asbestos--amosite and Pulmonary-Fibrosis

Human exposure to Libby amphibole (LA) asbestos increases risk of lung cancer, mesothelioma, and non-malignant respiratory disease. This study evaluated potency and time-course effects of LA and positive control amosite (AM) asbestos fibers in male F344 rats following nose-only inhalation exposure.. Rats were exposed to air, LA (0.5, 3.5, or 25.0 mg/m(3) targets), or AM (3.5 mg/m(3) target) for 10 days and assessed for markers of lung inflammation, injury, and cell proliferation. Short-term results guided concentration levels for a stop-exposure study in which rats were exposed to air, LA (1.0, 3.3, or 10.0 mg/m(3)), or AM (3.3 mg/m(3)) 6 h/day, 5 days/week for 13 weeks, and assessed 1 day, 1, 3, and 18 months post-exposure. Fibers were relatively short; for 10 mg/m(3) LA, mean length of all structures was 3.7 μm and 1% were longer than 20 μm.. Ten days exposure to 25.0 mg/m(3) LA resulted in significantly increased lung inflammation, fibrosis, bronchiolar epithelial cell proliferation and hyperplasia, and inflammatory cytokine gene expression compared to air. Exposure to 3.5 mg/m(3) LA resulted in modestly higher markers of acute lung injury and inflammation compared to AM. Following 13 weeks exposure, lung fiber burdens correlated with exposure mass concentrations, declining gradually over 18 months. LA (3.3 and 10.0 mg/m(3)) and AM produced significantly higher bronchoalveolar lavage markers of inflammation and lung tissue cytokines, Akt, and MAPK/ERK pathway components compared to air control from 1 day to 3 months post-exposure. Histopathology showed alveolar inflammation and interstitial fibrosis in all fiber-exposed groups up to 18 months post-exposure. Positive dose trends for incidence of alveolar epithelial hyperplasia and bronchiolar/alveolar adenoma or carcinoma were observed among LA groups.. Inhalation of relatively short LA fibers produced inflammatory, fibrogenic, and tumorigenic effects in rats which replicate essential attributes of asbestos-related disease in exposed humans. Fiber burden, inflammation, and activation of growth factor pathways may persist and contribute to lung tumorigenesis long after initial LA exposure. Fiber burden data are being used to develop a dosimetry model for LA fibers, which may provide insights on mode of action for hazard assessment.

Topics: Adenocarcinoma, Bronchiolo-Alveolar; Adenoma; Animals; Apoptosis; Asbestos, Amosite; Asbestos, Amphibole; Cell Proliferation; Cell Transformation, Neoplastic; Cytokines; Dose-Response Relationship, Drug; Epithelial Cells; Hyperplasia; Inflammation Mediators; Inhalation Exposure; Lung; Lung Neoplasms; Male; Pneumonia; Pulmonary Fibrosis; Rats, Inbred F344; Risk Assessment; Signal Transduction; Time Factors

COPD has been reported in workers exposed to particulates, and there is increasing evidence that high levels of ambient particulate pollutants may also be associated with COPD. The studies here investigate the hypothesis that particulates, including air pollution particles, can induce airway wall fibrosis, a process that can lead to COPD.. Rat tracheal explants were exposed to various occupationally encountered dusts, air pollution particles, and model air pollution particles. In some experiments, iron was loaded onto the particle surface. Gene expression and nuclear factor (NF)-kappaB activation were measured after 7 days of air culture. Adhesion to and uptake of dusts by the tracheal epithelium were also evaluated.. Known fibrogenic dusts such as amosite asbestos produced increased gene expression of procollagen, transforming growth factor-beta, and platelet-derived growth factor, and increased hydroxyproline in the explants, and the addition of iron increased these effects. The addition of iron also converted nonfibrogenic TiO2 into a fibrogenic dust. Dusts with surface complexed iron activated NF-kappaB via an oxidant mechanism. However, an ultrafine TiO2 with very low iron was also fibrogenic. In separate experiments, exogenous tumor necrosis factor-alpha increased dust adhesion to, and exogenous ozone increased dust uptake by, tracheal epithelial cells.. Mineral dusts can directly induce fibrosis in the airway wall. Exogenous inflammatory cells and exogenous agents are not required, but they probably exaggerate the fibrogenic effects. An iron-mediated oxidant mechanism underlies the fibrogenic effects of some, but not all, of these dusts. Particle-induced airway wall fibrosis may lead to COPD.

