Abstract
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(x)Fe(3-x)O(4) nanoparticles. Our work provides insight into the optimization of ultrasmall ferrite nanoparticle-based T(1) contrast agents by tuning their compositions and promotes the translation of these ultrasmall ferrite nanoparticles for clinical use of high-performance contrast-enhanced MRI.