Lipid metabolism: a new frontier in sleep apnea research

Unraveling the Complexities of Oxidative Stress and Inflammation Biomarkers in Obstructive Sleep Apnea Syndrome: A Comprehensive Review

BACKGROUND

Obstructive sleep apnea syndrome (OSAS), affecting approximately 1 billion adults globally, is characterized by recurrent airway obstruction during sleep, leading to oxygen desaturation, elevated carbon dioxide levels, and disrupted sleep architecture. OSAS significantly impacts quality of life and is associated with increased morbidity and mortality, particularly in the cardiovascular and cognitive domains. The cyclic pattern of intermittent hypoxia in OSAS triggers oxidative stress, contributing to cellular damage. This review explores the intricate relationship between OSAS and oxidative stress, shedding light on molecular mechanisms and potential therapeutic interventions.

METHODS

A comprehensive review spanning from 2000 to 2023 was conducted using the PubMed, Cochrane, and EMBASE databases. Inclusion criteria encompassed English articles focusing on adults or animals and reporting values for oxidative stress and inflammation biomarkers.

RESULTS

The review delineates the imbalance between pro-inflammatory and anti-inflammatory factors in OSAS, leading to heightened oxidative stress. Reactive oxygen species biomarkers, nitric oxide, inflammatory cytokines, endothelial dysfunction, and antioxidant defense mechanisms are explored in the context of OSAS. OSAS-related complications include cardiovascular disorders, neurological impairments, metabolic dysfunction, and a potential link to cancer. This review emphasizes the potential of antioxidant therapy as a complementary treatment strategy.

CONCLUSIONS

Understanding the molecular intricacies of oxidative stress in OSAS is crucial for developing targeted therapeutic interventions. The comprehensive analysis of biomarkers provides insights into the complex interplay between OSAS and systemic complications, offering avenues for future research and therapeutic advancements in this multifaceted sleep disorder.

A mediation analysis of metabolic and inflammatory factors in the severe sleep apnea-coronary heart disease association

BACKGROUND

It is unclear whether metabolic and inflammatory factors mediate the association between severe sleep apnea and coronary heart disease (CHD) in observational studies based on the large-scale population. This study aims to assess the association between severe sleep apnea and CHD and to explore the extent to which this association is mediated by metabolic factors and C-reactive protein (CRP).

METHODS

In UK Biobank, 213 442 CHD-free (mean age: 55.00) adults were followed up for 15 years to detect incident CHD. Metabolic factors included hyperglycemia, hypertension, dyslipidemia, hypertriglyceridemia, and hyperuricemia. A higher CRP concentration level was defined as a cutoff point of >3.0 mg/l. Data were analyzed using Cox proportional hazards models and the generalized structural equation model.

RESULTS

During follow-up, 9278 participants developed incident CHD (4.3%). The multi-adjusted hazard ratio and 95% confidence interval of CHD related to severe sleep apnea were 1.76 (1.44-2.15). In the mediation analysis, the strongest indirect association was for dyslipidemia, accounting for 20.8% of the association between severe sleep apnea and CHD (β = 0.22, 95% confidence interval = 0.16-0.28), followed by hypertriglyceridemia (12.3%). The proportion of mediation increased to 29.1% when CRP was added to the metabolic mediators.

CONCLUSIONS

Severe sleep apnea was associated with an increased risk of CHD. Lipid factors might play an essential role in the severe sleep apnea-CHD relationship. CRP increased the magnitude of mediation effects of overall metabolic factors. What is already known on this topic It is unknown whether the association between severe sleep apnea and CHD among the large population-based cohort study. Evidence on the mediating effect of metabolic and inflammatory factors in the severe sleep apnea-CHD association remains unclear. What this study adds Lipid factors were the biggest mediation driver in the severe sleep apnea-CHD path. C-reactive protein increased the magnitude of mediation effects of overall metabolic factors. How this study might affect research, practice or policy Investigating mediation analyses not only enhances comprehension of the pathophysiological connection between severe sleep apnea and CHD but also offers valuable insights into preventing CHD.

The association between biomarker angiopoietin-like protein five and obstructive sleep apnea in patients undergoing bariatric surgery

PURPOSE

Obstructive sleep apnea (OSA) is prevalent in the bariatric population. OSA should be recognized in patients undergoing bariatric surgery preoperatively to prevent peri- and post-operative complications. Lipid metabolism-related biomarkers are associated with OSA. Triglyceride metabolism is, among others, regulated by angiopoietin-like protein five (ANGPTL5). We aimed to evaluate the level of ANGPTL5 in patients with OSA of different severity levels before and after bariatric surgery.

