The water-soluble fullerene derivative ‘Radical Sponge®’ exerts cytoprotective action against UVA irradiation but not visible-light-catalyzed cytotoxicity in human skin keratinocytes

Fullerene was entrapped in polyvinylpyrrolidone of 60-80 kDa at a molar ratio range of 0.42–0.67:1, resulting in a water-soluble derivative with a mean particle diameter of about 688 nm, named ‘Radical Sponge®’ because of its ROS-scavenging ability as previously demonstrated, and examined in the present study for its photo-biological actions toward human skin keratinocytes HaCaT. The keratinocytes were repeatedly irradiated with a visible light of wavelengths of 400–2000 nm (approximately 19,800 lux) in the presence or absence of Radical Sponge® of 25–75 μM and did not exhibit any photo-cytotoxicity due to coexistent Radical Sponge® as compared with the sham-irradiation control. Radical Sponge® exerted a more marked cytoprotection at doses of 10–40 μM against UVA irradiation of 30 J/cm2 when it was pre-irradiationally administered and rinsed out immediately before the irradiation, than when administered only during or after the irradiation, indicating the preventive rather than therapeutic or ray-sheltering effect of Radical Sponge® on UVA injuries. Cytoprotection by Radical Sponge® against UVA was achieved at the advisable range doses of 10–40 μM in contrast to no effect of polyvinylpyrrolidone alone; its dose-dependency was advantageous over that of VC-IP, a tetra-alkyl-esterized provitamin C, which became less cytoprotective above 20 μM. Thus, Radical Sponge® is expected as an anti-UVA-preventive agent without visible-light-catalyzed cytotoxicity toward human skin keratinocytes.