Biopersistence and potential adverse health impacts of fibrous nanomaterials: what have we learned from asbestos?

Altered global gene expression profiles in human gastrointestinal epithelial Caco2 cells exposed to nanosilver

Extensive consumer exposure to food- and cosmetics-related consumer products containing nanosilver is of public safety concern. Therefore, there is a need for suitable in vitro models and sensitive predictive rapid screening methods to assess their toxicity. Toxicogenomic profile showing subtle changes in gene expressions following nanosilver exposure is a sensitive toxicological endpoint for this purpose. We evaluated the Caco2 cells and global gene expression profiles as tools for predictive rapid toxicity screening of nanosilver. We evaluated and compared the gene expression profiles of Caco-2 cells exposed to 20 nm and 50 nm nanosilver at a concentration 2.5 μg/ml. The global gene expression analysis of Caco2 cells exposed to 20 nm nanosilver showed that a total of 93 genes were altered at 4 h exposure, out of which 90 genes were up-regulated and 3 genes were down-regulated. The 24 h exposure of 20 nm silver altered 15 genes in Caco2 cells, out of which 14 were up-regulated and one was down-regulated. The most pronounced changes in gene expression were detected at 4 h. The greater size (50 nm) nanosilver at 4 h exposure altered more genes by more different pathways than the smaller (20 nm) one. Metallothioneins and heat shock proteins were highly up-regulated as a result of exposure to both the nanosilvers. The cellular pathways affected by the nanosilver exposure is likely to lead to increased toxicity. The results of our study presented here suggest that the toxicogenomic characterization of Caco2 cells is a valuable in vitro tool for assessing toxicity of nanomaterials such as nanosilver.

Carbon Nanotube Emissions from Arc Discharge Production: Classification of Particle Types with Electron Microscopy and Comparison with Direct Reading Techniques

Introduction:

An increased production and use of carbon nanotubes (CNTs) is occurring worldwide. In parallel, a growing concern is emerging on the adverse effects the unintentional inhalation of CNTs can have on humans. There is currently a debate regarding which exposure metrics and measurement strategies are the most relevant to investigate workplace exposures to CNTs. This study investigated workplace CNT emissions using a combination of time-integrated filter sampling for scanning electron microscopy (SEM) and direct reading aerosol instruments (DRIs).

Material and Methods:

Field measurements were performed during small-scale manufacturing of multiwalled carbon nanotubes using the arc discharge technique. Measurements with highly time- and size-resolved DRI techniques were carried out both in the emission and background (far-field) zones. Novel classifications and counting criteria were set up for the SEM method. Three classes of CNT-containing particles were defined: type 1: particles with aspect ratio length:width >3:1 (fibrous particles); type 2: particles without fibre characteristics but with high CNT content; and type 3: particles with visible embedded CNTs.

Results:

Offline sampling using SEM showed emissions of CNT-containing particles in 5 out of 11 work tasks. The particles were classified into the three classes, of which type 1, fibrous CNT particles contributed 37%. The concentration of all CNT-containing particles and the occurrence of the particle classes varied strongly between work tasks. Based on the emission measurements, it was assessed that more than 85% of the exposure originated from open handling of CNT powder during the Sieving, mechanical work-up, and packaging work task. The DRI measurements provided complementary information, which combined with SEM provided information on: (i) the background adjusted emission concentration from each work task in different particle size ranges, (ii) identification of the key procedures in each work task that lead to emission peaks, (iii) identification of emission events that affect the background, thereby leading to far-field exposure risks for workers other than the operator of the work task, and (iv) the fraction of particles emitted from each source that contains CNTs.

Conclusions:

There is an urgent need for a standardized/harmonized method for electron microscopy (EM) analysis of CNTs. The SEM method developed in this study can form the basis for such a harmonized protocol for the counting of CNTs. The size-resolved DRI techniques are commonly not specific enough to selective analysis of CNT-containing particles and thus cannot yet replace offline time-integrated filter sampling followed by SEM. A combination of EM and DRI techniques offers the most complete characterization of workplace emissions of CNTs today.

The path towards healthier societies, environments, and economies: a broader perspective for sustainable engineered nanomaterials

Economic value is no longer adequate by itself as a proxy for the value-added benefits (VAB) assumed to be generated by emerging technologies such as engineered nanomaterials (ENMs). This study was conducted to explore the potential to establish an integrated sociotechnical framework with the end goal to assess whether or not ENMs and nano-enabled products contribute VAB. Based on the research in this study, it is suggested that all stakeholders in the larger society-environment-economy (SEE) system should develop an understanding of the multiple interrelationships within and between the diverse constituents along the particle lifecycle trajectory to capture their influence on the system benefit and risk outcomes. Furthermore, the sociotechnical framework establishes an additional three-step process: (1) at the pre-design stage, the test of VAB should be assessed using an expert panel representing the different segments of SEE, the social principles of design are detailed and customized to the needs of ENMs and nano-enabled products, and an economic appraisal is conducted to justify the VAB on material grounds; (2) at the design stage, the technical principles should be examined and detailed to ensure the compatibility of stakeholder needs; and (3) an iterative adaptive cycle should be conducted to re-examine the sociotechnical principles on a periodic basis. Within this context, ENMs are considered sustainable when (a) the conditions of VAB and minimal risk elements are satisfied in a sequential order, with VAB demonstrated at the pre-design stage, then at the design stage ENMs posing no harm greater than minimal levels to the SEE constituents; and (b) ENMs and nano-enabled products are bounded by a finite time limit. In addition, to reach the conditions of sustainability, the role of all SEE stakeholders should be broadened (e.g., regulatory agencies should transform their roles from not only the control of risks of negative implications, but also the establishment of positive implications as well).

Coupled elasticity-diffusion model for the effects of cytoskeleton deformation on cellular uptake of cylindrical nanoparticles

Molecular dynamic simulations and experiments have recently demonstrated how cylindrical nanoparticles (CNPs) with large aspect ratios penetrate animal cells and inevitably deform cytoskeletons. Thus, a coupled elasticity-diffusion model was adopted to elucidate this interesting biological phenomenon by considering the effects of elastic deformations of cytoskeleton and membrane, ligand-receptor binding and receptor diffusion. The mechanism by which the binding energy drives the CNPs with different orientations to enter host cells was explored. This mechanism involved overcoming the resistance caused by cytoskeleton and membrane deformations and the change in configurational entropy of the ligand-receptor bonds and free receptors. Results showed that deformation of the cytoskeleton significantly influenced the engulfing process by effectively slowing down and even hindering the entry of the CNPs. Additionally, the engulfing depth was determined quantitatively. CNPs preferred or tended to vertically attack target cells until they were stuck in the cytoskeleton as implied by the speed of vertically oriented CNPs that showed much faster initial engulfing speeds than horizontally oriented CNPs. These results elucidated the most recent molecular dynamics simulations and experimental observations on the cellular uptake of carbon nanotubes and phagocytosis of filamentous Escherichia coli bacteria. The most efficient engulfment showed the stiffness-dependent optimal radius of the CNPs. Cytoskeleton stiffness exhibited more significant influence on the optimal sizes of the vertical uptake than the horizontal uptake.

