Extensive evaluations of the cytotoxic effects of gold nanoparticles

BACKGROUND

Many in vitro studies have revealed that the interference of dye molecules in traditional nanoparticle cytotoxicity assays results in controversial conclusions. The aim of this study is to establish an extensive and systematic method for evaluating biological effects of gold nanoparticles in mammalian cell lines.

METHODS

We establish the cell-impedance measurement system, a label-free, real-time cell monitoring platform that measures electrical impedance, displaying results as cell index values, in a variety of mammalian cell lines. Cytotoxic effects of gold nanoparticles are also evaluated with traditional in vitro assays.

RESULTS

Among the six cell lines, gold nanoparticles induce a dose-dependent suppression of cell growth with different levels of severity and the suppressive effect of gold nanoparticles was indirectly associated with their sizes and cellular uptake. Mechanistic studies revealed that the action of gold nanoparticles is mediated by apoptosis induction or cell cycle delay, depending on cell type and cellular context. Although redox signaling is often linked to the toxicity of nanoparticles, in this study, we found that gold nanoparticle-mediated reactive oxygen species generation was not sustained to notably modulate proteins involved in antioxidative defense system.

CONCLUSION

The cell-impedance measurement system, a dye-free, real-time screening platform, provides a reliable analysis for monitoring gold nanoparticle cytotoxicity in a variety of mammalian cell lines. Furthermore, gold nanoparticles induce cellular signaling and several sets of gene expression to modulate cellular physical processes.

GENERAL SIGNIFICANCE

The systematic approach, such as cell-impedance measurement, analyzing the toxicology of nanomaterials offers convincing evidence of the cytotoxicity of gold nanomaterials.

Effect of functionalized gold nanoparticles on floating lipid bilayers

The development of novel nano-engineered materials poses important questions regarding the impact of these new materials on living systems. Possible adverse effects must be assessed in order to prevent risks for health and the environment. On the other hand, a thorough understanding of their interaction with biological systems might also result in the creation of novel biomedical applications. We present a study on the interaction of model lipid membranes with gold nanoparticles (AuNP) of different surface modifications. Neutron reflectometry experiments on zwitterionic lipid double bilayers were performed in the presence of AuNP functionalized with cationic and anionic head groups. Structural information was obtained that provided insight into the fate of the AuNPs with regard to the integrity of the model cell membranes. The AuNPs functionalized with cationic head groups penetrate into the hydrophobic moiety of the lipid bilayers and cause membrane disruption at an increased concentration. In contrast, the AuNPs functionalized with anionic head groups do not enter but seem to impede the destruction of the lipid bilayer at an alkaline pH. The information obtained might influence the strategy for a better nanoparticle risk assessment based on a surface charge evaluation and contribute to nano-safety considerations during their design.

The 'nanobig rod' class of gold nanorods: optimized dimensions for improved in vivo therapeutic and imaging efficacy

Currently, gold nanorods can be synthesized in a wide range of sizes. However, for the intended biological applications gold nanorods with approximate dimensions 50 nm × 15 nm are used. We investigate by computer simulation the effect of particle dimensions on the optical and thermal properties in the context of the specific applications of photoacoustic imaging. In addition we discuss the influence of particle size in overcoming the following biophysical barriers when administrated in vivo: extravasation, avoidance of uptake by organs of the reticuloendothelial system, penetration through the interstitium, binding capability and uptake by the target cells. Although more complex biological influences can be introduced in future analysis, the present work illustrates that larger gold nanorods, designated by us as 'nanobig rods', may perform better at meeting the requirements for successful in vivo applications compared to their smaller counterparts, which are conventionally used.

Photoacoustic imaging: a potential tool to detect early indicators of metastasis

The metastasis of cancer is a multistage process involving complex biological interactions and difficult to predict outcomes. Accurate assessment of the extent of metastasis is critical for clinical practice; unfortunately, medical imaging methods capable of identifying the early stages of invasion and metastasis are lacking. Photoacoustic imaging is capable of providing noninvasive, real-time imaging of significant anatomical and physiological changes. indicating the progression of cancer invasion and metastasis. Preclinically, photoacoustic methods have been used to image lymphatic anatomy, including the sentinel lymph nodes, to identify circulating tumor cells within vasculature and to detect micrometastases. Progress has begun toward the development of clinically applicable photoacoustic imaging systems to assist with the determination of cancer stage and likelihood of metastatic invasion.

Quantifying and imaging engineered nanomaterials in vivo: challenges and techniques

Quantifying and imaging the engineered nanomaterials (ENMs) in vivo can provide information on the bio-distribution and fate of ENMs in living systems. A necessary amount of in vivo quantitative data is indispensable to verify the extrapolation from in vitro tests, to modify the predictive models of ENM exposure, and to underpin the risk management strategy for ENMs. However, it remains a challenge to quantitatively assess the bio-distribution of ENMs under realistic exposure, their long-term deposition (especially in non-targeted tissues), their passage across the natural barriers, and the impacts of nano-bio interactions on their in vivo behaviors. Some commonly used techniques for in vivo ENM quantification, such as electron microscopy, fluorescence-based detection, atomic spectroscopy, radiotracing, and techniques basing on synchrotron radiation are reviewed, and their technical characteristics, the state of the art, limitations, and future prospects are addressed.

