The role of mitochondrial genomics in patients with non-alcoholic steatohepatitis (NASH)

Non-alcoholic Steatohepatitis in Asians: Current Perspectives and Future Directions

Non-alcoholic steatohepatitis (NASH) is a subset of non-alcoholic fatty liver disease (NAFLD), which, apart from excess fat in the liver, may be characterised by some level of inflammatory infiltration and fibrogenesis, occasionally progressing to liver cirrhosis or hepatocellular carcinoma (HCC). The objective of the current review is to elucidate the rising prevalence, the role of microbiome and genetics in pathogenesis, diagnostic challenges, and novel treatment alternatives for NASH. Newer diagnostic techniques are being developed since using liver biopsy in a larger population is not a reasonable option and is primarily restricted to clinical research, at least in developing countries. Besides these technical challenges, another important factor leading to deviation from guideline practice is the lack of health insurance coverage in countries like India. It leads to reluctance on the part of physicians and patients to delay required tests to curb out-of-pocket expenditure. There is no cure for NASH, with liver transplantation remaining the last option for those who progress to end-stage liver disease (ESLD) or are detected with early-stage HCC. Thus, lifestyle modification remains the only viable option for many, but compliance and long-term adherence remain major challenges. In obese individuals, bariatric surgery and weight reduction have shown favourable results. In patients with less severe obesity, endoscopic bariatric metabolic therapies (EBMT) are rapidly emerging as less invasive therapies. However, access and acceptability remain poor for these weight reduction methods. Therefore, intense research is being conducted for potential newer drug classes with several agents currently in phase II or III of clinical development. Some of these have demonstrated promising results, such as a reduction in hepatic fat content, and attenuation of fibrosis with an acceptable tolerability profile in phase II studies. The developments in the management of NASH have been fairly encouraging. Further well-designed long-term prospective studies should be undertaken to generate evidence with definitive results.

Mitochondrial DNA methylation in metabolic associated fatty liver disease

Introduction

Hepatic lipid accumulation and mitochondrial dysfunction are hallmarks of metabolic associated fatty liver disease (MAFLD), yet molecular parameters underlying MAFLD progression are not well understood. Differential methylation within the mitochondrial DNA (mtDNA) has been suggested to be associated with dysfunctional mitochondria, also during progression to Metabolic Steatohepatitis (MeSH). This study further investigates whether mtDNA methylation is associated with hepatic lipid accumulation and MAFLD.

Methods

HepG2 cells were constructed to stably express mitochondria-targeted viral and prokaryotic cytosine DNA methyltransferases (mtM.CviPI or mtM.SssI for GpC or CpG methylation, respectively). A catalytically inactive variant (mtM.CviPI-Mut) was constructed as a control. Mouse and human patients' samples were also investigated. mtDNA methylation was assessed by pyro- or nanopore sequencing.

Results and discussion

Differentially induced mtDNA hypermethylation impaired mitochondrial gene expression and metabolic activity in HepG2-mtM.CviPI and HepG2-mtM.SssI cells and was associated with increased lipid accumulation, when compared to the controls. To test whether lipid accumulation causes mtDNA methylation, HepG2 cells were subjected to 1 or 2 weeks of fatty acid treatment, but no clear differences in mtDNA methylation were detected. In contrast, hepatic Nd6 mitochondrial gene body cytosine methylation and Nd6 gene expression were increased in mice fed a high-fat high cholesterol diet (HFC for 6 or 20 weeks), when compared to controls, while mtDNA content was unchanged. For patients with simple steatosis, a higher ND6 methylation was confirmed using Methylation Specific PCR, but no additional distinctive cytosines could be identified using pyrosequencing. This study warrants further investigation into a role for mtDNA methylation in promoting mitochondrial dysfunction and impaired lipid metabolism in MAFLD.

