Spindle disturbances in mammalian cells III. Toxicity, c-mitosis and aneuploidy with 22 different compounds. Specific and unspecific mechanisms

Cytogenetic and genotoxic effects of 2-chlorophenol on Allium cepa L. root meristem cells

2-Chlorophenol (2-CP), a class of chlorinated organic pollutants like other chlorophenols, is used as intermediate in the synthesis of the higher chlorinated congeners, certain dyes, preservatives, herbicides, fungicides, and plastics. In this study, cytotoxic and genotoxic effects of 2-CP were investigated on the root meristem cells of Allium cepa for its effects on root growth, mitotic index (MI), mitotic phases, chromosomal abnormalities (CAs), and DNA damage by using Allium anaphase-telophase and Comet assays. EC₅₀ of 2-CP value was determined as approximately 25 mg/L by Allium root growth inhibition test. Three concentrations of 2-CP (12.5, 25, and 50 mg/L), distilled water (negative control), and methyl methane sulfonate (MMS, 10 mg/L, positive control) were applied to onion stem cells under different exposure periods (24, 48, 72, and 96 h). All the applied doses of 2-CP slightly decreased MIs. 2-CP induced total CAs such as disturbed anaphase-telophase, chromosome laggards, stickiness, and bridges and also DNA damage at significant levels. These results demonstrate that 2-CP has genotoxic effects in A. cepa root meristematic cells.

Detection of genotoxic effects of drinking water disinfection by-products using Vicia faba bioassay

Plant-based bioassays have gained wide use among the toxicological and/or ecotoxicological assessment procedures because of their simplicity, sensitivity, low cost, and reliability. The present study describes the use of Vicia faba (V. faba) micronucleus (MN) test and V. faba comet assay in the evaluation of the genotoxic potential of disinfection by-products (DBPs) commonly found in chlorine-disinfected drinking water. Five haloacetic acids and three halogenated acetonitriles were chosen as representatives of DBPs in this study because they are of potentially great public health risk. Results of the MN test indicated that monochloroacetic acid (MCA), monobromoacetic acid (MBA), dichloroacetic acid (DCA), dibromoacetic acid (DBA), trichloroacetic acid (TCA), and trichloroacetonitrile (TCAN) caused a statistically significant increase in MN frequency in V. faba root tip cells. However, no genotoxic response was observed for dichloroacetonitrile (DCAN) and dibromoacetonitrile (DBAN). Results of the comet assay showed that all tested DBPs induced a statistically significant increase in genomic DNA damage to V. faba root tip cells. On considering the capacity to detect genomic damage of a different nature, we suggest that a combination of V. faba MN test and V. faba comet assay is a useful tool for the detection of genotoxic effects of DBPs. It is worthy of assessing the feasibility of using V. faba comet assay combined with V. faba MN test to screen for the genotoxic activity of chlorinated drinking water in future work.

Evaluation of toxicity and genotoxicity of 2-chlorophenol on bacteria, fish and human cells

Due to the extensive use of chlorophenols (CPs) in anthropogenic activities, 2-Chlorophenol (2-CP), among other CPs, can enter aquatic ecosystems and can be harmful to a variety of organisms, including bacteria, fish and humans, that are exposed directly and/or indirectly to such contaminated environments. Based on the existing knowledge and in order to move a step forward, the purpose of this study is to investigate the toxic and mainly the genotoxic effects of 2-CP using a combination of bioassays. The tests include the marine bacterium Vibrio fischeri and micronuclei induction in the erythrocytes of Carassius auratus as well as in cultured human lymphocytes. The results obtained reveal that 2-CP is able to induce dose-dependent toxic and genotoxic effects on the selected tested concentrations under the specific experimental conditions.

Genetic damage, but limited evidence of oxidative stress markers in diethyl maleate-induced glutathione depleted mouse lymphoma L5178Y (TK(+/-)) cell cultures

Depletion of glutathione (GSH) in cells exposed to certain xenobiotics has been proposed to result in oxidative stress, which could lead to damage of cellular macromolecules such as proteins, lipids, and DNA. Diethyl maleate (DEM) is known to conjugate with GSH and rapidly lower cellular GSH levels. The objective of this study was to investigate the influence of DEM-induced GSH depletion on various genotoxicity and gene expression end points in mouse lymphoma L5178Y (TK(+/-)) cell cultures. Cells were exposed to DEM for 4 h at concentrations of 0, 6.7, 13.5, 26.9, 53.8, 107.6, 215.3, and 430.6 µg/mL (0.039-2.5 mM). Genotoxicity was evaluated by examining the induction of in vitro micronuclei (20 h post-treatment) and DNA strand breaks as measured by comet (immediately following treatment), and correlating these observations to cellular GSH levels. In the current study, GSH was decreased more than 50% at the lowest test concentration (6.7 µg/mL) and more than 95% at ≥ 107.6 µg/mL. A significant increase in micronuclei and DNA strand breaks was observed at concentrations of ≥ 26.9 µg/mL. Gene expression of seven apoptosis and oxidative-stress related genes showed significant alterations in only three genes only at the highest test concentration. Quantifiable levels of 8-OH-dG (≥ 2 adducts per 1 × 10(8) NT) were not detected at any treatment concentration. These results demonstrate an association between DEM-induced genotoxicity and GSH depletion in mouse lymphoma L5178Y (TK(+/-)) cells, but not with other oxidative markers.

