Estradiol Protects Against Cardiorespiratory Dysfunctions and Oxidative Stress in Intermittent Hypoxia

Chronic intermittent hypoxia-induced hypertension: the impact of sex hormones

Obstructive sleep apnea, a common form of sleep-disordered breathing, is characterized by intermittent cessations of breathing that reduce blood oxygen levels and contribute to the development of hypertension. Hypertension is a major complication of obstructive sleep apnea that elevates the risk of end-organ damage. Premenopausal women have a lower prevalence of obstructive sleep apnea and cardiovascular disease than men and postmenopausal women, suggesting that sex hormones play a role in the pathophysiology of sleep apnea-related hypertension. The lack of protection in men and postmenopausal women implicates estrogen and progesterone as protective agents but testosterone as a permissive agent in sleep apnea-induced hypertension. A better understanding of how sex hormones contribute to the pathophysiology of sleep apnea-induced hypertension is important for future research and possible hormone-based interventions. The effect of sex on the pathophysiology of sleep apnea and associated intermittent hypoxia-induced hypertension is of important consideration in the screening, diagnosis, and treatment of the disease and its cardiovascular complications. This review summarizes our current understanding of the impact of sex hormones on blood pressure regulation in sleep apnea with a focus on sex differences.

Loss of testosterone induces postprandial insulin resistance and increases the expression of the hepatic antioxidant flavin-containing monooxygenases in mice exposed to intermittent hypoxia

AIM

We tested the hypothesis that low testosterone alters the effects of intermittent hypoxia (IH) on glucose homeostasis, hepatic oxidative stress, and transcriptomic profile in male mice.

METHODS

We used sham-operated or orchiectomized (ORX) mice exposed to normoxia (Nx) or IH for 2 weeks. We performed fasting insulin and glucose tolerance tests and assessed fasting and postprandial insulin resistance with the HOMA-IR. The activity of hepatic prooxidant (NADPH oxidase-NOX), antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase-SOD, Cat, GPx), lipid peroxidation (MDA concentration), and the total concentration of glutathione (GSH) were measured under postprandial conditions. mRNA sequencing and pathway enrichment analyses were used to identify hepatic genes underlying the interactions between IH and testosterone.

RESULTS

In Sham mice, IH improves fasting insulin sensitivity and glucose tolerance, while there are no effects of IH in ORX mice. In ORX mice, IH induces postprandial hyperinsulinemia, insulin resistance, and a prooxidant profile of enzyme activity (low SOD activity) without altering hepatic MDA and GSH content. ORX and IH altered the expression of genes involved in oxidoreductase activities, cytochromes-dependent pathways, and glutathione metabolism. Among the genes upregulated in ORX-IH mice, the flavin-containing monooxygenases (FMO) are particularly relevant since these are potent hepatic antioxidants that could help prevent overt oxidative stress in ORX-IH mice.

CONCLUSION

Low levels of testosterone in male mice exposed to IH induce post-prandial hyperinsulinemia and insulin resistance and determine the mechanisms by which the liver handles IH-induced oxidative stress.

On the origins of sleep disordered breathing, cardiorespiratory and metabolic dysfunction: which came first, the chicken or the egg?

Sleep disordered breathing (SDB) is a complex, sex specific and highly heterogeneous group of respiratory disorders. Nevertheless, sleep fragmentation and repeated fluctuations of arterial blood gases for several hours per night are at the core of the problem; together, they impose significant stress to the organism with deleterious consequences on physical and mental health. SDB increases the risk of obesity, diabetes, depression and anxiety disorders; however, the same health issues are risk factors for SDB. So, which came first, the chicken or the egg? What causes the appearance of the first significant apnoeic events during sleep? These are important questions because although moderate to severe SDB affects ∼500 million adults globally, we still have a poor understanding of the origins of the disease, and the main treatments (and animal models) focus on the symptoms rather than the cause. Because obesity, metabolic dysfunction and stress-related neurological disorders generally appear progressively, we discuss how the development of these diseases can lead to specific anatomical and non-anatomical traits of SDB in males and females while considering the impacts of sex steroids. In light of the growing evidence indicating that the carotid bodies are important sensors of key metabolic and endocrine signals associated with stress and dysmetabolism, we propose that these organs play a key role in the process.

Pathophysiological mechanisms and therapeutic approaches in obstructive sleep apnea syndrome

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

Intermittent Hypoxia and Weight Loss: Insights into the Etiology of the Sleep Apnea Phenotype

Sleep apnea (SA) is a major respiratory disorder with increased risk for hypertension and obesity; however, our understanding of the origins of this complex disorder remains limited. Because apneas lead to recurrent drops in O₂ during sleep, intermittent hypoxia (IH) is the main animal model to explore the pathophysiology of SA. Here, we assessed the impacts of IH on metabolic function and related signals. Adult male rats were exposed to 1 week of moderate IH (FiO₂ = 0.10-30 s, ten cycles/hour, 8 h/day). Using whole-body plethysmography, we measured respiratory variability and apnea index during sleep. Blood pressure and heart rate were measured by the tail-cuff method; blood samples were taken for multiplex assay. At rest, IH augmented arterial blood pressure, respiratory instability, but not apnea index. IH induced weight, fat, and fluid loss. IH also reduced food intake and plasma leptin, adrenocorticotropic hormone (ACTH), and testosterone levels but increased inflammatory cytokines. We conclude that IH does not replicate the metabolic clinical features of SA patient, thus raising our awareness of the limitations of the IH model. The fact that the risk for hypertension occurs before the appearance of apneas provides new insights into the progression of the disease.

A Narrative Review of Sex and Gender Differences in Sleep Disordered Breathing: Gaps and Opportunities

INTRODUCTION

Sleep disordered breathing (SDB) is a common condition, associated with multiple comorbidities including cardiovascular and metabolic disease. It has been previously established that SDB is more prevalent in men than women, shifting the literature's focus away from the latter population. As such, underdiagnosis, and thus undertreatment, of SDB in women exists.

METHODS

To establish the differences in prevalence, clinical presentation, and pathophysiology of SDB between the two sexes, a narrative review of the current literature was performed.

RESULTS

Rates of SDB are higher among men, likely driven by differences in symptom presentation between men and women, with women presenting with more "atypical" symptoms, and lack of sensitivity in SDB screening tools to detect SDB in women. In addition to the cardiovascular risks of SDB, women with SDB may have worse quality of life, higher prevalence of insomnia, and respiratory issues.

DISCUSSION

More research is needed to better define the unique pathophysiology and clinical presentation of SDB in women. In addition, an increased awareness among health care providers and the lay public of the SDB-specific sex and gender differences will serve to minimize disparities in identification and treatment of SDB in women.

Intermittent Hypoxia-Induced Cardiomyocyte Death Is Mediated by HIF-1 Dependent MAM Disruption

Rationale: Intermittent hypoxia (IH) is one of the main features of sleep-disordered breathing (SDB). Recent findings indicate that hypoxia inducible factor-1 (HIF-1) promotes cardiomyocytes apoptosis during chronic IH, but the mechanisms involved remain to be elucidated. Here, we hypothesize that IH-induced ER stress is associated with mitochondria-associated ER membrane (MAM) alteration and mitochondrial dysfunction, through HIF-1 activation. Methods: Right atrial appendage biopsies from patients with and without SDB were used to determine HIF-1α, Grp78 and CHOP expressions. Wild-type and HIF-1α^+/− mice were exposed to normoxia (N) or IH (21–5% O₂, 60 cycles/h, 8 h/day) for 21 days. Expressions of HIF-1α, Grp78 and CHOP, and apoptosis, were measured by Western blot and immunochemistry. In isolated cardiomyocytes, we examined structural integrity of MAM by proximity ligation assay and their function by measuring ER-to-mitochondria Ca²⁺ transfer by confocal microscopy. Finally, we measured mitochondrial respiration using oxygraphy and calcium retention capacity (CRC) by spectrofluorometry. MAM structure was also investigated in H9C2 cells incubated with 1 mM CoCl₂, a potent HIF-1α inducer. Results: In human atrial biopsies and mice, IH induced HIF-1 activation, ER stress and apoptosis. IH disrupted MAM, altered Ca²⁺ homeostasis, mitochondrial respiration and CRC. Importantly, IH had no effect in HIF-1α^+/− mice. Similar to what observed under IH, HIF-1α overexpression was associated with MAM alteration in H9C2. Conclusion: IH-induced ER stress, MAM alterations and mitochondrial dysfunction were mediated by HIF-1; all these intermediate mechanisms ultimately inducing cardiomyocyte apoptosis. This suggests that HIF-1 modulation might limit the deleterious cardiac effects of SDB.