Mitochondrial alterations in fatty liver diseases

Fatty liver diseases can result from common metabolic diseases, as well as from xenobiotic exposure and excessive alcohol use, all of which have been shown to exert toxic effects on hepatic mitochondrial functionality and dynamics. Invasive or complex methodology limits large-scale investigations of mitochondria in human livers. Nevertheless, abnormal mitochondrial function, such as impaired fatty acid oxidation and oxidative phosphorylation, drives oxidative stress and has been identified as an important feature of human steatohepatitis. On the other hand, hepatic mitochondria can be flexible and adapt to the ambient metabolic condition to prevent triglyceride and lipotoxin accumulation in obesity. Experience from studies on xenobiotics has provided important insights into the regulation of hepatic mitochondria. Increasing awareness of the joint presence of metabolic disease-related (lipotoxic) and alcohol-related liver diseases further highlights the need to better understand their mutual interaction and potentiation in disease progression. Recent clinical studies have assessed the effects of diets or bariatric surgery on hepatic mitochondria, which are also evolving as an interesting therapeutic target in non-alcoholic fatty liver disease. This review summarises the current knowledge on hepatic mitochondria with a focus on fatty liver diseases linked to obesity, type 2 diabetes and xenobiotics.

Attribution of diabetes to the development of severe liver disease in the general population

BACKGROUND AND AIMS

Diabetes is associated with advanced liver disease and predicts mortality regardless of the primary aetiology of the liver disease. Even a family history of diabetes has been linked to advanced liver fibrosis in non-alcoholic fatty liver disease (NAFLD). However, the fraction of liver-related outcomes in the general population that are attributable to diabetes remains unclear.

METHODS

The population attributable fraction (PAF) of diabetes for liver disease as a time-dependent exposure was estimated in the Finnish FINRISK study (n = 28 787) and the British Whitehall II study (n = 7855). We also assessed the predictive ability of a family history of diabetes for liver-related outcomes. Incident diabetes data were from drug purchase/reimbursement and healthcare registries (FINRISK) or follow-up examinations (Whitehall II). Incident severe liver outcomes were identified through linkage with national healthcare registries.

RESULTS

Diabetes was associated with a two-fold risk of liver-related outcomes in both the FINRISK (HR, 1.92; p < .001) and Whitehall II (HR, 2.37; p < .001) cohorts, and this remained significant after adjusting for multiple confounders. PAF analyses demonstrated that diabetes explained 12-14% of the risk for severe liver-related outcomes after 10 and 20 years of follow-up. Also, maternal diabetes increased the risk of liver-related outcomes in the FINRISK (HR, 1.43; p = .044) and Whitehall II (HR, 2.04; p = .051) cohorts.

CONCLUSION

Approximately 12%-14% of severe liver-related outcomes are attributable to diabetes at the population level. The association between maternal diabetes and liver disease might suggest a mitochondrial genetic mechanism.

Update on Non-Alcoholic Fatty Liver Disease-Associated Single Nucleotide Polymorphisms and Their Involvement in Liver Steatosis, Inflammation, and Fibrosis: A Narrative Review

Genetic factors are involved in the development, progression, and severity of NAFLD. Polymorphisms in genes regulating liver functions may increase liver susceptibility to NAFLD. Therefore, we conducted this literature study to present recent findings on NAFLD-associated polymorphisms from published articles in PubMed from 2016 to 2021. From 69 selected research articles, 20 genes and 34 SNPs were reported to be associated with NAFLD. These mutated genes affect NAFLD by promoting liver steatosis (PNPLA3, MBOAT7, TM2SF6, PTPRD, FNDC5, IL-1B, PPARGC1A, UCP2, TCF7L2, SAMM50, IL-6, AGTR1, and NNMT), inflammation (PNPLA3, TNF-α, AGTR1, IL-17A, IL-1B, PTPRD, and GATAD2A), and fibrosis (IL-1B, PNPLA3, MBOAT7, TCF7L2, GATAD2A, IL-6, NNMT, UCP, AGTR1, and TM2SF6). The identification of these genetic factors helps to better understand the pathogenesis pathways of NAFLD

It Is High Time Physicians Thought of Natural Products for Alleviating NAFLD. Is There Sufficient Evidence to Use Them?

