Nonalcoholic steatohepatitis: association of insulin resistance and mitochondrial abnormalities

Pathogenic effects of Desulfovibrio in the gut on fatty liver in diet-induced obese mice and children with obesity

BACKGROUND

Although we know the key role of gut dysbiosis in nonalcoholic fatty liver disease (NAFLD), it remains unclear what microbe(s) are responsible. This study aims to identify the microbes that cause NAFLD.

METHODS

C57BL/6JNarl male mice fed a high-fat diet (HFD) were orally administered Lactobacillus reuteri (L. reuteri) or Lactobacillus rhamnosus GG plus Bifidobacterium animalis subsp. lactis BB12 (LGG plus BB12). Their fecal microbiomes identified by 16S rRNA sequencing were correlated with the severity of fatty liver. We then used a human cohort to confirm the role of the microbe(s). The HFD-fed mice were administrated with the identified bacterium, Desulfovibrio. The histopathological changes in the liver and ileum were analyzed.

RESULTS

Lactobacillus and Bifidobacterium improved hepatic steatosis and fibrosis in HFD-fed mice, which was related to the decreased abundance of Desulfovibrio in feces. Further human study confirmed the amount of D. piger in the fecal microbiota of obese children with NAFLD was increased. We then administered D. piger and found aggravated hepatic steatosis and fibrosis in HFD-fed mice. Hepatic expression of CD36 was significantly increased in HFD-fed mice gavaged with D. piger. In HepG2 cells, overexpression of CD36 increased lipid droplets, whereas knockdown of CD36 decreased lipid droplets. HFD-fed mice gavaged with D. piger had a decrease in the villus length, crypt depth, and zonula occludens-1 density in the ileum tissue.

CONCLUSIONS

Our findings provide novel insights into the role of Desulfovibrio dysregulation in NAFLD. Modulation of Desulfovibrio may be a potential target for the treatment of NAFLD.

Potential Therapeutic Implication of Herbal Medicine in Mitochondria-Mediated Oxidative Stress-Related Liver Diseases

Mitochondria are double-membrane organelles that play a role in ATP synthesis, calcium homeostasis, oxidation-reduction status, apoptosis, and inflammation. Several human disorders have been linked to mitochondrial dysfunction. It has been found that traditional therapeutic herbs are effective on alcoholic liver disease (ALD) and nonalcoholic fatty liver disease (NAFLD) which are leading causes of liver cirrhosis and hepatocellular carcinoma. The generation of reactive oxygen species (ROS) in response to oxidative stress is caused by mitochondrial dysfunction and is considered critical for treatment. The role of oxidative stress, lipid toxicity, and inflammation in NAFLD are well known. NAFLD is a chronic liver disease that commonly progresses to cirrhosis and chronic liver disease, and people with obesity, insulin resistance, diabetes, hyperlipidemia, and hypertension are at a higher risk of developing NAFLD. NAFLD is associated with a number of pathological factors, including insulin resistance, lipid metabolic dysfunction, oxidative stress, inflammation, apoptosis, and fibrosis. As a result, the improvement in steatosis and inflammation is enough to entice researchers to look into liver disease treatment. However, antioxidant treatment has not been very effective for liver disease. Additionally, it has been suggested that the beneficial effects of herbal medicines on immunity and inflammation are governed by various mechanisms for lipid metabolism and inflammation control. This review provided a summary of research on herbal medicines for the therapeutic implementation of mitochondria-mediated ROS production in liver disease as well as clinical applications through herbal medicine. In addition, the pathophysiology of common liver disorders such as ALD and NAFLD would be investigated in the role that mitochondria play in the process to open new therapeutic avenues in the management of patients with liver disease.

MitoQ alleviates carbon tetrachloride-induced liver fibrosis in mice through regulating JNK/YAP pathway

Background

Liver fibrosis is a pathological wound-healing response caused by chronic liver damage. Mitochondria regulate hepatic energy metabolism and oxidative stress. Accumulating evidence has revealed that increased mitochondrial oxidative stress contributes to the activation of fibrogenesis. However, the roles and underlying mechanisms of mitochondrial oxidative stress in liver fibrosis remain unknown.

Methods and results

In this study, C57BL/6 mice were used to establish a model of liver fibrosis via oral gavage with CCl4 treatment for 8 weeks. Furthermore, intervention experiments were achieved by CCl4 combined with the intraperitoneal injection of mitoquinone mesylate (mitoQ). We demonstrated that the chronic CCl4 exposure resulted in severe hepatic fibrogenesis and significantly promoted the production of reactive oxygen species (ROS) and mitochondrial abnormalities. Besides, JNK/YAP pathway was also activated. By contrast, the administration of mitoQ markedly inhibited the expression of pro-fibrogenic transforming growth factor-β as well as type I collagen. The antifibrotic effects of mitoQ were also confirmed by hematoxylin and eosin staining and Sirius red staining. Moreover, mitoQ substantially reduced CCl4-induced mitochondrial damage and the release of ROS. Further studies suggested that this protection against liver fibrosis was mechanistically related to the inhibition of phosphorylation of JNK and the nuclear translocation of YAP.

Conclusion

In conclusion, these findings revealed that mitoQ attenuated liver fibrosis by inhibiting ROS production and the JNK/YAP signaling pathway. Selective targeting JNK/YAP may serve as a therapeutic strategy for retarding progression of chronic liver disease.

Glial cell derived neurotrophic factor prevents western diet and palmitate-induced hepatocyte oxidative damage and death through SIRT3

Nonalcoholic fatty liver disease (NAFLD) is associated with increased oxidative stress that leads to hepatocyte and mitochondrial damage. In this study we investigated the mechanisms involved in the induction of oxidative stress and impairment of mitochondrial quality control and mitophagy in hepatocytes by the saturated fatty acid palmitate and Western diet feeding in mice and if their harmful effects could be reversed by the neurotrophic factor glial cell derived neurotrophic factor (GDNF). Western diet (WD)-feeding increased hepatic lipid peroxidation in control mice and, in vitro palmitate induced oxidative stress and impaired the mitophagic clearance of damaged mitochondria in hepatocytes. This was accompanied by reductions in hepatocyte sirtuin 3 (SIRT3) deacetylase activity, gene expression and protein levels as well as in superoxide dismutase enzyme activity. These reductions were reversed in the liver of Western diet fed GDNF transgenic mice and in hepatocytes exposed to palmitate in the presence of GDNF. We demonstrate an important role for Western diet and palmitate in inducing oxidative stress and impairing mitophagy in hepatocytes and an ability of GDNF to prevent this. These findings suggest that GDNF or its agonists may be a potential therapy for the prevention or treatment of NAFLD.

S100 Proteins in Fatty Liver Disease and Hepatocellular Carcinoma

Non-alcoholic fatty liver disease (NAFLD) is a highly prevalent and slow progressing hepatic pathology characterized by different stages of increasing severity which can ultimately give rise to the development of hepatocellular carcinoma (HCC). Besides drastic lifestyle changes, few drugs are effective to some extent alleviate NAFLD and HCC remains a poorly curable cancer. Among the deregulated molecular mechanisms promoting NAFLD and HCC, several members of the S100 proteins family appear to play an important role in the development of hepatic steatosis, non-alcoholic steatohepatitis (NASH) and HCC. Specific members of this Ca²⁺-binding protein family are indeed significantly overexpressed in either parenchymal or non-parenchymal liver cells, where they exert pleiotropic pathological functions driving NAFLD/NASH to severe stages and/or cancer development. The aberrant activity of S100 specific isoforms has also been reported to drive malignancy in liver cancers. Herein, we discuss the implication of several key members of this family, e.g., S100A4, S100A6, S100A8, S100A9 and S100A11, in NAFLD and HCC, with a particular focus on their intracellular versus extracellular functions in different hepatic cell types. Their clinical relevance as non-invasive diagnostic/prognostic biomarkers for the different stages of NAFLD and HCC, or their pharmacological targeting for therapeutic purpose, is further debated.

