Lung response to particulates with emphasis on asbestos and other fibrous dusts

Our plain-English summary of Lung response to particulates with emphasis on asbestos and other fibrous dusts, by K.P. Lee (Critical Reviews in Toxicology, 1985).

The study

• Author: K.P. Lee
• Journal: Critical Reviews in Toxicology
• Published: 1985;14(1):33-86
• Type of article: Review
• Cited by: 44 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Many theories have been proposed to explain asbestosis and asbestos-related pulmonary disease. However, none of the theories give a completely plausible explanation for the pathogenesis. Recently, attention has been drawn to a theory that the fibrogenicity or carcinogenicity of fibrous dust particles is related to fiber diameter and length rather than to chemical properties. This theory may help partially elucidate the disease process but is still far from solving the enigma of pulmonary fibrosis or carcinogenesis. The theory cannot explain the absence of these pathological effects among fiberglass workers or experimental animals exposed by inhalation (even though mesotheliomas are induced by intrapleural implantation and fiber dimension-related fibrogenicity is demonstrated by intratracheal injection). Little information regarding the pulmonary response to manmade fibrous particles is available in animals following inhalation exposure. Attempts should be made to confirm the absence of adverse effects using animal inhalation experiments even though to this point there is no conclusive evidence that either lung cancer or pulmonary diseases can be produced among employees in manmade fiber industries. A new research trend seems concentrated on testing the durability of asbestos or manmade fibers. This is based on the concept that biological effects of fibrous particles are the result of relative durability and that particles which can be fragmented or shortened may be less pathogenic. In the last two decades, considerable understanding about pulmonary fibrosis and carcinogenesis of asbestos has been achieved by clinical and animal experiments. In vitro tests including cytotoxicity, hemolysis, immunology, and enzyme biochemistry have provided important information on the interrelationships among these various biological effects of asbestos.

In plain English

This article was a narrative review, not a new study. The author reviewed published human, animal and laboratory work on how the lungs respond to inhaled dusts. It covered so-called nuisance dusts, asbestos, manmade inorganic fibers such as glass fibers and potassium titanate, and organic manmade fibers. The review stated that mesothelioma usually develops 25 to 30 years after first exposure. It said mesothelioma appears closely related to crocidolite, alone or mixed with other fiber types, while the role of chrysotile remained controversial. It described lung cancer risk as 50-fold greater in asbestos workers who smoke than in nonsmokers not exposed to asbestos. It cited an inhalation study in which potassium titanate fibers caused dose-related lung fibrosis in rats, guinea pigs and hamsters, but mesotheliomas only in hamsters. In animal implantation studies, fibers thinner than 1.5 micrometres and longer than 8 micrometres were most effective at inducing mesothelioma. The author cautioned that injection studies have little relevance to human exposure. The author concluded that no theory fully explained asbestos disease and that the fiber-size theory was still far from doing so.

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: Narrative review of published human, animal and laboratory studies; no new study population
• Who was studied: No study population of its own; the review drew on published studies of workers, urban residents and laboratory animals (rats, hamsters, guinea pigs, mice, baboons)
• Exposure: Nuisance dusts; asbestos (chrysotile, crocidolite, amosite, anthophyllite, actinolite, tremolite); manmade inorganic fibers (fiberglass, mineral wool, potassium titanate and others); organic manmade fibers (nylon, polyester, acrylic)
• Main results:
  • The review stated that mesotheliomas develop many years after first exposure, in most cases after 25 to 30 years
  • The review stated that mesothelioma occurrence appears closely related to crocidolite, alone or in a mixture of fiber types
  • The review stated that the role of chrysotile in human mesothelioma was not well known and remained controversial
  • Citing other studies, the review stated that lung cancer risk is 50-fold greater in asbestos workers who smoke than in nonsmokers not exposed to asbestos
  • In a cited inhalation study, rats, guinea pigs and hamsters exposed to potassium titanate fibers developed dose-related lung fibrosis in all three species, but mesotheliomas only in hamsters
  • In rat studies using implantation into the chest cavity, the optimal fiber size for inducing mesothelioma was less than 1.5 micrometres in diameter and greater than 8 micrometres in length
  • The review stated that, unlike in laboratory animals, lung fibrosis in humans continues to progress after asbestos exposure stops
  • The review stated that there is no evidence that pleural plaques are precursors of malignant mesothelioma, and that plaques do not indicate asbestosis
  • Citing a recent review, the article stated that manmade vitreous fibers do not cause an increased risk of lung cancer or nonmalignant lung disease
• The authors' conclusion: The author concluded that none of the proposed theories fully explains asbestos-related disease. In the author's view, the fiber-dimension theory may partly explain the disease process but is still far from solving the problem of pulmonary fibrosis or carcinogenesis.
• Limitations the authors state:
  • The author stated that injecting fibers into the chest or abdominal cavity of animals has little relevance to human exposure, because of the unnatural route and the large quantities used
  • The author noted that the relative potency of asbestos types in animal studies does not match the incidence of human mesothelioma
  • The author noted that little animal inhalation information was available on manmade fibers

Topics

Medical terms in this study, explained in our Lexicon: Pulmonary Fibrosis, Carcinogenesis, Mesothelioma, Fiber Dimensions, Lung Cancer.

Related studies

• Quantitative assessment of inorganic fibrous particulates in dust samples with an analytical transmission electron microscope — F.D. Pooley, N.J. Clark (1979)
• The pulmonary response to fibrous dusts of diverse compositions — P. Gross, R.T. deTreville, et al. (1970)
• Evaluation of the dose-response and fate in the lung and pleura of chrysotile-containing brake dust compared to chrysotile or crocidolite asbestos in a 28-day quantitative inhalation toxicology study — D.M. Bernstein, B. Toth, et al. (2018)
• Fibrous dust particles and ferruginous bodies. Methods for quantitating them and some results from the lungs of city dwellers — P. Gross, J. Tuma, et al. (1970)
• Dose-response relationship of fibrous dusts in intraperitoneal studies — M. Roller, F. Pott, et al. (1997)
• Evaluation of the fate and pathological response in the lung and pleura of brake dust alone and in combination with added chrysotile compared to crocidolite asbestos following short-term inhalation exposure — D.M. Bernstein, R.A. Rogers, et al. (2015)

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