The Pulmonary Response and Clearance of Ludox Colloidal Silica after a 4-Week Inhalation Exposure in Rats

Rats were exposed to Ludox colloidal silica (CS) at concentrationsof 0, 10, 50, and 150 mg/m³ for 6 hr/day, 5 days/week for 4weeks. Rats were killed after 4 weeks of exposure and 10 daysor 3 months post exposure (PE). The exposure concentration of10 mg/m³ Ludox CS is considered to be the no-effect concentration.There were no exposure-related clinical signs in any group.After 4 weeks exposure, lung weights were increased significantlyin rats exposed to 50 and 150 mg/m³ Ludox CS, but lung weightswere similar to those of controls at 3 months PE. After 4 weeksexposure to 50 mg/m³ Ludox CS, a slight alveolar macrophageresponse, polymorphonuclear leukocytic infiltration, and TypeII pneumocyte hyperplasia in alveolar duct regions were present.After 3 months PE, these pulmonary lesions had almost disappearedwith removal of most dust-laden alveolar macrophages (AMs).The pulmonary response to 150 mg/m³ Ludox CS was similar incharacter but increased in magnitude from that seen at 50 mg/m³At 3 months PE, most particleladen AMs had disappeared and theremaining AMs were aggregated and sharply demarcated. A fewaggregates of particle-laden AMs appeared to transform intosilicotic nodules comprising macrophages, epithelioid cells,and lymphocytic infiltration in some animals. Some silicoticnodules showed reticular fiber networks with minute collagenfiber deposition. Tracheobronchial lymph nodes were enlargedwith aggregates of particle-laden AMs and hyperplastic histiocyticcells. Lung-deposited Ludox cleared rapidly from the lungs withhalf-times of approximately 40 and 50 days for the 50 and 150mg/m³ groups, respectively.     

INHALATION TOXICITY OF POTASSIUM OCTATITANATE FIBERS (TISMO) IN RATS FOLLOWING 13 WEEKS OF AEROSOL EXPOSURE

One hundred and forty male and 140 female rats were divided into 1 control and 3 test groups of 35 rats each, per sex, and exposed by whole-body inhalation to test compound at target concentrations of 0, 1 mg/m³ (1700 fibers/cm³, 123 WHO fibers/cm³), 10 mg/m³ (5900 fibers/cm³, 952 WHO fibers/cm³), and 100 mg/m³ (112,700 fibers/cm³, 7440 WHO fibers/cm³) for 6 h/day, 5 days/wk for 13 wk. Ten rats from each group were killed after 13 wk of exposure and 13 wk of recovery, respectively, for histopathological evaluation. The other 15 rats from each group were killed to study lung clearance after 91 days of exposure, and approximately 1.5 and 3 mo of recovery following the end of the 13 wk of exposure. The mean fiber length of the chamber atmosphere was 2.8, 2.7, and 2.8 µm, while the mean fiber width was 0.48, 0.48, and 0.45 µm for the 1-, 10-, and 100-mg/m³ chambers, respectively. In the 1-mg/m³ (123 WHO fibers/cm³) exposure group, inhaled particles were mostly retained in a few fiberladen alveolar macrophages (AMs) within the alveoli adjacent to alveolar ducts without any adverse tissue response throughout 13 wk of exposure and following 13 wk of recovery. This exposure concentration was considered to be a no-observable-adverse-effect level (NOAEL), since the alveoli containing fiber-laden AMs preserved normal structure. After 13 wk of exposure to 10 mg/m³ (952 WHO fibers/cm³), fiber-laden AMs were mainly retained at the alveoli adjacent to the alveolar ducts. Infrequently, slight fibrotic thickening was observed in the alveolar ducts and adjoining alveoli, with proliferating fibroblasts and hyperplastic Type II pneumocytes, and microgranulomas. Occasionally, trace amounts of collagenous material were deposited in the thickened alveolar ducts and adjoining alveolar walls. In addition, minimal alveolar bronchiolarization was occasionally found in the alveoli adjacent to the terminal bronchioles. The peribronchial lymphoid tissue and thymic lymph nodes contained migrated fiber-laden AMs. After 13 wk of recovery, fiber-laden AMs had mostly disappeared from alveoli located in the peripheral acini, but they localized in the alveolar ducts region, suggesting there was active lung clearance of fibers by the AMs via airways. Thickened alveolar ducts and adjacent alveoli were decreased in thickness, a reversible change manifested by reduction of proliferating Type II pneumocytes and fibroblasts. Collagenized fibrosis was slightly more pronounced in the thickened alveolar ducts and adjoining alveoli. The lung response following 13 wk of exposure to 100 mg/m³ (7440 WHO fibers/cm³) and after 13 wk of recovery was similar to those findings of the 952 WHO fibers/cm³ group but more pronounced, demonstrating a clear concentration-related response. Alveolar ducts and adjoining alveolar walls in the central acini were irregularly thickened with more frequent evidence of minimal collagenized fibrosis. The lung burden and clearance of fibers were estimated by measuring the total content of titanium (Ti) in the lungs, but high variability of Ti content in control and exposed groups prevented meaningful lung clearance analysis.     

