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M Lemaire

Publications and source records attributed to M Lemaire.

At least 55 records · Page 3Linked to original sources
PubMed1998

In vitro and in situ absorption of SDZ-RAD using a human intestinal cell line (Caco-2) and a single pass perfusion model in rats: comparison with rapamycin.

PURPOSE: To compare the intestinal absorption and active efflux protein susceptibility of a new immunosuppressive agent (SDZ-RAD) with that of its analog rapamycin. METHODS: Caco-2 cell monolayers were used to examine bidirectional transport of the two compounds at low micromolar concentrations. Single pass rat intestinal perfusion was also used to examine steady state permeability. RESULTS: Rapamycin and SDZ-RAD showed a distinct preference for transport in the basolateral to apical direction of Caco-2 monolayers as efflux was >20 times greater than apical to basolateral transport. Efflux of SDZ-RAD was completely inhibited by verapamil while efflux of rapamycin was mostly inhibited by verapamil and partially inhibited by probenecid. Passive permeability was shown to be 20 x 10(-6) cm/sec for SDZ-RAD and 10 x 10(-6) cm/sec for rapamycin. In situ rat studies also showed the permeability of rapamycin to be half that of SDZ-RAD with permeabilities of 12.6 X 10(-6) for rapamycin and 24.8 x 10(-6) cm/sec for SDZ-RAD. CONCLUSIONS: SDZ-RAD and rapamycin are strong substrates for P-gp-like mediated efflux. Rapamycin is also partially removed from cells by a second efflux system that is not responsive to SDZ-RAD. When these efflux pumps are inhibited SDZ-RAD is likely to be absorbed across the intestine at a faster rate than rapamycin.

Animals↗
PubMed1998

Role of lipoproteins in the plasma binding of SDZ PSC 833, a novel multidrug resistance-reversing cyclosporin.

AIMS: The plasma binding of the cyclosporin D analogue SDZ PSC 833 was investigated in vitro. METHODS: The plasma total binding constant (corresponding to the bound-to-free concentration or binding ratio) was determined at 37 degrees C by the erythrocyte partitioning technique on plasma samples from three healthy volunteers and three cancer patients. Lipoproteins were also removed from plasma samples from three healthy volunteers by a standard ultracentrifugal technique. RESULTS: SDZ PSC 833 plasma binding was 97.8 +/- 1.1% and 97.3 +/- 0.2% in samples from three healthy volunteers and three cancer patients respectively. More than 95% of blood SDZ PSC 833 was distributed in plasma. When the original plasma samples of three individuals were delipidated, SDZ PSC 833 binding was strongly decreased (58% bound to plasma proteins) and when lipoproteins were resuspended in the delipidated plasma samples to produce varying lipoprotein plasma concentrations, the binding increased continuously with the fraction of added lipoproteins. When lipoproteins were resuspended to restore the original lipoprotein plasma content, the % plasma-bound SDZ PSC 833 increased to 98.2%, close to the value observed with the original plasma (98.7%). CONCLUSIONS: These results clearly indicate that SDZ PSC 833 plasma binding is mainly determined by lipoproteins and that in blood, most of SDZ PSC 833 is distributed in plasma.

Cyclosporine↗
PubMed1998

Calretinin expression as a critical component in the control of dentate gyrus long-term potentiation induction in mice.

We have recently reported that mice homozygous (Cr-/-) for a null mutation in the calretinin gene have impaired long-term potentiation (LTP) induction in the dentate gyrus (S. Schurmans et al. (1997) Proc. Natl. Acad. Sci. USA, 94, 10415 ). Here, we investigated dentate LTP induction in mice heterozygous (Cr+/-) for the same mutation. Despite the presence of calretinin in neurons of these mice, although at reduced levels as compared with normal mice, LTP induction in dentate gyrus was totally impaired. Spatial memory and learning were found unaffected in Cr+/- mice, such as in Cr-/- mice. Altogether, our results suggest that calretinin is a critical component in the control of dentate synaptic plasticity in mice, and that levels of calretinin higher than those observed in Cr+/- mice are required to induce LTP in this area. The possible mechanisms leading to the absence of correlation between gene dosage and biological effects are discussed.

