Characterization of a novel model for atherosclerosis imaging: the apolipoprotein E-deficient rat

The apolipoprotein E-deficient (apoE^-/-) mouse is a well-established model for studying atherosclerosis. However, its small size limits its use in longitudinal positron emission tomography (PET) imaging studies. Recently, the apoE^-/- rat has emerged as an alternative. With this study, we investigate the feasibility of using apoE^-/- rats as an in vivo model for longitudinal atherosclerotic PET/CT imaging.

ApoE^-/- rats showed significantly higher [¹⁸F]FDG uptake than controls in the aortic arch (+ 18.5%, p < 0.001) and abdominal aorta (+ 31.0%, p < 0.001) at weeks 12, 26, and 51. ApoE^-/- rats exhibited hypercholesterolemia, as evidenced by plasma cholesterol levels that were up to tenfold higher, and total hepatic cholesterol levels that were up to threefold higher than the control rats at the end of the study. Fast protein liquid chromatography cholesterol profiling indicated very high levels of pro-atherogenic apoB-containing very low-density lipoprotein and low-density lipoprotein fractions in the apoE^-/- rats. Atherosclerotic lesions cover 19.9% of the surface of the aortic arch (p = 0.0013), and there was a significantly higher subendothelial accumulation of ED1-positive macrophages in the abdominal aorta of the apoE^-/- rats compared to control rats (Ctrl) (p = 0.01). No differences in neutral sterols were observed but higher levels of bile acids were found in the apoE^-/- rats.

These data demonstrate early signs of hypercholesterolemia, high levels of bile acids, the development of atherosclerotic lesions, and macrophage accumulation in apoE^-/- rats. Therefore, this model shows promise for atherosclerosis imaging studies.