Toxicologic significance of histologic change in the larynx of the rat following inhalation exposure: a critical review

Differences in the anatomy and physiology of the human and rat respiratory tracts and impact on toxicological assessments

Inhalation is a critical route through which substances can exert adverse effects in humans; therefore, it is important to characterize the potential effects that inhaled substances may have on the human respiratory tract by using fit for purpose, reliable, and human relevant testing tools. In regulatory toxicology testing, rats have primarily been used to assess the effects of inhaled substances as they-being mammals-share similarities in structure and function of the respiratory tract with humans. However, questions about inter-species differences impacting the predictability of human effects have surfaced. Disparities in macroscopic anatomy, microscopic anatomy, or physiology, such as breathing mode (e.g., nose-only versus oronasal breathing), airway structure (e.g., complexity of the nasal turbinates), cell types and location within the respiratory tract, and local metabolism may impact inhalation toxicity testing results. This review shows that these key differences describe uncertainty in the use of rat data to predict human effects and supports an opportunity to harness modern toxicology tools and a detailed understanding of the human respiratory tract to develop testing approaches grounded in human biology. Ultimately, as the regulatory purpose is protecting human health, there is a need for testing approaches based on human biology and mechanisms of toxicity.

Conventional and multi-omics assessments of subacute inhalation toxicity due to propylene glycol and vegetable glycerin aerosol produced by electronic cigarettes

Propylene glycol (PG) and vegetable glycerin (VG) are the most common solvents used in electronic cigarette liquids. No long-term inhalation toxicity assessments have been performed combining conventional and multi-omics approaches on the potential respiratory effects of the solvents in vivo. In this study, the systemic toxicity of aerosol generated from a ceramic heating coil-based e-cigarette was evaluated. First, the aerosol properties were characterized, including carbonyl emissions, the particle size distribution, and aerosol temperatures. To determine toxicological effects, rats were exposed, through their nose only, to filtered air or a propylene glycol (PG)/ glycerin (VG) (50:50, %W/W) aerosol mixture at the target concentration of 3 mg/L for six hours daily over a continuous 28-day period. Compared with the air group, female rats in the PG/VG group exhibited significantly lower body weights during both the exposure period and recovery period, and this was linked to a reduced food intake. Male rats in the PG/VG group also experienced a significant decline in body weight during the exposure period. Importantly, rats exposed to the PG/VG aerosol showed only minimal biological effects compared to those with only air exposure, with no signs of toxicity. Moreover, the transcriptomic, proteomic, and metabolomic analyses of the rat lung tissues following aerosol exposure revealed a series of candidate pathways linking aerosol inhalation to altered lung functions, especially the inflammatory response and disease. Dysregulated pathways of arachidonic acids, the neuroactive ligand-receptor interaction, and the hematopoietic cell lineage were revealed through integrated multi-omics analysis. Therefore, our integrated multi-omics approach offers novel systemic insights and early evidence of environmental-related health hazards associated with an e-cigarette aerosol using two carrier solvents in a rat model.

Subchronic inhalation of a novel electronic nicotine delivery system formulation and its corresponding base formulation

BACKGROUND

Fresh Menthol 3% Nicotine (FM3) is a novel JUUL e-liquid formulation. Its potential toxicity and that of the corresponding base formulation relative to a filtered air (FA) control was studied in a subchronic inhalation study conducted in general accordance with OECD 413.

METHODS

Aerosols generated with an intense puffing regime were administered to rats in a nose-only fashion at 1400 µg aerosol collected mass/L on a 6 hour/day basis for 90 days with a 42-day recovery. Exposure atmospheres met target criteria. Systemic exposure was confirmed by plasma measurement of nicotine.

RESULTS

No test article-related mortality, clinical signs (other than reversible lower body weight gains in males), clinical pathology or gross findings were noted during this study. No microscopic lesions related to base formulation exposure were identified. Minimal microscopic lesions were observed in the FM3 6-hour exposure group. Microscopic lesions observed in the FM3 6-hour exposure group comprised only minimal laryngeal squamous metaplasia in one male and one female animal. No microscopic lesions related to FM3 exposure remained after the recovery period.

