Chronic intermittent hypoxia leads to insulin resistance and impaired glucose tolerance through dysregulation of adipokines in non-obese rats

Intermittent hypoxia increases lipid insulin resistance in healthy humans: A randomized crossover trial

Sympathetic overactivity caused by chronic intermittent hypoxia is a hallmark of obstructive sleep apnea. A high sympathetic tone elicits increases in plasma free fatty acid and insulin. Our objective was to assess the impact of 14 nights of chronic intermittent hypoxia exposure on sympathetic activity, glucose control, lipid profile and subcutaneous fat tissue remodelling in non-obese healthy humans. In this prospective, double-blinded crossover study, 12 healthy subjects were randomized, among them only nine underwent the two phases of exposures of 14 nights chronic intermittent hypoxia versus air. Sympathetic activity was measured by peroneal microneurography (muscle sympathetic nerve activity) before and after each exposure. Fasting glucose, insulin, C-peptide and free fatty acid were assessed at rest and during a multisampling oral glucose tolerance test. We assessed histological remodelling, adrenergic receptors, lipolysis and lipogenesis genes expression and functional changes of the adipose tissue. Two weeks of exposure of chronic intermittent hypoxia versus ambient air significantly increased sympathetic activity (p = 0.04). Muscle sympathetic nerve activity increased from 24.5 [18.9; 26.8] before to 21.7 [13.8; 25.7] after ambient air exposure, and from 20.6 [17.4; 23.9] before to 28.0 [24.4; 31.5] bursts per min after exposure to chronic intermittent hypoxia. After chronic intermittent hypoxia, post-oral glucose tolerance test circulating free fatty acid area under the curve increased (p = 0.05) and free fatty acid sensitivity to insulin decreased (p = 0.028). In adipocyte tissue, intermittent hypoxia increased expression of lipolysis genes (adipocyte triglyceride lipase and hormone-sensitive lipase) and lipogenesis genes (fatty acid synthase; p < 0.05). In this unique experimental setting in healthy humans, chronic intermittent hypoxia induced high sympathetic tone, lipolysis and decreased free fatty acid sensitivity to insulin. This might participate in the trajectory to systemic insulin resistance and diabetes for patients with obstructive sleep apnea.

Sulfonylurea Use in Patients with Type 2 Diabetes and COPD: A Nationwide Population-Based Cohort Study

We conducted this study to investigate the long-term outcomes of sulfonylurea (SU) use in patients with chronic obstructive pulmonary disease (COPD) and type 2 diabetes (T2D). We used propensity-score matching to identify 6008 pairs of SU users and nonusers from Taiwan's National Health Insurance Research Database from 1 January 2000 to 31 December 2017. Cox proportional hazard models were used to compare the risks of mortality, cardiovascular events, non-invasive positive pressure ventilation, invasive mechanical ventilation, bacterial pneumonia, lung cancer, and hypoglycemia between SU users and nonusers. In the matched cohorts, the mean follow-up time for SU users and nonusers was 6.57 and 5.48 years, respectively. Compared with nonusers, SU users showed significantly lower risks of mortality [aHR 0.53(0.48-0.58)], cardiovascular events [aHR 0.88(0.81-0.96)], non-invasive positive pressure ventilation [aHR 0.74(0.6-0.92)], invasive mechanical ventilation [aHR 0.57(0.5-0.66)], and bacterial pneumonia [aHR 0.78(0.7-0.87)]. A longer cumulative duration of SU use was associated with a lower risk of these outcomes. This nationwide cohort study demonstrated that SU use was associated with significantly lower risks of cardiovascular events, ventilation use, bacterial pneumonia, and mortality in patients with COPD and T2D. SU may be a suitable option for diabetes management in these patients.

Are levels of adipokines and micronutrients different in male adult smokers and non-smokers? A case-control study

OBJECTIVE

Smoking is a common public problem leading to increases in oxidative stress and decreases in the levels of some micronutrients, finally affecting adipokine levels. The aim of this study was to compare the serum levels of omentin (intelectin-1), chemerin, TNF-α, and some micronutrient intakes in male smokers and non-smokers.

METHODS

40 male smokers and 40 male non-smokers with a mean age of 38.6±14.1 years were included in this study. Serum levels of omentin, chemerin, and TNF-α were measured. To calculate the daily intake of energy, carbohydrate, protein, fat, and some of the micronutrients, the 24-h recall and semi-quantitative food frequency questionnaire (FFQ) was used.

RESULTS

Omentin, chemerin, and TNF-α levels in male smokers were lower than non-smokers, but these differences were not statistically significant. However, after adjustment for total and saturated fat intakes and age, omentin (β=138.4, p=0.027) and TNF-α (β=144.5, p=0.015) revealed significant differences.

CONCLUSION

The serum levels of omentin, chemerin, TNF-α, and some micronutrient intakes were not significantly different between smokers and non-smokers. Further population studies are needed to clarify this subject.

