The Role of NADPH Oxidases (NOXs) in Liver Fibrosis and the Activation of Myofibroblasts

The effect of saraglitazar on TGF-β-induced smad3 phosphorylation and expression of genes related to liver fibrosis in LX2 cell line

BACKGROUND AND PURPOSE

Liver fibrosis is a reversible liver injury that occurs as a result of many chronic inflammatory diseases and can lead to cirrhosis, which is irreversible and fatal. So, we studied the anti-fibrotic effects of saroglitazar on LX-2 cell lines, as a dual PPARα/γ agonist.

METHODS

Cells, after 80% confluence, were treated with TGF-β (2 ng/mL) for 24 h. Then cells were treated with saroglitazar at different doses (2.5, 5, 10 µM) for 24 h. After same incubation, the cells of control group, TGF-β group, and TGF-β + saroglitazar group were harvested for RNA and protein extraction to determine the effects of saroglitazar. RT-PCR and western blot methods were used to express genes related to fibrosis.

RESULTS

Our results show that the relative expression of α-SMA, collagen1α, N-cadherin, NOX (1, 2, and 4), and phosphorylated Smad3 protein was significantly higher in TGF-β-treated cells compared with the normal group, and E-cadherin expression was decreased in TGF-β-treated cells. After TGF-β-treated cells were exposed to saroglitazar, the expression of these genes was significantly reversed (P < 0.05).

CONCLUSIONS

Our results clearly show the short-term inhibitory role of saroglitazar in the expression of fibrotic factors using the TGF-β/Smad signaling pathway. These results suggest that saroglitazar can be considered as a suitable therapeutic strategy for fibrotic patients. Although more studies are needed.

Mitochondrial reactive oxygen species impact human fibroblast responses to protracted γ-ray exposures

Purpose: Continuous exposure to ionizing radiation at a low dose rate poses significant health risks to humans on deep space missions, prompting the need for mechanistic studies to identify countermeasures against its deleterious effects. Mitochondria are a major subcellular locus of radiogenic injury, and may trigger secondary cellular responses through the production of reactive oxygen species (mtROS) with broader biological implications. Methods and Materials: To determine the contribution of mtROS to radiation-induced cellular responses, we investigated the impacts of protracted γ-ray exposures (IR; 1.1 Gy delivered at 0.16 mGy/min continuously over 5 days) on mitochondrial function, gene expression, and the protein secretome of human HCA2-hTERT fibroblasts in the presence and absence of a mitochondria-specific antioxidant mitoTEMPO (MT; 5 µM). Results: IR increased fibroblast mitochondrial oxygen consumption (JO2) and H2O2 release rates (JH2O2) under energized conditions, which corresponded to higher protein expression of NADPH Oxidase (NOX) 1, NOX4, and nuclear DNA-encoded subunits of respiratory chain Complexes I and III, but depleted mtDNA transcripts encoding subunits of the same complexes. This was associated with activation of gene programs related to DNA repair, oxidative stress, and protein ubiquination, all of which were attenuated by MT treatment along with radiation-induced increases in JO2 and JH2O2. IR also increased secreted levels of interleukin-8 and Type I collagens, while decreasing Type VI collagens and enzymes that coordinate assembly and remodeling of the extracellular matrix. MT treatment attenuated many of these effects while augmenting others, revealing complex effects of mtROS in fibroblast responses to IR. Conclusion: These results implicate mtROS production in fibroblast responses to protracted radiation exposure, and suggest potentially protective effects of mitochondrial-targeted antioxidants against radiogenic tissue injury in vivo.

NADPH oxidase 1 promotes hepatic steatosis in obese mice and is abrogated by augmented skeletal muscle mass

Exercise as a lifestyle modification is a frontline therapy for nonalcoholic fatty liver disease (NAFLD), but how components of exercise attenuate steatosis is unclear. To uncouple the effect of increased muscle mass from weight loss in obesity, myostatin knockout mice were bred on a lean and obese db/db background. Myostatin deletion increases gastrocnemius (Gastrocn.) mass and reduces hepatic steatosis and hepatic sterol regulatory element binding protein 1 (Srebp1) expression in obese mice, with no impact on adiposity or body weight. Interestingly, hypermuscularity reduces hepatic NADPH oxidase 1 (Nox1) expression but not NADPH oxidase 4 (Nox4) in db/db mice. To evaluate a deterministic function of Nox1 on steatosis, Nox1 knockout mice were bred on a lean and db/db background. NOX1 deletion significantly attenuates hepatic oxidant stress, steatosis, and Srebp1 programming in obese mice to parallel hypermuscularity, with no improvement in adiposity, glucose control, or hypertriglyceridemia to suggest off-target effects. Directly assessing the role of NOX1 on SREBP1, insulin (Ins)-mediated SREBP1 expression was significantly increased in either NOX1, NADPH oxidase organizer 1 (NOXO1), and NADPH oxidase activator 1 (NOXA1) or NOX5-transfected HepG2 cells versus ?-galactosidase control virus, indicating superoxide is the key mechanistic agent for the actions of NOX1 on SREBP1. Metabolic Nox1 regulators were evaluated using physiological, genetic, and diet-induced animal models that modulated upstream glucose and insulin signaling, identifying hyperinsulinemia as the key metabolic derangement explaining Nox1-induced steatosis in obesity. GEO data revealed that hepatic NOX1 predicts steatosis in obese humans with biopsy-proven NAFLD. Taken together, these data suggest that hypermuscularity attenuates Srebp1 expression in db/db mice through a NOX1-dependent mechanism.NEW & NOTEWORTHY This study documents a novel mechanism by which changes in body composition, notably increased muscle mass, protect against fatty liver disease. This mechanism involves NADPH oxidase 1 (NOX1), an enzyme that increases superoxide and increases insulin signaling, leading to increased fat accumulation in the liver. NOX1 may represent a new early target for preventing fatty liver to stave off later liver diseases such as cirrhosis or liver cancer.

Mitochondrial quality control in liver fibrosis: Epigenetic hallmarks and therapeutic strategies

BACKGROUND AND AIM

Mitochondrial quality control (MQC) plays a significant role in the progression of liver fibrosis, with key processes such as mitochondrial fission, fusion, mitophagy and biogenesis maintaining mitochondrial homeostasis. To understand the molecular mechanisms underlying epigenetic regulation of mitochondrial quality control in liver fibrosis, with the aim of uncovering novel therapeutic targets for treating, mitigating, and potentially reversing liver fibrosis, in light of the most recent advances in this field.

METHODS

We searched PubMed, Web of Science, and Scopus for published manuscripts using terms "mitochondrial quality control" "mitochondrial fission" "mitochondrial fusion" "mitochondrial biogenesis" "mitophagy" "liver fibrosis" "epigenetic regulation" "DNA methylation" "RNA methylation" "histone modification" and "non-coding RNA". Manuscripts were collated, studied and carried forward for discussion where appropriate.

RESULTS

Mitochondrial fission, fusion, biogenesis, and mitophagy regulate the homeostasis of mitochondria, and the imbalance of mitochondrial homeostasis can induce liver fibrosis. Epigenetic regulation, including DNA methylation, RNA methylation, histone modifications, and non-coding RNAs, plays a significant role in regulating the processes of mitochondrial homeostasis.

CONCLUSION

Mitochondrial quality control and epigenetic mechanisms are intricately linked to the pathogenesis of liver fibrosis. Understanding these molecular interactions provides insight into potential therapeutic strategies. Further research is necessary to translate these findings into clinical applications, with a focus on developing epigenetic drugs to ameliorate liver fibrosis by modulating MQC and epigenetic pathways.

Roles of oxidative stress/JNK/ERK signals in paraquat-triggered hepatic apoptosis

Paraquat (PQ), a toxic and nonselective bipyridyl herbicide, is one of the most extensively used pesticides in agricultural countries. In addition to pneumotoxicity, the liver is an important target organ for PQ poisoning in humans. However, the mechanism of PQ in hepatotoxicity remains unclear. In this study, we found that exposure of rat hepatic H4IIE cells to PQ (0.1-2 mM) induced significant cytotoxicity and apoptosis, which was accompanied by mitochondria-dependent apoptotic signals, including loss of mitochondrial membrane potential (MMP), cytosolic cytochrome c release, and changes in the Bcl-2/Bax mRNA ratio. Moreover, PQ (0.5 mM) exposure markedly induced JNK and ERK1/2 activation, but not p38-MAPK. Blockade of JNK and ERK1/2 signaling by pretreatment with the specific pharmacological inhibitors SP600125 and PD98059, respectively, effectively prevented PQ-induced cytotoxicity, mitochondrial dysfunction, and apoptotic events. Additionally, PQ exposure stimulated significant oxidative stress-related signals, including reactive oxygen species (ROS) generation and intracellular glutathione (GSH) depletion, which could be reversed by the antioxidant N-Acetylcysteine (NAC). Buffering the oxidative stress response with NAC also effectively abrogated PQ-induced hepatotoxicity, MMP loss, apoptosis, and phosphorylation of JNK and ERK1/2 protein, however, the JNK or ERK inhibitors did not suppress ROS generation in PQ-treated cells. Collectively, these results demonstrate that PQ exposure induces hepatic cell toxicity and death via an oxidative stress-dependent JNK/ERK activation-mediated downstream mitochondria-regulated apoptotic pathway.

