Continuous exposure to chrysotile asbestos can cause transformation of human mesothelial cells via HMGB1 and TNF-α signaling

Our plain-English summary of Continuous exposure to chrysotile asbestos can cause transformation of human mesothelial cells via HMGB1 and TNF-α signaling, by F. Qi, G. Okimoto, S. Jube, et al (The American Journal of Pathology, 2013).

The study

• Authors: F. Qi, G. Okimoto, S. Jube, A. Napolitano, H.I. Pass, R. Laczko, R.M. Demay, G. Khan, M. Tiirikainen, C. Rinaudo, A. Croce, H. Yang, G. Gaudino, M. Carbone
• Journal: The American Journal of Pathology
• Published: 2013;183(5):1654-66
• Cited by: 89 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant mesothelioma is strongly associated with asbestos exposure. Among asbestos fibers, crocidolite is considered the most and chrysotile the least oncogenic. Chrysotile accounts for more than 90% of the asbestos used worldwide, but its capacity to induce malignant mesothelioma is still debated. We found that chrysotile and crocidolite exposures have similar effects on human mesothelial cells. Morphological and molecular alterations suggestive of epithelial-mesenchymal transition, such as E-cadherin down-regulation and β-catenin phosphorylation followed by nuclear translocation, were induced by both chrysotile and crocidolite. Gene expression profiling revealed high-mobility group box-1 protein (HMGB1) as a key regulator of the transcriptional alterations induced by both types of asbestos. Crocidolite and chrysotile induced differential expression of 438 out of 28,869 genes interrogated by oligonucleotide microarrays. Out of these 438 genes, 57 were associated with inflammatory and immune response and cancer, and 14 were HMGB1 targeted genes. Crocidolite-induced gene alterations were sustained, whereas chrysotile-induced gene alterations returned to background levels within 5 weeks. Similarly, HMGB1 release in vivo progressively increased for 10 or more weeks after crocidolite exposure, but returned to background levels within 8 weeks after chrysotile exposure. Continuous administration of chrysotile was required for sustained high serum levels of HMGB1. These data support the hypothesis that differences in biopersistence influence the biological activities of these two asbestos fibers.

Copyright © 2013 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.

In plain English

In this laboratory study, the authors exposed human mesothelial cells from patients with benign conditions to chrysotile or crocidolite asbestos and injected female mice with either fiber. In culture, chrysotile killed more cells and induced more TNF-α than crocidolite. Both fibers caused HMGB1 release. Both also reduced E-cadherin and shifted beta-catenin into the nucleus, changes the authors called suggestive of epithelial-mesenchymal transition. Crocidolite produced more transformed-cell clusters (foci) than chrysotile: 53 versus 21 with added TNF-α, 12 versus 3 with macrophages. With macrophages, gene changes lasted to 5 weeks with crocidolite but faded with chrysotile; with added TNF-α, they lasted regardless of fiber. In mice given two large doses, blood HMGB1 kept rising after crocidolite but fell to background within 6 to 10 weeks after chrysotile. With ten smaller weekly doses, it stayed above controls up to 10 weeks for both. The authors concluded that only continuous chrysotile exposure maintained processes that may lead to mesothelioma. They noted that the results do not address chrysotile carcinogenesis in humans, that cell-culture concentrations likely exceeded human pleural levels, and that no long-term tumor experiment was done.

