Nocturnal hypoxic stress activates invasive ability of monocytes in patients with obstructive sleep apnoea syndrome

Background and objective: Obstructive sleep apnoea syndrome (OSAS) is known to be a risk factor for cardiovascular events. However, the precise mechanism has not been fully elucidated. OSAS-induced hypoxic stress may promote the production of inflammatory cytokines and chemokines by monocytes, which has a crucial role in the development of atherosclerosis. In addition, adhesion to the vascular endothelium and transendothelial migration of monocytes are considered to induce atherosclerosis. The aim of this study was to investigate the effects of hypoxic stress on the invasive ability of monocytes in OSAS. Methods: Twenty-one male patients with OSAS and 17 healthy male control subjects, who were matched for age and BMI, were enrolled. Venous blood samples were collected before and after sleep, and also after CPAP titration, for the purpose of monocyte isolation. The invasive ability of monocytes was evaluated by counting the number of invading cells using a BD BioCoat Matrigel Invasion Chamber. Results: The number of cells, which represents the invasive ability of monocytes, was significantly higher in patients with OSAS compared with control subjects, in the early morning (P < 0.001). In patients with OSAS, invasive ability in the early morning after sleep was significantly elevated as compared with that before sleep (P < 0.001), and was positively correlated with the oxygen desaturation index (P < 0.05). CPAP titration led to a decrease in the invasive ability (P < 0.001). Conclusions: These results indicate that OSAS-induced hypoxic stress activates the invasive ability of monocytes, and that the occurrence of this phenomenon during sleep may contribute to the development of atherosclerosis in OSAS.