Effects of the presence or absence of a protein corona on silica nanoparticle uptake and impact on cells

Nanoparticles inhibit DNA replication by binding to DNA: modeling and experimental validation

Predictive models are beneficial tools for researchers to use in prioritizing nanoparticles (NPs) for toxicological tests, but experimental evaluation can be time-consuming and expensive, and thus, priority should be given to tests that identify the NPs most likely to be harmful. For characterization of NPs, the physical binding of NPs to DNA molecules is important to measure, as interference with DNA function may be one cause of toxicity. Here, we determined the interaction energy between 12 types of NPs and DNA based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) model and then predicted the affinity of the NPs for DNA. Using the single-molecule imaging technique known as atomic force microscopy (AFM), we experimentally determined the binding affinity of those NPs for DNA. Theoretical predictions and experimental observations of the binding affinity agreed well. Furthermore, the effect of NPs on DNA replication in vitro was investigated with the polymerase chain reaction (PCR) technique. The results showed that NPs with a high affinity for DNA strongly inhibited DNA replication, whereas NPs with low affinity had no or minimal effects on DNA replication. The methodology here is expected to benefit the genotoxicological testing of NPs as well as the design of safe NPs.

Alzheimer's disease: pathophysiology and applications of magnetic nanoparticles as MRI theranostic agents

Alzheimer's disease (AD) is the most common form of dementia. During the recent decade, nanotechnology has been widely considered, as a promising tool, for theranosis (diagnosis and therapy) of AD. Here we first discuss pathophysiology and characteristics of AD with a focus on the amyloid cascade hypothesis. Then magnetic nanoparticles (MNPs) and recent works on their applications in AD, focusing on the superparamagnetic iron oxide nanoparticles (SPIONs), are reviewed. Furthermore, the amyloid-nanoparticle interaction is highlighted, with the scope to be highly considered by the scientists aiming for diagnostics and/or treatment of AD employing nanoparticles. Furthermore, recent findings on the "ignored" parameters (e.g., effect of protein "corona" at the surface of nanoparticles on amyloid-β (Aβ) fibrillation process) are discussed.

Revealing the binding structure of the protein corona on gold nanorods using synchrotron radiation-based techniques: understanding the reduced damage in cell membranes

Regarding the importance of the biological effects of nanomaterials, there is still limited knowledge about the binding structure and stability of the protein corona on nanomaterials and the subsequent impacts. Here we designed a hard serum albumin protein corona (BSA) on CTAB-coated gold nanorods (AuNRs) and captured the structure of protein adsorption using synchrotron radiation X-ray absorption spectroscopy, microbeam X-ray fluorescent spectroscopy, and circular dichroism in combination with molecular dynamics simulations. The protein adsorption is attributed to at least 12 Au-S bonds and the stable corona reduced the cytotoxicity of CTAB/AuNRs. These combined strategies using physical, chemical, and biological approaches will improve our understanding of the protective effects of protein coronas against the toxicity of nanomaterials. These findings have shed light on a new strategy for studying interactions between proteins and nanomaterials, and this information will help further guide the rational design of nanomaterials for safe and effective biomedical applications.

Silica nanoparticles for cell imaging and intracellular sensing

There is increasing interest in the use of nanoparticles (NPs) for biomedical applications. In particular, nanobiophotonic approaches using fluorescence offers the potential of high sensitivity and selectivity in applications such as cell imaging and intracellular sensing. In this review, we focus primarily on the use of fluorescent silica NPs for these applications and, in so doing, aim to enhance and complement the key recent review articles on these topics. We summarize the main synthetic approaches, namely the Stöber and microemulsion processes, and, in this context, we deal with issues in relation to both covalent and physical incorporation of different types of dyes in the particles. The important issue of NP functionalization for conjugation to biomolecules is discussed and strategies published in the recent literature are highlighted and evaluated. We cite recent examples of the use of fluorescent silica NPs for cell imaging in the areas of cancer, stem cell and infectious disease research, and we review the current literature on the use of silica NPs for intracellular sensing of oxygen, pH and ionic species. We include a short final section which seeks to identify the main challenges and obstacles in relation to the potential widespread use of these particles for in vivo diagnostics and therapeutics.

Myoglobin on silica: a case study of the impact of adsorption on protein structure and dynamics

If protein structure and function changes upon adsorption are well documented, modification of adsorbed protein dynamics remains a blind spot, despite its importance in biological processes. The adsorption of metmyoglobin on a silica surface was studied by isotherm measurements, microcalorimetry, circular dichroïsm, and UV-visible spectroscopy to determine the thermodynamic parameters of protein adsorption and consequent structure modifications. The mean square displacement and the vibrational densities of states of the adsorbed protein were measured by elastic and inelastic neutron scattering experiments. A decrease of protein flexibility and depletion in low frequency modes of myoglobin after adsorption on silica was observed. Our results suggest that the structure loss itself is not the entropic driving force of adsorption.

