Mitochondrial dysfunction in non-alcoholic fatty liver disease and insulin resistance: Cause or consequence?

Exploring the effect and mechanism of Hippophae rhamnoides L. triterpenoid acids on improving NAFLD based on network pharmacology and experimental validation in vivo and in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

Sea buckthorn (Hippophae rhamnoides L.) is a traditional Chinese medicinal and possesses a rich medical history in terms of treating gastric disorders, sputum and cough and liver injuries in oriental medicinal system. By reason of the complicated chemical constituents, the material basis and potential pharmacological mechanism of sea buckthorn acting on Non-alcoholic fatty liver disease (NAFLD) has not been clearly elucidated.

AIM OF THE STUDY

To explore the pharmacological efficacy and underlying mechanism of sea buckthorn triterpenoid acid enrichment (STE) in the treatment of NAFLD.

MATERIALS AND METHODS

The approaches of Network pharmacology and experiment validation in vitro and in vivo were applied in this study. Firstly, targets of triterpenoid acid compounds and NAFLD were collected from databases. The crucial targets were screened by the construction of protein-protein interaction (PPI) network. Furthermore, the potential signaling pathways and targets affected by STE was predicted by GO together with KEGG enrichment analysis. Finally, the experiment validation was carried out through high-fat feeding NAFLD mice and lipid accumulation HepG2 cell model. Lipids and liver related biochemical indicators were determined, Oil Red O and H&E staining were employed to observe fat accumulation. In addition, the expression levels of proteins of key target and signal pathway anticipated in network pharmacology were detected to elaborated its action mechanism.

RESULTS

A total of 180 intersecting potential targets for enhancing NAFLD with STE were eventually identified. 6 key targets including AKT1, TNF, IL6, INS, JUN, STAT3 and TP53 were further identified and the AMPK-SREBP1 pathway was enriched. Animal experiment result showed that STE treatment could significantly reduce the levels of TG, TC, LDL-C, ALT and AST, increase the levels of HDL-C in serum, and improve lipid accumulation of epididymal fat and liver. The results of the lipid accumulation cell model indicated that STE and key compound oleanolic acid could diminish intracellular lipid levels of TG, TC, LDL-C and number of lipid droplets. Western blot results showed that the above beneficial effects could be achieved by regulating the expression of p-AMPK/AMPK, SREBP1, FAS, ACC, SCD protein.

CONCLUSION

This study confirmed the effect of STE on improving NAFLD and the potential action mechanism was involved in the regulation of the AMPK-SREBP1 pathway.

Hepatic-specific Pgc-1α ablation drives fibrosis in a MASH model

BACKGROUND & AIMS

Metabolic dysfunction-associated steatohepatitis (MASH) is a growing cause of chronic liver disease, characterized by fat accumulation, inflammation and fibrosis, which development depends on mitochondrial dysfunction and oxidative stress. Highly expressed in the liver during fasting, peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) regulates mitochondrial and oxidative metabolism. Given the relevant role of mitochondrial function in MASH, we investigated the relationship between PGC-1α and steatohepatitis.

METHODS

We measured the hepatic expression of Pgc-1α in both MASH patients and wild-type mice fed a western diet (WD) inducing steatosis and fibrosis. We then generated a pure C57BL6/J strain loss of function mouse model in which Pgc-1α is selectively deleted in the liver and we fed these mice with a WD supplemented with sugar water that accurately mimics human MASH.

RESULTS

We observed that the hepatic expression of Pgc-1α is strongly reduced in MASH, in both humans and mice. Moreover, the hepatic ablation of Pgc-1α promotes a considerable reduction of the hepatic mitochondrial respiratory capacity, setting up a bioenergetic harmful environment for liver diseases. Indeed, the lack of Pgc-1α decreases mitochondrial function and increases inflammation, fibrosis and oxidative stress in the scenario of MASH. Intriguingly, this profibrotic phenotype is not linked with obesity, insulin resistance and lipid disbalance.

CONCLUSIONS

In a MASH model the hepatic ablation of Pgc-1α drives fibrosis independently from lipid and glucose metabolism. These results add a novel mechanistic piece to the puzzle of the specific and crucial role of mitochondrial function in MASH development.

VDAC1-Based Peptides as Potential Modulators of VDAC1 Interactions with Its Partners and as a Therapeutic for Cancer, NASH, and Diabetes

This review presents current knowledge related to the voltage-dependent anion channel-1 (VDAC1) as a multi-functional mitochondrial protein that acts in regulating both cell life and death. The location of VDAC1 at the outer mitochondrial membrane (OMM) allows control of metabolic cross-talk between the mitochondria and the rest of the cell, and also enables its interaction with proteins that are involved in metabolic, cell death, and survival pathways. VDAC1's interactions with over 150 proteins can mediate and regulate the integration of mitochondrial functions with cellular activities. To target these protein-protein interactions, VDAC1-derived peptides have been developed. This review focuses specifically on cell-penetrating VDAC1-based peptides that were developed and used as a "decoy" to compete with VDAC1 for its VDAC1-interacting proteins. These peptides interfere with VDAC1 interactions, for example, with metabolism-associated proteins such as hexokinase (HK), or with anti-apoptotic proteins such as Bcl-2 and Bcl-xL. These and other VDAC1-interacting proteins are highly expressed in many cancers. The VDAC1-based peptides in cells in culture selectively affect cancerous, but not non-cancerous cells, inducing cell death in a variety of cancers, regardless of the cancer origin or genetics. They inhibit cell energy production, eliminate cancer stem cells, and act very rapidly and at low micro-molar concentrations. The activity of these peptides has been validated in several mouse cancer models of glioblastoma, lung, and breast cancers. Their anti-cancer activity involves a multi-pronged attack targeting the hallmarks of cancer. They were also found to be effective in treating non-alcoholic fatty liver disease and diabetes mellitus. Thus, VDAC1-based peptides, by targeting VDAC1-interacting proteins, offer an affordable and innovative new conceptual therapeutic paradigm that can potentially overcome heterogeneity, chemoresistance, and invasive metastatic formation.

Diet and physical exercise as key players to tackle MASLD through improvement of insulin resistance and metabolic flexibility

Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) has emerged as a prevalent health concern, encompassing a wide spectrum of liver-related disorders. Insulin resistance, a key pathophysiological feature of MASLD, can be effectively ameliorated through dietary interventions. The Mediterranean diet, rich in whole grains, fruits, vegetables, legumes, and healthy fats, has shown promising results in improving insulin sensitivity. Several components of the Mediterranean diet, such as monounsaturated fats and polyphenols, exert anti-inflammatory and antioxidant effects, thereby reducing hepatic steatosis and inflammation. Furthermore, this dietary pattern has been associated with a higher likelihood of achieving MASLD remission. In addition to dietary modifications, physical exercise, particularly resistance exercise, plays a crucial role in enhancing metabolic flexibility. Resistance exercise training promotes the utilization of fatty acids as an energy source. It enhances muscle glucose uptake and glycogen storage, thus reducing the burden on the liver to uptake excess blood glucose. Furthermore, resistance exercise stimulates muscle protein synthesis, contributing to an improved muscle-to-fat ratio and overall metabolic health. When implemented synergistically, the Mediterranean diet and resistance exercise can elicit complementary effects in combating MASLD. Combined interventions have demonstrated additive benefits, including greater improvements in insulin resistance, increased metabolic flexibility, and enhanced potential for MASLD remission. This underscores the importance of adopting a multifaceted approach encompassing dietary modifications and regular physical exercise to effectively manage MASLD. This narrative review explores the biological mechanisms of diet and physical exercise in addressing MASLD by targeting insulin resistance and decreased metabolic flexibility.

Induction of steatosis in primary human hepatocytes recapitulates key pathophysiological aspects of metabolic dysfunction-associated steatotic liver disease

BACKGROUND & AIMS

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most common cause of chronic liver disease. Owing to limited available treatment options, novel pre-clinical models for target selection and drug validation are warranted. We have established and extensively characterized a primary human steatotic hepatocyte in vitro model system that could guide the development of treatment strategies for MASLD.

METHODS

Cryopreserved primary human hepatocytes from five donors varying in sex and ethnicity were cultured with free fatty acids in a 3D collagen sandwich for 7 days and the development of MASLD was followed by assessing classical hepatocellular functions. As proof of concept, the effects of the drug firsocostat (GS-0976) on in vitro MASLD phenotypes were evaluated.

