Response to statin therapy in obstructive sleep apnea syndrome: a multicenter randomized controlled trial

Continuous Positive Airway Pressure but Not GLP1-mediated Weight Loss Improves Early Cardiovascular Disease in Obstructive Sleep Apnea: A Randomized Proof-of-Concept Study

Rationale: Obstructive sleep apnea (OSA) is an independent risk factor for cardiovascular (CV) morbidity and mortality, but the benefit of continuous positive airway pressure (CPAP) is uncertain. However, most randomized controlled trials have focused on the role of CPAP in secondary prevention, although there is growing evidence of a potential benefit on early CV disease. Weight loss in combination with CPAP may be superior but is difficult to achieve and maintain with conventional measures alone. Objectives: The aim of this study was to gain insights into the effect of CPAP on early atherosclerotic processes and to compare it with a glucagon-like peptide (GLP)-1-mediated weight loss regimen in patients with OSA. Methods: We performed a randomized proof-of-concept study comparing CPAP, a GLP1-mediated weight-loss regimen (liraglutide [Lir]), and both in combination for 24 weeks in 30 consecutive patients with OSA (apnea-hypopnea index >15 events/h; body mass index 30-40 kg/m2; and no history of diabetes, heart failure, or unstable CV disease). In addition to extensive evaluation for CV risk factors and endothelial function at baseline and end of study, subjects underwent 18F-fluoro-2-deoxy-D-glucose positron emission tomography-computed tomography (18F-FDG PET-CT) for the measurement of aortic wall inflammation (target-to-background ratio) and coronary computed tomography angiography for semiautomated coronary plaque analysis. Results: Baseline characteristics were similar between groups. CPAP alone and in combination resulted in greater reduction in apnea-hypopnea index than Lir alone (mean difference, -45 and -43 events/h, respectively, vs. -12 events/h; P < 0.05). Both Lir and combination treatment led to significant weight loss, but only CPAP alone resulted in significant decrease in vascular inflammation (aortic wall target-to-background ratio from 2.03 ± 0.34 to 1.84 ± 0.43; P = 0.010), associated with an improvement in endothelial function and a decrease in C-reactive protein. Low-attenuation coronary artery plaque volume as a marker of unstable plaque also decreased with CPAP (from 571 ± 490 to 334 ± 185 mm3) and with combination therapy (from 401 ± 145 to 278 ± 126 mm3) but not with Lir. Conclusions: These data suggest that CPAP therapy, but not GLP1-mediated weight loss, improves vascular inflammation and reduces unstable plaque volume in patients with OSA. Further large randomized controlled studies are warranted to assess the benefit of CPAP therapy in modifying early CV disease. Clinical trial registered with www.clinicaltrials.gov (NCT04186494).

Statin's role on blood pressure levels: Meta-analysis based on randomized controlled trials

Statins have been proven to be effective in minimizing the risk of cardiovascular adverse events, however, their effect on BP variability is debatable with respect to their significance and their use as a potential anti-hypertensive. Using a meta-analysis approach, the aim of this study was to explore whether certain statins have the potential to lower blood pressure (BP). For the period 2002-2022, Scopus, PubMed, Web of Science, and the Cochrane Central Register of Controlled Trials databases were searched for the studies that examined the effect of statins on blood pressure in normotensive or hypertensive individuals. Randomized controlled clinical trials that investigated this effect were included based on our inclusion criteria. Our primary outcomes were changes in systolic and diastolic blood pressure (DBP). The final analysis of the study included 49 RCTs involving 45 173 participants randomized to receive either statins or placebo. Among the two groups, the total weighted mean difference (WMD) for systolic blood pressure (ΔSBP) was -1.42 (95% CI: -2.38, -0.46; p = .004) and diastolic blood pressure (ΔDBP) was 0.82 (95% CI: -1.28, -0.36; p = .0005). Despite various studies suggesting the efficacy of statins in blood pressure lowering to be significant and non-significant both, we observed a decrease in SBP and DBP both, although the change was not as large and could be considered significant. A large multicenter, multi-ethnic, large sample pool size, and a long period follow-up study is still required to assert these claims.

