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Biomedical subjects

A Dumoulin

Publications and source records attributed to A Dumoulin.

At least 19 recordsLinked to original sources
PubMed2006

[Management of complicated retinal detachment using a heavy silicon oil as temporary tamponade].

PURPOSE: To assess the efficacy and safety of a heavy silicon oil (a silicon oil-RMN3 mixture, a mixed fluorinated and hydrocarbonated olefin) as temporary internal tamponade in selected cases of retinal detachment with inferior breaks. PATIENTS AND METHODS: Forty-six patients were operated on (inferior and/or posterior breaks: 38; proliferative vitreoretinopathy > or =C2: 18; anterior proliferative vitreoretinopathy: 14), with a mean follow-up of 39 months. Seventeen patients were operated on with a heavy silicon oil of a 1.03 g/cm3 density and 29 patients with a silicon oil of a 1.02 g/cm3 density. Heavy silicon oil was removed in 41 patients after a mean of 9.3 weeks. RESULTS: Anatomic success was achieved in 35 cases after a mean follow-up of 39 months. Recurrent retinal detachment with proliferative vitreoretinopathy occurred in eight cases during heavy silicon oil tamponade. The removal was difficult in three cases with the 1.02 g/cm3 density silicon oil. Complications included glaucoma (eight eyes), major emulsification (two eyes), and an intraocular inflammation reaction to topical steroids (five eyes). CONCLUSION: Heavy silicon oil (Oxane Hd) is as safe and effective as standard silicon oil in the treatment of selected retinal detachment, but intraocular manipulations are quite difficult. A prospective study is necessary to compare the efficacy of Oxane Hd and standard silicon oil in selected cases of retinal detachment with inferior breaks and in cases of large inferior retinectomy.

Adolescent↗
PubMed2003

Severe recurrent cytomegalovirus disease revealed by a colocutaneous fistula in a kidney transplant recipient.

Intestinal disorders are classical complications of cytomegalovirus (CMV) infection in kidney transplant recipients (Helderman JH, Goral S. Gastrointestinal complications of transplant immunosuppression. J Am Soc Nephrol 2002: 13: 277-287). Severe ulcerative colitis that is sometimes lethal has been reported (Foucar E, Mukai K, Foucar K, Sutherland DE, Van Buren CT. Colon ulceration in lethal cytomegalovirus infection. Am J Clin Pathol 1981: 76: 788-801 and Frankel AH, Barker F, Williams G, Benjamin IS, Lechler R, Rees AJ. Neutropenic enterocolitis in a renal transplant patient. Transplantation 1991: 52: 913-914). The immunosuppressive drugs currently used, and notably mycophenolate mofetil (Cellcept), cause significant changes in the incidence, duration, and viral load of CMV infections with severe atypical forms of CMV disease (De Maar EF, Verschuuren EA, Homan vd Heide JJ, et al. Effects of changing immunosuppressive regimen on the incidence, duration and viral load of cytomegalovirus infection in renal transplantation: a single center report. Transpl Infect Dis 2002: 4: 17-24 and Perez Valentin MA, Cofan F, Sole M, et al. Atypical cytomegalovirus in renal transplantation: a new form of presentation. Nefrologia 2002: 22: 381-385). This report describes a patient who suffered from several episodes of colitis due to an unusual and late-appearing CMV infection.

Antigens, Viral↗
PubMed2001

IPSC kinetics at identified GABAergic and mixed GABAergic and glycinergic synapses onto cerebellar Golgi cells.

