Role of fibroblast growth factor 21 in the early stage of NASH induced by methionine- and choline-deficient diet

FGF21 reverses MASH through coordinated actions on the CNS and liver

Metabolic dysfunction-associated steatotic liver disease (MASLD) and its progressive form, metabolic dysfunction-associated steatohepatitis (MASH), represent a growing public health burden with limited therapeutic options. Recent studies have revealed that fibroblast growth factor 21 (FGF21)-based analogs can significantly improve MASH, but the mechanisms for this effect are not well understood. Here, we demonstrate that the beneficial metabolic effects of FGF21 to reverse MASH are mediated through distinct mechanisms to independently lower hepatic triglyceride and cholesterol levels. Specifically, FGF21 signaling directly to glutamatergic neurons in the central nervous system (CNS) stimulates hepatic triglyceride reduction and reversal of fibrosis, whereas FGF21 signaling directly to hepatocytes is necessary and sufficient to reduce hepatic cholesterol levels in mice. Mechanistically, we show that FGF21 acts in the CNS to increase sympathetic nerve activity to the liver, which suppresses hepatic de novo lipogenesis. These results provide critical insights into a promising pharmacological target to treat MASH.

Treating metabolic dysfunction-associated steatohepatitis: The fat-trimming FGF21 approach

Metabolic dysfunction-associated steatohepatitis (MASH) is a condition characterized by hepatosteatosis, inflammation, and tissue damage, with steatosis as the initial stage, which involves chronic, excess deposition of lipids in hepatic lipid droplets. Despite the growing prevalence and serious risks it poses, including liver decompensation, the need for transplantation, and increased patient mortality, MASH currently faces no approved pharmacotherapy. Several promising treatment candidates have emerged from recent clinical trials, including analogs of FGF21 and agonists of the associated FGFR1-KLB complex. These agents were well-tolerated in trials and have demonstrated significant improvements in both histological and biochemical markers of liver fat content, inflammation, injury, and fibrosis in patients with MASH. Endocrine FGF21 plays a vital role in maintaining homeostasis of lipid, glucose, and energy metabolism. It achieves this through pathways that target lipids or lipid droplets in adipocytes and hepatocytes. Mechanistically, pharmacological FGF21 acts as a potent catabolic factor to promote lipid or lipid droplet lipolysis, fatty acid oxidation, mitochondrial catabolic flux, and heat-dissipating energy expenditure, leading to effective clearance of hepatic and systemic gluco-lipotoxicity and inflammatory stress, thereby preventing obesity, diabetes, and MASH pathologies. In this review, we aim to provide an update on the outcomes of clinical trials for several FGF21 mimetics. We compare these outcomes with preclinical studies and offer a lipid-centric perspective on the mechanisms underlying the clinical benefits of these agents for MASH.

FGF21 Signaling Exerts Antifibrotic Properties during Pulmonary Fibrosis

Rationale: Idiopathic pulmonary fibrosis (IPF) is a lethal disease with limited therapeutic options. FGF21 (fibroblast growth factor 21), an endocrine fibroblast growth factor that acts through the FGFR1 (fibroblast growth factor receptor 1)/KLB (β-Klotho) pathway, mitigates liver fibrosis. Objectives: We hypothesized that FGF21 could exert antifibrotic properties in the lung. Methods: The concentrations of FGF21 and KLB in the plasma of patients with IPF and control subjects were assessed. Pulmonary fibrosis development was assessed in Fgf21-deficient mice compared with wild-type littermates, at Day 14 (D14) after the intratracheal injection of bleomycin. We determined the effect of repeated subcutaneous injections of a PEGylated FGF21 analog at D7, D10, D14, and D17 after bleomycin on the development of pulmonary fibrosis. Mice were killed at D21. The effects of FGF21, alone or with KLB, on apoptosis in murine lung epithelial 15 cells and on the phenotype of human lung fibroblasts were assessed in vitro. Measurements and Main Results: In the plasma of patients with IPF, FGF21 concentrations were increased, while KLB concentrations were decreased. Fgf21-deficient mice showed increased sensitivity to bleomycin in comparison with their wild-type littermates. Treatment with PEGylated FGF21 mitigated lung fibrogenesis, as evidenced by a lower injury score and decreased fibrosis markers and profibrotic mediator expression compared with the control group receiving the diluent. In murine lung epithelial 15 cells, stimulation with FGF21 and KLB inhibited apoptosis, through the decrease of BAX and BIM. Fibroblastic phenotype remained unaltered. Conclusions: Our data indicate a possible antifibrotic effect of FGF21 in the lung achieved through the inhibition of alveolar type 2 cell apoptosis.

Cassia mimosoides L. decoction improves non-alcoholic fatty liver disease by modulating the pregnane X receptor

ETHNOPHARMACOLOGICAL RELEVANCE

Cassia mimosoides L. (CML) is a traditional Chinese medicine (TCM), which is frequently used in the clinical practice of TCM in the Lingnan region of China for the treatment of obesity. However, it is not clear whether decoction of cassia seeds has beneficial effects on non-alcoholic fatty liver disease (NAFLD).

OBJECTIVES

This study investigates the effect of CML on NAFLD and its underlying mechanisms.

MATERIALS AND METHODS

The high-fat diet (HFD) was used to induce NAFLD mice, and 40 male C57BL/6J mice were divided into Control, HFD, and CML groups (CML-low 1.5 g/kg, CML-medium 2.25 g/kg, CML-high 4.5 g/kg). The mouse primary hepatocytes (MPHs) of wild type (WT) and PXR-/- mice were induced using OAPA and divided into Control, OAPA, and CML groups (10 mg/L, 100 mg/L). Glycolipid metabolism, inflammation, and oxidative stress levels were detected in vivo and in vitro.

RESULTS

Compared to the HFD group, the CML groups demonstrated reduced body weight, triglycerides, total cholesterol, blood glucose, and mRNA levels of the lipid metabolism genes Srebp-1c and ACC1 in mice (p < 0.05 or 0.01). The ELISA results indicated that CML inhibited the production of IL-1β, IL-6, and TNF-α (p < 0.05). Furthermore, CML increased the SOD level (p < 0.01) to improve oxidative stress. RNA-seq expression showed that CML suppressed the transcriptional level of pregnane X receptor (PXR)(p < 0.05). In vitro experiments, the protective effect of CML against OAPA-induced lipid accumulation and inflammation observed in WT MPHs disappeared in PXR-/- MPHs (IC50: 1.04 mg/mL).

CONCLUSION

CML decoction ameliorates NAFLD mainly by inhibiting the PXR signaling pathway, which provides a theoretical basis for the broad application of CML in clinical practice.

Diverting hepatic lipid fluxes with lifestyles revision and pharmacological interventions as a strategy to tackle steatotic liver disease (SLD) and hepatocellular carcinoma (HCC)

Steatotic liver disease (SLD) and Hepatocellular Carcinoma (HCC) are characterised by a substantial rewiring of lipid fluxes caused by systemic metabolic unbalances and/or disrupted intracellular metabolic pathways. SLD is a direct consequence of the interaction between genetic predisposition and a chronic positive energy balance affecting whole-body energy homeostasis and the function of metabolically-competent organs. In this review, we discuss how the impairment of the cross-talk between peripheral organs and the liver stalls glucose and lipid metabolism, leading to unbalances in hepatic lipid fluxes that promote hepatic fat accumulation. We also describe how prolonged metabolic stress builds up toxic lipid species in the liver, and how lipotoxicity and metabolic disturbances drive disease progression by promoting a chronic activation of wound healing, leading to fibrosis and HCC. Last, we provide a critical overview of current state of the art (pre-clinical and clinical evidence) regarding mechanisms of action and therapeutic efficacy of candidate SLD treatment options, and their potential to interfere with SLD/HCC pathophysiology by diverting lipids away from the liver therefore improving metabolic health.

