Relationship between Obstructive Sleep Apnea and Liver Abnormalities in Morbidly Obese Patients: A Prospective Study

Metabolic Dysfunction-Associated Steatohepatitis and Progression to Hepatocellular Carcinoma: A Literature Review

The prevalence of metabolic-associated fatty liver disease (MAFLD) is increasing globally due to factors such as urbanization, obesity, poor nutrition, sedentary lifestyles, healthcare accessibility, diagnostic advancements, and genetic influences. Research on MAFLD and HCC risk factors, pathogenesis, and biomarkers has been conducted through a narrative review of relevant studies, with a focus on PubMed and Web of Science databases and exclusion criteria based on article availability and language. Steatosis marks the early stage of MASH advancement, commonly associated with factors of metabolic syndrome such as obesity and type 2 diabetes. Various mechanisms, including heightened lipolysis, hepatic lipogenesis, and consumption of high-calorie diets, contribute to the accumulation of lipids in the liver. Insulin resistance is pivotal in the development of steatosis, as it leads to the release of free fatty acids from adipose tissue. Natural compounds hold promise in regulating lipid metabolism and inflammation to combat these conditions. Liver fibrosis serves as a significant predictor of MASH progression and HCC development, underscoring the need to target fibrosis in treatment approaches. Risk factors for MASH-associated HCC encompass advanced liver fibrosis, older age, male gender, metabolic syndrome, genetic predispositions, and dietary habits, emphasizing the requirement for efficient surveillance and diagnostic measures. Considering these factors, it is important for further studies to determine the biochemical impact of these risk factors in order to establish targeted therapies that can prevent the development of HCC or reduce progression of MASH, indirectly decreasing the risk of HCC.

Effects of obstructive sleep apnea on non-alcoholic fatty liver disease in patients with obesity: a systematic review

INTRODUCTION

Obesity has been linked to non-alcoholic fatty liver disease (NAFLD), a widespread chronic liver ailment, as well as obstructive sleep apnea (OSA). The development of NAFLD is influenced by repeated intermittent hypoxia, a feature of OSA.

METHODS

This systematic review (SR) investigated CENTRAL, PubMed, and EMBASE databases. The endpoint of this SR was to assess which OSA-related indicators could predict the presence of NAFLD and the effect of bariatric metabolic surgery (BMS) on improving OSA and NAFLD over time.

RESULTS

Compared to previous SRs published in 2013, 14 new publications were added to our SR, alongside studies conducted prior to 2013. The SR ultimately included 28 studies (18 cross-sectional and 10 cohort trials). In the majority of studies, significant correlations were observed between OSA, OSA-related outcomes, and NAFLD. However, the apnea-hypopnea index (AHI) alone proved to be an inadequate predictor of NAFLD. Instead, respiratory and metabolic changes were found to alleviate oxidative stress induced by hypoxemia. Six studies involved patients who underwent BMS, with one evaluating patients before and after BMS, revealing associations between increased OSA and NAFLD improvement following BMS. Six months after surgery, 100% of patients in the mild-to-moderate OSA group were free from fatty liver, and an 89% reduction was observed in the severe OSA group.

CONCLUSION

For the first time, BMS has been tested in treating both OSA and NAFLD pre and postoperative with positive results. Further research, ideally with histological and functional data, is needed to confirm these findings. The SR identified 14 distinct liver outcome tests; however, high heterogeneity and incomplete data precluded a meta-analysis. It is imperative to pay greater attention to the influence of OSA-related factors and uniformity in liver outcomes testing concerning NAFLD. To accomplish this, study designs should be enhanced by incorporating more comprehensive pre- and postoperative evaluations, extending follow-up periods, and employing a more consistent methodology for liver diagnosis in patients with obesity.

Relationship between Obstructive Sleep Apnea and Liver Abnormalities in Older Patients: A Cross-Sectional Study

BACKGROUND

Older age is a risk factor for obstructive sleep apnea (OSA), which is associated with the development of nonalcoholic fatty liver disease (NAFLD). We aimed to investigate the correlation between OSA and liver injury among older patients. Study Design. This is a cross-sectional study.

METHODS

Consecutive older (≥60 years) snoring patients were included. Subjects were divided into no OSA, mild OSA, moderate OSA, and severe OSA groups according to the apnea-hypopnea index (AHI) and were also separated into liver injury and nonliver injury groups based on liver function. Logistic regression analysis was applied to analyze the independent risk factors for liver injury.

RESULTS

We studied 227 patients (155 male, 72 female). The prevalence of liver injury exhibited an increasing trend among groups with mild-to-severe OSA. In addition, body mass index, AHI, and TG showed significant differences between the liver injury and nonliver injury groups. Logistic regression analysis revealed that AHI and TG were the major contributing factors for liver injury in older patients (adjusted odds ratio [OR] = 1.055, p=0.013, and OR = 1.485, p=0.039, respectively).

CONCLUSIONS

Older patients with OSA have an increased risk of liver injury and NAFLD, and sleep apnea and high TG are important factors in contributing to the development of liver injury.

Heart Failure with Preserved Ejection Fraction and Obstructive Sleep Apnea: A Novel Paradigm for Additional Cardiovascular Benefit of SGLT2 Inhibitors in Subjects With or Without Type 2 Diabetes

After examining the complex interplay between heart failure (HF) in its various clinical forms, metabolic disorders like nonalcoholic fatty liver disease (NAFLD), and obstructive sleep apnea (OSA) syndrome, in this mini-review we described possible favorable effects of sodium-glucose cotransporter 2 inhibitors (SGLT2is) on HF with preserved (i.e., ≥ 50%) ejection fraction (HFpEF) through enhanced cardiorenal function and visceral-subcutaneous body fat redistribution. In greater detail, on the basis of pathophysiological mechanisms underlying OSA onset and the direct positive SGLT2i effect on renal function benefiting chronic kidney disease, we emphasized the promising role of SGLT2is in prevention, rehabilitation, and treatment of patients with OSA regardless of coexisting type 2 diabetes (T2DM). Indeed, SGLT2is enhance lipolysis and fatty acid beta-oxidation. These phenomena might prevent OSA by reducing the size of visceral and subcutaneous adipose tissue and, as proven in humans and animals with T2DM, counteract NAFLD onset and progression. The aforementioned mechanisms may represent an additional SGLT2i cardioprotective effect in terms of HFpEF prevention in patients with OSA, whose NAFLD prevalence is estimated to be over 50%.

Management of Patients With Non-alcoholic Steatohepatitis Undergoing Liver Transplantation: Considerations for the Anesthesiologist

Non-alcoholic fatty liver disease (NAFLD) currently affects more than 25% of the world population and is rising. NAFLD can progress to non-alcoholic steatohepatitis that is associated with hepatic inflammation and fibrosis and can result in cirrhosis with subsequent liver failure. Non-alcoholic steatohepatitis (NASH) has now emerged as one of the leading etiologies for a liver transplant among adults in the United States. Given the rising incidence of liver transplants in patients with NASH-related cirrhosis, it is essential for anesthesiologists to be familiar with this condition as well as with NASH-related comorbidities and perioperative complications. Not only is NASH linked to metabolic syndrome, but it also is independently associated with cardiovascular disease, renal and thyroid dysfunction, obstructive sleep apnea (OSA), and a hypercoagulable state. The association with these conditions can affect the perioperative outcome of these patients, particularly because of increased mortality from major adverse cardiovascular events and sepsis. In order to decrease the perioperative morbidity and mortality of patients with NASH undergoing a liver transplant, a multidisciplinary approach to their perioperative management is essential, along with careful preoperative evaluation and aggressive intraoperative and postoperative monitoring. The focus of this review article is to provide a comprehensive overview of challenges associated with liver transplants in patients with NASH and to provide suggestions for appropriate patient selection and perioperative management.

The association between obstructive sleep apnea and non-alcoholic steatohepatitis: a retrospective nationwide inpatient sample analysis

Aim of the study

The primary purpose of this study was to assess the association of obstructive sleep apnea (OSA) and non-alcoholic steatohepatitis (NASH) from a large national inpatient sample database.

Material and methods

We conducted a retrospective analysis using the Healthcare Cost and Utilization Project-Nationwide Inpatient Sample. OSA and NASH patients were identified using the ICD-10-CM code G47.33 and K75.81. Non-NASH patients (control) were randomly selected and matched by age and gender to each NASH patient in a 4 : 1 ratio. Weighted logistic regression models were used to calculate the association between OSA and NASH in addition to different comorbidities.

