Lung proliferative and clearance responses to inhaled para-aramid RFP in exposed hamsters and rats: comparisons with chrysotile asbestos fibers

Our plain-English summary of Lung proliferative and clearance responses to inhaled para-aramid RFP in exposed hamsters and rats: comparisons with chrysotile asbestos fibers, by D.B. Warheit, S.I. Snajdr, M.A. Hartsky, et al (Environmental Health Perspectives, 1997).

The study

• Authors: D.B. Warheit, S.I. Snajdr, M.A. Hartsky, S.R. Frame
• Journal: Environmental Health Perspectives
• Published: 1997;105 Suppl 5(Suppl 5):1219-22
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

This study compared pulmonary effects of para-aramid respirable-sized, fiber-shaped particles (RFP) (p-aramid fibrils) and chrysotile asbestos fiber exposures in rats. Additional p-aramid inhalation studies were conducted in hamsters to compare species responses. The hamster results are preliminary. The parameters studied were clearance/biopersistence of inhaled p-aramid RFP or size-separated asbestos fibers as well as pulmonary cell proliferation and inflammation indices after 2-week inhalation exposures. Rats were exposed nose only to chrysotile asbestos fibers at concentrations of 459 and 782 fibers/ml or to p-aramid RFP at 419 or 772 fibrils/ml. Hamsters were exposed whole body to p-aramid RFP at concentrations of 358 and 659 fibrils/ml. Subsequently, animals were assessed immediately (time 0) as well as 5 days (10 days for hamsters), 1, 3, 6, and 12 months postexposure. Lung burdens for the p-aramid-exposed rats were 4.8 x 10(7) and 7.6 x 10(7) fibrils/lung, with similar numbers of chrysotile fibers > 5 microns recovered from the lungs of asbestos-exposed rats. In comparison, 1.4 x 10(6) fibrils/lung were recovered in the high-dose hamster group. Biopersistence studies in p-aramid-exposed rats and hamsters demonstrated an initial increase (relative to time 0) in retained p-aramid fibrils during the first month postexposure, which indicated breakage or shortening of inhaled fibrils. This result was associated with a progressive reduction, and increased residence time in the lung, in the mean lengths of the fibrils, which signified biodegradability of inhaled p-aramid fibrils in both species. In contrast, clearance of short chrysotile asbestos fibers was rapid, but clearance of the long chrysotile fibers was slow or insignificant, as evidenced by a progressive increase over time in the mean lengths of fibers recovered from the lungs of exposed rats. Two-week, high-dose exposures to p-aramid in both rats and hamsters produced transient increases in pulmonary inflammatory and cell proliferative responses. In contrast, inhalation of size-separated chrysotile asbestos fibers in rats produced persistent increases in cell labeling indices of airway, alveolar, and subpleural cells measured through a period of 1 to 3 months postexposure. These results suggest that inhaled p-aramid RFP are biodegradable in the lungs of exposed rats and hamsters. In contrast, exposures to chrysotile asbestos fibers in rats resulted in a selective pulmonary retention of long chrysotile fibers.

In plain English

This was an animal inhalation experiment comparing para-aramid (Kevlar) fibrils with Canadian chrysotile asbestos. The article describes para-aramid as an asbestos substitute in products such as brake linings and gaskets. Male rats breathed chrysotile or para-aramid, and male hamsters para-aramid only, 6 hours a day, 5 days a week, for 2 weeks. Lungs were checked for fibers and cell proliferation for up to 12 months in rats and 3 months in hamsters. In both species, retained para-aramid fibrils grew shorter over time and increased in number during the first month, which the authors attributed to breakage or shortening. They were then cleared rapidly at 1 to 3 months. Short chrysotile fibers cleared rapidly, but long ones cleared slowly or insignificantly, so the average length of retained chrysotile fibers rose. After high-dose exposures, cell proliferation rose only briefly with para-aramid, but in rats given chrysotile it stayed raised for up to 3 months. The authors concluded that para-aramid is biodegradable in these rodents, supporting the theory that it is probably biodegradable in human lungs. They called the hamster results preliminary.

