Search PubMed⌕ Search

Biomedical subjects

G Siest

Publications and source records attributed to G Siest.

At least 289 records · Page 16Linked to original sources
PubMed1987

[Absence of a relationship between the prevalence of markers for hepatitis B virus and the moderate consumption of alcohol].

The prevalence of 3 serological markers of hepatitis B virus was studied in a sample population of 481 men between the ages of 40 and 60 examined in the course of a routine medical checkup, whose acknowledged intake of pure alcohol was under 120 g per day. No statistically significant relationship was found between the frequency of the markers (HBs antigen, anti-HBs and anti-HBc antibodies) and the level of acknowledged alcohol consumption. The frequencies of the major potential risk factors in hepatitis B virus infection were similar among patients claiming to drink less than 20 g per day and those claiming an intake of between 20 and 80 g daily. Finally, the activities of some of the plasma enzymes most frequent in hepatology increased in a statistically significant way with acknowledged consumption of alcohol--this, in the absence of any contact with hepatitis B virus. No relationship was shown between enzyme levels and the presence--or absence--of hepatitis B markers, whatever the acknowledged alcohol consumption.

Adult↗
PubMed1986

Liquid chromatographic assay for the measurement of glucuronidation of arylcarboxylic acids using uridine diphospho-[U-14C] glucuronic acid.

A general method for the assay of UDP-glucuronosyltransferase activity towards arylcarboxylic acids (clofibric acid, 1- and 2-naphthylacetic acid) using UDP-[U-14C] glucuronic acid in liver microsomes is described. The 14C-labelled glucuronide was separated by high-performance liquid chromatography, identified by hydrolysis by beta-glucuronidase, characterized by laser desorption mass spectrometry and quantified by scintillation counting. The coefficient of variation of the enzyme activity for the inter-assay repeatability was below 4.5%. As little as 2.5 nmol of the arylcarboxylic acid glucuronides could be detected and precisely quantified. The method was applied to the determination of the apparent kinetic constants for glucuronidation of the acids. Clofibric acid was the best substrate for UDP-glucuronosyltransferase (Vmax/KM, the ratio of the maximum initial velocity and the Michaelis-Menten constant, is 12.3). The two isomers, 1- and 2-naphthylacetic acids, were transformed at a similar rate. However, they exhibited different enzymatic affinities, as the KM values were 1.0 mM and 5.6 mM for 1- and 2-naphthylacetic acid, respectively. This indicates that the spatial organization of the substrates played a critical role in this acyl glucuronoconjugation.

Animals↗
PubMed1986

Inhibition of bilirubin UDPglucuronosyltransferase activity by triphenylacetic acid and related compounds.

Bilirubin UDPglucuronosyltransferase of rat or human liver microsomes was inhibited, in vitro, by triphenylacetic acid and by structurally related arylcarboxylic acids. This inhibition appeared to be competitive towards bilirubin, and mixed-type towards UDPglucuronic acid. A decrease in the number of phenyl rings or the absence of the carboxyl group in the molecule gave structures which did not affect enzyme activity, showing that both the triphenyl moiety and the carboxyl group were necessary for the inhibition. On the other hand, successive additions of methylene groups in the aliphatic chain progressively increased inhibitory potency. Kappi,bilirubin for triphenylacetic acid was 96 microM compared with 5 microM for 7,7,7-triphenylheptanoic acid. The inhibition of bilirubin UDPglucuronosyltransferase was not due to displacement of bilirubin from albumin. On the basis of these results an attempt was made to delineate the molecular events leading to glucuronidation of bilirubin.

Animals↗
PubMed1986

Stereospecific induction of rat liver bilirubin UDPglucuronosyltransferase and lauric acid 12-hydroxylation by the isomers of 2-phenylpropionic acid.

