Sleep-disordered breathing and cerebrovascular disease: a mechanistic approach

Mechanisms underlying the health benefits of intermittent hypoxia conditioning

Intermittent hypoxia (IH) is commonly associated with pathological conditions, particularly obstructive sleep apnoea. However, IH is also increasingly used to enhance health and performance and is emerging as a potent non-pharmacological intervention against numerous diseases. Whether IH is detrimental or beneficial for health is largely determined by the intensity, duration, number and frequency of the hypoxic exposures and by the specific responses they engender. Adaptive responses to hypoxia protect from future hypoxic or ischaemic insults, improve cellular resilience and functions, and boost mental and physical performance. The cellular and systemic mechanisms producing these benefits are highly complex, and the failure of different components can shift long-term adaptation to maladaptation and the development of pathologies. Rather than discussing in detail the well-characterized individual responses and adaptations to IH, we here aim to summarize and integrate hypoxia-activated mechanisms into a holistic picture of the body's adaptive responses to hypoxia and specifically IH, and demonstrate how these mechanisms might be mobilized for their health benefits while minimizing the risks of hypoxia exposure.

Identification biomarkers in disease progression of obstructive sleep apnea from children serum based on WGCNA and Mfuzz

Obstructive sleep apnea (OSA) syndrome is a prevalent form of respiratory sleep disorder, with an increasing prevalence among children. The consequences of OSA include obesity, diabetes, cardiovascular disease, and neuropsychological diseases. Despite its pervasive impact, a significant proportion of individuals especially children remain unaware that they suffer from OSA. Consequently, there is an urgent need for an accessible diagnostic approach. In this study, we conducted a bioinformatic analysis to identify potential biomarkers from a proteomics dataset comprising serum samples from children with OSA in the progression stage. In the Gene Set Enrichment Analysis (GSEA), we observed that the complement and immune response pathways persisted throughout the development of OSA and could be detected in the early stages. Subsequent to soft clustering and WGCNA analysis, it was revealed that the Hippo pathway, including ITGAL and FERMT3, plays a role in mild OSA. The analysis revealed a significant alteration of the complement and coagulation pathways, including TFPI and MLB2, in moderate OSA. In severe OSA, there was an association between hypoxia and the extracellular matrix (ECM) receptor interaction and collagen binding. In summary, it can be posited that the systemic inflammation may persist throughout the progression of OSA. Furthermore, severe OSA is characterized by abnormal vascular endothelial function, which may be attributed to chronic hypoxia. Finally, four potential biomarkers (ITGAL, TFPI, TTR, ANTXR1) were identified based on LASSO regression, and a prediction model for OSA progression was constructed based on the biomarkers.

Pathophysiological mechanisms and therapeutic approaches in obstructive sleep apnea syndrome

Obstructive sleep apnea syndrome (OSAS) is a common breathing disorder in sleep in which the airways narrow or collapse during sleep, causing obstructive sleep apnea. The prevalence of OSAS continues to rise worldwide, particularly in middle-aged and elderly individuals. The mechanism of upper airway collapse is incompletely understood but is associated with several factors, including obesity, craniofacial changes, altered muscle function in the upper airway, pharyngeal neuropathy, and fluid shifts to the neck. The main characteristics of OSAS are recurrent pauses in respiration, which lead to intermittent hypoxia (IH) and hypercapnia, accompanied by blood oxygen desaturation and arousal during sleep, which sharply increases the risk of several diseases. This paper first briefly describes the epidemiology, incidence, and pathophysiological mechanisms of OSAS. Next, the alterations in relevant signaling pathways induced by IH are systematically reviewed and discussed. For example, IH can induce gut microbiota (GM) dysbiosis, impair the intestinal barrier, and alter intestinal metabolites. These mechanisms ultimately lead to secondary oxidative stress, systemic inflammation, and sympathetic activation. We then summarize the effects of IH on disease pathogenesis, including cardiocerebrovascular disorders, neurological disorders, metabolic diseases, cancer, reproductive disorders, and COVID-19. Finally, different therapeutic strategies for OSAS caused by different causes are proposed. Multidisciplinary approaches and shared decision-making are necessary for the successful treatment of OSAS in the future, but more randomized controlled trials are needed for further evaluation to define what treatments are best for specific OSAS patients.

Hypothalamic Oxytocin Neuron Activation Attenuates Intermittent Hypoxia-Induced Hypertension and Cardiac Dysfunction in an Animal Model of Sleep Apnea

BACKGROUND

Obstructive sleep apnea is a prevalent and poorly treated cardiovascular disease that leads to hypertension and autonomic imbalance. Recent studies that restore cardiac parasympathetic tone using selective activation of hypothalamic oxytocin neurons have shown beneficial cardiovascular outcomes in animal models of cardiovascular disease. This study aimed to determine if chemogenetic activation of hypothalamic oxytocin neurons in animals with existing obstructive sleep apnea-induced hypertension would reverse or blunt the progression of autonomic and cardiovascular dysfunction.

METHODS

Two groups of rats were exposed to chronic intermittent hypoxia (CIH), a model of obstructive sleep apnea, for 4 weeks to induce hypertension. During an additional 4 weeks of exposure to CIH, 1 group was treated with selective activation of hypothalamic oxytocin neurons while the other group was untreated.

RESULTS

Hypertensive animals exposed to CIH and treated with daily hypothalamic oxytocin neuron activation had lower blood pressure, faster heart rate recovery times after exercise, and improved indices of cardiac function compared with untreated hypertensive animals. Microarray analysis suggested that, compared with treated animals, untreated animals had gene expression profiles associated with cellular stress response activation, hypoxia-inducible factor stabilization, and myocardial extracellular matrix remodeling and fibrosis.

CONCLUSIONS

In animals already presenting with CIH-induced hypertension, chronic activation of hypothalamic oxytocin neurons blunted the progression of hypertension and conferred cardioprotection after an additional 4 weeks of CIH exposure. These results have significant clinical translation for the treatment of cardiovascular disease in patients with obstructive sleep apnea.

Intermittent hypoxia treatments cause cellular priming in human microglia

Obstructive sleep apnoea syndrome (OSAS) is a sleep-disordered breathing characterized by nocturnal collapses of the upper airway resulting in cycles of blood oxygen partial pressure oscillations, which lead to tissue and cell damage due to intermittent hypoxia (IH) episodes. Since OSAS-derived IH may lead to cognitive impairment through not fully cleared mechanisms, herein we developed a new in vitro model mimicking IH conditions to shed light on its molecular effects on microglial cells, with particular attention to the inflammatory response. The in vitro model was set-up and validated by measuring the hypoxic state, HIF-1α levels, oxidative stress by ROS production and mitochondrial activity by MTS assay. Then, the mRNA and protein levels of certain inflammatory markers (NF-κB and interleukin 6 (IL-6)) after different IH treatment protocols were investigated. The IH treatments followed by a normoxic period were not able to produce a high inflammatory state in human microglial cells. Nevertheless, microglia appeared to be in a state characterized by increased expression of NF-κB and markers related to a primed phenotype. The microglia exposed to IH cycles and stimulated with exogenous IL-1β resulted in an exaggerated inflammatory response with increased NF-κB and IL-6 expression, suggesting a role for primed microglia in OSAS-driven neuroinflammation.