Female sex hormones and symptoms of obstructive sleep apnea in European women of a population-based cohort

Background

The prevalence of obstructive sleep apnea is higher in women after menopause. This is suggested to be a result of an altered sex hormone balance but has so far not been confirmed in a population-based study.

Objective

To investigate whether serum concentration of estrogens and progesterone are associated with the prevalence of sleep apnea symptoms in middle-aged women of the general population.

Methods

We analyzed data from 774 women (40–67 years) from 15 study centers in seven countries participating in the second follow-up of the European Community Respiratory Health Survey (2010–2012). Multiple logistic regression models were fitted with self-reported symptoms of sleep apnea as outcomes and serum concentrations of various estrogens and progesterone as predictors. All analyses were adjusted for relevant covariates including age, BMI, education, study center, smoking habits, and reproductive age.

Results

Among all included women, a doubling of serum concentrations of estrone and progesterone was associated with 19% respectively 9% decreased odds of snoring. Among snorers, a doubling of the concentrations of 17β-estradiol, estrone and estrone 3-sulfate was associated with 18%, 23% and 17% decreased odds of breathing irregularly, and a doubling of the progesterone concentration was further associated with 12% decreased odds of waking up suddenly with a chocking sensation. Other evaluated associations were not statistically significant.

Conclusions

Middle-aged women with low serum estrogen and progesterone levels are more likely to snore and report symptoms of obstructive sleep apnea.

Additive effects of orchiectomy and intermittent hypoxia on lung mechanics and inflammation in C57BL/6J male mice

NEW FINDINGS

What is the central question of this study? Does endogenous testosterone modulate the consequences of intermittent hypoxia (IH) in the lungs of male mice? What is the main finding and its importance? Orchiectomized mice exposed to IH develop a pattern that is similar to emphysema or obstructive lung disease with elevated lung volumes, low pulmonary elastance during a methacholine challenge test and high counts of lymphocytes in bronchoalveolar lavages. Since low testosterone levels and other respiratory diseases are common in sleep apnoea, there is a clear clinical relevance to these results.

ABSTRACT

We tested the hypothesis that low testosterone levels modulate the pulmonary responses to intermittent hypoxia (IH; used as a model of sleep apnoea (SA)) in male mice. We used intact (SHAM) or orchiectomized (ORX) mice exposed to IH for 14 days (12 h/day, 10 cycles/h, 6% oxygen) or to normoxia (Nx). We first measured ventilation and metabolic rates in freely behaving mice (whole-body plethysmography) and then respiratory mechanics in tracheotomized mice (flexiVent). We assessed the respiratory system resistance and elastance (E_rs ), Newtonian resistance (resistance of the large airways), tissue damping and tissue elastance (H) under baseline conditions and during a methacholine challenge test. We also measured the quasi-static compliance and inspiratory capacity with partial pressure-volume loops. Finally, inflammatory cells were counted in the broncho-alveolar lavage (BAL) and we measured lung volume by water displacement. ORX-IH mice had higher tidal volume, inspiratory capacity and lung volume compared to the other groups, but showed signs of low efficiency of O₂ exchange rate relative to minute ventilation. During the methacholine challenge, orchiectomy decreased the values of most mechanical parameters and IH reduced E_rs and H leading to very low values in ORX-IH mice. Finally, the total number of cells and the number of lymphocytes in BAL were both increased by IH in ORX mice. Since reduced lung elasticity, low O₂ extraction, increased lung volumes and inflammation are signs of emphysematous lung disease, we conclude that testosterone might prevent lung emphysema during IH exposures.

Beneficial Effects of High Intensity Interval Training and/or Linseed Oil Supplementation to Limit Obesity-Induced Oxidative Stress in High Fat Diet-Fed Rats

High-intensity interval training (HIIT) and linseed oil (LO) supplementation are effective strategies to reduce obesity-induced oxidative stress. Our aim was to determine whether the HIIT + LO combination prevents obesity-induced oxidative stress in high fat diet (HFD)-fed rats. HFD-fed 8-week-old, male, Wistar rats were subdivided in four groups: HFD, LO (2% of sunflower oil replaced with 2% of LO in the HFD), HIIT (4 days/week for 12 weeks), and HIIT + LO. Wistar rats fed a low-fat diet (LFD) were used as controls. Epididymal and subcutaneous adipose tissue, gastrocnemius muscle, liver, and plasma samples were collected to measure oxidative stress markers (AOPP, oxLDL), antioxidant (SOD, CAT, and GPx activities) and pro-oxidant (NOx and XO) enzyme activities. Compared with the LFD, the HFD altered the pro/antioxidant status in different tissues (increase of AOPP, oxLDL, SOD and catalase activities in plasma, and SOD activity increase in liver and decrease in adipose tissues) but not in gastrocnemius. LO upregulated CAT activity and decreased NOx in liver. HIIT alleviated HFD negative effects in liver by reducing SOD and NOx activities. Moreover, the HIIT + LO combination potentiated SOD activity upregulation in subcutaneous tissue. HIIT and LO supplementation have independent beneficial effects on the pro/antioxidant balance. Their association promotes SOD activity in subcutaneous adipose tissue.

High-intensity exercise in hypoxia improves endothelial function via increased nitric oxide bioavailability in C57BL/6 mice

AIM

The optimal exercise intensity to improve endothelial function remains unclear, as well as whether the addition of hypoxia could potentiate this function. Therefore, the aim of this study was to compare the effects of different exercise intensities in normoxia and hypoxia on vascular reactivity and nitric oxide (NO) bioavailability in mice.

METHODS

C57BL/6 mice underwent treadmill running three times per week, for 4 weeks at either low, maximal or supramaximal intensity in normoxia or hypoxia (inspire oxygen fraction = 0.13). Vascular reactivity and expression of genes and proteins involved in NO production/bioavailability were assessed in aorta using isolated vessel tension experiments, RT-qPCR and western blot, respectively. Circulating NO metabolites and pro-/antioxidant markers were measured.

RESULTS

Hypoxic exercise improved both acetylcholine-induced vasorelaxation and phenylephrine-induced vasoconstriction compared to normoxic exercise, independently of intensity. In hypoxia, a higher acetylcholine-induced vasorelaxation was observed with high intensities (supramaximal and maximal) compared to low intensity. Exercise protocols modulated endothelial nitric oxide synthase (eNOS) and α1-adrenergic receptor (α1 -AR) mRNA level, but not superoxide dismutase 3 (SOD3) and p47phox. No significant differences were observed for protein expression of α1 -AR, total eNOS, phosphorylated eNOS, SOD isoforms and p47phox. However, plasma SOD and catalase activities were significantly increased in hypoxic supramaximal compared to hypoxic low intensity, while concentration of nitrotyrosine significantly decreased. The latter was also observed in hypoxic maximal and supramaximal compared to the same intensities in normoxia.

CONCLUSION

Hypoxic high-intensity exercise increases NO bioavailability and improves vascular function, opening promising clinical perspectives for cardiovascular disease prevention.

The poorly conducted orchestra of steroid hormones, oxidative stress and inflammation in frailty needs a maestro: Regular physical exercise

This review outlines the various factors associated with unhealthy aging which includes becoming frail and dependent. With many people not engaging in recommended exercise, facilitators and barriers to engage with exercise must be investigated to promote exercise uptake and adherence over the lifespan for different demographics, including the old, less affluent, women, and those with different cultural-ethnic backgrounds. Governmental and locally funded public health messages and environmental facilitation (gyms, parks etc.) can play an important role. Studies have shown that exercise can act as a conductor to balance oxidative stress, immune and endocrine functions together to promote healthy aging and reduce the risk for age-related morbidities, such as cardiovascular disease and atherosclerosis, and promote cognition and mood over the lifespan. Like a classic symphony orchestra, consisting of four groups of related musical instruments - the woodwinds, brass, percussion, and strings - the aging process should also perform in harmony, with compassion, avoiding the aggrandizement of any of its individual parts during the presentation. This review discusses the wide variety of molecular, cellular and endocrine mechanisms (focusing on the steroid balance) underlying this process and their interrelationships.

