Formamidopyrimidine-DNA glycosylase enhances arsenic-induced DNA strand breaks in PHA-stimulated and unstimulated human lymphocytes

To confirm that arsenic (As) induces oxidative DNA damage in phytohemagglut inin (PHA)-stimulated and unstimulated human lymphocytes, we used the alkal ine comet assay combined with specific enzyme [formamidopyrimidine-DNA glyc osylase (FPG)] digestion to measure As-induced base damage. The results sho wed that the enzyme-sensitive sites were readily detected with the alkaline comet assay after the cells were treated with 10 muM AS for 2 hr. The repa ir patterns observed for FPG-created DNA single strand breaks (SSBs) in As- treated cells were comparable to those in hydrogen peroxide (H2O2)-treated cells. The enzyme-created SSBs, As-induced base damage, were more significa nt in PHA-stimulated lymphocytes. About 63% and 68% of SSBs induced by As a nd H2O2, respectively, were repaired in PHA-stimulated lymphocyces by 2-hr repair incubation, but about 34% and 43%, respectively, were repaired in un stimulated cells. About 40% and 49% of base damage induced by As and H2O2, respectively, were repaired in PHA-stimulated lymphocytes, but about 19% an d 21%, respectively, were repaired in unstimulated cells. These results ind icated that As induced oxidative DNA damage in human lymphocytes at micromo lar concentrations. The damaged bases could be chiefly purines or formamido pyrimidines. Like the damage induced by H2O2, As-induced DNA damage was rep aired more slowly in unstimulated lymphocytes.