Mussel-inspired polydopamine: a biocompatible and ultrastable coating for nanoparticles in vivo

Bioinspired polydopamine (PDA) has served as a universal coating to nanoparticles (NPs) for various biomedical applications. However, one remaining critical question is whether the PDA shell on NPs is stable in vivo. In this study, we modified gold nanoparticles (GNPs) with finely controlled PDA nanolayers to form uniform core/shell nanostructures (GNP@PDA). In vitro study showed that the PDA-coated GNPs had low cytotoxicity and could smoothly translocate to cancer cells. Transmission electron microscopy (TEM) analysis demonstrated that the PDA nanoshells were intact within cells after 24 h incubation. Notably, we found the GNP@PDA could partially escape from the endosomes/lysosomes to cytosol and locate close to the nucleus. Furthermore, we observed that the PDA-coated NPs have very different uptake behavior in two important organs of the liver and spleen: GNP@PDA in the liver were mainly uptaken by the Kupffer cells, while the GNP@PDA in the spleen were uptaken by a variety of cells. Importantly, we proved the PDA nanoshells were stable within cells of the liver and spleen for at least six weeks, and GNP@PDA did not show notable histological toxicity to main organs of mice in a long time. These results provided the direct evidence to support that the PDA surface modification can serve as an effective strategy to form ultrastable coatings on NPs in vivo, which can improve the intracellular delivery capacity and biocompatibility of NPs for biomedical application.

Rapid formation of plasma protein corona critically affects nanoparticle pathophysiology

In biological fluids, proteins bind to the surface of nanoparticles to form a coating known as the protein corona, which can critically affect the interaction of the nanoparticles with living systems. As physiological systems are highly dynamic, it is important to obtain a time-resolved knowledge of protein-corona formation, development and biological relevancy. Here we show that label-free snapshot proteomics can be used to obtain quantitative time-resolved profiles of human plasma coronas formed on silica and polystyrene nanoparticles of various size and surface functionalization. Complex time- and nanoparticle-specific coronas, which comprise almost 300 different proteins, were found to form rapidly (<0.5 minutes) and, over time, to change significantly in terms of the amount of bound protein, but not in composition. Rapid corona formation is found to affect haemolysis, thrombocyte activation, nanoparticle uptake and endothelial cell death at an early exposure time.

Negatively charged metal oxide nanoparticles interact with the 20S proteasome and differentially modulate its biologic functional effects

The multicatalytic ubiquitin-proteasome system (UPS) carries out proteolysis in a highly orchestrated way and regulates a large number of cellular processes. Deregulation of the UPS in many disorders has been documented. In some cases, such as carcinogenesis, elevated proteasome activity has been implicated in disease development, while the etiology of other diseases, such as neurodegeneration, includes decreased UPS activity. Therefore, agents that alter proteasome activity could suppress as well as enhance a multitude of diseases. Metal oxide nanoparticles, often developed as diagnostic tools, have not previously been tested as modulators of proteasome activity. Here, several types of metal oxide nanoparticles were found to adsorb to the proteasome and show variable preferential binding for particular proteasome subunits with several peptide binding "hotspots" possible. These interactions depend on the size, charge, and concentration of the nanoparticles and affect proteasome activity in a time-dependent manner. Should metal oxide nanoparticles increase proteasome activity in cells, as they do in vitro, unintended effects related to changes in proteasome function can be expected.

Silver nanoparticle protein corona composition in cell culture media

The potential applications of nanomaterials as drug delivery systems and in other products continue to expand. Upon introduction into physiological environments and driven by energetics, nanomaterials readily associate proteins forming a protein corona (PC) on their surface. This PC influences the nanomaterial's surface characteristics and may impact their interaction with cells. To determine the biological impact of nanomaterial exposure as well as nanotherapeutic applications, it is necessary to understand PC formation. Utilizing a label-free mass spectrometry-based proteomics approach, we examined the composition of the PC for a set of four silver nanoparticles (AgNPs) including citrate-stabilized and polyvinlypyrrolidone-stabilized (PVP) colloidal silver (20 or 110 nm diameter). To simulate cell culture conditions, AgNPs were incubated for 1 h in Dulbecco's Modified Eagle Medium supplemented with 10% fetal bovine serum, washed, coronal proteins solubilized, and proteins identified and quantified by label-free LC-MS/MS. To determine which attributes influence PC formation, the AgNPs were characterized in both water and cell culture media with 10% FBS. All AgNPs associated a common subset of 11 proteins including albumin, apolipoproteins, keratins, and other serum proteins. 110 nm citrate- and PVP-stabilized AgNPs were found to bind the greatest number of proteins (79 and 85 respectively) compared to 20 nm citrate- and PVP-stabilized AgNPs (45 and 48 respectively), suggesting a difference in PC formation based on surface curvature. While no relationships were found for other protein parameters (isoelectric point or aliphatic index), the PC on 20 nm AgNPs (PVP and citrate) consisted of more hydrophobic proteins compared to 110 nm AgNPs implying that this class of proteins are more receptive to curvature-induced folding and crowding in exchange for an increased hydration in the aqueous environment. These observations demonstrate the significance of electrostatic and hydrophobic interactions in the formation of the PC which may have broad biological and toxicological implications.

