Accumulation of iron oxide nanoparticles by cultured primary neurons

Local Administrations of Iron Oxide Nanoparticles in the Prefrontal Cortex and Caudate Putamen of Rats Do Not Compromise Working Memory and Motor Activity

Iron oxide nanoparticles (IONPs) have come into focus for their use in medical applications although possible health risks for humans, especially in terms of brain functions, have not yet been fully clarified. The present study investigates the effects of IONPs on neurobehavioural functions in rats. For this purpose, we infused dimercaptosuccinic acid-coated IONPs into the medial prefrontal cortex (mPFC) and caudate putamen (CPu). Saline (VEH) and ferric ammonium citrate (FAC) were administered as controls. One- and 4-week post-surgery mPFC-infused animals were tested for their working memory performance in the delayed alternation T-maze task and in the open field (OF) for motor activity, and CPu-infused rats were tested for their motor activity in the OF. After completion of the experiments, the brains were examined histologically and immunohistochemically. We did not observe any behavioural or structural abnormalities in the rats after administration of IONPs in the mPFC and the CPu. In contrast, administration of FAC into the CPu resulted in decreased motor activity and increased the number of microglia in the mPFC. Perls' Prussian blue staining revealed that FAC- and IONP-treated rats had more iron-containing ramified cells than VEH-treated rats, indicating iron uptake by microglia. Our results demonstrate that local infusions of IONPs into selected brain regions have no adverse impact on locomotor behaviour and working memory.

Evaluation of Dimercaptosuccinic Acid-Coated Iron Nanoparticles Immunotargeted to Amyloid Beta as MRI Contrast Agents for the Diagnosis of Alzheimer's Disease

Nanoparticle-based magnetic contrast agents have opened the potential for magnetic resonance imaging (MRI) to be used for early non-invasive diagnosis of Alzheimer's disease (AD). Accumulation of amyloid pathology in the brain has shown association with cognitive decline and tauopathy; hence, it is an effective biomarker for the early detection of AD. The aim of this study was to develop a biocompatible magnetic nanoparticle targeted to amyloid beta (Aβ) plaques to increase the sensitivity of T2-weighted MRI for imaging of amyloid pathology in AD. We presented novel iron core-iron oxide nanoparticles stabilized with a dimercaptosuccinic acid coating and functionalized with an anti-Aβ antibody. Nanoparticle biocompatibility and cellular internalization were evaluated in vitro in U-251 glioblastoma cells using cellular assays, proteomics, and transmission electron microscopy. Iron nanoparticles demonstrated no significant in vitro cytotoxicity, and electron microscopy results showed their movement through the endocytic cycle within the cell over a 24 h period. In addition, immunostaining and bio-layer interferometry confirmed the targeted nanoparticle's binding affinity to amyloid species. The iron nanoparticles demonstrated favourable MRI contrast enhancement; however, the addition of the antibody resulted in a reduction in the relaxivity of the particles. The present work shows promising preliminary results in the development of a targeted non-invasive method of early AD diagnosis using contrast-enhanced MRI.

Cellular and Molecular Processes Are Differently Influenced in Primary Neural Cells by Slight Changes in the Physicochemical Properties of Multicore Magnetic Nanoparticles

Herein, we use two exemplary superparamagnetic iron oxide multicore nanoparticles (SPIONs) to illustrate the significant influence of slightly different physicochemical properties on the cellular and molecular processes that define SPION interplay with primary neural cells. Particularly, we have designed two different SPION structures, NFA (i.e., a denser multicore structure accompanied by a slightly less negative surface charge and a higher magnetic response) and NFD (i.e., a larger surface area and more negatively charged), and identified specific biological responses dependent on SPION type, concentration, exposure time, and magnetic actuation. Interestingly, NFA SPIONs display a higher cell uptake, likely driven by their less negative surface and smaller protein corona, more significantly impacting cell viability and complexity. The tight contact of both SPIONs with neural cell membranes results in the significant augmentation of phosphatidylcholine, phosphatidylserine, and sphingomyelin and the reduction of free fatty acids and triacylglycerides for both SPIONs. Nonetheless, NFD induces greater effects on lipids, especially under magnetic actuation, likely indicating a preferential membranal location and/or a tighter interaction with membrane lipids than NFA, in agreement with their lower cell uptake. From a functional perspective, these lipid changes correlate with an increase in plasma membrane fluidity, again larger for more negatively charged nanoparticles (NFD). Finally, the mRNA expression of iron-related genes such as Ireb-2 and Fth-1 remains unaltered, while TfR-1 is only detected in SPION-treated cells. Taken together, these results demonstrate the substantial impact that minor physicochemical differences of nanomaterials may exert in the specific targeting of cellular and molecular processes. A denser multicore structure generated by autoclave-based production is accompanied by a slight difference in surface charge and magnetic properties that become decisive for the biological impact of these SPIONs. Their capacity to markedly modify the lipidic cell content makes them attractive as lipid-targetable nanomedicines.

