Unusual inflammatory and fibrogenic pulmonary responses to single-walled carbon nanotubes in mice

Pulmonary toxicity of multi-walled carbon nanotubes (Baytubes) relative to alpha-quartz following a single 6h inhalation exposure of rats and a 3 months post-exposure period

Manufactured multi-walled carbon nanotubes (MWCNT) have attracted a great deal of attention due to their unique structural, chemical, and physical characteristics. This study utilized a 1x 6h inhalation exposure protocol followed by a 3 months post-exposure period. Wistar rats were nose-only exposed to 11 and 241 mg/m(3) MWCNT (Baytubes) of respirable, solid aerosol. MWCNT depleted of residual metals (depletion from 0.53% to 0.12% Co) were compared at 11 mg/m(3). Rats similarly exposed to air and alpha-quartz (248 mg/m(3)) served as negative and positive controls, respectively. Pulmonary response was characterized by bronchoalveolar lavage (BAL), lung histopathology, organ burden determinations, and gene expression analyses of lung homogenates with emphasis on extracellular matrix components. This acute inhalation exposure protocol was suitable to characterize and distinguish acute deposition-related effects from the long-term sequelae of retained MWCNT. Subtle differences in acute pulmonary toxic potency due to differences in metal contaminations could be revealed by this protocol. Consistent with the long retention halftime of poorly soluble particles, even short-term inhalation studies may require post-exposure periods of at least 3 months to reveal MWCNT-specific dispositional and toxicological characteristics relative to alpha-quartz. Distinct differences in the time course of pulmonary inflammation of MWCNT and alpha-quartz could be demonstrated. Transcriptomics proved to be a useful tool to analyze the etiopathology of collagen detected by BAL and histopathology. In summary, the pulmonary inflammogenicity following exposure to MWCNT was concentration-dependent with evidence of regression over time. Conversely, alpha-quartz resulted in progressive changes over time. The time course of pulmonary inflammation associated with retained MWCNT was independent on the concentration of residual cobalt. This supports the conclusion that the predominant response to inhaled MWCNT is principally related to the assemblage structure and not catalyst impurities (if in the range of < or = 0.5%).

Carbon nanofibers and carbon nanotubes in regenerative medicine

Carbon nanotubes and carbon nanofibers have long been investigated for applications in composite structural materials, semiconductor devices, and sensors. With the recent well-documented ability to chemically modify nanofibrous carbon materials to improve their solubility and biocompatibility properties: a whole new class of bioactive carbon nanostructures has been created for biological applications. This review focuses on the latest applications of carbon nanofibers and carbon nanotubes in regenerative medicine.

Induction of aneuploidy by single-walled carbon nanotubes

Engineered carbon nanotubes are newly emerging manufactured particles with potential applications in electronics, computers, aerospace, and medicine. The low density and small size of these biologically persistent particles makes respiratory exposures to workers likely during the production or use of commercial products. The narrow diameter and great length of single-walled carbon nanotubes (SWCNT) suggest the potential to interact with critical biological structures. To examine the potential of nanotubes to induce genetic damage in normal lung cells, cultured primary and immortalized human airway epithelial cells were exposed to SWCNT or a positive control, vanadium pentoxide. After 24 hr of exposure to either SWCNT or vanadium pentoxide, fragmented centrosomes, multiple mitotic spindle poles, anaphase bridges, and aneuploid chromosome number were observed. Confocal microscopy demonstrated nanotubes within the nucleus that were in association with cellular and mitotic tubulin as well as the chromatin. Our results are the first to report disruption of the mitotic spindle by SWCNT. The nanotube bundles are similar to the size of microtubules that form the mitotic spindle and may be incorporated into the mitotic spindle apparatus.

Bacterial lipopolysaccharide enhances PDGF signaling and pulmonary fibrosis in rats exposed to carbon nanotubes