Metabolic improvement and liver regeneration by inhibiting CXXC5 function for non-alcoholic steatohepatitis treatment

Non-alcoholic steatohepatitis (NASH) is a chronic liver disease that results from multiple metabolic disorders. Considering the complexity of the pathogenesis, the identification of a factor mediating the multiple pathogenic phenotypes of NASH will be important for treatment. In this study, we found that CXXC5, a negative feedback regulator of the Wnt/β-catenin pathway, was overexpressed with suppression of Wnt/β-catenin signaling and its target genes involved in hepatic metabolism in obese-NASH patients. Cxxc5−/− mice were found to be resistant to NASH pathogenesis with metabolic improvements. KY19334, a small molecule that activates the Wnt/β-catenin pathway via interference of the CXXC5-Dvl interaction, reversed the overall pathogenic features of NASH as Cxxc5−/− mice. The improvement in NASH by KY19334 is attributed to its regenerative effects through restorative activation of the suppressed Wnt/β-catenin signaling. Overall, the pronounced metabolic improvements with the stimulation of liver regeneration by interfering with the CXXC5-Dvl interaction provide a therapeutic approach for NASH.

Spermidine-mediated hypusination of translation factor EIF5A improves mitochondrial fatty acid oxidation and prevents non-alcoholic steatohepatitis progression

Spermidine is a natural polyamine that has health benefits and extends life span in several species. Deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase (DOHH) are key enzymes that utilize spermidine to catalyze the post-translational hypusination of the translation factor EIF5A (EIF5A^H). Here, we have found that hepatic DOHH mRNA expression is decreased in patients and mice with non-alcoholic steatohepatitis (NASH), and hepatic cells treated with fatty acids. The mouse and cell culture models of NASH have concomitant decreases in Eif5a^H and mitochondrial protein synthesis which leads to lower mitochondrial activity and fatty acid β-oxidation. Spermidine treatment restores EIF5A^H, partially restores protein synthesis and mitochondrial function in NASH, and prevents NASH progression in vivo. Thus, the disrupted DHPS-DOHH-EIF5A^H pathway during NASH represents a therapeutic target to increase hepatic protein synthesis and mitochondrial fatty acid oxidation (FAO) and prevent NASH progression.

The atherogenic index of plasma: A novel factor more closely related to non-alcoholic fatty liver disease than other lipid parameters in adults

Background and aims

The relationship of non-alcoholic fatty liver disease (NAFLD) with the atherogenic index of plasma (AIP) is unclear. This study aims to detect the association between AIP and NAFLD, compare the discriminative power of AIP with other lipid parameters for NAFLD, and establish a discriminant model using physical examination data.

Methods

Participants aged over 20 years who underwent routine physical examination in Beijing Chaoyang Hospital from April 2016 to August 2020 were included. We categorized subjects based on hepatic ultrasound results and analyzed the association between NAFLD risk and AIP, conventional plasma lipids, remnant cholesterol (RC), triglyceride and glucose (TyG) index, and other atherogenic indices (n = 112,200) using logistic regression, restricted cubic spline regression, and receiver operating characteristic curve.

Results

Out of the 112,200 subjects, 30.4% had NAFLD. The body weight index, plasma glucose, conventional lipids, TyG index, AIP, atherogenic coefficient (AC), and coronary risk index (CRI) were significantly higher, while HDL-C was lower (p < 0.001) in patients with NAFLD than those without NAFLD (all p < 0.001). Compared with conventional lipids, RC, TyG index, AC, and CRI, AIP had a stronger correlation with the risk of NAFLD (OR 6.71, 95% CI 6.23–7.22, p < 0.001) after adjusting confounders and presented a non-linear dose–response relationship (p < 0.0001). The optimal cut-off value of AIP was 0.05 and the area under the curve (AUC) was 0.82 (95% CI: 0.81–0.82) with high sensitivity and specificity. The AUC of the simplified three-variable NAFLD discriminant model was 0.90 in both the training set and the validation set.

Conclusion

AIP was significantly associated with NAFLD and showed superior discriminative performance to other lipid parameters. These findings might help screen NAFLD in high-risk individuals and reduce the prevalence of NAFLD.

Autophagy Dysregulation in Metabolic Associated Fatty Liver Disease: A New Therapeutic Target

Metabolic associated fatty liver disease (MAFLD) is one of the most common causes of chronic liver disease worldwide. To date, there is no FDA-approved treatment, so there is an urgent need to determine its pathophysiology and underlying molecular mechanisms. Autophagy is a lysosomal degradation pathway that removes damaged organelles and misfolded proteins after cell injury through endoplasmic reticulum stress or starvation, which inhibits apoptosis and promotes cell survival. Recent studies have shown that autophagy plays an important role in removing lipid droplets from hepatocytes. Autophagy has also been reported to inhibit the production of pro-inflammatory cytokines and provide energy for the hepatic stellate cells activation during liver fibrosis. Thyroid hormone, irisin, melatonin, hydrogen sulfide, sulforaphane, DA-1241, vacuole membrane protein 1, nuclear factor erythroid 2-related factor 2, sodium-glucose co-transporter type-2 inhibitors, immunity-related GTPase M, and autophagy-related gene 7 have been reported to ameliorate MAFLD via autophagic induction. Lipid receptor CD36, SARS-CoV-2 Spike protein and leucine aminopeptidase 3 play a negative role in the autophagic function. This review summarizes recent advances in the role of autophagy in MAFLD. Autophagy modulates major pathological changes, including hepatic lipid metabolism, inflammation, and fibrosis, suggesting the potential of modulating autophagy for the treatment of MAFLD.

Hepatocyte Mitochondrial Dynamics and Bioenergetics in Obesity-Related Non-Alcoholic Fatty Liver Disease

PURPOSE OF THE REVIEW

Mitochondrial dysfunction has long been proposed to play a crucial role in the pathogenesis of a considerable number of disorders, such as neurodegeneration, cancer, cardiovascular, and metabolic disorders, including obesity-related insulin resistance and non-alcoholic fatty liver disease (NAFLD). Mitochondria are highly dynamic organelles that undergo functional and structural adaptations to meet the metabolic requirements of the cell. Alterations in nutrient availability or cellular energy needs can modify their formation through biogenesis and the opposite processes of fission and fusion, the fragmentation, and connection of mitochondrial network areas respectively. Herein, we review and discuss the current literature on the significance of mitochondrial adaptations in obesity and metabolic dysregulation, emphasizing on the role of hepatocyte mitochondrial flexibility in obesity and NAFLD.

RECENT FINDINGS

Accumulating evidence suggests the involvement of mitochondrial morphology and bioenergetics dysregulations to the emergence of NAFLD and its progress to non-alcoholic steatohepatitis (NASH). Most relevant data suggests that changes in liver mitochondrial dynamics and bioenergetics hold a key role in the pathogenesis of NAFLD. During obesity and NAFLD, oxidative stress occurs due to the excessive production of ROS, leading to mitochondrial dysfunction. As a result, mitochondria become incompetent and uncoupled from respiratory chain activities, further promoting hepatic fat accumulation, while leading to liver inflammation, insulin resistance, and disease's deterioration. Elucidation of the mechanisms leading to dysfunctional mitochondrial activity of the hepatocytes during NAFLD is of predominant importance for the development of novel therapeutic approaches towards the treatment of this metabolic disorder.

