The water-soluble fullerene derivative 'Radical Sponge super([registered])' 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 super([registered])' 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 super([registered]) of 25-75 mu M and did not exhibit any photo-cytotoxicity due to coexistent Radical Sponge super([registered]) as compared with the sham-irradiation control. Radical Sponge super([registered]) exerted a more marked cytoprotection at doses of 10-40 mu M against UVA irradiation of 30 J/cm super(2) 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 super([registered]) on UVA injuries. Cytoprotection by Radical Sponge super([registered]) against UVA was achieved at the advisable range doses of 10-40 mu M 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 mu M. Thus, Radical Sponge super([registered]) is expected as an anti-UVA- preventive agent without visible-light-catalyzed cytotoxicity toward human skin keratinocytes.