Iron, Oxidative Stress, and Metabolic Dysfunction-Associated Steatotic Liver Disease

Excess free iron is a substrate for the formation of reactive oxygen species (ROS), thereby augmenting oxidative stress. Oxidative stress is a well-established cause of organ damage in the liver, the main site of iron storage. Ferroptosis, an iron-dependent mechanism of regulated cell death, has recently been gaining attention in the development of organ damage and the progression of liver disease. We therefore summarize the main mechanisms of iron metabolism, its close connection to oxidative stress and ferroptosis, and its particular relevance to disease mechanisms in metabolic-dysfunction-associated fatty liver disease and potential targets for therapy from a clinical perspective.

Kindlin-2 maintains liver homeostasis by regulating GSTP1-OPN-mediated oxidative stress and inflammation in mice

Hepatocyte plays a principal role in preserving integrity of the liver homeostasis. Our recent study demonstrated that Kindlin-2, a focal adhesion protein that activates integrins and regulates cell-extracellular matrix interactions, plays an important role in regulation of liver homeostasis by inhibiting inflammation pathway; however, the molecular mechanism of how Kindlin-2 KO activates inflammation is unknown. Here, we show that Kindlin-2 loss largely downregulates the antioxidant glutathione-S-transferase P1 in hepatocytes by promoting its ubiquitination and degradation via a mechanism involving protein-protein interaction. This causes overproduction of intracellular reactive oxygen species and excessive oxidative stress in hepatocytes. Kindlin-2 loss upregulates osteopontin in hepatocytes partially because of upregulation of reactive oxygen species and consequently stimulates overproduction of inflammatory cytokines and infiltration in liver. The molecular and histological deteriorations caused by Kindlin-2 deficiency are markedly reversed by systemic administration of an antioxidant N-acetylcysteine in mice. Taken together, Kindlin-2 plays a pivotal role in preserving integrity of liver function.

Combined quercetin and simvastatin attenuate hepatic fibrosis in rats by modulating SphK1/NLRP3 pathways

Liver fibrosis involves several signalling pathways working in concert regulating the deposition of extracellular matrix. In this study, we evaluated the effect of quercetin and simvastatin alone and their combination on the treatment of experimentally induced hepatic fibrosis in rats. To decipher the potential mechanisms involved, liver fibrosis was induced in rats by administration of 40 % carbon tetrachloride (CCl4) (1 μl/g rat, i.p., twice weekly) for 6 weeks. Quercetin (50 mg/kg, orally), simvastatin (40 mg/kg, orally) either individually or combined were administered for another 4 weeks. The three treatment groups ameliorated hepatic dysfunction and altered parameters of sphingolipid and pyroptosis pathways. Yet, the combined group showed a more pronounced effect. Treatments lowered serum levels of GOT, GPT, ALP and elevated albumin and total protein levels. Histopathological and electron microscope examination of liver tissue revealed diminished fibrosis and inflammation. Protein expression levels of α-SMA, IL-1β, PPAR-γ, TGF-β1, caspase-1 and caspase-3 expression in liver tissues were reduced. Additionally, hepatic mRNA levels of SphK1 and NLRP3 decreased after treatment. Furthermore, the three groups lowered MDA levels and elevated total antioxidant capacity, GSH and Nrf2 expression levels. Treatments downregulated sphingolipid pathway and NLRP3-mediated pyroptosis and stimulated an anti-apoptotic, anti-proliferative and antioxidant activity. This suggests that targeting the SphK1/NLRP3 pathway could be a prospective therapeutic strategy against liver fibrosis.

Curcumin Modulates NOX Gene Expression and ROS Production via P-Smad3C in TGF-β-Activated Hepatic Stellate Cells

Background

Liver fibrosis, associated with hepatic stellate cells (HSCs), occurs when a healthy liver sustains damage, thereby impairing its function. NADPH oxidases (NOXs), specifically isoforms 1, 2, and 4, play a role in reactive oxygen species (ROS) production during hepatic injuries, resulting in fibrosis. Curcumin has shown strong potential in mitigating liver fibrosis. Our research aimed to investigate the effects of curcumin on lowering NOX and ROS levels. This compound was also studied for its effects on NOXs, ROS concentrations through the inhibition of Smad3 phosphorylation in transforming growth factor beta (TGF-β)-activated human HSCs.

Methods

MTT assay investigated the cytotoxic effects of curcumin on HSCs. The cells were activated by exposure to TGF-β (2 ng/mL) for 24 hours. After activating, the cells were treated with curcumin at 25-150 μM concentrations. After administering curcumin to the cells, we employed RT-PCR and Western blot techniques to evaluate the related gene and protein expression levels. This evaluation was primarily focused on the mRNA expression levels of NOX1, NOX2, NOX4 and phosphorylated Smad3C.

Results

The mRNA expression level of aforesaid NOXs as well as α-smooth muscle actin (α-SMA), collagen1-α, and ROS levels were significantly reduced following 100 μM curcumin treatment. Furthermore, curcumin significantly decreased the p-Smad3C protein level in TGF-β-activated cells, with fold changes of 3 and 2 observed at 75 and 100 μM, respectively.

Conclusion

Curcumin decreased the levels of ROS and NOX, as well as the expression of α-SMA and collagen1-α. The primary mechanism for this reduction could be linked to the level of p-Smad3C. Hence, curcumin could serve as an effective therapeutic agent for liver fibrosis.

Curcumin and saroglitazar attenuate diet-induced nonalcoholic steatohepatitis by activating the Nrf2 pathway and suppressing ERK1/2 signaling

Objectives

Non-alcoholic fatty liver disease (NAFLD) is a chronic steatohepatitis disorder. If left untreated, it can progress to hepatocellular carcinoma. Several studies have shown that saroglitazar, a PPARα/γ dual agonist, and curcumin (the principal constituent of turmeric) may be effective in the treatment of NAFLD. This research aimed to study the pharmacological mechanism of these compounds in rats with NAFLD.

Materials and Methods

NAFLD was induced in male Wistar rats (aged 6-8 weeks) by feeding them a high-fat diet (HFD) for 6 weeks. Subsequently, the rats were divided into four groups, with Group 1 continuing on HFD, while groups 2, 3, and 4 received HFD supplemented with saroglitazar, curcumin, and both saroglitazar and curcumin, respectively. We evaluated the expression of Nrf2, ERK1/2, NOX1,2,4, antioxidant enzymes, PPARα, γ, and genes regulating lipid metabolism in the liver. Histopathology of liver tissue was also examined. Furthermore, we analyzed serum levels of lipid profiles and hepatic enzymes.

Results

Rats with NAFLD that received treatment involving saroglitazar and curcumin showed a significant decrease in the expression of ERK1/2, SREBP1, PPARγ, pro-inflammatory cytokines, NOXs, and ROS levels. Additionally, the levels of Nrf2, PPARα, and antioxidant enzymes showed a significant increase. The serum levels of lipid profiles and hepatic enzymes also decreased significantly after drug treatment.

Conclusion

Our results confirm that both saroglitazar and curcumin ameliorate NAFLD by regulating the Nrf2 and ERK1/2 signaling pathways. These findings suggest that curcumin could serve as a suitable substitute for saroglitazar, although they appear to have a synergistic effect.

Targeting ROS production through inhibition of NADPH oxidases

NADPH oxidases (NOXs) are transmembrane enzymes that are devoted to the production of reactive oxygen species (ROS). In cancers, dysregulation of NOX enzymes affects ROS production, leading to redox unbalance and tumor progression. Consequently, NOXs are a drug target for cancer therapeutics, although current therapies have off-target effects: there is a need for isoenzyme-selective inhibitors. Here, we describe fully validated human NOX inhibitors, obtained from an in silico screen, targeting the active site of Cylindrospermum stagnale NOX5 (csNOX5). The hits are validated by in vitro and in cellulo enzymatic and binding assays, and their binding modes to the dehydrogenase domain of csNOX5 studied via high-resolution crystal structures. A high-throughput screen in a panel of cancer cells shows activity in selected cancer cell lines and synergistic effects with KRAS modulators. Our work lays the foundation for the development of inhibitor-based methods for controlling the tightly regulated and highly localized ROS sources.

