Nitrovasodilators inhibit platelet-derived growth factor-induced proliferation and migration of activated human hepatic stellate cells

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.

Mechanobiology of portal hypertension

The interplay between mechanical stimuli and cellular mechanobiology orchestrates the physiology of tissues and organs in a dynamic balance characterized by constant remodelling and adaptative processes. Environmental mechanical properties can be interpreted as a complex set of information and instructions that cells read continuously, and to which they respond. In cirrhosis, chronic inflammation and injury drive liver cells dysfunction, leading to excessive extracellular matrix deposition, sinusoidal pseudocapillarization, vascular occlusion and parenchymal extinction. These pathological events result in marked remodelling of the liver microarchitecture, which is cause and result of abnormal environmental mechanical forces, triggering and sustaining the long-standing and progressive process of liver fibrosis. Multiple mechanical forces such as strain, shear stress, and hydrostatic pressure can converge at different stages of the disease until reaching a point of no return where the fibrosis is considered non-reversible. Thereafter, reciprocal communication between cells and their niches becomes the driving force for disease progression. Accumulating evidence supports the idea that, rather than being a passive consequence of fibrosis and portal hypertension (PH), mechanical force-mediated pathways could themselves represent strategic targets for novel therapeutic approaches. In this manuscript, we aim to provide a comprehensive review of the mechanobiology of PH, by furnishing an introduction on the most important mechanisms, integrating these concepts into a discussion on the pathogenesis of PH, and exploring potential therapeutic strategies.

DNMT3a-mediated methylation of TCF21/hnRNPA1 aggravates hepatic fibrosis by regulating the NF-κB signaling pathway

Hepatic fibrosis is caused by liver damage as a consequence of wound healing response. Recent studies have shown that hepatic fibrosis could be effectively reversed, partly through regression of activated hepatic stellate cells (HSCs). Transcription factor 21 (TCF21), a member of the basic helix-loop-helix (bHLH) transcription factor, is involved in epithelial-mesenchymal transformation in various diseases. However, the mechanism by which TCF21 regulates epithelial-mesenchymal transformation in hepatic fibrosis has not been elucidated. In this research, we found that hnRNPA1, the downstream binding protein of TCF21, accelerates hepatic fibrosis reversal by inhibiting the NF-κB signaling pathway. Furthermore, the combination of DNMT3a with TCF21 promoter results in TCF21 hypermethylation. Our results suggest that DNMT3a regulation of TCF21 is a significant event in reversing hepatic fibrosis. In conclusion, this research identifies a novel signaling axis, DNMT3a-TCF21-hnRNPA1, that regulates HSCs activation and hepatic fibrosis reversal, providing a novel treatment strategy for hepatic fibrosis. The clinical trial was registered in the Research Registry (researchregistry9079).

Survival benefits of adding simvastatin to standard therapy for secondary prevention of bleeding esophageal varices in patients with hepatitis C-related liver cirrhosis

Background

The combination of endoscopic band ligation and beta-blockers is the standard of care treatment for secondary prevention of variceal bleeding; however, rebleeding still occurs with associated high mortality. Simvastatin (a lipid-lowering agent) was found to reduce portal hypertension and decrease hepatic fibrosis. This study aimed to assess the effect of adding simvastatin to the standard therapy to prevent variceal rebleeding and its impact on survival in patients with liver cirrhosis.

Results

This single-center randomized controlled clinical trial included 80 patients with cirrhosis receiving the standard secondary prophylaxis for variceal bleeding composed of endoscopic variceal ligation and non-selective β-blockers (either propranolol or carvedilol). Two weeks after the first attack of hematemesis, patients were randomized into two groups: group I who received the standard therapy (40 patients) and group II who administered simvastatin (20 mg daily for 2 weeks and 40 mg daily after that). Patients were followed up for 1 year. The primary endpoints were rebleeding and overall survival. Thirty patients of group I completed the study while ten patients died during the follow-up period. The simvastatin group showed a significantly better overall 1-year survival (3 deaths during follow-up) compared to the control group (37/40, 92.5% vs. 30/40; 75%) (p-value 0.034); however, this was lacking in Child C patients. No similar difference was present in rebleeding rates between the two groups (5/40, 12.5% vs. 3/40, 7.5%) (p-value 0.456) in groups I and II, respectively.

Conclusions

Adding simvastatin to the standard therapy in secondary prevention of variceal bleeding could be associated with survival benefits in patients with Child A and B cirrhosis, while was incapable of reducing rebleeding.

Molecular Mechanisms That Link Oxidative Stress, Inflammation, and Fibrosis in the Liver

Activated hepatic stellate cells (HSCs) and myofibroblasts are the main producers of extracellular matrix (ECM) proteins that form the fibrotic tissue that leads to hepatic fibrosis. Reactive oxygen species (ROS) can directly activate HSCs or induce inflammation or programmed cell death, especially pyroptosis, in hepatocytes, which in turn activates HSCs and fibroblasts to produce ECM proteins. Therefore, antioxidants and the nuclear factor E2-related factor-2 signaling pathway play critical roles in modulating the profibrogenic response. The master proinflammatory factors nuclear factor-κB (NF-κB) and the nucleotide-binding oligomerization domain (NOD)-like receptor protein 3 (NLRP3) inflammasome may coordinate to produce and activate profibrogenic molecules such as interleukins 1β and 18, which effectively activate HSCs, to produce large amounts of fibrotic proteins. Furthermore, the NLRP3 inflammasome activates pro-caspase 1, which is upregulated by NF-κB, to produce caspase 1, which induces pyroptosis via gasdermin and the activation of HSCs. ROS play central roles in the activation of the NF-κB and NLRP3 signaling pathways via IκB (an inhibitor of NF-κB) and thioredoxin-interacting protein, respectively, thereby linking the molecular mechanisms of oxidative stress, inflammation and fibrosis. Elucidating these molecular pathways may pave the way for the development of therapeutic tools to interfere with specific targets.

BAY 41-2272 Attenuates CTGF Expression via sGC/cGMP-Independent Pathway in TGFβ1-Activated Hepatic Stellate Cells

Activation of hepatic stellate cells (HSCs) is a critical pathogenic feature of liver fibrosis and cirrhosis. BAY 41-2272 is a canonical non-nitric oxide (NO)-based soluble guanylyl cyclase (sGC) stimulator that triggers cyclic guanosine monophosphate (cGMP) signaling for attenuation of fibrotic disorders; however, the impact of BAY 41-2272 on HSC activation remains ill-defined. Transforming growth factor (TGF)β and its downstream connective tissue growth factor (CTGF or cellular communication network factor 2, CCN2) are critical fibrogenic cytokines for accelerating HSC activation. Here, we identified that BAY 41-2272 significantly inhibited the TGFβ1-induced mRNA and protein expression of CTGF in mouse primary HSCs. Indeed, BAY 41-2272 increased the sGC activity and cGMP levels that were potentiated by two NO donors and inhibited by a specific sGC inhibitor, ODQ. Surprisingly, the inhibitory effects of BAY 41-2272 on CTGF expression were independent of the sGC/cGMP pathway in TGFβ1-activated primary HSCs. BAY 41-2272 selectively restricted the TGFβ1-induced phosphorylation of Akt but not canonical Smad2/3 in primary HSCs. Together, we illustrate a unique framework of BAY 41-2272 for inhibiting TGFβ1-induced CTGF upregulation and HSC activation via a noncanonical Akt-dependent but sGC/cGMP-independent pathway.

