Beneficial effects of photo-inactive titanium dioxide specimens on plasmid DNA, human cells and yeast cells exposed to UVA/UVB simulated sunlight

Photoactive TiO2 specimens extracted from commercial sunscreen lotions had been shown earlier [R. Dunford, A. Salinaro, L. Cai, N. Serpone, S. Horikoshi, H. Hidaka, J. Knowland, FEBS Lett. 418 (1997) 87] to cause damage to both DNA plasmids in vitro and to whole human skin cells in cultures by photoproduced OH radicals. This article reports on the effects of TiO2 specimens, whose particle surface was modified by a thermally assisted procedure to produce TiO2 specimens of considerably reduced photo-activity. Deactivation of the photocatalytic activity of TiO2 impacts on the kinetics of photooxidation of phenol and has a significant effect in diminishing, if not suppressing completely, damage caused to DNA plasmids, to human cells, and to yeast cells compared to non-modified specimens exposed to UVB/UVA simulated solar radiation. Photo-inactive TiO2 could be beneficial in sunscreen formulations and in polymer blends, since they also completely retain their UVB/UVA absorption/scattering (screening) characteristics. Synergistic effects of titania specimens with an organic sunscreen active agent (Padimate-O) on DNA plasmids and the survival of yeast cells in the presence of titanium dioxide, and in the presence of such UV filters as Padimate-O and Parsol 1789 (i.e., avobenzone) under UV irradiation are reported.