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

Comparison of the biological activity between ultrafine and fine titanium dioxide particles in RAW 264.7 cells associated with oxidative stress

Ultrafine or fine titanium dioxide (TiO(2)) particles are widely used in the production of white pigments, for sunscreens, and in cleanup techniques. However, currently knowledge is deficient concerning cellular responses to these particles. The study evaluated and compared the biological activity of ultrafine and fine TiO(2) particles in RAW 264.7 macrophages according to an oxidative stress paradigm. In vitro exposure of macrophages to ultrafine or fine TiO(2) in the range of 0.5-200 microg/ml did not significantly alter cell viability. However, ultrafine TiO(2) enhanced intracellular generation of reactive oxygen species (ROS) to a greater extent than fine TiO(2) at each exposure concentration. Ultrafine TiO(2) induced ERK1/2 activation in a concentration-dependent manner, while the fine TiO(2)-induced changes were minimal. Phosphorylation of ERK1/2 occurred following 10 min exposure to higher concentrations of ultrafine TiO(2) (> or = 25 microg/ml). Similarly, ultrafine TiO(2) exposure significantly enhanced tumor necrosis factor (TNF)-alpha and macrophage inflammatory protein (MIP)-2 secretion in a concentration-dependent manner, and its potency was higher than fine TiO(2). These findings suggest that when exposure concentration is based upon equivalent mass, ultrafine TiO(2) exerts greater biological activity as measured by ROS generation, ERK 1/2 activation, and proinflammatory mediator secretion in RAW 264.7 macrophages than fine TiO(2).

Rosette nanotubes show low acute pulmonary toxicity in vivo

Nanotubes are being developed for a large variety of applications ranging from electronics to drug delivery. Common carbon nanotubes such as single-walled and multi-walled carbon nanotubes have been studied in the greatest detail but require solubilization and removal of catalytic contaminants such as metals prior to being introduced to biological systems for medical application. The present in vivo study characterizes the degree and nature of inflammation caused by a novel class of self-assembling rosette nanotubes, which are biologically inspired, naturally water-soluble and free of metal content upon synthesis. Upon pulmonary administration of this material we examined responses at 24 h and 7d post-exposure. An acute inflammatory response is triggered at 50 and 25 microg doses by 24 h post-exposure but an inflammatory response is not triggered by a 5 microg dose. Lung inflammation observed at a 50 microg dose at 24 h was resolving by 7d. This work suggests that novel nanostructures with biological design may negate toxicity concerns for biomedical applications of nanotubes. This study also demonstrates that water-soluble rosette nanotube structures represent low pulmonary toxicity, likely due to their biologically inspired design, and their self-assembled architecture.

Sequential exposure to carbon nanotubes and bacteria enhances pulmonary inflammation and infectivity

Carbon nanotubes (CNT), with their applications in industry and medicine, may lead to new risks to human health. CNT induce a robust pulmonary inflammation and oxidative stress in rodents. Realistic exposures to CNT may occur in conjunction with other pathogenic impacts (microbial infections) and trigger enhanced responses. We evaluated interactions between pharyngeal aspiration of single-walled CNT (SWCNT) and bacterial pulmonary infection of C57BL/6 mice with Listeria monocytogenes (LM). Mice were given SWCNT (0, 10, and 40 mug/mouse) and 3 days later were exposed to LM (10(3) bacteria/mouse). Sequential exposure to SWCNT/LM amplified lung inflammation and collagen formation. Despite this robust inflammatory response, SWCNT pre-exposure significantly decreased the pulmonary clearance of LM-exposed mice measured 3 to 7 days after microbial infection versus PBS/LM-treated mice. Decreased bacterial clearance in SWCNT-pre-exposed mice was associated with decreased phagocytosis of bacteria by macrophages and a decrease in nitric oxide production by these phagocytes. Pre-incubation of naïve alveolar macrophages with SWCNT in vitro also resulted in decreased nitric oxide generation and suppressed phagocytizing activity toward LM. Failure of SWCNT-exposed mice to clear LM led to a continued elevation in nearly all major chemokines and acute phase cytokines into the later course of infection. In SWCNT/LM-exposed mice, bronchoalveolar lavage neutrophils, alveolar macrophages, and lymphocytes, as well as lactate dehydrogenase level, were increased compared with mice exposed to SWCNT or LM alone. In conclusion, enhanced acute inflammation and pulmonary injury with delayed bacterial clearance after SWCNT exposure may lead to increased susceptibility to lung infection in exposed populations.

Single-walled carbon nanotubes: geno- and cytotoxic effects in lung fibroblast V79 cells

With the development of nanotechnology, there is a tremendous growth of the application of nanomaterials, which increases the risk of human exposure to these nanomaterials through inhalation, ingestion, and dermal penetration. Among different types of nanoparticles, single-walled carbon nanotubes (SWCNT) with extremely small size (1 nm in diameter) exhibit extraordinary properties and offer possibilities to create materials with astounding features. Since the release of nanoparticles in an enclosed environment is of great concern, a study of possible genotoxic effects is important. Our previous data showed that pharyngeal aspiration of SWCNT elicited pulmonary effects in C57BL/6 mice that was promoted by a robust, acute inflammatory reaction with early onset resulting in progressive interstitial fibrogenic response and the formation of granulomas. In the present study, the genotoxic potential of SWCNT was evaluated in vitro. The genotoxic effects of nanoparticles were examined using three different test systems: the comet assay and micronucleus (MN) test in a lung fibroblast (V79) cell line, and the Salmonella gene mutation assay in strains YG1024/YG1029. Cytotoxicity tests showed loss of viability in a concentration- and time-dependent manner after exposure of cells to SWCNT. Results from the comet assay demonstrated the induction of DNA damage after only 3 h of incubation with 96 microg/cm2 of SWCNT. The MN test indicated some but not significant micronucleus induction by SWCNT in the V79 cell line at the highest concentrations tested. With two different strains of Salmonella typhimurium, no mutations were found following SWCNT exposure.

Alteration of deposition pattern and pulmonary response as a result of improved dispersion of aspirated single-walled carbon nanotubes in a mouse model

Nanoparticles have a fundamental dimension of <100 nm. However, on suspension in media, agglomerates of nanoparticles are the more common structure. This is particularly evident in prior intratracheal instillation or aspiration studies of single-walled carbon nanotubes (SWCNT), in which granulomatous lesions encased by epithelioid macrophages were produced by large agglomerates. In this study, we tested the hypothesis of whether exposure to more dispersed SWCNT structures would alter pulmonary distribution and response. A dispersed preparation of single-walled carbon nanotubes (DSWCNT) with a mean diameter of 0.69 microm was given by pharyngeal aspiration to C57BL/6 mice. Electron microscopy demonstrated a highly dispersed, interstitial distribution of DSWCNT deposits by 1 day postexposure. Deposits were generally <1 microm. Macrophage phagocytosis of DSWCNT was rarely observed at any time point. Lung responses were studied by lavage and morphometry at 1 h, 1 day, 7 day, and 1 mo after a single DSWCNT exposure of 10 microg/mouse. Lung sections and lavage cells demonstrated an early, transient neutrophilic and inflammatory phase that rapidly resolved and was similar to that observed with large agglomerates. No granulomatous lesions or epithelioid macrophages were detected. Morphometric measurement of Sirius red staining was used to assess the connective tissue response. The average thickness of connective tissue in alveolar regions was 0.10 +/- 0.02, 0.09 +/- 0.02, 0.10 +/- 0.01, 0.48 +/- 0.04, and 0.88 +/- 0.19 microm for PBS and 1-h, 1-day, 7-day, and 1-mo postexposure groups, respectively. The results demonstrate that dispersed SWCNT are rapidly incorporated into the alveolar interstitium and that they produce an increase in collagen deposition.