Thirteen-week study of toxicity of fiber-like multi-walled carbon nanotubes with whole-body inhalation exposure in rats

Abstract

Cancer development due to fiber-like straight type of multi-walled carbon nanotubes (MWCNTs) has raised concerns for human safety because of its shape similar to asbestos. To set concentrations of MWCNT for a rat carcinogenicity study, we conducted a 13-week whole body inhalation study. F344 male and female rats, 6-week-old at the commencement of the study, were exposed by whole-body inhalation to MWCNT at concentrations of 0, 0.2, 1 and 5?mg/m³ with a generation and exposure system utilizing the cyclone sieve method. Measured concentrations in the exposure chambers were 0.20?±?0.02, 1.01?±?0.11 and 5.02?±?0.25?mg/m³ for 13 weeks. The MMAD (GSD) of MWCNT were 1.4–1.6?μm (2.3–3.0), and mean width and length were 94.1–98.0?nm and 5.53–6.19?μm, respectively, for each target concentration. Lung weights were increased 1.2-fold with 1?mg/m³ and 1.3-fold with 5?mg/m³ in both sexes compared to the controls. In the bronchoalveolar lavage fluid (BALF) analyses, inflammatory parameters were increased concentration-dependently in both sexes from 0.2?mg/m³. Granulomatous changes in the lung were induced at 1 and 5?mg/m³ in females and even at 0.2?mg/m³ in males. Focal fibrosis of the alveolar wall was observed in both sexes at 1?mg/m³ or higher. Inflammatory infiltration in the visceral pleural and subpleural areas was induced only at 5?mg/m³. In conclusion, we determined 0.2?mg/m³ as the low-observed-adverse-effect level (LOAEL) for respiratory tract toxicity in the present inhalation exposure study of rats.     

Pulmonary fibrotic response to inhalation of ZnO nanoparticles and toluene co-exposure through directed flow nose only exposure chamber

Abstract

The increasing use of Zinc Oxide nanoparticles (ZnONPs) in paint industry is not supplemented with adequate toxicology data. This report focuses on the fibrogenic toxicity caused due to co-exposure of ZnONPs and toluene in male Wistar rats, exposed for 28 days, through directed flow nose only exposure chamber. The rats were grouped as air control, toluene control (200?ppm), zinc oxide control (10?mg/m³), low dose co-exposed (5?mg/m³ ZnO and 200?ppm of toluene) and high dose co-exposed (10?mg/m³ of ZnO and 200?ppm of toluene). Our study demonstrates that co-exposure of ZnONPs and toluene (as in paint industry), even at their respective permissible exposure level (5?mg/m³ for ZnO and 200?ppm for toluene) have the potential to produce a progressive inflammatory and fibrotic response in the alveolar tissues of the lungs. We observed a significant increase in inflammatory markers in BAL fluid and elevated malondialdehyde (MDA) levels with lower levels of intracellular reduced glutathione (GSH) in lungs of rats of co-exposed group. Significant increase in the levels of pro-inflammatory mediators (IL-6, Ikβα, Cox-II, p-NF-κB) in lung tissues also indicated pulmonary damage. To best of our knowledge this is the first study which highlights the toxicity of co-exposed ZnO NPs and toluene.     

Changing the dose metric for inhalation toxicity studies: Short-term study in rats with engineered aerosolized amorphous silica nanoparticles

Inhalation toxicity and exposure assessment studies for nonfibrous particulates have traditionally been conducted using particle mass measurements as the preferred dose metric (i.e., mg or μg/m³). However, currently there is a debate regarding the appropriate dose metric for nanoparticle exposure assessment studies in the workplace. The objectives of this study were to characterize aerosol exposures and toxicity in rats of freshly generated amorphous silica (AS) nanoparticles using particle number dose metrics (3.7?×?10⁷ or 1.8?×?10⁸ particles/cm³) for 1- or 3-day exposures. In addition, the role of particle size (d₅₀?=?37 or 83?nm) on pulmonary toxicity and genotoxicity endpoints was assessed at several postexposure time points. A nanoparticle reactor capable of producing, de novo synthesized, aerosolized amorphous silica nanoparticles for inhalation toxicity studies was developed for this study. SiO₂ aerosol nanoparticle synthesis occurred via thermal decomposition of tetraethylorthosilicate (TEOS). The reactor was designed to produce aerosolized nanoparticles at two different particle size ranges, namely d₅₀?=?～30?nm and d₅₀?=?～80?nm; at particle concentrations ranging from 10⁷ to 10⁸ particles/cm³. AS particle aerosol concentrations were consistently generated by the reactor. One- or 3-day aerosol exposures produced no significant pulmonary inflammatory, genotoxic, or adverse lung histopathological effects in rats exposed to very high particle numbers corresponding to a range of mass concentrations (1.8 or 86?mg/m³). Although the present study was a short-term effort, the methodology described herein can be utilized for longer-term inhalation toxicity studies in rats such as 28-day or 90-day studies. The expansion of the concept to subchronic studies is practical, due, in part, to the consistency of the nanoparticle generation method.     

