Mammalian cell transformation induced by Cr(VI) compounds in the presence of nitrilotriacetic acid (NTA)

Abstract

NTA, which was frequently proposed as a substitute for polyphosphates as a builder in household detergents, at high doses is an established animal renal carcinogen, whose mutagenicity is still questionable, so that it is generally considered as an indirect, non mutagenic carcinogen. In short-term tests, NTA was found able to induce mammalian cell transformation in cultured BALB/c 3T3 mouse cells as well as in rat embryo cells infected with leukemia virus. The induction of anchorage-independent growth (soft-agar assay) in BHK 13–21 Syrian hamster fibroblasts was studied by scoring colonies visible to the naked eye at 20–25 days after plating: cells capable of extended anchorage-independent growth are defined as transformants. Survival was determined by plating control and treated cells in liquid medium without agar, and by counting the number of macroscopic colonies after 7 days. Mitomycin C and 4-nitroquinoline oxide were used as reference direct transforming agents. No significant increase in the spontaneous transformation rate of BHK cells was induced by NTA concentrations ranging from 2×10 −3 to 10 −2 M although the survival index was significantly reduced above 4×10 −3 M NTA. NTA can very efficiently sequester metal ions as water soluble complexes, and the genotoxicity of metal compounds is generally increased in the presence of NTA. Two Cr(VI) compounds, K 2Cr 2O 7 which is highly soluble in water, and CaCrO 4 which is only partially soluble, were tested in the soft agar assay either in the absence or in the presence of NTA. When used alone, both compounds behaved as positive transforming agents. NTA increased up to ten times the cytotoxicity and the transforming activity of both Cr(VI) compounds. On the basis of the amounts of Cr(VI) detectable in the K 2Cr 2O 7 and CaCrO 4 solutions in the absence and in the presence of NTA, a synergistic interaction between NTA and soluble Cr(VI) can be inferred.