Impact of endothelial nitric oxide synthase polymorphisms on urothelial cell carcinoma development

OBJECTIVES

Urothelial cell carcinoma (UCC), a major malignancy of the genitourinary tract, is induced through carcinogenic etiological factors. Endothelial nitric oxide synthase (eNOS) is one of the major isoforms of nitric oxide synthase and is involved in various pathophysiologic and physiologic processes. In this study, eNOS single-nucleotide polymorphisms were investigated to evaluate UCC susceptibility and clinicopathological characteristics.

MATERIALS AND METHODS

Two single-nucleotide polymorphisms of eNOS in 431 patients with UCC and 862 controls without cancer were analyzed using real-time polymerase chain reaction.

RESULTS

The results showed that 272 men with UCC having eNOS 894 G > T rs1799983 "GT + TT" variants had a high risk of developing a large tumor (T1-T4, P = 0.038). Furthermore, a correlation was observed between the expressions of eNOS and invasive tumor, metastasis and poor survival in urothelial carcinoma in The Cancer Genome Atlas data set.

CONCLUSION

Our results indicated that male patients with UCC carrying eNOS 894 G > T rs1799983 "GT + TT" genetic variants have a high risk of developing a large tumor, and eNOS polymorphisms may serve as a marker or therapeutic target in UCC treatment.

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.

Evaluation of portal pressure by doppler ultrasound in patients with cirrhosis before and after simvastatin administration - a randomized controlled trial

Background: Portal hypertension is one of the most frequent complications of cirrhosis. β-adrenergic blockers, with or without organic nitrates, are currently used as hypotensive agents. Statins such as simvastatin seem to be safe for patients with chronic liver diseases and exert multiple pleiotropic actions. This study aimed to assess PTH using Doppler ultrasound in patients with cirrhosis before and after simvastatin administration.

Methods: This randomized controlled clinical trial was conducted on 40 patients with cirrhosis who were randomized into 2 groups: group I included 20 patients with cirrhosis who were administered 20 mg of simvastatin daily for 2 weeks and then 40 mg daily for another 2 weeks, and group II included 20 patients with cirrhosis who did not receive simvastatin as a control group. All patients underwent full clinical examination, laboratory investigations, and abdominal Doppler ultrasound at baseline and after 30 days to evaluate portal vein diameter, blood flow volume, direction and velocity of portal vein blood flow, hepatic artery resistance and pulsatility indices, splenic artery resistance index, portal hypertension index (PHI), liver vascular index, and modified liver vascular index (MLVI).

Results: There was a highly significant decrease in the hepatic artery resistance index  in group I, from 0.785 ± 0.088 to 0.717 ± 0.086 (P < 0.001). There was a significant decrease in the PHI in group I , from 3.915 ± 0.973 m/sec to 3.605 ± 1.168 m/sec (P = 0.024). Additionally, there was a significant increase in the MLVI in group I from 11.540 ± 3.266 cm/sec to 13.305 ± 3.222 cm/sec, an increase of 15.3% from baseline (P = 0.009). No significant adverse effects were detected.

Conclusions: Simvastatin is safe and effective in lowering portal hypertension.

[ClinicalTrials.gov Identifier: NCT02994485]

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.

A comparative study on the anti-schistosomal and hepatoprotective effects of vinpocetine and isosorbide-5-mononitrate on Schistosoma mansoni-infected mice

Schistosomiasis is a remarkable public health problem in developing countries. Presently, praziquantel is the optional drug for all human schistosomiasis. Owing to the increased praziquantel resistance, there is an urgent need to develop new alternatives. This study aims at determining the anti-schistosomal and/or the hepatoprotective effects of the anti-inflammatory drug; vinpocetine, and the vasodilator and the nitric oxide donor; isosorbide-5-mononitrate, in comparison to praziquantel. In the present research, the therapeutic efficacies of these drugs were assessed in Swiss albino female mice (CD-I strain) experimentally infected with an Egyptian strain of Schistosoma mansoni, using some general, parasitological, and histopathological parameters. In this work, praziquantel significantly reduced worm burden and hepatic egg load, increased the percentage of dead eggs in the small intestine and decreased granuloma count, but did not reduce granuloma diameter. While, either vinpocetine or isosorbide-5-mononitrate monotherapy did not induce significant reduction in the worm count, hepatic egg load or shift in the oogram pattern, but significantly reduced granuloma count and diameter. Moreover, isosorbide-5-mononitrate significantly reduced hepatic inflammation and necrosis. The best results were obtained in the mice groups treated with isosorbide-5-mononitrate combined with praziquantel or vinpocetine. Our results point to vinpocetine and isosorbide-5-mononitrate as a convenient and promising adjuvant to praziquantel for ameliorating schistosomal liver pathology. Further studies are recommended to reveal the actual pathways responsible for the different activities of vinpocetine and isosorbide-5-mononitrate.

Role of DDAH/ADMA pathway in TGF-β1-mediated activation of hepatic stellate cells

Asymmetric dimethylarginine (ADMA) is catalyzed by the enzyme dimethylarginine dimethylaminohydrolase (DDAH) in humans, and the role for ADMA has been associated with hepatic fibrogenesis. Transforming growth factor‑β (TGF‑β) has been shown to mediate the myofibroblastic transformation of quiescent hepatic stellate cells (HSCs), a pivotal step in liver fibrogenesis. However, the underlying molecular mechanisms are not well understood. Accumulation of ADMA due to low activity of DDAH has been reported to be associated with liver damage and hepatic fibrosis. In this study, the role of the DDAH/ADMA pathway in the TGF‑β1‑induced HSC activation was assessed. Freshly harvested primary HSCs from rat liver were used in this study. It was demonstrated that TGF‑β1 treatment significantly suppressed the DDAH protein expression and activity, and increased levels of ADMA in the culture medium of rat primary HSCs. Notably, the TGF‑β1‑mediated effects on DDAH/ADMA were significantly abrogated by the p38 mitogen activated protein kinase specific inhibitor, SB203580. Furthermore, it was demonstrated that excessive ADMA led to an increase in the number of TGF‑β1‑positive HSCs and induced the expression of α‑smooth muscle actin and collagen type I in rat primary HSCs. In addition, rat primary HSCs exposed to excessive ADMA showed a significant increase in the expressions of α‑SMA and collagen type I. Finally, it was revealed that ADMA treatment promoted the proliferation of rat primary HSCs. In conclusion, the results obtained from the study suggest a potentially novel role for the ADMA/DDAH1 signaling pathway in TGF‑β1‑induced HSC activation, and along with the studies of others, suppression of the ADMA/DDAH1 pathway may be an alterative approach for the treatment of liver fibrosis.

Liver Sinusoidal Endothelial Cell: An Update

This update focuses on two main topics. First, recent developments in our understanding of liver sinusoidal endothelial cell (LSEC) function will be reviewed, specifically elimination of blood-borne waste, immunological function of LSECs, interaction of LSECs with liver metastases, LSECs and liver regeneration, and LSECs and hepatic fibrosis. Second, given the current emphasis on rigor and transparency in biomedical research, the update discusses the need for standardization of methods to demonstrate identity and purity of isolated LSECs, pitfalls in methods that might lead to a selection bias in the types of LSECs isolated, and questions about long-term culture of LSECs. Various surface markers used for immunomagnetic selection are reviewed.

"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.

