Metformin ameliorates activation of hepatic stellate cells and hepatic fibrosis by succinate and GPR91 inhibition

Chrysin-loaded calixarene-cyclodextrin ternary drug delivery system inhibits TGF-β and galectin-1 mediated pathways in diabetic liver fibrosis

This study investigated the efficacy of a new chrysin-loaded calixarene-cyclodextrin ternary drug delivery system (DDS) in reversing liver fibrosis in a mouse model of chronic diabetes. The system was designed to enhance the solubility and bioavailability of chrysin (CHR) and calixarene 0118 (OTX008). Adult male CD1 mice received streptozotocin (STZ) injections to induce diabetes. After 20 weeks, they underwent intraperitoneal treatments twice weekly for a two-week period. Histological analyses revealed that long-term hyperglycaemia increased liver fibrosis and altered hepatic ultrastructure, characterized by lipid accumulation, hepatic stellate cell activation, and collagen deposition. The treatment with the chrysin-loaded DDS restored liver structure closely to normal levels, as opposed to the minimal impact observed with sulfobutylated β-cyclodextrin (SBECD) alone. The treatment significantly decreased serum activities of alanine /aspartate transaminases and reduced the gene expression of collagen type I (Col-I). It also modulated the transforming growth factor beta 1 (TGF-β1)/Smad signalling pathway, inhibiting the activation and proliferation of hepatic stellate cells. The treatment led to a downregulation of the TGF-β1 gene and its receptors TGFβR1 and TGFβR2, together with a decrease in Smad 2 and 3 mRNA levels. Conversely, Smad 7 mRNA expression was increased by the DDS. Furthermore, it downregulated galectin-1 (Gal-1) gene and protein levels, which correlated with fibrotic markers. In conclusion, the chrysin-loaded calixarene-cyclodextrin ternary DDS presents a promising therapeutic approach for diabetic liver fibrosis, effectively targeting fibrotic pathways and restoring hepatic function and structure.

SUCNR1 regulates insulin secretion and glucose elevates the succinate response in people with prediabetes

Pancreatic β-cell dysfunction is a key feature of type 2 diabetes, and novel regulators of insulin secretion are desirable. Here we report that the succinate receptor (SUCNR1) is expressed in β-cells and is up-regulated in hyperglycemic states in mice and humans. We found that succinate acts as a hormone-like metabolite and stimulates insulin secretion via a SUCNR1-Gq-PKC-dependent mechanism in human β-cells. Mice with β-cell-specific Sucnr1 deficiency exhibit impaired glucose tolerance and insulin secretion on a high-fat diet, indicating that SUCNR1 is essential for preserving insulin secretion in diet-induced insulin resistance. Patients with impaired glucose tolerance show an enhanced nutritional-related succinate response, which correlates with the potentiation of insulin secretion during intravenous glucose administration. These data demonstrate that the succinate/SUCNR1 axis is activated by high glucose and identify a GPCR-mediated amplifying pathway for insulin secretion relevant to the hyperinsulinemia of prediabetic states.

The interplay between diabetes and non-alcoholic fatty liver disease: a cross-sectional study from Pakistan

Background and objectives

Non-alcoholic fatty liver disease (NAFLD) is characterized by ectopic deposition of fat in the liver, in the absence of other secondary causes of fat buildup. The relationship between NAFLD, including alanine aminotransferase (ALT), and glycated haemoglobin (HbA1c), is important for predicting the severity of disease and prognosis. This study aims to investigate the association of HbA1c in type 2 diabetes mellitus (T2DM) patients with NAFLD via measuring the ALT levels.

Materials and methods

This retrospective cross-sectional study enroled 130 patients with T2DM and NAFLD. The association between levels of HbA1c and ALT in patients of NAFLD with controlled and uncontrolled T2DM, respectively, was investigated. Stratification was done based on gender and diabetic control, using HbA1c levels as a marker of glycemic control. Serum ALT levels were also compared in both groups.

Results

The mean age of the participants was 50.2±5.7 years. The total participants were 130, of which 77 (59.3%) were females and 53 (40.7%) were males. The numbers of patients having uncontrolled T2DM (HbA1c>7%), and controlled T2DM (HbA1c <7%) were 78 (60%) and 52 (40%), respectively. Moreover, 46 (35.3%) females and 32 (24.7%) males had uncontrolled T2DM, and 31 (23.8%) females and 21 (16.2%) males had controlled T2DM. The mean ALT level for uncontrolled and controlled T2DM in female patients was found to be 24.6±3.4 and 13.5±2.4, respectively, (P <0.05). For male patients, it was found to be 54.0±4.9 and 29.1±5.4, respectively (P=0.008).

Conclusion

There is a positive association between elevated HbA1c and ALT levels in T2DM patients with NAFLD.

Metformin: update on mechanisms of action on liver diseases

Substantial attention has been paid to the various effects of metformin on liver diseases; the liver is the targeted organ where metformin exerts its antihyperglycemic properties. In non-alcoholic fatty liver disease (NAFLD), studies have shown that metformin affects the ATP/AMP ratio to activate AMPK, subsequently governing lipid metabolism. The latest research showed that low-dose metformin targets the lysosomal AMPK pathway to decrease hepatic triglyceride levels through the PEN2-ATP6AP1 axis in an AMP-independent manner. Metformin regulates caspase-3, eukaryotic initiation factor-2a (eIF2a), and insulin receptor substrate-1 (IRS-1) in palmitate-exposed HepG2 cells, alleviating endoplasmic reticulum (ER) stress. Recent observations highlighted the critical association with intestinal flora, as confirmed by the finding that metformin decreased the relative abundance of Bacteroides fragilis while increasing Akkermansia muciniphila and Bifidobacterium bifidum. The suppression of intestinal farnesoid X receptor (FXR) and the elevation of short-chain fatty acids resulted in the upregulation of tight junction protein and the alleviation of hepatic inflammation induced by lipopolysaccharide (LPS). Additionally, metformin delayed the progression of cirrhosis by regulating the activation and proliferation of hepatic stellate cells (HSCs) via the TGF-β1/Smad3 and succinate-GPR91 pathways. In hepatocellular carcinoma (HCC), metformin impeded the cell cycle and enhanced the curative effect of antitumor medications. Moreover, metformin protects against chemical-induced and drug-induced liver injury (DILI) against hepatotoxic drugs. These findings suggest that metformin may have pharmacological efficacy against liver diseases.

