Cytotoxic and genotoxic effects of 4-hydroxynonenal in cerebral endothelial cells

Oxygen free radicals are produced in the central nervous system (CNS) as a consequence of normal physiological metabolic reactions of neuronal cells, but there is evidence accumulating that they are also implicated in the processes leading to a number of pathological changes in the brain. A general mechanism whereby oxygen free radicals induce tissue damage is lipid peroxidation (LPO), which generates a large variety of water-soluble carbonyl compounds. Due to their high reactivity, we focused our investigations on 4-hydroxyalkenals, in particular on 4-hydroxynonenal (HNE), the major 4-hydroxyalkenal. Two phenotypes of cerebral endothelial cells (cECs) were treated with various concentrations of 4-hydroxynonenal and the cyto- and genotoxic effects studied. The cytogenetic endpoints determined were chromosomal aberrations and the induction of micronuclei. Three hours of incubation with HNE induced significantly elevated levels of chromosomal aberrations at concentrations ≥1 μM and micronuclei at concentrations ≥10 μM in both cEC phenotypes, compared to the controls. Cytotoxicity was observed at a concentration of 50 μM HNE and was significantly higher in the elongated and spindle-shaped cEC phenotype (type II) than in the epithelial cEC phenotype (type I). The results indicate that cECs are affected by HNE even at low concentrations with minor differences between the two cEC phenotypes.     

Genotoxic properties of 4-hydroxyalkenals and analogous aldehydes

4-Hydroxynonenal (HNE), one of the major products of lipid peroxidation, has been demonstrated to induce genotoxic effects in the micromolar range. HNE has too structural domains, a lipophilic tail and a polar head with three functional groups: the aldehyde and hydroxy groups and the trans CC double bond. To evaluate their relative importance, the genotoxic effects of HNE were compared with those of the homologous aldehydes 4-hydroxyhexenal and 4-hydroxyundecenal (different lengths of the lipophilic tail), and the analogous aldehydes 2-trans-nonenal (lacking the OH group) and nonanal (lacking the OH group and the trans CC double bond). This investigation was carried out on primary cultures of adult rat hepatocytes in order to further determine the influence of biotransformation- and/or detoxification reactions.

A 3-h treatment with HNE induces statistically significant levels of SCE at concentrations ≥0.1 μM, micronuclei at concentrations ≥ 1 μM and chromosomal aberrations at a concentration of 10 μM. Compared to HNE the homologous aldehydes induced a significant genotoxic effect at higher concentrations. Statistically significant increases in SCE frequency were obtained at concentrations ≥ 1 μM for 4-hydroxyundecenal and at a concentration of 10 μM for 4-hydroxyhexenal. The induction of chromosomal aberrations was significantly elevated at concentrations of ≥ 10 μM and 10 μM for 4-hydroxyhexenal and 4-hydroxyundecenal, respectively. Except for a 4-hydroxyhexenal concentration of 1 μM, both aldehydes did not induce statistically significant levels of micronucleis.

The HNE analogous aldehydes 2-trans-nonenal and nonanal induced statistically significant frequencies of SCE at concentrations of ≥ 1 μM (nonanal) and ≥ 10 μM (2-trans-nonenal). No significant induction of chromosomal aberrations or micronuclei could be demonstrated.

The structure of the aldehydes investigated appears to influence the cyto- and genotoxic potential in the following ways. (1) The lenght of the lipophilic tail has no influence on chromosomal aberration induction, but appears to determine the yield of SCE and micronuclei, and the cytotoxic potential. (2) The lack of the OH group (2-trans-nonenal) reduces the SCE-inducing potential of the aldehyde shifting the dose-effect curve to higher concentrations. The similar shape compared to SCE induction by HNE indicates that possibly the same active metabolite is formed. (3) The lack of both the OH group and the CC double bond (nonanal) does not result in a complete loss of the SCE-inducing activity. The different shape of the dose-response curve suggests a different metabolism and/or a different mode of interaction with DNA.     