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 experiments on primary human mesothelial cells in tissue culture (including gene-expression microarrays) and an animal experiment in mice
• Who was studied: Primary human mesothelial cells isolated from pleural fluids of patients with congestive heart failure or other benign conditions, cultured at the University of Hawai'i Cancer Center. The animal work used female BALB/c mice aged 6 to 8 weeks, with 10 animals per group.
• Exposure: Reference fibers from the International Union against Cancer (UICC): chrysotile B (Canadian), chrysotile A (from Zimbabwe, used to repeat the in vitro experiments other than the microarrays), and crocidolite (Koegas mine, South Africa). The culture dose is printed as "5 mg/cm2". Mice received intraperitoneal injections, 1 week apart, in one of two schedules: two injections of 2.5 mg (high-dose, short-term) or 10 injections of 0.5 mg (low-dose, long-term), for a total of 5 mg of fiber in each case. Control mice received PBS vehicle.
• Main results:
  • After 48 hours, fewer chrysotile-exposed cells than crocidolite-exposed cells remained adherent (46 plus or minus 9% versus 73 plus or minus 12%; P less than 0.0001).
  • More of the surviving chrysotile-exposed cells became spindle-shaped than crocidolite-exposed cells (48 plus or minus 6% versus 26 plus or minus 8%; P = 0.0173).
  • Both fibers were cytotoxic depending on fiber density, and chrysotile was significantly more cytotoxic than crocidolite.
  • Chrysotile caused the cells to express and release higher levels of TNF-α than crocidolite. Pretreating the cells with TNF-α significantly reduced the cytotoxicity of both fibers.
  • With added TNF-α, chrysotile-exposed cells formed fewer foci after 4 weeks than crocidolite-exposed cells (21 plus or minus 1 versus 53 plus or minus 5; P = 0.021). Cells exposed to either fiber without TNF-α died within 2 weeks.
  • In co-culture with macrophages, after 8 weeks there were more foci in crocidolite-exposed cells than in chrysotile-exposed cells (12 plus or minus 2 versus 3 plus or minus 1 foci; P = 0.008). No foci developed in co-cultures without asbestos.
  • Of 28,869 genes tested, 438 were differentially expressed, and 57 of these were associated with inflammatory and immune response and cancer.
  • In cells given added TNF-α, activation of the 57 genes persisted from 48 hours to 5 weeks, whatever the fiber exposure.
  • In the macrophage co-cultures, the gene activation persisted with crocidolite. With chrysotile, it was seen at 48 hours but had declined to baseline levels at 5 weeks. HMGB1 was a top predicted upstream regulator for both fibers in these co-cultures at 48 hours, but at 5 weeks only crocidolite still showed a similar activation pattern among HMGB1 target genes.
  • In mice on the high-dose, short-term schedule, serum HMGB1 increased constantly after crocidolite. After chrysotile, the increase was transient and declined to background levels within 6 to 10 weeks.
  • In mice on the low-dose, long-term schedule, serum HMGB1 stayed higher than in the control group up to 10 weeks, for both fiber types.
  • Both fibers reduced E-cadherin, with a significantly sharper reduction from chrysotile. Exogenous TNF-α further reduced E-cadherin, and a TNF-α neutralizing antibody impaired the reduction. Both fibers also increased beta-catenin phosphorylation at Y142 and movement of beta-catenin into the nucleus. The authors considered these findings, together with increases in vimentin and alpha-smooth muscle actin, supportive of epithelial-mesenchymal transition.
  • Chrysotile A from Zimbabwe produced effects largely overlapping those of chrysotile B from Canada in the repeated in vitro experiments.
• The authors' conclusion: The authors concluded that, in human mesothelial cells, chrysotile can induce molecular changes similar to those of crocidolite, but that these changes are transitory. In their view, the results support the notion that only continuous exposure to chrysotile maintains, over a prolonged time span, the processes that may lead to malignant mesothelioma. They named fiber biopersistence as one of the main differences between the two fibers.
• Limitations the authors state:
  • The asbestos concentration used, which the authors described as suitable for in vitro studies, likely exceeds the concentrations reached in the pleura of people exposed to asbestos.
  • No long-term experiment assessed mesothelioma incidence in the mice under the two injection schedules; the authors state that such an experiment was under way.
  • The authors state that their results do not address the overall issue of chrysotile carcinogenesis in humans.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Koegas, Cape Province
• Shabani mine, Zimbabwe

All asbestos mines

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Mesothelial Cells, High Mobility Group Box 1 (HMGB1), Malignant Mesothelioma, Asbestos Exposure, Crocidolite, Translocation, biopersistence.

Related studies

• Asbestos induces mesothelial cell transformation via HMGB1-driven autophagy — J. Xue, S. Patergnani, et al. (2020)
• Asbestos-induced mesothelioma: is fiber biopersistence really a critical factor? — E. Kagan (2013)
• Programmed necrosis induced by asbestos in human mesothelial cells causes high-mobility group box 1 protein release and resultant inflammation — H. Yang, Z. Rivera, et al. (2010)
• Erionite and asbestos differently cause transformation of human mesothelial cells — P. Bertino, A. Marconi, et al. (2007)
• HMGB1 released by mesothelial cells drives the development of asbestos-induced mesothelioma — J.S. Suarez, F. Novelli, et al. (2023)
• HMGB1 targeting by ethyl pyruvate suppresses malignant phenotype of human mesothelioma — L. Pellegrini, J. Xue, et al. (2017)

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