Interleukin-6 and Tumor Necrosis Factor-α in Patients with Obstructive Sleep Apnea-Hypopnea Syndrome

Evaluation of Serum/Plasma Levels of Interleukins (IL-6, IL-12, IL-17, IL-18, and IL-23) in Adults and Children with Obstructive Sleep Apnea: A Systematic Review, Meta-Analysis, and Trial Sequential Analysis

Obstructive sleep apnea (OSA) is a chronic inflammatory disease characterized by partial or complete upper airway obstruction during sleep. We aimed to evaluate serum/plasma levels of several cytokines (interleukin [IL]-6, IL-12, IL-17, IL-18, and IL-23) in a systematic review meta-analysis in both adults and children with OSA compared with controls. We conducted a comprehensive search of 4 digital databases (PubMed, Web of Science, Scopus, and Cochrane Library) up until October 19, 2023, without any limitations. For our meta-analysis, we used Review Manager, version 5.3, and displayed the data as the standardized mean difference (SMD) and 95% confidence interval (CI) to assess the correlation between cytokine levels and OSA. We utilized Comprehensive Meta-Analysis version 3.0 software to conduct bias analyses, meta-regression, and sensitivity analyses. From 1881 records, 84 articles were included in the systematic review and meta-analysis. In adults, the pooled SMDs for IL-6 level were 0.79 (P value < 0.00001), for IL-17 level were 0.74 (P value = 0.14), and for IL-18 level were 0.43 (P value = 0.00002). In children, the pooled SMD for IL-6 was 1.10 (P value < 0.00001), for IL-12 was 0.47 (P value = 0.10), for IL-17 was 2.21 (a P value = 0.24), for IL-18 was 0.19 (P value = 0.07), and for IL-23 was 2.46 (P value < 0.0001). The subgroup analysis showed that the ethnicity, mean body mass index, and mean apnea-hypopnea index for IL-6 levels in adults and the ethnicity for IL-6 levels in children were effective factors in the pooled SMD. The findings of the trial sequential analysis revealed that adequate evidence has been obtained. The analysis of IL levels in adults and children with OSA compared with those without OSA revealed significant differences. In adults, IL-6 and IL-18 levels were significantly higher in the OSA group, while in children, only IL-6 and IL-23 levels were significantly elevated.

Association of Tumor Necrosis Factor-Alpha, Interleukin-1β, Interleukin-8, and Interferon-γ with Obstructive Sleep Apnea in Both Children and Adults: A Meta-Analysis of 102 Articles

Background: Cytokines may have a significant impact on sleep regulation. In this meta-analysis, we present the serum/plasma levels of tumor necrosis factor-alpha (TNF-α), interleukin (IL)-8, IL-1β, and interferon-gamma (IFN-γ) in both children and adults with obstructive sleep apnea (OSA) in comparison to controls. Methods: Four electronic databases were systematically searched (PubMed, Web of Science, Scopus, and Cochrane Library) through 19 October 2023, without any restrictions on language, date, age, and sex. We used Review Manager version 5.3 to perform meta-analysis and presented the data as standardized mean difference (SMD) and 95% confidence interval (CI) values to evaluate the relationships between the levels of cytokines and OSA. Results: A total of 102 articles (150 independent studies) were included in the meta-analysis. The pooled SMDs in adults were 1.42 (95%CI: 1.11, 1.73; p < 0.00001), 0.85 (95%CI: 0.40, 1.31; p = 0.0002), 0.69 (95%CI: 0.22, 1.16; p = 0.004), and 0.39 (95%CI: -0.37, 1.16; p = 0.31) for TNF-α, IL-8, IL-1β, and IFN-γ, respectively. The pooled SMDs in children were 0.84 (95%CI: 0.35, 1.33; p = 0.0008), 0.60 (95%CI: 0.46, 0.74; p < 0.00001), 0.25 (95%CI: -0.44, 0.93; p = 0.49), and 3.70 (95%CI: 0.75, 6.65; p = 0.01) for TNF-α, IL-8, IL-1β, and IFN-γ, respectively. Conclusions: The levels of proinflammatory cytokines of TNF-α, IL-8, and IL-1β in adults, and TNF-α, IL-8, and IFN-γ in children with OSA, are significantly higher than those in controls.

The Role of Interleukin-18 in the Development and Progression of Atherosclerosis

Atherosclerosis (AS), as a chronic inflammatory disorder of the cardiovascular system, is one of the leading causes of ischemic heart disease, stroke and peripheral vascular disease. There is growing evidence on the role of innate and adaptive immunity in the pathogenesis of atherosclerosis. Interleukin-18 is one of the novel proinflammatory cytokines involved in atherogenesis, atherosclerotic plaque instability and plaque rupture. In this review, we overview the findings of preclinical and clinical studies about the role and mechanism of action of IL-18 in the pathogenesis of AS, which could offer novel prognostic and therapeutic approaches.

Does the Severity of Obstructive Sleep Apnea Have an Independent Impact on Systemic Inflammation?

Background and Objectives: This paper aims to show whether obstructive sleep apnea (OSA) severity increases the level of systemic inflammation markers regardless of body mass index (BMI) and body composition. Materials and Methods: In total, 128 patients with OSA were included in the study. Examinees were divided into two groups: one with mild OSA (apnea-hypopnea index (AHI) < 15) and one with moderate and severe OSA (AHI ≥ 15). Nutritional status was assessed using body mass index, body composition by dual X-ray absorptiometry. Systemic inflammation was assessed on the basis of plasma concentrations of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and serum level of C-reactive protein (CRP). Results: We found elevated mean values of the evaluated systemic inflammation markers (CRP, TNF-α, IL-6) in a group with AHI ≥ 15, although there was no statistical significance. Our research found a significant positive correlation with BMI (r = 0.633, p < 0.001), as well as with body fat percentage (r = 0.450, p = 0.024) and serum CRP values. Significant correlation was found between the plasma IL-6 concentration and body fat percentage (FM%) (r = 0.579, p = 0.003) and lean body mass (r = -0.501, p = 0.013). Multivariate regression analysis did not show any independent predictor (parameters of OSA, nutritional status, body composition) of the systemic inflammation markers. Conclusions: Neither one tested parameter (nutritional status and body composition) of the severity of OSA was identified as an independent prognostic factor for the severity of systemic inflammation in patients with OSA.

Association between tumor necrosis factor alpha and obstructive sleep apnea in adults: a meta-analysis update

BACKGROUND

Tumor necrosis factor-α (TNF-α) has been reported to play a part in the development of obstructive sleep apnea (OSA) and its complications. However, the relationship between TNF-α and OSA still remains inconclusive. We aimed to systematically review and synthesize studies published to date on association between the two in adults.

METHODS

We searched for English-language articles containing original human data from case-control study studies in adults≥18 years of age. The selection criteria were set according to the PICOS framework. Articles were independently reviewed by three investigators. Data regarding demographics, clinical characteristics, and TNF-α levels were obtained. A random-effects model was applied to evaluate the overall effect sizes by calculating standard mean difference (SMD) and its 95% confidence intervals (CIs).

RESULTS

Of 393 identified abstracts, 50 articles (3503 OSA patients and 3379 health controls) were ultimately included in this meta-analysis. The results indicated that the TNF-α level in patients with OSA was 1.77 (95%CI, 1.37 to 2.17, I² = 97.8%, P < 0.0001) times higher than in the control group. Subgroup analyses showed a positive correlation between the level of TNF-α and OSA severity. According to meta-regression, we noted that aging significantly predicted an increased effect size of TNF-α level in OSA patients (P < 0.007).