Iron oxide nanoparticles cause surface coating- and core chemistry-dependent endothelial cell ferroptosis

Iron oxide nanoparticles (IONPs) are mostly intended to be administrated intravenously, understanding the interaction of IONPs with vascular endothelial cells is extremely crucial for developing safe application regimes of IONPs. In this work, interactions of three kinds of IONPs to endothelial cells were investigated both in human umbilical vein endothelial cells (HUVECs) and in healthy mice. Both meso-2,3-dimercaptosuccinic acid (DMSA) coated Fe₃O₄ NPs (DMSA-Fe₃O₄ NPs) and DMSA-Fe₂O₃ NPs induced cell growth inhibition, while polyglucose sorbitol carboxymethyether coated Fe₂O₃ NPs(PSC-Fe₂O₃ NPs) did not. The PSC coating inhibited the cellular uptake of the IONPs. Both DMSA-Fe₃O₄ and DMSA-Fe₂O₃ NPs induced ferroptosis of HUVEC through upregulating phospholipid peroxides, which could be inhibited by typical ferroptosis inhibitors ferrostatin-1, Trolox and deferoxamine. Moreover, transforming growth factor beta 1 (TGFβ1) was upregulated by DMSA-Fe₃O₄ NPs at protein and gene level. The inhibitor of TGFβ1 receptor LY210 could reduce the effect. When being intravenously injected in mice, DMSA-Fe₃O₄ NPs were observed locating in the liver, increased the levels of lipid peroxidation (4-hydroxynonenal), acyl-CoA synthetase long-chain family member 4(ACSL4) and TGFβ1, indicating ferroptosis occurrence in vivo. The ferroptosis of vascular endothelial cells in exposure with IONPs depended on the surface coating and core chemistry of the NPs. Both DMSA-Fe₃O₄ NPs and DMSA-Fe₂O₃ NPs could induce the ferroptosis of endothelial cells, while PSC-Fe₂O₃ NPs did not induce ferroptosis and apoptosis possibly due to the very low cellular uptake. DMSA-Fe₃O₄ NPs and TGFβ1 formed feedforward loop to induce ferroptosis.

Effects of Local Administration of Iron Oxide Nanoparticles in the Prefrontal Cortex, Striatum, and Hippocampus of Rats

Iron oxide nanoparticles (IONPs) are used for diverse medical approaches, although the potential health risks, for example adverse effects on brain functions, are not fully clarified. Several in vitro studies demonstrated that the different types of brain cells are able to accumulate IONPs and reported a toxic potential for IONPs, at least for microglia. However, little information is available for the in vivo effects of direct application of IONPs into the brain over time. Therefore, we examined the cellular responses and the distribution of iron in the rat brain at different time points after local infusion of IONPs into selected brain areas. Dispersed IONPs or an equivalent amount of low molecular weight iron complex ferric ammonium citrate or vehicle were infused into the medial prefrontal cortex (mPFC), the caudate putamen (CPu), or the dorsal hippocampus (dHip). Rats were sacrificed 1 day, 1 week, or 4 weeks post-infusion and brain sections were histologically examined for treatment effects on astrocytes, microglia, and neurons. Glial scar formation was observed in the mPFC and CPu 1 week post-infusion independent of the substance and probably resulted from the infusion procedure. Compared to vehicle, IONPs did not cause any obvious additional adverse effects and no additional tissue damage, while the infusion of ferric ammonium citrate enhanced neurodegeneration in the mPFC. Results of iron staining indicate that IONPs were mainly accumulated in microglia. Our results demonstrate that local infusions of IONPs in selected brain areas do not cause any additional adverse effects or neurodegeneration compared to vehicle.

