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G Siest

Publications and source records attributed to G Siest.

At least 253 records · Page 14Linked to original sources
PubMed1988

Total, tartrate-resistant, and tartrate-inhibited acid phosphatases in serum: biological variations and reference limits.

We studied several factors affecting biological variation in serum acid phosphatases in a population of 1195 apparently healthy subjects four years old or older. We assayed total acid phosphatase activities in the presence of a transphosphorylating agent and using alpha-naphthyl phosphate as substrate. The main factors modifying total and tartrate-resistant acid phosphatases activities in serum are similar to those observed for total and bone alkaline phosphatases activities: age, sex, and hormonal state (puberty or menopause). The tartrate-inhibited acid phosphatase activity is, however, independent of biological variations. Finally, we propose reference limits for total, tartrate-resistant, and tartrate-inhibited acid phosphatases in serum.

Acid Phosphatase↗
PubMed1988

Micro-scale two-dimensional electrophoresis of alkaline phosphatase from serum.

Isoenzymes of alkaline phosphatase (EC 3.1.3.1) were separated by micro-scale two-dimensional electrophoresis, with isoelectric focusing in capillary gels in the first dimension and polyacrylamide gradient-gel electrophoresis in the second. The isoenzymes detected were identified by several treatments--e.g., incubation with sialidase, papain, Triton X-100, and wheat-germ agglutinin--and by comparison with alkaline phosphatase from liver microsomes. Liver and bone isoforms in normal sera showed overlapping isoelectric points but differed in molecular mass, estimated as 172 and 185 kDa, respectively. Sera of patients with liver disease showed several additional groups of alkaline phosphatase isoforms, two of which were found to consist of multi-molecular complexes. Others probably correspond to incompletely glycated enzyme proteins. A further isoform with a mass of about 250 kDa does not seem to correspond to any known isoform of alkaline phosphatase in serum. With this technique, we demonstrated intra- and interindividual variations of the placental alkaline phosphatase isoenzyme in pregnancy sera.

Adult↗
PubMed1988

[Biological constants in migrants].

Until now, clinical chemists, clinicians, physicians dealing with the problem of migrant biology dispose only reference limits established for an autochtone population. But can these really be applied? We compared 28 blood constituents of a migrant population with those of the french population. We defined five geographic areas: Italy, the Iberian Peninsula, Northern Africa, Northern and Central Europe and the Near and Middle East.

Adult↗
PubMed1988

Albendazole sulfonation by rat liver cytochrome P-450c.

The metabolism of albendazole (ABZ) was studied in perfused livers from control and ABZ-treated rats (10.6 mg/kg, per os, each day for 10 days). In the perfusion fluid, the concentration of ABZ-sulfoxide (SO-ABZ) remained unchanged in treated, as compared to control animals, whereas ABZ-sulfone (SO2-ABZ) was increased in treated animals. In bile, only SO-ABZ was present. The transformation kinetics of SO-ABZ to SO2-ABZ in microsomes from rats treated with ABZ, 3-methylcholanthrene, Aroclor and isosafrole were biphasic. This suggests that enzyme activity was a consequence of two enzyme systems, one characterized by low affinity and high capacity, the other by high affinity and low capacity, the latter could be induced by 3-methylcholanthrene, ABZ, Aroclor and isosafrole. Cytochrome P-450c was induced potently in vivo by ABZ as proven by increased monooxygenase (7-ethoxyresorufin and 7-ethoxycoumarin-O-deethylase) activities and by Elisa test (a 5-fold increase in hemoprotein concentration was observed). Purified and reconstituted cytochrome P-450c from 3-methylcholanthrene or ABZ-treated rat liver were able to produce SO2-ABZ (2.01 and 1.70 nmol/mg/15 min, respectively, whereas cytochrome P-450b produced 10 times less SO2-ABZ). Immunological assays, as well as activity measurements showed a relationship between cytochrome P-450c-3-methylcholanthrene and cytochrome P-450c-ABZ. We conclude that induction of cytochrome P-450c by ABZ is the probable explanation for the enhanced formation of SO2-ABZ in vivo.

Albendazole↗
PubMed1987

Comparative study of clofibric acid and bilirubin glucuronidation in human liver microsomes.

Hepatic microsomal glucuronoconjugation of the hypolipidemic drug clofibric acid was characterized in human liver and compared to the acylglucuronide formation of an endogenous substrate, bilirubin. The affinity of UDP-glucuronosyltransferase for bilirubin was 15-fold higher than for clofibric acid; the Vmax for the transformation of the two substrates were similar. The analysis of the specific activity in 32 liver biopsies showed that glucuronidation of clofibric acid or bilirubin were comparable in man and in rat. However, UDP-glucuronosyltransferase activity towards clofibric acid exhibited a large interindividual variation in man. Sex or age did not influence the glucuronidation of bilirubin and clofibric acid. Among the drugs given to the patients only clofibrate was able to increase the bilirubin conjugation. No effect of alcohol or smoking on the conjugation of the two substrates was observed. The absence of correlation between UDP-glucuronosyltransferase activities towards clofibric acid and bilirubin together with the specific induction of bilirubin glucuronidation by clofibrate suggested that these arylcarboxylic substrates were conjugated by separate forms of UDP-glucuronosyltransferase in human.

Adult↗
PubMed1987

Induction of hepatic cytochrome P-450c-dependent monooxygenase activities by dantrolene in rat.