Hepatoprotective Mechanisms Induced by Spinach Methanolic Extract in Rats with Hyperglycemia-An Immunohistochemical Analysis

Spinach methanolic extract (SME) has a hepatoprotective effect due to its polyphenolic antioxidants; however, its action in parenchymal (PQ) and non-parenchymal (nPQ) cells remains unknown. This study investigates the hepatoprotective effect of SME on streptozotocin-induced hyperglycemic rats (STZ), focusing on immunohistochemical analyses. Methods: The extract was prepared, and the total polyphenols and antioxidant activity were quantified. Adult male Wistar rats were divided into four groups (n = 8): normoglycemic rats (NG), STZ-induced hyperglycemic (STZ), STZ treated with 400 mg/kg SME (STZ-SME), and NG treated with SME (SME) for 12 weeks. Serum liver transaminases and lipid peroxidation levels in tissue were determined. The distribution pattern and relative levels of markers related to oxidative stress [reactive oxygen species (ROS), superoxide dismutase-1, catalase, and glutathione peroxidase-1], of cytoprotective molecules [nuclear NRF2 and heme oxygenase-1 (HO-1)], of inflammatory mediators [nuclear NF-κB, TNF-α], proliferation (PCNA), and of fibrogenesis markers [TGF-β, Smad2/3, MMP-9, and TIMP1] were evaluated. Results: SME had antioxidant capacity, and it lowered serum transaminase levels in STZ-SME compared to STZ. It reduced NOX4 staining, and lipid peroxidation levels were related to low formation of ROS. In STZ-SME, the immunostaining for antioxidant enzymes increased in nPQ cells compared to STZ. However, enzymes were also localized in extra and intracellular vesicles in STZ. Nuclear NRF2 staining and HO-1 expression in PQ and nPQ were higher in STZ-SME than in STZ. Inflammatory factors were decreased in STZ-SME and were related to the percentage decrease in NF-κB nuclear staining in nPQ cells. Similarly, TGF-β (in the sinusoids) and MMP-9 (in nPQ) were increased in the STZ-SME group compared to the other groups; however, staining for CTGF, TIMP1, and Smad2/3 was lower. Conclusions: SME treatment in hyperglycemic rats induced by STZ may have hepatoprotective properties due to its scavenger capacity and the regulation of differential expression of antioxidant enzymes between the PQ and nPQ cells, reducing inflammatory and fibrogenic biomarkers in liver tissue.

HCV and HCC Tango-Deciphering the Intricate Dance of Disease: A Review Article

Hepatitis C virus (HCV) is a major cause of hepatocellular carcinoma (HCC) accounting for around one-third of all HCC cases. Prolonged inflammation in chronic hepatitis C (CHC), maintained through a variety of pro- and anti-inflammatory mediators, is one of the aspects of carcinogenesis, followed by mitochondrial dysfunction and oxidative stress. Immune response dysfunction including the innate and adaptive immunity also plays a role in the development, as well as in the recurrence of HCC after treatment. Some of the tumor suppressor genes inhibited by the HCV proteins are p53, p73, and retinoblastoma 1. Mutations in the telomerase reverse transcriptase promoter and the oncogene catenin beta 1 are two more important carcinogenic signaling pathways in HCC associated with HCV. Furthermore, in HCV-related HCC, numerous tumor suppressor and seven oncogenic genes are dysregulated by epigenetic changes. Epigenetic regulation of gene expression is considered as a lasting "epigenetic memory", suggesting that HCV-induced changes persist and are associated with liver carcinogenesis even after cure. Epigenetic changes and immune response dysfunction are recognized targets for potential therapy of HCC.

Advancing Perfusion Models: Dual-Vessel Ex Vivo Rat Liver Perfusion Based on a Clinical Setup

Normothermic ex vivo liver machine perfusion (NEVLP) has been developed to address the increasing organ shortage in liver transplantation, through optimal preservation, assessment, and conditioning of grafts from extended criteria donors. There remains a need to establish simple and standardized animal models that simulate clinical NEVLP to test novel therapies. Liver grafts from 36 Sprague-Dawley rats were perfused for 6 h in a dual-vessel NEVLP system with a Dulbecco's modified Eagles medium-based perfusate supplemented with rat plasma and erythrocytes. Varying doses of the clinically used vasodilator epoprostenol, Kupffer cell inhibitor glycine, and a Steen™-based perfusate were assessed. Perfusion pressures and bile production were recorded, and perfusate was analyzed for transaminase secretion. Tissue samples were evaluated histologically, and levels of cytokines and 8-Isoprostane were measured. Increasing levels of epoprostenol and the addition of glycine resulted in a stepwise decrease of transaminase secretion and improved bile production. Steen further decreased transaminase release and interleukin 1 beta levels. Liver grafts perfused with the optimized Steen-based protocol exhibited lowest levels of oxidative stress and best-preserved liver integrity. In conclusion, epoprostenol seemed to ameliorate liver function and prevent cellular damage beyond its vasodilatory effect, with glycine acting synergistically. The anti-inflammatory and antioxidative properties of Steen further improved the outcome of perfusion. Our rodent NEVLP system may be used to rapidly test new agents for the pharmacologic conditioning of livers and help translate findings from bench-to-bedside.

Cellular stress in the pathogenesis of nonalcoholic steatohepatitis and liver fibrosis

The burden of chronic liver disease is rising substantially worldwide. Fibrosis, characterized by excessive deposition of extracellular matrix proteins, is the common pathway leading to cirrhosis, and limited treatment options are available. There is increasing evidence suggesting the role of cellular stress responses contributing to fibrogenesis. This Review provides an overview of studies that analyse the role of cellular stress in different cell types involved in fibrogenesis, including hepatocytes, hepatic stellate cells, liver sinusoidal endothelial cells and macrophages.

Emerging Therapeutic Strategies in The Fight Against Primary Biliary Cholangitis

The liver has a vital role in many metabolic and regulatory processes in the body. Primary biliary cholangitis (PBC), previously known as primary biliary cirrhosis, is a chronic cholestatic autoimmune disease of the intrahepatic bile ducts associated with loss of tolerance to mitochondrial antigens. At this time there is no definitive cure for PBC; however, ursodeoxycholic acid (UDCA) has been shown to reduce injury when administered as the first line of treatment. Additional therapeutics can be given concurrently or as an alternative to UDCA to manage the symptoms and further curb disease progression. Currently, a liver transplant is the only potentially curative option when the patient has developed end-stage liver disease or intractable pruritus. This review aims to delineate the pathogenesis of primary biliary cholangitis and shed light on current therapeutic strategies in the treatment of PBC.

Oxidative Stress in Liver Pathophysiology and Disease

The liver is an organ that is particularly exposed to reactive oxygen species (ROS), which not only arise during metabolic functions but also during the biotransformation of xenobiotics. The disruption of redox balance causes oxidative stress, which affects liver function, modulates inflammatory pathways and contributes to disease. Thus, oxidative stress is implicated in acute liver injury and in the pathogenesis of prevalent infectious or metabolic chronic liver diseases such as viral hepatitis B or C, alcoholic fatty liver disease, non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH). Moreover, oxidative stress plays a crucial role in liver disease progression to liver fibrosis, cirrhosis and hepatocellular carcinoma (HCC). Herein, we provide an overview on the effects of oxidative stress on liver pathophysiology and the mechanisms by which oxidative stress promotes liver disease.

Cellular heterogeneity and plasticity during NAFLD progression

Nonalcoholic fatty liver disease (NAFLD) is a progressive liver disease that can progress to nonalcoholic steatohepatitis (NASH), NASH-related cirrhosis, and hepatocellular carcinoma (HCC). NAFLD ranges from simple steatosis (or nonalcoholic fatty liver [NAFL]) to NASH as a progressive form of NAFL, which is characterized by steatosis, lobular inflammation, and hepatocellular ballooning with or without fibrosis. Because of the complex pathophysiological mechanism and the heterogeneity of NAFLD, including its wide spectrum of clinical and histological characteristics, no specific therapeutic drugs have been approved for NAFLD. The heterogeneity of NAFLD is closely associated with cellular plasticity, which describes the ability of cells to acquire new identities or change their phenotypes in response to environmental stimuli. The liver consists of parenchymal cells including hepatocytes and cholangiocytes and nonparenchymal cells including Kupffer cells, hepatic stellate cells, and endothelial cells, all of which have specialized functions. This heterogeneous cell population has cellular plasticity to adapt to environmental changes. During NAFLD progression, these cells can exert diverse and complex responses at multiple levels following exposure to a variety of stimuli, including fatty acids, inflammation, and oxidative stress. Therefore, this review provides insights into NAFLD heterogeneity by addressing the cellular plasticity and metabolic adaptation of hepatocytes, cholangiocytes, hepatic stellate cells, and Kupffer cells during NAFLD progression.

