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Research published in Cell, July 9, 2010, provides compelling evidence for an environmental component for cancer survival, that is a macro environmental component. While other studies have examined the effects of diet and exercise and even toxicological components on cancer susceptibility, Cao et al. studied mice living in an “enriched housing environment” that included more opportunities for social interaction (mice housed in groups of 18–20, versus control groups of 5 mice), for learning experiences due to a variety of ‘toys’ and with increased living space.
The enriched environment was tested with a model where cancer cells proliferated after transplantation (a mouse melanoma model), and with a mouse model for colon cancer, the MC38 model.
The mice challenged with transplanted melanoma cells were first weaned (at 3 weeks of age) and randomly assigned housing groups, either the complex environment group or control housing. At either 3 or 6 weeks later, the mice were inoculated with melanoma cells, then returned to their respective housing settings; 17–19 days later, tumor size was determined.
For the mice housed in the enriched conditions for 3 weeks before inoculation, tumor size was 43% smaller than for the mice housed in a control setting for 3 weeks pre-inoculation. For mice housed in both settings for 6 weeks before inoculation, tumor size was 77% smaller for the mice in the more complex housing, compared to controls. All of the control mice had solid tumors, compared to 95% of enriched housing/3 week mice, and after 6 weeks, only 83% of mice in the enriched housing had tumors.
The researchers further investigated the effect on melanoma cells, incubated with serum from the control and enriched housing mice, using a cell proliferation assay. Serum taken from the mice in enriched housing slowed the melanoma cell growth in vitro significantly compared to the effect of serum from control mice on melanoma cells.
Using the MC38 model the authors inoculated mice first, then initiated the enriched housing group, either 4 days after inoculation or after visible tumors had developed (6 days). For the colon cancer mice that were moved to enriched housing 4 days after inoculation, tumor size was reduced by approximately 30% compared to control mice. The mice that were moved to enriched housing after tumor development showed a markedly reduced tumor size. These mice were moved to enriched housing at 6 days post inoculation and at day 12 had 44% smaller tumors than the control mice.
Systemic metabolic changes were noted in the enriched environment mice as well. This study and previous ones noted elevated levels of the stress hormone corticosterone, while serum leptin levels were markedly reduced. Leptin is a major adipocyte hormone, conveying metabolic information to the brain and also is involved with peripheral organs as a metabolic regulator or angiogenic factor. Several reports have linked elevated serum leptin levels to increased risk for prostate and breast cancers as well as melanoma. Further studies by these authors showed a consistent and inverse relationship between circulating leptin levels and tumor size.
The authors also examined whether the effects in reduced tumor size could be related to diet and exercise and in both cases, found that neither weight gain or loss or differences in wheel running by the mouse groups explained the reduction in tumor size for the mice in a complex living situation.
Here is the article:
Cao L, Liu X, Lin EJ, Wang C, Choi EY, Riban V, Lin B, & During MJ (2010). Environmental and genetic activation of a brain-adipocyte BDNF/leptin axis causes cancer remission and inhibition. Cell, 142 (1), 52-64 PMID: 20603014
As one whose housing is routinely confounded by dogs and cats running around, and a constant miscellany of mail, magazines and other paper goods, I’m hoping this household stress-as-cancer-inhibitor model applies.
We continually hear that social interaction is good for brain health. These authors put into place mechanistic evidence of how this occurs.