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Biomedical subjects

G Siest

Publications and source records attributed to G Siest.

At least 343 records · Page 19Linked to original sources
PubMed1983

[Biological variations and reference values of transferrin, immunoglobulin A and orosomucoid].

To explain laboratory test results, it is necessary to know for each parameter the biological variation factors and the reference values. The principal biological variations factors for transferrin, IgA and orosomucoid (age, sex, body weight, exercise, puberty, menstrual cycle, professional class and work conditions) have been studied on a sample of the population who have come to the Center for Preventive Medicine (Vandoeuvre-Lès-Nancy, France) for a health check-up (males and females, 4-60 years). We have assembled bibliographical data concerning the other main variations factors. Our results (variations calculated on the medians) and literature results (variations calculated on the medians or on the means) are presented together. These are respectively: 1. For transferrin: age (new-born/20-30 years: -29 to -71%, 50-60 years/20-30 years: -15%), menstrual cycle (+15%), pregnancy (+37 to +70%), exercise (+9 to +13%), oral contraceptives (+10 to +62%), medications (danazol: +60%, testosterone: -13%, D-penicillamine: -13 to -30%, L-asparaginase: -68%); 2. For IgA: age (new-born/20-30 years: -98 to 100%, 3-5 years/20-30 years: about -50%, 50-60 years/20-30 years: up to +60%), sex (men/women: up to +30%), exercise (+14%), pregnancy (-20%), obesity (+30%), season (winter/summer: +10 to +14%, in Africa humid season/dry season: +20%), oral contraceptives (-11 to -40%), medications (L-asparaginase: +36 to +60%), socio-economical factors (black/white: +20 to +75%); 3. For orosomucoid: age (new-born/20-30 years: -70 to -95%, 60-80 years/20-30 years: up to +50%), sex (men/women: up to +15%), obesity (+26%), menstrual cycle (+14%), pregnancy (-20 to -30%), oral contraceptives (-21 to -36%), medications (L-asparaginase: +17%, anabolic steroids: +68%). We determined the three proteins reference values with a nephelometric method.

Age Factors↗
PubMed1983

Comparative study of four hypolipidaemic agents on the activity of drug-metabolizing enzymes in rat liver microsomes.

In order to understand the secondary effects of hypolipidaemic agents in human therapy, the authors have studied the inductive properties of four of these drugs, clofibrate, F1379, fenofibrate and probucol, on hepatic drug metabolizing enzymes in the rat. Each hypolipidaemic molecule was administered once a day for five days at doses ranging from 100 to 450 mg/kg/day. All the drugs tested caused hepatomegaly, the effect being particularly marked in the case of F1379 and fenofibrate; on the other hand they decreased the microsomal protein content, especially after F1379 or probucol treatment. Cytochrome P-450 concentration was not greatly affected, with only a 40% increase by clofibrate (dose 200 mg/kg/day) and by F1379 at the lower dose. It is of interest that all the hypolipidaemic agents tested enhanced the activity of epoxide hydrolase with 4, 5 benzo(a)pyrene oxide as the substrate. Except for fenofibrate and probucol at the lower dose, they all strongly increased the activity. The greatest change was effected by F1379 which led to a three to eight-fold increase over the control values. We also measured UDP-glucuronosyltransferase activities using two substrates belonging to group I (4-nitrophenol) and group II (4-hydroxybiphenyl). It appears that the changes in enzyme activity found depended both on the type and the dose of the drug administered and on the chemical structure of the substrate. This study showed that hypolipidaemic drugs which are chemically related to clofibrate could greatly modify the activity of drug metabolizing enzymes and therefore alter the transformation of drugs administered concomitantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Total bone and liver alkaline phosphatases in plasma: biological variations and reference limits.

We have studied factors affecting biological variation in total plasma alkaline phosphatase in a population of 32 329 apparently healthy subjects four years old or older. Quantification of the bone and liver isoenzymes after thermal denaturation made it possible to specify the contributions of each isoenzyme to variations in the total activities. The main factors that modify plasma alkaline phosphatase activity are age, sex, hormonal state (puberty or menopause), and morphometric parameters (height, body weight, or degree of overweight). The bone isoenzyme is mainly responsible for the variations associated with age, sex, and puberty and to some extent with the menopause. Activity of the liver isoenzyme was also altered at the menopause and by certain drugs, such as oral contraceptives and blood-lipid-lowering agents. These data allow us to propose reference limits for total plasma, bone, and liver alkaline phosphatases according to age and sex.

