DNA repair capacity of cultured human lymphocytes exposed to mutagens measured by the comet assay and array expression analysis

Repair of mutagen-induced DNA lesions during transportation, storage and cultivation of lymphocytes may have a significant impact on results obtained in human biomonitoring after occupational and environmental exposure of human populations to genotoxic chemicals. Using the comet assay in combination with the repair inhibitor aphidicolin and array gene expression analysis of 92 DNA repair genes, we investigated the repair of DNA lesions induced by methyl methanesulfonate (MMS) and benzo[a]pyrenediolepoxide (BPDE) in phytohaemagglutinin (PHA)-stimulated cultured human lymphocytes in the time segment before replication. The comet assay indicated fast repair of MMS-induced damage during the first hours of cultivation. In contrast, removal of BPDE-induced lesions was slower and significant amounts of damage seem to persist until S-phase. Gene expression analysis revealed that PHA stimulation had a clear effect on gene regulation in lymphocytes already during the first 18h of cultivation. Under the conditions of this study, genotoxic concentrations of MMS did not induce significant changes in gene expression. In contrast, exposure to BPDE led to altered expression of several genes in a time- and concentration-related manner. Of the significantly up-regulated genes, only two genes (XPA and XPC) were directly related to nucleotide excision repair. Our results suggest that PHA stimulation of human lymphocytes influences the expression of DNA repair genes in human lymphocytes. The effect of induced DNA damage on gene expression is comparatively low and depends on the mutagens used. PHA-stimulated lymphocytes repair induced DNA damage before they start to replicate but the repair activity during the first 18h of cultivation is not affected by changes in the expression of DNA repair genes during this period of time.