Imaging approach to mechanistic study of nanoparticle interactions with the blood-brain barrier

Inducing a Transient Increase in Blood-Brain Barrier Permeability for Improved Liposomal Drug Therapy of Glioblastoma Multiforme

The blood-brain barrier (BBB) selectively controls the passage of endogenous and exogenous molecules between systemic circulation and the brain parenchyma. Nanocarrier-based drugs such as liposomes and nanoparticles are an attractive prospect for cancer therapy since they can carry a drug payload and be modified to improve targeting and retention at the desired site. However, the BBB prevents most therapeutic drugs from entering the brain, including physically restricting the passage of liposomes and nanoparticles. In this paper, we show that a low dose of systemically injected recombinant human vascular endothelial growth factor induces a short period of increased BBB permeability. We have shown increased delivery of a range of nanomedicines to the brain including contrast agents for imaging, varying sizes of nanoparticles, small molecule chemotherapeutics, tracer dyes, and liposomal chemotherapeutics. However, this effect was not uniform across all brain regions, and permeability varied depending on the drug or molecule measured. We have found that this window of BBB permeability effect is transient, with normal BBB integrity restored within 4 h. This strategy, combined with liposomal doxorubicin, was able to significantly extend survival in a mouse model of human glioblastoma. We have found no evidence of systemic toxicity, and the technique was replicated in pigs, demonstrating that this technique could be scaled up and potentially be translated to the clinic, thus allowing the use of nanocarrier-based therapies for brain disorders.

Brain Targeting by Liposome-Biomolecular Corona Boosts Anticancer Efficacy of Temozolomide in Glioblastoma Cells

Temozolomide (TMZ) is the current first-line chemotherapy for treatment of glioblastoma multiforme (GBM). However, similar to other brain therapeutic compounds, access of TMZ to brain tumors is impaired by the blood-brain barrier (BBB) leading to poor response for GBM patients. To overcome this major hurdle, we have synthesized a set of TMZ-encapsulating nanomedicines made of four cationic liposome (CL) formulations with systematic changes in lipid composition and physical-chemical properties. The targeting nature of this nanomedicine is provided by the recruitment of proteins, with natural targeting capacity, in the biomolecular corona (BC) layer that forms around CLs after exposure to human plasma (HP). TMZ-loaded CL-BC complexes were thoroughly characterized by dynamic light scattering (DLS), electrophoretic light scattering (ELS), and nanoliquid chromatography tandem mass spectrometry (nano-LC MS/MS). BCs were found to be enriched of typical BC fingerprints (BCFs) (e.g., Apolipoproteins, Vitronectin, and vitamin K-dependent protein), which have a substantial capacity in binding to receptors that are overexpressed at the BBB (e.g., scavenger receptor class B, type I and low-density lipoprotein receptor). We found that the CL formulation exhibiting the highest levels of targeting BCFs had larger uptake in human umbilical vein endothelial cells (HUVECs) that are commonly used as an in vitro model of the BBB. This formulation could also deliver TMZ to the human glioblastoma U-87 MG cell line and thus substantially enhance their antitumor efficacy compared to corona free CLs. Thus, we propose that the BC-based nanomedicines may pave a more effective way for efficient treatment of GBM.

Probing Amino Acid Interaction with a Polystyrene Nanoparticle Surface Using Saturation-Transfer Difference (STD)-NMR

The interaction between individual amino acids and the surface of carboxylate-modified polystyrene nanoparticles in solution was studied using Saturation-Transfer Difference (STD)-Nuclear Magnetic Resonance (NMR). Individual amino acids were screened for nanoparticle binding using an STD-NMR experiment at a fixed saturation time, and STD buildup curves were measured for those amino acids that exhibited significant STD difference signals in the initial screening. The strongest STD effects were measured for protons of aromatic side chains, with relatively weaker effects observed for protons in long-chain aliphatic and positively charged side chains. This indicates that there are several modes of binding to these polystyrene nanoparticles: electrostatic attraction between the negatively charged surface of the carboxylate-modified polystyrene nanoparticle and positively charged amino acids, hydrophobic effects between long aliphatic side chains and the nanoparticle surface, and π-π interactions between aromatic amino acids and aromatic groups in styrene. This information can be used in future studies to predict and understand interactions between nanoparticle surfaces and specific amino acid residues in small peptides and proteins.

Effect of the development of a cell barrier on nanoparticle uptake in endothelial cells

In order to improve the current success of nanomedicine, a better understanding of how nano-sized materials interact with and are processed by cells is required. Typical in vitro nanoparticle-cell interaction studies often make use of cells cultured at different cell densities. However, in vivo, for their successful delivery to the target tissue, nanomedicines need to overcome several barriers, such as endothelial and epithelial cell barriers. Unlike sub-confluent or confluent cell cultures, cell barriers are tight cell monolayers, expressing a series of specialized tight junction proteins between adjacent cells to limit paracellular transport and ensure close cell-to-cell interactions. A clear understanding on how the development of cells into a cell barrier may affect the uptake of nano-sized drug carriers is still missing. To this aim, here, human primary umbilical vein endothelial cells (HUVEC) are used as a model cell line to form endothelial cell barriers. Then, nanoparticle uptake is assessed in the developed endothelial barriers and compared to the uptake in sub-confluent or confluent HUVEC cultures. The results clearly show that the organization of cells into a cell barrier leads to a differential gene expression of endocytic markers, and - interestingly - this is accompanied by reduced nanoparticle uptake levels. Transport inhibitors are used to characterise the mechanisms involved in the uptake. However, we show that some of them can strongly compromise barrier integrity, thus impairing the interpretation of the outcomes, and overall, only a partial inhibition of nanoparticle uptake could be obtained.

