Light and electron microscope studies of the rat digestive tract following prolonged and short-term ingestion of chrysotile asbestos

Our plain-English summary of Light and electron microscope studies of the rat digestive tract following prolonged and short-term ingestion of chrysotile asbestos, by R. Jacobs, J. Humphrys, K.S. Dodgson, et al (British Journal of Experimental Pathology, 1978).

The study

• Authors: R. Jacobs, J. Humphrys, K.S. Dodgson, R.J. Richards
• Journal: British Journal of Experimental Pathology
• Published: 1978;59(5):443-53
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Free full text

Abstract

Rats were fed diets containing 0.5 mg or 50 mg of chrysotile asbestos each day for 1 week or 14 months and tissues of the gastrointestinal tract were examined by light and electron microscopy. At the light microscope level the oesophagus, stomach and caecum in treated animals appeared unaffected, whereas accumulation of cellular debris and Alcian blue-positive material was apparent in the ileal, rectal and colonic lumens. Electron microscope examination of the colon and ileum of rats ingesting 50 mg chrysotile/day for 14 months confirmed these findings and indicated changes in the mucosal lining cells of the ileum which were consistent with a mineral-induced cytotoxicity. These results are compared with those reported in a similar previous biochemical study and the specificity of asbestos action on certain regions of the gastrointestinal tract is discussed.

In plain English

This was an animal experiment. Three-month-old male rats were fed ordinary rat pellets alone (controls) or pellets with 0.5 mg or 50 mg of Rhodesian chrysotile asbestos a day, for 1 week or 14 months. The article does not say how many rats were in each group. Under the light microscope, the oesophagus, stomach and caecum of treated rats looked practically like controls. The ileum (small intestine) changed most, at both doses and durations: disorganized villi, vacuolization, and lining cells separating from underlying tissue. In the rectum and colon, clumps of nuclei and mucus-like material collected in the gut space. Under the electron microscope, ileal lining cells of rats fed 50 mg a day for 14 months pulled apart and lost their brush border. The colon showed separated cells and debris with bacteria. No asbestos fibres were detected between or inside the lining cells of the ileum or colon. The authors concluded that the findings suggest mineral-induced toxicity specific to certain regions of the gut. They said no firm conclusions could be drawn about fibres penetrating cells.

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 with light and electron microscope examination of gut tissue, comparing asbestos-fed rats with control rats
• Who was studied: Three-month-old male MRC hooded rats, kept in individual cages; the number of animals per group is not reported
• Exposure: UICC standard reference Rhodesian chrysotile asbestos added to rat pellets at 0.5 mg/day or 50 mg/day, fed for 1 week or 14 months; controls received pellets only (15 g/day)
• Main results:
  • Ileum, light microscopy, after 1 week: rats on 0.5 mg/day and on 50 mg/day showed similar changes compared with controls. These were disorganized villus tips, vacuolization of surface cells and of the villus core, and separation of the lining cells from the villus core.
  • Ileum, light microscopy, after 14 months at either dose: similar changes were seen. In addition, sections were often thinner than in controls, and the villus connective tissue looked loose and amorphous.
  • Rectum, all doses and durations: clumps of nuclei and Alcian blue-staining mucinous material were seen in the lumen of asbestos-fed rats but not in controls. No changes were seen in the rectal tissue itself.
  • Colon, light microscopy: the lumen showed changes like those in the rectum. After long-term feeding, the lamina propria looked more amorphous with some vacuolization. These changes were less marked than in the ileum.
  • Oesophagus, stomach and caecum: sections from asbestos-treated and control rats were practically identical.
  • Ileum, electron microscopy, rats fed 50 mg/day for 14 months: absorptive lining cells detached from each other with loss of tight junctions and enlarged spaces between cells. Other changes included loss of the brush border, vacuolization, discharge of cell contents into the lumen, blebbing of microvilli, and swollen mitochondria in cells that stayed intact.
  • Colon, electron microscopy, rats fed 50 mg/day for 14 months: vacuolization, separation of cells, and densely staining microvilli were seen. The lumen was filled with mucus-containing cell debris and bacteria. The cells did not show the isolated cells or the discharge of cell contents seen in the ileum.
  • The authors made an extensive search by electron microscopy. They detected no asbestos fibres in the spaces between the lining cells or inside the lining cells of the colon or ileum. They also found no evidence of fibres retained in the debris in the colonic lumen.
• The authors' conclusion: The authors concluded that their findings add to earlier biochemical findings suggesting that ingested chrysotile causes toxicity specific to certain regions of the gastrointestinal tract.
• Limitations the authors state:
  • The authors stated that definitive conclusions cannot be drawn about fibres penetrating the lining cells or passing through the gut wall. Neither was seen, possibly because of the limits of the techniques used.
  • The authors could not exclude that the large spaces between cells in the colon were caused by cutting tissue that contained asbestos fibres.
  • The authors suggested that chrysotile may have been lost from the tissue during fixation or sectioning, or cleared from the gut during the 24-hour fast before the rats were killed.
  • The authors noted that light microscopy alone gave little evidence of cell damage in the small intestine lining, unless the mucus and free nuclei in the lumen are taken as a sign of damage.

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile.

Related studies

• Nucleic acid metabolism in the rat following short-term and prolonged ingestion of chrysotile asbestos or cigarette-smoke condensate — R. Jacobs, M. Weinzweig, et al. (1978)
• The short-term effects of chronic asbestos ingestion in rats — R.E. Bolton, J.M. Davis (1976)
• 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)
• 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)
• Experimental lung tumors following specific intrabronchial application of chrysotile asbestos. Longitudinal light and electron microscopic investigations in rats — E. Fasske (1988)
• Ingestion of asbestos — S.H. Zaidi (1974)

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