Endothelin-1 modulates intrahepatic resistance in a rat model of noncirrhotic portal hypertension

Pathophysiology of Hepatorenal Syndrome

Hepatorenal syndrome type 1 (HRS-1) is a unique form of acute kidney injury that affects individuals with decompensated cirrhosis with ascites. The primary mechanism leading to reduction of kidney function in HRS-1 is hemodynamic in nature. Cumulative evidence points to a cascade of events that led to a profound reduction in kidney perfusion. A state of increased intrahepatic vascular resistance characteristic of advanced cirrhosis and portal hypertension is accompanied by maladaptive peripheral arterial vasodilation and reduction in systemic vascular resistance and mean arterial pressure. As a result of a fall in effective arterial blood volume, there is a compensatory activation of the sympathetic nervous system and the renin-angiotensin system, local renal vasoconstriction, loss of renal autoregulation, decrease in renal blood flow, and ultimately a fall in glomerular filtration rate. Systemic release of nitric oxide stimulated by the fibrotic liver, bacterial translocation, and inflammation constitute key components of the pathogenesis. While angiotensin II and noradrenaline remain the critical mediators of renal arterial and arteriolar vasoconstriction, other novel molecules have been recently implicated. Although the above-described mechanistic pathway remains the backbone of the pathogenesis of HRS-1, other noxious elements may be present in advanced cirrhosis and likely contribute to the renal impairment. Direct liver-kidney crosstalk via the hepatorenal sympathetic reflex can further reduce renal blood flow independently of the systemic derangements. Tense ascites may lead to intraabdominal hypertension and abdominal compartment syndrome. Cardio-hemodynamic processes have also been increasingly recognized. Porto-pulmonary hypertension, cirrhotic cardiomyopathy, and abdominal compartment syndrome may lead to renal congestion and complicate the course of HRS-1. In addition, a degree of ischemic or toxic (cholemic) tubular injury may overlap with the underlying circulatory dysfunction and further exacerbate the course of acute kidney injury. Improving our understanding of the pathogenesis of HRS-1 may lead to improvements in therapeutic options for this seriously ill population.

Current and investigational drugs in early clinical development for portal hypertension

Introduction

The development of portal hypertension leads to a majority of complications associated with chronic liver disease. Therefore, adequate treatment of portal hypertension is crucial in the management of such patients. Current treatment options are limited and consist mainly of medications that decrease the hyperdynamic circulation, such as non-selective beta blockers, and treatment of hypervolemia with diuretics. Despite these options, mortality rates have not improved over the last two decades. Newer, more effective treatment options are necessary to help improve survival and quality of life in these patients.

Areas covered

Multiple preclinical models and clinical studies have demonstrated potential efficacy of a variety of new treatment modalities. We introduce treatment options including the use of vasodilation promotors, vasoconstriction inhibitors, anticoagulants, antiangiogenics, and anti-inflammatory drugs. We examine the most recent studies for treatment options within these drug classes and offer insights as to which show the most promise in this field.

Methodology

Published studies that identified novel medical treatment options of portal hypertension were searched using PubMed (https://pubmed.ncbi.nlm.nih.gov/). Clinical trials listed in Clinicaltrials.gov were also searched with a focus on more recent and ongoing studies, including those with completed recruitment. Searching with key terms including "portal hypertension" as well as individually searching specific treatment medications that were listed in other publications was carried out. Finally, current societal guidelines and recent review articles relevant to the management of portal hypertension were evaluated, and listed references of interest were included.

Conclusion

Many ongoing early phase studies demonstrate promising results and may shape the field of portal hypertension management in future. As concrete results become available, larger RCTs will be required before making definitive conclusions regarding safety and efficacy and whether or not they can be incorporated into routine clinical practice. Statins, anticoagulants, and PDE inhibitors have been among the most studied and appear to be most promising.

Abdominal applications of quantitative 4D flow MRI

4D flow MRI is a quantitative MRI technique that allows the comprehensive assessment of time-resolved hemodynamics and vascular anatomy over a 3-dimensional imaging volume. It effectively combines several advantages of invasive and non-invasive imaging modalities like ultrasound, angiography, and computed tomography in a single MRI acquisition and provides an unprecedented characterization of velocity fields acquired non-invasively in vivo. Functional and morphological imaging of the abdominal vasculature is especially challenging due to its complex and variable anatomy with a wide range of vessel calibers and flow velocities and the need for large volumetric coverage. Despite these challenges, 4D flow MRI is a promising diagnostic and prognostic tool as many pathologies in the abdomen are associated with changes of either hemodynamics or morphology of arteries, veins, or the portal venous system. In this review article, we will discuss technical aspects of the implementation of abdominal 4D flow MRI ranging from patient preparation and acquisition protocol over post-processing and quality control to final data analysis. In recent years, the range of applications for 4D flow in the abdomen has increased profoundly. Therefore, we will review potential clinical applications and address their clinical importance, relevant quantitative and qualitative parameters, and unmet challenges.

