Mitochondrial adaptations and dysfunctions in nonalcoholic fatty liver disease

Mesenchymal stem cell-conditioned medium improved mitochondrial function and alleviated inflammation and apoptosis in non-alcoholic fatty liver disease by regulating SIRT1

Non-alcoholic fatty liver disease (NAFLD), an emerging risk factor for diabetes, is now recognized as the most common liver disease worldwide. Mesenchymal stem cells (MSCs), a promising tool in regenerative medicine, release abundant molecules into the conditioned medium (CM). Increasing evidence showed that MSC-CM is beneficial for diabetes-associated NAFLD. However, the mechanism of how MSC-CM improves NAFLD remains uncertain. In this study, to determine the effects of MSC-CM on NAFLD, streptozotocin (STZ) and high-fat diet (HFD) induced T2DM mice model and palmitic acid (PA)-stimulated L-O2 cells were used and treated with MSC-CM. Our results demonstrated that MSC-CM improved insulin resistance in diabetic mice, amended the pathological structure of the liver, enhanced the liver's total antioxidant capacity and mitochondrial function, reduced inflammation and cell apoptosis. We further verified that SIRT1 played a key role in mediating the protective effect of MSC-CM. These findings provide novel evidence that MSC-CM has the potential to treat T2DM patients with NAFLD clinically.

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

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

Vascular Adhesion Protein 1 Mediates Gut Microbial Flagellin-Induced Inflammation, Leukocyte Infiltration, and Hepatic Steatosis

Toll-like receptor 5 ligand, flagellin, and vascular adhesion protein 1 (VAP-1) are involved in non-alcoholic fatty liver disease. This study aimed to determine whether VAP-1 mediates flagellin-induced hepatic fat accumulation. The effects of flagellin on adipocyte VAP-1 expression were first studied in vitro. Then, flagellin (100 ng/mouse) or saline was intraperitoneally injected into C57BL/6J (WT) and C57BL/6-Aoc3-/- (VAP-1 KO) mice on a high-fat diet twice a week every 2 weeks for 10 weeks. After that, the effects on inflammation, insulin signaling, and metabolism were studied in liver and adipose tissues. Hepatic fat was quantified histologically and biochemically. Because flagellin challenge increased VAP-1 expression in human adipocytes, we used VAP-1 KO mice to determine whether VAP-1 regulates the inflammatory and metabolic effects of flagellin in vivo. In mice, VAP-1 mediated flagellin-induced inflammation, leukocyte infiltration, and lipolysis in visceral adipose tissue. Consequently, an increased release of glycerol led to hepatic steatosis in WT, but not in KO mice. Flagellin-induced hepatic fibrosis was not mediated by VAP-1. VAP-1 KO mice harbored more inflammation-related microbes than WT mice, while flagellin did not affect the gut microbiota. Our results suggest that by acting on visceral adipose tissue, flagellin increased leukocyte infiltration that induced lipolysis. Further, the released glycerol participated in hepatic fat accumulation. In conclusion, the results describe that gut microbial flagellin through VAP-1 induced hepatic steatosis.

Hepatocyte-specific PKCβ deficiency protects against high-fat diet-induced nonalcoholic hepatic steatosis

OBJECTIVE

Nonalcoholic hepatic steatosis, also known as fatty liver, is a uniform response of the liver to hyperlipidic-hypercaloric diet intake. However, the post-ingestive signals and mechanistic processes driving hepatic steatosis are not well understood. Emerging data demonstrate that protein kinase C beta (PKCβ), a lipid-sensitive kinase, plays a critical role in energy metabolism and adaptation to environmental and nutritional stimuli. Despite its powerful effect on glucose and lipid metabolism, knowledge of the physiological roles of hepatic PKCβ in energy homeostasis is limited.

METHODS

The floxed-PKCβ and hepatocyte-specific PKCβ-deficient mouse models were generated to study the in vivo role of hepatocyte PKCβ on diet-induced hepatic steatosis, lipid metabolism, and mitochondrial function.

RESULTS

We report that hepatocyte-specific PKCβ deficiency protects mice from development of hepatic steatosis induced by high-fat diet, without affecting body weight gain. This protection is associated with attenuation of SREBP-1c transactivation and improved hepatic mitochondrial respiratory chain. Lipidomic analysis identified significant increases in the critical mitochondrial inner membrane lipid, cardiolipin, in PKCβ-deficient livers compared to control. Moreover, hepatocyte PKCβ deficiency had no significant effect on either hepatic or whole-body insulin sensitivity supporting dissociation between hepatic steatosis and insulin resistance.

CONCLUSIONS

The above data indicate that hepatocyte PKCβ is a key focus of dietary lipid perception and is essential for efficient storage of dietary lipids in liver largely through coordinating energy utilization and lipogenesis during post-prandial period. These results highlight the importance of hepatic PKCβ as a drug target for obesity-associated nonalcoholic hepatic steatosis.

The L-α-Lysophosphatidylinositol/G Protein-Coupled Receptor 55 System Induces the Development of Nonalcoholic Steatosis and Steatohepatitis

BACKGROUND AND AIMS

G protein-coupled receptor (GPR) 55 is a putative cannabinoid receptor, and l-α-lysophosphatidylinositol (LPI) is its only known endogenous ligand. Although GPR55 has been linked to energy homeostasis in different organs, its specific role in lipid metabolism in the liver and its contribution to the pathophysiology of nonalcoholic fatty liver disease (NAFLD) remains unknown.

APPROACH AND RESULTS

We measured (1) GPR55 expression in the liver of patients with NAFLD compared with individuals without obesity and without liver disease, as well as animal models with steatosis and nonalcoholic steatohepatitis (NASH), and (2) the effects of LPI and genetic disruption of GPR55 in mice, human hepatocytes, and human hepatic stellate cells. Notably, we found that circulating LPI and liver expression of GPR55 were up-regulated in patients with NASH. LPI induced adenosine monophosphate-activated protein kinase activation of acetyl-coenzyme A carboxylase (ACC) and increased lipid content in human hepatocytes and in the liver of treated mice by inducing de novo lipogenesis and decreasing β-oxidation. The inhibition of GPR55 and ACCα blocked the effects of LPI, and the in vivo knockdown of GPR55 was sufficient to improve liver damage in mice fed a high-fat diet and in mice fed a methionine-choline-deficient diet. Finally, LPI promoted the initiation of hepatic stellate cell activation by stimulating GPR55 and activation of ACC.

CONCLUSIONS

The LPI/GPR55 system plays a role in the development of NAFLD and NASH by activating ACC.

Effects of Pyrroloquinoline Quinone on Lipid Metabolism and Anti-Oxidative Capacity in a High-Fat-Diet Metabolic Dysfunction-Associated Fatty Liver Disease Chick Model

Metabolic dysfunction-associated fatty liver disease (MAFLD) and its interaction with many metabolic pathways raises global public health concerns. This study aimed to determine the therapeutic effects of Pyrroloquinoline quinone (PQQ, provided by PQQ.Na₂) on MAFLD in a chick model and primary chicken hepatocytes with a focus on lipid metabolism, anti-oxidative capacity, and mitochondrial biogenesis. The MAFLD chick model was established on laying hens by feeding them a high-energy low-protein (HELP) diet. Primary hepatocytes isolated from the liver of laying hens were induced for steatosis by free fatty acids (FFA) and for oxidative stress by hydrogen peroxide (H₂O₂). In the MAFLD chick model, the dietary supplementation of PQQ conspicuously ameliorated the negative effects of the HELP diet on liver biological functions, suppressed the progression of MAFLD mainly through enhanced lipid metabolism and protection of liver from oxidative injury. In the steatosis and oxidative stress cell models, PQQ functions in the improvement of the lipid metabolism and hepatocytes tolerance to fatty degradation and oxidative damage by enhancing mitochondrial biogenesis and then increasing the anti-oxidative activity and anti-apoptosis capacity. At both the cellular and individual levels, PQQ was demonstrated to exert protective effects of hepatocyte and liver from fat accumulation through the improvement of mitochondrial biogenesis and maintenance of redox homeostasis. The key findings of the present study provide an in-depth knowledge on the ameliorative effects of PQQ on the progression of fatty liver and its mechanism of action, thus providing a theoretical basis for the application of PQQ, as an effective nutrient, into the prevention of MAFLD.

