Enhanced allergic airway disease in old mice is associated with a Th17 response

BACKGROUND

The prevalence of asthma in the elderly is increasing and associated with higher mortality than in children or young adults. However, the effects of age on the development and character of allergic asthma have been understudied. It has been suggested that mixed Th2/Th17 responses cause more severe forms of asthma, but the role of Th17 response in allergic airway disease and aging is not well understood.

OBJECTIVE

To investigate age-dependent characteristics and Th17 immune response in allergic airway disease in a murine house dust mite (HDM)-allergen model.

METHODS

Twelve-week-old and 15-month-old male BALB/c mice were sensitized and challenged with HDM. Bronchoalveolar lavage fluid (BALF), airway inflammation and hyperresponsiveness (AHR), serum immunoglobulin and splenic T cells were assessed. Age-related T cell activation was analyzed in a co-culture with bone marrow-derived dendritic cells (BMDC) and splenic CD4(+) T cells from young and old mice.

RESULTS

Features of allergic airway disease such as mucous cell hyperplasia, infiltration of airway eosinophils and lymphocytes, Th2 cytokine expression and serum IgG1 levels were greater in old compared to young mice. In contrast to the more marked inflammatory/immune responses to HDM in old mice, AHR was greater in young HDM-treated mice. Only the old mice developed airway neutrophil infiltration and a Th17 immune response upon HDM exposure, with increases in BALF cytokines IL-17A and KC, and Th17 cytokine producing T cells in the spleen. Stimulation of CD4(+) T cells and BMDC co-cultures with HDM, resulted in an enhanced Th17 cytokine response in cells isolated from old mice.

CONCLUSIONS AND CLINICAL RELEVANCE

Our findings in mice suggest that the severity and character of allergic airway disease are age dependent, with a bias towards a Th17 immune response with aging. Elderly, asthmatics may be prone to develop severe allergic airway inflammation with a mixed Th2/Th17 immune response.

Magnetic resonance imaging and computational fluid dynamics (CFD) simulations of rabbit nasal airflows for the development of hybrid CFD/PBPK models

The percentages of total airflows over the nasal respiratory and olfactory epithelium of female rabbits were calculated from computational fluid dynamics (CFD) simulations of steady-state inhalation. These airflow calculations, along with nasal airway geometry determinations, are critical parameters for hybrid CFD/physiologically based pharmacokinetic models that describe the nasal dosimetry of water-soluble or reactive gases and vapors in rabbits. CFD simulations were based upon three-dimensional computational meshes derived from magnetic resonance images of three adult female New Zealand White (NZW) rabbits. In the anterior portion of the nose, the maxillary turbinates of rabbits are considerably more complex than comparable regions in rats, mice, monkeys, or humans. This leads to a greater surface area to volume ratio in this region and thus the potential for increased extraction of water soluble or reactive gases and vapors in the anterior portion of the nose compared to many other species. Although there was considerable interanimal variability in the fine structures of the nasal turbinates and airflows in the anterior portions of the nose, there was remarkable consistency between rabbits in the percentage of total inspired airflows that reached the ethmoid turbinate region (approximately 50%) that is presumably lined with olfactory epithelium. These latter results (airflows reaching the ethmoid turbinate region) were higher than previous published estimates for the male F344 rat (19%) and human (7%). These differences in regional airflows can have significant implications in interspecies extrapolations of nasal dosimetry.

Differential association of MUC5AC and CLCA1 expression in small cartilaginous airways of RAO-affected and control horses

REASONS FOR PERFORMING STUDY

Airway mucus accumulation is associated with indoor irritant and allergen exposure in horses with recurrent airway obstruction (RAO). Epidermal growth factor receptor (EGFR) and a chloride channel (calcium activated, family member 1; CLCA1) are key signalling molecules involved in mucin gene expression.

OBJECTIVES

We hypothesised that exposure to irritants and aeroallergens would lead to increased expression of the mucin gene eqMUC5AC and increased stored mucosubstance in the airways of RAO-affected horses, associated with increased neutrophils and CLCA1 and EGFR mRNA levels.

METHODS

We performed quantitative RT-PCR of eqMUC5AC, CLCA1 and EGFR; volume density measurements of intraepithelial mucosubstances; and cytological differentiation of intraluminal inflammatory cells in small cartilaginous airways from cranial left and right and caudal left and right lung lobes of 5 clinically healthy and 5 RAO-affected horses that had been exposed to indoor stable environment for 5 days before euthanasia.

RESULTS

Neutrophils were increased in RAO-affected horses compared to clinically healthy controls. EqMUC5AC mRNA levels were positively correlated with both CLCA1 and EGFR mRNA levels in RAO-affected horses but only with CLCA1 in controls. The relationship between eqMUC5AC and CLCA1 differed in the 2 groups of horses with RAO-affected animals overexpressing CLCA1 in relation to eqMUC5AC.

CONCLUSIONS

These data implicate CLCA1 as a signalling molecule in the expression of eqMUC5AC in horses but also suggest differential regulation by CLCA1 and EGFR between horses with RAO and those with milder degrees of airway inflammation.

Gamma-tocopherol prevents airway eosinophilia and mucous cell hyperplasia in experimentally induced allergic rhinitis and asthma

BACKGROUND

Traditional therapies for asthma and allergic rhinitis (AR) such as corticosteroids and antihistamines are not without limitations and side effects. The use of complementary and alternative approaches to treat allergic airways disease, including the use of herbal and dietary supplements, is increasing but their efficacy and safety are relatively understudied. Previously, we have demonstrated that gamma-tocopherol (gammaT), the primary form of dietary vitamin E, is more effective than alpha-tocopherol, the primary form found in supplements and tissue, in reducing systemic inflammation induced by non-immunogenic stimuli.

OBJECTIVE

We used allergic Brown Norway rats to test the hypothesis that a dietary supplement with gammaT would protect from adverse nasal and pulmonary responses to airway allergen provocation.

METHODS

Ovalbumin (OVA)-sensitized Brown Norway rats were treated orally with gammaT before intranasal provocation with OVA. Twenty-four hours after two challenges, histopathological changes in the nose, sinus and pulmonary airways were compared with gene expression and cytokine production in bronchoalveolar lavage fluid and plasma.

RESULTS

We found that acute dosing for 4 days with gammaT was sufficient to provide broad protection from inflammatory cell recruitment and epithelial cell alterations induced by allergen challenge. Eosinophil infiltration into airspaces and tissues of the lung, nose, sinus and nasolacrimal duct was blocked in allergic rats treated with gammaT. Pulmonary production of soluble mediators PGE(2), LTB(4) and cysteinyl leukotrienes, and nasal expression of IL-4, -5, -13 and IFN-gamma were also inhibited by gammaT. Mucous cell metaplasia, the increase in the number of goblet cells and amounts of intraepithelial mucus storage, was induced by allergen in both pulmonary and nasal airways and decreased by treatment with gammaT.

CONCLUSIONS

Acute treatment with gammaT inhibits important inflammatory pathways that underlie the pathogenesis of both AR and asthma. Supplementation with gammaT may be a novel complementary therapy for allergic airways disease.

Specific biological effects of an anti-rat PMN antiserum intraperitoneally infected into f344/n rats

Neutropenia can be produced with antimitotic chemicals, but this method lacks specificity. An alternative is to use antibody-dependent cytotoxicity to produce neutropenia; however, this method has not been completely evaluated with respect to efficacy, specificity, and potential collateral damage, especially to constituents of bone marrow. This study used in vitro and in vivo methods to evaluate specific biological effects of a commercially available rabbit anti-rat neutrophil (PMN) antiserum in F344/N rats. The viability of rat pulmonary alveolar macrophages (PAMs), PMNs, and lymphocytes in vitro was quantified using a trypan blue dye exclusion test. Amounts of antiserum in vitro that rendered PMNs 100% nonviable did not decrease the viability or phagocytic ability of the PAMs and did not decrease the viability of the lymphocytes. Intraperitoneal (IP) injection of the antiserum into rats resulted in complete depletion of the PMNs and about a 50% depletion of the lymphocytes in circulating blood within 24 hours. The numbers of both cell types remained lowered for 5 days, but returned to control values by Day 6 after the IP injection. The antiserum had no effect on the numbers of PAMs or lymphocytes in the pulmonary alveolar airspaces, as determined by quantifying the numbers of these cell types in bronchoalveolar lavage fluid (BALF). The numbers of PMNs in BALF, however, decreased on Days 3 and 4 after IP injection of antiserum, but were not different from control values by Day 5. The viability of the PAMs in BALF of treated rats was not different from control values at any time point. There were no morphological indications that the injected antiserum damaged lung tissue or stem cells in bone marrow. Results demonstrate that the anti-rat PMN antiserum administered IP to F344/N rats depletes circulating PMNs and partially depletes lymphocytes for a period of about 6 days without adversely affecting the precursors of red or white blood cells in bone marrow. We concluded that the antiserum is a relatively specific way to temporarily render rats neutropenic without damaging precursor cells in bone marrow.

Persistent mucin glycoprotein alterations in equine recurrent airway obstruction

Horses with the episodic asthmalike condition of recurrent airway obstruction (RAO) have bouts of inflammation and bronchoconstriction associated with indoor housing. To assess the potential differences in airway secretions between RAO-affected and control horses, methods to quantify mucus secretions were developed and applied to bronchoalveolar lavage fluid. The relative difference in the amount of mucin glycoproteins between control and RAO-affected horses was assessed with a carbohydrate side chain-specific monoclonal antibody (4E4) in an enzyme-linked immunosorbent assay and by carbohydrate-specific enzyme-linked lectin assays. Significantly increased levels of 4E4-immunoreactive glycoprotein and the mucin-associated carbohydrates fucose (alpha-1,2 linkage) and N-acetylglucosamine were detected in RAO-affected horses in acute disease. RAO-affected horses in remission maintained significantly elevated levels of alpha-1,2-fucose and N-acetylglucosamine, whereas the 4E4-immunoreactive glycoprotein levels displayed a trend toward an increase over control levels. These results indicated that persistent changes in the quantity and/or quality of mucus glycoproteins occurred in the RAO-affected horses.