METHODS

We performed a single-center prospective cohort study including a consecutive series of patients who underwent bariatric surgery. We collected the clinical data, polysomnography (PSG) or polygraphy (PG) parameters, and plasma derived via venipuncture before and 6 to 12 months after surgery. Lipid profile, glucose levels, and ANGPTL5 levels were assessed. ANGPTL5 levels were measured using an enzyme-linked immunosorbent assay (ELISA).

RESULTS

The study included 88 patients for analysis. The patients were divided into two subgroups: no or mild OSA (apnea-hypopnea index (AHI) < 15 events/hour, n = 57) and moderate-to-severe OSA (AHI ≥ 15 events/hour, n = 31). The ANGPTL5 level was higher in the moderate-to-severe OSA group (20.5 [15.6, 26.5] ng/mL) compared to the no or mild OSA group (16.3 [12.5, 19.4] ng/mL) (p = 0.008). A significant positive correlation was observed between ANGPTL5 and AHI (ρ = 0.256, p = 0.017), apnea index (AI) (ρ = 0.318, p = 0.003), and triglyceride levels (ρ = 0.240, p = 0.025). ANGPTL5 levels were reduced significantly after bariatric surgery in both moderate-to-severe OSA (15.6 [10.3, 18.7] ng/mL) and no or mild OSA (13.4 [9.2, 15.8] ng/mL) groups, though to a lower level in the group without or mild OSA. Post-surgery, the significant positive correlation between ANGPTL5 and AHI (ρ = 0.210, p = 0.047), AI (ρ = 0.230, p = 0.034), and triglyceride (ρ = 0.397, p < 0.001) remained.

CONCLUSION

The data showed increased levels of ANGPTL5 in patients with moderate-to-severe OSA. Both AHI and ANGPTL5 levels decreased significantly after bariatric surgery. We also report an association between ANGPTL5 levels and OSA severity.

Pathophysiological mechanisms and therapeutic approaches in obstructive sleep apnea syndrome

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

Increased plasma ANGPTL7 levels with increased obstructive sleep apnea severity

BACKGROUND

Weight-loss surgery is one of the recommended methods for treating obstructive sleep apnea (OSA) in obese patients. While weight reduction is critical to relieve symptoms of OSA, the biochemical factors involved in post-surgery improvement are still unknown. We aimed to explore the link between ANGPTL7 and OSA in patients with different OSA severity. Furthermore, we examined the effect of treating OSA with bariatric surgery on ANGPTL7 level.

METHODS

We quantified levels of circulating ANGPTL7 in fasting plasma and adipose tissue samples of 88 participants before and after bariatric surgery. Confocal microscopy analyses were also performed to assess the ANGPTL7 expression in subcutaneous white adipose tissue biopsies obtained from people with moderate-to-severe OSA compared to those with none or mild OSA. The study involved 57 individuals with none or mild OSA and 31 patients with moderate-to-severe OSA.

RESULTS

Levels of circulating ANGPTL7 were significantly higher in people with moderate-to-severe OSA (1440 ± 1310 pg/ml) compared to the none or mild OSA group (734 ± 904 pg/ml, p = 0.01). The increase in ANGPTL7 correlated significantly and positively with the apnea-hypopnea index (AHI, r = .226, p = .037), and AHI-supine (r = .266, p = .019) in participants with moderate-to-severe OSA. Multivariate logistic regression analysis demonstrated an association between ANGPTL7 and OSA severity (log₂ ANGPTL7; OR =1.24, p = 0.024). ANGPTL7 levels exhibited significant positive correlations with the levels of TG and oxLDL (p-value = 0.002 and 0.01 respectively). Bariatric surgery reduced the levels of both ANGPTL7 and AHI significantly.

CONCLUSION

Here we report significantly increased levels of ANGPTL7 both in the circulation and in adipose tissue of patients with OSA, which concurred with increased inflammation and OSA severity. Levels of ANGPTL7 decreased significantly as OSA showed a significant improvement post-surgery supporting a potential role for ANGPTL7 in either OSA progression or a role in an OSA-related mechanism.

