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M L Viriot

Publications and source records attributed to M L Viriot.

13 recordsLinked to original sources
PubMed2006

Fate of coagulant species and conformational effects during the aggregation of a model of a humic substance with Al13 polycations.

A model of a humic substance (MHS) obtained from auto-oxidation of catechol and glycine, was aggregated at pH 6 and 8 with Al(13) polycations. The fate of Al(13) coagulant species upon association with MHS functional groups was studied using solid state (27)Al Magic-angle spinning (MAS) NMR and CP-MAS (13)C NMR. Electrophoretic measurements and steady-state fluorescence spectroscopy with pyrene as a fluoroprobe, were combined to investigate structural re-organization of humic material with aluminum concentration. MAS (27)Al NMR revealed that the coagulant species are Al(13) polycations or oligomers of Al(13) units at both pHs. CP MAS (13)C spectra indicated that, at low Al concentration, hydrolyzed aluminum species bind selectively to carboxylic groups at pH 6 and to phenolic moieties at pH 8. At higher coagulant concentrations, the remaining functional groups also interact with hydrolyzed Al to yield similar CP MAS (13)C spectra in the optimum concentration range. Negative values of electrophoretic mobility were obtained at optimum coagulant concentrations even though an overall charge balance was achieved between MHS anionic charge and Al(13) cationic charge at pH 6. The polarity-sensitive fluorescence of pyrene revealed that the interaction of Al(13) coagulant species with MHS functional groups induces the formation of intramolecular hydrophobic microenvironments. Such structural changes were reversed upon further addition of Al(13) polycations.

Aluminum Compounds↗
PubMed2003

Coumarin-like fluorescent molecular rotors for bioactive polymers probing.

Polysaccharides are interesting and often essential macromolecules but are difficult to analyse due to their lack of convenient chromophores. We propose an efficient labelling procedure for polysaccharides such as functionalized dextrans with coumarin derivatives: the fluorescent tracers present inter alia properties of emission of fluorescence dependent on the molecular environment (polarity, viscosity, temperature, pH, etc.). Hence, with in mind the understanding of cell-polysaccharide interactions, the labelled polymers were studied by in vitro tests on a line of endothelial cells sensitive to the proliferative effect of these dextran polysaccharides. Using 3D fluorescence microscopy, the fixation and internalization of fluorescent functionalized dextrans were observed in endothelial cells.

Cell Division↗
PubMed2003

New glycosylated porphyrins for PDT applications.

A good sensitizer for photodynamic therapy (PDT) should be a very selective reagent, which should fastly eliminate from healthy tissues. Furthermore it should have a strong absorption in the red light and good energy transfer properties to molecular oxygen to produce singlet oxygen. All these specifications imply that many second generation photosensitizers (porphyrins, chlorins, bacteriochlorins...) have been modified in order to improve their properties, but however, few have received the approval by regulatory authorities. One way to increase the selectivity of a photosensitizer is coupling it to a vector. Carbohydrate-bound porphyrins were found to be of great interest because of the specific affinity of particular carbohydrates for some tumour cells, the increasing of plasmatic life time and solubility. In this study, we report the synthesis and the photophysical properties (absorption, fluorescence, singlet oxygen formation) of new glycosylated porphyrins. Then, in vitro photocytotoxic properties were evaluated on the human colon adenocarcinoma cell line HT29.

Computer Graphics↗
PubMed1999

Membrane fluidity and oxygen diffusion in cholesterol-enriched endothelial cells.

In this study, we measured the influence of cholesterol rigidification on oxygen permeability in human endothelial cell monolayer membranes (ECs). Cholesterol-induced membrane rigidification was assessed at different membrane depths by a fluorescence polarization method with diphenyl-hexatriene (DPH) and 1-(4-trimethylamino)-6-phenylhexatriene (TMA-DPH). Fluorescence quenching by oxygen was probed in preferentially labelled membrane with pyrene butyric acid (PyC4) and pyrene dodecanoic acid (PyC12), as shown with a 3D fluorescence microscope (CellScan System). With both probes the experiments revealed a decrease in oxygen diffusion as the cholesterol concentration increased in the medium culture (from 3.42 microM to 17.11 microM). We showed that very low concentrations of cholesterol (about 1000 times below normal value, 6.2 mM) particularly decrease oxygen levels or diffusion rate in the middle region of the membrane. In conclusion, these findings prove in a direct manner that cholesterol significantly affect the endothelial barrier function and molecular oxygen transfer to underlying tissues. Risk factors (cholesterol) directly would contribute to tissue ischemia.