Metformin ameliorates liver fibrosis induced by congestive hepatopathy via the mTOR/HIF-1α signaling pathway

INTRODUCTION AND OBJECTIVES

Congestive hepatopathy (CH) is a hepatic vascular disease that results in chronic liver congestion, which can lead to liver fibrosis. New uses of metformin have been discovered over the years. However, the function of metformin in congestive liver fibrosis is not yet fully understood. This study aimed to investigate the effect of metformin on liver fibrosis in a mouse model of CH.

MATERIALS AND METHODS

Partial ligation of the inferior vena cava (pIVCL) was used to establish a mouse model of liver congestion. Metformin (0.1%) was added to the daily drinking water of the animals, and the effect of metformin on liver tissue was studied after 6 weeks. Hepatic stellate cells (HSCs) were also stimulated with CoCl2 to investigate the inhibitory impact of metformin on the mammalian target of rapamycin (mTOR)/hypoxia-inducible factor-1α (HIF-1α) pathway.

RESULTS

Metformin attenuated liver congestion; decreased the expression of collagen, fibronectin, α-smooth muscle actin (α-SMA), and HIF-1α; and ameliorated liver fibrosis in pIVCL mice. The proliferation and migration of HSCs were inhibited by metformin in vitro, which prevented α-SMA expression and restrained HSC activation. The expression levels of phosphorylated-mTOR, HIF-1α, and vascular endothelial growth factor were also decreased.

CONCLUSIONS

Metformin inhibits CH-induced liver fibrosis. Functionally, this beneficial effect may be the result of inhibition of HSC activation and of the mTOR/HIF-1α signaling pathway.

Aerobic exercise and vitamin E improve high-fat diet-induced NAFLD in rats by regulating the AMPK pathway and oxidative stress

BACKGROUND AND AIMS

Non-alcoholic fatty liver disease (NAFLD) has emerged as a major chronic liver disease. We explored simple and effective ways to improve NAFLD and investigate the mechanism of action.

METHODS

NAFLD was induced in 40 rats fed a high-fat diet (HFD). Magnetic resonance imaging was used to evaluate the progression and improvement of NAFLD. The treatment-related interventions included aerobic exercise (E) and vitamin E (VE) supplementation. Expression levels of proteins related to fat metabolism were also assessed. The activities of antioxidant enzymes in the liver and serum lipid metabolism were analyzed using biochemical methods.

RESULTS

Aerobic exercise and vitamin E effectively improved NAFLD in rats, resulting in decreased hepatic fat accumulation, reduced hepatocyte ballooning, and decreased triglyceride levels. Combination therapy achieved the best effect. Both aerobic exercise and vitamin E activate the AMPK pathway to phosphorylate acetyl-CoA carboxylase (ACC) and reduce fatty acid synthesis. The expression of sterol regulatory element-binding protein-1 (SREBP-1) was decreased significantly in the treated groups, particularly in the E + VE + HFD group. The expression of carnitine palmitoyl-transferase 1C (CPT1C) significantly increased in the treated groups, particularly in the E + VE + HFD group. Compared with the control group, reactive oxygen species (ROS) in the E + HFD group were slightly decreased, while that in the VE + HFD group were significantly decreased, with the even greater reduction observed in the E + VE + HFD group.

CONCLUSION

Aerobic exercise and vitamin E supplementation can improve HFD-induced NAFLD in rats by regulating the AMPK pathway and reducing oxidative stress.

Tcf20 deficiency is associated with increased liver fibrogenesis and alterations in mitochondrial metabolism in mice and humans

BACKGROUND & AIMS

Transcription co-activator factor 20 (TCF20) is a regulator of transcription factors involved in extracellular matrix remodelling. In addition, TCF20 genomic variants in humans have been associated with impaired intellectual disability. Therefore, we hypothesized that TCF20 has several functions beyond those described in neurogenesis, including the regulation of fibrogenesis.

METHODS

Tcf20 knock-out (Tcf20-/- ) and Tcf20 heterozygous mice were generated by homologous recombination. TCF20 gene genotyping and expression was assessed in patients with pathogenic variants in the TCF20 gene. Neural development was investigated by immufluorescense. Mitochondrial metabolic activity was evaluated with the Seahorse analyser. The proteome analysis was carried out by gas chromatography mass-spectrometry.

RESULTS

Characterization of Tcf20-/- newborn mice showed impaired neural development and death after birth. In contrast, heterozygous mice were viable but showed higher CCl4 -induced liver fibrosis and a differential expression of genes involved in extracellular matrix homeostasis compared to wild-type mice, along with abnormal behavioural patterns compatible with autism-like phenotypes. Tcf20-/- embryonic livers and mouse embryonic fibroblast (MEF) cells revealed differential expression of structural proteins involved in the mitochondrial oxidative phosphorylation chain, increased rates of mitochondrial metabolic activity and alterations in metabolites of the citric acid cycle. These results parallel to those found in patients with TCF20 pathogenic variants, including alterations of the fibrosis scores (ELF and APRI) and the elevation of succinate concentration in plasma.

CONCLUSIONS

We demonstrated a new role of Tcf20 in fibrogenesis and mitochondria metabolism in mice and showed the association of TCF20 deficiency with fibrosis and metabolic biomarkers in humans.

Protective effects of the succinate/SUCNR1 axis on damaged hepatocytes in NAFLD

OBJECTIVE

Succinate and succinate receptor 1 (SUCNR1) are linked to fibrotic remodeling in models of non-alcoholic fatty liver disease (NAFLD), but whether they have roles beyond the activation of hepatic stellate cells remains unexplored. We investigated the succinate/SUCNR1 axis in the context of NAFLD specifically in hepatocytes.

METHODS

We studied the phenotype of wild-type and Sucnr1^-/- mice fed a choline-deficient high-fat diet to induce non-alcoholic steatohepatitis (NASH), and explored the function of SUCNR1 in murine primary hepatocytes and human HepG2 cells treated with palmitic acid. Lastly, plasma succinate and hepatic SUCNR1 expression were analyzed in four independent cohorts of patients in different NAFLD stages.

RESULTS

Sucnr1 was upregulated in murine liver and primary hepatocytes in response to diet-induced NASH. Sucnr1 deficiency provoked both beneficial (reduced fibrosis and endoplasmic reticulum stress) and detrimental (exacerbated steatosis and inflammation and reduced glycogen content) effects in the liver, and disrupted glucose homeostasis. Studies in vitro revealed that hepatocyte injury increased Sucnr1 expression, which when activated improved lipid and glycogen homeostasis in damaged hepatocytes. In humans, SUCNR1 expression was a good determinant of NAFLD progression to advanced stages. In a population at risk of NAFLD, circulating succinate was elevated in patients with a fatty liver index (FLI) ≥60. Indeed, succinate had good predictive value for steatosis diagnosed by FLI, and improved the prediction of moderate/severe steatosis through biopsy when added to an FLI algorithm.

