Oxidative stress and oxidant signaling in obstructive sleep apnea and associated cardiovascular diseases

Oxidative Stress-induced Telomere Length Shortening of Circulating Leukocyte in Patients with Obstructive Sleep Apnea

The main mechanism of pathogenesis which causes systemic complications in obstructive sleep apnea (OSA) patients is believed to be intermittent hypoxia-induced intermediary effect and it depends on the burden of oxidative stress during sleep. We aimed to search the predictive markers which reflect the burden of systemic oxidative stress in patients with OSA and whether excessive telomere length shortening is a characteristic feature that can assess oxidative stress levels. We used quantitative PCR to measure telomere length using peripheral blood genomic DNA. Telomere lengths were compared in an age- and body mass index (BMI)-dependent manner in 34 healthy volunteers and 43 OSA subjects. We also performed reactive oxygen species assay to measure the concentration of hydrogen peroxide in the peripheral blood of healthy volunteers and OSA subjects. We found that the serum concentration of hydrogen peroxide was considerably higher in OSA patients, and that this was closely related with the severity of OSA. Significantly shortened telomere length was observed in the circulating leukocytes of the peripheral blood of OSA patients, and telomere length shortening was aggravated more acutely in an age- and BMI-dependent manner. An inverse correlation was observed between the concentration of hydrogen peroxide and the telomere length of OSA patients and excessive telomere length shortening was also linked to severity of OSA. The results provided evidence that telomere length shortening or excessive cellular aging might be distinctive in circulating leukocyte of OSA patients and may be an predictive biomarker for reflect the burden of oxidative stress in the peripheral blood of OSA patients.

Role of Oxidative Stress in the Neurocognitive Dysfunction of Obstructive Sleep Apnea Syndrome

Obstructive sleep apnea syndrome (OSAS) is characterized by chronic nocturnal intermittent hypoxia and sleep fragmentations. Neurocognitive dysfunction, a significant and extraordinary complication of OSAS, influences patients' career, family, and social life and reduces quality of life to some extent. Previous researches revealed that repetitive hypoxia and reoxygenation caused mitochondria and endoplasmic reticulum dysfunction, overactivated NADPH oxidase, xanthine oxidase, and uncoupling nitric oxide synthase, induced an imbalance between prooxidants and antioxidants, and then got rise to a series of oxidative stress (OS) responses, such as protein oxidation, lipid peroxidation, and DNA oxidation along with inflammatory reaction. OS in brain could trigger neuron injury especially in the hippocampus and cerebral cortex regions. Those two regions are fairly susceptible to hypoxia and oxidative stress production which could consequently result in cognitive dysfunction. Apart from continuous positive airway pressure (CPAP), antioxidant may be a promising therapeutic method to improve partially reversible neurocognitive function. Understanding the role that OS played in the cognitive deficits is crucial for future research and therapeutic strategy development. In this paper, recent important literature concerning the relationship between oxidative stress and cognitive impairment in OSAS will be summarized and the results can provide a rewarding overview for future breakthrough in this field.

Animal Model of Gestational Diabetes Mellitus with Pathophysiological Resemblance to the Human Condition Induced by Multiple Factors (Nutritional, Pharmacological, and Stress) in Rats

This study attempts to develop an experimental gestational diabetes mellitus (GDM) animal model in female Sprague-Dawley rats. Rats were fed with high fat sucrose diet, impregnated, and induced with Streptozotocin and Nicotinamide on gestational day 0 (D0). Sleeping patterns of the rats were also manipulated to induce stress, a lifestyle factor that contributes to GDM. Rats were tested for glycemic parameters (glucose, C-peptide, and insulin), lipid profiles (total cholesterol, triglycerides, HDL, and LDL), genes affecting insulin signaling (IRS-2, AKT-1, and PCK-1), glucose transporters (GLUT-2 and GLUT-4), proinflammatory cytokines (IL-6, TNF-α), and antioxidants (SOD, CAT, and GPX) on D6 and D21. GDM rats showed possible insulin resistance as evidenced by high expression of proinflammatory cytokines, PCK-1 and CRP. Furthermore, low levels of IRS-2 and AKT-1 genes and downregulation of GLUT-4 from the initial to final phases indicate possible defect of insulin signaling. GDM rats also showed an impairment of antioxidant status and a hyperlipidemic state. Additionally, GDM rats exhibited significantly higher body weight and blood glucose and lower plasma insulin level and C-peptide than control. Based on the findings outlined, the current GDM animal model closely replicates the disease state in human and can serve as a reference for future investigations.

Waist circumference and postmenopause stages as the main associated factors for sleep apnea in women: a cross-sectional population-based study

OBJECTIVE

The current study aimed to investigate stages of reproductive aging as an associated factor for obstructive sleep apnea syndrome (OSAS) among women in a representative sample of Sao Paulo, Brazil.

METHODS

Four hundred seven women underwent clinical evaluation, polysomnography, and biochemical analysis. Stages of reproductive aging were defined as premenopause, early postmenopause, and late postmenopause.

RESULTS

OSAS was more frequent in the postmenopausal groups, with 68.4% of women affected by severe OSAS belonging to the late postmenopause group. After adjustment for potential confounding factors, associated factors for OSAS, regardless of its severity, were waist circumference, modified Mallampati score IV, and both postmenopause stages. For moderate to severe OSAS and severe OSAS, we found waist circumference and both postmenopause stages to be the main factors. We carried out a receiver operating characteristic curve analysis, which demonstrated that the cutoff value for waist circumference was 87.5 cm, with a maximum of 75.7% accuracy for the classification of women as OSAS or non-OSAS.

CONCLUSIONS

OSAS is prevalent in postmenopausal women, especially in late postmenopause. This study highlights the association between waist circumference, early postmenopause and late postmenopause, and severity of OSAS. Our findings suggest that postmenopause stages may potentially exacerbate the presence of sleep disturbance and that reducing waist circumference may be an important strategy for managing OSAS in women.

Association of Anterior Cingulate Glutathione with Sleep Apnea in Older Adults At-Risk for Dementia

STUDY OBJECTIVES

Sleep disordered breathing (SDB) is common in older adults and is strongly associated with cognitive decline, with increasing evidence suggesting that it may represent a risk factor for dementia. Given that SDB is characterized by intermittent episodes of hypoxemia during sleep, it is possible that cognitive impairment may relate to cerebral oxidative stress. This study aimed to examine the relationship between nocturnal markers of hypoxemia and proton magnetic resonance spectroscopy ((1)H-MRS) markers of oxidative stress within the anterior cingulate cortex (ACC) of the brain.