Biological Transport↗
PubMed1998

Molecular rotors as fluorescent probes for biological studies.

Molecular rotors, which structure can be 4-(N,N-dimethylamino)-benzene, -benzylidene and -cinnamylidene derivatives and, also, coumarine-like compounds, have photophysical characteristics which strongly depend on the environmental parameters (polarity, viscosity, temperature, etc.). In this paper, a basic knowledge on molecular fluorescent rotors will be reminded and two fields of applications using molecular fluorescent rotors as optical sensors will be described: firstly, in polymer and, more particularly to detect the formation of hydrophobic microdomains, in the case of the aggregation of amphiphilic polymers (as models for globular proteins and/or enzymes) and, secondly, in cell biology, especially in liposomes (as models for biological membranes) to follow their thermotropic behavior and in endothelial cells under 3D fluorescence microscopy.

Fluorescent Dyes↗
PubMed1997

Membrane fluidity and oxygen diffusion in cholesterol-enriched erythrocyte membrane.

This work studied the effect of cholesteryl hemisuccinate incorporation on membrane fluidity and on the kinetics of oxygen diffusion at different depths in the erythrocyte membrane. Cholesterol concentration in the membrane was expressed as the cholesterol-protein ratio (C/Pt). The membrane fluidity, as assessed by a fluorescence polarization method with diphenyl-hexatriene and 1-(4-trimethylamino)-6-phenylhexa-1,3,5-triene, decreased as the C/Pt ratio increased. Time-resolved fluorescence spectroscopy of pyrene dodecanoic acid (PDA) under an increasing C/Pt ratio in the erythrocyte membrane revealed enhanced oxygen diffusion in the middle of the membrane bilayer (in which PDA was incorporated), which was not the case with pyrene butyric acid (PBA) incorporated in the internal part of the membrane surface. It has generally been accepted that increased membrane fluidity reduces the physical barrier to oxygen permeation. Such conflicting observations on oxygen permeation in the rigidified erythrocyte membrane could be due to variations in oxygen solubility (preferential partitioning) in different polarity microdomains (cholesterol and phospholipid partitions).

Cholesterol↗
PubMed1990

Differential action of thyroid hormones and chemically related compounds on the activity of UDP-glucuronosyltransferases and cytochrome P-450 isozymes in rat liver.

The effect of thyroid hormones and chemically related compounds, on the activity of UDP-glucuronosyltransferases (EC 2.4.1.17) and cytochrome P-450-dependent monooxygenases in rat liver microsomes was investigated. The animals were thyroidectomized and treated with different doses of the drugs for 3 weeks. Opposite effects were observed depending on the isoenzyme of UDP-glucuronosyltransferase considered. While 3,3',5-triiodo-L-thyronine, 3,3',5-triiodothyroacetic acid, 3,3',5-triiodothyropropionic acid, isopropyldiiodothyronine and L- and D-thyroxine strongly increased 4-nitrophenol glucuronidation in a dose-dependent fashion, they decreased markedly bilirubin glucuronidation. However, the activity toward nopol, a monoterpenoid alcohol, was not significantly changed regardless of which compound or dose was used. Variation of UDP-glucuronosyltransferase observed with 4-nitrophenol and bilirubin was related to the thyromimetic effect of the drugs estimated from the increase in alpha-glycerophosphate dehydrogenase. Thyronine and 3,5-diiodo-L-tyrosine, which did not enhance this activity, also failed to affect glucuronidation. Variations in UDP-glucuronosyltransferase activity were more likely due to changes in protein expression rather than changes in enzyme latency, since lipid organization of the microsomal membrane, as estimated from the mean anisotropy of 1,6-diphenyl-1,3,5-hexatriene by fluorescence polarization was not significantly modified by the drug administration. Although some of the drugs could significantly decrease the triacylglycerol and cholesterol contents in plasma, all failed to affect lauric acid hydroxylation. The activities of catalase, palmitoyl-CoA dehydrogenase (CN- insensitive) and carnitine acetyltransferase in the fraction enriched in peroxisomes were also not significantly affected by treatment with the thyroid hormone LT3. In contrast, the activity of 7-ethoxycoumarine O-deethylase was increased by large doses of thyronine and by 3,3',5-triiodothyropropionic acid. The concentration of total cytochrome P-450 was decreased in a dose-dependent fashion by all the compounds used, except thyronine. Finally, significant correlations were observed between glucuronidation of bilirubin and 4-nitrophenol and the content in cytochrome P-450. This suggests a possible coordinate regulation of the two processes, which depends on the physicochemical characteristics of the thyroid hormones and related compounds.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1984

Interests and limits of continuous excitation photo-physical methods applied to cellular rheology.