Elucidation of toxicity pathways in lung epithelial cells induced by silicon dioxide nanoparticles

A study into the effects of amorphous nano-SiO2 particles on A549 lung epithelial cells was undertaken using proteomics to understand the interactions that occur and the biological consequences of exposure of lung to nanoparticles. Suitable conditions for treatment, where A549 cells remained viable for the exposure period, were established by following changes in cell morphology, flow cytometry, and MTT reduction. Label-free proteomics was used to estimate the relative level of proteins from their component tryptic peptides detected by mass spectrometry. It was found that A549 cells tolerated treatment with 100 µg/ml nano-SiO2 in the presence of 1.25% serum for at least 4 h. After this time detrimental changes in cell morphology, flow cytometry, and MTT reduction were evident. Proteomics performed after 4 h indicated changes in the expression of 47 proteins. Most of the proteins affected fell into four functional groups, indicating that the most prominent cellular changes were those that affected apoptosis regulation (e.g. UCP2 and calpain-12), structural reorganisation and regulation of actin cytoskeleton (e.g. PHACTR1), the unfolded protein response (e.g. HSP 90), and proteins involved in protein synthesis (e.g. ribosomal proteins). Treatment with just 10 µg/ml nano-SiO2 particles in serum-free medium resulted in a rapid deterioration of the cells and in medium containing 10% serum the cells were resistant to up to 1000 µg/ml nano-SiO2 particles, suggesting interaction of serum components with the nanoparticles. A variety of serum proteins were found which bound to nano-SiO2 particles, the most prominent of which were albumin, apolipoprotein A-I, hemoglobin, vitronectin and fibronectin. The use of a proteomics platform, with appropriately designed experimental conditions, enabled the early biological perturbations induced by nano-SiO2 in a model target cell system to be identified. The approach facilitates the design of more focused test systems for use in tiered evaluations of nanomaterials.

Temperature: the "ignored" factor at the NanoBio interface

Upon incorporation of nanoparticles (NPs) into the body, they are exposed to biological fluids, and their interaction with the dissolved biomolecules leads to the formation of the so-called protein corona on the surface of the NPs. The composition of the corona plays a crucial role in the biological fate of the NPs. While the effects of various physicochemical parameters on the composition of the corona have been explored in depth, the role of temperature upon its formation has received much less attention. In this work, we have probed the effect of temperature on the protein composition on the surface of a set of NPs with various surface chemistries and electric charges. Our results indicate that the degree of protein coverage and the composition of the adsorbed proteins on the NPs' surface depend on the temperature at which the protein corona is formed. Also, the uptake of NPs is affected by the temperature. Temperature is, thus, an important parameter that needs to be carefully controlled in quantitative studies of bionano interactions.

Identifying specific protein residues that guide surface interactions and orientation on silica nanoparticles

We identify specific acylphosphatase (AcP) residues that interact with silica nanoparticles (SNPs) using a combined NMR spectroscopy and proteomics-mass spectrometry approach. AcP associated with 4- and 15-nm diameter SNPs through a common and specific interaction surface formed by amino acids from the two α-helices of the protein. Greater retention of native protein structure was obtained on 4-nm SNPs than on 15-nm particles, presumably due to greater surface curvature-induced protein stabilization with the smaller SNPs. These results demonstrate that proteins may undergo specific and size-dependent orientation on nanoparticle surfaces. Our approach can be broadly applied to various protein-material systems to help understand in much greater detail the protein-nanomaterial interface; it would also encourage better modeling, and thus prediction and design, of the behavior of functional proteins adsorbed onto different surfaces.

