Mixed endothelin receptor antagonist, SB209670, decreases portal pressure in biliary cirrhotic rats in vivo by reducing portal venous system resistance

GARP on hepatic stellate cells is essential for the development of liver fibrosis

BACKGROUND & AIMS

Glycoprotein A repetitions predominant (GARP) is a membrane protein that functions as a latent TGF-β docking molecule. While the immune regulatory properties of GARP on blood cells have been studied, the function of GARP on tissue stromal cells remains unclear. Here, we investigate the role of GARP expressed on hepatic stellate cells (HSCs) in the development of liver fibrosis.

METHODS

The function of GARP on HSCs was explored in toxin-induced and metabolic liver fibrosis models, using conditional GARP-deficient mice or a newly generated inducible system for HSC-specific gene ablation. Primary mouse and human HSCs were isolated to evaluate the contribution of GARP to the activation of latent TGF-β. Moreover, cell contraction of HSCs in the context of TGF-β activation was tested in a GARP-dependent fashion.

RESULTS

Mice lacking GARP in HSCs were protected from developing liver fibrosis. Therapeutically deleting GARP on HSCs alleviated the fibrotic process in established disease. Furthermore, natural killer T cells exacerbated hepatic fibrosis by inducing GARP expression on HSCs through IL-4 production. Mechanistically, GARP facilitated fibrogenesis by activating TGF-β and enhancing endothelin-1-mediated HSC contraction. Functional GARP was expressed on human HSCs and significantly upregulated in the livers of patients with fibrosis. Lastly, deletion of GARP on HSCs did not augment inflammation or liver damage.

CONCLUSIONS

GARP expressed on HSCs drives the development of liver fibrosis via cell contraction-mediated activation of latent TGF-β. Considering that systemic blockade of TGF-β has major side effects, we highlight a therapeutic niche provided by GARP and surface-mediated TGF-β activation. Thus, our findings suggest an important role of GARP on HSCs as a promising target for the treatment of liver fibrosis.

IMPACT AND IMPLICATIONS

Liver fibrosis represents a substantial and increasing public health burden globally, for which specific treatments are not available. Glycoprotein A repetitions predominant (GARP) is a membrane protein that functions as a latent TGF-β docking molecule. Here, we show that GARP expressed on hepatic stellate cells drives the development of liver fibrosis. Our findings suggest GARP as a novel target for the treatment of fibrotic disease.

Emerging Therapeutic Targets for Portal Hypertension

Purpose of Review

Portal hypertension is responsible of the main complications of cirrhosis, which carries a high mortality. Recent treatments have improved prognosis, but this is still far from ideal. This paper reviews new potential therapeutic targets unveiled by advances of key pathophysiologic processes.

Recent Findings

Recent research highlighted the importance of suppressing etiologic factors and a safe lifestyle and outlined new mechanisms modulating portal pressure. These include intrahepatic abnormalities linked to inflammation, fibrogenesis, vascular occlusion, parenchymal extinction, and angiogenesis; impaired regeneration; increased hepatic vascular tone due to sinusoidal endothelial dysfunction with insufficient NO availability; and paracrine liver cell crosstalk. Moreover, pathways such as the gut-liver axis modulate splanchnic vasodilatation and systemic inflammation, exacerbate liver fibrosis, and are being targeted by therapy. We have summarized studies of new agents addressing these targets.

Summary

New agents, alone or in combination, allow acting in complementary mechanisms offering a more profound effect on portal hypertension while simultaneously limiting disease progression and favoring regression of fibrosis and of cirrhosis. Major changes in treatment paradigms are anticipated.

Endothelin receptor B enhances liver injury and pro-inflammatory responses by increasing G-protein-coupled receptor kinase-2 expression in primary biliary cholangitis

