Development and evaluation of an aerosol generation and supplying system for inhalation experiments of manufactured nanoparticles

Pulmonary toxicity of tungsten trioxide nanoparticles in an inhalation study and an intratracheal instillation study

Objectives

We conducted inhalation and intratracheal instillation studies in order to examine the effects of tungsten trioxide (WO₃) nanoparticles on the lung, and evaluated whether or not the nanoparticles would cause persistent lung inflammation.

Methods

In the inhalation study, male 10‐week‐old Fischer 334 rats were classified into 3 groups. The control, low‐dose, and high‐dose groups inhaled clean air, 2, and 10 mg/m³ WO₃ nanoparticles, respectively, for 6 h each day for 4 weeks. The rats were dissected at 3 days, 1 month, and 3 months after the inhalation, and the bronchoalveolar lavage fluid (BALF) and lung tissue were examined. In the intratracheal instillation study, male 12‐week‐old Fischer 334 rats were divided into 3 subgroups. The control, low‐dose, and high‐dose groups were intratracheally instilled 0.4 ml distilled water, 0.2, and 1.0 mg WO₃ nanoparticles, respectively, dissolved in 0.4 ml distilled water. The rats were sacrificed at 3 days, 1 week, and 1 month after the intratracheal instillation, and the BALF and lung tissue were analyzed as in the inhalation study.

Results

The inhalation and instillation of WO₃ nanoparticles caused transient increases in the number and rate of neutrophils, cytokine‐induced neutrophil chemoattractant (CINC)‐1, and CINC‐2 in BALF, but no histopathological changes or upregulation of heme oxygenase (HO)‐1 in the lung tissue.

Conclusion

Our results suggest that WO₃ nanoparticles have low toxicity to the lung. According to the results of the inhalation study, we also propose that the no observed adverse effect level (NOAEL) of WO₃ nanoparticles is 2 mg/m³.

Assessment of Cytokine-Induced Neutrophil Chemoattractants as Biomarkers for Prediction of Pulmonary Toxicity of Nanomaterials

This work determines whether cytokine-induced neutrophil chemoattractants (CINC)-1, CINC-2 and CINC-3 can be markers for predicting high or low pulmonary toxicity of nanomaterials (NMs). We classified NMs of nickel oxide (NiO) and cerium dioxide (CeO₂) into high toxicity and NMs of two types of titanium dioxides (TiO₂ (P90 and rutile)) and zinc oxide (ZnO) into low toxicity, and we analyzed previous data of CINCs in bronchoalveolar lavage fluid (BALF) of rats from three days to six months after intratracheal instillation (0.2 and 1.0 mg) and inhalation exposure (0.32–10.4 mg/m³) of materials (NiO, CeO₂, TiO₂ (P90 and rutile), ZnO NMs and micron-particles of crystalline silica (SiO₂)). The concentration of CINC-1 and CINC-2 in BALF had different increase tendency between high and low pulmonary toxicity of NMs and correlated with the other inflammatory markers in BALF. However, CINC-3 increased only slightly in a dose-dependent manner compared with CINC-1 and CINC-2. Analysis of receiver operating characteristics for the toxicity of NMs by CINC-1 and CINC-2 showed the most accuracy of discrimination of the toxicity at one week or one month after exposure and CINC-1 and CINC-2 in BALF following intratracheal instillation of SiO₂ as a high toxicity could accurately predict the toxicity at more than one month after exposure. These data suggest that CINC-1 and CINC-2 may be useful biomarkers for the prediction of pulmonary toxicity of NMs relatively early in both intratracheal instillation and inhalation exposure.

Development of a novel aerosol generation system for conducting inhalation exposures to ambient particulate matter (PM)

In this study, we developed a novel method for generating aerosols that are representative of real-world ambient particulate matter (PM) in terms of both physical and chemical characteristics, with the ultimate objective of using them for inhalation exposure studies. The protocol included collection of ambient PM on filters using a high-volume sampler, which were then extracted with ultrapure Milli-Q water using vortexing and sonication. As an alternative approach for collection, ambient particles were directly captured into aqueous slurry samples using the versatile aerosol concentration enrichment system (VACES)/aerosol-into-liquid collector tandem technology. The aqueous samples from both collection protocols were then re-aerosolized using commercially available nebulizers. The physical characteristics (i.e., particle size distribution) of the generated aerosols were examined by the means of a scanning mobility particle sizer (SMPS) connected to a condensation particle counter (CPC) at different compressed air pressures of the nebulizer, and dilution air flow rates. In addition, the collected PM samples (both ambient and re-aerosolized) were chemically analyzed for water-soluble organic carbon (WSOC), elemental and organic carbon (EC/OC), inorganic ions, polycyclic aromatic hydrocarbons (PAHs), and metals and trace elements. Using the aqueous filter extracts, we were able to effectively recover the water-soluble components of ambient PM (e.g., water-soluble organic matter, and water-soluble inorganic ions); however, this method was deficient in recovering some of the important insoluble components such as EC, PAHs, and many of the redox-active trace elements and metals. In contrast, using the VACES/aerosol-into-liquid collector tandem technology for collecting ambient PM directly into water slurry, we were able to preserve the water-soluble and water-insoluble components very effectively. These results illustrate the superiority of the VACES/aerosol-into liquid collector tandem technology to be used in conjunction with the re-aerosolization setup to create aerosols that fully represent ambient PM, making it an attractive choice for application in inhalation exposure studies.

