Comparative pulmonary and genotoxic responses to inhaled nickel subsulfide and nickel sulfate in F344 rats.

Inhalation studies with nickel (Ni) subsulfide (Ni3 S2 ) and Ni sulfate hexahydrate (NiSO4 ·6H2 O) investigated differences in mode of action that could explain why the former induced lung tumors in rats and the latter did not. Male rats were exposed to ≤0.22 mg Ni/m3 NiSO4 ·6H2 O or 0.44 mg Ni/m3 Ni3 S2 , 6 h/day, 5 days/week for 3 and 13 weeks; subsets of the rats exposed for 13 weeks were held for an additional 13 weeks. Analyses of bronchoalveolar lavage fluid, isolated cells, and whole lung tissue were conducted to compare the extent and persistence of any induced lung effects. Histological findings were qualitatively identical for both compounds and consistent with lesions reported in earlier studies. After 13 weeks of exposure, the incidence and severity of pulmonary inflammation and epithelial cell hyperplasia were greater among Ni3 S2 -exposed rats, whereas the reverse response was seen for apoptosis. Only Ni3 S2 exposure significantly increased epithelial and non-epithelial cell proliferation after 13 weeks of exposure. Both compounds induced DNA damage in isolated lung cells and DNA hypermethylation of whole lung tissue after 13 weeks of exposure at the highest exposure concentrations. Increases in cell proliferation, DNA damage, and tissue DNA hypermethylation did not persist during the 13-week recovery period. In summary, the highest concentrations of each compound produced marked pulmonary toxicity, but the lowest concentrations produced minimal or no effects. Differences in the proliferative and apoptotic responses between the two compounds may help explain differences in carcinogenicity, whereas the identification of no observed adverse effect concentrations (NOAECs) contributes to the risk characterization for inhalation exposure to nickel compounds.

5-Azacytidine inhaled dry powder formulation profoundly improves pharmacokinetics and efficacy for lung cancer therapy through genome reprogramming.

BACKGROUND: Epigenetic therapy through demethylation of 5-methylcytosine has been largely ineffective in treating lung cancer, most likely due to poor tissue distribution with oral or subcutaneous delivery of drugs such as 5-azacytidine (5AZA). An inhalable, stable dry powder formulation of 5AZA was developed. METHODS: Pharmacokinetics of inhaled dry powder and aqueous formulations of 5AZA were compared to an injected formulation. Efficacy studies and effect of therapy on the epigenome were conducted in an orthotopic rat lung cancer model for inhaled formulations. RESULTS: Inhaled dry powder 5AZA showed superior pharmacokinetic properties in lung, liver, brain and blood compared to the injected formulation and for all tissues except lung compared to an inhaled aqueous formulation. Only dry powder 5AZA was detected in brain (~4-h half-life). Inhaled dry powder was superior to inhaled aqueous 5AZA in reducing tumour burden 70-95%. Superiority of inhaled 5AZA dry powder was linked to effectively reprogramming the cancer genome through demethylation and gene expression changes in cancer signalling and immune pathways. CONCLUSIONS: These findings could lead to widespread use of this drug as the first inhaled dry powder therapeutic for treating local and metastatic lung cancer, for adjuvant therapy, and in combination with immunotherapy to improve patient survival.

PROPHYLACTIC ANTIBODY TREATMENT AND INTRAMUSCULAR IMMUNIZATION REDUCE INFECTIOUS HUMAN RHINOVIRUS 16 LOAD IN THE LOWER RESPIRATORY TRACT OF CHALLENGED COTTON RATS.

Human rhinoviruses (HRV) represent the single most important etiological agents of the common cold and are the most frequent cause of acute respiratory infections in humans. Currently the performance of available animal models for immunization studies using HRV challenge is very limited. The cotton rat (Sigmodon hispidus) is a well-recognized model for the study of human respiratory viral infections. In this work we show that, without requiring any genetic modification of either the host or the virus, intranasal infection of cotton rats with HRV16 resulted in measurable lower respiratory tract pathology, mucus production, and expression of interferon-activated genes. Intramuscular immunization with live HRV16 generated robust protective immunity that correlated with high serum levels of neutralizing antibodies. In addition, cotton rats treated prophylactically with hyperimmune anti-HRV16 serum were protected against HRV16 intranasal challenge. Finally, protection by immunization was efficiently transferred from mothers to newborn animals resulting in a substantial reduction of infectious virus loads in the lung following intranasal challenge. Overall, our results demonstrate that the cotton rat provides valuable additional model development options for testing vaccines and prophylactic therapies against rhinovirus infection.

