Gene transfer of the neuronal NO synthase isoform to cirrhotic rat liver ameliorates portal hypertension

Stellate cell-specific adhesion molecule protocadherin 7 regulates sinusoidal contraction

BACKGROUND AND AIMS

Sustained inflammation and hepatocyte injury in chronic liver disease activate HSCs to transdifferentiate into fibrogenic, contractile myofibroblasts. We investigated the role of protocadherin 7 (PCDH7), a cadherin family member not previously characterized in the liver, whose expression is restricted to HSCs.

APPROACH AND RESULTS

We created a PCDH7 fl/fl mouse line, which was crossed to lecithin retinol acyltransferase-Cre mice to generate HSC-specific PCDH7 knockout animals. HSC contraction in vivo was tested in response to the HSC-selective vasoconstrictor endothelin-1 using intravital multiphoton microscopy. To establish a PCDH7 null HSC line, cells were isolated from PCDH7 fl/fl mice and infected with adenovirus-expressing Cre. Hepatic expression of PCDH7 was strictly restricted to HSCs. Knockout of PCDH7 in vivo abrogated HSC-mediated sinusoidal contraction in response to endothelin-1. In cultured HSCs, loss of PCDH7 markedly attenuated contractility within collagen gels and led to altered gene expression in pathways governing adhesion and vasoregulation. Loss of contractility in PCDH7 knockout cells was impaired Rho-GTPase signaling, as demonstrated by altered gene expression, reduced assembly of F-actin fibers, and loss of focal adhesions.

CONCLUSIONS

The stellate cell-specific cadherin, PCDH7, is a novel regulator of HSC contractility whose loss leads to cytoskeletal remodeling and sinusoidal relaxation.

The evolving role of liver sinusoidal endothelial cells in liver health and disease

LSECs are a unique population of endothelial cells within the liver and are recognized as key regulators of liver homeostasis. LSECs also play a key role in liver disease, as dysregulation of their quiescent phenotype promotes pathological processes within the liver including inflammation, microvascular thrombosis, fibrosis, and portal hypertension. Recent technical advances in single-cell analysis have characterized distinct subpopulations of the LSECs themselves with a high resolution and defined their gene expression profile and phenotype, broadening our understanding of their mechanistic role in liver biology. This article will review 4 broad advances in our understanding of LSEC biology in general: (1) LSEC heterogeneity, (2) LSEC aging and senescence, (3) LSEC role in liver regeneration, and (4) LSEC role in liver inflammation and will then review the role of LSECs in various liver pathologies including fibrosis, DILI, alcohol-associated liver disease, NASH, viral hepatitis, liver transplant rejection, and ischemia reperfusion injury. The review will conclude with a discussion of gaps in knowledge and areas for future research.

β-PIX cooperates with GIT1 to regulate endothelial nitric oxide synthase in sinusoidal endothelial cells

Previous studies have demonstrated that G protein-coupled receptor kinase interacting-1 protein (GIT1) associates with endothelial nitric oxide synthase (eNOS) to regulate nitric oxide production in sinusoidal endothelial cells (SECs). Here, we hypothesized that GIT1's tightly associated binding partner, β-PIX (p21-activated kinase-interacting exchange factor β, ARHGEF7) is specifically important in the regulation of eNOS activity. We examined β-PIX expression in normal rat liver by immunohistochemistry and explored β-PIX protein-protein interactions using immunoprecipitation and immunoblotting. The role of β-PIX in regulating eNOS enzymatic activity was studied in GIT1-deficient SECs. Finally, structural analysis of interaction sites in GIT1 and β-PIX required to regulate eNOS activity were mapped. β-PIX was expressed primarily in SECs in normal liver and was either absent or expressed at extremely low levels in other liver cells (stellate cells, Kupffer cells, and hepatocytes). β-PIX interacted with GIT1 and eNOS to form a trimolecular signaling module in normal SECs and was important in stimulating eNOS activity. Of note, GIT1-β-PIX interaction led to synergistic enhancement of eNOS activity, and β-PIX-driven increase in eNOS activity was GIT1 dependent. Disruption of β-PIX or GIT1 in normal SECs using β-PIX siRNA or GIT1-deficient SECs led to reduced eNOS activity. Finally, specific GIT1 domains [Spa2 homology domain (SHD) and synaptic localization domain (SLD), aa 331-596] and the β-PIX COOH terminal (aa 496-555) appeared to be critical in the regulation eNOS activity. The data indicate that β-PIX regulates eNOS phosphorylation and function in normal SECs and highlight the importance of the GIT1/β-PIX/eNOS trimolecular complex in normal liver SEC function.NEW & NOTEWORTHY β-PIX is a multidomain protein known to be a GIT1 binding partner. We report here that in the normal liver, the distribution and cellular localization of β-PIX are restricted largely to sinusoidal endothelial cells. Furthermore, β-PIX interacts with eNOS and GIT1 promotes eNOS activity and NO production and therefore exerts a novel posttranslational regulatory function on eNOS activity in sinusoidal endothelial cells. We also have identified specific molecular domains important in GIT1 and β-PIX's interaction with eNOS, which may represent novel therapeutic targets in the control of sinusoidal blood flow and intrahepatic resistance.

Macula Densa SGLT1-NOS1-Tubuloglomerular Feedback Pathway, a New Mechanism for Glomerular Hyperfiltration during Hyperglycemia

BACKGROUND

Glomerular hyperfiltration is common in early diabetes and is considered a risk factor for later diabetic nephropathy. We propose that sodium-glucose cotransporter 1 (SGLT1) senses increases in luminal glucose at the macula densa, enhancing generation of neuronal nitric oxide synthase 1 (NOS1)-dependent nitric oxide (NO) in the macula densa and blunting the tubuloglomerular feedback (TGF) response, thereby promoting the rise in GFR.

METHODS

We used microperfusion, micropuncture, and renal clearance of FITC-inulin to examine the effects of tubular glucose on NO generation at the macula densa, TGF, and GFR in wild-type and macula densa-specific NOS1 knockout mice.

RESULTS

Acute intravenous injection of glucose induced hyperglycemia and glucosuria with increased GFR in mice. We found that tubular glucose blunts the TGF response in vivo and in vitro and stimulates NO generation at the macula densa. We also showed that SGLT1 is expressed at the macula densa; in the presence of tubular glucose, SGLT1 inhibits TGF and NO generation, but this action is blocked when the SGLT1 inhibitor KGA-2727 is present. In addition, we demonstrated that glucose increases NOS1 expression and NOS1 phosphorylation at Ser1417 in mouse renal cortex and cultured human kidney tissue. In macula densa-specific NOS1 knockout mice, glucose had no effect on NO generation, TGF, and GFR.

CONCLUSIONS

We identified a novel mechanism of acute hyperglycemia-induced hyperfiltration wherein increases in luminal glucose at the macula densa upregulate the expression and activity of NOS1 via SGLT1, blunting the TGF response and promoting glomerular hyperfiltration.