Stress and Loss of Ovarian Function: Novel Insights into the Origins of Sex-Based Differences in the Manifestations of Respiratory Control Disorders During Sleep

The respiratory system of women and men develops and functions in distinct neuroendocrine milieus. Despite differences in anatomy and neural control, homeostasis of arterial blood gases is ensured in healthy individuals regardless of sex. This convergence in function differs from the sex-based differences observed in many respiratory diseases. Sleep-disordered breathing (SDB) results mainly from episodes of upper airway closure. This complex and multifactorial respiratory disorder shows significant sexual dimorphism in its clinical manifestations and comorbidities. Guided by recent progress from basic research, this review discusses the hypothesis that stress is necessary to reveal the sexual dimorphism of SDB.

Protective Effects of Estrogen on Cardiovascular Disease Mediated by Oxidative Stress

Perimenopause is an important stage of female senescence. Epidemiological investigation has shown that the incidence of cardiovascular disease in premenopausal women is lower than that in men, and the incidence of cardiovascular disease in postmenopausal women is significantly higher than that in men. This phenomenon reveals that estrogen has a definite protective effect on the cardiovascular system. In the cardiovascular system, oxidative stress is considered important in the pathogenesis of atherosclerosis, myocardial dysfunction, cardiac hypertrophy, heart failure, and myocardial ischemia. From the perspective of oxidative stress, estrogen plays a regulatory role in the cardiovascular system through the estrogen receptor, providing strategies for the treatment of menopausal women with cardiovascular diseases.

Mirabegron Ameliorated Atherosclerosis of ApoE-/- Mice in Chronic Intermittent Hypoxia but Not in Normoxia

PURPOSE

It has been established that obstructive sleep apnea (OSA) is an independent risk factor for atherosclerosis. Chronic intermittent hypoxia (CIH) activates sympathoadrenal system and upregulates β3 adrenergic receptor (β3 AR). However, the effect of selective β3 AR agonist mirabegron in CIH-induced atherosclerosis remains unknown.

METHODS

We generated a CIH-induced atherosclerosis model through exposing ApoE^-/- mice to CIH (8 h per day, cyclic inspiratory oxygen fraction 5-21%, 60-s cycle) for 6 weeks after 4-week high-fat dieting and investigated the effects of mirabegron, a selective β3 AR agonist, on CIH-induced atherosclerosis. The coronary endarterectomy (CE) specimens from coronary artery disease patients with OSA and without OSA were collected.

RESULTS

The expression of β3 AR was significantly elevated in CIH-induced atherosclerosis model. Furthermore, treatment with mirabegron (10mg/kg per day by oral administration for 6 weeks) ameliorated atherosclerosis in ApoE^-/- mice in CIH but not in normoxia. Mechanistically, mirabegron activated β3 AR and ameliorated intraplaque oxidative stress by suppressing p22phox expression and reactive oxygen species (ROS) level. In addition, in human CE specimens, β3 AR was also upregulated associated with increased p22phox expression and ROS level both in the lumen and in the plaque of coronary artery in OSA subjects.

CONCLUSION

This study first demonstrated that mirabegron impeded the progression of CIH-induced atherosclerosis, at least in part, via β3 AR-mediated oxidative stress, suggesting a promising therapeutic strategy for protecting against atherosclerosis induced by CIH.

Sex-Specific Effects of Stress on Respiratory Control: Plasticity, Adaptation, and Dysfunction

As our understanding of respiratory control evolves, we appreciate how the basic neurobiological principles of plasticity discovered in other systems shape the development and function of the respiratory control system. While breathing is a robust homeostatic function, there is growing evidence that stress disrupts respiratory control in ways that predispose to disease. Neonatal stress (in the form of maternal separation) affects "classical" respiratory control structures such as the peripheral O₂ sensors (carotid bodies) and the medulla (e.g., nucleus of the solitary tract). Furthermore, early life stress disrupts the paraventricular nucleus of the hypothalamus (PVH), a structure that has emerged as a primary determinant of the intensity of the ventilatory response to hypoxia. Although underestimated, the PVH's influence on respiratory function is a logical extension of the hypothalamic control of metabolic demand and supply. In this article, we review the functional and anatomical links between the stress neuroendocrine axis and the medullary network regulating breathing. We then present the persistent and sex-specific effects of neonatal stress on respiratory control in adult rats. The similarities between the respiratory phenotype of stressed rats and clinical manifestations of respiratory control disorders such as sleep-disordered breathing and panic attacks are remarkable. These observations are in line with the scientific consensus that the origins of adult disease are often found among developmental and biological disruptions occurring during early life. These observations bring a different perspective on the structural hierarchy of respiratory homeostasis and point to new directions in our understanding of the etiology of respiratory control disorders. © 2021 American Physiological Society. Compr Physiol 11:1-38, 2021.

A5 noradrenergic neurons and breathing control in neonate rats

The pontine A5 noradrenergic group contributes to the maturation of the respiratory system before birth in rats. These neurons are connected to the neural network responsible for respiratory rhythmogenesis. In the present study, we investigated the participation of A5 noradrenergic neurons in neonates (P7-8 and P14-15) in the control of ventilation during hypoxia and hypercapnia in in vivo experiments using conjugated saporin anti-dopamine beta-hydroxylase (DβH-SAP) to specifically ablate noradrenergic neurons. Thus, DβH-SAP (420 ng/μL) or saporin (SAP, control) was injected into the A5 region of neonatal male Wistar rats. Hypoxia reduced respiratory variability in control animals; however, A5 lesion prevented this effect in P7-8 rats. Our data suggest that noradrenergic neurons of the A5 region in neonate rats do not participate in the control of ventilation under baseline and hypercapnic conditions, but exert an inhibitory modulation on breathing variability under hypoxic challenge in early life (P7-8).

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).

Evaluation and Management of Adults with Obstructive Sleep Apnea Syndrome

Obstructive sleep apnea syndrome (OSAS) is a common and underdiagnosed medical condition characterized by recurrent sleep-dependent pauses and reductions in airflow. While a narrow, collapsible oropharynx plays a central role in the pathophysiology of OSAS, there are other equally important nonanatomic factors including sleep-stage dependent muscle tone, arousal threshold, and loop gain that drive obstructive apneas and hypopneas. Through mechanisms of intermittent hypoxemia, arousal-related sleep fragmentation, and intrathoracic pressure changes, OSAS impacts multiple organ systems. Risk factors for OSAS include obesity, male sex, age, specific craniofacial features, and ethnicity. The prevalence of OSAS is rising due to increasing obesity rates and improved sensitivity in the tools used for diagnosis. Validated questionnaires have an important but limited role in the identification of patients that would benefit from formal testing for OSA. While an in-laboratory polysomnography remains the gold standard for diagnosis, the widespread availability and accuracy of home sleep apnea testing modalities increase access and ease of OSAS diagnosis for many patients. In adults, the most common treatment involves the application of positive airway pressure (PAP), but compliance continues to be a challenge. Alternative treatments including mandibular advancement device, hypoglossal nerve stimulator, positional therapies, and surgical options coupled with weight loss and exercise offer possibilities of an individualized personal approach to OSAS. Treatment of symptomatic patients with OSAS has been found to be beneficial with regard to sleep-related quality of life, sleepiness, and motor vehicle accidents. The benefit of treating asymptomatic OSA patients, particularly with regard to cardiovascular outcomes, is controversial and more data are needed.

Subclinical left ventricular systolic dysfunction detected in obstructive sleep apnea with automated function imaging and its association with nocturnal hypoxia

BACKGROUND

Early detection of left ventricular (LV) dysfunction is crucial in obstructive sleep apnea (OSA) due to its close relationship with cardiovascular diseases. Global longitudinal strain (GLS) derived from automated function imaging (AFI) can precisely assess global longitudinal function. The aim of this study was to determine if LV GLS was reduced in patients with OSA and a normal LV ejection fraction (LVEF) and to assess any associated determinants.

