Nucleic acid metabolism in the rat following short-term and prolonged ingestion of chrysotile asbestos or cigarette-smoke condensate

Our plain-English summary of Nucleic acid metabolism in the rat following short-term and prolonged ingestion of chrysotile asbestos or cigarette-smoke condensate, by R. Jacobs, M. Weinzweig, K.S. Dodgson, et al (British Journal of Experimental Pathology, 1978).

The study

• Authors: R. Jacobs, M. Weinzweig, K.S. Dodgson, R.J. Richards
• Journal: British Journal of Experimental Pathology
• Published: 1978;59(6):594-600
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Free full text

Abstract

Rats which have ingested a natural diet containing chrysotile asbestos (50 mg/day) both in the short (one week) and long term (5-15 months) show a statistically significant increase in the incorporation of [3H]-thymidine into DNA in the small intestine mucosa, colon and rectum, stomach and spleen and a significant decrease in the incorporation of this radiolabel into liver DNA. However, short-term ingestion of similar quantities of chrysotile produced no significant change in the incorporation of [3H]-uridine into RNA in any tissues, although prolonged ingestion of the mineral induced alterations in RNA metabolism in the lung and liver. By contrast, animals ingesting a natural diet containing cigarette-smoke condensate show a significantly high incorporation of [3H]-uridine into RNA in the mucosa, submucosa, spleen and heart following short-term exposure. Long-term ingestion of this diet produces similar changes in the submucosa, spleen and lung. The apparent specificity and the mechanism whereby ingested chrysotile interferes with DNA metabolism in some body tissues is discussed.

In plain English

This was an experiment in three-month-old male MRC hooded rats. For one week or 5 to 15 months, rats ate plain pellets, pellets with 50 mg a day of UICC Rhodesian chrysotile asbestos, or pellets containing cigarette-smoke condensate. The authors injected radioactive building blocks of DNA (thymidine) or RNA (uridine) and measured their incorporation per microgram of tissue DNA or RNA per hour. The DNA groups had 4 rats (one week) or 6 (long term). In chrysotile-fed rats, thymidine incorporation was significantly higher in the stomach, small-intestinal lining, colon and rectum, and spleen at both times, and in the oesophagus and caecum after one week; it was significantly lower in the liver. Uridine incorporation showed no statistically significant change after one week of chrysotile, but rose significantly in the lung and fell in the liver after long feeding. The smoke diet significantly raised uridine incorporation in several tissues, which differed between short and long feeding. The authors concluded that ingested chrysotile interferes with DNA metabolism in the rat gut and other organs, and called for more study of mechanism and dose.

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 feeding experiment measuring incorporation of radiolabelled thymidine into DNA and uridine into RNA in rat tissues
• Who was studied: Three-month-old male MRC hooded rats. In the DNA (thymidine) experiment there were 4 rats per group for short-term feeding and 6 rats per group for long-term feeding. Group sizes for the RNA experiment are not legible in the text.
• Exposure: UICC Rhodesian chrysotile asbestos at 50 mg/day, fed as a paste with crushed rat pellets, for one week or for 5 to 15 months. Separate groups ate pellets mixed with water through which smoke from one cigarette had been bubbled (cigarette-smoke condensate).
• Main results:
  • Short-term (one week) chrysotile-fed rats: thymidine incorporation into DNA was significantly higher in the small intestinal mucosa, oesophagus, caecum, colon and rectum, stomach, and spleen.
  • Short-term chrysotile-fed rats: thymidine incorporation into liver DNA was significantly decreased.
  • Long-term (5 to 15 months) chrysotile-fed rats: thymidine incorporation into DNA was significantly increased in the small intestinal mucosa, colon and rectum, spleen and stomach, and significantly decreased in the liver.
  • In chrysotile-fed rats, DNA metabolism in the small-intestinal submucosa appeared unaffected, while the lining mucosal cells showed increased incorporation.
  • Short-term chrysotile-fed rats: no statistically significant changes in uridine incorporation into RNA in any tissue examined.
  • Long-term chrysotile-fed rats: uridine incorporation into RNA was significantly increased in the lung and significantly decreased in the liver.
  • Short-term cigarette-smoke-condensate diet: significant increases in uridine incorporation into RNA in 4 tissues (small-intestinal mucosa, small-intestinal submucosa, spleen and heart).
  • Long-term smoked diet: significant increases in uridine incorporation into RNA in the small-intestinal submucosa, spleen and lung.
  • The authors also reported a decrease in thymidine incorporation into liver DNA after short-term ingestion of 0.5 mg/day of chrysotile, but did not give the data.
• The authors' conclusion: The authors concluded that ingestion of chrysotile asbestos interferes with DNA metabolism in rat tissues in the gastrointestinal tract and other body organs. They said the specificity and mechanism of these changes require further experimentation.
• Limitations the authors state:
  • The authors said further studies using different concentrations of chrysotile are needed to determine how specific the mineral's effect on nucleic acid metabolism is.
  • The authors said that assessing any possible environmental hazard from ingested chrysotile would need more information on the concentration required to produce metabolic changes in specific organs.

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile, Short-Term Exposure.

Related studies

• Light and electron microscope studies of the rat digestive tract following prolonged and short-term ingestion of chrysotile asbestos — R. Jacobs, J. Humphrys, et al. (1978)
• A preliminary study of biochemical changes in the rat small intestine following long-term ingestion of chrysotile asbestos — R. Jacobs, K.S. Dodgson, et al. (1977)
• Distribution of 6-6(n)-3[H]sucrose and its radiolabeled degradation products from isolated, perfused rat small intestine loops following prolonged ingestion of chrysotile asbestos — R. Jacobs, R.J. Richards (1980)
• Effects of cigarette smoke and asbestos on airway, vascular and mesothelial cell proliferation — H. Sekhon, J. Wright, et al. (1995)
• Synergistic effects of mineral fibres and cigarette smoke on the production of tumour necrosis factor by alveolar macrophages of rats — Y. Morimoto, M. Kido, et al. (1993)
• Cigarette smoke, asbestos, and small irregular opacities — W. Weiss (1984)

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