Historical Changes in Weight Classes and the Influence of NAFLD Prevalence: A Population Analysis of 34,486 Individuals

Background: Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease globally in tandem with the growing obesity epidemic. However, there is a lack of data on the relationship between historical weight changes 10 years ago and at present on NAFLD prevalence at the population level. Therefore, we sought to evaluate the relationship between weight classes and the prevalence of NAFLD. Methods: Data were used from the United States National Health and Nutrition Examination Survey (NHANES) from 1999 to 2018. Univariate and multivariate general linear model analyses were used to obtain risk ratio (RR) estimations of NAFLD events. Results: In total, 34,486 individuals were analysed, with those who were lean at both time points as the control group. Overweight (RR: 14.73, 95%CI: 11.94 to 18.18, p < 0.01) or obese (RR: 31.51, 95%CI: 25.30 to 39.25, p < 0.01) individuals at both timepoints were more likely to develop NAFLD. Residual risk exists where previously obese individuals became overweight (RR: 14.72, 95%CI: 12.36 to 17.52, p < 0.01) or lean (RR: 2.46, 95%CI: 1.40 to 4.31, p = 0.02), and previously overweight individuals who became lean (RR 2.24, 95%CI 1.42 to 3.54, p = 0.01) had persistent elevated risk of developing NAFLD despite weight regression. Sensitivity analysis identified that a higher proportion of individuals with regression in weight class were diabetics and Mexican Americans, while fewer African Americans saw weight-class regression. Conclusions: Residual risk exists in patients who lost weight despite the smaller magnitude of effect, and targeted weight reductions should still be used to mitigate the risk of NAFLD at the population level.

Fibroblasts: Immunomodulatory factors in refractory diabetic wound healing

Diabetes is a systemic disease in which patients with diabetes may develop peripheral neuropathy of the lower extremities and peripheral vascular disease due to long-term continuous exposure to high glucose. Delayed wound healing in diabetes is one of the major complications of diabetes. Slow wound healing in diabetic patients is associated with high glucose toxicity. When the condition deteriorates, the patient needs to be amputated, which seriously affects the quality of life and even endangers the life of the patient. In general, the delayed healing of diabetes wound is due to the lack of chemokines, abnormal inflammatory response, lack of angiogenesis and epithelial formation, and fibroblast dysfunction. The incidence of several chronic debilitating conditions is increasing in patients with diabetes, such as chronic renal insufficiency, heart failure, and hepatic insufficiency. Fibrosis is an inappropriate deposition of extracellular matrix (ECM) proteins. It is common in diabetic patients causing organ dysfunction. The fibrotic mechanism of diabetic fibroblasts may involve direct activation of permanent fibroblasts. It may also involve the degeneration of fibers after hyperglycemia stimulates immune cells, vascular cells, or organ-specific parenchymal cells. Numerous studies confirm that fibroblasts play an essential role in treating diabetes and its complications. The primary function of fibroblasts in wound healing is to construct and reshape the ECM. Nowadays, with the widespread use of single-cell RNA sequencing (scRNA-seq), an increasing number of studies have found that fibroblasts have become the critical immune sentinel cells, which can detect not only the activation and regulation of immune response but also the molecular pattern related to the injury. By exploring the heterogeneity and functional changes of fibroblasts in diabetes, the manuscript discusses that fibroblasts may be used as immunomodulatory factors in refractory diabetic wound healing, providing new ideas for the treatment of refractory diabetic wound healing.

Nonalcoholic steatohepatitis and mechanisms by which it is ameliorated by activation of the CNC-bZIP transcription factor Nrf2

Non-alcoholic steatohepatitis (NASH) represents a global health concern. It is characterised by fatty liver, hepatocyte cell death and inflammation, which are associated with lipotoxicity, endoplasmic reticulum (ER) stress, mitochondrial dysfunction, iron overload and oxidative stress. NF-E2 p45-related factor 2 (Nrf2) is a transcription factor that combats oxidative stress. Remarkably, Nrf2 is downregulated during the development of NASH, which probably accelerates disease, whereas in pre-clinical studies the upregulation of Nrf2 inhibits NASH. We now review the scientific literature that proposes Nrf2 downregulation during NASH involves its increased ubiquitylation and proteasomal degradation, mediated by Kelch-like ECH-associated protein 1 (Keap1) and/or β-transducin repeat-containing protein (β-TrCP) and/or HMG-CoA reductase degradation protein 1 (Hrd1, also called synoviolin (SYVN1)). Additionally, downregulation of Nrf2-mediated transcription during NASH may involve diminished recruitment of coactivators by Nrf2, due to increased levels of activating transcription factor 3 (ATF3) and nuclear factor-kappaB (NF-κB) p65, or competition for promoter binding due to upregulation of BTB and CNC homology 1 (Bach1). Many processes that downregulate Nrf2 are triggered by transforming growth factor-beta (TGF-β), with oxidative stress amplifying its signalling. Oxidative stress may also increase suppression of Nrf2 by β-TrCP through facilitating formation of the DSGIS-containing phosphodegron in Nrf2 by glycogen synthase kinase-3. In animal models, knockout of Nrf2 increases susceptibility to NASH, while pharmacological activation of Nrf2 by inducing agents that target Keap1 inhibits development of NASH. These inducing agents probably counter Nrf2 downregulation affected by β-TrCP, Hrd1/SYVN1, ATF3, NF-κB p65 and Bach1, by suppressing oxidative stress. Activation of Nrf2 is also likely to inhibit NASH by ameliorating lipotoxicity, inflammation, ER stress and iron overload. Crucially, pharmacological activation of Nrf2 in mice in which NASH has already been established supresses liver steatosis and inflammation. There is therefore compelling evidence that pharmacological activation of Nrf2 provides a comprehensive multipronged strategy to treat NASH.

Evaluation of nonalcoholic fatty liver disease (NAFLD) in severe obesity using noninvasive tests and imaging techniques

The prevalence of nonalcoholic fatty liver disease (NAFLD) and the more severe and inflammatory type, nonalcoholic steatohepatitis (NASH), is increasing rapidly. Especially in high-risk patients, that is those with obesity, metabolic syndrome, and type 2 diabetes mellitus, the prevalence of NAFLD can be as high as 80% while NASH may be present in 20% of these subjects. With the worldwide increase of obesity, it is most likely that these numbers will rise. Since advanced stages of NAFLD and NASH are strongly associated with morbidity and mortality-in particular, cardiovascular disease, liver cirrhosis, and hepatocellular carcinoma-it is of great importance to identify subjects at risk. A great variety of noninvasive tests has been published to diagnose NAFLD and NASH, especially using blood- and imaging-based tests. Liver biopsy remains the gold standard for NAFLD/NASH. This review aims to summarize the different mechanisms leading to NASH and liver fibrosis, the different noninvasive liver tests to diagnose and evaluate patients with severe obesity.

Association of sorting and assembly machinery component 50 homolog gene polymorphisms with nonalcoholic fatty liver disease susceptibility

BACKGROUND

Sorting and assembly machinery component 50 homolog (SAMM50) gene single-nucleotide polymorphisms (SNPs) have been connected with the susceptibility of nonalcoholic fatty liver disease (NAFLD), but with inconsistent results across the current evidence. The present work was schemed to explore the association between SAMM50 gene SNPs and NAFLD vulnerability via meta-analysis.

METHODS

PubMed, Web of Science, Cochrane Library, China National Knowledge Infrastructure (CNKI), and Wanfang were retrieved for eligible literature previous to June 10, 2021. The odds ratios (ORs) of the dichotomic variables and the standardized mean difference of quantitative variables with corresponding 95% confidence intervals (95% CIs) were computed to evaluate the strength of the associations. The quality of included studies was assessed using Newcastle-Ottawa Scale (NOS).

RESULTS

In total, 8 case-control studies encompassing 6297 NAFLD patients and 7306 disease-free controls in this meta-analysis. Ultimately, this analysis included 8, 6, and 5 studies for rs2143571, rs3761472, and rs738491 polymorphisms respectively. The pooled data revealed that the 3 polymorphisms had conspicuous associations with NAFLD susceptibility: rs2143571, A vs. G, OR=1.51, 95% CI, 1.37-1.66, P < .01; rs3761472, A vs. G, OR=1.50, 95% CI, 1.35-1.67, P < .01; rs738491, A vs. G, OR=1.51, 95% CI, 1.40-1.63, P < .01.

