Thomas Gebel

Arsenic and antimony: comparative approach on mechanistic toxicology.

A chemico-toxicological similarity between arsenic and antimony exists and their toxicology is often seen. Indeed, both elements possess several common properties, e.g. they are clastogenic but not mutagenic in the trivalent state and they have a carcinogenic potential: trivalent arsenicals are known to be human carcinogens and antimony(III) oxide (by inhalation) has been shown to cause lung cancer in female rats. For years, arsenic has been known to be environmentally toxic. Elevated human exposure to this element, mostly caused by the intake of contaminated tap water, is associated with increased incidences of cancer at various sites. It is still not clear how arsenic compounds exert their genotoxic effect. It may be connected with an inhibition of DNA repair or the induction of oxidative stress. Little work has been done on the toxicology of antimony as it is less widely present in the environment. There is evidence that in mammals antimony, unlike arsenic, is not detoxified via methylation but it still remains unclear what mechanism is responsible for antimonys genotoxicity. In general, there is little information known about this element to accurately determine its impact on human health. Thus, the aim of this paper is to review current knowledge for future risk assessment and further scientific work.

Genotoxicity of arsenical compounds.

With respect to global human health hazard, arsenic (As) is one of the most important environmental single substance toxicants. Currently, millions of people all over the world are exposed to the ubiquitous element in exposure levels leading to long-term toxicity, in particular cancer. Unfortunately, it has not been elucidated up to now how As mechanistically leads to the induction of neoplasia. Besides its tumorigenic potential, As has been shown to be genotoxic in a wide variety of different experimental set-ups and biological endpoints. In vitro, the element was shown to induce chromosomal mutagenicity like micronuclei, chromosome aberrations, and sister chromatid exchanges. It mainly acts clastogenic but also has an aneugenic potential. Instead, its potential to induce point mutations is very low in bacterial as well as in mammalian cell systems. However, in combined exposure with point mutagens in vitro, As was shown to enhance the frequency of chemical mutations in a synergistic manner. Additionally, As was shown to induce chromosome aberrations and micronuclei in vivo in experiments with mice. After long-term exposure to As-contaminated drinking water, the great majority of human biomonitoring studies found elevated frequencies of DNA lesions like micronuclei or chromosome aberrations. Respective occupational studies are few. Like it is the case for As carcinogenicity, it is not known through which mechanism the genotoxicity of As is mediated, although the data available indicate that As may act indirectly on DNA, i.e. via mechanisms like interference of regulation of DNA repair or integrity. Because of the indirect mode of action, it has been discussed as well that Ass genotoxicity may underlie a sublinear dose-response relationship. However, various problems like non-standardized test systems and experimental variability make it impossible to prove such statement. Basically, to be able to improve risk assessment, it is of crucial importance to scientifically approach the mechanistic way of induction of Ass genotoxicity and carcinogenicity.

In vivo genotoxicity of selected herbicides in the mouse bone-marrow micronucleus test.

Abstract The herbicides alachlor, atrazine, terbuthylazine, gluphosinate-ammonium, isoproturon, pendimethaline and trifluralin were tested for genotoxicity in the mouse bone-marrow micronucleus test (MNT). Both atrazine and trifluraline caused a significant increase in the number of micronuclei at doses of 1400 mg/kg body weight in female mice only. Alachlor, terbuthylazine, gluphosinate-ammonium, isoproturon and pendimethaline did not have any genotoxic effect in the mouse bone-marrow micronucleus test in either female or male animals.

Genotoxicity of platinum and palladium compounds in human and bacterial cells

Platinum and palladium belong to the group of platinum elements and thus share many chemical properties. Platinum coordination complexes are known to be carcinogenic and genotoxic in mammalian and bacterial cells. However, little is known about palladium genotoxicity. This study compares and evaluates the genotoxic potential of selected platinum and palladium metal salts in mammalian and bacterial cells using the cytokinesis-block micronucleus test (MNT) with human lymphocytes and the bacterial SOS chromotest. Carboplatin, cisplatin(II), transplantin(II), PtCl4(IV), and K2PtCl4(II) caused a significantly elevated genotoxicity in the MNT and the SOS chromotest. The platinum compounds PtCl2(II) and K2PtCl6(IV), and the divalent palladium salts PdCl2(II), K2PdCl4(II), Pd(NH3)2J2(II), Pd(NH3)4Cl2(II), and transpalladium(II) were not genotoxic in the MNT nor in the SOS chromotest. Therefore, evidence for palladium genotoxicity seems to be low in mammalian and bacterial cells.

