Development of an in vitro photosafety evaluation method utilizing intracellular ROS production in THP-1 cells

PhotoSENSIL-18 assay development: Enhancing the safety testing of cosmetic raw materials and finished products to support the in vitro photosensitization assessment?

Although photosensitization remains a major toxicological endpoint for the safety assessment of cosmetic products and their raw materials, there is no validated in vitro method available for the evaluation of this adverse effect so far. Given that previous studies have proposed that the Interleukine-18 (IL-18) plays a key role in keratinocyte-driven pro-inflammatory responses specific of the skin sensitization process, we hypothesize that IL-18 might be used as a specific biomarker for in vitro photosensitization assessment. The aim of the present study was the set-up of a new in vitro assay using IL-18 as a biomarker for the identification of photosensitizers in a reconstructed human epidermis (RHE) model. EpiCS™ RHE were incubated with a set of 16 known sensitising / phototoxic / photosensitizing substances and exposed to ultra-violet (UV) irradiation. Then, the cell viability was analysed by MTT assay, while the IL-18 secretion was quantified by ELISA. Preliminary assays have shown that 1 h of incubation followed by a recovery period of 23 h induced the highest IL-18 production in response to UV exposure. This protocol was used to test 16 substances and a ratio of IL-18 production (UV+/UV- ratio) was then generated. Our data shows that the cut-off of 1.5 (UV+/UV- ratio) is the most predictive model among the tested conditions, being capable of identifying true positive photosensitizers (8 of 9) with a good prediction in comparison with in vivo data. In a nutshell, our data suggests that the PhotoSENSIL-18 is a promising in vitro method for identification of photosensitizing substances. Although further studies are necessary to optimize the model, we foresee that the PhotoSENSIL-18 assay can be used in the context of an Integrative Approach to Testing and Assessment (IATA) of chemicals.

Development of photo-amino acid derivative reactivity assay: a novel in chemico alternative method for predicting photoallergy

Photoallergy test of cosmetics and several types of pharmaceutical substances is often necessary for obtaining approval from authorities. However, there are no official test guidelines for photoallergy evaluation. Therefore, we tried to establish a photoallergy test by utilizing an in chemico alternative sensitization method, amino acid derivative reactivity assay (ADRA). To determine the criteria for judging the photoallergy potential, photo-ADRA with or without photoirradiation was performed using 60 photoallergenic chemicals, and cysteine and lysine derivatives were detected using high-performance liquid chromatography either by absorbance or fluorescence measurement. The accuracy of prediction was 81.4% (48 of 59) and 80.0% (48 of 60) using the absorbance and fluorescence methods, respectively. However, as chemicals can breakdown into multiple chemicals during photoirradiation, the absorbance method often cannot perform accurate detection due to co-elution, whereas the fluorescence method can do this due to lack of co-elution. Moreover, all eight chemicals that were found to be negative or false-positive for photoirritation in the 3T3 neutral red uptake phototoxicity test were confirmed as positive for photoallergy using this method. Furthermore, we prepared three types of pseudo-mixtures where we added one photoallergen along with five nonphotoallergens and performed the photo-ADRA by the ultraviolet and fluorescence methods. The result of the fluorescence method was almost the same as that obtained with the use of a single photoallergen and hence the outcome was not affected by the mixture. Thus, this study not only showed a method of evaluating the photoallergy potential of a single chemical but also a mixture, making it useful as an in chemico photoallergy alternative test.