The Role of Inflammation in Cognitive Impairment of Obstructive Sleep Apnea Syndrome

Obstructive sleep apnea syndrome (OSAS) has become a major worldwide public health concern, given its global prevalence. It has clear links with multiple comorbidities and mortality. Cognitive impairment is one related comorbidity causing great pressure on individuals and society. The clinical manifestations of cognitive impairment in OSAS include decline in attention/vigilance, verbal–visual memory loss, visuospatial/structural ability impairment, and executive dysfunction. It has been proven that chronic intermittent hypoxia (CIH) may be a main cause of cognitive impairment in OSAS. Inflammation plays important roles in CIH-induced cognitive dysfunction. Furthermore, the nuclear factor kappa B and hypoxia-inducible factor 1 alpha pathways play significant roles in this inflammatory mechanism. Continuous positive airway pressure is an effective therapy for OSAS; however, its effect on cognitive impairment is suboptimal. Therefore, in this review, we address the role inflammation plays in the development of neuro-impairment in OSAS and the association between OSAS and cognitive impairment to provide an overview of its pathophysiology. We believe that furthering the understanding of the inflammatory mechanisms involved in OSAS-associated cognitive impairment could lead to the development of appropriate and effective therapy.

Incidence and risk of periodontitis in obstructive sleep apnea: A meta-analysis

Introduction

At present, the possible relationship between obstructive sleep apnea and periodontitis has been reported. The link remains ambiguous and unclear. The objective of this study is to assess the association between OSA and periodontitis.

Methods

Three databases, including Pubmed, Embase, and the Web of Science, were systematically searched to identify eligible studies that from their establishment to February 2022 for relevant studies. Subsequently, a meta-analysis was conducted to determine the relationship of pooled-effects more accurately.

Results

A summary analysis of the 9 results from the studies covering 43,414 individuals showed a statistical association results of the between OSA and the incidence rate of periodontitis(OR = 0.52; 95% CI: 0.49–0.55; I² = 98.43%; P = 0.000). In addition, OSA patients and the risk of the population were statistically significantly associated with an increased risk of periodontitis.(OR = 1.56; 95% CI: 1.06–2.06; P = 0.00).

Conclusions

Our results indicated that OSA may be associated with an increased risk of periodontitis. Further studies are required to confirm the link and explore the underlying mechanism of the link.

Detecting Obstructive Apnea Episodes using Dynamic Bayesian Networks and ECG-based Time-Series

In this study, we proposed an automatic detector for obstructive apnea episodes using only ECG-based time-series from a single-ECG channel. Several obstructive apnea episodes were provoked for different separated sequences of 15 minutes in anesthetized Sprague-Dawley rats. In this recurrent obstructive sleep apnea (OSA) model, each episode lasted 15s, while the number of total events per sequence was randomly selected. The beat-to-beat interval ( RR) and the R-wave amplitude ( Ra) time-series were extracted and processed for each sequence, and used to train Dynamic Bayesian Networks with different lags. An optimal trade-off between the lag ( L) and RMSE values was considered to select the best model to be used when detecting apnea episodes. The selected models were then used to estimate the occurrence probability of apnea episodes, p(A_t), by using a filtering approach. Finally, the time-series of the estimated probabilities were post-processed using non-overlapped 15-s epochs, to determine whether they are classified as apneic or non-apneic segments. Results showed that those lagged models with orders greater than 5, presented suitable RMSE values and become more sensitive as the order increased. A detection threshold of 0.2 seems to provide the best apnea detection performance overall, with Acc=0.81, Se=0.83 and Sp=0.79, using two ECG parameters and L=10. Clinical relevance- Dynamic Bayesian Networks represent a powerful tool to develop personalized models for apnea detection and diagnosis in OSA patients.

Inflammatory Biomarkers for Children with Sleep Disorders: A Review

Introduction Obstructive sleep apnea (OSA) syndrome is a highly prevalent problem in children. Unfortunately sleep disorders in children remain largely unreported and underdiagnosed due to various reasons. Overnight in-laboratory polysomnography (PSG) is the gold standard diagnostic method for OSA; however, it has several drawbacks. Hence there is a need for simple alternative diagnostic methods, such as biomarkers. Children with OSA seem to have an inflammatory aspect to its pathophysiology; thus the rationale for evaluating inflammatory biomarkers.

Objective This narrative review aimed to evaluate the existing knowledge regarding inflammatory biomarkers for children with sleep disorders.

Materials and Methods An extensive search of all literature linked to the topic was performed in PubMed, Medline, EBSCOhost, Cochrane library database CENTRAL, and Google Scholar search engine. Keywords used in the search included combinations of the following: inflammation, sleep disorders, children, and biomarkers. Studies in the list of references of relevant literature were also included. A total of 155 articles published in the period from 1997 to 2021 were initially included in this review. Selected articles comprised original research, meta-analysis, and systematic reviews.

Results Studies have mainly centered their investigations on serum inflammatory biomarkers, namely interleukin-6, tumor necrosis factor-α, and C-reactive protein. Very few studies investigated salivary inflammatory biomarkers in children.

Conclusion Evidence suggests that children with sleep disorders have elevated levels of salivary as well as serum inflammatory biomarkers in comparison to normal healthy children. Also increased levels of these biomarkers correlate with disease severity. However, more studies are needed to determine the sensitivity and specificity of salivary inflammatory biomarkers for children with sleep disorders.

Relationship between Sleep Stages and HRV response in Obstructive Sleep Apnea Patients

Patients suffering from obstructive sleep apnea (OSA) usually present an increased sympathetic activity caused by the intermittent hypoxia effect on autonomic control. This study evaluated the relationship between sleep stages and the apnea duration, frequency, and type, as well as their impact on HRV markers in different groups of disease severity. The hypnogram and R-R interval signals were extracted in 81 OSA patients from night polysomnographic (PSG) recordings. The apnea-hypopnea index (AHI) defined patient classification as mild-moderate (AHI<=30, n=44) or severe (AHI>30, n=37). The normalized power in VLH, LF, and HF bands of RR series were estimated by a time-frequency approach and averaged in 1-min epochs of normal and apnea segments. The autonomic response and the impact of sleep stages were assessed in both segments to compare patient groups. Deeper sleep stages (particularly S2) concentrated the shorter and mild apnea episodes (from 10 to 40 s) compared to light (SWS) and REM sleep. Longer episodes (>50 s) although less frequent, were of similar incidence in all stages. This pattern was more pronounced for the group of severe patients. Moreover, during apnea segments, LF_nu was higher (p=0.044) for the severe group, since V LF_nu and HF_nu presented the greatest changes when compared to normal segments. The non-REM sleep seems to better differentiate OSA patients groups, particularly through VLF_nu and HF_nu(p<0.001). A significant difference in both sympathetic and vagal modulation between REM and non-REM sleep was only found within the severe group. These results confirm the importance of considering sleep stages for HRV analysis to further assess OSA disease severity, beyond the traditional and clinically limited AHI values.Clinical relevance-Accounting for sleep stages during HRV analysis could better assess disease severity in OSA patients.

