Relation of endothelins to volume regulating neurohumoral systems in patients with cirrhosis of the liver

Engineered SPIONs functionalized with endothelin a receptor antagonist ameliorate liver fibrosis by inhibiting hepatic stellate cell activation

Endothelin-1/endothelin A receptor (ET-1/ETAR) pathway plays an important role in the progression of liver fibrosis by activating hepatic stellate cells (HSCs) - a key cell type involved in the pathogenesis of liver fibrosis. Inactivating HSCs by blocking the ET-1/ETAR pathway using a selective ETAR antagonist (ERA) represents a promising therapeutic approach for liver fibrosis. Unfortunately, small-molecule ERAs possess limited clinical potential due to poor bioavailability, short half-life, and rapid renal clearance. To improve the clinical applicability, we conjugated ERA to superparamagnetic iron-oxide nanoparticles (SPIONs) and investigated the therapeutic efficacy of ERA and ERA-SPIONs in vitro and in vivo and analyzed liver uptake by in vivo and ex vivo magnetic resonance imaging (MRI), HSCs-specific localization, and ET-1/ETAR-pathway antagonism in vivo. In murine and human liver fibrosis/cirrhosis, we observed overexpression of ET-1 and ETAR that correlated with HSC activation, and HSC-specific localization of ETAR. ERA and successfully synthesized ERA-SPIONs demonstrated significant attenuation in TGFβ-induced HSC activation, ECM production, migration, and contractility. In an acute CCl4-induced liver fibrosis mouse model, ERA-SPIONs exhibited higher liver uptake, HSC-specific localization, and ET-1/ETAR pathway antagonism. This resulted in significantly reduced liver-to-body weight ratio, plasma ALT levels, and α-SMA and collagen-I expression, indicating attenuation of liver fibrosis. In conclusion, our study demonstrates that the delivery of ERA using SPIONs enhances the therapeutic efficacy of ERA in vivo. This approach holds promise as a theranostic strategy for the MRI-based diagnosis and treatment of liver fibrosis.

Plasma nitrate/nitrite and endothelin-1 in patients with liver cirrhosis

The aims of this study were to examine the plasma nitrate/nitrite (NOx; two end products of nitric oxide metabolism) and endothelin-1 (ET-1) concentrations in patients with liver cirrhosis, and to investigate whether there is a relationship between these two vasoactive parameters and the course of disease. Twenty-eight patients with liver cirrhosis (11 HBV-related, four HCV-related, four alcohol-related, and nine with idiopathic etiology) and 25 healthy subjects (controls) were included in the study. The venous plasma concentrations of NOx and ET-1 were significantly higher (P<0.01 and P<0.001) in the patients with cirrhosis than in the controls. A significant increase in ET-1 was observed in the Child B subgroup vs. Child A (P<0.05), and in the Child C subgroup vs. either subgroup A or B (P<0.05). There were no statistical differences between study subgroups (Child A-C) in the mean of NOx values. Plasma NOx and ET-1 were significantly increased in patients with ascites compared to those without ascites (P<0.05 and P<0.01). Increased nitric oxide synthesis may be a compensation mechanism against endothelial injury. The highest ET-1 levels in Child C and moderately increased ET-1 levels in Child B, and the lower increase of ET-1 levels in Child A patients suggest that plasma ET-1 increases with the progression of the disease. The fact that NOx and ET-1 levels were higher in patients with decompensated cirrhosis (patients with ascites) than in those with compensated cirrhosis (patients without ascites), and the presence of a strong correlation between ET-1, NOx, and the degree of varices, supports the suggestion that there is a relationship between NOx, ET-1, and portal hypertension. Our study demonstrates that increased ET and nitric oxide metabolism is associated with the hemodynamic alterations induced by portal hypertension.

Does gender influence human cardiovascular and renal responses to water immersion?

