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Biomedical subjects

G Desmet

Publications and source records attributed to G Desmet.

At least 19 recordsLinked to original sources
PubMed1995

Maternal serum screening for fetal Down's syndrome, a retrospective study.

A retrospective study of the different biochemical markers used in screening for Down's syndrome was carried out on serum from 18,600 women between their 15th and 18th week of pregnancy. Thirty-two sera were from women with fetal Down's syndrome. The retrospective study of these 32 sera involves: (a) the screening of the maternal serum concentrations of human chorionic gonadotropin (hCG) and of alpha-fetoprotein (AFP); (b) the evaluation of the risk of Down's syndrome when screening maternal serum concentrations of hCG alone, then the combination of the two markers and finally the maternal serum concentrations of unconjugated estriol (uE3). The mean of MOM (multiples of the median) for the pathological sera were calculated for hCG (1.91), for AFP (0.63), for the ratio hCG over AFP (3.02) and for uE3 (0.72). With the use of hCG alone we estimated a 41% detection rate for an amniocentesis rate of 5.3%, whereas when hCG was combined with AFP the detection rate approached 65% for an amniocentesis rate of 5.5% at a risk cut-off of 1:300. The results of the uE3 determination confirm the validity of this marker. The comparison of these results with other retrospective studies shows the incidence of different factors in the detection rate such as the choice of markers, the age group studied, the modes of calculating the risk and the actual cut-off chosen.

Adult↗
PubMed1995

A simple and automated HPLC method for determination of total hydroxyproline in urine. Comparison with excretion of pyridinolines.

An HPLC method for measuring total hydroxyproline in human urine was validated. Hydroxyproline derivatization was achieved with 9-fluorenylmethyl chloroformate after blocking primary amino acids with orthophthaldialdehyde. The derivatives (hydroxyproline and internal standard) were separated by reversed phase high-performance liquid chromatography and detected by absorbance at 254 nm. Duplicate measurements of hydroxyproline have a coefficient of variation of 3.9% and the recovery in spiked urine samples is between 99.5 and 100.8%. We have compared the HPLC procedure with a commercial colorimetric assay. Analytical criteria of these methods are identical. Regression analysis, involving 50 samples, shows an excellent correlation between hydroxyproline chromatographic (y) and colorimetric (x) procedures: y = 0.989x + 2.99 (r = 0.976). Hydroxyproline excretion was determined in urine samples from 76 women more than 5 years post-menopause. The mean hydroxyproline/creatinine ratio in this group was 19.3 +/- 5.6 mumol/mmol (range 10.6-34.7). Finally, we compared in the same urinary samples hydroxyproline excretion with pyridinoline excretion (hydroxylysylpyridinoline and lysylpyridinoline), a new marker of bone resorption. The values show a significant correlation, with r = 0.417 for hydroxylysylpyridinoline and r = 0.443 for lysylpyridinoline.

Aged↗
PubMed1995

Multiple molecular forms of pyridinolines cross-links excreted in human urine evaluated by chromatographic and immunoassay methods.

The measurement of the collagen cross-links, hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP), excreted in urine either in free or peptide-bound forms represents the most extensively investigated biochemical marker of bone collagen degradation. We studied the urinary molecular forms of pyridinolines after separation in free and peptide-linked fractions by chromatography and serial dialysis. The pyridinoline amounts of molecular species (free, < 1000 D, 1000-3500 D, 3500-10,000 D, and > 10,000 D) were evaluated by high performance liquid chromatography (HPLC) as well as with the two newly introduced enzyme-linked immunosorbent assay (ELISA) methods for determination of free pyridinolines (collagen Pyrilinks and collagen Pyrilinks-D). The variability of urinary pyridinoline forms were studied in healthy adult control subjects (n = 10, 38.4 +/- 7.5) years), in adolescents (n = 10, 16 +/- 3.3 years), and in elderly subjects with vitamin D insufficiency (n = 10, 87.3 +/- 4.3 years). Free and peptide-conjugated pyridinolines with MW < 1000 D constitute the major part of urinary cross-links in all groups, with a significantly lesser excretion in elderly patients than in adolescent groups. Expressed as a percent of total cross-links, urinary free pyridinolines assessed by direct HPLC are less in elderly subjects (HP = 34.2 +/- 6.2%, LP = 32.7 +/- 7.6%) than in adolescents (HP = 45.8 +/- 10.8%, p = 0.0065 and LP = 47.8 +/- 12.1%, p = 0.012) and in healthy adults (HP = 39.3 +/- 11.5%, NS and LP = 38.1 +/- 9.3%, NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