Intracellular metabolism of 4-hydroxynonenal

4-hydroxynonenal (HNE) is a major aldehydic product of lipid peroxidation known to exert a multitude of biological, cytotoxic, and signal effects. Mammalian cells possess highly active pathways of HNE metabolism. The metabolic fate of HNE was investigated in various mammalian cells and organs such as hepatocytes, intestinal enterocytes, renal tubular cells, aortic and brain endothelial cells, synovial fibroblasts, neutrophils, thymocytes, heart, and tumor cells. The experiments were carried out at 37 degrees C at initial HNE concentrations between 1 microM--that means in the range of physiological and pathophysiologically relevant HNE levels--to 100 microM. In all cell types which were investigated, 90-95% of 100 microM HNE were degraded within 3 min of incubation. At 1 microM HNE the physiological blood serum level of about 0.1-0.2 microM was restored already after 10-30 s. As primary products of HNE in hepatocytes and other cell types the glutathione-HNE-1:1-conjugate, the hydroxynonenoic acid and the corresponding alcohol of HNE, the 1,4-dihydroxynonene, were identified. Furthermore, the beta-oxidation of hydroxynonenoic acid including the formation of water was demonstrated. The quantitative share of HNE binding to proteins was low with about 2-8% of total HNE consumption. The glycine-cysteine-HNE, cysteine-HNE adducts and the mercapturic acid from glutathione-HNE adduct were not formed in the most cell types, but in kidney cells and neutrophils. The rapid metabolism underlines the role of HNE degrading pathways in mammalian cells as important part of the secondary antioxidative defense mechanisms in order to protect proteins from modification by aldehydic lipid peroxidation products.     

Genetic damage in mammalian somatic cells exposed to radiofrequency radiation: a meta-analysis of data from 63 publications (1990-2005)

During the last several decades, numerous researchers have examined the potential of in vitro and /or in vivo exposure of radiofrequency( RF) radiation to damage the genetic material in mammalian somatic cells. A meta-analysis of reported data was conducted to obtain a quantitative estimate ( with 95% confidence intervals) of genotoxicity in RF-radiation-exposed cells compared with sham-exposed/unexposed control cells. The extent of genotoxicity was assessed for various end points, including single- and double-strand breaks in the DNA, incidence of chromosomal aberrations, micronuclei and sister chromatid exchanges. Among the several variables in the experimental protocols used in individual investigations, the influence of three specific variables related to RF-radiation exposure characteristics was examined in the meta-analysis: frequency, specific absorption rate, and exposure as continuous-wave, pulsed-wave and occupationally exposed/cell phone users. The overall data indicated that (1) the difference between RF-radiation exposure was small with few exceptions; (2) at certain RF radiation exposure conditions, there were statistically significant increases in genotoxicity for some end points; and (3) the mean indices for chromosomal aberrations and micronuclei in RF-radiation -exposed and sham-/unexposed controls were within the spontaneous levels reported in the historical database. Considerable evidence for publication bias was found in the meta-analysis.     

Toxicity and genotoxicity of wastewater from gasoline stations

The toxicity and genotoxicity of wastewater from eight gasoline stations in Brasília, Brazil's capital city, was studied by assessing chromosomal aberrations, chromosomal malsegregation and the mitotic index in Alliumcepa root cells, and the occurrence of micronucleus and nuclear abnormalities in peripheral erythrocytes of tilapia fish (Oreochromis niloticus). The content of gasoline station effluents was also analyzed based on several physico-chemical parameters. None of the wastewater samples was genotoxic to A. cepa root cells, although cell proliferation was significantly inhibited, especially at the highest concentrations. Likewise, no micronuclei were observed in O. niloticus peripheral erythrocytes, even after exposure to high concentrations, but there was an increase in the number of nuclear abnormalities and fish mortality. These results show that although the effluent from gasoline stations is processed by an oil/water separation system before being discharged into the main sewage system, the wastewater still contains toxic compounds.     

Possible mutagens derived from lipids and lipid precursors

Free radicals can initiate the oxidative decomposition of cellular membranes by lipid peroxidation. In this process a great variety of reactive aldehydes are produced intracellularly. Some of them, such as 4-hydroxynonenal or malonaldehyde, are biologically very active and might be involved in free radical-mediated DNA damage. A short review of the effects of aldehydic lipid peroxidation products on isolated DNA, their genotoxic effect in prokaryotes and eukaryotes and their in vivo carcinogenicity is given. Additionally own experiments on cytotoxic and genotoxic effects of 4-hydroxynonenal, 2-nonenal and nonanal in primary cultures of rat hepatocytes are reported. 4-Hydroxynonenal was highly cytotoxic at 100 microM, at subcytotoxic concentrations of 0.1-10 microM 4-hydroxynonenal increased the frequency of micronuclei, chromosomal aberrations and sister-chromatid exchange. 2-Nonenal and nonanal were not cytotoxic at 100 microM, the maximum dose tested. At 100 microM 2-nonenal led to a slight increase in micronuclei; chromosomal aberrations were not significantly altered. Nonanal had no detectable genotoxic effects. The level of endogenous 4-hydroxynonenal in tissues is in the range of 0.1-3.0 microM and can increase to 10 microM in conditions of oxidative stress; such levels appear to be sufficiently high to produce DNA damages, whether such damages are transient or irreversible is not known.     

