Abstract
Introduction
Obstructive sleep apnea (OSA) is a chronic condition that is characterized by intermittent hypoxia. Key regulator of oxygen metabolism is hypoxia inducible factor (HIF), which consists of oxygen sensitive subunit and continuously produced subunit. Circadian clock is composed of set of genes, which function as activators - CLOCK and BMAL 1, who similarly to HIF are basic helix-loop-helix-PER-ARNT-SIM transcription factors. Therefore, the aim of the study was to assess the relationship between HIF-1alpha, HIF-1beta, CLOCK, BMAL1 and polysomnography (PSG) variables in healthy individuals and severe OSA patients.
Methods
The study included 20 individuals, who underwent PSG and based on apnea-hypopnea index (AHI) were divided into severe OSA group (n=10; AHI30; 90% male) and healthy control (n=10; AHI<5; 70% male). All participants had their peripheral blood collected in the evening (9:00-10:00 pm) before and in the morning (6:00-7:00 am) after the PSG. HIF-1alpha, HIF-1beta, CLOCK and BMAL1 protein concertation measurements were performed using ELISA.
Results
Significant difference was observed in the following protein measurements between study groups: evening and morning HIF-1 (p=0.020 and p=0.043, respectively), evening HIF-1alpha (p=0.047), evening and morning CLOCK (p=0.037 and p=0.019, respectively) and morning BMAL1 (p=0.016). No differences were observed between morning and evening protein levels in both groups. Evening HIF-1beta corraleted with evening CLOCK and morning BMAL1 (R=0.511, p=0.21 and R=0.594, p=0.006, respectively), while morning HIF-1 with evening BMAL1 (R=474, p=0.35). Furthermore, evening and morning HIF-1 correlated with evening BMAL1 (R=564, p=0.010 and R=0.689, p=0.001, respectively). Additionally, morning CLOCK and BMAL1 correlated with AHI (R=0.510, p=0.022 and R=0.560, p=0.010, respectively) and desaturation index (R=0.487, p=0.209 and R=0.570, p=0.009, respectively).
Conclusion
There is significant correlation between both subunits of HIF-1 protein and circadian clock proteins: CLOCK and BMAL1, which further correlate with increased disease severity. This suggests OSA patients are in risk of circadian clock disruption due to present hypoxia.
Support
The study was financed by Polish National Centre Grant no. 2018/31/N/NZ5/03931.
Hitting two birds with one stone: the potential role of serum hypoxia-inducible factor-1α protein levels in obstructive sleep apnea–related cardiovascular disease. Authors' reply