RESULTS

Incubation with free fatty acids induced steatosis, insulin resistance, mitochondrial dysfunction, inflammation, and alterations in prominent human gene signatures similar to patients with MASLD, indicating the recapitulation of human MASLD in this system. The application of firsocostat rescued clinically observed fatty liver disease pathologies, highlighting the ability of the in vitro system to test the efficacy and potentially characterize the mode of action of drug candidates.

CONCLUSIONS

Altogether, our human MASLD in vitro model system could guide the development and validation of novel targets and drugs for the treatment of MASLD.

IMPACT AND IMPLICATIONS

Due to low drug efficacy and high toxicity, clinical treatment options for metabolic dysfunction-associated steatotic liver disease (MASLD) are currently limited. To facilitate earlier stop-go decisions in drug development, we have established a primary human steatotic hepatocyte in vitro model. As the model recapitulates clinically relevant MASLD characteristics at high phenotypic resolution, it can serve as a pre-screening platform and guide target identification and validation in MASLD therapy.

BNIP3 in hypoxia-induced mitophagy: Novel insights and promising target for non-alcoholic fatty liver disease

BNIP3 localizes to the outer mitochondrial membrane, has been demonstrated to be extensively involved in abnormalities to mitochondrial metabolic function and dynamicsand in non-alcoholic fatty liver disease (NAFLD). However, its role in NAFLD under hypoxia remains unclear. This study aimed to investigate the expression and the role of BNIP3 in NAFLD under hypoxia, and explore its involvement in regulating NAFLD mitophagy, fatty acid β-oxidation both in vivo and in vitro. BNIP3-mediated mitophagy level was analyzed using real-time quantitative polymerase chain reaction, Western blotting, immunofluorescence and electron microscopy. The role of BNIP3 in fatty acid β-oxidation was evaluated using lipid droplet staining, triglyceride content determination, and cellular energy metabolism. The results showed that compared with the HFD-2200 m, the body weight, inflammatory liver injury, and lipid deposition were significantly reduced in the HFD-4500 m group (P < 0.05), but autophagy and mitophagy were increased, and the expression of the mitophagy receptor BNIP3 was increased (P < 0.05). Compared to the control group, BNIP3 knockdown in the hypoxia group resulted in decreased levels of CPT1, ATGL, and p-HSL in lipid-accumulating hepatocytes, lipid droplet accumulation and triglyceride content increased (P < 0.05). Moreover, the ability of lipid-accumulating hepatocytes to oxidize fatty acids was reduced by BNIP3 knockdown in the hypoxia group (P < 0.05). Therefore, it can be concluded that, in NAFLD mice under hypoxia, BNIP3-mediated mitophagy promotes fatty acid β-oxidation. This study elucidated the role of BNIP3 in promoting fatty acid β-oxidation in NAFLD under hypoxia, and suggests BNIP3 may serve as a novel potential therapeutic target for NAFLD.

Role of Quercetin in DNA Repair: Possible Target to Combat Drug Resistance in Diabetes

Diabetes Mellitus (DM) is referred to as hyperglycemia in either fasting or postprandial phases. Oxidative stress, which is defined by an excessive amount of reactive oxygen species (ROS) production, increased exposure to external stress, and an excessive amount of the cellular defense system against them, results in cellular damage. Increased DNA damage is one of the main causes of genomic instability, and genetic changes are an underlying factor in the emergence of cancer. Through covalent connections with DNA and proteins, quercetin has been demonstrated to offer protection against the creation of oxidative DNA damage. It has been found that quercetin shields DNA from possible oxidative stress-related harm by reducing the production of ROS. Therefore, Quercetin helps to lessen DNA damage and improve the ability of DNA repair mechanisms. This review mainly focuses on the role of quercetin in repairing DNA damage and compensating for drug resistance in diabetic patients. Data on the target topic was obtained from major scientific databases, including SpringerLink, Web of Science, Google Scholar, Medline Plus, PubMed, Science Direct, and Elsevier. In preclinical studies, quercetin guards against DNA deterioration by regulating the degree of lipid peroxidation and enhancing the antioxidant defense system. By reactivating antioxidant enzymes, decreasing ROS levels, and decreasing the levels of 8-hydroxydeoxyguanosine, Quercetin protects DNA from oxidative damage. In clinical studies, it was found that quercetin supplementation was related to increased antioxidant capacity and decreased risk of type 2 diabetes mellitus in the experimental group as compared to the placebo group. It is concluded that quercetin has a significant role in DNA repair in order to overcome drug resistance in diabetes.

Nonalcoholic Fatty Liver Disease and Staging of Hepatic Fibrosis

Nonalcoholic fatty liver disease (NAFLD) is in parallel with the obesity epidemic, and it is the most common cause of liver diseases. The patients with severe insulin-resistant diabetes having high body mass index (BMI), high-grade adipose tissue insulin resistance, and high hepatocellular triacylglycerols (triglycerides; TAG) content develop hepatic fibrosis within a 5-year follow-up. Insulin resistance with the deficiency of insulin receptor substrate-2 (IRS-2)-associated phosphatidylinositol 3-kinase (PI3K) activity causes an increase in intracellular fatty acid-derived metabolites such as diacylglycerol (DAG), fatty acyl CoA, or ceramides. Lipotoxicity-related mechanism of NAFLD could be explained still best by the "double-hit" hypothesis. Insulin resistance is the major mechanism in the development and progression of NAFLD/nonalcoholic steatohepatitis (NASH). Metabolic oxidative stress, autophagy, and inflammation induce NASH progression. In the "first hit" the hepatic concentrations of diacylglycerol increase with an increase in saturated liver fat content in human NAFLD. Activities of mitochondrial respiratory chain complexes are decreased in the liver tissue of patients with NASH. Hepatocyte lipoapoptosis is a critical feature of NASH. In the "second hit," reduced glutathione levels due to oxidative stress lead to the overactivation of c-Jun N-terminal kinase (JNK)/c-Jun signaling that induces cell death in the steatotic liver. Accumulation of toxic levels of reactive oxygen species (ROS) is caused at least by two ineffectual cyclical pathways. First is the endoplasmic reticulum (ER) oxidoreductin (Ero1)-protein disulfide isomerase oxidation cycle through the downstream of the inner membrane mitochondrial oxidative metabolism and the second is the Kelch like-ECH-associated protein 1 (Keap1)-nuclear factor (erythroid-derived 2)-like 2 (Nrf2) pathways. In clinical practice, on ultrasonographic examination, the elevation of transaminases, γ-glutamyltransferase, and the aspartate transaminase to platelet ratio index indicates NAFLD. Fibrosis-4 index, NAFLD fibrosis score, and cytokeratin18 are used for grading steatosis, staging fibrosis, and discriminating the NASH from simple steatosis, respectively. In addition to ultrasonography, "controlled attenuation parameter," "magnetic resonance imaging proton-density fat fraction," "ultrasound-based elastography," "magnetic resonance elastography," "acoustic radiation force impulse elastography imaging," "two-dimensional shear-wave elastography with supersonic imagine," and "vibration-controlled transient elastography" are recommended as combined tests with serum markers in the clinical evaluation of NAFLD. However, to confirm the diagnosis of NAFLD, a liver biopsy is the gold standard. Insulin resistance-associated hyperinsulinemia directly accelerates fibrogenesis during NAFLD development. Although hepatocyte lipoapoptosis is a key driving force of fibrosis progression, hepatic stellate cells and extracellular matrix cells are major fibrogenic effectors. Thereby, these are pharmacological targets of therapies in developing hepatic fibrosis. Nonpharmacological management of NAFLD mainly consists of two alternatives: lifestyle modification and metabolic surgery. Many pharmacological agents that are thought to be effective in the treatment of NAFLD have been tried, but due to lack of ability to attenuate NAFLD, or adverse effects during the phase trials, the vast majority could not be licensed.

Changes of insulin receptors in high fat and high glucose diet mice with insulin resistance

This study aimed to observe the expression of insulin-signaling molecules in different organs of mice with insulin resistance (IR). Firstly, mice were fed a high-fat and high-sugar diet (HF group) to establish an IR model, and the controls (NF group) were fed with a normal diet. Next, the weight, fasting blood glucose (FBG), serum insulin and insulin tolerance were detected. Pathological changes of liver tissues were observed by H&E staining. The expressions of INSR, IRS-1 and IRS-2 in the liver, skeletal muscle and ovary were measured by qRT-PCR and western blotting. As a result, compared with the NF group, the HF group mice had increased weight, FBG, insulin and IR index after 6-week of feeding as well as a worse performance in the insulin tolerance test and H&E staining showed fatty liver-like changes after 12-week of feeding, exhibited lower expression of INSR, IRS-1 and IRS-2 in the liver of mice at 6 and 12 weeks. The expression of INSR and IRS-1 in skeletal muscle tissues exhibited the same trend, while those in ovary organs showed the opposite trend. These results suggested that the insulin signaling alters in the liver, skeletal muscle and ovary organs with the progress of IR.

