Inhalation Toxicity Studies Research Articles

P20-28 Toxicological effects caused by particles which exhibit no or very low intrinsic toxicity in inhalation toxicity studies: what are the challenges

P20-28 Toxicological effects caused by particles which exhibit no or very low intrinsic toxicity in inhalation toxicity studies: what are the challenges

Subchronic inhalation toxicity study of diethylbenzene in Wistar rats

Subchronic inhalation toxicity study of diethylbenzene in Wistar rats

Highly Drug-Loaded Nanoaggregate Microparticles for Pulmonary Delivery of Cyclosporin A.

Nanoparticles have the advantages of improving the solubility of poorly water-soluble drugs, facilitating the drug across biological barriers, and reducing macrophage phagocytosis in pulmonary drug delivery. However, nanoparticles have a small aerodynamic particle size, which makes it difficult to achieve optimal deposition when delivered directly to the lungs. Therefore, delivering nanoparticles to the lungs effectively has become a popular research topic. Nanoaggregate microparticles were used as a pulmonary drug delivery strategy for the improvement of the bioavailability of cyclosporine A (CsA). The nanoaggregate microparticles were prepared with polyvinyl pyrrolidone (PVP) as the excipient by combining the anti-solvent method and spray drying process. The physicochemical properties, aerodynamic properties, in vivo pharmacokinetics and inhalation toxicity of nanoaggregate microparticles were systematically evaluated. The optimal nanoparticles exhibited mainly spherical shapes with the particle size and zeta potential of 180.52 nm and -19.8 mV. The nanoaggregate microparticles exhibited irregular shapes with the particle sizes of less than 1.6 µm and drug loading (DL) values higher than 70%. Formulation NM-2 as the optimal nanoaggregate microparticles was suitable for pulmonary drug delivery and probably deposited in the bronchiole and alveolar region, with FPF and MMAD values of 89.62% and 1.74 μm. In addition, inhaled NM-2 had C max and AUC0-∞ values approximately 1.7-fold and 1.8-fold higher than oral cyclosporine soft capsules (Neoral®). The inhalation toxicity study suggested that pulmonary delivery of NM-2 did not result in lung function damage, inflammatory responses, or tissue lesions. The novel nanoaggregate microparticles for pulmonary drug delivery could effectively enhance the relative bioavailability of CsA and had great potential for clinical application.

Safety evaluation of synthesized magnesium carbonate hydrate particles following inhalation exposure

Numerous fine particles or mist from environmental substances significantly contribute to human beings, affecting health issues for both humans and the environment by irritating the respiratory system. To achieve scarcity of information regarding exposure routes and the relationship between substance and health effects needs to be investigated more. Here, we investigated flame retardants (FRs): magnesium carbonate was synthesized, and its inhalation toxicity was examined for the first time by applying it to Sprague-Dawley rats using a mist aerosol-supplying chamber condition. The synthesized magnesium carbonate was fully physiochemically characterized, exhibiting a mesoporous sheet-like morphology, size distribution of 4.971 ± 2.363 μm, the dypingite phase, a surface area of 10.718 m² g−1, and a pore volume of 0.051 cm³ g−1. As a result of the inhalation toxicity study, the 50% lethal concentration (LC50) of magnesium carbonate was determined to be equal to or greater than 1.91 mg m−3. Microscopic examination for assessing pulmonary residue levels of magnesium carbonate reveals the presence of residues in the lungs up to 3 days post-administration. However, over time, there is a gradual decrease of pulmonary residues, and by the 14th day of administration, it is regarded that no residual presence is observable within the pulmonary system.

Eosinophilic globules (syn. hyaline inclusions) and protein crystalloids in the nasal mucosa of rats treated with synthetic amorphous silica, an unspecific chitinase-like-protein-positive background lesion