Results

A total of 54,169 participants were included in our analysis; 10,740 cases of NASH were matched to 43,429 controls (non-NASH). NASH was significantly higher in the white population (82.12% vs. 76.64%, p < 0.001). The prevalence of OSA among NASH patients was significantly higher compared to the control group (15.8% vs. 8.9%, adjusted OR: 1.34, 95% CI: 1.14-1.56, p = 0.0003). The prevalence of celiac disease and Crohn’s disease was significantly higher in patients with NASH (0.7% vs. 0.2%, p < 0.0002 and 1.28% vs. 0.76%, p < 0.0001). Multiple comorbidities were significantly elevated in the NASH group compared to the non-NASH group, including diabetes mellitus (DM; 36% vs. 17.6%, p < 0.0001), obesity (36.4% vs. 18.2%, p < 0.0001) and metabolic syndrome (0.86% vs. 0.06%, p < 0.0001). The mortality rate was significantly higher in the NASH group (3.8% vs. 2%, p < 0.0001).

Conclusions

This is the first study using the ICD-10-CM code with a specific search code for NASH. Our large population database results emphasize that there is a significant association between OSA and NASH.

Sleep disorder in patients with chronic liver disease: a narrative review

Sleep disturbance is a common feature of chronic liver disease (CLD) with impact on health-related quality of life; 60-80% of patients with CLD report subjective poor sleep; frequent presentations of sleep disturbance include insomnia, reduced sleep efficiency, increased sleep latency, reduced time in rapid eye movement (REM) sleep, restless leg syndrome and excessive daytime sleepiness (EDS). Key contributors to sleep disturbance include hepatic encephalopathy (HE) and circadian rhythm imbalance due to altered melatonin metabolism. Specific conditions causing CLD, such as non-alcoholic fatty liver disease (NAFLD), chronic viral hepatitis and primary biliary cholangitis (PBC) result in different types of sleep disturbance, and the treatment of these conditions can often also lead to sleep disturbance. There are currently limited management options for sleep disturbance in CLD. Obstructive sleep apnoea (OSA) is a common condition that causes chronic intermittent hypoxia due to airway collapse during sleep. This chronic intermittent hypoxia appears to contribute to the development of NAFLD. The presence of reactive oxygen species and the overexpression of hypoxia inducible factor 1-alpha secondary to hypoxia may be responsible for the second 'hit' of the 'two-hit' hypothesis of NAFLD. Treatment of the intermittent hypoxia with continuous positive airway pressure therapy has limited efficacy against liver dysfunction. There remain many outstanding areas of investigation in the management of sleep disturbance in CLD, and of liver dysfunction in OSA.

How frequent is sleep-disordered breathing among Egyptian cirrhotic adults?

AIM OF THE STUDY

Liver cirrhosis is an irreversible destructive liver disease that is associated with a wide range of complications. Among the recognized comorbidities of liver cirrhosis are sleep-disordered breathing (SDB), which is being more and more often described among cirrhotics. This study aimed to detect the prevalence of SDB among Egyptian post-viral cirrhotic adults.

MATERIAL AND METHODS

This study enrolled 48 post-viral cirrhotic patients and 16 apparently healthy control subjects. All patients and controls were evaluated by thorough history taking, full clinical examination, laboratory investigations, the Epworth Sleepiness Scale questionnaire, the Berlin Questionnaire and polysomnography.

RESULTS

Patients and controls were comparable as regards baseline demographics. Patients with liver cirrhosis had higher frequency of SDB compared to controls (56.2% vs. 12.5%, p = 0.002). The most frequently encountered SBD patterns among cirrhotics were obstructive sleep apnea and apnea hypopnea index. Moreover, SDB was more severe among cirrhotics (25% were mild, 16.6% were moderate and 14.6% were severe obstructive sleep apnea - OSA) compared to the healthy controls (all were mild).

CONCLUSIONS

It seems that post-viral cirrhotic patients had a wide range of SDB with variable degrees of severity compared to the healthy controls.

Single-layered ultra-soft washable smart textiles for all-around ballistocardiograph, respiration, and posture monitoring during sleep

Good sleep is considered to be the cornerstone for maintaining both physical and mental health. However, nearly one billion people worldwide suffer from various sleep disorders. To date, polysomnography (PSG) is the most commonly used sleep-monitoring technology,however, it is complex, intrusive, expensive and uncomfortable. Unfortunately, present noninvasive monitoring technologies cannot simultaneously achieve high sensitivity, multi-parameter monitoring and comfort. Here, we present a single-layered, ultra-soft, smart textile for all-around physiological parameters monitoring and healthcare during sleep. With a high-pressure sensitivity of 10.79 mV/Pa, a wide working frequency bandwidth from 0 Hz to 40 Hz, good stability, and decent washability, the single-layered ultra-soft smart textile is simultaneously capable of real-time detection and tracking of dynamic changes in sleep posture, and subtle respiration and ballistocardiograph (BCG) monitoring. Using the set of patient generated health data, an obstructive sleep apnea-hypopnea syndrome (OSAHS) monitoring and intervention system was also developed to improve the sleep quality and prevent sudden death during sleep. This work is expected to pave a new and practical pathway for physiological monitoring during sleep.

Obstructive sleep apnea and dyslipidemia: from animal models to clinical evidence

Lipid metabolism deregulation constitutes the pathogenic basis for the development of atherosclerosis and justifies a high incidence of cardiovascular-related morbidity and mortality. Some data suggest that dyslipidemia may be associated with sleep-disordered breathing, mainly obstructive sleep apnea (OSA), due to alterations in fundamental biochemical processes, such as intermittent hypoxia (IH). The aim of this systematic review was to identify and critically evaluate the current evidence supporting the existence of a possible relationship between OSA and alterations in lipid metabolism. Much evidence shows that, during the fasting state, OSA and IH increase lipid delivery from the adipose tissue to the liver through an up-regulation of the sterol regulatory element-binding protein-1 and stearoyl-CoA desaturase-1, increasing the synthesis of cholesterol esters and triglycerides. In the postprandial state, lipoprotein clearance is delayed due to lower lipoprotein lipase activity, probably secondary to IH-up-regulation of angiopoietin-like protein 4 and decreased activity of the peroxisome proliferator-activated receptor alpha. Moreover, oxidative stress can generate dysfunctional oxidized lipids and reduce the capacity of high-density lipoproteins (HDL) to prevent low-density lipoprotein (LDL) oxidation. In the clinical field, several observational studies and a meta-regression analysis support the existence of a link between OSA and dyslipidemia. Although there is evidence of improved lipid profile after apnea-hypopnea suppression with continuous positive airway pressure (CPAP), the majority of the data come from observational studies. In contrast, randomized controlled trials evaluating the effects of CPAP on lipid metabolism present inconclusive results and two meta-analyses provide contradictory evidence.

Obstructive sleep apnea and liver injury in severely obese patients with nonalcoholic fatty liver disease

OBJECTIVES

Obstructive sleep apnea (OSA) and nonalcoholic fatty liver disease (NAFLD) are common in subjects with severe obesity. It has been suggested that insulin resistance and systemic inflammation may play a role in the development of nonalcoholic steatohepatitis (NASH), but the mechanisms remain controversial. The aim of this study was to explore the influence of OSA on liver injury and its potential mechanisms in severely obese patients with NAFLD.

METHODS

Severely obese patients requiring bariatric surgery were consecutively recruited between November 2017 and June 2018. Demographic, biochemical, liver ultrasound, and ambulatory polygraph data were collected.

RESULTS

One hundred fifty-three subjects with liver ultrasound-verified NAFLD were classified into three groups according to the apnea-hypopnea index (AHI). The level of serum alanine aminotransferase (ALT) and gamma-glutamyl transpeptidase (GGT) tended to increase with more severe OSA (P = 0.024 and P = 0.004, respectively). In the unadjusted analysis, both ALT and GGT were positively correlated with AHI, oxygen desaturation index, percentage of total sleep time spent with oxyhemoglobin saturation below 90%, male sex, homeostasis model assessment of insulin resistance (HOMA-IR), and total cholesterol, while liver enzymes were negatively related to lowest oxygen saturation. In multiple regression analysis, AHI (odds ratio (OR) = 1.052, P = 0.044) and HOMA-IR (OR = 1.135, P = 0.001) were independent risk factors for an elevated ALT level. High-sensitivity C-reactive protein (hs-CRP) was positively associated with BMI and GGT (r = 0.349 and r = 0.164 (P < 0.05), respectively), and no correlation was found between hs-CRP and AHI or other parameters of hypoxia. hs-CRP and GGT remained significantly correlated after adjusting for confounding parameters (OR = 2.509, P = 0.013).