Quercetin Alleviates Oxidative Damage by Activating Nuclear Factor Erythroid 2-Related Factor 2 Signaling in Porcine Enterocytes

Oxidative stress has been implicated in the etiology of multiple gastrointestinal disorders, such as irritable bowel syndrome and inflammatory bowel disease. This study was conducted to evaluate effects of natural product quercetin on diquat-induced oxidative stress in porcine enterocytes and underlying mechanisms. Intestinal porcine epithelial cell line 1 (IPEC-1) cells pretreated with or without quercetin (5 μM, 24 h) were incubated with vehicle or diquat (100 μM) for 6 h. The results showed that diquat treatment induced apoptosis in a caspase-3-dependent manner, as accompanied by elevated reactive oxygen species (ROS) production, increased mitochondrial depolarization, and reduced the abundance of tight junction proteins. These adverse effects of diquat were remarkably abrogated by quercetin administration. Further study indicated that the protective effect of quercetin was associated with elevated protein abundance of nuclear factor erythroid 2-related factor 2 (Nrf2) and increased intracellular glutathione (GSH) content. Interestingly, the beneficial effects of quercetin on diquat-induced oxidative damage were abolished by all-trans-retinoic acid (Atra), a specific inhibitor of Nrf2, indicating a Nrf2-dependent regulation manner. The results show that quercetin attenuates diquat-induced cell injury by promoting protein abundance of Nrf2 and regulating GSH-related redox homeostasis in enterocytes. These findings provide new insights into a function role of quercetin in maintaining intestinal homeostasis.

Cytochrome P450 2E1 should not be neglected for acetaminophen-induced liver injury in metabolic diseases with altered insulin levels or glucose homeostasis

Acetaminophen (APAP) hepatotoxicity is mediated by N-acetyl-p-benzoquinone imine (NAPQI), a highly toxic metabolite generated by cytochrome P450 2E1 (CYP2E1). Thus, pathological conditions increasing CYP2E1 activity can favour APAP-induced liver injury, which is characterized by massive hepatocellular necrosis and secondary sterile inflammation. In a recent work, Wang et al. showed that APAP-induced hepatotoxicity was exacerbated in a murine model of type 1 diabetes induced by the administration of streptozotocin (STZ). Higher hepatotoxicity was in particular associated with a stronger proinflammatory response of the resident macrophages. Although the authors carried out numerous investigations, they did not study hepatic CYP2E1, nor discussed the possible role of this enzyme in the exacerbation of APAP hepatotoxicity. However, numerous investigations reported hepatic CYP2E1 induction in STZ-treated rodents, which could be secondary to insulinopenia and ketosis. This commentary also discusses the role of insulin resistance in CYP2E1 induction observed in obesity and nonalcoholic fatty liver disease. Investigators studying APAP-induced liver injury in the context of insulinopenia or hyperinsulinemia are thus encouraged to consider CYP2E1 as a significant player in the observed phenotypic changes.

Chemerin/CMKLR1 ameliorates nonalcoholic steatohepatitis by promoting autophagy and alleviating oxidative stress through the JAK2-STAT3 pathway

Nonalcoholic steatohepatitis (NASH) is a global public health challenge. Overwhelmed oxidative stress and impaired autophagy play an important role in the progression of NASH. Chemerin is an adipokine that has attracted much attention in inflammation and metabolic diseases. This study aimed to examine the effects of chemerin in NASH and its association with oxidative stress and autophagy. In this study, chemerin was found to significantly ameliorate high-fat diet (HFD) induced NASH, marked by decreased serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α), decreased insulin resistance (IR) and leptin resistance (LR), and improved liver lesions. Besides, chemerin prevented enhanced oxidative stress in NASH mice by regulating the antioxidant defense system (MDA downregulation and upregulation of superoxide dismutase (SOD)). Moreover, chemerin contributed to the alleviation of NASH through autophagy activation (p62 downregulation, and upregulation of beclin-1 and LC3). Furthermore, these effects were related to increased phosphorylation of JAK2-STAT3 stimulated by chemerin, which could be inhibited by the CMKLR1 specific inhibitor α-NETA. In conclusion, excess chemerin highly probably ameliorated NASH by alleviating oxidative stress and promoting autophagy, the mechanism responsible for this process was related, at least in part, to the increased phosphorylation of JAK2-STAT3 stimulated by chemerin/CMKLR1. Rh-chemerin may represent promising therapeutic targets in the treatment of NASH.

Plant sterol ester of α-linolenic acid ameliorates high-fat diet-induced nonalcoholic fatty liver disease in mice: association with regulating mitochondrial dysfunction and oxidative stress via activating AMPK signaling

Plant sterol ester of α-linolenic acid prevents nonalcoholic fatty liver disease by improving mitochondrial function, modifying lipid metabolism, and inhibiting oxidative stress via AMPK signaling.

Mitochondrial Dysfunction is a Key Pathway that Links Saturated Fat Intake to the Development and Progression of NAFLD

Non-Alcoholic fatty liver disease (NAFLD) is the most common form of liver disease and is characterized by fat accumulation in the liver. Hypercaloric diets generally increase hepatic fat accumulation, whereas hypocaloric diets decrease liver fat content. In addition, there is evidence to suggest that moderate amounts of unsaturated fatty acids seems to be protective for the development of a fatty liver, while consumption of saturated fatty acids (SFA) appears to predispose toward hepatic steatosis. Recent studies highlight a key role for mitochondrial dysfunction in the development and progression of NAFLD. It is proposed that changes in mitochondrial structure and function are key mechanisms by which SFA lead to the development and progression of NAFLD. In this review, it is described how SFA intake is associated with liver steatosis and decreases the efficiency of the respiratory transport chain. This results in the production of reactive oxygen species and damage to nearby structures, eventually leading to inflammation, apoptosis, and scarring of the liver. Furthermore, studies demonstrating that SFA intake affects the composition of mitochondrial membranes are presented, and this process accelerates the progression of NAFLD. It is likely that events are intertwined and reinforce each other, leading to a constant deterioration in health.

Nonalcoholic Fatty Liver Disease and Non-Alcoholic Steatohepatitis: Current Issues and Future Perspectives in Preclinical and Clinical Research

Nonalcoholic fatty liver disease (NAFLD) is a continuum of liver abnormalities often starting as simple steatosis and to potentially progress into nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis and hepatocellular carcinoma. Because of its increasing prevalence, NAFLD is becoming a major public health concern, in parallel with a worldwide increase in the recurrence rate of diabetes and metabolic syndrome. It has been estimated that NASH cirrhosis may surpass viral hepatitis C and become the leading indication for liver transplantation in the next decades. The broadening of the knowledge about NASH pathogenesis and progression is of pivotal importance for the discovery of new targeted and more effective therapies; aim of this review is to offer a comprehensive and updated overview on NAFLD and NASH pathogenesis, the most recommended treatments, drugs under development and new drug targets. The most relevant in vitro and in vivo models of NAFLD and NASH will be also reviewed, as well as the main molecular pathways involved in NAFLD and NASH development.

Improvement of the hepatic lipid status in intrauterine growth retarded pigs by resveratrol is related to the inhibition of mitochondrial dysfunction, oxidative stress and inflammation

Mitochondrial dysfunction, oxidative stress and inflammation are crucial contributors to liver damage and nonalcoholic fatty liver disease (NAFLD) in adulthood in offspring affected by intrauterine growth retardation (IUGR). Resveratrol (RSV) has been reported to treat and/or prevent hepatic diseases under various pathological conditions. However, the therapeutic and/or preventive effects of RSV on hepatic abnormality in IUGR adults have not been investigated until now. The effects of IUGR and RSV on the hepatic metabolic status, mitochondrial function, redox homeostasis and inflammation in pigs in adulthood were investigated. A total of 36 pairs of IUGR and normal birth weight piglets were orally fed with 80 mg RSV per kg body weight per d or vehicle (0.5% carboxymethylcellulose) for 7-21 d after birth. And then the offspring were fed with a basal diet supplemented with 300 mg RSV per kg feed or a basal diet from weaning to slaughter at 150 d. The plasma and liver samples were collected for subsequent analysis. RSV exerted beneficial effects on hepatic injury and metabolic alterations in IUGR pigs, which may be due to improved mitochondrial function and fatty acid oxidation by intensified mitochondrial biogenesis, enhanced antioxidant levels such as glutathione reductase and total superoxide dismutase activities, increased interleukin 10 gene expression and repolarization of macrophages. RSV alleviated hepatic lipid accumulation in IUGR pigs by improving mitochondrial function, redox status and inflammation, implying that it is a potential candidate for further development as an effective clinical treatment for NAFLD associated with IUGR.