CONCLUSION

Exposure atmosphere characterization indicated that conditions were achieved to permit thorough assessment of test articles and results indicate a low order of toxicity for the FM3 Electronic nicotine delivery systems (ENDS) formulation and its base formulation.

Assessment of inhalation toxicity of cigarette smoke and aerosols from flavor mixtures: 5-week study in A/J mice

Most flavors used in e-liquids are generally recognized as safe for oral consumption, but their potential effects when inhaled are not well characterized. In vivo inhalation studies of flavor ingredients in e-liquids are scarce. A structure-based grouping approach was used to select 38 flavor group representatives (FGR) on the basis of known and in silico-predicted toxicological data. These FGRs were combined to create prototype e-liquid formulations and tested against cigarette smoke (CS) in a 5-week inhalation study. Female A/J mice were whole-body exposed for 6 h/day, 5 days/week, for 5 weeks to air, mainstream CS, or aerosols from (1) test formulations containing propylene glycol (PG), vegetable glycerol (VG), nicotine (N; 2% w/w), and flavor (F) mixtures at low (4.6% w/w), medium (9.3% w/w), or high (18.6% w/w) concentration or (2) base formulation (PG/VG/N). Male A/J mice were exposed to air, PG/VG/N, or PG/VG/N/F-high under the same exposure regimen. There were no significant mortality or in-life clinical findings in the treatment groups, with only transient weight loss during the early exposure adaptation period. While exposure to flavor aerosols did not cause notable lung inflammation, it caused only minimal adaptive changes in the larynx and nasal epithelia. In contrast, exposure to CS resulted in lung inflammation and moderate-to-severe changes in the epithelia of the nose, larynx, and trachea. In summary, the study evaluates an approach for assessing the inhalation toxicity potential of flavor mixtures, thereby informing the selection of flavor exposure concentrations (up to 18.6%) for a future chronic inhalation study.

Mainstream Cigarette Smoke Impacts the Mouse Vocal Fold Epithelium and Mucus Barrier

OBJECTIVES/HYPOTHESIS

Cigarette smoke (CS) is a primary risk factor for the development of numerous benign and malignant laryngeal diseases. The epithelium and mucus lining the vocal folds (VF) are the first barriers against CS. The primary objective of this study was to investigate epithelial and mucus barrier changes in the mouse laryngeal mucosa upon exposure to subacute CS. The secondary objective was to compare mucus barrier changes in mice and human smokers and nonsmokers. Study Design Animal model.

METHODS

Mice were exposed to CS for 4 weeks for 4 hours (N = 12, high dose [HD]) or 1 hour (N = 12, low dose [LD]) per day. Air-exposed mice were used as a control group (N = 10). Larynges were harvested and VF epithelial barrier integrity was evaluated including cellular proliferation and expression of cell junctions. We also investigated mucus production by examining mucus cell area and mucin expression in mice and human smokers and nonsmokers.

RESULTS

HD CS increased VF epithelial cellular proliferation but did not alter the expression of cell junctions. HD CS also induced hypertrophy of the mucus-producing submucosal glands. However, only LD CS increased MUC5AC gene expression. MUC5AC staining appeared elevated in laryngeal specimens from smokers, but this was not significant as compared to nonsmokers.

CONCLUSIONS

These findings help us identify potential adaptive mechanisms to CS exposure as well as set the foundation for further study of key aspects of epithelial and mucus barrier integrity that may be implicated in laryngeal disease development following prolonged smoking.

LEVEL OF EVIDENCE

NA Laryngoscope, 131:2530-2539, 2021.

Respiratory Effects of Exposure to Aerosol From the Candidate Modified-Risk Tobacco Product THS 2.2 in an 18-Month Systems Toxicology Study With A/J Mice