CONCLUSIONS

OSA may play a role in liver injury among severely obese individuals with NAFLD. Insulin resistance and systemic inflammation were possible contributing factors in this process.

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.

Extra-Hepatic Manifestations of Nonalcoholic Fatty Liver Disease: A Review

Nonalcoholic fatty liver disease (NAFLD) is now the leading cause of chronic liver disease worldwide with a strong association with metabolic syndrome. NAFLD is truly a systemic disease and is associated with a plethora of extra-hepatic manifestations or comorbidities. These are either related to secondary effects of associated obesity or from pathophysiological effects of insulin resistance in NAFLD. Three most common causes of increased morbidity and mortality associated with NAFLD are cardiovascular disease, liver disease, and cancer. In this narrative review, we will discuss comprehensively on cardiovascular disease, type 2 diabetes mellitus, and chronic kidney disease and will also highlight on malignancy especially colorectal cancer, pulmonary disorders including obstructive sleep apnea, endocrine disorders such as hypothyroidism and polycystic ovarian syndrome, dermatological disorders especially psoriasis, and hematological associations including iron overload and susceptibility to thrombosis. In addition to focusing on pathogenesis of these extrahepatic manifestations, we will highlight their clinical implications for physicians in routine clinical practice. Further, there remains an unmet need for safe and effective therapies and examining their benefits on these extra-hepatic manifestations among patients with NAFLD.

A new sensitive and accurate model to predict moderate to severe obstructive sleep apnea in patients with obesity

Obstructive sleep apnea (OSA) has a high prevalence in patients with obesity. Only patients with clinical symptoms of OSA are admitted to polysomnography; however, many patients with OSA are asymptomatic. We aimed to create and validate a population-based risk score that predicts the severity of OSA in patients with obesity.We here report the cross-sectional analysis at baseline of an ongoing study investigating the long-term effect of bariatric surgery on OSA. One-hundred sixty-one patients of the Obesity Center of the Catholic University Hospital in Rome, Italy were included in the study. The patients underwent overnight cardiorespiratory monitoring, blood chemistry analyses, hepatic ultrasound, and anthropometric measurements. The patients were divided into 2 groups according OSA severity assessed by the apnea-hypopnea index (AHI): AHI < 15 = no or mild and AHI ≥ 15 moderate to severe OSA. A statistical prediction model was created and validated. C statistics was used to evaluate the discrimination performance of the model.The prevalence of OSA was 96.3% with 74.5% of the subjects having moderate/severe OSA. Sex, body mass index, diabetes, and age were included in the final prediction model that had excellent discrimination ability (C statistics equals to 83%). An OSA risk chart score for clinical use was created.Patients with severe obesity are at a very high risk for moderate or severe OSA in particular if they are men, older, more obese, and/or with type 2 diabetes. The OSA risk chart can be useful for general practitioners and patients as well as for bariatric surgeons to select patients with high risk of moderate to severe OSA for further polysomnography.

Increased liver stiffness in patients with severe sleep apnoea and metabolic comorbidities

The goal of this study was to assess the relationship between the severity of obstructive sleep apnoea (OSA) and liver stiffness measurement (LSM), one of the most accurate noninvasive screening tools for liver fibrosis in nonalcoholic fatty liver disease.The study included 147 patients with at least one criterion for the metabolic syndrome, assessed by polysomnography for suspected OSA. LSM was performed using transient elastography (FibroScan). Significant liver disease and advanced liver fibrosis were defined as LSM ≥7.3 and ≥9.6 kPa, respectively.23 patients were excluded because of unreliable LSM. Among 124 patients, 34 (27.4%) had mild OSA, 38 (30.6%) had moderate OSA and 52 (42.0%) had severe OSA. LSM values were 7.3- <9.6 kPa in 18 (14.5%) patients and ≥9.6 kPa in 15 (12.1%) patients. A dose-response relationship was observed between OSA severity and LSM values (p=0.004). After adjustment for age, sex, metabolic syndrome and insulin resistance, severe OSA was associated with an increased risk of LSM ≥7.3 kPa (OR 7.17, 95% CI 2.51-20.50) and LSM ≥9.6 kPa (OR 4.73, 95% CI 1.25-17.88).In patients with metabolic comorbidities, severe OSA is independently associated with increased liver stiffness, which may predispose to a higher risk of significant liver disease and poorer prognosis.

The association of nonalcoholic steatohepatitis and obstructive sleep apnea

BACKGROUND AND AIM

The association between obstructive sleep apnea (OSA) and abnormal liver enzymes has been reported in multiple studies. The existing literature regarding the relationship between OSA and nonalcoholic steatohepatitis (NASH) is conflicting. Thus we aimed to determine the relationship between OSA and NASH from a large database.

PATIENTS AND METHODS

A cross-sectional study was performed using the 2012 Nationwide Inpatient Sample. We identified adult patients (18-90 years) who had a diagnosis of OSA using the International Classification of Diseases 9th version codes. The control group was comprised of adult individuals with no discharge records of OSA. NASH diagnosis was also identified using the International Classification of Diseases 9th version codes. The association between OSA and NASH was calculated using univariable and multivariable logistic regression.

RESULTS

A total of 30 712 524 hospitalizations were included. The OSA group included 1 490 150 patients versus 29 222 374 in the control non-OSA group. The OSA group average age was 61.8±0.07 years (44.2% females) compared with 57.0±0.11 years (60.1% females) in the non-OSA group. NASH prevalence was significantly higher in the OSA group compared with the non-OSA group [2% (95% confidence interval (CI): 1.9, 2.1) vs. 0.65% (95% CI: 0.63, 0.66), P<0.001]. After adjusting for obesity, diabetes, hypertension, dyslipidemia, the metabolic syndrome and Charlson comorbidity index, OSA patients were three times more likely to have NASH [adjusted odds ratio: 3.1 (95% CI: 3.0-3.3), P<0.001].

CONCLUSION

Patients with OSA are three times more likely to have NASH compared with patients without OSA after controlling for other confounders. These data indicate that OSA should be considered as an independent risk factor for developing NASH.

Hepatocyte Hypoxia Inducible Factor-1 Mediates the Development of Liver Fibrosis in a Mouse Model of Nonalcoholic Fatty Liver Disease

Background

Obstructive sleep apnea (OSA) is associated with the progression of non-alcoholic fatty liver disease (NAFLD) to steatohepatitis and fibrosis. This progression correlates with the severity of OSA-associated hypoxia. In mice with diet induced obesity, hepatic steatosis leads to liver tissue hypoxia, which worsens with exposure to intermittent hypoxia. Emerging data has implicated hepatocyte cell signaling as an important factor in hepatic fibrogenesis. We hypothesized that hepatocyte specific knockout of the oxygen sensing α subunit of hypoxia inducible factor-1 (HIF-1), a master regulator of the global response to hypoxia, may be protective against the development of liver fibrosis.

Methods

Wild-type mice and mice with hepatocyte-specific HIF-1α knockout (Hif1a^-/-hep) were fed a high trans-fat diet for six months, as a model of NAFLD. Hepatic fibrosis was evaluated by Sirius red stain and hydroxyproline assay. Liver enzymes, fasting insulin, and hepatic triglyceride content were also assessed. Hepatocytes were isolated from Hif1a^-/-hep mice and wild-type controls and were exposed to sustained hypoxia (1% O₂) or normoxia (16% O₂) for 24 hours. The culture media was used to reconstitute type I collagen and the resulting matrices were examined for collagen cross-linking.

Results

Wild-type mice on a high trans-fat diet had 80% more hepatic collagen than Hif1a^-/-hep mice (2.21 μg collagen/mg liver tissue, versus 1.23 μg collagen/mg liver tissue, p = 0.03), which was confirmed by Sirius red staining. Body weight, liver weight, mean hepatic triglyceride content, and fasting insulin were similar between groups. Culture media from wild-type mouse hepatocytes exposed to hypoxia allowed for avid collagen cross-linking, but very little cross-linking was seen when hepatocytes were exposed to normoxia, or when hepatocytes from Hif1a^-/-hep mice were used in hypoxia or normoxia.