Visualization and quantitative analysis of nanoparticles in the respiratory tract by transmission electron microscopy

Nanotechnology in its widest sense seeks to exploit the special biophysical and chemical properties of materials at the nanoscale. While the potential technological, diagnostic or therapeutic applications are promising there is a growing body of evidence that the special technological features of nanoparticulate material are associated with biological effects formerly not attributed to the same materials at a larger particle scale. Therefore, studies that address the potential hazards of nanoparticles on biological systems including human health are required. Due to its large surface area the lung is one of the major sites of interaction with inhaled nanoparticles. One of the great challenges of studying particle-lung interactions is the microscopic visualization of nanoparticles within tissues or single cells both in vivo and in vitro. Once a certain type of nanoparticle can be identified unambiguously using microscopic methods it is desirable to quantify the particle distribution within a cell, an organ or the whole organism. Transmission electron microscopy provides an ideal tool to perform qualitative and quantitative analyses of particle-related structural changes of the respiratory tract, to reveal the localization of nanoparticles within tissues and cells and to investigate the 3D nature of nanoparticle-lung interactions.This article provides information on the applicability, advantages and disadvantages of electron microscopic preparation techniques and several advanced transmission electron microscopic methods including conventional, immuno and energy-filtered electron microscopy as well as electron tomography for the visualization of both model nanoparticles (e.g. polystyrene) and technologically relevant nanoparticles (e.g. titanium dioxide). Furthermore, we highlight possibilities to combine light and electron microscopic techniques in a correlative approach. Finally, we demonstrate a formal quantitative, i.e. stereological approach to analyze the distributions of nanoparticles in tissues and cells.This comprehensive article aims to provide a basis for scientists in nanoparticle research to integrate electron microscopic analyses into their study design and to select the appropriate microscopic strategy.

Tocopheryl Polyethylene Glycol Succinate as a Safe, Antioxidant Surfactant for Processing Carbon Nanotubes and Fullerenes

This work investigates the physical interactions between carbon nanomaterials and tocopheryl polyethylene glycol succinate (TPGS). TPGS is a synthetic amphiphile that undergoes enzymatic cleavage to deliver the lipophilic antioxidant, alpha-tocopherol (vitamin E) to cell membranes, and is FDA approved as a water-soluble vitamin E nutritional supplement and drug delivery vehicle. Here we show that TPGS 1000 is capable of dispersing multi-wall and single-wall carbon nanotubes in aqueous media, and for multiwall tubes is more effective than the commonly used non-ionic surfactant Triton X-100. TPGS is also capable of solubilizing C(60) in aqueous phases by dissolving fullerene in the core of its spherical micelles. Drying of these solutions leads to fullerene/TPGS phase separation and the self-assembly of highly ordered asymmetric nanoparticles, with fullerene nanocrystals attached to the hydrophobic end of crystalline TPGS nanobrushes. The article discusses surface charge, colloidal stability, and the potential applications of TPGS as a safe surfactant for "green" processing of carbon nanomaterials.

Ethical and scientific issues of nanotechnology in the workplace

In the absence of scientific clarity about the potential health effects of occupational exposure to nanoparticles, a need exists for guidance in decisionmaking about hazards, risks, and controls. An identification of the ethical issues involved may be useful to decision makers, particularly employers, workers, investors, and health authorities. Because the goal of occupational safety and health is the prevention of disease in workers, the situations that have ethical implications that most affect workers have been identified. These situations include the a) identification and communication of hazards and risks by scientists, authorities, and employers; b) workers' acceptance of risk; c) selection and implementation of controls; d) establishment of medical screening programs; and e) investment in toxicologic and control research. The ethical issues involve the unbiased determination of hazards and risks, nonmaleficence (doing no harm), autonomy, justice, privacy, and promoting respect for persons. As the ethical issues are identified and explored, options for decision makers can be developed. Additionally, societal deliberations about workplace risks of nanotechnologies may be enhanced by special emphasis on small businesses and adoption of a global perspective.

Nano neurology and the four P's of central nervous system regeneration: preserve, permit, promote, plasticity

True nanomaterials are delivered as a specific structure, or combination of structures, designed to deliver the therapeutic intact, directly to the site, requiring a much lower dose. These materials use very specific and deliberate molecular structures that can interact with neurons or protein structures inside the cells. Until recently, functional recovery of the central nervous system (CNS) was an unattainable goal and nanotechnology was an invisible science. A well-planned treatment spaced over time will produce functional return in the CNS. The four P's of CNS regeneration is a new framework for approaching CNS injury and evidence shows that nanotechnology is currently being used for stroke rehabilitation and, in several clinical trials, the treatment of scar formation blockade in the spinal cord. The four components are preserve, permit, promote, and plasticity.

Evaluation of Resveratrol and Piceatannol Cytotoxicity in Macrophages, T Cells, and Skin Cells

The cytotoxicity of resveratrol and of piceatannol, a structural analog of resveratrol, was examined in cultured cells. Using a MTT-based assay, which measures the conversion of 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) to a colored formazan product in living cells, resveratrol was found to inhibit the viability of transformed mouse macrophages, tumor-derived human T cells and human epidermoid carcinoma cells in a concentration-dependent manner, with the effect decreasing in the order: T cells (LC50 ~27 μmol L-1, 24 h; ~9 μmol L-1; 48h) > macrophages (LC50~29 μmol L-1, 24 h; 39 μmol L-1, 48 h) > skin cells (LC50 ~91 μmol L-1, 24 h; ~66 μmol L-1, 48 h). Paradoxically, a high concentration of resveratrol (50 μmol L-1) inhibited the proliferation of all three cell types, and a low concentration (5 μmol L-1) stimulated the proliferation of macrophages. The viability of macrophages was also decreased by piceatannol in a concentration-dependent manner. The stimulation of macrophages with zymosan lowered the cytotoxicity of both resveratrol and piceatannol. Scanning electron microscopy of cells treated with resveratrol revealed changes in cellular morphology that were consistent with toxicity. In macrophages and skin cells, resveratrol (50 μmol L-1) induced a time-dependent increase in reduced glutathione levels but did not alter the background levels of thiobarbituric acid-reactive substances. Taken together, the present data indicate that resveratrol is toxic to cultured macrophages, T cells and skin cells at concentrations ≥25 μmol L-1, and that the cytotoxicity occurs via a mechanism that does not involve oxidative stress. Furthermore, the degree of toxicity of both resveratrol and piceatannol towards macrophages depends on the activation status of these cells, with zymosan-activated cells appearing more resistant than nonstimulated cells.

