title: Singlet molecular oxygen generated from lipid hydroperoxides by the russell mechanism: studies using 18(O)-labeled linoleic acid hydroperoxide and monomol light emission measurements.
abstract: The decomposition of lipid hydroperoxides into peroxyl radicals is a potential source of singlet oxygen ((1)O(2)) in biological systems. We report herein on evidence of the generation of (1)O(2) from lipid hydroperoxides involving a cyclic mechanism from a linear tetraoxide intermediate proposed by Russell. Using (18)O-labeled linoleic acid hydroperoxide (LA(18)O(18)OH) in the presence of Ce(4+) or Fe(2+), we observed the formation of (18)O-labeled (1)O(2) ((18)[(1)O(2)]) by chemical trapping of (1)O(2) with 9,10-diphenylanthracene (DPA) and detected the corresponding (18)O-labeled DPA endoperoxide (DPA(18)O(18)O) by high-performance liquid chromatography coupled to tandem mass spectrometry. Spectroscopic evidence for the generation of (1)O(2) was obtained by measuring (i) the dimol light emission in the red spectral region (lambda > 570 nm); (ii) the monomol light emission in the near-infrared (IR) region (lambda = 1270 nm); and (iii) the quenching effect of sodium azide. Moreover, the presence of (1)O(2) was unequivocally demonstrated by the direct spectral characterization of the near-IR light emission. For the sake of comparison, (1)O(2) deriving from the H(2)O(2)/OCl(-) and H(2)O(2)/MoO(4)(2)(-) systems or from the thermolysis of the endoperoxide of 1,4-dimethylnaphthalene was also monitored. These chemical trapping and photoemission properties clearly demonstrate that the decomposition of LA(18)O(18)OH generates (18)[(1)O(2)], consistent with the Russell mechanism and pointing to the involvement of (1)O(2) in lipid hydroperoxide mediated cytotoxicity.
authors.affiliation: Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, CP26077, CEP 05513-970, Brazil.
authors.forename: Sayuri
authors.initials: S
authors.lastname: Miyamoto
authors.forename: Glaucia R
authors.initials: GR
authors.lastname: Martinez
authors.forename: Marisa H G
authors.initials: MH
authors.lastname: Medeiros
authors.forename: Paolo
authors.initials: P
authors.lastname: Di Mascio
mesh_terms: D002563:Cerium / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry; D008027:Light; D008041:Linoleic Acids / Q000737:chemistry* / Q000378:metabolism; D008054:Lipid Peroxides / Q000737:chemistry* / Q000378:metabolism; D008163:Luminescent Measurements; D010103:Oxygen Isotopes; D010777:Photochemistry; D026082:Singlet Oxygen / Q000737:chemistry* / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D019265:Spectroscopy, Near-Infrared / Q000379:methods
chemical_list: D005296:Ferrous Compounds; D008041:Linoleic Acids; D008054:Lipid Peroxides; D010103:Oxygen Isotopes; D026082:Singlet Oxygen; C008285:linoleic acid hydroperoxide; D002563:Cerium