Biomarkers of oxidative stress following continuous positive airway pressure withdrawal: data from two randomised trials

The effect of supplemental oxygen and continuous positive airway pressure withdrawal on endocan levels

PURPOSE

Endocan is a biomarker of endothelial dysfunction, which is a precursor to cardiovascular disease. Obstructive sleep apnoea (OSA) is associated with elevated endocan levels but the effects of treatment on endocan levels in OSA are not fully established. We aimed to determine whether endocan levels could be detected by immunoassay and to determine the effect of supplemental oxygen during continuous positive airway pressure (CPAP) withdrawal on circulating endocan levels.

METHODS

We conducted an exploratory analysis from a randomised controlled crossover study which included participants with OSA. Participants stopped their CPAP therapy and were randomised to receive either supplemental oxygen or sham for 14 nights before crossing over. Supplemental oxygen blocked the rise in blood pressure seen in the sham group. We analysed plasma endocan levels by immunoassay at baseline and after 14 nights of intervention in both groups.

RESULTS

Twenty-five participants were included, with a total of 100 samples. Endocan levels were detectable at all time points in 22 participants (88%), and in 93 (93%) samples. Supplemental oxygen had no effect on endocan levels compared to sham (+ 0.52 ng/ml, 95%CI -0.21 to + 1.25, p = 0.16), and there was no significant difference in endocan levels from baseline to follow-up in either the sham (-0.30 ng/ml, 95%CI -0.89 to + 0.30, p = 0.31) or supplemental oxygen (+ 0.22 ng/ml, 95%CI 0.00 to + 0.44, p = 0.05) arm.

CONCLUSIONS

We have shown that endocan levels are detectable before and after CPAP withdrawal. However, we found no effect of supplemental oxygen following CPAP withdrawal on circulating endocan levels.

TRIAL REGISTRATION AND DATE

ISRCTN 17,987,510 19/02/2015.

Role of Oxidative Stress in the Occurrence and Development of Cognitive Dysfunction in Patients with Obstructive Sleep Apnea Syndrome

Obstructive sleep apnea syndrome (OSAS) causes recurrent apnea and intermittent hypoxia at night, leading to several complications such as cognitive dysfunction. However, the molecular mechanisms underlying cognitive dysfunction in OSAS are unclear, and oxidative stress mediated by intermittent hypoxia is an important mechanism. In addition, the improvement of cognitive dysfunction in patients with OSAS varies by different treatment regimens; among them, continuous positive airway pressure therapy (CPAP) is mostly recognized for improving cognitive dysfunction. In this review, we discuss the potential mechanisms of oxidative stress in OSAS, the common factors of affecting oxidative stress and the Links between oxidative stress and inflammation in OSAS, focusing on the potential links between oxidative stress and cognitive dysfunction in OSAS and the potential therapies for neurocognitive dysfunction in patients with OSAS mediated by oxidative stress. Therefore, further analysis on the relationship between oxidative stress and cognitive dysfunction in patients with OSAS will help to clarify the etiology and discover new treatment options, which will be of great significance for early clinical intervention.

Pde5 Inhibition Reduced Blood Pressure and Alleviated Target Organ Damage in Chronic Intermittent Hypoxia