Smoking cessation is the most effective measure for reducing the risk of smoking-related diseases. However, switching to less harmful products (modified-risk tobacco products [MRTP]) can be an alternative to help reduce the risk for adult smokers who would otherwise continue to smoke. In an 18-month chronic carcinogenicity/toxicity study in A/J mice (OECD Test Guideline 453), we assessed the aerosol of Tobacco Heating System 2.2 (THS 2.2), a candidate MRTP based on the heat-not-burn principle, compared with 3R4F cigarette smoke (CS). To capture toxicity- and disease-relevant mechanisms, we complemented standard toxicology endpoints with in-depth systems toxicology analyses. In this part of our publication series, we report on integrative assessment of the apical and molecular exposure effects on the respiratory tract (nose, larynx, and lungs). Across the respiratory tract, we found changes in inflammatory response following 3R4F CS exposure (eg, antimicrobial peptide response in the nose), with both shared and distinct oxidative and xenobiotic responses. Compared with 3R4F CS, THS 2.2 aerosol exerted far fewer effects on respiratory tract histology, including adaptive tissue changes in nasal and laryngeal epithelium and inflammation and emphysematous changes in the lungs. Integrative analysis of molecular changes confirmed the substantially lower impact of THS 2.2 aerosol than 3R4F CS on toxicologically and disease-relevant molecular processes such as inflammation, oxidative stress responses, and xenobiotic metabolism. In summary, this work exemplifies how apical and molecular endpoints can be combined effectively for toxicology assessment and further supports findings on the reduced respiratory health risks of THS 2.2 aerosol.

Short-term whole body cigarette smoke exposure induces regional differences in cellular response in the mouse larynx

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Short-term CSE induced regional differences in murine laryngeal cellular responses.

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Basal cell hyperplasia accompanies adaptive cell proliferation in the vocal folds.

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Increased subglottic cell proliferation persists even after CS cessation.

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SEM revealed vocal fold microprojection damage with possible necrotic features.

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Subglandular acidic mucins decreased and neutral mucins increased post-CSE.

The larynx is an essential organ in the respiratory tract and necessary for airway protection, respiration, and phonation. Cigarette smoking is a significant risk factor associated with benign and malignant laryngeal diseases. Despite this association, the underlying mechanisms by which cigarette smoke (CS) drives disease development are not well elucidated. In the current study, we developed a short-term murine whole body inhalation model to evaluate the first CS-induced cellular responses in the glottic [i.e. vocal fold (VF)] and subglottic regions of the larynx. Specifically, we investigated epithelial cell proliferation, cell death, surface topography, and mucus production, at various time points (1 day, 5 days, 10 days) after ∼ 2 h exposure to 3R4F cigarettes (Delivered dose: 5.6968 mg/kg per cigarette) and following cessation for 5 days after a 5 day CS exposure (CSE). CSE elevated levels of BrdU labeled proliferative cells and p63 labeled epithelial basal cells on day 1 in the VF. CSE increased proliferative cells in the subglottis at days 5, 10 and following cessation in the subglottis. Cleaved caspase-3 apoptotic activity was absent in VF at all time points and increased at day 1 in the subglottis. Evaluation of the VF surface by scanning electron microscopy (SEM) revealed significant epithelial microprojection damage at day 10 and early signs of necrosis at days 5 and 10 post-CSE. SEM visualizations additionally indicated the presence of deformed cilia at days 5 and 10 after CSE and post-cessation in the respiratory epithelium lined subglottis. In terms of mucin content, the impact of short-term CSE was observed only at day 10, with decreasing acidic mucin levels and increasing neutral mucin levels. Overall, these findings reveal regional differences in murine laryngeal cellular responses following short-term CSE and provide insight into potential mechanisms underlying CS-induced laryngeal disease development.

Multisite Analysis of Lesions in the Respiratory Tract of the Rat and Nonhuman Primate (Cynomolgus Monkey) Exposed to Air, Vehicle, and Inhaled Small Molecule Compounds

This paper presents a review of the nature, range, and incidences of background pathology findings in the respiratory tract of cynomolgus monkeys and rats. Data were collected from 81 inhalation studies and 133 non-inhalation studies evaluated at 3 geographically distinct contract research organization facilities. The inhalation studies were comprised of 44 different small molecule pharmaceuticals or chemicals which were also analyzed in order to understand the patterns of induced changes within the respiratory tract. The lung was the most frequently affected organ in both species, with increased alveolar macrophages being the most common background and test article-related finding. In the upper respiratory tract (URT), inflammatory cell infiltrates were the most common background findings in the nasal cavity in monkeys. Induced URT findings were more frequent in rats than monkeys, with squamous metaplasia in the larynx, and goblet cell hyperplasia in the nasal cavity being the most common. Overall, the data revealed a limited pattern of response to inhaled molecules in the respiratory tract, with background and test article-related findings often occurring in the same regions. It is hoped that these data will assist in the interpretation of findings in the respiratory tract induced by novel inhaled small molecule entities.

