Early proximal tubule injury in experimental aristolochic acid nephropathy: functional and histological studies.

BACKGROUND: Aristolochic acid (AA), the plant extract of Aristolochia species, is involved in the onset of progressive tubulointerstitial renal fibrosis in humans. Clinical and in vitro findings have previously suggested that the proximal tubule was the target of AA. METHODS: Using a rat model of AA nephropathy, the proximal tubular lesions induced by daily subcutaneous injections of AA for 35 or 5 days were characterized biochemically and histologically. Urinary excretion of proteins, albumin, low molecular weight proteins, N-acetyl-beta-d-glucosaminidase, alpha-glutathione S-transferase, leucine aminopeptidase and neutral endopeptidase (NEP) was determined and related to histological conventional findings and immunostainings of NEP and megalin. RESULTS: In both protocols, an acute phase of release of urinary markers was observed within the first 3 days of AA treatment in parallel with a significant increase of specific AA-related DNA adducts reflecting early tubular intoxication. A dramatic loss of the proximal tubule brush border was histologically confirmed, while the expression of megalin decreased at the damaged apical epithelium (mainly of the S3 segment). CONCLUSION: Proximal tubule injury occurs early after AA intoxication in rats, with a link between specific AA-DNA adduct formation, decreased megalin expression and inhibition of receptor-mediated endocytosis of low molecular weight proteins, bringing in vivo confirmation of previous in vitro studies.

Basolateral chloride transporters in autosomal dominant polycystic kidney disease.

Transepithelial Cl(-) secretion mediated by apical cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channels plays a key role in cyst fluid accumulation in autosomal dominant polycystic kidney disease (ADPKD). The molecular identity of the basolateral transporter(s) responsible for Cl(-) entry in ADPKD cells is unknown, although pharmacological studies suggest that a bumetanide-sensitive Na(+)-K(+)-2Cl(-) cotransporter (NKCC/BSC) is involved. We investigated the expression of NKCC1, CFTR and anion exchanger type I (AE1) in ADPKD kidneys and cultured ADPKD cells. Immunoblotting and immunoprecipitation detected NKCC1 at ~170 kDa in ADPKD cells and kidney extracts. Immunostaining located NKCC1 in one-third of ADPKD cysts, with a pattern of basolateral reactivity. Staining of serial sections showed that cysts positive for NKCC1 also stained for CFTR. Additional studies demonstrated that AE1 is expressed in ADPKD kidneys, and is located at the basolateral pole of CFTR-positive ADPKD cysts that do not express NKCC1. RT-PCR and sequence analyses confirmed the selective expression of NKCC1 or AEI in cultured ADPKD cells that also express CFTR. The fact that most CFTR-positive ADPKD cysts also express NKCC1 suggests that transepithelial Cl(-) secretion in ADPKD involves molecular mechanisms similar to secretory epithelia. AE1 might be an alternative basolateral pathway for Cl(-) in a minority of cysts.