Vasoconstrictor antagonism improves functional and structural vascular alterations and liver damage in rats with early NAFLD

Abstract

Background & AimsIntrahepatic vascular resistance is increased in early non-alcoholic fatty liver disease (NAFLD), potentially leading to tissue hypoxia and triggering disease progression. Hepatic vascular hyperreactivity to vasoconstrictors has been identified as an underlying mechanism. This study investigates vasoconstrictive agonism and antagonism in 2 models of early NAFLD and in non-alcoholic steatohepatitis (NASH).MethodsThe effects of endothelin-1 (ET-1), angiotensin II (ATII) and thromboxane A2 (TxA2) agonism and antagonism were studied by in situ ex vivo liver perfusion and preventive/therapeutic treatment experiments in a methionine-choline-deficient diet model of steatosis. Furthermore, important results were validated in Zucker fatty rats after 4 or 8 weeks of high-fat high-fructose diet feeding. In vivo systemic and portal pressures, ex vivo transhepatic pressure gradients (THPG) and transaminase levels were measured. Liver tissue was harvested for structural and mRNA analysis.ResultsThe THPG and consequent portal pressure were significantly increased in both models of steatosis and in NASH. ET-1, ATII and TxA2 increased the THPG even further. Bosentan (ET-1 receptor antagonist), valsartan (ATII receptor blocker) and celecoxib (COX-2 inhibitor) attenuated or even normalised the increased THPG in steatosis. Simultaneously, bosentan and valsartan treatment improved transaminase levels. Moreover, bosentan was able to mitigate the degree of steatosis and restored the disrupted microvascular structure. Finally, beneficial vascular effects of bosentan endured in NASH.ConclusionsAntagonism of vasoconstrictive mediators improves intrahepatic vascular function. Both ET-1 and ATII antagonists showed additional benefit and bosentan even mitigated steatosis and structural liver damage. In conclusion, vasoconstrictive antagonism is a potentially promising therapeutic option for the treatment of early NAFLD.Lay summaryIn non-alcoholic fatty liver disease (NAFLD), hepatic blood flow is impaired and the blood pressure in the liver blood vessels is increased as a result of an increased response of the liver vasculature to vasoconstrictors. Using drugs to block the constriction of the intrahepatic vasculature, the resistance of the liver blood vessels decreases and the increased portal pressure is reduced. Moreover, blocking the vasoconstrictive endothelin-1 pathway restored parenchymal architecture and reduced disease severity.