FGF21 agonists: An emerging therapeutic for metabolic dysfunction-associated steatohepatitis and beyond

The worldwide epidemics of obesity, hypertriglyceridemia, dyslipidaemia, type 2 diabetes, and metabolic dysfunction-associated steatotic liver disease (MASLD)/metabolic dysfunction-associated steatohepatitis (MASH) represent a major economic burden on healthcare systems. Patients with at-risk MASH, defined as MASH with moderate or significant fibrosis, are at higher risk of comorbidity/mortality, with a significant risk of cardiovascular diseases and/or major adverse liver outcomes. Despite a high unmet medical need, there is only one drug approved for MASH. Several drug candidates have reached the phase III development stage and could lead to several potential conditional drug approvals in the coming years. Within the armamentarium of future treatment options, FGF21 analogues hold an interesting position thanks to their pleiotropic effects in addition to their significant effect on both MASH resolution and fibrosis improvement. In this review, we summarise preclinical and clinical data from FGF21 analogues for MASH and explore additional potential therapeutic indications.

Tanshinone IIA Inhibits the Endoplasmic Reticulum Stress-Induced Unfolded Protein Response by Activating the PPARα/FGF21 Axis to Ameliorate Nonalcoholic Steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a critical stage in the progression of nonalcoholic fatty liver disease (NAFLD). Tanshinone IIA (TIIA) is a tanshinone extracted from Salvia miltiorrhiza; due to its powerful anti-inflammatory and antioxidant biological activities, it is commonly used for treating cardiovascular and hepatic diseases. A NASH model was established by feeding mice a methionine and choline-deficient (MCD) diet. Liver surface microblood flow scanning, biochemical examination, histopathological examination, cytokine analysis through ELISA, lipidomic analysis, transcriptomic analysis, and Western blot analysis were used to evaluate the therapeutic effect and mechanism of TIIA on NASH. The results showed that TIIA effectively reduced lipid accumulation, fibrosis, and inflammation and alleviated endoplasmic reticulum (ER) stress. Lipidomic analysis revealed that TIIA normalized liver phospholipid metabolism in NASH mice. A KEGG analysis of the transcriptome revealed that TIIA exerted its effect by regulating the PPAR signalling pathway, protein processing in the ER, and the NOD-like receptor signalling pathway. These results suggest that TIIA alleviates NASH by activating the PPARα/FGF21 axis to negatively regulate the ER stress-induced unfolded protein response (UPR).

FGF21 protects against ischaemia reperfusion injury in normal and fatty livers

BACKGROUND

Liver ischaemia/reperfusion (I/R) injury, which is an inevitable clinical problem of liver resection, liver transplantation and haemorrhagic shock. Fibroblast growth factor 21 (FGF21) was intimately coupled with multiple metabolic processes and proved to protect against apoptosis and inflammatory response in hepatocytes during hepatic I/R injury. However, the regulatory mechanisms of FGF21 in hepatic I/R injury remains unknown. Therefore, we hypothesize that FGF21 protects hepatic tissues from I/R injury.

METHODS

Blood samples were available from haemangiomas patients undergoing hepatectomy and murine liver I/R model and used to further evaluate the serum levels of FGF21 both in humans and mice. We further explored the regulatory mechanisms of FGF21 in murine liver I/R model by using FGF21-knockout mice (FGF21-KO mice) and FGF21-overexpression transgenic mice (FGF21-OE mice) fed a high-fat or ketogenic diet.

RESULTS

Our results show that the circulating levels of FGF21 were robustly decreased after liver I/R in both humans and mice. Silencing FGF21 expression with FGF21-KO mice aggravates liver injury at 6 h after 75 min of partial liver ischaemia, while FGF21-OE mice display alleviated hepatic I/R injury and inflammatory response. Compared with chow diet mice, exogenous FGF21 decreases the levels of aminotransferase, histological changes, apoptosis and inflammatory response in hepatic I/R injury treatment mice with a high-fat diet. Meanwhile, ketogenic diet mice are not sensitive to hepatic I/R injury.

CONCLUSIONS

The circulating contents of FGF21 are decreased during liver warm I/R injury and exogenous FGF21 exerts hepatoprotective effects on hepatic I/R injury. Thus, FGF21 regulates hepatic I/R injury and may be a key therapeutic target.

The endocrine FGFs axis: A systemic anti-fibrotic response that could prevent pulmonary fibrogenesis?

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal disease for which therapeutic options are limited, with an unmet need to identify new therapeutic targets. IPF is thought to be the consequence of repeated microlesions of the alveolar epithelium, leading to aberrant epithelial-mesenchymal communication and the accumulation of extracellular matrix proteins. The reactivation of developmental pathways, such as Fibroblast Growth Factors (FGFs), is a well-described mechanism during lung fibrogenesis. Secreted FGFs with local paracrine effects can either exert an anti-fibrotic or a pro-fibrotic action during this pathological process through their FGF receptors (FGFRs) and heparan sulfate residues as co-receptors. Among FGFs, endocrine FGFs (FGF29, FGF21, and FGF23) play a central role in the control of metabolism and tissue homeostasis. They are characterized by a low affinity for heparan sulfate, present in the cell vicinity, allowing them to have endocrine activity. Nevertheless, their interaction with FGFRs requires the presence of mandatory co-receptors, alpha and beta Klotho proteins (KLA and KLB). Endocrine FGFs are of growing interest for their anti-fibrotic action during liver, kidney, or myocardial fibrosis. Innovative therapies based on FGF19 or FGF21 analogs are currently being studied in humans during liver fibrosis. Recent data report a similar anti-fibrotic action of endocrine FGFs in the lung, suggesting a systemic regulation of the pulmonary fibrotic process. In this review, we summarize the current knowledge on the protective effect of endocrine FGFs during the fibrotic processes, with a focus on pulmonary fibrosis.

Oligonucleotide therapies for nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) represents a severe disease subtype of nonalcoholic fatty liver disease (NAFLD) that is thought to be highly associated with systemic metabolic abnormalities. It is characterized by a series of substantial liver damage, including hepatocellular steatosis, inflammation, and fibrosis. The end stage of NASH, in some cases, may result in cirrhosis and hepatocellular carcinoma (HCC). Nowadays a large number of investigations are actively under way to test various therapeutic strategies, including emerging oligonucleotide drugs (e.g., antisense oligonucleotide, small interfering RNA, microRNA, mimic/inhibitor RNA, and small activating RNA) that have shown high potential in treating this fatal liver disease. This article systematically reviews the pathogenesis of NASH/NAFLD, the promising druggable targets proven by current studies in chemical compounds or biological drug development, and the feasibility and limitations of oligonucleotide-based therapeutic approaches under clinical or pre-clinical studies.

Establishment of Novel Mouse Model of Dietary NASH Rapidly Progressing into Liver Cirrhosis and Tumors

Non-alcoholic steatohepatitis (NASH), which is the most severe manifestation of non-alcoholic fatty liver disease (NAFLD), has been recognized as a major hepatocellular carcinoma (HCC) catalyst. However, the molecular mechanism of NASH-liver fibrosis-HCC sequence remains unclear and a specific and effective treatment for NASH has not yet been established. The progress in this field depends on the availability of reliable preclinical models which show the steady progression to NASH, liver cirrhosis, and HCC. However, most of the NASH mouse models that have been described to date develop NASH generally for more than 24 weeks and there is an uncertainty of HCC development. To overcome such shortcomings of experimental NASH studies, we established a novel NASH-HCC mouse model with very high reproducibility, generality, and convenience. We treated male C57BL/6J mice with a newly developed choline-deficient and methionine-restricted high-fat diet, named OYC-NASH2 diet, for 60 weeks. Treatment of OYC-NASH2 diet for 3 weeks revealed marked steatosis, lobular inflammation, and fibrosis, histologically diagnosed as NASH. Liver cirrhosis was observed in all mice with 48-week treatment. Liver nodules emerged at 12 weeks of the treatment, > 2 mm diameter liver tumors developed in all mice at 24 weeks of the treatment and HCC appeared after 36-week treatment. In conclusion, our rapidly progressive and highly reproducible NASH-liver cirrhosis-HCC model is helpful for preclinical development and research on the pathogenesis of human NAFLD-NASH-HCC. Our mouse model would be useful for the development of novel chemicals for NASH-HCC-targeted therapies.

