Nitric oxide promotes caspase-independent hepatic stellate cell apoptosis through the generation of reactive oxygen species

Hybrid non-animal modeling: A mechanistic approach to predict chemical hepatotoxicity

Developing mechanistic non-animal testing methods based on the adverse outcome pathway (AOP) framework must incorporate molecular and cellular key events associated with target toxicity. Using data from an in vitro assay and chemical structures, we aimed to create a hybrid model to predict hepatotoxicants. We first curated a reference dataset of 869 compounds for hepatotoxicity modeling. Then, we profiled them against PubChem for existing in vitro toxicity data. Of the 2560 resulting assays, we selected the mitochondrial membrane potential (MMP) assay, a high-throughput screening (HTS) tool that can test chemical disruptors for mitochondrial function. Machine learning was applied to develop quantitative structure-activity relationship (QSAR) models with 2536 compounds tested in the MMP assay for screening new compounds. The MMP assay results, including QSAR model outputs, yielded hepatotoxicity predictions for reference set compounds with a Correct Classification Ratio (CCR) of 0.59. The predictivity improved by including 37 structural alerts (CCR = 0.8). We validated our model by testing 37 reference set compounds in human HepG2 hepatoma cells, and reliably predicting them for hepatotoxicity (CCR = 0.79). This study introduces a novel AOP modeling strategy that combines public HTS data, computational modeling, and experimental testing to predict chemical hepatotoxicity.

Elucidating the Molecular Pathways and Therapeutic Interventions of Gaseous Mediators in the Context of Fibrosis

Fibrosis, a pathological alteration of the repair response, involves continuous organ damage, scar formation, and eventual functional failure in various chronic inflammatory disorders. Unfortunately, clinical practice offers limited treatment strategies, leading to high mortality rates in chronic diseases. As part of investigations into gaseous mediators, or gasotransmitters, including nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S), numerous studies have confirmed their beneficial roles in attenuating fibrosis. Their therapeutic mechanisms, which involve inhibiting oxidative stress, inflammation, apoptosis, and proliferation, have been increasingly elucidated. Additionally, novel gasotransmitters like hydrogen (H2) and sulfur dioxide (SO2) have emerged as promising options for fibrosis treatment. In this review, we primarily demonstrate and summarize the protective and therapeutic effects of gaseous mediators in the process of fibrosis, with a focus on elucidating the underlying molecular mechanisms involved in combating fibrosis.

Tofogliflozin Delays Portal Hypertension and Hepatic Fibrosis by Inhibiting Sinusoidal Capillarization in Cirrhotic Rats

BACKGROUND

Liver cirrhosis leads to portal hypertension (PH) with capillarization of liver sinusoidal endothelial cells (LSECs), although drug treatment options for PH are currently limited. Sodium glucose transporter 2 inhibitors, which are antidiabetic agents, have been shown to improve endothelial dysfunction. We aimed to elucidate the effect of tofogliflozin on PH and liver fibrosis in a rat cirrhosis model.

METHODS

Male-F344/NSlc rats repeatedly received carbon tetrachloride (CCl4) intraperitoneally to induce PH and liver cirrhosis alongside tofogliflozin (10 or 20 mg/kg). Portal hemodynamics and hepatic phenotypes were assessed after 14 weeks. An in vitro study investigated the effects of tofogliflozin on the crosstalk between LSEC and activated hepatic stellate cells (Ac-HSC), which are relevant to PH development.

RESULTS

Tofogliflozin prevented PH with attenuated intrahepatic vasoconstriction, sinusoidal capillarization, and remodeling independent of glycemic status in CCl4-treated rats. Hepatic macrophage infiltration, proinflammatory response, and fibrogenesis were suppressed by treatment with tofogliflozin. In vitro assays showed that tofogliflozin suppressed Ac-HSC-stimulated capillarization and vasoconstriction in LSECs by enhancing the antioxidant capacity, as well as inhibited the capilliarized LSEC-stimulated contractive, profibrogenic, and proliferative activities of Ac-HSCs.

CONCLUSIONS

Our study provides strong support for tofogliflozin in the prevention of liver cirrhosis-related PH.

Schisantherin A protects hepatocyte via upregulating DDAH1 to ameliorate liver fibrosis in mice

BACKGROUND

Hepatic fibrosis is the pivotal determinant in the progression of chronic liver diseases towards cirrhosis or advanced stages. Studies have shown that Schisantherin A (Sin A), the primary active compound from Schizandra chinensis (Turcz.) Baill., exhibits anti-hepatic fibrosis effects. However, the mechanism of Sin A in liver fibrosis remain unclear.

PURPOSE

To examine the effects and underlying mechanism of Sin A on hepatic fibrosis.

STUDY DESIGN AND METHODS

The effects and mechanism of Sin A were investigated using liver fibrosis mouse models induced by carbon tetrachloride (CCl4) or dimethylnitrosamine (DMN), as well as H2O2-induced hepatocyte injury in vitro.

RESULTS

Sin A treatment ameliorated hepatocyte injury, inflammation, hepatic sinusoidal capillarization, and hepatic fibrosis in both CCl4-induced and DMN-induced mice. Sin A effectively reversed the reduction of DDAH1 expression, the p-eNOS/eNOS ratio and NO generation and attenuated the elevation of hepatic ADMA level induced by CCl4 and DMN. Knockdown of DDAH1 in hepatocytes not only triggered hepatocyte damage, but it also counteracted the effect of Sin A on protecting hepatocytes in vitro.

CONCLUSION

Our findings indicate that Sin A ameliorates liver fibrosis by upregulating DDAH1 to protect against hepatocyte injury. These results provide compelling evidence for Sin A treatment in liver fibrosis.

Gastro‑oesophageal reflux disease in liver cirrhosis: Possible pathogenesis and clinical intervention (Review)

Oesophageal variceal bleeding is a common complication of decompensated liver cirrhosis (LC). Some studies have reported that reflux oesophagitis (RE) is a risk factor for upper gastrointestinal bleeding, and greatly impacts the quality of life. However, the frequency and mechanism of gastro-oesophageal reflux disease (GERD) in LC remain unclear. The present review explored the possible pathogenesis, and analysed the advantages and disadvantages of the interventional measures and the need for implementation of these measures. By combining the comprehensive terms associated with LC, GERD and RE, EMBASE, Medline/PubMed and the Cochrane Library were systematically searched. The underlying pathological mechanism of GERD in LC was summarized: Transient relaxation of the lower oesophageal sphincter, delayed gastric emptying, increased intra-abdominal pressure, increased intragastric pressure and excessive nitric oxide production destroyed the 'anti-reflux barrier', causing gastric content reflux. Proton pump inhibitors (PPIs) have been widely used empirically to lower the risk of oesophageal venous rupture and bleeding. However, long-term use of acid inhibitors in patients with LC may induce complications, such as spontaneous bacterial peritonitis. The metabolic half-life of PPIs is prolonged in patients with severe liver function impairment. Therefore, the indications for using acid inhibitors lack clarity. However, after endoscopic oesophageal variceal eradication, additional benefits may be gained from the long-term use of PPIs in small doses.

