Superparamagnetic iron oxide nanoparticles as a liver MRI contrast agent: contribution of microencapsulation to...

We have developed a new method of synthetizing superparamagnetic iron oxide nanoparticles, consisting in the modifications of Molday's method, which ensures high relaxivity (2.4 10(5) s-1.M-1.L), good chemical stability, singular biodistribution and a considerable safety margin. The ED (Efficace Dose) to LD50 ratio is 1/2400 instead of 1/50 for Gd-DTPA. In order to develop a magnetite-delivery system to the liver we have incorporated the nanoparticles into biodegradable synthetic microcapsules. Encapsulated 59Fe oxide nanoparticles are injected into rats; in these conditions the sequestration is 9-fold greater in liver and 6 and 5 times lower in blood and carcase, respectively. This modification of the biodistribution enables the use of magnetite containing microcapsules at only 0.3 mg/kg iron to obtain an improved contrast in liver.