SGI-110 and entinostat therapy reduces lung tumor burden and reprograms the epigenome.

The DNA methyltransferase (DNMT) inhibitor vidaza (5-Azacytidine) in combination with the histone deacetylase inhibitor entinostat has shown promise in treating lung cancer and this has been replicated in our orthotopic lung cancer model. However, the effectiveness of DNMT inhibitors against solid tumors is likely impacted by their limited stability and rapid inactivation by cytidine deaminase (CDA) in the liver. These studies were initiated to test the efficacy of SGI-110, a dinucleotide containing decitabine that is resistant to deamination by CDA, as a single agent and in combination with entinostat. Evaluation of in vivo plasma concentrations and pharmacokinetic properties of SGI-110 showed rapid conversion to decitabine and a plasma half-life of 4 hr. SGI-110 alone or in combination with entinostat reduced tumor burden of a K-ras/p53 mutant lung adenocarcinoma cell line (Calu6) engrafted orthotopically in nude rats by 35% and 56%, respectively. SGI-110 caused widespread demethylation of more than 300 gene promoters and microarray analysis revealed expression changes for 212 and 592 genes with SGI-110 alone or in combination with entinostat. Epigenetic therapy also induced demethylation and expression of cancer testis antigen genes that could sensitize tumor cells to subsequent immunotherapy. In the orthotopically growing tumors, highly significant gene expression changes were seen in key cancer regulatory pathways including induction of p21 and the apoptotic gene BIK. Moreover, SGI-110 in combination with entinostat caused widespread epigenetic reprogramming of EZH2-target genes. These preclinical in vivo findings demonstrate the clinical potential of SGI-110 for reducing lung tumor burden through reprogramming the epigenome.

Safety assessment of nebulized xylitol in beagle dogs.

Xylitol, a potential cystic fibrosis treatment, lowers the salt concentration of airway surface liquid and enhances innate immunity of human airways. The study objective was to evaluate the potential toxicity/recovery from a 14-consecutive day (7 days/week), facemask inhalation administration of nebulized xylitol solution in Beagle dogs. Aerosolized xylitol was generated through three Aerotech II nebulizers operating at approximately 40 psi driving pressure. Test article groups were exposed to the same concentration of aerosolized xylitol for 1, 0.5, or 0.25 h for the high, mid, and low exposures, respectively. A control group was exposed for 1 h to a nebulized normal saline solution. Animals were sacrificed the day following the last exposure or subsequently after 14 non-exposure days. Study endpoints included clinical observations, body weights, ophthalmology, and physical examinations, food consumption, clinical pathology, urinalyses, organ weights, and histopathology. Mean xylitol aerosol concentrations for all groups were approximately 3.5 mg/l. Mean total deposited doses to the pulmonary region were estimated as 21, 11, and 5 mg/kg, for the high-, mid-, and low-exposure groups, respectively. All dogs survived to the scheduled necropsy. No treatment-related findings were observed due to xylitol exposure in any end point examined. Lung findings (mild interstitial infiltration, macrophage hyperplasia, alveolitis, and bronchitis) were consistent among exposed and control groups. No exposure-related effect of xylitol in any parameter assessed was seen during or after the 14-day exposure in Beagle dogs. The No Observed Effect Level was the high-exposure level and suggests that inhaled xylitol is safe for clinical administration.

Antioxidant diet protects against emphysema, but increases mortality in cigarette smoke-exposed mice.