Engineered multi-walled carbon nanotubes (MWCNT) represent a possible health risk for pulmonary fibrosis due to their fiber-like shape and potential for persistence in the lung. We postulated that bacterial lipopolysaccharide (LPS), a ubiquitous agent in the environment that causes lung inflammation, would enhance fibrosis caused by MWCNT. Rats were exposed to LPS and then intratracheally instilled with MWCNT or carbon black (CB) nanoparticles 24 hours later. Pulmonary fibrosis was observed 21 days after MWCNT exposure, but not with CB. LPS alone caused no fibrosis but enhanced MWCNT-induced fibrosis. LPS plus CB did not significantly increase fibrosis. MWCNT increased platelet-derived growth factor-AA (PDGF-AA), a major mediator of fibrosis. PDGF-AA production in response to MWCNT, but not CB, was synergistically enhanced by LPS. Immunostaining showed PDGF-AA in bronchiolar epithelial cells and macrophages. Since macrophages engulfed MWCNT, were positive for PDGF-AA, and mediate fibroblast responses, experiments were performed with rat lung macrophages (NR8383 cells) and rat lung fibroblasts in vitro. LPS exposure increased PDGF-A mRNA levels in NR8383 cells and enhanced MWCNT-induced PDGF-A mRNA levels. Moreover, LPS increased MWCNT- or CB-induced PDGF receptor-alpha (PDGF-Ralpha) mRNA in fibroblasts. Our data suggest that LPS exacerbates MWCNT-induced lung fibrosis by amplifying production of PDGF-AA in macrophages and epithelial cells, and by increasing PDGF-Ralpha on pulmonary fibroblasts. Our findings also suggest that individuals with pre-existing pulmonary inflammation are at greater risk for the potential adverse effects of MWCNT.

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

Human diseases associated with exposure to asbestos fibers include pleural fibrosis and plaques, pulmonary fibrosis (asbestosis), lung cancer, and diffuse malignant mesothelioma. The critical determinants of fiber bioactivity and toxicity include not only fiber dimensions, but also shape, surface reactivity, crystallinity, chemical composition, and presence of transition metals. Depending on their size and dimensions, inhaled fibers can penetrate the respiratory tract to the distal airways and into the alveolar spaces. Fibers can be cleared by several mechanisms, including the mucociliary escalator, engulfment, and removal by macrophages, or through splitting and chemical modification. Biopersistence of long asbestos fibers can lead to inflammation, granuloma formation, fibrosis, and cancer. Exposure to synthetic carbon nanomaterials, including carbon nanofibers and carbon nanotubes (CNTs), is considered a potential health hazard because of their physical similarities with asbestos fibers. Respiratory exposure to CNTs can produce an inflammatory response, diffuse interstitial fibrosis, and formation of fibrotic granulomas similar to that observed in asbestos-exposed animals and humans. Given the known cytotoxic and carcinogenic properties of asbestos fibers, toxicity of fibrous nanomaterials is a topic of intense study. The mechanisms of nanomaterial toxicity remain to be fully elucidated, but recent evidence suggests points of similarity with asbestos fibers, including a role for generation of reactive oxygen species, oxidative stress, and genotoxicity. Considering the rapid increase in production and use of fibrous nanomaterials, it is imperative to gain a thorough understanding of their biologic activity to avoid the human health catastrophe that has resulted from widespread use of asbestos fibers.

Inhaled fluorescent magnetic nanoparticles induced extramedullary hematopoiesis in the spleen of mice

OBJECTIVES

Nanomaterials are used in a wide variety of industrial materials such as semiconductors, magnetic resonance imaging, gene delivery carriers for gene therapy and many others; thus, human seems to be frequently exposed to them. Such diverse applications of nanoparticles elicit the need to identify the positive aspects of nanomaterials while avoiding the potential toxic effects. In this study, inhalation toxicity of manufactured nanomaterials using fluorescent magnetic nanoparticles (FMNPs) was assessed to address the issue of potential nanoparticle toxicity.

METHODS

Biological samples from a previous mouse FMNP exposure experiment were analyzed for potential FMNP toxicity. Mice inhaled FMNPs for 4 wk through a nose-only exposure chamber developed by our group for 4 wk and the potential toxicity of FMNPs was analyzed.

RESULTS

The nanoparticle distribution by scanning mobility particle sizer (SMPS) analysis showed that the mean values of number concentration (mass concentrations) in the nose-only exposure chamber were maintained at 4.89 x 10(5)/cm3 (approximately 159.4 microg/m3) for the low concentration and 9.34 x 10(5)/cm3 (approximately 319.5 microg/m3) for the high concentration, respectively. Inhalation of FMNPs caused a decrease of body weight and significant changes of white blood cells (WBCs) levels in whole blood. The FMNPs induced extramedullary hematopoiesis in the spleen without having a pulmonary effect.

CONCLUSIONS

Our results support the proposition that extensive toxicity evaluation is needed for practical applications of anthropogenic nanomaterials and suggest that careful regulation of nanoparticle applications may be necessary to maintain a high quality of life as well as for facilitating the development of nanotechnology.

