CPAP Therapy for Obstructive Sleep Apnea Improves Levels of Inflammatory Biomarkers

The use of continuous positive airway pressure (CPAP) in the treatment of obstructive sleep apnea (OSA) improves serum levels of 3 inflammatory markers associated with extensive morbidity, including atherosclerotic vascular disease. This was the conclusion of a meta-analysis published recently in the Journal of Inflammation. The 3 inflammatory markers selected for the analysis were C-reactive protein (CRP), tumor necrosis factor alpha (TNF-α), and interleukin-6 (IL-6) (see below). 

Evidence has been accumulating that strengthens an observed link between OSA and both cardiovascular (CV) and cerebrovascular disease and associated morbidity. Many of the physiologic and biochemical abnormalities that result from OSA (eg, severe hypoxemia, sleep interruption) cause increased expression of systemic inflammatory markers, sustained sympathetic activation, and endothelial dysfunction-mechanisms all known to be atherogenic. CPAP is the primary treatment for OSA and is proved to reduce CV morbidity and risk. The current study aimed to discover whether the therapy would also reduce levels of disease precursors.

The authors analyzed the published data from studies of adults with OSA that addressed values of at least one of the specified markers before and after CPAP treatment. A total of 3835 studies were reviewed for inclusion; 23 case-controlled studies were pooled for analysis.

Using a P value of <.05 to mark significance, the levels of CRP and TNF-α were significantly decreased after the use of CPAP therapy. Levels of IL-6 were not significantly reduced; however, a general trend of decreasing IL-6 values with CPAP use was seen. 

Small sample size was found to be the primary reason that some studies in each of the 3 categories did not support the overall finding that CPAP significantly improves levels of inflammatory markers. The authors also note that the available literature is “. . . largely low-level evidence.” They also point out that data exclusion based on language and presentation form (ie, graphical only) may have introduced publication bias.

Overall, however, reduced levels of inflammatory markers suggest that CPAP therapy for OSA may modulate the CV risk profile through multiple mechanisms, including modulation of systemic inflammation. Future studies to explore this dimension of the CV risk profile will need to examine the impact of OSA treatment on atherosclerosis and vasculopathy.

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A Trio of Inflammatory Indicators CRP is synthesized in the liver and is thought to play a direct role in the initiation and progression of atherosclerosis. Its pro-inflammatory and pro-atherongenic properties have been found in endothelial cells, vascular smooth muscle cells, and monocyte-macrophages. CRP levels are also associated with oxidative stress.

IL-6 is a circulating cytokine known to be secreted from activated macrophages and lymphocytes, among other cell types. Inflammation is the primary stimulus for IL-6 release, but other identified triggers are cigarette smoking and adiposity.

TNF-α is also a pro-inflammatory cytokine known to play a role in host defense as well as in the pathogenesis of disease processes, including atherogenesis, septic shock, and  autoimmune disorders.

Reference
Baessler A, Nadeem R, Harvey M, et al. Treatment for sleep apnea by continuous positive airway pressure improves levels of inflammatory markers-a meta-analysis. J Inflammation. 2013;10:13. http://www.journal-inflammation.com/content/pdf/1476-9255-10-13.pdf