LRP1 loss in airway epithelium exacerbates smoke-induced oxidative damage and airway remodeling

The LDL receptor-related protein 1 (LRP1) partakes in metabolic and signaling events regulated in a tissue-specific manner. The function of LRP1 in airways has not been studied. We aimed to study the function of LRP1 in smoke-induced disease. We found that bronchial epithelium of patients with chronic obstructive pulmonary disease and airway epithelium of mice exposed to smoke had increased LRP1 expression. We then knocked out LRP1 in human bronchial epithelial cells in vitro and in airway epithelial club cells in mice. In vitro, LRP1 knockdown decreased cell migration and increased transforming growth factor β activation. Tamoxifen-inducible airway-specific LRP1 knockout mice (club Lrp1-/-) induced after complete lung development had increased inflammation in the bronchoalveolar space and lung parenchyma at baseline. After 6 months of smoke exposure, club Lrp1-/- mice showed a combined restrictive and obstructive phenotype, with lower compliance, inspiratory capacity, and forced expiratory volume0.05/forced vital capacity than WT smoke-exposed mice. This was associated with increased values of Ashcroft fibrotic index. Proteomic analysis of room air exposed-club Lrp1-/- mice showed significantly decreased levels of proteins involved in cytoskeleton signaling and xenobiotic detoxification as well as decreased levels of glutathione. The proteome fingerprint created by smoke eclipsed many of the original differences, but club Lrp1-/- mice continued to have decreased lung glutathione levels and increased protein oxidative damage and airway cell proliferation. Therefore, LRP1 deficiency leads to greater lung inflammation and damage and exacerbates smoke-induced lung disease.

Potential Mechanisms Underlying Hypoxia-Induced Diabetes in a Rodent Model: Implications for COVID-19

Previous studies reported that repetitive hypoxia in rat pups reduces insulin secretion and elevates fasting blood glucose levels; these sequelae persisted for several months. This report describes how episodic hypoxic events elevate a chloride ion exporter, K⁺-Cl⁻ cotransporter-2 (KCC2), in the plasma membrane of insulin-secreting pancreatic β-cells. We assume that acute diabetic symptoms observed in rat pups with periodic oxygen desaturation could result from a lack of blood insulin levels due to disturbed β-cell function. This acute hypo-insulinemia may result from a disruption in chloride balance in β-cells arising from an imbalanced KCC2-NKCC1 (chloride exporter-importer) density as a consequence of periodic oxygen desaturation. Mechanistically, we postulate that a reduced insulin secretion due to the KCC2-NKCC1 imbalance subsequent to acute oxygen desaturation could result in hyperglycemia in rat pups, paralleling symptoms shown in patients with COVID-19 who experienced acute respiratory distress.

A rapid juvenile murine model of nonalcoholic steatohepatitis (NASH): Chronic intermittent hypoxia exacerbates Western diet-induced NASH

AIMS

Many dietary NASH models require a long duration to establish (4-6 months). Chronic intermittent hypoxia (CIH), a cardinal hallmark of obstructive sleep apnea (OSA), may accelerate the progression of pediatric nonalcoholic fatty liver disease (NAFLD). However, diet-induced obese (DIO) mice exposed to CIH have not been perceived as a fast or reliable tool in NASH research. This study was designed to establish a rapid juvenile murine NASH model, and determine whether the combination of CIH and a western-style diet (hypercaloric fatty diet plus high fructose) can fully display key pathologic features of NASH.

METHODS

C57BL/6 N mice (3 weeks old) fed a control diet or western diet (WD) were exposed to CIH (9% nadir of inspired oxygen levels) or room air for 6 and 12 weeks.

KEY FINDINGS

The Control/CIH group mainly exhibited hyperinsulinemia and insulin resistance (IR). In contrast, mice fed a WD developed weight gain after 3 weeks, microvesicular steatosis in 6 weeks, and indices of metabolic disorders at 12 weeks. Furthermore, CIH exposure accelerated WD- induced macromicrovesicular steatosis (liver triglycerides and de novo lipogenesis), liver injury (ballooned hepatocytes and liver enzymes), lobular/portal inflammation (inflammatory cytokines and macrophage recruitment), and fibrogenesis (hydroxyproline content and TGF-β protein). Notably, only the WD/CIH group exhibited elevated hepatic MDA content, protein levels of NOX4, α-SMA and collagen I, as well as reduced Nrf2 and HO-1 protein expression.

SIGNIFICANCE

WD/CIH treatment rapidly mimics the histological characteristics of pediatric NASH with metabolic dysfunction and fibrosis, representing an appropriate experimental model for NASH research.

Pentobarbital Anesthesia Suppresses the Glucose Response to Acute Intermittent Hypoxia in Rat

A key feature of sleep disordered breathing syndromes, such as obstructive sleep apnea is intermittent hypoxia. Intermittent hypoxia is well accepted to drive the sympathoexcitation that is frequently associated with hypertension and diabetes, with measurable effects after just 1 h. The aim of this study was to directly measure the glucose response to 1 h of acute intermittent hypoxia in pentobarbital anesthetized rats, compared to conscious rats. However, we found that while a glucose response is measurable in conscious rats exposed to intermittent hypoxia, it is suppressed in anesthetized rats. Intermittent hypoxia for 1, 2, or 8 h increased blood glucose by 0.7 ± 0.1 mmol/L in conscious rats but had no effect in anesthetized rats (-0.1 ± 0.2 mmol/L). These results were independent of the frequency of the hypoxia challenges, fasting state, vagotomy, or paralytic agents. A supraphysiological challenge of 3 min of hypoxia was able to induce a glycemic response indicating that the reflex response is not abolished under pentobarbital anesthesia. We conclude that pentobarbital anesthesia is unsuitable for investigations into glycemic response pathways in response to intermittent hypoxia in rats.