Genotoxicity of selected pesticides in the mouse bone-marrow micronucleus test and in the sister-chromatid exchange test with human lymphocytes in vitro.

Selected pesticides (aldicarb, 1,3-dichloropropene, methidathion, parathion, triadimefon, vinclozolin) were tested for their clastogenic and aneugenic activities in the mouse bone-marrow micronucleus (MN) test in vivo and for their sister-chromatid exchange-inducing activities in human lymphocytes in vitro in the presence and absence of an exogenous metabolizing system from rat-liver S9. 1,3-Dichloropropene significantly increased the frequencies of micronucleated polychromatic erythrocytes (PCE) in bone-marrow cells of female mice from 3.3 MN/1000 PCE to 15.3 MN/1000 PCE (187 mg per kg body weight). 1,3-Dichloropropene (100 microM) induced 16.0 SCE/metaphase after 24 h of incubation as compared with the basal rate of 11.2 SCE/metaphase (-S9) and of 15.4 SCE/metaphase as compared with 10.5 SCE/metaphase of the control (+S9). These values were statistically significantly different from each other. The other pesticides tested did neither increase the rate of micronuclei significantly in polychromatic erythrocytes in male nor in female animals. Aldicarb and methidathion induced a significant increase in SCEs in human lymphocytes in vitro only without the metabolic activating system: aldicarb, 5 microM, 24 h incubation: 15.5 SCE/metaphase; control: 12.6 SCE/metaphase; methidathion, 100 microM, 24 h incubation: 15.8 SCE/metaphase, control: 11.1 SCE/metaphase. Parathion, triadimefon and vinclozolin did not have any SCE-inducing effects.

Genotoxicity of selected metal compounds in the SOS chromotest

Knowledge concerning the genotoxicity of inorganic metal compounds in the SOS chromotest is limited. Up to now, only Cr(VI), Sn(II) and the platinum antitumor compound cisplatin(II) were shown to be genotoxic in this test system. However, for Cr(VI) and Sn(II), a positive reaction could only be achieved in cytotoxic dose ranges. The aim of the present study was to provide additional data concerning metal salt genotoxicity in the SOS chromotest. Therefore, 14 metal/metalloid salt compounds of platinum, palladium, rhodium, arsenic, antimony and chromium were tested. Four platinum salts, K2PtCl4, cis-Pt(NH3)2Cl2 (cisplatin), trans-Pt(NH3)2Cl2 (transplatin) and PtCl4 as well as two rhodium compounds tested, K2RhCl5 and (NH4)3RhCl6, could be shown to be genotoxic in the chromotest using the tester strain Escherichia coli PQ37. A moderate genotoxicity was shown by the two Cr(VI) compounds K2CrO4 and K2Cr2O7. All palladium compounds and all the other metal salts tested were unable to induce a significant SOS response.

Suppression of arsenic-induced chromosome mutagenicity by antimony

Arsenic and antimony are two semimetals sharing some chemical as well as toxicological properties. Both elements are clastogenic but not point mutagenic in their trivalent state of valency. Environmental exposure to arsenic was proven to be associated with increased rates of various types of cancers. Antimony is suspected to be carcinogenic to humans. Arsenic and antimony can be found as environmental co-contaminants resulting in co-exposure to man. However, in most regions where arsenic was found in elevated environmental amounts, it was not investigated whether an additional exposure to antimony was predominating. In this study, the chromosome mutagenicity induced by arsenic(III) was significantly suppressed by antimony(III) in the micronucleus test with V79 cells. The results demonstrate the necessity to identify putative environmental co-contaminations of antimony in the regions contaminated with arsenic and to determine the impact of antimony co-exposure on arsenic genotoxicity and carcinogenicity in man in vivo.

Human effect monitoring in cases of occupational exposure to antineoplastic drugs: a method comparison.

