In this study, we analysed the physico-chemical properties of positively charged magnetic fluids consisting of magnetic nanoparticles (MNPs) functionalised by different amino acids (AAs): glycine (Gly), lysine (Lys) and tryptophan (Trp), and the influence of AA–MNP complexes on the MRI relaxivity. We found that the AA coating affects the size of dispersed particles and isoelectric point, as well as the zeta potential of AA–MNPs differently, depending on the AA selected. Moreover, we showed that a change in hydrodynamic diameter results in a change to the relaxivity of AA–MNP complexes. On the one hand, we observed a decrease in the relaxivity values, r1 and r2, with an increase in hydrodynamic diameter (the relaxivity of r1 and r2 were comparable with commercially available contrast agents); on the other hand, we observed an increase in r2* value with an increase in hydrodynamic size. These findings provide an interesting preliminary look at the impact of AA coating on the relaxivity properties of AA–MNP complexes, with a specific application in molecular contrast imaging originating from magnetic nanoparticles and magnetic resonance techniques.

Various pathological processes in humans are associated with biogenic iron accumulation and the mineralization of iron oxide nanoparticles, especially magnetite. Ferritin has been proposed as a precursor to pathological magnetite mineralization. This study quantifies spectroscopically the release of ferrous ions from native ferritin and magnetoferritin as a model system for pathological ferritin in the presence of potent natural reducing agents (vitamins C and B2) over time. Ferrous cations are required for the transformation of ferrihydrite (physiological) into a magnetite (pathological) mineral core and are considered toxic at elevated levels. The study shows a significant difference in the reduction and iron release from native ferritin compared to magnetoferritin for both vitamins. The amount of reduced iron formed from a magnetoferritin mineral core is two to five times higher than from native ferritin. Surprisingly, increasing the concentration of the reducing agent affects only iron release from native ferritin. Magnetoferritin cores with different loading factors seem to be insensitive to different concentrations of vitamins. An alternative hypothesis of human tissue magnetite mineralization and the process of iron-induced pathology is proposed. The results could contribute to evidence of the molecular mechanisms of various iron-related pathologies, including neurodegeneration.

Magnetite mineralization in human tissue is associated with various pathological processes, especially neurodegenerative disorders. Ferritin’s mineral core is believed to be a precursor of magnetite mineralization. Magnetoferritin (MF) was prepared with different iron loading factors (LFs) as a model system for pathological ferritin to analyze its MRI relaxivity properties compared to those of native ferritin (NF). The results revealed that MF differs statistically significantly from NF, with the same LF, for all studied relaxation parameters at 7 T: r1, r2, r2*, r2/r1, r2*/r1. Distinguishability of MF from NF may be useful in non-invasive MRI diagnosis of pathological processes associated with iron accumulation and magnetite mineralization (e.g., neurodegenerative disorders, cancer, and diseases of the heart, lung and liver). In addition, it was found that MF samples possess very strong correlation and MF’s relaxivity is linearly dependent on the LF, and the transverse and longitudinal ratios r2/r1 and r2*/r1 possess complementary information. This is useful in eliminating false-positive hypointensive artefacts and diagnosis of the different stages of pathology. These findings could contribute to the exploitation of MRI techniques in the non-invasive diagnosis of iron-related pathological processes in human tissue.