DNA strand breaking capacity of acrylamide and glycidamide in mammalian cells

We compared the DNA damaging potency of acrylamide (AA) and its metabolite glycidamide (GA) in the comet assay in cell systems differing with respect to species origin and cytochrome P450-depended monooxygenase (CYP2E1) expression (V79, Caco-2, primary rat hepatocytes). Only after 24 h incubation in the highest concentration of AA (6 mM) a slight but significant increase in DNA damage was observed in V79 and Caco-2 cells. In primary rat hepatocytes, however, expressing substantial amounts of CYP2E1, no induction of DNA strand breaks was found. At the end of the incubation time period (24 h), still 67+/-19% of the CYP2E1 protein was detected by Western blotting. Direct treatment with GA resulted in a significant increase in DNA damage in V79 cells and primary rat hepatocytes at concentrations > or =100 microM (24 h). Caco-2 cells were found to be less sensitive, exhibiting an increase in DNA strand breaks at concentrations > or 300 microM GA. These data confirm the higher genotoxic potential of GA compared to AA but also indicate that high expression of CYP2E1 per se is not necessarily associated with increased genotoxicity of AA. We, therefore, investigated whether the intracellular glutathione (GSH) level might be a critical determinant for the genotoxicity of AA in cells with different CYP2E1 status. Depletion of intracellular GSH by dl-buthionine-[S,R]-sulfoxime (BSO) in rat hepatocytes and V79 cells resulted in a significant induction of DNA strand breaks after incubation with 1 mM AA. However, at higher concentrations (> or =1.25 mM) a strong increase in cytotoxicity, resulting in a severe loss of viability, was observed. In summary, the DNA strand breaking effect of AA appeared not to be directly correlated with the CYP2E1 status of the cells. Depletion of GSH is associated with an increase in AA genotoxicity but seems also to lead to a substantial enhancement of cytotoxicity.     

Genotoxicity studies on the organophosphorus insecticide chloracetophone

Chloracetophone (O,O-dimethyl-2,2,2-trichloro-1-(chloroacetoxy)phosphonate), a new insecticide of the organophosphorus group of pesticides, was tested for genotoxicity in a variety of systems with different genetic end-points and varying parameters. The test systems included 2 microbial systems, Salmonella and Aspergillus for point mutations and mitotic segregation, respectively, and human lymphocyte cultures and mammalian bone marrow cells (from rats and hamsters treated acutely and subacutely) for chromosomal aberrations and micronuclei. Chloracetophone was negative in Aspergillus at concentrations of 1-500 micrograms/ml, in human lymphocyte cultures at concentrations of 2.5-40 micrograms/ml, in rats at doses of 420-21 mg/kg b.w. and in hamsters at doses of 210-42 mg/kg b.w. for chromosomal aberrations. It did not cause any increase of micronuclei in human lymphocytes and rat bone marrow cells but did cause a significant increase in hamster bone marrow cells. Chloracetophone induced base-pair substitutions in strain TA100 of Salmonella with and without metabolic activation at a concentration range of 2000-6000 micrograms/plate.     

The correlation between the frequency of micronuclei and specific chromosome aberrations in human lymphocytes exposed to microwave radiation in vitro.

Human whole-blood samples were exposed to continuous microwave radiation, frequency 7.7 GHz, power density 0.5, 10 and 30 mW/cm2 for 10, 30 and 60 min. A correlation between specific chromosomal aberrations and the incidence of micronuclei after in vitro exposure was observed. In all experimental conditions, the frequency of all types of chromosomal aberrations was significantly higher than in the control samples. In the irradiated samples the presence of dicentric and ring chromosomes was established. The incidence of micronuclei was also higher in the exposed samples. The results of the structural chromosome aberration test and of the micronucleus test were comparatively analyzed. The values obtained showed a positive correlation between micronuclei and specific chromosomal aberrations (acentric fragments and dicentric chromosomes). The results of the study indicate that microwave radiation causes changes in the genome of somatic human cells and that the applied tests are equally sensitive for the detection of the genotoxicity of microwaves.     