NLRP3 Deficiency Protects Against Intermittent Hypoxia-Induced Neuroinflammation and Mitochondrial ROS by Promoting the PINK1-Parkin Pathway of Mitophagy in a Murine Model of Sleep Apnea

Obstructive sleep apnea (OSA) associated neurocognitive impairment is mainly caused by chronic intermittent hypoxia (CIH)-triggered neuroinflammation and oxidative stress. Previous study has demonstrated that mitochondrial reactive oxygen species (mtROS) was pivotal for hypoxia-related tissue injury. As a cytosolic multiprotein complex that participates in various inflammatory and neurodegenerative diseases, NLRP3 inflammasome could be activated by mtROS and thereby affected by the mitochondria-selective autophagy. However, the role of NLRP3 and possible mitophagy mechanism in CIH-elicited neuroinflammation remain to be elucidated. Compared with wild-type mice, NLRP3 deficiency protected them from CIH-induced neuronal damage, as indicated by the restoration of fear-conditioning test results and amelioration of neuron apoptosis. In addition, NLRP3 knockout mice displayed the mitigated microglia activation that elicited by CIH, concomitantly with elimination of damaged mitochondria and reduction of oxidative stress levels (malondialdehyde and superoxide dismutase). Elevated LC3 and beclin1 expressions were remarkably observed in CIH group. In vitro experiments, intermittent hypoxia (IH) significantly facilitated mitophagy induction and NLRP3 inflammasome activation in microglial (BV2) cells. Moreover, IH enhanced the accumulation of damaged mitochondria, increased mitochondrial depolarization and augmented mtROS release. Consistently, NLRP3 deletion elicited a protective phenotype against IH through enhancement of Parkin-mediated mitophagy. Furthermore, Parkin deletion or pretreated with 3MA (autophagy inhibitor) exacerbated these detrimental actions of IH, which was accompanied with NLRP3 inflammasome activation. These results revealed NLRP3 deficiency acted as a protective promotor through enhancing Parkin-depended mitophagy in CIH-induced neuroinflammation. Thus, NLRP3 gene knockout or pharmacological blockage could be as a potential therapeutic strategy for OSA-associated neurocognitive impairment.

Use of antidiabetic medications and risk of chronic obstructive pulmonary disease exacerbation requiring hospitalization: a disease risk score-matched nested case-control study

BACKGROUND

Exacerbation of chronic obstructive pulmonary disease (COPD) severely impacts the quality of life and causes high mortality and morbidity. COPD is involved with systemic and pulmonary inflammation, which may be attenuated with antidiabetic agents exerting anti-inflammatory effects. Real-world evidence is scant regarding the effects of antidiabetic agents on COPD exacerbation. Accordingly, we conducted a disease risk score (DRS)-matched nested case-control study to systemically assess the association between each class of oral hypoglycemic agents (OHAs) and risk of severe COPD exacerbation in a nationwide COPD population co-diagnosed with diabetes mellitus (DM).

METHODS

We enrolled 23,875 COPD patients receiving at least one OHA for management of DM by analyzing the Taiwan National Health Insurance claims database between January 1, 2000, and December 31, 2015. Cases of severe exacerbation were defined as those who had the first hospital admission for COPD. Each case was individually matched with four randomly-selected controls by cohort entry date, DRS (the estimated probability of encountering a severe COPD exacerbation), and COPD medication regimens using the incidence density sampling approach. Conditional logistic regressions were performed to estimate odds ratios (OR) of severe COPD exacerbation for each type of OHAs.

RESULTS

We analyzed 2700 cases of severe COPD exacerbation and 9272 corresponding controls after DRS matching. Current use of metformin versus other OHAs was associated with a 15% (adjusted OR [aOR], 0.85; 95% confidence interval [CI] 0.75-0.95) reduced risk of severe COPD exacerbation, whereas the reduced risk was not observed with other types of antidiabetic agents. When considering the duration of antidiabetic medication therapy, current use of metformin for 91-180 and 181-365 days was associated with a 28% (aOR, 0.72; 95% CI 0.58-0.89) and 37% (aOR, 0.63; 95% CI 0.51-0.77) reduced risk of severe COPD exacerbation, respectively. Similarly, 91-180 days of sulfonylureas therapy led to a 28% (aOR, 0.72; 95% CI 0.58-0.90) lower risk, and longer treatments consistently yielded 24-30% lower risks. Current use of thiazolidinediones for more than 181 days yielded an approximately 40% decreased risk.

CONCLUSIONS

Duration-dependent beneficial effects of current metformin, sulfonylurea, and thiazolidinedione use on severe COPD exacerbation were observed in patients with COPD and DM.

