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Biomedical subjects

G Siest

Publications and source records attributed to G Siest.

At least 271 records · Page 15Linked to original sources
PubMed1987

Changes of cerebral gamma glutamyltransferase activities after treatment with exogenous inducers.

The activity of gamma-glutamyltransferase localized in isolated brain synaptic membranes- and microvessels-enriched fractions was assayed after treatment of rats with either phenobarbital or ethanol. Phenobarbital increased the activity of gamma-glutamyltransferase in microvessels, without alteration of synaptic membranes activity. An increase of enzyme activity was also obtained after a chronic intoxication with ethanol. These results suggest that the isoform of gamma-glutamyltransferase localized in brain microvessels may respond to exogenous inducers.

Animals↗
PubMed1987

A new enzyme immunoassay of microsomal rat liver epoxide hydrolase.

Antiserum against purified rat liver microsomal epoxide hydrolase was produced in the rabbit. We developed an enzyme-linked immunosorbent assay which is reliable with regard to its analytical criteria. The concentration of epoxide hydrolase was measured in liver microsomes of control rats and animals treated with F 1379 (250 mg/kg/day) for 5, 7, 14, and 21 days. This hypolipidemic drug was able to induce strong epoxide hydrolase activity and enhance protein concentration. The gradual increase in epoxide hydrolase concentration paralleled the increase of epoxide hydrolase activity, with stabilization occurring after the 14th until the 21st day of treatment.

Animals↗
PubMed1987

The activity of 1-naphthol-UDP-glucuronosyltransferase in the brain.

Cerebral microsomes catalysed efficiently the glucuronidation of 1-naphthol, this formation of glucuronide being activated by treatment with Triton X-100 or digitonin. Activated microsomes from the brain of the rat conjugated 1-naphthol with an apparent Km of 95 microM and a Vmax of 5.47 nmol/hr mg protein at 30 degrees C. Microsomal uridine diphosphate (UDP)-glucuronosyltransferase activity in brain towards 1-naphthol was not significantly induced by pretreatment of animals with 3-methylcholanthrene or phenobarbital. These data suggest that UDP-glucuronosyltransferases in brain are different from the hepatic enzymes with regard to biochemical parameters and in response to inducers of drug metabolism. The hepatic UDP-glucuronosyltransferase deficiency in Gunn rats was also observed in the brain.

Animals↗
PubMed1987

Quantitative measurement of cerebral cytochrome P-450 by second derivative spectrophotometry.

Second order derivative spectrophotometry was used to improve the accuracy and reproducibility of cytochrome P-450 measurements in subcellular fractions obtained from the brain. This method allowed better resolution of the overlapping bands of cytochrome P-450 and other iron proteins, as well as a reduction of the effects of turbidity and non-specific components. Using this method, the cytochrome P-450 content of rat brain mitochondrial and microsomal fractions was measured to be 74.2 +/- 2.3 and 5.9 +/- 0.3 pmol/mg protein, respectively.

Animals↗
PubMed1987

Heterogeneity of hepatic microsomal UDP-glucuronosyltransferases activities: use and comparison of differential inductions in some mammalian species.

1. The co-injection in rats of the inducers 3-methylcholanthrene or phenobarbital and of a protein synthesis inhibitor (cycloheximide) shows that two clusters of hepatic UDP-Glucuronosyltransferases (GT1 and GT2) are under separate genomic expression and differentially regulated. 2. The administration of cycloheximide alone even suggests a distinct turn-over for these two groups of isoenzymes. 3. Indirect evidence for a UDPGT isoform specialized for some structurally-related exogenous substrates, the monoterpenoid alcohols, is brought. Their conjugation exhibits a small deficiency and a marked response to phenobarbital treatment in the Gunn rat and an exclusive inducibility by phenobarbital in the guinea-pig.

Animals↗
PubMed1987

Differential induction profile of drug-metabolizing enzymes after treatment with hypolipidaemic agents.

Various hypolipidaemic agents differentially induced microsomal drug-metabolizing enzymes. Clofibrate, clofibric acid, fenofibric acid and dulofibrate, which are mainly hypotriglyceridaemic, increased the content in cytochromes P-450 (77-185% over control), and especially cytochrome P-452-dependent lauric acid 12-hydroxylation (5.6- to 8.4-fold increase). Bilirubin glucuronidation was 2.1- to 2.8-fold stimulated; epoxide hydrolase activity (benzo(a)pyrene-oxide) was only slightly increased by the drugs. By contrast, F1379, which lowers plasma cholesterol only, did not change cytochromes P-450 content and slightly affected the 12-hydroxylation of lauric acid. It dramatically enhanced the epoxide hydrolase activity (7.6-fold), and increased (200%) the glucuronidation of planar group I substrates (4-nitrophenol, 4-methylumbelliferone, 1-naphthol). These effects were accompanied by a highly positive staining of gamma-glutamyltransferase in the liver characterized by a great number of intensively coloured foci in the periportal and perilobular area of the tissue. Treatment of rats for three weeks with F1379 did not modify this typical profile in enzyme induction. Such continuous effect could reveal some biochemical changes of hepatocytes with important toxicological relevance. Compared to the parent compound, treatment of rats with two metabolites of F1379 led to a decrease in the induction potency on epoxide hydrolase and on the forms I of UDP-glucuronosyltransferase; by contrast, the content in cytochromes P-450 was increased.

