The effect of butylated hydroxytoluene on the chromosomal damage induced by bleomycin in Chinese hamster ovary cells

Abstract

The effect of butylated hydroxytoluene (BHT) on chromosomal damage induced by bleomycin (BLM) in CHO cells was studied. Treatments were performed in cells at quiescent state (90/95% at G 0–G 1), 2 h after subculture (G 1) or 3 h before fixation (G 2). Cells were treated for 20 min with BLM plus BHT and subsequently incubated in the presence of BHT until fixation. Results were compared with those obtained from untreated and DMSO-treated controls, from treatments with BLM or BHT alone, from treatments with BLM followed by treatment with DMSO until fixation, and from treatments with BLM plus BHT for 20 min without post-treatment with BHT. BLM induced chromatid- and chromosome-type aberrations in cells treated at G 0/G 1 or G 1 and chromatid-type aberrations in cells treated at the G 2 stage. Post-treatment with BHT strongly decreased the frequency of chromosome- but not of chromatid-type aberrations in G 0/G 1 and G 1 and of chromatid-type aberrations in G 2. These results are explained assuming that chromosome-type aberrations induced at G 0/G 1 and G 1, and chromatid-type aberrations induced at G 2 are originated by the induction of double-strand breaks by BLM through the formation of free radicals. Thus, the observed effect of BHT post-treatment could be considered as evidence that chromosome aberrations are induced by BLM following a two-step mechanism. On the other hand, it is necessary to differentiate between chromatid-type aberrations induced by BLM at G 0/G 1 and those produced by G 2 treatment on the basis of replication errors for the former and DNA repair errors for the latter. In addition, the induction of chromatid-type aberrations by BHT itself at G 0/G 1 must be taken into account. As BHT acts as an S-dependent agent, chromatid-type aberrations observed after treatment with BLM and BHT in G 0/G 1 could arise from single-strand breaks induced by BLM and DNA primary lesions induced by BHT.