In a 13-week inhalation toxicity study with three recovery periods (3, 6, and 12 months), Crl: WI rats were allocated to nine groups, each containing 25 animals per sex. Eight groups were treated daily by inhalation with the test items at concentrations of 0.5, 1.0, 2.5, or 5.0 mg/m3 (SAS 1 groups 2, 3, 4, or 5, respectively; SAS 2 groups 6, 7, 8, or 9, respectively). Controls (group 1) were treated with air only.In nasal cavities, the major lesions consisted of increased eosinophilic globules and chitinase-3-like-protein-positive crystalloids* in the nasal mucosa, mainly in nasal cavity levels 2–4 up to week 26 of recovery without any further injury in olfactory mucosa, mainly in SAS 1-treated animals. Eosinophilic globules in the rodent nasal cavity are common and increase with age; they represent a particular finding of the rodent nasal mucosa. The relevance of chitinase-3-like protein (Ym1 + Ym2) expression in the rodent nasal mucosa is unknown but is normal in control animals. Both findings developed without any indicator for inflammatory processes. The increase of these unspecific background findings is considered an indicator of minor irritative effects.Due to the clear lack of nasal tissue injury or concurrent changes (degeneration, necrosis, inflammatory infiltrate, dysplasia, and/or neoplasia) following repeated inhalation exposure to SAS, it is deemed that the eosinophilic globules (hyaline inclusions) combined with the formation of eosinophilic protein crystalloids in this study represent an adaptive response.

Acute Inhalation Toxicity Study of 3-Methoxybutyl Acetate in Sprague-Dawley Rats

3-Methoxybutyl acetate is an organic solvent used in a wide range of industrial and consumer applications, such as coatings, adhesives, chemical intermediates, paints, and washing products. We conducted an acute inhalation toxicity study of 3-Methoxybutyl acetate using an inhalation exposure system (nose-only) in Sprague-Dawley rats. Male and female rats were exposed to 3-Methoxybutyl acetate for 4 h/day. The tests were conducted according to the Organisation for Economic Cooperation and Development Guidelines for the Testing of Chemicals (OECD TG) 436. The analytical concentrations of the exposure chamber were 9.76 ± 0.51 mg/L. Clinical signs, mean body weight changes, and gross necropsy results were observed. No deaths, abnormal clinical signs, gross findings at necropsy, or abnormal mean body weight changes related to exposure to the test substance were observed in either sex. Based on these results, we suggested that 3-Methoxybutyl acetate does not have acute toxic effects at the technically acceptable concentration of 10 mg/L.

Enhanced study design for acute inhalation studies with hydrophobic surface-treated particles to determine toxicological effects including suffocation

High concentrations of low-density particles may cause effects in acute inhalation toxicity studies which can be easily underestimated or misinterpreted following strictly the OECD TG 436, i.e., limited parameters as mortality and gross lesions will be evaluated only. Seven particle types (synthetic amorphous silica (SAS) HMDZ-SAS, silica gel, pyrogenic SAS, and precipitated SAS, calcium carbonate, aluminum oxide pyrogenic alumina, organic red pigment) were chosen at the highest technically feasible concentration of approximately 500 mg/m3 for acute inhalation studies with an expanded endpoint setup. Therefore additional parameters and a thorough histopathological evaluation of an extensive set of organs, including the respiratory tract emphasizing the nasal cavities were added. Six Crl:WI rats per study were exposed for four hours from which three animals were sacrificed after 24 hours and three animals after 14 days. HMDZ-SAS caused early death in all animals due to blockage of the nasal passages caused by its hydrophobicity. For all other Si-containing compounds, histology revealed minor inflammatory and reactive lesions in lungs after 24 hours that were still present after 14 days, except in silica gel-treated animals. After 14 days, for pyrogenic SAS, precipitated SAS, and pyrogenic alumina, granulomas formed in the BALT and lung-associated lymph nodes. In contrast, the calcium carbonate induced almost no findings, and the red pigment (also tested for the additional dose of 1000 mg/m3) stuck partially to the nasal mucosa without causing pathological damage and partly entered the lungs without showing any adverse effects. The results of the present study highlight the advantage of improving the rather simple study design of acute inhalation studies by implementing an extended study design.