It is possible to characterize the cohesion of the lipidic zones in cells or in membranes by using molecular emission spectroscopy techniques such as : fluorescence polarization, quenching reactions, intramolecular reactions. However, applying these techniques in biology can be improved by the use of pulsed excitations leading to the time-resolved evolutions of some properties of the probe, which can themselves be a function of their environment. The first and the last techniques, based on the use of diphenylhexatriene and dipyrenylpropane respectively are used in practice by steady state excitation. In the case of fluorescence polarization, it can be shown that the method can be applied, within certain limits, which have to be precised when studying the modifications in the membranes. This is also partly true for methods based on the use of intramolecular reactions. However these continuous excitation techniques usually only lead to a global result which is a function of several spectroscopic parameters and of the "cohesion" of the membrane. Then it can be shown that to go beyond this step of semi-quantitative analysis, it is necessary to use pulsed or modulated excitation methods. Moreover this more sophisticated technical approach implies a new theoretical effort to understand the molecular dynamics of the membranes.

Animals↗
PubMed1984

Investigation of human blood platelets with fluorescence spectroscopy.

Intramolecular excimer formation of dipyrenylpropane was investigated in human blood platelets. The ratio of the emission intensities of excimer to monomer (IE/IM) is sensitive to changes in lipidic membrane structure, induced by external perturbations, such as cholesteryl hemisuccinate introduction and temperature. Lack of reliable "microviscosities" determinations could be due to poor solubility of the probe in aqueous cells suspensions. Results were compared to those obtained with the fluorescence polarization technique.

Blood Platelets↗
PubMed1983

Pressure effects on the apparent viscosity of artificial dipalmitoylphosphatidylcholine and dimyristoylphosphatidylcholine membranes using intramolecular excimer probe.

Emission spectroscopy of intramolecular excimer probes allows the determination of 'equivalent viscosity' of membranes. While increasing the pressure on artificial membrane suspensions, variations in viscosity - essentially related to an increase in the order parameter in the membranes - are observed. In the case of mixed phospholipids, the effect of pressure is amplified, probably due to the existence of holes on the molecular scale between the two lipidic layers.

Dimyristoylphosphatidylcholine↗
PubMedDate not supplied

Spectrofluorimetric methods for the measurement of the so called "microviscosity" of lipidic structures.

The cellular interactions involving the membrane depend on its physico-chemical nature and on the topographical distribution of the membrane receptors. At present, the role of the lipidic regions is not well defined; however, it is known than the fluidity or "microviscosity" of the lipidic components controls important processes in cellular biology. Different spectrofluorimetric methods, continuous or time resolved, susceptible to the cohesion of lipidic regions have been developed: 1. The anisotropy of fluorescence where the rotation of probes is studied (linked to the coefficient of diffusional rotation). 2. The inhibition of fluorescence where the kinetics of the reaction is practically diffusion controlled. 3. The formation of emissive intramolecular complexes where the internal rotations of interchromophoric bonds are studied. After the development of kinetic models, the methods have been tested with synthetic and natural organized assemblies. The values of "microviscosity" obtained with these methods may be different because the environments of probes are different. Therefore, the concept of "microviscosity", applied to biological membranes is limited.

Chemical Phenomena↗
PubMedDate not supplied

Effect of glutaraldehyde on hemoglobin-dependent quenching of pyrene fluorescence. Application to oxygen diffusion in erythrocyte.

In the present study, we investigate the effect of glutaraldehyde incorporation on the erythrocyte deformability, membrane fluidity and process of molecular oxygen diffusion. The erythrocyte deformability variations were inversely related with the glutaraldehyde concentration incorporated. The membrane fluidity, as assessed by a method based on the kinetics of pyrene dodecanoic acid excimers formation, decreased as the glutaraldehyde concentration increased. So, we verified that glutaraldehyde incorporation was accompanied by membrane rigidification. In the presence of glutaraldehyde, decreased absorption of hemoglobin heme group (420 nm) and decreased hemoglobin-dependent quenching of pyrene butyric acid (PBA) fluorescence would result from hemoglobin polymerization. Using a technique of fluorescence intensity quenching by molecular oxygen (accessibility to oxygen), we showed that oxygen diffusion was decreased in the presence of glutaraldehyde. To conclude, membrane rigidification induced by glutaraldehyde incorporation would affect oxygen molecular process.

Butyrates↗