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Biomedical subjects

P Hubert

Publications and source records attributed to P Hubert.

At least 19 recordsLinked to original sources
PubMed1999

Elimination of adsorption effects in the analysis of water-soluble vitamins in pharmaceutical formulations by capillary electrophoresis.

A tendency to an increase in migration times was observed when different water-soluble vitamins were analysed repeatedly in pharmaceutical preparations by capillary electrophoresis. In order to better understand the origin of this effect, the influence of the vitamins and the excipients, such as cellulose derivatives, was investigated. These studies indicated that the increase in analyte migration times was most probably due to the adsorption of different kinds of constituents to the capillary wall. Different rinsing procedures were tested in order to eliminate these unfavourable effects. A rinse of the capillary with a 25 mM sodium dodecyl sulfate (SDS) solution in the running buffer between successive runs was found to be particularly effective when the analysis was performed by free solution capillary zone electrophoresis (CZE). When the vitamins were determined by micellar electrokinetic chromatography (MEKC) using SDS as surfactant, a short capillary rinse with the running buffer was sufficient to obtain reproducible migration times. The CZE and MEKC methods developed were validated and compared. Both methods could be applied to the determination of water-soluble vitamins in different multivitamin formulations.

Chemistry, Pharmaceutical↗
PubMed1999

Riluzole series. Synthesis and in vivo "antiglutamate" activity of 6-substituted-2-benzothiazolamines and 3-substituted-2-imino-benzothiazolines.

Two series of analogues of riluzole, a blocker of excitatory amino acid mediated neurotransmission, have been synthesized: monosubstituted 2-benzothiazolamines and 3-substituted derivatives. Of all the compounds prepared in the first series, only 2-benzothiazolamines bearing alkyl, polyfluoroalkyl, or polyfluoroalkoxy substituents in the 6-position showed potent anticonvulsant activity against administration of glutamic acid in rats. The most active compounds displaying in vivo "antiglutamate" activity were the 6-OCF(3) (riluzole), 6-OCF(2)CF(3), 6-CF(3), and 6-CF(2)CF(3) substituted derivatives with ED(50) values between 2.5 and 3.2 mg/kg i.p. Among the second series of variously substituted benzothiazolines, compounds as active as riluzole or up to 3 times more potent were identified in two series: benzothiazolines bearing a beta-dialkylaminoethyl moiety and compounds with an alkylthioalkyl chain and their corresponding sulfoxides and sulfones. The most potent derivatives were 2-imino-3-(2-methylthio)- and 2-imino-3-(2-methylsulfinyl)-ethyl-6-trifluoromethoxybenzothiazolines (61 and 64, ED(50) = 1.0 and 1.1 mg/kg i.p., respectively). In addition, intraperitoneal administration of some of the best benzothiazolines protected mice from mortality produced by hypobaric hypoxia.

Animals↗
PubMed1999

Metformin modulates insulin receptor signaling in normal and cholesterol-treated human hepatoma cells (HepG2).

The effects of the biguanide anti-hyperglycemic agent, metformin (N,N'-dimethyl-biguanide), on insulin signaling was studied in a human hepatoma cell line (HepG2). Cells were cultured in the absence (control cells) or in the presence of 100 microM of a cholesterol derivative, hemisuccinate of cholesterol. Cholesterol hemisuccinate-treatment alters cholesterol and lipid content of HepG2 and modulates membrane fluidity. Cholesterol hemisuccinate-treatment induces a decrease in insulin responsiveness and creates an 'insulin-resistant' state in these cells. Exposure to 100 microM of metformin resulted in a significant enhancement of insulin-stimulated lipogenesis in control and cholesterol hemisuccinate-treated cells. In control cells, metformin altered glycogenesis in a biphasic manner. In cholesterol hemisuccinate-treated cells, metformin inhibited basal glycogenesis but restored insulin-stimulated glycogenesis. Hence, to understand the mechanism of metformin action, we analyzed early steps in the insulin signaling pathway, including insulin receptor autophosphorylation, mitogen-activated-protein kinase and phosphatidylinositol 3-kinase activities, in both control and cholesterol hemisuccinate-treated cells. Overall, the results suggest that metformin may interact with the insulin receptor and/or a component involved in the early steps of insulin signal transduction.

