Analysis of the influence of cell heterogeneity on nanoparticle dose response

The impact of macrophage phenotype and heterogeneity on the total internalized gold nanoparticle counts

Macrophages play a pivotal role in the internalization and processing of administered nanoparticles (NPs). Furthermore, the phagocytic capacity and immunological properties of macrophages can vary depending on their microenvironment, exhibiting a spectrum of polarization states ranging from pro-inflammatory M1 to anti-inflammatory M2. However, previous research investigating this phenotype-dependent interaction with NPs has predominantly relied on semi-quantitative techniques or conventional metrics to assess intracellular NPs. Here, we focus on the interaction of human monocyte-derived macrophage phenotypes (M1-like and M2-like) with gold NPs (AuNPs) by combining population-based metrics and single-cell analysis by focused ion beam-scanning electron microscopy (FIB-SEM). The multimodal analysis revealed phenotype-dependent response and uptake behavior differences, becoming more pronounced after 48 hours. The study also highlighted phenotype-dependent cell-to-cell heterogeneity in AuNPs uptake and variability in particle number at the single-cell level, which was particularly evident in M2-like macrophages, which increases with time, indicating enhanced heteroscedasticity. Future efforts to design NPs targeting macrophages should consider the phenotypic variations and the distribution of NPs concentrations within a population, including the influence of cell-to-cell heterogeneity. This comprehensive understanding will be critical in developing safe and effective NPs to target different macrophage phenotypes.

Nanotherapeutic Heterogeneity: Sources, Effects, and Solutions

Nanomaterials have revolutionized medicine by enabling control over drugs' pharmacokinetics, biodistribution, and biocompatibility. However, most nanotherapeutic batches are highly heterogeneous, meaning they comprise nanoparticles that vary in size, shape, charge, composition, and ligand functionalization. Similarly, individual nanotherapeutics often have heterogeneously distributed components, ligands, and charges. This review discusses nanotherapeutic heterogeneity's sources and effects on experimental readouts and therapeutic efficacy. Among other topics, it demonstrates that heterogeneity exists in nearly all nanotherapeutic types, examines how nanotherapeutic heterogeneity arises, and discusses how heterogeneity impacts nanomaterials' in vitro and in vivo behavior. How nanotherapeutic heterogeneity skews experimental readouts and complicates their optimization and clinical translation is also shown. Lastly, strategies for limiting nanotherapeutic heterogeneity are reviewed and recommendations for developing more reproducible and effective nanotherapeutics provided.

Cell cycle-dependent Cu uptake explained the heterogenous responses of Chlamydomonas to Cu exposure

Growing evidence suggested that microorganisms exhibited heterogeneous sensitivity to toxicants, but their underlying mechanisms remain largely unknown. The asynchronous cell cycle progression in natural population implies the connection between cell cycle and heterogeneity. Here, the heterogenous responses of Chlamydomonas reinhardtii upon Cu stress were confirmed with the aid of a fluorometric probe for imaging Cu(I), implying the connection with cell cycle. Our results further indicated that the increase of labile Cu(I) was related to the cell division, leading to the fluctuation of labile Cu(I) with diurnal cycle and cell cycle, respectively. However, lack of Cu mainly influenced the cell division. We demonstrated that G2/M phase was the critical stage requiring high Cu quota during cell division. Specifically, algae at G2/M phase required 10-fold of Cu quota compared with that at G1 phase, which was related to the mitochondrial replication. Eventually, the heterogeneous Cu uptake ability of algae at different cell phases led to the heterogeneous responses to Cu exposure. Overall, Cu could influence the cell cycle through mediating the cell division, and in turn algae at different cell phases exhibited different Cu sensitivities. This study firstly uncovered the underlying mechanisms of heterogeneous Cu sensitivity for phytoplankton, which could help to evaluate the potential ecological risks of Cu.

On predicting heterogeneity in nanoparticle dosage

Nanoparticles are increasingly employed as a vehicle for the targeted delivery of therapeutics to specific cell types. However, much remains to be discovered about the fundamental biology that dictates the interactions between nanoparticles and cells. Accordingly, few nanoparticle-based targeted therapeutics have succeeded in clinical trials. One element that hinders our understanding of nanoparticle-cell interactions is the presence of heterogeneity in nanoparticle dosage data obtained from standard experiments. It is difficult to distinguish between heterogeneity that arises from stochasticity in nanoparticle-cell interactions, and that which arises from heterogeneity in the cell population. Mathematical investigations have revealed that both sources of heterogeneity contribute meaningfully to the heterogeneity in nanoparticle dosage. However, these investigations have relied on simplified models of nanoparticle internalisation. Here we present a stochastic mathematical model of nanoparticle internalisation that incorporates a suite of relevant biological phenomena such as multistage internalisation, cell division, asymmetric nanoparticle inheritance and nanoparticle saturation. Critically, our model provides information about nanoparticle dosage at an individual cell level. We perform model simulations to examine the influence of specific biological phenomena on the heterogeneity in nanoparticle dosage in the absence of heterogeneity in the cell population. Under certain modelling assumptions, we derive analytic approximations of the nanoparticle dosage distribution. We demonstrate that the analytic approximations are accurate, and show that nanoparticle dosage can be described by a Poisson mixture distribution with rate parameters that are a function of Beta-distributed random variables. We discuss the implications of the analytic results with respect to parameter estimation and model identifiability from standard experimental data. Finally, we highlight extensions and directions for future research.