Graphene Oxide Upregulates the Homeostatic Functions of Primary Astrocytes and Modulates Astrocyte-to-Neuron Communication

Graphene-based materials are the focus of intense research efforts to devise novel theranostic strategies for targeting the central nervous system. In this work, we have investigated the consequences of long-term exposure of primary rat astrocytes to pristine graphene (GR) and graphene oxide (GO) flakes. We demonstrate that GR/GO interfere with a variety of intracellular processes as a result of their internalization through the endolysosomal pathway. Graphene-exposed astrocytes acquire a more differentiated morphological phenotype associated with extensive cytoskeletal rearrangements. Profound functional alterations are induced by GO internalization, including the upregulation of inward-rectifying K⁺ channels and of Na⁺-dependent glutamate uptake, which are linked to the astrocyte capacity to control the extracellular homeostasis. Interestingly, GO-pretreated astrocytes promote the functional maturation of cocultured primary neurons by inducing an increase in intrinsic excitability and in the density of GABAergic synapses. The results indicate that graphene nanomaterials profoundly affect astrocyte physiology in vitro with consequences for neuronal network activity. This work supports the view that GO-based materials could be of great interest to address pathologies of the central nervous system associated with astrocyte dysfunctions.

Uptake and transcytosis of functionalized superparamagnetic iron oxide nanoparticles in an in vitro blood brain barrier model

Two major hurdles in nanomedicine are the limited strategies for synthesizing stealth nanoparticles and the poor efficacy of the nanoparticles in translocating across the blood brain barrier (BBB). Here we examined the uptake and transcytosis of iron oxide nanoparticles (IONPs) grafted with biomimetic phosphorylcholine (PC) brushes in an in vitro BBB model system, and compared them with bare, PEG or PC-PEG mixture grafted IONPs. Hyperspectral imaging indicated IONP co-localization with cells. Quantitative analysis with total reflection X-ray fluorescence spectrometry showed that after 24 h, 78% of PC grafted, 68-69% of PEG or PC-PEG grafted, and 30% of bare IONPs were taken up by the BBB. Transcytosis of IONPs was time-dependent and after 24 h, 16-17% of PC or PC-PEG mixture grafted IONPs had passed the BBB model, significantly more than PEG grafted or bare IONPs. These findings point out that grafting of IONPs with PC is a viable strategy for improving the uptake and transcytosis of nanoparticles.

Induction of a Na+/K+-ATPase-dependent form of autophagy triggers preferential cell death of human immunodeficiency virus type-1-infected macrophages

Although antiretroviral therapy is highly effective in suppressing human immunodeficiency virus type-1 (HIV) replication, treatment has failed to eliminate viral reservoirs and discontinuation of treatment results in viral reactivation. Here, we demonstrate that peptides Tat-vFLIP-α2 and Tat-Beclin 1/BECN1 which have been shown to induce a Na⁺/K⁺-ATPase- and a macroautophagy/autophagy-dependent form of cell death, autosis, can preferentially kill HIV-infected macrophages while preventing virological rebound. To improve bioavailability and drug delivery, Tat-vFLIP-α2 was encapsulated into biodegradable PLGA (poly lactic-co-glycolic acid)-lipid-PEG (polyethylene glycol) nanoparticles for long-lasting intracellular delivery. After a single dose of NP-vFLIP-α2, HIV-infected macrophages were preferentially killed in a dose-dependent manner compared to uninfected or untreated HIV-infected cells with complete inhibition of HIV infection at 10 μM of peptide. HIV-infected macrophages treated with NP-vFLIP-α2 exhibited increased markers of autophagy including LC3B lipidation, SQSTM1/p62 degradation and Na⁺/K⁺-ATPase expression compared to untreated uninfected or infected cells. Moreover, the increased cell death observed in HIV-infected cells was not altered by treatment with bafilomycin A₁ (BAF) or the caspase inhibitor Z-VAD-FMK, but could be reversed following treatment with the Na⁺/K⁺-ATPase inhibitor, digoxin, or knockdown of ATG5 or ATG7. NP-vFLIP-α2 induced preferential killing was also detected in HIV-infected macrophages under antiretroviral suppression without inducing viral reactivation. Additionally, we found that Na⁺/K⁺-ATPase was upregulated in HIV-infected cells, which enhanced NP-vFLIP-α2 induced cell death. These findings provide a novel strategy to eradicate HIV-infected macrophages by selectively killing infected cells through the induction of Na⁺/K⁺-ATPase dependent autophagy, while preventing reactivation of virus and new infection of uninfected bystander cells.

Nano-delivery systems for encapsulation of dietary polyphenols: An experimental approach for neurodegenerative diseases and brain tumors

Neurodegenerative diseases (NDs) and brain tumors are severe, disabling, and incurable disorders that represent a critical problem regarding human suffering and the economic burden on the healthcare system. Because of the lack of effective therapies to treat NDs and brain tumors, the challenge for physicians is to discover new drugs to improve their patients' quality of life. In addition to risk factors such as genetics and environmental influences, increased cellular oxidative stress has been reported as one of the potential common etiologies in both disorders. Given their antioxidant and anti-inflammatory potential, dietary polyphenols are considered to be one of the most bioactive natural agents in chronic disease prevention and treatment. Despite the protective activity of polyphenols, their inefficient delivery systems and poor bioavailability strongly limit their use in medicine and functional food. A potential solution lies in polymeric nanoparticle-based polyphenol delivery systems that are able to enhance their absorption across the gastrointestinal tract, improve their bioavailability, and transport them to target organs. In the present manuscript, we provide an overview of the primary polyphenols used for ND and brain tumor prevention and treatment by focusing on recent findings, the principal factors limiting their application in clinical practice, and a promising delivery strategy to improve their bioavailability.

