Pro-oxidant activity of polyphenols and its implication on cancer chemoprevention and chemotherapy

Our plain-English summary of Pro-oxidant activity of polyphenols and its implication on cancer chemoprevention and chemotherapy, by A.J. León-González, C. Auger, V.B. Schini-Kerth (Biochemical Pharmacology, 2015).

The study

• Authors: A.J. León-González, C. Auger, V.B. Schini-Kerth
• Journal: Biochemical Pharmacology
• Published: 2015;98(3):371-80
• Cited by: 194 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Reactive oxygen species (ROS) play a major role in carcinogenesis: pro-oxidant agents like tobacco smoke, asbestos or N-nitrosamines, are known as mutagenic and carcinogenic, and cancer cells show increased levels of ROS and redox deregulation. However, pro-oxidant molecules can also act as selective cytotoxic agents against cancer cells by achieving toxic levels of ROS. Although polyphenols are well-known as potent antioxidants, a pro-oxidant effect has been associated with their pro-apoptotic effect in various types of tumor cells. The aim of the present review is to present the main evidences of the pro-oxidant-related cytotoxic activity of naturally occurring polyphenols and their underlying mechanisms.

Copyright © 2015 Elsevier Inc. All rights reserved.

In plain English

This article, labelled a commentary in the journal, was a review by laboratory pharmacology researchers in Strasbourg, France. It did not study asbestos. Asbestos appeared once in the opening summary, alongside tobacco smoke and N-nitrosamines, as an example of a pro-oxidant agent known to cause mutations and cancer. The review covered published laboratory and animal research on polyphenols, plant compounds found in foods such as tea, berries, wine, turmeric and olive oil. It looked at whether these compounds, usually known as antioxidants, can instead raise levels of reactive oxygen species and kill cancer cells. The authors described studies in cancer cell lines in which many classes of polyphenols triggered cell death linked to reactive oxygen species. They noted that the effect of soy isoflavones on cancer remains controversial. They wrote that whether reactive oxygen species cause this cell death or result from it is debated, and that the role of this mechanism in living animals is still poorly understood. The authors concluded that polyphenols seem to act as antioxidants to prevent cancer and as pro-oxidants to kill cancer cells. They said more studies in animals and humans are needed.

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: Narrative review (published as a commentary) of laboratory and animal studies on the pro-oxidant activity of polyphenols in cancer
• Who was studied: No study population of its own; the review drew on published cell-culture studies of many cancer cell lines and some animal (mouse and rat) studies
• Exposure: Naturally occurring polyphenols (for example EGCG from green tea, curcumin, resveratrol, quercetin). Asbestos was mentioned only once, in the abstract, as an example of a pro-oxidant agent known to cause mutations and cancer; it was not a subject of the review
• Main results:
  • The authors stated that phenolic compounds can act as antioxidants or as pro-oxidants depending on concentration and the cellular environment
  • The review described conditions under which polyphenols act as pro-oxidants: high concentrations, high pH and the presence of redox-active transition metals
  • Among the mechanisms the authors listed for polyphenols' toxic effects on cancer cells were promotion of mitochondrial dysfunction and cell death, and inhibition of the cells' antioxidant defenses
  • The authors noted debate over whether reactive oxygen species cause polyphenol-induced cell death or are a consequence of it
  • The authors described the effect of isoflavones on cancer as controversial, citing a study in which dietary soy isoflavones increased metastatic tumor nodules in the lungs in a mouse model of breast cancer
• The authors' conclusion: The authors concluded that polyphenols seem to act as antioxidants to prevent cancer and as pro-oxidants to kill cancer cells, and that more studies in living animals and in humans are needed
• Limitations the authors state:
  • The authors stated that the role of reactive oxygen species in the anticancer effects seen in animals is poorly understood, because most animal studies reported only tumor growth and cell death data
  • The authors stated that bioavailability, the role of polyphenol breakdown products, the active chemical structure and clinical evidence remain to be clarified

Topics

Medical terms in this study, explained in our Lexicon: Chemotherapy, Reactive Oxygen Species (ROS), Carcinogenesis, Carcinogenic.

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