Analysis of the nitric oxide-cyclic guanosine monophosphate pathway in experimental liver cirrhosis suggests phosphodiesterase-5 as potential target to treat portal hypertension

AIM

To investigate the potential effect of inhibitors of phosphodiesterase-5 (PDE-5) for therapy of portal hypertension in liver cirrhosis.

METHODS

In the rat model of thioacetamide-induced liver fibrosis/cirrhosis the nitric oxide-cyclic guanosine monophosphate (NO-cGMP) pathway was investigated. Expression and localization of PDE-5, the enzyme that converts vasodilating cGMP into inactive 5’-GMP, was in the focus of the study. Hepatic gene expression of key components of the NO-cGMP pathway was determined by qRT-PCR: Endothelial NO synthase (eNOS), inducible NO synthase (iNOS), soluble guanylate cyclase subunits α1 and β1 (sGCa1, sGCb1), and PDE-5. Hepatic PDE-5 protein expression and localization were detected by immunohistochemistry. Serum cGMP concentrations were measured using ELISA. Acute effects of the PDE-5 inhibitor Sildenafil (0.1 mg/kg or 1.0 mg/kg) on portal and systemic hemodynamics were investigated using pressure transducers.

RESULTS

Hepatic gene expression of eNOS (2.2-fold; P = 0.003), sGCa1 (1.7-fold; P = 0.003), sGCb1 (3.0-fold; P = 0.003), and PDE-5 (11-fold; P = 0.003) was increased in cirrhotic livers compared to healthy livers. Overexpression of PDE-5 (7.7-fold; P = 0.006) was less pronounced in fibrotic livers. iNOS expression was only detected in fibrotic and cirrhotic livers. In healthy liver, PDE-5 protein was localized primarily in zone 3 hepatocytes and to a lesser extent in perisinusoidal cells. This zonation was disturbed in cirrhosis: PDE-5 protein expression in perisinusoidal cells was induced approximately 8-fold. In addition, PDE-5-expressing cells were also found in fibrous septa. Serum cGMP concentrations were reduced in rats with cirrhotic livers by approximately 40%. Inhibition of PDE-5 by Sildenafil caused a significant increase in serum cGMP concentrations [+ 64% in healthy rats (P = 0.024), + 85% in cirrhotic rats (P = 0.018)]. Concomitantly, the portal venous pressure was reduced by 19% in rats with liver cirrhosis.

CONCLUSION

Overexpression and abrogated zonation of PDE-5 likely contribute to the pathogenesis of cirrhotic portal hypertension. PDE-5 inhibition may therefore be a reasonable therapeutic approach for portal hypertension.

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]

Intrahepatic vascular changes in non-alcoholic fatty liver disease: Potential role of insulin-resistance and endothelial dysfunction

Metabolic syndrome is a cluster of several clinical conditions characterized by insulin-resistance and high cardiovascular risk. Non-alcoholic fatty liver disease is the liver expression of the metabolic syndrome, and insulin resistance can be a frequent comorbidity in several chronic liver diseases, in particular hepatitis C virus infection and/or cirrhosis. Several studies have demonstrated that insulin action is not only relevant for glucose control, but also for vascular homeostasis. Insulin regulates nitric oxide production, which mediates to a large degree the vasodilating, anti-inflammatory and antithrombotic properties of a healthy endothelium, guaranteeing organ perfusion. The effects of insulin on the liver microvasculature and the effects of IR on sinusoidal endothelial cells have been studied in animal models of non-alcoholic fatty liver disease. The hypotheses derived from these studies and the potential translation of these results into humans are critically discussed in this review.

Addition of simvastatin to carvedilol non responders: A new pharmacological therapy for treatment of portal hypertension

AIM

To determine whether addition of simvastatin could be an important pharmacological rescue therapy for carvedilol non-responders.

METHODS

One hundred and two consecutive patients of cirrhosis of liver with significant portal hypertension were included. Hepatic venous pressure gradient (HVPG) was measured at the base line and after proper optimization of dose; chronic response was assessed at 3 mo. Carvedilol non-responders were given simvastatin 20 mg per day (increased to 40 mg per day at day 15). Carvedilol plus simvastatin was continued for 1 mo and hemodynamic response was again measured at 1 mo.

RESULTS

A total of 102 patients with mean age of 58.3 ± 6.6 years were included. Mean baseline HVPG was 16.75 ± 2.12 mmHg and after optimization of dose and reassessment of HVPG at 3 mo, mean reduction of HVPG from baseline was 5.5 ± 1.7 mmHg and 2.8 ± 1.6 mmHg among responders and non-responders respectively (P < 0.001). Addition of simvastatin to carvedilol non-responders resulted in significant response in 16 patients (42.1%) and thus overall response with carvedilol and carvedilol plus simvastatin was seen in 78 patients (80%). Two patients were removed in chronic protocol study with carvedilol and three patients were removed in carvedilol plus simvastatin study due to side effects.

CONCLUSION

Addition of simvastatin to carvedilol non-responders may prove to be an excellent rescue therapy in patients with portal hypertension.

The Molecular Basis of Portal Hypertension

Cirrhosis leads to portal hypertension and vascular abnormalities in multiple vascular beds. There is intense vasoconstriction in the liver and the kidneys, but also vasodilation in the other vascular beds, including the periphery, lungs, brain, and mesentery. The derangement in each of these beds leads to specific clinical disease. The vasoconstrictive phenotype in the liver ultimately leads to clinical portal hypertension, and is caused by an imbalance of vasoconstrictive and vasorelaxing molecules, which will be the focus of this review.

Wuweizi protects against liver cirrhosis by promoting endogenous stem cell proliferation

AIM: To investigate the mechanism for Wuweizi to treat liver cirrhosis.

METHODS: A rat model of liver cirrhosis was developed with CCl₄. Rats were randomly divided into five groups: three treatment groups [small dose Wuweizi group (A1), middle dose group (A2) and high dose group (A3)], a blank group (C) and a model group (M). Except group C, liver cirrhosis was induced in all other groups. Groups A1, A2 and A3 were given 1.0, 1.5 and 2.0 mg/200 g Wuweizi, respectively. After treatment, histopathology, liver function [aspartate transaminase (AST), alanine transaminase (ALT) and albumin (ALB)], hepatic fibrosis, stem cell proliferation, and the expression ofCK-18, ALB and α-fetoprotein (AFP) were assessed.

RESULTS: In the treatment groups, there was an improvement in the degree of hepatic fibrosis and the condition of liver cell degeneration and necrosis, as revealed by HE staining and Masson staining, and the liver fibrosis scores were different among each treatment group (P < 0.05). Compared with group M, the liver fibrosis score of group A2 was improved most obviously (P < 0.01). Immunohistochemistry analysis showed that the expression of CK-18, ALB and AFP was different between each treatment group (P < 0.05). By labeling liver tissue stem cells with BrdU, the proliferation and division of stem cells were observed through the method of "regional coexistence". Immunofluorescence analysis revealed that the expression of CK-18, ALB and AFP were different among each treatment group (P < 0.01), with group A2 having the most prominent expression (P < 0.01). Liver function was improved differently in each treatment group (P < 0.05). Compared with group M, AST and ALT were decreased most significantly and ALB increased most obviously in group A2 (P < 0.01).