The Association of Sleep Disorders, Obesity and Sleep-Related Hypoxia with Cancer

BACKGROUND

Sleep disorders have emerged as potential cancer risk factors.

OBJECTIVE

This review discusses the relationships between sleep, obesity, and breathing disorders with concomitant risks of developing cancer.

RESULTS

Sleep disorders result in abnormal expression of clock genes, decreased immunity, and melatonin release disruption. Therefore, these disorders may contribute to cancer development. Moreover, in sleep breathing disorder, which is frequently experienced by obese persons, the sufferer experiences intermittent hypoxia that may stimulate cancer cell proliferation.

DISCUSSION

During short- or long- duration sleep, sleep-wake rhythm disruption may occur. Insomnia and obstructive sleep apnea increase cancer risks. In short sleepers, an increased risk of stomach cancer, esophageal squamous cell cancer, and breast cancer was observed. Among long sleepers (>9 hours), the risk of some hematologic malignancies is elevated.

CONCLUSION

Several factors including insomnia, circadian disruption, obesity, and intermittent hypoxia in obstructive sleep apnea are contributing risk factors for increased risk of several types of cancers. However, further studies are needed to determine the more significant of these risk factors and their interactions.

Effects of different obesity-related adipokines on the occurrence of obstructive sleep apnea

Obstructive sleep apnea (OSA), characterized by recurrent episodes of apnea during sleep and daytime sleepiness, seriously affects human health and may lead to systemic organ dysfunction. The pathogenesis of OSA is complex and still uncertain, but multiple surveys have shown that obesity is an important factor, and the incidence of OSA in people with obesity is as high as 30%. Adipokines are a group of proteins secreted from adipocytes, which are dysregulated in obesity and may contribute to OSA. Here, we review the most important and representative research results regarding the correlation between obesity-related adipokines including leptin, adiponectin, omentin-1, chemerin, and resistin and OSA in the past 5 years, provide an overview of these key adipokines, and analyze possible intrinsic mechanisms and influencing factors. The existing research shows that OSA is associated with an increase in the serum levels of leptin, chemerin, and resistin and a decrease in the levels of adiponectin and omentin-1; the findings presented here can be used to monitor the development of OSA and obesity, prevent future comorbidities, and identify risk factors for cardiovascular and other diseases, while different adipokines can be linked to OSA through different pathways such as insulin resistance, intermittent hypoxia, and inflammation, among others. We hope our review leads to a deeper and more comprehensive understanding of OSA based on the relevant literature, which will also provide directions for future clinical research.

Effects of CPAP therapy on subcutaneous adipose tissue in patients with obstructive sleep apnea: a meta-analysis

PURPOSE

Continuous positive airway pressure (CPAP) is an effective treatment for obstructive sleep apnea (OSA). However, studies provide conflicting results on the effects of CPAP on subcutaneous adipose tissue (SAT) in patients with OSA. We therefore performed a meta-analysis to evaluate whether or not CPAP has an effect on SAT in patients with OSA.

METHODS

Studies were retrieved by searching the Cochrane Library, Web of Science, Embase, and Pubmed. Information on study and patient characteristics, study design, and SAT pre- and post-CPAP treatment was extracted for analysis. Different methods for measurement of SAT were also notated. Standardized mean difference (SMD) and 95% confidence interval (CI) were measured to estimate the change in SAT before and after CPAP treatment. Meta-analysis was performed using the RevMan v.5.3 and Stata 14.0.

RESULTS

A total of 10 studies met inclusion criteria encompassing 309 patients in the final analysis. The pooled estimate showed that CPAP treatment resulted in no significant change in SAT (SMD = - 0.014, 95% CI = - 0.161 to 0.133, p = 0.896). Meta-regression analyses revealed no predictor, including methods of measuring SAT, that influenced the CPAP effect on SAT.

CONCLUSION

Our meta-analysis demonstrated that after CPAP therapy, there was no significant change in SAT in patients with OSA.

Cancer cachexia has many symptoms but only one cause: anoxia

During nearly 100 years of research on cancer cachexia (CC), science has been reciting the same mantra: it is a multifactorial syndrome. The aim of this paper is to show that the symptoms are many, but they have a single cause: anoxia. CC is a complex and devastating condition that affects a high proportion of advanced cancer patients. Unfortunately, it cannot be reversed by traditional nutritional support and it generally reduces survival time. It is characterized by significant weight loss, mainly from fat deposits and skeletal muscles. The occurrence of cachexia in cancer patients is usually a late phenomenon. The conundrum is why do similar patients with similar tumors, develop cachexia and others do not? Even if cachexia is mainly a metabolic dysfunction, there are other issues involved such as the activation of inflammatory responses and crosstalk between different cell types.  The exact mechanism leading to a wasting syndrome is not known, however there are some factors that are surely involved, such as anorexia with lower calorie intake, increased glycolytic flux, gluconeogenesis, increased lipolysis and severe tumor hypoxia. Based on this incomplete knowledge we put together a scheme explaining the molecular mechanisms behind cancer cachexia, and surprisingly, there is one cause that explains all of its characteristics: anoxia.  With this different view of CC we propose a treatment based on the physiopathology that leads from anoxia to the symptoms of CC.  The fundamentals of this hypothesis are based on the idea that CC is the result of anoxia causing intracellular lactic acidosis. This is a dangerous situation for cell survival which can be solved by activating energy consuming gluconeogenesis. The process is conducted by the hypoxia inducible factor-1α. This hypothesis was built by putting together pieces of evidence produced by authors working on related topics.