Severe diseases like cirrhosis and liver failure can be developed from primary biliary cholangitis (PBC). Endothelin-2 (EDN2) and endothelin receptor B (EDNRB) are related to the pathogenesis of PBC. However, the roles of EDN2 and EDNRB in PBC-related liver injury and inflammation along with molecular mechanisms are poorly defined. In this study, histopathologic alterations of liver tissues were assessed through hematoxylin-eosin staining. Alanine transaminase (ALT), alkaline phosphatase (ALP), aspartate transaminase (AST), and γ-Glutamyltranspetidase (GGT) (4 liver function indexes) serum levels were detected with corresponding activity assay kits. Also, we determined the levels of M2 subtype anti-mitochondrial antibody (AMA-M2), interferon-gamma (IFN-γ), and tumor-necrosis factor alpha (TNFα) in serum with ELISA assay. Later, RT-qPCR assay was used to measure the expression of genes at mRNA levels, while western blotting and immunohistochemical techniques were used to detect protein levels of genes. Our results showed that the liver tissues of PBC patients and mice presented with severe hepatocyte injury and inflammatory cell infiltration as well as destruction of intrahepatic small bile ducts. ALP, AST, ALT, GGT, AMA-M2, IFN-γ, and TNF-α serum levels were higher in PBC patients and mice. Besides, EDN2 and EDNRB were highly expressed in serums and livers of PBC patients and mice. EDNRB potentiated PBC-related liver injury and pro-inflammatory responses, as evidenced by observation of serious liver pathologic injury and increased serum levels of ALP, AST, ALT, AMA-M2, IFN-γ, and TNF-α in PBC mice following EDNRB overexpression. EDNRB overexpression or activation via its agonist IRL-1620 TFA triggered liver injury and pro-inflammatory responses, increased GRK2 expression and induced NF-κB expression and activation in wild-type mice. EDNRB knockdown or inhibition by Bosentan alleviated liver damage and inflammation, reduced GRK2 expression, and inhibited NF-κB in PBC mice. These findings suggested EDNRB loss or inhibition weakened liver injury and pro-inflammatory responses by down-regulating GRK2 and inhibiting the NF-κB pathway in PBC mice.

Synergic effect of atorvastatin and ambrisentan on sinusoidal and hemodynamic alterations in a rat model of NASH

In non-alcoholic steatohepatitis (NASH), decreased nitric oxide and increased endothelin-1 (ET-1, also known as EDN1) released by sinusoidal endothelial cells (LSEC) induce hepatic stellate cell (HSC) contraction and contribute to portal hypertension (PH). Statins improve LSEC function, and ambrisentan is a selective endothelin-receptor-A antagonist. We aimed to analyse the combined effects of atorvastatin and ambrisentan on liver histopathology and hemodynamics, together with assessing the underlying mechanism in a rat NASH model. Diet-induced NASH rats were treated with atorvastatin (10 mg/kg/day), ambrisentan (30 mg/kg/day or 2 mg/kg/day) or a combination of both for 2 weeks. Hemodynamic parameters were registered and liver histology and serum biochemical determinations analysed. Expression of proteins were studied by immunoblotting. Conditioned media experiments were performed with LSEC. HSCs were characterized by RT-PCR, and a collagen lattice contraction assay was performed. Atorvastatin and ambrisentan act synergistically in combination to completely normalize liver hemodynamics and reverse histological NASH by 75%. Atorvastatin reversed the sinusoidal contractile phenotype, thus improving endothelial function, whereas ambrisentan prevented the contractile response in HSCs by blocking ET-1 response. Additionally, ambrisentan also increased eNOS (also known as Nos3) phosphorylation levels in LSEC, via facilitating the stimulation of endothelin-receptor-B in these cells. Furthermore, the serum alanine aminotransferase of the combined treatment group decreased to normal levels, and this group exhibited a restoration of the HSC quiescent phenotype. The combination of atorvastatin and ambrisentan remarkably improves liver histology and PH in a diet-induced NASH model. By recovering LSEC function, together with inhibiting the activation and contraction of HSC, this combined treatment may be an effective treatment for NASH patients.

Summary: Combining atorvastatin with ambrisentan is safe and effective in reducing intrahepatic resistance and portal hypertension in an experimental model of NASH. This liver histology amelioration highlights a promising therapeutic strategy.

Novel treatment options for portal hypertension

Portal hypertension is most frequently associated with cirrhosis and is a major driver for associated complications, such as variceal bleeding, ascites or hepatic encephalopathy. As such, clinically significant portal hypertension forms the prelude to decompensation and impacts significantly on the prognosis of patients with liver cirrhosis. At present, non-selective β-blockers, vasopressin analogues and somatostatin analogues are the mainstay of treatment but these strategies are far from satisfactory and only target splanchnic hyperemia. In contrast, safe and reliable strategies to reduce the increased intrahepatic resistance in cirrhotic patients still represent a pending issue. In recent years, several preclinical and clinical trials have focused on this latter component and other therapeutic avenues. In this review, we highlight novel data in this context and address potentially interesting therapeutic options for the future.

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.

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.