CONCLUSIONS

We identify hepatocytes as target cells of extracellular succinate during NAFLD progression and uncover a hitherto unknown function for SUCNR1 as a regulator of hepatocyte glucose and lipid metabolism. Our clinical data highlight the potential of succinate and hepatic SUCNR1 expression as markers to diagnose fatty liver and NASH, respectively.

Metformin induces mitochondrial fission and reduces energy metabolism by targeting respiratory chain complex I in hepatic stellate cells to reverse liver fibrosis

The activation and proliferation of hepatic stellate cells (HSCs) are critical processes for the treatment of liver fibrosis. It is necessary to identify effective drugs for the treatment of liver fibrosis and elucidate their mechanisms of action. Metformin can inhibit HSCs; however, no systematic studies demonstrating the effects of metformin on mitochondria in HSCs have been reported. This study demonstrated that metformin induces mitochondrial fission by phosphorylating AMPK/DRP1 (S616) in HSCs to decrease the expression of α-SMA and collagen. Additionally, metformin repressed the total ATP production rate, especially the production rate of ATP produced through mitochondrial oxidative phosphorylation, by inhibiting the enzymatic activity of complex I. Further analysis revealed that metformin strongly constrained the transcription of mitochondrial genes (ND1-ND6 and ND4L) that encode the core subunits of respiratory chain I. Upregulation of the mRNA expression of HK2 and GLUT1 slightly enhanced glycolysis. Additionally, metformin increased mitochondrial DNA (mtDNA) copy number to suppress the proliferation and activation of HSCs, indicating that mtDNA copy number can alter the fate of HSCs. In conclusion, metformin can induce mitochondrial fragmentation and low-level energy metabolism in HSCs, thereby suppressing HSCs activation and proliferation to reverse liver fibrosis.

Metformin Impacts Human Syncytiotrophoblast Mitochondrial Function from Pregnancies Complicated by Obesity and Gestational Diabetes Mellitus in a Sexually Dimorphic Manner

Maternal obesity and gestational diabetes mellitus (GDM) are associated with placental dysfunction, small for gestational age (SGA) offspring, and programming of adult-onset disease. We examine how metformin, commonly used to treat type A2 GDM, affects placental metabolism as well as mitochondrial content and function. Syncytiotrophoblasts (STBs) were prepared from placentas of male and female fetuses collected at term cesarean section from lean (pre-pregnancy BMI < 25), obese (BMI > 30), and obese A2GDM women. Metformin treatment (0.001-10 mM) of STB caused no change in non-mitochondrial respiration but significant concentration-dependent (1 and 10 mM) decreases in basal, maximal, and ATP-linked respiration and spare capacity. Respiration linked to proton leak was significantly increased in STB of male A2GDM placentas at low metformin concentrations. Metformin concentrations ≥1 mM increased glycolysis in STB from placentas from lean women, but only improved glycolytic capacity in female STB. Whereas metformin had little effect on superoxide generation from male STB of any group, it gave a concentration-dependent decrease in superoxide generation from female STB of lean and obese women. Fewer mitochondria were observed in STB from obese women and male STB from lean women with increasing metformin concentration. Metformin affects STB mitochondrial function in a sexually dimorphic manner but at concentrations above those reported in maternal circulation (approximately 0.01 mM) in women treated with metformin for GDM.

Research progress of metformin in the treatment of liver fibrosis

Liver fibrosis is a disease with significant morbidity and mortality. It is a chronic pathological process characterized by an imbalance of extracellular matrix production and degradation in liver tissue. Metformin is a type of hypoglycemic biguanide drug, which can be used in the treatment of liver fibrosis, but its anti-fibrotic effect and mechanism of action are unclear. The purpose of this article is to review the research progress of metformin in the treatment of liver fibrosis and to provide a theoretical basis for its application in the treatment of liver fibrosis.

HBO1 as an Important Target for the Treatment of CCL4-Induced Liver Fibrosis and Aged-Related Liver Aging and Fibrosis

The liver is the largest digestive organ in the human body. The increasing incidence of chronic liver fibrosis is one of the major health challenges in the world. Liver fibrosis is a wound-healing response to acute or chronic cellular damage of liver tissue. At present, despite a series of research progress on the pathophysiological mechanism of fibrosis that has been made, there is still a gap in identifying antifibrotic targets and converting them into effective treatments. Therefore, it is extremely important to seek a molecular target that can alleviate or reverse liver fibrosis, which has important scientific and clinical significance. In the current study, to evaluate the therapeutic effect of HBO1 as a molecular target on liver aging and fibrosis, naturally-aged mice and CCL4-induced liver fibrosis mice were used as animal models, and multiple experiments were performed. Experimental results showed that HBO1 knockdown could strongly mitigate the accumulation of hepatic collagen by Masson and Sirius Red staining. Further study showed that HBO1 knockdown reduced the expression of fibrosis-related marker molecules (α-SMA, collagen type I (ColI), and fibronectin). Further work showed that HBO1 knockdown could significantly alleviate HSC activation. On this basis, we analyzed the underlying mechanism by which HBO1 alleviates liver fibrosis. It was found that HBO1 knockdown may modulate liver fibrosis by regulating the processes of EMT, inflammation, and oxidative stress. We further studied the effect of HBO1 knockdown on liver aging and aging-related liver fibrosis, and the results showed that HBO1 knockdown could significantly reduce the level of aging-related liver fibrosis and relieve liver aging. In conclusion, we systematically investigated the potential of HBO1 as a therapeutic target to attenuate liver fibrosis and liver aging. The current study found a crucial target for liver fibrosis and liver-aging therapy, which has laid a solid foundation for the liver fibrosis-related research.

Advances in metformin for the treatment of non-alcoholic fatty liver disease in children

INTRODUCTION

The increased economic and social burdens for NAFLD worldwide make treating such a disease a significant public health issue. Metformin, a kind of insulin sensitizer generally used to treat type 2 diabetes, has been recently found to have efficacy on children's NAFLD in various areas such as glucolipid metabolism, intestinal bacterial metabolism, oxidative stress, and anti-inflammatory response. This article aims to provide an overview of the possible mechanisms of NAFLD in children and the potential therapeutic application of metformin.

AREAS COVERED

The Cochrane Library, PubMed, Scopus, and EMBASE database was systematically searched on 12 April 2022, using the keywords metformin; non-alcoholic fatty liver disease; and children to identify similar studies. An additional search for recently published research was performed in June 2020.