Effects of amlodipine combined with atorvastatin on Th17/Treg imbalance and vascular microcirculation in hypertensive patients with atherosclerosis: A double-blind, single-center randomized controlled trial

OBJECTIVE

Helper T cells 17 (Th17) and regulatory T cells (Treg), as CD4+T lymphocyte subsets, play an important role in the process of atherosclerosis. However, there are few studies on the regulation and efficacy of atorvastatin combined with amlodipine on Th17/Treg balance in hypertension combined with carotid atherosclerosis. Therefore, this study aims to verify the efficacy and immunomodulatory effects of atorvastatin combined with amlodipine in the treatment of hypertension combined with carotid atherosclerosis.

METHODS

A total of 260 patients with hypertension and carotid atherosclerosis were randomly divided into atorvastatin or combined treatment group. Inflammatory factors and Th17 and Treg levels were detected by enzyme-linked immunosorbent assay and flow cytometry. The messenger ribonucleic acid expression of retinoic acid receptor-related orphan receptor gamma and forkhead spiral transcription factor were detected by real-time quantitative polymerse chain reaction.

RESULTS

We found that the total effective rate in the treatment group was significantly higher than that in the control group. The levels of whole blood high shear viscosity, whole blood low shear viscosity, plasma specific viscosity and fibrin content in the 2 groups were significantly decreased after treatment, and the combined group was significantly lower than the control group (all P < .05). The improvement of endothelial function in the treatment group was also significantly higher than that in the control group (all P < .05). In addition, we found that there were statistically significant differences in Th17 percentage, Treg percentage and Treg/Th17 between the treatment group and the control group (P < .05). The messenger ribonucleic acid levels of retinoic acid receptor-related orphan receptor gamma and forkhead spiral transcription factor showed the same trend. Further detection of Th17-related inflammatory factors showed that the expression of interleukin (IL)-17, IL-6, IL-23 and tumor necrosis factor-α in the treatment group was significantly decreased, which was better than that in the control group (all P < .05).

CONCLUSION

These data indicate that amlodipine combined with atorvastatin can improve Th17/Treg imbalance, vascular endothelial function and efficacy in patients with hypertension and atherosclerosis.

A systematic review and meta-analyses on the effects of atorvastatin on blood pressure and heart rate

AIMS

Considering the inconsistencies in the literature on the atorvastatin effect on blood pressure (BP), we performed these meta-analyses.

METHODS AND RESULTS

Through a search of the Excerpta Medica Database (EMBASE), PubMed, and Web of Science databases, 1412 articles were identified, from which 33 randomized clinical trials (RCT) and 44 pre-clinical were selected. Populations from RCT were stratified according to baseline BP and lipid levels. We performed meta-analyses of the effect of atorvastatin on systolic (SBP), diastolic and mean BP; heart rate (HR); HR variability, and baroreflex. Atorvastatin reduced SBP in the overall population (P = 0.05 vs. placebo; P = 0.03 vs. baseline), in normotensive and hyperlipidaemic (P = 0.04 vs. placebo; P = 0.0001 vs. baseline) and in hypertensive and hyperlipidaemic (P = 0.02 vs. placebo; P = 0.008 vs. baseline) individuals in parallel RCT, but it did not affect SBP in normotensive and normolipidaemic individuals (P = 0.51 vs. placebo; P = 0.4 vs. baseline). Although an effect of atorvastatin was detected in hyperlipidaemic individuals, the meta-regression coefficient for the association of low density lipoprotein (LDL)-cholesterol reduction with SBP reduction in the overall population demonstrated that SBP reduction is not dependent on the changes in LDL-cholesterol. A meta-analysis of preclinical reports demonstrated that SBP was reduced in atorvastatin-treated hypertensive and normolipidaemic rats (spontaneously hypertensive rats: P < 0.00001), but not in normotensive and normolipidaemic rats (control rats: P = 0.97). Atorvastatin also reduced the HR in spontaneously hypertensive rat.

CONCLUSION

Atorvastatin lowers BP independent of LDL-cholesterol levels. Additional studies are needed to estimate the involvement of the autonomic nervous system in the BP-lowering effect of atorvastatin.

Correlation of Dyslipidemia and Inflammation With Obstructive Sleep Apnea Severity

Introduction: Obstructive sleep apnea (OSA) is a serious condition linked with various metabolic disorders and associated with increased all-cause and cardiovascular mortality. Although the potential mechanisms of pathophysiological processes related to OSA are relatively well known, the data regarding the correlation between obstructive sleep apnea, dyslipidemia, and systemic inflammation are still inconclusive.