Activated hepatic stellate cells promote liver cancer by induction of myeloid-derived suppressor cells through cyclooxygenase-2

Hepatic stellate cells (HSCs) are critical mediators of immunosuppression and the pathogenesis of hepatocellular carcinoma (HCC). Our previous work indicates that HSCs promote HCC progression by enhancing immunosuppressive cell populations including myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs). MDSCs are induced by inflammatory cytokines (e.g., prostaglandins) and are important in immune suppression. However, how HSCs mediate expansion of MDSCs is uncertain. Thus, we studied activated HSCs that could induce MDSCs from bone marrow cells and noted that HSC-induced MDSCs up-regulated immunosuppressive activity via iNOS, Arg-1, and IL-4Rα. After treating cells with a COX-2 inhibitor or an EP4 antagonist, we established that HSC-induced MDSC accumulation was mediated by the COX2-PGE₂-EP4 signaling. Furthermore, in vivo animal studies confirmed that inhibition of HSC-derived PGE₂ could inhibit HSC-induced MDSC accumulation and HCC growth. Thus, our data show that HSCs are required for MDSC accumulation mediated by the COX2-PGE₂-EP4 pathway, and these data are the first to link HSC and MDSC subsets in HCC immune microenvironment and provide a rationale for targeting PGE₂ signaling for HCC therapy.

Proteinase-activated receptor 2 (PAR2) in hepatic stellate cells - evidence for a role in hepatocellular carcinoma growth in vivo

BACKGROUND

Previous studies have established that proteinase-activated receptor 2 (PAR2) promotes migration and invasion of hepatocellular carcinoma (HCC) cells, suggesting a role in HCC progression. Here, we assessed the impact of PAR2 in HCC stromal cells on HCC growth using LX-2 hepatic stellate cells (HSCs) and Hep3B cells as model.

METHODS

PAR2 expression and function in LX-2 cells was analysed by RT-PCR, confocal immunofluorescence, electron microscopy, and [Ca(2+)]i measurements, respectively. The impact of LX-2-expressed PAR2 on tumour growth in vivo was monitored using HCC xenotransplantation experiments in SCID mice, in which HCC-like tumours were induced by coinjection of LX-2 cells and Hep3B cells. To characterise the effects of PAR2 activation in LX-2 cells, various signalling pathways were analysed by immunoblotting and proteome profiler arrays.

RESULTS

Following verification of functional PAR2 expression in LX-2 cells, in vivo studies showed that these cells promoted tumour growth and angiogenesis of HCC xenografts in mice. These effects were significantly reduced when F2RL1 (encoding PAR2) was downregulated by RNA interference (RNAi). In vitro studies confirmed these results demonstrating RNAi mediated inhibition of PAR2 attenuated Smad2/3 activation in response to TGF-β1 stimulation in LX-2 cells and blocked the pro-mitotic effect of LX-2 derived conditioned medium on Hep3B cells. Furthermore, PAR2 stimulation with trypsin or a PAR2-selective activating peptide (PAR2-AP) led to activation of different intracellular signalling pathways, an increased secretion of pro-angiogenic and pro-mitotic factors and proteinases, and an enhanced migration rate across a collagen-coated membrane barrier. Silencing F2RL1 by RNAi or pharmacological inhibition of Src, hepatocyte growth factor receptor (Met), platelet-derived growth factor receptor (PDGFR), p42/p44 mitogen activated protein kinase (MAPK) or matrix-metalloproteinases (MMPs) blocked PAR2-AP-induced migration.

CONCLUSION

PAR2 in HSCs plays a crucial role in promoting HCC growth presumably by mediating migration and secretion of pro-angiogenic and pro-mitotic factors. Therefore, PAR2 in stromal HSCs may have relevance as a therapeutic target of HCC.

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.

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.

Liver sinusoidal endothelial cells in hepatic fibrosis

Capillarization, lack of liver sinusoidal endothelial cell (LSEC) fenestration, and formation of an organized basement membrane not only precedes fibrosis, but is also permissive for hepatic stellate cell activation and fibrosis. Thus, dysregulation of the LSEC phenotype is a critical step in the fibrotic process. Both a vascular endothelial growth factor (VEGF)-stimulated, nitric oxide (NO)-independent pathway and a VEGF-stimulated NO-dependent pathway are necessary to maintain the differentiated LSEC phenotype. The NO-dependent pathway is impaired in capillarization and activation of this pathway downstream from NO restores LSEC differentiation in vivo. Restoration of LSEC differentiation in vivo promotes HSC quiescence, enhances regression of fibrosis, and prevents progression of cirrhosis.

Molecular pathophysiology of portal hypertension

Over the past two decades the advances in molecular cell biology have led to significant discoveries about the pathophysiology of portal hypertension (PHT). In particular, great progress has been made in the study of the molecular and cellular mechanisms that regulate the increased intrahepatic vascular resistance (IHVR) in cirrhosis. We now know that the increased IHVR is not irreversible, but that both the structural component caused by fibrosis and the active component caused by hepatic sinusoidal constriction can be, at least partially, reversed. Indeed, it is now apparent that the activation of perisinusoidal hepatic stellate cells, which is a key event mediating the augmented IHVR, is regulated by multiple signal transduction pathways that could be potential therapeutic targets for PHT treatment. Furthermore, the complexity of the molecular physiology of PHT can also be appreciated when one considers the complex signals capable of inducing vasodilatation and hyporesponsiveness to vasoconstrictors in the splanchnic vascular bed, with several vasoactive molecules, controlled at multiple levels, working together to mediate these circulatory abnormalities. Added to the complexity is the occurrence of pathological angiogenesis during the course of disease progression, with recent emphasis given to understanding its molecular machinery and regulation. Although much remains to be learned, with the current availability of reagents and new technologies and the exchange of concepts and data among investigators, our knowledge of the molecular basis of PHT will doubtless continue to grow, accelerating the transfer of knowledge generated by basic research to clinical practice. This will hopefully permit a better future for patients with PHT.

Shenzhang granules inhibit cell proliferation and reduce α-SMA expression in hepatic stellate cells

AIM: To assess the effects of different concentrations of Shenzhang granules on cell proliferation and the expression of alpha smooth muscle actin (α-SMA) in hepatic stellate cells (HSCs).

METHODS: After HSCs were cultured with different concentrations of serum containing Shenzhang granules, α-SMA mRNA and protein expression was detected by RT-PCR and Western blot, respectively, cell cycle progression was assessed using flow cytometry, and cell migration was assessed using cell scratch assay.

RESULTS: After treatment with serum containing Shenzhang granules, the expression of α-SMA mRNA and protein was significantly reduced, cell cycle was arrested in G2 phase, and cell proliferation and migration were inhibited.

CONCLUSION: Treatment with Shenzhang granules can reduce α-SMA expression and inhibit cell proliferation in HSCs.

Role of differentiation of liver sinusoidal endothelial cells in progression and regression of hepatic fibrosis in rats

BACKGROUND & AIMS

Capillarization, characterized by loss of differentiation of liver sinusoidal endothelial cells (LSECs), precedes the onset of hepatic fibrosis. We investigated whether restoration of LSEC differentiation would normalize crosstalk with activated hepatic stellate cells (HSC) and thereby promote quiescence of HSC and regression of fibrosis.

METHODS

Rat LSECs were cultured with inhibitors and/or agonists and examined by scanning electron microscopy for fenestrae in sieve plates. Cirrhosis was induced in rats using thioacetamide, followed by administration of BAY 60-2770, an activator of soluble guanylate cyclase (sGC). Fibrosis was assessed by Sirius red staining; expression of α-smooth muscle actin was measured by immunoblot analysis.