ABSTRACT

The role of phosphodiesterase 5 (Pde5) in obstructive sleep apnea-induced damage remains unclear. Our study aimed to investigate the role of Pde5 in the chronic intermittent hypoxia (CIH) model. C57BL/6J wild-type (WT) mice (n = 48) and Pde5 knockout (Pde5 -/- ) mice (n = 24) were randomly assigned to CIH group and room air group. After 6 weeks, some WT mice (n = 24) in CIH group were given sildenafil or saline gavage for another 4 weeks. Blood pressure was regularly measured during the experiment. Echocardiography was used to estimate cardiac function. We collected organs from each group of mice and measured their physical indicators. Histochemical staining was used to explore the size of cardiomyocyte and fibrosis area of various organs. Cyclic guanosine monophosphate and malondialdehyde concentrations in serum were measured by ELISA assay. Compared with the RA-treated group, the 6-week CIH resulted in a significant increase in blood pressure, altered heart structure, and reduced serum cyclic guanosine monophosphate in WT mice. Pde5 -/- mice and sildenafil intragastric administration significantly reduced systolic blood pressure in CIH condition and attenuated the damage of target organs. In CIH model, we found that the cardiomyocyte size and fibrosis area of heart and kidney significantly reduced in Pde5 -/- groups. Besides, endogenous and exogenous inhibition of Pde5 reduced malondialdehyde level and inflammatory and oxidative stress markers expression in CIH condition. In this study, we found that Pde5 inhibition could reduce blood pressure and alleviate target organ damage in the CIH model, which may be mediated through the oxidative stress pathway.

The effect of continuous positive airway pressure on total antioxidant capacity in obstructive sleep apnea: a systematic review and meta-analysis

BACKGROUND

Obstructive sleep apnea (OSA), a sleep-related disorder with high prevalence, is associated with an imbalance in oxidative stress and is linked to cardiovascular disease. There are conflicting reports regarding the effectiveness of continuous positive airway pressure (CPAP) therapy on oxidative stress/antioxidant markers in patients with OSA. This review was performed to evaluate the influence of therapy with CPAP on serum/plasma total antioxidant capacity (TAC) in patients with OSA.

METHODS

The Cochrane Library, Web of Science, Scopus, Embase, and PubMed were searched through June 2022 to obtain studies evaluating CPAP treatment on TAC in patients with OSA. Overall results were tested using standardized mean difference (SMD) with a 95% confidence interval (CI). Comprehensive Meta-Analysis V2 software was employed to perform analyses.

RESULTS

Ten studies with 12 effect sizes were eligible for inclusion in this analysis. The overall SMD revealed that CPAP therapy significantly increased TAC [SMD 0.497; 95% CI: 0.21 to 0.77; p: 0.00] in OSA. Analyses based on subgroups showed that the effect of CPAP therapy was significant in all subgroups according to therapy duration, age, BMI, and AHI. Whereas the meta-regression results indicated that the impact of therapy with CPAP on TAC is associated with AHI, BMI, and age in patients with OSA.

CONCLUSIONS

The finding of this meta-analysis demonstrated a favorable impact of CPAP therapy on TAC levels in patients suffering from OSA.

Continuous positive airway pressure affects mitochondrial function and exhaled PGC1-α levels in obstructive sleep apnea

Purpose: Subjects with obstructive sleep apnea (OSA) exhibit systemic and upper airway oxidative stress and inflammation, which cause mitochondrial dysfunction. The intend of this study is to estimate mitochondrial function (mitochondrial DNA/nuclear DNA [Mt/N] ratio) and protein levels of peroxisome proliferator-coactivated receptor gamma co-activator 1-alpha (PGC1-α) in the exhaled breath condensate (EBC) and plasma before and after continuous positive airway pressure (CPAP) treatment. Materials and methods: Twenty healthy individuals (control) and 40 subjects with severe or moderate OSA were recruited to undergo CPAP treatment and evaluation in a sleep study. The Mt/N ratio in the EBC and blood were assayed by quantitative real-time polymerase chain reaction. Enzyme-linked immunosorbent assay was used to measure the protein concentration of PGC1-α in the EBC and plasma. All experiments were performed after 3 months of CPAP treatment in subjects with OSA. Results: We observed no noteworthy differences between the control and treatment groups. Moreover, there were no differences in the Mt/N ratio in the blood and plasma levels of PGC1-α in subjects with OSA before and after treatment. However, the Mt/N ratio and protein levels of PGC1-α in the EBC of OSA subjects were higher than those in the control group and returned to normal levels after CPAP treatment. Conclusions: We successfully treated subjects with OSA by CPAP, which restored the Mt/N ratio and levels of PGC1-α in the EBC.

