title: Interactions of dietary carotenoids with activated (singlet) oxygen and free radicals: potential effects for human health.
abstract: Molecular mechanisms associated with the anti-/pro-oxidative properties of carotenoids (CARs) are described in organic solvents, micro-heterogeneous environments and model lipid membranes and in cellular suspensions. Singlet oxygen is important in the skin and eye and CARs are efficient singlet oxygen (SO) quenchers with corresponding rate constants near diffusion controlled (typically app. 10¹⁰ M⁻¹ s⁻¹) with lycopene (LYC) exhibiting the most efficient quenching in organic solvents. However, in membrane environments there is little or no difference in the quenching efficiency between the dietary CARs. Furthermore, aggregation of CARs, particularly those in the macula (lutein and zeaxanthin), markedly reduces SO quenching efficiency. Free radical interactions with CARs leads to at least three processes, electron and hydrogen atom transfer and adduct formation. The most studied is electron transfer where the CAR loses an electron to become a radical cation. The reactivity/lifetime of such CAR radicals may lead to a switch from anti- to pro-oxidant behaviour of CARs. These reactions are related to CAR redox potentials with LYC being the lowest (most easily oxidised) allowing LYC to reduce/repair all other CAR radical cations and LYC 'sacrificed' where mixtures of CARs are present in oxidative environments. Such redox-controlled reactions may lead to deleterious as well as beneficial health effects.
authors.affiliation: Department of Dermatology, Charité-Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Fritz
authors.initials: F
authors.lastname: Böhm
authors.forename: Ruth
authors.initials: R
authors.lastname: Edge
authors.forename: George
authors.initials: G
authors.lastname: Truscott
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000502:physiology*; D002338:Carotenoids / Q000737:chemistry* / Q000494:pharmacology* / Q000502:physiology; D002986:Clinical Trials as Topic; D004032:Diet; D005609:Free Radicals / Q000378:metabolism; D006801:Humans; D014975:Lutein / Q000378:metabolism; D018384:Oxidative Stress; D017382:Reactive Oxygen Species; D026082:Singlet Oxygen / Q000378:metabolism; D024341:Xanthophylls / Q000378:metabolism; D065146:Zeaxanthins
chemical_list: D000975:Antioxidants; D005609:Free Radicals; D017382:Reactive Oxygen Species; D024341:Xanthophylls; D065146:Zeaxanthins; D026082:Singlet Oxygen; D002338:Carotenoids; D014975:Lutein