SOD2 ameliorates pulmonary hypertension in a murine model of sleep apnea via suppressing expression of NLRP3 in CD11b+ cells

Background

High prevalence of obstructive sleep apnea (OSA) in the pulmonary hypertension (PH) population suggests that chronic intermittent hypoxia (CIH) is an important pathogenic factor of PH. However, the exact mechanism of CIH induced PH is not clear. One of the molecules that plays a key role in regulating pulmonary artery function under hypoxic conditions is superoxide dismutase 2 (SOD₂).

Methods

Our study utilized heterozygous SOD₂^−/+ mice firstly in CIH model to explore the exact role of SOD₂ in CIH causing PH. Expression of SOD2 was analyzed in CIH model. Echocardiography and pulmonary hypertension were measured in wild type (WT) and SOD2^−/+ mice under normal air or CIH condition. Hematoxylin–Eosin (H&E) staining and masson staining were carried out to evaluate pulmonary vascular muscularization and remodeling. Micro-PET scanning of in vivo ^99mTc-labelled- MAG3-anti-CD11b was applied to assess CD11b in quantification and localization. Level of nod-like receptor pyrin domain containing 3 (NLRP3) was analyzed by real time PCR and immunohistochemistry (IHC).

Results

Results showed that SOD₂ was down-regulated in OSA/CIH model. Deficiency of SOD2 aggravated CIH induced pulmonary hypertension and pulmonary vascular hypertrophy. CD11b⁺ cells, especially monocytic myeloid cell line-Ly6C⁺Ly6G⁻ cells, were increased in the lung, bone marrow and the blood under CIH condition, and down-regulated SOD2 activated NLRP3 in CD11b⁺ cells. SOD₂-deficient-CD11b⁺ myeloid cells promoted the apoptosis resistance and over-proliferation of human pulmonary artery smooth muscle cells (PASMCs) via up-regulating NLRP3.

Conclusion

CIH induced down-regulating of SOD2 increased pulmonary hypertension and vascular muscularization. It could be one of the mechanism of CIH leading to PH.

Epidemiological and pathophysiological evidence supporting links between obstructive sleep apnoea and Type 2 diabetes mellitus

Obstructive sleep apnoea (OSA) and Type 2 diabetes mellitus (T2DM) are common diseases. The global prevalence of OSA is between 2% and 7% in general population cohorts. The worldwide prevalence of T2DM among adults (aged 20-79 years) was estimated to be 6.4%. The concurrent presence of OSA and T2DM can be expected in the same patient, given their high prevalence and similar predisposition. We reviewed the overlapping pathophysiology of OSA and T2DM in this article.

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.

2-Methoxyestradiol attenuates chronic-intermittent-hypoxia-induced pulmonary hypertension through regulating microRNA-223

Pulmonary hypertension (PH) is prevalent in patients with obstructive sleep apnea (OSA) syndrome, and coexistence of PH and OSA indicates a worse prognosis and higher mortality. Chronic intermittent hypoxia (CIH) is the key pathogenesis of OSA. Also, microRNA-223 (miR-223) plays a role in the regulation of CIH-induced PH process. However, the detailed mechanism of CIH inducing PH is still unclear. This study aimed to investigate the pathological process of CIH associated PH and explore the potential therapeutic methods. In this study, adult Sprague-Dawley rats were exposed to CIH or normoxic (N) conditions with 2-methoxyestradiol (2-Me) or vehicle treatment for 6 weeks. The results showed that 2-Me treatment reduced the progression of pulmonary angiogenesis in CIH rats, and alleviated proliferation, cellular migration, and reactive oxygen species formation was induced by CIH in pulmonary artery smooth muscle cells (PASMCs). CIH decreased the expression of miR-223, whereas 2-Me reversed the downregulation of miR-223 both in vivo and in vitro. Furthermore, the antiangiogenic effect of 2-Me observed in PASMCs was abrogated by miR-223 inhibitor, while enhanced by miR-223 mimic. These findings suggested that miR-223 played an important role in the process of CIH inducing PH, and 2-Me might reverse CIH-induced PH via upregulating miR-223.

Leptin and Leptin Resistance in the Pathogenesis of Obstructive Sleep Apnea: A Possible Link to Oxidative Stress and Cardiovascular Complications

Obesity-related sleep breathing disorders such as obstructive sleep apnea (OSA) and obesity hypoventilation syndrome (OHS) cause intermittent hypoxia (IH) during sleep, a powerful trigger of oxidative stress. Obesity also leads to dramatic increases in circulating levels of leptin, a hormone produced in adipose tissue. Leptin acts in the hypothalamus to suppress food intake and increase metabolic rate. However, obese individuals are resistant to metabolic effects of leptin. Leptin also activates the sympathetic nervous system without any evidence of resistance, possibly because these effects occur peripherally without a need to penetrate the blood-brain barrier. IH is a potent stimulator of leptin expression and release from adipose tissue. Hyperleptinemia and leptin resistance may upregulate generation of reactive oxygen species, increasing oxidative stress and promoting inflammation. The current review summarizes recent data on a possible link between leptin and oxidative stress in the pathogenesis of sleep breathing disorders.