Unlocking mammalian regeneration through hypoxia inducible factor one alpha signaling

Historically, the field of regenerative medicine has aimed to heal damaged tissue through the use of biomaterials scaffolds or delivery of foreign progenitor cells. Despite 30 years of research, however, translation and commercialization of these techniques has been limited. To enable mammalian regeneration, a more practical approach may instead be to develop therapies that evoke endogenous processes reminiscent of those seen in innate regenerators. Recently, investigations into tadpole tail regrowth, zebrafish limb restoration, and the super-healing Murphy Roths Large (MRL) mouse strain, have identified ancient oxygen-sensing pathways as a possible target to achieve this goal. Specifically, upregulation of the transcription factor, hypoxia-inducible factor one alpha (HIF-1α) has been shown to modulate cell metabolism and plasticity, as well as inflammation and tissue remodeling, possibly priming injuries for regeneration. Since HIF-1α signaling is conserved across species, environmental or pharmacological manipulation of oxygen-dependent pathways may elicit a regenerative response in non-healing mammals. In this review, we will explore the emerging role of HIF-1α in mammalian healing and regeneration, as well as attempts to modulate protein stability through hyperbaric oxygen treatment, intermittent hypoxia therapy, and pharmacological targeting. We believe that these therapies could breathe new life into the field of regenerative medicine.

Molecular determinants of obstructive sleep apnea

Obstructive sleep apnea (OSA) is characterized as recurrent episodes of obstruction in the upper airway during the period of sleep. The condition occurs in approximately 11% and 4% of middle-aged men and middle-aged women, respectively. Polysomnography is a diagnostic procedure that involves the constant observation of oxygen saturation and unsaturation during sleep. Usually, positive airway pressure is considered a benchmark treatment for OSA. This review summarizes the recent developments and emerging evidence from molecular biology-based research studies that show that genetic factors have an influence on OSA. The genetic aspects of OSA that have been identified include heritability and other phenotypic co-factors such as anatomical morphology. It also draws attention to the results of a polymorphic-based study that was conducted to determine the causative single nucleotide mutations associated with obesity and adverse cardiovascular risk in OSA. However, the role of such mutations and their linkage to OSA can not yet be established. Nonetheless, a large body of evidence supports a strong association between inflammatory cytokine polymorphism and obesity in the development of OSA. There are also probable intermediate factors with several gene-gene interactions. Therefore, advanced applications and modern techniques should be applied to facilitate new findings and to minimize the risk of developing OSA.

Effects of chronic intermittent hypoxia caused by obstructive sleep apnea on lipopolysaccharide-induced acute lung injury

AIM OF THE STUDY

Obstructive sleep apnea (OSA) is a common disease associated with significant morbidity and mortality. Sleep quality is an important issue; some patients with acute lung injury (ALI) have underlying OSA. However, the potential influences of OSA on ALI have not been reported until now. In this study, we evaluated the impact of preceding intermittent hypoxia (IH), a typical characteristic of OSA, on lipopolysaccharide (LPS)-induced ALI in a mouse model.

METHODS

C57BL/6J mice were randomly divided into four groups: room air-control (RA-CTL), intermittent hypoxia-control (IH-CTL), room air-lipopolysaccharide (RA-LPS), and intermittent hypoxia-lipopolysaccharide (IH-LPS) groups. The mice were exposed to RA or IH (20 cycles/h, FiO₂ nadir 7 ± 0.5%, 8 h/day) for 30 days. The LPS groups received intratracheal LPS on day 28.

RESULTS

The IH-LPS group tended to exhibit more severe inflammation, fibrosis, and oxidative stress compared to the other groups, including the RA-LPS group. Total cell, neutrophil, and eosinophil counts in bronchoalveolar lavage fluid increased significantly in the IH-LPS group compared to the RA-LPS group. Compared to the RA-LPS group, the hydroxyproline level increased significantly in the IH-LPS group. In addition, the IH-LPS group exhibited significantly more terminal deoxynucleotidyl transferase dUTP nick end labeled-positive cells compared to the RA-LPS group.

CONCLUSIONS

We found that prior IH may negatively impact LPS-induced ALI in a mouse model. This result suggests that ALI in patients with OSA may be more of a concern. Further research into the mechanisms underlying the effects of IH on ALI is needed.

Hypoxia-induced Effects on ECG Depolarization by Time Warping Analysis during Recurrent Obstructive Apnea

In this work, we evaluated a non-linear approach to estimate morphological variations in ECG depolarization, in the context of intermittent hypoxia (IH). Obstructive apnea sequences were provoked for 15 minutes in anesthetized Sprague-Dawley rats, alternating with equal periods of normal breathing, in a recurrent obstructive sleep apnea (OSA) model. Each apnea episode lasted 15 s, while the frequency used for each sequence was randomly selected. Average heartbeats obtained before the start and at the end of each episode, were delineated to extract only the QRS wave. Then, the segmented QRS waves were non-linearly aligned using the dynamic time warping (DWT) algorithm. Morphological QRS changes in both the amplitude and temporal domains were estimated from this alignment procedure. The hypoxic and basal segments were analyzed using ECG (lead I) recordings acquired during the experiment. To assess the effects of IH over time, the changes relative to the basal QRS wave were determined, in the intervals prior to each successive events until the end of the experiment. The results showed a progressive increase in the amplitude and time-domain morphological markers of the QRS wave along the experiment, which were strongly correlated with the changes in traditional QRS markers (r ≈ 0.9). Significant changes were found between pre-apnea and hypoxic measures only for the time-domain analysis (p<0.001), probably due to the short duration of the simulated apnea episodes.Clinical relevance Increased variability in ECG depolarization morphology during recurrent hypoxic episodes would be closely related to the expression of cardiovascular dysfunction in OSA patients.

Non-linear HRV Analysis to Quantify the Effects of Intermittent Hypoxia Using an OSA Rat Model

In this paper, a non-linear HRV analysis was performed to assess fragmentation signatures observed in heartbeat time series after intermittent hypoxia (IH). Three markers quantifying short-term fragmentation levels, PIP, IALS and PSS, were evaluated on R-R interval series obtained in a rat model of recurrent apnea. Through airway obstructions, apnea episodes were periodically simulated in six anesthetized Sprague-Dawley rats. The number of apnea events per hour (AHI index) was varied during the first half of the experiment while apnea episodes lasted 15 s. For the second part, apnea episodes lasted 5, 10 or 15 s, but the AHI index was fixed. Recurrent apnea was repeated for 15-min time intervals in all cases, alternating with basal periods of the same duration. The fragmentation markers were evaluated in segments of 5 minutes, selected at the beginning and end of the experiment. The impact of the heart and breathing rates (HR and BR, respectively) on the parameter estimates was also investigated. The results obtained show a significant increase (from 5 to 10%, p <; 0.05) in fragmentation measures of heartbeat time series after IH, indicating a clear deterioration of the initial conditions. Moreover, there was a strong linear relationship (r > 0.9) between these markers and BR, as well as with the ratio given by HR/BR. Although fragmentation may be impacted by IH, we found that it is highly dependent on HR and BR values and thus, they should be considered during its calculation or used to normalize the fragmentation estimates.

Obstructive sleep apnea, nighttime arousals, and leukocyte telomere length: the Multi-Ethnic Study of Atherosclerosis

STUDY OBJECTIVES

Sleep disturbances and sleep apnea are associated with increased vulnerability to age-related disease, altering molecular pathways affecting biological aging. Telomere length captures one component of biological aging. We evaluated whether objectively assessed sleep and sleep apnea relate to leukocyte telomere length (LTL) in the Multi-Ethnic Study of Atherosclerosis (MESA).

METHODS

Men and women aged 44-84 years (n = 672) from the MESA Stress and MESA Sleep studies underwent polysomnography and 7 day actigraphy (at Exam 5) and assessment of LTL (at baseline [Exam 1] and about 10 years later [Exam 5]).

