Obstructive Sleep Apnea Dynamically Increases Nocturnal Plasma Free Fatty Acids, Glucose, and Cortisol During Sleep

Journey towards a personalised medicine approach for OSA: Can a similar approach to adult OSA be applied to paediatric OSA?

The concept of personalised medicine is likely to revolutionise the treatment of adult obstructive sleep apnoea as a result of recent advances in the understanding of disease heterogeneity by identifying clinical phenotypes, pathophysiological endotypes, biomarkers and treatable traits. Children with the condition show a similar level of heterogeneity and paediatric obstructive sleep apnoea would also benefit from a more targeted approach to diagnosis and management. This review aims to summarise the adult literature on the phenotypes and endotypes of obstructive sleep apnoea and assess whether a similar approach may also be suitable to guide the development of new diagnostic and management approaches for paediatric obstructive sleep apnoea.

Dynamic changes in nocturnal blood glucose levels are associated with sleep-related features in patients with obstructive sleep apnea

Obstructive sleep apnea (OSA) has a bidirectional relationship with insulin resistance conditions; however, the mechanism remains unclear. This study aimed to compare dynamic nocturnal glucose changes among patients with OSA of varying levels of severity and evaluate temporal changes associated with the cardinal features of OSA (sympathetic hyperactivation, intermittent hypoxemia, and sleep fragmentation) in nondiabetic subjects. Nocturnal glucose was measured with a continuous glucose monitoring device every 5 min during polysomnography (PSG). The OSA features were evaluated using heart rate variability (HRV), minimum saturation, and electroencephalography. Eleven subjects with moderate to severe OSA and 12 subjects with no or mild OSA were evaluated. Those with moderate to severe OSA showed an increasing trend in blood glucose levels after sleep onset, whereas those without or with mild OSA showed a decreasing trend (F = 8.933, p < 0.001). Delta band power also showed different trends during sleep between the two groups (F = 2.991, p = 0.009), and minimum saturation remained lower in the moderate to severe OSA group than in the no or mild OSA group. High degrees of coupling between nocturnal glucose levels and each OSA feature were observed. Altered trends in nocturnal glucose in moderate to severe OSA may reflect glucose intolerance and result in metabolic consequences. Managing the features of sleep-related OSA may have implications for metabolic management in the future.

Sleep apnea in men is associated with altered lipid metabolism, glucose tolerance, insulin sensitivity, and body fat percentage

PURPOSE

Obstructive sleep apnea (OSA) is associated with obesity and risk for type 2 diabetes. In this community-based study, we thoroughly investigated fatty acid metabolism, incretin response, glucose tolerance, insulin secretion and insulin sensitivity, and autonomic nerve activity in men with or without OSA.

METHODS

Fifteen men without diabetes but with signs of severe OSA, defined as apnea-hypopnea index (AHI) >30, and 15 age- and BMI-matched men without OSA (AHI < 5) were recruited from a community-based cohort. Assessments included clinical and anthropometric measurements, a 2-h oral glucose tolerance test (OGTT), and autonomic nerve activity using heart rate variability (HRV).

RESULTS

Men with OSA had higher body fat % than BMI-matched men without OSA (p = 0.046) and it was associated with markers of insulin resistance. The area under the curve for nonesterified fatty acids (NEFA) during OGTT was higher in men with OSA (p = 0.021) and fasting NEFA levels were numerically higher (p = 0.097). The plasma glucose at fasting and during OGTT was higher in men with OSA (p < 0.001). Incretin response was similar between groups. Fasting and OGTT-derived indices indicated impaired insulin sensitivity in men with OSA. Compared with men without OSA, Matsuda index (p = 0.068) and Gutt index (p < 0.01) were lower in men with OSA. The HRV measures did not differ between groups.

CONCLUSIONS

Our study suggests that fatty acid handling, glucose tolerance, and insulin sensitivity are impaired in men with severe OSA. This might partly be explained by the increased body fat percentage.

Quantifications of Lipid Kinetics In Vivo Using Stable Isotope Tracer Methodology

Like other bodily materials, lipids such as plasma triacylglycerol, cholesterols, and free fatty acids are in a dynamic state of constant turnover (i.e., synthesis, breakdown, oxidation, and/or conversion to other compounds) as essential processes for achieving dynamic homeostasis in the body. However, dysregulation of lipid turnover can lead to clinical conditions such as obesity, fatty liver disease, and dyslipidemia. Assessment of “snap-shot” information on lipid metabolism (e.g., tissue contents of lipids, abundance of mRNA and protein and/or signaling molecules) are often used in clinical and research settings, and can help to understand one's health and disease status. However, such “snapshots” do not provide critical information on dynamic nature of lipid metabolism, and therefore may miss “true” origin of the dysregulation implicated in related diseases. In this regard, stable isotope tracer methodology can provide the in vivo kinetic information of lipid metabolism. Combining with “static” information, knowledge of lipid kinetics can enable the acquisition of in depth understanding of lipid metabolism in relation to various health and disease status. This in turn facilitates the development of effective therapeutic approaches (e.g., exercise, nutrition, and/or drugs). In this review we will discuss 1) the importance of obtaining kinetic information for a better understanding of lipid metabolism, 2) basic principles of stable isotope tracer methodologies that enable exploration of “lipid kinetics” in vivo, and 3) quantification of some aspects of lipid kinetics in vivo with numerical examples.

Understanding the pathophysiological mechanisms of cardiometabolic complications in obstructive sleep apnoea: towards personalised treatment approaches

In January 2019, a European Respiratory Society research seminar entitled "Targeting the detrimental effects of sleep disturbances and disorders" was held in Dublin, Ireland. It provided the opportunity to critically review the current evidence of pathophysiological responses of sleep disturbances, such as sleep deprivation, sleep fragmentation or circadian misalignment and of abnormalities in physiological gases such as oxygen and carbon dioxide, which occur frequently in respiratory conditions during sleep. A specific emphasis of the seminar was placed on the evaluation of the current state of knowledge of the pathophysiology of cardiovascular and metabolic diseases in obstructive sleep apnoea (OSA). Identification of the detailed mechanisms of these processes is of major importance to the field and this seminar offered an ideal platform to exchange knowledge, and to discuss pitfalls of current models and the design of future collaborative studies. In addition, we debated the limitations of current treatment strategies for cardiometabolic complications in OSA and discussed potentially valuable alternative approaches.