In vivo Cell Tracking Using Non-invasive Imaging of Iron Oxide-Based Particles with Particular Relevance for Stem Cell-Based Treatments of Neurological and Cardiac Disease

Stem cell-based therapeutics is a rapidly developing field associated with a number of clinical challenges. One such challenge lies in the implementation of methods to track stem cells and stem cell-derived cells in experimental animal models and in the living patient. Here, we provide an overview of cell tracking in the context of cardiac and neurological disease, focusing on the use of iron oxide-based particles (IOPs) visualized in vivo using magnetic resonance imaging (MRI). We discuss the types of IOPs available for such tracking, their advantages and limitations, approaches for labeling cells with IOPs, biological interactions and effects of IOPs at the molecular and cellular levels, and MRI-based and associated approaches for in vivo and histological visualization. We conclude with reviews of the literature on IOP-based cell tracking in cardiac and neurological disease, covering both preclinical and clinical studies.

Understanding Nanoparticle Toxicity to Direct a Safe-by-Design Approach in Cancer Nanomedicine

Nanomedicine is a rapidly growing field that uses nanomaterials for the diagnosis, treatment and prevention of various diseases, including cancer. Various biocompatible nanoplatforms with diversified capabilities for tumor targeting, imaging, and therapy have materialized to yield individualized therapy. However, due to their unique properties brought about by their small size, safety concerns have emerged as their physicochemical properties can lead to altered pharmacokinetics, with the potential to cross biological barriers. In addition, the intrinsic toxicity of some of the inorganic materials (i.e., heavy metals) and their ability to accumulate and persist in the human body has been a challenge to their translation. Successful clinical translation of these nanoparticles is heavily dependent on their stability, circulation time, access and bioavailability to disease sites, and their safety profile. This review covers preclinical and clinical inorganic-nanoparticle based nanomaterial utilized for cancer imaging and therapeutics. A special emphasis is put on the rational design to develop non-toxic/safe inorganic nanoparticle constructs to increase their viability as translatable nanomedicine for cancer therapies.

Tailoring Iron Oxide Nanoparticles for Efficient Cellular Internalization and Endosomal Escape

Iron oxide nanoparticles (IONs) have been widely explored for biomedical applications due to their high biocompatibility, surface-coating versatility, and superparamagnetic properties. Upon exposure to an external magnetic field, IONs can be precisely directed to a region of interest and serve as exceptional delivery vehicles and cellular markers. However, the design of nanocarriers that achieve an efficient endocytic uptake, escape lysosomal degradation, and perform precise intracellular functions is still a challenge for their application in translational medicine. This review highlights several aspects that mediate the activation of the endosomal pathways, as well as the different properties that govern endosomal escape and nuclear transfection of magnetic IONs. In particular, we review a variety of ION surface modification alternatives that have emerged for facilitating their endocytic uptake and their timely escape from endosomes, with special emphasis on how these can be manipulated for the rational design of cell-penetrating vehicles. Moreover, additional modifications for enhancing nuclear transfection are also included in the design of therapeutic vehicles that must overcome this barrier. Understanding these mechanisms opens new perspectives in the strategic development of vehicles for cell tracking, cell imaging and the targeted intracellular delivery of drugs and gene therapy sequences and vectors.

Developmental Neurotoxicity Screening for Nanoparticles Using Neuron-Like Cells of Human Umbilical Cord Mesenchymal Stem Cells: Example with Magnetite Nanoparticles

Metallic nanoparticles (NPs), as iron oxide NPs, accumulate in organs, cross the blood-brain barrier and placenta, and have the potential to elicit developmental neurotoxicity (DNT). Human stem cell-derived in vitro models may provide more realistic platforms to study NPs effects on neural cells, and to obtain relevant information on the potential for early or late DNT effects in humans. Primary neuronal-like cells (hNLCs) were generated from mesenchymal stem cells derived from human umbilical cord lining and the effects caused by magnetite (Fe₃O₄NPs, 1-50 μg/mL) evaluated. Neuronal differentiation process was divided into stages: undifferentiated, early, mid- and fully-differentiated (from day-2 to 8 of induction) based on different neuronal markers and morphological changes over time. Reduction in neuronal differentiation induction after NP exposure was observed associated with NP uptake: β-tubulin III (β-Tub III), microtubule-associated protein 2 (MAP-2), enolase (NSE) and nestin were downregulated (10-40%), starting from 25 μg/mL at the early stage. Effects were exacerbated at higher concentrations and persisted up to 8 days without cell morphology alterations. Adenosine triphosphate (ATP) and caspase-3/7 activity data indicated Fe₃O₄NPs-induced cell mortality in a concentration-dependent manner and increases of apoptosis: effects appeared early (from day-3), started at low concentrations (≥5 μg/mL) and persisted. This new human cell-based model allows different stages of hNLCs to be cultured, exposed to NPs/chemicals, and analyzed for different endpoints at early or later developmental stage.