Study of charge-dependent transport and toxicity of peptide-functionalized silver nanoparticles using zebrafish embryos and single nanoparticle plasmonic spectroscopy

Nanomaterials possess unusually high surface area-to-volume ratios and surface-determined physicochemical properties. It is essential to understand their surface-dependent toxicity in order to rationally design biocompatible nanomaterials for a wide variety of applications. In this study, we have functionalized the surfaces of silver nanoparticles (Ag NPs, 11.7 ± 2.7 nm in diameter) with three biocompatible peptides (CALNNK, CALNNS, CALNNE) to prepare positively (Ag-CALNNK NPs(+ζ)), negatively (Ag-CALNNS NPs(-2ζ)), and more negatively charged NPs (Ag-CALNNE NPs(-4ζ)), respectively. Each peptide differs in a single amino acid at its C-terminus, which minimizes the effects of peptide sequences and serves as a model molecule to create positive, neutral, and negative charges on the surface of the NPs at pH 4-10. We have studied their charge-dependent transport into early developing (cleavage-stage) zebrafish embryos and their effects on embryonic development using dark-field optical microscopy and spectroscopy (DFOMS). We found that all three Ag-peptide NPs passively diffused into the embryos via their chorionic pore canals, and stayed inside the embryos throughout their entire development (120 h), showing charge-independent diffusion modes and charge-dependent diffusion coefficients. Notably, the NPs create charge-dependent toxic effects on embryonic development, showing that the Ag-CALNNK NPs(+ζ) (positively charged) are the most biocompatible while the Ag-CALNNE NPs(-4ζ) (more negatively charged) are the most toxic. By comparing with our previous studies of the same sized citrated Ag and Au NPs, the Ag-peptide NPs are much more biocompatible than the citrated Ag NPs, and nearly as biocompatible as the Au NPs, showing the dependence of nanotoxicity upon the surface charges, surface functional groups, and chemical compositions of the NPs. This study also demonstrates powerful applications of single NP plasmonic spectroscopy for quantitative analysis of single NPs in vivo and in tissues, and reveals the possibility of rational design of biocompatible NPs.

Gold nanoparticle delivery of modified CpG stimulates macrophages and inhibits tumor growth for enhanced immunotherapy

Gold nanoparticle accumulation in immune cells has commonly been viewed as a side effect for cancer therapeutic delivery; however, this phenomenon can be utilized for developing gold nanoparticle mediated immunotherapy. Here, we conjugated a modified CpG oligodeoxynucleotide immune stimulant to gold nanoparticles using a simple and scalable self-assembled monolayer scheme that enhanced the functionality of CpG in vitro and in vivo. Nanoparticles can attenuate systemic side effects by enhancing CpG delivery passively to innate effector cells. The use of a triethylene glycol (TEG) spacer on top of the traditional poly-thymidine spacer increased CpG macrophage stimulatory effects without sacrificing DNA content on the nanoparticle, which directly correlates to particle uptake. In addition, the immune effects of modified CpG-AuNPs were altered by the core particle size, with smaller 15 nm AuNPs generating maximum immune response. These TEG modified CpG-AuNP complexes induced macrophage and dendritic cell tumor infiltration, significantly inhibited tumor growth, and promoted survival in mice when compared to treatments with free CpG.

Therapeutic platforms based on gold nanoparticles and their covalent conjugates with drug molecules

This review will first look at the various covalent strategies that have been developed to attach drugs to gold nanoparticles as well as the strengths and limitations of such strategies. After examining general strategies for the synthesis of gold nanoparticles and their subsequent covalent functionalization, this review will focus on nanoparticle conjugates for gene therapy, antibacterial, and anticancer applications including the use of gold nanoparticles with intrinsically therapeutic properties. The effects of targeting and cellular uptake of gold nanoparticles will also be discussed.

Biomimetic metal oxides for the extraction of nanoparticles from water

Contamination of nanomaterials in the environment will pose significant health risks in the future. A viable purification method is necessary to address this problem. Here we report the synthesis and application of a series of metal oxides prepared using a biological template for the removal of nanoparticles from the aqueous environment. A simple synthesis of metal oxides such as ZnO, NiO, CuO, Co3O4 and CeO2 employing eggshell membrane (ESM) as a biotemplate is reported. The morphology of the metal oxide powders was characterized using electron microscopes and the lattice structure was established using X-ray diffraction methods. Extraction of nanoparticles from water was carried out to compare the efficiency of metal oxides. NiO showed good extraction efficiency in removing gold and silver nanoparticles from spiked water samples within an hour. Easy access and enhanced stability of metal oxides makes them interesting candidates for applications in industrial effluent treatments and water purifications.