Obstructive sleep apnea and cardiovascular comorbidity: common pathophysiological mechanisms to cardiovascular disease

Obstructive sleep apnea (OSA) is associated with many cardiovascular and metabolic diseases. Sleep apnea causes intermittent hypoxemia, chest pressure fluctuations and a reaction from the cerebral cortex in the form of a short awakening during sleep (EEG-activation). The consequences of pathological pathways are studied in experimental models involving cell cultures, animals, and healthy volunteers. At present, the negative impact of intermittent hypoxemia on a variety of pathophysiological disorders of the heart and blood vessels (vascular tone fluctuations, thickening of the intimamedia complex in the vascular wall, direct damaging effect on the myocardium) has a great evidence base. Two other pathological components of OSA (pressure fluctuations and EEG-activation) can also affect cardiovascular system, mainly affecting the increase in blood pressure and changing cardiac hemodynamics. Although these reactions are considered separately in the review, with the development of sleep apnea they occur sequentially and are closely interrelated. As a result, these pathological pathways trigger further pathophysiological mechanisms acting on the heart and blood vessels. It is known that these include excessive sympathetic activation, inflammation, oxidative stress and metabolic dysregulation. In many respects being links of one process, these mechanisms can trigger damage to the vascular wall, contributing to the formation of atherosclerotic lesions. The accumulated data with varying degrees of reliability confirm the participation of OSA through these processes in the formation of cardiovascular disorders. There are factors limiting direct evidence of this interaction (sleep deprivation, causing similar changes, as well as the inability to share the contribution of other risk factors for cardiovascular diseases, in particular arterial hypertension, obesity, which are often associated with OSA). It is necessary to continue the study of processes that implement the pathological effect of OSA on the cardiovascular system.

The effect of acute intermittent hypoxia on postprandial triglyceride levels in humans: a randomized crossover trial

Background

Obstructive sleep apnea (OSA), a sleep disorder frequently observed in individuals living with obesity, consists of repeated involuntary breathing obstructions during sleep, leading to intermittent hypoxia (IH). In humans, acute continuous hypoxia slightly increases plasma triglycerides (TG). However, no study yet compared the postprandial TG response of individuals with or without OSA under intermittent hypoxia.

Methods

Using a randomized crossover design, seven individuals diagnosed with moderate OSA and eight healthy individuals without OSA were given a meal after which they were exposed for 6 h to normoxia or intermittent hypoxia (e.g., 15 hypoxic events per hour). Blood lipid levels were measured hourly during each session.

Results

Peak postprandial TG concentrations tended to be 22% higher under IH irrespective of group (IH × time interaction, p = 0.068). This trend toward higher total plasma TG was attributable to increased levels of denser TG-rich lipoproteins such as very low-density lipoproteins (VLDL) and chylomicrons (CM) remnants. Irrespective of group, the postprandial TG concentrations in denser TG-rich lipoproteins was 20% higher under IH (IH × time interaction, p = 0.036), although IH had virtually no impact on denser TG-rich lipoprotein concentrations in the OSA group.

Conclusion

Acute intermittent hypoxia tends to negatively affect postprandial TG levels in healthy individuals, which is attributable to an increase in denser TG-carrying lipoprotein levels such as VLDL and CM remnants. This altered postprandial TG response to acute intermittent hypoxia was not observed in individuals with OSA.

Association of lipoprotein levels with sleep apnea: role of autonomic dysfunction

Objectives. Although multiple mechanisms, including autonomic dysfunction, seem to link sleep-disordered breathing (SDB) with dyslipidemia in animal studies, the data in clinical studies are limited. The aim of this study was to explore the association of lipoprotein levels with SDB measures in healthy habitual snorers. We supposed that autonomic dysfunction is the linking mechanism.Methods. We enrolled 110 previously healthy subjects with complaints of habitual snoring. To assess SDB, polysomnography was performed. Blood samples for the analysis of total cholesterol (TC), high-density lipoprotein (HDL), low-density lipoprotein cholesterol (LDL), and triglycerides (TG) were obtained in a fasting condition after the polysomnography. Baroreflex sensitivity (BRS) was used to assess the autonomic dysfunction.Results. In stepwise multiple linear regression analysis, minimal nocturnal blood oxygen saturation (beta=-0.240, p=0.020) and neck circumference (beta=0.224, p=0.03) were the only significant contributors in model predicting TG. SDB measures were not identified as significant contributors in models predicting TC, LDL, and HDL. We failed to find any significant difference in BRS in SDB subjects when compared according to the presence or absence of hypercholesterolemia/ hypertriglyceridemia. In SDB subjects, the area under the curve in a receiver operating curve to predict hypercholesterolemia and hypertriglyceridemia by BRS was 0.468 (95% CI: 0.328-0.608) and 0.425 (95% CI: 0.304-0.546), respectively.Conclusions. Our results suggest that minimal nocturnal blood oxygen saturation is significant contributor in model predicting TG. No significant decrease in BRS was found in SDB subjects with hypercholesterolemia and hypertriglyceridemia. In SDB subjects, the role of autonomic dys-function in the development of dyslipidemia remains controversial.

