The effects of patulin and patulin-cysteine mixtures on DNA synthesis and the frequency of sister-chromatid exchanges in human lymphocytes.

The effects of patulin and patulin-cysteine mixtures on DNA synthesis in human blood lymphocytes were measured by assaying incorporation of [3H]thymidine into cellular DNA. Patulin inhibited and patulin-cysteine mixtures stimulated the incorporation of [3H]thymidine into DNA. The inhibitory action of patulin diminished with time in culture. Patulin was found to be unstable in the culture medium. The sister-chromatid exchange (SCE) frequency was significantly elevated by intermediate concentrations (0 . 1-0 . 2 micrograms/ml culture) of the toxin. The cells are protected from the effect at low concentrations of the toxin. There may be excessive damage at higher concentrations but only the unaffected cells go into mitosis. Therefore an increased frequency of SCEs is detected only at intermediate concentrations, or, at higher concentrations, with early harvesting. Cysteine seems to potentiate the effect of patulin on SCE frequency.