Upper respiratory tract lesions in inhalation toxicology

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

•

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

•

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

•

Increased subglottic cell proliferation persists even after CS cessation.

•

SEM revealed vocal fold microprojection damage with possible necrotic features.

•

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.

Numerical analysis of nanoparticle transport and deposition in a cynomolgus monkey nasal passage

Environmental exposure to toxic agents is commonly encountered by occupational and residential populations. However, in vivo exposure data in human subjects is limited by measurement and ethical restrictions. Monkey represents a suitable surrogate for human exposure studies, but the particle transport and deposition features in monkey airways are still not well understood. As a response to this research challenge, this paper presents a virtual exposure study that numerically investigated the nanoparticle transport process through a realistic cynomolgus monkey nasal airway. Particles with size of 1 nm to 1 μm were considered and the transport process was modelled by the Lagrangian discrete phase model. Overall and local deposition as well as particle dispersion along the airway were examined by using a variety of non-dimensional parameters including combined diffusion parameter, deposition enhancement factor and particle flux enhancement factor. Consistent deposition patterns were observed in present and literature nasal models. Most particles tended to pass the nasal airway through certain spatial regions, including the middle section of the nasal valve, the lower half of the middle coronal plane, and the central regions of the choana. While naturally inhaled nanoparticles can hardly be delivered to the olfactory region as it is located apart from the mainstream with high particle flux. Research findings provide insight into nanoparticle inhalation exposure characteristics in the monkey airway and can contribute in formulating data extrapolation schemes between monkey and human airways.

Evidence of SARS-CoV2 Entry Protein ACE2 in the Human Nose and Olfactory Bulb

Usually, pandemic COVID-19 disease, caused by SARS-CoV2, presents with mild respiratory symptoms such as fever, cough, but frequently also with anosmia and neurological symptoms. Virus-cell fusion is mediated by angiotensin-converting enzyme 2 (ACE2) and transmembrane serine protease 2 (TMPRSS2) with their organ expression pattern determining viral tropism. Clinical presentation suggests rapid viral dissemination to the central nervous system leading frequently to severe symptoms including viral meningitis. Here, we provide a comprehensive expression landscape of ACE2 and TMPRSS2 proteins across human postmortem nasal and olfactory tissue. Sagittal sections through the human nose complemented with immunolabelling of respective cell types represent different anatomically defined regions including olfactory epithelium, respiratory epithelium of the nasal conchae and the paranasal sinuses along with the hardly accessible human olfactory bulb. ACE2 can be detected in the olfactory epithelium as well as in the respiratory epithelium of the nasal septum, the nasal conchae, and the paranasal sinuses. ACE2 is located in the sustentacular cells and in the glandular cells in the olfactory epithelium as well as in the basal cells, glandular cells, and epithelial cells of the respiratory epithelium. Intriguingly, ACE2 is not expressed in mature or immature olfactory receptor neurons and basal cells in the olfactory epithelium. Similarly, ACE2 is not localized in the olfactory receptor neurons albeit the olfactory bulb is positive. Vice versa, TMPRSS2 can also be detected in the sustentacular cells and the glandular cells of the olfactory epithelium. Our findings provide the basic anatomical evidence for the expression of ACE2 and TMPRSS2 in the human nose, olfactory epithelium, and olfactory bulb. Thus, they are substantial for future studies that aim to elucidate the symptom of SARS-CoV2 induced anosmia via the olfactory pathway.

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.

Comparative Effects of 1/4-inch and 1/8-inch Corncob Bedding on Cage Ammonia Levels, Behavior, and Respiratory Pathology of Male C57BL/6 and 129S1/Svlm Mice

Corncob is a common bedding material used in laboratory rodents, but little is known about differences in the effects of the 2 available sizes on rodent models and health. This study compared the effects of these 2 corncob bedding sizes on cage ammonia levels, behavior, and respiratory pathology in mice. We hypothesized that the beddings would not differ significantly in their effects on these parameters. Two strains of male mice (C57BL/6 and 129S1/Svlm) were housed in static, filter-top cages containing 1 of the 2 bedding types for the duration of the study (12 wk). Intracage ammonia was measured during 1 wk of the study on days 0, 3, 5, and 7. Behavior was evaluated by using circadian rhythm, open field, and Morris water-maze tests. Animals were euthanized with injectable euthanasia solution to collect respiratory and ocular tissues for histopathologic lesion scoring. Animals that were euthanized immediately upon arrival from the vendor served as negative controls. Bedding size did not significantly affect behavior or ammonia levels. Average intracage ammonia levels on day 7 were 525 ppm for 1/4-in. bedding and 533 ppm for 1/8-in. bedding. Regardless of the bedding size, lesions noted in both strains of mice were of similar incidence and severity, were limited to the nose, and consisted of minimal to mild suppurative rhinitis. The eyes, trachea, and lungs were not affected. In conclusion, 1/4-in. and 1/8-in. corncob beddings have comparable effects on cage ammonia levels and the behavior and respiratory pathology in male mice of the strains tested.