Nanoparticles-a thoracic toxicology perspective

A substantial literature demonstrates that the main ultrafine particles found in ambient urban air are combustion-derived nanoparticles (CDNP) which originate from a number of sources and pose a hazard to the lungs. For CDNP, three properties appear important-surface area, organics and metals. All of these can generate free radicals and so induce oxidative stress and inflammation. Inflammation is a process involved in the diseases exhibited by the individuals susceptible to the effects of PM- development and exacerbations of airways disease and cardiovascular disease. It is therefore possible to implicate CDNP in the common adverse effects of increased PM. The adverse effects of increases in PM on the cardiovascular system are well-documented in the epidemiological literature and, as argued above, these effects are likely to be driven by the combustion-derived NP. The epidemiological findings can be explained in a number of hypotheses regarding the action of NP:-1) Inflammation in the lungs caused by NP causes atheromatous plaque development and destabilization; 2) The inflammation in the lungs causes alteration in the clotting status or fibrinolytic balance favouring thrombogenesis; 3) The NP themselves or metals/organics released by the particles enter the circulation and have direct effects on the endothelium, plaques, the clotting system or the autonomic nervous system/ heart rhythm. Environmental nanoparticles are accidentally produced but they provide a toxicological model for a new class of purposely 'engineered' NP arising from the nanotechnology industry, whose effects are much less understood. Bridging our toxicological knowledge between the environmental nanoparticles and the new engineered nanoparticles is a considerable challenge.

Immunological properties of engineered nanomaterials

Most research on the toxicology of nanomaterials has focused on the effects of nanoparticles that enter the body accidentally. There has been much less research on the toxicology of nanoparticles that are used for biomedical applications, such as drug delivery or imaging, in which the nanoparticles are deliberately placed in the body. Moreover, there are no harmonized standards for assessing the toxicity of nanoparticles to the immune system (immunotoxicity). Here we review recent research on immunotoxicity, along with data on a range of nanotechnology-based drugs that are at different stages in the approval process. Research shows that nanoparticles can stimulate and/or suppress the immune responses, and that their compatibility with the immune system is largely determined by their surface chemistry. Modifying these factors can significantly reduce the immunotoxicity of nanoparticles and make them useful platforms for drug delivery.

Reviewing the environmental and human health knowledge base of carbon nanotubes

Carbon nanotubes (CNTs) are considered one of the most promising materials in nanotechnology, with attractive properties for many technologic applications. The different synthesis, purification, and postprocessing methods produce CNTs with different physical characteristics, which can be applied in different fields ranging from composite materials, medical applications, and electronics to energy storage. The widespread projected use of CNTs makes it important to understand their potential harmful effects. In this environmental health review we observed a remarkable range of results of some of the toxicology studies. The comparability should be improved by further standardization and introduction of reference materials. However, at present the findings of this review suggest several key points: a) there are different types of CNTs, and therefore they cannot be considered a uniform group of substances; and b) in environmental compartments, CNTs can be bioavailable to organisms. The properties of CNTs suggest a possible accumulation along the food chain and high persistence. In organisms the absorption, distribution, metabolism, excretion, and toxicity of CNTs depend on the inherent physical and chemical characteristics such as CNT functionalization, coating, length, and agglomeration state that are influenced by the external environmental conditions during CNT production, use, and disposal stages. Characterized exposure scenarios could therefore be useful when conducting toxicologic studies. However, CNTs produce a toxic response upon reaching the lungs in sufficient quantity; this reaction is produced in a time-and dose-dependent manner. The identification of possible risks to human health and environment is a prerequisite for a successful introduction of CNTs in future applications.

High resolution FESEM and TEM reveal bacterial spore attachment

Transmission electron microscopy (TEM) studies in the 1960s and early 1970s using conventional thin section and freeze fracture methodologies revealed ultrastructural bacterial spore appendages. However, the limited technology at that time necessitated the time-consuming process of imaging serial sections and reconstructing each structure. Consequently, the distribution and function of these appendages and their possible role in colonization or pathogenesis remained unknown. By combining high resolution field emission electron microscopy with TEM images of identical bacterial spore preparations, we have been able to obtain images of intact and sectioned Bacillus and Clostridial spores to clearly visualize the appearance, distribution, resistance (to trypsin, chloramphenicol, and heat), and participation of these structures to facilitate attachment of the spores to glass, agar, and human cell substrates. Current user-friendly commercial field emission scanning electron microscopes (FESEMs), permit high resolution imaging, with high brightness guns at lower accelerating voltages for beam sensitive intact biological samples, providing surface images at TEM magnifications for making direct comparisons. For the first time, attachment structures used by pathogenic, environmental, and thermophile bacterial spores could be readily visualized on intact spores to reveal how specific appendages and outer spore coats participated in spore attachment, colonization, and invasion.

Pulmonary and Systemic Immune Response to Inhaled Multiwalled Carbon Nanotubes

Inhalation of multiwalled carbon nanotubes (MWCNTs) at particle concentrations ranging from 0.3 to 5 mg/m3 did not result in significant lung inflammation or tissue damage, but caused systemic immune function alterations. C57BL/6 adult (10- to 12-week) male mice were exposed by whole-body inhalation to control air or 0.3, 1, or 5 mg/m3 respirable aggregates of MWCNTs for 7 or 14 days (6 h/day). Histopathology of lungs from exposed animals showed alveolar macrophages containing black particles; however, there was no inflammation or tissue damage observed. Bronchial alveolar lavage fluid also demonstrated particle-laden macrophages; however, white blood cell counts were not increased compared to controls. MWCNT exposures to 0.3 mg/m3 and higher particle concentrations caused nonmonotonic systemic immunosuppression after 14 days but not after 7 days. Immunosuppression was characterized by reduced T-cell-dependent antibody response to sheep erythrocytes as well as T-cell proliferative ability in presence of mitogen, Concanavalin A. Assessment of nonspecific natural killer (NK) cell activity showed that animals exposed to 1 mg/m(3) had decreased NK cell function. Gene expression analysis of selected cytokines and an indicator of oxidative stress were assessed in lung tissue and spleen. No changes in gene expression were observed in lung; however, interleukin-10 (IL-10) and NAD(P)H oxidoreductase 1 mRNA levels were increased in spleen.

A comparison of dispersing media for various engineered carbon nanoparticles

BACKGROUND

With the increased manufacture and use of carbon nanoparticles (CNP) there has been increasing concern about the potential toxicity of fugitive CNP in the workplace and ambient environment. To address this matter a number of investigators have conducted in vitro and in vivo toxicity assessments. However, a variety of different approaches for suspension of these particles (culture media, Tween 80, dimethyl sulfoxide, phosphate-buffered saline, fetal calf serum, and others), and different sources of materials have generated potentially conflicting outcomes. The quality of the dispersion of nanoparticles is very dependent on the medium used to suspend them, and this then will most likely affect the biological outcomes.

