Cell Tracking by Magnetic Particle Imaging: Methodology for Labeling THP-1 Monocytes with Magnetic Nanoparticles for Cellular Imaging

Abstract

Magnetic particle imaging (MPI) is a noninvasive tomographic imaging modality for the quantitative visualization of magnetic nanoparticles (MNPs) with high temporal and spatial resolution. The general capability of MPI for cell tracking (e.g., monitoring living cells labeled with MNPs) has successfully been shown. MNPs in cell culture media are often subjected to structural and magnetic changes. In addition to the deteriorating reproducibility, this also complicates the systematic study of the relationship between the MNP properties and their cellular uptake for MPI. Here, we present a method for the preparation of magnetically labeled THP-1 (Tamm–Horsfall Protein-1) monocytes that are used in MPI cell tracking. The method development was performed using two different MPI tracers, which exhibited electrostatic and steric stabilizations, respectively. In the first step, the interaction between the MNPs and cell culture media was investigated and adjusted to ensure high structural and magnetic stability. Furthermore, the influences of the incubation time, MNP concentration used for cellular uptake, and individual preparation steps (e.g., the washing of cells) were systematically investigated. Finally, the success of the developed loading method was demonstrated by the MPI measurements. The presented systematic investigation of the factors that influence the MNP loading of cells will help to develop a reliable and reproducible method for MPI monocyte tracking for the early detection of inflammation in the future.

Counting cells in motion by quantitative real-time magnetic particle imaging

“…Note that all cell samples underwent a special washing procedure before and after incubation with MNP according to 29 .…”

“…Various factors, including incubation time, culture medium conditions, and the structural properties of MNPs, can affect the internalization of MNPs by cells. When loading cells with MNPs for MPI, it must be considered that the magnetic properties of the MNPs, and thus the quality of the MPI signal, may be altered 29 – 32 . However, these changes could not be attributed to changes in the MNP microstructure and the environment.…”

Monitoring magnetic nanoparticle clustering and immobilization with thermal noise magnetometry using optically pumped magnetometers

“…MNPs are known to form clusters during cellular uptake, which impacts their magnetization dynamics 9,15,[67][68][69] . For their usage in biomedical application as MPI and hyperthermia treatment, the change in their magnetic state can heavily influence their performance 16,19,20,22,70,71 . However, the change in the thermal noise of the MNPs due to cellular uptake is unknown so far.…”

“…9,15,[67][68][69] For their usage in biomedical applications as MPI and hyperthermia treatment, the change in their magnetic state can heavily inuence their performance. 16,19,20,22,70,71 However, the change in the thermal noise of the MNPs due to cellular uptake is unknown so far. Especially the absence of an external magnetic excitation during a TNM experiment can be seen as an advantage in the determination of the precise clustering mechanism, since cluster formation and aggregation due to an external perturbation are eliminated in this technique.…”

Progress in magnetic particle imaging signal and iron quantification methods in vivo – application to long circulating SPIONs

“…This quantication allows for the monitoring of tracer behaviour in vivo across various applications such as cancer imaging, cell tracking and inammation imaging. [1][2][3][4] With the growth in MPI usage, agreement on a reliable and user-independent method to process and quantify MPI signals from 2D and 3D images is crucial. The majority of in vivo MPI studies describe either a region of interest (ROI) determined manually or by growing an ROI from a seed of the maximum signal, the quantied signal is then converted to an iron amount by using a standard curve.…”