On the distribution of genotoxic factors in various organs of mice treated with cycasin

Induction of genotoxic effects by chlorohydroxyfuranones, byproducts of water disinfection, in E. coli K-12 cells recovered from various organs of mice

The genotoxic effects of three chlorohydroxyfuranones (CHFs), 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone (MX), 3-chloro-4-(chloromethyl)-5-hydroxy-2[5H]furanone (CMCF) and 3,4,-dichloro-5-hydroxy-2[5H]furanone (MCA), which are formed as byproducts of water disinfection with chlorine, were investigated in bacterial differential DNA repair assays in vitro and in animal-mediated assays in vivo. As indicators of DNA damage, E. coli K-12 strains were used that differ in their repair capacity (uvrB/recA vs. uvr+/rec+). Liquid incubation of the compounds without metabolic activation caused a pronounced reduction of the viability of the repair-deficient strain relative to the repair-proficient wild-type strain. The order of potency of genotoxic activity in vitro (dose range 0.004-10 micrograms/ml) was MX > CMCF > MCA. Addition of mouse S-9 mix or bovine serum albumin to the incubation mixtures resulted in an almost complete loss of the activity of all three test compounds. In the animal-mediated assays, mixtures of the indicator bacteria were injected intravenously into mice which were subsequently treated with the test compounds (200 mg/kg b.w.). Two hours later, the cells were recovered from various organs and the relative survival frequencies determined. Under these conditions, all three compounds caused pronounced genotoxic effects, MX and CMCF being stronger genotoxins than MCA. The strongest effects were consistently found in the gastrointestinal tract, but statistically significant DNA damage was also observed in indicator cells recovered from lungs, liver, spleen and kidneys. In a further experiment, the effects of lower doses of MX (4.3, 13 and 40 mg/kg) were investigated. In these experiments dose-dependent effects were measured in all organs. CMCF and MA caused only marginal effects at 40 mg/kg except in the stomach where approximately a 50% reduction of relative survival frequency was observed with CMCF. The results of these animal-mediated assays indicate that (i) all three CHFs cause genotoxic effects in the living animal, and (ii) the potencies of the three compounds observed under in vivo conditions are not commensurate with their extremely high activities measured in vitro. One possible explanation for the weaker responses observed in the animal-mediated assays might be that CHFs are inactivated by non-specific protein binding.

An evaluation of the E. coli K-12 uvrB/recA DNA repair host-mediated assay. II. In vivo results for 36 compounds tested in the mouse

The aim of this study was to further evaluate the E. coli K-12 DNA repair host-mediated assay, as a short-term in vivo genotoxicity test, to be used as a complement to the micronucleus test in the routine testing of chemicals and drugs. The assay involves the administration of the test substance to mice by the route of choice, followed by the intravenous administration of a mixture of DNA repair deficient and proficient derivatives of E. coli K-12. After an incubation period the relative survival of the two strains was determined in blood, liver, lungs, kidneys and testes of the host. A significant preferential reduction of the DNA repair deficient strain in any organ indicates that the test substance possesses genotoxic properties. A total of 36 substances, 26 carcinogens, 4 weak or non-carcinogens and 6 unclassified substances, were tested in this assay. Positive results were obtained for 23 compounds. Of the carcinogens 18 were positive and of the non-carcinogens 3 were negative. The overall concordance between the assay and carcinogenicity was 72%. In general, alkylating agents and direct-acting nitroso compounds showed genotoxic activity in all organs tested, while the other substances were positive in a limited number of organs. With oral administration, which was the most commonly used administration route in the study, the organ showing a positive response most often was the blood. The results from the present study were compared with results from the micronucleus test, which were available for 26 of the substances. Results were in agreement for 15 of the substances, while 8 substances were positive in the present assay and negative in the micronucleus test: 4-aminobiphenyl, 2-anisidine, epichlorohydrin, formaldehyde, 1- and 2-naphthylamine, 2-nitrophenylenediamine and 4-nitroquinoline-N-oxide. The substances negative in the E. coli DNA repair host-mediated assay, but positive in the micronucleus test were: benzene, catechol and cyclophosphamide. It is concluded from this evaluation that the E. coli K-12 DNA repair host-mediated assay detects a number of carcinogens that are negative in the micronucleus test, while detecting most of the compounds that are positive in the latter. The advantages of this test are that differential DNA repair measures a broad spectrum of genetic damage, an in vitro/in vivo comparison is possible with the same test organisms, results can be obtained from various organs and the test is rapid.(ABSTRACT TRUNCATED AT 400 WORDS)

Use of differential DNA-repair host mediated assays to investigate the biotransformation of xenobiotics in Drosophila melanogaster. I. Genotoxic effects of nitrosamines