CONCLUSION: Wuweizi has a protective effect on injured liver cells. Wuweizi could delay the process of liver cirrhosis via mechanisms possibly related to promoting the proliferation of endogenous stem cells.

Evolution in the understanding of the pathophysiological basis of portal hypertension: How changes in paradigm are leading to successful new treatments

Among the common complication of cirrhosis portal hypertension witnessed a major improvement of prognosis during the past decades. Principally due to the introduction of rational treatments based on new pathophysiological paradigms (concepts of thought) developed in the 1980s. The best example being the use of non-selective beta-blockers and of vasopressin analogs, somatostatin, and its analogs. Further refinement in the knowledge of the molecular mechanisms involved in the regulation of both the splanchnic and hepatic circulation has led to the emergence of new treatments, which are based on evidence that show not only structural but also vasoactive components increase the hepatic vascular resistance, as well as of angiogenesis. This knowledge and future improvements will most likely result in more effective treatment of portal hypertension and effective prevention of its complications in early stages.

Integrin-linked kinase regulates endothelial cell nitric oxide synthase expression in hepatic sinusoidal endothelial cells

BACKGROUND & AIMS

Portal hypertension results from endothelial dysfunction after liver injury caused in part by abnormal production of endothelial cell derived nitric oxide synthase (eNOS). Here, we have postulated that endothelial mechanosensing pathways involving integrin-linked kinase (ILK) may play a critical role in portal hypertension, eNOS expression and function. In this study, we investigated the role of ILK and the small GTP-binding protein, Rho, in sinusoidal endothelial cell (SEC) eNOS regulation and function.

METHODS

Primary liver SECs were isolated using standard techniques. Liver injury was induced by performing bile duct ligation (BDL). To examine the expression of Rho and ILK in vivo during wound healing, SECs were infected with constitutively active Rho (V14), a dominant negative Rho (N19) and constructs encoding ILK and a short hairpin-inhibiting ILK.

RESULTS

Integrin-linked kinase expression was increased in SECs after liver injury; endothelin-1, vascular endothelial growth factor, and transforming growth factor beta-1 stimulated ILK expression in SECs. ILK expression in turn led to eNOS upregulation and to enhance eNOS phosphorylation and NO production. ILK knockdown or ILK (kinase) inhibition reduced eNOS mRNA expression, promoter activity, eNOS expression and ultimately NO production. In contrast, ILK overexpression had the opposite effect. Inhibition of ILK activity also disrupted the actin cytoskeleton in isolated SECs. Rho overexpression suppressed phosphorylation of the serine-threonine kinase, Akt and inhibited eNOS phosphorylation. Finally, inhibition of Rho function with the RGS domain of the p115-Rho-specific GEF (p115-RGS) significantly increased eNOS phosphorylation.

CONCLUSIONS

Our data suggest a potential role for ILK, the cytoskeleton and ILK signalling partners including Rho in regulating intrahepatic SEC eNOS expression and function.

Pathophysiology of Portal Hypertension

The bases of our current knowledge on the physiology of the hepatic portal system are largely owed to the work of three pioneering vascular researchers from the sixteenth and the seventeenth centuries: A. Vesalius, W. Harvey, and F. Glisson. Vesalius is referred to as the founder of modern human anatomy, and in his influential book, De humani corporis fabrica libri septem, he elaborated the first anatomical atlas of the hepatic portal venous system (Vesalius 2013). Sir William Harvey laid the foundations of modern cardiovascular research with his Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus (Harvey 1931) in which he established the nature of blood circulation. Finally, F. Glisson characterized the gastrointestinal-hepatic vascular system (Child 1955). These physiological descriptions were later complemented with clinical observations. In the eighteenth and nineteenth centuries, Morgagni, Puckelt, Cruveilhier, and Osler were the first to make the connection between common hepatic complications – ascites, splenomegaly, and gastrointestinal bleeding – and obstruction of the portal system (Sandblom 1993). These were the foundations that allowed Gilbert, Villaret, and Thompson to establish an early definition of portal hypertension at the beginning of the twentieth century. In this period, Thompson performed the first direct measurement of portal pressure by laparotomy in some patients (Gilbert and Villaret 1906; Thompson et al. 1937). Considering all these milestones, and paraphrasing Sir Isaac Newton, if hepatologists have seen further, it is by standing on the shoulders of giants.

Nowadays, our understanding of the pathogenesis of portal hypertension has largely improved thanks to the progress in preclinical and clinical research. However, this field is ever-changing and hepatologists are continually identifying novel pathological mechanisms and developing new therapeutic strategies for this clinical condition. Hence, the aim of this chapter is to summarize the current knowledge about this clinical condition.

Vascular pathobiology in chronic liver disease and cirrhosis - current status and future directions

Chronic liver disease is associated with remarkable alterations in the intra- and extrahepatic vasculature. Because of these changes, the fields of liver vasculature and portal hypertension have recently become closely integrated within the broader vascular biology discipline. As developments in vascular biology have evolved, a deeper understanding of vascular processes has led to a better understanding of the mechanisms of the dynamic vascular changes associated with portal hypertension and chronic liver disease. In this context, hepatic vascular cells, such as sinusoidal endothelial cells and pericyte-like hepatic stellate cells, are closely associated with one another, where they have paracrine and autocrine effects on each other and themselves. These cells play important roles in the pathogenesis of liver fibrosis/cirrhosis and portal hypertension. Further, a variety of signaling pathways have recently come to light. These include growth factor pathways involving cytokines such as transforming growth factor β, platelet derived growth factor, and others as well as a variety of vasoactive peptides and other molecules. An early and consistent feature of liver injury is the development of an increase in intra-hepatic resistance; this is associated with changes in hepatic vascular cells and their signaling pathway that cause portal hypertension. A critical concept is that this process aggregates signals to the extrahepatic circulation, causing derangement in this system's cells and signaling pathways, which ultimately leads to the collateral vessel formation and arterial vasodilation in the splanchnic and systemic circulation, which by virtue of the hydraulic derivation of Ohm's law (pressure = resistance × flow), worsens portal hypertension. This review provides a detailed review of the current status and future direction of the basic biology of portal hypertension with a focus on the physiology, pathophysiology, and signaling of cells within the liver, as well as those in the mesenteric vascular circulation. Translational implications of recent research and the future directions that it points to are also highlighted.

Efficient hepatic delivery of drugs: novel strategies and their significance

Liver is a vital organ responsible for plethora of functions including detoxification, protein synthesis, and the production of biochemicals necessary for the sustenance of life. Therefore, patients with chronic liver diseases such as viral hepatitis, liver cirrhosis, and hepatocellular carcinoma need immediate attention to sustain life and as a result are often exposed to the prolonged treatment with drugs/herbal medications. Lack of site-specific delivery of these medications to the hepatocytes/nonparenchymal cells and adverse effects associated with their off-target interactions limit their continuous use. This calls for the development and fabrication of targeted delivery systems which can deliver the drug payload at the desired site of action for defined period of time. The primary aim of drug targeting is to manipulate the whole body distribution of drugs, that is, to prevent distribution to non-target cells and concomitantly increase the drug concentration at the targeted site. Carrier molecules are designed for their selective cellular uptake, taking advantage of specific receptors or binding sites present on the surface membrane of the target cell. In this review, various aspects of liver targeting of drug molecules and herbal medications have been discussed which elucidate the importance of delivering the drugs/herbal medications at their desired site of action.

