In vitro biodegradation of chrysotile fibres by alveolar macrophages and mesothelial cells in culture: comparison with a pH effect

Our plain-English summary of In vitro biodegradation of chrysotile fibres by alveolar macrophages and mesothelial cells in culture: comparison with a pH effect, by M.C. Jaurand, A. Gaudichet, S. Halpern, et al (British Journal of Industrial Medicine, 1984).

The study

• Authors: M.C. Jaurand, A. Gaudichet, S. Halpern, J. Bignon
• Journal: British Journal of Industrial Medicine
• Published: 1984;41(3):389-95
• Cited by: 34 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The modification of the chemistry of asbestos chrysotile fibres (Mg3(Si2O5)(OH)4) after their ingestion by cultured cells has been studied. Two types of cells involved in asbestos related pulmonary disease were used, rabbit alveolar macrophages (AM), recovered by bronchoalveolar lavage, and pleural mesothelial cells (PMC) obtained from the rat parietal pleura. Chemical characterisation of intracellular fibres was performed on unstained ultrathin sections by electron probe microanalysis. The results showed a progressive leaching of Mg, characterised by a time dependent decrease of Mg/Si. AM were more efficient than PMC at leaching intracellular chrysotile fibres since it took longer to obtain the same proportion of leached fibres with PMC than with AM. As in vitro Mg-leaching can be obtained by acid treatment, chrysotile fibres were incubated, either untreated or pretreated with cell membranes, at pH 4 or 7 for various times. The data show that the kinetic of leaching by AM was comparable with leaching at pH 4. The leaching by PMC was of the same order as leaching at pH 7. When membranes were adsorbed on to the fibres, a delayed leaching was observed. The results indicate that the solubilisation of chrysotile by AM could be an intraphagolysosomal event due to a pH effect. With PMC, however, it is not possible to draw this conclusion since nothing is known about the intracellular pH.

In plain English

This laboratory study asked whether cells remove magnesium from chrysotile asbestos fibres, a process the authors call biodegradation or leaching. The authors added Rhodesian chrysotile (from the UICC) to rabbit alveolar macrophages and to cultured rat pleural mesothelial cells. They then measured the magnesium-to-silicon (Mg/Si) ratio of fibres inside the cells, analysing 30 fibres per series. Fibres with Mg/Si of 0.8 or less were counted as leached. Among control fibres, 85% had Mg/Si above 0.8. Half of the fibres inside macrophages were leached after 45 minutes, while mesothelial cells took seven days to reach the same proportion. Fibres were also incubated in acidic (pH 4) or neutral (pH 7) solutions, with or without a coating of red blood cell membranes. Leaching was higher and faster at pH 4, and the coating delayed it. Macrophage results were close to pH 4 values, and mesothelial results were in the pH 7 range. The authors concluded that leaching in macrophages may occur inside the cells' phagolysosomes as an effect of acidity. For mesothelial cells, they said more must be known about intracellular pH before drawing a conclusion.

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: In vitro laboratory experiment using cultured animal cells and cell-free incubation of fibres at different pH
• Who was studied: Alveolar macrophages obtained by bronchoalveolar lavage from normal rabbits, and pleural mesothelial cells from normal rat parietal pleura, grown in culture; 30 fibres analysed per series
• Exposure: Rhodesian chrysotile fibres from the UICC. Macrophages received 4 micrograms per square centimetre for 45 minutes, four hours, or 20 hours (24 hours in Table 1). Mesothelial cells received 2 micrograms per square centimetre for 20 hours, were washed, and were fixed 2, 4, 6 and 7 days later. Fibres were also incubated at pH 7 (60 hours, 12 days) or pH 4 (70 hours, 8 days), with or without a coating of red blood cell membranes.
• Main results:
  • In control (unexposed) chrysotile, the Mg/Si ratio was always higher than 0.6, and 85% of fibres had Mg/Si higher than 0.8
  • 50% of fibres inside macrophages were leached (Mg/Si 0.8 or less) after 45 minutes; seven days were needed for fibres inside mesothelial cells to reach the same proportion
  • 59% of fibres were leached by macrophages after 24 hours, compared with 13% after two days in mesothelial cells
  • In mesothelial cells, fibres with Mg/Si lower than 0.4 were observed after seven days
  • In cell-free solutions, magnesium leaching occurred at both pH 4 and pH 7 but was higher and faster at pH 4; at pH 7 no fibre had Mg/Si of 0.4 or less
  • Coating fibres with red blood cell membranes had a low protective effect: it delayed leaching but did not inhibit it
  • Mg/Si values for fibres in macrophages were close to those at pH 4, while values for mesothelial cells were in the range of those at pH 7
• The authors' conclusion: The authors concluded that chrysotile is soluble in biological media. In macrophages, solubilisation may be an intraphagolysosomal event due to a pH effect. In mesothelial cells it did not correlate with acid solubilisation, and more must be known about their intracellular pH. They suggested that the lower magnesium content of fibres from human lungs could be partly due to attack by pulmonary cells.
• Limitations the authors state:
  • Mg/Si varied along single fibres and between fibres. The authors said variation along a fibre could be due to instability of the analytical method or to natural variation in the chrysotile, and variation between fibres might also reflect differences in how long fibres were retained in the cells.
  • The two cell types were treated differently: mesothelial cells were washed after 20 hours, while with macrophages all fibres stayed in the medium and could be ingested throughout. The authors gave this as the probable reason the macrophage kinetics were variable.
  • The stability of the membranes adsorbed on the fibres in the buffered solutions was not known
  • The intracellular pH of mesothelial cells was not known, so no conclusion about the mechanism could be drawn for those cells

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Chrysotile, Alveolar Macrophage, Mesothelial Cells, Bronchoalveolar Lavage (BAL), Parietal Pleura.

Related studies

• In vitro reactivity of alveolar macrophages and red blood cells with asbestos fibres treated with oxalic acid, sulfur dioxide and benzo-3,4-pyrene — M.C. Jaurand, L. Magne, et al. (1981)
• Leaching of chrysotile asbestos in human lungs. Correlation with in vitro studies using rabbit alveolar macrophages — M.C. Jaurand, J. Bignon, et al. (1977)
• Cytotoxic effects of quartz and chrysotile asbestos: in vitro interspecies comparison with alveolar macrophages — J. Schimmelpfeng, A. Seidel (1991)
• Cytotoxic effects of aramid fibres on rat pulmonary macrophages: comparison with chrysotile asbestos — J. Dunnigan, D. Nadeau, et al. (1984)
• In vitro transformation of rat pleural mesothelial cells by chrysotile fibres and/or benzo[a]pyrene — M.J. Paterour, J. Bignon, et al. (1985)
• Comparison of effects on macrophage cultures of glass fibre, glass powder, and chrysotile asbestos — E.G. Beck, P.F. Holt, et al. (1972)

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