RESULTS

General linear models adjusting for age, sex, race/ethnicity, BMI, physical activity, and smoking found that severe obstructive sleep apnea (OSA; apnea-hypopnea index > 30) was cross-sectionally associated with shorter LTL (p = 0.007). Modest associations of shorter LTL with less rapid eye movement sleep, more stage 1 sleep, wake after sleep onset >30 min, and long sleep duration were found, but these effects were diminished after adjusting for lifestyle and OSA. Exploratory analyses found that higher arousal index at Exam 5 was associated with greater LTL decline over the prior 10 years (p = 0.004).

CONCLUSIONS

OSA was associated with shorter LTL. Individuals with high-arousal frequency had greater leukocyte telomere attrition over the prior decade. These findings suggest that sleep apnea and sleep fragmentation are associated with accelerated biological aging.

Alteration of Inflammatory Mediators in the Upper and Lower Airways under Chronic Intermittent Hypoxia: Preliminary Animal Study

Purpose

We hypothesized that CIH may affect the upper airway immune system and aimed to verify whether CIH can induce airway inflammation in a murine obstructive sleep apnea (OSA) model.

Methods

C57BL6 male mice were exposed to intermittent hypoxia (CIH group; 5 ~ 21% FiO₂, 120 sec cycles, 12 h/d, n = 6) or room air (Sham group, n = 6) for up to 4 weeks in identical chambers. Nasal and lung tissues and lavage fluid were collected and analyzed by multiplex assay. Lung lavage fluid was also utilized for FACS analysis to determine eosinophil count.

Results

We determined the protein level of 24 different cytokines, chemokines, and inflammatory mediators. Among various cytokines, levels of IL-1α, IL-1β, IL-4, IL-6, and IL-13 were significantly elevated in nose or lung tissue from the CIH group. In addition, MCP-1 and periostin were elevated in nose and lung tissue and lavage fluid from the CIH group.

Conclusions

CIH for 4 weeks altered the levels of inflammatory mediators in both the nose and lungs of mouse model. We suggest that the airway immune system may be deteriorated by CIH and allergic inflammation in the upper or lower airway could be worsened by sleep apnea.

Impaired plasma clot lysis and its determinants in patients with obstructive sleep apnea syndrome

Evidence indicates that hypercoagulability and impaired fibrinolysis have been observed in patients with obstructive sleep apnea syndrome (OSAS). It is unclear which factors determine prolonged fibrin clot lysis in OSAS. One hundred and sixty-five consecutive patients suspected of OSAS underwent overnight polysomnography. Prior to polysomnography, we determined plasma clot lysis time (CLT), plasminogen activator inhibitor (PAI)-1 antigen, activated thrombin-activatable fibrinolysis inhibitor (TAFIa), plasmin, and antiplasmin. OSAS was diagnosed in 110 (66.7%) patients, including 35 (31.8%) with severe OSAS, 26 (23.6%) with moderate OSAS, and 49 (44.6%) mild OSAS. Compared with 55 (33.3%) individuals in whom OSAS was not confirmed, OSAS patients had prolonged CLT (+12.8%), associated with higher PAI-1 antigen (+18.1%) (after adjustment for age, diabetes, and body mass index; both P < 0.01) and similar levels of TAFIa, plasmin, or antiplasmin. PAI-1, TAFIa, and CLT correlated positively with apnea/hypopnea index, which reflects the severity of OSAS (R = 0.66, P < 0.001; R = 0.29, P = 0.002; R = 0.55, P = 0.001, respectively), and with other polysomnography parameters, with the most potent correlations observed for desaturation index. Regression analysis adjusted for potential confounders showed that in OSAS, CLT was independently predicted by apnea/hypopnea index (B = 0.29, P = 0.002), PAI-1 (B = 0.42, P < 0.001), and TAFIa (B = 0.81, P = 0.044), whereas both PAI-1 and TAFIa were predicted only by desaturation index (B = 0.24, P = 0.002; and B = 0.14, P = 0.001, respectively). The severity of OSAS is closely associated with hypofibrinolysis measured in a global plasma-based assay, driven largely by PAI-1. Attenuated fibrinolysis might contribute to high risk of thromboembolic events in this disease.

Dynamic changes in sleep-related breathing abnormalities in bilateral paramedian mesencephalon and thalamus stroke: a follow-up case study

BACKGROUND

Bilateral paramedian thalamic stroke is characterized by hypersomnia, vertical gaze palsy, amnestic alteration, and apathic state. Combined lesion of the paramedian thalamus and mesencephalon bilaterally is extremely rare. Little is known about the breathing disturbances of the particular region due to the lesion. The following describes the specific case of a woman, age 62, with bilateral paramedian thalamic and mesencephalic stroke. Initially, the patient's complaints exhibited altered vigilance and vertical gaze palsy. Notably, following the acute phase, fluctuating hypersomnia was detected. The MRI (brain) revealed an ischemic lesion in the medial part of the mesencephalon and paramedian thalamus, bilaterally.

AIMS

The aim of the present study is to elucidate the involvement and characteristics of sleep-related breathing abnormalities in the clinical manifestation of the combined paramedian thalamic and mesencephalic stroke.

METHODS

Polysomnographic recordings were accomplished seven times with 1-week interval between the consecutive recordings, toward investigating the early changes of sleep and sleep-related breathing abnormalities.

RESULTS

Sleep structure examination featured a decrease in N3 and REM ratio and an increase in N1 and N2 ratio with minimal improvement during the recovery period. In contrast, significant changes were found in the breathing pattern: the initial central apnea dominance was followed by obstructive apneas with a gradual decrease of the total pathological respiratory events.

CONCLUSION

In addition to the structural abnormality of the sleep regulating network, sleep-disordered breathing is another possible cause of hypersomnia in patients afflicted with the present localization of the lesion.

Antioxidants inhibit the inflammatory and apoptotic processes in an intermittent hypoxia model of sleep apnea

BACKGROUND

Sleep apnea causes intermittent hypoxia (IH). We aimed to investigate the proteins related to oxidative stress, inflammation and apoptosis in liver tissue subjected to IH as a simulation of sleep apnea in conjunction with the administration of either melatonin (MEL, 200 μL/kg) or N-acetylcysteine (NAC, 10 mg/kg).

METHODS

Seventy-two adult male Balb-C mice were divided: simulation of IH (SIH), SIH + MEL, SIH + NAC, IH, IH + MEL and IH + NAC. The animals were subjected to simulations of sleep apnea for 8 h a day for 35 days. The data were analyzed with ANOVA and Tukey tests with the significance set at p < 0.05.

RESULTS

In IH, there was a significant increase in oxidative stress and expression of HIF-1a. In addition, we observed increase in the activation levels of NF-kB. This increase may be responsible for the increased expression of TNF-alpha and iNOS as well as the significant increase of VEGF signaling and expression of caspase-3 and caspase-6, which suggests an increase in apoptosis. In the groups treated with antioxidants, the analysis showed that the enzyme activity and protein levels were similar to those of the non-simulated group.

CONCLUSIONS

Thus, we show that IH causes liver inflammation and apoptosis, which may be protected with either MEL or NAC.