Interfacing Graphene-Based Materials With Neural Cells

The scientific community has witnessed an exponential increase in the applications of graphene and graphene-based materials in a wide range of fields, from engineering to electronics to biotechnologies and biomedical applications. For what concerns neuroscience, the interest raised by these materials is two-fold. On one side, nanosheets made of graphene or graphene derivatives (graphene oxide, or its reduced form) can be used as carriers for drug delivery. Here, an important aspect is to evaluate their toxicity, which strongly depends on flake composition, chemical functionalization and dimensions. On the other side, graphene can be exploited as a substrate for tissue engineering. In this case, conductivity is probably the most relevant amongst the various properties of the different graphene materials, as it may allow to instruct and interrogate neural networks, as well as to drive neural growth and differentiation, which holds a great potential in regenerative medicine. In this review, we try to give a comprehensive view of the accomplishments and new challenges of the field, as well as which in our view are the most exciting directions to take in the immediate future. These include the need to engineer multifunctional nanoparticles (NPs) able to cross the blood-brain-barrier to reach neural cells, and to achieve on-demand delivery of specific drugs. We describe the state-of-the-art in the use of graphene materials to engineer three-dimensional scaffolds to drive neuronal growth and regeneration in vivo, and the possibility of using graphene as a component of hybrid composites/multi-layer organic electronics devices. Last but not least, we address the need of an accurate theoretical modeling of the interface between graphene and biological material, by modeling the interaction of graphene with proteins and cell membranes at the nanoscale, and describing the physical mechanism(s) of charge transfer by which the various graphene materials can influence the excitability and physiology of neural cells.

Neuro-Nano Interfaces: Utilizing Nano-Coatings and Nanoparticles to Enable Next-Generation Electrophysiological Recording, Neural Stimulation, and Biochemical Modulation

Neural interfaces provide a window into the workings of the nervous system-enabling both biosignal recording and modulation. Traditionally, neural interfaces have been restricted to implanted electrodes to record or modulate electrical activity of the nervous system. Although these electrode systems are both mechanically and operationally robust, they have limited utility due to the resultant macroscale damage from invasive implantation. For this reason, novel nanomaterials are being investigated to enable new strategies to chronically interact with the nervous system at both the cellular and network level. In this feature article, the use of nanomaterials to improve current electrophysiological interfaces, as well as enable new nano-interfaces to modulate neural activity via alternative mechanisms, such as remote transduction of electromagnetic fields are explored. Specifically, this article will review the current use of nanoparticle coatings to enhance electrode function, then an analysis of the cutting-edge, targeted nanoparticle technologies being utilized to interface with both the electrophysiological and biochemical behavior of the nervous system will be provided. Furthermore, an emerging, specialized-use case for neural interfaces will be presented: the modulation of the blood-brain barrier.

Neurobehavioral assessment of rats exposed to pristine polystyrene nanoplastics upon oral exposure

The increasing use of plastics has raised concerns about pollution of freshwater by these polymeric materials. Knowledge about their potential effects on environmental and public health is limited. Recent publications have suggested that the degradation of plastics will result in the release of nano-sized plastic particles to the environment. Therefore, it is of utmost importance to gain knowledge about whether and how nanoplastics affect living organisms. The present study aimed to analyse potential neurobehavioral effects of polystyrene nanoparticles (PS-NPs) after long-term exposure on rat. Potential effects of PS-NPs were investigated using four test dosages (1, 3, 6, and 10 mg PS-NPs/kg of body weight/day) administrated orally with adult Wistar male rats for five weeks. Neurobehavioral tests were chosen to assess a variety of behavioral domains. Particle diameters in test suspensions were determined through dynamic light scattering and showed an average hydrodynamic diameter of approximately 38.92 nm. No statistically significant behavioral effects were observed in all tests performed (p > 0.05). In the elevated plus maze, PS-NPs-exposed rats showed greater number of entries into open arms compared to controls. Also, PS-NPs had no significant influence on body weight of animals. Taking into account the subtle and transient nature of neurobehavioral consequences, however, these results underline the possibility of even pristine plastic nanoparticles to induce behavioral alteration in the rest of the food web, including for marine biota and humans. Indeed even though studied neurobehavioral effects in our study was not statistically significant, the observed subtle effects may be clinically considerable.

Comparative ecotoxicity of polystyrene nanoparticles in natural seawater and reconstituted seawater using the rotifer Brachionus plicatilis

The impact of nanoplastics using model polystyrene nanoparticles (PS NPs), anionic (PS-COOH) and cationic (PS-NH₂), has been investigated on the marine rotifer Brachionus plicatilis, a major component of marine zooplanktonic species. The role of different surface charges in affecting PS NP behaviour and toxicity has been considered in high ionic strength media. To this aim, the selected media were standardized reconstituted seawater (RSW) and natural sea water (NSW), the latter resembling more natural exposure scenarios. Hatched rotifer larvae were exposed for 24h and 48h to both PS NPs in the range of 0.5-50μg/ml using PS NP suspensions made in RSW and NSW. No effects on lethality upon exposure to anionic NPs were observed despite a clear gut retention was evident in all exposed rotifers. On the contrary, cationic NPs caused lethality to rotifer larvae but LC₅₀ values resulted lower in rotifers exposed in RSW (LC₅₀=2.75±0.67µg/ml) compared to those exposed in NSW (LC₅₀=6.62±0.87µg/ml). PS NPs showed similar pattern of aggregation in both high ionic strength media (RSW and NSW) but while anionic NPs resulted in large microscale aggregates (Z-average 1109 ± 128nm and 998±67nm respectively), cationic NP aggregates were still in nano-size forms (93.99 ± 11.22nm and 108.3 ± 12.79nm). Both PDI and Z-potential of PS NPs slightly differed in the two media suggesting a role of their different surface charges in affecting their behaviour and stability. Our findings confirm the role of surface charges in nanoplastic behaviour in salt water media and provide a first evidence of a different toxicity in rotifers using artificial media (RSW) compared to natural one (NSW). Such evidence poses the question on how to select the best medium in standardized ecotoxicity assays in order to properly assess their hazard to marine life in natural environmental scenarios.

