Chronic kidney disease (CKD) represents a progressive impairment of renal function, leading to severe health complications, with a prevalence of about 10 % globally, and poses a substantial public health challenge [1], [2]. This condition manifests as a progressive and irreversible deterioration of nephrons, coupled with microvascular injury, impaired repair mechanisms, renal fibrosis, low-grade and restored inflammation, oxidative stress, and metabolic imbalances, ultimately resulting in renal failure and end-stage kidney disease (ESKD) [3]. Examining the link between CKD and renal fibrosis is essential for understanding the disease's causes and developing effective treatments. Among various pathomechanisms, epithelial-mesenchymal transition (EMT), a process in which epithelial cells transition into a mesenchymal phenotype, is characterized by the loss of polarity and an increase in migratory capacity. The transforming growth factor-beta (TGF-β) is a pivotal mediator of fibrosis, promoting EMT, activating mesenchymal cells, and enhancing extracellular matrix (ECM) production, which establishes a microenvironment contributive to fibrosis progression [4], [5].

Rodent models are frequently employed to study kidney disease mechanisms and to validate new treatment strategies for evaluating novel therapeutic agents. Kidney fibrosis, a prevalent outcome of CKD, serves as a reliable marker of disease progression. The unilateral ureteral obstruction (UUO) model is widely accepted for in-vivo studies of kidney fibrosis, as it rapidly reproduces key pathological features of CKD, including tubular damage, inflammatory infiltration, myofibroblast activation, ECM accumulation, fibrotic changes, and microvascular loss. This model is typically induced by ureteral ligation in rodents and studied over periods ranging from 3 days to 4 weeks [6], [7]. Due to its consistent fibrotic phenotype and independence from genetic or sex-related variables, this model is particularly advantageous for experiments involving transgenic animals [8].

Various signaling systems play a role in the progression of CKD, one of which is the endothelin (ET) system. It is composed of vasoconstrictive peptides derived mainly from endothelial cells and plays a pivotal role in the pathogenesis of glomerular and tubulointerstitial kidney diseases. In the kidney, ETs are synthesized by mesangial cells and podocytes, and within the glomerular basement membrane. Their actions are mediated through endothelin receptor type A (ETA) and endothelin receptor type B (ETB), which are widely distributed in epithelial cells, renal tubules, and collecting ducts, contributing to kidney dysfunction and disease progression [9], [10]. ETA receptor-mediated activation of the endothelin system in CKD promotes prolonged vasoconstriction, leading to hyperfiltration, podocyte damage, proteinuria, and a progressive decline in glomerular filtration rate (GFR). Hence, recent research underscores the potential benefits of endothelin receptor antagonists in kidney diseases, with reports indicating their effectiveness in reducing proteinuria and slowing GFR decline [9], [11].

To alleviate CKD, several therapeutic agents have been explored over the past few decades; however, validated approaches to regulate inflammation or halt the progression of renal fibrosis remain elusive, and these approaches often carry notable side effects [12]. Drug repurposing has thus emerged as a promising strategy, facilitating drug discovery and development in a more time- and cost-efficient manner [13]. Ambrisentan (AMB), a selective endothelin receptor antagonist, is indicated in the management of pulmonary arterial hypertension and has shown promising renoprotective effects in ischemia-reperfusion injury (IRI). It enhances nitric oxide (NO) production, which supports endothelial function and vascular relaxation and helps to mitigate the inflammatory response in IRI. These actions collectively suggest potential therapeutic application of AMB in renal protection [14]. AMB significantly attenuated albuminuria and nephrinuria while reducing the expression of kidney injury markers. Moreover, it effectively prevented glomerular hypertrophy, thickening of Bowman’s capsule, glomerulosclerosis, vascular congestion, and podocyte injury [15]. Another study reported that AMB ameliorates inflammation, oxidative stress and apoptosis in acute kidney injury (AKI) by downregulating the death receptor P75NTR, thereby improving renal blood flow, maintaining oxidative homeostasis, and regulating signaling pathways such as p53, VEGF/eNOS, NF-κB, and the Bcl-2/Bax/caspase-3 cascade [16]. Despite its therapeutic relevance, the role of AMB in renal fibrosis remains unexplored. Hence, based on the literature review and conceptual analysis, we propose that AMB may mitigate UUO-induced renal fibrosis in male Sprague-Dawley (SD) rats and recombinant human-transforming growth factor-beta1 (rh-TGF-β1) -induced fibrosis in NRK-52E (rat kidney tubular epithelial cells) by modulating AKT/GSK-3β (protein kinase B/glycogen synthase kinase-3 beta) signaling pathway in obstructed kidneys.