Acute sleep fragmentation does not alter pro-inflammatory cytokine gene expression in brain or peripheral tissues of leptin-deficient mice

Obesity and sleep fragmentation (SF) are often co-occurring pro-inflammatory conditions in patients with obstructive sleep apnea. Leptin is a peptide hormone produced by adipocytes that has anorexigenic effects upon appetite while regulating immunity. The role of leptin in mediating inflammatory responses to SF is incompletely understood. Male C57BL/6j (lean) and ob/ob mice (leptin-deficient mice exhibiting obese phenotype) were subjected to SF or control conditions for 24 h using an automated SF chamber. Trunk blood and tissue samples from the periphery (liver, spleen, fat, and heart) and brain (hypothalamus, prefrontal cortex, and hippocampus) were collected. Quantitative PCR was used to determine relative cytokine gene expression of pro-inflammatory (IL-1β, TNF-α) and anti-inflammatory (TGF-β1) cytokines. Enzyme-linked immunosorbent assay (ELISA) was used to determine serum corticosterone concentration. Ob/ob mice exhibited elevated cytokine gene expression in liver (TNF-α, TGF-β1), heart (TGF-β1), fat (TNF-α), and brain (hippocampus, hypothalamus, prefrontal cortex: IL-1β, TNF-α) compared with wild-type mice. Conversely, leptin deficiency decreased pro-inflammatory cytokine gene expression in heart (IL-1β, TNF-α). SF significantly increased IL-1β and TNF-α gene expression in fat and TGF-β1 expression in spleen relative to controls, but only in wild-type mice. SF increased basal serum corticosterone regardless of genotype. Taken together, these findings suggest that leptin deficiency affects cytokine gene expression differently in the brain compared to peripheral tissues with minimal interaction from acute SF.

[One-hour post-load plasma glucose: a better indicator of glucose metabolism for obstructive sleep apnea?]

OBJECTIVE

To assess the value of blood glucose at different time points in oral glucose tolerance test (OGTT), particularly one?hour post load plasma glucose (1 hPG), in evaluating glucose metabolism in adult patients with obstructive sleep apnea (OSA).

METHODS

Eighty nine adultswith newly diagnosed OSA were analyzed retrospectively for sleep architecture assessed using polysomnography and glucose metabolism assessed by OGTT at different time points (0, 30, 60, 120, and 180 min). Pearson's correlatives and multiple linear regression models were established to investigate the correlations between glucose metabolism and other indices including sleep architecture, apnea hypopnea index (AHI), mean and lowest oxygen saturation (MSO₂ and LSO₂) and obesity measurements.

RESULTS

The majority (67.4%) of the patients had abnormal 1 hPG, and 41.6% had abnormal 2 hPG. 1 hPG was positively correlated with neck circumference (r=0.245), abdomen circumference (r=0.231), systolic blood pressure (r=0.213), diastolic blood pressure (r=0.276) and AHI (r=0.324), and was negatively associated with MSO₂ (r=-0.341) and LSO₂ (r=-0.387) (all P<0.05). After controlling for age, BMI, neck and abdomen circumferences, 1 hPG was found to inversely correlated with MSO₂ (r=-0.253, P=0.032) and LSO₂ (r=-0.311, P=0.008). In non-obese OSA subgroup, 1 hPG was significantly associated with OSA-related indices, and regression models showed that LSO₂ and N2 were the two most important contributors to 1 hPG (adjusted R²=0.349, P<0.001); plasma glucose at other time points did not show such correlations.

CONCLUSIONS

1 hPG abnormality occurs earlier than 2 hPG in OSA patients. 1 hPG is significantly associated with OSA independent of obesity and may serve as a better index for measuring OSA-related glucose disorder.

Visceral White Adipose Tissue after Chronic Intermittent and Sustained Hypoxia in Mice

Angiogenesis, a process induced by hypoxia in visceral white adipose tissues (vWAT) in the context of obesity, mediates obesity-induced metabolic dysfunction and insulin resistance. Chronic intermittent hypoxia (IH) and sustained hypoxia (SH) induce body weight reductions and insulin resistance of different magnitudes, suggesting different hypoxia inducible factor (HIF)-1α-related activity. Eight-week-old male C57BL/6J mice (n = 10-12/group) were exposed to either IH, SH, or room air (RA). vWAT were analyzed for insulin sensitivity (phosphorylated (pAKT)/AKT), HIF-1α transcription using chromatin immunoprecipitation (ChIP)-sequencing, angiogenesis using immunohistochemistry, and gene expression of different fat cell markers and HIF-1α gene targets using quantitative polymerase chain reaction or microarrays. Body and vWAT weights were reduced in hypoxia (SH > IH > RA; P < 0.001), with vWAT in IH manifesting vascular rarefaction and increased proinflammatory macrophages. HIF-1α ChIP-sequencing showed markedly increased binding sites in SH-exposed vWAT both at 6 hours and at 6 weeks compared with IH, the latter also showing decreased vascular endothelial growth factor, endothelial nitric oxide synthase, P2RX5, and PAT2 expression, and insulin resistance (IH > > > SH = RA; P < 0.001). IH induces preferential whitening of vWAT, as opposed to prominent browning in SH. Unlike SH, IH elicits early HIF-1α activity that is unsustained over time and is accompanied by concurrent vascular rarefaction, inflammation, and insulin resistance. Thus, the dichotomous changes in HIF-1α transcriptional activity and brown/beige/white fat balance in IH and SH should enable exploration of mechanisms by which altered sympathetic outflow, such as that which occurs in apneic patients, results in whitening, rather than the anticipated browning of adipose tissues that occurs in SH.

