Development and evaluation of a quality control system based on transdermal electrical resistance for skin barrier function in vitro.

BACKGROUND: In vitro skin permeation experiments are highly relevant for pharmaceutical, cosmetic, agricultural developments, and regulatory evaluation. A key requirement is the skin barrier integrity, that is accompanied by an intact stratum corneum (SC) which implements high skin quality. A variety of integrity tests are currently available, for example, measurement of transepidermal water loss, monitoring the permeation of tritiated water and the measurement of transdermal electrical resistance (TER). MATERIALS AND METHODS: We aimed for a non-destructive examination of barrier integrity as quality control system, based on TER. Therefore, the in-house developed instrument SkinTER measures electrical resistance on excised human skin samples in a non-invasive and easy-to-use pattern. In this proof of concept study, we compared three human in vitro skin models with focus on their TER and permeation properties. The skin integrity was impaired to mimic conditions of skin during age, lifestyle (eg, shaving) or diseases (eg, obesity, psoriasis, and atopic dermatitis). The OECD permeation marker caffeine was correlated to the corresponding TER value. RESULTS: A correlation between both was obtained by having a Pearson coefficient of -0.830. Hereby, a minimum TER value for intact skin samples of ~1.77 kΩ*cm2 was suggested. Intact samples are significantly different (α = ≤0.05) to their impaired counterparts in flux and TER values. CONCLUSION: The new SkinTER instrument gives a quick and non-invasive feedback on skin quality before a permeation experiment.

Modulating the Barrier Function of Human Alveolar Epithelial (hAELVi) Cell Monolayers as a Model of Inflammation.

The incidence of inflammatory lung diseases such as acute respiratory distress syndrome (ARDS) remains an important problem, particularly in the present time with the Covid-19 pandemic. However, an adequate in vitro test system to monitor the barrier function of the alveolar epithelium during inflammation and for assessing anti-inflammatory drugs is urgently needed. Therefore, we treated human Alveolar Epithelial Lentivirus-immortalised cells (hAELVi cells) with the pro-inflammatory cytokines TNF-α (25 ng/ml) and IFN-γ (30 ng/ml), in the presence or absence of hydrocortisone (HC). While TNF-α and IFN-γ are known to reduce epithelial barrier properties, HC could be expected to protect the barrier function and result in an anti-inflammatory effect. We investigated the impact of anti-inflammatory/inflammatory treatment on transepithelial electrical resistance (TEER) and the apparent permeability coefficient (Papp) of the low permeability marker sodium fluorescein (NaFlu). After incubating hAELVi cells for 48 hours with a combination of TNF-α and IFN-γ, there was a significant decrease in TEER and a significant increase in the Papp. The presence of HC maintained the TEER values and barrier properties, so that no significant Papp change was observed. By using hAELVi cells to study anti-inflammatory drugs in vitro, the need for animal experiments could be reduced and pulmonary drug development accelerated.