Field size effects on DNA damage and proliferation in normal human cell populations irradiated with X-ray microbeams

Abstract

To clarify the health risks of internal radiation exposure, it is important to investigate the radiological effects of local exposure at cell levels from radioactive materials taken up by organs. Focusing on the response of cell populations post-irradiation, X-ray microbeams are very effective at reproducing the effects of local exposure within an internal exposure in vitro. The present study aims to clarify the effects of local exposure by investigating the response of normal human cell (MRC-5) populations irradiated with X-ray microbeams of different beam sizes to DNA damage. The populations of MRC-5 were locally irradiated with X-ray microbeams of 1 Gy at 0.02–1.89 mm2 field sizes, and analyzed whether the number of 53BP1 foci as DSB (DNA double strand break) per cell changed with the field size. We found that even at the same dose, the number of DSB per cell increased depending on the X-irradiated field size on the cell population. This result indicated that DNA damage repair of X-irradiated cells might be enhanced in small size fields surrounded by non-irradiated cells. This study suggests that X-irradiated cells received some signal (a rescue signal) from surrounding non-irradiated cells may be involved in the response of cell populations post-irradiation.

Inflammatory Signaling and DNA Damage Responses after Local Exposure to an Insoluble Radioactive Microparticle

“…Meanwhile, the protective effects were maximal at the smallest in-field size of 25% ( Figure S6B ). Ojima et al reported the increase in nuclear 53BP1 foci with X-irradiated field size [ 12 ], and Lam et al reported rescue effects on 53BP1 foci at 12 h post-irradiation with a 2.5% irradiated cell population [ 46 ]. The tendency of survival data ( Figure S6 ) agrees well with these data on 53BP1 foci [ 12 , 46 ].…”

“…Ojima et al reported the increase in nuclear 53BP1 foci with X-irradiated field size [ 12 ], and Lam et al reported rescue effects on 53BP1 foci at 12 h post-irradiation with a 2.5% irradiated cell population [ 46 ]. The tendency of survival data ( Figure S6 ) agrees well with these data on 53BP1 foci [ 12 , 46 ]. The potential underlying mechanisms of protective effects might be attributable to the reduction in early DNA damage by antioxidants [ 8 , 59 ] or stimulated DNA repair [ 52 , 53 , 54 ].…”

“…There are several reports on responses of human normal cells to local radiation exposure [ 8 , 11 , 12 ]. Among them, our previous in vitro study reported on the spatial distribution of DNA double-strand breaks (DSBs), which was detected by the histone H2AX phosphorylated on serine 139 (γ-H2AX foci) at DSB sites [ 13 , 14 ], after 24 h exposure to Cs-BMP with 505.7 Bq [ 8 ].…”

Effects of spatial variation in dose delivery: what can we learn from radon-related lung cancer studies?

“…The larger the field area, the higher the incidence of skin disorders, even with the same absorbed skin dose (Coggle et al 1984 ; Peel et al 1984 ; Hopewell et al 1993 ). Recently, Ojima et al ( 2021 ) was able to demonstrate RIFSE utilizing an X-ray microbeam setup to expose human cell populations with different exposure field sizes. Shortly after 1 Gy exposure, significantly more nuclear repair foci (53BP1) were observed in cells present in the larger exposure fields compared to cells in the smaller fields.…”

Radiation-Induced Rescue Effect: Insights from Microbeam Experiments

“…The Radiation-Induced Field Size Effect (RIFSE) refers to the phenomenon that radiobiological effects in a cell population depend on the irradiation field size and volume in addition to the absorbed dose [ 17 ]. RIFSE was reported by Coggle et al [ 18 ] and Peel et al [ 19 ] almost 40 years ago when they found that different β-particle doses were required for skin reactions with different irradiation field size.…”