Cholesterol↗
PubMed1999

In vivo inhibition of NF-kappa B in T-lineage cells leads to a dramatic decrease in cell proliferation and cytokine production and to increased cell apoptosis in response to mitogenic stimuli, but not to abnormal thymopoiesis.

To understand the role of NF-kappa B complexes in T cell development and activation, we have generated transgenic mice in which RelA and c-Rel complexes were selectively inhibited in the T-lineage cells by specific expression of a trans-dominant form of I kappa B alpha. Transgene expression did not affect the thymic development, but led to lowered numbers of splenic T cells and to a dramatic decrease in the ex vivo proliferative response of splenic T lymphocytes. Analysis of IL-2 and IL-2R alpha expression demonstrated that the perturbation of the proliferation response was not attributable to an abnormal expression of these genes. In contrast, expression of IL-4, IL-10, and IFN-gamma was strongly inhibited in the transgenic T cells. The proliferative deficiency of the transgenic T cells was associated with an increased apoptosis. These results point out the involvement of NF-kappa B/Rel family proteins in growth signaling pathways by either regulating proteins involved in the IL-2 signaling or by functionally interfering with the cell cycle progression.

Animals↗
PubMed1999

Incorporation of exogenous lipids modulates insulin signaling in the hepatoma cell line, HepG2.

The lipid content of cultured cells can be experimentally modified by supplementing the culture medium with specific lipids or by the use of phospholipases. In the case of the insulin receptor, these methods have contributed to a better understanding of lipid disorder-related diseases. Previously, our laboratory demonstrated that experimental modification of the cellular lipid composition of an insulin-sensitive rat hepatoma cell line (ZHC) resulted in an alteration in insulin receptor binding and biological action (Bruneau et al., Biochim. Biophys. Acta 928 (1987) 287-296/297-304). In this paper, we have examined the effects of lipid modification in another hepatoma cell line, HepG2. Exogenous linoleic acid (LA, n-6), eicosapentaenoic acid (EPA, n-3) or hemisuccinate of cholesterol (CHS) was added to HepG2 cells, to create a cellular model in which membrane composition was modified. In this model, we have shown that: (1) lipids were incorporated in treated HepG2 cells, but redistributed differently when compared to treated ZHC cells; (2) that insulin signaling events, such as insulin receptor autophosphorylation and the phosphorylation of the major insulin receptor substrate (IRS-1) were altered in response to the addition of membrane lipids or cholesterol derived components; and (3) different lipids affected insulin receptor signaling differently. We have also shown that the loss of insulin receptor autophosphorylation in CHS-treated cells can be correlated with a decreased sensitivity to insulin. Overall, the results suggest that the lipid environment of the insulin receptor may play an important role in insulin signal transduction.

Animals↗
PubMed1999

Hyaluronate-alginate gel as a novel biomaterial: mechanical properties and formation mechanism.

With the aim of producing a biomaterial for surgical applications, the alginate-hyaluronate association has been investigated to combine the gel-forming properties of alginate with the healing properties of hyaluronate. Gels were prepared by diffusion of calcium into alginate-hyaluronate mixtures, with an alginate content of 20 mg/mL. The hyaluronate source was shown to have significant effect on the aspect and the properties of the gels. The gels have viscoelastic behaviour and the transient measurements carried out in creep mode could be interpreted through a Kelvin-Voigt generalised model: experimental data led to the steady state hardness and a characteristic viscosity of the gel. Gels prepared from Na rooster comb hyaluronate with weight ratio up to 0.50 have satisfactory mechanical properties, and fully stable gels are obtained after a few days; on the contrary, use of lower molecular weight hyaluronate led to loose gels for hyaluronate contents over 0.25. Gel formation was investigated by measurements of the exchange fluxes between the calcium chloride solution and the forming gel, which allowed thorough investigations of the occuring diffusion phenomena of water, calcium ion and hyaluronate. Strong interactions of water with hyaluronate reduce significantly the rate of weight loss from the gel beads and allows higher water content in steady-state gels. Calcium content in the gel samples could be correlated to the actual alginate concentration, whatever the nature and the weight ratio of hyaluronate.