Methods: The study was conducted as a retrospective cohort study including 328 patients with newly diagnosed obstructive sleep apnea during the period between April 2018, and May 2020, in University Clinical Hospital Center “Bezanijska kosa”, Belgrade, Serbia. Polysomnography was performed in all patients according to the protocol. Numerous demographic, antropometric, laboratory, and clinical data were correlated to Apnea-Hypopnea Index (AHI) as a dependent variable, with a particular review on the relation between lipid abnormalities, inflammatory parameters, and obstructive sleep apnea severity. Multivariate logistic regression model was used to assess predictors of severe OSA (AHI ≥30 per hour).

Results: A total of 328 patients were included in the study. The mean age of the patients was 54.0 ± 12.5 years and more than two-thirds were male (68.8%). The majority of the patients had an AHI of at least 30 events per hour. Patients with severe OSA were more frequently male, obese, hypertensive and hyperlipidemic, and had increased neck circumference (both male and female patients). One hundred and thirty-two patients had metabolic syndrome. Patients with severe OSA more frequently had metabolic syndrome and significantly higher levels of glucose, creatinine, uric acid, AST, ALT, CK, microalbumine/creatinine ratio, triglyceride, total cholesterol, HDL, total cholеsterol to HDL‐C ratio, CRP, and ESR. In the multivariate linear regression model with AHI (≥30 per hour) as a dependent variable, of demographic and clinical data, triglycerides ≥1.7 mmol/L and CRP >5 mg/L were significantly associated with AHI≥30 per hour.

Conclusion: The present study on 328 patients with newly diagnosed obstructive sleep apnea revealed significant relation of lipid abnormalities, inflammatory markers, and other clinically important data with obstructive sleep apnea severity. These results can lead to a better understanding of the underlying pathophysiological processes and open the door to a new world of potentially useful therapeutic modalities.

Atorvastatin attenuates intermittent hypoxia-induced myocardial oxidative stress in a mouse obstructive sleep apnea model

Chronic intermittent hypoxia (CIH), a hallmark of obstructive sleep apnea (OSA), is associated with various cardiovascular diseases. In the present study, we assessed the effect of the lipid reducing agent atorvastatin on CIH-induced myocardial oxidative stress and apoptosis in a mouse OSA model. Forty-eight C57BL/6J mice were evenly divided among normoxia + vehicle, normoxia + atorvastatin, CIH + vehicle, and CIH + atorvastatin groups. CIH consisted of a hypoxia-reoxygenation cycle in which oxygen concentrations fluctuated from 21% to 6% and back over two minutes for 8 hours each day (30 events/hour). CIH exposure continued for 12 weeks. Atorvastatin (5 mg/kg) was administered from week 6 through the end of the experiment. CIH increased malondialdehyde levels and decreased superoxide dismutase activity, total antioxidant capacity, and nuclear factor erythroid 2-related factor 2 levels in cardiac tissue, indicating a reduction in antioxidant activity. Atorvastatin significantly reversed those effects (p < 0.05). CIH also increased B-cell lymphoma 2-associated protein X and cleaved caspased-3 levels as well as the myocardial apoptotic rate, as indicated by terminal deoxynucleotidyl transferase dUTP nick-end labeling. Atorvastatin had no effect on those changes (p > 0.05). Thus, atorvastatin administration exerts antioxidant but not anti-apoptotic effects after CIH and may therefore have therapeutic potential in OSA patients with cardiovascular comorbidities.

Beneficial Effect of Statin Therapy on Arterial Stiffness

Arterial stiffness describes the increased rigidity of the arterial wall that occurs as a consequence of biological aging and several diseases. Numerous studies have demonstrated that parameters to assess arterial stiffness, especially pulse-wave velocity, are predictive of those individuals that will suffer cardiovascular morbidity and mortality. Statin therapy may be a pharmacological strategy to improve arterial elasticity. It has been shown that the positive benefits of statin therapy on cardiovascular disease is attributable not only to their lipid-lowering capacity but also to various pleiotropic effects, such as their anti-inflammatory, antiproliferative, antioxidant, and antithrombotic properties. Additionally, statins reduce endothelial dysfunction, improve vascular and myocardial remodeling, and stabilize atherosclerotic plaque. The aim of the present review was to summarize the evidence from human studies showing the effects of statins on arterial stiffness.