EFFECT OF MULTI-WALLED CARBON NANOTUBES ON VIABILITY AND SUPEROXIDE DISMUTASE EXPRESSION IN HUMAN WOUND PATHOGENS

Recently, a wide variety of bionanocomposites and biocomposites are being developed to be used as extracellular matrix for chronic wound healing. Majority of the chronic wound situations arise due to infections caused by drug-resistant microbes like Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. In particular S. aureus has become refractory to the current armamentarium of antimicrobial drugs. Therefore, it is imperative while designing nanobiocomposites for use as extracellular matrices to profile their antimicrobial activity. MWNT (multi-wall carbon nanotube) has been exploited previously in designing biocompatible nanocomposite for medical applications. Keeping in view, we studied the antimicrobial effect of MWNT on human clinical burn/wound pathogens, which were Methicillin-resistant Staphylococci and one Vancomycin intermediate Staphylococcus isolate. We also studied E. coli NCTC 10418 and Pseudomonas aeruginosa NCTC 10662, two surrogate gram negative microbes to understand their behavior in the presence of MWNT. Apart from reduction in viable counts of the test panel, organism's extracellular expression of the enzyme Superoxide dismutase (SOD) was also taken into account as this is the probable mechanism adopted by bacteria in general to survive and sustain under nutritional and other stress situation including pathogenesis. The present study indicated that all Staphylococcal isolates were susceptible to MWNT which reduced the bacterial count between 3–9 logs barring Sau G19 which only exhibited 1 log reduction. Sau G17, Sau G18, and Sau G19 expressed a higher SOD activity, Sau G9 exhibited a lower SOD expression and in Sau G16, the SOD expression was nearly the same as compared to control. Thus, from this study, it could be inferred that MWNT, apart from being antimicrobial, induces oxidative stress on S. aureus.

Characterization and evaluation of nanoparticle release during the synthesis of single-walled and multiwalled carbon nanotubes by chemical vapor deposition

Airborne nanoparticles released during the synthesis of single-walled and multi-walled carbon nanotubes were measured and characterized. This study reported the field measurements during the development of carbon nanotube production. Monitoring data were taken and the sampling methods to characterize aerosol release were developed along with the modification of carbon nanotube production in a time period from 2006 to 2009. Particle number concentrations for diameters from 5 nm to 20 microm were measured using the fast mobility particle sizer and the aerodynamic particle sizer; the particles released from the furnace were found to be less than 500 nm in diameter. The morphology and elemental composition of the released nanoparticles were characterized by scanning and transmission electron microscopy and energy dispersive spectroscopy. Different operating conditions of multi-walled carbon nanotubes (MWCNT) production were studied to evaluate their effects on the number and morphology of aerosol particles, and the number of particles released. Carbon nanotube filaments and carbon particles in clusters were found among the released aerosol particles during production of multiwalled carbon nanotubes.

A predictive toxicological paradigm for the safety assessment of nanomaterials

The rate of expansion of nanomaterials calls for the consideration of appropriate toxicological paradigms in the safety assessment of nanomaterials. We advocate a predictive toxicological paradigm for the assessment of nanomaterial hazards. The predictive toxicological approach is defined as establishing and using mechanisms and pathways of injury at a cellular and molecular level to prioritize screening for adverse biological effects and health outcomes in vivo. Specifically as it relates to nanomaterials, a predictive approach has to consider the physicochemical properties of the material that leads to molecular or cellular injury and also has to be valid in terms of disease pathogenesis in whole organisms.

Inhalation toxicity of multiwall carbon nanotubes in rats exposed for 3 months

Carbon nanotubes (CNT) are of great commercial interest. Theoretically, during processing and handling of CNT and in abrasion processes on composites containing CNT, inhalable CNT particles might be set free. For hazard assessment, we performed a 90-day inhalation toxicity study with a multiwall CNT (MWCNT) material (Nanocyl NC 7000) according to Organisation for Economic Co-operation and Development test guideline 413. Wistar rats were head-nose exposed for 6 h/day, 5 days/week, 13 weeks, total 65 exposures, to MWCNT concentrations of 0 (control), 0.1, 0.5, or 2.5 mg/m(3). Highly respirable dust aerosols were produced with a proprietary brush generator which neither damaged the tube structure nor increased reactive oxygen species on the surface. Inhalation exposure to MWCNT produced no systemic toxicity. However, increased lung weights, pronounced multifocal granulomatous inflammation, diffuse histiocytic and neutrophilic inflammation, and intra-alveolar lipoproteinosis were observed in lung and lung-associated lymph nodes at 0.5 and 2.5 mg/m(3). These effects were accompanied by slight blood neutrophilia at 2.5 mg/m(3). Incidence and severity of the effects were concentration related. At 0.1 mg/m(3), there was still minimal granulomatous inflammation in the lung and in lung-associated lymph nodes; a no observed effect concentration was therefore not established in this study. The test substance has low dust-forming potential, as demonstrated by dustiness measurements, but nonetheless strict industrial hygiene measures must be taken during handling and processing. Toxicity and dustiness data such as these can be used to compare different MWCNT materials and to select the material with the lowest risk potential for a given application.