Alginates↗
PubMed1999

Generation of T lymphocytes from the epithelium and stroma of squamous pre-neoplastic lesions of the uterine cervix.

In this study, we have developed a simple and efficient technique for the isolation of viable lymphocytes from the epithelium and stroma of small pre-neoplastic squamous intraepithelial lesions (SIL) of the uterine cervix. Following the separation of the epithelium from the stroma using dispase II, both biopsy fragments were used to generate T lymphocytes. The stroma-derived lymphocytes were obtained by collecting and culturing the cells migrating out of the biopsy in the presence of IL2 (50 U/ml). An average of 0.7 x 10(6) and 1.4 x 10(6) lymphocytes could be obtained after 20 and 30 days of culture, respectively. For the expansion of lymphocytes derived from the pre-neoplastic epithelium (SIL) it was necessary to use a combination of irradiated peripheral blood mononuclear cells (PBMC) as a feeder layer with PHA (0.1%), in addition to IL2 (50 U/ml). Interestingly, these lymphocytes could be obtained using either allogeneic or syngeneic PBMCs. With this protocol, we were able to generate up to 100 x 10(6) lymphocytes from the epithelium, the majority of which were T lymphocytes.

Carcinoma in Situ↗
PubMed1999

Hyaluronate-alginate combination for the preparation of new biomaterials: investigation of the behaviour in aqueous solutions.

With the aim of producing a biomaterial for surgical applications, the alginate-hyaluronate association has been investigated. Crossed techniques were used to assess the existence of polymer interactions in aqueous solutions up to 20 mg/ml. Alginate was obtained from algae and hyaluronate was purified from rooster comb. Viscometry measurements using the capillary technique or the Couette flow, together with circular dichroism investigations, evidenced the moderate significance of interactions between the two polysaccharides in dilute solutions. In addition, the case of more concentrated solutions and containing 20 mg/ml alginate was approached by rheological measurements in the flow mode; the behaviour of the polymer associations appeared as a compromise between those of individual polysaccharides.

Alginates↗
PubMed1999

Colonization of in vitro-formed cervical human papillomavirus- associated (pre)neoplastic lesions with dendritic cells: role of granulocyte/macrophage colony-stimulating factor.

The purpose of this study was to investigate the ability of CD1a+ Langerhans/dendritic cells (LCs/DCs) to infiltrate human papillomavirus (HPV)-associated (pre)neoplastic lesions of the uterine cervix. Migration of LCs/DCs in the presence of keratinocytes derived from normal cervix and HPV-transformed cell lines was evaluated in Boyden chambers and in organotypic cultures and correlated with granulocyte/macrophage colony-stimulating factor (GM-CSF) production by the cells, as determined by ELISA. Conditioned media of HPV-transformed keratinocytes contained lower amounts of GM-CSF and induced a decreased motile response of LCs/DCs in the Boyden chamber assay compared with those of normal cervical keratinocytes. The migration of LCs/DCs in the presence of conditioned media from normal keratinocytes could be blocked by an anti-GM-CSF antibody, and the migration of LCs/DCs in the presence of conditioned media from HPV-transformed keratinocytes could be increased by supplementing the media with recombinant GM-CSF. GM-CSF was also a potent factor in enhancing the colonization of LCs/DCs into organotypic cultures of HPV-transformed keratinocytes, as the infiltration of LCs/DCs in the in vitro-formed (pre)neoplastic epithelium was minimal under basal conditions and dramatically increased after the addition of GM-CSF to the cultures. These results suggest that GM-CSF could play an important role in the recruitment of LCs/DCs into the HPV-transformed (pre)neoplastic cervical epithelium and be useful as a new immunotherapeutic approach for cervical (pre)cancers.