Endocytosis: The Nanoparticle and Submicron Nanocompounds Gateway into the Cell

Nanoparticles (NPs) and submicron particles are increasingly used as carriers for delivering therapeutic compounds to cells. Their entry into the cell represents the initial step in this delivery process, being most of the nanoparticles taken up by endocytosis, although other mechanisms can contribute to the uptake. To increase the delivery efficiency of therapeutic compounds by NPs and submicron particles is very relevant to understand the mechanisms involved in the uptake process. This review covers the proposed pathways involved in the cellular uptake of different NPs and submicron particles types as well as the role that some of the physicochemical nanoparticle characteristics play in the uptake pathway preferentially used by the nanoparticles to gain access and deliver their cargo inside the cell.

Cytotoxicity, cellular uptake and apoptotic responses in human coronary artery endothelial cells exposed to ultrasmall superparamagnetic iron oxide nanoparticles

Ultrasmall superparamagnetic iron oxide nanoparticles (USPION) possess reactive surfaces, are metabolized and exhibit unique magnetic properties. These properties are desirable for designing novel theranostic biomedical products; however, toxicity mechanisms of USPION are not completely elucidated. The goal of this study was to investigate cell interactions (uptake and cytotoxicity) of USPION using human coronary artery endothelial cells as a vascular cell model. Polyvinylpirrolidone-coated USPION were characterized: average diameter 17 nm (transmission electron microscopy [TEM]), average hydrodynamic diameter 44 nm (dynamic light scattering) and zeta potential -38.75 mV. Cells were exposed to 0 (control), 25, 50, 100 or 200 μg/mL USPION. Concentration- and time-dependent cytotoxicity were observed after 3-6 hours through 24 hours of exposure using Alamar Blue and Real-Time Cell Electronic Sensing assays. Cell uptake was evaluated by imaging using live-dead confocal microscopy, actin and nuclear fluorescent staining, and TEM. Phase-contrast, confocal microscopy, and TEM imaging showed significant USPION internalization as early as 3 hours after exposure to 25 μg/mL. TEM imaging demonstrated particle internalization in secondary lysosomes with perinuclear localization. Three orthogonal assays were conducted to assess apoptosis. TUNEL staining demonstrated a marked increase in fragmented DNA, a response pathognomonic of apoptosis, after a 4-hour exposure. Cells subjected to agarose gel electrophoresis exhibited degraded DNA 3 hours after exposure. Caspase-3/7 activity increased after a 3-hour exposure. USPION uptake resulted in cytotoxicity involving apoptosis and these results contribute to further mechanistic understanding of the USPION toxicity in vitro in cardiovascular endothelial cells.

Magnetic iron oxide nanoparticles for imaging, targeting and treatment of primary and metastatic tumors of the brain

Magnetic nanoparticles in general, and iron oxide nanoparticles in particular, have been studied extensively during the past 20 years for numerous biomedical applications. The main applications of these nanoparticles are in magnetic resonance imaging (MRI), magnetic targeting, gene and drug delivery, magnetic hyperthermia for tumor treatment, and manipulation of the immune system by macrophage polarization for cancer treatment. Recently, considerable attention has been paid to magnetic particle imaging (MPI) because of its better sensitivity compared to MRI. In recent years, MRI and MPI have been combined as a dual or multimodal imaging method to enhance the signal in the brain for the early detection and treatment of brain pathologies. Because magnetic and iron oxide nanoparticles are so diverse and can be used in multiple applications such as imaging or therapy, they have attractive features for brain delivery. However, the greatest limitations for the use of MRI/MPI for imaging and treatment are in brain delivery, with one of these limitations being the brain-blood barrier (BBB). This review addresses the current status, chemical compositions, advantages and disadvantages, toxicity and most importantly the future directions for the delivery of iron oxide based substances across the blood-brain barrier for targeting, imaging and therapy of primary and metastatic tumors of the brain.

