Initial assessment of magnetoferritin biokinetics and proton relaxation enhancement in rats.
OBJECTIVE
We evaluated the biokinetics and proton relaxation enhancement of magnetoferritin, a recently developed class of superparamagnetic iron oxides, in rats.


METHODS
"Equine" magnetoferritin was administered intravenously at 5 mg protein and 1.4 mg Fe/kg in nude rats carrying subcutaneous xenografted human small-cell lung carcinoma with and without preinjection of 100 mg/kg equine apoferritin. Blood clearance, in vivo biodistribution, and proton relaxation enhancement were assessed by variable field relaxometry, immunohistochemistry, and magnetic resonance (MR) imaging at 1.5 T.


RESULTS
Magnetoferritin clearance from blood followed biexponential kinetics, with a short initial half-life of 1.4-1.7 min. A second, longer component lasted for several hours. Histochemical staining, MR imaging, and ex vivo relaxometry revealed rapid uptake of magnetoferritin in the liver, spleen, and lymph nodes. There was no difference in biodistribution after apoferritin preinjection.


CONCLUSIONS
In the rat, equine magnetoferritin is rapidly sequestered by cells of the reticuloendothelial system, with no direct involvement of ferritin receptors. These properties may allow the use of magnetoferritin as an MR contrast agent for the liver and spleen.
Bulte
J W
JW
Laboratory of Diagnostic Radiology Research, National Institutes of Health, Bethesda, MD 20892, USA.
Douglas
T
T
Mann
S
S
Vymazal
J
J
Laughlin
P G
PG
Frank
J A
JA
D000818:Animals; D001052:Apoferritins / Q000031:analogs & derivatives* / Q000097:blood / Q000493:pharmacokinetics; D018288:Carcinoma, Small Cell / Q000175:diagnosis / Q000378:metabolism; D003287:Contrast Media; D005260:Female; D007501:Iron / Q000097:blood / Q000493:pharmacokinetics*; D008099:Liver / Q000378:metabolism; D008175:Lung Neoplasms / Q000175:diagnosis / Q000378:metabolism; D008198:Lymph Nodes / Q000378:metabolism; D008279:Magnetic Resonance Imaging; D010087:Oxides / Q000097:blood / Q000493:pharmacokinetics*; D051381:Rats; D011923:Rats, Nude; D013154:Spleen / Q000378:metabolism
D003287:Contrast Media; D010087:Oxides; C088922:magnetoferritin; D001052:Apoferritins; D007501:Iron