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J C Vincent

Publications and source records attributed to J C Vincent.

At least 19 recordsLinked to original sources
PubMed2001

An improved assay for the N-acetyl-D-glucosamine reducing ends of polysaccharides in the presence of proteins.

Hyaluronan concentration and hyaluronidase activity can be assayed by using different techniques including turbidimetry, viscosimetry, ELISA, chromatography, and colorimetry. The most popular colorimetric method is that of J. Reissig et al. (1955, J. Biol. Chem. 217, 959-966), in which the color results from a reaction between the Ehrlich's reagent (DMAB) and the N-acetyl-d-glucosamine reducing end of each hyaluronan chain. Nevertheless, there are problems with this method when proteins are present in the medium. Here we propose a new interpretation of the Reissig signal for estimating such reducing ends in media containing enzymes or other proteins. This interpretation is based on the fact that the absorbance obtained by using the Reissig method results from two factors: a turbidity due to the formation of polysaccharide-protein complexes and a color resulting from the action of DMAB on the reducing end of the polysaccharide chains. The turbidity at 585 nm, the wavelength at which the color intensity is maximal, may be estimated by curve fitting the spectrum between 450 and 650 nm. Subtracting the turbidity from the absorbance gives the colorimetric intensity which represents the concentration of polysaccharide chains. Moreover, the turbidity may give additional information about the existence of polysaccharide-protein complexes and their nature.

Acetylglucosamine↗
PubMed1998

Phosphate poisoning by ingestion of clothes washing liquid and fabric conditioner.

A case of deliberate ingestion of clothes washing liquid and fabric conditioner is described. Tracheal intubation and controlled ventilation became necessary because of respiratory muscle dysfunction associated with hypocalcaemia. We suggest that the phosphate component of the clothes washing liquid was responsible for the dramatic metabolic upset and subsequent need for admission to the Intensive Care Unit.

Adult↗
PubMed1997

Influence of stiripentol on cytochrome P450-mediated metabolic pathways in humans: in vitro and in vivo comparison and calculation of in vivo inhibition constants.

OBJECTIVE: The spectrum of cytochrome P450 inhibition of stiripentol, a new anticonvulsant, was characterized in vitro and in vivo. METHODS: Stiripentol was incubated in vitro with (R)-warfarin, coumarin, (S)-warfarin, (S)-mephenytoin, bufuralol, p-nitrophenol, and carbamazepine as probes for CYPs 1A2, 2A6, 2C9, 2C19, 2D6, 2E1, and 3A4, respectively. Caffeine demethylation and the 6 beta-hydroxycortisol/cortisol ratio were monitored in vivo before and after 14 days of treatment with stiripentol as measures of CYP1A2 and CYP3A4 activity, and dextromethorphan O- and N-demethylation were used to measure CYP2D6 and CYP3A4 activity, respectively. In vivo inhibition constants for CYP3A4 were calculated with use of data that previously documented the interaction between stripentol and carbamazepine. RESULTS: In vitro, stiripentol inhibited CYPs 1A2, 2C9, 2C19, 2D6, and 3A4, with inhibition constant values at or slightly higher than therapeutic (total) concentrations of stiripentol, but it did not inhibit CYPs 2A6 and 2E1 even at tenfold therapeutic concentrations. In vivo inhibition of caffeine demethylation and dextromethorphan N-demethylation were consistent with inhibition of CYP1A2 and CYP3A4, respectively. The 6 beta-hydroxycortisol/cortisol ratio did not provide a reliable index of CYP3A4 inhibition. Inhibition of CYP2D6-mediated O-demethylation was not observed in vivo. With use of carbamazepine, in vivo inhibition constants for CYP3A4 ranged between 12 and 35 mumol/L, whereas the corresponding in vitro value was 80 mumol/L. CONCLUSIONS: Stiripentol appears to inhibit several CYP450 enzymes in vitro and in vivo. In vivo inhibition constants show that stiripentol inhibition of CYP3A4 is linearly related to plasma concentration in patients with epilepsy.