Evaluating genotoxicity data to identify a mode of action and its application in estimating cancer risk at low doses: A case study involving carbon tetrachloride

In the new USEPA cancer risk assessment guidelines, mode of action (MoA) information, combined with a determination of whether or not a chemical is mutagenic, plays an important role in determining whether a linear or nonlinear approach should be used to estimate cancer risks at low doses. In this article, carbon tetrachloride (CT) is used as an example to illustrate how mixed genotoxicity data can be evaluated and used to identify a likely MoA. CT is essentially negative in inducing gene mutations in Salmonella, but is consistently positive in inducing recombination and aneuploidy in fungi. Negative or equivocal results were seen in most in vitro and in vivo studies in mammals, including mutation studies in transgenic mice. However, DNA adducts, primarily those derived from oxidation- and lipid-peroxidation-derived products as well as DNA double-strand breaks and micronucleated cells, have been seen repeatedly in the liver of CT-treated animals. On the basis of the weight of evidence, CT should not be considered a directly mutagenic agent. Mutagenic as well as other genotoxic effects, as they occur, will most likely be generated through indirect mechanisms resulting from oxidative and lipid peroxidative damage and/or damage occurring during necrosis or apoptosis. As key events in this process are expected to occur in a nonlinear fashion, the expected relationship between CT dose and carcinogenic response in the liver is likely to be nonlinear with a steep dose response. This conclusion is consistent with rodent cancer bioassay results in which steep nonlinear dose responses have been seen.

Genotoxic effects of environmental estrogen-like compounds in CHO-K1 cells

Some environmental estrogen-like compounds, such as bisphenol A (BPA), 4-nonylphenol (NP), 4-octylphenol (OP), propyl p-hydroxybenzoate (P-PHBA), and butyl p-hydroxybenzoate (B-PHBA), synthetic estrogen, diethylstilbestrol (DES), and natural estrogen, 17beta-estradiol (E2), were studied for their genotoxicity in CHO-K1 cells using sister-chromatid exchange (SCE), chromosome aberration (CA), and DNA strand break (comet) assays. Six of the chemicals, excluding E2, caused DNA migration in the comet assay and induced SCEs at one or more of the highest doses. Among the chemicals, OP produced an especially high incidence of SCEs. Structural CA was induced by five of the chemicals, excluding OP and NP, and BPA, E2, and DES also induced aneuploid cells. E2 and DES particularly increased the rate of polyploidy at high doses. The incidence of colchicine-mitosis-like (c-mitotic) figures suggesting spindle disrupting effects was also detected with five of the chemicals, excluding OP and NP, and six of the chemicals, excluding E2, caused endoreduplication (ERD), a form of nuclear polyploidization induced by block of cell cycle at G2 phase, at one or more high doses. Our present results suggest that OP and NP cause repairable DNA damage, including SCEs, and do not result in CA, while the damage caused by DES, BPA, P-PHBA, and B-PHBA results in the induction of CAs together with SCEs probably because of imperfect repair. We are unable to explain the observation that the DNA damage caused by E2 resulted in CA induction but not DNA migration or SCE induction, except for speculating that the DNA damage is different from that caused by DES and the estrogen-like chemicals. Our findings also suggest that E2, DES and BPA have aneuploidogenic properties, and that the former two of chemicals also are polyploidy-inducing agents.

Nicotine alters bovine oocyte meiosis and affects subsequent embryonic development

The effects of nicotine on nuclear maturation and meiotic spindle dynamics of bovine oocytes and subsequent embryonic development were investigated. Maturation rates (85%-94%) derived from nicotine treatments at 0.01 to 1.0 mM were similar to the control (86%), but significantly decreased at 2.0 to 6.0 mM. Haploid complements of metaphase II oocytes in 0.01 to 1.0 mM nicotine (approximately 90%) were similar to the control, while lower (ranged from 63% to 76%, P < 0.05 or P < 0.01) haploid oocytes were observed in the 2.0 to 6.0 mM nicotine groups. The majority of the PB1-free oocytes derived from 3.0 to 6.0 mM nicotine treatments were diploidy (2n = 60). Spindle microtubules changed from characteristically being asymmetrical in the controls to being equally distributed into two separate chromosome groups in the nicotine treatments. Nicotine disorganized the microfilament organization and inhibited the movement of anaphase or telophase chromosomes to the cortical area. The inhibited two chromosome groups became two spindles that either moved close in proximity or merged entirely together resulting in diploidy within the affected oocyte. Nicotine treatment significantly reduced the rate of cleavage and blastocyst development after parthenogenetic activation. Diploidy and cell number were drastically reduced in the resultant blastocysts. In conclusion, nicotine can alter the normal process of bovine oocyte meiosis and affects subsequent embryonic development.