High-performance liquid chromatographic determination of 3-hydroxypyridinium derivatives as new markers of bone resorption.

Hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP) are intermolecular cross-linking amino acids of collagen and their urinary excretion reflects bone resorption. An isocratic high-performance liquid chromatographic assay using a reversed-phase column with a prefractionation step and fluorescence detection was developed. The accuracy and reproducibility were assessed by loading experiments and by double analysis of urinary samples. The recoveries after various loads were above 90% for HP and between 87 and 94% for LP, with an intra-assay relative standard deviation (R.S.D.) of 5% for HP and 8% for LP. The inter-assay R.S.D.s were 8% for HP and 12.4% for LP. The fasting and 24-h urinary excretions of HP and LP were measured in 40 healthy subjects (mean age 35 years) of both sexes. There was no difference between males and females. Mean adult normal values were 33.6 +/- 8.1 pmol/mumol creatinine for HP and 7.0 +/- 2.5 pmol/mumol creatinine for LP in morning fasting urine and 2-.9 +/- 7.0 pmol/mumol creatinine for HP and 5.8 +/- 1.9 pmol/mumol creatinine for LP after 24-h urinary collection. HP and LP excretions were significantly higher in morning fasting urine than in 24-h collections, in agreement with the physiological circadian rythm of bone resorption. This simplified and optimized procedure is a good method for the determination of pyridinolines and should be useful for the evaluation of bone resorption.

Adult↗
PubMed1992

Thyroid hormone extraction by plasma exchange: a study of extraction rate.

How to obtain an optimal efficiency of plasma exchanges in the treatment of severe hyperthyroidism has not been defined. In order to evaluate how long the exchanges must be continued to be fully effective in extracting thyroid hormones, we evaluated the extraction rate by repeated plasma sampling in two hyperthyroid patients and three euthyroid subjects who underwent a total of seven exchanges. Plasma concentrations of thyroid hormones were also determined just before, just after, and 24 hours following the exchange. The hormonal removal rate did not fall dramatically during the exchange, so that its efficiency--in terms of hormone extraction--depends closely on its duration. The determination of plasma thyroid hormone concentrations after the exchange does not appear to be useful in evaluating the thyroid hormone loss since these concentrations may not change in spite of the hormonal extraction.

Humans↗
PubMed1991

[Fluoride bioavailability from sodium fluoride alone or in association with different calcium salts].

Fluoride pharmacokinetics were studied in twelve healthy subjects after oral administration of one tablet of osteofluor-containing 25 mg of sodium fluoride alone or associated with different calcium salts (500 mg Ca element) given as microcrystalline hydroxyapatite compound or powdered tri-calcium phosphate. Fluoride was measured in plasma and urine with a specific electrode and fluoride bioavailability from the three drugs was compared. Calcium absorption after oral load was assessed by measuring variations from the fasting state of plasma calcium and parathyroid hormone and of the urinary calcium to creatinine ratio. The bioavailability of fluoride is significantly decreased by the association to sodium fluoride of hydroxyapatite but not of tri-calcium phosphate. Calcium absorption seems greater after administration of hydroxyapatite compound. The decrease of the fluoride bioavailability is probably dependent on the capacity of calcium absorption from the calcium salts. The association of calcium to fluoride is absolutely required for treatment of osteoporosis. The microcrystalline hydroxyapatite compound seems preferable in view of its greater calcium absorption and of its limited decrease in fluoride bioavailability.