Current concepts on the role of nitric oxide in portal hypertension

Portal hypertension (PHT) is defined as a pathological increase in portal venous pressure and frequently accompanies cirrhosis. Portal pressure can be increased by a rise in portal blood flow, an increase in vascular resistance, or the combination. In cirrhosis, the primary factor leading to PHT is an increase in intra-hepatic resistance to blood flow. Although much of this increase is a mechanical consequence of architectural disturbances, there is a dynamic and reversible component that represents up to a third of the increased vascular resistance in cirrhosis. Many vasoactive substances contribute to the development of PHT. Among these, nitric oxide (NO) is the key mediator that paradoxically regulates the sinusoidal (intra-hepatic) and systemic/splanchnic circulations. NO deficiency in the liver leads to increased intra-hepatic resistance while increased NO in the circulation contributes to the hyperdynamic systemic/splanchnic circulation. NO mediated-angiogenesis also plays a role in splanchnic vasodilation and collateral circulation formation. NO donors reduce PHT in animals models but the key clinical challenge is the development of an NO donor or drug delivery system that selectively targets the liver.

Transplantation of endothelial progenitor cells ameliorates vascular dysfunction and portal hypertension in carbon tetrachloride-induced rat liver cirrhotic model

BACKGROUND AND AIM

In cirrhosis, sinusoidal endothelial cell injury results in increased endothelin-1 (ET-1) and decreased nitric oxide synthase (NOS) activity, leading to portal hypertension. However, the effects of transplanted endothelial progenitor cells (EPCs) on the cirrhotic liver have not yet been clarified. We investigated whether EPC transplantation reduces portal hypertension.

METHODS

Cirrhotic rats were created by the administration of carbon tetrachloride (CCl(4) ) twice weekly for 10 weeks. From week 7, rat bone marrow-derived EPCs were injected via the tail vein in this model once a week for 4 weeks. Endothelial NOS (eNOS), vascular endothelial growth factor (VEGF) and caveolin expressions were examined by Western blots. Hepatic tissue ET-1 was measured by a radioimmunoassay (RIA). Portal venous pressure, mean aortic pressure, and hepatic blood flow were measured.

RESULTS

Endothelial progenitor cell transplantation reduced liver fibrosis, α-smooth muscle actin-positive cells, caveolin expression, ET-1 concentration and portal venous pressure. EPC transplantation increased hepatic blood flow, protein levels of eNOS and VEGF. Immunohistochemical analyses of eNOS and isolectin B4 demonstrated that the livers of EPC-transplanted animals had markedly increased vascular density, suggesting reconstitution of sinusoidal blood vessels with endothelium.

CONCLUSIONS

Transplantation of EPCs ameliorates vascular dysfunction and portal hypertension, suggesting this treatment may provide a new approach in the therapy of portal hypertension with liver cirrhosis.

Endothelial dysfunction in the regulation of cirrhosis and portal hypertension

Portal hypertension is caused by an increased intrahepatic resistance, a major consequence of cirrhosis. Endothelial dysfunction in liver sinusoidal endothelial cells (LSECs) decreases the production of vasodilators, such as nitric oxide, and favours vasoconstriction. This contributes to an increased vascular resistance in the intrahepatic/sinusoidal microcirculation and develops portal hypertension. Portal hypertension, in turn, causes endothelial dysfunction in the extrahepatic, i.e. splanchnic and systemic, circulation. Unlike dysfunction in LSECs, endothelial dysfunction in the splanchnic and systemic circulation causes overproduction of vasodilator molecules, leading to arterial vasodilation. In addition, portal hypertension leads to the formation of portosystemic collateral vessels. Both arterial vasodilation and portosystemic collateral vessel formation exacerbate portal hypertension by increasing the blood flow through the portal vein. Pathological consequences, such as oesophageal varices and ascites, result. While the sequence of pathological vascular events in cirrhosis and portal hypertension has been elucidated, the underlying cellular and molecular mechanisms causing endothelial dysfunctions are not yet fully understood. This review article summarizes the current cellular and molecular studies on endothelial dysfunctions found during the development of cirrhosis and portal hypertension with a focus on the intra- and extrahepatic circulations. The article ends by discussing the future directions of the study for endothelial dysfunction.

Pathophysiology of portal hypertension and its clinical links

Portal hypertension is a major cause of morbidity and mortality in patients with liver cirrhosis. Intrahepatic vascular resistance due to architectural distortion and intrahepatic vasoconstriction, increased portal blood flow due to splanchnic vasodilatation, and development of collateral circulation have been considered as major factors for the development of portal hypertension. Recently, sinusoidal remodeling and angiogenesis have been focused as potential etiologic factors and various researchers have tried to improve portal hypertension by modulating these new targets. This article reviews potential new treatments in the context of portal hypertension pathophysiology concepts.

G protein-coupled receptor kinases: more than just kinases and not only for GPCRs

G protein-coupled receptor (GPCR) kinases (GRKs) are best known for their role in homologous desensitization of GPCRs. GRKs phosphorylate activated receptors and promote high affinity binding of arrestins, which precludes G protein coupling. GRKs have a multidomain structure, with the kinase domain inserted into a loop of a regulator of G protein signaling homology domain. Unlike many other kinases, GRKs do not need to be phosphorylated in their activation loop to achieve an activated state. Instead, they are directly activated by docking with active GPCRs. In this manner they are able to selectively phosphorylate Ser/Thr residues on only the activated form of the receptor, unlike related kinases such as protein kinase A. GRKs also phosphorylate a variety of non-GPCR substrates and regulate several signaling pathways via direct interactions with other proteins in a phosphorylation-independent manner. Multiple GRK subtypes are present in virtually every animal cell, with the highest expression levels found in neurons, with their extensive and complex signal regulation. Insufficient or excessive GRK activity was implicated in a variety of human disorders, ranging from heart failure to depression to Parkinson's disease. As key regulators of GPCR-dependent and -independent signaling pathways, GRKs are emerging drug targets and promising molecular tools for therapy. Targeted modulation of expression and/or of activity of several GRK isoforms for therapeutic purposes was recently validated in cardiac disorders and Parkinson's disease.

