Effects of various degrees of oxidative stress induced by intermittent hypoxia in rat myocardial tissues

TRPC5 channel participates in myocardial injury in chronic intermittent hypoxia

OBJECTIVE

The purpose of this study is to develop an animal model of Chronic Intermittent Hypoxia (CIH) and investigate the role of the TRPC5 channel in cardiac damage in OSAHS rats.

METHODS

Twelve male Sprague Dawley rats were randomly divided into the CIH group and the Normoxic Control (NC) group. Changes in structure, function, and pathology of heart tissue were observed through echocardiography, transmission electron microscopy, HE-staining, and TUNEL staining.

RESULTS

The Interventricular Septum thickness at diastole (IVSd) and End-Diastolic Volume (EDV) of rats in the CIH group significantly increased, whereas the LV ejection fraction and LV fraction shortening significantly decreased. TEM showed that the myofilaments in the CIH group were loosely arranged, the sarcomere length varied, the cell matrix dissolved, the mitochondrial cristae were partly flocculent, the mitochondrial outer membrane dissolved and disappeared, and some mitochondria were swollen and vacuolated. The histopathological examination showed that the cardiomyocytes in the CIH group were swollen with granular degeneration, some of the myocardial fibers were broken and disorganized, and most of the nuclei were vacuolar and hypochromic.

CONCLUSION

CIH promoted oxidative stress, the influx of Ca2+, and the activation of the CaN/NFATc signaling pathway, which led to pathological changes in the morphology and ultrastructure of cardiomyocytes, the increase of myocardial apoptosis, and the decrease of myocardial contractility. These changes may be associated with the upregulation of TRPC5.

Effects of obstructive sleep apnea on myocardial injury and dysfunction: a review focused on the molecular mechanisms of intermittent hypoxia

Obstructive sleep apnea (OSA) is characterized by intermittent hypoxia (IH) and is strongly associated with adverse cardiovascular outcomes. Myocardial injury and dysfunction have been commonly observed in clinical practice, particularly in patients with severe OSA. However, the underlying mechanisms remain obscure. In this review, we summarized the molecular mechanisms by which IH impact on myocardial injury and dysfunction. In brief, IH-induced cardiomyocyte death proceeds through the regulation of multiple biological processes, including differentially expressed transcription factors, alternative epigenetic programs, and altered post-translational modification. Besides cell death, various cardiomyocyte injuries, such as endoplasmic reticulum stress, occurs with IH. In addition to the direct effects on cardiomyocytes, IH has been found to deteriorate myocardial blood and energy supply by affecting the microvascular structure and disrupting glucose and lipid metabolism. For better diagnosis and treatment of OSA, further studies on the molecular mechanisms of IH-induced myocardial injury and dysfunction are essential.

Association between the circulating superoxide dismutase and obstructive sleep apnea: a meta-analysis

PURPOSE

Although it has been reported that superoxide dismutase (SOD) is related to obstructive sleep apnea (OSA), the results are controversial. In addition, the effects of the continuous positive airway pressure (CPAP) treatment on SOD levels are also inconsistent. The primary purpose of the present meta-analysis is to determine the relationship between the circulating SOD levels and OSA.

METHODS

The studies included in this meta-analysis were selected from the PubMed, Embase, Cochrane Library, and Scopus databases. Two researchers independently reviewed the studies. Data analysis was performed using Stata 15.1. The overall effects were measured using the standardized mean difference (SMD) with a 95% confidence interval (CI). A random-effects model or a fixed-effects model was used, depending on the heterogeneity of the studies.

RESULTS

A total of 14 studies were included, comprising 1240 patients and 457 controls. The results showed that the circulating SOD levels of the patients with OSA were significantly lower than that of the control group (SMD = - 1.645, 95% CI = - 2.279 to - 1.011, P < 0.001). We also studied changes in the circulating SOD levels in patients with OSA after the CPAP treatment. No significant difference was observed in the circulating SOD levels after the CPAP treatment (SMD = - 0.028, 95% CI = - 0.218 to 0.162, P = 0.772).

CONCLUSION

The results suggested that patients with OSA have reduced levels of SOD and were related to disease severity. The results also indicated that circulating SOD levels may be a reliable marker for detecting systemic oxidative stress in patients with OSA. However, the circulating SOD levels were not affected by the short-term (4-12 weeks) CPAP treatment. Therefore, further large-scale, well-designed randomized controlled trials with a longer CPAP therapy (more than 6 months preferably) and good adherence to the treatment are needed to investigate this issue.