Identification of mucosal injury in the murine nasal airways by magnetic resonance imaging: site-specific lesions induced by 3-methylindole

A magnetic resonance imaging (MRI) technique was developed to identify mucosal damage to the nasal passages of mice resulting from exposure to respiratory toxicants. 3-Methylindole (3-MI) was chosen as a model nasal toxicant because systemic administration of this compound in mice results in a well-characterized necrotizing nasal lesion that is restricted to the olfactory mucosa. MRI technology allows imaging of the same mice before and at time points after injection. In addition, morphological alterations and increases in the area of sinus cavity airspace can be followed as a function of dose and time following exposure. For 3-MI, the cross-sectional area of the sinus airspaces increased by 1.7-fold in mice injected with 200 mg/kg and 2.6-fold in mice injected with 300 mg/kg at 3 days after injection. Alterations in the nasal turbinates lined by olfactory mucosa were identified 1, 3, and 6 days postadministration of 3-MI using MRI. Postmortem histological examination of the nasal tissue confirmed the intranasal location and distribution of the 3-MI-induced lesions observed by MRI. MRI can be a useful technique to identify toxicant-induced mucosal injury in the nasal passages at an in-plane resolution less than 60 microm.

Effects of ozone and endotoxin coexposure on rat airway epithelium: potentiation of toxicant-induced alterations

Tropospheric ozone is the major oxidizing component in photochemical smog and is one of the most pervasive problems to human health of the criteria air pollutants for which the National Ambient Air Quality Standards have been designated by the Clean Air Act. Although many adverse health effects of ozone exposure have been documented in both humans and laboratory animals, controversy surrounds the establishment and implementation of ozone standards set forth by the U.S. Environmental Protection Agency. Because people are commonly exposed to more than one air pollutant at a time, studies that examine coexposures to airborne materials may be more relevant for assessing their risks to human health. Airborne biogenic substances such as pollens, spores, and bacterial products are ubiquitous in the environment, and when inhaled can cause adverse respiratory symptoms. One such biogenic agent, bacterial endotoxin, is a potent stimulus of airway inflammation and is a ubiquitous airborne contaminant commonly found in domestic, agricultural, and industrial settings. Little is known about the interaction of exposures to biogenic substances and criteria air pollutants such as ozone. In the last few years we have performed a series of studies in rodents that examined the biologic responses of the respiratory epithelium after airway exposures to both endotoxin and ozone. When exposed to ozone (0.5 ppm 8 hr/day for 3 days), Fischer rats develop lesions in the nasal transitional epithelium, whereas intranasal instillation of endotoxin (20 microg) elicits epithelial lesions in the respiratory epithelium of the nose and conducting airways. Our studies were designed to examine how exposure to one toxicant may affect the airway epithelial lesions induced by the other toxicant. We investigated the potential role of acute inflammation in the enhancement of airway epithelial lesions after exposure of these two toxicants in neutrophil-sufficient and neutrophil-deficient rodents. A summary of these results indicates that epithelial and inflammatory responses to coexposure of these two pollutants are greater than those elicited by either agent alone. Interestingly, each toxicant enhances the epithelial alterations induced by the other. Furthermore, the synergistic effects elicited by coexposure to ozone and endotoxin are mediated partly by neutrophils. These studies provided some new insights into how inhaled co-pollutants interact to initiate and promote alterations of airway epithelium. Further studies with these and other air pollutants will help define their true risk to human health.

Endotoxin enhancement of ozone-induced mucous cell metaplasia is neutrophil-dependent in rat nasal epithelium

Ozone, the primary oxidant gas in photochemical smog, causes neutrophilic inflammation and mucous cell metaplasia (MCM) in the nasal transitional epithelium (NTE) of rats and monkeys. Bacterial endotoxin is another common airborne agent that induces acute neutrophilic inflammation, but not MCM, in NTE. It does, however, enhance ozone-induced MCM in rat nasal airways (Fanucchi et al., 1998, Toxicol. Appl. Pharmacol. 152, 1-9). In the present study, F344 rats exposed to filtered air or 0.5 ppm ozone (8 h/day for 3 days) were intranasally instilled with sterile saline or 100 microg endotoxin 24 h and 48 h after the third ozone exposure. To determine the role of neutrophilic inflammation in endotoxin-induced potentiation of the MCM caused by ozone, half of the rats were depleted of circulating neutrophils prior to saline or endotoxin instillations. Rats were killed 6 h or 3 days after the last intranasal instillation, and nasal tissues were processed for (1) light microscopy and morphometric analysis to determine the number of infiltrating neutrophils and the volume amount (density) of stored mucosubstances in the NTE, and (2) quantitative RT-PCR analysis of steady-state mucin gene (rMuc-5AC) mRNA levels in the NTE. Endotoxin induced a transient influx of neutrophils in both air- and ozone-exposed rats that was completely blocked by neutrophil depletion. Endotoxin increased rMuc-5AC mRNA levels in the NTE of ozone-exposed rats. Neutrophil depletion, however, had no effect on endotoxin-induced upregulation of mucin gene mRNA levels. Endotoxin enhanced the ozone-induced increase in stored mucosubstances (4-fold increase), but only in neutrophil-sufficient rats. These data indicate that endotoxin enhancement of ozone-induced upregulation of rMuc-5AC mRNA levels is neutrophil-independent, while its effects on intraepithelial production and storage of mucus glycoproteins is dependent on the presence of neutrophils.

Respiratory tract toxicity in rats exposed to Mexico City air

The rat has been used extensively as a health sentinel, indicator, or monitor of environmental health hazards, but this model has not been directly validated against human exposures. Humans in Mexico City show upper respiratory tract lesions and evidence of pulmonary damage related to their environmental inhalation exposure. In this study, male and female F344 rats were exposed (23 hr/day) in Mexico City to local Mexico City air (MCA)* for up to seven weeks. Controls were maintained at the same location under filtered air. Prior to these exposures, several steps were taken. First, the nasal passages of normal male rats shipped from the United States and housed in Mexico City were examined for mycoplasma infection; no evidence of infection was found. In addition, a mobile exposure and monitoring system was assembled and, with an ozone (O3) exposure atmosphere, was tested along with supporting histopathology techniques and analysis of rat nasal and lung tissues. Last, the entire exposure model (equipment and animals) was transported to Mexico City and validated for a three-week period. During the seven-week study there were 18 one-hour intervals during which the average O3 concentration of MCA in the exposure chamber exceeded the US National Ambient Air Quality Standard (NAAQS) of 0.120 ppm 03 (hourly average, not to be exceeded more than once per year). This prolonged exposure of healthy F344 rats to MCA containing episodically low to moderate concentrations of 03 (as well as other urban air pollutants) did not induce inflammatory or epithelial lesions in the nasal airways or lung as measured by qualitative histologic techniques or quantitative morphometric techniques. These findings agree with those of previous controlled O3 inhalation studies, but they are in contrast to reports indicating that O3-polluted MCA causes significant nasal mucosal injury in adults and children living in southwestern Mexico City. Taken together, these findings may suggest that human airways are markedly more susceptible to the toxic effects of MCA than are the airways of the F344 rat.

Production of interferon-gamma by influenza hemagglutinin-specific CD8 effector T cells influences the development of pulmonary immunopathology

This study examined the inflammation, lung function impairment, and immune protection associated with either wild-type or interferon (IFN)-gamma-deficient Tc1- or Tc2-CD8 effector cells responding to influenza pneumonia. The adoptive transfer of influenza hemagglutinin-specific Tc1 effectors afforded protection and elicited only minimal impairment of lung function. IFN-gamma-deficient Tc1 effector cells were equally protective, but were associated with an eosinophil influx and slightly more lung function impairment early in the response. Relative to Tc1, Tc2 effector cells were less protective, elicited an eosinophil influx and a greater impairment of lung functions. IFN-gamma-deficient Tc2 effector cells were not protective and were associated with the severest impairment of lung function throughout the response, an accumulation of neutrophils, and extensive pulmonary vasculitis and alveolar hemorrhaging. Deletion of IFN-gamma was associated with a delay in effector cell recruitment and the elicitation of a more intense inflammatory response that resulted in more severe lung function impairment in the recipients of either Tc1 or Tc2 IFN-gamma-deficient effector cells. Thus, during influenza infections, IFN-gamma production by the responding CD8 T cells is associated with effector cell recruitment and mitigation of the associated inflammation and of the resulting impairment in lung functions but is not necessary for optimal protection.

Nitric oxide diminishes apoptosis and p53 gene expression after renal ischemia and reperfusion injury

BACKGROUND

The role of nitric oxide in the ischemic injury of the kidney is still controversial. The aim of this study was to reevaluate the beneficial effect of exogenous nitric oxide and define its effects as regulator of gene p53 expression and apoptosis in the ischemic renal injury.

METHODS

Sprague-Dawley rats were subjected to 75 min of renal warm ischemia and contralateral nephrectomy. The animals were divided into six groups (n=6 per group): Two sham groups at 4 and 24 hr, two ischemic control (IC) at same times and two treated groups (Na-NP), studied at same intervals, where sodium nitroprusside (5 mg/kg) was given 15 min before reperfusion. The parameters evaluated included: serum creatinine, blood urea nitrogen, neutrophil infiltration determined by myeloperoxidase, gene p53 expression determined by reverse transcriptase polymerase chain reaction, apoptosis determined by peroxidase in situ technique and light histology.

RESULTS

There were significant improvements in serum creatinine and blood urea nitrogen at 24 hr in the NA-NP group when compared with the IC group (P<0.05). Myeloperoxidase levels were higher in the IC when evaluated against the Na-NP groups. Na-NP exhibited a downregulating effect in the expression of gene p53 when compared to the IC group. Apoptosis was more evident in the IC group and had moderately increased histological damage when compared to the Na-NP group.

CONCLUSIONS

Nitric oxide demonstrated a protective effect in the ischemic injury of the kidney and exerted an antiapoptotic action dowregulating the expression of gene p53.

