Researchers have found reduction in the development of chronic pain in mice with increased levels of physical activity. The effect was found to be mediated, at least in part, by increased levels of the anti-inflammatory molecule, IL-10.
Population-based research has previously revealed that people who have a higher levels of physical activity are at lower risk of developing chronic pain. Based on this research, which suggests a protective effect of physical activity, scientists from the University of Iowa, United States, designed a study to further investigate the mechanisms involved in this effect.
The researchers designed a series of experiments in mice to determine whether changes in inflammatory markers occur in response to regular physical activity. One group of mice were placed in cages with free access to a running wheel, while a second group of mice was placed in a cage with no running wheels. After 8 weeks the running wheels were removed from the ‘active’ group of mice, and the researchers injected both groups of mice with acidic (pH 4.0) saline, to induce chronic pain.
The results revealed that there were differences in types of macrophages (a type of immune cell) found in the muscle tissues of the mice, when comparing between the physically active and physically inactive group. The physically active mice tended to have a greater amount of macrophages expressing the protein CD206. These types of macrophages, ‘regulatory macrophages’ are responsible for the production of anti-inflammatory molecules, and are involved in reducing inflammation, and inducing tissue repair.
The researchers also found that when the physically inactive mice were injected with the anti-inflammatory molecule, IL-10, they were able to mimic the protective effects seen in the active group of mice. Conversely, they were able to block the beneficial effects of exercise in the active mice by blocking IL-10.
Overall the researchers state that the results support a role for the molecule IL-10 in the beneficial effects of exercise on development of chronic pain. The researchers hypothesize that long-term physical activity reduces the levels of inflammatory molecules, and increases levels of anti-inflammatory molecules, such as IL-10. This positive balance of anti-inflammatory molecules may therefore prevent the development of chronic pain.
Leung, Audrey, Gregory, Nicholas S, Allen, Lee-Ann H, Sluka, Kathleen A. “Regular physical activity prevents chronic pain by altering resident muscle macrophage phenotype and increasing interleukin-10 in mice” Pain January 2016 – Volume 157 – Issue 1 – p 70–79.
Written by Deborah Tallarigo, PhD