M. Duverger-van Bogaert

Liver extract mediated mutagenicity of acrylonitrile.

The mutagenic activity of acrylonitrile vapours towards Salmonella typhimurium strains strictly depends upon the presence of a liver postmitochondrial fraction. The reversion rate varies according to the animal species from which the S9 fraction is obtained as well as to the pretreatment of the animals. The comparatively weak activating effect of the microsomal fraction and the inability of both SKF525A and carbon monoxide to inhibit the S9 mediated mutagenicity of acrylonitrile (ACN) suggest that the cytochrome P-450-dependent monooxygenases do not play a major role in the metabolic activation of ACN into a mutagenic intermediate (s).

Metabolic activation by a supernatant from human hepatoma cells: a possible alternative in mutagenic tests.

The supernatant from human Hep G2 hepatoma cells was examined for typical enzymatic activities involved in the metabolism of xenobiotics. Neither cytochrome P-450 nor b5 was detectable, but associated enzymatic activities were found especially after induction with hydrocortisone (HC) and benzanthracene (BA) suggesting that this Hep G2 supernatant contains cyt P-450 IA1 and IA2. Other critical enzymes are also present, but, as expected, at lower activities than in Aroclor 1254 rat liver S9, except for NADH and NADPH cytochrome c reductase. Results of the Ames test indicate that the induced Hep G2 supernatant is a suitable activator for the evaluation of genotoxicity of indirect mutagens.

Influence of Experimental Factors on the Mutagenicity of Vinylic Monomers

The results obtained by testing the mutagenicity of several vinylic monomers, styrene, butadiene, acrylonitrile, vinyl chloride on strains of Salmonella typhimurium in various experimental conditions, modes of incubation, and in the presence of different metabolic activating systems, demonstrate that these parameters have a variable effect on the mutagenic potency of those monomers.

Biochemical effects of acrylonitrile on the rat liver, as influenced by various pretreatments of the animals.

Abstract Acrylonitrile is extensively used in the synthesis of plastics, some of which are used for the packaging of food and beverage. A single dose of AN causes an increase in serum lactate and sorbitol dehydrogenase levels, as well as a decrease of liver cytochrome P-450 content and microsomal aldrin oxide synthetase activity. Those effects are prevented by pretreatments of the animals with either inducers of the mixed function oxidases or L-cysteine; diethylmaleate pretreatment enhances the increase of the soluble enzyme levels.

Styrene induced modifications of some rat liver enzymes involved in the activation and inactivation of xenobiotics.

Abstract Rats were injected intraperitoneally with single doses of styrene. Its effects on the kinetic parameters of liver microsomal monooxygenases and epoxide hydratase were investigated. The results were compared with those produced either by ethylbenzene, the vinyl-saturated analog of styrene or by phenobarbital and 3-methylcholanthrene, the classical inducers of those enzymes. The biochemical modifications were correlated with the altered ability of homogenates obtained from similarly pretreated rats to activate benzo(a)pyrene into intermediates mutagenic towards Salmonella typhimurium . Administration of styrene or 3-methylcholanthrene decreased the K m , of benzo(a)pyrene hydroxylase and aldrin epoxidase; styrene, but not 3-methylcholanthrene, decreased the K m of styrene oxide hydratase; none of the two compounds modified the K m of styrene epoxidase. Pretreatment of the rats by styrene or 3-methylcholanthrene enhanced the S 9 mediated mutagenicity of benzo(a)pyrene several-fold, when compared to the mutagenic response mediated by liver preparations from control rats. Phenobarbital and ethylbenzene did not modify either the K m of the investigated enzymes or the liver-mediated mutagenicity of benzo(a)pyrene.

Mutagenic activation of aromatic amines by a human hepatoma cell (Hep G2) supernatant tested by means of Salmonella typhimurium strains with different acetyltransferase activities.

The study was carried out to characterize hepatoma cells (Hep G2) as activation system relevant to man and to investigate which are the tester strains most suitable for the mutagenic assay of aromatic amines. A supernatant prepared from the human hepatoma cell line Hep G2 was used to activate benzidine, 2-aminofluorene (2-AF) and 2-acetylaminofluorene (2-AAF) in the Salmonella typhimurium reversion assay. Activation by Hep G2 supernatant was studied with increasing concentrations of the three compounds, in tester strains TA98, YG1024, DJ400 and DJ460. Benz[alpha]anthracene (BA) pretreatment of cells increases the mutagenicity of benzidine in strains YG1024, DJ460 and DJ400. Activation of 2-AAF and 2-AF was observed in strains YG1024, DJ400 and, at the highest tested dose, in DJ460. These results were compared with those obtained with S9 from control and Aroclor 1254 (Aro)-pretreated rat liver. With strain TA98 comparable responses were obtained except for 2-AF which was better activated using rat liver S9. The use of strain YG1024 greatly increases the sensitivity of the response. Strain DJ460 makes it possible to detect activation of 2-AF and 2-AAF by Aro-induced rat liver. These results indicate that Hep G2 supernatant is a useful metabolic activation system of human origin that can be used to replace rat liver S9. An appropriate choice of the Salmonella strain not only can increase the sensitivity of the response, but may also help to overcome certain metabolic shortcomings of the Hep G2 cell line and rat liver S9.

Oxidative Activation of 2-aminofluorene By Human Red-blood-cell Cytosol

Purified red blood cell cytosol is able to activate 2-aminofluorene (2AF) to N-hydroxy-2-aminofluorene. Apparent kinetic parameters are determined with and without methylene blue. The latter, which maintains haemoglobin in the reduced form and stimulates NADPH production, increases the affinity of the enzyme for the 2AF. This activity is inhibited by carbon monoxide while cyanide is without effect. The involvement of a peroxidative reaction or a one-electron oxidative mechanism involving free radicals may be excluded.

Population Monitoring for Genetic-damage Induced By Environmental Physical and Chemical-agents

The short-term tests performed in vitro on different systems, from phage to human cells, or in vivo, on laboratory animals, allow only a qualitative estimate of the action of mutagenic agents, and the extrapolation of such experimental results to man may encounter many difficulties.Direct biomonitoring of populations exposed to chemicals could represent a more realistic approach for an evaluation of the hazards to man. Certain methods are still under development. Nevertheless, other ones can already by used routinely, e.g. the cytogenetic observations on peripheral blood lymphocytes and the Ames test for mutagenic substances in urine, and can provide useful suggestions how to set threshold limits for chemical substances encountered in the working environment.

Activation of some aromatic amines to mutagenic products by human red blood cell cytosol

The ability of human red blood cell cytosol to activate aromatic amines was evaluated with the Ames test using Salmonella typhimurium TA98 in the liquid preincubation condition. While negative results were obtained with 4-acetylaminofluorene (4AAF) and 1-naphtylamine (1NA), a slight response was observed for 4-aminobiphenyl (4ABP) and 2-naphthylamine (2NA). Human red blood cell cytosol was able to activate 2-aminofluorene (2AF), 2-acetylaminofluorene (2AAF) and 2-aminoanthracene (2AA) to mutagenic intermediates. Extracts of human red blood cell cytosol incubated with 2AF were analyzed by gas chromatography: N-hydroxy-2-aminofluorene was identified as a metabolite.

Enzymic N-demethylation reaction catalysed by red blood cell cytosol

Red blood cell cytosol promotes enzymic N-demethylation reactions which display typical Michaelis-Menten kinetics with respect to N-methylaniline as substrate. The demethylase activity is linked with hemoglobin (Hb) and is enhanced in the presence of NADH and the NADH-methemoglobin reductase system. It has been adduced that Hb in its oxygenated form is involved in the reaction.