Molecular and cellular regulation of thermogenic fat

Thermogenic fat, consisting of brown and beige adipocytes, dissipates energy in the form of heat, in contrast to the characteristics of white adipocytes that store energy. Increasing energy expenditure by activating brown adipocytes or inducing beige adipocytes is a potential therapeutic strategy for treating obesity and type 2 diabetes. Thus, a better understanding of the underlying mechanisms of thermogenesis provides novel therapeutic interventions for metabolic diseases. In this review, we summarize the recent advances in the molecular regulation of thermogenesis, focusing on transcription factors, epigenetic regulators, metabolites, and non-coding RNAs. We further discuss the intercellular and inter-organ crosstalk that regulate thermogenesis, considering the heterogeneity and complex tissue microenvironment of thermogenic fat.

Investigation of FGF21 mRNA levels and relative mitochondrial DNA copy number levels and their relation in nonalcoholic fatty liver disease: a case-control study

Background: Although the exact mechanisms of nonalcoholic fatty liver disease (NAFLD) are not fully understood, numerous pieces of evidence show that the variations in mitochondrial DNA (mtDNA) level and hepatic Fibroblast growth factor 21 (FGF21) expression may be related to NAFLD susceptibility. Objectives: The main objective of this study was to determine relative levels of mtDNA copy number and hepatic FGF21 expression in a cohort of Iranian NAFLD patients and evaluate the possible relationship. Methods: This study included 27 NAFLD patients (10 with nonalcoholic fatty liver (NAFL) and 17 with non-alcoholic steatohepatitis (NASH)) and ten healthy subjects. Total RNA and genomic DNA were extracted from liver tissue samples, and then mtDNA copy number and FGF21 expression levels were assessed by quantitative real-time PCR. Results: The relative level of hepatic mtDNA copy number was 3.9-fold higher in patients than in controls (p < 0.0001). NAFLD patients showed a 2.9-fold increase in hepatic FGF21 expression compared to controls (p < 0.013). Results showed that hepatic FGF21 expression was positively correlated with BMI, serum ALT, and AST levels (p < 0.05). The level of mitochondrial copy number and hepatic FGF21 expression was not significantly associated with stages of change in hepatic steatosis. Finally, there was a significant correlation between FGF21 expression and mitochondrial copy number in NAFLD patients (p = 0.027). Conclusion: Our findings suggest a considerable rise of hepatic FGF21 mRNA levels and mtDNA-CN and show a positive correlation between them in the liver tissue of NAFLD patients.

Design and pharmaceutical evaluation of bifunctional fusion protein of FGF21 and GLP-1 in the treatment of nonalcoholic steatohepatitis

Fibroblast growth factor 21 (FGF21) and glucagon-like peptide-1 (GLP-1) may be useful for the treatment of type 2 diabetes, obesity, and non-alcoholic fatty liver disease (NAFLD). Previous studies have shown that GLP-1 may synergize with FGF21 in the regulation of glucose and lipid metabolism. Currently, no approved drug therapy is available for non-alcoholic steatohepatitis (NASH). Here, we constructed and screened dual-targeting fusion proteins of GLP-1 and FGF21, connected by elastin-like polypeptides (ELPs), to investigate whether a combination of these two hormones would have therapeutic effects in models of NASH. The temperature phase transition and release of the hormones under physiological conditions were studied to identify a bifunctional fusion protein of FGF21 and GLP-1 (GEF) that was highly stable and showed sustained release. We further evaluated the quality and therapeutic efficacy of GEF in three mouse models of NASH. We successfully synthesized a novel recombinant bifunctional fusion protein with high stability and low immunogenicity. The GEF protein synthesized ameliorated hepatic lipid accumulation, hepatocyte damage, and inflammation; prevented the progression of NASH in the three models; reduced glycemia; and caused weight loss. This novel GEF molecule may be suitable for clinical use for the treatment of NAFLD/NASH and related metabolic diseases.

Toxicokinetics of recombinant human fibroblast growth factor 21 for injection in cynomolgus monkey for 3 months

Introduction: Recombinant human fibroblast growth factor 21 (FGF-21) is a potential therapeutic agent for multiple metabolic diseases. However, little is known about the toxicokinetic characteristics of FGF-21. Methods: In the present study, we investigated the toxicokinetics of FGF-21 delivered via subcutaneous injection in vivo. Twenty cynomolgus monkeys were injected subcutaneously with different doses of FGF-21 for 86 days. Serum samples were collected at eight different time points (0, 0.5, 1.5, 3, 5, 8, 12, and 24 h) on day 1, 37 and 86 for toxicokinetic analysis. The serum concentrations of FGF-21 were measured using a double sandwich Enzyme-linked immunosorbent assay. Blood samples were collected on day 0, 30, 65, and 87 for blood and blood biochemical tests. Necropsy and pathological analysis were performed on d87 and d116 (after recovery for 29 days). Results: The average AUC_(0-24h) values of low-dose FGF-21 on d1, d37, and d86 were 5253, 25268, and 60445 μg h/L, and the average AUC_(0-24h) values of high-dose FGF-21 on d1, d37, and d86 were 19964, 78999, and 1952821 μg h/L, respectively. Analysis of the blood and blood biochemical indexes showed that prothrombin time and AST content in the high-dose FGF-21 group increased. However, no significant changes in other blood and blood biochemical indexes were observed. The anatomical and pathological results showed that continuous subcutaneous injection of FGF-21 for 86 days did not affect organ weight, the organ coefficient, and histopathology in cynomolgus monkeys. Discussion: Our results have guiding significance for the preclinical research and clinical use of FGF-21.

Intestinal BMP-9 locally upregulates FGF19 and is down-regulated in obese patients with diabetes

Bone morphogenetic protein (BMP)-9, a member of the TGFβ-family of cytokines, is believed to be mainly produced in the liver. The serum levels of BMP-9 were reported to be reduced in newly diagnosed diabetic patients and BMP-9 overexpression ameliorated steatosis in the high fat diet-induced obesity mouse model. Furthermore, injection of BMP-9 in mice enhanced expression of fibroblast growth factor (FGF)21. However, whether BMP-9 also regulates the expression of the related FGF19 is not clear. Because both FGF21 and 19 were described to protect the liver from steatosis, we have further investigated the role of BMP-9 in this context. We first analyzed BMP-9 levels in the serum of streptozotocin (STZ)-induced diabetic rats (a model of type I diabetes) and confirmed that BMP-9 serum levels decrease during diabetes. Microarray analyses of RNA samples from hepatic and intestinal tissue from BMP-9 KO- and wild-type mice (C57/Bl6 background) pointed to basal expression of BMP-9 in both organs and revealed a down-regulation of hepatic Fgf21 and intestinal Fgf19 in the KO mice. Next, we analyzed BMP-9 levels in a cohort of obese patients with or without diabetes. Serum BMP-9 levels did not correlate with diabetes, but hepatic BMP-9 mRNA expression negatively correlated with steatosis in those patients that did not yet develop diabetes. Likewise, hepatic BMP-9 expression also negatively correlated with serum LPS levels. In situ hybridization analyses confirmed intestinal BMP-9 expression. Intestinal (but not hepatic) BMP-9 mRNA levels were decreased with diabetes and positively correlated with intestinal E-Cadherin expression. In vitro studies using organoids demonstrated that BMP-9 directly induces FGF19 in gut but not hepatocyte organoids, whereas no evidence of a direct induction of hepatic FGF21 by BMP-9 was found. Consistent with the in vitro data, a correlation between intestinal BMP-9 and FGF19 mRNA expression was seen in the patients' samples. In summary, our data confirm that BMP-9 is involved in diabetes development in humans and in the control of the FGF-axis. More importantly, our data imply that not only hepatic but also intestinal BMP-9 associates with diabetes and steatosis development and controls FGF19 expression. The data support the conclusion that increased levels of BMP-9 would most likely be beneficial under pre-steatotic conditions, making supplementation of BMP-9 an interesting new approach for future therapies aiming at prevention of the development of a metabolic syndrome and liver steatosis.