Obstructive sleep apnea and effects of continuous positive airway pressure on triglyceride-rich lipoprotein metabolism

This study aimed to explore lipoprotein metabolism in obstructive sleep apnea (OSA) and the effects of continuous positive airway pressure (CPAP). We studied 15 men with severe OSA [apnea-hypopnea index (AHI) ≥30 events/hour] and 12 age-, BMI-, and waist circumference-matched volunteers without OSA (AHI <5 events/hour). Carotid intima-media thickness (CIMT) was determined by a blind examiner. After 12 h fasting, a triglyceride-rich chylomicron-like emulsion, labeled with [¹⁴C]cholesteryl oleate and [³H]triolein, was injected intravenously followed by blood sample collection at preestablished times. Fractional clearance rate (FCR) of the radiolabeled lipids was estimated by compartmental analysis of radioisotope decay curves. Compared with controls, patients with OSA showed a significant delay in both cholesteryl ester FCR (0.0126 ± 0.0187 vs. 0.0015 ± 0.0025 min^-1; P = 0.0313) and triglycerides FCR (0.0334 ± 0.0390 vs. 0.0051 ± 0.0074 min^-1; P = 0.0001). CIMT was higher in the OSA group: 620 ± 17 vs. 725 ± 29 µm; P = 0.004. Cholesteryl ester FCRs were inversely related to total sleep time <90% (r = -0.463; P = 0.029) and CIMT (r = -0.601; P = 0.022). The triglyceride FCR was inversely correlated with AHI (r = -0.537; P = 0.04). In a subgroup of patients treated with CPAP for 3 months (n = 7), triglyceride FCR increased 5-fold (P = 0.025), but the cholesteryl ester FCR was unchanged. In conclusion, severe OSA decreased lipolysis of triglyceride-rich lipoproteins and delayed removal of remnants. CPAP treatment may be effective to restore the lipolysis rates.

[Cardiovascular risk and obstructive sleep apnea]

Le syndrome d'apnées obstructives du sommeil (SAOS) touche environ 4% des hommes et 2% des femmes d'âge moyen mais beaucoup de ces patients ne sont ni diagnostiqués ni traités. Une morbidité et une mortalité cardio et cérébrovasculaires sont associées aux apnées du sommeil. La notion de lien de causalité s'est confirmée ces dernières années sur des données épidémiologiques, expérimentales et thérapeutiques. La prévalence dans la population générale et l'impact sur la genèse et l'évolution de l'hypertension artérielle systémique et pulmonaire, des troubles du rythme cardiaque, de la maladie coronarienne, de l'insuffisance cardiaque et des accidents vasculaires cérébraux doivent inciter à diagnostiquer et à traiter précocement les troubles respiratoires du sommeil et si possible à les prévenir.

Which place of pharmacological approaches beyond continuous positive airway pressure to treat vascular disease related to obstructive sleep apnea?

Obstructive sleep apnea (OSA) is characterized by recurrent episodes of partial or complete upper airway obstruction, occurring during sleep, leading to chronic intermittent hypoxia (IH), which harms the cardiovascular system. OSA is associated with both functional and structural vascular alterations that contribute to an increased prevalence of fatal and non-fatal cardiovascular events. OSA is a heterogeneous disease with respect to the severity of hypoxia, the presence of daytime symptoms, obesity, and cardiovascular comorbidities. Various clusters of OSA phenotypes have been described leading to more highly personalized treatment. The aim of this review is to describe the various therapeutic strategies including continuous positive airway pressure (CPAP), oral appliances, surgery, weight loss, and especially pharmacological interventions that have been evaluated to reduce vascular alterations in both OSA patients and preclinical animal models. Conventional therapies, predominantly CPAP, have a limited impact on vascular alterations in the presence of co-morbidities. A better knowledge of pharmacological therapies targeting IH-induced vascular alterations will facilitate the use of combined therapies and is crucial for designing clinical trials in well-defined OSA phenotypes.