Nicorandil/ morphine crosstalk accounts for antinociception and hepatoprotection in hepatic fibrosis in rats: Distinct roles of opioid/cGMP and NO/KATP pathways

Previous report indicated that nicorandil potentiated morphine antinociception and attenuated hepatic injury in liver fibrotic rats. Herein, the underlying mechanisms of nicorandil/morphine interaction were investigated using pharmacological, biochemical, histopathological, and molecular docking studies. Male Wistar rats were injected intraperitoneally (i.p.) with carbon tetrachloride (CCl4, 40%, 2 ml/kg) twice weekly for 5 weeks to induce hepatic fibrosis. Nicorandil (15 mg/kg/day) was administered per os (p.o.) for 14 days in presence of the blockers; glibenclamide (KATP channel blocker, 5 mg/kg, p.o.), L-NG-nitro-arginine methyl ester (L-NAME, nitric oxide synthase inhibitor, 15 mg/kg, p.o.), methylene blue (MB, guanylyl cyclase inhibitor, 2 mg/kg, i.p.) and naltrexone (opioid antagonist, 20 mg/kg, i.p.). At the end of the 5th week, analgesia was evaluated using tail flick and formalin tests along with biochemical determinations of liver function tests, oxidative stress markers and histopathological examination of liver tissues. Naltrexone and MB inhibited the antinociceptive activity of the combination. Furthermore, combined nicorandil/morphine regimen attenuated the release of endogenous peptides. Docking studies revealed a possible interaction of nicorandil on µ, κ and δ opioid receptors. Nicorandil/morphine combination protected against liver damage as evident by decreased liver enzymes, liver index, hyaluronic acid, lipid peroxidation, fibrotic insults, and increased superoxide dismutase activity. Nicorandil/morphine hepatoprotection and antioxidant activity were inhibited by glibenclamide and L-NAME but not by naltrexone or MB. These findings implicate opioid activation/cGMP versus NO/KATP channels in the augmented antinociception, and hepatoprotection, respectively, of the combined therapy and implicate provoked cross talk by nicorandil and morphine on opioid receptors and cGMP signaling pathway. That said, nicorandil/morphine combination provides a potential multitargeted therapy to alleviate pain and preserve liver function.

Nicorandil reduces morphine withdrawal symptoms, potentiates morphine antinociception, and ameliorates liver fibrosis in rats

AIMS

Chronic liver disease (CLD) is a serious medical condition affecting patients globally and pain management poses a unique challenge. ATP-sensitive potassium channels (K_ATP) are expressed in nociceptive neurons and hepatic cells. We tested the hypothesis whether morphine and nicorandil, K_ATP channel opener, alone and in combination possess hepatoprotective, antinociceptive effect and alter morphine physical dependence.

MAIN METHODS

Intraperitoneal injection (i.p.) of carbon tetrachloride (CCl₄) induced liver fibrosis in male Wistar rats. Nicorandil (15 mg/kg/day) was administered per os for two weeks. Morphine (3.8, 5, 10 mg/kg, i.p.) was administered prior to antinociception testing in tail flick and formalin tests. Morphine physical dependence following naloxone injection, fibrotic, oxidative stress markers, and liver histopathology were assessed.

KEY FINDINGS

Morphine alone, produced insignificant changes of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), hyaluronic acid (HA), hepatic hydroxyproline (Hyp), malondialdehyde (MDA), and superoxide dismutase (SOD) levels and exerted significant antinociception in the pain models. Nicorandil alone protected against liver damage (decreased serum ALT, AST, HA, hepatic Hyp, MDA, increased SOD levels, improved fibrosis scores). Nicorandil/morphine combination produced remarkable hepatoprotection and persistent analgesia compared to morphine alone as evidenced by reduced (EC50) of morphine. Nicorandil augmented morphine analgesia and markedly decreased withdrawal signs in morphine-dependent rats.

SIGNIFICANCE

The data showed for the first time, the hepatoprotection and augmented antinociception mediated by nicorandil/morphine combination in liver fibrosis via antioxidant and antifibrotic mechanisms. Nicorandil ameliorated withdrawal signs in morphine dependence in CLD. Thus, combining nicorandil/morphine provides a novel treatment strategy to ameliorate hepatic injury, potentiate antinociception and overcome morphine-induced physical dependence in liver fibrosis.

Crosstalk of TNF-α, IFN-γ, NF-kB, STAT1 and redox signaling in lipopolysaccharide/D-galactosamine/dimethylsulfoxide-induced fulminant hepatic failure in mice

Purpose

The clinical study of fulminant hepatic failure is challenging due to its high mortality and relative rarity, necessitating reliance on pre-clinical models to gain insight into its pathophysiology and develop potential therapies.

Methods and Results

In our study, the combination of the commonly used solvent dimethyl sulfoxide to the current-day model of lipopolysaccharide/d-galactosamine-caused fulminant hepatic failure was found to cause significantly greater hepatic damage, as indicated by alanine aminotransferase level. The effect was dose-dependent, with the maximum increase in alanine aminotransferase observed following 200 μl/kg dimethyl sulfoxide co-administration. Co-administration of 200 μl/kg dimethyl sulfoxide also remarkably increased histopathological changes induced by lipopolysaccharide/d-galactosamine. Importantly, alanine aminotransferase levels and survival rate in the 200 μl/kg dimethyl sulfoxide co-administration groups were both greater than those in the classical lipopolysaccharide/d-galactosamine model. We found that dimethyl sulfoxide co-administration aggravated lipopolysaccharide/d-galactosamine-caused liver damage by stimulating inflammatory signaling, as indicated by tumor necrosis factor alpha (TNF-α), interferon gamma (IFN-γ), inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2) levels. Further, nuclear factor kappa B (NF-kB) and transcription factor activator 1 (STAT1) were upregulated, as was neutrophil recruitment, indicated by myeloperoxidase activity. Hepatocyte apoptosis was also increased, and greater nitro-oxidative stress was noted, as determined based on nitric oxide, malondialdehyde, and glutathione levels.

Conclusion

Co-treatment with low doses of dimethyl sulfoxide enhanced the lipopolysaccharide/d-galactosamine-caused hepatic failure in animals, with higher toxicity and greater survival rates. The current findings also highlight the potential danger of using dimethyl sulfoxide as a solvent in experiments involving the hepatic immune system, suggesting that the new lipopolysaccharide/d-galactosamine/dimethyl sulfoxide model described herein could be used for pharmacological screening with the goal to better understand hepatic failure and evaluate treatment approaches.

Critical Role for Hepatocyte-Specific eNOS in NAFLD and NASH

Regulation of endothelial nitric oxide synthase (eNOS) in hepatocytes may be an important target in nonalcoholic fatty liver disease (NAFLD) development and progression to nonalcoholic steatohepatitis (NASH). In this study, we show genetic deletion and viral knockdown of hepatocyte-specific eNOS exacerbated hepatic steatosis and inflammation, decreased hepatic mitochondrial fatty acid oxidation and respiration, increased mitochondrial H₂O₂ emission, and impaired the hepatic mitophagic (BNIP3 and LC3II) response. Conversely, overexpressing eNOS in hepatocytes in vitro and in vivo increased hepatocyte mitochondrial respiration and attenuated Western diet-induced NASH. Moreover, patients with elevated NAFLD activity score (histology score of worsening steatosis, hepatocyte ballooning, and inflammation) exhibited reduced hepatic eNOS expression, which correlated with reduced hepatic mitochondrial fatty acid oxidation and lower hepatic protein expression of mitophagy protein BNIP3. The current study reveals an important molecular role for hepatocyte-specific eNOS as a key regulator of NAFLD/NASH susceptibility and mitochondrial quality control with direct clinical correlation to patients with NASH.

