Animal models of nonalcoholic fatty liver disease

The Polyphenolic Profile and Antioxidant Activity of Five Vegetal Extracts with Hepatoprotective Potential

Oxidative stress is among the major triggers for many important human functional disorders, which often lead to various metabolic or tissue diseases. The aim of the study is to obtain five standardized vegetal extracts (Cynarae extractum-CE, Rosmarini extractum-RE, Taraxaci extractum-TE, Cichorii extractum-CHE, and Agrimoniae extractum-AE) that contain active principles with an essential role in protecting liver cells against free radicals and quantify their antioxidant actions. The compounds of therapeutic interest from the analyzed extracts were identified and quantified using the UHPLC-HRMS/MS technique. Thus, the resulting identified compounds were 28 compounds in CE, 48 compounds in RE, 39 compounds in TE, 43 compounds in CHE, and 31 compounds in AE. These compounds belong to the class of flavonoids, isoflavones, phenolic acids and dicarboxylic acids, depsides, diterpenes, triterpenes, sesquiterpenes, proanthocyanidins, or coumarin derivatives. From the major polyphenolic compounds quantified in all the extracts analyzed by UHPLC-HRMS/MS, considerable amounts have been found for chlorogenic acid (619.8 µg/g extract for TE-2032.4 µg/g extract for AE), rutoside (105.1 µg/g extract for RE-1724.7 µg/g extract for AE), kaempferol (243 µg/g extract for CHE-2028.4 µg/g extract for CE), and for naringenin (383 µg/g extract for CHE-1375.8 µg/g extract for AE). The quantitative chemical analysis showed the highest content of total phenolic acids for AE (24.1528 ± 1.1936 g chlorogenic acid/100 g dry extract), the highest concentration of flavones for RE (6.0847 ± 0.3025 g rutoside/100 g dry extract), and the richest extract in total polyphenols with 31.7017 ± 1.2211 g tannic acid equivalent/100 g dry extract for AE. Several methods (DPPH, ABTS, and FRAP) have been used to determine the in vitro total antioxidant activity of the extracts to evaluate their free radical scavenging ability, influenced by the identified compounds. As a result, the correlation between the content of the polyphenolic compounds and the antioxidant effect of the extracts has been demonstrated. Statistically significant differences were found when comparing the antiradical capacity within the study groups. Although all the analyzed extracts showed good IC50 values, which may explain their antihepatotoxic effects, the highest antioxidant activity was obtained for Agrimoniae extractum (IC50ABTS = 0.0147 mg/mL) and the lowest antioxidant activity was obtained for Cynarae extractum (IC50ABTS = 0.1588 mg/mL). Furthermore, the hepatoprotective potential was evaluated in silico by predicting the interactions between the determined phytochemicals and key molecular targets relevant to liver disease pathophysiology. Finally, the evaluation of the pharmacognostic and phytochemical properties of the studied extracts validates their use as adjuvants in phytotherapy, as they reduce oxidative stress and toxin accumulation and thus exert a hepatoprotective effect at the cellular level.

Liver PP2A-Cα Protects From Parenteral Nutrition-associated Hepatic Steatosis

BACKGROUND & AIMS

Parenteral nutrition (PN) is a lifesaving therapy for patients with intestinal failure. Hepatic steatosis is a potentially fatal complication of long-term PN, but the involved pathological mechanisms are incompletely unclarified. Herein, we identify the role of protein phosphatase 2A (PP2A) in the pathogenesis of parenteral nutrition-associated hepatic steatosis (PNAHS).

METHODS

Proteomic/phosphoproteomic analyses of liver samples from patients with PNAHS were applied to identify the mechanism of PNAHS. Total parenteral nutrition (TPN) mice model, in vivo, and in vitro experiments were used to assess the effect of PP2A-Cα on liver fatty acid metabolism.

RESULTS

Reduced expression of PP2A-Cα (catalytic subunit) enhanced activation of serine/threonine kinase Akt2 and decreased activation of adenosine monophosphate-activated protein kinase (AMPK) were associated with hepatic steatosis in patients with PNAHS. Mice given PN for 14 days developed hepatic steatosis, down-regulation of PP2A-Cα, activation of Akt2, and inhibition of AMPK. Hepatocyte-specific deletion of PP2A-Cα in mice given PN exacerbated Akt2 activation, AMPK inhibition, and hepatic steatosis through an effect on fatty acid degradation, whereas hepatocyte-specific PP2A-Cα overexpression significantly ameliorated hepatic steatosis accompanied with Akt2 suppression and AMPK activation. Additionally, pharmacological activation of Akt2 in mice overexpressing PP2A-Cα led to the aggravation of hepatic steatosis.

CONCLUSIONS

Our findings demonstrate that hepatic PP2A-Cα serves as a protective factor of PNAHS due to ameliorating hepatic steatosis and improving liver function. Our study provides a strong rationale that PP2A-Cα may be involved in the pathogenesis of PNAHS.

Celastrol-loaded lactosylated albumin nanoparticles attenuate hepatic steatosis in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a multifactorial disease with several liver-associated pathologic characteristics such as aberrant lipid accumulation, persistent chronic inflammation and hyperactive endoplasmic reticulum (ER) stress. Plant-derived celastrol (CEL) appeared to be a promising anti-inflammatory and anti-obesity drug but the clinical application was delayed by low oral bioavailability. The present study was designed for developing biodegradable albumin-based nanoparticles to deliver CEL to the liver for treating NAFLD. CEL was entrapped into lactosylated bovine serum albumin (Lac-BSA) by high pressure homogenization to generate CEL-loaded Lac-BSA nanoparticles (CEL-Lac-BSA). CEL-Lac-BSA displayed spherical morphology, narrow size distribution at 158.6 ± 3.4 nm and reasonable drug-loading efficiency at 13.62 ± 0.13%. CEL-Lac-BSA not only showed better hepatocyte uptake and hepatic deposition than free CEL, but also outperformed in reducing lipid deposition, ameliorating liver function and enhancing insulin sensitivity in a mouse model of diet-induced NAFLD. Mechanistic studies indicated that CEL-Lac-BSA more effectively downregulated the mRNA levels of genes for lipogenesis and lipid transporter while upregulated the mRNA levels of lipolysis mediators. Western blot analysis confirmed the outperformance of CEL-Lac-BSA in enhancing the activation of AMP-activated protein kinase (AMPK) and silent information regulation 2 homolog (SIRT1) and the protein levels of fatty acid synthase (FASN) and sterol regulatory element-binding protein-1c (SREBP1c) in NAFLD mice. Taken together, CEL-Lac-BSA showed better potential in the treatment of diet-induced NAFLD. Lactose-coating of albumin-based nanoparticles effectively facilitated the liver-targeting release of hydrophobic drug CEL for ameliorating hepatic steatosis. Therefore, CEL-Lac-BSA may be translated into a potential clinical therapy against obesity and NAFLD.

Jiangzhi granule attenuates non-alcoholic steatohepatitis through modulating bile acid in mice fed high-fat vitamin D deficiency diet

Vitamin D deficiency is a common phenomenon in non-alcoholic fatty liver disease (NAFLD) and the progressive non-alcoholic steatohepatitis (NASH). Jiangzhi Granule (JZG) formula is a Traditional Chinese medicine prescription, and has been found effective against NAFLD/NASH. Here we showed that vitamin D deficiency could accelerate NASH development, and reduce vitamin D receptor (VDR) expression. JZG treatment alleviated high-fat vitamin D deficient (HF-VDD) diet-induced NASH in C57BL/6 J mice, and up-regulated both the liver and intestinal VDR expression independent of 1,25-dihydroxy-vitamin D₃ level. We analyzed the fecal BA profile using liquid chromatography coupled with triple quadrupole mass spectrometry (UPLC-TQMS) -based metabolomics, and found that JZG modulated fecal BA profile, predominantly increased the ratio of secondary BA species, as well as the expression of tight junction proteins Zona occludens 1(ZO-1) and occludin in the colon. In vitro experiment further confirmed the representative secondary BA species lithocholic acid (LCA) and keto-LCA upregulated the expression of and ZO-1 through VDR in LPS-stressed Caco-2 cells. Our results identified the endogenous VDR activation by JZG through modulating BA species in vitamin D deficiency-related NASH mice, thus providing evidence for the clinical application of JZG in treating NASH.

Indole alkaloids of Alstonia scholaris (L.) R. Br. alleviated nonalcoholic fatty liver disease in mice fed with high-fat diet

Alstonia scholaris (L.) R. Br (Apocynaceae) is a well-documented medicinal plant for treating respiratory diseases, liver diseases and diabetes traditionally. The current study aimed to investigate the effects of TA on non-alcoholic fatty liver disease (NAFLD). A NAFLD model was established using mice fed a high-fat diet (HFD) and administered with TA (7.5, 15 and 30 mg/kg) orally for 6 weeks. The biochemical parameters, expressions of lipid metabolism-related genes or proteins were analyzed. Furthermore, histopathological examinations were evaluated with Hematoxylin-Eosin and MASSON staining. TA treatment significantly decreased the bodyweight of HFD mice. The concentrations of low-density lipoprotein (LDL), triglyceride (TG), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were also decreased significantly in TA-treated mice group, accompanied by an increase in high-density lipoprotein (HDL). Furthermore, TA alleviated hepatic steatosis injury and lipid droplet accumulation of liver tissues. The liver mRNA levels involved in hepatic lipid synthesis such as sterol regulatory element-binding protein 1C (SREBP-1C), regulators of liver X receptor α (LXRα), peroxisome proliferator activated receptor (PPAR)γ, acetyl-CoA carboxylase (ACC1) and stearyl coenzyme A dehydrogenase-1 (SCD1), were markedly decreased, while the expressions involved in the regulation of fatty acid oxidation, PPARα, carnitine palmitoyl transterase 1 (CPT1A), and acyl coenzyme A oxidase 1 (ACOX1) were increased in TA-treated mice. TA might attenuate NAFLD by regulating hepatic lipogenesis and fatty acid oxidation.

