PubMed Health⌕ Search

Biomedical subjects

P Poulet

Publications and source records attributed to P Poulet.

At least 19 recordsLinked to original sources
PubMed2000

Oxygen consumption through metabolism and photodynamic reactions in cells cultured on microbeads.

Oxygen consumption by cultured cells, through metabolism and photosensitization reactions, has been calculated theoretically. From this result, we have derived the partial oxygen pressure PO2 in the perfusion medium flowing across sensitized cultured cells during photodynamic experiments. The PO2 variations in the perfusate during light irradiation are related to the rate of oxygen consumption through photoreactions, and to the number of cells killed per mole of oxygen consumed through metabolic processes. After irradiation, the reduced metabolic oxygen consumption yields information on the cell death rate, and on the photodynamic cell killing efficiency. The aim of this paper is to present an experimental set-up and the corresponding theoretical model that allows us to control the photodynamic efficiency for a given cell-sensitizer pair, under well defined and controlled conditions of irradiation and oxygen supply. To demonstrate the usefulness of the methodology described, CHO cells cultured on microbeads were sensitized with pheophorbide a and irradiated with different light fluence rates. The results obtained, i.e. oxygen consumption of about 0.1 microM s(-1) m(-3) under a light fluence rate of 1 W m(-2), 10(5) cells killed per mole of oxygen consumed and a decay rate of about 1 h(-1) of living cells after irradiation, are in good agreement with the theoretical predictions and with previously published data.

Animals↗
PubMed1998

Magnetic resonance imaging of PLP-induced experimental allergic encephalomyelitis in Lewis rats.

An in vivo magnetic resonance (MR) imaging study was performed on experimental allergic encephalomyelitis (EAE) induced in Lewis rats through proteolipid protein (PLP). PLP was solubilized in water or in an aqueous solution of 1% 10-tridecyl ether (TDE), a non-ionic detergent used in membrane protein research. All 16 rats immunized with 500 microg of TDE-solubilized PLP developed clinical signs and MR abnormalities fully comparable to those observed in MBP-induced EAE. Total paraplegia was observed in 12.5% of rats, mild or moderate paraparesis in 68.8% of rats and tail paralysis in the remaining 18.7% of rats. Whereas only 37.5% of the eight rats immunized with 500 microg of water-solubilized PLP developed minor clinical signs (tail weakness or paralysis). Our observations confirm that the difficulties encountered when trying to induce EAE by means of PLP arise from the highly hydrophobic nature of this protein. Accordingly, if a reproducible model is to be developed, it seems more judicious to use non-ionic detergents in both the extraction and solubilization phases of PLP preparation, this would allow maximal solubilization of the protein while avoiding aggregates, which may otherwise form during either of the PLP preparation.

Animals↗
PubMed1996

Reduction of traumatic brain injury-induced cerebral oedema by a free radical scavenger.

Oxygen derived free radicals have been proposed to be in part responsible for the cerebral oedema resulting from head injury. In the present study the effects of free radical suppression with MDL 74,180 (2,3-dihydro-2,2,4,6,7-pentamethyl-3-(4-methylpiperazino)-methyl-1 - benzofuran-5-ol dihydrochloride), an alpha-tocopherol analogue free radical scavenger, on the development of cerebral oedema resulting from head injury has been assessed. Fluid percussion head injury in rats caused a regional oedema 48 h after injury. Infusion of MDL 74,180 for 2 h after the injury significantly attenuated oedema development in a dose-related manner. Using magnetic resonance imaging, cerebral oedema development was monitored in head injured mice. Oedema was apparent 4 h after head injury and was greatest in the vicinity of the olfactory bulb and surrounding the ventricles. Treatment with MDL 74,180 (1-10 micrograms/kg intravenously, administered 3-5 min after the injury) significantly reduced the oedema development. MDL 74,180 is a potential treatment for the oedema caused as a result of head injury.

Animals↗
PubMed1994

Local administration of 7 beta-hydroxycholesteryl-3-oleate inhibits growth of experimental rat C6 glioblastoma.

