Chronic intermittent hypoxia causes hepatitis in a mouse model of diet-induced fatty liver

Association between sleep apnea and ultrasound-defined liver fibrosis: Results from NHANES 2017 to 2020

Liver fibrosis is a critical factor in the advancement of nonalcoholic fatty liver disease towards cirrhosis. There is limited research exploring the association between obstructive sleep apnea (OSA) and liver fibrosis among community populations. The present study aimed to assess the association between sleep apnea (SA) and liver fibrosis based on the National Health and Nutrition Examination Survey (NHANES). Data were acquired from NHANES survey cycle 2017 to 2020. We assessed liver fibrosis by the median values of liver stiffness measurement (LSM). The diagnosis of SA was based on participants' response to sleep questionnaire. Univariate and multivariate logistic regression were used to validate the association of SA and liver fibrosis. A total of 7615 participants were included in this study. The LSM level of SA group was significantly higher than non-SA group. The proportion of liver fibrosis in SA group was markedly higher than that in non-SA group (14.0% vs 7.3%, P < .001). Univariate logistic analysis showed that SA was positively associated with liver fibrosis (OR = 2.068, 95%CI = 1.715-2.494, P < .001). Further multivariate logistic analysis revealed that SA was independently associated with increased risk of liver fibrosis after adjusting for confounding factors (OR = 1.277, 95%CI = 1.003-1.625, P = .048). The current study demonstrated an independent association between self-reported SA and increased risk of ultrasound-defined liver fibrosis in community-based sample.

Non-alcoholic fatty liver disease and sleep disorders

Studies have shown that non-alcoholic fatty liver disease (NAFLD) may be associated with sleep disorders. In order to explore the explicit relationship between the two, we systematically reviewed the effects of sleep disorders, especially obstructive sleep apnea (OSA), on the incidence of NAFLD, and analyzed the possible mechanisms after adjusting for confounding factors. NAFLD is independently associated with sleep disorders. Different sleep disorders may be the cause of the onset and aggravation of NAFLD. An excessive or insufficient sleep duration, poor sleep quality, insomnia, sleep-wake disorders, and OSA may increase the incidence of NAFLD. Despite that some research suggests a unidirectional causal link between the two, specifically, the onset of NAFLD is identified as a result of changes in sleep characteristics, and the reverse relationship does not hold true. Nevertheless, there is still a lack of specific research elucidating the reasons behind the higher risk of developing sleep disorders in individuals with NAFLD. Further research is needed to establish a clear relationship between NAFLD and sleep disorders. This will lay the groundwork for earlier identification of potential patients, which is crucial for earlier monitoring, diagnosis, effective prevention, and treatment of NAFLD.

Intermittent hypoxia induces hepatic senescence through promoting oxidative stress in a mouse model

PURPOSE

Metabolic-associated fatty liver disease (MAFLD) is an aging-related disease. Obstructive sleep apnea (OSA) may cause MAFLD. This study aimed to explore whether or not intermittent hypoxia (IH), the hallmark of OSA, induces liver aging through oxidative stress.

METHODS

C57BL/6J male mice were administered normal air (control), IH, or antioxidant tempol + IH daily for 6 weeks before the collection of serum and liver tissue samples. A histological examination was conducted to assess liver aging. ELISA was performed to measure liver function indicator levels in the serum and oxidative stress indicator activities in the liver. Western blot analysis was carried out to determine the protein expression of the markers related to oxidative stress, inflammation, and senescence.

RESULTS

Compared with control, IH resulted in significant increases in serum ALT, AST, and TG levels in mice (all P < 0.001), along with lobular inflammation and accumulation of collagen and fat in the liver. The protein levels of inflammatory factors and senescent markers were significantly increased in the IH mouse liver compared with those in the control mouse liver. Meanwhile, IH significantly reduced SOD and CAT activities while enhancing p22phox and Nrf2 protein expression in mouse liver compared with control. Importantly, antioxidant therapy with tempol effectively abrogated the effects of IH on oxidative stress response and aging-related liver injury.

CONCLUSIONS

Our findings suggest that IH induces liver inflammation and aging through oxidative stress. OSA may exacerbate target organ aging and participate in target organ damage. Strategies targeting oxidative stress may prevent and treat OSA-related MAFLD.

Weight loss induced alleviation of sleep-disordered breathing is associated with improvement of non-alcoholic fatty liver disease

INTRODUCTION

Sleep-disordered breathing (SDB) and non-alcoholic fatty liver disease (NAFLD) are both common comorbidities in obese patients. Structured weight loss programs are effective and can reduce the incidence and severity of obesity-related comorbidities. The objective of the present analysis is to test whether weight loss induced alleviation of SDB is a predictor for improvement of NAFLD.

METHODS

Obese participants underwent a standardized non-surgical 3 months weight reduction program (800 kilocalories per day with low carbohydrate and fat content). Abdominal sonography for NAFLD (grade 0 to 3) and monitoring for SDB (defined as apnea-hypopnea index [AHI] ≥ 15/h) were performed at baseline and after 3 months. Alleviation of SDB was defined as a shift from AHI≥ 15/h to <15/h.

RESULTS

48 patients (48% female, age 42 ± 12 years, body-mass index 40.3 ± 8.1 kg/m2, AHI 14 ± 17/h, 85% NAFLD grade ≥1) participated in the weight loss program. In contrast to the no SDB group, in patients with SDB weight loss of 27.1 ±0 .9 kg (8.4 ± 2.8 kg/m2) after three months was paralleled by a reduction in AHI (-22 ± 17/h), prevalence of SDB (from 31% to 13%), and oxidized low-density lipoprotein (-13 ± 11 U/l). In individuals with preexisting SDB NAFLD grade improved more (2 versus 1, p<0.001) and was at a lower degree at 3 months than in those without SDB (0 versus 1, p = 0.015). In multivariable analysis models, SDB at baseline was associated with improvement of NAFLD grade (B 0.908; 95% CI 0.125, 1.691; p = 0.024), independently of age, sex, and BMI (each p>0.05, respectively). Decreasing BMI (B 0.16 [95%-CI 0.08; 0.23], p<0.001) and alleviation of SDB (B 0.90 [95%-CI 0.21; 1.58], p = 0.012) were independently associated with improvement of NAFLD grade.

CONCLUSION

Preexisting SDB and weight loss induced alleviation of SDB are predictors for improvement in NAFLD grade, independent of the extent of weight loss. SDB may contribute to the pathogenesis of NAFLD via SDB-induced oxidative stress and inflammation, but the causal mechanism remains unclear.

The effects of intermittent hypoxia on hepatic expression of fatty acid translocase CD36 in lean and diet-induced obese mice

BACKGROUND

Both obstructive sleep apnea (OSA) and non-alcoholic fatty liver disease (NAFLD) are prevalent within obese individuals. We aimed to investigate the effects of intermittent hypoxia (IH), a clinical feature of OSA, on hepatic expression of fatty acid translocase (CD36) in relation to liver injury in lean and diet-induced obese mice.

METHODS

Four-week-old male C57BL/6J mice were randomized to standard diet (SD) or high fat (HF) diet groups. At 13-week-old, all mice were exposed to either air or IH (IH30; thirty hypoxic episodes per hour) for four weeks. We assessed liver injury through lipid profile, oxidative and inflammatory stress, histological scoring and hepatic CD36 expression.

RESULTS

In lean mice, IH elevated serum and hepatic triglyceride and free fatty acid (FFA) levels, in line with upregulation of hepatic CD36 expression and myeloperoxidase (MPO)-positive cells in support of inflammatory infiltrates along with increase in serum malondialdehyde (MDA), C-X-C motif chemokine ligand 1(CXCL-1) and monocyte chemoattractant protein-1 (MCP-1). In diet-induced obese mice, an increase in hepatic alanine transaminase (ALT) activity, serum and hepatic levels of lipid parameters and inflammatory markers, serum MDA level, hepatic expressions of CD36 and α-smooth muscle actin (α-SMA), and MPO-positive cells was observed. IH potentiated hepatic ALT activity, serum CXCL-1 and hepatic interleukin-6 (IL-6), in line with inflammatory infiltrates, but paradoxically, reduced hepatic FFA level and hepatic CD36 expression, compared to obese mice without IH exposure. However, IH further augmented diet-induced liver steatosis and fibrosis as shown by histological scores.

CONCLUSION

This study contributes to support that IH featuring OSA may lead to liver injury via differential regulation of hepatic CD36 expression in lean and diet-induced obese mice.

