Biochemical and Morphologic Responses of Rat Nasal Epithelia to Hyperoxia

Biochemical and Morphologic Responses of Rat Nasal Epitheliato Hyperoxia. NIKULA, K. J., SABOURIN, P. J., FRIETAG, B. C,BIRDWHISTELL, A. J., HOTCHKISS, J. A., AND HARKEMA, J. R. (1991).Fundam. Appl. Toxicol 17, 675–683. While performing itsfunctions in olfaction, modification of inspired air, and protectionof the lower respiratory tract from high concentrations of potentiallyharmful inhalants, the nasal mucosa can be injured by a numberof inhalants. In this study, F344/N male rats were exposed tofiltered air or hyperoxia (85 or 87% oxygen), 24 hr/day, 7 days/week,for 1 (acute exposure) or 11 (chronic exposure) weeks. Therewere distinct differences between the different epithelial regionsexamined in replicative and morphologic responses as well asaltered enzyme activities in response to oxygen exposure. Neitheracute nor chronic hyperoxic exposure caused degenerative, necrotizing,or inflammatory changes in any of the nasal epithelial examined.Hyperoxia-induced hypertrophy, but not hyperplasia, of the non-ciliatedoiboidal (NCC) epithelium occurred after both acute and chronicexposure. Cell replication was increased in portions of theNCC and respiratory epithelia after acute hyperoxia exposure.There were significant increases, compared to controls, in thespecific activity of glucose-6-phosphate dehydrogenase in thenasal turbinates, maxilloturbinates, and lateral wall epithelium(NCC epithelium), the nasal septum (respiratory epithelium),and the ethmoturbinates (olfactory epithelium), and in the specificactivity of glutathione peroxidase in the NCC epithelium andethmoturbinates after acute hyperoxia exposure. The specificactivity of cytochrome P450-dependent monooxy-genase-catalyzedO-deethylation of 3-cyano-7-ethoxycoumarin was significantlydecreased, compared to controls, in the NCC epithelium. Theseresults suggest that hyperoxia exposure induces morphologicand biochemical alterations in nasal epithelia which appearto be protective responses of certain cell types to hyperoxia.     

Olfactory Mucosal Lesions in F344 Rats Following Inhalation Exposure to Pyridine at Threshold Limit Value Concentrations

Pyridine is a volatile solvent used as an intermediate in theproduction of insecticides, herbicides, pharmaceuticals, anddyes. Pyridine is also found in tobacco smoke. Because inhalationis a primary route of exposure to pyridine, we examined theeffect of inhaled pyridine on morphology at the portal of entry,the nose. Nasal tissues from F344/N rats exposed using a noseonlymode 6 hr/day for 4 days to either filtered air (controls) orone of two concentrations of pyridine vapor were examined histologically.The rats had been killed 18 hr after the last exposure. Thetwo pyridine concentrations were the current threshold limitvalue (TLV, 5 ppm) and a high concentration (444 ppm). Olfactoryepithelial lesions in rats exposed to both concentrations ofpyridine included vacuolar degeneration of sustentacular cells;focal, marked attenuation of the epithelium; loss of vacuolardegeneration of sustentacular cells; focal, marked attenuationof the epithelium; loss of neurons; and the presence of intraepithelialluminal structures. The lesions were only slightly more severein the rats exposed to 444 ppm compared to those rats exposedto 5 ppm pyridine. The results show that inhalation of pyridineat the current TLV concentration of 5 or 444 ppm causes lesionsin the olfactory epithelium of rats.     

Effect of Chronic Cigarette Smoke Exposure on Lung Clearance of Tracer Particles Inhaled by Rats