Animals↗
PubMed1998

Characterization of the transport of a cationic octapeptide, octreotide, in rat bile canalicular membrane: possible involvement of P-glycoprotein.

The cyclic cationic octapeptide octreotide is known to be taken up by hepatocytes, with more than 70% of an intravenous dose being excreted into bile in unchanged form. We have already reported that a transporter other than the canalicular multispecific organic anion transporter (cMOAT) is responsible for the biliary excretion of octreotide in vivo. The aim of this study is to obtain an insight into the transporter of octreotide in bile canalicular membrane. The effect of various compounds on the ATP-dependent uptake of octreotide by rat bile canalicular membrane vesicles (CMV) was investigated. The ATP-dependent uptake of [14C]octreotide by CMV was inhibited by verapamil, vincristine and PSC833 in a concentration-dependent manner, the maximum inhibitory effects of these compounds being almost equal to that of excess unlabeled octreotide, while taurocholic acid (TCA) caused no inhibition at concentrations much higher than the Km of TCA uptake by CMV. Mutual inhibition between octreotide and dinitrophenylglutathione (DNP-SG), a representative substrate for cMOAT was only minor and could only be observed at concentrations much higher than the Km for each ligand uptake. To examine the contribution of P-glycoprotein to the biliary excretion of octreotide in vivo, biliary excretion of octreotide was compared between P-glycoprotein-induced rats by phenothiazine (PTZ) treatment and normal rats. A significant increase in the biliary excretion rate was observed in PTZ-treated rats. Only a slight decrease in biliary excretion was observed in mdr1a knock-out mice compared with normal mice, which may be explained by the associated induction of mdr1b. These results demonstrate that the transporter for octreotide is different from cMOAT and the bile acid transporter. The involvement of P-glycoprotein in the biliary excretion of octreotide is suggested.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1998

Effect of the Mdr1a P-glycoprotein gene disruption on the tissue distribution of SDZ PSC 833, a multidrug resistance-reversing agent, in mice.

The involvement of mdr1a P-glycoprotein (P-gP) on the tissue distribution of the multidrug resistance-reversing agent SDZ PSC 833 was assessed by use of mdr1a (-/-) mice. The mdr1a (-/-) and wild-type mdr1a (+/+) mice received a 4-h constantrate i.v. infusion (2 micrograms/min) of [14C]SDZ PSC 833. Mice were sacrificed at 0, 0.5, 1, 2 and 4 h during infusion and at 0.5, 1, 3, 8 and 24 h after stopping the infusion. Blood and tissues were analyzed on total (14C) and parental SDZ PSC 833 concentrations. Mdr1a (-/-) mice exhibited increased SDZ PSC 833 accumulation in cerebrum, cerebellum and somewhat in testes and small intestine compared with the wild-type mice. The difference between mdr1a (-/-) and (+/+) brain (cerebrum and cerebellum) penetration depended on SDZ PSC 833 blood concentrations, because this cyclosporin analog apparently governs its own brain penetration by inhibiting the P-glycoprotein pump in mdr1a (+/+) mice. Thus the mdr1a (-/-)/(+/+) ratio of brain concentrations tended to decrease and increase at high and low blood concentrations, respectively. These findings clearly demonstrate the interaction of SDZ PSC 833 with the P-glycoprotein present at the blood-brain barrier. The SDZ PSC 833 distribution in other mdr1a P-glycoprotein-expressed tissues, as well as its metabolism and elimination, was not affected by the mdr1a gene disruption. This suggests that factors other than mdr1a P-gP are involved in the disposition of this multidrug resistance-reversing agent.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1998

Modulation of the tumor disposition of vinca alkaloids by PSC 833 in vitro and in vivo.