RESULTS

In this work, the distributions of different CNP (sources and types) have been characterized in various media. Furthermore, the outcome of instilling the different agglomerates, or size distributions, was examined in mouse lungs after one and seven days. Our results demonstrated that CNP suspended in serum produced particle suspensions with the fewest large agglomerates, and the most uniform distribution in mouse lungs. In addition, no apparent clearance of instilled CNP took place from lungs even after seven days.

CONCLUSION

This work demonstrates that CNP agglomerates are present in all dispersing vehicles to some degree. The vehicle that contains some protein, lipid or protein/lipid component disperses the CNP best, producing fewer large CNP agglomerates. In contrast, vehicles absent of lipid and protein produce the largest CNP agglomerates. The source of the CNP is also a factor in the degree of particle agglomeration within the same vehicle.

Nanotechnology safety concerns revisited

Nanotechnology is an emerging science involving manipulation of matter at the nanometer scale. Due to concerns over nanomaterial risks, there has been a dramatic increase in focused safety research. The present review provides a summary of these published findings, identifying areas of agreement and discordance with regard to: (1) the potential for nanomaterial exposure, (2) the relative hazard nanomaterials pose to humans and the environment, and (3) the present deficits in our understanding of risk. Special attention is paid to study design and methodologies, offering valuable insight into the complexities encountered with nanomaterial safety assessment. Recent data highlight the impact of surface characteristics on nanomaterial biocompatibility and point to the inadequacy of the current size-dependent mechanistic paradigms, with nanoscale materials lacking unique or characteristic toxicity profiles. The available data support the ability of the lung, gastrointestinal tract, and skin to act as a significant barrier to the systemic exposure of many nanomaterials. Furthermore, the acute systemic toxicity of many nanomaterials appear to be low. By contrast, the potential pulmonary toxicity of certain nanomaterials, such as carbon nanotubes, is significant, requiring a better understanding of exposure to further evaluate their risk. While these findings arrive at an overall picture of material-specific rather than nanogeneralized risk, any conclusions should clearly be tempered by the fact that nanomaterial safety data are limited. Until such time as the exposures, hazards, and environmental life cycle of nanomaterials have been more clearly defined, cautious development and implementation of nanotechnology is the most prudent course.

Enhanced peripheral thrombogenicity after lung inflammation is mediated by platelet-leukocyte activation: role of P-selectin

BACKGROUND

Inhaled ultrafine particles trigger peripheral thrombotic complications.

METHODS

We have analyzed the systemic prothrombotic risk following lung inflammation induced by pulmonary carbon nanotubes (CNTs).

RESULTS

Intratracheal instillation in Swiss mice of 200 and 400 microg of multiwall ground CNTs triggered substantial lung neutrophil, but not macrophage influx, 24 h later. The detection of circulating platelet-leukocyte conjugates exclusively 6 h after CNT instillation pointed to early but transient activation of circulating platelets. At 24 h, elevated plasma procoagulant microvesicular tissue factor activity was found in CNT-exposed but not in saline-exposed mice. However, at 24 h, both the tail and jugular vein bleeding times were prolonged in CNT-exposed but not in saline-exposed mice, arguing against strong CNT-induced platelet activation at this point. Nevertheless, at 24 h, enhanced peripheral thrombogenicity was detected in CNT-exposed but not in saline-exposed mice, via quantitative photochemically induced carotid artery thrombosis measurements. P-selectin neutralization abrogated platelet-leukocyte conjugate formation and microvesicular tissue factor generation, and abolished the CNT-induced thrombogenicity amplification. In contrast, the weak vascular injury-triggered thrombus formation in saline-treated mice was not affected by P-selectin neutralization at 24 h.

CONCLUSIONS

The mild CNT-induced lung inflammation translates via rapid but mild and transient activation of platelets into P-selectin-mediated systemic inflammation. Leukocyte activation leads to tissue factor release, in turn eliciting inflammation-induced procoagulant activity and an associated prothrombotic risk.

Mechanisms of action of inhaled fibers, particles and nanoparticles in lung and cardiovascular diseases

BACKGROUND

A symposium on the mechanisms of action of inhaled airborne particulate matter (PM), pathogenic particles and fibers such as silica and asbestos, and nanomaterials, defined as synthetic particles or fibers less than 100 nm in diameter, was held on October 27 and 28, 2005, at the Environmental Protection Agency (EPA) Conference Center in Research Triangle Park, North Carolina. The meeting was the eighth in a series of transatlantic conferences first held in Penarth, Wales, at the Medical Research Council Pneumoconiosis Unit (1979), that have fostered long-standing collaborations between researchers in the fields of mineralogy, cell and molecular biology, pathology, toxicology, and environmental/occupational health.

RESULTS

The goal of this meeting, which was largely supported by a conference grant from the NHLBI, was to assemble a group of clinical and basic research scientists who presented and discussed new data on the mechanistic effects of inhaled particulates on the onset and development of morbidity and mortality in the lung and cardiovascular system. Another outcome of the meeting was the elucidation of a number of host susceptibility factors implicated in adverse health effects associated with inhaled pathogenic particulates.

CONCLUSION

New models and data presented supported the paradigm that both genetic and environmental (and occupational) factors affect disease outcomes from inhaled particulates as well as cardiopulmonary responses. These future studies are encouraged to allow the design of appropriate strategies for prevention and treatment of particulate-associated morbidity and mortality, especially in susceptible populations.

Nanoparticle effects on rat alveolar epithelial cell monolayer barrier properties

Inhaled nanoparticles have been reported to contribute to deleterious effects on human health. In this study, we investigated the effects of ultrafine ambient particulate suspensions (UAPS), polystyrene nanoparticles (PNP; positively and negatively charged; 20, 100, 120 nm), quantum dots (QD; positively and negatively charged; 30 nm) and single-wall carbon nanotubes (SWCNT) on alveolar epithelial cell barrier properties. Transmonolayer resistance (R(t)) and equivalent short-circuit current (I(eq)) of primary rat alveolar epithelial monolayers were measured in the presence and absence of varying concentrations of apical nanoparticles. In some experiments, apical-to-basolateral fluxes of radiolabeled mannitol or inulin were determined with or without apical UAPS exposure and lactate dehydrogenase (LDH) release was analyzed after UAPS or SWCNT exposure. Results revealed that exposure to UAPS decreased R(t) and I(eq) significantly over 24 h, although neither mannitol nor inulin fluxes changed. Positively charged QD decreased R(t) significantly (with subsequent recovery), while negatively charged QD did not. R(t) decreased significantly after SWCNT exposure (with subsequent recovery). On the other hand, PNP exposure had no effects on R(t) or I(eq). No significant increases in LDH release were observed after UAPS or SWCNT exposure. These data indicate that disruption of alveolar epithelial barrier properties due to apical nanoparticle exposure likely involves alteration of cellular transport pathways and is dependent on specific nanoparticle composition, shape and/or surface charge.

