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Biomedical subjects

M Roberfroid

Publications and source records attributed to M Roberfroid.

At least 109 records · Page 6Linked to original sources
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↗
PubMed1980

Induction, activation, and inhibition of hamster and rat liver microsomal arylamide and arylamine N-hydroxylase.

By applying a new and highly sensitive assay for measuring N-hydroxy metabolites, the biochemical properties of the microsomal N-hydroxylase from control and 3-methylcholanthrene-treated rat and hamster liver have been analyzed, and the following conclusions have been drawn. (a) Due to a difference in enzyme affinity, the metabolic activation of acetylaminofluorene is more pronounced than that of aminofluorene, a fact which correlates with the difference in the carcinogenic potency of the two compounds. (b) Arylamine N-hydroxylase differs qualitatively as well as quantitatively from arylamide N- hydroxylase mainly in terms of sensitivity to various in vitro inhibitors. (c) 7,8-Benzoflavone and 3-methylcholanthrene are strong inhibitors of liver microsomal N-hydroxylases. This effect could partly explain the inhibition of the hepatic tumorigenicity of acetylaminofluorene in animals simultaneously fed 3-methylcholanthrene. (d) The metabolism of acetylaminofluorene proceeds via both ring- (C-1, C-3, C-5, or C-7) and N-hydroxylation. There is clear reciprocal interaction between these various microsomal pathways. (e) The apparent increase in Km following pretreatment of the rat with 3-methylcholanthrene is due to competitive inhibition of the N-hydroxylase by some of the C-hydroxy metabolites. This effect is not seen in hamster liver.

2-Acetylaminofluorene↗
PubMed1979

Determination of Kováts retention indices with a capillary column and electron-capture detection: application to the assay of the enzymatic conversion of 3,4-epoxy-1-butene into diepoxybutane.

A method is described that allows for alternate operation of a "pin and cup"-type electron-capture detector (ECD) in the normal ECD mode and in the metastable argon ionization mode. By such means, marker n-alkanes can be run without a change of the gas or temperature parameters, and measurements can be made of the Kováts retention indices of unknown compounds that are detectable in trace amounts by ECD only. As an application, tests are reported which support the probable enzymatic conversion of 3,4-epoxy-1-butene into diepoxybutane during incubation of the former with rat liver microsomes.

Animals↗
PubMed1979

Microsomal vinyl oxide synthetase: modification of its kinetic parameters by chemical carcinogens.

The kinetic parameters of liver microsomal vinyl oxide synthetase as well as their modifications under the influence of various pretreatments have been evaluated, using 1,1,2-trichlorethylene (TCE) as a substrate. The results were correlated with those obtained using aldrin oxide synthetase and benzpyrene hydroxylase as typical cytochrome P-450 dependent enzymatic activity. The treatments of animals with chemical carcinogens selectively increase the affinity of those enzymes for their substrates.

Aldrin↗
PubMed1979

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).

Acrylonitrile↗