Gasotransmitters: Potential Therapeutic Molecules of Fibrotic Diseases

Fibrosis is defined as the pathological progress of excessive extracellular matrix (ECM), such as collagen, fibronectin, and elastin deposition, as the regenerative capacity of cells cannot satisfy the dynamic repair of chronic damage. The well-known features of tissue fibrosis are characterized as the presence of excessive activated and proliferated fibroblasts and the differentiation of fibroblasts into myofibroblasts, and epithelial cells undergo the epithelial-mesenchymal transition (EMT) to expand the number of fibroblasts and myofibroblasts thereby driving fibrogenesis. In terms of mechanism, during the process of fibrosis, the activations of the TGF-β signaling pathway, oxidative stress, cellular senescence, and inflammatory response play crucial roles in the activation and proliferation of fibroblasts to generate ECM. The deaths due to severe fibrosis account for almost half of the total deaths from various diseases, and few treatment strategies are available for the prevention of fibrosis as yet. Recently, numerous studies demonstrated that three well-defined bioactive gasotransmitters, including nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S), generally exhibited anti-inflammatory, antioxidative, antiapoptotic, and antiproliferative properties. Besides these effects, a number of studies have reported that low-dose exogenous and endogenous gasotransmitters can delay and interfere with the occurrence and development of fibrotic diseases, including myocardial fibrosis, idiopathic pulmonary fibrosis, liver fibrosis, renal fibrosis, diabetic diaphragm fibrosis, and peritoneal fibrosis. Furthermore, in animal and clinical experiments, the inhalation of low-dose exogenous gas and intraperitoneal injection of gaseous donors, such as SNAP, CINOD, CORM, SAC, and NaHS, showed a significant therapeutic effect on the inhibition of fibrosis through modulating the TGF-β signaling pathway, attenuating oxidative stress and inflammatory response, and delaying the cellular senescence, while promoting the process of autophagy. In this review, we first demonstrate and summarize the therapeutic effects of gasotransmitters on diverse fibrotic diseases and highlight their molecular mechanisms in the process and development of fibrosis.

Roles of nuclear receptors in hepatic stellate cells

Introduction: Hepatic stellate cells (HSCs) are essential for physiological homeostasis of the liver extracellular matrix (ECM). Excessive transdifferentiation of HSC from a quiescent to an activated phenotype contributes to disrupt this balance and can lead to liver fibrosis. Accumulating evidence has suggested that nuclear receptors (NRs) are involved in the regulation of HSC activation, proliferation, and function. Therefore, these NRs may be therapeutic targets to balance ECM homeostasis and inhibit HSC activation in liver fibrosis.Areas covered: In this review, the authors summarized the recent progress in the understanding of the regulatory role of NRs in HSCs and their potential as drug targets in liver fibrosis.Expert opinion: NRs are still potential therapy targets for inhibiting HSCs activation and liver fibrosis. However, the development of NRs agonists or antagonists to inhibit HSCs requires fully consideration of systemic effects.

The Power of Plasticity-Metabolic Regulation of Hepatic Stellate Cells

Hepatic stellate cells (HSCs) are resident non-parenchymal liver pericytes whose plasticity enables them to regulate a remarkable range of physiologic and pathologic responses. To support their functions in health and disease, HSCs engage pathways regulating carbohydrate, mitochondrial, lipid, and retinoid homeostasis. In chronic liver injury, HSCs drive hepatic fibrosis and are implicated in inflammation and cancer. To do so, the cells activate, or transdifferentiate, from a quiescent state into proliferative, motile myofibroblasts that secrete extracellular matrix, which demands rapid adaptation to meet a heightened energy need. Adaptations include reprogramming of central carbon metabolism, enhanced mitochondrial number and activity, endoplasmic reticulum stress, and liberation of free fatty acids through autophagy-dependent hydrolysis of retinyl esters that are stored in cytoplasmic droplets. As an archetype for pericytes in other tissues, recognition of the HSC's metabolic drivers and vulnerabilities offer the potential to target these pathways therapeutically to enhance parenchymal growth and modulate repair.

Autophagy in liver diseases

Autophagy is the liver cell energy recycling system regulating a variety of homeostatic mechanisms. Damaged organelles, lipids and proteins are degraded in the lysosomes and their elements are re-used by the cell. Investigations on autophagy have led to the award of two Nobel Prizes and a health of important reports. In this review we describe the fundamental functions of autophagy in the liver including new data on the regulation of autophagy. Moreover we emphasize the fact that autophagy acts like a two edge sword in many occasions with the most prominent paradigm being its involvement in the initiation and progress of hepatocellular carcinoma. We also focused to the implication of autophagy and its specialized forms of lipophagy and mitophagy in the pathogenesis of various liver diseases. We analyzed autophagy not only in well studied diseases, like alcoholic and nonalcoholic fatty liver and liver fibrosis but also in viral hepatitis, biliary diseases, autoimmune hepatitis and rare diseases including inherited metabolic diseases and also acetaminophene hepatotoxicity. We also stressed the different consequences that activation or impairment of autophagy may have in hepatocytes as opposed to Kupffer cells, sinusoidal endothelial cells or hepatic stellate cells. Finally, we analyzed the limited clinical data compared to the extensive experimental evidence and the possible future therapeutic interventions based on autophagy manipulation.

Vitamin A and Its Multi-Effects on Pancreas: Recent Advances and Prospects

Vitamin A (VA), which is stored in several forms in most tissues, is required to maintain metabolite homeostasis and other processes, including the visual cycle, energy balance, epithelial cell integrity, and infection resistance. In recent years, VA molecules, also known as retinoids, have been extensively explored and used in the treatment of skin disorders and immune-related tumors. To date, several observational and interventional studies have explored the relationship between VA status and the pathogenesis of diabetes. In particular, VA micronutrients have been shown to regulate pancreatic development, β-cell function, pancreatic innate immune responses, and pancreatic stellate cells phenotypes through multiple mechanisms. However, there are still many problems to be proven or resolved. In this review, we summarize and discuss recent and available evidence on VA biological metabolism in the pancreas. Analysis of the effects of VA on metabolism in the pancreas will contribute to our understanding of the supportive physiological roles of VA in pancreas protection.

The Emerging Role of Hepatocellular eNOS in Non-alcoholic Fatty Liver Disease Development

Non-alcoholic fatty liver disease (NAFLD) is comprised of a spectrum of liver injury ranging from excess fat accumulation in the liver (steatosis), to steatohepatitis (NASH), to its end stage of cirrhosis. A hallmark of NAFLD progression is the decline in function of hepatic mitochondria, although the mechanisms remain unresolved. Given the important role endothelial nitric oxide synthase (eNOS) plays in mitochondrial dynamics in other tissues, it has emerged as a potential mediator of maintaining mitochondrial function in the liver. In this mini review, we summarize the most relevant findings that extends current understanding of eNOS as a regulator of mitochondrial biogenesis, and identifies a potential additional role in mitochondrial turnover and attenuating inflammation during NAFLD development and progression.

Liver fibrosis: Pathophysiology and clinical implications

Liver fibrosis is a clinically significant finding that has major impacts on patient morbidity and mortality. The mechanism of fibrosis involves many different cellular pathways, but the major cell type involved appears to be hepatic stellate cells. Many liver diseases, including Hepatitis B, C, and fatty liver disease cause ongoing hepatocellular damage leading to liver fibrosis. No matter the cause of liver disease, liver-related mortality increases exponentially with increasing fibrosis. The progression to cirrhosis brings more dramatic mortality and higher incidence of hepatocellular carcinoma. Fibrosis can also affect outcomes following liver transplantation in adult and pediatric patients and require retransplantation. Drugs exist to treat Hepatitis B and C that reverse fibrosis in patients with those viral diseases, but there are currently no therapies to directly treat liver fibrosis. Several mouse models of chronic liver diseases have been successfully reversed using novel drug targets with current therapies focusing mostly on prevention of myofibroblast activation. Further research in these areas could lead to development of drugs to treat fibrosis, which will have invaluable impact on patient survival. This article is categorized under: Metabolic Diseases > Molecular and Cellular Physiology.

Improved Hepatic Reserve and Fibrosis in a Case of "Portal-Systemic Liver Failure" by Portosystemic Shunt Occlusion

Patient: Female, 67-year-old

Final Diagnosis: Portal-systemic liver failure

Symptoms: None (second opinion)

Medication: None

Clinical Procedure: Balloon-occluded retrograde transvenous obliteration (BRTO) Specialty: Radiology

The Roles of Notch Signaling in Liver Development and Disease

The Notch signaling pathway plays major roles in organ development across animal species. In the mammalian liver, Notch has been found critical in development, regeneration and disease. In this review, we highlight the major advances in our understanding of the role of Notch activity in proper liver development and function. Specifically, we discuss the latest discoveries on how Notch, in conjunction with other signaling pathways, aids in proper liver development, regeneration and repair. In addition, we review the latest in the role of Notch signaling in the pathogenesis of liver fibrosis and chronic liver disease. Finally, recent evidence has shed light on the emerging connection between Notch signaling and glucose and lipid metabolism. We hope that highlighting the major advances in the roles of Notch signaling in the liver will stimulate further research in this exciting field and generate additional ideas for therapeutic manipulation of the Notch pathway in liver diseases.