Oxidative stress plays an important role in cigarette smoke-induced lung inflammation and emphysema. We produced an enriched diet by adding freeze-dried fruits and vegetables and additional supplements to the 8604 Teklad Rodent Diet, a standard rodent diet. In this study, we examined the effects of the antioxidant-enriched diet on cigarette smoke-induced lung inflammation and emphysema. CH3/HeN mice were fed either a regular diet or the supplemented diet. These mice were exposed to filtered air, a low concentration of cigarette smoke (total particulate matter: 100 mg/m3) or a high concentration of cigarette smoke (total particulate matter: 250 mg/m3) for 6 h/day, 5 days/week for total 16 weeks. Surprisingly, increased mortality (53%) was observed in the high concentration of cigarette smoke-exposed mice fed the antioxidant diet compared to the high concentration of cigarette smoke-exposed mice that were fed a regular diet (13%). The necropsy analysis revealed nasal passage obstruction due to mucous plugging in cigarette smoke-exposed mice on the antioxidant diet. However, the antioxidant diet significantly reduced neutrophilic inflammation and emphysema in the high concentration of cigarette smoke-exposed mice as compared to the regular diet /high concentration of cigarette smoke controls. The antioxidant capacity in the bronchoalveolar fluid or oxidative damage to the lung tissue was not affected by the antioxidant diet. Pro-MMP-2, MMP-2, and MMP-9 activity did not correlate with the protective effects of AOD on cigarette smoke-induced emphysema. These data suggest that the antioxidant diet reduced cigarette smoke-induced inflammation and emphysema, but increased mortality in the obligate nose-breathing mice.

The acute toxicity, tissue distribution, and histopathology of inhaled ricin in Sprague Dawley rats and BALB/c mice.

Ricin is a highly toxic ribosome-inactivating protein derived from the castor bean (Ricinus communis). Due to the relative ease of producing ricin, it is characterized as a category B priority pathogen by the Center for Disease Control and Prevention. The purpose of this study was to compare the acute toxicity, associated histopathology, as well as the regional respiratory tract deposition and clearance kinetics of inhaled ricin in rats and mice using a single pure preparation. Acute toxicity was evaluated in five groups of six animals per species exposed nose-only to ricin aerosols and followed up to 7 days post-exposure. Tissues were collected for histopathology. The calculated median lethal doses (LD50s) were 0.24 µg/kg (rats) and 0.58 µg/kg (mice). Histological changes were noted in nose, larynges, trachea, lung, thymus, and spleen of both species. Pulmonary deposition in rats inhaling 94-99 ng/L ricin for 20 min (low dose) or 40 min (high dose) were 45.9 and 96 ng/g lung, respectively. Clearance was best described by a single-component negative exponential function. Estimated lung doses were 0.38 and 1.43 µg/g·h among the low and high dose rats, respectively. In mice inhaling 94 ng/L ricin for 20 min, pulmonary deposition was 91.1 ng/g lung and the estimated tissue dose was 1.72 µg/g·h. No ricin was detected in extra-respiratory tract tissue or in excreta. Results of this study demonstrate differences exist in pulmonary deposition, clearance rates, and tissue dose and histopathological changes between rats and mice inhaling ricin.

Time course of lesion development in the hairless guinea-pig model of sulfur mustard-induced dermal injury.

The objective of these studies was to provide detailed analyses of the time course of sulfur mustard (SM) vapor-induced clinical, histological, and biochemical changes following cutaneous exposure in hairless guinea-pigs. Three 6 cm(2) sites on the backs of each guinea-pig were exposed to SM vapor (314 mg(3) ) for 6 minutes (low dose) or 12 minutes (high dose). Animals were killed at 6, 24, and 48 hours, or 2 weeks postexposure. Erythema, edema, histopathology, and analysis of matrix metalloproteinase (MMP)-2 and -9 content were evaluated. Erythema was observed by 6 hours, and edema by 24 hours postexposure. Vapor exposure caused epidermal necrosis with varying degrees of dermatitis, ulceration, hemorrhage, and separation of the dermis from the epidermis. Later changes included epidermal regeneration with hyperplasia and formation of granulation tissue in the dermis with loss of hair follicles and glandular structures. Relative amounts of pro and active MMP-2 and MMP-9 were significantly increased in the high-dose SM group at 2 weeks. Erythema, edema, and histologic changes are consistent with findings among human victims of SM attack. This model, with observations to 2 weeks, will be useful in assessing the efficacy of countermeasures against SM.

Chronic carcinogenicity study of gasoline vapor condensate (GVC) and GVC containing methyl tertiary-butyl ether in F344 rats.

