title: Involvement of semiquinone radicals in the in vitro cytotoxicity of cigarette mainstream smoke.
abstract: Free radicals in cigarette smoke have attracted a great deal of attention because they are hypothesized to be responsible in part for several of the pathologies related to smoking. Hydroquinone, catechol, and their methyl-substituted derivatives are abundant in the particulate phase of cigarette smoke, and they are known precursors of semiquinone radicals. In this study, the in vitro cytotoxicity of these dihydroxybenzenes was determined using the neutral red uptake (NRU) assay, and their radical-forming capacity was determined by electron paramagnetic resonance (EPR). All of the dihydroxybenzenes studied were found to generate appreciable amounts of semiquinone radicals when dissolved in the cell culture medium employed in the NRU assay. Hydroquinone exhibited by far the highest capacity to form semiquinone radicals at physiological pH, even though it is not the most cytotoxic dihydroxybenzene. Methyl-substituted dihydroxybenzenes were found to be more cytotoxic than either hydroquinone or catechol. The formation of semiquinone radicals via auto-oxidation of the dihydroxybenzenes was found to be dependent on the reduction potential of the corresponding quinone/semiquinone radical redox couple. The capacity to generate semiquinone radicals was found to be insufficient to explain the variance in the cytotoxicity among the dihydroxybenzenes in our study; consequently, other mechanisms of toxicity must also be involved. The observed interactions between 2,6-dimethylhydroquinone and hydroquinone in the cytotoxicity assay and EPR analysis suggest that care needs to be taken when the bioactivity of cigarette smoke constituents is evaluated, i.e., the effect of the cigarette smoke complex matrix on the activity of the single constituent studied must be taken into consideration.
authors.affiliation: Philip Morris USA Research Center, 4201 Commerce Road, Richmond, Virginia 23234, USA. salem.chouchane@pmusa.com
authors.forename: Salem
authors.initials: S
authors.lastname: Chouchane
authors.forename: Jan B
authors.initials: JB
authors.lastname: Wooten
authors.forename: Franz J
authors.initials: FJ
authors.lastname: Tewes
authors.forename: Arno
authors.initials: A
authors.lastname: Wittig
authors.forename: Boris P
authors.initials: BP
authors.lastname: Müller
authors.forename: Detlef
authors.initials: D
authors.lastname: Veltel
authors.forename: Joerg
authors.initials: J
authors.lastname: Diekmann
mesh_terms: D000818:Animals; D041702:BALB 3T3 Cells; D016227:Benzoquinones / Q000009:adverse effects* / Q000302:isolation & purification; D002470:Cell Survival / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004578:Electron Spin Resonance Spectroscopy; D051379:Mice; D015394:Molecular Structure; D014028:Tobacco Smoke Pollution / Q000009:adverse effects* / Q000032:analysis
chemical_list: D016227:Benzoquinones; D014028:Tobacco Smoke Pollution; C025232:semiquinone radicals