Insulin resistance and metabolic flexibility as drivers of liver and cardiac disease in T2DM

Metabolic flexibility refers to the ability of tissues to adapt their use of energy sources according to substrate availability and energy demands. This review aims to disentangle the emerging mechanisms through which altered metabolic flexibility and insulin resistance promote NAFLD and heart disease progression. Insulin resistance and metabolic inflexibility are central drivers of hepatic and cardiac diseases in individuals with type 2 diabetes. Both play a critical role in the complex interaction between glucose and lipid metabolism. Disruption of metabolic flexibility results in hyperglycemia and abnormal lipid metabolism, leading to increased accumulation of fat in the liver, contributing to the development and progression of NAFLD. Similarly, insulin resistance affects cardiac glucose metabolism, leading to altered utilization of energy substrates and impaired cardiac function, and influence cardiac lipid metabolism, further exacerbating the progression of heart failure. Regular physical activity promotes metabolic flexibility by increasing energy expenditure and enabling efficient switching between different energy substrates. On the contrary, weight loss achieved through calorie restriction ameliorates insulin sensitivity without improving flexibility. Strategies that mimic the effects of physical exercise, such as pharmacological interventions or targeted lifestyle modifications, show promise in effectively treating both diabetes and NAFLD, finally reducing the risk of advanced liver disease.

Deletion of hepatic small heterodimer partner ameliorates development of nonalcoholic steatohepatitis in mice

Small heterodimer partner (SHP, Nr0b2) is an orphan nuclear receptor that regulates bile acid, lipid, and glucose metabolism. Shp-/- mice are resistant to diet-induced obesity and hepatic steatosis. In this study, we explored the potential role of SHP in the development of nonalcoholic steatohepatitis (NASH). A 6-month Western diet (WD) regimen was used to induce NASH. Shp deletion protected mice from NASH progression by inhibiting inflammatory and fibrotic genes, oxidative stress, and macrophage infiltration. WD feeding disrupted the ultrastructure of hepatic mitochondria in WT mice but not in Shp-/- mice. In ApoE-/- mice, Shp deletion also effectively ameliorated hepatic inflammation after a 1 week WD regimen without an apparent antisteatotic effect. Moreover, Shp-/- mice resisted fibrogenesis induced by a methionine- and choline-deficient diet. Notably, the observed protection against NASH was recapitulated in liver-specific Shp-/- mice fed either the WD or methionine- and choline-deficient diet. Hepatic cholesterol was consistently reduced in the studied mouse models with Shp deletion. Our data suggest that Shp deficiency ameliorates NASH development likely by modulating hepatic cholesterol metabolism and inflammation.

Fructose aggravates copper-deficiency-induced non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD), is the most common cause of chronic liver disease, affecting 24% of the global population. Accumulating evidence demonstrates that copper deficiency (CuD) is implicated in the development of NAFLD, besides, high fructose consumption by promoting inflammation contributes to NAFLD. However, how CuD and/or fructose (Fru) causes NAFLD is not clearly delineated. The present study aims to investigate the role of CuD and/or fructose supplement on hepatic steatosis and hepatic injury. We established a CuD rat model by feeding weaning male Sprague-Dawley rats for 4 weeks with CuD diet. Fructose was supplemented in drinking water. We found the promoting role of CuD or Fructose (Fru) in the progress of NAFLD, which was aggravated by combination of the two. Furthermore, we presented the alteration of hepatic lipid profiles (including content, composition, and saturation), especially ceramide (Cer), cardiolipin (CL), phosphatidylcholine (PC) and phosphatidylethanolamine (PE) was closely associated with CuD and/or Fru fed induced-NAFLD in rat models. In conclusion, insufficient copper intake or excessive fructose supplement resulted in adverse effects on the hepatic lipid profile, and fructose supplement causes a further hepatic injury in CuD-induced NAFLD, which illuminated a better understanding of NAFLD.

Mitochondrial protease ClpP supplementation ameliorates diet-induced NASH in mice

BACKGROUND & AIMS

Mitochondrial dysfunction is considered a pathogenic linker in the development of non-alcoholic steatohepatitis (NASH). Inappropriate mitochondrial protein-quality control, possibly induced by insufficiency of the mitochondrial matrix caseinolytic protease P (ClpP), can potentially cause mitochondrial dysfunction. Herein, we aimed to investigate hepatic ClpP levels in a diet-induced model of NASH and determine whether supplementation of ClpP can ameliorate diet-induced NASH.

METHODS

NASH was induced by a high-fat/high-fructose (HF/HFr) diet in C57BL/6J mice. Stress/inflammatory signals were induced in mouse primary hepatocytes (MPHs) by treatment with palmitate/oleate (PA/OA). ClpP levels in hepatocytes were reduced using the RNAi-mediated gene knockdown technique but increased through the viral transduction of ClpP. ClpP activation was induced by administering a chemical activator of ClpP.

RESULTS

Hepatic ClpP protein levels in C57BL/6J mice fed a HF/HFr diet were lower than the levels in those fed a normal chow diet. PA/OA treatment also decreased the ClpP protein levels in MPHs. Overexpression or activation of ClpP reversed PA/OA-induced mitochondrial dysfunction and stress/inflammatory signal activation in MPHs, whereas ClpP knockdown induced mitochondrial dysfunction and stress/inflammatory signals in these cells. On the other hand, ClpP overexpression or activation improved HF/HFr-induced NASH characteristics such as hepatic steatosis, inflammation, fibrosis, and injury in the C57BL/6J mice, whereas ClpP knockdown further augmented steatohepatitis in mice fed a HF/HFr diet.

CONCLUSIONS

Reduced ClpP expression and subsequent mitochondrial dysfunction are key to the development of diet-induced NASH. ClpP supplementation through viral transduction or chemical activation represents a potential therapeutic strategy to prevent diet-induced NASH.

LAY SUMMARY

Western diets, containing high fat and high fructose, often induce non-alcoholic steatohepatitis (NASH). Mitochondrial dysfunction is considered pathogenically linked to diet-induced NASH. We observed that the mitochondrial protease ClpP decreased in the livers of mice fed a western diet and supplementation of ClpP ameliorated western diet-induced NASH.

Tanshinone IIA Ameliorates Nonalcoholic Steatohepatitis in Mice by Modulating Neutrophil Extracellular Traps and Hepatocyte Apoptosis

Salvia miltiorrhiza Bunge, a traditional Chinese medicine, is widely used in the treatment of a variety of diseases and syndromes. Tanshinone IIA (TIIA), a phenanthrenequinone-class derivative extracted from S. miltiorrhiza, is one of its main active components and has anti-inflammatory effects on various tissues and cells. This study aimed to investigate the beneficial effects of TIIA on nonalcoholic steatohepatitis (NASH) induced in mice using a methionine choline deficiency (MCD) diet and the underlying mechanism of these. Our results reveal that TIIA remarkably ameliorated hepatic steatosis and inflammation and decreased the serum levels of liver dysfunction markers while increasing the levels of serum total cholesterol and triglycerides in MCD-fed mice. TIIA significantly reduced mRNA levels of the inflammatory factors TNF-α, IL-6, and TGF-β. Similarly, TIIA inhibited caspase-3 and Bax-mediated apoptosis in MCD-fed mice. Together, our data indicate that TIIA inhibits the formation of MPO and CitH3 in neutrophil extracellular traps and inhibits apoptosis mediated by caspase-3 and Bax in hepatocytes, thereby mitigating inflammatory progression in an MCD diet-induced NASH mouse model.

Roles of organelle-specific autophagy in hepatocytes in the development and treatment of non-alcoholic fatty liver disease

ABSTRACT

Non-alcoholic fatty liver disease (NAFLD) is a disorder of lipid metabolism. The lipotoxic intermediates of lipid metabolism cause mitochondrial dysfunction and endoplasmic reticulum stress. Organelle-specific autophagy is responsible for the removal of dysfunctional organelles to maintain intracellular homeostasis. Lipophagy contributes to lipid turnover by degrading lipid droplets. The level of autophagy changes during the course of NAFLD, and the activation of hepatocyte autophagy might represent a method of treating NAFLD.

