Patterson Matthew, Vogel Hans J, Prenner Elmar J
Biochemistry Research Group, Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
Biochemistry Research Group, Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
Biochim Biophys Acta. 2016 Feb;1858(2):403-14. doi: 10.1016/j.bbamem.2015.11.025. Epub 2015 Nov 30.
The tear film protects the eye from foreign particles and pathogens, prevents excess evaporation, provides lubrication, and maintains a high quality optical surface necessary for vision. The anterior layer of tear film consists of polar and non-polar lipid layers. The polar lipids form a monolayer on the aqueous subphase, acting as surfactants for the non-polar lipid multilayer. A tear film polar lipid biomimetic consisting of dipalmitoyl phosphatidylcholine (DPPC), dipalmitoyl phosphatidylethanolamine (DPPE), palmitoyl glucosylceramide (PGC), and palmitoyl sphingomyelin (PSM) was characterized using Langmuir monolayers and Brewster angle microscopy (BAM). Lipid combinations formed very stable monolayers, especially those containing DPPC or PSM. Surface experiments and elasticity analyses revealed that PGC resulted in more condensed and rigid mixed monolayers. DPPE provided resistance to large changes in lipid ordering over a wide surface pressure range. Ternary mixtures containing DPPE and PGC with either DPPC or PSM experienced the greatest lipid ordering within the natural tear film surface pressure range suggesting that these lipids are important to maintain tear film integrity during the inter-blink period. Finally, BAM images revealed unique structures within monolayers of DPPC, DPPE, and PGC at the natural tear film surface pressure. 3D analysis of these domains suggested either the formation of multilayers or outward protrusions at surface pressures far below the point of irreversible collapse as seen on the isotherm. This entails that the polar lipids of tear film may be capable of multilayer formation or outward folding as a mechanism to prevent rupture of the tear film during a blink.
泪膜可保护眼睛免受异物和病原体侵害，防止过度蒸发，提供润滑，并维持视觉所需的高质量光学表面。泪膜的前层由极性和非极性脂质层组成。极性脂质在水相亚层上形成单分子层，作为非极性脂质多层的表面活性剂。使用朗缪尔单分子层和布鲁斯特角显微镜（BAM）对由二棕榈酰磷脂酰胆碱（DPPC）、二棕榈酰磷脂酰乙醇胺（DPPE）、棕榈酰葡萄糖神经酰胺（PGC）和棕榈酰鞘磷脂（PSM）组成的泪膜极性脂质仿生物进行了表征。脂质组合形成了非常稳定的单分子层，尤其是那些含有DPPC或PSM的组合。表面实验和弹性分析表明，PGC导致形成更致密和刚性更强的混合单分子层。DPPE在很宽的表面压力范围内对脂质有序性的大变化具有抗性。含有DPPE和PGC以及DPPC或PSM的三元混合物在天然泪膜表面压力范围内经历了最大的脂质有序化，这表明这些脂质对于在眨眼间隔期间维持泪膜完整性很重要。最后，BAM图像揭示了在天然泪膜表面压力下DPPC、DPPE和PGC单分子层内的独特结构。对这些区域的三维分析表明，在远低于等温线上不可逆塌陷点的表面压力下形成了多层或向外突出。这意味着泪膜的极性脂质可能能够形成多层或向外折叠，作为一种在眨眼期间防止泪膜破裂的机制。
