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M Roberfroid

Publications and source records attributed to M Roberfroid.

At least 73 records · Page 4Linked to original sources
PubMed1983

Effects of diethyl maleate on protein synthesis in isolated hepatocytes.

Diethyl maleate is commonly used in toxicological and drug metabolism research using isolated adult rat hepatocytes. At the highest concentrations used the effect of diethyl maleate is, however, not limited to glutathione depletion. In these conditions it inhibits protein synthesis and it impairs the "L" system for amino acid transport. It has, however, no effect on the cytochrome P-450 content or its dependent aldrin monooxygenase. The present report shows that a concentration of diethyl maleate as low as 0.2 mM is sufficient to deplete glutathione without affecting glycogen and protein synthesis, transport of amino acid or monooxygenase activity in isolated adult rat hepatocytes.

Animals↗
PubMed1983

Rabbit liver microsomal 2-acetylamino- and 2-aminofluorene N-hydroxylase.

Rabbit liver microsomes N-hydroxylate both 2-acetylaminofluorene (2-AAF) and 2-aminofluorene (2-AF). They also deacetylate N-hydroxy-2-acetylaminofluorene (N-OH-2-AAF). The enzymic activity towards the two substrates is the same but the enzyme has a higher affinity for the arylamide than for the arylamine. With regard to various modifiers added in vitro, rabbit liver microsomal N-hydroxylase behaves like those of rat, hamster and mouse. However, it is less effectively inhibited by the substituted imidazole derivative, Miconazole (MN). None of the enzymic properties of the rabbit liver microsomal N-hydroxylase investigated explains the resistance of this tissue to the carcinogenic effect of 2-AAF.

2-Acetylaminofluorene↗
PubMed1983

Comparative study of rat, dog and human liver microsomal arylamide N-hydroxylases.

As compared to rat liver microsomal arylamide N-hydroxylase both the dog and the human enzymes have lower affinity but higher activity. SKF525A, a well known effector of cytochrome P-450 dependent mixed function oxidases, activates the hepatic N-hydroxylase of all three species. This effect is concentration dependent and tends to plateau at 50 X 10(-6)M. As previously demonstrated with rat liver microsomes, the ring-hydroxylated, non-toxic, metabolites of 2-acetylaminofluorene, interact with the N-hydroxylating enzyme. These interactions are both compound- and species-specific. The most striking differences are seen with the paraphenolic product which activates the rat, does not affect the dog and inhibits the human liver enzyme. In the liver of this last species, that compound is the main metabolite of 2-acetylaminofluorene (2-AAF).

2-Acetylaminofluorene↗
PubMed1983

Mutagenicity of 1,2-dimethylhydrazine towards Salmonella typhimurium, co-mutagenic effect of secondary biliary acids.

Even though 1,2-dimethylhydrazine (DMH) is highly carcinogenic in experimental animals, it has not been shown to be clearly mutagenic in any of the short term tests in vitro. The present report demonstrates that DMH is mutagenic in the Ames test when it is incubated together with lithocholic or deoxycholic acid with or without metabolic activation. Such a co-mutagenic effect seems to be restricted to the secondary biliary acids since neither cholic nor chenodeoxycholic acid had the same activity. The secondary biliary acids are present in the colon where they are formed by bacteria. Such a co-mutagenic effect could thus be of importance with regard to the carcinogenic activity of DMH. It could also be relevant to colon carcinogenesis in humans.

1,2-Dimethylhydrazine↗
PubMed1983

Structure-activity relationship amongst biliary acids showing comutagenic activity towards 1,2-dimethylhydrazine.

Secondary biliary acids act, in vitro, as co-mutagenic agents towards 1,2-dimethylhydrazine incubated in the presence of Salmonella typhimurium strain TA 100. The present report demonstrates an important structure-activity relationship with regard to this effect. The number and position of hydroxyl substituents, the configuration at various C atoms and the stereochemistry of the junction between rings A and B of the steroid moiety are parameters which influence the cogenotoxic activity. Beyond these structural parameters, the basic physico-chemical properties of the biliary acids could be the key factor controlling their effects. Co-incubation of the various biliary acids reveals that the so-called secondary compounds antagonise each other's activity; moreover, in the presence of a constant concentration of primary bile acids, the co-mutagenic effect is directly related to the amount of the secondary bile acids. The co-mutagenic activity of the secondary biliary acids and its modulation by their mixing could be a key factor in the etiology of colon cancer.

1,2-Dimethylhydrazine↗
PubMed1983

Morphological alterations and DNase deficiency in phenobarbital promotion of N-nitrosomorpholine initiated rat hepatocarcinogenesis.

Tumorigenic effect in rat liver was increased when phenobarbital was given chronically after N-nitrosomorpholine. In these rats the liver parenchyma surrounding pre- and neo-plastic lesions demonstrated distinct, mainly centrilobular zones of hypertrophic hepatocytes with abundant eosinophilic, filamentous cytoplasm, increase in nucleic acids and decrease in DNase activity. These alterations might be considered as signs of tumor-promoting activity of phenobarbital.