Complement promotes endothelial von Willebrand factor and angiopoietin-2 release in obstructive sleep apnea

STUDY OBJECTIVE

Obstructive sleep apnea (OSA) is highly prevalent and triples vascular thromboembolic risk. Intermittent hypoxia (IH) during transient cessation of breathing in OSA impairs endothelial protection against complement. Complement activation stimulates the endothelial release of a pro-thrombotic von Willebrand factor (vWF). We investigated whether increased complement activity in OSA promotes the endothelial release of vWF and pro-inflammatory angiopoietin-2. We further investigated whether improving complement protection with statins reverses these changes.

METHODS

Using endothelial cells (ECs) and blood collected from OSA patients (n = 109) and controls (n = 67), we assessed whether altered cellular localization of complement inhibitor CD59 in OSA modulates exocytosis of Weibel-Palade bodies (WPB), secretory granules that store vWF and angiopoietin-2. These interactions were also assessed in vitro in ECs exposed to normoxia or IH with or without recombinant complement C9 and with or without atorvastatin.

RESULTS

Circulating levels of angiopoietin-2 were greater in OSA than controls and levels of vWF cleavage products correlated with OSA severity. In cultured ECs, IH enhanced complement-stimulated angiopoietin-2 and vWF release by reducing EC surface and increasing intracellular expression of complement inhibitor CD59. Intracellular CD59 co-localized with WPB in OSA. IH increased binding of intracellular CD59 to syntaxin-3, which dissociated syntaxin-3 from voltage-sensitive calcium channel Cav1.2, and activated WPB exocytosis in a calcium-dependent manner. Atorvastatin reversed IH-enhanced endothelial release of vWF and angiopoietin-2.

CONCLUSIONS

IH promotes the complement-mediated release of vWF and angiopoietin-2, which may contribute to pro-thrombotic and pro-inflammatory conditions in OSA. Statin reversed these effects, suggesting a potential approach to reduce cardiovascular risk in OSA.

Effect of 12-month intervention with low-dose atorvastatin on pulse wave velocity in subjects with type 2 diabetes and dyslipidaemia

Cardiovascular disease is the leading cause of morbidity and mortality in subjects with type 2 diabetes mellitus. Increased aortic stiffness, assessed with the carotid-femoral pulse wave velocity, is an independent risk factor for cardiovascular disease. Statins reduce effectively cardiovascular disease and mortality in high-risk patients. The aim of this prospective non-randomized, observational study was to examine the impact of treatment with either 10 mg atorvastatin plus diet or diet alone on carotid-femoral pulse wave velocity in subjects with type 2 diabetes mellitus and dyslipidaemia. A total of 79 subjects with type 2 diabetes mellitus and dyslipidaemia were included; 46 subjects were treated with atorvastatin 10 mg daily plus diet and 33 were managed by diet alone for 12 months. Carotid-femoral pulse wave velocity and carotid-radial pulse wave velocity were measured using applanation tonometry. In the atorvastatin-treated group, carotid-femoral pulse wave velocity reduced significantly during the study and there was a trend for reduction in the carotid-radial pulse wave velocity. Total cholesterol, low-density lipoprotein cholesterol, triglycerides and C-reactive protein were reduced only in the atorvastatin-treated participants. No significant changes were found in body mass index, blood pressure, heart rate, diabetes control and high-density lipoprotein cholesterol in either study group. Treatment with low-dose atorvastatin for 12 months improves carotid-femoral pulse wave velocity in subjects with type 2 diabetes mellitus and dyslipidaemia.

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.

Impairment of vascular strain in patients with obstructive sleep apnea

Background

Obstructive sleep apnea (OSA) is an independent risk factor for the development of cardiovascular diseases. Aim of this present study was to evaluate and extend recent research on the influence of obstructive sleep apnea on vascular strain.

Methods

A total number of 98 patients were integrated in the study. Patients were grouped according to the Apnea-Hypopnea-Index (AHI) in patients with mild-to-moderate OSA (5/h ≤ AHI < 30/h), severe OSA (AHI ≥ 30/h) and controls (AHI < 5/h). Groups were matched in age, body-mass-index and cardiovascular risks. Vascular strain of common carotid arteries was assessed by ultrasound speckle-tracking. A minor group of 30 patients and controls further underwent assessment of vascular strain of brachial and femoral arteries. Additionally, all patients underwent blood testing to reveal potential influences of inflammatory markers on arterial stiffness. In additional analysis we examined the effect of statin therapy on vascular strain.