Cigarette smoking can influence the pulmonary disposition ofother inhaled materials in humans and laboratory animals. Thisstudy was undertaken to investigate the influence of cigarettesmoke exposures of rats on the pulmonary clearance of inhaled,relatively insoluble radioactive tracer particles. Following13 weeks of whole-body exposure to air or mainstream cigarettesmoke for 6 hr/day, 5 days/week at concentrations of 0, 100,or 250 mg total particulate matter (TPM)/m³, rats were acutelyexposed pernasally to ⁸⁵Sr-labeled fused aluminosilicate (⁸⁵Sr-FAP)tracer particles, then air or smoke exposures were resumed.A separate group of rats was exposed to the ⁸⁵Sr-FAP then seriallyeuthanized through 6 months after exposure to confirm the relativeinsolubility of the tracer particles. We observed decreasedtracer particle clearance from the lungs that was smoke concentration-dependent.By 180 days after exposure to the tracer aerosol, about 14,20, and 40% of the initial activity of tracer was present incontrol, 100 mg TPM/m³, and 250 mg TPM/m³ groups, respectively.Body weight gains were less in smoke-exposed rats than in controls.Smoke exposure produced lung lesions which included increasednumbers of pigmented alveolar macrophages distributed throughoutthe parenchyma and focal collections of enlarged alveolar macrophageswith concomitant alveolar epithelial hyperplasia and neutro-philicalveolitis. The severity of the lesions increased with smokeexposure duration and concentration to include interstitialaggregates of pigmented macrophages and interstitial fibrosis.Our data confirm previous findings that exposure to cigarettesmoke decreases the ability of the lungs to clear inhaled materials.We further demonstrate an exposure-concentration related magnitudeof effect, suggesting that the cigarette smoke-exposed rat constitutesa useful model for studies of the effects of cigarette smokeon the disposition of inhaled particles.     

Thirteen-Week, Repeated Inhalation Exposure of F344/N Rats and B6C3F1 Mice to Ferrocene

Ferrocene (dicyclopentadienyl iron; CAS No. 102-54-5) is a relativelyvolatile compound used as a chemical intermediate, a catalyst,and an antiknock additive in gasoline. This organometallic chemicalis of particular interest because of its structural similaritiesto other metallocenes, some of which are carcinogenic. F344/Nrats and B6C3F₁ mice were exposed to 0, 3.0, 10, and 30 mg ferrocenevapor/m³, 6 hr/day, 5 days/week, for 13 weeks. During theseexposures, no rats or mice died, nor were any clinical signsof ferrocene-related toxicity observed. At the end of the exposures,male rats exposed to the lowest and highest level of ferrocenehad decreased body weight gains compared to filtered-air-exposedcontrol male rats, while body weight gains for all groups ofboth ferrocene- and filtered-air-exposed female rats were similar.Male mice exposed to ferrocene had no differences in body weightgains, compared to controls, but female mice had decreases inbody weight gains at the 10 and 30 mg/m³ exposure levels. Therewere exposure concentration- and exposure-time-related increasesin lung burdens of iron. The mean iron lung burden in rats exposedto 30 mg ferrocene vapor/m³ for 90 days was four times greaterthan the burden in control rats. No exposure-related changesin respiratory function, lung biochemistry, bronchoalveolarlavage cytology, total lung collagen, clinical chemistry, andhematology parameters were observed. This suggests that theaccumulations of iron in lung did not cause an inflammatoryresponse nor any functional impairment of the lung. There wereno indications of developing pulmonary fibrosis nor of any hematologictoxicity. No exposure-related gross lesions were seen in anyof the rats or mice at necropsy. Exposure-related histopathologicalterations, primarily pigment accumulations, were observedin the nose, larynx, trachea, lung, and liver of both species,and in the kidneys of mice. Lesions were most severe in thenasal olfactory epithelium where pigment accumulation, necrotizinginflammation, metaplasia, and epithelial regeneration occurred.Nasal lesions were observed in all ferrocene-exposed animalsand differed only in severity, which was dependent on the exposureconcentration. Histochernical stains of these target tissuesshowed the presence of iron ions. The results suggest that themechanism of ferrocene toxicity may be the intracellular releaseof ferrous ion through ferrocene metabolism, followed by eitheriron-catalyzed lipid peroxidation of cellular membranes or theiron-catalyzed Fenton reaction to form hydroxyl radicals thatdirectly react with other key cellular components, such as proteinor DNA.     