Non-alcoholic fatty liver disease (NAFLD) is the most common form of liver disease all over the world due to the obesity pandemic; currently, therapeutic options for NAFLD are scarce, except for diet recommendations and physical activity. NAFLD is characterized by excessive accumulation of fat deposits (>5%) in the liver with subsequent inflammation and fibrosis. Studies in the literature show that insulin resistance (IR) may be considered as the key mechanism in the onset and progression of NAFLD. Recently, using natural products as an alternative approach in the treatment of NAFLD has drawn growing attention among physicians. In this review, the authors present the most recent randomized controlled trials (RCTs) and lines of evidence from animal models about the efficacy of nutraceutics in alleviating NAFLD. Among the most studied substances in the literature, the following molecules were chosen because of their presence in the literature of both clinical and preclinical studies: spirulina, oleuropein, garlic, berberine, resveratrol, curcumin, ginseng, glycyrrhizin, coffee, cocoa powder, epigallocatechin-3-gallate, and bromelain.

Nonalcoholic Fatty Liver Disease (NAFLD). Mitochondria as Players and Targets of Therapies?

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease and represents the hepatic expression of several metabolic abnormalities of high epidemiologic relevance. Fat accumulation in the hepatocytes results in cellular fragility and risk of progression toward necroinflammation, i.e., nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and eventually hepatocellular carcinoma. Several pathways contribute to fat accumulation and damage in the liver and can also involve the mitochondria, whose functional integrity is essential to maintain liver bioenergetics. In NAFLD/NASH, both structural and functional mitochondrial abnormalities occur and can involve mitochondrial electron transport chain, decreased mitochondrial β-oxidation of free fatty acids, excessive generation of reactive oxygen species, and lipid peroxidation. NASH is a major target of therapy, but there is no established single or combined treatment so far. Notably, translational and clinical studies point to mitochondria as future therapeutic targets in NAFLD since the prevention of mitochondrial damage could improve liver bioenergetics.

Mitochondrial Mutations and Genetic Factors Determining NAFLD Risk

NAFLD (non-alcoholic fatty liver disease) is a widespread liver disease that is often linked with other life-threatening ailments (metabolic syndrome, insulin resistance, diabetes, cardiovascular disease, atherosclerosis, obesity, and others) and canprogress to more severe forms, such as NASH (non-alcoholic steatohepatitis), cirrhosis, and HCC (hepatocellular carcinoma). In this review, we summarized and analyzed data about single nucleotide polymorphism sites, identified in genes related to NAFLD development and progression. Additionally, the causative role of mitochondrial mutations and mitophagy malfunctions in NAFLD is discussed. The role of mitochondria-related metabolites of the urea cycle as a new non-invasive NAFLD biomarker is discussed. While mitochondria DNA mutations and SNPs (single nucleotide polymorphisms) canbe used as effective diagnostic markers and target for treatments, age and ethnic specificity should be taken into account.

Remodeling of Mitochondrial Plasticity: The Key Switch from NAFLD/NASH to HCC

Hepatocellular carcinoma (HCC) is the most common primary malignancy of the liver and the third-leading cause of cancer-related mortality. Currently, the global burden of nonalcoholic fatty liver disease (NAFLD) has dramatically overcome both viral and alcohol hepatitis, thus becoming the main cause of HCC incidence. NAFLD pathogenesis is severely influenced by lifestyle and genetic predisposition. Mitochondria are highly dynamic organelles that may adapt in response to environment, genetics and epigenetics in the liver ("mitochondrial plasticity"). Mounting evidence highlights that mitochondrial dysfunction due to loss of mitochondrial flexibility may arise before overt NAFLD, and from the early stages of liver injury. Mitochondrial failure promotes not only hepatocellular damage, but also release signals (mito-DAMPs), which trigger inflammation and fibrosis, generating an adverse microenvironment in which several hepatocytes select anti-apoptotic programs and mutations that may allow survival and proliferation. Furthermore, one of the key events in malignant hepatocytes is represented by the remodeling of glucidic-lipidic metabolism combined with the reprogramming of mitochondrial functions, optimized to deal with energy demand. In sum, this review will discuss how mitochondrial defects may be translated into causative explanations of NAFLD-driven HCC, emphasizing future directions for research and for the development of potential preventive or curative strategies.