Biofertilizers and nanofertilizers for sustainable agriculture: Phycoprospects and challenges

Increased food demands and ceasing nutrient deposits have resulted in a great shortfall between the food supply and demand and would be worse in the years to come. Higher inputs of synthetic fertilizers on lands have resulted in environmental pollution, persistent changes in the soil ecology, and physicochemical conditions. This has greatly decreased the natural soil fertility thereby hindering agricultural productivity, human health, and hygiene. Bio-based resilient nutrient sources as wastewater-derived algae are promising as a complete nutrient for agriculture and have the potential to be used in soilless cultivations. Innovations in nano-fortification and nano-sizing of minerals and algae have the potential to facilitate nutrients bioavailability and efficacy for a multifold increase in productivity. In this context, various options on minerals nanofertilizer application in agricultural food production besides efficient biofertilizer have been investigated. Algal biofertilizer with the nanoscale application has huge prospects for further agriculture productivities and fosters suitable development.

Sources of variability in nanoparticle uptake by cells

Understanding how nano-sized objects are taken up by cells is important for applications within medicine (nanomedicine), as well as to avoid unforeseen hazard due to nanotechnology (nanosafety). Even within the same cell population, one typically observes a large cell-to-cell variability in nanoparticle uptake, raising the question of the underlying cause(s). Here we investigate cell-to-cell variability in polystyrene nanoparticle uptake by HeLa cells, with generalisations of the results to silica nanoparticles and liposomes, as well as to A549 and primary human umbilical vein endothelial cells. We show that uptake of nanoparticles is correlated with cell size within a cell population, thereby reproducing and generalising previous reports highlighting the role of cell size in nanoparticle uptake. By repeatedly isolating (using fluorescence-activated cell sorting) the cells that take up the most and least nanoparticles, respectively, and performing RNA sequencing on these cells separately, we examine the underlying gene expression that contributes to high and low polystyrene nanoparticle accumulation in HeLa cells. We can thereby show that cell size is not the sole driver of cell-to-cell variability, but that other cellular characteristics also play a role. In contrast to cell size, these characteristics are more specific to the object (nanoparticle or protein) being taken up, but are nevertheless highly heterogeneous, complicating their detailed identification. Overall, our results highlight the complexity underlying the cellular features that determine nanoparticle uptake propensity.

Data-Driven Modeling of the Cellular Pharmacokinetics of Degradable Chitosan-Based Nanoparticles

Nanoparticle drug delivery vehicles introduce multiple pharmacokinetic processes, with the delivery, accumulation, and stability of the therapeutic molecule influenced by nanoscale processes. Therefore, considering the complexity of the multiple interactions, the use of data-driven models has critical importance in understanding the interplay between controlling processes. We demonstrate data simulation techniques to reproduce the time-dependent dose of trimethyl chitosan nanoparticles in an ND7/23 neuronal cell line, used as an in vitro model of native peripheral sensory neurons. Derived analytical expressions of the mean dose per cell accurately capture the pharmacokinetics by including a declining delivery rate and an intracellular particle degradation process. Comparison with experiment indicates a supply time constant, τ = 2 h. and a degradation rate constant, b = 0.71 h⁻¹. Modeling the dose heterogeneity uses simulated data distributions, with time dependence incorporated by transforming data-bin values. The simulations mimic the dynamic nature of cell-to-cell dose variation and explain the observed trend of increasing numbers of high-dose cells at early time points, followed by a shift in distribution peak to lower dose between 4 to 8 h and a static dose profile beyond 8 h.

In situ High-Throughput Single-Cell Analysis Reveals the Crosstalk between Nanoparticle-Induced Cell Responses

Nanomaterials are widely used in a variety of industrial, biological, and medical applications. Therefore, high concerns about their possible impact on human and environmental health have been raised. Here, we describe a high-throughput single-cell imaging method to reveal the crosstalk among quantum dot (QDot)-induced ROS generation, apoptosis, and changes in nucleus size in macrophages. In triple marker combinations, we assessed the correlations of three QDot-induced cellular responses via divided subsets based on single-cell analysis. In contrast to the results obtained from the cell population, we demonstrated that the change in nucleus size was positively correlated with ROS generation. We found that QDot exposure induced ROS generation, which led to cell apoptosis, followed by a change in nucleus size. In general, these observations on crosstalk of cellular responses provide detailed insights into the heterogeneity of nanoparticle exposure.

