Intercellular Communication in the Propagation of Bystander Effect and Genomic Instabilty in Human Cells after X-ray, Proton and Carbon

Purpose: Radiation-induced bystander effect and genomic instability have important implication in radiotherapy. Their persistence in the progeny may contribute to risk of long-term effect, including cancer. This study investigates the role of gap junction intercellular communication (GJIC) and the quality of radiation in the propagation of stressful effect in bystander cells and their progeny.\nMaterial and methods: Confluent Human skin fibroblasts were exposed to microbeam irradiations with different linear energy transfer (LET) at mean absorbed dose of 0.4 Gy, in the presence or absence of GJIC inhibitor (AGA) by which 0.036-0.4% of cells were directly targeted by radiation. After 4 h irradiation or following 20 population doublings, the cells were harvested and assayed for micronucleus (MN) formation, gene mutation and protein oxidation.\nResults: Our results showed that high-LET carbon microbeams (LET ～103 keV/um) and high-LET proton microbeams (LET ～11 keV/um) were more effective than low-LET X ray microbeam (LET ～6 keV/um) in the induction of DNA damage in bystander cells. Interestingly, significant attenuation of MN formation occurred in bystander cells in the presence of AGA after proton and carbon microbeams. In contrast, incubation of the cells with AGA did not significantly affect the induction of MN formation in bystander cells after X irradiation. Further, the progeny of bystander cells exposed to X rays or protons showed persistent oxidative stress which correlated MN formation and mutation frequency. Such effects were not observed after carbon ions. Importantly, the progeny of bystander cells from cultures exposed to protons or carbon ions under conditions where GJIC was inhibited harbored reduced oxidative and genetic damage. This mitigating effect was not detected when the cultured were exposed to X rays. The overall results show the expression of stressful effects in the bystander cells and their progeny are dependent on LET.\nConclusions: Our findings suggest that the involvement of GJIC-dependent of radiation quality in the propagation of radiation-induced stress to bystander cells and their progeny. In addition, this work provides a strong support to the fact that carbon can significantly reduce the risk of cancer and have potential implications in the therapeutic outcome of radiotherapy.15th International Congress of Radiation Researc