Sex-Specific Differential Responses of Circulating Biomarkers in Obstructive Sleep Apnea Treatment. A Post Hoc Analysis of a Randomized Controlled Trial

Rationale: Knowledge of sex-specific changes of cardiovascular biomarkers in response to continuous positive airway pressure (CPAP) therapy for obstructive sleep apnea (OSA) is limited.Objectives: We hypothesized a differential sex-specific cardiovascular biomarker response with CPAP therapy for OSA.Methods: Participants with moderate-severe OSA (apnea-hypopnea index, 15 events/h) were randomized to CPAP versus sham and completed polysomnography and collection of biomarkers of inflammation (myeloperoxidase, fibrinogen, paraoxonase, interleukin [IL]-6, IL-6 soluble receptor, aryl esterase, oxidized low-density lipoprotein, lipoprotein A, plasminogen activator inhibitor 1, and F₂-isoprostane urine/creatinine ratio) and vascular measures at baseline and 8 weeks of therapy with either CPAP (n = 72) or sham treatment (n = 70). Post hoc secondary analyses of sex-study arm interaction relative to change in inflammatory biomarkers were evaluated via linear regression with adjustment for baseline biomarker value, age, race, body mass, index, waist circumference, and CPAP adherence. Interactions were further evaluated via sex-stratified analyses.Results: The study sample comprised a total of 149 participants aged 50.8 ± 11.7 years; 55% were male, and 55% were white. Participants had a median apnea-hypopnea index of 26.3 events per hour (interquartile range, 13-37). There were substantial interactions between study arm and sex for myeloperoxidase, paraoxonase, and fibrinogen (P = 0.03, P = 0.03, and P = 0.08, respectively). No significant interactions were found for the vascular measures. Estimates were similar but with decreased power in sex-stratified analyses, with decreased biomarkers in women and increased biomarkers in men.Conclusions: Differential sex-specific responses to CPAP therapy for OSA were observed for circulating inflammatory biomarkers, which persisted after adjustment for confounders. These findings set the stage for validation studies and, if confirmed, biochemical pathway elucidation to inform sex-specific personalized treatment approaches.Clinical trial registered with www.clinicaltrials.gov (NCT00607893).

Oxidative Stress and Inflammation Biomarker Expression in Obstructive Sleep Apnea Patients

Obstructive Sleep Apnea Syndrome (OSAS) is a respiratory sleep disorder characterised by repeated episodes of partial or complete obstruction of the upper airway during the night. This obstruction usually occurs with a reduction (hypopnea) or complete cessation (apnea) of the airflow in the upper airways with the persistence of thoracic-diaphragmatic respiratory movements. During the hypopnea/apnea events, poor alveolar ventilation reduces the oxygen saturation in the arterial blood (SaO₂) and a gradual increase in the partial arterial pressure of carbon dioxide (PaCO₂). The direct consequence of the intermittent hypoxia is an oxidative imbalance, with reactive oxygen species production and the inflammatory cascade’s activation with pro and anti-inflammatory cytokines growth. Tumour necrosis factors, inflammatory cytokines (IL2, IL4, IL6), lipid peroxidation, and cell-free DNA have been found to increase in OSAS patients. However, even though different risk-related markers have been described and analysed in the literature, it has not yet been clarified whether specified inflammatory bio-markers better correlates with OSAS diagnosis and its clinical evolution/comorbidities. We perform a scientific literature review to discuss inflammatory and oxidative stress biomarkers currently tested in OSAS patients and their correlation with the disease’s severity and treatment.

Effects of continuous positive airway pressure on resolvin and matrix metalloproteinase-9 in patients with obstructive sleep apnea

PURPOSE

Resolvin is a checkpoint controller in inflammation. Matrix metalloproteinase-9 (MMP-9) is an airway remodeling regulator. We evaluated the levels of resolvin and MMP-9 protein in the serum and exhaled breath condensate (EBC) before and after continuous positive airway pressure (CPAP) treatment.