Topics: Air Pollutants; Air Pollutants, Occupational; Animals; Asbestos, Amosite; Collagen Type I; Drug Synergism; Dust; Humans; Hydroxyproline; Iron; NF-kappa B; Oxidants, Photochemical; Ozone; Particle Size; Procollagen; Pulmonary Disease, Chronic Obstructive; Pulmonary Fibrosis; Rats; Tobacco Smoke Pollution; Trachea

To investigate the role of iron and active oxygen species (AOS) in asbestos-induced fibrosis, we loaded increasing amounts of Fe(II)/Fe(III) onto the surface of amosite asbestos fibers and then applied the fibers to rat tracheal explants. Explants were harvested after 7 d in air organ culture. Asbestos by itself doubled procollagen gene expression, and a further increase was seen with increasing iron loading; actual collagen content measured as hydroxyproline was increased in a similar pattern. Iron loading also increased gene expression of platelet-derived growth factor (PDGF)-A and transforming growth factor (TGF)-beta(1). Neither asbestos alone nor iron-loaded asbestos affected gene expression of PDGF-B, tumor necrosis factor-alpha, or TGF-alpha. The AOS scavenger tetramethylthiourea or treatment of fibers with the iron chelator deferoxamine prevented asbestos-induced increases in procollagen, PDGF-A, and TGF-beta gene expression, whereas glutathione had no effect. The proteasome inhibitor MG-132 abolished asbestos-induced increases in procollagen gene expression but did not affect increases in PDGF-A or TGF-beta(1) expression, whereas the extracellular signal-regulated protein kinase (ERK) inhibitor PD98059 had exactly the opposite effect. We conclude that surface iron as well as the iron-catalyzed generation of AOS play a role in asbestos-induced matrix (procollagen) production and that this process is driven in part through oxidant-induced nuclear factor kappa B activation. Surface iron and AOS also play a role in PDGF-A and TGF-beta gene expression, but through an ERK-dependent mechanism.

Topics: Animals; Asbestos, Amosite; Cells, Cultured; Cysteine Proteinase Inhibitors; Enzyme Inhibitors; Flavonoids; Gene Expression; Iron; Leupeptins; Male; MAP Kinase Signaling System; NF-kappa B; Platelet-Derived Growth Factor; Procollagen; Pulmonary Fibrosis; Rats; Rats, Sprague-Dawley; Reactive Oxygen Species; RNA, Messenger; Trachea; Transforming Growth Factor beta; Transforming Growth Factor beta1; Tumor Necrosis Factor-alpha

This article describes the activity of an E-glass microfiber (104E) during chronic inhalation and intraperitoneal injection studies in rats. Results are compared with another microfiber of similar dissolution rate (k(dis)), code 100/475, and the more durable amosite asbestos, both of which we had previously used in similar experiments (Davis et al., 1996). Rats were exposed to aerosol concentrations of 1000 fibers (longer than 5 microm)/ml, as measured by optical microscopy, for 7 h/day, 5 days/wk. Subgroups of rats were followed for mean lung burden, early and late signs of fibrosis, and tumor incidence. At the end of 12 mo of exposure, the mean number of 104E fibers of all lengths in the lungs was approximately double that for amosite but two-thirds of that for 100/475. For fibers longer than 15 microm, the mean 104E burden was similar to that for the amosite and more than twice that of the 100/475. After a 12-mo recovery period, the retained lung burdens (of fibers of all lengths) were approximately 30% of those at 12 mo for both microfibers, and somewhat higher (approximately 44%) for amosite. Amosite and 100/475 fibers longer than 15 microm were more persistent in the lungs than 104E fibers. The chemical composition of 104E fibers did not appear to have been significantly altered by up to 24 mo of residence in lung tissue, whereas the composition of 100/475 was substantially altered over the same time period. From the inhalation study, out of the pathology subgroup of 43 animals exposed to 104E microfibers, 10 had lung tumors (7 carcinoma, 3 adenoma) and 2 had mesotheliomas, whereas in 42 rats exposed to amosite asbestos, there were 16 lung tumors (7 carcinoma, 9 adenoma) and 2 mesotheliomas. The 104E- and amosite-treated animals had similar levels of fibrosis. In contrast, 38 animals treated with 100/475 had little fibrosis, 4 lung tumors (adenomas), and no mesotheliomas. The greater pathogenicity of the 104E fibers, compared to 100/475 fibers, might be partly explained by the greater numbers of long fibers retained in the lung after 12 mo of inhalation. However, we speculate that modification of surface properties by extensive selective leaching of some glass components reduces the toxic potential of 100/475. In a parallel intraperitoneal injection study, 104E caused considerably more mesotheliomas (21 rats out of 24) than 100/475 (8 rats out of 24). In addition, 104E appeared to be more active than amosite asbestos, since mesotheliomas appeared mu