Proteome and phosphoproteome characterization of liver in the postprandial state from diet-induced obese and lean mice

A metabolic consequence of obesity is hepatosteatosis, which can develop into more serious diseases in the non-alcoholic fatty liver disease (NAFLD) spectrum. The goal of this study was to identify the protein signature of liver in the postprandial state in obesity compared to leanness. The postprandial state is of interest due to the central role of the liver in regulating macronutrient and energy homeostasis during the fed-fast cycle and lack of previously reported controlled studies in the postprandial state. Therefore, we assessed the proteome and phosphoproteome of liver in the postprandial state from diet-induced obese (DIO) and lean mice using untargeted LC-MS/MS analysis. We identified significant alterations in the levels of proteins involved in fatty acid oxidation, activation, and transport, as well as proteins involved in energy metabolism including ketogenesis, tricarboxylic acid cycle, and electron transport chain in liver of DIO compared to lean mice. Additionally, phosphorylated proteins in liver of DIO and lean mice reflect possible regulatory mechanisms controlling fatty acid metabolism and gene expression that may contribute to hepatic metabolic alterations in obesity. Our data indicates PPARα-mediated transcriptional regulation of lipid metabolism and adaptation to hepatic lipid overload. The results of this study expand our knowledge of the molecular changes that occur in liver in the postprandial state in obesity compared to leanness. SIGNIFICANCE: Proteome and phosphoproteome studies of liver in a controlled postprandial state in obesity and leanness are lacking; however, this information is crucial to understanding how obesity-associated hepatosteatosis influences postprandial nutrient and energy metabolism. In this global shotgun proteome and phosphoproteome analysis, we identified unique protein signatures defining obesity and leanness in liver in the postprandial state and identified potential mechanisms contributing to hepatic metabolic alterations in obesity. The results of this study provide a foundation to focus future experiments on the contribution of altered protein and phosphorylation patterns to postprandial metabolism in obesity-associated hepatosteatosis.

Non-Alcoholic Steatohepatitis Decreases Microsomal Liver Function in the Absence of Fibrosis

The incidence of non-alcoholic fatty liver disease (NAFLD) is rising across the globe, with the presence of steatohepatitis leading to a more aggressive clinical course. Currently, the diagnosis of non-alcoholic steatohepatitis (NASH) is based on histology, though with the high prevalence of NAFLD, a non-invasive method is needed. The 13C-aminopyrine breath test (ABT) evaluates the microsomal liver function and could be a potential candidate. We aimed to evaluate a potential change in liver function in NASH patients and to evaluate the diagnostic power of ABT to detect NASH. We performed a retrospective analysis on patients suspected of NAFLD who underwent a liver biopsy and ABT. 440 patients were included. ABT did not decrease in patients with isolated liver steatosis but decreased significantly in the presence of NASH without fibrosis and decreased even further with the presence of significant fibrosis. The predictive power of ABT as a single test for NASH was low but improved in combination with ALT and ultrasonographic steatosis. We conclude that microsomal liver function of patients with NASH is significantly decreased, even in the absence of fibrosis. The ABT is thus a valuable tool in assessing the presence of NASH; and could be used as a supplementary diagnostic tool in clinical practice.

Impaired liver regeneration and lipid homeostasis in CCl4 treated WDR13 deficient mice

WDR13 - a WD repeat protein, is abundant in pancreas, liver, ovary and testis. Absence of this protein in mice has been seen to be associated with pancreatic β-cell proliferation, hyperinsulinemia and age dependent mild obesity. Previously, we have reported that the absence of WDR13 in diabetic Lepr^db/db mice helps in amelioration of fatty liver phenotype along with diabetes and systemic inflammation. This intrigued us to study direct liver injury and hepatic regeneration in Wdr13^−/0 mice using hepatotoxin CCl₄. In the present study we report slower hepatic regeneration in Wdr13^−/0 mice as compared to their wild type littermates after CCl₄ administration. Interestingly, during the regeneration phase, hepatic hypertriglyceridemia was observed in Wdr13^−/0 mice. Further analyses revealed an upregulation of PPAR pathway in the liver of CCl₄- administered Wdr13^−/0 mice, causing de novo lipogenesis. The slower hepatic regeneration observed in CCl₄ administered Wdr13^−/0 mice, may be linked to liver hypertriglyceridemia because of activation of PPAR pathway.

Significance of Simple Steatosis: An Update on the Clinical and Molecular Evidence

Non-alcoholic fatty liver disease (NAFLD) is defined clinicopathologically by the accumulation of lipids in >5% of hepatocytes and the exclusion of secondary causes of fat accumulation. NAFLD encompasses a wide spectrum of liver damage, extending from simple steatosis or non-alcoholic fatty liver (NAFL) to non-alcoholic steatohepatitis (NASH)—the latter is characterized by inflammation and hepatocyte ballooning degeneration, in addition to the steatosis, with or without fibrosis. NAFLD is now the most common cause of chronic liver disease in Western countries and affects around one quarter of the general population. It is a multisystem disorder, which is associated with an increased risk of type 2 diabetes mellitus as well as liver- and cardiovascular-related mortality. Although earlier studies had suggested that NAFL is benign (i.e., non-progressive), cumulative evidence challenges this dogma, and recent data suggest that nearly 25% of those with NAFL may develop fibrosis. Importantly, NAFLD patients are more susceptible to the toxic effects of alcohol, drugs, and other insults to the liver. This is likely due to the functional impairment of steatotic hepatocytes, which is virtually undetectable by current clinical tests. This review provides an overview of the current evidence on the clinical significance of NAFL and discusses the molecular basis for NAFL development and progression.

Endogenous ethanol produced by intestinal bacteria induces mitochondrial dysfunction in non-alcoholic fatty liver disease

BACKGROUND AND AIM

A causal relationship between changes of the gut microbiome and non-alcoholic fatty liver disease (NAFLD) remains unclear. We demonstrated that endogenous ethanol (EnEth) produced by intestinal microbiota is likely a causative agent of NAFLD.

METHODS

Two mutants with different alcohol-producing abilities, namely, W14-adh and W14Δadh, were constructed using the clinical high alcohol-producing (HiAlc) Klebsiella pneumoniae strain W14 as a parent. Damage to hepatocytes caused by bacteria with different alcohol-producing capacities was evaluated (EtOH group as positive control). The ultrastructural changes of mitochondria were assessed via transmission electron microscopy (TEM). Hepatic levels of mitochondrial reactive oxygen species (ROS), DNA damage, and adenosine triphosphate were examined.

RESULTS

The results illustrated that steatosis was most severe in the W14-adh group, followed by the W14 group, whereas the W14Δadh group had few fatty droplets. TEM and examination of related protein expression revealed that the mitochondrial integrity of HepG2 hepatocytes was considerably damaged in the EtOH and bacteria treatment groups. The impaired mitochondrial function in HepG2 hepatocytes was evidenced by reduced adenosine triphosphate content and increased mitochondrial ROS accumulation and DNA damage in the EtOH and bacteria treatment groups, especially the W14-adh group. Meanwhile, liver injury and mitochondrial damage were observed in the hepatocytes of mice. The livers of mice in the W14-adh group, which had the highest ethanol production, exhibited the most serious damage, similar to that in the EtOH group.

CONCLUSIONS

EnEth produced by HiAlc bacteria induces mitochondrial dysfunction in NAFLD.

Prebiotic Xylo-Oligosaccharides Ameliorate High-Fat-Diet-Induced Hepatic Steatosis in Rats

Understanding the importance of the gut microbiota (GM) in non-alcoholic fatty liver disease (NAFLD) has raised the hope for therapeutic microbes. We have shown that high hepatic fat content associated with low abundance of Faecalibacterium prausnitzii in humans and, further, the administration of F. prausnitzii prevented NAFLD in mice. Here, we aimed at targeting F. prausnitzii by prebiotic xylo-oligosaccharides (XOS) to treat NAFLD. First, the effect of XOS on F. prausnitzii growth was assessed in vitro. Then, XOS was supplemented or not with high (HFD, 60% of energy from fat) or low (LFD) fat diet for 12 weeks in Wistar rats (n = 10/group). XOS increased F. prausnitzii growth, having only a minor impact on the GM composition. When supplemented with HFD, XOS ameliorated hepatic steatosis. The underlying mechanisms involved enhanced hepatic β-oxidation and mitochondrial respiration. Nuclear magnetic resonance (¹H-NMR) analysis of cecal metabolites showed that, compared to the HFD, the LFD group had a healthier cecal short-chain fatty acid profile and on the HFD, XOS reduced cecal isovalerate and tyrosine, metabolites previously linked to NAFLD. Cecal branched-chain fatty acids associated positively and butyrate negatively with hepatic triglycerides. In conclusion, XOS supplementation can ameliorate NAFLD by improving hepatic oxidative metabolism and affecting GM.