Therapeutic potential of intermittent hypoxia: a matter of dose

Intermittent hypoxia (IH) has been the subject of considerable research in recent years, and triggers a bewildering array of both detrimental and beneficial effects in multiple physiological systems. Here, we review the extensive literature concerning IH and its impact on the respiratory, cardiovascular, immune, metabolic, bone, and nervous systems. One major goal is to define relevant IH characteristics leading to safe, protective, and/or therapeutic effects vs. pathogenesis. To understand the impact of IH, it is essential to define critical characteristics of the IH protocol under investigation, including potentially the severity of hypoxia within episodes, the duration of hypoxic episodes, the number of hypoxic episodes per day, the pattern of presentation across time (e.g., within vs. consecutive vs. alternating days), and the cumulative time of exposure. Not surprisingly, severe/chronic IH protocols tend to be pathogenic, whereas any beneficial effects are more likely to arise from modest/acute IH exposures. Features of the IH protocol most highly associated with beneficial vs. pathogenic outcomes include the level of hypoxemia within episodes and the number of episodes per day. Modest hypoxia (9-16% inspired O2) and low cycle numbers (3-15 episodes per day) most often lead to beneficial effects without pathology, whereas severe hypoxia (2-8% inspired O2) and more episodes per day (48-2,400 episodes/day) elicit progressively greater pathology. Accumulating evidence suggests that "low dose" IH (modest hypoxia, few episodes) may be a simple, safe, and effective treatment with considerable therapeutic potential for multiple clinical disorders.

Ceftriaxone preserves glutamate transporters and prevents intermittent hypoxia-induced vulnerability to brain excitotoxic injury

Hypoxia alters cellular metabolism and although the effects of sustained hypoxia (SH) have been extensively studied, less is known about chronic intermittent hypoxia (IH), commonly associated with cardiovascular morbidity and stroke. We hypothesize that impaired glutamate homeostasis after chronic IH may underlie vulnerability to stroke-induced excitotoxicity. P16 organotypic hippocampal slices, cultured for 7 days were exposed for 7 days to IH (alternating 2 min 5% O₂ - 15 min 21% O₂), SH (5% O₂) or RA (21% O₂), then 3 glutamate challenges. The first and last exposures were intended as a metabolic stimulus (200 µM glutamate, 15 min); the second emulated excitotoxicity (10 mM glutamate, 10 min). GFAP, MAP2, and EAAT1, EAAT2 glutamate transporters expression were assessed after exposure to each hypoxic protocol. Additionally, cell viability was determined at baseline and after each glutamate challenge, in presence or absence of ceftriaxone that increases glutamate transporter expression. GFAP and MAP2 decreased after 7 days IH and SH. Long-term IH but not SH decreased EAAT1 and EAAT2. Excitotoxic glutamate challenge decreased cell viability and the following 200 µM exposure further increased cell death, particularly in IH-exposed slices. Ceftriaxone prevented glutamate transporter decrease and improved cell viability after IH and excitotoxicity. We conclude that IH is more detrimental to cell survival and glutamate homeostasis than SH. These findings suggest that impaired regulation of extracellular glutamate levels is implicated in the increased brain susceptibility to excitotoxic insult after long-term IH.

The polymorphic and contradictory aspects of intermittent hypoxia

Intermittent hypoxia (IH) has been extensively studied during the last decade, primarily as a surrogate model of sleep apnea. However, IH is a much more pervasive phenomenon in human disease, is viewed as a potential therapeutic approach, and has also been used in other disciplines, such as in competitive sports. In this context, adverse outcomes involving cardiovascular, cognitive, metabolic, and cancer problems have emerged in obstructive sleep apnea-based studies, whereas beneficial effects of IH have also been identified. Those a priori contradictory findings may not be as contradictory as initially thought. Indeed, the opposite outcomes triggered by IH can be explained by the specific characteristics of the large diversity of IH patterns applied in each study. The balance between benefits and injury appears to primarily depend on the ability of the organism to respond and activate adaptive mechanisms to IH. In this context, the adaptive or maladaptive responses can be generally predicted by the frequency, severity, and duration of IH. However, the presence of underlying conditions such as hypertension or obesity, as well as age, sex, or genotypic variance, may be important factors tilting the balance between an appropriate homeostatic response and decompensation. Here, the two possible facets of IH as derived from human and experimental animal settings will be reviewed.

Obstructive sleep apnea and cognitive impairment: addressing the blood-brain barrier

Increasing data support a connection between obstructive sleep apnea (OSA) and cognitive impairment but a causal link has yet to be established. Although neuronal loss has been linked to cognitive impairment, emerging theories propose that changes in synaptic plasticity can cause cognitive impairment. Studies demonstrate that disruption to the blood-brain barrier (BBB), which is uniquely structured to tightly maintain homeostasis inside the brain, leads to changes in the brain's microenvironment and affects synaptic plasticity. Cyclical intermittent hypoxia is a stressor that could disrupt the BBB via molecular responses already known to occur in either OSA patients or animal models of intermittent hypoxia. However, we do not yet know if or how intermittent hypoxia can cause cognitive impairment by mechanisms operating at the BBB. Therefore, we propose that initially, adaptive homeostatic responses at the BBB occur in response to increased oxygen and nutrient demand, specifically through regulation of influx and efflux BBB transporters that alter microvessel permeability. We further hypothesize that although these responses are initially adaptive, these changes in BBB transporters can have long-term consequences that disrupt the brain's microenvironment and alter synaptic plasticity leading to cognitive impairment.

Melatonin ameliorates endothelial dysfunction, vascular inflammation, and systemic hypertension in rats with chronic intermittent hypoxia

The pathogenesis of hypertension in patients with obstructive sleep apnea (OSA) is associated with endothelial dysfunction induced by chronic intermittent hypoxia (IH). Studies have shown that administration of melatonin ameliorates oxidative injury and inflammation. This study examined the effect of melatonin on the oxidative stress, endothelial dysfunction, and inflammation during the pathogenesis of hypertension in chronic IH. Adult Sprague-Dawley rats that had received a daily injection of melatonin or vehicle were exposed to IH treatment mimicking a severe OSA condition for 14-21 days. Systolic pressure was significantly higher in the vehicle-treated (144 ± 2.7 mmHg) but not in the melatonin-treated rats (123 ± 5.1 mmHg) by 21-day IH treatment when compared with the normoxic control. Levels of malondialdehyde and the expressions of NADPH oxidase, pro-inflammatory mediators (TNF-α, inducible NO synthase, COX-2), and adhesion molecules (ICAM-1, VCAM-1, and E-selectin) of the thoracic aorta were markedly increased by 14-day IH treatment preceding the hypertensive response. Also, levels of nitric oxide (NO˙), endothelial-dependent relaxation, and the expressions of endothelial NO synthase (eNOS) and antioxidant enzymes (GPx, CAT, and Cu/Zn SOD) were significantly lowered in the IH rats. Melatonin treatment significantly mitigated the increased expression of NADPH oxidase, pro-inflammatory mediators, and adhesion molecules. Moreover, melatonin prevented the endothelial dysfunction with ameliorated levels of NO˙, endothelial-dependent relaxation, and expressions of eNOS and antioxidant enzymes. These results suggest that melatonin is protective against IH-induced hypertension and endothelial dysfunction via an antioxidant and anti-inflammatory mechanism.

