Person: YÜKSEL, MERAL
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YÜKSEL
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MERAL
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Publication Open Access Effect of Vitamin D Deficiency and Replacement on Endothelial Function in Asymptomatic Subjects(ENDOCRINE SOC, 2009-10-01) VELİOĞLU ÖĞÜNÇ, AYLİZ; Tarcin, Ozlem; Yavuz, Dilek Gogas; Ozben, Beste; Telli, Ahu; Ogunc, Ayliz Velioglu; Yuksel, Meral; Toprak, Ahmet; Yazici, Dilek; Sancak, Seda; Deyneli, Oguzhan; Akalin, SemaContext: Vitamin D receptors are present in many tissues. Hypovitaminosis D is considered to be a risk factor for atherosclerosis. Objective: This study explores the effects of vitamin D replacement on insulin sensitivity, endothelial function, inflammation, oxidative stress, and leptin in vitamin D-deficient subjects. Design, Setting, and Patients: Twenty-three asymptomatic vitamin D-deficient subjects with 25-hydroxyvitamin D [25(OH)D] levels below 25 nmol/liter were compared with a control group that had a mean 25(OH)D level of 75 nmol/liter. The vitamin D-deficient group received 300,000 IU im monthly for 3 months. The following parameters were evaluated before and after treatment: vitamin D metabolites, leptin, endothelial function by brachial artery flow mediated dilatation (FMD), insulin sensitivity index based on oral glucose tolerance test, and lipid peroxidation as measures of thiobarbituric acid reactive substances (TBARS). Results: FMD measurements were significantly lower in 25(OH)D-deficient subjects than controls (P = 0.001) and improved after replacement therapy (P = 0.002). Posttreatment values of TBARS were significantly lower than pretreatment levels (P < 0.001). A positive correlation between FMD and 25(OH)D (r = 0.45; P = 0.001) and a negative correlation between FMD and TBARS (r = -0.28; P < 0.05) were observed. There was a significant increase in leptin levels after therapy, and the leptin levels were positively correlated with 25(OH)D levels (r = 0.45; P < 0.05). Conclusions: This study shows that 25(OH)D deficiency is associated with endothelial dysfunction and increased lipid peroxidation. Replacement of vitamin D has favorable effects on endothelial function. Vitamin D deficiency can be seen as an independent risk factor of atherosclerosis. Hypovitaminosis D-associated endothelial dysfunction may predispose to higher rates of cardiovascular disease in the winter. (J Clin Endocrinol Metab 94: 4023-4030, 2009)Publication Open Access Diurnal Blood Pressure Abnormalities Are Related to Endothelial Dysfunction in Patients with Non-Complicated Type 1 Diabetes(NATURE PUBLISHING GROUP, 2008-11) YAVUZ, DİLEK; Deyneli, Oguzhan; Yazici, Dilek; Toprak, Ahmet; Yuksel, Meral; Aydin, Hasan; Tezcan, Hakan; Yavuz, Dilek Gogas; Akalin, SemaPatients with diabetes have an increased cardiovascular morbidity and mortality despite interventions to prevent these outcomes. Abnormalities in diurnal blood pressure patterns are also associated with excess cardiovascular mortality. The aim of this study was to determine the effects of diurnal blood pressure patterns on endothelial function and oxidative stress in patients with uncomplicated type 1 diabetes mellitus. Thirty-two normotensive and normoalbuminuric type 1 diabetic patients (21 dipper and 11 nondipper) and 37 healthy (27 dipper and 10 nondipper) volunteers underwent 24-h ambulatory blood pressure monitoring. Their endothelial functions were evaluated using flow mediated dilatation (FMD) and by measuring nitric oxide and thiobarbituric acid reactive substances (TBARS). Dippers were defined as subjects who exhibited an average reduction in both systolic and diastolic blood pressure of greater than 10% between day and night periods. Nondipper type 1 diabetic patients and controls had nighttime systolic and diastolic blood pressure values that were significantly higher than those of dipper diabetic patients (p<0.05) and dipper controls (p<0.01). Values of FMD for nondipper diabetic patients (5.12 +/- 2.2%) were significantly lower than those In dipper diabetic patients (10.19 +/- 2.5%, p<0.01), nondipper (10.08 +/- 2.9%, p<0.001) and dipper controls (11.76 +/- 0.8%, p<0.001). Additionally, levels of TBARS In the dipper diabetic group and dipper controls were significantly lower than those in the nondipper diabetic group (p<0.05). In conclusion, only type 1 diabetic patients with a nondipping pattern of blood pressure exhibited changes that may lead to endothelial dysfunction and atherosclerosis. (Hypertens Res 2008; 31: 2065-2073)Publication Metadata only Exogenous subclinical hyperthyroidism impairs endothelial function in nodular Goiter patients(MARY ANN LIEBERT, INC, 2008) YAVUZ, DİLEK; Yavuz, Dilek Gogas; Yazici, Dilek; Toprak, Ahmet; Deyneli, Oguzhan; Aydin, Hasan; Yuksel, Meral; Akalin, SemaBackground: Exogenous subclinical hyperthyroidism is associated with cardiovascular and metabolic changes. The aim of this study was to evaluate the effect of levothyroxine ( LT4) suppression on endothelial function and insulin sensitivity in euthyroid nodular goiter patients. Methods: Twenty-two euthyroid patients with multinodular goiter (MNG) and 22 matched healthy controls were studied. LT4 was administered in doses ranging from 50 to 150 mu g/day to reach target serum thyroid-stimulating hormone ( TSH) levels < 0.5mIU/L. Patients were studied before and after 8 weeks after the target TSH level < 0.5mIU/L. The control group was studied twice, 16 weeks apart. Flow mediated vasodilatation ( FMD), insulin sensitivity index (ISI), lipid peroxidation, and high-sensitivity C-reactive protein (hsCRP) were the outcome measures. Results: LT4 treatment significantly suppressed TSH levels to 0.2 +/- 0.1mIU/L ( minimum and maximum range was 0.05-0.3 mIU/L). FMD decreased from 10.7 +/- 2.7% to 5.4 +/- 1.7% ( p < 0.001) and mean ISI decreased from 2.56 +/- 1.10 to 1.41 +/- 0.50 ( p < 0.001) with LT4 treatment in the MNG group. Lipid peroxidation measured as thiobarbituric acid reactive substances ( Tbars) ( p < 0.05), and hsCRP ( p < 0.001) levels significantly increased compared to the baseline in the MNG group. FMD measurement inversely correlated with free T4 ( p =0.008) and Tbars ( p = 0.004), and positively correlated with ISI ( p 0.004). Serum Tbars and hsCRP were independent predictors of FMD ( p= 0.004) in multivariate analysis. All results expressed as mean +/- SD. Conclusions: TSH suppression therapy with LT4 leading to subclinical hyperthyroidism may cause impaired endothelial function, increased oxidative stress, and decreased insulin sensitivity in euthyroid nodular goiter patients.