Mutagenic activity of structurally related oxiranes and siloranes in Salmonella typhimurium

The in vitro and in vivo genotoxicity of parthenin, a sesquiterpene lactone from Parthenium hysterophorus L. with allergenic and irritant action, was assessed in three short-term tests: bacterial reversion in Salmonella typhimurium and Escherichia coli, in vitro chromosomal aberrations in peripheral blood lymphocytes and micronuclei in mouse peripheral blood. Parthenin was not mutagenic in S. typhimurium strains TA 1535, TA 1537, TA 98 and TA 100 but a weak response was observed in TA 102 (+S9) from 0.19 to 1.22 micromole per plate. Concentrations of 7.62 micromole per plate or higher were toxic, but the effect was reduced when S9 was present. Screening of oxidative mutagenesis with E. coli strains IC 188 and IC 203 gave negative results. Parthenin induced chromosomal aberrations, mainly chromatid breaks, in blood lymphocytes exposed to 10-60 microM during 20 h. An association was found with cytotoxicity, since concomitant nuclear alterations such as pycnosis, micronuclei and karyorrhexis were observed. Sister chromatid exchanges (SCEs) in lymphocytes were not influenced by exposure to parthenin; rather a decrease was observed at 60 microM. On the other hand, a minor increment in polyploid metaphases was found at 40 microM. When a single intraperitoneal (i.p.) dose of 4-31 mg/kg of parthenin was administered to mice, a positive increase in the micronucleated reticulocyte (RET) frequency was observed at 48 h for both sexes at the highest dose.     

Amelioration of genotoxic damage by certain phytoproducts in human lymphocyte cultures

The antigenotoxic effect of some phytoproducts like carotenoid (beta-carotene), curcumin, ascorbic acid and flavonoid (genistein)was demonstrated on the genotoxicity induced by hydrocortisone. Human lymphocyte cultures were studied for the induction of chromosomal aberrations, sister chromatid exchanges and effect on cell cycle kinetics with or without the presence of metabolic activation (S9 mix). The phytoproducts were studied in two most effective doses viz. carotenoid (0.5 and 0.7 microM), curcumin (15 and 25 microM), ascorbic acid (60 and 80 microM) and flavonoid (25 and 40 microM) in 24, 48 and 72 h cultures, and they were found to reduce chromosomal aberrations, sister chromatid exchange and increase replication index. The present study showed that the ascorbic acid and curcumin were more effective than carotenoid and flavonoid, though all provide protection against the genotoxicity of hydrocortisone.     

Genotoxicity of streptozotocin

Streptozotocin (Streptozocin, STZ, CAS No. 18883-66-4) is a monofunctional nitrosourea derivative isolated from Streptomyces achromogenes. It has broad spectrum antibiotic activity and antineoplastic properties and is often used to induce diabetes mellitus in experimental animals through its toxic effects on pancreatic beta cells. STZ is a potent alkylating agent known to directly methylate DNA and is highly genotoxic, producing DNA strand breaks, alkali-labile sites, unscheduled DNA synthesis, DNA adducts, chromosomal aberrations, micronuclei, sister chromatid exchanges, and cell death. This antibiotic was found to be mutagenic in bacterial assays and eukaryotic cells. STZ is also carcinogenic; a single administration induces tumors in rat kidney, liver, and pancreas. Several lines of evidence indicate that free radicals are involved in the production of DNA and chromosome damage by this compound. Because of the use of STZ as an antineoplastic agent, the study of its genotoxicity has considerable practical significance. The purpose of this review is to present our current knowledge regarding the genotoxicity of STZ.     

The influence of 4-hydroxy-2-nonenal on proliferation, differentiation and apoptosis of human osteosarcoma cells

The product of lipid peroxidation, 4-hydroxy-2-nonenal (HNE) is known to cause cell death at high concentrations, while at lower concentrations it can influence cell proliferation and differentiation. In our experiments we used human osteosarcoma cells (HOS), to test the influence of HNE on cell proliferation, differentiation and induction of apoptosis. Apoptosis induction was estimated by TiterTACS TUNEL test. The cells were in parallel counted and the DAPI staining method was used to distinguish between apoptotic and necrotic cells as well as to define the proportion of cells in mitosis. To test the influence of HNE on HOS cell differentiation, cells were treated every second day with HNE. After 10 days, the cells were stained for alkaline phosphatase, a marker for osteoblast differentiation. Cell growth inhibition was caused by supraphysiological concentrations of 10 or 100 microM HNE, while apoptosis was induced with supraphysiological as well as by the physiological amount of the aldehyde (1 microM). Necrosis appeared when cells were treated with 10 or 100 microM, but not with 1 microM HNE. The proportion of cells in mitosis gradually declined with increased HNE concentration. Multiple exposures of HOS cells to 10 microM HNE prevented HOS cell differentiation. These results indicated that HNE inhibits proliferation and differentiation of HOS cells in the same concentration dependent manner as it causes apoptosis. We thus assume that HNE might be one of the important signaling molecules regulating the growth of the human osteosarcoma cells.     

