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Biomedical subjects

J Chopineau

Publications and source records attributed to J Chopineau.

28 records · Page 2Linked to original sources
PubMed1991

Solid-phase extraction of midazolam and two of its metabolites from plasma for high-performance liquid chromatographic analysis.

A rapid, sensitive and selective assay of midazolam and two of its metabolites in plasma, based on high-performance liquid chromatography, has been developed. The compounds are subjected to solid-phase extraction, using C18 cartridges (Bond-Elut). Recoveries are in excess of 90% for midazolam and its metabolites. The limit of quantitation of the assay is 50 ng/ml of plasma for each compound.

Chromatography, High Pressure Liquid↗
PubMed1989

Dynamic interactions between enzyme activity and the microstructured environment.

A new approach for the study of an enzyme's relationship with its own reaction medium has been developed. One technique of micellar enzymology is the use of pseudohomogeneous systems composed of surfactant/water/organic solvent. In such systems, the physicochemical properties and textures of the medium depend on the relative ratios of the different components. Enzymes are catalytically active in such systems and up to the present have been studied in different microenvironments, such as micelles, microemulsions and lyotropic liquid crystals. Our purpose was to develop a system in which the enzyme could, by its activity, modify one of the components in such a way that the relative ratios among them changed sufficiently to produce a transition from one phase domain to another. The three components, water (or glucose in water), octanol and octyl-beta-D-glucoside, form a classical ternary water/oil/surfactant system. The relevant phase diagram shows different macroheterogeneous phases and microstructured domains. The enzyme beta-D-glucosidase hydrolyses octyl-beta-D-glucoside to form glucose and octanol. The enzyme was found to change the relative ratios of water (or glucose in water), octanol and octyl-beta-D-glucoside in such a manner that the physicochemical structure of the medium was modified. At the beginning of the reaction beta-D-glucosidase was present in a micellar solution of octyl-beta-D-glucoside in water. As the enzymatic reaction proceeded, the medium became biphasic. One of the two phases was the micellar solution of octyl beta-D-glucoside in water, while the other phase was either a microemulsion or a liquid crystalline phase. In addition the enzyme, through its catalytic activity, was able to modify the physiocochemical properties of the reaction medium.

Chemical Phenomena↗
PubMedDate not supplied

Study of hydrophobic interactions between acylated proteins and phospholipid bilayers using BIACORE.

Intracellular proteins of eukaryotic cells are frequently covalently modified by the addition of long chain fatty acids. These modifications are thought to allow otherwise soluble proteins to associate with membranes by lipid-lipid based hydrophobic interactions. The purpose of this work was to quantify the effect of acyl chain length on hydrophobic interactions between acylated proteins and phospholipid monolayers. The binding of an artificially acylated model protein to electrically neutral phospholipids was studied by surface plasmon resonance, using BIACORE. Kinetic rates for the binding of bovine pancreatic ribonuclease A (RNase A), monoacylated on its N-terminal lysine with fatty acids of 10, 12, 14, 16 or 18 carbon atoms, to phospholipids on hydrophobic sensor chips, were measured. Unlike unmodified ribonuclease, acylated RNase A bound to the phospholipids, and the association level increased with the acyl chain length to reach a maximum for C16. Reproducible kinetics were obtained which did not fit a 1:1 Langmuir model but rather a two-step binding profile.

Acylation↗
PubMedDate not supplied

Self-evolving microstructured systems upon enzymatic catalysis.

The consequences of cell microstructuration on enzyme functions is discussed in the framework of self-evolving microstructured systems. Molecular assemblies of amphiphiles or lipids are spontaneously formed by self-organisation. Among these different structures, reversed micelles, liquid crystalline mesophases and vesicles are hosts for enzymatic reaction studies. Inside a living cell, phospholipid metabolism is responsible for membrane structural modifications; the catalytic behaviour of lipolytic enzymes, mainly phospholipase (PL) A2, is described in relation with structural aspects of biological membranes. The implication in cellular regulation events of PLC and PLD is discussed in relation with the role of their reaction products as second messengers in membrane fusion processes. The in vitro synthesis of dialkyl phosphatidylcholines, via the enzymatic 'salvage pathway' which leads to the formation of vesicles upon phospholipid formation, is considered in relation with autopoiesis. More recent studies on self-evolving systems based on enzyme-surfactants reactions are detailed. The interactions between amphiphilic aggregates and enzymes allow to explore the OG/octanol/water phase diagram. Enzymatic formation of dipalmitoylphosphatidylcholine (DPPC) liposomes and non-ionic surfactant vesicles (NSV), starting from mixed micelles or open structures, finally sets an example of a biomimetic self-evolving system.

Cholesterol↗
PubMedDate not supplied

Induction of a catabolic state in rats by dexamethasone: dose or time dependency?