Usefulness of myeloperoxidase as a biomarker for the ranking of pulmonary toxicity of nanomaterials

BACKGROUND

In order to examine whether myeloperoxidase (MPO) can be a useful marker for evaluating the pulmonary toxicity of nanomaterials, we analyzed MPO protein in bronchoalveolar lavage fluid (BALF) samples obtained from previous examinations of a rat model. In those examinations we performed intratracheal instillation exposures (dose: 0.2-1.0 mg) and inhalation exposures (exposure concentration: 0.32-10.4 mg/m3) using 9 and 4 nanomaterials with different toxicities, respectively. Based on those previous studies, we set Nickel oxide nanoparticles (NiO), cerium dioxide nanoparticles (CeO2), multi wall carbon nanotubes with short or long length (MWCNT (S) and MWCNT (L)), and single wall carbon nanotube (SWCNT) as chemicals with high toxicity; and titanium dioxide nanoparticles (TiO2 (P90) and TiO2 (Rutile)), zinc oxide nanoparticles (ZnO), and toner with external additives including nanoparticles as chemicals with low toxicity. We measured the concentration of MPO in BALF samples from rats from 3 days to 6 months following a single intratracheal instillation, and from 3 days to 3 months after the end of inhalation exposure.

RESULTS

Intratracheal instillation of high toxicity NiO, CeO2, MWCNT (S), MWCNT (L), and SWCNT persistently increased the concentration of MPO, and inhalation of NiO and CeO2 increased the MPO in BALF. By contrast, intratracheal instillation of low toxicity TiO2 (P90), TiO2 (Rutile), ZnO, and toner increased the concentration of MPO in BALF only transiently, and inhalation of TiO2 (Rutile) and ZnO induced almost no increase of the MPO. The concentration of MPO correlated with the number of total cells and neutrophils, the concentration of chemokines for neutrophils (cytokine-induced neutrophil chemoattractant (CINC)-1 and heme oxygenase (HO)-1), and the activity of released lactate dehydrogenase (LDH) in BALF. The results from the receiver operating characteristics (ROC) for the toxicity of chemicals by the concentration of MPO proteins in the intratracheal instillation and inhalation exposures showed that the largest areas under the curves (AUC) s in both examinations occurred at 1 month after exposure.

CONCLUSION

These data suggest that MPO can be a useful biomarker for the ranking of the pulmonary toxicity of nanomaterials, especially at 1 month after exposure, in both intratracheal instillation and inhalation exposure.

Oxidative DNA damage in the rat lung induced by intratracheal instillation and inhalation of nanoparticles

Nanoparticles are widely used as useful industrial materials. Therefore, their possible adverse health effects must be appraised. We assessed and compared the oxidative DNA damage caused by four different nanoparticles (TiO₂, NiO, ZnO and CeO₂). The effects of the administration methods, intratracheal instillation and inhalation, were also evaluated. Rats were subjected to intratracheal instillations or 4 weeks of inhalation exposure to the nanoparticles, and the 8-hydroxydeoxyguanosine (8-OHdG) levels in the lung were analyzed by an HPLC-EC detector method. The 8-OHdG levels were increased in a dose-dependent manner with the inhalation of NiO. ZnO also increased the 8-OHdG levels with inhalation. In comparison with the control, the 8-OHdG levels were significantly and persistently higher with the CeO₂ nanoparticle administration, by both intratracheal instillation and inhalation. In contrast, there were no significant differences in the 8-OHdG levels between the control and TiO₂ nanoparticle-treated groups, with either intratracheal instillation or inhalation during the observation period. These results indicated that NiO, ZnO and CeO₂ nanoparticles generate significant amounts of free radicals, and oxidative stress may be responsible for the lung injury caused by these nanoparticles. In addition, both intratracheal instillation and inhalation exposure induced similar tendencies of oxidative DNA damage with these nanoparticles.

Spatial-Temporal Dispersion of Aerosolized Nanoparticles During the Use of Consumer Spray Products and Estimates of Inhalation Exposure

We evaluated the spatial-temporal dispersion of airborne nanomaterials during the use of spray consumer products and estimated the level of consumer inhalation exposure. A total of eight spray products including five propellant and three pump types were selected to evaluate the dispersion of airborne nanoparticles across time and space in a cleanroom which could control the background particles. Four products were advertised to contain silver and one contained titanium nanoparticles, while three products were specified no ENM but as being manufactured through the use of nanotechnology. We used direct-reading instruments with a thermodesorber unit to measure the particles (number, mass, surface area), as well as filter sampling to examine physicochemical characteristics. Sampling was conducted simultaneously at each location (1 m, near-field; 2, 3 m, far-field) by distance from the source. We estimated the inhaled doses at the breathing zone, and the doses deposited in each part of the respiratory tract using the experimental data and mathematical models. Nanoparticles released from the propellant sprays persisted in the air and dispersed over a large distance due to their small size (1466-5565 particles/cm³). Conversely, the pump sprays produced larger droplets that settled out of the air relatively close to the source, so the concentration was similar to background level (<200 particles/cm³). The estimates of inhalation exposure also suggested that exposure to nanoparticles was greater with propellant sprays (1.2 × 10⁸ ± 4.0 × 10⁷ particles/kgbw/day) than pump sprays (2.7 × 10⁷ ± 6.5 × 10⁶ particles/kgbw/day). We concluded that the propellant sprays create a higher risk of exposure than the pump sprays.

Characterization of Aerosols of Titanium Dioxide Nanoparticles Following Three Generation Methods Using an Optimized Aerosolization System Designed for Experimental Inhalation Studies

Nanoparticles (NPs) can be released in the air in work settings, but various factors influence the exposure of workers. Controlled inhalation experiments can thus be conducted in an attempt to reproduce real-life exposure conditions and assess inhalation toxicology. Methods exist to generate aerosols, but it remains difficult to obtain nano-sized and stable aerosols suitable for inhalation experiments. The goal of this work was to characterize aerosols of titanium dioxide (TiO₂) NPs, generated using a novel inhalation system equipped with three types of generators-a wet collision jet nebulizer, a dry dust jet and an electrospray aerosolizer-with the aim of producing stable aerosols with a nano-diameter average (<100 nm) and monodispersed distribution for future rodent exposures and toxicological studies. Results showed the ability of the three generation systems to provide good and stable dispersions of NPs, applicable for acute (continuous up to 8 h) and repeated (21-day) exposures. In all cases, the generated aerosols were composed mainly of small aggregates/agglomerates (average diameter <100 nm) with the electrospray producing the finest (average diameter of 70-75 mm) and least concentrated aerosols (between 0.150 and 2.5 mg/m³). The dust jet was able to produce concentrations varying from 1.5 to 150 mg/m³, and hence, the most highly concentrated aerosols. The nebulizer collision jet aerosolizer was the most versatile generator, producing both low (0.5 mg/m³) and relatively high concentrations (30 mg/m³). The three optimized generators appeared suited for possible toxicological studies of inhaled NPs.

