Inflammatory Mediators in Obstructive Sleep Apnoea Syndrome; Mechanisms of Production and the Effect of Long Term Antioxidants Administration

Obstructive Sleep Apnea Syndrome (OSAS) is associated with elevated plasma levels of IL-6 and TNF-α, which cannot be accounted for by obesity (Vgontzas et al Sleep Med Rev 2005;9:211-24, Ciftci et al Cytokine 2004;28:87-91\]. Obstructive apneas-hypopneas are accompanied by strenuous diaphragmatic contractions before the ensuing arousals and re-establishment of airway patency. We have shown that strenuous diaphragmatic contractions induced by resistive loading lead to elevated plasma levels of IL-6, TNF-α, and IL-1β (Vassi-lakopoulos et al AJRCCM 2002;166:1572-8) with concomitant up-regulation of the cytokines within the diaphragmatic myofibers (Vassilakopoulos et al AJRCCM 2004;170:154-61). OSAS patients exhibit frequent episodes of hypoxemia during the night. Loaded breathing is a form exercise for the respiratory muscles, and both acute and chronic hypoxia lead to an augmented plasma IL-6 response to exercise compared to normoxia (Lundby et al Eur J Appl Physiol 2004;91:88-93). In OSAS, monocytes have oxidative stress (Dyugovskaya et al AJRCCM 2002;165:934-9) and produce more cytokines (TNF-α) in vitro (Minoguchi et al Chest 204;126:1473-9). Hypothesis #1: plasma levels of IL-6 and TNF-α are increased during the night in OSAS patients secondary to the intermittent strenuous diaphragmatic contractions and the episodes of hypoxia-reoxygenation associated with the obstructive apneas-hypopneas. Hypothesis #2: monocytes from sleep apnea patients, exhibit augmented intracellular expression of IL-6 and TNF-α during the night. Hypothesis #3: Oxidative stress is a stimulus for cytokine upregulation in OSAS.