Antibodies↗
PubMed1999

Leukemic CD3+ LGL share functional properties with their CD8+ CD57+ cell counterpart expanded after BMT.

Leukemic T-LGL (large granular lymphocyte) composed of clonal CD3+ TCR alphabeta+ CD8+ CD57+ cells were compared with oligoclonally CD3+ CD8hi+ CD57- lymphocytes expanded after BMT. Leukemic CD3+ CD8hi+ CD57+ LGL showed several phenotypic differences such as an upregulation of CD16 and adhesion molecules (mainly CD11c, CD58 and CD54), activation markers and an exclusive CD45RA isoform expression. Unstimulated CD3+ CD8+ CD57+ LGL from both leukemic and BMT donors spontaneously developed an ex vivo CTL-like CD3-redirected cytotoxicity but no NK cell activity. Different stimuli (PHA, PMA or rhIL-2) induced similar cytotoxic profiles after a 6-day culture involving a CD3-redirected lysis predominating over a low NK cell activity. However, culture of leukemic LGL with these stimuli allowed either a 2 week persistence (PMA or rhIL-2) of CD8+ CD57+ LGL or their disappearance after 3 days (PHA). Furthermore, leukemic CD8hi+ CD57+ T lymphocytes produced an inhibitor of cytotoxic functions as previously described for BMT recipients' CD8+ CD57+ cells. Thus, despite some phenotypic differences between both cell sources, leukemic CD57+ T-LGL display the same functional characteristics of cytotoxic effector and immunoregulatory T cells as CD8+ CD57+ T cells from BMT recipients which might represent their normal counterpart.

Bone Marrow Transplantation↗
PubMed1999

Pharmacokinetics and tolerance of flunitrazepam in neonates and in infants.

OBJECTIVE: To study the pharmacokinetics of flunitrazepam (used for sedation in neonates and infants), to determine the influence of both gestational and postnatal age on the pharmacokinetic parameters, and to analyze the relationship between the hemodynamic parameters and flunitrazepam plasma concentration. METHODS: Flunitrazepam was infused for 20 minutes as a single dose (0.2 mg x kg(-1)) and as multiple doses (0.1 mg x kg(-1)). Six to eight 1-mL blood samples were collected per patient. Flunitrazepam plasma concentration was measured by gas chromatography-mass spectrometry. RESULTS: Thirty-one patients (25 neonates and six infants) were included in the study. Only three of them received multiple doses. After the single dose (n = 28), half-life was 22.6 +/- 7.3 hours, clearance was 0.15 +/- 0.14 L x kg x h(-1), and volume of distribution was 4.6 +/- 4.1 L x kg(-1) (mean +/- SD). Plasma clearance and volume of distribution significantly increased with postnatal age (P < .05), but no pharmacokinetic parameter varied significantly with gestational age. Diastolic blood pressure significantly decreased with increasing flunitrazepam plasma concentrations (P < .05). CONCLUSION: Postnatal age but not gestational age influenced flunitrazepam pharmacokinetic parameters in neonates and infants. Diastolic blood pressure was inversely correlated to flunitrazepam plasma concentration.

Age Factors↗
PubMed1999

Substitution of the insulin receptor transmembrane domain with that of glycophorin A inhibits insulin action.

