Hypochlorous acid impairs endothelium-derived nitric oxide bioactivity through a superoxide-dependent mechanism.
OBJECTIVE
To determine how hypochlorous acid (HOCl), the principal product of myeloperoxidase, modulates vascular function.


RESULTS
Rabbit arterial rings exposed to HOCl (0 to 500 micromol/L) exhibited dose- and time-dependent impairment of endothelium-dependent arterial relaxation to acetylcholine and A23187, but not the NO donor, diethylamine NONOate, suggesting that HOCl targets the endothelium. This effect was not because of cytotoxicity, as HOCl treatment produced no significant change in endothelial cell morphology or lactate dehydrogenase release. We observed HOCl-mediated endothelial cell protein oxidation by immunoreactivity to HOP-1, a monoclonal antibody specific for HOCl-oxidized protein. In support of this notion, known HOCl scavengers, such as methionine and N-acetylcysteine, partially preserved endothelium-derived NO bioactivity in response to HOCl. In an unanticipated observation, HOCl-mediated impairment of NO bioactivity was prevented by manganese superoxide dismutase in a manner dependent on its enzymatic activity. Finally, we found that HOCl reduced endothelial nitric oxide synthase dimer stability, an effect that was also inhibited by superoxide dismutase.


CONCLUSIONS
Taken together, these data indicate that HOCl imparts a defect in endothelial NO production due to a superoxide-dependent reduction in endothelial nitric oxide synthase dimer stability. These data provide another mechanism whereby myeloperoxidase-derived oxidants can contribute to the impairment of NO bioactivity that is characteristic of atherosclerosis.
Evans Memorial Department of Medicine and Whitaker Cardiovascular Institute, Boston University School of Medicine, Mass 02118, USA.
Roland
R
Stocker
Annong
A
Huang
Erin
E
Jeranian
Jing Yun
JY
Hou
Tina T
TT
Wu
Shane R
SR
Thomas
John F
JF
Keaney
D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism; D000975:Antioxidants / Q000494:pharmacology; D001011:Aorta / Q000166:cytology / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D002478:Cells, Cultured; D019281:Dimerization; D004730:Endothelium, Vascular / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism* / Q000503:physiopathology; D005260:Female; D006997:Hypochlorous Acid / Q000494:pharmacology*; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III; D011506:Proteins / Q000276:immunology / Q000378:metabolism; D011817:Rabbits; D013194:Staining and Labeling / Q000379:methods; D013481:Superoxides / Q000378:metabolism*; D013552:Swine / Q000235:genetics
D000911:Antibodies, Monoclonal; D000975:Antioxidants; D011506:Proteins; D013481:Superoxides; D009569:Nitric Oxide; D006997:Hypochlorous Acid; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III