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M Hoebeke

Publications and source records attributed to M Hoebeke.

At least 19 recordsLinked to original sources
PubMed2006

Photochemistry of 2,6-diisopropylphenol (propofol).

The photochemistry of the anaesthetic agent propofol (PPF) was investigated in three different solvents of quite different polarity (cyclohexane, methanol and phosphate buffer pH 7) by means of nanosecond laser flash photolysis and absorption spectroscopy. GC-MS spectrometry measurements of PPF in cyclohexane have revealed the formation of two major products upon low intensity UV continuous irradiation of PPF in aerated solution: the diphenol derivative of PPF and 2,6-diisopropyl-p-benzoquinone (PPFQ). Only the diphenol compound was obtained in anaerobic solution. PPF phenoxyl radical (PPF ) generation has been assigned as the original step leading to the formation of both the diphenol compound and PPFQ in cyclohexane as revealed by laser flash photolysis at 266 nm and by electron paramagnetic resonance spectroscopy as well. Investigation of PPF by nanosecond flash photolysis at 266 nm in the other solvents revealed the occurrence of different photochemical processes depending on the nature and the polarity of the solvent. A reaction scheme is proposed in order to discuss the mechanism of reaction of PPF in all media.

Electron Spin Resonance Spectroscopy↗
PubMed2006

AGMIAL: implementing an annotation strategy for prokaryote genomes as a distributed system.

We have implemented a genome annotation system for prokaryotes called AGMIAL. Our approach embodies a number of key principles. First, expert manual annotators are seen as a critical component of the overall system; user interfaces were cyclically refined to satisfy their needs. Second, the overall process should be orchestrated in terms of a global annotation strategy; this facilitates coordination between a team of annotators and automatic data analysis. Third, the annotation strategy should allow progressive and incremental annotation from a time when only a few draft contigs are available, to when a final finished assembly is produced. The overall architecture employed is modular and extensible, being based on the W3 standard Web services framework. Specialized modules interact with two independent core modules that are used to annotate, respectively, genomic and protein sequences. AGMIAL is currently being used by several INRA laboratories to analyze genomes of bacteria relevant to the food-processing industry, and is distributed under an open source license.

Bacterial Proteins↗
PubMed2005

Reactivity towards singlet oxygen of propofol inside liposomes and neuronal cells.

Singlet oxygen (1O2), a reactive oxygen species, has been found to be implicated in many cellular events and pathological disorders. Herein, we investigated the reactivity of 1O2 towards the anaesthetic agent propofol (PPF) encapsulated within DMPC liposomes. By time resolved luminescence, the rate constant of 1O2 quenching by PPF was evaluated, depending on the location of the sensitizer, with following values: 1.35+/-0.05x10(7) M(-1) s(-1) for deuteroporphyrin (as embedded source) and 0.8+/-0.04x10(7) M(-1) s(-1) for uroporphyrin (as external source), respectively. The nature of the oxidation product, resulting from the reaction of 1O2 with PPF, was determined using absorption and HPLC techniques. Finally, the in vitro protective effect of PPF towards the 1O2-induced neuronal cell toxicity was evaluated in terms of cell viability.

Anesthetics, Intravenous↗
PubMed2003

[Diffuse retinal epitheliopathy: study of 30 eyes].

Retrospective study of 17 patients (30 eyes) with diffuse retinal epitheliopathy followed for at least 5 years. The study is based on clinical data, ophthalmoscopic findings and fluorescein angiograms. The patients (16 men and 1 woman) are all caucasian with a mean age of 43 years. The disease is bilateral in 13 patients. We report an association with systemic corticosteroid treatment after kidney transplantation in 10 cases. Nine patients have arterial hypertension. Two patients are diabetic and 2 present high level of psychological stress. After a mean follow-up of 12 years, a loss of vision of at least 3 lines is noted in 17 eyes. The decrease in vision is related to an enlargement of the pigment epithelium atrophy to the fovea (15 eyes) or with permanent retrofoveolar serous detachment (2 eyes).

Adrenal Cortex Hormones↗
PubMed2001

Increase of the photosensitizing efficiency of the Bacteriochlorin a by liposome-incorporation.

