DNA damage and metallothionein synthesis in human hepatoma cells (HepG2) exposed to cadmium.
Cadmium is an important heavy metal environmental toxicant, which is classified as a human carcinogen. The comet assay was used to evaluate the levels of DNA damage in a metabolically competent HepG2 cell line after treatment with low, non-cytotoxic and physiologically relevant concentrations of cadmium, alone and in combination with the dietary mutagen 2-amino-3-methyl-imidazo[4,5-f]quinoline (IQ) and with the environmental mutagen benzo[a]pyrene (B(a)P). After exposure of the cells to 10, 100 and 1000 nM CdCl(2), a dose- and time-dependent increase of DNA damage was detected. Maximal damage was found after 12 h of treatment, but declined with further incubation with CdCl(2). The increased synthesis of metallothioneins on exposure to CdCl(2) up to 12 h suggests that they are responsible for the adaptation of HepG2 cells to the DNA damaging effects of CdCl(2). Co-treatment of the cells with CdCl(2) (10-1000 nM) and IQ (300 microM) induced a dose-dependent increase of DNA damage compared to cells treated with IQ alone. Co-genotoxic activity was also observed by increased formation of micronuclei in cells exposed to IQ and 1000 nM CdCl(2); at this concentration, CdCl(2) alone also induced micronuclei in HepG2 cells. Our results support the hypothesis that direct and indirect mechanisms are involved in cadmium-induced DNA damage.
Fatur
T
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Department of Genetic Toxicology and Cancer Biology, National Institute of Biology, Vecna pot 111, 1000, Ljubljana, Slovenia.
Tusek
M
M
Falnoga
I
I
Scancar
J
J
Lah
T T
TT
Filipic
M
M
D000222:Adaptation, Physiological; D001564:Benzo(a)pyrene / Q000633:toxicity; D002104:Cadmium / Q000008:administration & dosage / Q000633:toxicity*; D002273:Carcinogens / Q000008:administration & dosage / Q000633:toxicity*; D006528:Carcinoma, Hepatocellular; D002470:Cell Survival / Q000187:drug effects; D020552:Comet Assay; D004249:DNA Damage / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008099:Liver / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D008113:Liver Neoplasms; D008668:Metallothionein / Q000096:biosynthesis*; D009153:Mutagens; D011804:Quinolines / Q000633:toxicity; D013997:Time Factors; D014407:Tumor Cells, Cultured
D002273:Carcinogens; D009153:Mutagens; D011804:Quinolines; D002104:Cadmium; C029216:2-amino-3-methylimidazo(4,5-f)quinoline; D001564:Benzo(a)pyrene; D008668:Metallothionein