Western Diet Causes Obesity-Induced Nonalcoholic Fatty Liver Disease Development by Differentially Compromising the Autophagic Response

Nonalcoholic fatty liver disease (NAFLD) is characterized by the development of steatosis, which can ultimately compromise liver function. Mitochondria are key players in obesity-induced metabolic disorders; however, the distinct role of hypercaloric diet constituents in hepatic cellular oxidative stress and metabolism is unknown. Male mice were fed either a high-fat (HF) diet, a high-sucrose (HS) diet or a combined HF plus HS (HFHS) diet for 16 weeks. This study shows that hypercaloric diets caused steatosis; however, the HFHS diet induced severe fibrotic phenotype. At the mitochondrial level, lipidomic analysis showed an increased cardiolipin content for all tested diets. Despite this, no alterations were found in the coupling efficiency of oxidative phosphorylation and neither in mitochondrial fatty acid oxidation (FAO). Consistent with unchanged mitochondrial function, no alterations in mitochondrial-induced reactive oxygen species (ROS) and antioxidant capacity were found. In contrast, the HF and HS diets caused lipid peroxidation and provoked altered antioxidant enzyme levels/activities in liver tissue. Our work provides evidence that hepatic oxidative damage may be caused by augmented levels of peroxisomes and consequently higher peroxisomal FAO-induced ROS in the early NAFLD stage. Hepatic damage is also associated with autophagic flux impairment, which was demonstrated to be diet-type dependent. The HS diet induced a reduction in autophagosomal formation, while the HF diet reduced levels of cathepsins. The accumulation of damaged organelles could instigate hepatocyte injuries and NAFLD progression.

Resolvin D1 mitigates non-alcoholic steatohepatitis by suppressing the TLR4-MyD88-mediated NF-κB and MAPK pathways and activating the Nrf2 pathway in mice

AIMS

Resolvin D1 (RvD1), a potent endogenous lipid mediator converted from docosahexaenoic acid (DHA), has exert anti-inflammatory and antioxidant effects in many preclinical disease models, but its potential role in non-alcoholic steatohepatitis (NASH) remains elusive. This study was performed to investigate the protective effects and mechanisms of RvD1 in NASH.

MAIN METHODS

In vivo, male C57BL/6 mice were fed an MCD diet for 4 weeks to induce NASH. RvD1 was added in the last 2 weeks of the feeding period. In vitro, lipopolysaccharide (LPS)-activated RAW264.7 macrophages were pretreated with increasing concentrations of RvD1. Serum liver functional markers and hepatic oxidative stress indicators were measured biochemically. Mouse liver tissue sections were stained with hematoxylin-eosin, oil red O, and Masson's trichrome to assess the severity of steatohepatitis, steatosis and fibrosis. The qRT-PCR, immunohistochemistry and Western blotting assays were applied to analyse mechanisms underlying RvD1 protection in NASH.

KEY FINDINGS

In vivo, RvD1 significantly attenuates steatohepatitis in MCD diet-fed mice by modulating key events, including steatosis, inflammation, oxidative stress and fibrosis in the progression of NASH. In vitro, RvD1 also represses LPS-induced inflammation in RAW264.7 cells. These effects may be mainly attributed to RvD1 markedly suppressing excessive inflammatory responses via the inhibition of the TLR4-MyD88-mediated NF-κB and MAPK signalling pathways as well as enhancing antioxidation capacity via the activation of the Nrf2 pathway.

SIGNIFICANCE

These results demonstrate that RvD1 is a promising hepatoprotective agent for the therapy of NASH.

Drug discovery and treatment paradigms in nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in western populations, and is closely associated with features of the metabolic syndrome. The burden of disease is set to rise exponentially, and this is further compounded by the lack of good medications. In addition, these patients tend to have multiple comorbidities that may not be adequately managed. In this article, we review the biological basis of potential therapies in nonalcoholic steatohepatitis (NASH), the current drugs being tested in clinical trials, as well some practical considerations in managing patients in the clinic.

Hypothyroidism and Nonalcoholic Fatty Liver Disease: Pathophysiological Associations and Therapeutic Implications

Nonalcoholic fatty liver disease (NAFLD) is a complex clinical entity which can be secondary to many other diseases including hypothyroidism, characterized by lowering of thyroid hormones and increased thyroid stimulating hormone (TSH). A lot of emerging data published recently advocates the hypothesis that hypothyroid induced NAFLD could be a separate clinical entity, even suggesting possible treatment options for NAFLD involving substitution therapy for hypothyroidism along with lifestyle modifications. In addition, a whole new field of research is focused on thyromimetics in NAFLD/NASH treatment, currently in phase 3 clinical trials. In this critical review we summarized epidemiological and pathophysiological evidence linking these two clinical entities and described specific treatment options with the accent on promising new agents in NAFLD treatment, specifically thyroid hormone receptor (THR) agonist and its metabolites.

Prolonged Lipid Accumulation in Cultured Primary Human Hepatocytes Rather Leads to ER Stress than Oxidative Stress

Overweight has become a major health care problem in Western societies and is accompanied by an increasing incidence and prevalence of non-alcoholic fatty liver disease (NAFLD). The progression from NAFLD to non-alcoholic steatohepatitis (NASH) marks a crucial tipping point in the progression of severe and irreversible liver diseases. This study aims to gain further insight into the molecular processes leading to the evolution from steatosis to steatohepatitis. Steatosis was induced in cultures of primary human hepatocytes by continuous five-day exposure to free fatty acids (FFAs). The kinetics of lipid accumulation, lipotoxicity, and oxidative stress were measured. Additionally, ER stress was evaluated by analyzing the protein expression profiles of its key players: PERK, IRE1a, and ATF6a. Our data revealed that hepatocytes are capable of storing enormous amounts of lipids without showing signs of lipotoxicity. Prolonged lipid accumulation did not create an imbalance in hepatocyte redox homeostasis or a reduction in antioxidative capacity. However, we observed an FFA-dependent increase in ER stress, revealing thresholds for triggering the activation of pathways associated with lipid stress, inhibition of protein translation, and apoptosis. Our study clearly showed that even severe lipid accumulation can be attenuated by cellular defenses, but regenerative capacities may be reduced.

Branched chain amino acids and carbohydrate restriction exacerbate ketogenesis and hepatic mitochondrial oxidative dysfunction during NAFLD

Mitochondrial adaptation during non-alcoholic fatty liver disease (NAFLD) include remodeling of ketogenic flux and sustained tricarboxylic acid (TCA) cycle activity, which are concurrent to onset of oxidative stress. Over 70% of obese humans have NAFLD and ketogenic diets are common weight loss strategies. However, the effectiveness of ketogenic diets toward alleviating NAFLD remains unclear. We hypothesized that chronic ketogenesis will worsen metabolic dysfunction and oxidative stress during NAFLD. Mice (C57BL/6) were kept (for 16-wks) on either a low-fat, high-fat, or high-fat diet supplemented with 1.5X branched chain amino acids (BCAAs) by replacing carbohydrate calories (ketogenic). The ketogenic diet induced hepatic lipid oxidation and ketogenesis, and produced multifaceted changes in flux through the individual steps of the TCA cycle. Higher rates of hepatic oxidative fluxes fueled by the ketogenic diet paralleled lower rates of de novo lipogenesis. Interestingly, this metabolic remodeling did not improve insulin resistance, but induced fibrogenic genes and inflammation in the liver. Under a chronic "ketogenic environment," the hepatocyte diverted more acetyl-CoA away from lipogenesis toward ketogenesis and TCA cycle, a milieu which can hasten oxidative stress and inflammation. In summary, chronic exposure to ketogenic environment during obesity and NAFLD has the potential to aggravate hepatic mitochondrial dysfunction.