Analysis of Requirements for Inhalation Toxicity Studies of Chemicals

SCIENTIFIC RELEVANCE. Studies of the inhalation administration of chemicals are associated with challenges in designing experiments. The parameters to be selected include the experimental animal species, the inhalation chamber, and the mode of inhalation (dynamic or static).AIM. This study aimed to analyse the practical application of regulatory requirements to non-clinical studies of the inhalation toxicity of chemicals.DISCUSSION. This review compares international and Russian standards for studying the inhalation toxicity of chemicals, including GOST 32542-2013, GOST 326432020, GOST 32636-2020, GOST 32383-2013, and GOST 2646-2014. The improvement of the legal and regulatory framework correlates with adopting the Good Laboratory Practice and the risk-based approach to categorising test substances into hazard classes. Hazard classes are determined in rodents without dose extrapolation to humans. The authors present the differences between the main guidelines on inhalation exposure in rodent studies of acute, subacute, subchronic, and chronic toxicity. The article describes current approaches to assessing the inhalation toxicity of chemicals, which allow researchers to replace animal studies with in vitro tests.CONCLUSIONS. According to the current regulatory standards, inhalation toxicity is studied in rats/mice, which have anatomical differences from humans. As an alternative to animal studies, researchers are developing and validating in vitro methods, which yet require regulatory review and approval.

Repeated intratracheal instillation of whole-cigarette smoke condensate to assess lung damage in a rat model.

Cigarette smoke induces an inflammatory response in the lungs by recruiting inflammatory cells, leading to lung diseases such as lung cancer, chronic obstructive pulmonary disease, and pulmonary fibrosis. Existing inhalation exposure methods for assessing the adverse effects of cigarette smoke require expensive equipment and are labor-intensive. Therefore, we attempted to develop a novel method to assess these adverse effects using intratracheal instillation (ITI) of whole cigarette smoke condensate (WCSC). The WCSC (0, 5, 10, or 20 mg/mL) was administered by ITI once daily for 6 or 12 days using an automatic video instillator. Repeated WCSC ITI increased the lung weight, and monocyte chemoattractant protein-1 (MCP-1), neutrophil, and lymphocyte levels within bronchoalveolar lavage fluid compared to the control. In the histopathological analysis of the lung tissue, a mild inflammatory response was observed in the 6 and 12 days 20 mg/mL WCSC exposure groups. The genome-wide RNA-seq expression patterns revealed that inflammatory and immune response-related genes, such as the chemokine signaling pathway, Th1/Th2 cell differentiation, and cytokine-cytokine receptor interaction, were employed following WCSC exposure. In addition, MCP-1 was time-dependent and increased in the 10 mg/mL exposure group compared to the control group. These results suggested that the WCSC might induce the potential pulmonary inflammatory response. Furthermore, we proposed that ITI may be a rapid and effective method of evaluating the adverse effects of WCSC within a short exposure period (less than 2 weeks), and it can be used to evaluate cigarette inhalation toxicity studies as an alternative method.

The acute vapour inhalation toxicity of 2-butoxyethanol. Points considered when designing and conducting a study in Guinea pigs and evaluating existing inhalation toxicity data on low volatility solvents

This publication reports the outcome of an acute inhalation toxicity study with guinea pigs by nose-only exposure to the substance 2-butoxyethanol at exposures close to the maximum attainable saturation vapour concentration. We describe the methods used to ensure exposure only to saturation vapour at a level as high as could be practically achieved whilst avoiding aerosol formation. We consider the practical difficulties and implications of testing substances at or close to their saturation vapour concentration and the criteria that should be used to critically assess such studies, especially with reference to the GHS (Globally Harmonised System) for classification and labelling, where a clear differentiation between gases, vapours and dust and mists applies. Guinea pigs showed no adverse effects when exposed for 4 h to the maximum attainable concentration of pure 2-butoxyethanol vapour. If guinea pigs are regarded as the most appropriate species to assess short term toxicity to humans from exposure to 2-butoxyethanol, because they are like humans not sensitive to haemolysis of red blood cells caused by exposure to the substance, then the data from this study shows that 2-butoxyethanol presents a low acute inhalation toxicity hazard.

Comparison of the toxicological potential of two JUUL ENDS products to reference cigarette 3R4F and filtered air in a 90-day nose-only inhalation toxicity study.