Continuous Positive Airway Pressure Treatment, Glycemia, and Diabetes Risk in Obstructive Sleep Apnea and Comorbid Cardiovascular Disease

OBJECTIVE

Despite evidence of a relationship among obstructive sleep apnea (OSA), metabolic dysregulation, and diabetes, it is uncertain whether OSA treatment can improve metabolic parameters. We sought to determine effects of long-term continuous positive airway pressure (CPAP) treatment on glycemic control and diabetes risk in patients with cardiovascular disease (CVD) and OSA.

RESEARCH DESIGN AND METHODS

Blood, medical history, and personal data were collected in a substudy of 888 participants in the Sleep Apnea cardioVascular Endpoints (SAVE) trial in which patients with OSA and stable CVD were randomized to receive CPAP plus usual care, or usual care alone. Serum glucose and glycated hemoglobin A_1c (HbA_1c) were measured at baseline, 6 months, and 2 and 4 years and incident diabetes diagnoses recorded.

RESULTS

Median follow-up was 4.3 years. In those with preexisting diabetes (n = 274), there was no significant difference between the CPAP and usual care groups in serum glucose, HbA_1c, or antidiabetic medications during follow-up. There were also no significant between-group differences in participants with prediabetes (n = 452) or new diagnoses of diabetes. Interaction testing suggested that women with diabetes did poorly in the usual care group, while their counterparts on CPAP therapy remained stable.

CONCLUSIONS

Among patients with established CVD and OSA, we found no evidence that CPAP therapy over several years affects glycemic control in those with diabetes or prediabetes or diabetes risk over standard-of-care treatment. The potential differential effect according to sex deserves further investigation.

Circulating MicroRNA Profile Associated with Obstructive Sleep Apnea in Alzheimer's Disease

The diagnosis of obstructive sleep apnea (OSA) in Alzheimer's disease (AD) by polysomnography (PSG) is challenging due to the required collaboration of the patients. In addition, screening questionnaires have demonstrated limited usefulness with this subpopulation. Considering this, we investigated the circulating microRNA (miRNA) profile associated with OSA in AD patients. This study included a carefully selected cohort of females with mild-moderate AD confirmed by biological evaluation (n = 29). The individuals were submitted to one-night PSG to diagnose OSA (apnea-hypopnea index ≥ 15/h) and the blood was collected in the following morning. The plasma miRNA profile was evaluated using RT-qPCR. The patients had a mean (SD) age of 75.8 (5.99) years old with a body mass index of 28.6 (3.83) kg m^-2. We observed a subset of 15 miRNAs differentially expressed between OSA and non-OSA patients, of which 10 were significantly correlated with the severity of OSA. Based on this, we built a prediction model that generated an AUC (95% CI) of 0.95 (0.88-1.00) including 5 of the differentially expressed miRNAs that correlated with OSA severity: miR-26a-5p, miR-30a-3p, miR-374a-5p, miR-377-3p, and miR-545-3p. Our preliminary results suggest a plasma miRNA signature associated with the presence of OSA in AD patients. Further studies will be necessary to validate these findings.

Maternal Sleep-Disordered Breathing in Pregnancy and Increased Nocturnal Glucose Levels in Women with Gestational Diabetes Mellitus

BACKGROUND

Women with hyperglycemia during pregnancy are at high risk for adverse perinatal outcomes. Maternal sleep-disordered breathing (SDB) during pregnancy is common and is a risk factor for gestational diabetes mellitus (GDM). However, the relationship between SDB severity and glucose control is unknown.

RESEARCH QUESTION

Is there an association between SDB severity and glucose levels as assessed by continuous glucose monitoring in GDM?

STUDY DESIGN AND METHODS

Women with GDM underwent sleep recordings and 72-hour continuous glucose monitoring. Linear mixed models were used to estimate the association of the apnea-hypopnea index (AHI), rapid eye movement (REM)-AHI, and non-REM-AHI with mean glucose levels during nighttime (two periods: 11 pm to 3 am and 3 am to 6 am), daytime (8 am to 9 pm), and 24-hours. Models were adjusted for BMI and antihyperglycemic medications.

RESULTS

In 65 participants who were 35 ± 5 (mean ± SD) years of age with BMI of 33 ± 7 kg/m², 31% were undergoing insulin and/or metformin therapy. A ten-unit increase in AHI was associated with elevated nocturnal glucose levels (11 pm to 3 am: 0.20 mmol/L [95% CI, 0.04-0.40]) with persistent elevations into the morning (8 am: 0.26 mmol/L [95% CI, 0.08-0.4]) when adjusted for BMI and medications. REM-AHI was also associated with higher nocturnal and morning glucose levels, whereas non-REM was not. AHI was not associated with either mean daytime or 24-hour glucose levels.

INTERPRETATION

Greater severity of SDB was associated with higher nocturnal and morning glucose levels in women with GDM.

Obstructive sleep apnea and dyslipidemia: from animal models to clinical evidence

Lipid metabolism deregulation constitutes the pathogenic basis for the development of atherosclerosis and justifies a high incidence of cardiovascular-related morbidity and mortality. Some data suggest that dyslipidemia may be associated with sleep-disordered breathing, mainly obstructive sleep apnea (OSA), due to alterations in fundamental biochemical processes, such as intermittent hypoxia (IH). The aim of this systematic review was to identify and critically evaluate the current evidence supporting the existence of a possible relationship between OSA and alterations in lipid metabolism. Much evidence shows that, during the fasting state, OSA and IH increase lipid delivery from the adipose tissue to the liver through an up-regulation of the sterol regulatory element-binding protein-1 and stearoyl-CoA desaturase-1, increasing the synthesis of cholesterol esters and triglycerides. In the postprandial state, lipoprotein clearance is delayed due to lower lipoprotein lipase activity, probably secondary to IH-up-regulation of angiopoietin-like protein 4 and decreased activity of the peroxisome proliferator-activated receptor alpha. Moreover, oxidative stress can generate dysfunctional oxidized lipids and reduce the capacity of high-density lipoproteins (HDL) to prevent low-density lipoprotein (LDL) oxidation. In the clinical field, several observational studies and a meta-regression analysis support the existence of a link between OSA and dyslipidemia. Although there is evidence of improved lipid profile after apnea-hypopnea suppression with continuous positive airway pressure (CPAP), the majority of the data come from observational studies. In contrast, randomized controlled trials evaluating the effects of CPAP on lipid metabolism present inconclusive results and two meta-analyses provide contradictory evidence.