Pathophysiology and clinical practice analysis on endothelin system and portal hypertension

Portal hypertension (PHT) is a common clinical syndrome which leads to various severe, even lethal complications. The concentration of endothelin-1 (ET-1) in plasma is increased both in human body and PHT animal model. The effect of ET-1 depends on the kind of tissue and the expression of ET-1 receptor in this tissue. However, the expression of ET-1 receptor is not identical even in the same tissue at different PHT phases. This review aims to give an update on the endothelin syetem in PHT and elucidate a potential novel strategy.

Increased sinusoidal resistance is responsible for the basal state and endothelin-induced venoconstriction in perfused cirrhotic rat liver

The localization of increased intrahepatic vascular resistance and the segmental vascular responsiveness to endothelin-1 are not well known in liver cirrhosis. We determined the segmental vascular resistances and their response to endothelin-1 of isolated portally perfused bile duct ligation (BDL)-induced cirrhotic rat livers. The portal occlusion pressure (Ppo) and the hepatic venous occlusion pressure (Phvo) were obtained by analyzing the profiles of the portal (Ppv) and hepatic venous (Phv) pressures during the double occlusion maneuver of simultaneous occlusions of the inflow and outflow perfusion lines. From the pressure gradients among Ppv, Ppo, Phvo, and Phv, the portal-hepatic venous resistance was assigned to three segments of the portal [Rpv = (Ppv - Ppo)/blood flow (Q)], sinusoidal [Rsinus = (Ppo - Phvo)/Q] and hepatic venous [Rhv = (Phvo - Phv)/Q] resistances. Rsinus, but not Rpv or Rhv, was significantly greater in BDL livers than in sham livers. Endothelin-1 (0.1-1 nM) increased Rpv and Rsinus to a similar magnitude, but not Rhv, in both sham and BDL. At 3 nM, the responsiveness of Rpv was smaller in BDL than in sham, but that of Rsinus were similar between in BDL and sham. In conclusion, increased sinusoidal resistance accounts for increased intrahepatic resistance of BDL-induced liver cirrhosis. Endothelin-1 contracts portal veins and sinusoids, but not hepatic veins, in both sham and cirrhotic livers. Sinusoidal contractility to endothelin-1 is not impaired in cirrhotic livers.

Infection et rupture de varice œsophagienne au cours de la cirrhose

Endotoxemia and bacterial infection are frequent in patients with cirrhosis. They alter systemic and splanchnic hemodynamics, worsen coagulation disorders, impair liver function and thus may induce variceal bleeding. In variceal bleeding, bacterial infection favours failure to control bleeding, early rebleeding, and death. In patients with cirrhosis and variceal bleeding, antibiotic-prophylaxis decreases bacterial infection and the incidence of early rebleeding, and, more important, significantly decreases the death rate in these patients.

Local regulator adrenomedullin contributes to the circulatory disturbance in cirrhotic rats

AIM: To investigate whether adrenomedullin, a potent vasodilator peptide, plays a role in the circulatory disturbance in cirrhosis.

METHODS: Cirrhosis was induced in rats by weekly gavage of carbon tetrachloride. Hemodynamic studies were performed in vivo using radioactive microspheres and in vitro using isolated aortic rings. The adrenomedullin concentrations were measured by radioimmunoassay.

RESULTS: Acute administration of adrenomedullin to the control rats reduced the systemic arterial pressure along with an increase of serum levels of the stable metabolite of nitric oxide (NOx), in a dose-dependent manner. Chronic infusion of adrenomedullin reduced the vascular resistance and increased the blood flow in the systemic and splanchnic circulation. Intravenous administration of anti-adrenomedullin antibody did not affect any hemodynamic parameters in the cirrhotic rats, whereas this antibody ameliorated the blunted contractile response to phenylephrine, α-adrenergic receptor agonist, in the aortic rings of the cirrhotic rats. The adrenomedullin concentrations in the aorta were higher in the cirrhotic rats than in the controls, and correlated with the mean arterial pressure in the cirrhotic rats. Moreover, adrenomedullin blunted the contractile response to phenylephrine in both of the control aorta and cirrhotic aorta, but not in the presence of NG-nitro-L-arginine methyl ester, an NO synthase inhibitor.

CONCLUSION: Adrenomedullin overproduced in the vascular wall may contribute to the circulatory disturbance in cirrhosis as a local regulator of the vascular tonus rather than a circulating hormone.

Defective RhoA/Rho-kinase signaling contributes to vascular hypocontractility and vasodilation in cirrhotic rats

BACKGROUND & AIMS

Portal hypertension is associated with arterial hypotension and vascular hypocontractility, which persists despite elevated plasma levels of vasoconstrictors. We investigated the role of the RhoA/Rho-kinase pathway in vascular smooth muscle hypocontractility of rats with secondary biliary cirrhosis.