To describe the action mechanisms of Bacteriochlorin a (BCA), a second generation photosensitizer, in phosphate buffer (PB) and in dimyristoyl phosphatidylcholine (DMPC) liposomes we carried out oxygen consumption and ESR measurements. In PB, where BCA was in a monomer-dimer equilibrium, our results suggested that the oxygen consumption was related to the BCA monomers concentration in solution. Incorporation of BCA in DMPC liposomes, by promoting the monomerization of BCA, increased 9-fold the oxygen consumption in comparison to the value in PB. The use of specific singlet oxygen quenchers (Azide and 9,10-Anthracenedipropionic acid) in ESR and oxygen consumption experiments allowed us to assert that BCA was mainly a type II sensitizer when it was incorporated in DMPC. Finally, the cell survival of WiDr cells after a PDT treatment was measured for cells incubated with BCA in cell culture medium and cells incubated with BCA in DMPC. Irrespective of the dye concentration, the cell survival was lower when liposomes were used. This effect could be the result of a better BCA monomerization and/or a different BCA uptake in cells.

Buffers↗
PubMed2001

SPiD: a subtilis protein interaction database.

MOTIVATION: Protein-protein interactions are a potential source of valuable clues in determining the functional role of as yet uncharacterized gene products in metabolic pathways. Graph-like structures emerging from the accumulation of interaction data make it difficult to maintain a consistent and global overview by hand. Bioinformatics tools are needed to perform this graph visualization while maintaining a link to the experimental data. RESULTS: "SPiD" is an online database for exploring networks of interacting proteins in Bacillus subtilis characterized by the two-hybrid system. Graphical displays of interaction networks are created dynamically as users interactively navigate through these networks. Third party applications can interface the database through a Common Object Request Broker Architecture (CORBA) tier. AVAILABILITY: SPiD is available through its web site at http://www-mig.versailles.inra.fr/bdsi/SPiD, and through an Interoperable Object Reference (IOR) and its associated Interface Definition Language (IDL). CONTACT: hoebeke@versailles.inra.fr

Bacillus subtilis↗
PubMed1999

Fluorescence, absorption and electron spin resonance study of bacteriochlorin a incorporation into membrane models.

Analysis of the bacteriochlorin a absorption spectra suggests the existence of a monomer-dimer equilibrium, particularly intense in phosphate buffer and favored by a decrease of the pH. The dye in methanolic solution is predominantly in monomeric form. Fluorescence and electron spin resonance nitroxide spin labeling measurements indicate that incorporation into the lipid phase of dimyristoyl-L-alpha-phosphatidylcholine liposomes induces dye monomerization. Moreover, the molecules are bound in the external surface of the vesicles and a complete incorporation is ensured by a lipid-to-dye ratio greater than 125.

Dimerization↗
PubMed1998

Propofol reacts with peroxynitrite to form a phenoxyl radical: demonstration by electron spin resonance.

Peroxynitrite (ONOO-), resulting from the reaction of nitric oxide with superoxide anion, is a powerful oxidant produced in activated macrophages, during ischemia-reperfusion processes as well as in neurodegenerative disorders. This study investigated the reaction of the anesthetic agent propofol (PPF) with ONOO-, using electron spin resonance (ESR) and UV-visible spectrometry. Peroxynitrite was synthetized either from acidified hydrogen peroxide and nitrite, or from sodium azide and ozone. The addition of ONOO- to PPF in alkaline solution (pH 12) allowed to detect a, short lifetime, ESR signal corresponding to a phenoxyl radical. This finding was confirmed by a UV-visible study, resulting in the appearance of 427 nm peak and the disappearance of the peak located at 239 nm. The 291 nm peak remained unchanged. The identification of the end-product of the reaction of PPF with ONOO- needs further investigations.

Anesthetics↗
PubMed1998

The antibiotic ceftazidime is a singlet oxygen quencher as demonstrated by ultra-weak chemiluminescence and by inhibition of AAP consumption.

We demonstrated that the cephalosporin antibiotic ceftazidime (CAZ) deactivated singlet oxygen (1O2). We then studied the mechanisms of the CAZ effects on the ultra weak chemiluminescence (uwCL) associated with the energy decay of 1O2 generated by the Mallet reaction (H2O2 + HOCl --> HCl + H2O + 1O2), and on the anthracene-9,10-dipropionic acid (AAP) consumption by 1O2 generated by irradiation of Rose Bengal (RB). The uwCL generated by the Mallet reaction was amplified (6.2 times) by CAZ. The use of red and blue filters, which absorb radiation below 610 nm and between 470 and 700 nm respectively, demonstrated that CAZ increased the uwCL by a radiation emission at wavelengths shorter than the 633 and 704 nm wavelength emissions of 1O2. CAZ was excited by scavenging the energy excess of 1O2, which so returned to its fundamental state, while CAZ deactivated with light emission between 430-480 nm. CAZ also inhibited in a dose-dependent manner the consumption of AAP by 1O2 generated by the irradiation of RB. The protection of AAP by 5 x 10(-3) M CAZ was equivalent to that of 10(-3) M histidine and 3 X 10(-6) M sodium azide. This process of 1O2 deactivation will be useful in diseases characterized by an excessive PMN activation with a release of activated oxygen species.

