Mitochondria-Mediated Pathogenesis and Therapeutics for Non-Alcoholic Fatty Liver Disease

Pharmacological approaches to enhance mitochondrial biogenesis: focus on PGC-1Α, AMPK, and SIRT1 in cellular health

BACKGROUND

Mitochondrial biogenesis is essential for cellular energy balance and metabolic stability. Its dysregulation is linked to various metabolic and neurodegenerative diseases, making it a significant therapeutic target. Pharmacological approaches aimed at enhancing mitochondrial function have gained attention for their potential to restore cellular metabolism.

OBJECTIVES

This review examines recent advancements in pharmacological strategies targeting mitochondrial biogenesis, focusing on the roles of PGC-1α, AMPK, and SIRT1, alongside novel therapeutic agents and drug delivery systems.

METHODS

A systematic review of studies published between 2018 and 2023 was conducted using databases such as PubMed, Web of Science, and Elsevier. Keywords related to mitochondrial biogenesis and pharmacological modulation were used to identify relevant literature.

RESULTS

Various pharmacological agents, including resveratrol, curcumin, and metformin, activate mitochondrial biogenesis through different pathways. SIRT1 activators and AMPK agonists have shown promise in improving mitochondrial function. Advances in mitochondria-targeted drug delivery systems enhance therapeutic efficacy, yet challenges remain in clinical translation due to the complexity of mitochondrial regulation.

CONCLUSION

Pharmacological modulation of mitochondrial biogenesis holds therapeutic potential for metabolic and neurodegenerative diseases. While preclinical studies are promising, further research is needed to optimize drug efficacy, delivery methods, and personalized treatment strategies.

Curcumol ameliorates alcohol and high-fat diet-induced fatty liver disease via modulation of the Ceruloplasmin/iron overload/mtDNA signaling pathway

Fatty liver disease (FLD), a chronic liver disease characterized by excessive lipid deposition, is affecting more and more people worldwide owing to the increasing global incidence of obesity and heavy alcohol consumption. However, there is still no effective strategy for prevention or treatment of alcohol and high-fat diet (HFD)-induced FLD. The purpose of this study was to investigate the effect of curcumol on alcohol and HFD-induced FLD and the underlying molecular mechanisms. The results showed that curcumol ameliorated alcohol and HFD-induced hepatocyte injury in vivo and in vitro, and the mechanism might be related to its up-regulation of ceruloplasmin and subsequent alleviation of iron overload. Moreover, curcumol inhibited alcohol and HFD-induced mitochondrial damage and mtDNA release in hepatocytes by modulating iron overload. Furthermore, curcumol's inhibition of mtDNA release could suppress the activation of cGAS-STING and subsequent inflammation, and this phenomenon could be reversed by cGAS overexpression. Notably, alcohol and HFD-induced mtDNA release from hepatocytes contributed to HSC activation and this effect could be weakened by curcumol. In conclusion, these findings elucidated that curcumol ameliorated alcohol and HFD-induced FLD via modulating ceruloplasmin/iron overload/mtDNA signaling pathway, which lead to the inhibition of inflammation and HSCs activation.

PDZD8 Augments Endoplasmic Reticulum-Mitochondria Contact and Regulates Ca2+ Dynamics and Cypd Expression to Induce Pancreatic β-Cell Death during Diabetes

BACKGRUOUND

Diabetes mellitus (DM) is a chronic metabolic disease that poses serious threats to human physical and mental health worldwide. The PDZ domain-containing 8 (PDZD8) protein mediates mitochondria-associated endoplasmic reticulum (ER) membrane (MAM) formation in mammals. We explored the role of PDZD8 in DM and investigated its potential mechanism of action.

METHODS

High-fat diet (HFD)- and streptozotocin-induced mouse DM and palmitic acid (PA)-induced insulin 1 (INS-1) cell models were constructed. PDZD8 expression was detected using immunohistochemistry, quantitative real-time polymerase chain reaction (qRT-PCR), and Western blotting. MAM formation, interactions between voltage-dependent anion-selective channel 1 (VDAC1) and inositol 1,4,5-triphosphate receptor type 1 (IP3R1), pancreatic β-cell apoptosis and proliferation were detected using transmission electron microscopy (TEM), proximity ligation assay (PLA), terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, immunofluorescence staining, and Western blotting. The mitochondrial membrane potential, cell apoptosis, cytotoxicity, and subcellular Ca2+ localization in INS-1 cells were detected using a JC-1 probe, flow cytometry, and an lactate dehydrogenase kit.

RESULTS

PDZD8 expression was up-regulated in the islets of HFD mice and PA-treated pancreatic β-cells. PDZD8 knockdown markedly shortened MAM perimeter, suppressed the expression of MAM-related proteins IP3R1, glucose-regulated protein 75 (GRP75), and VDAC1, inhibited the interaction between VDAC1 and IP3R1, alleviated mitochondrial dysfunction and ER stress, reduced the expression of ER stress-related proteins, and decreased apoptosis while increased proliferation of pancreatic β-cells. Additionally, PDZD8 knockdown alleviated Ca2+ flow into the mitochondria and decreased cyclophilin D (Cypd) expression. Cypd overexpression alleviated the promoting effect of PDZD8 knockdown on the apoptosis of β-cells.

CONCLUSION

PDZD8 knockdown inhibited pancreatic β-cell death in DM by alleviated ER-mitochondria contact and the flow of Ca2+ into the mitochondria.

BRUCE liver-deficiency potentiates MASLD/MASH in PTEN liver-deficient background by impairment of mitochondrial metabolism in hepatocytes and activation of STAT3 signaling in hepatic stellate cells

Metabolic dysfunction-associated steatotic liver disease (MASLD) is currently the most common liver disease, affecting up to 25% of people worldwide, featuring excessive fat accumulation in hepatocytes. Its advanced form, metabolic dysfunction-associated steatohepatitis (MASH), is a serious disease with hepatic inflammation and fibrosis, increasing the need for liver transplants. However, the pathogenic mechanism of MASLD and MASH is not fully understood. We reported that BRUCE ( BIRC6) is a liver cancer suppressor and is downregulated in MASLD/MASH patient liver specimens, though the functional role of BRUCE in MASLD/MASH remains to be elucidated. To this end, we generated liver-specific double KO (DKO) mice of BRUCE and PTEN, a major tumor suppressor and MASLD/MASH suppressor. By comparing liver histopathology among 2-3-month-old mice, there were no signs of MASLD or MASH in BRUCE liver-KO mice and only onset of steatosis in PTEN liver-KO mice. Interestingly, DKO mice had developed robust hepatic steatosis with inflammation and fibrosis. Further analysis of mitochondrial function with primary hepatocytes found moderate reduction of mitochondrial respiration, ATP production and fatty acid oxidation in BRUCE KO and the greatest reduction in DKO hepatocytes. Moreover, aberrant activation of pro-fibrotic STAT3 signaling was found in hepatic stellate cells (HSCs) in DKO mice which was prevented by administered STAT3-specific inhibitor (TTI-101). Collectively, the data demonstrates by maintaining mitochondrial metabolism BRUCE works in concert with PTEN to suppress the pro-fibrogenic STAT3 activation in HSCs and consequentially prevent MASLD/MASH. The findings highlight BRUCE being a new co-suppressor of MASLD/MASH.