Conclusions

Hepatocyte HIF-1 mediates an increase in liver fibrosis in a mouse model of NAFLD, perhaps due to liver tissue hypoxia in hepatic steatosis. HIF-1 is necessary for collagen cross-linking in an in vitro model of fibrosis.

The association between continuous positive airway pressure therapy and liver disease development in obstructive sleep apnea/hypopnea syndrome patients: a nationwide population-based cohort study in Taiwan

PURPOSE

Studies on the association between continuous positive airway pressure (CPAP) treatment and liver diseases such as non-alcoholic fatty liver disease (NAFLD) and cirrhosis in patients with obstructive sleep apnea/hypopnea syndrome (OSAHS) are limited. To the best of our knowledge, none exists that makes use of a national database in an Asian population. This study aims to evaluate the effects of CPAP treatment on patients with these two disorders in a retrospective, population-based study in Taiwan.

METHODS

Using the Taiwan National Health Insurance claims database, this study collected the data of OSAHS patients diagnosed between 2000 and 2008 and divided them into CPAP treatment and non-CPAP treatment groups. All subjects were followed up until 2010. Liver disease incidence and risk were calculated.

RESULTS

The CPAP group had a lower cumulative incidence rate of developing liver disease than the non-CPAP group within the observation periods (p < 0.001). After adjusting for age, gender, urbanization level, and comorbidities, the CPAP treatment group showed a lower risk of developing liver disease compared with the non-CPAP treatment group (sub-aHR of 0.66 (95% CI 0.55-0.80), p < 0.001).

CONCLUSIONS

Our observations suggest that CPAP treatment may play an important role to delay the progression of liver disease in OSAHS patients and decreases the incidence of liver disease among OSAHS patients. Thus, CPAP therapy may be a feasible way to decrease the risk of liver disease among patients with OSAHS.

Hypoxia-regulated mechanisms in the pathogenesis of obesity and non-alcoholic fatty liver disease

The pandemic rise in obesity has resulted in an increased incidence of metabolic complications. Non-alcoholic fatty liver disease is the hepatic manifestation of the metabolic syndrome and has become the most common chronic liver disease in large parts of the world. The adipose tissue expansion and hepatic fat accumulation characteristics of these disorders compromise local oxygen homeostasis. The resultant tissue hypoxia induces adaptive responses to restore oxygenation and tissue metabolism and cell survival. Hypoxia-inducible factors (HIFs) function as master regulators of this hypoxia adaptive response, and are in turn hydroxylated by prolyl hydroxylases (PHDs). PHDs are the main cellular oxygen sensors and regulate HIF proteasomal degradation in an oxygen-dependent manner. HIFs and PHDs are implicated in numerous physiological and pathological conditions. Extensive research using genetic models has revealed that hypoxia signaling is also a key mechanism in adipose tissue dysfunction, leading to adipose tissue fibrosis, inflammation and insulin resistance. Moreover, hypoxia affects liver lipid metabolism and deranges hepatic lipid accumulation. This review summarizes the molecular mechanisms through which the hypoxia adaptive response affects adipocyte and hepatic metabolism, and the therapeutic possibilities of modulating HIFs and PHDs in obesity and fatty liver disease.

Nonalcoholic fatty liver disease and obstructive sleep apnea

Obstructive sleep apnea (OSA) and more importantly its hallmark, chronic intermittent hypoxia (CIH), are established factors in the pathogenesis and exacerbation of nonalcoholic fatty liver disease (NAFLD). This has been clearly demonstrated in rodent models exposed to intermittent hypoxia, and strong evidence now also exists in both paediatric and adult human populations. OSA and CIH induce insulin-resistance and dyslipidemia which are involved in NAFLD physiopathogenesis. CIH increases the expression of the hypoxia inducible transcription factor HIF1α and that of downstream genes involved in lipogenesis, thereby increasing β-oxidation and consequently exacerbating liver oxidative stress. OSA also disrupts the gut liver axis, increasing intestinal permeability and with a possible role of gut microbiota in the link between OSA and NAFLD. OSA patients should be screened for NAFLD and vice versa those with NAFLD for OSA. To date there is no evidence that treating OSA with continuous positive airway pressure (CPAP) will improve NAFLD but it might at least stabilize and slow its progression. Nevertheless, these multimorbid patients should be efficiently treated for all their metabolic co-morbidities and be encouraged to follow weight stabilization or weight loss programs and physical activity life style interventions.

Pharyngeal collapsibility during sleep is elevated in insulin-resistant females with morbid obesity

Insulin resistance is associated with sleep apnoea, leading us to hypothesise that it is also associated with elevations in pharyngeal collapsibility, even in the absence of sleep apnoea.90 bariatric patients were characterised for sleep apnoea, pharyngeal collapsibility and insulin resistance. Patients with a respiratory disturbance index (RDI) >10 events·h(-1), diabetes mellitus, tonsillar hypertrophy and pulmonary disease were excluded. The remaining 14 females underwent collapsibility measurements (passive critical pressure, Pcritp ) during non-rapid eye movement sleep. The homeostasis model assessment (HOMA) index, a measure of insulin resistance, was derived from measurements of fasting glucose and insulin levels, and compared to Pcritp Groups with high Pcritp compared to low Pcritp did not differ in age, body mass index or RDI. HOMA and insulin were elevated in the high Pcritp group compared to the low Pcritp group (p<0.02). Pcritp correlated with HOMA (Spearman's ρ=0.565, 95% CI 0.104-0.862; p=0.035) and insulin (Spearman's ρ=0.609 95% CI 0.196-0.835; p=0.021).Obese insulin-resistant subjects without frank diabetes or sleep apnoea demonstrate preclinical elevations in pharyngeal collapsibility, which may increase their susceptibility to sleep apnoea. Our findings suggest that insulin resistance could play a significant role in sleep apnoea pathogenesis by generating requisite elevations in pharyngeal collapsibility.

Extrahepatic Manifestations of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease worldwide with an increased prevalence of metabolic, macro- and microvascular complications. The primary causes of mortality in NAFLD are cardiovascular disease (CVD), malignancy and liver disease. NAFLD is a multisystem disease that affects a variety of extra-hepatic organ systems. The main focus of this review is to summarize the reported extra-hepatic associations, which include CVD, chronic kidney disease, obstructive sleep apnea, osteoporosis, psoriasis, colorectal cancer, iron overload and various endocrinopathies (e.g. type 2 diabetes mellitus, thyroid dysfunction, and polycystic ovarian syndrome). Due to the systemic manifestations of NAFLD patients require a multidisciplinary assessment and may benefit from more rigorous surveillance and early treatment interventions to decrease mortality related to malignancy or cardiometabolic diseases.

Managing Sleep Disturbances in Cirrhosis

Sleep disturbances, particularly daytime sleepiness and insomnia, are common problems reported by patients suffering from liver cirrhosis. Poor sleep negatively impacts patients' quality of life and cognitive functions and increases mortality. Although sleep disturbances can be an early sign of hepatic encephalopathy (HE), many patients without HE still complain of poor quality sleep. The pathophysiology of these disturbances is not fully understood but is believed to be linked to impaired hepatic melatonin metabolism. This paper provides an overview for the clinician of common comorbidities contributing to poor sleep in patients with liver disease, mainly restless leg syndrome and obstructive sleep apnea. It discusses nondrug and pharmacologic treatment options in these patients, such as the use of light therapy and histamine (H1) blockers.

Obstructive Sleep Apnea Is Associated with Liver Damage and Atherosclerosis in Patients with Non-Alcoholic Fatty Liver Disease

Background/Aims

We assessed whether obstructive sleep apnea (OSA) and nocturnal hypoxemia are associated with severity of liver fibrosis and carotid atherosclerosis in patients with biopsy-proven NAFLD and low prevalence of morbid obesity. Secondary aim was to explore the association of OSA and hypoxemia with NASH and severity of liver pathological changes.

Methods

Consecutive patients (n = 126) with chronically elevated ALT and NAFLD underwent STOP-BANG questionnaire to estimate OSA risk and ultrasonographic carotid assessment. In patients accepting to perform cardiorespiratory polygraphy (PG, n = 50), OSA was defined as an apnea/hypopnea index ≥5. A carotid atherosclerotic plaque was defined as a focal thickening >1.3 mm.