Cellular uptake and intracellular localization of poly (acrylic acid) nanoparticles in a rainbow trout (Oncorhynchus mykiss) gill epithelial cell line, RTgill-W1

The ever-growing production of engineered nanoparticles (NPs) for use in many agricultural, commercial, consumer, and industrial applications will lead to their accidental or intentional release into the environment. Potential routes of environmental exposure include manufacturing or transport spills, disposal of NP-containing products down the drain and/or in landfills, as well as direct usage on agricultural land. Therefore, NPs will inevitably contaminate aquatic environments and interact with resident organisms. However, there is limited information regarding the mechanisms that regulate NP transport into fish from the environment. Thus, our primary objective was to elucidate the mechanism(s) underlying cellular uptake and intracellular fate of 3-9nm poly (acrylic acid) NPs loaded with the fluorescent dye Nile red using a rainbow trout (Oncorhynchus mykiss) gill epithelial cell line (RTgill-W1). In vitro measurements with NP-treated RTgill-W1 cells were carried out using a combination of laser scanning confocal microscopy, flow cytometry, fluorescent biomarkers (transferrin, cholera toxin B subunit, and dextran), endocytosis inhibitors (chlorpromazine, genistein, and wortmannin), and stains (4', 6-diamidino-2-phenylindole, Hoechst 33342, CellMask Deep Red, and LysoTracker Yellow). Clathrin-mediated endocytosis (CME), caveolae-mediated endocytosis and macropinocytosis pathways were active in RTgill-W1 cells, and these pathways were exploited by the non-cytotoxic NPs to enter these cells. We have demonstrated that NP uptake by RTgill-W1 cells was impeded when clathrin-coated pit formation was blocked by chlorpromazine. Furthermore, colocalization analysis revealed a moderate positive relationship between NPs and LysoTracker Yellow-positive lysosomal compartments indicating that CME was the dominant operative mechanism involved in NP internalization by RTgill-W1 cells. Overall, our results clearly show that fish gill epithelial cells internalized NPs via energy-dependent endocytotic processes. This study enhances our understanding of complex NP-cell interactions and the results obtained in vitro imply a potential risk to aquatic organisms.

Towards a classification strategy for complex nanostructures

The range of possible nanostructures is so large and continuously growing, that collating and unifying the knowledge connected to them, including their biological activity, is a major challenge. Here we discuss a concept that is based on the connection of microscopic features of the nanomaterials to their biological impacts. We also consider what would be necessary to identify the features that control their biological interactions, and make them resemble each other in a biological context.

Influence of Size and Shape on the Anatomical Distribution of Endotoxin-Free Gold Nanoparticles

The transport and the delivery of drugs through nanocarriers is a great challenge of pharmacology. Since the production of liposomes to reduce the toxicity of doxorubicin in patients, a plethora of nanomaterials have been produced and characterized. Although it is widely known that elementary properties of nanomaterials influence their in vivo kinetics, such interaction is often poorly investigated in many preclinical studies. The present study aims to evaluate the actual effect of size and shape on the biodistribution of a set of gold nanoparticles (GNPs) after intravenous administration in mice. To this goal, quantitative data achieved by inductively coupled plasma mass spectrometry and observational results emerging from histochemistry (autometallography and enhanced dark-field hyperspectral microscopy) were combined. Since the immune system plays a role in bionano-interaction we used healthy immune-competent mice. To keep the immune surveillance on the physiological levels we synthesized endotoxin-free GNPs to be tested in specific pathogen-free animals. Our study mainly reveals that (a) the size and the shape greatly influence the kinetics of accumulation and excretion of GNPs in filter organs; (b) spherical and star-like GNPs showed the same percentage of accumulation, but a different localization in liver; (c) only star-like GNPs are able to accumulate in lung; (d) changes in the geometry did not improve the passage of the blood brain barrier. Overall, this study can be considered as a reliable starting point to drive the synthesis and the functionalization of potential candidates for theranostic purposes in many fields of research.

The effect of nanoparticle size on the ability to cross the blood-brain barrier: an in vivo study

AIM

Our goal was to develop an efficient nanoparticle-based system that can overcome the restrictive mechanism of the blood-brain barrier (BBB) by targeting insulin receptors and would thus enable drug delivery to the brain.

METHODS

Insulin-coated gold nanoparticles (INS-GNPs) were synthesized to serve as a BBB transport system. The effect of nanoparticle size (20, 50 and 70 nm) on their ability to cross the BBB was quantitatively investigated in Balb/C mice.

RESULTS

The most widespread biodistribution and highest accumulation within the brain were observed using 20 nm INS-GNPs, 2 h post injection. In vivo CT imaging revealed that particles migrated to specific brain regions, which are involved in neurodegenerative and neuropsychiatric disorders.

CONCLUSION

These findings promote the optimization of nanovehicles for transport of drugs through the BBB. The insulin coating of the particles enabled targeting of specific brain regions, suggesting the potential use of INS-GNPs for delivery of various treatments for brain-related disorders.

Blood-brain-barrier spheroids as an in vitro screening platform for brain-penetrating agents

Culture-based blood–brain barrier (BBB) models are crucial tools to enable rapid screening of brain-penetrating drugs. However, reproducibility of in vitro barrier properties and permeability remain as major challenges. Here, we report that self-assembling multicellular BBB spheroids display reproducible BBB features and functions. The spheroid core is comprised mainly of astrocytes, while brain endothelial cells and pericytes encase the surface, acting as a barrier that regulates transport of molecules. The spheroid surface exhibits high expression of tight junction proteins, VEGF-dependent permeability, efflux pump activity and receptor-mediated transcytosis of angiopep-2. In contrast, the transwell co-culture system displays comparatively low levels of BBB regulatory proteins, and is unable to discriminate between the transport of angiopep-2 and a control peptide. Finally, we have utilized the BBB spheroids to screen and identify BBB-penetrant cell-penetrating peptides (CPPs). This robust in vitro BBB model could serve as a valuable next-generation platform for expediting the development of CNS therapeutics.

