title: Mechanism of cytotoxicity of catechols and a naphthalenediol in PC12-AC cells: the connection between extracellular autoxidation and molecular electronic structure.
abstract: ortho-Hydroxyphenols (catechols) form a common structural unit in naturally occurring antioxidants such as polyphenols. They also show pro-oxidant characteristics which depend on their particular structure. Here we examined the acetylated versions of three catechols and a naphthalenediol for cytotoxicity to adrenal PC12-AC cells. We found that the three catechols H1 (a p-methoxycatechol), H2 (a catechol analog of alpha-tocopherol), and H4 (a dioxymethylene-substituted catechol) strongly upregulate glutathione (GSH) in 24 h, whereas 1,4-dipropyl-2,3-naphthalenediol (DPND) does not. Upregulation of GSH is primarily caused by oxidative stress in the form of hydrogen peroxide generation, and both GSH upregulation and the rate of H(2)O(2) generation correlate well with the cytotoxicity. The major source of H(2)O(2) is autoxidation in the extracellular space, which results from transport of the (deacetylated) hydroquinone form outside the cell, rather than internal redox cycling. DPND is much less cytotoxic than any of the catechols. We show that this is because it cannot form a naphthoquinone due to the energy penalty associated with the loss of aromaticity in the benzene ring adjacent to the diol functional group. The relevance of these results to the design of antioxidants is discussed.
authors.affiliation: Department of Chemistry, Carleton University, 1125 Colonel By Drive, Ottawa, ON, Canada K1S 5B6.
authors.forename: Alexandru
authors.initials: A
authors.lastname: Chichirau
authors.forename: Mihaela
authors.initials: M
authors.lastname: Flueraru
authors.forename: Leonid L
authors.initials: LL
authors.lastname: Chepelev
authors.forename: James S
authors.initials: JS
authors.lastname: Wright
authors.forename: William G
authors.initials: WG
authors.lastname: Willmore
authors.forename: Tony
authors.initials: T
authors.lastname: Durst
authors.forename: Helmi H
authors.initials: HH
authors.lastname: Hussain
authors.forename: Martin
authors.initials: M
authors.lastname: Charron
mesh_terms: D000818:Animals; D002396:Catechols / Q000737:chemistry / Q000633:toxicity*; D002470:Cell Survival / Q000187:drug effects; D002999:Clone Cells / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004583:Electrons; D005978:Glutathione / Q000187:drug effects / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism; D015394:Molecular Structure; D009284:Naphthols / Q000737:chemistry / Q000633:toxicity*; D010084:Oxidation-Reduction; D016716:PC12 Cells; D051381:Rats; D013329:Structure-Activity Relationship; D013997:Time Factors
chemical_list: D002396:Catechols; D009284:Naphthols; C107946:2,7-dihydroxynaphthalene; D006861:Hydrogen Peroxide; D005978:Glutathione