Preparation And Evaluation Of Mr Molecular Probes Targeting Thrombus

Objective：To prepare a kind of MR molecular probes targetingthrombus (Gd-PLGA-RGDS microparticles) and evaluate its relatedcharacteristics, such as physical and chemical properties, the ability oftargeting thrombus in vitro and of magnetic resonance imaging. In order tolay the foundation for the therapy of targeting thrombus and the judgmentof efficacy.Materials and methods： Double emulsion solvent-evaporationtechnique (water/oil/water, W/O/W) was used to encapsulate magneticresonance contrast agent Gd-DTPA in PLGA particles taking PLGA-COOHas the carrier. RGDS peptides were further immobilized by carbodiimidemethod (EDC/NHS) to prepare the MR molecular probes targetingthrombus. The morphology and inner of these molecular probes wereseparately observed by optical microscope and transmission electronmicroscope, and the average diameter were measured by laser particle sizeanalyzer. The Gd-DTPA loading of the probes was determined by inductivecoupled plasma emission spectrometer (ICP). The rate of carrying RGDSpeptides was tested by flow cytometry after FITC-labeled on the RGDS. Fresh blood direct smear method was used to simulate the thrombus invitro, and then the ability of targeting thrombus was assessed by confocallaser scanning microscopy after rhodamine6G was encapsulated in theprobes. The imaging ability of the probes was observed by1.5T MRscanner. The longitudinal relaxation time was measured by T1mappingsoftware and the longitudinal relaxation rate was calculated.Results：MR molecular probes targeting thrombus were successfullyprepared by these methods. It showed the regular shape, smooth surface,non-aggregated and relatively uniform size microparticles in the opticalmicroscope, and it also showed a large number of electron dense materialsfilled with the probes in the transmission electron microscope.The probeshad a mean diameter of2.04μm. The encapsulation rate of Gd-DTPAmeasured by ICP was39.53%. Because of conjunction with RGDSpeptides, the wavelength of the probes shell changed and the rate ofcarrying RGDS tested by flow cytometry was up to89.69%. In theexperiments in vitro, the rhodamine RGDS-Gd-PLGA particles were seengathered at the surface of thrombus in the confocal microscopy after beingwashed by PBS buffer many times, which proved that the probes hadsuccessfully been bonded to the thrombus. It can realize the imaging at1.5T MR scanner, and at the same time as Gd-DTPA concentrationincreased, the longitudinal relaxation rate increased too. Conclusions： MR molecular probes targeting thrombus weresuccessfully prepared by double emulsion solvent-evaporation techniqueand carbodiimide method. The probes had regular shape, small size and theability of targeting thrombus in vitro, they can realize the imaging at1.5TMR scanner at the same time. It was helpful to provide a new method and anew technology to diagnose thrombosis at the molecular level and treatthrombus and judge the efficacy.