Obstructive Sleep Apnea, Hypoxia, and Nonalcoholic Fatty Liver Disease

Recent studies have demonstrated that obstructive sleep apnea (OSA) is associated with the development and evolution of nonalcoholic fatty liver disease (NAFLD), independent of obesity or other shared risk factors. Like OSA, NAFLD is a prevalent disorder associated with major adverse health outcomes: Patients with NAFLD may develop cirrhosis, liver failure, and hepatocellular carcinoma. One major finding that has emerged from these studies is that the OSA-NAFLD association is related to the degree of nocturnal hypoxemia in OSA. Animal models have therefore largely focused on intermittent hypoxia, a key manifestation of OSA, to shed light on the mechanisms by which OSA may give rise to the complex metabolic disturbances that are seen in NAFLD. Intermittent hypoxia leads to tissue hypoxia and can result in oxidative stress, mitochondrial dysfunction, inflammation, and overactivation of the sympathetic nervous system, among many other maladaptive effects. In such models, intermittent hypoxia has been shown to cause insulin resistance, dysfunction of key steps in hepatic lipid metabolism, atherosclerosis, and hepatic steatosis and fibrosis, each of which is pertinent to the development and/or progression of NAFLD. However, many intriguing questions remain unanswered: Principally, how aggressively should the clinician screen for NAFLD in patients with OSA, and vice versa? In this review, we attempt to apply the best evidence from animal and human studies to highlight the relationship between these two disorders and to advocate for further trials aimed at defining these relationships more precisely.

Individual differences in glucocorticoid regulation: Does it relate to disease risk and resilience?

Glucocorticoid (GC) signaling varies among individuals, and this variation may relate to individual differences in health outcomes. To determine if and which aspects of signaling (basal, circadian, integrative, or reactivity) are associated with specific health outcomes, we reviewed recent studies that relate GCs to health outcomes. We identified papers through PubMed and reviewed 100 original research articles related to mental health, cardiovascular health, cancer, diabetes, obesity, pulmonary health, sleep, and fitness. Many studies reported elevated GC secretion associated with worse health, but this was only particularly true for integrative GC measures. On the other hand, accentuated cortisol awakening response and a steeper circadian rhythm were both associated with positive health outcomes. Overall, relationships between GC secretion and health outcomes were relatively weak. This systematic review of relationships between GC metrics and health outcomes highlights the importance of careful consideration when selecting methods to measure GC regulation in health research.

Ruiz J, Buela-Casal G. Anxiety and Depression in Patients with Obstructive Sleep Apnoea before and after Continuous Positive Airway Pressure: The ADIPOSA Study

The prevalence and treatment response of depression and anxiety symptoms in obstructive sleep apnoea (OSA), although widely addressed in research and clinical settings, still remain unclear due to overlapping symptoms. The ADIPOSA study sought to elucidate the presence of non-overlapping symptoms of depression and anxiety in patients with moderate to severe OSA before and after continuous positive airway pressure (CPAP) treatment. Forty-eight adults aged 18-80 (68.75% men) with moderate to severe OSA were enrolled in this twelve-week longitudinal single-arm trial and completed a full-night ambulatory sleep diagnostic test and an assessment of cognitive-affective depression and anxiety symptoms using the Beck-Depression Inventory-Fast Screen (BDI-FS), the State-Trait Depression Inventory (IDER) and the State-Trait Anxiety Inventory (STAI). We found no cognitive-affective depression or anxiety symptoms of clinical relevance at baseline. The amelioration of depression and anxiety symptoms after CPAP use was only statistically significant when considering anxiety-trait (p < 0.01; d = 0.296) and euthymia (p < 0.05; d = 0.402), the distinctive component of depression. Although dysthymia or high negative affect remained unchanged, CPAP may be effective at reducing the lack of positive affect, a well-established health-protective factor. However, not until depression and anxiety disorders related to OSA are accurately measured in clinical and research settings will it be possible to obtain robust conclusions on the occurrence and amelioration of these symptoms after treatment.

Adrenal gland size in obstructive sleep apnea: Morphological assessment of hypothalamic pituitary adrenal axis activity

OBJECTIVES

The association of obstructive sleep apnea (OSA) with hypothalamic pituitary adrenal (HPA) axis activation has not been fully understood from results of previous studies using hormonal assessments. We aimed to investigate the relationship between adrenal size, a potential marker reflecting HPA axis activity, and sleep parameters related to OSA.

METHODS

We retrospectively reviewed data on 284 consecutive adult patients aged 20 to 80 y who had undergone polysomnography and abdominal computed tomography (CT). OSA was defined as none/mild (apnea-hypopnea index [AHI] <15, n = 75), moderate (AHI 15 to 30, n = 80), and severe OSA (AHI ≥30, n = 129). Widths of adrenal body and limbs were measured by abdominal CT.

RESULTS

Adrenal size was greater in participants with severe OSA than in those with none/mild or moderate OSA (adrenal body width: 6.03 mm, none/mild OSA; 6.09 mm, moderate OSA; 6.78 mm, severe OSA; p <0.001; adrenal limb width: 3.75 mm, none/mild OSA; 3.95 mm, moderate OSA; 4.26 mm, severe OSA, p <0.001). Multivariate regression analysis showed that not the 3% oxygen desaturation index and time of SpO2 <90% but a higher arousal index was the only determinant factor for increased adrenal limb width (β = 0.27, p <0.001) after adjusting for other variables that could affect adrenal size. Neither the arousal index nor hypoxic parameters were associated with adrenal body width.

CONCLUSIONS

Results indicated that adrenal glands may enlarge in response to longstanding sleep fragmentation, suggesting the involvement of OSA in HPA axis augmentation.