BACKGROUND: Daily injections of dexamethasone (DEX) given to adult rats are a recognized but nonstandardized model of stress. The aim of this work was to establish a reproducible and accurate model of stress in adult rats by chronic injection of DEX in order to standardize it. For this purpose, the effect of the duration of treatment and the effect of DEX dose were tested. To help understand the mechanisms of the catabolic effect of DEX, the study was extended to the metabolism of glutamine (GLN). In experiment 1, 60 male Sprague-Dawley rats (3 months old) were divided into 8 groups of 6 rats: groups G3, G5, G7, and G9 received 1.50 mg/kg/d of DEX by intraperitoneal (i.p.) injection for 3, 5, 7, or 9 days, respectively. Groups G3PF, G5PF, G7PF, or G9PF were pair-fed to groups G3, G5, G7, or G9, respectively. Group AL (n = 12) was healthy rats fed ad libitum. RESULTS: In treated rats, nitrogen balance reached its lowest value at day 5. After 9 days treatment by DEX, the catabolic state was reduced. An increase in GLN-synthetase activity and a decrease in muscle GLN content were related to DEX per se not to DEX-induced anorexia. In experiment 2, 25 rats were divided into 5 groups of 5 animals. Groups G0.75, G1.50, and G2.50 received 0.75, 1.50, and 2.50 mg/kg/d, respectively, of DEX by i.p. injection for 5 days. Group PF was pair-fed to group G2.50 and group AL was control rats. RESULTS: DEX induced a decrease in nitrogen balance that was dose-independent. GLN-synthetase activity was increased maximally in gastrocnemius by 0.75 mg/kg. CONCLUSIONS: Five days of treatment by DEX and a dose of 0.75 mg/kg/d induced a marked catabolic state.

Animals↗
PubMedDate not supplied

[Effects of optotoxic substances on several glycolytic enzyme activities in the retina of the pig (author's transl)].

1. The authors report the results obtained after the action of certain optotoxic substances on several enzyme activities in the retina of the pig. 2. This in vitro study involved enzyme interferences of the following optotoxic agents : ethionamide, d-penicillamine, ethylene diaminotetra-acetic acid (EDTA), disodium and dicobalt salts. The enzyme activities studied involved glycolysis, the enzymes selected being as follows: glucose phosphate isomerase (GPI, E.C. 5.3.1.9), fructose-1,6-diphosphate aldolase (F1-6diPA, E.C. 4.1.2.13), lactate dehydrogenase (LDH, E.C. 1.1.1.27). 3. Following the action of the effectors studied, a marked decrease in the enzyme activities examined was found in the retina. This decrease, of varying rapidity and regularity, went as far in some cases as total inhibition; there was disturbance of glycolysis. 4. These results indicate the existence of interactions with a complex mechanism. It may be noted that all of the effectors studied were chelating agents of divalent metals and the changes which they induced in the enzyme activities examined may be explained by interference of the chelates formed with metal cations, such as Zn++, co-factors or effectors of these glycolysis enzymes (with the exception of GPI). These stable chelates are formed by virtue of the primary amine--NH2, thiol--SH, thionyl-[Formula: see text] groups, i.e. groups belonging to molecules essential to cell metabolism.

Animals↗
PubMedDate not supplied

[Analysis of opiates in the urine of children with gas chromatography coupled to mass spectrometry].

Acute intoxication by opiates is quite frequent and very serious, especially in children whence the need to assay these compounds in biological fluids. The authors have developed an assay for opiates (codeine, codethyline, morphine and pholcodine) by gas chromatography/mass spectrometry (GC/MS) on a capillary column. This assay can identify different opiates due to its high specificity. Before chromatography, urine from children undergoes acid hydrolysis and solid phase extraction. The compounds are derivatized by acetylation before being chromatographied. This assay is carried out after a first search for opiates in urine by immunoenzymology. Each sample containing opiates is then analysed by GC/MS in order to determine specifically the opiates responsible for intoxication.

Child↗
PubMedDate not supplied

[Use of a dynamometer in hospital pharmacy. Its use to study the mechanical properties of plastic materials].

The stretching test is in current use in Pharmaceutical Industry to characterize the mechanical properties of materials or to control medical devices such as catheters. Given the lack of official standards in the French Pharmacopée, we present here the results of an experiment carried out in Hospital Pharmacy. The value of the results will be depending on the manual gesture of the operator and on the experimental conditions for a given material. The factors which appear to be essential are the following: numerous samples, necessary to assess a good repeatability, the stretching speed and the place of the rupture that have to be defined, so as the manual fixation of the samples. This test is interesting in Hospital Pharmacy but the methodology remains a problem so that it cannot be recommended for an occasional use, in spite of an apparent simplicity.

Catheterization↗
PubMedDate not supplied

[4-Arylpiperazine derivatives: a seedbed of drugs for various therapeutic indications].

The main focus of this review is the pharmacology and the therapeutic use of chemical related agents, the arylpiperazine derivatives. These compounds produce a variety of behavioural responses and pharmacological effects which directly and principally result from activation of serotonin systems. However, minor modifications in the chemical structure of these products involve important changes in affinity and selectivity for 5-HT receptors since it can also display significant affinity for dopaminergic, adrenergic or histaminergic receptors. The different arylpiperazine drugs therapeutically used are described as well as some compounds presently under investigation.

Animals↗