CONCLUSION

This study identified a significant association between OSA and elevated TNF-α level in adults. Meanwhile, TNF-α levels were consistently correlated with severity of OSA, which indicated it might be a promising biomarker for the development of OSA. However, well-designed, large-scale, case-control cohorts are needed to better understand the relationship of TNF-α in the context of adult OSA.

Evaluation of Serum and Plasma Interleukin-6 Levels in Obstructive Sleep Apnea Syndrome: A Meta-Analysis and Meta-Regression

Obstructive sleep apnea syndrome (OSAS) is considered a low-grade chronic inflammatory disease. Interleukin-6 (IL-6) is one of the most significant inflammatory markers and an excellent proxy for the inflammatory/immune system. The present meta-analysis and meta-regression aimed at comparing plasma and serum levels of IL-6 between individuals (children and adults) with OSAS and healthy controls. Four databases, PubMed/Medline, Scopus, Cochrane Library, and Web of Science, were comprehensively searched to retrieve articles published up to December, 2019, with no further restrictions. RevMan 5.3 software was used to calculate the crude mean difference (MD) and 95% confidence interval (CI). The results of funnel plots and meta-regression were analyzed by the CMA 2.0 software. Sixty-three studies (57 with adults; six with children) were included in the present meta-analysis. For adults, 37 studies reported significantly higher serum IL-6 levels and 20 reported significantly higher plasma IL-6 levels for those with OSAS than for healthy controls [pooled MD of 2.89 pg/ml (P < 0.00001) and pooled MD of 2.89 pg/ml (P < 0.00001), respectively]. The pooled analysis of serum and plasma IL-6 levels in children with OSAS compared with controls revealed that only the MD of plasma IL-6 levels was significant (MD = 0.84 pg/ml, P = 0.004). Results of the meta-regression showed that greater age was associated with higher serum IL-6 levels. Egger's test revealed a publication bias across the studies for serum and plasma IL-6 levels (P = 0.00044 and P = 0.01445, respectively). In summary, the meta-analysis and meta-regression confirmed that, compared to healthy controls, individuals with OSAS (children and adults) had higher serum/plasma IL-6 levels.

Serum and Plasma Tumor Necrosis Factor Alpha Levels in Individuals with Obstructive Sleep Apnea Syndrome: A Meta-Analysis and Meta-Regression

BACKGROUND

Obstructive sleep apnea syndrome (OSAS) is associated with a variety of inflammatory factors. Specifically, proinflammatory cytokines appear to be associated with the pathogenesis of OSAS.

METHODS

For the present meta-analysis and meta-regression on serum and plasma tumor necrosis factor alpha (TNF-α) levels in individuals with and without OSAS, we performed a systematic search without any restrictions of the PubMed/Medline, Scopus, Cochrane Library, and Web of Science databases to find relevant articles published up to February 1, 2020.

RESULTS

Fifty-five (adults: 29 studies on serum and 17 studies on plasma; children: 4 studies on serum and 5 studies on plasma) were included and analyzed. Always compared to age-matched healthy controls, the pooled MDs were as follows: adults, serum: 10.22 pg/mL (95% CI = 8.86, 11.58; p < 0.00001); adults, plasma: 5.90 pg/mL (95% CI = 4.00, 7.80; p < 0.00001); children, serum: 0.21 pg/mL (95% CI = 0.05, 0.37; p = 0.01); children, plasma: 5.90 pg/mL (95% CI = 4.00, 7.80; p < 0.00001).

CONCLUSIONS

Compared to healthy and age-matched controls, adult individuals with OSAS had significantly higher serum/plasma TNF-α levels. For children with OSAS, significantly higher levels were observed for TNF-α in serum but not in plasma.

Neck Grasp Predicts Obstructive Sleep Apnea in Type 2 Diabetes Mellitus

Aims

Obstructive sleep apnea (OSA) is a common disorder with high morbidity, mortality, and an increasing prevalence in the general population. It has an even higher prevalence among individuals with type 2 diabetes mellitus (DM). The snoring, tiredness, observed apnea, high blood pressure, body-mass-index, age, neck circumference and male gender (STOP-BANG) questionnaire and Berlin Questionnaire can be cumbersome in clinical practice and require subjective data on sleepiness. We proposed prospectively studying a primary care population with type 2 DM comparing neck grasp, neck circumference, and common screening questionnaires to identify OSA.

Methods

Persons with a diagnosis of type 2 DM were recruited from a primary care clinic. Participants were screened using Easy Sleep Apnea Predictor (ESAP), STOP-Bang questionnaire, and Berlin questionnaire. A positive ESAP was defined as a 1cm gap when a patient encircled their hands around the neck. All subjects underwent in-laboratory PSG testing.

Results

Forty-three participants were enrolled and the prevalence of OSA was 90.7% (AHI ≥ 5). The median BMI was 38.0. The prevalence of mild OSA by PSG (AHI 5-14) was 27.9%, moderate OSA (AHI 15-29) was 25.6%, and severe OSA (AHI >30) was 37.2%. For mild OSA both ESAP and neck circumference showed 100% specificity.

Conclusions

This study reinforces the need for screening diabetic persons for obstructive sleep apnea. ESAP and neck circumference are useful for identifying persons with type 2 DM who are at risk for OSA. Together these findings could improve recognition of OSA in persons at risk for cardiovascular disease. Trial Registration of “Neck grasp as a predictor of Sleep Apnea,” https://clinicaltrials.gov/ct2/show/NCT02474823, Clinical Trials.gov Identifier, is NCT02474823.

Obstructive Sleep Apnea and Inflammation: Proof of Concept Based on Two Illustrative Cytokines

Obstructive sleep apnea syndrome (OSAS) is a markedly prevalent condition across the lifespan, particularly in overweight and obese individuals, which has been associated with an independent risk for neurocognitive, behavioral, and mood problems as well as cardiovascular and metabolic morbidities, ultimately fostering increases in overall mortality rates. In adult patients, excessive daytime sleepiness (EDS) is the most frequent symptom leading to clinical referral for evaluation and treatment, but classic EDS features are less likely to be reported in children, particularly among those with normal body-mass index. The cumulative evidence collected over the last two decades supports a conceptual framework, whereby sleep-disordered breathing in general and more particularly OSAS should be viewed as low-grade chronic inflammatory diseases. Accordingly, it is assumed that a proportion of the morbid phenotypic signature in OSAS is causally explained by underlying inflammatory processes inducing end-organ dysfunction. Here, the published links between OSAS and systemic inflammation will be critically reviewed, with special focus on the pro-inflammatory cytokines tumor necrosis factor α (TNF-α) and interleukin 6 (IL-6), since these constitute classical prototypes of the large spectrum of inflammatory molecules that have been explored in OSAS patients.