A new perspective on liver diseases: Focusing on the mitochondria-associated endoplasmic reticulum membranes

The pathogenesis of liver diseases is multifaceted and intricate, posing a persistent global public health challenge with limited therapeutic options. Therefore, further research into liver diseases is imperative for better comprehension and advancement in treatment strategies. Numerous studies have confirmed the endoplasmic reticulum (ER) and mitochondria as key organelles driving liver diseases. Notably, the mitochondrial-associated ER membranes (MAMs) establish a physical and functional connection between the ER and mitochondria, highlighting the importance of inter-organelle communication in maintaining their functional homeostasis. This review delves into the intricate architecture and regulative mechanism of the integrated MAM that facilitate the physiological transfer of signals and substances between organelles. Additionally, we also provide a detailed overview regarding the varied pathogenic roles of malfunctioning MAM in liver diseases, focusing on its involvement in the progression of ER stress and mitochondrial dysfunction, the regulation of mitochondrial dynamics and Ca2+ transfer, as well as the disruption of lipid and glucose homeostasis. Furthermore, the current challenges and prospects associated with MAM in liver disease research are thoroughly discussed. In conclusion, elucidating the specific structure and function of MAM in different liver diseases may pave the way for novel therapeutic strategies.

Mettl3-m6A-YTHDF1 axis promotion of mitochondrial dysfunction in metabolic dysfunction-associated steatotic liver disease

BACKGROUND

N6-methyladenosine (m6A) mRNA modification and mitochondrial function hold paramount importance in the advancement of metabolic dysfunction-associated steatotic liver disease (MASLD).

AIM

The aim of this study was to elucidate the impact of m6A on hepatic mitochondrial dysfunction and provide a novel perspective for a more comprehensive understanding of the pathogenesis of MASLD.

METHODS

High-throughput screening methods were used to identify the underlying transcriptome and proteome changes in MASLD model mice. Western blotting, blue native gel electrophoresis (BNGE), dot blot, and Seahorse analyses were conducted to identify and validate the underlying regulatory mechanisms of m6A on mitochondria.

RESULTS

In vivo, abnormal m6A modification in MASLD was attributed to the upregulation of methyltransferase like 3 (Mettl3) and the downregulation of YTH N6-methyladenosine RNA binding protein 1 (YTHDF1) induced by high-fat foods. In vitro, knockdown of Mettl3 inhibited hepatic oxidative phosphorylation (OXPHOS) and the mitochondrial respiratory chain (MRC), while overexpression of Mettl3 promoted these processes. However, knockout of the reader protein YTHDF1, which plays a crucial role in the m6A modification process, counteracted the effect of Mettl3 and suppressed mitochondrial OXPHOS.

CONCLUSIONS

In MASLD, damage to the MRC may be regulated by the Mettl3-m6A-YTHDF1 axis, particularly by the role of YTHDF1. Modulation of the Mettl3-m6A-YTHDF1 axis has the potential to improve mitochondrial function, alleviate MASLD symptoms, and decrease the likelihood of disease progression.

Dual Phytochemical/Activity-Guided Optimal Preparation and Bioactive Material Basis of Orthosiphon Stamineus Benth. (Shen Tea) against Nonalcoholic Fatty Liver Disease

Orthosiphon stamineus Benth. (OSB) is a popular plant used for making "Shen tea" or "Java tea". It has been demonstrated with antioxidant, anti-inflammatory, and hepatoprotective activities. However, its potential beneficial effects and bioactive material basis for nonalcoholic fatty liver disease (NAFLD) has not been convincingly studied. In the present work, we conducted dual phytochemical/activity-guided extraction optimization and component fractionation of OSB, and evaluated its beneficial effects on NAFLD. Flavonoids and polyphenols (caffeic acid/protocatechuic acid derivatives) were determined as the dominant phytochemicals in OSB. The extraction process for these phytochemicals was optimized by using response surface methodology. Noticeably, flavonoids showed a stronger correlation with the antioxidant activities of OSB than polyphenols. Likewise, the flavonoid-rich fraction of OSB exerted antioxidant activities stronger than those of other fractions. As expected, in vitro and in vivo studies demonstrated that the flavonoid-rich fraction effectively attenuated weight increase, improved lipid metabolism, alleviated hepatic steatosis, and reversed hepatic inflammation. Importantly, this fraction showed equivalent beneficial effects to the total extract of OSB, suggesting that flavonoids were the main bioactive constituents of OSB. The action mechanism was indicated as direct antioxidant effect through chemical interaction with free radicals and indirect mitochondria-mediated antioxidant defense. Our research offers bioactive substances for further exploitation and expands the potential application of OSB.

Gut microbial metabolites in MASLD: Implications of mitochondrial dysfunction in the pathogenesis and treatment

With an increasing prevalence, metabolic dysfunction-associated steatotic liver disease (MASLD) has become a major global health problem. MASLD is well-known as a multifactorial disease. Mitochondrial dysfunction and alterations in the gut bacteria are 2 vital events in MASLD. Recent studies have highlighted the cross-talk between microbiota and mitochondria, and mitochondria are recognized as pivotal targets of the gut microbiota to modulate the host's physiological state. Mitochondrial dysfunction plays a vital role in MASLD and is associated with multiple pathological changes, including hepatocyte steatosis, oxidative stress, inflammation, and fibrosis. Metabolites are crucial mediators of the gut microbiota that influence extraintestinal organs. Additionally, regulation of the composition of gut bacteria may serve as a promising therapeutic strategy for MASLD. This study reviewed the potential roles of several common metabolites in MASLD, emphasizing their impact on mitochondrial function. Finally, we discuss the current treatments for MASLD, including probiotics, prebiotics, antibiotics, and fecal microbiota transplantation. These methods concentrate on restoring the gut microbiota to promote host health.

Mitochondria-Derived Vesicles, Sterile Inflammation, and Pyroptosis in Liver Cancer: Partners in Crime or Innocent Bystanders?

Alterations in cellular signaling, chronic inflammation, and tissue remodeling contribute to hepatocellular carcinoma (HCC) development. The release of damage-associated molecular patterns (DAMPs) upon tissue injury and the ensuing sterile inflammation have also been attributed a role in HCC pathogenesis. Cargoes of extracellular vesicles (EVs) and/or EVs themselves have been listed among circulating DAMPs but only partially investigated in HCC. Mitochondria-derived vesicles (MDVs), a subpopulation of EVs, are another missing link in the comprehension of the molecular mechanisms underlying the onset and progression of HCC biology. EVs have been involved in HCC growth, dissemination, angiogenesis, and immunosurveillance escape. The contribution of MDVs to these processes is presently unclear. Pyroptosis triggers systemic inflammation through caspase-dependent apoptotic cell death and is implicated in tumor immunity. The analysis of this process, together with MDV characterization, may help capture the relationship among HCC development, mitochondrial quality control, and inflammation. The combination of immune checkpoint inhibitors (i.e., atezolizumab and bevacizumab) has been approved as a synergistic first-line systemic treatment for unresectable or advanced HCC. The lack of biomarkers that may allow prediction of treatment response and, therefore, patient selection, is a major unmet need. Herein, we overview the molecular mechanisms linking mitochondrial dysfunction, inflammation, and pyroptosis, and discuss how immunotherapy targets, at least partly, these routes.

Mitochondrial-mediated nuclear remodeling and macrophage polarizations: A key switch from liver fibrosis to HCC progression

Liver fibrosis is a significant health burden worldwide and has emerged as the leading cause of Hepatocellular carcinoma (HCC) incidence. Mitochondria are the dynamic organelles that regulate the differentiation, survival, and polarization of macrophages. Nuclear-DNA-associated proteins, micro-RNAs, as well as macrophage polarization are essential for maintaining intracellular and extra-cellular homeostasis in the liver parenchyma. Dysregulated mitochondrial coding genes (ETS complexes I, II, III, IV, and V), non-coding RNAs (mitomiRs), and nuclear alteration lead to the production of reactive oxygen species (ROS) and inflammation which are implicated in the transition of liver fibrosis into HCC. Recent findings indicated the protecting effect of E74-like factor 3/peroxisome proliferator-activated receptor-γ (Elf-3/PPAR-γ). HDAR-y inhibits the deacetylation of PPAR-y and maintains the PPAR-y pathway. Elf-3 plays a tumor suppressive role through epithelial-mesenchymal transition-related gene and zinc finger E-box binding homeobox 2 (ZEB-2) domain. Additionally, the development of HCC includes the PI3K/Akt/mTOR and transforming Growth Factor β (TGF-β) pathway that promotes the Epithelial-mesenchymal transition (EMT) through Smad/Snail/Slug signaling cascade. In contrast, the TLR2/NOX2/autophagy axis promotes M2 polarization in HCC. Thus, a thorough understanding of the mitochondrial and nuclear reciprocal relationship related to macrophage polarization could provide new research opportunities concerning diseases with a significant impact on liver parenchyma towards developing liver fibrosis or liver cancer. Moreover, this knowledge can be used to develop new therapeutic strategies to treat liver diseases.

