Abstract
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.
Highlights
K2Cr2O7 stimulates the uptake of labelled thymidine into the soluble intracellular pool while Cr3+ always exerts an inhibitory action
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 Cr6+ at the plasma membrane level on the mechanisms involved in nucleoside uptake, and to the interaction of Cr3+ at the intracellular level with nucleophilic targets on the DNA molecule
Chromium (Cr) compounds are carcinogenic in man (Browning, 1969; Furst and Haro, 1969, IARC, 1973) and experimental animals (Hueper, 1961; IARC, 1973; Maltoni, 1974) induce cell transformation in vitro (Fradkin et al, 1975) and give rise to several cytogenetic effects in different biological systems: point mutations (Venitt and Levy, 1974; Nishioka, 1975; Bonatti, Meini and Abbondandolo, 1976), alterations of nucleic acid physico-chemical properties (Herrmann and Speck, 1954; Huff et al, 1964), chromosome aberrations (Glass, 1956) and DNA repair synthesis (Raffetto et al, 1977)
Summary
Treatment of BHK cell cultures for 1-4 h with 10-5M-1_0-3M K2Cr2O7 stimulates nucleoside uptake into the intracellular pool, inhibiting on the contrary nucleic acid synthesis (Levis et al, 1978). The effects of K2Cr2O7 on TdR uptake and on DNA synthesis have been determined in HEp cultures and compared with
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