Synthesis, metabolism and structure-mutagenicity relationships of novel 4-nitro-(imidazoles and pyrazoles) in Salmonella typhimurium

A new series of 4-nitro-(imidazoles and pyrazoles) were synthesized as novel antimycotics and tested for their activation to mutagenic forms using Salmonella typhimurium TA98 and TA100, in the presence and in the absence of metabolic activation. TA100NR, TA100/1,8-DNP6, YG1026 and YG1029 strains were employed to identify a specific metabolic reaction which governs the mutagenic potency. Derivatives in the pyrazole group were generally found to be non mutagenic and active imidazoles were weak-direct-acting mutagens. For most of the compounds the mutagenic responses in TA98 were absent or 12- to 22-fold lower compared to TA100. The presence of a methyl or a benzylic group on the imidazole ring and substituents on the N1 and N3 positions were determinant for mutagenicity. Metabolism by bacterial enzyme systems was important to the expression of genotoxicity. Active compounds showed no mutagenicity toward the strain defective in classical nitroreductase and increased mutagenicity, from 2- to 7-fold depending on the test compound, toward the corresponding overproducing bacteria. On the other hand, compounds displayed reduced mutagenicity to the O-acetyltransferase strain without having increased activity in the corresponding overproducing bacteria, YG1029.

Analysis of radiation-induced micronuclei by FISH using a combination of painting and centromeric DNA probes

In situ hybridization with whole chromosome painting probes (chromosome 1, 7, 11, 14, 17 and 21) in combination with a human pancentromeric alpha-satellite probe was used to analyse the presence of specific chromosomal material in micronuclei (MN) induced in human lymphocytes by ionizing radiation. The purpose was to investigate the nature of radiation-induced cytogenetic damage, especially to study whether the fraction of paint-positive MN is proportional to the relative DNA content of the respective chromosomes which might indicate a random breakage of chromosomes. Flow-sorted MN and MN in binucleated cells were analysed with the six chromosome specific painting probes. It was found that the fraction of paint-positive MN increased linearly with the DNA content of the respective chromosomes. About 13% radiation-induced MN in human lymphocytes were found to contain centromeric signals independent of the presence of specific chromosome painting signals. The data obtained on flow-sorted MN and MN in binucleated cells agreed well, indicating that flow-sorted MN can be used for studying their chromosomal content with the FISH technique. If it is assumed that the chromosomal content of MN reflects radiation-induced damage, then these results support a random model of radiation-induced cytogenetic damage in human lymphocytes for the six chromosomes studied.

The genetic and non-genetic toxicity of the fungicide Vinclozolin

The mutagenic/cocarcinogenic potential of the fungicide Vinclozolin was assessed by a comprehensive examination of toxicity mechanisms at both the genetic and the metabolic level. Vinclozolin did not induce any significant increase in chromosomal aberrations in human pheripheral blood lymphocytes cultured in vitro, both in the presence and in the absence of metabolic activation. However, significant dose-related increases in micronucleated erythrocytes (up to 4-fold over the control) were found in the bone marrow cells of mice 24 h after treatment with the fungicide over a range of concentrations from 312.5 to 1250 mg/kg. The morphology and the size of micronuclei induced was suggestive of a predominantly clastogenic mode of action. Several cytochrome P450 (CYP)-dependent reactions have been monitored in liver, kidney and lung microsomes of male and female Swiss Albino CD1 mice in order to ascertain certain toxic non-genetic properties (related to carcinogenesis) of Vinclozolin. It was found to be a selective inducer towards CYP 3A (liver, kidney) and 2E1 (liver), as exemplified by the significant increases of the demethylation of aminopyrine (APND, up to 2.3-fold, female liver), and hydroxylation of p-nitrophenol (pNPH, up to 5.6-fold, male liver). In general, however, Vinclozolin has a complex pattern of induction and suppression of CYP-dependent enzymes, as shown from the reduced expression of various monooxygenases depending upon dose, sex or organ considered. For example, pNPH activity was suppressed in kidney (up to 48% loss, averaged between male and female), whereas ethoxycoumarin O-deethylase was reduced in lung up to 53% in male (at the highest dose). These data were sustained by means of Western immunoblotting using rabbit polyclonal antibodies anti-CYP 3A and 2E1. Northern blotting analysis using CYP 3A1/2 and 2E1 cDNA biotinylated probes showed that the expression of such isozymes is regulated at the mRNA level. Taken together, the findings indicate the clastogenic activity and the possible cotoxic, cocarcinogenic and promoting potential of Vinclozolin.