Obstructive Sleep Apnea: From Intermittent Hypoxia to Cardiovascular Complications via Blood Platelets

Obstructive sleep apnea is a chronic condition characterized by recurrent episodes of apneas or hypopneas during sleep leading to intermittent hypoxemia and arousals. The prevalence of the sleep disordered breathing is estimated that almost 50% of men and 24% of women suffer from moderate to severe form of the disorder. Snoring, collapse of upper airways and intermittent hypoxia are main causes of smoldering systemic inflammation in patients suffering from obstructive sleep apnea. The systematic inflammation is considered one of the key mechanisms leading to significant cardiovascular complications. Blood platelets, formerly not even recognized as cells, are currently gaining attention as crucial players in the immune continuum. Platelet surface is endowed with receptors characteristic for cells classically belonging to the immune system, which enables them to recognize pathogens, immune complexes, and interact in a homo- and heterotypic aggregates. Platelets participate in the process of transcellular production of bioactive lipids by delivering both specific enzymes and substrate molecules. Despite their lack of nucleus, platelets synthetize proteins in a stimuli-dependent manner. Atherosclerosis and consequent cardiovascular complications result from disruption in homeostasis of both of the platelet roles: blood coagulation and inflammatory processes modulation. Platelet parameters, routinely evaluated as a part of complete blood count test, were proposed as markers of cardiovascular comorbidity in patients with obstructive sleep apnea. Platelets were found to be excessively activated in this group of patients, especially in obese subjects. Persistent activation results in enhanced spontaneous aggregability and change in cytokine production. Platelet-lymphocyte ratio was suggested as an independent marker for cardiovascular disease in obstructive sleep apnea syndrome and continuous positive air pressure therapy was found to have an impact on platelet parameters and phenotype. In this literature review we summarize the current knowledge on the subject of platelets involvement in obstructive sleep apnea syndrome and consider the possible pathways in which they contribute to cardiovascular comorbidity.

Tumor necrosis factor alpha is a promising circulating biomarker for the development of obstructive sleep apnea syndrome: a meta-analysis

Obstructive sleep apnea syndrome (OSAS) is a chronic inflammatory disorder. The relationship between tumor necrosis factor alpha (TNF-alpha) and OSAS has been widely evaluated, but the results thus far remain inconclusive. We thereby decided to quantify the changes of TNF-alpha between OSAS patients and controls by a meta-analysis. This study complies with the MOOSE guidelines. Two reviewers independently searched articles and abstracted relevant data. In total, 47 articles (59 studies) were analyzed, including 2857 OSAS patients and 2115 controls. Overall, OSAS patients had a significantly higher level of circulating TNF-alpha than controls (weighted mean difference [WMD]: 9.66 pg/mL, 95% confidence interval [CI]: 8.66 to 11.24, P<0.001), but with significant heterogeneity (I²: 99.7%). After adjusting for potential missing studies, the overall estimate was weakened but still significant (filled WMD: 2.63 pg/mL, 95% CI: 2.56 to 2.70, P<0.001). When studies were stratified by OSAS severity, the changes in circulating TNF-alpha between patients and controls increased gradually with the more severe grades of OSAS. In patients with mild, mild-to-moderate, moderate, moderate-to-severe and severe OSAS, circulating TNF-alpha was higher than respective controls by 0.99, 1.48. 7.79, 10.08 and 8.85 pg/mL, with significant heterogeneity (I²: 91.2%, 74.5%, 97.6%, 99.0% and 98.1%). In conclusion, our findings demonstrated that circulating TNF-alpha was significantly higher in OSAS patients than in controls, and this difference became more pronounced with the more severe grades of OSAS, indicating that TNF-alpha might be a promising circulating biomarker for the development of OSAS.

Obstructive sleep apnea: Is it a biomarker of metabolic health in obesity

Context

The prevalence of obstructive sleep apnea (OSA) increases with obesity, and OSA has been linked to increased cardiovascular risk via hypoxemia and sleep disruption.

Objective and Main Outcome Measures

We hypothesized that if OSA contributes to cardio-metabolic risk, then 1) obese individuals with OSA will have more cardio-metabolic disease, and 2) patients with OSA who are non-adherent to CPAP treatment will have a greater incidence of cardio-metabolic abnormalities.

Design setting and patients

We prospectively recruited obese patients (n = 83; BMI 49 ± 9 kg/m²). All patients had polysomnography and were stratified by 1) the absence/presence of OSA, and 2) metabolic health. Detailed CPAP reports were analyzed for compliance and OSA severity in 38 subjects.

Results

OSA by polysomnography was present in 69% of patients. While 79% of patients with OSA and 54% without OSA were categorized as MAO (χ² = 5.47, p < 0.02), when adjusted for age, gender and BMI this difference was not significant (p = 0.36). Insulin levels were higher in the OSA group, but when adjusted there was no significant difference (p = 0.350). In patients on CPAP therapy, there was a negative associative trend between OSA control (apnea-hypopnea index) and beta-cell function (HOMA-β) (r = -0.406, p = 0.076), but no association between CPAP compliance and AHI with age, BMI, glucose, insulin, adiponectin, or insulin resistance.

Conclusions

OSA is not independently associated with overall cardio-metabolic health and insulin resistance in obese patients, even when accounting for treatment compliance. The strongest predictors of the obese metabolic healthy phenotype in OSA patients are age, gender and BMI.

The relationship between sleep apnea, metabolic dysfunction and inflammation: The gender influence

Obstructive sleep apnea (OSA) has been associated with increased risk of cardiovascular morbidity and mortality. Although inflammatory markers may mediate this association, it is unknown the influence of gender in this mechanism. Thus, we aimed to evaluate the interaction effects between OSA and gender on metabolic and inflammatory profile in a population sample. This study is part of EPISONO cohort, in which 1042 participants underwent polysomnography, answered questionnaires, and had their blood collected for analysis of fasting glucose, total cholesterol and fractions, leptin, ghrelin, liver transaminases, tumor necrosis factor (TNF)-α, interleukin (IL)-6, and C-reactive protein. The results showed that men with OSA had higher leptin levels, shorter sleep latency and lower N3 sleep stage compared to men control (CTRL). They also presented higher apnea index and number of central apneas compared to both CTRL men and OSA women. In women, OSA was related to longer REM sleep latency, higher apnea-hypopnea index (AHI) during REM sleep and increased TNF-α levels compared to CTRL women. A multivariate model showed that male gender, ghrelin and total cholesterol were negatively associated with TNF-α, while IL-6, triglycerides and hypopnea index were positively associated (R²=0.21). Additionally, gender (men), body mass index, ghrelin, apnea index and smoking were positive predictors of leptin levels (R²=0.55). Of note, postmenopause was associated with changes observed in both TNF-α and AHI during REM sleep in women with OSA. Taken together, our study suggests that OSA consequences may differ between genders and this could indicate a need for different OSA management in women according to their reproductive life's stage.

An update on cardiovascular effects of obstructive sleep apnoea syndrome

Obstructive sleep apnoea syndrome is an important health problem which may cause or worsen systemic diseases. Chronic intermittent hypoxia during repetitive airflow cessations may cause endothelial dysfunction. Sleep apnoea is also shown to be associated with hypercoagulability which may be due to decreased nitric oxide levels and impaired vasodilatation. Endothelial dysfunction, increased systemic inflammation, sympathetic nervous system activation, increased oxidative stress and dysglycaemia may all contribute to cardiovascular processes such as hypertension, arrhythmia, stroke, heart failure and coronary artery disease in patients with obstructive sleep apnoea. Treatment approaches in patients with obstructive sleep apnoea mainly focus on maintaining upper airway patency either with positive airway pressure devices or upper airway appliances. Strategies involving positive airway pressure therapy are associated with decreased morbidity and mortality. Obstructive sleep apnoea should be suspected as an underlying mechanism in patients with cardiovascular disease and warrants appropriate treatment.

How has our interest in the airway changed over 100 years?

Since the beginning of our specialty, our understanding of the link between function and facial growth and development has progressively improved. Today, we know that children with sleep-related breathing problems will often develop distinctive facial characteristics. In adults, sleep apnea can result in serious morbidity and mortality. Orthodontists can ask sleep-related questions in the health history to help identify sleep breathing disorders. Treating these patients presents unique opportunities for orthodontists to collaborate with other medical specialties to improve a patient's health and treatment outcome. Research presented in our Journal in the next century may shed new light that will help us better identify the problem and aid the specialty in developing more effective evidence-based treatment. Additional efforts are needed to understand the physiology, neurology, and genetics of sleep breathing disorders.

