Superparamagnetic Ferrite Nanoparticle Contrast Agents

Superparamagnetic iron oxide particle (SPIO) is a new type of magnetic material used in the Magnetic Resonance Imaging (MRI), which can be developed as reticuloendothelial system MRI contrast agents. This kind of material has the advantages of high signal to noise ratio and safe in application of MRI. In order to expand the application of MRI contrast agent in clinical studies, in this paper the lyophilized SPIO was prepared. First, SPIO colloid was prepared with ferric chloride and ferrous chloride by chemical precipitation reaction. Total iron content was determined by o-phenanthroline colorirnetry. Based on single factor studies, which took the appearance of SPIO colloid, yield and specific magnetization as criteria, the optimal manufacturing condition and formulation were obtained by orthogonal design test. The iron yield of optimal SPIO colloid and the specific magnetization was 49.3%, 0.64 emulg respectively (n=3). On the basis of SPIO colloid, the lyophilized SPIO was prepared in order to improve the stability of SPIO colloid. Two methods of sterilization, Arnold steam sterilization and Micropore sterilization were studied, which had little effect on the quantity of SPIO colloid. The eutectic temperature of SPIO colloid with different cryoprotectant was detennined by conductant method. 2% mannitol as cryoprotectant was the best concentration by appearance and state of rehydration. Stability studies of lyophilized SPIO demonstrated that light, temperature had little effect. The accelerated stability experiment indicated the shelf life of lyophilized SPIO was about two years. The physicochemical properties of lyophilized SPIO were described. Transmission electron microscopy showed that SPIO particle was nanoparticle with iron oxide crystal diameter of 3Onm. Laser scattering measurement showed the average size of rehydrated lyophilized SPIO was 98.7nm. X-ray diffraction 3 ABSTRACT and electron diffraction were consistent with the content of Fe304 crystal in SPIO. X-ray diffiaction line-broadening indicated the size of SPIO became smaller.. The results of vibrating sample magnetometer measurement demonstrated the characteristic of superparamagnetic material of rehydrated lyophilized SPIO. The safety experiments of rehydrated lyophilized SPIO, such as vessel irritation and hemolysis, were tested for intravenous administration. It was showed that lyophilized SPIO was safe formulation and nonirritant. LD50 was more than 177mg/kg in mouse. The preliniinazy studies of pharmacokinetics were evaluated in rats. The plasma Fe3~ concentration was determined by 5-Br-PADAP-OP-Fe2~ colorimetxy. The pharmacokinetic characteristics of rehydrated lyophilized SPIO conformed two compartments model. The efficacy of rehydrated lyophilized SPIO as MRI contrast agent was investigated in tumor-mouse with T2-weighted imaging. After intravenous administration, it was showed that the MRI signal intensity in normal hepar reduced significantly(P