Topics: Administration, Inhalation; Aerosols; Animals; Asbestos, Amosite; Body Burden; Carcinoma; Glass; Inhalation Exposure; Injections, Intraperitoneal; Lung; Lung Neoplasms; Male; Mesothelioma; Mineral Fibers; Neoplasms, Experimental; Particle Size; Pulmonary Fibrosis; Rats; Rats, Wistar; Survival Analysis; Survival Rate; Toxicity Tests

Asbestos fibers are an important cause of lung fibrosis; however, the biological mechanisms are incompletely understood. The lung epithelium serves an important barrier function in the lung, and disrupting the epithelial barrier can contribute to lung fibrosis. Lung epithelial permeability is increased in patients with asbestosis, and asbestos fibers increase permeability across cultured human lung epithelium. However, the mechanism of this increased permeability is not known. Many of the biological effects of asbestos are postulated to be due to its ability to generate oxidants, and oxidants are known to increase epithelial permeability. However, we previously reported that altering the iron content of asbestos (important in oxidant generation) had no effect on its ability to increase permeability. For that reason, we undertook these studies to determine whether asbestos increases epithelial permeability through nonoxidant pathways. Both extracellular (H2O2) and intracellular (menadione) oxidants increase paracellular permeability across human lung epithelial monolayers. Extracellular catalase but not superoxide dismutase prevented increased permeability after both oxidant exposures. However, catalase offered no protection from asbestos-induced permeability. We next depleted the cells of glutathione or catalase to determine whether depleting normal cellular antioxidants would increase the sensitivity to asbestos. Permeability was the same in control cells and in cells depleted of these antioxidants. In addition to generating oxidants, asbestos also activates signal transduction pathways. Blocking protein kinase C activation did not prevent asbestos-induced permeability; however, blocking tyrosine kinase with tyrophostin A25 did prevent asbestos-induced permeability, and blocking tyrosine phosphatase with sodium vanadate enhanced the effect of asbestos. These data demonstrate that asbestos may increase epithelial permeability through nonoxidant pathways that involve tyrosine kinase activation. This model offers an important system for studying pathways involved in regulating lung epithelial permeability.

Topics: Amitrole; Asbestos, Amosite; Asbestos, Serpentine; Buthionine Sulfoximine; Catalase; Cell Membrane Permeability; Cells, Cultured; Epithelial Cells; Glutathione; Humans; Hydrogen Peroxide; Kinetics; Lung; Mannitol; Oxidants; Phorbol 12,13-Dibutyrate; Pulmonary Fibrosis; Time Factors; Vitamin K

Exposure to mineral dusts is associated with the development of chronic airflow obstruction, probably mediated in part by dust-induced fibrosis of the small airways. To investigate the mechanism of fibrosis, we exposed rat tracheal explants to amosite asbestos, iron oxide, or titanium dioxide. Explants were then maintained in air organ culture, and the expression of genes encoding for various mediators and matrix components assessed by reverse transcriptase-polymerase chain reaction (RT-PCR). At 7 d, all dusts produced significant increases in platelet-derived growth factor-A (PDGF-A) and transforming growth factor-beta1 (TGF-beta1) gene expression compared with control; asbestos and titanium dioxide produced increases in PDGF-B, and titanium dioxide increased TGF-alpha expression. Only asbestos caused increases in procollagen expression. No dust increased expression of tumor necrosis factor-alpha (TNF-alpha), fibronectin, or tropoelastin. Elevations in these factors coincided temporally with transport of particles into the epithelium and then to the subepithelial space. By in situ hybridization, TGF-beta gene expression was found in both the epithelium and subepithelial (interstitial) space, and PDGF-B and procollagen gene expression in the subepithelial space. Chemical analysis showed a small increase in hydroxyproline, a measure of collagen content, in asbestos-treated explants. We conclude that mineral dusts can induce airway wall fibrosis by directly upregulating proliferative and fibrogenic mediators as well as matrix components in the airway epithelium and interstitium, and that neither airspace nor circulating inflammatory cells are required for these effects. Different mineral dusts produce different patterns of reaction.

