Differential responses of murine alveolar macrophages to elongate mineral particles of asbestiform and non-asbestiform varieties: Cytotoxicity, cytokine secretion and transcriptional changes

Our plain-English summary of Differential responses of murine alveolar macrophages to elongate mineral particles of asbestiform and non-asbestiform varieties: Cytotoxicity, cytokine secretion and transcriptional changes, by T.O. Khaliullin, E.R. Kisin, S. Guppi, et al (Toxicology and Applied Pharmacology, 2020).

The study

• Authors: T.O. Khaliullin, E.R. Kisin, S. Guppi, N. Yanamala, V. Zhernovkov, A.A. Shvedova
• Journal: Toxicology and Applied Pharmacology
• Published: 2020;409:115302
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Human exposures to asbestiform elongate mineral particles (EMP) may lead to diffuse fibrosis, lung cancer, malignant mesothelioma and autoimmune diseases. Cleavage fragments (CF) are chemically identical to asbestiform varieties (or habits) of the parent mineral, but no consensus exists on whether to treat them as asbestos from toxicological and regulatory standpoints. Alveolar macrophages (AM) are the first responders to inhaled particulates, participating in clearance and activating other resident and recruited immunocompetent cells, impacting the long-term outcomes. In this study we address how EMP of asbestiform versus non-asbestiform habit affect AM responses. Max Planck Institute (MPI) cells, a non-transformed mouse line that has an AM phenotype and genotype, were treated with mass-, surface area- (s.a.), and particle number- (p.n.) equivalent concentrations of respirable asbestiform and non-asbestiform riebeckite/tremolite EMP for 24 h. Cytotoxicity, cytokines secretion and transcriptional changes were evaluated. At the equal mass, asbestiform EMP were more cytotoxic, however EMP of both habits induced similar LDH leakage and decrease in viability at s.a. and p.n. equivalent doses. DNA damage assessment and cell cycle analysis revealed differences in the modes of cell death between asbestos and respective CF. There was an increase in chemokines, but not pro-inflammatory cytokines after all EMP treatments. Principal component analysis of the cytokine secretion showed close clustering for the s.a. and p.n. equivalent treatments. There were mineral- and habit-specific patterns of gene expression dysregulation at s.a. equivalent doses. Our study reveals the critical nature of EMP morphometric parameters for exposure assessment and dosing approaches used in toxicity studies.

Published by Elsevier Inc.

In plain English

This was a laboratory study in cells, not people. The authors exposed mouse alveolar macrophage-like cells (MPI cells, derived from mouse fetal livers) for 24 hours to four respirable mineral preparations: riebeckite asbestos (crocidolite), tremolite asbestos, and non-asbestiform cleavage fragments of riebeckite and of tremolite. Doses were matched three ways: by total mass, by surface area of particles longer than 5 µm with aspect ratio over 3:1, and by number of those particles. All treatments lowered the ratio of live to dead cells to 90-70% of untreated controls. At equal mass, the asbestos forms caused significantly more cell-membrane damage (LDH leakage). For riebeckite, leakage was similar at surface-area-matched doses. A marker of DNA double-strand breaks was highest in asbestos-treated cells, especially riebeckite asbestos. All treatments raised several chemokines but not IL-6 or TNF-alpha. Gene-expression changes were largest with riebeckite asbestos. They were broadly similar between the two riebeckite forms but quite divergent between the two tremolite forms. The authors concluded that asbestiform habit itself may be an important determinant for some minerals, like tremolite. They noted that cell studies cannot account for lung deposition, clearance or biopersistence.

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 a mouse alveolar macrophage-like cell line
• Who was studied: MPI cells (alveolar macrophage-like cells) originally derived from the fetal livers of C57BL/6J mice; no human subjects
• Exposure: Respirable asbestiform and non-asbestiform (cleavage fragment) riebeckite and tremolite: UICC riebeckite asbestos (crocidolite), non-asbestiform riebeckite from Pikes Peak, Colorado, tremolite asbestos from Lone Pine, California, and non-asbestiform tremolite prepared by the U.S. Bureau of Mines. Cells were exposed for 24 hours at doses matched for total mass, surface area, or number of particles longer than 5 µm with aspect ratio over 3:1.
• Main results:
  • All treatments reduced the ratio of viable to dead cells at 24 hours to 90-70% of untreated controls
  • At equal mass doses, the asbestiform particles caused significantly greater LDH leakage (cell-membrane damage) than the cleavage fragments
  • For riebeckite, LDH leakage was similar for the asbestos and the cleavage fragments at surface-area-equivalent doses
  • At equal particle numbers, cleavage fragments trended toward more cytotoxicity than the asbestiform forms, but the difference never reached statistical significance
  • The DNA double-strand break marker (gamma-H2AX) was highest in asbestos-treated cells, specifically riebeckite asbestos
  • All treatments significantly increased secretion of IL-1 alpha, MCP-1, MIP-1 alpha, MIP-1 beta and KC, but not other cytokines such as IL-6 or TNF-alpha
  • At surface-area-equivalent doses, the numbers of genes significantly up- and down-regulated were 492 and 302 for riebeckite asbestos, 374 and 220 for riebeckite cleavage fragments, 224 and 70 for tremolite asbestos, and 258 and 118 for tremolite cleavage fragments
  • Gene expression changes were greatest with riebeckite asbestos, followed similar patterns for riebeckite asbestos and riebeckite cleavage fragments, and were quite divergent between the two tremolite forms
• The authors' conclusion: The authors concluded that, beyond similar cytotoxicity at equal surface-area doses, distinct gene expression and DNA damage patterns suggest that asbestiform habit itself may be an important determinant for some minerals, like tremolite
• Limitations the authors state:
  • In vitro studies cannot address the complexity of interactions among tissues and organs
  • The study did not account for deposition patterns, mucociliary clearance or biopersistence
  • The artificial sample preparation is not exactly representative of typical human exposures
  • The results do not allow confident conclusions about the main mode of cell death in each treatment
  • The cytokine results cannot be reliably translated to living animals or people

Topics

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

Medical terms in this study, explained in our Lexicon: Alveolar Macrophage, elongate mineral particles (EMPs), Asbestiform, Non-Asbestiform, Cytokine, Fibrosis, Lung Cancer, Malignant Mesothelioma.

Related studies

• Distinctive profile of alveolar macrophage-derived cytokine release induced by fibrogenic and nonfibrogenic mineral dusts — I. Lemaire, S. Ouellet (1996)
• Human alveolar macrophage cytokine release in response to in vitro and in vivo asbestos exposure — R.C. Perkins, R.K. Scheule, et al. (1993)
• Asbestos stimulation triggers differential cytokine release from human monocytes and alveolar macrophages — L.J. Geist, L.S. Powers, et al. (2000)
• Cytokine and free radical responses of alveolar macrophages in vitro to asbestos fibres — L.C. Mongan, T. Jones, et al. (2000)
• Refractory ceramic fibers activate alveolar macrophage eicosanoid and cytokine release — G.D. Leikauf, S.P. Fink, et al. (1995)
• Alveolar macrophage cytokine and growth factor production in a rat model of crocidolite-induced pulmonary inflammation and fibrosis — K.E. Driscoll, J.K. Maurer, et al. (1995)

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