Combination of Broccoli Sprout Extract and Zinc Provides Better Protection against Intermittent Hypoxia-Induced Cardiomyopathy Than Monotherapy in Mice

Nuclear factor-E2-related factor 2 (Nrf2) and metallothionein have each been reported to protect against chronic intermittent hypoxia- (IH-) induced cardiomyopathy. Sulforaphane-rich broccoli sprout extract (BSE) and zinc can effectively induce Nrf2 and metallothionein, respectively, to protect against IH-induced cardiomyopathy via antioxidative stress. However, whether the cardiac protective effects of the combination of BSE and zinc can be synergistic or the same has not been evaluated. In this study, we treated 8-week-old C57BL/6J mice with BSE and/or zinc during exposure to IH for 8 weeks. Cardiac dysfunction, as determined by echocardiography, and pathological remodeling and abnormalities, including cardiac fibrosis, inflammation, and oxidative damage, examined by histopathology and western blotting, were clearly observed in IH mice but were not significant in IH mice treated with either BSE, zinc, or zinc/BSE. Furthermore, the effects of the combined treatment with BSE and zinc were always greater than those of single treatments. Nrf2 function and metallothionein expression in the heart increased to a greater extent using the combination of BSE and zinc than using BSE or zinc alone. These findings for the first time indicate that the dual activation of Nrf2 and metallothionein by combined treatment with BSE and zinc may be more effective than monotherapy at preventing the development of IH-induced cardiomyopathy.

Sustained Intermittent Hypoxemia Induces Adiponectin Oligomers Redistribution and a Tissue-Specific Modulation of Adiponectin Receptor in Mice

Introduction: Hypoxemia is a critical component of several respiratory diseases and is known to be involved in the processes underlying co-morbidities associated to such disorders, notably at the cardiovascular level. Circulating level of Adiponectin (Ad), known as a metabolic regulator and cardio-protective hormone was previously suggested to be reduced by hypoxia but consequences of such variation are unclear. The evaluation of the specific effect of hypoxemia on Ad forms and receptors could improve the understanding of the involvement of Ad axis in hypoxemia-related diseases.

Methods: Ad-pathway components were investigated in a murine model of sustained intermittent hypoxemia (FiO₂ 10%, 8 h/day, 35 days).

Results: Sustained intermittent hypoxemia (SIH) induced a redistribution of Ad multimers in favor of HMW forms, without change in total plasmatic level. Mice submitted to hypoxia also exhibited tissue-specific modification of adiporeceptor (AdipoR) protein level without mRNA expression change. A decreased AdipoR2 abundance was observed in skeletal muscle and heart whereas AdipoR1 level was only reduced in muscle. No change was observed in liver regarding AdipoR. Lipid profile was unchanged but glucose tolerance increased in hypoxemic mice.

Conclusion: Sustained intermittent hypoxemia, per se, modify Ad oligomerization state as well as AdipoR protein abundance in a tissue-specific way. That suggests alteration in Ad-dependant pathways in pathological conditions associated to SIH. Investigation of Ad-pathway components could therefore constitute useful complementary criteria for the clustering of patients with hypoxemia-related diseases and management of co-morbidities, as well as to develop new therapeutic strategies.

Elevated Levels of Apelin-36 in Heart Failure Due to Chronic Systemic Hypoxia

Apelin is a novel adipokine identified as an endogenous ligand of the specific orphan receptor APJ. Among the various isoforms of apelin, an increase in the apelin-36 plasma level has been associated with oxidative stress, and this isoform has various biological effects, such as positive inotropic, vasodilatory, and antiatherosclerotic effects. Therefore, apelin-36 may be used as a biomarker of heart failure (HF). Advances in the understanding of the molecular mechanisms underlying HF cannot be achieved without the use of animal models. However, it is unclear whether chronic systemic hypoxia can cause HF in rats. The present study aimed to determine whether chronic systemic hypoxia can cause HF in rats and whether apelin-36 can be used as a biomarker of HF. The study included Sprague-Dawley rats. The rats were randomly divided into seven groups ( n  = 4). One of the groups was a control group, and the six other groups were exposed to hypoxia (8% O2) for different durations (6 hours, 1 day, 3 days, 5 days, 7 days, and 14 days). The exposure groups showed ventricular hypertrophy accompanied by myocardial structural damage, which indicated ventricular remodeling. In addition, the exposure groups showed elevated apelin-36 plasma levels and signs of oxidative stress. Moreover, gel electrophoresis of heart tissue showed five bands that corresponded to apelin isotypes, including apelin-36. In an experimental rat HF model with chronic systemic hypoxia, apelin-36 was elevated along with oxidative stress. Apelin-36 along with oxidative stress may serve as a biomarker of HF in this model.

