Design of a cell specific macromolecular contrast agent for higher resolution of magnietic resonance imaging

点击翻译按钮获取中文摘要

The purpose of this study was to establish a novel imaging concept which depict micro-environmental differences in pathological and/or physiological states between normal and damaged tissues. For the purpose we newly designed an intelligent contrast agent whose signal intensity is activated only at the lower pH.MRI contrast agents consisting of Gd ions shorten the T1 relaxation time of protons of its surrounding water molecules to enhance MRI signals. The signal enhancement activity of Gd ions is closely related with hydration behavior of the agent. Thus, one can modify the signal enhancement activity of Gd ions by regulating its hydration behavior. We employed polyion complex composed of a couple of weakly acidic and basic polymers to design pH-sensitive contrast agents. These oppositely charged polyions form stable polyion complex accompanying with release of water molecules when the charge in the complex is electrostatically equivalent. But it adsorbs water molecules when the charge balance is disordered by pH variation, In this study, pH-sensitive polyion complex containing Gd ions was prepared as an intelligent contrast agent and its pH-dependent enhancement in MRI signal was evaluated.From the results of this study, this novel MRI contrast agent can specifically enhance MRI signal only at lower pH, even if it might be equally distributed. This reversible pH-dependent signal switching behavior of our newly designed MRI contrast agent will be an excellent tool for cancer diagnosis, since the extracellular fluid of tumor is more acidic than normal tissue and blood stream.