Mitochondrial dynamics and nonalcoholic fatty liver disease (NAFLD): new perspectives for a fairy-tale ending?

Nonalcoholic fatty liver disease (NAFLD) includes a broad spectrum of liver dysfunctions and it is predicted to become the primary cause of liver failure and hepatocellular carcinoma. Mitochondria are highly dynamic organelles involved in multiple metabolic/bioenergetic pathways in the liver. Emerging evidence outlined that hepatic mitochondria adapt in number and functionality in response to external cues, as high caloric intake and obesity, by modulating mitochondrial biogenesis, and maladaptive mitochondrial response has been described from the early stages of NAFLD. Indeed, mitochondrial plasticity is lost in progressive NAFLD and these organelles may assume an aberrant phenotype to drive or contribute to hepatocarcinogenesis. Severe alimentary regimen and physical exercise represent the cornerstone for NAFLD care, although the low patients' compliance is urging towards the discovery of novel pharmacological treatments. Mitochondrial-targeted drugs aimed to recover mitochondrial lifecycle and to modulate oxidative stress are becoming attractive molecules to be potentially introduced for NAFLD management. Although the path guiding the switch from bench to bedside remains tortuous, the study of mitochondrial dynamics is providing intriguing perspectives for future NAFLD healthcare.

Mitochondrial haplogroup G is associated with nonalcoholic fatty liver disease, while haplogroup A mitigates the effects of PNPLA3

Objectives

Mitochondrial dysfunction plays a pivotal role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). We hypothesized that mitochondrial DNA (mtDNA) haplogroups affect the risk of NAFLD in Han Chinese patients and interact with PNPLA3 genotypes.

Design

NAFLD and control patients were recruited from a tertiary care centre. The mitochondrial genome was amplified in overlapping segments and sequenced. Mitochondrial haplogroups were determined using Mitomaster. PNPLA3 rs738409 genotyping was performed using restriction fragment length polymorphism analysis.

Patients

We enrolled 655 NAFLD patients and 504 controls.

Results

More NAFLD patients encoded haplogroup G; odds ratio (OR) 1.85 (95% confidence interval [CI] 1.16, 2.80). Subhaplogroup G3 was present more frequently in NAFLD patients (25.8% vs 6.5%). The PNPLA3 CG genotype resulted in an OR of 1.66 (95% CI 1.25, 2.21), and the GG genotype resulted in an OR of 2.33 (95% CI 1.72, 3.17) for NAFLD. Patients with mitochondrial haplogroup A had a significantly higher frequency of genotype GG. Among patients with haplogroup A, no PNPLA3 genotype was associated with increased NAFLD risk (CG: OR 1.17, 95% CI 0.55, 2.34; GG: OR 1.04 95% CI 0.66, 2.65). Excluding haplogroup A, the OR for CG was 1.58 (95% CI 1.18, 2.12), and the OR for GG was 1.81 (95% CI 1.30, 2.51).

Conclusion

Haplogroup G was associated with an increased risk of NAFLD PNPLA3 GG genotype was overrepresented among patients encoding haplogroup A and was not associated with NAFLD risk among haplogroup A patients. Mitochondrial genetics influence NAFLD risk and interact with PNPLA3 genotypes.

Protocols for Mitochondria as the Target of Pharmacological Therapy in the Context of Nonalcoholic Fatty Liver Disease (NAFLD)

Nonalcoholic fatty liver disease (NAFLD) is one of the most frequent metabolic chronic liver diseases in developed countries and puts the populations at risk of progression to liver necro-inflammation, fibrosis, cirrhosis, and hepatocellular carcinoma. Mitochondrial dysfunction is involved in the onset of NAFLD and contributes to the progression from NAFLD to nonalcoholic steatohepatitis (NASH). Thus, liver mitochondria could become the target for treatments for improving liver function in NAFLD patients. This chapter describes the most important steps used for potential therapeutic interventions in NAFLD patients, discusses current options gathered from both experimental and clinical evidence, and presents some novel options for potentially improving mitochondrial function in NAFLD.