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: rats and hamsters given 2-week inhalation exposures, then examined for lung fiber clearance and retention and for cell proliferation at set times afterward
• Who was studied: Male Crl:CDBR rats and male Syrian golden hamsters, 7 to 8 weeks old, plus age-matched sham controls. Four animals per exposure group per time period were used for cell proliferation and lung tissue studies. Hamsters were evaluated immediately after exposure and at 10 days, 1 month and 3 months.
• Exposure: Rats breathed UICC chrysotile asbestos (Canadian chrysotile) prepared to increase the share of longer fibers, or para-aramid respirable-sized, fiber-shaped particles (Kevlar). Exposure was 6 hours a day, 5 days a week, for 2 weeks. Rats were exposed nose only to chrysotile at 459 and 782 fibers/ml or to para-aramid at 419 or 772 fibrils/ml. Hamsters were exposed whole body to para-aramid at 358 and 659 fibrils/ml. The article describes para-aramid fibrils as asbestos fiber substitutes in products such as brake linings and gaskets.
• Main results:
  • Lung burdens in para-aramid-exposed rats were 4.8 x 10^7 and 7.6 x 10^7 fibrils per lung. Similar numbers of chrysotile fibers longer than 5 micrometers were recovered from asbestos-exposed rats. The high-dose hamster group had 1.4 x 10^6 fibrils per lung.
  • In para-aramid-exposed rats and hamsters, the number of retained fibrils rose during the first month after exposure, compared with time 0. The authors took this as indicating breakage or shortening of the fibrils.
  • Clearance of para-aramid fibrils in rats and hamsters was at first slower than clearance of chrysotile, alongside shortening of the retained fibrils. At 1 to 3 months after exposure, para-aramid was cleared rapidly.
  • In chrysotile-exposed rats, short fibers were cleared rapidly, but a subpopulation of longer fibers was cleared at a slower or insignificant rate.
  • In chrysotile-exposed rats, the mean length of fibers recovered from lung tissue increased the longer the fibers stayed in the lung.
  • In para-aramid-exposed rats and hamsters, cell-labeling (proliferation) indices rose relative to controls immediately after exposure. In rats these effects were no different from controls after a 5-day postexposure period. The authors' summary describes these as transient increases after 2-week high-dose para-aramid exposures.
  • In asbestos-exposed rats, significant increases in cell labeling were measured in the high-dose groups immediately after exposure and at 5 days, 1 month and 3 months. Labeling returned to control levels at 6 months.
• The authors' conclusion: The authors concluded that the cell proliferative effects and enhanced biodurability of chrysotile, which they associate with chronic disease, do not occur with inhaled para-aramid fibrils. They stated that biodegradability in two rodent species supports the theory that para-aramid fibrils are probably biodegradable in exposed human lungs.
• Limitations the authors state:
  • The authors state that the hamster results are preliminary.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Fibril, biopersistence, Inflammation.

Related studies

• Pulmonary effects in rats inhaling size-separated chrysotile asbestos fibres or p-aramid fibrils: differences in cellular proliferative responses — D.B. Warheit, M.A. Hartsky, et al. (1996)
• A comparative study of the clearance of respirable para-aramid, chrysotile and glass fibres from rat lungs — A. Searl (1997)
• A review of inhalation toxicology studies with para-aramid fibrils — D.B. Warheit (1995)
• Cytotoxic effects of aramid fibres on rat pulmonary macrophages: comparison with chrysotile asbestos — J. Dunnigan, D. Nadeau, et al. (1984)
• Man-made respirable-sized organic fibers: what do we know about their toxicological profiles? — D.B. Warheit, K.L. Reed, et al. (2001)
• Comparative proliferative and histopathologic changes in rat lungs after inhalation of chrysotile or crocidolite asbestos — K.A. BéruBé, T.R. Quinlan, et al. (1996)

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