Novel Therapeutic Approaches to Liver Fibrosis Based on Targeting Oxidative Stress

Chronic liver disease (CLD) constitutes a growing global health issue, with no effective treatments currently available. Oxidative stress closely interacts with other cellular and molecular processes to trigger stress pathways in different hepatic cells and fuel the development of liver fibrosis. Therefore, inhibition of reactive oxygen species (ROS)-mediated effects and modulation of major antioxidant responses to counteract oxidative stress-induced damage have emerged as interesting targets to prevent or ameliorate liver injury. Although many preclinical studies have shown that dietary supplements with antioxidant properties can significantly prevent CLD progression in animal models, this strategy has not proved effective to significantly reduce fibrosis when translated into clinical trials. Novel and more specific therapeutic approaches are thus required to alleviate oxidative stress and reduce liver fibrosis. We have reviewed the relevant literature concerning the crucial role of alterations in redox homeostasis in different hepatic cell types during the progression of CLD and discussed current pharmacological approaches to ameliorate fibrosis by reducing oxidative stress focusing on selective modulation of enzymatic oxidant sources, antioxidant systems and ROS-mediated pathogenic processes.

Molecular Mechanism Pathways of Natural Compounds for the Treatment of Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in the world, and its incidence continues to increase each year. Yet, there is still no definitive drug that can stop its development. This review focuses mainly on lipotoxicity, oxidative stress, inflammation, and intestinal flora dysbiosis to understand NAFLD's pathogenesis. In this review, we used NCBI's PubMed database for retrieval, integrating in vivo and in vitro experiments to reveal the therapeutic effects of natural compounds on NAFLD. We also reviewed the mechanisms by which the results of these experiments suggest that these compounds can protect the liver from damage by modulating inflammation, reducing oxidative stress, decreasing insulin resistance and lipid accumulation in the liver, and interacting with the intestinal microflora. The natural compounds discussed in these papers target a variety of pathways, such as the AMPK pathway and the TGF-β pathway, and have significant therapeutic effects. This review aims to provide new possible therapeutic lead compounds and references for the development of novel medications and the clinical treatment of NAFLD. It offers fresh perspectives on the development of natural compounds in preventing and treating NAFLD.

Primary Biliary Cholangitis: Promising Emerging Innovative Therapies and Their Impact on GLOBE Scores

Primary biliary cholangitis (PBC), previously referred to as primary biliary cirrhosis, is an autoimmune disorder leading to the destruction of intra-hepatic bile ducts. If untreated, progressive bile duct damage and cholestasis can lead to ductopenia and result in cirrhosis. Ursodiol, the first drug approved for PBC, has changed the natural history of this disease and improved patient outcomes. Subsequently, several new prediction models incorporating a response to ursodiol were developed. These include the GLOBE score, which was shown to predict long-term outcomes in patients with PBC. In 2016, obeticholic acid (OCA) became the second drug to be approved by the FDA, predominantly based on improvement in alkaline phosphatase (ALP) levels. This trial has subsequently influenced the design of clinical trials. Several drugs are currently being evaluated as therapeutic options for PBC, with improvement in ALP being a main endpoint. In this review, we will discuss the impact of new therapies on GLOBE scores in patients with PBC.

Label-Free Imaging Techniques to Evaluate Metabolic Changes Caused by Toxic Liver Injury in PCLS

Abuse with hepatotoxic agents is a major cause of acute liver failure. The search for new criteria indicating the acute or chronic pathological processes is still a challenging issue that requires the selection of effective tools and research models. Multiphoton microscopy with second harmonic generation (SHG) and fluorescence lifetime imaging microscopy (FLIM) are modern label-free methods of optical biomedical imaging for assessing the metabolic state of hepatocytes, therefore reflecting the functional state of the liver tissue. The aim of this work was to identify characteristic changes in the metabolic state of hepatocytes in precision-cut liver slices (PCLSs) under toxic damage by some of the most common toxins: ethanol, carbon tetrachloride (CCl4) and acetaminophen (APAP), commonly known as paracetamol. We have determined characteristic optical criteria for toxic liver damage, and these turn out to be specific for each toxic agent, reflecting the underlying pathological mechanisms of toxicity. The results obtained are consistent with standard methods of molecular and morphological analysis. Thus, our approach, based on optical biomedical imaging, is effective for intravital monitoring of the state of liver tissue in the case of toxic damage or even in cases of acute liver injury.

Effect of Hepatic Pathology on Liver Regeneration: The Main Metabolic Mechanisms Causing Impaired Hepatic Regeneration

Liver regeneration has been studied for many decades, and the mechanisms underlying regeneration of normal liver following resection are well described. However, no less relevant is the study of mechanisms that disrupt the process of liver regeneration. First of all, a violation of liver regeneration can occur in the presence of concomitant hepatic pathology, which is a key factor reducing the liver's regenerative potential. Understanding these mechanisms could enable the rational targeting of specific therapies to either reduce the factors inhibiting regeneration or to directly stimulate liver regeneration. This review describes the known mechanisms of normal liver regeneration and factors that reduce its regenerative potential, primarily at the level of hepatocyte metabolism, in the presence of concomitant hepatic pathology. We also briefly discuss promising strategies for stimulating liver regeneration and those concerning methods for assessing the regenerative potential of the liver, especially intraoperatively.

Activation of Kupffer cells in NAFLD and NASH: mechanisms and therapeutic interventions

Non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) are emerging as the leading causes of liver disease worldwide. These conditions can lead to cirrhosis, liver cancer, liver failure, and other related ailments. At present, liver transplantation remains the sole treatment option for end-stage NASH, leading to a rapidly growing socioeconomic burden. Kupffer cells (KCs) are a dominant population of macrophages that reside in the liver, playing a crucial role in innate immunity. Their primary function includes phagocytosing exogenous substances, presenting antigens, and triggering immune responses. Moreover, they interact with other liver cells during the pathogenesis of NAFLD, and this crosstalk may either delay or exacerbate disease progression. Stimulation by endogenous signals triggers the activation of KCs, resulting in the expression of various inflammatory factors and chemokines, such as NLRP3, TNF-α, IL-1B, and IL-6, and contributing to the inflammatory cascade. In the past 5 years, significant advances have been made in understanding the biological properties and immune functions of KCs in NAFLD, including their interactions with tissue molecules, underlying molecular mechanisms, signaling pathways, and relevant therapeutic interventions. Having a comprehensive understanding of these mechanisms and characteristics can have enormous potential in guiding future strategies for the prevention and treatment of NAFLD.

Synergistic effects of combined treatment of 1,2-dichloroethane and high-dose ethanol on liver damage in mice and the related mechanisms

Our previous studies have shown that the metabolism of 1,2-dichloroethane (1,2-DCE) mediated by CYP2E1 could result in oxidative damage in the liver of mice. In the current study, we further investigated the effects of combined treatment with 1,2-DCE and high dose ethanol on liver and the mechanisms since both of them can be metabolized by CYP2E1 in the liver. There are several novel findings in the current study. First, combined treatment of mice with 1,2-DCE and high-dose ethanol could synergistically upregulate both protein and mRNA levels of CYP2E1, which might aggravate liver damage through CYP2E1-mediated oxidative stress. Second, the combined treatment could also synergistically trigger NLRP3 inflammasome activation and inflammatory responses in the liver. Third, the combined treatment synergistically upregulated the antioxidant defence systems in response to oxidative stress, however the compensatory mechanisms of antioxidant defence systems appeared to be insufficient to protect liver damage in the mice. Finally, the upregulated CYP2E1 expression was confirmed by using its specific inhibitor to play the crucial roles in liver damage in the mice during the combined treatment.

NOX4-TIM23 interaction regulates NOX4 mitochondrial import and metabolic reprogramming

Pulmonary fibrosis is a progressive lung disease characterized by macrophage activation. Asbestos-induced expression of nicotinamide adenine dinucleotide phosphate hydrogen oxidase 4 (NOX4) in lung macrophages mediates fibrotic progression by the generation of mitochondrial reactive oxygen species (ROS), modulating mitochondrial biogenesis, and promoting apoptosis resistance; however, the mechanism(s) by which NOX4 localizes to mitochondria during fibrosis is not known. Here, we show that NOX4 localized to the mitochondrial matrix following asbestos exposure in lung macrophages via direct interaction with TIM23. TIM23 and NOX4 interaction was found in lung macrophages from human subjects with asbestosis, while it was absent in mice harboring a conditional deletion of NOX4 in lung macrophages. This interaction was localized to the proximal transmembrane region of NOX4. Mechanistically, TIM23 augmented NOX4-induced mitochondrial ROS and metabolic reprogramming to oxidative phosphorylation. Silencing TIM23 decreased mitochondrial ROS and oxidative phosphorylation. These observations highlight the important role of the mitochondrial translocase TIM23 interaction with NOX4. Moreover, this interaction is required for mitochondrial redox signaling and metabolic reprogramming in lung macrophages.