Chronic inhalation studies were conducted to compare the toxicity and potential carcinogenicity of evaporative emissions from unleaded gasoline (GVC) and gasoline containing the oxygenate methyl tertiary-butyl ether (MTBE; GMVC). The test materials were manufactured to mimic vapors people would be exposed to during refueling at gas stations. Fifty F344 rats per gender per exposure level per test article were exposed 6 h/d, 5 d/wk for 104 wk in whole body chambers. Target total vapor concentrations were 0, 2, 10, or 20 g/m³ for the control, low-, mid-, and high-level exposures, respectively. Endpoints included survival, body weights, clinical observations, organs weights, and histopathology. GVC and GMVC exerted no marked effects on survival or clinical observations and few effects on organ weights. Terminal body weights were reduced in all mid- and high-level GVC groups and high-level GMVC groups. The major proliferative lesions attributable to gasoline exposure with or without MTBE were renal tubule adenomas and carcinomas in male rats. GMV exposure led to elevated testicular mesothelioma incidence and an increased trend for thyroid carcinomas in males. GVMC inhalation caused an increased trend for testicular tumors with exposure concentration. Mid- and high-level exposures of GVC and GMVC led to elevated incidences of nasal respiratory epithelial degeneration. Overall, in these chronic studies conducted under identical conditions, the health effects in F344 rats following 2 yr of GVC or GMVC exposure were comparable in the production of renal adenomas and carcinomas in male rats and similar in other endpoints.

Combination therapy with vidaza and entinostat suppresses tumor growth and reprograms the epigenome in an orthotopic lung cancer model.

Epigenetic therapy for solid tumors could benefit from an in vivo model that defines tumor characteristics of responsiveness and resistance to facilitate patient selection. Here we report that combining the histone deacetylase inhibitor entinostat with the demethylating agent vidaza profoundly affected growth of K-ras/p53 mutant lung adenocarcinomas engrafted orthotopically in immunocompromised nude rats by targeting and ablating pleomorphic cells that occupied up to 75% of the tumor masses. A similar reduction in tumor burden was seen with epigenetic therapy in K-ras or EGFR mutant tumors growing orthotopically. Increased expression of proapoptotic genes and the cyclin-dependent kinase inhibitor p21 was seen. Hundreds of genes were demethylated highlighted by the reexpression of polycomb-regulated genes coding for transcription factor binding proteins and the p16 gene, a key regulator of the cell cycle. Highly significant gene expression changes were seen in key regulatory pathways involved in cell cycle, DNA damage, apoptosis, and tissue remodeling. These findings show the promise for epigenetic therapy in cancer management and provide an orthotopic lung cancer model that can assess therapeutic efficacy and reprogramming of the epigenome in tumors harboring different genetic and epigenetic profiles to guide use of these drugs.

Brevetoxin inhalation alters the pulmonary response to influenza A in the male F344 rat.

Epidemiological studies demonstrated that the number of emergency-room visits for respiratory indications increases during periods of Florida Red Tides. The purpose of this study was to examine whether or not repeated brevetoxin inhalation, as may occur during a Florida Red Tide, affects pulmonary responses to influenza A. Male F344 rats were divided into four groups: (1) sham aerosol/no influenza; (2) sham aerosol/influenza; (3) brevetoxin/no influenza; and (4) brevetoxin/influenza. Animals were exposed by nose-only inhalation to vehicle or 50 µg brevetoxin-3/m3, 2 h/d for 12 d. On d 6 of aerosol exposure, groups 2 and 4 were administered 10,000 plaque-forming units of influenza A, strain HKX-31 (H3N2), by intratracheal instillation. Subgroups were euthanized at 2, 4, and 7 d post influenza treatment. Lungs were evaluated for viral load, cytokine content, and histopathologic changes. Influenza virus was cleared from the lungs over the 7-d period; however, there was significantly more virus remaining in the group 4 lungs compared to group 2. Influenza virus significantly increased interleukins-1α and -6 and monocyte chemotactic protein-1 in lung; brevetoxin exposure significantly enhanced the influenza-induced response. At 7 d, the severity of perivascular and peribronchiolar inflammatory cell infiltrates was greatest in group 4. Bronchiolitis persisted, with low incidence and severity, only in group 4 at d 7. These results suggest that repeated inhalation exposure to brevetoxin may delay virus particle clearance and recovery from influenza A infection in the rat lung.

In utero exposure of female CD-1 Mice to AZT and/or 3TC: I. Persistence of microscopic lesions in cardiac tissue.

