Cosmetic efficacy claims in vitro using a three-dimensional human skin model

A tissue engineered human skin equivalent is successfully used for the testing of raw materials and cosmetic formulations. This reconstructed skin is supported by a collagen-glycosaminoglycan-chitosan biopolymer in which human keratinocytes and dermal fibroblasts were co-cultured to form a tissue that closely reproduces the in vivo architecture of normal human skin and takes into account the complex interactions between epidermis and dermis. On the other hand, dermal and epidermal responses can be assessed separately in the dermal or skin equivalent. The three-dimensional model has important advantages compared to monolayer cell cultures and epidermis models in efficacy testing: (i) the possibility of long-term cultivation with repeated application of cream formulations containing bioactives and (ii) the similarity to human skin concerning the interaction between dermis and epidermis. These similarities include the expression of keratinocyte differentiation markers such as cytokeratin 10, filaggrin and transglutaminase, as well as proteins of the basal lamina (laminin, collagen type IV) and extracellular matrix proteins such as elastin. The efficacy of selected bioactives was determined using different endpoints, for example, stimulation of collagen synthesis in the dermal and skin equivalents was shown in comparison to vitamin C as a positive control. On skin equivalents using immunofluorescence techniques we also demonstrated stimulation of the differentiation marker filaggrin, which is important for skin moisturization. The results could be used for claim substantiation, e.g. for the treatment of dry and aged skin.