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Biomedical subjects

P Labbé

Publications and source records attributed to P Labbé.

15 recordsLinked to original sources
PubMed2006

Unraveling the spatial distribution of immunoglobulins, enzymes, and polyelectrolytes within layer-by-layer self-assembled multilayers. Ellipsometric studies.

The ellipsometric characterization of a layer-by-layer electrostatically self-assembled multilayer of polyphenol oxidase and alkaline phosphatase with the polycation poly(dimethyldiallylammonium chloride) built on an immunologic layer formed by immunoglobulin G (IgG) and glucose oxidase-conjugated anti-IgG (IgG-GOD) on glassy carbon is reported. The step-by-step evolution of the psi-Delta ellipsometric angles was followed during film growth. Two optical models, named the three-layer film model and reorganization film model, were employed and found suitable for ellipsometric data interpretation. A comparative analysis of film optical properties, film thickness, and ellipsometric mass assessed from both models is also presented.

Alkaline Phosphatase↗
PubMed2005

Multivalent ion/polyelectrolyte exchange processes in exponentially growing multilayers.

We show, in this paper that multivalent ferrocyanide anions can penetrate into exponentially growing (PGA/PAH)n multilayer films whatever the nature of the last deposited layer. These ions are not able to diffuse out of the film when it is brought in contact with a pure buffer solution. However, the contact of this film with a poly(allylamine) (PAH) or a poly(L-glutamic acid) (PGA) solution leads to the release of ferrocyanide ions from the multilayer. It is shown that the release of ferrocyanide anions, when the film is in contact with a PGA solution, is due to the diffusion of the PGA chains into the film so that an exchange between ferrocyanide ions and PGA chains takes place inside the film. On the other hand, PAH chains do not diffuse into PGA/PAH multilayers. When the film is then brought in contact with a PAH solution, the PAH chains from the solution are expected to strongly interact with the ferrocyanide ions and thus induce a diffusion mechanism of the multivalent anions out of the film, the film/solution interface playing the role of a sink for these ions. This work thus shows that interactions between multivalent ions and exponentially growing films are much more complex than expected at first sight and that polyelectrolyte multilayers must be seen as dynamic entities in which diffusion and exchange processes can take place.

Adsorption↗
PubMed2001

Phosphate tungsten bronze series: crystallographic and structural properties of low-dimensional conductors.

Phosphate tungsten bronzes have been shown to be conductors of low dimensionality. A review of the crystallographic and structural properties of this huge series of compounds is given here, corresponding to the present knowledge of the different X-ray studies and electron microscopy investigations. Three main families are described, monophosphate tungsten bronzes, Ax(PO2)4(WO3)2m, either with pentagonal tunnels (MPTBp) or with hexagonal tunnels (MPTBh), and diphosphate tungsten bronzes, Ax(P2O4)2(WO3)2m, mainly with hexagonal tunnels (DPTBh). The general aspect of these crystal structures may be described as a building of polyhedra sharing oxygen corners made of regular stacking of WO3-type slabs with a thickness function of m, joined by slices of tetrahedral PO4 phosphate or P2O7 diphosphate groups. The relations of the different slabs with respect to the basic perovskite structure are mentioned. The structural description is focused on the tilt phenomenon of the WO6 octahedra inside a slab of WO3-type. In this respect, a comparison with the different phases of the WO3 crystal structures is established. The various modes of tilting and the different possible connections between two adjacent WO3-type slabs involve a great variety of structures with different symmetries, as well as the existence of numerous twins in MPTBp's. Several phase transitions, with the appearance of diffuse scattering and modulation phenomena, were analysed by X-ray scattering measurements and through the temperature dependence of various physical properties for the MPTBp's. The role of the W displacements within the WO3-type slabs, in two modulated structures (m = 4 and m = 10), already solved, is discussed. Finally, the complexity of the structural aspects of DPTBh's is explained on the basis of the average structures which are the only ones solved.

Journal Article↗
PubMed2001

Amplification of amperometric biosensor responses by electrochemical substrate recycling. 3. Theoretical and experimental study of the phenol-polyphenol oxidase system immobilized in Laponite hydrogels and layer-by-layer self-assembled structures.