CONCLUSION

This meta-analysis suggests that rs2143571, rs3761472, and rs738491 polymorphisms of the SAMM50 gene are appreciably associated with augmented risk of NAFLD vulnerability. It will provide the latest evidence to support the susceptibility of SAMM50 gene polymorphisms and NAFLD, and provide strategies for the prevention and treatment of NAFLD.

Protective effects of oyster protein hydrolysates on alcohol-induced liver disease (ALD) in mice: based on the mechanism of anti-oxidative metabolism

Many bioactivities of hydrolysates from oyster (Crassostrea gigas) muscle have been reported, while there is no knowledge about their protective effects on alcohol-induced liver disease (ALD). In the present study, the anti-oxidative activities in vitro and molecular weight distribution of oyster protein hydrolysates (OPH) were detected and the OPH released by alcalase (AOPH) was used to treat C57BL/6 mice. C57BL/6 mice were treated with a Lindros control diet to establish an ethanol-exposed model. The content of small-weight components (<2.0 kDa) of OPH reached 90.85%. AOPH showed more potent antioxidant activities in vitro with higher reducing power and ferric reducing antioxidant power (FRAP), and those capacities could be maintained at a high level after simulated gastrointestinal digestion. Compared to the model mice, oral administration (4 weeks) of AOPH at 800 mg per kg body weight could lead to a decline in T-AOC, GSH-PX, and ADH in the liver. The hepatocellular lesions were effectively relieved and impaired liver tissue development was successfully inhibited. A total of 834 genes and 54 proteins showed differential expression in the AOPH group and the oxidative metabolic pathways of ethanol such as oxidative phosphorylation, glutathione metabolism, peroxisomes, the PPAR signaling pathway and drug metabolism-cytochrome P450 play a preeminent role in ALD according to the results of transcriptomics and proteomics. The beneficial effects of AOPH were available in the improvement of ALD. These results revealed that AOPH intervention ameliorated ALD by affecting oxidative metabolism and highlighting AOPH's potential application as a functional food.

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.

Cinnamaldehyde Mitigates Atherosclerosis Induced by High-Fat Diet via Modulation of Hyperlipidemia, Oxidative Stress, and Inflammation

Atherosclerosis is a disease in which plaque builds up inside arteries. Cinnamaldehyde (Ci) has many biological properties that include anti-inflammatory and antioxidant activities. Thus, this study was designed to explore the protective effect of Ci against atherosclerosis induced by a high-fat diet (HFD) in Wistar rats. Atherosclerosis was induced by an oral administration of an HFD for 10 weeks. Atherosclerosis-induced rats were supplemented with Ci at a dose of 20 mg/kg bw dissolved in 0.5% dimethyl sulfoxide (DMSO), daily by oral gavage for the same period. Rats were divided into three groups of 10 rats each fed with (a) ND, (b) HFD, and (c) HFD+Ci, daily for 10 weeks. Treatment of rats with Ci significantly reduced the elevated levels of serum total cholesterol (T.Ch), triglycerides (TG), low-density lipoprotein-cholesterol (LDL-Ch), very low-density lipoprotein-cholesterol (VLDL-Ch), and free fatty acids (FFAs) and significantly increased the lowered levels of high-density lipoprotein-cholesterol (HDL-Ch) level. Ci ameliorated the increased cardiovascular risk indices 1 and 2 and the decreased antiatherogenic index. Moreover, Ci reduced the elevated serum creatine kinase (CK), creatine kinase-MB (CK-MB), lactate dehydrogenase (LDH), and aspartate aminotransferase (AST) activities. Ci also improved the heart antioxidant activities by decreasing malondialdehyde (MDA) and increasing glutathione S-transferase (GST), superoxide dismutase (SOD), catalase (CAT), reduced glutathione (GSH), and glutathione peroxidase (Gpx) activities. Furthermore, the supplementation with Ci downregulated the mRNA expression levels of interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-17 (IL-17), and tumor necrosis factor-α (TNF-α). Thus, Ci successfully elicited a therapeutic impact against atherosclerosis induced by HFD via its hypolipidemic, antioxidant, and anti-inflammatory actions.

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

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

Metabolic dysfunction and cancer in HCV: Shared pathways and mutual interactions

HCV hijacks many host metabolic processes in an effort to aid viral replication. The resulting hepatic metabolic dysfunction underpins many of the hepatic and extrahepatic manifestations of chronic hepatitis C (CHC). However, the natural history of CHC is also substantially influenced by the host metabolic status: obesity, insulin resistance and hepatic steatosis are major determinants of CHC progression toward hepatocellular carcinoma (HCC). Direct-acting antivirals (DAAs) have transformed the treatment and natural history of CHC. While DAA therapy effectively eradicates the virus, the long-lasting overlapping metabolic disease can persist, especially in the presence of obesity, increasing the risk of liver disease progression. This review covers the mechanisms by which HCV tunes hepatic and systemic metabolism, highlighting how systemic metabolic disturbance, lipotoxicity and chronic inflammation favour disease progression and a precancerous niche. We also highlight the therapeutic implications of sustained metabolic dysfunction following sustained virologic response as well as considerations for patients who develop HCC on the background of metabolic dysfunction.

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.

NAFLD: Mechanisms, Treatments, and Biomarkers

Nonalcoholic fatty liver disease (NAFLD), recently renamed metabolic-associated fatty liver disease (MAFLD), is one of the most common causes of liver diseases worldwide. NAFLD is growing in parallel with the obesity epidemic. No pharmacological treatment is available to treat NAFLD, specifically. The reason might be that NAFLD is a multi-factorial disease with an incomplete understanding of the mechanisms involved, an absence of accurate and inexpensive imaging tools, and lack of adequate non-invasive biomarkers. NAFLD consists of the accumulation of excess lipids in the liver, causing lipotoxicity that might progress to metabolic-associated steatohepatitis (NASH), liver fibrosis, and hepatocellular carcinoma. The mechanisms for the pathogenesis of NAFLD, current interventions in the management of the disease, and the role of sirtuins as potential targets for treatment are discussed here. In addition, the current diagnostic tools, and the role of non-coding RNAs as emerging diagnostic biomarkers are summarized. The availability of non-invasive biomarkers, and accurate and inexpensive non-invasive diagnosis tools are crucial in the detection of the early signs in the progression of NAFLD. This will expedite clinical trials and the validation of the emerging therapeutic treatments.

When Sugar Reaches the Liver: Phenotypes of Patients with Diabetes and NAFLD

Type 2 diabetes mellitus (T2DM) and non-alcoholic fatty liver disease (NAFLD) have been traditionally linked to one another. Recent studies suggest that NAFLD may be increasingly common in other types of diabetes such as type 1 diabetes (T1DM) and less frequently ketone-prone and Maturity-onset Diabetes of the Young (MODY) diabetes. In this review, we address the relationship between hyperglycemia and insulin resistance and the onset and progression of NAFLD. In addition, despite the high rate of patients with T2DM and other diabetes phenotypes that can alter liver metabolism and consequently develop steatosis, fibrosis, and cirrhosis, NALFD screening is not still implemented in the daily care routine. Incorporating a clinical algorithm created around a simple, non-invasive, cost-effective model would identify high-risk patients. The principle behind managing these patients is to improve insulin resistance and hyperglycemia states with lifestyle changes, weight loss, and new drug therapies.

