Silica and asbestos: contrasts in tissue response

Our plain-English summary of Silica and asbestos: contrasts in tissue response, by A.G. Heppleston (Annals of the New York Academy of Sciences, 1979).

The study

• Author: A.G. Heppleston
• Journal: Annals of the New York Academy of Sciences
• Published: 1979;330:725-44
• Type of article: Review
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy.

In plain English

This 1979 article was a review by a single author comparing how body tissues respond to silica and to asbestos. It drew on human lung pathology, animal experiments and cell-culture work, including the author's own earlier experiments. It covered scarring (fibrosis), damage to cells, fatty build-up in the air sacs, and cancer. The review described the human silicotic nodule as sharply defined, while asbestos scarring was more irregular. In the author's earlier cell experiments, only extracts of quartz-treated intact macrophages significantly raised a collagen marker in fibroblasts. The author summarised asbestos damage to cells as mild and selective and silica's as severe and nonselective. One reviewed study, however, found chrysotile as toxic as silica to peritoneal macrophages. The review stated that lung cancer in men exposed to silica was similar to that in nonminers. Asbestos workers followed in cohorts had an increased lung cancer risk when exposure was severe. Crocidolite had mainly been incriminated in mesothelioma, but amosite and chrysotile had also been implicated. The author concluded that the contrasts appeared qualitative rather than quantitative.

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: review comparing tissue responses to silica and asbestos, drawing on human pathology, animal experiments and cell-culture studies (including the author's earlier work)
• Who was studied: No single study population; the review discussed human lung tissue, experimental animals (such as rats and guinea pigs) and cell cultures from published studies
• Exposure: Silica (quartz, tridymite, cristobalite, amorphous silica) compared with asbestos (chrysotile and the amphiboles, including amosite, crocidolite and anthophyllite)
• Main results:
  • The human silicotic nodule was described as a sharply circumscribed lesion, whereas the asbestos lesion had a more irregular distribution
  • In severe asbestosis (from the author's earlier work cited), there was no relationship between the severity of asbestosis and how long the mineral had been in the lungs
  • In the author's cell-culture experiment, only the extract of quartz-treated intact macrophages significantly raised hydroxyproline (a collagen marker) in fibroblasts. Quartz alone, extract of untreated macrophages and quartz-treated disintegrated macrophages did not.
  • In a cited study, PNO (a substance that inhibits quartz fibrosis) failed to inhibit pleural fibrosis from injected chrysotile
  • In a cited rat inhalation study of reference asbestos samples, Canadian chrysotile and anthophyllite were most fibrogenic, Rhodesian chrysotile and crocidolite less so, and amosite least
  • In one cited study of peritoneal macrophages, amosite and crocidolite were innocuous while chrysotile was as toxic as silica; the author's summary table rated asbestos cytotoxicity as mild and selective
  • In a cited rat study, inhaled chrysotile produced surface tension and pressure/volume changes in the lungs similar to silica
  • The review stated that lung cancer prevalence in men exposed to silica was similar to that in nonminers
  • Cited cohort studies of asbestos workers showed an increased lung cancer risk when exposure was severe; no one fiber type had been particularly connected with lung cancer
  • The review stated that cigarette smoking combined with asbestos exposure evidently had a multiplicative effect on bronchial cancer
  • For pleural and peritoneal mesothelioma, crocidolite had mainly been incriminated, but amosite and chrysotile exposure had also been implicated
  • From animal studies, the author judged that magnesium was not pivotal in tumor induction, and that fiber structure (small diameter, greater length) mattered more than chemical properties
• The authors' conclusion: The author concluded that, on the balance of available evidence, the contrasts in tissue response to compact (silica) and fibrous (asbestos) particles appeared to be qualitative rather than quantitative
• Limitations the authors state:
  • The author noted that the rat silica experiments used intratracheal injection and histological grading, which are not the most reliable methods
  • The author stated that injection and implantation techniques do not deliver fibers at the proper rate or manner and eliminate interaction with lung surfactant
  • The author stated it is not yet justifiable to assume that cytotoxicity tests are sufficient to indicate occupational risk

Topics

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

Related studies

• Effect of SiO2-liberated macrophage factor on protein synthesis in connective tissue in vitro — M. Aalto, H. Turakainen, et al. (1979)
• One agent, many diseases: exposure-response data and comparative risks of different outcomes following silica exposure — K. Steenland (2005)
• Mesothelial cell proliferation: a nonspecific response to lung injury associated with fibrosis — I.Y. Adamson, J. Bakowska, et al. (1994)
• Indications for distinct pathogenic mechanisms of asbestos and silica through gene expression profiling of the response of lung epithelial cells — T.N. Perkins, P.M. Peeters, et al. (2015)
• Silicosis and smoking strongly increase lung cancer risk in silica-exposed workers — N. Kurihara, O. Wada (2004)
• Silica exposure and altered regulation of autoimmunity — S. Lee, H. Matsuzaki, et al. (2014)

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