METHODS

Twenty-four older adults (mean age = 67.9 y) at-risk for dementia were recruited from our Healthy Brain Ageing Research Clinic. At-risk was defined as participants seeking help for assessment and/or intervention for cognitive decline, including those with subjective and/or objective cognitive complaints. This could occur in the context of prior depression or risk factors (e.g., vascular) for dementia. All participants underwent psychiatric, medical and neuropsychological assessment followed by overnight polysomnography. In addition, participants underwent (1)H-MRS to derive levels of ACC metabolite glutathione (GSH) reported as a ratio to creatine (GSH/Cr).

RESULTS

Increased levels of GSH/Cr were associated with lower oxygen desaturation (r = -0.54, P = 0.007) and more severe apnea-hypopnea index scores during rapid eye movement sleep (r = 0.42, P = 0.050). In addition, ACC GSH/Cr correlated with poorer executive functioning (i.e., response inhibition: r = -0.49, P = 0.015; set shifting: r = -0.43, P = 0.037).

CONCLUSIONS

Markers of nocturnal hypoxemia and SDB are associated with cerebral oxidative stress in older people at-risk for dementia, suggesting a potential mechanism by which SDB may contribute to brain degeneration, cognitive decline, and dementia. Further work focused on utilizing this biomarker for the early identification and treatment of this possible modifiable risk factor in older persons is now warranted.

Influence of obstructive sleep apnea on ischemia-modified albumin levels and carotid intima-media thickness

Obstructive sleep apnea (OSA) is associated with an increased risk of atherosclerosis. Carotid intima-media thickness (CIMT) is strongly associated with the presence of significant risk factors for cardiovascular disturbances. A disturbance in the oxidative/antioxidative balance is involved in the pathogenesis of OSA and cardiovascular diseases. Ischemia-modified albumin (IMA) is suggested as a novel marker of oxidative stress; IMA can be defined as decreased binding of transitional metal ions to serum albumin in oxidative status. The purpose of this research was to evaluate the influence of OSA on IMA levels and CIMT. In total, 61 individuals with OSA with no comorbidities and 24 healthy controls with a similar body mass index and age were enrolled in this study. Serum levels of IMA, CIMT (estimated radiologically), and polysomnographic parameters, were determined and interpreted. Serum IMA levels were significantly higher in individuals with OSA compared with the control group (p=0.0003). CIMT was significantly higher in the OSA group compared with the control group (0.88± 0.26 mm vs 0.75±0.17 mm, p=0.005). The CIMT and serum IMA levels were positively correlated with the apnea-hypopnea index (r=0.35 and r=0.32, respectively), and with the oxygen desaturation index (r=0.34 and r=0.29, respectively) at baseline. Increased IMA levels and CIMT may be related to increased oxidative stress and risk of atherosclerosis in individuals with OSA.

Peripheral chemoreception and arterial pressure responses to intermittent hypoxia

Carotid bodies are the principal peripheral chemoreceptors for detecting changes in arterial blood oxygen levels, and the resulting chemoreflex is a potent regulator of blood pressure. Recurrent apnea with intermittent hypoxia (IH) is a major clinical problem in adult humans and infants born preterm. Adult patients with recurrent apnea exhibit heightened sympathetic nerve activity and hypertension. Adults born preterm are predisposed to early onset of hypertension. Available evidence suggests that carotid body chemoreflex contributes to hypertension caused by IH in both adults and neonates. Experimental models of IH provided important insights into cellular and molecular mechanisms underlying carotid body chemoreflex-mediated hypertension. This article provides a comprehensive appraisal of how IH affects carotid body function, underlying cellular, molecular, and epigenetic mechanisms, and the contribution of chemoreflex to the hypertension.

Oxidative stress parameters and their correlation with clinical, metabolic and polysomnographic parameters in severe obstructive sleep apnea syndrome

The aim of the present study was to assess the levels of oxidative stress markers, catalase (CAT), glutathione peroxidase (GPX) and malondialdehyde (MDA) in severe OSAS and to investigate any correlation between oxidative stress markers and clinical, metabolic and polysomnographic parameters. A total of 30 patients with severe OSAS and 30 healthy controls were included in this cross-sectional, clinical study. Demographic data, polysomnographic, biochemical and clinical indices as well as serum levels of CAT, MDA and GPX were measured and compared in OSAS and control groups. Furthermore, OSAS patients with and without pulmonary hypertension (PHT) were evaluated in terms of levels of CAT, MDA and GPX. Patients with severe OSAS exhibited significantly lower serum levels of CAT (P<0.001) and GPX (P<0.001). Serum MDA levels were remarkably higher in OSAS group (P<0.001). Correlation analysis revealed that levels of CAT and GPX were correlated with apnea-hypopnea index and there was a correlation between serum levels of MDA and CRP. Severe OSAS patients with and without PHT did not reveal any differences for CAT (P=0.789), MDA (P=0.805) and GPX levels (P=0.281). Our results have shown that oxidative stress markers significantly changed in patients with severe OSAS. This information is noteworthy because documentation of the role of oxidative stress in OSAS may have important implications regarding diagnosis, monitoring, treatment and prognosis.

miR-103 Regulates Oxidative Stress by Targeting the BCL2/Adenovirus E1B 19 kDa Interacting Protein 3 in HUVECs

Oxidative stress plays a critical role in cardiovascular diseases. Salidroside, a glycoside from Rhodiola rosea, has been used as an antioxidative therapy for oxidative injury in cardiac diseases. However, the mechanism underlying its antioxidant effect needs to be elucidated. Treatment of HUVECs with H₂O₂ significantly decreased the expression of miR-103 in a dose- and time-dependent manner, whereas pretreatment with salidroside significantly inhibited this decrease. Subsequent analysis showed that overexpression of miR-103 abrogated cell activity and ROS production induced by H₂O₂. Bcl2/adenovirus E1B 19 kDa interacting protein 3 (BNIP3) was determined to be a novel miR-103 target in HUVECs. Interestingly, H₂O₂ treatment upregulated BNIP3 expression; in turn, this effect was inhibited by pretreatment with salidroside. Further studies confirmed that the knockdown of BNIP3 enhanced cell activity and suppressed the ROS production induced by H₂O₂. These results demonstrated for the first time that salidroside protects HUVECs in part by upregulating the expression of miR-103, which mediates BNIP3 downregulation and plays an important role in the cytoprotective actions.

Effect of Short Term CPAP Therapy in Obstructive Sleep Apnea Patients with Metabolic Syndrome

BACKGROUND

Patients of obstructive sleep apnea (OSA) with metabolic syndrome (MetS) are at increased risk of cardiovascular morbidity and mortality. The role of oxidative stress in pathogenesis of OSA and MetS has been widely reported. Continuous positive airway pressure (CPAP) therapy remains the first-line of treatment in OSA. The beneficial effect of long term CPAP therapy in OSA is well-known. However, the effect of short term CPAP on the components of MetS and oxidative stress-antioxidant levels is still unclear.