Topics: Airway Obstruction; Animals; Asbestos, Amosite; Culture Techniques; Dust; Epithelium; Extracellular Matrix Proteins; Ferric Compounds; Fibronectins; Gene Expression Regulation; Hydroxyproline; Inflammation Mediators; Irritants; Lung; Male; Mineral Fibers; Minerals; Platelet-Derived Growth Factor; Procollagen; Protein-Tyrosine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-sis; Pulmonary Fibrosis; Rats; Rats, Sprague-Dawley; Titanium; Transforming Growth Factor beta; Tropoelastin; Tumor Necrosis Factor-alpha; Up-Regulation

The Cape Boards Plant at Uxbridge produced insulation board containing amosite asbestos between 1947 and 1973 with only small amounts of chrysotile. After 1973 only amosite was used. In this study we examined lung samples from 48 workers who had been employed at the plant and who had come to autopsy. The study investigated the fiber levels against the lung pathology including amount of interstitial fibrosis and numbers of ferruginous bodies. The degree of interstitial fibrosis and number of asbestos bodies were graded and the tissues were analyzed by transmission electron microscopy and energy dispersive X-ray analysis and the fibers counted and typed. The 48 cases included 5 mesotheliomas and 14 lung cancers. The mineral analysis results were dominated by the amosite fiber levels. The amounts of chrysotile were relatively small. There were higher levels in lung cancer cases than mesotheliomas and higher levels in mesothelioma cases than those who had died from nonasbestos related diseases. Analysis of the lung tissues showed a consistent pattern of high amosite levels, which confirms the impression that amosite was the predominant form of asbestos used and also indicates that the factory had been a very dusty one.

Topics: Asbestos, Amosite; Asbestosis; Humans; Lung Diseases; Lung Neoplasms; Mesothelioma; Occupational Diseases; Pulmonary Fibrosis

Experimental inhalation in a number of studies has demonstrated that chrysotile asbestos can cause pulmonary fibrosis and both benign and malignant pulmonary tumours, two lesions which are associated in that the studies reporting high tumour rates also found high levels of asbestosis. One comparison reported that animals with malignant tumours had approximately twice the amount of fibrosis in the lung parenchyma as those of similar age without tumours. Many studies have examined the pathogenicity of asbestos administered by ingestion and most of these included chrysotile asbestos: the results have been universally negative apart from one study with amosite that contained no control animals and is best discarded. Only one inhalation study has reported an examination of the larynxes of animals: this found no pathological changes. In many studies, tumours other than the lung had been listed, but significant numbers of kidney tumours have never been recorded. Injection studies inducing mesothelioma have indicated that fibre geometry is important with long thin fibres (> 8 microns in length and < 0.25 microns in diameter) being the most carcinogenic. This has been difficult to confirm for inhaled fibres although fibres less than 5 microns in length appear to cause neither fibrosis nor pulmonary tumours. Similar results have been found with amosite for fibres up to 10-15 microns although longer fibres do produce these conditions. It is suggested that to produce pulmonary fibrosis and neoplasia fibres may need to be longer than 20 microns. Chrysotile has been shown in many studies to be removed from lung tissue much more rapidly than amphibole fibres.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Administration, Inhalation; Animals; Asbestos, Amosite; Asbestos, Amphibole; Asbestos, Serpentine; Asbestosis; Cricetinae; Dust; Injections; Laryngeal Neoplasms; Lung Neoplasms; Mesothelioma; Pleural Neoplasms; Pulmonary Fibrosis; Rats

