title: 5-methyltetrahydrofolate rapidly improves endothelial function and decreases superoxide production in human vessels: effects on vascular tetrahydrobiopterin availability and endothelial nitric oxide synthase coupling.
abstract: BACKGROUND
  The circulating form of folic acid, 5-methyltetrahydrofolate (5-MTHF), may have beneficial effects on endothelial function; however, its mechanisms of action remain uncertain. Decreased nitric oxide (NO) bioavailability and increased vascular superoxide production in vascular disease states are due in part to endothelial NO synthase (eNOS) uncoupling related to deficiency of the eNOS cofactor tetrahydrobiopterin (BH4), but whether this mechanism is important in human atherosclerosis and represents a rational therapeutic target remains unclear. We hypothesized that 5-MTHF would improve endothelial function by decreasing superoxide and peroxynitrite production and by improving eNOS coupling, mediated by BH4 availability.
  
  
  RESULTS
  Vascular superoxide/peroxynitrite production and vasomotor responses to acetylcholine and bradykinin were determined in saphenous veins and internal mammary arteries from 117 patients undergoing CABG. The effects of 5-MTHF were examined ex vivo (n = 61) by incubating vessels with 5-MTHF (1 to 100 micromol/L) and in vivo by intravenous infusion of 5-MTHF or placebo before vessel harvest (n = 56). 5-MTHF improved NO-mediated endothelium-dependent vasomotor responses and reduced vascular superoxide, both ex vivo and in vivo. These changes were not explained by direct superoxide scavenging by 5-MTHF in vitro or by changes in plasma total homocysteine in vivo. Rather, 5-MTHF was a strong peroxynitrite scavenger and increased vascular BH4 and the BH4/total biopterin ratio. Furthermore, 5-MTHF reversed eNOS uncoupling, as assessed by NG-nitro-l-arginine methyl ester-inhibitable superoxide production, increased the eNOS dimer:monomer ratio, and enhanced eNOS activity.
  
  
  CONCLUSIONS
  5-MTHF has beneficial effects on endothelial function and vascular superoxide production in human atherosclerosis, by preventing peroxynitrite-mediated BH4 oxidation and improving eNOS coupling.
authors.affiliation: Department of Cardiovascular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, OX3 9DU, UK.
authors.forename: Charalambos
authors.initials: C
authors.lastname: Antoniades
authors.forename: Cheerag
authors.initials: C
authors.lastname: Shirodaria
authors.forename: Nicholas
authors.initials: N
authors.lastname: Warrick
authors.forename: Shijie
authors.initials: S
authors.lastname: Cai
authors.forename: Joseph
authors.initials: J
authors.lastname: de Bono
authors.forename: Justin
authors.initials: J
authors.lastname: Lee
authors.forename: Paul
authors.initials: P
authors.lastname: Leeson
authors.forename: Stefan
authors.initials: S
authors.lastname: Neubauer
authors.forename: Chandi
authors.initials: C
authors.lastname: Ratnatunga
authors.forename: Ravi
authors.initials: R
authors.lastname: Pillai
authors.forename: Helga
authors.initials: H
authors.lastname: Refsum
authors.forename: Keith M
authors.initials: KM
authors.lastname: Channon
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000975:Antioxidants / Q000494:pharmacology; D050197:Atherosclerosis / Q000378:metabolism*; D001682:Biological Availability; D001708:Biopterins / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D001920:Bradykinin / Q000494:pharmacology; D001026:Coronary Artery Bypass; D003324:Coronary Artery Disease; D004311:Double-Blind Method; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000378:metabolism*; D006710:Homocysteine / Q000097:blood; D006801:Humans; D009569:Nitric Oxide / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D030421:Peroxynitrous Acid / Q000378:metabolism; D011485:Protein Binding; D013481:Superoxides / Q000378:metabolism*; D013763:Tetrahydrofolates / Q000494:pharmacology*
chemical_list: D000975:Antioxidants; D013763:Tetrahydrofolates; D006710:Homocysteine; D013481:Superoxides; D030421:Peroxynitrous Acid; D001708:Biopterins; D009569:Nitric Oxide; D052250:Nitric Oxide Synthase Type III; C003402:sapropterin; D000109:Acetylcholine; D001920:Bradykinin; C005984:5-methyltetrahydrofolate