EXPERT OPINION

Although metformin has been proved to have an excellent therapeutic effect on children's NAFLD; we can still explore its potential impacts and mechanisms from different angles, such as combined medication. At the same time, we should also pay attention to its side effects.

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.

Metformin treatment reverses high fat diet- induced non-alcoholic fatty liver diseases and dyslipidemia by stimulating multiple antioxidant and anti-inflammatory pathways

Purpose

This current study investigated the effect of metformin treatment on hepatic oxidative stress and inflammation associated with nonalcoholic fatty liver disease (NADLD) in high fat diet (HFD) fed rats.

Method

Wistar rats were fed with a HFD or laboratory chow diet for 8 weeks. Metformin was administered orally at a dose of 200 mg/kg. Body weight, food and water intake were recorded on daily basis. Oral glucose tolerance test (OGTT), biochemical analysis and histological examinations were conducted on plasma and tissue samples. Antioxidant and anti-inflammatory mRNA expression was analyzed using reverse transcription polymeric chain reaction (RT-PCR).

Results

Metformin treatment for 8 weeks prevented HFD-induced weight gain and decreased fat deposition in HFD fed rats. Biochemical analysis revealed that metformin treatment significantly attenuated nitro-oxidative stress markers malondialdehyde (MDA), advanced protein oxidation product (APOP), and excessive nitric oxide (NO) levels in the liver of HFD fed rats. Gene expression analysis demonestrated that metformin treatment was associated with an enhanced expression of antioxidant genes such as Nrf-2, HO-1, SOD and catalase in liver of HFD fed rats. Metformin treatment also found to modulate the expression of fat metabolizing and anti-inflammatory genes including PPAR--γ, C/EBP-α, SREBP1c, FAS, AMPK and GLUT-4. Consistent with the biochemical and gene expression data, the histopathological examination unveiled that metformin treatment attenuated inflammatory cells infiltration, steatosis, hepatocyte necrosis, collagen deposition, and fibrosis in the liver of HFD fed rats.

Conclusion

In conclusion, this study suggests that metformin might be effective in the prevention and treatment of HFD-induced steatosis by reducing hepatic oxidative stress and inflammation in the liver.

Foresight regarding drug candidates acting on the succinate-GPR91 signalling pathway for non-alcoholic steatohepatitis (NASH) treatment

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease, and it is a liver manifestation of metabolic syndrome, with a histological spectrum from simple steatosis to non-alcoholic steatohepatitis (NASH). NASH can evolve into progressive liver fibrosis and eventually lead to liver cirrhosis. The pathological mechanism of NASH is multifactorial, involving a series of metabolic disorders and changes that trigger low-level inflammation in the liver and other organs. In the pathogenesis of NASH, the signal transduction pathway involving succinate and the succinate receptor (G-protein-coupled receptor 91, GPR91) regulates inflammatory cell activation and liver fibrosis. This review describes the mechanism of the succinate-GPR91 signalling pathway in NASH and summarizes the drugs that act on this pathway, with the aim of providing a new approach to NASH treatment.

Metformin attenuates the epithelial-mesenchymal transition of lens epithelial cells through the AMPK/TGF-β/Smad2/3 signalling pathway

Posterior capsule opacification (PCO) is a common ocular fibrosis disease related to the epithelial-mesenchymal transition (EMT) of human lens epithelial cells (HLECs). However, safe and effective drugs that prevent or treat PCO are lacking. Metformin (Mtf) has been used to treat fibrosis-related diseases affecting many organs and tissues, but its effect on ocular fibrosis-related diseases is unclear. We investigated whether Mtf can inhibit EMT and fibrosis in HLECs to prevent and treat PCO and elucidated the potential molecular mechanism. Here, we established an HLEC model of TGF-β-induced EMT and found that 400 μM Mtf inhibited vertical and lateral migration and EMT-related gene and protein expression in HLECs. Smad2/3 are downstream molecules of TGF-β that enter the nucleus to regulate EMT-related gene expression during the occurrence and development of PCO. We revealed that Mtf suppressed TGF-β-induced Smad2/3 phosphorylation and nuclear translocation. Mtf induces AMP-activated protein kinase (AMPK) phosphorylation. In this study, we found that Mtf induced the activation of AMPK phosphorylation in HLECs. To further explore the mechanism of Mtf, we pretreated HLECs with Compound C (an AMPK inhibitor) to repeat the above experiments and found that Compound C abolished the inhibitory effect of Mtf on HLEC EMT and the TGF-β/Smad2/3 signalling pathway. Thus, Mtf targets AMPK phosphorylation to inhibit the TGF-β/Smad2/3 signalling pathway and prevent HLEC EMT. Notably, we first illustrated the AMPK/TGF-β/Smad2/3 signalling pathway in HLECs, which may provide a new therapeutic strategy for PCO.

Rethinking succinate: an unexpected hormone-like metabolite in energy homeostasis

There has been an explosion of interest in the signaling capacity of energy metabolites. A prime example is the Krebs cycle substrate succinate, an archetypal respiratory substrate with functions beyond energy production as an intracellular and extracellular signaling molecule. Long associated with inflammation, emerging evidence supports a key role for succinate in metabolic processes relating to energy management. As the natural ligand for SUCNR1, a G protein-coupled receptor, succinate is akin to hormones and likely functions as a reporter of metabolism and stress. In this review, we reconcile new and old observations to outline a regulatory role for succinate in metabolic homeostasis. We highlight the importance of the succinate-SUCNR1 axis in metabolic diseases as an integrator of macrophage immune response, and we discuss new metabolic functions recently ascribed to succinate in specific tissues. Because circulating succinate has emerged as a promising biomarker in chronic metabolic diseases, a better understanding of the physiopathological role of the succinate-SUCNR1 axis in metabolism might open new avenues for clinical use in patients with obesity or diabetes.

Cellular protein markers, therapeutics, and drug delivery strategies in the treatment of diabetes-associated liver fibrosis

Liver fibrosis is the excessive accumulation of extracellular matrix due to chronic injuries, such as viral infection, alcohol abuse, high-fat diet, and toxins. Liver fibrosis is reversible before it progresses to cirrhosis and hepatocellular carcinoma. Type 2 diabetes significantly increases the risk of developing various complications including liver diseases. Abundant evidence suggests that type 2 diabetes and liver diseases are bidirectionally associated. Patients with type 2 diabetes experience more severe symptoms and accelerated progression of live diseases. Obesity and insulin resistance resulting from hyperlipidemia and hyperglycemia are regarded as the two major risk factors that link type 2 diabetes and liver fibrosis. This review summarizes possible mechanisms of the association between type 2 diabetes and liver fibrosis. The cellular protein markers that can be used for diagnosis and therapy of type 2 diabetes-associated liver fibrosis are discussed. We also highlight the potential therapeutic agents and their delivery systems that have been investigated for type 2 diabetes-associated liver fibrosis.

