BPS2026 - Solid-state MAS NMR to examine fluorescent small-molecule binding to pathological calcification minerals

The abnormal deposition of calcium phosphate minerals in tissues is prevalent in chronic and age-related diseases, including cardiovascular disease, age-related macular degeneration (AMD), and Alzheimer’s disease (AD). Ectopic calcification is associated with disease progression in AMD and AD and with increased mortality in cardiovascular disease, but the precise mechanisms that drive the calcification process are poorly understood. In fact, the specific mineral composition of calcified deposits and whether different minerals have distinct pathological implications is unknown. New tools are needed to detect the presence of individual minerals and examine the calcification process in vivo. A variety of small molecule dyes have been described as calcification sensors due to their ability to bind hydroxyapatite (HAP), which is known to be a major mineral component in calcified deposits. However, the HAP-binding selectivity of these dyes varies and the atomic-level details of their binding to calcified mineral surfaces remain unresolved. Employing fluorescence-based methods and solid-state magic-angle spinning (MAS) NMR spectroscopy, we are developing means to examine the binding of small molecule dyes to individual calcification minerals. Here, we describe the mineral specificity and atomic-level interactions between the small molecule dye xylenol orange and HAP as well as whitlockite (WHT), whose presence and role in pathological calcification is now emerging. We expect these methods will be instrumental in elucidating key mineral-binding interactions that can be leveraged in the design of new mineral-selective sensors and diagnostic tools.