Preparation and evaluation of 111In-labeled liposomes containing phosphatidylglycerol for detection of macrophages in atherosclerotic plaques.

Macrophage infiltration is a characteristic feature of atherosclerotic plaque progression. Since liposomes containing 1,2-distearoyl-sn-glycero-3-phosphoglycerol (DSPG) are efficiently phagocytosed by macrophages, we deduced that radiolabeled liposomes containing DSPG could potentially be used for nuclear imaging of vulnerable atherosclerotic plaques. Indium-111 (111In)-labeled liposomes containing different ratios of DSPG were developed with a high labeling efficiency. 111In-labeled liposomes with higher DSPG content showed higher uptake by macrophage-like RAW264 cells. A biodistribution study demonstrated rapid blood clearance and selective accumulation in the liver and spleen, especially in normal mice injected with 111In-labeled liposomes with higher DSPG content. Accumulation in atherosclerotic plaques was evaluated using 111In-labeled DSPG liposomes, which had the highest DSPG content among the studied liposomes. 111In-labeled DSPG liposomes accumulated in the plaques and the radioactive regions were mostly consistent with the distribution of macrophages. The target-to-non-target ratio of 111In-labeled DSPG liposomes was higher than that of 111In-labeled control liposomes without DSPG. These results suggest that 111In-labeled liposomes containing DSPG are useful for nuclear medical diagnosis of atherosclerotic plaques.