Acute pulmonary toxicity following inhalation exposure to aerosolized VX in anesthetized rats

ABSTRACT

This study evaluated acute toxicity and pulmonary injury in rats at 3, 6 and 24?h after an inhalation exposure to aerosolized O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (VX). Anesthetized male Sprague-Dawley rats (250–300?g) were incubated with a glass endotracheal tube and exposed to saline or VX (171, 343 and 514?mg×min/m³ or 0.2, 0.5 and 0.8?LCt₅₀, respectively) for 10?min. VX was delivered by a small animal ventilator at a volume of 2.5?ml?×?70 breaths/minute. All VX-exposed animals experienced a significant loss in percentage body weight at 3, 6, and 24?h post-exposure. In comparison to controls, animals exposed to 514?mg×min/m³ of VX had significant increases in bronchoalveolar lavage (BAL) protein concentrations at 6 and 24?h post-exposure. Blood acetylcholinesterase (AChE) activity was inhibited dose dependently at each of the times points for all VX-exposed groups. AChE activity in lung homogenates was significantly inhibited in all VX-exposed groups at each time point. All VX-exposed animals assessed at 20 min and 3, 6 and 24?h post-exposure showed increases in lung resistance, which was prominent at 20 min and 3?h post-exposure. Histopathologic evaluation of lung tissue of the 514?mg×min/m³ VX-exposed animals at 3, 6 and 24?h indicated morphological changes, including perivascular inflammation, alveolar exudate and histiocytosis, alveolar septal inflammation and edema, alveolar epithelial necrosis, and bronchiolar inflammatory infiltrates, in comparison to controls. These results suggest that aerosolization of the highly toxic, persistent chemical warfare nerve agent VX results in acute pulmonary toxicity and lung injury in rats.     

Subchronic Inhalation Study of Toner in Rats

Abstract

A subchronic inhalation study of a special test toner was conducted by exposure of groups of F-344 SPF (specific pathogen free) rats for 6 hlday, 5 dayslwk for 13 wk. The test material was a special 9000 type xerographic toner, enriched in respirable size particles compared to commercial toner, such that it was about 35% respirable according to the ACGIH criteria. The nominal aerosol exposure concentrations were 0, 7.0, 4.0, 76.0, and 64.0 mg/m³ Body weight, clinical chemistry values, food consumption, and organ weights were normal except for a 40% increase in lung weight for the highest exposure group. Histopathological examination of the lungs indicated an exposure-related accumulation of particle-laden alveolar macrophages. A very slight degree of septal thickening of the alveolar structure was noted in the highest exposure group. Clearance results for the test material and a superimposed spike of ⁵⁹Fe₂O₃ were essentially unchanged at exposure concentrations of 0, 1, and 4 mg/m³. At 76 mg/m³, some indications of retarded clearance were noted and at 64 mg/m³, no appreciable toner clearance was observed. The pulmonary changes observed at the two highest exposure levels are interpreted on the basis of the “lung overloading” concept. Based upon the above observations, as well as the increase in lung weight, both the maximum tolerated dose (MTD) and the maximum functionally tolerated dose of test toner (MFTD) in this subchronic study were exceeded at the 64 mg/m³ exposure level.     

Siderite (FeCO3) and magnetite (Fe3O4) overload-dependent pulmonary toxicity is determined by the poorly soluble particle not the iron content

