Comparison of endothelin receptors in normal versus cirrhotic human liver and in the liver from endothelial cell-specific ETB knockout mice

Aims: Endothelin (ET) antagonists show promise in animal models of cirrhosis and portal hypertension. The aim was to pharmacologically characterise the expression of endothelin receptors in human liver, hepatic artery and portal vein.

Main methods: Immunofluorescence staining, receptor autoradiography and competition binding assays were used to localise and quantify ET receptors on hepatic parenchyma, hepatic artery and portal vein in human cirrhotic or normal liver. Additional experiments were performed to determine the affinity and selectivity of ET antagonists for liver ET endothelin receptors. An endothelial cell ETB knockout murine model was used to examine the function of sinusoid endothelial ETB receptors.

Key findings: ETB receptors predominated in normal human liver and displayed the highest ratio (ETB:ETA 63:47) compared with other peripheral tissues. In two patients examined, liver ETB expression was upregulated in cirrhosis (ETB:ETA 83:17). Both sub-types localised to the media of normal portal vein but ETB receptors were downregulated fivefold in the media of cirrhotic portal vein. Sinusoid diameter was fourfold smaller in endothelial cell ETB knockout mice. The liver morphology of ETB knockout mice was markedly different to normal murine liver, with loss of the wide spread sinusoidal pattern. In the knockout mice, sinusoids were reduced in both number and absolute diameter, while large intrahepatic veins were congested with red blood cells.

Significance: These data support a role for the ET system in cirrhosis of the liver and suggest that endothelial ETB blockade may cause sinusoidal constriction which may contribute to hepatotoxicity associated with some endothelin antagonists. (c) 2012 Elsevier Inc. All rights reserved.