Neutrophil-dependent and neutrophil-independent alterations in the nasal epithelium of ozone-exposed rats

Ozone induces epithelial hyperplasia and mucous cell metaplasia (MCM) in nasal transitional epithelium (NTE) of rats. A transient neutrophil influx accompanies upregulation of mucin messenger RNA (mRNA) before the onset of MCM. The present study was designed to examine the role of neutrophils in ozone-induced epithelial changes in the NTE of rats. Fourteen hours before inhalation exposure, male F344/N rats were injected intraperitoneally with antirat neutrophil antiserum to deplete circulating neutrophils, or were injected with normal (control) serum. Rats were then exposed to 0 ppm (filtered air) or 0.5 ppm ozone (8 h/d) for 1 or 3 d. Maxilloturbinates lined with NTE were analyzed to determine the epithelial labeling index; numeric densities of neutrophils, total epithelial cells, and mucous secretory cells; amount of stored intraepithelial mucosubstances; and steady-state ratMUC-5AC (mucin) mRNA levels. At 2 h after 3 d of exposure, rats treated with antiserum had 90% fewer circulating neutrophils than did rats treated with control serum. Antiserum-treated, ozone-exposed rats had 87% fewer infiltrating neutrophils than did control serum-treated, ozone-exposed rats. At 4 d after 3 d of exposure, antiserum-treated, ozone-exposed rats had 66% less stored intraepithelial mucosubstances and 58% fewer mucous cells in their NTE than did control serum-treated, ozone-exposed rats. Antiserum treatment had no effects on ozone-induced epithelial cell proliferation or mucin mRNA upregulation. The results of this study indicated that ozone-induced MCM was neutrophil-dependent, whereas ozone-induced epithelial cell proliferation and mucin gene upregulation were neutrophil-independent.

Synergistic hepatotoxicity from coexposure to bacterial endotoxin and the pyrrolizidine alkaloid monocrotaline

Individuals are commonly exposed to bacterial endotoxin (lipopolysaccharide [LPS]) through gram-negative bacterial infection and from its translocation from the gastrointestinal lumen into the circulation. Inasmuch as noninjurious doses of LPS augment the hepatotoxicity of certain xenobiotic agents, exposure to small amounts of LPS may be an important determinant of susceptibility to chemical intoxication. Monocrotaline (MCT) is a pyrrolizidine alkaloid phytotoxin that at large doses produces centrilobular liver lesions in rats. In the present study, MCT was coadministered with LPS to determine whether LPS would enhance its hepatotoxicity. Doses of MCT (100 mg/kg, ip) and LPS (7.4 x 10(6) EU/kg, iv), which were nonhepatotoxic when administered separately, produced significant liver injury in male, Sprague-Dawley rats when given in combination. Within 18 h after MCT administration, this cotreatment resulted in enhanced plasma alanine aminotransferase and aspartate aminotransferase activities, two markers of liver injury. Histologically, overt hemorrhage and necrosis appeared between 12 and 18 h. The lesions were centrilobular and midzonal and exhibited characteristics similar to lesions associated with larger doses of MCT and LPS, respectively. In the presence of LPS, the threshold for MCT toxicity was reduced to 13-33% of the dose required for toxicity with MCT alone. A study in isolated, hepatic parenchymal cells revealed no interaction between MCT and LPS in producing cytotoxicity. In summary, coexposure of rats to noninjurious doses of MCT and LPS resulted in pronounced liver injury. Results in vitro suggest that the enhanced toxicity does not result from a direct interaction of MCT and LPS with hepatic parenchymal cells. These results provide additional evidence that exposure to small amounts of LPS may be a determinant of susceptibility to food-borne hepatotoxins.

Lipopolysaccharide and the trichothecene vomitoxin (deoxynivalenol) synergistically induce apoptosis in murine lymphoid organs

Human exposure to Gram-negative bacterial lipopolysaccharide (LPS) is common and may have an important influence on chemical toxicity. LPS has been shown previously to enhance synergistically the toxicity of trichothecene mycotoxins. Because either of these toxin groups alone characteristically target lymphoid organs at high doses, we evaluated the effects of coexposure to subthreshold doses of Salmonella typhimurium LPS and vomitoxin (VT) administered by intraperitoneal injection and oral gavage of B6C3F1 mice, respectively, on apoptosis in lymphoid tissues after 12-h exposure. The capacity of LPS (0.5 mg/kg body weight) and VT (25 mg/kg body weight) to act synergistically in causing apoptosis in thymus, spleen, and Peyer's patches was suggested by increased internucleosomal DNA fragmentation in whole cell lysates as determined by gel electrophoresis. Following terminal deoxynucleotidyl transferase (TdT)-mediated fluorescein-dUTP nick end-labeling (TUNEL) of tissue sections, a dramatic enhancement of fluorescence intensity indicative of apoptosis was observed in thymus, spleen, Peyer's patches, and bone marrow from coexposed animals as compared to those given the agents alone. Evaluation of hematoxylin and eosin-stained tissue sections of treatment mice revealed the characteristic features of lymphocyte apoptosis, including marked condensation of nuclear chromatin, fragmentation of nuclei, and formation of apoptotic bodies in tissues from mice. Combined treatment with VT (25 mg/kg body weight) and LPS (0.5 mg/kg body weight) significantly increased (p<0.05) the amount of apoptotic thymic and splenic tissue as compared to the expected additive responses of mice receiving either toxin alone. When apoptosis was examined in cell suspensions of thymus, spleen, Peyer's patches, and bone marrow by flow cytometry in conjunction with propidium iodide staining, the percentage of apoptotic cells was significantly increased (p<0.05) in cotreatment groups as compared to the additive responses to LPS and VT given alone. The results provide qualitative and quantitative evidence for the hypothesis that LPS exposure markedly amplifies the toxicity of trichothecenes and that the immune system is a primary target for these interactive effects.

Histopathology of nasal olfactory mucosa from selected inhalation toxicity studies conducted with volatile chemicals

In recent years, histopathologic changes have been reported in the olfactory mucosa of rodents exposed, by inhalation, to a variety of volatile chemicals. In order to better characterize these lesions, a panel of experienced pathologists reviewed microscopic lesions of the olfactory epithelium of rats reported in 10 inhalation studies conducted with 8 different chemicals. The objectives were to determine if the olfactory epithelial lesions are morphologically similar or different for the chemicals of interest, to develop and recommend appropriate diagnostic criteria and nomenclature to characterize the morphology of these olfactory lesions, and to provide specific criteria for judging the degree of severity of the olfactory changes in these studies. The results indicated that the distribution and nature of the lesions were similar in all the examined studies in which olfactory changes were observed. Recommended standardized nomenclature and diagnostic criteria and a uniform method for scoring lesion severity based on the extent of distribution and severity of tissue damage are presented.

Inflammatory and epithelial responses during the development of ozone-induced mucous cell metaplasia in the nasal epithelium of rats

Rats repeatedly exposed to high ambient concentrations of ozone develop mucous cell metaplasia (MCM) in the nasal transitional epithelium (NTE). The present study was designed to determine the temporal relationships of ozone-induced inflammatory and epithelial responses and their correlation with subsequent MCM in the NTE of rats. Male F344/N rats were exposed to 0.5 ppm ozone, 8 h/day for 1, 2, or 3 days. Two h prior to sacrifice, all the rats were injected intraperitoneally with 5'-bromo-2-deoxyuridine (BrdU) to label epithelial cells undergoing DNA synthesis. Rats exposed to ozone for 1 or 2 days were killed 2 h after the exposure. Rats exposed to ozone for 3 days were killed 2 h or 1, 2, or 4 days after the exposure. Control rats were killed after a 7-day exposure to filtered air. One nasal passage from the anterior nasal cavity of each rat was fixed and processed for light microscopy to morphometrically determine the numeric densities of epithelial cells, neutrophils, and mucous cells, and the amount of intraepithelial mucosubstances in the NTE. The maxilloturbinate from the other nasal passage was processed for analysis of an airway mucin-specific gene (i.e., rMuc-5AC mRNA). Acute ozone exposure induced a rapid increase in rMuc-5AC mRNA levels prior to the onset of MCM, and the increased levels of rMuc-5AC mRNA persisted with MCM. Neutrophilic inflammation coincided with epithelial DNA synthesis and upregulation of rMuc-5AC, but was resolved when MCM first appeared in the NTE. The results of the present study suggest that upregulation of mucin mRNA by acute ozone exposure may be associated with the concurrent neutrophilic inflammation and epithelial hyperplasia in the NTE. Ozone-induced MCM may be dependent on these important pre-metaplastic responses (i.e., mucin mRNA upregulation, neutrophilic inflammation, and epithelial proliferation).

Effects of pre-existing rhinitis on ozone-induced mucous cell metaplasia in rat nasal epithelium

Ozone causes rhinitis and nasal epithelial alterations. The toxicity of ozone on nasal airways with pre-existing rhinitis has not been investigated. The present study was designed to determine the effect of endotoxin-induced rhinitis on ozone-induced epithelial alterations, especially mucous cell metaplasia (MCM), in the nasal transitional epithelium (NTE) of rats. Six h prior to daily inhalation exposure, male F344/N rats were intranasally instilled with saline or endotoxin (100 microgram/day). Rats were killed 2 h or 4 days after 3-day (8 h/day) exposure to ozone (0.5 ppm) or filtered air (0 ppm). The maxilloturbinate from one nasal passage was processed for morphometric analyses of the numbers of neutrophils and epithelial cells and the amount of intraepithelial mucosubstances (IM) in the NTE. The maxilloturbinate from the other nasal passage was processed for a mucin-specific (rMuc-5AC) mRNA analysis. At 2 h postexposure, endotoxin/ozone-exposed rats had 48 and 3 times more neutrophils in the NTE than did saline/air- and saline/ozone-exposed rats, respectively. Ozone-exposed rats had 35% more NTE cells and 2-fold more mucin mRNA than did saline/air-exposed rats, independent of endotoxin exposure. At 4 days postexposure, endotoxin/ozone-exposed rats had 5 and 2 times more IM and mucous cells, respectively, than did saline/air- and saline/ozone-exposed rats. Though endotoxin/air-exposed rats killed at 2 h postexposure had more neutrophils (40-fold), epithelial cells (27%) and mucin mRNA (2-fold) in the NTE than did saline/air-exposed rats, no MCM was present in those rats killed at 4 days postexposure. The results of the present study indicated that pre-existing rhinitis augments ozone-induced MCM.