Effects of inorganic nanoparticles on liver fibrosis: Optimizing a double-edged sword for therapeutics

Liver fibrosis is a condition of sustained wound healing in response to chronic liver injury caused by various factors such as viral, cholestatic and inflammatory diseases. Despite significant advances in the understanding of the mechanistic details of fibrosis, therapeutic intervention with the use of anti-fibrotic drugs achieved only marginal efficacy. Among which, pharmacokinetics profile of agents leading to off-targeting and suboptimal distribution are the principal limiting factors. Concurrently, inorganic nanoparticles (NPs) have gained significant recognition in biomedicine, owning to their unique physicochemical properties. Since NPs are known to accumulate in well vascularised organs, the intuitive therapeutic targeting of the liver using engineered NPs seems to be a plausible approach in treating liver fibrosis. However, the application of inorganic NPs also raised concerns of its potential long-term impact to humans. Current literatures have reported both negative risks as well as surprising benefits, thus sparking off a needful discussion about the feasibility of using inorganic NPs in treating liver fibrosis. Inorganic NPs entrapped in the liver may pose health risks, particularly due to their non-biodegradability and potential toxicity when accumulated in undesirable concentrations. This highlighted the need to assess the health risk of using inorganic NPs, and also to establish a framework to evaluate the conditions when the beneficial effects of these NPs would outweigh potential risks. Hence, this review takes a balanced approach on assessing the mechanistic details behind inorganic NP-induced biochemical perturbations, which could either alleviate or worsen liver fibrosis. Consequently, it attempts to chart out possibilities for future directions through optimizing therapeutic outcomes by design.

The potential role of vascular alterations and subsequent impaired liver blood flow and hepatic hypoxia in the pathophysiology of non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) covers a spectrum of disease ranging from steatosis to steatohepatitis (NASH) and fibrosis, but the underlying pathophysiological mechanisms remain largely unknown. As there is currently no approved pharmacological therapy and the prevalence of NAFLD keeps increasing, understanding of its pathophysiology is crucial. We hypothesise that vascular alterations in early NAFLD play a role in the progression of the disease by inducing an increased intrahepatic vascular resistance and consequently relative hypoxia in the liver. Evidence of the detrimental effects of hypoxia in NAFLD has already been observed in liver surgery, where the outcomes of steatotic livers after ischaemia-reperfusion are worse than in healthy livers, and in obstructive sleep apnoea, which is an independent risk factor of NAFLD. Moreover, early histological damage in NAFLD is situated in the pericentral zone, which is also the first zone to be affected by a decreased oxygen tension because of the unique hepatic vacsular anatomy that causes the pericentral oxygen tension to be the lowest. Angiogenesis is also a characteristic of NAFLD, driven by hypoxia-induced mechanisms, as demonstrated in both animal models and in humans with NAFLD. Relative hypoxia is most probably induced by impaired blood flow to the liver, caused by increased intrahepatic vascular resistance. An increased intrahepatic vascular resistance early in the development of disease has been convincingly demonstrated in several animal models of NAFLD, whereas an increased portal pressure, a consequence of increased intrahepatic vascular resistance, has been proven in patients with NAFLD. Animal studies demonstrated a decreased intrahepatic effect of vasodilators and an increased reactivity to vasoconstrictors that results in an increased intrahepatic vascular resistance, thus the presence of a functional component. Pharmacological products that target vasoregulation can hence improve the intrahepatic vascular resistance and this might prevent or reverse progression of NAFLD, representing an important therapeutic option to study. Some of the drugs currently under evaluation in clinical trials for NASH have interesting properties related to the hepatic vasculature. Some other interesting drugs have been tested in animal models but further study in patients with NAFLD is warranted. In summary, in this paper we summarise the evidence that leads to the hypothesis that an increased intrahepatic vascular resistance and subsequent parenchymal hypoxia in early NAFLD is an important pathophysiological driving mechanism for the progression of the disease.

Effectiveness of vinpocetine and isosorbide-5-mononitrate on experimental schistosomiasis mansoni: Biochemical and immunohistochemical study

Schistosomiasis is one of the most important tropical and subtropical devastating diseases, where praziquantel is the sole drug of choice. Praziquantel effectively kills the adult worms, however, drug resistance has been repeatedly reported. Moreover, there is currently no efficient anti-fibrotic therapy available for chronic schistosomiasis. So, novel drugs which exert anti-fibrotic efficacy are urgently needed. This research is complementary to our previous work that evaluated the anti-schistosomal effects of the anti-inflammatory vinpocetine, as well as the vasodilator and the anti-oxidant isosorbide-5-mononitrate. In the present study, we assessed the therapeutic efficacies of drugs in Swiss albino female mice experimentally infected with an Egyptian strain of Schistosoma mansoni, using some biochemical and immunohistochemical parameters. Our results revealed that both vinpocetine and isosorbide-5-mononitrate monotherapy significantly decreased hepatic nuclear factor-kappaB, 10 weeks post infection. The best effects were seen in mice administered praziquantel combined with isosorbide-5-mononitrate, as detected by reduction in hydroxyproline and collagen contents of the liver, and significant increase in the hepatic nitric oxide content. The data provides insight into the potential effects of the assessed drugs with isosorbide-5-mononitrate being more superior to vinpocetine, hence it can be used as novel adjuvant to praziquantel to alleviate schistosomal hepatic fibrosis. However, molecular mechanism/s and clinical trials are worthy to be scrutinized.

Effective Amelioration of Liver Fibrosis Through Lentiviral Vector Carrying Toxoplasma gondii gra15II in Murine Model

Our previous investigations indicated that in vitro polarization of mouse macrophages by Toxoplasma gondii type II strain dense granule protein 15 (GRA15 II ), one of the genotype-associated effectors of T. gondii, induced the phenotypes of classically activated macrophage (M1). Transfusion of the cells to mice may effectively alleviated hepatic fibrosis caused by schistosomiasis. The purpose of the study was to identify whether liver macrophages can be in vivo driven to M1 macrophages by lentiviral vector (LV) carrying GRA15 II gene (LV-gra15 II ) and to explore the potential mechanism by which the LV-gra15 II -activated liver macrophage (LV-gra15 II -M) ameliorates the hepatic fibrosis in schistosomiasis. The mice were treated with LV-gra15 II by hydrodynamic injection via the tail vein followed by challenge of Schistosoma japonicum (S. japonicum). Our experiments showed that LV-gra15 II was successfully delivered to liver macrophages and GRA15II was persistently expressed in the macrophages of mice for at least 2 months. Furthermore, the LV-gra15 II infected macrophages were polarized to M1 macrophages in vivo. Consequently, mice with schistosomiasis receiving LV-gra15 II injection displayed a remarkable amelioration of liver granuloma formation and collagen deposition in association with downregulated expression of transforming growth factor-beta1, arginase 1 (Arg-1), α-smooth muscle actin, and an increased expression of matrix metalloproteinase 13 (MMP13). Simultaneously, no negative effects of liver function and vitality of mice were noted. The in vitro experiments indicated that the C-C motif chemokine ligand 2 and nitric oxide level were elevated in LV-gra15 II -M cultural supernatants; hepatocyte growth factor expression was enhanced in LV-gra15 II -M. In addition, LV-gra15 II -M not only secreted MMP13, which greatly degraded type I collagen, but also induced murine hepatic stellate cell (HSC) line (JS1) apoptosis in the co-culture system. Taken together, we identified for the first time that LV-gra15 II may in vivo drive liver macrophages to M1 macrophage phenotypes, which helps for alteration of the liver fibrotic microenvironment with collagen dissolution, HSC deactivation, apoptosis and hepatocyte protection. Our study gives an insight into the use of gene delivery with parasite-derived immunomodulatory factor as a potential immune cell activating agent to re-equilibrate the other pathogen-induced immune response in some chronic diseases.

