Functionalized low-density lipoprotein nanoparticles for in vivo enhancement of atherosclerosis on magnetic resonance images.

To allow visualization of macrophage-rich and miniature-sized atheromas by magnetic resonance (MR) imaging, we have converted low-density lipoprotein (LDL) into MR-active nanoparticles via the intercalation of a 1,4,7,10-tetraazacyclodecane-1,4,7-triacetic acid (DO3A) derivative and the subsequent coordination reaction with Gd3+. After careful removal of nonchelated Gd3+, an MR-active LDL (Gd3+-LDL) with a remarkably high payload of Gd3+ (in excess of 200 Gd3+ atoms per particle) and a high relaxivity (r(1) = 20.1 s(-1) mM(-1) per Gd3+. or 4040 s(-1) mM(-1) per LDL) was obtained. Dynamic light-scattering photon correlation spectroscopy (DLS) and cryo transmission electron microscope (cryoTEM) images showed that Gd3+-LDL particles did not aggregate and remained of a similar size (25-30 nm) to native LDL. Intravenous injection of Gd3+-LDL into an atherosclerotic mouse model (ApoE(-/-)) resulted in an extremely high enhancement of the atheroma-bearing aortic walls at 48 h after injection. Free Gd3+ dissociation from Gd3+-LDL was not detected over the imaging time window (96 h). Because autologous LDL can be isolated, modified, and returned to the same patient, our results suggest that MR-active LDL can potentially be used as a noninfectious and nonimmunogenic imaging probe for the enhancement of atheroplaques presumably via the uptake into macrophages inside the plaque.