Nrf2 expression and function, but not MT expression, is indispensable for sulforaphane-mediated protection against intermittent hypoxia-induced cardiomyopathy in mice

We reported previously that nuclear factor erythroid 2-related factor 2 (Nrf2) and metallothionein (MT) play critical roles in preventing intermittent hypoxia (IH)-induced cardiomyopathy. In addition, positive feedback regulation between Nrf2 and MT is required for the efficient compensative responses of the heart to IH. As an activator of Nrf2, sulforaphane (SFN) has attracted attention as a potential protective agent against cardiovascular disease. Here, we investigated whether SFN can up-regulate cardiac Nrf2 expression and function, as well as MT expression, to prevent IH-induced cardiomyopathy, and if so, whether Nrf2 and MT are indispensable for this preventive effect. Nrf2-knock-out (Nrf2-KO) or MT-KO mice and their wild-type (WT) equivalents were exposed to IH for 4 weeks with or without SFN treatment. SFN almost completely prevented IH-induced cardiomyopathy in WT mice, and this preventive effect was abolished in Nrf2-KO mice but retained in MT-KO mice. In IH-exposed WT mice, SFN induced significant increases in the expression levels of Nrf2 and its downstream antioxidant target genes, as well as those of MT, but these effects were not seen in IH-exposed Nrf2-KO mice. By contrast, KO of MT did not affect the ability of SFN to up-regulate the expression of Nrf2 and its downstream antioxidant targets. These results suggest that SFN-induced MT expression is Nrf2-dependent, and SFN prevents IH-induced cardiomyopathy in a Nrf2-dependent manner, for which MT is dispensable. This study provides important information that is relevant to the potential use of SFN to prevent IH-induced cardiomyopathy.

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Sulforaphane (SFN) protects from intermittent-hypoxia (IH)-induced cardiomyopathy;

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SFN can increase both Nrf2 and metallothionein (MT) but the latter is Nrf2 dependent.

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SFN protects the heart from IH in wild-type and MT-KO mice, but not in Nrf2 mice.

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Nrf2 is indispensable, but not MT, for SFN to protect from IH-induced cardiomyopathy.

β-Adrenergic signaling, monoamine oxidase A and antioxidant defence in the myocardium of SHR and SHR-mtBN conplastic rat strains: the effect of chronic hypoxia

The β-adrenergic signaling pathways and antioxidant defence mechanisms play important roles in maintaining proper heart function. Here, we examined the effect of chronic normobaric hypoxia (CNH, 10% O2, 3 weeks) on myocardial β-adrenergic signaling and selected components of the antioxidant system in spontaneously hypertensive rats (SHR) and in a conplastic SHR-mtBN strain characterized by the selective replacement of the mitochondrial genome of SHR with that of the more ischemia-resistant Brown Norway strain. Our investigations revealed some intriguing differences between the two strains at the level of β-adrenergic receptors (β-ARs), activity of adenylyl cyclase (AC) and monoamine oxidase A (MAO-A), as well as distinct changes after CNH exposure. The β2-AR/β1-AR ratio was significantly higher in SHR-mtBN than in SHR, apparently due to increased expression of β2-ARs. Adaptation to hypoxia elevated β2-ARs in SHR and decreased the total number of β-ARs in SHR-mtBN. In parallel, the ability of isoprenaline to stimulate AC activity was found to be higher in SHR-mtBN than that in SHR. Interestingly, the activity of MAO-A was notably lower in SHR-mtBN than in SHR, and it was markedly elevated in both strains after exposure to hypoxia. In addition to that, CNH markedly enhanced the expression of catalase and aldehyde dehydrogenase-2 in both strains, and decreased the expression of Cu/Zn superoxide dismutase in SHR. Adaptation to CNH intensified oxidative stress to a similar extent in both strains and elevated the IL-10/TNF-α ratio in SHR-mtBN only. These data indicate that alterations in the mitochondrial genome can result in peculiar changes in myocardial β-adrenergic signaling, MAO-A activity and antioxidant defence and may, thus, affect the adaptive responses to hypoxia.