Electronic nicotine delivery systems (ENDS) are generally recognized as less harmful alternatives for those who would otherwise continue to smoke cigarettes. The potential toxicity of aerosols generated from JUUL Device and Virginia Tobacco (VT3) or Menthol (ME3) JUULpods at 3.0% nicotine concentration was assessed in rats exposed at target aerosol concentrations of 1400μg/L for up to 6h/day on a 5 day/week basis for at least 90 days (general accordance with OECD 413). 3R4F reference cigarette smoke (250μg/L) and Filtered Air were used as comparators. JUUL ENDS product aerosol exposures at >5x the 3R4F cigarette smoke level resulted in greater plasma nicotine and cotinine levels (up to 2x). Notable cigarette smoke related effects included pronounced body weight reductions in male rats, pulmonary inflammation evidenced by elevated lactate dehydrogenase, pro-inflammatory cytokines and neutrophils in bronchoalveolar lavage fluid, increased heart and lung weights, and minimal to marked respiratory tract histopathology. In contrast, ENDS aerosol exposed animals had minimal body weight changes, no measurable inflammatory changes and minimal to mild laryngeal squamous metaplasia. Despite the higher exposure levels, VT3 and ME3 did not result in significant toxicity or appreciable respiratory histopathology relative to 3R4F cigarette smoke following 90 days administration.

Natural mineral fibers: conducting inhalation toxicology studies—part B: development of a nose-only exposure system for repeat-exposure in vivo study of Libby amphibole aerosol

Background Exposure to asbestos is associated with malignant and nonmalignant respiratory disease. To strengthen the scientific basis for risk assessment on fibers, the National Institute of Environmental Health Sciences (NIEHS) has initiated a series of studies to address fundamental questions on the toxicology of naturally occurring asbestos and related mineral fibers after inhalation exposure. A prototype nose-only exposure system was previously developed and validated. The prototype system was expanded to a large-scale exposure system in this study for conducting subsequent in vivo rodent inhalation studies of Libby amphibole (LA) 2007, selected as a model fiber. Results The exposure system consisting of six exposure carousels was able to independently deliver stable LA 2007 aerosol to individual carousels at target concentrations of 0 (control group), 0.1, 0.3, 1, 3, or 10 mg/m3. A single aerosol generator was used to provide aerosol to all carousels to ensure that exposure atmospheres were chemically and physically similar, with aerosol concentration as the only major variable among the carousels. Transmission electron microscopy (TEM) coupled with energy dispersive spectrometry (EDS) and selected area electron diffraction (SAED) analysis of aerosol samples collected at the exposure ports indicated the fiber dimensions, chemical composition, and mineralogy were equivalent across exposure carousels and were comparable to the bulk LA 2007 material. Conclusion The exposure system developed is ready for use in conducting nose-only inhalation toxicity studies of LA 2007 in rats. The exposure system is anticipated to have applicability for the inhalation toxicity evaluation of other natural mineral fibers of concern.

Natural mineral fibers: conducting inhalation toxicology studies – part A: Libby Amphibole aerosol generation and characterization method development

Background Asbestos has been classified as a human carcinogen, and exposure may increase the risk of diseases associated with impaired respiratory function. As the range of health effects and airborne concentrations that result in health effects across asbestos-related natural mineral fiber types are not fully understood, the National Institute of Environmental Health Sciences has established a series of research studies to characterize hazards of natural mineral fibers after inhalation exposure. This paper presents the method development work of this research project. Results A prototype nose-only exposure system was fabricated to explore the feasibility of generating natural mineral fiber aerosol for in vivo inhalation toxicity studies. The prototype system consisted of a slide bar aerosol generator, a distribution/delivery system and an exposure carousel. Characterization tests conducted using Libby Amphibole 2007 (LA 2007) demonstrated the prototype system delivered stable and controllable aerosol concentration to the exposure carousel. Transmission electron microscopy (TEM) analysis of aerosol samples collected at the exposure port showed the average fiber length and width were comparable to the bulk LA 2007. TEM coupled with energy dispersive spectrometry (EDS) and selected area electron diffraction (SAED) analysis further confirmed fibers from the aerosol samples were consistent with the bulk LA 2007 chemically and physically. Conclusions Characterization of the prototype system demonstrated feasibility of generating LA 2007 fiber aerosols appropriate for in vivo inhalation toxicity studies. The methods developed in this study are suitable to apply to a multiple-carousel exposure system for a rat inhalation toxicity testing using LA 2007.

