FN1 and diabetic kidney disease: Curcumin, a polyphenolic compound found in Curcuma Longa L. (Zingiberaceae), has been reported to down-regulate SphK1 and S1P expression, inhibit FN and TGF-β1 production mediated by the SphK1-S1P signaling pathway, and exert nephroprotective effects by ameliorating DKD fibrosis (103, 104).