The first study on the effect of crocodile oil from Crocodylus siamensis on hepatic mitochondrial function for energy homeostasis in rats

Background and Aim:

Consumption of fatty acids (FA) can alter hepatic energy metabolism and mitochondrial function in the liver. Crocodile oil (CO) is rich in mono-and polyunsaturated FAs, which have natural anti-inflammatory and healing properties. In rat livers, we investigated the effect of CO on mitochondrial function for energy homeostasis.

Materials and Methods:

Twenty-one male Sprague-Dawley rats were divided into three groups at random. Group 1 rats were given sterile water (RO), Group 2 rats were given CO (3% v/w), and Group 3 rats were given palm oil (PO) (3% v/w). For 7 weeks, rats were given sterile water, CO, and PO orally. The researchers looked at body weight, food intake, liver weight, energy intake, blood lipid profiles, and mitochondria-targeted metabolites in the liver. The liver’s histopathology, mitochondrial architecture, and hydrolase domain containing 3 (HDHD3) protein expression in liver mitochondria were studied.

Results:

Body weight, liver weight, liver index, dietary energy intake, and serum lipid profiles were all unaffected by CO treatment. The CO group consumed significantly less food than the RO group. The CO group also had significantly higher levels of oxaloacetate and malate than the PO group. CO treatment significantly ameliorated hepatic steatosis, as evidenced by a greater decrease in the total surface area of lipid particles than PO treatment. CO administration preserved mitochondrial morphology in the liver by upregulating the energetic maintenance protein HDHD3. Furthermore, chemical-protein interactions revealed that HDHD3 was linked to the energy homeostatic pathway.

Conclusion:

CO may benefit liver function by preserving hepatic mitochondrial architecture and increasing energy metabolic activity.

Developmental Programming: Prenatal Testosterone Excess on Liver and Muscle Coding and Noncoding RNA in Female Sheep

Prenatal testosterone (T)-treated female sheep manifest peripheral insulin resistance, ectopic lipid accumulation, and insulin signaling disruption in liver and muscle. This study investigated transcriptional changes and transcriptome signature of prenatal T excess-induced hepatic and muscle-specific metabolic disruptions. Genome-wide coding and noncoding (nc) RNA expression in liver and muscle from 21-month-old prenatal T-treated (T propionate 100 mg intramuscular twice weekly from days 30-90 of gestation; term: 147 days) and control females were compared. Prenatal T (1) induced differential expression of messenger RNAs (mRNAs) in liver (15 down, 17 up) and muscle (66 down, 176 up) (false discovery rate < 0.05, absolute log2 fold change > 0.5); (2) downregulated mitochondrial pathway genes in liver and muscle; (3) downregulated hepatic lipid catabolism and peroxisome proliferator-activated receptor (PPAR) signaling gene pathways; (4) modulated noncoding RNA (ncRNA) metabolic processes gene pathway in muscle; and (5) downregulated 5 uncharacterized long noncoding RNA (lncRNA) in the muscle but no ncRNA changes in the liver. Correlation analysis showed downregulation of lncRNAs LOC114112974 and LOC105607806 was associated with decreased TPK1, and LOC114113790 with increased ZNF470 expression. Orthogonal projections to latent structures discriminant analysis identified mRNAs HADHA and SLC25A45, and microRNAs MIR154A, MIR25, and MIR487B in the liver and ARIH1 and ITCH and miRNAs MIR369, MIR10A, and MIR10B in muscle as potential biomarkers of prenatal T excess. These findings suggest downregulation of mitochondria, lipid catabolism, and PPAR signaling genes in the liver and dysregulation of mitochondrial and ncRNA gene pathways in muscle are contributors of lipotoxic and insulin-resistant hepatic and muscle phenotype. Gestational T excess programming of metabolic dysfunctions involve tissue-specific ncRNA-modulated transcriptional changes.

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.

Impact of Silibinin A on Bioenergetics in PC12APPsw Cells and Mitochondrial Membrane Properties in Murine Brain Mitochondria

Age-related multifactorial diseases, such as the neurodegenerative Alzheimer’s disease (AD), still remain a challenge to today’s society. One mechanism associated with AD and aging in general is mitochondrial dysfunction (MD). Increasing MD is suggested to trigger other pathological processes commonly associated with neurodegenerative diseases. Silibinin A (SIL) is the main bioactive compound of the Silymarin extract from the Mediterranean plant Silybum marianum (L.) (GAERTN/Compositae). It is readily available as a herbal drug and well established in the treatment of liver diseases as a potent radical scavenger reducing lipid peroxidation and stabilize membrane properties. Recent data suggest that SIL might also act on neurological changes related to MD. PC12APP_sw cells produce low levels of human Aβ and thus act as a cellular model of early AD showing changed mitochondrial function. We investigated whether SIL could affect mitochondrial function by measuring ATP, MMP, as well as respiration, mitochondrial mass, cellular ROS and lactate/pyruvate concentrations. Furthermore, we investigated its effects on the mitochondrial membrane parameters of swelling and fluidity in mitochondria isolated from the brains of mice. In PC12APP_sw cells, SIL exhibits strong protective effects by rescuing MMP and ATP levels from SNP-induced mitochondrial damage and improving basal ATP levels. However, SIL did not affect mitochondrial respiration and mitochondrial content. SIL significantly reduced cellular ROS and pyruvate concentrations. Incubation of murine brain mitochondria with SIL significantly reduces Ca²⁺ induced swelling and improves membrane fluidity. Although OXPHOS activity was unaffected at this early stage of a developing mitochondrial dysfunction, SIL showed protective effects on MMP, ATP- after SNP-insult and ROS-levels in APPsw-transfected PC12 cells. Results from experiments with isolated mitochondria imply that positive effects possibly result from an interaction of SIL with mitochondrial membranes and/or its antioxidant activity. Thus, SIL might be a promising compound to improve cellular health when changes to mitochondrial function occur.

Astragaloside IV ameliorates fat metabolism in the liver of ageing mice through targeting mitochondrial activity

Astragaloside IV (AST) is a major bioactive compound of Radix Astragali with medical and health benefits. Previous studies have found that AST can reduce the body weights of high-fat diet fed mice. However, the effect of AST on fat metabolism of ageing mice is unclear. In this study, naturally ageing mice were administered intragastrically with AST at 30 mg/kg/day (ageing + AST-L group) and 90 mg/kg/day (ageing + AST-H group) for 16-20 months. Adult (4 months old) and ageing mice were given 1% sodium carboxyl methylcellulose as vehicle. Energy metabolism-related biological parameters of living mice were examined. Moreover, mRNA and protein levels of key enzymes/proteins involved in triglyceride (TG) lipolysis, fatty acid β-oxidation (FAO), ketone body (KB) production and mitochondrial respiratory chain were also examined after sacrifice. Results demonstrated that treatment with AST significantly reduced body weight, white fat and liver/body weight ratio of ageing mice, significantly reduced serum/hepatic TG levels, respiratory quotient, promoted fatty acid mobilization in white adipose tissue, mitochondrial FAO and KB production and mitochondrial biosynthesis/functions in the liver of ageing mice. AST also up-regulated the expression of phosphorylated AMP-activated protein kinase, acetyl-CoA carboxylase, acetyl-coenzyme A synthetase, carnitine palmitoyltransferase 1a/1b, enoyl coenzyme A hydratase-short chain, acyl-CoA dehydrogenase medium chain and mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase-2 involved in fat metabolism. These results indicated that mitochondrial activity could be the target of AST to treat abnormal fat metabolism during ageing.

Inhibition of Estrogen-Related Receptor α Blocks Liver Steatosis and Steatohepatitis and Attenuates Triglyceride Biosynthesis

The estrogen-related receptor (ERR) family of orphan nuclear receptors are transcriptional activators for genes involved in mitochondrial bioenergetics and metabolism. The goal of this study was to explore the role of ERRα in lipid metabolism and the potential effect of inhibiting ERRα on the development of nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). In the current study, three experimental mouse models: high-fat diet, high-carbohydrate diet, and a genetic model of hepatic insulin resistance where the liver hyperinsulinemia signal is mimicked via hepatic deletion of Pten (phosphatase and tensin homolog deleted on chromosome 10), the negative regulator of the insulin/phosphatidylinositol 3-kinase signaling pathway, were used. A recently developed small-molecule inhibitor for ERRα was used to demonstrate that inhibiting ERRα blocked NAFLD development induced by either high-carbohydrate diet or high-fat diet feeding. ERRα inhibition also diminished lipid accumulation and attenuated NASH development in the Pten null mice. Glycerolipid synthesis was discovered as an additional mechanism for ERRα-regulated NAFLD/NASH development and glycerophosphate acyltransferase 4 was identified as a novel transcriptional target of ERRα. In summary, these results establish ERRα as a major transcriptional regulator of lipid biosynthesis in addition to its characterized primary function as a regulator for mitochondrial function. This study recognizes ERRα as a potential target for NAFLD/NASH treatment and elucidates novel signaling pathways regulated by ERRα.