Kinetics of nanoparticle uptake into and distribution in human cells

Whether one wishes to optimise drug delivery using nano-sized carriers or avoid hazard posed by engineered nanomaterials, the kinetics of nanoparticle uptake into human cells and their subsequent intracellular distribution is key. Unique properties of the nanoscale implies that such nanoparticles are taken up and trafficked in a different fashion compared to molecular species. In this review, we discuss in detail how to describe the kinetics of nanoparticle uptake and intracellular distribution, using previous studies for illustration. We also cover the extracellular kinetics, particle degradation, endosomal escape and cell division, ending with an outlook on the future of kinetic studies.

Cytotoxic effects of polystyrene nanoplastics with different surface functionalization on human HepG2 cells

Nanoplastics in the environment lead to the human exposure to these particles. However, the consequences of this exposure are not yet fully understood. Here, the cytotoxicity of polystyrene nanoparticles (PS-NPs) with a uniform size (50 nm) but distinct surface functionalization (pristine polystyrene, PS; carboxy and amino functionalized, PS-COOH and PS-NH₂, respectively), and at an exposure dosage of 10, 50 and 100 μg/mL, were assessed in the human hepatocellular carcinoma (HepG2) cell line. Although all PS-NPs could be internalized by the HepG2 cells, according to the fluorescent intensities, more of PS-COOH and PS-NH₂ than PS, accumulated in the cells. The cell viability was significantly affected in a positively dose-related manner. Functionalized PS-NPs exhibited greater inhibition of cell viability than PS, and the viability inhibition peaked (46%) at 100 μg/mL of PS-NH₂ exposure. Superoxide dismutase (SOD) activity was maximum when HepG2 cells were exposed to 10 μg/mL of PS-COOH (1.8 folds higher than that without PS-COOH exposure). The glutathione (GSH) content was maximum when the cells were treated with 50 μg/mL of PS (3.75 fold increase compared to untreated cells). Although the difference in inhibition of cell viability was not significant between PS-NH₂ and PS-COOH exposure, 100 μg/mL of PS-NH₂ exposure caused the most severe oxidative stress due to dramatically increased accumulation of malondialdehyde (MDA); however, a decrease in the antioxidants levels as the SOD activity and GSH content were also found. The results demonstrated that the cellular oxidative damage occurred and that the antioxidation enzymes may not be able to maintain the balance between the generation of oxidant species and the antioxidant defense. Consequently, 100 μg/mL of PS-NH₂ exposure triggered the destruction of antioxidant structures. This study defines the cytotoxic effects of PS-NPs on HepG2 cells and emphasizes the significance of investigating the cytotoxic outcomes of nanoplastics in humans.

Isolating the sources of heterogeneity in nano-engineered particle-cell interactions

Nano-engineered particles have the potential to enhance therapeutic success and reduce toxicity-based treatment side effects via the targeted delivery of drugs to cells. This delivery relies on complex interactions between numerous biological, chemical and physical processes. The intertwined nature of these processes has thus far hindered attempts to understand their individual impact. Variation in experimental data, such as the number of particles inside each cell, further inhibits understanding. Here, we present a mathematical framework that is capable of examining the impact of individual processes during particle delivery. We demonstrate that variation in experimental particle uptake data can be explained by three factors: random particle motion; variation in particle-cell interactions; and variation in the maximum particle uptake per cell. Without all three factors, the experimental data cannot be explained. This work provides insight into biological mechanisms that cause heterogeneous responses to treatment, and enables precise identification of treatment-resistant cell subpopulations.

Morphofunctional characteristics of mouse (Mus musculus musculus) liver on the application of various doses of nanostructural sapropel

The liver is considered to be the main organ in the processes of regulating metabolism, neutralizing toxins and maintaining the constancy of the internal environment of the body. The goal of the research was to study the morphofunctional state of the liver under the effect of different concentrations of nanostructured sapropel. The experiments were carried out on non-linear (outbred) white mice weighing 24.9 ± 1.8 g. Twelve mature males were allotted to four groups. Mice of the experimental groups I, II and III intragastrically through the atraumatic flexible probe were once injected with nanostructured sapropel (particle size of 45.0–180.0 nm) in the following doses: lethal – 3.0 g/kg of the body weight; toxic – 1.8 g/kg of the body weight and safe – 0.6 g/kg of the body weight. Mice of group IV served as a control one and received deionized water in the same way. The choice of liver as the organ for analyzing is justified by the fact that the liver did not have direct contact with sapropel nanoparticles in the process of its intragastric administration into the body of white mice. Four hours after the introduction of nanostructured sapropel, three mice from each group were killed by cervical dislocation. After preparation and staining with hematoxylin and eosin, identical pieces of the liver were evaluated using light microscopy. Histological studies have established that the introduction of a lethal dose of nanostructured sapropel caused hemodynamic vascular disorders; focal necrosis and necrobiosis of hepatocytes were also observed in the research. Furthermore, the research noted a migration of reticuloendotheliocytes to the centrolobular regions of the lobules and enhancement of their activity. The microstructure of the liver when introducing a toxic dose of nanostructured sapropel was characterized by moderate plethora of sinusoidal capillaries, deformation of hepatocytes, focal destruction with the development of karyopiknosis, karyorhexis and karyolysis. The study revealed the activation of reticuloendothelial cells. Liver histology when introducing a safe dose of nanostructured sapropel was characterized by the preservation of the integrity of the structural elements, polyploid (two- and multi-core) hepatocytes were identified in the periportal part of the lobes. The changes in the structural and functional state of the mice liver were found to be depending on the dose of the nanostructured sapropel.