#3351 TRIAL OF ISOLATED HAEMODIALYSIS WITH PATIENT-ENTRY TENT AND HYPOCHLORITE MIST

Abstract Background and Aims The global spread of COVID-19 has posed a serious threat to patients receiving renal replacement therapy and to the staff who treat them. Every time they treat a patient or operate a machine, they have to wear personal protective equipment (PPE). In order to reduce the burden on our staff, we have introduced two pieces of equipment. One is a hypochlorous acid mist for room and surface disinfection using CLFine®. The other is an AIR ZIPPER® patient isolation tent in the existing isolation room. Both products were manufactured by Nipro Corporation of Osaka, Japan. However, there was no evidence to support the use of hypochlorous acid in an ultrasonic humidifier. Therefore, Nipro Corporation conducted a “28-day repeated inhalation toxicity study” on rats with a third party organisation and confirmed the results as toxicologically safe. According to the Occupational Safety and Health Act, also in the school environmental health, the concentration of chlorine in the air is 0.5 ppm or less (8 hours/day, 5 days/week or less). CL Fine® has shown an antiviral effect within these regulations. The size of the AIR ZIPPER® is about a fifth of the standard 10m3 size, down to about 2m3. Powerful, high-efficiency particulate air filter pumps have been fitted to replace the air in the tent in less than 5 minutes at low flow rates (0.4 m3/min airflow), enabling it to operate below the negative pressure standard of 2.5 Pascal. In addition, the AIR ZIPPER® is equipped with air intake valves that open and close in a single direction towards the inside of the tent. Prior to the introduction of the AIR ZIPPER®, staff had to wear PPE with an N95 mask when operating the machine, puncturing and returning blood to the patient. Method Patients with a fever or who have been in contact with COVID-19 patients and infected patients were asked to enter the AIRZIPPER®. The haemodialysis machine is placed outside. The zipper of the AIRZIPPER® could not be closed until the puncture procedure had been completed. To reduce the spread of viruses outside the tent, the high air volume (air flow rate 0.9 m3/min) allows a one-way air flow from the outside to the inside. Following the puncture, the tent zipper was sealed and the air pressure was adjusted to reach the recommended negative pressure of 2.5 Pa and above within 1 minute. Furthermore, the hypochlorous acid mist with CLFine® has the ability to disinfect viruses from the outside of the AIR ZIPPER®. Therefore, after the 30 minutes with the zip closed in the isolation room, the outside of the AIR ZIPPER® was operated as a safe zone. Results On 13 January 2022, two pieces of equipment arrived at the Toshin Clinic and all patients carrying COVID-19 who subsequently developed the disease were isolated and haemodialysed. Quarantine dialysis was performed in 156 patients, including those who had close contact with a COVID-19 patient or who had fever. A total of 96 isolation haemodialysis sessions using AIR ZIPPER® and CL Fine® were performed on 22 COVID-19 patients (male/female: 19/3, age: 69.8 ± 14.2 years, HD duration: 5.38 ± 3.8 years) with SARS-CoV-2 infection in our clinic. Fortunately, there was no transmission to staff or other patients, and no patients died. Conclusion These infection control measures helped to reduce staff workload and prevent infections. In conclusion, the present method should be equipped by all haemodialysis providers to deal with Covid 19 infections as well as with new infections in the future.

88 Microplastic References for Inhalation Studies

Abstract Microplastic research has been increasing due to the uncertainty of potential effects on the environment and human health. However, microplastic references are currently missing. Not only is there a lack of references there is also a lack of diversity in polymer type for references, especially in toxicological studies. In specific, inhalation studies must rely on microplastics that are respirable and/or inhalable (< 10 µm) to result in toxicological outcomes. Therefore, in this project, we focus on using solvent precipitation to produce microplastic references from TPU, PA-6, PET, and LDPE for microplastic inhalation toxicity studies. Particle size distribution of the dispersion is used to verify that the desired size range is achieved. To demonstrate that the produced microplastic references are representative from its original material, molecular and particle descriptors are characterized. Chemical composition, molecular weight, crystallinity, solidity, density, are among the descriptors tested for both the produced microplastic references and its corresponding commercial counterpart. Preliminary results have shown that quantities needed for in-vitro testing and particle size range desired is achieved with successful production of sub-100 nm constituent particle counts and all-respirable mass-based diameters. SEM images confirm the size distribution and show distribution of particle shapes. Chemical composition via spontaneous Raman Scattering illustrates clear polymer spectra signals from the microplastic dispersions. These microplastic reference materials are complemented by toxicology controls. In addition, the in-vitro screening uses both submersed and air-liquid interface cultures to expose cells. This study will thus provide information on microplastic material descriptors relevant for inhalation toxicity.