Molecular mechanisms in thioacetamide-induced acute and chronic liver injury models

Thioacetamide (TAA) undergoes bioactivation in the liver by the CYP450 2E1 enzyme, resulting in the formation of TAA-S-oxide and TAA-S-dioxide. TAA-S-dioxide induces oxidative stress via lipid peroxidation of the hepatocellular membrane. A single TAA dose (50-300 mg/kg) administration initiates hepatocellular necrosis around the pericentral region after its covalent binding to macromolecules in the liver. Intermittent TAA administration (150-300 mg/kg, weekly thrice, for 11-16 weeks) activates transforming growth factor (TGF)-β/smad3 downstream signaling in injured hepatocytes, causing hepatic stellate cells (HSCs) to acquire myofibroblast like phenotype. The activated HSCs synthesize a variety of extracellular matrix, leading to liver fibrosis, cirrhosis, and portal hypertension. The TAA induced liver injury varies depending on the animal model, dosage, frequency, and routes of administration. However, TAA induces hepatotoxicity in a reproducible manner, and it is an ideal model to evaluate the antioxidant, cytoprotective, and antifibrotic compounds in experimental animals.

Mitochondria-derived H2O2 triggers liver regeneration via FoxO3a signaling pathway after partial hepatectomy in mice

Reactive oxygen species (ROS) can induce oxidative injury and are generally regarded as toxic byproducts, although they are increasingly recognized for their signaling functions. Increased ROS often accompanies liver regeneration (LR) after liver injuries, however, their role in LR and the underlying mechanism remains unclear. Here, by employing a mouse LR model of partial hepatectomy (PHx), we found that PHx induced rapid increases of mitochondrial hydrogen peroxide (H2O2) and intracellular H2O2 at an early stage, using a mitochondria-specific probe. Scavenging mitochondrial H2O2 in mice with liver-specific overexpression of mitochondria-targeted catalase (mCAT) decreased intracellular H2O2 and compromised LR, while NADPH oxidases (NOXs) inhibition did not affect intracellular H2O2 or LR, indicating that mitochondria-derived H2O2 played an essential role in LR after PHx. Furthermore, pharmacological activation of FoxO3a impaired the H2O2-triggered LR, while liver-specific knockdown of FoxO3a by CRISPR-Cas9 technology almost abolished the inhibition of LR by overexpression of mCAT, demonstrating that FoxO3a signaling pathway mediated mitochondria-derived H2O2 triggered LR after PHx. Our findings uncover the beneficial roles of mitochondrial H2O2 and the redox-regulated underlying mechanisms during LR, which shed light on potential therapeutic interventions for LR-related liver injury. Importantly, these findings also indicate that improper antioxidative intervention might impair LR and delay the recovery of LR-related diseases in clinics.

Structure, regulation, and physiological functions of NADPH oxidase 5 (NOX5)

NOX5 is the last member of the NADPH oxidase (NOXs) family to be identified and presents some specific characteristics differing from the rest of the NOXs. It contains four Ca²⁺ binding domains at the N-terminus and its activity is regulated by the intracellular concentration of Ca²⁺. NOX5 generates superoxide (O₂^•-) using NADPH as a substrate, and it modulates functions related to processes in which reactive oxygen species (ROS) are involved. Those functions appear to be detrimental or beneficial depending on the level of ROS produced. For example, the increase in NOX5 activity is related to the development of various oxidative stress-related pathologies such as cancer, cardiovascular, and renal diseases. In this context, pancreatic expression of NOX5 can negatively alter insulin action in high-fat diet-fed transgenic mice. This is consistent with the idea that the expression of NOX5 tends to increase in response to a stimulus or a stressful situation, generally causing a worsening of the pathology. On the other hand, it has also been suggested that it might have a positive role in preparing the body for metabolic stress, for example, by inducing a protective adipose tissue adaptation to the excess of nutrients supplied by a high-fat diet. In this line, its endothelial overexpression can delay lipid accumulation and insulin resistance development in obese transgenic mice by inducing the secretion of IL-6 followed by the expression of thermogenic and lipolytic genes. However, as NOX5 gene is not present in rodents and human NOX5 protein has not been crystallized, its function is still poorly characterized and further extensive research is required.

Mesenchymal stem cells in fibrotic diseases-the two sides of the same coin

Fibrosis is caused by extensive deposition of extracellular matrix (ECM) components, which play a crucial role in injury repair. Fibrosis attributes to ~45% of all deaths worldwide. The molecular pathology of different fibrotic diseases varies, and a number of bioactive factors are involved in the pathogenic process. Mesenchymal stem cells (MSCs) are a type of multipotent stem cells that have promising therapeutic effects in the treatment of different diseases. Current updates of fibrotic pathogenesis reveal that residential MSCs may differentiate into myofibroblasts which lead to the fibrosis development. However, preclinical and clinical trials with autologous or allogeneic MSCs infusion demonstrate that MSCs can relieve the fibrotic diseases by modulating inflammation, regenerating damaged tissues, remodeling the ECMs, and modulating the death of stressed cells after implantation. A variety of animal models were developed to study the mechanisms behind different fibrotic tissues and test the preclinical efficacy of MSC therapy in these diseases. Furthermore, MSCs have been used for treating liver cirrhosis and pulmonary fibrosis patients in several clinical trials, leading to satisfactory clinical efficacy without severe adverse events. This review discusses the two opposite roles of residential MSCs and external MSCs in fibrotic diseases, and summarizes the current perspective of therapeutic mechanism of MSCs in fibrosis, through both laboratory study and clinical trials.

Therapeutic interventions of acute and chronic liver disorders: A comprehensive review

Liver disorders are one of the most common pathological problems worldwide. It affects more than 1.5 billion worldwide. Many types of hepatic cells have been reported to be involved in the initiation and propagation of both acute and chronic liver diseases, including hepatocytes, Kupffer cells, sinusoidal endothelial cells, and hepatic stellate cells (HSCs). In addition, oxidative stress, cytokines, fibrogenic factors, microRNAs, and autophagy are also involved. Understanding the molecular mechanisms of liver diseases leads to discovering new therapeutic interventions that can be used in clinics. Recently, antioxidant, anti-inflammatory, anti-HSCs therapy, gene therapy, cell therapy, gut microbiota, and nanoparticles have great potential for preventing and treating liver diseases. Here, we explored the recent possible molecular mechanisms involved in the pathogenesis of acute and chronic liver diseases. Besides, we overviewed the recent therapeutic interventions that targeted liver diseases and summarized the recent studies concerning liver disorders therapy.

Exosomes of Whartons' jelly mesenchymal stem cell reduce the NOX genes in TGF-β-induced hepatic fibrosis

Objectives

Activated cells which are called star-shaped cells, are some of the key factors in the development of liver fibrosis. Activation of NADPH oxidase (NOX) is associated with increased HSCs activity and progression of hepatic fibrosis. In this study, the effects of human exosomes derived from WJ-MSCs on NOX1, NOX2, and NOX4 gene expression in TGF-β-induced hepatic fibrosis were investigated.

Materials and Methods

LX2 cell line was treated with 2 ng/ml TGF-β for 24 hr, in order to induce liver fibrosis after starvation. In the next step, the cells were treated with several concentrations of the exosomes derived from WJ-MSCs (10, 20, 30, 40, and 50 μg/ml). Finally, Smad3C phosphorylated protein expression level and NOX1, NOX2, and NOX4 gene expression levels were measured.

Results

The results demonstrated that the level of NOX1, NOX2, and NOX4 mRNA expressions decreased significantly during 24 hrs at concentrations of 40 and 50 μg/ml of WJ-MSCs exosomes in TGF-β-induced-HSCs. The p-Smad3C proteins were significantly decreased (fold change: 1.83, P-value<0.05) after exposure to WJ-MSC-derived exosomes.

Conclusion

Treatment with exosomes prevents further activation of HSCs by inhibiting the level of Smad3C phosphorylation. The experimental data of our study suggested that in liver fibrosis, the protection of HSCs activation against TGF-β by inhibiting the NOX pathway via human exosomes of WJ-MSCs is extremely important. It needs further research as a treatment method.

Adiponectin alleviates non-alcoholic fatty liver injury via regulating oxidative stress in liver cells

BACKGROUND

The aim of the present study was to investigate the role of adiponectin in non-alcoholic fatty liver cell model and its mechanism.