Human Mesenchymal Stromal Cells Resolve Lipid Load in High Fat Diet-Induced Non-Alcoholic Steatohepatitis in Mice by Mitochondria Donation

Mesenchymal stromal cells (MSC) increasingly emerge as an option to ameliorate non-alcoholic steatohepatitis (NASH), a serious disease, which untreated may progress to liver cirrhosis and cancer. Before clinical translation, the mode of action of MSC needs to be established. Here, we established NASH in an immune-deficient mouse model by feeding a high fat diet. Human bone-marrow-derived MSC were delivered to the liver via intrasplenic transplantation. As verified by biochemical and image analyses, human mesenchymal stromal cells improved high-fat-diet-induced NASH in the mouse liver by decreasing hepatic lipid content and inflammation, as well as by restoring tissue homeostasis. MSC-mediated changes in gene expression indicated the switch from lipid storage to lipid utilization. It was obvious that host mouse hepatocytes harbored human mitochondria. Thus, it is feasible that resolution of NASH in mouse livers involved the donation of human mitochondria to the mouse hepatocytes. Therefore, human MSC might provide oxidative capacity for lipid breakdown followed by restoration of metabolic and tissue homeostasis.

Gender Difference in Liver Enzymes in Newly Defined Subgroups of Diabetes Revealed by a Data-Driven Cluster Analysis

BACKGROUND

Recently, a newly proposed data-driven approach for classifying diabetes has challenged the status quo of the classification of adult-onset patients with diabetes. This study investigated the association between liver injury and diabetes, classified by data-driven cluster analysis, as liver injury is a significant risk factor for diabetes.

METHODS

We enrolled 822 adult patients with newly diagnosed diabetes. Two-step cluster analysis was performed using six parameters, including age at diagnosis, body mass index, hemoglobin A1C, homoeostatic assessment model 2 estimates about insulin resistance (HOAM2-IR) and beta-cell function (HOMA2-B), and glutamic acid decarboxylase antibodies (GADA) positivity. Patients were allocated into five clusters. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activity were compared as indicators of liver injury among clusters.

RESULTS

Serum ALT and AST activities were significantly different among clusters (P=0.002), even among those without GADA positivity (P=0.004). Patients with severe insulin-resistant diabetes (SIRD) and mild obesity-related diabetes (MOD) had a more severe liver injury. Gender dimorphism was also found for serum ALT and AST activities among subgroups. Female patients had better liver function than males with SIRD and MOD.

CONCLUSIONS

We verified the feasibility of a newly proposed diabetes classification system and found robust and significant relationship and gender differences between serum ALT and AST activities and diabetes in some specific subgroups. Our findings indicate that more attention should be paid to diabetes subgroups when studying risk factors, indicators, or treatment in diabetic research.

Hepatic Mitochondrial Dysfunction and Risk of Liver Disease in an Ovine Model of “PCOS Males”

First-degree male relatives of polycystic ovary syndrome (PCOS) sufferers can develop metabolic abnormalities evidenced by elevated circulating cholesterol and triglycerides, suggestive of a male PCOS equivalent. Similarly, male sheep overexposed to excess androgens in fetal life develop dyslipidaemia in adolescence. Dyslipidaemia, altered lipid metabolism, and dysfunctional hepatic mitochondria are associated with the development of non-alcoholic liver disease (NAFLD). We therefore dissected hepatic mitochondrial function and lipid metabolism in adolescent prenatally androgenized (PA) males from an ovine model of PCOS. Testosterone was directly administered to male ovine fetuses to create prenatal androgenic overexposure. Liver RNA sequencing and proteomics occurred at 6 months of age. Hepatic lipids, glycogen, ATP, reactive oxygen species (ROS), DNA damage, and collagen were assessed. Adolescent PA males had an increased accumulation of hepatic cholesterol and glycogen, together with perturbed glucose and fatty acid metabolism, mitochondrial dysfunction, with altered mitochondrial transport, decreased oxidative phosphorylation and ATP synthesis, and impaired mitophagy. Mitochondrial dysfunction in PA males was associated with increased hepatic ROS level and signs of early liver fibrosis, with clinical relevance to NAFLD progression. We conclude that excess in utero androgen exposure in male fetuses leads to a PCOS-like metabolic phenotype with dysregulated mitochondrial function and likely lifelong health sequelae.

Influence of NAFLD and bariatric surgery on hepatic and adipose tissue mitochondrial biogenesis and respiration

Impaired mitochondrial oxidative phosphorylation (OXPHOS) in liver tissue has been hypothesised to contribute to the development of nonalcoholic steatohepatitis in patients with nonalcoholic fatty liver disease (NAFLD). It is unknown whether OXPHOS capacities in human visceral (VAT) and subcutaneous adipose tissue (SAT) associate with NAFLD severity and how hepatic OXPHOS responds to improvement in NAFLD. In biopsies sampled from 62 patients with obesity undergoing bariatric surgery and nine control subjects without obesity we demonstrate that OXPHOS is reduced in VAT and SAT while increased in the liver in patients with obesity when compared with control subjects without obesity, but this was independent of NAFLD severity. In repeat liver biopsy sampling in 21 patients with obesity 12 months after bariatric surgery we found increased hepatic OXPHOS capacity and mitochondrial DNA/nuclear DNA content compared with baseline. In this work we show that obesity has an opposing association with mitochondrial respiration in adipose- and liver tissue with no overall association with NAFLD severity, however, bariatric surgery increases hepatic OXPHOS and mitochondrial biogenesis.

Impaired mitochondrial function in liver tissue may contribute to the pathogenesis and disease progression of nonalcoholic fatty liver disease (NAFLD). Here the authors report that patients with obesity have lower mitochondrial capacity in adipose tissues but higher capacity in the liver, without overall associations to NAFLD severity, and that bariatric surgery increases hepatic mitochondrial respiration and mitochondrial biogenesis.

GLP-1 mimetics as a potential therapy for nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH), as a severe form of nonalcoholic fatty liver disease (NAFLD), is characterized by liver steatosis, inflammation, hepatocellular injury and different degrees of fibrosis. The pathogenesis of NASH is complex and multifactorial, obesity and type 2 diabetes mellitus (T2DM) have been implicated as major risk factors. Glucagon-like peptide-1 receptor (GLP-1R) is one of the most successful drug targets of T2DM and obesity, and its peptidic ligands have been proposed as potential therapeutic agents for NASH. In this article we provide an overview of the pathophysiology and management of NASH, with a special focus on the pharmacological effects and possible mechanisms of GLP-1 mimetics in treating NAFLD/NASH, including dual and triple agonists at GLP-1R, glucose-dependent insulinotropic polypeptide receptor or glucagon receptor.

Interaction of SAMM50-rs738491, PARVB-rs5764455 and PNPLA3-rs738409 Increases Susceptibility to Nonalcoholic Steatohepatitis

BACKGROUND AND AIMS

Previous studies have reported that the single nucleotide polymorphisms (SNPs) of SAMM50-rs738491, PARVB-rs5764455 and PNPLA3-rs738409 are associated with nonalcoholic fatty liver disease (NAFLD). However, no studies have examined the effect of interactions between these three genotypes to affect liver disease severity. We assessed the effect of these three SNPs on nonalcoholic steatohepatitis (NASH) and also examined the gene-gene interactions in a Chinese population with biopsy-confirmed NAFLD.

METHODS

We enrolled 415 consecutive adult individuals with biopsy-proven NAFLD. Multivariable logistic regression analysis was undertaken to test associations between NASH and SNPs in SAMM50-rs738491, PARVB-rs5764455 and PNPLA3-rs738409. Gene-gene interactions were analyzed by performing a generalized multifactor dimensionality reduction (GMDR) analysis.

RESULTS

The mean ± standard deviation age of these 415 patients was 41.3±12.5 years, and 75.9% were men. Patients with SAMM50-rs738491 TT, PARVB-rs5764455 AA or PNPLA3-rs738409 GG genotypes had a higher risk of NASH, even after adjustment for age, sex and body mass index. GMDR analysis showed that the combination of all three SNPs was the best model for predicting NASH. Additionally, the odds ratio of the haplotype T-A-G for predicting the risk of NASH was nearly three times higher than that of the haplotype G-C-C.