Toxicogenomic responses of human liver HepG2 cells to silver nanoparticles

The increased use of silver nanoparticles (AgNPs) in foods and cosmetics has raised public safety concerns. However, only limited knowledge exists on the effect of AgNPs on the cellular transcriptome. This study evaluated global gene expression profiles of human liver HepG2 cells exposed to 20 and 50 nm AgNPs for 4 and 24 h at 2.5 µg ml(-1) . Exposure to 20 nm AgNPs resulted in 811 altered genes after 4 h, but much less after 24 h. Exposure to 50 nm AgNPs showed minimal altered genes at both exposure times. The HepG2 cells responded to the toxic insult of AgNPs by transiently upregulating stress response genes such as metallothioneins and heat shock proteins. Functional analysis of the altered genes showed more than 20 major biological processes were affected, of which metabolism, development, cell differentiation and cell death were the most dominant categories. Several cellular pathways were also impacted by AgNP exposure, including the p53 signaling pathway and the NRF2-mediated oxidative stress response pathway, which may lead to increased oxidative stress and DNA damage in the cell and potentially result in genotoxicity and carcinogenicity. Together, these results indicate that HepG2 cells underwent a multitude of cellular processes in response to the toxic insult of AgNP exposure, and suggest that toxicogenomic characterization of human HepG2 cells could serve as an alternative model for assessing toxicities of NPs.

Titanium dioxide nanoparticles induce an adaptive inflammatory response and invasion and proliferation of lung epithelial cells in chorioallantoic membrane

Titanium dioxide nanoparticles (TiO2 NPs) studies have been performed using relatively high NPs concentration under acute exposure and limited studies have compared shape effects. We hypothesized that midterm exposure to low TiO2 NPs concentration in lung epithelial cells induces carcinogenic characteristics modulated partially by NPs shape. To test our hypothesis we synthesized NPs shaped as belts (TiO2-B) using TiO2 spheres (TiO2-SP) purchased from Sigma Aldrich Co. Then, lung epithelial A549 cells were low-exposed (10 µg/cm(2)) to both shapes during 7 days and internalization, cytokine release and invasive potential were determined. Results showed greater TiO2-B effect on agglomerates size, cell size and granularity than TiO2-SP. Agglomerates size in cell culture medium was 310 nm and 454 nm for TiO2-SP and TiO2-B, respectively; TiO2-SP and TiO2-B induced 23% and 70% cell size decrease, respectively, whilst TiO2-SP and TiO2-B induced 7 and 14-fold of granularity increase. NOx production was down-regulated (31%) by TiO2-SP and up-regulated (70%) by TiO2-B. Both NPs induced a transient cytokine release (IL-2, IL-6, IL-8, IL-4, IFN-γ, and TNF-α) after 4 days, but cytokines returned to basal levels in TiO2-SP exposed cells while TiO2-B induced a down-regulation after 7 days. Midterm exposure to both shapes of NPs induced capability to degrade cellular extracellular matrix components from chorioallantoic membrane and Ki-67 marker showed that TiO2-B had higher proliferative potential than TiO2-SP. We conclude that midterm exposure to low NPs concentration of NPs has an impact in the acquisition of new characteristics of exposed cells and NPs shape influences cellular outcome.

Single-walled carbon nanotubes induce cell death and transcription of TNF-α in macrophages without affecting nitric oxide production

Single-walled carbon nanotubes (SWCNTs) are potent nanomaterials that have diverse shapes and features. The utilization of these molecules for drug delivery is being investigated; thus, it is important to determine whether they alter immune responses against pathogens. In this study, we show that macrophages treated with a mixture of lipopolysaccharide and SWCNTs produced normal levels of nitric oxide and inducible nitric oxide synthase mRNA. However, these treatments induced cell death, presumably via necrosis. In addition, treating cells with SWCNTs induced the expression of tumor necrosis factor-α mRNA, a potent pro-inflammatory cytokine. These results suggest that SWCNTs may influence immune responses, which could result in unexpected effects following their administration for the purpose of drug delivery.

USNCTAM perspectives on mechanics in medicine

Over decades, the theoretical and applied mechanics community has developed sophisticated approaches for analysing the behaviour of complex engineering systems. Most of these approaches have targeted systems in the transportation, materials, defence and energy industries. Applying and further developing engineering approaches for understanding, predicting and modulating the response of complicated biomedical processes not only holds great promise in meeting societal needs, but also poses serious challenges. This report, prepared for the US National Committee on Theoretical and Applied Mechanics, aims to identify the most pressing challenges in biological sciences and medicine that can be tackled within the broad field of mechanics. This echoes and complements a number of national and international initiatives aiming at fostering interdisciplinary biomedical research. This report also comments on cultural/educational challenges. Specifically, this report focuses on three major thrusts in which we believe mechanics has and will continue to have a substantial impact. (i) Rationally engineering injectable nano/microdevices for imaging and therapy of disease. Within this context, we discuss nanoparticle carrier design, vascular transport and adhesion, endocytosis and tumour growth in response to therapy, as well as uncertainty quantification techniques to better connect models and experiments. (ii) Design of biomedical devices, including point-of-care diagnostic systems, model organ and multi-organ microdevices, and pulsatile ventricular assistant devices. (iii) Mechanics of cellular processes, including mechanosensing and mechanotransduction, improved characterization of cellular constitutive behaviour, and microfluidic systems for single-cell studies.

Amphibole, but not chrysotile, asbestos induces anti-nuclear autoantibodies and IL-17 in C57BL/6 mice

Abstract Exposure to amphibole asbestos has been associated with production of autoantibodies in mice and humans, and increases the risk of systemic autoimmune disease. However, epidemiological studies of chrysotile exposure have not indicated a similar induction of autoimmune responses. To demonstrate this difference in controlled exposures in mice, and to explore possible mechanistic explanations for the difference, C57BL/6 mice were exposed intratracheally to amphibole or chrysotile asbestos, or to saline only. Serum antinuclear antibodies (ANA), antibodies to extractable nuclear antigens (ENA), serum cytokines, and immunoglobulin isotypes were evaluated 8 months after the final treatment. The percentages of lymphocyte sub-sets were determined in the spleen and lungs. The results show that amphibole, but not chrysotile, asbestos increases the frequency of ANA/ENA in mice. Amphibole and chrysotile both increased multiple serum cytokines, but only amphibole increased IL-17. Both fibers decreased IgG1, without significant changes in other immunoglobulin isotypes. Although there were no gross changes in overall percentages of T- and B-cells in the spleen or lung, there was a significant increase in the normally rare populations of suppressor B-cells (CD19(+), CD5(+), CD1d(+)) in both the spleen and lungs of chrysotile-exposed mice. Overall, the results suggest that, while there may be an inflammatory response to both forms of asbestos, there is an autoimmune response in only the amphibole-exposed, but not the chrysotile-exposed mice. These data have critical implications in terms of screening and health outcomes of asbestos-exposed populations.