Mitochondrial Quality Control: Its Role in Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD)

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as non-alcoholic fatty liver disease, is characterized by hepatic steatosis and metabolic dysfunction and is often associated with obesity and insulin resistance. Recent research indicates a rapid escalation in MASLD cases, with projections suggesting a doubling in the United States by 2030. This review focuses on the central role of mitochondria in the pathogenesis of MASLD and explores potential therapeutic interventions. Mitochondria are dynamic organelles that orchestrate hepatic energy production and metabolism and are critically involved in MASLD. Dysfunctional mitochondria contribute to lipid accumulation, inflammation, and liver fibrosis. Genetic associations further underscore the relationship between mitochondrial dynamics and MASLD susceptibility. Although U.S. Food and Drug Administration-approved treatments for MASLD remain elusive, ongoing clinical trials have highlighted promising strategies that target mitochondrial dysfunction, including vitamin E, metformin, and glucagon-like peptide-1 receptor agonists. In preclinical studies, novel therapeutics, including nicotinamide adenine dinucleotide+ precursors, urolithin A, spermidine, and mitoquinone, have shown beneficial effects, such as improving mitochondrial quality control, reducing oxidative stress, and ameliorating hepatic steatosis and inflammation. In conclusion, mitochondrial dysfunction is central to MASLD pathogenesis. The innovative mitochondria-targeted approaches discussed in this review offer a promising avenue for reducing the burden of MASLD and improving global quality of life.

Thyroid Hormone and Mitochondrial Dysfunction: Therapeutic Implications for Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD)

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly termed nonalcoholic fatty liver disease (NAFLD), is a widespread global health concern that affects around 25% of the global population. Its influence is expanding, and it is anticipated to overtake alcohol as the leading cause of liver failure and liver-related death worldwide. Unfortunately, there are no approved therapies for MASLD; as such, national and international regulatory health agencies undertook strategies and action plans designed to expedite the development of drugs for treatment of MASLD. A sedentary lifestyle and an unhealthy diet intake are important risk factors. Western countries have a greater estimated prevalence of MASLD partly due to lifestyle habits. Mitochondrial dysfunction is strongly linked to the development of MASLD. Further, it has been speculated that mitophagy, a type of mitochondrial quality control, may be impaired in MASLD. Thyroid hormone (TH) coordinates signals from the nuclear and mitochondrial genomes to control mitochondrial biogenesis and function in hepatocytes. Mitochondria are known TH targets, and preclinical and clinical studies suggest that TH, thyroid receptor β (TR-β) analogs, and synthetic analogs specific to the liver could be of therapeutic benefit in treating MASLD. In this review, we highlight how mitochondrial dysfunction contributes to development of MASLD, and how understanding the role of TH in improving mitochondrial function paved the way for innovative drug development programs of TH-based therapies targeting MASLD.

Exploring the potential mechanism of Rubus corchorifolius L. fruit polyphenol-rich extract in mitigating non-alcoholic fatty liver disease by integration of metabolomics and transcriptomics profiling

Nonalcoholic fatty liver disease (NAFLD), as the commonest chronic liver disease, is accompanied by liver oxidative stress and inflammatory responses. Herein, the extract obtained from Rubus corchorifolius fruits was purified and characterized for its polyphenol composition. The liver protective effect of the purified R. corchorifolius fruit extract (RCE) on mice with high-fat-diet (HFD)-induced NAFLD were investigated, and the potential mechanisms were explored through the integration of transcriptomics and metabolomics. Results showed that the polyphenolic compounds in RCE mainly included (-)-epigallocatechin, procyanidin B2, keracyanin, vanillin, dihydromyricetin, and ellagic acid. In addition, RCE intervention ameliorated liver and mitochondrial damage, which was evidenced by decreased indices of oxidative stress, liver function markers, and lipid profile levels. The liver metabonomics research revealed that RCE intervention affected the metabolic pathways of metabolites, including linoleic acid metabolism, galactose metabolism, alanine, aspartate and glutamate metabolism, retinol metabolism, glycine, serine and threonine metabolism, tryptophan metabolism, aminoacyl-tRNA biosynthesis, riboflavin metabolism, starch and sucrose metabolism, and arachidonic acid metabolism. Additionally, liver transcriptomics research indicated that pathways like fatty acid degradation, circadian rhythm, valine, leucine and isoleucine degradation, primary bile acid biosynthesis, cytokine-cytokine receptor interaction, adipocytokine signaling pathway, glutathione metabolism, lipid and atherosclerosis were significantly enriched. The transcriptomics and metabolomics analysis demonstrated that RCE intervention had significant modulatory effects on the metabolic pathways associated with glycolipid metabolism. Moreover, RT-PCR results verified that RCE intervention regulated liver mRNA levels associated with the inflammatory response. Therefore, our findings suggest that the intake of RCE might be an effective strategy to alleviate liver damage.

Natural polysaccharides protect against diet-induced obesity by improving lipid metabolism and regulating the immune system

Unhealthy dietary patterns-induced obesity and obesity-related complications pose a great threat to human health all over the world. Accumulating evidence suggests that the pathophysiology of obesity and obesity-associated metabolic disorders is closely associated with dysregulation of lipid and energy metabolism, and metabolic inflammation. In this review, three potential anti-obesity mechanisms of natural polysaccharides are introduced. Firstly, natural polysaccharides protect against diet-induced obesity directly by improving lipid and cholesterol metabolism. Since the immunity also affects lipid and energy metabolism, natural polysaccharides improve lipid and energy metabolism by regulating host immunity. Moreover, diet-induced mitochondrial dysfunction, prolonged endoplasmic reticulum stress, defective autophagy and microbial dysbiosis can disrupt lipid and/or energy metabolism in a direct and/or inflammation-induced manner. Therefore, natural polysaccharides also improve lipid and energy metabolism and suppress inflammation by alleviating mitochondrial dysfunction and endoplasmic reticulum stress, promoting autophagy and regulating gut microbiota composition. Specifically, this review comprehensively summarizes underlying anti-obesity mechanisms of natural polysaccharides and provides a theoretical basis for the development of functional foods. For the first time, this review elucidates anti-obesity mechanisms of natural polysaccharides from the perspectives of their hypolipidemic, energy-regulating and immune-regulating mechanisms.

The newly proposed alanine aminotransferase to high-density lipoprotein cholesterol ratio has shown effectiveness in identifying non-alcoholic fatty liver disease

Objective

Alanine aminotransferase (ALT) and high-density lipoprotein cholesterol (HDL-C) are important predictive factors for non-alcoholic fatty liver disease (NAFLD). The aim of this study was to analyze the association between the ALT/HDL-C ratio and NAFLD.

Methods

We conducted a retrospective analysis of data from 14,251 individuals participating in the NAGALA project's health screening program. The presence of NAFLD was diagnosed based on the participants' alcohol consumption status and liver ultrasonography images. Multivariable logistic regression models were used to assess the association between the ALT/HDL-C ratio and NAFLD. Receiver operating characteristic (ROC) analysis was performed to determine and compare the effectiveness of ALT, HDL-C, the aspartate aminotransferase to HDL-C (AST/HDL-C) ratio, the gamma-glutamyl transferase to HDL-C (GGT/HDL-C) ratio and the ALT/HDL-C ratio in identifying NAFLD.

