Initial interaction of citrate-coated iron oxide nanoparticles with the glycocalyx of THP-1 monocytes assessed by real-time magnetic particle spectroscopy and electron microscopy

Interaction with biological material can alter physicochemical parameters of magnetic nanoparticles and might thereby change their magnetic behavior with potentially important implications for various nanoparticle applications. Little is known about changes of the magnetic behavior that occur during the initial phase of cell binding and uptake. We investigate the magnetic behavior of very small superparamagnetic iron-oxide nanoparticles (VSOP) during initial contact with THP-1 monocytes. We combine real-time magnetic particle spectroscopy (MPS), a fast and sensitive method for specific detection of magnetic nanoparticles in biological specimen with high-pressure-freezing/freeze-substitution transmission electron microscopy (HPF/FS-TEM), enabling us to generate snapshots of the interaction of VSOP with the cellular glycocalyx. MPS reveals significant changes of the dynamic magnetic behavior within seconds after VSOP injection into monocyte suspensions that correlate with the formation of nanoparticle clusters in the glycocalyx. The combination of real-time MPS and HPF/FS-TEM provides an ideal platform to analyze magnetic behaviors of nanoparticles upon interaction with cells and tissues

A multi-purpose phantom kit for magnetic particle imaging

Phantoms are essential tools for the development and characterization of Magnetic Particle Imaging (MPI), an imaging technique that can quantitatively map the spatial distribution of magnetic nanoparticles (MNP). The objective of this study was to develop and validate a modular MPI phantom kit with high versatility for platform-independent quality assurance and the assembling of defined geometries in MPI. It was shown that the developed MPI phantom kit can be used for both application scenario testing and quality assurance in MPI which provides the basis for future reference phantoms to directly compare existing scanners within the MPI community

Uremic Toxin-Induced Exosome-like Extracellular Vesicles Contain Enhanced Levels of Sulfated Glycosaminoglycans which Facilitate the Interaction with Very Small Superparamagnetic Iron Oxide Particles

Uremic toxins exert pathophysiological effects on cells and tissues, such as the generation of a pro-calcifying subtype of exosome-like extracellular vesicles (EVs) in vascular cells. Little is known about the effects of the toxins on the surface structure of EVs. Thus, we studied the effects of uremic toxins on the abundance of sulfated glycosaminoglycans (GAGs) in EVs, and the implications for binding of ligands such as very small superparamagnetic iron oxide particles (VSOPs) which could be of relevance for radiological EV-imaging. Vascular cells were treated with the uremic toxins NaH2PO4 and a mixture of urea and indoxyl sulfate. Uremia in rats was induced by adenine feeding. EVs were isolated from culture supernatants and plasma of rats. By proton T1-relaxometry, magnetic particle spectroscopy, and analysis of genes, proteins, and GAG-contents, we analyzed the roles of GAGs in the ligand binding of EVs. By influencing GAG-associated genes in host cells, uremic toxins induced higher GAG contents in EVs, particularly of sulfated chondroitin sulfate and heparan sulfate chains. EVs with high GAG content interacted stronger with VSOPs compared to control ones. This was confirmed by experiments with GAG-depleted EVs from genetically modified CHO cells and with uremic rat-derived EVs. Mechanistically, uremic toxin-induced PI3K/AKT-signaling and expression of the sulfate transporter SLC26A2 in host cells contributed to high GAG contents in EVs. In conclusion, uremic conditions induce enhanced GAG contents in EVs, which entails a stronger interaction with VSOPs. VSOPs might be suitable for radiological imaging of EVs rich in GAGs

3D printed measurement phantoms for evaluation of magnetic particle imaging scanner

To assess the potential and capability of different MPI scanner designs and architectures, defined reference phantoms for imaging studies are required. For the preparation of well-defined structures as well as realistic vessel structures, 3D printed molds were filled with magnetic nanoparticles embedded into a long term stable polymeric matrix or perfused with a flowing ferrofluid. Different types and layouts of 3D printed phantoms will be presented which were imaged by means of MPI successfully

Magnetic nanoparticle-gel materials for development of joint phantoms for MPI and MRI