Neuron-Like Cells Generated from Human Umbilical Cord Lining-Derived Mesenchymal Stem Cells as a New In Vitro Model for Neuronal Toxicity Screening: Using Magnetite Nanoparticles as an Example

The wide employment of iron nanoparticles in environmental and occupational settings underlines their potential to enter the brain. Human cell-based systems are recommended as relevant models to reduce uncertainty and to improve prediction of human toxicity. This study aimed at demonstrating the in vitro differentiation of the human umbilical cord lining-derived-mesenchymal stem cells (hCL-MSCs) into neuron-like cells (hNLCs) and the benefit of using them as an ideal primary cell source of human origin for the neuronal toxicity of Fe3O4NPs (magnetite-nanoparticles). Neuron-like phenotype was confirmed by: live morphology; Nissl body staining; protein expression of different neuronal-specific markers (immunofluorescent staining), at different maturation stages (i.e., day-3-early and day-8-full differentiated), namely β-tubulin III, MAP-2, enolase (NSE), glial protein, and almost no nestin and SOX-2 expression. Synaptic makers (SYN, GAP43, and PSD95) were also expressed. Fe3O4NPs determined a concentration- and time-dependent reduction of hNLCs viability (by ATP and the Trypan Blue test). Cell density decreased (20-50%) and apoptotic effects were detected at ≥10 μg/mL in both types of differentiated hNLCs. Three-day-differentiated hNLCs were more susceptible (toxicity appeared early and lasted for up to 48 h) than 8-day-differentiated cells (delayed effects). The study demonstrated that (i) hCL-MSCs easily differentiated into neuronal-like cells; (ii) the hNCLs susceptibility to Fe3O4NPs; and (iii) human primary cultures of neurons are new in vitro model for NP evaluation.

Evaluation of cytotoxicity and genotoxicity induced by oleic acid-coated iron oxide nanoparticles in human astrocytes

Iron oxide nanoparticles (ION) are gaining importance as diagnostic and therapeutic tool of central nervous system diseases. Although oleic acid-coated ION (O-ION) have been described as stable and biocompatible, their potential neurotoxicity was scarcely evaluated in human nervous cells so far. The primary aim of this work was to assess the molecular and cellular effects of O-ION on human astrocytes (A172 cells) under different experimental conditions. An extensive set of cyto- and genotoxicity tests was carried out, including lactate dehydrogenase release assay, cell cycle alterations, and cell death production, as well as comet assay, γH2AX assay, and micronucleus (MN) test, considering also iron ion release capacity and alterations in DNA repair ability. Results showed a moderate cytotoxicity related to cell cycle arrest and cell death promotion, regardless of serum presence. O-ION induced genotoxic effects, namely primary DNA damage, as detected by the comet assay and H2AX phosphorylation, but A172 cells were able to repair this particular damage because no chromosome alterations were found (confirmed by MN test results). Accordingly, no effects on the DNA repair ability were observed. The presence of serum proteins did not influence O-ION toxicity. Iron ions released from the O-ION surface seemed not to be responsible for the cytotoxic and genotoxic effects observed. Environ. Mol. Mutagen. 2019. © 2019 Wiley Periodicals, Inc.

A Multidisciplinary Approach Toward High Throughput Label-Free Cytotoxicity Monitoring of Superparamagnetic Iron Oxide Nanoparticles