RESULTS

Maintenance of LSEC differentiation requires vascular endothelial growth factor-A stimulation of nitric oxide-dependent signaling (via sGC and cyclic guanosine monophosphate) and nitric oxide-independent signaling. In rats with thioacetamide-induced cirrhosis, BAY 60-2770 accelerated the complete reversal of capillarization (restored differentiation of LSECs) without directly affecting activation of HSCs or fibrosis. Restoration of differentiation to LSECs led to quiescence of HSCs and regression of fibrosis in the absence of further exposure to BAY 60-2770. Activation of sGC with BAY 60-2770 prevented progression of cirrhosis, despite continued administration of thioacetamide.

CONCLUSIONS

The state of LSEC differentiation plays a pivotal role in HSC activation and the fibrotic process.

Celecoxib, a selective cyclooxygenase-2 inhibitor, lowers plasma cholesterol and attenuates hepatic lipid peroxidation during carbon-tetrachloride-associated hepatotoxicity in rats

Cyclooxygenase-2 (COX-2) expression and prostaglandin production are suggested to play important, complex roles in the pathogenesis of various liver diseases. Studies on the effects of COX-2 inhibitors on the progression of liver fibrosis present controversial results, and the proposed therapeutic potential of these agents in chronic liver disease is predicated largely on their effectiveness in modulating hepatic stellate cell activation in vitro. This study investigated the modulatory effect of celecoxib, a selective COX-2 inhibitor, in CCl(4)-mediated hepatotoxicity in rats. Thirty Wistar albino rats, weighing 120-180 g, were assigned into five groups of 6 rats/group. Groups 1 and 2 received saline (10 mL/kg) and CCl(4) (80 mg/kg), respectively. Group 3 was given celecoxib (5.7 mg/kg), whereas groups 4 and 5 were pretreated with 2.9 and 5.7 mg/kg/day of celecoxib, respectively, 1 hour before CCl(4) treatment. Plasma aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase activities increased significantly by 118.5, 150.0, and 51.3%, respectively, with an accompanying decrease (P < 0.05) in total protein and albumin after CCl(4) treatment. Hepatotoxicity was associated with a significant increase in plasma cholesterol, hepatic lipid peroxidation (LPO), and severe hepatic necrosis with marked fatty and cellular (i.e., mononuclear cells) infiltration. Although celecoxib neither reduced CCl(4)-induced increases in marker enzymes of hepatotoxicity nor significantly attenuated hepatic necrosis, it, however, was effective in reducing elevated cholesterol by 16.5 and 20.8% and LPO by 12.9 and 35.5% at 2.9 and 5.7 mg/kg, respectively. Data suggest that COX-2 inhibitors may be effective in controlling hypercholesterolemia and peroxidative changes associated with liver injury.

Insulin resistance and liver microcirculation in a rat model of early NAFLD

BACKGROUND & AIMS

Insulin contributes to vascular homeostasis in peripheral circulation, but the effects of insulin in liver microvasculature have never been explored. The aim of this study was to assess the vascular effects of insulin in the healthy and fatty liver.

METHODS

Wistar rats were fed a control or a high fat diet (HFD) for 3days, while treated with a placebo, the insulin-sensitizer metformin, or the iNOS inhibitor 1400W. Vascular responses to insulin were evaluated in the isolated liver perfusion model. Insulin sensitivity at the sinusoidal endothelium was tested by endothelium-dependent vasodilation in response to acetylcholine in the presence or absence of insulin and by the level of liver P-eNOS after an insulin injection.

RESULTS

Rats from the HFD groups developed liver steatosis. Livers from the control group showed a dose-dependent hepatic vasodilation in response to insulin, which was blunted in livers from HFD groups. Metformin restored liver vascular insulin-sensitivity. Pre-treatment with insulin enhanced endothelium-dependent vasodilation of the hepatic vasculature and induced hepatic eNOS phosphorylation in control rats but not in HFD rats. Treatment with metformin or 1400W restored the capacity of insulin to enhance endothelium dependent vasodilation and insulin induced eNOS phosphorylation in HFD rats.

CONCLUSIONS

The administration of a HFD induces insulin resistance in the liver sinusoidal endothelium, which is mediated, at least in part, through iNOS upregulation and can be prevented by the administration of metformin. Insulin resistance at the hepatic vasculature can be detected earlier than inflammation or any other sign of advanced NALFD.

Hepatic stellate cells produce vascular endothelial growth factor via phospho-p44/42 mitogen-activated protein kinase/cyclooxygenase-2 pathway

Vascular endothelial growth factor (VEGF) is one of the major cytokines secreted by activated hepatic stellate cells (HSCs). VEGF is involved in hepatic angiogenesis and plays an important role in the development of liver fibrosis. TNP-470, an angiogenic inhibitor, attenuates the development of rat liver fibrosis with reduced angiogenesis, as demonstrated in our previous study. HSCs were prepared from specific pathogen-free Wister rat livers. The isolated HSCs were activated and stimulated with platelet-derived growth factor BB (PDGF-BB) or prostaglandin E2 with or without pretreatment with MAPK cascade inhibitors (PD98059, which inhibits MEK activation), SB203580 (a selective pharmacologic inhibitor of p38 MAPK), and SP600125 (a selective inhibitor of the c-Jun N-terminal kinase, JNK). VEGF production and those of related molecules were assayed at the protein and mRNA levels by immunostaining, western blot analysis, and real-time quantitative PCR. The activated HSCs produced more VEGF than the quiescent ones. Those that received PDGF-BB stimulation showed enhanced cyclooxygenase-2 (COX-2) expression and activation of phosphor-mitogen-activated protein kinase (MAPK) p44/p42. Pretreatment with PD98059 significantly inhibited COX-2 expression and VEGF production within the PDGF-activated HSCs, but the effect was nullified by exogenous prostaglandin E2. pJNK and p38 inhibitors do not show similar inhibitory effects on VEGF and COX-2 expression, and pJNK and p38 MAPK signals are not involved in the COX-2/MAPK signaling cascade. VEGF production in PDGF-stimulated HSCs is dependent on the overexpression of COX-2 protein via the phospho-p42/44 MAP kinase activation, based on PD98059 inhibition.

S-Nitroso-N-acetylcysteine induces de-differentiation of activated hepatic stellate cells and promotes antifibrotic effects in vitro

Nitric oxide (NO) has been shown to act as a potent antifibrogenic agent by decreasing myofibroblast differentiation. S-Nitroso-N-acetylcysteine (SNAC), a NO donor, attenuates liver fibrosis in rats, but the cellular and molecular mechanisms on liver myofibroblast-like phenotype still remain unknown. Here, we investigate the antifibrotic effects of SNAC on hepatic stellate cells, the major fibrogenic cell type in the liver. A murine GRX cell line was incubated with SNAC (100μM) or vehicle (control group) for 72h. Cell viability was measured by MTT colorimetric assay and the conversion of myofibroblast into quiescent fat-storing cell phenotype was evaluated by Oil-Red-O staining. TGFβ-1, TIMP-1, and MMP-13 levels were measure in the supernatant by ELISA. Profibrogenic- and fibrolytic-related gene expression was quantified using real-time qPCR. SNAC induced phenotype conversion of myofibroblast-like phenotype into quiescent cells. SNAC decreased gene and protein expression of TGFβ-1 and MMP-2 compared to control groups. Besides, SNAC down-regulated profibrogenic molecules and up-regulated MMP-13 gene expression, which plays a key role in the degradation of interstitial collagen in liver fibrosis. In conclusion, these findings demonstrate that SNAC efficiently can modulate the activation and functionality of murine hepatic stellate cells and could be considered as an antifibrotic treatment to human liver fibrosis.