Results

We observed a significant positive association between the ALT/HDL-C ratio and the prevalence of NAFLD. For each standard deviation (SD) increase in the ALT/HDL-C ratio, the adjusted odds ratio (OR) for NAFLD among the participants was 3.05 [95% confidence interval (CI): 2.63, 3.53], with the highest quartile of ALT/HDL-C ratio having a 9.96-fold increased risk compared to the lowest quartile. In further subgroup analyses stratified by gender, age, and waist circumference (WC), we observed a significantly higher risk of NAFLD associated with the ALT/HDL-C ratio among individuals aged ≥45 years, males, and those who were abdominal obesity. Furthermore, based on the results of ROC analysis, we found that the ALT/HDL-C ratio [area under the curves (AUC): 0.8553] was significantly superior to ALT, HDL-C, AST/HDL-C ratio and GGT/HDL-C ratio in identifying NAFLD (All Delong P<0.05); the threshold of suggested ALT/HDL-C ratio for identifying NAFLD was 15.97.

Conclusion

This population-based study demonstrates a positive association between the ALT/HDL-C ratio and NAFLD. The ALT/HDL-C ratio can effectively identify individuals with NAFLD.

Mitochondrial metabolic dysfunction and non-alcoholic fatty liver disease: new insights from pathogenic mechanisms to clinically targeted therapy

Metabolic dysfunction-associated fatty liver disease (MAFLD) is among the most widespread metabolic disease globally, and its associated complications including insulin resistance and diabetes have become threatening conditions for human health. Previous studies on non-alcoholic fatty liver disease (NAFLD) were focused on the liver's lipid metabolism. However, growing evidence suggests that mitochondrial metabolism is involved in the pathogenesis of NAFLD to varying degrees in several ways, for instance in cellular division, oxidative stress, autophagy, and mitochondrial quality control. Ultimately, liver function gradually declines as a result of mitochondrial dysfunction. The liver is unable to transfer the excess lipid droplets outside the liver. Therefore, how to regulate hepatic mitochondrial function to treat NAFLD has become the focus of current research. This review provides details about the intrinsic link of NAFLD with mitochondrial metabolism and the mechanisms by which mitochondrial dysfunctions contribute to NAFLD progression. Given the crucial role of mitochondrial metabolism in NAFLD progression, the application potential of multiple mitochondrial function improvement modalities (including physical exercise, diabetic medications, small molecule agonists targeting Sirt3, and mitochondria-specific antioxidants) in the treatment of NAFLD was evaluated hoping to provide new insights into NAFLD treatment.

The Role of Fucoxanthin in Non-Alcoholic Fatty Liver Disease

Chronic liver disease (CLD) has emerged as a leading cause of human deaths. It caused 1.32 million deaths in 2017, which affected men more than women by a two-to-one ratio. There are various causes of CLD, including obesity, excessive alcohol consumption, and viral infection. Among them, non-alcoholic fatty liver disease (NAFLD), one of obesity-induced liver diseases, is the major cause, representing the cause of more than 50% of cases. Fucoxanthin, a carotenoid mainly found in brown seaweed, exhibits various biological activities against NAFLD. Its role in NAFLD appears in several mechanisms, such as inducing thermogenesis in mitochondrial homeostasis, altering lipid metabolism, and promoting anti-inflammatory and anti-oxidant activities. The corresponding altered signaling pathways are the β3-adorenarine receptor (β3Ad), proliferator-activated receptor gamma coactivator (PGC-1), adenosine monophosphate-activated protein kinase (AMPK), peroxisome proliferator-activated receptor (PPAR), sterol regulatory element binding protein (SREBP), nuclear factor kappa B (NF-κB), mitogen-activated protein kinase (MAPK), protein kinase B (AKT), SMAD2/3, and P13K/Akt pathways. Fucoxanthin also exhibits anti-fibrogenic activity that prevents non-alcoholic steatohepatitis (NASH) development.

Hepatic Mitochondria-Gut Microbiota Interactions in Metabolism-Associated Fatty Liver Disease

The prevalence of metabolism-associated fatty liver disease (MAFLD) represents an urgent pandemic, complicated by a higher risk of morbidity and mortality as well as an increased socio-economic burden. There is growing evidence proving the impact of gut microbiota modifications on the development and progression of MAFLD through changes in metabolic pathways, modulation of the immune response, and activation of pro-inflammatory signals. Concurrently, metabolites produced by gut microbiota consisting of short chain fatty acids and bile acids contribute to the regulation of hepatic homeostasis by interacting with mitochondria. Evolving research indicates that innovative therapeutic targets for MAFLD may focus on gut microbiota-mitochondria interplay to regulate hepatic homeostasis. Recent investigations have explored the potential of new treatment strategies, such as prebiotics, probiotics, and metabolites, to change the composition of gut microbiota and simultaneously exert a positive impact on mitochondrial function to improve MAFLD. This review summarizes the significance of mitochondria and reports modifications in the composition of gut microbiota and its metabolites in MAFLD in order to illustrate the fascinating interplay between liver mitochondria and intestinal microbiota, discussing the potential effects of innovative treatments to modulate gut microbiota.

The Non-Invasive Assessment of Circulating D-Loop and mt-ccf Levels Opens an Intriguing Spyhole into Novel Approaches for the Tricky Diagnosis of NASH

Nonalcoholic fatty liver disease (NAFLD) is the commonest liver disease worldwide affecting both adults and children. Nowadays, no therapeutic strategies have been approved for NAFLD management, and hepatic biopsy remains the gold standard procedure for its diagnosis. NAFLD is a multifactorial disease whose pathogenesis is affected by environmental and genetic factors, and it covers a spectrum of conditions ranging from simple steatosis up to nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). Several studies underlined the urgent need to develop an NAFLD risk prediction model based on genetics, biochemical indicators, and metabolic disorders. The loss of mitochondrial dynamics represents a typical feature of progressive NAFLD. The imbalance of mitochondrial lifecycle together with the impairment of mitochondrial biomass and function trigger oxidative stress, which in turn damages mitochondrial DNA (mtDNA). We recently demonstrated that the main genetic predictors of NAFLD led to mitochondrial dysfunction. Moreover, emerging evidence shows that variations in the displacement loop (D-loop) region impair mtDNA replication, and they have been associated with advanced NAFLD. Finally, lower levels of mitophagy foster the overload of damaged mitochondria, resulting in the release of cell-free circulating mitochondrial DNA (mt-ccf) that exacerbates liver injury. Thus, in this review we summarized what is known about D-loop region alterations and mt-ccf content during NAFLD to propose them as novel non-invasive biomarkers.

The role of hepatic microenvironment in hepatic fibrosis development

AIM

Fibrosis is a common pathological feature of most types of chronic liver injuries. There is no specific treatment for liver fibrosis at present. The liver microenvironment, which fosters the survival and activity of liver cells, plays an important role in maintaining the normal structure and physiological function of the liver. The aim of this review is to deeply understand the role of the liver microenvironment in the dynamic and complicated development of liver fibrosis.

METHODS

After searching in Elsevier ScienceDirect, PubMed and Web of Science databases using 'liver fibrosis' and 'microenvironment' as keywords, studies related to microenvironment in liver fibrosis was compiled and examined.

RESULTS

The homeostasis of the liver microenvironment is disrupted during the development of liver fibrosis, affecting liver cell function, causing various types of cell reactions, and changing the cell-cell and cell-matrix interactions, eventually affecting fibrosis formation.

CONCLUSION

Liver microenvironment may be important for identifying potential therapeutic targets, and restoring microenvironment homeostasis may be an important strategy for promoting the reversal of liver fibrosis.KEY MESSAGESThe homeostasis of the liver microenvironment is disrupted in liver fibrosis;A pro-fibrotic microenvironment is formed during the development of liver fibrosis;Restoring microenvironment homeostasis may be an important strategy for promoting the reversal of liver fibrosis.