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.

Inhalation toxicity of benzalkonium chloride and triethylene glycol mixture in rats

Benzalkonium chloride (BAC), a disinfectant, and triethylene glycol (TEG), an organic solvent/sanitizer, are frequently combined in commercially available household sprays. To assess the respiratory effect of this combination, Sprague-Dawley rats were exposed to an aerosol containing BAC (0.5%, w/v) and TEG (10%, w/v) for up to 2 weeks in a whole-body inhalation chamber. BAC (4.1-4.5 mg/m³, sprayed from 0.5% solution) promoted pulmonary cell damage and inflammation as depicted by the increase in total protein, lactate dehydrogenase, polymorphonuclear leukocytes, and macrophage inflammatory protein-2 in the bronchoalveolar lavage fluid, whereas TEG (85.3-94.5 mg/m³, sprayed from 10% solution) did not affect the lung. Rats exposed to the BAC/TEG mixture for 2 weeks showed severe respiratory symptoms (sneezing, wheezing, breath shortness, and chest tightness), but no lung damage or inflammation was observed. However, significant ulceration and degenerative necrosis were observed in the nasal cavities of rats repeatedly exposed to the BAC/TEG mixture. The mass median aerodynamic diameters of the aqueous, BAC, TEG and BAC/TEG aerosols were 1.24, 1.27, 3.11 and 3.24 μm, respectively, indicating that TEG-containing aerosols have larger particles than those of the aqueous and BAC alone aerosols. These results suggest that the toxic effects of BAC and BAC/TEG aerosols on the different respiratory organs may be associated with the difference in particle diameter, since particle size is important in determining the deposition site of inhaled materials.

Immunopathology of the Respiratory System

Respiratory immunity is accomplished using multiple mechanisms including structure/anatomy of the respiratory tract, mucosal defense in the form of the mucociliary apparatus, innate immunity using cells and molecules and acquired immunity. There are species differences of the respiratory immune system that influence the response to environmental challenges and pharmaceutical, industrial and agricultural compounds assessed in nonclinical safety testing and hazard identification. These differences influence the interpretation of respiratory system changes after exposure to these challenges and compounds in nonclinical safety assessment and hazard identification and their relevance to humans.

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.

Normal Anatomy, Histology, and Spontaneous Pathology of the Nasal Cavity of the Cynomolgus Monkey (Macaca fascicularis)

The evaluation of inhalation studies in monkeys is often hampered by the scarcity of published information on the relevant nasal anatomy and pathology. We examined nasal cavities of 114 control cynomolgus monkeys from 11 inhalation studies evaluated 2008 to 2013, in order to characterize and document the anatomic features and spontaneous pathology. Compared to other laboratory animals, the cynomolgus monkey has a relatively simple nose with 2 unbranched, dorsoventrally stacked turbinates, large maxillary sinuses, and a nasal septum that continues into the nasopharynx. The vomeronasal organ is absent, but nasopalatine ducts are present. Microscopically, the nasal epithelium is thicker than that in rodents, and the respiratory (RE) and transitional epithelium (TE) rest on a thick basal lamina. Generally, squamous epithelia and TE line the vestibule, RE, the main chamber and nasopharynx, olfactory epithelium, a small caudodorsal region, while TE is observed intermittently along the passages. Relatively high incidences of spontaneous pathology findings, some resembling induced lesions, were observed and included inflammation, luminal exudate, scabs, squamous and respiratory metaplasia or hyperplasia, mucous cell hyperplasia/metaplasia, and olfactory degeneration. Regions of epithelial transition were the most affected. This information is considered helpful in the histopathology evaluation and interpretation of inhalation studies in monkeys.

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.