Lower adiposity does not protect beta-2 syntrophin null mice from hepatic steatosis and inflammation in experimental non-alcoholic steatohepatitis

Visceral adiposity is strongly associated with liver steatosis, which predisposes to the development of non-alcoholic steatohepatitis (NASH). Mice with loss of the molecular adapter protein beta-2 syntrophin (SNTB2) have greatly reduced intra-abdominal fat mass. Hepatic expression of proteins with a role in fatty acid metabolism such as fatty acid synthase was nevertheless normal. This was also the case for proteins regulating cholesterol synthesis and uptake. Yet, a slight induction of hepatic cholesterol was noticed in the mutant mice. When mice were fed a methionine choline deficient (MCD) diet to induce NASH, liver cholesteryl ester content was induced in the wild type but not the mutant mice. Serum cholesterol of the mice fed a MCD diet declined and this was significant for the SNTB2 null mice. Though the mutant mice lost less fat mass than the wild type animals, hepatic triglyceride levels were similar between the groups. Proteins involved in fatty acid or cholesterol metabolism such as fatty acid synthase, apolipoprotein E and low-density lipoprotein receptor did not differ between the genotypes. Hepatic oxidative stress and liver inflammation of mutant and wild type mice were comparable. Mutant mice had lower hepatic levels of secondary bile acids and higher cholesterol storage in epididymal fat, and this may partly prevent hepatic cholesterol deposition. In summary, the current study shows that SNTB2 null mice have low intra-abdominal fat mass and do not accumulate hepatic cholesteryl esters when fed a MCD diet. Nevertheless, the SNTB2 null mice develop a similar NASH pathology as wild type mice suggesting a minor role of intra-abdominal fat and liver cholesteryl esters in this model.

Homocysteine-induced endoplasmic reticulum stress activates FGF21 and is associated with browning and atrophy of white adipose tissue in Bhmt knockout mice

Betaine-homocysteine methyltransferase (BHMT) catalyzes the transfer of methyl groups from betaine to homocysteine (Hcy), producing methionine and dimethylglycine. In this work, we characterize Bhmt wild type (Bhmt-WT) and knockout (Bhmt-KO) mice that were fully backcrossed to a C57Bl6/J background. Consistent with our previous findings, Bhmt-KO mice had decreased body weight, fat mass, and adipose tissue weight compared to WT. Histological analyses and gene expression profiling indicate that adipose browning was activated in KO mice and contributed to the adipose atrophy observed. BHMT is not expressed in adipose tissue but is abundant in liver; thus, a signal must originate from the liver that modulates adipose tissue. We found that, in Bhmt-KO mice, homocysteine-induced endoplasmic reticulum (ER) stress is associated with activation of the hepatic transcription factor cyclic AMP response element binding protein (CREBH), and an increase in hepatic and plasma concentrations of fibroblast growth factor 21 (FGF21), which is known to induce adipose browning. Our data indicate that the deletion of a single gene in one-carbon metabolism modifies adipose biology and energy metabolism. Future studies could focus on identifying if functional polymorphisms in BHMT result in a similar adipose atrophy phenotype.

Development of the Rabbit NASH Model Resembling Human NASH and Atherosclerosis

Non-alcoholic steatohepatitis (NASH) is a chronic liver disease which may progress into liver fibrosis and cancer. Since NASH patients have a high prevalence of atherosclerosis and ensuing cardiovascular diseases, simultaneous management of NASH and atherosclerosis is required. Currently, rodents are the most common animal models for NASH and accompanying liver fibrosis, but there are great differences in lipoprotein profiles between rodents and humans, which makes it difficult to reproduce the pathology of NASH patients with atherosclerosis. Rabbits can be a promising candidate for assessing NASH and atherosclerosis because lipoprotein metabolism is more similar to humans compared with rodents. To develop the NASH model using rabbits, we treated the Japanese White rabbit with a newly developed high-fat high-cholesterol diet (HFHCD) containing palm oil 7.5%, cholesterol 0.5%, and ferrous citrate 0.5% for 16 weeks. HFHCD-fed rabbits exhibited NASH at 8 weeks after commencing the treatment and developed advanced fibrosis by the 14th week of treatment. In addition to hypercholesterolemia, atherosclerotic lesion developed in the aorta after 8 weeks. Therefore, this rabbit NASH model might contribute to exploring the concurrent treatment options for human NASH and atherosclerosis.

Fibroblast Growth Factor-21 as a Potential Therapeutic Target of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a highly prevalent disease without any approved treatment to-date despite intensive research efforts by researchers and pharmaceutical industry. Fibroblast growth factor (FGF)-21 has been gaining increasing attention as a possible contributing factor and thus therapeutic target for obesity-related metabolic disorders, including NAFLD, mainly due to its effects on lipid and carbohydrate metabolism. Most animal and human observational studies have shown higher FGF-21 concentrations in NAFLD than non-NAFLD, implying that FGF-21 may be increased to counteract hepatic steatosis and inflammation. However, although Mendelian Randomization studies have revealed that variations of FGF-21 levels within the physiological range may have effects in hyperlipidemia and possibly nonalcoholic steatohepatitis, they also indicate that FGF-21, in physiological concentrations, may fail to reverse NAFLD and may not be able to control obesity and other diseases, indicating a state of FGF-21 resistance or insensitivity that could not respond to administration of FGF-21 in supraphysiological concentrations. Interventional studies with FGF-21 analogs (eg, pegbelfermin, efruxifermin, BOS-580) in humans have provided some favorable results in Phase 1 and Phase 2 studies. However, the definite effect of FGF-21 on NAFLD may be clarified after the completion of the ongoing clinical trials with paired liver biopsies and histological endpoints. The aim of this review is to critically summarize experimental and clinical data of FGF-21 in NAFLD, in an attempt to highlight existing knowledge and areas of uncertainty, and subsequently, to focus on the potential therapeutic effects of FGF-21 and its analogs in NAFLD.

The potential function and clinical application of FGF21 in metabolic diseases

As an endocrine hormone, fibroblast growth factor 21 (FGF21) plays a crucial role in regulating lipid, glucose, and energy metabolism. Endogenous FGF21 is generated by multiple cell types but acts on restricted effector tissues, including the brain, adipose tissue, liver, heart, and skeletal muscle. Intervention with FGF21 in rodents or non-human primates has shown significant pharmacological effects on a range of metabolic dysfunctions, including weight loss and improvement of hyperglycemia, hyperlipidemia, insulin resistance, cardiovascular disease, and non-alcoholic fatty liver disease (NAFLD). Due to the poor pharmacokinetic and biophysical characteristics of native FGF21, long-acting FGF21 analogs and FGF21 receptor agonists have been developed for the treatment of metabolic dysfunction. Clinical trials of several FGF21-based drugs have been performed and shown good safety, tolerance, and efficacy. Here we review the actions of FGF21 and summarize the associated clinical trials in obesity, type 2 diabetes mellitus (T2DM), and NAFLD, to help understand and promote the development of efficient treatment for metabolic diseases via targeting FGF21.

