Biomedical subjects

Philippe Dubois

Publications and source records attributed to Philippe Dubois.

24 records · Page 2Linked to original sources

PubMed2002

Reactive oxygen species (ROS) production by amoebocytes of Asterias rubens (Echinodermata).

An adapted peroxidase, luminol-enhanced chemiluminescence method in an EDTA-free, Ca++-containing medium is described and used to characterise reactive oxygen species (ROS) production by starfish immunocytes using a standard microplate reader luminometer. ROS production was stimulated by direct interaction of immunocytes with bacteria or bacterial wall components, but not by the soluble stimulant PMA nor the lectin concanavalin A. Produced ROS detected by this method are apparently superoxide anions, hydrogen peroxide and peroxynitrite. Comparison with other chemiluminescence methods indicates that the described method is the only one to detect the stimulation of starfish immunocytes by the Gram-positive bacteria, Micrococcus luteus, a fact that questions previous reports indicating a lack of stimulation by pathogens. The adapted method provides a rapid determination of the overall ROS production, which is suitable for both disease control and immunotoxicological studies in echinoderms.

Animals↗

PubMed2002

Local relapse in patients treated for squamous cell vulvar carcinoma: incidence and prognostic value.

To evaluate the risk factors for local relapse in vulvar cancer patients and its impact on survival as a function of its different patterns, which include local recurrences at the primary tumor site, recurrences remote from the primary tumor, and skin bridge recurrences. Between January 1978 and June 1999, 215 patients were treated for vulvar squamous cell carcinoma. The median follow-up was 38 months. To evaluate the role of local relapse in survival, a Cox regression multivariable analysis was performed using local relapse as a time-dependent covariate. The local relapse-free survival rate was 78.6% (+/- 7.1%) at 5 years. Multivariable analyses showed that the local relapse was increased by the factors margin status and depth of invasion. Pathologic nodal status, tumor size, margin status, and depth of invasion were predictors of cancer-related death in the Cox multivariable model with fixed covariates. The contribution of local relapse for disease-specific survival at the site of the primary tumor (relative risk [RR] 6.35; 95% confidence interval [CI] 2.07, 15.76) or skin bridge recurrence (RR 6.48; 95% CI 2.54, 16.49) was highly significant, whereas the contribution of local relapse at the other sites was not (RR 2.29; 95% CI 0.53, 9.91). In this model, margin status was not significant. The risk of cancer-related death after local relapse was 58.4% (+/- 18.3%) at 1 year and 70.9% (+/- 17.6%) at 3 years.Local relapses at the site of the primary tumor or skin bridge recurrences are strong predictors for cancer-related death, but not local relapse at a distant site.

Adult↗

PubMed2002

Differentiation of immune cells challenged by bacteria in the common European starfish, Asterias rubens (Echinodermata).

Amoebocytes are the main effector cells of the echinoderm immune system. In starfishes, a taxon in which bacterial diseases have been rarely reported, amoebocytes are considered to be the only circulating and immune cell type. The present paper addresses the question of amoebocyte differentiation in the starfish Asterias rubens when challenged by bacteria. Starfishes were injected with FITC-coupled bacteria (Micrococcus luteus). Amoebocytes were collected at regular time intervals for 24 h. The cytometric characteristics and the phagocytic activity were studied by flow cytometry. Three amoebocyte groups of different size were identified. The cell concentrations of the two largest and more numerous of these groups (G2 and G3) were modulated by immune stimulation while the group of smallest, less numerous, cells (G1) was unaffected. All of these cell groups were phagocytic but their kinetics of cell activation and bacteria ingestion differed. G1 cells showed the lowest phagocytic activity while G3 cells had the highest and fastest phagocytic activity. Starfish amoebocytes appear to be segregated in three groups, two of them (G2 and G3) being immunomodulated and one of them presenting a very fast reaction to bacteria. It is suggested that the high efficiency of the immune system in starfishes is related to this fast reaction.

Animals↗

PubMedDate not supplied

Impact of silicone-based block copolymer surfactants on the surface and bulk microscopic organization of a biodegradable polymer, poly(epsilon-caprolactone).