Intermittent hypoxia-induced cardiomyopathy and its prevention by Nrf2 and metallothionein

The mechanism for intermittent hypoxia (IH)-induced cardiomyopathy remains obscure. We reported the prevention of acute and chronic IH-induced cardiac damage by selective cardiac overexpression of metallothionein (MT). Herein we defined that MT-mediated protection from IH-cardiomyopathy is via activation of nuclear factor erythroid 2-related factor 2 (Nrf2), a critical redox-balance controller in the body. For this, mice were exposed to IH for 3 days (acute) or 4 or 8 weeks (chronic). Cardiac Nrf2 and MT expression in response to IH were significantly increased acutely yet decreased chronically. Interestingly, cardiac overexpression (Nrf2-TG) or global deletion of the Nrf2 gene (Nrf2-KO) made mice highly resistant or highly susceptible, respectively, to IH-induced cardiomyopathy and MT expression. Mechanistically, 4-week IH exposure significantly decreased cardiac Nrf2 binding to the MT gene promoter, and thus, depressed both MT transcription and translation in WT mice but not Nrf2-TG mice. Likewise, cardiac MT overexpression prevented chronic IH-induced cardiomyopathy and down-regulation of Nrf2 likely via activation of a PI3K/Akt/GSK-3β/Fyn-dependent signaling pathway. These results reveal an integrated relationship between cardiac Nrf2 and MT expression in response to IH -- acute compensatory up-regulation followed by chronic down-regulation and cardiomyopathy. Cardiac overexpression of either Nrf2 or MT offered cardioprotection from IH via complicated PI3K/Akt/GSK3B/Fyn signaling. Potential therapeutics may target either Nrf2 or MT to prevent chronic IH-induced cardiomyopathy.

Estradiol Regulates Txnip and Prevents Intermittent Hypoxia-Induced Vascular Injury

Chronic intermittent hypoxia (IH) contributes to obstructive sleep apnea (OSA)-related cardiovascular diseases through increasing oxidative stress. It has been widely recognized that estradiol decreases the risk for cardiovascular disease, but the estrogen replacement therapy is limited for its side effects. Thioredoxin (Trx) and its endogenous inhibitor, thioredoxin-interacting protein (Txnip), are associated with the protective effect of estradiol in some conditions. In this study, we aimed to explore whether estradiol could protect against IH-induced vascular injury, and the possible effect of Trx-1/Txnip in this process. Forty-eight adult female C57/BL6J mice were randomly divided into 4 groups, ovariectomy combined with IH group, sham operation combined with IH group, IH group and the control group. The mice treated with IH for 8 hrs/day, and 28 days. IH induced the injury of aorta, and ovariectomized mice were more prone to the IH-induced aortic injury, with higher level of oxidative stress. In vitro, estradiol increased Trx-1 level, but decreased the level of Txnip and oxidative stress in human umbilical vein endothelial cells (HUVECs) treated with IH for 16 hrs. Knock-down of Txnip by specific siRNA rescued oxidative stress and apoptosis. In conclusion, estradiol protects against IH-induced vascular injury, partially through the regulation of Trx-1/Txnip pathway.

Hypoxia inhibits expression and function of mitochondrial thioredoxin 2 to promote pulmonary hypertension

Pulmonary hypertension (PH) is characterized by increased pulmonary vascular resistance, pulmonary vascular remodeling, and increased pulmonary vascular pressures that often result in right ventricular dysfunction, leading to right heart failure. Evidence suggests that reactive oxygen species (ROS) contribute to PH pathogenesis by altering pulmonary vascular cell proliferation and intracellular signaling pathways. However, the role of mitochondrial antioxidants and oxidant-derived stress signaling in the development of hypoxia-induced PH is largely unknown. Therefore, we examined the role of the major mitochondrial redox regulator thioredoxin 2 (Trx2). Levels of Trx2 mRNA and protein were examined in human pulmonary arterial endothelial cells (HPAECs) and smooth muscle cells (HPASMCs) exposed to hypoxia, a common stimulus for PH, for 72 h. Hypoxia decreased Trx2 mRNA and protein levels. In vitro overexpression of Trx2 reduced hypoxia-induced H₂O₂ production. The effects of increased Trx2 protein level were examined in transgenic mice expressing human Trx2 (Tg^hTrx2) that were exposed to hypoxia (10% O₂) for 3 wk. Tg^hTrx2 mice exposed to hypoxia had exacerbated increases in right ventricular systolic pressures, right ventricular hypertrophy, and increased ROS in the lung tissue. Trx2 overexpression did not attenuate hypoxia-induced increases in Trx2 oxidation or Nox4 expression. Expression of a dominant negative C93S Trx2 mutant that mimics Trx2 oxidation exacerbated hypoxia-induced increases in HPASMC H₂O₂ levels and cell proliferation. In conclusion, Trx2 overexpression failed to attenuate hypoxia-induced HPASMC proliferation in vitro or hypoxia-induced PH in vivo. These findings indicate that strategies to enhance Trx2 expression are unlikely to exert therapeutic effects in PH pathogenesis.