Vitamin E deficiency enhances pulmonary inflammatory response and oxidative stress induced by single-walled carbon nanotubes in C57BL/6 mice

Exposure of mice to single-walled carbon nanotubes (SWCNTs) induces an unusually robust pulmonary inflammatory response with an early onset of fibrosis, which is accompanied by oxidative stress and antioxidant depletion. The role of specific components of the antioxidant protective system, specifically vitamin E, the major lipid-soluble antioxidant, in the SWCNT-induced reactions has not been characterized. We used C57BL/6 mice, maintained on vitamin E-sufficient or vitamin E-deficient diets, to explore and compare the pulmonary inflammatory reactions to aspired SWCNTs. The vitamin E-deficient diet caused a 90-fold depletion of alpha-tocopherol in the lung tissue and resulted in a significant decline of other antioxidants (GSH, ascorbate) as well as accumulation of lipid peroxidation products. A greater decrease of pulmonary antioxidants was detected in SWCNT-treated vitamin E-deficient mice as compared to controls. Lowered levels of antioxidants in vitamin E-deficient mice were associated with a higher sensitivity to SWCNT-induced acute inflammation (total number of inflammatory cells, number of polymorphonuclear leukocytes, released LDH, total protein content and levels of pro-inflammatory cytokines, TNF-alpha and IL-6) and enhanced profibrotic responses (elevation of TGF-beta and collagen deposition). Exposure to SWCNTs markedly shifted the ratio of cleaved to full-length extracellular superoxide dismutase (EC-SOD). Given that pulmonary levels of vitamin E can be manipulated through diet, its effects on SWCNT-induced inflammation may be of practical importance in optimizing protective strategies.

Alveolar macrophages from normal subjects lack the NOS-related system y+ for arginine transport

Systems y+ and y+L represent the main routes for arginine transport in mammalian cells. While system y+ activity is needed for the stimulated NO production in rodent alveolar macrophages (AM), no information is yet available about arginine transport in human AM. We study here arginine influx and genes for arginine transporters in AM from bronchoalveolar lavage of normal subjects. These cells express the y+ -related genes SLC7A1/CAT1 and SLC7A2/CAT2B, as well as the y+L genes SLC7A7/y+LAT1 and SLC7A6/y+LAT2. However, compared with human endothelial cells, AM express much less SLC7A2 mRNA and higher levels of SLC7A7 mRNA. Granulocyte macrophage colony-stimulating factor or IFN-gamma do not change the expression of any transporter gene, while lipopolysaccharide induces SLC7A2/CAT2B. Under all the conditions tested, leucine inhibits most of the arginine transport in the presence of Na+ and N-ethylmaleimide, an inhibitor of system y+, is completely ineffective, indicating that system y+L operates most of the arginine influx. Comparable results are obtained in AM from patients with interstitial lung disease, such as Nonspecific Interstitial Pneumonia (NSIP), although these cells have a higher SLC7A1 and a lower SLC7A7 expression than AM from normal subjects. It is concluded that AM from normal subjects or patients with NSIP lack a functional transport system y+, a situation that may limit arginine availability for NO synthesis. Moreover, since mutations of SLC7A7/y+LAT1 cause Lysinuric Protein Intolerance, a disease often associated with AM impairment and alveolar proteinosis, the high SLC7A7 expression observed in human AM suggests that y+LAT1 activity is important for the function of these cells.

The adsorption–desorption process of bovine serum albumin on carbon nanotubes

The aim of this work is to study the adsorption-desorption process of bovine serum albumin (BSA) on carbon nanotubes (CNT) by reflectometry. The effect of the surface properties was analyzed by comparing the behavior of BSA on silica. The experiments were performed by reflectometry at different BSA concentrations, at pH 3.0, 4.8, and 7.0 and at two ionic strengths. Protein desorption was induced by either dilution with buffer or the addition of SDS. The initial adsorption rate is controlled by the attachment of BSA molecules to the surface, and strongly diminishes at pH 7. Adsorption isotherms reflect the high affinity of BSA for both sorbent surfaces and reach well-defined plateau values that depend on the pH, being the highest at pH 4.8 on CNT. Experiments performed at different ionic strengths (NaCl added) showed a less pronounced effect. Dilution does not induce desorption on either surface however, the addition of SDS removes protein only from the silica surface.

Toxicological aspects and applications of nanoparticles in paediatric respiratory disease

Most research in the area of micro- and nano-particles as applied to respiratory disease has been on potential toxic effects. Particulate emissions from industrial processes, coal burning and diesel exhaust have been shown to cause a variety of adverse effects both in vitro and in vivo. However, the vast majority of these studies has focused on larger, micron-sized particles. It is only within the last few years that the emphasis has shifted to nanoparticles as nanotechnology research and its applications have increased. Investigations have also begun into how nanoparticles may be used for therapeutic and imaging purposes in pulmonary diseases such as tuberculosis and cystic fibrosis. Some of these applications, along with recent studies on the toxic effects of nanoparticulate emissions will be reviewed in this article.

Cardiovascular effects of pulmonary exposure to single-wall carbon nanotubes

BACKGROUND

Engineered nanosized materials, such as single-wall carbon nanotubes (SWCNT), are emerging as technologically important in different industries.

OBJECTIVE

The unique physical characteristics and the pulmonary toxicity of SWCNTs raised concerns that respiratory exposure to these materials may be associated with cardiovascular adverse effects.

METHODS

In these studies we evaluated aortic mitochondrial alterations by oxidative stress assays, including quantitative polymerase chain reaction of mitochondrial (mt) DNA and plaque formation by morphometric analysis in mice exposed to SWCNTs.

RESULTS

A single intrapharyngeal instillation of SWCNTs induced activation of heme oxygenase-1 (HO-1), a marker of oxidative insults, in lung, aorta, and heart tissue in HO-1 reporter transgenic mice. Furthermore, we found that C57BL/6 mice, exposed to SWCNT (10 and 40 mug/mouse), developed aortic mtDNA damage at 7, 28, and 60 days after exposure. mtDNA damage was accompanied by changes in aortic mitochondrial glutathione and protein carbonyl levels. Because these modifications have been related to cardiovascular diseases, we evaluated whether repeated exposure to SWCNTs (20 mug/mouse once every other week for 8 weeks) stimulates the progression of atherosclerosis in ApoE(-/-) transgenic mice. Although SWCNT exposure did not modify the lipid profiles of these mice, it resulted in accelerated plaque formation in ApoE(-/-) mice fed an atherogenic diet. Plaque areas in the aortas, measured by the en face method, and in the brachiocephalic arteries, measured histopathologically, were significantly increased in the SWCNT-treated mice. This response was accompanied by increased mtDNA damage but not inflammation.

CONCLUSIONS

Taken together, the findings are of sufficient significance to warrant further studies to evaluate the systemic effects of SWCNT under workplace or environmental exposure paradigms.