Cloning of human ABCB11 gene in E. coli required the removal of an intragenic Pribnow-Schaller Box before it's Insertion into genomic safe harbor AAVS1 site using CRISPR-Cas9

Background: Genomic safe harbors are sites in the genome which are safe for gene insertion such that the inserted gene will function properly, and the disruption of the genomic location doesn't cause any foreseeable risk to the host. The AAVS1 site is the genetic location which is disrupted upon integration of adeno associated virus (AAV) and is considered a 'safe-harbor' in human genome because about one-third of humans are infected with AAV and so far there is no apodictic evidence that AAV is pathogenic or disruption of AAVS1 causes any disease in man.  Therefore, we chose to target the AAVS1 site for the insertion of ABCB11, a bile acid transporter which is defective in progressive familial intra hepatic cholestasis type-2 (PFIC-2), a lethal disease of children where cytotoxic bile salts accumulate inside hepatocytes killing them and eventually the patient. Methods: We used the CRISPR Cas9 a genome editing system to insert the ABCB11 gene at AAVS1 site in human cell-lines. Results: We found that human ABCB11 sequence has a "Pribnow- Schaller Box" which allows its expression in bacteria and expression of ABCB11 protein which is toxic to E. coli; the removal of this was required for successful cloning. We inserted ABCB11 at AAVS1 site in HEK 293T using CRISPR-Cas9 tool.  We also found that the ABCB11 protein has similarity with E. coli endotoxin (lipid A) transporter MsbA. Conclusions: We inserted ABCB11 at AAVS1 site using CRISPR-Cas9; however, the frequency of homologous recombination was very low for this approach to be successful in vivo.

Hepatic erythropoietin response in cirrhosis. A contemporary review

The main function of erythropoietin (EPO) is to maintain red blood cell mass, but in recent years, increasing evidence has suggested a wider biological role not solely related to erythropoiesis, e.g. angiogenesis and tissue protection. EPO is produced in the liver during fetal life, but the main production shifts to the kidney after birth. The liver maintains a production capacity of up to 10% of the total EPO synthesis in healthy controls, but can be up-regulated to 90-100%. However, the hepatic EPO synthesis has been shown not to be adequate for correction of anemia in the absence of renal-derived EPO. Elevated circulating EPO has been reported in a number of diseases, but data from cirrhotic patients are sparse and the level of plasma EPO in patients with cirrhosis is controversial. Cirrhosis is characterized by liver fibrosis, hepatic dysfunction and the release of proinflammatory cytokines, which lead to arterial hypotension, hepatic nephropathy and anemia. An increase in EPO due to renal hypoperfusion, hypoxia and anemia or an EPO-mediated hepato-protective and regenerative mechanism is plausible. However, poor hepatic synthesis capacity, a decreasing co-factor level and inflammatory feedback mechanisms may explain a potential insufficient EPO response in end-stage cirrhosis. Finally, the question remains as to whether a potential increase in EPO production in certain stages of cirrhosis originates from the kidney or liver. This paper aims to review contemporary aspects of EPO relating to chronic liver disease.

Obliterative portal venopathy: a clinical and histopathological review

Non-cirrhotic portal hypertension (NCPH) is characterized by the elevation of the portal pressure in the absence of cirrhosis. Obliterative portal venopathy (OPV) as a cause of NCPH is being increasingly diagnosed, especially after recent reports of its occurrence in patients with HIV using didanosine. Patients usually present with episodes of variceal hemorrhage and other features of portal hypertension including jaundice, ascites, encephalopathy and hepatopulmonary syndrome. Hepatic synthetic function is typically well preserved and the laboratory evaluation in OPV patients typically reveals only mild nonspecific hematological abnormalities chiefly related to hypersplenism. Its diagnosis remains a challenge and patients are often mistakenly diagnosed as having cirrhosis. Despite the increasing recognition of OPV, its etiology and pathogenesis are still unclear. A number of etiologies have been proposed including genetic predisposition, recurrent bacterial infections, HIV infection and highly active antiretroviral therapy, an altered immune response, hypercoagulability, and exposure to chemicals and certain medications. Histopathological evaluation remains critical in excluding cirrhosis and other causes of portal hypertension, and is the only way of definitively establishing the diagnosis of OPV. Clinicians should have a high index of suspicion for OPV in patients who present with variceal bleeding and splenomegaly and who do not have other features of cirrhosis. The purpose of this review is to summarize the known etiologies for OPV and its associated clinical aspects and correlations, and to also provide ample histophotomicrographs of OPV to aid in the diagnosis. It will also help raise awareness of this entity amongst pathologists and clinicians alike.

Endothelin-1 and -3 induce choleresis in the rat through ETB receptors coupled to nitric oxide and vagovagal reflexes

We have reported previously that centrally applied ET (endothelin)-1 and ET-3 induce either choleresis or cholestasis depending on the dose. In the present study, we sought to establish the role of these endothelins in the short-term peripheral regulation of bile secretion in the rat. Intravenously infused endothelins induced significant choleresis in a dose-dependent fashion, ET-1 being more potent than ET-3. Endothelins (with the exception of a higher dose of ET-1) did not affect BP (blood pressure), portal venous pressure or portal blood flow. ET-1 and ET-3 augmented the biliary excretion of bile salts, glutathione and electrolytes, suggesting enhanced bile acid-dependent and -independent bile flows. ET-induced choleresis was mediated by ET(B) receptors coupled to NO and inhibited by truncal vagotomy, atropine administration and capsaicin perivagal application, supporting the participation of vagovagal reflexes. RT (reverse transcription)-PCR and Western blot analysis revealed ETA and ET(B) receptor expression in the vagus nerve. Endothelins, through ET(B) receptors, augmented the hepatocyte plasma membrane expression of Ntcp (Na⁺/taurocholate co-transporting polypeptide; Slc10a1), Bsep (bile-salt export pump; Abcb11), Mrp2 (multidrug resistance protein-2; Abcc2) and Aqp8 (aquaporin 8). Endothelins also increased the mRNAs of these transporters. ET-1 and ET-3 induced choleresis mediated by ET(B) receptors coupled to NO release and vagovagal reflexes without involving haemodynamic changes. Endothelin-induced choleresis seems to be caused by increased plasma membrane translocation and transcriptional expression of key bile transporters. These findings indicate that endothelins are able to elicit haemodynamic-independent biological effects in the liver and suggest that these peptides may play a beneficial role in pathophysiological situations where bile secretion is impaired.