Mitigation of liver fibrosis via hepatic stellate cells mitochondrial apoptosis induced by metformin

Liver fibrosis, a disease characterized by the excessive accumulation of extracellular matrix originating from activated hepatic stellate cells (HSCs), is a common pathological response to chronic liver injury resulting from a variety of insults. However, drugs that effectively block the activation of HSCs have still not been adequately investigated. This study demonstrates that metformin decreased the number of activated-HSCs through induction of apoptosis, but did not impact numbers of hepatocytes. Metformin upregulated BAX activation with facilitation of BIM, BAD and PUMA; downregulated Bcl-2 and Bcl-xl, but did not affect Mcl-1. Additionally, metformin induced cytochrome c release from mitochondria into the cytoplasm, directly triggering caspase-9-mediated mitochondrial apoptosis. The decline in mitochondrial membrane potential (ΔΨm) and deposition of superoxide in mitochondria accelerated the destruction of the integrity of mitochondrial membrane. Moreover, we verified the therapeutic effect of metformin in our mouse model of liver fibrosis associated with nonalcoholic steatohepatitis (NASH) in which hepatic function, NASH lesions and fibrosis were improved by metformin. In conclusion, this study indicated that metformin has significant therapeutic value in NASH-derived liver fibrosis by inducing apoptosis in HSCs, but does not affect the proliferation of hepatocytes.

Rodent models and metabolomics in non-alcoholic fatty liver disease: What can we learn?

Non-alcoholic fatty liver disease (NAFLD) prevalence has increased drastically in recent decades, affecting up to 25% of the world’s population. NAFLD is a spectrum of different diseases that starts with asymptomatic steatosis and continues with development of an inflammatory response called steatohepatitis, which can progress to fibrosis. Several molecular and metabolic changes are required for the hepatocyte to finally vary its function; hence a “multiple hit” hypothesis seems a more accurate proposal. Previous studies and current knowledge suggest that in most cases, NAFLD initiates and progresses through most of nine hallmarks of the disease, although the triggers and mechanisms for these can vary widely. The use of animal models remains crucial for understanding the disease and for developing tools based on biological knowledge. Among certain requirements to be met, a good model must imitate certain aspects of the human NAFLD disorder, be reliable and reproducible, have low mortality, and be compatible with a simple and feasible method. Metabolism studies in these models provides a direct reflection of the workings of the cell and may be a useful approach to better understand the initiation and progression of the disease. Metabolomics seems a valid tool for studying metabolic pathways and crosstalk between organs affected in animal models of NAFLD and for the discovery and validation of relevant biomarkers with biological understanding. In this review, we provide a brief introduction to NAFLD hallmarks, the five groups of animal models available for studying NAFLD and the potential role of metabolomics in the study of experimental NAFLD.

Application of Disulfiram and its Metabolites in Treatment of Inflammatory Disorders

Disulfiram has been used clinically for decades as an anti-alcoholic drug. Recently, several studies have demonstrated the anti-inflammatory effects of disulfiram and its metabolism, which can alleviate the progression of inflammation in vivo and in vitro. In the current study, we summarize the anti-inflammatory mechanisms of disulfiram and its metabolism, including inhibition of pyroptosis by either covalently modifying gasdermin D or inactivating nod-like receptor protein 3 inflammasome, dual effects of intracellular reactive oxygen species production, and inhibition of angiogenesis. Furthermore, we review the potential application of disulfiram and its metabolism in treatment of inflammatory disorders, such as inflammatory bowel disease, inflammatory injury of kidney and liver, type 2 diabetes mellitus, sepsis, uveitis, and osteoarthritis.

METTL3-m6A-Rubicon axis inhibits autophagy in nonalcoholic fatty liver disease

N6-methyladenosine (m⁶A) mRNA modification plays critical roles in various biological events and is involved in multiple complex diseases. However, the role of m⁶A modification in autophagy in nonalcoholic fatty liver disease (NAFLD) remains largely unknown. Here, we report that m⁶A modification was increased in livers of NAFLD mouse models and in free fatty acid (FFA)-treated hepatocytes, and the abnormal m⁶A modification was attributed to the upregulation of methyltransferase like 3 (METTL3) induced by lipotoxicity. Knockdown of METTL3 promoted hepatic autophagic flux and clearance of lipid droplets (LDs), while overexpression of METTL3 inhibited these processes. Mechanistically, METTL3 directly bound to Rubicon mRNA and mediated the m⁶A modification, while YTH N6-methyladenosine RNA binding protein 1 (YTHDF1), as a partner of METTL3, interacted with the m⁶A-marked Rubicon mRNA and promoted its stability. Subsequently, RUBICON inhibited autophagosome-lysosome fusion and further blocked clearance of LDs. Taken together, our results showed a critical role of METTL3 and YTHDF1 in regulating lipid metabolism via the autophagy pathway and provided a novel insight into m⁶A mRNA methylation in NAFLD.

Vasoconstrictor antagonism improves functional and structural vascular alterations and liver damage in rats with early NAFLD

BACKGROUND & AIMS

Intrahepatic vascular resistance is increased in early non-alcoholic fatty liver disease (NAFLD), potentially leading to tissue hypoxia and triggering disease progression. Hepatic vascular hyperreactivity to vasoconstrictors has been identified as an underlying mechanism. This study investigates vasoconstrictive agonism and antagonism in 2 models of early NAFLD and in non-alcoholic steatohepatitis (NASH).

METHODS

The effects of endothelin-1 (ET-1), angiotensin II (ATII) and thromboxane A2 (TxA2) agonism and antagonism were studied by in situ ex vivo liver perfusion and preventive/therapeutic treatment experiments in a methionine-choline-deficient diet model of steatosis. Furthermore, important results were validated in Zucker fatty rats after 4 or 8 weeks of high-fat high-fructose diet feeding. In vivo systemic and portal pressures, ex vivo transhepatic pressure gradients (THPG) and transaminase levels were measured. Liver tissue was harvested for structural and mRNA analysis.

RESULTS

The THPG and consequent portal pressure were significantly increased in both models of steatosis and in NASH. ET-1, ATII and TxA2 increased the THPG even further. Bosentan (ET-1 receptor antagonist), valsartan (ATII receptor blocker) and celecoxib (COX-2 inhibitor) attenuated or even normalised the increased THPG in steatosis. Simultaneously, bosentan and valsartan treatment improved transaminase levels. Moreover, bosentan was able to mitigate the degree of steatosis and restored the disrupted microvascular structure. Finally, beneficial vascular effects of bosentan endured in NASH.

CONCLUSIONS

Antagonism of vasoconstrictive mediators improves intrahepatic vascular function. Both ET-1 and ATII antagonists showed additional benefit and bosentan even mitigated steatosis and structural liver damage. In conclusion, vasoconstrictive antagonism is a potentially promising therapeutic option for the treatment of early NAFLD.

LAY SUMMARY

In non-alcoholic fatty liver disease (NAFLD), hepatic blood flow is impaired and the blood pressure in the liver blood vessels is increased as a result of an increased response of the liver vasculature to vasoconstrictors. Using drugs to block the constriction of the intrahepatic vasculature, the resistance of the liver blood vessels decreases and the increased portal pressure is reduced. Moreover, blocking the vasoconstrictive endothelin-1 pathway restored parenchymal architecture and reduced disease severity.

A Comparison of the Gene Expression Profiles of Non-Alcoholic Fatty Liver Disease between Animal Models of a High-Fat Diet and Methionine-Choline-Deficient Diet

Non-alcoholic fatty liver disease (NAFLD) embraces several forms of liver disorders involving fat disposition in hepatocytes ranging from simple steatosis to the severe stage, namely, non-alcoholic steatohepatitis (NASH). Recently, several experimental in vivo animal models for NAFLD/NASH have been established. However, no reproducible experimental animal model displays the full spectrum of pathophysiological, histological, molecular, and clinical features associated with human NAFLD/NASH progression. Although methionine-choline-deficient (MCD) diet and high-fat diet (HFD) models can mimic histological and metabolic abnormalities of human disease, respectively, the molecular signaling pathways are extremely important for understanding the pathogenesis of the disease. This review aimed to assess the differences in gene expression patterns and NAFLD/NASH progression pathways among the most common dietary animal models, i.e., HFD- and MCD diet-fed animals. Studies showed that the HFD and MCD diet could induce either up- or downregulation of the expression of genes and proteins that are involved in lipid metabolism, inflammation, oxidative stress, and fibrogenesis pathways. Interestingly, the MCD diet model could spontaneously develop liver fibrosis within two to four weeks and has significant effects on the expression of genes that encode proteins and enzymes involved in the liver fibrogenesis pathway. However, such effects in the HFD model were found to occur after 24 weeks with insulin resistance but appear to cause less severe fibrosis. In conclusion, assessing the abnormal gene expression patterns caused by different diet types provides valuable information regarding the molecular mechanisms of NAFLD/NASH and predicts the clinical progression of the disease. However, expression profiling studies concerning genetic variants involved in the development and progression of NAFLD/NASH should be conducted.