Results

Prevalence of high OSA risk was similar in patients refusing or accepting PG (76% vs 68%, p = 0.17). Among those accepting PG, overall OSA prevalence was significantly higher in patients with F2-F4 fibrosis compared to those without (72% vs 44%; p = 0.04). Significant fibrosis was independently associated with mean nocturnal oxygen saturation (SaO₂)<95% (OR 3.21, 95%C.I. 1.02–7.34; p = 0.04). Prevalence of OSA tended to be higher in patients with, than in those without, carotid plaques (64% vs 40%; p = 0.08). Carotid plaques were independently associated with %time at SaO2<90% >1 (OR 6.30, 95%C.I. 1.02–12.3; p = 0.01).

Conclusions

In NAFLD patients with chronically elevated ALT at low prevalence of morbid obesity, OSA was highly prevalent and indexes of SaO₂ resulted independently associated with severity of liver fibrosis and carotid atherosclerosis. These data suggest to consider sleep disordered breathing as a potential additional therapeutic target in severe NAFLD patients.

Association Between the Severity of Nocturnal Hypoxia in Obstructive Sleep Apnea and Non-Alcoholic Fatty Liver Damage

BACKGROUND

Obstructive sleep apnea (OSA) is a major disease that can cause significant mortality and morbidity. Chronic intermittent hypoxia is a potential causal factor in the progression from fatty liver to nonalcoholic steatohepatitis.

OBJECTIVES

This study evaluated the association between the degree of liver steatosis and severity of nocturnal hypoxia.

PATIENTS AND METHODS

In this study, between December 2011 and December 2013, patients with ultrasound-diagnosed NAFLD evaluated by standart polysomnography were subsequentally recorded. Patients with alcohol use, viral hepatitis and other chronic liver diseases were excluded. We analyzed polysomnographic parameters, steatosis level and severity of obstructive sleep apnea (OSA) in consideration of body mass index (BMI), biochemical tests and ultrasonographic liver data of 137 subjects. Patients with sleep apnea and AHI scores of < 5, 5 - 14, 15 - 29 and ≥30 are categorized as control, mild, moderate and severe, respectively.

RESULTS

One hundred and thirty-seven patients (76 women, 61 men) with a mean age of 55.75 ± 10.13 years who underwent polysomnography were included in the study. Of 118 patients diagnosed with OSA, 19 (16.1%) had mild OSA, 39 (33.1%) moderate OSA and 60 (50.8%) severe OSA. Nineteen cases formed the control group. Apnea/hypopnea index and oxygen desaturation index (ODI) values were significantly higher in moderate and severe non-alcoholic fatty liver disease (NAFLD) compared to the non-NAFLD group. Mean nocturnal SpO2 values were significantly lower in mild NAFLD and severe NAFLD compared to the non-NAFLD group. Lowest O2 saturation (LaSO2) was found low in mild, moderate and severe NAFLD compared to the non-NAFLD group in a statistically significant manner.

CONCLUSIONS

We assessed polysomnographic parameters of AHI, ODI, LaSO2 and mean nocturnal SpO2 levels, which are especially important in the association between NAFLD and OSAS. We think that it is necessary to be attentive regarding NAFLD development and progression in patients with OSA whose nocturnal hypoxia is severe.

Elevated Serum Liver Enzymes in Patients with Obstructive Sleep Apnea-hypopnea Syndrome

BACKGROUND

Obstructive sleep apnea-hypopnea syndrome (OSAS) is associated with elevated liver enzymes and fatty liver. The purpose of this study was to measure serum liver enzyme levels in patients evaluated by polysomnography (PSG) and the factors associated with liver injury in OSAS patients.

METHODS

All patients referred to PSG for evaluation of sleep apnea symptoms between June 2011 and November 2014 were included in this study. Demographic data and PSG parameters were recorded. Serum alanine aminotransferase, aspartate aminotransferase, and gamma-glutamyl transferase levels were systematically measured. OSAS patients were divided into mild, moderate, and severe groups according to the apnea-hypopnea index (AHI) values of 5-14 events/h, 15-29 events/h, and ≥30 events/h.

RESULTS

A total of 540 patients were enrolled in this study; among these patients, 386 were male. Elevated liver enzymes were present in 42.3% of OSAS patients (32.4% in mild/moderate group; 51.0% in severe group) and 28.1% patients without OSAS. Patients with OSAS had higher body mass index (BMI) (P < 0.01). In the bivariate correlation, the liver enzymes level was negatively correlated with age and the lowest arterial oxygen saturation (SaO 2 ), and was positively correlated with BMI, oxygen desaturation index, percent of total time with oxygen saturation level <90% (TS90%), AHI, total cholesterol (TC), and triglyceride (TG). In logistic regression analysis, Age, BMI, TS90%, TC, and TG were included in the regression equation.

CONCLUSIONS

Our data suggest that OSAS is a risk factor for elevated liver enzymes. The severity of OSAS is correlated with liver enzyme levels; we hypothesize that hypoxia is one of main causes of liver damage in patients with OSAS.

Clinical manifestations of sleep apnea

Obstructive sleep apnea (OSA) may manifest in a number of ways from subtle intrusion into daily life to profound sleepiness, snoring, witnessed apneas and other classic symptoms. Although there is increasing evidence suggesting OSA can adversely affect health in a variety of ways, this disorder remains underdiagnosed. The most well-escribed health consequences of OSA relate to the cardiovascular system. Hypertension and arrhythmias have a strong association with OSA, and evidence suggests that treatment of OSA in patients with refractory hypertension and in patients planning cardioversion for atrial fibrillation may be of particularly importance. Significant associations between heart failure and OSA as well as complex sleep apnea have also been well-described. Cerebrovascular insult, impaired neurocognition, and poorly controlled mood disorder are also associated with in OSA. Therapy for OSA may ameliorate atherosclerotic progression and improve outcomes post-cerebrovascular accident (CVA). OSA should be considered in patients complaining of poor concentration at work, actual or near-miss motor vehicle accidents, and patients with severe sleepiness as a component of their co-morbid mood disorders. The metabolic impact of OSA has also been studied, particularly in relation to glucose homeostasis. Also of interest is the potential impact OSA has on lipid metabolism. The adverse effect untreated OSA has on glucose tolerance and lipid levels has led to the suggestion that OSA is yet another constituent of the metabolic syndrome. Some of these metabolic derangements may be related to the adverse effects untreated OSA has on hepatic health. The cardiovascular, neurocognitive, and metabolic manifestations of OSA can have a significant impact on patient health and quality of life. In many instances, evidence exists that therapy not only improves outcomes in general, but also modifies the severity of co-morbid disease. To mitigate the long-term sequela of this disease, providers should be aware of the subtle manifestations of OSA and order appropriate testing as necessary.

Obstructive sleep apnea with excessive daytime sleepiness is associated with non-alcoholic fatty liver disease regardless of visceral fat

BACKGROUND/AIMS

Obstructive sleep apnea (OSA) is associated with an increased risk of obesity and non-alcoholic fatty liver disease (NAFLD), but it remains unclear whether the risk of NAFLD is independently related to OSA regardless of visceral obesity. Thus, the aim of the present study was to examine whether OSA alone or in combination with excessive daytime sleepiness (EDS) or short sleep duration was associated with NAFLD independent of visceral fat in Korean adults.

METHODS

A total of 621 participants were selected from the Korean Genome and Epidemiology Study (KoGES). The abdominal visceral fat area (VFA) and hepatic fat components of the participants were assessed using computed tomography scans and they were then categorized into four groups depending on the presence of OSA and EDS.

RESULTS

The proportions of NAFLD were 21.1%, 18.5%, 32.4%, and 46.7% in participants without OSA/EDS, with only EDS, with only OSA, and with both OSA and EDS, respectively. A combination of OSA and EDS increased the odds ratio (OR) for developing NAFLD (OR, 2.75; 95% confidence interval [CI], 1.21 to 6.28) compared to those without OSA/EDS, and this association remained significant (OR, 2.38; 95% CI, 1.01 to 5.59) even after adjusting for VFA. In short sleepers (< 5 hours) with OSA, the adjusted OR for NAFLD was 2.50 (95% CI, 1.08 to 5.75) compared to those sleeping longer than 5 hours without OSA.

CONCLUSIONS

In the present study, OSA was closely associated with NAFLD in Korean adults. This association was particularly strong in those with EDS or short sleep duration regardless of VFA.

Obstructive Sleep Apnea Is Associated with Nonalcoholic Steatohepatitis and Advanced Liver Histology

BACKGROUND AND AIMS

Nonalcoholic fatty liver disease (NAFLD) and obstructive sleep apnea (OSA) are growing in prevalence in the USA. Existing data on the relationship between OSA and NAFLD are conflicting and limited by the use of various histologic definitions of nonalcoholic steatohepatitis (NASH). Using a robust definition of NASH in a large, well-characterized cohort, we sought to evaluate whether OSA was associated with NASH and advanced fibrosis.