Croix CM, Watkins SC, Kisin ER, Kotchey GP, Balasubramanian K, Vlasova II, Yu J, Kim K, Seo W, Mallampalli RK, Star A, Shvedova AA. Lung macrophages "digest" carbon nanotubes using a superoxide/peroxynitrite oxidative pathway

In contrast to short-lived neutrophils, macrophages display persistent presence in the lung of animals after pulmonary exposure to carbon nanotubes. While effective in the clearance of bacterial pathogens and injured host cells, the ability of macrophages to "digest" carbonaceous nanoparticles has not been documented. Here, we used chemical, biochemical, and cell and animal models and demonstrated oxidative biodegradation of oxidatively functionalized single-walled carbon nanotubes via superoxide/NO* → peroxynitrite-driven oxidative pathways of activated macrophages facilitating clearance of nanoparticles from the lung.

Immunopathological effects of malaria pigment or hemozoin and other crystals

Blood-stage malaria parasites produce insoluble hemozoin (Hz) crystals that are released in the blood circulation upon schizont rupture. In general, endogenous crystal formation or inhalation of crystalline materials is often associated with pathology. As the immune system responds differently to crystalline particles than to soluble molecules, in this review, the properties, immunological recognition, and pathogenic responses of Hz are discussed, and compared with two other major pathogenic crystals, monosodium urate (MSU) and asbestos. Because of the size and shape of MSU crystals and asbestos fibers, phagolysosomal formation is inefficient and often results in leakage of lysosomal content in the cell cytoplasm and/or in the extracellular environment with subsequent cell damage and cell death. Phagolysosomal formation after Hz ingestion is normal, but Hz remains stored inside these cells for months or even longer without any detectable degradation. Nonetheless, the different types of crystals are recognized by similar immune receptors, involving Toll-like receptors, the inflammasome, antibodies, and/or complement factors, and through similar signaling cascades, they activate both proinflammatory and anti-inflammatory immune responses that contribute to inflammation-associated pathology.

Graphene-based nanomaterials for drug delivery and tissue engineering

Nanomaterials offer interesting physicochemical and biological properties for biomedical applications due to their small size, large surface area and ability to interface/interact with the cells/tissues. Graphene-based nanomaterials are fast emerging as "two-dimensional wonder materials" due to their unique structure and excellent mechanical, optical and electrical properties and have been exploited in electronics and other fields. Emerging trends show that their exceptional properties can be exploited for biomedical applications, especially in drug delivery and tissue engineering. This article presents a comprehensive review of various types and properties of graphene family nanomaterials. We further highlight how these properties are being exploited for drug delivery and tissue engineering applications.

Towards predicting the lung fibrogenic activity of nanomaterials: experimental validation of an in vitro fibroblast proliferation assay

Background

Carbon nanotubes (CNT) can induce lung inflammation and fibrosis in rodents. Several studies have identified the capacity of CNT to stimulate the proliferation of fibroblasts. We developed and validated experimentally here a simple and rapid in vitro assay to evaluate the capacity of a nanomaterial to exert a direct pro-fibrotic effect on fibroblasts.

Methods

The activity of several multi-wall (MW)CNT samples (NM400, the crushed form of NM400 named NM400c, NM402 and MWCNTg 2400) and asbestos (crocidolite) was investigated in vitro and in vivo. The proliferative response to MWCNT was assessed on mouse primary lung fibroblasts, human fetal lung fibroblasts (HFL-1), mouse embryonic fibroblasts (BALB-3T3) and mouse lung fibroblasts (MLg) by using different assays (cell counting, WST-1 assay and propidium iodide PI staining) and dispersion media (fetal bovine serum, FBS and bovine serum albumin, BSA). C57BL/6 mice were pharyngeally aspirated with the same materials and lung fibrosis was assessed after 2 months by histopathology, quantification of total collagen lung content and pro-fibrotic cytokines in broncho-alveolar lavage fluid (BALF).

Results

MWCNT (NM400 and NM402) directly stimulated fibroblast proliferation in vitro in a dose-dependent manner and induced lung fibrosis in vivo. NM400 stimulated the proliferation of all tested fibroblast types, independently of FBS- or BSA- dispersion. Results obtained by WST1 cell activity were confirmed with cell counting and cell cycle (PI staining) assays. Crocidolite also stimulated fibroblast proliferation and induced pulmonary fibrosis, although to a lesser extent than NM400 and NM402. In contrast, shorter CNT (NM400c and MWCNTg 2400) did not induce any fibroblast proliferation or collagen accumulation in vivo, supporting the idea that CNT structure is an important parameter for inducing lung fibrosis.

Conclusions

In this study, an optimized proliferation assay using BSA as a dispersant, MLg cells as targets and an adaptation of WST-1 as readout was developed. The activity of MWCNT in this test strongly reflects their fibrotic activity in vivo, supporting the predictive value of this in vitro assay in terms of lung fibrosis potential.

Animal models of fibrotic lung disease

Interstitial lung fibrosis can develop as a consequence of occupational or medical exposure, as a result of genetic defects, and after trauma or acute lung injury leading to fibroproliferative acute respiratory distress syndrome, or it can develop in an idiopathic manner. The pathogenesis of each form of lung fibrosis remains poorly understood. They each result in a progressive loss of lung function with increasing dyspnea, and most forms ultimately result in mortality. To better understand the pathogenesis of lung fibrotic disorders, multiple animal models have been developed. This review summarizes the common and emerging models of lung fibrosis to highlight their usefulness in understanding the cell-cell and soluble mediator interactions that drive fibrotic responses. Recent advances have allowed for the development of models to study targeted injuries of Type II alveolar epithelial cells, fibroblastic autonomous effects, and targeted genetic defects. Repetitive dosing in some models has more closely mimicked the pathology of human fibrotic lung disease. We also have a much better understanding of the fact that the aged lung has increased susceptibility to fibrosis. Each of the models reviewed in this report offers a powerful tool for studying some aspect of fibrotic lung disease.

Graphene microsheets enter cells through spontaneous membrane penetration at edge asperities and corner sites

Understanding and controlling the interaction of graphene-based materials with cell membranes is key to the development of graphene-enabled biomedical technologies and to the management of graphene health and safety issues. Very little is known about the fundamental behavior of cell membranes exposed to ultrathin 2D synthetic materials. Here we investigate the interactions of graphene and few-layer graphene (FLG) microsheets with three cell types and with model lipid bilayers by combining coarse-grained molecular dynamics (MD), all-atom MD, analytical modeling, confocal fluorescence imaging, and electron microscopic imaging. The imaging experiments show edge-first uptake and complete internalization for a range of FLG samples of 0.5- to 10-μm lateral dimension. In contrast, the simulations show large energy barriers relative to kBT for membrane penetration by model graphene or FLG microsheets of similar size. More detailed simulations resolve this paradox by showing that entry is initiated at corners or asperities that are abundant along the irregular edges of fabricated graphene materials. Local piercing by these sharp protrusions initiates membrane propagation along the extended graphene edge and thus avoids the high energy barrier calculated in simple idealized MD simulations. We propose that this mechanism allows cellular uptake of even large multilayer sheets of micrometer-scale lateral dimension, which is consistent with our multimodal bioimaging results for primary human keratinocytes, human lung epithelial cells, and murine macrophages.

Biocompatibility of pristine graphene for neuronal interface

OBJECT

Graphene possesses unique electrical, physical, and chemical properties that may offer significant potential as a bioscaffold for neuronal regeneration after spinal cord injury. The purpose of this investigation was to establish the in vitro biocompatibility of pristine graphene for interface with primary rat cortical neurons.

