transported DHA. Only GLUT2 and GLUT8, known to be expressed in intestines, transported DHA with apparent transport affinities (Km) of 2.33 and 3.23 mM and maximal transport rates (Vmax) of 25.9 and 10.1 pmol/min/oocyte, respectively. Maximal rates for DHA transport mediated by GLUT2 and GLUT8 in oocytes were lower than maximal rates for 2-deoxy-D-glucose (Vmax of 224 and 32 pmol/min/oocyte for GLUT2 and GLUT8, respectively) and fructose (Vmax of 406 and 116 pmol/min/oocyte for GLUT2 and GLUT8, respectively). These findings may be explained by differences in the exofacial binding of substrates, as shown by inhibition studies with ethylidine glucose. DHA transport activity in GLUT2- and GLUT8-expressing oocytes was inhibited by glucose, fructose, and by the flavonoids phloretin and quercetin. These studies indicate intestinal DHA transport may be mediated by the facilitative sugar transporters GLUT2 and GLUT8. Furthermore, dietary sugars and flavonoids in fruits and vegetables may modulate Asc bioavailability via inhibition of small intestinal GLUT2 and GLUT8. © 2013 by The American Society for Biochemistry and Molecular Biology, Inc.

Vandenplas G.,Ghent University | De Bacquer D.,Ghent University | Calders P.,Ghent University | Fiers T.,Ghent University | And 3 more authors.
Heart | Year: 2012

Context: The literature provides no clear answer as to whether total oestradiol (E2) concentrations increase the risk of incident cardiovascular disease (CVD) in healthy men. Objective: The authors conducted a systematic review and meta-analysis to estimate the predictive value of E2 for CVD, and to identify study features explaining conflicting results. Data sources: Articles were identified by a Medline and Embase search and citation tracking. Study selection: Eligible articles were prospective population-based cohorts and nested case-control studies on E2 and incident cardiovascular disease (CVD), including myocardial infarction, stroke or death from coronary heart disease. Data-extraction: Independent researchers re-expressed associations of E2 and incident CVD in a uniform manner to be used in meta-regression analyses for identification of study features explaining conflicting results, and to estimate the predictive value of E2 for CVD. Results and conclusions: 14 studies out of 128 electronically identified articles were eligible. Data to be used for meta-analysis could be calculated in seven cases, and in the remaining seven cases, data of three more became available by contacting those authors. Overall, a non-significant association was found with an estimated summary RR of 0.98 for a change of >75th versus <25th percentile in E2 (95% CI 0.74 to 1.31). Mean body mass index (BMI) of the study population (βs -0.8, p<0.004), and quality of E2 assay (βs -0.6, p<0.08) may have modified the relationship between E2 and incident CVD. The present systematic review does not provide evidence for a pronounced harmful or beneficial effect of E2 on risk for incident CVD in healthy men. If present, an effect of E2 on risk for CVD might be modulated by BMI.

Ruige J.B.,Ghent University | Ouwens D.M.,Ghent University | Ouwens D.M.,Institute for Clinical Biochemistry and Pathobiochemistry | Kaufman J.-M.,Ghent University
Journal of Clinical Endocrinology and Metabolism | Year: 2013

Context: The widespread use of T therapy, particularly in aging males, necessitates knowledge of the relationship between T and the cardiovascular system. Evidence Acquisition: The review is based on a 1970 to 2013 PubMed search with terms related to androgens in combination with cardiovascular disease, including T, dihydrotestosterone, trial, mortality, cardiovascular disease, myocardial infarction, blood pressure, endothelial function, dyslipidemia, thrombosis, ventricular function, and arrhythmia. Original articles, systematic reviews and meta-analyses, and relevant citations were screened. Evidence Synthesis: Low T has been linked to increased blood pressure, dyslipidemia, atherosclerosis, arrhythmia, thrombosis, endothelial dysfunction, as well as to impaired left ventricular function. On the one hand, a modest association is suggested between low endogenous T and incident cardiovascular disease or cardiovascular mortality, implying unrecognized beneficial T effects, residual confounding, or a relationship with health status. On the other hand, treatments with T to restore "normal concentrations" have so far not been proven to be beneficial with respect to cardiovascular disease; neither have they definitely shown specific adverse cardiovascular effects. The cardiovascular risk-benefit profile of T therapy remains largely evasive in view of a lack of well-designed and adequately powered randomized clinical trials. Conclusions: The important knowledge gap as to the exact relationship between T and cardiovascular disease would support a cautious, restrained approach to T therapy in aging men, pending clarification of benefits and risks by adequately powered clinical trials of sufficient duration. Copyright © 2013 by The Endocrine Society.

Wiza C.,Institute for Clinical Biochemistry and Pathobiochemistry | Herzfeld De Wiza D.,Institute for Clinical Biochemistry and Pathobiochemistry | Nascimento E.B.M.,Karolinska Institutet | Lehr S.,Institute for Clinical Biochemistry and Pathobiochemistry | And 3 more authors.
Diabetologia | Year: 2013

Aims/hypothesis: The proline-rich Akt substrate of 40 kDa (PRAS40) is a component of the mammalian target of rapamycin complex 1 (mTORC1) and among the most prominent Akt substrates in skeletal muscle. Yet the cellular functions of PRAS40 are incompletely defined. This study assessed the function of PRAS40 in insulin action in primary human skeletal muscle cells (hSkMC). Methods: Insulin action was examined in hSkMC following small interfering RNA-mediated silencing of PRAS40 (also known as AKT1S1) under normal conditions and following chemokine-induced insulin resistance. Results: PRAS40 knockdown (PRAS40-KD) in hSkMC decreased insulin-mediated phosphorylation of Akt by 50% (p < 0.05) as well as of the Akt substrates glycogen synthase kinase 3 (40%) and tuberous sclerosis complex 2 (32%) (both p < 0.05). Furthermore, insulin-stimulated glucose uptake was reduced by 20% in PRAS40-KD myotubes (p < 0.05). Exposing PRAS40-KD myotubes to chemokines caused no additional deterioration of insulin action. PRAS40-KD further reduced insulin-mediated phosphorylation of the mTORC1-regulated proteins p70S6 kinase (p70S6K) (47%), S6 (43%), and eukaryotic elongation 4E-binding protein 1 (100%), as well as protein levels of growth factor receptor bound protein 10 (35%) (all p < 0.05). The inhibition of insulin action in PRAS40-KD myotubes was associated with a reduction in IRS1 protein levels (60%) (p < 0.05), and was reversed by pharmacological proteasome inhibition. Accordingly, expression of the genes encoding E3-ligases F-box protein 32 (also known as atrogin-1) and muscle RING-finger protein-1 and activity of the proteasome was elevated in PRAS40-KD myotubes. Conclusions/interpretation: Inhibition of insulin action in PRAS40-KD myotubes was found to associate with IRS1 degradation promoted by increased proteasome activity rather than hyperactivation of the p70S6K-negative-feedback loop. These findings identify PRAS40 as a modulator of insulin action. © 2013 Springer-Verlag Berlin Heidelberg.

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