The current study was designed to delineate temporal changes in cardiomyocytes and mitochondria at the light and electron microscopic levels in hearts of mice exposed transplacentally to commonly used nucleoside analogs (NRTIs). Pregnant CD-1 mice were given 80 mg AZT/kg, 40 mg 3TC/kg, 80 mg AZT/kg plus 40 mg 3TC/kg, or vehicle alone during the last 7 days of gestation, and hearts from female mouse pups were examined at 13 and 26 weeks postpartum for histopathological or ultrastructural changes in cross-sections of both the ventricles and the interventricular septum. Using light microscopy and special staining techniques, transplacental exposure to AZT, 3TC, or AZT/3TC was shown to induce significant histopathological changes in myofibrils; these changes were more widespread at 13 weeks than at 26 weeks postpartum. While most light microscopic lesions resolved, some became more severe between 13 and 26 weeks postpartum. Transplacental NRTI exposure also resulted in progressive drug-specific changes in the number and ultrastructural integrity of cardiac mitochondria. These light and electron microscopic findings show that a subset of changes in cardiac mitochondria and myofibrils persisted and progressed months after transplacental exposure of an animal model to NRTIs, with combined AZT/3TC exposure yielding additive effects compared with either drug alone.

Rosiglitazone prevents the progression of preinvasive lung cancer in a murine model.

There is a critical need to identify efficacious chemopreventive agents for lung cancer that can be taken chronically with no side effects and whose mechanisms of action do not involve genotoxicity that could drive, rather than impede, cancer progression. We evaluated the ability of a chemopreventive cocktail that included selenium (antioxidant), rosiglitazone (peroxisome proliferator-activated receptor gamma agonist), sodium phenylbutyrate or valproic acid (histone deacetylase inhibitors) and hydralazine (cytosine-demethylating agent) to prevent the progression of lung cancer in A/J mice treated with NNK. Agents were administered alone or in various combinations. Effects of the chemopreventive agents were quantified based on the proportion of hyperplasias and adenomas within the mouse lung. Significant effects on tumor progression were seen in all treatment groups that included rosiglitazone as reflected by a 47-57% increase in number of hyperplasias and a 10-30% decrease in adenomas. Cell proliferation was also reduced in these treatment groups by approximately 40%. Interestingly, while treatment with rosiglitazone alone did not significantly affect lesion size, striking effects were seen in the combination therapy group that included sodium phenylbutyrate, with the volume of hyperplasias and adenomas decreasing by 40 and 77%, respectively. These studies demonstrate for the first time that chronic in vivo administration of rosiglitazone, used in the management of diabetes mellitus, can significantly block the progression of premalignant lung cancer in the A/J mouse model.

Histone deacetylase 2 is phosphorylated, ubiquitinated, and degraded by cigarette smoke.

Cigarette smoke (CS)-induced lung inflammation involves the reduction of histone deacetylase 2 (HDAC2) abundance, which is associated with steroid resistance in patients with chronic obstructive pulmonary disease and in individuals with severe asthma who smoke cigarettes. However, the molecular mechanism of CS-mediated reduction of HDAC2 is not clearly known. We hypothesized that HDAC2 is phosphorylated and subsequently degraded by the proteasome in vitro in macrophages (MonoMac6), human bronchial and primary small airway epithelial cells, and in vivo in mouse lungs in response to chronic CS exposure. Cigarette smoke extract (CSE) exposure in MonoMac6 and in bronchial and airway epithelial cells led to phosphorylation of HDAC2 on serine/threonine residues by a protein kinase CK2-mediated mechanism, decreased HDAC2 activity, and increased ubiquitin-proteasome-dependent HDAC2 degradation. CK2 and proteasome inhibitors reversed CSE-mediated HDAC2 degradation, whereas serine/threonine phosphatase inhibitor, okadaic acid, caused phosphorylation and subsequent ubiquitination of HDAC2. CS-induced HDAC2 phosphorylation was detected in mouse lungs from 2 weeks to 4 months of CS exposure, and mice showed significantly lower lung HDAC2 levels. Thus, CS-mediated down-regulation of HDAC2 in human macrophages and lung epithelial cells in vitro and in mouse lung in vivo involves the induction of serine/threonine phosphorylation and proteasomal degradation, which may have implications for steroid resistance and abnormal inflammation caused by cigarette smoke.

Radiation-induced lung adenocarcinoma is associated with increased frequency of genes inactivated by promoter hypermethylation.