Epithelial Alteration Associated With Recovery From Laryngeal Squamous Metaplasia in Rats: Kinetics of Recovery From a Test Item-Related Change

Squamous metaplasia is a nonspecific adaptive response to chronic irritation in the larynx and is often diagnosed as a test item-related change in rat inhalation studies. Investigating scientists are frequently asked to assess the adversity of laryngeal squamous metaplasia and to interpret its relevance to human risk. One factor in predicting relevance to human risk is the kinetics (degree and speed) of recovery following the cessation of exposure to the test item. Most reports describing recovery from squamous metaplasia in the rat larynx discuss the more severe end of the spectrum of metaplastic change (moderate to severe) and include relatively long (6 weeks or more) recovery periods. We conducted 2 studies to evaluate the toxicity and recovery from any potential effects of 4-(Chloro-2-methylphenoxy) butyric (MCPB) acid, a herbicide, when administered by inhalation to young male Sprague Dawley rats for 3 to 4 weeks. The studies resulted in minimal to moderate laryngeal squamous metaplasia for which we describe the kinetics of recovery over 1 to 4 weeks. We found that the microscopic change epithelial alteration, which is normally considered to be a precursor in the development of squamous metaplasia, can occur as a transitional stage between squamous and normal epithelium during recovery.

Evaluation of toxicity of aerosols from flavored e-liquids in Sprague-Dawley rats in a 90-day OECD inhalation study, complemented by transcriptomics analysis

The use of flavoring substances is an important element in the development of reduced-risk products for adult smokers to increase product acceptance and encourage switching from cigarettes. In a first step towards characterizing the sub-chronic inhalation toxicity of neat flavoring substances, a study was conducted using a mixture of the substances in a base solution of e-liquid, where the standard toxicological endpoints of the nebulized aerosols were supplemented with transcriptomics analysis. The flavor mixture was produced by grouping 178 flavors into 26 distinct chemical groups based on structural similarities and potential metabolic and biological effects. Flavoring substances predicted to show the highest toxicological effect from each group were selected as the flavor group representatives (FGR). Following Organization for Economic Cooperation and Development Testing Guideline 413, rats were exposed to three concentrations of the FGR mixture in an e-liquid composed of nicotine (23 µg/L), propylene glycol (1520 µg/L), and vegetable glycerin (1890 µg/L), while non-flavored and no-nicotine mixtures were included as references to identify potential additive or synergistic effects between nicotine and the flavoring substances. The results indicated that the inhalation of an e-liquid containing the mixture of FGRs caused very minimal local and systemic toxic effects. In particular, there were no remarkable clinical (in-life) observations in flavored e-liquid-exposed rats. The biological effects related to exposure to the mixture of neat FGRs were limited and mainly nicotine-mediated, including changes in hematological and blood chemistry parameters and organ weight. These results indicate no significant additive biological changes following inhalation exposure to the nebulized FGR mixture above the nicotine effects measured in this sub-chronic inhalation study. In a subsequent study, e-liquids with FGR mixtures will be aerosolized by thermal treatment and assessed for toxicity.

A 90-day OECD TG 413 rat inhalation study with systems toxicology endpoints demonstrates reduced exposure effects of the aerosol from the carbon heated tobacco product version 1.2 (CHTP1.2) compared with cigarette smoke. I. Inhalation exposure, clinical pathology and histopathology