In vivo validation of 4D flow MRI for assessing the hemodynamics of portal hypertension

PURPOSE

To implement and validate in vivo radial 4D flow MRI for quantification of blood flow in the hepatic arterial, portal venous, and splanchnic vasculature of healthy volunteers and patients with portal hypertension.

MATERIALS AND METHODS

Seventeen patients with portal hypertension and seven subjects with no liver disease were included in this Health Insurance Portability and Accountability Act (HIPAA)-compliant and Institutional Review Board (IRB)-approved study. Exams were conducted at 3T using a 32-channel body coil with large volumetric coverage and 1.4 mm isotropic true spatial resolution. Using postprocessing software, cut-planes orthogonal to vessels were used to quantify flow (L/min) in the hepatic and splanchnic vasculature.

RESULTS

Flow quantification was successful in all cases. Portal vein and supraceliac aorta flow demonstrated high variability among patients. Measurements were validated indirectly using internal consistency at three different locations within the portal vein (error = 4.2 ± 3.9%) and conservation of mass at the portal confluence (error = 5.9 ± 2.5%) and portal bifurcation (error = 5.8 ± 3.1%).

CONCLUSION

This work demonstrates the feasibility of radial 4D flow MRI to quantify flow in the hepatic and splanchnic vasculature. Flow results agreed well with data reported in the literature, and conservation of mass provided indirect validation of flow quantification. Flow in patients with portal hypertensions demonstrated high variability, with patterns and magnitude consistent with the hyperdynamic state that commonly occurs in portal hypertension.

Endothelin-1 derived from spleen-activated Rho-kinase pathway in rats with secondary biliary cirrhosis

AIM

  Splenectomy or partial splenic embolism has been reported to improve liver function in patients with hypersplenism and liver dysfunction. The aim of this study was to investigate the mechanism of improvement after splenectomy.

METHODS

  Liver cirrhosis was induced by bile duct ligation (BDL). Rats underwent sham operation, splenectomy (Sp group), BDL, or BDL plus splenectomy (BDL + Sp group), and were subjected to experiments at 2 weeks after the operation. Portal venous pressure (PVP) and hepatic tissue blood flow (HTBF) were measured in each group. The plasma concentration of endothelin-1 (ET-1) and endothelial nitric oxide synthase (eNOS), RhoA and Rho-kinase expressions were studied.

RESULTS

  There were significant differences in PVP (17.9 ± 0.91 vs 23.3 ± 3.91 cmH(2) O; P < 0.01) and HTBF (16.6 ± 1.72 vs 13.3 ± 1.82 mL/min; P < 0.01) between the BDL + Sp and BDL groups. In the liver of BDL rats, eNOS phosphorylation and NOx levels were decreased, accompanied by RhoA activation compared with the BDL + Sp group. Splenectomy decreased serum ET-1 levels, RhoA activation and consequently increased eNOS phosphorylation.

CONCLUSION

  ET-1 derived from the spleen might increase intrahepatic resistance by downregulating Rho signaling in liver cirrhosis. Splenectomy for splenomegaly in liver cirrhosis might partially improve liver function by enhancing intrahepatic microcirculation.

Acute effects of endothelin receptor antagonists on hepatic hemodynamics of cirrhotic and noncirrhotic rats

Hepatic and circulating endothelin-1 (ET-1) are increased in patients with cirrhosis and in cirrhotic animals. However, the distinct roles of ET receptor subtypes ETA and ETB in cirrhosis and portal hypertension (PHT) have not been clearly elucidated. Thus, we studied the effects of selective ET-1 antagonists (ETA-ant or ETB-ant) and nonselective ET-1 antagonist (ETA/B-ant) on hepatic hemodynamics in cirrhotic rats. Liver fibrosis and PHT were induced by complete bile duct ligation (BDL) in rats. Two weeks after BDL or sham surgery, hemodynamic responses were measured during intraportal infusion of incremental doses of the following ET-ants: (i) BQ-123, (ii) BQ-788, and (iii) bosentan. After equilibration with vehicle, doses of ET-ants were infused for 30 min periods, and steady-state systemic and hepatic hemodynamics, portal venous pressure (PVP), and hepatic blood flow (HBF) were measured. BDL induced significant PHT and elevated concentrations of plasma ET-1 compared with sham. ETA-ant decreased PVP of cirrhotic rats but had no effect on sham, whereas ETB-ant increased PVP in sham but had no effect in BDL. Nonselective ETA/B-ant decreased PVP of BDL similarly to ETA-ant. Both ETA-ant and ETB-ant decreased local HBF, whereas a nonselective antagonist did not change HBF in sham; however no significant changes were observed in HBF of BDL rats with any of the antagonists. These findings suggest ETA activation contributes to PHT in cirrhotic rats, whereas ETB-mediated portal depressor effects are attenuated in cirrhotic rats compared with noncirrhotic rats.

Endothelin receptor antagonism in portal hypertension

BACKGROUND

Endothelin receptor antagonists (ERAs) have recently become prominent therapies for pulmonary arterial hypertension, and are being explored clinically in several areas, including resistant hypertension, idiopathic pulmonary fibrosis, and cancer.

OBJECTIVE

To review the available preclinical and clinical data surrounding ERAs and their potential role to treat portal hypertension.

METHODS

A systematic search of peer-reviewed publications was performed using PubMed and Ovid/Medline/EMBASE databases.

RESULTS

Several preclinical in vivo studies have evaluated ERAs in models of portal hypertension. The majority of these studies employ nonselective ERAs, and support the hypothesis that endothelin participates in the development and maintenance of portal hypertension. A limited number of studies have addressed whether ET(A) receptor-selective ERAs provide an advantage over nonselective agents in ameliorating the effects of portal hypertension, and the majority of these data indicate that selective ERAs may be sufficient. Very few clinical studies have evaluated ERAs in portal hypertension patients. What has been described in humans supports a role for endothelin, but is not sufficient to draw conclusions regarding ERA selectivity.

