The aim of this study was to test the effectiveness of two potent PARP inhibitors in vivo, and to measure their effect on cellular apoptosis and DNA breakage following a low level genotoxic insult in C57Bl/6 mice. Animals were injected intraperitoneally with either PBS vehicle, 3-aminobenzamide (3-AB) or 5-aminoisoquinolinone (5-AIQ). Half of the animals were then subjected to 3 Gy whole body g-irradiation, and sacrificed three hours later. PARP activity was measured in spleen, and was found to be significantly stimulated following g-irradiation. Neither 3-AB nor 5-AIQ displayed significant inhibitory effects in the absence of the genotoxic insult, but both modulated the rise in PARP activity induced by radiation, significantly in the case of 3-AB. Apoptotic index (AI) was assessed in histological sections of spleen and colon by TUNEL assay, but although irradiation induced a significant multiple-fold increase of AI in both tissues after 3 hours, this was not affected by the inhibitory actions of 3-AB or 5-AIQ. Furthermore, neither inhibitor affected the induction of reticulocyte micronuclei, a measure of chromosomal damage, 48 h after treatment in irradiated or unirradiated mice. Our data suggest that inhibitors of PARP activity used in vivo do not abolish residual activity present in resting tissues, but can effectively stifle an excess of activity induced by DNA strand breakage. However, we also conclude that this excess has no measurable effect on the associated increase in cellular apoptosis and chromosomal breakage.

Keywords: PARP, 3-aminobenzamide, 5-aminoisoquinolinone, g-irradiation, micronuclei