Immunomagnetic isolation of magnetoferritin-labeled cells in a modified ferrograph

Hyperthermostable recombinant human heteropolymer ferritin derived from a novel plasmid design

Mammalian ferritins are predominantly heteropolymeric species consisting of 2 structurally similar, but functionally and genetically distinct subunit types, called H (Heavy) and L (Light). The two subunits co-assemble in different H and L ratios to form 24-mer shell-like protein nanocages where thousands of iron atoms can be mineralized inside a hollow cavity. Here, we use differential scanning calorimetry (DSC) to study ferritin stability and understand how various combinations of H and L subunits confer aspects of protein structure-function relationships. Using a recently engineered plasmid design that enables the synthesis of complex ferritin nanostructures with specific H to L subunit ratios, we show that homopolymer L and heteropolymer L-rich ferritins have a remarkable hyperthermostability (Tm = 115 ± 1°C) compared to their H-ferritin homologues (Tm = 93 ± 1°C). Our data reveal a significant linear correlation between protein thermal stability and the number of L subunits present on the ferritin shell. A strong and unexpected iron-induced protein thermal destabilization effect (ΔTm up to 20°C) is observed. To our knowledge, this is the first report of recombinant human homo- and hetero-polymer ferritins that exhibit surprisingly high dissociation temperatures, the highest among all known ferritin species, including many known hyperthermophilic proteins and enzymes. This extreme thermostability of our L and L-rich ferritins may have great potential for biotechnological applications.

Design of a high-throughput bio-ferrograph for isolation of cancer cells from whole blood

Enumeration and morphological characterization of circulating tumor cells (CTCs) can be useful in diagnosis and prognosis of metastatic cancer patients. The bio-ferrograph (BF) with its five flow channels, which was developed in the late 1990s for magnetic isolation of biological cells and tissue fragments from fluids, is a modification of the analytical ferrograph. Its use for isolation of rare CTCs from human whole blood (HWB) is a novel approach for the detection of cancer at a cellular level. The isolation process is facilitated by the interaction of specifically magnetized cells with a strong external magnetic field, yielding high recovery rates with no morphological alternation of cells that are isolated on a coverslip glass slide, thus allowing complementary microscopic, chemical, biological, and mechanical analyses. Here, a full mechanical and magnetostatic design of a novel high-throughput BF is presented. The system design is based on an optimized procedure for bio-ferrographic isolation of CTCs from HWB. It incorporates a semi-automated CTC separation system consisting of sample preparation, labeling, and staining; magnetic isolation; and system recovery. The design process was optimized based on experimental feasibility tests and finite element analyses. The novel bench-top system consists of 100 flow channels, allowing simultaneous analysis of multiple samples from 20 patients in each run, with the potential to become a decision-making tool for medical doctors when monitoring patients in a hospital setting. It opens a new route for early diagnosis, prognosis, and treatment of cancers, as well as other diseases, such as osteoarthritis.

Synthesis of Cationized Magnetoferritin for Ultra-fast Magnetization of Cells

Many important biomedical applications, such as cell imaging and remote manipulation, can be achieved by labeling cells with superparamagnetic iron oxide nanoparticles (SPIONs). Achieving sufficient cellular uptake of SPIONs is a challenge that has traditionally been met by exposing cells to elevated concentrations of SPIONs or by prolonging exposure times (up to 72 hr). However, these strategies are likely to mediate toxicity. Here, we present the synthesis of the protein-based SPION magnetoferritin as well as a facile surface functionalization protocol that enables rapid cell magnetization using low exposure concentrations. The SPION core of magnetoferritin consists of cobalt-doped iron oxide with an average particle diameter of 8.2 nm mineralized inside the cavity of horse spleen apo-ferritin. Chemical cationization of magnetoferritin produced a novel, highly membrane-active SPION that magnetized human mesenchymal stem cells (hMSCs) using incubation times as short as one minute and iron concentrations as lows as 0.2 mM.

Physical limits to magnetogenetics

This is an analysis of how magnetic fields affect biological molecules and cells. It was prompted by a series of prominent reports regarding magnetism in biological systems. The first claims to have identified a protein complex that acts like a compass needle to guide magnetic orientation in animals (Qin et al., 2016). Two other articles report magnetic control of membrane conductance by attaching ferritin to an ion channel protein and then tugging the ferritin or heating it with a magnetic field (Stanley et al., 2015; Wheeler et al., 2016). Here I argue that these claims conflict with basic laws of physics. The discrepancies are large: from 5 to 10 log units. If the reported phenomena do in fact occur, they must have causes entirely different from the ones proposed by the authors. The paramagnetic nature of protein complexes is found to seriously limit their utility for engineering magnetically sensitive cells.