Uptake and toxicity of copper oxide nanoparticles in cultured primary brain astrocytes

To test for consequences of an exposure of brain cells to copper oxide nanoparticles (CuO-NPs), we synthesised and characterised dimercaptosuccinate-coated CuO-NPs. These particles had a diameter of around 5 nm as determined by transmission electron microscopy, while their average hydrodynamic diameter in aqueous dispersion was 136 ± 4 nm. Dispersion in cell-culture medium containing 10% fetal calf serum increased the hydrodynamic diameter to 178 ± 12 nm and shifted the zeta potential of the particles from -49 ± 7 mV (in water) to -10 ± 3 mV. Exposure of cultured primary brain astrocytes to CuO-NPs increased the cellular copper levels and compromised the cell viability in a time-, concentration- and temperature-dependent manner. Application of CuO-NPs in concentrations above 100 µM copper (6.4 µg/ml) severely compromised the viability of the cells, as demonstrated by a lowered 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction capacity, a lowered cellular lactate dehydrogenase activity and an increased membrane permeability for the fluorescent dye propidium iodide. Copper internalisation as well as cell toxicity of astrocytes exposed to CuO-NPs were similar to that observed for cells that had been incubated with copper salts. The CuO-NP-induced toxicity was accompanied by an increase in the generation of reactive oxygen species (ROS) in the cells. Both, ROS formation and cell toxicity in CuO-NP-treated astrocytes, were lowered in the presence of the cell-permeable copper chelator tetrathiomolybdate. These data demonstrate that CuO-NPs are taken up by cultured astrocytes and suggest that excess of internalised CuO-NPs cause cell toxicity by accelerating the formation of ROS.

Preformed albumin corona, a protective coating for nanoparticles based drug delivery system

The non-specific interaction between nanoparticles (NPs) and plasma proteins occurs immediately after NPs enter the blood, resulting in the formation of the protein corona that thereafter replaces the original NPs and becomes what the organs and cells really see. Consequently, the in vivo fate of NPs and the biological responses to the NPs are changed. This is one substantial reason for the two main problems of the NPs based drug delivery system, i.e. nanotoxicity and rapid clearance of NPs from the blood after intravenous injection. Here, we demonstrate the successful application of the preformed albumin corona in inhibiting the plasma proteins adsorption and decreasing the complement activation, and ultimately in prolonging the blood circulation time and reducing the toxicity of the polymeric PHBHHx NPs. Since the interaction of proteins with various nano-materials and/or -particles is ubiquitous, pre-forming albumin corona has a great potential to be a versatile strategy for optimizing the NPs based drug delivery system.

Surface and size effects on cell interaction of gold nanoparticles with both phagocytic and nonphagocytic cells

With the development of nanotechnology and its application in biomedicine, studies on the interaction between nanoparticles and cells have become increasingly important. To understand the surface and size effects on cell interaction of nanoparticles, the cellular uptake behaviors of two series of gold nanoparticles (AuNPs) with both positively and negatively charged surfaces and sizes range from ~16 to ~58 nm were investigated in both phagocytic RAW 264.7 and nonphagocytic HepG2 cells. The internalization of AuNPs was quantified by ICP-MS, and the intracellular fate of NPs was evaluated by TEM analysis. The results showed that the AuNPs with positive surface charge have much higher cell internalization ability than those with negative surface charge in nonphagocytic HepG2 cells. However, the uptake extent of negatively charged AuNPs was similar with that of the positively charged AuNPs when in phagocytic RAW 264.7 cells. Among the tested size range, negatively charged AuNPs with a diameter of ~40 nm had the highest uptake in both cells, while the positively charged AuNPs did not show a certain tendency. Intracellular TEM analysis demonstrated the different fate of AuNPs in different cells, where both the positively and negatively charged AuNPs were mainly trapped in the lysosomes in HepG2 cells, but many of them were localized in phagosomes when in RAW 264.7 cells. Cytotoxicity of these AuNPs was tested by both MTT and LDH assays, which suggested NP's toxicity is closely related to the tested cell types besides the surface and size of NPs. It demonstrates that cell interaction between nanoparticles and cells is not only affected by surface and size factors but also strongly depends on cell types.

Interaction of nanoparticles with proteins: relation to bio-reactivity of the nanoparticle

Interaction of nanoparticles with proteins is the basis of nanoparticle bio-reactivity. This interaction gives rise to the formation of a dynamic nanoparticle-protein corona. The protein corona may influence cellular uptake, inflammation, accumulation, degradation and clearance of the nanoparticles. Furthermore, the nanoparticle surface can induce conformational changes in adsorbed protein molecules which may affect the overall bio-reactivity of the nanoparticle. In depth understanding of such interactions can be directed towards generating bio-compatible nanomaterials with controlled surface characteristics in a biological environment. The main aim of this review is to summarise current knowledge on factors that influence nanoparticle-protein interactions and their implications on cellular uptake.