Dimming the Powerhouse: Mitochondrial Dysfunction in the Liver and Skeletal Muscle of Intrauterine Growth Restricted Fetuses

Intrauterine growth restriction (IUGR) of the fetus, resulting from placental insufficiency (PI), is characterized by low fetal oxygen and nutrient concentrations that stunt growth rates of metabolic organs. Numerous animal models of IUGR recapitulate pathophysiological conditions found in human fetuses with IUGR. These models provide insight into metabolic dysfunction in skeletal muscle and liver. For example, cellular energy production and metabolic rate are decreased in the skeletal muscle and liver of IUGR fetuses. These metabolic adaptations demonstrate that fundamental processes in mitochondria, such as substrate utilization and oxidative phosphorylation, are tempered in response to low oxygen and nutrient availability. As a central metabolic organelle, mitochondria coordinate cellular metabolism by coupling oxygen consumption to substrate utilization in concert with tissue energy demand and accretion. In IUGR fetuses, reducing mitochondrial metabolic capacity in response to nutrient restriction is advantageous to ensure fetal survival. If permanent, however, these adaptations may predispose IUGR fetuses toward metabolic diseases throughout life. Furthermore, these mitochondrial defects may underscore developmental programming that results in the sequela of metabolic pathologies. In this review, we examine how reduced nutrient availability in IUGR fetuses impacts skeletal muscle and liver substrate catabolism, and discuss how enzymatic processes governing mitochondrial function, such as the tricarboxylic acid cycle and electron transport chain, are regulated. Understanding how deficiencies in oxygen and substrate metabolism in response to placental restriction regulate skeletal muscle and liver metabolism is essential given the importance of these tissues in the development of later lifer metabolic dysfunction.

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.

Aging-induced aberrant RAGE/PPARα axis promotes hepatic steatosis via dysfunctional mitochondrial β oxidation

Non‐alcoholic fatty liver disease (NAFLD), characterized by an increase in hepatic triglyceride (TG) content, is the most common liver disease worldwide. Aging has been shown to increase susceptibility to NAFLD; however, the underlying molecular mechanism remains poorly understood. In the present study, we examined hepatic TG content and gene expression profiles in body weight‐matched young (3 months old), middle‐aged (10 months old), and old (20 months old) C57BL/6 mice and found that TGs were markedly accumulated while mitochondrial β‐oxidation‐related genes, including PPARα, were downregulated in the liver of old mice. In addition, advanced glycation end product receptor (RAGE), a key regulator of glucose metabolism, was upregulated in the old mice. Mechanistically, suppression of RAGE upregulated PPARα and its downstream target genes, which in turn led to reduced TG retention. Finally, we found that hepatic RAGE expression was increased in aging patients, a finding that correlated with decreased PPARα levels. Taken together, our findings demonstrate that the upregulation of RAGE may play a critical role in aging‐associated liver steatosis.

Assessment of mitochondrial function in metabolic dysfunction-associated fatty liver disease using obese mouse models

Metabolic dysfunction-associated fatty liver disease (MAFLD) is characterized by deregulated hepatic lipid metabolism; however, the association between MAFLD development and mitochondrial dysfunction has yet to be confirmed. Herein, we employed high-resolution respirometry, blue native polyacrylamide gel electrophoresis-based in-gel activity measurement and immunoblot analysis to assess mitochondrial function in obesity-induced mouse models with varying degrees of MAFLD. Results showed a slight but significant decrease in hepatic mitochondrial respiration in some MAFLD mice compared to mice fed a standard diet. However, the activities and levels of mitochondrial oxidative phosphorylation complexes remained unchanged during obesity-induced MAFLD progression. These results suggest that mitochondrial function, particularly oxidative phosphorylation, was mildly affected during obesity-induced MAFLD development. Moreover, transcriptome profiling of mouse and human liver tissues with varying degrees of MAFLD revealed that the decreased activation of mitochondria-related pathways was only associated with MAFLD of a high histological grade, whereas the major regulators of mitochondrial biogenesis were not altered in mice or humans during MAFLD development. Collectively, our results suggest that impaired hepatic mitochondrial function is not closely associated with obesity-induced MAFLD. Therefore, therapeutic strategies targeting mitochondria for the treatment of MAFLD should be reconsidered.

Role and Mechanisms of Mitophagy in Liver Diseases

The mitochondrion is an organelle that plays a vital role in the regulation of hepatic cellular redox, lipid metabolism, and cell death. Mitochondrial dysfunction is associated with both acute and chronic liver diseases with emerging evidence indicating that mitophagy, a selective form of autophagy for damaged/excessive mitochondria, plays a key role in the liver’s physiology and pathophysiology. This review will focus on mitochondrial dynamics, mitophagy regulation, and their roles in various liver diseases (alcoholic liver disease, non-alcoholic fatty liver disease, drug-induced liver injury, hepatic ischemia-reperfusion injury, viral hepatitis, and cancer) with the hope that a better understanding of the molecular events and signaling pathways in mitophagy regulation will help identify promising targets for the future treatment of liver diseases.

The VDAC1-based R-Tf-D-LP4 Peptide as a Potential Treatment for Diabetes Mellitus

Diabetes mellitus is a metabolic disorder approaching epidemic proportions. Non-alcoholic fatty liver disease (NAFLD) regularly coexists with metabolic disorders, including type 2 diabetes, obesity, and cardiovascular disease. Recently, we demonstrated that the voltage-dependent anion channel 1 (VDAC1) is involved in NAFLD. VDAC1 is an outer mitochondria membrane protein that serves as a mitochondrial gatekeeper, controlling metabolic and energy homeostasis, as well as crosstalk between the mitochondria and the rest of the cell. It is also involved in mitochondria-mediated apoptosis. Here, we demonstrate that the VDAC1-based peptide, R-Tf-D-LP4, affects several parameters of a NAFLD mouse model in which administration of streptozotocin (STZ) and high-fat diet 32 (STZ/HFD-32) led to both type 2 diabetes (T2D) and NAFLD phenotypes. We focused on diabetes, showing that R-Tf-D-LP4 peptide treatment of STZ/HFD-32 fed mice restored the elevated blood glucose back to close to normal levels, and increased the number and average size of islets and their insulin content as compared to untreated controls. Similar results were obtained when staining the islets for glucose transporter type 2. In addition, the R-Tf-D-LP4 peptide decreased the elevated glucose levels in a mouse displaying obese, diabetic, and metabolic symptoms due to a mutation in the obese (ob) gene. To explore the cause of the peptide-induced improvement in the endocrine pancreas phenotype, we analyzed the expression levels of the proliferation marker, Ki-67, and found it to be increased in the islets of STZ/HFD-32 fed mice treated with the R-Tf-D-LP4 peptide. Moreover, peptide treatment of STZ/HFD-32 fed mice caused an increase in the expression of β-cell maturation and differentiation PDX1 transcription factor that enhances the expression of the insulin-encoding gene, and is essential for islet development, function, proliferation, and maintenance of glucose homeostasis in the pancreas. This increase occurred mainly in the β-cells, suggesting that the source of their increased number after R-Tf-D-LP4 peptide treatment was most likely due to β-cell proliferation. These results suggest that the VDAC1-based R-Tf-D-LP4 peptide has potential as a treatment for diabetes.

Differential Effects of Silibinin A on Mitochondrial Function in Neuronal PC12 and HepG2 Liver Cells

The Mediterranean plant Silybum marianum L., commonly known as milk thistle, has been used for centuries to treat liver disorders. The flavonolignan silibinin represents a natural antioxidant and the main bioactive ingredient of silymarin (silybin), a standard extract of its seeds. Mitochondrial dysfunction and the associated generation of reactive oxygen/nitrogen species (ROS/RNS) are involved in the development of chronic liver and age-related neurodegenerative diseases. Silibinin A (SIL A) is one of two diastereomers found in silymarin and was used to evaluate the effects of silymarin on mitochondrial parameters including mitochondrial membrane potential and ATP production with and without sodium nitroprusside- (SNP-) induced nitrosative stress, oxidative phosphorylation, and citrate synthase activity in HepG2 and PC12 cells. Both cell lines were influenced by SIL A, but at different concentrations. SIL A significantly weakened nitrosative stress in both cell lines. Low concentrations not only maintained protective properties but also increased basal mitochondrial membrane potential (MMP) and adenosine triphosphate (ATP) levels. However, these effects could not be associated with oxidative phosphorylation. On the other side, high concentrations of SIL A significantly decreased MMP and ATP levels. Although SIL A did not provide a general improvement of the mitochondrial function, our findings show that SIL A protects against SNP-induced nitrosative stress at the level of mitochondria making it potentially beneficial against neurological disorders.