The two poorly soluble iron containing solid aerosols of siderite (FeCO₃) and magnetite (Fe₃O₄) were compared in a 4-week inhalation study on rats at similar particle mass concentrations of approximately 30 or 100?mg/m³. The particle size distributions were essentially identical (MMAD ≈1.4 μm). The iron-based concentrations were 12 or 38 and 22 or 66?mg Fe/m³ for FeCO₃ and Fe₃O₄, respectively. Modeled and empirically determined iron lung burdens were compared with endpoints suggestive of pulmonary inflammation by determinations in bronchoalveolar lavage (BAL) and oxidative stress in lung tissue during a postexposure period of 3 months. The objective of study was to identify the most germane exposure metrics, that are the concentration of elemental iron (mg Fe/m³), total particle mass (mg PM/m³) or particle volume (μl PM/m³) and their associations with the effects observed. From this analysis it was apparent that the intensity of pulmonary inflammation was clearly dependent on the concentration of particle-mass or -volume and not of iron. Despite its lower iron content, the exposure to FeCO₃ caused a more pronounced and sustained inflammation as compared to Fe₃O₄. Similarly, borderline evidence of increased oxidative stress and inflammation occurred especially following exposure to FeCO₃ at moderate lung overload levels. The in situ analysis of 8-oxoguanine in epithelial cells of alveolar and bronchiolar regions supports the conclusion that both FeCO₃ and Fe₃O₄ particles are effectively endocytosed by macrophages as opposed to epithelial cells. Evidence of intracellular or nuclear sources of redox-active iron did not exist. In summary, this mechanistic study supports previous conclusions, namely that the repeated inhalation exposure of rats to highly respirable pigment-type iron oxides cause nonspecific pulmonary inflammation which shows a clear dependence on the particle volume-dependent lung overload rather than any increased dissolution and/or bioavailability of redox-active iron.     

Endotracheal aerosolization of atropine sulfate protects against soman-induced acute respiratory toxicity in guinea pigs

The efficacy of endotracheal aerosolization of atropine sulfate for protection against soman (GD)-induced respiratory toxicity was investigated using microinstillation technique in guinea pigs. GD (841?mg/m³, 1.3 LCt₅₀ or 1121?mg/m³, 1.7 LCt₅₀) was aerosolized endotracheally to anesthetized male guinea pigs that were treated with atropine sulfate (5.0?mg/kg) 30 s postexposure by endotracheal microinstillation. Animals exposed to 841?mg/m³ and 1121?mg/m³GD resulted in 31 and 13% while treatment with atropine sulfate resulted in 100 and 50% survival, respectively. Cholinergic symptoms and increased body weight loss were reduced in atropine-treated animals compared to GD controls. Diminished pulse rate and blood O₂ saturation in GD-exposed animals returned to normal levels after atropine treatment. Increased cell death, total cell count and protein in the bronchoalveolar fluid (BALF) in GD-exposed animals returned to normal levels following atropine treatment. GD exposure increased glutathione and superoxide dismutase levels in BALF and that were reduced in animals treated with atropine. Respiratory parameters measured by whole-body barometric plethysmography revealed that treatment with atropine sulfate resulted in normalization of respiratory frequency, tidal volume, time of expiration, time of inspiration, end expiratory pause, pseudo lung resistance (Penh) and pause at 4 and 24?h post 841?mg/m³ GD exposure. Lung histopathology showed that atropine treatment reduced bronchial epithelial subepithelial inflammation and multifocal alveolar septal edema. These results suggest that endotracheal aerosolization of atropine sulfate protects against respiratory toxicity and lung injury induced by microinstillation inhalation exposure to lethal doses of GD.     

Pulmonary toxicity of printer toner following inhalation and intratracheal instillation

Abstract

The pulmonary effects of a finished toner were evaluated in intratracheal instillation and inhalation studies, using toners with external additives (titanium dioxide nanoparticles and amorphous silica nanoparticles). Rats received an intratracheal dose of 1?mg or 2?mg of toner and were sacrificed at 3 days, 1 week, 1 month, 3 months and 6 months. The toner induced pulmonary inflammation, as evidenced by a transient neutrophil response in the low-dose groups and persistent neutrophil infiltration in the high-dose groups. There were increased concentrations of heme oxygenase-1 (HO-1) as a marker of oxidative stress in the bronchoalveolar lavage fluid (BALF) and the lung. In a 90-day inhalation study, rats were exposed to well-dispersed toner (mean of MMAD: 3.76?µm). The three mass concentrations of toner were 1, 4 and 16?mg/m³ for 13 weeks, and the rats were sacrificed at 6 days and 91 days after the end of the exposure period. The low and medium concentrations did not induce neutrophil infiltration in the lung of statistical significance, but the high concentration did, and, in addition, upon histopathological examination not only showed findings of inflammation but also of fibrosis in the lung. Taken together, the results of our studies suggest that toners with external additives lead to pulmonary inflammation and fibrosis at lung burdens suggest beyond the overload. The changes observed in the pulmonary responses in this inhalation study indicate that the high concentration (16?mg/m³) is an LOAEL and that the medium concentration (4?mg/m³) is an NOAEL.     

