PubMed Health⌕ Search

Biomedical subjects

M Roberfroid

Publications and source records attributed to M Roberfroid.

At least 91 records · Page 5Linked to original sources
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↗
PubMed1980

Subcellular fractionation of isolated rat hepatocytes. A comparison with liver homogenate.

An improved method for the homogenization and the subsequent subcellular fractionation of hepatocytes isolated from adult rat liver is described. The homogenization procedure developed in the present study allows the preservation of the integrity of subcellular structures, as demonstrated by measurement of the activities of representative enzymes as well as by determination of their latency. The activities of representative marker enzymes, as calculated on subcellular fractions obtained by differential centrifugation of the homogenate, are identical whether the homogenate arises from isolated hepatocytes or from the whole liver. Moreover, there is a close similitude between the kinetic parameters (Km and V) of two microsomal cytochrome P450-dependent mixed-function oxidases, namely aniline hydroxylase and aminopyrine demethylase determined on microsomal preparations obtained either from isolated cells or from the whole liver.

Animals↗
PubMed1980

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.

Animals↗
PubMed1980

Interference of chemicals with glycogen metabolism in isolated hepatocytes.

Freshly isolated hepatocytes in suspension were used to evaluate the possible effects of certain chemicals. Conditions including the choice of the incubation medium have been defined for maintaining the cells competent for a sufficient length of time. Using paracetamol alone or in combination with diethylmaleate, we have been able to show that these chemicals markedly alter the metabolic state of the cells, as indicated by an inhibition of glycogen synthesis and even by an enhancement of glycogen degradation, without modifying membrane integrity. These effects are dose-dependent and probably mediated through modification of glycogen phosphorylase activity.

Acetaminophen↗
PubMed1980

Separate isolation of cells from nodules and surrounding parenchyma of the same precancerous rat liver: biochemical and cytochemical characterization.

Various enzyme and metabolic alterations have been observed in the hyperplastic nodules which appear during the hepatocarcinogenesis. These alterations have been mainly specified by histochemical observations. In this report, a technique of hepatocyte isolation is described which enables the separation of 2 cellular fractions, respectively, from the nodules and from the surrounding parenchyma of the same liver of a rat previously treated with a hepatocarcinogen. Such a technique allowed parallel analysis of both cellular populations by biochemical and cytochemical techniques.

Animals↗
PubMed1980

Characterization of the guinea pig liver microsomal 2-fluorenylamine and N-2-fluorenylacetamide N-hydroxylase.

Many reports in the literature have indicated that the guinea-pig is resistant to the carcinogenic effect of N-2-fluorenylacetamide (2FAA); this refractoriness has been attributed to its lack of N-hydroxylating enzymes. The present communication, however, supports the results of contradictory reports which demonstrate that guinea-pig liver microsomes are in fact able to N-hydroxylate both 2-fluorenamine and 2FAA. The guinea-pig N-hydroxylase activity toward 2-fluorenamine is found to be even greater than the reported activity in the rat and hamster. It is similarly inhibited by 3-methylcholanthrene (3MC), 7,8-benzoflavone (7,8 BF) or miconazole. Activity toward N-2-fluorenacetamide is present in the microsomal preparation from the control guinea-pig. There is slight activation by SKF525A, paraoxon (PX) or sodium fluoride. Under optimum conditions, in the presence of both paraoxon and sodium fluoride, activity is equivalent to that of rat liver microsomal enzymes.

2-Acetylaminofluorene↗
PubMed1980

Competitive inhibitory effect of microsomal N-hydroxylase, a possible explanation for the in vivo in inhibition of 2-acetylaminofluorene carcinogenicity by 3-methylcholanthrene.

The kinetic properties of the N-hydroxylation of 2-acetylaminofluorene (2-AAF) are studied with microsomal preparations of livers from both control and 3-methylcholanthrene (3-MC)-pretreated rats and hamsters. The level of basal enzymatic activity is higher in hamster than in rat liver; 3-MC induces the activity in both animals. When added in vitro to incubation mixture, 3-MC competitively inhibits the N-hydroxylase activity. When fed to rats simultaneously with 2-AAF, 3-MC suppresses the carcinogenicity of the acetylated arylamine by inhibiting the first step in its activation pathway. Hamster tissues are not protected by this pretreatment because the level of N-hydroxylase activity is too high.

2-Acetylaminofluorene↗
PubMed1980

The mutagenicity of butadiene towards Salmonella typhimurium.

Gaseous butadiene (BUT) was mutagenic towards S. typhimurium strain TA 1530 when the incubation mixture was supplemented with a NADPH-fortified rat liver microsomal preparation; mutagenicity increased with the dose. A significant mutagenic effect was similarly observed when the petri dishes, containing the bacteria but no metabolic activation system, were incubated in the presence of butadiene, in a desiccator in which plates containing the S-9 rat liver fraction had been placed. This indirect mutagenic effect was attributed to the formation, by the S-9 mix, of volatile intermediate(s) that migrated and induced mutations in neighbouring bacteria.

Animals↗