Enzymatic and nonenzymatic protein acetylations control glycolysis process in liver diseases

Impaired glycolysis has pathologic effects on the occurrence and progression of liver diseases, and it appears that glycolysis is increased to different degrees in different liver diseases. As an important post-translational modification, reversible lysine acetylation regulates almost all cellular processes, including glycolysis. Lysine acetylation can occur enzymatically with acetyltransferases or nonenzymatically with acetyl-coenzyme A. Accompanied by the progression of liver diseases, there seems to be a temporal and spatial variation between enzymatic and nonenzymatic acetylations in the regulation of glycolysis. Here, we summarize the most recent findings on the functions and targets of acetylation in controlling glycolysis in the different stages of liver diseases. In addition, we discuss the differences and causes between enzymatic and nonenzymatic acetylations in regulating glycolysis throughout the progression of liver diseases. Then, we review these new discoveries to provide the potential implications of these findings for therapeutic interventions in liver diseases.-Li, J., Wang, T., Xia, J., Yao, W., Huang, F. Enzymatic and nonenzymatic protein acetylations control glycolysis process in liver diseases.

Hepatic alterations during the development and progression of cancer cachexia

Cancer-associated bodyweight loss (cachexia) is a hallmark of many cancers and is associated with decreased quality of life and increased mortality. Hepatic function can dramatically influence whole-body energy expenditure and may therefore significantly influence whole-body health during cancer progression. The purpose of this study was to examine alterations in markers of hepatic metabolism and physiology during cachexia progression. Male C57BL/6J mice were injected with 1 × 10⁶ Lewis Lung Carcinoma cells dissolved in 100 μL PBS and cancer was allowed to develop for 1, 2, 3, or 4 weeks. Control animals were injected with an equal volume of phosphate-buffered saline. Livers were analyzed for measures of metabolism, collagen deposition, protein turnover, and mitochondrial quality. Animals at 4 weeks had ∼30% larger livers compared with all other groups. Cancer progression was associated with altered regulators of fat metabolism. Additionally, longer duration of cancer development was associated with ∼3-fold increased regulators of collagen deposition as well as phenotypic collagen content, suggesting increased liver fibrosis. Mitochondrial quality control regulators appeared to be altered before any phenotypic alterations to collagen deposition. While induction of Akt was noted, downstream markers of protein synthesis were not altered. In conclusions, cancer cachexia progression is associated with hepatic pathologies, specifically liver fibrosis. Alterations to mitochondrial quality control mechanisms appear to precede this fibrotic phenotype, potentially suggesting mitochondrial mechanisms for the development of hepatic pathologies during the development and progression of cancer cachexia. Novelty Cachexia progression results in liver collagen deposition and fibrosis. Alterations in mitochondrial quality control may precede liver pathologies during cachexia.

Mitophagy in Hepatic Insulin Resistance: Therapeutic Potential and Concerns

Metabolic syndrome, characterized by central obesity, hypertension, and hyperlipidemia, increases the morbidity and mortality of cardiovascular disease, type 2 diabetes, nonalcoholic fatty liver disease, and other metabolic diseases. It is well known that insulin resistance, especially hepatic insulin resistance, is a risk factor for metabolic syndrome. Current research has shown that hepatic fatty acid accumulation can cause hepatic insulin resistance through increased gluconeogenesis, lipogenesis, chronic inflammation, oxidative stress and endoplasmic reticulum stress, and impaired insulin signal pathway. Mitochondria are the major sites of fatty acid β-oxidation, which is the major degradation mechanism of fatty acids. Mitochondrial dysfunction has been shown to be involved in the development of hepatic fatty acid–induced hepatic insulin resistance. Mitochondrial autophagy (mitophagy), a catabolic process, selectively degrades damaged mitochondria to reverse mitochondrial dysfunction and preserve mitochondrial dynamics and function. Therefore, mitophagy can promote mitochondrial fatty acid oxidation to inhibit hepatic fatty acid accumulation and improve hepatic insulin resistance. Here, we review advances in our understanding of the relationship between mitophagy and hepatic insulin resistance. Additionally, we also highlight the potential value of mitophagy in the treatment of hepatic insulin resistance and metabolic syndrome.

Gene Expression Predicts Histological Severity and Reveals Distinct Molecular Profiles of Nonalcoholic Fatty Liver Disease

The heterogeneity of biological processes driving the severity of nonalcoholic fatty liver disease (NAFLD) as reflected in the transcriptome and the relationship between the pathways involved are not well established. Well-defined associations between gene expression profiles and disease progression would benefit efforts to develop novel therapies and to understand disease heterogeneity. We analyzed hepatic gene expression in controls and a cohort with the full histological spectrum of NAFLD. Protein-protein interaction and gene set variation analysis revealed distinct sets of coordinately regulated genes and pathways whose expression progressively change over the course of the disease. The progressive nature of these changes enabled us to develop a framework for calculating a disease progression score for individual genes. We show that, in aggregate, these scores correlate strongly with histological measures of disease progression and can thus themselves serve as a proxy for severity. Furthermore, we demonstrate that the expression levels of a small number of genes (~20) can be used to infer disease severity. Finally, we show that patient subgroups can be distinguished by the relative distribution of gene-level scores in specific gene sets. While future work is required to identify the specific disease characteristics that correspond to patient clusters identified on this basis, this work provides a general framework for the use of high-content molecular profiling to identify NAFLD patient subgroups.

Antioxidant Versus Pro-Apoptotic Effects of Mushroom-Enriched Diets on Mitochondria in Liver Disease

Mitochondria play a central role in non-alcoholic fatty liver disease (NAFLD) progression and in the control of cell death signalling during the progression to hepatocellular carcinoma (HCC). Associated with the metabolic syndrome, NAFLD is mostly driven by insulin-resistant white adipose tissue lipolysis that results in an increased hepatic fatty acid influx and the ectopic accumulation of fat in the liver. Upregulation of beta-oxidation as one compensatory mechanism leads to an increase in mitochondrial tricarboxylic acid cycle flux and ATP generation. The progression of NAFLD is associated with alterations in the mitochondrial molecular composition and respiratory capacity, which increases their vulnerability to different stressors, including calcium and pro-inflammatory molecules, which result in an increased generation of reactive oxygen species (ROS) that, altogether, may ultimately lead to mitochondrial dysfunction. This may activate further pro-inflammatory pathways involved in the progression from steatosis to steatohepatitis (NASH). Mushroom-enriched diets, or the administration of their isolated bioactive compounds, have been shown to display beneficial effects on insulin resistance, hepatic steatosis, oxidative stress, and inflammation by regulating nutrient uptake and lipid metabolism as well as modulating the antioxidant activity of the cell. In addition, the gut microbiota has also been described to be modulated by mushroom bioactive molecules, with implications in reducing liver inflammation during NAFLD progression. Dietary mushroom extracts have been reported to have anti-tumorigenic properties and to induce cell-death via the mitochondrial apoptosis pathway. This calls for particular attention to the potential therapeutic properties of these natural compounds which may push the development of novel pharmacological options to treat NASH and HCC. We here review the diverse effects of mushroom-enriched diets in liver disease, emphasizing those effects that are dependent on mitochondria.

Impact of Lipotoxicity on Tissue "Cross Talk" and Metabolic Regulation

Obesity-associated comorbidities include non-alcoholic fatty liver disease, Type 2 diabetes, and cardiovascular disease. These diseases are associated with accumulation of lipids in non-adipose tissues, which can impact many intracellular cellular signaling pathways and functions that have been broadly defined as "lipotoxic." This review moves beyond understanding intracellular lipotoxic outcomes and outlines the consequences of lipotoxicity on protein secretion and inter-tissue "cross talk," and the impact this exerts on systemic metabolism.