METHODS

Graphene films were prepared by chemical vapor deposition on a copper foil catalytic substrate and subsequent apposition on bare Permanox plastic polymer dishes. Rat neuronal cell culture was grown on graphene-coated surfaces, and cell growth and attachment were compared with those on uncoated and poly-d-lysine (PDL)-coated controls; the latter surface is highly favorable for neuronal attachment and growth. Live/dead cell analysis was conducted with flow cytometry using ethidium homodimer-1 and calcein AM dyes. Lactate dehydrogenase (LDH) levels-indicative of cytotoxicity-were measured as markers of cell death. Phase contrast microscopy of active cell culture was conducted to assess neuronal attachment and morphology.

RESULTS

Statistically significant differences in the percentage of live or dead neurons were noted between graphene and PDL surfaces, as well as between the PDL-coated and bare surfaces, but there was little difference in cell viability between graphene-coated and bare surfaces. There were significantly lower LDH levels in the graphene-coated samples compared with the uncoated ones, indicating that graphene was not more cytotoxic than the bare control surface. According to phase contrast microscopy, neurons attached to the graphene-coated surface and were able to elaborate long, neuritic processes suggestive of normal neuronal metabolism and morphology.

CONCLUSIONS

Further use of graphene as a bioscaffold will require surface modification that enhances hydrophilicity to increase cellular attachment and growth. Graphene is a nanomaterial that is biocompatible with neurons and may have significant biomedical applications.

Mechanisms of toxicity by carbon nanotubes

Carbon nanotubes (CNTs) consist of a family of carbon built nanoparticles, whose biological effects depend on their physical characteristics and other constitutive chemicals (impurities and functions attached). CNTs are considered the twenty first century material due to their unique physicochemical characteristics and applicability to industrial product. The use of these materials steadily increases worldwide and toxic outcomes need to be studied for each nanomaterial in depth to prevent adverse effects to humans and the environment. Entrance into the body is physical, and usually few nanoparticles enter the body; however, once there, they are persistent due to their limited metabolisms, so their removal is slow, and chronic cumulative health effects are studied. Oxidative stress is the main mechanism of toxicity but size, agglomeration, chirality as well as impurities and functionalization are some of the structural and chemical characteristic contributing to the CNTs toxicity outcomes. Among the many toxicity pathways, interference with cytoskeleton and fibrous mechanisms, cell signaling, membrane perturbations and the production of cytokines, chemokines and inflammation are some of the effects resulting from exposure to CNTs. The aim of this review is to offer an up-to-date scope of the effects of CNTs on biological systems with attention to mechanisms of toxicity.

Length-dependent effect of single-walled carbon nanotube exposure in a dynamic cell growth environment of human alveolar epithelial cells

Despite the great use of nanomaterials for engineering and medical applications, nanomaterials may have adverse consequences by accidental exposure, because of their nanoscale size, composition and shape. Like many nanomaterials, carbon nanotubes (CNTs) have been used for many proven applications, but the size of the CNTs makes them more readily become airborne and can therefore create the risk of being inhaled by a worker. In this study, we evaluated single-walled CNT (SWCNT)-induced effects on cellular responses such as cell proliferation, inflammatory response and oxidative stress in dynamic cell growth condition. A dynamic cell growth environment was established to mimic the dynamic changes in the amount of circumferential and longitudinal expansion and contraction occurred during normal breathing movement in the lung. Two different length (short: outer diameter (OD) 1-2 nm, length 0.5-2 μm; long: OD 1-2 nm, length 5-30 μm) of SWCNTs were used at different exposure concentrations (5, 10 and 20 μg/ml) during the different exposure duration (24, 48 and 72 h). Dynamic environment facilitated altered interaction between SWCNTs and A549 monolayer. Cellular responses in dynamic condition were significantly different from those in static condition. Moreover, cellular responses were dependent on the length of SWCNTs both in static and dynamic cell growth conditions.

Arsenic, asbestos and radon: emerging players in lung tumorigenesis

The cause of lung cancer is generally attributed to tobacco smoking. However lung cancer in never smokers accounts for 10 to 25% of all lung cancer cases. Arsenic, asbestos and radon are three prominent non-tobacco carcinogens strongly associated with lung cancer. Exposure to these agents can lead to genetic and epigenetic alterations in tumor genomes, impacting genes and pathways involved in lung cancer development. Moreover, these agents not only exhibit unique mechanisms in causing genomic alterations, but also exert deleterious effects through common mechanisms, such as oxidative stress, commonly associated with carcinogenesis. This article provides a comprehensive review of arsenic, asbestos, and radon induced molecular mechanisms responsible for the generation of genetic and epigenetic alterations in lung cancer. A better understanding of the mode of action of these carcinogens will facilitate the prevention and management of lung cancer related to such environmental hazards.

Silicon, a Possible Link between Environmental Exposure and Autoimmune Diseases: The Case of Rheumatoid Arthritis

Silicon is one of the most common chemicals on earth. Several compounds such as silica, asbestos, silicone or, nanoparticles are built from tetrahedral units with silicon as the central atom. Despite these, structural similarities, they have rarely been analyzed as a group. These compounds generate significant biological alterations that include immune hyperactivation, production of the reactive species of oxygen and tissue injury. These pathological processes may trigger autoimmune responses and lead to the development of rheumatoid arthritis. Populations at risk include those that constantly work in industrial process, mining, and agriculture as well as those that undergo silicone implants. Herein a review on the main features of these compounds and how they may induce autoimmune responses is presented.

Distinct affinity of nuclear proteins to the surface of chrysotile and crocidolite

The inhalation of asbestos is a risk factor for the development of malignant mesothelioma and lung cancer. Based on the broad surface area of asbestos fibers and their ability to enter the cytoplasm and nuclei of cells, it was hypothesized that proteins that adsorb onto the fiber surface play a role in the cytotoxicity and carcinogenesis of asbestos fibers. However, little is known about which proteins adsorb onto asbestos. Previously, we systematically identified asbestos-interacting proteins and classified them into eight sub-categories: chromatin/nucleotide/RNA-binding proteins, ribosomal proteins, cytoprotective proteins, cytoskeleton-associated proteins, histones and hemoglobin. Here, we report an adsorption profile of proteins for the three commercially used asbestos compounds: chrysotile, crocidolite and amosite. We quantified the amounts of adsorbed proteins by analyzing the silver-stained gels of sodium dodecyl sulfate-polyacrylamide gel electrophoresis with ImageJ software, using the bands for amosite as a standard. We found that histones were most adsorptive to crocidolite and that chromatin-binding proteins were most adsorptive to chrysotile. The results suggest that chrysotile and crocidolite directly interact with chromatin structure through different mechanisms. Furthermore, RNA-binding proteins preferably interacted with chrysotile, suggesting that chrysotile may interfere with transcription and translation. Our results provide novel evidence demonstrating that the specific molecular interactions leading to carcinogenesis are different between chrysotile and crocidolite.