Duration of intermittent hypoxia impacts metabolic outcomes and severity of murine NAFLD

Rationale

Obstructive sleep apnea (OSA) is associated with metabolic dysfunction, including progression of nonalcoholic fatty liver disease (NAFLD). Chronic intermittent hypoxia (IH) as a model of OSA worsens hepatic steatosis and fibrosis in rodents with diet induced obesity. However, IH also causes weight loss, thus complicating attempts to co-model OSA and NAFLD. We sought to determine the effect of various durations of IH exposure on metabolic and liver-related outcomes in a murine NAFLD model. We hypothesized that longer IH duration would worsen the NAFLD phenotype.

Methods

Male C57BL/6J mice (n = 32) were fed a high trans-fat diet for 24 weeks, to induce NAFLD with severe steatohepatitis. Mice were exposed to an IH profile modeling severe OSA, for variable durations (0, 6, 12, or 18 weeks). Intraperitoneal glucose tolerance test was measured at baseline and at six-week intervals. Liver triglycerides, collagen and other markers of NAFLD were measured at sacrifice.

Results

Mice exposed to IH for 12 weeks gained less weight (p = 0.023), and had lower liver weight (p = 0.008) relative to room air controls. These effects were not observed in the other IH groups. IH of longer duration transiently worsened glucose tolerance, but this effect was not seen in the groups exposed to shorter durations of IH. IH exposure for 12 or 18 weeks exacerbated liver fibrosis, with the largest increase in hepatic collagen observed in mice exposed to IH for 12 weeks.

Discussion

Duration of IH significantly impacts clinically relevant outcomes in a NAFLD model, including body weight, fasting glucose, glucose tolerance, and liver fibrosis.

Causal relationship between nonalcoholic fatty liver disease and different sleep traits: a bidirectional Mendelian randomized study

Background and aims

Non-alcoholic fatty liver disease(NAFLD) is common worldwide and has previously been reported to be associated with sleep traits. However, it is not clear whether NAFLD changes sleep traits or whether the changes in sleep traits lead to the onset of NAFLD. The purpose of this study was to investigate the causal relationship between NAFLD and changes in sleep traits using Mendelian randomization.

Methods

We proposed a bidirectional Mendelian randomization (MR) analysis and performed validation analyses to dissect the association between NAFLD and sleep traits. Genetic instruments were used as proxies for NAFLD and sleep. Data of genome-wide association study(GWAS) were obtained from the center for neurogenomics and cognitive research database, Open GWAS database and GWAS catalog. Three MR methods were performed, including inverse variance weighted method(IVW), MR-Egger, weighted median.

Results

In total,7 traits associated with sleep and 4 traits associated with NAFLD are used in this study. A total of six results showed significant differences. Insomnia was associated with NAFLD (OR(95% CI)= 2.25(1.18,4.27), P = 0.01), Alanine transaminase levels (OR(95% CI)= 2.79(1.70, 4.56), P =4.71×10-5) and percent liver fat(OR(95% CI)= 1.31(1.03,1.69), P = 0.03). Snoring was associated with percent liver fat (1.15(1.05,1.26), P =2×10-3), alanine transaminase levels (OR(95% CI)= 1.27(1.08,1.50), P =0.04).And dozing was associated with percent liver fat(1.14(1.02,1.26), P =0.02).For the remaining 50 outcomes, no significant or definitive association was yielded in MR analysis.

Conclusion

Genetic evidence suggests putative causal relationships between NAFLD and a set of sleep traits, indicating that sleep traits deserves high priority in clinical practice. Not only the confirmed sleep apnea syndrome, but also the sleep duration and sleep state (such as insomnia) deserve clinical attention. Our study proves that the causal relationship between sleep characteristics and NAFLD is the cause of the change of sleep characteristics, while the onset of non-NAFLD is the cause of the change of sleep characteristics, and the causal relationship is one-way.

Development of albumin monitoring system with hepatic hypoxia-on-a-chip

Hypoxia plays an essential role in the pathogenesis of various liver diseases, and albumin is one of the important biomarkers secreted by the liver. In this study, we developed an albumin monitoring system composed of hepatic hypoxia-on-a-chip and an albumin sensor to study liver function change due to hypoxia. In hepatic hypoxia-on-a-chip, we vertically stack an oxygen-scavenging channel on a liver on a chip with a thin gas-permeable membrane in the middle. This unique design of the hepatic hypoxia-on-a-chip can help to induce hypoxia quickly, attaining <5% within 10 min. An electrochemical albumin sensor was fabricated based on the covalent immobilization of antibodies on the Au electrode to monitor albumin secreting function on the hepatic hypoxia-on-a-chip. Standard albumin samples spiked in PBS, and culture media were measured by the electrochemical impedance spectroscopy using the fabricated immunosensor. The LOD was calculated to be 10 ag/mL in both cases. Using the electrochemical albumin sensor, we measured albumin secretion in normoxia and hypoxia in the chips. The albumin concentration decreased to 27% after 24 h in hypoxia compared to normoxia. This response was consistent with physiological studies. With technical refinements, the present albumin monitoring system can be a powerful tool in studying hepatic hypoxia with real-time liver function monitoring.

Investigating the Relationship between Obstructive Sleep Apnoea, Inflammation and Cardio-Metabolic Diseases

Obstructive sleep apnoea (OSA) is a prevalent underdiagnosed disorder whose incidence increases with age and weight. Uniquely characterised by frequent breathing interruptions during sleep-known as intermittent hypoxia (IH)-OSA disrupts the circadian rhythm. Patients with OSA have repeated episodes of hypoxia and reoxygenation, leading to systemic consequences. OSA consequences range from apparent symptoms like excessive daytime sleepiness, neurocognitive deterioration and decreased quality of life to pathological complications characterised by elevated biomarkers linked to endocrine-metabolic and cardiovascular changes. OSA is a well-recognized risk factor for cardiovascular and cerebrovascular diseases. Furthermore, OSA is linked to other conditions that worsen cardiovascular outcomes, such as obesity. The relationship between OSA and obesity is complex and reciprocal, involving interaction between biological and lifestyle factors. The pathogenesis of both OSA and obesity involve oxidative stress, inflammation and metabolic dysregulation. The current medical practice uses continuous positive airway pressure (CPAP) as the gold standard tool to manage OSA. It has been shown to improve symptoms and cardiac function, reduce cardiovascular risk and normalise biomarkers. Nonetheless, a full understanding of the factors involved in the deleterious effects of OSA and the best methods to eliminate their occurrence are still poorly understood. In this review, we present the factors and evidence linking OSA to increased risk of cardiovascular conditions.

Association Between Metabolic-Associated Fatty Liver Disease and Obstructive Sleep Apnea: A Cross-Sectional Study

AIM

Emerging evidence has revealed that obstructive sleep apnea (OSA) is an independent risk factor for the development of a variety of adverse metabolic disease states. In this study, we evaluated the association between OSA severity and metabolic dysfunction-associated fatty liver disease (MAFLD) among Asian populations.

MATERIALS AND METHODS

This was a cross-sectional, single-center study. The study cohort consisted of patients undergoing polysomnography and abdominal ultrasonography. Logistic regression analysis was used to evaluate the independent risk factors of MAFLD in patients with OSA.

RESULTS

A total of 1065 patients (277 non-MAFLD and 788 MAFLD) were included in the study. The prevalence of MAFLD in non-OSA, mild-moderate OSA, and severe OSA patients was 58.16%, 72.41%, and 78.0%, respectively (p < 0.001). We identified significant differences in body mass index (BMI), apnea-hypopnea index (AHI), oxygen desaturation index (ODI), and lowest O₂ saturation (LaSO₂) between non-MAFLD and MAFLD patients (all p < 0.001). After adjusting for confounding variables, we used multivariate regression analysis to show that BMI, ODI, and triglyceride (TG) levels independently predicted the occurrence of MAFLD (odds ratio [OR] = 1.234, p < 0.001; OR = 1.022, p = 0.013; OR = 1.384, p = 0.001, respectively). Moreover, stratified analysis according to BMI indicated that TG levels were the predominant risk factor for MAFLD in a group of patients with a BMI < 23 kg/m², while BMI, ODI, TG levels, and total cholesterol (TC) were the major risk factors for MAFLD in a group of patients with a BMI ≥ 23 kg/m² (all p < 0.05).

CONCLUSION

OSA-associated chronic intermittent hypoxia was independently associated with the risk of MAFLD, especially in OSA patients with a BMI ≥ 23 kg/m², suggesting that oxidative stress might play an important role in the pathogenesis of MAFLD in patients with OSA.

