Inhibition of Na+/H+ exchange decreases albumin-induced NF-kappa B activation in renal proximal tubular cell lines (OK and LLC-PK1 cells)

Filtered proteins play a role in the pathogenesis of renal interstitial inf lammation and fibrosis. At least part of these effects are mediated by the nuclear factor kappaB (NF-kappaB). Receptor-mediated endocytosis of protein s like albumin in renal M p mal tubular cells is in part dependent on Na+/H + exchanger (NHE) isoform 3. We tested the hypothesis that pharmacological inhibition of NHE-3 reduces albumin-induced NF-kappaB activation - and ther efore albumin-induced renal interstitial inflammation and fibrosis - using established proximal tubular cell lines (OK and LLC-PK1). 5-(N-ethyl-N-isoropyl)-amiloride (EIPA) or HOE694 were use to inhibit NHE. Albumin endocytosis was determined by fluorometric analysis of FITC-BSA upt ake. Electromobility gel shift assays were performed in order to determine the NF-kappaB-specific DNA-binding activity. EIPA reduced albumin uptake in OK and LLC-PK1 cells and HOE694 decreased al bumin uptake in LLC-PK1 cells, with IC50 values corresponding to NHE-3 inhi bition. Furthermore, albumin-induced increases in NF-kappaB DNA-binding act ivity were partially inhibited by EIPA in OK and LLC-PK1 cells. HOE694 at a concentration of 100 mu mol/l similarly decreased albumin-induced NF-kappa B DNA-binding activity. Cytosolic acidification by propionic acid did not p revent BSA-induced activation of NF-kappaB. Inhibition of BSA endocytosis b y chlorpromazine decreased NF-kappaB activation. NHE-dependent albumin endocytosis induces an increase in NF-kappaB-specific protein activity in renal proximal tubular cells in culture, which is decr eased by EIPA and HOE694. Thus, inhibition of albumin uptake might be a the rapeutical strategy to prevent albumin-induced NF-kappaB activation and alb umin-associated inflammatory or fibrotic renal pathomechanisms in vivo.