Moderate radiation prolongs life

MIPT scientists have found out that weak doses of gamma radiation prolong the life of fruit flies, and this effect is more pronounced in females than in males. The results obtained will help to identify genes that contribute to prolonging life, and in the future – to create anti-aging products for humans. The results of the study are published in the prestigious scientific journal PLoS ONE (Zhikrevetskaya et al. Effect of Low Doses (5-40 cGy) of Gamma-irradiation on Lifespan and Stress-related Genes Expression Profile in Drosophila melanogaster. A group of scientists from the Laboratory of Genetics of Aging and Longevity at MIPT, the Engelhardt Institute of Molecular Biology of the Russian Academy of Sciences, as well as the Scientific Center of the Russian Academy of Sciences in Komi and Syktyvkar University under the leadership of Alexey Moskalev is studying the mechanisms of hormesis – a phenomenon in which moderate stress has a stimulating effect on the body and contributes to the prolongation of life.

For the first time this effect was discovered at the end of the XIX century by the German pharmacologist Hugo Schultz: he discovered that small doses of poison accelerate the growth of yeast cells. Subsequently, the effect was found in many other organisms, in particular, peppermint and roundworms. 

"Small doses of poisons or moderate exposure to other stressful factors affect the body so that the stimulating effect overrides the harm. As a result, this can lead to an increase in life expectancy," explains the lead author of the article Svetlana Zhikrivetskaya. 

In recent years, scientists have been actively studying the phenomenon of radiation hormesis – the beneficial effects of small doses of ionizing radiation. According to conventional wisdom, there are no safe doses of radiation, since any radiation damages DNA molecules. A background in which the increase in the risk of cancer is negligible is considered acceptable. 

However, a number of experiments showed an improvement in vital signs "under radiation" in mice and in cell cultures. Indirect confirmation of radiation hormesis can be cases of unintentional exposure of large groups of people for a long time. 

In particular, in 1982, 20 thousand tons of metal were accidentally contaminated with cobalt-60 in Taiwan during steel smelting. Then this steel was used for building metal structures, and for about 20 years about 10 thousand people were exposed to radiation about 1 thousand times higher than the natural background. Scientists who studied these people came to the conclusion that the number of cancer cases in this group of unwitting subjects was lower than usual. However, these conclusions are criticized, and the very idea of radiation hormesis remains controversial. 

Moskalev's group investigated the effect of low doses of radiation. Previously, scientists have already established that radiation has a statistically significant effect on the larvae of fruit flies: their life expectancy increases, in addition, their resistance to stress, for example, to overheating, increases. In a new study, the group found out how gamma radiation affects adult fruit flies, and most importantly, how the activity of certain genes changes. 

"There are assumptions that hormesis is universal, that the mechanisms of its work, stress genes and stress pathways, are very similar in different animals. We look for these common pathways and compile a list of the corresponding genes. And on flies it can be done quickly, simply and inexpensively compared to mice and so on," says Zhikrivetskaya. 

About 2 thousand fruit flies (one thousand males and females each) were studied in the experiment, and 2 thousand flies were in the control group. The experimental group was divided into four subgroups, each of which received its own dose of radiation from a radium-266 source – from 0.05 to 0.4 gray (Gr). In gray, the amount of radiation energy absorbed by a substance (for example, by the tissues of the body) is measured. A dose of 6-8 Gy received by a person leads to acute radiation sickness and death within a few days, a dose of 3 Gy – for several weeks, and 0.05 Gy is the maximum permissible dose for people whose work is associated with radiation. 

Adult flies, unlike humans, tolerate radiation well, even a giant dose of 1000 gray does not lead them to instant death, but only slightly shortens their life span. Therefore, doses in tenths and hundredths of gray, which for a person means radiation sickness, are not serious for flies. 

"The results of our experiment confirmed that the life expectancy of fruit flies is increasing, and in females this effect was much more pronounced: in females, the average life expectancy increased by 7.6%, and in males – only 3.4%. On average, fruit flies live for about two months, that is, this is a noticeable increase – about a week," adds Svetlana Zhikrivetskaya.

But much more scientists were interested in how and which genes are activated at the same time. "If we understand how the genetic mechanisms work in this case, in the future we will be able to launch them without stress, that is, for example, to launch the mechanisms of the beneficial effects of small doses of radiation without radiation itself," the researcher explains. 

Scientists in an experiment with fruit flies investigated the change in the activity of 29 genes, and measurements were carried out many times: immediately after irradiation, after 6 hours, a day, two and three days. 

"For example, we have found that some genes that are responsible for DNA repair (repair) are overexpressed 48-77 hours after exposure to radiation has ended. Moreover, a number of genes showed overexpression precisely depending on gender," says Zhikrivetskaya. 

According to her, in the future, scientists plan to investigate the phenomenon of radiation hormesis in other animals, in particular, in mice. "Ultimately, this will allow us to find ways to prolong life for a person," the researcher concludes.

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17.08.2015