In the rat cerebellum, Golgi cells receive serotonin-evoked inputs from Lugaro cells (L-IPSCs), in addition to spontaneous inhibitory inputs (S-IPSCs). In the present study, we analyze the pharmacology of these IPSCs and show that S-IPSCs are purely GABAergic events occurring at basket and stellate cell synapses, whereas L-IPSCs are mediated by GABA and glycine. Corelease of the two transmitters at Lugaro cell synapses is suggested by the fact that both GABA(A) and glycine receptors open during individual L-IPSCs. Double immunocytochemical stainings demonstrate that GABAergic and glycinergic markers are coexpressed in Lugaro cell axonal varicosities, together with the mixed vesicular inhibitory amino acid transporter. Lugaro cell varicosities are found apposed to glycine receptor (GlyR) clusters that are localized on Golgi cell dendrites and participate in postsynaptic complexes containing GABA(A) receptors (GABA(A)Rs) and the anchoring protein gephyrin. GABA(A)R and GlyR/gephyrin appear to form segregated clusters within individual postsynaptic loci. Basket and stellate cell varicosities do not face GlyR clusters. For the first time the characteristics of GABA and glycine cotransmission are compared with those of GABAergic transmission at identified inhibitory synapses converging onto the same postsynaptic neuron. The ratio of the decay times of L-IPSCs and of S-IPSCs is a constant value among Golgi cells. This indicates that, despite a high cell-to-cell variability of the overall IPSC decay kinetics, postsynaptic Golgi cells coregulate the kinetics of their two main inhibitory inputs. The glycinergic component of L-IPSCs is responsible for their slower decay, suggesting that glycinergic transmission plays a role in tuning the IPSC kinetics in neuronal networks.

Amino Acid Transport Systems↗
PubMed2000

Transposing sequences between fetal and adult hemoglobins indicates which subunits and regulatory molecule interfaces are functionally related.

To correlate amino acid sequence changes with hemoglobin function we are carrying out a detailed recombinant analysis of the adult hemoglobin/fetal hemoglobin (HbA/HbF) systems. The important physiological differences between these two tetramers lie at unspecified sites in the 39 sequence substitutions of the 146 amino acids in their beta and gamma chains. In this paper, significant differences in the tetramer-dimer dissociation constants (referred to as tetramer "strength" or "stability") of adult (HbA) and fetal (HbF) hemoglobin tetramers have been used to probe the relationship between the allosteric, sliding interface and the effects of the allosteric regulator, 2,3-DPG, in promoting oxygen release. The single amino acid difference at the allosteric interfaces of these two hemoglobins, Glu-43(beta) --> Asp-43(gamma), which is not near the DPG binding site, leads to a significantly lower DPG response, approaching that of HbF. The results are inconsistent with the long-held idea that the replacement of His-143(beta) in HbA to Ser-143(gamma) in HbF is solely responsible for the lowered DPG response in HbF. On the other hand, the Val-1(beta) --> Gly-1(gamma) replacement near the DPG binding site has no effect on the DPG response. The replacement of His-116(beta) by the hydrophobic Ile-116(gamma) at the rigid alpha(1)beta(1) interface has a marginal yet detectable effect on the allosteric alpha(1)beta(2) interface. The results, overall, are interpreted using a model involving electrostatic coupling between certain side chains and extend the concept of a long-range relationship between some distant regions of the tetramer that are likely mediated through the central cavity.

2,3-Diphosphoglycerate↗
PubMed2000

Serotonin-driven long-range inhibitory connections in the cerebellar cortex.

Disturbances of the serotoninergic neuromodulation in the cerebellar cortex have been involved in several types of ataxia, but the physiological action of serotonin in this structure remains poorly understood. We report that in slices of the rat cerebellar vermis, serotonin triggers the firing of an inhibitory interneuron presynaptic to Golgi cells. The Lugaro cell, a neglected interneuronal type, satisfies the expected criteria for this input, whereas basket cells, stellate cells, or Golgi cells do not. Lugaro cells are selectively excited by serotonin, and their firing behavior (sustained steady frequency in the 5-15 Hz range) resembles the pattern of occurrence of serotonin-evoked IPSCs in Golgi cells. Immunohistochemical stainings and single cell reconstructions show that Lugaro cell axons form a parasagittal plexus but also extend long transverse branches that run parallel to the parallel fibers and are partly myelinated. Electrophysiological data suggest that these transverse axons participate in synaptic contacts of the Lugaro cells with Golgi cells, and we calculated that in the intact cerebellum a given Lugaro cell contacts >100 Golgi cells. Serotonin modulation of Lugaro cells may constitute an intracortical switch involved in information patterning at the level of Golgi cells and granule cells populations, and particularly in synchronizations recorded along the transverse axis in vivo.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed2000

Transmission of Pneumocystis carinii disease from immunocompetent contacts of infected hosts to susceptible hosts.