METHODS

Aortic expressions of RhoA and Rho-kinase were analyzed in sham-operated and BDL rats by reverse-transcription polymerase chain reaction (RT-PCR) and immunoblots. Activation of aortic RhoA was examined by pull down of guanosine triphosphate (GTP)-RhoA and membrane translocation of RhoA. Rho-kinase activity was assessed as phosphorylation of its substrate, moesin. Contractility of isolated aortic rings was determined myographically. The hemodynamic effect of the Rho-kinase inhibitor (R)-(+)-trans-N-(4-pyridyl)-4-(1-aminoethyl)-cyclohexanecarboxamide (Y-27632) was determined in vivo by measuring changes in mean arterial pressure and systemic vascular resistance (SVR) (microspheres).

RESULTS

Contraction of aortic rings from BDL rats was impaired in response to the alpha(1)-adrenergic receptor agonist methoxamine but not to high molar KCl. Aortic expression of RhoA was unchanged in cirrhotic rats, whereas Rho-kinase was down-regulated posttranscriptionally. Methoxamine-induced activation of RhoA as well as basal and methoxamine-induced phosphorylation of moesin were strongly reduced in aortas from cirrhotic rats. Aortic rings from cirrhotic rats precontracted with methoxamine showed an increased sensitivity to relaxation with Y-27632. The drop in SVR induced by Y-27632 was larger in cirrhotic rats than in sham-operated rats.

CONCLUSIONS

An impaired vascular activation of RhoA and a down-regulation of Rho-kinase might contribute to vasodilation and vascular hypocontractility in BDL-induced cirrhosis.

Vascular, hemodynamic and renal effects of low-dose losartan in rats with secondary biliary cirrhosis

BACKGROUND

In cirrhosis, splanchnic and systemic vasodilatation induce a hyperdynamic circulatory dysfunction, portal hypertension and renal sodium retention. This vasodilatation is in part because of an impaired vascular response to alpha1-adrenoceptor agonists. Recently, the angiotensin II type 1-receptor antagonist losartan has been shown to attenuate portal hypertension. We hypothesized that losartan decreases portal pressure by counteracting the impaired vascular responsive to alpha1-adrenoceptor agonists.

METHODS

We studied, in rats with secondary biliary cirrhosis and sham-operated rats, the effect of 0.5 and 10 mg losartan/kg x day on aortic responsiveness to alpha1-adrenoceptor stimulation with methoxamine and angiotensin II (myograph), splanchnic and systemic hemodynamics (colored microspheres), plasma noradrenaline levels and kidney function.

RESULTS

In cirrhotic rats, 10 mg losartan/kg x day completely inhibited aortic contractility to angiotensin II, decreased vascular resistance and arterial pressure and induced renal failure. In contrast, 0.5 mg losartan/kg x day only partially inhibited aortic contractility to angiotensin II, but improved aortic contractility to methoxamine, increased splanchnic and systemic vascular resistance, decreased portal pressure, decreased plasma norepinephrine levels and induced natriuresis.

CONCLUSIONS

In cirrhotic rats, losartan at a very low dose increases splanchnic vascular resistance, decreases portal pressure and improves kidney function, possibly by an increased vascular responsiveness to alpha1-adrenoceptor agonists.

Effects of endothelin-1 on portal-systemic collaterals of common bile duct-ligated cirrhotic rats

BACKGROUND/AIMS

Endothelin-1 (ET-1) may induce intrahepatic vasoconstriction and consequently increase portal pressure. Endothelin-1 has been shown to exert a direct vasoconstrictive effect on the collateral vessels in partially portal vein-ligated rats with a high degree of portal-systemic shunting. This study investigated the collateral vascular responses to ET-1, the receptors in mediation and the regulation of ET-1 action by nitric oxide and prostaglandin in cirrhotic rats with a relatively low degree of portal-systemic shunting.

METHODS

The portal-systemic collaterals of common bile duct-ligated (BDL) cirrhotic rats were tested by in situ perfusion. The concentration-response curves of collaterals to graded concentrations of ET-1 (10(-10)-10(-7) m) with or without BQ-123 (ET(A) receptor antagonist, 2 x 10(-6) m), BQ-788 (ET(B) receptor antagonist, 10(-7) m) or both were recorded. In addition, the collateral responses to ET-1 with preincubation of N(omega)-nitro-L-arginine (NNA, 10(-4) M), indomethacin (INDO, 10(-5) M) or in combination were assessed.