DOI:http://dx.doi.org/10.7554/eLife.17210.001

How biological systems interact with magnetic fields is of great interest both from a basic science perspective and for technological applications. Certain animal species can sense the Earth’s magnetic field for the purposes of navigation. How that compass sense works is perhaps the last true mystery of sensory biology. If we knew how the magnetic field affects the activity of nerve cells, we could harness that mechanism to create new biomedical tools. One technological goal is to genetically engineer specific cells in the brain or elsewhere so their activity can be controlled using an external magnet. This dream has been called “magnetogenetics”.

In recent months a string of reports claimed to have solved both the scientific and the technological challenges of magnetogenetics. They all involved the discovery or the engineering of protein molecules that are sensitive to magnetic fields. Markus Meister has now checked whether those claims were consistent with well-established physical laws.

For each case, Meister calculated how strongly the protein in question would link magnetic fields to cellular activity. The results show that the predicted effects are too weak to account for the reported measurements by huge margins: between five and ten orders of magnitude. It therefore appears that none of these reports have hit on a solution to magnetogenetics.

All of the proposed proteins use iron atoms to couple to the magnetic field, but Meister concludes that these proteins contain far too few iron atoms. How safe is that conclusion? There has been enormous technological interest in making tiny magnets; for example, to design the ever-denser data storage drives inside computers. Hence the magnetism of small clusters of atoms is exceedingly well understood. If any of the biological reports of magnetogenetics turned out correct, they would force a revolutionary rethinking of basic physics.

With the recognition that magnetogenetics remains unsolved, and that different approaches are needed, Meister hopes that other investigators will feel motivated to continue innovating in this area.

DOI:http://dx.doi.org/10.7554/eLife.17210.002

Ultra-fast stem cell labelling using cationised magnetoferritin

Magnetic cell labelling with superparamagnetic iron oxide nanoparticles (SPIONs) facilitates many important biotechnological applications, such as cell imaging and remote manipulation. However, to achieve adequate cellular loading of SPIONs, long incubation times (24 hours and more) or laborious surface functionalisation are often employed, which can adversely affect cell function. Here, we demonstrate that chemical cationisation of magnetoferritin produces a highly membrane-active nanoparticle that can magnetise human mesenchymal stem cells (hMSCs) using incubation times as short as one minute. Magnetisation persisted for several weeks in culture and provided significant T2* contrast enhancement during magnetic resonance imaging. Exposure to cationised magnetoferritin did not adversely affect the membrane integrity, proliferation and multi-lineage differentiation capacity of hMSCs, which provides the first detailed evidence for the biocompatibility of magnetoferritin. The combination of synthetic ease and flexibility, the rapidity of labelling and absence of cytotoxicity make this novel nanoparticle system an easily accessible and versatile platform for a range of cell-based therapies in regenerative medicine.

Application of magnetic cytosmear for the estimation of Plasmodium falciparum gametocyte density and detection of asexual stages in asymptomatic children

Background

Conventional malaria parasite detection methods, such as rapid diagnostic tests (RDT) and light microscopy (LM), are not sensitive enough to detect low level parasites and identification of gametocytes in the peripheral blood. A modified and sensitive laboratory prototype, Magnetic Deposition Microscopy (MDM) was developed to increase the detection of sub-microscopic parasitaemia and estimation of gametocytes density in asymptomatic school children.

Methods

Blood samples were collected from 303 asymptomatic school children from seven villages in Bagamoyo district in Tanzania. Participants were screened for presence of malaria parasites in the field using RDT and MDM whereas further examination of malaria parasites was done in the laboratory by LM. LM and MDM readings were used to calculate densities and estimate prevalence of asexual and sexual stages of the parasite.

Results

Plasmodium falciparum parasites (asexual and sexual stages) were detected in 23 (7.6 %), 52 (17.2 %), and 59 (19.5 %) out of 303 samples by LM, RDT and MDM respectively. Gametocytes were detected in 4 (1.3 %) and 12 (4.0 %) out of the same numbers of samples by LM, and MDM, respectively. Likewise, in vitro results conducted on two laboratory strains of P. falciparum, 3D7 and NF54 to assess MDM sensitivity on gametocytes detection and its application on concentrating gametocytes indicated that gametocytes were enriched by MDM by 10-fold higher than LM. Late stages of the parasite strains, 3D7 and NF54 were enriched by MDM by a factor of 20.5 and 35.6, respectively. MDM was more specific than LM and RDT by 87.5 % (95 %, CI 71.2–89.6 %) and 89.0 % (95 % CI 82.9–91.4) respectively. It was also found that MDM sensitivity was 62.5 % (95 % CI 49.5–71.8) when compared with RDT while with LM was 36.5 % (95 % CI 32.2–60.5).

Conclusions

These findings provide strong evidence that MDM enhanced detection of sub-microscopic P. falciparum infections and estimation of gametocyte density compared to current malaria diagnostic tools. In addition, MDM is superior to LM in detecting sub-microscopic gametocytaemia. Therefore, MDM is a potential tool for low-level parasitaemia identification and quantification with possible application in malaria transmission research.