More Than the Sum of the Respiratory Events: Personalized Medicine Approaches for Obstructive Sleep Apnea

Traditionally, the presence and severity of obstructive sleep apnea (OSA) have been defined by the apnea-hypopnea index (AHI). Continuous positive airway pressure is generally first-line therapy despite low adherence, because it reliably reduces the AHI when used, and the response to other therapies is variable. However, there is growing appreciation that the underlying etiology (i.e., endotype) and clinical manifestation (i.e., phenotype) of OSA in an individual are not well described by the AHI. We define and review the important progress made in understanding and measuring physiological mechanisms (or endotypes) that help define subtypes of OSA and identify the potential use of genetics to further refine disease classification. This more detailed understanding of OSA pathogenesis should influence clinical treatment decisions as well as help inform research priorities and clinical study design. In short, treatments could be individualized on the basis of the underlying cause of OSA; patients could better understand which symptoms and outcomes will respond to OSA treatment and by how much; and researchers could select populations most likely to benefit from specific treatment approaches for OSA.

Obstructive Sleep Apnea Is Associated With Altered Glycemic Patterns in Pregnant Women With Obesity

OBJECTIVE

Often unrecognized, obstructive sleep apnea (OSA) worsens over pregnancy and is associated with poorer perinatal outcomes. The association between OSA in late pregnancy and metabolic biomarkers remains poorly understood. We tested the hypothesis that OSA in pregnant women with obesity is positively correlated with 24-hour patterns of glycemia and IR despite controlling for diet.

DESIGN

Pregnant women (32 to 34 weeks' gestation; body mass index, 30 to 40 kg/m2) wore a continuous glucose monitor for 3 days. OSA was measured in-home by WatchPAT 200™ [apnea hypopnea index (AHI), oxygen desaturation index (ODI; number per hour)]. Fasting blood was collected followed by a 2-hour, 75-g, oral glucose tolerance test to measure IR. Association between AHI and 24-hour glucose area under the curve (AUC) was the powered outcome.

RESULTS

Of 18 women (29.4 ± 1.4 years of age [mean ± SEM]), 12 (67%) had an AHI ≥5 (mild OSA). AHI and ODI were correlated with 24-hour glucose AUC (r = 0.50 to 0.54; P ≤ 0.03) and mean 24-hour glucose (r = 0.55 to 0.59; P ≤ 0.02). AHI and ODI were correlated with estimated hepatic IR (r = 0.59 to 0.74; P < 0.01), fasting free fatty acids (fFFAs; r = 0.53 to 0.56; P < 0.05), and waking cortisol (r = 0.49 to 0.64; P < 0.05).

CONCLUSIONS

Mild OSA is common in pregnant women with obesity and correlated with increased glycemic profiles, fFFAs, and estimates of hepatic IR. OSA is a potentially treatable target to optimize maternal glycemia and metabolism, fetal fuel supply, and pregnancy outcomes.

[Pathophysiological aspects of neuro-endocrine regulation system in patients with obstructive sleep apnea syndrome]

AIM

To reveal the changes in the pituitary-thyroid, pituitary-gonadal, adrenal components and in the prolactinergic system of neuroendocrine regulation in patients with severe obstructive sleep apnea syndrome (OSAS).

MATERIAL AND METHODS

The study involved 51 men aged 46-55 years. The main group (BG) included 37 patients with severe OSAS. The duration of clinical manifestations of OSAS was 10.5±1.5 years. OSAS was verified on the basis of clinical and functional studies and polysomnographic monitoring in accordance with the AASM criteria (2014). The control group (CG) consisted of 14 age-matched men without sleep-disordered breathing. The body mass index in BG was 34.2±1.8 compared to 28.2±2.1 kg/m² in CG. Serum concentrations of thyroid-stimulating hormone (TTG), free thyroxine (T4), triiodothyronine (T3), cortisol, prolactin, testosterone, luteonizing (LH) and follicle-stimulating (FSH) hormones were determined by the immunoradiological method using the standard DIA test system (Russia) and the analyzer 'Immunotest-800'.

RESULTS

Patients with severe OSAS had decreased concentration of free thyroxine (T4) and decreased activity of thyroid stimulating hormone (TSH) (р<0.001), increased concentration of prolactin and cortisol (р<0.001), decreased concentration of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone compared to the controls (р<0.001).

CONCLUSION

The changes in the hypothalamic-pituitary-gonadal system are a manifestation of disturbances of the mechanisms of self-regulation and compensation that indicates the presence of maladaptive reactions of the neuroendocrine system.

Associations of variants In the hexokinase 1 and interleukin 18 receptor regions with oxyhemoglobin saturation during sleep

Sleep disordered breathing (SDB)-related overnight hypoxemia is associated with cardiometabolic disease and other comorbidities. Understanding the genetic bases for variations in nocturnal hypoxemia may help understand mechanisms influencing oxygenation and SDB-related mortality. We conducted genome-wide association tests across 10 cohorts and 4 populations to identify genetic variants associated with three correlated measures of overnight oxyhemoglobin saturation: average and minimum oxyhemoglobin saturation during sleep and the percent of sleep with oxyhemoglobin saturation under 90%. The discovery sample consisted of 8,326 individuals. Variants with p < 1 × 10(-6) were analyzed in a replication group of 14,410 individuals. We identified 3 significantly associated regions, including 2 regions in multi-ethnic analyses (2q12, 10q22). SNPs in the 2q12 region associated with minimum SpO2 (rs78136548 p = 2.70 × 10(-10)). SNPs at 10q22 were associated with all three traits including average SpO2 (rs72805692 p = 4.58 × 10(-8)). SNPs in both regions were associated in over 20,000 individuals and are supported by prior associations or functional evidence. Four additional significant regions were detected in secondary sex-stratified and combined discovery and replication analyses, including a region overlapping Reelin, a known marker of respiratory complex neurons.These are the first genome-wide significant findings reported for oxyhemoglobin saturation during sleep, a phenotype of high clinical interest. Our replicated associations with HK1 and IL18R1 suggest that variants in inflammatory pathways, such as the biologically-plausible NLRP3 inflammasome, may contribute to nocturnal hypoxemia.