The effect of 7 beta-hydroxycholesteryl-3-oleate on rat brain C6 glioblastoma cells was studied. Three days after the inoculation of 2 x 10(5) C6 cells into the frontal cortex of 6-day-old Wistar rats, two types of liposomes [consisting of either phosphatidylcholine and monosialoganglioside (PG:GM1, 10:1 mol/mol) only, or containing 7 beta-hydroxycholesterol, 7 beta-hydroxycholesteryl-3-oleate, 7 alpha-hydroxycholesteryl-3-oleate, or 7-ketocholesteryl-3-oleate] were injected into the xenograft. Ten days later, the animals were sacrificed, the tumors were stained with cresyl violet or hematoxylin/eosin, their volumes determined by image analysis, and their development followed by magnetic resonance imaging. The mean (+/- SE) tumor volume was 4.4 +/- 1.0 mm3. The injection of liposomes without oxysterol had no effect on tumor growth, whereas injection of liposomes containing 7 beta-hydroxycholesteryl-3-oleate (36 nmol) gave rise to a marked decrease in tumor volume (from 4.4 +/- 1.0 to 0.7 +/- 0.4 mm3). Seven nmol had no effect on tumor growth, 72 nmol were as efficient as 36 nmol, and 144 nmol attenuated the tumor volume by 50% only. Liposomes containing 72 nmol of oleic acid enhanced the tumor volume 4-fold. These findings were confirmed by magnetic resonance imaging. Thus, following induction of tumors in both the right and left sides of the cortex and treatment of the right side, magnetic resonance imaging indicated a significant decrease in tumor volume on the right side only. When C6 cells and 7 beta-hydroxycholesteryl-3-oleate were simultaneously injected, tumors did not develop in 80% of the animals. The clearance of [3H]7 beta-hydroxycholesteryl-3-oleate, of which 75% was converted to cholesterol, reached 99% after 48 h. Other oxysterols did not affect the tumor volume except that 7-keto-cholesteryl-3-oleate decreased the tumor volume by 50%. Thus, the 3-fatty acyl ester and 7 beta-hydroxyl groups are apparently required for the antitumor growth effect. Taken together, these data suggest that 7 beta-hydroxycholesteryl-3-oleate might be useful for local glioblastoma chemotherapy.

Administration, Topical↗
PubMed1994

Localized T2 measurements using an OSIRIS-CPMG method. Application to measurements of blood oxygenation and transverse relaxation free of diffusion effect.

This work presents a new method allowing localized T2 measurements, based upon the OSIRIS scheme. A train of 180 degrees pulses is applied after the OSIRIS preparation cycle, recording directly the transverse magnetization decay. The method was verified for two nuclei, 1H and 19F, with phantoms and in vivo on rats. The accuracy of the T2 values is discussed, as well as possible applications of the OSIRIS-CPMG method to proton transverse spin relaxation measurements, free of diffusion effects, and to non-invasive in vivo blood oxygenation measurements, through the use of an emulsion of perfluorooctylbromide, a blood substitute containing fluorine.

Animals↗
PubMed1994

Hyperbaric oxygen treatment in acute experimental allergic encephalomyelitis. Contribution of magnetic resonance imaging study.

Magnetic resonance imaging (MRI) has been performed to determine the efficacy of hyperbaric oxygen treatment (HBO) on experimental allergic encephalomyelitis (EAE) in Lewis rats. The animals were exposed for 2 x 3 h in a 24-h period at 2 ATA pure O2. Three HBO treatment protocols were used: a 10-day preventive treatment (beginning on the 1st day postimmunization), a 3-day preventive treatment (beginning on the 1st day postimmunization), and a 10-day symptomatic treatment (beginning on the 11th day postimmunization). Based on clinical and MRI observations, this study demonstrates: (i) that HBO treatment does not reduce the blood-brain barrier (BBB) disturbance and cerebral edema in EAE, (ii) that in an opposite way, it provokes reversible BBB breakdown, and (iii) that preventive HBO treatments results in modification of the course of EAE, possibly by immunosuppression effect during the initial sensitization step.

Animals↗
PubMed1994

Magnetic resonance imaging of antibody-mediated demyelinating experimental allergic encephalomyelitis.

