G. Conti

Non-disjunction and crossing-over induced by pharmaceutical drugs in Aspergillus nidulans

Summary A system has been developed to test rapidly, with diploids of Aspergillus nidulans , the non-disjunction and crossing-over induced by drugs. The test permits a semiquantitation of the induced damage. 110 pharmaceutical specialities were tested. 13 of them strongly increased the incidence of somatic segregation. The spontaneous rate was approximately 1 · 10 -5 of non-disjunction. The drugs that were mutagenic belong to the following classes. (1) Quinolines—4 specialities containing quinolines of various types were tested. All increased the incidence of non-disjunction up to 36% of the plated conidia. (2) Sulfa drugs—6 were tested and all but 3 induced crossing-over. Maximal incidence was 45% of the plated conidia. (3) Benzodiazepines—8 were tested. Only one significantly increases non-disjunction. The frequency was 5%. (4) Pyrazolidines—9 were tested of which two induced non-disjunction. The frequency was 10%. (5) Various—chemicals of widely different composition were also mutagenic. These were: Entobex 15%, Mucoxin 11%, Tanderil 10%, Nitrofurin (nitrofurantoin) 12%, Lipopill (phentermine) 14%, Esidrex 96%.

Mutagenicity spectra in bacterial strains of airborne and engine exhaust particulate extracts

The mutagenicity spectra of the organic extracts of both airborne particulate matter and diesel and gasoline soot particles were determined using a battery of 9 bacterial strains of different genetic specificity. The assays with crude extracts and with fractionated acidic, neutral and basic components revealed striking differences in the patterns of mutagenic responses produced by each of the complex mixtures investigated. The mutagenicity of air particulate matter was shown to depend mainly on direct-acting acidic and neutral compounds, with a lesser contribution of basic promutagens which required exogenous metabolic activation by liver S9. The assays with a diesel soot extract indicated the prevailing contribution of direct-acting acidic and neutral compounds, and suggested an important role also for nitro derivatives other than nitropyrenes. The gasoline exhaust was characterized by powerful promutagenic compounds, belonging to either the acidic, neutral or basic fractions. The implications of these results are discussed with respect to the contribution of engine exhausts to air pollution, and the possible use of mutagenicity spectra in the analysis of environmental complex mixtures.

Mutagenicity of trichloroethylene, trichloroethanol and chloral hydrate in Aspergillus nidulans

A trichloroethylene (TCE) sample, free of epoxides, has been assayed for its ability to induce gene mutations (methionine suppressors) and mitotic segregation in the mould Aspergillus nidulans. No increase in the spontaneous frequency of methionine suppressors was observed when conidia of a haploid strain were plated on selective medium and exposed to TCE vapours. A weak but statistically significant increase in methionine suppressors was detected, however, when conidia of cultures grown and conidiated in the presence of TCE vapours were plated onto selective media. Growing colonies of a heterozygous diploid strain were exposed to TCE vapours to investigate the induction of mitotic segregation. Scoring and phenotypic analysis of segregant sectors showed a significant increase in the frequency of haploids and non-disjunctional diploids but not of cross-overs. Treatment of quiescent conidia in liquid medium was ineffective. Trichloroethanol and chloral hydrate, two main TCE metabolites in mammals, shared the ability to induce somatic segregation demonstrated by TCE vapours. On the grounds of these results the possible endogenous metabolic conversion of TCE into trichloroethanol and chloral hydrate is hypothesized.

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.

The induction of mitotic chromosome malsegregation in Aspergillus nidulans. quantitative structure activity relationship (QSAR) 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.

Induction of somatic segregation by halogenated aliphatic hydrocarbons in Aspergillus nidulans.

8 halogenated aliphatic hydrocarbons were assayed for their ability to induce somatic segregation in the mould Aspergillus nidulans. Induction of haploidization, mitotic non-disjunction and mitotic crossing-over was studied in heterozygous colonies exposed to the tested chemicals through the detection and phenotypic analysis of segregated sectors. The results obtained show that 1,2-dibromoethane induced all kinds of segregated sectors; 1,2-dichloroethane, allyl chloride, 2-chloroethanol, 2,2-dichloroethanol and 2,2-dichloroacetaldehyde significantly increased the frequency of haploid sectors and diploid non-disjunctional sectors; chloroform and 1,2-dichloropropane were ineffective.

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.

Induction of cytoplasmic “petite” mutation by antibacterial antibiotics

Abstract The induction of petite mutation by three antibiotics known to inhibit microbial protein synthesis has been studied in two strains of yeast. Erythromycin and tetracycline, but not chloramphenicol, were affective in inducing petites. However, the two strains studied showed a considerable difference in sensitivity to the mutagenic action of the antibiotics used.

Growth-mediated metabolic activation of promutagens in Aspergillus nidulans

7 procarcinogens belonging to different chemical classes (nitrosamines, hydrazoalkanes, oxazaphosphorines and aromatic amines) were tested in A. nidulans for the induction of point mutations with two genetic systems (8-AG resistance and induction of methionine suppressors). Dimethylnitrosamine, diethylnitrosamine, nitrosomorpholine, dimethylhydrazine, procarbazine and cyclophosphamide gave positive results with a good dose--effect relationship in the growth-mediated assay, whereas they gave negative or borderline positive results in the plate incorporation assay. 2-Aminoanthracene was completely negative with both experimental procedures. DMN, DEN and NM were also tested for their ability to induce somatic segregation: all were positive when assayed in the growth-mediated assay.