Chronological Change of Right Ventricle by Chronic Intermittent Hypoxia in Mice

Augmented O-GlcNAcylation exacerbates right ventricular dysfunction and remodeling via enhancement of hypertrophy, mitophagy, and fibrosis in mice exposed to long-term intermittent hypoxia

Previously, we showed that augmented O-linked N-acetylglucosaminylation (O-GlcNAcylation) mitigates cardiac remodeling in O-GlcNAc transferase-transgenic (Ogt-Tg) mice exposed to acute (2-week) intermittent hypoxia (IH) by suppressing nuclear factor of activated T cells (NFAT) and nuclear factor kappa B (NF-κB) via the O-GlcNAcylation of glycogen synthase kinase 3 beta (GSK-3β) and NF-κB p65. Because this effect is time dependent, we exposed Ogt-Tg mice to IH for 4 weeks (IH4W) in the present study. O-GlcNAcylation was significantly enhanced in Ogt-Tg mice vs. wild-type (WT) mice exposed to normoxia and IH4W. Total O-GlcNAcylation levels were significantly increased in WT and Ogt-Tg mice after IH4W vs. normoxia. After IH4W, Ogt-Tg mice displayed significantly exacerbated signs of cardiac hypertrophy and fibrosis in the right ventricles (RVs) but not the left ventricles (LVs). Echocardiography revealed IH4W-induced right ventricular dysfunction. Phosphorylated GSK-3β levels were increased in Ogt-Tg mice vs. WT mice after IH4W, whereas phosphorylated NF-κB p65 levels were unaffected. Mitophagy, which is associated with cardiac dysfunction, was increased in the RVs of Ogt-Tg mice after IH4W. Furthermore, the levels of phosphorylated dynamin-related protein 1 (p-Drp1) were significantly increased, and the expression of mitofusin-2 (MFN2) was significantly decreased. In human embryonic kidney cells, mitochondrial uncoupler-induced mitochondrial dysfunction was accelerated in Ogt-overexpressing cells. In addition to increasing the levels of phosphorylated Smad2, IH4W promoted cardiac fibrosis in the RVs of Ogt-Tg mice. Thus, augmented O-GlcNAcylation may aggravate IH4W-induced right ventricular dysfunction and remodeling by promoting hypertrophy, mitophagy, and fibrosis via GSK-3β inactivation, an increased p-Drp-1/MFN2 ratio, and Smad2 activation, respectively.

Is obstructive sleep apnea associated with erythrocytosis? A systematic review and meta‐analysis

Objective

The aim of this systematic review and meta‐analysis was to investigate the association between obstructive sleep apnea (OSA) and erythrocytosis.

Methods

The PubMed, Web of Science, and Cochrane Library databases were searched for articles examining hematocrit values in patients with OSA and control individuals published till September 1, 2021. The pooled standardized mean difference (SMD) with 95% confidence interval (CI) was calculated, and subgroup analyses were performed.

Results

Eleven eligible studies with a total of 4608 patients with OSA were included in this meta‐analysis. Pooled outcomes revealed that hematocrit values were significantly higher in patients with OSA than in controls (SMD, 0.19; 95% CI, 0.08–0.29; p < .01). When studies were stratified by disease severity, the significant differences in hematocrit values between patients and controls were only observed in the severe OSA group (SMD, 0.34; 95% CI, 0.08–0.59; p < .01), but not in the mild and moderate OSA groups. In subgroup analyses according to sex and publication year, significant differences in hematocrit values between patients and controls remained stable in studies with only female patients (SMD, 0.25; 95% CI, 0.12–0.38; p < .01) and in studies published after 2012 (SMD, 0.17; 95% CI, 0.06–0.28, p < .01).

Conclusion

Our meta‐analysis revealed that the hematocrit value was significantly increased in patients with OSA, particularly in severe patients, compared with that in controls. However, the elevation was modest, and the hematocrit value is expected to be within the normal range in patients with OSA. These data suggest that OSA leads to slight increases in hematocrit but does not cause clinically significant erythrocytosis.

Serum high-mobility group box 1 protein level correlates with the lowest SaO2 in patients with sleep apnea: a preliminary study

Introduction

Serum level of high-mobility group box 1 protein is reportedly correlated with the severity of obstructive sleep apnea.

Objective

We tried to evaluate the possibility of using the serum high-mobility group box 1 protein level as a biologic marker in obstructive sleep apnea patients.

Methods

We generated a chronic intermittent hypoxia murine model that reflected human obstructive sleep apnea. Obstructive sleep apnea patients who underwent polysomnography were prospectively enrolled. Serum samples were obtained from mice and obstructive sleep apnea patients, and the serum high-mobility group box1 protein level was measured by enzyme-linked immunosorbent assay.

Results

Serum high-mobility group box 1 protein level was 56.16 ± 30.33 ng/mL in chronic intermittent hypoxia and 18.63 ± 6.20 ng/mL in control mice (p < 0.05). The mean apnea-hypopnea index and respiratory disturbance index values of enrolled obstructive sleep apnea patients were 50.35 ± 27.96 and 51.56 ± 28.53, respectively, and the mean serum high-mobility group box 1 protein level was 30.13 ± 19.97 ng/mL. The apnea–hypopnea index and respiratory disturbance index were not significantly correlated with the serum high-mobility group box 1 protein level (p > 0.05). Instead, this protein level was significantly correlated with lowest arterial oxygen concentration (SaO₂) (p < 0.05).