To study the role of transmembrane (TM) domains interactions in the activation of the insulin receptor, we have replaced the insulin receptor TM domain with that of glycophorin A (GpA), an erythrocyte protein that spontaneously forms detergent-resistant dimers through TM-TM interactions. Insulin receptor cDNA sequences with the TM domain replaced by that of GpA were constructed and stably transfected in CHO cells. Insulin binding to cells and solubilized receptors was not modified. Electrophoresis after partial reduction of disulfide bonds revealed an altered structure for the soluble chimeric receptors, seen as an altered mobility apparently due to increased interactions between the beta subunits of the receptor. Insulin signaling was markedly decreased for cells transfected with chimeric receptors compared with cells transfected with normal receptors. A decrease in insulin-induced receptor kinase activity was observed for solubilized chimeric receptors. In conclusion, substitution by the native GpA TM domain of the insulin receptor results in structurally modified chimeric receptors that are unable to transmit the insulin signal properly. It is hypothesized that this substitution may impose structural constraints that prevent the proper changes in conformation necessary for activation of the receptor kinase. Other mutants modifying the structure or the membrane orientation of the glycophorin A TM domain are required to better understand these constraints.

Amino Acid Sequence↗
PubMed1998

Simultaneous determination of methylphenobarbital enantiomers and phenobarbital in human plasma by on-line coupling of an achiral precolumn to a chiral liquid chromatographic column.

A fully automated liquid chromatographic (LC) method for the simultaneous determination of methylphenobarbital enantiomers and phenobarbital in human plasma has been developed. The method is based on the use of a precolumn packed with an internal-surface reversed-phase packing material (LiChrospher ADS) for sample clean-up coupled to LC analysis on a cellulose tris(4-methylbenzoate) based chiral stationary phase (Chiralcel OJ-R). A 100-microliter plasma sample was injected directly on the precolumn packed with LiChrospher RP-18 ADS using a mixture of pH 5.0 phosphate buffer-methanol (97:3, v/v) as washing liquid. The analytes were then eluted in the back-flush mode with the LC mobile phase. The enantiomeric separation of methylphenobarbital was achieved on Chiralcel OJ-R). The retention times were modelled using a D-optimal design with ten experimental points in order to optimise the LC mobile phase for the separation of phenobarbital from the enantiomers of mephobarbital. The factors selected were the acetonitrile content, the pH and the sodium perchlorate concentration in the mobile phase. A Derringer's desirability function was used to find an optimal and robust solution within the experimental domain. The mobile phase selected consisted of a mixture of pH 7.0 phosphate buffer-acetonitrile (60:40, v/v). The elution profiles of phenobarbital, methylphenobarbital and blank plasma samples on the precolumn and the time needed for analyte transfer from the precolumn to the analytical column were then determined. Finally, the method developed was validated.

Chromatography, Liquid↗
PubMed1998

Simultaneous determination of pirlindole enantiomers and dehydropirlindole by chiral liquid chromatography.

Liquid chromatography was employed for the determination of pirlindole enantiomers and its oxidation product dehydropirlindole (DHP). The direct separation of pirlindole enantiomers and DHP was achieved on a cellulose tris-(3,5-dimethylphenylcarbamate) chiral stationary phase (Chiralcel OD-R). Acetonitrile was used as the organic modifier and sodium perchlorate was used as an ionic additive in the mobile phase. The influence of acetonitrile and sodium perchlorate concentrations on enantioselectivity and achiral selectivity towards DHP was investigated in order to find suitable conditions for the determination of low amounts of each analyte. The mobile phase selected consisted of a mixture of acetonitrile and phosphate buffer (pH 5.0) containing sodium perchlorate (0.05 M) (35:65, v/v) and the UV detector was set at 220 nm. The method developed was validated and was found to be linear in the 0.1-5 microg ml(-1) range (r2 = 0.999 for the three compounds). Repeatability and the intermediate precision for the three analytes at a concentration of 0.1 microg ml(-1) were about 3 and 4%, respectively. This concentration corresponds to the quantification of 0.1% for the minor enantiomer. Actual determinations of enantiomeric purity for single enantiomers of pirlindole were performed.

Acetonitriles↗
PubMed1998

Time resolved fluorescence properties of phenylalanine in different environments. Comparison with molecular dynamics simulation.