The origin of heterogeneous nanoparticle uptake by cells

Understanding nanoparticle uptake by biological cells is fundamentally important to wide-ranging fields from nanotoxicology to drug delivery. It is now accepted that the arrival of nanoparticles at the cell is an extremely complicated process, shaped by many factors including unique nanoparticle physico-chemical characteristics, protein-particle interactions and subsequent agglomeration, diffusion and sedimentation. Sequentially, the nanoparticle internalisation process itself is also complex, and controlled by multiple aspects of a cell's state. Despite this multitude of factors, here we demonstrate that the statistical distribution of the nanoparticle dose per endosome is independent of the initial administered dose and exposure duration. Rather, it is the number of nanoparticle containing endosomes that are dependent on these initial dosing conditions. These observations explain the heterogeneity of nanoparticle delivery at the cellular level and allow the derivation of simple, yet powerful probabilistic distributions that accurately predict the nanoparticle dose delivered to individual cells across a population.

Cross-Correlative Single-Cell Analysis Reveals Biological Mechanisms of Nanoparticle Radiosensitization

Nanoparticle radiosensitization has been demonstrated well to enhance the effects of radiotherapy, motivate the improvement of therapeutic ratios, and decrease morbidity in cancer treatment. A significant challenge exists in optimizing formulations and translation due to insufficient knowledge of the associated mechanisms, which have historically been limited to physical concepts. Here, we investigated a concept for the role of biological mechanisms. The mere presence of gold nanoparticles led to a down-regulation of thymidylate synthase, important for DNA damage repair in the radioresistant S-phase cells. By developing a cross-correlative methodology to reveal probabilistic gold nanoparticle uptake by cell sub-populations and the associated sensitization as a function of the uptake, a number of revealing observations have been achieved. Surprisingly, for low numbers of nanoparticles, a desensitization action was observed. Sensitization was discovered to preferentially impact S-phase cells, in which impairment of the DNA damage response by the homologous recombination pathway dominates. This small but radioresistant cell population correlates with much greater proliferative ability. Thus, a paradigm is presented whereby enhanced DNA damage is not necessarily due to an increase in the number of DNA double-strand breaks (DSBs) created but can be from a nanoparticle-induced impairment of the damage response by down-regulating repair proteins such as thymidylate synthase.

Nanotoxicity of Silver Nanoparticles on HEK293T Cells: A Combined Study Using Biomechanical and Biological Techniques

Human embryonic kidney 293T cells (HEK293T cells) before and after treatment with silver nanoparticles (AgNPs) were measured using advanced atomic force microscopy (AFM) force measurement technique, and the biomechanical property of cells was analyzed using a theoretical model. The biomechanical results showed that the factor of viscosity of untreated HEK293T cells reduced from 0.65 to 0.40 for cells exposure to 40 μg/mL of AgNPs. Comet assay indicated that significant DNA damage occurred in the treated cells, measured as tail DNA% and tail moment. Furthermore, gene expression analysis showed that for the cells treated with 40 μg/mL of AgNPs, the antiapoptosis genes Bcl2-t and Bclw were, respectively, downregulated to 0.65- and 0.66-fold of control, and that the proapoptosis gene Bid was upregulated to 1.55-fold of control, which indicates that apoptosis occurred in cells exposed to AgNPs. Interestingly, excellent negative correlations were found between the factor of viscosity and tail DNA%, and tail moment, which suggest that the biomechanical property can be correlated with genotoxicity of nanoparticles on the cells. Based on the above results, we conclude that (1) AgNPs can lead to biomechanical changes in HEK293T cells, concomitantly with biological changes including cell viability, DNA damage, and cell apoptosis; (2) the factor of viscosity can be exploited as a promising label-free biomechanical marker to assess the nanotoxicity of nanoparticles on the cells; and (3) the combination of AFM-based mechanical technique with conventional biological methods can provide more comprehensive understanding of the nanotoxicity of nanoparticles than merely by using the biological techniques.

