Experimental studies on asbestos carcinogenicity

Our plain-English summary of Experimental studies on asbestos carcinogenicity, by L.M. Shabad, L.N. Pylev, L.V. Krivosheeva, et al (Journal of the National Cancer Institute, 1974).

The study

• Authors: L.M. Shabad, L.N. Pylev, L.V. Krivosheeva, T.F. Kulagina, B.A. Nemenko
• Journal: Journal of the National Cancer Institute
• Published: 1974;52(4):1175-87
• Cited by: 44 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy.

Abstract

The carcinogenic activity of different types of asbestos of the USSR was investigated. All samples of chrysotile had traces of benzo[a]pyrene (BP). Chrysotile asbestos had a high adsorption activity. BP was not found in anthophyllite and magnesioarfvedsonite. Intratracheal injections and inhalations of different kinds of chrysotile induced pulmonary carcinomas, sarcomas, and precancerous lesions in rats. The number of such lesions was higher if asbestos and BP were introduced together. Intrapleural administration of chrysotile asbestos induced several types of mesothelioma and premesotheliomatous lesions in rats. A transplantable mesothelioma (MSh-71) is in its twenty-sixth generation.

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

In plain English

This 1974 report described rat experiments with chrysotile asbestos from Ural and Kazakhstan mines in the USSR. It also measured benzo[a]pyrene (BP), a cancer-causing chemical, in asbestos samples. Chrysotile alone injected into the windpipe caused a few precancerous lung changes and no tumors. Combined with BP, chrysotile produced tumors in 6 of 21 (29%) and 6 of 11 (55%) longer-surviving rats in two series, and lung carcinomas occurred only with this combination. Rats that breathed chrysotile mill dust developed no tumors, possibly, the authors said, because the experiment was short. Precancerous lesions affected 20% of rats given dust alone, 57% given dust plus BP and 38% given dust plus cigarette smoke. After chrysotile was injected into the chest cavity, pleural mesotheliomas were found in 31 of 67 rats (46%) that survived 8 to 24.5 months, and some spread to other organs. One tumor was kept growing by transplantation (MSh-71). All chrysotile samples contained small amounts of BP, but none was found in the anthophyllite and magnesiaarfvedsonite samples tested. The authors concluded that their types of asbestos were carcinogenic and said the mechanism was unclear.

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 experiments in rats (intratracheal injection, inhalation and intrapleural injection of chrysotile, with and without BP or cigarette smoke), plus laboratory measurement of BP content and BP adsorption in asbestos samples
• Who was studied: Randombred male and female rats. The intratracheal series used 1-month-old rats weighing 90-100 g. Each series was split into early deaths (weeks) and longer survivors (months): series 1 had 12 and 49 rats, series 2 had 30 and 21, series 3 had 24 and 11, and series 4 had 9 and 19. The inhalation series had 46 rats (asbestos alone), 21 (asbestos plus BP) and 16 (asbestos plus cigarette smoke). The intrapleural experiment used rats weighing 100 g: 67 surviving 8-24.5 months and 3 surviving 2-2.5 months. Asbestos samples came from USSR mines and mills.
• Exposure: Chrysotile from Ural and Kazakhstan mines. Intratracheal: 2 mg three times, given alone, with adsorbed BP, or with 5 mg BP; one group got 5 mg BP alone. Inhalation: Kazakhstan chrysotile mill dust at 230 mg per cubic metre (unit garbled in the scan), 2 hours 5 times a week for 13.5 months, alone or with intratracheal BP or cigarette smoke. Intrapleural: Ural chrysotile filter dust, 20 mg three times. BP was also measured in chrysotile, anthophyllite and magnesiaarfvedsonite samples.
• Main results:
  • Intratracheal chrysotile alone (series 1): precancerous lesions only at the end of the experiments, and no tumors.
  • Chrysotile with adsorbed BP (series 2): tumors in 6 of the 21 rats surviving 10.5-25.5 months (29%). These were lung papillomas or reticulosarcomas, with no carcinomas.
  • Chrysotile plus 5 mg BP (series 3): tumors in 6 of the 11 rats surviving 9-28 months (55%). These were 1 lung papilloma, 3 lung carcinomas and 2 pleural mesotheliomas.
  • Lung carcinomas occurred only when asbestos and BP were combined.
  • Inhalation of chrysotile dust produced no tumors in any series.
  • Inhalation: precancerous lesions in 20% of rats given asbestos alone (9 of 46), 57% with added BP (12 of 21) and 38% with added tobacco smoke (6 of 16). The authors reported the difference between series 1 and 2 as significant, and the difference they printed as between series 2 and 3 as of borderline significance.
  • Intrapleural chrysotile, by the running text: mesotheliomas in 13 of 46 rats that died at 8-17 months and in 15 of 21 rats that died at 18-25 months.
  • Intrapleural chrysotile, by Table 3: 31 mesotheliomas (46%) among the 67 rats surviving 8-24.5 months. The text calls this 46% of all treated rats, but the table also lists 3 rats surviving 2-2.5 months. The first mesothelioma was found at 8 months.
  • Some sarcoma-like pleural mesotheliomas spread to the kidneys, liver and mediastinal lymph nodes.
  • A mixed pleural mesothelioma from a chrysotile-injected rat was transplanted. By September 1973 it was in its 26th transplant generation, with 68% of transplantations successful.
  • All chrysotile samples contained small amounts of BP. Levels were lower in ore and highest in the commercial product: 36.97 and 16.00 micrograms per kg in the two chrysotile sources.
  • No BP was found in the magnesiaarfvedsonite and anthophyllite samples tested.
  • Chrysotile dust strongly adsorbed BP from solution, slightly less than thermal carbon black did.
• The authors' conclusion: The authors concluded that the types of asbestos they tested were carcinogenic in rats. They suggested that asbestos fibers may adsorb BP and enhance its effect, without ruling out a carcinogenic effect of asbestos itself, especially for mesothelial tumors. They stated that the mechanism was not clear and that more investigation was needed.
• Limitations the authors state:
  • The authors said the lack of tumors after inhalation was possibly due to the short duration of the experiment.
  • The authors said they lacked sufficient evidence to classify the adenomatous pleural proliferations as tumors.
  • The authors stated that the mechanism of asbestos carcinogenesis was not clear.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Carcinogenic, Chrysotile, Anthophyllite, Magnesio-arfvedsonite, Carcinoma, Sarcoma, Mesothelioma.

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