Recent Progress on Manganese‐Based Nanostructures as Responsive MRI Contrast Agents

Abstract

Manganese-based nanostructured contrast agents (CAs) entered the field of medical diagnosis through magnetic resonance imaging (MRI) some years ago. Although some of these Mn-based CAs behave as classic T contrast enhancers in the same way as clinical Gd-based molecules do, a new type of Mn nanomaterials have been developed to improve MRI sensitivity and potentially gather new functional information from tissues by using traditional T contrast enhanced MRI. These nanomaterials have been designed to respond to biological environments, mainly to pH and redox potential variations. In many cases, the differences in signal generation in these responsive Mn-based nanostructures come from intrinsic changes in the magnetic properties of Mn cations depending on their oxidation state. In other cases, no changes in the nature of Mn take place, but rather the nanomaterial as a whole responds to the change in the environment through different mechanisms, including changes in integrity and hydration state. This review focusses on the chemistry and MR performance of these responsive Mn-based nanomaterials.

Manganese-Based Targeted Nanoparticles for Postoperative Gastric Cancer Monitoring via Magnetic Resonance Imaging

“…The paramagnetic strength of the ions depends on the number of unpaired electrons in the 3d orbital. Thus, more unpaired electrons will have stronger paramagnetic strength (31). The unpaired electron number of the trivalent Mn is less than that of divalent Mn; therefore, the r 1 value of Mn 3 O 4 is relatively low.…”

“…However, magnetic susceptibility artifacts and dark signals impede the clinical promotion of T2 contrast agents (29,30). Mn is a necessary trace element that has a high relaxation spin and bright signal; thus, Mn-based contrast agents have attracted considerable attention in recent decades (31). However, Mn is difficult to use in MRI directly.…”

GMBP1-conjugated manganese oxide nanoplates for in vivo monitoring of gastric cancer MDR using magnetic resonance imaging

“…The more unpaired electrons, the stronger the paramagnetic strength. 30 However, Mn 3 O 4 contains one divalent Mn and two trivalent Mn. The unpaired electron number of Mn 3+ (4) is less than Mn 2+ (5), resulting in a relatively low r 1 value.…”

“…28,29 Since Mn is an essential trace element in living organisms, this molecule has a good biocompatibility, high relaxation spin and a bright signal, that make Mn-based contrast agents ideal candidates for MRI CAs. 30 Furthermore, manganese oxide nanoparticles, with favorable monodispersity and excellent crystallinity, have been shown to be synthesized on a massive scale in an air atmosphere under mild conditions. 31 In previous studies, nanoprobes based on Mn 3 O 4 nanospheres have been used for in vivo PET/MR 28,32 and uorescence/MR 33 imaging of tumors.…”

A pH‐Sensitive Zwitterionic Iron Complex Probe with High Biocompatibility for Tumor‐Specific Magnetic Resonance Imaging

“…The pH microenvironmento ft umor tissues is one of the most promising endogenouss timuli for investigating this concept, given that acidosisi saunique feature and au niversal phenomenon observed in solid tumors. [5] Smart agents that respond to the tumor-specific microenvironment have shown better performance in mapping of tumor tissues.F or instance, gadolinium complexes [6] or gadolinium-containing polymericn anoparticles [7][8][9][10] with pH-sensitive switchable structures or manganese-based nanostructures with the ability to release paramagnetic Mn 2 + ions in the acidic tumor microenvironment [11][12][13][14][15][16] have been reported to selectively enhancet he MR contrasto f tumortissues.However,the practical application of mostnanoparticle-based agents was hampered because of its high uptake by the reticuloendothelial system organs (such as the liver and spleen), resulting in slow and inefficient elimination. [17,18] Small gadolinium complexes may be eliminated via the relatively safe renal clearance pathway, but the unavoidable leakage of toxic Gd 3 + ions from these complexes still pose ap otential risk of causing nephrogenic systemic fibrosis (NSF) [19,20] and Gd retention in organs such as brain, bones, and skin.…”