Two amphiphilic AB block copolymers, containing a highly compatible poly(epsilon-caprolactone) (PCL) block connected to a poly(dimethylsiloxane) (PDMS) block having a low surface energy, are synthesized and characterized in terms of their dispersion in a presynthesized PCL matrix. X-ray photoelectron spectroscopy, contact angle measurements, atomic force microscopy, and optical microscopy are used to describe the evolution of the surface chemical composition, as well as the surface and bulk morphology of the PCL/copolymer blends as a function of the nature and weight surface free energy and the dispersion of the copolymers in the blends, leading to important modifications of the bulk and the surface morphology. These differences are interpreted in terms of the impact of the block copolymers on the semicrystalline polymer structure and related properties in the prospect of using the surfactants to improve the synthesis of PCL in supercritical CO(2).

Biodegradation, Environmental↗

PubMedDate not supplied

Silylation reaction of dextran: effect of experimental conditions on silylation yield, regioselectivity, and chemical stability of silylated dextrans.

The controlled synthesis of biodegradable copolymers of dextran grafted with aliphatic polyesters first requires the preparation of polysaccharide derivatives soluble in organic solvents. Silylation of dextran can thus lead to such organosoluble derivatives and allows the polymerization of cyclic esters initiated from the nonsilylated OH functions. Silylation of dextran was studied in DMSO by different reactants such as 1,1,1,3,3,3-hexamethyldisilazane (HMDS) in the presence of various catalysts and N,O-bis(trimethylsilyl)acetamide (BSA). According to the silylating agent and the used experimental conditions, it was possible to obtain highly or totally silylated dextrans. In parallel, an investigation of the chemical stability of the dextran chain during silylation was performed. Thus, it was found that, when used at 50 degrees C, HMDS with or without catalysts gives a relatively high silylation yield and does not alter the dextran chain length, whereas at 80 degrees C, dextran degradation was observed. BSA is a very good silylating agent, which allows reaching 100% silylation even at 50 degrees C but provokes the degradation of the polysaccharide chains. The work was completed by a study of the reactivity order of the glucosidic OH functions toward silylation reaction. This order was found to be (OH(2) > OH(4) > OH(3)) as already reported for other reactions. 2D-NMR of highly silylated dextrans demonstrated that they are constituted of both quantitatively silylated glucose units and two types of disilylated ones.

Dextrans↗

PubMedDate not supplied

Production of starch foams by twin-screw extrusion: effect of maleated poly(butylene adipate-co-terephthalate) as a compatibilizer.

Free-radical-initiated grafting of maleic anhydride (MA) onto poly(butylene adipate-co-terephthalate) (PBAT), a biodegradable aliphatic-aromatic copolyester, was performed by reactive extrusion. 2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane was used as the free-radical initiator. The peroxide concentration was varied between 0.0 and 0.5 wt % at 3.0 wt % MA concentration; the MA concentration was varied between 1.0 and 5.0 wt % at 0.5 wt % peroxide concentration. The reaction temperature was maintained at 185 degrees C for all experiments. Under these conditions, between 0.194% and 0.691% MA was grafted onto the polyester backbone. Size-exclusion chromatography, melt flow index, intrinsic viscosity measurements, thermal gravimetric analysis, and differential scanning calorimetry were used to characterize the maleated copolyester. Increasing the initiator concentration at a constant MA concentration of 3% resulted in an increase in the grafting of MA while decreasing the molecular weight of the resulting polymer. Increasing the feed MA concentration also increased the grafting percentage. The maleation of the polyester proved to be very efficient in promoting strong interfacial adhesion with high amylose cornstarch in starch foams as prepared by melt blending. Thus, the use of maleated copolyester as a compatibilizer between starch and PBAT allowed the reduction of the density of resulting starch foams to approximately 21 kg/m3 and improved the resilience from 84% to as high as 95%. Also, the resulting starch foams exhibited improved hydrophobic properties in terms of lower weight gain and higher dimensional stability on moisture sorption.

Biodegradation, Environmental↗