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Kidney Int. 2003 May;63(5):1671-80.

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

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Department of Pharmacology, Tokyo Women's Medical University, School of Medicine, Tokyo, Japan.



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).


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.


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.


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.

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