A Review of the Comparative Anatomy, Histology, Physiology and Pathology of the Nasal Cavity of Rats, Mice, Dogs and Non-human Primates. Relevance to Inhalation Toxicology and Human Health Risk Assessment

There are many significant differences in the structural and functional anatomy of the nasal cavity of man and laboratory animals. Some of the differences may be responsible for the species-specific nasal lesions that are often observed in response to inhaled toxicants. This paper reviews the comparative anatomy, physiology and pathology of the nasal cavity of the rat, mouse, dog, monkey and man, highlighting factors that may influence the distribution of nasal lesions. Gross anatomical variations such as turbinate structure, folds or grooves on nasal walls, or presence or absence of accessory structures, may influence nasal airflow and species-specific uptake and deposition of inhaled material. In addition, interspecies variations in the morphological and biochemical composition and distribution of the nasal epithelium may affect the local tissue susceptibility and play a role in the development of species-specific nasal lesions. It is concluded that, while the nasal cavity of the monkey might be more similar to that of man, each laboratory animal species provides a model that responds in a characteristic and species-specific manner. Therefore for human risk assessment, careful consideration must be given to the anatomical differences between a given animal model and man.

Toxicity and carcinogenicity studies of Ginkgo biloba extract in rat and mouse: liver, thyroid, and nose are targets

Ginkgo biloba extract (GBE) is a popular herbal supplement that is used to improve circulation and brain function. In spite of widespread human exposure to relatively high doses over potentially long periods of time, there is a paucity of data from animal studies regarding the toxicity and carcinogenicity associated with GBE. In order to fill this knowledge gap, 3-month and 2-year toxicity and carcinogenicity studies with GBE administered by oral gavage to B6C3F1/N mice and F344/N rats were performed as part of the National Toxicology Program's Dietary Supplements and Herbal Medicines Initiative. The targets of GBE treatment were the liver, thyroid, and nose. These targets were consistent across exposure period, sex, and species, albeit with varying degrees of effect observed among studies. Key findings included a notably high incidence of hepatoblastomas in male and female mice and evidence of carcinogenic potential in the thyroid gland of both mice and rats. Various nonneoplastic lesions were observed beyond control levels in the liver, thyroid gland, and nose of rats and mice administered GBE. Although these results cannot be directly extrapolated to humans, the findings fill an important data gap in assessing risk associated with GBE use.

A 26-Week Toxicity Assessment of AIR001 (Sodium Nitrite) by Inhalation Exposure in Rats and by Intravenous Administration in Dogs

Historically, nitrogen oxides (NO_x) in food, drinking water, as well as in the atmosphere have been believed to be associated with adverse health consequences. More recently, NO_x have been implicated in normal homeostatic regulation, and exogenous administration has been associated with health benefits. One such potential health benefit is the prospect that inhaled nitrite will lower pulmonary blood pressure (BP) in patients with pulmonary arterial hypertension (PAH), a disease with poor prognosis due to the lack of effective treatment. To characterize potential chronic toxicity associated with inhaled AIR001 (sodium nitrite) for use in the treatment of PAH, 26-week exposures to AIR001 were carried out by inhalation administration in rats and by intravenous infusion in dogs. The studies revealed that methemoglobinemia was the primary adverse effect in both species. Methemoglobin levels less than 40% were well tolerated in both species, while levels greater than 50% methemoglobin caused death in some rats. Additionally, a decrease in systemic BP was also observed with inhaled AIR001 exposure in dogs. These acute secondary and exaggerated pharmacological effects occurred daily throughout the 26-week treatment period. Chronic exposure did not alter the magnitude of either methemoglobinemia or hypotension or result in additional toxicity or compensatory responses. Based on the exposure levels that produced these pharmacodynamic responses in animals, relative to those measured in early clinical studies, it appears that an adequate margin of safety exists to support the continued clinical development of inhaled AIR001.

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.

Nasal passages of Göttingen minipigs from the neonatal period to young adult

Histopathological examination of the nasal passages requires a standardized approach for recording lesion distribution patterns. Nasal diagrams provide guidance to map the lesions. Information on lesions exists for rodents, dogs, and monkeys, which all have been used in inhalation studies. Recently, minipigs have garnered interest as an inhalation model because minipigs resemble humans in many features of anatomy, physiology, and biochemistry and may be a good alternative to monkeys and dogs. The present work explored the microanatomy and histology of the nasal passages of Göttingen minipigs from postnatal day 1 until 6 months of age. Six nasal levels were selected, which allow examination of the squamous, transitional (nonciliated) and ciliated respiratory, and olfactory epithelia; the nasopharynx; and relevant structures such as the vomeronasal organ, olfactory bulb, and nasal/nasopharynx-associated lymphoid tissue.