Response of Rat Tracheal Epithelium to Ozone and Oxygen Exposure in Vitro

Response of Rat Tracheal Epithelium to ozone and Oxygen Exposurein Vitro. NIKULA, K. J., AND WILSON, D. W. (1990). Fundam. Appl.Toxicol. 15, 121–131. Although ozone-induced epithelialinjury in vivo has been morphologically characterized, effectsof gaseous oxidants on respiratory epithelium in organ culture,where tissue organization is maintained but systemic influencesare eliminated, have not been thoroughly investigated. In thisstudy, we exposed tracheal organ cultures from rats to 95% oxygenand 1 ppm ozone, alone and in combination, to determine (1)whether epithelial responses to ozone similar to those observedin vivo occur in airways separated from systemic physiologic,secretory, and inflammatory reactions; (2) whether concentrationsof oxygen sufficient to potentially cause oxidant injury resultin morphologic epithelial alterations similar to those thatoccur in ozone toxicity; and (3) if the combined oxidant insultof oxygen and ozone results in more severe damage to the trachealepithelium than occurs with ozone in air. Tracheal organ cultureswere exposed to filtered air and 5% carbon dioxide; filteredair, 5% carbon dioxide, and 1 ppm ozone; 95% oxygen and 5% carbondioxide; or 95% oxygen, 5% carbon dioxide, and 1 ppm ozone for96 hr. Light- and quantitative electron-microscopic evaluationshowed that epithelia exposed to 1 ppm ozone in air exhibitedloss of ciliated cells and ciliated cell damage. The epitheliaexposed to 95% oxygen and 5% carbon dioxide were pseudostratified,columnar, ciliated, and hyperplastic. Epithelia exposed to 95%oxygen plus 1 ppm ozone were stratified and nonciliated or verysparsely ciliated. The predominant cell types in epithelia exposedto oxygen plus ozone were serous cells and metaplastic cells,and focal aggregates of adherent necrotic cells were present.We conclude that there was a synergism between oxygen and ozoneexposure leading to enhanced epithelial injury and metaplasia.     

Comparative Pulmonary Toxicities and Carcinogenicities of Chronically Inhaled Diesel Exhaust and Carban Black in F344 Rats

Diesel exhaust (DE) is a known pulmonary carcinogen in rats,and the carcinogenic response is known to require the presenceof soot. Many estimates of human lung cancer risk from inhaledDE have been developed from rat bioassay data or from the comparativemutagenic potencies of DE soot extract and known human chemicalcarcinogens. To explore the importance of the DE soot-associatedorganic compounds in the lung tumor response of rats, male andfemale F344 rats were exposed chroni cally to diluted wholeDE or aerosolized carbon black (CB) 16 hr/day, 5 days/week attarget particle concentrations of 2.5 mg/m³ (LDE, LCB) or 6.5mg/m³ (HDE, HCB) or to filtered air. The CB served as a surrogatefor the elemental carbon matrix of DE soot. Considering boththe mass fraction of solvent-extractable matter and its mutagenicityin the Ames Salmonella assay, the mutagenicity in revertantsper unit particle mass of the CB was three orders of magnitudeless than that of the DE soot. Both DE soot and CB particlesaccumulated progressively in the lungs of exposed rats, butthe rate of accumulation was higher for DE soot. In general,DE and CB caused similar, dose-related, nonneoplastic lesions.CB and DE caused significant, exposure concentration-relatedincreases, of similar magnitudes, in the incidences and prevalencesof the same types of malignant and benign lung neoplasms infemale rats. The incidences of neoplasms were much lower inmales than females, and the mci dences were slightly higheramong DE- than CB-exposed males. Survival was shortened in theCB-exposed males, and the short ened survival may have suppressedthe expression of carcinoge nicity as measured by crude incidence.Logistic regression mod eling did not demonstrate significantdifferences between the carcinogenic potencies of CB and DEin either gender. The re sults suggest that the organic fractionof DE may not play an important role in the carcinogenicityof DE in rats.     

BIOLOGICAL AND IMMUNOLOGICAL ACTIVITY OF HUMAN CHORIONIC GONADOTROPHIN IN MATERNAL SERUM DURING EARLY PREGNANCY

Serum chorionic gonadotrophin (hCG) levels were measured by three different assay methods in 20 women admitted to legal abortion and 21 patients having insulin-dependent diabetes, both during 8 to 14 weeks of pregnancy. Biological activity of hCG was determined with a mouse Leydig cell in-vitro bioassay, binding activity of the hormone to LH receptors by rat testis radioreceptorassay, and immunoreactivity by fluorimmunoassay. Bioassay and radioreceptorassay gave 1.4 and 1.7-fold higher hCG concentrations than fluoroimmunoassay using the same standard. Correlations between hCG levels measured by bioassay and fluoroimmunoassay (r = 0.81; P less than 0.01) and radioreceptorassay and fluoroimmunoassay (r = 0.95; P less than 0.01) were good. The results emphasize the heterogeneity of hCG in the pregnancy serum. Different domains of the molecules are recognized by assay methods based on antigenicity, receptor binding and biopotency of the hormone.