Carboxyfullerenes protect human keratinocytes from ultraviolet-B-induced apoptosis

Carboxyfullerene, a water-soluble carboxylic acid derivative of a fullerene , which acts as a free-radical scavenger, was investigated as a protective agent against ultraviolet-light-induced damage in human keratinocytes. Firs t, we demonstrate that carboxyfullerene is not cytotoxic for these cells. I n addition, this compound significantly reduces the ultraviolet-B-induced i nhibition of keratinocyte proliferation and protects keratinocytes from apo ptosis caused by ultraviolet B irradiation in a time- and dose-dependent fa shion. Furthermore, the percentage of cells with depolarized mitochondria i s significantly lower in ultraviolet-B-irradiated keratinocytes pretreated with carboxyfullerene than in cells provided with diluent alone. Carboxyful lerene also protects human keratinocytes from apoptosis induced by exposure to deoxy-D-ribose, a sugar that causes cell death through a pathway involv ing oxidative stress. On the other hand, ultraviolet B downregulates bcl-2 levels in human keratinocytes, and carboxyfullerene fails to prevent this e ffect. These results suggest that carboxy- fullerene protects human keratin ocytes from ultraviolet B damage possibly via a mechanism interfering with the generation of reactive oxygen species from depolarized mitochondria wit hout the involvement of bcl-2.