MR Imaging Of Brain Glioma In Rat Model Using Transferrin-conjugated SPIONs As A Specific Contrast Agent

Objective:By testing Tf-SPIONs of rat C6 glioma both in vitro and in vivo on MRI imaging, to explore whether transferrin-conjugated superparamagnetic iron oxide nanoparticles(Tf-SPIONs)could used as a specific MR contrast agent for detecting glioma in rat.Methods:(1) Tf conjuated with SPIONs was testing by Fourier transform infrared spectroscopy (FTIR) .The morphology and particle size of nanoparticles were observed by transmission electron microscope (TEM). The range of 1-20μg/ml concentration of Tf-SPIONs and SPIONs were scanned using 3.0T MRI of T2WI sequence and calculated the value of r₂ relaxation rates. (2) The different concentrations 0, 5, 10, 15 and 20ug/ml of Tf-SPIONs and SPIONs were incubated with C6 glioma cells respectively, which were scanned by the T2WI sequence and compared between the two signal strength. Two samples of different concentrations of intracellular iron content were measured. The concentration 20μg/mL of Tf-SPIONs and SPIONs were separately incubated with C6 glioma cells and then underwent Prussian blue staining. (3) The rat glioma model was established by brain stereotaxic injection of C6 glioma cells. Planted about 14 days, Tf-SPIONs and SPIONs were separately injected via the tumor-bearing rat tail vein, then the rats were scanned by T2WI, T1WI and SWI sequence after 2 hours, 24 hours, 48 hours to evaluate the effectiveness of the contrast agent. And the tumor signal changes were observed. Finally, the tumor biopsy specimens were separately performed Prussian blue staining and HE staining as the biochemical and pathological study. (4) SPSS16.0 software was used to test the study data by line independent samples t test, p <0.05 indicating a significant statistically difference.Results:①The successfully coupling of Tf and SPIONs was confirmed by FTIR. TEM showed the overall size of SPIONs was 9.3±0.5 nm, Tf-SPIONs was 14.1±0.6 nm. From the concentration-relaxation rate curve, showing the concentration of Tf-SPIONs and SPIONs and T2 relaxation time was linear, with the sample concentration increasing, the relaxation rate increasing. The r2 value of SPIONs was 120.4mM^-1S^-1 according to MRI imaging, and Tf-SPIONs was 64.3 mM^-1S^-1.②MRI imaging revealed that Tf-SPIONs group with C6 cells in T2 signal intensity is more obvious than SPIONs group in vitro. The results of the concentration-iron content curve showed that iron content the Tf-SPIONs groups were higher than the control in the 0-20μg/mL concentration range. Prussian blue staining confirmed that the number of positive cells was significantly higher than the control group.③The tumors showed as heterogenous hyperintensity on T2WI images and hypointensity on T1WI imaging. 2h after the injection of Tf-SPIONs, the T2WI and SWI image signal started to decrease in tumor tissues. After 24 and 48 hours the low signal area became obvious and the scope increased. However, the control group observed no significant signal change in the tumor area.The normal brain tissue was invaded by glioma tumor cells on HE staining. Prussian blue staining confirmed that large number of Tf-SPIONs accumulated in tumor site .However, rare SPIONs were accumulated.Conclution:Tf-SPIONs could improve the sensitivity and specificity of visualizing the glioma on T2WI and SWI images, and could maintain a longer time window. It may served as an ideal MR contrast agent in targeting glioma in the future.