Anthracenes↗
PubMed1997

Electron spin resonance evidence of the generation of superoxide anion, hydroxyl radical and singlet oxygen during the photohemolysis of human erythrocytes with bacteriochlorin a.

Photodynamic therapy with bacteriochlorin a (BCA) as sensitizer induces damage to red blood cells in vivo. To assess the extent of the contributuion of reactive oxygen species (ROS) and to determine a possible reaction mechanism, competition experiments with assorted ROS quenching or/and enhancing agents were performed in human erythrocytes as model system and in phosphate buffer. In the erythrocyte experiments, a 2% suspension was incubated with BCA for 1 h, washed with phosphate-buffered saline, resuspended and subsequently illuminated with a diode laser using a fluence rate of 2.65 mW/cm2. Potassium leakage and hemolysis were light and BCA dose dependent. Adding tryptophan (3.3 mM), azide (1 mM) or histidine (10 mM) to the erythrocyte suspension before illumination delayed the onset of K-leakage and hemolysis suggesting a type II mechanism. The D2O did not affect K-leakage nor photohemolysis. Adding mannitol (13.3 mM) or glycerol (300 nM) also caused a delay in the onset of K-leakage and hemolysis, suggesting the involvement of radicals. In phosphate buffer experiments, it was shown using electron spin resonance (ESR) associated with spin-trapping techniques that BCA is able to generate O2-. and OH. radicals without production of aqueous electron. Visible or UV irradiation of the dye in the presence of the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) gave an ESR spectrum characteristic of the DMPO-hydroxyl radical spin adduct DMPO-OH. Addition of ethanol or sodium formate produced supplementary hyperfine splittings due to the respective CH3CHOH. and CO2-. radical adducts, indicating the presence of free OH.. Production of DMPO-OH was partly inhibited by superoxide dismutase (SOD), catalase and desferrioxamine, suggesting that the iron-catalyzed decomposition of H2O2 was partly involved in the formation of one part of the observed OH.. The complementary inhibition of DMPO-OH production by azide and 9,10-anthracenedipropionic acid (ADPA) was consistent with 1O2 production by BCA followed by reaction of 1O2 with DMPO and decay of the intermediate complex to form DMPO-OH and free OH.. All our results seem to indicate that BCA is a 50%/50% type 1/type 2 sensitizer in buffered aqueous solutions and confirmed that the dye-induced hemolysis of erythrocytes was cell caused by a mixed type 1/type 2 mechanism.

Cyclic N-Oxides↗
PubMed1995

The importance of liposomes as models and tools in the understanding of photosensitization mechanisms.

The various applications of liposomes in understanding photosensitization are described in this paper, with particular emphasis on the various kinds of information that these models allow to obtain in phototherapy. Liposomes are simple vesicles in which an aqueous phase is enclosed by a phospholipidic membrane. They are suitable models mimicking specific situations occurring in vivo and they allow study of the influence of physicochemical, photobiological and biochemical factors on the uptake of photosensitizers by tissues, their mechanisms of action and the subsequent photoinduced tumor necrosis. Moreover, solubilization of the sensitizer into the bilayer seems to improve its tumoral selectivity and its photodynamic efficiency.

Animals↗
PubMed1995

Endonasal dacryocystorhinostomy: indications, technique and results.

Dacryocystorhinostomy (DCR) allows an obstructed lachrymal drainage system to be drained into the nasal fossa. Since the development of endonasal microsurgical techniques, the endonasal approach presents itself as an alternative choice to the conventional external approach. It is far less traumatic, yet as efficacious as the conventional approach, and avoids the need for a skin incision and the disruption of the medial canthal structures. Twenty-six patients suffering from lachrymal system obstruction underwent 28 endonasal dacryocystorhinostomies under microscopical (n = 25) or endoscopic control (n = 3). Pre-operative assessment included clinical symptoms (sac swelling, purulent secretions, epiphora) and outflow obstruction on X-rays (conventional dacryocystography and/or subtraction macrodacryocystography). Post-operatively, 23 DCR were free of symptoms. Two presented occasional epiphora and three were unsuccessful. The presence of pre-operative purulent secretions was significantly correlated with post-operative success and with lachrymal sac patency, which is also confirmed by X-ray examination (p<0.001). Thus in cases of purulent secretion with epiphora, X-ray examination is redundant and may be avoided. On the contrary, when epiphora is an isolated symptom, X-rays must be performed in order to determine where the obstruction is located and to provide information on lachrymal sac morphology.

