On the importance of chain branching in tear film lipid layer wax and cholesteryl esters

The tear film lipid layer (TFLL) is important to the maintenance of ocular surface health. Surprisingly, information on the individual roles of the myriad of unique lipids found therein is limited. The most abundant lipid species are the wax esters (WE) and cholesteryl esters (CE), and, especially their branched analogs. The isolation of these lipid species from the TFLL has proved to be tedious, and as a result, insights on their biophysical profiles and role in the TFLL is currently lacking. Herein, we circumvent these issues by a total synthesis of the most abundant iso-methyl branched WEs and CEs found in the TFLL. Through a detailed characterization of the biophysical properties, by the use of Langmuir monolayer and wide-angle X-ray scattering techniques, we demonstrate that chain branching alters the behavior of these lipid species on multiple levels. Taken together, our results fill an important knowledge gap concerning the structure and function of the TFLL on the whole.

Automated summary

The tear film lipid layer (TFLL) plays a crucial role in maintaining ocular surface health. However, there is limited knowledge about the specific functions of the unique lipids found in the TFLL. This study focuses on the synthesis and characterization of the most abundant iso-methyl branched wax esters and cholesteryl esters in the TFLL, demonstrating that chain branching affects the behavior of these lipid species on multiple levels. The results of this study provide important insights into the structure and function of the TFLL.