METHODS

Polysomnography (PSG) and echocardiography were done in consecutive patients with suspected OSA and normal LVEF in this prospective study. Patients were divided into two groups according to apnea-hypopnea index (AHI) (Group 1, normal or mild OSA: AHI < 15/h; Group 2, moderate-to-severe OSA: AHI ≥ 15/h). Clinical, PSG, and echocardiographic parameters were compared between the two groups and the associated factors were investigated.

RESULTS

Of 425 consecutive patients, 244 were analyzed after exclusions. Patients in Group 2 had significantly worse GLS than those in Group 1 (p < 0.001). The prevalence of GLS reduction (defined as < - 19.7%) was 25% and 76%, respectively (χ² = 34.19, p < 0.001). Nocturnal lowest pulse oxygen saturation (SpO₂), AHI, body mass index (BMI), and gender were associated with GLS reduction (all p < 0.05). Further multivariate analysis showed that the lowest SpO₂ (OR: 2.15), gender (OR: 2.45), and BMI (OR: 2.66) remained independent (all p < 0.05), and the lowest SpO₂ was the most powerful determinant (χ² = 33.0, p < 0.001) in forward regression analysis. The intra- and inter-operator variability for AFI and coefficient of repeatability was low even in those with relatively poor images.

CONCLUSIONS

In patients with normal LVEF, more severe OSA was associated with a worse GLS. The major determinants were lowest nocturnal SpO₂, gender, and obesity, but not AHI. GLS can be rapidly and reliably assessed using AFI.

Lung oxidative stress and transcriptional regulations induced by estradiol and intermittent hypoxia

We determined the effects of chronic intermittent hypoxia (CIH) and estradiol (E₂) on oxidative stress and gene expression in the lungs. Female Sprague-Dawley rats were left intact (sham) or ovariectomized (OVX) and implanted with pumps delivering vehicle or E₂ (0.5 mg/kg/day). Two weeks following surgery, the rats were exposed to room air (RA) or CIH for 7 days (10% O₂, 10 cycles/hour, 8 h/day). Lung samples were used to measure the activities of pro- (NADPH and xanthine oxidases) and antioxidant (superoxide dismutase, catalase and glutathione peroxidase) enzymes, and concentrations of advanced oxidation of protein products (AOPP). We determined gene expression with an RNA microarray and enrichment analysis of differentially expressed genes. In rats exposed to RA, OVX and E₂ supplementation increased pro- and antioxidant activities and AOPP concentration. In rats exposed to CIH, AOPP concentration, pro- and antioxidant enzymes activities increased in sham, did not changed in OVX-Veh rats, and were reduced in OVX-E₂ rats. In rats exposed to RA, genes involved in extracellular matrix were up-regulated by OVX and down-regulated by E₂, while E₂ up-regulated genes involved in cell mobility/adherence and leukocytes migration. OVX downregulated expression of roughly 200 olfactory receptor genes without effect of E₂. CIH altered gene expression in sham and OVX-E₂, but not in OVX-Veh rats. Enrichment analysis confirmed the antioxidant effects of E₂ under CIH. There are important interactions between ovarian hormones and CIH that can be relevant to better understand the consequences of sleep apnea (i.e. CIH) on the occurrence of lung pathologies in women.

Metabolic responses to intermittent hypoxia are regulated by sex and estradiol in mice

The roles of sex and sex-hormones on the metabolic consequences of intermittent hypoxia (IH, a reliable model of sleep apnea) are unknown. We used intact male or female mice and ovariectomized (OVX) females treated with vehicle (Veh) or estradiol (E₂) and exposed to normoxia (Nx) or IH (6% O₂, 10 cycles/h, 12 h/day, 2 wk). Mice were then fasted for 6 h, and we measured fasting glucose and insulin levels and performed insulin or glucose tolerance tests (ITT or GTT). We also assessed liver concentrations of glycogen, triglycerides (TGs), and expression levels of genes involved in aerobic or anaerobic metabolism. In males, IH lowered fasting levels of glucose and insulin, slightly improved glucose tolerance, but altered glucose tolerance in females. In OVX-Veh females, IH reduced fasting glucose and insulin levels and strongly impaired glucose tolerance. E₂ supplementation reversed these effects and improved homeostasis model assessment of β-cell function (HOMA-β), a marker of pancreatic glucose-induced insulin released. IH decreased liver TG concentration in males and slightly increased glycogen in OVX-Veh females. Liver expression of glycolytic (Ldha) and mitochondrial (citrate synthase, Pdha1) genes was reduced by IH in males and in OVX-Veh females, but not in intact or OVX-E₂ females. We conclude that 1) IH reduced fasting levels of glycemia in males and in ovariectomized females. 2) IH improves glucose tolerance only in males. 3) In females IH decreased glucose tolerance, this effect was amplified by ovariectomy, and reversed by E₂ supplementation. 4) During IH exposures, E₂ supplementation appears to improve pancreatic β cells functions.NEW & NOTEWORTHY We assessed fasting glycemic control, and tolerance to insulin and glucose in male and female mice exposed to intermittent hypoxia. IH improves glucose tolerance in males but had opposite effects in females. This response was amplified following ovariectomy in females and prevented by estradiol supplementation. Metabolic consequences of IH differ between males and females and are regulated by estradiol in female mice.

Sex differences in integrated neurocardiovascular control of blood pressure following acute intermittent hypercapnic hypoxia

Repetitive hypoxic apneas, similar to those observed in sleep apnea, result in resetting of the sympathetic baroreflex to higher blood pressures (BP). This baroreflex resetting is associated with hypertension in preclinical models of sleep apnea (intermittent hypoxia, IH); however, the majority of understanding comes from males. There are data to suggest that female rats exposed to IH do not develop high BP. Clinical data further support sex differences in the development of hypertension in sleep apnea, but mechanistic data are lacking. Here we examined sex-related differences in the effect of IH on sympathetic control of BP in humans. We hypothesized that after acute IH we would observe a rise in muscle sympathetic nerve activity (MSNA) and arterial BP in young men (n = 30) that would be absent in young women (n = 19). BP and MSNA were measured during normoxic rest before and after 30 min of IH. Baroreflex sensitivity (modified Oxford) was evaluated before and after IH. A rise in mean BP following IH was observed in men (+2.0 ± 0.7 mmHg, P = 0.03), whereas no change was observed in women (-2.7 ± 1.2 mmHg, P = 0.11). The elevation in MSNA following IH was not different between groups (4.7 ± 1.1 vs. 3.8 ± 1.2 bursts/min, P = 0.65). Sympathetic baroreflex sensitivity did not change after IH in either group (P > 0.05). Our results support sex-related differences in the effect of IH on neurovascular control of BP and show that any BP-raising effects of IH are absent in young women. These data enhance our understanding of sex-specific mechanisms that may contribute to BP changes in sleep apnea.

Influence of Oxidative Stress Biomarkers and Genetic Polymorphisms on the Clinical Severity of Hydroxyurea-Free Senegalese Children with Sickle Cell Anemia

Oxidative stress would play a role in the pathophysiology of sickle cell anemia (SCA). We tested the impact of common SCA genetic modifiers (alpha-thalassemia, G6PD deficiency, HbF quantitative trait loci; QTL) and pro/antioxidant genes polymorphisms (SOD2 rs4880, XO rs207454, MPO rs233322) on oxidative stress biomarkers (AOPP, MDA, MPO, XO, MnSOD, CAT, GPx) and clinical severity in 301 Senegalese SCA hydroxyurea-free children at steady-state (median age 9.1 years, sex ratio H/F = 1.3). Plasma oxidative stress biomarkers were compared with those of a control group (AA). CAT activity, AOPP, and MDA levels were higher in SCA than in AA individuals while XO, GPX, and MnSOD activities were lower. The presence of alpha-thalassemia decreased MDA level and MPO activity but no effect of the HbF QTL or G6PD deficiency was observed. SCA children who experienced their first hospitalized complication before 3 years old had higher MnSOD and CAT activities than the other children while those with no hospitalized VOC in the previous 2 years presented higher GPX activity. Age of the first hospitalized complication and AOPP levels were affected by the MPO rs2333227 SNP. Our results suggest that alpha-thalassemia modulates oxidative stress in SCA, presumably because of a reduction in the MPO activity.

