Biomedical subjects

D Fournier

Publications and source records attributed to D Fournier.

At least 37 records · Page 2Linked to original sources

PubMed1999

High-resolution ultrasound evaluation of internal jugular venous valves.

Although the presence of valves in the distal portion of the internal jugular veins has been widely described by anatomists and pathologists, their existence remains underscored in the medical literature. We set out to demonstrate their sonographic aspect and to evaluate their morphology, location and prevalence. Seventy-five cadavers were evaluated for the presence and aspect of such valves through neck dissections. Concurrent evaluation of the sonographic character of these structures was performed in another cohort of 75 adults. Valves of the distal portion of the internal jugular veins were found in 93 % of the cadaveric studies. Ultrasonography easily demonstrated the valve leaflets in 87 % of patients; all were observed in the distal portion of the internal jugular (IJ) veins. Sixty percent were bilateral with the majority of unilateral veins found on the right side. High-resolution ultrasonography easily demonstrates valves in the distal portion of the IJ veins which are present in the great majority of persons. Their evaluation may be of use in percutaneous procedures using this venous access.

Aged↗

PubMed1999

Ventral transdural herniation of the thoracic spinal cord: surgical treatment in four cases and review of literature.

BACKGROUND: A specific cause of progressive Brown-Sequard syndrome has been identified: a ventral herniation of the thoracic spinal cord through the dural sleeve on one side. METHOD: Four female patients who were affected by a progressive Brown Sequard syndrome related to a transdural spinal cord herniation have been investigated and were submitted to surgery and postoperative evaluation. FINDINGS: The MRI scan showed atrophy and forward displacement of the spinal cord on one side and adhesion of the spinal cord to the dura mater. CT myelography demonstrated the disappearance of the premedullar rim at the level of the herniation and the shadow of the extradural herniation. Surgical treatment consisted in the excision of the arachnoid cyst when there was one, section of the dentate ligament, release of the adhesions, detachment of the spinal cord from the hernial orifice, and lastly suture of the dural tear or placement by a patch. Follow-up examination showed motor improvement with persistent sensory deficit in two cases and stabilisation in two cases. INTERPRETATION: The cause of the dural tear, either traumatic or congenital could not be confirmed in the four cases. Symptoms probably occur when herniation fills the orifice and strangulation happens which explains the late appearance and progressive evolution of this myelopathy. Mobilisation of the herniated spinal cord back into the intradural space can be achieved by surgery and may stop the evolution of the symptoms and signs.

Adult↗

PubMed1999

Cholinesterases from the marine mussels Mytilus galloprovincialis Lmk. and M. edulis L. from the freshwater bivalve Corbicula fluminea Müller.

In order to improve the molecular basis for the use of bivalve cholinesterases as a reliable biomarker for aquatic pollution, the polymorphism and characterization of these enzymes in Mytilus edulis, Mytilus galloprovincialis and Corbicula fluminea were investigated. All results are consistent with the presence of only one pharmacological form of cholinesterase in each species. The molecular masses were 180 kDa for the two marine mussels and 240 kDa for C. fluminea. The cholinesterases are anchored to the membrane by a glycosyl inositol phosphate like the Ga form (type I) described in vertebrates. Surprisingly, these cholinesterases were poorly inhibited by organophosphorous compounds compared to enzymes from other sources. This suggests that these bivalves could be used as a biomarker for acute rather than chronic contaminations by anticholinesterase insecticides.

Animals↗

PubMed1999

Mechanism of an insect glutathione S-transferase: kinetic analysis supporting a rapid equilibrium random sequential mechanism with housefly I1 isoform.

The steady-state kinetics of glutathione S-transferase I1 (GST I1) from housefly Musca domestica expressed in Escherichia coli were investigated with glutathione (GSH) and 1-chloro-2,4-dinitrobenzene (CDNB). Concentrations of the varied substrates were from 0.03 to 1 mM for GSH and 0.05 to 1 mM for CDNB. Within this range, Michaelis-Menten behaviour was observed and convergent straight lines in double reciprocal plots excluded a ping-pong kinetic mechanism. Instead, data were consistent either with rapid-equilibrium random or with steady-state ordered sequential mechanisms because of abscissa convergence. Discrimination was achieved by studying the reaction with another electrophilic partner, p-nitrophenyl-acetate (PNPA). Concentrations of PNPA and GSH varied within the ranges 0.5 to 10 mM and 0.03 to 0.6 mM, respectively. The complete set of data supports the proposal of a rapid-equilibrium random-sequential model with strictly independent sites for GSH and CDNB or PNPA. Kinetic parameters are thus true dissociation equilibrium constants with values of 0.15 mM for GSH, 0.15 mM for CDNB, and 7 mM for PNPA. Analysis of the inhibition by the product (S-(2,4-dinitrophenyl)-glutathione, 10 to 100 microM), on the coupling reaction between GSH and CDNB with either GSH (0.05 to 0.5 mM, CDNB 0.2 mM) or CDNB (0.05 to 0.5 mM, GSH 0.2 mM) varied, consistent with the proposed mechanism. Binding of product to the free enzyme excludes GSH (competitive inhibition pattern with Kp = 12 microM) but only slightly hinders binding of CDNB. Binding free energies, together with the inhibition pattern, suggest that the non-peptidic moiety of product interacts with an alternative sub-site within the large open pocket accommodating the various electrophilic substrates. These results lead us to propose a model for intra-pocket shifting of the non-peptidic moiety upon product formation which contributes to the product release.