OBJECTIVES: To investigate whether DNA damage increased in subjects possibly exposed to high amounts of antineoplastic agents. METHODS: The level of genetic damage was determined in peripheral mononuclear blood cells with the sister chromatid exchange test, the alkaline elution technique, and the cytokinesis block micronucleus test. RESULTS: The supposed increased exposure of the study subjects was caused by a malfunction of a safety hood resulting in leakage of air during preparation of an infusion of an antineoplastic drug. Two months after a new safety hood was installed, the frequencies of micronuclei and sister chromatid exchanges of exposed nurses (n = 10) were still significantly increased when compared with a matched control group (p < 0.01 and p < 0.05, one sided Wilcoxon test, respectively). In a second examination seven months later, the frequency of micronuclei had significantly decreased to control values (p < 0.05, one sided Wilcoxon test, n = 6). Moreover, the study subjects who smoked (n = 8) had significantly increased frequencies of micronuclei and sister chromatid exchanges (p < 0.01 and p < 0.05, one sided U test, respectively). No differences in the rate of DNA damage could be detected with the alkaline elution technique. CONCLUSIONS: Control measures on the level of biological effect should be performed regularly to ensure maximum safety precautions for workers potentially exposed to genotoxic agents.

Assessment of a possible genotoxic environmental risk in sheep bred on grounds with strongly elevated contents of mercury, arsenic and antimony.

A part of Northern Palatinate country (Germany) was formerly influenced by mercury mining. Today, in many cases agricultural and housing areas are placed onto or near to former dump grounds of rubble. In the soil of these areas the concentration of mercury, arsenic and antimony was found ranging from basic natural contents up to strongly elevated levels. In a biomonitoring project, sheep bred on grounds contaminated with mercury (range 1-435 mg Hg/kg dry matter), arsenic (range 17-147 mg As/kg dry matter) and antimony (range 2-15 mg Sb/kg dry matter) were taken as example on the uptake of these elements from the environment and for possible effects of this exposure. Significantly elevated mercury levels were found in wool of one collective of exposed sheep (0.107 mg/kg mean vs. 0.048 mg/kg mean, p < 0.001, U-test). Surprisingly, the arsenic content of wool taken from sheep bred in the urban referential area was approx. 10 times higher than that of the sheep bred on the grounds contaminated with arsenic (0.57 mg/kg mean vs. 0.051 mg/kg mean, p < 0.001, U-test). In general, element concentrations in the examined blood samples were low and the differences between the collectives were small: mercury was found in concentrations ranging from 0.9 microgram/l up to 2.0 micrograms/l (means), arsenic and antimony were generally found in concentrations below 1 microgram/l. Neither in the alkaline elution technique nor in the sister chromatid exchange (SCE) analysis significant increases in the rate of DNA-damaging effects between the different sheep collectives were detected. This indicates that the transfer rate of genotoxic compounds of mercury, arsenic or antimony from the environment is too low to register effects with AFE and SCE although the soil was highly contaminated.

Impact of dimethyl sulfoxide and examples of combined genotoxicity in the SOS chromotest.

The bacterial SOS chromotest with Escherichia coli PQ37 was used for the assessment of genotoxicity of combined xenobiotic treatments. The modulation of test compound genotoxicity by dimethyl sulfoxide (DMSO), a common solvent for test compounds, was assessed as well. It was shown that DMSO modulated SOS chromotest genotoxicity of several xenobiotics: in comparison to test compound dissolution in water, the commonly used addition of 3.2% (v/v) DMSO as solvent lead to a significant increase in the genotoxicity of K(2)RhCl(5) and beta-propiolactone (BPL). However, the effects of cisplatin decreased significantly when DMSO was added. Thus, albeit DMSO is not genotoxic in this test itself, it can interfere with SOS chromotest responses. Further experiments were performed in the absence of DMSO. BPL and cisplatin in combination showed an over-additive synergism in SOS genotoxicity as well as K(2)RhCl(5) and cisplatin did. Addition of Pd(NH(3))(4)Cl(2) and NaAsO(2), which are non-genotoxic in the SOS chromotest, did not enhance the K(2)RhCl(5)- or BPL-mediated SOS sfiA induction. Nevertheless, at the highest subcytotoxic dose of NaAsO(2) tested (200 microM), a slight yet significant suppression of BPL-mediated SOS genotoxicity was observed. These results confirm that the SOS chromotest is a useful tool for the rapid evaluation of the combined genotoxicity of compound mixtures. However, the use of DMSO as test solvent has to be taken with caution.