The inductive effects of racemic 2-phenylpropionic acid and its isomers on rat liver bilirubin UDP-glucuronosyltransferase activity and lauric acid 12-hydroxylation (cytochrome P-452-dependent) were compared. The (S)-(+)-enantiomer and the racemic mixture gave the greatest induction of both enzyme activities, whereas (R)-(-)-2-phenylpropionic acid produced increases of only one-third of those of its antipode. The determination of the enantiomeric composition of the excreted 2-phenylpropionic acid after a single oral dose indicated that the (R)-(-)-enantiomer given as such or in the racemate was inverted to its antipode, which strongly suggests that (S)-(+)-2-phenylpropionic acid is responsible for the inductive effects observed. The demonstration of the same stereospecificity for the induction of bilirubin UDPglucuronosyltransferase and lauric acid 12-hydroxylation further indicates a close mechanistic link between these two processes.

Animals↗
PubMed1986

Interactions of perhexiline maleate and arylalkylamine derivatives with cytochrome P-450 and in-vitro hydroxylation.

In order to find a substitute for perhexiline maleate, an antiangina drug, for which several side effects due to poor hydroxylation have been reported, an arylalkylamine series with antianginal properties has been synthesized. The aim of the present work was to select a more rapidly hydroxylated compound than perhexiline maleate in this series. Two criteria have been retained. The binding of the molecules to liver microsomal cytochrome P-450 and their rate of hydroxylation were both studied in vitro using phenobarbital induced rat liver microsomes. Incubation with cofactors and extraction procedures have been tested on one of the molecules of the series taken as example: N-2-dicyclohexyl-2-phenethylamine. All of the molecules tested in the series substrates were type I substrates; nevertheless, no correlation was found between binding on cytochrome P-450 and oxidative metabolism of the drugs. Two of the studied molecules were more easily hydroxylated than the others and than perhexiline maleate: (N-2-dicyclohexyl-2-phenethylamine) and (II) (N-cyclohexyl-2-diphenylethylamine) with the following respective kinetics: Apparent Vmax: 0.073 and 0.32 units, apparent Km: 6.9 X 10(-5) M and 22.2 X 10(-5) M.

Animals↗
PubMed1986

ELISA of 6-beta-hydroxycortisol in human urine: diurnal variations and effects of antiepileptic therapy.

An enzyme-linked immunosorbent assay for urinary 6-beta-hydroxycortisol (6-beta-OHF) was developed. A highly specific antiserum against 6-beta-OHF-21-hemisuccinate bovine serum albumin (6-beta-OHF-21-HS-BSA) raised in rabbit was used. The enzyme-labelled hapten was prepared by the mixed anhydride method using horse radish peroxidase (HRP). The limit of detection is very low (10 pg), the intra-assay variation ranges from 5.2-6.6%, the inter-assay variation is 8.2-8.3%. Cross reactivities of various steroids are very low. The diurnal variations in urinary 6-beta-OHF and it's ratio to 17-hydroxycorticosteroids (17-OHCS) were studied in six healthy volunteers. No significant difference was found within the 24 h for the ratio of 6-beta-OHF to 17-OHCS. A large increase of 8-12 h urinary 6-beta-OHF was observed in patients receiving chronic treatment with antiepileptics.

17-Hydroxycorticosteroids↗
PubMed1986

Subcellular distribution of cytochrome P-450 in the brain.

The subcellular distribution of the monooxygenase complexes in the brain was studied by using subcellular fractionation and characterization of these fractions by marker enzymes. Cytochrome P-450 was found to be mainly localized in both synaptic and non-synaptic mitochondria; only a small quantity of enzyme was also found in the microsomal fraction. Peeling off the outer membrane of mitochondria showed that the protein was retained in the inner membrane fraction. A comparative study among some other species confirmed the mitochondrial prevalence of cerebral cytochrome P-450. A partial purification of the rat brain mitochondrial P-450 was obtained.

Animals↗
PubMed1986

Immobilization of pig liver microsomes. Stability of cytochrome P-450-dependent monooxygenase activities.

