Unravelling polyphenol skin permeation: A comparative study using full-thickness 3D in vitro and ex vivo human skin...

The evaluation of cosmetic ingredients permeation through human skin is a key aspect in the safety and efficacy development of topical formulations. However, conventional approaches are limited by the low availability, inter-donor variability and ethical constraints associated with ex vivo human skin explants. In this context, 3D in vitro skin models have emerged as promising alternatives, although their predictive capacity still requires further validation.

This study aimed to assess and compare the permeation of catechin, epicatechin, chlorogenic acid (CGA), neochlorogenic acid (NCGA) and their mixture using a 3D full-thickness skin model and ex vivo human skin explants.

The 3D full-thickness model was independently prepared using dermal (HDF) and epidermal (HaCaT) cell lines cultured under air-liquid interface conditions. Separately, ex vivo human skin explants were mounted on Franz diffusion cells. 3D full-thickness model barrier formation was monitored by transepithelial electrical resistance (TEER), while permeation was quantified by liquid chromatography coupled with diode array detection and mass spectrometry (LC-DAD-MS) in both models. Cytocompatibility was evaluated using the MTT assay.

The 3D co-culture model exhibited a progressive increase in TEER, reaching stable values above 200 Ω.cm², indicating a functional skin barrier formation. In vitro permeation studies enabled the detection of all tested compounds and revealed compound-specific permeation profiles strongly influenced by the structural characteristics of flavan-3-ols and hydroxycinnamic acids. In contrast, ex vivo human skin explants exhibited a more restrictive barrier, with only CGA and NCGA being quantifiable, achieving 44%-50% permeation after 24 h and displaying high skin retention rates (63%-70%). None of the tested compounds induced cytotoxic effects.

This work demonstrates that full-thickness 3D skin models represent a robust and ethically advantageous screening platform for cosmetic ingredients, bridging the gap between conventional 2D monocultures and ex vivo human skin explants, and contributing to the reduction of human tissue use in dermal absorption studies.