ABSTRACT
Seven different test systems were utilized to investigate the genetic activity of chromium compounds: infidelity of DNA replication in vitro by DNA pol alpha from calf thymus, damage of DNA detected by alkaline elution in treated mammalian cells or in DNA purified and treated in vitro, DNA repair synthesis in mammalian cells in vitro detected by autoradiography or scintillation counting after labelling with [3H]dThd, gene mutations in the Salmonella typhimurium Ames test, gene mutations (6TG resistance) in cultured hamster cells, sister-chromatid exchanges in different rodent cell cultures, and transformation to anchorage-independent growth of hamster cells in vitro (soft-agar assay). Potassium dichromate and chromium chloride were used as water-soluble Cr(VI) and Cr(III) salts. Several reference mutagens (EMS, MMS, MMC, 4NQO) were included in the single tests as positive controls. Cr(VI) was active in all the tested systems, except in the induction of DNA damage and DNA repair synthesis in cultured cells. Cr(III), on the other hand, was absolutely inactive unless a direct interaction with purified DNA was permitted by the test conditions. The relevance of data from the various tests to the understanding of the mechanisms of the genotoxic activity of chromium is discussed. Effects other than the direct interaction of Cr(III) with DNA are inferred, which can cause infidelity of the DNA polymerase functions.
Subject(s)
Chromium/toxicity , Mutagens , Mutation , Animals , Cell Adhesion/drug effects , Cell Line , Cricetinae , Cricetulus , DNA Repair/drug effects , DNA Replication/drug effects , DNA-Directed DNA Polymerase/metabolism , Drug Resistance , Lung , Mutagenicity Tests , Salmonella typhimurium/drug effects , Sister Chromatid Exchange/drug effects , Structure-Activity RelationshipSubject(s)
Chromates/pharmacology , Chromium Compounds , Chromium/pharmacology , DNA/metabolism , Kidney/drug effects , Polynucleotides/metabolism , Potassium Dichromate/pharmacology , RNA/metabolism , Animals , Cell Line , Chlorides/pharmacology , Cricetinae , Hot Temperature , Nucleic Acid Denaturation/drug effects , Nucleic Acid Renaturation/drug effects , Spectrophotometry, UltravioletABSTRACT
Our observations about the cytotoxic and cytogenetic effects of hexavalent and trivalent chromium compounds in mammalian cells cultured in vitro are reviewed. Additional data concerning the induction of chromosomal aberrations and sister chromatid exchanges, the inhibition of nucleic acid and protein synthesis, the interference with nucleotide metabolism, and the modification of membrane-linked enzyme activity are reported. A possible mechanism of chromium action is proposed.
Subject(s)
Chromium/toxicity , Animals , Carcinogens/toxicity , Cell Line , Chromium/metabolism , DNA/biosynthesis , Mutagens/toxicity , Protein BiosynthesisABSTRACT
The cytotoxic effects of hexavalent (k(2)Cr(2)O(7)) and trivalent (CrCl(3)) chromium compounds have been studied in cultured hamster fibroblasts (BHK line) and human epithelial-like cells (HEp line).K(2)Cr(2)O(7) stimulates the uptake of labelled thymidine into the soluble intracellular pool (the stimulation of nucleoside uptake represents a specific effect of Cr(6+)) while Cr(3+) always exerts an inhibitory action. DNA Synthesis is inhibited by treatment with both chromium compounds, but especially by K(2)Cr(2)O(7). Moreover, the effective CrCl(3) concentrations reduce the sensitivity of DNA and RNA to hydrolysis with perchloric acid. Treatments with k(2)Cr(2)O(7) in balanced salt solution, where Cr(6+) reduction is less marked, induce more pronounced cytotoxic effects than treatments in complete growth medium.HEp cells turned out to be more sensitive to K(2)Cr(2)O(7) than BHK fibroblasts: in the former line TdR uptake is less stimulated, DNA synthesis and cell survival are more affected. Survival of BHK cells to K(2)Cr(2)O(7) indicates a multi-hit mechanism of cell inactivation, the extrapolation number being about 10.On the basis of quantitative Cr determinations in the treatment solutions and in the treated cells, the cytotoxic effects of Cr are attributed to the action of Cr(6+) at the plasma membrane level on the mechanisms involved in nucleoside uptake, and to the interaction of Cr(3+) at the intracellular level with nucleophilic targets on the DNA molecule.
