The influence of nonprotein thiols on DNA damage induced by bleomycin in single human cells.

Nonprotein thiols are considered radioprotectors, preventing DNA damage by ionizing radiation. Because bleomycin (BLM) is a radiomimetic agent, it was proposed that thiols may prevent DNA damage produced by this antibiotic. However, results obtained with treatments combining thiols and BLM in living cells are contradictory. The goal of this study was to analyze the DNA damage induced by BLM and the influence of 3 nonprotein thiols of different electrical charges and chemical compositions at the level of single cells (comet assay). We also studied the morphological signs of apoptosis produced by BLM in these same conditions. We found that all thiols potentiated DNA damage induced by BLM, most probably by reactivating the BLM complex once it generated free radicals. Cysteamine (positive) potentiated BLM action the most, glutathione (negative) potentiated this antibiotic the least, whereas cysteine had an intermediate effect compared with the other two.