Abstract
Langmuir monolayers containing different amounts of cholesterol and cholesteryl stearate were studied at two different temperatures (24 °C and 35 °C). The main goal was to contribute towards the understanding of how the variations in the chemical composition may affect the physico-chemical properties of these specific lipid monolayers. The model mixture was chosen considering that cholesteryl esters are present in cell membranes and some other biological systems, including human tear lipids. Therefore, an investigation into the effect of the lipid monolayer composition on their interfacial properties may elucidate some of the fundamental reasons for the deficiencies in cell membranes and tear film functioning in vivo. The experimental results have shown that the molar ratio of the mixture plays a crucial role in the modulation of the Langmuir film properties. The condensing effects of the cholesterol and the interactions between the lipids in the monolayer were the main factors altering the monolayer response to dilatational deformation. The modification of the mixture compositions leads to significant changes in the Langmuir films and the mechanical performance, altering the ability of the monolayer to reduce the surface tension and the viscoelastic properties of the monolayers. This suggests that subtle modifications of the biomembrane composition may significantly alter its physiological function.
Highlights
Cholesteryl esters and cholesterol together with wax esters are counted among the most important components of the fatty secretion of the meibomian glands [1,2,3], driving the decrease in the surface tension and contributing to the Marangoni-driven homogeneous spreading of the tears upon blinking [4,5,6]
The equilibrium behavior and the response against controlled dilational stresses of Langmuir monolayers formed for mixtures of cholesterol and cholesteryl stearate have been studied as function of the temperature at 24 ◦ C and 35 ◦ C, aiming at an understanding of the potential effects of the composition on the physico-chemical properties of the biologically relevant model Langmuir monolayers
The analysis of the surface-pressure-area per molecule isotherms has evidenced the existence of a strong synergism between cholesterol and cholesteryl stearate, such synergism being the maximum for specific compositions, which depends on the temperature
Summary
Cholesteryl esters and cholesterol together with wax esters are counted among the most important components of the fatty secretion of the meibomian glands [1,2,3], driving the decrease in the surface tension and contributing to the Marangoni-driven homogeneous spreading of the tears upon blinking [4,5,6] They contribute to counteracting the film thinning by retarding the water evaporation, and by lubricating and stabilizing the tear film [7,8,9,10]. Different factors can influence the stability and physiological function of tear film, including autoimmune, environmental, hormonal or toxic factors These lead to different alterations in the structural order of the lipid molecules and the mechanical properties of meibum, which can result in different pathological states [16,17,18]. This makes it necessary to explore the origin of such pathological states and seek potential therapeutic approaches for minimizing its impact on human health [19]
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