METHOD

We enrolled 20 non-OSA snorers and 40 patients with moderate to severe OSA scheduled for CPAP treatment. ELISA was used to assess resolvin and MMP-9 levels in the serum and EBC. All patients underwent sleep assessment at baseline and 3 months after CPAP.

RESULTS

There was no between-group difference; moreover, there were no differences in the pre- and post-treatment serum levels of resolvin and MMP-9 in patients with OSA. Compared with non-OSA snorers, patients with OSA had lower resolvin and higher MMP-9 levels in the EBC. After CPAP treatment, the EBC levels of resolvin and MMP-9 in patients with OSA returned to normal.

CONCLUSIONS

Successful OSA treatment by CPAP can normalize EBC levels of resolvin and MMP-9.

Effects of continuous positive airway pressure on exhaled transforming growth factor-β and vascular endothelial growth factor in patients with obstructive sleep apnea

Background

Both transforming growth factor β (TGF-β) and vascular endothelial growth factor (VEGF) are master regulators of airway remodeling; however, their pathological roles in obstructive sleep apnea (OSA) remain unclear. The aim of the present study was to evaluate the expression of TGF-β and VEGF protein in the serum and exhaled breath condensate (EBC) before and after continuous positive airway pressure (CPAP) treatment in OSA patients.

Methods

Forty patients with moderate to severe OSA requiring CPAP and 20 healthy subjects were prospectively recruited. The concentrations of TGF-β and VEGF protein in the serum and EBC were evaluated by enzyme-linked immunosorbent assay. All OSA patients underwent a sleep study that was repeated 3 months after receiving CPAP therapy.

Results

Protein concentrations of TGF-β and VEGF in the serum did not differ between healthy controls and OSA patients before CPAP treatment. There was also no difference in the serum protein concentrations of TGF-β and VEGF of the OSA patients before and after CPAP treatment. However, both the TGF-β and VEGF protein concentrations in the EBC were higher in the OSA patients than those in control subjects, and recovered to normal levels after CPAP.

Conclusions

Successful treatment of OSA by CPAP can restore the TGF-β and VEGF protein concentrations in the EBC.

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 apnoea in acute coronary syndrome

Obstructive sleep apnoea (OSA) syndrome affects about 13% of the male and 7-9% of the female population. Hypoxia, oxidative stress and systemic inflammation link OSA and cardiovascular and metabolic consequences, including coronary artery disease. Current research has identified several clinical phenotypes, and the combination of breathing disturbances during sleep, systemic effects and end-organ damage might help to develop personalised therapeutic approaches. It is unclear whether OSA is a risk factor for acute coronary syndrome (ACS) and might affect its outcome. On the one hand, OSA in patients with ACS may worsen prognosis; on the other hand, OSA-related hypoxaemia could favour the development of coronary collaterals, thereby exerting a protective effect. It is unknown whether positive airway pressure treatment may influence adverse events and consequences of ACS. In non-sleepy patients with OSA and stable coronary artery disease, randomised controlled trials failed to show that continuous positive airway pressure (CPAP) treatment protected against cardiovascular events. Conversely, uncontrolled studies suggested positive effects of CPAP treatment in such patients. Fewer data are available in subjects with ACS and OSA, and results of randomised controlled studies on the effects of CPAP are expected shortly. Meanwhile, the search for reliable markers of risk continues. Recent studies suggest that daytime sleepiness may indicate a more severe OSA phenotype with regard to cardiovascular risk. Finally, some studies suggest sex-related differences. The picture is still incomplete, and the potential role of OSA in patients with ACS awaits confirmation, as well as clear definition of subgroups with different degrees of risk.

Circulating adipocyte fatty acid-binding protein is reduced by continuous positive airway pressure treatment for obstructive sleep apnea-a randomized controlled study

PURPOSE

The circulating level of adipocyte fatty acid-binding protein (AFABP), a biomarker with prognostic and therapeutic importance in metabolic disorders, has been shown to be elevated in obstructive sleep apnea (OSA). This randomized controlled study aimed to investigate the effect of continuous positive airway pressure (CPAP) treatment for OSA on AFABP levels.

