title: Pristine (C60) and hydroxylated [C60(OH)24] fullerene phototoxicity towards HaCaT keratinocytes: type I vs type II mechanisms.
abstract: The increasing use of fullerene nanomaterials has prompted widespread concern over their biological effects. Herein, we have studied the phototoxicity of gamma-cyclodextrin bicapped pristine C 60 [(gamma-CyD) 2/C 60] and its water-soluble derivative C 60(OH) 24 toward human keratinocytes. Our results demonstrated that irradiation of (gamma-CyD) 2/C 60 or C 60(OH) 24 in D 2O generated singlet oxygen with quantum yields of 0.76 and 0.08, respectively. Irradiation (>400 nm) of C 60(OH) 24 generated superoxide as detected by the EPR spin trapping technique; superoxide generation was enhanced by addition of the electron donor nicotinamide adenine dinucleotide (reduced) (NADH). During the irradiation of (gamma-CyD) 2/C 60, superoxide was generated only in the presence of NADH. Cell viability measurements demonstrated that (gamma-CyD) 2/C 60 was about 60 times more phototoxic to human keratinocytes than C 60(OH) 24. UVA irradiation of human keratinocytes in the presence of (gamma-CyD) 2/C 60 resulted in a significant rise in intracellular protein-derived peroxides, suggesting a type II mechanism for phototoxicity. UVA irradiation of human keratinocytes in the presence of C 60(OH) 24 produced diffuse intracellular fluorescence when the hydrogen peroxide probe Peroxyfluor-1 was present, suggesting a type I mechanism. Our results clearly show that the phototoxicity induced by (gamma-CyD) 2/C 60 is mainly mediated by singlet oxygen with a minor contribution from superoxide, while C 60(OH) 24 phototoxicity is mainly due to superoxide.
authors.affiliation: Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA. zhaob2@niehs.nih.gov
authors.forename: Baozhong
authors.initials: B
authors.lastname: Zhao
authors.forename: Yu-Ying
authors.initials: YY
authors.lastname: He
authors.forename: Piotr J
authors.initials: PJ
authors.lastname: Bilski
authors.forename: Colin F
authors.initials: CF
authors.lastname: Chignell
mesh_terms: D002460:Cell Line; D002470:Cell Survival; D005609:Free Radicals / Q000737:chemistry / Q000378:metabolism; D037741:Fullerenes / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D006900:Hydroxylation; D015603:Keratinocytes / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism; D015394:Molecular Structure; D010100:Oxygen / Q000378:metabolism; D010777:Photochemistry; D013053:Spectrophotometry
chemical_list: D005609:Free Radicals; D037741:Fullerenes; C530172:pristine (C60); D006861:Hydrogen Peroxide; D010100:Oxygen