METHODS

The serum were collected from patients with non-alcoholic fatty liver disease and healthy controls. Then the expression of APN in the serum was detected using APN kit. Furthermore, an in vitro model of NAFLD was established using mixed fatty acids treated HepG2 cells, and APN was highly expressed in the culture solution to a concentration of 10 μg/mL. The normal control group (Normal) was normal cells, the model group (NAFLD) was mixed fatty acids treated HepG2 cells, the experimental group (NAFLD+APN) was model cells transfected with high APN expression, and the negative control group (NAFLD+PBS) was model cells transfected with PBS. The expression of NOX2 in each group was detected by Western blot. The corresponding kit was used to detect the level of triglyceride (TG), the activity of superoxide dismutase (SOD), the content of malondialdehyde (MDA), and the ratio of GSH/GSSG in each group of cells.

RESULTS

The expression level of APN was greatly decreased in the serum of NAFLD patients (P<0.01), and the TG content was significantly increased in HepG2 cells treated with fatty acids (P<0.001), indicating successful modeling. The cells had high expression of APN (P<0.001) showed low expression of NOX2 (P<0.001). The kit test results showed that the high expression of APN could reverse the decrease of SOD activity, the increase of MDA level, the decrease of GSH/GSSG ratio and the increase of TG content (P<0.001), all of which were restored to the modeling level after application of NOX2's activator TBCA.

CONCLUSIONS

APN was lowly expressed in the serum of NAFLD patients. Its effect mechanism was to alleviate the injury of NAFLD cells by reducing oxidative stress via regulating NOX2 expression.

Role of Oxidative Stress in Liver Disorders

Oxygen is vital for life as it is required for many different enzymatic reactions involved in intermediate metabolism and xenobiotic biotransformation. Moreover, oxygen consumption in the electron transport chain of mitochondria is used to drive the synthesis of ATP to meet the energetic demands of cells. However, toxic free radicals are generated as byproducts of molecular oxygen consumption. Oxidative stress ensues not only when the production of reactive oxygen species (ROS) exceeds the endogenous antioxidant defense mechanism of cells, but it can also occur as a consequence of an unbalance between antioxidant strategies. Given the important role of hepatocytes in the biotransformation and metabolism of xenobiotics, ROS production represents a critical event in liver physiology, and increasing evidence suggests that oxidative stress contributes to the development of many liver diseases. The present review, which is part of the special issue “Oxidant stress in Liver Diseases”, aims to provide an overview of the sources and targets of ROS in different liver diseases and highlights the pivotal role of oxidative stress in cell death. In addition, current antioxidant therapies as treatment options for such disorders and their limitations for future trial design are discussed.

Aucubin ameliorates liver fibrosis and hepatic stellate cells activation in diabetic mice via inhibiting ER stress-mediated IRE1α/TXNIP/NLRP3 inflammasome through NOX4/ROS pathway

Type 2 diabetes (T2DM) is closely associated with hepatic injury, which could promote/exacerbate hepatic inflammation, steatosis, and accelerate liver fibrosis progression. Aucubin (AU), as an active ingredient isolated from Eucommia ulmoides, exists a nutritional value in hepatoprotective effect and diabetic complications. However, whether it possesses more outstanding features on improving liver injury in diabetic conditions and the underlying mechanism is unclear. Our research investigated the treatment of AU on liver fibrosis and potential mechanisms on high-fat diet/streptozotocin-induced diabetic mice and high glucose (HG)&TGF-β1-induced LX-2 cells. Results showed that AU restored hepatic function without affecting blood sugar levels in diabetic mice. Meanwhile, the enhanced levels of total cholesterol, triglycerides, and LDL-c were reversed in hepatic tissue after AU treatment. Histomorphology assays including H&E, Masson, PAS, Oil red and Sirius red staining showed that AU treatment reduced liver swelling, steatosis and fibrosis. Mechanistic studies showed that AU alleviated NLRP3 inflammasome activation and inflammatory responses via inhibiting ER stress-mediated IRE1α/TXNIP signaling pathway, which could postpone the development of T2DM induced hepatic fibrosis. In addition, the ROS generation and the up-regulated expression of NADHP oxidase 4 (NOX4) in the liver tissue were suppressed by AU treatment. Moreover, in vitro model, NOX4 activation was prominently enhanced and AU treatment blocked HG&TGF-β1-induced NOX4 derived superoxide generation and thereby ameliorating hepatic stellate cell activation, which can be abrogated in the overexpression of NOX4 LX-2 cells. In addition, inhibition effects on ER stress-mediated IRE1α/TXNIP/NLRP3 inflammasome by AU treatment also were abolished in the overexpression of NOX4 LX-2 cells. Meanwhile, molecular docking results indicated that AU and NOX4 protein have a higher affinity. Taken together, AU might be a potential nutraceutical or therapeutic drug to ameliorate hepatic impairment and fibrosis in T2DM.

Loss of heat shock factor 1 promotes hepatic stellate cell activation and drives liver fibrosis

Liver fibrosis is an aberrant wound healing response that results from chronic injury and is mediated by hepatocellular death and activation of hepatic stellate cells (HSCs). While induction of oxidative stress is well established in fibrotic livers, there is limited information on stress‐mediated mechanisms of HSC activation. Cellular stress triggers an adaptive defense mechanism via master protein homeostasis regulator, heat shock factor 1 (HSF1), which induces heat shock proteins to respond to proteotoxic stress. Although the importance of HSF1 in restoring cellular homeostasis is well‐established, its potential role in liver fibrosis is unknown. Here, we show that HSF1 messenger RNA is induced in human cirrhotic and murine fibrotic livers. Hepatocytes exhibit nuclear HSF1, whereas stellate cells expressing alpha smooth muscle actin do not express nuclear HSF1 in human cirrhosis. Interestingly, despite nuclear HSF1, murine fibrotic livers did not show induction of HSF1 DNA binding activity compared with controls. HSF1‐deficient mice exhibit augmented HSC activation and fibrosis despite limited pro‐inflammatory cytokine response and display delayed fibrosis resolution. Stellate cell and hepatocyte‐specific HSF1 knockout mice exhibit higher induction of profibrogenic response, suggesting an important role for HSF1 in HSC activation and fibrosis. Stable expression of dominant negative HSF1 promotes fibrogenic activation of HSCs. Overactivation of HSF1 decreased phosphorylation of JNK and prevented HSC activation, supporting a protective role for HSF1. Our findings identify an unconventional role for HSF1 in liver fibrosis. Conclusion: Our results show that deficiency of HSF1 is associated with exacerbated HSC activation promoting liver fibrosis, whereas activation of HSF1 prevents profibrogenic HSC activation.

Niacin regresses collagen content in human hepatic stellate cells from liver transplant donors with fibrotic non-alcoholic steatohepatitis (NASH)

In patients with non-alcoholic steatohepatitis (NASH), the onset of fibrosis is a major predictor of cirrhosis and its deadly complications. There is no approved effective pharmacologic therapy for liver fibrosis. Niacin (in pharmacologic concentrations or dose) reverses hepatic steatosis and steatohepatitis. Niacin's efficacy on human hepatic fibrosis is unknown. We investigated the effect of niacin on reversal of preexisting collagen content, in cultured primary human hepatic stellate cells (HSC) obtained from 7 donor livers (processed for transplantation) selected from 5 deceased patients having histologically diagnosed NASH with fibrosis (F1-F3) and 2 non-NASH-fibrosis subjects (Samsara Sciences, Inc., now LifeNet Health). Pharmacologically relevant concentrations of niacin produced a robust and significant dose and time-dependent regression of pre-existing fibrosis by an average of 47.6% and 60.1% (0.25 and 0.5 mM niacin at 48 h incubation) and 53.5% and 65.0% (0.25 and 0.5 mM niacin at 96 h incubation), respectively. In stellate cells from non-NASH-fibrosis subjects, niacin prevented, and regressed fibrosis induced by liver fibrosis stimulators, transforming growth factor-β (TGF-β) and hydrogen peroxide. Niacin significantly inhibited oxidative stress induced by stressors, palmitic acid, or hydrogen peroxide by 52% and 50%, respectively. Translationally, these human HSC data, coupled with emerging in vivo animal data and in vitro human hepatocyte data, suggest that niacin (used clinically for dyslipidemia) could be repurposed as an effective drug for the clinical treatment of patients with NASH-fibrosis or liver cirrhosis. This is in addition to its known efficacy for reversing steatohepatitis and steatosis which can also result in liver cirrhosis.