The role of protein kinases as key drivers of metabolic dysfunction-associated fatty liver disease progression: New insights and future directions

Metabolic dysfunction-associated fatty liver disease (MAFLD), proposed in 2020 is a novel term for non-alcoholic fatty liver disease (NAFLD) which was coined for the first time in 1980. It is a leading cause of the most chronic liver disease and hepatic failure all over the world, and unfortunately, with no licensed drugs for treatment yet. The progress of the disease is driven by the triggered inflammatory process, oxidative stress, and insulin resistance in many pathways, starting with simple hepatic steatosis to non-alcoholic steatohepatitis, fibrosis, cirrhosis, and liver cancer. Protein kinases (PKs), such as MAPK, ErbB, PKC, PI3K/Akt, and mTOR, govern most of the pathological pathways by acting on various downstream key points in MAFLD and regulating both hepatic gluco- lipo-neogenesis and inflammation. Therefore, modulating the function of those potential protein kinases that are effectively involved in MAFLD might be a promising therapeutic approach for tackling this disease. In the current review, we have discussed the key role of protein kinases in the pathogenesis of MAFLD and performed a protein-protein interaction (PPI) network among the main proteins of each kinase pathway with MAFLD-related proteins to predict the most likely targets of the PKs in MAFLD. Moreover, we have reported the experimental, pre-clinical, and clinical data for the most recent investigated molecules that are activating p38-MAPK and AMPK proteins and inhibiting the other PKs to improve MAFLD condition by regulating oxidation and inflammation signalling.

Contribution of organokines in the development of NAFLD/NASH associated hepatocellular carcinoma

Globally the incidence of hepatocellular carcinoma (HCC) is on an upsurge. Evidence is accumulating that liver disorders like nonalcoholic fatty liver disease (NAFLD) and its more progressive form nonalcoholic steatohepatitis (NASH) are associated with increased risk of developing HCC. NAFLD has a prevalence of about 25% and 50%-90% in obese population. With the growing burden of obesity epidemic worldwide, HCC presents a major healthcare burden. While cirrhosis is one of the major risk factors of HCC, available literature suggests that NAFLD/NASH associated HCC also develops in minimum or noncirrhotic livers. Therefore, there is an urgent need to understand the pathogenesis and risk factors associated with NAFLD and NASH related HCC that would help in early diagnosis and favorable prognosis of HCC secondary to NAFLD. Adipokines, hepatokines and myokines are factors secreted by adipocytes, hepatocytes and myocytes, respectively, playing essential roles in cellular homeostasis, energy balance and metabolism with autocrine, paracrine and endocrine effects. In this review, we endeavor to focus on the role of these organokines in the pathogenesis of NAFLD/NASH and its progression to HCC to augment the understanding of the factors stimulating hepatocytes to acquire a malignant phenotype. This shall aid in the development of novel therapeutic strategies and tools for early diagnosis of NAFLD/NASH and HCC.

Clinically Relevant Dose of Pemafibrate, a Novel Selective Peroxisome Proliferator-Activated Receptor α Modulator (SPPARMα), Lowers Serum Triglyceride Levels by Targeting Hepatic PPARα in Mice

Pemafibrate (PEM) is a novel lipid-lowering drug classified as a selective peroxisome proliferator-activated receptor α (PPARα) modulator whose binding efficiency to PPARα is superior to that of fibrates. This agent is also useful for non-alcoholic fatty liver disease and primary biliary cholangitis with dyslipidemia. The dose of PEM used in some previous mouse experiments is often much higher than the clinical dose in humans; however, the precise mechanism of reduced serum triglyceride (TG) for the clinical dose of PEM has not been fully evaluated. To address this issue, PEM at a clinically relevant dose (0.1 mg/kg/day) or relatively high dose (0.3 mg/kg/day) was administered to male C57BL/6J mice for 14 days. Clinical dose PEM sufficiently lowered circulating TG levels without apparent hepatotoxicity in mice, likely due to hepatic PPARα stimulation and the enhancement of fatty acid uptake and β-oxidation. Interestingly, PPARα was activated only in the liver by PEM and not in other tissues. The clinical dose of PEM also increased serum/hepatic fibroblast growth factor 21 (FGF21) without enhancing hepatic lipid peroxide 4-hydroxynonenal or inflammatory signaling. In conclusion, a clinically relevant dose of PEM in mice efficiently and safely reduced serum TG and increased FGF21 targeting hepatic PPARα. These findings may help explain the multiple beneficial effects of PEM observed in the clinical setting.

Factors Associated with White Fat Browning: New Regulators of Lipid Metabolism

Mammalian adipose tissue can be divided into white and brown adipose tissue based on its colour, location, and cellular structure. Certain conditions, such as sympathetic nerve excitement, can induce the white adipose adipocytes into a new type of adipocytes, known as beige adipocytes. The process, leading to the conversion of white adipocytes into beige adipocytes, is called white fat browning. The dynamic balance between white and beige adipocytes is closely related to the body’s metabolic homeostasis. Studying the signal transduction pathways of the white fat browning might provide novel ideas for the treatment of obesity and alleviation of obesity-related glucose and lipid metabolism disorders. This article aimed to provide an overview of recent advances in understanding white fat browning and the role of BAT in lipid metabolism.

Fibroblast growth factor 21: A "rheostat" for metabolic regulation?

Fibroblast growth factor 21 is an evolutionarily conserved factor that plays multiple important roles in metabolic homeostasis. During the past two decades, extensive investigations have improved our understanding of its delicate metabolic roles and identified its pharmacological potential to mitigate metabolic disorders. However, most clinical trials have failed to obtain the desired results, which raises issues regarding its clinical value. Fibroblast growth factor 21 is dynamically regulated by nutrients derived from food intake and hepatic/adipose release, which in turn act on the central nervous system, liver, and adipose tissues to influence food preference, hepatic glucose, and adipose fatty acid output. Based on this information, we propose that fibroblast growth factor 21 should not be considered merely an anti-hyperglycemia or anti-obesity factor, but rather a means of balancing of nutrient fluctuations to maintain an appropriate energy supply. Hence, the specific functions of fibroblast growth factor 21 in glycometabolism and lipometabolism depend on specific metabolic states, indicating that its pharmacological effects require further consideration.

FGF21: A Novel Regulator of Glucose and Lipid Metabolism and Whole-Body Energy Balance

Fibroblast growth factor (FGF) 21 is a recently recognized metabolic regulator that evokes interest due to its beneficial action of maintaining whole-body energy balance and protecting the liver from excessive triglyceride production and storage. Together with FGF19 and FGF23, FGF21 belongs to the FGF family with hormone-like activity. Serum FGF21 is generated primarily in the liver under nutritional stress stimuli like prolonged fasting or the lipotoxic diet, but also during increased mitochondrial and endoplasmic reticulum stress. FGF21 exerts its endocrine action in the central nervous system and adipose tissue. Acting in the ventromedial hypothalamus, FGF21 diminishes simple sugar intake. In adipose tissue, FGF21 promotes glucose utilization and increases energy expenditure by enhancing adipose tissue insulin sensitivity and brown adipose tissue thermogenesis. Therefore, FGF21 favors glucose consumption for heat production instead of energy storage. Furthermore, FGF21 specifically acts in the liver, where it protects hepatocytes from metabolic stress caused by lipid overload. FGF21 stimulates hepatic fatty acid oxidation and reduces lipid flux into the liver by increasing peripheral lipoprotein catabolism and reducing adipocyte lipolysis. Paradoxically, and despite its beneficial action, FGF21 is elevated in insulin resistance states, that is, fatty liver, obesity, and type 2 diabetes.

Endocrine Fibroblast Growth Factors in Relation to Stress Signaling

Fibroblast growth factors (FGFs) play important roles in various growth signaling processes, including proliferation, development, and differentiation. Endocrine FGFs, i.e., atypical FGFs, including FGF15/19, FGF21, and FGF23, function as endocrine hormones that regulate energy metabolism. Nutritional status is known to regulate the expression of endocrine FGFs through nuclear hormone receptors. The increased expression of endocrine FGFs regulates energy metabolism processes, such as fatty acid metabolism and glucose metabolism. Recently, a relationship was found between the FGF19 subfamily and stress signaling during stresses such as endoplasmic reticulum stress and oxidative stress. This review focuses on endocrine FGFs and the recent progress in FGF studies in relation to stress signaling. In addition, the relevance of the stress-FGF pathway to disease and human health is discussed.

