title: Homocysteine-induced inhibition of endothelium-dependent relaxation in rabbit aorta: role for superoxide anions.
abstract: Hyperhomocysteinemia is associated with endothelial dysfunction, although its mechanism is unknown. Isometric tension recordings and lucigenin chemiluminescence were used to assess the effects of homocysteine exposure on endothelium-dependent and -independent relaxation in isolated rabbit aortic rings and superoxide anion (O(2)(-)) production by cultured porcine aortic endothelial cells, respectively. Homocysteine (0.1 to 10 mmol/L) produced a significant (P<0.001) concentration- and time-dependent inhibition of endothelium-dependent relaxation in response to both acetylcholine and the calcium ionophore A23187. Only the intracellular O(2)(-) scavenger 4,5-dihydroxy-1,3-benzene disulfonic acid (Tiron, 10 mmol/L) significantly (P<0.001) inhibited the effect of homocysteine on acetylcholine- and A23187-induced relaxation. Incubation of porcine aortic endothelial cells with homocysteine (0.03 to 1 mmol/L for up to 72 hours) caused a significant (P<0.001) time-dependent increase in the O(2)(-) released by these cells on the addition of Triton X-100 (1% [vol/vol]), with levels returning to values comparable to those of control cells at the 72-hour time point. These changes in O(2)(-) levels were associated with a time-dependent increase in endothelial cell superoxide dismutase activity, becoming significant (P<0.001) after 72 hours. Furthermore, the homocysteine-induced increase in endothelial cell O(2)(-) levels was completely inhibited (P<0.001) by the concomitant incubation with either Tiron (10 mmol/L), vitamin C (10 micromol/L), or vitamin E (10 micromol/L). These data suggest that the inhibitory effect of homocysteine on endothelium-dependent relaxation is due to an increase in the endothelial cell intracellular levels of O(2)(-) and provide a possible mechanism for the endothelial dysfunction associated with hyperhomocysteinemia.
authors.affiliation: Cardiovascular Sciences Research Group, Department of Pharmacology, Therapeutics, and Toxicology, University of Wales College of Medicine, Heath Park, Cardiff, UK. langd@cf.ac.uk
authors.forename: D
authors.initials: D
authors.lastname: Lang
authors.forename: M B
authors.initials: MB
authors.lastname: Kredan
authors.forename: S J
authors.initials: SJ
authors.lastname: Moat
authors.forename: S A
authors.initials: SA
authors.lastname: Hussain
authors.forename: C A
authors.initials: CA
authors.lastname: Powell
authors.forename: M F
authors.initials: MF
authors.lastname: Bellamy
authors.forename: H J
authors.initials: HJ
authors.lastname: Powers
authors.forename: M J
authors.initials: MJ
authors.lastname: Lewis
mesh_terms: D000166:Acridines; D000818:Animals; D001011:Aorta / Q000187:drug effects* / Q000502:physiology; D004730:Endothelium, Vascular / Q000378:metabolism / Q000502:physiology*; D006710:Homocysteine / Q000494:pharmacology*; D008163:Luminescent Measurements; D008297:Male; D011817:Rabbits; D017382:Reactive Oxygen Species / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism; D013552:Swine; D014661:Vasoconstriction; D014664:Vasodilation / Q000187:drug effects*
chemical_list: D000166:Acridines; D017382:Reactive Oxygen Species; D006710:Homocysteine; D013481:Superoxides; C033472:10,10'-dimethyl-9,9'-biacridinium