Kinetics of silica nanoparticles in the human placenta

The potential medical applications of nanoparticles (NPs) warrant their investigation in terms of biodistribution and safety during pregnancy. The transport of silica NPs across the placenta was investigated using two models of maternal-foetal transfer in human placenta, namely, the BeWo b30 choriocarcinoma cell line and the ex vivo perfused human placenta. Nanotoxicity in BeWo cells was examined by the MTT assay which demonstrated decreased cell viability at concentrations >100 µg/mL. In the placental perfusion experiments, antipyrine crossed the placenta rapidly, with a foetal:maternal ratio of 0.97 ± 0.10 after 2 h. In contrast, the percentage of silica NPs reaching the foetal perfusate after 6 h was limited to 4.2 ± 4.9% and 4.6 ± 2.4% for 25 and 50 nm NPs, respectively. The transport of silica NPs across the BeWo cells was also limited, with an apparent permeability of only 1.54 × 10(-6) ± 1.56 × 10(-6) cm/s. Using confocal microscopy, there was visual confirmation of particle accumulation in both BeWo cells and in perfused placental tissue. Despite the low transfer of silica NPs to the foetal compartment, questions regarding biocompatibility could limit the application of unmodified silica NPs in biomedical imaging or therapy.

Internalization pathways of anisotropic disc-shaped zeolite L nanocrystals with different surface properties in HeLa cancer cells

Information about the mechanisms underlying the interactions of nanoparticles with living cells is crucial for their medical application and also provides indications of the putative toxicity of such materials. Here the uptake and intracellular delivery of disc-shaped zeolite L nanocrystals as porous aminosilicates with well-defined crystal structure, uncoated as well as with COOH-, NH2 -, polyethyleneglycol (PEG)- and polyallylamine hydrochloride (PAH) surface coatings are reported. HeLa cells are used as a model system to demonstrate the relation between these particles and cancer cells. Interactions are studied in terms of their fates under diverse in vitro cell culture conditions. Differently charged coatings demonstrated dissimilar behavior in terms of agglomeration in media, serum protein adsorption, nanoparticle cytotoxicity and cell internalization. It is also found that functionalized disc-shaped zeolite L particles enter the cancer cells via different, partly not yet characterized, pathways. These in vitro results provide additional insight about low-aspect ratio anisotropic nanoparticle interactions with cancer cells and demonstrate the possibility to manipulate the interactions of nanoparticles and cells by surface coating for the use of nanoparticles in medical applications.

Protein binding modulates the cellular uptake of silver nanoparticles into human cells: implications for in vitro to in vivo extrapolations?

Nanoparticles (NP) absorbed in the body will come in contact with blood proteins and form NP/protein complexes termed protein coronas, which may modulate NP cellular uptake. This study quantitated human epidermal keratinocyte (HEK) uptake of silver (Ag) NP complexed to different human serum proteins. Prior to HEK dosing, AgNP (20nm and 110nm citrate BioPure™; 40nm and 120nm silica-coated) were preincubated for 2h at 37°C without (control) or with physiological levels of albumin (44mg/ml), IgG (14.5mg/ml) or transferrin (3mg/ml) to form protein-complexed NP. HEK were exposed to the protein incubated AgNP for 3h, rinsed and incubated for 24h, rinsed in buffer and lysed. Ag was assayed by inductively-coupled plasma optical emission spectrometry. Uptake of Ag in HEK was <4.1% of applied dose with proteins suppressing citrate, but not silica coated Ag uptake. IgG exposure dramatically reduced 110nm citrate AgNP uptake. In contrast, greatest uptake of 20nm silica AgNP was seen with IgG, while 110nm silica AgNP showed minimal protein effects. Electron microscopy confirmed cellular uptake of all NP but showed differences in the appearance and agglomeration state of the NP within HEK vacuoles. This work suggests that NP association with different serum proteins, purportedly forming different protein coronas, significantly modulates Ag uptake into HEK compared to native NP uptake, suggesting caution in extrapolating in vitro uptake data to predict behavior in vivo where the nature of the protein corona may determine patterns of cellular uptake, and thus biodistribution, biological activity and toxicity.