Association Between Serum Fetuin-A levels, Carotid Artery Stiffness, and Intima–Media Thickness in Patients With Normotensive Obstructive Sleep Apnea Syndrome

Increased carotid intima–media thickness (cIMT) and stiffness, reflecting subclinical atherosclerosis, are associated with obstructive sleep apnea syndrome (OSAS). The relationship between serum fetuin-A, which inhibits ectopic calcification, and atherosclerosis is unclear. Therefore, we investigated the association between serum fetuin-A levels and carotid artery stiffness and cIMT in patients with normotensive OSAS (n = 50) and non-OSAS controls (n = 38). Compared with controls, there were lower fetuin-A levels (59.4 ± 6.5 vs 68.2 ± 5.8 ng/mL, P = .029), higher mean cIMT (0.73 ± 0.2 vs 0.63 ± 0.3 mm, P < .001), and greater stiffness (β) index (7.45 ± 0.9 vs 5.2 ± 0.7, P = .001) in the OSAS group. The cIMT and stiffness (β) index were inversely correlated with fetuin-A levels ( r = −.324, P = .033; r = −.466, P < .001, respectively) and positively correlated with apnea hypopnea index ( r = .498, P < .001; r = .422, P = .001, respectively) in the OSAS group. Decreased serum fetuin-A levels were associated with subclinical carotid atherosclerosis in patients with normotensive OSAS.

Serum cardiotrophin-1 and IL-6 levels in patients with obstructive sleep apnea syndrome

Obstructive sleep apnea syndrome (OSAS) is associated with increased rates of cardiovascular diseases (CVD). Basic mechanisms involved in the increased cardiovascular risk of OSAS remain unclear. Inflammation has been shown to potentially play a critical role in this association. The aim of the present study was to investigate the level of cardiotrophin-1 (CT-1) in patients with OSAS. Forty-eight newly diagnosed OSAS patients and 37 nonapneic controls were enrolled in this study. Demographic data, cigarette smoking status, previous history of chronic diseases including CVD and metabolic diseases and drugs, and habits were obtained by a standardized questionnaire. All patients underwent polysomnographic evaluation. The mean age was 48.3 ± 12.3 (24-74) years in OSAS group. Median apnea-hypopnea index was 23.6 (6-91.8) and median body mass index was 30.4 (24.2-49.4) in the OSAS group. Plasma CT-1 levels in OSAS and control groups, respectively, were 12.03 ± 1.08 and 11.85 ± 1.18 pg/ml. There was no significant difference in the plasma levels of CT-1 and IL-6 between the OSAS group and the controls.

Simulating sleep apnea by exposure to intermittent hypoxia induces inflammation in the lung and liver

Sleep apnea is a breathing disorder that results from momentary and cyclic collapse of the upper airway, leading to intermittent hypoxia (IH). IH can lead to the formation of free radicals that increase oxidative stress, and this mechanism may explain the association between central sleep apnea and nonalcoholic steatohepatitis. We assessed the level of inflammation in the lung and liver tissue from animals subjected to intermittent hypoxia and simulated sleep apnea. A total of 12 C57BL/6 mice were divided into two groups and then exposed to IH (n = 6) or a simulated IH (SIH) (n = 6) for 35 days. We observed an increase in oxidative damage and other changes to endogenous antioxidant enzymes in mice exposed to IH. Specifically, the expression of multiple transcription factors, including hypoxia inducible factor (HIF-1α), nuclear factor kappa B (NF-κB), and tumor necrosis factor (TNF-α), inducible NO synthase (iNOS), vascular endothelial growth factor (VEGF), and cleaved caspase 3 were shown to be increased in the IH group. Overall, we found that exposure to intermittent hypoxia for 35 days by simulating sleep apnea leads to oxidative stress, inflammation, and increased activity of caspase 3 in the liver and lung.

Cardiac response to chronic intermittent hypoxia with a transition from adaptation to maladaptation: the role of hydrogen peroxide

Obstructive sleep apnea (OSA) is a highly prevalent respiratory disorder of sleep, and associated with chronic intermittent hypoxia (CIH). Experimental evidence indicates that CIH is a unique physiological state with potentially “adaptive” and “maladaptive” consequences for cardio-respiratory homeostasis. CIH is also a critical element accounting for most of cardiovascular complications of OSA. Cardiac response to CIH is time-dependent, showing a transition from cardiac compensative (such as hypertrophy) to decompensating changes (such as failure). CIH-provoked mild and transient oxidative stress can induce adaptation, but severe and persistent oxidative stress may provoke maladaptation. Hydrogen peroxide as one of major reactive oxygen species plays an important role in the transition of adaptive to maladaptive response to OSA-associated CIH. This may account for the fact that although oxidative stress has been recognized as a driver of cardiac disease progression, clinical interventions with antioxidants have had little or no impact on heart disease and progression. Here we focus on the role of hydrogen peroxide in CIH and OSA, trying to outline the potential of antioxidative therapy in preventing CIH-induced cardiac damage.

Wake-up or unclear-onset strokes: are they waking up to the world of thrombolysis therapy?

Wake-up or unclear-onset strokes occur in up to one-fourth of patients with ischemic stroke. Although stroke severity and clinical outcomes appear to be poorer in wake-up strokes than nonwake-up strokes, many patients with wake-up strokes do not receive thrombolytic therapy because stroke onset time cannot be determined. Recent studies have suggested, however, that the actual onset time of wake-up stroke is close to the wake-up time. Furthermore, advanced imaging technologies may enable us to identify patients with favorable risk-benefit profiles for thrombolysis. Indeed, empirical thrombolytic treatments have suggested safety and feasibility of such therapy in these patients. Based on these promising results and the development of multimodal imaging methods, prospective thrombolysis trials using predefined imaging criteria are currently under way to test the safety and efficacy of thrombolysis in patients with wake-up or unclear-onset strokes. The establishment of optimal acute treatment strategies in this important yet so far neglected group of patients is eagerly awaited.

Sleep apnea and risk of deep vein thrombosis: a non-randomized, pair-matched cohort study

BACKGROUND

Patients with sleep apnea have been reported to be associated with increased prevalence of deep vein thrombosis (DVT) in some papers, which were criticized for either a small sample size or lack of a prospective control. Our study strived to explore the relationship of sleep apnea and the subsequent development of DVT using a nationwide, population-based database.

METHODS

From 2000 to 2007, we identified a study cohort consisting of newly diagnosed sleep apnea cases in the National Health Insurance Research Database. A control cohort without sleep apnea, matched for age, sex, comorbidities, major operation, and fractures, was selected for comparison. The 2 cohorts were followed-up, and we observed the occurrence of DVT by registry of DVT diagnosis.

RESULTS

Of the 10,185 sampled patients (5680 sleep apnea patients vs. 4505 control), 40 (0.39%) cases developed DVT during a mean follow-up period of 3.56 years, including 30 (0.53%) from the sleep apnea cohort and 10 (0.22 %) from the control group. Subjects with sleep apnea experienced a 3.113-fold (95% confidence interval, 1.516-6.390; P=.002) increase in incident DVT, which was independent of age, sex, and comorbidities. Kaplan-Meier analysis also revealed the tendency of sleep apnea patients toward DVT development (log-rank test, P=.001). The risk of DVT was even higher in sleep apnea cases who needed continuous positive airway pressure treatment (hazard ratio 9.575; 95% confidence interval, 3.181-28.818; P <.001).

CONCLUSION

Sleep apnea may be an independent risk factor for DVT.