Inhibiting NADPH Oxidases to Target Vascular and Other Pathologies: An Update on Recent Experimental and Clinical Studies

Reactive oxygen species (ROS) can be beneficial or harmful in health and disease. While low levels of ROS serve as signaling molecules to regulate vascular tone and the growth and proliferation of endothelial cells, elevated levels of ROS contribute to numerous pathologies, such as endothelial dysfunctions, colon cancer, and fibrosis. ROS and their cellular sources have been extensively studied as potential targets for clinical intervention. Whereas various ROS sources are important for different pathologies, four NADPH oxidases (NOX1, NOX2, NOX4, and NOX5) play a prominent role in homeostasis and disease. NOX1-generated ROS have been implicated in hypertension, suggesting that inhibition of NOX1 may be a promising therapeutic approach. NOX2 and NOX4 oxidases are of specific interest due to their role in producing extra- and intracellular hydrogen peroxide (H₂O₂). NOX4-released hydrogen peroxide activates NOX2, which in turn stimulates the release of mitochondrial ROS resulting in ROS-induced ROS release (RIRR) signaling. Increased ROS production from NOX5 contributes to atherosclerosis. This review aims to summarize recent findings on NOX enzymes and clinical trials inhibiting NADPH oxidases to target pathologies including diabetes, idiopathic pulmonary fibrosis (IPF), and primary biliary cholangitis (PBC).

NADPH Oxidases Connecting Fatty Liver Disease, Insulin Resistance and Type 2 Diabetes: Current Knowledge and Therapeutic Outlook

Nonalcoholic fatty liver disease (NAFLD), characterized by ectopic fat accumulation in hepatocytes, is closely linked to insulin resistance and is the most frequent complication of type 2 diabetes mellitus (T2DM). One of the features connecting NAFLD, insulin resistance and T2DM is cellular oxidative stress. Oxidative stress refers to a redox imbalance due to an inequity between the capacity of production and the elimination of reactive oxygen species (ROS). One of the major cellular ROS sources is NADPH oxidase enzymes (NOX-es). In physiological conditions, NOX-es produce ROS purposefully in a timely and spatially regulated manner and are crucial regulators of various cellular events linked to metabolism, receptor signal transmission, proliferation and apoptosis. In contrast, dysregulated NOX-derived ROS production is related to the onset of diverse pathologies. This review provides a synopsis of current knowledge concerning NOX enzymes as connective elements between NAFLD, insulin resistance and T2DM and weighs their potential relevance as pharmacological targets to alleviate fatty liver disease.

Social isolation triggers oxidative status and impairs systemic and hepatic insulin sensitivity in normoglycemic rats

Drug-naïve psychotic patients show metabolic and hepatic dysfunctions. The rat social isolation model of psychosis allows to investigate mechanisms leading to these disturbances to which oxidative stress crucially contributes. Here, we investigated isolation-induced central and peripheral dysfunctions in glucose homeostasis and insulin sensitivity, along with redox dysregulation. Social isolation did not affect basal glycemic levels and the response to glucose and insulin loads in the glucose and insulin tolerance tests. However, HOMA-Index value were increased in isolated (ISO) rats. A hypothalamic reduction of AKT phosphorylation and a trend toward an increase in AMPK phosphorylation were observed following social isolation, accompanied by reduced GLUT-4 levels. Social isolation also induced a reduction of phosphorylation of the insulin receptor, of AKT and GLUT-2, and a decreased phosphorylation of AMPK in the liver. Furthermore, a significant reduction in hepatic CPT1 and PPAR-α levels was detected. ISO rats also showed significant elevations in hepatic ROS amount, lipid peroxidation and NOX4 expression, whereas no differences were detected in NOX2 and NOX1 levels. Expression of SOD2 in the mitochondrial fraction and SOD1 in the cytosolic fraction was not altered following social isolation, whereas SOD activity was increased. Furthermore, a decrease of hepatic CAT and GSH amount was observed in ISO rats compared to GRP animals. Our data suggest that the increased oxidant status and antioxidant capacity modifications may trigger hepatic and systemic insulin resistance, by altering signal hormone pathway and sustaining subsequent alteration of glucose homeostasis and metabolic impairment observed in the social isolation model of psychosis.

Mulberrin confers protection against hepatic fibrosis by Trim31/Nrf2 signaling

Mulberrin (Mul) is a key component of the traditional Chinese medicine Romulus Mori with various biological functions. However, the effects of Mul on liver fibrosis have not been addressed, and thus were investigated in our present study, as well as the underlying mechanisms. Here, we found that Mul administration significantly ameliorated carbon tetrachloride (CCl4)-induced liver injury and dysfunction in mice. Furthermore, CCl4-triggerd collagen deposition and liver fibrosis were remarkably attenuated in mice with Mul supplementation through suppressing transforming growth factor β1 (TGF-β1)/SMAD2/3 signaling pathway. Additionally, Mul treatments strongly restrained the hepatic inflammation in CCl4-challenged mice via blocking nuclear factor-κB (NF-κB) signaling. Importantly, we found that Mul markedly increased liver TRIM31 expression in CCl4-treated mice, accompanied with the inactivation of NOD-like receptor protein 3 (NLRP3) inflammasome. CCl4-triggered hepatic oxidative stress was also efficiently mitigated by Mul consumption via improving nuclear factor E2-related factor 2 (Nrf2) activation. Our in vitro studies confirmed that Mul reduced the activation of human and mouse primary hepatic stellate cells (HSCs) stimulated by TGF-β1. Consistently, Mul remarkably retarded the inflammatory response and reactive oxygen species (ROS) accumulation both in human and murine hepatocytes. More importantly, by using hepatocyte-specific TRIM31 knockout mice (TRIM31Hep-cKO) and mouse primary hepatocytes with Nrf2-knockout (Nrf2KO), we identified that the anti-fibrotic and hepatic protective effects of Mul were TRIM31/Nrf2 signaling-dependent, relieving HSCs activation and liver fibrosis. Therefore, Mul-ameliorated hepatocyte injury contributed to the suppression of HSCs activation by improving TRIM31/Nrf2 axis, thus providing a novel therapeutic strategy for hepatic fibrosis treatment.

Receptor-interacting protein kinase-1 ablation in liver parenchymal cells promotes liver fibrosis in murine NASH without affecting other symptoms

Non-alcoholic steatohepatitis (NASH), a chronic liver disease that emerged in industrialized countries, can further progress into liver fibrosis, cirrhosis, and hepatocellular carcinoma. In the next decade, NASH is predicted to become the leading cause of liver transplantation, the only current interventional therapeutic option. Hepatocyte death, triggered by different death ligands, plays key role in its progression. Previously, we showed that the receptor-interacting protein kinase-1 (RIPK1) in hepatocytes exhibits a protective role in ligand-induced death. Now, to decipher the role of RIPK1 in NASH, Ripk1^LPC-KO mice, deficient for RIPK1 only in liver parenchymal cells, and their wild-type littermates (Ripk1^fl/fl) were fed for 3, 5, or 12 weeks with high-fat high-cholesterol diet (HFHCD). The main clinical signs of NASH were analyzed to compare the pathophysiological state established in mice. Most of the symptoms evolved similarly whatever the genotype, whether it was the increase in liver to body weight ratio, the steatosis grade or the worsening of liver damage revealed by serum transaminase levels. In parallel, inflammation markers followed the same kinetics with significant equivalent inductions of cytokines (hepatic mRNA levels and blood cytokine concentrations) and a main peak of hepatic infiltration of immune cells at 3 weeks of HFHCD. Despite this identical inflammatory response, more hepatic fibrosis was significantly evidenced at week 12 in Ripk1^LPC-KO mice. This coincided with over-induced rates of transcripts of genes implied in fibrosis development (Tgfb1, Tgfbi, Timp1, and Timp2) in Ripk1^LPC-KO animals. In conclusion, our results show that RIPK1 in hepatocyte limits the progression of liver fibrosis during NASH.

Pathophysiological mechanisms of hepatic stellate cells activation in liver fibrosis

Liver fibrosis is a complex pathological process controlled by a variety of cells, mediators and signaling pathways. Hepatic stellate cells play a central role in the development of liver fibrosis. In chronic liver disease, hepatic stellate cells undergo dramatic phenotypic activation and acquire fibrogenic properties. This review focuses on the pathophysiological mechanisms of hepatic stellate cells activation in liver fibrosis. They enter the cell cycle under the influence of various triggers. The “Initiation” phase of hepatic stellate cells activation overlaps and continues with the “Perpetuation” phase, which is characterized by a pronounced inflammatory and fibrogenic reaction. This is followed by a resolution phase if the injury subsides. Knowledge of these pathophysiological mechanisms paved the way for drugs aimed at preventing the development and progression of liver fibrosis. In this respect, impairments in intracellular signaling, epigenetic changes and cellular stress response can be the targets of therapy where the goal is to deactivate hepatic stellate cells. Potential antifibrotic therapy may focus on inducing hepatic stellate cells to return to an inactive state through cellular aging, apoptosis, and/or clearance by immune cells, and serve as potential antifibrotic therapy. It is especially important to prevent the formation of liver cirrhosis since the only radical approach to its treatment is liver transplantation which can be performed in only a limited number of countries.