CONCLUSION

While preclinical evidence suggests a role for endothelin and ERAs in portal hypertension, scant and equivocal clinical data highlight a need for human studies with current selective and nonselective ERAs.

Catalase delivery for inhibiting ROS-mediated tissue injury and tumor metastasis

Reactive oxygen species (ROS) have been suggested to be involved in a variety of human diseases. Catalase, an enzyme degrading hydrogen peroxide, can be used as a therapeutic agent for such diseases, but its successful application will depend on the distribution of the enzyme to the sites where ROS are generated. Chemical modification techniques have been used to control the tissue distribution of catalase, and delivery to hepatocytes (galactosylation), liver nonparenchymal cells (mannosylation or succinylation), kidney (cationization) and the blood pool (PEGylation) has been achieved. The effectiveness of catalase delivery has been demonstrated in animal models for hepatic ischemia/reperfusion injury, chemical-induced tissue injuries and tumor metastasis to the liver, lung and peritoneal organs. Significant inhibition was observed in the ROS-mediated oxidative tissue damages and ROS-mediated upregulation of expression of genes responsible for recruitment of inflammatory cells and for metastatic growth of tumor cells. Because oxygen plays a fundamental key role in our life and oxidative stress is implicated in a wide variety of human diseases, catalase delivery could have wide application in the near future.

Experimental investigation of the role of endothelin-1 in idiopathic portal hypertension

BACKGROUND AND AIM

The authors' previous report revealed that endothelin-1 might be released from B lymphocytes in cirrhotic patients with hypersplenism. Other investigators have shown that persistent exposure to environmental contaminants including arsenic might induce idiopathic portal hypertension. The aim of this study was to experimentally identify how endothelin-1 is involved in the development of idiopathic portal hypertension and which cells produce endothelin-1 in the spleen.

METHODS

Portal pressure and venous endothelin-1 concentrations were measured in rats that were given sodium arsenate orally for long periods, and endothelin-1 expression levels in the spleen were assessed by staining. In a second experiment, B and T lymphocytes and monocyte-derived macrophages cultured from healthy human peripheral blood were stimulated with sodium arsenite, sodium arsenate, lipopolysaccharide and interferon-gamma. Endothelin-1 concentrations in the supernatants were measured by ELISA.

RESULTS

Arsenic exposure gradually increased portal pressure and venous endothelin-1 levels in rats. Endothelin-1 concentration in the supernatant did not change in every cell type stimulated with arsenic, but it increased in B lymphocytes and monocyte-derived macrophages treated with lipopolysaccharide and interferon-gamma.

CONCLUSIONS

The in vivo study indicated that arsenic might elevate portal pressure through mechanisms involving endothelin-1. In the in vitro study, lipopolysaccharide and interferon-gamma clearly induced endothelin-1 synthesis not only in monocyte-derived macrophages but also in B lymphocytes, although arsenic treatment did not affect those cells. This study partially supports the hypothesis that idiopathic portal hypertension might be promoted by endothelin-1 overproduction from splenic B lymphocytes in response to certain substances.

Animal models of portal hypertension

Animal models have allowed detailed study of hemodynamic alterations typical of portal hypertension and the molecular mechanisms involved in abnormalities in splanchnic and systemic circulation associated with this syndrome. Models of prehepatic portal hypertension can be used to study alterations in the splanchnic circulation and the pathophysiology of the hyperdynamic circulation. Models of cirrhosis allow study of the alterations in intrahepatic microcirculation that lead to increased resistance to portal flow. This review summarizes the currently available literature on animal models of portal hypertension and analyzes their relative utility. The criteria for choosing a particular model, depending on the specific objectives of the study, are also discussed.

Analysis of In Vivo Nuclear Factor-κB Activation during Liver Inflammation in Mice: Prevention by Catalase Delivery

Nuclear factor-kappaB (NF-kappaB) is a transcription factor that plays crucial roles in inflammation, immunity, cell proliferation, and apoptosis. Until now, there have been few studies of NF-kappaB activation in whole animals because of experimental difficulties. Here, we show that mice receiving a simple injection of plasmid vectors can be used to examine NF-kappaB activation in the liver. Two plasmid vectors, pNF-kappaB-Luc (firefly luciferase gene) and pRL-SV40 (Renilla reniformis luciferase gene), were injected into the tail vein of mice by the hydrodynamics-based procedure, an established method of gene transfer to mouse liver. Then, the ratio of the firefly and R. reniformis luciferase activities (F/R) was used as an indicator of the NF-kappaB activity in the liver. Injection of thioacetamide or lipopolysaccharide plus d-galactosamine increased the F/R ratio in the liver, and this was significantly (P<0.001) inhibited by an intravenous injection of catalase derivatives targeting liver nonparenchymal cells. Imaging the firefly luciferase expression in live mice clearly demonstrated that the catalase derivatives efficiently prevented the NF-kappaB-mediated expression of the firefly luciferase gene. Plasma transaminases and the survival rate of mice supported the findings obtained by the luminescence-based analyses. Thus, this method, which requires no genetic recombination techniques, is highly sensitive to the activation of NF-kappaB and allows us to continuously examine the activation in live animals. In conclusion, this novel, simple, and sensitive method can be used not only for analyzing the NF-kappaB activation in the organ under different inflammatory conditions but also for screening drug candidates for the prevention of liver inflammation.