Animals↗

PubMed1999

Interaction of 3-alkylpyridinium polymers from the sea sponge Reniera sarai with insect acetylcholinesterase.

3-Alkylpyridinium polymers (poly-APS), composed of 29 or 99 N-butyl-3-butyl pyridinium units, were isolated from the marine sponge Reniera sarai. They act as potent cholinesterase inhibitors. The inhibition kinetics pattern reveals several successive phases ending in irreversible inhibition of the enzyme. To provide more information on mechanism of inhibition, interaction of poly-APS and N-butyl-3-butyl pyridinium iodide (NBPI) with soluble dimeric and monomeric insect acetylcholinesterase (AChE) was studied by using enzyme intrinsic fluorescence and light scattering, conformational probes ANS and trypsin, and SDS-PAGE. Poly-APS quenched tryptophan fluorescence emission of AChE more extensively than NBPI. Both inhibitors exhibited a pseudo-Lehrer type of quenching. Interaction of poly-APS with dimeric AChE did not induce significant changes of the enzyme conformation as assayed by using the hydrophobic probe ANS and trypsin digestion. In contrast to NBPI, titration of both monomeric and dimeric AChE with poly-APS resulted in the appearance of large complexes detected by measuring light scattering. An excess of poly-APS produced AChE precipitation as proved on SDS-PAGE. None of the effects were observed with trypsin as a control. It was concluded that AChE aggregation and precipitation rather than the enzyme conformational changes accounted for the observed irreversible component of poly-APS inhibition.

Acetylcholinesterase↗

PubMed1999

Is the insect glutathione S-transferase I gene family intronless?

The genes coding for class I glutathione S-transferases in insects were believed to be intronless because the coding sequence was not interrupted by an intron. But sequences of the untranslated 5' end of transcripts revealed the presence of an intron in housefly and Drosophila genes suggesting that most insect GSTI genes are in fact interrupted.

Animals↗

PubMed1999

Subclavian steal syndrome and flow-related aneurysm. Another reason to treat.

A 48-year-old woman presented with a symptomatic right subclavian steal syndrome due to proximal subclavian artery stenosis. Anatomically the innominate artery was absent. Collateral circulation followed the vertebro-vertebral pathway with reversal of blood flow in the ipsilateral vertebral artery. There was also multiple dilated intervertebral collaterals and an associated saccular aneurysm on one of them. Surgical carotid-subclavian transposition permitted relief of clinical symptoms, disappearance of collateral circulation and subtotal regression of the aneurysm. This spontaneous evolution confirmed the role of high-flow in the pathogenesis of some aneurysms and the habitually good prognosis of flow-related aneurysms with correction of the cause. Arteriography still appears essential in diagnosis, pretherapeutic assessment and sometimes post-treatment evaluation in subclavian steal syndrome.

Aneurysm↗

PubMed1999

[Spontaneous spinal cord herniation: a little-known cause of Brown-Sequard syndrome. Report of two cases and review of the literature].

We report two cases of spinal cord herniation. The first one concerns a 28 year-old female who presented with an eighteen-month past history of spasticity of the right lower limb associated with somesthetic sensorial disturbances of the left side with a T4 level, related to a T3-T4 spinal cord herniation. The second case concerned a 58 year-old female with a past history of a left lower limb pyramidal syndrome associated with somesthetic and proprioceptive sensibilities disturbances of the right side with a T5 level related to a T4-T5 spinal cord herniation. Spinal cord herniation is an uncommon and underestimated cause of a progressive Brown-Sequard syndrome. The diagnosis is now easy on the MRI, showing a ventral attraction of the cord. The outcome is usually good, following the surgical reduction of the herniation.

Adult↗

PubMed1999

[Post-traumatic intracranial arterial aneurysm. Two cases with review of the literature].