Animals↗
PubMed1982

Removal of O6-methylguanine from DNA by human liver fractions.

In in vitro assays using methylated DNAs as substrates, human liver fractions were shown to be able to catalyze the removal of O6-methylguanine. The amount of removal was proportional to the amount of protein added, and the loss of O6-methylguanine occurred with stoichiometric formation of guanine in the DNA and S-methylcysteine in protein. This indicates that human liver contains a protein similar to that previously found in bacteria exposed to alkylating agents. This protein acts as a transmethylase, transferring the intact methyl group from O6-methylguanine in DNA to a cysteine residue on that protein. A similar activity is present in rodent liver, but it was found that human liver was about 10 times more active in carrying out this reaction. In contrast, there was no difference between the human and rat liver extracts in catalyzing the loss of another methylation product, 7-methylguanine, from alkylated DNA. The liver is the organ most likely to be alkylated after exposure to exogenous potential alkylating agents such as dimethylnitrosamine. The present results show that human liver has a significant capacity to repair O6-methylguanine in DNA, which has been implicated as a critical product in carcinogenesis and mutagenesis.

Animals↗
PubMed1982

Genetic differences in the enzymic properties of the aromatic hydrocarbon inducible N-hydroxylation of 2-acetylaminofluorene in mouse liver.

3-Methylcholanthrene (3-MC) pretreatment induces the liver microsomal 2-acetylaminofluorene (2-AAF) N-hydroxylase activity of C57BL6 responsive mice. The same pretreatment modifies this enzyme by significantly increasing its apparent Km value which, moreover, becomes protein concentration dependent. After 3-MC induction, the C57BL6 mouse liver microsomal 2-AAF N-hydroxylase is activated by paraoxon and 8-hydroxyquinoline. This last chemical does not, however, inhibit the microsomal metabolism of N-hydroxy-2-acetylaminofluorene (N-OH-2-AAF) as it does in the presence of guinea pig liver microsomes. The hypothesis is formulated that 3-MC pretreatment of C57BL6 mice induces not only cytochrome P448 dependent mixed function oxidase but also the synthesis of a microsomal protein which reversibly binds 2-AAF. Mutagenicity data are presented which corroborate this hypothesis. As in guinea pig liver microsomes, N-OH-2-AAF is further metabolized by both C57BL6 and DBA2 mouse liver microsomes. This metabolism is not inhibited by NaF which acts as an inhibitor of microsomal arylamidase. This is a possible contributing reason why 2-AAF is only weakly carcinogenic for mice.

2-Acetylaminofluorene↗
PubMed1982

Hepatic microsomal metabolism of 1,3-butadiene.

1. In rat liver microsomes, 1,3-butadiene was metabolized to butadiene monoxide, which was subsequently transformed into 3-butene-1,2-diol by microsomal epoxide hydrolase. 2. In the metabolism of butadiene oxide in microsomes, four metabolites were detected, namely two stereoisomers of DL-diepoxybutane, and two stereoisomers of 3,4-epoxy-1,2-butanediol. No meso-diepoxybutane was detected.

Animals↗
PubMed1982

Induction and modification of rat liver microsomal arylamide N-hydroxylase by various pretreatments.

3-Methycholantrene, benzoanthracene, benzo[e]pyrene, and pyrene induce N-hydroxylase activity and modify the enzyme by increasing its apparent Km. As exemplified by the effect of 3-methylcholanthrene, the polycyclic aromatic hydrocarbons also induce other mixed-function oxidases such as aryl hydrocarbon hydroxylase and the various arylamide C-hydroxylases. Acute or chronic pretreatment of rats with acetylaminofluorenes induces N-hydroxylase and modifies the enzyme affinity by decreasing its apparent Km. Among the various-position isomers, 4-acetylaminofluorene is completely inactive and 2-acetylaminofluorene is the most potent. Its effect is both dose- and time dependent, and it seems to be specific for N-hydroxylase, the same pretreatment having no effect on arylhydrocarbon hydroxylase or arylamide C-hydroxylases. After simultaneous treatment of rats with 3-methylcholanthrene and 2-acetylaminofluorene, even though N-hydroxylase activity as measured on hepatic microsomes in vitro is significantly induced, the urinary excretion of N-hydroxy-2-acetylaminofluorene is significantly reduced over a 24-hr period. This observation is discussed in relationship to the well-known inhibitory effect of 3-methylcholanthrene on the hepatocarcinogenicity of 2-acetylaminofluorene.

2-Acetylaminofluorene↗
PubMed1982

Metabolism of N-hydroxy-2-acetylaminofluorene and N-hydroxy-2-aminofluorene by guinea pig liver microsomes.

