Oxidative stress-mediated cytotoxicity and apoptosis induction by TiO2 nanofibers in HeLa cells

Our plain-English summary of Oxidative stress-mediated cytotoxicity and apoptosis induction by TiO2 nanofibers in HeLa cells, by K.M. Ramkumar, C. Manjula, G. Gnanakumar, et al (European Journal of Pharmaceutics and Biopharmaceutics, 2012).

The study

• Authors: K.M. Ramkumar, C. Manjula, G. Gnanakumar, M.A. Kanjwal, T.V. Sekar, R. Paulmurugan, P. Rajaguru
• Journal: European Journal of Pharmaceutics and Biopharmaceutics
• Published: 2012;81(2):324-33
• Cited by: 43 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Titanium dioxide nanoparticles are increasingly being used in pharmaceutical and cosmetic products. The high aspect ratio of fibrous nanomaterials, such as carbon nanotubes and TiO(2) nanofibers (TiO(2)NFs), similar to the one used in this study makes them an attractive structural material and has attracted a lot of attention due to their possible negative health effects as suggested by their morphological similarities with asbestos. In the present study, therefore, toxicity of TiO(2)NFs was evaluated in human cervical adenocarcinoma HeLa cells. The TEM and XRD analyses showed that TiO(2)NFs used in this study are pure with uniform diameter of around 200 nm, and their length to width aspect ratio ranged between 5 and 15. Exposure of HeLa cells to TiO(2)NFs induced significant cytotoxicity even at doses as low as 2 μg/ml. The intracellular uptake of TiO(2)NFs in cells was shown by Alizarin Red S (ARS) labeled nanofibers. The mechanism of toxicity is mainly due to the induction of cellular oxidative stress, as revealed by elevated ROS levels, reduced antioxidant levels, and increased lipid peroxidation leading to apoptosis. The cell cycle analysis indicated G(2)/M cell cycle arrest in the cells exposed to TiO(2)NF. TiO(2)NFs treatment to HeLa cells resulted in increased expression of proapoptotic proteins Bax with an increase in cytosolic Cytochrome-C and inhibition of anti-apoptotic protein Bcl-2. Our results revealed the potential mechanism of cellular effects of TiO(2)NFs.

Copyright © 2012 Elsevier B.V. All rights reserved.

In plain English

This laboratory study used cells grown in dishes, not people or animals. The authors made titanium dioxide nanofibers, about 200 nm wide and 5 to 15 times longer than wide, and tested them on HeLa cells, a human cervical adenocarcinoma cell line. Asbestos itself was not tested. They chose these fibers because fibrous nanomaterials resemble asbestos in shape, raising health concerns. Cell survival fell with higher dose (up to 20 micrograms per milliliter) and longer exposure. At 10 micrograms per milliliter, about 50% of cells died within 24 hours. Labeled fibers were seen inside the cells. Treated cells showed more reactive oxygen species, more lipid damage and less of the antioxidant glutathione. In the 24-hour annexin-v test, apoptotic (programmed-death) cells rose from 0.01% in untreated cells to 6.15% at 5 and 45.98% at 10 micrograms per milliliter. More treated cells were stalled in the G2/M phase of the cell cycle, and cell-death proteins changed. The authors concluded that oxidative stress may cause the toxicity. They noted it is unknown whether workplace or environmental exposure could reach a threshold dose in the body.

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 (cell culture) laboratory experiment
• Who was studied: HeLa cells, a human cervical adenocarcinoma cell line, obtained from the American Type Culture Collection; no people or animals were studied
• Exposure: Titanium dioxide nanofibers made by electrospinning and heating, reported as anatase, about 200 nm in diameter with a length-to-width ratio of 5 to 15. Doses were 0 to 20 micrograms per milliliter for 1 to 24 hours. Most experiments used up to 10 micrograms per milliliter for 24 hours. No asbestos was tested.
• Main results:
  • Cell viability decreased with dose and time. In HeLa cells, 10 micrograms per milliliter caused about 50% cell death at 24 hours.
  • Significant cytotoxicity was seen in HeLa cells at doses as low as 2 micrograms per milliliter.
  • Fluorescently labeled nanofibers were detected inside HeLa cells.
  • Treated cells had a significant (P less than 0.05) decrease in reduced glutathione (GSH) and an increase in oxidized glutathione (GSSG). Reactive oxygen species levels correlated negatively with GSH (R2 = 0.995).
  • In treated HeLa cells, the share of cells in the sub-G0 and G2/M phases rose significantly with dose. In untreated cells these were 1.52% sub-G0 and 18.25% G2/M. At 10 micrograms per milliliter they were 18.62% and 33.01%.
  • After 24 hours of treatment, apoptotic HeLa cells measured by annexin-v were 0.01% in untreated controls, 6.15% at 5 micrograms per milliliter and 45.98% at 10 micrograms per milliliter.
  • Treated cells showed higher Bax, cleaved caspase-3 and cytosolic cytochrome-c, and significantly decreased Bcl-2 protein. Bax and Bcl-2 mRNA changed in the same directions with dose.
• The authors' conclusion: The authors concluded that TiO2 nanofibers induced dose- and time-dependent cytotoxicity in HeLa cells, and that reactive oxygen species generation and oxidative stress may be the cause.
• Limitations the authors state:
  • The authors stated it is unknown whether workplace or environmental exposure would be sufficient to reach a threshold dose in the living body.

Topics

Medical terms in this study, explained in our Lexicon: Oxidative Stress, Apoptosis, Aspect Ratio (Length-to-diameter ratio), Adenocarcinoma.

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