Aristolochic acid impedes endocytosis and induces DNA adducts in proximal tubule cells

Background. Aristolochic acid (AA), present in Aristolochia plants, appears to be the toxin responsible for Chinese herbs nephropathy (CHN), a rapidly progressive tubulointerstitial nephritis. One of the earliest sign of CHN is the urinary excretion of low-molecular-weight proteins (LMWP), suggesting that AA is toxic to proximal tubules (PT). Methods. The effects of AA on PT functions including reabsorption of LMWP were investigated on the well-established opossum kidney (OK) cell line, a model for PT. and compared with those of the classical PT toxin cadmium chloride (CdCl2). Results. OK cell monolayers internalized albumin and beta2-microglobulin by receptor-mediated endocytosis, both proteins apparently competing for the same receptor, a complex of megalin and cubulin. The process was significantly impaired by 24-hour preincubation with AA (10 or 20 mu mol/L) or CdCl2 (15 mu mol/L). Furthermore, 24-hour exposure to AA followed by its removal during one to six days led to a persistent inhibition of the uptake of albumin, in contrast to the substantial recovery observed after CdCl2 removal. Neither AA nor CdCl2 affected cell viability, Na+-glucose cotransport or total rate of protein synthesis. A A significantly decreased megalin expression and formed specific DNA adducts in OK cells, similar to those found in kidneys from CHN patients. Conclusions. The present data support the involvement of AA in the early PT dysfunction found in CHN; furthermore, they suggest a causal relationship between DNA adduct formation. decreased megalin expression, and inhibition of receptor-mediated endocytosis of LMWP.