Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
Spectrum of chromosomal aberrations in peripheral lymphocytes of hospital workers occupationally exposed to low doses of ionizing radiation
Introduction
Ionizing radiation is known to induce mutations and cell transformations, predominantly by causing single-strand and double-strand DNA breakage, thereby leading to chromosome instability and carcinogenesis [1], [2]. Human cytogenetic biomonitoring studies using somatic cells have been proposed as pertinent tools to assess the possible genotoxic effects of a hazardous exposure [3], [4]. In particular, longitudinal studies have shown that raised chromosome aberration (CA) frequency in peripheral lymphocytes is associated with increased cancer risk [5], [6], [7]. CA frequency is therefore considered a relevant biomarker for cancer predisposition [5], [6], [7].
CA analysis in peripheral lymphocytes using conventional Giemsa staining has been applied as a suitable approach for detecting the genetic effects of ionizing radiation exposure [8]. Increased CA frequencies were found in accidentally irradiated subjects [9], [10], [11] and in populations living in areas with high levels of environmental radioactivity [12], [13]. Almost all the studies on workers occupationally exposed to ionizing radiation have recorded increased CA frequencies with respect to the general population [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27]. However, the relationship between ionizing radiation exposure levels and the increase of the frequencies of different types of structural chromosome aberrations is not yet completely clarified [14], [15], [16], [21], [22], [27]. While increase of both chromosome rearrangements (dicentric) and breakages have been found in workers exposed to high levels of ionizing radiation [14], [15], [16], [17], [24], [25], in populations with very low accumulated doses the only reported differences have regarded acentric fragments and total aberrant cells [18], [19], [21]. Taken together, these reports suggest that different types of chromosome damage occur at low and high doses of ionizing radiation.
To shed more light on the kinds of genetic damage associated with low-dose exposure, we investigated the frequencies of various types of CA by conventional Giemsa staining in peripheral lymphocytes from hospital workers exposed to low levels of ionizing radiation and from control subjects. In particular, the CA yield was analyzed by considering the effects of dose equivalent over time. Other variables, such as the effects of donor age, gender, smoking status on chromosomal aberration frequencies were also taken into account.
Section snippets
Subjects
The study population of 34 professionals occupationally exposed to ionizing radiation comprised 19 physicians and 15 technicians in the units of radiology, radiotherapy and cardiology at the S. Orsola-Malpighi Hospital in Bologna, Italy. None of these workers were professionally exposed to any carcinogenic agent other than the ionizing radiation. The control group comprised 35 individuals (20 physicians, and 15 administrative staff) working in the same hospital without any work-related exposure
Results
CA assay results are shown in Table 2. The mean frequencies of aberrant cells and of chromosome breaks (at analysis of the spectrum of scored structural CA) were significantly higher in the exposed group (P=0.007; P=0.001). Seven dicentric chromosome exchanges were detected in the exposed group and only three in controls, but the mean frequencies were not significantly different (the very low frequency of this aberration type excluded its use in further statistical analysis). No chromatid
Discussion
In the present study, we investigated the frequencies of various type of CA in peripheral lymphocytes of hospital workers occupationally exposed to very low levels of ionizing radiation. As expected, our results indicated that the overall frequency of aberrant cells was significantly higher in exposed workers than in controls. As regards the spectrum of structural CA, in keeping with other studies [20], [21], [27], we found that exposed workers exhibited significantly increased frequencies of
Acknowledgements
We are grateful to Robin M.T. Cooke for editing the manuscript. This work was jointly supported by a MURST (Ministry of the University and of the Scientific Technology Research) grant (ex 60%) and a special grant to Francesca Maffei from University of Bologna for the project “Giovani Ricercatori”.
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