RESULTS

Endothelin-1 significantly increased the perfusion pressures of portal-systemic collaterals. The ET-1-induced constrictive effects were inhibited by BQ-123 or BQ-123 plus BQ-788 but not by BQ-788 alone. The inhibitory effect was greater in the combination group. Pretreatment of NNA or NNA plus INDO equivalently enhanced the response of ET-1 while pretreatment of INDO alone exerted no effect.

CONCLUSION

Endothelin-1 has a direct vasoconstrictive effect on the collaterals of BDL cirrhotic rats, mainly mediated by ET(A) receptor. Endogenous nitric oxide may play an important role in modulating the effects of ET-1 in the portal-systemic collaterals of BDL cirrhotic rats.

Effects of tumor necrosis factor, endothelin and nitric oxide on hyperdynamic circulation of rats with acute and chronic portal hypertension

AIM: To evaluate the effect of tumor necrosis factor (TNF), endothelin (ET) and nitric oxide (NO) on hyperdynamic circulation (HC) of rats with acute and chronic portal hypertension (PHT).

METHODS: Chronic portal hypertension was induced in Wistar rats by injection of carbon tetrachloride. After two weeks of cirrhosis formation, L-NMMA (25 mg/kg) was injected into one group of cirrhotic rats via femoral vein and the experiment was begun immediately. Another group of cirrhotic rats was injected with anti-rat TNFα (300 mg/kg) via abdominal cavity twice within 48 h and the experiment was performed 24 h after the second injection. The blood concentrations of TNFα, ET-1 and NO in portal vein and the nitric oxide synthase (NOS) activity in hepatic tissue were determined pre-and post-injection of anti-rat TNFα or L-NMMA. Stroke volume (SV), cardiac output (CO), portal pressure (PP), superior mesenteric artery blood flow (SMA flow) and iliac artery blood flow (IAflow) were measured simultaneously. Acute portal hypertension was established in Wistar rats by partial portal-vein ligation (PVL). The parameters mentioned above were determined at 0.5 h, 24 h, 48 h, 72 h and 120 h after PVL. After the formation of stable PHT, the PVL rats were injected with anti-rat TNFα or L-NMMA according to different groups, the parameters mentioned above were also determined.

RESULTS: In cirrhotic rats, the blood levels of TNFα, NO in portal vein and the liver NOS activity were significantly increased (P < 0.05) while the blood level of ET-1 was not statistically different (P > 0.05) from the control animals (477.67 ± 83.81 pg/mL vs 48.87 ± 32.79 pg/mL, 278.41 ± 20.11 µmol/L vs 113.28 ± 14.51 µmol/L, 1.81 ± 0.06 u/mg·prot vs 0.87 ± 0.03 u/mg·prot and 14.33 ± 4.42 pg/mL vs 8.72 ± 0.79 pg/mL, respectively). After injection of anti-rat TNFα, the blood level of TNFα was lower than that in controls (15.17 ± 18.79 pg/mL vs 48.87 ± 32.79 pg/mL). The blood level of NO and the liver NOS activity were significantly decreased, but still higher than those of the controls. The blood level of ET-1 was not significantly changed. PP, SV, CO, SMAflow and IAflow were ameliorated. After injection of L-NMMA, the blood level of NO and the liver NOS activity were recovered to those of the controls. PP and CO were also recovered to those of the controls. SV, SMAflow and IAflow were ameliorated. In PVL rats, the blood levels of TNFα, NO in portal vein and the liver NOS activity were gradually increased and reached the highest levels at 48 h after PVL. The blood level of ET-1 among different staged animals was not significantly different from the control animals. PP among different staged animals (2.4 ± 0.18 kPa at 0.5 h, 1.56 ± 0.08 kPa at 24 h, 1.74 ± 0.1 kPa at 48 h, 2.38 ± 0.05 kPa at 72 h, 2.39 ± 0.16 kPa at 120 h) was significantly higher than that in controls (0.9 ± 0.16 kPa). After injection of anti-rat TNFα in 72 h PVL rats, the blood level of TNFα was lower than that in controls (14 ± 14 pg/mL vs 48.87 ± 32.79 pg/mL). The blood level of NO and the liver NOS activity were significantly decreased, but still higher than those of the controls. The blood level of ET-1 was not significantly changed. PP was decreased from 2.38 ± 0.05 kPa to 1.68 ± 0.12 kPa, but significantly higher than that in controls. SV, CO, SMAflow and IAflow were ameliorated. After injection of L-NMMA in 72 h PVL rats, the blood level of NO and the liver NOS activity were recovered to those of the controls. PP, SV, CO, SMAflow and IAflow were also recovered to those of the controls.