Loss of expression of miR-335 is implicated in hepatic stellate cell migration and activation

Activation and migration of resident stellate cells (HSCs) within the hepatic space of Disse play an important role in hepatic fibrosis, which accounts for the increased numbers of activated HSCs in areas of inflammation during hepatic fibrosis. Currently, microRNAs have been found to play essential roles in HSC differentiation, proliferation, apoptosis, fat accumulation and collagen production. However, little is known about microRNA mediated HSC activation and migration. In this study, the miRNA expression profiles of quiescent HSCs, partially activated HSCs and fully activated HSCs were compared in pairs. Gene ontology (GO) and GO-Map network analysis indicated that the activation of HSCs was regulated by microRNAs. Among them miR-335 was confirmed to be significantly reduced during HSC activation by qRT-PCR, and restoring expression of miR-335 inhibited HSC migration and reduced α-SMA and collagen type I. Previous study revealed that tenascin-C (TNC), an extracellular matrix glycoprotein involved in cell migration, might be a target of miR-335. Therefore, we further studied the TNC expression in miR-335 over-expressed HSCs. Our data showed that exogenous TNC could enhance HSC migration in vitro and miR-335 restoration resulted in a significant inhibition of TNC expression. These results demonstrated that miR-335 restoration inhibited HSC migration, at least in part, via downregulating the TNC expression.

Increased expression of cyclooxygenase-2 is associated with the progression to cirrhosis

BACKGROUND/AIMS

To investigate the degree of cyclooxygenase-2 (COX-2) protein expression in chronic hepatitis and cirrhosis.

METHODS

COX-2 protein expression was evaluated in 43 cases of chronic hepatitis and 24 cases of cirrhosis using immunohistochemical techniques. The COX-2 immunohistochemical staining score was assessed using the scoring systems of Pazirandeh et al and Qiu et al. and each scoring system was based on a sum of the parameters of staining intensity and distribution.

RESULTS

The mean COX-2 expression scores in chronic hepatitis and cirrhosis were 2.5 ± 1.3 vs. 3.3 ± 1.1 (p = 0.008), and 3.2 ± 2.0 vs. 4.5 ± 1.7 (p = 0.006), respectively, based on the Pazirandeh et al. and Qiu et al. scoring systems. The percentage samples of high COX-2 expression score (4 to 5) in chronic hepatitis and cirrhosis were 16.3% vs. 45.8% (p = 0.022), and 23.3% vs. 50% (p = 0.021), respectively, based on the two scoring systems. The mean COX-2 expression scores based on the severity of hepatic fibrosis scored using Ishak's modified staging system (fibrosis score 0 to 3 vs. 4 to 6) were 2.4 ± 1.3 vs. 3.2 ± 1.1 (p = 0.009), and 3.1 ± 2.0 vs. 4.3 ± 1.8 (p = 0.009), respectively, based on the two scoring systems.

CONCLUSIONS

COX-2 expression was significantly higher in liver cirrhosis group than in chronic hepatitis. COX-2 expression scores according to Ishak's staging was significantly higher in the advanced fibrosis group. COX-2 may play a role in the progression of hepatic fibrosis.

PPARgamma as a potential therapeutic target in pulmonary hypertension

Pulmonary hypertension (PH) is a progressive disorder of the pulmonary circulation associated with significant morbidity and mortality. The pathobiology of PH involves a complex series of derangements causing endothelial dysfunction, vasoconstriction and abnormal proliferation of pulmonary vascular wall cells that lead to increases in pulmonary vascular resistance and pressure. Recent evidence indicates that the ligand-activated transcription factor, peroxisome proliferator-activated receptor gamma (PPARgamma) can have a favorable impact on a variety of pathways involved in the pathogenesis of PH. This review summarizes PPARgamma biology and the emerging evidence that therapies designed to activate this receptor may provide novel approaches to the treatment of PH. Mediators of PH that are regulated by PPARgamma are reviewed to provide insights into potential mechanisms underlying therapeutic effects of PPARgamma ligands in PH.

Hepatic endothelial dysfunction and abnormal angiogenesis: new targets in the treatment of portal hypertension

Portal hypertension is the main cause of complications in patients with chronic liver disease. Over the past 25 years, progress in the understanding of the pathophysiology of portal hypertension was followed by the introduction of an effective pharmacological therapy, consisting mainly of treatments aimed at correcting the increased splanchnic blood flow. It is only recently that this paradigm has been changed. Progress in our knowledge of the mechanisms of increased resistance to portal blood flow, of the formation of portal-systemic collaterals, and of mechanisms other than vasodilatation maintaining the increased splanchnic blood flow have opened entirely new perspectives for developing more effective treatment strategies. This is the aim of the current review, which focuses on: (a) the modulation of hepatic vascular resistance by correcting the increased hepatic vascular tone due to hepatic endothelial dysfunction, and (b) correcting the abnormal angiogenesis associated with portal hypertension, which contributes to liver inflammation and fibrogenesis, to the hyperkinetic splanchnic circulation, and to the formation of portal-systemic collaterals and varices.

Hepatoprotective effects of the nitric oxide donor isosorbide-5-mononitrate alone and in combination with the natural hepatoprotectant, silymarin, on carbon tetrachloride-induced hepatic injury in rats

The aim of this study was to investigate the effect of the nitric oxide donor isosorbide-5-mononitrate (5-ISMN) alone or in combination with the natural hepatoprotectant with anti-oxidant activity silymarin on the carbon tetrachloride (CCl(4))-induced hepatic injury in rats. 5-ISMN (1.8, 3.6 or 7.2 mg/kg), silymarin (25 mg/kg) or 5-ISMN (1.8, 3.6 or 7.2 mg/kg) combined with silymarin was given once daily orally simultaneously with CCl(4) and for 15 days thereafter. Liver damage was assessed by determining serum enzyme activities and hepatic histopathology. 5-ISMN given at the above doses conferred significant protection against the hepatotoxic actions of CCl(4) in rats, reducing serum alanine aminotransferase (ALT) levels by 31.2, 39.3 and 61.6%, respectively, when compared with controls. Serum aspartate aminotransferase (AST) levels decreased by 19.8, 22.7 and 59.4%, respectively, while alkaline phosphatase (ALP) decreased by 26.1 and 32.6% by the drug at 3.6 and 7.2 mg/kg, respectively. When silymarin was added to 5-ISMN (1.8, 3.6 or 7.2 mg/kg), ALT decreased by 32.8, 59.6, 70.2% and AST by 28.7, 50.3, 60%, when compared with CCl(4) control group levels. Silymarin in combination with 3.6 or 7.2 mg/kg 5-ISMN resulted in 37.5 and 39.2% reductions in ALP when compared with CCl(4) control group. Meanwhile, silymarin alone reduced ALT, AST and ALP levels by 65.9, 52 and 62.3%, respectively. Blood levels of reduced glutathione were markedly decreased in CCl(4)-treated rats. Reduced glutathione levels were increased by the administration of 5-ISMN and restored to near normal values by silymarin treatment. Histopathological alterations by CCl(4) were markedly reduced after treatment with 5-ISMN alone or in combination with silymarin. Histopathologic examination of the livers of CCl(4)-treated rats administered 5-ISMN at 7.2 mg/kg showed marked restoration of the normal architecture of the liver tissue and minimal fibrosis. Silymarin co-administered with 5-ISMN resulted in further improvement of the histologic picture. These results indicates that treatment with 5-ISMN protects against hepatocellular necrosis induced by CCl(4). The study suggests a potential therapeutic use for 5-ISMN in combination with silymarin in liver injury.