Understanding biophysicochemical interactions at the nano-bio interface

Rapid growth in nanotechnology is increasing the likelihood of engineered nanomaterials coming into contact with humans and the environment. Nanoparticles interacting with proteins, membranes, cells, DNA and organelles establish a series of nanoparticle/biological interfaces that depend on colloidal forces as well as dynamic biophysicochemical interactions. These interactions lead to the formation of protein coronas, particle wrapping, intracellular uptake and biocatalytic processes that could have biocompatible or bioadverse outcomes. For their part, the biomolecules may induce phase transformations, free energy releases, restructuring and dissolution at the nanomaterial surface. Probing these various interfaces allows the development of predictive relationships between structure and activity that are determined by nanomaterial properties such as size, shape, surface chemistry, roughness and surface coatings. This knowledge is important from the perspective of safe use of nanomaterials.

Mechanisms for how inhaled multiwalled carbon nanotubes suppress systemic immune function in mice

The potential health effects of inhaling carbon nanotubes are important because of possible exposures in occupational settings. Previously, we have shown mice that have inhaled multiwalled carbon nanotubes have suppressed systemic immune function. Here, we show the mechanisms for this immune suppression. Mice were exposed to 0, 0.3 or 1 mg m(-3) multiwalled carbon nanotubes for 6 h per day for 14 consecutive days in whole-body inhalation chambers. Only those exposed to a dose of 1 mg m(-3) presented suppressed immune function; this involved activation of cyclooxygenase enzymes in the spleen in response to a signal from the lungs. Spleen cells from exposed animals partially recovered their immune function when treated with ibuprofen, a drug that blocks the formation of cyclooxygenase enzymes. Knockout mice without cyclooxygenase enzymes were not affected when exposed to multiwalled carbon nanotubes, further confirming the importance of this enzyme in suppression. Proteins from the lungs of exposed mice suppressed the immune function of spleen cells from normal mice, but not those from knockout mice. Our findings suggest that signals from the lung can activate signals in the spleen to suppress the immune function of exposed mice.

Nanomaterials – the Next Great Challenge for Qsar Modelers

In this final chapter a new perspective for the application of QSAR in the nanosciences is discussed. The role of nanomaterials is rapidly increasing in many aspects of everyday life. This is promoting a wide range of research needs related to both the design of new materials with required properties and performing a comprehensive risk assessment of the manufactured nanoparticles. The development of nanoscience also opens new areas for QSAR modelers. We have begun this contribution with a detailed discussion on the remarkable physical–chemical properties of nanomaterials and their specific toxicities. Both these factors should be considered as potential endpoints for further nano-QSAR studies. Then, we have highlighted the status and research needs in the area of molecular descriptors applicable to nanomaterials. Finally, we have put together currently available nano-QSAR models related to the physico-chemical endpoints of nanoparticles and their activity. Although we have observed many problems (i.e., a lack of experimental data, insufficient and inadequate descriptors), we do believe that application of QSAR methodology will significantly support nanoscience in the near future. Development of reliable nano-QSARs can be considered as the next challenging task for the QSAR community.

Alternative estimation of human exposure of single-walled carbon nanotubes using three-dimensional tissue-engineered human lung

