School of Science and Health, University of Western Sydney, Penrith, NSW 2751, Australia.
Exp Eye Res. 2013 Oct;115:57-64. doi: 10.1016/j.exer.2013.06.016. Epub 2013 Jun 21.
(O-acyl) ω-hydroxy fatty acids (OAHFAs) are a recently found group of polar lipids in meibum. Since these lipids can potentially serve as a surfactant in the tear film lipid layer, the surface properties of a molecule of this lipid class was investigated and compared with a structurally related wax ester and a fatty acid. (O-oleyl) ω-hydroxy palmitic acid was synthesized and used as the model OAHFA. It was spread either alone or mixed with human meibum on an artificial tear buffer in a Langmuir trough, and pressure-area isocycle profiles were recorded at different temperatures and compared with those of palmityl oleate and oleic acid. These measurements were accompanied by fluorescence microscopy of meibum mixed films during pressure-area isocycles. The pressure area curves indicated that pure films of the model OAHFA are as surface active as oleic acid films, cover a much larger surface area than either palmityl oleate or oleic acid and show a distinct biphasic pressure-area isocycle profile. The OAHFAs appeared to remain on the aqueous surface and show only a minor re-arrangement into multi-layered structures during repetitive pressure area isocycles. All these properties can be explained by OAHFAs binding weakly to the aqueous surface via an ester group and strongly via a carboxyl group. By contrast, the pressure area profiles of palmityl oleate films indicate that they form multi-layers and oleic acid presumably forms micelles and desorbs into the subphase. When mixed with meibum, similar features as for pure films were observed. In addition, meibum-OAHFA films appeared very homogeneous; a feature not seen with other mixtures. In conclusion these data support the notion that the tested OAHFA is a very potent surfactant which is important in spreading and stabilising meibomian lipid films.
（O-酰基）ω-羟基脂肪酸（OAHFAs）是在睑脂中发现的一组新的极性脂质。由于这些脂质有可能在泪膜脂质层中充当表面活性剂，因此研究了这种脂质类别的分子的表面性质，并将其与结构上相关的蜡酯和脂肪酸进行了比较。（O-油酰基）ω-羟基棕榈酸被合成并用作模型 OAHFA。它单独或与人睑脂混合在Langmuir 槽中的人工泪液缓冲液中展开，并在不同温度下记录压力-面积等温线曲线，并与棕榈酸油酸酯和油酸进行比较。这些测量还伴随着压力-面积等温线循环中混合的睑脂荧光显微镜。压力-面积曲线表明，模型 OAHFA 的纯膜与油酸膜一样具有表面活性，覆盖的表面积比棕榈酸油酸酯或油酸大得多，并且表现出明显的两相压力-面积等温线曲线。OAHFAs 似乎仍留在水相表面上，并且在重复的压力-面积等温线循环中仅发生轻微的重新排列成多层结构。所有这些性质都可以通过 OAHFAs 通过酯基与水相弱结合以及通过羧基与水相强结合来解释。相比之下，棕榈酸油酸酯膜的压力-面积曲线表明它们形成多层，而油酸可能形成胶束并解吸到亚相中。当与睑脂混合时，观察到与纯膜相似的特征。此外，睑脂-OAHFA 膜看起来非常均匀；与其他混合物不同。总之，这些数据支持了这样的观点，即测试的 OAHFA 是一种非常有效的表面活性剂，它对于扩散和稳定睑脂膜很重要。