Circulating metabolites as a concept beyond tumor biology determining disease recurrence after resection of colorectal liver metastasis

BACKGROUND

Micro-metastatic growth is considered the main source of early cancer recurrence. Nutritional and microenvironmental components are increasingly recognized to play a significant role in the liver. We explored the predictive potential of preoperative plasma metabolites for postoperative disease recurrence in colorectal cancer liver metastasis (CRCLM) patients.

METHODS

All included patients (n = 71) had undergone R0 liver resection for colorectal cancer liver metastasis in the years between 2012 and 2018. Preoperative blood samples were collected and assessed for 180 metabolites using a preconfigured mass-spectrometry kit (Biocrates Absolute IDQ p180 kit). Postoperative disease-free (DFS) and overall survival (OS) were prospectively recorded. Patients that recurred within 6 months after surgery were defined as "high-risk" and, subsequently, a three-metabolite model was created which can assess DFS in our collective.

RESULTS

Multiple lysophosphatidylcholines (lysoPCs) and phosphatidylcholines (PCs) significantly predicted disease recurrence within 6 months (strongest: PC aa C36:1 AUC = 0.83, p = 0.003, PC ae C34:0 AUC = 0.83, p = 0.004 and lysoPC a C18:1 AUC = 0.8, p = 0.006). High-risk patients had a median DFS of 183 days versus 522 days in low-risk population (p = 0.016, HR = 1.98 95% CI 1.16-4.35) with a 6 months recurrence rate of 47.6% versus 4.7%, outperforming routine predictors of oncological outcome.

CONCLUSION

Circulating metabolites identified CRCLM patients at highest risk for 6 months disease recurrence after surgery. Our data also suggests that circulating metabolites might play a significant pathophysiological role in micro-metastatic growth and concomitant early tumor recurrences after liver resection. However, the clinical applicability and performance of this proposed metabolomic concept needs to be independently validated in future studies.

Hepatocyte-specific deletion of adipose triglyceride lipase (adipose triglyceride lipase/patatin-like phospholipase domain containing 2) ameliorates dietary induced steatohepatitis in mice

BACKGROUND AND AIMS

Increased fatty acid (FA) flux from adipose tissue to the liver contributes to the development of NAFLD. Because free FAs are key lipotoxic triggers accelerating disease progression, inhibiting adipose triglyceride lipase (ATGL)/patatin-like phospholipase domain containing 2 (PNPLA2), the main enzyme driving lipolysis, may attenuate steatohepatitis.

APPROACH AND RESULTS

Hepatocyte-specific ATGL knockout (ATGL LKO) mice were challenged with methionine-choline-deficient (MCD) or high-fat high-carbohydrate (HFHC) diet. Serum biochemistry, hepatic lipid content and liver histology were assessed. Mechanistically, hepatic gene and protein expression of lipid metabolism, inflammation, fibrosis, apoptosis, and endoplasmic reticulum (ER) stress markers were investigated. DNA binding activity for peroxisome proliferator-activated receptor (PPAR) α and PPARδ was measured. After short hairpin RNA-mediated ATGL knockdown, HepG2 cells were treated with lipopolysaccharide (LPS) or oleic acid:palmitic acid 2:1 (OP21) to explore the direct role of ATGL in inflammation in vitro. On MCD and HFHC challenge, ATGL LKO mice showed reduced PPARα and increased PPARδ DNA binding activity when compared with challenged wild-type (WT) mice. Despite histologically and biochemically pronounced hepatic steatosis, dietary-challenged ATGL LKO mice showed lower hepatic inflammation, reflected by the reduced number of Galectin3/MAC-2 and myeloperoxidase-positive cells and low mRNA expression levels of inflammatory markers (such as IL-1β and F4/80) when compared with WT mice. In line with this, protein levels of the ER stress markers protein kinase R-like endoplasmic reticulum kinase and inositol-requiring enzyme 1α were reduced in ATGL LKO mice fed with MCD diet. Accordingly, pretreatment of LPS-treated HepG2 cells with the PPARδ agonist GW0742 suppressed mRNA expression of inflammatory markers. Additionally, ATGL knockdown in HepG2 cells attenuated LPS/OP21-induced expression of proinflammatory cytokines and chemokines such as chemokine (C-X-C motif) ligand 5, chemokine (C-C motif) ligand (Ccl) 2, and Ccl5.

CONCLUSIONS

Low hepatic lipolysis and increased PPARδ activity in ATGL/PNPLA2 deficiency may counteract hepatic inflammation and ER stress despite increased steatosis. Therefore, lowering hepatocyte lipolysis through ATGL inhibition represents a promising therapeutic strategy for the treatment of steatohepatitis.

In Vivo Dynamic Nuclear Polarization Magnetic Resonance Imaging for the Evaluation of Redox-Related Diseases and Theranostics

Significance:In vivo molecular and metabolic imaging is an emerging field in biomedical research that aims to perform noninvasive detection of tissue metabolism in disease states and responses to therapeutic agents. The imbalance in tissue oxidation/reduction (Redox) states is related to the onset and progression of several diseases. Tissue redox metabolism provides biomarkers for early diagnosis and drug treatments. Thus, noninvasive imaging of redox metabolism could be a useful, novel diagnostic tool for diagnosis of redox-related disease and drug discovery. Recent Advances:In vivo dynamic nuclear polarization magnetic resonance imaging (DNP-MRI) is a technique that enables the imaging of free radicals in living animals. DNP enhances the MRI signal by irradiating the target tissue or solution with the free radical molecule's electron paramagnetic resonance frequency before executing pulse sequence of the MRI. In vivo DNP-MRI with redox-sensitive nitroxyl radicals as the DNP redox contrast agent enables the imaging of the redox metabolism on various diseases. Moreover, nitroxyl radicals show antioxidant effects that suppress oxidative stress. Critical Issues: To date, considerable progress has been documented preclinically in the development of animal imaging systems. Here, we review redox imaging of in vivo DNP-MRI with a focus on the recent progress of this system and its uses in patients with redox-related diseases. Future Directions: This technique could have broad applications in the study of other redox-related diseases, such as cancer, inflammation, and neurological disorders, and facilitate the evaluation of treatment response as a theranostic tool. Antioxid. Redox Signal. 36, 172-184.

Mitigation of MAFLD in High Fat-High Sucrose-Fructose Fed Mice by a Combination of Genistein Consumption and Exercise Training

PURPOSE

Metabolic dysfunction-associated fatty liver disease (MAFLD) is fueled by escalations in both sedentary behavior and caloric intake and is noted in obese type 2 diabetic (T2DM) patients. This study aimed to examine the effects of exercise and the phytoestrogen genistein in mice fed a high fat (60% fat) high sugar (55% fructose with 45% sucrose), HFHS diet.

METHODS

Male C57BL/6J mice were assigned to five groups: HFHS, HFHS with genistein (600 mg/kg diet, HFHS+Gen), HFHS with moderate exercise (HFHS+Ex), and HFHS with combined genistein and moderate exercise (HFHS-Gen+Ex). Control lean mice were fed standard chow and water. Exercise consisted of 30-minute sessions of treadmill running five days/week for the 12-week study duration. Body weight was assessed weekly. Liver, kidney, fecal pellets and serum were extracted at the end of the study and maintained at -80°C.

RESULTS

After 12 weeks of treatment, mice in the HFHS group had the highest hepatic lipid content. Plasma levels of glucose, insulin, leptin, cholesterol, amylin, and total fat content were significantly elevated in HFHS mice compared to control mice. HFHS feeding increased protein expression of carnitine palmitoyltransferase 1b (CPT-1b isoform) in gastrocnemius, CPT1a, glucose transporter protein 2 (GLUT2), glucocorticoid receptor (GR), and fructose 1,6-bisphosphate 1 (FBP1) expression in liver. Exercise alone had minor effects on these metabolic abnormalities. Genistein alone resulted in improvements in body weight, fat content, amylin, insulin sensitivity, and liver histopathology, GR, FBP1, and acetyl-CoA carboxylase 1 (ACC1). Combination treatment resulted in additional metabolic improvements, including reductions in hepatic lipid content and lipid area, alanine transferase activity, CPT1b, and CPT1a.

CONCLUSION

Our results indicate that a HFHS diet is obesogenic, inducing metabolic perturbations consistent with T2DM and MAFLD. Genistein alone and genistein combined with moderate intensity exercise were effective in reducing MAFLD and the aberrations induced by chronic HFHS feeding.

