Mimicking liver iron overload using liposomal ferritin preparations

Close monitoring of liver iron content is necessary to prevent iron overload in transfusion‐dependent anemias. Liver biopsy remains the gold standard; however, MRI potentially offers a noninvasive alternative. Iron metabolism and storage is complicated and tissue/disease‐specific. This report demonstrates that iron distribution may be more important than iron speciation with respect to MRI signal changes. Simple synthetic analogs of hepatic lysosomes were constructed from noncovalent attachment of horse‐spleen ferritin to 0.4 μm diameter phospholipid liposomes suspended in agarose. Graded iron loading was achieved by varying ferritin burden per liposome as well as liposomal volume fraction. T 1 and T 2 relaxation times were measured on a 60 MHz NMR spectrometer and compared to simple ferritin‐gel combinations. Liposomal‐ferritin had 6‐fold stronger T 2 relaxivity than unaggregated ferritin but identical T 1 relaxivity. Liposomal‐ferritin T 2 relaxivity also more closely matched published results from hemosiderotic marmoset liver, suggesting a potential role as an iron‐calibration phantom. Magn Reson Med 51:607–611, 2004. © 2004 Wiley‐Liss, Inc.