CONCLUSIONS

NAFLD patients carrying the SAMM50-rs738491 TT, PARVB-rs5764455 AA or PNPLA3-rs738409 GG genotypes are at greater risk of NASH. These three SNPs may synergistically interact to increase susceptibility to NASH.

Physical exercise positively modulates nonalcoholic steatohepatitis-related hepatic endoplasmic reticulum stress

Obesity is a predictive factor for the development of nonalcoholic steatohepatitis (NASH). Although some of the mechanisms associated with NASH development are still elusive, its pathogenesis relies on a complex broad spectrum of (interconnected) metabolic-based disorders. We analyzed the effects of voluntary physical activity (VPA) and endurance training (ET), as preventive and therapeutic nonpharmacological strategies, respectively, against hepatic endoplasmic reticulum (ER) stress, ER-related proapoptotic signaling, and oxidative stress in an animal model of high-fat diet (HFD)-induced NASH. Adult male Sprague-Dawley rats were divided into standard control liquid diet (SCLD) or HFD groups, with sedentary, VPA, and ET subgroups in both (sedentary animals with access to SCLD [SS], voluntarily physically active animals with access to SCLD [SV], and endurance-trained animals with access to SCLD [ST] in the former and sedentary animals with access to liquid HFD [HS], voluntarily physically active animals with access to liquid HFD [HV], and endurance-trained animals with access to liquid HFD [HT] in the latter, respectively). Hepatic ER stress and ER-related proapoptotic signaling were evaluated by Western blot and reverse transcriptase-polymerase chain reaction; redox status was evaluated through quantification of lipid peroxidation, protein carbonyls groups, and glutathione levels as well as antioxidant enzymes activity. In SCLD-treated animals, VPA significantly decreased eukaryotic initiation factor-2 alpha (eIF2α). In HFD-treated animals, VPA significantly decreased eIF2α and phospho-inositol requiring enzyme-1 alpha (IRE1α) but ET significantly decreased eIF2α and significantly increased both spliced X-box binding protein 1 (sXBP1) and unspliced X-box binding protein 1; a significant increase of phosphorylated-eIF2α (p-eIF2α) to eIF2α ratio occurred in ET versus VPA. HS compared to SS disclosed a significant increase of total and reduced glutathione, HV compared to SV a significant increase of oxidized glutathione, HT compared to ST a significant increase of p-eIF2α to eIF2α ratio and sXBP1. Physical exercise counteracts NASH-related ER stress and its associated deleterious consequences through a positive and dynamical modulation of the hepatic IRE1α-X-box binding protein 1 pathway.

Nonalcoholic Fatty Liver Disease: Could It Be the Next Medical Tsunami?

Nonalcoholic fatty liver disease (NAFLD) is a rapidly increasing cause of chronic liver disease with excess fat deposition in the liver, without an identifiable cause. NAFLD's benign form is called nonalcoholic fatty liver (NAFL), which can progress to nonalcoholic steatohepatitis (NASH) with or without fibrosis. Over time, NASH can progress to cirrhosis and eventually hepatocellular carcinoma (HCC) or progress to HCC without cirrhosis. Its incidence and prevalence are increasing to epidemic proportions, making it the most common cause of chronic liver disease in the western world. This review article attempts to understand the epidemiology, pathophysiology, evaluation, and management, and, most importantly, to generate awareness of this disease process.

Impaired Hepatic Mitochondrial Capacity in Nonalcoholic Steatohepatitis Associated With Type 2 Diabetes

OBJECTIVE

Individuals with type 2 diabetes are at higher risk of progression of nonalcoholic fatty liver (steatosis) to steatohepatitis (NASH), fibrosis, and cirrhosis. The hepatic metabolism of obese individuals adapts by upregulation of mitochondrial capacity, which may be lost during the progression of steatosis. However, the role of type 2 diabetes with regard to hepatic mitochondrial function in NASH remains unclear.

RESEARCH DESIGN AND METHODS

We therefore examined obese individuals with histologically proven NASH without (OBE) (n = 30; BMI 52 ± 9 kg/m2) or with type 2 diabetes (T2D) (n = 15; 51 ± 7 kg/m2) as well as healthy individuals without liver disease (CON) (n = 14; 25 ± 2 kg/m2). Insulin sensitivity was measured by hyperinsulinemic-euglycemic clamps with d-[6,6-2H2]glucose. Liver biopsies were used for assessing mitochondrial capacity by high-resolution respirometry and protein expression.

RESULTS

T2D and OBE had comparable hepatic fat content, lobular inflammation, and fibrosis. Oxidative capacity in liver tissue normalized for citrate synthase activity was 59% greater in OBE than in CON, whereas T2D presented with 33% lower complex II-linked oxidative capacity than OBE and higher H2O2 production than CON. Interestingly, those with NASH and hepatic fibrosis score ≥1 had lower oxidative capacity and antioxidant defense than those without fibrosis.

CONCLUSIONS

Loss of hepatic mitochondrial adaptation characterizes NASH and type 2 diabetes or hepatic fibrosis and may thereby favor accelerated disease progression.

Metabolic dysfunction-associated fatty liver disease: advances in genetic and epigenetic implications

PURPOSE OF REVIEW

Fatty liver associated with metabolic dysfunction, also known under the acronym NAFLD (nonalcoholic fatty liver disease) is the leading global cause of chronic liver disease. In this review, we address the state of research on genetics and epigenetics of NAFLD with focus on key discoveries and conceptual advances over the past 2 years.

RECENT FINDINGS

The analysis of NAFLD-associated genetic variant effects on the whole-transcriptome, including quantitative trait loci (QTL) associated with gene expression (eQTL) or splicing (sQTL) may explain pleiotropic effects. Functional experiments on NAFLD-epigenetics, including profiling of liver chromatin accessibility quantitative trait loci (caQTL) show co-localization with numerous genome-wide association study signals linked to metabolic and cardiovascular traits. Novel studies provide insights into the modulation of the hepatic transcriptome and epigenome by tissue microbiotas. Genetic variation of components of the liver cellular respirasome may result in broad cellular and metabolic effects. Mitochondrial noncoding RNAs may regulate liver inflammation and fibrogenesis. RNA modifications as N6-methyladenosine may explain sex-specific differences in liver gene transcription linked to lipid traits.

SUMMARY

The latest developments in the field of NAFLD-genomics can be leveraged for identifying novel disease mechanisms and therapeutic targets that may prevent the morbidity and mortality associated with disease progression.

VIDEO ABSTRACT

http://links.lww.com/COL/A23.

Non-alcoholic Fatty Liver Disease and Steatohepatitis: Risk Factors and Pathophysiology

Non-alcoholic fatty liver disease (NAFLD) and its progressive subtype non-alcoholic steatohepatitis (NASH) are the most prevalent liver diseases, often leading to hepatocellular carcinoma (HCC). This review aims to describe the present knowledge of the risk factors responsible for the development of NAFLD and NASH. I performed a literature review identifying studies focusing on the complex pathogenic pathway and risk factors of NAFLD and steatohepatitis. The relationship between NAFLD and metabolic syndrome is well established and widely recognized. Obesity, dyslipidemia, type 2 diabetes, hypertension, and insulin resistance are the most common risk factors associated with NAFLD. Among the components of metabolic syndrome, current evidence strongly suggests obesity and type 2 diabetes as risk factors of NASH and HCC. However, other elements, namely gender divergences, ethnicity, genetic factors, participation of innate immune system, oxidative stress, apoptotic pathways, and adipocytokines, take a leading role in the onset and promotion of NAFLD. Pathophysiological mechanisms that are responsible for NAFLD development and subsequent progression to NASH are insulin resistance and hyperinsulinemia, oxidative stress, hepatic stellate cell (HSC) activation, cytokine/adipokine signaling pathways, and genetic and environmental factors. Major pathophysiological findings of NAFLD are dysfunction of adipose tissue through the enhanced flow of free fatty acids (FFAs) and release of adipokines, and altered gut microbiome that generate proinflammatory signals and cause NASH progression. Understanding the pathophysiology and risk factors of NAFLD and NASH; this review could provide insight into the development of therapeutic strategies and useful diagnostic tools.