Recent discoveries of various forms of carbon nanostructure have stimulated research on their applications and hold promise for applications in medicine and other related engineering areas. Although carbon nanotubes (CNTs) are already being produced on a massive scale, few studies have been performed which test the potential harmful effects of this new technology. The authors used a three-dimensional in vitro model of the human airway using a coculture of normal human bronchial epithelial cells and normal human fibroblasts for the health risk assessment of CNTs on the human respiratory systems. The authors used aqueous single-walled carbon nanotube (SWCNT) solution. The average length and diameter of nanotube ropes were about 500 nm and less than 10 nm, respectively. The authors measured the production of nitric oxide (NO) as an inflammatory marker and mitochondrial activity using MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay as a cytotoxic response of the cell layers following exposure of different concentration of aqueous SWCNT solution. The results indicated that NO production was dramatically increased and cell viability was decreased following exposure of different concentrations of SWCNTs. Transepithelial electrical resistance (TER) across the coculture layers was measured to observe the changes in airway physiological function following exposure of different concentrations of SWCNTs. TER value was dramatically decreased following exposure of 20% SWCNT (8 microg/ml). In this study, the authors presented viable alternatives to in vivo tests to evaluate the toxicity of engineered SWCNTs. Cytotoxic/inflammatory responses and barrier function of the human lung layers following exposure of SWCNTs were observed using in vitro coculture system of airway.

Oxidative stress induced by zero-valent iron nanoparticles and Fe(II) in human bronchial epithelial cells

To identify the mechanism through which nanoparticulate zero-valent iron (nZVI; Fe0(s)) damages cells, a series of experiments were conducted in which nZVI in phosphate-buffered saline (PBS) was exposed to oxygen in the presence and absence of human bronchial epithelial cells. When nZVI is added to PBS, a burst of oxidants is produced as Fe0 and ferrous iron (Fe[II]) are converted to ferric iron (Fe[II]). Cytotoxicity and internal reactive oxygen species (ROS) production in cells exposed to nZVI is equivalent to the response observed when cells are exposed to the same concentration of dissolved Fe(II). Experiments conducted in the absence of cells indicate that the oxidant produced during Fe(II) oxidation reacts with methanol and dimethyl sulfoxide, but not with compounds such as tert-butanol and benzoate that react exclusively with hydroxyl radical. The role of reactive oxidants produced during Fe(II) oxidation in cytotoxicity and internal ROS production is further supported by experiments in which cell damage was limited by the addition of ligands that prevented Fe(II) oxidation and by the absence of cell damage when the nanoparticles were oxidized prior to exposure. The behavior of the oxidant produced by nZVI is consistent with an oxidant such as the ferryl ion, rather than hydroxyl radical.

Aging of nanocarbons in ambient conditions: probable metastability of carbon nanotubes

We studied the physicochemical properties of several commercially available single- and multi-walled carbon nanotubes (SWNTs and MWNTs) and fullerenes stored in normal ambient conditions for 24 months. We found that SWNTs exhibit a trend of decreasing surface area and pore volume up to 7-15 months but then stabilized, no longer being impacted by sample age or outgassing temperatures. Using X-ray Photoelectron Spectroscopy, we also observed a trend of decreasing surface oxygen in all samples from the beginning with much lower % oxygen observed after 12-15 months of aging under ambient conditions. The surface oxygen then stabilized for the duration of this study. There was also evidence that the total structural-defect concentration, estimated from Raman spectroscopy, was somehow lowered during the aging process. The decrease in surface oxygen is an unexpected phenomenon because most other carbons, such as activated carbons or carbon molecular sieves, either oxidize or remain unaffected by age. We believe that nanocarbons are meta-stable materials (in pseudo-thermodynamic equilibrium), and that their aging in ambient conditions makes them more thermodynamically stable with fixed properties. This new information about the properties of nanocarbons should be further explored as it can help resolve some of the conflicting reports such as those about the environmental impacts of nanomaterials.

Health effects of exposure to carbon nanofibers: systematic review, critical appraisal, meta analysis and research to practice perspectives

BACKGROUND

Literature reviews examining the relationship between exposure to carbon nanofibers (CNFs) and health consequences are qualitative in nature and do not employ an evidence-based assessment.

OBJECTIVE

This research deals with a systematic review, critical appraisal, and meta-analysis designed to examine the potential health effects associated with exposure to CNFs. The utilization of research findings into practice is also explored.

METHODS

Published articles were obtained from a search of electronic databases and bibliographies of identified articles. A critical appraisal was conducted using an 'Experimental Appraisal Instrument' developed in this study. The meta-analysis was established using statistical techniques with/without the incorporation of overall study quality. The likelihood of utilizing research findings into practice (i.e., from research to practice) was computed using a four-step algorithm based on the criteria of: strength of association, consistency among studies, temporality, biological gradient, type of experimental unit, type of CNF (single- and multi-wall nanotubes), CNF grade (commercial or altered), exposure dose, exposure duration, and support by analogy from the published literature.