High Cortisol and the Risk of Dementia and Alzheimer's Disease: A Review of the Literature

Introduction: Cortisol effects on the brain are exerted through two distinct receptors, inducing complex and even opposite effects on the cerebral structures implicated in the various cognitive functions. High cortisol may also have deleterious effects on the brain structures and contribute to neurodegeneration, in particular Alzheimer’s disease (AD), via different mechanisms.

Objective: To examine the interrelationships between cortisol, cognitive impairment and AD.

Methods: Review of the literature.

Results: Clinical studies found that elevated cortisol was associated with poorer overall cognitive functioning, as well as with poorer episodic memory, executive functioning, language, spatial memory, processing speed, and social cognition; while in animals, glucocorticoid administration resulted in cognitive impairment and abnormal behavior. In cognitively healthy subjects, higher cortisol levels have been associated with an increased risk of cognitive decline and AD. Subjects with dementia and Mild Cognitive Impairment (MCI) due to AD have been found to have higher CSF cortisol levels than cognitively healthy controls. Elevated CSF cortisol may also be associated with a more rapid cognitive decline in MCI due to AD. Elevated cortisol levels have been also found in delirium. High cortisol may mediate the impact of stressful life events, high neuroticism, depression, sleep disturbances, as well as cardiovascular risk factors on cognitive performance, neurodegeneration, and cognitive decline. High cortisol may also exert neurotoxic effects on the hippocampus, and promote oxidative stress and amyloid β peptide toxicity. Further possible underlying mechanisms include the interactions of cortisol with inflammatory mediators, neurotransmitters, and growth factors.

Conclusion: Elevated cortisol levels may exert detrimental effects on cognition and contribute to AD pathology. Further studies are needed to investigate cortisol-reducing and glucocorticoidreceptor modulating interventions to prevent cognitive decline.

Sleep duration and risk of diabetes: Observational and Mendelian randomization studies

Inadequate sleep could contribute to type 2 diabetes, but observational studies are inconsistent and open to biases, particularly from confounding. We used Mendelian randomization (MR) to obtain an unconfounded estimate of the effect of sleep duration on diabetes, fasting glucose (FG) and hemoglobin A1c (HbA1c), and an observation study to assess differences by sex. Using MR, we assessed the effects of genetically instrumented sleep on diabetes, based on 68 single nucleotide polymorphisms (SNPs), applied to the DIAbetes Genetics Replication and meta-analysis case (n = 26,676)-control (n = 132,532) study and on FG and HbA1c, based on 55 SNPs, applied to the Meta-Analyses of Glucose and Insulin-related traits Consortium (MAGIC) study of FG (n = 122,743) and HbA1c (n = 123,665). In the population-representative Hong Kong Chinese "Children of 1997" birth cohort we assessed whether associations of sleep duration at ~17.5 years with FG and HbA1c differed by sex. Using inverse variance weighting with multiplicative random effects, sleep duration was not associated with diabetes (odds ratio (OR) 0.85 per hour of sleep, 95% confidence interval (CI) 0.64 to 1.13), FG (-0.032 mmol/l per hour of sleep, 95% CI -0.126 to 0.063) or HbA1c (-0.022% per hour of sleep, 95% CI -0.069 to 0.024). In "Children of 1997", the associations of sleep duration with FG differed by sex (p for interaction 0.05) but not with HbA1c. Overall sleep duration does not appear to be related to diabetes, FG or HbA1c, but the possibility of sex differences merits investigation.

Short-term effects of continuous positive airway pressure on oxidative stress in severe sleep apnea

PURPOSE

Obstructive sleep apnea (OSA) is associated with oxidative stress that is involved in the pathogenesis of cardiovascular and metabolic complications. The concentrations of salivary markers of oxidative stress in patients with OSA increase considerably during the night. The dynamics is not affected by continuous positive airway pressure (CPAP) in mild to moderate OSA. The aim of this study was to analyze the short-term effects of CPAP on salivary oxidative stress markers in patients with severe OSA.

METHODS

Salivary samples were collected from 24 patients with apnea-hypopnea index higher than 30 during the first (diagnostic) night, who were treated by CPAP during the second (therapeutic) night.

RESULTS

The salivary markers of oxidative stress (TBARS, AGEs, and AOPP) were higher in the morning after the diagnostic night when compared to the evening concentrations (p < 0.01 for TBARS and p < 0.05 for AGEs and AOPP). Treatment by CPAP significantly decreased the morning concentrations of TBARS, AOPP (p < 0.01 for both), and AGEs (p < 0.05). Also, TBARS and AGEs positively correlated with apnea-hypopnea index (r = 0.48 and 0.49, respectively; p < 0.05). Antioxidant statuss was not affected.

CONCLUSION

Severe OSA is associated with increased levels of saliva markers for lipid peroxidation, protein oxidative damage, and carbonyl damage. Even short-term CPAP partially prevents oxidative and carbonyl stress during the night and this can be monitored non-invasively using saliva.

Dose-dependent effects of continuous positive airway pressure for sleep apnea on weight or metabolic function: Individual patient-level clinical trial meta-analysis

Therapeutic-continuous positive airway pressure seems to increase weight compared with placebo-continuous positive airway pressure. It is not known whether weight gain with therapeutic-continuous positive airway pressure dose is dependent or whether it causes metabolic dysfunction. Data synthesis of three randomised placebo-continuous positive airway pressure-controlled trials (2-3 months) was performed to test whether there is a dose-dependent effect of continuous positive airway pressure on weight. Fasting glucose, insulin, insulin resistance (homeostatic model assessment), lipids and visceral abdominal fat were also tested to determine any effect on metabolic function. Mixed-model analysis of variance was used to quantify these effects. One-hundred and twenty-eight patients were analysed. Overall there was a small increase in weight with therapeutic-continuous positive airway pressure use compared with placebo-continuous positive airway pressure (difference: 1.17 kg; 0.37-1.97, p = 0.005), which was greater with high-use therapeutic-continuous positive airway pressure compared with high-use placebo-continuous positive airway pressure (1.45 kg; 0.10-2.80, p = 0.04). Continuous positive airway pressure use as a continuous variable was also significantly associated with weight change in continuous positive airway pressure users (0.30 kg hr^-1  night^-1 ; 0.04-0.56, p = 0.001), but not in placebo users (0.04 kg hr^-1  night^-1 ; -0.22 to 0.26, p = 0.76). Neither therapeutic-continuous positive airway pressure nor the dose of therapeutic-continuous positive airway pressure caused any changes to metabolic outcomes. The weight gain effects of medium-term therapeutic-continuous positive airway pressure appear modest and are not accompanied by any adverse metabolic effects.