Postulated carbon tetrachloride mode of action: a review

Under the 2005 U.S. EPA Guidelines for Carcinogen Risk Assessment (1), evaluations of carcinogens rely on mode of action data to better inform dose response assessments. A reassessment of carbon tetrachloride, a model hepatotoxicant and carcinogen, provides an opportunity to incorporate into the assessment biologically relevant mode of action data on its carcinogenesis. Mechanistic studies provide evidence that metabolism of carbon tetrachloride via CYP2E1 to highly reactive free radical metabolites plays a critical role in the postulated mode of action. The primary metabolites, trichloromethyl and trichloromethyl peroxy free radicals, are highly reactive and are capable of covalently binding locally to cellular macromolecules, with preference for fatty acids from membrane phospholipids. The free radicals initiate lipid peroxidation by attacking polyunsaturated fatty acids in membranes, setting off a free radical chain reaction sequence. Lipid peroxidation is known to cause membrane disruption, resulting in the loss of membrane integrity and leakage of microsomal enzymes. By-products of lipid peroxidation include reactive aldehydes that can form protein and DNA adducts and may contribute to hepatotoxicity and carcinogenicity, respectively. Natural antioxidants, including glutathione, are capable of quenching the lipid peroxidation reaction. When glutathione and other antioxidants are depleted, however, opportunities for lipid peroxidation are enhanced. Weakened cellular membranes allow sufficient leakage of calcium into the cytosol to disrupt intracellular calcium homeostasis. High calcium levels in the cytosol activate calcium-dependent proteases and phospholipases that further increase the breakdown of the membranes. Similarly, the increase in intracellular calcium can activate endonucleases that can cause chromosomal damage and also contribute to cell death. Sustained cell regeneration and proliferation following cell death may increase the likelihood of unrepaired spontaneous, lipid peroxidation- or endonuclease-derived mutations that can lead to cancer. Based on this body of scientific evidence, doses that do not cause sustained cytotoxicity and regenerative cell proliferation would subsequently be protective of liver tumors if this is the primary mode of action. To fulfill the mode of action framework, additional research may be necessary to determine alternative mode(s) of action for liver tumors formed via carbon tetrachloride exposure.

Urinary levels of insecticide metabolites and DNA damage in human sperm

BACKGROUND

Members of the general population are exposed to non-persistent insecticides at low levels. The present study explored whether environmental exposures to carbaryl and chlorpyrifos are associated with DNA damage in human sperm.

METHODS

Subjects (n=260) were recruited through a Massachusetts infertility clinic. Individual exposures were measured as spot urinary metabolite concentrations of chlorpyrifos [3,5,6-trichloro-2-pyridinol (TCPY)] and carbaryl [1-naphthol (1N)], adjusted using specific gravity. Sperm DNA integrity was assessed by neutral comet assay and reported as comet extent, percentage DNA in comet tail (Tail%) and tail distributed moment (TDM).

RESULTS

A statistically significant increase in Tail% was found for an interquartile range (IQR) increase in both 1N [coefficient=4.1; 95% confidence interval (CI) 1.9-6.3] and TCPY (2.8; 0.9-4.6), while a decrease in TDM was associated with IQR changes in 1N (-2.2; -4.9 to 0.5) and TCPY (-2.5; -4.7 to -0.2). A negative correlation between Tail% and TDM was present only when stratified by comet extent, suggesting that Tail% and TDM may measure different types of DNA damage within comet extent strata.

CONCLUSIONS

Environmental exposure to carbaryl and chlorpyrifos may be associated with increased DNA damage in human sperm, as indicated by a change in comet assay parameters.

Evaluation of the aneugenic potential of the fungicide Ferbam in mice

Ferbam, a potent dithiocarbamate fungicide is used as a protectant against a wide variety of fungal diseases in fruits, vegetables, and ornamental plants. The wide-spread use of this chemical is likely to pollute the environment. Hence, it was planned to test the possible genotoxicity of Ferbam through its aneugenic potential in the in vivo mouse (Mus musculus) test system. Four different doses of Ferbam, namely, 7.5, 15.0, 30.0, 60.0 mg/kg body weight were administered orally to mice Mus musculus suspended in gum tragacanth representing, respectively, 1/16, 1/8, 1/4;, 1/2 th of the LD50 value. They were sacrificed at 6-, 12-, 24-, and 48-h intervals along with a distilled water negative control at 2 mg/kg body weight. Colchicine treated animals were used as positive controls. Bone marrow preparations were made following the standard Hypotonic flame dry Giemsa staining technique to study the dose and time yield effect of Ferbam. The aneugenic potential was evaluated for C-mitotic effects by scoring the mitotic index, c-mitoses frequency, anaphase reduction, and hyper/hypodiploidy induction. Ferbam showed a significant increase in the mitotic index and C-mitoses effects and anaphase decreased at the highest doses of 30 and 60 mg/kg at 12- and 24-h intervals. Colchicine induced significant effects in all the aneugenic parameters observed at all the time intervals. There was no significant induction of either hyperdiploidy or hypodiploidy by Ferbam, unlike colchicine, indicating that the fungicide Ferbam is not aneugenic in the mouse test system.

Evaluation of acute hepatotoxic effects exerted by environmental estrogens nonylphenol and 4-octylphenol in immature male rats

Nonylphenol (NP) and 4-Octylphenol (4OP) have shown estrogenic properties both in vivo and in vitro. Researchers have known for years that estrogens induce a wide number of hepatotoxic actions in rodents. In order to study the acute hepatic effects exerted by NP and 4OP on rat liver the following endpoints were evaluated: relative liver weight (RLW), morphology, cell cycle and ploidy status, monooxygenase enzymes content and levels of both, cytosolic estrogen receptor (cER) and microsomal binding sites for estrogens (mEBS). Immature male Sprague-Dawley rats were injected intraperitoneally (i.p.) with 60 mg/kg of NP or 4OP for 1, 5 or 10 days. Despite the fact that RLW of the animals was not modified but any treatment, the histopathological study revealed the presence of an increase in the percentage of both, mitotic activity and Ki-67-labeling index (LI) in the livers from animals treated with alkylphenols in absence of any degenerative lesion. Furthermore, all the livers from alkylphenols-treated groups showed the presence of abnormal mitosis and c-mitosis. Although the levels of both, cER and cytochrome P450 (Cyt. P450) were not affected by any treatment, concentration of the mEBS was decreased after 10 days of treatment with alkylphenols. These findings taken together suggest that the exposition to alkylphenols induce cell proliferation and spindle disturbances and that these compounds are capable of modulating the expression of putative membrane receptors for estrogens.

