Tests which distinguish induced crossing-over and aneuploidy from secondary segregation in Aspergillus treated with chloral hydrate or gamma-rays

Carcinogenicity of chloral hydrate administered in drinking water to the male F344/N rat and male B6C3F1 mouse

Male B6C3F1 mice and male F344/N rats were exposed to chloral hydrate (chloral) in the drinking water for 2 years. Rats: Measured chloral hydrate drinking water concentrations for the study were 0.12 g/L, 0.58 g/L, and 2.51 g/L chloral hydrate that yielded time-weighted mean daily doses (MDDs) of 7.4, 37.4, and 162.6 mg/kg per day. Water consumptions, survival, body weights, and organ weights were not altered in any of the chloral hydrate treatments. Life-time exposures to chloral hydrate failed to increase the prevalence (percentage of animals with a tumor) or the multiplicity (tumors/animal) of hepatocellular neoplasia. Chloral hydrate did not increase the prevalence of neoplasia at any other organ site. Mice: Measured chloral hydrate drinking water concentrations for the study were 0.12 g/L, 0.58 g/L, and 1.28 g/L that gave MDDs of 13.5, 65.0, and 146.6 mg/kg per day. Water consumptions, survival, body and organ weights, were not altered from the control values by any of the chloral hydrate treatments. Enhanced neoplasia was observed only in the liver. Prevalence and multiplicity of hepatocellular carcinoma (HC) were increased only for the high-dose group (84.4%; 0.72 HC/animal; p < or = 0.05). Values of 54.3%; 0.72 HC/animal and 59%; 1.03 HC/animal were observed for the 13.5- and 65.0-mg/kg per day treatment groups. Prevalence and multiplicity for the control group were 54.8%; 0.74 HC/animal. Hepatoadenoma (HA) prevalence and multiplicity were significantly increased (p < or = 0.05) at all chloral hydrate concentrations: 43.5%; 0.65 HA/animal, 51.3%; 0.95 HA/animal and 50%; 0.72 HA/animal at 13.5, 65.0, and 146.6 mg/kg per day chloral hydrate compared to 21.4%; 0.21 HA/animal in the untreated group. Altered foci of cells were evident in all doses tested in the mouse, but no significant differences were observed over the control values. Hepatocellular necrosis was minimal and did not exceed that seen in untreated rats and mice. Chloral hydrate exposure did not alter serum chemistry and hepatocyte proliferation in rats and mice or increase hepatic palmitoyl CoA oxidase in mice at any of the time periods monitored. It was concluded that chloral hydrate was carcinogenic (hepatocellular neoplasia) in the male mouse, but not in the rat, following a lifetime exposure in the drinking water. Based upon the increased HA and combined tumors at all chloral hydrate doses tested, a no observed adverse effect level was not determined.

Genotoxicity of an extract of Calendula officinalis L

A fluid extract of Calendula officinalis L. displayed genotoxic properties when assayed for mitotic segregation in the heterozygous diploid D-30 of Aspergillus nidulans. The extract of Calendula exhibited dose-dependent toxicity and genotoxicity (both mitotic crossing-over and chromosome malsegregation being observed) to Aspergillus in the range of five plate concentrations from 0.1 to 1.0 mg of solids/ml assayed. Mutagenicity testing with the Salmonella/microsome assay in strains TA 1535, TA 1537, TA 98 and TA 100 was negative in a plate incorporation protocol, with concentrations ranging from 50 to 5000 microg/plate (+/- S9). The mouse bone marrow micronucleus test, where the extract was dosed orally up to 1 g/kg for 2 days, was also negative.

Mutagenicity of three disinfection by-products: di- and trichloroacetic acid and chloral hydrate in L5178Y/TK +/- (-)3.7.2C mouse lymphoma cells

The disinfection of water, required to make it safe for human consumption, leads to the presence of halogenated organic compounds. Three of these carcinogenic 'disinfection by-products', dichloroacetic acid (DCA), trichloroacetic acid (TCA) and chloral hydrate (CH) have been widely evaluated for their potential toxicity. The mechanism(s) by which they exert their activity and the steps in the etiology of the cancers that they induce are important pieces of information that are required to develop valid biologically-based quantitative models for risk assessment. Determining whether these chemicals induce tumors by genotoxic or nongenotoxic mechanisms (or a combination of both) is key to this evaluation. We evaluated these three chemicals for their potential to induce micronuclei and aberrations as well as mutations in L5178Y/TK +/- (-)3.7.2C mouse lymphoma cells. TCA was mutagenic (only with S9 activation) and is one of the least potent mutagens that we have evaluated. Likewise, CH was a very weak mutagen. DCA was weakly mutagenic, with a potency (no. of induced mutants/microgram of chemical) similar to (but less than) ethylmethanesulfonate (EMS), a classic mutagen. When our information is combined with that from other studies, it seems reasonable to postulate that mutational events are involved in the etiology of the observed mouse liver tumors induced by DCA at drinking water doses of 0.5 to 3.5 g/l, and perhaps chloral hydrate at a drinking water dose of 1 g/l. The weight-of-evidence for TCA suggest that it is less likely to be a mutagenic carcinogen. However, given the fact that DCA is a weak mutagen in the present and all of the published studies, it seems unlikely that it would be mutagenic (or possibly carcinogenic) at the levels seen in finished drinking water.