Relationship between sleep-disordered breathing and markers of systemic inflammation in women from the general population

Sleep-disordered breathing (SDB) is a risk factor for cardiovascular disease (CVD). The underlying pathogenesis is not clear. In patients with obstructive sleep apnoea syndrome (OSAS) elevated levels of inflammatory markers, such as C-reactive protein (CRP), interleukin-6 (IL-6) and tumour necrosis factor α (TNFα) have been found. These markers have also been shown as independent markers of CVD in other populations. The aim of the study was to investigate the association between SDB and systemic inflammation in a population-based cohort of women. From 6817 women who previously answered a questionnaire concerning snoring habits, 230 habitually snoring women and 170 women regardless of snoring status went through polysomnography, anthropometric measurements and blood sampling. Analyses were made for CRP, TNFα, IL-6, myeloperoxidase (MPO) and lysozyme. The levels of CRP, IL-6 and lysozyme were significantly higher in subjects with apnoea-hypopnoea index (AHI) ≥15 compared with women with lower AHI. All inflammatory markers except MPO correlated to AHI and oxygen desaturation measures, and to waist circumference. In multiple linear regressions adjusting for age, waist circumference and smoking, independent correlations between oxygen desaturation indices (ODI) and inflammation were found for IL-6 (P = 0.03 for % sleep time with saturation <90%) and TNFα (P = 0.03 for ODI 3%). No significant correlations were found between AHI and inflammation. Also, for women from the general population there is an independent correlation between SDB and inflammation, even after adjusting for obesity. The results indicate that intermittent hypoxia, and not the AHI, is related to systemic inflammation seen in OSAS.

Impact of obstructive sleep apnea on cognitive performance

OBJECTIVE: To evaluate the impact of obstructive sleep apnea (OSA) on cognition. METHOD: We compared the performance of 17 patients with polysomnographic diagnosis of OSA in brief cognitive tests to that of 20 healthy controls, matched for age and education. The testing battery included the Mini-Mental State Examination (MMSE), Brief Cognitive Screening Battery (BCSB), Digit-Symbol (DS) and Phonemic Verbal Fluency (FAS). Anthropometric measures and scores from the Epworth Sleepiness Scale were also recorded. RESULTS: OSA patients performed significantly worse than controls in the MMSE, in memory items from the BCSB, in DS and also in FAS. OSA patients also exhibited higher body mass index, increased neck circumference and higher scores in Epworth Sleepiness Scale than controls. CONCLUSION: OSA significantly impairs cognitive performance, especially within the domains of attention, memory and executive functioning. These deficits may be detected by brief and easy-to-administer cognitive tests.

Endothelial mechanisms of endothelial dysfunction in patients with obstructive sleep apnea

BACKGROUND

Obstructive sleep apnea (OSA) occurs in 2% of middle-aged women and 4% of middle-aged men in the general population and the prevalence is much higher in specific patient groups. Intermittent hypoxia (IH, oxygen desaturation and re-oxygenation) cycle, a major pathophysiologic character of OSA, and the physiological responses this evokes are thought to be responsible for its association with increased cardiovascular morbidity and mortality. Endothelial dysfunction, resulting from IH and as a key early event in atherosclerosis, was demonstrated repeatedly in patients with OSA and in animal models of IH, providing an important mechanistic link between the acute cyclical IH during sleep and the increased prevalence of chronic vascular diseases.

CONCLUSIONS

From this work, we conclude that IH from OSA may result in endothelial dysfunction, as a potential promoter of atherosclerosis, through nitric oxide unavailability, oxidative stress and inflammation, cell apoptosis, the crosstalk between endothelial cells and circulating inflammatory cells, microparticles, and damage repairing process. Though effective continuous positive airway pressure (CPAP) may specifically improve endothelial function, more controlled larger interventional trials that will include multiple centers and randomized allocation of CPAP therapy are needed to see if such changes are reversible before cause and effect can be implied finally, while further studies on cellular and animal level are also needed to elucidate molecular biologic/pathologic pathways.

Sleep-disordered breathing and pregnancy: potential mechanisms and evidence for maternal and fetal morbidity

PURPOSE OF REVIEW

This article reviews current data on pathophysiologic mechanisms by which sleep-disordered breathing during pregnancy may cause harm, and explores biological pathways for associated adverse maternal and fetal outcomes, especially pregnancy-induced hypertension and gestational diabetes.

RECENT FINDINGS

Accumulating data indicate that snoring and sleep apnea during pregnancy are likely to increase the risk for gestational hypertension and preeclampsia. Several new studies have observed that sleep-disordered breathing and short sleep duration also increase the risk of gestational diabetes, similar to observations in the general population. There are varying levels of emerging evidence for potential mechanisms, including oxidative stress, increased sympathetic activity and inflammation, adipokine levels and insulin resistance, linking sleep-disordered breathing events during pregnancy to adverse outcomes.

SUMMARY

Sleep-disordered breathing and adverse maternal-fetal outcomes such as preeclampsia and gestational diabetes share a number of mechanistic pathways, and growing data in pregnant women indicate that snoring and sleep apnea increase the risk of these and other complications for both the mother and the fetus. Nevertheless, direct evidence of the pathophysiologic mechanisms by which sleep-disordered breathing during pregnancy exerts negative effects remains sparse.

Cardiovascular consequences of sleep apnea

Cardiovascular disease has been the leading cause of death since 1900. Strategies for cardiovascular disease and prevention have helped to reduce the burden of disease, but it remains an important public health challenge. Therefore, understanding the underlying pathophysiology and developing novel therapeutic approaches for cardiovascular disease is of crucial importance. Recognizing the link between sleep and cardiovascular disease may represent one such novel approach. Obstructive sleep apnea (OSA), a common form of sleep-disordered breathing, has a high and rising prevalence in the general adult population, attributable in part to the emerging epidemic of obesity and enhanced awareness. OSA has been independently linked to specific cardiovascular outcomes such as hypertension, stroke, myocardial ischemia, arrhythmias, fatal and nonfatal cardiovascular events, and all-cause mortality. Treatment of OSA may represent a novel target to reduce cardiovascular health outcomes.

Obstructive sleep apnea causes oxidative damage to plasma lipids and proteins and decreases adiponectin levels

PUPOSE: Obstructive sleep apnea (OSA) is associated with various metabolic disorders, and oxidative stress was suggested to play an important role. In the present study, we aimed to investigate serum adiponectin and oxidative stress markers, especially protein carbonyls, and to evaluate the correlation between these parameters and lipid, insulin and fasting glucose concentrations in OSA patients and controls.

METHOD

Blood was drawn from healthy male volunteers following full-night polysomnographic evaluation. Subjects were classified as controls (n = 24), mild OSA group (n = 9) and moderate-severe OSA group (n = 17) according to their apnea-hypopnea indices (AHIs). Serum lipids, fasting glucose, adiponectin, malondialdehyde (MDA), protein carbonyl concentrations, and paraoxonase activities were measured in all subjects.

RESULTS

Results of this study indicated that serum adiponectin concentrations were significantly decreased and MDA and protein carbonyl concentrations were significantly elevated in OSA patients compared to the controls. Protein carbonyl and MDA concentrations were significantly and positively correlated with AHI, while a significant negative correlation was found between adiponectin concentrations and AHI. Adiponectin levels were negatively correlated with MDA levels.