Phytochemicals targeting NAFLD through modulating the dual function of forkhead box O1 (FOXO1) transcription factor signaling pathways

Literature evidence reveals that natural compounds are potential candidates for ameliorating obesity-associated non-alcoholic fatty liver disease (NAFLD) by targeting forkhead box O1 (FOXO1) transcription factor. FOXO1 has a dual and complex role in regulating both increase and decrease in lipid accumulation in hepatocytes and adipose tissues (AT) at different stages of NAFLD. In insulin resistance (IR), it is constitutively expressed, resulting in increased hepatic glucose output and lipid metabolism irregularity. The studies on different phytochemicals indicate that dysregulation of FOXO1 causes disturbance in cellular nutrients homeostasis, and the natural entities have an enduring impact on the mitigation of these abnormalities. The current review communicates and evaluates certain phytochemicals through different search engines, targeting FOXO1 and its downstream cellular pathways to find lead compounds as potential therapeutic agents for treating NAFLD and related metabolic disorders. The findings of this review confirm that polyphenols, flavonoids, alkaloids, terpenoids, and anthocyanins are capable of modulating FOXO1 and associated signaling pathways, and they are potential therapeutic agents for NAFLD and related complications. HIGHLIGHTS: • FOXO1 has the potential to be targeted by novel drugs from natural sources for the treatment of NAFLD and obesity. • FOXO1 regulates cellular autophagy, inflammation, oxidative stress, and lipogenesis through alternative mechanisms. • Phytochemicals treat NAFLD by acting on FOXO1 or SREBP1c and PPARγ transcription factor signaling pathways.

Mitochondrial Dysfunction Plays Central Role in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a global pandemic that affects one-quarter of the world’s population. NAFLD includes a spectrum of progressive liver disease from steatosis to nonalcoholic steatohepatitis (NASH), fibrosis, and cirrhosis and can be complicated by hepatocellular carcinoma. It is strongly associated with metabolic syndromes, obesity, and type 2 diabetes, and it has been shown that metabolic dysregulation is central to its pathogenesis. Recently, it has been suggested that metabolic- (dysfunction) associated fatty liver disease (MAFLD) is a more appropriate term to describe the disease than NAFLD, which puts increased emphasis on the important role of metabolic dysfunction in its pathogenesis. There is strong evidence that mitochondrial dysfunction plays a significant role in the development and progression of NAFLD. Impaired mitochondrial fatty acid oxidation and, more recently, a reduction in mitochondrial quality, have been suggested to play a major role in NAFLD development and progression. In this review, we provide an overview of our current understanding of NAFLD and highlight how mitochondrial dysfunction contributes to its pathogenesis in both animal models and human subjects. Further we discuss evidence that the modification of mitochondrial function modulates NAFLD and that targeting mitochondria is a promising new avenue for drug development to treat NAFLD/NASH.

Downregulation of hepatic fat accumulation, inflammation and fibrosis by nerolidol in purpose built western-diet-induced multiple-hit pathogenesis of NASH animal model

Western diet style (fast food), which includes fatty frozen junk food, lard, processed meats, whole-fat dairy foods, cream, mayonnaise, butter, snacks, and fructose, is a primary etiological determinant for developing nonalcoholic steatohepatitis (NASH) worldwide. Here the primary focus is to see the impact of naturally identified essential oil on disease mechanisms developed in an animal model using the same ingredients. Currently, symptomatic therapies are recommended for the management of NASH due to non-availability of specific treatments. Therefore, the present study was designed to evaluate the potential anti-NASH effect of nerolidol in a rat model fed with a purpose-built diet. The diet substantially induced insulin resistance, hepatic steatosis, dyslipidemia, and elevation of liver enzymes in the experimental animals. The levels of liver oxidative stress markers, nitrites (NO₂^-), serum pro-inflammatory cytokine (TNF-α) and hepatic collagen were increased in disease control rats. Nerolidol oral treatment in ascending dose order of 250 and 500 mg/kg substantially reduced the steatosis (macrovesicular and microvesicular), degeneration of hepatocytes, and inflammatory cells infiltration. The amounts of circulatory TNF-α and tissue collagen were also reduced at 500 mg/kg dose of nerolidol, expressing its anti-fibrotic effect. The current study described the multiple-hit pathophysiology of NASH as enhanced steatosis, pro-inflammatory markers, and oxidative stress in rats, which resulted in the development of vicious insulin resistance. Nerolidol treatment significantly reduced hepatic lipid accumulation and halted disease progression induced by a hypercaloric diet.

Transcriptomic analysis in zebrafish larvae identifies iron-dependent mitochondrial dysfunction as a possible key event of NAFLD progression induced by benzo[a]pyrene/ethanol co-exposure

Non-alcoholic fatty liver disease (NAFLD) is a worldwide epidemic for which environmental contaminants are increasingly recognized as important etiological factors. Among them, the combination of benzo[a]pyrene (B[a]P), a potent environmental carcinogen, with ethanol, was shown to induce the transition of steatosis toward steatohepatitis. However, the underlying mechanisms involved remain to be deciphered. In this context, we used high-fat diet fed zebrafish model, in which we previously observed progression of steatosis to a steatohepatitis-like state following a 7-day-co-exposure to 43 mM ethanol and 25 nM B[a]P. Transcriptomic analysis highlighted the potent role of mitochondrial dysfunction, alterations in heme and iron homeostasis, involvement of aryl hydrocarbon receptor (AhR) signaling, and oxidative stress. Most of these mRNA dysregulations were validated by RT-qPCR. Moreover, similar changes were observed using a human in vitro hepatocyte model, HepaRG cells. The mitochondria structural and functional alterations were confirmed by transmission electronic microscopy and Seahorse technology, respectively. Involvement of AhR signaling was evidenced by using in vivo an AhR antagonist, CH223191, and in vitro in AhR-knock-out HepaRG cells. Furthermore, as co-exposure was found to increase the levels of both heme and hemin, we investigated if mitochondrial iron could induce oxidative stress. We found that mitochondrial labile iron content was raised in toxicant-exposed larvae. This increase was prevented by the iron chelator, deferoxamine, which also inhibited liver co-exposure toxicity. Overall, these results suggest that the increase in mitochondrial iron content induced by B[a]P/ethanol co-exposure causes mitochondrial dysfunction that contributes to the pathological progression of NAFLD.

CRISPR screen identified that UGT1A9 was required for bisphenols-induced mitochondria dyshomeostasis

Exposure to bisphenols chemicals could cause various adverse health effects, including non-alcoholic fatty liver disease (NAFLD), which have been associated with cellular mitochondria stress. However, the biological mechanism underlying the mitochondria stress-mediated cell death by bisphenols was poorly understood. Here, CRISPR screens were performed to identify the critical genes which were involved in cell death caused by exposure to four bisphenols (BPA, BPB, BPE and BPS). Results of CRISPR screens showed that UGT1A9 was the primary genetic factor facilitating cell death induced by all of the four bisphenols. Systematic toxicological tests demonstrated that UGT1A9 was required for BPA-induced mitochondria dyshomeostasis in vitro and in vivo, and UGT1A9-mediated mitochondria dyshomeostasis was an important cause of facilitating cell death. Liver injury caused by exposure to BPA in wild-type mice was accompanied with suppression of mitophagy and increased expression of C-Caspase 3, but UGT1A9 knockout attenuated these adverse effects induced by BPA. Finally, molecular epidemiology analysis suggested that the five genetic variants of UGT1A9 could be potential genetic risk factors of NAFLD when people were exposed to BPA. The biological mechanism uncovered here provided mechanistic evidence for identification of susceptible populations of liver injury associated with exposure to BPA.

