Caffeine post-treatment causes a shift in the chromosome aberration types induced by mitomycin C, suggesting a caffeinesensitive mechanism of DNA repair in G2

Human lymphocytes were exposed in G₁ to mitomycin C (2.5 µMfor 2 h) and harvested at 3-h intervals from 48 to 84 h afterstimulation. All cultures were also post-treated in G₂ withcaffeine (2mM). Different types of chromosomal aberrations werescored in the first division metaphases. Caffeine increasesall chromosome aberration types by promoting a premature mitosisof damaged cells. However, when the frequency of damaged cellsis not affected by the caffeine post-treatment, a reductionof the frequency of the exchange-type aberrations was shown.The possibility that caffeine interferes with some mechanismof G₂ repair is discussed. ¹To whom correspondence should be addressed