Adult↗
PubMed1996

Experimental procedure for a hydrogen peroxide assay based on the peroxidase-oxidase reaction.

A low-cost assay method that is able to measure H2O2 concentrations as low as the nano-molar range is described. The assay solution contains NADH, horseradish peroxidase, and superoxide dismutase at PH 7.5. After the addition of the sample, the decrease in NADH concentration measured by spectrophotometry is proportional to the H2O2 concentration. Because of superoxide dismutation, a high amplification factor defined as moles NADH oxidised per mole H2O2 added is obtained, which allows the sensitivity limit of the method to be greatly improved. We have established the conditions under which the amplification factor can be stabilised at a high level: the best compromise is to increase both the horseradish peroxidase and superoxide dismutase concentrations. Finally, we have also shown that coupled to specific oxidases, our assay method is suitable for measuring very low concentrations of biochemicals that can be oxidized by oxygen with H2O2 production.

Computer Simulation↗
PubMed1994

A hydrogen peroxide assay based on the peroxidase-oxidase reaction. Numerical simulation of the reaction mechanism.

In order to explain an assay method for H2O2, based on the horseradish peroxidase/NADH/H2O2 system, we performed a numerical simulation of this complex reaction mechanism. For this purpose, we applied a simplified version of a model designed by Yokota and Yamazaki to our experimental conditions [Yokota, K. & Yamazaki, I. (1977) Biochemistry 16, 1913-1918]. This modification leads to a kinetic behaviour of the system very similar to our experimental results when the presence of superoxide dismutase is simulated. These simulations confirm that hydrogen peroxide concentrations are proportional to the total amount of NADH oxidized. We also showed that superoxide dismutase activity can be determined by this assay method. Moreover, in samples containing superoxide dismutase and hydrogen peroxide, the simulations showed that both superoxide dismutase and hydrogen peroxide can be determined using our assay method.

Catalysis↗
PubMed1993

Kinetic study of the alpha-chymotrypsin-catalyzed hydrolysis and synthesis of a peptide bond in a monophasic aqueous/organic reaction medium.

We have studied the hydrolysis and synthesis reactions of the peptide bond involved in N-Cbz-L-tryptophanyl-glycineamide as catalyzed by alpha-chymotrypsin in various mixtures of water and 1,4-butanediol. Using a constant nonsaturating concentration of substrate, the initial reaction rates decreased exponentially with decreasing water content in the solvent mixture. When the water content was decreased from 100 to 20% (v/v), the maximum rate of reaction did not vary by more than a factor of 2 to 4, whereas the Michaelis constant increased exponentially. This exponential variation of the Michaelis constant was due to changes in the partitioning of the substrate between the active site of the enzyme and the solvent. In these processes, the actual rate constants did not vary when the relative contents of water and 1,4-butanediol were varied.

Animals↗
PubMed1993

Spatial distribution of viable cells immobilized in agar membranes.

The biocatalytic structures obtained by immobilizing microorganisms in planar gel slabs have been studied and modeled to better understand the dynamics of systems controlled by diffusion-reaction-growth couplings. The theoretical results give two kinds of information: the time evolution of the extra-membrane system due to the intra-membrane reactions which can easily be compared to experiments, and the intra-membrane behaviour which is mainly characterized by the concentration profiles. The steady state cell concentration profile is one of the most important elements of a system's behaviour. In addition to photographs taken at different depths in the membrane, we have developed an original, simple and reproducible technique for the experimental determination of the intra-membrane cell concentration profiles. The technique uses a home-made microtome to obtain gel slices, in which the cell concentration is determined using visible spectroscopy. By using this technique, we have shown a good agreement between the theoretical predictions and the experimental profiles, which validates the modeling.

Agar↗
PubMed1992

An enzymatic determination of hydrogen peroxide by using spectrophotometry.