In vitro blood-brain barrier (BBB) models are crucial tools for screening brain-penetrating compounds. Here the authors develop a self-assembling BBB spheroid model with superior performance to the standard transwell BBB model, and use their platform to identify cell-penetrating peptides that can cross the BBB.

Low uptake of silica nanoparticles in Caco-2 intestinal epithelial barriers

Cellular barriers, such as the skin, the lung epithelium or the intestinal epithelium, constitute one of the first obstacles facing nanomedicines or other nanoparticles entering organisms. It is thus important to assess the capacity of nanoparticles to enter and transport across such barriers. In this work, Caco-2 intestinal epithelial cells were used as a well-established model for the intestinal barrier, and the uptake, trafficking and translocation of model silica nanoparticles of different sizes were investigated using a combination of imaging, flow cytometry and transport studies. Compared to typical observations in standard cell lines commonly used for in vitro studies, silica nanoparticle uptake into well-developed Caco-2 cellular barriers was found to be very low. Instead, nanoparticle association to the apical outer membrane was substantial and these particles could easily be misinterpreted as internalised in the absence of imaging. Passage of nanoparticles through the barrier was very limited, suggesting that the low amount of internalised nanoparticles was due to reduced uptake into cells, rather than a considerable transport through them.

Nanoparticle diffusion in crowded and confined media

We identify distinct mechanisms controlling slowing of nanoparticle diffusion through complex media featuring both rigid geometrical confinement and soft mobile crowders. Towards this end, we use confocal microscopy and single particle tracking to probe the diffusion of 400 nm nanoparticles suspended in Newtonian water, in a Newtonian glycerol/water mixture, or in a non-Newtonian polymer solution through a model porous medium, a packed bed of microscale glass beads. The mobility of nanoparticles, as quantified by the long-time diffusion coefficient extracted from the particle mean-squared displacement, slows as the average pore size of the packed bed media decreases for both Newtonian and non-Newtonian solutions. The distribution of particle displacements is non-Gaussian, consistent with the spatial heterogeneity of the geometrical confinement imposed by the packed bed. The slowing of nanoparticle mobility in all solutions follows the predictions of models that describe hydrodynamic interactions with the packed bed. In non-Newtonian solutions, depletion interactions due to the polymers near the glass beads result in temporary adsorption of particles onto the bead surface, as indicated by a stretched-exponential distribution of residence times. Our results therefore suggest that the confined diffusive dynamics of nanoparticles in polymer solutions is controlled by two competing mechanisms: hydrodynamic interactions between particles and spatial obstacles, which dictate the long-time slowing of diffusion, and depletion interactions between particles and confining walls due to the macromolecules, which control transient adsorption and hence alter the statistics of the short-time motion.

Effects of nanomaterials on marine invertebrates

The development of nanotechnology will inevitably lead to the release of consistent amounts of nanomaterials (NMs) and nanoparticles (NPs) into marine ecosystems. Ecotoxicological studies have been carried out to identify potential biological targets of NPs, and suitable models for predicting their impact on the health of the marine environment. Recent studies in invertebrates mainly focused on NP accumulation and sub-lethal effects, rather than acute toxicity. Among marine invertebrates, bivalves represent by large the most studied group, with polychaetes and echinoderms also emerging as significant targets of NPs. However, major scientific gaps still need to be filled. In this work, factors affecting the fate of NPs in the marine environment, and their consequent uptake/accumulation/toxicity in marine invertebrates will be summarized. The results show that in different model species, NP accumulation mainly occurs in digestive tract and gills. Data on sub-lethal effects and modes of action of different types of NPs (mainly metal oxides and metal based NPs) in marine invertebrates will be reviewed, in particular on immune function, oxidative stress and embryo development. Moreover, the possibility that such effects may be influenced by NP interactions with biomolecules in both external and internal environment will be introduced. In natural environmental media, NP interactions with polysaccharides, proteins and colloids may affect their agglomeration/aggregation and consequent bioavailability. Moreover, once within the organism, NPs are known to interact with plasma proteins, forming a protein corona that can affect particle uptake and toxicity in target cells in a physiological environment. These interactions, leading to the formation of eco-bio-coronas, may be crucial in determining particle behavior and effects also in marine biota. In order to classify NPs into groups and predict the implications of their release into the marine environment, information on their intrinsic properties is clearly insufficient, and a deeper understanding of NP eco/bio-interactions is required.

Ultra-small lipid-polymer hybrid nanoparticles for tumor-penetrating drug delivery

Lipid-polymer hybrid nanoparticles, consisting of a polymeric core coated by a layer of lipids, are a class of highly scalable, biodegradable nanocarriers that have shown great promise in drug delivery applications. Here, we demonstrate the facile synthesis of ultra-small, sub-25 nm lipid-polymer hybrid nanoparticles using an adapted nanoprecipitation approach and explore their utility for targeted delivery of a model chemotherapeutic. The fabrication process is first optimized to produce a monodisperse population of particles that are stable under physiological conditions. It is shown that these ultra-small hybrid nanoparticles can be functionalized with a targeting ligand on the surface and loaded with drug inside the polymeric matrix. Further, the in vivo fate of the nanoparticles after intravenous injection is characterized by examining the blood circulation and biodistribution. In a final proof-of-concept study, targeted ultra-small hybrid nanoparticles loaded with the cancer drug docetaxel are used to treat a mouse tumor model and demonstrate improved efficacy compared to a clinically available formulation of the drug. The ability to synthesize a significantly smaller version of the established lipid-polymer hybrid platform can ultimately enhance its applicability across a wider range of applications.