Soluble Receptor for Advanced Glycation End Product Ameliorates Chronic Intermittent Hypoxia Induced Renal Injury, Inflammation, and Apoptosis via P38/JNK Signaling Pathways

Obstructive sleep apnea (OSA) associated chronic kidney disease is mainly caused by chronic intermittent hypoxia (CIH) triggered tissue damage. Receptor for advanced glycation end product (RAGE) and its ligand high mobility group box 1 (HMGB1) are expressed on renal cells and mediate inflammatory responses in OSA-related diseases. To determine their roles in CIH-induced renal injury, soluble RAGE (sRAGE), the RAGE neutralizing antibody, was intravenously administered in a CIH model. We also evaluated the effect of sRAGE on inflammation and apoptosis. Rats were divided into four groups: (1) normal air (NA), (2) CIH, (3) CIH+sRAGE, and (4) NA+sRAGE. Our results showed that CIH accelerated renal histological injury and upregulated RAGE-HMGB1 levels involving inflammatory (NF-κB, TNF-α, and IL-6), apoptotic (Bcl-2/Bax), and mitogen-activated protein kinases (phosphorylation of P38, ERK, and JNK) signal transduction pathways, which were abolished by sRAGE but p-ERK. Furthermore, sRAGE ameliorated renal dysfunction by attenuating tubular endothelial apoptosis determined by immunofluorescence staining of CD31 and TUNEL. These findings suggested that RAGE-HMGB1 activated chronic inflammatory transduction cascades that contributed to the pathogenesis of the CIH-induced renal injury. Inhibition of RAGE ligand interaction by sRAGE provided a therapeutic potential for CIH-induced renal injury, inflammation, and apoptosis through P38 and JNK pathways.

Early improvement in obstructive sleep apnea and increase in orexin levels after bariatric surgery in adolescents and young adults

BACKGROUND

Obstructive sleep apnea (OSA) associated with obesity is known to improve after bariatric surgery, but little is known about early changes in this condition after surgery.

OBJECTIVES

To study the clinical course of OSA after bariatric surgery SETTING: Children's hospital in the United States METHODS: Adolescents and young adults with obstructive sleep apnea undergoing vertical sleeve gastrectomy (n = 6) or gastric bypass (n = 1) were enrolled in this prospective study. Participants underwent formal polysomnography before and at 3 and 5 weeks after bariatric surgery. Anthropometric measurements and assay for orexin and leptin were also performed at study visits. Thirty-one adolescents who underwent 2 polysomnography studies that were 4 weeks apart served as control patients.

RESULTS

Baseline mean (range) age of participants was 17.8 (15.4-20.7) years, 71% were male, with body mass index of 55.2 (41.3-61.6) kg/m² and had a median apnea hypopnea index (AHI) of 15.8 (7.1-23.8) events/hour. Differences in least-square means from longitudinal analysis did not show significant differences in AHI in the control group but showed significant postoperative decline in AHI relative to baseline. AHI declined postoperatively from baseline by 9.2 events/hour (95% confidence interval: 3.8 to 14.5) at 3 weeks (P = .002) and 9.1 events/hour (95% confidence interval: 3.8 to 14.5) at 5 weeks (P = .002); there was no significant change from 3 to 5 weeks in AHI. Leptin decreased and orexin levels increased significantly by 3 weeks postoperatively.

CONCLUSIONS

These observations suggest that OSA responds early and out of proportion to weight loss after metabolic and or bariatric surgery, thus weight independent factors may at least in part be responsible for early improvement in OSA postoperatively.

Sleep Apnea in Type 2 Diabetes

IN BRIEF Obstructive sleep apnea (OSA) alters glucose metabolism, promotes insulin resistance, and is associated with development of type 2 diabetes. Obesity is a key moderator of the effect of OSA on type 2 diabetes. However, chronic exposure to intermittent hypoxia and other pathophysiological effects of OSA affect glucose metabolism directly, and treatment of OSA can improve glucose homeostasis.