Pneumocystis carinii organisms constitute a large group of heterogeneous atypical microscopic fungi that are able to infect immunocompromised mammals by an airborne route and to proliferate in their lungs, inducing Pneumocystis carinii pneumonia. This pneumonia remains a crucial epidemiological challenge, since neither the source of Pneumocystis carinii infection in humans nor the process by which humans become infected has been clearly established. Polymerase chain reaction (PCR) assays have shown that profoundly immunosuppressed patients without pneumocystosis can be subclinically infected with Pneumocystis. Other PCR-based studies have suggested that healthy immunocompetent hosts are not latent carriers of the parasite. However, recent reports have indicated that Pneumocystis carinii can persist for limited periods in the lungs of convalescent rats after recovery from corticosteroid-induced pneumocystosis, and also that immunocompetent mammals can be transiently parasitized by Pneumocystis carinii after close contact with hosts with Pneumocystis carinii pneumonia. Can transiently parasitized hosts be a source of infection for immunosuppressed hosts? In order to investigate this important clinical question, the ability of immunocompetent BALB/c mice, which were carrying subclinical levels of Pneumocystis carinii, to transmit the infection by the airborne route to highly susceptible, uninfected mice with severe combined immunodeficiency was studied. The results indicated that the immunocompetent mice, transiently parasitized by Pneumocystis carinii organisms after close contact with Pneumocystis carinii-infected mice, were able to transmit the infection to Pneumocystis carinii-free mice with severe combined immunodeficiency.

Animals↗
PubMed2000

Transplantation of embryonic Raphe cells regulates the modifications of the gabaergic phenotype occurring in the injured spinal cord.

Transection of the spinal cord yields a permanent deficit due to the interruption of descending and ascending tracts which subserve the supraspinal control of spinal cord functions. We have shown previously that transplantation below the level of the section of embryonic monoaminergic neurons can promote the recovery of some segmental functions via a local serotonergic and noradrenergic reinnervation. Moreover, the up-regulation of the corresponding receptors resulting from the section was corrected by the transplants. The aim of the present work was to determine whether such a graft could also influence non-monoaminergic local neurons, the GABAergic interneurons of the spinal cord. Following spinal cord transection, the number of cells which express glutamate decarboxylase (mol. wt 67,000) messenger RNA--a marker of GABA synthesis--increased significantly below the lesion compared with the intact animal. In contrast, in lesioned animals which had been grafted one week later with raphe neuroblasts, this number was close to control level. These post-grafting modifications were further associated with increased GABA immunoreactivity in the host tissue. These data suggest that the graft of embryonic raphe cells which compensates the deficit of serotonin in the distal segment also regulates the expression of the GABAergic phenotype in the host spinal cord. This regulation could be mediated by the re-establishment of a local functional innervation by both serotonin and GABAergic transplanted neurons and/or by trophic factors released from the embryonic cells. It appears then that grafted cells influence the host tissue in a complex manner, through the release and/or regulation of several neurotransmitter systems.

Animals↗
PubMed2000

Expression and properties of recombinant HbA2 (alpha2delta2) and hybrids containing delta-beta sequences.

Hemoglobin A2 (alpha2delta2), which is present at low concentration (1-2%) in the circulating red cells of normal individuals, has two important features that merit its study, i.e., it inhibits polymerization of sickle HbS and its elevated concentration in some thalassemias is a useful clinical diagnostic. However, reports on its functional properties regarding O2 binding are conflicting. We have attempted to resolve these discrepancies by expressing, for the first time, recombinant hemoglobin A2 and systematically studying its functional properties. The construct expressing HbA2 contains only alpha and delta genes so that the extensive purification required to isolate natural HbA2 is circumvented. Although natural hemoglobin A2 is expressed at low levels in vivo, the amount of recombinant alpha2delta2 expressed in yeast is similar to that found for adult hemoglobin A and for fetal hemoglobin F when the alpha + beta or the alpha + gamma genes, respectively, are present on the construct. Recombinant HbA2 is stable, i.e., not easily oxidized, and it is a cooperative functional hemoglobin with tetramer-dimer dissociation properties like those of adult HbA. However, its intrinsic oxygen affinity and response to the allosteric regulators chloride and 2,3-diphosphoglycerate are lower than the corresponding properties for adult hemoglobin. Molecular modeling studies which attempt to understand these properties of HbA2 are described.