Prebiotic administration modulates gut microbiota and faecal short-chain fatty acid concentrations but does not prevent chronic intermittent hypoxia-induced apnoea and hypertension in adult rats

BACKGROUND

Evidence is accruing to suggest that microbiota-gut-brain signalling plays a regulatory role in cardiorespiratory physiology. Chronic intermittent hypoxia (CIH), modelling human sleep apnoea, affects gut microbiota composition and elicits cardiorespiratory morbidity. We investigated if treatment with prebiotics ameliorates cardiorespiratory dysfunction in CIH-exposed rats.

METHODS

Adult male rats were exposed to CIH (96 cycles/day, 6.0% O2 at nadir) for 14 consecutive days with and without prebiotic supplementation (fructo- and galacto-oligosaccharides) beginning two weeks prior to gas exposures.

FINDINGS

CIH increased apnoea index and caused hypertension. CIH exposure had modest effects on the gut microbiota, decreasing the relative abundance of Lactobacilli species, but had no effect on microbial functional characteristics. Faecal short-chain fatty acid (SCFA) concentrations, plasma and brainstem pro-inflammatory cytokine concentrations and brainstem neurochemistry were unaffected by exposure to CIH. Prebiotic administration modulated gut microbiota composition and diversity, altering gut-metabolic (GMMs) and gut-brain (GBMs) modules and increased faecal acetic and propionic acid concentrations, but did not prevent adverse CIH-induced cardiorespiratory phenotypes.

INTERPRETATION

CIH-induced cardiorespiratory dysfunction is not dependant upon changes in microbial functional characteristics and decreased faecal SCFA concentrations. Prebiotic-related modulation of microbial function and resultant increases in faecal SCFAs were not sufficient to prevent CIH-induced apnoea and hypertension in our model. Our results do not exclude the potential for microbiota-gut-brain axis involvement in OSA-related cardiorespiratory morbidity, but they demonstrate that in a relatively mild model of CIH, sufficient to evoke classic cardiorespiratory dysfunction, such changes are not obligatory for the development of morbidity, but may become relevant in the elaboration and maintenance of cardiorespiratory morbidity with progressive disease.

FUNDING

Department of Physiology and APC Microbiome Ireland, University College Cork, Ireland. APC Microbiome Ireland is funded by Science Foundation Ireland, through the Government's National Development Plan.

Progesterone decreases apnoea and reduces oxidative stress induced by chronic intermittent hypoxia in ovariectomized female rats

NEW FINDINGS

What is the central question of this study? Does progesterone reduce the effect of chronic intermittent hypoxia (CIH) on arterial blood pressure, respiratory control and oxidative stress in the central nervous system in ovariectomized rats? What is the main finding and its importance? Progesterone does not prevent the elevation of arterial blood pressure in rats exposed to CIH, but normalizes respiratory control, and reduces cerebral oxidative stress. This study draws focus to a potential role of progesterone and the consequences of sleep apnoea in menopausal women.

ABSTRACT

We tested the hypothesis that progesterone (Prog) reduces the effect of chronic intermittent hypoxia (CIH) on arterial blood pressure, respiratory chemoreflexes and oxidative stress in the central nervous system. Ovariectomized female rats were implanted with osmotic pumps delivering vehicle (Veh) or Prog (4 mg kg^-1  day^-1 ). Two weeks following the surgery, rats were exposed to room air (Air) or CIH (7 days, 10% O₂ , 10 cycles h^-1 , 8 h day^-1 ). We studied three groups: Veh-Air, Veh-CIH and Prog-CIH. After the CIH exposures, we measured the mean arterial pressure (MAP; tail cuff) and assessed the frequency of apnoeas at rest and ventilatory responses to hypoxia and hypercapnia (whole body plethysmography). The activities of the pro-oxidant enzyme NADPH oxidase (NOX) and antioxidant enzymes superoxide dismutase (SOD; in mitochondrial and cytosolic fractions) and glutathione peroxidase (GPx), as well as the concentration of malondialdehyde (MDA), a marker of lipid peroxidation, were measured in brain cortex and brainstem samples. CIH exposure increased the MAP, the frequency of apnoeas, and the respiratory frequency response to hypoxia and hypercapnia. Prog did not prevent the CIH-induced elevation in MAP, but it reduced the CIH-induced frequency of apnoeas and increased hypoxic and hypercapnic ventilatory responses. In the brain cortex, CIH increased NOX activity, and decreased the cytosolic and mitochondrial SOD activities. These effects were prevented by Prog. NOX activity was increased by CIH in the brainstem, and this was also blocked by Prog. The study draws focus to the links between ovarian hormones and the consequences of sleep apnoea in women.

Sleep Disordered Breathing, a Novel, Modifiable Risk Factor for Hypertensive Disorders of Pregnancy

PURPOSE OF REVIEW

Pathophysiology of hypertensive disorders of pregnancy (HDP), especially preeclampsia, has not been fully elucidated. Most trials aimed at the prevention of preeclampsia have failed to show significant benefit and investigation of novel, modifiable risk factors is sorely needed. Sleep disordered breathing (SDB), a group of disorders for which treatments are available, meets these criteria. SDB impacts about a third of all pregnancies and is associated with hypertension in the general non-pregnant population.

RECENT FINDINGS

Recent studies have shown a high prevalence of SDB, especially in complicated pregnancies. Several studies have shown that pregnant women with SDB have a higher risk for developing HDP, and these two disorders are associated with similar maternal long-term cardiovascular outcomes. Based on limited animal models of gestational intermittent hypoxia and human studies, SDB and HDP share similar risk factors and some pathophysiological mechanisms. However, there is paucity of studies addressing causality of this association and identifying therapeutic targets for intervention. Maternal SDB represents a novel and modifiable risk factor of HDP. Further studies are needed in order to establish the exact mechanisms underlying this association and to identify specific areas for clinical interventions.

Cardiovascular Disease in Women Across the Lifespan: The Importance of Sleep

Cardiovascular disease (CVD) and sleep disturbances are both common and associated with significant morbidity and mortality. Compared with men, women are more likely to report insufficient sleep. During the 2018 Research Conference on Sleep and the Health of Women sponsored by the National Heart, Lung, and Blood Institute, researchers in cardiology, integrative physiology and sleep medicine reviewed the current understanding of how sleep and sleep disturbances influence CVD in women across the lifespan. Women may be particularly vulnerable to the negative effects of sleep disturbances at important stages of their life, including during pregnancy and after menopause. The proposed pathways linking sleep disturbances and adverse cardiovascular outcomes in women are numerous and the complex interaction between them is not well understood. Future research focused on understanding the scope of sleep disorders in women, defining the underlying mechanisms, and testing interventions to improve sleep are critical for improving the cardiovascular health of all women.

Sex and age differentially affect GABAergic neurons in the mouse prefrontal cortex and hippocampus following chronic intermittent hypoxia

Obstructive sleep apnea (OSA), a chronic sleep disorder characterized by repetitive reduction or cessation of airflow during sleep, is widely prevalent and is associated with adverse neurocognitive sequelae including increased risk of Alzheimer's disease (AD). In humans, OSA is more common in elderly males. OSA is characterized by sleep fragmentation and chronic intermittent hypoxia (CIH), and recent epidemiological studies point to CIH as the best predictor of neurocognitive sequelae associated with OSA. The sex- and age- specific effects of OSA-associated CIH on specific cell populations such as γ-aminobutyric acid (GABA)-ergic neurons in the hippocampus and the medial prefrontal cortex (mPFC), regions important for cognitive function, remain largely unknown. The present study examined the effect of 35 days of either moderate (10% oxygen) or severe (5% oxygen) CIH on GABAergic neurons in the mPFC and hippocampus of young and aged male and female mice as well as post-accelerated ovarian failure (AOF) female mice. In the mPFC and hippocampus, the number of GABA-labeled neurons increased in aged and young severe CIH males compared to controls but not in young moderate CIH males. This change was not representative of the individual GABAergic cell subpopulations, as the number of parvalbumin-labeled neurons decreased while the number of somatostatin-labeled neurons increased in the hippocampus of severe CIH young males only. In all female groups, the number of GABA-labeled cells was not different between CIH and controls. However, in the mPFC, CIH increased the number of parvalbumin-labeled neurons in young females and the number of somatostatin-labeled cells in AOF females but decreased the number of somatostatin-labeled cells in aged females. In the hippocampus, CIH decreased the number of somatostatin-labeled neurons in young females. CIH decreased the density of vesicular GABA transporter in the mPFC of AOF females only. These findings suggest sex-specific changes in GABAergic neurons in the hippocampus and mPFC with males showing an increase of this cell population as compared to their female counterparts following CIH. Age at exposure and severity of CIH also differentially affect the GABAergic cell population in mice.

