A little stress could be good
Study shows mice put into stressful situations fight cancer better than those left to chill out
Some stress can be good for the body, helping fight off cancer, researchers reported on Thursday.
Living in an environment rich with physical, mental and social stimulation — a setting that causes mild stress — might by itself curb cancer growth, according to a new study led by researchers at The Ohio State University Comprehensive Cancer Center — Arthur G. James Cancer Hospital and Richard J. Solove Research Institute.
Experiments with mice showed that animals put into a stressful situation, even fighting with other mice, did a better job of fighting tumors than mice left to chill out.
They said their findings, published in the July 9 issue of the journal Cell, point to a possible neurological treatment for cancer.
“The way we live, and how we live, may well have a much bigger impact on the prognosis of cancer than we recognized previously,” said Matthew During, a professor of neuroscience who worked on the study, in a telephone interview.
Dr. During’s team injected mice with melanoma, a type of fast-growing skin cancer, and let the tumors grow. They put some of the mice in a large cage, with lots of toys, space and many more other mice than usual.
Other mice stayed in ordinary lab cages.
After three weeks, tumors shrank almost in half in the mice in the “stimulating” cage and they shrank 77 per cent after six weeks. The tumors completely disappeared in 17 per cent of the mice, with no other cancer treatment.
Dr. During believes that more than simple stimulation is at work in the mice. The mice in the “enriched” cages were a little stressed out.
“You find some of them with little bite marks and fight marks,” said Dr. During. “It’s not all friendly.”
Although common wisdom holds that stress is not healthful, the body’s response to stress is complex, and hormones released in response to stress can have positive effects.
To show the benefits were not simply due to exercise, the researchers placed running wheels in the smaller cage. The mice ran up to three times as far as the mice in the large cage, but were not more resistant to cancer.
Experiments to see what was happening biologically in the mice showed the stressed mice were producing more of a brain chemical called brain-derived neurotrophic factor.
The enriched environment created for this study housed 20 mice in large containers equipped with toys, hiding places and running wheels, along with unlimited food and water. Control mice were housed in groups of five in smaller, standard laboratory containers with no toys but with unlimited food and water.
The researchers injected human melanoma cells under the skin in both sets of animals. After three weeks of enriched housing, mice had tumors that were about half the size of those in control mice. With six weeks of enrichment, those tumors were 80 percent smaller than those in control animals, and almost 20 percent of the animals in the enriched group had no visible tumors at all. Control animals, on the other hand, all had visible tumors.
Investigating this effect further, During and his colleagues looked for changes in several metabolic hormones in the blood. Of those, leptin showed a dramatic drop in the enriched group.
A series of experiments demonstrated that leptin and the nervous system pathway really did influence tumor growth. Blocking the hormone altogether, for example, mimicked the enriched-environment effect, and the animals developed smaller tumors.
This compound reduces the production of leptin, a hormone linked with appetite and also associated with melanoma, prostate and breast cancer. The more leptin the mice produced, the smaller their tumors were.
Leptin acts differently in mice than it does in humans, and cancer grows differently in mice injected with tumors than it does in people. But Dr. During believes the findings may nonetheless apply to people.
“The key is that we believe that this pathway that we’ve defined here exists in humans,” he said.
“This suggests we can also start considering treating cancer by operating on the brain as well and introducing a gene to activate this pathway,” he added.
Up to now, scientists have only studied mice in situations of severe stress. That mice do better in situations of moderate stress has implications for cancer patients, Dr. During said.
“We shouldn’t be simply avoiding stress and looking for happiness,” Dr, During said. “We should be getting involved in team sports, getting involved in social groups, where there’s sort of an interactive dynamics which are a little bit challenging for us.”
http://www.sciencedaily.com/releases/2010/07/100708122611.htm
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