Sumas Mountain chrysotile induces greater lung fibrosis in Fischer344 rats than Libby amphibole, El Dorado tremolite, and Ontario ferroactinolite

The physical properties of different types of asbestos may strongly affect health outcomes in exposed individuals. This study was designed to provide understanding of the comparative toxicity of naturally occurring asbestos (NOA) fibers including Libby amphibole (LA), Sumas Mountain chrysotile (SM), El Dorado tremolite (ED), and Ontario ferroactinolite (ON) cleavage fragments. Rat-respirable fractions (PM₂.₅) were prepared by water elutriation. Surface area was greater for SM (64.1 m²/g) than all other samples (range: 14.1-16.2 m²/g), whereas mean lengths and aspect ratios (ARs) for LA and SM were comparable and greater than ED and ON. Samples were delivered via a single intratracheal (IT) instillation at doses of 0.5 and 1.5mg/rat. One day post-IT instillation, low-dose NOA exposure resulted in a 3- to 4-fold increase in bronchoalveolar lavage fluid (BALF) cellularity compared with dispersion media (DM) controls, whereas high-dose exposure had a more severe effect on lung inflammation which varied by source. Although inducing less neutrophilic inflammation than ON and ED, exposure to either LA or SM resulted in a greater degree of acute lung injury. Three months post-IT instillation, most BALF parameters had returned to control levels, whereas the development of fibrosis persisted and was greatest in SM-exposed rats (SM > LA > ON > ED). These data demonstrate that fiber length and higher AR are directly correlated with the severity of fibrosis and that, in the rat, exposure to SM is more fibrogenic than LA which suggests that there may be cause for concern for people at risk of being exposed to NOA from the Sumas Mountain landslide.

Surface-structure-regulated penetration of nanoparticles across a cell membrane

The cell uptake rate of nanoparticles (NPs) coated with mixed hydrophilic/hydrophobic ligands is known to be strongly influenced by the ligand pattern on the nanoparticle surface. To help reveal the physical mechanism behind this intriguing phenomenon, here we perform dissipative particle dynamics simulations to analyze the evolution of free energy as the ligand-coated NPs pierce through a lipid bilayer. Four characteristic ligand patterns are considered: striated NPs with alternating hydrophilic and hydrophobic groups compared to NPs with randomly mixed ligands at the same hydrophilic to hydrophobic ratio, as well as NPs coated with homogeneous hydrophilic or hydrophobic ligands. The free energy analysis indicates that among the four ligand patterns under study, the striated NP encounters the lowest energy barrier during translocation across the membrane. Further analysis reveals that the translocation of the striated NP is facilitated by the constraint of its rotational degree of freedom by the anisotropic ligand pattern, which prevented the free energy of the system from sinking to a deeper valley as the NP passes through the hydrophobic core of the bilayer. Finally, the critical forces required for almost instant penetration of these patterned NPs across the bilayer are calculated and shown to be consistent with the free energy analysis. These findings provide useful guidelines for the molecular design of patterned NPs for controllable cell penetrability.

Ninety-day inhalation toxicity study with a vapor grown carbon nanofiber in rats

A subchronic inhalation toxicity study of inhaled vapor grown carbon nanofibers (CNF) (VGCF-H) was conducted in male and female Sprague Dawley rats. The CNF test sample was composed of > 99.5% carbon with virtually no catalyst metals; Brunauer, Emmett, and Teller (BET) surface area measurements of 13.8 m2/g; and mean lengths and diameters of 5.8 µm and 158 nm, respectively.Four groups of rats per sex were exposed nose-only, 6 h/day, for 5 days/week to target concentrations of 0, 0.50, 2.5, or 25 mg/m3 VGCF-H over a 90-day period and evaluated 1 day later. Assessments included conventional clinical and histopathological methods, bronchoalveolar lavage fluid (BALF) analysis, and cell proliferation (CP) studies of the terminal bronchiole (TB), alveolar duct (AD), and subpleural regions of the respiratory tract. In addition, groups of 0 and 25 mg/m3 exposed rats were evaluated at 3 months postexposure (PE). Aerosol exposures of rats to 0.54 (4.9 f/cc), 2.5 (56 f/cc), and 25 (252 f/cc) mg/m(3) of VGCF-H CNFs produced concentration-related small, detectable accumulation of extrapulmonary fibers with no adverse tissue effects. At the two highest concentrations, inflammation of the TB and AD regions of the respiratory tract was noted wherein fiber-laden alveolar macrophages had accumulated. This finding was characterized by minimal infiltrates of inflammatory cells in rats exposed to 2.5mg/m(3) CNF, inflammation along with some thickening of interstitial walls, and hypertrophy/hyperplasia of type II epithelial cells, graded as slight for the 25mg/m(3) concentration. At 3 months PE, the inflammation in the high dose was reduced. No adverse effects were observed at 0.54mg/m(3). BALF and CP endpoint increases versus controls were noted at 25mg/m(3) VGCF-H but not different from control values at 0.54 or 2.5mg/m(3). After 90 days PE, BALF biomarkers were still increased at 25mg/m(3), indicating that the inflammatory response was not fully resolved. Greater than 90% of CNF-exposed, BALF-recovered alveolar macrophages from the 25 and 2.5mg/m(3) exposure groups contained nanofibers (> 60% for 0.5mg/m(3)). A nonspecific inflammatory response was also noted in the nasal passages. The no-observed-adverse-effect level for VGCF-H nanofibers was considered to be 0.54mg/m(3) (4.9 fibers/cc) for male and female rats, based on the minimal inflammation in the terminal bronchiole and alveolar duct areas of the lungs at 2.5mg/m(3) exposures. It is noteworthy that the histopathology observations at the 2.5mg/m(3) exposure level did not correlate with the CP or BALF data at that exposure concentration. In addition, the results with CNF are compared with published findings of 90-day inhalation studies in rats with carbon nanotubes, and hypotheses are presented for potency differences based on CNT physicochemical characteristics. Finally, the (lack of) relevance of CNF for the high aspect ratio nanomaterials/fiber paradigm is discussed.

Multi-walled carbon nanotubes induce COX-2 and iNOS expression via MAP kinase-dependent and -independent mechanisms in mouse RAW264.7 macrophages

BACKGROUND

Carbon nanotubes (CNTs) are engineered graphene cylinders with numerous applications in engineering, electronics and medicine. However, CNTs cause inflammation and fibrosis in the rodent lung, suggesting a potential human health risk. We hypothesized that multi-walled CNTs (MWCNTs) induce two key inflammatory enzymes in macrophages, cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS), through activation of extracellular signal-regulated kinases (ERK1,2).

METHODS

RAW264.7 macrophages were exposed to MWCNTs or carbon black nanoparticles (CBNPs) over a range of doses and time course. Uptake and subcellular localization of MWCNTs was visualized by transmission electron microscopy (TEM). Protein levels of COX-2, iNOS, and ERK1,2 (total ERK and phosphorylated ERK) were measured by Western blot analysis. Prostaglandin-E(2) (PGE(2)) and nitric oxide (NO) levels in cell supernatants were measured by ELISA and Greiss assay, respectively.