RESULTS

Twenty-one experimental studies satisfied the inclusion criteria and were performed on human cells, experimental animal models and animal cells as experimental units. The methodological qualities of published studies ranged from 'very poor' to 'excellent', with 'overall study description' scoring 'good' and 'study execution' equal to 'moderate'. The random-effects model was applied in the meta-analysis calculations as heterogeneity was significant at the 10% for all outcomes reported. The mean standardized meta-estimates for the experimental groups were significantly lower than those for the control groups for cell viability and cell death, respectively. Incorporating the effect of overall study quality score widened the gap between the experimental and control groups. Assessment of research findings on the basis of the four-step algorithm revealed that the likelihood of the results to occur in practice is 'somewhat possible' at this time. That is, if exposure conditions to CNF in the reported studies are similar to those in nano-manufacturing plants, it is somewhat possible that CNFs alter the function of human cells resulting in loss of cell viability and cell death.

CONCLUSIONS

Our findings suggest that it is 'somewhat possible' for the CNF to penetrate the human cells in the targeted organs and to cause cellular damage. Although the weight of evidence is not sufficient, it is advisable that actions be taken to ensure the protection of workers exposed to CNFs, that is, (a) engineering controls should be established to contain exposure to CNF, and (b) simultaneously rigorous personnel protective equipment should be planned to further minimize the risk of CNF exposure.

Absence of carcinogenic response to multiwall carbon nanotubes in a 2-year bioassay in the peritoneal cavity of the rat

Toxicological investigations of carbon nanotubes have shown that they can induce pulmonary toxicity, and similarities with asbestos fibers have been suggested. We previously reported that multiwall carbon nanotubes (MWCNT) induced lung inflammation, granulomas and fibrotic reactions. The same MWCNT also caused mutations in epithelial cells in vitro and in vivo. These inflammatory and genotoxic activities were related to the presence of defects in the structure of the nanotubes. In view of the strong links between inflammation, mutations and cancer, these observations prompted us to explore the carcinogenic potential of these MWCNT in the peritoneal cavity of rats. The incidence of mesothelioma and other tumors was recorded in three groups of 50 male Wistar rats injected intraperitoneally with a single dose of MWCNT with defects (2 or 20 mg/animal) and MWCNT without defects (20 mg/animal). Two additional groups of 26 rats were used as positive (2 mg UICC crocidolite/animal) and vehicle controls. After 24 months, although crocidolite induced a clear carcinogenic response (34.6% animals with mesothelioma vs. 3.8% in vehicle controls), MWCNT with or without structural defects did not induce mesothelioma in this bioassay (4, 0, or 6%, respectively). The incidence of tumors other than mesothelioma was not significantly increased across the groups. The initial hypothesis of a contrasting carcinogenic activity between MWCNT with and without defects could not be verified in this bioassay. We discuss the possible reasons for this absence of carcinogenic response, including the length of the MWCNT tested (< 1 mum on average), the absence of a sustained inflammatory reaction to MWCNT, and the capacity of these MWCNT to quench free radicals.

NanoGenotoxicology: the DNA damaging potential of engineered nanomaterials

With the rapid expansion in the nanotechnology industry, it is essential that the safety of engineered nanomaterials and the factors that influence their associated hazards are understood. A vital area governing regulatory health risk assessment is genotoxicology (the study of genetic aberrations following exposure to test agents), as DNA damage may initiate and promote carcinogenesis, or impact fertility. Of late, considerable attention has been given to the toxicity of engineered nanomaterials, but the importance of their genotoxic potential on human health has been largely overlooked. This comprehensive review focuses on the reported abilities of metal nanoparticles, metal-oxide nanoparticles, quantum dots, fullerenes, and fibrous nanomaterials, to damage or interact with DNA, and their ecogenotoxicity is also considered. Many of the engineered nanomaterials assessed were found to cause genotoxic responses, such as chromosomal fragmentation, DNA strand breakages, point mutations, oxidative DNA adducts and alterations in gene expression profiles. However, there are clear inconsistencies in the literature and it is difficult to draw conclusions on the physico-chemical features of nanomaterials that promote genotoxicity, largely due to study design. Hence, areas that require that further attention are highlighted and recommendations to improve our understanding of the genotoxic potential of engineered nanomaterials are addressed.

Oxidatively damaged DNA in rats exposed by oral gavage to C60 fullerenes and single-walled carbon nanotubes

BACKGROUND

C60 fullerenes and single-walled carbon nanotubes (SWCNT) are projected to be used in medicine and consumer products with potential human exposure. The hazardous effects of these particles are expected to involve oxidative stress with generation of oxidatively damaged DNA that might be the initiating event in the development of cancer.