Endothelin regulates intermittent hypoxia-induced lipolytic remodelling of adipose tissue and phosphorylation of hormone-sensitive lipase

Obstructive sleep apnoea syndrome is characterized by repetitive episodes of upper airway collapse during sleep resulting in chronic intermittent hypoxia (IH). Obstructive sleep apnoea syndrome, through IH, promotes cardiovascular and metabolic disorders. Endothelin-1 (ET-1) secretion is upregulated by IH, and is able to modulate adipocyte metabolism. Therefore, the present study aimed to characterize the role of ET-1 in the metabolic consequences of IH on adipose tissue in vivo and in vitro. Wistar rats were submitted to 14 days of IH-cycles (30 s of 21% FiO2 and 30 s of 5% FiO2 ; 8 h day(-1) ) or normoxia (air-air cycles) and were treated or not with bosentan, a dual type A and B endothelin receptor (ETA-R and ETB-R) antagonist. Bosentan treatment decreased plasma free fatty acid and triglyceride levels, and inhibited IH-induced lipolysis in adipose tissue. Moreover, IH induced a 2-fold increase in ET-1 transcription and ETA-R expression in adipose tissue that was reversed by bosentan. In 3T3-L1 adipocytes, ET-1 upregulated its own and its ETA-R transcription and this effect was abolished by bosentan. Moreover, ET-1 induced glycerol release and inhibited insulin-induced glucose uptake. Bosentan and BQ123 inhibited these effects. Bosentan also reversed the ET-1-induced phosphorylation of hormone-sensitive lipase (HSL) on Ser(660) . Finally, ET-1-induced lipolysis and HSL phosphorylation were also observed under hypoxia. Altogether, these data suggest that ET-1 is involved in IH-induced lipolysis in Wistar rats, and that upregulation of ET-1 production and ETA-R expression by ET-1 itself under IH could amplify its effects. Moreover, ET-1-induced lipolysis could be mediated through ETA-R and activation of HSL by Ser(660) phosphorylation.

Circulating Endocannabinoids and Insulin Resistance in Patients with Obstructive Sleep Apnea

Objectives. The purpose of this study is to investigate the relationship between plasma endocannabinoids and insulin resistance (IR) in patients with obstructive sleep apnea (OSA). Methods. A population of 64 with OSA and 24 control subjects was recruited. Body mass index (BMI), waist circumference, lipids, blood glucose and insulin, homeostasis model of assessment for insulin resistance index (HOMA-IR), anandamide (AEA), 1/2-arachidonoylglycerol (1/2-AG), and apnea-hypopnea index (AHI) were analyzed. Results. Fasting blood insulin (22.9 ± 7.8 mIU/L versus 18.5 ± 7.2 mIU/L, P < 0.05), HOMA-IR (2.9 ± 1.0 versus 2.4 ± 0.9, P < 0.01), AEA (3.2 ± 0.7 nmol/L versus 2.5 ± 0.6 nmol/L, P < 0.01), and 1/2-AG (40.8 ± 5.7 nmol/L versus 34.3 ± 7.7 nmol/L, P < 0.01) were higher in OSA group than those in control group. In OSA group, AEA, 1/2-AG, and HOMA-IR increase with the OSA severity. The correlation analysis showed significant positive correlation between HOMA-IR and AHI (r = 0.44, P < 0.01), AEA and AHI (r = 0.52, P < 0.01), AEA and HOMA-IR (r = 0.62, P < 0.01), and 1/2-AG and HOMA-IR (r = 0.33, P < 0.01). Further analysis showed that only AEA was significantly correlated with AHI and HOMA-IR after adjusting for confounding factors. Conclusions. The present study indicated that plasma endocannabinoids levels, especially AEA, were associated with IR and AHI in patients with OSA.

Effect of Intermittent Hypoxia and Rimonabant on Glucose Metabolism in Rats: Involvement of Expression of GLUT4 in Skeletal Muscle

Background

Obstructive sleep apnea (OSA) and its main feature, chronic intermittent hypoxia (IH) during sleep, is closely associated with insulin resistance (IR) and diabetes. Rimonabant can regulate glucose metabolism and improve IR. The present study aimed to assess the effect of IH and rimonabant on glucose metabolism and insulin sensitivity, and to explore the possible mechanisms.

Material/Methods

Thirty-two rats were randomly assigned into 4 groups: Control group, subjected to intermittent air only; IH group, subjected to IH only; IH+NS group, subjected to IH and treated with normal saline; and IH+Rim group, subjected to IH and treated with 10 mg/kg/day of rimonabant. All rats were killed after 28 days of exposure. Then, the blood and skeletal muscle were collected. We measured fasting blood glucose levels, fasting blood insulin levels, and the expression of glucose transporter 4 (GLUT4) in both mRNA and protein levels in skeletal muscle.

Results

IH can slow weight gain, increase serum insulin level, and reduce insulin sensitivity in rats. The expressions of GLUT4 mRNA, total GLUT4, and plasma membrane protein of GLUT4 (PM GLUT4) in skeletal muscle were decreased. Rimonabant treatment was demonstrated to improve weight gain and insulin sensitivity of the rats induced by IH. Rimonabant significantly upregulated the expression of GLUT4 mRNA, PM GLUT4, and total GLUT4 in skeletal muscle.

Conclusions

The present study demonstrates that IH can cause IR and reduced expression of GLUT4 in both mRNA and protein levels in skeletal muscle of rats. Rimonabant treatment can improve IH – induced IR, and the upregulation of GLUT4 expression may be involved in this process.