In a recent study, researchers used mice to determine the effects of sleep apnea on the growth of cancer.
Sleep apnea is a disorder in which an individual’s breathing stops and starts again periodically during sleep. The two types of sleep apnea are central sleep apnea and obstructive sleep apnea. With central sleep apnea, the brain does not signal the muscles involved in breathing and breathing stops, but with obstructive sleep apnea, an individual’s throat muscles relax, causing their airways to become constricted.
Sleep apnea causes intermittent hypoxia
The repeated constriction of the airways results in periods of low oxygen, known as intermittent hypoxia. Intermittent hypoxia has many consequences, but in recent research, intermittent hypoxia as a result of obstructive sleep apnea has been shown to play a role in cancer development. Using mice, researchers explored the effects of sleep apnea on cancer in a study that was published in the American Journal of Respiratory and Critical Care Medicine.
The researchers used 21 mice that were 20 months old and 24 mice that were only 2 months old to mimic older and younger humans, respectively. After they exposed the mice to six hours of room air or intermittent hypoxia every day for 10 days, the researchers injected the mice with lung cancer cells. The tumors were allowed to grow for a month, after which time the researchers euthanized the mice to examine their tumors.
Mice exposed to intermittent hypoxia are more prone to cancer growth
Compared to young mice exposed to room air, young mice exposed to intermittent hypoxia had increased tumor growth. Examination of the tumors showed that the tumors of young mice exposed to intermittent hypoxia had more tumor-associated macrophages and these macrophages were shown to promote tumor growth.
Overall, the researchers showed that the effects of sleep apnea, specifically intermittent hypoxia, in young mice is a risk factor for cancer growth. This difference between young and old mice is likely due to differences in immunological pathways involving cells such as tumor-associated macrophages, however, the exact causes of these differences in immune responses are still unclear. Future research should focus on delineating how intermittent hypoxia promotes these responses.
Written by Monica Naatey-Ahumah, BSc
References:
- Torres, M., Campillo, N., Nonaka, P.N., Montserrat, J.M., Gozal, D., Martinez-Garcia, A.,… Almendros, I. (2018). Aging Reduces Intermittent Hypoxia-induced Lung Carcinoma Growth in a Mouse Model of Sleep Apnea. The Journal of Respiratory and Critical Care Medicine.https://doi.org/10.1164/rccm.201805-0892LE
- Mayo Clinic. (2018, July 25). Sleep Apnea. Retrieved from, https://www.mayoclinic.org/diseases-conditions/sleep-apnea/symptoms-causes/syc-20377631