Evaluation of Pulmonary Toxicity of Zinc Oxide Nanoparticles Following Inhalation and Intratracheal Instillation

We conducted inhalation and intratracheal instillation studies of zinc oxide (ZnO) nanoparticles in order to examine their pulmonary toxicity. F344 rats were received intratracheal instillation at 0.2 or 1 mg of ZnO nanoparticles with a primary diameter of 35 nm that were well-dispersed in distilled water. Cell analysis and chemokines in bronchoalveolar lavage fluid (BALF) were analyzed at three days, one week, one month, three months, and six months after the instillation. As the inhalation study, rats were exposed to a concentration of inhaled ZnO nanoparticles (2 and 10 mg/m³) for four weeks (6 h/day, 5 days/week). The same endpoints as in the intratracheal instillation study were analyzed at three days, one month, and three months after the end of the exposure. In the intratracheal instillation study, both the 0.2 and the 1.0 mg ZnO groups had a transient increase in the total cell and neutrophil count in the BALF and in the expression of cytokine-induced neutrophil chemoattractant (CINC)-1, CINC-2, chemokine for neutrophil, and heme oxygenase-1 (HO-1), an oxidative stress marker, in the BALF. In the inhalation study, transient increases in total cell and neutrophil count, CINC-1,-2 and HO-1 in the BALF were observed in the high concentration groups. Neither of the studies of ZnO nanoparticles showed persistent inflammation in the rat lung, suggesting that well-dispersed ZnO nanoparticles have low toxicity.

Comparison between whole-body inhalation and nose-only inhalation on the deposition and health effects of nanoparticles

OBJECTIVES

We performed the two inhalation exposures, whole-body inhalation and nose-only inhalation, to investigate the pulmonary deposition and health effects of the two inhalation methods.

METHODS

In both methods, we exposed rats to the same TiO2 nanoparticles at almost the same exposure concentration for 6 h and compared the deposited amounts of nanoparticles and histopathological changes in the lungs. Rats were exposed to rutile-type TiO2 nanoparticles generated by the spray-dry method for 6 h. The exposure concentration in the whole-body chamber was 4.10 ± 1.07 mg/m(3), and that in nose-only chamber was 4.01 ± 1.11 mg/m(3). The particle sizes were 230 and 180 nm, respectively. A control group was exposed to fresh air.

RESULTS

The amounts of TiO2 deposited in the lungs as measured by ICP-AES after acid digestion just after the exposure were: 42.6 ± 3.5 μg in the whole-body exposure and 46.0 ± 7.7 μg in the nose-only exposure groups. The histopathological evaluation was the same in both exposure groups: no infiltration of inflammatory cells in the alveolar space and interstitium, and no fibrosis.

CONCLUSION

The two inhalation methods using the same material under the same exposure conditions resulted in the same particle deposition and histopathology in the lung.

Pulmonary toxicity of well-dispersed cerium oxide nanoparticles following intratracheal instillation and inhalation

We performed inhalation and intratracheal instillation studies of cerium dioxide (CeO₂) nanoparticles in order to investigate their pulmonary toxicity, and observed pulmonary inflammation not only in the acute and but also in the chronic phases. In the intratracheal instillation study, F344 rats were exposed to 0.2 mg or 1 mg of CeO₂ nanoparticles. Cell analysis and chemokines in bronchoalveolar lavage fluid (BALF) were analyzed from 3 days to 6 months following the instillation. In the inhalation study, rats were exposed to the maximum concentration of inhaled CeO₂ nanoparticles (2, 10 mg/m³, respectively) for 4 weeks (6 h/day, 5 days/week). The same endpoints as in the intratracheal instillation study were examined from 3 days to 3 months after the end of the exposure. The intratracheal instillation of CeO₂ nanoparticles caused a persistent increase in the total and neutrophil number in BALF and in the concentration of cytokine-induced neutrophil chemoattractant (CINC)-1, CINC-2, chemokine for neutrophil, and heme oxygenase-1 (HO-1), an oxidative stress marker, in BALF during the observation time. The inhalation of CeO₂ nanoparticles also induced a persistent influx of neutrophils and expression of CINC-1, CINC-2, and HO-1 in BALF. Pathological features revealed that inflammatory cells, including macrophages and neutrophils, invaded the alveolar space in both studies. Taken together, the CeO₂ nanoparticles induced not only acute but also chronic inflammation in the lung, suggesting that CeO₂ nanoparticles have a pulmonary toxicity that can lead to irreversible lesions.

Risk Assessment of the Carbon Nanotube Group

This study assessed the health risks via inhalation and derived the occupational exposure limit (OEL) for the carbon nanotube (CNT) group rather than individual CNT material. We devised two methods: the integration of the intratracheal instillation (IT) data with the inhalation (IH) data, and the "biaxial approach." A four-week IH test and IT test were performed in rats exposed to representative materials to obtain the no observed adverse effect level, based on which the OEL was derived. We used the biaxial approach to conduct a relative toxicity assessment of six types of CNTs. An OEL of 0.03 mg/m(3) was selected as the criterion for the CNT group. We proposed that the OEL be limited to 15 years. We adopted adaptive management, in which the values are reviewed whenever new data are obtained. The toxicity level was found to be correlated with the Brunauer-Emmett-Teller (BET)-specific surface area (BET-SSA) of CNT, suggesting the BET-SSA to have potential for use in toxicity estimation. We used the published exposure data and measurement results of dustiness tests to compute the risk in relation to particle size at the workplace and showed that controlling micron-sized respirable particles was of utmost importance. Our genotoxicity studies indicated that CNT did not directly interact with genetic materials. They supported the concept that, even if CNT is genotoxic, it is secondary genotoxicity mediated via a pathway of genotoxic damage resulting from oxidative DNA attack by free radicals generated during CNT-elicited inflammation. Secondary genotoxicity appears to involve a threshold.