Characterizing Nanoparticles in Biological Matrices: Tipping Points in Agglomeration State and Cellular Delivery In Vitro

Understanding the delivered cellular dose of nanoparticles is imperative in nanomedicine and nanosafety, yet is known to be extremely complex because of multiple interactions between nanoparticles, their environment, and the cells. Here, we use 3-D reconstruction of agglomerates preserved by cryogenic snapshot sampling and imaged by electron microscopy to quantify the "bioavailable dose" that is presented at the cell surface and formed by the process of individual nanoparticle sequestration into agglomerates in the exposure media. Critically, using 20 and 40 nm carboxylated polystyrene-latex and 16 and 85 nm silicon dioxide nanoparticles, we show that abrupt, dose-dependent "tipping points" in agglomeration state can arise, subsequently affecting cellular delivery and increasing toxicity. These changes are triggered by shifts in the ratio of the total nanoparticle surface area to biomolecule abundance, with the switch to a highly agglomerated state effectively changing the test article midassay, challenging the dose-response paradigm for nanosafety experiments. By characterizing nanoparticle numbers per agglomerate, we show these tipping points can lead to the formation of extreme agglomeration states whereby 90% of an administered dose is contained and delivered to the cells by just the top 2% of the largest agglomerates. We thus demonstrate precise definition, description, and comparison of the nanoparticle dose formed in different experimental environments and show that this description is critical to understanding cellular delivery and toxicity. We further empirically "stress-test" the commonly used dynamic light scattering approach, establishing its limitations to present an analysis strategy that significantly improves the usefulness of this popular nanoparticle characterization technique.

A new mild hyperthermia device to treat vascular involvement in cancer surgery

Surgical margin status in cancer surgery represents an important oncologic parameter affecting overall prognosis. The risk of disease recurrence is minimized and survival often prolonged if margin-negative resection can be accomplished during cancer surgery. Unfortunately, negative margins are not always surgically achievable due to tumor invasion into adjacent tissues or involvement of critical vasculature. Herein, we present a novel intra-operative device created to facilitate a uniform and mild heating profile to cause hyperthermic destruction of vessel-encasing tumors while safeguarding the encased vessel. We use pancreatic ductal adenocarcinoma as an in vitro and an in vivo cancer model for these studies as it is a representative model of a tumor that commonly involves major mesenteric vessels. In vitro data suggests that mild hyperthermia (41-46 °C for ten minutes) is an optimal thermal dose to induce high levels of cancer cell death, alter cancer cell's proteomic profiles and eliminate cancer stem cells while preserving non-malignant cells. In vivo and in silico data supports the well-known phenomena of a vascular heat sink effect that causes high temperature differentials through tissues undergoing hyperthermia, however temperatures can be predicted and used as a tool for the surgeon to adjust thermal doses delivered for various tumor margins.

Pancreatic adenocarcinoma response to chemotherapy enhanced with non-invasive radio frequency evaluated via an integrated experimental/computational approach

Although chemotherapy combined with radiofrequency exposure has shown promise in cancer treatment by coupling drug cytotoxicity with thermal ablation or thermally-induced cytotoxicity, limited access of the drug to tumor loci in hypo-vascularized lesions has hampered clinical application. We recently showed that high-intensity short-wave capacitively coupled radiofrequency (RF) electric-fields may reach inaccessible targets in vivo. This non-invasive RF combined with gemcitabine (Gem) chemotherapy enhanced drug uptake and effect in pancreatic adenocarcinoma (PDAC), notorious for having poor response and limited therapeutic options, but without inducing thermal injury. We hypothesize that the enhanced cytotoxicity derives from RF-facilitated drug transport in the tumor microenvironment. We propose an integrated experimental/computational approach to evaluate chemotherapeutic response combined with RF-induced phenotypic changes in tissue with impaired transport. Results show that RF facilitates diffusive transport in 3D cell cultures representing hypo-vascularized lesions, enhancing drug uptake and effect. Computational modeling evaluates drug vascular extravasation and diffusive transport as key RF-modulated parameters, with transport being dominant. Assessment of hypothetical schedules following current clinical protocol for Stage-IV PDAC suggests that unresponsive lesions may be growth-restrained when exposed to Gem plus RF. Comparison of these projections to experiments in vivo indicates that synergy may result from RF-induced cell phenotypic changes enhancing drug transport and cytotoxicity, thus providing a potential baseline for clinically-focused evaluation.

Spatially-resolved profiling of carbon nanotube uptake across cell lines

The internalisation and intra-cellular distribution of carbon nanotubes (CNT) has been quantitatively assessed using imaging flow cytometry. Spatial analysis of the bright field images indicates the presence of a small sub-population (5% of cells) in which the internalised CNTs are packed into pronounced clusters, visible as dark spots due to strong optical scattering by the nanotubes. The area of these spots can be used as a label-free metric of CNT dose and we assess the relative uptake of charge-neutral CNTs, over a 24 hours exposure period across four cell types: J774 mouse macrophage cells, A549 and Calu-6 human lung cancer cells, and MCF-7 human breast cells. The relative dose as indicated by the spot-area metric closely correlates to results using the same CNT preparation, conjugated to a FITC-label and shows pronounced uptake by the J774 cells leading to a mean dose that is >60% higher than for the other cell types. Spatial evaluation of dosing clusters is also used to quantify differences in uptake by J774 cells of CNTs with different surface functionalisation. While the percentage of CNT-cluster positive cells increases from 5% to 19% when switching from charge-neutral CNTs to poly-cationic, dendron functionalised CNTs, the single cell level analysis of internalised clusters indicates a lower dose per cell of poly-cationic CNTs relative to the charge-neutral CNTs. We concluded that there is dose homeostasis i.e., the population-averaged cellular dose of CNTs remained unchanged.

