title: A reappraisal of xanthine dehydrogenase and oxidase in hypoxic reperfusion injury: the role of NADH as an electron donor.
abstract: Xanthine oxidase (XO) is conventionally known as a generator of reactive oxygen species (ROS) which contribute to hypoxic-reperfusion injury in tissues. However, this role for human XO is disputed due to its distinctive lack of activity towards xanthine, and the failure of allopurinol to suppress reperfusion injury. In this paper, we have employed native gel electrophoresis together with activity staining to investigate the role human xanthine dehydrogenase (XD) and XO in hypoxic reperfusion injury. This approach has provided information which cannot be obtained by conventional spectrophotometric assays. We found that both XD and XO of human umbilical vein endothelial cells (HUVECs) and lymphoblastic leukaemic cells (CEMs) catalysed ROS generation by oxidising NADH, but not hypoxanthine. The conversion of XD to XO was observed in both HUVECs and CEMs in response to hypoxia, although the level of conversion varied. Purified human milk XD generated ROS more efficiently in the presence of NADH than in the presence of hypoxanthine. This NADH oxidising activity was blocked by the FAD site inhibitor, diphenyleneiodonium (DPI), but was not suppressible by the molybdenum site inhibitor, allopurinol. However, in the presence of both DPI and allopurinol the activities of XD/XO were completely blocked with either NADH or hypoxanthine as substrates. We conclude that both human XD and XO can oxidise NADH to generate ROS. Therefore, the conversion of XD to XO is not necessary for post-ischaemic ROS generation. The hypoxic-reperfusion injury hypothesis should be reappraised to take into account the important role played by XD and XO in oxidising NADH to yield ROS.
authors.affiliation: Bone and Joint Research Unit, St Bartholomew's and the Royal London School of Medicine and Dentistry, University of London, UK. Z.ZHANG@MDS.QMW.AC.UK
authors.forename: Z
authors.initials: Z
authors.lastname: Zhang
authors.forename: D R
authors.initials: DR
authors.lastname: Blake
authors.forename: C R
authors.initials: CR
authors.lastname: Stevens
authors.forename: J M
authors.initials: JM
authors.lastname: Kanczler
authors.forename: P G
authors.initials: PG
authors.lastname: Winyard
authors.forename: M C
authors.initials: MC
authors.lastname: Symons
authors.forename: M
authors.initials: M
authors.lastname: Benboubetra
authors.forename: R
authors.initials: R
authors.lastname: Harrison
mesh_terms: D000493:Allopurinol / Q000494:pharmacology*; D015687:Cell Hypoxia; D002478:Cells, Cultured; D004591:Electrophoresis, Polyacrylamide Gel; D010450:Endopeptidases / Q000378:metabolism; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D000860:Hypoxia / Q000150:complications*; D007511:Ischemia / Q000150:complications / Q000378:metabolism; D008214:Lymphocytes / Q000378:metabolism* / Q000473:pathology; D008895:Milk, Human / Q000201:enzymology; D009243:NAD / Q000378:metabolism*; D009861:Onium Compounds / Q000494:pharmacology*; D010084:Oxidation-Reduction; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000473:pathology; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015427:Reperfusion Injury / Q000201:enzymology* / Q000209:etiology; D013053:Spectrophotometry; D013379:Substrate Specificity; D014407:Tumor Cells, Cultured; D014471:Umbilical Veins; D014968:Xanthine Dehydrogenase / Q000502:physiology*; D014969:Xanthine Oxidase / Q000502:physiology*
chemical_list: D004791:Enzyme Inhibitors; D009861:Onium Compounds; D017382:Reactive Oxygen Species; D009243:NAD; D000493:Allopurinol; C007517:diphenyleneiodonium; D014968:Xanthine Dehydrogenase; D014969:Xanthine Oxidase; D010450:Endopeptidases