Plasma level of hypoxanthine/xanthine as markers of oxidative stress with different stages of obstructive sleep apnea syndrome

BACKGROUND AND OBJECTIVES: Tissue hypoxia due to repeated apneas among patients of obstructive sleep apnea syndrome (OSAS) leads to cumulative oxidative stress. It is established that an increased plasma level of hypoxanthine/xanthine may serve as a criterion of tissue hypoxia. We presumed that plasma levels of hypoxanthine/xanthine might be high among patients of OSAS due to oxidative stress. Nobody studied this relationship earlier. The aim of this study was to estimate their plasma levels as markers of hypoxia. DESIGN AND SETTINGS: This case-control study was performed for a period of 1-year including patients referred to a tertiary care hospital, New Delhi, India. MATERIALS AND METHODS: It was a case-control study. A total of 43 patients of OSAS, diagnosed by overnight polysomnography (PSG), were included in the study. Age- and sex-matched 43 subjects in whom the presence of OSAS was not confirmed by overnight PSG were enrolled as healthy controls. The severity of disease was classified on the basis of apnea-hypopnea index (AHI). Out of 43 patients, 9 were moderate and 14 were severe. None was with mild OSAS. The venous blood sample was collected in the morning after PSG. Hematological and biochemical assays were also performed. Plasma levels of hypoxanthine/xanthine were measured by fluorometric analysis (normal laboratory reference <2.00 mmol/L). Data collected was analyzed statistically by SPSS version 14.0, student unpaired t test, chi-square test, Mann-Whitney U test, and Pearson correlation coefficient. RESULTS: The mean plasma level of hypoxanthine/xanthine in patients of OSAS was found to be 5.4 (5.1) mmol/L, and in controls it was 1.2 (0.4) mmol/L. A statistically significant (P=.000) difference was found between both groups. Among patients, a positive correlation between hypoxanthine/xanthine levels with age, AHI, and serum triglyceride levels was observed. The joint explanatory power of these significant factors was found to be 59.6% (P<.001). CONCLUSION: Plasma levels of xanthine/hypoxanthine were significantly elevated in patients of OSAS, and these were positively correlated with age, serum triglyceride levels, AHI, and severity of the disease.