METHODS

Consecutive subjects attending sleep study were invited if they were confirmed to have severe OSA and were free of metabolic diseases. Participants were randomized (1:1) into CPAP or observation group for 4 weeks. Demographics, anthropometric data, and circulating biomarkers were checked at baseline and after the 4-week study period.

RESULTS

Ninety subjects were randomized. The mean age was 46 ± 9 years old; 82% were male. Their mean body mass index (BMI) was 29 ± 5 kg/m². By intention-to-treat approach, the CPAP group showed significant reductions in Epworth sleepiness scale and morning systolic blood pressure (- 7.2 mmHg, - 12.7 to - 1.7 mmHg, p = 0.011), but no significant difference in AFABP, adiponectin, C-reactive protein (CRP), and 8-isoprostane levels. In the per-protocol analysis, when only those who were compliant to CPAP were included, a significant reduction in AFABP (- 7.32 ng/ml, - 13.58, - 1.06, p = 0.023) were found in the CPAP-treated group compared with the control group, along with improvements in clinical parameters. Changes in AFABP were independently associated with both systolic blood pressure (β = 0.289, p = 0.028) and diastolic blood pressure (β = 0.217, p = 0.030).

CONCLUSION

CPAP therapy used regularly over 4 weeks for severe OSA lowered circulating AFABP level, suggesting a potential beneficial effect of OSA treatment on alleviating metabolic risks.

TRIAL REGISTRATION

The research protocol was registered at the National Institutes of Health clinical trials registry (NCT01173432).

Strategies to decrease oxidative stress biomarker levels in human medical conditions: A meta-analysis on 8-iso-prostaglandin F2α

The widespread detection of elevated oxidative stress levels in many medical conditions has led to numerous efforts to design interventions to reduce its effects. Efforts have been wide-ranging, from dietary changes to administration of antioxidants, supplements, e.g., omega-3-fatty acids, and many medications. However, there is still no systemic assessment of the efficacy of treatments for oxidative stress reduction across a variety of medical conditions. The goal of this meta-analysis is, by combining multiple studies, to quantitate the change in the levels of the popular oxidative stress biomarker 8-iso-prostaglandin F2α (8-iso-PGF2α) after a variety of treatment strategies in human populations. Nearly 350 unique publications with 180 distinct strategies were included in the analysis. For each strategy, the difference between pre- or placebo and post-treatment levels calculated using Hedges' g value of effect. In general, administration of antibiotics, antihyperlipidemic agents, or changes in lifestyle (g = - 0.63, - 0.54, and 0.56) had the largest effect. Administration of supplements, antioxidants, or changes in diet (g = - 0.09, - 0.28, - 0.12) had small quantitative effects. To fully interpret the effectiveness of these treatments, comparisons to the increase in g value for each medical condition is required. For example, antioxidants in populations with coronary artery disease (CAD) reduce the 8-iso-PGF2α levels by g = - 0.34 ± 0.1, which is quantitatively considered a small effect. However, CAD populations, in comparison to healthy populations, have an increase in 8-iso-PGF2α levels by g = 0.38 ± 0.04; therefore, the overall reduction of 8-iso-PGF2α levels is ≈ 90% by this treatment in this specific medical condition. In conclusion, 8-iso-PGF2α levels can be reduced not only by antioxidants but by many other strategies. Not all strategies are equally effective at reducing 8-iso-PGF2α levels. In addition, the effectiveness of any strategy can be assessed only in relation to the medical condition investigated.

