Abstract
Purpose :
Cholesteryl esters (CE) are the second largest class of meibomian lipids (ML) in mammals. However, the biophysical roles of CE played in health and ocular pathologies such as dry eye (DE) and meibomian gland dysfunction (MGD) are still unclear. The purpose of this study was to develop a novel in vitro experimental methodology to systematically characterize the biophysical functions of meibomian CE in the norm and pathology using a CE-ablated Soat1-knockout (KO) mouse model.
Methods :
ML were extracted from tarsal plates of wild type (WT) and homozygous KO 6+/-2 mos old male mice. The lipid compositions of pooled ML samples of each kind were established using liquid chromatography-mass spectrometry (LC-MS). The biophysical properties of WT and KO ML samples were thoroughly evaluated and compared in side-by-side experiments using a novel experimental methodology called constrained drop surfactometry (CDS). CDS is a new generation of droplet-based tensiometry technique capable of versatile biophysical assays under rigorously controlled environmental conditions (Figure 1). We have further developed the CDS into a ventilated, closed-chamber evaporimeter, designed for studying the evaporation resistance of ML films. In conjunction with direct film imaging using atomic force microscopy, we have systematically studied major biophysical properties of the ML films, such as dynamic surface activity, interfacial dilational rheology, evaporation resistance, and lateral structure of the lipid films with submicron resolution.
Results :
The LC-MS experiments confirmed an almost complete ablation of ML-type CE in KO mice and a multifold increase in free cholesterol. In comparison to WT mice, the ML film of the KO mice demonstrated a decreased film stability (indicated by a larger hysteresis area for the compression-expansion loop of the surface tension – surface area curves), reduced viscous modulus, disrupted film structures, and less resistance to water evaporation.
Conclusions :
These findings illustrate the likely biophysical role of cholesterol and CE in pathophysiology of DE, MGD, and other related pathologies. Our results also demonstrate that CDS is a reliable, easy-to-use, and versatile biophysical model for in vitro characterization of ML.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.