RESULTS

MWCNTs, but not CBNPs, induced COX-2 and iNOS in a time- and dose-dependent manner. COX-2 and iNOS induction by MWCNTs correlated with increased PGE(2) and NO production, respectively. MWCNTs caused ERK1,2 activation and inhibition of ERK1,2 (U0126) blocked MWCNT induction of COX-2 and PGE2 production, but did not reduce the induction of iNOS. Inhibition of iNOS (L-NAME) did not affect ERK1,2 activation, nor did L-NAME significantly decrease COX-2 induction by MWCNT. Nickel nanoparticles (NiNPs), which are present in MWCNTs as a residual catalyst, also induced COX-2 via ERK-1,2. However, a comparison of COX-2 induction by MWCNTs containing 4.5 and 1.8% Ni did not show a significant difference in ability to induce COX-2, indicating that characteristics of MWCNTs in addition to Ni content contribute to COX-2 induction.

CONCLUSION

This study identifies COX-2 and subsequent PGE(2) production, along with iNOS induction and NO production, as inflammatory mediators involved in the macrophage response to MWCNTs. Furthermore, our work demonstrates that COX-2 induction by MWCNTs in RAW264.7 macrophages is ERK1,2-dependent, while iNOS induction by MWCNTs is ERK1,2-independent. Our data also suggest contributory physicochemical factors other than residual Ni catalyst play a role in COX-2 induction to MWCNT.

Genotoxicity and molecular response of silver nanoparticle (NP)-based hydrogel

Background

Since silver-nanoparticles (NPs) possess an antibacterial activity, they were commonly used in medical products and devices, food storage materials, cosmetics, various health care products, and industrial products. Various silver-NP based medical devices are available for clinical uses, such as silver-NP based dressing and silver-NP based hydrogel (silver-NP-hydrogel) for medical applications. Although the previous data have suggested silver-NPs induced toxicity in vivo and in vitro, there is lack information about the mechanisms of biological response and potential toxicity of silver-NP-hydrogel.

Methods

In this study, the genotoxicity of silver-NP-hydrogel was assayed using cytokinesis-block micronucleus (CBMN). The molecular response was studied using DNA microarray and GO pathway analysis.

Results and discussion

The results of global gene expression analysis in HeLa cells showed that thousands of genes were up- or down-regulated at 48 h of silver-NP-hydrogel exposure. Further GO pathway analysis suggested that fourteen theoretical activating signaling pathways were attributed to up-regulated genes; and three signal pathways were attributed to down-regulated genes. It was discussed that the cells protect themselves against silver NP-mediated toxicity through up-regulating metallothionein genes and anti-oxidative stress genes. The changes in DNA damage, apoptosis and mitosis pathway were closely related to silver-NP-induced cytotoxicity and chromosome damage. The down-regulation of CDC14A via mitosis pathway might play a role in potential genotoxicity induced by silver-NPs.

Conclusions

The silver-NP-hydrogel induced micronuclei formation in cellular level and broad spectrum molecular responses in gene expression level. The results of signal pathway analysis suggested that the balances between anti-ROS response and DNA damage, chromosome instability, mitosis inhibition might play important roles in silver-NP induced toxicity. The inflammatory factors were likely involved in silver-NP-hydrogel complex-induced toxic effects via JAK-STAT signal transduction pathway and immune response pathway. These biological responses eventually decide the future of the cells, survival or apoptosis.

Focused actions to protect carbon nanotube workers

There is still uncertainty about the potential health hazards of carbon nanotubes (CNTs) particularly involving carcinogenicity. However, the evidence is growing that some types of CNTs and nanofibers may have carcinogenic properties. The critical question is that while the carcinogenic potential of CNTs is being further investigated, what steps should be taken to protect workers who face exposure to CNTs, current and future, if CNTs are ultimately found to be carcinogenic? This paper addresses five areas to help focus action to protect workers: (i) review of the current evidence on the carcinogenic potential of CNTs; (ii) role of physical and chemical properties related to cancer development; (iii) CNT doses associated with genotoxicity in vitro and in vivo; (iv) workplace exposures to CNT; and (v) specific risk management actions needed to protect workers.

Factoring-in agglomeration of carbon nanotubes and nanofibers for better prediction of their toxicity versus asbestos

Background

Carbon nanotubes (CNT) and carbon nanofibers (CNF) are allotropes of carbon featuring fibrous morphology. The dimensions and high aspect ratio of CNT and CNF have prompted the comparison with naturally occurring asbestos fibers which are known to be extremely pathogenic. While the toxicity and hazardous outcomes elicited by airborne exposure to single-walled CNT or asbestos have been widely reported, very limited data are currently available describing adverse effects of respirable CNF.

Results

Here, we assessed pulmonary inflammation, fibrosis, oxidative stress markers and systemic immune responses to respirable CNF in comparison to single-walled CNT (SWCNT) and asbestos. Pulmonary inflammatory and fibrogenic responses to CNF, SWCNT and asbestos varied depending upon the agglomeration state of the particles/fibers. Foci of granulomatous lesions and collagen deposition were associated with dense particle-like SWCNT agglomerates, while no granuloma formation was found following exposure to fiber-like CNF or asbestos. The average thickness of the alveolar connective tissue - a marker of interstitial fibrosis - was increased 28 days post SWCNT, CNF or asbestos exposure. Exposure to SWCNT, CNF or asbestos resulted in oxidative stress evidenced by accumulations of 4-HNE and carbonylated proteins in the lung tissues. Additionally, local inflammatory and fibrogenic responses were accompanied by modified systemic immunity, as documented by decreased proliferation of splenic T cells ex vivo on day 28 post exposure. The accuracies of assessments of effective surface area for asbestos, SWCNT and CNF (based on geometrical analysis of their agglomeration) versus estimates of mass dose and number of particles were compared as predictors of toxicological outcomes.

Conclusions

We provide evidence that effective surface area along with mass dose rather than specific surface area or particle number are significantly correlated with toxicological responses to carbonaceous fibrous nanoparticles. Therefore, they could be useful dose metrics for risk assessment and management.

Mesothelial cell and anti-nuclear autoantibodies associated with pleural abnormalities in an asbestos exposed population of Libby MT

Despite data linking amphibole asbestos exposure with production of autoantibodies, the role of autoantibodies in subsequent disease is unknown. Residents of Libby, Montana have experienced significant exposure to amphibole asbestos due to the mining of asbestos-contaminated vermiculite near the community over several decades. This population predominantly exhibits pleural disease, and an autoimmune-like disorder that has yet to be well defined. This study sought to determine whether autoantibodies from asbestos-exposed subjects were associated with pleural lesions. Serum samples of subjects from Libby were evaluated for anti-nuclear antibodies (ANA) and mesothelial cell autoantibodies (MCAA) using cell based ELISA. The presence of radiographic abnormalities detected during the time frame of serum collection was determined from screening records. In accord with previous studies, 61.3% (76/124) of the Libby samples were ANA positive, a frequency much higher than expected for a healthy population. The odds of having pleural or interstitial abnormalities in Libby was nearly 3.55 times greater for individuals that tested positive for ANA compared with individuals negative for ANA (p=0.004). MCAA were also detected at a strikingly high frequency (18.5%; 23/124) in samples from Libby. Individuals with MCAA had 4.9 times the risk of having pleural abnormalities compared to MCAA-negative subjects (p=0.044). In conclusion, ANA and MCAA were elevated in a study population that was known to have chronic exposure to asbestos, and these autoantibodies were associated with pleural abnormalities, the predominant finding in the asbestos-exposed population of Libby. Additional research is needed to determine the role these autoantibodies may play in pulmonary disease.

