A comparison of the DNA-damaging, the cytotoxic and genotoxic properties of tetracycline in human fibroblasts in the presence and absence of light.

The reduction of the colony-forming ability, the induction of DNA strand breaks and DNA repair were determined in human fibroblasts after treatment with tetracycline (TC) in the presence and absence of light. In all experiments human fibroblasts were more sensitive to incubations of TC in the light than in the dark. Induction of DNA single-strand breaks and DNA repair were detected in the cells after a 1-h incubation with TC under light but not in the dark. In contrast to these results, TC induced single-strand breaks in isolated PM2 DNA in the dark, however, to a lower extent than in the presence of light. In both cases strand break formation was totally suppressed by adding catalase. The formation of a TC-derived radical by ESR and a decomposition product by UV-vis spectroscopy was observed in the presence and absence of light; their rate of formation in the dark was much smaller than in the light.