Barrier function and epidermal homeostasis
Actives with an effect on epidermal homeostasis can be screened by monitoring tissue cohesion markers and differentiation markers.
The biological endpoints of interest are assessed by immunofluorescence of proteins involved in tight junctions (like claudins, occludin and ZO-1), (corneo)desmosomes (corneodesmosin, desmogleins), and proteins involved in the cornified envelope (involucrin, loricrin, filaggrin, K10, matriptase, cystatin M/E, SPRRs).
The effects of a test item on skin barrier can also be evaluated by measuring the trans-epidermal electric resistance (TEER), skin diffusion of chromogenic dyes and skin penetration of reference molecules.
Re-epithelialization and wound healing
Re-epithelialization and wound healing properties of actives are addressed using in vitro tests targeting cell proliferation (BrdU incorporation assay), migration ("scratch" assay, Boyden chambers) and invasion (Boyden chambers) and sequential expression of tissue repair markers (cytokine secretion, protease activities).