Osteopontin mRNA expression by rat mesothelial cells exposed to multi-walled carbon nanotubes as a potential biomarker of chronic neoplastic transformation in vitro

Our plain-English summary of Osteopontin mRNA expression by rat mesothelial cells exposed to multi-walled carbon nanotubes as a potential biomarker of chronic neoplastic transformation in vitro, by S. Sridharan, A. Taylor-Just, J.C. Bonner (Toxicology in Vitro, 2021).

The study

• Authors: S. Sridharan, A. Taylor-Just, J.C. Bonner
• Journal: Toxicology in Vitro
• Published: 2021;73:105126
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Mesothelioma is a cancer of the lung pleura primarily associated with inhalation of asbestos fibers. Multi-walled carbon nanotubes (MWCNTs) are engineered nanomaterials that pose a potential risk for mesothelioma due to properties that are similar to asbestos. Inhaled MWCNTs migrate to the pleura in rodents and some types cause mesothelioma. Like asbestos, there is a diversity of MWCNT types. We investigated the neoplastic potential of tangled (tMWCNT) versus rigid (rMWCNT) after chronic exposure using serial passages of rat mesothelial cells in vitro. Normal rat mesothelial (NRM2) cells were exposed to tMWCNTs or rMWCNTs for 45 weeks over 85 passages to determine if exposure resulted in transformation to a neoplastic phenotype. Rat mesothelioma (ME1) cells were used as a positive control. Osteopontin (OPN) mRNA was assayed as a biomarker of transformation by real time quantitative polymerase chain reaction (qPCR) and transformation was determined by a cell invasion assay. Exposure to rMWCNTs, but not tMWCNTs, resulted in transformation of NRM2 cells into an invasive phenotype that was similar to ME1 cells. Moreover, exposure of NRM2 cells to rMWCNTs increased OPN mRNA that correlated with cellular transformation. These data suggest that OPN is a potential biomarker that should be further investigated to screen the carcinogenicity of MWCNTs in vitro.

Copyright © 2021 Elsevier Ltd. All rights reserved.

In plain English

This was a laboratory study of cells, not people; no asbestos was tested. The authors exposed a normal rat pleural mesothelial cell line (NRM2) for 45 weeks, through 85 passages, to one of two kinds of multi-walled carbon nanotubes: tangled or rigid (Mitsui-7). A rat mesothelioma cell line (ME1) served as a comparison. The authors measured osteopontin (OPN) mRNA, a possible cancer marker, and the cells' ability to invade. ME1 cells made significantly more OPN mRNA and were more invasive than unexposed NRM2 cells. Cells exposed to rigid nanotubes formed dense clusters and had significantly higher OPN mRNA than unexposed cells. Compared with cells exposed to tangled nanotubes, the difference was significant at passages 42, 46, 51 and 61 but not at 55 and 58. Both nanotube types increased invasion at passage 85, rigid more than tangled. The authors concluded that rigid nanotubes could have neoplastic potential similar to asbestos in humans. They noted that the transformation findings came from one rat mesothelial cell line, that passage-85 cells were not tested for OPN, and that these nanotubes have not been shown to cause mesothelioma in humans.

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: chronic exposure of a rat cell line to carbon nanotubes with serial sub-passaging, measuring OPN mRNA (real-time qPCR), cell appearance and cell invasion
• Who was studied: Normal rat pleural mesothelial cells (NRM2 cell line, from the parietal pleura of a male Fischer-344 rat). Rat mesothelioma cells (ME1, from spontaneous peritoneal mesothelioma tumors of a male Fischer-344 rat) were used as a positive control. No humans or live animals were studied.
• Exposure: Multi-walled carbon nanotubes (MWCNTs) of two types: tangled (tMWCNT, Helix Materials Solutions) and rigid (rMWCNT, Mitsui-7, obtained from NIOSH). At each passage, 0.1 μg/ml was re-added, for a final concentration of 0.02 μg/cm2 per well, over 45 weeks. No asbestos was used.
• Main results:
  • At passage 80, NRM2 cells exposed to rigid MWCNTs showed altered appearance with optically dense foci of cell clusters, similar to ME1 mesothelioma cells. Cells exposed to tangled MWCNTs kept a dense monolayer.
  • Without nanotube exposure, ME1 mesothelioma cells produced significantly more OPN mRNA than NRM2 cells and were also more invasive.
  • OPN mRNA in NRM2 cells exposed to rigid MWCNTs, but not tangled MWCNTs, was significantly higher than in unexposed control cells. Levels varied among passages.
  • Compared with cells exposed to tangled MWCNTs, cells exposed to rigid MWCNTs had significantly higher OPN mRNA at passages 42, 46, 51 and 61, but not at passages 55 and 58.
  • At passage 85, both MWCNT types increased the number of invading NRM2 cells compared with unexposed late-passage cells. Unexposed passage-85 cells had a similar number of invading cells to passage-12 cells.
  • At passage 85, NRM2 cells exposed to rigid MWCNTs had more invading cells than those exposed to tangled MWCNTs.
• The authors' conclusion: The authors concluded that OPN could be a potential biomarker of neoplastic-like transformation in these cells. They also concluded that rigid MWCNTs could have a neoplastic potential similar to asbestos in humans and could lead to mesothelioma, while tangled MWCNTs appear to have low potential to transform mesothelial cells.
• Limitations the authors state:
  • The passage-85 cells used for the invasion assays were not tested for OPN mRNA.
  • OPN mRNA levels varied among passages for unknown reasons, and the long experiment made further investigation of this variability not feasible.
  • Soft agar colony formation and tumor formation in immunosuppressed nude mice were not tested. The authors said these would be needed to conclude more thoroughly that rigid MWCNTs cause neoplastic transformation.
  • The observations of neoplastic-like transformation by rigid MWCNTs come from a single rat mesothelial cell line.
  • It has not been shown that MWCNTs cause mesothelioma in humans, and it is not yet known whether OPN would help predict mesothelioma in exposed people.

Topics

Medical terms in this study, explained in our Lexicon: Osteopontin, Mesothelial Cells, Biomarker, Mesothelioma, Pleura.

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