[DNA damage in human pleural mesothelial cells induced by exposure to carbon nanotubes]

OBJECTIVES

Nanomaterials are currently used in electronics, industrial materials, cosmetics, and medicine because they have useful physicochemical properties, such as strength, conductivity, durability, and chemical stability. As these materials have become widespread, many questions have arisen regarding their effects on health and the environment. In particular, recent studies have demonstrated that carbon nanotubes (CNTs) cause significant inflammation and mesothelioma in vivo. In this study, we investigated the potential risk posed by singlewalled carbon nanotube (SWCNT) and multiwalled carbon nanotube (MWCNT) exposure in human pleural mesothelial cells.

METHODS

CNT cytotoxicity was determined by a trypan blue exclusion assay, and DNA damage was detected by an alkaline comet assay. The concentration of 8-oxodeoxyguanosine (8-OHdG) in DNA was measured by high perhormance liquid chromatography with electrochemical detection. The expression of base excision repair enzymes in the cell was estimated by immunoblot analysis.

RESULTS

We observed inhibitory effects on cell proliferation and the induction of DNA damage following exposure of cells to purified CNTs that were suspended in dispersion medium. However, accumulation of 8-OHdG in DNA was not found. In addition, the expression levels of base excision enzymes that are involved in hOGG1, hMTH1, and MYH in MeT-5A cells remained unchanged for 24 h after carbon nanotube exposure.

CONCLUSIONS

CNTs significantly inhibit cell proliferation and decrease DNA damage in human pleural mesothelial cells. Our results indicate that the mechanism of CNT-induced genotoxicity is different from that following exposure to reactive oxygen species, which causes oxidative DNA modifications and 8-OHdG production. Further investigation is required to characterize the specific DNA mutations that occur following CNT exposure.

Pulmonary Toxicity, Distribution, and Clearance of Intratracheally Instilled Silicon Nanowires in Rats

Silicon nanowires (Si NWs) are being manufactured for use as sensors and transistors for circuit applications. The goal was to assess pulmonary toxicity and fate of Si NW using an in vivo experimental model. Male Sprague-Dawley rats were intratracheally instilled with 10, 25, 50, 100, or 250 μg of Si NW (~20-30 nm diameter; ~2-15 μm length). Lung damage and the pulmonary distribution and clearance of Si NW were assessed at 1, 3, 7, 28, and 91 days after-treatment. Si NW treatment resulted in dose-dependent increases in lung injury and inflammation that resolved over time. At day 91 after treatment with the highest doses, lung collagen was increased. Approximately 70% of deposited Si NW was cleared by 28 days with most of the Si NW localized exclusively in macrophages. In conclusion, Si NW induced transient lung toxicity which may be associated with an early rapid particle clearance; however, persistence of Si NW over time related to dose or wire length may lead to increased collagen deposition in the lung.

Effect of chemical composition and state of the surface on the toxic response to high aspect ratio nanomaterials

Nanomaterials often act as a double sword. On the one hand they offer exceptional new properties, but on the other hand show signs of toxicity. High aspect ratio nanomaterials (HARNs) cause more concern than isometric nanoparticles owing to their physical similarity with asbestos. Many compounds may be prepared in fibrous shape with nano-sized diameter differing one from the other in various ways. This article reports a comparative picture of the chemical features and related toxic responses to a variety of HARNs, namely carbon nanotubes, asbestos, carbon nanofibers, oxide and metal wires and rods. In spite of similarities in form, durability and several biological responses elicited in vitro and in vivo, carbon nanotubes - opposite to asbestos - quench radicals, are hydrophobic and may be fully purified from metal impurities. Most of the other HARNs produced so far are metal or metal oxide compounds, less biopersistent than carbon nanotubes.

Meeting report: mode(s) of action of asbestos and related mineral fibers

BACKGROUND

Although asbestos in general is well known to cause a range of neoplastic and non-neoplastic human health effects, not all asbestos fiber types have the same disease-causing potential, and the mode of action (MOA) of specific types of asbestos and related fibers for various health outcomes are not well understood.

OBJECTIVES

A workshop was held to discuss the state of the science of the MOA for asbestos-related disease. The objective was to review the range of asbestos-induced health effects (including those at sites remote to the respiratory tract). We sought to identify existing knowledge gaps and define what research is needed to address these gaps and advance asbestos research.

DISCUSSION

Discussions centered on areas of uncertainty in the field, including the ways asbestos is defined and characterized, the role of different fiber characteristics (e.g., length and mineralogy) in disease, and the impact of low-dose exposures on human health. Studying the dosimetry and mode of action of multiple fiber types would enhance our understanding of asbestos-related disease. To better elucidate the MOA of specific asbestos fibers, the risk assessor requires data as to specific characteristics of asbestos in determining fiber toxicity (e.g., surface area, mineral type), which may inform efforts to assess and control exposures and prevent adverse human health outcomes for the diverse range of fiber types. Specific research aims were defined for these topics and for overarching issues to be addressed, including the use of standardized terminology, test materials, and better experimental models to aid in data extrapolation to humans.

CONCLUSION

To resolve these and other issues, participants agreed that diverse scientific disciplines must coordinate to better understand the MOA leading to the various asbestos-related disease end points.

Biological interactions of graphene-family nanomaterials: an interdisciplinary review

Graphene is a single-atom thick, two-dimensional sheet of hexagonally arranged carbon atoms isolated from its three-dimensional parent material, graphite. Related materials include few-layer-graphene (FLG), ultrathin graphite, graphene oxide (GO), reduced graphene oxide (rGO), and graphene nanosheets (GNS). This review proposes a systematic nomenclature for this set of Graphene-Family Nanomaterials (GFNs) and discusses specific materials properties relevant for biomolecular and cellular interactions. We discuss several unique modes of interaction between GFNs and nucleic acids, lipid bilayers, and conjugated small molecule drugs and dyes. Some GFNs are produced as dry powders using thermal exfoliation, and in these cases, inhalation is a likely route of human exposure. Some GFNs have aerodynamic sizes that can lead to inhalation and substantial deposition in the human respiratory tract, which may impair lung defense and clearance leading to the formation of granulomas and lung fibrosis. The limited literature on in vitro toxicity suggests that GFNs can be either benign or toxic to cells, and it is hypothesized that the biological response will vary across the material family depending on layer number, lateral size, stiffness, hydrophobicity, surface functionalization, and dose. Generation of reactive oxygen species (ROS) in target cells is a potential mechanism for toxicity, although the extremely high hydrophobic surface area of some GFNs may also lead to significant interactions with membrane lipids leading to direct physical toxicity or adsorption of biological molecules leading to indirect toxicity. Limited in vivo studies demonstrate systemic biodistribution and biopersistence of GFNs following intravenous delivery. Similar to other smooth, continuous, biopersistent implants or foreign bodies, GFNs have the potential to induce foreign body tumors. Long-term adverse health impacts must be considered in the design of GFNs for drug delivery, tissue engineering, and fluorescence-based biomolecular sensing. Future research is needed to explore fundamental biological responses to GFNs including systematic assessment of the physical and chemical material properties related to toxicity. Complete materials characterization and mechanistic toxicity studies are essential for safer design and manufacturing of GFNs in order to optimize biological applications with minimal risks for environmental health and safety.