Results

Patients with OSA showed significantly reduced values of vascular strain of common carotid arteries. Radial and circumferential strains were significantly lower in both patients with mild-to-moderate (p = .05) and patients with severe OSA (p = .001) compared to control. Vascular strain parameters of brachial and femoral arteries showed no consistent results. There were no significant correlations of inflammatory markers with vascular strain parameters. No significant differences in vascular strain were detected between statin and non-statin groups.

Conclusion

Patients with OSA show significantly reduced vascular strain assessed by ultrasound-based speckle-tracking. Vascular stiffness increases with the severity of the disease. Target vessels to assess vascular strain in patients with OSA are common carotid arteries, whereas other sites of the arterial tree are not reliable. No significant impact of current statin therapy on vascular strain was found. Further studies are needed to evaluate potential benefit of statins in secondary prevention of atherosclerosis in OSA.

Effect of statin therapy on pulse wave velocity: A meta-analysis of randomized controlled trials

BACKGROUND AND OBJECTIVE

Arterial stiffness (AS) is an independent cardiovascular risk factor. A number of studies have reported a beneficial role of statins on AS albeit with controversial results, in addition to their effects on lipid profile. Therefore, we carried out a meta-analysis of the available randomized controlled trials assessing the effects of statin therapy on AS, in the attempt to reach more definitive conclusions.

METHODS

A systematic search of the on-line databases available up to March 2017 was conducted, including intervention studies reporting AS expressed by carotid-femoral pulse wave velocity (PWV), as difference between the effects of treatment with or without statins. For each study, mean difference (MD) and 95% confidence intervals (CI) were pooled using a random effect model.

RESULTS

Eleven studies met the pre-defined inclusion criteria, for a total of 573 participants and 2-144 weeks' intervention time. In the pooled analysis, statin therapy was associated with a -6.8% (95% C.I.: -11.7 to -1.8) reduction in PWV. There was significant heterogeneity among studies (I² = 96%); none of the study characteristics seems to have influenced the effect of statin use on PWV.

CONCLUSIONS

The results of this meta-analysis suggest that statin therapy reduces AS. This effect appears to be at least in part independent of the changes in blood pressure and lipid profile.

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.

Changes in inflammatory mediators as a result of intermittent hypoxia in obstructive sleep apnea syndrome

BACKGROUND

Inflammation plays an important role in obstructive sleep apnea syndrome (OSAS). The objective of this study was to investigate the relationship of serum C-reactive protein (CRP), pentraxin-3 (PTX-3), procalcitonin (ProCT), interleukin-33 (IL-33) and its soluble receptor ST2 (sST2) with the syndrome severity and to show theirs importance as biomarkers.

METHODS

This study comprises a total of 84 identical (sex and age wise) cases. Full-night polysomnography was performed in each patient. OSAS diagnosis and severity index being based on the widely used criterion known as Apnea Hypopnea Index(AHI). Subgroups were as follows: 24(AHI < 5) controls, 28 mild-moderate OSAS(AHI 5-30) and 32 severe OSAS(AHI > 30).

RESULTS

PTX-3, IL-33 and sST2 receptors were significantly higher in OSAS groups than the control group (P < .001). However, both CRP and ProCT levels were similar in all subjects. There was a positive correlation between PTX-3 and BMI (r = 0.446; P < .01), ODI (r = 0.555; P < .01), IL-33 (r = 0.348; P = .001) and sST2 (r = 326; P = .002), while there was a negative correlation with minimum SaO₂ (r = -0.672; P < .01) in patient group. PTX-3 as a predictor of OSAS showed highest specificity (%91.7) and sensitivity (%91.7) (P < .001).

CONCLUSIONS

PTX-3 can be a new indicator reflecting the inflammatory state in patients with OSAS. Since patients with OSAS could have more hypoxic state during sleep, we found higher PTX-3 level in those patients and a negative correlation between PTX-3 and minimum SaO₂ , which could explain that PTX-3 levels can increase with the severity of disease. Our results suggest that PTX-3 as an inflammatory biomarker may play a crucial role as an indicator of syndrome severity in OSAS.

