Abstract
The measurement of skin electrical resistance (SER) has drawn a great deal of attention for the rapid screening of transdermal penetration enhancers (PEs). However, the mechanisms underlying the SER measurement are still unclear. This study was to investigate the effects and mechanisms of seven oxygen-containing terpenes on the SER kinetics. Stratum corneum (SC) lipids were proved to play a key role in SER measurement. Then, the factors affecting the SER measurement were optimized. By the determination of SER kinetics, cyclic terpenes (1,8-cineole, terpinen-4-ol, menthol and α-terpineol) were demonstrated to possess higher enhancement ratio (ER) values compared with linear terpenes (linalool, geraniol and citral). For the first time, the linear correlation was found between ER of terpenes and the interaction energy of terpene–ceramide complexes revealed by molecular simulation. The attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) analysis revealed that the effect of cyclic terpenes on SC lipid arrangement was obviously stronger than that of linear terpenes. In addition, by evaluating HaCaT skin cell viability, little difference was found between the toxicities of cyclic and linear terpenes. In conclusion, measurement of SER could be a feasible approach for the efficient evaluation of the PEs that mainly act on SC lipids.
Highlights
Transdermal drug delivery (TDD) offers several advantages over other routes of drug administration, such as avoiding gut and hepatic first-pass metabolism, improving patient compliance, decreasing administration frequency and reducing side effects
We further investigated the factors affecting the measurement of skin electrical resistance (SER) kinetics
The SER measurement was proved to be directly dependent on the stratum corneum (SC) barrier, especially SC
Summary
Transdermal drug delivery (TDD) offers several advantages over other routes of drug administration, such as avoiding gut and hepatic first-pass metabolism, improving patient compliance, decreasing administration frequency and reducing side effects. TDD is an effective and preferred route of administration [1]. Application of TDD is limited primarily by low skin permeability. The skin acts as an effective barrier to protect the organism against undesirable. Molecules 2019, 24, 523; doi:10.3390/molecules24030523 www.mdpi.com/journal/molecules effects2019, of the The Molecules. FOR main permeation barrier resides in the outermost layer of the ofskin, 22 of stratum corneum (SC), a composite of proteins and lipids in which protein-rich corneocytes are surrounded lipid bilayers. Ordered structure and low permeability of these lipid bilayers are corneocytes arebysurrounded by lipid bilayers
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