METHODS

Two hundred and thirteen subjects undergoing weight loss surgery were queried for OSA and then underwent liver biopsy. NASH was defined, as recommended by the American Association for the Study of Liver Disease, by the presence of all of the following: >5 % macrovesicular steatosis, lobular inflammation, and hepatocyte ballooning. NAFLD activity score (NAS) was also determined for each subject.

RESULTS

Subjects with OSA had significantly higher alanine and aspartate aminotransferase levels than subjects without OSA (ALT 54.1 vs. 37.7 U/L, P = 0.0007; AST 31.7 vs. 20.5 U/L, P = 0.0007). OSA was associated with the presence of NASH, and this remained significant after adjusting for age, gender, race, and diabetes mellitus (P = 0.03 OR 2.01; 95 %, 1.05-3.87). Steatosis grade, lobular inflammation grade, NAS score, and fibrosis stage were all significantly associated with the presence of OSA and remained so after adjustment.

CONCLUSIONS

OSA is associated with elevated aminotransferase levels, the presence of NASH, and advanced NASH histology. Further studies are needed to evaluate the impact of OSA treatment on NASH.

Relationship between obstructive sleep apnea and nonalcoholic fatty liver disease in nonobese adults

PURPOSE

Obstructive sleep apnea (OSA) is closely related to nonalcoholic fatty liver disease (NAFLD), though the mechanism is not conclusive as obesity is a confounder. The objective of this observational study was to investigate the correlation between these disorders in nonobese subjects.

METHODS

We consecutively enrolled nonobese individuals undergoing polysomnography and abdominal ultrasonography and analyzed differences in NAFLD patients grouped by the apnea-hypopnea index (AHI) and in OSA patients according to the presence or absence of NAFLD. Multivariate regression analysis was used to evaluate the independent risks of NAFLD in OSA patients.

RESULTS

A total of 175 participants were included. The 106 ultrasound-diagnosed NAFLD patients were classified into four groups by AHI. There were no significant differences in triglycerides (TG), serum aminotransferase levels of alanine aminotransferase and aspartate aminotransferase, high-sensitivity C-reactive protein, and homeostasis model assessment of insulin resistance (HOMA-IR) with worsening OSA. In both OSA patients with NAFLD and those without NAFLD, body mass index (BMI), the lowest oxygen saturation (LaSO2), HOMA-IR, and TG were significantly associated. Additionally, BMI, LaSO2, and TG independently predicted the development of NAFLD after adjustments (odds ratio [OR] = 1.562, p = 0.003; OR = 0.960, p = 0.03; OR = 3.410, p < 0.001, respectively).

CONCLUSIONS

In nonobese subjects, OSA itself does not appear to induce significant changes in liver enzymes. With reference to lipid metabolism, weight control and OSA-related hypoxemia are key factors in reducing the risk of NAFLD in OSA patients. Additional large-scale, prospective studies are warranted to investigate the impact of OSA on liver injury in nonobese adults.

Impact of Obstructive Sleep Apnea on Liver Fat Accumulation According to Sex and Visceral Obesity

Rationale

Associations between obstructive sleep apnea (OSA) and liver fat accumulation have been frequently investigated because both morbidities are common. Visceral fat was reported to be closely related to OSA and liver fat accumulation. Recently, sex differences in the association between OSA and mortality have gained much attention.

Objectives

To investigate the associations among OSA, liver fat accumulation as determined by computed tomography, and visceral fat area and their sex differences.

Methods

Studied were 188 males and 62 females who consecutively underwent polysomnography and computed tomography.

Results

Although the apnea-hypopnea index was positively correlated with liver fat accumulation in the total males, none of the OSA-related factors was independently associated with liver fat accumulation in either the total male or female participants in the multivariate analyses. When performing subanalyses using a specific definition for Japanese of obesity or visceral obesity (body mass index (BMI) ≥25 kg/m² or visceral fat area ≥100 cm²), in only males without visceral obesity, percent sleep time with oxygen saturation <90%, in addition to BMI, insulin resistance, and serum triglyceride values, was independently correlated with liver fat accumulation (R² = 15.1%, P<0.001). In males, percent sleep time of oxygen saturation <90% was also a determining factor for alanine aminotransferase values regardless of visceral fat area. In contrast, OSA was not associated with liver fat accumulation or alanine aminotransferase values in females whether or not visceral obesity was absent.

Conclusions

Sex differences in the visceral fat-dependent impact of OSA on liver fat accumulation existed. Although the mechanisms are not known and ethnic differences may exist in addition to the specific criteria of visceral obesity in Japan, the treatment of male patients with OSA might be favorable from the viewpoint of preventing liver fat accumulation and liver dysfunction even in patients without obvious visceral fat accumulation.

Antioxidants inhibit the inflammatory and apoptotic processes in an intermittent hypoxia model of sleep apnea

BACKGROUND

Sleep apnea causes intermittent hypoxia (IH). We aimed to investigate the proteins related to oxidative stress, inflammation and apoptosis in liver tissue subjected to IH as a simulation of sleep apnea in conjunction with the administration of either melatonin (MEL, 200 μL/kg) or N-acetylcysteine (NAC, 10 mg/kg).

METHODS

Seventy-two adult male Balb-C mice were divided: simulation of IH (SIH), SIH + MEL, SIH + NAC, IH, IH + MEL and IH + NAC. The animals were subjected to simulations of sleep apnea for 8 h a day for 35 days. The data were analyzed with ANOVA and Tukey tests with the significance set at p < 0.05.

RESULTS

In IH, there was a significant increase in oxidative stress and expression of HIF-1a. In addition, we observed increase in the activation levels of NF-kB. This increase may be responsible for the increased expression of TNF-alpha and iNOS as well as the significant increase of VEGF signaling and expression of caspase-3 and caspase-6, which suggests an increase in apoptosis. In the groups treated with antioxidants, the analysis showed that the enzyme activity and protein levels were similar to those of the non-simulated group.

CONCLUSIONS

Thus, we show that IH causes liver inflammation and apoptosis, which may be protected with either MEL or NAC.

Hypoxia and fatty liver

The liver is a central organ that metabolizes excessive nutrients for storage in the form of glycogen and lipids and supplies energy-producing substrates to the peripheral tissues to maintain their function, even under starved conditions. These processes require a considerable amount of oxygen, which causes a steep oxygen gradient throughout the hepatic lobules. Alcohol consumption and/or excessive food intake can alter the hepatic metabolic balance drastically, which can precipitate fatty liver disease, a major cause of chronic liver diseases worldwide, ranging from simple steatosis, through steatohepatitis and hepatic fibrosis, to liver cirrhosis. Altered hepatic metabolism and tissue remodeling in fatty liver disease further disrupt hepatic oxygen homeostasis, resulting in severe liver hypoxia. As master regulators of adaptive responses to hypoxic stress, hypoxia-inducible factors (HIFs) modulate various cellular and organ functions, including erythropoiesis, angiogenesis, metabolic demand, and cell survival, by activating their target genes during fetal development and also in many disease conditions such as cancer, heart failure, and diabetes. In the past decade, it has become clear that HIFs serve as key factors in the regulation of lipid metabolism and fatty liver formation. This review discusses the molecular mechanisms by which hypoxia and HIFs regulate lipid metabolism in the development and progression of fatty liver disease.

Sleep apnea and fatty liver disease: The growing link and management issues

Obstructive sleep apnea (OSA) is associated with metabolic, cardiovascular and neuropsychological disorders, with substantial morbidity and economic costs. OSA has been estimated to affect 4%-11% of the population, depending on age. Obesity is a significant risk factor for OSA. Non alcoholic fatty liver disease (NAFLD) has emerged as an integral component of the metabolic syndrome, with insulin resistance as the central pathogenic feature. Estimates based on imaging and autopsy studies suggest that about 20%-30% of adults in the United States and other Western countries have NAFLD. Evidence now suggests that NAFLD is independently correlated to insulin resistance regardless of adiposity. Some authors have suggested that OSA may be another contributor to NAFLD development. In complex diseases, several or many different genes interact with environmental factors in determining disease presence or its phenotype. Individual genes only have a small effect on disease risk and can therefore be very difficult to identify. The genetic and hormonal determinants of OSA and NAFLD have received little attention. A wide variety of intermediate phenotypes and genes are involved in OSA and NAFLD which makes this syndrome genetically complex. Various adipokines, the most important of which are leptin, adiponectin, tumor necrosis factor-alpha, resistin and interleukin-6, have a key role in NAFLD and OSA. Some studies have suggested that oxidative stress may also contribute to the development of NAFLD and OSA. Lifestyle intervention, insulin sensitizer drugs and bariatric surgery aim to improve metabolic syndrome, OSA and NAFLD but need further investigation.