Diabetic fibrosis

Diabetes-associated morbidity and mortality is predominantly due to complications of the disease that may cause debilitating conditions, such as heart and renal failure, hepatic insufficiency, retinopathy or peripheral neuropathy. Fibrosis, the excessive and inappropriate deposition of extracellular matrix in various tissues, is commonly found in patients with advanced type 1 or type 2 diabetes, and may contribute to organ dysfunction. Hyperglycemia, lipotoxic injury and insulin resistance activate a fibrotic response, not only through direct stimulation of matrix synthesis by fibroblasts, but also by promoting a fibrogenic phenotype in immune and vascular cells, and possibly also by triggering epithelial and endothelial cell conversion to a fibroblast-like phenotype. High glucose stimulates several fibrogenic pathways, triggering reactive oxygen species generation, stimulating neurohumoral responses, activating growth factor cascades (such as TGF-β/Smad3 and PDGFs), inducing pro-inflammatory cytokines and chemokines, generating advanced glycation end-products (AGEs) and stimulating the AGE-RAGE axis, and upregulating fibrogenic matricellular proteins. Although diabetes-activated fibrogenic signaling has common characteristics in various tissues, some organs, such as the heart, kidney and liver develop more pronounced and clinically significant fibrosis. This review manuscript summarizes current knowledge on the cellular and molecular pathways involved in diabetic fibrosis, discussing the fundamental links between metabolic perturbations and fibrogenic activation, the basis for organ-specific differences, and the promises and challenges of anti-fibrotic therapies for diabetic patients.

Metformin Inhibits Transforming Growth Factor β-Induced Fibrogenic Response of Human Dermal Fibroblasts and Suppresses Fibrosis in Keloid Spheroids

ABSTRACT

Accumulation of excessive extracellular matrix (ECM) and aberrant transforming growth factor β (TGF-β) signaling pathway function can be potential therapeutic targets for keloid treatment. In this study, we examined the antifibrotic effect of metformin as a suppressor of TGF-β signaling pathways in human dermal fibroblasts (HDFs) and keloid spheroids. Human dermal fibroblasts were stimulated with TGF-β (10 ng/mL) and treated with metformin (10 mM). The mRNA and protein expression of ECM components were evaluated by quantitative polymerase chain reaction, western blot, and immunofluorescence assay. In addition, we immunohistochemically examined the expression levels of ECM proteins in keloid spheroids. After addition of metformin (10 mM), collagen types I and III and elastin mRNA levels were significantly decreased in HDFs, and collagen type I protein level was significantly decreased. In addition, the expression levels of collagen types I and III, fibronectin, and elastin were significantly reduced in keloid spheroids after treatment with metformin (100 mM). Collagen types I and III and p-Smad2/3 complex proteins were decreased in metformin-treated keloid spheroids. These findings indicated that metformin inhibits the expression of ECM components in TGF-β-stimulated HDFs and keloid spheroids. Therefore, we suggest the potential of metformin as an effective agent for the treatment of keloids.

Role of G Protein-Coupled Receptors in Hepatic Stellate Cells and Approaches to Anti-Fibrotic Treatment of Non-Alcoholic Fatty Liver Disease

The prevalence of non-alcoholic fatty liver disease (NAFLD) is globally increasing. Gaining control over disease-related events in non-alcoholic steatohepatitis (NASH), an advanced form of NAFLD, is currently an unmet medical need. Hepatic fibrosis is a critical prognostic factor in NAFLD/NASH. Therefore, a better understanding of the pathophysiology of hepatic fibrosis and the development of related therapies are of great importance. G protein-coupled receptors (GPCRs) are cell surface receptors that mediate the function of a great variety of extracellular ligands. GPCRs represent major drug targets, as indicated by the fact that about 40% of all drugs currently used in clinical practice mediate their therapeutic effects by acting on GPCRs. Like many other organs, various GPCRs play a role in regulating liver function. It is predicted that more than 50 GPCRs are expressed in the liver. However, our knowledge of how GPCRs regulate liver metabolism and fibrosis in the different cell types of the liver is very limited. In particular, a better understanding of the role of GPCRs in hepatic stellate cells (HSCs), the primary cells that regulate liver fibrosis, may lead to the development of drugs that can improve hepatic fibrosis in NAFLD/NASH. In this review, we describe the functions of multiple GPCRs expressed in HSCs, their roles in liver fibrogenesis, and finally speculate on the development of novel treatments for NAFLD/NASH.

Metformin and Fibrosis: A Review of Existing Evidence and Mechanisms

Fibrosis is a physiological response to organ injury and is characterized by the excessive deposition of connective tissue components in an organ, which results in the disruption of physiological architecture and organ remodeling, ultimately leading to organ failure and death. Fibrosis in the lung, kidney, and liver accounts for a substantial proportion of the global burden of disability and mortality. To date, there are no effective therapeutic strategies for controlling fibrosis. A class of metabolically targeted chemicals, such as adenosine monophosphate-activated protein kinase (AMPK) activators and peroxisome proliferator-activated receptor (PPAR) agonists, shows strong potential in fighting fibrosis. Metformin, which is a potent AMPK activator and is the only recommended first-line drug for the treatment of type 2 diabetes, has emerged as a promising method of fibrosis reduction or reversion. In this review, we first summarize the key experimental and clinical studies that have specifically investigated the effects of metformin on organ fibrosis. Then, we discuss the mechanisms involved in mediating the antifibrotic effects of metformin in depth.

Succinate Receptor 1: An Emerging Regulator of Myeloid Cell Function in Inflammation

The rapidly evolving area of immunometabolism has shed new light on the fundamental properties of products and intermediates of cellular metabolism (metabolites), highlighting their key signaling roles in cell-to-cell communication. Recent evidence identifies the succinate-succinate receptor 1 (SUCNR1) axis as an essential regulator of tissue homeostasis. Succinate signaling via SUCNR1 guides divergent responses in immune cells, which are tissue and context dependent. Herein, we explore the main cellular pathways regulated by the succinate-SUCNR1 axis and focus on the biology of SUCNR1 and its roles influencing the function of myeloid cells. Hence, we identify new therapeutic targets and putative therapeutic approaches aimed at resolving detrimental myeloid cell responses in tissues, including those occurring in the persistently inflamed central nervous system (CNS).