Animal models of portal hypertension

Animal models have allowed detailed study of hemodynamic alterations typical of portal hypertension and the molecular mechanisms involved in abnormalities in splanchnic and systemic circulation associated with this syndrome. Models of prehepatic portal hypertension can be used to study alterations in the splanchnic circulation and the pathophysiology of the hyperdynamic circulation. Models of cirrhosis allow study of the alterations in intrahepatic microcirculation that lead to increased resistance to portal flow. This review summarizes the currently available literature on animal models of portal hypertension and analyzes their relative utility. The criteria for choosing a particular model, depending on the specific objectives of the study, are also discussed.

Portopulmonary hypertension

Portopulmonary hypertension (PPHT) is defined as precapillary pulmonary hypertension accompanied by hepatic disease or portal hypertension. Pulmonary hypertension results from excessive pulmonary vascular remodeling and vasoconstriction. These histological alterations have been indistinguishable from those of other forms of pulmonary arterial hypertension. Factors involved in the pathogenesis of PPHT include volume overload, hyperdynamic circulation, and circulating vasoactive mediators. The disorder has a substantial impact on survival and requires focused treatment. Liver transplantation in patients with moderate to severe PPHT is associated with a significantly reduced survival rate. The best medical treatment for patients with PPHT is controversial; most authors currently regard continuous intravenous application of prostacyclin as the treatment of choice for patients with severe PPHT. There is only very limited reported experience with inhaled prostacyclin or its analog, iloprost. Increasing evidence of the efficacy of the endothelin-receptor antagonist bosentan and of the phosphodiesterase-5 inhibitor sildenafil is emerging in highly selected patients with PPHT. In the future, a combination therapy of the above-mentioned agents might become a therapeutic option. Other agents such as beta-blockers seem to be harmful to patients with moderate to severe portopulmonary hypertension. Up-to-date, randomized, double-blind, controlled clinical trials are lacking and are needed urgently.

Modelos animales en el estudio de la hipertensión portal

Animal models allow detailed study of the hemodynamic alterations in portal hypertension syndrome and of the molecular mechanisms involved in the abnormalities in splenic and systemic circulation associated with this syndrome. Models of prehepatic portal hypertension can be used to study alterations in the splenic circulation and the physiopathology of hyperdynamic circulation. Moreover, models of cirrhosis allow the alterations in intrahepatic microcirculation that lead to increased resistance to portal flow to be studied. The present review summarizes currently available animal models of portal hypertension and analyzes their relative utility in investigating the distinct disorders associated with this entity. The criteria for the choice of a particular model, depending on the specific objectives of the study, are also discussed.

A proteomic analysis of thioacetamide-induced hepatotoxicity and cirrhosis in rat livers

Thioacetamide (TAA) administration is an established technique for generating rat models of liver fibrosis and cirrhosis. Oxidative stress is believed to be involved as TAA-induced liver fibrosis is initiated by thioacetamide S-oxide, which is derived from the biotransformation of TAA by the microsomal flavine-adenine dinucleotide (FAD)-containing monooxygense (FMO) and cytochrome P450 systems. A two-dimensional gel electrophoresis-mass spectrometry approach was applied to analyze the protein profiles of livers of rats administered with sublethal doses of TAA for 3, 6 and 10 weeks respectively. With this approach, 59 protein spots whose expression levels changed significantly upon TAA administration were identified, including three novel proteins. These proteins were then sorted according to their common biochemical properties and functions, so that pathways involved in the pathogenesis of rat liver fibrosis due to TAA-induced toxicity could be elucidated. As a result, it was found that TAA-administration down-regulated the enzymes of the primary metabolic pathways such as fatty acid beta-oxidation, branched chain amino acids and methionine breakdown. This phenomenon is suggestive of the depletion of succinyl-CoA which affects heme and iron metabolism. Up-regulated proteins, on the other hand, are related to oxidative stress and lipid peroxidation. Finally, these proteomics data and the data obtained from the scientific literature were integrated into an "overview model" for TAA-induced liver cirrhosis. This model could now serve as a useful resource for researchers working in the same area.

FK 409 ameliorates small-for-size liver graft injury by attenuation of portal hypertension and down-regulation of Egr-1 pathway

OBJECTIVE

To investigate whether low-dose nitric oxide donor FK 409 could attenuate small-for-size graft injury in liver transplantation using small-for-size grafts.

SUMMARY BACKGROUND DATA

The major concern of live donor liver transplantation is small-for-size graft injury at the early phase after transplantation. Novel therapeutic strategies should be investigated.

METHODS

We employed a rat orthotopic liver transplantation model using small-for-size (40%) graft. FK 409 was given at 30 minutes before graft harvesting (2 mg/kg) to the donor and immediately after reperfusion (1 mg/kg) to the recipient (FK group). Graft survival, intragraft genes expression, portal hemodynamics, and hepatic ultrastructural changes were compared between the 2 groups.

RESULTS

Seven-day graft survival rates in the FK group were significantly improved compared with those of rats not receiving FK 409 (control group; 80% versus 28.6%, P = 0.018). In the FK group, portal pressure was significantly decreased within the first 60 minutes after reperfusion whereas in the control group, transient portal hypertension was observed. Intragraft expression (both mRNA and protein) of early growth response-1, endothelin-1, endothelin-1 receptor A, tumor necrosis factor-alpha, macrophage-inflammatory protein-2, and inducible nitric oxide synthase was significantly down-regulated accompanied with up-regulation of heme oxygenase-1, A20, interferon-gamma-inducible protein-10, and interleukin-10 during the first 24 hours after reperfusion. Hepatic ultrastructure, especially the integrity of sinusoids was well protected in the FK group.

CONCLUSIONS

Low-dose FK 409 rescues small-for-size grafts in liver transplantation by attenuation of portal hypertension and amelioration of acute phase inflammatory response by down-regulation of Egr-1, together with prior induction of heat shock proteins.