A rapid differential DNA-repair assay procedure was developed to investigate the biotransformation of xenobiotics in Drosophila melanogaster in vivo. Indicator of genotoxic activity was a pair of streptomycin-dependent Escherichia coli strains differing vastly in DNA repair capacity (uvr+/rec+ vs. uvrB/recA). Prior to the experiments with test compounds, mixtures of the two strains were injected into the abdomina of untreated animal hosts (male Berlin-K flies) and the time-dependent recovery kinetics determined. Subsequently, different aliphatic and aromatic nitrosamines were tested. Solutions of the compounds were injected simultaneously with the indicator cells. Three hours later, the flies were killed, homogenized and the induction of (repairable) DNA damage determined by comparison of the survival rates of the two strains in single animals. Eight carcinogenic compounds (nitrosodiethylamine, NDEA; nitrosodimethylamine, NDMA; nitrosodi-npropylamine, NDPA; nitrosodiethanolamine, NDELA; nitrosomethylaniline, NMA; 4-methyl-nitrosopiperidine, MNPIP; nitrosopyrrolidine, NPYR; nitrosomorpholine, NMOR) and one whose tumorigenic activities are still controversially discussed (nitrosodiphenylamine, NDPhA) induced dose-dependent differential killing effects in the present system. One agent which has not been found carcinogenic in rodents (2.6-dimethyl-nitrosopiperidiine. NDMPIP) gave negative results. The ranking order of genotoxic activities of the nitrosamines found in Drosophila in vivo is in good agreement with those of carcinogenic potencies established on the basis of experiments with rats. The most pronounced exceptions are the rather weak response towards NMA and the stronger DNA damaging activity of NMPIP compared to NDMA. Phenobarbital (5-ethyl-5-phenyl-2,4,6-trioxohepatahydropyramidine) (PB) feeding of the flies resulted in an increase of the DNA damaging potencies of all nitrosamines tested. Substantial enhancement of the induction of DNA damage was however, restricted to NDEA, NPYR and NMOR, whereas with nitrosodiphenylamine (NDPhA), NDELA and NDMA only a moderate (less than 25%) increase of differential killing effects was found. In the case of the two latter compounds, these results might be due to the fact that enzymes other than the MFO are involved in their activation. Attempts to localize the formation and/or distribution of metabolites in the bodies of fruitflies by separation of the tagmata of chemically treated animals and determination of genotoxic effects in the different segments indicate that the most pronounced effects occur in the abdomina whereas in heads and thoraxes comparatively lower activities are detectable.

Investigations on the use of EDTA-permeabilized E. coli cells in liquid suspension and animal-mediated genotoxicity assays

The potential use of EDTA-permeabilized E. coli cells for the investigation of genotoxic effects of compounds with a large molecular configuration in vitro and in animal-mediated differential DNA-repair assays was studied. The indicator for the induction of (repairable) DNA damage was a pair of E. coli K-12 strains (343/765 and 343/753) differing vastly in DNA-repair capacity (uvr+/rec+ vs. uvrB/recA). Investigations on the influence of EDTA treatment on the viability of these strains show that during short-term exposure (3 min), the EDTA level should not exceed 0.5 mmole/l in the pretreatment mix, since at higher concentrations a marginal titer reduction of the repair-deficient strain occurs, thus indicating a weak genotoxic activity of this chelating agent. Comparisons of the results gained in vitro with permeabilized and untreated cells demonstrate that EDTA exposure leads to a substantial enhancement of the sensitivity of the indicator bacteria towards DNA damage induced by B(a)P and N-Ac-2AAF which is essential for the detection of genotoxic activities of these polycyclic aromatic compounds. Experiments to elucidate the possibility of employing EDTA-treated cells in vivo show that following intravenous and oral administration the recovery rates of permeabilized indicator strains from various mouse organs are substantially lower than those found under identical conditions (exposure time 150 min) with untreated strains. Nevertheless enough viable cells can be recovered from liver, spleen, kidneys, lungs and stomach to allow the investigation of organ-specific genotoxicity. It is furthermore noteworthy that exposure of permeabilized indicator cells in control animals (for 150 min) resulted in a marginal reduction of the relative survival of the repair-deficient strain in all organs investigated, whereas with non-treated strains such effects are only detectable after extended exposure periods. The observation of a slightly elevated genotoxic background under in vivo conditions does not prevent the assessment of the organ distribution of genotoxic effects induced by mutagens and/or carcinogens: in the case of B(a)P, intraperitoneal administration to mice in the dose range of 10-50 mg/kg body weight resulted in a pronounced dose-dependent inactivation of the uvrB/recA cells in the liver. Also in the lungs differential killing effects occurred at the highest dose tested, whereas no genotoxic activities were detectable in stomach, kidneys and spleen of the host animals.