Higd1a Protects Cells from Lipotoxicity under High-Fat Exposure

Hypoxia-inducible gene domain family member 1A (Higd1a) has recently been reported to protect cells from hypoxia by helping to maintain normal mitochondrial function. The potential induction of Higd1a under high-fat exposure and whether it could protect cells from oxidative stress attracted our attention. Initially, 0.4 mM oleic acid and 0.2 mM palmitate were added to the growth media of HepG2 and LO2 cells for 72 hours. We discovered increased Higd1a expression, and knocking down Higd1a impaired mitochondrial transmembrane potential and induced cell apoptosis. We then identified that elevated reactive oxygen species (ROS) is responsible for increased Higd1a expression. Furthermore, we found that ROS promoted Higd1a expression by upregulating HIF-1a and PGC-1a expressions, and these two proteins could exert synergistic effects in inducing Higd1a expression. Taken together, these data suggest that Higd1a plays positive roles in protecting cells from oxidative stress, and ROS could induce Higd1a expression by upregulating PGC-1a and HIF-1a expressions.

Hepatic HKDC1 Expression Contributes to Liver Metabolism

Glucokinase (GCK) is the principal hexokinase (HK) in the liver, operating as a glucose sensor to regulate glucose metabolism and lipid homeostasis. Recently, we proposed HK domain-containing 1 (HKDC1) to be a fifth HK with expression in the liver. Here, we reveal HKDC1 to have low glucose-phosphorylating ability and demonstrate its association with the mitochondria in hepatocytes. As we have shown previously that genetic deletion of HKDC1 leads to altered hepatic triglyceride levels, we also explored the influence of overexpression of HKDC1 in hepatocytes on cellular metabolism, observing reduced glycolytic capacity and maximal mitochondrial respiration with concurrent reductions in glucose oxidation and mitochondrial membrane potential. Furthermore, we found that acute in vivo overexpression of HKDC1 in the liver induced substantial changes in mitochondrial dynamics. Altogether, these findings suggest that overexpression of HKDC1 causes mitochondrial dysfunction in hepatocytes. However, its overexpression was not enough to alter energy storage in the liver but led to mild improvement in glucose tolerance. We next investigated the conditions necessary to induce HKDC1 expression, observing HKDC1 expression to be elevated in human patients whose livers were at more advanced stages of nonalcoholic fatty liver disease (NAFLD) and similarly, found high liver expression in mice on diets causing high levels of liver inflammation and fibrosis. Overall, our data suggest that HKDC1 expression in hepatocytes results in defective mitochondrial function and altered hepatocellular metabolism and speculate that its expression in the liver may play a role in the development of NAFLD.

A mix of dietary fermentable fibers improves lipids handling by the liver of overfed minipigs

Obesity induced by overfeeding ultimately can lead to nonalcoholic fatty liver disease, whereas dietary fiber consumption is known to have a beneficial effect. We aimed to determine if a supplementation of a mix of fibers (inulin, resistant starch and pectin) could limit or alleviate overfeeding-induced metabolic perturbations. Twenty female minipigs were fed with a control diet (C) or an enriched fat/sucrose diet supplemented (O + F) or not (O) with fibers. Between 0 and 56 days of overfeeding, insulin (+88%), HOMA (+102%), cholesterol (+45%) and lactate (+63%) were increased, without any beneficial effect of fibers supplementation. However, fibers supplementation limited body weight gain (vs. O, -15% at D56) and the accumulation of hepatic lipids droplets induced by overfeeding. This could be explained by a decreased lipids transport potential (-50% FABP1 mRNA, O + F vs. O) inducing a down-regulation of regulatory elements of lipids metabolism / lipogenesis (-36% SREBP1c mRNA, O + F vs. O) but not to an increased oxidation (O + F not different from O and C for proteins and mRNA measured). Glucose metabolism was also differentially regulated by fibers supplementation, with an increased net hepatic release of glucose in the fasted state (diet × time effect, P<.05 at D56) that can be explained partially by a possible increased glycogen synthesis in the fed state (+82% GYS2 protein, O + F vs. O, P=.09). The direct role of short chain fatty acids on gluconeogenesis stimulation is questioned, with probably a short-term impact (D14) but no effect on a long-term (D56) basis.

Hepatic growth hormone - JAK2 - STAT5 signalling: Metabolic function, non-alcoholic fatty liver disease and hepatocellular carcinoma progression

The rising prevalence of obesity came along with an increase in associated metabolic disorders in Western countries. Non-alcoholic fatty liver disease (NAFLD) represents the hepatic manifestation of the metabolic syndrome and is linked to primary stages of liver cancer development. Growth hormone (GH) regulates various vital processes such as energy supply and cellular regeneration. In addition, GH regulates various aspects of liver physiology through activating the Janus kinase (JAK) 2- signal transducer and activator of transcription (STAT) 5 pathway. Consequently, disrupted GH - JAK2 - STAT5 signaling in the liver alters hepatic lipid metabolism and is associated with NAFLD development in humans and mouse models. Interestingly, while STAT5 as well as JAK2 deficiency correlates with hepatic lipid accumulation, recent studies suggest that these proteins have unique ambivalent functions in chronic liver disease progression and tumorigenesis. In this review, we focus on the consequences of altered GH - JAK2 - STAT5 signaling for hepatic lipid metabolism and liver cancer development with an emphasis on lessons learned from genetic knockout models.

Impact of 17β-estradiol on complex I kinetics and H2O2 production in liver and skeletal muscle mitochondria

Naturally or surgically induced postmenopausal women are widely prescribed estrogen therapies to alleviate symptoms associated with estrogen loss and to lower the subsequent risk of developing metabolic diseases, including diabetes and nonalcoholic fatty liver disease. However, the molecular mechanisms by which estrogens modulate metabolism across tissues remain ill-defined. We have previously reported that 17β-estradiol (E2) exerts antidiabetogenic effects in ovariectomized (OVX) mice by protecting mitochondrial and cellular redox function in skeletal muscle. The liver is another key tissue for glucose homeostasis and a target of E2 therapy. Thus, in the present study we determined the effects of acute loss of ovarian E2 and E2 administration on liver mitochondria. In contrast to skeletal muscle mitochondria, E2 depletion via OVX did not alter liver mitochondrial respiratory function or complex I (CI) specific activities (NADH oxidation, quinone reduction, and H2O2 production). Surprisingly, in vivo E2 replacement therapy and in vitro E2 exposure induced tissue-specific effects on both CI activity and on the rate and topology of CI H2O2 production. Overall, E2 therapy protected and restored the OVX-induced reduction in CI activity in skeletal muscle, whereas in liver mitochondria E2 increased CI H2O2 production and decreased ADP-stimulated respiratory capacity. These results offer novel insights into the tissue-specific effects of E2 on mitochondrial function.

Bacupari peel extracts (Garcinia brasiliensis) reduces the biometry, lipogenesis and hepatic steatosis in obese rats

The aim was to evaluate the effect of the ethanol extract of bacupari peel (EEB) on biometric measurements, hepatic lipogenesis and progression of non-alcoholic fatty liver disease (NAFLD) in obese Wistar rats. Chemical analysis of the bacupari peel extract identified 7-epiclusianone as the major constituent (140.02 mg/g) followed by morelloflavone (35.86 mg/g). Animals treated with high fat diet plus EEB (BHFD) reduced body mass index (BMI), liver weight and hepatosomatic index in relation to the obese control. The food intake was similar between hyperlipid group (HFD) groups with or without EEB. However, the normal control group (AIN-93 M) presented higher food intake and lower final weight compared to the obese control (HFD). The PPAR-α, CPT-1a and the ADIPOR2 genes expressions, and the concentration of the PPAR-α and the adiponectin protein level increased in the BHFD group in relation to the obese control. The EEB promoted reduction of the SREBP-1c gene expression and the percentage of hepatic fat and the degree of steatosis in relation to HFD. It was concluded that EEB showed a protective effect on NAFLD, as it promoted a reduction in BMI, induced lipid oxidation, reduced lipogenesis and hepatic steatosis. Moreover, our results suggest an interaction that can lead to an agonist activity of the EEB to the PPAR-α receptor.

Sensitive and early detection of mitochondrial dysfunction in the liver of NASH model mice by PET imaging with 18F-BCPP-BF

BACKGROUND

Nonalcoholic fatty liver disease is a common disorder that progresses from simple fatty liver (steatosis) to nonalcoholic steatohepatitis (NASH). It is thought that mitochondrial dysfunction plays a critical role in the progression of NASH. In this study, we developed a non-invasive method for early diagnosis and staging of NASH that directly measures mitochondrial complex-I (MC-I) activity in the liver of NASH model mice by positron emission tomography (PET) imaging using the novel tracer 2-tert-butyl-4-chloro-5-[6-(4-[¹⁸F]fluorobutoxy)-pyridin-3-ylmethoxy]-2H-pyridazin-3-one (¹⁸F-BCPP-BF). Liver uptake of ¹⁸F-BCPP-BF in NASH and age-matched control mice was measured as a standard uptake value over a period of 1 to 12 weeks. Histopathological evaluation of the liver tissue was performed by haematoxylin and eosin staining, and fibrosis was assessed by Masson's trichrome staining.