Preventive Effect of Apple Polyphenol Extract on High-Fat Diet-Induced Hepatic Steatosis in Mice through Alleviating Endoplasmic Reticulum Stress

In this work, the protective effect of apple polyphenol extract (APE) on hepatic steatosis was investigated. Thirty-two C57BL/6J mice were assigned randomly to control group, hepatic steatosis group, lovastatin group, and APE group. After 8 weeks of intervention, APE supplementation markedly decreased the body weight gain, liver weight, liver index, epididymal adipose weight, epididymal adipose index, serum, and hepatic lipid levels. Hematoxylin and eosin staining revealed that APE supplementation alleviated histopathological changes of hepatic steatosis. Western blot revealed that APE downregulated the protein levels of GRP78, IRE1α, p-IRE1α, XBP1, PERK, p-PERK, p-eIF2α, ATF6, PPAR-γ, SREBP-1c, FAS, and ACC1. In conclusion, this study found that APE inhibited IRE1α-XBP1, PERK-eIF2α, and ATF6 signaling pathways to alleviate endoplasmic reticulum stress, thereby improving HFD-induced hepatic steatosis.

Protective Roles of Shilajit in Modulating Resistin, Adiponectin, and Cytokines in Rats with Non-alcoholic Fatty Liver Disease

OBJECTIVE

To evaluate the effect of Shilajit, a medicine of Ayurveda, on the serum changes in cytokines and adipokines caused by non-alcoholic fatty liver disease (NAFLD).

METHODS

After establishing fatty liver models by feeding a high-fat diet (HFD) for 12 weeks, 35 Wistar male rats were randomly divided into 5 groups, including control (standard diet), Veh (HFD + vehicle), high-dose Shilajit [H-Sh, HFD + 250 mg/(kg·d) Shilajit], low-dose Shilajit [L-Sh, HFD + 150 mg/(kg·d) Shilajit], and pioglitazone [HFD + 10 mg/(kg·d) pioglitazone] groups, 7 rats in each group. After 2-week of gavage administration, serum levels of glucose, insulin, interleukin 1beta (IL-1β), IL-6, IL-10, tumor necrosis factor-alpha (TNF-α), adiponectin, and resistin were measured, and insulin resistance index (HOMA-IR) was calculated.

RESULTS

After NAFLD induction, the serum level of IL-10 significantly increased and serum IL-1β, TNF-α levels significantly decreased by injection of both doses of Shilajit and pioglitazone (P<0.05). Increases in serum glucose level and homeostasis model of HOMA-IR were reduced by L-Sh and H-Sh treatment in NAFLD rats (P<0.05). Both doses of Shilajit increased adiponectin and decreased serum resistin levels (P<0.05).

CONCLUSION

The probable protective role of Shilajit in NAFLD model rats may be via modulating the serum levels of IL-1β, TNF-α, IL-10, adipokine and resistin, and reducing of HOMA-IR.

Altered Mitochondrial Quality Control in Rats with Metabolic Dysfunction-Associated Fatty Liver Disease (MAFLD) Induced by High-Fat Feeding

Metabolic dysfunction-associated fatty liver disease (MAFLD) is defined as the presence of hepatic steatosis in addition to one of three metabolic conditions: overweight/obesity, type 2 diabetes mellitus, or metabolic dysregulation. Chronic exposure to excess dietary fatty acids may cause hepatic steatosis and metabolic disturbances. The alteration of the quality of mitochondria is one of the factors that could contribute to the metabolic dysregulation of MAFDL. This study was designed to determine, in a rodent model of MAFLD, the effects of a long-term high-fat diet (HFD) on some hepatic processes that characterize mitochondrial quality control, such as biogenesis, dynamics, and mitophagy. To mimic the human manifestation of MAFLD, the rats were exposed to both an HFD and a housing temperature within the rat thermoneutral zone (28–30 °C). After 14 weeks of the HFD, the rats showed significant fat deposition and liver steatosis. Concomitantly, some important factors related to the hepatic mitochondrial quality were markedly affected, such as increased mitochondrial reactive oxygen species (ROS) production and mitochondrial DNA (mtDNA) damage; reduced mitochondrial biogenesis, mtDNA copy numbers, mtDNA repair, and mitochondrial fusion. HFD-fed rats also showed an impaired mitophagy. Overall, the obtained data shed new light on the network of different processes contributing to the failure of mitochondrial quality control as a central event for mitochondrial dysregulation in MAFLD.

Steatosis induced by nonylphenol in HepG2 cells and the intervention effect of curcumin

Non-alcoholic fatty liver disease (NAFLD) has increasingly become a serious public health problem. There is growing evidence that nonylphenol (NP) exposure may cause steatosis, but the underlying mechanism is not fully understood. Curcumin (CUR) improves NAFLD-related lipid metabolism disorders and oxidative stress, but its preventive and therapeutic effects on NP-induced steatosis have not been reported. The objective of this investigation was to determine the capability and potential mechanism of NP to induce steatosis in vitro and the intervention of curcumin. HepG2 cells were treated with 0 μM, 20 μM, 30 μM, 40 μM NP for 24 h. Lipid droplets accumulated significantly in HepG2 cells after NP treatment, and the concentration of triglyceride (TG) and total cholesterol (T-CHO) increased significantly. Simultaneously, lipogenesis gene expression was up-regulated significantly, fatty acid oxidation (FAO) gene expression was significantly down-regulated, and reactive oxygen species (ROS) were overproduced. Meanwhile, the expression of p-AMPK/AMPK in the AMPK/mTOR signaling pathway was significantly down-regulated and the expression of p-mTOR/mTOR was markedly up-regulated. However, blocking ROS production with N-acetyl-L-cysteine (NAC) can reverse these phenomena. In addition, our study found that curcumin effectively ameliorated the effects of NP-induced steatosis. Our study indicates that NP can induce steatosis in HepG2 cells, and may be implicated in inhibiting the ROS-dependent AMPK/mTOR pathway, and that curcumin ameliorates the NAFLD-like changes induced by NP in HepG2 cells.

Molecular targets regulating endoplasmic reticulum-mitochondria crosstalk for NAFLD treatment

Non-alcoholic fatty liver disease (NAFLD) as the most common chronic liver disease poses a significant impact on public healthcare and economic risk worldwide. As a multifactorial disease, NAFLD is usually associated with many comorbidities such as obesity, insulin resistance, hypertension, hyperlipidemia, diabetes, and cardiovascular disease. Without effectively preventive intervention, the advanced stage of NAFLD, non-alcoholic steatohepatitis (NASH), can progress to cirrhosis and hepatocellular carcinoma (HCC). However, there is no approved therapeutic treatment. Excessive fat accumulation in the liver is the hallmark of NAFLD, which can lead to mitochondrial dysfunction and endoplasmic reticulum (ER) stress. Dysfunction of two organelles also induces the upregulation of reactive oxygen species (ROS), activation of the unfolded protein response (UPR), and disruption of calcium transport, which promote NAFLD progression. Herein, this review summarized the current understanding of the roles of mitochondrial dysfunction and ER stress in the pathogenesis of NAFLD. Specifically, this review focused on the key molecules associated with the ER-mitochondria communication and different treatment options by targeting ER stress and mitochondrial dysfunction to treat NAFLD or NASH. Clinical trials to evaluate the therapeutic efficacy of representative agents, such as natural products, metabolites, and modulators of stress, have been reviewed and analyzed. Overall, recent findings suggest that targeting ER stress and mitochondrial dysfunction holds a promise for NAFLD treatment.

Environmental toxicant-induced maladaptive mitochondrial changes: A potential unifying mechanism in fatty liver disease?

Occupational and environmental exposures to industrial chemicals are well known to cause hepatotoxicity and liver injury. However, despite extensive evidence showing that exposure can lead to disease, current research approaches and regulatory policies fail to address the possibility that subtle changes caused by low level exposure to chemicals may also enhance preexisting conditions. In recent years, the conceptual understanding of the contribution of environmental chemicals to liver disease has progressed significantly. Mitochondria are often target of toxicity of environmental toxicants resulting in multisystem disorders involving different cells, tissues, and organs. Here, we review persistent maladaptive changes to mitochondria in response to environmental toxicant exposure as a mechanism of hepatotoxicity. With better understanding of the mechanism(s) and risk factors that mediate the initiation and progression of toxicant-induced liver disease, rational targeted therapy can be developed to better predict risk, as well as to treat or prevent this disease.