Portopulmonary hypertension: a tale of two circulations

Pulmonary involvement is common in patients with portal hypertension and can manifest in diverse manners. Changes in pulmonary arterial resistance, manifesting either as the hepatopulmonary syndrome or portopulmonary hypertension (PPHTN), have been increasingly recognized in these patients in recent years. This review summarizes the clinicopathologic features, diagnostic criteria, as well as the latest concepts in the pathogenesis and management of PPHTN, which is defined as an elevated pulmonary artery pressure in the setting of an increased pulmonary vascular resistance and a normal wedge pressure in a patient with portal hypertension.

Impact of dopamine and endothelin-1 antagonism on portal venous blood flow during laparoscopic surgery

BACKGROUND

Recent data indicate that pneumoperitoneal carbondioxide (CO2) insufflation impairs hepatic macro- and microcirculation. Whether dopamine and endothelin-1 (ET-1) antagonists might restore liver blood during laparoscopic surgery has not yet been investigated.

METHODS

For this study, 30 male WAG/Rij rats were randomized into two groups to obtain pneumoperitoneum with CO2 (n=15) or helium (n = 15). All the animals were implanted with a polyethylene-50 cannula into the right vena jugularis and a Doppler ultrasound flow probe around the portal vein. In each group, the rats were administered dopamine (n = 5); JKC-10, JKC-301, which is a selective endothelin-1 (ET-1) antagonist (n = 5), or sodium chloride as a control (n = 5). Portal blood flow was measured during intraabdominal pressures 2 to 12 mmHg. Data were analyzed using the Kruskal-Wallis h-test.

RESULTS

The application of dopamine and ET-1 antagonists significantly improved portal blood flow over that of the control animals (p <0.05). No significant differences were found between CO2 and helium insufflation (P > 0.05).

CONCLUSIONS

Dopamine and ET-1 antagonism restore portal blood flow during laparoscopic surgery independently of the insufflation gas. Whether improved hepatic perfusion might have beneficial effects on liver function needs further investigation.

Effects of endothelins on hepatic stellate cell synthesis of endothelin-1 during hepatic wound healing

Endothelin-1 production is increased after liver injury and the subsequent wounding response. Further, endothelin-1 has prominent effects on hepatic stellate cells (key effectors of the hepatic wounding response), including on collagen synthesis, proliferation, and expression of smooth muscle proteins. We tested the hypothesis that endothelins (ETs) may regulate endothelin-1 production during hepatic wounding, and have investigated potential mechanisms underlying this process. Studies were performed on isolated stellate cells from normal and injured livers; in addition, potential autocrine effects of ET were assessed in vivo using an ET receptor antagonist in a model of liver injury. In stellate cells isolated from either normal or injured rat livers, ET receptor stimulation with endothelin-3 or sarafotoxin S6C (preferential ET(B) agonists) caused a dose-dependent increase in endothelin-1 production. Additionally, administration of a mixed ET antagonist in vivo during injury led to reduced stellate cell production of endothelin-1. The mechanism by which ETs stimulated endothelin-1 in this system appeared to be through upregulation of ET converting enzyme-1 (which converts precursor ET to mature peptide), rather than by modulation of precursor endothelin-1. We conclude that during liver injury and wound healing, stellate cell endothelin-1 production is, at least partially, stimulated by ETs via autocrine mechanisms that occur at the level of ET converting enzyme-1.

Reproducible production of thioacetamide-induced macronodular cirrhosis in the rat with no mortality

BACKGROUND/AIMS

Hepatotoxin-induced rat models of liver cirrhosis are limited by the wide heterogeneity of cirrhosis produced. The present study developed a modified, reliable, and reproducible technique by which hepatic and systemic responses to thioacetamide during induction of cirrhosis were monitored by weekly weight changes.

METHODS

Male Wistar rats (200-230 g) were divided into three groups. Group 1 (n=20) received continuous administration of 0.03% (w/v) thioacetamide in the drinking water for 12 weeks. Group 2 (n=20) received the same concentration of 0.03% thioacetamide as an initial concentration that was modified according to weekly weight changes in response to thioacetamide during the induction of cirrhosis. Group 3 (n=6) received normal water and served as controls.

RESULTS

Mortality of Group 1 was 30% and the production of cirrhosis was only 45%. In contrast, there were no deaths in Group 2 and well-developed macronodular cirrhosis was found in 90% of the rats which was associated with significant portal hypertension, as indicated by increased portal venous pressure (13.6+/-0.4 vs. 9.1+/-0.3 mmHg, cirrhotic vs. control, respectively, P<0.01, Student's unpaired t-test).

CONCLUSIONS

Variations in responses to thioacetamide can be easily monitored by weekly weight changes to reduce mortality to zero and simultaneously increase the production and quality of cirrhosis induced in rats.

Pathogenesis of portal hypertensive gastropathy: a clinical and experimental review

Portal hypertensive gastropathy (PHG) is recognized as a clinical entity in portal hypertension, but the pathogenesis of PHG is still unclear. Therefore, we reviewed the current state of knowledge concerning the portal hypertensive gastric mucosa and hypothesized the pathogenesis of PHG. Elevated portal pressure can induce changes of local hemodynamics, thus causing congestion in the upper stomach and gastric tissue damage. These changes may then activate cytokines and growth factors, such as tumor necrosis factor alpha, which are substances that activate endothelial constitutive nitric oxide synthase and endothelin 1 in the portal hypertensive gastric mucosa. Overexpressed nitric oxide synthase produces an excess of nitric oxide, which induces hyperdynamic circulation and peroxynitrite overproduction. The overproduction of peroxynitrite, together with endothelin overproduction may cause an increased susceptibility of gastric mucosa to damage. When combined with the characteristics of impaired mucosal defense and healing, these factors may together produce PHG in patients with portal hypertension.