AIM

The present study explored the effects of one night of CPAP therapy on the oxidant-antioxidant status and components of MetS in patients of OSA with MetS.

MATERIALS AND METHODS

Twenty adult males and postmenopausal females with MetS and symptoms suggestive of OSA were enrolled in the study. None of the subjects were smoker or alcoholic. They did not consume any drugs that would alter their antioxidant levels. Overnight polysomnography was done to confirm diagnosis and assess CPAP pressure. Following which they spent one night in the sleep lab for CPAP therapy. Blood pressure data and blood samples were collected at baseline and after CPAP. Collected samples were transferred immediately to the laboratory for analysis of serum thiol, lipid peroxidation, insulin resistance (HOMA-IR) and lipid profile.

RESULTS

Paired t-test with two-tail significance was used to compare the changes in study parameters in the same patient before and after treatment. The antioxidant level increased and oxidative stress decreased as evidenced by serum thiol concentration (204.2±65.7 vs 254.9±72 μmol/L, p<0.001) and lipid peroxidation levels (13.1±6.2 vs 8.4±3.1 μmol/L, p<0.01).There was a significant decrease in both systolic (132.1±16.1 vs 127.2±14.3 mmHg, p<0.01) and diastolic blood pressure (86.4±9.4 vs 81.2±9.8 mmHg, p<0.01) after one night of CPAP. However, there was no change in lipid parameters and the reduction seen in insulin resistance was not statistically significant.

CONCLUSION

One night of CPAP therapy seems to be helpful in reducing oxidative stress, improving antioxidant levels and decreasing the severity of various components of MetS.

HIF-1α activation by intermittent hypoxia requires NADPH oxidase stimulation by xanthine oxidase

Hypoxia-inducible factor 1 (HIF-1) mediates many of the systemic and cellular responses to intermittent hypoxia (IH), which is an experimental model that simulates O2 saturation profiles occurring with recurrent apnea. IH-evoked HIF-1α synthesis and stability are due to increased reactive oxygen species (ROS) generated by NADPH oxidases, especially Nox2. However, the mechanisms by which IH activates Nox2 are not known. We recently reported that IH activates xanthine oxidase (XO) and the resulting increase in ROS elevates intracellular calcium levels. Since Nox2 activation requires increased intracellular calcium levels, we hypothesized XO-mediated calcium signaling contributes to Nox activation by IH. We tested this possibility in rat pheochromocytoma PC12 cells subjected to IH consisting alternating cycles of hypoxia (1.5% O2 for 30 sec) and normoxia (21% O2 for 5 min). Kinetic analysis revealed that IH-induced XO preceded Nox activation. Inhibition of XO activity either by allopurinol or by siRNA prevented IH-induced Nox activation, translocation of the cytosolic subunits p47phox and p67phox to the plasma membrane and their interaction with gp91phox. ROS generated by XO also contribute to IH-evoked Nox activation via calcium-dependent protein kinase C stimulation. More importantly, silencing XO blocked IH-induced upregulation of HIF-1α demonstrating that HIF-1α activation by IH requires Nox2 activation by XO.

Mechanisms and clinical consequences of untreated central sleep apnea in heart failure

Central sleep apnea (CSA) is a highly prevalent, though often unrecognized, comorbidity in patients with heart failure (HF). Data from HF population studies suggest that it may present in 30% to 50% of HF patients. CSA is recognized as an important contributor to the progression of HF and to HF-related morbidity and mortality. Over the past 2 decades, an expanding body of research has begun to shed light on the pathophysiologic mechanisms of CSA. Armed with this growing knowledge base, the sleep, respiratory, and cardiovascular research communities have been working to identify ways to treat CSA in HF with the ultimate goal of improving patient quality of life and clinical outcomes. In this paper, we examine the current state of knowledge about the mechanisms of CSA in HF and review emerging therapies for this disorder.

Epigenetic Regulation of Carotid Body Oxygen Sensing: Clinical Implications

Recurrent apnea with intermittent hypoxia (IH) is a major clinical problem in infants born preterm. Recent epidemiological studies showed that adults who were born preterm exhibit increased incidence of sleep-disordered breathing and hypertension. Thus, apnea of prematurity predisposes individuals to autonomic dysfunction in adulthood. Experimental studies showed that adult rats exposed to IH as neonates exhibit augmented carotid body and adrenal chromaffin cells (AMC) response to hypoxia and irregular breathing with apneas and hypertension. The enhanced hypoxic sensitivity of the carotid body and AMC in adult rats exposed to neonatal IH was associated with increased oxidative stress, decreased expression of genes encoding anti-oxidant enzymes, and increased expression of pro-oxidant enzymes. Epigenetic mechanisms including DNA methylation leads to long-term changes in gene expression. The decreased expression of the Sod2 gene, which encodes the anti-oxidant enzyme, superoxide dismutase 2, was associated with DNA hypermethylation of a single CpG dinucleotide close to the transcription start site. Treating neonatal rats with decitabine, an inhibitor of DNA methylation, during IH exposure prevented the oxidative stress, enhanced hypoxic sensitivity, and autonomic dysfunction in adult rats. These findings suggest that epigenetic mechanisms, especially DNA methylation contributes to neonatal programming of hypoxic sensitivity and the ensuing autonomic dysfunction in adulthood.

Aberrant spontaneous low-frequency brain activity in male patients with severe obstructive sleep apnea revealed by resting-state functional MRI

BACKGROUND

The majority of previous neuroimaging studies have demonstrated both structural and functional abnormalities in obstructive sleep apnea (OSA). However, few studies have focused on the regional intensity of spontaneous fluctuations during the resting state and the relationship between the abnormal properties and the behavioral performances. In the present study, we employed the amplitude of low-frequency fluctuation (ALFF) method to explore the local features of spontaneous brain activity in OSA patients (OSAs).

METHODS

Twenty-five untreated male severe OSAs and 25 age-matched and years-of-education-matched male good sleepers (GSs) were included in this study. The ALFF method was used to assess the local features of spontaneous brain activity. The mean signal values of the altered ALFF areas were analyzed with receiver operating characteristic curve. Partial correlation analysis was used to explore the relationship between the observed mean ALFF values of the different areas and the behavioral performances.