Investigation of Changes in Liver Microanatomy in the Steatosis Model Created by Permanent Canula in Rats

Objective: The knowledge of nonalcoholic fatty liver disease (NAFLD) and Nonalcoholic Steatohepatitis (NASH) is limited to the findings from available suitable models for this disease. A number of rodent models have been described in which relevant liver pathology develops in an appropriate metabolic context. In this experimental study, it was aimed to create a new liver fat model by giving fat from the portal vein of rats and to visualize the changes in the liver with advanced microscopic techniques. Methods: 28 female rats were used in the study. Permanent intraabdominal cannulas were inserted into the portal vein of the rats. Rats were randomly divided four group. Intralipid 20% substance was injected through cannula to the experimental groups during the test period. Control group received saline at the same rate. At the end of the experiment, the animals were visualized with a laser speckle microscope and livers were divided into sections according to the stereological method. The sections were painted with Hematoxylin-Eosin, Oil red o, Masson trichoma, Bodipy, Nile red. Sections were evaluated under a microscope. Results: Ballooning, inflammation and fibrosis were observed in the 2 week intralipid group. In the 1 week intralipid group, the rate of parenchyma decreased while the sinusoid rate increased, and sinusoid rate increased significantly in the 2 week intralipid (p˂0.05). Conclusion: According to the findings, steatohepatitis was detected in the 2 week intralipid, whereas only steatosis was observed in the 1 week intralipid. Thus, it was concluded that the newly formed rat model causes steatosis.

Study of lipid proton difference evaluation via 9.4T MRI analysis of fatty liver induced by exposure to methionine and choline-deficient (MCD) diet and high-fat diet (HFD) in an animal model

The selection of an animal model is based on the pathological mechanism appropriate for experimental investigation because the therapeutic effect was low depending on the pathological occurrence mechanism. The purpose of this study is to elucidate the changes in lipid proton concentration in two animal models of nonalcoholic fatty liver disease (NAFLD): methionine and choline-deficient (MCD) diet and high-fat diet (HFD). We calculated the T2 relaxation time of 7 lipid protons (LP) in the 9.4 T MRS phantom experiment. The concentrations of LPs were adjusted for T2 and T2* of MCD, HFD, and CCl₄ fatty liver animal models. Multivariate analysis and Pearson correlation were performed to analyze LP concentration, and the difference was investigated via Kendall correlation and independent t-test using LP composition ratio. The T2 relaxation time of each LP was accurately determined using phantom experiments. The in vivo magnetic resonance spectroscopy (MRS) data were obtained by quantifying the t2/t2* corrected LP concentration in the liver of the animal model. In case of MCD and HFD, there was an average difference in all LPs except 0.9 ppm LP, and the MCD and CCl₄ groups showed differences in the average of all LPs. However, there was no difference between LP of HFD and CCl₄ groups. A higher level of unsaturated fatty acids was found in the MCD fatty liver model than in HFD induced fatty liver.

MCLR-elicited hepatic fibrosis and carcinogenic gene expression changes persist in rats with diet-induced nonalcoholic steatohepatitis through a 4-week recovery period

Nonalcoholic steatohepatitis (NASH) causes liver extracellular matrix (ECM) remodeling and is a risk factor for fibrosis and hepatocellular carcinoma (HCC). Microcystin-LR (MCLR) is a hepatotoxin produced by fresh-water cyanobacteria that causes a NASH-like phenotype, liver fibrosis, and is also a risk factor for HCC. The focus of the current study was to investigate and compare hepatic recovery after cessation of MCLR exposure in healthy versus NASH animals. Male Sprague-Dawley rats were fed either a control or a high fat/high cholesterol (HFHC) diet for eight weeks. Animals received either vehicle or 30 μg/kg MCLR (i.p: 2 weeks, alternate days). Animals were euthanized at one of three time points: at the completion of the MCLR exposure period and after 2 and 4 weeks of recovery. Histological staining suggested that after four weeks of recovery the MCLR-exposed HFHC group had less steatosis and more fibrosis compared to the vehicle-exposed HFHC group and MCLR-exposed control group. RNA-Seq analysis revealed dysregulation of ECM genes after MCLR exposure in both control and HFHC groups that persisted only in the HFHC groups during recovery. After 4 weeks of recovery, MCLR hepatotoxicity in pre-existing NASH persistently dysregulated genes related to cellular differentiation and HCC. These data demonstrate impaired hepatic recovery and persistent carcinogenic changes after MCLR toxicity in pre-existing NASH.

Sugar kelp (Saccharina latissima) inhibits hepatic inflammation and fibrosis in a mouse model of diet-induced nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH), closely associated with obesity, is a health concern worldwide. We investigated whether the consumption of U.S.-grown sugar kelp (Saccharina latissima), an edible brown alga, can prevent obesity-associated metabolic disturbances and NASH in a mouse model of diet-induced NASH. Male C57BL/6J mice were fed a low-fat diet, a high-fat/high-sucrose/high-cholesterol diet (HF), or a HF diet containing sugar kelp (HF-Kelp) for 14 weeks. HF-Kelp group showed lower body weight with increased O2 consumption, CO2 production, physical activity, and energy expenditure compared with the HF. In the liver, there were significant decreases in weight, triglycerides, total cholesterol, and steatosis with HF-Kelp. The HF-Kelp group decreased hepatic expression of a macrophage marker adhesion G protein-coupled receptor E1 (Adgre1) and an M1 macrophage marker integrin alpha x (Itgax). HF-Kelp group also exhibited decreased liver fibrosis, as evidenced by less expression of fibrogenic genes and collagen accumulation than those of HF group. In epididymal white adipose tissue (eWAT), HF-Kelp group exhibited decreases in eWAT weight and adipocyte size compared with those of the HF. HF-Kelp group showed decreased expression of collagen type VI alpha 1 chain, Adgre1, Itgax, and tumor necrosis factor α in eWAT. We demonstrated, for the first time, that the consumption of U.S-grown sugar kelp prevented the development of obesity and its associated metabolic disturbances, steatosis, inflammation, and fibrosis in the liver and eWAT of a diet-induced NASH mouse model.

A Novel Humanized Model of NASH and Its Treatment With META4, A Potent Agonist of MET

BACKGROUND & AIMS

Nonalcoholic fatty liver disease is a frequent cause of hepatic dysfunction and is now a global epidemic. This ailment can progress to an advanced form called nonalcoholic steatohepatitis (NASH) and end-stage liver disease. Currently, the molecular basis of NASH pathogenesis is poorly understood, and no effective therapies exist to treat NASH. These shortcomings are due to the paucity of experimental NASH models directly relevant to humans.

METHODS

We used chimeric mice with humanized liver to investigate nonalcoholic fatty liver disease in a relevant model. We carried out histologic, biochemical, and molecular approaches including RNA-Seq. For comparison, we used side-by-side human NASH samples.

RESULTS

Herein, we describe a "humanized" model of NASH using transplantation of human hepatocytes into fumarylacetoacetate hydrolase-deficient mice. Once fed a high-fat diet, these mice develop NAFLD faithfully, recapitulating human NASH at the histologic, cellular, biochemical, and molecular levels. Our RNA-Seq analyses uncovered that a variety of important signaling pathways that govern liver homeostasis are profoundly deregulated in both humanized and human NASH livers. Notably, we made the novel discovery that hepatocyte growth factor (HGF) function is compromised in human and humanized NASH at several levels including a significant increase in the expression of the HGF antagonists known as NK1/NK2 and marked decrease in HGF activator. Based on these observations, we generated a potent, human-specific, and stable agonist of human MET that we have named META4 (Metaphor) and used it in the humanized NASH model to restore HGF function.

CONCLUSIONS

Our studies revealed that the humanized NASH model recapitulates human NASH and uncovered that HGF-MET function is impaired in this disease. We show that restoring HGF-MET function by META4 therapy ameliorates NASH and reinstates normal liver function in the humanized NASH model. Our results show that the HGF-MET signaling pathway is a dominant regulator of hepatic homeostasis.

A Systematic Review of Animal Models of NAFLD Finds High-Fat, High-Fructose Diets Most Closely Resemble Human NAFLD

BACKGROUND AND AIMS

Animal models of human disease are a key component of translational hepatology research, yet there is no consensus on which model is optimal for NAFLD.

APPROACH AND RESULTS

We generated a database of 3,920 rodent models of NAFLD. Study designs were highly heterogeneous, and therefore, few models had been cited more than once. Analysis of genetic models supported the current evidence for the role of adipose dysfunction and suggested a role for innate immunity in the progression of NAFLD. We identified that high-fat, high-fructose diets most closely recapitulate the human phenotype of NAFLD. There was substantial variability in the nomenclature of animal models: a consensus on terminology of specialist diets is needed. More broadly, this analysis demonstrates the variability in preclinical study design, which has wider implications for the reproducibility of in vivo experiments both in the field of hepatology and beyond.

CONCLUSIONS

This systematic analysis provides a framework for phenotypic assessment of NAFLD models and highlights the need for increased standardization and replication.

