GdIOPs/MRI And DCM-KPV Fluorescence Imaging For Studying The Ulcerative Colitis Inflammatory Activity

Objective:This study was designed to investigate the influence of the size of iron oxide nanoparticles in the iron and gadolinium synthetic materials on the signal intensity,and to explore the application of T1-T2 dual modal contrast agents in the ulcerative colitis（UC）.Furthermore,a peptide receptor-targeted fluorescent probe DCM-KPV was designed for tracking inflammatory activity of ulcerative colitis diagnosis.Methods:Two types of GdIOPs with different size of Fe₃O₄ nanoparticles were synthesized respectively.TEM test and MTS assay were performed to characterize the GdIOPs.△SNR%of the ROIs in pre and post contrast MRI was calculated,to compared T1 and T2 enhancement abilities.Peptide receptor-targeted fluorescent probe DCM-KPV was synthesized.The high resolution mass spectrometry（HRMS）,and ¹H NMR were performed to fully characterize the fluorescent probe DCM-KPV.The photostability of DCM-KPV was evaluated by time-course fluorescence measurements via uninterrupted continuous exposure to the light irradiation.Cell cytotoxicity of DCM-KPV was evaluated by MTS assay and TUNEL test.Cell tracing studies of DCM-KPV treated with Caco-2 cells was conducted by confocal laser scanning microscope（CLSM）imaging.T1WI of mice models,fluorescence imaging of colon tissue ROIs and HE staining of corresponding colon tissue were performed to assess the relationship among the MRI signal intensity,fluorescence intensity and mucous injury degree.Results:The diameter of iron oxide NPs in Fe₃O₄@DOPA（Gd-DTPA）NPs and Fe₃O₄@PEI（Gd-DTPA）NPs was 3 nm and 15 nm respectively（p<0.05）.MTS assay demonstrated the cell viability was more than 80%in the designed concentration（0,2.5,12.5,25,and 50μg/m L）.In vivo experiments,the most powerful extent of△SNR%inT1WIbytheintravenousinjectionwas29.3%（Fe₃O₄@DOPA（Gd-DTPA）NPs/colitisgroup）,10.1%（Fe₃O₄@PEI（Gd-DTPA）NPs/colitisgroup）,3.1%（Fe₃O₄@DOPA（Gd-DTPA）NPs/controlgroup）and2.4%（Fe₃O₄@PEI（Gd-DTPA）NPs/control group）respectively.Similarly,the most powerful extent of△SNR%in T2WI by the intravenous injection was 6.1%,16.3%,1.2%and2.5%respectively.The most powerful extent of△SNR%inT1WI by intraperitoneal injection was 37.3%,10.3%,4.9%and 3.2%respectively.The most powerful extent of△SNR%in T2WI by intraperitoneal injection was 7.1%,16.2%,1.2%and 0.9%respectively.The significant difference of△SNR%between colitis and control group was found（p<0.01）.Peptide receptor-targeted fluorescent probe DCM-KPV displayed the favorable long emission at 629 nm and large stokes shift（170 nm）,along with the long fluorescence half-life period（420 s）.MTS assay demonstrated the cell viability was more than 90%in the designed concentration of DCM-KPV（0,1,10 and 30μM）.The average fluorescence intensity of colon ROIs in chronic,acute and control group was 9.33E+08,4.08E+08 and 2.25E+08 respectively,showing the significant difference（p<0.05）.Conclusion:As T1-T2 dual MRI contrast agents,Fe₃O₄@DOPA（Gd-DTPA）NPs displayed more obvious T1 enhancement ability and Fe₃O₄@PEI（Gd-DTPA）NPs displayed more obvious T2 enhancement ability.Two types of GdIOPs above showed significant difference in the△SNR%between the colitis mice and normal mice,indicating the potential application in the diagnosis of ulcerative colitis in the active stage.The desirable diagnostic ability of DCM-KPV can guarantee the real-time tracking and visualization of intracellular KPV,providing an alternative diagnostic target of PepT1 to judge the active and remission stage of UC by molecular imaging.