The amperometric response toward phenol of PPO-based rotating disk bioelectrodes is analyzed on the basis of a kinetic model taking into account internal and external mass transport effects and a CEC' electroenzymatic mechanism. Monophenolase activity of PPO catalyses the oxidation of phenol to o-quinone (step C). o-Quinone can then enter an amplification recycling process involving electrochemical reduction (step E) and enzymatic reoxidation (step C': catecholase activity). The rate-limiting steps such as monophenolase activity, catecholase recycling, permeability of the membrane, and activity and accessibility of the catalytic enzyme sites are theoretically considered and experimentally demonstrated for different electrode configurations including PPO immobilized in Laponite hydrogels and layer-by-layer self-assembled multilayers of PPO and poly(diallyldimethylammonium).

Biosensing Techniques↗
PubMed1999

Cluster configurations in modulated EuVxMo8+/-yO14 crystals.

Three orthorhombic crystals of chemical formula Eu(x)V(y)Mo(8+/-z)O(14) were investigated by X-ray diffraction (Mo Kalpha radiation, lambda = 0.71073 Å). They have nearly the same lattice parameters (a approximately 11.3, b approximately 10.0, c approximately 9.2 Å), display one-dimensional incommensurate modulations of wavevector q* = gammac* and are characterized by the same superspace group Cmca(00gamma)s00. The crystals differ both in their compositions (namely Eu(0.976(6))V(1.13(5))Mo(7.10(5))O(14), Eu(0.986(4))V(1.10(3))Mo(7.30(1))O(14) and EuMo(7.96(1))O(14)) and in their gamma components [0.195 (2), 0.245 (2) and 0.286 (3), respectively]. The average structures of these crystals appear closely related to the structures of LaMo(7.7)O(14) (not modulated) and LaMo(8)O(14) (modulated); however, two main differences are outlined: first, the modulation direction is c in the Eu-containing crystals but b in the modulated La-containing crystal [q* = (1/3)b*], second, the Eu-containing crystals have centrosymmetric structures while the La-containing crystals have polar structures (space group C2ca). The Mo (or Mo and V) atoms are stacked to form (001) layers of metallic clusters. The density modulation of these structures implies the existence of the new types of clusters Mo(9), Mo(10), Mo(6)V(4), Mo(7)V(3) and Mo(8)V(2) besides the clusters M(8) (Mo(8), Mo(6)V(2) and Mo(7)V) and M(7) (Mo(7) and Mo(6)V) which are already known. Mo(8) units with cis and trans configurations and Mo(6)V(2) units with a trans configuration appear as the main cluster types in these crystals. The nature of the metallic clusters changes along c, but inside one (001) layer it is likely that only one cluster type with a given configuration is present. The main structural result is the formation, in some unit cells, of strong intercluster Mo-Mo, Mo-V or V-V bonds with distances close to 2.6 Å within a layer as well as between two neighbouring layers.

Journal Article↗
PubMed1998

Functional responses of human neutrophils to sodium sulfite (Na2SO3) in vitro.

An influx of neutrophils into the airways is a common feature observed during pulmonary inflammation induced by air pollutants, including sulfur dioxide and sulfates. In the present study focusing on the in vitro interactions of sodium sulfite (Na2SO3) with human neutrophils, we confirm results indicating that this sulfite induces superoxide production (O2-) by itself. We demonstrated that this response can occur more rapidly than previously reported (within 5 min), and that Na2SO3 can act as a priming agent, in a concentration-dependent fashion, to the bacterial tripeptide N-formyl-methionine-leucine-phenylalanine (fMLP) by increasing O2-production. In addition, our results show that Na2SO3 induces gene expression in human neutrophils in a concentration-dependent manner as assessed by incorporation of 5-[3H] uridine into total RNA. However, it does not induce cell shape changes. We also demonstrated that Na2SO3 does not modulate neutrophil apoptosis nor reverse the well-known delaying effect of granulocyte-macrophage colony-stimulating factor (GM-CSF) on apoptosis. We conclude that Na2SO3 acts rapidly on neutrophil physiology, within a few minutes with respect to superoxide production, and a few hours (4 h) with respect to gene expression without altering a biological process such as the rate of apoptosis evaluated after a long period of incubation (20 h). We further conclude that Na2SO3-induced production of O2does not drive neutrophils to undergo apoptosis, a mechanism known to occur in other conditions. Therefore, the potential toxicity of Na2SO3 during pulmonary inflammation or lung-associated diseases may be related to its ability to induce superoxide production without altering neutrophil apoptosis rate.

Apoptosis↗
PubMed1997

Human coproporphyrinogen oxidase. Biochemical characterization of recombinant normal and R231W mutated enzymes expressed in E. coli as soluble, catalytically active homodimers.

