thioguanine-anhydrous and lead-chromate

The genotoxicity of soluble and insoluble hexavalent chromium compounds was studied in mammalian cell assays which detect base substitution, deletion, addition, and frameshift mutations [6-thioguanine resistance in Chinese hamster ovary cells], primarily base substitution mutations [ouabain resistance in Chinese hamster ovary and C3H/10T1/2 Cl 8 mouse embryo fibroblasts (10T1/2)] and morphological transformation [focus formation] in 10T1/2 cells. Soluble hexavalent CaCrO4, administered in either acute (5-h) or subacute (24-h) dosing regimens, induced dose-dependent cytotoxicity and mutation to 6-thioguanine resistance in Chinese hamster ovary cells but no mutation to ouabain resistance or focus formation in transformation assays, although the acute treatment induced a high frequency of conversion of 10T1/2 cells to adipocytes. Cell lines established from cloned adipocytic cells were not morphologically transformed and did not grow in soft agarose. PbCrO4 did not induce mutation to either 6-thioguanine or ouabain resistance but did induce a reproducible dose-dependent, low frequency of focus formation in 10T1/2 cells. Cell lines established from PbCrO4-induced foci stably formed foci when coseeded with 10T1/2 cells, had 3-5-fold increased saturation densities relative to nontransformed 10T1/2 cells, and formed colonies in soft agarose, indicating their likelihood to be neoplastic. Long term exposure of 10T1/2 cells to either CaCrO4 or PbCl2, even at 85% cytotoxic concentrations, or pretreatment of cells with either CaCrO4 or PbCl2 followed by treatment with the alternate compound, did not induce morphological transformation. Treatment of cells with insoluble hexavalent PbCrO4 resulted in progressive and extensive vacuolization of cells in contact with the particles. Progressive cytoplasmic engulfment of PbCrO4 particles was observed using scanning electron microscopy, although PbCrO4 particles were not observed inside vacuoles. These results indicate that the soluble clastogens K2Cr2O7 and CaCrO4 were probably mutagenic by a non-base substitution mechanism but could not transform 10T1/2 cells. In contrast, PbCrO4 was not detectably mutagenic but induced transformation, which could not be explained solely by acute or chronic exposure to dissolution products of either lead or chromate alone. Since PbCrO4 particles were found to be intracytoplasmic in extensively vacuolated cells, we suggest that the unique physiochemical properties of PbCrO4 particles, leadi

Topics: Adipose Tissue; Animals; Calcium Compounds; Cell Transformation, Neoplastic; Cells, Cultured; Chromates; Lead; Mice; Mice, Inbred C3H; Microscopy, Electron; Mutagenicity Tests; Ouabain; Thioguanine

We used the V79 Chinese hamster cell line to detect the induction by NTA of 6-thioguanine resistance, due to mutation at the HGPRT locus, with direct and indirect mutagens as positive controls. NTA was tested within the 10(-4)-1.5 X 10(-2) M concentration range: although it was cytotoxic above the 10(-2) M dose, it did not increase the frequency of mutations at any of the tested concentrations, independently of metabolic activation (rat-liver S9 fraction). NTA is known to dissolve heavy metals and therefore to increase their genotoxicity. We found that an insoluble Cr(VI) compound, lead chromate (PbCrO4), was not cytotoxic nor mutagenic on V79 cells, probably because it is taken up by the cells very slowly, whereas the presence of NTA (2.5 X 10(-3) M in water) elicited a direct cytotoxicity and mutagenicity, which was dose-dependent from 5 X 10(-5) M to 10(-4) M PbCrO4. This effect was due to solubilization of the chromate anion by NTA, as determined by comparing spectrophotometric determinations of Cr(VI) in PbCrO4 treatment solutions with a mutagenicity titration curve obtained with a completely soluble Cr(VI) salt (potassium dichromate, K2Cr2O7).

Topics: Acetates; Animals; Cell Line; Cell Survival; Chromates; Cricetinae; Cricetulus; Drug Resistance; Lead; Mutation; Nitrilotriacetic Acid; Potassium Compounds; Solubility; Thioguanine