CONCLUSION: NO plays a critical role in the development and maintenance of HC in acute PHT and is a key factor for maintenance of HC in chronic PHT. TNFα may not participate in the hemodynamic changes of HC directly, while play an indirect role by inducing the production of NO through activating NOS. No evidence that circulating ET-1 plays a role in both models of portal hypertension has been found.

Acute haemodynamic effects of losartan in anaesthetized cirrhotic rats

BACKGROUND

Portal hypertension in cirrhosis is the result of increased intrahepatic vascular resistance to portal outflow as well as increased portal tributary blood flow. The angiotensin II type 1 receptor antagonist losartan has been suggested as a portal pressure-lowering drug in patients with cirrhosis.

AIM

To investigate the systemic and splanchnic haemodynamic effects of different doses of losartan.

METHODS

In 35 anaesthetized rats with secondary biliary cirrhosis, 3, 10 or 30 mg of losartan kg(-1) or solvent were administered intravenously. Ten sham-operated rats served as controls. Mean arterial pressure and portal pressure were measured by catheters in the femoral artery or portal vein. Systemic and splanchnic haemodynamics and mesenterico-systemic shunt rate were determined by the coloured microsphere method.

RESULTS

Losartan reduced portal pressure (sham: 9.1 +/- 0.4. cirrhosis: 19.3 +/- 1.1, after 3 mg kg(-1) of losartan 16.4 +/- 0.4, after 10 mg kg(-1) of losartan 15.6 +/- 0.6, after 30 mg kg(-1) of losartan 14.9 +/- 0.6 mmHg) without reducing portal sinusoidal resistance. However, in cirrhotic rats it reduced portal tributary blood flow (sham: 4.3 +/- 0.6. cirrhosis: 8.6 +/- 1.4, after 3 mg kg(-1) of losartan 3.8 +/- 0.7, after 10 mg kg(-1) of losartan 4.7 +/- 0.5, after 30 mg kg(-1) of losartan 5.9 +/- 0.9 mmHg). This was owing either to an increase in splanchnic vascular resistance at the 3 mg kg(-1) dose or to a reduction in the splanchnic perfusion-pressure gradient secondary to a reduction in mean arterial pressure at the 10 and 30 mg kg(-1) doses (mean arterial pressure: sham: 109.7 +/- 4.8. cirrhosis: 109.4 +/- 2.8, after 3 mg kg(-1) of losartan 99.7 +/- 2.9, after 10 mg kg(-1) of losartan 89.9 +/- 3.4, after 30 mg kg(-1) of losartan 81.0 +/- 2.9 mmHg).

CONCLUSIONS

Low doses of losartan reduce portal hypertension by an increase in splanchnic vascular resistance without hypotensive side-effects on arterial pressure.

Enrasentan, an antagonist of endothelin receptors

Endothelins are powerful vasoconstrictor agents produced by endothelial cells and identified by Yanagisawa et al. in 1988. Two types of receptors for endothelins have been identified: ET(A) receptors are located on smooth muscle cells of the vascular wall and are responsible for endothelin-induced vasoconstriction while ET(B) receptors are located on endothelial cells and induce these cells to release NO and prostacyclin. Moreover, these peptides not only cause a potent and prolonged vasoconstriction but are also known to enhance cell proliferation and to stimulate extracellular matrix accumulation. High levels of plasma or tissue endothelins have been found in patients with heart failure, diabetes, stroke, primary pulmonary hypertension, liver cirrhosis and other diseases. Given these effects of endothelins, blocking their receptors might be a new way to reduce blood pressure and to treat other illnesses. Accordingly, many endothelin antagonists have been developed and evaluated in animals and humans. Enrasentan is a mixed ET(A) and ET(B) receptor antagonist with a higher affinity for ET(A) receptors, although it cannot be considered a selective antagonist. In an animal model of hypertension and cardiac hypertrophy the drug has reduced blood pressure, prevented cardiac hypertrophy and preserved myocardial function. In rats with hyperinsulinemia and hypertension enrasentan normalized blood pressure and prevented cardiac and renal damage. In rats with stroke the drug reduced the ischemic area in the brain. Enrasentan has been added to conventional treatment in patients with heart failure (NYHA Class 2-3) and no addictive effect of the drug has been observed. This is in contrast with results obtained in animal models and still has not been explained. In conclusion, many possible clinical applications can be suggested for this drug, but further studies are necessary to better evaluate its therapeutic efficacy.