Antifibrotic effects of ZK14, a novel nitric oxide-donating biphenyldicarboxylate derivative, on rat HSC-T6 cells and CCl4-induced hepatic fibrosis

AIM

To study the pharmacologic effect of ZK(14), a novel nitric oxide-donating biphenyldicarboxylate (DDB) derivative, on HSC-T6 cells and on CCl(4)-induced hepatic fibrosis.

METHODS

Inhibition of HSC-T6 cell growth by ZK(14) was evaluated by MTT assay. The effect of ZK(14) on the percentage of HSC-T6 cells undergoing apoptosis was measured using Annexin-V/PI double-staining and TUNEL assay. Mitochondrial membrane potential (MMP) and caspase activities were tested. Hepatic fibrosis was induced in Sprague-Dawley rats by intraperitoneal injection with 14% CCl(4). Rats with hepatic fibrosis were randomly divided into four groups: model control, ZK(14) (20 mg/kg), ZK(14) (10 mg/kg) and DDB (5 mg/kg). Levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), hyaluronic acid (HA), type III collagen (PCIII), and nitric oxide (NO) were assessed, and liver samples were stained with hematoxylin-eosin. The NO level in cells treated with ZK(14) in vitro was also measured.

RESULTS

The effect of ZK(14) on HSC-T6 cell apoptosis was concentration- and time-dependent, with up to 50% of cells becoming apoptotic when exposed to 100 mumol/L ZK(14) for 18 h. ZK(14) treatment resulted in mitochondrial membrane depolarization and activation of caspases 3 and 9. At a dose of 20 mg/kg, ZK(14) significantly decreased serum transaminase (AST, ALT) activities and fibrotic index (HA, PCIII) levels and significantly inhibited fibrogenesis.

CONCLUSION

These data indicate that ZK(14), a novel NO-donating DDB derivative, promotes HSC-T6 apoptosis in vitro through a signaling mechanism involving mitochondria and caspase activation and it inhibits CCl(4)-induced hepatic fibrosis in vivo. The results suggest that ZK(14) has potential therapeutic value in the treatment of hepatic fibrosis.

Simvastatin lowers portal pressure in patients with cirrhosis and portal hypertension: a randomized controlled trial

BACKGROUND & AIMS

Simvastatin improves liver generation of nitric oxide and hepatic endothelial dysfunction in patients with cirrhosis, so it could be an effective therapy for portal hypertension. This randomized controlled trial evaluated the effects of continuous simvastatin administration on the hepatic venous pressure gradient (HVPG) and its safety in patients with cirrhosis and portal hypertension.

METHODS

Fifty-nine patients with cirrhosis and portal hypertension (HVPG > or =12 mm Hg) were randomized to groups that were given simvastatin 20 mg/day for 1 month (increased to 40 mg/day at day 15) or placebo in a double-blind clinical trial. Randomization was stratified according to whether the patient was being treated with beta-adrenergic blockers. We studied splanchnic and systemic hemodynamics and variables of liver function and safety before and after 1 month of treatment.

RESULTS

Simvastatin significantly decreased HVPG (-8.3%) without deleterious effects in systemic hemodynamics. HVPG decreases were observed in patients who were receiving beta-adrenergic blockers (-11.0%; P = .033) and in those who were not (-5.9%; P = .013). Simvastatin improved hepatic, fractional, and intrinsic clearance of indocyanine green, showing an improvement in effective liver perfusion and function. No significant changes in HVPG and liver function were observed in patients receiving placebo. The number of patients with adverse events did not differ significantly between groups. No patient was withdrawn from the study based on adverse events.

CONCLUSIONS

Simvastatin decreased HVPG and improved liver perfusion in patients with cirrhosis. These effects were additive with those of beta-adrenergic blockers. The beneficial effects of simvastatin should be confirmed in long-term clinical trials for portal hypertension.

Reactive nitrogen species switch on early extracellular matrix remodeling via induction of MMP1 and TNFalpha

BACKGROUND & AIMS

Liver injury leads to generation of reactive oxygen and nitrogen species, which can react to produce peroxynitrite (ONOO-). We investigated whether ONOO- and its metabolites modulate extracellular matrix remodeling.

METHODS

Stellate cells (HSC) were incubated with pure ONOO- or SIN-1 (a ONOO- donor). Western blot, nuclear in vitro transcription, Northern blot, qPCR, and promoter transactivation analysis for COL1A1 and COL1A2 were carried out. Rats were fed alcohol or injected with CCl4 to cause alcohol-induced liver injury and an early fibrogenic response.

RESULTS

HSC incubated with ONOO- or SIN-1 showed similar viability, proliferation, COL1A1 and COL1A2 transcription rates, and mRNA levels as controls. There was a time- and dose-dependent down-regulation of collagen I and alpha-Sma proteins and up-regulation of MMP1 and TNFalpha, indicating decreased HSC activation. These effects were blocked by ONOO- scavengers. SIN-1 or ONOO- increased nitrosylation of MMP1/MMP13 and transactivation of the MMP1, MMP13, and TNFalpha promoters. A TNFalpha neutralizing antibody or GSH-ethyl ester blocked MMP1 promoter transactivation; whereas TNFalpha or l-buthionine sulfoximine, which depletes GSH, further enhanced it. Pretreatment with SIN-1 or ONOO- reduced the TGFbeta pro-fibrogenic response in HSC. In vivo experiments validated the protective role of ONOO- on the early fibrogenic response. However, highly activated HSC, such as myofibroblasts and HSC from chronic alcohol-fed rats, were resistant to the anti-fibrogenic actions of ONOO- due to higher levels of GSH, a ONOO- scavenger, overproduction of pro-fibrogenic TGFbeta, and reactive oxygen species.

CONCLUSION

ONOO- could induce a protective mechanism in HSC in early stages of liver injury.

Oxidative and nitrosative stress and fibrogenic response

Uncontrolled production of collagen I is the main feature of liver fibrosis. Following a fibrogenic stimulus such as alcohol, hepatic stellate cells (HSC) transform into an activated collagen-producing cell. In alcoholic liver disease, numerous changes in gene expression are associated with HSC activation, including the induction of several intracellular signaling cascades, which help maintain the activated phenotype and control the fibrogenic and proliferative state of the cell. Detailed analyses for understanding the molecular basis of the collagen I gene regulation have revealed a complex process involving reactive oxygen species (ROS) as key mediators. Less is known, however, about the contribution of reactive nitrogen species (RNS). In addition, a series of cytokines, growth factors, and chemokines, which activate extracellular matrix (ECM)-producing cells through paracrine and autocrine loops, contribute to the fibrogenic response.

Redox mechanisms in hepatic chronic wound healing and fibrogenesis

Reactive oxygen species (ROS) generated within cells or, more generally, in a tissue environment, may easily turn into a source of cell and tissue injury. Aerobic organisms have developed evolutionarily conserved mechanisms and strategies to carefully control the generation of ROS and other oxidative stress-related radical or non-radical reactive intermediates (that is, to maintain redox homeostasis), as well as to 'make use' of these molecules under physiological conditions as tools to modulate signal transduction, gene expression and cellular functional responses (that is, redox signalling). However, a derangement in redox homeostasis, resulting in sustained levels of oxidative stress and related mediators, can play a significant role in the pathogenesis of major human diseases characterized by chronic inflammation, chronic activation of wound healing and tissue fibrogenesis. This review has been designed to first offer a critical introduction to current knowledge in the field of redox research in order to introduce readers to the complexity of redox signalling and redox homeostasis. This will include ready-to-use key information and concepts on ROS, free radicals and oxidative stress-related reactive intermediates and reactions, sources of ROS in mammalian cells and tissues, antioxidant defences, redox sensors and, more generally, the major principles of redox signalling and redox-dependent transcriptional regulation of mammalian cells. This information will serve as a basis of knowledge to introduce the role of ROS and other oxidative stress-related intermediates in contributing to essential events, such as the induction of cell death, the perpetuation of chronic inflammatory responses, fibrogenesis and much more, with a major focus on hepatic chronic wound healing and liver fibrogenesis.

