Analysis of the biological and chemical reactivity of zeolite-based aluminosilicate fibers and particulates

Our plain-English summary of Analysis of the biological and chemical reactivity of zeolite-based aluminosilicate fibers and particulates, by E. Fach, W.J. Waldman, M. Williams, et al (Environmental Health Perspectives, 2002).

The study

• Authors: E. Fach, W.J. Waldman, M. Williams, J. Long, R.K. Meister, P.K. Dutta
• Journal: Environmental Health Perspectives
• Published: 2002;110(11):1087-96
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Environmental and/or occupational exposure to minerals, metals, and fibers can cause lung diseases that may develop years after exposure to the agents. The presence of toxic fibers such as asbestos in the environment plus the continuing development of new mineral or vitreous fibers requires a better understanding of the specific physical and chemical features of fibers/particles responsible for bioactivity. Toward that goal, we have tested aluminosilicate zeolites to establish biological and chemical structure-function correlations. Zeolites have known crystal structure, are subject to experimental manipulation, and can be synthesized and controlled to produce particles of selected size and shape. Naturally occurring zeolites include forms whose biological activity is reported to range from highly pathogenic (erionite) to essentially benign (mordenite). Thus, we used naturally occurring erionite and mordenite as well as an extensively studied synthetic zeolite based on faujasite (zeolite Y). Bioactivity was evaluated using lung macrophages of rat origin (cell line NR8383). Our objective was to quantitatively determine the biological response upon interaction of the test particulates/fibers with lung macrophages and to evaluate the efficacy of surface iron on the zeolites to promote the Fenton reaction. The biological assessment included measurement of the reactive oxygen species by flow cytometry and chemiluminescence techniques upon phagocytosis of the minerals. The chemical assessment included measuring the hydroxyl radicals generated from hydrogen peroxide by iron bound to the zeolite particles and fibers (Fenton reaction). Chromatography as well as absorption spectroscopy were used to quantitate the hydroxyl radicals. We found that upon exposure to the same mass of a specific type of particulate, the oxidative burst increased with decreasing particle size, but remained relatively independent of zeolite composition. On the other hand, the Fenton reaction depended on the type of zeolite, suggesting that the surface structure of the zeolite plays an important role.

In plain English

This was a laboratory study of three zeolite minerals: natural erionite, natural mordenite and a synthetic mineral called zeolite Y. No asbestos was tested. The authors exposed rat lung macrophage cells grown in the lab (cell line NR8383) to the minerals and measured the cells' release of reactive oxygen species. Separately, they measured hydroxyl radicals produced from hydrogen peroxide by iron loaded onto each mineral's surface (the Fenton reaction). The cell response rose with dose. For fractionated mordenite it rose from 946 ± 139 at 10 µg to 8382 ± 1,855 at 250 µg (arbitrary units). For the same mass, smaller particles gave larger responses, and similar-sized particles gave similar responses regardless of mineral. Ammonium chloride, which reduced particle uptake, cut the response by about 70%. In the chemical tests, at similar surface iron, erionite produced more hydroxyl radicals than mordenite, which produced more than zeolite Y. The authors concluded that particle size drove the cell response, while mineral structure determined hydroxyl radical production. They noted they did not know how many particles entered the 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: Laboratory (in vitro) experiment combining tests on a cultured rat lung macrophage cell line with cell-free chemical tests of iron-loaded minerals
• Who was studied: Rat pulmonary alveolar macrophage-derived cell line NR8383, grown in culture. The minerals tested were erionite and mordenite from Minerals Research (Clarkson, NY) and zeolite Y from Union Carbide.
• Exposure: Erionite, mordenite and zeolite Y in unfractionated and size-fractionated forms. Doses in the chemiluminescence tests were 10, 50 or 250 µg per well of 100,000 cells. Iron-exchanged forms of the three zeolites were used for the Fenton reaction tests. No asbestos was tested.
• Main results:
  • The chemiluminescence (oxidative burst) response of the cells was dose-dependent for all minerals. For fractionated mordenite it rose from 946 ± 139 at 10 µg to 8382 ± 1,855 at 250 µg (arbitrary units).
  • For the same mass of particles, the oxidative burst signal was inversely related to particle size for each zeolite. At 50 µg, fine erionite (0.8 µm) gave 1,904, fractionated erionite (3 µm) 965 ± 361, and unfractionated erionite (10 µm) 695 ± 288.
  • For particles of comparable size, the authors reported no significant difference in oxidative burst between the minerals, especially between erionite and mordenite.
  • All mineral-induced responses were 10- to 100-fold smaller than the response to zymosan, the positive control. Flow cytometry did not detect an oxidative response to the minerals.
  • Treating the cells with the uptake inhibitor ammonium chloride reduced chemiluminescence by about 70%. In electron micrographs, the treatment did not affect binding of fibers to the cell membrane. It reduced fibers inside cells from about eight per cell to one to two per cell, based on four micrographs.
  • In the chemical (Fenton reaction) tests, at similar surface iron levels, erionite produced more hydroxyl radicals than mordenite, which produced more than zeolite Y. Increasing surface iron on zeolite Y did not increase hydroxyl radical production.
  • When surface iron was removed with the polymer, leaving only iron inside the mineral, no hydroxyl radical product (MSA) was detected.
• The authors' conclusion: The authors concluded that particle size (presumably through surface area) affected the macrophage oxidative burst more than mineral structure. They concluded that mineral structure determined iron-driven hydroxyl radical production, in the order erionite, then mordenite, then zeolite Y. They suggested that mordenite should also be toxic because of its Fenton reactivity and that zeolite Y should be considerably less toxic.
• Limitations the authors state:
  • The authors did not know how many particles entered the cells when samples of different particle sizes were used.
  • Flow cytometry could not detect an oxidative response to the minerals despite repeated modifications of the method.
  • At the highest iron solution concentration, zeolite Y lost crystallinity, so its highest surface iron value also includes iron incorporated into amorphous material.

Topics

Medical terms in this study, explained in our Lexicon: Zeolite, Occupational Exposure, Vitreous, Crystal Structure, erionite, Macrophage, Fenton Reaction, Reactive Oxygen Species (ROS).

Related studies

• Fenten chemistry of Fe(III)-exchanged zeolitic minerals treated with antioxidants — T.A. Ruda, P.K. Dutta (2005)
• In vitro interaction of zeolite fibers with individual cells (macrophages NR8383): measurement of intracellular oxidative burst — B.D. Hogg, P.K. Dutta, et al. (1996)
• Natural fibrous zeolites and their carcinogenicity-a review — K.R. Spurny (1983)
• The effects of intrapleural injections of alumina and aluminosilicate (ceramic) fibres — G.H. Pigott, J. Ishmael (1992)
• Peculiarities of the clastogenic properties of chrysotile-asbestos fibers and zeolite particles — A.D. Durnev, N.O. Daugel-Dauge, et al. (1993)
• Biological effects of naturally occurring and man-made fibres: in vitro cytotoxicity and mutagenesis in mammalian cells — R. Okayasu, L. Wu, et al. (1999)

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