Use of the occlusive patch to evaluate the photosensitive properties of chemicals in guinea-pigs

A novel in vitro method for the detection and characterization of photosensitizers

Photoactivation and binding of photoactive chemicals to proteins is a known prerequisite for the formation of immunogenic photoantigens and the induction of photoallergy. The intensive use of products and the availability of new chemicals, along with an increasing exposure to sun light contribute to the risk of photosensitizing adverse reactions. Dendritic cells (DC) play a pivotal role in the induction of allergic contact dermatitis. Human peripheral blood monocyte derived dendritic cells (PBMDC) were thus perceived as an obvious choice for the development of a novel in vitro photosensitization assay using the modulation of cell surface protein expression in response to photosensitizing agents. In this new protocol, known chemicals with photosensitizing, allergenic or non-allergenic potential were pre-incubated with PBMDCs prior to UVA irradiation (1 J/cm(2)). Following a 48 h incubation, the expression of the cell surface molecules CD86, HLA-DR and CD83 was measured by flow cytometry. All tested photosensitizers induced a significant and dose-dependent increase of CD86 expression after irradiation compared to non-irradiated controls. Moreover, the phototoxicity of the chemicals could also be determined. In contrast, (i) CD86 expression was not affected by the chosen irradiation conditions, (ii) increased CD86 expression induced by allergens was independent of irradiation and (iii) no PBMDC activation was observed with the non-allergenic control. The assay proposed here for the evaluation of the photoallergenic potential of chemicals includes the assessment of their allergenic, phototoxic and toxic potential in a single and robust test system and is filling a gap in the in vitro photoallergenicity test battery.

Phototoxicity, photoallergy, and contact sensitization of nitro musk perfume raw materials

The potential of 4 related nitro musk substances (musk tibetene, musk ketone, musk xylol, and musk moskene) to cause photoallergy, phototoxicity, and/or contact sensitivity was compared to that of musk ambrette, a known photoallergen. Musk ambrette caused a high incidence of photoallergy as indicated by the severity of the skin grades as compared to a control group. Musk tibetene and musk moskene were negative for phototoxicity, photoallergenicity and contact sensitivity under the test conditions. Musk xylol was shown to be a weak contact sensitizer. Musk ketone gave challenge responses suggestive of a weak phototoxin and a weak contact sensitizer. The latter was not affected by light exposure. These data suggest that except for musk ambrette, the nitro musks as a group do not have the potential to produce photoallergy. Some members of this type of perfume raw material could be classified as weak sensitizers (musk xylol, musk ketone) or weakly phototoxic (musk ketone). These latter biological qualities have not been expressed clinically.