Nitric oxide regulates tumor cell cross-talk with stromal cells in the tumor microenvironment of the liver

Tumor progression is regulated through paracrine interactions between tumor cells and stromal cells in the microenvironment, including endothelial cells and myofibroblasts. Nitric oxide (NO) is a key molecule in the regulation of tumor-microenvironment interactions, although its precise role is incompletely defined. By using complementary in vitro and in vivo approaches, we studied the effect of endothelial NO synthase (eNOS)-derived NO on liver tumor growth and metastasis in relation to adjacent stromal myofibroblasts and matrix because liver tumors maintain a rich, vascular stromal network enriched with phenotypically heterogeneous myofibroblasts. Mice with an eNOS deficiency developed liver tumors more frequently in response to carcinogens compared with control animals. In a surgical model of pancreatic cancer liver metastasis, eNOS overexpression in the tumor microenvironment attenuated both the number and size of tumor implants. NO promoted anoikis of tumor cells in vitro and limited their invasive capacity. Because tumor cell anoikis and invasion are both regulated by myofibroblast-derived matrix, we explored the effect of NO on tumor cell protease expression. Both microarray and Western blot analysis revealed eNOS-dependent down-regulation of the matrix protease cathepsin B within tumor cells, and silencing of cathepsin B attenuated tumor cell invasive capacity in a similar manner to that observed with eNOS overexpression. Thus, a NO gradient within the tumor microenvironment influences tumor progression through orchestrated molecular interactions between tumor cells and stroma.

Experimental schistosomal hepatitis: protective effect of coenzyme-Q10 against the state of oxidative stress

Schistosoma mansoni (S. mansoni) eggs trapped in the host liver elicit a chain of oxidative processes that may be, at least in part, responsible for the pathology and progression of fibrosis associated with schistosomal hepatitis. This study was designed to assess the protective effect of the antioxidant coenzyme-Q10 (Co-Q10) against experimental S. mansoni-induced oxidative stress in the liver, and its potential role as an adjuvant to praziquantel (PZQ) therapy. The oxidative stress and overall liver function were improved under Co-Q10 therapy as evidenced by significant reduction in oxidative stress markers and preservation of antioxidant factors. Liver fibrosis was also reduced with a positive impact on liver function. Moreover, addition of Co-Q10 to PZQ therapy caused: significant reduction of liver egg load, significant improvement of the redox status, and lastly decreased liver fibrosis.

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

Hepatic stellate cells (HSCs) contribute to portal hypertension through multiple mechanisms that include collagen deposition, vasoconstriction, and regulation of sinusoidal structure. Under normal physiologic conditions, endothelial nitric oxide (NO) synthase-derived NO exerts paracrine effects on HSCs; however, in cirrhosis, NO generation is impaired in association with concomitant HSC activation and changes in sinusoidal structure, events that contribute significantly to the development of portal hypertension. These concepts, in combination with recent evidence that induction of HSC-selective apoptosis may represent a useful target for treatment of chronic liver disease, led us to examine if NO may further limit HSC function through apoptosis. Indeed, both NO donors and endothelial NO synthase overexpression promoted HSC apoptotic pathways. HSC death conferred by NO occurred through mitochondrial membrane depolarization and through a caspase-independent pathway. Furthermore, NO-induced apoptosis of HSC did not occur through the canonical pathways of soluble guanylate cyclase or protein nitration, but rather through the generation of superoxide and hydroxyl radical intermediates. Lastly, HSC isolated from rats after bile duct ligation were more susceptible to NO-induced apoptosis. These data indicate that NO promotes HSC apoptosis through a signaling mechanism that involves mitochondria, is mediated by reactive oxygen species, and occurs independent of caspase activation.

CONCLUSION

We postulate that NO-dependent apoptosis of HSCs may maintain sinusoidal homeostasis, and may represent an additional beneficial effect of NO donors for therapy of portal hypertension.

Inhibition of inducible nitric oxide synthase activity prevents liver recovery in rat thioacetamide-induced fibrosis reversal

BACKGROUND

Stimulation of nitric oxide (NO) synthesis similar to the application of NO donors could be of benefit in liver fibrosis. Many authors believe that activation of NO synthesis by pharmacological agents is promising in the treatment of liver fibrosis. However, there is considerable controversy in understanding the role of NO in fibrogenesis and fibrolysis. The aims of our study were to evaluate the effects of L-arginine, as an NO metabolic precursor, and those of NO synthase (NOS) inhibitors, L-nitroarginine methyl ester (L-NAME) and aminoguanidine (AG) in rats with thioacetamide (TAA)-induced liver fibrosis reversal.

MATERIALS AND METHODS

Male Wistar rats, 230-240 g, received TAA (200 mg kg(-1), intraperitoneally) twice a week for 3 months. Liver resolution was simulated by withdrawal of TAA administration. Thereafter the animals were subdivided into five groups and treated by intragastric intubation with: L-arginine (100 and 300 mg kg(-1)); L-NAME as an inhibitor of both constitutively expressed NOS (eNOS) and inducible NOS (iNOS) (20 mg kg(-1)), AG as a specific inhibitor of iNOS (100 mg kg(-1)) or placebo. The severity of liver fibrosis was assessed by morphometric evaluation of liver slides stained with Azan-Mallory, hydroxyproline (Hyp) determination and mRNA steady state levels of collagen I, transforming growth factor (TGF)-beta1, metalloproteinases (MMP)-13, -14, tissue inhibitor of MMP (TIMP)-1 and plasminogen activator inhibitor (PAI)-1 were quantified by real time PCR. The activities of serum marker enzyme, alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase, were measured.

RESULTS

TAA treatment during 3 months induced micronodular liver fibrosis with a pronounced deposition of collagen fibres. L-Arginine did not affect this deposition nor did it affect both relative and total liver hydroxyproline content. Both NOS inhibitors significantly increased the square of the liver connective tissue stained by Azan-Mallory and the above parameters characterizing liver hydroxyproline content. Both NOS inhibitors up-regulated procollagen alpha1 (I), MMP-13, TIMP-1 and PAI-1 mRNA expression. The AG effects were more pronounced. than those of L-NAME. AG treatment also increased mRNA expression of TGF-beta1 and PAI-1.

CONCLUSIONS

Both NOS inhibitors developed a clear pro-fibrotic effect in the liver. Aminoguanidine was more fibrotic than L-NAME. Our data suggest a significant anti-fibrotic role for iNOS rather than for eNOS. L-Arginine did not show any anti-fibrotic properties in the TAA-model used.

