Comparing the Genotoxic Effects Induced by Folate Deficiency to Those Induced By Ionizing Radiation in Cultured Human Lymphocytes

DNA double-strand breaks (DSB) which is the primary cause of chromosomal aberrations and cancer and the most serious DNA lesion caused by ionizing radiation, are also caused by several common vitamin or mineral deficiencies such as folate, B6, or B12. In the current study, cultured human lymphocytes were either irradiated at low and high doses or cultured at different levels of folate deficiency to assess: cell proliferation, apoptosis, cell cycle, DNA single-strand (SSB) and double strand (DSB) breaks and changes in gene expression. Both, radiation and folate deficiency, decreased cell proliferation and induced DNA breaks, apoptosis, and cell cycle arrest. Cells irradiated with 1 Gy had proliferation rate of ∼50% that of unirradiated cells; 5 Gy completely abolished lymphocyte proliferation. The proliferation rate of cells cultured in 12 nM folate was 46% that of control cells and lymphocytes cultured in 0 nM folate did not proliferate. Irradiated lymphocytes showed cell cycle arrest in G2/M phase in a dose dependant manner. The G2/M arrest was still evident 72 h after irradiation. In contrast to radiation, folate deficiency caused an arrest in the S phase of the cell cycle in an apparently dosedependent manner. DNA breaks as measured by the alkaline Comet assay were increased for radiation doses of 1 Gy and higher, although statistical significance was achieved only at 5 Gy. Similarly, cells cultured in low folate showed a dose-dependent increase in DNA breaks. For the conditions used in this study, physiological concentrations of folate deficiency (12 nM) induced as much DNA damage as did 1 Gy of radiation, a relatively high dose. Results suggest that physiological levels of folate deficiency cause as much DNA damage as relatively high levels of ionizing radiation, but with a different cellular response. The results also suggest that low doses of radiation can induce radio adaptive response, protecting the cells from damage induced by subsequent irradiation. This adaptive response has not been observed for folate deficiency.