Abstract: This paper focuses on cytotoxicity examination of superparamagnetic iron oxide nanoparticles (SPIONs) using different methods, including impedance spectroscopy. Recent advances of SPIONs for clinical and research applications have triggered the need to understand their effects in cells. Despite the great advances in adapting various biological and chemical methods to assess in-vitro toxicity of SPIONs, less attention has been paid on the development of a high throughput label-free screening platform to study the interaction between the cells and nanoparticles including SPIONs. In this paper, we have taken the first step toward this goal by proposing a label-free impedimetric method for monitoring living cells treated with SPIONs. We demonstrate the effect of SPIONs on the adhesion, growth, proliferation, and viability of neuroblastoma 2A (N2a) cells using impedance spectroscopy as a label-free method, along with other standard microscopic and cell viability testing methods as control methods. Our results have shown a decreased viability of the cells as the concentration of SPIONs increases with percentages of 59%, 47%, and 40% for 100 µg/mL (C4), 200 µg/mL (C5), 300 µg/mL (C6), respectively. Although all SPIONs concentrations have allowed the growth of cells within 72 hours, C4, C5, and C6 showed slower growth compared to the control (C1). The growth and proliferation of N2a cells are faster in the absence or low concentration of SPIONS. The percent coefficient of variation (% CV) was used to compare cell concentrations obtained by TBDE assay and a Scepter cell counter. Results also showed that the lower the SPIONs concentration, the lower the impedance is expected to be in the sensing electrodes without the cells. Meanwhile, the variation of surface area (∆S) was affected by the concentration of SPIONs. It was observed that the double layer capacitance was almost constant because of the higher attachment of cells, the lower surface area coated by SPIONs. In conclusion, impedance changes of electrodes exposed to the mixture of cells and SPIONs offer a wide dynamic range (>1 MΩ using Electric Cell-substrate Impedance electrodes) suitable for cytotoxicity studies. Based on impedance based, viability testing and microscopic methods' results, SPIONs concentrations higher than 100 ug/mL and 300 ug/mL cause minor and major effects, respectively. We propose that a high throughput impedance-based label-free platform provides great advantages for studying SPIONs in a cell-based context, opening a window of opportunity to design and test the next generation of SPIONs with reduced toxicity for biomedical or medical applications.

Monitoring of the Cytoskeleton-Dependent Intracellular Trafficking of Fluorescent Iron Oxide Nanoparticles by Nanoparticle Pulse-Chase Experiments in C6 Glioma Cells

Iron oxide nanoparticles (IONPs) are used for various biomedical and therapeutic approaches. To investigate the uptake and the intracellular trafficking of IONPs in neural cells we have performed nanoparticle pulse-chase experiments to visualize the internalization and the fate of fluorescent IONPs in C6 glioma cells and astrocyte cultures. Already a short exposure to IONPs for 10 min at 4 °C (nanoparticle pulse) allowed binding of substantial amounts of nanoparticles to the cells, while internalization of IONPs into the cell was prevented. The uptake of bound IONPs and the intracellular trafficking was started by increasing the temperature to 37 °C (chase period). While hardly any cellular fluorescence nor any iron staining was detectable directly after the nanoparticle pulse, dotted cellular fluorescence and iron patterns appeared already within a few minutes after start of the chase incubation and became intensified in the perinuclear region during further incubation for up to 90 min. Longer chase incubations resulted in separation of the fluorescent coat from the core of the internalized IONPs. Disruption of actin filaments in C6 cells strongly impaired the internalization of IONPs, whereas destabilization of microtubules traped IONP-containing vesicles to the plasma membrane. In conclusion, nanoparticle pulse-chase experiments allowed to synchronize the cellular uptake of fluorescent IONPs and to identify for C6 cells an actin-dependent early and a microtubule-dependent later process in the intracellular trafficking of fluorescent IONPs.

How to Study the Uptake and Toxicity of Nanoparticles in Cultured Brain Cells: The Dos and Don't Forgets

Due to their exciting properties, engineered nanoparticles have obtained substantial attention over the last two decades. As many types of nanoparticles are already used for technical and biomedical applications, the chances that cells in the brain will encounter nanoparticles have strongly increased. To test for potential consequences of an exposure of brain cells to engineered nanoparticles, cell culture models for different types of neural cells are frequently used. In this review article we will discuss experimental strategies and important controls that should be used to investigate the physicochemical properties of nanoparticles for the cell incubation conditions applied as well as for studies on the biocompatibility and the cellular uptake of nanoparticles in neural cells. The main focus of this article will be the interaction of cultured neural cells with iron oxide nanoparticles, but similar considerations are important for studying the consequences of an exposure of other types of cultured cells with other types of nanoparticles. Our article aims to improve the understanding of the special technical challenges of working with nanoparticles on cultured neural cells, to identify potential artifacts and to prevent misinterpretation of data on the potential adverse or beneficial consequences of a treatment of cultured cells with nanoparticles.

