Effective Tracking Of Bone Mesenchymal Stem Cells In Vivo By Magneticresonance Imaging Using Melanin-based Gadolinium³⁺ Nanoparticles

Objective: With the development of regenerative medicine and stem cell transplant treatment technology,tracking transplanted stem cells is necessary to clarify cellular properties and improve transplantation success.In this study,we designed and synthesized melanin-based gadolinium³⁺(Gd³⁺)-chelate nanoparticles(MNP-Gd³⁺)of about 7-10 nm for stem cell tracking in vivo.Method: 1.We synthesized MNP-Gd³⁺ nanoparticles by one-step method.And the characteristics of MNP-Gd³⁺ nanoparticles were measured by TEM,DLS and ICP-MS.2.MNP-Gd³⁺,MNP,and Gd-DTPA aqueous solutions on PCR plateswas performed in vitro using 3.0T clinical MRI equipment.Then we measured the T1 value of MNP-Gd³⁺ and MNP,calculated and compared the relaxation rate.3.BMSCs were co-incubated with MNP-Gd³⁺ nanoparticles.Thedistribution of MNP-Gd³⁺ in the cells was observed by Masson-Fontana melanin staining,laser confocal microscopy and transmission electron microscopy.The toxicity of MNP-Gd³⁺ was observed by MTT assay.Labeled cells with different concentrations were observed by 3.0T clinical MRI equipment.4.MNP-Gd³⁺labeled BMSCs were intramuscularly injected into the left thigh of rat.MRI was performed on 1,4,7,14,21 and 28 after injection.Results: 1.MNP-Gd³⁺ nanoparticles are round or oval black particles,which are good stability and relatively uniform dispersion in the TEM images.The size distribution of MNP-Gd³⁺ nanoparticles is about 7-10 nm,and each MNP molecule could chelate 112 Gd³⁺.2.We found that the T1 relaxivity?r1?of MNP-Gd³⁺ was significantlyhigher than that of Gd-DTPA.3.The nanoparticles were taken up by bone mesenchymal stem cells?BMSCs?via endocytosis and were broadly distributed in the cytoplasm.Based on MTT assay,no cyto-toxicity of labeled stem cells was observed for MNP-Gd³⁺ concentrations of less than 800 ? g/m L.Furthermore,we founded that high concentrationslabeled cells produce higher signal intensity than low concentrations.4.We tracked MNP-Gd³⁺-labeled BMSCs in vivo using 3.0T MRIequipment.After intramuscularly injection,MNP-Gd³⁺-labeled BMSCs were detected,even after four weeks,by 3.0T MRI.Conclusion: MNP-Gd³⁺ nanoparticles possesses many beneficial properties,such as its high stability and sensitivity,shorter T1 relaxation time,higher cell labeling efficiency,and lower cytotoxicity compared with commercial imaging agents.We concluded that MNP-Gd³⁺ nanoparticles at appropriate concentrations can be used to effectively monitor and track BMSCs in vivo.MNP-Gd³⁺ nanoparticles have potential as a new positive MRI contrast agent in clinical applications.