Optical imaging of hydroxyapatite in the calcified vasculature of transgenic animals.

OBJECTIVE To detect the hydroxyapatite component of vascular calcification in vivo so that the process of calcium deposition can be studied in transgenic model systems. METHODS AND RESULTS We have previously developed a near-infrared fluorescent bisphosphonate derivative that binds with high affinity and specificity to hydroxyapatite, and an intraoperative near-infrared fluorescence imaging system for small animals. Using these tools, and a transgenic mouse strain with homozygous deletion of the matrix GLA protein (Mgp(-/-)), we demonstrate that the hydroxyapatite component of vascular calcification can be detected in vivo with high sensitivity, specificity, and resolution. CONCLUSIONS The hydroxyapatite component of vascular calcification can be detected optically, in real-time, without sacrifice of the animal. It is now possible to study the earliest events associated with vascular mineralization, at the cell and organ level, and to monitor the process in living animals.