Disrupted intestinal structure in a rat model of intermittent hypoxia

Obstructive sleep apnea (OSA) is a chronic condition characterized by chronic intermittent hypoxia (IH) and subsequent reoxygenation (ROX). The gastrointestinal system, which is particularly sensitive to tissue hypoxia and reduced perfusion, is likely to be affected by OSA. A rat model of IH was used to analyze oxidative stress-associated genes and tight junction proteins by reverse transcription‑quantitative polymerase chain reaction. Subsequently, altered morphology of the duodenal mucosa and elevated Chiu scores were observed in the IH‑exposed rats. In addition, IH exposure resulted in upregulation of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits, NADPH oxidase 2 and p22phox, in the small intestine, and upregulation of transcription factors, including hypoxia‑inducible factor-1, nuclear factor‑κB and activator protein-1. Furthermore, the mRNA expression levels of intestinal tight junction (TJ)-related proteins, claudin-1 and claudin-4, were decreased in the IH‑exposed group, as compared with in the control group. In conclusion, the present study demonstrated that OSA, which is characterized by IH and ROX, may lead to disruption of the duodenum. The mechanism underlying the effects of OSA on duodenal morphology may be associated with increased oxidative stress and activation of transcription factors, subsequently inducing intestinal TJ disruption and intestinal injury.

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.

Adiponectin protects the kidney against chronic intermittent hypoxia-induced injury through inhibiting endoplasmic reticulum stress

PURPOSE

The current study was carried out to assess the effects of chronic intermittent hypoxia (CIH) on the kidney, the intervention roles of adiponectin (Ad), and the associated mechanisms.

METHODS

Sixty Wistar rats were randomly divided into four groups: the normal control (NC), normal control plus Ad supplement (NC + Ad), CIH, and CIH plus Ad supplement (CIH + Ad) groups. The rats in both CIH and CIH + Ad groups were submitted to a CIH environment for 4 months, while the rats in NC and NC + Ad groups were housed with the normal air for 4 months. In addition, the rats in NC + Ad and CIH + Ad groups were treated with an intravenous injection of Ad at a dosage of 10 μg per injection, twice a week, for four successive months.

RESULTS

The production level of reactive oxygen species (ROS) and the protein levels of endoplasmic reticulum (ER) stress, as well as the cell apoptosis level in kidney, were all higher in the CIH group than in the NC and NC + Ad groups (all p < 0.05). However, the ROS production, the protein of ER stress, and cell apoptosis levels in kidney were all lower in the CIH + Ad group than those in the CIH group (all p < 0.05).

CONCLUSION

Ad could protect against CIH-induced renal cell apoptosis through inhibiting ROS-related ER stress.

Chronic intermittent hypoxia increases rat sternohyoid muscle NADPH oxidase expression with attendant modest oxidative stress

Chronic intermittent hypoxia (CIH) causes upper airway muscle dysfunction. We hypothesized that the superoxide generating NADPH oxidase (NOX) is upregulated in CIH-exposed muscle causing oxidative stress. Adult male Wistar rats were exposed to intermittent hypoxia (5% O₂ at the nadir for 90 s followed by 210 s of normoxia), for 8 h per day for 14 days. The effect of CIH exposure on the expression of NOX subunits, total myosin and 4-hydroxynonenal (4-HNE) protein adducts in sternohyoid muscle was determined by western blotting and densitometry. Sternohyoid protein free thiol and carbonyl group contents were determined by 1D electrophoresis using specific fluorophore probes. Aconitase and glutathione reductase activities were measured as indices of oxidative stress. HIF-1α content and key oxidative and glycolytic enzyme activities were determined. Contractile properties of sternohyoid muscle were determined ex vivo in the absence and presence of apocynin (putative NOX inhibitor). We observed an increase in NOX 2 and p47 phox expression in CIH-exposed sternohyoid muscle with decreased aconitase and glutathione reductase activities. There was no evidence, however, of increased lipid peroxidation or protein oxidation in CIH-exposed muscle. CIH exposure did not affect sternohyoid HIF-1α content or aldolase, lactate dehydrogenase, or glyceraldehyde-3-phosphate dehydrogenase activities. Citrate synthase activity was also unaffected by CIH exposure. Apocynin significantly increased sternohyoid force and power. We conclude that CIH exposure upregulates NOX expression in rat sternohyoid muscle with concomitant modest oxidative stress but it does not result in a HIF-1α-dependent increase in glycolytic enzyme activity. Constitutive NOX activity decreases sternohyoid force and power. Our results implicate NOX-dependent reactive oxygen species in CIH-induced upper airway muscle dysfunction which likely relates to redox modulation of key regulatory proteins in excitation-contraction coupling.

