The Effects of Cholesterol Oxidation on Erythrocyte Plasma Membranes: A Monolayer Study.

Cholesterol plays a key role in the molecular and mesoscopic organisation of lipid membranes and it is expected that changes in its molecular structure (e.g., through environmental factors such as oxidative stress) may affect adversely membrane properties and function. In this study, we present evidence that oxidation of cholesterol has significant effects on the mechanical properties, molecular and mesoscopic organisation and lipid-sterol interactions in condensed monolayers composed of the main species found in the inner leaflet of the erythrocyte membrane. Using a combination of experimental methods (static area compressibility, surface dilatational rheology, fluorescence microscopy, and surface sensitive X-ray techniques) and atomistic molecular dynamics simulations, we show that oxidation of cholesterol to 7-ketocholesterol leads to stiffening of the monolayer (under both static and dynamic conditions), significant changes in the monolayer microdomain organisation, disruption in the van der Waals, electrostatic and hydrophobic interactions between the sterol and the other lipid species, and the lipid membrane hydration. Surface sensitive X-ray techniques reveal that, whilst the molecular packing mode is not significantly affected by cholesterol oxidation in these condensed phases, there are subtle changes in membrane thickness and a significant decrease in the coherence length in monolayers containing 7-ketocholesterol.

Assessment of Compressive Raman versus Hyperspectral Raman for Microcalcification Chemical Imaging.

We experimentally implement a compressive Raman technology (CRT) that incorporates chemometric analysis directly into the spectrometer hardware by means of a digital micromirror device (DMD). The DMD is a programmable optical filter on which optimized binary filters are displayed. The latter are generated with an algorithm based on the Cramer-Rao lower bound. We compared the developed CRT microspectrometer with two conventional state-of-the-art Raman hyperspectral imaging systems on samples mimicking microcalcifications relevant for breast cancer diagnosis. The CRT limit of detection significantly improves, when compared to the CCD based system, and CRT ultimately allows 100× and 10× faster acquisition speeds than the CCD- and EMCCD-based systems, respectively.