Mesothelioma Induced By Intrapleural Injection of Different Types of Fibres in Rats - Synergistic Effect of Other Carcinogens

Our plain-English summary of Mesothelioma Induced By Intrapleural Injection of Different Types of Fibres in Rats - Synergistic Effect of Other Carcinogens, by J. Lafuma, M. Morin, J.L. Poncy, et al (1980).

The study

• Authors: J. Lafuma, M. Morin, J.L. Poncy, R. Masse, A. Hirsch, J. Bigon, G. Monchaux
• Published: BIOLOGICAL EFFECTS OF MINERAL FIBRES (J.C. WAGNER, EDITOR), LYON: IARC SCIENTIFIC PUBLICATIONS, VOLUME 30., PP 311-320 (1980)
• Type of article: Conference paper
• Our copy: from Johns-Manville's own medical library. The article is still under copyright, so we describe it here rather than post it.

In plain English

This French animal experiment injected 20 mg of mineral fibres into the chest lining (pleura) of three-month-old rats. The fibres were UICC chrysotile, untreated or leached to different degrees, UICC crocidolite, and a glass fibre. Of 35 rats given unleached chrysotile, 13 developed mesotheliomas and 2 lung carcinomas; none of 32 saline controls developed either. Chrysotile leached to 20% produced 15 mesotheliomas in 32 rats; more heavily leached chrysotile produced fewer, down to 1 in 36 rats at 100% leaching by oxalic acid. Crocidolite produced mesotheliomas in 20 of 41 rats, and glass fibres in 6 of 44. Nine abdominal mesotheliomas were seen; the authors could not establish whether they spread from chest tumours or arose during injection through the abdomen. In small preliminary groups, rats received a tenfold smaller 2 mg chrysotile dose combined with radon or with earlier neutron radiation. All 8 radon-group rats developed lung tumours, 7 of them mesotheliomas; 3 of 9 neutron-group rats developed mesotheliomas. The authors concluded that leaching reduced chrysotile's toxicity and cancer effect, and that the radiation experiments showed increased sensitivity to intrapleurally injected asbestos fibres.

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 experiment: intrapleural (into the chest lining) injection of fibres in rats, plus small preliminary experiments combining radiation with chrysotile
• Who was studied: Three-month-old Sprague-Dawley SPF rats. Groups ranged from 16 to 52 rats in the main fibre experiments (32 saline controls). The preliminary radiation groups had 8 to 10 rats, with 20 to 30 irradiated controls.
• Exposure: 20 mg of UICC standard fibre by intrapleural injection. Fibres were untreated chrysotile; chrysotile leached to 20%, 50%, 70% or 100% by oxalic acid, or to 100% by hydrochloric acid; UICC crocidolite; and glass fibres (J.M. 104). Preliminary groups received 2 mg intrapleural chrysotile combined either with radon (3000 WLM over one month; the damaged text leaves unclear whether radon came before or after the injection) or with whole-body neutron irradiation given 125 days before the injection. One further irradiated group was fed chrysotile in its diet.
• Main results:
  • Unleached chrysotile: of 35 rats, 2 had lung carcinomas and 13 had mesotheliomas (43% as printed). Saline controls: 0 of 32 had either.
  • Chrysotile leached to 20% (printed '201'): 0 carcinomas and 15 mesotheliomas in 32 rats (47%). That is not fewer than with unleached chrysotile.
  • Chrysotile leached to 100% by oxalic acid: 1 mesothelioma in 36 rats (3%). Chrysotile leached to 100% by hydrochloric acid: 0 tumours in 16 rats.
  • Leaching decreased chrysotile's toxic action. Mean survival was longer with more leaching (unleached 363 days; saline controls 468 days).
  • Mean latent period to tumours was 384 days for unleached chrysotile and 585 days for chrysotile leached to 100%.
  • Crocidolite: 0 carcinomas and 20 mesotheliomas in 41 rats.
  • Glass fibres: 0 carcinomas and 6 mesotheliomas in 44 rats (14%).
  • Nine abdominal mesotheliomas were observed across the chrysotile, crocidolite and glass fibre groups.
  • Extrathoracic cancers: 5.1 were expected and 6 were observed, which the authors described as no excess.
  • Radon combined with 2 mg chrysotile: all 8 rats developed lung tumours, 7 of them mesotheliomas.
  • Neutron irradiation followed 125 days later by 2 mg chrysotile: 4 carcinomas and 3 mesotheliomas in 9 rats. Irradiated controls: 1 carcinoma and 0 mesotheliomas in 20 rats.
• The authors' conclusion: The authors concluded that leaching reduced chrysotile's toxicity and carcinogenic effect. They concluded that preliminary experiments with radiation showed increased sensitivity to asbestos fibres injected intrapleurally.
• Limitations the authors state:
  • The synergism (combined-effect) studies were described as preliminary.
  • The original protocol was modified: rats were added from the metabolism experiment, and some animals were lost to cannibalism and infection.
  • The authors could not establish whether the abdominal mesotheliomas spread from chest tumours or were caused at the time of injection through the abdominal cavity.
  • Tumour figures for the neutron-irradiated animals did not demonstrate significant radiosensitivity, because few cancers were observed in controls.

Topics

Medical terms in this study, explained in our Lexicon: Mesothelioma, Synergistic Effect, Pleura, UICC, Chrysotile, Crocidolite, Carcinoma.

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