Antioxidants can accelerate tumour growth, suggests study

The chemicals inactivate a protein that works as tumour suppressor and prevents cancer

By Kundan Pandey
Published: Thursday 30 January 2014

Till now, the world knew that antioxidants can help in preventing life-threatening diseases such as cancer. But a new study, published in the journal Science Translational Medicine, states that antioxidants may have detrimental effect in development of lung cancer.

The study also provides evidence to suggest that antioxidants can play a procarcinogenic role in people (such as smokers), who are already at a high risk of cancer.

The research, published on January 29, was conducted on mice to define the impact of antioxidant supplementation on tumour progression, severity and lethality. Swedish researchers, associated with the University of Gothenburg, divided the sample in two groups—controlled and the one administered fixed quantities of Vitamin E and N-acetylcysteine (NAC), the anti-oxidants with different molecular properties and generally used by human beings.

The researchers first induced mutations, which are likely to convert in lung cancer, in both the groups of subjects. Then, one of the groups was administered antioxidants. All the mice were euthanised after 8 to 10 weeks. Just before ending their lives, the researchers studied the impact of antioxidants and found that the tumour was 2.8 fold higher in the mice which were given antioxidants as compared to the controlled group.

In other words, when mice with an increased risk of lung cancer were treated with antioxidants, their early precancerous wound progressed faster and the mice developed more tumours. These tumours, just before the death of mice, were found to be at more advanced stage.

To make these findings relevant for human beings, researchers used the same antioxidants on human lung cancer cell lines and found that mice tissue respond to them in the same way.

‘Smokers should avoid supplementary intake of antioxidants’

The finding suggests that people, especially smokers, who are at a high risk of lung disease, should avoid taking supplementary antioxidants as they can accelerate tumour progression.

Referring to other experimental studies and clinical trials, researchers assert that antioxidants should never be recommended for prevention of lung cancer.

Limitations of the study

However, they admit that the research has allowed them to study only the impact of antioxidants on tumour progression and not on tumour initiation or prevention. Some of them have also suggested that further studies are needed to establish the findings.

Antioxidants and their new role
Antioxidants— including vitamins, carotenes and minerals—are natural or man-made substances added to food, cosmetic products and pharmaceutical drugs.

They are the molecules that inhibit oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons from a substance to an oxidising agent and can produce free radicals. In turn, these radicals can start chain reactions. When the chain reaction occurs in a cell, it can cause damage or death to the cell. Antioxidants terminate these chain reactions by removing free radical intermediates, and inhibit other oxidation reactions.

In this research, the antioxidants reduced oxidative stress and DNA damage as expected, but at the same time they also inactivated p53, a protein that also works as tumour suppressor and prevents cancer. This nullified the other possible benefits of antioxidants.

"When we knocked out p53 in the mice and in human lung cancer cell lines, the antioxidants had no effect," said Martin O Bergö, an expert in molecular and clinical medicine who led the research.

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