Associations between polysomnography and actigraphy-based sleep indices and glycemic control among those with and without type 2 diabetes: the Multi-Ethnic Study of Atherosclerosis

Study Objectives

To examine the associations of sleep measures with hemoglobin A1c (HbA1c) among individuals with and without type 2 diabetes.

Methods

Data were from 2049 Multi-Ethnic Study of Atherosclerosis participants taking part in a sleep ancillary study. Cross-sectional linear regression models examined associations of actigraphy estimates of sleep (sleep duration, variability, and maintenance efficiency) and polysomnography measures (obstructive sleep apnea [OSA] and hypoxemia) with HbA1c, stratified by diabetes status. Primary models were adjusted for demographics, lifestyle behaviors, and obesity.

Results

Among individuals with diabetes (20 per cent population), those who slept <5 hr/night had greater HbA1c than those who slept 7-8 hr/night (7.44 vs. 6.98 per cent, ptrend = 0.04), with no attenuation of associations after adjusting for OSA/hypoxemia. In women with diabetes, but not men, those in the lowest quartile of sleep maintenance efficiency had greater HbA1c than those in the highest quartile of sleep maintenance efficiency (7.60 vs. 6.97 per cent, ptrend < 0.01). Among those without diabetes, individuals with severe OSA or in the highest quartile of hypoxemia had significantly greater HbA1c than those without OSA or who were in the lowest quartile of hypoxemia (5.76 vs. 5.66 per cent, ptrend = 0.01; 5.75 vs. 5.66 per cent, ptrend < 0.01, respectively). Associations did not meaningfully differ by race/ethnicity.

Conclusions

Among individuals with diabetes, HbA1c was significantly higher in men and women with short sleep duration and in women with poor sleep maintenance efficiency, suggesting a role for behavioral sleep interventions in the management of diabetes. Among individuals without diabetes, untreated severe OSA/hypoxemia may adversely influence HbA1c.

Obstructive sleep apnea and the metabolic syndrome: The road to clinically-meaningful phenotyping, improved prognosis, and personalized treatment

Obstructive sleep apnea (OSA) is an increasingly prevalent sleep disorder characterized by upper airway obstruction during sleep, resulting in breathing pauses, intermittent hypoxia, and fragmented sleep. In parallel, the constellation of adverse health outcomes associated with prolonged obesity, such as insulin resistance, elevated blood pressure, triglycerides, and reduced high-density lipoprotein cholesterol - termed metabolic syndrome -raises the risk of cardiovascular morbidity and mortality, type 2 diabetes, and all-cause mortality. Affecting 35-40% of U.S. adults, risk factors for metabolic syndrome, including obesity, middle age, sedentary behavior, and genetics, share considerable overlap with those for OSA. Thus, it has been difficult to disentangle cause, effect, and whether certain treatments, such as CPAP, can improve these outcomes. In this paper, we provide an update to our 2005 review which explored the association between OSA and metabolic syndrome, highlighting visceral obesity as the common etiological factor of both conditions. This update includes (a) recent data on physiological and biochemical mechanisms, (b) new data in nonobese men and women as well as children and adolescents, (c) insight from the latest treatment studies, (d) the role of aging in understanding clinically-meaningful phenotypes of the disorder, and (e) the potential diagnostic/prognostic utility of biomarkers in identifying OSA patients with the strongest cardiometabolic risk.

The Bidirectional Relationship Between Obstructive Sleep Apnea and Metabolic Disease

Obstructive sleep apnea (OSA) is a common sleep disorder, effecting 17% of the total population and 40-70% of the obese population (1, 2). Multiple studies have identified OSA as a critical risk factor for the development of obesity, diabetes, and cardiovascular diseases (3-5). Moreover, emerging evidence indicates that metabolic disorders can exacerbate OSA, creating a bidirectional relationship between OSA and metabolic physiology. In this review, we explore the relationship between glycemic control, insulin, and leptin as both contributing factors and products of OSA. We conclude that while insulin and leptin action may contribute to the development of OSA, further research is required to determine the mechanistic actions and relative contributions independent of body weight. In addition to increasing our understanding of the etiology, further research into the physiological mechanisms underlying OSA can lead to the development of improved treatment options for individuals with OSA.

Association of sleep disturbances with obesity, insulin resistance and the metabolic syndrome

Insufficient sleep, which has become endemic in recent years, has been variably associated with increased risk of obesity, disorders of glucose and insulin homeostasis, and the metabolic syndrome; to a lesser degree, so has excessive sleep. This review summarizes recent epidemiological and pathophysiological evidence linking sleep disturbances (primarily abnormalities of sleep duration) with obesity, insulin resistance, type 2 diabetes and the metabolic syndrome in children and adults.

Sleep biology updates: Hemodynamic and autonomic control in sleep disorders

Sleep disorders like obstructive sleep apnea syndrome, periodic limb movements in sleep syndrome, insomnia and narcolepsy-cataplexy are all associated with an increased risk of cardiovascular diseases. These disorders share an impaired autonomic nervous system regulation that leads to increased cardiovascular sympathetic tone. This increased cardiovascular sympathetic tone is, in turn, likely to play a major role in the increased risk of cardiovascular disease. Different stimuli, such as intermittent hypoxia, sleep fragmentation, decrease in sleep duration, increased respiratory effort, and transient hypercapnia may all initiate the pathophysiological cascade leading to sympathetic overactivity and some or all of these are encountered in these different sleep disorders. In this manuscript, we outline the different pathways leading to sympathetic over-activity in different sleep conditions. This augmented sympathetic tone is likely to play an important role in the development of cardiovascular disease in patients with sleep disorders, and it is further hypothesized to that sympathoexcitation contributes to the metabolic dysregulation associated with these sleep disorders.

