The development of a highly efficient, low-toxicity, ultrasmall ferrite nanoparticle-based T
1
contrast agent for high-resolution magnetic resonance imaging (MRI) is highly desirable. However, the correlations between the chemical compositions,
in vitro
T
1
relaxivities,
in vivo
nano-bio interactions and toxicities remain unclear, which has been a challenge in optimizing the
in vivo
T
1
contrast efficacy.
Methods
: Ultrasmall (3 nm) manganese ferrite nanoparticles (Mn
x
Fe
3-x
O
4
) with different doping concentrations of the manganese ions (x = 0.32, 0.37, 0.75, 1, 1.23 and 1.57) were used as a model system to investigate the composition-dependence of the
in vivo
T
1
contrast efficacy. The efficacy of liver-specific contrast-enhanced MRI was assessed through systematic multiple factor analysis, which included the
in vitro
T
1
relaxivity,
in vivo
MRI contrast enhancement, pharmacokinetic profiles (blood half-life time, biodistribution) and biosafety evaluations (
in vitro
cytotoxicity testing,
in vivo
blood routine examination,
in vivo
blood biochemistry testing and H&E staining to examine the liver).
Results
: With increasing Mn doping, the T
1
relaxivities initially increased to their highest value of 10.35 mM
-1
s
-1
, which was obtained for Mn
0.75
Fe
2.25
O
4
, and then the values decreased to 7.64 m M
-1
s
-1
, which was obtained for the Mn
1.57
Fe
1.43
O
4
nanoparticles. Nearly linear increases in the
in vivo
MRI signals (ΔSNR) and biodistributions (accumulation in the liver) of the Mn
x
Fe
3-x
O
4
nanoparticles were observed for increasing levels of Mn doping. However, both the
in vitro
and
in vivo
biosafety evaluations suggested that Mn
x
Fe
3-x
O
4
nanoparticles with high Mn-doping levels (x > 1) can induce significant toxicity.
Conclusion
: The systematic multiple factor assessment indicated that the Mn
x
Fe
3-x
O
4
(x = 0.75-1) nanoparticles were the optimal T
1
contrast agents with higher
in vivo
efficacies for liver-specific MRI than those of the other compositions of the Mn
...