Administration, Oral↗
PubMed1991

Pharmacokinetics of butyric acid derivative with xylitol.

The short chain fatty acids, especially butyric acid salts have interesting biological properties. In some cases, transformed cells can recover a normal phenotype and in animal, butyrate salts increase antitumor resistance. Butyrate may be considered as possibly useful for antitumor therapy. But these products exhibit two essential disadvantages which restrict their clinical use in man: high concentrations required to achieve therapeutic effects and rapid excretion with short half life. In order to optimize the clinical use of butyrate, we studied a n-butyric acid ester obtained with xylitol selected for its physiological and metabolic inertia. Structure determination of tributyryl xylitol was carried out by mass and NMR spectrometry (MW = 344). The low toxicity and the antitumor effects of this ester, especially in association with Corynebacterium parvum and interferon, confirm its therapeutic interest. The slow excretion of this prodrug should make butyrate clinical use easier by preventing extensive systemic metabolism and metabolic side-effects due to cations of butyrate salts.

Animals↗
PubMed1989

Pharmacokinetic study of butyric acid administered in vivo as sodium and arginine butyrate salts.

Considering that butyrate-treated malignant cells can recover in a transitory fashion a non-cancerous phenotype, the authors carried out a pharmacokinetics study of butyric acid injected as sodium or arginine salts for possible antitumor therapies. In the case of 1-14C-labelled butyrate, the appearance of radioactivity in the blood of injected mice is rapid and some of it is maintained for relatively long periods in different organs, mainly the liver. However, no precision can be given about the structure of radioactive compounds in blood and tissues. Using gas-liquid chromatography, the authors studied the metabolism of butyrate in both animals and man. In mice and rabbits, the half-life is less than 5 min. In man, the butyric acid elimination curve can be divided into two parts corresponding to two half-lives: for the first (0.5 min), the slope suggests an accelerated excretion, while for the following (13.7 min), a slow plateau is observed. The rapid elimination of butyrate is a limiting factor for practical applications. However, the lack of toxicity supports its use in human therapy.

Adult↗
PubMed1989

Reaction mechanisms responsible for transformation of pertechnetate in photoautotrophic organisms.

Experimental data on the physiological effects of Tc on photoautotrophic and N2-fixing organisms all suggest a relation between their ability to generate strong reducing power and the incorporation of Tc. A series of biochemical experiments were undertaken to elucidate this problem. Isolated spinach chloroplasts, thylakoids and purified compounds of the photosynthetic electron transport chain were incubated with TcO4-. After illumination, the quantity of TcO4- transformed was measured with gel filtration chromatography. For part of the samples, the amount of extractable Tc(V) was determined. Isolated thylakoids showed reduction of TcO4- in the light, suggesting direct interference of TcO4- with the electron transport chain. Use of specific inhibitors and artificial electron carriers indicated that TcO4- withdraws electrons from ferredoxin. Competitive inhibition of TcO4- reduction by O2 and NADP+, as well as its capacity to function as a terminal acceptor in the diaphorase reaction with NADPH, indicates its interaction with the transport chain to be comparable to that of O2. In suspensions of thylakoids, TcO4- is mainly reduced into an extractable Tc(V) compound. Only part of the Tc fraction reduced by intact chloroplasts could, however, be extracted, whereas negligible quantities of unstable Tc(V) complexes were detected in intact plants. The stable complexes in vivo are supposed to originate through ligand exchange with strong complexing agents, such as thiol compounds. Disproportionation reactions of unstable Tc(V) compounds might result in complexes with Tc in lower oxidation states.

Chloroplasts↗
PubMed1989

Dissociation of immunocomplexes by ionic shock for the development of immunosensors: application to measurement of alpha 1-fetoprotein.