RESULTS

Compared with GSs, OSAs had significantly higher scores for body mass index, apnea-hypopnea index, arterial oxygen saturation <90%, arousal index, and Epworth Sleepiness Scale (ESS) score; furthermore, OSAs had significantly lower scores for rapid eye movement sleep and in the Montreal Cognitive Assessment (MoCA). Compared with GSs, OSAs showed significant lower-ALFF areas in the cluster of the right precuneus and bilateral posterior cingulate gyrus, as well as a higher-ALFF area in the left inferior frontal gyrus. The area under the curve values of the lower- and higher-ALFF areas were 0.90 and 0.93, respectively. Further diagnostic analysis exhibited that the sensibility and specificity of the two clusters were 80% and 92%, respectively. The mean signal value of the lower-ALFF cluster displayed significant positive correlations with lowest oxygen saturation (r=0.447, P=0.025) and MoCA score (r =0.405, P=0.045).

CONCLUSION

OSAs may involve in a dysfunction in the default mode network and an adaptive compensatory response in the frontal lobe, which reflect the underlying pathophysiology of cognitive impairment.

Intermittent hypoxia: a low-risk research tool with therapeutic value in humans

Intermittent hypoxia has generally been perceived as a high-risk stimulus, particularly in the field of sleep medicine, because it is thought to initiate detrimental cardiovascular, respiratory, cognitive, and metabolic outcomes. In contrast, the link between intermittent hypoxia and beneficial outcomes has received less attention, perhaps because it is not universally understood that outcome measures following exposure to intermittent hypoxia may be linked to the administered dose. The present review is designed to emphasize the less recognized beneficial outcomes associated with intermittent hypoxia. The review will consider the role intermittent hypoxia has in cardiovascular and autonomic adaptations, respiratory motor plasticity, and cognitive function. Each section will highlight the literature that contributed to the belief that intermittent hypoxia leads primarily to detrimental outcomes. The second segment of each section will consider the possible risks associated with experimentally rather than naturally induced intermittent hypoxia. Finally, the body of literature indicating that intermittent hypoxia initiates primarily beneficial outcomes will be considered. The overarching theme of the review is that the use of intermittent hypoxia in research investigations, coupled with reasonable safeguards, should be encouraged because of the potential benefits linked to the administration of a variety of low-risk intermittent hypoxia protocols.

Effects of 8 weeks of CPAP on lipid-based oxidative markers in obstructive sleep apnea: a randomized trial

Dyslipidaemia and increased oxidative stress have been reported in severe obstructive sleep apnea, and both may be related to the development of cardiovascular disease. We have previously shown in a randomized crossover study in patients with moderate to severe obstructive sleep apnea that therapeutic continuous positive airway pressure treatment for 8 weeks improved postprandial triglycerides and total cholesterol when compared with sham continuous positive airway pressure. From this study we have now compared the effect of 8 weeks of therapeutic continuous positive airway pressure and sham continuous positive airway pressure on oxidative lipid damage and plasma lipophilic antioxidant levels. Unesterified cholesterol, esterified unsaturated fatty acids (cholesteryl linoleate: C18:2; and cholesteryl arachidonate: C20:4; the major unsaturated and oxidizable lipids in low-density lipoproteins), their corresponding oxidized products [cholesteryl ester-derived lipid hydroperoxides and hydroxides (CE-O(O)H)] and antioxidant vitamin E were assessed at 20:30 hours before sleep, and at 06:00 and 08:30 hours after sleep. Amongst the 29 patients completing the study, three had incomplete or missing [CE-O(O)H] data. The mean apnea -hypopnoea index, age and body mass index were 38 per hour, 49 years and 32 kg m(-2) , respectively. No differences in lipid-based oxidative markers or lipophilic antioxidant levels were observed between the continuous positive airway pressure and sham continuous positive airway pressure arms at any of the three time-points [unesterified cholesterol 0.01 mm, P > 0.05; cholesteryl linoleate: C18:2 0.05 mm, P > 0.05; cholesteryl arachidonate: C20:4 0.02 mm, P = 0.05; CE-O(O)H 2.5 nm, P > 0.05; and lipid-soluble antioxidant vitamin E 0.03 μm, P > 0.05]. In this study, accumulating CE-O(O)H, a marker of lipid oxidation, does not appear to play a role in oxidative stress in obstructive sleep apnea.

Antioxidants inhibit the inflammatory and apoptotic processes in an intermittent hypoxia model of sleep apnea

BACKGROUND

Sleep apnea causes intermittent hypoxia (IH). We aimed to investigate the proteins related to oxidative stress, inflammation and apoptosis in liver tissue subjected to IH as a simulation of sleep apnea in conjunction with the administration of either melatonin (MEL, 200 μL/kg) or N-acetylcysteine (NAC, 10 mg/kg).

METHODS

Seventy-two adult male Balb-C mice were divided: simulation of IH (SIH), SIH + MEL, SIH + NAC, IH, IH + MEL and IH + NAC. The animals were subjected to simulations of sleep apnea for 8 h a day for 35 days. The data were analyzed with ANOVA and Tukey tests with the significance set at p < 0.05.

RESULTS

In IH, there was a significant increase in oxidative stress and expression of HIF-1a. In addition, we observed increase in the activation levels of NF-kB. This increase may be responsible for the increased expression of TNF-alpha and iNOS as well as the significant increase of VEGF signaling and expression of caspase-3 and caspase-6, which suggests an increase in apoptosis. In the groups treated with antioxidants, the analysis showed that the enzyme activity and protein levels were similar to those of the non-simulated group.

CONCLUSIONS

Thus, we show that IH causes liver inflammation and apoptosis, which may be protected with either MEL or NAC.

Cardiovascular mortality in obstructive sleep apnoea treated with continuous positive airway pressure or oral appliance: an observational study

BACKGROUND AND OBJECTIVE

The objective of this study was to evaluate the long-term cardiovascular mortality in patients with severe obstructive sleep apnoea (OSA) treated with either continuous positive airway pressure (CPAP) or mandibular advancing device (MAD).

METHODS

A non-concurrent cohort study of 570 subjects with severe OSA (apnoea/hypopnoea index (AHI) ≥ 30/h) and a control group of 269 subjects (AHI < 5/h) were followed up for a median of 79 months (interquartile range 76-88 months). All patients received CPAP initially. MAD was offered for those who were non-adherent to CPAP. The endpoint was cardiovascular death.