In vitro culture of microdissected rat nasal airway tissues

The surface epithelium lining the nasal airways is a potential target for inhaled contaminants such as ozone, endotoxin, formaldehyde, tobacco smoke, and organic dusts. The epithelial response to injury may depend on the toxicant, the type of epithelium, the severity of the injury, and the presence of inflammatory cells and their secreted products. To study mechanisms of toxicant-induced epithelial injury and repair, in the absence of cellular inflammation or other systemic effects, we have developed a culture system to maintain morphologically distinct nasal airway epithelium in vitro. Microdissected maxilloturbinates and proximal nasal septa of male F344/N rats were cultured at an air-liquid interface for up to 14 d in supplemented serum-free medium. Maxilloturbinates are lined by nonciliated cuboidal nasal transitional epithelium (NTE) with few or no mucous cells. The proximal nasal septum is lined by a mucociliary respiratory epithelium (RE) that normally contains numerous mucous cells. Preservation of the normal RE and NTE phenotype in culture was assessed by light and electron microscopy, and analysis of an airway mucin gene (rMuc-5AC) messenger RNA (mRNA). Both RE and NTE retained normal cell morphology for 14 d in culture (DIC). After 14 DIC there were 20% fewer RE cells in the septa (equal loss of ciliated and mucous cells) and 25% more NTE cells in the maxilloturbinates (increased number of basal cells). Compared with the RE, the NTE expressed consistently low levels of rMuc-5AC mRNA and had little to no histochemically detectable intraepithelial mucosubstances (IM) after 0, 3, 7, or 14 DIC. The amount of stored IM and the steady-state levels of rMuc-5AC mRNA in the RE decreased with time in culture. In summary, this culture system can maintain fully differentiated secretory and nonsecretory rat airway epithelia in vitro for up to 14 d. This study was an essential first step in developing a system to study the pathogenesis of toxicant-induced airway epithelial injury and mechanisms of cellular repair and adaptation in the absence of cellular inflammation and other systemic influences.

Amplified proinflammatory cytokine expression and toxicity in mice coexposed to lipopolysaccharide and the trichothecene vomitoxin (deoxynivalenol)

A single oral exposure to the trichothecene vomitoxin (VT) has been previously shown in the mouse to increase splenic mRNA levels for several cytokines in as little as 2 h. Since one underlying mechanism for these effects likely involves superinduction of transiently expressed cytokine genes, VT may also potentially amplify cytokine responses to inflammatory stimuli. To test this possibility, the effects of oral VT exposure on tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and IL-1beta expression were measured in mice that were intraperitoneally injected with lipopolysaccharide (LPS), a prototypic inflammatory agent. As anticipated, VT alone at 1, 5, and 25 mg/kg body weight increased splenic mRNA expression of all three cytokines after 3 h in a dose-response fashion. LPS injection at 1 and 5 mg/kg body weight also induced proinflammatory cytokine mRNA expression. There was a synergistic increase in TNF-alpha splenic mRNA levels in mice treated with both VT and LPS as compared to mice treated with either toxin alone, whereas the effects were additive for IL-6 and IL-1beta mRNA expression. When relative mRNA levels were examined over a 12-h period in mice given LPS (1 mg/kg) and/or VT (5 mg/kg), significant enhancement was observed up to 6, 12, and 3 h for TNF-alpha, IL-6, and IL-1beta, respectively. When plasma cytokine concentrations were measured, TNF-alpha was found to peak at 1 h and was significantly increased at 1, 3, and 6 h if mice were given LPS and VT, whereas LPS or VT alone caused much smaller increases in plasma TNF-alpha Plasma IL-6 peaked at 3 h in LPS, VT, and LPS/VT groups, with the combined toxin group exhibiting additive effects. Plasma IL-1beta was not detectable. The potential for VT and LPS to enhance toxicity was examined in a subsequent study. Mortality was not observed up to 72 h in mice exposed to a single oral dose of VT at 25 mg/kg body weight or to an intraperitoneal dose of LPS at 1 or 5 mg/kg body weight; however, all mice receiving VT and either LPS dose became moribund in less than 40 h. The principal histologic lesions in the moribund mice treated with VT and LPS were marked cell death and loss in thymus, Peyer's patches, spleen, and bone marrow. In all of these lymphoid tissues, treatment-induced cell death had characteristic histologic features of apoptosis causing lymphoid atrophy. These results suggest that LPS exposure may markedly increase the toxicity of trichothecenes and that the immune system was a primary target of these interactive effects.

Breathing pattern response and epithelial labeling in ozone-induced airway injury in neutrophil-depleted rats

To test the hypothesis that neutrophils enhance the repair of ozone (O3)-injured airway epithelium, we investigated breathing pattern responses and airway epithelial injury and repair in rats depleted of neutrophils using rabbit antirat neutrophil serum (ANS) and control rats treated with normal rabbit serum (NRS). Thirty-seven Wistar rats were exposed to O3 (1 ppm) or filtered air (FA) for 8 h followed by 8 h in FA. O3-exposed NRS- and ANS-treated rats showed similar progressive decreases in tidal volume and increase in breathing frequency, with maximal changes occurring at 8 h of exposure, whereas FA-exposed rats showed no significant changes. O3-exposed ANS-treated rats showed more epithelial necrosis in the nasal cavity, bronchi, and distal airways than did O3-exposed NRS-treated rats. Incorporation of 5-bromo-2-deoxyuridine (BrdU), a measure of cellular proliferation, was assessed using an optical disector to count BrdU- labeled terminal bronchiolar epithelial cells. O3-exposed ANS-treated rats had significantly less BrdU- labeled epithelial cells than did O3-exposed NRS-treated rats. We conclude that neutrophils contribute to the repair process by enhancing the proliferation of O3-injured airway epithelial cells.

Long-lasting effects of chronic ozone exposure on rat nasal epithelium

Ozone, the principal oxidant pollutant in photochemical smog, causes airway epithelial injury in the upper and lower respiratory tract of laboratory animals. We have recently reported that long-term inhalation exposure to ozone causes mucous-cell metaplasia (MCM) in the surface epithelium lining the nasal airways of F344 rats. The principal objective of the present study was to determine the persistence of ozone-induced MCM in the nasal epithelium after the end of a chronic exposure. Male F344/N rats were exposed to 0, 0.25, or 0.5 ppm ozone, for 8 h/d, 7 d/wk for 13 wk. Animals were killed 8 h, 4 wk, or 13 wk after the end of the chronic exposure. Ozone-related alterations in the nasal epithelium were qualitatively and quantitatively characterized through histochemistry, image analysis, and morphometric techniques. Some rats were exposed for an additional 8 h to 0.5 ppm ozone at 13 wk after the end of the chronic exposure to determine whether previous ozone exposure results in persistent changes in the sensitivity of nasal epithelium to acute injury. At the end of the chronic exposure, hyperplasia was present in the nasal epithelium of rats exposed to 0.25 and 0.5 ppm ozone. By 13 wk postexposure, this proliferative alteration was still evident only in the rats exposed to 0.5 ppm ozone. Ozone-induced MCM with associated intraepithelial mucosubstances was evident only in the nasal tissues of rats exposed to 0.5 ppm ozone. Though attenuated, these alterations in the nasal mucous apparatus were still detectable at 13 wk after the end of the exposure. At this same time after the chronic exposure, an acute (8 h) exposure to 0.5 ppm ozone induced an additional increase of mucosubstances in the nasal epithelium of rats previously exposed to 0.5 ppm ozone, but not in rats chronically exposed to 0 or 2.5 ppm ozone. The persistent nature of the ozone-induced MCM in rats documented in this report suggests that ozone exposure may have the potential to induce similar long-lasting alterations in the airways of humans.

Capsaicin-sensitive C-fiber-mediated protective responses in ozone inhalation in rats

To assess the role of lung sensory C fibers during and after inhalation of 1 part/million ozone for 8 h, we compared breathing pattern responses and epithelial injury-inflammation-repair in rats depleted of C fibers by systemic administration of capsaicin as neonates and in vehicle-treated control animals. Capsaicin-treated rats did not develop ozone-induced rapid, shallow breathing. Capsaicin-treated rats showed more severe necrosis in the nasal cavity and greater inflammation throughout the respiratory tract than did control rats exposed to ozone. Incorporation of 5-bromo-2'-deoxyuridine (a marker of DNA synthesis associated with proliferation) into terminal bronchiolar epithelial cells was not significantly affected by capsaicin treatment in rats exposed to ozone. However, when normalized to the degree of epithelial necrosis present in each rat studied, there was less 5-bromo-2'-deoxyuridine labeling in the terminal bronchioles of capsaicin-treated rats. These observations suggest that the ozone-induced release of neuropeptides does not measurably contribute to airway inflammation but may play a role in modulating basal and reparative airway epithelial cell proliferation.

Ozone-induced pulmonary inflammation and epithelial proliferation are partially mediated by PAF

Ozone (O3) exposure stimulates airway inflammation and epithelial sloughing in a number of species, including mice. Platelet-activating factor (PAF) is a lipid mediator released by activated mast cells, macrophages, and epithelial cells and causes pulmonary inflammation and hyperpermeability. We hypothesized that the activation of PAF receptors is central to the development of inflammation and epithelial injury induced by acute O3 exposure in mice. To test this hypothesis, O3-susceptible C57BL/6J mice were treated with a PAF-receptor antagonist, UK-74505, or vehicle either before or immediately after 3-h exposure to O3 (2 parts/million) or filtered air. Bronchoalveolar lavage (BAL) fluids were collected 6 and 24 h after exposure. Differential cell counts and protein content of the lavage were used as indicators of inflammation in the airways. O3-induced epithelial injury was assessed by light microscopy, and DNA synthesis in epithelium of terminal bronchioles was estimated by using a bromodeoxyuridine-labeling index. Intercellular adhesion molecule 1 (ICAM-1) expression was also examined in the lung by immunohistochemical localization. O3 caused significant increases in polymorphonuclear leukocytes and protein in the BAL fluid, increased pulmonary epithelial proliferation, and increased epithelial expression of ICAM-1 compared with air-exposed, vehicle-treated control mice. Relative to O3-exposed, vehicle-treated control mice, UK-74505 before exposure significantly (P < 0.05) decreased BAL protein, polymorphonuclear leukocytes, and epithelial cells. O3-induced inflammation was similarly attenuated in mice treated with UK-74505 after exposure. These experiments thus support the hypothesis that O3-induced airways inflammation and epithelial damage in mice are partially mediated by activation of PAF receptors, possibly through modulation of ICAM-1 expression.