The Association Between Obstructive Sleep Apnea and Carotid Intima-Media Thickness: A Systematic Review and Meta-Analysis

Obstructive sleep apnea (OSA) has been suggested as a risk factor for carotid atherosclerosis. The present meta-analysis aimed to evaluate the association between OSA and carotid intima-media thickness (CIMT). Eighteen studies comparing CIMT of patients with OSA versus non-OSA patients were included. Quantitative data synthesis was used to pool weighted standardized difference in means (SMD) of CIMT in a random-effects model. Compared to healthy controls, patients with OSA had a significantly higher CIMT (SMD: 0.881; 95% confidence interval [CI]: 0.647-1.115; P < .001). Due to the great heterogeneity, a subgroup analysis was conducted based on the study design. The pooled SMD of CIMT between patients with OSA and healthy controls were 0.810 (95% CI: 0.676-0.943; P < .001) and 1.008 (95% CI: 0.506-1.510; P < .001) in matched and unmatched group, respectively. Moreover, the correlation of apnea-hypopnea index and CIMT was moderate ( r = .389; 95% CI: 0.315-0.459; P < .001). After adjustment for several major confounders, OSA is an independent risk factor for CIMT. These findings remind clinicians to screen for cardiovascular diseases in patients with OSA.

Targeting the ROS-HIF-1-endothelin axis as a therapeutic approach for the treatment of obstructive sleep apnea-related cardiovascular complications

Obstructive sleep apnea (OSA) is now recognized as an independent and important risk factor for cardiovascular diseases such as hypertension, coronary heart disease, heart failure and stroke. Clinical and experimental data have confirmed that intermittent hypoxia is a major contributor to these deleterious consequences. The repetitive occurrence of hypoxia-reoxygenation sequences generates significant amounts of free radicals, particularly in moderate to severe OSA patients. Moreover, in addition to hypoxia, reactive oxygen species (ROS) are potential inducers of the hypoxia inducible transcription factor-1 (HIF-1) that promotes the transcription of numerous adaptive genes some of which being deleterious for the cardiovascular system, such as the endothelin-1 gene. This review will focus on the involvement of the ROS-HIF-1-endothelin signaling pathway in OSA and intermittent hypoxia and discuss current and potential therapeutic approaches targeting this pathway to treat or prevent cardiovascular disease in moderate to severe OSA patients.

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.

Beneficial effect of continuous positive airway pressure on lipid profiles in obstructive sleep apnea: a meta-analysis

Purpose

Dyslipidemia is considered as one mechanism causing cardiovascular sequelae in obstructive sleep apnea (OSA). Continuous positive airway pressure (CPAP) can reduce cardiovascular morbidities but its effect on lipid profiles is inconclusive. This study aimed to investigate the effects of CPAP on lipid profiles by a meta-analysis of the existing randomized controlled trials.

Methods

Studies were retrieved from MEDLINE/PubMed, EMBASE, CENTRAL, commercial websites, and article references up to August 2013 following the protocols (PROSPERO CRD42012002636). Randomized controlled trials investigating the CPAP effects on changes in lipid profiles in adult patients with OSA were included. Two independent researchers extracted relevant data in duplicate. The pooled effect was analyzed by fixed-effect generic inverse variance, and the heterogeneity was assessed using the I² statistic.

Results

Six trials with 348 patients and 351 controls were included. CPAP significantly lowered total cholesterol (mean, −6.23 mg/dl; 95% CI, −8.73 to –3.73; I², 0 %; p < 0.001), triglyceride (mean, −12.60 mg/dl; 95% CI, −18.80 to −6.41; I², 25 %; p < 0.001), and high-density lipoprotein (mean, −1.05 mg/dl; 95% CI, −1.69 to −0.40; I², 0 %; p = 0.001), but not low-density lipoprotein (mean, −1.01 mg/dl; 95% CI, −5.04 to 3.02; I², 0 %; p = 0.62). The lipid-lowering effects were homogeneous across the studies. By subgroup analysis, the reductions of lipid profiles were associated with the cross-over design, subtherapeutic CPAP as placebo, enrolled patients with moderate-to-severe OSA or daytime sleepiness, and CPAP treatment with short-term duration or good compliance.

Conclusions

This meta-analysis validates the observation that CPAP can reduce lipid profiles in patients with OSA.

Electronic supplementary material

The online version of this article (doi:10.1007/s11325-014-1082-x) contains supplementary material, which is available to authorized users.