Concentration dependent cholesteryl-ester and wax-ester structural relationships and meibomian gland dysfunction

Area of Science:

• Ophthalmology and Vision Science
• Biophysics
• Materials Science

Background:

• Dry eye disease is associated with a reduced cholesteryl ester (CE) to wax ester (WE) ratio in meibum.
• The functional and structural implications of this lipid ratio alteration remain largely speculative.

Purpose of the Study:

• To quantify the CE/WE ratio in human meibum from dry eye patients.
• To investigate the impact of varying CE/WE ratios on lipid structure and thermodynamics using a model system.

Main Methods:

• Infrared spectroscopy was employed to determine CE and WE concentrations in human meibum.
• A model system of cholesteryl behenate (CE) and stearyl stearate (WE) was used to analyze hydrocarbon chain conformation and thermodynamics.

Main Results:

• Meibum from dry eye donors exhibited a 36% lower CE/WE molar ratio compared to controls.
• As little as 5% CE significantly increased the phase transition temperature of WE from -0.12°C to 63°C.
• CE incorporation increased lipid order and induced a monoclinic geometry in hydrocarbon chains above 10% CE.

Conclusions:

• The CE/WE ratio is demonstrably lower in meibum affected by dry eye due to meibomian gland dysfunction.
• Significant conformational changes in lipid hydrocarbon chains occur with CE concentrations of 5% and above.
• Understanding CE-WE interactions is crucial for elucidating lipid layer function on ocular, skin, and plant surfaces.