Obstructive jaundice activates nitroxidergic neurons of the vago-vagal neural circuit that regulates the hepatobiliary system in rabbits

In this study, we investigated the expression of neuronal nitric oxide synthase (nNOS) and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d), two specific enzymes for nitric oxide (NO) synthesis, in the development of liver fibrosis induced by chronic bile duct ligation (BDL) in the rabbit. We specifically studied the liver-innervated nitroxidergic neurons that originate in the nodose ganglion (NG), nucleus of the solitary tract (NTS) and dorsal motor vagal nucleus (DMV). Our data showed that BDL resulted in overexpression of NADPH-d/nNOS in the NG, NTS and DMV neurons. Using densitometric analysis, we found a significant increase in NADPH-d expression as a result of BDL in the NG, NTS and DMV (72.6, 79.4 and 57.4% increase, respectively). These findings were corroborated by serum biochemistry and hepatic histopathological examination, which were influenced by NADPH-d/nNOS-generated NO in the liver following BDL. Upregulation of NADPH-d/nNOS expression may have important implications, including (1) facilitation of extrahepatic biliary parasympathetic tone that promotes gallbladder emptying of excess stagnant bile; (2) relaxation of smooth muscles of bile canaliculi thus participating in the pathogenesis of cholestasis; (3) dilation of hepatic sinusoids to counter BDL-induced intrahepatic portal hypertension in which endothelia may be damaged, and (4) alterations in hepatic metabolism, such as glycogenesis, bile formation and secretion, and bilirubin clearance.

Tempol administration, a superoxide dismutase mimetic, reduces hepatic vascular resistance and portal pressure in cirrhotic rats

BACKGROUND & AIMS

Increased superoxide in cirrhotic livers, by reducing nitric oxide bioavailability, contributes to increase intrahepatic vascular resistance to portal blood flow and as a consequence portal pressure. We aimed to evaluate whether a strategy directed to reduce superoxide using tempol, a small membrane permeable SOD-mimetic, is able to modulate intrahepatic nitric oxide content and reduce portal pressure in cirrhotic rats.

METHODS

Superoxide and nitric oxide were evaluated in control sinusoidal endothelial cells (SEC) pre-treated with the pro-oxidant diethyldithiocarbamate (DDC) and in CCl(4)-cirrhotic rat livers treated with tempol or vehicle. Mean arterial pressure, portal pressure, and portal blood flow were measured in control and cirrhotic rats treated with tempol (180μmol/kg/h; via ileocholic vein) or vehicle. In a subset of animals, hemodynamic measurements were performed after NO-inhibition with l-NAME.

RESULTS

Tempol reduced superoxide content and increased NO both in SEC and cirrhotic livers. In cirrhotic rats, but not in controls, tempol significantly reduced portal pressure, and increased portal blood flow, which most likely reflects a reduction in intrahepatic vascular resistance. Tempol significantly reduced mean arterial pressure. l-NAME prevented all these effects.

CONCLUSIONS

Tempol reduces superoxide, increases nitric oxide, and reduces portal pressure in sinusoidal endothelial cells and in cirrhotic livers. These results confirm that oxidative stress has a role in the pathogenesis of portal hypertension and supports the use of antioxidants in its treatment. However, when considering the use of antioxidants as additional therapy to treat portal hypertension, the potential to produce deleterious effects on systemic hemodynamics needs to be carefully evaluated.

Chronic intermittent hypoxia induces NMDA receptor-dependent plasticity and suppresses nitric oxide signaling in the mouse hypothalamic paraventricular nucleus

Chronic intermittent hypoxia (CIH) is a concomitant of sleep apnea that produces a slowly developing chemosensory-dependent blood pressure elevation ascribed in part to NMDA receptor-dependent plasticity and reduced nitric oxide (NO) signaling in the carotid body. The hypothalamic paraventricular nucleus (PVN) is responsive to hypoxic stress and also contains neurons that express NMDA receptors and neuronal nitric oxide synthase (nNOS). We tested the hypothesis that extended (35 d) CIH results in a decrease in the surface/synaptic availability of the essential NMDA NR1 subunit in nNOS-containing neurons and NMDA-induced NO production in the PVN of mice. As compared with controls, the 35 d CIH-exposed mice showed a significant increase in blood pressure and an increased density of NR1 immunogold particles located in the cytoplasm of nNOS-containing dendrites. Neither of these between-group differences was seen after 14 d, even though there was already a reduction in the NR1 plasmalemmal density at this time point. Patch-clamp recording of PVN neurons in slices showed a significant reduction in NMDA currents after either 14 or 35 d exposure to CIH compared with sham controls. In contrast, NO production, as measured by the NO-sensitive fluorescent dye 4-amino-5-methylamino-2',7'-difluorofluorescein, was suppressed only in the 35 d CIH group. We conclude that CIH produces a reduction in the surface/synaptic targeting of NR1 in nNOS neurons and decreases NMDA receptor-mediated currents in the PVN before the emergence of hypertension, the development of which may be enabled by suppression of NO signaling in this brain region.

[Treatment update on portal hypertension and complications]

Current understanding of the pathophysiology of portal hypertension has resulted in therapeutic approaches aimed at correcting the increased splanchnic blood flow and some of which have been already used in clinical practice. Recently new perspectives opened and erstwhile paradigm has been changed to focus on increased resistance to portal blood flow and the formation of portosystemic collateralization. Several studies revealed the clear-cut mechanisms of hepatic endothelial dysfunction and abnormal angiogenesis contributing to the development of portal hypertension. Thus the modulations of hyperdynamic circulation or angiogenesis seem to be valuable therapeutic targets. In the current review update, we discuss the multidisciplinary management of modulating hepatic vascular resistance and abnormal angiogenesis associated with portal hypertension. However, these new pharmacological approaches are still under investigation and widescale clinical application are needed to develop effective strategies.

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.

A real-time, telemetric method for continuous measurement of portal pressures

The ability to longitudinally monitor portal and splanchnic pressures would greatly enhance the understanding of acute and chronic liver disease by helping to assess the immediate and long-term impact of therapeutic manipulations. However, a technique for measuring portal pressures in the ambulatory setting is not currently available. To overcome this difficulty, we utilized an approach that involved the implantation of a miniature telemetric device, equipped with a specially-designed pressure transmission catheter, into the spleen of an anesthetized mouse. Using this approach, portal pressures were measured continuously over 5 d in conscious, unrestrained animals, the availability of which will help facilitate studies of the portal circulation requiring long-term stability.

The hepatic microcirculation: mechanistic contributions and therapeutic targets in liver injury and repair

The complex functions of the liver in biosynthesis, metabolism, clearance, and host defense are tightly dependent on an adequate microcirculation. To guarantee hepatic homeostasis, this requires not only a sufficient nutritive perfusion and oxygen supply, but also a balanced vasomotor control and an appropriate cell-cell communication. Deteriorations of the hepatic homeostasis, as observed in ischemia/reperfusion, cold preservation and transplantation, septic organ failure, and hepatic resection-induced hyperperfusion, are associated with a high morbidity and mortality. During the last two decades, experimental studies have demonstrated that microcirculatory disorders are determinants for organ failure in these disease states. Disorders include 1) a dysregulation of the vasomotor control with a deterioration of the endothelin-nitric oxide balance, an arterial and sinusoidal constriction, and a shutdown of the microcirculation as well as 2) an overwhelming inflammatory response with microvascular leukocyte accumulation, platelet adherence, and Kupffer cell activation. Within the sequelae of events, proinflammatory mediators, such as reactive oxygen species and tumor necrosis factor-alpha, are the key players, causing the microvascular dysfunction and perfusion failure. This review covers the morphological and functional characterization of the hepatic microcirculation, the mechanistic contributions in surgical disease states, and the therapeutic targets to attenuate tissue injury and organ dysfunction. It also indicates future directions to translate the knowledge achieved from experimental studies into clinical practice. By this, the use of the recently introduced techniques to monitor the hepatic microcirculation in humans, such as near-infrared spectroscopy or orthogonal polarized spectral imaging, may allow an early initiation of treatment, which should benefit the final outcome of these critically ill patients.

