Clothier, R. and H. Cox. The Uptake and Photoactivation of Hypericin by Human Keratinocytes and the Protective Effects of Three UV-Filters. ATLA 27: 318. 1999.

Hypericin – 00548-04-9; benzophenone-3 – 00131-57-7; benzophenone-4 – 04065-45-6; Parsol 1789 – 70356-09-1

The objectives of this study were: a) to demonstrate the photoactivation of the anti-depressant hypericin by UV radiation; and b) to evaluate the protective effects of benzophenone-3, benzophenone-4 and Parsol 1789 on this photoactivation in vitro. The targets were a human keratinocyte cell line (HaCaT). The UVA source was the Sol 500 lamp as employed in the ECVAM/COLIPA UV filter study (Spielmann et al. ATLA 26, 679-708, 1998). UV tubes were used for the UVB source and chlorpromazine was used as the positive control. The hypericin was photoactivated, at 10^-8 M following 5 J/cm² UVA, and reduced cell viability by 77 ± 18%. No toxicity was noted up to 10^-7 M on exposure to 60 mJ/cm² UVB. If the hypericin was removed from the cells after the 1-hour pre-treatment, and the cells were exposed to UVA, phototoxicity was still evident, at 10^-8 M, with a loss of viability of 57 ± 24% in the cells. Benzophenone-3, benzophenone-4 and Parsol 1798 were unable to modulate this hypericin-induced photo-damage, when suspended in the culture medium. Benzophenone-3 and Parsol 1789 were cytotoxic with EC50 values of 100.5 ug/ml and 36.4 ug/ml respectively in the presence of 12 J/cm² UVA. However, when dissolved in mineral oil, and floated over the cells’ aqueous medium, cytotoxicity was reduced allowing higher concentrations to be used. Screening of direct UVA-induced damage was observed with 10 mg/ml of benzophenone-3 and Parsol 1789. They failed to reduce the hypericin-induced photo-damage, while reducing that cause by 1 ug/ml chlorpromazine respectively.