Effect of nitrilotriacetate (NTA) on cation balance in the rat

NTA and Fe(III)NTA: differential patterns of renal toxicity in subchronic studies

Differential patterns in terms of nephropathology and 8-hydroxyguanine formation in the course of oral 28-day studies were observed with nitrilotriacetic acid (NTA) and FeNTA. FeNTA, but not NTA, caused enhanced 8-hydroxyguanine formation in kidney DNA after oral and intraperitoneal administration. Enhanced lipid peroxidation in the kidney homogenate was observed with FeNTA as well as with NTA. For NTA, the low dose (9 mg/kg per day) was without adverse effect. The kidney toxicity of oral FeNTA (50, 200, and 1000 mg/kg per day) was only mild, 50 mg/kg per day; however, it still led to an increased 8-hydroxyguanine content. The relevance of Iron(III) (Fe(III)) or Fe(III)NTA formation as a relevant mediator of NTA-related toxicity was excluded on the basis of these data. Also, a thermodynamic consideration presented here, supports the view that zinc (Zn), and not Fe, is likely to mediate the tubular cell cytotoxicity of NTA.

A review of the environmental and mammalian toxicology of nitrilotriacetic acid

This article provides a review of available information on the chemistry, environmental toxicology, and mammalian toxicology of nitrilotriacetic acid (NTA). The ability of NTA to chelate metal ions such as Mg++ and Ca++ into water soluble complexes makes NTA useful as an additive to boiler water, as a builder in laundry detergents, and as a stabilizer in textile, paper, and pulp processing. Environmental fate studies show NTA biodegrades in wastewater treatment plants, in natural waters, and in soils under a wide variety of conditions. Studies on the environmental effects of NTA indicate that no adverse effects occur in treatment plants or receiving waters at anticipated levels. Monitoring programs have established that only low steady-state concentrations of NTA occur in natural waters as a result of NTA usage. In mammalian systems, NTA is not metabolized and is excreted rapidly by filtration in the kidney. No reproductive, teratogenic, or adverse bone effects have been observed at highly exaggerated doses. In numerous genotoxicity assay systems, both in vivo and in vitro, NTA is nongenotoxic. Chronic oral exposure of rodents to high doses of NTA is associated with tumorigenicity in, and restricted to, the urinary tract. The urinary tract tumors are the consequence of chronic toxicity that is caused by changes in Zn and Ca distributions between the urinary tract tissues and urine at high doses of NTA. Thresholds for the effects of NTA on Zn and Ca distributions are 10(5) to 10(6) greater than the possible maximum human exposure resulting from the low levels of NTA that are known to occur in the environment.

Reversibility of renal cortical lesions induced in rats by high doses of nitrilotriacetate in chronic feeding studies

The effects in the renal cortex of the male rat of continuous administration of a high dose of nitrilotriacetate (NTA) for 24 months were compared with those of the administration of a similar dose for 18 months followed by a 6-month recovery period on the control diet. The results suggest that discontinuation of treatment interrupts the sequence of events leading to tumour formation. This study indicates that all stages in the proposed pathogenesis of renal tubular tumour formation by NTA, up to the occurrence of adenomatous hyperplasia and neoplasia, are reversible. Apparently, tumour development is dependent on the continuous administration of high doses of NTA in the presence of toxic injury to the majority of nephrons.

Alterations of renal tissue structure during a 30-day gavage study with nitrilotriacetate

Nitrilotriacetate (NTA), as the monohydrated trisodium salt, was administered by gavage to male Sprague-Dawley rats at levels of 0, 0.73 or 7.3 mmol/kg body weight/day for periods of up to 30 days. Two animals from each of the groups were killed 24 hr after dosing on day 9, 13, 16, 20, 23, 27 or 30. Cytoplasmic vacuolation and hyperplasia of the proximal convoluted tubules were the most prominent alterations observed by light microscopic examination of kidney tissue from both groups of NTA-treated rats. The number and severity of the lesions was greater in the high-dose group and in this group, erosion and hyperplasia of the pelvic transitional epithelium were also noted. The results of this study suggest that NTA-associated urinary tract lesions develop in a sequential pattern and that the rate and extent of these lesions is dose dependent.

The effects of nitrilotriacetate on cation disposition and urinary tract toxicity

In this review a summary is presented of the experimental evidence that has led to the development of hypotheses to explain how the chronic ingestion of nitrilotriacetate (NTA), which is a non-mutagenic, non-metabolized and non-accumulating compound, might induce urinary tract toxicity that can lead to neoplasia. The hypotheses attribute the toxic process to alterations in divalent cation (M2+) distribution in the urinary tract during the processing of NTA for excretion in the urine. The hypotheses do not identify a 'carcinogen' per se but rather define conditions that must exist for the initiation and propagation of toxicity that is an essential precursor of and accompanies tumours associated with chronic, high dosage NTA ingestion. The proposed hypotheses are consistent with all available information on NTA toxicity and define ingestion doses that do not alter urinary tract M2+ distributions and do not initiate urinary tract toxicity after chronic exposure. The existence of no-effect doses that must be exceeded for the initiation and propagation of toxicity negates the validity of mathematical extrapolations of possible tumour incidence at doses below the threshold levels from the results obtained in chronic, high dosage experiments. The thresholds determined in the experimental animals are several orders of magnitude greater than human exposure via drinking-water based upon measured NTA concentrations in Canada where NTA has been used in detergents since 1970.

Short-term effects of dietary nitrilotriacetic acid in the male Charles River rat kidney

Trisodium nitrilotriacetate monohydrate was fed to male weanling Charles River rats for 28 days. Clinical evidence of urinary tract toxicity included hydronephrosis and nephromegaly. Microscopically, severe renal injury was recognized specifically as convoluted tubular cytoplasmic vacuolation and pelvic epithelial erosion. Hyperplasis occurred as a sequela to these specific cytotoxic alterations.