Endotoxin potentiates ozone-induced mucous cell metaplasia in rat nasal epithelium

People are exposed to a combination of environmental pollutants throughout their lives. Repeated exposures of one common pollutant, ozone, have been reported to cause the development of mucous cell metaplasia in the nasal transitional epithelium (NTE) of rats. The present study was designed to test the hypothesis that exposure to bacterial endotoxin, another toxicant ubiquitous to the environment, potentiates this metaplastic response in rat NTE. Rats were exposed to 0 or 0.5 ppm ozone 8 h/day for 3 days. After ozone exposure, rats were intranasally instilled with saline containing 0 or 100 micrograms endotoxin once daily for 2 days. Rats were killed 6 h or 3 days after the last intranasal instillation. Nasal tissue was processed for light microscopy and image analysis, or for isolation of total RNA. Mucous cell metaplasia was not detected in air/endotoxin-exposed rats, was observed in ozone/saline-exposed rats, and was most severe in ozone/endotoxin-exposed rats. At 6 h after instillation, amounts of intraepithelial mucosubstances (IM) were 4-fold greater in NTE of ozone/endotoxin-exposed rats as compared to controls. These IM levels were similar to those of ozone/saline-exposed rats. Mucin-specific mRNA (rMuc-5AC) levels were elevated in all treatment groups at this timepoint. At 3 days after instillation, amounts of IM in ozone/endotoxin-exposed rats were 10-fold greater than in controls and 5-fold greater than in ozone/saline-exposed rats. rMuc-5AC mRNA levels remained elevated in the ozone/endotoxin-exposed rats. Despite the fact that bacterial endotoxin alone does not cause a phenotypic change in rat NTE, it can augment the mucous cell metaplasia induced by a previous exposure to ozone.

Expression of the Bcl-2 protein in nasal epithelia of F344/N rats during mucous cell metaplasia and remodeling

Exposure to ozone induces mucous cell metaplasia in rat airway epithelia. During the regeneration process, apoptotic mechanisms may be responsible for eliminating metaplastic cells. Therefore, the present study investigated expression of Bcl-2, a regulator of apoptosis, in ozone-induced mucous cell metaplasias. Adjacent metaplastic mucous cells in nasal airway epithelia that were exposed to ozone were heterogeneous in their expression of Bcl-2; some cells expressed high levels, whereas others expressed low levels or no Bcl-2. On Western blot analysis, Bcl-2 was detected in protein extracts from nasal epithelia of rats exposed to 0.5 ppm ozone for 1 mo but not in control rats exposed to filtered air. The number of metaplastic mucous cells in transitional epithelia of rat nasal airways was increased from 0 to about 200 after 3 and 6 mo of exposure to ozone; only 0 to 10 metaplastic mucous cells remained after a recovery period of 13 wk in rats exposed to ozone for 3 mo. The number of mucous cells of the respiratory epithelium lining the midseptum did not change after ozone exposure or recovery. The percentage of Bcl-2-positive cells lining the midseptum increased from 7 to 14% after a 3- and 6-mo ozone exposure, respectively. In transitional epithelia of the lateral wall and the nasoturbinates and maxilloturbinates, 35 to 55% of cells were Bcl-2-positive after a 1-mo exposure and 10 to 18% after both a 3- and a 6-mo exposure to ozone. Bcl-2 reactivity decreased to 0 to 8% after a recovery period of 13 wk. These observations suggest that Bcl-2 plays a role in the development and resolution of mucous cell metaplasias. This model may be useful in uncovering the role of Bcl-2 during the development and maintenance of metaplastic mucous cells. Disregulation of Bcl-2 expression may be responsible for the sustained mucous cell metaplasia in asthmatics or may allow cells to accumulate and become more susceptible to transformation leading to neoplasia.

Fluticasone propionate attenuates ozone-induced rhinitis and mucous cell metaplasia in rat nasal airway epithelium

Ozone (O3) is the principal oxidant pollutant in photochemical smog. Repeated exposures to O3 induces inflammation and mucous cell metaplasia in the nasal airways of laboratory animals. Our study was designed to determine the efficacy of a topical anti-inflammatory corticosteroid in preventing O3-induced rhinitis and mucous cell metaplasia in rat nasal epithelium. Male F344 rats were exposed to filtered air (0 ppm O3; air-controls) or 0.5 ppm O3, 8 h/day, for 3 or 5 days. Immediately before and after each exposure, rats received an intranasal instillation (50 microl/nasal passage) of a topical corticosteroid, fluticasone propionate (FP; 25 microg/nasal passage) or its vehicle only (0.01% ethanol in saline). Rats were killed 2 h after the third exposure (3-day exposure) or 3 days after the fifth exposure (5-day exposure) and nasal tissues were processed for light microscopy. Numeric densities of epithelial cells and neutrophils, and the amount of intraepithelial mucosubstances (IM) in the epithelium lining the maxilloturbinates were morphometrically determined. There were no significant differences in any measured parameter in air-exposed rats instilled with FP compared with air-exposed rats instilled with vehicle. Vehicle-treated rats exposed to ozone had neutrophilic rhinitis with 3.3- and 1.6-fold more intraepithelial neutrophils (3-day and 5-day exposure, respectively) and marked mucous cell metaplasia (5-day exposure only) with numerous mucous cells and approximately 60 times more IM in the nasal transitional epithelium compared with vehicle-treated air-controls. FP-treated rats exposed to ozone had minimal nasal inflammation (1.3-fold more intraepithelial neutrophils only after 3-day exposure) and minimal mucous cell metaplasia (5-fold more IM only after 5-day exposure) compared with vehicle-instilled, air-exposed rats. Results of this study indicate that FP-treatment is effective in attenuating not only O3-induced rhinitis (30-60% reduction) but also O3-induced mucous cell metaplasia (85% reduction) in rat nasal transitional epithelium. The cellular and molecular mechanisms involved in FP-induced attenuation of O3-induced nasal lesions remain to be determined.

A comparative analysis of primate nasal airways using magnetic resonance imaging and nasal casts

The nasal cavity is an intricate part of the respiratory tract. It is not only the site of olfaction, but also serves as a filter to protect the lower respiratory tract from inhaled pollutants. A substantial fraction of inhaled particles deposit in this region and may pose potential health risks. To predict possible sites of inhaled aerosol deposition and better understand health risks associated with inhaled aerosols in this region, it is necessary to examine the morphometry of the nasal passage. Magnetic resonance imaging (MRI) of the nose was done from the anterior to the posterior, in 3-mm sections, on five anesthetized rhesus monkeys and on two nasal casts (one human and one rhesus monkey). The MRI images were analyzed for perimeter and cross-sectional areas of each section. Results indicated that the left and right nasal passages were very symmetric for the five monkeys but not for the human cast. The cross-sectional area and, consequently, the volume varied greatly among monkeys in vivo. Measurements from the monkey cast exhibited 1.4-fold differences normalized body weight in cross-sectional areas, but with smaller differences in perimeter when compared to the MRI in vivo images. The human cast exhibited a volume three times greater than that of the monkey cast, while the surface area was approximately doubled. Results from this comparison showed many similarities in the structure of the monkey and human nose suggesting that the rhesus monkey would be a good human surrogate in aerosol deposition studies.

Is exposure to bacterial endotoxin a determinant of susceptibility to intoxication from xenobiotic agents?

Why certain individuals are more susceptible than others to harmful effects of chemical exposure remains incompletely understood. One understudied but potentially important determinant of susceptibility is concurrent or preexisting inflammation that may influence the pathogenic outcome of chemical exposure. Endotoxin from gram-negative bacteria is a potent inducer of inflammation. We are all exposed to endotoxin, and such exposure varies considerably among individuals depending on environment, bacterial infection, and conditions that affect its translocation from the lumen of the gastrointestinal tract into the circulation. Mammals have a vigorous response to endotoxin that includes recruitment and activation of inflammatory cells and release of many soluble mediators that affect cellular homeostasis. These and other results have led to the hypothesis that altered tissue homeostasis initiated by small, otherwise nontoxic doses of xenobiotic agents can progress to overt toxicity in the presence of inflammatory factors generated by concurrent endotoxin exposure. This hypothesis is supported by studies in animals, in which considerable evidence has accumulated indicating that endotoxin exposure can influence the magnitude of responses to toxic chemicals. For example, exposure to small amounts of endotoxin markedly augments liver injury from a variety of hepatotoxicants including carbon tetrachloride, ethanol, cadmium, halothane, allyl alcohol, and others. Although support for this hypothesis exists, much remains to be learned about the mechanisms by which endotoxin augments chemical toxicity and the implications for human health. Given the ubiquitous and variable exposure of people and animals to endotoxin, this inducer of inflammation should receive serious consideration as a potential determinant of susceptibility to toxic chemicals.

Mucous cell metaplasia in rat nasal epithelium after a 20-month exposure to ozone: a morphometric study of epithelial differentiation

The present study was designed to examine the effects of long-term ozone exposure on nasal epithelia and intraepithelial mucosubstances (IM) throughout the nasal airways of F344/N rats. Animals were exposed to 0 (controls), 0.12, 0.5, or 1.0 ppm ozone, 6 h/day, 5 days/wk, for 20 mo. Rats were killed 1 wk after the end of the exposure, and nasal tissues were processed for light and electron microscopy. Standard morphometric techniques were used to determine epithelial cell densities and the amounts of IM in the surface epithelium lining the nasal airways. No mucous cells or IM were present in the epithelia lining the nasal lateral meatus and maxillary sinus of rats exposed to 0 or 0.12 ppm ozone. In contrast, rats exposed to 0.5 or 1.0 ppm ozone had marked mucous cell metaplasia (MCM) with numerous mucous cells and conspicuous amounts of IM in the surface epithelium lining these upper airways. Ozone-induced increases in total epithelial cells (i.e., epithelial hyperplasia) were present only in rats exposed to 1.0 ppm. The results of this study indicate that rats chronically exposed to 1.0 or 0.5 ppm, but not 0.12 ppm, ozone can develop marked MCM with significant increases in IM in both proximal and distal nasal airways. The epithelial changes observed throughout the nasal passages of ozone-exposed rats may be adaptive responses in an attempt to protect the upper and lower respiratory tract from further ozone-induced injury.

