Antioxidants favor metastases

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Vitamin C, beta-carotene and Co. - antioxidants were previously considered extremely healthy. The radical scavengers are supposed to protect against oxidative stress. In other words, aggressive oxygen species that cause mutations in the genetic material and thus promote uncontrolled cell growth - i.e. the development of cancer. But the antioxidants harbor an undreamt-of danger: they seem to promote the formation of metastases in cancer patients.

Last year, researchers at the University of Gothenburg in Sweden found that antioxidants in mice with lung cancer did not inhibit tumor growth as expected, but instead promoted it. In addition, the mice developed more aggressive tumors when they were given antioxidants. Experiments with human lung cancer cells confirmed the negative effects of the radical scavengers. "The results suggest that lung tumor cells multiply faster when there is little reactive oxygen - and that is exactly what antioxidants can do," the researchers write.

Influence on skin cancer?

Martin Bergö and his colleagues, also from the University of Gothenburg, have now investigated these results further. They looked at the effects of antioxidants on another type of cancer, skin cancer. To do this, they gave mice with the most dangerous form of skin cancer, malignant melanoma, the antioxidant N-acetylcysteine ​​(NAC) in their drinking water. "The antioxidant concentration corresponded to a dose of 665 to 1,330 milligrams per day in relation to humans. This is within the range recommended for nutritional supplements and medical applications," the scientists said.

Double the rate of metastases

The result was clear: the mice that had been administered the antioxidant developed twice as many metastases compared to the control group. But not only was the number of metastases increased, but also the number of malignant tumor cells in the individual metastases. Experiments with NAC and a vitamin E analog on cell cultures from patients with malignant melanoma supported these results.

“It is possible that the tumor cells that have left the primary tumor are exposed to oxidative stress, which reduces their ability to migrate, penetrate new tissue and form metastases,” the researchers report. The antioxidant NAC helps the tumor cells to overcome this obstacle.

“In contrast to the lung cancer study, the primary melanoma tumor did not increase. But the antioxidant increases the ability of the tumor cells to metastasize, "reports Bergö. But this is an even bigger problem, he emphasizes:" Because in melanoma, it is not the primary tumor per se that is dangerous; the metastases lead to death. "

Dietary supplements - not for cancer patients

Antioxidants are not only found in fresh vegetables and fruits, but above all in food supplements. In the hope of a therapeutic effect, cancer patients in particular often turn to dietary supplements with antioxidants, as studies by the University of Gothenburg have shown. "But we have proven that it is precisely antioxidants in at least two types of cancer that promote the progression of the cancer," says Bergö. "Our current results, combined with data from large clinical trials of antioxidants, suggest that people with cancer should avoid such supplements."

Also skin and sun creams under suspicion

Antioxidants play a special role in skin cancer: because here they also have an external effect. "Skin and sun creams sometimes contain beta-carotene or vitamin E, both of which may affect the malignant melanoma cells in the same way as the antioxidants in dietary supplements," says Bergö. The scientists are currently researching exactly how the additives in lotions influence skin cancer. "We are testing whether antioxidants that are applied directly to malignant melanomas accelerate the progression of the cancer just as much as antioxidants taken orally," says the expert.

He also points out that the effect of various antioxidants with regard to other cancer diseases urgently needs to be investigated. "Because if we want to properly assess the role that free radicals and antioxidants play in cancer, we need more data."

Sources:

Le Gal K. et al .: Antioxidants can increase melanoma metastasis in mice. Science Translational Medicine. DOI: 10.1126 / scitranslmed.aad3740

Press release of the University of Gothenburg from October 8th, 2015

Tags:  Diseases drugs womenshealth