Epigenetic inactivation of genes by promoter hypermethylation, a major mechanism in the initiation and progression of tobacco-induced cancer, has also been associated with lung cancer induced through environmental and occupational exposures. Our previous study of gene methylation in workers from the MAYAK nuclear enterprise identified a significantly higher prevalence for methylation of the p16 gene (CDKN2A) in adenocarcinomas from workers compared to tumors from non-worker controls. The purpose of this investigation was to determine whether genes in addition to p16 are "targeted" for silencing and whether overall gene methylation was more common in radiation-induced adenocarcinoma. A significant increase in the prevalence of methylation of GATA5 was seen in tumors from workers compared to tumors from controls. The prevalence for methylation of PAX5 beta and H-cadherin did not differ in tumors from workers and controls. Evaluating the frequency for methylation of a five-gene panel revealed that 93% of adenocarcinomas from workers compared to 66% of tumors from controls were methylated for at least one gene. Moreover, a twofold increase was seen in the number of tumors methylated for three or more genes for tumors from workers compared to controls. Increased frequency for inactivation of genes by promoter hypermethylation and targeting of tumor suppressor genes such as GATA5 may be factors that contribute to the increased risk for lung cancer associated with radiation exposure.

A review of the histopathology of cigarette smoke-induced lung cancer in rats and mice.

In the past several years an increased number of lung tumors has been reported in laboratory studies of rats and mice after lifetime exposure to mainstream cigarette smoke. Proliferative epithelial lesions are present in the lungs of both species and are apparent antecedent lesions to benign and malignant tumors. Both species have alveolar epithelia hyperplasia, alveolar adenomas, and alveolar carcinomas. The incidence of all three are more in the rats. In addition, mice also have bronchiolar epithelial hyperplasia and bronchial papillomas not found in rats. Rats have a low incidence of squamous cyst that is not found in mice. Lung tumors in rats and mice are found at the end of the life span and rarely metastasize. The characteristics of the lung tumors, and the proliferative changes associated with the tumors, are important in helping understand the mechanisms of lung cancer induction. These studies in rats and mice allow new approaches to the study of cigarette smoke-induced changes in the lung.

Subchronic inhalation of soluble manganese induces expression of hypoxia-associated angiogenic genes in adult mouse lungs.

Although the lung constitutes the major exposure route for airborne manganese (Mn), little is known about the potential pulmonary effects and the underlying molecular mechanisms. Transition metals can mimic a hypoxia-like response, activating the hypoxia inducible factor-1 (HIF-1) transcription factor family. Through binding to the hypoxia-response element (HRE), these factors regulate expression of many genes, including vascular endothelial growth factor (VEGF). Increases in VEGF, an important biomarker of angiogenesis, have been linked to respiratory diseases, including pulmonary hypertension. The objective of this study was to evaluate pulmonary hypoxia-associated angiogenic gene expression in response to exposure of soluble Mn(II) and to assess the genes' role as intermediaries of potential pulmonary Mn toxicity. In vitro, 0.25 mM Mn(II) altered morphology and slowed the growth of human pulmonary epithelial cell lines. Acute doses between 0.05 and 1 mM stimulated VEGF promoter activity up to 3.7-fold in transient transfection assays. Deletion of the HRE within the promoter had no effect on Mn(II)-induced VEGF expression but decreased cobalt [Co(II)]-induced activity 2-fold, suggesting that HIF-1 may not be involved in Mn(II)-induced VEGF gene transcription. Nose-only inhalation to 2 mg Mn(II)/m(3) for 5 days at 6 h/day produced no significant pulmonary inflammation but induced a 2-fold increase in pulmonary VEGF mRNA levels in adult mice and significantly altered expression of genes associated with murine angiogenesis. These findings suggest that even short-term exposures to soluble, occupationally relevant Mn(II) concentrations may alter pulmonary gene expression in pathways that ultimately could affect the lungs' susceptibility to respiratory disease.

Modulators of cigarette smoke-induced pulmonary emphysema in A/J mice.

