Does Radioadaptive Response also Apply to the Case of Heavy-ion Irradiations in Fetal and Adult Mice? Part II. Priming Low Dose of Heavy-ion Irradiations Modifies Detrimental Effects from Challenging High Dose of X-irradiations.

Radiation-induced adaptive response (AR) was described in numerous biological systems. AR research is of great concern as investigations on the conditions essential for AR induction provide important scientific basis for risk estimates and offer significant insight into the novel biological defense mechanisms. However, at whole body level most of the investigations were performed using X-irradiations. In a series of study in progress, possible induction of AR by high LET irradiation of accelerated heavy ions is being tested both in vivo in young adult mice and in utero in fetal mice. Investigations are to verify 1) if priming low-dose X-rays could reduce the detrimental effects, i.e., growth retardation, death or malformation induced by the challenging high dose from heavy-ion irradiations, 2) if low dose of heavy-ion irradiation could induce any AR against the detrimental effects from high dose of X-rays, and 3) if low-dose heavy-ion irradiations could induce any AR against the detrimental effects from the high dose of heavy-ion irradiations. Accelerated heavy ion particles from mono beams of carbon, silicon and ion generated by HIMAC, with the LET values of about 15, 55, and 200 keV/micrometer respectively, are being examined. At the 51st annual meeting of JRRS, we reported that priming low-dose X-rays could modify the detrimental effects from challenging high dose of heavy-ion irradiations. In this work, we will present the new data obtained on AR induction by heavy-ion irradiations in vivo. This is for the first time, at the whole body level, that AR is demonstrated by priming low dose of high LET irradiations. Interestingly, the essential conditions for successful AR induction seem to be dependent on the particle and/or the LET value of the irradiation.