Analysis of pulmonary surfactant in rat lungs after inhalation of nanomaterials: Fullerenes, nickel oxide and multi-walled carbon nanotubes

The health risks of inhalation exposure to engineered nanomaterials in the workplace are a major concern in recent years, and hazard assessments of these materials are being conducted. The pulmonary surfactant of lung alveoli is the first biological entity to have contact with airborne nanomaterials in inhaled air. In this study, we retrospectively evaluated the pulmonary surfactant components of rat lungs after a 4-week inhalation exposure to three different nanomaterials: fullerenes, nickel oxide (NiO) nanoparticles and multi-walled carbon nanotubes (MWCNT), with similar levels of average aerosol concentration (0.13-0.37 mg/m(3)). Bronchoalveolar lavage fluid (BALF) of the rat lungs stored after previous inhalation studies was analyzed, focusing on total protein and the surfactant components, such as phospholipids and surfactant-specific SP-D (surfactant protein D) and the BALF surface tension, which is affected by SP-B and SP-C. Compared with a control group, significant changes in the BALF surface tension and the concentrations of phospholipids, total protein and SP-D were observed in rats exposed to NiO nanoparticles, but not in those exposed to fullerenes. Surface tension and the levels of surfactant phospholipids and proteins were also significantly different in rats exposed to MWCNTs. The concentrations of phospholipids, total protein and SP-D and BALF surface tension were correlated significantly with the polymorphonuclear neutrophil counts in the BALF. These results suggest that pulmonary surfactant components can be used as measures of lung inflammation.

Inhalation Exposure to Carbon Nanotubes (CNT) and Carbon Nanofibers (CNF): Methodology and Dosimetry

Carbon nanotubes (CNT) and nanofibers (CNF) are used increasingly in a broad array of commercial products. Given current understandings, the most significant life-cycle exposures to CNT/CNF occur from inhalation when they become airborne at different stages of their life cycle, including workplace, use, and disposal. Increasing awareness of the importance of physicochemical properties as determinants of toxicity of CNT/CNF and existing difficulties in interpreting results of mostly acute rodent inhalation studies to date necessitate a reexamination of standardized inhalation testing guidelines. The current literature on pulmonary exposure to CNT/CNF and associated effects is summarized; recommendations and conclusions are provided that address test guideline modifications for rodent inhalation studies that will improve dosimetric extrapolation modeling for hazard and risk characterization based on the analysis of exposure-dose-response relationships. Several physicochemical parameters for CNT/CNF, including shape, state of agglomeration/aggregation, surface properties, impurities, and density, influence toxicity. This requires an evaluation of the correlation between structure and pulmonary responses. Inhalation, using whole-body exposures of rodents, is recommended for acute to chronic pulmonary exposure studies. Dry powder generator methods for producing CNT/CNF aerosols are preferred, and specific instrumentation to measure mass, particle size and number distribution, and morphology in the exposure chambers are identified. Methods are discussed for establishing experimental exposure concentrations that correlate with realistic human exposures, such that unrealistically high experimental concentrations need to be identified that induce effects under mechanisms that are not relevant for workplace exposures. Recommendations for anchoring data to results seen for positive and negative benchmark materials are included, as well as periods for postexposure observation. A minimum data set of specific bronchoalveolar lavage parameters is recommended. Retained lung burden data need to be gathered such that exposure-dose-response correlations may be analyzed and potency comparisons between materials and mammalian species are obtained considering dose metric parameters for interpretation of results. Finally, a list of research needs is presented to fill data gaps for further improving design, analysis, and interpretation and extrapolation of results of rodent inhalation studies to refine meaningful risk assessments for humans.

Human exposure to conventional and nanoparticle--containing sprays-a critical review

The release of pesticides from conventional spray products has been investigated in depth, and suitable analytical techniques detecting the mass of the released substances are available. In contrast, nanoparticle-containing sprays are less studied, although they are perceived as critical for consumers because inhalation exposure can occur to potentially toxic nanoparticles. A few recent studies presented analytical concepts for exposure experiments and generated data for exposure assessment. This study attempts to review and compare the current approaches to characterize nanosprays and to identify challenges for future research. Furthermore, experimental setups used for exposure assessment from conventional sprays are reviewed and compared to setups used for nanoparticle-containing sprays. National and international norms dealing with nanoparticle characterization, spray characterization and exposure are inspected with regard to their usefulness for standardizing exposure assessment. Different approaches in the field of exposure modeling are reviewed and compared. The conclusion is that due to largely varying experimental setups to date exposure values for nanosprays are difficult to compare. All studies are only conducted with a limited set of sprays, and no systematic evaluation of the study conditions is available. A suitable set of experimental setups as well as minimum reporting requirements should be agreed upon to enable the systematic evaluation of consumer sprays in the future. Indispensable features of such experimental setups are developed in this review.

Quantitative assessment of inhalation exposure and deposited dose of aerosol from nanotechnology-based consumer sprays

This study provides a quantitative assessment of inhalation exposure and deposited aerosol dose in the 14 nm to 20 μm particle size range based on the aerosol measurements conducted during realistic usage simulation of five nanotechnology-based and five regular spray products matching the nano-products by purpose of application. The products were also examined using transmission electron microscopy. In seven out of ten sprays, the highest inhalation exposure was observed for the coarse (2.5-10 μm) particles while being minimal or below the detection limit for the remaining three sprays. Nanosized aerosol particles (14-100 nm) were released, which resulted in low but measurable inhalation exposures from all of the investigated consumer sprays. Eight out of ten products produced high total deposited aerosol doses on the order of 10¹-10³ ng kg^-1 bw per application, ~85-88% of which were in the head airways, only <10% in the alveolar region and <8% in the tracheobronchial region. One nano and one regular spray produced substantially lower total deposited doses (by 2-4 orders of magnitude less), only ~52-64% of which were in the head while ~29-40% in the alveolar region. The electron microscopy data showed nanosized objects in some products not labeled as nanotechnology-based and conversely did not find nano-objects in some nano-sprays. We found no correlation between nano-object presence and abundance as per the electron microscopy data and the determined inhalation exposures and deposited doses. The findings of this study and the reported quantitative exposure data will be valuable for the manufacturers of nanotechnology-based consumer sprays to minimize inhalation exposure from their products, as well as for the regulators focusing on protecting the public health.