Cytotoxicity of the venom of Pelagia noctiluca forskål (Cnidaria: Scyphozoa)

The activity of Pelagia noctiluca venom was never assessed on cultured cells; therefore, we have evaluated on V79 cells the cytotoxicity, genotoxicity and ATP depletion induced after treatment. Venom did not cause alteration on cell DNA, but showed remarkable cytotoxic properties. With the highest nematocyst concentration (150,000 nematocyst/ml) 74 and 39% cells survived after 1 and 3 h, respectively, when evaluated by Trypan blue. Treated cells showed increased ATP levels during the same time. Preliminary HPLC analyses have showed the occurrence of a protein containing peak.

Are baseline frequencies of SCEs, CAs, and MN in human lymphocytes related to hematological values?

In the present study, the correlation among several hematic values and the baseline frequencies of sister chromatid exchanges (SCEs), chromosome aberrations (CAs), and micronucleus (MN) were evaluated in human peripheral blood lymphocytes from a group of 1429 volunteers. Donors were selected to be representative of the general population of people living in the city of Pisa (Italy). By the use of the principal component analysis (PCA), principal components (PCs) were extracted from the complex pattern of correlations intrinsic in the hematic values (for example such as those among hemoglobin content, hematocrit, and erythrocyte count), and were tested for correlation on SCE, CA and MN frequencies. The seven PCs extracted (among 20 hematic values) were either positively or negatively correlated with the three cytogenetic endpoints. However, after correction by independent confounding factors (such as the age), with the use of the coefficient of partial correlation (CPC) analysis, only one PC significantly held the correlation with MN frequencies. This PC had the main contribution from the correlation between the concentration of potassium and the activity of alkaline phosphatase. These variables are known to be markers for bone (calcium) metabolism and are negatively correlated with MN frequencies. Because MN can arise from aneuploidy, the hematic concentrations of calcium may be important for stabilizing the mitotic process in stimulated lymphocytes. Finally, our study shows that the analysis of the hematic values adds very little information and removes a meaningless part of variance of the total variability observed for SCEs, CAs and MN.

Validation of single cell gel assay in human leukocytes with 18 reference compounds

To validate the alkaline single cell gel (SCG) assay as a tool for the detection of DNA damage in human leukocytes, we investigated the in vitro activity of 18 chemicals. Thirteen of these chemicals (pyrene (PY), benzo(a)pyrene (BaP), cyclophosphamide (CP), 4-nitroquinoline-1-oxide (4NQO), bleomycin (BLM), methylmercury chloride (MMC), mitomycin C (MTC), hydrogen peroxide (HP), diepoxybutane (DEB), glutaraldehyde (GA), formaldehyde (FA), griseofulvin (GF), sodium azide (NA)) are genotoxic in at least one cell system, while five compounds (ascorbic acid (AA), glucose (GL), D-mannitol (MAN), O-vanillin (VAN), chlorophyllin (CHL)) are classified as non-genotoxic. In this in vitro SCG assay, PY, BaP and CP were positive with exogeneous metabolic activation (rat S9 mix) while 4NQO, BLM, MMC, MTC, hydrogen peroxide, and diepoxbutane were positive in the absence of metabolic activation. CHL and VAN were unexpectedly found to induce a dose-dependent increase in DNA migration. AA, GL, and MAN were negative in a non-toxic range of doses. GF gave equivocal results, while FA and GA increased DNA migration at low doses and decreased DNA migration at higher doses. This behaviour is consistent with the known DNA damaging and crosslinking properties of these compounds. These data support the sensitivity and specificity of this assay for identifying genotoxic agents.

Sensitivity of cytokinesis to hydrophobic interactions. Chemical induction of bi-and multinucleated cells

We have tested whether cytokinesis is as sensitive to hydrophobic interactions as karyokinesis, and evaluated the usefulness of the frequency of binucleated cells as end-point. Treating cultured cells for 2 or 24 h, with different lipophilic alcohols and chlorinated hydrocarbons made this possible. Colcemid and cytochalasin B were applied as positive controls for inhibition of karyokinesis and cytokinesis, respectively. Several-fold increases of binucleated cells could be seen with cytochalasin B after 2 h of treatment, while there was no increase with colcemid, which instead blocked cells in prometaphase/metaphase. The solvent acted primarily through hydrophobic interactions. For each solvent, the blocking of cells in prometaphase/metaphase and a minor increase in binucleated cells, were seen at approximately the same concentration; the binucleated cells probably emanated from cells in anaphase/telophase at the start of treatment. We conclude that the spindle function and cleavage show similar sensitivity to hydrophobic interactions. After prolonged treatment, allowing escape from the metaphase block, the solvents induced binucleated and multinucleated cells. By forming the quotient between multinucleated (MULTI) and binucleated (BIN) cells one could distinguish between effects primarily on the spindle or cytokinesis, respectively. All solvents, and a combination of colcemid and cytochalasin B, showed quotients intermediate between those observed with colcemid (high MULTI/BIN) and cytochalasin B (low MULTI/BIN), respectively. Both protocols revealed the same relationship between lowest active concentration and lipophilicity for the solvents, implying that concentration, not dose were of prime importance. The specific inhibitors acted at low concentrations in relation to lipophilicity, clearly demonstrating their chemical mechanisms. This approach can be used for rapid screening of potential aneugens, distinguishing between routes, and when lipophilicity is known, also reveal the principal mechanism of action, i.e. physico-chemical or chemical.