Obstructive sleep apnoea

Obstructive sleep apnoea (OSA) is increasing in prevalence due to rising obesity. While OSA is a disorder primarily of the upper airway during sleep, its pathophysiological impact on other body systems is increasingly recognised. There has been interest in the prevalence of OSA in different ophthalmic conditions and possible causation has been postulated. As OSA is common, it can be expected that people with co-existent OSA will be found in any ophthalmic disease population studied. To determine with confidence the significance of finding patients with OSA in a particular cohort requires a well matched control group, ideally matched for age, obesity, gender and co-morbidities. Only if one can say with certainty that the prevalence of OSA is higher in a group with a particular co-existent ophthalmic disease can we begin to speculate about possible mechanisms for the overlap in these conditions. Possible mechanisms for how OSA might affect the eye are discussed in this review. The current literature is reviewed with respect to diabetic retinopathy, glaucoma, floppy eyelid syndrome, non-arteritic ischaemic optic neuropathy, keratoconus and AMD. Associations with OSA have been found, but robust prospective studies using multi-channel sleep studies to diagnose OSA are lacking. Gaps remain in the evidence and in our knowledge. It is hoped that this review will highlight the need for ophthalmologists to consider OSA in their patients. It also makes recommendations for future research, especially to consider whether therapies for OSA can also be effective for ophthalmic disorders.

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.

Intermittent hypoxia, cardiovascular disease and obstructive sleep apnoea

Obstructive sleep apnoea (OSA) is a common disorder and is associated with cardiovascular disease. Continuous positive airway pressure (CPAP), whilst reducing blood pressure, has not been shown to reduce cardiovascular events when used as a treatment solely for this purpose in patients with previous cardiovascular disease. Developing a better understanding of the mechanisms underlying cardiovascular disease in OSA is important to develop new treatments. Potential causative mechanisms for cardiovascular disease in OSA include arousal induced sympathetic activation, large intrathoracic pressure swings leading to shear stress on the heart and great vessels, and intermittent hypoxia (IH). This review discusses the role of IH, as a major physiological consequence of OSA, in the development of cardiovascular disease.

Association between obstructive sleep apnea severity and endothelial dysfunction in patients with type 2 diabetes

Background

Obstructive sleep apnea (OSA) and type 2 diabetes (T2D) are associated with endothelial dysfunction a main predictor of late cardiovascular (CV) events. Despite the high prevalence of OSA in patients with T2D, the impact of OSA severity on endothelial function has not been clearly elucidated. The aim of this cross-sectional study was to determine whether increasing OSA severity is associated with poorer endothelial function in patients with T2D.

Methods

140 patients with T2D and no overt CV disease underwent polysomnography, peripheral arterial tonometry, clinic blood pressure (BP) measurement, biological assessment for CV risk factors, daytime sleepiness and health related quality of life (HRQL) questionnaires. The following commonly used cut-offs for apnea-hypopnea index (AHI) were used to define 3 categories of disease severity: AHI < 15 (no OSA or mild OSA), 15 ≤ AHI < 30 (moderate OSA), and AHI ≥ 30 (severe OSA). The primary outcome was the reactive hyperemia index (RHI), a validated assessment of endothelial function.

Results

21.4% of patients had moderate OSA and 47.6% had severe OSA. Increasing OSA severity and nocturnal hypoxemia were not associated with a significant decrease in RHI. Endothelial dysfunction (RHI < 1.67) was found in 47.1, 44.4 and 39.2% of patients with no OSA or mild OSA, moderate OSA and severe OSA, respectively (p = 0.76). After adjustment for confounders including body mass index, increasing OSA severity was associated with higher systolic BP (p = 0.03), lower circulating levels of adiponectin (p = 0.0009), higher levels of sP-selectin (p = 0.03), lower scores in 3 domains of HRQL including energy/vitality (p = 0.02), role functioning (p = 0.01), and social functioning (p = 0.04).

Conclusions

Moderate to severe OSA is very common but has no impact on digital micro-vascular endothelial function in patients with T2D.

