Effects of radiation quality and dose rate on radiation-induced nucleoplasmic bridges in human peripheral blood lymphocytes

https://doi.org/10.1016/j.mrgentox.2021.503321Get rights and content

Highlights

  • 12C6+ induced NPB have a good dose-response relationship at 0–8 Gy.

  • The RBE values of 12C6+ to 60Co γ-rays decrease with increased NPB frequencies.

  • 60Co γ- rays-induced NPB frequencies are affected by the specific dose rates.

Abstract

Previous studies showed that the yield of cobalt-60 γ-rays-induced nucleoplasmic bridges (NPB) in human peripheral blood lymphocytes is dose dependent. However, the influence of the radiation quality and dose rates on NPB frequencies has not been investigated. The present study aimed to investigate NPB frequencies in human peripheral blood lymphocytes induced by carbon ions and explore the dose rate effect on cobalt-60 γ-rays-induced NPB. To establish dose-response curves, human peripheral blood samples were irradiated with 0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 and 8.0 Gy of carbon ions at a dose rate of 3.0 Gy/min in vitro. To explore the dose rate effect, human peripheral blood samples were irradiated with 2.0 and 5.0 Gy of cobalt-60 γ-rays at dose rates of 0.2, 0.5, 1.0, 3.0, 5.0 and 10.0 Gy/min in vitro. NPB and micronuclei (MN) in binucleated cells were analyzed with the cytokinesis-block micronucleus cytome assay. Results showed that the dose-response curve of carbon ion-induced NPB frequencies follow a linear-quadratic model (R2 = 0.934). The relative biological effectiveness (RBE) values of carbon ions to cobalt-60 γ-rays decreased with increased NPB frequencies (ranging from 2.47 to 5.86). Compared with group 1.0 Gy/min, the NPB frequencies in groups 10.0 Gy/min (2.0 Gy), 5.0 and 10.0 Gy/min (5.0 Gy) were decreased significantly (P < 0.05). Carbon ion-induced NPB in human peripheral blood lymphocytes have a good dose-response relationship. Cobalt-60 γ-rays-induced NPB frequencies are affected by the specific dose rate.

Introduction

With the development and utilization of nuclear energy and radiation resource, accidental exposures are frequently occurring. These accidents, such as Chernobyl accident in 1986 or Fukushima accident in 2011, are attracting increased attention because radiation significantly pollutes the environment and affects the health status of populations in a long period. In addition to mass casualty accidents, isolated radiation accidents or industrial accidents can also cause human death and injury. Biological dose assessment of individuals is the key to emergency preparedness and clinical treatment, thus an accurate and rapid radiation biodosimetry is very important after radiation accident [1]. Moreover, biodosimetry for the determination of biological effects should also be focused.

The cytokinesis-block micronucleus (CBMN) assay for scoring micronuclei (MN) has been the efficient method in the field of radiation emergencies [2]. CBMN assay is a rapid and simple method for measuring DNA damage events. Since 2007, this method has been developed as the CBMN cytome assay by Fenech [3] and becomes a comprehensive system for measuring chromosome breakage, DNA misrepair, chromosome loss, nondisjunction, necrosis, apoptosis and cytostasis [4]. Nucleoplasmic bridge (NPB) is a continuous DNA-containing structure linking the two main nuclei in a binucleated cell, which could also be scored because it is a biomarker of chromosome rearrangement, DNA misrepair, and telomere end fusions [5].

NPB frequencies in human peripheral blood lymphocytes and lymphoblastoid cell lines increase after exposure to X-ray, neutron and radon [[6], [7], [8]]. Our previous studies have shown that the yield of cobalt-60 γ-rays-induced NPB in human peripheral blood lymphocytes are dose-dependent [9,10], similar results have also been found by Cheong et al. and Thomas et al. [11,12]. These studies have suggested that NPB is a sensitive biomarker of ionizing radiation exposure, and NPB frequencies increase with the increased absorbed dose of ionizing radiation.