Influence of iron-overload on DNA damage and its repair in human leukocytes in vitro

Iron is an important element that modulates the production of reactive oxygen species, which are thought to play a causative role in biological processes such as mutagenesis and carcinogenesis. The potential genotoxicity of dietary iron has been seldom studied in human leukocyte and only few reports have investigated in human colon tumor cells. Therefore, DNA damage and repair capacity of human leukocytes were examined using comet assay for screening the potential toxicity of various iron-overloads such as ferric-nitrilotriacetate (Fe-NTA), FeSO(4), hemoglobin and myoglobin, and compared with 200μM of H(2)O(2) and HNE. The iron-overloads tested were not cytotoxic in the range of 10-1000 microM by trypan blue exclusion assay. The exposure of leukocytes to Fe-NTA (500 and 1000 microM), FeSO(4) (250-1000 microM), hemoglobin (10 microM) and myoglobin (250 microM) for 30 min induced significantly higher DNA damage than NC. Treatment with 500 and 1000 microM of Fe-NTA showed a similar genotoxic effect to H(2)O(2), and a significant higher genotoxic effect than HNE. The genotoxicity of FeSO(4) (250-1000 microM), hemoglobin (10 microM) and myoglobin (250 microM) was not significantly different from that of H(2)O(2) and HNE. Iron-overloads generated DNA strand break were rejoined from the first 1h. Their genotoxic effect was not observed at 24h. These data from this study provide additional information on the genotoxicity of iron-overloads and self-repair capacity in human leukocytes.     

Chromothripsis in Hepatocarcinogenesis: The Role of a Micronuclear Aberration and Polyploidy

In this study, we used the mouse model of chemically induced hepatocarcinogenesis to investigate the chromosomal aberrations in hepatic cells. The model was obtained by combined treatment of mice with Dipin (radiomimetic drug) followed by partial hepatectomy. Cytological analysis of isolated liver cells treated with Dipin has demonstrated a number of hepatocytes with structural nuclear abnormalities and multiple micronuclei. Karyotype analysis of polyploid hepatocytes has shown numerous chromosomal aberrations including alleged morphological manifestations of chromothripsis, a special type of genomic reorganization characterized by the local disintegration of chromosomes. Micronuclei with chromosomal fragments have developed as a result of double-strand DNA breaks and might serve as the initial substrate for chromothripsis. The emergence of micronuclei containing chromosomal fragments is the most important result of the treatment employed. Therefore, the presented model of liver cancer (hepatocarcinogenesis) can be used to study the process of chromothripsis in the future.     

Effect of various concentrations of acyclovir on cell survival and micronuclei induction on cultured HeLa cells

The HeLa cells were treated with 0, 0.01, 0.1, 1, 10 and 100 microM acyclovir (ACV) for 8 h duration and the growth kinetics, cell survival and micronuclei induction were determined. Treatment of HeLa cells with various concentrations of ACV resulted in a concentration-dependent decline in growth kinetics, cell proliferation indices and cell survival. ACV, 100 microM, completely inhibited cell division, where no appreciable changes in cell number were observed from 1 to 5 days post-treatment. This is reflected in cell survival, where the surviving fraction of cells was reduced to 1/2 at 100 microM ACV. Conversely, the frequency of micronuclei showed a concentration-dependent elevation at 20, 30 and 40 h post-treatment. ACV not only induced one micronuclei-bearing binucleate cell but also binucleate cells bearing two and multiple micronuclei in a concentration-dependent manner. The micronuclei frequency increased with time up to 30 h post-treatment and declined thereafter. The relationship between micronuclei induction and cell survival was determined by plotting the former on Y- and the latter on X-axes, respectively. The surviving fraction of cells declined with the elevation in micronuclei frequency and a best fit was observed for linear quadratic formalism.     

