The quinoid dihydropteridine reductase (QDPR) has been suggested to be an important modulator of diabetic nephropathy through the regulation of the TGF-β1/Smad3 signaling pathway [93] and to play an important role as a protective factor against oxidative stress [94], while NQO1 polymorphism has been recently associated with the risk of diabetic nephropathy [95]. Here, SMAD3 is linked to diabetic kidney disease.