Female Sex and Gender in Lung/Sleep Health and Disease. Increased Understanding of Basic Biological, Pathophysiological, and Behavioral Mechanisms Leading to Better Health for Female Patients with Lung Disease

Female sex/gender is an undercharacterized variable in studies related to lung development and disease. Notwithstanding, many aspects of lung and sleep biology and pathobiology are impacted by female sex and female reproductive transitions. These may manifest as differential gene expression or peculiar organ development. Some conditions are more prevalent in women, such as asthma and insomnia, or, in the case of lymphangioleiomyomatosis, are seen almost exclusively in women. In other diseases, presentation differs, such as the higher frequency of exacerbations experienced by women with chronic obstructive pulmonary disease or greater cardiac morbidity among women with sleep-disordered breathing. Recent advances in -omics and behavioral science provide an opportunity to specifically address sex-based differences and explore research needs and opportunities that will elucidate biochemical pathways, thus enabling more targeted/personalized therapies. To explore the status of and opportunities for research in this area, the NHLBI, in partnership with the NIH Office of Research on Women's Health and the Office of Rare Diseases Research, convened a workshop of investigators in Bethesda, Maryland on September 18 and 19, 2017. At the workshop, the participants reviewed the current understanding of the biological, behavioral, and clinical implications of female sex and gender on lung and sleep health and disease, and formulated recommendations that address research gaps, with a view to achieving better health outcomes through more precise management of female patients with nonneoplastic lung disease. This report summarizes those discussions.

Effect of experimentally induced hypertension on cerebellum of postmenopausal rat

Cerebellum seems to be a specific target for both the decrease of estrogen and hypertension in menopause. The aim of this study was to investigate the hypertension and menopause-induced changes in rat's cerebellar cortex and the possible mechanisms of these changes. Rats were divided into four groups: the sham-operated control (SC-group), the ovariectomized (OVX-group), the hypertensive (H-group), and the ovariectomized-hypertensive (OVX-H-group) group. The mean arterial pressure (MAP), serum nitric oxide (NO), lipid peroxides and antioxidant catalase enzyme levels were assayed. Cerebellar tissue homogenization for analysis of lipid peroxides, antioxidant catalase enzyme, tumor necrosis factor-α (TNF-α), and estradiol was done. Quantification of adrenomedullin (AM) and interleukin-10 (IL-10) mRNA was also done. Cerebella were processed for histological, immunohistochemical and transmission electron microscopic examination. In the OVX-group, insignificant structural and biochemical changes were observed compared with the SC-group apart from the significantly increased lipid peroxides and decreased NO and catalase levels in serum. The H-group showed an elevated lipid peroxides and TNF-α levels, reduced catalase level, numerous degenerated Purkinje cells, vacuolations of the neuropil, some axonal degeneration, and few ghosts in the granular cell layer (GL). However, in OVX-H-group, oxidative stress, inflammation, and cerebellar damage were exacerbated and cerebellar estrogen was reduced associated with reduction in GL thickness and decreased Purkinje cells number. Most axoplasms had degenerated neurofilaments with abnormal myelination. The immunoexpression of glial fibrillary acidic protein were significantly increased in both OVX-group and H-group and significantly decreased in OVX-H group. Gene expression of AM and IL-10 were increased in cerebellar tissues of H-group compared with the SC-group but it was significantly decreased in OVX-H-group compared with H-group. Taken together, postmenopausal rats with hypertension suffered from structural cerebellar changes than rats with only hypertension or estrogen deficiency separately due to augmentation of the increased oxidative stress markers and the proinflammatory cytokines (TNF-α) with down regulation of the anti-inflammatory cytokine (IL-10) and the blood pressure regulator, AM. These suggested that high blood pressure is a critical factor for postmenopausal cerebellum.

Effects of Individualized Treadmill Endurance Training on Oxidative Stress in Skeletal Muscles of Transgenic Sickle Mice

Oxidative stress is a key feature in the pathophysiology of sickle cell disease. Endurance training has been shown to reduce oxidative stress in the heart and the liver of sickle mice. However, the effects of endurance training on skeletal muscles, which are major producers of reactive oxygen species during exercise, are currently unknown. The aim of this study was to evaluate the effect of sickle genotype on prooxidant/antioxidant response to individualized endurance training in skeletal muscles of sickle mice. Healthy and homozygous Townes sickle mice were divided into trained or sedentary groups. Maximal aerobic speed and V̇O₂ peak were determined using an incremental test on a treadmill. Trained mice ran at 40% to 60% of maximal aerobic speed, 1 h/day, 5 days/week for 8 weeks. Oxidative stress markers, prooxidant/antioxidant response, and citrate synthase enzyme activities were assessed in the gastrocnemius, in the plantaris, and in the soleus muscles. Maximal aerobic speed and V̇O₂ peak were significantly reduced in sickle compared to healthy mice (-57% and -17%; p < 0.001). NADPH oxidase, superoxide dismutase, and catalase activities significantly increased after training in the gastrocnemius of sickle mice only. A similar trend was observed for citrate synthase activity in sickle mice (p = 0.06). In this study, we showed an adaptive response to individualized endurance training on the prooxidant/antioxidant balance in the gastrocnemius, but neither in the plantaris nor in the soleus of trained sickle mice, suggesting an effect of sickle genotype on skeletal muscle response to endurance treadmill training.

Tissue-Specific Oxidative Stress Modulation by Exercise: A Comparison between MICT and HIIT in an Obese Rat Model

Background and Aim

Exercise is an effective strategy to reduce obesity-induced oxidative stress. The purpose of this study was to compare the effects of two training modalities (moderate-intensity continuous training (MICT) and high-intensity interval training (HIIT)) on the pro/antioxidant status of different tissues in obese Zucker rats.

Methods

Eight-week-old male Zucker rats (fa/fa, n = 36) were subdivided in three groups: MICT, HIIT, and control (no exercise) groups. Trained animals ran on a treadmill (0° slope), 5 days/week for 10 weeks (MICT: 51 min at 12 m·min^-1; HIIT: 6 sets of 3 min at 10 m·min^-1 followed by 4 min at 18 m·min^-1). Epididymal (visceral) and subcutaneous adipose tissue, gastrocnemius muscle, and plasma samples were collected to measure oxidative stress markers (advanced oxidation protein products (AOPP), oxidized low-density lipoprotein (oxLDL)), antioxidant system markers (ferric-reducing ability of plasma (FRAP), superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPx) activities), and prooxidant enzymes (NADPH oxidase and xanthine oxidase (XO) activities, myeloperoxidase content).

Results

Compared with the control, MICT increased GPx and catalase activities and the FRAP level in epididymal adipose tissue. HIIT increased the AOPP level in subcutaneous adipose tissue. In the muscle, HIIT increased both SOD and GPx activities and reduced the AOPP level, whereas MICT increased only SOD activity. Finally, plasma myeloperoxidase content was similarly decreased by both training modalities, whereas oxLDL was reduced only in the MICT group.

Conclusion

Both HIIT and MICT improved the pro/antioxidant status. However, HIIT was more efficient than MICT in the skeletal muscle, whereas MICT was more efficient in epididymal adipose tissue. This suggests that oxidative stress responses to HIIT and MICT are tissue-specific. This could result in ROS generation via different pathways in these tissues. From a practical point of view, the two training modalities should be combined to obtain a global response in people with obesity.