Screening of medicinal plants for induction of somatic segregation activity in Aspergillus nidulans

Knowledge about mutagenic properties of plants commonly used in traditional medicine is limited. A screening for genotoxic activity was carried out in aqueous or alcoholic extracts prepared from 13 medicinal plants widely used as folk medicine in Cuba: Lepidium virginicum L. (Brassicaceae): Plantago major L. and Plantago lanceolata L. (Plantaginaceae); Ortosiphon aristatus Blume, Mentha x piperita L., Melissa officinalis L. and Plectranthus amboinicus (Lour.) Spreng. (Lamiaceae); Cymbopogon citratus (DC.) Stapf (Poaceae); Passiflora incarnata L. (Passifloraceae); Zingiber officinale Roscoe (Zingiberaceae); Piper auritum HBK. (Piperaceae); Schinus terebinthifolius Raddi (Anacardeaceae) and Momordica charantia L. (Cucurbitaceae). A plate incorporation assay with Aspergillus nidulans was employed, allowing detection of somatic segregation as a result of mitotic crossing-over, chromosome malsegregation or clastogenic effects. Aspergillus nidulans D-30, a well-marked strain carrying four recessive mutations for conidial color in heterozygosity, which permitted the direct visual detection of segregants, was used throughout this study. As a result, only in the aqueous extract of one of the plants screened (Momordica charantia) a statistical significant increase in the frequency of segregant sectors per colony was observed, and consequently, a genotoxic effect is postulated.

Micronuclei induced in round spermatids of mice after stem-cell treatment with chloral hydrate: evaluations with centromeric DNA probes and kinetochore antibodies

The chromosomal effects of chloral hydrate (CH) on germ cells of male mice were investigated using two methods to detect and characterize spermatid micronuclei (SMN); (a) anti-kinetochore immunofluorescence (SMN-CREST) and (b) multicolor fluorescence in situ hybridization with DNA probes for centromeric DNA and repetitive sequences on chromosome X (SMN-FISH). B6C3F1 mice received single intraperitoneal (i.p.) injections of 82.7, 165.4, or 413.5 mg/kg and round spermatids were sampled at three time intervals representing cells treated in late meiosis, early meiosis, or as spermatogonial stem cells. No increases in the frequencies of SMN were detected for cells treated during meiosis using either SMN-CREST or SMN-FISH methods. After spermatogonial stem-cell treatment, however, elevated frequencies of SMN were detected by both methods. With SMN-FISH, dose trends were observed both in the frequencies of spermatids containing micronuclei and in the frequency of spermatids carrying centromeric label. These findings corroborate the recent report by Allen and colleagues [Allen JW et al.(1994): Mutat. Res. 323:81-88] that CH treatment of spermatogenic stem cells induced SMN. Furthermore, our findings suggest that chromosomal malsegregation or loss may occur in spermatids long after CH treatment of stem cells. Further studies are needed to understand the mechanism of action of the CH effect on stem cells and to determine whether similar effects are induced in human males treated with CH.

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.

Potential carcinogenicity of chloral hydrate--a review

Chloral hydrate is commonly used to sedate children for diagnostic or therapeutic procedures. The drug has been extensively used for many years, but there are remarkably few data on its long-term health effects. Concern in this regard is raised by recent studies showing chloral hydrate to be genotoxic, causing chromosome changes and other effects in vivo and in vitro. In addition, chloral hydrate is a reactive metabolite of trichloroethylene, a known carcinogen, and is structurally similar to other carcinogenic intermediates. Two carcinogenicity studies performed using the oral route of administration in mice indicate that the drug is potentially carcinogenic--in one case after a single dose lower than the typical dose used for sedation. Practitioners should be aware of chloral hydrate's genotoxicity and potential carcinogenicity. Discretion in its use seems appropriate until further studies clarify its long term health consequences.