Targeted delivery of ursolic acid and oleanolic acid to lungs in the form of an inhaler for the management of tuberculosis: Pharmacokinetic and toxicity assessment.

Ursolic acid (UA) and oleanolic acid (OA) are triterpenoids. They are used to treat numerous diseases, including tuberculosis. Combinations of these drugs provide new insight into the management of tuberculosis. The major obstacle is the effective delivery of these drugs to the lungs, which are mainly affected due to M. tuberculosis. A metered-dose inhaler (MDI) was developed to address this issue containing UA and OA, followed by in-vitro and in-vivo evaluation. In the present study, MDI formulation was prepared by incorporating UA and OA at the dose level of 120 μg/ml in each actuation. In-vitro evaluation of this MDI formulation was performed to ensure its suitability to deliver UA and OA preciously. With prior approval of IAEC, a pharmacokinetic and acute inhalation toxicity study was conducted using MDI on Wistar rats. The pharmacokinetic study showed an increased biological half-life of UA (9.23±0.104 h) and OA (8.93±0.166 h) in combination therapy. In-vivo toxicity study demonstrated no adverse effects on body weight and vital organs in the treatment group compared with the control group. Histopathology examination of these essential organs showed no abnormalities. Mild alternation in the biochemical and hematological parameters was observed. However, these alterations did not affect the overall health of the animals. The present study documents a detailed study for the safety and pharmacokinetics of UA and OA in-vivo for their advanced application in tuberculosis disease.

The effects of 4-week inhalation exposure to titanium nitride on lungs of Sprague-Dawley rats.

Titanium nitride (TiN) is a ceramic material with physical properties such as extreme hardness, high decomposition temperature, defect structure, and gold-yellow color. TiN is generally considered non-toxic and safe; however, hazards have not been identified, especially in workers after inhalation exposure. Here, we conducted a four-week inhalation toxicity study of TiN using a nose-only inhalation exposure system in Sprague-Dawley rats. Rats were exposed to TiN for 4 weeks (6h a day, 5 days per week) at target concentrations of 45, 90, and 180mg/m3. Clinical signs, mean body weight changes, hematology, blood biochemistry, necropsy, organ weight, bronchoalveolar lavage fluid analysis, and histopathological findings were observed. Analytical concentrations of the low, middle, and high-concentration groups were 45.55 ± 3.18mg/m3, 90.69 ± 7.30mg/m3, and 183.87 ± 15.21mg/m3, respectively. The mass median aerodynamic diameter (MMAD) for the low, middle, and high-concentration groups were 1.44 ± 0.07μm, 1.47 ± 0.18μm, and 1.68 ± 0.16μm, and the geometric standard deviation (GSD) was 2.24 ± 0.03, 2.31 ± 0.16, and 2.43 ± 0.11, respectively. No systemic adverse effects were observed after inhalation exposure to TiN; however, histopathological findings (increased phagocytic macrophages and alveolar/bronchiolar epithelial hyperplasia) and Bronchoalveolar Lavage Fluid (BALF) analysis (elevated lactate dehydrogenase and gamma-glutamyltransferase values) showed adverse effects on the lungs in the middle and high-concentration groups. Based on these results, the no observed adverse effect concentration (NOAEC) is suggested to be 45mg/m3.

Sodium dichloroisocyanurate toxicity in rats during a 90-day inhalation toxicity study