Chronic intermittent hypoxia promotes early intrahepatic endothelial impairment in rats with nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a progressive disease that ranges from simple steatosis to cirrhosis. Obstructive sleep apnea syndrome (OSAS) and chronic intermittent hypoxia (CIH) are implicated in the pathogenesis of NAFLD. However, the overlapping consequences of CIH on liver sinusoidal endothelial function over time in NAFLD are largely unknown. We explored endothelial dysfunction in a rat model of NAFLD with a high-fat diet exposed to CIH [12 h/day, every 30 s to fractional concentration of oxygen ([Formula: see text] 8%-10%]. The livers were isolated and perfused, and the endothelial function was determined by testing the vasodilation of the liver circulation to increased concentrations of acetylcholine and von Willebrand factor (vWF) and intercellular adhesion molecule 1 (ICAM-1) expression. Phosphorylated endothelial nitric oxide synthase (p-eNOS), cGMP, and oxidative stress were assessed to determine nitric oxide bioavailability. Inflammation and fibrosis were evaluated by transaminases, myeloperoxidase activity, hydroxyproline, and histological evaluation. Hypoxia-inducible factors (HIFs) were studied as a marker of hypoxia and after a second insult with acetaminophen. CIH exposure provoked typical systemic features of OSAS and provoked a decreased response in vasodilation to acetylcholine. This was associated with increased oxidative stress and reduced p-eNOS and cGMP. The microcirculation impairment due to CIH preceded significant hepatic inflammation and fibrotic changes, despite the presence of HIF expression. In conclusion, CIH exacerbates endothelial dysfunction in NAFLD rats associated with increased oxidative stress and reduced nitric oxide bioavailability. This occurs before inflammation and fibrosis establish. Our results suggest that with CIH endothelial dysfunction should be considered an early target.NEW & NOTEWORTHY We believe the findings are of relevance because we demonstrate that chronic intermittent hypoxia further augments impaired hepatic endothelial dysfunction in nonalcoholic fatty liver disease rats. Because obstructive sleep apnea syndrome is associated with systemic endothelial dysfunction in cardiovascular disorders, and chronic intermittent hypoxia is an independent and reversible risk factor for hypertension and coronary artery disease, we hypothesized that this entity may be of potential relevance in the pathophysiology of nonalcoholic fatty liver disease.

Atherosclerosis and Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is a common disease defined by excess fat deposition in the liver. The course of NAFLD is not fully understood, however, some pathogenic mechanisms have been identified. Accumulation of fat in liver cells is associated with insulin resistance, central obesity, triglyceride accumulation in the liver and hepatic fatty acid metabolism dysregulation that cause steatosis. The other process leads to hepatocyte inflammation and necrosis, which leads to severe hepatic disease; non-alcoholic steatohepatitis. Many clinical studies have underlined the link between NAFLD and atherosclerosis. NAFLD may alter the balance lipid-glucose metabolism as well as increase the risk of hypertension and systemic inflammation. This results in a greater risk of vascular events. The present review considers the link between NAFLD and atherosclerosis.

Non-alcoholic Fatty Liver Disease and Steatohepatitis: Risk Factors and Pathophysiology

Non-alcoholic fatty liver disease (NAFLD) and its progressive subtype non-alcoholic steatohepatitis (NASH) are the most prevalent liver diseases, often leading to hepatocellular carcinoma (HCC). This review aims to describe the present knowledge of the risk factors responsible for the development of NAFLD and NASH. I performed a literature review identifying studies focusing on the complex pathogenic pathway and risk factors of NAFLD and steatohepatitis. The relationship between NAFLD and metabolic syndrome is well established and widely recognized. Obesity, dyslipidemia, type 2 diabetes, hypertension, and insulin resistance are the most common risk factors associated with NAFLD. Among the components of metabolic syndrome, current evidence strongly suggests obesity and type 2 diabetes as risk factors of NASH and HCC. However, other elements, namely gender divergences, ethnicity, genetic factors, participation of innate immune system, oxidative stress, apoptotic pathways, and adipocytokines, take a leading role in the onset and promotion of NAFLD. Pathophysiological mechanisms that are responsible for NAFLD development and subsequent progression to NASH are insulin resistance and hyperinsulinemia, oxidative stress, hepatic stellate cell (HSC) activation, cytokine/adipokine signaling pathways, and genetic and environmental factors. Major pathophysiological findings of NAFLD are dysfunction of adipose tissue through the enhanced flow of free fatty acids (FFAs) and release of adipokines, and altered gut microbiome that generate proinflammatory signals and cause NASH progression. Understanding the pathophysiology and risk factors of NAFLD and NASH; this review could provide insight into the development of therapeutic strategies and useful diagnostic tools.

The Cardiovascular and Metabolic Effects of Chronic Hypoxia in Animal Models: A Mini-Review

Animal models are useful to understand the myriad physiological effects of hypoxia. Such models attempt to recapitulate the hypoxemia of human disease in various ways. In this mini-review, we consider the various animal models which have been deployed to understand the effects of chronic hypoxia on pulmonary and systemic blood pressure, glucose and lipid metabolism, atherosclerosis, and stroke. Chronic sustained hypoxia (CSH)-a model of chronic lung or heart diseases in which hypoxemia may be longstanding and persistent, or of high altitude, in which effective atmospheric oxygen concentration is low-reliably induces pulmonary hypertension in rodents, and appears to have protective effects on glucose metabolism. Chronic intermittent hypoxia (CIH) has long been used as a model of obstructive sleep apnea (OSA), in which recurrent airway occlusion results in intermittent reductions in oxyhemoglobin saturations throughout the night. CIH was first shown to increase systemic blood pressure, but has also been associated with other maladaptive physiological changes, including glucose dysregulation, atherosclerosis, progression of nonalcoholic fatty liver disease, and endothelial dysfunction. However, models of CIH have generally been implemented so as to mimic severe human OSA, with comparatively less focus on milder hypoxic regimens. Here we discuss CSH and CIH conceptually, the effects of these stimuli, and limitations of the available data.

Obstructive Sleep Apnea Affects Lacrimal Gland Function

Purpose

To determine the effect of obstructive sleep apnea syndrome (OSA) on lacrimal gland function and its mechanism.

Methods

Male mice aged seven to eight weeks were housed in cages with cyclic intermittent hypoxia to mimic OSA, and the control group was kept in a normal environment. Slit-lamp observation, fluorescein staining, and corneal sensitivity detection are used to assess cornea changes. Tear secretion was detected by phenol red cotton thread, and the pathological changes of lacrimal gland were observed by hematoxylin and eosin staining, oil red O staining, cholesterol and triglyceride kits, immunofluorescence staining, immunohistochemical staining, real-time polymerase chain reaction, transmission electron microscopy, and Western blot.

Results

Studies revealed a decreased tear secretion, corneal epithelial defects and corneal hypersensitivity. Myoepithelial cell damage, abnormal lipid accumulation, reduced cell proliferation, increased apoptosis and inflammatory cell infiltration in the lacrimal gland were also seen. Hifα and NF-κB signaling pathways, moreover, were activated, while Pparα was downregulated, in the lacrimal glands of OSA mice. Fenofibrate treatment significantly alleviated pathological changes of the lacrimal gland induced by OSA.

Conclusion

OSA disturbs the Hifα/Pparα/NF-κB signaling axis, which affects lacrimal gland structure and function and induces dry eye.

Enhanced hepatic respiratory capacity and altered lipid metabolism support metabolic homeostasis during short-term hypoxic stress

BACKGROUND

Tissue hypoxia is a key feature of several endemic hepatic diseases, including alcoholic and non-alcoholic fatty liver disease, and organ failure. Hypoxia imposes a severe metabolic challenge on the liver, potentially disrupting its capacity to carry out essential functions including fuel storage and the integration of lipid metabolism at the whole-body level. Mitochondrial respiratory function is understood to be critical in mediating the hepatic hypoxic response, yet the time-dependent nature of this response and the role of the respiratory chain in this remain unclear.

RESULTS

Here, we report that hepatic respiratory capacity is enhanced following short-term exposure to hypoxia (2 days, 10% O2) and is associated with increased abundance of the respiratory chain supercomplex III2+IV and increased cardiolipin levels. Suppression of this enhanced respiratory capacity, achieved via mild inhibition of mitochondrial complex III, disrupted metabolic homeostasis. Hypoxic exposure for 2 days led to accumulation of plasma and hepatic long chain acyl-carnitines. This was observed alongside depletion of hepatic triacylglycerol species with total chain lengths of 39-53 carbons, containing palmitic, palmitoleic, stearic, and oleic acids, which are associated with de novo lipogenesis. The changes to hepatic respiratory capacity and lipid metabolism following 2 days hypoxic exposure were transient, becoming resolved after 14 days in line with systemic acclimation to hypoxia and elevated circulating haemoglobin concentrations.

