Does low dose radiation induced adaptive response influence initial DNA-DSB formation? Evidence from γH2AX foci...

Low-dose radiation-induced adaptive response (LDRIAR) is well documented, but its role in early DNA damage signaling remains unclear. This study aimed to investigate whether adaptive response influences initial DNA double-strand break (DSB) recognition, as reflected by γH2AX foci formation, and to evaluate its time-dependent expression in human lymphocytes.

Peripheral blood lymphocytes from three healthy donors were exposed to a priming dose followed by a challenging dose at defined time intervals. DNA damage was assessed using γH2AX foci analysis, comparing acute and split-dose exposures in both PHA-stimulated (large) and non-stimulated (small) lymphocytes.

A clear time-dependent adaptive response was observed. No significant reduction in γH2AX foci was detected at 1 h (p > 0.05). At 2 h, a significant decrease was observed (∼7-8% in large and ∼13% in small lymphocytes; p < 0.01), which increased at 4 h (∼12% and ∼22%, respectively; p < 0.001). The maximal response occurred at 15 h, with reductions of ∼40-43% in large and ∼27% in small lymphocytes (p < 0.001). Small lymphocytes exhibited an earlier response, while large lymphocytes showed a greater magnitude at later time points. The temporal trend was consistent across donors, with minor variability at later intervals.

The findings demonstrate that LDRIAR is reflected at the level of DNA damage signaling and follows a defined temporal pattern with cell-type specificity. This suggests that adaptive response may influence early DSB-associated processes, contributing to a better understanding of radiation response mechanisms in radiobiology.