PSC 833, a nonimmunosuppressive cyclosporin, is able to inhibit the efflux of antitumor drugs mediated by P-glycoprotein (P-gp). The purpose of the present study is to compare the effect of PSC 833 on the tumor disposition of [3H]vincristine ([3H]VCR) and [3H]vinblastine ([3H]VBL) in in vitro and in vivo experiments from a pharmacokinetic point of view. In in vitro experiments, the effect of PSC 833 was investigated on the cellular uptake of [3H]VCR and [3H]VBL by HCT-15 and COLO 205, human colorectal tumor cell lines with extensive and minimal expression of P-gp, respectively. PSC 833 (2 microM) increased the cellular uptake of [3H]VCR and [3H]VBL by HCT-15 cells, but not that by COLO 205 cells, 8- and 6-fold, respectively, without affecting the initial influx rates. In addition, 2 microM PSC 833 reduced the efflux of [3H]VCR from HCT-15 cells to a level comparable with that from COLO 205 cells. Furthermore, the effect of PSC 833 on the tumor disposition of intravenously administered [3H]VCR and [3H]VBL was studied in tumor inoculated mice. Infusion of PSC 833 (10 microg/hr/mouse) increased the HCT-15 tumor disposition of [3H]VBL and [3H]VCR in vivo to a level comparable with that observed in vitro. These findings demonstrate that PSC 833 enhances the tumor disposition of vinca alkaloids by inhibition of P-gp-mediated efflux not only in vitro but also in vivo in a solid tumor model.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1998

[Corticosteroid-induced epidural lipomatosis. Efficacy of medical treatment].

We describe a further case of cauda equina compression secondary to steroid-induced epidural lipomatosis in a patient treated for IBD. The diagnosis was rapidly confirmed by MRI allowing conservative management by corticosteroid withdrawal as well as use of hygiene and dietary measures. Therapeutic efficacy was noted on a clinical basis and confirmed by repeated follow-up MRI exams which showed regression of fat accumulation. Symptomatic epidural lipomatosis is probably underestimated because physicians concerned by steroid treatment are not fully informed about this potentially severe and usually iatrogenic disease. Also, proper medical attention to the first neurological symptom in these patients might help limit therapeutic management to a medical measurer, before requiring surgical decompressive surgery.

Adult↗
PubMed1997

Impaired long-term potentiation induction in dentate gyrus of calretinin-deficient mice.

Calretinin (Cr) is a Ca2+ binding protein present in various populations of neurons distributed in the central and peripheral nervous systems. We have generated Cr-deficient (Cr-/-) mice by gene targeting and have investigated the associated phenotype. Cr-/- mice were viable, and a large number of morphological, biochemical, and behavioral parameters were found unaffected. In the normal mouse hippocampus, Cr is expressed in a widely distributed subset of GABAergic interneurons and in hilar mossy cells of the dentate gyrus. Because both types of cells are part of local pathways innervating dentate granule cells and/or pyramidal neurons, we have explored in Cr-/- mice the synaptic transmission between the perforant pathway and granule cells and at the Schaffer commissural input to CA1 pyramidal neurons. Cr-/- mice showed no alteration in basal synaptic transmission, but long-term potentiation (LTP) was impaired in the dentate gyrus. Normal LTP could be restored in the presence of the GABAA receptor antagonist bicuculline, suggesting that in Cr-/- dentate gyrus an excess of gamma-aminobutyric acid (GABA) release interferes with LTP induction. Synaptic transmission and LTP were normal in CA1 area, which contains only few Cr-positive GABAergic interneurons. Cr-/- mice performed normally in spatial memory task. These results suggest that expression of Cr contributes to the control of synaptic plasticity in mouse dentate gyrus by indirectly regulating the activity of GABAergic interneurons, and that Cr-/- mice represent a useful tool to understand the role of dentate LTP in learning and memory.

Animals↗
PubMed1997

Effect of the P-glycoprotein inhibitor, SDZ PSC 833, on the blood and brain pharmacokinetics of colchicine.