CONCLUSIONS

The liver maintains metabolic homeostasis in response to shorter term hypoxic exposure through transient enhancement of respiratory chain capacity and alterations to lipid metabolism. These findings may have implications in understanding and treating hepatic pathologies associated with hypoxia.

Effects of Intermittent Hypoxia on Cytokine Expression Involved in Insulin Resistance

Sleep apnea syndrome (SAS) is a prevalent disorder characterized by recurrent apnea or hypoxia episodes leading to intermittent hypoxia (IH) and arousals during sleep. Currently, the relationship between SAS and metabolic diseases is being actively analyzed, and SAS is considered to be an independent risk factor for the development and progression of insulin resistance/type 2 diabetes (T2DM). Accumulating evidence suggests that the short cycles of decreased oxygen saturation and rapid reoxygenation, a typical feature of SAS, contribute to the development of glucose intolerance and insulin resistance. In addition to IH, several pathological conditions may also contribute to insulin resistance, including sympathetic nervous system hyperactivity, oxidative stress, vascular endothelial dysfunction, and the activation of inflammatory cytokines. However, the detailed mechanism by which IH induces insulin resistance in SAS patients has not been fully revealed. We have previously reported that IH stress may exacerbate insulin resistance/T2DM, especially in hepatocytes, adipocytes, and skeletal muscle cells, by causing abnormal cytokine expression/secretion from each cell. Adipose tissues, skeletal muscle, and the liver are the main endocrine organs producing hepatokines, adipokines, and myokines, respectively. In this review, we focus on the effect of IH on hepatokine, adipokine, and myokine expression.

Association between Hepatic Steatosis and Obstructive Sleep Apnea in Children and Adolescents with Obesity

BACKGROUND

Owing to the increasing rate of pediatric obesity, its complications such as non-alcoholic fatty liver disease (NAFLD) and obstructive sleep apnea (OSA) have become prevalent already in childhood. We aimed to assess the relationship between these two diseases in a cohort of children with obesity.

METHODS

We enrolled 153 children with obesity (mean age 10.5 ± 2.66, mean BMI 30.9 ± 5.1) showing OSA. Subjects underwent a laboratory evaluation, a cardio-respiratory polysomnography (PSG), and a liver ultrasound.

RESULTS

All subjects had a clinical diagnosis of OSA based on the AHI > 1/h (mean AHI 8.0 ± 5.9; range 2.21-19.0). Of these, 69 showed hepatic steatosis (62.3% as mild, 20.3% as moderate, and 17.4% as severe degree). A strong association between ALT and apnea/hypopnea index (AHI) was observed (p = 0.0003). This association was not confirmed after adjusting for hepatic steatosis (p = 0.53). By subdividing our population according to the presence/absence of steatosis, this association was found only in the steatosis group (p = 0.009). As the severity of steatosis increased, the significance of its association with AHI compared to the absence of steatosis became progressively stronger (all p < 0.0001).

CONCLUSIONS

Hepatic steatosis seems to drive the association between OSA and ALT levels, suggesting a potential pathogenic role of OSA in NAFLD.

Obstructive sleep apnea and severity of nonalcoholic fatty liver disease

BACKGROUND

Mechanisms involving obstructive sleep apnea (OSA) and nonalcoholic fatty liver disease (NAFLD) are under increasing assessment. This study evaluated the correlation of OSA with the severity of NAFLD.

MATERIALS AND METHODS

Prospective study in which patients with at least one of metabolic syndrome (MS) criteria were initially assessed by the NAFLD fibrosis score and according to the outcome (intermediate or high risk of advanced fibrosis) underwent liver biopsy (exception of patients with clinical, ultrasound or endoscopic diagnosis of cirrhosis). All patients performed polysomnography. For statistical analysis, the patients were assembled into two groups: (1) without apnea or mild apnea and (2) moderate or severe apnea. In the correlation of OSA with the severity of NAFLD, the risk factors evaluated were: degree of steatosis, presence and severity of nonalcoholic steatohepatitis (NASH) and fibrosis.

RESULTS

Fifty-one patients were evaluated, 80.4% had systemic arterial hypertension (SAH), 68.6% type 2 diabetes mellitus, 62.7% dyslipidemia and 96.1% MS. Regarding the histological evaluation (n = 48), all had steatosis, 95.8% steatohepatitis and 83.3% fibrosis. In polysomnography, 80.4% were group 1 and 19.6% group 2. In univariate analysis, no correlation was found between steatosis severity, NASH and presence or severity of fibrosis with OSA. A multivariate analysis adjusted for obesity level, found that patients with moderate to severe OSA had an increased risk of hepatic fibrosis (odds ratio 1.22, 95% confidence interval: 1.02-1.45, P = 0.027).

CONCLUSION

The present study demonstrated an association between fibrosis and moderate to severe OSA, regardless of obesity.

Untargeted Metabolomic Profiling of Liver in a Chronic Intermittent Hypoxia Mouse Model

Obstructive sleep apnea (OSA) has been demonstrated to be associated with liver injury. Nevertheless, the mechanisms linking the two disorders remain largely unexplored to date. Based on UHPLC/Q-TOF MS platform, the present study aimed to study the hepatic metabolomic profiling in a chronic intermittent hypoxia (CIH) mouse model to identify altered metabolites and related metabolic pathways. C57BL/6 Mice (n = 12 each group) were exposed to intermittent hypoxia or control conditions (room air) for 12 weeks. At the end of the exposure, liver enzymes and histological changes were assessed. Untargeted metabolomics approach by UHPLC/Q-TOF MS and orthogonal partial least squares-discriminant analysis (OPLS-DA) were applied to screen altered metabolites in mice liver. Bioinformatics analyses were applied to identify the related metabolic pathways. CIH treatment caused a remarkable liver injury in mice. A total of 27 differential metabolites in negative ion mode and 44 in positive ion mode were identified between the two groups. These metabolites were correlated to multiple biological and metabolic processes, including various amino acid metabolism, membrane transport, lipid metabolism, carbohydrate metabolism, nucleotide metabolism, ferroptosis, etc. three differential metabolites including glutathione, glutathione disulfide, arachidonic acid (peroxide free) were identified in the ferroptosis pathway. CIH was associated with a significant metabolic profiling change in mice liver. The metabolites in amino acid metabolism, membrane transport, lipid metabolism, carbohydrate metabolism, nucleotide metabolism, and ferroptosis played an important role in CIH-induced liver injury. These findings contribute to a better understanding of the mechanisms linking OSA and liver injury and help identify potential therapeutic targets.

Impact of continuous positive airway pressure therapy for nonalcoholic fatty liver disease in patients with obstructive sleep apnea

BACKGROUND

Obstructive sleep apnea (OSA) has been suggested as an independent risk factor for nonalcoholic fatty liver disease (NAFLD), and continuous positive airway pressure (CPAP) is the first-line therapy for OSA.

AIM

To clarify the efficacy of effective CPAP therapy on NAFLD of OSA patients by serum markers and transient elastography (TE) using FibroScan^® (Echosens, Paris, France).

METHODS

We prospectively enrolled 123 consecutive patients with OSA who met the indications for CPAP. Liver fibrosis and steatosis were assessed using TE. Before and after 6 mo of CPAP therapy, serum markers and TE were assessed for all patients. The mean usage rate of CPAP therapy for 6 mo was arbitrarily calculated in each patient and expressed as “mean compliance index” (m-CI).

RESULTS

In 50 OSA patients with NAFLD, both aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were significantly decreased after 6 mo of CPAP therapy. Univariate analysis showed that decreased body weight (BW), decreased body mass index (BMI), decreased AST level, decreased hemoglobin A1c, and high m-CI were significantly related with improved ALT level. In multivariate regression model adjusted for quantities of BW change during 6 mo of CPAP therapy, high m-CI tended to improve ALT level (P = 0.051). All 17 OSA patients with NAFLD, high m-CI and no BMI changes showed significant improvements in AST and ALT levels. Meanwhile, no significant changes in TE data or serum fibrosis markers were seen.

CONCLUSION

Some NAFLD could be associated with chronic intermittent hypoxia due to OSA independent of BW changes. In those cases, adequate reoxygenation from effective CPAP therapy may improve NAFLD.

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.