Proceedings of the 2011 National Toxicology Program Satellite Symposium

The 2011 annual National Toxicology Program (NTP) Satellite Symposium, entitled "Pathology Potpourri," was held in Denver, Colorado in advance of the Society of Toxicologic Pathology's 30th Annual Meeting. The goal of the NTP Symposium is to present current diagnostic pathology or nomenclature issues to the toxicologic pathology community. This article presents summaries of the speakers' presentations, including diagnostic or nomenclature issues that were presented, along with select images that were used for audience voting or discussion. Some lesions and topics covered during the symposium include: proliferative lesions from various fish species including ameloblastoma, gas gland hyperplasia, nodular regenerative hepatocellular hyperplasia, and malignant granulosa cell tumor; spontaneous cystic hyperplasia in the stomach of CD1 mice and histiocytic aggregates in the duodenal villous tips of treated mice; an olfactory neuroblastoma in a cynomolgus monkey; various rodent skin lesions, including follicular parakeratotic hyperkeratosis, adnexal degeneration, and epithelial intracytoplasmic accumulations; oligodendroglioma and microgliomas in rats; a diagnostically challenging microcytic, hypochromic, responsive anemia in rats; a review of microcytes and microcytosis; nasal lesions associated with green tea extract and Ginkgo biloba in rats; corneal dystrophy in Dutch belted rabbits; valvulopathy in rats; and lymphoproliferative disease in a cynomolgus monkey.

Non-clinical safety and pharmacokinetic evaluations of propylene glycol aerosol in Sprague-Dawley rats and Beagle dogs

Aerosolized propylene glycol (PG) was generated as log-normally distributed particulate clouds in different concentrations using a novel capillary aerosol generator (CAG) and evaluated in a battery of non-clinical studies intended to assess its potential inhalation and systemic toxicity in 2 species before ICH-compliant "first-time-in-man" studies. Exposures were nose-only in rats, and via face mask with oropharyngeal tube in dogs. The CAG-generated PG aerosol had a mass median aerodynamic diameter (MMAD) of 2.29μm, with a 1.56 geometric standard deviation (GSD) in the rat studies, and a MMAD of 1.34μm (1.45 GSD) in the dog studies, consistent with expected particle size exposures in man. International Congress on Harmonization (ICH) Guidelines were followed, which recommend preliminary non-clinical safety studies using the vehicle and device (CAG-PG) prior to the first human exposure including safety pharmacology, pharmacokinetic (PK) studies, single dose toxicity studies, and repeated dose toxicity studies in two species. In the rat, the only biologically relevant findings included clinical signs of ocular and nasal irritation indicated by minor bleeding around the eyes and nose, and minimal laryngeal squamous metaplasia. This finding is commonly observed in inhalation studies in the rat, and likely related to the unique sensitivity of the tissue, as well as the circuitous airflow pathway through the larynx which increases particle deposition. In the female Beagle dog, treatment-related decreases in hemoglobin, red blood cells and hematocrit were observed in the two highest exposure groups, equivalent to approximately 18 and 60mg/kg/day. In male dogs from the high dose group, similar small decreases, albeit, non-statistically significant decreases were observed in these hematological markers as well. PK studies in rats and dogs showed that the absorption of PG following pulmonary inhalation exposure occurs rapidly, and equilibrium between lung tissue and plasma is achieved quickly. With daily inhalations of PG aerosols, there is evidence of minor tissue accumulation of PG in each species. Inhalation exposure to CAG-generated PG aerosols achieved PG concentrations in the systemic circulation that were similar to those attained via the oral route. Systemic elimination of PG appears to be saturable, presumably via hepatic metabolism. PG elimination in the high dose groups for both species showed terminal plasma and lung concentration-time profiles suggesting a zero-order elimination process. There was no apparent tissue toxicity of the lung, liver and kidney in these studies. Under the conditions of these studies, the NOEL for the rat was determined to be 20mg/kg/day for the 28-day study. In the Beagle dog, the NOEL was approximately 6.05mg/kg/day for the 28-day study. Overall, these studies allowed us to conclude that PG aerosol generated with the capillary aerosol generator could be administered safely in man, with an adequate margin of safety needed to conduct "first-time-in-man" human exposure studies.

Proliferative and nonproliferative lesions of the rat and mouse respiratory tract

The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP) and North America (STP) to develop an internationally-accepted nomenclature for proliferative and non-proliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in the respiratory tract of laboratory rats and mice, with color photomicrographs illustrating examples of some lesions. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous developmental and aging lesions as well as lesions induced by exposure to test materials. A widely accepted and utilized international harmonization of nomenclature for respiratory tract lesions in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.