Metal-based nanoparticle interactions with the nervous system: the challenge of brain entry and the risk of retention in the organism

This review of metal-based nanoparticles focuses on factors influencing their distribution into the nervous system, evidence they enter brain parenchyma, and nervous system responses. Gold is emphasized as a model metal-based nanoparticle and for risk assessment in the companion review. The anatomy and physiology of the nervous system, basics of colloid chemistry, and environmental factors that influence what cells see are reviewed to provide background on the biological, physical-chemical, and internal milieu factors that influence nervous system nanoparticle uptake. The results of literature searches reveal little nanoparticle research included the nervous system, which about equally involved in vitro and in vivo methods, and very few human studies. The routes of uptake into the nervous system and mechanisms of nanoparticle uptake by cells are presented with examples. Brain nanoparticle uptake inversely correlates with size. The influence of shape has not been reported. Surface charge has not been clearly shown to affect flux across the blood-brain barrier. There is very little evidence for metal-based nanoparticle distribution into brain parenchyma. Metal-based nanoparticle disruption of the blood-brain barrier and adverse brain changes have been shown, and are more pronounced for spheres than rods. Study concentrations need to be put in exposure contexts. Work with dorsal root ganglion cells and brain cells in vitro show the potential for metal-based nanoparticles to produce toxicity. Interpretation of these results must consider the ability of nanoparticles to distribute across the barriers protecting the nervous system. Effects of the persistence of poorly soluble metal-based nanoparticles are of particular concern.

Influence of the surface coating on the cytotoxicity, genotoxicity and uptake of gold nanoparticles in human HepG2 cells

The toxicological profile of gold nanoparticles (AuNPs) remains controversial. Significant efforts to develop surface coatings to improve biocompatibility have been carried out. In vivo biodistribution studies have shown that the liver is a target for AuNPs accumulation. Therefore, we investigated the effects induced by ~20 nm spherical AuNPs (0-200 μM Au) with two surface coatings, citrate (Cit) compared with 11-mercaptoundecanoic acid (11-MUA), in human liver HepG2 cells. Cytotoxicity was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction and lactate dehydrogenase (LDH) release assays after 24 to 72 h of incubation. DNA damage was assessed by the comet assay, 24 h after incubation with the capped AuNPs. Uptake and subcellular distribution of the tested AuNPs was evaluated by quantifying the gold intracellular content by graphite furnace atomic absorption spectrometry (GFAAS) and transmission electron microscopy (TEM), respectively. The obtained results indicate that both differently coated AuNPs did not induce significant cytotoxicity. An inverse concentration-dependent increase in comet tail intensity and tail moment was observed in Cit-AuNPs- but not in MUA-AuNPs-exposed cells. Both AuNPs were internalized in a concentration-dependent manner. However, no differences were found in the extent of the internalization between the two types of NPs. Electron-dense deposits of agglomerates of Cit- and MUA-AuNPs were observed either inside endosomes or in the intercellular spaces. In spite of the absence of cytotoxicity, DNA damage was observed after exposure to the lower concentrations of Cit- but not to MUA-AuNPs. Thus, our data supports the importance of the surface properties to increase the biocompatibility and safety of AuNPs.

The gold standard: gold nanoparticle libraries to understand the nano-bio interface

Since the late 1980s, researchers have prepared inorganic nanoparticles of many types--including elemental metals, metal oxides, metal sulfides, metal selenides, and metal tellurides--with excellent control over size and shape. Originally many researchers were primarily interested in exploring the quantum size effects predicted for such materials. Applications of inorganic nanomaterials initially centered on physics, optics, and engineering but have expanded to include biology. Many current nanomaterials can serve as biochemical sensors, contrast agents in cellular or tissue imaging, drug delivery vehicles, or even as therapeutics. In this Account we emphasize that the understanding of how nanomaterials will function in a biological system relies on the knowledge of the interface between biological systems and nanomaterials, the nano-bio interface. Gold nanoparticles can serve as excellent standards to understand more general features of the nano-bio interface because of its many advantages over other inorganic materials. The bulk material is chemically inert, and well-established synthetic methods allow researchers to control its size, shape, and surface chemistry. Gold's background concentration in biological systems is low, which makes it relatively easy to measure it at the part-per-billion level or lower in water. In addition, the large electron density of gold enables relatively simple electron microscopic experiments to localize it within thin sections of cells or tissue. Finally, gold's brilliant optical properties at the nanoscale are tunable with size, shape, and aggregation state and enable many of the promising chemical sensing, imaging, and therapeutic applications. Basic experiments with gold nanoparticles and cells include measuring the toxicity of the particles to cells in in vitro experiments. The species other than gold in the nanoparticle solution can be responsible for the apparent toxicity at a particular dose. Once the identity of the toxic agent in nanoparticle solutions is known, researchers can employ strategies to mitigate toxicity. For example, the surfactant used at high concentration in the synthesis (0.1 M) of gold nanorods remains on their surface in the form of a bilayer and can be toxic to certain cells at 200 nM concentrations. Several strategies can alleviate the toxic response. Polyelectrolyte layer-by-layer wrapping can cover up the surfactant bilayer, or researchers can exchange the surfactant with chemically similar molecules. Researchers can also replace the surfactant with a biocompatible thiol or use a polymerizable surfactant that can be "stitched" onto the nanorods and reduce its lability. In all these cases, however, proteins or other molecules from the cellular media cover the engineered surface of the nanoparticles, which can drastically change the charges and functional groups on the nanoparticle surface.

