Use of in vitro dermal equivalent and skin equivalent kits for evaluating cutaneous toxicity of cosmetic products

Fourteen cosmetic products reflecting a range of irritancy levels were evaluated for cutaneous irritation potential using dermal equivalent (DE) and skin equivalent (SE) kits. Our two in vitro models are presented in 12 culture inserts (Transwell, Costar) allowing air-liquid interphase culture and topical application. Dermal equivalent includes a collagen-glycosaminoglycans-chitosan porous matrix populated by human normal fibroblasts and skin equivalent is realized by seeding keratinocytes onto the DE. The pure cosmetic products were applied in triplicate by topical application (10 mul) onto a surface delimited by a silicone assay ring placed onto DE and SE. After 24 h contact with the cosmetic products, the residual cellular viability was measured using a MTT test on treated and untreated tissues. The purpose of this preliminary validation study was to evaluate to what extent the in vitro results can predict in vivo skin irritation. Consequently, 11 cosmetic products with known Draize irritation classes were tested on DE. Ten of 11 were correlated if we considered only the irritancy potential prediction (irritant or nonirritant) but considering the binary correlation with three classes of irritation (irritant, slightly irritant, or nonirritant), 8 of 11 were correlated. Moreover, the parameters of validation were calculated. Second, three cosmetic products with known Draize primary irritation index (PDII) were tested both on DE and SE. The correlation of the in vitro MTT values to the in vivo data using a regression line was found to be r = 0.99 for DE and r = 0.99 for SE. These preliminary results are encouraging and suggest that the two models, DE kit and SE kit, could be used as in vivo alternative methods after a complete validation study involving the testing of the different chemical classes and various cosmetic forms.