We hypothesized that women and men exhibit similar cardiovascular and renal responses to thermoneutral water immersion (WI) to the neck. Ten women and nine men underwent two sessions in random order: 1) seated nonimmersed for 5.5 h (control) and 2) WI for 3 h, with subjects seated nonimmersed for 1.5 h pre- and 1 h postimmersion. We measured left atrial diameter, heart rate, arterial pressure, urine volume and osmolality, and urinary endothelin, urodilatin, sodium, and potassium excretion. No significant difference existed between groups in cardiovascular responses. The groups also exhibited mostly similar renal responses to immersion after adjustment for body mass. However, female urodilatin excretion per kilogram during immersion was over twofold that of men, and the female kaliuretic response to immersion was delayed and less pronounced relative to that in men. Men may excrete more potassium than women during immersion because men possess greater lean body mass (potassium per kilogram). Results obtained in men during WI may be cautiously extrapolated to women, yet urodilatin and potassium responses exhibit gender differences.

Renal effects of transjugular intrahepatic portosystemic shunt in cirrhosis: comparison of patients with ascites, with refractory ascites, or without ascites

Renal effects of the transjugular intrahepatic portosystemic shunt (TIPS) were compared in 6 patients without ascites (group 1), 11 patients with ascites responding to diuretic treatment (group 2), and 6 patients with refractory ascites (group 3). Seven days after insertion of TIPS, 24-hour urinary sodium excretion had increased in patients with ascites: 113 +/- 16 mmol to 170 +/- 30 mmol (P = .012) in group 2, and 22 +/- 8 mmol to 77 +/- 27 mmol (P = .050) in group 3. In group 3, fractional sodium excretion tended to increase from 0.26% +/- 0.14% to 0.62% +/- 18% (P = .081). The relative increase of urinary sodium excretion (to 444% +/- 122%) and fractional sodium excretion (to 413% +/- 127%) in group 3 was significantly (P < .05) higher than in group 1 and group 2, respectively. Creatinine clearance and 24-hour urinary volume were not significantly changed in either group. Patients with Child-Pugh class C had a more pronounced effect of TIPS on urinary sodium excretion (increase to 396% +/- 115% vs. 139% +/- 15%; P = .066) and on fractional sodium excretion (increase to 415% +/- 103% vs. 94% +/- 15%; P = .020) than patients with less-severe liver disease. Fractional sodium excretion of less than 0.35% before TIPS was found to be an indicator of renal response to TIPS. The effect of TIPS on urinary sodium excretion and on fractional sodium excretion was related to the patients' Child-Pugh score (r = .55; P = .007 and r = .68; P = .001, respectively) and inversely to their fractional sodium excretion (r = -.44; P = .047 and r = -.54; P = .012, respectively) before TIPS. These data demonstrate that TIPS affects renal sodium handling in patients with ascites, particularly in patients with refractory ascites. Severity of liver disease and fractional sodium excretion before TIPS are parameters to predict the extent of the renal response.

The effect of endothelin and its antagonist Bosentan on hemodynamics and microvascular exchange in cirrhotic rat liver

BACKGROUND/AIMS

To characterize the effects of endothelin-1 and of Bosentan, a mixed endothelin antagonist, on hepatic hemodynamics in cirrhotic animals in vivo and on hepatic microvascular exchange in the perfused rat liver.

METHODS

Biliary cirrhosis was induced by bile duct ligation, and micronodular cirrhosis by chronic exposure to phenobarbital/CCl4 in male rats. Hepatic hemodynamics were studied under basal conditions and after administration of Bosentan (3-30 mg/kg) by the microsphere technique. Microvascular exchange was assessed in the in situ perfused rat liver by the multiple indicator dilution technique.

RESULTS

Bosentan lowered portal pressure in a dose-dependent fashion; at the highest dose tested, this decrease averaged -29+/-11 and -26+/-8% in biliary and micronodular cirrhosis, respectively (p<0.01). This was achieved mainly via a marked decrease in hepatic arterial flow. In the perfused liver, endothelin-1 induced a dose-dependent vasoconstriction; up to 10(-9) mol/l; this was not associated with any effect on viability. At this dose, endothelin-1 markedly decreased extravascular albumin space in both controls and micronodular cirrhosis; this could be antagonized by Bosentan 10(-5) mol/l.