Biomarkers associated with obstructive sleep apnea: A scoping review

The overall validity of biomarkers in the diagnosis of obstructive sleep apnea (OSA) remains unclear. We conducted a scoping review to provide assessments of biomarkers characteristics in the context of obstructive sleep apnea (OSA) and to identify gaps in the literature. A scoping review of studies in humans without age restriction that evaluated the potential diagnostic value of biological markers (blood, exhaled breath condensate, salivary, and urinary) in the OSA diagnosis was undertaken. Retained articles were those focused on the identification of biomarkers in subjects with OSA, the latter being confirmed with a full overnight or home-based polysomnography (PSG). Search strategies for six different databases were developed. The methodology of selected studies was classified using an adaptation of the evidence quality criteria from the American Academy of Pediatrics. Additionally the biomarkers were classified according to their potential clinical application. We identified 572 relevant studies, of which 117 met the inclusion criteria. Eighty-two studies were conducted in adults, 34 studies involved children, and one study had a sample composed of both adults and children. Most of the studies evaluated blood biomarkers. Potential diagnostic biomarkers were found in nine pediatric studies and in 58 adults studies. Only nine studies reported sensitivity and specificity, which varied substantially from 43% to 100%, and from 45% to 100%, respectively. Studies in adults have focused on the investigation of IL-6, TNF-α and hsCRP. There was no specific biomarker that was tested by a majority of authors in pediatric studies, and combinatorial urine biomarker approaches have shown preliminary promising results. In adults IL-6 and IL-10 seem to have a favorable potential to become a good biomarker to identify OSA.

Obstructive Sleep Apnoea and Vascular Disease in Patients with Type 2 Diabetes

Obstructive sleep apnoea (OSA) is common and is associated with many vascular risk factors, such as hypertension, insulin resistance, albuminuria, dyslipidaemia, increased inflammation and endothelial dysfunction. Epidemiological studies have shown that OSA is associated with increased cardiovascular disease (CVD) and that continuous positive airway pressure (CPAP) might reduce CVD events in patients with OSA. In addition, OSA has also been shown to be associated with albuminuria, chronic kidney disease, a wide range of ocular diseases and peripheral neuropathy. Considering that CVD and microvascular complications are major contributors to the morbidity, mortality and the economic burden of diabetes and that OSA is common in patients with type 2 diabetes (T2D), it is important to understand the role of OSA in the development and/or progression of vascular disease in patients with T2D and to explore the impact of CPAP on diabetes-related vascular outcomes. The purpose of this article is to review the evidence for the relationship and impact of OSA on vascular disease and vascular risk factors particularly in patients with T2D.

Genetic variants associated with sleep disorders

OBJECTIVE

The diagnostic boundaries of sleep disorders are under considerable debate. The main sleep disorders are partly heritable; therefore, defining heritable pathophysiologic mechanisms could delineate diagnoses and suggest treatment. We collected clinical data and DNA from consenting patients scheduled to undergo clinical polysomnograms, to expand our understanding of the polymorphisms associated with the phenotypes of particular sleep disorders.

METHODS

Patients at least 21 years of age were recruited to contribute research questionnaires, and to provide access to their medical records, saliva for deoxyribonucleic acid (DNA), and polysomnographic data. From these complex data, 38 partly overlapping phenotypes were derived indicating complaints, subjective and objective sleep timing, and polysomnographic disturbances. A custom chip was used to genotype 768 single-nucleotide polymorphisms (SNPs). Additional assays derived ancestry-informative markers (eg, 751 participants of European ancestry). Linear regressions controlling for age, gender, and ancestry were used to assess the associations of each phenotype with each of the SNPs, highlighting those with Bonferroni-corrected significance.

RESULTS

In peroxisome proliferator-activated receptor gamma, coactivator 1 beta (PPARGC1B), rs6888451 was associated with several markers of obstructive sleep apnea. In aryl hydrocarbon receptor nuclear translocator-like (ARNTL), rs10766071 was associated with decreased polysomnographic sleep duration. The association of rs3923809 in BTBD9 with periodic limb movements in sleep was confirmed. SNPs in casein kinase 1 delta (CSNK1D rs11552085), cryptochrome 1 (CRY1 rs4964515), and retinoic acid receptor-related orphan receptor A (RORA rs11071547) were less persuasively associated with sleep latency and time of falling asleep.

CONCLUSIONS

SNPs associated with several sleep phenotypes were suggested, but due to risks of false discovery, independent replications are needed before the importance of these associations can be assessed, followed by investigation of molecular mechanisms.

Diagnostic capability of biological markers in assessment of obstructive sleep apnea: a systematic review and meta-analysis

OBJECTIVE

The purpose of this systematic review is to evaluate the diagnostic value of biological markers (exhaled breath condensate, blood, salivary and urinary) in the diagnosis of OSA in comparison to the gold standard of nocturnal PSG.

METHODS

Studies that differentiated OSA from controls based on PSG results, without age restriction, were eligible for inclusion. The sample of selected studies could include studies in obese patients and with known cardiac disease. A detailed individual search strategy for each of the following bibliographic databases was developed: Cochrane, EMBASE, MEDLINE, PubMed, and LILACS. The references cited in these articles were also crosschecked and a partial grey literature search was undertaken using Google Scholar. The methodology of selected studies was evaluated using the 14-item Quality Assessment Tool for Diagnostic Accuracy Studies.

RESULTS

After a two-step selection process, nine articles were identified and subjected to qualitative and quantitative analyses. Among them, only one study conducted in children and one in adults found biomarkers that exhibit sufficiently satisfactory diagnostic accuracy that enables application as a diagnostic method for OSA.

CONCLUSION

Kallikrein-1, uromodulin, urocotin-3, and orosomucoid-1 when combined have enough accuracy to be an OSA diagnostic test in children. IL-6 and IL-10 plasma levels have potential to be good biomarkers in identifying or excluding the presence of OSA in adults.

Biomarkers to improve diagnosis and monitoring of obstructive sleep apnea syndrome: current status and future perspectives

Obstructive sleep apnea syndrome (OSAS) is characterized by recurrent episodes of upper airway collapse associated with oxygen desaturation and sleep disruption. It is proposed that these periodic changes lead to molecular variations that can be detected by assessing serum biomarkers. Studies have identified inflammatory, oxidative, and metabolic perturbations attributable to sleep-disordered breathing. Given that OSAS is associated with increased cardiovascular and cerebrovascular morbidity, the ideal biomarker should enable timely recognition with the possibility of intervention. There is accumulating data on the utility of serum biomarkers for the evaluation of disease severity, prognosis, and response to treatment. However, current knowledge is limited by data collection techniques, disease complexity, and potential confounding factors. The current paper reviews the literature on the use of serum biomarkers in OSAS. It is concluded that the ideal serum biomarker still needs to be discovered, while caution is needed in the interpretation of hitherto available results.

