[Effect of sleep apnea syndrome on the vascular endothelium]

Obstructive sleep apnoea (OSA) is a common disorder associated with an increased risk of cardiovascular disease and stroke. As it is strongly associated with known cardiovascular risk factors, including obesity, insulin resistance, and dyslipidemia, OSA is an independent risk factor for hypertension. Although the association between OSA and the metabolic syndrome tends to confound studies of the independent effects of OSA on vascular disease, recent evidences from basic science to epidemiological and clinical studies suggest that OSA may add worsening pathophysiological conditions to obesity. OSA contributes to the imbalance between vasodilators and vasoconstrictors, in particular through oxidative stress-dependent catabolism of nitric oxide, increased sympathetic nerve activity, enhanced renin-angiotensin system activity and endothelin synthesis. Additionally, several recent studies suggest that OSA may be a circumstance favouring central and vascular resistance to leptin. The beneficial effects of this hormone in normal subjects, are lost during endothelial dysfunction and OSA. Moreover, high leptin concentrations, within a range observed during OSA, display adverse effects on endothelial function and vascular physiology. Through of a yet unknown mechanism, OSA per se accounts for part of the elevated serum leptin concentration reported in patients. The current standard treatment for OSA-nasal continuous positive airway pressure (CPAP)-eliminates apnoea and the ensuing acute hemodynamic changes during sleep. Accordingly, vasopressor mediators and leptin concentration are shifted toward normal values by CPAP. Thus, in addition to this effective therapy, evaluation of specific strategies targeting leptin sensitivity and vasopressor mediators may open novel perspectives for treatment of OSA and its associated end-organ damages.