The effect of the multidrug resistance-reversing agent, SDZ PSC 833, on blood and brain pharmacokinetics of a P-glycoprotein substrate, colchicine, was investigated using simultaneous blood and brain microdialysis in freely moving rats. The use of microdialysis for pharmacokinetic studies was validated by comparing the blood concentrations of colchicine obtained by microdialysis with those obtained by direct blood sampling. The rats received either SDZ PSC 833 (2.3 mg/kg i.v. bolus followed by 16.7 microg/min/kg i.v. infusion during all the experiment) and colchicine (1 mg/kg i.v. bolus followed by 12.5 microg/min/kg i.v. infusion during 2 hours) or colchicine alone (the same dosage with SDZ PSC 833 vehicle). The SDZ PSC 833 treatment resulted in important modifications of colchicine blood pharmacokinetics: the unbound colchicine blood concentration at steady-state was enhanced from 149.6 +/- 9.9 to 333.5 +/- 81.7 ng/ml indicating a two-fold decrease in colchicine clearance. Moreover the coadministration of SDZ PSC 833 increased the brain penetration of colchicine by a factor of 10, at least. This enhancement could not be exactly assessed because the brain dialysate concentrations of control group were below the limit of detection. Nevertheless, the large increase of colchicine brain penetration is consistent with the hypothesis that SDZ PSC 833 is able to inhibit the P-glycoprotein pump present at the blood-brain barrier.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Modulation of the Escherichia coli sigmaE (RpoE) heat-shock transcription-factor activity by the RseA, RseB and RseC proteins.

The sigma(E) (RpoE) transcription factor of Escherichia coli regulates the expression of genes whose products are devoted to extracytoplasmic activities. The sigma(E) regulon is induced upon misfolding of proteins in the periplasm or the outer membrane. Similar to other alternative sigma factors, the activity of sigma(E) is tightly regulated in E. coli. We have previously shown that sigma(E) is positively autoregulated at the transcriptional level. DNA sequencing, coupled with transcriptional analyses, have shown that sigma(E) is encoded by the first gene of a four-gene operon. The second gene of this operon, rseA, encodes an anti-sigma(E) activity. This was demonstrated at both the genetic and biochemical levels. For example, mutations in rseA constitutively increase sigma(E) activity. Consistent with this, overproduction of RseA leads to an inhibitory effect on sigma(E) activity. Topological analysis of RseA suggests the existence of one transmembrane domain, with the N-terminal part localized in the cytoplasm. Overproduction of this N-terminal domain alone was shown to inhibit sigma(E) activity. These observations were confirmed in vitro, because either purified RseA or only its purified N-terminal domain inhibited transcription from Esigma(E)-dependent promoters. Furthermore, RseA and sigma(E) co-purify, and can be co-immunoprecipitated, and chemically cross-linked. The sigma(E) activity is further modulated by the products of the remaining genes in this operon, rseB and rseC. RseB is a periplasmic protein, which negatively regulates sigma(E) activity and specifically interacts with the C-terminal periplasmic domain of RseA. In contrast, RseC is an inner membrane protein that positively modulates sigma(E) activity. Most of these protein-protein interactions were verified in vivo using the yeast two-hybrid system.

Bacterial Proteins↗
PubMed1997

Functions of S-layers.

Although S-layers are being increasingly identified on Bacteria and Archaea, it is enigmatic that in most cases S-layer function continues to elude us. In a few instances, S-layers have been shown to be virulence factors on pathogens (e.g. Campylobacter fetus ssp. fetus and Aeromonas salmonicida), protective against Bdellovibrio, a depository for surface-exposed enzymes (e.g. Bacillus stearothermophilus), shape-determining agents (e.g. Thermoproteus tenax) and nucleation factors for fine-grain mineral development (e.g. Synechococcus GL 24). Yet, for the vast majority of S-layered bacteria, the natural function of these crystalline arrays continues to be evasive. The following review up-dates the functional basis of S-layers and describes such diverse topics as the effect of S-layers on the Gram stain, bacteriophage adsorption in lactobacilli, phagocytosis by human polymorphonuclear leukocytes, the adhesion of a high-molecular-mass amylase, outer membrane porosity, and the secretion of extracellular enzymes of Thermoanaerobacterium. In addition, the functional aspect of calcium on the Caulobacter S-layer is explained.

Abortion, Veterinary↗
PubMed1997

Modeling the route of administration-based enhancement in the brain delivery of EAB 515, studied by microdialysis.