OBJECTIVE

In this study we investigated the effect of a single oral administration of C60 fullerenes and SWCNT.

METHODS

We measured the level of oxidative damage to DNA as the premutagenic 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in the colon mucosa, liver, and lung of rats after intragastric administration of pristine C60 fullerenes or SWCNT (0.064 or 0.64 mg/kg body weight) suspended in saline solution or corn oil. We investigated the regulation of DNA repair systems toward 8-oxodG in liver and lung tissue.

RESULTS

Both doses of SWCNT increased the levels of 8-oxodG in liver and lung. Administration of C60 fullerenes increased the hepatic level of 8-oxodG, whereas only the high dose generated 8-oxodG in the lung. We detected no effects on 8-oxodG in colon mucosa. Suspension of particles in saline solution or corn oil yielded a similar extent of genotoxicity, whereas corn oil per se generated more genotoxicity than the particles. Although there was increased mRNA expression of 8-oxoguanine DNA glycosylase in the liver of C60 fullerene-treated rats, we found no significant increase in repair activity.

CONCLUSIONS

Oral exposure to low doses of C60 fullerenes and SWCNT is associated with elevated levels of 8-oxodG in the liver and lung, which is likely to be caused by a direct genotoxic ability rather than an inhibition of the DNA repair system.

The limits of testing particle-mediated oxidative stress in vitro in predicting diverse pathologies; relevance for testing of nanoparticles

In vitro studies with particles are a major staple of particle toxicology, generally used to investigate mechanisms and better understand the molecular events underlying cellular effects. However, there is ethical and financial pressure in nanotoxicology, the new sub-specialty of particle toxicology, to avoid using animals. Therefore an increasing amount of studies are being published using in vitro approaches and such studies require careful interpretation. We point out here that 3 different conventional pathogenic particle types, PM₁₀, asbestos and quartz, which cause diverse pathological effects, have been reported to cause very similar oxidative stress effects in cells in culture. We discuss the likely explanation and implications of this apparent paradox, and its relevance for testing in nanotoxicology.

Nanoparticle penetration and transport in living pumpkin plants: in situ subcellular identification

BACKGROUND

In recent years, the application of nanotechnology in several fields of bioscience and biomedicine has been studied. The use of nanoparticles for the targeted delivery of substances has been given special attention and is of particular interest in the treatment of plant diseases. In this work both the penetration and the movement of iron-carbon nanoparticles in plant cells have been analyzed in living plants of Cucurbita pepo.

RESULTS

The nanoparticles were applied in planta using two different application methods, injection and spraying, and magnets were used to retain the particles in movement in specific areas of the plant. The main experimental approach, using correlative light and electron microscopy provided evidence of intracellular localization of nanoparticles and their displacement from the application point. Long range movement of the particles through the plant body was also detected, particles having been found near the magnets used to immobilize and concentrate them. Furthermore, cell response to the nanoparticle presence was detected.

CONCLUSION

Nanoparticles were capable of penetrating living plant tissues and migrating to different regions of the plant, although movements over short distances seemed to be favoured. These findings show that the use of carbon coated magnetic particles for directed delivery of substances into plant cells is a feasible application.

Effects of multi-walled carbon nanotubes on a murine allergic airway inflammation model

The development of nanotechnology has increased the risk of exposure to types of particles other than combustion-derived particles in the environment, namely, industrial nanomaterials. On the other hand, patients with bronchial asthma are sensitive to inhaled substances including particulate matters. This study examined the effects of pulmonary exposure to a type of nano-sized carbon nanotube (multi-walled nanotubes: MWCNT) on allergic airway inflammation in vivo and their cellular mechanisms in vitro. In vivo, ICR mice were divided into 4 experimental groups. Vehicle, MWCNT (50 microg/animal), ovalbumin (OVA), and OVA+MWCNT were repeatedly administered intratracheally. Bronchoalveolar lavage (BAL) cellularity, lung histology, levels of cytokines related to allergic inflammation in lung homogenates/BAL fluids (BALFs), and serum immunoglobulin levels were studied. Also, we evaluated the impact of MWCNT (0.1-1 microg/ml) on the phenotype and function of bone marrow-derived dendritic cells (DC) in vitro. MWCNT aggravated allergen-induced airway inflammation characterized by the infiltration of eosinophils, neutrophils, and mononuclear cells in the lung, and an increase in the number of goblet cells in the bronchial epithelium. MWCNT with allergen amplified lung protein levels of Th cytokines and chemokines compared with allergen alone. MWCNT exhibited adjuvant activity for allergen-specific IgG(1) and IgE. MWCNT significantly increased allergen (OVA)-specific syngeneic T-cell proliferation, particularly at a lower concentration in vitro. Taken together, MWCNT can exacerbate murine allergic airway inflammation, at least partly, via the promotion of a Th-dominant milieu. In addition, the exacerbation may be partly through the inappropriate activation of antigen-presenting cells including DC.