A subset of Kupffer cells regulates metabolism through the expression of CD36

Tissue macrophages are immune cells whose phenotypes and functions are dictated by origin and niches. However, tissues are complex environments, and macrophage heterogeneity within the same organ has been overlooked so far. Here, we used high-dimensional approaches to characterize macrophage populations in the murine liver. We identified two distinct populations among embryonically derived Kupffer cells (KCs) sharing a core signature while differentially expressing numerous genes and proteins: a major CD206^loESAM^- population (KC1) and a minor CD206^hiESAM⁺ population (KC2). KC2 expressed genes involved in metabolic processes, including fatty acid metabolism both in steady-state and in diet-induced obesity and hepatic steatosis. Functional characterization by depletion of KC2 or targeted silencing of the fatty acid transporter Cd36 highlighted a crucial contribution of KC2 in the liver oxidative stress associated with obesity. In summary, our study reveals that KCs are more heterogeneous than anticipated, notably describing a subpopulation wired with metabolic functions.

An update on drug development for the treatment of metabolic (dysfunction) associated fatty liver disease: Progress and opportunities

Despite the rising health burden of metabolic (dysfunction) associated fatty liver disease (MAFLD), there are no approved pharmacotherapies for MAFLD currently. This situation led to a significant escalation in drug development and randomized controlled trials for MAFLD, particularly as novel information about its molecular pathogenesis unfolds. Currently, there are numerous investigational candidate drugs for MAFLD in various stages of clinical development that act on different pathophysiological processes, such as metabolism/steatosis, inflammation or fibrosis. Here, we provide an update on drug development for the treatment of MAFLD and discuss the prospects and challenges for improving and accelerating the nonalcoholic fatty liver disease drug discovery pipeline.

Effect of Microbiome on Non-Alcoholic Fatty Liver Disease and the Role of Probiotics, Prebiotics, and Biogenics

Non-alcoholic fatty liver disease (NAFLD) is a leading cause of liver cirrhosis and hepatocellular carcinoma. NAFLD is associated with metabolic disorders such as obesity, insulin resistance, dyslipidemia, steatohepatitis, and liver fibrosis. Liver-resident (Kupffer cells) and recruited macrophages contribute to low-grade chronic inflammation in various tissues by modulating macrophage polarization, which is implicated in the pathogenesis of metabolic diseases. Abnormalities in the intestinal environment, such as the gut microbiota, metabolites, and immune system, are also involved in the pathogenesis and development of NAFLD. Hepatic macrophage activation is induced by the permeation of antigens, endotoxins, and other proinflammatory substances into the bloodstream as a result of increased intestinal permeability. Therefore, it is important to understand the role of the gut–liver axis in influencing macrophage activity, which is central to the pathogenesis of NAFLD and nonalcoholic steatohepatitis (NASH). Not only probiotics but also biogenics (heat-killed lactic acid bacteria) are effective in ameliorating the progression of NASH. Here we review the effect of hepatic macrophages/Kupffer cells, other immune cells, intestinal permeability, and immunity on NAFLD and NASH and the impact of probiotics, prebiotics, and biogenesis on those diseases.

The role of biofactors in the prevention and treatment of age-related diseases

The present demographic changes toward an aging society caused a rise in the number of senior citizens and the incidence and burden of age-related diseases (such as cardiovascular diseases [CVD], cancer, nonalcoholic fatty liver disease [NAFLD], diabetes mellitus, and dementia), of which nearly half is attributable to the population ≥60 years of age. Deficiencies in individual nutrients have been associated with increased risks for age-related diseases and high intakes and/or blood concentrations with risk reduction. Nutrition in general and the dietary intake of essential and nonessential biofactors is a major determinant of human health, the risk to develop age-related diseases, and ultimately of mortality in the older population. These biofactors can be a cost-effective strategy to prevent or, in some cases, even treat age-related diseases. Examples reviewed herein include omega-3 fatty acids and dietary fiber for the prevention of CVD, α-tocopherol (vitamin E) for the treatment of biopsy-proven nonalcoholic steatohepatitis, vitamin D for the prevention of neurodegenerative diseases, thiamine and α-lipoic acid for the treatment of diabetic neuropathy, and the role of folate in cancer epigenetics. This list of potentially helpful biofactors in the prevention and treatment of age-related diseases, however, is not exhaustive and many more examples exist. Furthermore, since there is currently no generally accepted definition of the term biofactors, we here propose a definition that, when adopted by scientists, will enable a harmonization and consistent use of the term in the scientific literature.

The role of iron homeostasis in adipocyte metabolism

Iron plays a vital role in the metabolism of adipose tissue. On the one hand, iron is essential for differentiation, endocrine, energy supply and other physiological functions of adipocytes. Iron homeostasis affects the progression of many chronic metabolic diseases such as obesity, type 2 diabetes mellitus, and non-alcoholic fatty liver disease. In adipose tissue, iron deficiency is associated with obesity, mainly due to inflammation. Nevertheless, excessive iron in adipose tissue leads to decreased insulin sensitivity owing to mitochondrial dysfunction and adipokine changes. On the other hand, iron has an effect on the thermogenesis of adipocytes. Iron deficiency affects the production of beige fat and the direction of the differentiation of brown fat. In this review, we summarize the current understanding of the crosstalk between iron homeostasis and metabolism in adipose tissue.

Acetylation of lactate dehydrogenase B drives NAFLD progression by impairing lactate clearance

BACKGROUND & AIMS

Lactate has recently been reported to accumulate in the livers of patients progressing from simple steatosis to non-alcoholic steatohepatitis (NASH). However, the underlying mechanism(s) of lactate accumulation and the role of lactate in the progression of non-alcoholic fatty liver disease (NAFLD) are essentially unknown.

METHODS

We compared the acetylome in liver samples taken from healthy individuals, patients with simple steatosis and patients with NASH to identify potential targets of acetylation with a role in lactate metabolism. Interactions between the acetylated target and acetyltransferases were measured in multiple cell lines. An acetyltransferase inhibitor was injected into high-fat diet (HFD)-fed mice to determine the role of lactate on NAFLD progression in vivo.

RESULTS

Hyperacetylation of lactate dehydrogenase B (LDHB) was found to be associated with lactate accumulation in NAFL and NASH livers in humans and mice. P300/CBP-associated factor (PCAF)-mediated acetylation of LDHB K82 was found to significantly decrease LDHB activity and impair hepatic lactate clearance, resulting in lactate accumulation. Acetylated LDHB induced lactate accumulation which exacerbated lipid deposition and inflammatory responses by activating histone hyperacetylation in HFD-induced NASH. The administration of embelin, a PCAF inhibitor, and the generation of an acetylation-deficient mutant of LDHB ameliorated NASH.

CONCLUSION

PCAF-dependent LDHB acetylation plays a key role in hepatic lipid accumulation and inflammatory responses by impairing lactate clearance; this process might be a potential therapeutic target for the treatment of NASH.

LAY SUMMARY

Lactate is known to accumulate in the livers of patients during the progression of non-alcoholic fatty liver disease (NAFLD); however, the underlying mechanism(s) of this accumulation and its importance in disease progression are unknown. Herein, we show that the acetylation of an enzyme involved in lactate metabolism leads to impaired lactate clearance and exacerbates NAFLD progression.

TWIST2 and the PPAR signaling pathway are important in the progression of nonalcoholic steatohepatitis

BACKGROUND

To investigate the roles of the transcription factors twist family bHLH transcription factor 1 (TWIST1), twist family bHLH transcription factor 2 (TWIST2), and peroxisome proliferator activated receptor gamma (PPARγ) in the progression of nonalcoholic steatohepatitis.

METHODS

The protein levels of TWIST1, TWIST2 and PPARγ were determined in the serum of nonalcoholic fatty liver disease (NAFLD) patients and healthy controls by enzyme-linked immunosorbent assay (ELISA). An in vivo model for fatty liver was established by feeding C57BL/6 J mice a high-fat diet (HFD). An in vitro model of steatosis was established by treating LO-2 cells with oleic acid (OA). RNA sequencing was performed on untreated and OA-treated LO-2 cells followed by TWIST1, TWIST2 and PPARγ gene mRNA levels analysis, Gene Ontology (GO) enrichment and pathway analysis.

RESULTS

The TWIST2 serum protein levels decreased significantly in all fatty liver groups (P < 0.05), while TWIST1 varied. TWIST2 tended to be lower in mice fed an HFD and was significantly lower at 3 months. Similarly, in the in vitro model, the TWIST2 protein level was downregulated significantly at 48 and 72 h after OA treatment. RNA sequencing of LO-2 cells showed an approximately 2.3-fold decrease in TWIST2, with no obvious change in TWIST1 and PPARγ. The PPAR signaling pathway was enriched, with 4 genes upregulated in OA-treated cells (P = 0.0018). The interleukin (IL)-17 and tumor necrosis factor (TNF) signaling pathways were enriched in OA-treated cells.

CONCLUSIONS

The results provide evidence that the TWIST2 and PPAR signaling pathways are important in NAFLD and shed light on a potential mechanism of steatosis.

