Study On The Distribution Of Superparamagnetic Iron Oxide Nanoparticles Modified With Different Functional Molecules In Rat Brain

Poly(ethylene glycol)(PEG)and poly(ethylene imine)(PEI)co-modified superparamagnetic iron oxide nanoparticles(SPIONs)(PEG/PEI-SPIONs),and PEG and maleic anhydride(Mal)co-modified SPIONs(Mal-SPIONs)were synthesized by thermal decomposition.PEG and PEI provided excellent water dispersibility and stability.We further conjugated phospholipids which is the main components of cell membrane to PEG/PEI-SPIONs.The bovine serum albumin which is the prevalent in living organisms was conjugated to MalSPIONs,The RGD which can bind to integrin on cell membrane was conjugated to MalSPIONs,in order to study the diffusion of SPIONs modified with different functional molecules in rat brain.The nanoparticles were unilaterally injected into the left substantia nigra of rat brains.The distributions of the nanoparticles in the left brains of the rats were examined by ICP-OES(inductively coupled plasma optical emission spectrometer)and TEM(transmission electron microscopy)at 24 h after the injection.We focused on the distribution of iron oxide nanoparticles in five regions: thalamus,temporal lobe,prefrontal cortex,olfactory bulb,and brain stem.The uptake of PEG/PEI-SPIONs and DMPC-SPIONs by PC-12 cells were also studied.The main results are as follows:(1)We synthesized and characterized the superparamagnetic iron oxide nanoparticles(SPIONs)modified with poly(ethylene glycol)(PEG)and polyethylenimine(PEI)(PEG/PEISPIONs),and with dimyristoylphosphatidylcholine(DMPC)(DMPC-SPIONs).The nanoparticles were unilaterally injected into the left substantia nigra of rat brains.The distributions of the nanoparticles in the left brains of the rats were examined by ICP-OES and TEM at 24 h after the injection.Iron was found in the olfactory bulb,temporal lobe,frontal cortex,thalamus and brain stem at 24 h after the injection of DMPC-SPIONs and PEG/PEISPIONs.In the rat substantia nigra,most DMPC-SPIONs were distributed in and on the myelin sheath around axons or on cell membranes,some were in cells.As a comparison,less iron was found in the rat brains at 24 h after the injection of PEG/PEI-SPIONs.Our experiments suggest DMPC modification on SPIONs be a safe and effective method for increasing SPIONs distribution on the cell membranes.(2)We incubated DMPC-SPIONs with PC-12 cells.The nanoparticles internalized into PC-12 cells were observed by TEM and quantified by ICP-OES.There was a much greater uptake of DMPC-SPIONs than PEG/PEI-SPIONs into PC-12 cells and remarkable amounts of accumulated nanoparticles were found in the lysosome,endoplasmic reticulum,mitochondria,vesicles,and around the nucleus,and some nanoparticles remained on the cell membrane.This can be attributed to the similarity between the chemical structures of DMPC and membrane phospholipids which result in the fusion of DMPC and cell membranes.Our results encourage further research on DMPC-SPIONs as drug carriers,transfection agents,MRI contrast agents for cells and hyperthermia agents.(3)We synthesized and characterized the superparamagnetic iron oxide nanoparticles(SPIONs)modified with maleic anhydride(Mal)(Mal-SPIONs)and RGD(RGD/Mal-SPIONs),and with bovine serum albumin(BSA)(BSA/Mal-SPIONs).The nanoparticles were unilaterally injected into the left substantia nigra of rat brains.The distributions of the nanoparticles in the left brains of the rats were examined by ICP-OES and TEM at 24 h after the injection to investigate the distribution of iron nanoparticles in rat brain.It was found that Mal-SPIONs mainly concentrated on the thalamus,and there was no significant change in iron content in the other four different brain regions.After the RGD/Mal-SPIONs injection,the iron content in different brain areas was significantly increased.And the diffusion distance was significantly increased.After the injection of BSA/Mal-SPIONs,the iron content in thalamus and temporal lobe near the substantia nigra was significantly increased.While the iron content in the other four brain regions did not increase significantly.A conclution can be drawn according to the results of each group: RGD is important for the distribution of the iron oxide nanoparticles in brains.BSA which has a larger molecular weight can promote the diffusion of iron oxide nanoparticles from the left substantia nigra to the thalamus and temporal lobe to some extent.This work is encouraging for further study on using DMPC-SPIONs and RGD/MalSPIONs s for efficient drug delivery or for deep brain stimulation of neurons in a magnetic field.