To evaluate the performance of commercial as well as custom-made scanners, dedicated phantoms with defined magnetic nanoparticle (MNP) distributions are required. Prerequisite for the development of such phantoms is the establishment of suitable MNP-matrix combinations. In this study, two different gel types were investigated as potential matrix materials: water-based biopolymers and synthetic polymers. These materials exhibit similar imaging behaviour to body tissue in MRI and MPI. Aqueous suspensions of MNP coated with different types of functionalized dextranes were used for embedding particles into the biopolymers, and organic fluids with oleic acid coated MNP for synthetic polymers, respectively. The obtained MNP-matrix combinations were tested for their shape stability. The homogeneity of MNP distribution and immobilization within the matrix was determined by optical investigation of the samples with a microscope, and the magnetic properties of the composite materials measured by vibrating sample magnetometry. From the tested combinations of MNP and matrix material, oleic acid coated MNP embedded in Permagel was found to be the most suitable for the construction of MPI phantoms. This was based on the reliable and homogeneous fixation of the MNP within the matrix without agglomeration of the particles

Human alveolar progenitors generate dual lineage bronchioalveolar organoids

Mechanisms of epithelial renewal in the alveolar compartment remain incompletely understood. To this end, we aimed to characterize alveolar progenitors. Single-cell RNA-sequencing (scRNA-seq) analysis of the HTII-280+/EpCAM+ population from adult human lung revealed subclusters enriched for adult stem cell signature (ASCS) genes. We found that alveolar progenitors in organoid culture in vitro show phenotypic lineage plasticity as they can yield alveolar or bronchial cell-type progeny. The direction of the differentiation is dependent on the presence of the GSK-3β inhibitor, CHIR99021. By RNA-seq profiling of GSK-3β knockdown organoids we identified additional candidate target genes of the inhibitor, among others FOXM1 and EGF. This gives evidence of Wnt pathway independent regulatory mechanisms of alveolar specification. Following influenza A virus (IAV) infection organoids showed a similar response as lung tissue explants which confirms their suitability for studies of sequelae of pathogen-host interaction

Concentration Dependent MPI Tracer Performance

Magnetic Particle Imaging (MPI) and Magnetic Particle Spectroscopy (MPS) usually require a reference sample measurement to provide information about the non-linear dynamic magnetic behavior of a specific magnetic nanoparticle (MNP) type. This reference sample based approach presupposes that this dynamic magnetization behavior of MNP is concentration independent. We investigated Resovist® and its precursor Ferucarbotran at different concentrations to verify this assumption by means of MPS. Remarkably, for Resovist® we found a strong concentration dependence of the MPS signal. Above an iron concentration of about 150 mmol/L the shape of the moment and phase spectra changed with increasing iron concentration. In contrast, for Ferucarbotran we found no concentration dependence of the dynamic magnetic behavior even though at a two?fold higher initial concentration. Our experimental results indicate that the dynamic magnetic behavior of MPI tracers may be altered at higher concentrations and should be studied prior to MPI by MPS experiments

Magnetic particle spectroscopy for monitoring the cellular uptake of magnetic nanoparticles: Impact of the excitation field amplitude

Magnetic particle spectroscopy (MPS) is a sensitive method for the quantification of magnetic nanoparticles (MNP). MPS is based on the detection of nonlinear magnetic AC susceptibility and has been established as a rapid and straightforward method for tracer characterization. MPS is also excellent for monitoring the uptake of MNP by cells. The magnetic excitation fields of several millitesla used in MPS measurement raises the possibility of field-induced changes in the MNP sample (e.g., chain formation, aggregation, etc.). In this work, we aim to investigate the field-induced changes in monitoring the uptake of different MNP by THP-1 cells. By using different excitation field amplitudes and measurement scripts, the influence of dynamic magnetic fields on the MPS signal of MNP is investigated and recommendations for continuous MPS measurements of MNP in biological environment are given. We found that the excitation field amplitude and field exposure time can impact the uptake kinetics and influences the temporal resolution. In addition, high SNR can be achieved with a field strength of 12 mT, while at the same time reducing excitation field changes occurring at higher field strengths (such as 25 mT)

Enhanced characterization of a Magnetic Particle Imaging tracer combining field-flow fractionation and Magnetic Particle Spectroscopy

For a more detailed assessment of the performance of magnetic nanoparticles used as tracer in Magnetic Particle Imaging, we applied centrifugal flow-field fractionation (CF3) to separate a tracer according to their density and mass. The fractions were then magnetically and physically characterized by MPS, DLS, MALS and UV/Vis. Combining these findings with the results of magnetic characterization will allow a better understanding of the underlying mechanisms of MPI signal generation and tracer performance. &nbsp