Bioconjugation of oligonucleotides for treating liver fibrosis

Liver fibrosis results from chronic liver injury due to hepatitis B and C, excessive alcohol ingestion, and metal ion overload. Fibrosis culminates in cirrhosis and results in liver failure. Therefore, a potent antifibrotic therapy is urgently needed to reverse scarring and eliminate progression to cirrhosis. Although activated hepatic stellate cells (HSCs) remain the principle cell type responsible for liver fibrosis, perivascular fibroblasts of portal and central veins as well as periductular fibroblasts are other sources of fibrogenic cells. This review will critically discuss various treatment strategies for liver fibrosis, including prevention of liver injury, reduction of inflammation, inhibition of HSC activation, degradation of scar matrix, and inhibition of aberrant collagen synthesis. Oligonucleotides (ODNs) are short, single-stranded nucleic acids, which disrupt expression of target protein by binding to complementary mRNA or forming triplex with genomic DNA. Triplex forming oligonucleotides (TFOs) provide an attractive strategy for treating liver fibrosis. A series of TFOs have been developed for inhibiting the transcription of alpha1(I) collagen gene, which opens a new area for antifibrotic drugs. There will be in-depth discussion on the use of TFOs and how different bioconjugation strategies can be utilized for their site-specific delivery to HSCs or hepatocytes for enhanced antifibrotic activities. Various insights developed in individual strategy and the need for multipronged approaches will also be discussed.

Proangiogenic cytokines as hypoxia-dependent factors stimulating migration of human hepatic stellate cells

Pathological angiogenesis is associated with the fibrogenic progression of chronic liver diseases. Experimental data suggest that hypoxia and vascular endothelial growth factor (VEGF) may stimulate proliferation and synthesis of type I collagen in activated, myofibroblast-like rat hepatic stellate cells (HSC/MFs). In this study, we investigated whether hypoxia, recombinant VEGF, or angiopoietin 1 (Ang-1) may affect other crucial profibrogenic features. In human HSC/MFs, which constitutively express VEGF receptor-1 and -2 (VEGFR-1, VEGFR-2) and the Ang-1 receptor Tie-2, exposure to hypoxia, VEGF, or Ang-1 resulted in a Ras/Erk-dependent stimulation of chemokinesis and chemotaxis. Migration of human HSC/MFs under hypoxic conditions involved up-regulation of VEGF-A, Ang-1, and related receptors and was mainly dependent on VEGFR-2 (Flk-1). In specimens from either cirrhotic rat livers or from patients with hepatitis C virus-related cirrhosis, HSC/MFs expressed proangiogenic factors and related receptors in areas of active fibrogenesis (ie, at the leading or lateral edge of developing incomplete fibrotic septa). Data presented herein suggest that VEGF and Ang-1 may contribute to fibrogenesis by acting as hypoxia-inducible, autocrine, and paracrine factors able to recruit myofibroblast-like cells. Moreover, HSC/MFs, in addition to their established profibrogenic role, may also contribute to neoangiogenesis during chronic hepatic wound healing.

Hemodynamic and antifibrotic effects of a selective liver nitric oxide donor V-PYRRO/NO in bile duct ligated rats

AIM: To assess whether a liver specific nitric oxide (NO) donor (V-PYRRO/NO) would prevent the development of portal hypertension and liver fibrosis in rats with bile duct ligation (BDL).

METHODS: Treatment (placebo or V-PYRRO/NO 0.53 μmol/kg per hour) was administered i.v. to rats 2 d before BDL (D-2) and maintained until the day of hemodynamic measurement (D26). Intra-hepatic NO level was estimated by measuring liver cGMP level. Effects of V-PYRRO/NO on liver fibrosis and lipid peroxidation were also assessed.

RESULTS: Compared to placebo treatment, V-PYRRO/NO improved splanchnic hemodynamics in BDL rats: portal pressure was significantly reduced by 27% (P < 0.0001) and collateral circulation development was almost completely blocked (splenorenal shunt blood flow by 74%, P = 0.007). Moreover, V-PYRRO/NO significantly prevented liver fibrosis development in BDL rats (by 30% in hepatic hydroxyproline content and 31% in the area of fibrosis, P < 0.0001 respectively), this effect being probably due to a decrease in lipid peroxidation by 44% in the hepatic malondialdehyde level (P = 0.007). Interestingly, we observed a significant and expected increase in liver cGMP, without any systemic hemodynamic effects (mean arterial pressure, vascular systemic resistance and cardiac output) in both sham-operated and BDL rats treated with V-PYRRO/NO. This result is in accordance with studies on V-PYRRO/NO metabolism showing a specific release of NO in the liver.

CONCLUSION: Continuous administrations of V-PYRRO/NO in BDL rats improved liver fibrosis and splanchnic hemodynamics without any noxious systemic hemo-dynamic effects.

Defects in cGMP-PKG pathway contribute to impaired NO-dependent responses in hepatic stellate cells upon activation

NO antagonizes hepatic stellate cell (HSC) contraction, although activated HSC in cirrhosis demonstrate impaired responses to NO. Decreased NO responses in activated HSC and mechanisms by which NO affects activated HSC remain incompletely understood. In normal rat HSC, the NO donor diethylamine NONOate (DEAN) significantly increased cGMP production and reduced serum-induced contraction by 25%. The guanylate cyclase (sGC) inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ) abolished 50% of DEAN effects, whereas the cGMP analog 8-bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP) reiterated half the observed DEAN response, suggesting both cGMP-dependent protein kinase G (PKG)-dependent and -independent mechanisms of NO-mediated antagonism of normal HSC contraction. However, NO donors did not increase cGMP production from in vivo activated HSC from bile duct-ligated rats and showed alterations in intracellular Ca(2+) accumulation suggesting defective cGMP-dependent effector pathways. The LX-2 cell line also demonstrated lack of cGMP generation in response to NO and a lack of effect of ODQ and 8-BrcGMP in modulating the NO response. However, cGMP-independent effects in response to NO were maintained in LX-2 and were associated with S-nitrosylation of proteins, an effect reiterated in primary HSC. Adenovirus-based overexpression of PKG significantly attenuated contraction of LX-2 by 25% in response to 8-BrcGMP. In summary, these studies demonstrate that NO affects HSC through cGMP-dependent and -independent pathways. The HSC activation process is associated with maintenance of cGMP-independent actions of NO but defects in cGMP-PKG-dependent NO signaling that are improved by PKG gene delivery in LX-2 cells. Activating targets downstream from NO-cGMP in activated HSC may represent a novel therapeutic target for portal hypertension.

Effect of celecoxib on experimental liver fibrosis in rat

BACKGROUND/AIM

Cyclooxygenase-2 (COX-2), an inducible enzyme that catalyzes prostaglandin synthesis, has been implicated in a number of hepatic stellate cell (HSC) functions. In the current study, we assessed the in vivo effect of celecoxib, a COX-2-selective inhibitor, in experimental liver fibrosis in rats.

METHODS

Male Sprague-Dawley rats received experimental treatments for 5 weeks. Serum alanine transminase at the time of sacrifice was measured. Quantitative assessment of liver fibrosis was performed by computerized morphometry. Expression of COX-2, alpha smooth muscle actin and connective tissue growth factor (CTGF) was evaluated by immunohistochemistry. Real-time quantitative PCR was used to determine the expression of genes associated with fibrogenesis and extracellular matrix degradation.

RESULTS

Liver fibrosis was significantly worse in rats that received both carbon tetrachloride (CCl4) and celecoxib, compared with rats that received CCl4 and gavage of water (P = 0.037). There was also more HSC activation, and upregulation of collagen alpha1(I), heat-shock protein 47, alphaB crystallin, matrix metalloproteinase (MMP)-2, MMP-9 and tissue inhibitor of MMP (TIMP)-2. The expression of TIMP-1 and CTGF was not significantly different between the two groups. The pro-fibrogenic effect of celecoxib in toxin-induced liver fibrosis in rats was further confirmed in thioacetamide model of liver injury.

CONCLUSIONS

Celecoxib potentiates experimental liver fibrosis; further studies are warranted to investigate the potential pro-fibrogenic effect of celecoxib in other animal models of liver fibrosis and in patients with chronic hepatitis.