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.