Choose your cell model wisely: The in vitro nanoneurotoxicity of differentially coated iron oxide nanoparticles for neural cell labeling

Currently, there is a large interest in the labeling of neural stem cells (NSCs) with iron oxide nanoparticles (IONPs) to allow MRI-guided detection after transplantation in regenerative medicine. For such biomedical applications, excluding nanotoxicity is key. Nanosafety is primarily evaluated in vitro where an immortalized or cancer cell line of murine origin is often applied, which is not necessarily an ideal cell model. Previous work revealed clear neurotoxic effects of PMA-coated IONPs in distinct cell types that could potentially be applied for nanosafety studies regarding neural cell labeling. Here, we aimed to assess if DMSA-coated IONPs could be regarded as a safer alternative for this purpose and how the cell model impacted our nanosafety optimization study. Hereto, we evaluated cytotoxicity, ROS production, calcium levels, mitochondrial homeostasis and cell morphology in six related neural cell types, namely neural stem cells, an immortalized cell line and a cancer cell line from human and murine origin. The cell lines mostly showed similar responses to both IONPs, which were frequently more pronounced for the PMA-IONPs. Of note, ROS and calcium levels showed opposite trends in the human and murine NSCs, indicating the importance of the species. Indeed, the human cell models were overall more sensitive than their murine counterpart. Despite the clear cell type-specific nanotoxicity profiles, our multiparametric approach revealed that the DMSA-IONPs outperformed the PMA-IONPs in terms of biocompatibility in each cell type. However, major cell type-dependent variations in the observed effects additionally warrant the use of relevant human cell models.

STATEMENT OF SIGNIFICANCE

Inorganic nanoparticle (NP) optimization is chiefly performed in vitro. For the optimization of iron oxide (IO)NPs for neural stem cell labeling in the context of regenerative medicine human or rodent neural stem cells, immortalized or cancer cell lines are applied. However, the use of certain cell models can be questioned as they phenotypically differ from the target cell. The impact of the neural cell model on nanosafety remains relatively unexplored. Here we evaluated cell homeostasis upon exposure to PMA- and DMSA-coated IONPs. Of note, the DMSA-IONPs outperformed the PMA-IONPs in each cell type. However, distinct cell type-specific effects were witnessed, indicating that nanosafety should be evaluated in a human cell model that represents the target cell as closely as possible.

Micellar nanocomplexes for biomagnetic delivery of intracellular proteins to dictate axon formation during neuronal development

During mammalian embryonic development, neurons polarize to create distinct cellular compartments of axon and dendrite that inherently differ in form and function, providing the foundation for directional signaling in the nervous system. Polarization results from spatio-temporal segregation of specific proteins' activities to discrete regions of the neuron to dictate axonal vs. dendritic fate. We aim to manipulate axon formation by directed subcellular localization of crucial intracellular protein function. Here we report critical steps toward the development of a nanotechnology for localized subcellular introduction and retention of an intracellular kinase, LKB1, crucial regulator of axon formation. This nanotechnology will spatially manipulate LKB1-linked biomagnetic nanocomplexes (LKB1-NCs) in developing rodent neurons in culture and in vivo. We created a supramolecular assembly for LKB1 rapid neuronal uptake and prolonged cytoplasmic stability. LKB1-NCs retained kinase activity and phosphorylated downstream targets. NCs were successfully delivered to cultured embryonic hippocampal neurons, and were stable in the cytoplasm for 2 days, sufficient time for axon formation. Importantly, LKB1-NCs promoted axon formation in these neurons, representing unique proof of concept for the sufficiency of intracellular protein function in dictating a central developmental event. Lastly, we established NC delivery into cortical progenitors in live rat embryonic brain in utero. Our nanotechnology provides a viable platform for spatial manipulation of intracellular protein-activity, to dictate central events during neuronal development.

Are iron oxide nanoparticles safe? Current knowledge and future perspectives

Due to their unique physicochemical properties, including superparamagnetism, iron oxide nanoparticles (ION) have a number of interesting applications, especially in the biomedical field, that make them one of the most fascinating nanomaterials. They are used as contrast agents for magnetic resonance imaging, in targeted drug delivery, and for induced hyperthermia cancer treatments. Together with these valuable uses, concerns regarding the onset of unexpected adverse health effects following exposure have been also raised. Nevertheless, despite the numerous ION purposes being explored, currently available information on their potential toxicity is still scarce and controversial data have been reported. Although ION have traditionally been considered as biocompatible - mainly on the basis of viability tests results - influence of nanoparticle surface coating, size, or dose, and of other experimental factors such as treatment time or cell type, has been demonstrated to be important for ION in vitro toxicity manifestation. In vivo studies have shown distribution of ION to different tissues and organs, including brain after passing the blood-brain barrier; nevertheless results from acute toxicity, genotoxicity, immunotoxicity, neurotoxicity and reproductive toxicity investigations in different animal models do not provide a clear overview on ION safety yet, and epidemiological studies are almost inexistent. Much work has still to be done to fully understand how these nanomaterials interact with cellular systems and what, if any, potential adverse health consequences can derive from ION exposure.

