Interactions Between Amyloid-β (1-42) and Hydroxyapatite-Cholesterol Spherules Associated with Age-Related Macular Degeneration

Drusen deposition on sub-retinal pigment epithelium is the causal factor for age-related macular degeneration for the old-aged individuals. These deposits contain hydroxyapatite-cholesterol spherules on which several proteins and lipids accumulate to cover the retina and choroid, causing blurred vision and blindness. Amyloid-β, the known culprit in Alzheimer's disease, is one among the few major proteins known to occur in these deposits. In the present article, we report preliminary analyses of interactions between amyloid-β and hydroxyapatite-cholesterol composites using Thioflavin-T binding kinetics, solid-state NMR and transmission electron microscopy (TEM). Thioflavin-T fluorescence kinetics shows that amyloid-β (1-42) aggregates only under certain conditions of concentration of cholesterol in the hydroxyapatite-cholesterol composites prepared by two different methods. These results were confirmed by 1D C CPMAS solid-state NMR. TEM imaging revealed that there is an exposure of the cholesterol surface in the composites prepared by sonication method. These imaging experiments explain the dependence of aggregation kinetics on the exposure and availability of cholesterol surface in the composites to a certain extent.