Original article Prevalence of endothelial nitric oxide synthase E298D polymorphism in Turkish patients with essential hypertension Figen Esin Kayhan a,1 , Meliha Koldemir a,1 , Penbe Cagatay b , Cavlan Ciftci c , Belgin Susleyici-Duman a, * a Department of Biology, Marmara University, Istanbul, Turkey b Department of Biostatistic and Medical Informatics, Istanbul University, Istanbul, Turkey c Department of Cardiology, Istanbul Bilim University, Istanbul, Turkey 1. Introduction Nitric oxide (NO), produced by the nitric oxide synthase in the endothelial cells, regulates vasomotor tone and blood flow through its activation of the endothelium-derived relaxing factor (EDRF) [1]. Association exists between NOS3 gene single nucleotide polymorphisms (SNPs) and hypertension [2]. Both human and animal studies have shown onset of hypertension due to loss of nitric oxide, which act as endothelium-derived relaxing factor [3]. Nitric oxide is catalyzed by endothelial nitric oxide synthase (eNOS), an enzyme with multiple genetic variants that might confer risk for hypertension [4]. An association between eNOS polymorphism and reduced eNOS expression and activity has been reported. Human eNOS gene is located on chromosome 7q35–36, consists of 26 exons spanning approximately 21 kb with multiple polymorphisms [5]. The common polymorphism G894T in exon 7 of the eNOS gene results in the substitution of glutamic acid (E) at codon 298 by aspartic acid (D) (E298D). This is the only known polymorphism changing the eNOS protein sequence, leading to speculation that genetic variation at this site may alter eNOS activity or regulation and possibly leads to endothelial dysfunction and to pathogenesis of several cardiovascular diseases [6]. The biological significance of the substitution of G to T in the eNOS gene locus is unclear. Fatini et al. have published a LightCycler assay for the analysis of this polymorphism [7]. E298D polymorphism of the eNOS gene has been extensively studied, and reported to be associated with the reduced expression and activity of eNOS [8]. Tesauro et al. [9] suggested that the eNOS E298 is subject to selective proteolytic cleavage in endothelial cells and vascular tissues and therefore individuals with Asp 298 may display low eNOS activity. Further, The codon 298 falls between the critical residues of the heme domain (100–200) and the binding sites for L- arginine and tetrahydrobiopterin (350–450) [10]. It has been speculated that in the absence of tetrahydrobiopterin, the eNOS enzyme becomes dysfunctional leading to decreased generation of NO and increased superoxide synthesis. By some investigators it has been suggested that Glu298Asp substitution may affect the response of vascular endothelium to increased oxidative stress [11,12]. Whether the E298D mutation has any effect on the binding Diabetes & Metabolic Syndrome: Clinical Research & Reviews 7 (2013) 12–16 A R T I C L E I N F O Keywords: E298D polymorphism eNOS Lipid Fat mass Obesity A B S T R A C T Aims: Our aim was to evaluate the effects of endothelial nitric oxide synthase (eNOS) E298D polymorphism in obesity variables and essential hypertension (eHT) development risk. The genotype frequencies of E298D polymorphism in eHT patients and non-hypertensive (non-HT) controls (proven to have normal coronaries angiographically) were analyzed for their association with demographic and obesity related data of the eHT patients and controls. Materials and methods: eNOS gene E298D genotypes were determined with qPCR. Results: The eNOS E298D polymorphism frequencies for 298E/E, 298E/D and 298D/D genotypes were respectively as 41.1%, 44.6%, 14.3% in subjects eHT and 52.8%, 38.9%, 8.3% in the non-HT groups. The combined E298D homozygous polymorphic and heterozygous genotypes were found to have a decreasing effect on serum total-cholesterol levels in comparison to wild-type genotypes in eHT patients but not controls. Conclusions: Our results support the idea that, the eNOS E298D polymorphism, which is not associated with hypertension, may increase the risk of hypertension when associated with high serum total- cholesterol levels. ß 2013 Diabetes India. Published by Elsevier Ltd. All rights reserved. * Corresponding author at: Marmara University, Faculty of Science and Arts, Department of Biology, Goztepe-Istanbul, Turkey. Tel.: +90 216 346 45 53; fax: +90 216 347 87 83. E-mail address: belgin.susleyici@marmara.edu.tr (B. Susleyici-Duman). 1 These authors participated equally to this publication. Contents lists available at SciVerse ScienceDirect Diabetes & Metabolic Syndrome: Clinical Research & Reviews jo ur n al h o mep ag e: www .elsevier .c om /loc ate/d s x 1871-4021/$ – see front matter ß 2013 Diabetes India. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.dsx.2013.02.001