The tricarboxylic acid cycle activity in cultured primary astrocytes is strongly accelerated by the protein tyrosine kinase inhibitor tyrphostin 23

Tyrphostin 23 (T23) is a well-known inhibitor of protein tyrosine kinases and has been considered as potential anti-cancer drug. T23 was recently reported to acutely stimulate the glycolytic flux in primary cultured astrocytes. To investigate whether T23 also affects the tricarboxylic acid (TCA) cycle, we incubated primary rat astrocyte cultures with [U-¹³C]glucose in the absence or the presence of 100 μM T23 for 2 h and analyzed the ¹³C metabolite pattern. These incubation conditions did not compromise cell viability and confirmed that the presence of T23 doubled glycolytic lactate production. In addition, T23-treatment strongly increased the molecular carbon labeling of the TCA cycle intermediates citrate, succinate, fumarate and malate, and significantly increased the incorporation of ¹³C-labelling into the amino acids glutamate, glutamine and aspartate. These results clearly demonstrate that, in addition to glycolysis, also the mitochondrial TCA cycle is strongly accelerated after exposure of astrocytes to T23, suggesting that a protein tyrosine kinase may be involved in the regulation of the TCA cycle in astrocytes.

The Protein Tyrosine Kinase Inhibitor Tyrphostin 23 Strongly Accelerates Glycolytic Lactate Production in Cultured Primary Astrocytes

Tyrphostin 23 (T23) is a well-known inhibitor of protein tyrosine kinases. To investigate potential acute effects of T23 on the viability and the glucose metabolism of brain cells, we exposed cultured primary rat astrocytes to T23 for up to 4 h. While the viability and the morphology of the cultured astrocytes were not acutely affected by the presence of T23 in concentrations of up to 300 µM, this compound caused a rapid, time- and concentration-dependent increase in glucose consumption and lactate release. Maximal effects on glycolytic flux were found for incubations with 100 µM T23 for 2 h which doubled both glucose consumption and lactate production. The stimulation of glycolytic flux by T23 was reversible, completely abolished upon removal of the compound and not found in presence of other known inhibitors of endocytosis. Structurally related compounds such as tyrphostin 25 and catechol or modulators of AMP kinase activity did neither affect the basal nor the T23-stimulated lactate production by astrocytes. In contrast, the presence of the phosphatase inhibitor vanadate completely abolished the stimulation by T23 of astrocytic lactate production in a concentration-dependent manner. These data suggest that T23-sensitive phosphorylation/dephosphorylation events are involved in the regulation of astrocytic glycolysis.

Growth factor choice is critical for successful functionalization of nanoparticles

Nanoparticles (NPs) show new characteristics compared to the corresponding bulk material. These nanoscale properties make them interesting for various applications in biomedicine and life sciences. One field of application is the use of magnetic NPs to support regeneration in the nervous system. Drug delivery requires a functionalization of NPs with bio-functional molecules. In our study, we functionalized self-made PEI-coated iron oxide NPs with nerve growth factor (NGF) and glial cell-line derived neurotrophic factor (GDNF). Next, we tested the bio-functionality of NGF in a rat pheochromocytoma cell line (PC12) and the bio-functionality of GDNF in an organotypic spinal cord culture. Covalent binding of NGF to PEI-NPs impaired bio-functionality of NGF, but non-covalent approach differentiated PC12 cells reliably. Non-covalent binding of GDNF showed a satisfying bio-functionality of GDNF:PEI-NPs, but turned out to be unstable in conjugation to the PEI-NPs. Taken together, our study showed the importance of assessing bio-functionality and binding stability of functionalized growth factors using proper biological models. It also shows that successful functionalization of magnetic NPs with growth factors is dependent on the used binding chemistry and that it is hardly predictable. For use as therapeutics, functionalization strategies have to be reproducible and future studies are needed.