Induction of mitotic aneuploidy using Chinese hamster primary embryonic cells. Test results of 10 chemicals

Using primary Chinese hamster embryonic cells, 10 known or suspected aneugens supplied as a part of the EC 4th Environmental Research and Development Programme were evaluated by the technique described by Dulout and Natarajan (1987). The chemicals included cadmium chloride, chloral hydrate, colchicine, diazepam, econazole, hydroquinone, pyrimethamine, thiabendazole, thimerosal and vincristine. All chemicals except pyrimethamine gave clearly positive effect at most of the doses tested. The ease with which the assay is performed and reproducible results that are obtained with the suspected compounds indicate that this in vitro test using primary embryonic fibroblasts is a promising one for routine screening.

A mechanism for the development of Clara cell lesions in the mouse lung after exposure to trichloroethylene

Female CD-1 mice exposed to trichloroethylene (6 h/day) at concentrations from 20-2000 ppm developed a highly specific lung lesion after a single exposure, characterised by vacuolation of the Clara cells, the number of cells affected increasing with increasing dose level. At the highest dose levels pyknosis of the Clara cells was apparent. After 5 days of repeated exposures the lesion had resolved but exposure of mice following a 2-day break resulted in recurrence of the lesion. The changes in mouse lung Clara cells were accompanied by a marked loss of cytochrome P-450 activities. No morphological changes were seen in the lungs of rats exposed to either 500 or 1000 ppm trichloroethylene. Isolated mouse lung Clara cells were shown to metabolize trichloroethylene to chloral, trichloroethanol and trichloroacetic acid. Chloral was the major metabolite. Trichloroethanol glucuronide was not detected. In comparative experiments using mouse hepatocytes the major metabolites were trichloroethanol and its glucuronide conjugate. The activity of UDP-glucuronosyltransferase was compared in mouse lung Clara cells and hepatocytes using two phenolic substrates and trichloroethanol. Hepatocytes readily formed glucuronides from all three substrates whereas Clara cells were only active with the two phenolic substrates. The three major metabolites of trichloroethylene, chloral, trichloroethanol and trichloroacetic acid were each dosed to mice and of these metabolites, only chloral had an effect on mouse lung causing a lesion (Clara cell) identical to that seen with trichloroethylene. It is proposed that the failure of Clara cells to conjugate trichloroethanol leads to an accumulation of chloral which results in cytotoxicity. The known genotoxicity of chloral suggests that this lesion may be related to the development of lung tumours in mice exposed to trichloroethylene by inhalation.

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.

Fate of 2,2,2-trichloroacetaldehyde (chloral hydrate) produced during trichloroethylene oxidation by methanotrophs

Four different methanotrophs expressing soluble methane monooxygenase produced 2,2,2-trichloroacetaldehyde, or chloral hydrate, a controlled substance, during the oxidation of trichloroethylene. Chloral hydrate concentrations decreased in these cultures between 1 h and 24 h of incubation. Chloral hydrate was shown to be biologically transformed to trichloroethanol and trichloroacetic acid by Methylosinus trichosporium OB3b. At elevated pH and temperature, chloral hydrate readily decomposed and chloroform and formic acid were detected as products.

Botran and bleomycin induce crossing-over, and bleomycin also increases aneuploidy in diploid strains of Aspergillus

Both bleomycin, an antineoplastic drug, and botran (2,6-dichloro-4-nitro-aniline), a fungicide, are known to inhibit growth and induce genetic segregation in diploid tester strains of Aspergillus nidulans when present in agar media. To identify primary effects, samples of induced apparent crossover types were analysed in detail. For both compounds, coincident and consecutive events of mitotic crossing-over were found to be very frequent and such events showed a random distribution among isolated colour sectors. In the case of botran, a thorough search for imbalanced precursor types was negative and recessive lethals were found only rarely. Such segregants are therefore unlikely the result of terminal deletions. For bleomycin, induction of reciprocal crossing-over was confirmed by treatments of germinating conidia. On plating to normal growth medium, crossover segregants showed up as coloured half- or quarter-colonies, including some "twin spots". Whole coloured colonies were also frequent and these increased with dose levels which caused decreasing survival and increasing frequencies of abnormal colonies. Analysis of large fractions of such "abnormals" identified aneuploids in all cases. While botran, in plate tests, also increased haploid segregants and disomic precursors could be found, tests of germinating conidia "in liquid" were inconclusive, because botran is insoluble in water. Some increases of aneuploids were observed, but only when botran and the solvent DMSO both were present at increased levels.

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.

Genetic toxicology of 1,1,2-trichloroethylene

1,1,2-Trichloroethylene (TCE) is a widely used halogenated solvent, produced in hundreds of millions of kg each year for industrial purposes. Occupational and environmental exposure of human populations to TCE has been reported in industrialized areas. Long-term carcinogenicity studies in rodents demonstrate that exposure to high doses of TCE results in the induction of liver and lung tumors in the mouse, and tumors of the kidney and the testis in the rat. An indirect mechanism, based on the stimulation of liver peroxisome proliferation by TCE metabolites, was proposed to explain species differences in TCE hepatocarcinogenicity. Mutagenicity studies indicate that TCE is weakly active both in vitro, where liver microsomes produce electrophilic TCE metabolites, and also in vivo in mouse bone marrow, where high rates of micronuclei, but no structural chromosome aberrations, are found. Among TCE metabolites, trichloroacetic acid was reported to be carcinogenic to mouse liver. Furthermore, both trichloroacetic acid and chloral hydrate were found to be genotoxic in vivo, inducing structural and numerical chromosome abnormalities, respectively.