RESULTS

Significant mitochondrial dysfunction was detected as early as 1 week after commencing the diet, and MC-I activity in the liver measured by PET was reduced by > 50% relative to that in age-matched control mice after 6 weeks. Liver uptake of ¹⁸F-BCPP-BF was low throughout the 12-week experimental period. Histopathological examination revealed that steatosis, inflammation, and ballooning progressed from 1 to 6 weeks, with fibrosis observed from 6 to 12 weeks.

CONCLUSIONS

PET scans and histopathological analysis revealed that mitochondrial dysfunction in the liver contributed to the progression of NASH. PET imaging with ¹⁸F-BCPP-BF is a useful tool for detecting NASH at early stages and for monitoring therapeutic response.

NEFA-induced ROS impaired insulin signalling through the JNK and p38MAPK pathways in non-alcoholic steatohepatitis

The aim of this study was to investigate the changes in hepatic oxidative phosphorylation (OXPHOS) complexes (COs) in patients and cows with non‐alcoholic steatohepatitis (NASH) and to investigate the mechanism that links mitochondrial dysfunction and hepatic insulin resistance induced by non‐esterified fatty acids (NEFAs). Patients and cows with NASH displayed high blood NEFAs, TNF‐α and IL‐6 concentrations, mitochondrial dysfunction and insulin resistance. The protein levels of peroxisome proliferator‐activated receptor‐γ coactivator‐1α (PGC‐1α), mitofusin‐2 (Mfn‐2) and OXPHOS complexes (human: COI and COIII; cow: COI‐IV) were significantly decreased in patients and cows with NASH. NEFA treatment significantly impaired mitochondrial function and, increased reactive oxygen species (ROS) production, and excessive ROS overactivated the JNK and p38MAPK pathways and induced insulin resistance in cow hepatocytes. PGC‐1α and Mfn‐2 overexpression significantly decreased the NEFA‐induced ROS production and TNF‐α and IL‐6 mRNA expressions, reversed the inhibitory effect of NEFAs on mitochondrial function and attenuated the overactivation of the ROS‐JNK/p38MAPK pathway, alleviated insulin resistance induced by NEFAs in cow hepatocytes and HepG2 cells. These findings indicate that NEFAs induce mitochondrial dysfunction and insulin resistance mediated by the ROS‐JNK/p38MAPK pathway. PGC‐1α or Mfn‐2 overexpression reversed the lipotoxicity of NEFAs on mitochondrial dysfunction and insulin resistance. Our study clarified the mechanism that links hepatic mitochondrial dysfunction and insulin resistance in NASH.

Effects of exposure to malathion on blood glucose concentration: a meta-analysis

Exposure to malathion (an organophosphate pesticide widely used around the world) has been associated with alterations in blood glucose concentration in animal models. However, the results are inconsistent. The aim of this meta-analysis was to evaluate whether malathion exposure can disturb the concentrations of blood glucose in exposed rats. We performed a literature search of online databases including PubMed, EBSCO, and Google Scholar and reviewed original articles that analyzed the relation between malathion exposure and glucose levels in animal models. The selection of articles was based on inclusion and exclusion criteria. The database search identified thirty-five possible articles, but only eight fulfilled our inclusion criteria, and these studies were included in the meta-analysis. The effect of malathion on blood glucose concentration showed a non-monotonic dose-response curve. In addition, pooled analysis showed that blood glucose concentrations were 3.3-fold higher in exposed rats than in the control group (95% CI, 2-5; Z = 3.9; p < 0.0001) in a random-effect model. This result suggested that alteration of glucose homeostasis is a possible mechanism of toxicity associated with exposure to malathion.

Increased lipogenesis in spite of upregulated hepatic 5'AMP-activated protein kinase in human non-alcoholic fatty liver

AIMS

Molecular adaptations in human non-alcoholic fatty liver disease (NAFLD) are incompletely understood. This study investigated the main gene categories related to hepatic de novo lipogenesis and lipid oxidation capacity.

METHODS

Liver specimens of 48 subjects were histologically classified according to steatosis severity. In-depth analyses were undertaken using real-time polymerase chain reaction, immunoblotting, and immunohistochemistry. Lipid profiles were analyzed by gas chromatography/flame ionization detection, and effects of key fatty acids were studied in primary human hepatocytes.

RESULTS

Real-time polymerase chain reaction, immunoblotting, and immunohistochemistry indicated 5'AMP-activated protein kinase (AMPK) to be increased with steatosis score ≥ 2 (all P < 0.05), including various markers of de novo lipogenesis and lipid degradation (all P < 0.05). Regarding endoplasmic reticulum stress, X-Box binding protein-1 (XBP1) was upregulated in steatosis score ≥ 2 (P = 0.029) and correlated with plasma palmitate (r = 0.34; P = 0.035). Palmitate incubation of primary human hepatocytes increased XBP1 and downstream stearoyl CoA desaturase-1 mRNA expression (both P < 0.05). Moreover, plasma and liver tissue exposed a NAFLD-related lipid profile with reduced polyunsaturated/saturated fatty acid ratio, increased palmitate and palmitoleate, and elevated lipogenesis and desaturation indices with steatosis score ≥ 2 (all P < 0.05).

CONCLUSION

In humans with advanced fatty liver disease, hepatic AMPK protein is upregulated, potentially in a compensatory manner. Moreover, pathways of lipid synthesis and degradation are co-activated in subjects with advanced steatosis. Palmitate may drive lipogenesis by activating XBP1-mediated endoplasmic reticulum stress and represent a target for future dietary or pharmacological intervention.

Antioxidant dietary approach in treatment of fatty liver: New insights and updates

Non-alcoholic fatty liver disease (NAFLD) is a common clinicopathological condition, encompassing a range of conditions caused by lipid deposition within liver cells. To date, no approved drugs are available for the treatment of NAFLD, despite the fact that it represents a serious and growing clinical problem in the Western world. Identification of the molecular mechanisms leading to NAFLD-related fat accumulation, mitochondrial dysfunction and oxidative balance impairment facilitates the development of specific interventions aimed at preventing the progression of hepatic steatosis. In this review, we focus our attention on the role of dysfunctions in mitochondrial bioenergetics in the pathogenesis of fatty liver. Major data from the literature about the mitochondrial targeting of some antioxidant molecules as a potential treatment for hepatic steatosis are described and critically analysed. There is ample evidence of the positive effects of several classes of antioxidants, such as polyphenols (i.e., resveratrol, quercetin, coumestrol, anthocyanins, epigallocatechin gallate and curcumin), carotenoids (i.e., lycopene, astaxanthin and fucoxanthin) and glucosinolates (i.e., glucoraphanin, sulforaphane, sinigrin and allyl-isothiocyanate), on the reversion of fatty liver. Although the mechanism of action is not yet fully elucidated, in some cases an indirect interaction with mitochondrial metabolism is expected. We believe that such knowledge will eventually translate into the development of novel therapeutic approaches for fatty liver.

Embrionary way to create a fatty liver in portal hypertension

Portal hypertension in the rat by triple partial portal vein ligation produces an array of splanchnic and systemic disorders, including hepatic steatosis. In the current review these alterations are considered components of a systemic inflammatory response that would develop through three overlapping phenotypes: The neurogenic, the immune and the endocrine. These three inflammatory phenotypes could resemble the functions expressed during embryonic development of mammals. In turn, the inflammatory phenotypes would be represented in the embryo by two functional axes, that is, a coelomic-amniotic axis and a trophoblastic yolk-sac or vitelline axis. In this sense, the inflammatory response developed after triple partial portal vein ligation in the rat would integrate both functional embryonic axes on the liver interstitial space of Disse. If so, this fact would favor the successive development of steatosis, steatohepatitis and fibrosis. Firstly, these recapitulated embryonic functions would produce the evolution of liver steatosis. In this way, this fat liver could represent a yolk-sac-like in portal hypertensive rats. After that, the systemic recapitulation of these embryonic functions in experimental prehepatic portal hypertension would consequently induce a gastrulation-like response in which a hepatic wound healing reaction or fibrosis occur. In conclusion, studying the mechanisms involved in embryonic development could provide key results for a better understanding of the nonalcoholic fatty liver disease etiopathogeny.