Subchronic inhalation toxicity of iron oxide (magnetite, Fe(3) O(4) ) in rats: pulmonary toxicity is determined by the particle kinetics typical of poorly soluble particles

Wistar rats were nose‐only exposed to pigment‐sized iron oxide dust (Fe₃O₄, magnetite) in a subchronic 13‐week inhalation study according to the OECD testing guidelines TG#413 and GD#39. A 4 week pilot study with a 6 month post exposure period served as basis for validating the kinetic modeling approaches utilized to design the subchronic study. Kinetic analyses made during this post exposure period demonstrated that a diminution in particle clearance and lung inflammation occurred at cumulative exposure levels exceeding the lung overload threshold. Animals were exposed 6 h per day, five days per week for 13 consecutive weeks at actual concentrations of 0, 4.7, 16.6 and 52.1 mg m^?3 (mass median aerodynamic diameter ≈1.3 μm, geometric standard deviation = 2). The exposure to iron oxide dust was tolerated without mortality, consistent changes in body weights, food and water consumption or systemic toxicity. While general clinical pathology and urinalysis were unobtrusive, hematology revealed changes of unclear toxicological significance (minimally increased differential neutrophil counts in peripheral blood). Elevations of neutrophils in bronchoalveolar lavage (BAL) appeared to be the most sensitive endpoint of study. Histopathology demonstrated responses to particle deposition in the upper respiratory tract (goblet cell hyper‐ and/or metaplasia, intraepithelial eosinophilic globules in the nasal passages) and the lower respiratory tract (inflammatory changes in the bronchiolo‐alveolar region). Consistent changes suggestive of pulmonary inflammation were evidenced by BAL, histopathology, increased lung and lung‐associated‐lymph node (LALN) weights at 16.6 and 52.1 mg m^?3. Increased septal collagenous fibers were observed at 52.1 mg m^?3. Particle translocation into LALN occurred at exposure levels causing pulmonary inflammation. In summary, the retention kinetics iron oxide reflected that of poorly soluble particles. The empirical no‐observed‐adverse‐effect level (NOAEL) and the lower bound 95% confidence limit on the benchmark concentration (BMCL) obtained by benchmark analysis was 4.7 and 4.4 mg m^?3, respectively, and supports an OEL (time‐adjusted chronic occupational exposure level) of 2 mg m^?3 (alveolar fraction). Copyright © 2011 John Wiley & Sons, Ltd.     

Chronic Inhalation Exposure of Wistar Rats and two Different Strains of Mice to Diesel Engine Exhaust,Carbon Black,and Titanium Dioxide

Abstract

Wistar rats were exposed for 2 yr to diesel engine exhaust, carbon black (Printex 90, Degussa, FR. G), and ultraline TiO₂ (P25, Degussa, FRG) and were subsequently kept in clean air for 6 mo. Particle exposure concentration was increased during the course of the experiment for carbon black and TiO₂ to reach particle lung loads similar to those found in the diesel soot-exposed rats. The average particle exposure concentrations for diesel soot, carbon black, and TiO₂ were 7, 11.6, and 10 mg/m³, respectively. Lung tumor rates in these rats increased with increasing cumulative particle exposure (mg/m³ x h) independent of the type of particle employed. The exposure to 2.5 mg/m¹ diesel soot also induced a significantly increased lung tumor rate, but 0.8 mg/m³ diesel soot did not. With this study, it could be demonstrated that the carbon core of diesel soot is mainly responsible for the occurrence of diesel engine exhaust-related lung tumors; the role of diesel soot-attached polycyclic aromatic hydrocarbons (PAH) and NO₂-PAH is probably of minor importance in the rat lung. Agglomerates of ultrafine carbon and TiO₂ particles seem particularly suited to exert toxic effects primarily on alveolar macrophages and alveolar lung particle clearance. Although such lung toxic effects were also seen with the lowest diesel soot exposure concentration (0.8 mg/m³) used, no increased lung tumor rate was detected in this group of rats. Whether this result implies a threshold for the particle-related lung tumor induction mechanism as already discussed by Vostal (1986) or whether the tumor effect was simply not observed because of statistical reasons needs further research on the possible mode of action of ultra-fine insoluble particles in the lung. NMR. I mice that were kept in the same exposure atmospheres (high diesel soot, carbon black, TiO₂) as the rats did not show an increased lung tumor rate. Furthermore, there was no treatment-related tumor response in NMRI nor in C57BL/6N mice exposed to diesel exhaust containing 4.5 mg/m³ diesel soot or to the same exhaust dilution but devoid of soot particles. C57BU6N mice were exposed for 24 mo and were subsequently kept in clean air for another 6 mo. Not only the average survival time but also the particle load per gram lung wet weight of the C57BU6N mice was very similar to rats exposed to 7 mg/m³ diesel soot.     

