Gadolinium mixed-micelles: effect of the amphiphile on in vitro and in vivo efficacy in apolipoprotein E knockout mouse models of atherosclerosis.

Gadolinium (Gd) micelles are nanoparticles that incorporate phospholipids, surfactants, and lipophilic Gd complexes. Preliminary studies have shown that lipid-based nanoparticles may penetrate atherosclerotic plaque. The aim of the current study was to prepare, characterize, and evaluate in vivo the efficacy of two Gd micelle formulations using apolipoprotein E knockout (ApoE(-/-)) mouse models of atherosclerosis. Gd micelles were prepared using two different amphiphiles but similar GdDTPA lipids, surfactants, and fluorescent labels. The results indicate that the choice of amphiphile may affect the particle size, relaxivity, and blood clearance in wild-type mice (WT). However, the in vivo MR efficacy, with respect to uptake in the vessel wall of ApoE(-/-) mice, was not affected by the amphiphile used. Significant wall enhancement of ApoE(-/-) mice was observed following administration of 0.015 and 0.038 mmol Gd/kg of both micelle formulations. No significant enhancement of the vessel wall of WT mice was observed for any of the dosages or formulations tested. Additionally, liver uptake 24 hr post-injection (p.i.) was not influenced by the choice of amphiphile. The results of this study strongly suggest that liver uptake and wall enhancement may be regulated by the surface properties of the micelle and not by other factors, such as micelle size.