Internalization of SiO₂ nanoparticles by alveolar macrophages and lung epithelial cells and its modulation by the lung surfactant substitute Curosurf

Because of an increasing exposure to environmental and occupational nanoparticles (NPs), the potential risk of these materials for human health should be better assessed. Since one of the main routes of entry of NPs is via the lungs, it is of paramount importance to further characterize their impact on the respiratory system. Here, we have studied the uptake of fluorescently labeled SiO₂ NPs (50 and 100 nm) by epithelial cells (NCI-H292) and alveolar macrophages (MHS) in the presence or absence of pulmonary surfactant. The quantification of NP uptake was performed by measuring cell-associated fluorescence using flow cytometry and spectrometric techniques in order to identify the most suitable methodology. Internalization was shown to be time and dose dependent, and differences in terms of uptake were noted between epithelial cells and macrophages. In the light of our observations, we conclude that flow cytometry is a more reliable technique for the study of NP internalization, and importantly, that the hydrophobic fraction of lung surfactant is critical for downregulating NP uptake in both cell types.

Polymer-coated nanoparticles interacting with proteins and cells: focusing on the sign of the net charge

To study charge-dependent interactions of nanoparticles (NPs) with biological media and NP uptake by cells, colloidal gold nanoparticles were modified with amphiphilic polymers to obtain NPs with identical physical properties except for the sign of the charge (negative/positive). This strategy enabled us to solely assess the influence of charge on the interactions of the NPs with proteins and cells, without interference by other effects such as different size and colloidal stability. Our study shows that the number of adsorbed human serum albumin molecules per NP was not influenced by their surface charge. Positively charged NPs were incorporated by cells to a larger extent than negatively charged ones, both in serum-free and serum-containing media. Consequently, with and without protein corona (i.e., in serum-free medium) present, NP internalization depends on the sign of charge. The uptake rate of NPs by cells was higher for positively than for negatively charged NPs. Furthermore, cytotoxicity assays revealed a higher cytotoxicity for positively charged NPs, associated with their enhanced uptake.

Multimodality imaging using SPECT/CT and MRI and ligand functionalized 99mTc-labeled magnetic microbubbles

Background

In the present study, we used multimodal imaging to investigate biodistribution in rats after intravenous administration of a new ^99mTc-labeled delivery system consisting of polymer-shelled microbubbles (MBs) functionalized with diethylenetriaminepentaacetic acid (DTPA), thiolated poly(methacrylic acid) (PMAA), chitosan, 1,4,7-triacyclononane-1,4,7-triacetic acid (NOTA), NOTA-super paramagnetic iron oxide nanoparticles (SPION), or DTPA-SPION.

Methods

Examinations utilizing planar dynamic scintigraphy and hybrid imaging were performed using a commercially available single-photon emission computed tomography (SPECT)/computed tomography (CT) system. For SPION containing MBs, the biodistribution pattern of ^99mTc-labeled NOTA-SPION and DTPA-SPION MBs was investigated and co-registered using fusion SPECT/CT and magnetic resonance imaging (MRI). Moreover, to evaluate the biodistribution, organs were removed and radioactivity was measured and calculated as percentage of injected dose.

Results

SPECT/CT and MRI showed that the distribution of ^99mTc-labeled ligand-functionalized MBs varied with the type of ligand as well as with the presence of SPION. The highest uptake was observed in the lungs 1 h post injection of ^99mTc-labeled DTPA and chitosan MBs, while a similar distribution to the lungs and the liver was seen after the administration of PMAA MBs. The highest counts of ^99mTc-labeled NOTA-SPION and DTPA-SPION MBs were observed in the lungs, liver, and kidneys 1 h post injection. The highest counts were observed in the liver, spleen, and kidneys as confirmed by MRI 24 h post injection. Furthermore, the results obtained from organ measurements were in good agreement with those obtained from SPECT/CT.

Conclusions

In conclusion, microbubbles functionalized by different ligands can be labeled with radiotracers and utilized for SPECT/CT imaging, while the incorporation of SPION in MB shells enables imaging using MR. Our investigation revealed that biodistribution may be modified using different ligands. Furthermore, using a single contrast agent with fusion SPECT/CT/MR multimodal imaging enables visualization of functional and anatomical information in one image, thus improving the diagnostic benefit for patients.

Gold nanoparticles downregulate interleukin-1β-induced pro-inflammatory responses

Interleukin 1 beta (IL-1β)-dependent inflammatory disorders, such as rheumatoid arthritis and psoriasis, pose a serious medical burden worldwide, where patients face a lifetime of illness and treatment. Organogold compounds have been used since the 1930s to treat rheumatic and other IL-1β-dependent diseases and, though their mechanisms of action are still unclear, there is evidence that gold interferes with the transmission of inflammatory signalling. Here we show for the first time that citrate-stabilized gold nanoparticles, in a size dependent manner, specifically downregulate cellular responses induced by IL-1β both in vitro and in vivo. Our results indicate that the anti-inflammatory activity of gold nanoparticles is associated with an extracellular interaction with IL-1β, thus opening potentially novel options for further therapeutic applications.