NPB frequencies in binucleated cells are strongly correlated with dicentric and ring chromosome (dic + r) frequencies in metaphases of the same environment condition cultures [9,12,13] Moreover, the background frequency of NPB in healthy population is relatively low [[14], [15], [16]], which is close to the background frequency of dic + r, but much lower than that of MN. NPB can also be easily identified because of its simple morphological criteria, and may have the possibility of autonomous analysis [17,18]. Therefore, NPB combines the advantages of chromosome aberration (CA) and CBMN assays.

When nuclear or radiation accidents occur, high and low linear energy transfer (LET) radiations at different dose rates are usually combined. LET is the energy deposited per unit length along the trajectory of an ionizing radiation quantum or particle. The biological effects of ionizing radiation depend on the absorbed dose; and these effects are also affected by energy distribution. High LET radiations are generally based on an energy deposition peak (Bragg peak) at the end of their tracks. When exposed to the same dose of ionizing radiation, biological effect induced by high LET radiation is higher than that by low LET radiation. High LET radiations also lead to a higher relative biological effectiveness (RBE) value than low LET radiation for cell killing, reduced oxygen effect and cell cycle [19]. The RBE of an ionizing radiation, which depends on radiation quality, dose and cell radiosensitivity, is the most important parameter of information in clinical radiobiology and radiotherapy. This value is generally measured for a particular biological endpoint relative to observation made in a reference field, such as the cobalt-60 γ-rays or X-ray. Therefore, information on both radiation quality and dose rate is indispensable for accurately estimated the biological dose.

An ideal radiation biodosimeter should have a good dose-dependent manner on both high and low LET ionizing radiations. However, effects of radiation quality and dose rate on radiation-induced NPB have not been systematically investigated yet. This study aimed to establish the dose-response curve of NPB in human peripheral blood lymphocytes induced by carbon ions, to explore the RBE values of carbon ions to cobalt-60 γ-rays, and the dose rate effect of γ-rays-induced NPB.

Section snippets

Subjects and human peripheral blood samples

This work was conducted at the National Institute for Radiological Protection (NIRP), Chinese Center for Disease Control and Prevention. The ethics committee of NIRP approved all the designed experiments in this study. The scope of this study was explained to each subject, and signed informed consents were obtained.

Human peripheral blood samples, donated by 2 males, were collected to establish the carbon ion-induced NPB dose-response curve as well as to explore the dose rate effect on NPB. The

Dose-response curve of carbon ion-induced NPB

To establish the dose-response curve of carbon ion-induced NPB, around 125–2000 binucleated cells were analyzed from each dose level. The number of binucleated cells available for each sample decreased with the increased absorbed dose of carbon ions (Table 1). About 1000 or more binucleated cells could be observed after exposure to around 0–4.0 Gy of carbon ions, whereas the number of binucleated cells available was less than 300 after exposure to more than 6.0 Gy of irradiation. NDI decreased

Discussion

In the present study, high LET ionizing radiation (carbon ions)-induced NPB in human peripheral blood lymphocytes in vitro was investigated. The dose-response curve between the NPB yield and the absorbed doses of carbon ions (0–8.0 Gy) was established. The RBE value of carbon ions to cobalt-60 γ-rays and the dose rate effect of ionizing radiation-induced NPB were also analyzed.

To establish the dose-response curve of carbon ion-induced NPB, sufficient binucleated cells from each dose level were

Conclusions

NPB is a sensitive biomarker of early chromosome damage events induced by both high and low LET ionizing radiations. High LET ionizing radiation (carbon ions)-induced NPB in human peripheral blood lymphocytes have a good dose-response relationship at 0–8 Gy. Carbon ions has higher RBE value than cobalt-60 γ-rays. Cobalt-60 γ-rays-induced NPB frequencies are affected by the specific dose rate.

Funding

National Natural Science Foundation of China [Grant number: 81573081].

Declaration of Competing Interest

The authors have no conflict of interest to declare.

Acknowledgments

This work was supported by the National Natural Science Foundation of China [grant number 81573081]. We thank the blood donors in this study for their contributions.

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      Such a DNA-containing connection forms a NPB after one cell division. Ionizing radiation-induced NPB frequency increases with absorbed dose [20,21]. Our previous studies indicated favorable dose-effect relationships for NPB frequency at both high doses and relatively low doses.

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