Mutation Research/Genetic Toxicology and Environmental Mutagenesis
Antioxidant status and cytogenetic damage in hospital workers occupationally exposed to low dose ionizing radiation
Introduction
Ionizing radiation (IR) is like a double-edged sword. It is either useful in medicine for diagnosis and treatment of human diseases or an important contributor to the occurrence of occupational diseases such as cataracts, cardiovascular disturbance, and cancer. [[1], [2], [3]] High doses of IR are clearly known to induce acute and chronic effects in humans, but the risk of LDIR remains controversial. Many factors, such as adaptive responses, non-target effects, and low-dose hypersensitivity, affect the long term outcome of low-dose exposures [4,5]. Still, effects associated with exposure to IR in the low-dose range led to damaging changes such as genomic instability, chromosomal aberrations, and cell death [4,[6], [7], [8], [9], [10]]. The ICRP recommends an effective dose limit of 20 mSv per year, averaged over 5 years, with the further provision that the effective dose should not exceed 50 mSv in any year [11]. Hospital workers are the occupational group that is most consistently exposed to LDIR [12]. Although in many hospital radiology units the radiation exposure remains below these levels, there is a higher risk for hospital workers handling diagnostic X-ray machines and cameras due to their chronic exposure to LDIR. Consequently, the potential risk for detrimental effects associated with LDIR in hospital workers is still a matter of debate. [6,13]
It is known that IR can induce oxidative stress through the generation of reactive oxygen species (ROS), resulting in oxidative damage to biomolecules such as DNA, proteins, and lipids. [[14], [15], [16]] Otherwise, evidence indicates that the involvement of ROS in primary pathological mechanisms is a feature mainly of extraneous physical or chemical perturbations, in which radiation is perhaps the major contributor [17]. Oxygen radicals are known to induce membrane peroxidation and MDA formation which are both harmful to cellular function [18]. MDA can cause DNA damage and directly inhibit proteins such as sodium/potassium adenosine triphosphatase (Na-K-ATPase) and glutamate transporters [19]. Cells in eukaryotic organisms maintain their vital functions against oxidative stress status with the help of an antioxidant defense system that includes three major classes of antioxidant enzymes: SOD, CAT, and selenium-dependent glutathione peroxidase (Se-GPx) [18,20]. The first line of defense against ROS is SOD, which utilizes superoxide anions to hydrogen peroxide [21]. CAT, a heme-containing enzyme that utilizes hydrogen peroxide produced by SOD [22], functions directly as a free radical scavenger.
High levels of ROS are dangerous and can cause cell damage, resulting in illness. It is a predisposing factor for cancer. [23,24] Many studies have shown that LDIR exposure can generate ROS by upsetting the balance between oxidants and antioxidants in many organs, leading to oxidative DNA damage. The cytokinesis-block micronucleus cytome (CBMN Cyt) assay has been widely used to evaluate DNA damage, cytostasis and cytotoxicity [25,26]. The CBMN technique with cytochalasin-B as the cytokinesis inhibitor, allows evaluation of the MN frequency in dividing cells accumulated in the bi-nucleated stage to overcome the uncertainties associated with in vitro cell-division kinetics that can affect MN expression. The formation of MN is the result of chromosome breakage and loss due to unrepaired DNA damage or chromosome separation caused by mitotic disorders.
MN is considered to be an effective biomarker of diseases and of processes associated with DNA damage. [[27], [28], [29]] Furthermore, the CBMN assay also allows one to calculate the nuclear division index (NDI), providing information on a cell cycle’s delay with regard to exposure [30].
The aim of the present study was to assess occupationally induced oxidative damage and chromosomal damage in a large population of hospital workers exposed to ionizing radiation. To evaluate the status of oxidative stress in hospital staff exposed to chronic LDIR, we measured blood antioxidant enzyme activities (CuZn-SOD, GSH-PX, and CAT) and MDA levels. Scoring of MN formation is a cytogenetic assay commonly used in biodosimetry. We also determined the influence of confounding factors such as age, gender, years of employment, exposure dose, smoking status and alcohol consumption status on antioxidant enzymes, LP and MN frequency.
Section snippets
Study population
The study population comprised 336 participants: 218 full-time medical workers, including technicians, physicians and nurses, were engaged as the exposed group and 118 healthy volunteers were non-exposed controls. The exposed population consisted of 142 male and 76 female participants randomly selected from diagnostic radiology, radiotherapy, interventional radiology and nuclear medicine departments of the same hospital in Chongqing, China, who were chronically occupationally exposed to LDIR.
Characteristics of participants
Demographic characteristics of hospital workers occupationally exposed to LDIR, as well as the non-exposed controls, are presented in Table 1. The median age for both groups was 33 years. Also, the two groups were well balanced with respected to sex distribution. Although fewer exposed participants than controls were smokers and non-drinkers, these differences were not statistically significant. The median value of annual effective dose in exposed workers was 0.48 mSv (25th to 75th
Discussion
In the present study, occupational dosimetry records over the last year ranged from 0.12 to 1.67 mSv and were within the limit established by the ICRP. The levels of exposure in hospitals have been decreased in recent decades below the regulatory limit, although the increasing use of relatively high-dose procedures raises some concerns. A personal dosimeter may underestimate the real exposure, not only because of the detection threshold of dosimeters but also because of improper wearing. [34]
Funding
This study was supported by the National Natural Science Foundation of China (No. 81273105).
Declaration of Competing Interest
The authors declare that there is no conflict of interest.
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