Continuous-flow differential mobility analysis of nanoparticles and biomolecules

The differential mobility analyzer (DMA) is a powerful instrument that continuously separates aerosol particles according to their migration velocities in an electric field with high resolution. Because of the low fields employed, the mobility can be related to particle size or ion cross section. Combined with a sensitive detector, such as a continuous-flow condensation particle counter, the DMA enables differential size distribution measurements to be made within minutes to seconds. Over the past few decades, these capabilities have made the DMA a central tool for aerosol characterization in the 10-1,000-nm size range. DMAs have been adapted recently for measurement of particles as small as 1 nm and are now contributing to our understanding of nucleation, nanotechnology, and gas ions. Moreover, the opposed migration classifier, a new approach to differential mobility analysis, expands the dynamic range and shows promise both for increasing resolution beyond present levels and for changing the way that instruments are built. Thus, the DMA continues to advance methods and capabilities for physical characterization at transition from molecules to clusters to particles.

Comparison of dose-response relations between 4-week inhalation and intratracheal instillation of NiO nanoparticles using polimorphonuclear neutrophils in bronchoalveolar lavage fluid as a biomarker of pulmonary inflammation

Inhalation studies and intratracheal instillation studies using laboratory animals are commonly conducted for pulmonary toxicity tests of nanomaterials. In our study, male Wister rats were exposed to nickel oxide (NiO) particles including a nano-scale, even for aerosols and suspensions, in a 4-week inhalation and intratracheal instillation. Using polymorphonuclear neutrophils (PMNs) in bronchoalveolar lavage fluid as a biomarker of inflammation, we attempted to quantify the relationship between responses to inhalation and intratracheal instillation of the nanoparticles, based on surface area doses. Four kinds of NiO suspension samples with different specific surface areas were singly injected via the tracheas of the rats. The relationship between the instilled doses and PMN production was examined 3 days and 1 month after the instillation. In parallel, 4-week inhalation studies, using two of the suspensions, were conducted for aerosols generated by a pressurized nebulizer. NiO samples induced PMN responses 3 days after instillation according to the surface area doses, but not the mass doses, as has been reported in many studies. When the same NiO samples were tested in a 4-week inhalation and intratracheal instillation, the amount of pulmonary deposition of the sample after the 4-week inhalation, and an intratracheally instilled dose about ten-times higher, induced similar PMN responses 3 days after termination of inhalation and instillation. Using the relationship between these responses to 4-week inhalation and intratracheal instillation, it may be possible to estimate what aerosol concentrations of other nanomaterials might cause the same responses of PMN production as intratracheal instillation tests.

Inhalation toxicity assessment of carbon-based nanoparticles

Although the demand for nanomaterials has grown, researchers have not conclusively determined the effects of nanomaterials on the human body. To understand the effects of nanomaterials on occupational health, we need to estimate the respiratory toxicity of nanomaterials through inhalation studies, intratracheal instillation studies, and pharyngeal aspiration studies. The discrepancies observed among these studies tend to result from differences in the physiochemical properties of nanomaterials, such as aggregation and dispersion. Therefore, in all toxicity studies, identification of the physicochemical properties of nanomaterials is essential. This Account reviews the inhalation toxicity of manufactured nanomaterials and compares them with inhalation and intratracheal instillation studies of well-characterized fullerene and carbon nanotubes. In many reports, pulmonary inflammation and injury served as pulmonary endpoints for the inhalation toxicity. To assess pulmonary inflammation, we examined neutrophil and macrophage infiltration in the alveolar and/or interstitial space, and the expression of the neutrophil and/or monocyte chemokines. We also reported the release of lactate dehydrogenase (LDH) and alkaline phosphatase (ALP) in the bronchoalveolar lavage fluid (BALF), the expression of oxidative stress-related genes characteristic of lung injury, and the presence of granulomatous lesion and pulmonary fibrosis. In the inhalation and intratracheal instillation studies of well-characterized fullerenes, exposure to fullerene did not induce pulmonary inflammation or transient inflammation. By contrast, in an inhalation study, a high concentration of multiwall carbon nanotubes (MWCNTs) and single-wall carbon nanotubes (SWCNTs) induced neutrophil inflammation or granulomatous formations in the lung, and intratracheal instillation of MWCNTs and SWCNTs induced persistent inflammation in the lung. Among the physicochemical properties of carbon nanotubes, the increased surface area is associated with inflammatory activity as measured by the increase in the rate of neutrophils measured in bronchoalveolar lavage fluid. Metal impurities such as iron and nickel enhanced the pulmonary toxicity of carbon nanotubes, and SWCNTs that included an amorphous carbon induced multifocal granulomas in the lung while purer SWCNTs did not. The aggregation state also affects pulmonary response: Exposure to well-dispersed carbon nanotubes led to the thickening of the alveolar wall and fewer granulomatous lesions in the lung, while agglomerated carbon nanotubes produced granulomatous inflammation. The values of the acceptable exposure concentration in some countries were based on the data of subacute and subchronic inhalation and intratracheal instillation studies of well-characterized fullerene and carbon nanotubes. In Japan, the acceptable exposure concentration of fullerene is 0.39 mg/m³. In Europe, the proposal concentration is 44.4 μg/m³ for acute toxicity and 0.27 μg/m³ for chronic toxicity. The proposal acceptable exposure concentrations of carbon nanotubes are 0.03, 0.05, and 0.007 mg/m³ in Japan, Europe, and the United States, respectively.

