Serum midkine levels in patients with obstructive sleep apnea

Abstract

Introduction: Obstructive sleep apnea (OSA) is a highly prevalent disease. The unique form of hypoxia and re-oxygenation in the circulation is termed “intermittent hypoxia” which is responsible to initiation of inflammatory response. Midkine (MK) is a heparin binding protein and plays key role in angiogenesis, inflammation and its expression is increased during hypoxic conditions. Thus we hypothesed that serum MK levels will be found higher in patients with OSA. Methods: Patients who underwent full polysomnography with suspicion of OSA were eligible for study. Serum MK and C-reactive protein (CRP) levels were compared between OSA and control groups. Results: Twenty four control and 53 OSA patients were enrolled the study. Median serum MK levels were found significantly lower in OSA than control group 85.93 pg/ml, 131.86 pg/ml respectively, p=0.001. But there was no significant correlation between OSA severity and serum MK levels. Median serum CRP levels were higher in OSA than control group 2.8 mg/L vs 2.05 mg/L respectively p=0.075 but it was significant only severe OSA vs control group 4.3 mg/L vs 2.05, p<0.01. Conclusions: Unexcepted lower serum levels of MK were found in OSA patients than control group but the mechanism underlying this condition is unclear. Rapidly endocytosis or internalization of serum MK or the different inflammatory response to IH may be responsible of this results.