Post-traumatic intracranial aneurysms are rare entity, which can appear following even benign head injuries. Their clinical manifestations are various, from a typical SAH to an uncommon intracerebral hematoma. Medical history runs usually from a couple of days to several years. Two cases of intracranial aneurysm have been observed from 1995 to 1998. The first case presented as a cortical aneurysm in a cerebral contusion following a week of evolution. The second case presented as a cortical hematoma with a head trauma 10 years before. All patients were operated on with uneventful follow-up. Post-traumatic intracranial aneurysms can exhibit an increase in size or a spontaneous thrombosis. Diagnosis is made by angiography, which has to be repeated if treatment has to be delayed. Best results are obtained by exclusion of the lesion, if allowed by the patient's condition.

Adult↗

PubMed1998

A putative kinetic model for substrate metabolisation by Drosophila acetylcholinesterase.

Insect acetylcholinesterase, an enzyme whose catalytic site is located at the bottom of a gorge, can metabolise its substrate in a wide range of concentrations (from 1 microM to 200 mM) since it is activated at low substrate concentrations. It also presents inhibition at high substrate concentrations. Among the various rival kinetic models tested to analyse the kinetic behaviour of the enzyme, the simplest able to explain all the experimental data suggests that there are two sites for substrate molecules on the protein. Binding on the catalytic site located at the bottom of the gorge seems to be irreversible, suggesting that each molecule of substrate which enters the active site gorge is metabolised. Reversible binding at the peripheral site of the free enzyme has high affinity (2 microM), suggesting that this binding increases the probability of the substrate entering the active site gorge. Peripheral site occupation decreases the entrance rate constant of the second substrate molecule to the catalytic site and strongly affects the catalytic activity of the enzyme. On the other hand, catalytic site occupation lowers the affinity of the peripheral site for the substrate (34 mM). These effects between the two sites result both in apparent activation at low substrate concentration and in general inhibition at high substrate concentration.

Acetylcholine↗

PubMed1998

Inhibition of acetylcholinesterase by an alkylpyridinium polymer from the marine sponge, Reniera sarai.

Large polymeric 3-alkylpyridinium salts have been isolated from the marine sponge Reniera sarai. They are composed of N-butyl(3-butylpyridinium) repeating subunits, polymerized head-to-tail, and exist as a mixture of two main polymers with molecular weights without counterion of about 5520 and 18900. The monomer analogue of the inhibitor, N-butyl-3-butylpyridinium iodide has been synthesized. This molecule shows mixed reversible inhibition of acetylcholinesterase. The polymers also act as acetylcholinesterase inhibitors and show an unusual inhibition pattern. We tentatively describe it as quick initial reversible binding, followed by slow binding or irreversible inhibition of the enzyme. This kinetics suggests that there are several affinity binding sites on the acetylcholinesterase molecule where the polymer can bind. The first binding favors binding to other sites which leads to an apparently irreversibly linked enzyme-inhibitor complex.

Animals↗

PubMed1998

Engineering sensitive acetylcholinesterase for detection of organophosphate and carbamate insecticides.

High quantities of various acetylcholinesterases can now be produced following in vitro expression and it is possible to use them as biosensors to detect organophosphates and carbamates insecticides. In order to check the potentialities of acetylcholinesterase from various sources, we have studied enzyme from bovine erythrocyte, Electrophorus electricus, Drosophila melanogaster, Torpedo californica and Caenorhabditis elegans. It appears that insect acetylcholinesterase is more susceptible to a broad range of organophosphates and carbamates insecticides than the other tested enzymes. D. melanogaster is 8-fold more sensitive than E. electricus enzyme and this sensitivity has been increased to 12-fold by introducing a mutation at position 408.

Acetylcholinesterase↗

PubMed1998

Two invertebrate acetylcholinesterases show activation followed by inhibition with substrate concentration.

In vertebrates there are two cholinesterases, with differences in catalytic behaviour with respect to substrate concentration: butyrylcholinesterase displays an increased activity at low substrate concentrations, whereas acetylcholinesterase displays inhibition by excess substrate. In two invertebrates, Drosophila melanogaster and Caenorhabditis elegans, we found cholinesterases that showed both kinetic complexities: substrate activation at low substrate concentrations followed by inhibition at higher concentrations. These triphasic kinetics can be explained by the presence of two enzymes with different kinetic behaviours or more probably by the existence of a single enzyme regulated by the substrate concentration.

Acetylcholinesterase↗

PubMed1998

Drosophila acetylcholinesterase: effect of post-translational [correction of post-traductional] modifications on the production in the baculovirus system and substrate metabolization.