Consequences of prolonged inhalation of ozone on F344/N rats: collaborative studies. Part XII: Atrophy of bone in nasal turbinates

As part of the National Toxicology Program/Health Effects Institute collaborative study of the health effects of prolonged ozone exposure, it was observed that rats chronically exposed to ozone had marked histopathologic changes in the upper respiratory tract, including atrophy of the nasal turbinates. The principal objective of the present study was to morphometrically assess the severity of the ozone-induced changes in the bony tissue of the maxilloturbinates in these chronically exposed rats. Male and female F344/N rats were exposed to 0, 0.12, 0.5, or 1.0 part per million (ppm) ozone, 6 hours/day, 5 days/week for 20 or 24 months. Rats were killed one week after the end of the exposure, and nasal tissues were processed for light and electron microscopy. Using image analysis and standard morphometric techniques, the amounts of bone, surface epithelium, and lamina propria comprising the maxilloturbinates were estimated by measuring the cross-sectional area of each tissue compartment at a defined location in the proximal nasal passage. Both male and female rats had significant morphologic and morphometric changes in the maxilloturbinates after prolonged exposures to 0.5 or 1.0 ppm ozone, but not to 0.12 ppm ozone. Ozone-exposed rats had significant reductions in the cross-sectional area of turbinate bone, reflecting the loss of bone in the maxilloturbinate after prolonged exposure. This ozone-induced bony atrophy was more severe in male than in female rats. Using electron microscopy, numerous bone-resorption sites were identified on the outer, periosteal, surface of the turbinate bone in ozone-exposed animals. Rats with bony atrophy also had a conspicuous influx and mixed inflammatory cells into the lamina propria surrounding the turbinate bone. In addition, ozone exposures caused reductions in the area of lamina propria, due to blood vessel constriction, and increases the in the area of the surface epithelium, due to hyperplasia and metaplasia. The results of the present tudy demonstrated that prolonged exposure of rats to ozone can cause marked loss of turbinate bone. The severity of this ozone-induced bony atrophy in rats is dependent on both concentration and gender.

Gadolinium chloride pretreatment protects against hepatic injury but predisposes the lungs to alveolitis after lipopolysaccharide administration

Exposure to lipopolysaccharide (LPS) can result in multi-organ failure and death. After an intravenous injection of LPS into rats, neutrophils (PMN) rapidly accumulate in the liver sinusoids and pulmonary vasculature, and PMN play a critical role in producing both hepatic and pulmonary injury. Kupffer cells (KC), the resident macrophages of the liver, phagocytose LPS and produce inflammatory mediators which may be chemotactic and stimulatory for PMN. The purpose of this study was to determine whether inhibition of KC function affects PMN accumulation and the development of parenchymal injury in the liver and lungs after systemic administration of LPS. Female, Sprague-Dawley rats (180-230 g) were pretreated with either gadolinium chloride-6H2O (GdCl3; 10 mg/kg, intravenously), to inactivate KC, or saline vehicle 24 h before receiving either LPS (4 mg/kg, intravenously) or saline vehicle. Rats were killed 1.5, 6, and 24 h after LPS administration. In a preliminary study, exposure to GdCl3 decreased uptake of carbon in the liver, indicating inhibition of phagocytosis by KC. Ninety minutes after administration of LPS, PMN accumulated in the livers of LPS-treated rats, and this effect was not altered by pretreatment with GdCl3. Similarly, exposure to LPS resulted in PMN accumulation in the pulmonary tissue, which was unaffected by GdCl3 pretreatment. Exposure to GdCl3 before LPS administration resulted in a significant increase in the number of PMN recovered by bronchoalveolar lavage at 24 h, indicating diffuse acute alveolitis. LPS-induced hepatic injury was prevented by pretreatment with GdCl3; however, the increased wet lung/body weight ratio observed after LPS administration was unaffected by GdCl3. These results confirm that inactivation of KC protects against hepatic injury and extend this finding by ruling out inhibition of hepatic PMN accumulation as a mechanism for this effect. The data also suggest that treatment with GdCl3 predisposes the lungs to alveolitis during systemic exposure to LPS.

Kinetics of nasal epithelial cell loss and proliferation in F344 rats following a single exposure to 0.5 ppm ozone

Repeated exposure to 0.5 ppm ozone (O3) induces mucous cell metaplasia in the nasal transitional epithelium (NTE) of rats. The cellular events which commit the NTE to undergo this phenotypic alteration occur during the first 3 days of exposure. To examine the kinetics of the early cellular responses of NTE to O3, F344 rats were exposed to filtered air or 0.5 ppm O3 for 8 hr and euthanized 2, 4, 6, 8, 12, 16, 20, 24, and 36 hr postexposure (PE). Two hours before euthanization, rats were injected with bromodeoxyuridine (BrdU) to label S-phase cells. The nasal cavities were fixed and processed for light microscopy. Sections from the anterior nasal cavity were immunostained to detect BrdU-labeled cells and analyzed to determine the numeric densities of NTE cells and intraepithelial neutrophils, and the labeling index (LI; [BrdU-labeled epithelial cells/total epithelial cells] x 100) and unit length labeling index (ULLI; BrdU-labeled epithelial cells/mm basal lamina) of the NTE overlying maxilloturbinates. O3 exposure induced a transient influx of neutrophils 2-4 hr PE and a significant (17%) loss of NTE cells 2-4 hr PE. An increase in epithelial DNA synthesis was first detected 12 hr PE. In this study, there was no difference in the sensitivity of the two measures of epithelial cell DNA synthesis. Both the LI and ULLI were greatest 20-24 hr PE and were reduced, but still greater than those of controls, by 36 hr PE. The numeric density of NTE cells returned to control levels 20-24 hr PE. This study has defined the kinetics of acute O3-induced NTE cell injury, loss, and proliferation in vivo. The transit time from Go to S, after O3-induced injury, was 12-20 hr and the duration of G2 + M was 8-12 hr. These data may be used to further explore the early cellular and molecular events that lead to ozone-induced mucous cell metaplasia.

Responses of rat nasal epithelium to short- and long-term exposures of ozone: image analysis of epithelial injury, adaptation and repair

This article reviews the use of computerized image analysis and standard morphologic techniques to characterize the responses of nasal epithelium in laboratory rats to single or repeated exposures to a common urban air-pollutant, ozone. Alterations in the number and composition of the epithelial cell populations after either short- or long-term exposures are described. The principal nasal epithelial alteration induced by repeated exposures to this irritating, oxidant pollutant is mucous cell metaplasia (i.e., transformation of airway epithelium, normally devoid of mucous cells, to a secretory epithelium containing numerous mucus-secreting cells). This metaplastic change, induced by acute or chronic ozone exposures, has been morphometrically examined at various times post-exposure. In this article, we describe our current understanding of the pathogenesis and persistence of ozone-induced mucous cell metaplasia in nasal epithelium based on the results of these morphometric studies.

Neutrophil involvement in the retention and clearance of dust intratracheally instilled into the lungs of F344/N rats

This study evaluated polymorphonuclear leukocyte (PMN) involvement in translocation of dust to bronchial lymph nodes after deposition of dust in the lungs of control and neutropenic F344/N rats. Rats were rendered neutropenic with an intraperitoneal (IP) injection of anti-rat PMN antiserum (APA); control rats were injected IP with 0.9% saline solution. Eighteen hours after IP injections, control and APA-treated rats were instilled intratracheally with 5 x 10(8) microspheres suspended in 0.9% saline solution, which caused an influx of PMNs into the pulmonary airspaces of control rats, but not of APA-treated rats. One day postinstillation (PI), 77.2% of the microspheres recovered in bronchoalveolar lavage fluid (BALF) from control rats were associated with pulmonary alveolar macrophages (PAMs) and 18.8% with PMNs; 4.0% were free. In BALF from the APA-treated rats, 66.3% of the microspheres were associated with PAMs and 0.3% with PMNs; 36.3% were free. Two days PI, about 95% of the microspheres in BALF from control and APA-treated rats were associated with PAMs; by 4 and 7 days PI, essentially 100% were with PAMs. Amounts of microspheres translocated to bronchial lymph nodes of control rats were four fold less than in the APA-treated rats on days 2, 4, and 7 PI (p < .05). The results suggest that PMNs in pulmonary airspaces of F344/N rats phagocytize dust and thereby interfere with the mechanism(s) involved in dust penetration into the pulmonary interstitium.

A small proline-rich protein, SPRR1, is upregulated early during tobacco smoke-induced squamous metaplasia in rat nasal epithelia

Small proline-rich proteins, believed to be precursor proteins for the crosslinked envelope formation in cells undergoing squamous differentiation, are encoded by the SPRR genes. To further investigate the role of these proteins, the time course of increased synthesis of SPRR1 mRNA in nasal epithelia of rats exposed to cigarette smoke was determined, and the deduced amino acid sequence of the rat SPRR1 was compared with those of other species. Using the pig homologue (20K) antisense cRNA probe, high levels of SPRR1 transcript were detected by in situ hybridization in squamous epithelia that line the nasal vestibule and hard palate of the rat. Basal cells of both the vestibule and palate contained low levels of the transcript, and increasing amounts were detected in the squamous layers. In rats exposed to 250 mg/m3 (total particulate matter) cigarette smoke 6 h/day for 5 days, the number of small mucous cells increased in the respiratory epithelium of the nasal septum in the early stages of squamous differentiation, but were gradually replaced by squamous metaplastic cells. During this transition, hybridization of the 20K antisense cRNA probe increased in the epithelial and mesenchymal cells, indicating that SPRR1 protein could have roles in cellular differentiation other than as a building block of the crosslinked envelope. Similarly, high levels of SPRR1 transcript were detected in the nasal transitional epithelium lining internal walls and maxilloturbinates that had undergone squamous metaplasia after cigarette smoke exposure. At 5 days after the withdrawal of cigarette smoke exposure, the morphology of the midseptal epithelium returned to that of a pseudostratified mucociliary epithelium and the epithelia lining the maxilloturbinates to that of a transitional epithelium. Accompanying this change in morphology of the tissues, the levels of SPRR1 transcripts significantly decreased in the epithelia. However, in the mesenchyme no significant decrease was observed during this recovery. RNA prepared from the external nose surrounding the nasal vestibule contained a transcript of about 0.9 kb that hybridized to the 20K cDNA probe on Northern blot analysis. DNA sequence analysis of the transcript confirmed the identity as that of the SPRR mRNA with its characteristic repeat encoding the oligopeptide with the general consensus -EPC*PKVP-. However, the rat homologue rSPRR1 contained more repeats of the oligopeptide compared with those of higher mammals such as the rabbit, pig, and human, suggesting a possible inverse relation between number of repeats and evolution development. This finding suggests that the number of repeats in the protein may be redundant; however, the conserved sequence of the peptide indicates that this region is essential for the function of this protein.

