| MRI is characterized by high spatial resolution and complete noninvasiveness,is often used to interpret the clinical diagnosis of brain diseases.About 40%of clinical patients need to use contrast agents for MRI diagnosis.Common gadolinium agents have the disadvantages of high cost and high dose.SPIONs,as an emerging contrast agent for MRI,is superior to gadolinium in both theoretical research and clinical trails,with high imaging resolution in brain soft tissue.Spinal canal administration can bypass the blood-brain barrier which hinders the diagnosis and treatment of brain diseases.At present,there are few studies on the application of intrathecal tube embedding technique and spinal canal administration of SPIONs for brain MRI.Therefore,it has important theoretical significance and broad application prospect to study the application of efficient SPIONs contrast agent in combination with spinal canal administration in MRI diagnosis of brain diseases.Oil-soluble SPIONs were synthesised by an improved high-temperature thermal decomposition method in this study,having a good morphology and particle size distribution with an average particle size of 5 nm and saturation magnetization of 81.83emu/g.In order to increase the water solubility and improve its stability,we modified SPIONs with DSPE-PEG2000 by thin film ultrasonic dispersion method.The DSPE-PEG2000-SPIONs have zeta average size around 70 nm,Zeta potential about-18 mv,PDI0.107.The aqueous solution has a clear brown appearance,PDI remained below 0.2 under4℃for 30 days without aggregation.The relaxation rate of DSPE-PEG2000-SPIONs was396.3 mm-1·s-1,which was higher than Feridex,suggesting high magnetic sensitivity.Biosecurity is a primary consideration for materials application in biomedical field.Based on the potential toxicity of SPIONs,side effects of iron overload in liver,high cost and long period in animal study,we used mouse primary hepatocytes sandwich model to evaluate the toxicity of SPIONs which established by an improved collagenase perfusion method.The activity of the hepatocytes obtained by following vena cava perfusion was about 90%and（1-4）×106hepatocytes could be obtained from the liver of each mouse.The AST ALT,AKP of cell culture supernatant in sandwich model can maintain a high state in one week.LDH levels declined gradually and BUN is rising which both then tend to stable.Hepatocytes are characterized by special multilateral morphology in 2 weeks period.The AST and ALT levels of cell culture supernatant showed a density dependence of hepatocytes.The cell viability of hepatocytes was 87.94%when DSPE-PEG2000-SPIONs concentration was 200μg/m L.The AST,ALT level of hepatocytes did not decrease significantly compared with control when the SPIONs concentration was 0-200μg/m L.these results indicated that DSPE-PEG2000-SPIONs had no significant effect on the function of hepatocytes and with low toxicity.In addition,we found that there was no significant change in the UV-Vis absorption spectra of culture medium after co-incubation with DSPE-PEG2000-SPIONs,suggesting that the toxicity of DSPE-PEG2000-SPIONs was independent of the changes in culture medium.Spinal canal administration can ignore the influence of blood-brain barrier.In order to explore the feasibility of SPIONs spinal canal administration and the enhancement of brain MRI signal in diseases diagnosis,we constructed a long-term spinal canal administration model of rats with an improved lumbar embedding technique.The results of catheter permeability test and spinal canal anatomy showed that catheter location was accurate and have a good permeability which can realize spinal canal administration and rats can recover quickly without complications after the operation.These results indicated that the model we have established was stable and reliable.MRI results of rats with 40μL DSPE-PEG2000-SPIONs for spinal canal administration showed that DSPE-PEG2000-SPIONs could enter into the brain through cerebrospinal fluid circulation within 30 minutes and achieve MRI enhancement.After 4 hours,the DSPE-PEG2000-SPIONs could be excreted in large quantities through urine,indicating good biological safety. |
