US EPA

2210300 

Journal Article 

The induction of sister-chromatid exchanges in Chinese hamster ovary cells by prolonged exposure to 2-acetylaminofluorene and S-9 mix 

Takehisa, S; Wolff, S 

1978 

1 

Mutation Research
ISSN: 0027-5107
EISSN: 1873-135X 

HEEP/79/04754 

58 

1 

103-106 

HEEP COPYRIGHT: BIOL ABS. Mutagenic carcinogens induce sister-chromatid exchanges (SCE) in cells at concentrations that do not increase ordinary chromosome aberrations. Therefore, the SCE test has been established as a sensitive test for the effects of DNA-damaging chemicals in mammalian cells. This test can detect effects on DNA not only by direct-acting chemicals, but also by some procarcinogens that require metabolic activation. When cells were treated with 10-4 M 2-AAF (2-acetylaminofluorene) alone for 24 h there was only a slight increase in SCE. A 30 min treatment with 10-4 M 2-AAF plus S-9 Mix (rat liver microsomes supplemented with an NADPH generating system) gave no increase. If, however, the time of treatment with 2-AAF plus S-9 Mix was extended to 2.5 h, the yield of SCE was approximately doubled. The same effect was noted after treatment with an activating system containing the supernatant from the gently centrifuged homogenate of Aroclor-induced rat liver. When the activating system contained the supernatant from uninduced liver or phenobarbital-induced liver there was no marked increase. In these cases, however, there always was a slight increase over the yields obtained without metabolic activation. Increasing the treatment time of cells with 2-AAF plus S-9 Mix from 2.5 to 5 h brought about a greater increase in SCE. Treatment of cells for 30 min with medium containing 2-AAF and S-9 Mix that had been pre-incubated for 5 h without cells significantly increased the yield of SCE. Pre-incubation without cells for only 2.5 h resulted in a higher yield than in controls, but the difference was not significant. With time the active metabolites of 2-AAF produced by in vitro enzymatic activity accumulate in the medium. Although coincubation of the in vitro metabolic activation system with CHO (Chinese hamster ovary) cells was not necessary to bring about an increase in SCE, such coincubation led to a far greater increase.