Oxidative Stress and Redox Signaling in the Pathophysiology of Liver Diseases

The increased production of derivatives of molecular oxygen and nitrogen in the form of reactive oxygen species (ROS) and reactive nitrogen species (RNS) lead to molecular damage called oxidative stress. Under normal physiological conditions, the ROS generation is tightly regulated in different cells and cellular compartments. Any disturbance in the balance between the cellular generation of ROS and antioxidant balance leads to oxidative stress. In this article, we discuss the sources of ROS (endogenous and exogenous) and antioxidant mechanisms. We also focus on the pathophysiological significance of oxidative stress in various cell types of the liver. Oxidative stress is implicated in the development and progression of various liver diseases. We narrate the master regulators of ROS-mediated signaling and their contribution to liver diseases. Nonalcoholic fatty liver diseases (NAFLD) are influenced by a "multiple parallel-hit model" in which oxidative stress plays a central role. We highlight the recent findings on the role of oxidative stress in the spectrum of NAFLD, including fibrosis and liver cancer. Finally, we provide a brief overview of oxidative stress biomarkers and their therapeutic applications in various liver-related disorders. Overall, the article sheds light on the significance of oxidative stress in the pathophysiology of the liver. © 2022 American Physiological Society. Compr Physiol 12:3167-3192, 2022.

HIIT and MICT attenuate high-fat diet-induced hepatic lipid accumulation and ER stress via the PERK-ATF4-CHOP signaling pathway

Fatty liver can be induced by dietary habits and lifestyle and is directly related to obesity. Although the benefits of exercise interventions for reduction of liver fat have recently been acknowledged, the underlying mechanisms remain unclear. Thus, our present study investigated the effects of high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) on high-fat diet-induced hepatic lipid accumulation, and explored the role of endoplasmic reticulum (ER) stress signaling pathways. To establish an obesity model, rats were fed with a normal standard diet or a high-fat diet (45% kcal as fat). Then, both lean and obese rats were divided into three subgroups: sedentary control (LC, OC) groups, high-intensity interval training (LHI, OHI) groups, and moderated-intensity continuous training (LMI, OMI) groups (n = 10). Rats in the exercise group underwent a swimming training protocol for 8 weeks. After the experimental period, serum and liver tissues from different groups were dissected for morphological and biochemical analyses. The results showed that with HIIT and MICT interventions, body weight and serum inflammatory markers (e.g., MCP-1, IL-1β, and TNF-α) were reduced in obese rats. Interestingly, HIIT was more effective in ameliorating liver triglyceride content and enhancing mitochondrial metabolic-enzymatic activity than was MICT in obese rats. Both HIIT and MICT conferred beneficial properties through upregulating Nrf2 expression, improving antioxidant enzyme activities and reduction of hepatic ER stress, which may have been regulated by the Bip-mediated PERK-ATF4-CHOP pathway. In conclusion, our findings confirmed the effectiveness of HIIT and MICT, particularly HIIT, in mitigating hepatic lipid accumulation.

Garcinia Biflavonoid 1 Improves Lipid Metabolism in HepG2 Cells via Regulating PPARα

Garcinia biflavonoid 1 (GB1) is one of the active chemical components of Garcinia kola and is reported to be capable of reducing the intracellular lipid deposition, which is the most significant characteristic of non-alcoholic fatty liver disease. However, its bioactive mechanism remains elusive. In the current study, the lipid deposition was induced in HepG2 cells by exposure to oleic acid and palmitic acid (OA&PA), then the effect of GB1 on lipid metabolism and oxidative stress and the role of regulating PPARα in these cells was investigated. We found that GB1 could ameliorate the lipid deposition by reducing triglycerides (TGs) and upregulate the expression of PPARα and SIRT6, suppressing the cell apoptosis by reducing the oxidative stress and the inflammatory factors of ROS, IL10, and TNFα. The mechanism study showed that GB1 had bioactivity in a PPARα-dependent manner based on its failing to improve the lipid deposition and oxidative stress in PPARα-deficient cells. The result revealed that GB1 had significant bioactivity on improving the lipid metabolism, and its potential primary action mechanism suggested that GB1 could be a potential candidate for management of non-alcoholic fatty liver disease.

Distinct contributions of metabolic dysfunction and genetic risk factors in the pathogenesis of non-alcoholic fatty liver disease

BACKGROUND & AIMS

There is substantial inter-individual variability in the risk of non-alcoholic fatty liver disease (NAFLD). Part of which is explained by insulin resistance (IR) ('MetComp') and part by common modifiers of genetic risk ('GenComp'). We examined how IR on the one hand and genetic risk on the other contribute to the pathogenesis of NAFLD.

METHODS

We studied 846 individuals: 492 were obese patients with liver histology and 354 were individuals who underwent intrahepatic triglyceride measurement by proton magnetic resonance spectroscopy. A genetic risk score was calculated using the number of risk alleles in PNPLA3, TM6SF2, MBOAT7, HSD17B13 and MARC1. Substrate concentrations were assessed by serum NMR metabolomics. In subsets of participants, non-esterified fatty acids (NEFAs) and their flux were assessed by D5-glycerol and hyperinsulinemic-euglycemic clamp (n = 41), and hepatic de novo lipogenesis (DNL) was measured by D2O (n = 61).

RESULTS

We found that substrate surplus (increased concentrations of 28 serum metabolites including glucose, glycolytic intermediates, and amino acids; increased NEFAs and their flux; increased DNL) characterized the 'MetComp'. In contrast, the 'GenComp' was not accompanied by any substrate excess but was characterized by an increased hepatic mitochondrial redox state, as determined by serum β-hydroxybutyrate/acetoacetate ratio, and inhibition of hepatic pathways dependent on tricarboxylic acid cycle activity, such as DNL. Serum β-hydroxybutyrate/acetoacetate ratio correlated strongly with all histological features of NAFLD. IR and hepatic mitochondrial redox state conferred additive increases in histological features of NAFLD.

CONCLUSIONS

These data show that the mechanisms underlying 'Metabolic' and 'Genetic' components of NAFLD are fundamentally different. These findings may have implications with respect to the diagnosis and treatment of NAFLD.

LAY SUMMARY

The pathogenesis of non-alcoholic fatty liver disease can be explained in part by a metabolic component, including obesity, and in part by a genetic component. Herein, we demonstrate that the mechanisms underlying these components are fundamentally different: the metabolic component is characterized by hepatic oversupply of substrates, such as sugars, lipids and amino acids. In contrast, the genetic component is characterized by impaired hepatic mitochondrial function, making the liver less able to metabolize these substrates.