EAB 515 (S-alpha-amino-5-phosphonomethyl[1,1'biphenyl]-3-propanoic acid) is an extremely hydrophilic N-methyl-D-aspartate antagonist. It shows marked CNS activity, in that it is a potent neuroprotector in models of cerebral ischemia, and also demonstrates social and non-social behavioral alteration following systemic administration in animals. Because of its high degree of ionization at physiologic pH, one would not expect appreciable brain uptake of EAB 515 across tight junctions of the blood-brain barrier. This is in contrast to its pharmacologic effect as well as brain/plasma ratios measured during systemic administration in rats. These observations lead us to investigate other transport pathways that might account for its brain uptake. Such mechanistic information is imperative in rational drug delivery and drug design strategies. Upon intracerebroventricular administration, the observed steady-state cortical extracellular fluid concentrations of EAB 515 were over 100-fold higher than those observed following intravenous administration, when normalized for the dosing rate. This increased distribution into the brain, based upon the route of administration, suggests the transport of drug directly between the cerebrospinal fluid and the brain extracellular space. The parameters of the model that adequately describes the data obtained from the two routes of administration in individual animals were estimated. The clinical significance of these results is in the use of intracerebroventricular administration for enhanced brain delivery of hydrophilic drugs that poorly cross the blood-brain barrier.

Animals↗
PubMed1997

Carrier-mediated hepatic uptake of the cationic cyclopeptide, octreotide, in rats. Comparison between in vivo and in vitro.

The plasma concentration and biliary excretion profiles of a cationic cyclic octapeptide, octreotide, were compared between control rats and rats given an intravenous infusion of a bile acid, taurocholate (TCA), and an organic anion, dibromosulfophthalein (DBSP). Both TCA and DBSP reduced the plasma elimination and biliary excretion of octreotide after its intravenous bolus administration. Two mechanisms accounting for this phenomenon were considered a priori: decreased hepatic uptake from blood to liver and decreased biliary excretion from liver to bile. The tissue uptake clearance (CLup) of octreotide in plasma and several tissues was determined, and extensive uptake of octreotide (0.20 ml/min/g liver) was observed only in liver. The kinetic analysis indicated that CLup in liver fell to 10% of controls after administration of both TCA and DBSP. To compare CLup between in vivo and in vitro, the initial velocity of octreotide uptake by isolated hepatocytes and primary cultured hepatocytes was measured. The estimated kinetic parameters KM and Vmax were approximately 100 microM and 200 pmol/min/10(6) cells in both systems, respectively. Hepatic uptake clearance estimated from the in vitro data was comparable with that observed in vivo. Biliary excretion of octreotide is reduced in Eisai hyperbilirubinemic rats (EHBRs), which have a heredity defect of multispecific organic anion transporter on the bile canalicular membrane, compared with that of Sprague-Dawley rats. The kinetic analysis demonstrated that the hepatic uptake was reduced in EHBRs. The uptake study using primary cultured hepatocytes suggested that a high level of unidentified endogenous substrate(s) in EHBR plasma may be responsible for the reduction of hepatic uptake of octreotide in EHBRs. In conclusion, we have demonstrated in vivo that carrier-mediated hepatic uptake of octreotide is inhibited by TCA and DBSP and that the CLup obtained in vivo is comparable with the CLup obtained in vitro in isolated hepatocytes and primary cultured hepatocytes.

Animals↗
PubMed1997

[The organization of helicopter emergency services for the rescue of aircraft crash victims in the topical forest].

The purpose of this report was to describe lessons learned from experience in the tropical forest of Guyana and one helicopter rescue mission in that hostile environment. With previous data reported in the literature several guidelines for organizing these operations can be proposed. These rescue operations involve hoisting the victim to helicopter, medical treatment itself, and penetration into a hostile environment. Effectiveness and safety mandate that the physicians involved receive regular training in the techniques of helicopter evacuation, first aid, and survival. It is necessary to adapt conventional first aid kits for the purpose and to develop light and adequate survival equipment as listed exhaustively by the author.

Accidents, Aviation↗
PubMed1997

P-Glycoprotein mediates the efflux of quinidine across the blood-brain barrier.