Carnosol alleviates nonalcoholic fatty liver disease by inhibiting mitochondrial dysfunction and apoptosis through targeting of PRDX3

Mitochondrial dysfunction is a major factor in nonalcoholic fatty liver disease (NAFLD), preceding insulin resistance and hepatic steatosis. Carnosol (CAR) is a kind of diterpenoid with antioxidant, anti-inflammatory and antitumor activities. Peroxiredoxin 3 (PRDX3), a mitochondrial H2O2-eliminating enzyme, undergoes overoxidation and subsequent inactivation under oxidative stress. The purpose of this study was to investigate the protective effect of the natural phenolic compound CAR on NAFLD via PRDX3. Mice fed a high-fat diet (HFD) and AML-12 cells treated with palmitic acid (PA) were used to detect the molecular mechanism of CAR in NAFLD. We found that pharmacological treatment with CAR notably moderated HFD- and PA- induced steatosis and liver injury, as shown by biochemical assays, Oil Red O and Nile Red staining. Further mechanistic investigations revealed that CAR exerted anti-NAFLD effects by inhibiting mitochondrial oxidative stress, perturbation of mitochondrial dynamics, and apoptosis in vivo and in vitro. The decreased protein and mRNA levels of PRDX3 were accompanied by intense oxidative stress after PA intervention. Interestingly, CAR specifically bound PRDX3, as shown by molecular docking assays, and increased the expression of PRDX3. However, the hepatoprotection of CAR in NAFLD was largely abolished by specific PRDX3 siRNA, which increased mitochondrial dysfunction and exacerbated apoptosis in vitro. In conclusion, CAR suppressed lipid accumulation, mitochondrial dysfunction and hepatocyte apoptosis by activating PRDX3, mitigating the progression of NAFLD, and thus, CAR may represent a promising candidate for clinical treatment of steatosis.

Network Pharmacology Exploration Reveals Anti-Apoptosis as a Common Therapeutic Mechanism for Non-Alcoholic Fatty Liver Disease Treated with Blueberry Leaf Polyphenols

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease characterized by excessive fat accumulation in the liver. The aim of this study is to elucidate the multi-target mechanism of polyphenols in blueberry leaves (PBL) on NAFLD by network pharmacology and to validate its results via biological experiments. Twenty constituents in PBL were preliminarily determined by liquid chromatography-tandem mass spectrometry. Subsequently, 141 predicted drug targets and 1226 targets associated with NAFLD were retrieved from public databases, respectively. The herb-compound-target network and the target protein–protein interaction network (PPI) were established through Cytoscape software, and four compounds and 53 corresponding targets were identified. Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment were performed to explore the biological processes of the predicted genes. The results of cell experiments demonstrated that PBL could significantly improve the viability of the NAFLD cell model, and the protein expressions of caspase-3 and Bcl-2 were consistent with the expected mechanism of action of PBL. Those results systematically revealed that the multi-target mechanism of PBL against NAFLD was related to the apoptosis pathway, which could bring deeper reflections into the hepatoprotective effect of PBL.

Tebuconazole Fungicide Induces Lipid Accumulation and Oxidative Stress in HepG2 Cells

Tebuconazole (TEB), a triazole fungicide, is frequently applied to agriculture for the increase of food production. Although TEB causes liver toxicity, its effects on cellular lipid accumulation are rarely investigated. Therefore, this study aimed to study the effects of TEB on lipid metabolism and accumulation in HepG2 cells. HepG2 cells were exposed to 0-320 µM TEB for 1-24 h. TEB (20-80 µM, 24 h)-treated cells showed lipid accumulation. Further, TEB (20-80 µM, 1-12 h) increased the nuclear translocation of peroxisome proliferator-activated receptors and the expression of lipid uptake and oxidation-related markers such as cluster of differentiation 36, fatty acid transport protein (FATP) 2, FATP5, and carnitine palmitoyltransferase 1. Oxidative stress levels in TEB-treated cells (20-80 µM, 24 h) were higher, compared to those in the control. TEB (20-80 µM, 24 h) also induced the loss of mitochondrial membrane potential and lower levels of microsomal triglyceride transfer protein in the cells. Thus, TEB can induce lipid accumulation by altering the expression of lipid-metabolizing molecules and can therefore impair lipid metabolism. Our data suggest that human exposure to TEB may be a risk factor for non-alcoholic fatty liver disease.

3,4-dihydroxytoluene, a metabolite of rutin, suppresses the progression of nonalcoholic fatty liver disease in mice by inhibiting p300 histone acetyltransferase activity

3,3',4',5,7-Pentahydroxyflavone-3-rhamnoglucoside (rutin) is a flavonoid with a wide range of pharmacological activities. Dietary rutin is hardly absorbed because the microflora in the large intestine metabolize rutin into a variety of compounds including quercetin and phenol derivatives such as 3,4-dihydroxyphenolacetic acid (DHPAA), 3,4-dihydroxytoluene (DHT), 3,4-hydroxyphenylacetic acid (HPAA) and homovanillic acid (HVA). We examined the potential of rutin and its metabolites as novel histone acetyltransferase (HAT) inhibitors. DHPAA, HPAA and DHT at the concentration of 25 μM significantly inhibited in vitro HAT activity with DHT having the strongest inhibitory activity. Furthermore, DHT was shown to be a highly efficient inhibitor of p300 HAT activity, which corresponded with its high degree of inhibition on intracellular lipid accumulation in HepG2 cells. Docking simulation revealed that DHT was bound to the p300 catalytic pocket, bromodomain. Drug affinity responsive target stability (DARTS) analysis further supported the possibility of direct binding between DHT and p300. In HepG2 cells, DHT concentration-dependently abrogated p300-histone binding and induced hypoacetylation of histone subunits H3K9, H3K36, H4K8 and H4K16, eventually leading to the downregulation of lipogenesis-related genes and attenuating lipid accumulation. In ob/ob mice, administration of DHT (10, 20 mg/kg, iv, every other day for 6 weeks) dose-dependently improved the NAFLD pathogenic features including body weight, liver mass, fat mass, lipid accumulation in the liver, and biochemical blood parameters, accompanied by the decreased mRNA expression of lipogenic genes in the liver. Our results demonstrate that DHT, a novel p300 histone acetyltransferase inhibitor, may be a potential preventive or therapeutic agent for NAFLD.

Drug-like sphingolipid SH-BC-893 opposes ceramide-induced mitochondrial fission and corrects diet-induced obesity

Ceramide-induced mitochondrial fission drives high-fat diet (HFD)-induced obesity. However, molecules targeting mitochondrial dynamics have shown limited benefits in murine obesity models. Here, we reveal that these compounds are either unable to block ceramide-induced mitochondrial fission or require extended incubation periods to be effective. In contrast, targeting endolysosomal trafficking events important for mitochondrial fission rapidly and robustly prevented ceramide-induced disruptions in mitochondrial form and function. By simultaneously inhibiting ARF6- and PIKfyve-dependent trafficking events, the synthetic sphingolipid SH-BC-893 blocked palmitate- and ceramide-induced mitochondrial fission, preserved mitochondrial function, and prevented ER stress in vitro. Similar benefits were observed in the tissues of HFD-fed mice. Within 4 h of oral administration, SH-BC-893 normalized mitochondrial morphology in the livers and brains of HFD-fed mice, improved mitochondrial function in white adipose tissue, and corrected aberrant plasma leptin and adiponectin levels. As an interventional agent, SH-BC-893 restored normal body weight, glucose disposal, and hepatic lipid levels in mice consuming a HFD. In sum, the sphingolipid analog SH-BC-893 robustly and acutely blocks ceramide-induced mitochondrial dysfunction, correcting diet-induced obesity and its metabolic sequelae.

