title: Persistent effects of Libby amphibole and amosite asbestos following subchronic inhalation in rats.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, NC, 27711, USA. Gavett.Stephen@epa.gov.
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Gavett
authors.affiliation: The Hamner Institutes for Health Sciences, Research Triangle Park, NC, 27711, USA.
authors.forename: Carl U
authors.initials: CU
authors.lastname: Parkinson
authors.affiliation: Experimental Pathology Laboratories, Inc. (EPL®), Research Triangle Park, NC, 27711, USA.
authors.forename: Gabrielle A
authors.initials: GA
authors.lastname: Willson
authors.affiliation: National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, NC, 27711, USA.
authors.forename: Charles E
authors.initials: CE
authors.lastname: Wood
authors.affiliation: National Center for Environmental Assessment, U.S. Environmental Protection Agency, Research Triangle Park, NC, 27711, USA.
authors.forename: Annie M
authors.initials: AM
authors.lastname: Jarabek
authors.affiliation: The Hamner Institutes for Health Sciences, Research Triangle Park, NC, 27711, USA.
authors.forename: Kay C
authors.initials: KC
authors.lastname: Roberts
authors.affiliation: National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, NC, 27711, USA.
authors.forename: Urmila P
authors.initials: UP
authors.lastname: Kodavanti
authors.affiliation: The Hamner Institutes for Health Sciences, Research Triangle Park, NC, 27711, USA.
authors.forename: Darol E
authors.initials: DE
authors.lastname: Dodd
mesh_terms: D002282:Adenocarcinoma, Bronchiolo-Alveolar / Q000139:chemically induced* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D000236:Adenoma / Q000139:chemically induced* / Q000378:metabolism / Q000473:pathology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D017639:Asbestos, Amosite / Q000633:toxicity*; D017636:Asbestos, Amphibole / Q000633:toxicity*; D049109:Cell Proliferation / Q000187:drug effects; D002471:Cell Transformation, Neoplastic / Q000139:chemically induced; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D006965:Hyperplasia; D018836:Inflammation Mediators / Q000378:metabolism; D019570:Inhalation Exposure; D008168:Lung / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D008175:Lung Neoplasms / Q000139:chemically induced* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D008297:Male; D011014:Pneumonia / Q000139:chemically induced* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D011658:Pulmonary Fibrosis / Q000139:chemically induced* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D011916:Rats, Inbred F344; D018570:Risk Assessment; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors
chemical_list: D017636:Asbestos, Amphibole; D016207:Cytokines; D018836:Inflammation Mediators; D017639:Asbestos, Amosite
keywords: Adenoma; Amosite; Asbestos; Carcinoma; Dosimetry; Fibrosis; Inflammation; Inhalation; Libby amphibole; Risk assessment