FGF21 alleviates acute liver injury by inducing the SIRT1-autophagy signalling pathway

Liver injury can lead to different hepatic diseases, which are the mainly causes of high global mortality and morbidity. Autophagy and Sirtuin type 1 (SIRT1) have been shown protective effects in response to liver injury. Previous studies have showed that Fibroblast growth factor 21 (FGF21) could alleviate acute liver injury (ALI), but the mechanism remains unclear. Here, we verified the relationship among FGF21, autophagy and SIRT1 in carbon tetrachloride (CCl₄)‐induced ALI. We established CCl₄‐induced ALI models in C57BL/6 mice and the L02 cell line. The results showed that FGF21 was robustly induced in response to stress during the development of ALI. After exogenous FGF21 treatment in ALI models, liver damage in ALI mice was significantly reduced, as well as serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels. Consistently, FGF21 also greatly reduced the levels of ALT, AST, pro‐inflammatory cytokines interleukin 6 (IL6) and tumour necrosis factor‐alpha (TNFα) in ALI cell lines. Mechanistically, exogenous FGF21 treatment efficiently upregulated the expression of autophagy marker microtubule‐associated protein light chain‐3 beta (LC3 II) and autophagy key molecule coiled‐coil myosin‐like BCL2‐interacting protein (Beclin1), which was accompanied by alleviating hepatotoxicity in CCl₄‐treated wild‐type mice. Then, we examined how FGF21 induced autophagy expression and found that SIRT1 was also upregulated by FGF21 treatment. To further verify our results, we constructed an anti‐SIRT1 lentit‐RNAi to inhibit SIRT1 expression in mice and L02 cells, which reversed the protective effect of FGF21 on ALI. In summary, these results indicate that FGF21 alleviates ALI by enhancing SIRT1‐mediated autophagy.

Non-Alcoholic Steatohepatitis Severity Associates with FGF21 Level and Kidney Glucose Uptake

Background: Nonalcoholic steatohepatitis (NASH) is a severe form of fatty liver disease that has been shown to be associated with chronic kidney disease (CKD). Mechanism for the association of NASH with CKD remains unclear. In this study, we examined the association between NASH severity and kidney glucose uptake and the liver-secreted signaling molecule fibroblast growth factor 21 (FGF21). Methods: Kinetic parameters for kidney glucose transport rate (K₁) and standardized uptake value (SUV) were determined using dynamic positron emission tomography after injection of ¹⁸F-fluorodeoxyglucose. Liver biopsies were scored for NASH activity (inflammation and ballooning), fibrosis, and steatosis FGF21 was measured from fasting serum samples. Patients were categorized by liver biopsy and multivariate analyses were performed to evaluate the associations. Results: Of 41 NASH patients 73% were females, 71% white, 51% with steatosis ≥2, 39% with NASH activity ≥4 and fibrosis ≥3. With severe NASH activity, kidney SUV significantly increased even when adjusted for underlying insulin-resistant (IR) state. Kidney K₁ decreased significantly in higher liver activity in unadjusted models but not when adjusted for IR. FGF21 decreased with severe liver activity in adjusted models (P < 0.05) and associated with kidney K1 but not SUV. Conclusion: Our pilot data indicate that kidney glucose metabolism associates with NASH activity and FGF21 levels, suggesting a potential mechanism to NASH-induced CKD. Clinical Trials.gov ID: NCT02754037.

Gut microbiota mediate the FGF21 adaptive stress response to chronic dietary protein-restriction in mice

Chronic dietary protein-restriction can create essential amino acid deficiencies and induce metabolic adaptation through the hepatic FGF21 pathway which serves to maintain host fitness during prolonged states of nutritional imbalance. Similarly, the gut microbiome undergoes metabolic adaptations when dietary nutrients are added or withdrawn. Here we confirm previous reports that dietary protein-restriction triggers the hepatic FGF21 adaptive metabolic pathway and further demonstrate that this response is mediated by the gut microbiome and can be tuned through dietary supplementation of fibers that alter the gut microbiome. In the absence of a gut microbiome, we discover that FGF21 is de-sensitized to the effect of protein-restriction. These data suggest that host-intrinsic adaptive pathways to chronic dietary protein-restriction, such as the hepatic FGF21 pathway, may in-fact be responding first to adaptive metabolic changes in the gut microbiome.

Pubertal FGF21 deficit is central in the metabolic pathophysiology of an ovine model of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS), affecting over 10% of women, is associated with insulin resistance, obesity, dyslipidaemia, fatty liver and adipose tissue dysfunction. Its pathogenesis is poorly understood and consequently treatment remains suboptimal. Prenatally androgenized (PA) sheep, a clinically realistic model of PCOS, recapitulate the metabolic problems associated with PCOS. Fibroblast Growth Factor 21 (FGF21) is a metabolic hormone regulating lipid homeostasis, insulin sensitivity, energy balance and adipose tissue function. We therefore investigated the role of FGF21 in the metabolic phenotype of PA sheep. In adolescence PA sheep had decreased hepatic expression and circulating concentrations of FGF21. Adolescent PA sheep show decreased FGF21 signalling in subcutaneous adipose tissue, increased hepatic triglyceride content, trend towards reduced fatty acid oxidation capacity and increased hepatic expression of inflammatory markers. These data parallel studies on FGF21 deficiency, suggesting that FGF21 therapy during adolescence may represent a treatment strategy to mitigate metabolic problems associated with PCOS.

The Roles and Pharmacological Effects of FGF21 in Preventing Aging-Associated Metabolic Diseases

With the continuous improvement of living standards but the lack of exercise, aging-associated metabolic diseases such as obesity, type 2 diabetes mellitus (T2DM), and non-alcoholic fatty liver disease (NAFLD) are becoming a lingering dark cloud over society. Studies have found that metabolic disorders are near related to glucose, lipid metabolism, and cellular aging. Fibroblast growth factor 21 (FGF21), a member of the FGFs family, efficiently regulates the homeostasis of metabolism and cellular aging. By activating autophagy genes and improving inflammation, FGF21 indirectly delays cellular aging and directly exerts anti-aging effects by regulating aging genes. FGF21 can also regulate glucose and lipid metabolism by controlling metabolism-related genes, such as adipose triglyceride lipase (ATGL) and acetyl-CoA carboxylase (ACC1). Because FGF21 can regulate metabolism and cellular aging simultaneously, FGF21 analogs and FGF21 receptor agonists are gradually being valued and could become a treatment approach for aging-associated metabolic diseases. However, the mechanism by which FGF21 achieves curative effects is still not known. This review aims to interpret the interactive influence between FGF21, aging, and metabolic diseases and delineate the pharmacology of FGF21, providing theoretical support for further research on FGF21.

FGF/FGFR Signaling in Hepatocellular Carcinoma: From Carcinogenesis to Recent Therapeutic Intervention

Simple Summary

As the most common primary liver cancer, HCC is a tricky cancer resistant to systemic therapies. The fibroblast growth factor family and its receptors are gaining more and more attention in various cancers. Noticing an explosion in the number of studies about aberrant FGF/FGFR signaling in HCC being studied, we were encouraged to summarize them. This review discusses how FGF/FGFR signaling influences HCC development and its implications in HCC prediction and target treatment, and combination treatment.

Abstract

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer, ranking third in cancer deaths worldwide. Over the last decade, several studies have emphasized the development of tyrosine kinase inhibitors (TKIs) to target the aberrant pathways in HCC. However, the outcomes are far from satisfactory due to the increasing resistance and adverse effects. The family of fibroblast growth factor (FGF) and its receptors (FGFR) are involved in various biological processes, including embryogenesis, morphogenesis, wound repair, and cell growth. The aberrant FGF/FGFR signaling is also observed in multiple cancers, including HCC. Anti-FGF/FGFR provides delightful benefits for cancer patients, especially those with FGF signaling alteration. More and more multi-kinase inhibitors targeting FGF signaling, pan-FGFR inhibitors, and selective FGFR inhibitors are now under preclinical and clinical investigation. This review summarizes the aberrant FGF/FGFR signaling in HCC initiating, development and treatment status, and provide new insights into the treatment of HCC.