Two models of demyelinating experimental allergic encephalomyelitis (EAE) were studied on Lewis rats in whom the disease was induced by injections of either (i) lentil-lectin binding myelin glycoproteins plus myelin basic protein (MBP)-specific T cells (36 rats), or (ii) myelin/oligodendrocyte glycoprotein-specific monoclonal antibody plus MBP-specific T cells (16 rats). In our 24 control rats, 20 received MBP-specific T cells only, and four received myelin glycoproteins plus purified protein derivative-specific T cells. The extent of the resulting blood-brain barrier (BBB) permeability, vasogenic oedema and/or demyelination was assessed in vivo using magnetic resonance imaging (MRI) techniques. The results show that in both demyelinating EAE models the disease appeared more quickly, progressed very rapidly and was more severe than when induced with a similar number of MBP-specific T cells alone. Almost all animals developed hyperacute EAE, with a very high mortality rate. MRI showed a very intense BBB breakdown and vasogenic oedema in all the normally 'leaky' areas of the central nervous system, and focal lesions corresponding to plaque formation in the brain stem or spinal cord near the 'leaky' areas. During the 40-day observation period, the rare survivors of this hyperacute form of EAE presented a chronic form of EAE with serious sequelae. Our results demonstrate that the synergistic effect observed between MBP-specific T cells and antibodies to myelin glycoproteins, especially to myelin/oligodendrocyte glycoprotein, does not only induce demyelinating lesions and chronic clinical signs, but is further responsible, via the normally 'leaky areas', for the fatal increase of the BBB breakdown and vasogenic oedema of which there are ample acute clinical signs.

Animals↗
PubMed1994

The role of Mycobacterium tuberculosis in experimental allergic encephalomyelitis.

Various detergents used in preparative membrane protein chemistry were added to a complete Freund's adjuvant/water emulsion in order to increase the solubility and/or immunologic availability of the Mycobacterium tuberculosis membrane and to explain its role in blood-brain barrier (BBB) permeability. Magnetic resonance imaging was used for in vivo determination of the BBB breakdown and cerebral edema. The results showed that with 1% 10 tridecyl ether, which increases emulsion stability, abundant BBB breakdown and cerebral edema were observed, similar to those encountered in experimental allergic encephalomyelitis (EAE). We suggest that the immunologic response triggered off by M. tuberculosis largely contributes to the BBB permeability changes observed during EAE, probably by an action on the endothelial cells of the cerebral blood vessels.

Animals↗
PubMed1993

Photoacoustic detection of photosensitized oxygenations in highly absorbing samples.

A photoacoustic (PA) study of the relaxation processes of the excited states of photosensitizers in the presence of oxygen and chemical acceptors is described. It has been predicted theoretically that the ratio of PA amplitudes with and without acceptor depends on two parameters alpha and beta, related to the sensitizer and to the acceptor properties, respectively. Experimental studies were carried out on solutions of hematoporphyrin IX and methylene blue. The addition of an acceptor, specific to the singlet oxygen, like tetramethyl ethylene or furfuryl alcohol, appears to decrease significantly the photoacoustic signal amplitude within the band of absorption.

Hematoporphyrins↗
PubMed1993

Blood-brain barrier breakdown in MBP-specific T cell induced experimental allergic encephalomyelitis. A quantitative in vivo MRI study.

Blood--brain barrier permeability in myelin basic protein (MBP)-specific T cell induced experimental allergic encephalomyelitis (EAE) was studied by magnetic resonance imaging (MRI) in Lewis rats. Myelin basic protein-specific T cells of different specificity and/or purified protein derivative (PPD)-specific T cells were used. During the course of EAE, the volume of the lesions and the T1 and T2 relaxation times were recorded and evaluated with respect to the clinical signs. The results showed that the severity of abnormalities seen on MRI, corresponding to the blood--brain barrier breakdown and cerebral oedema depended on the following two factors: (i) the specificity of the MBP-specific T cells used; (ii) the number of MBP-specific T cells transferred. It was also shown that the more specific the cells were, the less severe the cerebral blood--brain barrier rupture. Moreover, the blood--brain barrier breakdown increased when the number of cells increased. Our results demonstrated that a synergy exists between MBP and PPD-specific T cells which seems to result in an increase in central nervous system inflammation. This helps to explain the role of Mycobacterium tuberculosis in the induction of EAE.

