Department of Biochemistry and Molecular Biology, University of Southern Denmark, Denmark.
University of Copenhagen, Novo Nordisk Foundation Center for Protein Research, Denmark.
Biochim Biophys Acta Gen Subj. 2019 Jul;1863(7):1226-1233. doi: 10.1016/j.bbagen.2019.04.012. Epub 2019 Apr 15.
Knowledge regarding the barrier properties of human skin is important for understanding skin pathology, developing of transdermal drug delivery systems and computational skin absorption models; however, the molecular pathways through human skin remains to be fully investigated on a nanoscopic level. In particular the nanoscopic pathway of molecules passing the intercellular lipid bilayers separating the corneocytes in the stratum corneum (SC) is not fully elucidated.
Using stimulated emission depletion microscopy (STED) and Förster resonance energy transfer (FRET) the molecular pathways through the SC, the main barrier of the skin, are determined for lipophilic and water-soluble molecules at a nanoscopic resolution.
Using STED and confocal microscopy, water-soluble dyes, were observed to be present in both the corneocytes and in the intercellular lipid matrix, whereas the lipophilic dyes were predominately in the intercellular lipid bilayers. FRET was observed in the SC between the lipophilic and water-soluble dyes, the existence of a minimum possible distance between acceptor and donor molecules of 4.0 ± 0.1 nm was found.
The results indicate that lipophilic molecules penetrate the stratum corneum via the intercellular lipids bilayers separating the corneocytes in the SC, while the more water-soluble molecules penetrate the stratum corneum via the transcellular route through the corneocytes and intercellular lipid bilayers via the polar head groups of lipid molecules in the bilayers.
Knowledge of the nanoscopic molecular pathways through human skin will help understand the skin barrier function and will be of use for computational skin absorption models and transdermal drug delivery strategies.
了解人体皮肤的屏障特性对于理解皮肤病理学、开发透皮药物传递系统和计算皮肤吸收模型非常重要；然而，在纳米尺度上，人类皮肤的分子途径仍有待充分研究。特别是，穿过角质层（SC）中分离角质细胞的细胞间脂质双层的分子的纳米级途径尚未完全阐明。
使用受激发射损耗显微镜（STED）和Förster 共振能量转移（FRET），以纳米分辨率确定通过皮肤主要屏障——角质层的亲脂性和水溶性分子的分子途径。
使用 STED 和共聚焦显微镜，观察到水溶性染料既存在于角质细胞中，也存在于细胞间脂质基质中，而亲脂性染料则主要存在于细胞间脂质双层中。在 SC 中观察到亲脂性和水溶性染料之间的 FRET，发现受体和供体分子之间的最小可能距离为 4.0±0.1nm。
结果表明，亲脂性分子通过分离 SC 中角质细胞的细胞间脂质双层渗透角质层，而更亲水性的分子则通过穿过角质细胞的跨细胞途径渗透角质层，并通过双层中脂质分子的极性头基团穿过细胞间脂质双层。
了解人体皮肤的纳米级分子途径将有助于理解皮肤屏障功能，并将有助于计算皮肤吸收模型和透皮药物传递策略。