RESULTS

Two hundred and eight control subjects, 177 patients treated with CPAP, 72 with MAD and 212 who declined treatment were analysed. Forty-two patients had a fatal cardiovascular event during the course of the study. The non-apnoeic group had the lowest cardiovascular death rate (0.28 per 100 person-years (95% confidence interval (CI): 0.08-0.71)) followed by the CPAP-treated (0.56 per 100 person-years (95% CI: 0.20-1.23)) and the MAD-treated OSA group (0.61 per 100 person-years (95% CI: 0.13-1.78)), with the highest cardiovascular mortality rate observed in the untreated OSA group (2.1 per 100 person-years (95% CI: 1.37-2.92)). Although residual AHI for MAD-treated patients was significantly higher than CPAP-treated patients (16.3 ± 5.1/h vs. 4.5 ± 2.3/h; P < 0.001), there was no difference in cardiovascular death rate between the two groups (hazard ratio 1.08 (95% CI: 0.55-1.74); P = 0.71).

CONCLUSIONS

Both CPAP and MAD may be equally effective therapy in reducing the risk of fatal cardiovascular events in patients with severe OSA.

Obstructive sleep apnea and progression of coronary artery calcium: the multi-ethnic study of atherosclerosis study

Background

Obstructive sleep apnea (OSA) is a common condition associated with cardiovascular disease. Its potential effect on progression of subclinical atherosclerosis is not well understood. We tested the hypothesis that self‐reported OSA is associated with progression of coronary artery calcium (CAC). We also evaluated whether traditional cardiovascular risk factors accounted for the association.

Methods and Results

In the Multi‐Ethnic Study of Atherosclerosis (MESA) prospective cohort, we studied 2603 participants who at baseline (2002–2004) completed a sleep questionnaire and underwent coronary computed tomography (CT) and, then 8 years later (2010–2011), a repeat coronary CT. Participants were categorized by symptoms of habitual snoring or reported physician diagnosis of OSA. At baseline, 102 (3.9%) reported diagnosed OSA; 666 (25.6%) reported diagnosed habitual snoring; and 1835 (70.5%) reported neither habitual snoring nor OSA (“normal”). At baseline, CAC prevalence was highest among those with OSA but similar for those with and without habitual snoring. During 8 years of follow‐up, greater progression of CAC was observed among those with OSA versus normal (mean increase of 204.2 versus 135.5 Agatston units; P=0.01), after accounting for demographics, behaviors, and body habitus. Modest attenuation was observed after adjustment for cardiovascular risk factors (188.7 versus 138.8; P=0.06). CAC progression among habitual snorers was similar to that observed in the normal group.

Conclusions

OSA was associated with CAC score progression after adjustment for demographics, behaviors, and body mass index. However, the association was not significant after accounting for cardiovascular risk factors, which may mediate the association between OSA and CAC.

Effects of first-time overnight CPAP therapy for increasing the complexity of the patient's physiological system

Studies regarding the effects of short-term continuous positive airway pressure (CPAP) therapy are not sufficient. A total of 35 patients with moderate to severe untreated OSA were divided into 2 groups. Group 1 comprised 22 patients who underwent polysomnography (PSG) for one night, and Group 2 comprised 13 patients who received PSG combined with CPAP therapy. To evaluate the influence of receiving CPAP therapy for one night, we measured 5 min wrist pulse signals before and after the experiment to assess heart rate variability, as well as novel short time multiscale entropy (sMSE) indicator that examines complexity in physiological signals. The results show that the participants in Group 1 exhibited significant changes in normalized low-frequency power/normalized high-frequency power (nLF/nHF) (0.72 ± 0.09 versus 1.11 ± 0.11, P = 0.006) values before and after the PSG study. By contrast, the participants in Group 2 showed no significant changes in the 3 indicators. Regarding the sMSE indicator, Group 2 patients exhibited significant increases in the sMSE. CPAP therapy administered for one night can reduce the sympathovagal imbalance in patients with moderate to severe untreated OSA and increase the complexity of the patient's physiological system, thereby reflecting their overall improved health.

Relationship between hepcidin levels and periodic limb movement disorder in patients with obstructive sleep apnea syndrome

PURPOSE

This study was aimed to assess potential correlations between periodic leg movement (PLM) index, hepcidin levels, and iron status in patients with obstructive sleep apnea syndrome (OSAS).

METHODS

Forty-four newly diagnosed OSAS patients and 49 non-apneic controls were enrolled in this study. All patients underwent polysomnographic evaluation. The hepcidin, iron, ferritin, total iron binding capacity, and C-reactive protein levels were measured.

RESULTS

The mean age was 47.4 ± 7.2 years (18-68) in the OSAS group and 44.9 ± 11.1 years (23-65) in the control group. There were no differences in age, gender, and smoking between OSAS patients and controls. Mean apnea-hypopnea index (AHI) was 25.1 events/h. Mean serum hepcidin levels were significantly higher in OSAS subjects (725.9 ng/ml) than in control subjects (646.0 ng/ml) (p < 0.001). Serum iron levels were significantly lower in the OSAS and PLM disorder groups than in control subjects (p < 0.001). Serum hepcidin levels were significantly correlated with AHI (r = 0.453) and PLM index (r = 0.114). Serum iron levels were significantly negatively correlated with AHI (r = -0.169) and PLM index (r = -0.180).

CONCLUSIONS

In our study, the level of hepcidin was increased in patients with OSAS. Our study indicates that levels of hepcidin correlate with the AHI and PLM index severity of OSAS.

Obstructive sleep apnea and risk of osteoporosis: a population-based cohort study in Taiwan

BACKGROUND

Obstructive sleep apnea (OSA) is associated with metabolic, endocrine, and cardiovascular diseases. It is characterized by repetitive episodes of apnea/hypopnea and hypoxia in tissues, which might also impact bone metabolism. This study investigates the possible association between OSA and osteoporosis.

METHODS

Random samples of 1 million individuals were collected from Taiwan's National Health Insurance database. A total of 1377 patients with newly diagnosed OSA from 2000 to 2008 were recruited and compared with a matched cohort of 20 655 patients without OSA. All patients were tracked until an osteoporosis diagnosis, death, or the end of 2011.

RESULTS

During the 6-year follow-up period, the incidence rates of osteoporosis in the OSA cohort and comparison group were 2.52 and 1.00 per 1000 person-years, respectively. Patients with OSA were found to be at 2.74 times the risk of osteoporosis than patients without OSA (95% confidence interval 1.69-4.44, P < .05), after adjustment for age, gender, diabetes, hypertension, coronary artery disease, obesity, stroke, hyperlipidemia, chronic kidney disease, gout, monthly income, and geographical location. Subgroup analysis showed that older patients and female patients had a higher risk for osteoporosis than their younger and male counterparts. Log-rank analysis revealed that patients with OSA patients had significantly higher cumulative incidence rates of osteoporosis than the comparison group (P < .0001).

CONCLUSION

People diagnosed with OSA are at increased risk for subsequent osteoporosis.

