Socialising with others can “help fight cancer”, according to The Daily Telegraph. The newspaper said that the ‘positive stress’ from interaction causes tumours to shrink and even go into remission.
The research was an animal study comparing the progression of tumours in mice kept in standard cages and in mice given more space, a range of playthings and the freedom to interact with other mice. The researchers found that the enriched environment decreased tumour size and say that this was due to the brain sending chemical signals to fat cells. This then caused changes in the hormones the cells released, and an enhanced immune response.
It is not clear yet whether the brain and hormone changes observed in these mice are relevant to humans or could be equated with being more sociable. It has also not been determined what types of activity would create ‘positive stress’ in humans or whether this would have any effect on cancer.
This study does highlight interesting potential drug targets within the brain and circulating hormones that may warrant further research.
Where did the story come from?
The study was carried out by researchers from the Ohio State University in the US and Cornell University and was funded by the US National Institutes of Health. The study was published in the peer-reviewed journal Cell.
The newspapers have tended to overemphasise the relevance of this animal research to humans, as further research is needed to determine how a person’s psychology and environment affects the course of their cancer.
What kind of research was this?
This animal study looked at whether tumours in mice that had developed melanoma (skin cancer) or colon cancer were affected by their living environment. The researchers were interested in this as they said that the environment can affect the regulation of hormone release by the brain, which may be involved in changing how tumours grow.
As this was an animal study, at this stage its relevance to humans is uncertain.
What did the research involve?
The researchers used mice that were bred to develop colon cancer and normal mice that were induced to develop tumours following injection with skin or colon cancer tumour cells. They compared tumour growth in mice that were kept in an enriched environment with the growth in those mice in a more basic caged environment. They also compared growth in mice, which had access to a running wheel only. The enriched environment had increased space and playthings, and the mice could interact with other mice.
The researchers also looked at certain ‘biomarkers’, chemicals in the blood that indicate that a tumour is present. The researchers also looked at whether the enriched environment affected the amount of enzymes involved in tumour growth and looked at the expression of genes in the hypothalamus (the part of the brain that links the nervous system with the hormonal system. They also assessed whether the enriched environment affected the mice’s weight, and their hormone levels.
The researchers were particularly interested in a chemical called Brain Derived Neurotropic Factor (BDNF). Release of this chemical in the brain can trigger the activity of a group of neurones that affect the amount of the hormone leptin released by fat cells. Leptin also signals back to the brain to give information about the body’s metabolic demands.
What were the basic results?
The researchers found that the enriched environment caused reduced tumour growth and increased remission in mice compared to mice housed in standard cages. They found that the mice in the enriched environment weighed less than the control mice, although the effect on the tumours was not due to physical activity alone as mice that had access to a running wheel only did not show the same slowing of tumour growth.
They found that a fat cell hormone called adiponectin increased, while leptin hormone decreased in mice kept in the enriched environment.
The researchers also observed that the spleens of the mice in the enriched environment were more enlarged after they were injected with cancer cells, indicating they had a stronger immune response.
The gene producing BDNF (the chemical that governs leptin levels) was two times more active in the enriched environment mice when the researchers genetically modified the mice to produce more BDNF. This produced the same pattern of changes seen as in the enriched environment mice. Furthermore, if they switched off the gene, housing mice in an enriched environment no longer had the same effects on the tumours.
The researchers then explored the gene expression of leptin and adiponectin in fat cells. They found that the leptin gene was less active and the adiponectin gene was more active in the enriched environment mice. By blocking the activity of neurones that send signals to the fat cells, they blocked the effect the enriched environment had on tumour growth.
They also found that if they infused mice with leptin, the tumours were larger than mice not treated with the hormone.
How did the researchers interpret their results?
The researchers say that their research shows that an enriched environment reduces cancer burden and that this effect is associated with changes in hormones and an enhancement of the immune response of these mice. They say the enriched environment gave mice a ‘positive stress’ as they were exposed to new objects and other mice. The observed reduction in cancer burden was facilitated by BDNF in the hypothalamus, which, in turn, caused changes in the action of the fat cells. They also say that the roles of the hormones adiponectin and leptin in tumour growth were not yet fully known.
The researchers suggest that “at a clinical level, direct gene transfer of BDNF can mimic the antiproliferative (anti-tumour growth) effects of an enriched environment”. On this basis they believe that either environmental or drug-based interventions to induce BDNF expression in the hypothalamus “may have therapeutic potential”.
This research showed that cognitive and social stimulation combined with physical activity promoted by an enriched environment reduced tumour growth in mice. It has also determined brain and hormone activity that may underlie this effect.
The brain and hormone changes observed in mice housed under these experimental conditions may not relate to changes in humans commonly thought of as ‘more sociable’. It has not been determined what types of activity, if any, would create a ‘positive stress’ in humans, nor whether this would have any effect on cancer.
However, this study does highlight interesting potential drug targets within the brain and circulating hormones that warrant further research in humans.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
The Daily Telegraph, 9 July 2010
Daily Mail, 9 July 2010
Links to the science
Cell, Volume 142, Issue 1, 52-64, 9 July 2010