Recovery from silver-nanoparticle-exposure-induced lung inflammation and lung function changes in Sprague Dawley rats

Abstract

In a previous study, the lung function, as indicated by the tidal volume, minute volume, and peak inspiration flow, decreased during 90 days of exposure to silver nanoparticles and was accompanied by inflammatory lesions in the lung morphology. Therefore, this study investigated the recovery from such lung function changes in rats following the cessation of 12 weeks of nanoparticle exposure. Male and female rats were exposed to silver nanoparticles (14–15 nm diameter) at concentrations of 0.66 × 10⁶ particles/cm³ (49 μg/m³, low dose), 1.41 × 10⁶ particles/cm³ (117 μg/m³, middle dose), and 3.24 × 10⁶ particles/cm³ (381 μg/m³, high dose) for 6 h/day in an inhalation chamber for 12 weeks. The rats were then allowed to recover. The lung function was measured every week during the exposure period and after the cessation of exposure, plus animals were sacrificed after the 12-week exposure period, and 4 weeks and 12 weeks after the exposure cessation. An exposure-related lung function decrease was measured in the male rats after the 12-week exposure period and 12 weeks after the exposure cessation. In contrast, the female rats did not show a consistent lung function decrease either during the exposure period or following the exposure cessation. The histopathology showed a gradual recovery from the lung inflammation in the female rats, whereas the male rats in the high-dose group exhibited persistent inflammation throughout the 12-week recovery period. Therefore, the present results suggest a potential persistence of lung function changes and inflammation induced by silver nanoparticle exposure above the no observed adverse effect level.     

In vivo genotoxicity evaluation of lung cells from Fischer 344 rats following 28 days of inhalation exposure to MWCNTs,plus 28 days and 90 days post-exposure

Abstract

Despite their useful physico-chemical properties, carbon nanotubes (CNTs) continue to cause concern over occupational and human health due to their structural similarity to asbestos. Thus, to evaluate the toxic and genotoxic effect of multi-wall carbon nanotubes (MWCNTs) on lung cells in vivo, eight-week-old rats were divided into four groups (each group?=?25 animals), a fresh air control (0?mg/m³), low (0.17?mg/m³), middle (0.49?mg/m³), and high (0.96?mg/m³) dose group, and exposed to MWCNTs via nose-only inhalation 6?h per day, 5 days per week for 28 days. The count median length and geometric standard deviation for the MWCNTs determined by TEM were 330.18 and 1.72?nm, respectively, and the MWCNT diameters ranged from 10 to 15?nm. Lung cells were isolated from five male and five female rats in each group on day 0, day 28 (only from males) and day 90 following the 28-day exposure. The total number of animals used was 15 male and 10 female rats for each concentration group. To determine the genotoxicity of the MWCNTs, a single cell gel electrophoresis assay (Comet assay) was conducted on the rat lung cells. As a result of the exposure, the olive tail moments were found to be significantly higher (p?<?0.05) in the male and female rats from all the exposed groups when compared with the fresh air control. In addition, the high-dose exposed male and middle and high-dose exposed female rats retained DNA damage, even 90 days post-exposure (p?<?0.05). To investigate the mode of genotoxicity, the intracellular reactive oxygen species (ROS) levels and inflammatory cytokine levels (TNF-α, TGF- β, IL-1, IL-2, IL-4, IL-5, IL-10, IL-12 and IFN-γ) were also measured. For the male rats, the H₂O₂ levels were significantly higher in the middle (0 days post-exposure) and high- (0 days and 28 days post-exposure) dose groups (p?<?0.05). Conversely, the female rats showed no changes in the H₂O₂ levels. The inflammatory cytokine levels in the bronchoalveolar lavage (BAL) fluid did not show any statistically significant difference. Interestingly, the short-length MWCNTs deposited in the lung cells were persistent at 90 days post-exposure. Thus, exposing lung cells to MWCNTs with a short tube length may induce genotoxicity.     

Multiple-Dose Chronic Inhalation Toxicity Study of Size-Separated Kaolin Refractory Ceramic Fiber in Male Fischer 344 Rats