A novel technique to determine the cell type specific response within an in vitro co-culture model via multi-colour flow cytometry

Determination of the cell type specific response is essential towards understanding the cellular mechanisms associated with disease states as well as assessing cell-based targeting of effective therapeutic agents. Recently, there have been increased calls for advanced in vitro multi-cellular models that provide reliable and valuable tools correlative to in vivo. In this pursuit the ability to assess the cell type specific response is imperative. Herein, we report a novel approach towards resolving each specific cell type of a multi-cellular model representing the human lung epithelial tissue barrier via multi-colour flow cytometry (FACS). We proved via ≤ five-colour FACS that the manipulation of this in vitro model allowed each cell type to be resolved with no impact upon cell viability. Subsequently, four-colour FACS verified the ability to determine the biochemical effect (e.g. oxidative stress) of each specific cell type. This technique will be vital in gaining information upon cellular mechanics when using next-level, multi-cellular in vitro strategies.

Bio-identity and fate of albumin-coated SPIONs evaluated in cells and by the C. elegans model

Nanoparticles which surface adsorb proteins in an uncontrolled and non-reproducible manner will have limited uses as nanomedicinal products. A promising approach to avoid nanoparticle non-specific interactions with proteins is to design bio-hybrids by purposely pre-forming a protein corona around the inorganic cores. Here, we investigate, in vitro and in vivo, the newly acquired bio-identity of superparamagnetic iron oxide nanoparticles (SPIONs) upon their functionalization with a pre-formed and well-defined bovine serum albumin (BSA) corona. Cellular uptake, intracellular particle distribution and cytotoxicity were studied in two cell lines: adherent and non-adherent cells. BSA decreases nanoparticle internalization in both cell lines and protects the iron core once they have been internalized. The physiological response to the nanoparticles is then in vivo evaluated by oral administration to Caenorhabditis elegans, which was selected as a model of a functional intestinal barrier. Nanoparticle biodistribution, at single particle resolution, is studied by transmission electron microscopy. The analysis reveals that the acidic intestinal environment partially digests uncoated SPIONs but does not affect BSA-coated ones. It also discloses that some particles could enter the nematode's enterocytes, likely by endocytosis which is a different pathway than the one described for the worm nutrients.

STATEMENT OF SIGNIFICANCE

Unravelling meaningful relationships between the physiological impact of engineered nanoparticles and their synthetic and biological identity is of vital importance when considering nanoparticles biomedical uses and when establishing their nanotoxicological profile. This study contributes to better comprehend the inorganic nanoparticles' behavior in real biological milieus. We synthesized a controlled pre-formed BSA protein corona on SPIONs to lower unspecific cell uptake and decrease nanoparticle fouling with other proteins. Such findings may be of relevance considering clinical translation and regulatory issues of inorganic nanoparticles. Moreover, we have advanced in the validation of C. elegans as a simple animal model for assessing biological responses of engineering nanomaterials. The physiological response of BSA coated SPIONs was evaluated in vivo after their oral administration to C. elegans. Analyzing ultra-thin cross-sections of the worms by TEM with single-particle precision, we could track NP biodistribution along the digestive tract and determine unambiguously their translocation through biological barriers and cell membranes.

The impact of species and cell type on the nanosafety profile of iron oxide nanoparticles in neural cells

BACKGROUND

While nanotechnology is advancing rapidly, nanosafety tends to lag behind since general mechanistic insights into cell-nanoparticle (NP) interactions remain rare. To tackle this issue, standardization of nanosafety assessment is imperative. In this regard, we believe that the cell type selection should not be overlooked since the applicability of cell lines could be questioned given their altered phenotype. Hence, we evaluated the impact of the cell type on in vitro nanosafety evaluations in a human and murine neuroblastoma cell line, neural progenitor cell line and in neural stem cells. Acute toxicity was evaluated for gold, silver and iron oxide (IO)NPs, and the latter were additionally subjected to a multiparametric analysis to assess sublethal effects.

RESULTS

The stem cells and murine neuroblastoma cell line respectively showed most and least acute cytotoxicity. Using high content imaging, we observed cell type- and species-specific responses to the IONPs on the level of reactive oxygen species production, calcium homeostasis, mitochondrial integrity and cell morphology, indicating that cellular homeostasis is impaired in distinct ways.