Erythropoietin and caffeine exert similar protective impact against neonatal intermittent hypoxia: Apnea of prematurity and sex dimorphism

Apnea of prematurity (AoP) is associated with severe and repeated episodes of arterial oxygen desaturation (intermittent hypoxia - IH), which in turn increases the number of apneas. So far, there is no data addressing whether IH leads to sex-specific respiratory consequences, neither if drugs targeting AoP are more effective in males or females. We used rat pups for investigating whether IH-mediated increase of apneas is sex-specific. We also tested whether caffeine (treatment of choice of AoP), erythropoietin (Epo - a neuroprotective factor and potent respiratory stimulant), and combination of both (caffeine+Epo) prevent the IH-mediated formation of apneas in a sex-dependent manner. Newborn rats exposed to IH (21% - 10% FIO₂-8 h a day - 10 cycles per hour) during postnatal days (P) 3-10 were used in this work. Animals were administered drug vehicle, Epo, caffeine and Epo + caffeine (daily from P3 to P10) gavage. At P10 the frequency of apneas at rest (as an index of respiratory dysfunction induced by IH), and respiratory parameters were measured by plethysmography. Our results showed that IH significantly increases the number of apneas in male but not in female rat pups. Moreover, caffeine and Epo in males similarly prevented the increase of apneas induced by IH, and the administration of both drugs together did not provide a cumulative beneficial effect. No impact of drugs was evidenced in females. Apart from apneas, IH increased the normoxic basal ventilation (ventilation at rest) of male animals, and treatments did not prevent such alteration. Besides, no IH- nor treatment-mediated modulation of basal ventilation was found in the basal ventilation of female animals. Analysis of the activity of pro- and antioxidative molecules revealed that IH induces oxidative stress in the brainstem of male and female animals and that all tested treatments similarly prevented such oxidative imbalance in pups of both sexes. We concluded that neonatal IH and the treatments tested to prevent its respiratory consequences are sex-specific. The mechanics associated with such prevention are directly linked with the prevention of oxidative stress and the maturation of the brain. These findings are relevant to understanding better the AoP disorder and for proposing Epo as a new therapeutical tool.

Roles of oestradiol receptor alpha and beta against hypertension and brain mitochondrial dysfunction under intermittent hypoxia in female rats

AIM

Chronic intermittent hypoxia (CIH) induces systemic (hypertension) and central alterations (mitochondrial dysfunction underlying cognitive deficits). We hypothesized that agonists of oestradiol receptors (ER) α and β prevent CIH-induced hypertension and brain mitochondrial dysfunction.

METHODS

Ovariectomized female rats were implanted with osmotic pumps delivering vehicle (Veh), the ERα agonist propylpyraoletriol (PPT - 30 μg/kg/day) or the ERβ agonist diarylpropionitril (DPN - 100 μg/kg/day). Animals were exposed to CIH (21%-10% F_I O₂ - 10 cycles/hour - 8 hours/day - 7 days) or normoxia. Arterial blood pressure was measured after CIH or normoxia exposures. Mitochondrial respiration and H₂ O₂ production were measured in brain cortex with high-resolution respirometry, as well as activity of complex I and IV of the electron transport chain, citrate synthase, pyruvate, and lactate dehydrogenase (PDH and LDH).

RESULTS

Propylpyraoletriol but not DPN prevented the rise of arterial pressure induced by CIH. CIH exposures decreased O₂ consumption, complex I activity, and increased H₂ O₂ production. CIH had no effect on citrate synthase activity, but decreased PDH activity and increased LDH activity indicating higher anaerobic glycolysis. Propylpyraoletriol and DPN treatments prevented all these alterations.

CONCLUSIONS

We conclude that in OVX female rats, the ERα agonist prevents from CIH-induced hypertension while both ERα and ERβ agonists prevent the brain mitochondrial dysfunction and metabolic switch induced by CIH. These findings may have implications for menopausal women suffering of sleep apnoea regarding hormonal therapy.

Protective roles of estradiol against vascular oxidative stress in ovariectomized female rats exposed to normoxia or intermittent hypoxia

AIM

We tested the hypothesis that estradiol (E₂ ) reduces aortic oxidative stress and endothelial dysfunction in ovariectomized (OVX) female rats exposed to room air (RA) or chronic intermittent hypoxia (CIH).

METHODS

We used intact or OVX female rats treated with vehicle or E₂ (0.5 mg/kg/d) and exposed to RA or CIH (21%-10% O₂ , 10 cycles/h, 8 h/d) for 7 or 35 days, and measured the arterial pressure, heart rate and plasma endothelin-1 levels. We also measured in thoracic aortic samples, the activities of the pro-oxidant enzymes NADPH (NOX) and xanthine oxidase (XO), the antioxidant enzymes superoxide dismutase, catalase, glutathione peroxidase and the advanced oxidation protein products (AOPP-oxidative stress marker). Finally, we used aortic rings to assess the contractile response to phenylephrine and the vasodilatory response to acetylcholine.

RESULTS

After 7 or 35 days of CIH, E₂ supplementation reduced arterial pressure. E₂ reduced plasma endothelin-1 levels after 7 days of CIH, but not after 35 days. Ovariectomy, but not CIH for 7 days, increased aortic oxidative stress and E₂ treatment prevented this effect. Remarkably, in animals exposed to RA, this was achieved by a reduction in NOX and XO activities, but in animals exposed to CIH this was achieved by increased catalase activity. In OVX female rats exposed to CIH for 7 days, E₂ supplementation improved the NO-mediated vasodilation. After 35 days of CIH, enzymatic activities, AOPP and aortic reactivity were similar in all groups.

CONCLUSION

E₂ -based therapy could help prevent the vascular consequences of CIH in apneic women.

Maternal obstructive sleep apnea and neonatal birth outcomes in a population based sample

OBJECTIVE

Evaluate the association of OSA with birth outcomes including the risk of congenital anomalies and the need for a higher level of clinical care at delivery.

METHODS

Population-based study that linked newborn records with maternal records. Data from 95 perinatal centers across all geographic census divisions of the U.S. of women with a delivery diagnosis from 2010 to 2014 whose records could be linked to the corresponding newborn record. An International Classification of Diseases, ninth Revision (ICD-9) code for sleep apnea was used to identify exposure and outcome variables. Univariate and multivariate logistic regression analyses were performed with a model that included substance use, obesity, diabetes, maternal co-morbidities, and pregnancy complications.

RESULTS

In this study, 1,423,099 maternal records were linked to live newborn records. OSA was associated with a higher risk for congenital anomalies in offspring (aOR 1.26, 1.11 to 1.43), with the highest risk being that of musculoskeletal anomalies (aOR 1.89, 1.16 to 3.07) after adjusting for comorbidities and potential teratogens. Neonates born to mothers with OSA were more likely to be admitted to the intensive care unit (25.3% vs. 8.1%, p < 0.001), require resuscitation (aOR 2.76, 1.35 to 5.64) and have a longer hospital stay (aOR 2.25, 1.85 to 2.65).

CONCLUSIONS

Although our study does not establish causation, it is the first to demonstrate a higher risk of congenital anomalies and resuscitation at birth in neonates of mothers with OSA, emphasizing the importance of identifying OSA in pregnant women and women of reproductive age.

Sensory plasticity of carotid body is correlated with oxidative stress in paraventricular nucleus during chronic intermittent hypoxia

Chronic intermittent hypoxia (CIH) is known to induce hypertension, but the mechanism is not well understood. We hypothesized that sensory plasticity of the carotid body (CB) and oxidative stress in the paraventricular nucleus (PVN) are involved in CIH-induced hypertension. In this study, rats were exposed to CIH for 28 days (intermittent hypoxia of 21% O₂ for 60 s and 5% O₂ for 30 s, cyclically repeated for 8 hr/day) and then randomly grouped for intracerebroventricular injection of 5-HT2 receptor antagonist ritanserin, Rho-associated protein kinase (ROCK) inhibitor Y-27632, and NADPH oxidase (NOX) inhibitor diphenyleneiodonium (DPI), respectively. We found that CIH increased blood pressure (BP), elevated carotid sinus nerve (CSN) and renal sympathetic nerve (RSN) activities, oxidative stress, and cell apoptosis in PVN. NOX-derived reactive oxygen species (ROS) production and cell apoptosis decreased when CIH-induced activation of 5-HT/5-HT2AR/PKC signaling was inhibited by ritanserin. In addition, RhoA expression was downregulated when oxidative stress was attenuated by DPI, while Y-27632 decreased the expression of endothelin-1, which is overexpressed in the vascular wall during hypertension. Moreover, treatment with ritanserin, DPI or Y-27632 attenuated the sensory plasticity and sympathetic hyperactivity as well as CIH-induced elevation of BP. In conclusion, CIH-induced activation of 5-HT/5-HT2AR/PKC signaling contributes to NOX-derived oxidative stress in PVN, which may cause sensory plasticity of CB, RSN hyperactivity, and elevated BP.