The soluble guanylate cyclase stimulator riociguat reduces fibrogenesis and portal pressure in cirrhotic rats

In cirrhotic patients, portal hypertension (PHT) deteriorates survival, yet treatment options are limited. A major contributor to increased intrahepatic vasoconstriction in PHT is dysfunctional nitric-oxide signaling. Soluble guanylate cyclase (sGC) is the receptor of nitric-oxide and can be stimulated by riociguat. Riociguat is approved for pulmonary hypertension but has not been studied in liver cirrhosis. In this study we assessed the effects of riociguat on PHT and liver fibrosis in cholestatic (bile duct ligation, BDL) and toxic (carbon-tetrachloride, CCl4) rat models. In cirrhotic livers sGC expression was upregulated. In BDL rats, riociguat reduced liver fibrosis and decreased portal pressure without affecting systemic hemodynamics. In an early BDL disease stage, riociguat decreased bile duct proliferation, improved sinusoidal vascular dysfunction and inhibited angiogenesis. In advanced BDL riociguat exhibited anti-inflammatory effects. In CCl4 rats the beneficial effects of riociguat treatment were less pronounced and confined to an early disease stage. Similarly, in patients with cholestatic cirrhosis and PHT nitrates (that induce sGC activity) decreased portal pressure more effectively than in patients with non-cholestatic etiology. We also found an improvement of transaminases in patients with pulmonary hypertension receiving riociguat. Our findings support the clinical development of sGC stimulators in patients with cirrhotic PHT.

Role of Oxidative Stress in Pathophysiology of Nonalcoholic Fatty Liver Disease

Liver steatosis without alcohol consumption, namely, nonalcoholic fatty liver disease (NAFLD), is a common hepatic condition that encompasses a wide spectrum of presentations, ranging from simple accumulation of triglycerides in the hepatocytes without any liver damage to inflammation, necrosis, ballooning, and fibrosis (namely, nonalcoholic steatohepatitis) up to severe liver disease and eventually cirrhosis and/or hepatocellular carcinoma. The pathophysiology of fatty liver and its progression is influenced by multiple factors (environmental and genetics), in a “multiple parallel-hit model,” in which oxidative stress plays a very likely primary role as the starting point of the hepatic and extrahepatic damage. The aim of this review is to give a comprehensive insight on the present researches and findings on the role of oxidative stress mechanisms in the pathogenesis and pathophysiology of NAFLD. With this aim, we evaluated the available data in basic science and clinical studies in this field, reviewing the most recent works published on this topic.

Elevated mitochondrial activity distinguishes fibrogenic hepatic stellate cells and sensitizes for selective inhibition by mitotropic doxorubicin

Activation of hepatic stellate cells (HSCs) is an integral component of the wound‐healing process in liver injury/inflammation. However, uncontrolled activation of HSCs leads to constant secretion of collagen‐rich extracellular matrix (ECM) proteins, resulting in liver fibrosis. The enhanced ECM synthesis/secretion demands an uninterrupted supply of intracellular energy; however, there is a paucity of data on the bioenergetics, particularly the mitochondrial (mito) metabolism of fibrogenic HSCs. Here, using human and rat HSCs in vitro, we show that the mito‐respiration, mito‐membrane potential (Δψm) and cellular ‘bioenergetic signature’ distinguish fibrogenic HSCs from normal, less‐active HSCs. Ex vivo, HSCs from mouse and rat models of liver fibrosis further confirmed the altered ‘bioenergetic signature’ of fibrogenic HSCs. Importantly, the distinctive elevation in mito‐Δψm sensitized fibrogenic HSCs for selective inhibition by mitotropic doxorubicin while normal, less‐active HSCs and healthy human primary hepatocytes remained minimally affected if not, unaffected. Thus, the increased mito‐Δψm may provide an opportunity to selectively target fibrogenic HSCs in liver fibrosis.

Biology of portal hypertension

Portal hypertension develops as a result of increased intrahepatic vascular resistance often caused by chronic liver disease that leads to structural distortion by fibrosis, microvascular thrombosis, dysfunction of liver sinusoidal endothelial cells (LSECs), and hepatic stellate cell (HSC) activation. While the basic mechanisms of LSEC and HSC dysregulation have been extensively studied, the role of microvascular thrombosis and platelet function in the pathogenesis of portal hypertension remains to be clearly characterized. As a secondary event, portal hypertension results in splanchnic and systemic arterial vasodilation, leading to the development of a hyperdynamic circulatory syndrome and subsequently to clinically devastating complications including gastroesophageal varices and variceal hemorrhage, hepatic encephalopathy from the formation of portosystemic shunts, ascites, and renal failure due to the hepatorenal syndrome. This review article discusses: (1) mechanisms of sinusoidal portal hypertension, focusing on HSC and LSEC biology, pathological angiogenesis, and the role of microvascular thrombosis and platelets, (2) the mesenteric vasculature in portal hypertension, and (3) future directions for vascular biology research in portal hypertension.

Role and regulation of autophagy and apoptosis by nitric oxide in hepatic stellate cells during acute liver failure

BACKGROUND & AIMS

We previously found that hepatic stellate cell activation induced by autophagy maintains the liver architecture to prevent collapse during acute liver failure. Nitric oxide has shown to induce hepatic stellate cell apoptosis. Whether and how nitric oxide is involved in acute liver failure and autophagy remains unclear.

METHODS

Acute liver failure patients were recruited to investigate the correlation between plasma nitric oxide levels and clinical features. Liver tissues were collected from chronic hepatitis patients by biopsy and from acute liver failure patients who had undergone liver transplantation. The expression of nitric oxide synthases and hepatic stellate cell activation (alpha-SMA), and autophagic activity (LC3) were investigated by immunohistochemistry. Autophagy and apoptosis were investigated by immunoblot analysis, confocal microscopy, and flow cytometry in hepatic stellate cells treated with nitric oxide donors.

RESULTS

Plasma nitric oxide level was significantly increased in patients with acute liver failure compared to those with cirrhosis (53.60±19.74 μM vs 19.40±9.03 μM, Z=-7.384, P<.001) and positively correlated with MELD-Na score (r=.539, P<.001), implicating nitric oxide in acute liver failure. At least some Nitric oxide was produced by overexpression of inducible nitric oxide synthases and endothelial nitric oxide synthases, but not neuronal nitric oxide synthases in the liver tissue. In vivo observation revealed that autophagy was inhibited in hepatic stellate cells based on decreased LC3 immunostaining, and in vitro experiments demonstrated that Nitric oxide can inhibit autophagy. Moreover, nitric oxide promoted hepatic stellate cell apoptosis, which was rescued by an autophagy inducer.

CONCLUSIONS

Increased nitric oxide synthases/ nitric oxide promotes apoptosis through autophagy inhibition in hepatic stellate cells during acute liver failure, providing a novel strategy for the treatment of patients with acute liver failure.

"Non alcoholic fatty liver disease and eNOS dysfunction in humans"

Background

NAFLD is associated to Insulin Resistance (IR). IR is responsible for Endothelial Dysfunction (ED) through the impairment of eNOS function. Although eNOS derangement has been demonstrated in experimental models, no studies have directly shown that eNOS dysfunction is associated with NAFLD in humans. The aim of this study is to investigate eNOS function in NAFLD patients.

