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 microm diameter phospholipid liposomes suspended in agarose. Graded iron loading was achieved by varying ferritin burden per liposome as well as liposomal volume fraction. T1 and T2 relaxation times were measured on a 60 MHz NMR spectrometer and compared to simple ferritin-gel combinations. Liposomal-ferritin had 6-fold stronger T2 relaxivity than unaggregated ferritin but identical T1 relaxivity. Liposomal-ferritin T2 relaxivity also more closely matched published results from hemosiderotic marmoset liver, suggesting a potential role as an iron-calibration phantom.