Gold- and silver nanoparticles affect the growth characteristics of human embryonic neural precursor cells

Rapid development of nanotechnologies and their applications in clinical research have raised concerns about the adverse effects of nanoparticles (NPs) on human health and environment. NPs can be directly taken up by organs exposed, but also translocated to secondary organs, such as the central nervous system (CNS) after systemic- or subcutaneous administration, or via the olfactory system. The CNS is particularly vulnerable during development and recent reports describe transport of NPs across the placenta and even into brain tissue using in vitro and in vivo experimental systems. Here, we investigated whether well-characterized commercial 20 and 80 nm Au- and AgNPs have an effect on human embryonic neural precursor cell (HNPC) growth. After two weeks of NP exposure, uptake of NPs, morphological features and the amount of viable and dead cells, proliferative cells (Ki67 immunostaining) and apoptotic cells (TUNEL assay), respectively, were studied. We demonstrate uptake of both 20 and 80 nm Au- and AgNPs respectively, by HNPCs during proliferation. A significant effect on the sphere size- and morphology was found for all cultures exposed to Au- and AgNPs. AgNPs of both sizes caused a significant increase in numbers of proliferating and apoptotic HNPCs. In contrast, only the highest dose of 20 nm AuNPs significantly affected proliferation, whereas no effect was seen on apoptotic cell death. Our data demonstrates that both Au- and AgNPs interfere with the growth profile of HNPCs, indicating the need of further detailed studies on the adverse effects of NPs on the developing CNS.

Revealing rotational modes of functionalized gold nanorods on live cell membranes

A full understanding of cell mechanics requires knowledge of both translational and rotational dynamics. The single particle orientation and rotational tracking (SPORT) technique is combined here with correlation analysis to identify the fundamental rotational modes: in-plane rotation and out-of-plane tilting, as well as other more complex rotational patterns, from the vast image data captured at a temporal resolution of 5 ms for single gold nanorod probes in live cell imaging experiments. The unique capabilities of visualizing and understanding rotational motions of functional nanoparticles on live cell membranes allow correlation of the rotational and translational dynamics in unprecedented detail and provide new insights into complex membrane processes. Particles with functionalized surfaces, which interact with the membrane in fundamentally different ways, can exhibit distinct rotational modes and are, for the first time, directly visualized, and these show the early events for membrane approach and attachment.

In vivo study of spherical gold nanoparticles: inflammatory effects and distribution in mice

OBJECTIVES

Gold nanoparticles (AuNPs) of 21 nm have been previously well characterized in vitro for their capacity to target macrophages via active uptake. However, the short-term impact of such AuNPs on physiological systems, in particular resident macrophages located in fat tissue in vivo, is largely unknown. This project investigated the distribution, organ toxicity and changes in inflammatory cytokines within the adipose tissue after mice were exposed to AuNPs.

METHODS

Male C57BL/6 mice were injected intraperitoneally (IP) with a single dose of AuNPs (7.85 μg AuNPs/g). Body weight and energy intake were recorded daily. Tissues were collected at 1 h, 24 h and 72 h post-injection to test for organ toxicity. AuNP distribution was examined using electron microscopy. Proinflammatory cytokine expression and macrophage number within the abdominal fat pad were determined using real-time PCR.

RESULTS

At 72 hours post AuNP injection, daily energy intake and body weight were found to be similar between Control and AuNP treated mice. However, fat mass was significantly smaller in AuNP-treated mice. Following IP injection, AuNPs rapidly accumulated within the abdominal fat tissue and some were seen in the liver. A reduction in TNFα and IL-6 mRNA levels in the fat were observed from 1 h to 72 h post AuNP injection, with no observable changes in macrophage number. There was no detectable toxicity to vital organs (liver and kidney).

CONCLUSION

Our 21 nm spherical AuNPs caused no measurable organ or cell toxicity in mice, but were correlated with significant fat loss and inhibition of inflammatory effects. With the growing incidence of obesity and obesity-related diseases, our findings offer a new avenue for the potential development of gold nanoparticles as a therapeutic agent in the treatment of such disorders.