Continuous Positive Airway Pressure Does Not Improve Nonalcoholic Fatty Liver Disease in Patients with Obstructive Sleep Apnea. A Randomized Clinical Trial

Rationale: Obstructive sleep apnea (OSA) is associated with development of nonalcoholic fatty liver disease (NAFLD). The effects of continuous positive airway pressure (CPAP) on NAFLD in patients with concomitant OSA are unknown.Objectives: To investigate the effects of autoadjusting CPAP versus subtherapeutic CPAP treatment over 6 months on NAFLD activities.Methods: Patients with NAFLD and OSA, as defined by respiratory event index ≥5/h diagnosed by a validated level 3 Embletta device, were randomized into group A) autoadjusting CPAP (4-20 cm H₂O) or group B) subtherapeutic CPAP (pressure fixed at 4 cm H₂O). The primary endpoint was the difference in changes in intrahepatic triglyceride as measured by proton magnetic resonance spectroscopy after 6 months of therapy. Key secondary endpoints included changes in controlled attenuation parameter (CAP) and liver stiffness measurement measured with transient elastography, and serum cytokeratin-18 fragment.Measurements and Main Results: A total of 120 patients were randomized equally into two groups. There were significant correlations between CAP and respiratory event index (r = 0.203, P = 0.026), percentage of total recording time with Sa_O2 < 90% (r = 0.265, P = 0.003), and oxygen desaturation index (r = 0.214, P = 0.019). After 6 months of treatment, there were no significant differences of changes in primary and secondary endpoints between the two treatment groups. Regression analysis showed that weight change over 6 months correlated with changes in both intrahepatic triglyceride and CAP (P < 0.001).Conclusions: Despite significant correlations between hepatic steatosis and markers of severity of OSA, CPAP alone did not improve hepatic steatosis and fibrosis. However, the additional role of weight reduction through lifestyle modification deserves further investigation.

Association between obstructive sleep apnea and non-alcoholic fatty liver disease in pediatric patients: a meta-analysis

BACKGROUND

Some studies have reported a relationship between obstructive sleep apnea (OSA) and non-alcoholic fatty liver disease (NAFLD) in pediatric population. However, this issue remains controversial.

OBJECTIVES

The purpose of the present study was to investigate the association between OSA and NAFLD in pediatric population.

METHODS

We systematically searched PubMed, Web of Science, Embase for eligible studies. The data involving markers of NAFLD including alanine aminotransferase (ALT), aspartate aminotransferase (AST), hepatic inflammation, hepatic fibrosis of both OSA group and control group were extracted. Pooled standardised mean difference (SMD) and weighted mean difference (WMD) were appropriately calculated through a fixed or random-effect model.

RESULTS

Nine cross-sectional studies with 1133 children and adolescents were included. OSA was significantly associated with ALT, AST, and NAFLD fibrosis stage, but not NAFLD inflammation grade. Subgroup analysis indicated that both mild OSA and severe OSA were significantly associated with elevated ALT and AST. Furthermore, in the studies with all main confounding factors (age, gender, and BMI) matched, OSA group had higher ALT and AST levels than control group.

CONCLUSIONS

This meta-analysis suggested that OSA was associated with NAFLD evidenced by elevated liver enzymes and progressive hepatic fibrosis in pediatric population. Screening and monitoring of NAFLD in pediatric patients with obesity-related OSA are necessary.

Cognitive Dysfunction in Non-Alcoholic Fatty Liver Disease-Current Knowledge, Mechanisms and Perspectives

Non-alcoholic fatty liver disease (NAFLD) has emerged as the hepatic component of the metabolic syndrome and now seemingly affects one-fourth of the world population. Features associated with NAFLD and the metabolic syndrome have frequently been linked to cognitive dysfunction, i.e. systemic inflammation, vascular dysfunction, and sleep apnoea. However, emerging evidence suggests that NAFLD may be a cause of cognitive dysfunction independent of these factors. NAFLD in addition exhibits dysbiosis of the gut microbiota and impaired urea cycle function, favouring systemic ammonia accumulation and further promotes systemic inflammation. Such disruption of the gut–liver–brain axis is essential in the pathogenesis of hepatic encephalopathy, the neuropsychiatric syndrome associated with progressive liver disease. Considering the growing burden of NAFLD, the morbidity from cognitive impairment is expected to have huge societal and economic impact. The present paper provides a review of the available evidence for cognitive dysfunction in NAFLD and outlines its possible mechanisms. Moreover, the clinical challenges of characterizing and diagnosing cognitive dysfunction in NAFLD are discussed.

Understanding the pathophysiological mechanisms of cardiometabolic complications in obstructive sleep apnoea: towards personalised treatment approaches

In January 2019, a European Respiratory Society research seminar entitled "Targeting the detrimental effects of sleep disturbances and disorders" was held in Dublin, Ireland. It provided the opportunity to critically review the current evidence of pathophysiological responses of sleep disturbances, such as sleep deprivation, sleep fragmentation or circadian misalignment and of abnormalities in physiological gases such as oxygen and carbon dioxide, which occur frequently in respiratory conditions during sleep. A specific emphasis of the seminar was placed on the evaluation of the current state of knowledge of the pathophysiology of cardiovascular and metabolic diseases in obstructive sleep apnoea (OSA). Identification of the detailed mechanisms of these processes is of major importance to the field and this seminar offered an ideal platform to exchange knowledge, and to discuss pitfalls of current models and the design of future collaborative studies. In addition, we debated the limitations of current treatment strategies for cardiometabolic complications in OSA and discussed potentially valuable alternative approaches.

Leptin: Master Regulator of Biological Functions that Affects Breathing

Obesity is a global epidemic in developed countries accounting for many of the metabolic and cardiorespiratory morbidities that occur in adults. These morbidities include type 2 diabetes, sleep-disordered breathing (SDB), obstructive sleep apnea, chronic intermittent hypoxia, and hypertension. Leptin, produced by adipocytes, is a master regulator of metabolism and of many other biological functions including central and peripheral circuits that control breathing. By binding to receptors on cells and neurons in the brainstem, hypothalamus, and carotid body, leptin links energy and metabolism to breathing. In this comprehensive article, we review the central and peripheral locations of leptin's actions that affect cardiorespiratory responses during health and disease, with a particular focus on obesity, SDB, and its effects during early development. Obesity-induced hyperleptinemia is associated with centrally mediated hypoventilation with decrease CO₂ sensitivity. On the other hand, hyperleptinemia augments peripheral chemoreflexes to hypoxia and induces sympathoexcitation. Thus, "leptin resistance" in obesity is relative. We delineate the circuits responsible for these divergent effects, including signaling pathways. We review the unique effects of leptin during development on organogenesis, feeding behavior, and cardiorespiratory responses, and how undernutrition and overnutrition during critical periods of development can lead to cardiorespiratory comorbidities in adulthood. We conclude with suggestions for future directions to improve our understanding of leptin dysregulation and associated clinical diseases and possible therapeutic targets. Lastly, we briefly discuss the yin and the yang, specifically the contribution of relative adiponectin deficiency in adults with hyperleptinemia to the development of metabolic and cardiovascular disease. © 2020 American Physiological Society. Compr Physiol 10:1047-1083, 2020.

Correlation between Obstructive Sleep Apnea and Non-Alcoholic Fatty Liver Disease before and after Metabolic Bariatric Surgery

BACKGROUND

Emerging evidence has revealed that obstructive sleep apnea (OSA) is associated with non-alcoholic fatty liver disease (NAFLD). However, the impact of OSA on NAFLD among obese patients undergoing metabolic and bariatric surgery (MBS), especially during follow-up period, remains unclear.

OBJECTIVE

To analyze the correlation based on preoperative characteristics and postoperative conditions among bariatric patients with comorbid OSA and NAFLD.

METHODS

Clinical data of patients who underwent MBS in our institution between January 2016 and June 2019 were reviewed retrospectively. Correlation analysis and linear regressions were used to identify how OSA links with NAFLD before and after treatment of MBS.

RESULTS

Of 308 patients, 181 were diagnosed with OSA and enrolled in the present study, and 127 completed follow-up visits at 6 months. The proportion of NAFLD in the mild-moderate OSA and severe OSA groups was 75.0% and 96.0%, respectively. MBS was effective at improving sleep apnea and nocturnal hypoxia, as well as liver steatosis and fibrosis (P < 0.05). And we also found that there were significant correlations not only between OSA- and NAFLD-related characteristics at baseline but also between their improvements after surgery, eventually leading to similar prognosis of NAFLD for both groups (P < 0.05), no matter what presurgical differences existed. In addition, the results of the univariate and multivariate linear regression analyses supported preoperative liver/spleen Hounsfield units ratio (LSR) by computerized tomography (CT) as an independent predictor of the effect of MBS on liver steatosis.

CONCLUSION

In conclusion, MBS plays a pivotal role in the control of medical conditions in obese patients with OSA and NAFLD. Given the correlation between OSA and NAFLD in the present study, in the case of both the severity at baseline as well as the improvement after surgery, OSA may pose an impact on the prognosis of NAFLD in bariatric patients.