Effect of OSA on hypoxic and inflammatory markers during CPAP withdrawal: Further evidence from three randomized control trials

BACKGROUND AND OBJECTIVE

Obstructive sleep apnoea (OSA) is associated with cardiovascular disease. Intermittent hypoxia, endothelial dysfunction and adipose tissue-mediated inflammation have all been linked to cardiovascular disease in OSA. We therefore explored the effect of OSA on relevant associated blood markers: adrenomedullin (ADM), endocan, endothelin-1 (ET-1), resistin and vascular endothelial growth factor (VEGF).

METHODS

Patients with OSA, established on and compliant with continuous positive airways pressure (CPAP) therapy for >1 year were included from three randomized controlled trials, conducted at two centres. Patients were randomized to either continued therapeutic CPAP or sham CPAP (CPAP withdrawal) for 2 weeks. Blood markers were measured at baseline and at 14 days and the treatment effect between sham CPAP and therapeutic CPAP was analysed.

RESULTS

A total of 109 patients were studied (therapeutic CPAP n = 54, sham CPAP n = 55). Sham CPAP was associated with a return of OSA (between-group difference in oxygen desaturation index (ODI) 36.0/h, 95% CI 29.9-42.2, P < 0.001). Sham CPAP was associated with a reduction in ADM levels at 14 days (-26.0 pg/mL, 95% CI -47.8 to -4.3, P = 0.02), compared to therapeutic CPAP. Return of OSA was not associated with changes in endocan, ET-1, resistin or VEGF.

CONCLUSION

Whilst CPAP withdrawal was associated with return of OSA, it was associated with an unexpected significant reduction in the vasodilator ADM and not with expected increases in hypoxia-induced markers, markers of endothelial function or resistin. We propose that the vascular effects occurring in OSA may be brought about by other mechanisms, perhaps partly through a reduction in ADM.

Effect of Continuous Positive Airway Pressure on Airway Inflammation and Oxidative Stress in Patients with Obstructive Sleep Apnea

Background. Airway inflammation and oxidative stress may be linked in obstructive sleep apnea (OSA) patients. We determined the effectiveness of continuous positive airway pressure (CPAP) therapy in reducing fractional exhaled nitric oxide (FeNO) and malondialdehyde (MDA) levels in OSA patients. Methods. Thirteen patients with OSA and 13 normal controls were recruited. FeNO and MDA levels were measured in the controls and in OSA patients before and after three months of CPAP therapy. Results. FeNO and MDA levels were higher in the patients compared to the age and gender matched controls (FeNO: 25.9 ± 5.0 versus 17.5 ± 5.9 ppb, P < 0.001; MDA: 14.6 ± 7.8 versus 2.1 ± 0.3 μmol/L, P < 0.001). FeNO and MDA levels were lower post-CPAP compared to pre-CPAP (FeNO: 25.9 ± 5.0 versus 17.0 ± 2.3 ppb, P < 0.001; MDA: 14.6 ± 7.8 versus 10.0 ± 6.4 μmol/L, P < 0.01). Apnea-hypopnea index (15.9 ± 6.6 versus 4.1 ± 2.1/h, P < 0.001) and mean arterial pressure (P < 0.01) decreased following CPAP treatment. Daytime mean SpO₂ (P < 0.05) increased. Conclusion. Our study demonstrates that CPAP therapy yields clinical benefits by reducing upper airway inflammation and oxidative stress in OSA patients.

Effect of Continuous Positive Airway Pressure on Cardiovascular Biomarkers: The Sleep Apnea Stress Randomized Controlled Trial

BACKGROUND

Although existing research highlights the relationship of OSA and cardiovascular disease, the effect of OSA treatment on cardiovascular biomarkers remains unclear. We evaluated the effect of OSA treatment on oxidative stress/inflammation measures.

METHODS

We conducted a parallel, randomized controlled trial in moderate to severe OSA (apnea-hypopnea index ≥ 15) patients to examine effects of 2-month CPAP vs sham-CPAP on the primary outcome of oxidative stress/inflammation (F2-isoprostanes: ng/mg) and myeloperoxidase: pmol/L) and secondary oxidative stress measures. Exploratory secondary analyses included vascular and systemic inflammation markers. Linear models adjusted for baseline values examined effect of CPAP on biomarker change (least squares means, 95% CI) including secondary stratified analyses examining CPAP adherence and degree of hypoxia.

