Study of DNA damage induction and repair capacity of fresh and cryopreserved lymphocytes exposed to H2O2 and gamma-irradiation with the alkaline comet assay.

The alkaline SCGE assay was evaluated for use with cryopreserved lymphocytes in order to obtain results similar to the freshly isolated ones. The induction of DNA damage as well as the repair capacity of gamma-rays and H2O2 exposed cryopreserved human lymphocytes was found to be the same to that of the freshly isolated. Human lymphocytes (fresh or cryopreserved) responded differently to the effects of gamma-irradiation if compared to the H2O2 treatment. The distribution of DNA damage among gamma-irradiated lymphocytes was more homogeneous compared to H2O2, both in freshly isolated and in cryopreserved cells. 2.4 micrograms/ml phytohemagglutinin at the start of a 2-h incubation in RPMI of cryopreserved samples gave similar DNA repair and distribution patterns to the 2-h post-exposure incubation of freshly isolated lymphocytes. H2O2-induced DNA damage was not repaired completely. However, the repair of gamma-rays-induced DNA damage was more efficient. These findings confirm the different mode of action of the two agents on the induction of DNA damage, as well as, the different response of the lymphocytes' DNA repair system.