Extracellular vesicles derived from fat-laden hepatocytes undergoing chemical hypoxia promote a pro-fibrotic phenotype in hepatic stellate cells

BACKGROUND

The transition from steatosis to non-alcoholic steatohepatitis (NASH) is a key issue in non-alcoholic fatty liver disease (NAFLD). Observations in patients with obstructive sleep apnea syndrome (OSAS) suggest that hypoxia contributes to progression to NASH and liver fibrosis, and the release of extracellular vesicles (EVs) by injured hepatocytes has been implicated in NAFLD progression.

AIM

To evaluate the effects of hypoxia on hepatic pro-fibrotic response and EV release in experimental NAFLD and to assess cellular crosstalk between hepatocytes and human hepatic stellate cells (LX-2).

METHODS

HepG2 cells were treated with fatty acids and subjected to chemically induced hypoxia using the hypoxia-inducible factor 1 alpha (HIF-1α) stabilizer cobalt chloride (CoCl2). Lipid droplets, oxidative stress, apoptosis and pro-inflammatory and pro-fibrotic-associated genes were assessed. EVs were isolated by ultracentrifugation. LX-2 cells were treated with EVs from hepatocytes. The CDAA-fed mouse model was used to assess the effects of intermittent hypoxia (IH) in experimental NASH.

RESULTS

Chemical hypoxia increased steatosis, oxidative stress, apoptosis and pro-inflammatory and pro-fibrotic gene expressions in fat-laden HepG2 cells. Chemical hypoxia also increased the release of EVs from HepG2 cells. Treatment of LX2 cells with EVs from fat-laden HepG2 cells undergoing chemical hypoxia increased expression pro-fibrotic markers. CDAA-fed animals exposed to IH exhibited increased portal inflammation and fibrosis that correlated with an increase in circulating EVs.

CONCLUSION

Chemical hypoxia promotes hepatocellular damage and pro-inflammatory and pro-fibrotic signaling in steatotic hepatocytes both in vitro and in vivo. EVs from fat-laden hepatocytes undergoing chemical hypoxia evoke pro-fibrotic responses in LX-2 cells.

TLR4 mediates inflammation and hepatic fibrosis induced by chronic intermittent hypoxia in rats

Obstructive sleep apnea syndrome (OSAS) is a common and complex disorder that is associated with liver injury. Moreover, previous studies have revealed that chronic intermittent hypoxia (CIH) is associated with the development of non-alcoholic fatty liver disease and hepatic fibrosis. However, the underlying molecular mechanisms remain largely unknown. The present study aimed to investigate whether chronic intermittent hypoxia induced hepatic fibrosis, in addition to determining its underlying mechanisms, in CIH model rats using immunohistochemistry, western blotting and reverse transcription-quantitative PCR. The present results suggested that CIH caused hepatic fibrosis and increased the expression levels of interleukin (IL)-1β, IL-8, monocyte chemotactic-1, tumor necrosis factor-α, intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 in the liver; these conditions could be reversed by Toll-like receptor 4 (TLR4) short hairpin RNA lentivirus treatment. Moreover, immunohistochemistry and western blotting results indicated that TLR4 and NF-κB expression levels were significantly increased in the CIH and CIH-TLR4 empty vector lentivirus group. However, protein expression levels of TLR4, NF-κB, inhibitor of NF-κB and phosphorylated-mitogen-activated protein kinase (MAPK)-1 in the hypoxia/reoxygenation group were significantly higher compared with the control group (P<0.05), and these results were reversed by the MAPK inhibitor U0126 in vitro. Collectively, the present preliminary results suggested that inflammation and the TLR4/NF-κB/MAPK signaling pathway may be involved in CIH-induced liver fibrosis.

The role of ferroptosis in chronic intermittent hypoxia-induced liver injury in rats

PURPOSE

Obstructive sleep apnea (OSA) has been related to an increased risk of liver injury. Ferroptosis is a form of programmed cell death implicated in multiple physiological and pathological processes. This study aimed to explore the role of ferroptosis in chronic intermittent hypoxia (CIH)-induced liver injury as well as to uncover the underlying mechanisms using a CIH rat model.

METHODS

Fourteen male Sprague-Dawley rats were randomly allocated to either the normal control (NC) (n = 7) or the CIH group (n = 7). Rats were exposed to intermittent hypoxia for 8 weeks in CIH group. Liver function, histological changes, and markers of oxidative stress were evaluated. The protein levels of hypoxia-inducible factor-1α, nuclear factor E2-related factor 2 (Nrf2), Acyl-CoA synthetase long-chain family member 4 (ACSL4), and glutathione peroxidase 4 (GPX4) in liver were examined by Western blot analysis.

RESULTS

CIH treatment caused significant increase of serum alanine aminotransferase, aspartate aminotransferase, and malondialdehyde (MDA). Liver MDA was significantly higher in CIH group than that in NC group. Histology showed that CIH treatment induced discernible swelled, disordered hepatocytes, necrosis, and infiltrated inflammatory cells. CIH treatment significantly reduced the expression of GPX4, while markedly up-regulated expression of ACSL4, indicating elevation in hepatic ferroptosis. In addition, the protein expression of Nrf2 in CIH group was significantly lower than that in NC group.

CONCLUSIONS

Ferroptosis played a crucial role in CIH-induced liver injury. The hepatic ferroptosis in CIH rat model might be mediated by the dysregulation of Nrf2. This highlights a potential therapeutic target for the treatment of OSA-related liver injury.

Obstructive Sleep Apnea, Hypoxia, and Nonalcoholic Fatty Liver Disease

Recent studies have demonstrated that obstructive sleep apnea (OSA) is associated with the development and evolution of nonalcoholic fatty liver disease (NAFLD), independent of obesity or other shared risk factors. Like OSA, NAFLD is a prevalent disorder associated with major adverse health outcomes: Patients with NAFLD may develop cirrhosis, liver failure, and hepatocellular carcinoma. One major finding that has emerged from these studies is that the OSA-NAFLD association is related to the degree of nocturnal hypoxemia in OSA. Animal models have therefore largely focused on intermittent hypoxia, a key manifestation of OSA, to shed light on the mechanisms by which OSA may give rise to the complex metabolic disturbances that are seen in NAFLD. Intermittent hypoxia leads to tissue hypoxia and can result in oxidative stress, mitochondrial dysfunction, inflammation, and overactivation of the sympathetic nervous system, among many other maladaptive effects. In such models, intermittent hypoxia has been shown to cause insulin resistance, dysfunction of key steps in hepatic lipid metabolism, atherosclerosis, and hepatic steatosis and fibrosis, each of which is pertinent to the development and/or progression of NAFLD. However, many intriguing questions remain unanswered: Principally, how aggressively should the clinician screen for NAFLD in patients with OSA, and vice versa? In this review, we attempt to apply the best evidence from animal and human studies to highlight the relationship between these two disorders and to advocate for further trials aimed at defining these relationships more precisely.

Nonalcoholic Fatty Liver Disease in Adults: Current Concepts in Etiology, Outcomes, and Management

Nonalcoholic fatty liver disease (NAFLD) is a spectrum of disease, extending from simple steatosis to inflammation and fibrosis with a significant risk for the development of cirrhosis. It is highly prevalent and is associated with significant adverse outcomes both through liver-specific morbidity and mortality but, perhaps more important, through adverse cardiovascular and metabolic outcomes. It is closely associated with type 2 diabetes and obesity, and both of these conditions drive progressive disease toward the more advanced stages. The mechanisms that govern hepatic lipid accumulation and the predisposition to inflammation and fibrosis are still not fully understood but reflect a complex interplay between metabolic target tissues including adipose and skeletal muscle, and immune and inflammatory cells. The ability to make an accurate assessment of disease stage (that relates to clinical outcome) can also be challenging. While liver biopsy is still regarded as the gold-standard investigative tool, there is an extensive literature on the search for novel noninvasive biomarkers and imaging modalities that aim to accurately reflect the stage of underlying disease. Finally, although no therapies are currently licensed for the treatment of NAFLD, there are interventions that appear to have proven efficacy in randomized controlled trials as well as an extensive emerging therapeutic landscape of new agents that target many of the fundamental pathophysiological processes that drive NAFLD. It is highly likely that over the next few years, new treatments with a specific license for the treatment of NAFLD will become available.

Effect of chronic intermittent hypoxia on gene expression profiles of rat liver: a better understanding of OSA-related liver disease

PURPOSE

Obstructive sleep apnea (OSA) and OSA-associated chronic intermittent hypoxia (CIH) have been suggested to be associated with increased risk of liver disease. Little is known about the biological pathophysiology and underlying molecular mechanisms. Here we use whole-genome expression profiling to explore the transcriptomic changes induced by CIH in rat liver.

