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 (<i>r</i>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 (<i>ApoE</i>^{<i>–/–</i>}) 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