Nonlinearity of nuclear enlargement in hepatocytes induced by the carcinogen N'-nitrosomorpholine in Ovo

In this study we investigated the effects of different doses of the carcinogenic nitrosamine N'-nitrosomorpholine (NNM) on the occurrence of enlarged nuclei in embryonic turkey liver in order to evaluate whether this parameter might represent a quantitative indicator of chemically induced hepatocarcinogenesis. Therefore fertile embryo turkey eggs were injected with NNM over a dose range of 125 microg-8 mg/egg at the first day of incubation. After incubation for 24 days, the embryonic livers were removed and processed for histologic evaluation. The induction of hepatocytes with enlarged nuclei (nuclear profiles > 35 microm2 was quantitated morphometrically in hematoxylin and eosin (H&E)-stained sections. The NNM treatment increased both the number of enlarged hepatocyte nuclei and the areas of the individual profiles of the enlarged nuclei in a dose-dependent manner. Exposure to 500 microg-8 mg NNM/egg resulted in a statistically significant increase in the number of hepatocytes with enlarged nuclei. The lower doses of 250 microg and 125 microg NNM/egg showed a similar albeit not significant trend. Signs for cytotoxic effects on the hepatocytes, such as necrosis or enhanced cytoplasmic vacuolization, were observed in tissue samples of embryos exposed to 4 or 8 mg NNM, but not after treatment with lower doses. The dose-effect curve for the induction of the nuclear enlargement was nonlinear, with a moderate slope for lower dose levels of 125-500 microg/egg and a steep slope for higher dose levels of 1-8 mg. Findings in rodents indicate a pathogenic link between the occurrence of enlarged nuclei and hepatocarcinogenesis. Based on the results with NNM, it is suggested that the in ovo model may represent a rapid, convenient, and inexpensive experimental approach for dose effect investigations on chemically induced hepatocarcinogenesis.

Spindle disturbances induced by benzo[a]pyrene and 7, 12-dimethylbenz[a]anthracene in a Chinese hamster cell line (V79-MZ) and the stability of the numerical chromosome aberrations that follow

We previously reported that benzo[a]pyrene (BP) and 7, 12-dimethylbenz[a]anthracene (DMBA) induce aneuploidy and polyploidy, respectively, in the Chinese hamster cell line V79-MZ in the absence of S9 mix. In the present study we investigated the effect of BP and DMBA on the mitotic spindle. BP caused incomplete spindle formation and DMBA inhibited spindle formation completely. The combined results indicate that incomplete spindles caused by BP resulted in aneuploidy, and the absence of spindle formation caused by DMBA resulted in polyploidy. The induced polyploidy was stable for several serial passages in fresh medium. BP and DMBA induced different chromosome number distributions. After BP treatment, the normal distribution of chromosome number was restored in 4 days. After DMBA treatment, on the other hand, a tetraploid peak was maintained for 2 months following an initial transient broad distribution of chromosome number after 1 day. The results suggest that different mechanisms were involved in the induction of numerical aberrations by BP and DMBA. Furthermore the induction of numerical aberrations by BP and DMBA was reproducible over 5 months of passages. In four clones tested, the frequency of cells with the modal chromosome number in control cultures gradually decreased from 82% on the average just after cloning to 62% 5 months later. BP and DMBA induced characteristic ploidy changes following succeeding cell passages for up to 5 months, indicating that the ability to respond to BP and DMBA was stable for that period of time. Because these findings were specific to V79-MZ cells, this cell line might be a good tool for studying chemicals that induce numerical chromosome aberrations.

C-mitotic effects of trichloroethylene (TCE) on bone marrow cells of mice

The possible aneuploidy inducing activity of Trichloroethylene (TCE, CAS No. 79-01-6) an industrial chemical was investigated by employing three cytogenetic end points i.e., C-mitotic effects, Micronuclei (MN) and parallel chromosome structural aberration (CA) analysis in vivo. The experiments were conducted in mouse bone marrow cells. The animals were treated with TCE in the dose of 500, 1000, 2000 and 4000 mg/kg for 6, 12, 24, 48 hr. Colchicine (COL) was taken as positive control for its known aneuploidy-inducing effects and Cyclophosphamide as a model mutagen. TCE showed positive CM effects accompanied with increases of Mitotic Index and decreased frequencies of anaphases in higher doses. The chemical showed a positive MN response in bone marrow polychromatic erythrocytes but was negative in CA analysis. The preliminary results indicated that TCE is capable of inducing C-mitotic effects in mouse bone marrow cells which is suggestive of its possible aneuploidy induction potential.

