Quantitation of genome damage and transcriptional profile of DNA damage response genes in human peripheral blood mononuclear cells exposed in vitro to low doses of neutron radiation

Humans are exposed to ionizing radiation from different sources that include natural, occupational, medical, accidental exposures. Evaluation of the effect of low level of neutron exposure to human cells in vitro has important implications to human health. Attempts were made to measure genome damage, transcriptional profile of DNA damage response and repair genes in peripheral blood mono-nuclear cells (PBMCs) exposed to different doses of  neutron irradiation (241Am-9Be source) in vitro. Blood samples were collected from six random, healthy individuals with written informed consent. The frequency of micronuclei (MN), nucleoplasmic bridges (NPB), DNA strand breaks and gamma-H2AX foci intensity were measured in PBMCs exposed to low doses of neutron (3.0 to 12mGy). Transcription profile of ATM, P53, CDKN1A, GADD45A, TRF1, TRF2, PARP1, NEIL1, MUTYH, APE1, XRCC1, LIG3, FEN1 and LIG1 were analysed in PBMCs at 30 min and 4h post-irradiation using real time quantitative PCR. Our results revealed a significant increase (P≤0.05) in the frequency of MN at 9.0 and 12.0mGy as compared to control. A dose dependent increase in the percentage of DNA in tail and an increased intensity of gamma-H2AX foci were observed. CDKN1A and GADD45A showed marginal up-regulation at 30 min, whereas PARP1 showed increased expression at 4h post-irradiation across the doses studied. The present study revealed that GADD45A, CDKN1A and PARP1 can be used as early signatures for low-dose neutron exposure. However, further in vitro and in vivo studies are required to establish its implications in radiation protection science.