To obtain recombinant human coproporphyrinogen oxidase (CPX), a cDNA for the coding region of mature human CPX has been expressed in E. coli. CPX was produced as a fusion protein with glutathione S-transferase followed by the hexapeptide recognition site for thrombin cleavage just preceding first amino acid of the CPX protein. The human CPX was found to be in the soluble fraction. This previously unobtainable human heme synthetic enzyme was purified to electrophoretic homogeneity with a specific activity of 4200 nmol/hr./mg of protein using a Glutathione Sepharose 4B column and gel filtration. Recombinant human CPX exhibits homogeneous behavior during high performance liquid chromatography (HPLC) and the N-terminal sequence, confirmed by protein sequencing, revealed a single polypeptide chain. In its active form, human CPX is a homodimer. According to the hydrodynamic properties derived from analytical ultracentrifugation, dimeric CPX has a nearly globular shape. Additionally, naturally occurring Arg to Trp (R231W)-mutated CPX has been also expressed in E. coli and further characterized. The mutated enzyme has a Km value of 0.55 microM as compared to 0.30 microM for the wild type. The catalytic efficiency (specificity constant, kcat/Km) of the mutated CPX was four fold lower than wild-type enzyme. The activity measurement of the mutated enzyme showed higher thermal sensitivity as compared with wild type CPX. The measured pI for mutated CPX is 5.65, compared to 6.40 for wild type. The pH optima for the mutated and wild-type protein are 6.6 and 6.8, respectively. The R231W mutation of CPX does not affect dimer formation and both normal and mutated CPX exhibit identical sedimentation properties. The thermal denaturation of both wild type and mutant CPX was found to be irreversible. The mutated CPX contained a significant amount of tightly bound porphyrin coproporphyrin. No metal association was found either in wild type or in mutated CPX. The availability of the recombinant human CPX will aid in structural and mechanistic studies.

Amino Acid Sequence↗
PubMed1995

Characterization of a novel human antibody xenoreactive with fibronectin.

Recent reports have used bovine fibronectin (Fn) as source of antigen to study human anti-Fn autoantibodies. We have characterized a novel human antibody (Ab) reactive with bovine and marsupial Fn, but not with human Fn. Indirect immunofluorescence, wet cleaving and protein adherence assays, immunoblotting, blot-affinity purification, a cell adhesion inhibition assay, and competitive experiments with synthetic peptides were used to characterize the anti-Fn Ab in serum from a patient with an undifferentiated connective tissue disease. A characteristic Fn-like network was observed by indirect immunofluorescence on bovine MDBK and marsupial PtK2 cells, but not on various human cell lines. Double immunofluorescence revealed colocalization of the Ab with a mouse monoclonal anti-Fn Ab. A reactive polypeptide of 240 kDa corresponding to the M(r) of Fn was identified by immunoblotting using MDBK and PtK2 total cell lysates. The Ab reacted with the 240-kDa band of purified bovine Fn with an endpoint titer of 1:64,000, while no reactivity was observed with human cellular or plasma Fn. Blot-affinity purification of the Ab from the 240-kDa PtK2 region confirmed that the Fn-like fluorescent pattern observed was due to reactivity with the 240-kDa band and not with other regions of the blot. The Ab affinity-purified from the 240-kDa region also reacted with purified bovine Fn by immunoblotting. Functional analysis disclosed specific inhibition of PtK2 and MDBK cell adhesion by the affinity-purified anti-Fn Ab. Competitive experiments with synthetic peptides demonstrated that the epitope is located in the decapeptide RGDSPASSKP containing the cell-binding domain of Fn. Longitudinal analysis of the Ab revealed its persistence over 6 years. Bovine and marsupial Fn can be the focus of a highly specific and persistent human immune response. Reactivity of a human Ab with bovine Fn does not imply cross-reactivity with human Fn. In light of recent reports using bovine Fn to characterize human anti-Fn "autoantibodies," future studies on human anti-Fn should specifically employ purified human Fn as antigen.

Adult↗
PubMed1993

[Rheumatoid polyarthritis in the elderly--rhizomelic pseudopolyarthritis: what differences?].

The authors have conducted a comparative retrospective study between polymyalgia rheumatic (N = 26) and rheumatoid arthritis in the elderly (N = 44), including HLA DRB1 genotype determination by PCR-RFLP analysis. No clinical nor biological differences were significant between the 2 groups of patients. However 70% of RA patients had one ore more susceptibility alleles (shared epitope hypothesis) and 50% in polymyalgia rheumatica.

Aged↗