A new spectrophotometric method for determining low hydrogen peroxide concentrations by using horseradish peroxidase in the presence of NADH at pH 7.5 has been described. Both total NADH consumption and initial reaction rate may be used for the determination. Using the NADH consumption, a linear response with respect to hydrogen peroxide was observed in the concentration range 7 x 10(-8)-2.5 x 10(-6) M. Due to the presence of superoxide dismutase, hydrogen peroxide is partly regenerated and an amplification of the signal results, which explains the sensitivity.

Horseradish Peroxidase↗
PubMed1992

Gram-scale enzymatic synthesis of a peptide bond.

The synthesis reaction of the peptide, N-Cbz-L-tryptophanyl-glycineamide, catalyzed by alpha-chymotrypsin was performed in a 20% water/80%, 1,4-butanediol mixture. The synthesis yield reached 90.9% at the end of the reaction and 72.3% after purification. The effects on the yield of both pH and the ratio between total initial concentrations of glycineamide and N-Cbz-L-tryptophan are examined. The high yield, specificity, simplicity and reproducibility of this method make it complementary of the chemical methods.

Catalysis↗
PubMed1991

Euthanasia.

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Attitude of Health Personnel↗
PubMed1991

Stiripentol.

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Animals↗
PubMed1988

Angiotensin-converting enzyme inhibition, anti-hypertensive activity and hemodynamic profile of trandolapril (RU 44570).

Trandolapril (RU 44570), a new non-sulfhydryl angiotensin-converting enzyme (ACE) inhibitor chemically related to enalapril, and its diacid (RU 44403), were investigated for their ability to inhibit angiotensin-converting enzyme. Trandolapril attenuated angiotensin I (Ang I)-induced pressor responses following i.v. administration to rats and dogs with ID50 values of 13.1 +/- 1.3 and 21.1 +/- 2.3 micrograms/kg. RU 44403 produced corresponding values of 9.9 +/- 0.7 and 7.2 +/- 2.3 micrograms/kg. Trandolapril (3-300 micrograms/kg) produced a dose-related attenuation of Ang I-induced pressor responses (ID50 30 micrograms/kg) following oral administration to rats. Oral administration of trandolapril (30-1000 micrograms/kg) to dogs inhibited Ang I pressor responses for over 6 h. The depressor action of bradykinin in the rat was potentiated by i.v. trandolapril and RU 44403 with ED50 values of 5.5 +/- 0.8 and 4.9 +/- 0.3 micrograms/kg respectively. Trandolapril was 2.3-10-fold more potent than enalapril in all experiments, depending on species or route of administration. RU 44403 and MK 422 were approximately equipotent, implying that trandolapril was more readily hydrolysed than enalapril. Trandolapril (0.3-30 mg/kg) produced dose-related, long-lasting (greater than 24 h) reductions in blood pressure (BP) in spontaneously hypertensive rats (SHR) following oral administration. The anti-hypertensive effect was potentiated significantly in hydrochlorothiazide-pretreated SHR when the plasma renin activity was increased. Enalapril was 10-fold less potent than trandolapril in reducing BP. The anti-hypertensive action of trandolapril (3 mg/kg) was abolished in SHR that were bilaterally nephrectomized 24 h beforehand, but was maintained in SHR pretreated by indomethacin (5 mg/kg p.o.). Trandolapril (1 mg/kg i.v.) produced a modest and transient reduction in BP in anesthetized dogs. Trandolapril produced dose-related (30-1000 micrograms/kg) reductions in BP, total peripheral resistance and heart work in dogs pretreated with hydrochlorothiazide to increase plasma renin activity.

Angiotensin I↗
PubMed1988

How a soluble enzyme can be forced to work as a transport system: description of an experimental design.

