Uremic toxins of organic anions up-regulate PAI-1 expression by induction of NF-kappaB and free radical in proximal tubular cells

Kidney Int. 2003 May;63(5):1671-80. doi: 10.1046/j.1523-1755.2003.00906.x.


Background: Uremic toxins have been suggested to promote progression of chronic renal failure. We have shown that organic anion transporter-mediated uptake of uremic toxins induces oxidative stress in opossum kidney renal tubular cells overexpressing the transporter. Plasminogen activator inhibitor-1 (PAI-1) and nuclear factor-kappa B (NF-kappaB) are major factors known to promote tubulointerstitial fibrosis. The present study examined the signaling pathway that is activated by uremic toxins to induce PAI-1 and activate NF-kappaB in human renal proximal tubular cells (HK-2).

Methods: Uremic toxins in the form of organic anion were examined their ability to induce oxidative stress, PAI-1 gene expression, and NF-kappaB activation in HK-2. PAI-1 expression was measured by enzyme-linked immunosorbent assay (ELISA) and the Northern blotting. Human PAI-1 promoter activity was estimated by luciferase reporter gene (NKkappaB-luc) assay. NF-kappaB activation was measured by the pNFkappaB-luc reporter gene and electrophretic gel mobility shift assay.

Results: Among organic anion species tested, indoxyl sulfate and indoleacetic acid induced free radical production in HK-2. A nonspecific transporter inhibitor (probenecid) suppressed the IS-stimulated radical production. Indoxyl sulfate and indoleacetic acid dose dependently increased the expressions of PAI-1 mRNA and protein in these cells. The luciferase reporter gene assay revealed that indoxyl sulfate and indoleacetic acid dose dependently activated NF-kappaB and PAI-1 promoter. Activation of NF-kappaB was also confirmed by an electrophoretic gel mobility shift assay. Both antioxidant and NF-kappaB inhibitors dose dependently inhibited the activation of PAI-1 promoter by indoxyl sulfate.

Conclusion: Uremic toxins induce free radical production by renal tubular cells and activate NF-kappaB which, in turn, up-regulates PAI-1 expression. Thus, progression of chronic renal failure may be promoted by PAI-1 up-regulation induced by uremic toxins.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anions / pharmacokinetics
  • Cells, Cultured
  • Free Radicals / metabolism
  • Gene Expression / drug effects
  • Humans
  • Indican / pharmacokinetics*
  • Indoleacetic Acids / pharmacokinetics*
  • Kidney Failure, Chronic / physiopathology
  • Kidney Tubules, Proximal / cytology*
  • Kidney Tubules, Proximal / metabolism
  • NF-kappa B / metabolism*
  • Oxidative Stress / drug effects
  • Plasminogen Activator Inhibitor 1 / genetics*
  • Promoter Regions, Genetic / physiology
  • Signal Transduction / drug effects
  • Toxins, Biological / pharmacology
  • Up-Regulation / drug effects
  • Uremia / physiopathology


  • Anions
  • Free Radicals
  • Indoleacetic Acids
  • NF-kappa B
  • Plasminogen Activator Inhibitor 1
  • Toxins, Biological
  • indoleacetic acid
  • Indican