Genotoxicity of bergapten and bergamot oil in Saccharomyces cerevisiae.

In order to determine the genotoxic potential of bergapten (5-methoxypsoralen (5-MOP] and bergamot oil (BO), the genetic effects of 5-MOP and BO (containing equivalent amounts of 5-MOP) were studied in haploid and diploid yeast (Saccharomyces cerevisiae) using solar simulated radiation (SSR). At equal doses of SSR, equal concentrations of 5-MOP alone or 5-MOP in BO have a similar influence on survival and on the induction of cytoplasmic "petite" mutations, reverse and forward mutations, mitotic gene conversion and genetically aberrant colonies including mitotic crossing over. No reciprocity is found between SSR dose and 5-MOP concentration for cytotoxic, mutagenic and recombinogenic effects. In the presence of chemical filters (Parsol 1789, a UVA filter, and Parsol MCX, a cinnamate derivative acting as a UVB filter) considerable protection is observed against the induction of genetic effects by 5-MOP and BO containing 5-MOP in haploid and diploid cells. As indicated by the lower induction kinetics, the protection is higher than expected from the light-absorbing properties, suggesting photochemical interaction. The protection is slightly higher for BO than for 5-MOP. The induction of genetic effects by 5-MOP alone or BO containing 5-MOP is independent of oxygen. Experiments on suction blister fluids taken from patients after topical treatment with BO containing 5-MOP indicate that in comparison with water the bioavailability and thus the genotoxic effects of the compounds are decreased. Moreover, in addition to the filtering effect against the photoinduced genotoxic effects of BO, the presence of chemical filters apparently reduces the penetration of BO containing 5-MOP and provides a reduction in biological effectiveness.