Amino Acid Sensing in Metabolic Homeostasis and Health

Sensing and responding to changes in nutrient levels, including those of glucose, lipids, and amino acids, by the body is necessary for survival. Accordingly, perturbations in nutrient sensing are tightly linked with human pathologies, particularly metabolic diseases such as obesity, type 2 diabetes mellitus, and other complications of metabolic syndromes. The conventional view is that amino acids are fundamental elements for protein and peptide synthesis, while recent studies have revealed that amino acids are also important bioactive molecules that play key roles in signaling pathways and metabolic regulation. Different pathways that sense intracellular and extracellular levels of amino acids are integrated and coordinated at the organismal level, and, together, these pathways maintain whole metabolic homeostasis. In this review, we discuss the studies describing how important sensing signals respond to amino acid availability and how these sensing mechanisms modulate metabolic processes, including energy, glucose, and lipid metabolism. We further discuss whether dysregulation of amino acid sensing signals can be targeted to promote metabolic disorders, and discuss how to translate these mechanisms to treat human diseases. This review will help to enhance our overall understanding of the correlation between amino acid sensing and metabolic homeostasis, which have important implications for human health.

Hepatokines as a Molecular Transducer of Exercise

Exercise has health benefits and prevents a range of chronic diseases caused by physiological and biological changes in the whole body. Generally, the metabolic regulation of skeletal muscle through exercise is known to have a protective effect on the pathogenesis of metabolic syndrome, non-alcoholic fatty liver disease (NAFLD), type 2 diabetes (T2D), and cardiovascular disease (CVD). Besides this, the importance of the liver as an endocrine organ is a hot research topic. Hepatocytes also secrete many hepatokines in response to nutritional conditions and/or physical activity. In particular, certain hepatokines play a major role in the regulation of whole-body metabolic homeostasis. In this review, we summarize the recent research findings on the exercise-mediated regulation of hepatokines, including fibroblast growth factor 21, fetuin-A, angiopoietin-like protein 4, and follistatin. These hepatokines serve as molecular transducers of the metabolic benefits of physical activity in chronic metabolic diseases, including NAFLD, T2D, and CVDs, in various tissues.

Multiple organs involved in the pathogenesis of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) represents the leading cause of chronic liver disease worldwide and the anticipated health burden is huge. There are limited therapeutic approaches for NAFLD now. It’s imperative to get a better understanding of the disease pathogenesis if new treatments are to be discovered. As the hepatic manifestation of metabolic syndrome, this disease involves complex interactions between different organs and regulatory pathways. It’s increasingly clear that brain, gut and adipose tissue all contribute to NAFLD pathogenesis and development, in view of their roles in energy homeostasis. In the present review, we try to summarize currently available data regarding NAFLD pathogenesis and to lay a particular emphasis on the inter-organ crosstalk evidence.

Methionine metabolism in chronic liver diseases: an update on molecular mechanism and therapeutic implication

As one of the bicyclic metabolic pathways of one-carbon metabolism, methionine metabolism is the pivot linking the folate cycle to the transsulfuration pathway. In addition to being a precursor for glutathione synthesis, and the principal methyl donor for nucleic acid, phospholipid, histone, biogenic amine, and protein methylation, methionine metabolites can participate in polyamine synthesis. Methionine metabolism disorder can aggravate the damage in the pathological state of a disease. In the occurrence and development of chronic liver diseases (CLDs), changes in various components involved in methionine metabolism can affect the pathological state through various mechanisms. A methionine-deficient diet is commonly used for building CLD models. The conversion of key enzymes of methionine metabolism methionine adenosyltransferase (MAT) 1 A and MAT2A/MAT2B is closely related to fibrosis and hepatocellular carcinoma. In vivo and in vitro experiments have shown that by intervening related enzymes or downstream metabolites to interfere with methionine metabolism, the liver injuries could be reduced. Recently, methionine supplementation has gradually attracted the attention of many clinical researchers. Most researchers agree that adequate methionine supplementation can help reduce liver damage. Retrospective analysis of recently conducted relevant studies is of profound significance. This paper reviews the latest achievements related to methionine metabolism and CLD, from molecular mechanisms to clinical research, and provides some insights into the future direction of basic and clinical research.

Dietary Restriction Suppresses Steatosis-Associated Hepatic Tumorigenesis in Hepatitis C Virus Core Gene Transgenic Mice

BACKGROUND AND AIMS

Dietary restriction (DR) is a preventive strategy for obesity, metabolic syndrome, cardiovascular disease, and diabetes. Although an interconnection between obesity, metabolic syndrome, fatty liver, and hepatocellular carcinoma has been documented, the mechanism and impact of DR on steatosis-derived hepatocarcinogenesis are not fully understood. This study aimed to evaluate whether DR can prevent hepatic tumorigenesis.

METHODS

Male hepatitis C virus core gene transgenic (HCVcpTg) mice that develop spontaneous age-dependent insulin resistance, hepatic steatosis, and ensuing liver tumor development without apparent hepatic fibrosis, were fed with either a control diet ad libitum (control group) or 70% of the same control diet (DR group) for 15 months, and liver phenotypes were investigated.

RESULTS

DR significantly reduced the number and volume of liver tumors. DR attenuated hepatic oxidative and endoplasmic reticulum stress and markedly suppressed nuclear factor-κB, signal transducer and activator of transcription 3 (STAT3) and STAT5, and phosphorylation of extracellular signal-regulated kinase, leading to downregulation of several pro-oncogenic mediators, such as cyclin D1. Serum insulin and insulin-like growth factor 1 levels, as well as hepatic expression of insulin receptor substrate 1/2, phosphatidylinositol-3 kinase, and serine/threonine-protein kinase AKT, were downregulated by DR. A transcriptome analysis revealed that STAT3 signaling and lipogenesis were the most suppressed hepatocarcinogenic pathways affected by DR. Additionally, DR stimulated autophagy and p62/sequestosome 1 degradation, enhanced phosphorylation of AMP-activated protein kinase α, increased fibroblast growth factor 21 expression, and attenuated expression of senescence-associated secretory phenotypes.

CONCLUSION

DR suppressed steatosis-associated hepatic tumorigenesis in HCVcpTg mice, mainly due to attenuation of pathways involved in inflammation, cellular stress, cell proliferation, insulin signaling, and senescence. These findings support the notion that persistent 30% reduction of daily food intake is beneficial for preventing steatosis-associated hepatocarcinogenesis caused by HCV core protein.

Lack of FGF21 promotes NASH-HCC transition via hepatocyte-TLR4-IL-17A signaling

Rationale: Hepatocellular carcinoma (HCC) has been increasingly recognized in nonalcoholic steatohepatitis (NASH) patients. Fibroblast growth factor 21 (FGF21) is reported to prevent NASH and delay HCC development. In this study, the effects of FGF21 on NASH progression and NASH-HCC transition and the potential mechanism(s) were investigated. Methods: NASH models and NASH-HCC models were established in FGF21Knockout (KO) mice to evaluate NASH-HCC transition. IL-17A signaling was investigated in the isolated hepatic parenchymal cells, splenocytes, and hepatocyte and HCC cell lines. Results: Lack of FGF21 caused significant up-regulation of the hepatocyte-derived IL-17A via Toll-like receptor 4 (TLR4) and NF-κB signaling. Restoration of FGF21 alleviated the high NAFLD activity score (NAS) and attenuated the TLR4-triggered hepatocyte-IL-17A expression. The HCC nodule number and tumor size were significantly alleviated by treatments of anti-IL-17A antibody. Conclusion: This study revealed a novel anti-inflammatory mechanism of FGF21 via inhibiting the hepatocyte-TLR4-IL-17A signaling in NASH-HCC models. The negative feedback loop on the hepatocyte-TLR4-IL-17A axis could be a potential anti-carcinogenetic mechanism for FGF21 to prevent NASH-HCC transition.