Treatments in Covid-19 patients with pre-existing metabolic dysfunction-associated fatty liver disease: A potential threat for drug-induced liver injury?

Obese patients who often present metabolic dysfunction-associated fatty liver disease (MAFLD) are at risk of severe presentation of coronavirus disease 2019 (COVID-19). These patients are more likely to be hospitalized and receive antiviral agents and other drugs required to treat acute respiratory distress syndrome and systemic inflammation, combat bacterial and fungal superinfections and reverse multi-organ failure. Among these pharmaceuticals, antiretrovirals such as lopinavir/ritonavir and remdesivir, antibiotics and antifungal agents can induce drug-induced liver injury (DILI), whose mechanisms are not always understood. In the present article, we hypothesize that obese COVID-19 patients with MAFLD might be at higher risk for DILI than non-infected healthy individuals or MAFLD patients. These patients present several concomitant factors, which individually can favour DILI: polypharmacy, systemic inflammation at risk of cytokine storm, fatty liver and sometimes nonalcoholic steatohepatitis (NASH) as well as insulin resistance and other diseases linked to obesity. Hence, in obese COVID-19 patients, some drugs might cause more severe (and/or more frequent) DILI, while others might trigger the transition of fatty liver to NASH, or worsen pre-existing steatosis, necroinflammation and fibrosis. We also present the main mechanisms whereby drugs can be more hepatotoxic in MAFLD including impaired activity of xenobiotic-metabolizing enzymes, mitochondrial dysfunction, altered lipid homeostasis and oxidative stress. Although comprehensive investigations are needed to confirm our hypothesis, we believe that the current epidemic of obesity and related metabolic diseases has extensively contributed to increase the number of cases of DILI in COVID-19 patients, which may have participated in presentation severity and death.

Metabolic Profiling Reveals Aggravated Non-Alcoholic Steatohepatitis in High-Fat High-Cholesterol Diet-Fed Apolipoprotein E-Deficient Mice Lacking Ron Receptor Signaling

Non-alcoholic steatohepatitis (NASH) represents the progressive sub-disease of non-alcoholic fatty liver disease that causes chronic liver injury initiated and sustained by steatosis and necroinflammation. The Ron receptor is a tyrosine kinase of the Met proto-oncogene family that potentially has a beneficial role in adipose and liver-specific inflammatory responses, as well as glucose and lipid metabolism. Since its discovery two decades ago, the Ron receptor has been extensively investigated for its differential roles on inflammation and cancer. Previously, we showed that Ron expression on tissue-resident macrophages limits inflammatory macrophage activation and promotes a repair phenotype, which can retard the progression of NASH in a diet-induced mouse model. However, the metabolic consequences of Ron activation have not previously been investigated. Here, we explored the effects of Ron receptor activation on major metabolic pathways that underlie the development and progression of NASH. Mice lacking apolipoprotein E (ApoE KO) and double knockout (DKO) mice that lack ApoE and Ron were maintained on a high-fat high-cholesterol diet for 18 weeks. We observed that, in DKO mice, the loss of ligand-dependent Ron signaling aggravated key pathological features in steatohepatitis, including steatosis, inflammation, oxidation stress, and hepatocyte damage. Transcriptional programs positively regulating fatty acid (FA) synthesis and uptake were upregulated in the absence of Ron receptor signaling, whereas lipid disposal pathways were downregulated. Consistent with the deregulation of lipid metabolism pathways, the DKO animals exhibited increased accumulation of FAs in the liver and decreased level of bile acids. Altogether, ligand-dependent Ron receptor activation provides protection from the deregulation of major metabolic pathways that initiate and aggravate non-alcoholic steatohepatitis.

Apoptosis-inducing factor deficient mice fail to develop hepatic steatosis under high fat high fructose diet or bile duct ligation

Apoptosis-inducing factor (AIF) is a mitochondrial flavoprotein involved in redox signalling and programmed cell death. The role of AIF has been well recognized in diabetes and obesity. However, the aspect of AIF deficiency in the development of hepatic steatosis and liver injury is unknown. Therefore, in the current study, Harlequin (Hq mutant) mouse with markedly reduced content of AIF was investigated to explore the role of AIF on the initiation of liver injury. The wild type (WT) developed physiological and pathological features of non-alcoholic fatty liver disease (NAFLD) that were not seen in the Hq mice with AIF deficiency, when fed on high fat high fructose (HFHF) diet. Following bile duct ligation (BDL), the liver associated pathological changes were less conspicuous in Hq mice as compared to WT mice. The expression of AIF protein and apoptosis was markedly lesser as compared to their respective control in Hq mice on HFHF diet. Furthermore, the genes involved in fatty acid metabolism were also altered in the group of treated Hq mice. In conclusion, Hq mice failed to develop diet induced hepatic steatosis, suggestive of a role of AIF mediated pathway in the initiation and progression of liver inflammation. Thus, partial loss of AIF appears to be hepatoprotective. SIGNIFICANCE OF THE STUDY: AIF deficiency has multiple roles in altered pathology processes and cellular metabolism, thereby compromising the cellular homeostasis. Considering the molecular functions of AIF in other organ pathology little is known about its role in diet induced liver injury. Hence, the aim of the current study was to investigate the role of AIF deficiency in liver injury and diseases with focus on NAFLD. The study will help to deliniate the mechanisms of NAFLD using Harliquin Mice.

Neohesperidin enhances PGC-1α-mediated mitochondrial biogenesis and alleviates hepatic steatosis in high fat diet fed mice

BACKGROUNDS

Mitochondria plays a critical role in the development and pathogenesis of nonalcoholic fatty liver disease (NAFLD). Neohesperidin (NHP) could lower blood glucose and prevent obesity in mice. However, the direct effect of NHP on hepatic steatosis has not been reported.

METHODS

Mice were fed with either a chow diet or HFD with or without oral gavage of NHP for 12 weeks. A variety of biochemical and histological indicators were examined. In vitro cell culture model was utilized to demonstrate underlying molecular mechanism of the effect induced by NHP treatment.

RESULTS

NHP increases mitochondrial biogenesis, improves hepatic steatosis and systematic insulin resistance in high fat diet (HFD) fed mice. NHP elevates hepatic mitochondrial biogenesis and fatty acid oxidation by increasing PGC-1α expression. Mechanistically, the activation of AMP-activated protein kinase (AMPK) is involved in NHP induced PGC-1α expression.

CONCLUSIONS

PGC-1α-mediated mitochondrial biogenesis plays a vital role in the mitigation of hepatic steatosis treated by NHP. Our result suggests that NHP is a good candidate to be dietary supplement for the auxiliary treatment of NAFLD.

Hepatic Stellate Cell-Macrophage Crosstalk in Liver Fibrosis and Carcinogenesis

Chronic liver injury due to viral hepatitis, alcohol abuse, and metabolic disorders is a worldwide health concern. Insufficient treatment of chronic liver injury leads to fibrosis, causing liver dysfunction and carcinogenesis. Most cases of hepatocellular carcinoma (HCC) develop in the fibrotic liver. Pathological features of liver fibrosis include extracellular matrix (ECM) accumulation, mesenchymal cell activation, immune deregulation, and angiogenesis, all of which contribute to the precancerous environment, supporting tumor development. Among liver cells, hepatic stellate cells (HSCs) and macrophages play critical roles in fibrosis and HCC. These two cell types interplay and remodel the ECM and immune microenvironment in the fibrotic liver. Once HCC develops, HCC-derived factors influence HSCs and macrophages to switch to protumorigenic cell populations, cancer-associated fibroblasts and tumor-associated macrophages, respectively. This review aims to summarize currently available data on the roles of HSCs and macrophages in liver fibrosis and HCC, with a focus on their interaction.

