DIFFERENCES IN BASAL AND INDUCED DNA SINGLE-STRAND BREAKS BETWEEN HUMAN PERIPHERAL MONOCYTES AND LYMPHOCYTES

The aim of this study was to compare the susceptibility of peripheral monocytes and lymphocytes to oxidant-induced DNA single-strand breaks (SSB). DNA damage was assessed by the alkaline single-cell gel electro phoresis (SCGE) assay. Total peripheral mononuclear leukocytes (PML), PML enriched in lymphocytes and PML enriched in monocytes were used. T he basal rate of SSB was measured after in vitro incubation of cells f or 1 h in phosphate-buffered saline, and the induced rate after incuba tion in 10 mu M or 50 mu wM H2O2. Incubation was performed at 4 degree s C to limit the possible influence of DNA repair. Lymphocyte-enriched PML were obtained after adhesion of the monocytes to tissue-culture t reated plastic, and monocyte-enriched PML by removal of monocytes from the plastic through trypsin. In all samples, cell differentiation was performed using an immunofluorescence technique with antibodies again st T- and B-lymphocytes and cytospin preparations. The rate of SSB was determined by visual scoring according to 6 predefined categories of DNA damage and was expressed as mean score (range 0-500) per 100 cells . There was a linear relationship between the percentage of lymphocyte s in the samples and the basal rate of SSB (p < 0.001, slope 0.67 scor e units per %). The same was true for induced DNA damage after incubat ion in 10 mu M H2O2 (p < 0.001, slope 3.80 score units per %) or 50 mu M H2O2 (p < 0.001, slope 3.22 score units per %). These regression an alyses revealed a 2.9-fold greater rate of basal DNA damage in lymphoc ytes compared to monocytes and an 11.3-fold greater rate for the damag e induced by 10 mu M H2O2. We conclude that there are marked differenc es in the rate of basal and induced SSB between lymphocytes and monocy tes, suggesting differences in antioxidant capacity between the two ce ll populations. These findings indicate that the assessment of SSB for biomonitoring and genotoxicity testing using PML has to take into acc ount possible changes in cellular composition.