Role of selective endothelin-A receptor antagonism in the progression of acute kidney injury to chronic kidney disease

Abstract

Renal ischemia-reperfusion injury (IRI) is a detrimental event caused by many conditions, such as renal transplantation. IRI is a precipitant of acute kidney injury (AKI) which results in accelerated impairment of renal function and can lead to the development of chronic kidney disease (CKD). We investigated short-term administration of a selective endothelin A receptor antagonist, sitaxentan, in the reversal of AKI and the prevention of AKI to CKD development. Sitaxentan’s mechanism of action was also studied, investigating whether the beneficial effects previously seen with long term administration were a result of renal haemodynamic improvement and/or change in inflammatory cell phenotype. The anti-hypertensive verapamil was used as control for the vasodilatory actions of sitaxentan. Two studies were carried out using a mouse model of IRI which involved clamping of the left renal artery for 50 mins to induce ischemic damage. The first study lasted 28d and involved 7d drug treatment. The second study lasted 5d and involved 4d of treatment; Doppler ultrasound and CT scanning took place on day 5 to investigate renal haemodynamics. After the mice were culled and their tissues collected, RT-qPCR, ELISA, immunohistochemistry, histological analysis and flow cytometry were used to determine whether short-term treatment of sitaxentan was effective in reversing/preventing renal disease whilst also investigating the specific mechanism of action. Results from the first study suggested 7 day treatment of sitaxentan was not effective at reversing AKI and preventing CKD. This was due to there being little or mainly no changes when studying kidney weights and appearance, endothelin related gene expression, histology, urinary ET-1 content. Results from the second study suggest that the benefits of long term sitaxentan administration could be due to a change in inflammatory cell phenotype within the circulating blood and kidneys. Data from flow cytometry showed that drug treated groups exhibited a decrease in percentage of circulating non-classical monocytes compared to non-treatment (post IRI). This may suggest that the non-classical monocytes - known for exerting beneficial effects in pathological environments - could be migrating to the IRI kidney to aid repair. Due to some differences when comparing sitaxentan with verapamil treatment, there is a possibility that sitaxentan works via a differing pathway to verapamil. However, as verapamil also caused the significant changes in the innate immune system, differences in effects could relate to its stronger anti-hypertensive capacity.