Acetylcholinesterase cDNAs from Drosophila melanogaster modified on its primary sequence were cloned into baculovirus and were expressed in Sf9 cells with the aim to identify a mutant form that produces the enzyme at a high level. Directed mutagenesis was used in order to independently knockout different sites of post-translational modifications: exchange of the C-terminal hydrophobic peptide for a glycolipid molecule, dimerization by disulfide bridge, N-linked glycosylation at the five accessible sites, and subunit formation by proteolytic cleavage of a hydrophilic peptide found in the precursor. Another mutation involved the elimination of a free cysteine in the mature protein. All mutations involving post-translational modifications resulted in lower recoveries, suggesting that they are useful for maintaining high amounts of protein in the synapse. By contrast, elimination of a free cysteine in the mature protein permitted an increase in the level of production of the enzyme. These mutations did not affect specific activity of the enzyme at substrate concentrations ranging from 3 microM to 200 mM, suggesting that activation and inhibition of the enzyme activity does not originate from a polymorphism in post-translational modifications.

Acetylcholine↗

PubMed1998

Stabilization of recombinant Drosophila acetylcholinesterase.

The uses of pure and stable acetylcholinesterase can range from simple basic research to applications in environment quality assessment. In order to satisfy some of these needs its recombinant expression is routinely performed. Affinity-purified recombinant Drosophila melanogaster acetylcholinesterase proved to be instable; an apparent cause of this seemed to be the presence of contaminants with protease activity as evidenced by SDS-PAGE. The elimination of these accompanying products was achieved by anion-exchange, hydrophobic interaction, and cibacron blue affinity chromatography applied downstream from procainamide affinity chromatography. The utilization of a parallel affinity acting via an engineered histidine tail permitted the elimination of the copurified proteases as well. Despite the elimination of the contaminants, the apparently pure extracts were still unstable. It is shown that such instability can be counterbalanced by provoking protein-protein interactions, either between enzyme molecules or with other molecules such as bovine serum albumin. Another way to reduce instability is the addition of a reversible inhibitor or polyethylene glycol 3350.

Acetylcholinesterase↗

PubMed1998

Essential interactions between Thiobacillus ferrooxidans and heterotrophic microorganisms during a wastewater sludge bioleaching process.

The stimulating effect of heterotrophic microorganisms was investigated on the growth and on the ferrous iron oxidation of Thiobacillus ferrooxidans in synthetic media and in wastewater sludge. The addition of a sediment. Rhodotorula rubra isolate or a strain of T. acidophilus on two-layer agarose-gelled medium doubled the plating efficiency of T. ferrooxidans. In liquid cultures, R. rubra had a slight but significant effect on the growth rate of T. ferrooxidans. Moreover, the yeast allowed a faster initiation of the ferrous iron oxidation and acidification by T. ferrooxidans. In the bioleaching process, the co-culture of T. ferrooxidans with R. rubra or with the indigenous microbial assemblage from sludge was shown to be essential since the pure culture of T. ferrooxidans failed to oxidize ferrous iron and to acidify wastewater sludge. These results emphasize the importance of active heterotrophic microorganisms in the metal bioleaching activity of T. ferrooxidans in sludge.

Journal Article↗

PubMed1998

A new attempt to assess the effect of learning processes on the cholinergic system: studies on fruitflies and honeybees.

The effect of training on the functioning of the cholinergic system was investigated in fruitflies and in honeybees. Drosophila were submitted to a passive avoidance conditioning of the proboscis extension response (PER). Flies had to learn to suppress the sugar-induced PER to avoid an aversive quinine reinforcement. In a yoked control group, the punishment was administered with no relation to the response displayed. Honeybees underwent a five-trial olfactory conditioning of the PER elicited by an antennal gustatory stimulation. In the control group, olfactory and gustatory stimulations were unpaired to prevent a learning process from developing. Immediately at the end of the learning session, acetylcholinesterase (AChE) activity was individually measured on the whole animal for Drosophila and on the head for the honeybee in experimental and in control groups. In fruitflies and honeybees, the AChE rate did not differ between the experimental group and its respective control group. Moreover, no significant correlation could be found individually between the learning performance and the AChE rate in either Drosophila or in honeybees. This experiment did not reveal any modulatory effect of the learning acquisition level on the AChE activity in insects as was previously reported in honeybees.

Acetylcholinesterase↗

PubMed1997

[Thoracic ultrasound].

Ultrasonography is the best imaging modality for detection of pleural effusions and the presence of septations, but is not accepted as a reliable diagnostic tool for other thoracic problems. However, the technique is useful for analysis of parietal lesions and pulmonary masses arising in the periphery of the lung. Biopsy of such lesions and drainage of pleural effusions are often easier under sonographic guidance than with CT. Because of its advantages, sonography should be used more often as a diagnostic and therapeutic tool in thoracic imaging.

Humans↗