Comparative pulmonary responses to inhaled inorganic fibers with asbestos and fiberglass

Our plain-English summary of Comparative pulmonary responses to inhaled inorganic fibers with asbestos and fiberglass, by K.P. Lee, C.E. Barras, F.D. Griffith, et al (Environmental Research, 1981).

The study

• Authors: K.P. Lee, C.E. Barras, F.D. Griffith, R.S. Waritz, C.A. Lapin
• Journal: Environmental Research
• Published: 1981;24(1):167-91
• Cited by: 68 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

One group of rats, hamsters, and guinea pigs was exposed to amosite asbestos by inhalation of fibers of lengths greater than 5 µm at 3.1 x 10^6/liter, fiberglass at 0.7 x 10^6/liter, potassium octatitanate (Fybex, Du Pont's registered trademark for inorganic reinforcing titanate fibers) at 2.9 x 10^6/liter, and pigmentary potassium titanate (PKT) at 2.0 x 10^6/liter, respectively, for 6 hr/day for 3 months. One group of animals exposed to air alone was used as control. In addition, three groups of rats, hamsters, and guinea pigs were exposed to Fybex at 2.9 x 10^6/liter, 13.5 x 10^6/liter, and 41.8 x 10^6/liter, respectively, for 3 months. One group served as control. Asbestos, Fybex, and PKT produced essentially similar pulmonary responses but with marked differences in fibrogenicity and species differences. Asbestos was the most potent fibrogenic agent and was more than 10 times more fibrogenic than Fybex in terms of exposure concentration. Dose-related fibrogenic activity was found in the animals exposed to Fybex. PKT was the least fibrogenic and produced very minute pulmonary fibrosis in rats and hamsters but not in guinea pigs. Fine fiberglass particles were not fibrogenic. Rats revealed more fibrogenic pulmonary reactions than guinea pigs or hamsters. A few pulmonary tumors developed in animals exposed to asbestos, Fybex, and fiberglass, but their numbers were too small to allow any conclusions on carcinogenicity to be drawn. Fybex produced mesotheliomas in a few hamsters and its possible carcinogenic potential cannot be ruled out.

PubMed has no abstract for this study. This is the authors' abstract, copied from the article.