Microsomes from pig liver were covalently coupled to Sepharose activated by CNBr and to Sephadex activated by 1,1'-carbonyldiimidazole. Microsomes were also entrapped inside Ca-alginate and kappa-carrageenan gels. The concentration of immobilized cytochrome P-450 was determined by CO-difference spectra. The activity of the monooxygenase system was demonstrated by the N-demethylation of aminopyrine, the O-demethylation of p-nitroanisole, and the hydroxylation of perhexiline maleate. Upon immobilization, a 30-40% and a 60-70% decrease in Vappmax for the O- and N-demethylations were respectively observed. The Vappmax values for the hydroxylation of perhexiline maleate were essentially the same for the different immobilized forms and for the freely suspended microsomal cytochrome P-450. Under storage at 4 degrees C, microsomes entrapped inside kappa-carrageenan and Ca-alginate were less stable than the free microsomes, whereas immobilization on CNBr-activated Sepharose improved the stability of the hepatic microsomal monooxygenase system at the same temperature. These types of immobilized microsomes have the advantage of being easily recovered and reused for other assays. Finally, microsomes entrapped inside kappa-carrageenan or Ca-alginate can be used to follow up the continuous metabolization of p-nitroanisole for several hours in a stirred-batch reactor.

Animals↗
PubMed1986

Kinetic constant determination of liver microsomal and purified UDP-glucuronosyltransferase after phenobarbital and 3-methylcholanthrene treatments in rats.

After induction by phenobarbital and 3-methylcholanthrene, UDP-glucuronosyltransferase involved mainly in the conjugation of planar substrates was purified. Compared to the microsomal enzyme, the purified protein exhibited less affinity towards the substrates, but the corresponding Vmaxs were increased. These results were attributed to a change in the lipid environment of the purified enzyme. The conjugation rate for 4-hydroxycoumarine was 15-45 times less than that measured for the 7-hydroxyisomer with the microsomal or the purified enzymes. Immunoprecipitation studies of the enzyme revealed that the two compounds were transformed by the same enzyme, or metabolized by two separate enzymes presenting the same antigenic site. The orientation of the hydroxyl group of planar aglycones in the active site is the determinant for the efficiency of catalysis.

Animals↗
PubMed1986

Modulation of UDPglucuronosyltransferase activity in rats by dietary lipids.

Male Wistar rats were fed for 40 d a purified diet whose lipid source (60 g/kg diet) was coconut, peanut, corn or fish (herring) oil. A low lipid (lipid-deficient) diet (corn oil, 2 g/kg diet) was also fed to some rats. There were no significant differences in final body weights of rats fed the coconut, peanut, and corn oil diets. Rats fed the fish oil diet gained less weight than those fed any other diet. However, liver weight, ratio of liver to body weight, and protein content were not affected by any of the diets. The plasma cholesterol concentration of rats fed fish oil was lower than that of the other groups of rats. This diet resulted in the highest cytochrome P-450 concentration and markedly enhanced epoxide hydrolase activity. No difference in the level in cytochrome P-450 was noted between the groups of rats fed the vegetable oils. Epoxide hydrolase activity was also significantly higher with the corn oil diet. Interestingly, only glucuronidation of group I substrates was stimulated by the fish or corn oil diets and lowered by the coconut oil diet. Liver microsomes of rats fed fish oil contained a high level of lipid peroxides; this diet greatly stimulated NADPH-dependent peroxidation. The differential stimulation of UDPglucuronosyltransferase activity towards group I substrates could be the results of a toxic action of the fish oil diet as suggested by the concomitant enhancements of epoxide hydrolase, transaminase activities and peroxide content.

Animals↗
PubMed1986

Comparison of cytochrome P-450 content and activities in liver microsomes of seven animal species, including man.

The cytochrome P-450 content found in human livers obtained post mortem was between 0.21-0.42 nmol/mg protein. The kinetic parameters of the mono-oxygenase activities--Km and Vmax--were determined in liver microsomes for N-demethylation (aminopyrine, benzphetamine, ethylmorphine), O-demethylation (4-nitroanisole), O-deethylation (7-ethoxycoumarin) and hydroxylation (benzo[a]pyrene), in an attempt to establish an inter-species comparison between man and the six animal species studied. The four substrates studied (aminopyrine, benzphetamine, ethylmorphine, benzo[a]pyrene) were shown to be less active in humans than the male rat, which is the most commonly used model. However, other animal species, such as the female Sprague-Dawley rat and the pig, are much more similar to man. From a procedural point of view, the optimal substrate concentrations vary from one experimental species to another. Due to the apparent Km observed, for example, the activities of the guinea-pig require a higher substrate concentration.