CONCLUSIONS

Endothelin-1 affects hepatic microvascular exchange, presumably by a direct effect on hepatic sinusoidal endothelial cells. A mixed endothelin antagonist lowers portal pressure in vivo, presumably by acting on hepatic stellate cells, and counteracts the microvascular effects of endothelin-1 in vitro. These properties could prove useful in treatment of portal hypertension.

Daily profile of plasma endothelin-1 and -3 in pre-ascitic cirrhosis: relationships with the arterial pressure and renal function

BACKGROUND/AIMS

Measurements of plasma endothelin-1 and -3 in pre-ascitic cirrhosis have provided controversial results. Similarly, the role of the endothelin system in the pathogenesis of volume and hemodynamic disturbances of cirrhosis is still debated. To provide a further insight into this issue, we assessed the daily fluctuations of plasma endothelins and their relationship with arterial pressure and renal function in pre-ascitic cirrhosis.

METHODS

Endothelin-1 and -3, plasma renin activity, atrial natriuretic peptide, noradrenaline and mean arterial pressure were measured at 11 pm, 7 am, 9 am and 6 pm in 10 patients with pre-ascitic cirrhosis and in 10 healthy subjects on normal sodium diet and carrying on their usual activities (supine from 10 pm to 7 am, standing and mobile after 7 am). Glomerular filtration rate and daily renal sodium excretion were assessed during the supine period, and from 7 am to 12 am and from 12 am to 10 pm during the standing period.

RESULTS

Endothelin-1 was higher in patients than in control subjects (p=0.000) and did not change during the study. Endothelin-3 was also higher in patients (p=0.002) and showed slight fluctuation in control subjects. The mean daily level of plasma renin activity was lower (p=0.016) and that of atrial natriuretic peptide higher (p=0.000) in patients with cirrhosis. Norepinephrine and mean arterial pressure did not differ significantly between the two groups. No correlations were found between endothelins and either hemodynamic or neuro-hormonal and renal function parameters in the two groups.

CONCLUSIONS

Despite the presence of increased effective volemia (as suggested by the reduced plasma renin activity and elevated atrial natriuretic peptide) and normal adrenergic tone, patients with pre-ascitic cirrhosis show elevated levels of endothelin-1 and endothelin-3 throughout the day. In early cirrhosis circulating endothelins, although elevated, do not appear to play a more prominent role in setting arterial pressure than in normal subjects, and endothelin elevation is not detrimental to renal function.

Endothelins in chronic liver disease

This review describes recent progress in the accumulation of knowledge about the endothelins (ETs), a family of vasoactive 21-amino acid polypeptides, in chronic liver disease. Particular prominence is given to the dynamics of ET-1 and ET-3 and their possible relation to the disturbed circulation and neurohumoral dysregulation found in cirrhosis. Recent studies have shown that the ET system is highly activated in most cirrhotic patients. Circulating ET-1 and ET-3 levels have a positive relation to the severity of the disease and fluid retention, with the highest values recorded in patients with functional renal failure. Studies on liver biopsies have revealed synthesis of ET-1 in hepatic endothelial and other cells, and recent investigations have identified the hepatosplanchnic system as a major source of ET-1 and ET-3 spillover into the circulation, with a direct relation to portal venous hypertension. In addition, marked associations with disturbance of systemic haemodynamics and with abnormal distribution of blood volume have been reported. Although the pathophysiological importance of the ET system in chronic liver disease is not completely understood, similarities to other vasopressive and antinatriuretic regulatory systems (i.e. the sympathetic nervous system, renin-angiotensin-aldosterone and vasopressin) are apparent, with respect to kinetics and haemodynamic dysregulation. Cirrhosis seems to be a pathophysiological condition with indications of the occurrence of ETs, not only as local modulators, but also as a system with potential importance for systemic regulation.