CONCLUSION

Results of this study, which is the first human study investigating and describing serum protein carbonyl concentrations in OSA patients, reveal that OSA causes increments in oxidative damage and decreases adiponectin levels. The recurrent hypoxia-reoxygenation attacks in OSA patients may activate oxidative stress, elevating sympathetic activity and leading to low levels of adiponectin.

Obstructive sleep apnea and cardiovascular disease

PURPOSE OF REVIEW

To update the reader on the most recent developments linking obstructive sleep apnea to cardiovascular disease.

RECENT FINDINGS

Significant progress has been made in defining the relationship between obstructive sleep apnea and cardiovascular disease. However, much work remains to be done to clarify the pathophysiologic mechanisms and the potential role of treatment of sleep apnea in the prevention of cardiovascular morbidity and mortality.

SUMMARY

At present there is only limited evidence to recommend the routine treatment of obstructive sleep apnea specifically for the prevention of cardiovascular disease.

Heat-shock protein 70: expression in monocytes of patients with sleep apnoea and association with oxidative stress and tumour necrosis factor-alpha

Obstructive sleep apnoea (OSA) is associated with a variety of nightly stresses, including intermittent hypoxaemia, oxidative stress and sleep fragmentation. Heat-shock proteins (HSPs) are upregulated in response to an array of environmental and metabolic stresses. We hypothesized that the OSA-related stresses would affect the expression of HSP70 in monocytes. Basal (30 min, at 37 degrees C), heat stress-induced HSP70 (30 min, at 43 degrees C) and basal tumour necrosis factor-alpha (TNF-alpha) were determined by flow cytometry in monocytes of 10 patients with OSA and 10 controls matched by age, gender and body mass index. Oxidative stress was determined by thiobarbituric acid-reactive substances (TBARS) and antioxidant paraoxonase-1 activity. Basal HSP70 expression was 1.8-fold higher in patients with OSA as compared with controls (P < 0.0005) and was significantly positively correlated with TBARS (r = 0.56, P < 0.009). However, induction of HSP70 in response to heat stress treatment was lower by 40% in OSA monocytes as compared with controls (P < 0.0003). Furthermore, heat stress-induced HSP70 expression was significantly negatively correlated with basal HSP70 expression independently of apnoea severity (r = -0.69, P < 0.0006). Also, basal intracellular TNF-alpha expression was inversely correlated with heat-shock-induced HSP70 (r = -0.78, P < 0.015) in OSA monocytes but not in controls. In conclusion, basal HSP70 overexpression that is a protective mechanism indicative of disease-associated stress was significantly higher in patients with OSA and was correlated with oxidative stress. On the other hand, in response to a defined heat-stress treatment, the induction of HSP70 was lower in patients with OSA, indicative of a possible maladaptive response to an acute stress. Correlations with oxidative stress and TNF-alpha further support this conclusion.

Mechanisms of intermittent hypoxia induced hypertension

Exposing rodents to brief episodes of hypoxia mimics the hypoxemia and the cardiovascular and metabolic effects observed in patients with obstructive sleep apnoea (OSA), a condition that affects between 5% and 20% of the population. Apart from daytime sleepiness, OSA is associated with a high incidence of systemic and pulmonary hypertension, peripheral vascular disease, stroke and sudden cardiac death. The development of animal models to study sleep apnoea has provided convincing evidence that recurrent exposure to intermittent hypoxia (IH) has significant vascular and haemodynamic impact that explain much of the cardiovascular morbidity and mortality observed in patients with sleep apnoea. However, the molecular and cellular mechanisms of how IH causes these changes is unclear and under investigation. This review focuses on the most recent findings addressing these mechanisms. It includes a discussion of the contribution of the nervous system, circulating and vascular factors, inflammatory mediators and transcription factors to IH-induced cardiovascular disease. It also highlights the importance of reactive oxygen species as a primary mediator of the systemic and pulmonary hypertension that develops in response to exposure to IH.

Obstructive sleep apnea, inflammation, and the metabolic syndrome

The combination of metabolic syndrome and obstructive sleep apnea (OSA) has been termed "syndrome Z." The prevalence of both OSA and metabolic syndrome is increasing worldwide, in part linked to the epidemic of obesity. Beyond their epidemiologic relationship, growing evidence suggests that OSA may be causally related to metabolic syndrome. We are only beginning to understand the potential mechanisms underlying the OSA-metabolic syndrome interaction. Although there is no clear consensus, there is growing evidence that alterations in the hypothalamic-pituitary axis, generation of reactive oxygen species (ROS) due to repetitive hypoxia, inflammation, and generation of adipokines may be implicated in the changes associated with both OSA and metabolic syndrome. Whether some or all of these metabolic alterations mechanistically link OSA to metabolic syndrome remains to be proven, but it is an area of intense scientific interest.

Effects of allopurinol on cardiac function and oxidant stress in chronic intermittent hypoxia

RATIONALE

Obstructive sleep apnea is associated with left ventricular (LV) dysfunction, oxidant stress, and chronic intermittent hypoxia (CIH). Allopurinol (ALLO) is a xanthine oxidase inhibitor that also scavenges free radicals.

OBJECTIVES

Using an animal model of CIH we hypothesized that ALLO decreases oxidant stress and cardiac injury.

MATERIALS AND METHODS

Rats were exposed to either CIH (nadir 4-6%, approximately once per minute) or room air (handled controls, HC) for 8 h a day for 10 days. Four treatment groups (six to ten animals per group) were studied: CIH/ALLO, CIH/placebo (PLAC), HC/ALLO, and HC/PLAC. Outcomes included myocardial lipid peroxides (LPO) for oxidant stress, fraction shortening of the LV cavity for cardiac function (LVFS) and an assay for myocyte apoptosis.

RESULTS

LPO was lower in CIH/ALLO group compared to CIH/PLAC (179 +/- 102 vs. 589 +/- 68 mcg/mg protein, p < 0.05). LVFS was greater in ALLO animals than PLAC in both CIH and HC (CIH/ALLO 48.6 +/- 2.3% vs. CIH/PLAC 38 +/- 1.4%; HC/ALLO 64.9 +/- 1.8% vs. HC/PLAC 51.5 +/- 1.5%; both p < 0.05). Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay showed fewer apoptotic nuclei in LV myocardium in CIH/ALLO compared to CIH/PLAC (38.0 +/- 1.4 vs. 48.6 +/- 2.3 positive nuclei per 2.5 mm(2) area, p < 0.05).

CONCLUSION

ALLO is associated with improvement in CIH-associated oxidant stress, myocardial dysfunction, and apoptosis in rats.

Sleep disorders and home dialysis

Sleep disorders, such as restless legs, periodic limb movements and sleep apnea, and sleep complaints such as insomnia and daytime sleepiness, are very common in end-stage renal disease patients despite treatment with 3-times-a-week conventional hemodialysis. If left untreated, they are likely to impair quality of life and may alter cardiovascular outcomes in this patient population. Home dialysis has the potential to improve sleep disorders by offering more effective dialysis than conventional modalities. Although there has been little direct comparison between the impact of home dialysis and conventional dialysis on sleep disorders, there is evidence that both nocturnal peritoneal dialysis and nocturnal hemodialysis improve sleep apnea. The impact of home dialysis on other sleep disorders and sleep complaints is less impressive, but the data, thus far, have been limited. Further research is required to evaluate the impact of home dialysis on all sleep disorders and sleep complaints in this patient population and to determine whether this improves quality of life and cardiovascular morbidity and mortality.