Time-dependent 53BP1 foci kinetics in X-irradiated human hair follicle dermal papilla cells.

We investigated the feasibility of a biological dosimetry method using human hair follicle dermal papilla cells (HFDPCs). Cultured HFDPCs were X-irradiated at doses of 50-20 000 mGy, and 53BP1 foci were analyzed up to 96 h post-irradiation to assess DNA double-strand break repair kinetics and dose-response relationships. Up to 5 h post-irradiation, 53BP1 foci increased in a significant dose-dependent manner from 50 to 1000 mGy. By 24 h, the foci count at 50 mGy returned to background levels, whereas dose dependence persisted at higher doses. Notably, analysis of the focus size revealed that the proportion of large foci (diameter ≥ 1 μm) significantly increased at doses ≥ 3000 mGy at 24 h. At 96 h post-irradiation, while total focus counts showed limited discrimination, large-foci assessment maintained significant sensitivity for doses as low as 500 mGy). These findings demonstrate that 53BP1 focus counting in HFDPCs allows for dose estimation from 50 mGy at 5 h, while focus size analysis enhances the accuracy for threshold-based estimation of doses ≥ 500 mGy up to 96 h. This study provides foundational data demonstrating the potential of HFDPCs for biological dosimetry and medical triage, warranting further validation using intact hair samples.