Biomarkers to improve diagnosis and monitoring of obstructive sleep apnea syndrome: current status and future perspectives

Obstructive sleep apnea syndrome (OSAS) is characterized by recurrent episodes of upper airway collapse associated with oxygen desaturation and sleep disruption. It is proposed that these periodic changes lead to molecular variations that can be detected by assessing serum biomarkers. Studies have identified inflammatory, oxidative, and metabolic perturbations attributable to sleep-disordered breathing. Given that OSAS is associated with increased cardiovascular and cerebrovascular morbidity, the ideal biomarker should enable timely recognition with the possibility of intervention. There is accumulating data on the utility of serum biomarkers for the evaluation of disease severity, prognosis, and response to treatment. However, current knowledge is limited by data collection techniques, disease complexity, and potential confounding factors. The current paper reviews the literature on the use of serum biomarkers in OSAS. It is concluded that the ideal serum biomarker still needs to be discovered, while caution is needed in the interpretation of hitherto available results.

Serum resistin levels in children with primary snoring

Primary Snoring (PS) has been positioned at the milder end of the Sleep-Disordered Breathing severity continuum characterized by snoring and it is usually underestimated. PS is defined as snoring without apnea, frequent arousals, or gas exchange abnormalities and recent studies demonstrated that children with PS have increased blood pressure and reduced arterial distensibility. The association between adipokines and SDB has been recently investigated, though most of the studies were focused on OSAS where intermittent hypoxia characterizing the disease may lead to an inflammatory cascade and to the release of several adipokines, contributing to oxidative stress. Resistin, initially described s an adipokine increasing insulin resistance, has been recently identified as a novel important member of the cytokine family involved in the regulation of inflammation. The aim of our study was to investigate circulating resistin levels in normal weight children with PS. Sixty-five children of normal weight aged between 4 and 14 years of age were selected for habitual snoring. Children with positive polysomnography were excluded from the study. Serum resistin levels were detected in all children with PS. Thirty-three healthy non-snorer children with similar age, sex and BMI were selected as a control group. A significantly higher level of resistin was observed in patients with PS compared to the control group (4.67±1.91 ng/ml vs 3.98±1.58 ng/ml; p<0.01). Patients with inconclusive pulse oximetry showed significantly higher resistin levels than those with negative recordings recordings (5.29±1.91 ng/ml vs 4.20±1.93 ng/ml; p<0.008). Moreover, there was a significant increasing trend between sieric adipokine level and the frequency of snoring (p<0.006). Our results suggest that systemic inflammation and oxidative stress may also play a significant role in the pathophysiology of PS.

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.

Obstructive sleep apnea, oxidative stress and cardiovascular disease: lessons from animal studies

Obstructive sleep apnea (OSA) is an independent risk factor for cardiovascular (CV) diseases such as arterial hypertension, heart failure, and stroke. Based on human research, sympathetic activation, inflammation, and oxidative stress are thought to play major roles in the pathophysiology of OSA-related CV diseases. Animal models of OSA have shown that endothelial dysfunction, vascular remodelling, and systemic and pulmonary arterial hypertension as well as heart failure can develop in response to chronic intermittent hypoxia (CIH). The available animal data are clearly in favour of oxidative stress playing a key role in the development of all of these CV manifestations of OSA. Presumably, the oxidative stress is due to an activation of NADPH oxidase and other free oxygen radicals producing enzymes within the CV system as evidenced by data from knockout mice and pharmacological interventions. It is hoped that animal models of OSA-related CV disease will continue to contribute to a deeper understanding of their underlying pathophysiology and will foster the way for the development of cardioprotective treatment options other than conventional CPAP therapy.