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Laxman Mainali, Marija Raguz, William J O'Brien, Witold K Subczynski; Properties of Membranes Derived from the Total Lipids Extracted from the Clear and Cataractous Human Lenses of 61- to 70-Year-Old Donors. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1216.
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To compare the domain structure and properties of human lens lipid membranes prepared from the total lipids extracted from the clear and cataractous lens cortex and nucleus of 61- to 70-year-old donors. This research is important for further studies of intact human lens membranes, especially for the elucidation of the effect of membrane proteins on the lateral organization of the lipid bilayer portion of these membranes.
Human lens lipid membranes were prepared using a rapid solvent exchange method. Their properties and organization were investigated using electron paramagnetic resonance (EPR) spin-labeling methods. Formation of cholesterol crystals was detected using the differential scanning calorimetry (DSC). Measured membrane properties included: the phospholipid alkyl chain order, alkyl chain fluidity, oxygen transport parameter within the membranes, and hydrophobicity of membrane interior.
The measured cholesterol-to-phospholipid molar ratio in human lens membranes was 1.8 and 4.4, respectively, for cortex and nucleus of clear lenses and 1.14 and 1.45 for cataractous lenses. In the nucleus of clear lenses cholesterol crystals, formed presumably outside membranes. However, in the nucleus of cataractous lenses cholesterol crystals were not formed. In all investigated membranes cholesterol existed in two distinguished environments: (1) cholesterol dispersed in phospholipid bilayer and (2) cholesterol in non crystalline cholesterol domains (cholesterol bilayer domains, CBDs). Only in the preparation from clear lens nuclei was the third environment detected, namely cholesterol crystals.
All profiles of membrane properties were very similar to those reported for lens lipid membranes of 41- to 60-year-old donors. This confirms that saturation with cholesterol determines properties of the phospholipid bilayer of lens lipid membranes. The presence of the CBD ensures that the phospholipid bilayer in all investigated membranes was saturated with cholesterol. Formation of cholesterol crystals in aged fiber cells cannot be treated as precursors or signs of age-related cataract formation.
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