Detection of DNA primary damage by premature chromosome condensation in human peripheral blood lymphocytes treated with methyl methanesulfonate.

Abstract

Methyl methanesulfonate (MMS) is a direct acting methylating agent which produces apurinic sites that are transformed into DNA single-strand breaks by base excision repair. MMS-induced DNA lesions have to be transformed by DNA synthesis in order to give rise to chromosomal damage. In this study the premature chromosome condensation (PCC) technique was used in G(1) human lymphocytes treated with MMS to investigate whether, with this technique, chromosomal damage could be detected without the cell needing to undergo DNA synthesis. A dose-dependent increase in chromosomal fragmentation was indeed observed in G(1) lymphocytes. MMS treatment at 1.3, 2.5 and 5 mM was characterized by the appearance of highly fragmented chromosomes. This observation induced us to further investigate whether this effect was more connected with triggering of apoptotic cell death than a consequence of the PCC technique. Data obtained by nuclear morphology analysis, by Trypan blue exclusion assay and pulsed field gel electrophoresis seem to suggest that the observed chromosome fragmentation could be due to the onset of apoptosis. Consequently, one should bear in mind that the PCC technique can overestimate chromosomal damage when apoptosis is also induced.