Tear Film Lipid Layer Structure: Self-Assembly of O-Acyl-ω-hydroxy Fatty Acids and Wax Esters into Evaporation-Resistant Monolayers.

Tuomo Viitaja,Riku O Paananen,Jukka Moilanen,Kirsi Johanna Svedström,Filip S Ekholm

doi:10.1021/acs.nanolett.1c02475

Tuomo Viitaja, Riku O Paananen + Show 3 more

Open Access

https://doi.org/10.1021/acs.nanolett.1c02475

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Abstract

In healthy eyes, the tear film lipid layer (TFLL) is considered to act as an evaporation resistant barrier, which prevents eyes from drying. Seeking to understand the mechanisms behind the evaporation resistance of the TFLL, we studied mixtures of lipid layer wax esters and O-acyl-ω-hydroxy fatty acids. Analyzing their self-assembly and biophysical properties led to new discoveries concerning the structure and function of the TFLL. We discovered how these lipids self-assemble at the air-water interface and form an efficient antievaporative barrier, demonstrating for the first time how the interaction of different tear film lipid species can improve the evaporation resistance compared with individual lipid classes on their own. These results provide a potential mechanism for the evaporation resistance of the lipid layer. In addition, the results serve as a base for the future development of improved dry eye treatments and other applications where the evaporation of water represents a significant challenge.

Highlights

In healthy eyes, the tear film lipid layer (TFLL) is considered to act as an evaporation resistant barrier, which prevents eyes from drying
The thin tear film lipid layer (TFLL) secreted by the Meibomian glands on the tear film surface stabilizes the entire tear film by suppressing the evaporation of water from the underlying aqueous tear fluid. This ability is compromised in dry eye patients, the underlying factors are poorly understood.[4,5]. The reasons for these shortcomings are related to the complex composition of the TFLL, which features 200− 500 different lipid species from a variety of lipid classes.[6−8] lipidomic studies on Dry eye disease (DED) patients,[9−12] transgenic mouse studies,[13−15] and characterization of the biophysical properties of individual TFLL lipid species[16−21] have implicated that O-acyl-ω-hydroxy fatty acids (OAHFAs) and wax esters (WEs) may be central lipid classes with respect to evaporation resistance
To improve the mechanistic understanding of the TFLL function and to provide the first step toward improved solutions for dry eye patients, we set out to study the molecular level structure of films composed of OAHFAs and WEs and its correlation to evaporation resistance

Summary

■ ACKNOWLEDGMENTS

BAM, Brewster angle microscope; DED, dry eye disease; OAHFA, O-acyl-ω-hydroxy-fatty acid; TFLL, tear film lipid layer; WAXS, wide-angle X-ray scattering; WE, wax ester

■ REFERENCES

Major Neutral Lipid Classes in Human Meibum by Direct Infusion

Findings

Novel Interferometric Method to Investigate the Relation between