Needle crystals of vitamin B2 induce polyploidy in Chinese hamster lung (CHL/IU) cells

Induction of polyploidy by vitamin B2 (VB2) was investigated in cultured Chinese hamster lung (CHL/IU) cells. We report that VB2 in the form of needle crystals induces polyploidy via the formation of CHL/IU cells with more than one nucleus. The incidence of polyploid cells depended on the amount of needle crystals. No induction of polyploidy was observed when VB2 was used in solution. Electron-microscopic examination revealed that needle crystals adhered to the cell surface, and were enclosed by viscous cellular materials. These results indicate that needle crystals of VB2 have the ability to induce polyploidy in cultured CHL/IU cells, probably by physically fixing the shape of the cells and by this preventing normal mitosis.

The detection and evaluation of aneugenic chemicals

Although aneuploidy makes a significant contribution to both somatic and inherited disease the mechanisms by which environmental chemicals may induce numerical chromosome aberrations are only poorly defined. The European Union Project was aimed to further our understanding of those chemical interactions with the components of the mitotic and meiotic cell division cycle which may lead to aneuploidy and to characterise the parameters such as cellular metabolism which may influence the activity of aneugenic chemicals. C-mitosis can be induced by the highly lipophilic polychlorinated biphenyl and the completion of mitosis and cleavage can be modified by agents which deplete cellular levels of reduced glutathione. Modifications of the fidelity of chromosome segregation were produced by inhibiting the functioning of topoisomerase II during chromatid separation. In contrast, the modification of centromere integrity resulted in chromosome breakage as opposed to disturbance of segregation. Modifiers of tubulin assembly and centriolar functioning in somatic cells such as acrylamide, vinblastine and diazepam reproduced their activity in rodent bone marrow and male germ cells. The analysis of chromosome malsegregation in Aspergillus nidulans by a structurally related series of halogenated hydrocarbons was used to develop a QSAR model which had high predictive value for the results of fungal tests for previously untested related chemicals. Metabolic studies of potential aneugens in genetically engineered human lymphoblastoid cells demonstrated the detoxification of the aneugenic activity of chloral hydrate and the activation of 2,3-dichlorobutane, 1,1,2-trichloroethane and trichloroethylene by Phase I biotransforming enzymes. Cell transformation studies in Syrian hamster dermal cultures using a panel of 22 reference and or potential aneugens indicated that 15 of the 22 produced positive results following single exposures. Five of the aneugens which were negative following single exposures produced positive results where cultures were continuously exposed for up to 6 weeks to low concentrations following a single non-transforming exposure to the mutagen dimethyl sulphate. The transformation studies indicate that a significant proportion of chemical aneugens are potential complete carcinogens and/or co-carcinogens. To optimise the enumeration of chromosomes following exposure to potential chemical aneugens whole chromosome paints and centromere specific probes suitable for use in fluorescence in situ hybridisation (FISH) were developed for the rat, mouse and Chinese hamster and selected human probes evaluated for their suitability for routine use. Molecular chromosome probes were used to develop protocols for enumerating chromosomes in metaphase cells and centromeres and micronuclei in interphase cells. The analysis of segregation of specific centromeres in binucleate cells following cytochalasin B treatment was shown to be a potentially valuable system for characterising non-disjunction following chemical exposure. Whole chromosome paints and centromere specific probes were used to demonstrate the presence of dose-response thresholds following treatment with a reference panel of spindle inhibiting chemicals. These data indicate that the FISH technology is suitable for evaluating the relative hazards of low-dose exposures to aneugenic chemicals.

Paracetamol-induced spindle disturbances in V79 cells with and without expression of human CYP1A2

Spindle disturbing effects in terms of c-mitosis and cytotoxicity of paracetamol were investigated in two Chinese hamster V79 cell lines, one of which (V79MZh1A2) was transfected with human CYP1A2. This enzyme catalyses the oxidative formation of the reactive paracetamol metabolite, NAPQI, believed to initiate hepatoxicity by covalent binding to proteins after overdose. In the native V79 cell line paracetamol increased c-mitosis frequency in a concentration dependent manner from 8.7 + or - 3.5% (control) to 66 + or - 18% at 20 mM. A significant increase to 13.3 + or - 3.5% was first seen at 2.5 mM in the native cell line (P<0.05). In the V79MZh1A2 cells the concentration-effect curve was slightly shifted to the left (P<0.05) with c-mitosis frequency increased to 12.1 + or - 2.6% (P<0.05) at 1 mM paracetamol. At 5 mM paracetamol the c-mitosis frequency was 14.4 + or - 5.0% and 19.0 + or - 3.8% in the native and CYP1A2 expressing cell lines, respectively (P<0.05). At 20 mM paracetamol the c-mitosis frequency was 61 + or - 10% in the V79MZh1A2 cells. Cell survival was reduced to approximately 50% at 5-10 mM paracetamol in both cell lines. At 20 mM paracetamol survival was further decreased to 39 + or - 9% in V79MZh1A2 cells only (P<0.05). The present study demonstrated that paracetamol may disturb the spindle of dividing cells conveying a risk of aneuploidy. The spindle disturbing effect was only slightly enhanced by expression of CYP1A2, suggesting that metabolic activation plays only a minor role in this genotoxic effect. The reduction of survival mirrored the increase in c-mitosis frequency.