Amino Acid Sequence↗
PubMed2000

Formation of mixed glycine and GABAergic synapses in cultured spinal cord neurons.

In the spinal cord, GABA and glycine mediate inhibition at separate or mixed synapses containing glycine and/or GABA(A) receptors (GlyR and GABA(A)R, respectively). We have analysed here the sequence of events leading to inhibitory synapse formation during synaptogenesis of embryonic spinal cord neurons between 1 and 11 days in vitro (DIV). We used immunocytochemical methods to detect simultaneously an antigen specific to inhibitory terminals, the vesicular inhibitory amino acid transporter (VIAAT), and one of the following postsynaptic elements: GlyR, GABA(A)R or gephyrin, the anchoring protein of GlyR, which is also associated with GABA(A)R. Quantitative analysis revealed that until 5 DIV most gephyrin clusters were not adjacent to VIAAT-positive profiles, but became associated with them at later stages. In contrast, GlyR and GABAAR clustered predominantly in front of VIAAT-containing terminals at all stages. However, about 10% of receptor aggregates were detected at nonsynaptic loci. The two receptors colocalized in 66.2+/-2.5% of the inhibitory postsynaptic domains after 11 DIV, while 30.3+/-2.6% and 3.4+/-0.8% of them contained only GlyR and GABA(A)R, respectively. Interestingly, at 3 DIV GABA(A)R clustered at a postsynaptic location prior to gephyrin and GlyR; GABA(A)R could thus be the initiating element in the construction of mixed glycine and GABAergic synapses. The late colocalization of gephyrin with GABA(A)R, and the demonstration by other groups that, in the absence of gephyrin, postsynaptic GABA(A)R is not detected, suggest that gephyrin is involved in the stabilization of GABA(A)R rather than in its initial accumulation at synaptic sites.

Amino Acid Transport Systems↗
PubMed2000

[Cryptosporidium and wildlife: a risk for humans?].

The present review underlines the knowledge of Cryptosporidium, especially its biodiversity and transmission. The presence of the parasite in different mammal host species is discussed with real, potential risk of transmission to humans. The potential role of insects in mechanical transmission of the parasite is evaluated by experimental protocols. The cost of cryptosporidiosis at health and economic levels are mentioned, which emphasises the importance of detection and identification of the parasite in the environment and in wild mammal species, using specific molecular tools. Potential measures to be accomplished in order to fight off cryptosporidiosis are also noted.

Animals↗
PubMed1999

Presence of the vesicular inhibitory amino acid transporter in GABAergic and glycinergic synaptic terminal boutons.

The characterization of the Caenorhabditis elegans unc-47 gene recently allowed the identification of a mammalian (gamma)-amino butyric acid (GABA) transporter, presumed to be located in the synaptic vesicle membrane. In situ hybridization data in rat brain suggested that it might also take up glycine and thus represent a general Vesicular Inhibitory Amino Acid Transporter (VIAAT). In the present study, we have investigated the localization of VIAAT in neurons by using a polyclonal antibody raised against the hydrophilic N-terminal domain of the protein. Light microscopy and immunocytochemistry in primary cultures or tissue sections of the rat spinal cord revealed that VIAAT was localized in a subset (63-65%) of synaptophysin-immunoreactive terminal boutons; among the VIAAT-positive terminals around motoneuronal somata, 32.9% of them were also immunoreactive for GAD65, a marker of GABAergic presynaptic endings. Labelling was also found apposed to clusters positive for the glycine receptor or for its associated protein gephyrin. At the ultrastructural level, VIAAT immunoreactivity was restricted to presynaptic boutons exhibiting classical inhibitory features and, within the boutons, concentrated over synaptic vesicle clusters. Pre-embedding detection of VIAAT followed by post-embedding detection of GABA or glycine on serial sections of the spinal cord or cerebellar cortex indicated that VIAAT was present in glycine-, GABA- or GABA- and glycine-containing boutons. Taken together, these data further support the view of a common vesicular transporter for these two inhibitory transmitters, which would be responsible for their costorage in the same synaptic vesicle and subsequent corelease at mixed GABA-and-glycine synapses.