Microbial cytotoxicity of carbon-based nanomaterials: implications for river water and wastewater effluent

This study evaluates the cytotoxicity of four carbon-based nanomaterials (CBNs)--single-walled carbon nanotubes (SWNTs), multiwalled carbon nanotubes (MWNTs), aqueous phase C60 nanoparticles (aq-nC60), and colloidal graphite--in gram negative and gram positive bacteria. The potential impacts of CBNs on microorganisms in natural and engineered aquatic systems are also evaluated. SWNTs inactivate the highest percentage of cells in monocultures of Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, and Staphylococcus epidermis, as well as in the diverse microbial communities of river water and wastewater effluent. Bacterial cytotoxicity displays time dependence, with longer exposure times accentuating toxicity in monocultures with initial tolerance for SWNTs. In Bacillus subtilis, an additional 3.5 h of incubation produced a five fold increase in toxicity. Elevated concentration of NOM reduces the attachment of bacteria on SWNT aggregates by 50%, but does not mitigate toxicity toward attached cells. CBN toxicity in bacterial monocultures was a poor predictor of microbial inactivation in chemically and biologically complex environmental samples.

Phosphatidylserine targets single-walled carbon nanotubes to professional phagocytes in vitro and in vivo

Broad applications of single-walled carbon nanotubes (SWCNT) dictate the necessity to better understand their health effects. Poor recognition of non-functionalized SWCNT by phagocytes is prohibitive towards controlling their biological action. We report that SWCNT coating with a phospholipid "eat-me" signal, phosphatidylserine (PS), makes them recognizable in vitro by different phagocytic cells - murine RAW264.7 macrophages, primary monocyte-derived human macrophages, dendritic cells, and rat brain microglia. Macrophage uptake of PS-coated nanotubes was suppressed by the PS-binding protein, Annexin V, and endocytosis inhibitors, and changed the pattern of pro- and anti-inflammatory cytokine secretion. Loading of PS-coated SWCNT with pro-apoptotic cargo (cytochrome c) allowed for the targeted killing of RAW264.7 macrophages. In vivo aspiration of PS-coated SWCNT stimulated their uptake by lung alveolar macrophages in mice. Thus, PS-coating can be utilized for targeted delivery of SWCNT with specified cargoes into professional phagocytes, hence for therapeutic regulation of specific populations of immune-competent cells.

Carbon Nanotubes in Biology and Medicine: In vitro and in vivo Detection, Imaging and Drug Delivery

Carbon nanotubes exhibit many unique intrinsic physical and chemical properties and have been intensively explored for biological and biomedical applications in the past few years. In this comprehensive review, we summarize the main results from our and other groups in this field and clarify that surface functionalization is critical to the behavior of carbon nanotubes in biological systems. Ultrasensitive detection of biological species with carbon nanotubes can be realized after surface passivation to inhibit the non-specific binding of biomolecules on the hydrophobic nanotube surface. Electrical nanosensors based on nanotubes provide a label-free approach to biological detection. Surface-enhanced Raman spectroscopy of carbon nanotubes opens up a method of protein microarray with detection sensitivity down to 1 fmol/L. In vitro and in vivo toxicity studies reveal that highly water soluble and serum stable nanotubes are biocompatible, nontoxic, and potentially useful for biomedical applications. In vivo biodistributions vary with the functionalization and possibly also size of nanotubes, with a tendency to accumulate in the reticuloendothelial system (RES), including the liver and spleen, after intravenous administration. If well functionalized, nanotubes may be excreted mainly through the biliary pathway in feces. Carbon nanotube-based drug delivery has shown promise in various In vitro and in vivo experiments including delivery of small interfering RNA (siRNA), paclitaxel and doxorubicin. Moreover, single-walled carbon nanotubes with various interesting intrinsic optical properties have been used as novel photoluminescence, Raman, and photoacoustic contrast agents for imaging of cells and animals. Further multidisciplinary explorations in this field may bring new opportunities in the realm of biomedicine.