Different patterns of kidney toxicity after subacute administration of Na-nitrilotriacetic acid and Fe-nitrilotriacetic acid to Wistar rats.

Na-nitrilotriacetic acid (Na3NTA) and Fe-nitrilotriacetic acid (FeNTA) have both been described to cause tumors in the urinary tract of rodents. However, these effects were observed using different modes of administration at extremely different dose levels and explained by different mechanisms. Whereas FeNTA causes an iron overload of cells and is genotoxic in various assays, Na3NTA is predominantly bound to zinc in vivo and thereby causes cytotoxic effects in the urinary tract. In contrast to FeNTA, Na3NTA requires high dose levels to produce tumors. The aim of this study was to compare the effects of Na3NTA and FeNTA on cellular proliferation, histopathology, lipid peroxidation, and 8-OH-2'-deoxyguanosine levels in the kidneys as well as on the urinary excretion of Ca, Fe, and Zn. For evaluation of DNA synthesis both compounds were administered for 1 or 4 weeks to 14-week-old male Wistar rats at a tumor causing dose, Na3NTA via the diet at 150 ppm and 20,000 ppm (approximately 9 and approximately 1000 mg/kg/day) and FeNTA i.p. at 25 mg/kg/day. An osmotic minipump, containing 20 mg/ml BrdU, was implanted subcutaneously 7 days before necropsy. Na3NTA showed nearly no effect on DNA replication after 1 week but a strong reaction after 4 weeks. The increase was 10- to 18-fold in different renal compartments. The enhancement of proliferation in the proximal tubules was nearly twice that in the distal tubules. In contrast, FeNTA caused DNA replication during the first week, and this was restricted to the proximal tubules. After 4 weeks there was an 18-fold increase in the outer stripe and no effect in the inner stripe of the outer medulla. The data presented give evidence to the assumption that both substances increase cell proliferation as a compensatory mechanism, causing different pattern of tubular proliferation in terms of time course and affected cell types. Both Na3NTA at 20,000 ppm and FeNTA led to increased lipid peroxidation, whereas increased levels of 8-OH-2'-deoxyguanosine were observed only after treatment with FeNTA. Urinary excretion of Zn was increased 30-fold after administration of 20,000 ppm Na3NTA but only 2-fold after administration of FeNTA. Urinary excretion of Ca and Fe remained unchanged after treatment with either Na3NTA and FeNTA. These results show that the Na3NTA-related proliferative effects are not mediated by an internal formation of FeNTA.