Rizzo Domenico, Ravera Enrico, Fragai Marco, Parigi Giacomo, Luchinat Claudio
Magnetic Resonance Center (CERM), Department of Chemistry, University of Florence, Via Sacconi 6, Sesto Fiorentino, Florence, Italy.
Consorzio Interuniversitario Risonanze Magnetiche di Metalloproteine (CIRMMP), Sesto Fiorentino, Florence, Italy.
Bioinorg Chem Appl. 2021 Jan 5;2021:6666018. doi: 10.1155/2021/6666018. eCollection 2021.
Magnetic resonance imaging (MRI) often requires contrast agents to improve the visualization in some tissues and organs, including the gastrointestinal tract. In this latter case, instead of intravascular administration, oral agents can be used. Natural oral contrast agents, such as fruit juice, have the advantages of better taste, tolerability, and lower price with respect to the artificial agents. We have characterized the relaxometry profiles of pineapple juice in order to understand the origin of the increase in relaxation rates (and thus of the MRI contrast) in reference to its content of manganese ions. Furthermore, we have characterized the relaxometry profiles of pineapple juice in the presence of alginate in different amounts; the interaction of the manganese ions with alginate slows down their reorientation time to some extent, with a subsequent increase in the relaxation rates. The relaxometry profiles were also compared with those of manganese(II) solutions in 50 mmol/dm sodium acetate solution (same pH of pineapple juice), which revealed sizable differences, mostly in the number of water molecules coordinated to the metal ion, their lifetimes, and in the constant of the Fermi-contact interaction. Finally, the fit of the transverse relaxivity shows that the increased viscosity in the hydrogel formulations can improve significantly the negative contrast of pineapple juice at the magnetic fields relevant for clinical MRI.
磁共振成像（MRI）通常需要使用造影剂来改善某些组织和器官（包括胃肠道）的可视化效果。在后一种情况下，可以使用口服造影剂而非血管内给药。天然口服造影剂，如果汁，相对于人工造影剂具有口感更好、耐受性更佳和价格更低的优点。我们已经对菠萝汁的弛豫测量曲线进行了表征，以便根据其锰离子含量了解弛豫率增加（从而MRI对比度增加）的原因。此外，我们还对不同量藻酸盐存在下菠萝汁的弛豫测量曲线进行了表征；锰离子与藻酸盐的相互作用在一定程度上减缓了它们的重新取向时间，随后弛豫率增加。还将弛豫测量曲线与50 mmol/dm醋酸钠溶液（与菠萝汁pH相同）中锰（II）溶液的弛豫测量曲线进行了比较，结果显示存在显著差异，主要体现在与金属离子配位的水分子数量、它们的寿命以及费米接触相互作用常数方面。最后，横向弛豫率的拟合表明，水凝胶制剂中增加的粘度可以显著改善菠萝汁在临床MRI相关磁场下的负对比度。
