TGFB1 and chronic kidney disease: p-Cresol sulfate (PCS) and indoxyl sulfate (IS) contribute to CKD progression through renal tubular damage or tubulointerstitial fibrosis by activating free-radical production, upregulating nuclear factor (NF)-κB and plasminogen activator inhibitor type 1(PAI-1), and enhancing the expression of transforming growth factor beta 1 (TGFβ), tissue inhibitor of metalloproteinase (TIM), and pro-alpha 1 collagen [3].