The effect of dantrolene sodium, a skeletal muscle relaxant, on drug metabolizing enzymes has been investigated after treatment of rats with a dose of 200 mg/kg for five days. We observed an induction of cytochrome P-450c and epoxide hydrolase in immunoassays and activities. An enhancement of the UDP-glucuronosyltransferase (GT1) activity was observed. We also reported a decrease of both liver cytochrome P-450 content and microsomal cytochrome P-450b dependent N-demethylation activities. On the other hand, the binding of dantrolene on microsomal cytochrome P-450 produced a type I difference spectrum, these data were obtained with liver microsomal cytochrome P-450c induced by 3-methylcholanthrene.

Animals↗
PubMed1987

Brain mitochondrial cytochrome P-450scc: spectral and catalytic properties.

The cytochrome P-450-dependent cholesterol side chain cleavage system of the brain has been studied using nonsynaptic mitochondria as the source of enzymatic activity. The system has been found to bind cholesterol and 11-deoxycorticosterone, producing type I difference spectra, whereas the binding of pregnenolone induced a reverse type I difference spectrum. Inhibitors of cytochrome P-450-linked monooxygenase activities produced type II spectra. The formation of labeled pregnenolone after incubation of brain mitochondria with [4-14C]cholesterol has been obtained, and this formation was inhibited by glutethimide, a specific inhibitor of cytochrome P-450scc. The functional significance of this enzymatic activity is discussed.

Aminoglutethimide↗
PubMed1987

Ethoxyresorufin O-deethylase activity in rat brain subcellular fractions.

Non-polar, lipid-soluble drugs or xenobiotics are able to cross the blood-brain barrier. The brain cytochrome P-450-dependent monooxygenases may oxidize these molecules to more polar and somewhat hazardous metabolites responsible for neurotoxicity. In order to characterize the cytochrome P-450 dependent aryl hydrocarbon hydroxylase activity in brain subcellular fractions, we used 7-ethoxyresorufin as a substrate, as its O-deethylation reflects specifically the activity of the cytochrome P-450 isoform which metabolizes and is induced by polycyclic aromatic hydrocarbons. The results reported here show that this enzymatic activity occurs in both microsomal and mitochondrial fractions, and that the induction after 3-methylcholanthrene treatment remains limited, thus preventing the formation of high levels of harmful metabolites.

Animals↗
PubMed1987

Differential time-course of induction of rat liver gamma-glutamyltransferase and drug-metabolizing enzymes in the endoplasmic reticulum, Golgi and plasma membranes after a single phenobarbital injection. Evaluation of protein variations by two-dimensional electrophoresis.

This study was conducted to follow as a function of time the activity of gamma-glutamyltransferase in the various membranes of rat liver cells after a single dose of phenobarbital (PB) (75 mg kg-1 body weight). Gamma-glutamyltransferase induction was maximal 24 h after PB treatment in both the rough endoplasmic reticulum and the plasma membranes. This pattern of induction differed from that of some drug metabolizing enzymes. While total cytochrome P-450 content was enhanced mainly in endoplasmic reticulum until 48 h after PB treatment, UDP-glucuronosyltransferase activity was not greatly altered by PB under the same conditions. The comparison of two-dimensional electrophoretic polypeptide profiles of each subcellular membrane isolated from control and phenobarbital-treated rats revealed important variations induced by PB. In plasma membranes, the heaviest subunit (apparent Mr = 60 x 10(3)) of hepatic gamma-glutamyltransferase was provisionally identified as a collection of polypeptide which differ only by their pI. The concentration of these polypeptides was smaller in the endoplasmic reticulum where they were of lower apparent molecular mass. This suggests that the gamma-glutamyltransferase precursor is already processed at the level of the endoplasmic reticulum but it is still not completely mature or glycosylated. Five days of continuous PB treatment induced by appearance of new gamma-glutamyltransferase isoforms in plasma membranes. We demonstrate that after a single injection of PB, gamma-glutamyltransferase activity increases simultaneously with some drug-metabolizing enzymes, such as total cytochrome P-450 but not with others, such as UDP-glucuronosyltransferases.

Animals↗
PubMed1987

Properties of human hepatic UDP-glucuronosyltransferases. Relationship to other inducible enzymes in patients with cholestasis.

Glucuronidation of 4-nitrophenol, nopol (a monoterpenoid alcohol) and bilirubin, which in the rat, are catalyzed by three different enzymes, has been examined in liver biopsies from patients with various liver diseases, in particular cholestasis. These different activities were not correlated, which strongly suggests that at least three independently regulated forms of UDP-glucuronosyltransferases were present in the microsomes. Non ionic detergents (Triton X100, Emulgen 911) and deoxycholate produced similar activation (more than 2-fold) of the glucuronidation of 4-nitrophenol. Amphipathic substances, such as CHAPS (3-[3-cholamidopropyl-dimethylammonio]-1-propane sulfonate), and lysophosphatidylcholines maximally increased this UDP-glucuronosyltransferase activity, the most potent being oleoyl lysophosphatidylcholine (4-fold increase). Discriminant analysis of the data revealed no correlation between the three different UDP-glucuronosyltransferase activities and the age or sex of the patients. A good correlation was found on multidimensional analysis between form 1 of the enzyme (4-nitrophenol glucuronidation) and, in decreasing order of magnitude, epoxide hydrolase (measured with benzo(a)pyrene-4,5-oxide as substrate), cytochrome P-450, 7-ethoxycoumarin deethylase, aspartate aminotransferase and gamma-glutamyltransferase (r = 0.89); and between Form 3 of the enzyme (bilirubin glucuronidation) and NADPH cytochrome c reductase, alkaline phosphatase, (r = 0.81). These relationships may reflect the differential variation in enzymatic activities in various hepato-biliary diseases.

7-Alkoxycoumarin O-Dealkylase↗