Cytogenetic effects of Metalaxyl on human and animal chromosomes

The purpose of this study was to assess the cytogenetic effects in vitro and in vivo of a commonly used fungicide, Metalaxyl. Chromosome damage in vitro, quantified by cultured human peripheral blood lymphocytes, demonstrated dose-related effects not associated with mitotic inhibition or cell death. Significant induction of chromosomal aberrations was observed with between 300 and 1000 micrograms/ml Metalaxyl in the absence of microsomal activation. Incubation in the presence of S9 mix produced less cytogenetic damage. Single i.p. injections of 75-300 mg/kg Metalaxyl had no effect on the frequency of micronuclei, detected in murine polychromatic erythrocytes. Micronuclei results were not compromised by direct evidence of cytotoxicity in the bone marrow of treated animals. The results in the present study indicated that genotoxicity of Metalaxyl was detected only in vitro and not in vivo. Available data reported that Metalaxyl was non-carcinogenic and gave negative results in a battery of genotoxicity tests. So, clastogenicity of Metalaxyl may not be evidence for DNA reactivity, but it may indicate alterations in cell homeostasis which are well implicated in the process of carcinogenesis.

Analysis of metabolism and genotoxicity of 5-nitro-3-thiophenecarboxanilides in bacterial, mammalian and human cells

5-nitro-3-thiophenecarboxanilide (NTCA3) was clearly mutagenic in Salmonella typhimurium strains TA98, YG1021 (the strain with elevated nitroreductase) and YG1024 (the strain with elevated O-acetyltransferase) and only slightly mutagenic at the gpt locus in AS52 cells. Clastogenic activity in human lymphocytes was dependent on the length of exposure: detectable chromosome aberrations were observed following a 24 h treatment period, but not after 3 h exposure. S9 increased genotoxicity in both mammalian cells and human lymphocytes. Metabolites formed by incubation of NTCA3 with the different cell systems were examined. A time-course study in cell whole extracts showed that bacterial and mammalian cells can acetylate NTCA3 forming 5-acetylamino-3-thiophene-carboxanilide. The formation of this metabolite in human lymphocyte extracts was not confirmed. These data support the conclusions that: (i) both bacterial and mammalian activation pathways play a role in mutations by NTCA3; (ii) the N-acetylated derivative is generated by acyl-transferase after reduction and is the end product of the metabolism in both bacterial and mammalian cells; and (iii) different levels of reductase and acetyltransferase activity may contribute to the differential sensitivity of the different cellular species to the genotoxicity of NTCA3. The fact that NTCA3 serves as substrate for enzymatic activities of importance also in human metabolism needs consideration in assessing the potential risk posed by NTCAs.

Interactive effects between trichloroethylene and pesticides at metabolic and genetic level in mice

A combined cytogeneticurine metabolite analysis approach was used to assess potential interactive effects between Fenarimol (FN), a fungicide, and trichloroethylene (TRI), a halogenated solvent. FN was demonstrated to selectively induce P450-2B1 isoforms in different organs of treated mice. Since the rate of metabolism and the stereospecificity of metabolism are dependent on the types and amount of P450s available, FN might drastically alter the metabolic activation of a precarcinogen, such as TRI, and its toxicological consequences. Male CD1 mice were divided into untreated, vehicle control, and experimental groups. Animals of the latter groups were treated ip with 150 mg/kg bw FN in corn oil, 457 mg/kg bw TRI in corn oil, TRI plus FN separated by different time intervals. Bone marrow cells were harvested for determination of micronuclei (MN) frequencies in polychromatic erythrocytes (PCE). The presence of the known metabolite of TRI, trichloroethanol (TCE), was quantitated in collected urine by gas chromatography using an electron-capture detector. Linear regression analysis shows that MN frequency by TRI is correlated with TCE concentration in urine. Observed potentiation of genotoxicity of TRI by FN pretreatment (1 hr before TRI treatment) apparently reflects changes in the spectra of enzymes involved in TRI metabolism, and altered toxicokinetic, as witnessed by the 20% difference in TCE excretion from combined treated mice. However, no increased genetic or metabolic effects were observed when FN was administered 3 hr before TRI. No significant interactive effects were observed at a genetic level when FN was administered 1 hr and 3 hr after TRI whereas a 33 to 47% loss in TCE excretion was recorded.(ABSTRACT TRUNCATED AT 250 WORDS)