Effects on CD34+ haematopoietic stem cells induced by low doses of alpha irradiation

Abstract

To study the normal cell response to low doses of radiation we have irradiated CD34+ haematopoietic stem cells with alpha particles with doses between 0.3 and 0.6 Gy. Radiation sources used are 222Rn and his daughters 218Po and 214Po previously dissolved in culture medium. CD34+ cells are exposed to alpha radiation and cultured for different times and doses, and later, survival, apoptosis fraction and total cell death (apoptosis and necrosis) are analysed. There are significant differences between irradiated and control cultures on these three parameters. Increases of survival are observed on irradiated cells with regard to control cells, and with decreases on apoptosis and cellular total death. Also we observed that the most remarkable effect was produced on an initial period of 48 hours. This fact is probably due to the major initial sensibility of cells which gradually lose their stem or pluripotential character. That shows a better adaptation of irradiated culture to the stress they suffer. This stress is mainly due to the defrost before culture and growth. Finally, the results are discussed by analysing the observed responses. General mechanisms induced by ionising radiation are analysed, and even the particular ones due to high LET radiation. The relatively low percentage of direct interaction alpha particle-cell, and the observation of an extended response to the whole culture indicates the presence of another extranuclear target. In the same way this gives evidence of intercellular effect transmission. The responsible mechanisms of this bystander effect are also discussed in the conclusions.