Toxicology of halogenated aliphatic hydrocarbons: structural and molecular determinants for the disturbance of chromosome segregation and the induction of lipid peroxidation

The induction of mitotic chromosome malsegregation, mitotic arrest and lethality by a set of 55 halogenated hydrocarbons was investigated. To this aim, genetic assays in the mould Aspergillus nidulans, able to provide precise quantitative information on the end-points studied, were used throughout the work. The experimental data obtained were used to develop QSAR models for the induction of aneuploidy, which pointed to a major role of electrophilicity as molecular determinant for the aneugenic potential of the halogenated hydrocarbons investigated. Within the hypothesis of a link between the electrophilicity of haloalkanes and their propensity to undergo a reductive biotransformation, with production of free radical species, a subset of 27 compounds was also tested for the ability to induce lipid peroxidation in rat liver microsomes in vitro. The results obtained indicate a partial coincidence between the abilities to initiate lipid peroxidation and to disturb chromosome segregation at mitosis. The data base obtained was also used to investigate the relationship between chemical structure and peroxidative potential. The analysis indicated that electronic and structural parameters related to the ease of homolitic cleavage of the carbon-halogen bond play a pivotal role as determinants for the peroxidative character of haloalkanes.

Comparative QSAR in toxicology: examples from teratology and cancer chemotherapy of aniline mustards

During the past 30 years, thousands of quantitative structure-activity relationships (QSAR) have been published for all sorts of chemicals acting on many forms of life or parts thereof (DNA, enzymes, organelles, etc.). Very little effort has been made to show the relationship among these equations. In this report, we discuss two examples, the toxicity of phenols to rats and the effect of aniline mustards on a variety of living systems, where the electronic effects in the QSAR can be correlated to QSAR from physical organic chemistry. This enables one to make better mechanistic deductions about the biological structure-activity relationships. From this, it is concluded that radicals formed from the phenols cause birth defects.

A dichotomy between lipophilicity and in vivo and in vitro genotoxicity

An analysis of a number of data bases revealed a dichotomy between the lipophilicity of groups of agents capable of inducing genotoxicity in vitro and in vivo. Thus agents with the potential for reacting with cellular DNA, inducing mutations in Salmonella and clastogenicity in cultured cells were characteristically significantly more hydrophilic than agents which did not induce such effects. On the other hand, in vivo inducers of clastogenicity (micronuclei) were significantly more lipophilic than non-inducers. Cellular and systemic toxicants were also more lipophilic than non-toxicants.

Bombesin impairs spindle function in mitotic V79 Chinese hamster cells by a receptor-dependent mechanism

Bombesin belongs to a family of peptides acting as local hormones with roles in growth regulation, neural function and secretion. Upon binding to its receptor bombesin primarily elicits an increase of inositolphosphates and diacylglycerol, events leading to increased [Ca2+]i and activation of protein kinase C. When asynchronously growing V79 Chinese hamster cells were treated with bombesin in the 10(-9)-10(-7) M concentration range their content of inositolphosphates increased and so did the frequency of mitotic cells with abnormal chromosomal arrangements (c-mitoses). Both effects were abolished by simultaneous addition of the synthetic peptide antagonist D-Arg1,D-Phe5,D-Trpu7,9-Leu11-substance P that binds to certain bombesin receptors. These results demonstrate that the V79 cells most probably have receptors for bombesin and that the weak but significant c-mitotic effect is mediated by such receptors.

The induction of mitotic chromosome malsegregation in Aspergillus nidulans. Quantitative structure activity relationship (OSAR) analysis with chlorinated aliphatic hydrocarbons

The biological activity of 24 chlorinated aliphatic hydrocarbons has been studied in the mold Aspergillus nidulans. The ability to induce chromosome malsegregation, lethality and mitotic growth arrest has been experimentally determined for each chemical. These data, together with those of 11 related compounds previously investigated, generated a data base which was used for quantitative structure-activity relationship (QSAR) analysis. To this aim, both physico-chemical descriptors and electronic parameters of each compound have been calculated and included in the analysis. The QSAR analysis indicated that toxic effects induced by chlorinated aliphatics in A. nidulans are mainly dependent on steric factors, as indicated by the correlation with molar refractivity (MR). Conversely, the ease with which they accept electrons, parametrized by LUMO (energy of the lowest unoccupied molecular orbital), plays a prevailing role in determining the aneuploidizing properties. An involvement of free radicals, generated by the reductive metabolism of haloalkanes, is hypothesized as an explanation of the data.

Reproductive hazards of fire fighting. II. Chemical hazards

Studies of the health of fire fighters have historically focused on non-malignant respiratory disease and cancer. More recently, concerns have surfaced about reproductive health effects in many areas of the workforce, including fire fighting. These concerns prompted this review of chemical exposures that may contribute to adverse reproductive health outcomes in male as well as female fire fighters. A review of the industrial hygiene literature was undertaken to identify agents commonly found in fire smoke. These agents were then examined for evidence of reproductive toxicity or mutagenicity/carcinogenicity. This profile of chemical agents and their reproductive toxicities permits a qualitative determination that fire fighters are exposed to potential reproductive toxicants as a part of their normal fire fighting duties. Considerations for mitigating these risks are also discussed.