Graphene Oxide Nanosheets Disrupt Lipid Composition, Ca(2+) Homeostasis, and Synaptic Transmission in Primary Cortical Neurons

Graphene has the potential to make a very significant impact on society, with important applications in the biomedical field. The possibility to engineer graphene-based medical devices at the neuronal interface is of particular interest, making it imperative to determine the biocompatibility of graphene materials with neuronal cells. Here we conducted a comprehensive analysis of the effects of chronic and acute exposure of rat primary cortical neurons to few-layer pristine graphene (GR) and monolayer graphene oxide (GO) flakes. By combining a range of cell biology, microscopy, electrophysiology, and "omics" approaches we characterized the graphene-neuron interaction from the first steps of membrane contact and internalization to the long-term effects on cell viability, synaptic transmission, and cell metabolism. GR/GO flakes are found in contact with the neuronal membrane, free in the cytoplasm, and internalized through the endolysosomal pathway, with no significant impact on neuron viability. However, GO exposure selectively caused the inhibition of excitatory transmission, paralleled by a reduction in the number of excitatory synaptic contacts, and a concomitant enhancement of the inhibitory activity. This was accompanied by induction of autophagy, altered Ca(2+) dynamics, and a downregulation of some of the main players in the regulation of Ca(2+) homeostasis in both excitatory and inhibitory neurons. Our results show that, although graphene exposure does not impact neuron viability, it does nevertheless have important effects on neuronal transmission and network functionality, thus warranting caution when planning to employ this material for neurobiological applications.

In vitro screening of nanomedicines through the blood brain barrier: A critical review

The blood-brain barrier accounts for the high attrition rate of the treatments of most brain disorders, which therefore remain one of the greatest health-care challenges of the twenty first century. Against this background of hindrance to brain delivery, nanomedicine takes advantage of the assembly at the nanoscale of available biomaterials to provide a delivery platform with potential to raising brain levels of either imaging or therapeutic agents. Nevertheless, to prevent later failure due to ineffective drug levels at the target site, researchers have been endeavoring to develop a battery of in vitro screening procedures that can predict earlier in the drug discovery process the ability of these cutting-edge drug delivery platforms to cross the blood-brain barrier for biomedical purposes. This review provides an in-depth analysis of the currently available in vitro blood-brain barrier models (both cell-based and non-cell-based) with the focus on their suitability for understanding the biological brain distribution of forthcoming nanomedicines. The relationship between experimental factors and underlying physiological assumptions that would ultimately lead to a more predictive capacity of their in vivo performance, and those methods already assayed for the evaluation of the brain distribution of nanomedicines are comprehensively discussed.

Magnetic particle spectroscopy allows precise quantification of nanoparticles after passage through human brain microvascular endothelial cells

Crossing the blood-brain barrier is an urgent requirement for the treatment of brain disorders. Superparamagnetic iron oxide nanoparticles (SPIONs) are a promising tool as carriers for therapeutics because of their physical properties, biocompatibility, and their biodegradability. In order to investigate the interaction of nanoparticles with endothelial cell layers in detail, in vitro systems are of great importance. Human brain microvascular endothelial cells are a well-suited blood-brain barrier model. Apart from generating optimal conditions for the barrier-forming cell units, the accurate detection and quantification of SPIONs is a major challenge. For that purpose we use magnetic particle spectroscopy to sensitively and directly quantify the SPION-specific iron content. We could show that SPION concentration depends on incubation time, nanoparticle concentration and location. This model system allows for further investigations on particle uptake and transport at cellular barriers with regard to parameters including particles' shape, material, size, and coating.

Transcytosis-Targeting Peptide: A Conductor of Liposomal Nanoparticles through the Endothelial Cell Barrier

The ultimate goal in the area of drug-delivery systems is the development of a nanoparticle that can penetrate the endothelial cell monolayer for the targeting of tissue parenchyma. In the present study, we identify a transcytosis-targeting peptide (TTP) that permits polyethyleneglycol (PEG)-modified liposomes (PEG-LPs) to penetrate through monolayers of brain-derived endothelial cells. These endothelial cells were layered on a gelatin nanofiber sheet, a nanofiber meshwork that allows the evaluation of transcellular transport of nanosized particles (ca. 100 nm). Systematic modification of the sequences results in the identification of the consensus sequence of TTP as L(R/K)QZZZL, where Z denotes hydrophilic amino acids (R/K/S and partially D). The TTP-modified liposomes are bound on the heparin sulfate proteoglycan, and are then taken up via lipid raft-mediated endocytosis. Subsequent intracellular imaging of the particles reveals a unique intracellular sorting of TTP-modified PEG liposomes (TTP-PEG-LPs); namely the TTP-LPs are not localized with the lysosomes, whereas this co-localization is dominant in the unmodified PEG liposomes (PEG-LPs). The in vivo endothelial penetration of liposomes in adipose tissue is conferred by the dual modification of the particles with TTP and tissue-targeting ligands. This technology promises innovations in intravenously available delivery system to tissue parenchyma.

Stem Cell-Based Human Blood-Brain Barrier Models for Drug Discovery and Delivery

The development of novel neuropharmaceuticals requires the evaluation of blood-brain barrier (BBB) permeability and toxicity. Recent studies have highlighted differences in the BBB among different species, with the most important differences involving the expression of P-glycoprotein (P-gp), multidrug resistance-associated proteins, transporters, and claudins. In addition, functional studies have shown that brain pharmacokinetics of P-glycoprotein substrates are different in humans and rodents. Therefore, human BBB models may be an important platform for initial drug screening before in vivo studies. This strategy might help to reduce costs in drug development and failures in clinical studies. We review the differences in the BBB among species, recent advances in the generation of human BBB models, and their applications in drug discovery and delivery.

