Evidence against tetrahydrobiopterin depletion of vascular tissue exposed to nitric oxide/superoxide or nitroglycerin.
Several cardiovascular disorders, including atherosclerosis and tolerance to the antianginal drug nitroglycerin (GTN), may be associated with the generation of superoxide anions, which react with nitric oxide (NO) to yield peroxynitrite. According to a widely held view, oxidation of tetrahydrobiopterin (BH(4)) by peroxynitrite causes uncoupling of endothelial NO synthase (eNOS), resulting in reduced NO bioavailability and endothelial dysfunction under conditions of oxidative stress. In this study we determined the levels of reduced biopterins and endothelial function in cultured cells exposed to peroxynitrite and GTN as well as in blood vessels isolated from GTN-tolerant guinea pigs and rats. BH(4) was rapidly oxidized by peroxynitrite and 3-morpholino sydnonimine (SIN-1) in buffer, but this was prevented by glutathione and not observed in endothelial cells exposed to SIN-1 or GTN. Prolonged treatment of the cells with 0.1 mM GTN caused slow N(G)-nitro-l-arginine-sensitive formation of reactive oxygen species without affecting eNOS activity. Endothelial function and BH(4)/BH(2) levels were identical in blood vessels of control and GTN-tolerant animals. Our results suggest that peroxynitrite-triggered BH(4) oxidation does not occur in endothelial cells or GTN-exposed blood vessels. GTN seems to trigger minor eNOS uncoupling that is unrelated to BH(4) depletion and without observable consequence on eNOS function.
Department of Pharmacology and Toxicology, Karl-Franzens-Universität Graz, A-8010 Graz, Austria.
Kurt
K
Schmidt
Margit
M
Rehn
Heike
H
Stessel
Gerald
G
Wölkart
Bernd
B
Mayer
D000818:Animals; D001708:Biopterins / Q000031:analogs & derivatives* / Q000378:metabolism; D001808:Blood Vessels / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D005260:Female; D006168:Guinea Pigs; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism / Q000494:pharmacology*; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D005996:Nitroglycerin / Q000378:metabolism / Q000494:pharmacology*; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000187:drug effects; D013481:Superoxides / Q000378:metabolism / Q000494:pharmacology*
D013481:Superoxides; D001708:Biopterins; D009569:Nitric Oxide; D052250:Nitric Oxide Synthase Type III; C003402:sapropterin; D005996:Nitroglycerin