Adolescent↗
PubMed1995

[Effect of local medications on intraocular pressure control following trabeculectomy].

Longterm administration of topical antiglaucoma therapies had been indicated to be a serious risk for failure of trabeculectomy through inducing a subclinical inflammation of conjunctival tissues and stimulating secondary fibroblastic proliferation. Our study had 3 main aims: (1) to check if this pejorative effect is present in our population of glaucomatous patients, (2) in order to improve the rate of surgical success in theoretically high risk patients (duration of topical treatment longer than 36 months), to determine the usefulness of the following actions: suppression of beta blocking agents 8 days before surgery, suppression of miotics and eventual topical administration of fluorometholone one month before surgery. (3) to correlate the observed clinical results to the cellular profile of preoperative conjunctival biopsies. We presented in a first step the results of a retrospective analysis including 88 trabeculectomies performed between January '93 and April '95 in 62 GCAO patients older than 40 years and without any previous ocular surgery. The mean age of patients was 66,8 years (41 to 87 years). Patients were classified into "complete success", "qualified success" and "failures" according to the "target" IOP was or was not reached in the last examination. Mean follow up was 5,8 months (1 to 26 months). The second prospective part of our study included 20 trabeculectomies performed in 16 patients we chose according to the nature, the duration of the preoperative topical therapy and the preoperative eventual preparation of the conjunctiva. This study also included a semiquantitative count of the different conjunctival cellular colonies in peroperative biopsies. Mean follow up of this study was 2,3 months (1 to 5 months). 31 "complete success", 52 "qualified success" and 5 "failure" were observed in the retrospective study. The reduction of IOP following trabeculectomy was statistically significant at all examinations (mean IOP in the last examination: 14,9 +/- 4,3 mmHg) but the level of success was not significantly different according to the nature, (mono against polytherapy), the duration of preoperative medical topical treatment, as well as the preoperative actions in order to improve the operative success in high risk patients. Preliminary results of our second prospective study did not yet show any failure and did not exhibit any clear correlation between the counts of the different cellular colonies and the level of operative success on one hand and the different topical therapies in the other hand. The results and limitations of this study were compared to those of the literature.

Adrenergic beta-Antagonists↗
PubMed1994

Quenching of merocyanine 540 triplet state by nitroxyl radicals in liposomal systems: a laser flash photolysis study.

Laser flash photolysis experiments were undertaken to investigate the interaction between stearic acid nitroxide spin probes and photoexcited merocyanine 540 (MC540) in dimyristoyl-L-alpha-phosphatidylcholine liposomes (membrane model). The measurements of the paramagnetic signal decay kinetics of four different spin-labelled stearic acids (n-DSA) show that the direct interaction between the dye and the probe is affected by the position of the nitroxyl group along the carbon chain. Laser flash photolysis results reveal a significant decrease in the MC540 triplet lifetime in the presence of n-DSA, the effect depending on the depth at which the nitroxyl moiety is localized in the bilayer. Previous results on the rate of disappearance of the electron spin resonance (ESR) nitroxide signal on continuous photolysis of the same systems do not show the same dependence on the localization of the nitroxyl moiety in the liposome. Although the MC540 triplet state seems to be implicated in the reaction process, the results suggest that ESR and laser flash experiments demonstrate two different kinds of mechanism.

Dimyristoylphosphatidylcholine↗
PubMed1993

Destruction of stearic acid nitroxyl radicals mediated by photoexcited merocyanine 540 in liposomal and micellar systems.

Fatty acid spin labels have been included into liposomes and micelles, in order to study the photochemical behavior of merocyanine 540 toward nitroxyl radicals situated at various depths in the bilayer or the surfactant layer. Visible illumination of the dye, either free in ethanol or bound to liposomes or micelles, leads to the reduction of the electron spin resonance signal of the label. The efficiency of the interaction between merocyanine 540 and spin labels depends on the depth at which the nitroxyl moiety is localized in the micelle or vesicle. Fluorescence measurements indicate that the first excited singlet state of merocyanine 540 is not directly implicated in the reaction mechanism. Flash photolysis experiments conducted in aqueous solutions of hexadecyltrimethylammonium bromide micelles show that the presence of nitroxyl radical decreases the rate constant of triplet decay in a concentration-dependent fashion. The corresponding quenching rate constant (kq) is determined for the different spin labels. The kq values and the reduction rates of ESR signal show the same dependence on the localization of the nitroxyl moiety in the micelles.

Cetrimonium↗