Safflower extract: A novel renal fibrosis antagonist that functions by suppressing autocrine TGF‐beta

Progressive renal disease is characterized by the accumulation of extracellular matrix proteins in the renal interstitium. Hence, developing agents that antagonize fibrogenic signals is a critical issue facing researchers. The present study investigated the blood-circulation-promoting Chinese herb, safflower, on fibrosis status in NRK-49F cells, a normal rat kidney interstitial fibroblast, to evaluate the underlying signal transduction mechanism of transforming growth factor-beta (TGF-β), a potent fibrogenic growth factor. Safflower was characterized and extracted using water. Renal fibrosis model was established both in vitro with fibroblast cells treated with β-hydroxybutyrate and in vivo using rats undergone unilateral ureteral obstruction (UUO). Western blotting was used to examine protein expression in TGF-β-related signal proteins such as type I and type II TGF-β receptor, Smads2/3, pSmad2/3, Smads4, and Smads7. ELISA was used to analyze bioactive TGF-β1 and fibronectin levels in the culture media. Safflower extract (SE) significantly inhibited β-HB-induced fibrosis in NRK cells concomitantly with dose-dependent inhibition of the type I TGF-β1 receptor and its down-stream signals (i.e., Smad). Moreover, SE dose-dependently enhanced inhibitory Smad7. Thus, SE can suppress renal cellular fibrosis by inhibiting the TGF-β autocrine loop. Moreover, remarkably lower levels of tissue collagen were noted in the nephron and serum TGF-β1 of UUO rats receiving oral SE (0.15 g/3 ml/0.25 kg/day) compared with the untreated controls. Hence, SE is a potential inhibitor of renal fibrosis. We suggest that safflower is a novel renal fibrosis antagonist that functions by down-regulating TGF-β signals. J. Cell. Biochem. 104: 908–919, 2008. © 2008 Wiley-Liss, Inc.