Magnetoferritin: characterization of a novel superparamagnetic MR contrast agent.
A protein-encaged superparamagnetic iron oxide has been developed and characterized by using horse spleen apoferritin as a novel bioreactive environment. The roughly spherical magnetoferritin molecules, 120 A in diameter, are composed of a monocrystalline maghemite or magnetite core 73 A +/- 14 in diameter. Except for the additional presence of iron-rich molecules of higher molecular weight, the appearance and molecular weight (450 kd) of magnetoferritin are identical to that of natural ferritin; the molecules are externally indistinguishable from their precursor, with a pI (isoelectric point) in the range 4.3-4.6. The measured magnetic moment of the superparamagnetic cores is 13,200 Bohr magnetons per molecule, with T1 and T2 relaxivities (r1 and r2) of 8 and 175 L.mmol-1 (Fe).sec-1, respectively, at body temperature and clinical field strengths. The unusually high r2/r1 ratio of 22 is thought to arise from ideal core composition, with no evidence of crystalline paramagnetic inclusions. T2 relaxation enhancement can be well correlated to the field-dependent molecular magnetization, as given by the Langevin magnetization function, raised to a power in the range 1.4-1.6. With its nanodimensional biomimetic protein cage as a rigid, convenient matrix for complexing a plethora of bioactive substances, magnetoferritin may provide a novel template for specific targeting of selected cellular sites.
Bulte
J W
JW
Laboratory of Diagnostic Radiology, Research, National Institutes of Health, Bethesda, MD 20892.
Douglas
T
T
Mann
S
S
Frankel
R B
RB
Moskowitz
B M
BM
Brooks
R A
RA
Baumgarner
C D
CD
Vymazal
J
J
Strub
M P
MP
Frank
J A
JA
D000818:Animals; D001052:Apoferritins / Q000031:analogs & derivatives / Q000138:chemical synthesis / Q000737:chemistry; D003287:Contrast Media / Q000138:chemical synthesis / Q000737:chemistry; D003911:Dextrans; D052203:Ferrosoferric Oxide; D006736:Horses; D007501:Iron / Q000737:chemistry; D008279:Magnetic Resonance Imaging; D058185:Magnetite Nanoparticles; D010087:Oxides / Q000138:chemical synthesis / Q000737:chemistry
D003287:Contrast Media; D003911:Dextrans; D058185:Magnetite Nanoparticles; D010087:Oxides; C088922:magnetoferritin; D001052:Apoferritins; D007501:Iron; C065507:ferumoxides; D052203:Ferrosoferric Oxide