Animals↗
PubMed1992

In vivo dynamic MR imaging of MBP-induced acute experimental allergic encephalomyelitis in Lewis rat.

A dynamic in vivo study by MRI consisting of the measurement of relaxation times and in the visualization of the BBB permeability by Gd-DOTA was performed in an MBP-induced acute EAE model of Lewis rat. Fourteen rats were immunized with an MBP/CFA mixture, eight by CFA alone, and three control rats were used to test the harmless effect of repeatedly performed MRI examinations. Beginning on the 8th or 9th days and in parallel with the emergence of clinical signs, rats immunized by the MBP/CFA mixture showed slight increases of relaxation times and of the BBB permeability. These abnormalities, which always remain localized in the periventricular regions, become more pronounced toward the 10th and 11th days, just before (or at the same time) as paraplegia manifestations. After a plateau of a few days, they diminish with the clinical signs. This close correlation found in vivo establishes the essential role of BBB in the pathogenesis of clinical signs of this EAE model.

Animals↗
PubMed1992

Photoacoustic detection of triplet state and singlet oxygen in highly absorbing samples.

A photoacoustic (PA) effect theory taking into account two heat sources corresponding to the radiationless relaxation processes of two states of different lifetimes and to the heat diffusion across the sample is herewith presented. Results obtained demonstrate that the amplitude and the phase of the PA signal depend on the sample's thermal properties, on its optical absorption coefficient, on the lifetime of the long-lived excited state, and on the ratio of the two heat sources. This ratio can be expressed as a function of the product of the energy of the excited state times the quantum yield of its production. Simulations of PA amplitude and phase variations vs light modulation frequency exhibit new features of the PA signal:phase inversion and fast decrease of the amplitude. Experimental verifications were carried out on solutions and gels. Fitting of the amplitude and phase variations allow us to measure the lifetime and conversion yield of the intermediate state which can be a triplet state or singlet oxygen, O2(1 delta g). The addition of an acceptor, specific to O2(1 delta g), induces changes in the amplitude of the PA signal which can be used to study the production and deactivation of this excited form of oxygen. This work demonstrates the usefulness of PA in the detection of metastable excited states such as the triplet state and singlet oxygen and in their quantitative analysis.

Coloring Agents↗
PubMed1986

Chemical and molecular exchange effects on T2 relaxation of living tissues: a pulse spacing dependence study.

Contrast in magnetic resonance imaging depends principally on the longitudinal relaxation (R1) and the transverse relaxation rate (R2) of the observed nuclei, most often the protons. The spin-spin relaxation rate (R2) is the result of several mechanisms. The dependence of the interpulse delay of the Carr-Purcell-Meiboom-Gill sequence on the transverse relaxation rate of the water was studied in rat organs in vitro. It gives an insight into the exchange mechanisms involved. The increase of the interpulse delay from 0.2 ms to 5 ms gives an R2 increase of 23, 15, 3, and 2 s-1 for the heart, the liver, the spleen and the brain, respectively. These increases are compared to the R2 increases obtained in 17O-enriched water, amino acid and albumin solutions atomic exchange takes place. The concentration of these materials in organs cannot explain the R2 increase of the organs with the interpulse delay. Water exchange between intra and extracellular compartments is proposed to explain the R2 increase with interpulse delays in organs like the heart and the liver.

Albumins↗
PubMed1979

Erythrocyte copper levels in children with trisomy 21.

Erythrocyte superoxide dismutase is a cuproprotein displaying increased activity in cases of trisomy 21. In this study, the three erythrocyte copper fractions were compared at constant serum copper levels in children with and without trisomy 21. The labile erythrocyte copper level was found to be identical in both groups of children. Total erythrocyte copper, especially the stable fraction, was increased in cases of trisomy 21. The approximately fifty per cent ob served increase correlates with the augmented superoxide dismutase activity related to the presence of an extra chromosome 21. Measurement of the stable erythrocyte copper fraction could constitute an indirect method for evaluating superoxide dismutase activity.

Child↗