Analytical and theranostic applications of gold nanoparticles and multifunctional nanocomposites

Gold nanoparticles (GNPs) and GNP-based multifunctional nanocomposites are the subject of intensive studies and biomedical applications. This minireview summarizes our recent efforts in analytical and theranostic applications of engineered GNPs and nanocomposites by using plasmonic properties of GNPs and various optical techniques. Specifically, we consider analytical biosensing; visualization and bioimaging of bacterial, mammalian, and plant cells; photodynamic treatment of pathogenic bacteria; and photothermal therapy of xenografted tumors. In addition to recently published reports, we discuss new data on dot immunoassay diagnostics of mycobacteria, multiplexed immunoelectron microscopy analysis of Azospirillum brasilense, materno-embryonic transfer of GNPs in pregnant rats, and combined photodynamic and photothermal treatment of rat xenografted tumors with gold nanorods covered by a mesoporous silica shell doped with hematoporphyrin.

c(RGDfK) decorated micellar drug delivery system for intravesical instilled chemotherapy of superficial bladder cancer

The aim of this work was to develop a targeted drug delivery system with potentials for intravesical instilled chemotherapy of superficial bladder cancer. The amphiphilic diblock copolymer poly(ε-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) was first conjugated with the cyclic (Arginine-Glycine-Aspartic acid-d-Phenylalanine-Lysine) (c(RGDfK)) and fluorescein isothiocyannate (FITC) via the functional terminal groups of hydrophilic block, and then assembled into micelles. The interaction between micelles and various model cells was well studied by means of confocal laser scanning microscopy and flow cytometry. The c(RGDfK) on the surface of the micelle was confirmed by (1)H NMR analysis and cell affinity with human glioblastoma-astrocytoma cells (U87MG). The cell viability of bladder cancer cells (T-24 cells) after incubation with doxorubicin (DOX) loaded polymeric micelles was evaluated by in vitro cytotoxicity assay. The results revealed that c(RGDfK) modified micelles showed strong affinity to T-24 cells and strong inhibitory effect on the proliferation of T-24 cells when doxorubicin drug was loaded, indicating the high affinity of c(RGDfK) to bladder cancer cells. The c(RGDfK) modified micelles assembled from PCL-b-PEO diblock copolymers developed in this study are of great potentials as nano-scaled drug delivery system for intravesical instilled chemotherapy of superficial bladder cancer.

Equilibrium gold nanoclusters quenched with biodegradable polymers

Although sub-100 nm nanoclusters of metal nanoparticles are of interest in many fields including biomedical imaging, sensors, and catalysis, it has been challenging to control their morphologies and chemical properties. Herein, a new concept is presented to assemble equilibrium Au nanoclusters of controlled size by tuning the colloidal interactions with a polymeric stabilizer, PLA(1k)-b-PEG(10k)-b-PLA(1k). The nanoclusters form upon mixing a dispersion of ~5 nm Au nanospheres with a polymer solution followed by partial solvent evaporation. A weakly adsorbed polymer quenches the equilibrium nanocluster size and provides steric stabilization. Nanocluster size is tuned from ~20 to ~40 nm by experimentally varying the final Au nanoparticle concentration and the polymer/Au ratio, along with the charge on the initial Au nanoparticle surface. Upon biodegradation of the quencher, the nanoclusters reversibly and fully dissociate to individual ~5 nm primary particles. Equilibrium cluster size is predicted semiquantitatively with a free energy model that balances short-ranged depletion and van der Waals attractions with longer-ranged electrostatic repulsion, as a function of the Au and polymer concentrations. The close spacings of the Au nanoparticles in the clusters produce strong NIR extinction over a broad range of wavelengths from 650 to 900 nm, which is of practical interest in biomedical imaging.

Factors affecting T cell responses induced by fully synthetic glyco-gold-nanoparticles

We have synthesized and characterized nearly monodisperse and highly pure gold nanoparticles (2 and 5 nm) coated with non-immunoactive mono- and disaccharides, modelled after the capsular polysaccharide of serogroup A of the Neisseria meningitidis bacterium. We have used them to test their ability to induce immune cell responses as a consequence of their multivalency. The results indicate that they are indeed immunoactive and that immunoactivity is strongly dependent on size, and larger, 5 nm nanoparticles perform far better than smaller, 2 nm ones. Immune response (activation of macrophages) initiates with the whole nanoparticle recognition by the surface of antigen-presenting cells, independent of the saccharide oligomerization (or charge) on the nanoparticle surface. The induction of T cell proliferation and the increase of IL-2 levels, a consequence of the expression of MHC II involved in antigen presentation, require the presence of a disaccharide on the nanoparticle, not just a monosaccharide. A possible explanation is that, at this stage, the saccharides are detached from the gold surface. These results may provide leads for designing new saccharide-based, nanoparticle-conjugate vaccines.

Nanoparticles for imaging and treating brain cancer

Brain cancer tumors cause disruption of the selective properties of vascular endothelia, even causing disruptions in the very selective blood-brain barrier, which are collectively referred to as the blood-brain-tumor barrier. Nanoparticles (NPs) have previously shown great promise in taking advantage of this increased vascular permeability in other cancers, which results in increased accumulation in these cancers over time due to the accompanying loss of an effective lymph system. NPs have therefore attracted increased attention for treating brain cancer. While this research is just beginning, there have been many successes demonstrated thus far in both the laboratory and clinical setting. This review serves to present the reader with an overview of NPs for treating brain cancer and to provide an outlook on what may come in the future. For NPs, just like the blood-brain-tumor barrier, the future is wide open.