Effects of ET-1 and NO on hepatic hemodynamics at various stages of isolated perfused cirrhotic liver in rats

AIM

To investigate the effects of ET-1, NO on hepatic hemodynamics in isolated perfused rat liver at various stages of liver cirrhosis (LC).

METHODS

LC was induced by an intraperitoneal injection of CCL₄ combined with ethanol as drinking water. According to time points of CCL₄ injection, and combined with histopathological changes of liver and ascites, the isolated perfusion of liver was performed at a constant flow rate to determine the modulating effects of ET-1 and NO in the ends of 9th week (E-LC) and 14^th week (L-LC) after injected CCL₄.

RESULTS

After perfusion of L-NAME into the portal vein, there were no significant changes in the perfused pressure of portal vein (PP) and the hepatic venous pressure (Phv) of the L-LC group, the E-LC group and control group (P>0.05). After perfusion of ET-1, the PP of each group increased significantly (P<0.01). The elevated ranges of PP of the L-LC group was more than that of the E-LC group (P<0.01), both of which were higher than that of the control group (P<0.01). Compared with the ET-1 groups, the PP of the control group, the E-LC group and the L-LC group increased significantly (P<0.05) after perfusion of ET-1+L-NAME. There were no significant differences between the elevated ranges of PP of the L-LC and that of the E-LC group (P>0.05), both of which were more than that of the control group (P<0.01).

CONCLUSION

ET-1 plays a key role in elevating intra-hepatic resistance, facilitating synthesis of NO, which grow stronger in LC. With the development of LC, the compensation of NO decreases further. It is considered that antagonist of ET receptor and NO provider can increase synthesis of NO and be thus used in treatment of the high pressure of portal vein.

Role of thromboxane A2 in early BDL-induced portal hypertension

Although the mechanisms of cirrhosis-induced portal hypertension have been studied extensively, the role of thromboxane A(2) (TXA(2)) in the development of portal hypertension has never been explicitly explored. In the present study, we sought to determine the role of TXA(2) in bile duct ligation (BDL)-induced portal hypertension in Sprague-Dawley rats. After 1 wk of BDL or sham operation, the liver was isolated and perfused with Krebs-Henseleit bicarbonate buffer at a constant flow rate. After 30 min of nonrecirculating perfusion, the buffer was recirculated in a total volume of 100 ml. The perfusate was sampled for the enzyme immunoassay of thromboxane B(2) (TXB(2)), the stable metabolite of TXA(2). Although recirculation of the buffer caused no significant change in sham-operated rats, it resulted in a marked increase in portal pressure in BDL rats. The increase in portal pressure was found concomitantly with a significant increase of TXB(2) in the perfusate (sham vs. BDL after 30 min of recirculating perfusion: 1,420 +/- 803 vs. 10,210 +/- 2,950 pg/ml; P < 0.05). Perfusion with a buffer containing indomethacin or gadolinium chloride for inhibition of cyclooxygenase (COX) or Kupffer cells, respectively, substantially blocked the recirculation-induced increases in both portal pressure and TXB(2) release in BDL group. Hepatic detection of COX gene expression by RT-PCR revealed that COX-2 but not COX-1 was upregulated following BDL, and this upregulation was confirmed at the protein level by Western blot analysis. In conclusion, these results clearly demonstrate that increased hepatic TXA(2) release into the portal circulation contributes to the increased portal resistance in BDL-induced liver injury, suggesting a role of TXA(2) in liver fibrosis-induced portal hypertension. Furthermore, the Kupffer cell is likely the source of increased TXA(2), which is associated with upregulation of the COX-2 enzyme.

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.

Influence of indomethacin on effects of endothelin-1 on guinea pig isolated rings of common bile duct and sphincter of Oddi