Nanoparticles aggravate heat stress induced cognitive deficits, blood-brain barrier disruption, edema formation and brain pathology

Our knowledge regarding the influence of nanoparticles on brain function in vivo during normal or hyperthermic conditions is still lacking. Few reports indicate that when nanoparticles enter into the central nervous system (CNS) they may induce neurotoxicity. On the other hand, nanoparticle-induced drug delivery to the brain enhances neurorepair processes. Thus, it is likely that the inclusion of nanoparticles in body fluid compartments alters the normal brain function and/or its response to additional stress, e.g., hyperthermia. New data from our laboratory show that nanoparticles derived from metals (e.g., Cu, Ag or Al, approximately 50-60nm) are capable of inducing brain dysfunction in normal animals and aggravating the brain pathology caused by whole-body hyperthermia (WBH). Thus, normal animals treated with nanoparticles (for 1 week) exhibited mild cognitive impairment and cellular alterations in the brain. Subjection of these nanoparticle-treated rats to WBH resulted in profound cognitive and motor deficits, exacerbation of blood-brain barrier (BBB) disruption, edema formation and brain pathology compared with naive animals. These novel observations suggest that nanoparticles enhance brain pathology and cognitive dysfunction in hyperthermia. The possible mechanisms of nanoparticle-induced exacerbation of brain damage in WBH and its functional significance in relation to our current knowledge are discussed in this review.

Internalization of MWCNTs by microglia: Possible application in immunotherapy of brain tumors

There is a pressing need for new therapeutic, diagnostic, and drug delivery approaches for treating brain cancers. Nanotechnology offers a new method for targeted brain cancer therapy and could play a major role in gene and drug delivery. The goals of our study were to visualize in vitro ingestion, cytotoxicity, and loading capacity of Multi-Walled Carbon Nanotubes (MWCNTs) in microglia. Furthermore, we investigated internalization differences between microglia and glioma cells. BV2 microglia and GL261 glioma cells were incubated with MWCNTs, which were synthesized through catalytic chemical vapor deposition technique. Real-time RT-PCR, cell proliferation analysis, siRNA and DNA loading, electron microscopy, and flow cytometry were performed. We demonstrated that MWCNTs do not result in proliferative or cytokine changes in vitro, are capable of carrying DNA and siRNA and are internalized at higher levels in phagocytic cells as compared to tumor cells. This study suggests MWCNTs could be used as a novel, non-toxic, and biodegradable nano-vehicles for targeted therapy in brain cancers. Further studies are needed to demonstrate the full capacity of MWCNTs as nanovectors.

Ethical and scientific issues of nanotechnology in the workplace

In the absence of scientific clarity about the potential health effects of occupational exposure to nanoparticles, a need exists for guidance in decisionmaking about hazards, risks, and controls. An identification of the ethical issues involved may be useful to decision makers, particularly employers, workers, investors, and health authorities. Because the goal of occupational safety and health is the prevention of disease in workers, the situations that have ethical implications that most affect workers have been identified. These situations include the a) identification and communication of hazards and risks by scientists, authorities, and employers; b) workers' acceptance of risk; c) selection and implementation of controls; d) establishment of medical screening programs; and e) investment in toxicologic and control research. The ethical issues involve the unbiased determination of hazards and risks, nonmaleficence (doing no harm), autonomy, justice, privacy, and promoting respect for persons. As the ethical issues are identified and explored, options for decision makers can be developed. Additionally, societal deliberations about workplace risks of nanotechnologies may be enhanced by special emphasis on small businesses and adoption of a global perspective.

Nanoparticles: health effects--pros and cons

With the advent of nanotechnology, the prospects for using engineered nanomaterials with diameters of < 100 nm in industrial applications, medical imaging, disease diagnoses, drug delivery, cancer treatment, gene therapy, and other areas have progressed rapidly. The potential for nanoparticles (NPs) in these areas is infinite, with novel new applications constantly being explored. The possible toxic health effects of these NPs associated with human exposure are unknown. Many fine particles generally considered "nuisance dusts" are likely to acquire unique surface properties when engineered to nanosize and may exhibit toxic biological effects. Consequently, the nuisance dust may be transported to distant sites and could induce adverse health effects. In addition the beneficial uses of NPs in drug delivery, cancer treatment, and gene therapy may cause unintentional human exposure. Because of our lack of knowledge about the health effects associated with NP exposure, we have an ethical duty to take precautionary measures regarding their use. In this review we highlight the possible toxic human health effects that can result from exposure to ultrafine particles (UFPs) generated by anthropogenic activities and their cardiopulmonary outcomes. The comparability of engineered NPs to UFPs suggests that the human health effects are likely to be similar. Therefore, it is prudent to elucidate their toxicologic effect to minimize occupational and environmental exposure. Highlighting the human health outcomes caused by UFPs is not intended to give a lesser importance to either the unprecedented technologic and industrial rewards of the nanotechnology or their beneficial human uses.

Single-walled carbon nanotube (SWCNT)-induced interstitial fibrosis in the lungs of rats is associated with increased levels of PDGF mRNA and the formation of unique intercellular carbon structures that bridge alveolar macrophages in situ

Background

Nanotechnology is a rapidly advancing industry with many new products already available to the public. Therefore, it is essential to gain an understanding of the possible health risks associated with exposure to nanomaterials and to identify biomarkers of exposure. In this study, we investigated the fibrogenic potential of SWCNT synthesized by chemical vapor deposition using cobalt (Co) and molybdenum (Mo) as catalysts. Following a single oropharyngeal aspiration of SWCNT in rats, we evaluated lung histopathology, cell proliferation, and growth factor mRNAs at 1 and 21 days post-exposure. Comparisons were made to vehicle alone (saline containing a biocompatible nonionic surfactant), inert carbon black (CB) nanoparticles, or vanadium pentoxide (V₂O₅) as a known inducer of fibrosis.

Results

SWCNT or CB caused no overt inflammatory response at 1 or 21 days post-exposure as determined by histopathology and evaluation of cells (>95% macrophages) in bronchoalveolar lavage (BAL) fluid. However, SWCNT induced the formation of small, focal interstitial fibrotic lesions within the alveolar region of the lung at 21 days. A small fraction of alveolar macrophages harvested by BAL from the lungs of SWCNT-exposed rats at 21 days were bridged by unique intercellular carbon structures that extended into the cytoplasm of each macrophage. These "carbon bridge" structures between macrophages were also observed in situ in the lungs of SWCNT-exposed rats. No carbon bridges were observed in CB-exposed rats. SWCNT caused cell proliferation only at sites of fibrotic lesion formation as measured by bromodeoxyuridine uptake into alveolar cells. SWCNT increased platelet-derived growth factor (PDGF)-A, PDGF-B, and PDGF-C mRNA levels significantly at 1 day as measured by Taqman quantitative real-time RT-PCR. At 21 days, SWCNT did not increase any mRNAs evaluated, while V₂O₅ significantly increased mRNAs encoding PDGF-A, -B, and -C chains, PDGF-Rα, osteopontin (OPN), connective tissue growth factor (CTGF), and transforming growth factor (TGF)-β1.

Conclusion

Our findings indicate that SWCNT do not cause lung inflammation and yet induce the formation of small, focal interstital fibrotic lesioins in the alveolar region of the lungs of rats. Of greatest interest was the discovery of unique intercellular carbon structures composed of SWCNT that bridged lung macrophages. These "carbon bridges" offer a novel and easily identifiable biomarker of exposure.

