A preliminary study of biochemical changes in the rat small intestine following long-term ingestion of chrysotile asbestos

Our plain-English summary of A preliminary study of biochemical changes in the rat small intestine following long-term ingestion of chrysotile asbestos, by R. Jacobs, K.S. Dodgson, R.J. Richards (British Journal of Experimental Pathology, 1977).

The study

• Authors: R. Jacobs, K.S. Dodgson, R.J. Richards
• Journal: British Journal of Experimental Pathology
• Published: 1977;58(5):541-8
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Free full text

Abstract

Changes are reported in the DNA, RNA, protein and brush border enzymes in the small intestine mucosal lining cells and gut lumen, induced by maintaining rats on a diet containing chrysotile asbestos for 10 months. Intracellular levels of RNA, DNA and protein remained unchanged but significant alterations, consistent with a mineral-induced cytotoxicity, were found in the lumen level of DNA (increased) and RNA (decreased) in asbestos-treated rats. Most intracellular enzyme levels were consistently, but not significantly, elevated in animals maintained on diets containing asbestos whilst the activities within the lumen were significantly higher than those found in normal animals. The presence of cigarette smoke alone in the diet induced changes in intracellular RNA and lumen ATPase but the combined effect of cigarette smoke and asbestos was rarely different from the alterations induced by asbestos alone on the majority of parameters studied.

In plain English

This was a laboratory experiment in rats, which the authors called a preliminary study. Three-month-old male hooded rats were fed diets containing chrysotile asbestos at 0.5 mg/day or 50 mg/day for 10 months. In some groups the asbestos was first treated with cigarette smoke. Control rats ate normal diets or diets containing cigarette smoke alone. The authors measured DNA, RNA, protein and several enzymes in cells from the small intestine lining and in washings from the gut interior (lumen). In all asbestos-fed groups, lumen RNA was significantly lower and lumen DNA significantly higher than in controls. DNA and RNA in the lining cells were not significantly changed. Some lumen enzyme activities were significantly raised in asbestos-fed groups. Smoke-treated asbestos gave similar but not identical effects to asbestos alone. The authors suggested that asbestos may damage the lining cells. They noted that an earlier electron microscope study did not support this view and that further experiments were needed. The data tables cannot be read in this copy.

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 (feeding study in rats), described by the authors as a preliminary study
• Who was studied: Three-month-old male hooded rats (strain printed as '3MRC'), kept in individual cages and fed for 10 months, in four control and eight test diet groups, at the Department of Biochemistry, University College, Cardiff, Wales. The number of rats per group cannot be read in the text.
• Exposure: Chrysotile asbestos added to rat pellet or pellet-plus-margarine diets at a high dose (50 mg/day) or a low dose (0.5 mg/day, printed '0-5'). In 4 of the 8 test groups the asbestos was first pretreated with the smoke of one cigarette. Control diets included cigarette smoke alone.
• Main results:
  • In all groups of rats given asbestos (with or without cigarette smoke pretreatment), RNA in the gut lumen was significantly lower and DNA significantly higher than in control animals (Groups 1 and 4).
  • Asbestos in the diet did not significantly alter DNA or RNA levels in the mucosal cell lining layer.
  • Total mucosal cell protein was consistently, but not significantly, higher in rats given the low asbestos dose.
  • Only rats given the high asbestos dose pretreated with cigarette smoke (Group 6) had significantly lower lumen protein than rats on a normal diet (Group 1).
  • Cigarette smoke alone in the diet (Group 4) significantly reduced mucosal-cell RNA compared with normal rats (Group 1).
  • Among the enzymes, cigarette smoke alone (Group 4) significantly altered only total ATPase activity in the gut lumen.
  • The low asbestos dose alone (Group 2) significantly increased lumen beta-glucuronidase, sucrase and alkaline phosphatase activities, and mucosal cell beta-glucuronidase, compared with normal rats (Group 1).
  • The high asbestos dose (Group 3) produced significant changes in lumen beta-N-acetyl glucosaminidase, sucrase, ATPase and p-nitrophenyl acetate hydrolase activities compared with normal rats (Group 1).
  • Asbestos pretreated with cigarette smoke (Groups 5 and 6) produced effects similar, but not identical, to asbestos alone (Groups 2 and 3).
  • The authors stated that lumen DNA in asbestos-fed rats was invariably twice as high as in normal rats.
• The authors' conclusion: The authors concluded that the higher lumen DNA in asbestos-fed rats suggests faster shedding of lining cells, possibly due to cell damage caused by the mineral. They also offered an alternative explanation: asbestos might bind DNA.
• Limitations the authors state:
  • Some enzyme activities, particularly sucrase and alkaline phosphatase, fluctuated considerably despite precautions.
  • Comparison between experiments was difficult because of the wide range in enzyme activities.
  • Expressing enzyme activities per mg DNA partly masked the total enzyme activities in the lumen.
  • Electron microscope evidence from another research group (Davis et al., 1974) does not support the view that asbestos is cytotoxic to these cells.
  • The authors' hypotheses require further experimentation using histochemical and electron microscope techniques.
  • The physiological implications of the findings are unclear.

Topics

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

Related studies

• 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)
• 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)
• 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)
• Toxic effect on the rat small intestine of chronic administration of asbestos in drinking water — T.J. Delahunty, D. Hollander (1987)
• The mesotheliomas of the small intestine — M. Paul, G. Panabokke, et al. (1965)
• Functional and biochemical effects on rat lung following instillation of crocidolite and chrysotile asbestos — S. Hirano, M. Ono, et al. (1988)

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