Novel inhibitors of the cellular renin‐angiotensin system components, poricoic acids, target Smad3 phosphorylation and Wnt/β‐catenin pathway against renal fibrosis

Background and Purpose Tubulo‐interstitial fibrosis is the final pathway in the progression of chronic kidney disease (CKD) to kidney failure. The renin‐angiotensin system (RAS) plays a major role in CKD progression. Hence, we determined the efficacy of novel RAS inhibitors isolated from Poria cocos against renal fibrosis. Experimental Approach Effects of three novel tetracyclic triterpenoid compounds, poricoic acid ZC (PZC), poricoic acid ZD (PZD) and poricoic acid ZE (PZE), were investigated on TGFβ1‐ and angiotensin II (AngII)‐treated HK‐2 cells and unilateral ureteral obstruction (UUO) in mice. Immunofluorescence staining, quantitative real‐time PCR, siRNA, co‐immunoprecipitation and Western blot analyses were used to evaluate expression of key molecules in RAS, Wnt/β‐catenin and TGFβ/Smad pathways. Key Results Addition of the above compounds to culture media and their administration to UUO mice: (i) significantly attenuated epithelial‐to‐mesenchymal transition and extracellular matrix production in TGFβ1‐ and AngII‐treated HK‐2 cells and UUO mice by inhibiting Wnt/β‐catenin pathway activation and Smad3 phosphorylation; (ii) selectively inhibited Smad3 phosphorylation by blocking the interaction of TGFBR1 with Smad3; and (iii) specifically inhibited Smad3 activation. PZC and PZD showed a strong inhibitory effect on all RAS components, and PZE showed a strong inhibitory effect on renin. Furthermore, the secolanostane tetracyclic triterpenoids, PZC and PZD, showed a stronger inhibitory effect than the lanostane tetracyclic triterpenoid PZE. Therefore, compounds with secolanostance skeleton showed stronger bioactivity than those with lanostance skeleton. Conclusion and Implications The secolanostane tetracyclic triterpenoids effectively blocked RAS by simultaneously targeting multiple RAS components and lanostane tetracyclic triterpenoids inhibited renin and protected against tubulo‐interstitial fibrosis.