Differential uptake of ferumoxtran-10 and ferumoxytol, ultrasmall superparamagnetic iron oxide contrast agents in rabbit: Critical determinants of atherosclerotic plaque labeling

Purpose: To compare atherosclerotic plaque uptake of a first (ferumoxtran-10) and second generation (ferumoxytral) ultrasmall superparamagnetic iron oxide (USPIO) contrast agent with different pharmocokinetic/pharmacodynamic properties. Material and Methods: New Zealand White rabbits maintained on a high cholesterol/fat diet were. subjected to balloon injury to the abdominal aorta. Ferumoxtran-10 or ferumoxytol (500 mu mol/kg) was administered at 2, 4, and 8 weeks following injury. In vivo magnetic resonance imaging (MRI) was performed immediately prior to, immediately after, and 6 days post-contrast administration. Ex vivo MRI, histologic, and inductively coupled plasma-mass spectrometry (ICP-MS) iron analyses were performed on the excised vessels. Results: The blood pool clearance of ferumoxytol (t1/2 <= 6 hours) was more rapid than that of ferumoxtran-10 (t1/2 <= 48 hours). Decreased in vivo MRI signal intensity in the abdominal aorta was observed at 2, 4, and 8 weeks following injury with ferumoxtran-10, but not with ferumoxytol. Consistent with these. observations, ex vivo MRI signal intensity was decreased in the ferumoxtran-10 vessels, and to, a lesser degree in the ferumoxytol vs. control vessels (-contrast agent). In contrast, in vitro macrophage phagocytosis of USPIO was four to six fold greater with ferumoxytol than with ferumoxtran-10. Additionally, the absolute iron content correlated with ex vivo MRI signal intensity in a vessels (r = -0.86, P < 0.0001). Conclusions: These data suggest that the exposure period of atherosclerotic plaque to USPIO rather than the kinetics of the USPIO uptake by plaque alone is a critical criterion for experimental design of in vivo studies. 2005 Wiley-Liss, Inc.