The decomposition of lipid hydroperoxides into peroxyl radicals is a potential source of singlet oxygen (1O2) in biological systems. We report herein on evidence of the generation of 1O2 from lipid hydroperoxides involving a cyclic mechanism from a linear tetraoxide intermediate proposed by Russell. Using 18O-labeled linoleic acid hydroperoxide (LA18O18OH) in the presence of Ce4+ or Fe2+, we observed the formation of 18O-labeled 1O2 (18[1O2]) by chemical trapping of 1O2 with 9,10-diphenylanthracene (DPA) and detected the corresponding 18O-labeled DPA endoperoxide (DPA18O18O) by high-performance liquid chromatography coupled to tandem mass spectrometry.
Spectroscopic evidence for the generation of 1O2 was obtained by measuring (i) the dimol light emission in the red spectral region (λ > 570 nm); (ii) the monomol light emission in the near-infrared (IR) region (λ = 1270 nm); and (iii) the quenching effect of sodium azide. Moreover, the presence of 1O2 was unequivocally demonstrated by the direct spectral characterization of the near-IR light emission. For the sake of comparison, 1O2 deriving from the H2O2/OCl- and H2O2/MoO42- 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 LA18O18OH generates 18[1O2], consistent with the Russell mechanism and pointing to the involvement of 1O2 in lipid hydroperoxide mediated cytotoxicity.
Miyamoto, S., Martinez, G.R., Medeiros, M.H. and Di Mascio, P., 2003. Singlet molecular oxygen generated from lipid hydroperoxides by the Russell mechanism: studies using 18O-labeled linoleic acid hydroperoxide and monomol light emission measurements. Journal of the American Chemical Society, 125(20), pp.6172-6179.
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