Persistent effects of Libby amphibole and amosite asbestos following subchronic inhalation in rats

Table 3 Lung and trachea histopathology after exposure to AM or LA for 13 weeks

	Air control	AM 3.3	LA 1.0	LA 3.3	LA 10.0
Lung
Foreign Body^a
1 Day	0	8*	8*	8*	8*
1 Month	0	8*	8*	8*	8*
3 Months	0	8*	8*	8*	8*
18 Months	0	47*	40*	48*	49*
Alveolus Inflammation^b
1 Day	0	8 (1.0)*	8 (1.0)*	8 (1.0)*	8 (2.0)*
1 Month	0	8 (1.1)*	8 (1.0)*	8 (1.0)*	8 (2.0)*
3 Months	0	8 (1.0)*	8 (1.0)*	8 (1.1)*	8 (1.4)*
18 Months	0	45 (1.0)*	40 (0.9)*	47 (1.1)*	48 (1.1)*
Alveolar Epithelial Hyperplasia^c
1 Day	0	0	0	0	0
1 Month	0	0	0	0	1 (0.1)
3 Months	0	0	0	0	1 (0.1)
18 Months	1 (0.0)	9 (0.3)*	6 (0.2)	6 (0.2)	9 (0.4)*^
Bronchiole Epithelial Hyperplasia
1 Day	0	0	0	0	8 (1.0)*
1 Month	0	1 (0.1)	0	0	8 (1.0)*
3 Months	0	0	0	0	0
18 Months	0	0	0	0	0
Bronchiolization^d
1 Day	0	8 (1.0)*	7 (0.9)*	8 (1.0)*	8 (1.0)*
1 Month	0	7 (0.9)*	7 (0.9)*	7 (0.9)*	8 (1.4)*
3 Months	0	8 (1.0)*	8 (1.0)*	8 (1.0)*	8 (1.0)*
18 Months	0	5 (0.1)	5 (0.1)	0	0
Interstitial Fibrosis^e
1 Day	0	8 (1.0)*	8 (1.0)*	8 (1.0)*	8 (1.0)*
1 Month	0	8 (1.0)*	7 (0.9)*	8 (1.0)*	8 (1.0)*
3 Months	0	8 (1.0)*	8 (1.0)*	8 (1.0)*	8 (1.0)*
18 Months	0	42 (0.8)*	29 (0.6)*	43 (0.9)*	42 (0.9)*
(Sub) Pleural Fibrosis^e
18 Months	0	25 (0.5)*	16 (0.3)*	19 (0.4)*	22 (0.4)*
Bronchiolar/Alveolar Adenoma
18 Months	0	2	0	2	3^
Bronchiolar/Alveolar Carcinoma
18 Months	0	0	0	0	1
Bronchiolar/Alveolar Adenoma or Carcinoma
18 Months	0	2	0	2	4^
Trachea
Trachea, Chronic Inflammation
18 Months	0	0	4 (0.1)	2 (0.1)	9 (0.2)*
Trachea, Squamous Metaplasia
18 Months	0	1 (0.0)	0	0	0

Rats were exposed to AM or LA for 13 weeks and evaluated at 1 day, 1 month, 3 months, or 18 months after the end of the exposure period. Column headings indicated target mass concentrations (mg/m³). Values represent the number of animals with a finding in each group (total examined n = 8 at 1 day, 1, and 3 months, and n = 49–50 at 18 months). Average lesion severity scores for all rats in each group (shown in parentheses) were graded as follows: 1 = minimal, 2 = mild, 3 = moderate, 4 = marked, and 5 = severe. *P < 0.05 vs. air control; ^P < 0.05 for trend test among LA groups. ^aConsistent with fibers; not graded for severity. ^bPredominantly macrophages with lesser numbers of neutrophils and lymphocytes, often associated with foreign bodies; occasional granulomas with rare giant cells. ^cProliferation of cuboidal type II alveolar cells (without evidence of significant inflammation). ^dPresence of cells that resemble bronchiolar epithelial cells in alveolar ducts and adjacent alveoli. ^eConfirmed on Masson’s trichrome stain

ISSN: 1743-8977