Mass cells contribute to O3-induced epithelial damage and proliferation in nasal and bronchial airways of mice

Ozone (O3) exposure produces inflammation in the airways of humans and animal models. However, the mechanism by which O3 affects these changes is uncertain. Mast cells are strategically located below the epithelium of the airways and are capable of releasing a number of proinflammatory mediators. We tested the hypothesis that mast cells contribute to inflammation, epithelial sloughing, and epithelial proliferation in the nasal and terminal bronchiolar murine airways after O3 exposure. Mast cell-sufficient (+/+), mast cell-deficient (W/Wv), and mast cell-repleted [bone marrow-transplanted (BMT) W/Wv] mice were exposed to 2 ppm O3 or filtered air for 3 h. Nasal and bronchoalveolar lavage fluids were collected 6 and 24 h after exposure. Differential cell counts and protein content of the lavage fluids were used as indicators of inflammation and permeability changes in the airways. O3-induced epithelial injury was assessed by light microscopy, and O3-induced DNA synthesis in airway epithelium was estimated by using a 5-bromo-2'-deoxyuridine-labeling index in the nasal and terminal bronchiolar epithelia. Relative to air control mice, O3 caused significant increases in inflammation, epithelial injury, and epithelial DNA synthesis in +/+ mice. There was no significant effect of O3 exposure on any measured parameter in the W/Wv mice. To further assess the role of mast cells in O3-induced epithelial damage, mast cells were restored in W/Wv mice by BMT from +/+ congeners. Relative to sham-transplanted W/Wv mice, O3 caused significant increases in epithelial damage and DNA synthesis as well as inflammatory indicators in BMT W/Wv mice. These observations are consistent with the hypothesis that mast cells significantly modulate the inflammatory and proliferative responses of the murine airways to O3.

Mucous cell metaplasia in the airways of rats exposed to machining fluids

Occupational exposure to microbial-contaminated machining fluids is associated with a variety of adverse pulmonary effects including chronic bronchitis and increased sputum production. We have previously demonstrated in F344 rats that inhaled endotoxin can increase the amount of stored intraepithelial mucosubstances (Vs) in the respiratory tract. The purpose of the present study was to examine the effect of endotoxin-contaminated machining fluid aerosols on mucous production. Rats were exposed to aerosols of pyrogen-free water, 1 or 10 mg/m3 used machining fluid, or 10 mg/m3 unused machining fluid for 3 hr/day for 3 days. Twenty-four hours after the final exposure, right lung lobes were lavaged and the nasal cavity and left lung were fixed in formalin. The amount of Alcian blue/periodic acid-Schiff-stained mucosubstances was determined by morphometry. Exposure to 10 mg/m3 used machining fluid (equivalent to 0.8 micrograms/m3 endotoxin) produced a significant increase in Vs in the epithelial lining of both the nasal septum and intrapulmonary airways. These changes in Vs were accompanied by a significant increase in total cells and neutrophils in the lavage fluid. No changes in stored mucosubstances or lavage parameters were found in animals exposed to 1 mg/m3 used machining fluid aerosols. A significant increase in Vs was observed in the nasal septum but not in the intrapulmonary airways of animals exposed to 10 mg/m3 unused machining fluids (no measurable endotoxin). These results suggest that in addition to endotoxin, nonendotoxin components of machining fluids may contribute to the increase in sputum and chronic bronchitis reported for workers exposed to machining fluid aerosols.

Cotton dust produces an increase in intraepithelial mucosubstances in rat airways

Occupational exposure to endotoxin-contaminated organic dusts is associated with a variety of adverse pulmonary effects, including chronic bronchitis and sputum production. We have previously demonstrated in F344 rats that inhaled endotoxin rapidly induces an increase in the volume of stored intraepithelial mucosubstances (Vs) in the respiratory tract. The present study examined whether endotoxin-contaminated cotton dust can produce a similar increase in Vs in this animal model. Rats were exposed to air or 1.5 to 15.0 mg/m3 cotton dust for 2 h/d for 3 d. Twenty-four hours after the final exposure, the nasal cavity and lungs were fixed in formalin and the presence of Alcian blue/periodic acid-Schiff-staining mucosubstances determined by morphometry. Exposure to cotton dust produced concentration-dependent changes in Vs in the nasal septum and intrapulmonary airways. Statistically significant increases in Vs were observed in the epithelial lining of the nasal septum of animals exposed to 5.3 and 14.5 mg/m3 cotton dust (equivalent to 2.8 and 8.9 micrograms/m3 endotoxin). Vs in the intrapulmonary airways was also significantly increased at these concentrations. No significant changes were observed in the nasal septum or intrapulmonary airways after exposure to 1.8 mg/m3 cotton dust. These results are consistent with the hypothesis that endotoxin may contribute to the increase in human cases of chronic bronchitis reported in occupational settings in which endotoxin-contaminated dusts are encountered.

Regional differences in the effects of mainstream cigarette smoke on stored mucosubstances and DNA synthesis in F344 rat nasal respiratory epithelium

This study was designed to determine the effects of mainstream cigarette smoke (MCS) on stored intraepithelial mucosubstances (IM) and DNA synthesis within the nasal respiratory epithelium of F344 rats and whether such effects persist after cessation of exposure. Rats were exposed to filtered air or diluted MCS for 9 days over a 2-week period. Two hours prior to termination rats were injected with bromodeoxyuridine (BrdU) to label cells synthesizing DNA 1 or 14 days after the last exposure. Sections of nasal tissue blocks taken from a region immediately posterior to the incisor teeth were processed for light microscopy and histochemically stained to detect acidic and neutral IM and immunochemically stained to detect BrdU-labeled cells. The nasal septum was divided into three measurement zones (dorsal, mid-, and ventral) for morphometric quantitation of the volume density of IM and the unit length labeling index (ULLI). MCS-exposed rats terminated 1 day after the last exposure had 270% more IM in the dorsal septum, 58% less IM in the midseptum (due to regions of squamous metaplasia), and amounts of IM in the ventral septum similar to controls. MCS-exposed rats sacrificed 14 days after exposure still had increased amounts of IM in the dorsal septal region, but no regions of squamous metaplasia or amounts of IM in the mid- and ventral septal regions that were different from air-exposed controls. MCS exposure resulted in a significant increase in the ULLI 1 day but not 14 days after exposure in the ventral and midseptal regions only. The results of this study indicate that MCS exposure induces transient alterations in the mucous-producing apparatus in the rat anterior nasal cavity that are resolved following 2 weeks of recovery. However, the type and magnitude of the initial epithelial responses are dependent on the intranasal location of the airway epithelium examined.

A comparison of the inflammatory response of the lung to inhaled versus instilled particles in F344 rats

The potential pulmonary toxicity of poorly soluble airborne dusts generated in industrial and environmental settings is often evaluated by inhalation studies in rodents. Studies using intratracheal instillation of particles have been suggested as a less expensive alternative. We conducted a study to compare the inflammatory response of the lung to instilled versus inhaled particles. In one study, female F344/N rats, 11-13 weeks of age, were exposed for 6 hr/day, 5 days/week for 4 weeks by inhalation to 0, 0.1, 1.0, or 10 mg/m3 of either alpha-quartz (toxic particle) or TiO2 (relatively low toxicity particle) and the lung burdens were determined at 1 week after the end of the exposure. The lungs were evaluated by analysis of bronchoalveolar lavage fluid (BALF) at 1, 8, and 24 weeks after the end of the exposure and by histopathology at 24 weeks. In a second study, rats were exposed by instillation to the lung burdens present in the preceding study at 1 week after the inhalation exposure, and the rats were evaluated in the same manner as in the inhalation study. In general, the degree of alveolitis, as evaluated by histopathology and BALF analysis, was similar by the two methods of exposure. With lung burdens up to 750 micrograms/g lung, the TiO2 elicited no changes in BALF parameters at any time by either method of exposure, nor was any histopathology observed. The BALF changes elicited by alpha-quartz were of approximately the same magnitude and followed the same time course by either exposure method with the lowest dose delivered to the lung by either method being a "no-effect" dose. At the highest dose, microgranulomas were observed in bronchial-associated lymphoid tissue (BALT) in both sets of rats. However, the highest inhalation exposure induced pleural granulomatous lesions that were not observed in the animals instilled with alpha-quartz. The results indicate that the relative potentials of the two materials to produce bronchoalveolitis and granulomatous lesions in BALT could be appropriately evaluated using either intratracheal or inhalation exposures.

Consequences of prolonged inhalation of ozone on F344/N rats: collaborative studies. Part V: Effects on pulmonary function

The impact of a 20-month exposure to ozone on the pulmonary function of rats was assessed from a single series of measurements made after exposures were completed. Four to ten male and female F344/N rats per group were exposed six hours per day, five days per week, for 20 months to ozone at 0.12, 0.5, or 1.0 parts per million (ppm), or to clean air as controls. One to three days after the last exposure, the rats were anesthetized using halothane, fitted with oral endotracheal and esophageal catheters, and measured using plethysmographic techniques. The differences between mean values for control and treated rats were tested for significance by multiple comparisons. The values and intersubject variability for more than 30 measured and calculated parameters were similar to those reported previously for rats of similar age. The only consistent exposure-related effect was a small reduction of residual volume measured during slow lung deflation. This trend was observed in most exposure groups, but was most significant in females exposed to ozone at the 0.5 ppm level. Fibrosis and epithelial changes were observed in the terminal bronchiole-alveolar duct region in parallel studies of different rats from the same exposure groups. We hypothesized that these changes stiffened airspace walls and acted to maintain the patency of the air pathway at a lower than normal lung volume during deflation. Overall, the exposures had little impact on the integrated pulmonary function of the lung as measured in anesthetized rats.