Relationships between Obstructive Sleep Apnea Syndrome, Continuous Positive Airway Pressure Treatment, and Inflammatory Cytokines

The cardiovascular complications that frequently accompany obstructive sleep apnea syndrome (OSAS) are thought to develop as a result of inflammatory stress associated with cytokines such as IL-6 and TNF-α. We conducted the current study to compare levels of these cytokines in OSAS patients (n = 33) and nonapneic controls (n = 24). Furthermore, we investigated the impact of a three-month regime of continuous positive airway pressure (CPAP) on serum levels of IL-6 and TNF-α only in the OSAS patients. There were no significant differences in serum levels of either IL-6 (P = 0.782) or TNF- α (P = 0.722) or TNF-α (P = 0.722) between OSAS patients and nonapneic controls. Serum IL-6 levels correlated significantly with neck circumference in OSAS patients (P = 0.006). In OSAS patients, reduced levels of TNF-α and IL-6 correlated with increases in mean SaO₂ after CPAP treatment (P = 0.020 and P = 0.051, resp.). However, neither of cytokine levels was significantly impacted by CPAP therapy (both P > 0.137). We have demonstrated that plasma cytokine levels are similar in both otherwise healthy subjects with OSAS and in nonapneic control, and we conclude that OSAS-related parameters and CPAP treatment do not play a significant role in altering cytokine levels.

Pathophysiologic mechanisms of cardiovascular disease in obstructive sleep apnea syndrome

Obstructive sleep apnea syndrome (OSAS) is a highly prevalent sleep disorder, characterized by repeated disruptions of breathing during sleep. This disease has many potential consequences including excessive daytime sleepiness, neurocognitive deterioration, endocrinologic and metabolic effects, and decreased quality of life. Patients with OSAS experience repetitive episodes of hypoxia and reoxygenation during transient cessation of breathing that provoke systemic effects. Furthermore, there may be increased levels of biomarkers linked to endocrine-metabolic and cardiovascular alterations. Epidemiological studies have identified OSAS as an independent comorbid factor in cardiovascular and cerebrovascular diseases, and physiopathological links may exist with onset and progression of heart failure. In addition, OSAS is associated with other disorders and comorbidities which worsen cardiovascular consequences, such as obesity, diabetes, and metabolic syndrome. Metabolic syndrome is an emerging public health problem that represents a constellation of cardiovascular risk factors. Both OSAS and metabolic syndrome may exert negative synergistic effects on the cardiovascular system through multiple mechanisms (e.g., hypoxemia, sleep disruption, activation of the sympathetic nervous system, and inflammatory activation). It has been found that CPAP therapy for OSAS provides an objective improvement in symptoms and cardiac function, decreases cardiovascular risk, improves insulin sensitivity, and normalises biomarkers. OSAS contributes to the pathogenesis of cardiovascular disease independently and by interaction with comorbidities. The present review focuses on indirect and direct evidence regarding mechanisms implicated in cardiovascular disease among OSAS patients.

Elevation of plasma basic fibroblast growth factor after nocturnal hypoxic events in patients with obstructive sleep apnea syndrome

Obstructive sleep apnea syndrome (OSAS) is associated with recurrent nocturnal hypoxia during sleep; this hypoxia has been implicated in the pathogenesis of cardiovascular complication. However, a useful soluble factor that is sensitively correlated with OSAS severity for the diagnosis remains unidentified. We hypothesized that systemic levels of basic fibroblast growth factor (bFGF), a hypoxia-induced cytokine, were affected by nocturnal hypoxemia in OSAS patients, and we assessed whether the degree of change in the plasma bFGF concentrations before and after nocturnal hypoxia is correlated with the severity of OSAS. Thirty subjects who had suspected OSAS and had been investigated by nocturnal polysomnography (PSG) were enrolled. Plasma bFGF and vascular endothelial growth factor (VEGF) concentrations the night before PSG and the next morning were measured by sandwich enzyme-linked immunosorbent assay. Correlations between the changes in these factors and hypoxia-associated parameters for OSAS severity were analyzed. Patients with OSAS had significantly elevated levels of plasma bFGF but not VEGF and hemoglobin after rising. The degree of change in bFGF concentrations after nocturnal apnea episodes was significantly correlated with diagnostic parameters for OSAS severity. The change in plasma bFGF levels is associated with the degree of hypoxic state in OSAS patients, implying that bFGF might be a useful soluble factor for evaluating OSAS severity.

The interaction of obstructive sleep apnea and obesity on the inflammatory markers C-reactive protein and interleukin-6: the Icelandic Sleep Apnea Cohort

STUDY OBJECTIVES

To assess the relative roles and interaction of obstructive sleep apnea (OSA) severity and obesity on interleukin-6 (IL-6) and C-reactive protein (CRP) levels.

DESIGN

Cross-sectional cohort.

SETTING

The Icelandic Sleep Apnea Cohort.

PARTICIPANTS

454 untreated OSA patients (380 males and 74 females), mean ± standard deviation age 54.4 ± 10.6 yr.

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

Participants underwent a sleep study, abdominal magnetic resonance imaging to measure total abdominal and visceral fat volume, and had fasting morning IL-6 and CRP levels measured in serum. A significantly higher correlation was found for BMI than visceral fat volume with CRP and IL-6 levels. Oxygen desaturation index, hypoxia time, and minimum oxygen saturation (SaO₂) significantly correlated with IL-6 and CRP levels, but apnea-hypopnea index did not. When stratified by body mass index (BMI) category, OSA severity was associated with IL-6 levels in obese participants only (BMI > 30 kg/m²). A multiple linear regression model with interaction terms showed an independent association of OSA severity with IL-6 levels and an interaction between OSA severity and BMI, i.e., degree of obesity altered the relationship between OSA and IL-6 levels. An independent association of OSA severity with CRP levels was found for minimum SaO₂ only. A similar interaction of OSA severity and BMI on CRP levels was found for males and postmenopausal women.

CONCLUSIONS

OSA severity is an independent predictor of levels of IL-6 and CRP but interacts with obesity such that this association is found only in obese patients.

Sleep apnea determines soluble TNF-α receptor 2 response to massive weight loss

BACKGROUND

The effects of surgical weight loss (WL) on inflammatory biomarkers associated with sleep apnea remain unknown. We sought to determine if any biomarkers can predict amelioration of sleep apnea achieved by bariatric surgery. We hypothesized that surgical WL would substantially reduce severity of sleep apnea and levels of proinflammatory cytokines.

METHODS

Twenty-three morbidly obese adults underwent anthropometric measurements, polysomnography, and serum biomarker profiling prior to and 1 year following bariatric surgery. We examined the effect of WL and amelioration of sleep apnea on metabolic and inflammatory markers.

RESULTS

Surgical WL resulted in significant decreases in BMI (16.7 ± 5.97 kg/m(2)/median 365 days), apnea-hypopnea index (AHI), CRP, IL-6, sTNFαR1, sTNFαR2, and leptin levels, while ghrelin, adiponectin, and soluble leptin receptor concentrations increased significantly. Utilizing an AHI cutoff of 15 events/h, we found significantly elevated levels of baseline sTNFαR2 and greater post-WL sTNFαR2 decreases in subjects with baseline AHI ≥15 events/h compared to those with AHI <15 events/h despite no significant differences in baseline BMI, age, and ΔBMI. In a multivariable linear regression model adjusting for sex, age, impaired glucose metabolism, ΔBMI, and follow-up period, the post-WL decreases in AHI were an independent predictor of the decreases in sTNFαR2 and altogether accounted for 46% of the variance of ΔsTNFαR2 (P = 0.011) in the entire cohort.

CONCLUSIONS

Of all the biomarkers, the decrease in sTNFαR2 was independently determined by the amelioration of sleep apnea achieved by bariatric surgery. The results suggest that sTNFαR2 may be a specific sleep apnea biomarker across a wide range of body weight.

