Obstructive sleep apnea (OSA) is one of the risk factors for diabetes mellitus type 2 (DM2). As OSA is associated with the disruption of the circadian rhythm, it affects circadian clock proteins, including neuronal PAS domain protein 2 (NPAS2) and nuclear receptor subfamily 1 group D member 1 (Rev-Erb-α). These proteins have been shown to be related to metabolic abnormalities, i.a., insulin resistance. The present pilot study aimed to investigate the NPAS2 and Rev-Erb-α protein serum levels in the groups of patients with severe OSA and severe OSA+DM2 in comparison with healthy controls, taking into account correlations with polysomnography (PSG) parameters (e.g., oxygen saturation (SpO2) variables). A total of 40 participants were included in the study. They were split into 3 groups as follows: the OSA group (n = 17; apnea-hypopnea index (AHI) >30, no DM2); the OSA+DM2 group (n = 7; AHI > 30 and DM2); and the control group (n = 16; AHI < 5, no DM2). All participants underwent a nocturnal PSG examination and had their blood collected the following morning. The serum levels of NPAS2 and Rev-Erb-α proteins were assessed using the enzyme-linked immunosorbent assay (ELISA). The mean NPAS2 protein level was significantly lower in the OSA group as compared to healthy individuals (p = 0.017). Additionally, the OSA group presented with lower NPAS2 protein levels as compared to the OSA+DM2 group, but only a tendency was observed (p = 0.094). No differences in the Rev-Erb-α protein concentration were noticed. Furthermore, a negative correlation between AHI during rapid eye movement (REM) sleep and the NPAS2 protein serum level was observed (r = -0.478; p = 0.002). Serum NPAS2 protein might be involved in metabolic dysregulation present among OSA patients, while the mechanism itself may be associated with REM sleep.

Sleep is a complex physiological state, which can be divided into the non-rapid eye movement (NREM) phase and the REM phase. Both have some unique features and functions. This difference is best visible in electroencephalography recordings, respiratory system activity, arousals, autonomic nervous system activity, or metabolism. Obstructive sleep apnea (OSA) is a common condition characterized by recurrent episodes of pauses in breathing during sleep caused by blockage of the upper airways. This common condition has multifactorial ethiopathogenesis (e.g., anatomical predisposition, sex, obesity, and age). Within this heterogenous syndrome, some distinctive phenotypes sharing similar clinical features can be recognized, one of them being REM sleep predominant OSA (REM-OSA). The aim of this review was to describe the pathomechanism of REM-OSA phenotype, its specific clinical presentation, and its consequences. Available data suggest that in this group of patients, the severity of specific cardiovascular and metabolic complications is increased. Due to the impact of apneas and hypopneas predominance during REM sleep, patients are more prone to develop hypertension or glucose metabolism impairment. Additionally, due to the specific function of REM sleep, which is predominantly fragmented in the REM-OSA, this group presents with decreased neurocognitive performance, reflected in memory deterioration, and mood changes including depression. REM-OSA clinical diagnosis and treatment can alleviate these outcomes, surpassing the traditional treatment and focusing on a more personalized approach, such as using longer therapy of continuous positive airway pressure or oral appliance use.

Obstructive Sleep Apnea (OSA) is a disorder characterized by repeated upper airway collapse during sleep, leading to apneas and/or hypopneas, with associated symptoms like intermittent hypoxia and sleep fragmentation. One of the agents contributing to OSA occurrence and development seems to be serotonin (5-HT). Currently, the research focuses on establishing and interlinking OSA pathogenesis and the severity of the disease on the molecular neurotransmitter omnipresent in the human body—serotonin, its pathway, products, receptors, drugs affecting the levels of serotonin, or genetic predisposition. The 5-HT system is associated with numerous physiological processes such as digestion, circulation, sleep, respiration, and muscle tone—all of which are considered factors promoting and influencing the course of OSA because of correlations with comorbid conditions. Comorbidities include obesity, physiological and behavioral disorders as well as cardiovascular diseases. Additionally, both serotonin imbalance and OSA are connected with psychiatric comorbidities, such as depression, anxiety, or cognitive dysfunction. Pharmacological agents that target 5-HT receptors have shown varying degrees of efficacy in reducing the Apnea-Hypopnea Index and improving OSA symptoms. The potential role of the 5-HT signaling pathway in modulating OSA provides a promising avenue for new therapeutic interventions that could accompany the primary treatment of OSA—continuous positive airway pressure. Thus, this review aims to elucidate the complex role of 5-HT and its regulatory mechanisms in OSA pathophysiology, evaluating its potential as a therapeutic target. We also summarize the relationship between 5-HT signaling and various physiological functions, as well as its correlations with comorbid conditions.

Attention deficit hyperactivity disorder (ADHD) is a complex neurodevelopmental disorder that not only affects attention and behavior but is also intricately linked with sleep disturbances and immune system dysregulation. Recent research highlights that individuals with ADHD frequently experience sleep problems, which in turn exacerbate ADHD symptoms and contribute to cognitive and emotional difficulties. Immunological alterations, including elevated proinflammatory cytokines and hypothalamic–pituitary–adrenal axis dysfunction, have been observed among ADHD patients, suggesting a biological interplay between inflammation, sleep, and neurodevelopment. Genetic and environmental factors further modulate these relationships, influencing the onset and progression of the disorder. Thus, there is a need to find a key connecting such topics and the most vulnerable subjects in order to contribute towards a more personalized approach. This review examines the complex relationships between sleep, immunology, and ADHD, and explores the underlying mechanisms that involve circadian rhythm genes, neuroinflammation, and neurotransmitter imbalances. Our review outlines therapeutic strategies, emphasizing the importance of integrated pharmacological, behavioral, and lifestyle interventions to improve sleep quality, regulate immune responses, and ultimately enhance the overall management of ADHD.

Obstructive sleep apnea is a common sleep disorder characterized by chronic intermittent hypoxia (CIH), sleep fragmentation, and upper-airway collapse. Beyond respiratory issues, OSA significantly impacts the central nervous system, increasing the risk for mild cognitive impairment and dementia. This review synthesizes the dual nature of CIH-induced molecular cascades, describing pathways driving neurodegeneration, such as SUMOylation dysregulation, toll-like receptor signaling, and inflammasome overactivation (largely characterized in experimental and animal CIH models), and those activating endogenous neuroprotective adaptations. Physiological defense mechanisms, such as the upregulation of erythropoietin, shifts toward anaerobic glycolysis, and the activation of neurotrophic factors, may act to mitigate neuronal injury. Rather than acting as independent processes, these molecular responses form a dynamic balance between neuronal injury and endogenous neuroprotection. Here, we introduce the concept of ‘neuroprotective reserve’ as a novel, hypothesis-generating framework to describe this intrinsic buffering capacity against hypoxic stress. Understanding and clinically validating these pathways is critical for developing early diagnostic biomarkers and targeted adjunctive interventions that complement standard therapy to prevent irreversible neurocognitive decline.