Therapeutic targeting of aristolochic acid induced uremic toxin retention, SMAD 2/3 and JNK/ERK pathways in tubulointerstitial fibrosis: Nephroprotective role of propolis in chronic kidney disease

The nephrotoxicity of aristolochic acids (AAs), p-cresyl sulfate (PCS) and indoxyl sulfate (IS) were well-documented, culminating in tubulointerstitial fibrosis (TIF), advanced chronic kidney disease (CKD) and fatal urothelial cancer. Nonetheless, information regarding the attenuation of AAs-induced nephropathy (AAN) and uremic toxin retention is scarce. Propolis is a versatile natural product, exerting anti-oxidant, anti-cancer and anti-fibrotic properties. We aimed to evaluate nephroprotective effects of propolis extract (PE) in a murine model. AAN was developed to retain circulating PCS and IS using C57BL/6 mice, mimicking human CKD. The kidney sizes/masses, renal function indicators, plasma concentrations of PCS/IS, tissue expressions of TIF, α-SMA, collagen IaI, collagen IV and signaling pathways in transforming growth factor-β (TGF-β) family were analyzed among the control, PE, AAN, and AAN-PE groups. PE ameliorated AAN-induced renal atrophy, renal function deterioration, TIF, plasma retention of PCS and IS. PE also suppressed α-SMA expression and deposition of collagen IaI and IV in the fibrotic epithelial-mesenchymal transition. Notably, PE treatment in AAN model inhibited not only SMAD 2/3-dependent pathways but also SMAD-independent JNK/ERK activation in the signaling cascades of TGF-β family. Through disrupting fibrotic epithelial-mesenchymal transition and TGF-β signaling transduction pathways, PE improves TIF and thereby facilitates renal excretion of PCS and IS in AAN. In light of multi-faced toxicity of AAs, PE may be capable of developing a new potential drug to treat CKD patients exposed to AAs.