Consequences of prolonged inhalation of ozone on F344/N rats: collaborative studies. Part VII: Effects on the nasal mucociliary apparatus

Besides the centriacinar region of the lung, the nose is a principal target for ozone toxicity. Acute exposures to concentrations of ozone in ambient air induce secretory cell metaplasia in the nasal transitional epithelium of rats. This study examined the effects of chronic ozone exposure on the structure and function of the nasal mucociliary apparatus of the rat. Male and female F344/N rats were exposed to ozone concentrations of 0.0 (controls), 0.12, 0.5, or 1.0 parts per million (ppm), six hours per day, five days per week, for 20 months. All rats were killed seven or eight days after the end of the exposure. Immediately after death, mucous flow rates throughout the nasal passages were determined using in vitro video motion analysis. Following assessment of mucociliary function, the nasal tissues were processed for light microscopy and stained with Alcian blue (pH 2.5)/periodic acid-Schiff to detect intraepithelial mucus. Image analysis was used to quantitate the amount of mucus within the nasal transitional epithelium. In rats exposed to 0.5 or 1.0 ppm ozone, mucous flow rates were markedly slower over the lateral wall and turbinates of the proximal third of the nasal airways than they were in rats exposed to 0.0 or 0.12 ppm ozone. These intranasal regions in the rats exposed to 0.5 or 1.0 ppm ozone contained marked mucous cell metaplasia and 25 to 300 times more mucus in nasal transitional epithelium than was found in control rats. In addition, male and female rats exposed to 0.5 or 1.0 ppm ozone had marked epithelial hyperplasia in nasal transitional epithelium, increases in eosinophilic globules in the surface epithelium lining the distal nasal airways, and a mild to moderate inflammatory cell influx in the nasal mucosa in the proximal and middle nasal passages. Male rats also had conspicuous bony atrophy in maxilloturbinates and nasoturbinates. There were no significant decreases between the mucous flow rates of rats exposed to 0.12 ppm ozone and those of control rats. There were, however, mild increases in various flow rates in some areas of the nasal airways in rats exposed to 0.12 ppm ozone compared with control rats. No significant morphologic alterations were evident in the rats exposed to 0.0 or 0.12 ppm ozone. The results of this study indicate that rats chronically exposed to 0.5 or 1.0 ppm ozone have significant alterations in the function and structure of the nasal mucociliary apparatus. Though there was a mild increase in mucous flow rates in a few nasal regions of some rats exposed to 0.12 ppm ozone, this functional change was interpreted as a physiologic, rather than a pathologic, response to ozone at this relatively low concentration.

Morphometric approaches for evaluating pulmonary toxicity in mammals: implications for risk assessment

Recent advances in quantitative morphology provide all the tools necessary to obtain structural information in the lung that can be quantified and interpreted in the three-dimensional world of toxicology. Structural hierarchies of conducting airways and parenchyma of the lung provide: (1) numbers of cells per airway, lobe, or lung; (2) surface areas of cells, airways, and alveoli; (3) length of airways and vessels; and (4) volumes of cells, alveoli, airways, vessels, and individual lobes or the entire lung. Unbiased sampling of these subcompartments of the lung requires fractionation of lobes or individual airways. Individual airways of proximal and distal generations are obtained by airway microdissection along one axial pathway and comparisons made between airway generations. Vertical sections of selected airways are used to sample epithelium and interstitium. Using this unbiased approach of quantitative morphology, we have shown that inhalation of low ambient concentrations of ozone ([O3]0.15 ppm) near or at the United States National Ambient Air Quality Standard (NAAQS) (0.12 ppm O3) induces significant alterations in bronchiolar epithelium and interstitium in nonhuman primates but not rats. The alterations do not appear to be concentration- or time-dependent, thereby bringing into question the current NAAQS that may be at or above the threshold for distal airway injury in primates. Unbiased morphometric methods are critical in a quantitative evaluation of toxicological injury of mammalian tracheobronchial airways.

The rabbit lacrimal gland in vitamin A deficiency

PURPOSE

To investigate the morphology, ultrastructure, and protein secretion of the vitamin A-deficient rabbit lacrimal gland.

METHODS

The lacrimal glands of vitamin A-deficient rabbits and age-matched controls were fixed, processed by standard methods, and examined by light and transmission electron microscopy. Protein secreted by the lacrimal gland was analyzed using gel filtration chromatography and electrophoresis.

RESULTS

By light microscopy, the glands of experimental and control rabbits were indistinguishable. Electron microscopy showed little effect of vitamin A deficiency on the lacrimal acini, although occasional pyknotic nuclei were observed. The intralobular ductal epithelium was unaffected. Protein concentration and composition were essentially unchanged in lacrimal gland fluid of vitamin A-deficient rabbits compared to controls.

CONCLUSIONS

The rabbit lacrimal gland is minimally affected by vitamin A deficiency, suggesting species differences between rabbits and rats in the vitamin A requirements of the lacrimal gland. Normal lacrimal gland structure and function in vitamin A deficiency allow for the prompt secretion of retinol on the restoration of vitamin A to the diet.

A microspray nozzle for local administration of liquids or suspensions to lung airways via bronchoscopy

A microspray nozzle has been developed for the localized administration of solutions or suspensions to discrete pulmonary airway regions via bronchoscopy. Toxicants or tracer particles can be administered to single or multiple, specific lung airway segments. This permits studies of local-airway, whole-lung, and systemic responses to inhaled materials. The nozzle is fabricated by ultra-precision machining, has an overall length of 1 mm, and a diameter small enough to fit in the end of a 1.1-mm inner diameter, 1.2-mm outer diameter catheter. In vitro studies demonstrated the delivery efficiency for 99mTc solutions (98 +/- 1% SD) and for suspensions of 99mTc sulfur colloid or 3-mum 85Sr-labeled microspheres (55 +/- 15%). Photographic and gamma camera images of material deposited in the airways of Beagle dogs demonstrated in vivo that the deposition patterns are compact and uniform. The technique may also have therapeutic medical applications.

Effect of inhaled endotoxin on intraepithelial mucosubstances in F344 rat nasal and tracheobronchial airways

Increased sputum production and chronic bronchitis are associated with occupational exposure to endotoxin-contaminated organic ducts. The present study examined whether repeated exposure to occupationally relevant concentrations of airborne endotoxin in the F344 rat can alter the volume density of stored intraepithelial mucosubstances (Vs) in the respiratory tract. Rats were exposed to saline or endotoxin aerosols for 3 h/day for 3 days and were killed 24 h after the last exposure. Quantitative histochemistry of Vs in airway epithelium was examined at three distinct levels of the respiratory tract (nose, trachea, and lung). Exposure to endotoxin produced a dose-dependent increase in Vs in the intrapulmonary airways. The quantity of Vs in the intrapulmonary airways was significantly increased in animals exposed to as little as 0.3 micrograms/m3 endotoxin. Significant increases in Vs were observed in the trachea only after exposure to > or = 3.1 micrograms/m3 endotoxin, whereas no significant changes were observed in the nasal airways even at concentrations as high as 52.4 micrograms/m3. These results are consistent with earlier findings in which repeated instillation of endotoxin produced significant increases in Vs in the epithelial lining of the pulmonary airways and demonstrate that inhaled endotoxin may play a role in the increase in sputum and chronic bronchitis reported for workers exposed to organic dusts.

In vivo effects of endotoxin on DNA synthesis in rat nasal epithelium

Airway inflammation in bacterial infections is characterized by the presence of neutrophils and often epithelial injury and repair. Release of endotoxin from bacteria may contribute to these processes. The purpose of this study was to determine the in vivo effects of repeated endotoxin exposure on DNA synthesis in rat nasal epithelium in the presence and absence of neutrophilic influx. Rats were intranasally instilled, once a day for 3 days, with endotoxin or saline (controls). Before the first and third instillations, half of the saline and endotoxin-instilled animals were depleted of circulating blood neutrophils by administering a rabbit anti-rat neutrophil antiserum. Rats were sacrificed 6 or 24 h after the last instillation. Two hours prior to sacrifice, rats were intraperitoneally injected with bromodeoxyuridine (BrdU), an analog of thymidine that is incorporated in the nucleus of cells in the S-phase of the cell cycle. Nasal tissues were processed for light microscopy and immunohistochemical detection of BrdU in nasal epithelial cells. The numbers of nasal epithelial cells, BrdU-labeled epithelial nuclei, and neutrophils per millimeter of basal lamina in the epithelium lining the nasal turbinates in the proximal nasal passages were determined by morphometric analysis. We did not observe a neutrophilic influx in the nasal tissues of neutrophil-depleted rats at 6 or 24 h after the last endotoxin instillation; however, the numbers of nasal epithelial cells and the BrdU-labeling index were significantly increased compared to saline-instilled controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Response of macaque bronchiolar epithelium to ambient concentrations of ozone

Recently, we reported that exposure to ambient concentrations of ozone, near the U.S. National Ambient Air Quality Standard (0.12 ppm), induced significant nasal epithelial lesions in a non-human primate, the bonnet monkey. The present study defines the effects of ambient concentrations of ozone on the surface epithelium lining respiratory bronchioles and on the underlying bronchiolar interstitium in these same monkeys. Bonnet monkeys were exposed to filtered air or to 0.15 or 0.30 ppm ozone 8 hours/day for 6 or 90 days. At the end of exposures, monkeys were anesthetized and killed by exsanguination. Microdissected bronchiolar airways of infusion-fixed lungs were evaluated morphometrically by light microscopy and quantitatively by scanning and transmission electron microscopy for ozone-induced epithelial changes. Hyperplasia of nonciliated, cuboidal epithelial cells and intraluminal accumulation of macrophages characterized ozone-induced lesions in respiratory bronchioles. There were no significant differences in epithelial thickness or cell numbers among ozone-exposed groups. Ozone-exposed epithelium was composed of 80% cuboidal and 20% squamous cells compared with 40% cuboidal and 60% squamous cells in filtered air controls. In addition, the arithmetic mean thickness of the surface epithelium, a measure of tissue mass per unit area of basal lamina, was significantly increased in all of the ozone-exposed groups. The number of cuboidal epithelial cells per surface area of basal lamina was increased above control values by 780% after 6 days exposure to 0.15 ppm, 777% after 90 days to 0.15 ppm, and 996% after 90 days exposure to 0.30 ppm. There was also a significant ozone-induced increase in the thickness of the bronchiolar interstitium that was due to an increase in both cellular and acellular components. These results demonstrate that exposure to low ambient concentrations of ozone, near the current. National Ambient Air Quality Standard, induces pulmonary lesions in primates. The alterations do not appear to be concentration- or time-dependent, suggesting that the current National Ambient Air Quality Standard may be at or above the threshold for deep lung injury in primates.