The guinea pig is resistant to the hepatocarcinogenic effects of 2-acetylaminofluorene and 2-aminofluorene. This resistance, however, is not due to the lack of a N-hydroxylating enzyme in the liver which catalyzes the first and rate-limiting step to the activation of these chemicals to proximal carcinogens. It is shown that guinea pig liver microsomes can N-hydroxylate both of these compounds. The N-hydroxylation of 2-acetylaminofluorene but not 2-aminofluorene is inducible by pretreating the guinea pigs with benz(a)anthracene. The microsomal reaction is inhibited by 3-methylcholanthrene, miconazole, or 7,8-benzoflavone, 7-Iodo-2-acetylaminofluorene is N-hydroxylated by guinea pig liver microsomes at approximately the same rate as 2-acetylaminofluorene. The N-hydroxylation of 7-fluoro-2-acetyl-aminofluorene occurs at a much faster rate. The resistance of the guinea pig liver to the carcinogenic effect of the arylamides and arylamines may actually be due to the ability to further convert the N-hydroxylated metabolites to the inactive C7-hydroxylated product. The conversion of N-hydroxy-2-acetylaminofluorene to C7-hydroxy-2-acetylaminofluorene by guinea pig liver microsomes is inhibited by 8-hydroxyquinoline or miconazole. The microsomal metabolic activation of the 7-iodo-2-acetylaminofluorene used to confirm this new metabolic pathway proceeds via a deacetylation step which could explain the resistance of the rat to the carcinogenic effect of that chemical. The high yield of the N-hydroxy-7-fluoro-2-acetylaminofluorene produced by liver microsomes could be responsible for its high carcinogenic potency.

2-Acetylaminofluorene↗
PubMed1981

Mutagenicity of aflatoxin B1: observations in vivo and their relation to in vitro activation.

Aflatoxin B1 (AFB1) was shown to be clastogenic in vivo on the basis of its capacity to produce micronucleated cells and chromosomal aberrations in mouse bone marrow cells. On the other hand, in vitro studies on cultured human lymphocytes suggested only a slight mutagenic action of AFB1. If, however, a microsomal extract isolated from rat liver was added together with the AFB1 (1.92 X 10(-5) M) to the lymphocytes before the incubation period, the yield of chromosomal aberrations and of sister chromatid exchanges (SCE) increased markedly indicating that AFB1 must be metabolically converted before it can act as an active mutagen. The use of microsomal extracts for in vitro tests can thus considerably improve the reliability of such tests of mutagenicity although studies in vitro will not be able to entirely replace those in vitro.

Aflatoxin B1↗
PubMed1981

In vivo and in vitro effects of 3-methylcholanthrene on the microsome-mediated in vitro mutagenicity of 2-acetylaminofluorene.

Pretreatment of rat, hamster or mouse by 3-methylcholanthrene (3-MC) largely induces the liver microsomal N-hydroxylase activity. The same pretreatment given simultaneously with 2-acetylaminofluorene (2-AAF) inhibits the hepatocarcinogenicity in the rat but not in the hamster. The present report compared the in vivo and in vitro effects of 3-MC on liver microsomal N-hydroxylation and liver microsome-mediated mutagenicity of 2-AAF in hamster, rat and mouse. The induction of hamster or mouse liver microsomal N-hydroxylase activity correlated well with the increase in the microsome-mediated mutagenicity of 2-AAF. With rat, however, even though the N-hydroxylase activity is largely enhanced, microsome-mediated mutagenicity is significantly reduced after pretreatment with 3-MC. Such a reduction parallels a decrease in enzyme affinity. Added in vitro to the incubation medium, 3-MC (microM concentration) inhibits both the N-hydroxylase activity and the microsome-mediated mutagenicity of 2-AAF. Those data are discussed in relationship with the biological interactions between 3-MC and 2-AAF.

2-Acetylaminofluorene↗
PubMed1981

Preparation and analysis of a lung microsomal fraction from control and 3-methylcholanthrene treated rats.

In order to facilitate the homogenization of lung tissue it was previously incubated with collagenase during 30 minutes. Morphological observations were performed in order to ascertain the cell integrity. The enzymatically digested tissue was homogenized in a 0.25 M sucrose solution containing 1 mM EDTA, 3 mM imidazole (pH.7.3) and supplemented with 1 mM imipramine in order to stabilize the mitochondria, which otherwise might contaminate the microsomal fraction. The homogenate was then centrifuged and subdivided into four fractions which were analyzed for their content in protein and for the activities of so-called marker enzymes. The cytochrome P450 level was measured in both control and 3-methylcholanthrene preparations. The activities and the kinetic parameters of lung benzpyrene hydroxylase and aldrin epoxidase were measured using the lung microsomal fractions from control and previously 3-methylcholanthrene treated rats; 3-methylcholanthrene pretreatment modified the catalytiac properties of both enzymes.

Animals↗