Abstract

Refractory ceramic fibers (RCF) are man-made vitreous fibers used primarily in industrial high-temperature applications, especially for insulation of furnaces and kilns. Because of their increasing use and potential for human exposure an in an effort to define the dose-response, as a follow up to a maximum tolerated dose [30 mg/m³] study in rats (Mast et al., 1995), a multiple dose chronic toxicity/carcinogenicity inhalation study was conducted in Fischer 344 (F344) rats. Four groups of 140 weanling male F344 rats were exposed via noseonly inhalation to either HEPA-filtered air (chamber controls) or 3, 9, or 16 mg/m³(approximately 36, 91, and 162 fibers/cm³) of kaolin-based “size-selected” RCF fibers (approximately 1 µm in diameter and approximately 20 µm in length) for 6 h/day, 5 days/wk for 24 mo. They were then held unexposed until approximately 20% survival and sacrificed (30 mo). Croups of 3–6 animals were sacrificed at 3, 6, 12, 18, and 24 mo to follow the progression of pulmonary lesions and to determine fiber lung burdens. Additional groups of 3–6 rats were removed from exposure at 3, 6, 12, and 18 mo and were held until sacrificed at 24 mo (recovery groups) for similar determinations. A dose-related increase in fiber lung burden was observed. Lung burdens at 24 mo ranged from 5.6 × 10⁴ to 27.8 × 10⁴ fibers/mg dry lung tissue. Significant increases in lung weights and lung to body weight ratios were seen in the high-dose group. Treatment-related lesions were restricted to the lungs. To some extent, all doses of RCF resulted in minimal to mild macrophage infiltration, bronchiolization of proximal alveoli, and microgranuloma formation by 12 mo of exposure. Interstitial fibrosis was observed at 12 mo in the 9 and 16 mg/m³ groups but not in the low-dose group at any time point. A minimal amount of focal pleural fibrosis was first observed at 12 mo in the 9 and 76 mg/m³ dose groups and progressed to a mild severity in the high-dose group by the end of the study. The incidence of pulmonary neoplasm's was well within the range typically reported in the male F344 rat. Neoplasm's (bronchoalveolar adenomas and carcinomas) were observed in all groups 10 mg/m³ (air control), 1 of 129 (0.8%); 3 mg/m³, 2 of 123 (1.6%); 9 mg/m³, 5 of 127 (3.9%); 16 mg/m³, 2 of 124 (1.6%)]. A single pleural mesothelioma was observed in an animal exposed to 9 mg/m³ of kaolin RCF. The results of this study suggest that the dose response for primary lung neoplasms is steep, while that for mesothelioma may not be.     

Aerosol-based efficient delivery of azithromycin to alveolar macrophages for treatment of respiratory infections

The efficacy of aerosol-based delivery of azithromycin (AZM) for the treatment of respiratory infections caused by pathogenic microorganisms infected in alveolar macrophages (AMs) was evaluated by comparison with oral administration. The aerosol formulation of AZM (0.2?mg/kg) was administered to rat lungs using a Liquid MicroSprayer^®. The oral formulation of AZM (50?mg/kg) was used for comparison. Time-courses of concentrations of AZM in AMs following administration were obtained, and then the therapeutic availability (TA) was calculated. In addition, the area under the concentrations of AZM in AMs – time curve/minimum inhibitory concentration at which 90% of isolates ratio (AUC/MIC₉₀) were calculated to estimate the antibacterial effects in AMs. The TA of AZM in AMs following administration of aerosol formulation was markedly greater than that following administration of oral formulation. In addition, the AUC/MIC₉₀ of AZM in AMs was markedly higher than the effective values. This indicates that the aerosol formulation could be useful for the treatment of respiratory infections caused by pathogenic microorganisms infected in AMs. This study suggests that aerosolized AZM is an effective pulmonary drug delivery system for the treatment of respiratory infections.     

Repeated dose inhalation developmental toxicity study in rats exposed to cellulose insulation with boric acid additive

Abstract

Cellulose insulation (CI), a common building material, is a mixture of cellulose fibers and borates. Borates are approximately 20% of the product weight and act as a flame retardant. Given possible exposure to workers and consumers, an inhalation toxicity study was conducted following Organization for Economic Co-operation and Development (OECD) 414 for Prenatal Development Toxicity to evaluate if CI is a developmental toxicant. Pregnant female rats were exposed by nose-only inhalation to CI aerosols containing 20% boric acid for six h/day, from gestational day (GD) 6–19, and fetuses were evaluated for developmental parameters. Respirable CI was produced by grinding to produce respirable particles (MMAD 2.7–2.9?µm, geometric standard deviations (GSD) 1.9–2.6), which were then aerosolized. Target air concentrations were 15, 90, and 270?mg CI/m³. Controls were exposed to air only. Slight body weight reductions (average decrease <7% vs. control) were observed in male and female GD 20 fetuses in the mid and high dose groups. No embryo/fetal developmental toxicity or alterations in any other measured variable were reported at any dose. The no observed adverse effect level (NOAEL) for developmental outcomes was 270?mg/m³.     