Exercise Affects the Formation and Recovery of Alcoholic Liver Disease through the IL-6-p47phox Oxidative-Stress Axis

(1) Background: To explore the effect of exercise on the formation and recovery of alcoholic liver disease (ALD) and whether the IL-6−p47phox oxidative−stress axis is involved in that process. (2) Methods: Firstly, 23 six-week-old male C57BL/6J mice were randomly divided into the Con group, ALD group, ALD + NOXI group, ALD + Ex group, and ALD + Ex + NOXI group. The Liber−DeCarli alcoholic liquid diet was used for 6 weeks to establish the ALD mice model, and the Con group was given the TP4030C control diet. The remaining groups were fed with the TP4030B alcoholic diet, and exercise intervention was started after the ALD model establishment and lasted for another 6 weeks, with or without administration of the NOX inhibitor apocynin by intraperitoneal injection on every exercise training day. Secondly, 28 mice were randomly divided into the Sed group, Eth group, Eth + Ex group and Eth + Ex + NOXI group. The Sed group was given the TP4030C control diet. The remaining groups were fed with the TP4030B alcoholic diet and exercise intervention was started synchronously combined with or without administration of intraperitoneal apocynin injections on every exercise training day for 5 weeks. After each individual experiment was accomplished, physiological assessment and biochemical analysis of blood and tissue samples were examined. (3) Results: The levels of TG in serum and IL-6 protein content in liver tissue in the ALD group were significantly increased compared to the Con group (p < 0.05); compared with ALD, p47phox expression in muscle was increased significantly in the ALD + NOXI group (p < 0.05), and TG in serum decreased in the ALD + Ex group (p < 0.05). TG in serum, AST/ALT ratio, and IL-6 content in both liver and muscle decreased (p < 0.05) in the ALD + Ex + NOXI group with MDA in muscle significantly increased (p < 0.01). The AST/ALT ratio, TG in serum, SOD in liver, and p47phox in both liver and muscle in the ALD + Ex + NOXI group were significantly decreased compared with the ALD + NOXI group (p < 0.01). Compared with the ALD + Ex group, the liver index and HDL-C levels in serum were decreased (p < 0.05) in the ALD + Ex + NOXI group. The degree of hepatocyte steatosis and inflammatory infiltration were ameliorated after exercise intervention. In the Eth group, the relative epididymal fat content, HDL-C level, and AST/ALT ratio were significantly decreased, and TG and gp91phox in liver were significantly higher than in the Sed group (p < 0.05, p < 0.01). Compared with the Eth group, the AST/ALT ratio, MDA in the liver, and NOX4 and p47phox protein expression in the liver were significantly increased, and body weight decreased significantly in the Eth + Ex group (p < 0.05, p < 0.01), as did TG in the liver and MDA in muscle. In the th + Ex + NOXI group, gp91phox expression in the liver and body weight were significantly decreased (p < 0.05, p < 0.01). In the Eth + Ex + NOXI group, the ratio of AST/ALT and MDA in muscle were increased when compared with the Eth + Ex group, and the protein expression of gp91phox and p47phox were much lower (p < 0.01). (4) Conclusions: 6 weeks of exercise intervention during the recovery phase of ALD ameliorates hepatocyte damage and dyslipidemia through the IL-6−p47phox oxidative−stress axis, and applying a NOX inhibitor in combination could optimize this. However, drinking alcohol during exercise exacerbates dyslipidemia and oxidative stress, with hepatocyte IL-6−p47phox downregulated.

Factors affecting liver mitochondrial hydrogen peroxide emission

Mitochondria are key cellular sources of reactive oxygen species (ROS) and contain at least 12 known sites on multiple enzymes that convert molecular oxygen to superoxide and hydrogen peroxide (H₂O₂). Quantitation of site-specific ROS emission is critical to understand the relative contribution of different sites and the pathophysiologic importance of mitochondrial ROS. However, factors that affect mitochondrial ROS emission are not well understood. We characterized and optimized conditions for maximal total and site-specific H₂O₂ emission during oxidation of standard substrates and probed the source of the high H₂O₂ emission in unenergized rainbow trout liver mitochondria. We found that mitochondrial H₂O₂ emission capacity depended on the substrate being oxidized, mitochondrial protein concentration, and composition of the ROS detection system. Contrary to our expectation, addition of exogenous superoxide dismutase reduced H₂O₂ emission. Titration of conventional mitochondrial electron transfer system (ETS) inhibitors over a range of conditions revealed that one size does not fit all; inhibitor concentrations evoking maximal responses varied with substrate and were moderated by the presence of other inhibitors. Moreover, the efficacy of suppressors of electron leak (S1QEL1.1 and S3QEL2) was low and depended on the substrate being oxidized. We found that H₂O₂ emission in unenergized rainbow trout liver mitochondria was suppressed by GKT136901 suggesting that it is associated with NADPH oxidase activity. We conclude that optimization of assay conditions is critical for quantitation of maximal H₂O₂ emission and would facilitate more valid comparisons of mitochondrial total and site-specific H₂O₂ emission capacities between studies, tissues, and species.

Oxidative Stress and Redox Signaling in the Pathophysiology of Liver Diseases

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

Forsythiaside A Regulates Activation of Hepatic Stellate Cells by Inhibiting NOX4-Dependent ROS

Hepatic stellate cells (HSCs) activation is an important step in the process of hepatic fibrosis. NOX4 and reactive oxygen species expressed in HSCs play an important role in liver fibrosis. Forsythiaside A (FA), a phenylethanoid glycoside extracted and isolated from Forsythiae Fructus, has significant antioxidant activities. However, it is not clear whether FA can play a role in inhibiting the HSCs activation through regulating NOX4/ROS pathway. Therefore, our purpose is to explore the effect and mechanism of FA on HSCs activation to alleviate liver fibrosis. LX2 cells were activated by TGF-β1 in vitro. MTT assay and Wound Healing assay were used to investigate the effect of FA on TGF-β1-induced LX2 cell proliferation and migration. Elisa kit was used to measure the expression of MMP-1 and TIMP-1. Western blot and RT-qPCR were used to investigate the expression of fibrosis-related COLI, α-SMA, MMP-1 and TIMP-1, and inflammation-related TNF-α, IL-6 and IL-1β. The hydroxyproline content was characterized using a biochemical kit. The mechanism of FA to inhibit HSCs activation and apoptosis was detected by DCF-DA probe, RT-qPCR, western blot and flow cytometry. NOX4 siRNA was used to futher verify the effect of FA on NOX4/ROS pathway. The results showed that FA inhibited the proliferation and migration of LX2 cells and adjusted the expression of MMP-1, TIMP-1, COLI, α-SMA, TNF-α, IL-6 and IL-1β as well as promoted collagen metabolism to show potential in anti-hepatic fibrosis. Mechanically, FA down-regulated NOX4/ROS signaling pathway to improve oxidation imbalances, and subsequently inhibited PI3K/Akt pathway to suppress proliferation. FA also promoted the apoptosis of LX2 cells by Bax/Bcl2 pathway. Furthermore, the effects of FA on TGF-β1-induced increased ROS levels and α-SMA and COLI expression were weaken by silencing NOX4. In conclusion, FA had potential in anti-hepatic fibrosis at least in part by remolding of extracellular matrix and improving oxidation imbalances to inhibit the activation of HSCs and promote HSCs apoptosis.

Combination therapy based on targeted nano drug co-delivery systems for liver fibrosis treatment: A review

Liver fibrosis is the hallmark of liver disease and occurs prior to the stages of cirrhosis and hepatocellular carcinoma. Any type of liver damage or inflammation can result in fibrosis. Fibrosis does not develop overnight, but rather as a result of the long-term action of injury factors. At present, however, there are no good treatment methods or specific drugs other than removing the pathogenic factors. Drug application is still limited, which means that drugs with good performance in vitro cannot achieve good therapeutic effects in vivo, owing to various factors such as poor drug targeting, large side effects, and strong hydrophobicity. Hepatic stellate cells (HSC) are the primary effector cells in liver fibrosis. The nano-drug delivery system is a new and safe drug delivery system that has many advantages which are widely used in the field of liver fibrosis. Drug resistance and side effects can be reduced when two or more drugs are used in combination drug delivery. Combination therapy of drugs with different targets has emerged as a novel approach to treating liver fibrosis, and the nano co-delivery system enhances the benefits of combination therapy. While nano co-delivery systems can maximize benefits while avoiding drug side effects, this is precisely the advantage of the nano co-delivery system. This review briefly described the pathogenesis and current treatment strategies, the different co-delivery systems of combination drugs in the nano delivery system, and targeting strategies for nano delivery systems on liver fibrosis therapy. Because of their superior performance, nano delivery systems and targeting drug delivery systems have received a lot of attention in the new drug delivery system. The new delivery systems offer a new pathway in the treatment of liver fibrosis, and it is believed that it can be a new treatment for fibrosis in the future. Nano co-delivery system of combination drugs and targeting strategies has proven the effectiveness of anti-fibrosis at the experimental level.