Mice develop pulmonary emphysema after chronic exposure to cigarette smoke (CS). In this study, the influence of gender, exposure duration, and concentration of CS on emphysema, pulmonary function, inflammation, markers of toxicity, and matrix metalloproteinase (MMP) activity was examined in A/J mice. Mice were exposed to CS at either 100 or 250 mg total particulate material/m(3) (CS-100 or CS-250, respectively) for 10, 16, or 22 weeks. Evidence of emphysema was first seen in female mice after 10 weeks of exposure to CS-250, while male mice did not develop emphysema until 16 weeks. Female mice exposed to CS-100 did not have emphysema until 16 weeks, suggesting that disease development depends on the concentration and duration of exposure. Airflow obstruction and increased pulmonary compliance were observed in mice exposed to CS-250 for 22 weeks. Decreased elasticity was likely the major contributor to airflow obstruction because substantial remodeling of the conducting airways, beyond mild mucous cell hyperplasia, was lacking. Exposure to CS increased the number of macrophages, neutrophils, lymphocytes (B cells and activated CD4- and CD8-positive T cells), and activity of MMP-2 and -9 in the bronchoalveolar lavage fluid (BALF). Treatment with antioxidants N-acetylcysteine or epigallocatechin gallate (EGCG) did not decrease emphysema severity, but EGCG slightly decreased BALF inflammatory cell numbers and lactate dehydrogenase activity. Inflammation and emphysema persisted after a 17-week recovery period following exposure to CS-250 for 22 weeks. The similarities of this model to the human disease make it promising for studying disease pathogenesis and assessing new therapeutic interventions.

Life-span inhalation exposure to mainstream cigarette smoke induces lung cancer in B6C3F1 mice through genetic and epigenetic pathways.

Although cigarette smoke has been epidemiologically associated with lung cancer in humans for many years, animal models of cigarette smoke-induced lung cancer have been lacking. This study demonstrated that life time whole body exposures of female B6C3F1 mice to mainstream cigarette smoke at 250 mg total particulate matter/m(3) for 6 h per day, 5 days a week induces marked increases in the incidence of focal alveolar hyperplasias, pulmonary adenomas, papillomas and adenocarcinomas. Cigarette smoke-exposed mice (n = 330) had a 10-fold increase in the incidence of hyperplastic lesions, and a 4.6-fold (adenomas and papillomas), 7.25-fold (adenocarcinomas) and 5-fold (metastatic pulmonary adenocarcinomas) increase in primary lung neoplasms compared with sham-exposed mice (n = 326). Activating point mutations in codon 12 of the K-ras gene were identified at a similar rate in tumors from sham-exposed mice (47%) and cigarette smoke-exposed mice (60%). The percentages of transversion and transition mutations were similar in both the groups. Hypermethylation of the death associated protein (DAP)-kinase and retinoic acid receptor (RAR)-beta gene promoters was detected in tumors from both sham- and cigarette smoke-exposed mice, with a tendency towards increased frequency of RAR-beta methylation in the tumors from the cigarette smoke-exposed mice. These results emphasize the importance of the activation of K-ras and silencing of DAP-kinase and RAR-beta in lung cancer development, and confirm the relevance of this mouse model for studying lung tumorigenesis.

Inhalation toxicity of brevetoxin 3 in rats exposed for twenty-two days.

Brevetoxins are potent neurotoxins produced by the marine dinoflagellate Karenia brevis. Exposure to brevetoxins may occur during a K. brevis red tide when the compounds become aerosolized by wind and surf. This study assessed possible adverse health effects associated with inhalation exposure to brevetoxin 3, one of the major brevetoxins produced by K. brevis and present in aerosols collected along beaches affected by red tide. Male F344 rats were exposed to brevetoxin 3 at 0, 37, and 237 microg/m3 by nose-only inhalation 2 hr/day, 5 days/week for up to 22 exposure days. Estimated deposited brevetoxin 3 doses were 0.9 and 5.8 microg/kg/day for the low- and high-dose groups, respectively. Body weights of the high-dose group were significantly below control values. There were no clinical signs of toxicity. Terminal body weights of both low- and high-dose-group rats were significantly below control values. Minimal alveolar macrophage hyperplasia was observed in three of six and six of six of the low- and high-dose groups, respectively. No histopathologic lesions were observed in the nose, brain, liver, or bone marrow of any group. Reticulocyte numbers in whole blood were significantly increased in the high-dose group, and mean corpuscular volume showed a significant decreasing trend with increasing exposure concentration. Humoral-mediated immunity was suppressed in brevetoxin-exposed rats as indicated by significant reduction in splenic plaque-forming cells in both low- and high-dose-group rats compared with controls. Results indicate that the immune system is the primary target for toxicity in rats after repeated inhalation exposure to relatively high concentrations of brevetoxins.