Induction of micronuclei in human fibroblasts and keratinocytes by 25 kV x-rays

Abstract

A relative biological effectiveness (RBE) not much larger than unity is usually assumed for soft x-rays (up to approximately 50 keV) that are applied in diagnostic radiology such as mammography, in conventional radiotherapy and in novel radiotherapy approaches such as x-ray phototherapy. On the other hand, there have been recent claims of an RBE of more than 3 for mammography and respective conventional x-rays. Detailed data on the RBE of soft x-rays, however, are scarce. The aim of the present study was to determine the effect of low-energy x-rays on chromosomal damage in vitro, in terms of micronucleus induction. Experiments were performed with 25 kV x-rays and a 200 kV x-ray reference source. The studies were carried out on primary human epidermal keratinocytes (HEKn), human fibroblasts (HFIB) and NIH/3T3 mouse fibroblasts. Micronucleus (MN) induction was assayed after in vitro irradiation with doses ranging from 1 to 5.2 Gy. Compared to the effect of 200 kV x-rays, 25 kV x-rays resulted in moderately increased chromosomal damage in all cell lines studied. This increase was observed for the percentage of binucleated (BN) cells with micronuclei as well as for the number of micronuclei per BN cell. Moreover, the increased number of micronuclei per micronucleated BN cell in human keratinocytes and 3T3 mouse fibroblasts suggests that soft x-rays induce a different quality of damage. For all cell lines studied the analysis of micronucleus induction by 25 kV soft x-rays compared to 200 kV x-rays resulted in an RBE value of about 1.3. This indicates a somewhat enhanced potential of soft x-rays for induction of genetic effects.

Low-Dose Radiation Response of Primary Keratinocytes and Fibroblasts from Patients with Cervix Cancer

“…Comparison of the means of MN induction for fibroblasts and keratinocytes obtained after irradiation has shown keratinocytes to be at least twice as resistant as fibroblasts (Table 3). In the previous work (13), greater MN induction in human fibroblasts than in keratinocytes was found after X irradiation. Similarly, in cell survival studies, Geara et al (21) and D'Errico et al (22) found keratinocytes to be more radioresistant (higher surviving fraction) than fibroblasts after irradiation.…”

“…The MN assay has been described in detail (12,13). In brief, earlypassage cells (third-passage fibroblasts and second-passage keratinocytes) in exponential growth were seeded (at a density of 5 ϫ 10 4 /dish) onto 35-mm petri dishes (Nunc) with 2 ml medium as above, with two dishes per dose.…”

Multiparametric radiobiological assays show that variation of X-ray energy strongly impacts relative biological effectiveness: comparison between 220 kV and 4 MV

“…To date, no extensive study has compared two beams of X-rays with high and low energy at the same dose rate or has combined a wide range of biological outputs. Only few studies have reported a higher RBE for X-rays compared to the reference beam (200–250 kV) 12–15 . Nevertheless, these studies were performed on very low energy X-rays (below 50 kV) and not necessarily at the same dose rate than the reference X-rays beam.…”

“…1C). Interestingly, it is now known that exposure to very low-energy X-rays (25–30 kV) leads to high levels of DNA damage 12 or micronuclei 15 . But, surprisingly, our two beams are within the range of energy from 0.1 to 3 MeV for which an RBE of 1 is classically ascribed 1 .…”

Relation between DNA double-strand breaks and energy spectra of secondary electrons produced by different X-ray energies

“…Most of the observations reported in the literature concern mis-repair of DNA doublestrand breaks, including those of Mestres et al who showed an increase in chromosome aberrations in lymphocytes irradiated with 30 kV, 80 kV and 120 kV X-rays. Slonina et al showed induction of micronuclei with human fibroblasts and keratinocytes irradiated with 25 kV and Lehnert et al with human mammary epithelial cells irradiated with 25 kV and 10 kV X-rays (Slonina et al 2003;Lehnert et al 2006;Mestres et al 2008;Lehnert et al 2008). In addition, some studies have focused on clonogenic survival, including a study by Panteleeva et al, who showed a decrease in clonogenic survival with primary human epidermal keratinocytes and fibroblasts irradiated with 25 kV compared to 200 kV (Panteleeva et al 2003).…”