Adult↗
PubMed1986

An improved method for phenotyping individuals for the human serum paraoxonase arylesterase polymorphism.

Human serum paraoxonase/arylesterase is a polymorphic enzyme, determined by two allelic genes at one autosomal locus. These two isozymes are called (A) and (B), and the three corresponding phenotypes A, AB and B. We measure paraoxon hydrolysis (paraoxonase activity), with, or without 1 M NaCl, and phenylacetate hydrolysis (arylesterase activity) with, or without 0.1 mM chlorpromazine. The resulting four measurements make it possible to determined essentially every individual's phenotype. The combination of qualitative tests, based on distinctive characteristics of the two isozymes, greatly improves our ability to determine individual phenotypes and detect other isozymic variants of the esterase. For several years, we have been interested in the possible correlation of the phenotypes of paraoxonase/arylesterase and sensitivity or resistance to organophosphate exposure [1]. Recent reports show that the paraoxonase gene may be closely linked to the gene for cystic fibrosis [2]. If this will be confirmed, it could be another very practical reason for typing people for this polymorphic marker. Being able to identify those heterozygous for the paraoxonase/arylesterase polymorphism, about 43% of the European population, should greatly enhance the value of phenotyping for this simple, convenient, polymorphic trait.

Aryldialkylphosphatase↗
PubMed1986

6 beta-hydroxycortisol in serum and urine as determined by enzyme immunoassay on microtitre plates.

We modified our previous enzyme immunoassay (Clin Chim Acta 1986;157:267-76) for estimating 6 beta-hydroxycortisol (6 beta-OHF) to provide a more routine procedure for measuring it in urine and to increase sensitivity for its measurement in serum. Precision, analytical recovery, specificity, and detection limit are reported. 6 beta-OHF and 17-hydroxycorticosteroids in 24-h and 4-h (08:00-12:00 h) urine collections from healthy volunteers showed no significant day-to-day differences in excretion rate for either collection period. Mean values for 6 beta-OHF in serum of men, women, and women taking oral contraceptives showed no significant differences among these groups.

17-Hydroxycorticosteroids↗
PubMed1986

[Prevalence of viral hepatitis B markers in a sample population seen at a center of preventive medicine].

The frequency of hepatitis B markers was studied on 992 subjects attending health examinations in Preventive Medicine Center of Vandoeuvre-les-Nancy. The aim of this work was to precise some epidemiological factors in this population. Results of this study have specified that 9% of individuals have shown signs of past infection and 0.3% of subjects having at least one marker were positive for the HBs-antigen. Most results agree with the literature and markers prevalence was found associated with some parameters as age and ethnic origin.

Adolescent↗
PubMed1986

[Evaluation of the Coulter Counter S+IV LMG: estimation of the leukocyte formula. Comparison with microscopic methods].

The evaluation of a differential count instrument of the Coulter S+line, the S+IV LMG Coulter-Counter, in particular for the lymphocyte, monocyte and granulocyte count was carried out. This differential analysis was compared with more classical methods of the manual (microscope) or automatic type (image analyser, Hematrack 360 type, Geometric Data). The repeatability is very good and the correlations excellent. The instrument can even detect the presence of low percentages of abnormal cells. Placement of reagents and samples at room temperature is important and the samples can be kept at room temperature for at least 9 hours without disturbing the count. In addition, energetic shaking of the samples does not change the count for the three types of cells. Due to the alarms given by the instrument as regards the cell distributions and all of the parameters of the blood cell count, no pathology should be ignored. In their laboratory, the authors note that about 25% of the smears are further examined by microscope.

Autoanalysis↗