title: Inhibition of cellular respiration by endogenously produced carbon monoxide.
abstract: Endogenously produced nitric oxide (NO) interacts with mitochondrial cytochrome c oxidase, leading to inhibition of cellular respiration. This interaction has been shown to have important physiological and pathophysiological consequences. Exogenous carbon monoxide (CO) is also known to inhibit cytochrome c oxidase in vitro; however, it is not clear whether endogenously produced CO can inhibit cellular respiration and, if so, what the significance of this might be. In this study, we show that exogenous CO inhibits respiration in a moderate but persistent manner in HEK293 cells under ambient (21%) oxygen concentrations (K(i) = 1.44 microM). This effect of CO was increased (K(i) = 0.35 microM) by incubation in hypoxic conditions (1% oxygen). Endogenous CO, generated by HEK293 cells transfected with the inducible isoform of haem oxygenase (haem oxygenase-1; HO-1), also inhibited cellular respiration moderately (by 12%) and this was accompanied by inhibition (23%) of cytochrome c oxidase activity. When the cells were incubated in hypoxic conditions during HO-1 induction, the inhibitory effect of CO on cell respiration was markedly increased to 70%. Furthermore, endogenously produced CO was found to be responsible for the respiratory inhibition that occurs in RAW264.7 cells activated in hypoxic conditions with lipopolysaccharide and interferon-gamma, in the presence of N-(iminoethyl)-L-ornithine to prevent the synthesis of NO. Our results indicate that CO contributes significantly to the respiratory inhibition in activated cells, particularly under hypoxic conditions. Inhibition of cell respiration by endogenous CO through its interaction with cytochrome c oxidase might have an important role in inflammatory and hypoxic conditions.
authors.affiliation: Wolfson Institute for Biomedical Research, University College London, UK. s.moncada@ucl.ac.uk
authors.forename: Gabriela
authors.initials: G
authors.lastname: D'Amico
authors.forename: Francis
authors.initials: F
authors.lastname: Lam
authors.forename: Thilo
authors.initials: T
authors.lastname: Hagen
authors.forename: Salvador
authors.initials: S
authors.lastname: Moncada
mesh_terms: D000818:Animals; D002248:Carbon Monoxide / Q000378:metabolism* / Q000494:pharmacology*; D015687:Cell Hypoxia / Q000502:physiology; D002460:Cell Line; D019069:Cell Respiration / Q000187:drug effects*; D002478:Cells, Cultured; D003576:Electron Transport Complex IV / Q000037:antagonists & inhibitors / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D051547:Heme Oxygenase-1 / Q000096:biosynthesis / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D009569:Nitric Oxide / Q000096:biosynthesis / Q000494:pharmacology; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects; D013997:Time Factors
chemical_list: D009569:Nitric Oxide; D002248:Carbon Monoxide; D051547:Heme Oxygenase-1; D003576:Electron Transport Complex IV; D010100:Oxygen