The water-soluble
fullerene derivative
gamma-cyclodextrin bicapped C(60) [(gamma-CyD)(2)/C(60), CDF0] has several clinical applications, including use as a
drug carrier to bypass the blood ocular barriers or a
photosensitizer to treat
tumors in
photodynamic therapy. We have assessed the potential
ocular toxicity of (gamma-CyD)(2)/C(60) and its aggregated derivatives induced by UVA and visible light in vitro in human lens epithelial cells (HLE B-3). Cell viability using the MTS assay demonstrated that 2 microM (gamma-CyD)(2)/C(60) was highly phototoxic to HLE B-3 cells with UVA irradiation, while no effect was observed in the presence of visible light or when maintained in the dark. In contrast, the aggregated derivative (CDF150) showed neither cytotoxicity nor any phototoxic effect even at 30 microM with either UVA or visible light irradiation. In lens cells treated with (gamma-CyD)(2)/C(60),
phototoxicity was manifested as apoptosis.
Singlet oxygen production measurement using the EPR/TEMP trapping technique determined that (gamma-CyD)(2)/C(60) (CDF0) efficiently produced
singlet oxygen. The rate of
singlet oxygen production decreased with increased aggregation, with no production by the fully aggregated sample formed after 150 min of heating (CDF150). UVA irradiation of HLE B-3 in the presence of (gamma-CyD)(2)/C(60) resulted in a significant rise in intracellular
protein-derived
peroxides. The
singlet oxygen quenchers
sodium azide and
histidine each significantly protected lens cells against (gamma-CyD)(2)/C(60) photodamage, but
lutein and
Trolox (
vitamin E) did not. Clearly,
singlet oxygen is an important intermediate in the
phototoxicity of monomeric (gamma-CyD)(2)/
fullerene. Our results also demonstrate that UVA-blocking sunglasses can limit the ocular
phototoxicity of this nanomaterial, while nontoxic
endogenous antioxidants like
lutein or
Trolox cannot provide adequate protection.