CONCLUSIONS

Our data reveal cell type-specific toxicity profiles and demonstrate that a single cell line or toxicity end point will not provide sufficient information on in vitro nanosafety. We propose to identify a set of standard cell lines for screening purposes and to select cell types for detailed nanosafety studies based on the intended application and/or expected exposure.

Quantification of intracellular payload release from polymersome nanoparticles

Polymersome nanoparticles (PMs) are attractive candidates for spatio-temporal controlled delivery of therapeutic agents. Although many studies have addressed cellular uptake of solid nanoparticles, there is very little data available on intracellular release of molecules encapsulated in membranous carriers, such as polymersomes. Here, we addressed this by developing a quantitative assay based on the hydrophilic dye, fluorescein. Fluorescein was encapsulated stably in PMs of mean diameter 85 nm, with minimal leakage after sustained dialysis. No fluorescence was detectable from fluorescein PMs, indicating quenching. Following incubation of L929 cells with fluorescein PMs, there was a gradual increase in intracellular fluorescence, indicating PM disruption and cytosolic release of fluorescein. By combining absorbance measurements with flow cytometry, we quantified the real-time intracellular release of a fluorescein at a single-cell resolution. We found that 173 ± 38 polymersomes released their payload per cell, with significant heterogeneity in uptake, despite controlled synchronisation of cell cycle. This novel method for quantification of the release of compounds from nanoparticles provides fundamental information on cellular uptake of nanoparticle-encapsulated compounds. It also illustrates the stochastic nature of population distribution in homogeneous cell populations, a factor that must be taken into account in clinical use of this technology.

Misinterpretation in Nanotoxicology: A Personal Perspective

As an emerging field, nanotoxicology is gaining significant interest from scientists as well as from international regulatory firms in an attempt to build accumulated knowledge on this topic, which will be the basis for regulatory codes and safer nanotechnology. However, conflicting results and findings are abundant in the literature calling for more careful experimental design, result interpretation, and detailed reporting. In this perspective, we focus on misinterpretation in nanotoxicology and highlight the importance of proper experimental practice to avoid artifacts by discussing various examples from the literature.

How should the completeness and quality of curated nanomaterial data be evaluated?

Nanotechnology is of increasing significance. Curation of nanomaterial data into electronic databases offers opportunities to better understand and predict nanomaterials' behaviour. This supports innovation in, and regulation of, nanotechnology. It is commonly understood that curated data need to be sufficiently complete and of sufficient quality to serve their intended purpose. However, assessing data completeness and quality is non-trivial in general and is arguably especially difficult in the nanoscience area, given its highly multidisciplinary nature. The current article, part of the Nanomaterial Data Curation Initiative series, addresses how to assess the completeness and quality of (curated) nanomaterial data. In order to address this key challenge, a variety of related issues are discussed: the meaning and importance of data completeness and quality, existing approaches to their assessment and the key challenges associated with evaluating the completeness and quality of curated nanomaterial data. Considerations which are specific to the nanoscience area and lessons which can be learned from other relevant scientific disciplines are considered. Hence, the scope of this discussion ranges from physicochemical characterisation requirements for nanomaterials and interference of nanomaterials with nanotoxicology assays to broader issues such as minimum information checklists, toxicology data quality schemes and computational approaches that facilitate evaluation of the completeness and quality of (curated) data. This discussion is informed by a literature review and a survey of key nanomaterial data curation stakeholders. Finally, drawing upon this discussion, recommendations are presented concerning the central question: how should the completeness and quality of curated nanomaterial data be evaluated?

Time-Resolved Study of Nanoparticle Induced Apoptosis Using Microfabricated Single Cell Arrays

Cell fate decisions like apoptosis are heterogeneously implemented within a cell population and, consequently, the population response is recognized as sum of many individual dynamic events. Here, we report on the use of micro-patterned single-cell arrays for real-time tracking of nanoparticle-induced (NP) cell death in sets of thousands of cells in parallel. Annexin (pSIVA) and propidium iodide (PI), two fluorescent indicators of apoptosis, are simultaneously monitored after exposure to functionalized polystyrene (PS - NH 2) nanobeads as a model system. We find that the distribution of Annexin onset times shifts to later times and broadens as a function of decreasing NP dose. We discuss the mean time-to-death as a function of dose, and show how the EC 50 value depends both on dose and time of measurement. In addition, the correlations between the early and late apoptotic markers indicate a systematic shift from apoptotic towards necrotic cell death during the course of the experiment. Thus, our work demonstrates the potential of array-based single cell cytometry for kinetic analysis of signaling cascades in a high-throughput format.

