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Progression of lung inflammation and damage in rats after cessation of silica inhalation.

Authors

Porter-DW; Hubbs-AF; Mercer-R; Robinson-VA; Ramsey-D; McLaurin-J; Khan-A; Battelli-L; Brumbaugh-K; Teass-A; Castranova-V

Source

Toxicol Sci 2004 Mar; 79(2):370-380

Link

http://toxsci.oxfordjournals.org/cgi/content/abstract/79/2/370 

NIOSHTIC No.

20024935 

Abstract

Human epidemiologic studies have found that silicosis may develop or progress even after occupational exposure has ended, suggesting that there is a threshold lung burden above which silica-induced pulmonary disease progresses without further exposure. We previously described the time course of rat pulmonary responses to silica inhalation as biphasic, the initial phase characterized by increased but controlled pulmonary inflammation and damage. However, after a threshold lung burden was exceeded, rapid progression of silica-induced pulmonary disease occurred. To test the hypothesis that there is a threshold lung burden above which silica-induced pulmonary disease progresses without further exposure we initiated a study to investigate the relationship between silica exposure, the initiation and progression of silica-induced pulmonary disease, and recovery. Rats were exposed to silica (15 mg/m3, 6 h/day) for either 20, 40, or 60 days. A portion of the rats from each exposure were maintained without further exposure for 36 days to examine recovery. The major findings of this study are: (1) silica-exposed rats were not in pulmonary overload, and lung silica burden decreased with recovery; (2) pulmonary inflammation, damage and lipidosis increased with recovery for rats exposed to silica for 40 and 60 days, but not 20 days; (3) histopathology revealed changes in silica-induced alveolitis, epithelial hypertrophy and hyperplasia, and alveolar lipoproteinosis consistent with bronchoalveolar lavage (BAL) endpoints; and (4) pulmonary fibrosis developed even when exposure was stopped prior to its initial development.

Keywords

Silicosis; Silicates; Silica-dusts; Pulmonary-system; Pulmonary-system-disorders; Pulmonary-function; Respiratory-infections; Respiratory-irritants; Respiratory-system-disorders; Lung-disorders; Lung-disease; Lung-burden

Contact

Health Effects Laboratory Division, National Insitute for Occupational Safety and Health, 1095 Willowdale Road, M/S 2015, Morgantown WV, 26505

CODEN

TOSCF2

CAS No.

14808-60-7

Publication Date

20040331

Document Type

Journal Article

Fiscal Year

2004

NTIS Accession No.

NTIS Price

Issue of Publication

2

ISSN

1096-6080

NIOSH Division

HELD; DART

Source Name

Toxicological Sciences

State

WV; OH