Animals↗
PubMed1987

Production and certification of an enzyme reference material for gamma-glutamyltransferase (CRM 319). Part 1: Preparation and characterization.

We have produced a batch of lyophilized gamma-glutamyltransferase as enzyme reference material. The "light" enzyme form was purified from pig kidney to a relatively high specific activity (120 kU/g) and was essentially free of contaminating enzymes. The partly purified gamma-glutamyltransferase, lyophilized in a matrix containing bovine serum albumin (Fraction V, 60 g/L), yielded a batch of 4000 ampules and was stored at -20 degrees C. The vial-to-vial variability with respect to the catalytic concentration of the final product (CV 0.6%) and its stability (predicted loss of activity at -20 degrees C was less than 0.01% per year) were considered sufficient to allow the use of this preparation for a certification procedure. The behavior of the reference material in comparison with human serum samples was evaluated three ways: (a) by kinetic characteristics, (b) by the ratio of activities for duplicate determinations by different methods, and (c) by use of the reference material to convert values obtained by various methodologies to those by the IFCC proposed method. The material appeared to be commutable for the two methods studied. The difference in the ratios obtained for patients' samples and reference material was less than +/- 5%, and the recalculated values for patients' samples as determined with the reference material differed from values determined by the IFCC method by no more than 4.8%.

Animals↗
PubMed1987

Production and certification of an enzyme reference material for gamma-glutamyltransferase (CRM 319). Part 2: Certification campaign.

We describe the process of certification for a gamma-glutamyltransferase reference material (CRM no. 319). Fifteen laboratories participated to this interlaboratory evaluation. All steps of the measurements were controlled in an effort to locate potential sources of variations. In particular, the exclusion of some data was strictly documented or justified by the non-observance of the IFCC method and (or) discrepancies in instrumentation, reconstitution of the lyophilized samples, or measurement technique. Inaccuracy in the reconstitution of the lyophilized material was +/- 0.68%, and the molar absorptivity of the 5-amino-2-nitrobenzoate reported by each laboratory was within +/- 2% limits of the value reported by the IFCC. Calculated from the sets of accepted results, the total CV among samples was 2.6% and the overall CV was 3.2%. Within-day and between-day CVs were 1.1% and 1.4%, respectively. The greatest variation for a single component was the between-laboratory variability (CV 3.1%); the within-laboratory CV, including the day effect, was 1.8%. Finally, the certified value for the catalytic concentration of this enzyme in the reconstituted lyophilized reference material was 86.8 U/L with an uncertainty of +/- 2.1 U/L (0.95 confidence interval). The uncertainty appeared to be compatible with the end-use of this reference material.

Catalysis↗
PubMed1987

[Effects of the ingestion of oxidized fish oils on hepatic microsomal enzyme activities and membrane fluidity in rats. Influence of tocopherol overload].

Rats fed a dietary peroxidized fish oil showed an increase in cytochrome P-450 content and ethoxy-coumarin deethylase (ECDE) activity in liver microsomes. Administration of DL-alpha-tocopherol led to different effects according to the extent of the peroxidation in the fish oil. In rats fed a de-peroxidized oil, the inductive effect of phenobarbital on UDP-glucuronosyltransferase (UDGPT) activity was depressed by tocopherol. By the same time, induction of P-450 and ECDE remained unchanged, that of epoxide hydrase slightly increased. By contrast tocopherol strongly potentiated the inductive effect of phenobarbital toward UDPGT activity (group I substrates) in rats fed the peroxidized fish oil. The modification of the inductive effect of phenobarbital in combination with tocopherol on UDPGT activities was concomitant with an increase in seric transaminase activity and with a reverse effect as revealed from the study of the rate of fluorescent probes penetration in microsomes. The possible toxicity of the strong dose of tocopherol is discussed.

Animals↗
PubMed1987

Plasma apolipoproteins in Tangier disease, as studied with two-dimensional electrophoresis.