The role of inflammation in the association between gestational diabetes and obstructive sleep apnea: A pilot study

Background

Obstructive sleep apnea is associated with pregnancy complications including gestational diabetes. Mechanisms underlying the association between obstructive sleep apnea and gestational diabetes remain to be elucidated.

Methods

Twenty-three participants with gestational diabetes underwent home sleep apnea testing. Obstructive sleep apnea was defined as an apnea hypopnea index > 5. Fasting morning blood samples were measured using multianalyte profiling (xMAP) multiplexed bead array immunoassay for Interleukin 6, tumor necrosis factor-alpha, and Interleukin 8.

Results

Age, body mass index, and gestational age at enrollment were 31 + 4.4 years, 35.7 + 7.4 kg/m², and 28 ± 4 weeks, respectively. Participants were 52% Caucasian and 16% had obstructive sleep apnea. We observed positive correlations between apnea hypopnea index and Interleukin 6 (r = 0.62, p = 0.005), Interleukin 8 (r = 0.56, p = .56), and tumor necrosis factor-alpha (r = .58, p = .009). Women with obstructive sleep apnea had higher levels of Interleukin 6 (F = 5.01, p = .037) and Interleukin 8 (F = 6.33, p = .021) vs. women without obstructive sleep apnea.

Conclusion

These preliminary results indicate that in women with gestational diabetes, apnea hypopnea index is associated with an elevated inflammatory profile.

Brain-derived erythropoietin protects from intermittent hypoxia-induced cardiorespiratory dysfunction and oxidative stress in mice

Study Objectives

Based on the fact that erythropoietin (Epo) administration in rodents protects against spatial learning and cognitive deficits induced by chronic intermittent hypoxia (CIH)-mediated oxidative damage, here we tested the hypothesis that Epo in the brain protects against cardiorespiratory disorders and oxidative stress induced by CIH in adult mice.

Methods

Adult control and transgenic mice overexpressing Epo in the brain only (Tg21) were exposed to CIH (21%-10% O2-10 cycles/hour-8 hours/day-7 days) or room air. After CIH exposure, we used the tail cuff method to measure arterial pressure, and whole-body plethysmography to assess the frequency of apneic episodes at rest, minute ventilation, and ventilatory responses to hypoxia and hypercapnia. Finally, the activity of pro-oxidant (XO-xanthine oxidase, and NADPH) and antioxidant (super oxide dismutase) enzymes was evaluated in the cerebral cortex and brainstem.

Results

Exposure of control mice to CIH significantly increased the heart rate and arterial pressure, the number of apneic events, and the ventilatory response to hypoxia and hypercapnia. Furthermore, CIH increased the ratio of pro-oxidant to antioxidant enzymes in cortex and brainstem tissues. Both physiological and molecular changes induced by CIH were prevented in transgenic Tg21 mice.

Conclusions

We conclude that the neuroprotective effect of Epo prevents oxidative damage in the brain and cardiorespiratory disorders induced by CIH. Considering that Epo is used in clinics to treat chronic kidney disease and stroke, our data show convincing evidence suggesting that Epo may be a promising alternative drug to treat sleep-disorder breathing.

Sleep in Women Across the Life Span

There are many ways in which women experience sleep differently from men. Women contending with distinct sleep challenges respond differently to sleep disorders, as well as sleep deprivation and deficiency, and face particular health outcomes as a result of poor sleep. Idiosyncrasies, including changes that occur with the biological life cycles of menstruation, pregnancy, and menopause, make the understanding of sleep in women an important topic to study. Each phase of a woman's life, from childhood to menopause, increases the risk of sleep disturbance in unique ways that may require distinct management. Indeed, new research is unraveling novel aspects of sleep pathology in women and the fundamental role that sex hormones play in influencing sleep regulation and arousals and possibly outcomes of sleep conditions. Moreover, studies indicate that during times of hormonal change, women are at an increased risk for sleep disturbances such as poor sleep quality and sleep deprivation, as well as sleep disorders such as OSA, restless legs syndrome, and insomnia. This article reviews sleep changes in female subjects from neonatal life to menopause.

Effect of Gender on Chronic Intermittent Hypoxic Fosb Expression in Cardiorespiratory-Related Brain Structures in Mice

We aimed to delineate sex-based differences in neuroplasticity that may be associated with previously reported sex-based differences in physiological alterations caused by repetitive succession of hypoxemia-reoxygenation encountered during obstructive sleep apnea (OSA). We examined long-term changes in the activity of brainstem and diencephalic cardiorespiratory neuronal populations induced by chronic intermittent hypoxia (CIH) in male and female mice by analyzing Fosb expression. Whereas the overall baseline and CIH-induced Fosb expression in females was higher than in males, possibly reflecting different neuroplastic dynamics, in contrast, structures responded to CIH by Fosb upregulation in males only. There was a sex-based difference at the level of the rostral ventrolateral reticular nucleus of the medulla, with an increase in the number of FOSB/ΔFOSB-positive cells induced by CIH in males but not females. This structure contains neurons that generate the sympathetic tone and which are involved in CIH-induced sustained hypertension during waking hours. We suggest that the sex-based difference in neuroplasticity of this structure contributes to the reported sex-based difference in CIH-induced hypertension. Moreover, we highlighted a sex-based dimorphic phenomenon in serotoninergic systems induced by CIH, with increased serotoninergic immunoreactivity in the hypoglossal nucleus and a decreased number of serotoninergic cells in the dorsal raphe nucleus in male but not female mice. We suggest that this dimorphism in the neuroplasticity of serotoninergic systems predisposes males to a greater alteration of neuronal control of the upper respiratory tract associated with the greater collapsibility of upper airways described in male OSA subjects.

Divergent Mitochondrial Antioxidant Activities and Lung Alveolar Architecture in the Lungs of Rats and Mice at High Altitude

Compared with mice, adult rats living at 3,600 m above sea level (SL—La Paz, Bolivia) have high hematocrit, signs of pulmonary hypertension, and low lung volume with reduced alveolar surface area. This phenotype is associated with chronic mountain sickness in humans living at high altitude (HA). We tested the hypothesis that this phenotype is associated with impaired gas exchange and oxidative stress in the lungs. We used rats and mice (3 months old) living at HA (La Paz) and SL (Quebec City, Canada) to measure arterial oxygen saturation under graded levels of hypoxia (by pulse oximetry), the alveolar surface area in lung slices and the activity of pro- (NADPH and xanthine oxidases—NOX and XO) and anti- (superoxide dismutase, and glutathione peroxidase—SOD and GPx) oxidant enzymes in cytosolic and mitochondrial lung protein extracts. HA rats have a lower arterial oxygen saturation and reduced alveolar surface area compared to HA mice and SL rats. Enzymatic activities (NOX, XO, SOD, and GPx) in the cytosol were similar between HA and SL animals, but SOD and GPx activities in the mitochondria were 2–3 times higher in HA vs. SL rats, and only marginally higher in HA mice vs. SL mice. Furthermore, the maximum activity of cytochrome oxidase-c (COX) measured in mitochondrial lung extracts was also 2 times higher in HA rats compared with SL rats, while there was only a small increase in HA mice vs. SL mice. Interestingly, compared with SL controls, alterations in lung morphology are not observed for young rats at HA (15 days after birth), and enzymatic activities are only slightly altered. These results suggest that rats living at HA have a gradual reduction of their alveolar surface area beyond the postnatal period. We can speculate that the elevation of SOD, GPx, and COX activities in the lung mitochondria are not sufficient to compensate for oxidative stress, leading to damage of the lung tissue in rats.