Adolescent↗
PubMed1982

Conformational study of purified epoxide hydrolase from rat liver.

Hepatic epoxide hydrolase (EC 3.3.2.3) was purified from phenobarbital-treated rats by ion-exchange chromatography followed by hydrophobic chromatography. The enzyme had a specific activity of 300--400 nmol min-1 mg-1 protein with benzo[a]pyrene-4,5-oxide as the substrate. Circular dichroism (CD) spectra of the purified enzyme gave two negative bands, centered at 210 nm and 222 nm, respectively. The mean residue ellipticity at 222 nm was 12,9000 deg X cm(2) X dmol(-1), which indicated the presence of about 35% alpha-helical structures. Sodium dodecyl sulfate (SDS) greatly affected the shape of the CD spectra, which were gradually shifted to the blue. This suggested a decrease in the aggregation state of the protein. Electrostatic interactions were important in the organization of the enzyme structure since the conformation was stable between pH 7.4 and pH 10. At pH-values 5.0, 6.0 and 12.0, the CD bands underwent considerable changes in both amplitude and shape. Moreover there was a good correlation between the optimal pH range of the epoxide hydrolase activity and the organization state of the protein. After membrane reconstitution with liposomes, the conformation of the enzyme was not significantly modified by the presence of dimyristoyl L-alpha-phosphatidylcholine or other phospholipids. This constancy was obtained over a wide range of molar ratios of phospholipids to protein (0--500). However, phospholipids did increase the thermal stability of the enzyme. Fluorescence measurements of diphenylhexatriene (DPH) bound to dimyristoyl L-alpha-phosphatidylcholine indicated that addition of epoxide hydrolase modified the thermal transition of the lipid phase. On the other hand, electron paramagnetic resonance (EPR) signals of the nitroxide-labelled fatty acid, 2-(14-carboxy-tetradecyl)-2-ethyl-4,4-dimethyl-3,3,-oxazolidiny-oxyl, bound to the phospholipid, indicated that the presence of the protein decreased by about 53% the correlation time of the label, suggesting that its motion had increased. In conclusion, phospholipid-epoxide hydrolase interactions enhanced the fluidity of dimyristoyl L-alpha-phosphatidylcholine liposomes without changing the secondary structure of the enzyme. Electrostatic interactions also played an important role in the conformational stability of the protein.

Animals↗
PubMed1982

Effect of a dietary protein deficiency on the development of hepatic drug-metabolizing enzymes in young rats.

The effect of protein deprivation on the activities of hepatic drug-metabolizing enzymes was studied in young rats whose mothers had previously been on a protein-restricted diet during pregnancy. Dietary protein deficiency (5% lactic casein as the protein source) lowered the amount of cytochrome P-450 and the activities of epoxide hydrolase and UDP-glucuronosyltransferase (UDPGT) (l-borneol as the substrate) by about 45, 63, and 48%, for the first 8 weeks, respectively. Interestingly, UDPGT estimated with p-nitrophenol as the substrate was far less affected than that estimated from l-borneol glucuronidation. This finding provides further evidence of the heterogeneity of UDPGT. Restoration of a balanced diet for 15 days following protein deprivation quickly restored cytochrome P-450 and enzyme activities to control values. Our experiments showed that the development of drug-metabolizing enzymes was changed more by the diet in young rats than in older rats. This could affect the toxicity of drugs that are normally metabolized by these pathways.

Animals↗
PubMed1982

Phenobarbital induction of cytochrome P-450 and UDP-glucuronosyltransferase in rabbit liver plasma membranes.

The presence of cytochrome P-450 and UDP-glucuronosyltransferase was confirmed in rabbit liver plasma membranes. Their levels, expressed as amount or activity/mg protein, were 25 and 40% respectively of those found in hepatic microsomes. Both enzymes were induced by phenobarbital treatment of the animals: administration of the barbiturate for 4 days, produced a 150% increase in the cytochrome P-450 content and in the specific activity of UDP-glucuronosyltransferase. As compared with the microsomal enzymes, the plasma membrane enzymes were localized in a lipid environment characterized by high levels of cholesterol and sphingomyelin and a low level of phosphatidylcholine. Treatment with phenobarbital for 4 days also caused a significant increase of phosphatidylcholine and phosphatidylethanolamine content in plasma membranes.