Within the framework of a systems toxicology approach, the inhalation toxicity of aerosol from a novel tobacco-heating potentially modified risk tobacco product (MRTP), the carbon-heated tobacco product (CHTP) 1.2, was characterized and compared with that of mainstream smoke (CS) from the 3R4F reference cigarette in a 90-day nose-only rat inhalation study in general accordance with OECD TG 413. CHTP1.2 is a heat-not-burn product using a carbon heat source to produce an aerosol that contains nicotine and tobacco flavor. At equal or twice the nicotine concentration in the test atmospheres, inhalation of CHTP1.2 aerosol led to a significantly lower exposure to harmful constituents and induced less respiratory tract irritation, systemic, and pathological effects compared with CS. Nasal epithelial changes were less pronounced in the CHTP1.2- than in the CS-exposed groups and reverted in the nicotine concentration-matched group after a recovery period. Lung inflammation was minimal in the CHTP1.2-treated groups compared with the moderate extent seen in the 3R4F groups. Many other toxicological endpoints evaluated did not show CHTP1.2 aerosol exposure-related effects, and no effects not seen for 3R4F were observed. These observations were consistent with findings from previous studies in which rats were exposed to MRTP aerosols containing similar nicotine concentrations.

Toxicity of the main electronic cigarette components, propylene glycol, glycerin, and nicotine, in Sprague-Dawley rats in a 90-day OECD inhalation study complemented by molecular endpoints

While the toxicity of the main constituents of electronic cigarette (ECIG) liquids, nicotine, propylene glycol (PG), and vegetable glycerin (VG), has been assessed individually in separate studies, limited data on the inhalation toxicity of them is available when in mixtures. In this 90-day subchronic inhalation study, Sprague-Dawley rats were nose-only exposed to filtered air, nebulized vehicle (saline), or three concentrations of PG/VG mixtures, with and without nicotine. Standard toxicological endpoints were complemented by molecular analyses using transcriptomics, proteomics, and lipidomics. Compared with vehicle exposure, the PG/VG aerosols showed only very limited biological effects with no signs of toxicity. Addition of nicotine to the PG/VG aerosols resulted in effects in line with nicotine effects observed in previous studies, including up-regulation of xenobiotic enzymes (Cyp1a1/Fmo3) in the lung and metabolic effects, such as reduced serum lipid concentrations and expression changes of hepatic metabolic enzymes. No toxicologically relevant effects of PG/VG aerosols (up to 1.520  mg PG/L + 1.890 mg VG/L) were observed, and no adverse effects for PG/VG/nicotine were observed up to 438/544/6.6 mg/kg/day. This study demonstrates how complementary systems toxicology analyses can reveal, even in the absence of observable adverse effects, subtoxic and adaptive responses to pharmacologically active compounds such as nicotine.

Pulmonary Toxicity of Benzalkonium Chloride

The available toxicity data of benzalkonium chloride (BKC) clearly shows that it is toxic; however, the weight of evidence favors the view that at doses encountered in nasally and orally inhaled pharmaceutical preparations it is well tolerated. The adverse toxicological data predominantly come from in vitro and animal studies in which doses and exposure periods employed were excessive in relation to the clinical doses and their posology and, therefore, not directly applicable to the clinic. The conflict between the in vitro and animal data and the clinical experience can be reconciled by understanding some of the physicochemical properties of BKC, the nasal and respiratory tract microenvironments, the doses used, and the posology.

A Comparison of Rodent and Nonrodent Laryngeal and Tracheal Bifurcation Sensitivities in Inhalation Toxicity Studies and Their Relevance for Human Exposure

In inhalation toxicity studies, drug-induced lesions are frequently reported in the larynx and sometimes at the tracheal bifurcation (carina) in the rat, but less so in the dog or monkey, bringing into question the relevance of these rodent findings for humans. The rat larynx is widely considered to be more sensitive than that of the dog and monkey in its response to inhaled xenobiotics, although we could find no published data to support this. In this review, data from 52 inhalation studies involving rodent and nonrodent species were collated and reviewed. These data showed that the rodent larynx, and to a lesser extent the carina, was far more commonly affected by treatment than those of the nonrodent. This review indicates the greater susceptibility of the rodent larynx and carina and emphasizes their lack of relevance for man. Observations and data suggest that the human larynx is much closer to the beagle dog and cynomolgus monkey in its response to inhaled xenobiotics and that greater clinical relevance should be placed on any specific findings in these animal models.

Is It Adverse, Nonadverse, Adaptive, or Artifact?

