Filipa de Castro^{1 2}, Andrej Kováčik², Márcio Rodrigues¹, Gilberto Alves¹

1 – Faculty of Health Sciences, University of Beira Interior, Av. Infante D. Henrique, Covilhã, Portugal
2 – Faculty of Pharmacy in Hradec Králové, Charles University, Akademika Heyrovského 1203/8, 500 03 Hradec Králové 3, Czechia

The major function of the human skin is to protect the body against water loss and to prevent negative substances from entering it. This function is localised into the uppermost layer of the epidermis, the stratum corneum, which follows the “brick and mortar” model. An equimolar ratio of skin barrier lipids (Ceramides (Cer), Free Fatty Acids, and Cholesterol) is significant for epidermal homeostasis, therefore changes in the lipid content negatively influence the barrier properties. Lower portions of the skin barrier lipids, including Acylceramides, are typical for skin diseases, such as atopic dermatitis. One possible treatment and relief for the symptoms is the topical application of barrier lipids. In this work, we aimed to develop a skin lipid-based formulation, considering different types of Cer-based formulations applied to healthy and disrupted models of the skin barrier. Throughout permeability experiments in human stratum corneum, the barrier properties were studied using Transepidermal water loss (TEWL) and electrical impedance (EI). Using the Fourier-transform infrared (FTIR) spectroscopy we aimed to investigate the microstructure of studied healthy, disrupted and repaired models of stratum corneum. The changes in the TEWL values were in the majority statistically significant, however, there was more water being lost after applying the lipid-based formulation. The EI measurements correlated with the TEWL as the values decreased, indicating that the skin integrity was compromised. In contrast with
these results, the FTIR experiment revealed how the topical application of the selected Cer-based formulations positively changed the lipid chain order. However, these findings did not correlate with the values of the TEWL and EI. Overall, the results showed that the topically applied barrier lipids had a direct interaction with the skin barrier since it increased the lipids chain order that is necessary for the correct barrier function, although it did not positively change the barrier properties. The obtained results may be useful in the skin barrier (patho)physiology investigation and further support other studies developing the topically applied barrier lipids.