Quantitative analysis of nanoparticle transport through in vitro blood-brain barrier models

Nanoparticle transport through the blood-brain barrier has received much attention of late, both from the point of view of nano-enabled drug delivery, as well as due to concerns about unintended exposure of nanomaterials to humans and other organisms. In vitro models play a lead role in efforts to understand the extent of transport through the blood-brain barrier, but unique features of the nanoscale challenge their direct adaptation. Here we highlight some of the differences compared to molecular species when utilizing in vitro blood-brain barrier models for nanoparticle studies. Issues that may arise with transwell systems are discussed, together with some potential alternative methodologies. We also briefly review the biomolecular corona concept and its importance for how nanoparticles interact with the blood-brain barrier. We end with considering future directions, including indirect effects and application of shear and fluidics-technologies.

Nano-sized polystyrene affects feeding, behavior and physiology of brine shrimp Artemia franciscana larvae

Nano-sized polymers as polystyrene (PS) constitute one of the main challenges for marine ecosystems, since they can distribute along the whole water column affecting planktonic species and consequently disrupting the energy flow of marine ecosystems. Nowadays very little knowledge is available on the impact of nano-sized plastics on marine organisms. Therefore, the present study aims to evaluate the effects of 40nm anionic carboxylated (PS-COOH) and 50nm cationic amino (PS-NH2) polystyrene nanoparticles (PS NPs) on brine shrimp Artemia franciscana larvae. No signs of mortality were observed at 48h of exposure for both PS NPs at naplius stage but several sub-lethal effects were evident. PS-COOH (5-100μg/ml) resulted massively sequestered inside the gut lumen of larvae (48h) probably limiting food intake. Some of them were lately excreted as fecal pellets but not a full release was observed. Likewise, PS-NH2 (5-100µg/ml) accumulated in larvae (48h) but also adsorbed at the surface of sensorial antennules and appendages probably hampering larvae motility. In addition, larvae exposed to PS-NH2 undergo multiple molting events during 48h of exposure compared to controls. The activation of a defense mechanism based on a physiological process able to release toxic cationic NPs (PS-NH2) from the body can be hypothesized. The general observed accumulation of PS NPs within the gut during the 48h of exposure indicates a continuous bioavailability of nano-sized PS for planktonic species as well as a potential transfer along the trophic web. Therefore, nano-sized PS might be able to impair food uptake (feeding), behavior (motility) and physiology (multiple molting) of brine shrimp larvae with consequences not only at organism and population level but on the overall ecosystem based on the key role of zooplankton on marine food webs.

Destruction of amyloid fibrils by graphene through penetration and extraction of peptides

Current therapies for Alzheimer's disease (AD) can provide a moderate symptomatic reduction or delay progression at various stages of the disease, but such treatments ultimately do not arrest the advancement of AD. As such, novel approaches for AD treatment and prevention are urgently needed. We here provide both experimental and computational evidence that pristine graphene and graphene-oxide nanosheets can inhibit Aβ peptide monomer fibrillation and clear mature amyloid fibrils, thus impacting the central molecular superstructures correlated with AD pathogenesis. Our molecular dynamics simulations for the first time reveal that graphene nanosheets can penetrate and extract a large number of peptides from pre-formed amyloid fibrils; these effects seem to be related to exceptionally strong dispersion interactions between peptides and graphene that are further enhanced by strong π-π stacking between the aromatic residues of extracted Aβ peptides and the graphene surface. Atomic force microscopy images confirm these predictions by demonstrating that mature amyloid fibrils can be cut into pieces and cleared by graphene oxides. Thioflavin fluorescence assays further illustrate the detailed dynamic processes by which graphene induces inhibition of monomer aggregation and clearance of mature amyloid fibrils, respectively. Cell viability and ROS assays indicate that graphene oxide can indeed mitigate cytotoxicity of Aβ peptide amyloids. Our findings provide new insights into the underlying molecular mechanisms that define graphene-amyloid interaction and suggest that further research on nanotherapies for Alzheimer's and other protein aggregation-related diseases is warranted.

Surface decoration with gH625-membranotropic peptides as a method to escape the endo-lysosomal compartment and reduce nanoparticle toxicity

The membranotropic peptide gH625 is able to transport different cargos (i.e., liposomes, quantum dots, polymeric nanoparticles) within and across cells in a very efficient manner. However, a clear understanding of the detailed uptake mechanism remains elusive. In this work, we investigate the journey of gH625-functionalized polystyrene nanoparticles in mouse-brain endothelial cells from their interaction with the cell membrane to their intracellular final destination. The aim is to elucidate how gH625 affects the behavior of the nanoparticles and their cytotoxic effect. The results indicate that the mechanism of translocation of gH625 dictates the fate of the nanoparticles, with a relevant impact on the nanotoxicological profile of positively charged nanoparticles.

A TEM protocol for quality assurance of in vitro cellular barrier models and its application to the assessment of nanoparticle transport mechanisms across barriers

We report here a protocol to characterise and monitor the quality of in vitro human cellular barrier models using Transmission Electron Microscopy (TEM), which can be applied for transport assays, mechanistic studies and screening of drug/compound (including nanoparticle) penetration across such biological barriers. Data from two examples of biological barriers are given, namely the hCMEC/D3 endothelial blood-brain barrier model, and the Caco-2 intestinal epithelial barrier model, to show the general applicability of the method. Several aspects of this method are applicable to the quality assurance of in vitro barrier models, e.g., assessment of the multi or mono-layer structure of the endothelial cells; identification of any potential "holes" in the barrier that could confound transport assay results; validation of tight junction expression; and determination of the types and amounts of key cellular organelles present in the barrier to account for any significant changes in phenotype that may occur compared to the in vivo situation. The method described here provides a key advantage in that it prevents loss of the filter membrane during monolayer sectioning, thereby preserving critical details associated with the basal cell membrane. Applicability of the protocol for other in vitro biological barriers, such as the blood-foetus, blood-testes, blood-cerebrospinal fluid (CSF) and lung alveolar-capillary barriers is also discussed. Additionally, we demonstrate the use of the method for assessment of nanoparticle transport across cellular barriers and elucidation of transcytosis mechanisms. Sequential events of cellular endocytosis, localisation and transcytosis can be described in detail by TEM imaging, revealing useful sub-cellular details that provide evidence for the mechanism of nanoparticle transport in the hCMEC/D3 blood-brain barrier model and the Caco-2 intestinal epithelial cell model. Potential artefacts resulting from the nanoparticles interacting with the Transwell membranes can also be assessed.