Obstructive sleep apnea is associated with fatty liver and abnormal liver enzymes: a meta-analysis

BACKGROUND

Obstructive sleep apnea (OSA) is associated with the cluster of clinical conditions that comprise the metabolic syndrome, including nonalcoholic fatty liver disease (NAFLD). Our primary purpose was to estimate the effect of OSA on serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Our secondary purpose was to investigate the potential influence of OSA on histological severity of NAFLD to explore whether chronic intermittent hypoxia is associated with inflammation and fibrosis.

METHODS

Our literature search identified 11 studies, from which we extracted information about numbers of control subjects and OSA patients, and ALT, AST, and NAFLD.

RESULTS

From a total of 668 OSA patients and 404 controls, we found that the standardized difference in mean values of ALT and AST levels in patients with OSA was significantly different from that in the controls. Meta-regression showed that the association was independent of body mass index and type 2 diabetes. Fatty liver was associated with OSA in five studies with 400 subjects. OSA was significantly associated with liver fibrosis in 208 subjects, but not with lobular inflammation.

CONCLUSIONS

Routine assessment of liver enzymes and liver damage should be implemented in OSA patients because they have an increase of 13.3% of ALT and 4.4% of AST levels, and a 2.6-fold higher risk of liver fibrosis when they have NAFLD, which is 2.6 times more frequent in OSA patients.

Obstructive sleep apnea is associated with fatty liver and abnormal liver enzymes: a meta-analysis

BACKGROUND

Obstructive sleep apnea (OSA) is associated with the cluster of clinical conditions that comprise the metabolic syndrome, including nonalcoholic fatty liver disease (NAFLD). Our primary purpose was to estimate the effect of OSA on serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Our secondary purpose was to investigate the potential influence of OSA on histological severity of NAFLD to explore whether chronic intermittent hypoxia is associated with inflammation and fibrosis.

METHODS

Our literature search identified 11 studies, from which we extracted information about numbers of control subjects and OSA patients, and ALT, AST, and NAFLD.

RESULTS

From a total of 668 OSA patients and 404 controls, we found that the standardized difference in mean values of ALT and AST levels in patients with OSA was significantly different from that in the controls. Meta-regression showed that the association was independent of body mass index and type 2 diabetes. Fatty liver was associated with OSA in five studies with 400 subjects. OSA was significantly associated with liver fibrosis in 208 subjects, but not with lobular inflammation.

CONCLUSIONS

Routine assessment of liver enzymes and liver damage should be implemented in OSA patients because they have an increase of 13.3% of ALT and 4.4% of AST levels, and a 2.6-fold higher risk of liver fibrosis when they have NAFLD, which is 2.6 times more frequent in OSA patients.

Nonalcoholic fatty liver disease, nocturnal hypoxia, and endothelial function in patients with sleep apnea

BACKGROUND

Nocturnal hypoxia, the hallmark of OSA, is a potential contributing factor for nonalcoholic fatty liver disease (NAFLD). NAFLD severity and its implication in OSA-related endothelial dysfunction have not been investigated in a large, unselected OSA population, including nonobese subjects.

METHODS

Noninvasive blood tests (SteatoTest, NashTest, and FibroTest) were used to evaluate steatosis, nonalcoholic steatohepatitis (NASH), and fibrosis in a large cohort of patients with OSA. In the same group, endothelial function and its links with NAFLD severity were assessed.

RESULTS

Of the 226 subjects included who were referred for suspicion of OSA (men, 55%; median age, 56 years; median BMI, 34.2 kg/m2 [33% with BMI<30 kg/m2]), 61.5% exhibited moderate or severe steatosis. By multivariate analysis, independent factors for liver steatosis were, as expected, triglyceride levels (P<.0001) and insulin resistance (P=.0004) as well as nocturnal cumulative time spent<90% of oxygen saturation (CT90) (P=.01). Thirty-eight percent had borderline or possible NASH (N1 or N2 with NashTest). CT90 was significantly associated with borderline or possible NASH (P=.035) in univariate but not in multivariate analysis. The dose-response relationship between the severity of nocturnal hypoxia and liver injury was established only in morbid obesity and not in lean. Multivariate models showed that steatosis was independently associated with endothelial dysfunction after adjustment for confounders.

CONCLUSIONS

In a large, unselected OSA population, the severity of nocturnal hypoxia was independently associated with steatosis. Preexisting obesity exacerbated the effects of nocturnal hypoxemia. NAFLD is a potential mechanism of endothelial dysfunction in OSA.

Obstructive sleep apnea and hypoxemia are associated with advanced liver histology in pediatric nonalcoholic fatty liver disease

OBJECTIVE

To determine whether obstructive sleep apnea (OSA) and/or nocturnal hypoxemia are associated with the severity of liver injury in patients with pediatric nonalcoholic fatty liver disease (NAFLD).

STUDY DESIGN

Obese children aged 10-18 years with liver biopsy-proven NAFLD were enrolled. Demographic, clinical, and laboratory data were collected, polysomnography was performed, and liver histology was scored. Subjects were divided into those with OSA/hypoxemia and those without OSA/hypoxemia for analysis.

RESULTS

Of 25 subjects with NAFLD, OSA/hypoxemia was present in 15 (60%) (mean age, 12.8 ± 1.9 years; 68% male; 88% Hispanic; mean body mass index z-score, 2.3 ± 0.3). Subjects with and without OSA/hypoxemia had similar levels of serum aminotransferases, serum lipids, and inflammatory and insulin resistance markers. Although there were no differences between groups in the histological severity of steatosis, inflammation, ballooning degeneration, NAFLD activity score, or histological grade, subjects with OSA/hypoxemia had significantly more severe hepatic fibrosis. Moreover, oxygen saturation nadir during polysomnography was related to hepatic fibrosis stage (r = -0.49; P = .01) and aspartate aminotransferase level (r = 0.42; P < .05). Increasing percentage of time with oxygen saturation ≤90% was related to NAFLD inflammation grade (r = 0.44; P = .03), degree of hepatic steatosis (r = -0.50; P = .01), NAFLD activity score (r = 0.42; P = .04), aspartate aminotransferase level (r = 0.56; P = .004), and alanine aminotransferase level (r = 0.44; P = .03).

CONCLUSION

Moderate OSA/hypoxemia is common in pediatric patients with biopsy-proven NAFLD. OSA and the severity/duration of hypoxemia are associated with biochemical and histological measures of NAFLD severity.

Association of obstructive sleep apnoea with the presence and severity of non-alcoholic fatty liver disease. A systematic review and meta-analysis

Obstructive sleep apnoea syndrome (OSAS) and non-alcoholic fatty liver disease (NAFLD) are common in clinical practice. NAFLD encompasses simple steatosis and non-alcoholic steatohepatitis (NASH): both confer an increased risk of cardiovascular disease and diabetes; NASH increases also liver-related risk. Growing experimental evidence connects chronic intermittent hypoxia of OSAS to NAFLD. We reviewed English and non-English articles and international meeting abstracts through December 2012. Observational studies were included if they assessed OSAS by polysomnography and NAFLD by histological, radiological or biochemical criteria. Two reviewers evaluated retrieved articles by appropriate quality scores. Main outcomes were pooled using random- or fixed-effects models. The effect of age, sex and body mass index (BMI) on effect estimates was assessed by meta-regression. Eighteen cross-sectional studies (2,183 participants) were included. Pooled odds ratios (ORs) of OSAS for the presence of NAFLD, as defined by histology, radiology, and AST or ALT elevation, were 2.01(95% CI: 1.36-2.97), 2.99(1.79-4.99), 2.36(1.46-3.82) and 2.60(1.88-3.61), respectively. Pooled ORs of OSAS for NASH, fibrosis-any stage, or advanced fibrosis in biopsy-proven NAFLD patients were 2.37(1.59-3.51), 2.16(1.45-3.20) and 2.30(1.21-4.38). The magnitude and direction of effects were unaffected by age, sex and BMI. In conclusion, OSAS is associated with an increased risk of NAFLD, NASH and fibrosis. OSAS patients should be screened for the presence and severity of NAFLD.