The effect of hydroalcoholic Berberis integerrima fruits extract on the lipid profile, antioxidant parameters and liver and kidney function tests in patients with nonalcoholic fatty liver disease

Background

Non-alcoholic fatty liver disease (NAFLD) is one of the hepatic disorders which is characterized by increasing fat deposits in the liver. This disorder may lead to elevation the activity of liver enzymes and is associated with obesity, dyslipidemia, hypertension, and type II diabetes. The aim of present study was to investigate the effect of Berberis integerrima extract on NAFLD patients compare to placebo.

Methods

The present clinical trial was performed on 42 NAFLD patients who were randomly divided into two groups. The case group received a capsule (750 mg) containing hydro-alcoholic extract of Berberis integerrima extract every 12 h for 2 months, while the control (placebo) group received a capsule containing cellulose. Baseline characteristics, biochemical factors, antioxidant parameter, functional liver and renal test were evaluated before and after the treatment.

Results

Comparison rate of different parameters in case group before and after treatment demonstrated that BMI, cholesterol, triglyceride, LDL-C, fasting blood glucose, liver enzymes and renal parameters such as aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase were significantly decreased while HDL-C, glutathione peroxidase enzyme, and total antioxidant capacity were significantly elevated. The comparison of the mean parameters difference in two groups indicated that cholesterol, triglyceride, LDL-C, fasting blood glucose, liver enzymes and renal factors were significantly decreased, however HDL-C, glutathione peroxidase enzyme, and total antioxidant capacity were significantly increased in case group compared to control group.

Conclusion

The study findings revealed that the Berberis integerrima extract could reduce biochemical factors of blood, except HDL-C and increases total antioxidant capacity and glutathione peroxidase enzyme. Therefore, hydro-alcoholic extract of Berberis integerrima may be used as a great supplementary medicine in treating NAFLD.

Cellular Interactions in the Human Fatty Liver

Non-alcoholic steatohepatitis morbidity and mortality is on the rise due to the obesity pandemic. Its pathophysiology is not well understood and implies complex interactions between local hepatic cells populations, adipocytes, immune effectors that lead to hepatic lipid excess, lipotoxicity, cellular stress and inflammation, as well as programmed cell death. A better understanding of these pathogenic interactions would allow better identification of therapeutic targets in a disease that has no known pharmacological therapy until now.

European mitochondrial haplogroups predict liver-related outcomes in patients coinfected with HIV and HCV: a retrospective study

BACKGROUND

Mitochondrial DNA (mtDNA) haplogroups have been associated with advanced liver fibrosis and cirrhosis in patients coinfected with human immunodeficiency virus (HIV) and hepatitis C virus (HCV). Our aim was to determine whether mtDNA haplogroups are associated with liver-related events (LREs) in HIV/HCV-coinfected patients.

METHODS

We carried out a retrospective cohort study in HIV/HCV-coinfected patients who were potential candidates for therapy with interferon and ribavirin (IFN/Rib) between 2000 and 2009. The primary endpoint was the occurrence of LREs (decompensation or hepatocellular carcinoma). mtDNA genotyping was performed using the Sequenom MassARRAY platform. We used Fine and Gray proportional hazards model to test the association between mtDNA haplogroups and LREs, considering death as a competitive risk.

RESULTS

The study population comprised 243 patients, of whom 40 had advanced fibrosis or cirrhosis. After a median follow-up of 7.7 years, 90 patients treated with IFN/Rib achieved sustained viral response (SVR), 18 patients had LREs, and 11 patients died. Patients with haplogroup H had lower cumulative incidence than patients with other haplogroups (p = 0.012). However, patients with haplogroup T had higher cumulative incidence than patients with other haplogroups (p = 0.074). In the multivariate analysis, haplogroup T was associated with an increased hazard of developing LREs [adjusted subhazard ratio (aSHR) = 3.56 (95% CI 1.13;11.30); p = 0.030]; whereas haplogroup H was not associated with lower hazard of LREs [aSHR = 0.36 (95% CI 0.10;1.25); p = 0.105]. When we excluded patients who achieved SVR during follow-up, we obtained similar SHR values.

