Oxidative stress burdens obstructive sleep apnea patients

By Lucy Piper

Obstructive sleep apnea may be associated with increased oxidative burden, say researchers.

"This information is important since OSAS [obstructive sleep apnea syndrome] is associated with considerable morbidity which includes cardiovascular complications, and thus increased oxidative stress might be a plausible explanation for the relationship between OSAS and cardiovascular morbidity," Demosthenes Makris (University Hospital of Thessaly Biopolis, Larissa, Greece) and colleagues explain.

They found that overnight changes in reduced glutathione (GSH) and the ratio of GSH to oxidized glutathione (GSH:GSSG) in patients with severe OSAS differed significantly from those in individuals without the sleep disorder.

"Our findings suggest that OSAS patients presented a 'relative' insufficiency to increase their GSH level overnight compared to controls," the team writes in Sleep and Breathing. "This might be important in the natural course of OSAS since it has been suggested that high blood GSH concentrations correlates with long lifespan both in animals and humans."

The 18 patients with severe OSAS, defined as an apnea-hypopnea index (AHI) above 30, had received no previous treatment for OSAS and were free of comorbidities known to increase oxidative stress.

The patients with OSAS and 13 individuals with primary snoring but an AHI below 5 underwent spirometry, echocardiography, and full polysomnographic study. Before and on the morning following polysomnography, blood samples were collected to evaluate oxidative stress markers.

These included markers of lipid peroxidation (8-isoprostane and thiobarbituric acid-reactive substances [TBARS]), protein oxidation (carbonyl levels), and peroxidation (GSH and GSH:GSSG ratio as a measure of cellular toxicity), oxygen peroxide production (catalase and copper-zinc superoxide dismutase), and total antioxidant capacity.

The participants with and without OSAS had similar levels of the assessed oxidative stress markers before polysomnography. Overnight, however, GSH levels fell by an average 15% in patients with OSAS and increased by an average 63% in individuals without OSAS. A similar change was seen for the GSH:GSSG ratio. These differences were both significant.

But there was no difference between the two groups in the overnight change in the other oxidative stress markers.

Changes in the levels of biomarkers did not significantly correlate with AHI, arousal, or desaturation index, the researchers note.

"The present study provides evidence that oxidative stress increases overnight in OSAS patients, at least in GSH/GSSG pathway," they conclude.

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