Ameliorative effects and molecular mechanisms of vine tea on western diet-induced NAFLD

Non-alcoholic fatty liver disease (NAFLD) is a disease that is prevalent worldwide, and its prevention by dietary administration has recently been considered as an important strategy. In this study, we administered mice with vine tea polyphenol (VTP) extracted from Ampelopsis grossedentata, a Chinese herb, to investigate the preventive effect on western diet (WD)-induced NAFLD. Male C57BL/6N mice were fed either a normal diet (ND) or WD with or without VTP for 12 weeks. The results revealed that VTP supplementation decreased the serum levels of cholesterol and triglycerides, and reduced the accumulation of hepatic lipid droplets caused by WD. Molecular data revealed that VTP enhanced fatty acid oxidation by reactivating the WD-suppressed phosphorylation of AMP-activated protein kinaseα (AMPKα) and the expressions of peroxisome proliferator-activated receptor alpha (PPARα), carnitine palmitoyl transferase IA (CPT1A) and cytochrome P450, family 4, subfamily a1 (CYP4A1). VTP inhibited hepatic lipogenesis by reducing the WD-enhanced level of mature sterol regulatory element-binding protein 1 (SREBP1) and fatty acid synthase (FAS). Moreover, VTP activated nuclear factor (erythroid-derived 2)-like 2 (Nrf2)-mediated expressions of hemeoxygenase-1 (HO-1) and quinone oxidoreductase (NQO1), and reduced hepatic TBARS levels to prevent hepatic oxidative stress. On the other hand, VTP also increased intestinal zonula occludens-1 (ZO-1) expression and the relative abundance of gut Akkermansia, and reduced the ratio of Firmicutes/Bacteroidetes. Thus, VTP might prevent WD-induced NAFLD by balancing fatty acid oxidation and lipogenesis, hepatic oxidative stress, and gut microbiome, at least. These results suggest that vine tea, containing a high content of the bioactive compound dihydromyricetin, is a potential food resource for preventing NAFLD.

Liver-specific Prkn knockout mice are more susceptible to diet-induced hepatic steatosis and insulin resistance

Objective

PARKIN is an E3 ubiquitin ligase that regulates mitochondrial quality control through a process called mitophagy. Recent human and rodent studies suggest that loss of hepatic mitophagy may occur during the pathogenesis of obesity-associated fatty liver and contribute to changes in mitochondrial metabolism associated with this disease. Whole-body Prkn knockout mice are paradoxically protected against diet-induced hepatic steatosis; however, liver-specific effects of Prkn deficiency cannot be discerned in this model due to pleotropic effects of germline Prkn deletion on energy balance and subsequent protection against diet-induced obesity. We therefore generated the first liver-specific Prkn knockout mouse strain (LKO) to directly address the role of hepatic Prkn.

Methods

Littermate control (WT) and LKO mice were fed regular chow (RC) or high-fat diet (HFD) and changes in body weight and composition were measured over time. Liver mitochondrial content was assessed using multiple, complementary techniques, and mitochondrial respiratory capacity was assessed using Oroboros O₂K platform. Liver fat was measured biochemically and assessed histologically, while global changes in hepatic gene expression were measured by RNA-seq. Whole-body and tissue-specific insulin resistance were assessed by hyperinsulinemic-euglycemic clamp with isotopic tracers.

Results

Liver-specific deletion of Prkn had no effect on body weight or adiposity during RC or HFD feeding; however, hepatic steatosis was increased by 45% in HFD-fed LKO compared with WT mice (P < 0.05). While there were no differences in mitochondrial content between genotypes on either diet, mitochondrial respiratory capacity and efficiency in the liver were significantly reduced in LKO mice. Gene enrichment analyses from liver RNA-seq results suggested significant changes in pathways related to lipid metabolism and fibrosis in HFD-fed Prkn knockout mice. Finally, whole-body insulin sensitivity was reduced by 35% in HFD-fed LKO mice (P < 0.05), which was primarily due to increased hepatic insulin resistance (60% of whole-body effect; P = 0.11).

Conclusions

These data demonstrate that PARKIN contributes to mitochondrial homeostasis in the liver and plays a protective role against the pathogenesis of hepatic steatosis and insulin resistance.

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Mitochondrial respiratory capacity is reduced in liver-specific Prkn knockout mice.

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Liver-specific Prkn knockout mice develop more severe steatosis during high-fat diet feeding.

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Pathogenesis of NAFLD, including insulin resistance and markers of fibrosis, is enhanced in liver-specific Prkn knockout mice.

Bisphenol-A exposure worsens hepatic steatosis in ovariectomized mice fed on a high-fat diet: Role of endoplasmic reticulum stress and fibrogenic pathways

AIMS

Bisphenol (BP)-A exposure can impair glucose and lipid metabolism. However, it is unclear whether this endocrine disruptor (ED) modulates these processes in postmenopause, a period with organic changes that increase the risk for metabolic diseases. Herein, we evaluated the effects of BPA exposure on adiposity, glucose homeostasis and hepatic steatosis in ovariectomized (OVX) mice fed on a high-fat diet (HFD).

MAIN METHODS

Adult Swiss female mice were OVX and submitted to a normolipidic diet or HFD and drinking water without [control (OVX CTL) and OVX HFD groups, respectively] or with 1 μg/mL BPA (OVX CBPA and OVX HBPA groups, respectively), for 3 months.

KEY FINDINGS

OVX HFD females displayed increased adiposity, glucose intolerance, insulin resistance and moderate hepatic steatosis. This effect was associated with a high hepatic expression of genes involved in lipogenesis (Srebf1 and Scd1), β-oxidation (Cpt1a) and endoplasmic reticulum (ER) stress (Hspa5 and Hyou1). BPA did not alter adiposity or glucose homeostasis disruptions induced by HFD. However, this ED triggered severe steatosis, exacerbating hepatic fat and collagen depositions in OVX HBPA, in association with a reduction in Mttp mRNA, and up-regulation of genes involved in β-oxidation (Acox1 and Acadvl), mitochondrial uncoupling (Ucp2), ER stress (Hyou1 and Atf6) and chronic liver injury (Tgfb1and Casp8). Furthermore, BPA caused mild steatosis in OVX CBPA females, increasing the hepatic total lipids and mRNAs for Srebf1, Scd1, Hspa5, Hyou1 and Atf6.

SIGNIFICANCE

BPA aggravated hepatic steatosis in OVX mice. Especially when combined with a HFD, BPA caused NAFLD progression, which was partly mediated by chronic ER stress and the TGF-β1 pathway.

OSBPL2 Is Required for the Binding of COPB1 to ATGL and the Regulation of Lipid Droplet Lipolysis

The accumulation of giant lipid droplets (LDs) increases the risk of metabolic disorders including obesity and insulin resistance. The lipolysis process involves the activation and transfer of lipase, but the molecular mechanism is not completely understood. The translocation of ATGL, a critical lipolysis lipase, from the ER to the LD surface is mediated by an energy catabolism complex. Oxysterol-binding protein-like 2 (OSBPL2/ORP2) is one of the lipid transfer proteins that regulates intracellular cholesterol homeostasis. A recent study has proven that Osbpl2^−/− pigs exhibit hypercholesterolemia and obesity phenotypes with an increase in adipocytes. In this study, we identified that OSBPL2 links the endoplasmic reticulum (ER) with LDs, binds to COPB1, and mediates ATGL transport. We provide important insights into the function of OSBPL2, indicating that it is required for the regulation of lipid droplet lipolysis.

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LD lipolysis is impaired in OSBPL2/osbpl2b-mutant HepG2 cells and zebrafish

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OSBPL2 interacts with COPB1, a subunit of the COPI complex located on LDs

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Altered COPI complexes on LDs may perturb the trafficking of lipolysis lipase ATGL

Hepatic HuR modulates lipid homeostasis in response to high-fat diet

Lipid transport and ATP synthesis are critical for the progression of non-alcoholic fatty liver disease (NAFLD), but the underlying mechanisms are largely unknown. Here, we report that the RNA-binding protein HuR (ELAVL1) forms complexes with NAFLD-relevant transcripts. It associates with intron 24 of Apob pre-mRNA, with the 3′UTR of Uqcrb, and with the 5′UTR of Ndufb6 mRNA, thereby regulating the splicing of Apob mRNA and the translation of UQCRB and NDUFB6. Hepatocyte-specific HuR knockout reduces the expression of APOB, UQCRB, and NDUFB6 in mice, reducing liver lipid transport and ATP synthesis, and aggravating high-fat diet (HFD)-induced NAFLD. Adenovirus-mediated re-expression of HuR in hepatocytes rescues the effect of HuR knockout in HFD-induced NAFLD. Our findings highlight a critical role of HuR in regulating lipid transport and ATP synthesis.

Human antigen R (HuR) is a RNA binding protein involved in the regulation of many cellular functions. Here the authors show that, hepatocyte specific deletion of HuR exacerbates high-fat diet-induced NAFLD in mice by regulating transcripts involved in lipid transport and ATP synthesis.

