Hemolysis by asbestos

Our plain-English summary of Hemolysis by asbestos, by J.S. Harington, K. Miller, G. Macnab (Environmental Research, 1971).

The study

• Authors: J.S. Harington, K. Miller, G. Macnab
• Journal: Environmental Research
• Published: 1971;4(2):95-117
• Cited by: 157 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Summary of the article

This laboratory study examined how different types of asbestos and other minerals damage (lyse) red blood cells in vitro, how acidity (pH) affects this, and which chemical agents prevent it. Fourteen mineral dusts and fibers were tested, including Union Internationale Contre le Cancer (U.I.C.C.) standard reference asbestos samples. In the standard test, 50 mg of mineral was incubated with sheep erythrocytes in buffered saline for 50 minutes at 37°C, and the hemoglobin released was measured. Chrysotile lysed erythrocytes completely within 10 minutes over a pH range of 4-11. It was hemolytic to erythrocytes of all nine animal species tested. Amosite and crocidolite were relatively inactive on sheep cells (about 10%) but more active on cells of other species. Over 4 hours, their activity increased; with human erythrocytes it rose from 21% to 45% and from 15% to 44%. In nine forms of asbestos, hemolytic activity was related to the magnesium:silicon ratio. Adding specific surface area did not improve this relationship. EDTA (100 micromolar) reduced chrysotile hemolysis from 78% to 32% at a starting pH of 6.2, but had no effect at a starting pH of 7.2. PVPNO, which prevents hemolysis by silica, had little effect on chrysotile. Sialic acid reduced chrysotile hemolysis by 73%. The authors concluded that magnesium is the principal reactant on the chrysotile surface. They suggested that sialic acid on the erythrocyte surface may be the main group it reacts with. They also reported a tentative association between hemolytic activity and cytotoxicity.

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In plain English

This was a test-tube laboratory study, not a study of people. The authors exposed mainly sheep red blood cells to fourteen mineral dusts and fibers, including standard asbestos samples. They measured how much each broke open the cells (hemolysis). With sheep cells, chrysotile caused complete hemolysis within 10 minutes across pH 4 to 11, and it was hemolytic to cells of all nine species tested. Amosite and crocidolite were relatively inactive on sheep cells but more active on some other species' cells and over exposures of up to 4 hours. Hemolytic activity was related to magnesium-to-silicon ratio. EDTA reduced hemolysis by chrysotile only at lower pH. PVPNO had little effect on chrysotile. With amphibole asbestos it had little effect when washed off, but considerably reduced hemolysis when excess polymer was left in place. A digested mucoprotein containing sialic acid, not pure sialic acid, reduced hemolysis by chrysotile. The authors said their results supported the view that magnesium on the chrysotile surface is the principal reactant. They reported a reasonable association between hemolysis and cell toxicity, at least for acute effects, but called its significance unclear.

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: Laboratory (in vitro) experiment measuring the breakdown of red blood cells by mineral dusts and fibers
• Who was studied: Red blood cells (erythrocytes), mainly from sheep. Some experiments used red blood cells from nine species, including monkey and human. No human subjects or workers were studied.
• Exposure: Fourteen mineral dusts and fibers in 50 mg samples, including U.I.C.C. standard reference asbestos samples. The materials named include chrysotile, amosite, crocidolite, Bolivian crocidolite, anthophyllite, tremolite, three forms of actinolite, brucite, silica and carborundum. Exposures lasted 50 minutes as standard, and up to 4 hours in some tests.
• Main results:
  • Under the standard conditions, which used sheep red blood cells, chrysotile from several sources broke open the cells completely within 10 minutes over a pH range of 4 to 11.
  • In tests on red blood cells from nine species, the degree of hemolysis differed between species. Chrysotile was hemolytic to cells of every species. Amosite and crocidolite were more active on cells from some other species than on sheep cells, but no material classed as 'inactive' showed a very marked increase.
  • With longer exposure, hemolysis of sheep red blood cells by amosite rose from 6% in the first hour to 19% after 4 hours. With human red blood cells, hemolysis rose from 21% to 45%, and hemolysis by crocidolite rose from 15% to 44% over the same period.
  • Across nine forms of asbestos, hemolytic activity was related to the magnesium-to-silicon ratio. Taking specific surface area into account did not improve this relationship.
  • 100 micromolar Na3EDTA, at a starting pH of 6.2 and a final pH of 7.5, reduced hemolysis by chrysotile from 78% to 32% (59% protection). No reduction was found at a starting pH of 7.2 and a final pH of 8.2.
  • Brucite (magnesium hydroxide, the outer layer of chrysotile), tested at an amount containing magnesium equivalent to 50 mg of chrysotile, broke open 82% of sheep red blood cells, compared with 71% for chrysotile. EDTA gave 90% protection against brucite and 55% against chrysotile.
  • PVPNO, which inhibits hemolysis by silica, had little effect on hemolysis by chrysotile.
  • For amphibole forms of asbestos, PVPNO had little preventive effect when excess polymer was washed off. When it was not washed off, the hemolytic activity of the asbestos was considerably reduced, and almost abolished for anthophyllite.
  • A mucoprotein hydrolyzate containing 17.5 mg of sialic acid, incubated with 50 mg of chrysotile, reduced hemolysis by 73%.
  • The authors reported a reasonable association between cytotoxicity (toxicity to cells) and hemolytic activity, certainly for acute effects.
• The authors' conclusion: The authors stated that their findings accord with, and support, the view that magnesium on the asbestos surface is the principal agent in hemolysis. They also stated that the significance of the association between hemolysis and cell toxicity was not yet clear.
• Limitations the authors state:
  • The authors stated that the significance of the association between toxicity to cells and hemolysis was not yet clear.
  • In the neuraminidase experiment, the fragility of the red blood cells (20% hemolysis with inert carborundum) suggested that hemolysis by chrysotile was less extensive than the 68% figure indicates.
  • The authors noted that hemolysis itself appears to have little or nothing to do with how dust diseases develop.
  • Pure sialic acid could not be obtained, so a mucoprotein hydrolyzate was used. The authors assumed that the other materials in the hydrolyzate did not interfere.

Topics

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

Related studies

• Asbestos hemolysis — R.J. Schnitzer, F.L. Pundsack (1970)
• The prevention of asbestos-induced hemolysis — R. Desai, P. Hext, et al. (1975)
• Interrelationship between hemolysis and lipid peroxidation of human erythrocytes induced by silicic acid and silicate dusts — S.V. Singh, Q. Rahman (1987)
• Haemolytic activity of asbestos and other mineral dusts — G. Macnab, J.S. Harington (1967)
• Dusts causing pneumoconiosis generate .OH and produce hemolysis by acting as Fenton catalysts — T.P. Kennedy, R. Dodson, et al. (1989)
• Hemolysis by chrysotile asbestos fibers. I. Influence of the sialic acid content in human, rat, and sheep red blood cell membranes — J.P. Pelé, R. Calvert (1983)

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