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

Tuomo Viitaja; Jan-Erik Raitanen; Antti Hynynen; Jukka Moilanen; Kirsi Svedström; Riku O Paananen; Filip S Ekholm

doi:10.1016/j.colsurfb.2022.112429

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

Colloids Surf B Biointerfaces. 2022 Jun:214:112429. doi: 10.1016/j.colsurfb.2022.112429. Epub 2022 Feb 25.

Authors

Tuomo Viitaja¹, Jan-Erik Raitanen², Antti Hynynen², Jukka Moilanen³, Kirsi Svedström⁴, Riku O Paananen⁵, Filip S Ekholm⁶

Affiliations

¹ Department of Chemistry, University of Helsinki, P.O. Box 55, Helsinki FI-00014, Finland; Ophthalmology, University of Helsinki and Helsinki University Hospital, Haartmaninkatu 8, Helsinki FI-00290, Finland.
² Department of Chemistry, University of Helsinki, P.O. Box 55, Helsinki FI-00014, Finland.
³ Ophthalmology, University of Helsinki and Helsinki University Hospital, Haartmaninkatu 8, Helsinki FI-00290, Finland.
⁴ Department of Physics, University of Helsinki, P.O. Box 64, Helsinki FI-00014, Finland.
⁵ Department of Chemistry, University of Helsinki, P.O. Box 55, Helsinki FI-00014, Finland; Ophthalmology, University of Helsinki and Helsinki University Hospital, Haartmaninkatu 8, Helsinki FI-00290, Finland. Electronic address: riku.o.paananen@helsinki.fi.
⁶ Department of Chemistry, University of Helsinki, P.O. Box 55, Helsinki FI-00014, Finland. Electronic address: filip.ekholm@helsinki.fi.

PMID: 35278859
DOI: 10.1016/j.colsurfb.2022.112429

Abstract

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.

Keywords: Biophysics; Chemical synthesis; Structural elucidation; Tear film lipid layer.

MeSH terms

Biophysics
Cholesterol Esters* / chemistry
Esters
Lipids* / chemistry
Tears / chemistry

Substances

Cholesterol Esters
Esters
Lipids