Amino Acid Transport Systems↗
PubMed1998

The N-terminal sequence affects distant helix interactions in hemoglobin. Implications for mutant proteins from studies on recombinant hemoglobin felix.

The N-terminal 18-amino acid sequence of the beta-chain of hemoglobin, as far as the end of the A helix, has been replaced by the corresponding sequence of the gamma-chain of fetal hemoglobin with the remaining sequence of the beta-chain retained (helices B through H). The gamma-beta-chain had the correct mass, and its entire sequence was established by mass spectrometric analysis of its tryptic peptides; the alpha-chain also had the correct mass. This recombinant hemoglobin (named Hb Felix) retains cooperativity and has an oxygen affinity like that of HbA both in the presence and absence of the allosteric regulators, 2,3-diphosphoglycerate or chloride but differs from HbF in its 2,3-diphosphoglycerate response. However, Hb Felix has some features that resemble fetal hemoglobin, i.e. its significantly decreased tetramer-dimer dissociation and its circular dichroism spectrum, which measure the strength of the tetramer-dimer interface in the oxy conformation and its rearrangement to the deoxy conformation, respectively. Even though Hb Felix contains the HbA amino acids at its tetramer-dimer interface, which is located at a distance from the substitution sites, its interface properties resemble those of HbF. Therefore, the N-terminal sequence and not just those amino acids directly involved at the subunit interface contacts with alpha-chains must have a strong influence on this region of the molecule. The results reinforce the concept of fluid long range relationships among various parts of the hemoglobin tetramer (Dumoulin, A., Manning, L. R., Jenkins, W. T., Winslow, R. M., and Manning, J. M. (1997) J. Biol. Chem. 272, 31326-31332) and demonstrate the importance of the N-terminal sequence, especially in some mutant hemoglobins, in influencing its overall structure by affecting the relationship between helices.

Amino Acid Sequence↗
PubMed1998

Chimeric beta-EF3-alpha hemoglobin (Psi): energetics of subunit interaction and ligand binding.

Among the numerous strategies to design an oxygen carrier, we outline in this work the engineering of a stable homotetrameric hemoglobin, expressed in Escherichia coli. The chimeric globin (Psi) consists of the first 79 residues of human beta globin (corresponding to positions NA1 --> EF3) followed by the final 67 residues of human alpha globin (corresponding to positions EF3 --> HC3). The molecular mass for beta-EF3-alpha (Psi) globin was measured using mass spectrometry to be equal to its theoretical value: 15782 Da. Correct protein folding was assessed by UV/visible and fluorescence spectra. The subunit interaction free energies were estimated by HPLC gel filtration. In the cyanometHb species, the formation of the dimer-tetramer interface is 2 kcal/mol less favorable (Delta G = -7 kcal/mol) than that of Hb A (Delta G = -9 kcal/mol), whereas the dimer-monomer interface is tightly assembled (< -10 kcal/mol) as for the Hb A alpha 1 beta 1 interface. In contrast to Hb A, oxygen binding to Psi Hb is not cooperative. The free energy for binding four oxygen molecules to a Psi homotetramer is slightly increased compared to a Hb A heterotetramer (-28 and -27.5 kcal/4 mol of O2, respectively). The intrinsic O2 affinity of a Psi homodimer is 6-fold higher than that of a homotetramer. The linkage scheme between dimer-tetramer subunit assembly and the noncooperative oxygenation of Psi Hb predicts a stabilization of the tetramer after ligand release. This protein mechanism resembles that of Hb A for which the dimers exhibit a 100-fold higher O2 affinity relative to deoxy tetramers (which are 10(5) times more stable than oxy tetramers). A potent allosteric effector of Hb A, RSR4, binds to Psi Hb tetramers, inducing a decrease of the overall O2 affinity. Since RSR4 interacts specifically with two binding sites of deoxy Hb A, we propose that the chimeric tetramer folding is close to this native structure.

