Intestinal transport of some macromolecules in food

Our plain-English summary of Intestinal transport of some macromolecules in food, by M.L. Weiner (Food and Chemical Toxicology, 1988).

The study

• Author: M.L. Weiner
• Journal: Food and Chemical Toxicology
• Published: 1988;26(10):867-80
• Type of article: Review
• Cited by: 40 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This review focuses on the intestinal transport of macromolecules in food. Although it is known that neonates have the ability to absorb proteins from the intestine as a means of passive immunization, it has generally been assumed that adults do not retain this capability. A number of studies have shown that the adult mammalian small intestine is capable of transporting a variety of macromolecules in food to a very limited extent. The evidence demonstrating the transport of test substances in the micron-size range across the adult intestinal epithelial barrier is examined for a number of food substances and environmental contaminants. It will be shown that macromolecules can be transported across this barrier by endocytosis; by uptake into the gut-associated lymphoid tissue, and possibly by uptake into the goblet cells. It is considered highly unlikely that large micron-sized particles pass between intestinal cells due to the integrity of the tight junctions between cells that exclude particles in this size range. Quantitative estimates for macromolecular uptake are included along with a discussion of the physiological parameters influencing macromolecular transport.

In plain English

This article was a review, not a new study. The author reviewed published animal and human research on whether large molecules and small particles in food and water can pass through the wall of the adult intestine. The materials covered were proteins, latex and other inert particles, carrageenans, asbestos and other mineral fibres, and cellulose. Across the studies reviewed, the author reported that very small percentages of the amounts given crossed the intestinal barrier. Passage was mainly by uptake into intestinal cells or into the gut's lymphoid tissue (Peyer's patches). The author wrote that most of the evidence did not support passage between cells. For asbestos, the author described the animal studies as contradictory and noted problems with airborne fibre contamination. One reviewed human study found fibres in urine at an estimated 0.10% of the fibres swallowed in drinking water. A reviewed mouse study of chrysotile in drinking water found no fibres in intestinal tissue by light microscopy. The author concluded that the occasional asbestos fibres reported to cross the intestine were not considered to be of major concern, and also wrote that more work was required.

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: Review of published literature
• Who was studied: Published experimental studies in animals (rats, mice, pigs, monkeys, rabbits and others) and in humans on how material crosses the intestinal lining; no new subjects were studied
• Exposure: Ingested macromolecules and particles: proteins, inert particles such as latex and carbon, carrageenans, asbestos and other mineral fibres (including chrysotile, and amphibole fibres in drinking water), and cellulose and its derivatives. The review cites asbestos fibre widths of 0.1 to 2.0 micrometres and lengths of 0.5 to 25 micrometres.
• Main results:
  • The reviewed studies showed that proteins of about 0.005 micrometre can cross the adult intestinal barrier by being taken up into cells (endocytosis).
  • Uptake into the gut-associated lymphoid tissue was reported for particles up to 5.7 micrometres in diameter.
  • Passage of particles between intestinal cells ('persorption') was not supported by most of the scientific evidence reviewed.
  • Animal studies on whether mineral fibres penetrate the intestinal lining gave contradictory results.
  • In a reviewed human study (Cook and Olson, 1979) of people drinking a public water supply with a high mineral fibre content, fibres were found in urine at a concentration estimated at 0.10% of the ingested fibres. People who drank filtered water had a negligible fibre count in their urine.
  • In a reviewed mouse study (LeFevre et al., 1985b), mice drank water containing 1% chrysotile asbestos for 92 days. No asbestos fibres were seen by light microscopy in the intestinal tissue or Peyer's patches.
  • In the same mouse study, macrophages in the Peyer's patches of asbestos-fed mice appeared to contain more dense inclusions than those of control mice, but the inclusions contained no visible asbestos fibres.
  • Across the test substances reviewed, very small percentages of the administered material crossed the intestinal barrier.
• The authors' conclusion: The author concluded that the adult intestine transports macromolecules only to a limited degree. The author also concluded that the occasional asbestos fibres reported to cross the intestine and appear in urine are not considered to be of major concern.
• Limitations the authors state:
  • Animal studies of ingested fibres can be affected by contamination of tissue samples with airborne fibres and by inhalation of airborne fibres during oral feeding studies.
  • Studying asbestos fibre transport is difficult because the amount transported is very small and contamination is hard to avoid.
  • In the reviewed mouse chrysotile study, light microscopy may have missed some fibres.
  • The author stated that more work is needed on asbestos fibre transport.

Related studies

• An investigation of the penetration of ingested asbestos into the normal and abnormal intestinal mucosa of the rat — M.E. Meek, P. Grasso (1983)
• Transport of inhaled dust to extrapulmonary sites — P.F. Holt (1981)
• Effects of asbestos on membrane transport and metabolism of benzo(a)pyrene — C. Kandaswami, P.J. O'Brien (1980)
• Asbestos exposure increases paracellular transport of fibrin degradation products across human airway epithelium — T.J. Gross, S.M. Cobb, et al. (1994)
• A dynamical model of the transport of asbestos fibres in the human body — A. DeStefano, C.F. Martin, et al. (2017)
• Unusual intestinal talcosis — P.A. Anani, C. Ribaux, et al. (1987)

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