Conclusion

High-mobility group box 1 protein may be involved in the pathogenesis of obstructive sleep apnea, and the possibility of this protein being a useful biologic marker in obstructive sleep apnea should be further evaluated.

Potential Contribution of Carotid Body-Induced Sympathetic and Renin-Angiotensin System Overflow to Pulmonary Hypertension in Intermittent Hypoxia

PURPOSE OF REVIEW

Obstructive sleep apnea (OSA), featured by chronic intermittent hypoxia (CIH), is an independent risk for systemic hypertension (HTN) and is associated with pulmonary hypertension (PH). The precise mechanisms underlying pulmonary vascular remodeling and PH in OSA are not fully understood. However, it has been suggested that lung tissue hypoxia, oxidative stress, and pro-inflammatory mediators following CIH exposure may contribute to PH.

RECENT FINDINGS

New evidences obtained in preclinical OSA models support that an enhanced carotid body (CB) chemosensory reactiveness to oxygen elicits sympathetic and renin-angiotensin system (RAS) overflow, which contributes to HTN. Moreover, the ablation of the CBs abolished the sympathetic hyperactivity and HTN in rodents exposed to CIH. Accordingly, it is plausible that the enhanced CB chemosensory reactivity may contribute to the pulmonary vascular remodeling and PH through the overactivation of the sympathetic-RAS axis. This hypothesis is supported by the facts that (i) CB stimulation increases pulmonary arterial pressure, (ii) denervation of sympathetic fibers in pulmonary arteries reduces pulmonary remodeling and pulmonary arterial hypertension (PAH) in humans, and (iii) administration of angiotensin-converting enzyme (ACE) or blockers of Ang II type 1 receptor (ATR1) ameliorates pulmonary remodeling and PH in animal models. In this review, we will discuss the supporting evidence for a plausible contribution of the CB-induced sympathetic-RAS axis overflow on pulmonary vascular remodeling and PH induced by CIH, the main characteristic of OSA.

Sinomenine Attenuates Chronic Intermittent Hypoxia-Induced Lung Injury by Inhibiting Inflammation and Oxidative Stress

Background

In the present study, we aimed to investigate the effects of sinomenine (SIN) on chronic intermittent hypoxia (CIH)- induced lung injury in rats, and to explore the underlying mechanisms.

Material/Methods

To perform the investigation, a CIH rat model was established. ELISA assay was applied to detect the level of inflammatory cytokines. Oxidative stress bio-markers (MDA, SOD, and CAT) were determined in lung tissues. In addition, the expression level of NADPH oxidase 2 (Nox2) was analyzed by Western blotting and qRT-PCR, respectively.

Results

The results showed that compared with other groups, more obvious pulmonary pathological changes were observed in the CIH group. The level of inflammatory cytokines in the CIH group was markedly higher than that in the control and Con-S groups. Compared with the control and Con-S groups, oxidative stress was notably increased in the CIH group. Expression of Nox2 was also increased in the CIH group. The effects caused by CIH in rats were attenuated by SIN treatment.

Conclusions

SIN can reverse chronic intermittent hypoxia-induced lung injury through inhibiting inflammation and oxidative stress.

Intermittent hypoxia in utero damages postnatal growth and cardiovascular function in rats

Obstructive sleep apnea (OSA) is common in pregnancy and may compromise fetal and even postnatal development. We developed an animal model to determine if maternal OSA could have lasting effects in offspring. Pregnant Sprague-Dawley rats were exposed to reduced ambient O₂ from 21 to 4-5%, approximately once per minute [chronic intermittent hypoxia (CIH)] for 8 h/day during gestation days 3-19. Similarly handled animals exposed to ambient air served as controls (HC). Offspring were studied for body growth and cardiovascular function for 8 postnatal weeks. Compared with HC, prenatal CIH led to growth restriction, indicated by smaller body weight and tibial length, and higher arterial blood pressure in both male and female offspring. Compared with same-sex HC, CIH males showed abdominal obesity (greater ratio of abdominal fat weight to body weight or tibial length), left ventricular (LV) hypertrophy (greater heart weight-to-tibial length ratio and LV posterior wall diastolic thickness), elevated LV contractility (increases in LV ejection fraction, end-systolic pressure-volume relations, and preload recruitable stroke work), elevated LV and arterial stiffness (increased end-diastolic pressure-volume relationship and arterial elasticity), and LV oxidative stress (greater lipid peroxide content). Compared with female CIH offspring, male CIH offspring had more profound changes in blood pressure (BP), cardiac function, myocardial lipid peroxidase (LPO) content, and abdominal adiposity. Rodent prenatal CIH exposure, mimicking human maternal OSA, exerts detrimental morphological and cardiovascular effects on developing offspring; the model may provide useful insights of OSA effects in humans. NEW & NOTEWORTHY Obstructive sleep apnea is common in human pregnancy. Following maternal exposure to chronic intermittent hypoxia, a hallmark of sleep apnea, both sexes of rat offspring showed growth retardation, with males being more vulnerable to hypertension and dysfunctional left ventricular changes. This model is useful to study detrimental effects of maternal obstructive sleep apnea on developing offspring in humans.