Obstructive sleep apnea is a risk factor for Barrett's esophagus

BACKGROUND & AIMS

Common risk factors for obstructive sleep apnea (OSA) and Barrett's esophagus (BE) include obesity and gastroesophageal reflux disease (GERD). The aims of this study were to assess the association between OSA and BE and to determine whether the association is independent of GERD and body mass index (BMI).

METHODS

Patients who had undergone a diagnostic polysomnogram and esophagogastroduodenoscopy were identified by using Mayo Clinic (Rochester, Minnesota) databases from January 2000-November 2011. They were randomly matched for age, sex, and BMI at time of polysomnogram into the following groups: BE but no OSA (n = 36), OSA but no BE (n = 78), both (n = 74), or neither (n = 74). Clinical and demographic variables were abstracted from medical records. The association between OSA and BE was assessed by using a multiple variable logistic model that incorporated age, sex, BMI, clinical diagnosis of GERD, and smoking history.

RESULTS

Subjects with OSA had an 80% increased risk for BE compared with subjects without OSA (odds ratio, 1.8; 95% confidence interval, 1.1-3.2; P = .03). These findings were independent of age, sex, BMI, GERD, and smoking history. Increasing severity of OSA, measured by using the apnea-hypopnea index, was associated with an increased risk of BE (odds ratio, 1.2 per 10-unit increase in apnea-hypopnea index; 95% confidence interval, 1.0-1.3; P = .03).

CONCLUSIONS

In this case-control study, OSA was associated with an increased risk of BE, potentially through BMI and GERD independent mechanisms. Patients with OSA may benefit from evaluation for BE.

Cardiovascular complications of sleep apnea: role of oxidative stress

Obstructive sleep apnea (OSA) occurs in 2% of middle-aged women and 4% of middle-aged men with a higher prevalence among obese subjects. This condition is considered as an independent risk factor for cerebrovascular and cardiovascular diseases. One of the major pathophysiological characteristics of OSA is intermittent hypoxia. Hypoxia can lead to oxidative stress and overproduction of reactive oxygen species, which can lead to endothelial dysfunction, a hallmark of atherosclerosis. Many animal models, such as the rodent model of intermittent hypoxia, mimic obstructive sleep apnea in human patients and allow more in-depth investigation of biological and cellular mechanisms of this condition. This review discusses the role of oxidative stress in cardiovascular disease resulting from OSA in humans and animal models.

Arginase activity and nitric oxide levels in patients with obstructive sleep apnea syndrome

OBJECTIVE

Obstructive sleep apnea syndrome is characterized by repetitive obstruction of the upper airways, and it is a risk factor for cardiovascular diseases. There have been several studies demonstrating low levels of nitric oxide in patients with obstructive sleep apnea syndrome compared with healthy controls. In this study, we hypothesized that reduced nitric oxide levels would result in high arginase activity. Arginase reacts with L-arginine and produces urea and L-ornithine, whereas L-arginine is a substrate for nitric oxide synthase, which produces nitric oxide.

METHODS

The study group consisted of 51 obstructive sleep apnea syndrome patients (M/F: 43/8; mean age 49±10 years of age) and 15 healthy control subjects (M/F: 13/3; mean age 46±14 years of age). Obstructive sleep apnea syndrome patients were divided into two subgroups based on the presence or absence of cardiovascular disease. Nitric oxide levels and arginase activity were measured via an enzyme-linked immunosorbent assay of serum samples.

RESULTS

Serum nitric oxide levels in the control subjects were higher than in the obstructive sleep apnea patients with and without cardiovascular diseases (p<0.05). Arginase activity was significantly higher (p<0.01) in obstructive sleep apnea syndrome patients without cardiovascular diseases compared with the control group. Obstructive sleep apnea syndrome patients with cardiovascular diseases had higher arginase activity than the controls (p<0.001) and the obstructive sleep apnea syndrome patients without cardiovascular diseases (p<0.05).

CONCLUSION

Low nitric oxide levels are associated with high arginase activity. The mechanism of nitric oxide depletion in sleep apnea patients suggests that increased arginase activity might reduce the substrate availability of nitric oxide synthase and thus could reduce nitric oxide levels.

Melatonin ameliorates endothelial dysfunction, vascular inflammation, and systemic hypertension in rats with chronic intermittent hypoxia

The pathogenesis of hypertension in patients with obstructive sleep apnea (OSA) is associated with endothelial dysfunction induced by chronic intermittent hypoxia (IH). Studies have shown that administration of melatonin ameliorates oxidative injury and inflammation. This study examined the effect of melatonin on the oxidative stress, endothelial dysfunction, and inflammation during the pathogenesis of hypertension in chronic IH. Adult Sprague-Dawley rats that had received a daily injection of melatonin or vehicle were exposed to IH treatment mimicking a severe OSA condition for 14-21 days. Systolic pressure was significantly higher in the vehicle-treated (144 ± 2.7 mmHg) but not in the melatonin-treated rats (123 ± 5.1 mmHg) by 21-day IH treatment when compared with the normoxic control. Levels of malondialdehyde and the expressions of NADPH oxidase, pro-inflammatory mediators (TNF-α, inducible NO synthase, COX-2), and adhesion molecules (ICAM-1, VCAM-1, and E-selectin) of the thoracic aorta were markedly increased by 14-day IH treatment preceding the hypertensive response. Also, levels of nitric oxide (NO˙), endothelial-dependent relaxation, and the expressions of endothelial NO synthase (eNOS) and antioxidant enzymes (GPx, CAT, and Cu/Zn SOD) were significantly lowered in the IH rats. Melatonin treatment significantly mitigated the increased expression of NADPH oxidase, pro-inflammatory mediators, and adhesion molecules. Moreover, melatonin prevented the endothelial dysfunction with ameliorated levels of NO˙, endothelial-dependent relaxation, and expressions of eNOS and antioxidant enzymes. These results suggest that melatonin is protective against IH-induced hypertension and endothelial dysfunction via an antioxidant and anti-inflammatory mechanism.