CONCLUSIONS

European mitochondrial haplogroups may influence the natural history of chronic hepatitis C.

Mulberry Fruit Extract Ameliorates Nonalcoholic Fatty Liver Disease (NAFLD) through Inhibition of Mitochondrial Oxidative Stress in Rats

Mulberry is known to have pharmacological effects against cholesterol, obesity, and dyslipidemia. Many studies have revealed that mulberry leaf possesses hepatoprotective properties against nonalcoholic fatty liver disease (NAFLD); however, mulberry fruit is less studied in this context. Therefore, this study aimed to investigate the preventive effects of mulberry fruit against high fat diet- (HFD-) induced NAFLD. To evaluate the effects of mulberry fruit on NAFLD, two doses of mulberry fruit ethanol extracts [MB, 100, and 200 mg/kg BW (body weight)] were given to HFD-fed rats for 10 weeks. MB dramatically prevented liver damage as shown by biochemical analysis of the liver injury markers, alanine transaminase, and aspartate transaminase. MB treatment significantly inhibited the increased levels of total cholesterol, triacylglycerol, and low-density lipoprotein-cholesterol but restored the level of high-density lipoprotein-cholesterol in HFD-fed rats. Notably, histological analysis of liver tissues demonstrated that MB substantially ameliorated lipid accumulation. Expression of cholesterol-regulating genes was also suppressed by MB treatment. For its underlying mechanisms, MB suppressed hepatic reactive oxygen species (ROS) overproduction and mitochondrial oxidative stress in HFD-fed rats. MB potentially protects liver tissue against NAFLD by inhibition of mitochondrial oxidative stress, suggesting its possible use as a therapeutic agent for treatment of NAFLD.

Targeting mitochondria to oppose the progression of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a condition characterized by the excessive accumulation of triglycerides in hepatocytes. NAFLD is the most frequent chronic liver disease in developed countries, and is often associated with metabolic disorders such as obesity and type 2 diabetes. NAFLD definition encompasses a spectrum of chronic liver abnormalities, ranging from simple steatosis (NAFL), to steatohepatitis (NASH), significant liver fibrosis, cirrhosis, and hepatocellular carcinoma. NAFLD, therefore, represents a global public health issue. Mitochondrial dysfunction occurs in NAFLD, and contributes to the progression to the necro-inflammatory and fibrotic form (NASH). Disrupted mitochondrial function is associated with a decrease in the energy levels and impaired redox balance, and negatively affects cell survival by altering overall metabolism and subcellular trafficking. Such events reduce the tolerance of hepatocytes towards damaging hits, and favour the injurious effects of extra-cellular factors. Here, we discuss the role of mitochondria in NAFLD and focus on potential therapeutic approaches aimed at preserving mitochondrial function.

Adipose tissue and the physiologic underpinnings of metabolic disease

Adipose tissue dysfunction underlies the pathogenesis of metabolic disease. The metrics used to quantify adiposity and its association with metabolic disease, including body mass index, have limitations with important clinical implications. An understanding of the molecular and cellular mechanisms by which adipose tissue regulates systemic metabolism and contributes to metabolic disease will lead to next-generation adipose tissue-based therapy.

Mitochondria in non-alcoholic fatty liver disease

NAFLD is a common disease in Western society and ranges from steatosis to steatohepatitis and to end-stage liver disease. The molecular mechanisms that cause the progression of steatosis to severe liver damage are not fully understood. One suggested mechanism involves the oxidation of biomolecules by mitochondrial ROS which initiates a vicious cycle of exacerbated mitochondrial dysfunction and increased hepatocellular oxidative damage. This may ultimately pave the way for hepatic inflammation and liver failure. This review updates our current understanding of mitochondria-derived oxidative stress in the progression of NAFLD.

