title: NADPH oxidase 4 regulates homocysteine metabolism and protects against acetaminophen-induced liver damage in mice.
abstract: Glutathione is the major intracellular redox buffer in the liver and is critical for hepatic detoxification of xenobiotics and other environmental toxins. Hepatic glutathione is also a major systemic store for other organs and thus impacts on pathologies such as Alzheimer's disease, Sickle Cell Anaemia and chronic diseases associated with aging. Glutathione levels are determined in part by the availability of cysteine, generated from homocysteine through the transsulfuration pathway. The partitioning of homocysteine between remethylation and transsulfuration pathways is known to be subject to redox-dependent regulation, but the underlying mechanisms are not known. An association between plasma Hcy and a single nucleotide polymorphism within the NADPH oxidase 4 locus led us to investigate the involvement of this reactive oxygen species- generating enzyme in homocysteine metabolism. Here we demonstrate that NADPH oxidase 4 ablation in mice results in increased flux of homocysteine through the betaine-dependent remethylation pathway to methionine, catalysed by betaine-homocysteine-methyltransferase within the liver. As a consequence NADPH oxidase 4-null mice display significantly lowered plasma homocysteine and the flux of homocysteine through the transsulfuration pathway is reduced, resulting in lower hepatic cysteine and glutathione levels. Mice deficient in NADPH oxidase 4 had markedly increased susceptibility to acetaminophen-induced hepatic injury which could be corrected by administration of N-acetyl cysteine. We thus conclude that under physiological conditions, NADPH oxidase 4-derived reactive oxygen species is a regulator of the partitioning of the metabolic flux of homocysteine, which impacts upon hepatic cysteine and glutathione levels and thereby upon defence against environmental toxins.
authors.affiliation: Cardiovascular Division, King's College London, 125 Coldharbour Lane, London E5 0AD.
authors.forename: Thomas V A
authors.initials: TV
authors.lastname: Murray
authors.affiliation: Cardiovascular Division, King's College London, 125 Coldharbour Lane, London E5 0AD.
authors.forename: Xuebin
authors.initials: X
authors.lastname: Dong
authors.affiliation: Cardiovascular Division, King's College London, 125 Coldharbour Lane, London E5 0AD.
authors.forename: Greta J
authors.initials: GJ
authors.lastname: Sawyer
authors.affiliation: Mass Spectrometry Facility, King's College London, FWB, 150 Stamford Street London E1 9NH.
authors.forename: Anna
authors.initials: A
authors.lastname: Caldwell
authors.affiliation: Mass Spectrometry Facility, King's College London, FWB, 150 Stamford Street London E1 9NH.
authors.forename: John
authors.initials: J
authors.lastname: Halket
authors.affiliation: NHS Foundation Trust, King's College Hospital, Denmark Hill, London SE5 9RS.
authors.forename: Roy
authors.initials: R
authors.lastname: Sherwood
authors.affiliation: Institute of Liver Studies, King's College London, Denmark Hill, London SE5 9RS.
authors.forename: Alberto
authors.initials: A
authors.lastname: Quaglia
authors.affiliation: NHS Foundation Trust, King's College Hospital, Denmark Hill, London SE5 9RS.
authors.forename: Tracy
authors.initials: T
authors.lastname: Dew
authors.affiliation: Cardiovascular Division, King's College London, 125 Coldharbour Lane, London E5 0AD.
authors.forename: Narayana
authors.initials: N
authors.lastname: Anilkumar
authors.affiliation: Cardiovascular Division, King's College London, 125 Coldharbour Lane, London E5 0AD.
authors.forename: Simon
authors.initials: S
authors.lastname: Burr
authors.affiliation: Cardiovascular Division, King's College London, 125 Coldharbour Lane, London E5 0AD.
authors.forename: Rajesh K
authors.initials: RK
authors.lastname: Mistry
authors.affiliation: Cardiovascular Division, King's College London, 125 Coldharbour Lane, London E5 0AD.
authors.forename: Daniel
authors.initials: D
authors.lastname: Martin
authors.affiliation: Institut für Kardiovaskuläre Physiologie, Goethe-Universität, 60596 Frankfurt am Main, Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Schröder
authors.affiliation: Institut für Kardiovaskuläre Physiologie, Goethe-Universität, 60596 Frankfurt am Main, Germany.
authors.forename: Ralf P
authors.initials: RP
authors.lastname: Brandes
authors.affiliation: Institute of Liver Studies, King's College London, Denmark Hill, London SE5 9RS.
authors.forename: Robin D
authors.initials: RD
authors.lastname: Hughes
authors.affiliation: Cardiovascular Division, King's College London, 125 Coldharbour Lane, London E5 0AD.
authors.forename: Ajay M
authors.initials: AM
authors.lastname: Shah
authors.affiliation: Cardiovascular Division, King's College London, 125 Coldharbour Lane, London E5 0AD. Electronic address: alison.brewer@kcl.ac.uk.
authors.forename: Alison C
authors.initials: AC
authors.lastname: Brewer
mesh_terms: D000082:Acetaminophen / Q000633:toxicity*; D018712:Analgesics, Non-Narcotic / Q000633:toxicity*; D000818:Animals; D001622:Betaine / Q000378:metabolism; D015153:Blotting, Western; D002478:Cells, Cultured; D003545:Cysteine / Q000378:metabolism; D005260:Female; D005978:Glutathione / Q000378:metabolism; D056945:Hep G2 Cells; D006710:Homocysteine / Q000378:metabolism*; D006801:Humans; D007124:Immunoenzyme Techniques; D008099:Liver / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D008107:Liver Diseases / Q000209:etiology / Q000517:prevention & control*; D008715:Methionine / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases / Q000502:physiology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000378:metabolism
chemical_list: D018712:Analgesics, Non-Narcotic; D017382:Reactive Oxygen Species; D006710:Homocysteine; D000082:Acetaminophen; D001622:Betaine; D012436:S-Adenosylmethionine; D008715:Methionine; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases; C422943:Nox4 protein, mouse; D005978:Glutathione; D003545:Cysteine
keywords: Betaine-homocysteine-methyltransferase (BHMT); Glutathione; Hepatotoxicity; Nox4; Redox-signaling