The irritation potential of pharmaceutical, cosmetic and personal care products that are specifically formulated for application onto human mucosal tissues is evaluated using reconstructed tissue models such as EpiVaginal™ (MatTek Corporation, Ashland, MA, USA) or the Human Vaginal Epithelium (HVE) (EpiSkin, Lyon, France). The toxicity is determined by measuring the relative viability of the tissues treated with the test materials and compared to the negative/solvent control-treated tissues.
The safety of the pharmaceutical, cosmetic and personal care products that are specifically formulated for application onto human mucosal tissues can be performed using in vitro testing platforms based on reconstructed tissues that exhibit in vivo-like morphological and ultrastructural characteristics. The development of reconstructed, stratified, differentiated human vaginal epithelium tissue models replicating the native multilayered three-dimensional morphology, characteristic interdigitation of epithelial cells, glycogen and cytokeratin production has the potential to overcome some of the disadvantages of cell monolayers by the presence of a barrier layer that permits the topical application of active ingredients and final formulations, including those that are not water-soluble.
Furthermore, the use of the models such as EpiVaginal™ (MatTek Corporation, Ashland, MA, USA) or the Human Vaginal Epithelium (EpiSkin, Lyon, France) avoids animal welfare and inter-species extrapolation issues, and they allow a separation between the very mild products to which animal models are insensitive. The toxicity of the test materials is generally determined by measuring the relative conversion of MTT (3-[4,5 – dimethylthiazol-2-yl] – 2,5 – diphenyltetrazolium bromide) in the test material-treated tissues compared to the negative/solvent control-treated tissues and is evaluated on the basis of the relative tissue viability versus exposure time.
The toxicity is expressed as ET50 values representing the exposure time to a test article that reduces the viability of the tissues by 50% and they are dependent on the class of materials tested. Alternative assays that can be used to assess the toxicity of test materials expressed as tissue viability are LDH (lactate dehydrogenase) or ATP (adenosine triphosphate). Besides the tissue viability, other endpoints that can be used to compile the safety profile of test materials are cytokines (primary, secondary) release, TEER (transepithelial electrical resistance) and histology.
More endpoints can be investigated depending on the class of materials of interest and goals of each project. The results of the endpoints evaluated for the safety assessment of oral irritation potential are used to rank order the irritation potential of the test materials, to compare to reference materials or to evaluate the possibility to generate a prediction model (if animal or clinical data are available to establish the correlation).