Cytogenetic effects of hexavalent chromium in Bulgarian chromium platers

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Abstract

The aim of the present study was to evaluate the genotoxic effects of hexavalent chromium (Cr(VI)) in vivo in exposed Bulgarian chromium platers by using classical cytogenetic and molecular cytogenetic analyses of peripheral lymphocytes and exfoliated buccal cells. No significant difference was observed between the exposed workers and the controls with regard to the frequency of cells with chromosome aberrations (CAs) using conventional Giemsa staining and in the frequency of sister chromatid exchanges (SCEs). However, there was a significant increase in the number of cells with micronuclei (MN) in peripheral lymphocytes from chromium exposed workers as compared to the controls. In the buccal cells from these workers, this increase was even more pronounced. Cytosine arabinoside (AraC), an inhibitor of DNA synthesis and repair, was found to significantly increase the levels of MN in vitro in the lymphocytes of both groups. The increase was more expressed in the lymphocytes of chromium exposed workers. Both centromere positive (C+) as well as centromere negative (C) MN were observed by the fluorescence in situ hybridization (FISH) technique in both of the cell types studied. No difference between C+ and C MN frequencies was found in the lymphocytes as well as in the buccal cells. Thus, Cr(VI) appears to have both clastogenic as well as aneugenic effects in humans.

Introduction

Hexavalent chromium (Cr(VI)) is an established mutagen as well as human carcinogen of the respiratory system, particularly lung carcinogen [1], [2]. The carcinogenic action of some chromium compounds has been demonstrated in laboratory animals, too [3], [4]. Soluble Cr(VI) compounds have a corrosive action to skin and mucous membranes, especially to the nasal septum [3]. Inhaled aerosols of Cr(VI) are readily absorbed from the respiratory tract. In addition, some chromium compounds are found to be nephrotoxic, as well as allergenic [5], [6].

It is considered that genotoxic and carcinogenic activity of Cr(VI) is connected with its metabolism in the cell. Unlike trivalent chromium (Cr(III)), Cr(VI) penetrates easily the cell membrane, and is rapidly taken up by the cell. Intracellularly, Cr(VI) undergoes a complicated cascade of reductive metabolic processes, probably involving redox systems of ascorbate, glutathione or cysteine, etc. Passing through Cr(V) and Cr(IV), it is converted to Cr(III) which is stable. The latter reacts with several cellular constituents including nucleic acids and induces different types of DNA damage such as CAs, DNA strand breaks [5], [6], DNA–protein cross links, as well as homologous and non-homologous somatic recombination [3], [7], [8], [9].

In order to prove the relationship between exposure and cancer risk and to define safe levels of Cr(VI) exposure under occupational conditions, biological monitoring of exposed workers is of main importance. It should include estimations of external and internal exposure as well as studies of early biological effects, e.g. DNA damage, considered as early stages of carcinogenesis. The external exposure is measured by the concentration of Cr(VI) in the air at the working places. The internal exposure should be determined by analyses of body fluids, for example chromium content in urine. Early effects in carcinogenesis are genetic alterations such as chromosome aberrations (CAs), sister chromatid exchanges (SCEs), gene mutations, etc. [10]. The monitoring of these biomarkers is routinely carried out in blood lymphocytes. However, the existing data on the in vivo cytogenetic effects of Cr(VI) as studied on human blood cells are rather contradictory [11], [12], [13], [14] if opposed to the numerous papers reporting its genotoxicity if other end-points are investigated [1], [3], [7]. Whether peripheral blood lymphocytes (PBLs) are suitable for investigations of chromium genotoxic effects under occupational conditions, it is still a matter of dispute. Cr(VI) is known to cause cancer of the respiratory system, particularly lung cancer. Toxicokinetic studies of inhaled Cr(VI) have shown that only a small fraction of the total dose is distributed in the body while the bulk of Cr(VI) is deposited in the lungs where it remains for a very long time [15]. Therefore, it might be supposed that alternative cell test systems should be developed for or adapted to the purposes of human biomonitoring.

In this study the utility of peripheral lymphocytes as well as of buccal cells as target cells for genotoxic effects resulting from exposure to Cr(VI) has been investigated in a cohort of Bulgarian chromium platers.

Section snippets

The investigated cohort

For the chromium platers in Yambol, Bulgaria, relevant data on occupational history, health status, smoking habits, recent X-ray diagnostic examinations were collected by personal interviews and filled-up questionnaires (Table 1). All workers have reported regular use of personal protection devices like disposable masks, gloves, etc. Special interest was paid to perforation of the nasal septum due to chronic exposure by inhalation of chromium compounds. The identification of the exposed workers

CAs and SCEs

No differences were found between the study groups for the frequencies of CAs (1.38±0.20% in the exposed group versus 1.28±0.22% in the control workers, see Table 3) as well as SCEs/cell (7.07±0.21 in the workers versus 6.52±0.37 in the controls) as scored in the peripheral lymphocytes. Single dicentrics and minutes were found in individuals belonging to both study groups who were subjected to medical diagnostic X-ray examinations during the year preceding sampling. The frequency of CAs in both

Discussion

A bulk of evidence has been accumulated of the carcinogenic activity of Cr(VI) [1], [2], [4], [22]. Many authors have reported that Cr(VI) compounds show a genotoxic effects [3], [7], [13], [22]. Nevertheless, the mechanism of its action is not clarified and, on the basis of the contemporary knowledge, it is assumed to be a complex one [22], [23], [24].

In the present study a significant increase is found in the frequencies of MN in PBLs as well as in buccal mucosa cells of chromium platers as

Acknowledgements

This study has been supported by grants from EU INCO-Copernicus Project no. IC15CT960302 and by the National Swedish Environment Protection Agency.

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