Abstract:The keratinocyte growth and differentiation switch, tightly regulated by several mechanisms, is generally associated with decreased proliferation, cell cycle arrest in G0 ⁄ G1 phase and expression of epidermal differentiation markers, such as keratin 1 (K1), keratin 10 (K10) and involucrin. In vitro, the spontaneously immortalized human keratinocyte cell line HaCaT is often used as a model to study keratinocyte functions. Comparative differentiation studies between HaCaT cells and normal human keratinocytes (NHK) over an extended time-period have rarely been reported. Therefore, we studied their switch from a proliferating to a differentiated state over 13 days. As culture conditions involved changes in cellular responses, cells were cultured in a specific medium for keratinocyte growth and differentiation was induced by increasing extracellular calcium concentration from 0.09 to 1.2 mm. In NHK, addition of calciuminduced morphological changes and concomitant decreased proliferation. For HaCaT cells, calcium addition resulted in morphological changes, but in an unexpected manner, cells were more proliferative than when cultured at low calcium levels. HaCaT cell hyperproliferation correlated with cell cycle analysis, showing an accumulation in S ⁄ G2-M phases. Furthermore, RT-PCR and western blot analysis revealed a delay in the expression of the differentiation markers K1, K10 and involucrin in HaCaT cells compared with NHK. In conclusion, even though calcium-induced differentiation was not associated with a decreased cell proliferation, HaCaT cells conserved properties characteristic of differentiation.

An other mechanism of action of Avène TSW is described. Avène TSW treatment induced an enhanced constitutive calcium entry mediated by TRPV6 channel leading to the acceleration of human keratinocytes differentiation.

The association chitosan/linoleic acid/lactobionic acid in aqueous solution spontaneously led to the formation of stable microparticles with a liquid hydrophobic core consisting of linoleic acid surrounded by a shell of chitosan/lactobionic acid. The originality of the microparticles arises from the fact that they are formed by the association of three ingredients of cosmetic interest, including a skin penetration enhancer (linoleic acid). Dynamic light scattering (DLS) measurements showed microparticles with a mean diameter of 1-2 μm. The presence of a hydrophobic liquid core was observed by transmission electron microscopy (TEM). The ability of these microparticles to encapsulate phenylethyl resorcinol, a hydrophobic skin lightener, was evaluated and its encapsulation was confirmed thanks to T measurements and nuclear Overhauser effects (nOe) signs.

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