Pathophysiological mechanisms underlying MAFLD

BACKGROUND AND AIMS

The pathophysiology underlying metabolic associated fatty liver disease (MAFLD) involves a multitude of interlinked processes, including insulin resistance (IR) underlying the metabolic syndrome, lipotoxicity attributable to the accumulation of toxic lipid species, infiltration of proinflammatory cells causing hepatic injury and ultimately leading to hepatic stellate cell (HSC) activation and fibrogenesis. The proximal processes, such as IR, lipid overload and lipotoxicity are relatively well established, but the downstream molecular mechanisms, such as inflammatory processes, hepatocyte lipoapoptosis, and fibrogenesis are incompletely understood.

METHODS

A literature search was performed with Medline (PubMed), Scopus and Google Scholar electronic databases till June 2020, using relevant keywords (nonalcoholic fatty liver disease; metabolic associated fatty liver disease; nonalcoholic steatohepatitis; NASH pathogenesis) to extract relevant studies describing pathogenesis of MAFLD/MASH.

RESULTS

Several studies have reported new concepts underlying pathophysiology of MAFLD. Activation of HSCs is the common final pathway for diverse signals from damaged hepatocytes and proinflammatory cells. Activated HSCs then secrete excess extracellular matrix (ECM) which accumulates and impairs structure and function of the liver. TAZ (a transcriptional regulator), hedgehog (HH) ligands, transforming growth factor-β (TGF-β), bone morphogenetic protein 8B (BMP8B) and osteopontin play important roles in activating these HSCs. Dysfunctional gut microbiome, dysregulated bile acid metabolism, endogenous alcohol production, and intestinal fructose handling, modify individual susceptibility to MASH.

CONCLUSIONS

Newer concepts of pathophysiology underlying MASH, such as TAZ/Ihh pathway, extracellular vesicles, microRNA, dysfunctional gut microbiome and intestinal fructose handling present promising targets for the development of therapeutic agents.

Metformin: Sentinel of the Epigenetic Landscapes That Underlie Cell Fate and Identity

The biguanide metformin is the first drug to be tested as a gerotherapeutic in the clinical trial TAME (Targeting Aging with Metformin). The current consensus is that metformin exerts indirect pleiotropy on core metabolic hallmarks of aging, such as the insulin/insulin-like growth factor 1 and AMP-activated protein kinase/mammalian Target Of Rapamycin signaling pathways, downstream of its primary inhibitory effect on mitochondrial respiratory complex I. Alternatively, but not mutually exclusive, metformin can exert regulatory effects on components of the biologic machinery of aging itself such as chromatin-modifying enzymes. An integrative metabolo-epigenetic outlook supports a new model whereby metformin operates as a guardian of cell identity, capable of retarding cellular aging by preventing the loss of the information-theoretic nature of the epigenome. The ultimate anti-aging mechanism of metformin might involve the global preservation of the epigenome architecture, thereby ensuring cell fate commitment and phenotypic outcomes despite the challenging effects of aging noise. Metformin might therefore inspire the development of new gerotherapeutics capable of preserving the epigenome architecture for cell identity. Such gerotherapeutics should replicate the ability of metformin to halt the erosion of the epigenetic landscape, mitigate the loss of cell fate commitment, delay stochastic/environmental DNA methylation drifts, and alleviate cellular senescence. Yet, it remains a challenge to confirm if regulatory changes in higher-order genomic organizers can connect the capacity of metformin to dynamically regulate the three-dimensional nature of epigenetic landscapes with the 4th dimension, the aging time.

Metformin arrests the progression of established kidney disease in the subtotal nephrectomy model of chronic kidney disease

Metformin, an AMP-activated protein kinase (AMPK) activator, has been shown in previous studies to reduce kidney fibrosis in different models of experimental chronic kidney disease (CKD). However, in all of these studies, the administration of metformin was initiated before the establishment of renal disease, which is a condition that does not typically occur in clinical settings. The aim of the present study was to investigate whether the administration of metformin could arrest the progression of established renal disease in a well-recognized model of CKD, the subtotal kidney nephrectomy (Nx) model. Adult male Munich-Wistar rats underwent either Nx or sham operations. After the surgery (30 days), Nx rats that had systolic blood pressures of >170 mmHg and albuminuria levels of >40 mg/24 h were randomized to a no-treatment condition or to a treatment condition with metformin (300 mg·kg−1·day−1) for a period of either 60 or 120 days. After 60 days of treatment, we did not observe any differences in kidney disease parameters between Nx metformin-treated and untreated rats. However, after 120 days, Nx rats that had been treated with metformin displayed significant reductions in albuminuria levels and in markers of renal fibrosis. These effects were independent of any other effects on blood pressure or glycemia. In addition, treatment with metformin was also able to activate kidney AMPK and therefore improve mitochondrial biogenesis. It was concluded that metformin can arrest the progression of established kidney disease in the Nx model, likely via the activation of AMPK.

Epigenetic silencing of LncRNA ANRIL enhances liver fibrosis and HSC activation through activating AMPK pathway

Long non‐coding RNAs (LncRNAs) and DNA methylation are important epigenetic mark play a key role in liver fibrosis. Currently, how DNA methylation and LncRNAs control the hepatic stellate cell (HSC) activation and fibrosis has not yet been fully characterized. Here, we explored the role of antisense non‐coding RNA in the INK4 locus (ANRIL) and DNA methylation in HSC activation and fibrosis. The expression levels of DNA methyltransferases 3A (DNMT3A), ANRIL, α‐Smooth muscle actin (α‐SMA), Type I collagen (Col1A1), adenosine monophosphate‐activated protein kinase (AMPK) and p‐AMPK in rat and human liver fibrosis were detected by immunohistochemistry, qRT‐PCR and Western blotting. Liver tissue histomorphology was examined by haematoxylin and eosin (H&E), Sirius red and Masson staining. HSC was transfected with DNMT3A‐siRNA, over‐expressing ANRIL and down‐regulating ANRIL. Moreover, cell proliferation ability was examined by CCK‐8, MTT and cell cycle assay. Here, our study demonstrated that ANRIL was significantly decreased in activated HSC and liver fibrosis tissues, while Col1A1, α‐SMA and DNMT3A were significantly increased in activated HSC and liver fibrosis tissues. Further, we found that down‐regulating DNMT3A expression leads to inhibition of HSC activation. Reduction in DNMT3A elevated ANRIL expression in activated HSC. Furthermore, we performed the over expression ANRIL suppresses HSC activation and AMPK signalling pathways. In sum, our study found that epigenetic DNMT3A silencing of ANRIL enhances liver fibrosis and HSC activation through activating AMPK pathway. Targeting epigenetic modulators DNMT3A and ANRIL, and offer a novel approach for liver fibrosis therapy.