Mitochondria, oxidative stress and nonalcoholic fatty liver disease: A complex relationship

According to the 'multiple-hit' hypothesis, several factors can act simultaneously in nonalcoholic fatty liver disease (NAFLD) progression. Increased nitro-oxidative (nitroso-oxidative) stress may be considered one of the main contributors involved in the development and risk of NAFLD progression to nonalcoholic steatohepatitis (NASH) characterized by inflammation and fibrosis. Moreover, it has been repeatedly postulated that mitochondrial abnormalities are closely related to the development and progression of liver steatosis and NAFLD pathogenesis. However, it is difficult to determine with certainty whether mitochondrial dysfunction or oxidative stress are primary events or a simple consequence of NAFLD development. On the one hand, increasing lipid accumulation in hepatocytes could cause a wide range of effects from mild to severe mitochondrial damage with a negative impact on cell fate. This can start the cascade of events, including an increase of cellular reactive nitrogen species (RNS) and reactive oxygen species (ROS) production that promotes disease progression from simple steatosis to more severe NAFLD stages. On the other hand, progressing mitochondrial bioenergetic catastrophe and oxidative stress manifestation could be considered accompanying events in the vast spectrum of abnormalities observed during the transition from NAFL to NASH and cirrhosis. This review updates our current understanding of NAFLD pathogenesis and clarifies whether mitochondrial dysfunction and ROS/RNS are culprits or bystanders of NAFLD progression.

Polyene Phosphatidylcholine Ameliorates High Fat Diet-Induced Non-alcoholic Fatty Liver Disease via Remodeling Metabolism and Inflammation

Recent years have witnessed a rise in the morbidity of non-alcoholic fatty liver disease (NAFLD), in line with the global outbreak of obesity. However, effective intervention strategy against NAFLD is still unavailable. The present study sought to investigate the effect and mechanism of polyene phosphatidylcholine (PPC), a classic hepatoprotective drug, on NAFLD induced by high fat diet (HFD). We found that PPC intervention reduced the mass of liver, subcutaneous, epididymal, and brown fats in HFD mice. Furthermore, PPC supplementation significantly mitigated liver steatosis and improved glucose tolerance and insulin sensitivity in HFD mice, which was accompanied by declined levels of hepatic triglyceride, serum triglyceride, low density lipoprotein, aspartate aminotransferase, and alanine aminotransferase. Using transcriptome analysis, there were 1,789 differentially expressed genes (| fold change | ≥ 2, P < 0.05) including 893 upregulated genes and 896 downregulated genes in the HFD group compared to LC group. A total of 1,114 upregulated genes and 1,337 downregulated genes in HFD + PPC group were identified in comparison to HFD group. With the help of Gene Ontology (GO) analysis, these differentially expressed genes between HFD+PPC and HFD group were discovered related to “lipid metabolic process (GO: 0006629),” “lipid modification (GO: 0030258),” and “lipid homeostasis (GO: 0055088)”. Though Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, we found pathways associated with hepatic homeostasis of metabolism and inflammation. Notably, the pathway “Non-alcoholic fatty liver disease (mmu04932)” (P-value = 0.00698) was authenticated in the study, which may inspire the potential mechanism of PPC to ameliorate NAFLD. The study also found that lipolysis, fatty acid oxidation, and lipid export associated genes were upregulated, while the genes in uptake of lipids and cholesterol synthesis were downregulated in the liver of HFD mice after PPC supplementation. Interestingly, PPC attenuated the metabolic inflammation via inhibiting pro-inflammatory macrophage in the livers of mice fed by HFD. In summary, this study demonstrates that PPC can ameliorate HFD-induced liver steatosis via reprogramming metabolic and inflammatory processes, which inspire clues for further clarifying the intervention mechanism of PPC against NAFLD.

Hepatocyte nuclear factor 4α in the pathogenesis of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is emerging as the most common chronic liver disease worldwide. It refers to a range of liver conditions affecting people who drink little or no alcohol. NAFLD comprises non-alcoholic fatty liver and non-alcoholic steatohepatitis (NASH), the more aggressive form of NAFLD. NASH is featured by steatosis, lobular inflammation, hepatocyte injury, and various degrees of fibrosis. Although much progress has been made over the past decades, the pathogenic mechanism of NAFLD remains to be fully elucidated. Hepatocyte nuclear factor 4α (HNF4α) is a nuclear hormone receptor that is highly expressed in hepatocytes. Hepatic HNF4α expression is markedly reduced in NAFLD patients and mouse models of NASH. HNF4α has been shown to regulate bile acid, lipid, glucose, and drug metabolism. In this review, we summarize the recent advances in the understanding of the pathogenesis of NAFLD with a focus on the regulation of HNF4α and the role of hepatic HNF4α in NAFLD. Several lines of evidence have shown that hepatic HNF4α plays a key role in the initiation and progression of NAFLD. Recent data suggest that hepatic HNF4α may be a promising target for treatment of NAFLD.

Platelets in Non-alcoholic Fatty Liver Disease

Non alcoholic steatohepatitis (NASH) is the inflammatory reaction of the liver to excessive accumulation of lipids in the hepatocytes. NASH can progress to cirrhosis and hepatocellular carcinoma (HCC). Fatty liver is the hepatic manifestation of metabolic syndrome. A subclinical inflammatory state is present in patients with metabolic alterations like insulin resistance, type-2 diabetes, obesity, hyperlipidemia, and hypertension. Platelets participate in immune cells recruitment and cytokines-induced liver damage. It is hypothesized that lipid toxicity cause accumulation of platelets in the liver, platelet adhesion and activation, which primes the immunoinflammatory reaction and activation of stellate cells. Recent data suggest that antiplatelet drugs may interrupt this cascade and prevent/improve NASH. They may also improve some metabolic alterations. The pathophysiology of inflammatory liver disease and the implication of platelets are discussed in details.

Hepatic CDP-diacylglycerol synthase 2 deficiency causes mitochondrial dysfunction and promotes rapid progression of NASH and fibrosis

Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum of pathologies, ranging from steatosis to nonalcoholic steatohepatitis (NASH). The factors promoting the progression of steatosis to NASH are still unclear. Recent studies suggest that mitochondrial lipid composition is critical in NASH development. Here, we showed that CDP-DAG synthase 2 (Cds2) was downregulated in genetic or diet-induced NAFLD mouse models. Liver-specific deficiency of Cds2 provoked hepatic steatosis, inflammation and fibrosis in five-week-old mice. CDS2 is enriched in mitochondria-associated membranes (MAMs), and hepatic Cds2 deficiency impaired mitochondrial function and decreased mitochondrial PE levels. Overexpression of phosphatidylserine decarboxylase (PISD) alleviated the NASH-like phenotype in Cds2^f/f;AlbCre mice and abnormal mitochondrial morphology and function caused by CDS2 deficiency in hepatocytes. Additionally, dietary supplementation with an agonist of peroxisome proliferator-activated receptor alpha (PPARα) attenuated mitochondrial defects and ameliorated the NASH-like phenotype in Cds2^f/f;AlbCre mice. Finally, Cds2 overexpression protected against high-fat diet-induced hepatic steatosis and obesity. Thus, Cds2 modulates mitochondrial function and NASH development.

Oxidative Stress in Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is a challenging disease caused by multiple factors, which may partly explain why it still remains an orphan of adequate therapies. This review highlights the interaction between oxidative stress (OS) and disturbed lipid metabolism. Several reactive oxygen species generators, including those produced in the gastrointestinal tract, contribute to the lipotoxic hepatic (and extrahepatic) damage by fatty acids and a great variety of their biologically active metabolites in a “multiple parallel-hit model”. This leads to inflammation and fibrogenesis and contributes to NAFLD progression. The alterations of the oxidant/antioxidant balance affect also metabolism-related organelles, leading to lipid peroxidation, mitochondrial dysfunction, and endoplasmic reticulum stress. This OS-induced damage is at least partially counteracted by the physiological antioxidant response. Therefore, modulation of this defense system emerges as an interesting target to prevent NAFLD development and progression. For instance, probiotics, prebiotics, diet, and fecal microbiota transplantation represent new therapeutic approaches targeting the gut microbiota dysbiosis. The OS and its counter-regulation are under the influence of individual genetic and epigenetic factors as well. In the near future, precision medicine taking into consideration genetic or environmental epigenetic risk factors, coupled with new OS biomarkers, will likely assist in noninvasive diagnosis and monitoring of NAFLD progression and in further personalizing treatments.