One of the principal challenges facing a toxicologic pathologist is to determine and differentiate a true adverse effect from a nonadverse or an adaptive response. Recent publications from the Society of Toxicologic Pathology (STP) and the European STP provide guidance for determining and communicating adversity in nonclinical toxicology studies. In order to provide a forum to inform and engage in a discussion on this important topic, a continuing education (CE) course was held during the 2016 STP Annual meeting in San Diego, CA. The lectures at this course provided guidance on determining and communicating adversity using case studies involving both clinical pathology and anatomic pathology. In addition, one talk also focused on data quality, study design, and interpretation of artifacts that could hinder the determination of adversity. The CE course ended with a talk on understanding adversity in preclinical studies and engaging the regulatory agencies in the decision-making process. This manuscript is designed to provide brief summaries of all the talks in this well-received CE course.

Comparative pulmonary toxicity of inhaled metalworking fluids in rats and mice

Metalworking fluids (MWFs) are complex formulations designed for effective lubricating, cooling, and cleaning tools and parts during machining operations. Adverse health effects such as respiratory symptoms, dermatitis, and cancer have been reported in workers exposed to MWFs. Several constituents of MWFs have been implicated in toxicity and have been removed from the formulations over the years. However, animal studies with newer MWFs demonstrate that they continue to pose a health risk. This investigation examines the hypothesis that unrecognized health hazards exist in currently marketed MWF formulations that are presumed to be safe based on hazard assessments of individual ingredients. In vivo 13-week inhalation studies were designed to characterize and compare the potential toxicity of four MWFs: Trim VX, Cimstar 3800, Trim SC210, and Syntilo 1023. Male and female Wistar Han rats or Fischer 344N/Tac rats and B6C3F1/N mice were exposed to MWFs via whole-body inhalation at concentrations of 0, 25, 50, 100, 200, or 400 mg/m³ for 13 weeks, after which, survival, body and organ weights, hematology and clinical chemistry, histopathology, and genotoxicity were assessed following exposure. Although high concentrations were used, survival was not affected and toxicity was primarily within the respiratory tract of male and female rats and mice. Minor variances in toxicity were attributed to differences among species as well as in the chemical components of each MWF. Pulmonary fibrosis was present only in rats and mice exposed to Trim VX. These data confirm that newer MWFs have the potential to cause respiratory toxicity in workers who are repeatedly exposed via inhalation.

Symposium Summary: "Breathe In, Breathe Out, Its Easy: What You Need to Know About Developing Inhaled Drugs"

Developing inhaled drugs requires knowledge of lung anatomy, cell biology, respiratory physiology, particle physics, and some plumbing. Although dose makes the poison, in the context of an inhaled drug, the "dose" is not easily defined. This lack of clarity around dose poses issues and challenges in the design of inhalation toxicology programs. To better understand dose, the influence of ventilation is discussed as are the perturbations in pulmonary function observed with inhalation exposure that can affect dose. Methods for determining inhaled drug deposition to arrive at an estimate of lung dose are examined. Equally important to understanding dose are the techniques used to deliver aerosols to animals. With a better understanding of dose and inhalation exposure, species-specific histopathologic lesions, both common background and toxicologically significant lesions, are reviewed. Finally, insight into how regulators synthesize and evaluate these complex findings to assess clinical safety risks is presented.

Nanostructured calcium silicate hydrate seeds accelerate concrete hardening: a combined assessment of benefits and risks

Nanotechnology creates new possibilities to control and improve material properties for civil infrastructure. Special focus in this area is put on Portland cement and gypsum. Together their annual production is by far larger than for any other material worldwide. Nanomodification of these materials can be done during the few hours between dissolution and hardening, especially by nucleation of the re-crystallization with suitable colloids. Here we report first results in homogeneous seeding of the precipitation of calcium silicate hydrates within a real Portland cement composition. The occupational safety during the production phase and during mixing of concrete paste is addressed in detail by in vivo testing. We perform 5-day inhalation with 21-day recovery in rats and analyze organ-specific toxicity and 71 endpoints from bronchoalveolar lavage (BALF) and blood. In BALF parameters, no test-related changes were observed, indicating the generally low toxicity of the test material. Some mild lesions were observed in larynx level. In the lungs, all animals of the 50 mg/m³ concentration group revealed a minimal to mild increase in alveolar macrophages, which recovered back to control level.

