Sleep Apnea Produces Troubling Signs of Future Brain Disease
Tuesday, March 27, 2018
IRP researchers have discovered a link between disrupted breathing during sleep and biomarkers related to inflammation and poor brain health.
Like a bear leaves its ominous footprints in the snow, diseases and other biological processes often leave traces throughout our bodies. Recent technological and scientific advances have enabled clinicians to use measurements of these ‘biomarkers’ in their attempts to improve our health. A new study by IRP researchers revealed that patients with a sleep disorder called obstructive sleep apnea (OSA) have higher blood concentrations of certain biomarkers that may foreshadow poor brain health later in life.1
When people with OSA sleep, their throat muscles relax and block their windpipes, preventing proper breathing and often waking them up. As a result, these individuals get lower-quality sleep and their brains receive less oxygen at night.
“The overall idea is that those two conditions are not good for brain health, but nobody had really looked to see if some of the biomarkers we see in brain injury are also common in younger individuals with this type of disordered breathing,” says IRP Lasker Clinical Research Scholar Jessica Gill, Ph.D., R.N., the study’s senior author.
Between six and seventeen percent of adults have a moderate or severe form of OSA, and it is more common in older and heavier individuals, with some estimates placing its prevalence among older adults at nearly one in two.2 As a consequence, it is tough to determine whether biomarkers related to neurological damage or inflammation seen in OSA patients result from the illness itself, from the advanced age or extra pounds that tend to accompany it, or from other age- or weight-related conditions like type 2 diabetes. To overcome this obstacle, Dr. Gill’s study examined only younger, physically fit individuals.
Dr. Gill’s team first had their participants undergo sleep studies and gauged the severity of their OSA by counting the number of times their breathing was disrupted while they slept. After analyzing participants’ blood samples, Dr. Gill’s group found that individuals with moderate or severe OSA had higher levels of two compounds in their blood than those with mild OSA or controls without the condition. One of these substances, called interleukin-6, is a marker of inflammation that had been linked to OSA in prior studies. The other, called tau, is released from the brain when neurons are damaged and is associated with Alzheimer’s disease and traumatic brain injury. The more breathing disruptions a participant had during the sleep study, the higher the levels of tau tended to be in his or her blood.
“We think the oxygen deprivation is causing damage to neurons and that is then reflected in the release of tau from the brain that we can see in peripheral blood,” Dr. Gill says, “so when we see tau in the blood, we get concerned that there may be a subtle brain injury.”
Until recently, interleukin-6 and tau could only be measured by taking samples of cerebrospinal fluid from the spinal cord, which is much more invasive and medically risky than a blood draw. But Dr. Gill’s team took advantage of a new, ultra-sensitive technology that permitted these biomarkers to be detected in blood samples, allowing such assessments to become a part of more routine clinical care.
Dr. Gill cautions that the results of this particular study may not be applicable to the general population, as the sample was small, mostly male, and comprised entirely of active-duty military personnel. Her team is currently running a larger and more gender-diverse study that will follow participants over a longer period of time and include neurocognitive assessments. Her hope is that this research will spur doctors and patients to take a more proactive approach to OSA.
“Our results suggest that we really need to be monitoring people for this condition because if people are having prolonged periods of these biomarkers being elevated, that could indicate overall risk factors for neurological damage,” Dr. Gill says. “I think our research will make people aware that moderate or severe OSA is something we need to screen for and treat.”
 Elevated tau and interleukin-6 concentrations in adults with obstructive sleep apnea. Motamedi V, Kanefsky R, Matsangas P, Mithani S, Jeromin A, Brock MS6 Mysliwiec V, Gill J. Sleep Med. 2018 Mar;43:71-76. doi: 10.1016/j.sleep.2017.11.1121. Epub 2017 Nov 24.
 Prevalence of obstructive sleep apnea in the general population: a systematic review. Senaratna CV, Perret JL, Lodge CJ, Lowe AJ, Campbell BE, Matheson MC, Hamilton GS, Dharmage SC. Sleep Med Rev. 2017 Aug;34:70-81. doi: 10.1016/j.smrv.2016.07.002. Epub 2016 Jul 18.