title: Transient hyperoxic reoxygenation reduces cytochrome C oxidase activity by increasing superoxide dismutase and nitric oxide.
abstract: Oxygen therapies have been shown to be cytoprotective in a dose-dependent fashion. Previously, we have characterized the protective effects of moderate hyperoxia on cell viability of ischemic human cardiomyocytes and their mitochondrial membrane potential by transient addition of oxygenated perfluorocarbons to the cell medium. Now, we report that the activity and expression of cytochrome c oxidase (COX) after prolonged ischemia depend on the amount of oxygen delivered during reoxygenation. Transient hyperoxia during reoxygenation results in a decrease of COX activity by 62 +/- 15% and COX expression by 67 +/- 5%, when hyperoxic tensions of approximately = 300 mm Hg are reached in the cell medium. This decrease in COX expression is prevented by the inhibition of inducible nitric-oxide synthase (iNOS). Immunoblot analysis of ischemic human cardiomyocytes revealed that hyperoxic reoxygenation causes a 2-fold increase of iNOS, leading to a rise in nitric oxide production by 140 +/- 45%. Hyperoxic reoxygenation is further responsible for a 2-fold activation of hydrogen peroxide production and an increase in cytosolic superoxide dismutase expression by 35 +/- 10%. NADPH availability has no effect on the hyperoxia-induced decrease of superoxide. Overall, these results indicate that transient hyperoxic reoxygenation in optimal concentrations increases the level of nitric oxide by activation of iNOS and superoxide dismutase, thereby inducing respiration arrest in mitochondria of ischemic cardiomyocytes.
authors.affiliation: Department of Cardiology, University of Freiburg, Freiburg im Breisgau D-79106, Germany. amina.arab@uniklinik-freiburg.de
authors.forename: Amina
authors.initials: A
authors.lastname: Arab
authors.forename: Jin
authors.initials: J
authors.lastname: Wang
authors.forename: Kathrin
authors.initials: K
authors.lastname: Bausch
authors.forename: Katharina
authors.initials: K
authors.lastname: von Schmädel
authors.forename: Christoph
authors.initials: C
authors.lastname: Bode
authors.forename: Christoph
authors.initials: C
authors.lastname: Hehrlein
mesh_terms: D002470:Cell Survival; D003600:Cytosol / Q000201:enzymology; D003576:Electron Transport Complex IV / Q000737:chemistry*; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D018496:Hyperoxia / Q000378:metabolism*; D007511:Ischemia; D053078:Membrane Potential, Mitochondrial; D008954:Models, Biological; D032383:Myocytes, Cardiac / Q000201:enzymology; D009249:NADP / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D010100:Oxygen / Q000737:chemistry; D013482:Superoxide Dismutase / Q000378:metabolism*
chemical_list: D009569:Nitric Oxide; D009249:NADP; D052247:Nitric Oxide Synthase Type II; D013482:Superoxide Dismutase; D003576:Electron Transport Complex IV; D010100:Oxygen