Genotoxic effects of niclosamide in Aspergillus nidulans

A 2-5-month treatment with niclosamide, a widely used drug in developing countries, has been reported to induce lymphosarcomas in toad liver and kidney. The genotoxic effects of this drug have also been evaluated in Salmonella typhimurium, in somatic and germinal cells of mice and in human lymphocytes exposed in vitro and in vivo. The present study shows that niclosamide is also capable of inducing mitotic crossing-over and non-disjunction in Aspergillus nidulans, which points to the wide potential of this drug as a genotoxic agent.

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.

MMS-induced primary aneuploidy and other genotoxic effects in mitotic cells of Aspergillus

The possibility of more than 1 target for genotoxic effects of methyl methanesulphonate (MMS) was investigated, using mitotic test systems of the fungus Aspergillus. Haploid and diploid strains were exposed, either as dormant conidia or during mitosis, and analysed for induced aneuploidy and effects on genetic segregation. MMS treatment of haploid strains resulted in dose-dependent increases of stable mutants with altered phenotypes and semi-stable unbalanced aberrations (presumably duplications). In addition, but only in dividing cells, MMS induced unstable aneuploids. These mostly were hyperhaploid with few extra chromosomes and could be identified by comparison with standard disomic phenotypes. When well-marked diploids were treated 3 types of effect could be distinguished, using genetic and phenotypic criteria: (1) Clastogenic and mutagenic effects which caused dose-dependent increases of partial aneuploids with various abnormal phenotypes. These showed secondary genetic segregation of all types and produced euploid normal sectors by eliminating damaged chromosome segments. In addition, but only in dividing nuclei, MMS induced 2 types of segregation: (2) Reciprocal crossing-over at high frequency, recognisable as half or quarter colonies of mutant colour and in some cases as 'twin spots' (i.e., complementary pairs); (3) Trisomics and other aneuploids which showed characteristic phenotypes and expected segregation of markers: the types recovered indicate random malsegregation of chromosomes (occasional deviations resulted from coincidence with induced crossing-over). These results suggest that MMS may have 2 (or more) targets for genotoxic effects: DNA, as evident from induced mutations and aberrations, and from induced recombination in dividing cells; some non-DNA target (nucleotide or protein) essential for nuclear division and susceptible to alkylation, resulting in malsegregation and primary aneuploidy.

Genetic analysis of DNA repair in Aspergillus: evidence for different types of MMS-sensitive hyperrec mutants

To identify genes which affect DNA repair and possibly recombination in Aspergillus nidulans, mutants hypersensitive to methyl methanesulphonate (MMS) were induced with ultraviolet light (UV) or gamma-rays. About half of them contained associated translocations and many were hypersensitive to UV and/or defective in meiosis. Two are alleles of the known uvsB gene while most others define new genes. In addition, among available uvs mutants many were found to be MMS-sensitive. Some of the various uncharacterized ones were identified as alleles of known uvs, but 5 of them were mapped in 2 new genes, uvsH and uvsJ. To identify functional and epistatic groups, mutants from each uvs gene were tested for effects on recombination and mutation, and double mutant uvs strains were compared for UV survival to their component single mutant strains. 3 epistatic pairs were identified, (1) uvsF and H, (2) uvsB and D, and (3) uvsC and E. Conclusive interpair tests were difficult, because such double mutant combinations were frequently lethal or nearly so. The first pair, uvsF and H, shared some of the properties of excision-defective mutants, both uvs being very highly sensitive to UV for mutation as well as survival. But unlike such mutants, uvsH was also sensitive to gamma-rays and defective in meiosis. Both uvs showed normal levels of meiotic recombination, but greatly increased spontaneous mitotic crossing-over, being the most "hyperrec" types among all uvs. The second pair, uvsB and uvsC, which was similarly hyperrec showed only slight increases of UV-induced mutation (less than 2-fold). As a main effect, these uvs caused very high frequencies of unbalanced, unstable segregants from diploid conidia (30 X), but few of these were recognizable aneuploids. The third pair, uvsC and E, which are known to be rec- for gene conversion, caused reduced mitotic crossing-over in diploids and increased levels of haploid segregants. These mutants are spontaneous mutators, but showed less UV-induced mutation than wild-type controls.