Gut microbiota-derived succinate: Friend or foe in human metabolic diseases?

There is now a wealth of evidence showing that communication between microbiota and the host is critical to sustain the vital functions of the healthy host, and disruptions of this homeostatic coexistence are known to be associated with a range of diseases including obesity and type 2 diabetes. Microbiota-derived metabolites act both as nutrients and as messenger molecules and can signal to distant organs in the body to shape host pathophysiology. In this review, we provide a new perspective on succinate as a gut microbiota-derived metabolite with a key role governing intestinal homeostasis and energy metabolism. Thus, succinate is not merely a major intermediary of the TCA traditionally considered as an extracellular danger signal in the host, but also a by-product of some bacteria and a primary cross-feeding metabolite between gut resident microbes. In addition to maintain a healthy microbiome, specific functions of microbiota-derived succinate in peripheral tissues regulating host nutrient metabolism should not be rule out. Indeed, recent research point to some probiotic interventions directed to modulate succinate levels in the intestinal lumen, as a new microbiota-based therapies to treat obesity and related co-morbidities. While further research is essential, a large body of evidence point to succinate as a new strategic mediator in the microbiota-host cross-talk, which might provide the basis for new therapeutically approaches in a near future.

TGF-β in Hepatic Stellate Cell Activation and Liver Fibrogenesis-Updated 2019

Liver fibrosis is an advanced liver disease condition, which could progress to cirrhosis and hepatocellular carcinoma. To date, there is no direct approved antifibrotic therapy, and current treatment is mainly the removal of the causative factor. Transforming growth factor (TGF)-β is a master profibrogenic cytokine and a promising target to treat fibrosis. However, TGF-β has broad biological functions and its inhibition induces non-desirable side effects, which override therapeutic benefits. Therefore, understanding the pleiotropic effects of TGF-β and its upstream and downstream regulatory mechanisms will help to design better TGF-β based therapeutics. Here, we summarize recent discoveries and milestones on the TGF-β signaling pathway related to liver fibrosis and hepatic stellate cell (HSC) activation, emphasizing research of the last five years. This comprises impact of TGF-β on liver fibrogenesis related biological processes, such as senescence, metabolism, reactive oxygen species generation, epigenetics, circadian rhythm, epithelial mesenchymal transition, and endothelial-mesenchymal transition. We also describe the influence of the microenvironment on the response of HSC to TGF-β. Finally, we discuss new approaches to target the TGF-β pathway, name current clinical trials, and explain promises and drawbacks that deserve to be adequately addressed.

MicroRNA-29a Disrupts DNMT3b to Ameliorate Diet-Induced Non-Alcoholic Steatohepatitis in Mice

MicroRNA-29 (miR-29) has been found to reduce liver inflammation and fibrosis following a liver injury. Meanwhile, DNA methyltransferase has been reported to participate in the development of non-alcoholic steatohepatitis (NASH). The aim of this study is to investigate the miR-29a regulation of methyltransferase signaling and epigenetic program in NASH progression. Methods: miR-29a transgenic mice (miR-29aTg mice) and wild-type littermates were subjected to the methionine-choline-deficient (MCD) diet-induced animal model of NASH. Primary hepatic stellate cells were transfected with a miR-29a mimic and antisense inhibitor. We then analyzed gene expressions with qRT-PCR, immunohistochemical stain, Western blot, and luciferase reporter assay. The results demonstrated that increased miR-29a alleviated the MCD diet-induced body weight loss and steatosis and decreased aspartate aminotransferase (AST) levels in mice. Furthermore, hepatic tissue in miR-29aTg mice displayed a weak fibrotic matrix, as shown with Sirius Red staining concomitant with low fibrotic α-SMA expression within affected tissues compared to the wild-type mice fed the MCD diet. Forced miR-29a expression reduced the MCD diet exaggeration of reactive oxygen species (ROS) production by immunohistochemically staining 8-OHdG. Increased miR-29a signaling also resulted in the downregulation of DNMT3b, TGF-β, IL-6, heme oxygenase-1 (HO-1), p-SMAD3, PI3K, and L3BII expression within the liver tissue. An in vitro luciferase reporter assay further confirmed that miR-29a mimic transfection reduced DNMT3b expression in primary HSCs. Our data provide new insights that miR-29a improves MCD diet-induced liver inflammation, steatosis and fibrosis, and highlight the potential of miR-29a targeted therapy for treating NASH.

Chemokine (C-C motif) ligand 2 gene ablation protects low-density lipoprotein and paraoxonase-1 double deficient mice from liver injury, oxidative stress and inflammation

The risk of non-alcoholic fatty liver disease increases with obesity. Vulnerability to oxidative stress and/or inflammation represents a crucial step in non-alcoholic fatty liver disease progression through abnormal metabolic responses. In this study, we investigated the role of CCL2 gene ablation in mice that were double deficient in low density lipoprotein receptor and in paraoxonase-1. Mass spectrometry methods were used to assess the liver metabolic response in mice fed either regular chow or a high-fat diet. Dietary fat caused liver steatosis, oxidative stress and the accumulation of pro-inflammatory macrophages in the livers of double deficient mice. We observed alterations in energy metabolism-related pathways and in metabolites associated with the methionine cycle and the glutathione reduction pathway. This metabolic response was associated with impaired autophagy. Conversely, when we established CCL2 deficiency, histologic features of fatty liver disease were abrogated, hepatic liver oxidative stress decreased, and anti-inflammatory macrophage marker expression levels increased. These changes were associated with the normalization of metabolic disturbances and increased lysosome-associated membrane protein 2, expression, which suggests enhanced chaperone-mediated autophagy. This study demonstrates that CCL2 is a key molecule for the development of metabolic and histological alterations in the liver of mice sensitive to the development of hyperlipidemia and hepatic steatosis, a finding with potential to identify new therapeutic targets in liver diseases.

Paradoxical Roles of Oxidative Stress Response in the Digestive System before and after Carcinogenesis

Oxidative stress is recognized as a cancer-initiating stress response in the digestive system. It is produced through mitochondrial respiration and induces DNA damage, resulting in cancer cell transformation. However, recent findings indicate that oxidative stress is also a necessary anticancer response for destroying cancer cells. The oxidative stress response has also been reported to be an important step in increasing the anticancer response of newly developed molecular targeted agents. Oxidative stress might therefore be a cancer-initiating response that should be downregulated in the precancerous stage in patients at risk of cancer but an anticancer cell response that should not be downregulated in the postcancerous stage when cancer cells are still present. Many commercial antioxidant agents are marketed as “cancer-eliminating agents” or as products to improve one’s health, so cancer patients often take these antioxidant agents. However, care should be taken to avoid harming the anticancerous oxidative stress response. In this review, we will highlight the paradoxical effects of oxidative stress and antioxidant agents in the digestive system before and after carcinogenesis.

