MWCNTs Induce ROS Generation, ERK Phosphorylation, and SOD-2 Expression in Human Mesothelial Cells

Our plain-English summary of MWCNTs Induce ROS Generation, ERK Phosphorylation, and SOD-2 Expression in Human Mesothelial Cells, by M. Yu, R. Chen, Z. Jia, et al (International Journal of Toxicology, 2016).

The study

• Authors: M. Yu, R. Chen, Z. Jia, J. Chen, J. Lou, S. Tang, X. Zhang
• Journal: International Journal of Toxicology
• Published: 2016;35(1):17-26
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Biological oxidative responses are involved in the toxicity of multiwall carbon nanotubes (MWCNTs), which may cause asbestos-like pathogenicity. Superoxide dismutase 2 (SOD-2) has been proposed as a biomarker of early responses to mesothelioma-inducing fibers. This study was conducted to investigate the alteration of SOD-2 expression in the human mesothelial cell lines Met-5A after exposure to nontoxic doses of MWCNTs and the potential signaling pathway. The parameters measured included the viability, morphological change, superoxide formation, extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation, and messenger RNA (mRNA)/protein levels of SOD-2. Our results showed that MWCNTs upregulated SOD-2 expression at both mRNA and protein level. Coincidently, both superoxide formation and ERK1/2 phosphorylation were observed in Met-5A cells exposed to MWCNTs and were diminished by pretreatment with the reactive oxidative species (ROS) scavenger, N-acetyl-l-(+)-cysteine (NAC). To further investigate the role of ROS/ERK1/2 in MWCNTs-induced SOD-2 overexpression, prior to MWCNTs exposure, cells were pretreated with the Mitogen-activated protein kinase kinase 1/2 (MEK 1/2) inhibitor (U0126) or with NAC. Both pretreatments decreased the MWCNTs-induced overexpression of SOD-2. These results suggest that upregulation of SOD-2 in Met-5A cells exposed to MWCNTs is mediated by ROS formation and ERK1/2 activation.

© The Author(s) 2015.

In plain English

This laboratory study used cells grown in dishes, not people or animals, and did not test asbestos. The authors exposed Met-5A, a human mesothelial cell line, to multiwall carbon nanotubes (MWCNTs) for 24 hours. Mesothelial cells are the type that line the chest cavity. Doses are printed as 0 to 80 mg/mL, but this copy seems to drop the micro sign (a well volume reads 100 mL), so they may be micrograms per mL. At printed doses of 40 and below, the nanotubes did not significantly reduce cell survival; at 80 they did. Under the electron microscope, no nanotubes were seen inside cells at 20 or 40. The nanotubes raised reactive oxygen species (reactive oxygen-based molecules), by about 1.7-fold at 40. They also increased activation of a signaling protein, ERK1/2, and levels of an antioxidant enzyme, SOD-2. Pretreating cells with an antioxidant (NAC) or an ERK-pathway blocker (U0126) significantly reduced the SOD-2 increase. The authors concluded that this SOD-2 increase was driven by reactive oxygen species and ERK1/2 activation. They said its biological effects remain to be worked out.

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) cell culture experiment; no asbestos was tested
• Who was studied: Immortalized human mesothelial cell line Met-5A, obtained from the American Type Culture Collection. Viability results came from 5 experiments, Western blot results from 3, and mRNA results from at least 2.
• Exposure: Multiwall carbon nanotubes bought from Sigma-Aldrich (purity over 90%, metal contaminants under 0.1%), given for 24 hours at concentrations printed as 0, 10, 20, 40 and 80 mg/mL. The unit is uncertain because this copy appears to have lost the micro sign; the doses may be micrograms per mL. Some experiments used a 1-hour pretreatment before 40 (as printed) MWCNTs, either with NAC (2.5 mmol/L) or with U0126 (printed as 20 mmol/L).
• Main results:
  • In Met-5A cells, MWCNTs for 24 hours were not toxic at printed doses up to 40 (unit printed as mg/mL, possibly micrograms per mL).
  • In Met-5A cells, the highest printed dose (80, unit printed as mg/mL, possibly micrograms per mL) markedly reduced cell viability compared with untreated cells.
  • In cells exposed to printed doses of 20 or 40 (unit uncertain), electron microscopy showed neither significant structural changes nor nanotubes inside the cells.
  • In cells exposed to the printed dose of 80 (unit uncertain), some nanotubes were occasionally seen inside lysosome-like structures.
  • Reactive oxygen species rose with dose. Cells treated at the printed dose of 40 (unit uncertain) showed an approximately 1.7-fold increase after 24 hours, and NAC pretreatment significantly reduced this increase.
  • ERK1/2 phosphorylation (activation) rose with dose. In cells given the printed dose of 40, NAC pretreatment significantly decreased it.
  • SOD-2 mRNA rose in a dose-dependent way across printed doses of 0 to 40. SOD-2 protein rose in cells exposed to printed doses of 20 or 40.
  • In cells exposed to the printed dose of 40, pretreatment with NAC or U0126 significantly decreased the SOD-2 increase.
• The authors' conclusion: The authors concluded that MWCNT exposure enhanced SOD-2 expression in Met-5A cells, and that this was mediated by reactive oxygen species formation and ERK1/2 activation.
• Limitations the authors state:
  • The authors stated that two things remain to be clarified: the regulatory pathway of SOD-2 induction, and its biological effects on the pleural lining exposed to high-aspect-ratio materials.

Topics

Medical terms in this study, explained in our Lexicon: Mesothelial Cells, Superoxide, Biomarker, Mesothelioma, MeT-5A Cells.

Related studies

• Generation of reactive oxygen species by human mesothelioma cells — K. Kahlos, S. Pitkänen, et al. (1999)
• Raw single-wall carbon nanotubes induce oxidative stress and activate MAPKs, AP-1, NF-kappaB, and Akt in normal and malignant human mesothelial cells — M. Pacurari, X.J. Yin, et al. (2008)
• Mechanisms of oxidative stress and alterations in gene expression by Libby six-mix in human mesothelial cells — J.M. Hillegass, A. Shukla, et al. (2010)
• Effects of asbestos on initiation of DNA damage, induction of DNA-strand breaks, P53-expression and apoptosis in primary, SV40-transformed and malignant human mesothelial cells — B. Burmeister, T. Schwerdtle, et al. (2004)
• Chronic exposure to carbon nanotubes induces invasion of human mesothelial cells through matrix metalloproteinase-2 — W. Lohcharoenkal, L. Wang, et al. (2013)
• Different Cellular Response of Human Mesothelial Cell MeT-5A to Short-Term and Long-Term Multiwalled Carbon Nanotubes Exposure — L. Ju, W. Wu, et al. (2017)

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