Targeted RNA interference for hepatic fibrosis

Hepatic fibrosis is a common consequence in patients with chronic liver damage. To date, no agent has been approved for the treatment of hepatic fibrosis. RNA interference (RNAi) is known to be a powerful tool for post-transcriptional gene silencing and has opened new avenues in gene therapy. The problems of lack of cell specificity in vivo and subsequently the occurrence of side effects has hampered the development of hepatic fibrosis treatment. To overcome these shortcomings, several targeted strategies have been developed, such as hydrodynamics-based approaches, local administration, cell-type-selective ligands and cell-type-specific promoters or enhancers, etc. Here, we provide an overview of targeted strategies for the treatment of hepatic fibrosis, and particularly, targeted RNAi for hepatic fibrosis.

Role of endothelial nitric oxide synthase in the development of portal hypertension in the carbon tetrachloride-induced liver fibrosis model

Portal hypertension (PHT) is a complication of liver cirrhosis and directly increases mortality and morbidity by increasing the propensity of venous hemorrhage. There are two main underlying causations for PHT, increased hepatic resistance and systemic hyperdynamic circulation. Both are related to localized aberrations in endothelial nitric oxide synthase (eNOS) function and NO biosynthesis. This study investigates the importance of eNOS and systemic hyperdynamic-associated hyperemia to better understand the pathophysiology of PHT. Wild-type and eNOS(-/-) mice were given the hepatotoxin CCl(4) for 4-12 wk. Hepatic fibrosis was determined histologically following collagen staining. Portal venous pressure, hepatic resistance, and hyperemia were determined by measuring splenic pulp pressure (SPP), hepatic portal-venous perfusion pressure (HPVPP), abdominal aortic flow (Qao), and portal venous flow (Qpv). Hepatic fibrosis developed equally in wild-type and eNOS(-/-) CCl(4)-exposed mice. SPP, Qao, and Qpv increased rapidly in wild-type CCl(4)-exposed mice, but HPVPP did not. In eNOS(-/-) CCl(4) mice, Qao was not increased, SPP was partially increased, and HPVPP and Qpv were increased nonsignificantly. We concluded that the systemic hyperemia component of hyperdynamic circulation is eNOS dependent and precedes increased changes in hepatic resistance. Alternative mechanisms, possibly involving cyclooxygenase, may contribute. eNOS maintains normal hepatic resistance following CCl(4)-induced fibrosis. Consequently, increased portal pressure following chronic CCl(4) exposure is linked to hyperdynamic circulation in wild-type mice and increased hepatic resistance in eNOS(-/-) mice.

Phosphodiesterase-5 inhibitors have distinct effects on the hemodynamics of the liver

Background

The NO - cGMP system plays a key role in the regulation of sinusoidal tonus and liver blood flow with phosphodiesterase-5 (PDE-5) terminating the dilatory action of cGMP. We, therefore, investigated the effects of PDE-5 inhibitors on hepatic and systemic hemodynamics in rats.

Methods

Hemodynamic parameters were monitored for 60 min. after intravenous injection of sildenafil and vardenafil [1, 10 and 100 μg/kg (sil1, sil10, sil100, var1, var10, var100)] in anesthetized rats.

Results

Cardiac output and heart rate remained constant. After a short dip, mean arterial blood pressure again increased. Systemic vascular resistance transiently decreased slightly. Changes in hepatic hemodynamic parameters started after few minutes and continued for at least 60 min. Portal (var10 -31%, sil10 -34%) and hepatic arterial resistance (var10 -30%, sil10 -32%) decreased significantly (p < 0.05). At the same time portal venous (var10 +29%, sil10 +24%), hepatic arterial (var10 +34%, sil10 +48%), and hepatic parenchymal blood flow (var10 +15%, sil10 +15%) increased significantly (p < 0.05). The fractional liver blood flow (total liver flow/cardiac output) increased significantly (var10 26%, sil10 23%). Portal pressure remained constant or tended to decrease. 10 μg/kg was the most effective dose for both PDE-5 inhibitors.

Conclusion

Low doses of phosphodiesterase-5 inhibitors have distinct effects on hepatic hemodynamic parameters. Their therapeutic use in portal hypertension should therefore be evaluated.

[Progress in portal hypertension]

In patients with portal hypertension due to cirrhosis, the mechanisms responsible for circulatory modifications are well-known. An elevation in intrahepatic vascular resistance related to a hepatic endothelin hyperproduction and an arterial nitric oxide (NO) hyperproduction. The presence and the degree of portal hypertension might be determined by the measurement of the hepatic venous pressure gradient but non-invasive technique as FibroTest or FibroScan might be useful to estimate the presence of severe portal hypertension. Numerous substances decrease portal pressure either by reducing hepatic vascular resistance or by reducing portal tributary blood flow. The combination of both types of substances is probably the best pharmacological treatment of portal hypertension but further hemodynamic and clinical studies are needed.

Fibronectin stimulates endothelin-1 synthesis in rat hepatic myofibroblasts via a Src/ERK-regulated signaling pathway

BACKGROUND & AIMS

Liver injury serves as an excellent model of wound healing, characterized by increased synthesis of various cytokines and peptides, including the vasoactive peptide endothelin-1. In the liver, wound healing is mediated by effector cells such as hepatic stellate cells, which cause tissue contraction. Endothelin-1 has autocrine effects on stellate cells and induces their contractile activities. We explored the role of various extracellular matrix components, particularly of fibronectin, in regulating endothelin-1 production during liver injury.

METHODS

Hepatic stellate cells were isolated from normal and injured rats. Real-time polymerase chain reaction immunoblot and enzyme-linked immunosorbent assay analyses were used to measure specific variables, including endothelin-1 production. Preproendothelin-1 promoter activity was determined by a luciferase assay. Stellate cell contraction was measured by a gel contraction assay.

RESULTS

Fibronectin stimulated transcription of preproendothelin-1 messenger RNA and expression of endothelin through an integrin-dependent pathway in activated hepatic stellate cells. In these cells, fibronectin induced phosphorylation/activation of extracellular signal-regulated kinase (ERK) through a Shc- and Src-dependent mechanism; ERK activation was required for fibronectin-induced endothelin-1 expression. Fibronectin stimulation by stellate cells induced expression of smooth muscle alpha-actin and endothelin-1-mediated autocrine stellate cell contraction. Stellate cells isolated from injured livers of rats exhibited increased basal phosphorylation levels of Src, Shc, and ERK, as well as increased endothelin-1 synthesis.

