title: Effects of polymorphisms in endothelial nitric oxide synthase and folate metabolizing genes on the concentration of serum nitrate, folate, and plasma total homocysteine after folic acid supplementation: a double-blind crossover study.
abstract: OBJECTIVE
  A number of studies have explored the effects of dietary nitrate on human health. Nitrate in the blood can be recycled to nitric oxide, which is an essential mediator involved in many important biochemical mechanisms. Nitric oxide is also formed in the body from l-arginine by nitric oxide synthase. The aim of this study was to investigate whether genetic polymorphisms in endothelial nitric oxide synthase (eNOS) and genes involved in folate metabolism affect the concentration of serum nitrate, serum folate, and plasma total homocysteine in healthy individuals after folic acid supplementation.
  
  
  METHODS
  In a randomized double-blind, crossover study, participants were given either folic acid 800 μg/d (n = 52) or placebo (n = 51) for 2 wk. Wash-out period was 2 wk. Fasting blood samples were collected, DNA was extracted by salting-out method and the polymorphisms in eNOS synthase and folate genes were genotyped by polymerase chain reaction methods. Measurement of serum nitrate and plasma total homocysteine (p-tHcy) concentration was done by high-performance liquid chromatography.
  
  
  RESULTS
  The concentration of serum nitrate did not change in individuals after folic acid supplements (trial 1); however, the concentration of serum nitrate increased in the same individuals after placebo (P = 0.01) (trial 2). The individuals with three polymorphisms in eNOS gene had increased concentration of serum folate and decreased concentration of p-tHcy after folic acid supplementation. Among the seven polymorphisms tested in folate metabolizing genes, serum nitrate concentration was significantly decreased only in DHFR del 19 gene variant. A significant difference in the concentration of serum nitrate was detected among individuals with MTHFR C > T677 polymorphisms.
  
  
  CONCLUSIONS
  Polymorphisms in eNOS and folate genes affect the concentration of serum folate and p-tHcy but do not have any effect on the concentration of NO3 in healthy individuals after folic acid supplementation.
authors.affiliation: Department of Natural Sciences, University of Agder, Kristiansand, Norway. Electronic address: rona.n.cabo@uia.no.
authors.forename: Rona
authors.initials: R
authors.lastname: Cabo
authors.affiliation: Department of Public Health, Sport and Nutrition, University of Agder, Kristiansand, Norway.
authors.forename: Sigrunn
authors.initials: S
authors.lastname: Hernes
authors.affiliation: Department of Natural Sciences, University of Agder, Kristiansand, Norway.
authors.forename: Audun
authors.initials: A
authors.lastname: Slettan
authors.affiliation: Department of Public Health, Sport and Nutrition, University of Agder, Kristiansand, Norway.
authors.forename: Margaretha
authors.initials: M
authors.lastname: Haugen
authors.affiliation: William Harvey Research Institute, Queen Mary University London, UK.
authors.forename: Shu
authors.initials: S
authors.lastname: Ye
authors.affiliation: Department of Nutrition, University of Oslo, Oslo, Norway; Department of Clinical Service, Clinic of Cancer Medicine, Transplantation and Surgery, Oslo University Hospital, Oslo, Norway.
authors.forename: Rune
authors.initials: R
authors.lastname: Blomhoff
authors.affiliation: Department of Natural Sciences, University of Agder, Kristiansand, Norway.
authors.forename: M Azam
authors.initials: MA
authors.lastname: Mansoor
mesh_terms: D001120:Arginine / Q000378:metabolism; D018592:Cross-Over Studies; D004040:Dietary Carbohydrates / Q000008:administration & dosage; D004041:Dietary Fats / Q000008:administration & dosage; D004044:Dietary Proteins / Q000008:administration & dosage; D019587:Dietary Supplements; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005492:Folic Acid / Q000008:administration & dosage / Q000097:blood*; D005787:Gene Frequency; D060005:Genotyping Techniques; D064368:Healthy Volunteers; D006710:Homocysteine / Q000097:blood*; D006801:Humans; D009566:Nitrates / Q000097:blood*; D052250:Nitric Oxide Synthase Type III / Q000235:genetics* / Q000378:metabolism; D020641:Polymorphism, Single Nucleotide; D025101:Vitamin B 6 / Q000008:administration & dosage / Q000097:blood
chemical_list: D004040:Dietary Carbohydrates; D004041:Dietary Fats; D004044:Dietary Proteins; D009566:Nitrates; D006710:Homocysteine; D025101:Vitamin B 6; D005492:Folic Acid; D001120:Arginine; C496314:NOS3 protein, human; D052250:Nitric Oxide Synthase Type III
keywords: Genetic polymorphisms; HPLC; Plasma total homocysteine; Serum folate; Serum nitrate