Neuromedin U, a Key Molecule in Metabolic Disorders

Obesity is now a public health concern. The leading cause of obesity is an energy imbalance between ingested and expended calories. The mechanisms of feeding behavior and energy metabolism are regulated by a complex of various kinds of molecules, including anorexigenic and orexigenic neuropeptides. One of these neuropeptides, neuromedin U (NMU), was isolated in the 1980s, and its specific receptors, NMUR1 and NMUR2, were defined in 2000. A series of subsequent studies has revealed many of the physiological roles of the NMU system, including in feeding behavior, energy expenditure, stress responses, circadian rhythmicity, and inflammation. Particularly over the past decades, many reports have indicated that the NMU system plays an essential and direct role in regulating body weight, feeding behavior, energy metabolism, and insulin secretion, which are tightly linked to obesity pathophysiology. Furthermore, another ligand of NMU receptors, NMS (neuromedin S), was identified in 2005. NMS has physiological functions similar to those of NMU. This review summarizes recent observations of the NMU system in relation to the pathophysiology of obesity in both the central nervous systems and the peripheral tissues.

Eugenol modulates insulin sensitivity by upregulating insulin receptor substrate-2 in non-alcoholic fatty liver disease in rats

OBJECTIVES

The purpose of this study was to estimate the possible modulatory effect of Eugenol (EUG) on insulin resistance (IR) and liver fibrosis in high-fat diet (HFD)-induced experimental non-alcoholic fatty liver disease (NAFLD) in rats. It has been shown that EUG, a natural phenolic compound, has anti-hyperglycaemic, antioxidant and anti-inflammatory actions.

METHODS

For 8 consecutive weeks, standard rat chow diet (control group, EUG only treated group) or HFD (HFD group and HFD+EUG-treated group) were fed to rats daily. HFD+EUG-treated group and EUG only treated group were administered EUG (10 mg/kg) orally three times per week. Various indices of hepatotoxicity, oxidative stress, indicators of inflammation and liver fibrosis were investigated.

KEY FINDINGS

HFD-induced liver transaminases and triglycerides (TGs) were significantly decreased and histopathological lesions were improved with EUG treatment. EUG significantly improved IR evoked by HFD, as demonstrated by Homeostasis model assessment for insulin resistance (HOMA-IR) and increased insulin receptor substrate-2 (IRS-2) sensitivity. In addition, EUG improved oxidative stress damage elicited by HFD as shown by the restoration of reduced glutathione (GSH) level and nuclear factor erythroid-2-related factor 2 (Nrf-2) expression and plummeting lipid peroxidation. Further, EUG lessened pro-inflammatory cytokines surge [tumour necrosis factor-α (TNF-α) and IL-6] via inhibiting nuclear factor-κB (NF-κB) stimulation. As markers of fibrosis, EUG reduced collagen accumulation and smooth muscle alpha actin (SMaA) and TGF-β expression.

CONCLUSIONS

EUG may have protective effect against progression of fibrosis in NAFLD. The antifibrotic effect of EUG is probably due to EUG's antioxidant, anti-inflammatory and anti-hyperglycaemic.

BMP9 promotes methionine- and choline-deficient diet-induced nonalcoholic steatohepatitis in non-obese mice by enhancing NF-κB dependent macrophage polarization

Our previous study confirmed that bone morphogenetic protein 9 (BMP9) participated in the development of nonalcoholic steatohepatitis (NASH) by affecting macrophage polarization. The focus of this study was to further confirm the role of macrophages in BMP9-mediated NASH and to analyze the underlying mechanism. In vivo, mice that were administered adeno-associated viral (AAV) vectors containing a null transgene (AAV-null) or the BMP9 transgene (AAV-BMP9) were divided into methionine- and choline-deficient (MCD) and control diet (CD) groups, and they were administered either control liposomes or clodronate liposomes via tail vein injection, the latter to deplete macrophages. The mice were sacrificed after 4 weeks of MCD diet feeding. In vitro, RAW264.7 cells were pretreated with or without BAY11-7085 (an NF-κB inhibitor) and stimulated with recombinant human BMP9 (rh-BMP9). To explore the underlying mechanism of action of BMP9, primary human monocyte-derived macrophages were additionally investigated and immunohistochemistry, biochemical assays, qRT-PCR, and Western blotting were used. The characteristics of NASH-related inflammation were assessed by hepatic histological analysis. Serum AST and ALT and hepatic triglyceride were examined by biochemical assays. We found that the expression of M1 macrophage genes (including CD86, IL1β, IL6, MCP-1 and TNFα) and the number of M1 macrophages (iNOS⁺ macrophages) in the liver were significantly elevated after BMP9 overexpression and BMP9 directly upregulated TLR4 expression in MCD-induced NASH. These effects were eliminated by macrophage depletion. In vitro, we discovered that BMP9 enhanced the nuclear translocation of NF-κB to induce macrophage M1 polarization in RAW264.7 cells and it promoted LPS-mediated activation of the NF-κB pathway in primary human macrophages. Taken together, this study demonstrates that BMP9 promotes NASH development by directly acting on macrophages.

A human liver chimeric mouse model for non-alcoholic fatty liver disease

Background & Aims

The accumulation of neutral lipids within hepatocytes underlies non-alcoholic fatty liver disease (NAFLD), which affects a quarter of the world's population and is associated with hepatitis, cirrhosis, and hepatocellular carcinoma. Despite insights gained from both human and animal studies, our understanding of NAFLD pathogenesis remains limited. To better study the molecular changes driving the condition we aimed to generate a humanised NAFLD mouse model.

Methods

We generated TIRF (transgene-free Il2rg ^-/-/Rag2 ^-/-/Fah ^-/-) mice, populated their livers with human hepatocytes, and fed them a Western-type diet for 12 weeks.

Results

Within the same chimeric liver, human hepatocytes developed pronounced steatosis whereas murine hepatocytes remained normal. Unbiased metabolomics and lipidomics revealed signatures of clinical NAFLD. Transcriptomic analyses showed that molecular responses diverged sharply between murine and human hepatocytes, demonstrating stark species differences in liver function. Regulatory network analysis indicated close agreement between our model and clinical NAFLD with respect to transcriptional control of cholesterol biosynthesis.

Conclusions

These NAFLD xenograft mice reveal an unexpected degree of evolutionary divergence in food metabolism and offer a physiologically relevant, experimentally tractable model for studying the pathogenic changes invoked by steatosis.

Lay summary

Fatty liver disease is an emerging health problem, and as there are no good experimental animal models, our understanding of the condition is poor. We here describe a novel humanised mouse system and compare it with clinical data. The results reveal that the human cells in the mouse liver develop fatty liver disease upon a Western-style fatty diet, whereas the mouse cells appear normal. The molecular signature (expression profiles) of the human cells are distinct from the mouse cells and metabolic analysis of the humanised livers mimic the ones observed in humans with fatty liver. This novel humanised mouse system can be used to study human fatty liver disease.

Maternal exposure to high-fat diet during pregnancy and lactation predisposes normal weight offspring mice to develop hepatic inflammation and insulin resistance

Increasing evidence shows a potential link between the perinatal nutrient environment and metabolic outcome in offspring. Here, we investigated the effects of maternal feeding of a high-fat diet (HFD) during the perinatal period on hepatic metabolism and inflammation in male offspring mice at weaning and in early adulthood. Female C57BL/6 J mice were fed HFD or normal chow (NC) for 4 weeks before mating and during pregnancy and lactation. The male offspring mice were weaned onto an NC diet, and metabolic and molecular experiments were performed in early adulthood. At postnatal day 21, male offspring mice from HFD-fed dams (Off-HFD) showed significant increases in whole body fat mass and fasting levels of glucose, insulin, and cholesterol compared to male offspring mice from NC-fed dams (Off-NC). The RT-qPCR analysis showed two- to fivefold increases in hepatic inflammatory markers (MCP-1, IL-1β, and F4/80) in Off-HFD mice. Hepatic expression of G6Pase and PEPCK was elevated by fivefold in the Off-HFD mice compared to the Off-NC mice. Hepatic expression of GLUT4, IRS-1, and PDK4, as well as lipid metabolic genes, CD36, SREBP1c, and SCD1 were increased in the Off-HFD mice compared to the Off-NC mice. In contrast, CPT1a mRNA levels were reduced by 60% in the Off-HFD mice. At postnatal day 70, despite comparable body weights to the Off-NC mice, Off-HFD mice developed hepatic inflammation with increased expression of MCP-1, CD68, F4/80, and CD36 compared to the Off-NC mice. Despite normal body weight, Off-HFD mice developed insulin resistance with defects in hepatic insulin action and insulin-stimulated glucose uptake in skeletal muscle and brown fat, and these metabolic effects were associated with hepatic inflammation in Off-HFD mice. Our findings indicate hidden, lasting effects of maternal exposure to HFD during pregnancy and lactation on metabolic homeostasis of normal weight offspring mice.