CONCLUSIONS

Fibronectin stimulates activated stellate cells to produce endothelin-1 and contract, via an ERK-dependent signaling pathway. The resulting autocrine functional effects of endothelin-1 are likely to be important in the wound-healing process in injured liver.

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.

Advances in drug treatment of portal hypertension

Intrahepatic vascular resistance augmentation and portal blood flow increase are main mechanisms of portal hypertension. The former as an initial factor is mainly due to liver structure changes and motivity changes (reversible). It has been demonstrated that this reversible resistance can be reduced by 20%-30% with drugs. Portosystemic shunt or transjugular intrahepatic portosystemic shunt (TIPS) may induce many severe complications such as hepatic encephalopathy and stent re-obstruction. Therefore, researchers have performed plenty of experimental investigations about drug treatment of portal hypertension, and this article introduces their new advances in this field.

[The role of activated hepatic stellate cells in liver fibrosis, portal hypertension and cancer angiogenesis]

Although hepatic stellate cells, which are liver specific pericytes, have been recognized within the vasculature of the sinusoid for more than one hundred years, the biology and function of these cells is unclear. Recent studies have highlighted the key role of stellate cells in a number of fundamental processes that include wound healing/fibrosis, vasoregulation, and vascular remodeling/angiogenesis. In the liver, these processes are particularly important in the development of cirrhosis, portal hypertension and cancer. This article highlights the recent advances in our understanding of the biology of hepatic stellate cells and discusses some of the recently-ascribed functions that are relevant to liver fibrosis, portal hypertension and cancer angiogenesis.

Stellate cell contraction: role, regulation, and potential therapeutic target

The contraction of hepatic stellate cells has been proposed to mediate fibrosis by regulating sinusoidal blood flow and extracellular matrix remodeling. Abundant data from diverse, yet complementary, experimental methods support a robust model for the regulation of contractile force generation by stellate cells. In this model, soluble factors associated with liver injury, including endothelin 1 and nitric oxide, are transduced primarily through Rho signaling pathways that promote the myosin II-powered generation of contractile force by stellate cells. The enhanced knowledge of the role and differential regulation of stellate cell contraction may facilitate the discovery of new and targeted strategies for the prevention and treatment of hepatic fibrosis.

Divergent transforming growth factor-beta signaling in hepatic stellate cells after liver injury: functional effects on ECE-1 regulation

In liver wound healing, transforming growth factor-beta (TGF-beta) plays a critical role in stellate cell activation as well as signaling cascades in the fibrogenic response to injury. We postulate that the TGF-beta-dependent downstream signaling pathway may vary according to the mechanism of stellate cell activation; this study was undertaken to ascertain whether the downstream signaling pathways mediated by TGF-beta vary in different liver injury models. We measured Smad3 and MAP kinase activation after isolating stellate cells from rat livers injured by either bile duct ligation (BDL) or repeated carbon tetrachloride (CCl(4)) administration. Phospho-Smad3 was dramatically up-regulated in stellate cells after CCl(4) injury, but not after BDL-induced injury. TGF-beta signaling in stellate cells activated after BDL was mediated prominently through ERK activation, whereas activation induced by CCl(4) injury or culture led to a cross-signaling mechanism involving both Smad3 and p38. The divergent Smad signaling pathways observed appeared to be attributable to the differential regulation of the early growth response gene-1 (Egr-1), an apparent negative transcriptional factor for Smad3 in our system. In addition, inhibition of ERK activation in stellate cells from BDL-injured liver led to a decrease in expression of endothelin-converting enzyme-1, a critical regulator of endothelin-1. We speculate that TGF-beta signaling proceeds through differential signaling pathways depending on the mechanism of liver injury that leads to stellate cell activation.

Liposome-mediated gene transfer of endothelial nitric oxide synthase to cirrhotic rat liver decreases intrahepatic vascular resistance

BACKGROUND AND AIMS

Nitric oxide (NO) production by endothelial nitric oxide synthase (eNOS) in sinusoidal endothelial cells is reduced in the injured liver and leads to intrahepatic portal hypertension. The present study evaluates the effects of liposome-mediated gene transfer of eNOS on the intrahepatic vascular resistance and portal venous pressure (PVP) in cirrhotic rats.

METHODS

Hepatic cirrhosis was induced in male Sprague-Dawley rats by intraperitoneal injection of carbon tetrachloride (CCl(4)), whereas the control normal rats were given the same dose of peanut oil. Plasmid eukaryotic expression vector (liposome-pcDNA3/eNOS) was injected into the portal vein of CCl(4) cirrhotic rats, whereas cirrhotic controls received the same dose of naked plasmid (liposome-pcDNA3) or Tris buffer, and control normal rats received the same dose of Tris buffer. Five days after gene transfer, the levels of eNOS mRNA and protein, NO production, PVP and the changes of hepatic intrahepatic vascular resistance were investigated.

RESULTS

Five days after eNOS gene transfer, the levels of eNOS mRNA, eNOS protein and NO production in cirrhotic rats increased remarkably, while hepatic vascular resistance and PVP decreased significantly in cirrhotic rats.

CONCLUSION

Liposome-mediated eNOS gene transfer via intraportal injection is feasible and the increase of intrahepatic eNOS leads to a marked decrease in introhepatic vascular resistance and PVP. These data indicate that intrahepatic eNOS plays an important role in the pathogenesis of portal hypertension and gene transfer of eNOS is a potential and novel therapy for portal hypertension.

The management of portal hypertension: rational basis, available treatments and future options

Variceal bleeding is the last step in a chain of events initiated by an increase in portal pressure, followed by the development and progressive dilation of varices until these finally rupture and bleed. This sequence of events might be prevented - and reversed - by achieving a sufficient decrease in portal pressure. A different approach is the use of local endoscopic treatments at the varices. This article reviews the rationale for the management of patients with cirrhosis and portal hypertension, the current recommendations for the prevention and treatment of variceal bleeding, and outlines the unsolved issues and the perspectives for the future opened by new research developments.

Pressure loading and ethanol exposure differentially modulate rat hepatic stellate cell activation

Ethanol may cause an increase in sinusoidal pressure accompanied by portal hypertension. Hepatic stellate cells (HSCs) located in hepatic sinusoids may therefore be frequently exposed to dual stimulations of mechanical pressure and ethanol exposure in alcoholic liver injury. In this study, the effects of pressure loading and ethanol exposure on activation of rat cultured HSCs were investigated using an in vitro pressure-inducing apparatus. HSCs were cultured in media containing ethanol (0-100 mM) under different pressures (1-40 mmHg). Morphological changes and migration index were determined. We also determined the expression levels of alpha-smooth muscle actin (alpha-SMA) and mitogen-activated protein kinases (MAPKs) by Western blot analysis and the level of collagen IV and transforming growth factor beta1 (TGF-beta1) by ELISA. Pressure loading alone induced up-regulation of alpha-SMA via the extracellular signal-regulated kinases 1 and 2 (ERK1/2) and c-jun N-terminal kinase (JNK) signaling pathways, prolonged extension of marginal length, and increased production of collagen IV. In contrast, ethanol exposure alone increased only extension of marginal length and cell migration. Dual stimulations of pressure loading and ethanol exposure enhanced the production of TGF-beta1 and migration index. The TGF-beta1-dependent p38 MAPK pathway may operate for production of extracellular matrix (ECM) or enhanced migration in the case of dual stimulations. In conclusion, static pressure loading is an important factor directly accelerating the activation of HSCs. Although increased sinusoidal pressure and ethanol exposure might differentially modulate HSC activation, both stimuli are involved in an additive manner in some situations.