Lesions in the Larynx of Wistar RccHan: WIST Rats

Specific regions in the rat larynx exhibit cellular changes in response to inhaled xenobiotics. These regions include the base of the epiglottis, ventral pouch, and medial surfaces of the vocal processes of the arytenoid cartilages. 1 , 2 In order to collect information on the usefulness of trimming techniques, the influence of different vehicles, the impact of different application routes in toxicity studies, and differences between induced vs. spontaneous lesions, the data obtained from a large number of inhalation and non-inhalation studies performed in Wistar RCCHan^TM: Wist rats at Harlan Laboratories Ltd Switzerland, all evaluated or reviewed by the same pathologist, were compiled for a detailed review. The value of different trimming techniques was deemed to be greatest for transverse and sagittolongitudinal section techniques, as compared to horizontolongitudinally section techniques. The comparison of lesions encountered in control rats of inhalation studies treated with different vehicles did not reveal differences in the type, distribution pattern, incidence and/or severity of spontaneous lesions. The types of lesions were also independent of different application routes in non-inhalation studies compared to inhalation studies. The pattern of spontaneous lesions in the rodent larynx was determined by degenerative and inflammatory lesions starting most often in the submucosal glands by desiccated secretion followed by mineralization and local inflammation or were induced by impacted foreign bodies. Squamous metaplasia was recorded in the respiratory epithelium overlaying the ventral gland as a spontaneous lesion in male Wistar rats from inhalation studies with a maxim of 20.0% in an inhalation oncogenicity study. Induced metaplastic changes recorded in the larynx were reversible. Other induced lesions in inhalation studies consisted of submucosal edema, necrosis, inflammation and/or granuloma. Induced lesions in non-inhalation studies were found to be exclusively related to reflux laryngitis or food impaction. It is concluded, that in rodents induced lesions of the larynx differ in type, distribution pattern, severity and incidence from spontaneous lesions.

Carbon dioxide effects on olfactory functioning: behavioral, histological and immunohistochemical measurements

Most studies on toxic inhalation focus on solvent effects and few have dealt with gases on olfactory functioning. Among gases, the effects of carbon dioxide on general physiology have been well investigated contrary to the impact on olfactory neuroepithelium. Thus, this work was designed to evaluate in mice the possible effects of 3% CO(2) in two exposure periods: a 5h/day and a 12h/day conditions. Behavioral, histological and immunohistochemical observations were conducted every 2 weeks, i.e. before (W0), during (W2, W4) and after exposure (W6, W8). Firstly, behavioral evaluations of odor sensitivity showed differences in relation to the odor tested, i.e. no effect with congener urine odor and a reinforcement of 2,4,5-trimethythiazoline (TMT) (predator odor) repulsion. Secondly, histological evaluations showed a similar evolution of the epithelium thickness, i.e. a decrease along the exposure as well as during the post-exposure period and an increase of cell number (whatever the phenotype) although the kinetic appeared different in both experimental conditions. Thirdly, immunohistochemical quantification of olfactory marker protein (OMP)- and proliferating cell nuclear antigen (PCNA)-positive cells revealed that the number of mature olfactory neurons increased at the early beginning of exposure period in both conditions. While a decrease was observed in the following weeks (W4-W8) for the 12h/day condition, a stable amount of OMP-positive cells was maintained in the 5h/day condition. In contrast, the number of PCNA-positive cells followed a similar evolution, i.e. a constant decrease along the experiment. These findings indicate that the effects of CO(2) inhalation exposure are selectively dose-dependent.

Inhalation exposure to acetone induces selective damage on olfactory neuroepithelium in mice

Due to their specific position in the nasal cavity, the cells of olfactory neuroepithelium can be damaged by exposure to environmental airborne chemicals. However, few studies have been focused on selective damage, i.e. olfactory sensory neurons, basal cells, supporting and duct cells. As solvents are known to induce critical effects on olfactory neuroepithelium (OE), this study was designed to characterize histological and immunohistological effects induced by acetone exposure on OE in mice. Behavioral tests were conducted to evaluate olfactory sensitivity. Moreover, olfactory neuroepithelium was examined to evaluate the thickness and the total number of cells. Finally, different markers, olfactory marker protein (OMP) and proliferating cell nuclear antigen (PCNA), were used to characterize respectively olfactory sensory neurons and basal cells, and secondly to evaluate the dynamic of the tissue turnover. Results showed structural modifications, since the thickness and the number of cells in the OE were modified according to the time course of the exposure. Additionally, no changes for OMP-positive cells were observed whereas significant differences appeared for the density of PCNA-positive cells in relation to their location (main-body or basal layer of OE). These findings indicate that acetone exposure induces selective damage in olfactory neuroepithelium.