In vitro toxicity evaluation of single walled carbon nanotubes on human A549 lung cells

This paper describes the in vitro cytotoxicity assessment of single walled carbon nanotubes (SWCNT) on A549 cells, a human lung cell line. Cellular viability was determined using the alamar blue (AB), neutral red (NR) and MTT assays, which evaluated metabolic, lysosomal and mitochondrial activity respectively. In addition, the total protein content of the cells was measured using the coomassie brilliant (CB) blue assay. Supernatants were also assayed for Adenylate Kinase (AK) release and Interleukin 8 (IL-8) which indicated a loss of cell membrane integrity and an inflammation response respectively. To investigate the interactions between serum components in the test medium and the test materials, exposures were conducted both in serum containing (5%) and serum-free medium. Results from the cytotoxicity tests (AB, CB, MTT) revealed the SWCNT to have very low acute toxicity to the A549 cells as all but one of the reported 24h EC(50) values exceeded the top concentration tested (800 microg/ml). The SWCNT were found to interfere with a number of the dyes used in the cytotoxicity assessment and we are currently conducting a comprehensive spectroscopic study to further investigate these interactions. Of the multiple cytotoxicity assays used, the AB assay was found to be the most sensitive and reproducible. Transmission electron microscopy (TEM) studies confirmed that there was no intracellular localization of SWCNT in A549 cells following 24h exposure; however, increased numbers of surfactant storing lamellar bodies were observed in exposed cells.

Getting It Right the First Time: Developing Nanotechnology while Protecting Workers, Public Health, and the Environment

Nanotechnology, the design and manipulation of materials at the atomic scale, may well revolutionize many of the ways our society manufactures products, produces energy, and treats diseases. Innovative nanotechnology products are already reaching the market in a wide variety of consumer products. Some of the observed properties of nanomaterials call into question the adequacy of current methods for determining hazard and exposure, and for controlling resulting risks. Given the limitations of existing regulatory tools and policies, two distinct kinds of initiatives are urgently needed: first, a major increase in the federal investment nanomaterial risk research, and second, rapid development and implementation of voluntary standards of care pending development of adequate regulatory safeguards. The U.S. government should increase federal funding for nanomaterial risk research under the National Nanotechnology Initiative to at least $100 million annually for the next several years. Several voluntary programs are currently at various stages of evolution, though the eventual outputs of each of these are still far from clear. Ultimately, effective regulatory safeguards, harmonized globally, are necessary to provide a level playing field for industry while adequately protecting human health and the environment.

Nanoparticles in drug delivery and environmental exposure: same size, same risks?

Engineered nanoparticles are an important tool for future nanomedicines to deliver and target drugs or bring imaging agents to the targets where they are required. Since the original application of liposomes in the 1970s, a wealth of carrier and imaging systems has been developed, including magnetoliposomes, dendrimers, fullerenes and polymer carriers. However, to make use of this potential, toxicological issues must be addressed, in particular because of findings on combustion-derived nanoparticles in environmentally exposed populations, which show effects in those with respiratory or cardiovascular diseases. These effects are mediated by oxidative stress, lung and systemic inflammation and different mechanisms of internalization and translocation. Many effects found with combustion-derived nanoparticles have now tested positive with engineered nanoparticles, such as single-wall nanotubes. This article aims to identify common concepts in the action of nanoparticles in order to enable future cross-talk and mutual use of concepts.

Direct and indirect effects of single walled carbon nanotubes on RAW 264.7 macrophages: Role of iron

Single-walled carbon nanotubes (SWCNT), nano-cylinders with an extremely small diameter (1-2 nm) and high aspect ratio, have unique physico-chemical, electronic and mechanical properties and may exhibit unusual interactions with cells and tissues, thus necessitating studies of their toxicity and health effects. Manufactured SWCNT usually contain significant amounts of iron that may act as a catalyst of oxidative stress. Because macrophages are the primary responders to different particles that initiate and propagate inflammatory reactions and oxidative stress, we utilized two types of SWCNT: (1) iron-rich (non-purified) SWCNT (26 wt.% of iron) and (2) iron-stripped (purified) SWCNT (0.23 wt.% of iron) to study their interactions with RAW 264.7 macrophages. Ultrasonication resulted in predominantly well-dispersed and separated SWCNT strands as evidenced by scanning electron microscopy. Neither purified nor non-purified SWCNT were able to generate intracellular production of superoxide radicals or nitric oxide in RAW 264.7 macrophages as documented by flow-cytometry and fluorescence microscopy. SWCNT with different iron content displayed different redox activity in a cell-free model system as revealed by EPR-detectable formation of ascorbate radicals resulting from ascorbate oxidation. In the presence of zymosan-stimulated RAW 264.7 macrophages, non-purified iron-rich SWCNT were more effective in generating hydroxyl radicals (documented by EPR spin-trapping with 5,5-dimethyl-1-pyrroline-N-oxide, DMPO) than purified SWCNT. Similarly, EPR spin-trapping experiments in the presence of zymosan-stimulated RAW 264.7 macrophages showed that non-purified SWCNT more effectively converted superoxide radicals generated by xanthine oxidase/xanthine into hydroxyl radicals as compared to purified SWCNT. Iron-rich SWCNT caused significant loss of intracellular low molecular weight thiols (GSH) and accumulation of lipid hydroperoxides in both zymosan-and PMA-stimulated RAW 264.7 macrophages. Catalase was able to partially protect macrophages against SWCNT induced elevation of biomarkers of oxidative stress (enhancement of lipid peroxidation and GSH depletion). Thus, the presence of iron in SWCNT may be important in determining redox-dependent responses of macrophages.

In situ structure characterization of airborne carbon nanofibres by a tandem mobility-mass analysis

Carbon nanofibres aerosolized by the agitation of as-produced commercial powder have been characterized in situ by using the differential mobility analyser-aerosol particle mass analyser (DMA-APM) method to determine their structural properties such as the effective density and fractal dimension for toxicology study. The effective density of the aerosolized carbon nanofibres decreased from 1.2 to 0.4 g cm(-3) as the mobility diameters increased from 100 to 700 nm, indicating that the carbon nanofibres had open structures with an overall void that increased with increasing diameter, due to increased agglomeration of the nanofibres. This was confirmed by transmission electron microscopy (TEM) observation, showing that 100 nm mobility diameter nanofibres were predominantly single fibres, while doubly or triply attached fibres were seen at mobility diameters of 200 and 400 nm. Effective densities calculated using Cox's theory were in reasonable agreement with experimental values. The mass fractal dimension of the carbon nanofibres was found to be 2.38 over the size range measured and higher than that of single-walled carbon nanotubes (SWCNTs), suggesting that the carbon nanofibres have more compact structure than SWCNTs.

Reactivity of carbon nanotubes: free radical generation or scavenging activity?

Carbon nanotubes (CNTs) currently attract intense research efforts because of their unique properties which make them suitable for many industrial applications. When inhaled, CNTs constitute a possible hazard to human health. Several studies have shown that when instilled in the lung of experimental animals, CNTs induced an inflammatory and fibrotic response similar to that caused by other toxic particles which might be the result of oxidative stress caused by particle- and/or cell-derived free radicals. There is, however, no direct experimental evidence of a capacity of carbon nanotubes to generate directly free radicals. Here we report that multiwall carbon nanotubes (MWCNT) in aqueous suspension do not generate oxygen or carbon-centered free radicals in the presence of H2O2 or formate, respectively, as detected with the spin-trapping technique. Conversely, we observed that, when in contact with an external source of hydroxyl or superoxide radicals, MWCNT exhibit a remarkable radical scavenging capacity. It is therefore possible that the inflammatory reaction reported in vivo must be ascribed to MWCNT features other than particle-derived free radical generation.