Viburnum stellato-tomentosum Extract Suppresses Obesity and Hyperglycemia through Regulation of Lipid Metabolism in High-Fat Diet-Fed Mice

The potential biological activities of Viburnum stellato-tomentosum (VS), a plant mainly found in Costa Rica, have yet to be reported. Supplementation of VS extract for 17 weeks significantly decreased body weight gain, fat weight, fasting glucose, insulin, homeostasis model assessment of insulin resistance (HOMA-IR), and triglyceride levels in high-fat diet (HFD)-fed C57BL/6J mice. The molecular mechanisms underlying the anti-obesity and glucose-lowering effects of VS extract were investigated. VS extract suppressed adipocyte hypertrophy by regulating lipogenesis-related CCAAT/enhancer-binding protein α (C/EBPα) and insulin sensitivity-related peroxisome proliferator-activated receptor γ (Pparg) expression in adipose tissue (AT) and hepatic steatosis by inhibiting C/EBPα and lipid transport-related fatty acid binding protein 4 (FABP4) expression. VS extract enhanced muscular fatty acid β-oxidation-related AMP-activated protein kinase (AMPK) and PPARα expression with increasing Pparg levels. Furthermore, VS extract contained a much higher content of amentoflavone (AMF) (29.4 mg/g extract) compared to that in other Viburnum species. AMF administration decreased Cebpa and Fabp4 levels in the AT and liver, as well as improved insulin signaling-related insulin receptor substrate 1 (Irs1) and glucose transporter 1 (Glut1) levels in the muscle of HFD-fed mice. This study elucidated the in vivo molecular mechanisms of AMF for the first time. Therefore, VS extract effectively diminished obesity and hyperglycemia by suppressing C/EBPα-mediated lipogenesis in the AT and liver, enhancing PPARα-mediated fatty acid β-oxidation in muscle, and PPARγ-mediated insulin sensitivity in AT and muscle.

Gallic Acid Ameliorated Impaired Lipid Homeostasis in a Mouse Model of High-Fat Diet-and Streptozotocin-Induced NAFLD and Diabetes through Improvement of β-oxidation and Ketogenesis

Gallic acid (GA) is a simple polyphenol found in food and traditional Chinese medicine. Here, we determined the effects of GA administration in a combined mouse model of high-fat diet (HFD)-induced obesity and low-dose streptozotocin (STZ)-induced hyperglycemia, which mimics the concurrent non-alcoholic fatty liver disease (NAFLD) and type 2 diabetes pathological condition. By combining the results of physiological assessments, pathological examinations, metabolomic studies of blood, urine, liver, and muscle, and measurements of gene expression, we attempted to elucidate the efficacy of GA and the underlying mechanism of action of GA in hyperglycemic and dyslipidemic mice. HFD and STZ induced severe diabetes, NAFLD, and other metabolic disorders in mice. However, the results of liver histopathology and serum biochemical examinations indicated that daily GA treatment alleviated the high blood glucose levels in the mice and decelerated the progression of NAFLD. In addition, our results show that the hepatoprotective effect of GA in diabetic mice occurs in part through a partially preventing disordered metabolic pathway related to glucose, lipids, amino acids, purines, and pyrimidines. Specifically, the mechanism responsible for alleviation of lipid accumulation is related to the upregulation of β-oxidation and ketogenesis. These findings indicate that GA alleviates metabolic diseases through novel mechanisms.

Reduced hepatic global hydroxymethylation in mice treated with non-genotoxic carcinogens is transiently reversible with a methyl supplemented diet

Non-genotoxic carcinogens (NGCs) are known to cause perturbations in DNA methylation, which can be an early event leading to changes in gene expression and the onset of carcinogenicity. Phenobarbital (PB) has been shown to alter liver DNA methylation and hydroxymethylation patterns in mice in a time dependent manner. The goals of this study were to assess if clofibrate (CFB), a well-studied rodent NGC, would produce epigenetic changes in mice similar to PB, and if a methyl donor supplementation (MDS) would modulate epigenetic and gene expression changes induced by phenobarbital. CByB6F1 mice were treated with 0.5% clofibrate or 0.14% phenobarbital for 7 and 28 days. A subgroup of PB treated and control mice were also fed MDS diet. Liquid Chromatography-Ionization Mass Spectrometry (LC-MS) was used to quantify global liver 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) levels. Gene expression analysis was conducted using Affymetrix microarrays. A decrease in liver 5hmC but not 5mC levels was observed upon treatment with both CFB and PB with varying time of onset. We observed moderate increases in 5hmC levels in PB-treated mice when exposed to MDS diet and lower expression levels of several phenobarbital induced genes involved in cell proliferation, growth, and invasion, suggesting an early modulating effect of methyl donor supplementation. Overall, epigenetic profiling can aid in identifying early mechanism-based biomarkers of non-genotoxic carcinogenicity and increases the quality of cancer risk assessment for candidate drugs. Global DNA methylation assessment by LC-MS is an informative first step toward understanding the risk of carcinogenicity.

Impact of Parenteral Lipid Emulsion Components on Cholestatic Liver Disease in Neonates

Total parenteral nutrition (TPN) is a life-saving intervention for infants that are unable to feed by mouth. Infants that remain on TPN for extended periods of time are at risk for the development of liver injury in the form of parenteral nutrition associated cholestasis (PNAC). Current research suggests the lipid component of TPN is a factor in the development of PNAC. Most notably, the fatty acid composition, vitamin E concentration, and presence of phytosterols are believed key mediators of lipid emulsion driven PNAC development. New emulsions comprised of fish oil and medium chain triglycerides show promise for reducing the incidence of PNAC in infants. In this review we will cover the current clinical studies on the benefit of fish oil and medium chain triglyceride containing lipid emulsions on the development of PNAC, the current constituents of lipid emulsions that may modulate the prevalence of PNAC, and potential new supplements to TPN to further reduce the incidence of PNAC.

Transcriptional Regulation of Metabolic Pathways via Lipid-Sensing Nuclear Receptors PPARs, FXR, and LXR in NASH

Nonalcoholic fatty liver disease comprises a wide spectrum of liver injuries from simple steatosis to steatohepatitis and cirrhosis. Nonalcoholic steatohepatitis (NASH) is defined when liver steatosis is associated with inflammation, hepatocyte damage, and fibrosis. A genetic predisposition and environmental insults (ie, dietary habits, obesity) are putatively responsible for NASH progression. Here, we present the impact of the lipid-sensing nuclear receptors in the pathogenesis and treatment of NASH. In detail, we discuss the pros and cons of the putative transcriptional action of the fatty acid sensors (peroxisome proliferator-activated receptors), the bile acid sensor (farnesoid X receptor), and the oxysterol sensor (liver X receptors) in the pathogenesis and bona fide treatment of NASH.

Experimental models of metabolic and alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a multi-systemic disease that is considered the hepatic manifestation of metabolic syndrome (MetS). Because alcohol consumption in NAFLD patients is common, there is a significant overlap in the pathogenesis of NAFLD and alcoholic liver disease (ALD). Indeed, MetS also significantly contributes to liver injury in ALD patients. This “syndrome of metabolic and alcoholic steatohepatitis” (SMASH) is thus expected to be a more prevalent presentation in liver patients, as the obesity epidemic continues. Several pre-clinical experimental models that couple alcohol consumption with NAFLD-inducing diet or genetic obesity have been developed to better understand the pathogenic mechanisms of SMASH. These models indicate that concomitant MetS and alcohol contribute to lipid dysregulation, oxidative stress, and the induction of innate immune response. There are significant limitations in the applicability of these models to human disease, such as the ability to induce advanced liver injury or replicate patterns in human food/alcohol consumption. Thus, there remains a need to develop models that accurately replicate patterns of obesogenic diet and alcohol consumption in SMASH patients.

Pathogenesis of NASH and Promising Natural Products

Nonalcoholic steatohepatitis (NASH) is a common clinical condition that can lead to advanced liver diseases. The mechanism of the diaease progression, which is lacking effective therapy, remains obsure. Therefore, there is a need to understand the pathogenic mechanisms responsible for disease development and progression in order to develop innovative therapies. To accomplish this goal, experimental animal models that recapitulate the human disease are necessary. Currently, an increasing number of studies have focused on natural constituents from medicinal plants which have been emerged as a new hope for NASH. This review summarized the pathogenesis of NASH, animal models commonly used, and the promising targets for therapeutics. We also reviewed the natural constituents as potential NASH therapeutic agents.

The GLP-1R agonist liraglutide limits hepatic lipotoxicity and inflammatory response in mice fed a methionine-choline deficient diet

Nonalcoholic fatty liver disease (NAFLD) is the most common hepatic disorder related to type 2 diabetes (T2D). The disease can evolve toward nonalcoholic steatohepatitis (NASH), a state of hepatic inflammation and fibrosis. There is presently no drug that effectively improves and/or prevents NAFLD/NASH/fibrosis. GLP-1 receptor agonists (GLP-1Ra) are effective in treating T2D. As with the endogenous gut incretins, GLP-1Ra potentiate glucose-induced insulin secretion. In addition, GLP-1Ra limit food intake and weight gain, additional beneficial properties in the context of obesity/insulin-resistance. Nevertheless, these pleiotropic effects of GLP-1Ra complicate the elucidation of their direct action on the liver. In the present study, we used the classical methionine-choline deficient (MCD) dietary model to investigate the potential direct hepatic actions of the GLP-1Ra liraglutide. A 4-week infusion of liraglutide (570 µg/kg/day) did not impact body weight, fat accretion or glycemic control in MCD-diet fed mice, confirming the suitability of this model for avoiding confounding factors. Liraglutide treatment did not prevent lipid deposition in the liver of MCD-fed mice but limited the accumulation of C16 and C24-ceramide/sphingomyelin species. In addition, liraglutide treatment alleviated hepatic inflammation (in particular accumulation of M1 pro-inflammatory macrophages) and initiation of fibrosis. Liraglutide also influenced the composition of gut microbiota induced by the MCD-diet. This included recovery of a normal Bacteroides proportion and, among the Erysipelotrichaceae family, a shift between Allobaculum and Turicibacter genera. In conclusion, liraglutide prevents accumulation of C16 and C24-ceramides/sphingomyelins species, inflammation and initiation of fibrosis in MCD-diet-fed mice liver, suggesting beneficial hepatic actions independent of weight loss and global hepatic steatosis.