Nanotoxicology: advances and pitfalls in research methodology

As research progresses, nanoparticles (NPs) are becoming increasingly promising tools for medical diagnostics and therapeutics. Despite this rise, their potential risks to human health, together with environmental issues, has led to increasing concerns regarding their use. As such, a comprehensive understanding of the interactions that occur at the nano-bio interface is required in order to design safe, reliable and efficient NPs for biomedical applications. To this end, extensive studies have been dedicated to probing the factors that define various properties of the nano-bio interface. However, the literature remains unclear and contains conflicting reports on cytotoxicity and biological fates, even for seemingly identical NPs. This uncertainty reveals that we frequently fail to identify and control relevant parameters that unambiguously and reproducibly determine the toxicity of nanoparticles, both in vitro and in vivo. An effective understanding of the toxicological impact of NPs requires the consideration of relevant factors, including the temperature of the target tissue, plasma gradient, cell shape, interfacial effects and personalized protein corona. In this review, we discuss the factors that play a critical role in nano-bio interface processes and nanotoxicity. A proper combinatorial assessment of these factors substantially changes our insight into the cytotoxicity, distribution and biological fate of NPs.

Immunogold labeling reveals subcellular localisation of silica nanoparticles in a human blood-brain barrier model

Subcellular location of nanoparticles has been widely investigated with fluorescence microscopy, via fluorescently labeled antibodies to visualise target antigens in cells. However, fluorescence microscopy, such as confocal or live cell imaging, has generally limited 3D spatial resolution. Conventional electron microscopy can be useful in bridging resolution gap, but still not ideal in resolving subcellular organelle identities. Using the pre-embedding immunogold electron microscopic imaging, we performed accurate examination of the intracellular trafficking and gathered further evidence of transport mechanisms of silica nanoparticles across a human in vitro blood-brain barrier model. Our approach can effectively immunolocalise a variety of intracellular compartments and provide new insights into the uptake and subcellular transport of nanoparticles.

Exploiting the novel properties of protein coronas: emerging applications in nanomedicine

Protein coronas have been the focus of a great deal of study recently due to their inevitable formation and their impact on the biological consequences of nanomaterials. Although the field is still far from completely and definitively understanding protein coronas, we now have a good understanding of their behavior and their key characteristics. Protein corona composition changes with the environment and time, and also the physical properties of the underlying nanoparticle. More importantly, the protein corona has significant biological impact. Because we have a basic understanding of coronas, we can now move forward to exploiting their unique properties. Here, we discuss some emerging ways in which the protein corona is explicitly utilized for different applications in biology and medicine.

Intestinal absorption of fluorescently labeled nanoparticles

Characterization of intestinal absorption of nanoparticles is critical in the design of noninvasive anticancer, protein-based, and gene nanoparticle-based therapeutics. Here we demonstrate a general approach for the characterization of the intestinal absorption of nanoparticles and for understanding the mechanisms active in their processing within healthy intestinal cells. It is generally accepted that the cellular processing represents a major drawback of current nanoparticle-based therapeutic systems. In particular, endolysosomal trafficking causes degradation of therapeutic molecules such as proteins, lipids, acid-sensitive anticancer drugs, and genes. To date, investigations into nanoparticle processing within intestinal cells have studied mass transport through Caco-2 cells or everted rat intestinal sac models. We developed an approach to visualize directly the mechanisms of nanoparticle processing within intestinal tissue. These results clearly identify a mechanism by which healthy intestinal cells process nanoparticles and point to the possible use of this approach in the design of noninvasive nanoparticle-based therapies.

FROM THE CLINICAL EDITOR

Advances in nanomedicine have resulted in the development of new therapies for various diseases. Intestinal route of administration remains the easiest and most natural. The authors here designed experiments to explore and characterize the process of nanoparticle transport across the intestinal tissue. In so doing, further insights were gained for future drug design.

Different endocytotic uptake mechanisms for nanoparticles in epithelial cells and macrophages

Precise knowledge regarding cellular uptake of nanoparticles is of great importance for future biomedical applications. Four different endocytotic uptake mechanisms, that is, phagocytosis, macropinocytosis, clathrin- and caveolin-mediated endocytosis, were investigated using a mouse macrophage (J774A.1) and a human alveolar epithelial type II cell line (A549). In order to deduce the involved pathway in nanoparticle uptake, selected inhibitors specific for one of the endocytotic pathways were optimized regarding concentration and incubation time in combination with fluorescently tagged marker proteins. Qualitative immunolocalization showed that J774A.1 cells highly expressed the lipid raft-related protein flotillin-1 and clathrin heavy chain, however, no caveolin-1. A549 cells expressed clathrin heavy chain and caveolin-1, but no flotillin-1 uptake-related proteins. Our data revealed an impeded uptake of 40 nm polystyrene nanoparticles by J774A.1 macrophages when actin polymerization and clathrin-coated pit formation was blocked. From this result, it is suggested that macropinocytosis and phagocytosis, as well as clathrin-mediated endocytosis, play a crucial role. The uptake of 40 nm nanoparticles in alveolar epithelial A549 cells was inhibited after depletion of cholesterol in the plasma membrane (preventing caveolin-mediated endocytosis) and inhibition of clathrin-coated vesicles (preventing clathrin-mediated endocytosis). Our data showed that a combination of several distinguishable endocytotic uptake mechanisms are involved in the uptake of 40 nm polystyrene nanoparticles in both the macrophage and epithelial cell line.