Continuous separation principles using external microaction forces

During the past decade, methods for the continuous separation of microparticles with microaction forces have rapidly advanced. Various action forces have been used in designs of both microchannel and capillary continuous separation systems, which depend on properties such as conductivity, permittivity, absorptivity, refractive index, magnetic susceptibility, and compressibility. Particle migration velocity has been used to characterize the particles. Biological cells have been the most interesting targets of these continuous separation methods.

Iron transport in cancer cell culture suspensions measured by cell magnetophoresis

Cell motion in a magnetic field reveals the presence of intracellular paramagnetic elements, such as iron or manganese. Under controlled field and liquid media composition, such motion previously allowed us to compare the paramagnetic contribution to cell magnetic susceptibility in erythrocytes differing in the spin state of heme associated with hemoglobin. The method is now tested on cells with less obvious paramagnetic properties: cell cultures derived from human cancers to determine if the magnetophoretic mobility (MM) measurement is sufficiently sensitive to the dysregulation of the intracellular iron metabolism as suggested by reports on loss of iron homeostasis in cancer. The cell lines included hepatocellular carcinoma (Hep 3B 2.1-7 and Hep G2), promyelocytic (HL-60) and chronic myelogenous (K-562) leukemias, histiocytic lymphoma (U-937), tongue (CAL 27) and pharyngeal (Detroit 562) carcinomas, and epitheloid carcinoma (HeLa), whose MM was measured in complete media with standard and elevated soluble iron (ferric nitrate and ferric ammonium citrate), against oxy- and met-hemoglobin erythrocytes used as controls. Different cell lines responded differently to the magnetic field and the soluble iron concentrations in culture media establishing the possibility of single cell elemental analysis by magnetophoresis and magnetic cell separation based upon differences in intracellular iron concentration.

Development of multistage magnetic deposition microscopy

Magnetic deposition microscropy (MDM) combines magnetic deposition and optical analysis of magnetically tagged cells into a single platform. Our multistage MDM uses enclosed microfabricated channels and a magnet assembly comprising four zones in series. The enclosed channels alleviate the problem plaguing previous versions of MDM: scouring of the cell deposition layer by the air-liquid interface as the channel is drained. The four-zone magnet assembly was designed to maximize capture efficiency, and experiments yielded total capture efficiencies of >99% of fluorescent- and magnetically-labeled Jurkat cells at reasonable throughputs (10(3) cells/min). A digital image processing protocol was developed to measure the average pixel intensities of the deposited cells in different zones, indicative of the marker expression. Preliminary findings indicate that the multistage MDM may be suitable for depositing cells and particles in successive zones according to their magnetic properties (e.g., magnetic susceptibilities or magnetophoretic mobilities). The overall goal is to allow the screening of multiple disease conditions in a single platform.

Superparamagnetic gamma-Fe(2)O(3) nanoparticles with tailored functionality for protein separation

Polymer coated superparamagnetic gamma-Fe(2)O(3) nanoparticles were derivatized with a synthetic double-stranded RNA [poly(IC)], a known allosteric activator of the latent (2-5)A synthetase, to separate a single 35 kDa protein from a crude extract which cross reacted with antibodies raised against the sponge enzyme.

Binding affinities/avidities of antibody-antigen interactions: quantification and scale-up implications

Bioaffinity interactions have been, and continue to be, successfully adapted from nature for use in separation and detection applications. It has been previously reported that the magnetophoretic mobility of labeled cells show a saturation type phenomenon as a function of the concentration of the free antibody-magnetic nanoparticle conjugate which is consistent with other reports of antibody-fluorophore binding. Starting with the standard antibody-antigen relationship, a model was developed which takes into consideration multi-valence interactions, and various attributes of flow cytometry (FCM) and cell tracking velocimetry (CTV) measurements to determine both the apparent dissociation constant and the antibody-binding capacity (ABC) of a cell. This model was then evaluated on peripheral blood lymphocytes (PBLs) labeled with anti CD3 antibodies conjugated to FITC, PE, or DM (magnetic nanoparticles). Reasonable agreements between the model and the experiments were obtained. In addition, estimates of the limitation of the number of magnetic nanoparticles that can bind to a cell as a result of steric hinderance was consistent with measured values of magnetophoretic mobility. Finally, a scale-up model was proposed and tested which predicts the amount of antibody conjugates needed to achieve a given level of saturation as the total number of cells reaches 10(10), the number of cells needed for certain clinical applications, such as T-cell depletions for mismatched bone marrow transplants.

Synthesis of Nanophase Iron Oxide in Lumazine Synthase Capsids

An enzyme-based bio-nanoreactor: By acting as a mineralization template, lumazine synthase, a 60-subunit enzyme complex which has a hollow porous shell, can fabricate nanocrystalline iron oxide. Fe ions can permeate the capsid through hydrophilic funnel-shaped channels lined with glutamic acid residues and become encapsulated in the cavity as Fe^III oxide. The capsid increases in size from 15 to 30 nm in diameter through formation of a higher order structure as the concentration of Fe^III increases.