A comparative study on ethanol and acetaldehyde as inducers of chromosome malsegregation in Aspergillus nidulans

The activity of ethyl alcohol and acetaldehyde on mitotic chromosome segregation and conidial germination in Aspergillus nidulans was studied. Ethanol effectively induced malsegregation in a narrow range of concentrations (4.5-5.5%, v/v) and was inactive at doses which arrested conidial germination (above 6%). The same bell-shaped dose-response curve was shown by the spindle poison chloral hydrate, which was active in the range 6-10 mM. Acetaldehyde displayed a diphasic dose-response curve. Genetic analysis of induced segregants suggests that the disturbance of chromosome segregation is the primary genetic effect at low doses (0.025-0.037%), while at higher doses (above 0.1%), when growth was arrested, chromosome damage was primarily induced. The same pattern of segregants was produced by hydroquinone, a substance which indirectly affects chromosome segregation in A. nidulans. These differences in the genotoxic profiles of ethanol and acetaldehyde suggest that the effect exerted by ethanol on A. nidulans mitosis is not dependent on its conversion into acetaldehyde. In the absence of an effect of ethanol on in vitro polymerization of tubulin (actively inhibited by acetaldehyde at doses above 0.075%), a direct effect of ethanol on cell membranes is hypothesized. Comparison of the inhibition of growth and the effectiveness in aneuploidy induction displayed by ethanol, methanol, n-propanol and n-butanol demonstrates, in fact, a fair correlation with logP, a descriptor of lipophilicity related to the partitioning of compounds in biological membranes.

Chromosomal instability and progressive loss of chromosomes in HeLa cells during adaptation to hyperoxic growth conditions

By sequential selection for resistance to stepwise increased levels of atmospheric O2, a genetic variant of HeLa cells was obtained capable of stable proliferation under an atmosphere containing 80% O2 (HeLa-80). This cell strain has previously been characterized in terms of growth characteristics, morphology and antioxidant status (Joenje et al., 1985). In an attempt to find cytogenetic clues possibly related to the O2-tolerant character, metaphases of HeLa-80 cells were analyzed and compared to the parental (HeLa-20) strain. Numerical analysis revealed a progressive decrease in the number of chromosomes per cell during selection for O2 resistance, from a modal number of 112 in HeLa-20 cells to 84 in HeLa-80 cells. Cytogenetic endpoints for genetic damage revealed increased frequencies in HeLa-80 cells of both chromosomal aberrations (29.7 versus 6.9% aberrant cells) and sister-chromatid exchanges (0.46 +/- 0.13 versus 0.31 +/- 0.10 SCE/chromosome). G-banded metaphases failed to reveal cytogenetic evidence of gene amplification (homogeneously staining regions, double minutes) in the karyotype of HeLa-80 cells.

Mitotic arrest induced by fenvalerate in human lymphocyte cultures

The pyrethroid insecticide fenvalerate was tested for its ability to induce C-mitosis in cultured human peripheral blood lymphocytes at concentrations ranging from 2-50 micrograms/ml. We observed a significant increase in C-mitotic figures, indicating that this compound was effective in producing disturbance of spindle function.

Induction of chromosome malsegregation by halogenated organic solvents in Aspergillus nidulans: unspecific or specific mechanism?

Three chloromethanes (dichloromethane, chloroform and carbon tetrachloride) and 8 chlorinated ethanes (1,1- and 1,2-dichloroethane, 1,1,1- and 1,1,2-trichloroethane, 1,1,1,2- and 1,1,2,2-tetrachloroethane, pentachloroethane and hexachloroethane) were assayed in tests for the induction of mitotic segregation in Aspergillus nidulans diploid strain P1. Eight of the 11 compounds assayed (dichloromethane, chloroform, carbon tetrachloride, 1,1- and 1,2-dichloroethane, 1,1,2-trichloroethane, 1,1,1,2- and 1,1,2,2-tetrachloroethane) significantly increased the frequency of morphologically abnormal colonies which produced euploid whole-chromosome segregants (haploids and non-disjunctional diploids). Only in one case (1,1,1,2-tetrachloroethane) was a borderline increase in crossing-over frequency observed, thus suggesting the involvement of non-DNA targets in aneuploidy induction by these chlorinated hydrocarbons. Conclusive evidence for the induction of aneuploidy as the primary genetic event was provided by experiments in haploid strain 35 with 1,2-dichloroethane and 1,1,1,2-tetrachloroethane. Mutagenic, lethal and growth-arresting activities were quantitatively estimated and compared to a series of descriptors of physical and chemical properties of the molecules by means of multivariate statistical analysis. Lipophilicity, known to be related to c-mitotic activity, did not show any significant relationship with aneuploidizing activity, whereas a possible correlation among physico-chemical descriptors and toxic properties of test chemicals was highlighted.

The action of carbaryl and its metabolite alpha-naphthol on mitosis in V79 Chinese hamster fibroblasts. Indications of the involvement of some cholinester in cell division

Carbaryl (1-naphthyl-N-methylcarbamate) is a spindle-disturbing agent. A number of effects probably contribute to this activity. Carbaryl efficiently lowers the intracellular level of glutathione, thus endangering the integrity of the spindle. Carbaryl also causes lipid peroxidation. With anti-oxidant pretreatment, the frequency of c-mitotic cells is lowered which indicates that lipid peroxidation is a partial cause of the spindle-disturbing activity. At high concentrations of carbaryl, monopolar configurations in combination with cleavage are frequent and when tested, alpha-naphthol, which is thought to be formed from carbaryl in significant amounts at these concentrations, also gave monopolar configurations but with significantly lower frequencies of concomitant cleavage. Carbaryl inhibits cholinesterases and when tested, another cholinesterase inhibitor, diisopropylfluorophosphate, in combination with alpha-naphthol also increased the frequency of monopolar configuration in combination with cleavage. We therefore propose the involvement of some cholinester in the process of cell division.