The Effects of B1344, a Novel Fibroblast Growth Factor 21 Analog, on Nonalcoholic Steatohepatitis in Nonhuman Primates

Nonalcoholic steatohepatitis has emerged as a major cause of liver diseases with no effective therapies. Here, we evaluate the efficacies and pharmacokinetics of B1344, a long-acting polyethylene glycolylated (PEGylated) fibroblast growth factor 21 analog, in a nongenetically modified nonhuman primate species that underwent liver biopsy and demonstrate the potential for efficacies in humans. B1344 is sufficient to selectively activate signaling from the βKlotho/FGFR1c receptor complex. In cynomolgus monkeys with nonalcoholic fatty liver disease (NAFLD), administration of B1344 via subcutaneous injection for 11 weeks caused a profound reduction of hepatic steatosis, inflammation, and fibrosis, along with amelioration of liver injury and hepatocyte death, as evidenced by liver biopsy specimen and biochemical analysis. Moreover, improvement of metabolic parameters was observed in the monkeys, including reduction of body weight and improvement of lipid profiles and glycemic control. To determine the role of B1344 in the progression of murine NAFLD independent of obesity, B1344 was administered to mice fed a methionine- and choline-deficient diet. Consistently, B1344 administration prevented the mice from lipotoxicity damage and nonalcoholic steatohepatitis in a dose-dependent manner. These results provide preclinical validation for an innovative therapeutic approach to NAFLD and support further clinical testing of B1344 for treating nonalcoholic steatohepatitis and other metabolic diseases in humans.

Loss of Hepatocyte-Specific PPARγ Expression Ameliorates Early Events of Steatohepatitis in Mice Fed the Methionine and Choline-Deficient Diet

The prevalence of nonalcoholic fatty liver disease (NAFLD) is increasing worldwide. To date, there is not a specific and approved treatment for NAFLD yet, and therefore, it is important to understand the molecular mechanisms that lead to the progression of NAFLD. Methionine- and choline-deficient (MCD) diets are used to reproduce some features of NAFLD in mice. MCD diets increase the expression of hepatic peroxisome proliferator-activated receptor gamma (PPARγ, Pparg) and the fatty acid translocase (CD36, Cd36) which could increase hepatic fatty acid uptake and promote the progression of NAFLD in mice and humans. In this study, we assessed the contribution of hepatocyte-specific PPARγ and CD36 expression to the development of early events induced by the MCD diet. Specifically, mice with adult-onset, hepatocyte-specific PPARγ knockout with and without hepatocyte CD36 overexpression were fed a MCD diet for three weeks. Hepatocyte PPARγ and/or CD36 expression did not contribute to the development of steatosis induced by the MCD diet. However, the expression of inflammatory and fibrogenic genes seems to be dependent on the expression of hepatocyte PPARγ and CD36. The expression of PPARγ and CD36 in hepatocytes may be relevant in the regulation of some features of NAFLD and steatohepatitis.

A trans-fatty acid-rich diet promotes liver tumorigenesis in HCV core gene transgenic mice

Excess consumption of trans-fatty acid (TFA), an unsaturated fatty acid containing trans double bonds, is a major risk factor for cardiovascular disease and metabolic syndrome. However, little is known about the link between TFA and hepatocellular carcinoma (HCC) despite it being a frequent form of cancer in humans. In this study, the impact of excessive dietary TFA on hepatic tumorigenesis was assessed using hepatitis C virus (HCV) core gene transgenic mice that spontaneously developed HCC. Male transgenic mice were treated for 5 months with either a control diet or an isocaloric TFA-rich diet that replaced the majority of soybean oil with shortening. The prevalence of liver tumors was significantly higher in TFA-rich diet-fed transgenic mice compared with control diet-fed transgenic mice. The TFA-rich diet significantly increased the expression of pro-inflammatory cytokines, as well as oxidative and endoplasmic reticulum stress, and activated nuclear factor-kappa B (NF-κB) and nuclear factor erythroid 2-related factor 2 (NRF2), leading to high p62/sequestosome 1 (SQSTM1) expression. Furthermore, the TFA diet activated extracellular signal-regulated kinase (ERK) and stimulated the Wnt/β-catenin signaling pathway, synergistically upregulating cyclin D1 and c-Myc, driving cell proliferation. Excess TFA intake also promoted fibrogenesis and ductular reaction, presumably contributing to accelerated liver tumorigenesis. In conclusion, these results demonstrate that a TFA-rich diet promotes hepatic tumorigenesis, mainly due to persistent activation of NF-κB and NRF2-p62/SQSTM1 signaling, ERK and Wnt/β-catenin pathways and fibrogenesis. Therefore, HCV-infected patients should avoid a TFA-rich diet to prevent liver tumor development.

PPARs as Metabolic Regulators in the Liver: Lessons from Liver-Specific PPAR-Null Mice

Peroxisome proliferator-activated receptor (PPAR) α, β/δ, and γ modulate lipid homeostasis. PPARα regulates lipid metabolism in the liver, the organ that largely controls whole-body nutrient/energy homeostasis, and its abnormalities may lead to hepatic steatosis, steatohepatitis, steatofibrosis, and liver cancer. PPARβ/δ promotes fatty acid β-oxidation largely in extrahepatic organs, and PPARγ stores triacylglycerol in adipocytes. Investigations using liver-specific PPAR-disrupted mice have revealed major but distinct contributions of the three PPARs in the liver. This review summarizes the findings of liver-specific PPAR-null mice and discusses the role of PPARs in the liver.

Targeting FGF21 for the Treatment of Nonalcoholic Steatohepatitis

Nonalcoholic steatohepatitis (NASH), the severe stage of nonalcoholic fatty liver disease (NAFLD), is defined as the presence of hepatic steatosis with inflammation, hepatocyte injury, and different degrees of fibrosis. Although NASH affects 2-5% of the global population, no drug has been specifically approved to treat the disease. Fibroblast growth factor 21 (FGF21) and its analogs have emerged as a potential new therapeutic strategy for the treatment of NASH. In fact, FGF21 deficiency favors the development of steatosis, inflammation, hepatocyte damage, and fibrosis in the liver, whereas administration of FGF21 analogs ameliorates NASH by attenuating these processes. We review mechanistic insights into the beneficial and potential side effects of therapeutic approaches targeting FGF21 for the treatment of NASH.

FGF19 and FGF21 for the Treatment of NASH-Two Sides of the Same Coin? Differential and Overlapping Effects of FGF19 and FGF21 From Mice to Human

FGF19 and FGF21 analogues are currently in clinical development for the potential treatment of NASH. In Phase 2 clinical trials analogues of FGF19 and FGF21 decrease hepatic steatosis with up to 70% (MRI-PDFF) after 12 weeks and as early as 12-16 weeks of treatment an improvement in NASH resolution and fibrosis has been observed. Therefore, this class of compounds is currently of great interest in the field of NASH. FGF19 and FGF21 belong to the endocrine FGF19 subfamily and both require the co-receptor beta-klotho for binding and signalling through the FGF receptors. FGF19 is expressed in the ileal enterocytes and is released into the enterohepatic circulation in response to bile acids stimuli and in the liver FGF19 inhibits hepatic bile acids synthesis by transcriptional regulation of Cyp7A1, which is the rate limiting enzyme. FGF21 is, on the other hand, highly expressed in the liver and is released in response to high glucose, high free-fatty acids and low amino-acid supply and regulates energy, glucose and lipid homeostasis by actions in the CNS and in the adipose tissue. FGF19 and FGF21 are differentially expressed, have distinct target tissues and separate physiological functions. It is therefore of peculiar interest to understand why treatment with both FGF19 and FGF21 analogues have strong beneficial effects on NASH parameters in mice and human and whether the mode of action is overlapping This review will highlight the physiological and pharmacological effects of FGF19 and FGF21. The potential mode of action behind the anti-steatotic, anti-inflammatory and anti-fibrotic effects of FGF19 and FGF21 will be discussed. Finally, development of drugs is always a risk benefit analysis and the human relevance of adverse effects observed in pre-clinical species as well as findings in humans will be discussed. The aim is to provide a comprehensive overview of the current understanding of this drug class for the potential treatment of NASH.