Multicolor Microscopic In Vivo Imaging of the Formation and Disappearance of Lipid Droplets Using BODIPY-Based Red and Deep-Red Fluorescent Probes.

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide. As the number and size of lipid droplets (LDs) generally increase in hepatocytes during the early stages of NAFLD, visualization of LDs in living samples is of great importance for properly diagnosing and treating NAFLD. Here, red and deep-red fluorescent probes (BPMP-2Thia and BPMP-4Thia) based on boron-dipyrromethene (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene, BODIPY) are developed for the visualization of LDs in the liver of normal and NAFLD model mice as well as cultured cells. BPMP-2Thia and BPMP-4Thia exhibit bright emission in low-polarity solvents, which simulate the microenvironment of LDs, and they exhibit high selectivity for LDs, costaining capability, good biocompatibility, and high photostability in living cells and mice. Multicolor confocal microscopy combined with intravenous administration of an LD-specific probe, vascular endothelial marker, and nucleus-specific probe in mice enables the quantitative visualization of LD growth, including visualization of the disordered sinusoidal network and flattened hepatocyte nuclei. Furthermore, this simultaneous imaging method allows evaluation of the reduction in the number and size of LDs in the hepatic tissues of fatty liver model mice upon shifting from a high-fat to normal diet.