A provocative new study suggests that mice raised in spacious cages with lots of toys and companions are more resistant to cancer than mice living in standard cages. The work, which found that exercise alone does not explain the anti-cancer effect, attracts both excitement and skepticism.
The study is based on research from the 1960s, which found that the increase in mice in an "enriched environment" stimulates neuronal growth and learning. Recent research even suggests that stimulating cage environment in later life can help restore memory in animals with a neurodegenerative disease. Neuroscientists Matthew During and Cao Lei, both of Ohio State University and Cornell University, wondered if these profound effects on the brain may influence how the body reacts to cancer.
During his team studied the development of cancer in two sets of young male mice in groups of five animals housed in a standard cage (about the size of a bread box) with food, but nothing else, and groups of 18-20 mice raised in a larger cage (about the size of a portable crib) with food, toys, a maze, racing wheels, and where to hide. After the mouse has spent 3 to 6 weeks in their cages, the researchers injected under the skin with melanoma cancer cells and waited for tumors to develop.
The results were a surprise, says Durant. Mice who spent three weeks in enriched cages developed tumors that were 43% smaller in volume than those expressed in normal cages. The difference in mass of the tumor was 77% when mice past six weeks in special cages. And unlike mice bred in standard cages, some of those in enriched cages developed no tumors at all. The researchers obtained similar results for both types of mice prone to colon cancer.
Exercise alone did not explain the effect. high mouse in a typical cage connected to a wheel bearing tumors developed just as massive as those that have not cardio.
The anticancer effects seem related to metabolic changes, said Durant. Mice raised in the enriched environment had much lower blood levels of leptin, a hormone associated with obesity and cancer; they also had higher levels of corticosterone, a stress hormone. In addition, improved hypothalamuses caged mice had higher levels of brain-derived neurotrophic factor (BDNF), a growth factor that the researchers suggest sends signals to fat cells to produce less leptin. When the team turned off BDNF or ramp up in the brains of mice, they saw corresponding changes in leptin levels and tumor size, they report in tomorrow's issue of Cell .
speculates While mice in cages have improved "some anxiety" because of the life in a larger space and with more fellow mice to treat. "It is light stress. It is difficult system. "The moderate stress signals the brain to produce more BDNF and make less leptin promoting cancer, he suggests.
During said the results suggest that stress-free life can be less healthy than one with a slight stress. "Living a life of couch potato is not the best," During said.
Some researchers have shown the study with caution. First, it contradicts a lot of evidence that exercise protects against cancer, Henriette Van Praag says neuroscientist at the National Institute on Aging in Bethesda, Maryland. She said that a problem with the paper is that the mouse "runner" in standard cages have not had the chance to run individually; in a group, some males can monopolize the wheel bearing. "The concept is good, but I do not think they can say conclusively that exercise is not an important factor," said Van Praag.
physiologist John Hall of the University of Mississippi Medical Center in Jackson called the paper "an exciting new idea," but points to another reason to question whether the results will be applicable to persons: beta-blockers, which are drugs that block BDNF, have been widely used for heart disease since the 1960s, but there is "no evidence that they promote the tumor growth," he said.
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