Animals↗
PubMed1982

Effect of chronic ethanol administration on gamma-glutamyltransferase activities in plasma and in hepatic plasma membranes of male and female rats.

The effects of chronic ethanol administration on the activities of gamma-glutamyltransferase (GGT) in plasma and in hepatic plasma membranes of male and female rats are studied. The effects of alcohol on the lipid level in plasma are also investigated. After 4 weeks of treatment, GGT activity significantly increases in plasma either in male rats (131%, p less than 0.02) or in female ones (64%, p less than 0.05). In addition, chronic alcohol consumption simultaneously increases beta-lipoprotein and triglyceride levels in plasma only in male rats (181%, p less than 0.05 and 171%, p less than 0.01, respectively). In the liver, a significant elevation of GGT activity is observed in plasma membranes (146% in male rats, p less than 0.02, and 84% in female rats, p less than 0.02) but neither in homogenates nor in microsomal fractions. So, the variation of enzymatic activity in plasma as well as in hepatic plasma membranes is higher in male than in female rats. These results demonstrate, as for phenobarbital, that alcohol provokes an induction of GGT in rat liver only in the plasma membrane fraction.

Animals↗
PubMed1981

Measurement of plasma gamma-glutamyltransferase in clinical chemistry: kinetic basis and standardisation propositions.

The conditions for the measurement of gamma-glutamyltransferase (EC 2.3.2.2) activity of human plasma were studied at 30 degrees C using the kinetic technique of Szasz [3]. The optimum pH in Tris (hydroxymethylaminomethane) buffer and 2-amino-2-methyl-1.3-propanediol at a concentration of 100 mmol/1 are 8.0 and 8.1. The kinetic characteristics of human plasma gamma-glutamyltransferase were studied using gamma-L-glutamyl p-nitroanilide and its carboxyl derivative as donor substrates. Glycylglycine was chosen as the best acceptor of the gamma-glutamyl radical. Under these conditions, we have shown that the inhibition by the donor substrate was more important at acidic pH and vanished at alkaline pH. This inhibition was obviously related to the presence of the acceptor, but did not vary with glycylglycine concentration. At pH 8.0, by increasing the acceptor concentration some competition occurs at the donor binding site, as reported by other authors in relation to the known ping-pong bi-bi enzyme mechanism for the gamma-glutamyltransferase. Some displacement of donor substrate by increasing amounts of acceptor substrate could be observed at all pH values we studied. However, the influence of glycylglycine on the enzyme's maximum velocity and affinity for the donor substrate was also pH dependent. Studying the kinetic characteristics of the enzyme as a function of the pH suggests that the enzyme works with more than one active site at pH 7.5-8.0. Based on the results of this study, we propose measurement conditions for gamma-glutamyltransferase at 30 degrees C in routine clinical chemistry without preference in the choice of substrate.

1-Carboxyglutamic Acid↗
PubMed1981

Biological variations in hyperlipidemic children and adolescents treated with fenofibrate.

Beside their pharmacological action drugs may have unexpected side effects which must be known and taken into account in the interpretation of laboratory tests. In this work, we followed 17 hyperlipidemic subjects, aged 4-19 years, treated with fenofibrate only. We performed several plasma tests before and during treatment. The hypolipidemic action of fenofibrate was evident: decreases of cholesterol and triglycerides mean values were, respectively, 22% and 39% after 3 months of treatment. Other plasma constituents were also significantly decreased: uric acid, 20%; bilirubin, 19%; alkaline phosphatases, 15%. The aminotransferase activities (both AST and ALT) were increased in only four subjects after 3 months. The highest values were 88 U/l for AST and 109 U/l for ALT (the initial values were, respectively, 28 U/l and 23 U/l). These activities decreased when the treatment was stopped. These variations were isolated and transient.