Recent studies suggest that P-glycoprotein located on the blood-brain barrier restricts the brain uptake of its substrates. We examined the role of P-glycoprotein on the restricted entry of quinidine to the brain. Quinidine is a well known inhibitor of P-glycoprotein, although it is not yet clarified whether quinidine is the substrate for P-glycoprotein. Kinetic analysis of the uptake of quinidine into the rat brain after intravenous bolus administration revealed that the net uptake clearance is 25.5 microl/min/g brain. Intravenous administration of SDZ PSC 833, a multidrug resistance modifier, enhanced the net uptake clearance of quinidine by 15.7-fold. In contrast, no enhancement by SDZ PSC 833 was observed for the brain uptake of mannitol, a marker for the passive diffusion across the blood-brain barrier. The elimination of [3H] quinidine from the rat brain after microinjection into the cerebral cortex was inhibited by preadministered unlabeled quinidine and verapamil. In addition, the brain-to-plasma concentration ratio of quinidine at 10 min after intravenous administration was 27. 6-fold higher in mdr1a knock-out mice than in control mice. These results suggest that P-glycoprotein mediates the efflux of quinidine across the blood-brain barrier, resulting in its restricted entry to the brain.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Direct evidence for the different roles of the N- and C-terminal regulatory disulfides of sorghum leaf NADP-malate dehydrogenase in its activation by reduced thioredoxin.

Plant NADP-dependent malate dehydrogenase is activated through thiol/disulfide interchange with reduced thioredoxin. Previous studies showed that this process involves the reduction of two different disulfides per subunit: one N-terminal, the other C-terminal. Substitution of regulatory cysteines at each end by site-directed mutagenesis and comparison of activation kinetics of the mutants led us to propose a model for the activation mechanism where the C-terminal end shielded the access to the catalytic residues, whereas the N- terminal end was involved in the slow conformational change of the active site. In the present study, we took advantage of the previous identification of the catalytic histidine residue which can be specifically derivatized by diethyl pyrocarbonate to test the accessibility of the active site. The results clearly show that in the mutants where the C-terminal bridge is open the active site histidine is freely accessible to the reagent, whereas in the mutants where the N-terminal bridge is open, the active site cannot be reached without activation, thus demonstrating the validity of the model.

Disulfides↗
PubMed1996

High-performance liquid chromatographic analysis of (S)-alpha-amino-5-phosphonomethyl[1,1'-biphenyl]-3-propanoic acid (EAB 515) in brain and blood microdialysate (on-line) and in plasma ultrafiltrate of freely moving rats.

(S)-alpha-Amino-5-phosphonomethyl[1,1'-biphenyl]-3-propanoic acid (EAB 515, I), a competitive antagonist of the N-methyl-D-aspartate receptor, has significant pharmacological activity in the central nervous system (CNS). An extremely sensitive and selective analytical method was developed for the simultaneous analysis of I and its hydroxylated analog (RDC, II) in the microdialysate (MD) and plasma ultrafiltrate (UF) of rats. Microdialysis was used for in vivo sampling of unbound drug in the CSF, cortical extracellular fluid and in the blood of freely moving rats. Compound II was used for retrodialysis-based in vivo calibration of microdialysis probes to estimate the recovery of I. Compound I, being extremely hydrophilic with a high degree of ionization at the physiological pH of 7.4, has limited access to the brain regions. This, combined with its low microdialysis recovery, made the estimation of low brain concentrations of I a challenge. The analytes in MD and UF were separated (within 5 min) by reversed-phase HPLC on a 250 x 4.6 mm I.D. Maxsil 5 microns RP-2 column, and fluorescence of the eluent was monitored at 255 nm (lambda ex) and 320 nm (lambda em). A 0.09% (v/v) aqueous solution of trifluoroacetic acid (1 ml/min) was used as the mobile phase. The response for I in MD and UF samples was linear from 5 to 2000 ng/ml and from 20 to 10,000 ng/ml, respectively. The between-run (n = 6) and within-run (n = 3) variability of the assay was < 15%. Plasma-protein binding of I (fu = 0.68) was determined to be linear from 0.1 to 10 micrograms/ml. The analytical sensitivity, precision and accuracy of this method was suitable for the characterization of the pharmacokinetics and the CNS distribution of I, following administration of intravenous (i.v.) infusion, single i.v. bolus and multiple i.v. bolus doses of I to freely moving rats, with continuous microdialysate sampling of multiple tissues and simultaneous on-line HPLC analysis. Pharmacokinetic parameters for I, as determined from concentrations in blood MD samples with on-line analysis, were in good agreement with those estimated from concentrations in the UF of plasma samples obtained by conventional sampling.

Animals↗