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P Couvreur

Publications and source records attributed to P Couvreur.

At least 91 records · Page 5Linked to original sources
PubMed1998

[New approaches for encapsulation of peptides into poly(lactic/glycolic acid) microspheres].

The aim of the work was to develop small microspheres made from a biodegradable polymer, poly(lactide-co-glycolide), in order to entrap small peptides. Microspheres prepared by a water-in-oil-in-water emulsion solvent evaporation technique displayed a mean diameter below than 10 microns and showed high encapsulation efficiency of a 33 amino acid peptide (V3 BRU). In vitro release kinetics studies showed that such microparticles could be employed for both oral immunization and controlled release. The encapsulation of a seven aminoacid peptide in the same conditions, led to a very low encapsulation efficiency. In order to increase the entrapment efficiency, two strategies were adopted: taking into account the solubility of pBC 264 at different pH, a pH gradient was created to prevent the leakage of the encapsulated peptide into the outer aqueous phase. The inner aqueous phase was maintained at basic pH where the peptide was soluble, while the external aqueous phase was acidic: ovalbumin was added during preparation to stabilize the inner emulsion. These two strategies allowed to increase significantly the encapsulation rate of pBC 264. Nevertheless, the in vitro release kinetics of the peptide were strongly influenced by the presence of ovalbumin which seems to form pores in the microsphere structure (80% of the total peptide content was released after 30 minutes). By contrast, when ovalbumin was replaced by Pluronic F 68 microspheres did not have pores, thus the release profile and the extent of the burst were much smaller. When microspheres were stereotactically implanted in the rat brain, in vivo release profiles were in good agreement with the release observed in vitro. In conclusion, these microspheres are well suited for the slow delivery of neuropeptides in the brain, a feature expected to facilitate the study of long term effects of these compounds.

Animals↗
PubMed1997

On the use of ion-pair chromatography to elucidate doxorubicin release mechanism from polyalkylcyanoacrylate nanoparticles at the cellular level.

The major hypothesis underlying the remarkable efficiency of polyalkylcyanoacrylate particles loaded with doxorubicin against multidrug resistant tumor cells in vitro, is based on the ion-pair association of doxorubicin with soluble hydrolysis products of polyalkylcyanoacrylate. In an attempt to demonstrate the validity of this hypothesis, we have used ion-pair reversed-phase high-performance liquid chromatography and a laboratory-synthetized compound, i.e., the 2-cyano-2-butylhexanoic acid, as a model for polyalkylcyanoacrylate highly polydispersed degradation products. It is shown that, compared to a counter-ion, like heptane sulfonic acid, 2-cyano-2-butylhexanoic acid exhibits an effective ion-pairing effect at different pH values and organic mobile phase conditions. Moreover, at pH close to physiological conditions and at low mobile phase organic modifier percentage, this effect is experimentally observed, which strongly supports the initial hypothesis.

Antibiotics, Antineoplastic↗
PubMed1997

Multiple emulsion technology for the design of microspheres containing peptides and oligopeptides.

This paper reviews the preparation and characterization of small poly(lactic-co-glycolic acid) microspheres (mean size lower than 10 µm) containing small peptides and prepared by a water-in-oil-in-water emulsion solvent evaporation technique. These microspheres were shown to encapsulate very efficiently a 33 amino acid peptide (V3 BRU) and in vitro release kinetics studies showed that such microspheres could be employed for both oral vaccination and controlled release. The encapsulation of a seven amino acid peptide (pBC 264) led on the contrary to a very low encapsulation efficiency. In order to increase the encapsulation of pBC 264, two strategies were adopted: (i) taking into account the solubility of pBC 264 at different pH, the inner aqueous phase was maintained at a basic pH where the peptide was soluble, while the external aqueous phase was acidic; (ii) ovalbumin was added to stabilize the inner emulsion. These two strategies allowed us to increase significantly the encapsulation rate of pBC 264. Nevertheless, the in vitro release kinetics of the peptide were strongly influenced by the presence of ovalbumin which seems to form pores in the microsphere structure. By contrast, when ovalbumin was replaced by Pluronic(R) F68, microspheres did not have pores, thus the release profile and the extent of the burst were much smaller. When microspheres were stereotactically implanted in the rat brain, in vivo release profiles were in good agreement with the release observed in vitro. In conclusion, these microspheres are well suited for the slow delivery of neuropeptides in the brain, a feature expected to facilitate the study of long term effects of these compounds.

