The safety assessment of raw ingredients or finished products intended for human oral use or that can accidentally come in contact with humans’ oral tissues can be performed using in vitro testing platforms based on reconstructed tissue models. The oral irritation potential of oral care, pharmaceutical or tobacco products can be investigated using the tissue viability (%) as main endpoint in the evaluation of cytotoxicity.
The potential oral/buccal irritation of raw ingredients or finished products can be assessed using commercially available reconstructed tissue models such as the EpiOral™ and EpiGingival™ Models (MatTek Corporation, Ashland, MA, USA) or the Reconstructed human gingival (RGO) and reconstructed human oral (RHO) (EpiSkin, Lyon, France) derived from human oral/buccal cells.
The reconstructed tissues incorporate several key features, which make them advantageous in the study of potential oral/buccal toxicity. The test systems use a serum-free medium, which eliminates the possibility of interaction between the serum protein and test materials. The tissue models replicate many of the histological and functional features of the native tissues, including a multilayered three-dimensional morphology with a stratum filamentosum and s. distendum (for the oral models) or with a keratinized stratum corneum (specific for the gingival model). The test materials are applied directly to the tissue surface, at air interface, thus eliminating the challenges related to solubility in the cell culture media so often encountered when using cell culture-based systems.
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).