Immortalized equivalent human epidermis as a platform to evaluation hair dyes toxicity: Efficiency comparison between 3D and monolayer culture.

The use of 3D models in various scientific applications is becoming more popular to replace traditional monolayers models. In this work, we used a three-dimensional in-house model of epidermis using HaCaT immortalized cells to evaluate the dermal toxicity induced by Basic Blue 99 and Basic Red 51, both present in commercial hair dye formulations. Our data show that cells cultured in the 3D model respond differently to those cultured in monolayer. Basic Red 51 dye induces apoptosis an DNA breaks in both models, however, these effects is more pronounced in cells cultured in monolayer. The toxic mode of action of Basic Blue 99 seems to be the induction of cell death, without genotoxic effects, but while the necrotic pathway is observed in HaCaT monolayer cell culture, was apoptosis seen in the Equivalent Human Epidermis (EHE) model. We could also confirm that cells in EHE model, an environment that could better mimic human effects, react differently to chemical stressors than the cells cultivated in 2D.

Cytotoxic and genotoxic effects of two hair dyes used in the formulation of black color.

According to the International Agency for Research on Cancer (IARC), some hair dyes are considered mutagenic and carcinogenic in in vitro assays and exposed human populations. Epidemiological studies indicate that hairdressers occupationally exposed to hair dyes have a higher risk of developing bladder cancer. In Brazil, 26% of the adults use hair dye. In this study, we investigated the toxic effects of two hair dyes, Basic Red 51 (BR51) and Basic Brown 17 (BB17), which are temporary dyes of the azo group (R-N=N-R'), used in the composition of the black hair dye. To this end, MTT and trypan blue assays (cytotoxicity), comet and micronucleus assay (genotoxicity) were applied, with HepG2 cells. For cytotoxic assessment, dyes were tested in serial dilutions, being the highest concentrations those used in the commercial formula for hair dyes. For genotoxic assessment concentrations were selected according to cell viability. Results showed that both dyes induced significant cytotoxic and genotoxic effects in the cells, in concentrations much lower than those used in the commercial formula. Genotoxic effects could be related to the azo structure present in the composition of the dyes, which is known as mutagenic and carcinogenic. These results point to the hazard of the hair dye exposure to human health.