Obstructive sleep apnoea syndrome

Obstructive sleep apnoea syndrome (OSAS) is a common clinical condition in which the throat narrows or collapses repeatedly during sleep, causing obstructive sleep apnoea events. The syndrome is particularly prevalent in middle-aged and older adults. The mechanism by which the upper airway collapses is not fully understood but is multifactorial and includes obesity, craniofacial changes, alteration in upper airway muscle function, pharyngeal neuropathy and fluid shift towards the neck. The direct consequences of the collapse are intermittent hypoxia and hypercapnia, recurrent arousals and increase in respiratory efforts, leading to secondary sympathetic activation, oxidative stress and systemic inflammation. Excessive daytime sleepiness is a burden for the majority of patients. OSAS is also associated with cardiovascular co-morbidities, including hypertension, arrhythmias, stroke, coronary heart disease, atherosclerosis and overall increased cardiovascular mortality, as well as metabolic dysfunction. Whether treating sleep apnoea can fully reverse its chronic consequences remains to be established in adequately designed studies. Continuous positive airway pressure (CPAP) is the primary treatment modality in patients with severe OSAS, whereas oral appliances are also widely used in mild to moderate forms. Finally, combining different treatment modalities such as CPAP and weight control is beneficial, but need to be evaluated in randomized controlled trials. For an illustrated summary of this Primer, visit: http://go.nature.com/Lwc6te.

Clinical research strategies for fructose metabolism

Fructose and simple sugars are a substantial part of the western diet, and their influence on human health remains controversial. Clinical studies in fructose nutrition have proven very difficult to conduct and interpret. NIH and USDA sponsored a workshop on 13-14 November 2012, "Research Strategies for Fructose Metabolism," to identify important scientific questions and parameters to be considered while designing clinical studies. Research is needed to ascertain whether there is an obesogenic role for fructose-containing sugars via effects on eating behavior and energy balance and whether there is a dose threshold beyond which these sugars promote progression toward diabetes and liver and cardiovascular disease, especially in susceptible populations. Studies tend to fall into 2 categories, and design criteria for each are described. Mechanistic studies are meant to validate observations made in animals or to elucidate the pathways of fructose metabolism in humans. These highly controlled studies often compare the pure monosaccharides glucose and fructose. Other studies are focused on clinically significant disease outcomes or health behaviors attributable to amounts of fructose-containing sugars typically found in the American diet. These are designed to test hypotheses generated from short-term mechanistic or epidemiologic studies and provide data for health policy. Discussion brought out the opinion that, although many mechanistic questions concerning the metabolism of monosaccharide sugars in humans remain to be addressed experimentally in small highly controlled studies, health outcomes research meant to inform health policy should use large, long-term studies using combinations of sugars found in the typical American diet rather than pure fructose or glucose.

[Cardiovascular morbidity associated with obstructive sleep apnea syndrome]

INTRODUCTION

The obstructive sleep apnoea syndrome (OSAS) had become a major public health concern in modern society due to its high prevalence but, above all, to its associated morbidity, especially cardiovascular.

BACKGROUND

Untreated OSAS is associated with an increased incidence of fatal (myocardial infarction and stroke) (odds ratio: 2.87) and non-fatal cardiovascular events (myocardial infarction, stroke, coronary artery bypass surgery and coronary angiography) (odds ratio: 3.17). Moreover, the prevalence of hypertension in patients with OSAS is high, between 35 and 80%. The pathophysiological mechanisms leading to these complications are mainly due to intermittent hypoxia secondary to repeated episodes of apnoea/hypopnoea during sleep. These mechanisms include sympathetic hyperactivation, impairment of vasomotor reactivity, vascular inflammation, oxidative stress and metabolic disorders. In patients with OSAS, the impact of continuous positive pressure is proven in terms of prevention of cardiovascular events although blood pressure reduction is limited. Obviously these effects are proportional to observance.

CONCLUSION

OSAS does increase the cardiovascular risk, independently of other risk factors. Although the impact of treatment is relatively low in decreasing blood pressure, it seems essentially effective in preventing cardiovascular morbidity. Therefore, OSAS screening, and the association of specific treatments in cardio-metabolic patients and OSAS patients respectively, should be included in clinical strategies.

Obstructive sleep apnea and kidney disease: is there any direct link?

BACKGROUND

Obstructive sleep apnea (OSA) is a common and underrecognized disorder affecting at least 2% and 4% of women and men, respectively. Chronic kidney disease (CKD), on the other hand, affects around 13% of US adults. Both of these conditions share some risk factors such as age, obesity, and smoking and are associated with increased cardiovascular morbidity and mortality. By itself OSA may play a role in the development of arterial hypertension, metabolic syndrome, type 2 diabetes mellitus, and dyslipidemia with potential impact on CKD development and/or progression. But the data regarding OSA and CKD are relatively scant.

DISCUSSION

Moreover, several studies had shown possible harmful effects on kidney function independent from conventional risk factors. CKD is associated with excessive fluid volume, with potential shift during recumbency towards the neck area with increased upper airway resistance. Thus, OSA and CKD may be the results of each other and when present together may impose much greater cardiovascular risk than either disease alone.