Abstract

In vitro 3D skin models are able to recapitulate the major events in the process of skin homeostasis very well. Two cell biological assays have been applied on Phenion®-FT-skin models and demonstrated their usefulness for describing cellular activities in the process of skin renewal and homeostasis in vitro. A cell proliferation assay was applied to study the general proliferative responsiveness of basal keratinocytes and dermal fibroblasts, whereas the MTT-viability-assay was used to analyse the overall improvement of epidermal and dermal tissue viability. For demonstration purpose, single experiments have been performed in which skin models were systematically stimulated with known cosmetic and medical actives (atRA & 13cRA), whose time and dose dependent effectiveness are well characterized (18, 21).

INTRODUCTION

Skin homeostasis
Skin maintains its capability of self renewal throughout a whole human life. The continuum of keratinocyte birth, differentiation and desquamation comprises the core-principle of a physiological and physical skin barrier that holds fluids inside the body and acts as a protective shield against biological, chemical and physical environmental knoxes to the outside (3). Although skin continuously accumulates chronological and photo-induced signs of ageing, it still manages to keep up its skin barrier maintenance a life-long (6). The origin of interfollicular epidermal self regenerative capacity is located within a single, basal layer of keratinocytes, which is anchored to the papillar dermis via a range of connective structural proteins (6, 7). The first effective step in interfollicular regeneration takes place in the basal layer of epidermal keratinocytes. Undifferentiated basal keratinocytes undergo constantly acts of mitosis. New-born daughter cells detach from the underlying basement membrane and migrate into suprabasal epidermal layers. From that point on they withdraw from cell cycle and start th ...