Obstructive sleep apnea (OSA) is recognized as a risk factor for type 2 diabetes mellitus (DM2). Since OSA disrupts circadian rhythms, it can influence circadian clock proteins such as neuronal PAS domain protein 2 (NPAS2) and nuclear receptor subfamily 1 group D member 1 (Rev-Erb-α). These proteins have been linked to metabolic disturbances, including insulin resistance. This pilot study aimed to examine serum levels of NPAS2 and Rev-Erb-α in patients with severe OSA and those with severe OSA combined with DM2, compared to healthy controls, and to assess their correlations with polysomnography (PSG) parameters, including oxygen saturation (SpO₂) measures. Forty participants were enrolled and divided into three groups: OSA (n = 17; AHI > 30, without DM2), OSA+DM2 (n = 7; AHI > 30 with DM2), and controls (n = 16; AHI < 5, without DM2). All participants underwent overnight PSG followed by morning blood sampling. Serum NPAS2 and Rev-Erb-α levels were quantified using enzyme-linked immunosorbent assay (ELISA). Mean NPAS2 levels were significantly lower in the OSA group compared to healthy controls (p = 0.017). The OSA group also showed lower NPAS2 levels than the OSA+DM2 group, though this difference only approached significance (p = 0.094). No significant differences were observed in Rev-Erb-α concentrations. A negative correlation was found between AHI during REM sleep and NPAS2 serum levels (r = −0.478; p = 0.002). NPAS2 serum levels may play a role in the metabolic dysregulation observed in OSA patients, potentially through mechanisms linked to REM sleep.