Cyanidin-3-O-glucoside improves non-alcoholic fatty liver disease by promoting PINK1-mediated mitophagy in mice

BACKGROUND AND PURPOSE

Identifying safe and effective compounds that target to mitophagy to eliminate impaired mitochondria may be an attractive therapeutic strategy for non-alcoholic fatty liver disease. Here, we investigated the effects of cyanidin-3-O-glucoside (C3G) on non-alcoholic fatty liver disease (NAFLD) and the underlying mechanism.

EXPERIMENTAL APPROACH

Non-alcoholic fatty liver disease was induced by a high-fat diet for 16 weeks. C3G was administered during the last 4 weeks. In vivo, recombinant adenoviruses and AAV8 were used for overexpression and knockdown of PTEN-induced kinase 1 (PINK1), respectively. AML-12 and HepG2 cells were used for the mechanism study.

KEY RESULTS

C3G administration suppressed hepatic oxidative stress, NLR family pyrin domain containing 3 (NLRP3) inflammasome activation and steatosis and improved systemic glucose metabolism in mice with NAFLD. These effects of C3G were also observed in palmitic acid-treated AML-12 cells and hepatocytes from NAFLD patients. Mechanistic investigations revealed that C3G increased PINK1/Parkin expression and mitochondrial localization and promoted PINK1-mediated mitophagy to clear damaged mitochondria. Knockdown of hepatic PINK1 abolished the mitophagy-inducing effect of C3G, which blunted the beneficial effects of C3G on oxidative stress, NLRP3 inflammasome activation, hepatic steatosis and glucose metabolism.

CONCLUSION AND IMPLICATIONS

These results demonstrate that PINK1-mediated mitophagy plays an essential role in the ability of C3G to alleviate NAFLD and suggest that C3G may be a potential drug candidate for NAFLD treatment.

Moderate chronic ethanol consumption exerts beneficial effects on nonalcoholic fatty liver in mice fed a high-fat diet: possible role of higher formation of triglycerides enriched in monounsaturated fatty acids

PURPOSE

Several clinical studies suggested that light-to-moderate alcohol intake could alleviate nonalcoholic fatty liver disease (NAFLD), but the underlying mechanism is still poorly understood.

METHODS

Mice fed a high-fat diet (HFD) were submitted or not to moderate ethanol intake for 3 months (ca. 10 g/kg/day) via drinking water. Biochemical, analytical and transcriptomic analyses were performed in serum and liver.

RESULTS

Serum ethanol concentrations in ethanol-treated HFD mice comprised between 0.5 and 0.7 g/l throughout the experiment. NAFLD improvement was observed in ethanol-treated HFD mice as assessed by reduced serum transaminase activity. This was associated with less microvesicular and more macrovacuolar steatosis, the absence of apoptotic hepatocytes and a trend towards less fibrosis. Liver lipid analysis showed increased amounts of fatty acids incorporated in triglycerides and phospholipids, reduced proportion of palmitic acid in total lipids and higher desaturation index, thus suggesting enhanced stearoyl-coenzyme A desaturase activity. mRNA expression of several glycolytic and lipogenic enzymes was upregulated. Genome-wide expression profiling and gene set enrichment analysis revealed an overall downregulation of the expression of genes involved in collagen fibril organization and leukocyte chemotaxis and an overall upregulation of the expression of genes involved in oxidative phosphorylation and mitochondrial respiratory chain complex assembly. In addition, mRNA expression of several proteasome subunits was upregulated in ethanol-treated HFD mice.

CONCLUSIONS

Moderate chronic ethanol consumption may alleviate NAFLD by several mechanisms including the generation of non-toxic lipid species, reduced expression of profibrotic and proinflammatory genes, restoration of mitochondrial function and possible stimulation of proteasome activity.

Lipid Metabolism in Development and Progression of Hepatocellular Carcinoma

: Metabolic reprogramming is critically involved in the development and progression of cancer. In particular, lipid metabolism has been investigated as a source of energy, micro-environmental adaptation, and cell signalling in neoplastic cells. However, the specific role of lipid metabolism dysregulation in hepatocellular carcinoma (HCC) has not been widely described yet. Alterations in fatty acid synthesis, β-oxidation, and cellular lipidic composition contribute to initiation and progression of HCC. The aim of this review is to elucidate the mechanisms by which lipid metabolism is involved in hepatocarcinogenesis and tumour adaptation to different conditions, focusing on the transcriptional aberrations with new insights in lipidomics and lipid zonation. This will help detect new putative therapeutic approaches in the second most frequent cause of cancer-related death.

Role of oxidative stress in the pathogenesis of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) has emerged as the most common chronic liver disease worldwide and is strongly associated with the presence of oxidative stress. Disturbances in lipid metabolism lead to hepatic lipid accumulation, which affects different reactive oxygen species (ROS) generators, including mitochondria, endoplasmic reticulum, and NADPH oxidase. Mitochondrial function adapts to NAFLD mainly through the downregulation of the electron transport chain (ETC) and the preserved or enhanced capacity of mitochondrial fatty acid oxidation, which stimulates ROS overproduction within different ETC components upstream of cytochrome c oxidase. However, non-ETC sources of ROS, in particular, fatty acid β-oxidation, appear to produce more ROS in hepatic metabolic diseases. Endoplasmic reticulum stress and NADPH oxidase alterations are also associated with NAFLD, but the degree of their contribution to oxidative stress in NAFLD remains unclear. Increased ROS generation induces changes in insulin sensitivity and in the expression and activity of key enzymes involved in lipid metabolism. Moreover, the interaction between redox signaling and innate immune signaling forms a complex network that regulates inflammatory responses. Based on the mechanistic view described above, this review summarizes the mechanisms that may account for the excessive production of ROS, the potential mechanistic roles of ROS that drive NAFLD progression, and therapeutic interventions that are related to oxidative stress.

The Emerging Role of MicroRNAs in NAFLD: Highlight of MicroRNA-29a in Modulating Oxidative Stress, Inflammation, and Beyond

Non-alcoholic fatty liver disease (NAFLD) is a common cause of chronic liver disease and ranges from steatosis to steatohepatitis and to liver fibrosis. Lipotoxicity in hepatocytes, elevated oxidative stress and the activation of proinflammatory mediators of Kupffer cells, and fibrogenic pathways of activated hepatic stellate cells can contribute to the development of NAFLD. MicroRNAs (miRs) play a crucial role in the dysregulated metabolism and inflammatory signaling connected with NAFLD and its progression towards more severe stages. Of note, the protective effect of non-coding miR-29a on liver damage and its versatile action on epigenetic activity, mitochondrial homeostasis and immunomodulation may improve our perception of the pathogenesis of NAFLD. Herein, we review the biological functions of critical miRs in NAFLD, as well as highlight the emerging role of miR-29a in therapeutic application and the recent advances in molecular mechanisms underlying its liver protective effect.

PTPROt aggravates inflammation by enhancing NF-κB activation in liver macrophages during nonalcoholic steatohepatitis

Rationale: Inflammation plays a crucial role in the progression of nonalcoholic steatohepatitis (NASH). Protein tyrosine phosphatase receptor type O truncated isoform (PTPROt) is an integral membrane protein that has been identified in osteoclasts, macrophages, and B lymphocytes. However, its relationship between inflammation and NASH is largely unknown. Herein, we aimed to study the function of PTPROt in NASH progression.

Methods: We established a NASH mouse model in wild-type (WT), PTPRO knockout mice by western diet (WD) and methionine-choline-deficient diet (MCD). In addition, MCD-induced NASH model was established in BMT mice. Moreover, we determined the expression of PTPROt in liver macrophages in human subjects without steatosis, with simple steatosis, and with NASH to confirm the relationship between PTPROt and NASH. In vitro assays were also performed to study the molecular role of PTPROt in NASH progression.

Results: Human samples and animal model results illustrated that PTPROt is increased in liver macrophages during NASH progression and is positively correlated with the degree of NASH. Our animal model also showed that PTPROt in liver macrophages can enhance the activation of the NF-κB signaling pathway, which induces the transcription of genes involved in the inflammatory response. Moreover, PTPROt promotes the transcription of pro-oxidant genes and inhibits antioxidant and protective genes via increased activation of the NF-κB signaling pathway, thereby causing an increased level of reactive oxygen species (ROS) and damaged mitochondria. This triggers the NLRP3-IL1β axis and causes a heightened inflammatory response. Notably, PTPROt partially limits inflammation and ROS production by promoting mitophagy, which participates in a negative feedback loop in this model.