Multiscale benchmarking of drug delivery vectors

Cross-system comparisons of drug delivery vectors are essential to ensure optimal design. An in-vitro experimental protocol is presented that separates the role of the delivery vector from that of its cargo in determining the cell response, thus allowing quantitative comparison of different systems. The technique is validated through benchmarking of the dose-response of human fibroblast cells exposed to the cationic molecule, polyethylene imine (PEI); delivered as a free molecule and as a cargo on the surface of CdSe nanoparticles and Silica microparticles. The exposure metrics are converted to a delivered dose with the transport properties of the different scale systems characterized by a delivery time, τ. The benchmarking highlights an agglomeration of the free PEI molecules into micron sized clusters and identifies the metric determining cell death as the total number of PEI molecules presented to cells, determined by the delivery vector dose and the surface density of the cargo.

Excess titanium dioxide nanoparticles on the cell surface induce cytotoxicity by hindering ion exchange and disrupting exocytosis processes

To date, considerable effort has been devoted to determine the potential toxicity of nanoparticles to cells and organisms. However, determining the mechanism of cytotoxicity induced by different types of nanoparticles remains challenging. Herein, typically low toxicity nanomaterials were used as a model to investigate the mechanism of cytotoxicity induced by low toxicity nanomaterials. We studied the effect of nano-TiO2, nano-Al2O3 and nano-SiO2 deposition films on the ion concentration on a cell-free system simulating the cell membrane. The results showed that the ion concentration of K(+), Ca(2+), Na(+), Mg(2+) and SO4(2-) decreased significantly following filtration of the prepared deposition films. More specifically, at a high nano-TiO2 concentration (200 mg L(-1)) and a long nano-TiO2 deposition time (48 h), the concentration of Na(+) decreased from 2958.01 to 2775.72, 2749.86, 2757.36, and 2719.82 mg L(-1), respectively, for the four types of nano-TiO2 studied. Likewise, the concentration of SO4(2-) decreased from 38.83 to 35.00, 35.80, 35.40, and 35.27 mg L(-1), respectively. The other two kinds of typical low toxicity nanomaterials (nano-Al2O3 and nano-SiO2) have a similar impact on the ion concentration change trend. Adsorption of ions on nanoparticles and the hydrated shell around the ions strongly hindered the ions through the nanoparticle films. The endocytosed nanoparticles could be released from the cells without inducing cytotoxicity. Hindering the ion exchange and disrupting the exocytosis process are the main factors that induce cytotoxicity in the presence of excess nano-TiO2 on the cell surface. The current findings may offer a universal principle for understanding the mechanism of cytotoxicity induced by low toxicity nanomaterials.

Radiofrequency treatment alters cancer cell phenotype

The importance of evaluating physical cues in cancer research is gradually being realized. Assessment of cancer cell physical appearance, or phenotype, may provide information on changes in cellular behavior, including migratory or communicative changes. These characteristics are intrinsically different between malignant and non-malignant cells and change in response to therapy or in the progression of the disease. Here, we report that pancreatic cancer cell phenotype was altered in response to a physical method for cancer therapy, a non-invasive radiofrequency (RF) treatment, which is currently being developed for human trials. We provide a battery of tests to explore these phenotype characteristics. Our data show that cell topography, morphology, motility, adhesion and division change as a result of the treatment. These may have consequences for tissue architecture, for diffusion of anti-cancer therapeutics and cancer cell susceptibility within the tumor. Clear phenotypical differences were observed between cancerous and normal cells in both their untreated states and in their response to RF therapy. We also report, for the first time, a transfer of microsized particles through tunneling nanotubes, which were produced by cancer cells in response to RF therapy. Additionally, we provide evidence that various sub-populations of cancer cells heterogeneously respond to RF treatment.

Impact of nanoparticles on human and environment: review of toxicity factors, exposures, control strategies, and future prospects

Nanotechnology has revolutionized the world through introduction of a unique class of materials and consumer products in many arenas. It has led to production of innovative materials and devices. Despite of their unique advantages and applications in domestic and industrial sectors, use of materials with dimensions in nanometers has raised the issue of safety for workers, consumers, and human environment. Because of their small size and other unique characteristics, nanoparticles have ability to harm human and wildlife by interacting through various mechanisms. We have reviewed the characteristics of nanoparticles which form the basis of their toxicity. This paper also reviews possible routes of exposure of nanoparticles to human body. Dermal contact, inhalation, and ingestion have been discussed in detail. As very limited data is available for long-term human exposures, there is a pressing need to develop the methods which can determine short and long-term effects of nanoparticles on human and environment. We also discuss in brief the strategies which can help to control human exposures to toxic nanoparticles. We have outlined the current status of toxicological studies dealing with nanoparticles, accomplishments, weaknesses, and future challenges.

Suppression of nanoparticle cytotoxicity approaching in vivo serum concentrations: limitations of in vitro testing for nanosafety

Nanomaterials challenge paradigms of in vitro testing because unlike molecular species, biomolecules in the dispersion medium modulate their interactions with cells. Exposing cells to nanoparticles known to cause cell death, we observed cytotoxicity suppression by increasing the amount of serum in the dispersion medium towards in vivo-relevant conditions.