Treatment of bile duct-ligated rats with the nitric oxide synthase transcription enhancer AVE 9488 ameliorates portal hypertension

AIM

Nitric oxide levels are decreased in the cirrhotic liver and increased in the systemic vasculature. We investigated whether the nitric oxide synthase (NOS) transcription enhancer AVE 9488 ameliorates portal hypertension in cirrhotic rats.

METHODS

Rats with secondary biliary cirrhosis [bile duct ligation (BDL)] were treated with AVE 9488. BDL animals without treatment served as controls. Blood flow was determined with the microsphere technique. Intrahepatic resistance was measured by in situ perfusion. NOS-3 mRNA and protein levels in the liver, aorta and superior mesenteric artery (SMA) were measured.

RESULTS

Arterial pressure did not differ between treated and non-treated animals. Portal pressure, hepatic portal-vascular resistance and perfusion pressure of the in situ perfused liver were lower in the AVE 9488-treated animals. Arterial splanchnic resistance, portal venous inflow and shunt volume were increased by AVE 9488. N (G)-nitro-l-arginine methyl ester abolished the effect of AVE 9488. AVE 9488-treated rats had higher liver NOS-3 mRNA and protein levels, whereas NOS-3 mRNA and protein in the aorta and the SMA did not vary between groups. Phosphorylation of liver vasodilator-stimulated phosphoprotein (VASP) and NOS-3 as well as hepatic nitrite/nitrate was increased by AVE 9488.

CONCLUSIONS

Treatment of BDL rats with the NOS transcription enhancer AVE 9488 induces an increase in NOS-3 mRNA and protein in the liver. This is associated with an amelioration of portal hypertension.

Immunopathogenesis of hepatitis C virus infection and hepatic fibrosis: New insights into antifibrotic therapy in chronic hepatitis C

Fibrosis and cirrhosis represent the consequences of a sustained wound-healing response to chronic liver injury of any cause. Chronic hepatitis C virus (HCV) has emerged as a leading cause of cirrhosis in the USA and throughout the world. HCV may induce fibrogenesis directly by hepatic stellate cell activation or indirectly by promoting oxidative stress and apoptosis of infected cells. The ultimate result of chronic HCV injury is the accumulation of extracellular matrix with high density type I collagen within the subendothelial space of Disse, culminating in cirrhosis with hepatocellular dysfunction. The treatment of hepatitis C with the combination of pegylated interferon and ribavirin is still both problematic and costly, has suboptimal efficacy, serious side effects and a high level of intolerance, and is contraindicated in many patients. Hence, new approaches have assumed greater importance, for which there is an urgent need. The sustained progress in understanding the pathophysiology of hepatic fibrosis in the past two decades has increased the possibility of developing drugs specifically targeting the fibrogenic process. Future efforts should identify genetic markers associated with fibrosis risk in order to tailor the treatment of HCV infection based on genetically regulated pathways of injury and/or fibrosis. Such advances will expand the arsenal to overcome liver fibrosis, particularly in patients with hepatic diseases who have limited treatment options, such as those patients with chronic hepatitis C who have a high risk of fibrosis progression and recurrent HCV disease after liver transplantation.

Enhanced vasoconstrictor prostanoid production by sinusoidal endothelial cells increases portal perfusion pressure in cirrhotic rat livers

BACKGROUND/AIMS

Cyclooxygenase-1 (COX-1) is overexpressed in sinusoidal endothelial cells (SEC) of cirrhotic rat livers, and through an enhanced production of vasoconstrictor prostanoids contributes to increase intrahepatic resistance. Our study was aimed at investigating the role of enhanced AA bioavailability modulating the hepatic vascular tone of cirrhotic livers and identifying which prostanoid is involved.

METHODS

SEC isolated from control and cirrhotic rat livers were incubated with AA, methoxamine or vehicle. TXA(2) was quantified. In addition, portal perfusion pressure (PP) response curves to AA were performed in rat livers pre-incubated with vehicle, SC-560 (COX-1 inhibitor), Furegrelate (inhibitor of TXA(2) synthesis) and SQ-29548 (PGH(2)/TXA(2) receptor blocker). cPLA2 activity was determined in control and cirrhotic livers.

RESULTS

AA and methoxamine incubation promoted a significant increase in TXA(2) release by Cirrhotic-SEC, but not in Control-SEC. AA produced a dose-dependent increase in the PP, associated with increased TXA(2) release. These responses were significantly greater in cirrhotic livers. COX-1 inhibition and PGH(2)/TXA(2) receptor blockade, but not TXA(2) synthase inhibition, markedly attenuated the PP response to AA of cirrhotic livers. Additionally, cirrhotic livers exhibited significantly increased cPLA2 activity.

CONCLUSIONS

An enhanced production of vasoconstrictor prostanoids, probably PGH(2), by SEC contributes to increase vascular tone of cirrhotic livers.

Simvastatin treatment improves liver sinusoidal endothelial dysfunction in CCl4 cirrhotic rats

BACKGROUND/AIMS

Sinusoidal endothelial dysfunction with decreased nitric oxide (NO) production contributes to increased hepatic resistance in cirrhosis. Statins improve endothelial dysfunction in peripheral vasculature. This study was designed to characterize the hemodynamic and molecular effects of statins in cirrhotic rats.

METHODS

Systemic and splanchnic hemodynamics were evaluated in CCl(4) ascitic cirrhotic rats treated with placebo or simvastatin (25 mg/kg/day, for 3 days), at baseline and after volume expansion. Vascular responses of liver vasculature were evaluated after isolation and perfusion of the liver.

RESULTS

There were no differences in baseline hemodynamics in rats treated with simvastatin or placebo. However, in rats treated with simvastatin the increase in portal pressure induced by volume expansion was significantly attenuated. In isolated and perfused cirrhotic livers simvastatin pre-treatment significantly attenuated the pressure response to methoxamine, and significantly improved paradoxical vasoconstriction induced by acetylcholine. These effects were not observed in the presence of a nitric oxide synthase inhibitor. Simvastatin increased eNOS expression, Akt-dependent eNOS phosphorylation and cGMP liver content.

CONCLUSIONS

The administration of simvastatin might constitute a new way to selectively increase NO availability in the cirrhotic liver circulation and, therefore improve the vascular disturbances that contribute to portal hypertension.