The Distribution Of Nanoparticles In The Substantia Nigra Of Rats After Modification Of Extracellular Matrix

Due to their unique properties,superparamagnetic magnetic iron oxide nanoparticles（SPIONs）are widely used in targeted drug delivery,magnetic hyperthermia,cell labeling and other fields.The SPIONs with different modifications have different dispersion fates in the substantia nigra.Most of them were found to be distributed on the myelin membrane or endocytosed by cells.It is still a big challenge to locate SPIONs on or near the cell membrane.Chondroitin sulfate（CS）and hyaluronic acid（HA）,as important components of extracellular matrix,have good biocompatibility,and there are also a large number of specific receptors for CS and HA on the cell membranes.This work synthesizes superparamagnetic iron oxide nanoparticles（SPIONs）,whose surface is modified with hyaluronic acid and chondroitin sulfate.The effects of molecular weight,modification method and modification ratio on the properties of decorations were studied by material characterization.Materials with good dispersibility and sufficient amount of modification were selected for cell and animal experiments.Specific research results are as follows:（1）SPIONs with good water dispersion were prepared with Fe（acac）₃ and PEG as the main raw materials at 260℃.High molecular weight HA was degraded to low molecular weight oHA,and the viscosity of HA was changed.Hyaluronic acid is modified on the surface of nanoparticles with different concentrations,and the increase of hyaluronic acid viscosity leads to the serious agglomeration of nanoparticles.With the decrease of the molecular weight of the decorations,the water dispersion of the materials gradually increases,and the particle size conforms to the normal distribution,which meets the application requirements of biomedical field.（2）CS was modified to the SPIONs surface by chemical method and physical method at a ratio of 1:1,and it was found that the physical method had more graft and better dispersion.After adjusting the modification ratio,it was found that the average size and electronegativity of the products were the largest when the mixing ratio was 1:2.Therefore,the nano-particle system prepared in proportion was selected as the follow-up biological experiment object.（3）The cytotoxicity of hyaluronic acid-modified nanoparticles on PC-12 cells was studied,and the results showed that the cell compatibility of SPIONs and oHA-SPIONs-1:2was good.The modified nanoparticles were injected into the brain of rats,and the distribution of nanoparticles in the brain was observed by transmission electron microscope after slicing.The modified oHA can improve the retention of nanoparticles in the brain within 24 hours.Different brain regions are also distributed differently,with the highest in the temporal lobe.The distribution of subcellular structure in the substantia nigra was observed,and it was found that most of the aggregation was endocytosis into the cell,and the integrity of the cell structure was slightly damaged.oHA-SPIONs-1:2,which produces a reunion after injection,is not suitable for heat therapy,but can be loaded and transported to the brain with other drugs.（4）After the PC-12 cells were cultured with SPIONs and CS-SPIONs-1:2 for 24 hours,CS-SPIONs-1:2 had a promoting effect on cell growth.When the concentration of CS-SPIONs-1:2 was 200 g/mL,the promoting effect reached the maximum.After stereotopic injection of SPIONs and CS-SPIONs-1:2 into the substantia nirosa of rats for 24 h,the results of transmission electron microscopy showed that the iron content retained in the brain by CS-SPIONs-1:2 was higher,and it spread to the forecerebral cortex after injection.TEM observations have found that SPIONs randomly accumulate in the myelin sheath or mitochondria,and most CS-SPIONs-1:2 are concentrated on the outside of the cell,showing extremely low endocytosis,highly distributed in the extracellular space near the neuron cell body and synapses.CS-SPIONs-1:2 can be expected to have great application potential for therapies that require targeting or proximity to cell membranes.CS-SPIONs-1:2 can be used as a tool for deep brain stimulation neurons in external magnetic fields or as an efficient drug carrier.