title: Protection of endogenous beta-carotene in LDL oxidized by oxygen free radicals in the presence of supraphysiological concentrations of melatonin.
abstract: This study was designed to evaluate the effect of high concentrations of melatonin on the peroxidation of human low density lipoproteins (LDLs) initiated by O(2)(*-) and ethanol-derived peroxyl radicals (RO(2)(*)) from water gamma radiolysis in the presence of ethanol. LDL (3 g/l; total LDL concentration) was oxidized in the absence of melatonin or in its presence at three concentrations (50 x 10(-6), 100 x 10(-6) or 250 x 10(-6) mol/l) in ethanol. Radiolytic yields (i.e. number of mole consumed or produced per Joule) of the markers of lipid peroxidation were determined (i.e. decrease in the endogenous antioxidants alpha-tocopherol and beta-carotene, formation of conjugated dienes and of thiobarbituric acid-reactive substances [TBARS]). Melatonin decreased the yields of lipid peroxidation products and delayed the onset of the propagation phase for conjugated dienes and TBARS in a concentration-dependent manner. Nevertheless, melatonin did not protect endogenous alpha-tocopherol against peroxyl-induced oxidation (probably due to a lower scavenging capacity than that of alpha-tocopherol towards peroxyl radicals), but delayed the consumption of LDL endogenous beta-carotene and decreased its rate of disappearance. The effect of melatonin seemed to be the highest for a melatonin concentration of 250 x 10(-6) mol/l.
authors.affiliation: Laboratoire de Biochimie B, Hôpital de la Salpêtrière, Assistance Publique-Hôpitaux de Paris (AP-HP), Paris, France. dominique.rousselot@psl.ap-hop-paris.fr
authors.forename: Dominique
authors.initials: D
authors.lastname: Bonnefont-Rousselot
authors.forename: Virginie
authors.initials: V
authors.lastname: Guilloz
authors.forename: Sylvie
authors.initials: S
authors.lastname: Lepage
authors.forename: Catherine
authors.initials: C
authors.lastname: Bizard
authors.forename: Patrick
authors.initials: P
authors.lastname: Duriez
authors.forename: Daniel
authors.initials: D
authors.lastname: Lesieur
authors.forename: Jacques
authors.initials: J
authors.lastname: Delattre
authors.forename: Daniel
authors.initials: D
authors.lastname: Jore
authors.forename: Monique
authors.initials: M
authors.lastname: Gardès-Albert
mesh_terms: D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D000431:Ethanol / Q000494:pharmacology; D005609:Free Radicals; D005720:Gamma Rays; D006801:Humans; D015227:Lipid Peroxidation; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008550:Melatonin / Q000378:metabolism*; D008956:Models, Chemical; D010100:Oxygen / Q000378:metabolism*; D017392:Thiobarbituric Acid Reactive Substances / Q000378:metabolism; D024502:alpha-Tocopherol / Q000378:metabolism; D019207:beta Carotene / Q000378:metabolism*
chemical_list: D005609:Free Radicals; D008077:Lipoproteins, LDL; D017392:Thiobarbituric Acid Reactive Substances; D019207:beta Carotene; D000431:Ethanol; D024502:alpha-Tocopherol; D008550:Melatonin; D010100:Oxygen