Sleep-disordered breathing, circulating exosomes, and insulin sensitivity in adipocytes

BACKGROUND

Sleep-disordered-breathing (SDB), which is characterized by chronic intermittent hypoxia (IH) and sleep fragmentation (SF), is a prevalent condition that promotes metabolic dysfunction, particularly among patients suffering from obstructive hypoventilation syndrome (OHS). Exosomes are generated ubiquitously, are readily present in the circulation, and their cargo may exert substantial functional cellular alterations in both physiological and pathological conditions. However, the effects of plasma exosomes on adipocyte metabolism in patients with OHS or in mice subjected to IH or SF mimicking SDB are unclear.

METHODS

Exosomes from fasting morning plasma samples from obese adults with polysomnographically-confirmed OSA before and after 3 months of adherent CPAP therapy were assayed. In addition, C57BL/6 mice were randomly assigned to (1) sleep control (SC), (2) sleep fragmentation (SF), and (3) intermittent hypoxia (HI) for 6 weeks, and plasma exosomes were isolated. Equivalent exosome amounts were added to differentiated adipocytes in culture, after which insulin sensitivity was assessed using 0 nM and 5 nM insulin-induced pAKT/AKT expression changes by western blotting.

RESULTS

When plasma exosomes were co-cultured and internalized by human naive adipocytes, significant reductions emerged in Akt phosphorylation responses to insulin when compared to exosomes obtained after 24 months of adherent CPAP treatment (n = 24; p < 0.001), while no such changes occur in untreated patients (n = 8). In addition, OHS exosomes induced significant increases in adipocyte lipolysis that were attenuated after CPAP, but did not alter pre-adipocyte differentiation. Similarly, exosomes from SF- and IH-exposed mice induced attenuated p-AKT/total AKT responses to exogenous insulin and increased glycerol content in naive murine adipocytes, without altering pre-adipocyte differentiation.

CONCLUSIONS

Using in vitro adipocyte-based functional reporter assays, alterations in plasma exosomal cargo occur in SDB, and appear to contribute to adipocyte metabolic dysfunction. Further exploration of exosomal miRNA signatures in either human subjects or animal models and their putative organ and cell targets appears warranted.

Association between Erythrocyte Membrane Phospholipid Fatty Acids and Sleep Disturbance in Chinese Children and Adolescents

The relationship between circulating fatty acid (FA) composition and childhood sleep disturbance remains largely unclear. We aimed to investigate the association of erythrocyte membrane FA composition with prevalence of sleep disturbance in Chinese children and adolescents. A cross-sectional survey was conducted among 2337 school-aged children and adolescents who completed a clinical assessment in Beijing, China. Presence of sleep disturbance was self-reported or parent-reported by questionnaires. Erythrocyte FAs were measured by gas chromatography, and desaturase activities were estimated by FA ratios. Multivariable-adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for sleep disturbance across FA quartiles were calculated by a logistical regression model. We found higher proportions of erythrocyte phospholipid 24:0, 24:1n-9, and lower proportions of total n-3 polyunsaturated FA (PUFA), 22:5n-3 and 22:6n-3 in participants with sleep disturbance compared with those without. In the logistical regression models, significant inverse associations were found for total n-3 PUFA, 22:5n-3 and 22:6n-3, the highest versus lowest quartile ORs and 95% CIs were 0.57 (0.40, 0.82), 0.67 (0.47, 0.97) and 0.69 (0.49, 0.96), respectively. For per 1 SD difference of proportion, OR and 95% CI of prevalence of sleep disturbance was 0.91 (0.86, 0.97) for total n-3 PUFA, 0.90 (0.82, 0.98) for 22:5n-3, and 0.92 (0.86, 0.99) for 22:6n-3, respectively. No significant association was found for saturated fatty acids, monounsaturated fatty acids, n-6 polyunsaturated fatty acids or FA ratios. The present study suggested that erythrocyte n-3 PUFAs, especially 22:5n-3 and 22:6n-3, are inversely associated with prevalence of sleep disturbance in Chinese children and adolescents.

The Effect of Hypoxia and Metformin on Fatty Acid Uptake, Storage, and Oxidation in L6 Differentiated Myotubes

Metabolic impairments associated with obstructive sleep apnea syndrome (OSA) are linked to tissue hypoxia, however, the explanatory molecular and endocrine mechanisms remain unknown. Using gas-permeable cultureware, we studied the chronic effects of mild and severe hypoxia on free fatty acid (FFA) uptake, storage, and oxidation in L6 myotubes under 20, 4, or 1% O₂. Additionally, the impact of metformin and the peroxisome proliferator-activated receptor (PPAR) β/δ agonist, called GW501516, were investigated. Exposure to mild and severe hypoxia reduced FFA uptake by 37 and 32%, respectively, while metformin treatment increased FFA uptake by 39% under mild hypoxia. GW501516 reduced FFA uptake under all conditions. Protein expressions of CD36 (cluster of differentiation 36) and SCL27A4 (solute carrier family 27 fatty acid transporter, member 4) were reduced by 17 and 23% under severe hypoxia. Gene expression of UCP2 (uncoupling protein 2) was reduced by severe hypoxia by 81%. Metformin increased CD36 protein levels by 28% under control conditions and SCL27A4 levels by 56% under mild hypoxia. Intracellular lipids were reduced by mild hypoxia by 18%, while in controls only, metformin administration further reduced intracellular lipids (20% O₂) by 36%. Finally, palmitate oxidation was reduced by severe hypoxia, while metformin treatment reduced non-mitochondrial O₂ consumption, palmitate oxidation, and proton leak at all O₂ levels. Hypoxia directly reduced FFA uptake and intracellular lipids uptake in myotubes, at least partially, due to the reduction in CD36 transporters. Metformin, but not GW501516, can increase FFA uptake and SCL27A4 expression under mild hypoxia. Described effects might contribute to elevated plasma FFA levels and metabolic derangements in OSA.

