N Epsilon-(Hexanoyl) Lysine, A New Oxidative Stress Marker, is Increased in Metabolic Syndrome, but not in Obstructive Sleep Apnea

Abstract

BackgroundIt is well known that oxidative stress is induced by metabolic syndrome (MetS), leading to cardiovascular diseases. On the other hand, obstructive sleep apnea syndrome (OSAS) is frequently complicated with MetS, and OSAS is also considered to induce oxidative stress. Thus, we examined the plasma and urine markers of oxidative stress and antioxidant status in patients with OSAS with or without MetS. MethodsSixty-nine Japanese men suspected of having OSAS were recruited. We divided all patients into 3 groups: nonobese patients, obese patients without MetS, and patients with MetS. Oxidative stress markers, plasma and urine 8-hydroxydeoxyguanosine (8-OHdG) and plasma N epsilon-(hexanoyl) lysine (HEL), and an antioxidant status marker, plasma total antioxidant status, were measured by enzyme-linked immunosorbent assay. ResultsThe plasma HEL level was significantly increased in patients with MetS, whereas neither plasma and urine 8-OHdG levels nor plasma total antioxidant status level was different in patients with MetS. Furthermore, the plasma HEL level was significantly and positively correlated with fasting plasma glucose, serum insulin, and homeostasis model assessment-insulin resistance index in all subjects. ConclusionsThe oxidative stress is strongly associated with the presence of MetS but not related to the presence or severity of OSAS. Furthermore, we demonstrated that the plasma concentration of HEL is a more sensitive biomarker of oxidative stress in patients with MetS than the plasma and urine levels of 8-OHdG.