Inhibition of Na+/H+ exchange suppresses albumin-induced NF-kappa B activation

Several studies support a role of filtered albumin in the pathogenesis of r enal interstitial inflammation and fibrosis. At least, parts of these effec ts are mediated by the nuclear factor kappaB (NF-kappaB). Na+-H+ exchanger (NHE) isoform 3 supports receptor-mediated endocytosis of albumin in renal proximal tubular cells by a yet not completely understood mechanism. We tes ted the hypothesis that pharmacological inhibition of NHE reduces albumin-i nduced NF-kappaB activation using established proximal tubular cell lines. We exposed opossum (OK) and porcine (LLC-PK1) renal proximal tubular cells to bovine serum albumin (BSA). To inhibit NHE, 5-(N-ethyl-N-isopropyl)-amil oride (EIPA) was used. Albumin endocytosis was determined via FITC-BSA upta ke studies, and NF-kappaB-specific DNA-binding activity in BSA-exposed cell s was detected by electromobility gel shift assays (EMSAs). EIPA reduced al bumin uptake in OK and LLC-PK1 cells, with IC50 values corresponding to NHE -3 inhibition. The albumin-induced increase in NF-kappaB DNA-binding activi ty was prevented by EIPA in OK and LLC-PK1 cells. NF-kappaB activation by t he phorbol eater PMA was not affected by EIPA. We suggest that NHE-dependen t albumin endocytosis induces an increase in NF-kappaB-specific protein act ivity in renal proximal tubular cells in vitro, which is impaired by EIPA. Thus inhibition of albumin uptake in proximal tubular cells might be a ther apeutical strategy to prevent albumin-induced NF-kappaB activation and albu min-induced inflammatory or fibrotic renal pathomechanisms in vivo.