Time resolved fluorescence of the phenylalanine residue (Phe) alone and included in the transmembrane domain (TMD) sequences of the epidermal growth factor receptor (EGFR) and ErbB-2 was studied using the synchrotron radiation source of light, and compared to molecular dynamics (MD) simulations. The fluorescence intensity decay is strongly sensitive to the environment. A mono-exponential decay was obtained for Phe amino acid alone in two different solvents and for Phe included in EGFR transmembrane sequence, with fluorescence lifetime values varying from 1.7 ns (EGFR) to 7.4 ns (Phe dissolved in water). In ErbB-2 transmembrane sequence three lifetimes were detected. The relative amplitude of the shortest one (0.14 ns) is smaller than 10%, whereas the others (0.6 and 2.2 ns) are almost equally represented. They have been attributed to different rotamers exchanging slowly. This interpretation is supported by MD simulations which evidence transitions in time series of the chi 1 dihedral angle of Phe observed in the case of ErbB-2. The anisotropy decays are similar for both peptides and indicate the presence of a correlation time in the nanosecond range (1-4 ns) and the probable existence of a very fast one (< 0.05 ns). Autocorrelation functions computed from MD simulations corroborate these results.

Amino Acid Sequence↗
PubMed1998

Identification of a potential effector pathway for the trimeric Go protein associated with secretory granules. Go stimulates a granule-bound phosphatidylinositol 4-kinase by activating RhoA in chromaffin cells.

Besides having a role in signal transduction, heterotrimeric G proteins may be involved in membrane trafficking events. In chromaffin cells, Go is associated with secretory organelles, and its activation inhibits the ATP-dependent priming of exocytosis. By using permeabilized cells, we previously described that the control exerted by the granule-bound Go on exocytosis may be related to effects on the cortical actin network through a sequence possibly involving Rho. To provide further insight into the function of Rho in exocytosis, we focus here on its intracellular localization in chromaffin cells. By immunoreplica analysis, immunoprecipitation, and confocal immunofluorescence, we found that RhoA is specifically associated with the membrane of secretory chromaffin granules. Parallel subcellular fractionation experiments revealed the occurrence of a mastoparan-stimulated phosphatidylinositol 4-kinase activity in purified chromaffin granule membranes. This stimulatory effect of mastoparan was mimicked by GAP-43, an activator of the granule-associated Go, and specifically inhibited by antibodies against Galphao. In addition, Clostridium botulinum C3 exoenzyme completely blocked the activation of phosphatidylinositol 4-kinase by mastoparan. We propose that the control exerted by Go on peripheral actin and exocytosis is related to the activation of a downstream RhoA-dependent phosphatidylinositol 4-kinase associated with the membrane of secretory granules.

1-Phosphatidylinositol 4-Kinase↗
PubMed1998

CHARGE syndrome: report of 47 cases and review.

The acronym CHARGE refers to a syndrome of unknown cause. Here we report on 47 CHARGE patients evaluated for the frequency of major anomalies, namely coloboma (79%), heart malformation (85%), choanal atresia (57%), growth and/or mental retardation (100%), genital anomalies (34%), ear anomalies (91%), and/or deafness (62%). In addition, we comment on anomalies observed very frequently in neonates and infants with the CHARGE syndrome, including, minor facial anomalies, neonatal brain stem dysfunction with cranial nerve palsy, and, mostly, internal ear anomalies such as semicircular canal hypoplasia that were found in each patient that could be tested. We propose several criteria for poor survival including male gender, central nervous system and/or oesophageal malformations, and bilateral choanal atresia. No predictive factor regarding developmental prognosis could be identified in our series. A significantly higher mean paternal age at conception together with concordance in monozygotic twins and the existence of rare familial cases support the role of genetic factors such as de novo mutation of a dominant gene or subtle sub-microscopic chromosome rearrangement. Finally, the combination of malformations in CHARGE syndrome strongly supports the view that this multiple congenital anomalies/mental retardation syndrome is a polytopic developmental field defect involving the neural tube and the neural crests cells.

Abnormalities, Multiple↗