Cellular and molecular basis of portal hypertension

The molecular basis of the vascular wall abnormalities that contribute to development of portal hypertension are an area of active investigation. Studies to date suggest that diminution in eNOS-derived NO production in liver contributes to this process by causing increased intrahepatic resistance. This process seems to be mediated through inhibitory posttranslational regulatory mechanisms of eNOS. Endothelin-1 signaling is also increased in the intrahepatic vasculature. The mechanisms responsible for increased ET-1 signaling include increased ET-1 production and increased ET-A receptor expression, particularly within hepatic stellate cells, although the stimulus responsible for activation of the ET-1 system remains uncertain. In the splanchnic circulation, increases in eNOS-derived NO contribute to increased portal venous inflow through transcriptional and posttranslational regulation of eNOS. Development of the porto-systemic collateral circulation characteristic of portal hypertension occurs through a combination of NO-dependent dilation of preexisting vessels and through growth factor-mediated angiogenesis and neovascularization (Fig. 3). Further studies in vascular wall biology are continuing to elucidate more clearly the molecular mechanisms of portal hypertension. The [figure: see text] mechanism by which eNOS-derived NO production is increased in the splanchnic arteriolar endothelial cell but decreased in the liver endothelial cell and the role of specific ET receptor subtypes in the mechanism of activation of the ET-1 system and its effect on contractile cells in liver cirrhosis are areas that require further investigation. Further studies are needed to determine the intrahepatic site of pressure and perfusion regulation, be it the hepatic sinusoid and its unique, specialized cell types or the endothelial and smooth muscle cells in the hepatic and portal venules. The role of more recently delineated vasoactive pathways such as urotensin-II/GPR 14 and anandamide/CB1 receptor in portal hypertension must be examined. Most importantly, future studies must focus on novel experimental therapies, using pharmacologic and genetic approaches to modulate these vascular biologic systems and thereby to ameliorate complications and symptoms relating to portal hypertension in patients with cirrhosis.

Regional and systemic hemodynamic disturbances in cirrhosis

In cirrhosis of the liver there is an imbalance between factors mediating vasodilatation such as nitric oxide and factors mediating vasoconstriction such as endothelins. These imbalances result in portal hypertension, hepatorenal syndrome, portopulmonary hypertension, hepatopulmonary syndrome, as well as alterations in cerebral blood flow.

Cellular pathophysiology of portal hypertension and prospects for management with gene therapy

In summary, regulation of sinusoidal blood flow in normal and injured liver involves structural, cellular, and humoral components. Available data suggest that stellate cells, resident perisinusoidal mesenchymal cells with a histologic orientation in the sinusoid analogous to [figure: see text] vasoregulatory pericytes, modulate sinusoidal blood flow. This regulation by stellate cells is most evident in the context of liver injury but may apply also to the normal liver. The endothelin and NO systems are important in modulating stellate cell contractility, and their degree of equilibrium is significant in determining the level of local intrahepatic resistance, especially in the injured liver. Manipulation of either or both of these systems is feasible and effective in experimental models. Such findings have obvious clinical implications and are expected to set the [figure: see text] stage for novel gene therapy approaches for treatment of patients with portal hypertension.

Regulation of hepatic eNOS by caveolin and calmodulin after bile duct ligation in rats

In carbon tetrachloride-induced liver cirrhosis, diminution of hepatic endothelial nitric oxide synthase (eNOS) activity may contribute to impaired hepatic vasodilation and portal hypertension. The mechanisms responsible for these events remain unknown; however, a role for the NOS-associated proteins caveolin and calmodulin has been postulated. The purpose of this study is to characterize the expression and cellular localization of the NOS inhibitory protein caveolin-1 in normal rat liver and to then examine the role of caveolin in conjunction with calmodulin in regulation of NOS activity in cholestatic portal hypertension. In normal liver, caveolin protein is expressed preferentially in nonparenchymal cells compared with hepatocytes as assessed by Western blot analysis of isolated cell preparations. Additionally, within the nonparenchymal cell populations, caveolin expression is detected within both liver endothelial cells and hepatic stellate cells. Next, studies were performed 4 wk after bile duct ligation (BDL), a model of portal hypertension characterized by prominent cholestasis, as evidenced by a significant increase in serum cholesterol in BDL animals. After BDL, caveolin protein levels from detergent-soluble liver lysates are significantly increased as assessed by Western blot analysis. Immunoperoxidase staining demonstrates that this increase is most prominent within sinusoids and venules. Additionally, caveolin-1 upregulation is associated with a significant reduction in NOS catalytic activity in BDL liver lysates, an event that is corrected with provision of excess calmodulin, a protein that competitively binds eNOS from caveolin. We conclude that, in cholestatic portal hypertension, caveolin may negatively regulate NOS activity in a manner that is reversible by excess calmodulin.

