title: Comparing beta-carotene, vitamin E and nitric oxide as membrane antioxidants.
abstract: Singlet oxygen initiates lipid peroxidation via a nonfree radical mechanism by reacting directly with unsaturated lipids to form lipid hydroperoxides (LOOHs). These LOOHs can initiate free radical chain reactions leading to membrane leakage and cell death. Here we compare the ability and mechanism by which three small-molecule membrane antioxidants (beta-carotene, alpha-tocopherol and nitric oxide) inhibit lipid peroxidation in membranes. We demonstrate that beta-carotene provides protection against singlet oxygen-mediated lipid peroxidation, but does not slow free radical-mediated lipid peroxidation. Alpha-Tocopherol does not protect cells from singlet oxygen, but does inhibit free radical formation in cell membranes. Nitric oxide provides no direct protection against singlet oxygen exposure, but is an exceptional chain-breaking antioxidant as evident from its ability to blunt oxygen consumption during free radical-mediated lipid peroxidation. These three small-molecule antioxidants appear to have complementary mechanisms for the protection of cell membranes from detrimental oxidations.
authors.affiliation: Free Radical and Radiation Biology and ESR Facility, The University of Iowa, Iowa City 52242-1101, USA.
authors.forename: Freya Q
authors.initials: FQ
authors.lastname: Schafer
authors.forename: Hong P
authors.initials: HP
authors.lastname: Wang
authors.forename: Eric E
authors.initials: EE
authors.lastname: Kelley
authors.forename: Kate L
authors.initials: KL
authors.lastname: Cueno
authors.forename: Sean M
authors.initials: SM
authors.lastname: Martin
authors.forename: Garry R
authors.initials: GR
authors.lastname: Buettner
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000493:pharmacokinetics / Q000494:pharmacology*; D001692:Biological Transport; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D017323:Dihematoporphyrin Ether; D018922:HL-60 Cells; D006801:Humans; D020014:K562 Cells; D007939:Leukemia L1210; D008027:Light; D051379:Mice; D009569:Nitric Oxide / Q000493:pharmacokinetics / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D014810:Vitamin E / Q000493:pharmacokinetics / Q000494:pharmacology*; D019207:beta Carotene / Q000493:pharmacokinetics / Q000494:pharmacology*
chemical_list: D000975:Antioxidants; D019207:beta Carotene; D014810:Vitamin E; D009569:Nitric Oxide; D017323:Dihematoporphyrin Ether