Turnover and tissue uptake of rabbit ferritin from rabbit plasma

Biocompatibility of ferritin-based nanoparticles as targeted MRI contrast agents

Ferritin is a naturally occurring iron storage protein, proposed as a clinically relevant nanoparticle with applications as a diagnostic and therapeutic agent. Cationic ferritin is a targeted, injectable contrast agent to measure kidney microstructure with MRI. Here, the toxicity of horse spleen ferritin is assessed as a step to clinical translation. Adult male mice received cationic, native and high dose cationic ferritin (CF, NF, or HDCF) or saline and were monitored for 3weeks. Transient weight loss occurred in the ferritin groups with no difference in renal function parameters. Ferritin-injected mice demonstrated a lower serum iron 3weeks after administration. In ferritin-injected animals pre-treated with hydrocortisone, there were no structural or weight differences in the kidneys, liver, lung, heart, or spleen. This study demonstrates a lack of significant detrimental effects of horse-derived ferritin-based nanoparticles at MRI-detectable doses, allowing further exploration of these agents in basic research and clinical diagnostics.

Stability of radioiodinated ferritin

Ferritin which had been radioiodinated using chloramine T exhibited marked instability on storage at 4 degrees C. Both [125I]human liver and heart ferritins showed a similar rate of decline in immunoreactivity (t 1/2 = 20-23 days) indicating that deterioration with storage was not a function of isoferritin composition. The decrease in radioactivity associated with ferritin was due not only to loss of 125I from the molecule but also to protein degradation as shown by enzyme-linked immunoassay and gel filtration. The degradation products had an Mr of at least 69,000 although low Mr material could be identified by gel filtration when a marked reduction in immunoreactivity had occurred. Ferritin instability was much more pronounced than when other proteins such as immunoglobulin and albumin were radioiodinated with chloramine T. These observations indicate that when performing in vivo and in vitro studies with labeled ferritin, degradation of the protein during storage should be carefully monitored and the protein repurified before use.

Interaction of ferritin with serum: implications for ferritin turnover

An interaction between human and rabbit ferritins and serum was demonstrated by a coated tube binding assay, a shift in molecular size on gel filtration and by precipitation of complexes with 3.5% polyethylene glycol 6000. With polyethylene glycol and labelled ferritins, complex formation was inhibited by heating sera to 56 degrees C for 30 min and by addition of EDTA or excess unlabelled ferritins. Human heart ferritin showed the greatest interaction with serum, followed by human spleen ferritin and least of all human plasma ferritin. Ferritins did not appear to bind to IgG or IgM in normal sera. The interaction of 'H' subunit-containing ferritins with serum or plasma may be partly responsible for the rapid clearance of tissue ferritins from the circulation and the absence of acidic isoferritins in the plasma of normal subjects.