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M Roberfroid

Publications and source records attributed to M Roberfroid.

At least 91 records · Page 5Linked to original sources
PubMed1984

Critical biochemical functions of isolated hepatocytes as sensitive indicators of chemical toxicity.

Isolated hepatocytes from adult male Wistar rats are a suitable experimental model to study the cytotoxicity of chemicals. Indeed, the isolated cells incubated in suspension in a Waymouth medium supplemented with 10% newborn calf serum maintain critical biochemical functions such as cytochrome P-450-dependent monooxygenase activity, glycogen, and protein synthesis capacities. This cellular model is used to detect the early biochemical effects of various xenobiotics, i.e., chlorpromazine, promethazine, bromobenzene, paracetamol, and isoniazid. Both cellular lysis (measured by the LDH leakage) and metabolic competence of the hepatocytes (glycogen deposits and protein synthesis) are modified as a function of both the duration of exposure to, and the concentration of, the chemicals. These results point out that the evaluation of metabolic functions of isolated cells surviving in suspension might be a sensitive test to predict early cell injury. Indeed, changes in the cellular behavior may occur before or without cell death. Furthermore, since both the cytochrome P-450 content and its dependent monooxygenase activity together with critical biochemical functions of the isolated cells remain stable, this model is of significant interest in ascertaining the mechanisms of toxicity.

Acetaminophen↗
PubMed1984

Promoting effect of portocaval anastomosis in rat hepatocarcinogenesis.

The effect of a surgical intervention, portocaval anastomosis (PCA) has been investigated in three different phases of a triphasic protocol of rat hepatocarcinogenesis. This protocol consists of the i.p. injection of 200 mg/kg of diethylnitrosamine (initiation) followed 2 weeks later by a 2 weeks diet with 2-acetylaminofluorene (2-AAF) and in the middle a necrogenic dose of CC14 (selection). One week later, a promoter such as phenobarbital (PB) is given chronically (promotion). PCA or a sham operation is performed 5 months before the end of the experiment. PCA alone does not induce hyperplastic nodules, nor does it when rats are initiated 5 weeks before. However, PCA alters the evolution of established nodules: it can act as a promoter like PB. Indeed, 5 months after initiation and selection, the number of rats bearing hepatocarcinomas is zero out of seven with a sham operation and six out of seven with PCA performed one week after the end of the selection. The combination of PCA and PB is more potent than PB or PCB alone since six out of six, five out of eight and six out of seven rats, respectively, bear malignant liver tumours. Thus PCA, which induces many systemic perturbations, has a promoting effect. This suggests that the chronic administration of a xenobiotic is not the only way to promote cancer development.

Animals↗
PubMed1984

Comparison of different models of rat liver carcinogenesis: conclusions from a systemic analysis.

Different protocols of chemically induced hepatocarcinogenesis were applied to Wistar rats under identical experimental conditions. The following conclusions may be drawn after an analytic comparison of these results. Various chemical carcinogens show different carcinogenic capacities. Diethylnitrosamine is more potent than N-nitrosomorpholine which is more active than 2-acetylaminofluorene. A short-term exposure to such carcinogens is sufficient to initiate but not necessarily to complete the carcinogenic process. It can be promoted to completion by either a noncarcinogenic promoter or a carcinogen. From a systemic point of view, it appears that, as in the skin models, two-step protocols are not always equivalent to protocols using the same agent during the whole treatment. Moreover, the results observed with a multistep protocol indicate that during the initiating phase the carcinogen plays a selective role distinct both from a pure initiating role and from the promoting effect. The results obtained lead to the conclusion that the distinction between initiation and promotion remains purely operational as it still does not correspond to the nature of well-established biologic processes.

2-Acetylaminofluorene↗
PubMed1984

[Promoting effect of portacaval anastomosis in experimental hepatic carcinogenesis].

A promoting effect of portocaval anastomosis in a triphasic model of rat hepatocarcinogenesis is demonstrated since after initiation and selection premalignant lesions and hepatocellular carcinomas increase. This demonstrates that chronic administration of an exogenous compound is not the only way to promote cancer development.

2-Acetylaminofluorene↗
PubMed1984

[Dietary lipids and variations of fecal output and metabolic components in rats].

The amount of feces (g/day) and the concentration of fecal secondary bile acids have been measured in ninety-six male Wistar rats C.P.B.: W.U. which received diets varying in their content both in linoleic acid and in total fat (5-10-20 p. 100). The fecal outflow, water excretion and fecal concentration of deoxycholic and lithocholic acids increased exponentially with time of feeding. As early as two weeks after beginning the diets, the increases were significantly greater for the diet with saturated fatty acids than for the diet with polyunsaturated fatty acids. The amount of ingested fat had only a slow influence on fecal metabolic factors. Indeed, the effect of the diet with the highest fat content became significantly different from that of the diet with the lowest fat content only after seven weeks of feeding. The existence of a linear relationship between secondary bile acid concentrations and both fecal water outflow and fresh fecal outflow would seem to indicate that the increase in bile salt fecal excretion was strictly physiological. The proposed experimental protocol can be applied to study the relationship between fat intake, bile acid fecal excretion and tumor yield in experimental colonic tumorigenesis initiated by 1,2-dimethyl-hydrazine.

Animals↗
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↗