The mitochondria in lung fibrosis: friend or foe?

Idiopathic pulmonary fibrosis (IPF) and other forms of lung fibrosis are age-associated diseases with increased deposition of mesenchymal collagen that promotes respiratory malfunction and eventual death from respiratory failure. Our understanding of the pathobiology underlying pulmonary fibrosis is incomplete and current therapies available to slow or treat lung fibrosis are limited. Evidence reviewed herein demonstrates key involvement of mitochondrial dysfunction in diverse pulmonary cell populations, including alveolar epithelial cells (AEC), fibroblasts, and macrophages and/or immune cells that collectively advances the development of pulmonary fibrosis. The mitochondria have an important role in regulating whether fibrogenic stimuli results in the return of normal healthy function ("friend") or the development of pulmonary fibrosis ("foe"). In particular, we summarize the evidence suggesting that AEC mitochondrial dysfunction is important in mediating lung fibrosis signaling via mechanisms involving imbalances in the levels of reactive oxygen species, endoplasmic reticulum stress response, mitophagy, apoptosis and/or senescence, and inflammatory signaling. Further, we review the emerging evidence suggesting that dysfunctional mitochondria in AECs and other cell types play crucial roles in modulating nearly all aspects of the 9 hallmarks of aging in the context of pulmonary fibrosis as well as some novel molecular pathways that have recently been identified. Finally, we discuss the potential translational aspects of these studies as well as the key knowledge gaps necessary for better informing our understanding of the pathobiology of the mitochondria in mediating pulmonary fibrosis. We reason that targeting deficient mitochondria-derived pathways may provide innovative future treatment strategies that are urgently needed for lung fibrosis.

Curcumin inhibits hepatic stellate cell activation via suppression of succinate-associated HIF-1α induction

PURPOSE

Aberrant succinate accumulation emerges as a unifying mechanism for inflammation and oxidative stress. This study aims to investigate whether curcumin ameliorates hepatic fibrosis via blocking succinate signaling.

METHODS

We investigated the effects of curcumin on hepatic succinate accumulation and liver fibrosis in mice fed a high-fat diet (HFD). Meanwhile, we stimulated mouse primary hepatic stellate cells (HSCs) with succinate and observed the inhibitory effects of curcumin on succinate signaling.

RESULTS

Oral administration of curcumin and metformin combated mitochondrial fatty acid oxidation and reduced hepatic succinate accumulation due to the inhibition of succinate dehydrogenase (SDH) activity and demonstrated inhibitory effect on hepatic fibrosis. In mouse primary HSCs, curcumin prevented succinate- and CoCl₂-induced hypoxia-inducible transcription factor-1α (HIF-1α) induction via suppression of ROS production and effectively reduced gene expressions of Col1α, Col3α, fibronectin and TGF-β1 with inflammation inhibition. Knockdown of HIF-1α with small interfering RNA blocked the action of succinate to induce HSCs activation, indicative of the essential role of HIF-1α in succinate signaling.

CONCLUSIONS

Hepatic succinate accumulation served as a metabolic signal to promote liver fibrosis through HIF-1α induction. Curcumin reduced succinate accumulation by combating fatty acid oxidation and prevented HSCs activation by blocking succinate/HIF-1α signaling pathway.

Role of Metabolism in Hepatic Stellate Cell Activation and Fibrogenesis

Activation of hepatic stellate cell (HSC) involves the transition from a quiescent to a proliferative, migratory, and fibrogenic phenotype (i.e., myofibroblast), which is characteristic of liver fibrogenesis. Multiple cellular and molecular signals which contribute to HSC activation have been identified. This review specially focuses on the metabolic changes which impact on HSC activation and fibrogenesis.

Beneficial and Paradoxical Roles of Anti-Oxidative Nutritional Support for Non-Alcoholic Fatty Liver Disease

Oxidative stress is being recognized as a key factor in the progression of chronic liver disease (CLD), especially non-alcoholic fatty liver disease (NAFLD). Many NAFLD treatment guidelines recommend the use of antioxidants, especially vitamin E. Many prospective studies have described the beneficial effects of such agents for the clinical course of NAFLD. However, as these studies are usually short-term evaluations, lasting only a few years, whether or not antioxidants continue to exert favorable long-term effects, including in cases of concomitant hepatocellular carcinoma, remains unclear. Antioxidants are generally believed to be beneficial for human health and are often commercially available as health-food products. Patients with lifestyle-related diseases often use such products to try to be healthier without practicing lifestyle intervention. However, under some experimental NAFLD conditions, antioxidants have been shown to encourage the progression of hepatocellular carcinoma, as oxidative stress is toxic for cancer cells, just as for normal cells. In this review, we will highlight the paradoxical effects of antioxidants against NAFLD and related hepatocellular carcinoma.

Succinate as a Regulator of Hepatic Stellate Cells in Liver Fibrosis

The rapid increase of obesity rates worldwide is associated with chronic liver injury due to non-alcoholic fatty liver disease and non-alcoholic steatohepatitis. Chronic liver inflammation drives hepatic fibrosis, which is a highly conserved and coordinated protective response to tissue injury, and is a reversible process. Hepatocytes, immune cells, and hepatic stellate cells (HSCs) have been identified as key players in the mechanisms of hepatic fibrosis and inflammation. During the last decade, succinate, an intermediate of the tricarboxylic acid cycle in mitochondrial ATP production, has emerged as an important signaling molecule in various diseases. Succinate acts as an extracellular ligand for G-protein coupled receptor 91, also known as succinate receptor 1, which is mainly expressed in the kidney, heart, liver, immune cells, and retinal cells, suggesting a widespread function in cellular metabolism. Furthermore, succinate stabilizes hypoxia-inducible factor-1α in immune cells and tumors as a signaling molecule, and has been shown to post-translationally modify proteins. This review summarizes the recent evidence pointing to an additional role of succinate in profibrotic signaling, along with its downstream signaling pathways, and updates the current state of knowledge on the role of succinate in liver fibrosis through its action on HSCs. Further focus on this link can help identify succinate, its receptor, and its downstream signaling molecules as new targets for the treatment of liver fibrosis.