Mitochondria Matter: Systemic Aspects of Nonalcoholic Fatty Liver Disease (NAFLD) and Diagnostic Assessment of Liver Function by Stable Isotope Dynamic Breath Tests

The liver plays a key role in systemic metabolic processes, which include detoxification, synthesis, storage, and export of carbohydrates, lipids, and proteins. The raising trends of obesity and metabolic disorders worldwide is often associated with the nonalcoholic fatty liver disease (NAFLD), which has become the most frequent type of chronic liver disorder with risk of progression to cirrhosis and hepatocellular carcinoma. Liver mitochondria play a key role in degrading the pathways of carbohydrates, proteins, lipids, and xenobiotics, and to provide energy for the body cells. The morphological and functional integrity of mitochondria guarantee the proper functioning of β-oxidation of free fatty acids and of the tricarboxylic acid cycle. Evaluation of the liver in clinical medicine needs to be accurate in NAFLD patients and includes history, physical exam, imaging, and laboratory assays. Evaluation of mitochondrial function in chronic liver disease and NAFLD is now possible by novel diagnostic tools. "Dynamic" liver function tests include the breath test (BT) based on the use of substrates marked with the non-radioactive, naturally occurring stable isotope 13C. Hepatocellular metabolization of the substrate will generate 13CO2, which is excreted in breath and measured by mass spectrometry or infrared spectroscopy. Breath levels of 13CO2 are biomarkers of specific metabolic processes occurring in the hepatocyte cytosol, microsomes, and mitochondria. 13C-BTs explore distinct chronic liver diseases including simple liver steatosis, non-alcoholic steatohepatitis, liver fibrosis, cirrhosis, hepatocellular carcinoma, drug, and alcohol effects. In NAFLD, 13C-BT use substrates such as α-ketoisocaproic acid, methionine, and octanoic acid to assess mitochondrial oxidation capacity which can be impaired at an early stage of disease. 13C-BTs represent an indirect, cost-effective, and easy method to evaluate dynamic liver function. Further applications are expected in clinical medicine. In this review, we discuss the involvement of liver mitochondria in the progression of NAFLD, together with the role of 13C-BT in assessing mitochondrial function and its potential use in the prevention and management of NAFLD.

Quercetin and non-alcoholic fatty liver disease: A review based on experimental data and bioinformatic analysis

Quercetin, a polyphenol widely present in the plant kingdom, has received great interest due to pleiotropic effects. As evidenced by animal and cellular studies, quercetin exerts hepatoprotection against non-alcoholic fatty liver disease (NAFLD), particularly in hepatic steatosis and hepatitis. Mechanically, various hypotheses of such protective effects have been actively proposed, including improving fatty acid metabolism, anti-inflammation, anti-oxidant, modulating gut microbiota and bile acid, etc. Here, the role of quercetin in NAFLD was summarized. With a particular focus on molecular mechanism, we comprehensively discussed the pathways of quercetin on NAFLD based on the analysis from Gene Expression Omnibus (GEO) database and experimental evidence.

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.

Rosmarinic acid exerts an antagonistic effect on nonalcoholic fatty liver disease by regulating the YAP1/TAZ-PPARγ/PGC-1α signaling pathway

Rosmarinic acid (RA) is a water-soluble phenolic compound extracted from Boraginaceae and Lamiaceae. This study was designed to investigate the role and mechanism of action of RA in improving nonalcoholic fatty liver disease (NAFLD). Male SD rats maintained on a high fat diet and L02 cells stimulated with oleic acid were treated with RA. Our results showed that RA significantly reduced total cholesterol, triglycerides, low-density lipoprotein cholesterol, alanine aminotransferase, aspartate aminotransferase, and malondialdehyde levels and increased high-density lipoprotein cholesterol, superoxide dismutase and adenosine triphosphate levels both in vivo and in vitro. Hematoxylin and eosin staining and oil red O staining showed that RA had a good lipid-lowering effect and substantial protective effects on liver injury. Transmission electron microscopy and JC-1 fluorescence results showed that RA could improve mitochondrial damage in hepatocytes. Additionally, flow cytometry results indicated that RA inhibited ROS generation and apoptosis in L02 cells. The impaired hepatocytes were restored by using RA in NAFLD models characterized by down-regulating YAP1 and TAZ, meanwhile up-regulating PPARγ and PGC-1α. When YAP1 was over-expressed, RA reduced the expression of YAP1; however, the action of RA was significantly blocked by silencing YAP1. The experimental results indicated that RA markedly alleviated NAFLD by repairing mitochondrial damage and regulating the YAP1/TAZ-PPARγ/PGC-1α signaling pathway.

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.

Friend or Foe: Lipid Droplets as Organelles for Protein and Lipid Storage in Cellular Stress Response, Aging and Disease

Lipid droplets (LDs) were considered as a mere lipid storage organelle for a long time. Recent evidence suggests that LDs are in fact distinct and dynamic organelles with a specialized proteome and functions in many cellular roles. As such, LDs contribute to cellular signaling, protein and lipid homeostasis, metabolic diseases and inflammation. In line with the multitude of functions, LDs interact with many cellular organelles including mitochondria, peroxisomes, lysosomes, the endoplasmic reticulum and the nucleus. LDs are highly mobile and dynamic organelles and impaired motility disrupts the interaction with other organelles. The reduction of interorganelle contacts results in a multitude of pathophysiologies and frequently in neurodegenerative diseases. Contacts not only supply lipids for β-oxidation in mitochondria and peroxisomes, but also may include the transfer of toxic lipids as well as misfolded and harmful proteins to LDs. Furthermore, LDs assist in the removal of protein aggregates when severe proteotoxic stress overwhelms the proteasomal system. During imbalance of cellular lipid homeostasis, LDs also support cellular detoxification. Fine-tuning of LD function is of crucial importance and many diseases are associated with dysfunctional LDs. We summarize the current understanding of LDs and their interactions with organelles, providing a storage site for harmful proteins and lipids during cellular stress, aging inflammation and various disease states.

Phytotherapy using blueberry leaf polyphenols to alleviate non-alcoholic fatty liver disease through improving mitochondrial function and oxidative defense

BACKGROUND

Since non-alcoholic fatty liver disease (NAFLD) pathogenesis is multi-factorial, pharmacotherapy with a specific target commonly exhibits limited efficacy. Phytotherapy, whose therapeutic efficacy is based on the combined action of several active compounds, offers new treatment opportunity for NAFLD. As a representative, many natural polyphenols could be utilized in phytotherapy for NAFLD.

PURPOSE

In present work, we aimed to investigate the therapeutic effects and underlying mechanism of polyphenols in blueberry leaves (PBL) on NAFLD from a mitochondria-centric perspective since mitochondrial dysfunction could play a dominant role in NAFLD.

METHODS

Identification and quantification of PBL were performed using liquid chromatography coupled with tandem mass spectrometry. The beneficial effects, especially improving mitochondrial function, and potential mechanism of PBL on NAFLD were studied by in vitro and in vivo study.

RESULTS

Polyphenols were abundant in blueberry leaves making it advantaged in NAFLD phytotherapy. PBL effectively alleviated hepatic steatosis, oxidative stress and inflammation as indicated by both in vitro and in vivo study. Furthermore, PBL mediated improvement of mitochondrial dysfunction and antioxidant capability through activation of AMPK/PGC-1α/SIRT3 signaling axis.

CONCLUSION

Considering that mitochondrial dysfunction takes precedence over hepatic steatosis and induces NAFLD development, we conclude that PBL improve mitochondrial dysfunction and oxidative defense, subsequently alleviate hepatic steatosis, oxidative stress and inflammation, and eventually alleviate NAFLD.