Cell entry of one-dimensional nanomaterials occurs by tip recognition and rotation

Materials with high aspect ratio, such as carbon nanotubes and asbestos fibres, have been shown to cause length-dependent toxicity in certain cells because these long materials prevent complete ingestion and this frustrates the cell. Biophysical models have been proposed to explain how spheres and elliptical nanostructures enter cells, but one-dimensional nanomaterials have not been examined. Here, we show experimentally and theoretically that cylindrical one-dimensional nanomaterials such as carbon nanotubes enter cells through the tip first. For nanotubes with end caps or carbon shells at their tips, uptake involves tip recognition through receptor binding, rotation that is driven by asymmetric elastic strain at the tube-bilayer interface, and near-vertical entry. The precise angle of entry is governed by the relative timescales for tube rotation and receptor diffusion. Nanotubes without caps or shells on their tips show a different mode of membrane interaction, posing an interesting question as to whether modifying the tips of tubes may help avoid frustrated uptake by cells.

The role of iron in Libby amphibole-induced acute lung injury and inflammation

Complexation of host iron (Fe) on the surface of inhaled asbestos fibers has been postulated to cause oxidative stress contributing to in vivo pulmonary injury and inflammation. We examined the role of Fe in Libby amphibole (LA; mean length 4.99 µm ± 4.53 and width 0.28 µm ± 0.19) asbestos-induced inflammogenic effects in vitro and in vivo. LA contained acid-leachable Fe and silicon. In a cell-free media containing FeCl(3), LA bound #17 µg of Fe/mg of fiber and increased reactive oxygen species generation #3.5 fold, which was reduced by deferoxamine (DEF) treatment. In BEAS-2B cells exposure to LA, LA loaded with Fe (FeLA), or LA with DEF did not increase HO-1 or ferritin mRNA expression. LA increased IL-8 expression, which was reduced by Fe loading but increased by DEF. To determine the role of Fe in LA-induced lung injury in vivo, spontaneously hypertensive rats were exposed intratracheally to either saline (300 µL), DEF (1 mg), FeCl(3) (21 µg), LA (0.5 mg), FeLA (0.5 mg), or LA + DEF (0.5 mg). LA caused BALF neutrophils to increase 24 h post-exposure. Loading of Fe on LA but not chelation slightly decreased neutrophilic influx (LA + DEF > LA > FeLA). At 4 h post-exposure, LA-induced lung expression of MIP-2 was reduced in rats exposed to FeLA but increased by LA + DEF (LA + DEF > LA > FeLA). Ferritin mRNA was elevated in rats exposed to FeLA compared to LA. In conclusion, the acute inflammatory response to respirable fibers and particles may be inhibited in the presence of surface-complexed or cellular bioavailable Fe. Cell and tissue Fe-overload conditions may influence the pulmonary injury and inflammation caused by fibers.

The lung: the natural boundary between nature and nurture

Common lung diseases such as asthma, COPD, and pulmonary fibrosis cause significant morbidity and mortality in the U.S. and worldwide. Research investigating the mechanisms of disease etiology has clearly indicated that genetic attributes and environmental exposures each play important roles in the development of these diseases. Emerging evidence underscores the importance of the interplay between genetic predisposition and environmental factors in fully understanding the development of lung disease. Herein we discuss recent advances in knowledge and technology surrounding the role of genetics, the environment, and gene-environment interactions in these common lung diseases.

Low doses of pristine and oxidized single-wall carbon nanotubes affect mammalian embryonic development

Several in vitro and in vivo studies suggest local and systemic effects following exposure to carbon nanotubes. No data are available, however, on their possible embryotoxicity in mammals. In this study, we tested the effect of pristine and oxidized single-wall carbon nanotubes (SWCNTs) on the development of the mouse embryo. To this end, SWCNTs (from 10 ng to 30 μg/mouse) were administered to female mice soon after implantation (postcoital day 5.5); 10 days later, animals were sacrificed, and uteri, placentas, and fetuses examined. A high percentage of early miscarriages and fetal malformations was observed in females exposed to oxidized SWCNTs, while lower percentages were found in animals exposed to the pristine material. The lowest effective dose was 100 ng/mouse. Extensive vascular lesions and increased production of reactive oxygen species (ROS) were detected in placentas of malformed but not of normally developed fetuses. Increased ROS levels were likewise detected in malformed fetuses. No increased ROS production or evident morphological alterations were observed in maternal tissues. No fetal and placental abnormalities were ever observed in control animals. In parallel, SWCNT embryotoxicity was evaluated using the embryonic stem cell test (EST), a validated in vitro assay developed for predicting embryotoxicity of soluble chemical compounds, but never applied in full to nanoparticles. The EST predicted the in vivo data, identifying oxidized SWCNTs as the more toxic compound.

A 3-dimensional in vitro model of epithelioid granulomas induced by high aspect ratio nanomaterials

Background

The most common causes of granulomatous inflammation are persistent pathogens and poorly-degradable irritating materials. A characteristic pathological reaction to intratracheal instillation, pharyngeal aspiration, or inhalation of carbon nanotubes is formation of epithelioid granulomas accompanied by interstitial fibrosis in the lungs. In the mesothelium, a similar response is induced by high aspect ratio nanomaterials, including asbestos fibers, following intraperitoneal injection. This asbestos-like behaviour of some engineered nanomaterials is a concern for their potential adverse health effects in the lungs and mesothelium. We hypothesize that high aspect ratio nanomaterials will induce epithelioid granulomas in nonadherent macrophages in 3D cultures.

Results

Carbon black particles (Printex 90) and crocidolite asbestos fibers were used as well-characterized reference materials and compared with three commercial samples of multiwalled carbon nanotubes (MWCNTs). Doses were identified in 2D and 3D cultures in order to minimize acute toxicity and to reflect realistic occupational exposures in humans and in previous inhalation studies in rodents. Under serum-free conditions, exposure of nonadherent primary murine bone marrow-derived macrophages to 0.5 μg/ml (0.38 μg/cm²) of crocidolite asbestos fibers or MWCNTs, but not carbon black, induced macrophage differentiation into epithelioid cells and formation of stable aggregates with the characteristic morphology of granulomas. Formation of multinucleated giant cells was also induced by asbestos fibers or MWCNTs in this 3D in vitro model. After 7-14 days, macrophages exposed to high aspect ratio nanomaterials co-expressed proinflammatory (M1) as well as profibrotic (M2) phenotypic markers.

Conclusions

Induction of epithelioid granulomas appears to correlate with high aspect ratio and complex 3D structure of carbon nanotubes, not with their iron content or surface area. This model offers a time- and cost-effective platform to evaluate the potential of engineered high aspect ratio nanomaterials, including carbon nanotubes, nanofibers, nanorods and metallic nanowires, to induce granulomas following inhalation.