Nanomaterial inhalation exposure from nanotechnology-based cosmetic powders: a quantitative assessment

In this study we quantified exposures to airborne particles ranging from 14 nm to 20 µm due to the use of nanotechnology-based cosmetic powders. Three nanotechnology-based and three regular cosmetic powders were realistically applied to a mannequin's face while measuring the concentration and size distribution of inhaled aerosol particles. Using these data we calculated that the highest inhaled particle mass was in the coarse aerosol fraction (2.5-10 µm), while particles <100 nm made minimal contribution to the inhaled particle mass. For all powders, 85-93 % of aerosol deposition occurred in the head airways, while <10 % deposited in the alveolar and <5 % in the tracheobronchial regions. Electron microscopy data suggest that nanomaterials were likely distributed as agglomerates across the entire investigated aerosol size range (14 nm-20 µm). Thus, investigation of nanoparticle health effects should consider not only the alveolar region, but also other respiratory system regions where substantial nanomaterial deposition during the actual nanotechnology-based product use would occur.

Effects of inhaled nano-TiO2 aerosols showing two distinct agglomeration states on rat lungs

Nano-aerosols composed of large agglomerates (LA) (>100nm) are more likely to promote pulmonary clearance via macrophages phagocytosis. Small agglomerates (SA) (<100nm) seem to escape this first defense mechanism and are more likely to interact directly with biological material. These different mechanisms can influence pulmonary toxicity. This hypothesis was evaluated by comparing the relative pulmonary toxicity induced by aerosolized nano-TiO(2) showing two different agglomeration states: SA (<100nm) and LA (>100nm) at mass concentrations of 2 or 7mg/m(3). Groups of Fisher 344 male rats were nose-only exposed for 6h. The median number aerodynamic diameters were 30 and 185nm at 2mg/m(3), and 31 and 194nm at 7mg/m(3). We found in rat's bronchoalveolar lavage fluids (BALF) a significant 2.1-fold increase in the number of neutrophils (p<0.05) in the group exposed to the 7mg/m(3) LA nano-aerosol suggesting a mild inflammatory response. Rats exposed to the 7mg/m(3) SA nano-aerosol showed a 1.8-fold increase in LDH activity and 8-isoprostane concentration in BALF, providing evidence for cytotoxic and oxidative stress effects. Our results indicate that biological responses to nanoparticles (NP) might depend on the dimension and concentration of NP agglomerates.

Potential for inhalation exposure to engineered nanoparticles from nanotechnology-based cosmetic powders

BACKGROUND

The market of nanotechnology-based consumer products is rapidly expanding, and the lack of scientific evidence describing the accompanying exposure and health risks stalls the discussion regarding its guidance and regulation.

OBJECTIVES

We investigated the potential for human contact and inhalation exposure to nanomaterials when using nanotechnology-based cosmetic powders and compare them with analogous products not marketed as nanotechnology based.

METHODS

We characterized the products using transmission electron microscopy (TEM) and laser diffraction spectroscopy and found nanoparticles in five of six tested products. TEM photomicrographs showed highly agglomerated states of nanoparticles in the products. We realistically simulated the use of cosmetic powders by applying them to the face of a human mannequin head while simultaneously sampling the released airborne particles through the ports installed in the mannequin's nostrils.

RESULTS

We found that a user would be exposed to nanomaterial predominantly through nanoparticle-containing agglomerates larger than the 1-100-nm aerosol fraction.

CONCLUSIONS

Predominant deposition of nanomaterial(s) will occur in the tracheobronchial and head airways--not in the alveolar region as would be expected based on the size of primary nanoparticles. This could potentially lead to different health effects than expected based on the current understanding of nanoparticle behavior and toxicology studies for the alveolar region.

Biopersistence of inhaled MWCNT in rat lungs in a 4-week well-characterized exposure

It is important to conduct a risk assessment that includes hazard assessment and exposure assessment for the safe production and handling of newly developed nanomaterials. We conducted an inhalation study of a multi-wall carbon nanotube (MWCNT) as a hazard assessment. Male Wistar rats were exposed to well-dispersed MWCNT for 4 weeks by whole body inhalation. The exposure concentration in the chamber was 0.37 ± 0.18 mg/m³. About 70% of the MWCNTs in the chamber were single fiber. The geometric mean diameter (geometric standard deviation, GSD) and geometric mean length (GSD) of the aerosolized MWCNTs in the chamber were 63 nm (1.5) and 1.1 μm (2.7), respectively. The amounts of MWCNT deposited in the rat lungs were determined by the X-ray diffraction method and elemental carbon analysis. The average deposited amounts at 3 days after the inhalation were 68 μg/lung by the X-ray diffraction method and 76 μg/lung by elemental carbon analysis. The calculated deposition fractions were 18% and 20% in each analysis. The amount of retained MWCNT in the lungs until 3 months after the inhalation decreased exponentially and the calculated biological half times of MWCNT were 51 days and 54 days, respectively. The clearance was not delayed, but a slight increase in lung weight at 3 days after the inhalation was observed.

Foam cell formation of alveolar macrophages in Clara cell ablated mice inhaling crystalline silica

We investigated the function of Clara cells in vivo during exposure to inhaled crystalline silica by morphological and immunohistochemical examination of intra-alveolar cells and alveolar macrophages in Clara cell-ablated mice. The Clara cells of male FVB/n mice (8-12 weeks old) were ablated by intraperitoneal administration of naphthalene (300 mg/kg). The mice were then exposed to crystalline silica (Min-U-Sil-5, 97.1 ± 9.5 mg/m³, 6 hours/day, 5 days/week) for up to two weeks. The lungs were assessed by morphometry, as well as by immunohistochemistry of CD36, lectin-like oxygenated low-density lipoprotein receptor (LOX)-1, and matrix metalloproteinases (MMPs) -2, -9 and -12. There was a significantly greater number of intra-alveolar cells in Clara cell-ablated mouse groups than in wild-type mouse groups that were exposed to crystalline silica. A marked number of foamy alveolar macrophages were only detected in the Clara cell-ablated group exposed to crystalline silica, indicating that Clara cells inhibit infiltration and foam cell formation of alveolar macrophages. Immunohistochemical analysis indicated that foamy alveolar macrophages in the Clara cell-ablated group that inhaled crystalline silica overexpress CD36 and LOX-1, indicating upregulation of scavenger receptors of alveolar macrophages. These cells also express MMP-2, -9 and -12, suggesting increased gelatinolytic and elastolytic activities. Our findings suggest that Clara cells not only inhibit infiltration of alveolar macrophages but also their phagocytotic and gelatinolytic functions in silica-induced pulmonary injury.

