Astragaloside IV synergizes with ferulic acid to inhibit renal tubulointerstitial fibrosis in rats with obstructive nephropathy

BACKGROUND AND PURPOSE The combination of Chinese herbs, Astragali Radix and Angelicae Sinensis Radix, could alleviate renal interstitial fibrosis. Astragaloside IV (AS‐IV) and ferulic acid (FA) are the two major active constituents in this combination. In this study, we employed rats with unilateral ureteral obstruction to determine whether AS‐IV and FA have the same renoprotective effects and investigated the mechanisms of this action. EXPERIMENTAL APPROACH Renal pathological changes were evaluated after treatment with AS‐IV, FA or AS‐IV + FA (AF) for 10 days. Meanwhile, the expression of transforming growth factor β1 (TGF‐β1), fibronectin, α‐smooth muscle actin (α‐SMA), phosphorylation of c‐Jun NH2‐terminal kinase (p‐JNK) and nitric oxide (NO) production in kidney were determined. The expressions of fibronectin, α‐SMA, mitogen‐activated protein kinases [JNK, extracellular signal‐regulated kinases (ERK), P38] in TGF‐β1‐treated NRK‐49F cells or interleukin‐1‐treated HK‐2 cells after AS‐IV, FA or AF were assessed. KEY RESULTS AF alleviated the infiltration of mononuclear cells, tubular atrophy and interstitial fibrosis; reduced the expression of fibronectin, α‐SMA, TGF‐β1 and p‐JNK; and dramatically increased the production of NO in obstructed kidneys. Neither AS‐IV nor FA alone improved renal damage, but both increased NO production. AF inhibited α‐SMA and fibronectin expression in NRK‐49F or HK‐2 cells. Furthermore, AF significantly inhibited IL‐1β‐induced JNK phosphorylation, without affecting ERK or P38 phosphorylation. Neither AS‐IV nor FA alone had any effect on the cells. CONCLUSIONS AND IMPLICATIONS AS‐IV synergizes with FA to alleviate renal tubulointerstitial fibrosis; this was associated with inhibition of tubular epithelial–mesenchymal transdifferentiation (EMT) and fibroblast activation, as well as an increase in NO production in the kidney.