Intermittent hypoxia and hypercapnia induce pulmonary artery atherosclerosis and ventricular dysfunction in low density lipoprotein receptor deficient mice

Patients with obstructive sleep apnea, who experience episodic hypoxia and hypercapnia during sleep, often demonstrate increased inflammation, oxidative stress, and dyslipidemia. We hypothesized that sleep apnea patients would be predisposed to the development of atherosclerosis. To dissect the mechanisms involved, we developed an animal model in mice whereby we expose mice to intermittent hypoxia/hypercapnia (IHH) in normobaric environments. Two- to three-month-old low-density lipoprotein receptor deficient (Ldlr(-/-)) mice were fed a high-fat diet for 8 or 16 wk while being exposed to IHH for either 10 h/day or 24 h/day. Plasma lipid levels, pulmonary artery and aortic atherosclerotic lesions, and cardiac function were then assayed. Surprisingly, atherosclerosis in the aorta of IHH mice was similar compared with controls. However, in IHH mice, atherosclerosis was markedly increased in the trunk and proximal branches of the pulmonary artery of exposed mice; even though plasma cholesterol and triglycerides were lower than in controls. Hemodynamic analysis revealed that right ventricular maximum pressure and isovolumic relaxation constant were significantly increased in IHH exposed mice and left ventricular % fractional shortening was reduced. In conclusion, 1) Intermittent hypoxia/hypercapnia remarkably accelerated atherosclerotic lesions in the pulmonary artery of Ldlr(-/-) mice and 2) increased lesion formation in the pulmonary artery was associated with right and left ventricular dysfunction. These findings raise the possibility that patients with obstructive sleep apnea may be susceptible to atherosclerotic disease in the pulmonary vasculature, an observation that has not been previously recognized.

Salidroside protects against hydrogen peroxide-induced injury in HUVECs via the regulation of REDD1 and mTOR activation

Antioxidative therapy is considered an effective strategy for treating oxidative stress-induced apoptosis in cardiovascular diseases. Salidroside has been used as an antioxidative therapy for oxidative injury in cardiac diseases. However, the mechanism underlying its antioxidant effect is poorly understood. The present study aimed to investigate the pharmacological effects of salidroside on cultured human umbilical vein endothelial cells (HUVECs) under conditions of oxidative injury induced by hydrogen peroxide (H2O2) and the underlying mechanisms in vitro. HUVECs pretreated with or without salidroside for 24 h were exposed to H2O2-induced oxidative stress conditions for 6 h and then cell viability, apoptosis, HIF-1α, regulated in development and DNA damage responses-1 (REDD1) and the PI3K/Akt/mTOR pathway were investigated. The results demonstrated that salidroside effectively attenuated H2O2-impaired cell viability and the production of reactive oxygen species (ROS) in a concentration-dependent manner. Reduced H2O2-induced apoptosis and activation of the cellular PI3K/Akt/mTOR pathway were demonstrated in HUVECs pretreated with salidroside. Furthermore, the level of REDD1, a direct regulator of mitochondrial metabolism, significantly increased in parallel with the level of HIF-1α following pretreatment with salidroside. The antioxidative effect of salidroside was abrogated in REDD1 knockdown cells. However, LY294002, a PI3K inhibitor, attenuated the anti-apoptotic effect of salidroside and blocked the increase of Akt and mTOR; however, did not affect the antioxidative effect of salidroside. These findings suggested that salidroside was capable of protecting HUVECs against H2O2-induced apoptosis by activating the PI3K/Akt/mTOR-dependent pathway and inhibiting ROS production by activating REDD1.

Morbidities associated with obstructive sleep apnea

Obstructive sleep apnea (OSA)-induced biological changes include intermittent hypoxia, intermittent hypercapnia, intrathoracic pressure changes, sympathetic activation and sleep fragmentation. OSA can cause metabolic dysregulation, endothelial dysfunction, systemic inflammation, oxidative stress and hypercoagulation, and neurohumoral changes. There is evidence suggesting that OSA is independently associated with metabolic syndrome. OSA has been shown to increase the risk for systemic hypertension, pulmonary vascular disease, ischemic heart disease, cerebral vascular disease, congestive heart failure and arrhythmias. Although there are evidences accumulating that there may be a causal relationship between OSA and cardiovascular disorders, there is a need for more data from randomized controlled intervention trials to confirm this relationship. Many risk factors of OSA (age, male gender and obesity) are also known risk factors for cardiovascular disease. Severe OSA-hypopnea significantly increases the risk of fatal and nonfatal cardiovascular events in both men and women, and continuous positive airway pressure treatment reduces this risk in both. Neurocognitive consequences of OSA include daytime sleepiness, loss of alertness, memory deficit, reduced vigilance, impaired executive function, increased risk for automobile and occupational accidents, and decreased quality of life.

Tae-eum type as an independent risk factor for obstructive sleep apnea

Obstructive sleep apnea (OSA) is prevalent and associated with several kinds of chronic diseases. There has been evidence that a specific type of Sasang constitution is a risk factor for metabolic and cardiovascular diseases that can be found in patients with OSA, but there are no studies that address the association between the Sasang constitution type (SCT) and OSA. The purpose of this study was to investigate the association between the SCT and OSA. A total of 652 participants were included. All participants were examined for demographic information, medical history, and completed an interviewer-administered questionnaire on life style and sleep-related variables. Biochemical analyses were performed to determine the glucose and lipid profiles. An objective recording of OSA was done with an unattended home PSG using an Embla portable device. The apnea-hypopnea index (AHI) and oxygen desaturation index (ODI) were significantly higher in the Tae-eum (TE) type as compared to the So-eum (SE) and the So-yang (SY) types. Even after adjusting for confounding variables, the TE type still had a 2.34-fold (95% CI, 1.11–4.94; P = 0.0262) increased risk for OSA. This population-based cohort study found that the TE constitutional type is an independent risk factor for the development of OSA.

Intermittent hypoxia from obstructive sleep apnea may cause neuronal impairment and dysfunction in central nervous system: the potential roles played by microglia

Obstructive sleep apnea (OSA) is a common condition characterized by repetitive episodes of complete (apnea) or partial (hypopnea) obstruction of the upper airway during sleep, resulting in oxygen desaturation and arousal from sleep. Intermittent hypoxia (IH) resulting from OSA may cause structural neuron damage and dysfunction in the central nervous system (CNS). Clinically, it manifests as neurocognitive and behavioral deficits with oxidative stress and inflammatory impairment as its pathophysiological basis, which are mediated by microglia at the cellular level. Microglia are dominant proinflammatory cells in the CNS. They induce CNS oxidative stress and inflammation, mainly through mitochondria, reduced nicotinamide adenine dinucleotide phosphate oxidase, and the release of excitatory toxic neurotransmitters. The balance between neurotoxic versus protective and anti- versus proinflammatory microglial factors might determine the final roles of microglia after IH exposure from OSA. Microglia inflammatory impairments will continue and cascade persistently upon activation, ultimately resulting in clinically significant neuron damage and dysfunction in the CNS. In this review article, we summarize the mechanisms of structural neuron damage in the CNS and its concomitant dysfunction due to IH from OSA, and the potential roles played by microglia in this process.