Obesity hypoventilation syndrome

Obesity is becoming a major medical concern in several parts of the world, with huge economic impacts on health- care systems, resulting mainly from increased cardiovascular risks. At the same time, obesity leads to a number of sleep-disordered breathing patterns like obstructive sleep apnea and obesity hypoventilation syndrome (OHS), leading to increased morbidity and mortality with reduced quality of life. OHS is distinct from other sleep- related breathing disorders although overlap may exist. OHS patients may have obstructive sleep apnea/hypopnea with hypercapnia and sleep hypoventilation, or an isolated sleep hypoventilation. Despite its major impact on health, this disorder is under-recognized and under-diagnosed. Available management options include aggressive weight reduction, oxygen therapy and using positive airway pressure techniques. In this review, we will go over the epidemiology, pathophysiology, presentation and diagnosis and management of OHS.

Sleep apnea predicts distinct alterations in glucose homeostasis and biomarkers in obese adults with normal and impaired glucose metabolism

BACKGROUND

Notwithstanding previous studies supporting independent associations between obstructive sleep apnea (OSA) and prevalence of diabetes, the underlying pathogenesis of impaired glucose regulation in OSA remains unclear. We explored mechanisms linking OSA with prediabetes/diabetes and associated biomarker profiles. We hypothesized that OSA is associated with distinct alterations in glucose homeostasis and biomarker profiles in subjects with normal (NGM) and impaired glucose metabolism (IGM).

METHODS

Forty-five severely obese adults (36 women) without certain comorbidities/medications underwent anthropometric measurements, polysomnography, and blood tests. We measured fasting serum glucose, insulin, selected cytokines, and calculated homeostasis model assessment estimates of insulin sensitivity (HOMA-IS) and pancreatic beta-cell function (HOMA-B).

RESULTS

Both increases in apnea-hypopnea index (AHI) and the presence of prediabetes/diabetes were associated with reductions in HOMA-IS in the entire cohort even after adjustment for sex, race, age, and BMI (P = 0.003). In subjects with NGM (n = 30), OSA severity was associated with significantly increased HOMA-B (a trend towards decreased HOMA-IS) independent of sex and adiposity. OSA-related oxyhemoglobin desaturations correlated with TNF-α (r=-0.76; P = 0.001) in women with NGM and with IL-6 (rho=-0.55; P = 0.035) in women with IGM (n = 15) matched individually for age, adiposity, and AHI.

CONCLUSIONS

OSA is independently associated with altered glucose homeostasis and increased basal beta-cell function in severely obese adults with NGM. The findings suggest that moderate to severe OSA imposes an excessive functional demand on pancreatic beta-cells, which may lead to their exhaustion and impaired secretory capacity over time. The two distinct biomarker profiles linking sleep apnea with NGM and IGM via TNF-α and IL-6 have been discerned in our study to suggest that sleep apnea and particularly nocturnal oxyhemoglobin desaturations are associated with chronic metabolic fluxes and specific cytokine stressors that reflect links between sleep apnea and glucose metabolism. The study may help illuminate potential mechanisms for glucose dysregulation in OSA, and resolve some controversy over the associations of OSA with TNF-α and IL-6 in previous studies.

Sleep-disordered breathing is increased in obese adolescents with craniopharyngioma compared with obese controls

CONTEXT

Retrospective studies suggest that adolescents with craniopharyngioma and hypothalamic obesity have increased sleep-disordered breathing (SDB).

OBJECTIVES

The objectives of this study were to compare the prevalence of SDB in adolescents with craniopharyngioma-related obesity compared with body mass index (BMI)-matched controls and to explore possible relationships between SDB, insulin resistance, and adipocytokines.

DESIGN

This was a cross-sectional study of obese craniopharyngioma and obese control adolescents.

SETTING

Subjects were evaluated in the clinical investigation unit at the Hospital for Sick Children, Toronto.

PATIENTS

Fifteen patients with craniopharyngioma-related obesity and 15 BMI-matched controls were recruited and tested.

INTERVENTIONS

Each subject underwent fasting blood work, frequent sampled iv glucose tolerance test, polysomnography, and abdominal magnetic resonance imaging with calculation of visceral and sc adipose tissue.

MAIN OUTCOME MEASURES

Main measures included insulin sensitivity, sleep efficiency, and fragmentation.

RESULTS

Insulin sensitivity was lower in craniopharyngioma subjects compared with control subjects (0.96 +/- 0.34 vs. 1.67 +/- 0.7, P = 0.01). Sleep-onset latency (19.3 +/- 27.8 vs. 31.9 +/- 23.4, P = 0.03) and oxygen saturations (rapid eye movement sleep: 89.0 +/- 5.1 vs. 94.2 +/- 2.3, P < 0.001; non-rapid eye movement sleep: 88.4 +/- 5.6 vs. 94.3 +/- 1.5, P < 0.001) were lower in craniopharyngioma. Obstructive apnea-hypopnea index (OAHI) (7.5 +/- 9.0 vs. 1.5 +/- 1.5, P = 0.03) was higher in craniopharyngioma. Respiratory distress index and OAHI correlated negatively with adiponectin concentrations (r = -0.61, P = 0.03, r = -0.71, P = 0.006, respectively) in craniopharyngioma. On multiple regression, TNF-alpha and craniopharyngioma were independent positive predictors of sleep-onset latency and adiponectin and craniopharyngioma were significant predictors (negative and positive, respectively) of OAHI.

CONCLUSIONS

SDB is increased in adolescents with craniopharyngioma-related obesity compared with BMI-matched controls. Routine polysomnography should be considered in obese patients with craniopharyngioma and appropriate treatment initiated.

Sleep measures and morning plasma TNF-alpha levels in children with sleep-disordered breathing

BACKGROUND

Sleep disordered breathing in children is associated with severity-dependent increases in excessive daytime sleepiness (EDS). TNF-alpha is an inflammatory cytokine that has been implicated in EDS. Since, at any given level of apnea-hypopnea index, there is significant variability in EDS, we hypothesized that morning tumor necrosis factor (TNF)-alpha plasma levels may provide a biologic correlate of EDS.

METHODS

Children being evaluated for sleep disordered breathing underwent a blood draw after nocturnal polysomnography, and TNF-alpha plasma concentrations were assayed using ELISA. In a subset of 15 children with sleep disordered breathing and in 15 matched control subjects, whole blood cultures in the presence of lipopolysaccharide and Multiple Sleep Latency Test were conducted. Furthermore, 22 children with obstructive sleep apnea had TNF-alpha levels assayed and underwent nocturnal polysomnography and Multiple Sleep Latency Test before and after adenotonsillectomy.

RESULTS

In 298 children, morning TNF-alpha levels were globally increased in the presence of obstructive sleep apnea, particularly in more severe cases, and correlated with obstructive apnea-hypopnea index and sleep pressure score, a measure of respiratory-induced sleep fragmentation, but not with nadir Sa02. A stepwise logistic regression analysis revealed that sleep pressure score and body mass index accounted for 36.2% of the adjusted variance in TNF-alpha levels (P < 0.0001). Furthermore, multiple sleep latencies were correlated with whole blood culture-derived TNF-alpha levels (n = 15), and morning TNF-alpha levels decreased after adenotonsillectomy in 22 children.

CONCLUSIONS

TNF-alpha levels are increased in pediatric obstructive sleep apnea, are primarily driven by sleep fragmentation and body mass index, and are closely associated with the degree of sleepiness, as measured by Multiple Sleep Latency Test. Furthermore, surgical treatment of obstructive sleep apnea results in significant reductions in TNF-alpha levels with reciprocal prolongations in sleep latency.

Effect of continuous positive airway pressure therapy on aortic stiffness in patients with obstructive sleep apnea syndrome

OBJECTIVE

The most significant complications seen in patients with obstructive sleep apnea syndrome (OSAS) are associated with the cardiovascular system. The present study assessed aortic stiffness in patients with OSAS and evaluated the effect of continuous positive airway pressure (CPAP) therapy on aortic stiffness.