Apoptotic interactions of cytochrome c: redox flirting with anionic phospholipids within and outside of mitochondria

Since the (re)discovery of cytochrome c (cyt c) in the early 1920s and subsequent detailed characterization of its structure and function in mitochondrial electron transport, it took over 70 years to realize that cyt c plays a different, not less universal role in programmed cell death, apoptosis, by interacting with several proteins and forming apoptosomes. Recently, two additional essential functions of cyt c in apoptosis have been discovered that are carried out via its interactions with anionic phospholipids: a mitochondria specific phospholipid, cardiolipin (CL), and plasma membrane phosphatidylserine (PS). Execution of apoptotic program in cells is accompanied by substantial and early mitochondrial production of reactive oxygen species (ROS). Because antioxidant enhancements protect cells against apoptosis, ROS production was viewed not as a meaningless side effect of mitochondrial disintegration but rather playing some - as yet unidentified - role in apoptosis. This conundrum has been resolved by establishing that mitochondria contain a pool of cyt c, which interacts with CL and acts as a CL oxygenase. The oxygenase is activated during apoptosis, utilizes generated ROS and causes selective oxidation of CL. The oxidized CL is required for the release of pro-apoptotic factors from mitochondria into the cytosol. This redox mechanism of cyt c is realized earlier than its other well-recognized functions in the formation of apoptosomes and caspase activation. In the cytosol, released cyt c interacts with another anionic phospholipid, PS, and catalyzes its oxidation in a similar oxygenase reaction. Peroxidized PS facilitates its externalization essential for the recognition and clearance of apoptotic cells by macrophages. Redox catalysis of plasma membrane PS oxidation constitutes an important redox-dependent function of cyt c in apoptosis and phagocytosis. Thus, cyt c acts as an anionic phospholipid specific oxygenase activated and required for the execution of essential stages of apoptosis. This review is focused on newly discovered redox mechanisms of complexes of cyt c with anionic phospholipids and their role in apoptotic pathways in health and disease.

Tissue biodistribution and blood clearance rates of intravenously administered carbon nanotube radiotracers

Carbon nanotubes (CNT) are intensively being developed for biomedical applications including drug and gene delivery. Although all possible clinical applications will require compatibility of CNT with the biological milieu, their in vivo capabilities and limitations have not yet been explored. In this work, water-soluble, single-walled CNT (SWNT) have been functionalized with the chelating molecule diethylentriaminepentaacetic (DTPA) and labeled with indium ((111)In) for imaging purposes. Intravenous (i.v.) administration of these functionalized SWNT (f-SWNT) followed by radioactivity tracing using gamma scintigraphy indicated that f-SWNT are not retained in any of the reticuloendothelial system organs (liver or spleen) and are rapidly cleared from systemic blood circulation through the renal excretion route. The observed rapid blood clearance and half-life (3 h) of f-SWNT has major implications for all potential clinical uses of CNT. Moreover, urine excretion studies using both f-SWNT and functionalized multiwalled CNT followed by electron microscopy analysis of urine samples revealed that both types of nanotubes were excreted as intact nanotubes. This work describes the pharmacokinetic parameters of i.v. administered functionalized CNT relevant for various therapeutic and diagnostic applications.

Carbon nanotubes: a review of their properties in relation to pulmonary toxicology and workplace safety

Carbon nanotubes (CNT) are an important new class of technological materials that have numerous novel and useful properties. The forecast increase in manufacture makes it likely that increasing human exposure will occur, and as a result, CNT are beginning to come under toxicological scrutiny. This review seeks to set out the toxicological paradigms applicable to the toxicity of inhaled CNT, building on the toxicological database on nanoparticles (NP) and fibers. Relevant workplace regulation regarding exposure is also considered in the light of our knowledge of CNT. CNT could have features of both NP and conventional fibers, and so the current paradigm for fiber toxicology, which is based on mineral fibers and synthetic vitreous fibers, is discussed. The NP toxicology paradigm is also discussed in relation to CNT. The available peer-reviewed literature suggests that CNT may have unusual toxicity properties. In particular, CNT seem to have a special ability to stimulate mesenchymal cell growth and to cause granuloma formation and fibrogenesis. In several studies, CNT have more adverse effects than the same mass of NP carbon and quartz, the latter a commonly used benchmark of particle toxicity. There is, however, no definitive inhalation study available that would avoid the potential for artifactual effects due to large mats and aggregates forming during instillation exposure procedures. Studies also show that CNT may exhibit some of their effects through oxidative stress and inflammation. CNT represent a group of particles that are growing in production and use, and therefore, research into their toxicology and safe use is warranted.

Nanotechnology and Nanotoxicology

Nanotechnology is the manipulation of matter in dimensions <100 nm. At this size, matter can take on different chemical and physical properties, giving the products characteristics useful to industry, medicine and technology. Government funding and private investors provide billions of research dollars for the development of new materials and applications. The potential utility of these technologies is such that they are expected be a trillion-dollar industry within the next 10 years. However, the novel properties of nanoengineered materials lead to the potential for different toxicity compared with the bulk material. The field of nanotoxicology is still in its infancy, however, with very limited literature regarding potential health effects. Inhalational toxicity is to be expected, given the known effects of inhaled fine particulate matter. However, the degree to which most nanoparticles will aerosolise remains to be determined. It has been proposed that dermal exposure will be the most relevant route of exposure, but there is considerably less literature regarding dermal effects and absorption. Less defined still are the potential effects of nanoproducts on fetal development and the environment.

Nanomedicine and nanotoxicology: two sides of the same coin

Current advances in nanotechnology have led to the development of the new field of nanomedicine, which includes many applications of nanomaterials and nanodevices for diagnostic and therapeutic purposes. The same unique physical and chemical properties that make nanomaterials so attractive may be associated with their potentially calamitous effects on cells and tissues. Our recent study demonstrated that aspiration of single-walled carbon nanotubes elicited an unusual inflammatory response in the lungs of exposed mice with a very early switch from the acute inflammatory phase to fibrogenic events resulting in pulmonary deposition of collagen and elastin. This was accompanied by a characteristic change in the production and release of proinflammatory to anti-inflammatory profibrogenic cytokines, decline in pulmonary function, and enhanced susceptibility to infection. Chemically unmodified (nonfunctionalized) carbon nanotubes are not effectively recognized by macrophages. Functionalization of nanotubes results in their increased recognition by macrophages and is thus used for the delivery of nanoparticles to macrophages and other immune cells to improve the quality of diagnostic and imaging techniques as well as for enhancement of the therapeutic effectiveness of drugs. These observations on differences in recognition of nanoparticles by macrophages have important implications in the relationship between the potentially toxic health effects of nanomaterials and their applications in the field of nanomedicine.