Monolayers of Cholesterol and Cholesteryl Stearate at the Water/Vapor Interface: A Physico-Chemical Study of Components of the Meibum Layer

Investigation on the relationship between lipid composition and structure in model membranes composed of extracted natural phospholipids

HYPOTHESIS

Unravelling the structural diversity of cellular membranes is a paramount challenge in life sciences. In particular, lipid composition affects the membrane collective behaviour, and its interactions with other biological molecules.

EXPERIMENTS

Here, the relationship between membrane composition and resultant structural features was investigated by surface pressure-area isotherms, Brewster angle microscopy and neutron reflectometry on in vitro membrane models of the mammalian plasma and endoplasmic-reticulum-Golgi intermediate compartment membranes in the form of Langmuir monolayers. Natural extracted yeast lipids were used because, unlike synthetic lipids, the acyl chain saturation pattern of yeast and mammalian lipids are similar.

FINDINGS

The structure of the model membranes, orthogonal to the plane of the membrane, as well as their lateral packing, were found to depend strongly on their specific composition, with cholesterol having a major influence on the in-plane morphology, yielding a coexistence of liquid-order and liquid-disorder phases.

Interfacial Dynamics of Adsorption Layers as Supports for Biomedical Research and Diagnostics

The input of chemical and physical sciences to life sciences is increasingly important. Surface science as a complex multidisciplinary research area provides many relevant practical tools to support research in medicine. The tensiometry and surface rheology of human biological liquids as diagnostic tools have been very successfully applied. Additionally, for the characterization of pulmonary surfactants, this methodology is essential to deepen the insights into the functionality of the lungs and for the most efficient administration of certain drugs. Problems in ophthalmology can be addressed using surface science methods, such as the stability of the wetting films and the development of artificial tears. The serious problem of obesity is fast-developing in many industrial countries and must be better understood, while therapies for its treatment must also be developed. Finally, the application of fullerenes as a suitable system for detecting cancer in humans is discussed.

Fluid Films as Models for Understanding the Impact of Inhaled Particles in Lung Surfactant Layers

Pollution is currently a public health problem associated with different cardiovascular and respiratory diseases. These are commonly originated as a result of the pollutant transport to the alveolar cavity after their inhalation. Once pollutants enter the alveolar cavity, they are deposited on the lung surfactant (LS) film, altering their mechanical performance which increases the respiratory work and can induce a premature alveolar collapse. Furthermore, the interactions of pollutants with LS can induce the formation of an LS corona decorating the pollutant surface, favoring their penetration into the bloodstream and distribution along different organs. Therefore, it is necessary to understand the most fundamental aspects of the interaction of particulate pollutants with LS to mitigate their effects, and design therapeutic strategies. However, the use of animal models is often invasive, and requires a careful examination of different bioethics aspects. This makes it necessary to design in vitro models mimicking some physico-chemical aspects with relevance for LS performance, which can be done by exploiting the tools provided by the science and technology of interfaces to shed light on the most fundamental physico-chemical bases governing the interaction between LS and particulate matter. This review provides an updated perspective of the use of fluid films of LS models for shedding light on the potential impact of particulate matter in the performance of LS film. It should be noted that even though the used model systems cannot account for some physiological aspects, it is expected that the information contained in this review can contribute on the understanding of the potential toxicological effects of air pollution.

Human meibum and tear film derived cholesteryl and wax esters in meibomian gland dysfunction and tear film structure

PURPOSE

This study evaluated the presence and roles of cholesteryl esters (CEs) and wax esters (WEs) from human tear film and meibum in meibomian gland dysfunction (MGD).

METHODS

Out of 195 enrolled subjects, 164 and 179 subjects provided tear and meibum samples, respectively. Subjects were classified into normal, asymptomatic MGD, MGD, and mixed (MGD & aqueous deficient). The precorneal tear film (PCTF) thinning rate (evaporation) was measured using optical coherence tomography. Lipids extracted from tear and meibum samples were infused into a SCIEX 5600 TripleTOF mass spectrometer. CE and WE intensities quantified with Analyst 1.7 TF and LipidView 1.3 were compared across disease groups in MetaboAnalyst 5.0 and correlated with PCTF thinning rates.

RESULTS

The numbers of unique CEs and WEs identified in the samples were 125 and 86, respectively. Unsupervised Principal Component (PC) analysis and supervised Partial Least Square Discriminant analysis exhibited little separation among groups for both CEs and WEs in tears and meibum. Spearman's correlation analyses showed no association between either the first or second PC scores with PCTF thinning rates.

CONCLUSION

The abundances of human PCTF and meibum-derived CEs and WEs were independent of MGD disease status and PCTF thinning (evaporation). CEs and WEs alterations do not contribute to alterations in tear film dynamics in MGD, such as has been demonstrated by the (O-acyl) ω-hydroxy fatty acids (OAHFAs).