Conclusions: Our data strongly indicate that PTPROt plays a dual role in inflammation via the NF-κB signaling pathway in liver macrophages during NASH. Further studies are required to explore therapeutic strategies and prevention of this common liver disease through PTPROt.

San-Huang-Tang protects obesity/diabetes induced NAFLD by upregulating PGC-1α/PEPCK signaling in obese and galr1 knockout mice models

ETHNOPHARMACOLOGICAL RELEVANCE

San-Huang-Tang (ST), a classic prescription, has been clinically used to cure diabetes and diabetes-associated metabolic disorders. Established studies have reported that ST can alleviate inflammation, obesity, hyperglycemia and insulin resistance.

AIM OF THE STUDY

To the best of our knowledge, here, we reported for the first time the underlying mechanistic therapeutic efficacy of the ST against nonalcoholic fatty liver disease (NAFLD) in high-fat induced obese and galr1-deficient diabetic mice.

MATERIALS AND METHODS

The obese and galr1-deficient mice were treated with ST at a dose of 10 g/kg every day for three weeks. Then food intake, body weight and insulin resistance indexes were measured. Western blotting, qRT-PCR, and plasma biochemical analyses were applied.

RESULTS

ST reduced food intake, body weight, blood glucose level and insulin resistance, improved glucose tolerance in obese and galr1-deficient mice. Mechanistically, we confirmed that ST protected against NAFLD through activation of PGC-1α and its downstream signaling pathways as shown by the attenuated hepatic adipogenesis and lipid accumulation, increased hepatic fatty acid oxidation, regulated plasma lipid parameters, and increased energy expenditure and metabolic function in fat and muscle.

CONCLUSIONS

Reduction in food intake produced by ST may contribute to the observed metabolic effects. Our findings strongly suggest that ST might be a potential novel therapeutic drug against obesity/diabetes-induced NAFLD and other metabolic disorders.

The balance of protein farnesylation and geranylgeranylation during the progression of nonalcoholic fatty liver disease

Protein prenylation is an essential posttranslational modification and includes protein farnesylation and geranylgeranylation using farnesyl diphosphate or geranylgeranyl diphosphate as substrates, respectively. Geranylgeranyl diphosphate synthase is a branch point enzyme in the mevalonate pathway that affects the ratio of farnesyl diphosphate to geranylgeranyl diphosphate. Abnormal geranylgeranyl diphosphate synthase expression and activity can therefore disrupt the balance of farnesylation and geranylgeranylation and alter the ratio between farnesylated and geranylgeranylated proteins. This change is associated with the progression of nonalcoholic fatty liver disease (NAFLD), a condition characterized by hepatic fat overload. Of note, differential accumulation of farnesylated and geranylgeranylated proteins has been associated with differential stages of NAFLD and NAFLD-associated liver fibrosis. In this review, we summarize key aspects of protein prenylation as well as advances that have uncovered the regulation of associated metabolic patterns and signaling pathways, such as Ras GTPase signaling, involved in NAFLD progression. Additionally, we discuss unique opportunities for targeting prenylation in NAFLD/hepatocellular carcinoma with agents such as statins and bisphosphonates to improve clinical outcomes.

Effects and therapeutic mechanism of Yinzhihuang on steatohepatitis in rats induced by a high-fat, high-cholesterol diet

OBJECTIVES

We aimed to investigate the therapeutic mechanism of Yinzhihuang (YZH) liquid, a traditional Chinese medicine mainly composed of extracts of four components, on nonalcoholic steatohepatitis (NASH) induced by a high-fat, high-cholesterol diet (HFHCD) in rats.

METHODS

Altogether 30 Sprague-Dawley rats were randomized into three groups: control, the model group (HFHCD + saline) and the treatment group (HFHCD + YZH). Liver histological features and serum biochemical parameters were assessed by the end of the 16th week. RNA sequencing and protein mass spectrometry detection were performed. The genes and proteins expressed differentially were subjected to KEGG pathway enrichment analysis and included in a network-based regulatory model.

RESULTS

The weight, liver and fat indices and serum alanine transaminase, aspartate transaminase and total cholesterol levels of the HFHCD + YZH group were all significantly lower than those of the HFHCD + saline group. Moreover, their hepatic steatosis, ballooning and lobular inflammation were relieved, and 64 hepatic genes and 73 hepatic proteins were found to be reversed in their expression patterns after YZH treatment (P < 0.05). The network-based regulatory model showed that these deregulated genes and proteins were mainly involved in oxidative phosphorylation, Toll-like receptor, nucleotide-binding oligomerization domain-like receptor, peroxisome proliferator-activated receptor signaling, nuclear factor-kappa B tumor necrosis factor signaling pathways and fatty acid metabolism.

CONCLUSION

YZH could alleviate NASH in HFHCD-fed rats by inhibiting lipogenesis, accelerating lipid β-oxidation, alleviating oxidative stress and relieving necroinflammation in the liver.

Serum miR-379 expression is related to the development and progression of hypercholesterolemia in non-alcoholic fatty liver disease

Introduction

Non-alcoholic fatty liver disease (NAFLD) has a wide spectrum, eventually leading to cirrhosis and hepatic carcinogenesis. We previously reported that a series of microRNAs (miRNAs) mapped in the 14q32.2 maternally imprinted gene region (Dlk1-Dio3 mat) are related to NAFLD development and progression in a mouse model. We examined the suitability of miR-379, a circulating Dlk1-Dio3 mat miRNA, as a human NAFLD biomarker.

Methods

Eighty NAFLD patients were recruited for this study. miR-379 was selected from the putative Dlk1-Dio3 mat miRNA cluster because it exhibited the greatest expression difference between NAFLD and non-alcoholic steatohepatitis in our preliminary study. Real-time PCR was used to examine the expression levels of miR-379 and miR-16 as an internal control. One patient was excluded due to low RT-PCR signal.

Results

Compared to normal controls, serum miR-379 expression was significantly up-regulated in NAFLD patients. Receiver operating characteristic curve analysis suggested that miR-379 is a suitable marker for discriminating NAFLD patients from controls, with an area under the curve value of 0.72. Serum miR-379 exhibited positive correlations with alkaline phosphatase, total cholesterol, low-density-lipoprotein cholesterol and non-high-density-lipoprotein cholesterol levels in patients with early stage NAFLD (Brunt fibrosis stage 0 to 1). The correlation between serum miR-379 and cholesterol levels was lost in early stage NAFLD patients treated with statins. Software-based predictions indicated that various energy metabolism–related genes, including insulin-like growth factor-1 (IGF-1) and IGF-1 receptor, are potential targets of miR-379.

Conclusions

Serum miR-379 exhibits high potential as a biomarker for NAFLD. miR-379 appears to increase cholesterol lipotoxicity, leading to the development and progression of NAFLD, via interference with the expression of target genes, including those related to the IGF-1 signaling pathway. Our results could facilitate future research into the pathogenesis, diagnosis, and treatment of NAFLD.

Cellular Stress and General Pathological Processes

From the viewpoint of the general pathology, most of the human diseases are associated with a limited number of pathogenic processes such as inflammation, tumor growth, thrombosis, necrosis, fibrosis, atrophy, pathological hypertrophy, dysplasia and metaplasia. The phenomenon of chronic low-grade inflammation could be attributed to non-classical forms of inflammation, which include many neurodegenerative processes, pathological variants of insulin resistance, atherosclerosis, and other manifestations of the endothelial dysfunction. Individual and universal manifestations of cellular stress could be considered as a basic element of all these pathologies, which has both physiological and pathophysiological significance. The review examines the causes, main phenomena, developmental directions and outcomes of cellular stress using a phylogenetically conservative set of genes and their activation pathways, as well as tissue stress and its role in inflammatory and para-inflammatory processes. The main ways towards the realization of cellular stress and its functional blocks were outlined. The main stages of tissue stress and the classification of its typical manifestations, as well as its participation in the development of the classical and non-classical variants of the inflammatory process, were also described. The mechanisms of cellular and tissue stress are structured into the complex systems, which include networks that enable the exchange of information with multidirectional signaling pathways which together make these systems internally contradictory, and the result of their effects is often unpredictable. However, the possible solutions require new theoretical and methodological approaches, one of which includes the transition to integral criteria, which plausibly reflect the holistic image of these processes.