METHOD

Twenty-four patients with newly diagnosed, previously untreated, moderate or severe OSAS (apnea-hypopnea index > 15) and a control group of 17 healthy patients were included in the study. M-mode recordings of the ascending aorta were taken from the parasternal long axis by echocardiograhy, and systolic and diastolic diameters of the aorta were measured. Aortic elastic parameters, aortic strain, and distensibility were calculated. Measurements were repeated after 6 months of CPAP therapy in patients with OSAS and were compared with baseline values.

RESULTS

In patients with OSAS, compared with the control group, aortic strain (6.7%+/- 2.1% vs. 12.4%+/- 3.1%; P < 0.001) and aortic distensibility (2.8 +/- 0.9 x 10(-6) cm(2) dyn(-1) vs. 5.5 +/- 1.7 x 10(-6) cm(2) dyn(-1); P < 0.001) were evidently lower, and there was a significant correlation between aortic elastic parameters and AHI. After a 6-month course of CPAP therapy, significant increases were observed in aortic strain (6.1%+/- 1.5% vs. 7.3%+/- 1.7%; P < 0.001) and aortic distensibility (2.5 +/- 0.7 x 10(-6) cm(2) dyn(-1) vs. 3.1 +/- 0.9 x 10(-6) cm(2) dyn(-1); P < 0.001) in patients with OSAS.

CONCLUSION

Aortic strain and distensibility were lower in patients with OSAS than in control patients, and CPAP treatment provided improvement in aortic elastic parameters.

Influence of intermittent hypoxia on the signal transduction pathways to inflammatory response and circadian clock regulation

AIMS

Obstructive sleep apnea syndrome (OSAS), characterized by intermittent hypoxia/reoxygenation (IHR), is often associated with changing levels of circulating inflammatory cytokines and causes excessive daytime sleepiness, mood disturbances, and cardiovascular disease. An abnormal rhythm in the expression of circadian clock genes is observed in OSAS patients, and is also implicated in OSAS-related clinical symptoms. IHR-induced signal transduction is thought to underlie OSAS-associated complications. The aim of this study is to elucidate the influence of IHR on signal transduction pathways to inflammatory response and circadian clock regulation.

MAIN METHODS

To evaluate the direct action of IHR on intracellular signaling, we used a cell culture model to explore the underlying transcriptional events initiated by IHR.

KEY FINDINGS

Treatment of cultured human lung adenocarcinoma epithelial cells (A549) with IHR resulted in the elevation of mRNA levels of an inflammation cytokine interleukin-6 (IL-6), due to activation of the signaling pathway of nuclear factor-kappaB, a potent transcriptional activator of IL-6. On the other hand, the treatment of cells with IHR had little effect on clock gene response element-driven transcription. As a consequence, there was no significant change in mRNA levels of clock genes in IHR-treated cells.

SIGNIFICANCE

These results suggest that IHR can activate signal transduction to an inflammatory response, but not to circadian clock regulation. The abnormal rhythm in the expression of clock genes in OSAS patients is attributable to the changed levels of circulating factors that have the ability to modulate clock gene expression.

Association of chronic obstructive pulmonary disease and obstructive sleep apnea consequences

Obstructive sleep apnea syndrome (OSAS) and chronic obstructive pulmonary disease (COPD) are two diseases that often coexist within an individual. This coexistence is known as overlap syndrome and is the result of chance rather than a pathophysiological link. Although there are claims of a very high incidence of OSAS in COPD patients, recent studies report that it is similar to the general population. Overlap patients present sleep-disordered breathing associated to upper and lower airway obstruction and a reduction in respiratory drive. These patients present unique characteristics, which set them apart from either COPD or OSAS patients. COPD and OSAS are independent risk factors for cardiovascular events and their coexistence in overlap syndrome probably increases this risk. The mechanisms underlying cardiovascular risk are still unclear, but may involve systemic inflammation, endothelial dysfunction, and tonic elevation of sympathetic neural activity. The treatment of choice for overlap syndrome in stable patients is CPAP with supplemental oxygen for correction of upper airway obstructive episodes and hypoxemia during sleep.

Obstructive sleep apnea syndrome is a systemic disease. Current evidence

Obstructive sleep apnea syndrome (OSAS) is a highly prevalent sleep disorder, characterized by repeated disruptions of breathing during sleep. This disease has many potential consequences including excessive daytime sleepiness, neurocognitive deterioration, endocrinologic and metabolic effects, and decreased quality of life. Metabolic syndrome is another highly prevalence emerging public health problem that represents a constellation of cardiovascular risk factors. Each single component of the cluster increases the cardiovascular risk, but the combination of factors is much more significant. It has been suggested that the presence of OSAS may increase the risk of developing some metabolic syndrome features. Moreover, OSAS patients are at an increased risk for vascular events, which represent the greatest morbidity and mortality of all associated complications. Although the etiology of OSAS is uncertain, intense local and systemic inflammation is present. A variety of phenomena are implicated in this disease such as modifications in the autonomic nervous system, hypoxemia-reoxygenation cycles, inflammation, and coagulation-fibrinolysis imbalance. OSAS patients also present increased levels of certain biomarkers linked to endocrine-metabolic and cardiovascular alterations among other systemic consequences. All of this indicates that, more than a local abnormality, OSAS should be considered a systemic disease.

Effects of continuous positive airway pressure therapy on right ventricular function assessment by tissue Doppler imaging in patients with obstructive sleep apnea syndrome

OBJECTIVES

The effects of continuous positive airway pressure (CPAP) therapy on right ventricular (RV) function in patients with obstructive sleep apnea syndrome (OSAS) has not been previously studied by tissue Doppler imaging (TDI). The aim of this study was to assess RV function using TDI in patients with OSAS before and after CPAP therapy.

METHODS

Twenty-eight patients with newly diagnosed OSAS in the absence of any confounding factors and 18 controls were included in this study. The peak systolic velocity (S'm), early (E'm) and late (A'm) diastolic myocardial peak velocities at tricuspid lateral annulus, isovolumic acceleration (IVA), myocardial precontraction time (PCT'm), myocardial contraction time (CT'm), and myocardial relaxation time (RT'm) were measured. All echocardiographic parameters were calculated 6 months after CPAP therapy.

RESULTS

The RV diastolic parameters such as E'm velocity and E'm-to-A'm ratio were significantly lower, RT'm was significantly prolonged, A'm velocity was similar in patients with OSAS compared to controls; and the RV systolic parameters such as IVA and CT'm were significantly lower and S'm was similar in patients with OSAS compared to controls. At the end of the treatment, 20 of 28 patients were compliant with CPAP therapy. E'm velocity, E'm-to-A'm ratio, IVA, and CT'm increased, PCT'm, PCT'm-to-CT'm ratio, and RT'm decreased significantly after therapy, whereas S'm velocity and A'm velocity did not change after CPAP treatment in the compliant patients.

CONCLUSION

OSAS is associated with RV systolic and diastolic dysfunction, and 6 months of CPAP therapy improves the RV systolic and diastolic dysfunction.

High prevalence of small intestinal bacterial overgrowth in patients with morbid obesity: a contributor to severe hepatic steatosis

BACKGROUND

With the increasing prevalence of obesity, non-alcoholic fatty liver disease (NAFLD) has become a major cause of liver diseases. Small intestinal bacterial overgrowth (SIBO) could be related to NAFLD. Our aim was to determine the prevalence of SIBO and its relationship with liver lesions in morbidly obese patients.