Pathological features of rat lung following inhalation and intratracheal instillation of C(60) fullerene

We evaluated the pulmonary pathological features of rats that received a single intratracheal instillation and a 4-week inhalation of a fullerene. We used fullerene C(60) (nanom purple; Frontier Carbon Co. Ltd, Japan) in this study. Male Wistar rats received intratracheal dose of 0.1, 0.2, or 1 mg of C(60), and were sacrificed at 3 days, 1 week, 1 month, 3 months, 6 months, and 12 months. In the inhalation study, Wistar rats received C(60) or nickel oxide by whole-body inhalation for 6 h/day, 5 days/week, 4 weeks, and were sacrificed at 3 days, 1 month, and 3 months after the end of exposure. During the observation period, no tumors or granulomas were observed in either study. Histopathological evaluation by the point counting method (PCM) showed that a high dose of C(60) (1 mg) instillation led to a significant increase of areas of inflammation in the early phase (until 1 week). In the inhalation study of the C(60)-exposed group, PCM evaluation showed significant changes in the C(60)-exposed group only at 3 days after exposure; after 1 month, no significant changes were observed. The present study demonstrated that the pulmonary inflammation pattern after exposure to well-characterized C(60) via both intratracheal and inhalation instillation was slight and transient. These results support our previous studies that showed C(60) has no significant adverse effects in intratracheal and inhalation instillation studies.

Pulmonary toxicity of well-dispersed single-wall carbon nanotubes after inhalation

Single-wall carbon nanotubes (SWCNTs) were well-dispersed by ultrasonication to conduct an inhalation study. SWCNTs were generated using a pressurised nebuliser with liquid suspension of SWCNTs. Wistar rats were exposed to the well-dispersed SWCNT (diameter of bundle: 0.2 μm; length of bundle: 0.7 μm) for 4 weeks. The low and high mass concentrations of SWCNTs were 0.03 ± 0.003 and 0.13 ± 0.03 mg/m(3), respectively. The rats were sacrificed at 3 days, 1 month, and 3 months after the end of exposure. There were no increases of total cell or neutrophil counts in the bronchoalveolar lavage fluid (BALF), or the concentration of cytokine-induced neutrophil chemoattractant in the lungs or BALF in both the high and low concentration-exposed groups. Pulmonary infiltration of neutrophils was not observed in either exposed group throughout the observation period. Well-dispersed SWCNT did not induce neutrophil inflammation in the lung under the conditions in the present study.

Potential for exposure to engineered nanoparticles from nanotechnology-based consumer spray products

The potential for human exposure to engineered nanoparticles due to the use of nanotechnology-based consumer sprays (categorized as such by the Nanotechnology Consumer Products Inventory) is examined along with analogous products, which are not specified as nanotechnology-based (regular products). Photon correlation spectroscopy was used to obtain particle size distributions in the initial liquid products. Transmission electron microscopy was used to determine particle size, shape, and agglomeration of the particles. Realistic application of the spray products near the human breathing zone characterized airborne particles that are released during use of the sprays. Aerosolization of sprays with standard nebulizers was used to determine their potential for inhalation exposure. Electron microscopy detected the presence of nanoparticles in some nanotechnology-based sprays as well as in several regular products, whereas the photon correlation spectroscopy indicated the presence of particles <100 nm in all investigated products. During the use of most nanotechnology-based and regular sprays, particles ranging from 13 nm to 20 μm were released, indicating that they could he inhaled and consequently deposited in all regions of the respiratory system. The results indicate that exposures to nanoparticles as well as micrometer-sized particles can be encountered owing to the use of nanotechnology-based sprays as well as regular spray products.

Investigation of gene expression of MMP-2 and TIMP-2 mRNA in rat lung in inhaled nickel oxide and titanium dioxide nanoparticles

In order to investigate whether or not dispersed nanoparticles have an effect of inflammation and fibrosis on animals, we developed a nanoparticle generation system and examined the gene expression of matrix metalloproteinase (MMP) and tissue inhibitor matrix proteinase (TIMP) in rat lung containing inhaled nickel oxide (NiO) or titanium dioxide (TiO(2)) nanoparticles. In both experiments, Wistar male rats were exposed to NiO or TiO(2) nanoparticles for 4 wk (6 h/day). The geometric mean diameters of NiO and TiO(2) in the chamber were 139 ± 12 nm and 51 ± 9 nm, respectively. The average concentration of the particle number of NiO and TiO(2) was 1.0E+05 /cm(3) and 2.8E+05 /cm(3), respectively. At 4 d, 1 and 3 months after the end of the inhalation, the rats exposed to these particles were sacrificed and the gene expressions of MMP-2, TIMP-2 and type I collagen were measured using RT-PCR. Pathological finding revealed that there was minimum inflammation with nickel oxide only at 4 d and no change with titanium oxide. However, there were no changes of the gene expression of MMP-2, TIMP-2, and type I collagen in either the NiO or TiO(2) exposure groups. In this study, inhalation of nickel oxide and titanium dioxide nanoparticles did not induce the gene expression of MMP-2 and TIMP-2 mRNA in rat lungs.