The effects of endothelin-1 on motility of guinea pig extra-hepatic biliary tract portions were studied. Endothelin-1 (< or =100 nM) failed to contract rings of hepatic, cystic, proximal or distal common bile ducts, or choledochal or papillary halves of sphincter of Oddi. At 100 nM, endothelin-1 or sarafotoxin S6c (selective endothelin ET(B) receptor agonist) inhibited contractions of choledochal (but not papillary) sphincter of Oddi to carbachol (1 microM) by 63+/-5 and 45+/-9%, respectively. In distal common bile duct, indomethacin (5.6 microM) unmasked potent contractile effects of endothelin-1 [EC(50) 7.8 (5.5-11.1) nM; E(MAX) 80+/-6% of response to 80 mM KCl] and enhanced the contractile potency of carbachol (585-fold at EC(50) level), but not cholecystokinin C-terminal octapeptide. Inhibition of cholinergic responsiveness of the choledochal sphincter of Oddi by endothelin-1 was reduced by BQ-123 (1 microM; endothelin ET(A) receptor antagonist; cyclo[DTrp-DAsp-Pro-DVal-Leu]) and abolished by either BQ-123 plus BQ-788 (1 microM; endothelin ET(B) receptor antagonist; N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D-1-methoxycarboyl-D-norleucine) or indomethacin. Thus, eicosanoids of the cyclo-oxygenase pathway (i.e. prostanoids) suppress endothelin-1-induced contractions of distal common bile duct and mediate endothelin ET(A) and ET(B) receptor-dependent inhibition of cholinergic responsiveness of the choledochal portion of the sphincter of Oddi.

Plasma endothelin-1 levels in liver cirrhosis

The role of circulating endothelin- , a potent vasoconstricting peptide, in liver cirrhosis is still controversial. It has been postulated that endothelin-1 may play a role in the circulatory derangement occurring in cirrhotic subjects, and increased plasma endothelin-1 levels have been reported in these patients. In this study we looked for a relationship between the severity of the liver disease according to Child's classification and plasma endothelin-1 concentrations in a group of cirrhotic patients compared with a healthy control group. Twenty-two cirrhotic patients and 10 healthy controls, matched for sex and age, were selected for study after informed consent. The etiology of cirrhosis was posthepatitis B in 8 of 22 cases, posthepatitis C in 13 of 22 cases, and alcoholism in 1 patient. According to Child's classification, 6 patients were in class A, 6 in class B, and 10 in class C. Plasma endothelin-1 was measured by a commercial RIA kit (Amersham UK). Mean +/- SD plasma endothelin-1 levels were 8.8 +/- 0.9 pg/ml in controls and 9.2 +/- 1.1 pg/ml in all cirrhotic patients (P > 0.05). In each sub-group of cirrhotics, plasma endothelin- was 8.6 +/- 1.2 pg/ml in Child A, 8.9 +/- 1.9 pg/ml in Child B, and 10.6 +/- 1.5 pg/ml in Child C groups, respectively. There were no statistical differences between control subjects and Child A and B cirrhotic patients (P > 0.05). A significant increase in endothelinl was observed only in the Child C group versus either group A or B (P = 0.004). Our results show that alterations of circulating endothelin-1 do not occur in all cirrhotic patients; higher plasma levels than controls are only detectable in patients with more-severe hepatic failure. We do not know whether increased endothelin-1 levels are a consequence of hemodynamic disorders occurring in the advanced phase of liver cirrhosis or play a pathogenic role.

Endothelin-1 plays a major role in portal hypertension of biliary cirrhotic rats through endothelin receptor subtype B together with subtype A in vivo

BACKGROUND/AIMS

Endothelin-1 has been suggested to play a key role in cirrhotic portal hypertension, but a role of its receptors in vivo is not fully elucidated.

METHODS

Biliary cirrhosis was induced by bile duct ligation. Expressions of endothelin-1 and its receptors were evaluated by radioimmunoassay and/or reverse-transcription polymerase chain reaction. Hemodynamics were studied using endothelin receptor agonist or antagonist.

RESULTS

Portal pressure and hepatic endothelin-1 concentrations progressively increased in parallel after bile duct ligation. Gene expression of hepatic prepro-endothelin-1 and endothelin B receptor enhanced after bile duct ligation, while that of endothelin A receptor was unchanged. Intraportal administration of endothelin-1 or endothelin B receptor agonist sarafotoxin 6c (0.5 nmol/kg, respectively) progressively raised portal pressure in both sham and cirrhotic rats. Portal hypertensive effect of sarafotoxin 6c was more intense in cirrhotic rats than sham animals. Neither endothelin A receptor antagonist FR139317 (1 mg/kg) nor endothelin B receptor antagonist BQ788 (1 mg/kg) alone ameliorated cirrhotic portal hypertension. Only the combined endothelin A and B blockade was associated with a decrease in portal pressure in cirrhotic rats.

CONCLUSIONS

These results indicate that endothelin-1 plays a major role in cirrhotic portal hypertension through endothelin receptor subtype B together with subtype A in vivo.