Journal Article↗
PubMed1997

Development of sterically stabilized poly(isobutyl 2-cyanoacrylate) nanoparticles by chemical coupling of poly(ethylene glycol).

To develop rapidly biodegradable "stealth" nanoparticles, a physicochemical investigation was done on the formation of PEG-coated poly(isobutyl 2-cyanoacrylate) (PIBCA) nanoparticles. In particular, this study focused on the effect of polymerization conditions on particle size and surface properties, such as charge and hydrophilicity. Among the parameters involved, the pH of the polymerization medium was found to be a key to control the preparation of PEG-coated nanoparticles. Currently, poly(alkylcyanoacrylate) (PACA) nanoparticles are prepared in H2O at pH 2.5, the most appropriate for producing nanoparticles with a mean diameter of 200 nm and an unimodal size distribution. The presence of PEG in the polymerization medium was shown to affect particles formation: only a pH value < 1.5 led to the formation of colloidal nanoparticles, and slight pH variations dramatically affected particle size and PEG association. Polymer chemistry investigations and chemical determination of PEG strongly suggest that PEG associated with nanoparticles was well copolymerized with PIBCA.

Biocompatible Materials↗
PubMed1997

Complement consumption by poly(ethylene glycol) in different conformations chemically coupled to poly(isobutyl 2-cyanoacrylate) nanoparticles.

There is an increasing interest to develop injectable drug polymeric carriers not recognizable by the body as foreign particles and eliminated very quickly from the bloodstream. A polyethylene glycol (PEG)-coating onto injectable particles showed to reduce either protein adsorption and complement consumption, as a function of the PEG density. In this work we compared the complement rejecting ability of PEG in different conformations coupled to polyisobutylcyanoacrylate (PIBCA) nanoparticles, through the analysis of the residual hemolytic capacity of the human serum after contact with the particles. Nanoparticles were formed by chemical coupling of PEG during emulsion/polymerization of isobutylcyanoacrylate (IBCA). Nanoparticles characterization included an investigation of their surface properties, such as hydrophilicity and conformational mobility of the PEG chains grafted on the nanoparticles surface, and PEG total content. The polymerization kinetics of IBCA in presence of PEG or MePEG were also studied. Complement consumption was observed to be very sensitive to the number of particles in contact with human serum, as well as to the PEG conformation, suggesting PEG configuration could affect the particle exposed surface.

Complement System Proteins↗
PubMed1997

Evaluation of hepatic antioxidant systems after intravenous administration of polymeric nanoparticles.

We have investigated the modifications of the levels of intracellular markers of the oxidative stress in hepatocytes, after single or repeated injections of poly(isobutyl cyanoacrylate) (PIBCA) and polystyrene (PS) nanoparticles. Nanoparticles were administered intravenously at single doses of 20 and 100 mg kg 1 for 14 days. Levels of reduced (GSH) and oxidized (GSSG) glutathione, superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CT) and the peroxidation of membrane lipids were measured. Single and repeated administration of PIBCA and PS nanoparticles induced a transient depletion of GSH and GSSG levels, a transient inhibition of SOD activity and a slight increase in CT activity. However, GPx activity was not modified and lipid peroxidation was not observed, suggesting that hepatocytes are not strongly affected by these modifications. Since nanoparticles do not distribute in hepatocytes, oxidative species could proceed from hepatic macrophages, activated after nanoparticle phagocytosis. It is unlikely that poly(alkyl cyanoacrylate) degradation products might be responsible for the oxidative attack because non-biodegradable PS nanoparticles induced the same effect. Uptake of polymeric nanoparticles by Kupffer cells in the liver induce modifications in hepatocyte antioxidant systems, probably due to the production of radical oxygen species. However, the depletion in glutathione was not great enough to initiate hepatocyte damage, since no changes in lipid peroxidation and reversible alterations were observed. This is an important factor to be considered in the use of polymeric nanoparticles as drug carriers.