Adolescent↗
PubMed1981

Some kinetic properties of gamma-glutamyltransferase from rabbit liver.

gamma-Glutamyltransferase ((5-glutamyl)-peptide: amino-acid 5-glutamyltransferase, EC 2.3.2.2) of rabbit liver (detergent form) was purified 1100-fold in order to study its kinetic properties. Kinetic studies were conducted from pH 6.0 to 12.0 in the absence and presence of the acceptor substrate glycylglycine using gamma-glutamyl-3-carboxy-4-nitroanilide as the donor. The existence of more than one binding site for both donor and acceptor is postulated on kinetic evidence such as donor substrate activation, donor substrate inhibition and acceptor substrate activation. Homotropic interaction is also observed, in the form of negative cooperativity, in donor substrate binding, in the absence of acceptor at pH less than 9.0 and positive cooperativity (n = 2), in the absence or presence of acceptor at pH greater than 9.0. Hydrolase reaction reaches a maximum of activity at pH 10 (pK 8.6). Transferase activity under conditions of maximal velocity is maximal at pH 9.0 (pK 7.1). The ratio of transferase activity/hydrolase activity is maximal at pH 7.0-7.5. At low donor substrate concentrations, maximal activity is attained at pH 7.5.

1-Carboxyglutamic Acid↗
PubMed1981

Distribution, metabolism, and elimination of phenobarbital in rats: physiologically based pharmacokinetic model.

The distribution, metabolism, and elimination kinetics at two different doses of phenobarbital were examined in rats. After intravenous injection, phenobarbital distributed very rapidly to the liver and kidneys, less rapidly to the muscle and gut, and much more slowly to the brain. At the higher dose, a concentration rebound was observed 1 hr after injection. In addition, phenobarbital distributed unevenly in various organs as a result of a different extent of drug binding. A physiologically based model, including enterohepatic cycling and diffusion resistances between blood and tissue, is proposed for phenobarbital pharmacokinetics. It satisfactorily describes phenobarbital distribution in rats at the two doses and allows an evaluation of fundamental physicobiochemical parameters such as drug-tissue binding constants, blood-tissue transport coefficients, metabolism, and elimination rate constants.

Animals↗
PubMed1981

Effect of diphenylhydantoin and its main hydroxylated metabolite on the pharmacokinetics and the urinary and biliary excretion of phenobarbital and its p-hydroxy metabolite.

When rats which had been pretreated with a high dose of diphenylhydantoin (80 mg/kg) for 5 days were given a single intravenous dose of phenobarbital (30 mg/kg): (a) There was no increase in the rate at which phenobarbital (PB) disappeared from the plasma or the tissues of pretreated rats. (b) The percentages of phenobarbital and p-hydroxyphenobarbital (free and conjugated) excreted in the urine were similar in both treated and control animals. However, the percentage of conjugated p-hydroxyphenobarbital excreted, was almost twice that of the control group. (c) Pretreatment with diphenylhydantoin (DPH) markedly increased bile flow rates. Therefore these rats excreted more PB than their controls. The biliary excretion of hydroxylated metabolites of PB (free and conjugated), was similar to that found in urine. Hydroxylation was not increased although, there was a significant elevation in the percentage of conjugated metabolite excreted. In a study to establish whether the main metabolites of diphenylhydantoin interfered with the metabolism of phenobarbital the following results were obtained: (a) Intravenous administration of DPH together with PB caused a two-fold increase in the half-life of phenobarbital elimination. (b) Intravenous administration of PB, to bile duct cannulated rats which had been pretreated for 5 days with DPH, caused a significant reduction in the excretion of hydroxylated phenobarbital in comparison with their control group. However, all the excreted DPH was present in the conjugated form. (c) The DPH pretreated rats had significantly lower cytochrome P-450 and mono-oxygenase activities in their hepatic microsomes than the pretreated controls, and higher UDP-glucuronyltransferase activity with DPH itself as the substrate.

Animals↗
PubMed1981

Influence of oral contraceptives of differing dosages on alpha-1-antitrypsin, gamma-glutamyltransferase and alkaline phosphatase.

We have studied the effects of oral contraceptives on three glycoproteins, alpha-1-antitrypsin (A1AT), gamma-glutamyltransferase (GGT) and alkaline phosphatase (AP), in terms of age (20--40 years), duration of administration, and levels of estrogens. We have confirmed that oral contraceptives increase the concentration of A1AT and the activity of GGT and decrease the activity of AP, but that the modifications are less pronounced with pills containing low levels of estrogens for GGT and AP. We observed a decrease in A1AT and GGT after 2 and 5 years of treatment, respectively, but an increase in AP. Patient age seemed to have little influence on the change in AP activity and A1AT concentration but GGT activity was higher for the 25--30 year group.

Adult↗