Tangier disease is characterized by a deficiency of high-density lipoproteins and of their major protein constituent, apolipoprotein (apo) A-I. We used high-resolution two-dimensional electrophoresis to examine the principal plasma apolipoproteins (A-I, A-II, A-IV, E, C-II, and C-III) of three persons with Tangier disease, one homozygous patient and his two heterozygous children, comparing the patterns with those for healthy subjects. Characteristic abnormalities were found in the distribution of the isoproteins of apo A-I, there being a normal concentration of pro apo A-I but dramatically decreased concentrations of the other apo A-I isoproteins. We also found hitherto-undescribed polypeptide abnormalities in apo C-III: sialylated and nonsialylated forms of apo C-III appear as double spots having the same isoelectric points but different molecular masses. No other substantial difference was detected in the polypeptide distribution of the other plasma apolipoproteins.

Adult↗
PubMed1987

Evaluation of lipoproteins and apolipoproteins in serum of a Tangier patient by micro-scale two-dimensional electrophoresis.

We examined lipoproteins and apolipoproteins in serum of a Tangier-disease patient. We used three different techniques of micro-scale two-dimensional electrophoresis: (a) no denaturants; (b) with sodium dodecyl sulfate (SDS) used only in the slab gel electrophoresis; (c) and with urea and a detergent used in isoelectric focusing and with SDS in slab gel electrophoresis. By technique a, an extremely low concentration of high-density lipoproteins (HDL) in the Tangier serum was seen, and lipoproteins that cannot form HDL complexes were detected as multiple spots in the acidic (pl 4 approximately 5) and relatively low apparent molecular mass (20,000 approximately 80,000) region. By technique b, Tangier low-molecular-mass lipoproteins were dissociated into their constituent apolipoproteins, and we observed a higher proportion of apoC-III, together with lower proportions of apoA-I and apoA-II, than in the normal HDL fraction. Technique c showed the total content of apolipoproteins in the whole Tangier serum, as several workers have reported. The presence of low-molecular-mass lipoproteins and a high concentration of apoC-III in this lipoprotein fraction characterized the Tangier serum.

Adult↗
PubMed1987

[6 beta-hydroxycortisol: a non-invasive reflection of enzymes of drug metabolism].

6-beta-hydroxycortisol (6-beta-OHF) is the main unconjugated metabolite of cortisol in human urine. 6-beta-OHF could be assayed in urine by several methods : chromatography followed by colour reaction, high performance liquid chromatography, radioimmunoassay and enzyme immunoassay. Urinary 6-beta-OHF is increased in some physiological conditions (such as pregnancy) and pathological states (such as hypercortisolemia and liver disease). The measurement of 6-beta-OHF in human urine may provide a useful index of enzyme induction, its excretion being enhanced by many inducers of the mixed function oxygenase.

Enzyme Induction↗
PubMed1987

[Reference values of chemical constituents and plasma enzymes in minipigs].

Nine male minipigs Pitman Moore have been studied from weaning (To) and during 6 months and the following constituents have been measured: albumin, amylase, bilirubin, calcium, CK, cholesterol, creatinine, copper, iron, GGT, glucose, LDH, magnesium, PAL, phospholipids, potassium, proteins, sodium, ALT, ASP, triglycerides, urea, zinc. These animals were fed a standardized diet. At 6 months of age their weight increased progressively to 12 kg. Several factors of variation have been studied; time of blood sampling age of animals. We obtained the following results: values of bilirubin, CK and TGO were always lower at 8 a.m. than 12 a.m. and 6 p.m. The effects of age were variable. They are no variation in the values of only 4 parameters (calcium, sodium, potassium and triglycerides), while the others constituents were increased or decreased. Reference values for 21 blood parameters in Pitman Moore minipigs are described.

Aging↗
PubMed1987

[Evaluation of an immunological test for detecting occult fecal blood for case-finding in colorectal tumors].

Screening for colorectal tumours (cancers and polyps) by searching for blood in stools using the gaiac test is a well-known method. We evaluated a new gaiac test, the originality of which from its coupling with an enzyme immuno-assay specifically measuring human hemoglobin (Fecatest). The objectives of this new test were to decrease false positives and thus to improve the positive predictive value of screening. Subjects over 45 years of age attending health examinations at a Center of Preventive Medicine were studied. Of the 5,185 subjects who received the test, 4,376 (84 p. 100) performed it correctly, demonstrating good compliance in this population. For 664 (15 p. 100), the results of the gaiac test were positive. This positivity rate was higher for men than for women (20 p. 100 vs. 10 p. 100) but was not influenced by age. After positive results, 471 (70 p. 100) patients completed investigations decreasing the overall compliance to 80 p. 100. Fifteen cases of cancer and 78 cases of adenomas were found. The positive predictive value of the test was 20 p. 100 for tumours. A benign cause was found in 44 p. 100 of 471 patients, and investigations were negative in 36 p. 100. When the gaiac test was positive, the immunoenzymatic method significantly improved the positive predictive value for cancer (6 p. 100 vs. 3 p. 100) but not for polyps (20 p. 100 vs. 17 p. 100). Three of the 15 cancers and half of the 78 adenomas would not have been discovered with the immunoenzymatic method.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