Bridge over troubled waters: understanding the synthetic and biological identities of engineered nanomaterials

Engineered nanomaterials offer exciting opportunities for 'smart' drug delivery and in vivo imaging of disease processes, as well as in regenerative medicine. The ability to manipulate matter at the nanoscale enables many new properties that are both desirable and exploitable, but the same properties could also give rise to unexpected toxicities that may adversely affect human health. Understanding the physicochemical properties that drive toxicological outcomes is a formidable challenge as it is not trivial to separate and, hence, to pinpoint individual material characteristics of nanomaterials. In addition, nanomaterials that interact with biological systems are likely to acquire a surface corona of biomolecules that may dictate their biological behavior. Indeed, we propose that it is the combination of material-intrinsic properties (the 'synthetic identity') and context-dependent properties determined, in part, by the bio-corona of a given biological compartment (the 'biological identity') that will determine the interactions of engineered nanomaterials with cells and tissues and subsequent outcomes. The delineation of these entwined 'identities' of engineered nanomaterials constitutes the bridge between nanotoxicological research and nanomedicine.

Cellular Binding of Anionic Nanoparticles is Inhibited by Serum Proteins Independent of Nanoparticle Composition

Nanoparticles used in biological applications encounter a complex mixture of extracellular proteins. Adsorption of these proteins on the nanoparticle surface results in the formation of a "protein corona," which can dominate the interaction of the nanoparticle with the cellular environment. The goal of this research was to determine how nanoparticle composition and surface modification affect the cellular binding of protein-nanoparticle complexes. We examined the cellular binding of a collection of commonly used anionic nanoparticles: quantum dots, colloidal gold nanoparticles, and low-density lipoprotein particles, in the presence and absence of extracellular proteins. These experiments have the advantage of comparing different nanoparticles under identical conditions. Using a combination of fluorescence and dark field microscopy, flow cytometry, and spectroscopy, we find that cellular binding of these anionic nanoparticles is inhibited by serum proteins independent of nanoparticle composition or surface modification. We expect these results will aid in the design of nanoparticles for in vivo applications.

Formation and characterization of the nanoparticle-protein corona

Over the last decade the existence of "the corona," a natural interface between nanomaterials and living matter in biological milieu, evolved from a vague concept into broadly recognized fact. This robust shell arises (to some extent) on the surface of all nanoparticles (NPs), even the ones designed to avoid its formation upon contact with biological fluids and confers a biological identity to the nanomaterials such that they can engage with cellular machinery. The NP corona consists of those proteins (and other biomolecules such as lipids and sugars) residing on the NP surface for a sufficient timescale to influence the NP's properties and interactions with living systems. This chapter aims to provide simple protocols, as well as notes on potential pitfalls, to help researchers to perform basic experiments in this field as the basis for a more mechanistic approach to study and understand NP-protein corona complexes. This work has been supported by INSPIRE (Integrated NanoScience Platform for Ireland) funded by the Irish Government's Programme for Research in Third Level Institutions, Cycle 4, National Development Plan 2007-2013, and 3MICRON (NMP-2009-LA-245572), NAMDIATREAM (NMP4-LA-2010-246479) and QualityNano (INFRA-2010-262163) funded by the European Commission 7th Framework Programme.

Immobilization ofα-Chymotrypsin on the Surface of Magnetic/Gold Core/Shell Nanoparticles

Over the last decade, nanoparticles used as protein carriers have opened new avenues for a variety of biomedical applications. The main concern for these applications is changes in biological activity of immobilized proteins due to conformational changes on the surface of the carrier. To evaluate this concern, the preparation and biocatalyst activity ofα-chymotrypsin-Fe3O4@ Au core/shell nanoparticles were investigated. First, Fe3O4@ Au core/shell nanoparticles were synthesized by coprecipitation method and citrate reduction of HAuCl4. TEM imaging revealed a core size of 13 ± 3 nm and a shell thickness of 4 ± 1 nm for synthesized nanoparticles. X-ray diffraction (XRD) was used to study the crystalline structure of the nanoparticles. Next, the enzyme was immobilized on the surface of synthesized nanoparticles by covalent bonding of Au shell with thiol and amine groups present in the protein structure (e.g., cysteine and histidine residues). FTIR and fluorescence spectroscopy were utilized to study secondary and tertiary structures of the immobilized enzyme. Results show that the secondary and tertiary structures of the enzyme remain virtually unchanged after immobilization on the nanoparticles surface. However, the biocatalyst activity of the enzyme was reduced by thirty percent, indicating possible conformational changes or active site occlusion.