Simulating sleep apnea by exposure to intermittent hypoxia induces inflammation in the lung and liver

Sleep apnea is a breathing disorder that results from momentary and cyclic collapse of the upper airway, leading to intermittent hypoxia (IH). IH can lead to the formation of free radicals that increase oxidative stress, and this mechanism may explain the association between central sleep apnea and nonalcoholic steatohepatitis. We assessed the level of inflammation in the lung and liver tissue from animals subjected to intermittent hypoxia and simulated sleep apnea. A total of 12 C57BL/6 mice were divided into two groups and then exposed to IH (n = 6) or a simulated IH (SIH) (n = 6) for 35 days. We observed an increase in oxidative damage and other changes to endogenous antioxidant enzymes in mice exposed to IH. Specifically, the expression of multiple transcription factors, including hypoxia inducible factor (HIF-1α), nuclear factor kappa B (NF-κB), and tumor necrosis factor (TNF-α), inducible NO synthase (iNOS), vascular endothelial growth factor (VEGF), and cleaved caspase 3 were shown to be increased in the IH group. Overall, we found that exposure to intermittent hypoxia for 35 days by simulating sleep apnea leads to oxidative stress, inflammation, and increased activity of caspase 3 in the liver and lung.

Obstructive sleep apnea and non-alcoholic Fatty liver disease: is the liver another target?

Obstructive sleep apnea (OSA) is recurrent obstruction of the upper airway during sleep leading to intermittent hypoxia (IH). OSA has been associated with all components of the metabolic syndrome as well as with non-alcoholic fatty liver disease (NAFLD). NAFLD is a common condition ranging in severity from uncomplicated hepatic steatosis to steatohepatitis (NASH), liver fibrosis, and cirrhosis. The gold standard for the diagnosis and staging of NAFLD is liver biopsy. Obesity and insulin resistance lead to liver steatosis, but the causes of the progression to NASH are not known. Emerging evidence suggests that OSA may play a role in the progression of hepatic steatosis and the development of NASH. Several cross-sectional studies showed that the severity of IH in patients with OSA predicted the severity of NAFLD on liver biopsy. However, neither prospective nor interventional studies with continuous positive airway pressure treatment have been performed. Studies in a mouse model showed that IH causes triglyceride accumulation in the liver and liver injury as well as hepatic inflammation. The mouse model provided insight in the pathogenesis of liver injury showing that (1) IH accelerates the progression of hepatic steatosis by inducing adipose tissue lipolysis and increasing free fatty acids (FFA) flux into the liver; (2) IH up-regulates lipid biosynthetic pathways in the liver; (3) IH induces oxidative stress in the liver; (4) IH up-regulates hypoxia inducible factor 1 alpha and possibly HIF-2 alpha, which may increase hepatic steatosis and induce liver inflammation and fibrosis. However, the role of FFA and different transcription factors in the pathogenesis of IH-induced NAFLD is yet to be established. Thus, multiple lines of evidence suggest that IH of OSA may contribute to the progression of NAFLD but definitive clinical studies and experiments in the mouse model have yet to be done.

Novel links between HIFs, type 2 diabetes, and metabolic syndrome

Hypoxia inducible factors (HIFs) are master-regulators of cellular responses to hypoxia, and thus are crucial for survival. HIFs also play a role in regulating cellular processes in β-cells, liver, muscle, and adipose tissue, have effects on the regulation of weight, and play a role in type 2 diabetes (T2D). Indeed, in people with T2D the HIF pathway is dyregulated in major metabolic tissues involved in the pathogenesis of diabetes. This review covers the contrasting, complementary and conflicting effects of decreasing and increasing HIFs in various tissues, and shows that a delicate balance exists between HIF levels and optimal metabolic function. We propose that increasing the activity of HIFs might be a potential therapeutic strategy for treating T2D.

Hypoxia and hypoxia inducible factors: diverse roles in liver diseases

Hypoxia has been shown to have a role in the pathogenesis of several forms of liver disease. The hypoxia inducible factors (HIFs) are a family of evolutionarily conserved transcriptional regulators that affect a homeostatic response to low oxygen tension and have been identified as key mediators of angiogenesis, inflammation, and metabolism. In this review we summarize the evidence for a role of HIFs across a range of hepatic pathophysiology. We describe regulation of the HIFs and review investigations that demonstrate a role for HIFs in the development of liver fibrosis, activation of innate immune pathways, hepatocellular carcinoma, as well as other liver diseases in both human disease as well as murine models.

Hypoxia and hypoxia inducible factors: diverse roles in liver diseases

Hypoxia has been shown to have a role in the pathogenesis of several forms of liver disease. The hypoxia inducible factors (HIFs) are a family of evolutionarily conserved transcriptional regulators that affect a homeostatic response to low oxygen tension and have been identified as key mediators of angiogenesis, inflammation, and metabolism. In this review we summarize the evidence for a role of HIFs across a range of hepatic pathophysiology. We describe regulation of the HIFs and review investigations that demonstrate a role for HIFs in the development of liver fibrosis, activation of innate immune pathways, hepatocellular carcinoma, as well as other liver diseases in both human disease as well as murine models.

Nonalcoholic steatohepatitis in bariatric patients with a diagnosis of obstructive sleep apnea

OBJECTIVE

To study a possible association between obstructive sleep apnea (OSA) severity, managed with noninvasive ventilation, and nonalcoholic steatohepatitis (NASH) in bariatric surgical patients.

METHODS

Medical records of 218 bariatric surgical patients who underwent liver biopsy were reviewed. OSA severity was determined from preoperative polysomnography (apnea-hypopnea index (AHI) ≤ 15 no/mild OSA vs. AHI ≥ 16 moderate/severe OSA). Patients diagnosed with OSA were prescribed noninvasive ventilation. Patients were categorized according to liver histopathology into 3 groups: (i) no liver disease or simple steatosis, (ii) mild NASH (steatosis with necroinflammation and mild fibrosis (stage 0-1)), and iii) advanced NASH (steatosis with necroinflammation and more advanced fibrosis (stage ≥ 2)).

RESULTS

125 patients (57%) had no/mild OSA, and 93 (43%) had moderate/severe OSA. There was no difference in serum aminotransferases between patients by OSA severity classification. There was a high prevalence of hepatic histopathological abnormalities: 84% patients had steatosis, 57% had necroinflammation, 34% had fibrotic changes, and 14% had advanced NASH. There was no association between severity of NASH and severity of OSA.

CONCLUSIONS

There is no association between stage of steatohepatitis and OSA severity among morbidly obese patients managed with noninvasive ventilation.

Chronic intermittent hypoxia is a major trigger for non-alcoholic fatty liver disease in morbid obese

BACKGROUND & AIMS

Morbid obesity is frequently associated with low grade systemic inflammation, increased macrophage accumulation in adipose tissue (AT), obstructive sleep apnea (OSA), and nonalcoholic fatty liver disease (NAFLD). It has been suggested that chronic intermittent hypoxia (CIH) resulting from OSA could be an independent factor for early stage of NAFLD in addition to other well-recognized factors (dyslipidemia or insulin resistance). Moreover, macrophage accumulation in AT is associated with local hypoxia in fat tissue. We hypothesized that the association between CIH and morbid obesity could exert additional specific deleterious effects both in the liver and adipose tissues.

METHODS

One hundred and one morbidly obese subjects were prospectively recruited and underwent bariatric surgery during which a liver needle biopsy as well as surgical subcutaneous and omental AT biopsies were obtained. Oxygen desaturation index (ODI) quantified the severity of nocturnal CIH.

RESULTS

Histopathologic analysis of liver biopsies demonstrated that NAFLD lesions (ballooning of hepatocytes, lobular inflammation), NAFLD activity score (NAS), and fibrosis were significantly more severe in patients with the highest ODI tertile (p values ≤0.001 for all hepatic lesions). In multivariate analysis, after adjustment for age, obesity, and insulin resistance status, CIH remained independently associated with hepatic fibrosis, fibroinflammation, and NAS. By contrast, no association was found between CIH, macrophage accumulation, and adipocytes size in both subcutaneous and omental adipose tissue.

CONCLUSIONS

In morbidly obese patients, CIH was strongly associated with more severe liver injuries but did not worsen obesity induced macrophage accumulation in adipose tissue depots.