Serum Adropin as an Indicator of Endothelial Dysfunction and Disease Severity in Obstructive Sleep Apnea in Obese Patients

1. Background and Rationale ( Introduction): Obstructive Sleep Apnea (OSA) is a common sleep-related breathing disorder characterized by recurrent episodes of partial or complete upper airway obstruction during sleep, resulting in intermittent hypoxia, sleep fragmentation, and increased sympathetic nervous system activity. These pathophysiological disturbances promote oxidative stress and systemic inflammation, which contribute to vascular injury and increase cardiovascular risk in patients with OSA (Li et al., 2020). Intermittent hypoxia has been shown to induce endothelial oxidative stress and inflammatory signaling in a dose-dependent manner, with greater severity of OSA being associated with more pronounced vascular dysfunction (Ryan et al., 2021).

Endothelial dysfunction is considered a key early mechanism linking OSA to cardiovascular disease. Intermittent hypoxia impairs endothelial homeostasis mainly through reduced nitric oxide (NO) bioavailability, increased endothelin-1 activity, and activation of pro-inflammatory pathways, leading to abnormal vascular tone and progression of atherosclerosis and hypertension (Javaheri and Barbe, 2020). Importantly, endothelial dysfunction may precede overt cardiovascular disease, highlighting its value as an early therapeutic target in OSA patients.

Identifying early biomarkers of endothelial dysfunction in OSA is therefore of major clinical importance for risk stratification and prevention of cardiovascular complications. Such biomarkers may also help in monitoring disease severity and evaluating response to therapeutic interventions, including continuous positive airway pressure therapy (Ryan et al., 2021).

Adropin is a peptide hormone encoded by the ENHO gene and is involved in energy homeostasis, lipid metabolism, and endothelial function. It enhances endothelial nitric oxide synthase activity and NO production, exerting protective effects on the vascular endothelium. Experimental and clinical studies have demonstrated that reduced circulating adropin levels are associated with endothelial dysfunction, insulin resistance, and increased cardiovascular risk (Altamimi et al., 2021).

Recent studies have demonstrated significantly lower serum adropin levels in patients with obstructive sleep apnea compared to healthy controls, with negative correlations between adropin levels and apnea-hypopnea index severity, as well as positive associations with endothelial function markers (Yosaee et al., 2020; Aşkın et al., 2022). Given the central role of endothelial dysfunction in OSA-related cardiovascular morbidity and the vasoprotective properties of adropin, evaluating serum adropin levels may represent a simple and reliable marker of endothelial dysfunction in patients with obstructive sleep apnea.