Allosteric Regulation↗
PubMed1998

Tetramer-dimer equilibrium of oxyhemoglobin mutants determined from auto-oxidation rates.

One of the main difficulties with blood substitutes based on hemoglobin (Hb) solutions is the auto-oxidation of the hemes, a problem aggravated by the dimerization of Hb tetramers. We have employed a method to study the oxyHb tetramer-dimer equilibrium based on the rate of auto-oxidation as a function of protein concentration. The 16-fold difference in dimer and tetramer auto-oxidation rates (in 20 mM phosphate buffer at pH 7.0, 37 degrees C) was exploited to determine the fraction dimer. The results show a transition of the auto-oxidation rate from low to high protein concentrations, allowing the determination of the tetramer-dimer dissociation coefficient K4,2 = [Dimer] 2/[Tetramer]. A 14-fold increase in K4,2 was observed for addition of 10 mM of the allosteric effector inositol hexaphosphate (IHP). Recombinant hemoglobins (rHb) were genetically engineered to obtain Hb with a lower oxygen affinity than native Hb (Hb A). The rHb alpha2beta2 [(C7) F41Y/(G4) N102Y] shows a fivefold increase in K4,2 at pH 7.0, 37 degrees C. An atmosphere of pure oxygen is necessary in this case to insure fully oxygenated Hb. When this condition is satisfied, this method provides an efficient technique to characterize both the tetramer-dimer equilibrium and the auto-oxidation rates of various oxyHb. For low oxygen affinity Hb equilibrated under air, the presence of deoxy subunits accelerates the auto-oxidation. Although a full analysis is complicated, the auto-oxidation studies for air equilibrated samples are more relevant to the development of a blood substitute based on Hb solutions. The double mutants, rHb alpha2beta2 [(C7) F41Y/(G4) N102A] and rHb alpha2beta2 [(C7) F41Y/(E10) K66T], show a lower oxygen affinity and a higher rate of oxidation than Hb A. Simulations of the auto-oxidation rate versus Hb concentration indicate that very high protein concentrations are required to observe the tetramer auto-oxidation rate. Because the dimers oxidize much more rapidly, even a small fraction dimer will influence the observed oxidation rate.

Adult↗
PubMed1998

[Treatment of deep venous thrombosis at home: evolution from ideas to medical practice].

The diagnosis of Deep Venous Thrombosis (DVT) by duplex ultrasound is absolutely possible out of specialized centers. Low Molecular Weight Heparins (LMWH) allow to obtain a greater efficacy and safety compared to Unfractionated Heparin (UFH). The control of LMWH is very reduced. Two studies have just been published on the topic of treatment of DVT at home. The group of patients treated at home with LMWH is not presenting more complications than the group of patients initially treated at the hospital with UFH. Nevertheless, these studies concern a very selective population of patients. Our center has been proceeding to a study for 4 years (1993-1997) in comparing the treatment at home of proximal DVT by LMWH then oral anticoagulant, to the initial treatment (10 days) in hospital by also using LMWH then oral anticoagulant. The first results show that there is no difference between both groups in terms of end-points: death, extension or recurrence of the thrombus, pulmonary embolism, bleeding. Therefore, the treatment of some type of proximal DVT is possible at home. Nevertheless, it is necessary to be very cautions as the population studied so far is a selected one. Etiologies of DVT are a constant obsessive fear. DVT or pulmonary embolism represents a real general disease which is going to progress along life. The intervention of a specialized center is always necessary. It is a work in team which must get the upper hand compared to an isolated medical action.

Adolescent↗