METHODS

Rats (n = 3) were exposed to CIH for 8 weeks and were compared with rats exposed to normoxia (n = 3). Illumina HiSeq 4000 platform was used to examine differentially expressed genes (DEGs) in the liver between control group and CIH rat model. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to validate DEGs. Biological functions of DEGs were determined by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes.

RESULTS

Compared with control group, 318 genes were identified to be dysregulated in the liver of CIH rat model, with 211genes upregulated and 107 genes downregulated. Bioinformatics analysis showed that these genes were extensively related to various physiologic processes such as hepatic metabolism, apoptotic process, and oxidative stress. 10 genes with 5 upregulated and 5 downregulated were selected and further verified by qRT-PCR.

CONCLUSIONS

CIH resulted in altered gene expression patterns in the liver of rat. The DEGs were related to various physiological and pathological processes in CIH rat liver. These data provide a better understanding of the mechanisms and underlying molecular changes of OSA-related liver disease.

Myeloid cell deletion of Aryl hydrocarbon Receptor Nuclear Translocator (ARNT) induces non-alcoholic steatohepatitis. PLoS One. 2019;14:e0225332. [PMID: 31800592 PMCID: PMC6892561 DOI: 10.1371/journal.pone.0225332]

Background and aim

Non-alcoholic steatohepatitis (NASH) is predicted to become the most common cause of cirrhosis and liver failure. Risk factors include obesity, insulin resistance and diabetes. Macrophages and other myeloid cells play crucial roles in initiating and driving inflammation. Aryl hydrocarbon Receptor Nuclear Translocator (ARNT) is a transcription factor which binds to a range of partners to mediate responses to environmental signals, including the diet. In people with diabetes it is decreased in liver. We hypothesised that myeloid cell ARNT activity may contribute to the development of liver pathology.

Methods

Floxed-ARNT mice were bred with LysM-Cre mice to generate mice with reduced ARNT in myeloid cells. Animals were fed a high fat diet (HFD) and liver pathology was assessed. Histology, mRNA, fat accumulation and metabolism were studied.

Results

Animals with reduced myeloid ARNT developed steatohepatitis on a HFD, with additional alterations of metabolism and fat deposition. Steatohepatitis was accompanied by hepatic macrophage infiltration and expression of both M1 and M2 markers. Expression of mRNAs for Cxcl1, Mcp-1, Tnf-α and Tgf-β1 were increased. Human livers from controls and people with NASH were tested; ARNT mRNA was decreased by 80% (p = 0.0004).

Conclusions

Decreased myeloid ARNT may play a role in the conversion from non-alcoholic fatty liver to steatohepatitis. Increasing ARNT may be a therapeutic strategy to reduce NASH.

Induction of detrusor underactivity by extensive vascular endothelial damages of iliac arteries in a rat model and its pathophysiology in the genetic levels

We tried to establish a reliable detrusor underactivity (DUA) rat model and to investigate pathophysiology of chronic bladder ischemia (CBI) on voiding behavior and bladder function. Adult male rats were divided into five groups. The arterial injury (AI) groups (AI-10, AI-20, AI-30) underwent vascular endothelial damage (VED) of bilateral iliac arteries (with 10, 20, and 30 bilateral repetitions of injury, respectively) and received a 1.25% cholesterol diet. The sham group underwent sham operation and received the same diet. Controls received a regular diet. After 8 weeks, all rats underwent unanesthetized cystometrogram. Bladder tissues were processed for organ bath investigation, immunohistochemistry staining, and genome-wide gene expression analysis. Awake cystometry analysis showed that frequency of voiding contractions and micturition pressure were lower in the AI-30 group than in sham group (p < 0.01). Contractile responses to various stimuli were lower in AI-20 and AI-30 groups (both p < 0.001). In the AI-20 and AI-30 groups, atherosclerotic occlusion in the iliac arteries, tissue inflammation, fibrosis, denervation, and apoptosis of bladder muscle were prominent compared to the sham. Mechanistically, the expression of purinergic receptor P2X-1 was reduced in the AI-30 group, and the genome-wide gene expression analysis revealed that genes related to IL-17 and HIF-1 signaling pathways including INF-γ receptor-1 and C-X-C motif chemokine ligand-2 were upregulated in the CBI-induced DUA rat model. A rat model of progressive VED successfully induced DUA. Abnormal tissue inflammation, fibrosis, denervation, and bladder muscle tissue apoptosis may be involved in CBI-induced DUA pathophysiology.

Relationship Between Intermittent Hypoxia and Type 2 Diabetes in Sleep Apnea Syndrome

Sleep apnea syndrome (SAS) is a very common disease involving intermittent hypoxia (IH), recurrent symptoms of deoxygenation during sleep, strong daytime sleepiness, and significant loss of quality of life. A number of epidemiological researches have shown that SAS is an important risk factor for insulin resistance and type 2 diabetes mellitus (DM), which is associated with SAS regardless of age, gender, or body habitus. IH, hallmark of SAS, plays an important role in the pathogenesis of SAS and experimental studies with animal and cellular models indicate that IH leads to attenuation of glucose-induced insulin secretion from pancreatic β cells and to enhancement of insulin resistance in peripheral tissues and cells, such as liver (hepatocytes), adipose tissue (adipocytes), and skeletal muscles (myocytes). In this review, we focus on IH-induced dysfunction in glucose metabolism and its underlying molecular mechanisms in several cells and tissues related to glucose homeostasis.

Nocturnal Hypoxia Activation of the Hedgehog Signaling Pathway Affects Pediatric Nonalcoholic Fatty Liver Disease Severity

Chronic intermittent hypoxia and hedgehog (Hh) pathway dysregulation are associated with nonalcoholic fatty liver disease (NAFLD) progression. In this study, we determined the relationship between obstructive sleep apnea (OSA)/nocturnal hypoxia and Hh signaling in pediatric NAFLD. Adolescents with histologic NAFLD (n = 31) underwent polysomnogram testing, laboratory testing, and Sonic Hh (SHh), Indian hedgehog (IHh), glioblastoma‐associated oncogene 2 (Gli2), keratin 7 (K7), α‐smooth muscle actin (α‐SMA), and hypoxia‐inducible factor 1α (HIF‐1α) immunohistochemistry. Aspartate aminotransferase (AST) correlated with SHh, r = 0.64; Gli2, r = 0.4; α‐SMA, r = 0.55; and K7, r = 0.45 (P < 0.01), as did alanine aminotransferase (ALT) (SHh, r = 0.51; Gli2, r = 0.43; α‐SMA, r = 0.51; P < 0.02). SHh correlated with NAFLD activity score (r = 0.39), whereas IHh correlated with inflammation (r = −0.478) and histologic grade (r = −0.43); P < 0.03. Subjects with OSA/hypoxia had higher SHh (4.0 ± 2.9 versus 2.0 ± 1.5), Gli2 (74.2 ± 28.0 versus 55.8 ± 11.8), and α‐SMA (6.2 ± 3.3 versus 4.3 ± 1.2); compared to those without (P < 0.03). OSA severity correlated with SHh (r = 0.31; P = 0.09) and Gli2 (r = 0.37; P = 0.04) as did hypoxia severity, which was associated with increasing SHh (r = −0.53), Gli2 (r = −0.52), α‐SMA (r = −0.61), and K7 (r = −0.42); P < 0.02. Prolonged O₂ desaturations <90% also correlated with SHh (r = 0.55) and Gli2 (r = 0.61); P < 0.05. Conclusion: The Hh pathway is activated in pediatric patients with NAFLD with nocturnal hypoxia and relates to disease severity. Tissue hypoxia may allow for functional activation of HIF‐1α, with induction of genes important in epithelial‐mesenchymal transition, including SHh, and NAFLD progression.

Role of melanocortin 4 receptor in hypertension induced by chronic intermittent hypoxia

AIM

We previously demonstrated that central nervous system (CNS) melanocortin 4 receptors (MC4R) play a key role in regulating blood pressure (BP) in some conditions associated with increased SNS activity, including obesity. In this study, we examined whether activation of CNS MC4R contributes to chronic intermittent hypoxia (CIH)-induced hypertension and ventilatory responses to hypercapnia.

METHODS

Rats were instrumented with an intracerebroventricular (ICV) cannula in the lateral cerebral ventricle for continuous infusion of MC4R antagonist (SHU-9119) and telemetry probes for measuring mean arterial pressure (MAP) and heart rate (HR). Untreated and SHU-9119-treated rats as well as obese and lean MC4R-deficient rats were exposed to CIH for 7-18 consecutive days.

