The results of meantissue values in the presence and absence
of UV light werecompared and a test substance was considered to be phototoxic, if one or more test concentrations of the (+UVA) part of the experiment revealed a decrease in viability exceeding 30% when compared with identical concentrationsof the (−UVA) part of the experiment (Liebsch et al., 1997). Bergamot oil was used as positive control (Kejlová et al., 2007). The results obtained in the 3T3 Neutral Red Uptake Phototoxicity test showed that only avobenzone Epigenetics Compound Library in vitro was considered phototoxic, since it presented mean MPE of 0.327 and mean PIF of 11.478 (Table 1). Despite vitamin A palmitate presented a borderline mean MPE (0.106), some obtained values were classified as phototoxic or probably phototoxic, thuson the basis of these borderline results,
this vitamin was submitted to a UV dose/response study to confirm its phototoxic potential. The results obtained when avobenzone and vitamin A palmitate were submitted to 3T3 NRU Phototoxicity test under various intensities of UVA (2, 4 and 8 J/cm2) showed that avobenzone presented a pronounced phototoxicity enhancement (increased MPE) with higher UVA doses, showing that its phototoxicity was UVA dose dependent (Table 2). However when vitamin A was analyzed, no dose response effect was observed. Thus, the obtained results showed that vitamin A presented a tendency to a weak phototoxicpotential that was not confirmed in the dose response study (Table 2). When the combinations under study were analyzed, the phototoxicity test showed that only the combinations containing avobenzone, mTOR inhibitor comb 2 (OMC, AVB, MBC) and comb 4 (OMC, AVB, OC), presented phototoxic potential (Table 4). The other for combinations, comb 1 (OMC, BP-3 and OS) and comb 3 (OMC, BP-3 and OC), did not present any phototoxic potential, even when combined with vitamin A (Table 3). Both combination 2= and 4= (containing the different UV-filters in the same proportion used in the formulations under study) were not considered phototoxic (MPE lower than 0.15). There was an enhancement of MPE values, when vitamin A palmitate was added to these combinations (comb 2a= and
comb 4a=), however these combinations where still considered not phototoxic (Table 4). When combinations 2 and 4 (containing the different UV-filters in the proportion 1:1:1) were evaluated, there was an enhancement of MPE values, which were closer to borderline phototoxicity values. When vitamin A palmitate was added to these combinations, comb 2A and comb 4A had their MPE enhanced to 0.310 and 0.229, respectively, indicating a synergistic effect of vitamin A palmitate on phototoxicity of these combinations containing avobenzone. When a lower concentration of vitamin A was added to these UV-filters combinations, comb 2a and 4a (containing a proportion of UV-filters/vitamin A 1:0.1), a reduction of MPE values was observed (0.169 and 0.