Methods

Fifty-four NAFLD patients were consecutively enrolled. All patients underwent clinical and laboratory evaluation and liver biopsy. Patients were divided into two groups by the presence of NAFL or NASH. We measured vascular reactivity induced by patients’ platelets on isolated mice aorta rings. Immunoblot assays for platelet-derived phosphorylated-eNOS (p-eNOS) and immunohistochemistry for hepatic p-eNOS have been performed to evaluate eNOS function in platelets and liver specimens. Flow-mediated-dilation (FMD) was also performed. Data were compared with healthy controls.

Results

Twenty-one (38, 8%) patients had NAFL and 33 (61, 7%) NASH. No differences were found between groups and controls except for HOMA and insulin (p < 0.0001). Vascular reactivity demonstrated a reduced function induced from NAFLD platelets as compared with controls (p < 0.001), associated with an impaired p-eNOS in both platelets and liver (p < 0.001). NAFL showed a higher impairment of eNOS phosphorylation in comparison to NASH (p < 0.01). In contrast with what observed in vitro, the vascular response by FMD was worse in NASH as compared with NAFL.

Conclusions

Our data showed, for the first time in humans, that NAFLD patients show a marked eNOS dysfunction, which may contribute to a higher CV risk. eNOS dysfunction observed in platelets and liver tissue didn’t match with FMD.

Elevated nitric oxide levels associated with hepatic cell apoptosis during liver injury

Hepatic injury is a major event in liver surgery such as liver transplantation and it always leads to hepatic cell apoptosis. Nitric oxide (NO) is a key signaling regulation molecule. Many researchers have shown that increased NO level can influence liver cell apoptosis by promoting or inhibiting the relative signaling pathways that are involved in the caspase family, Bax/Bcl-2, mitochondria, oxidative stress, death receptors, and mitogen-activated protein kinases. Elucidating the relationships between NO and hepatic cell apoptosis is necessary for ameliorating prognosis of liver surgery. This article reviews the newest research progress in the relationships between higher NO levels and hepatic cell apoptosis in liver injury.

Interleukin-6 secreted by bipotential murine oval liver stem cells induces apoptosis of activated hepatic stellate cells by activating NF-κB-inducible nitric oxide synthase signaling

Liver fibrosis is now well recognized as the causative factor for increased mortality from complications associated with liver pathologies. Activated hepatic stellate cells (HSCs) play a critical role in the progression of liver fibrosis. Therefore, targeting these activated HSCs to prevent and (or) treat liver disease is a worthwhile approach to explore. In the present in vitro study, we investigated the use of bipotential murine oval liver cells (BMOL) in regulating the functions of activated HSCs to prevent progression of liver fibrosis. We used a conditioned medium-based approach to study the effect of BMOL cells on activated HSC survival and function. Our data showed that BMOL cells block the contraction of activated HSCs by inducing apoptosis of these cells. We demonstrated that BMOL cells secrete soluble factors, such as interleukin-6 (IL-6), which induced apoptosis of activated HSCs. Using both pharmacological and molecular inhibitor approaches, we further identified that IL-6-mediated activation of NF-κB-iNOS-NO-ROS signaling in activated HSCs plays a critical role in BMOL-cell-mediated apoptosis of activated HSCs. Thus, the present study provides an alternative cell-based therapeutic approach to treat liver fibrosis.

Hepatic sinusoids in liver injury, inflammation, and fibrosis: new pathophysiological insights

Changes of hepatic sinusoids are crucial in the pathogenesis of liver cirrhosis and portal hypertension. Liver injury leads to distinct morphological abnormalities such as loss of sinusoidal fenestration, vasoconstriction, and angiogenesis as well as molecular changes. Communication between the two key cells in this hepatic microenvironment-hepatic stellate cells (HSC) and sinusoidal endothelial cells (SEC)-has been studied for many years and several canonical pathways have been elucidated, such as decreased eNOS activity or increased PDGF and TGF-β production leading to activation and migration of HSC. In recent studies, alternative pathways of intercellular communication in liver diseases have been described such as cell-derived extracellular vesicles called exosomes, which deliver cell compounds to their target cells. Moreover, such extracellular vesicles may link injury to inflammation in alcoholic hepatitis. While inflammation leading to liver fibrosis has been studied in detail, in some circumstances pathways other than the known canonical inflammatory pathways may contribute to hepatic fibrogenesis. For example, in congestive hepatopathy, sinusoidal dilatation and fibrosis have been shown to be mediated by non-inflammatory mechanisms and associated with sinusoidal thrombi. A recently developed murine model further enables experimental studies of this disease entity. Increasing knowledge about these alternative disease pathways in liver injury, inflammation, and fibrosis may reveal possible target molecules for future therapies. This article builds upon a seminar given at the recent 3rd JSGE International Topic Conference in Sendai, Japan, and reviews the areas outlined above.

Contribution of Cyclooxygenase End Products and Oxidative Stress to Intrahepatic Endothelial Dysfunction in Early Non-Alcoholic Fatty Liver Disease

Introduction

Metabolic syndrome induces endothelial dysfunction, a surrogate marker of cardiovascular disease. In parallel, metabolic syndrome is frequently associated with non-alcoholic fatty liver disease (NAFLD), which may progress to cirrhosis. The aim of the present study was to evaluate intrahepatic endothelial dysfunction related to cyclooxygenase end products and oxidative stress as possible mechanisms involved in the pathophysiology of NAFLD.

Materials and Methods

Sprague-Dawley rats were fed standard diet (control-diet, CD) or high-fat-diet (HFD) for 6 weeks. Metabolic syndrome was assessed by recording arterial pressure, lipids, glycemia and rat body weight. Splanchnic hemodynamics were measured, and endothelial dysfunction was evaluated using concentration-effect curves to acetylcholine. Response was assessed with either vehicle, L-N^G-Nitroarginine (L-NNA), indomethacin, tempol, or a thromboxane receptor antagonist, SQ 29548. We quantified inflammation, fibrosis, oxidative stress, nitric oxide (NO) bioavailability and thromboxane B₂ levels.

Results

HFD rats exhibited metabolic syndrome together with the presence of NAFLD. Compared to control-diet livers, HFD livers showed increased hepatic vascular resistance unrelated to inflammation or fibrosis, but with decreased NO activity and increased oxidative stress. Endothelial dysfunction was observed in HFD livers compared with CD rats and improved after cyclooxygenase inhibition or tempol pre-incubation. However, pre-incubation with SQ 29548 did not modify acetylcholine response.

Conclusions

Our study provides evidence that endothelial dysfunction at an early stage of NAFLD is associated with reduced NO bioavailability together with increased cyclooxygenase end products and oxidative stress, which suggests that both pathways are involved in the pathophysiology and may be worth exploring as therapeutic targets to prevent progression of the disease.

Fusion protein of retinol-binding protein and albumin domain III reduces liver fibrosis

Activated hepatic stellate cells (HSCs) play a key role in liver fibrosis, and inactivating HSCs has been considered a promising therapeutic approach. We previously showed that albumin and its derivative designed for stellate cell-targeting, retinol-binding protein-albumin domain III fusion protein (referred to as R-III), inactivate cultured HSCs. Here, we investigated the mechanism of action of albumin/R-III in HSCs and examined the anti-fibrotic potential of R-III in vivo. R-III treatment and albumin expression downregulated retinoic acid (RA) signaling which was involved in HSC activation. RA receptor agonist and retinaldehyde dehydrogenase overexpression abolished the anti-fibrotic effect of R-III and albumin, respectively. R-III uptake into cultured HSCs was significantly decreased by siRNA-STRA6, and injected R-III was localized predominantly in HSCs in liver. Importantly, R-III administration reduced CCl4- and bile duct ligation-induced liver fibrosis. R-III also exhibited a preventive effect against CCl4-inducd liver fibrosis. These findings suggest that the anti-fibrotic effect of albumin/R-III is, at least in part, mediated by downregulation of RA signaling and that R-III is a good candidate as a novel anti-fibrotic drug.

