title: Superoxide activates uncoupling proteins by generating carbon-centered radicals and initiating lipid peroxidation: studies using a mitochondria-targeted spin trap derived from alpha-phenyl-N-tert-butylnitrone.
abstract: Although the physiological role of uncoupling proteins (UCPs) 2 and 3 is uncertain, their activation by superoxide and by lipid peroxidation products suggest that UCPs are central to the mitochondrial response to reactive oxygen species. We examined whether superoxide and lipid peroxidation products such as 4-hydroxy-2-trans-nonenal act independently to activate UCPs, or if they share a common pathway, perhaps by superoxide exposure leading to the formation of lipid peroxidation products. This possibility can be tested by blocking the putative reactive oxygen species cascade with selective antioxidants and then reactivating UCPs with distal cascade components. We synthesized a mitochondria-targeted derivative of the spin trap alpha-phenyl-N-tert-butylnitrone, which reacts rapidly with carbon-centered radicals but is unreactive with superoxide and lipid peroxidation products. [4-[4-[[(1,1-Dimethylethyl)-oxidoimino]methyl]phenoxy]butyl]triphenylphosphonium bromide (MitoPBN) prevented the activation of UCPs by superoxide but did not block activation by hydroxynonenal. This was not due to MitoPBN reacting with superoxide or the hydroxyl radical or by acting as a chain-breaking antioxidant. MitoPBN did react with carbon-centered radicals and also prevented lipid peroxidation by the carbon-centered radical generator 2,2'-azobis(2-methyl propionamidine) dihydrochloride (AAPH). Furthermore, AAPH activated UCPs, and this was blocked by MitoPBN. These data suggest that superoxide and lipid peroxidation products share a common pathway for the activation of UCPs. Superoxide releases iron from iron-sulfur center proteins, which then generates carbon-centered radicals that initiate lipid peroxidation, yielding breakdown products that activate UCPs.
authors.affiliation: Medical Research Council Dunn Human Nutrition Unit, Wellcome Trust-MRC Building, Hills Road, Cambridge CB2 2XY, United Kingdom. mpm@mrc-dunn.cam.ac.uk
authors.forename: Michael P
authors.initials: MP
authors.lastname: Murphy
authors.forename: Karim S
authors.initials: KS
authors.lastname: Echtay
authors.forename: Frances H
authors.initials: FH
authors.lastname: Blaikie
authors.forename: Jordi
authors.initials: J
authors.lastname: Asin-Cayuela
authors.forename: Helena M
authors.initials: HM
authors.lastname: Cocheme
authors.forename: Katherine
authors.initials: K
authors.lastname: Green
authors.forename: Julie A
authors.initials: JA
authors.lastname: Buckingham
authors.forename: Ellen R
authors.initials: ER
authors.lastname: Taylor
authors.forename: Fiona
authors.initials: F
authors.lastname: Hurrell
authors.forename: Gillian
authors.initials: G
authors.lastname: Hughes
authors.forename: Satomi
authors.initials: S
authors.lastname: Miwa
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Cooper
authors.forename: Dimitri A
authors.initials: DA
authors.lastname: Svistunenko
authors.forename: Robin A J
authors.initials: RA
authors.lastname: Smith
authors.forename: Martin D
authors.initials: MD
authors.lastname: Brand
mesh_terms: D000818:Animals; D002244:Carbon / Q000737:chemistry*; D002352:Carrier Proteins / Q000378:metabolism*; D003497:Cyclic N-Oxides; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D007473:Ion Channels; D015227:Lipid Peroxidation; D008565:Membrane Proteins / Q000378:metabolism*; D008930:Mitochondria, Liver / Q000378:metabolism*; D024101:Mitochondrial Proteins; D009589:Nitrogen Oxides / Q000737:chemistry*; D051381:Rats; D017382:Reactive Oxygen Species; D013113:Spin Labels; D013481:Superoxides / Q000378:metabolism*; D000071256:Uncoupling Protein 1
chemical_list: D002352:Carrier Proteins; D003497:Cyclic N-Oxides; D005609:Free Radicals; D007473:Ion Channels; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D009589:Nitrogen Oxides; D017382:Reactive Oxygen Species; D013113:Spin Labels; D000071256:Uncoupling Protein 1; D013481:Superoxides; C029217:phenyl-N-tert-butylnitrone; D002244:Carbon