Plant substance protects against radioactive radiation

Ingredient in broccoli and cabbage protects rats and mice from lethal radiation damage

Plant substance protects against radioactive radiation

Radioactive radiation: sickening in low doses, acutely fatal in high doses © SXC

Broccoli and cabbage are considered healthy: their ingredients combat cell stress, prevent cancer and are even said to slow down aging. Now it turns out: One of these substances could even protect against acute radioactive contamination. If rats and mice were given the substance 3,3- diindolylmethane (DIM), this saved them from certain radiation death. This protection worked even when the animals did not receive the drug until several hours after the lethal radiation, U.S. researchers report in the journal Proceedings of the National Academy of Sciences.

In a nuclear disaster like Chernobyl or Fukushima, rescue workers and laborers put themselves in deadly danger. This is because in the vicinity of the reactors, the radiation doses released are sometimes so high that a human being can develop fatal radiation sickness after only a short time. The consequences are irreparable cell damage, destruction of blood cells and organs, and often death after a few days.

But radiation in the context of cancer therapy also leaves damage in the body, albeit to a much lesser extent. Because to kill tumor cells, radiation doses must often be used that also damage healthy cells in the treated area. So far, there are few ways to cure radiation or reverse its effects. The side effects of radiation therapy can also only be alleviated, but not completely prevented.

Protection against cancer and cell damage

But now a remedy may be in sight. In experiments on rats and mice, a plant substance has proven to be surprisingly potent in protecting against radiation damage. The substance in question, 3,3-diindolylmethane (DIM), has been a focus of biomedical research for some time. Because experiments with cell cultures and animals already showed that the substance makes cells less susceptible to some types of cancer. The drug also appears to protect cells against oxidative stress.

Initial clinical tests also found that DIM has no harmful side effects when administered orally. "However, the mechanism by which DIM protects against cancer remains unknown," explain Saijun Fan of Georgetown University Medical Center in Washington DC and his colleagues. To get a closer look at the properties of this plant compound, the researchers decided to test whether and how DIM works against an extreme form of cell damage: radioactive radiation.

Plant substance protects against radioactive radiation

Immune to lethal radiation dose

For their study, they administered different concentrations of DIM to rats, which received one dose daily by injection for 14 days. Twenty-four hours after the first dose, the rats were irradiated with a whole-body dose of 13 grays of radioactivity – a normally absolutely lethal amount of radiation. "All the untreated animals died, but more than half of the rats treated with DIM were still alive even 30 days after irradiation," reports coauthor Eliot Rosen of Georgetown University Cancer Center. "This is the first evidence that DIM can also protect against radioactive radiation."

But especially promising is the result of another experiment. In this one, scientists began treating rats and mice with DIM only after the lethal dose of radiation had been administered. And here, too, the substance proved to be extremely effective: When DIM was first administered two hours after irradiation, more than half of the animals survived in this case as well. And even starting treatment as late as 24 hours after the lethal dose of radiation still saved a third of the animals from certain death.

According to the researchers, this suggests that DIM can still act against radiation damage after the fact – an important property in nuclear accidents. "Because then the affected individuals often cannot be recovered and treated earlier," the researchers said.

DNA repair accelerated

But what is the basis of the protective effect of the plant substance?? To find out, the scientists conducted additional experiments with cell cultures. This showed that the presence of DIM activates a signal substance in normal body cells that stimulates the repair of damaged DNA. This allows the cells to repair the destruction caused by the harsh radiation so quickly and effectively that the cell can continue to function. For this effect, DIM concentrations were already sufficient, which can be easily achieved by taking them via tablets and which are well tolerated, as the researchers point out.

And the scientists found out something else crucial: cancer cells do not seem to benefit from the protective effect of the DIM. The researchers report that the stimulation of DNA repair does not work for them. As a result, tumors and cancer cells in mice were still destroyed by irradiation, but the healthy cells were protected by the DIM in the process. This may also open up new possibilities for protecting cancer patients from the side effects of radiation therapy. "The DIM could protect patients’ healthy tissue during radiation treatment," Rosen says. The unprotected cancer cells, on the other hand, continue to be destroyed.

Well tolerated and effective

"DIM has several properties that make it a good protective agent against radiation," Fan and his colleagues state: "It is not toxic when administered orally, even in high doses, and is well absorbed by the body. It can also be administered by injection, for example, should the esophagus and digestive organs be affected by acute radiation.

In addition, it is able to protect against the consequences of radioactive irradiation even after the fact. "DIM increased the animals’ chance of survival over a wide range of radioactive doses between 5 and 13 grays," the researchers said. This shows that the substance protects against the destruction of blood cells as well as against the acute immediate consequences of radiation sickness. (Proceedings of the National Academy of Sciences, 2013; doi: 10.1073/pnas.1308206110)

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