Toxicity and occupational exposure assessment for hydroprocessed esters and fatty acids (HEFA) alternative jet fuels

ABSTRACT

The U.S. Air Force (USAF) has pursued development of alternative fuels to augment or replace petroleum-based jet fuels. Hydroprocessed esters and fatty acids (HEFA) renewable jet fuel is certified for use in commercial and USAF aircraft. HEFA feedstocks include camelina seed oil (Camelina sativa, HEFA-C); rendered animal fat (tallow, HEFA-T); and mixed fats and oils (HEFA-F). The aim of this study was to examine potential toxic effects associated with HEFA fuels exposures. All 3 HEFA fuels were less dermally irritating to rabbits than petroleum-derived JP-8 currently in use. Inhalation studies using male and female Fischer-344 rats included acute (1 day, with and without an 11-day recovery), 5-, 10- or 90-day durations. Rats were exposed to 0, 200, 700 or 2000 mg/m³ HEFA-F (6 hr/day, 5 days/week). Acute, 5 – and 10-day responses included minor urinalysis effects. Kidney weight increases might be attributed to male rat specific hyaline droplet formation. Nasal cavity changes included olfactory epithelial degeneration at 2000 mg/m³. Alveolar inflammation was observed at ≥700 mg/m³. For the 90-day study using HEFA-C, no significant neurobehavioral effects were detected. Minimal histopathological effects at 2000 mg/m³ included nasal epithelium goblet cell hyperplasia and olfactory epithelium degeneration. A concurrent micronucleus test was negative for evidence of genotoxicity. All HEFA fuels were negative for mutagenicity (Ames test). Sensory irritation (RD₅₀) values were determined to be 9578 mg/m³ for HEFA-C and greater than 10,000 mg/m³ for HEFA-T and HEFA-F in male Swiss-Webster mice. Overall, HEFA jet fuel was less toxic than JP-8. Occupational exposure levels of 200 mg/m³ for vapor and 5 mg/m³ for aerosol are recommended for HEFA-based jet fuels.     

Subacute inhalation toxicity study of synthetic amorphous silica nanoparticles in Sprague-Dawley rats

Synthetic amorphous silica nanoparticles (SiNPs) are one of the most applied nanomaterials and are widely used in a broad variety of industrial and biomedical fields. However, no recent long-term inhalation studies evaluating the toxicity of SiNPs are available and results of acute studies are limited. Thus, we conducted a subacute inhalation toxicity study of SiNPs in Sprague-Dawley rats using a nose-only inhalation system. Rats were separated into four groups and target concentrations selected in this study were as follows: control (fresh air), low- (0.407?±?0.066?mg/m³), middle- (1.439?±?0.177?mg/m³) and high-concentration group (5.386?±?0.729?mg/m³), respectively. The rats were exposed to SiNPs for four consecutive weeks (6 hr/day, 5 days/week) except for control group of rats which received filtered fresh air. After 28-days of inhalation exposure to SiNPs, rats were sacrificed after recovery periods of one, seven and 28 days. Although there were minimal toxic changes such as temporary decrease of body weight after exposure, increased levels of red blood cells (RBCs) and hemoglobin (Hb) concentration, the lung histopathological findings and inflammatory markers in bronchoalveolar lavage (BAL) fluid including polymorphonuclear (PMN) leukocyte, lactate dehydrogenase (LDH), albumin and protein did not show significant changes at any recovery period. The results of this study suggest that the subacute inhalation of SiNPs had no toxic effects on the lung of rats at the concentrations and selected time points used in this study.     

Measurement of various respiratory dynamics parameters following acute inhalational exposure to soman vapor in conscious rats

Abstract

Respiratory dynamics were investigated in head-out plethysmography chambers following inhalational exposure to soman in untreated, non-anesthetized rats. A multipass saturator cell was used to generate 520, 560 and 600?mg?×?min/m³ of soman vapor in a customized inhalational exposure system. Various respiratory dynamic parameters were collected from male Sprague-Dawley rats (300--350?g) during (20?min) and 24?h (10?min) after inhalational exposure. Signs of CWNA-induced cholinergic crisis were observed in all soman-exposed animals. Percentage body weight loss and lung edema were observed in all soman-exposed animals, with significant increases in both at 24?h following exposure to 600?mg?×?min/m³. Exposure to soman resulted in increases in respiratory frequency (RF) in animals exposed to 560 and 600?mg?×?min/m³ with significant increases following exposure to 560?mg?×?min/m³ at 24?h. No significant alterations in inspiratory time (IT) or expiratory time (ET) were observed in soman-exposed animals 24?h post-exposure. Prominent increases in tidal volume (TV) and minute volume (MV) were observed at 24?h post-exposure in animals exposed to 600?mg?×?min/m³. Peak inspiratory (PIF) and expiratory flow (PEF) followed similar patterns and increased 24?h post-exposure to 600?mg?×?min/m³ of soman. Results demonstrate that inhalational exposure to 600?mg?×?min/m³ soman produces notable alterations in various respiratory dynamic parameters at 24?h. The following multitude of physiological changes in respiratory dynamics highlights the need to develop countermeasures that protect against respiratory toxicity and lung injury.