Nitric oxide in liver fibrosis: The role of inducible nitric oxide synthase

The inducible form of nitric oxide synthase (iNOS) is expressed in hepatic cells in pathological conditions. Its induction is involved in the development of liver fibrosis, and thus iNOS could be a therapeutic target for liver fibrosis. This review summarizes the role of iNOS in liver fibrosis, focusing on 1) iNOS biology, 2) iNOS-expressing liver cells, 3) iNOS-related therapeutic strategies, and 4) future directions.

HOI-02 induces apoptosis and G2-M arrest in esophageal cancer mediated by ROS

Reactive oxygen species (ROS) are chemically reactive molecules that perform essential functions in living organisms. Accumulating evidence suggests that many types of cancer cells exhibit elevated levels of ROS. Conversely, generation of ROS has become an effective method to kill cancer cells. (E)-3-hydroxy-3-(4-(4-nitrophenyl)-2-oxobut-3-en-1-yl) indolin-2-one, which is an NO2 group-containing compound designated herein as HOI-02, generated ROS and, in a dose-dependent manner, decreased esophageal cancer cell viability and inhibited anchorage-independent growth, followed by apoptosis and G2-M arrest. Moreover, results of an in vivo study using a patient-derived xenograft mouse model showed that HOI-02 treatment suppressed the growth of esophageal tumors, without affecting the body weight of mice. The expression of Ki-67 was significantly decreased with HOI-02 treatment. In addition, the phosphorylation of c-Jun, and expression of p21, cleaved caspase 3, and DCFH-DA were increased in the HOI-02-treated group compared with the untreated control group. In contrast, treatment of cells with (E)-3-(4-(4-aminophenyl)-2-oxobut-3-en-1-yl)-3-hydroxyindolin-2-one, which is an NH2 group-containing compound designated herein as HOI-11, had no effect. Overall, we identified HOI-02 as an effective NO2 group-containing compound that was an effective therapeutic or preventive agent against esophageal cancer cell growth.

Caffeic Acid Phenethyl Ester inhibit Hepatic Fibrosis by Nitric Oxide Synthase and Cystathionine Gamma-Lyase in Rats

Background

Our aim was to study the effect of caffeic acid phenethyl ester (CAPE) on iNOS and cystathionine gamma-lyase (CSE) of hepatic fibrosis rat, and discuss the anti-hepatic fibrosis mechanism of caffeic acid phenethyl ester.

Material/Methods

We observed changes of NO and H₂S in serum of hepatic fibrosis rats. Enzyme-linked immunosorbent assay was used to test OD value of iNOS and CSE in serum of each. The expressions of iNOS and CSE protein in the liver were also detected by immunohistochemistry.

Results

Compared with the model group, the expression of NO and iNOS was decreased obviously and the level of H₂S and CSE was increased in the CAPE group.

Conclusions

CAPE has the effect of anti-hepatic fibrosis, which can be realized through adjusting the expression level of iNOS and CSE.

Angiogenesis and Fibrogenesis in Chronic Liver Diseases

Pathologic angiogenesis appears to be intrinsically associated with the fibrogenic progression of chronic liver diseases, which eventually leads to the development of cirrhosis and related complications, including hepatocellular carcinoma. Several laboratories have suggested that this association is relevant for chronic liver disease progression, with angiogenesis proposed to sustain fibrogenesis. This minireview offers a synthesis of relevant findings and opinions that have emerged in the last few years relating liver angiogenesis to fibrogenesis. We discuss liver angiogenesis in normal and pathophysiologic conditions with a focus on the role of hypoxia and hypoxia-inducible factors and assess the evidence supporting a clear relationship between angiogenesis and fibrogenesis. A section is dedicated to the critical interactions between liver sinusoidal endothelial cells and either quiescent hepatic stellate cells or myofibroblast-like stellate cells. Finally, we introduce the unusual, dual (profibrogenic and proangiogenic) role of hepatic myofibroblasts and emerging evidence supporting a role for specific mediators like vasohibin and microparticles and microvesicles.

Nitric oxide in liver diseases

Nitric oxide (NO) and its derivatives play important roles in the physiology and pathophysiology of the liver. Despite its diverse and complicated roles, certain patterns of the effect of NO on the pathogenesis and progression of liver diseases are observed. In general, NO derived from endothelial NO synthase (eNOS) in liver sinusoidal endothelial cells (LSECs) is protective against disease development, while inducible NOS (iNOS)-derived NO contributes to pathological processes. This review addresses the roles of NO in the development of various liver diseases with a focus on recently published articles. We present here two recent advances in understanding NO-mediated signaling - nitrated fatty acids (NO2-FAs) and S-guanylation - and conclude with suggestions for future directions in NO-related studies on the liver.

Adiponectin attenuates liver fibrosis by inducing nitric oxide production of hepatic stellate cells

Adiponectin protects against liver fibrosis, but the mechanisms have not been fully elucidated. Here, we showed that adiponectin upregulated inducible nitric oxide synthase (iNOS) messenger RNA (mRNA) and protein expression in hepatic non-parenchymal cells, particularly in hepatic stellate cells (HSCs), and increased nitric oxide (NO2-/NO3-) concentration in HSC-conditioned medium. Adiponectin attenuated HSC proliferation and migration but promoted apoptosis in a NO-dependent manner. More advanced liver fibrosis with decreased iNOS/NO levels was observed in adiponectin knockout mice comparing to wide-type mice when administered with CCI4 while NO donor supplementation rescued the phenotype. Further experiments demonstrated that adiponectin-induced iNOS/NO system activation is mediated through adipoR2-AMPK-JNK/Erk1/2-NF-κB signaling. These data suggest that adiponectin inhibits HSC function, further limiting the development of liver fibrosis at least in part through adiponectin-induced NO release. Therefore, adiponectin-mediated NO signaling may be a novel target for the treatment of liver fibrosis.

KEY MESSAGES

• Adiponectin activates HSC iNOS/NO and SEC eNOS/NO systems. • Adiponectin inhibits HSC proliferation and migration but promotes its apoptosis. • Adiponectin inhibits CCL4-induced liver fibrosis by modulation of liver iNOS/NO. • Adiponectin stimulates HSC iNOS/NO via adipoR2-AMPK-JNK/ErK1/2-NF-κB pathway.

The use of nanoparticles to deliver nitric oxide to hepatic stellate cells for treating liver fibrosis and portal hypertension

Polymeric nanoparticles are designed to transport and deliver nitric oxide (NO) into hepatic stellate cells (HSCs) for the potential treatment of both liver fibrosis and portal hypertension. The nanoparticles, incorporating NO donor molecules (S-nitrosoglutathione compound), are designed for liver delivery, minimizing systemic delivery of NO. The nanoparticles are decorated with vitamin A to specifically target HSCs. We demonstrate, using in vitro and in vivo experiments, that the targeted nanoparticles are taken up specifically by rat primary HSCs and the human HSC cell line accumulating in the liver. When nanoparticles, coated with vitamin A, release NO in liver cells, we find inhibition of collagen I and α-smooth muscle actin (α-SMA), fibrogenic genes associated with activated HSCs expression in primary rat liver and human activated HSCs without any obvious cytotoxic effects. Finally, NO-releasing nanoparticles targeted with vitamin A not only attenuate endothelin-1 (ET-1) which elicites HSC contraction but also acutely alleviates haemodynamic disorders in bile duct-ligated-induced portal hypertension evidenced by decreasing portal pressure (≈20%) and unchanging mean arterial pressure. This study clearly shows, for the first time, the potential for HSC targeted nanoparticle delivery of NO as a treatment for liver diseases with proven efficacy for alleviating both liver fibrosis and portal hypertension.