Physiological consequences of CPAP therapy withdrawal in patients with obstructive sleep apnoea-an opportunity for an efficient experimental model

Randomised controlled trials (RCTs) of continuous positive airway pressure (CPAP) in obstructive sleep apnoea (OSA) are time consuming, and their findings often inconclusive or limited due to suboptimal CPAP adherence in CPAP-naïve patients with OSA. Short-term CPAP withdrawal in patients with prior optimal CPAP adherence results in recurrence of OSA and its consequences. Thus, this experimental model serves as an efficient tool to investigate both the consequences of untreated OSA, and potential treatment alternatives to CPAP. The CPAP withdrawal protocol has been thoroughly validated, and applied in several RCTs focusing on cardiovascular and metabolic consequences of untreated OSA, as well as the assessment of treatment alternatives to CPAP.

Does Hypoxia Decrease the Metabolic Rate?

In some organisms and cells, oxygen availability influences oxygen consumption. In this review, we examine this phenomenon of hypoxic hypometabolism (HH), discussing its features, mechanisms, and implications. Small mammals and other vertebrate species exhibit "oxyconformism," a downregulation of metabolic rate and body temperature during hypoxia which is sensed by the central nervous system. Smaller body mass and cooler ambient temperature contribute to a high metabolic rate in mammals. It is this hypermetabolic state that is suppressed by hypoxia leading to HH. Larger mammals including humans do not exhibit HH. Tissues and cells also exhibit reductions in respiration during hypoxia in vitro, even at oxygen levels ample for mitochondrial oxidative phosphorylation. The mechanisms of cellular HH involve intracellular oxygen sensors including hypoxia-inducible factors, AMP-activated protein kinase (AMPK), and mitochondrial reactive oxygen species (ROS) which downregulate mitochondrial activity and ATP utilization. HH has a profound impact on cardiovascular, respiratory, and metabolic physiology in rodents. Therefore, caution should be exercised when extrapolating the results of rodent hypoxia studies to human physiology.

A Pilot Randomized-Controlled Trial on the Effect of CPAP Treatment on Glycemic Control in Gestational Diabetes: Study Design and Methods

Background: Gestational diabetes (GDM) is associated with adverse short- and long-term maternal and fetal outcomes. Observational data support a link between sleep-disordered breathing (SDB) during pregnancy and GDM. However, it is unknown whether treatment of SDB with continuous positive airway pressure (CPAP) improves glucose control in this patient population. In addition, CPAP adherence and feasibility as a treatment option in pregnancy is unknown. This pilot randomized, controlled trial aims to primarily determine the feasibility of CPAP treatment in pregnant women with SDB and GDM. This study is also investigating the effect of SDB treatment on 24-h glucose profiles as an exploratory outcome. Objectives: To describe the study methodology in this ongoing study of pregnant women with GDM and SDB. Patients and Methods: Pregnant women with GDM and SDB defined by apnea-hypopnea index (AHI) ≥10 (Chicago Scoring Criteria) on level 2 polysomnography are randomized to either auto titrating CPAP (experimental group) or a nasal dilator strip (control group) until delivery. The primary outcome, objectively-assessed adherence to CPAP, is measured over the course of the treatment period using device-specific software. Recruitment and retention rates will be calculated to assess the feasibility for planning future trials. Twenty-four hour glucose profiles are measured over a 72-h period using the continuous glucose monitoring (CGM) system, before and after the intervention. Conclusion: The results of this study will be highly informative to determine whether CPAP is a feasible treatment for pregnant women with GDM and SDB, a specialized population at risk for substantial comorbidity. The trial results will ultimately be useful in planning future SDB treatment trials in pregnancy and GDM. The study is registered on clinicaltrials.gov (NCT02245659).

Oxyhemoglobin Saturation Overshoot Following Obstructive Breathing Events Mitigates Sleep Apnea-Induced Glucose Elevations

Background: Obstructive sleep apnea (OSA) and nocturnal hypoxia are associated with disturbances in glucose regulation and diabetes. Temporal associations between OSA, oxygenation profiles and glucose have not been well-described. We hypothesized that oxyhemoglobin desaturation during apneic events and subsequent post-apnea saturation overshoot predict nocturnal glucose. Methods: In 30 OSA patients who underwent polysomnography while subjected to CPAP withdrawal, we characterized S_PO₂ swings by frequency, desaturation depth, and overshoot height relative to baseline. We examined the associations between frequently sampled glucose and S_PO₂ swings during the preceding 10 min. We developed multi-variable mixed effects linear regression to examine the independent associations between glucose and each level of these S_PO₂ swings, while controlling for OSA severity. Results: Desaturation depth was not associated with glucose (p > 0.05). In contrast, overshoot was associated with glucose in a dose-dependent manner. Each S_PO₂ peak that did not rise to within 1% of baseline was associated with incremental glucose elevations of 0.49 mg/dL (p = 0.01), whereas peaks that exceeded baseline by >1% were associated with glucose reductions of 0.46 mg/dL. Overshoot remained an independent predictor of glucose after adjustment for mean S_PO₂ and OSA severity (p > 0.05). Conclusions: Vigorous S_PO₂ improvements after apneic events may protect patients against OSA-related glucose elevations.

Sleep apnea: An overlooked cause of lipotoxicity?

Obstructive sleep apnea (OSA) is a common sleep disorder associated with diabetes and cardiovascular disease. However, the mechanisms by which OSA causes cardiometabolic dysfunction are not fully elucidated. OSA increases plasma free fatty acids (FFA) during sleep, reflecting excessive adipose tissue lipolysis. In animal studies, intermittent hypoxia simulating OSA also increases FFA, and the increase is attenuated by beta-adrenergic blockade. In other contexts, excessive plasma FFA can lead to ectopic fat accumulation, insulin resistance, vascular dysfunction, and dyslipidemia. Herein, we propose that OSA is a cause of excessive adipose tissue lipolysis contributing towards systemic "lipotoxicity". Since visceral and upper-body obesity contributes to OSA pathogenesis, OSA-induced lipolysis may further aggravate the consequences of this metabolically harmful state. If this hypothesis is correct, then OSA may represent a reversible risk factor for cardio-metabolic dysfunction, and this risk might be mitigated by preventing OSA-induced lipolysis during sleep.