The cellular transport systems which have been studied up to now have been found to be based on the functioning of specialized proteins anchored asymmetrically in cell membranes. In the present paper we show that a single soluble enzyme inserted at random in a gel slab can drive an uphill transport, provided that asymmetrical boundary conditions force the reversible reaction catalyzed by this enzyme to work forward on one face of the gel slab and backward on the other face. Experimentally, we have used a yeast alcohol dehydrogenase to induce an uphill transport of NADH. It cannot be excluded that comparable structurally symmetrical transport systems also exist in living cells. Such systems would be particularly well suited to preserving cell homeostasis with regard to small solutes.

Alcohol Dehydrogenase↗
PubMed1987

Immobilized cycling enzyme active transport systems. pH feedback control.

Active transport can be induced by applying a pH gradient across a membrane containing a homogeneous mixture of two cycling enzymes. When the two reactions are inversely 'pH active', one producing protons and the other consuming them, a pH feedback control of the functional structure occurs and the active transport function of the membrane can be either stabilized or inhibited according to whether the endogenic pH modifications tend to enhance or reduce the exergonic pH gradient. When it is stabilized, the system looks like a thin active layer surrounded by two diffusive layers, leading to a fairly good model for biological transport systems. Under particular conditions, signals can be emitted.

Biological Transport, Active↗
PubMed1985

Gastric cytoprotective, antisecretory and antiulcer activities of (E)-4-oxo-4-(3,4,5-trimethoxyphenyl)-2-butenoic acid (RU 38086).

As a result of trials of a large series of compounds, RU 38086 (E)-4-oxo-4-(3,4,5-trimethoxyphenyl)-2-butenoic acid) was selected because of its cytoprotective, antisecretory and antiulcer properties. In pylorus-ligated rats, RU 38086 dose-dependently decreased the total acid output, at 2.5, 5 and 10 mg/kg orally and at 10 and 50 mg/kg intraduodenally. In the perfused rat stomach, 1.2 mg/kg RU 38086 in situ inhibited acid secretion stimulated by histamine or pentagastrin but was inactive against carbachol. In the same test 5 mg/kg intravenously did not antagonize pentagastrin-induced acid secretion. In the cat Heidenhain pouch, 0.6 mg/kg RU 38086 was also antisecretory, reducing the acid concentration when in contact with the mucosa of the pouch. In ulcers induced in rats by ligature of the pylorus plus acetylsalicylic acid, RU 38086 at 2.5 and 5 mg/kg demonstrated much more striking activity after oral than after intraduodenal administration. It also had antiulcer activity against stress ulcers (restraint plus cold), starting at a dose of 5 mg/kg orally. RU 38086 had marked gastric cytoprotective activity in rats against the necrotizing effects of ethanol from the low dose of 0.3 mg/kg orally. This cytoprotective activity was not significantly affected by indomethacin pre-treatment. At 4 and 20 mg/kg orally, RU 38086 strongly increased prostaglandin E2 levels in gastric juice of pylorus-ligated rats and in stomach tissue of normal rats. These data indicate that RU 38086 is an orally effective cytoprotective, antisecretory and antiulcer agent.

Animals↗
PubMed1983

pH feedback control of enzyme membranes.

pH feedback on immobilized enzymes is theoretically examined with respect to substrate and pH levels, strength of acids produced by the reaction, buffering and asymmetry of the system. All the productions of proton by the different reactions are taken into account by using a 'symbolic species' H. The system of differential diffusion-reaction equations is then integrated using numerical methods. The local 'effective enzyme activity' modulated by an acidity factor enables us to predict and quantify evolutions of the systems: NonMichaelian behavior of an immobilized Michaelis-Menten-type enzyme is shown, even when pH back-actions are excluded; the analysis of intramembrane pH profiles shows that the shift of the optimal pH is a complex function of the substrate and pH levels, the intrinsic pH dependence of the enzyme, and the membrane characteristics. This study may easily be transposed to other types of effector such as divalent cations and used in examining self-regulations of multienzyme systems where pH-active reactions are involved.

Buffers↗