Simulating sleep apnea by exposure to intermittent hypoxia induces inflammation in the lung and liver

Sleep apnea is a breathing disorder that results from momentary and cyclic collapse of the upper airway, leading to intermittent hypoxia (IH). IH can lead to the formation of free radicals that increase oxidative stress, and this mechanism may explain the association between central sleep apnea and nonalcoholic steatohepatitis. We assessed the level of inflammation in the lung and liver tissue from animals subjected to intermittent hypoxia and simulated sleep apnea. A total of 12 C57BL/6 mice were divided into two groups and then exposed to IH (n = 6) or a simulated IH (SIH) (n = 6) for 35 days. We observed an increase in oxidative damage and other changes to endogenous antioxidant enzymes in mice exposed to IH. Specifically, the expression of multiple transcription factors, including hypoxia inducible factor (HIF-1α), nuclear factor kappa B (NF-κB), and tumor necrosis factor (TNF-α), inducible NO synthase (iNOS), vascular endothelial growth factor (VEGF), and cleaved caspase 3 were shown to be increased in the IH group. Overall, we found that exposure to intermittent hypoxia for 35 days by simulating sleep apnea leads to oxidative stress, inflammation, and increased activity of caspase 3 in the liver and lung.

Biomarkers of sleep apnea

Obstructive sleep apnea (OSA) is a condition of repetitive upper airway collapse, which occurs during sleep. Recent literature has emphasized the role of OSA in contributing to glucose intolerance, dyslipidemia, and hypertension. OSA is associated with the development of cardiovascular disease, although definitive data are sparse with regard to the prevention of cardiovascular disease and CPAP therapy. CPAP provides effective treatment for OSA, but patient adherence remains challenging. Aside from daytime symptom improvement, it is difficult to monitor the adequacy of treatment response. Thus, the search for a biomarker becomes critical. The discovery of an ideal biomarker for OSA has the potential to provide information related to diagnosis, severity, prognosis, and response to treatment. In addition, because large-scale randomized controlled trials are both ethically and logistically challenging in assessing hard cardiovascular outcomes, certain biomarkers may be reasonable surrogate outcome measures. This article reviews the literature related to potential biomarkers of OSA with the recognition that an ideal biomarker does not exist at this time.

Chronic intermittent hypoxia induces thioredoxin system changes in a gender-specific fashion in mice

Obstructive sleep apnea (OSA) is an independent risk factor of multisystem injury including liver and cardiovascular system. Chronic intermittent hypoxia (CIH) associated with recurrent apneas in patients with OSA is one of the most important causes of the increased various systems injury and oxidative stress induced by CIH is an important pathogenic mechanism. Reports indicated that females are less susceptible to oxidative stress injury. The goal of this study was to explore if there exists gender deference of thioredoxin system (Trx/Txnip) alterations by CIH and to clarify a clue for studying gender disparity of OSA-related multisystem injury. C57BL/6J mice of each gender were exposed to CIH with a fractional inspired O2 (FiO2) nadir of 5%. The oxidative and antioxidant biomarkers were evaluated, including serum OxLDL level and Trx/Txnip expression of liver tissue. Male mice exposed to CIH exhibited significant increases in serum OxLDL level than that of the male control (73.24 ± 22.43 μg/dL, 45.20 ± 28.53 μg/dL, P = 0.032) but no significant difference in the females. Male mice exposed to CIH also exhibited decreased expression of Trx than the female (0.4460 ± 0.1023 versus 1.0454 ± 0.1777, P = 0.013) and increased expression of Txnip than the female (0.0123 ± 0.0476 versus 0.0065 ± 0.0058, P = 0.022). These data suggest that CIH induces thioredoxin system change in a gender-specific fashion in mice.

Oxidative stress mediated arterial dysfunction in patients with obstructive sleep apnoea and the effect of continuous positive airway pressure treatment

Background

Several studies suggest an increase of oxidative stress and a reduction of endothelial function in obstructive sleep apnoea syndrome (OSAS). We assessed the association between OSAS, endothelial dysfunction and oxidative stress. Further aim was to evaluate the effect of nasal continuous positive airway pressure (nCPAP) on oxidative stress and arterial dysfunction.

Methods

We studied 138 consecutive patients with heavy snoring and possible OSAS. Patients underwent unattended overnight home polysomnography. Ten patients with severe OSAS were revaluated after 6 months of nCPAP therapy. To assess oxidative stress in vivo, we measured urinary 8-iso-PGF2α and serum levels of soluble NOX2-derived peptide (sNOX2-dp). Serum levels of nitrite/nitrate (NOx) were also determined. Flow-mediated brachial artery dilation (FMD) was measured to asses endothelial function.

Results

Patients with severe OSAS had higher urinary 8-iso-PGF2α (p<0.001) and serum NOX2 and lower NOx. A negative association was observed between FMD and OSA severity. Apnea/hypopnea index was significantly correlated with the indices of central obesity and with urinary 8-isoprostanes (r=0.298, p<0.001). The metabolic syndrome (t=-4.63, p<0.001) and urinary 8-isoprostanes (t=-2.02, p<0.05) were the only independent predictors of FMD. After 6-months nCPAP treatment, a significant decrease of serum NOX2, (p<0.005) and urinary 8-iso-PGF2α (p<0.01) was observed, while serum NOx showed only a minor increase. A statistically significant increase of FMD was observed (from 3.6% to 7.0%).

Conclusions

The results of our study indicate that patients with OSAS and cardiometabolic comorbidities have increased oxidative stress and arterial dysfunction that are partially reversed by nCPAP treatment.

Sympatho-adrenal activation by chronic intermittent hypoxia

Recurrent apnea with chronic intermittent hypoxia (CIH) is a major clinical problem in adult humans and infants born preterm. Patients with recurrent apnea exhibit heightened sympathetic activity as well as elevated plasma catecholamine levels, and these phenotypes are effectively recapitulated in rodent models of CIH. This article summarizes findings from studies addressing sympathetic activation in recurrent apnea patients and rodent models of CIH and the underlying cellular and molecular mechanisms. Available evidence suggests that augmented chemoreflex and attenuated baroreflex contribute to sympathetic activation by CIH. Studies on rodents showed that CIH augments the carotid body response to hypoxia and attenuates the carotid baroreceptor response to increased sinus pressures. Processing of afferent information from chemoreceptors at the central nervous system is also facilitated by CIH. Adult and neonatal rats exposed to CIH exhibit augmented catecholamine secretion from the adrenal medulla. Adrenal demedullation prevents the elevation of circulating catecholamines in CIH-exposed rodents. Reactive oxygen species (ROS)-mediated signaling is emerging as the major cellular mechanism triggering sympatho-adrenal activation by CIH. Molecular mechanisms underlying increased ROS generation by CIH seem to involve transcriptional dysregulation of genes encoding pro-and antioxidant enzymes by hypoxia-inducible factor-1 and -2, respectively.