The Effect\nof the Size of Gold Nanoparticle Contrast\nAgents on CT Imaging of the Gastrointestinal Tract and Inflammatory\nBowel Disease

Ulcerative colitis (UC) is a chronic inflammatory bowel\ndisease\n(IBD). CT imaging with contrast agents is commonly used for visualizing\nthe gastrointestinal (GI) tract in UC patients. Contrast agents that\nprovide enhanced imaging performance are highly valuable in this field.\nRecent studies have made significant progress in developing better\ncontrast agents for imaging the gastrointestinal tract using nanoparticles.\nHowever, the impact of nanoparticle size on this application remains\nunexplored. Gold nanoparticles (AuNPs) serve as an ideal model to\ninvestigate the effect of nanoparticle size on imaging of the gastrointestinal\ntract due to their controllable synthesis across a broad size range.\nIn this study, we synthesized AuNPs with core sizes ranging from 5\nto 75 nm to examine the effect of the size in this setting. AuNPs\nwere coated with poly(ethylene glycol) (PEG) to enhance stability\nand biocompatibility. In vitro tests show that gold nanoparticles\nare cytocompatible with macrophage cells (∼100% cell viability)\nand remain stable under acidic conditions, with no significant size\nchanges over time. Phantom imaging studies using a clinical CT scanner\nindicated that there was no effect of nanoparticle size on CT contrast\nproduction, as previously demonstrated. <i>In vivo</i> imaging\nusing a mouse model of acute colitis revealed a strong contrast generation\nthroughout the GI tract for all agents tested. For the most part, <i>in vivo</i> contrast was independent of AuNP size, although\nAuNP outperformed iopamidol (a clinically approved control agent).\nIn addition, differences in attenuation trends were observed between\nhealthy and colitis mice. We also observed almost complete clearance\nat 24 h of all formulations tested (less than 0.7% ID/g was retained),\nsupporting their value as a model platform for studying nanoparticle\nbehavior in imaging. In conclusion, this study highlights the potential\nof nanoparticles as effective contrast agents for CT imaging of the\ngastrointestinal tract (GIT) in the UC. Further systemic research\nis needed to explore contrast agents that can specifically image disease\nprocesses in this disease setting.