Nanoparticle toxicity by the gastrointestinal route: evidence and knowledge gaps

The increasing interest in nanoparticles for advanced technologies, consumer products, and biomedical applications has led to great excitement about potential benefits but also concern over the potential for adverse human health effects. The gastrointestinal tract represents a likely route of entry for many nanomaterials, both directly through intentional ingestion or indirectly via nanoparticle dissolution from food containers or by secondary ingestion of inhaled particles. Additionally, increased utilisation of nanoparticles may lead to increased environmental contamination and unintentional ingestion via water, food animals, or fish. The gastrointestinal tract is a site of complex, symbiotic interactions between host cells and the resident microbiome. Accordingly, evaluation of nanoparticles must take into consideration not only absorption and extraintestinal organ accumulation but also the potential for altered gut microbes and the effects of this perturbation on the host. The existing literature was evaluated for evidence of toxicity based on these considerations. Focus was placed on three categories of nanomaterials: nanometals and metal oxides, carbon-based nanoparticles, and polymer/dendrimers with emphasis on those particles of greatest relevance to gastrointestinal exposures.

Influence of gold nanoparticles on the kinetics of α-synuclein aggregation

α-synuclein (AS) is a small (140 amino acids), abundant presynaptic protein, which lacks a unique secondary structure in aqueous solution. Amyloid aggregates of AS in dopaminergic neurons of the midbrain are the hallmark of Parkinson's disease (PD). The process of aggregation involves a series of complex structural transitions from innocuous monomeric AS to oligomeric, presumably neurotoxic, forms and finally to fibril formation. Despite its potential importance for understanding PD pathobiology and devising rational, targeted therapeutic strategies, the details of the aggregation process remain largely unknown. Methodologies and reagents capable of controlling the aggregation kinetics are essential tools for the investigation of the molecular mechanisms of amyloid diseases. In this work, we investigated the influence of citrate-capped gold nanoparticles on the aggregation kinetics of AS using a fluorescent probe (MFC) sensitive to the polarity of the molecular microenvironment via excited state intramolecular proton transfer (ESIPT). The particular effects on the half time, nucleation time, and growth rate were ascertained. Gold nanoparticles produced a strong acceleration of protein aggregation with an influence on both the nucleation and growth phases of the overall mechanism. The effects were dependent on the size and concentration of the nanoparticles, being strongest for nanoparticles 10 nm in diameter, which produced a 3-fold increase in the overall aggregation rate at concentrations as low as 20 nM.

Hair fiber as a nanoreactor in controlled synthesis of fluorescent gold nanoparticles

The synthesis and detailed characterization of gold nanoparticles (AuNPs) inside human hair has been achieved by treatment of hair with HAuCl(4) in alkaline medium. The AuNPs, which show a strong red fluorescence under blue light, are generated inside the fiber and are arranged in the cortex in a remarkably regular pattern of whorls based on concentric circles, like a fingerprint. It opens an area of genuine nanocomposites with novel properties due to AuNPs inside the hair shaft.

Challenges and opportunities in the advancement of nanomedicines

Nanomedicine-based approaches to cancer treatment face several challenges that differ from those encountered by conventional medicines during clinical development. A systematic exploration of these issues has led us to identify the following needs and opportunities for further development: (1) robust and general methods for the accurate characterization of nanoparticle size, shape, and composition; (2) scalable approaches for producing nanomedicines with optimized bioavailability and excretion profiles; (3) particle engineering for maintaining low levels of nonspecific cytotoxicity and sufficient stability during storage; (4) optimization of surface chemistries for maximum targeted delivery and minimum nonspecific adsorption; (5) practical methods for quantifying ligand density and distributions on multivalent nanocarriers; and (6) the design of multifunctional nanomedicines for novel combination therapies with supportable levels of bioaccumulation.

A new approach to assess gold nanoparticle uptake by mammalian cells: combining optical dark-field and transmission electron microscopy

Toxicological effects of nanoparticles are associated with their internalization into cells. Hence, there is a strong need for techniques revealing the interaction between particles and cells as well as quantifying the uptake at the same time. For that reason, herein optical dark-field microscopy is used in conjunction with transmission electron microscopy to investigate the uptake of gold nanoparticles into epithelial cells with respect to shape, stabilizing agent, and surface charge. The number of internalized particles is strongly dependent on the stabilizing agent, but not on the particle shape. A test of metabolic activity shows no direct correlation with the number of internalized particles. Therefore, particle properties besides coating and shape are suspected to contribute to the observed toxicity.