In Vitro and In Vivo Models of Non-Alcoholic Fatty Liver Disease: A Critical Appraisal

Non-alcoholic fatty liver disease (NAFLD), including non-alcoholic fatty liver (NAFL) and non-alcoholic steatohepatitis (NASH), represents the hepatic manifestation of obesity and metabolic syndrome. Due to the spread of the obesity epidemic, NAFLD is becoming the most common chronic liver disease and one of the principal indications for liver transplantation. However, no pharmacological treatment is currently approved to prevent the outbreak of NASH, which leads to fibrosis and cirrhosis. Preclinical research is required to improve our knowledge of NAFLD physiopathology and to identify new therapeutic targets. In the present review, we summarize advances in NAFLD preclinical models from cellular models, including new bioengineered platforms, to in vivo models, with a particular focus on genetic and dietary mouse models. We aim to discuss the advantages and limits of these different models.

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

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

Quantification of non-alcoholic fatty liver disease progression in 3D liver microtissues using impedance spectroscopy

Non-alcoholic fatty liver disease (NAFLD) has become a global pandemic. However, a pharmacological cure has not been approved for NAFLD treatment. The greatest barriers to the development of new treatments are the ambiguous criteria among the NAFLD stages and the lack of quantitative methodologies for its disease assessment in a translatable preclinical model. In this study, we developed impedance assessment systems to quantify NAFLD progression in three-dimensional (3D) liver microtissue (hMT). The hMT model undergoing NAFLD represents clinical-like characteristics for a range of stages, such as lipid accumulation, cell ballooning, and stiffening. Each stage can be quantitatively assessed by an impedance system with microchannels under constant or dynamic pressure, depending on the relevant mechanical and morphological changes used in the clinical assessment of NAFLD. We determined a correlation between the impedance parameters and pathophysiological characteristics, such as gap widening and cytoplasmic deformation associated with NAFLD progression using bioimpedance simulation, showing hMTs struggling to return to normal states. In addition, we identified the relative stiffness to assess fibrogenesis from the correlation of resistance change and elongation length into the smaller channel of hMTs. We hope this methodology will have a significant impact on drug development by facilitating improved NAFLD assessment.

The nuclear and cytoplasmic roles of miR-320 in non-alcoholic fatty liver disease

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disorder worldwide. Multiple metabolic disorders, such as hyperlipidemia, hyperglycemia, insulin resistance and obesity, have been reportedly associated with NAFLD, but little is known about the detailed mechanisms.

METHODS AND RESULTS

Here, we explored the effects of multiple metabolic disorders, especially hyperglycemia on lipid accumulation in liver using several well-established animal models. We found that liver lipid deposition was increased in both type 1 diabetes and high-fat diet (HFD) induced hyperlipidemia models, suggesting that either hyperglycemia or hyperlipidemia alone or together was able to trigger NAFLD. Moreover, we tested whether miR-320, a miRNA promoting lipid accumulation in heart revealed by our previous study, also participated in NAFLD. Though miR-320 treatment further increased liver lipid deposition in type 1 diabetes and HFD-feeding mice, it showed no effect in leptin-receptor deficient db/db mice. Interestingly, miR-320 affected different target genes in cytosol and nucleus, respectively, which collectively led to liver lipid overload.

CONCLUSIONS

Our findings illustrated the complex roles of miRNAs in subcellular fractions including nucleus and cytoplasm, which may lead to new insights into the mechanisms and treatment strategies for NAFLD in the future.

Biomolecular Ultrasound Imaging of Phagolysosomal Function

Phagocytic clearance and lysosomal processing of pathogens and debris are essential functions of the innate immune system. However, the assessment of these functions in vivo is challenging because most nanoscale contrast agents compatible with noninvasive imaging techniques are made from nonbiodegradable synthetic materials that do not undergo regular lysosomal degradation. To overcome this challenge, we describe the use of an all-protein contrast agent to directly visualize and quantify phagocytic and lysosomal activities in vivo by ultrasound imaging. This contrast agent is based on gas vesicles (GVs), a class of air-filled protein nanostructures naturally expressed by buoyant microbes. Using a combination of ultrasound imaging, pharmacology, immunohistology, and live-cell optical microscopy, we show that after intravenous injection, GVs are cleared from circulation by liver-resident macrophages. Once internalized, the GVs undergo lysosomal degradation, resulting in the elimination of their ultrasound contrast. By noninvasively monitoring the temporal dynamics of GV-generated ultrasound signal in circulation and in the liver and fitting them with a pharmacokinetic model, we can quantify the rates of phagocytosis and lysosomal degradation in living animals. We demonstrate the utility of this method by showing how these rates are perturbed in two models of liver dysfunction: phagocyte deficiency and nonalcoholic fatty liver disease. The combination of proteolytically degradable nanoscale contrast agents and quantitative ultrasound imaging thus enables noninvasive functional imaging of cellular degradative processes.

Study on the hepatocellular carcinoma model with metastasis

Hepatocellular carcinoma (HCC) is one of the most common causes of cancer-related death around the world due to advanced clinical stage at diagnosis, high incidence of recurrence and metastasis after surgical treatment. It is in urgent need to create appropriate animal models to explore the mechanism, patterns, risk factors, and therapeutic strategies of HCC metastasis and recurrence. However, most of the established models lack the phenotype of invasion and metastasis in patient, or have unstable phenotype. To establish HCC models with stable metastasis phenotype requires profound understanding in cancer metastasis biology and scientific methodology. Over the past 3 decades, HCC models with stable metastasis have been extensively studied. This paper reviewed the history and development of HCC animal models and cell models, focusing on the screening and maintaining of metastatic potential and phenotype. In-depth studies using these models vastly promote the understanding of cellular and molecular mechanisms and development of therapeutic strategies on HCC metastasis.

A Translational Mouse Model for NASH with Advanced Fibrosis and Atherosclerosis Expressing Key Pathways of Human Pathology

Non-alcoholic steatohepatitis (NASH) is a fast-growing liver disorder that is associated with an increased incidence of cardiovascular disease and type 2 diabetes. Animal models adequately mimicking this condition are scarce. We herein investigate whether Ldlr−/−. Leiden mice on different high-fat diets represent a suitable NASH model. Ldlr−/−. Leiden mice were fed a healthy chow diet or fed a high-fat diet (HFD) containing lard or a fast food diet (FFD) containing milk fat. Additionally, the response to treatment with obeticholic acid (OCA) was evaluated. Both high-fat diets induced obesity, hyperlipidemia, hyperinsulinemia, and increased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels. Mice on both diets developed progressive macro- and microvesicular steatosis, hepatic inflammation, and fibrosis, along with atherosclerosis. HFD induced more severe hyperinsulinemia, while FFD induced more severe hepatic inflammation with advanced (F3) bridging fibrosis, as well as more severe atherosclerosis. OCA treatment significantly reduced hepatic inflammation and fibrosis, and it did not affect atherosclerosis. Hepatic transcriptome analysis was compared with human NASH and illustrated similarity. The present study defines a translational model of NASH with progressive liver fibrosis and simultaneous atherosclerosis development. By adaptation of the fat content of the diet, either insulin resistance (HFD) or hepatic inflammation and fibrosis (FFD) can be aggravated.

Propagule Powder of Japanese Yam (Dioscorea Japonica) Reduces High-Fat Diet-Induced Metabolic Stress in Mice through the Regulation of Hepatic Gene Expression

SCOPE

Japanese yam propagules are supposed to have high potential as a functional food. However, there are almost no studies examining their physiological function. This study aims to elucidate the physiological function of Japanese yam propagules that are heated, freeze-dried, and powdered.

METHODS AND RESULTS

A high-fat diet with Japanese yam propagules is administered to mice for 4 weeks. High-fat loading induces a decline in respiratory quotient, and a high-fat diet with propagules reduces it more. This result suggests that propagules increase fat oxidation, indicating fat utilization. The hepatic transcriptome is analyzed using a DNA microarray. Some of the genes affected by high-fat loading are reversed by simultaneous ingestion of propagules. Such genes are mainly involved in the immune system and fat metabolism. High-fat loading induces hepatic inflammation, which is repressed by simultaneous ingestion of propagules. For lipid metabolism, propagules repress an increase in cholesterol biosynthesis and catabolism by high-fat loading. Regarding carbohydrate metabolism, propagules decrease glycolysis and glycogen synthesis and increase gluconeogenesis. Moreover, amino acids are converted into pyruvate and then used for gluconeogenesis.

CONCLUSION

Propagules act to delay the occurrence of hepatic disease by suppressing carbohydrate and fat metabolism disorders in high-fat loaded mice.