Effects of serum on cytotoxicity of nano- and micro-sized ZnO particles

Although an increasing number of in vitro studies are being published regarding the cytotoxicity of nanomaterials, the components of the media for toxicity assays have often varied according to the needs of the scientists. Our aim for this study was to evaluate the influence of serum-in this case, fetal bovine serum-in a cell culture medium on the toxicity of nano-sized (50-70 nm) and micro-sized (<1 μm) ZnO on human lung epithelial cells (A549). The nano- and micro-sized ZnO both exhibited their highest toxicity when exposed to serum-free media, in contrast to exposure in media containing 5 or 10 % serum. This mainly comes not only from the fact that ZnO particles in the serum-free media have a higher dosage-per-cell ratio, which results from large aggregates of particles, rapid sedimentation, absence of protein protection, and lower cell growth rate, but also that extracellular Zn²⁺ release contributes to cytotoxicity. Although more extracellular Zn²⁺ release was observed in serum-containing media, it did not contribute to nano-ZnO cytotoxicity. Furthermore, non-dissolved particles underwent size-dependent particle agglomeration, resulting in size-dependent toxicity in both serum-containing and serum-free media. A low correlation between cytotoxicity and inflammation endpoints in the serum-free medium suggested that some signaling pathways were changed or induced. Since cell growth, transcription behavior for protein production, and physicochemical properties of ZnO particles all were altered in serum-free media, we recommend the use of a serum-containing medium when evaluating the cytotoxicity of NPs.

Emerging techniques in proteomics for probing nano-bio interactions

Nanoengineered particles that can facilitate drug formulation and improve specificity of delivery afford exciting opportunities for improved lesion-specific therapy. Understanding and controlling the nano-bio interactions of these materials is central to future developments in this area. Mass-spectrometry-based proteomics techniques, in conjunction with other emerging technologies, are enabling novel insights into the modulation of particle surfaces by biological fluids (formation of the protein corona) and subsequent particle-induced cellular responses. In this Perspective, we summarize important recent developments using proteomics-based techniques to understand nano-bio interactions and discuss the impact of such knowledge on improving particle design.

Biomolecular coronas provide the biological identity of nanosized materials

The search for understanding the interactions of nanosized materials with living organisms is leading to the rapid development of key applications, including improved drug delivery by targeting nanoparticles, and resolution of the potential threat of nanotechnological devices to organisms and the environment. Unless they are specifically designed to avoid it, nanoparticles in contact with biological fluids are rapidly covered by a selected group of biomolecules to form a corona that interacts with biological systems. Here we review the basic concept of the nanoparticle corona and its structure and composition, and highlight how the properties of the corona may be linked to its biological impacts. We conclude with a critical assessment of the key problems that need to be resolved in the near future.

Flotillin-involved uptake of silica nanoparticles and responses of an alveolar-capillary barrier in vitro

Drug and gene delivery via nanoparticles across biological barriers such as the alveolar-capillary barrier of the lung constitutes an interesting and increasingly relevant field in nanomedicine. Nevertheless, potential hazardous effects of nanoparticles (NPs) as well as their cellular and systemic fate should be thoroughly examined. Hence, this study was designed to evaluate the effects of amorphous silica NPs (Sicastar) and (poly)organosiloxane NPs (AmOrSil) on the viability and the inflammatory response as well as on the cellular uptake mechanisms and fate in cells of the alveolar barrier. For this purpose, the alveolar epithelial cell line (NCI H441) and microvascular endothelial cell line (ISO-HAS-1) were used in an experimental set up resembling the alveolar-capillary barrier of the lung. In terms of IL-8 and sICAM Sicastar resulted in harmful effects at higher concentrations (60 μg/ml) in conventional monocultures but not in the coculture, whereas AmOrSil showed no significant effects. Immunofluorescence counterstaining of endosomal structures in NP-incubated cells showed no evidence for a clathrin- or caveolae-mediated uptake mechanism. However, NPs were enclosed in flotillin-1 and -2 marked vesicles in both cell types. Flotillins appear to play a role in cellular uptake or trafficking mechanisms of NPs and are discussed as indicators for clathrin- or caveolae-independent uptake mechanisms. In addition, we examined the transport of NPs across this in vitro model of the alveolar-capillary barrier forming a tight barrier with a transepithelial electrical resistance of 560±8 Ω cm(2). H441 in coculture with endothelial cells took up much less NPs compared to monocultures. Moreover, coculturing prevented the transport of NP from the epithelial compartment to the endothelial layer on the bottom of the filter insert. This supports the relevance of coculture models, which favour a differentiated and polarised epithelial layer as in vitro test systems for nanoparticle uptake.