Role of nanoparticle surface functionality in the disruption of model cell membranes

Lipid bilayers are biomembranes common to cellular life and constitute a continuous barrier between cells and their environment. Understanding the interaction of engineered nanomaterials (ENMs) with lipid bilayers is an important step toward predicting subsequent biological effects. In this study, we assess the effect of varying the surface functionality and concentration of 10-nm-diameter gold (Au) and titanium dioxide (TiO(2)) ENMs on the disruption of negatively charged lipid bilayer vesicles (liposomes) using a dye-leakage assay. Our findings show that Au ENMs having both positive and negative surface charge induce leakage that reaches a steady state after several hours. Positively charged particles with identical surface functionality and different core compositions show similar leakage effects and result in faster and greater leakage than negatively charged particles, which suggests that surface functionality, not particle core composition, is a critical factor in determining the interaction between ENMs and lipid bilayers. The results suggest that particles permanently adsorb to bilayers and that only one positively charged particle is required to disrupt a liposome and trigger the leakage of its entire contents in contrast to mellitin molecules, the most widely studied membrane lytic peptide, which requires hundred of molecules to generate leakage.

Modulation of G protein-coupled adenosine receptors by strategically functionalized agonists and antagonists immobilized on gold nanoparticles

Gold nanoparticles (AuNPs) allow the tuning of pharmacokinetic and pharmacodynamic properties by active or passive targeting of drugs for cancer and other diseases. We have functionalized gold nanoparticles by tethering specific ligands, agonists and antagonists, of adenosine receptors (ARs) to the gold surface as models for cell surface interactions with G protein-coupled receptors (GPCRs). The AuNP conjugates with chain-extended AR ligands alone (PEGylated nucleosides and nonnucleosides, anchored to the Au via thioctic acid) were found to be insoluble in water due to hydrophobic entities in the ligand. Therefore, we added a second, biologically inactive pendant moiety to increase the water solubility, consisting of a PEGylated chain terminating in a carboxylic or phosphate group. The purity and stability of the immobilized biologically active ligand were examined by ultrafiltration and HPLC. Pharmacological receptor binding studies on these GPCR ligand-derivatized AuNPs (2-5 nm in diameter), performed using membranes of mammalian cells stably expressing human A1, A2A, and A3ARs, showed that the desired selectivity was retained with K(i) values (nanomolar) of A3AR agonist 21b and A2AAR antagonists 24 and 26a of 14 (A3), 34 (A2A), and 69 (A2A), respectively. The corresponding monomers displayed K i values of 37, 61, and 1,420 nM, respectively. In conclusion, we have synthesized stable, water-soluble AuNP derivatives of tethered A3 and A2AAR ligands that retain the biological properties of their monomeric ligands and are intended for therapeutic and imaging applications. This is the first prototypical application to gold carriers of small molecule (nonpeptide) GPCR ligands, which are under investigation for treatment of cancer and inflammatory diseases.

Preparation of concentrated colloids of gold core-silica shell nanoparticles for biomedical applications

Encapsulation of gold nanoparticles within a silica shell is highly beneficial to the preparation of highly concentrated gold nanoparticles that can strongly absorb X-ray and hence be used as an X-ray contrast agent. This chapter describes a method for preparing highly concentrated colloidal gold nanoparticles suitable for an X-ray contrast agent application. It describes specific details of procedures for preparing spherical gold nanoparticles, forming thin silica shell on each gold nanoparticle, and enriching the silica-encapsulated gold nanoparticles.

Effects of gestational age and surface modification on materno-fetal transfer of nanoparticles in murine pregnancy

Nanoparticle exposure in pregnancy may result in placental damage and fetotoxicity; however, the factors that determine fetal nanoparticle exposure are unclear. Here we have assessed the effect of gestational age and nanoparticle composition on fetal accumulation of maternally-administered nanomaterials in mice. We determined the placental and fetal uptake of 13 nm gold nanoparticles with different surface modifications (ferritin, PEG and citrate) following intravenous administration at E5.5-15.5. We showed that prior to E11.5, all tested nanoparticles could be visualized and detected in fetal tissues in significant amounts; however, fetal gold levels declined dramatically post-E11.5. In contrast, Au-nanoparticle accumulation in the extraembryonic tissues (EET) increased 6–15 fold with gestational age. Fetal and EET accumulation of ferritin- and PEG-modified nanoparticles was considerably greater than citrate-capped nanoparticles. No signs of toxicity were observed. Fetal exposure to nanoparticles in murine pregnancy is, therefore, influenced by both stage of embryonic/placental maturation and nanoparticle surface composition.

DNA damage enhancement from gold nanoparticles for clinical MV photon beams

In this study, we quantify the relative damage enhancement due to the presence of gold nanoparticles (GNP) in vitro in a clinical 6 MV beam for various delivery parameters and depths. It is expected that depths and delivery modes that produce a larger proportions of low-energy photons will have a larger effect on the cell samples containing GNP. HeLa cells with and without 50 nm GNP were irradiated at depths of 1.5, 5, 10, 15 and 20 cm. Conventional beams with square aperture sizes 5, 10 and 15 cm at isocenter, and flattening filter free (FFF) beams were used. Relative DNA damage enhancement with GNP was evaluated by γ-H2AX staining. Statistically significant increases in DNA damage with GNP, compared to the absence of GNP, were observed for all depths and delivery modes. Relative to the shallowest depth, damage enhancement was observed to increase as a function of increasing depth for all deliveries. For the conventional (open field) delivery, DNA damage enhancement with GNP was seen to increase as a function of field size. For FFF delivery, a substantial increase in enhancement was found relative to the conventional field delivery. The measured relative DNA damage enhancement validates the theoretically predicted trends as a function of depth and delivery mode for clinical MV photon beams. The results of this study open new possibilities for the clinical development of gold nanoparticle-aided radiation therapy.

