Borchman Douglas
Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY 40202.
J Lipid Res. 2021;62:100039. doi: 10.1194/jlr.TR120000874. Epub 2021 Feb 6.
Lens and tear film lipids are as unique as the systems they reside in. The major lipid of the human lens is dihydrosphingomylein, found in quantity only in the lens. The lens contains a cholesterol to phospholipid molar ratio as high as 10:1, more than anywhere else in the body. Lens lipids contribute to maintaining lens clarity, and alterations in lens lipid composition due to age are likely to contribute to cataract. Lens lipid composition reflects adaptations to the unique characteristics of the lens: no turnover of lens lipids or proteins; the lowest amount of oxygen of any tissue; and contains almost no intracellular organelles. The tear film lipid layer (TFLL) is also unique. The TFLL is a thin (100 nm) layer of lipid on the surface of tears covering the cornea that contributes to tear film stability. The major lipids of the TFLL are wax esters and cholesterol esters that are not found in the lens. The hydrocarbon chains associated with the esters are longer than those found anywhere else in the body (as long as 32 carbons), and many are branched. Changes in the composition and structure of the 30,000 different moieties of TFLL contribute to the instability of tears. The focus of the current review is how spectroscopy has been used to elucidate the relationships between lipid composition, conformational order and function, and the etiology of cataract and dry eye.
晶状体和泪膜脂质与它们所在的系统一样独特。人晶状体的主要脂质是二氢鞘磷脂，仅在晶状体中大量存在。晶状体中胆固醇与磷脂的摩尔比高达10:1，比身体其他任何部位都高。晶状体脂质有助于维持晶状体的透明度，而由于年龄导致的晶状体脂质组成变化可能会导致白内障。晶状体脂质组成反映了对晶状体独特特征的适应性：晶状体脂质或蛋白质无更新；是所有组织中含氧量最低的；且几乎不含有细胞内细胞器。泪膜脂质层（TFLL）也很独特。TFLL是覆盖在角膜上的泪液表面的一层薄（100纳米）脂质层，有助于泪膜稳定。TFLL的主要脂质是蜡酯和胆固醇酯，这些在晶状体中并不存在。与这些酯相关的烃链比身体其他任何部位的都长（长达32个碳），且许多是分支的。TFLL的30000种不同成分的组成和结构变化会导致泪液不稳定。本综述的重点是光谱学如何被用于阐明脂质组成、构象有序性与功能之间的关系，以及白内障和干眼症的病因。
