J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, 18223 Prague, Czech Republic.
Department of Biomedical Engineering, Faculty of Fundamental Problems of Technology, Wroclaw University of Science and Technology, Wroclaw, Poland.
Biochim Biophys Acta Biomembr. 2020 Sep 1;1862(9):183300. doi: 10.1016/j.bbamem.2020.183300. Epub 2020 Mar 31.
The Tear Film Lipid Layer (TFLL) covering the surface of the aqueous film at human cornea forms a first barrier between the eye and environment. Its alterations are related to dry eye disease. TFLL is formed by a complex mixture of lipids, with an excess of nonpolar components and a minor fraction of polar molecules. Its thickness is up to 160 nm, hence a multilayer-like structure of TFLL is assumed. However, details of TFLL organization are mostly unavailable in vivo due to the dynamic nature of the human tear film. To overcome this issue, we employ a minimalistic in vitro lipid model of TFLL. We study its biophysical characteristics by using a combination of the Langmuir trough with fluorescence microscopy. The model consists of two-component polar-nonpolar lipid films with a varying component ratio spread on the aqueous subphase at physiologically relevant temperature. We demonstrate that the model lipid mixture undergoes substantial structural reorganization as a function of lateral pressure and polar to nonpolar lipid ratio. In particular, the film is one-molecule-thick and homogenous under low lateral pressure. Upon compression, it transforms into a multilayer structure with inhomogeneities in the form of polar-nonpolar lipid assemblies. Based on this model, we hypothesize that TFLL in vivo has a duplex polar-nonpolar structure and it contains numerous mixed lipid aggregates formed because of film restructuring. These findings, despite the simplified character of the model, seem relevant for TFLL physiology as well as for understanding pathological conditions related to the lipids of the tear film.
泪膜脂质层（TFLL）覆盖在人眼角膜表面的水膜上，形成眼睛和环境之间的第一道屏障。其变化与干眼症有关。TFLL 由复杂的脂质混合物组成，含有过多的非极性成分和少量极性分子。其厚度可达 160nm，因此假设 TFLL 具有多层样结构。然而，由于人泪膜的动态性质，其组织细节在体内大多不可用。为了克服这个问题，我们采用了一种简化的体外 TFLL 脂质模型。我们通过使用 Langmuir 槽和荧光显微镜的组合来研究其生物物理特性。该模型由两种成分的极性-非极性脂质膜组成，其成分比在生理相关温度下在水亚相中展开。我们证明，模型脂质混合物随着层间压力和极性与非极性脂质比的变化会发生显著的结构重组。特别是，在低层间压力下，薄膜是单分子厚且均匀的。在压缩过程中，它会转变成具有极性-非极性脂质组装不均匀的多层结构。基于这个模型，我们假设体内 TFLL 具有双极性-非极性结构，并且由于膜重构而包含许多混合脂质聚集体。尽管模型具有简化的性质，但这些发现似乎与 TFLL 的生理学以及与泪膜脂质相关的病理条件有关。