We report here our experimental results on the reaction rate of immunological complexes and on potential repeated use of membranes as a result of dissociation of the complexes between alpha 1-fetoprotein and catalase-labeled antibodies by different buffers with various ionic strengths. The measurement consists of an immunological process and an enzymatic reaction. The protein membrane activated by glutaraldehyde for the immobilization of antibodies is fixed over an oxygen electrode. After incubation with antibody/alpha 1-fetoprotein and antibody/alpha 1-fetoprotein antibodies coupled to catalase, the reaction medium is introduced into a continuous-flow cell. Oxygen production by the catalase is measured on-line, with the electrode in contact with hydrogen peroxide. This response is correlated to the alpha 1-fetoprotein concentration of the sample. We show a typical calibration curve between 0.5 and 120 micrograms/L. Replicate (n = 20) equilibrium measurement with the same membrane gave a CV of 2.2%. The reversible immunochemical sensor has been tested for 30 measurements without significant loss of activity.

Antigen-Antibody Complex↗
PubMed1986

[Immobilization of enzymatic inhibitors for the isolation of reversible immunologic sensors].

The authors propose the use of specific sensors immobilized by ligands onto artificial supports, and the elaboration of a computerized system for the determination of various antigens, haptens or antibodies in biological fluids according to enzyme-linked immunosorbent assay techniques. Two enzymes are applied in this technique: the first (ribonuclease) for reversibly linking the immunocomplex to the insoluble support via disulphur bridges; the second (beta-D-glucose oxidase) for labelling the antigen. Enzyme activity is measured in the presence of glucose oxidase by fixing the immunocomplex onto a pO2 electrode. After incubation of the antigen labelled with glucose oxidase and the free antigen with specific antibodies linked with ribonuclease, to reduce the pre-established concentration, the reaction medium is introduced into the continuous flow cell. O2 consumption due to the enzyme reaction is measured by the actual time that the electrode is in contact with a glucose standard solution. Cleavage of the disulphur bridges is caused by an injection of dithiothreitol solution. Treatment of the signal obtained is realized with an automatic microcomputer system. The preliminary results show that reproducibility with the same membrane for ten measurements is less than 5%. Elution performed using dithiothreitol for example, shows that cleavage between the immunocomplex and the thiol-containing support is obtained after a few minutes, and 98% of the immunocomplex is eluted.

Animals↗
PubMed1986

[Photometric measurement of cell density in microplate cultures].

A rapid technique for measuring cellular density in microplates cultures is described. Cells are stained by toluidine blue (0% to 1% acetic acid), washed in 1% acetic acid and digested by trypsin (1%) or pronase (0.1%). Absorbance rate is read in an automated spectrophotometer for microplates. The correlation coefficient between absorbance and cellular number is higher than 0.99. The measures accuracy is satisfactory in the experimental conditions used.

Cell Count↗
PubMed1985

[Biosensor development in clinical analysis].

The use of enzymes immobilized or as markers formed the subject of more than thousand publications in the field of industry or biomedical applications, during the last five years. Recently, some authors published works concerning immobilization of total microorganisms for catalytic purposes, others use the enzymatic activity for marking molecules involved in immunological analysis processes. Together industrial biotechnology and medical analysis laboratory are interested with the evolution of these procedures involving the activity of immobilized enzymes. Enzyme immobilization allowed the lowering of analysis costs for, in this case, the enzyme can be used several times. We take account of the two main cases which are encountered during utilization of immobilized enzymes of analytical purposes. The enzyme is used directly for the catalysed reaction or it is used as enzymatic marker. These both aspects are developed mainly for the elaboration of enzymatic and immunoenzymatic electrodes and the realization of automatic computerized devices allowing continuous estimation of numerous biological blood parameters. From these two precise examples, glucose and antigen determination, the authors show the evolution of these technologies in the field of immobilized enzymes or captors and the analysis of signals given by these electrodes requiring a computerized treatment. This new technology opens to important potentialities in the analytical field. The automatization of these devices allowing the control in real time, will probably make easier the optimization steps of procedures actually used in the biomedical sphere.

Acetylcholine↗