The role of endothelin in the pathogenesis of Chagas' disease

Infection with Trypanosoma cruzi causes a generalised vasculitis of several vascular beds. This vasculopathy is manifested by vasospasm, reduced blood flow, focal ischaemia, platelet thrombi, increased platelet aggregation and elevated plasma levels of thromboxane A(2) and endothelin-1. In the myocardium of infected mice, myonecrosis and a vasculitis of the aorta, coronary artery, smaller myocardial vessels and the endocardial endothelium are observed. Immunohistochemistry studies employing anti-endothelin-1 antibody revealed increased expression of endothelin-1, most intense in the endocardial and vascular endothelium. Elevated levels of mRNA for prepro endothelin-1, endothelin converting enzyme and endothelin-1 were observed in the infected myocardium. When T. cruzi-infected mice were treated with phosphoramidon, an inhibitor of endothelin converting enzyme, there was a decrease in heart size and severity of pathology. Mitogen-activated protein kinases and the transcription factor activator-protein-1 regulate the expression of endothelin-1. Therefore, we examined the activation of mitogen-activated protein kinases in the myocardium by T. cruzi. Western blot demonstrated an extracellular signal regulated kinase. In addition, the activator-protein-1 DNA binding activity, as determined by electrophoretic mobility shift assay, was increased. Increased expression of cyclins A and cyclin D1 was observed in the myocardium, and immunohistochemistry studies revealed that interstitial cells and vascular and endocardial endothelial cells stained intensely with antibodies to these cyclins. These data demonstrate that T. cruzi infection of the myocardium activates extracellular signal regulated kinase, activator-protein-1, endothelin-1, and cyclins. The activation of these pathways is likely to contribute to the pathogenesis of chagasic heart disease. These experimental observations suggest that the vasculature plays a role in the pathogenesis of chagasic cardiomyopathy. Additionally, the identification of these pathways provides possible targets for therapeutic interventions to ameliorate or prevent the development of cardiomyopathy during T. cruzi infection.

Levels of circulating endothelin-1 and nitrates/nitrites in patients with virus-related hepatocellular carcinoma

A balance between endothelins (ET) and nitric oxide (NO) might interfere with liver haemodynamics and disease progression in various liver diseases. Increased levels of endothelin 1 (ET-1) and nitrites and nitrates (NOx, the end products of NO metabolism) have been reported in hepatocellular carcinoma (HCC), but the balance has not been studied. The purpose of this study was to assess the ratio of NOx to ET-1 in patients with virus-related hepatocellular carcinoma and to investigate its correlation with the extent of the disease. Eighteen patients with virus-related HCC (six Okuda stage I, six Okuda stage II and six Okuda stage III) were included in the study and were compared with 22 patients with viral cirrhosis (14 decompensated, eight compensated) and seven normal controls. ET-1 was measured with an ELISA assay and NOx with a modification of the Griess reaction. Patients with virus-related HCC had the highest levels of circulating ET-1 and NOx (13.24 +/- 0.82 pg/ml and 112.28 +/- 18.56 micromol/l) compared to compensated cirrhosis (9.47 +/- 0.50 pg/ml, P < 0.004 and 54.47 +/- 2.36 micromol/l, P < 0.01), decompensated cirrhosis (9.57 +/- 0.32 pg/ml, P < 0.001 and 90.20 +/- 11.23 micromol/l, NS) and normal controls (8.84 +/- 0.61 pg/ml, P < 0.001 and 51.17 +/- 6.18 micromol/l, P < 0.01). There was a significant increase of ET-1 and NOx at HCC stage III compared to HCC stages I and II, cirhotics and controls. HCC stage III patients also had a NOx/ET-1 ratio that was higher than HCC stages I and II patients, normal controls and patients with compensated cirrhosis. Virus-related HCC patients have high levels of circulating ET-1, compared to compensated or decompensated cirrhosis. Highest levels of ET-1 are produced in Okuda III tumours. NOx are also increased but only in Okuda stage III tumours. The NOx/ET-1 ratio is increased in virus-related HCC and DC. This increase may account for the known increase in tumour blood flow.

Enhanced synthesis and reduced metabolism of endothelin-1 (ET-1) by hepatocytes--an important mechanism of increased endogenous levels of ET-1 in liver cirrhosis

BACKGROUND/AIMS

Hepatic concentration of endothelin-1 (ET-1) is increased in human and experimental liver cirrhosis. Because of its potent actions in the liver, ET-1 has been suggested to play an important role in the pathophysiology of cirrhosis. Since hepatocytes are the major cell type to metabolize ET-1, we investigated whether their reduced capacity to degrade ET-1 is a mechanism of its elevated levels in cirrhosis.

METHODS

The expression of ET-1 receptors, ET-1 and endothelin converting enzyme (ECE), and metabolism of ET-1 and ECE activity were compared in hepatocytes isolated from control and carbon tetrachloride-induced cirrhotic rats.

RESULTS

ET-1 receptor density and receptor-mediated internalization of ET-1 were significantly increased in cirrhotic hepatocytes relative to the control cells. However, compared to control hepatocytes, metabolism of ET-1 by the cirrhotic cells was reduced significantly. Interestingly, hepatocytes were found to contain preproET-1 mRNA, ECE-1 mRNA and ET-1. PreproET-1 mRNA and ET-1 levels were increased in cirrhotic hepatocytes but their ECE mRNA and ECE activity were not altered.

CONCLUSIONS

These results provide the first evidence that hepatocytes have the ability to synthesize ET-1 and demonstrate that decreased metabolism and enhanced synthesis, of ET-1 in hepatocytes are an important mechanism of its elevated levels in cirrhosis.

The cell and molecular biology of hepatic fibrogenesis. Clinical and therapeutic implications

Much has been learned in the past 2 decades about the cellular and molecular mechanisms underlying hepatic fibrogenesis and about potential therapeutic approaches in patients with liver disease. The central event in fibrogenesis seems to be the activation of hepatic stellate cells. Stellate cell activation is characterized by several important features, including enhanced matrix synthesis and a prominent contractile phenotype, processes that probably contribute to the physical distortion and dysfunction of the liver in advanced disease. It is important to emphasize that the factors controlling activation are multifactorial and complex. The extracellular matrix is a dynamic, active constituent of the fibrogenic response and undergoes active remodeling, including synthesis and degradation. Effective therapy for hepatic fibrogenesis will probably also be multifactorial, based on the basic mechanisms underlying the fibrogenic process. The most effective therapies will probably be directed at the stellate cell. Approaches that address matrix remodeling (i.e., by enhancing matrix degradation or by inhibiting factors that prevent matrix breakdown) may be effective.