RESULTS

Chronic intermittent hypoxia reduced cumulative food intake by 18 ± 5 g while MAP and HR increased by 10 ± 3 mm Hg and 9 ± 5 bpm in untreated rats. SHU-9119 increased food intake (from 15 ± 1 to 46 ± 3 g) and prevented CIH-induced reduction in food intake. CIH-induced hypertension was not attenuated by MC4R antagonism (average increase of 10 ± 1 vs 9 ± 1 mm Hg for untreated and SHU-9119 treated rats). In obese MC4R-deficient rats, CIH for 7 days raised BP by 11 ± 4 mm Hg. However, when MC4R-deficient rats were food restricted to prevent obesity, CIH-induced hypertension was attenuated by 32%. We also found that MC4R deficiency was associated with impaired ventilatory responses to hypercapnia independently of obesity.

CONCLUSION

These results show that obesity and the CNS melanocortin system interact in complex ways to elevate BP during CIH and that MC4R may be important in the ventilatory responses to hypercapnia.

Melatonin prevents chronic intermittent hypoxia-induced injury by inducing sirtuin 1-mediated autophagy in steatotic liver of mice

BACKGROUND

Hepatic steatosis that occasionally results in nonalcoholic steatohepatitis (NASH) is related to obstructive sleep apnea (OSA). Many studies have shown that autophagy exerts protective effects on liver damage caused by various diseases and melatonin exhibits hepatoprotective properties. However, the mechanisms of liver injury induced by chronic intermittent hypoxia (CIH) and the effect of melatonin on the regulation of liver injury remain unclear.

PURPOSE

This study was aimed to evaluate the role of CIH in steatohepatitis progression and the regulatory function of melatonin on fatty liver sensitivity to CIH injury, mainly focusing on autophagy signaling.

METHODS

A high-fat diet (FD)-induced obesity mouse model was subjected to intermittent hypoxia/normoxia events for approximately 8 h per day using an autophagy agonist, rapamycin, or an inhibitor, 3-methyladenine (3-MA), and SRT1720, a sirtuin 1 (SIRT1) activator, or sirtinol, a SIRT1 inhibitor, with or without melatonin for a total of six successive weeks, followed by assessment of expression of autophagy-related genes and activity of serum aminotransferase as well as histological evaluation of tissue morphology.

RESULTS

Neither FD nor CIH alone causes significant liver injury; however, the combination yielded higher serum aminotransferase activities and more severe histological changes, accompanied by a decrease in autophagy activity. Melatonin markedly inhibited FD/CIH-stimulated liver injury by enhancing autophagy. In contrast, SIRT1 inhibition resulted in a decrease in the expression of melatonin-induced autophagy-related genes as well as diminished its protective effects on FD/CIH-induced liver injury.

CONCLUSION

These results suggest that melatonin could ameliorate FD/CIH-induced hepatocellular damage by activating SIRT1-mediated autophagy signaling.

Somatostatin analogue, Octreotide, improves restraint stress-induced liver injury by ameliorating oxidative stress, inflammatory response, and activation of hepatic stellate cells

The aim of this study is to investigate the effect of somatostatin (SST) analogue, Octreotide, on some features of liver injury induced by immobilization stress (IS) in adult male albino rats. Eighteen adult male albino rats were randomly divided into three equal groups: control, IS, and Octreotide-treated stressed groups. Octreotide (40 μg/kg body weight, subcutaneously) was administrated twice daily for 8 days during the exposure to IS. Octreotide was found to reduce the IS significantly and induce elevations in the plasma level of corticosterone, liver transaminases, and tumor necrosis factor α (TNF-α) as compared with IS group. Furthermore, Octreotide administration has significantly elevated the decline in the total antioxidant capacities (TAC) and lowered the elevated malondialdehyde (MDA) levels observed with IS in the hepatic tissue. Additionally, Octreotide treatment provided protection against the histopathological changes in the stressed liver in the form of significant reduction in the mean number of degenerated hepatocytes, the area % of collagen fibers, and glial fibrillary acid protein (GFAP) immunostaining with a significant increase in the mean number of normal hepatocytes. In conclusion, stressed rats showed disturbed liver functions and its oxidant-antioxidant status with highly expression hepatic stellate cells (HSCs), which were all improved by Octreotide administration, SST analogue.

Continuous Positive Airway Pressure Therapy on Nonalcoholic Fatty Liver Disease in Patients With Obstructive Sleep Apnea

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) is associated with nonalcoholic fatty liver disease (NAFLD) and related advanced fibrosis. We studied the treatment of OSA with continuous positive airway pressure (CPAP) in a population with NAFLD.

METHODS

Using an institutional database (2010-2014), we identified patients with NAFLD and OSA and studied changes in serum aminotransferases before and after CPAP use. We defined suspected NAFLD (sNAFLD) as serum alanine aminotransferase (ALT) > 30 U/L for men and > 19 U/L for women in the absence of known causes of chronic liver disease. The aspartate aminotransferase (AST) to platelet ratio index (APRI) was used to determine significant fibrosis. Consistent CPAP use for more than 3 months with adequate adherence parameters defined good adherence.

RESULTS

Of 351 patients with OSA on CPAP treatment, majority (mean age 57.6 years, 59.3% male) had abnormal ALT, and 89.4% met the criteria for sNAFLD. The prevalence of sNAFLD was higher among patients with moderate to severe OSA (90.6%) versus mild OSA (86.3%). There was a statistically significant improvement in AST, ALT, and APRI with CPAP therapy (all P < .01). There was an apparent dose-response relationship: patients with good adherence to CPAP showed a significantly larger decrease in AST and ALT than did those with poor adherence (P < .01). Multivariable logistic regression analysis showed CPAP treatment with adequate adherence (odds ratio = 3.93, 95% confidence interval = 1.29-11.94) was an independent predictor of regression of sNAFLD after adjusting for obesity class and severity of OSA.

CONCLUSIONS

OSA treatment with CPAP was associated with significant biochemical improvement and reduction in NAFLD-related fibrosis.

The Bidirectional Relationship Between Obstructive Sleep Apnea and Metabolic Disease

Obstructive sleep apnea (OSA) is a common sleep disorder, effecting 17% of the total population and 40-70% of the obese population (1, 2). Multiple studies have identified OSA as a critical risk factor for the development of obesity, diabetes, and cardiovascular diseases (3-5). Moreover, emerging evidence indicates that metabolic disorders can exacerbate OSA, creating a bidirectional relationship between OSA and metabolic physiology. In this review, we explore the relationship between glycemic control, insulin, and leptin as both contributing factors and products of OSA. We conclude that while insulin and leptin action may contribute to the development of OSA, further research is required to determine the mechanistic actions and relative contributions independent of body weight. In addition to increasing our understanding of the etiology, further research into the physiological mechanisms underlying OSA can lead to the development of improved treatment options for individuals with OSA.

Intermittent hypoxia suppression of growth hormone and insulin-like growth factor-I in the neonatal rat liver

OBJECTIVES

Extremely low gestational age neonates with chronic lung disease requiring oxygen therapy frequently experience fluctuations in arterial oxygen saturation or intermittent hypoxia (IH). These infants are at risk for multi-organ developmental delay, reduced growth, and short stature. The growth hormone (GH)/insulin-like growth factor-I (IGF-1) system, an important hormonal regulator of lipid and carbohydrate metabolism, promotes neonatal growth and development. We tested the hypothesis that increasing episodes of IH delay neonatal growth by influencing the GH/IGF-I axis.

DESIGN

Newborn rats were exposed to 2, 4, 6, 8, 10, or 12 hypoxic episodes (12% O₂) during hyperoxia (50% O₂) from P0-P7, P0-P14 (IH), or allowed to recover from P7-P21 or P14-P21 (IHR) in room air (RA). RA littermates at P7, P14, and P21 served as RA controls; and groups exposed to hyperoxia only (50% O₂) served as zero IH controls. Histopathology of the liver; hepatic levels of GH, GHBP, IGF-I, IGFBP-3, and leptin; and immunoreactivities of GH, GHR, IGF-I and IGF-IR were determined.

RESULTS

Pathological findings of the liver, including cellular swelling, steatosis, necrosis and focal sinusoid congestion were seen in IH, and were particularly severe in the P7 animals. Hepatic GH levels were significantly suppressed in the IH groups exposed to 6-12 hypoxic episodes per day and were not normalized during IHR. Deficits in the GH levels were associated with reduced body length and increase body weight during IHR suggesting increased adiposity and catchup fat. Catchup fat was also associated with elevations in GHBP, IGF-I, leptin.

CONCLUSIONS

IH significantly impairs hepatic GH/IGF-1 signaling during the first few weeks of life, which is likely responsible for hepatic GH resistance, increased body fat, and hepatic steatosis. These hormonal perturbations may contribute to long-term organ and body growth impairment, and metabolic dysfunction in preterm infants experiencing frequent IH and/or apneic episodes.