Investigation of the performance of TiO2 photocatalytic coatings

TiO₂ photocatalysts were prepared and coated on surfaces. Ultrathin TiO₂ coatings were obtained by wash-coating and screen-printing techniques. The latter provides films of excellent adhesion that could tolerate washing under water jet. The scratch-proof coatings were characterized, and X-ray diffraction (XRD), atomic force microscopy (AFM) and N₂ physisorption indicated that the addition of polyethylene glycol (PEG) not only improved the coating properties of TiO₂ but also served as poragen to produce high surface area, mesoporous TiO₂. The coated TiO₂ displayed better activity than the commercial P25 TiO₂ for photocatalytic oxidation of ethylene, ethanol, acetaldehyde, isopropanol and acetone. The catalyst also exhibited excellent bactericidal, fungicidal and virucidal activities against a wide variety of Gram-positive and Gram-negative bacteria, fungal spores and T2 bacterial phage. A simple photoreactor with tangential air flow was designed and tested in a chamber, before incorporating in a prototype air purifier. The study showed that there is good agreement between laboratory catalyst reaction data (i.e., 110 mmol h^-1 for acetone) and the prototype test results (69 mmol h^-1).

Hazard assessments of manufactured nanomaterials

BACKGROUND

It has been difficult to make reliable hazard assessments of manufactured nanomaterials, because the nanomaterials form large agglomerations in both in vitro and in vivo studies.

OBJECTIVE

In the New Energy and Industrial Technology Development Organization (NEDO) Project of Japan, the physicochemical properties of many manufactured nanomaterials are being measured, and in vitro and in vivo studies are being performed to determine which endpoints are correspond to the hazards and risks of nanomaterials. Focusing on titanium dioxide, fullerenes and carbon nanotubes, we introduce findings made in inhalation and intratracheal installation studies overseas, and together with the findings made in the NEDO project, and also assess the hazards presented by manufactured nanomaterials.

RESULTS AND CONCLUSION

A project by NEDO has succeeded in ensuring the stability of dispersion (nanoscale <100 nm) of manufactured nanomaterials, and is developing hazard assessments of manufactured nanomaterials. In these interim reports, the acceptable exposure concentration of titanium dioxide and fullerene was proposed to be 1.2 mg/m(3) and 0.8 mg/m(3) respirable dust in working environment, respectively.

Identification of potential biomarkers from gene expression profiles in rat lungs intratracheally instilled with C(60) fullerenes

The use of C(60) fullerenes is expected to increase in various industrial fields. Little is known about the potential toxicological mechanism of action of water-soluble C(60) fullerenes. In our previous research, gene expression profiling of the rat lung was performed after whole-body inhalation exposure to C(60) fullerenes to gain insights into the molecular events. These DNA microarray-based data closely matched the pathological findings that C(60) fullerenes caused no serious adverse pulmonary effects under the inhalation exposure condition. Taking advantage of this, we attempted to characterize time-dependent changes in the gene expression profiles after intratracheal instillation with C(60) fullerenes at different dosages and to identify the candidate expressed genes as potential biomarkers. The hierarchical cluster analysis revealed that the up- or downregulation of genes after intratracheal instillation with 1.0 mg C(60) fullerene particles in rat lung tissue was significantly over-represented in the "response to stimulus" and "response to chemical stimulus" categories of biological processes and in the "extracellular space" category of the cellular component. These results were remarkable for 1 week after the instillation with C(60) fullerenes. In the lung tissues instilled with 1.0 mg C(60) fullerene particles, many representative genes involved in "inflammatory response," such as the Cxcl2, Cxcl6, Orm1, and Spp1 genes, and in "matrix metalloproteinase activity," such as the Mmp7 and Mmp12 genes, were upregulated for over 6 months. The expression levels of 89 and 21 genes were positively correlated with the C(60) fullerene dose at 1 week and 6 months after the instillation, respectively. Most of them were involved in "inflammatory response", and the Ccl17, Ctsk, Cxcl2, Cxcl6, Lcn6, Orm1, Rnase9, Slc26a4, Spp1, Mmp7, and Mmp12 genes were overlapped. Meanwhile, the expression levels of 16 and 4 genes were negatively correlated with the C(60) fullerene dose at 1 week and 6 months after the instillation, respectively. Microarray-based gene expression profiling suggested that the expression of some genes is correlated with the dose of intratracheally instilled C(60) fullerenes. We propose that these genes are useful for identifying potential biomarkers in acute-phase or persistent responses to C(60) fullerenes in the lung tissue.

Inflammogenic effect of well-characterized fullerenes in inhalation and intratracheal instillation studies

Background

We used fullerenes, whose dispersion at the nano-level was stabilized by grinding in nitrogen gas in an agitation mill, to conduct an intratracheal instillation study and an inhalation exposure study. Fullerenes were individually dispersed in distilled water including 0.1% Tween 80, and the diameter of the fullerenes was 33 nm. These suspensions were directly injected as a solution in the intratracheal instillation study. The reference material was nickel oxide in distilled water. Wistar male rats intratracheally received a dose of 0.1 mg, 0.2 mg, or 1 mg of fullerenes and were sacrificed after 3 days, 1 week, 1 month, 3 months, and 6 months. In the inhalation study, Wistar rats were exposed to fullerene agglomerates (diameter: 96 ± 5 nm; 0.12 ± 0.03 mg/m³; 6 hours/days for 5 days/week) for 4 weeks and were sacrificed at 3 days, 1 month, and 3 months after the end of exposure. The inflammatory responses and gene expression of cytokine-induced neutrophil chemoattractants (CINCs) were examined in rat lungs in both studies.

Results

In the intratracheal instillation study, both the 0.1 mg and 0.2 mg fullerene groups did not show a significant increase of the total cell and neutrophil count in BALF or in the expression of CINC-1,-2αβ and-3 in the lung, while the high-dose, 1 mg group only showed a transient significant increase of neutrophils and expression of CINC-1,-2αβ and -3. In the inhalation study, there were no increases of total cell and neutrophil count in BALF, CINC-1,-2αβ and-3 in the fullerene group.

Conclusion

These data in intratracheal instillation and inhalation studies suggested that well-dispersed fullerenes do not have strong potential of neutrophil inflammation.