Recovery kinetics of micronucleus formation by fractionated X-ray irradiation in various types of human cells

Abstract

High-dose ionizing radiation is sufficient for breaking DNA strands, leading to cell death and mutations. By contrast, the effects of fractionated ionizing radiation on human-derived cells remain unclear. To better understand the genotoxic effects of fractionated ionizing radiation, as well as the cellular recovery rate, we investigated the frequency of micronucleus (MN) formation in various types of human cells. We irradiated cells with fractionated X-ray doses of 2 Gy at a rate of 0.0635 Gy/min, separated into two to eight smaller doses. After irradiation, we investigated the frequency of MN formation. In addition, we investigated the rate of decrease in MN frequency after irradiation with 1 or 2 Gy X-rays at various recovery periods. Fractionated irradiation decreased MN frequency in a dose-dependent manner. When the total dose of X-rays was the same, the MN frequencies were lower after fractionated X-ray irradiation than acute irradiation in every cell type examined. The rate of MN decrease was faster in KMST-6 cells, which were derived from a human embryo, than in the other cells. The rate of MN decrease was higher in cells exposed to fractionated X-rays than in those exposed to acute irradiation. Recovery rates were very similar among cell lines, except in KMST-6 cells, which recovered more rapidly than other cell types.

Variation of 4 MV X-ray dose rate in fractionated irradiation strongly impacts biological endothelial cell response in vitro

“…Dose fractionation is a powerful means of enabling healthy tissues to tolerate high doses of exposure. Numerous studies have focused on in vitro fractionated irradiations (Terashima et al, 2017;Koyama et al, 2018), with most of the work essentially being based on normofractionated schemes (daily fraction of 2 Gy) on cancerous human cells (Brodin et al, 1991;Hedman et al, 2011;van den Berg et al, 2020). Nevertheless, several studies have investigated fractionated irradiation on normal human cells (Boerma et al, 2003;Cerv elli et al, 2014) with the dose per fraction usually being up to 2 Gy.…”

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“…Moreover, low frequency electromagnetic field is itself is composed of extremely low frequency (ELF) with frequencies up to 300 Hz, and intermediate frequency with frequencies between 300 Hz and 10 MHz. Induction-heating ovens, computers, compact fluorescent lamps, inductive metal heating and welding and anti-theft systems at the exits of shops are examples of intermediate frequency electromagnetic fields sources [6,7]. Also, it should be noted that the use and transmission of electricity in general generate the ELF-electromagnetic field (EMF) [8].…”