In plain English

This was an animal inhalation study from a Du Pont laboratory. In a first experiment, rats, hamsters and guinea pigs breathed one of four dusts for 6 hours a day, 5 days a week, for 90 days: amosite asbestos, ball-milled fiberglass, potassium octatitanate fibers (Fybex) or pigmentary potassium titanate (PKT). Control animals breathed air. A second experiment exposed the three species to Fybex at three concentrations. Animals were examined up to 24 months after exposure. Asbestos was the most fibrogenic (scar-forming) material; the authors judged it at least 10 times more fibrogenic than Fybex. Fybex caused dose-related fibrosis. PKT caused minute fibrosis in rats, occasionally in hamsters, and none in guinea pigs. The authors found the fine fiberglass dust not fibrogenic, with only occasional negligible collagen deposition at two years. Rats developed more fibrosis than hamsters or guinea pigs. Lung tumors appeared in a few rats, including 3 of 16 asbestos-exposed rats examined at 18 or 24 months after exposure in the first experiment. Three Fybex-exposed hamsters developed pleural mesothelioma. The authors stated that tumor numbers were too small for conclusions about carcinogenicity, but that a Fybex link to the mesotheliomas could not be ruled out.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Animal inhalation experiment (two experiments) in rats, hamsters and guinea pigs, with air-exposed control groups and serial sacrifices during and after exposure
• Who was studied: Experiment 1: 230 young adult male Charles River Caesarian-Derived Sprague-Dawley rats (five groups of 46), 167 albino male guinea pigs and 170 hamsters (five groups of 34). Experiment 2: 160 male rats (four groups of 40), 139 guinea pigs and 146 hamsters. The work was done at Haskell Laboratory, Du Pont, Wilmington, Delaware. Animals were killed at intervals during exposure and at 6, 12, 18 and 24 months after exposure. Study dates are not given.
• Exposure: Experiment 1: amosite (UICC standard reference sample) at 3.1 million fibers longer than 5 micrometers per liter, ball-milled fiberglass at 0.7 million, Fybex at 2.9 million and PKT at 2.0 million per liter, or air alone. Exposure was 6 hours a day, 5 days a week, for 90 days. Experiment 2: Fybex at 2.9, 13.5 or 41.8 million fibers longer than 5 micrometers per liter, or air, for about 3 months. The article prints the concentrations as OCR-damaged '10Vliter'; Table 2 confirms they are times 10 to the 6th per liter. Only 7% of the fiberglass dust particles were fibrous in shape.
• Main results:
  • Based on how severe the lung fibrosis was at the various exposure concentrations, asbestos (amosite) appeared at least 10 times more fibrogenic than Fybex.
  • Fibrogenic activity in Fybex-exposed animals was dose-related.
  • PKT was the least fibrogenic of the fibers. It induced minute collagenized fibrosis in rats, occasionally in hamsters, and none in guinea pigs.
  • The authors found the fine fiberglass dust not fibrogenic. It caused a macrophage reaction and slight alveolar proteinosis, which appeared at 90 days of exposure and disappeared by 1 year after exposure. At 2 years, negligible collagen deposition was found occasionally where dust cells were trapped.
  • Collagenized fibrosis was most marked in rats, slightly more marked in hamsters than in guinea pigs, and least marked in guinea pigs.
  • Experiment 1 rats exposed to asbestos and examined at 18 or 24 months after exposure: 3 of 16 had lung tumors (2 bronchioloalveolar adenomas, 1 epidermoid carcinoma).
  • Experiment 1 rats exposed to fiberglass and examined at 18 or 24 months after exposure: 2 of 19 developed bronchioloalveolar adenomas.
  • Experiment 1 rats: 1 of 21 exposed to Fybex developed a bronchioloalveolar adenoma. None of 20 PKT-exposed rats and none of 19 control rats had primary lung tumors.
  • Experiment 2 rats exposed to Fybex: 3 of 25 rats in group 3 (13.5 million fibers per liter) had lung tumors. Across both experiments, the 10 lung tumors in rats exposed to fiberglass, asbestos and Fybex were 7 bronchioloalveolar adenomas, 2 epidermoid carcinomas and 1 adenocarcinoma.
  • Experiment 1 hamsters: 1 of 12 exposed to Fybex developed an epithelial-type pleural mesothelioma.
  • Experiment 2 hamsters: 1 of 13 in Fybex group 3 developed a biphasic pleural mesothelioma. Of 16 in Fybex group 4 (41.8 million fibers per liter), 1 had a pleural mesothelioma and 1 had a bronchioloalveolar adenoma.
  • Fybex-exposed hamsters had a high incidence of fibrotic pleuritis with mesothelial hyperplasia compared with rats or guinea pigs.
  • Guinea pigs: in Experiment 2, 2 of 17 control guinea pigs had bronchioloalveolar adenomas, and no Fybex-exposed guinea pig had a lung tumor. In Experiment 1, 2 of 7 fiberglass-exposed guinea pigs had bronchioloalveolar adenoma at 24 months, compared with none of 5 controls.
  • Hamsters exposed to asbestos had greater mortality than control hamsters.
• The authors' conclusion: The authors concluded that asbestos was the most potent fibrogenic agent tested and that the few lung tumors were too few for conclusions on carcinogenicity. They also concluded that, given the rarity of mesothelioma in hamsters and the frequent pleural changes seen, a relationship between Fybex exposure and the hamster mesotheliomas could not be ruled out.
• Limitations the authors state:
  • Too few animals remained at the 2-year post-exposure sacrifice to draw meaningful conclusions about carcinogenic potential.
  • The highest Fybex concentration (41.8 million fibers per liter) was unrealistically high and overloaded the lungs' clearance mechanisms.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Amosite.

Medical terms in this study, explained in our Lexicon: Amosite, Fibrogenic, Pulmonary Fibrosis, Mesothelioma, Carcinogenic.

Related studies

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• Historical cohort study of US man-made vitreous fiber production workers: I. 1992 fiberglass cohort follow-up: initial findings — G.M. Marsh, A.O. Youk, et al. (2001)
• Chronic inhalation study of fiber glass and amosite asbestos in hamsters: twelve-month preliminary results — T.W. Hesterberg, C. Axten, et al. (1997)
• Comparative epidemiology of men exposed to asbestos and man-made mineral fibers — J.R. Goldsmith (1986)
• Assessments of lung digestion methods for recovery of fibers — D.B. Warheit, H.C. Hwang, et al. (1991)
• A comparative study of the clearance of respirable para-aramid, chrysotile and glass fibres from rat lungs — A. Searl (1997)

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