A case of caffeine-mediated cancellation of mitotic delay without enhanced breakage in V79 cells

Chinese hamster cells (V79 379A) were grown for 17 h in the presence of 10 micrograms/ml bromodeoxyuridine (BrdU) to obtain cells with potential sister-chromatid differentiation. At this time batches were irradiated (1.5 Gy, 250 kVp X-rays) and the medium of all flasks replaced with one containing 10 micrograms/ml thymidine with or without 400 micrograms/ml caffeine. Metaphases from irradiated and unirradiated batches were sampled every hour for 7 h and FPG stained. All categories of chromatid-type aberrations were scored in G2 and S phase cells. As expected, mitotic delay in the presence of caffeine, (measured by a shift in the portion of the fraction of differentially stained metaphases (FDM) curve and a reduced fall in the mitotic index) was largely cancelled, but there was a negligible increase in chromatid-aberration frequency (all categories), only achieving significance if the consistency of the whole 7-h sampling period was considered. Caffeine had no effect on the frequencies of light/dark chromatid involvement, nor in the completeness of chromatid interchanges. We conclude that the enhanced breakage frequency often observed with post-irradiation caffeine treatment is not necessarily causally related to the cancellation of delay.