Inhibition of bergaptene toxicity by UV-A filters

Synopsis It is well known that 5-methoxypsoralen (5-MOP, bergaptene) exerts several biological actions on irradiation with long wavelength (UV-A, lambda > 320 nm) UV light. The present study had the purpose of evaluating if the phototoxic activity elicited in guinea-pigs by topical application of 5-MOP followed by irradiation, could be reduced or inhibited by the simultaneous application of substances which absorb in the UV-A region. The photo-sensitizing solutions were: an alcoholic solution of 5-MOP, diluted bergamot oil, and an experimental perfume. Of the filters tested, two dibenzoylmethane derivatives proved particularly effective. Interestingly, the inhibitory activity of the filters was significantly greater when these were co-administered with bergamot oil or with the perfume, with respect to the activity shown in the 5-MOP alcoholic solution. A distyrylbiphenyl derivative showing an absorption maximum at 350 nm, was also found particularly effective.