Intermittent hypoxia is a proinflammatory stimulus resulting in IL-6 expression and M1 macrophage polarization

The biological factors that promote inflammation or nonalcoholic steatohepatitis (NASH) in the setting of nonalcoholic fatty liver disease remain incompletely understood. Clinical studies have demonstrated an association between obstructive sleep apnea (OSA) and both inflammation and fibrosis in NASH, but the mechanism has not been identified. In this study, we use in vitro modeling to examine the impact of intermittent hypoxia on the liver. Hepatocyte, stellate cell, and macrophage cell lines were exposed to intermittent or sustained hypoxia. Candidate genes associated with inflammation, fibrosis, and lipogenesis were analyzed. Circulating cytokines were assessed in human serum of patients with nonalcoholic fatty liver disease. Intermittent hypoxia results in significant induction of interleukin (IL)-6 expression in both hepatocytes and macrophages. The increase in IL-6 expression was independent of hypoxia inducible factor 1 induction but appeared to be in part related to antioxidant response element and nuclear factor kappa B activation. Mature microRNA 365 (miR-365) has been demonstrated to regulate IL-6 expression, and we found that miR-365 expression was decreased in the setting of intermittent hypoxia. Furthermore, macrophage cell lines showed polarization to an M1 but not M2 phenotype. Finally, we found a trend toward higher circulating levels of IL-6 in patients with OSA and NASH. Conclusion: Intermittent hypoxia acts as a potent proinflammatory stimulus, resulting in IL-6 induction and M1 macrophage polarization. Increased IL-6 expression may be due to both induction of antioxidant response element and nuclear factor kappa B as well as inhibition of miR-365 expression. Higher levels of IL-6 were observed in human samples of patients with OSA and NASH. These findings provide biological insight into mechanisms by which obstructive sleep apnea potentiates inflammation and fibrosis in patients with fatty liver disease. (Hepatology Communications 2017;1:326-337).

Clinical implications of understanding the association between oxidative stress and pediatric NAFLD

Oxidative stress is central to the pathogenesis of non-alcoholic steatohepatitis. The reactive oxygen species (ROS) that characterise oxidative stress are generated in several cellular sites and their production is influence by multi-organ interactions. Areas covered: Mitochondrial dysfunction is the main source of ROS in fatty liver and is closely related to endoplasmic reticulum stress. Both are caused by lipotoxicity and together these three factors form a cycle of progressive organelle damage, resulting in sterile inflammation and apoptosis. Adipose tissue inflammation and intestinal dysbiosis provide substrates for ROS formation and trigger immune activation. Obstructive sleep apnea and abnormal divalent metal metabolism may also play a role. Expert commentary: The majority of available high-quality data originates from studies in adults and there are fewer therapeutic trials performed in pediatric cohorts, therefore conclusions are generalised to children. Establishing the role of organelle interactions, and its relationship with oxidative stress in steatohepatitis, is a rapidly evolving area of research.

Mitochondrial Adaptation in Nonalcoholic Fatty Liver Disease: Novel Mechanisms and Treatment Strategies

Nonalcoholic fatty liver disease (NAFLD) is prevalent in patients with obesity or type 2 diabetes. Nonalcoholic steatohepatitis (NASH), encompassing steatosis with inflammation, hepatocyte injury, and fibrosis, predisposes to cirrhosis, hepatocellular carcinoma, and even cardiovascular disease. In rodent models and humans with NAFLD/NASH, maladaptation of mitochondrial oxidative flux is a central feature of simple steatosis to NASH transition. Induction of hepatic tricarboxylic acid cycle closely mirrors the severity of oxidative stress and inflammation in NASH. Reactive oxygen species generation and inflammation are driven by upregulated, but inefficient oxidative flux and accumulating lipotoxic intermediates. Successful therapies for NASH (weight loss alone or with incretin therapy, or pioglitazone) likely attenuate mitochondrial oxidative flux and halt hepatocellular injury. Agents targeting mitochondrial dysfunction may provide a novel treatment strategy for NAFLD.