Fluorescence-tagged gold nanoparticles for rapidly characterizing the size-dependent biodistribution in tumor models

Nanoparticle vehicles may improve the delivery of contrast agents and therapeutics to diseased tissues, but their rational design is currently impeded by a lack of robust technologies to characterize their in vivo behavior in real-time. This study demonstrates that fluorescent-labeled gold nanoparticles can be optimized for in vivo detection, perform pharmacokinetic analysis of nanoparticle designs, analyze tumor extravasation, and clearance kinetics in tumor-bearing animals. This optical imaging approach is non-invasive and high-throughput. Interestingly, these fluorescent gold nanoparticles can be used for multispectral imaging to compare several nanoparticle designs simultaneously within the same animal and eliminates the host-dependent variabilities across measured data. Together these results describe a novel platform for evaluating the performance of tumor-targeting nanoparticles, and provide new insights for the design of future nanotherapeutics.

Shedding light on nanomedicine

Light is an electromagnetic radiation that can convert its energy into different forms (e.g., heat, chemical energy, and acoustic waves). This property has been exploited in phototherapy (e.g., photothermal therapy and photodynamic therapy (PDT)) and optical imaging (e.g., fluorescence imaging) for therapeutic and diagnostic purposes. Light-controlled therapies can provide minimally- or noninvasive spatiotemporal control as well as deep tissue penetration. Nanotechnology provides numerous advantages, including selective targeting of tissues, prolongation of therapeutic effect, protection of active payloads, and improved therapeutic indices. This review explores the advances that nanotechnology can bring to light-based therapies and diagnostics, and vice versa, including photo-triggered systems, nanoparticles containing photoactive molecules, and nanoparticles that are themselves photoactive. Limitations of light-based therapies such as photic injury and phototoxicity are discussed.

Gold nanoparticles: emerging paradigm for targeted drug delivery system

The application of nanotechnology in medicine, known as nanomedicine, has introduced a plethora of nanoparticles of variable chemistry and design considerations for cancer diagnosis and treatment. One of the most important field is the design and development of pharmaceutical drugs, based on targeted drug delivery system (TDDS). Being inspired by physio-chemical properties of nanoparticles, TDDS are designed to safely reach their targets and specifically release their cargo at the site of disease for enhanced therapeutic effects, thereby increasing the drug tissue bioavailability. Nanoparticles have the advantage of targeting cancer by simply being accumulated and entrapped in cancer cells. However, even after rapid growth of nanotechnology in nanomedicine, designing an effective targeted drug delivery system is still a challenging task. In this review, we reveal the recent advances in drug delivery approach with a particular focus on gold nanoparticles. We seek to expound on how these nanomaterials communicate in the complex environment to reach the target site, and how to design the effective TDDS for complex environments and simultaneously monitor the toxicity on the basis of designing such delivery complexes. Hence, this review will shed light on the research, opportunities and challenges for engineering nanomaterials with cancer biology and medicine to develop effective TDDS for treatment of cancer.

Synthesis and in vivo pharmacokinetic evaluation of degradable shell cross-linked polymer nanoparticles with poly(carboxybetaine) versus poly(ethylene glycol) surface-grafted coatings

Nanoparticles with tunable pharmacokinetics are desirable for various biomedical applications. Poly(ethylene glycol) (PEG) is well-known to create "stealth" effects to stabilize and extend the blood circulation of nanoparticles. In this work, poly(carboxybetaine) (PCB), a new nonfouling polymer material, was incorporated as surface-grafted coatings, conjugated onto degradable shell cross-linked knedel-like nanoparticles (dSCKs) composed of poly(acrylic acid)-based shells and poly(lactic acid) cores, to compare the in vivo pharmacokinetics to their PEG-functionalized analogues. A series of five dSCKs was prepared from amphiphilic block copolymers, having different numbers and lengths of either PEG or PCB grafts, by supramolecular assembly in water followed by shell cross-linking, and then studied by a lactate assay to confirm their core hydrolytic degradabilities. Each dSCK was also conjugated with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid macrocyclic chelators and tyramine moieties to provide for (64)Cu and/or radiohalogen labeling. The high specific activity of (64)Cu radiolabeling ensured nanogram administration of dSCKs for in vivo evaluation of their pharmacokinetics. Biodistribution studies demonstrated comparable in vivo pharmacokinetic profiles of PCB-grafted dSCKs to their PEG-conjugated counterparts. These results indicated that PCB-functionalized dSCKs have great potential as a theranostic platform for translational research.