To study the long-term effect of inhaled asbestos, guinea-pigs were exposed to airborne amosite at a concentration of 49 mg/m3, 2 h/day for 3 or 6 weeks and examined up to 2 years after exposure. Macrophages in lung lavage fluid (LLF) were increased at 16, 24 and 93 weeks and lymphocytes at 24 weeks. Examination of lung wall cells (LWC) 2 years after exposure compared to cells obtained by LLF showed higher proportions of LWC lymphocytes and neutrophils. Percoll gradient centrifugation of these cells showed a higher proportion of high density macrophages in LLF from the amosite-exposed animal and an increased number of low density lymphocytes in the LW. Cathepsin D was increased in LLF at 8 and 24 weeks and in alveolar macrophages 24 weeks and 2 years after exposure. Fibroblast cultures exposed to LLF did not show any statistical significant changes in their collagen synthesis. Histology 93 weeks after exposure showed macrophage and mediastinal lymph node accumulation of asbestos, as well as collagen in alveolar walls. Granulomas were found in the vicinity of blood vessels and in connection with the bronchioles. The data suggest that amosite at low doses ultimately causes fibrosis with a reaction pattern different from that seen in silicosis. The inflammation and fibrosis seems to develop only within the interstitium.

Topics: Administration, Inhalation; Animals; Asbestos; Asbestos, Amosite; Fibroblasts; Guinea Pigs; Lung; Lysosomes; Macrophages; Proline; Pulmonary Fibrosis

For many years it has been accepted that fibre dimensions are the most important factor in the development of asbestos related disease with long fibres being more dangerous than short for all types of asbestos. This information has been derived from in vitro experiments and injection or implantation experiments since the kilogramme quantities of specially prepared dusts that are necessary for long term inhalation have not been available. The present study has taken advantage of the availability of a sample of amosite produced so that almost all fibres were less than 5 micron in length. The effects of this dust were compared to dust prepared from raw amosite that contained a very high proportion of long fibres. Previous data from studies with UICC amosite, which was intermediate in length, were also available for comparison. At the end of 12 months of dust inhalation, significantly more short fibre amosite was present in the lung tissue compared to the long but while the long fibre dust caused the development of widespread pulmonary fibrosis, no fibrosis at all was found in animals treated with short fibre. One third of animals treated with long fibre dust developed pulmonary tumours or mesotheliomas but no pulmonary neoplasms were found in animals treated with short fibre dust. Following intraperitoneal injection, the long fibre amosite produced mesotheliomas in 95% of animals with a mean induction period of approximately 500 days. With short fibre dust, only a single mesothelioma developed after 837 days. In previous inhalation studies with UICC amosite, relatively little pulmonary fibrosis had developed and only two benign pulmonary tumours. This would suggest that to produce a significant carcinogenic response in rat lung tissue amosite fibres must be longer than those in the UICC preparation. Following the injection of UICC amosite, however, mesotheliomas developed in the same proportion of animals and with the same mean induction period as with long fibre dust. From this it would appear that while very short fibres exhibit little carcinogenicity to either lung or mesothelial tissues, mesotheliomas can be produced by dust preparations consisting of shorter fibres than are needed to produce tumours.

Topics: Animals; Asbestos; Asbestos, Amosite; Bronchi; Granulation Tissue; Lung; Lung Neoplasms; Macrophages; Male; Microscopy, Electron; Pulmonary Fibrosis; Rats; Rats, Inbred Strains

To determine whether asbestos dust produces pathologic changes in the small airways, and to determine where the anatomic lesions of asbestosis commence, the authors examined lungs from guinea pigs exposed to 10 or 30 mg of amosite asbestos by intratracheal instillation and sacrificed 6 months later. Measurement of airway wall thickness revealed that membranous and respiratory bronchioles of all sizes in exposed animals were significantly thicker than those of controls. Amosite fibers were found embedded in the walls of bronchi and in membranous and respiratory bronchioles; where these fibers penetrated the airway walls, an interstitial inflammatory and fibrotic reaction (asbestosis) occurred. It is concluded that 1) amosite asbestos produces diffuse abnormalities throughout the noncartilagenous airways and possibly the cartilagenous airways as well; 2) this effect is independent of interstitial fibrosis of the parenchyma (classical asbestosis); 3) asbestosis, at least that induced by amosite, commences at any site in the parenchyma to which the asbestos fibers can gain access, either by deposition in alveoli and alveolar ducts or by direct passage of fibers through the walls of all types and sizes of small airways.

Topics: Animals; Asbestos; Asbestos, Amosite; Asbestosis; Bronchi; Disease Models, Animal; Guinea Pigs; Pulmonary Fibrosis