Type II cyclic guanosine monophosphate-dependent protein kinase inhibits Rac1 activation in gastric cancer cells

Enhanced motility of cancer cells is a critical step in promoting tumor metastasis, which remains the major cause of gastric cancer-associated mortality. The small GTPase Rac1 is a key signaling component in the regulation of cell migration. Previous studies have demonstrated that Rac1 activity may be regulated by protein kinase G (PKG); however, the underlying mechanism is not yet clear. The current study aimed to investigate the effect of type II cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG II) on Rac1 activity. The human gastric cancer cell line AGS was infected with adenoviral constructs encoding PKG II to increase the expression of this enzyme, and treated with a cGMP analog (8-pCPT-cGMP) to induce its activation. A Transwell assay was employed to measure cell migration, and the activity of Rac1 was assessed using a pull-down assay. Immunoprecipitation was used to isolate the Rac1 protein. Phosphorylation of phosphatidylinositol 4,5 bisphosphate 3 kinase (PI3K) and its downstream effecter protein kinase B (Akt) are associated with lysophosphatidic acid (LPA)-induced motility/migration of cancer cells. Extracellular signal regulated kinase (ERK) is the major signaling molecule of the Mitogen activated protein kinase (MAPK) mediated signaling pathway. ERK and its upstream activator MAPK kinase (MEK) are also involved in LPA-induced motility/migration of cancer cells. Phosphorylation of PI3K/Akt, MEK/ERK and enriched Rac1 were detected by western blotting. The results revealed that blocking the activation of Rac1 by ectopically expressing an inactive Rac1 mutant (T17N) impeded LPA-induced cell migration. Increased PKG II activity inhibited LPA-induced migration and LPA-induced activation of Rac1; however, it had no effect on the phosphorylation of Rac1. PKG II also inhibited the activation of PI3K/Akt and MEK/ERK mediated signaling, which is important for LPA-induced Rac1 activation. These results suggest that PKG II affects LPA-stimulated migration of AGS cells by blocking Rac1 activation, via inhibition of PI3K/Akt and MEK/ERK mediated signaling.

Antifibrotic therapies in the liver

Significant progress has been made in understanding the principles underlying the development of liver fibrosis. This includes appreciating its dynamic nature, the importance of active fibrolysis in fibrosis regression, and the plasticity of cell populations endowing them with fibrogenic or fibrolytic properties. This is complemented by an increasing array of therapeutic targets with known roles in the progression or regression of fibrosis. With a key role for fibrosis in determining clinical outcomes and encouraging data from recently Food and Drug Administration-approved antifibrotics for pulmonary fibrosis, the development and validation of antifibrotic therapies has taken center stage in translational hepatology. In addition to summarizing the recent progress in antifibrotic therapies, the authors discuss some of the challenges ahead, such as achieving a better understanding of the interindividual heterogeneity of the fibrotic response, how to match interventions with the ideal patient population, and the development of better noninvasive methods to assess the dynamics of fibrogenesis and fibrolysis. Together, these advances will permit a better targeting and dose titration of individualized therapies. Finally, the authors discuss combination therapy with different antifibrotics as possibly the most potent approach for treating fibrosis in the liver.

LPSF/GQ-02 inhibits the development of hepatic steatosis and inflammation in a mouse model of non-alcoholic fatty liver disease (NAFLD)

Non-alcoholic fatty liver disease (NAFLD) defines a wide spectrum of liver diseases that extends from simple steatosis to non-alcoholic steatohepatitis. Although the pathogenesis of NAFLD remains undefined, it is recognized that insulin resistance is present in almost all patients who develop this disease. Thiazolidinediones (TZDs) act as an insulin sensitizer and have been used in the treatment of patients with type 2 diabetes and other insulin-resistant conditions, including NAFLD. Hence, therapy of NAFLD with insulin-sensitizing drugs should ideally improve the key hepatic histological changes, while also reducing cardiometabolic and cancer risks. Controversially, TZDs are associated with the development of cardiovascular events and liver problems. Therefore, there is a need for the development of new therapeutic strategies to improve liver function in patients with chronic liver diseases. The aim of the present study was to assess the therapeutic effects of LPSF/GQ-02 on the liver of LDLR-/- mice after a high-fat diet. Eighty male mice were divided into 4 groups and two different experiments: 1-received a standard diet; 2-fed with a high-fat diet (HFD); 3–HFD+pioglitazone; 4–HFD+LPSF/GQ-02. The experiments were conducted for 10 or 12 weeks and in the last two or four weeks respectively, the drugs were administered daily by gavage. The results obtained with an NAFLD murine model indicated that LPSF/GQ-02 was effective in improving the hepatic architecture, decreasing fat accumulation, reducing the amount of collagen, decreasing inflammation by reducing IL-6, iNOS, COX-2 and F4 / 80, and increasing the protein expression of IκBα, cytoplasmic NFκB-65, eNOS and IRS-1 in mice LDLR -/-. These results suggest a direct action by LPSF/GQ-02 on the factors that affect inflammation, insulin resistance and fat accumulation in the liver of these animals. Further studies are being conducted in our laboratory to investigate the possible mechanism of action of LPSF/GQ-02 on hepatic lipid metabolism.

Endothelial Gab1 deficiency aggravates splenomegaly in portal hypertension independent of angiogenesis

Certain pathological changes, including angiogenesis, actively contribute to the pathogenesis of splenomegaly in portal hypertension (PH), although the detailed molecular and cellular mechanisms remain elusive. In this study, we demonstrated that endothelial Grb-2-associated binder 1 (Gab1) plays a negative role in PH-associated splenomegaly independent of angiogenesis. PH, which was induced by partial portal vein ligation, significantly enhanced Gab1 expression in endothelial cells in a time-dependent manner. Compared with controls, endothelium-specific Gab1 knockout (EGKO) mice exhibited a significant increase in spleen size while their PH levels remained similar. Pathological analysis indicated that EGKO mice developed more severe hyperactive white pulp and fibrosis in the enlarged spleen but less angiogenesis in both the spleen and mesenteric tissues. Mechanistic studies showed that the phosphorylation of endothelial nitric oxide synthase (eNOS) in EGKO mice was significantly lower than in controls. In addition, the dysregulation of fibrosis and inflammation-related transcription factors [e.g., Krüppel-like factor (KLF) 2 and KLF5] and the upregulation of cytokine genes (e.g., TNF-α and IL-6) were observed in EGKO mice. We thus propose that endothelial Gab1 mediates multiple pathways in inhibition of the pathogenesis of splenomegaly in PH via prevention of endothelial dysfunction and overproduction of proinflammatory/profibrotic cytokines.

Fibronectin peptides as potential regulators of hepatic fibrosis through apoptosis of hepatic stellate cells

The turnover of extracellular matrix (ECM) components can generate signals that regulate several cellular functions such as proliferation, differentiation, and apoptosis. During liver injury, matrix metalloproteases (MMPs) production is enhanced and increased levels of peptides derived from extracellular matrix proteins can be generated. Synthetic peptides with sequences present in extracellular matrix proteins were previously found to induce both stimulating and apoptotic effects on several cell types including the inflammatory cells monocytes/macrophages. Therefore, in inflammatory liver diseases, locally accumulated peptides could be also important in regulating hepatic fibrosis by inducing apoptosis of hepatic stellate cells (HSC), the primary cellular source of extracellular matrix components. Here, we describe the apoptotic effect of fibronectin peptides on the cell line of human hepatic stellate cells LX-2 based on oligonucleosomal DNA fragmentation, caspase-3 and -9 activation, Bcl-2 depletion, and accumulation of Bax protein. We also found that these peptides trigger the activation of Src kinase, which in turn mediated the increase of JNK and p38 activities. By the use of specific inhibitors we demonstrated the involvement of Src, JNK, and p38 in apoptosis induced by fibronectin peptides on HSC. Moreover, fibronectin peptides increased iNOS expression in human HSC, and specific inhibition of iNOS significantly reduced the sustained activity of JNK and the programmed cell death caused by these peptides. Finally, the possible regulatory effect of fibronectin peptides in liver fibrosis was further supported by the ability of these peptides to induce metalloprotease-9 (MMP-9) expression in human monocytes.