Sodium dichloroisocyanurate-96% (NaDCC) is commonly used to treat drinking water, industrial water, and wastewater. However, exposure to NaDCC by inhalation can have toxic pulmonary effects in humans. In the present study, we evaluated the potential toxicity of NaDCC following a 90-day inhalation toxicity study in Sprague-Dawley/Crl:CD (SD) rats. The animals were exposed to 0.4, 2.0, or 10.0 mg/m3 NaDCC for 90 days. In addition, male and female rats from the 10.0 mg/m3 group were set up as the recovery group for 14 days. The bronchoalveolar lavage fluid showed a concentration-dependent increase in the total cell count, with a significant increase in neutrophils in both the sexes in the 10.0 mg/m3 group compared to the negative control group. In the 10.0 mg/m3 group, lung organ weight was significantly increased among the female rats. Histopathological examination showed eosinophilic droplets in the olfactory/respiratory epithelium, mucous cell hyperplasia, atrophy/degeneration of the tracheal branches, and wall thickening of the alveolar ducts in the nasal cavity of both sexes in the 10.0 mg/m3 group. The adverse effects of NaDCC exposure were observed to decrease during the 14-day recovery period in both sexes. Based on pathological observations, the “no observed adverse effect concentration (NOAEC)” of inhaled NaDCC was 2.0 mg/m3 for both sexes. These results are expected to provide a scientific basis for inhalation toxicity data of NaDCC.

Combined biological effects and lung proteomics analysis in mice reveal different toxic impacts of electronic cigarette aerosol and combustible cigarette smoke on the respiratory system.

Combustible cigarettes produce many toxic substances that have been linked to diseases, such as lung cancer and chronic obstructive pulmonary disease. For those smokers unable or unwilling to quit, electronic cigarettes (e-cigarettes) could be used as an alternative to cigarettes. However, the effects and mechanisms of e-cigarette aerosol (ECA) on respiratory function have not been fully elucidated, and in vivo studies of its safety are limited compared to cigarette smoke (CS). In this article, we chose nicotine levels as dosing references and C57BL/6 mice for a 10-week subchronic inhalation toxicity study. A comprehensive set of toxicological endpoints was used to study the effect of exposure. Both CS (6 mg/kg) and ECA (6 or 12 mg/kg) inhalation had decreased the animal’s lung function and increased levels of inflammation markers, along with pathological changes in the airways and lungs, with ECA displaying a relatively small effect at the same dose. Proteomic analysis of lung tissue showed greater overall protein changes by CS than that of ECA, with more severe inflammatory network perturbations. Compared with ECA, KEGG analysis of CS revealed upregulation of more inflammatory and virus-related pathways. Protein–protein interactions (PPI) showed that both ECA and CS significantly changed ribosome and complement system-related proteins in mouse lung tissue. The results support that e-cigarette aerosol is less harmful to the respiratory system than cigarette smoke at the same dose using this animal model, thus providing additional evidence for the relative safety of e-cigarettes.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00204-022-03378-z.

Acute, repeated inhalation toxicity, respiratory system irritation, and mutagenicity studies of 1,1,2,2-tetrafluoroethane (HFC-134) as the impurity in the pharmaceutical propellant 1,1,1,2-tetrafluoroethane (HFA-134a)

HFC-134 is the main impurity of HFA-134a. In order to verify the rationality of HFC-134 limits in HFA-134a and ensure the safety of HFA-134a as propellant in pharmaceutical metered-dose inhalers, acute inhalation toxicity, seven-day repeat dose inhalation irritation study, 21-day repeat dose inhalation toxicity study and reverse mutation assay of HFC-134 were tested to evaluate its inhalation safety. In acute inhalation studies, Sprague-Dawley rats were exposed nose-only to HFC-134 at levels of 100 000, 200 000, 400 000, 600 000, and 800 000 ppm for 4 h. Based on the mortality incidence, the calculated four-hour LC50 value for HFC-134 is 532 069 ppm for males and 502 058 ppm for females and acute inhalation toxicity is manifested as the lung lobes turn dark red. Exposures to 836 ± 67 ppm for 4 hours/day 7 days/week continuously did not induce local irritation of the respiratory system in Sprague-Dawley rats. Sprague-Dawley rats were exposed nose-only to HFC-134 at levels of 0 (control), 203 929 ppm and 394 871 ppm 2 h/day for 21 consecutive days, no significant treatment-related adverse effects was noted. Results from Ames studies demonstrated that HFC-134 was not mutagenic. Although HFC-134 has a very low acute inhalation toxicity, considering that its acute inhalation toxicity is higher than that of HFA-134a, and due to the high frequency of use of MDI by asthma patients, acceptance criteria of HFC-134 as the impurity in aerosol propellant HFA-134a should be lower than 8-h TWA WEEL value of 1000 ppm to ensure the safety of the MDI.