METHODS

A glucose hydrogen (H(2)) breath test (positive if fasting breath H(2) concentration > 20 ppm and/or an increase of > 10 ppm over baseline within the first 2 h) was performed in obese patients referred for bariatric surgery (body mass index [BMI] > 40 kg/m(2) or > 35 in association with comorbidities) and in healthy non-obese subjects. In obese patients, a surgical liver biopsy was performed.

RESULTS

One hundred and forty-six patients (129 women, age [mean+/-SE]: 40.7 +/- 11.4 years) were prospectively included in the study. The mean BMI was 46.1+/-6.4 kg/m(2). A liver biopsy was available in 137 patients and a breath test in 136. The frequency of positive breath tests was higher in obese patients (24/136, 17.1%) than in healthy subjects (1/40, 2.5%; P=0.031). In the univariate analysis, SIBO was not associated with clinical variables, but tended to be associated with more frequent severe hepatic steatosis (26.3 vs. 10.3%, P=0.127), whereas the frequency of sinusoidal or portal fibrosis, lobular necrosis and non-alcoholic steatohepatitis (NASH) were not different. In the multivariate analysis, SIBO (P=0.005) and the presence of a metabolic syndrome (P=0.006) were independent factors of severe hepatic steatosis.

CONCLUSION

In morbidly obese patients, bacterial overgrowth prevalence is higher than in healthy subjects and is associated with severe hepatic steatosis.

Cytokines and pathological sleep

Cytokines are proteins produced by leukocytes and other cells that function as intercellular mediators acting on several target tissues, resulting in multiple biologic actions. Over the last decade, medical research has explored the interaction between cytokines and sleep disorders. The aim of this review is to illustrate recent advances in knowledge about the relationship between cytokines and disorders of excessive sleepiness. Cytokines may have an important role in mediating excessive daytime sleepiness in sleep loss or insomnia. Alterations of the immune system have also been associated with narcolepsy. The relationship between cytokines and hormonal regulatory mechanisms may explain symptoms like fatigue and sleepiness in chronic inflammatory diseases. Cytokines may play an important role in the pathogenesis of obstructive sleep apnea and cardiovascular consequences of this condition. New biologic treatments targeting cytokines have been investigated in conditions characterized by sleep disturbance.

Cardiovascular morbidity in obstructive sleep apnea: oxidative stress, inflammation, and much more

Sleep-disordered breathing and obstructive sleep apnea (OSA) are highly prevalent disorders throughout the lifespan, which may affect up to 2-10% of the population, and have now been firmly associated with an increased risk for cardiovascular and neurobehavioral complications. Nevertheless, the overall pathophysiologic mechanisms mediating end-organ injury in OSA remain undefined, particularly due to the very frequent coexistence of other disease states, such as obesity, that clearly complicate the potential cause-effect relationships. Two major, and to some extent overlapping, mechanisms have been proposed to explain the morbid consequences of OSA, namely increased generation and propagation of reactive oxygen species and initiation and amplification of inflammatory processes. The evidence supporting the validity of these concepts as well as that detracting from such mechanisms will be critically reviewed in the context of clinical and laboratory-based approaches. In addition, some of the contradictory issues raised by such evaluation of the literature will be interpreted in the context of putative modifications of the individual responses to OSA, as determined by genetic variants among susceptibility-related genes, and also by potential environmental modulators of the phenotypic expression of any particular end-organ morbidity associated with OSA.

Alveolar-derived exhaled nitric oxide is reduced in obstructive sleep apnea syndrome

BACKGROUND

Obstructive sleep apnea syndrome (OSAS) is associated with cardiovascular diseases, in particular systemic arterial hypertension. We postulated that intermittent nocturnal hypoxia in OSAS may be associated to decreased fractional exhaled nitric oxide (FENO) levels from distal airspaces.

METHODS

Multiple flow rate measurements have been used to fractionate nitric oxide (NO) from alveolar and bronchial sources in 34 patients with OSAS, in 29 healthy control subjects, and in 8 hypertensive non-OSAS patients. The effect of 2 days of treatment with nasal continuous positive airway pressure (nCPAP) on FENO was examined in 18 patients with severe OSAS.

RESULTS

We found that the mean [+/- SE] concentrations of exhaled NO at a rate of 50 mL/s was 21.8 +/- 1.9 parts per billion (ppb) in patients with OSAS, 25.1 +/- 3.3 ppb in healthy control subjects, and 15.4 +/- 1.7 ppb in hypertensive control patients. The mean fractional alveolar NO concentration (CANO) in OSAS patients was significantly lower than that in control subjects (2.96 +/- 0.48 vs 5.35 +/- 0.83 ppb, respectively; p < 0.05). In addition, CANO values were significantly lower in OSAS patients with systemic hypertension compared to those in normotensive OSAS patients and hypertensive patients without OSAS. The mean values of CANO significantly improved after nCPAP therapy (2.67 +/- 0.41 to 4.69 +/- 0.74 nL/L, respectively; p = 0.01).

CONCLUSIONS

These findings suggest that alveolar FENO, and not bronchial FENO, is impaired in patients with OSAS and that this impairment is associated with an increased risk of hypertension. NO production within the alveolar space is modified by treatment with nCPAP.

TNFalpha siRNA reduces brain TNF and EEG delta wave activity in rats

Tumor necrosis factor alpha (TNFalpha) is a pleiotropic cytokine with several CNS physiological and pathophysiological actions including sleep, memory, thermal and appetite regulation. Short interfering RNAs (siRNA) targeting TNFalpha were incubated with cortical cell cultures and microinjected into the primary somatosensory cortex (SSctx) of rats. The TNFalpha siRNA treatment specifically reduced TNFalpha mRNA by 45% in vitro without affecting interleukin-6 or gluR1-4 mRNA levels. In vivo the TNFalpha siRNAalpha reduced TNFalpha mRNA, interleukin-6 mRNA and gluR1 mRNA levels compared to treatment with a scrambled control siRNA. After in vivo microinjection, the density of TNFalpha-immunoreactive cells in layer V of the SSctx was also reduced. Electroencephalogram (EEG) delta wave power was decreased on days 2 and 3 on the side of the brain that received the TNFalpha siRNA microinjection relative to the side receiving the control siRNA. These findings support the hypothesis that TNFalpha siRNA attenuates TNFalpha mRNA and TNFalpha protein in the rat cortex and that those reductions reduce cortical EEG delta power. Results also are consistent with the notion that TNFalpha is involved in CNS physiology including sleep regulation.

Obesity, metabolic syndrome and sleep apnoea: all pro-inflammatory states

Obesity is associated with significant morbidity and mortality and is increasing in prevalence worldwide. Associated conditions include insulin resistance (IR), diabetes, hypertension and dyslipidaemia; a clustering of these has recently been termed as metabolic syndrome. Weight gain is a major predictor of the metabolic syndrome with waist circumference being a more sensitive indicator than body mass index as it reflects both abdominal subcutaneous adipose tissue and visceral adipose tissue (VAT). VAT has more metabolic activity and secretes a number of hormones and pro-inflammatory cytokines which are linked with the metabolic abnormalities listed above. Central obesity also increases the risk of obstructive sleep apnoea syndrome (OSAS), where the sleep disordered breathing may also independently lead to/or exacerbate IR, diabetes and cardiovascular risk. The contribution of OSAS to the metabolic syndrome has been under-recognized. The putative mechanisms by which OSAS causes or exacerbates these other abnormalities are discussed. We propose that activation of nuclear factor kappa B by stress hypoxia and/or by increased adipokines and free fatty acids released by excess adipose tissue is the final common inflammatory pathway linking obesity, OSAS and the metabolic syndrome both individually and, in many cases, synergistically.