Influence of antimonite, selenite, and mercury on the toxicity of arsenite in primary rat hepatocytes

The long-term toxicity of arsenic (As) as a result of exposure to contaminated drinking water might be modified by coinciding exposures to elements like selenium, antimony, or mercury. In this study the influence of tetravalent selenite, trivalent antimonite, and divalent mercury was investigated in vitro using cultured primary rat hepatocytes. The cell vitality was assessed in the 3-[4,5-dimethylthiazol-2-yl-2,5-diphenyltetrazolium bromide] (MTT), assay with concurrent exposures of the cells to up to 50 microM sodium arsenite(III) and a potential modifier [50 microM sodium(IV) selenite, 10 microM antimony(III) chloride, 25 microM mercuric(II) chloride], which indicated an additive increase in the combined cytotoxicity. Sodium arsenite was tested for genotoxicity in the micronucleus test in a concentration range of 0.25 up to 7.5 microM. In this range, the MTT conversion was at least 80%, indicating high cell viability. Adose-dependent induction of micronuclei was observed. The lowest concentration causing a significantly elevated frequency of micronuclei was 1 microM As (p < 0.05). A significant influence (i.e., reduction of the combined genotoxicity as a result of the presence of a potential modifier) was only observed for 10 and 25 microM antimony chloride (p < 0.05, Fisher's exact test). The metabolic methylation of arsenite was not affected by concurrent incubation with any of the potential modifiers.     

DNA methyltransferase I is a mediator of doxorubicin-induced genotoxicity in human cancer cells

Doxorubicin can induce the formation of extra-nuclear bodies during mitosis termed micronuclei but the underlying causes remain unknown. Here, we show that sub-lethal exposure to doxorubicin-induced micronuclei formation in human cancer cells but not in non-tumorigenic cells. Occurrence of micronuclei coincided with stability of DNMT1 upon doxorubicin assault, and DNMT1 was localized to the micronuclei structures. Furthermore, 5-aza-2′-deoxycytidine-mediated DNMT1 depletion or siDNMT1 knock-down attenuated the frequency of doxorubicin-induced micronucleated cells. Human DNMT1^−/− cells displayed significantly fewer micronuclei compared to DNMT1^+/+ cells when challenged with doxorubicin, providing additional evidence for the involvement of DNMT1 in mediating such chromosomal aberrations. Collectively, our results demonstrate a role for DNMT1 in promoting DNA damage-induced genotoxicity in human cancer cells. DNMT1, recently identified as a candidate for doxorubicin-mediated cytotoxicity, is over-expressed in various cancer cell types. We propose that DNMT1 levels in tumor cells may determine the effectiveness of doxorubicin in chemotherapy.     

Induction of micronuclei by ochratoxin A is a sensitive parameter of its genotoxicity in cultured cells

In order to better characterize the ochratoxin A (OTA)-induced DNA damage and to further investigate factors which may modulate dose-effect relationships in cells, the induction of micronuclei was studied in V79 Chinese hamster fibroblast cells and in primary cultures of porcine urothelial bladder epithelial cells (PUBEC). OTA was able to induce micronuclei in PUBEC and V79 cells at concentrations below those which were overtly cytotoxic. OTA concentrations between 0.03 and 1 μM caused a dose-dependent increase of micronuclei in V79 cells (up to 3-fold compared to controls); but the lowest tested concentration of 0.01 μM OTA did not induce a higher frequency of micronuclei than in the solvent control, indicative of an apparent threshold. Clear evidence for genotoxic effects was also found in PUBEC cultures treated with OTA concentrations of 1 μM and more, although the dose-effect relationship in PUBEC was more variable for several freshly isolated cell batches, pointing to differences in susceptibility to OTA between bladder cells from different donor animals. The chromosomal genotoxicity of OTA demonstrated in this study is in general accord with previous findings on the induction of clastogenic effects and oxidative DNA damage by OTA. In both cases, the shape of the dose-response curve at very low OTA concentrations supports the existence of a threshold for its genotoxicity. Presented at the 28^th Mykotoxin-Workshop, Bydgoszcz, Poland, May 29–31, 2006     

Protective effect of zinc on cadmium-induced micronuclei in V79 cells

The induction of micronuclei (MN) in mitotically active cells has been widely used and promoted as a biological marker of exposure to environmental toxins. In our study the effect of zinc on cadmium genotoxicity was investigated in V 79 cells. The results indicate that cadmium chloride exposure for 24 h increased micronucleus frequency and the percentage of binucleated cells in dose-dependent manner. At the highest concentration of cadmium (50 microM Cd) 23 MN were found in 1000 cells. The protective effect of zinc on cadmium genotoxicity was investigated at lower concentrations (5-25 microM CdCl2). At 50 microM Cd, the number of MN increased significantly (16 MN).