RESULTS

Of 153 participants, 76 were randomized to CPAP and 77 to sham-CPAP. In an intent-to-treat analyses, no significant change was observed in the sham and CPAP groups respectively: F2-isoprostanes (-0.02 [-0.12 to 0.10] vs -0.08 [-0.18 to 0.03]) or myeloperoxidase (-3.33 [-17.02 to 10.37] vs -5.15 [-18.65 to 8.35]), nor other oxidative markers; findings that persisted in analyses stratified by adherence and hypoxia. Exploratory analyses revealed percentage reduction of soluble IL-6 receptor (ng/mL) levels (-0.04 [-0.08 to -0.01] vs 0.02 [-0.02 to 0.06], P = .019) and augmentation index (%) (-6.49 [-9.32 to -3.65] vs 0.44 [-2.22 to 3.10], P < .001) with CPAP compared with sham, respectively.

CONCLUSIONS

In moderate to severe OSA, 2-month CPAP vs sham did not reduce oxidative stress despite consideration of a broad range of measures, positive airway pressure adherence, and hypoxia burden. These findings suggest that nonoxidative stress pathways primarily modulate OSA-related cardiovascular consequences.

TRIAL REGISTRATION

ClinicalTrials.govNCT00607893.

Perioperative sleep apnea: a real problem or did we invent a new disease?

Depending on the subpopulation, obstructive sleep apnea (OSA) can affect more than 75% of surgical patients. An increasing body of evidence supports the association between OSA  and perioperative complications, but some data indicate important perioperative outcomes do not differ between patients with and without OSA. In this review we will provide an overview of the pathophysiology of sleep apnea and the risk factors for perioperative complications related to sleep apnea. We also discuss a clinical algorithm for the identification and management of OSA patients facing surgery.

Oxidative stress and inflamatory plasma biomarkers in respiratory syncytial virus bronchiolitis

INTRODUCTION

Oxidative stress (OS) plays a crucial role in the pathogenesis of inflammatory lung diseases.

OBJECTIVES

(i) We determined whether acute bronchiolitis (AB) caused by respiratory syncytial virus (RSV) induced OS; (ii) assessed whether OS biomarkers correlated with the severity of RSV-AB; and (iii) studied whether the levels of interleukins are associated with OS biomarkers.

METHODS

We performed an observational study by comparing healthy infants (Group 1) with RSV-AB infants, classified as Group 2 (pulse oximetry (SpO₂ ) >93%), and Group 3 (SpO₂  ≤ 92%), which needed oxygen therapy. Blood samples were collected to determine the levels of lipid peroxidation (LPO) products (LPO), total glutathione (TG), oxidised glutathione (GSSG), reduced glutathione (GSH), glutathione peroxidase (GPx), interleukins (ILs) IL-10, IL-6, IL-8, interferon-gamma (IFNγ), tumour necrosis factor-alpha (TNFα) and macrophage inflammatory proteins (MIP α and MIP β).

RESULTS

Forty-six RSV-AB infants (47% needed oxygen therapy) and 27 healthy infants were included. The GSH/GSSG ratio was lower in RSV-AB infants than in Group 1 (P<0.001). GSSG and GPx were significantly higher in Group 3. GSSG predicted the need for oxygen therapy with an optimal cut-off point of 15 µM/g for haemoglobin. The GSH/GSSG ratio negatively correlated with IL-6 (P: 0.014), IL-8 (P: 0.014) and IL-10 (P: 0.033). Group 3 exhibited a direct correlation between GPx and IL-10 levels (P: 0.024) and between LPO and MIP β (P: 0.003).

CONCLUSIONS

RSV induced OS in AB. An increase in GSSG correlated with the disease severity in the infants. OS may contribute to the pathogenesis of RSV-AB.