Presence of task-1 channel in the laryngeal mucosa in the newborn lamb

Nearly 40 potassium channels have been described in respiratory epithelial cells. Of these are found several members of the 4-transmembrane domain, 2-pore K(+) channel family (K2P family), namely Twik-1 and -2, Trek-1 and -2, Task-2, -3, and -4, Thik-1, and KCNK7. The aim of this study was to verify whether the Twik-related acid-sensitive K(+) channel, subtype 1 (Task-1) (also known as KCNK3), is present in the laryngeal mucosa in the newborn lamb. Through the use of immunohistochemistry and nested polymerase chain reaction (PCR) amplification, results indicate that Task-1 protein and mRNA are present in the laryngeal mucosa, in both the ciliated, pseudostratified columnar (respiratory) epithelium and the nonkeratinized, stratified squamous epithelium. The complete ovine Task-1 protein sequence showed high homology levels with previously reported mouse, bovine, and human Task-1 sequences. This includes a complete homology for the C-terminal amino acid sequence, which is mandatory for protein trafficking to the cell membrane. These results represent the first demonstration that Task-1, a pH-sensitive channel responsible for setting membrane potential, is present in the laryngeal mucosa of a newborn mammal.

Histopathological changes of rat larynx mucosa with exposure to chronic thinner inhalation

Objective: Histopathological changes in nasal mucosa, trachea, and pulmonary system with exposure to chronic thinner inhalation have been studied in the literature. However, the possible changes in larynx mucosa, which is a part of the upper airway tract, have not been studied yet. The aim of this study is to determine the histopathological changes of rat larynx mucosa with exposure to chronic thinner inhalation.

Study Design and Setting: Randomized trial. The study was conducted at the animal care facility of Haydarpasa Numune Education and Research Hospital.

Subjects and Methods: Fifty-one Sprague-Dawley rats were used throughout the experiment. Four groups of rats inhaled thinner in a glass cage for 2, 4, 8, and 12 weeks respectively. Seven rats inhaled only the air in the room as the control group.

Results: The comparison of inflammation and exocytosis in the control and 2 week groups revealed no significant difference ( P > 0.05), but from the beginning of 4 weeks of thinner inhalation, statistically significant differences were observed ( P < 0.05). From the beginning of 8 weeks of thinner inhalation, statistically significant differences were observed in larynx mucosa when we assessed metaplasia and cilia loss distribution among groups ( P < 0.05).

Conclusion: On the basis of histopathological evaluations, it was shown that the harmful effect of inhalation of thinner in high concentrations to larynx mucosa is similar to the effect on other organs of the respiratory system.

The inhalation toxicity of di- and triethanolamine upon repeated exposure

Systemic and respiratory tract (RT) toxicity of triethanolamine (TEA) was assessed in a 28-day nose-only inhalation study in Wistar rats (10animals/sex, concentrations: 0, 20, 100, 500mg/m3; 5 days/week, 6h/day). In two nose-only 90-day inhalation studies, with similar exposure design, Wistar rats were exposed to 0, 15, 150, 400mg/m3 diethanolamine (DEA) (DEA Study 1:13animals/sex, general subchronic study) and to 0, 1.5, 3, 8mg/m3 (DEA Study 2:10animals/sex) to specifically investigate respiratory tract toxicity. Only DEA induced systemic toxicity at or above 150mg/m3 (body and organ weight changes, clinical- and histo-pathological changes indicative for mild blood, liver, kidney and testicular effects). Neurotoxicity was not observed for both substances. Exposure to both substances resulted in laryngeal epithelial changes starting from 3mg/m3 for DEA (reversible metaplasia at the base of the epiglottis, inflammation at higher concentrations extending into the trachea) or from 20mg/m3 for TEA (focal inflammation, starting in single male animals). TEA appears to be less potent with respect to systemic toxicity and RT irritancy than DEA. The 90-day no adverse effect concentration" (NOAEC) for changes due to TEA exposure in the respiratory tract was 4.7mg/m3 derived by extrapolation from the NOAEC of the 28day study.