Animals↗
PubMed1997

Poly(alkyl cyanoacrylate) nanospheres for oral administration of insulin.

Poly(alkyl cyanoacrylate) nanocapsules have been successfully used for oral administration of insulin in diabetic rats. This work reports a suitable formulation for insulin-loaded nanospheres composed of full polymeric structures formed by polymerization of isobutyl cyanoacrylate (IBCA) in an acidic medium, insulin (15 U/mL) being added to the polymerization medium 60 min after the onset of polymerization. These nanospheres (MW 364) displayed a mean size of 145 nm and an association rate of 1 U of insulin/mg of polymer. They protected insulin from the degradation by proteolytic enzymes in vitro, especially when they were dispersed in an oily medium (Miglyol 812) containing surfactive agents (Poloxamer 188 and deoxycholic acid). When dispersed in the same medium, insulin-loaded nanospheres (100 U/kg of body weight), administered perorally in streptozotocin-induced diabetic rats, provoked a 50% decrease of fasted glycemia from the second hour up to 10-13 days. This effect was shorter (2 days) or absent when nanospheres were dispersed in water with surfactive agents or not. Using 14C-labeled nanospheres loaded with [125I]insulin, it was found that nanospheres increased the uptake of [125I]insulin or its metabolites in the gastrointestinal tract, blood, and liver while the excretion was delayed when compared to [125I]insulin nonassociated to nanospheres; in addition, 14C- and 125I-radioactivities disappeared progressively as a function of time, parallel to the biological effect. Thus insulin-loaded nanospheres can be considered as a convenient delivery system for oral insulin at the prerequisite that they were dispersed in an oily phase containing surfactants.

Administration, Oral↗
PubMed1997

Splenic trapping of nanoparticles: complementary approaches for in situ studies.

PURPOSE: To identify more accurately in the spleen, the areas and the cells where nanoparticulate carriers were taken up from the blood flow, a series of complementary approaches were used. METHODS: First, in and ex vivo examination of the whole spleen led to a global view of all the trapping areas. Then, histological studies on frozen sections of the same organ allowed for a more precise localization of these areas and image analysis gave an evaluation of tissue distribution of the nanoparticles. Finally, immunological and enzymological characteristics of the capturing cells were determined in situ, using monoclonal antibodies (F4/80 and anti-sialoadhesin) and cytochemical reactions (esterases and acid phosphatase). Furthermore incubation of spleen slices with different nanoparticles was used so as to know if the capture was due to a high capturing capacity of these cells or to a high blood flow in their vicinity. RESULTS: It was shown that more than 90% of the splenic capture was localized in the marginal zone of the follicles. The capturing cells form a special population of macrophages inserted in a reticular meshwork, showing low esterase and acid phosphatase activities, giving faint or no reaction with F4/80 or anti-sialoadhesin antibodies. The circulating nanoparticles were quickly trapped with rather low specificity by these cells. CONCLUSIONS: Combination of coherent approaches allowed for the tracking of capturing cells from in vivo observations to their in situ identification on immunological and enzymological criteria.

Animals↗
PubMed1997

Reversion of multidrug resistance with polyalkylcyanoacrylate nanoparticles: towards a mechanism of action.

Polyalkylcyanoacrylate (PACA) nanoparticles loaded with doxorubicin allowed multidrug resistance to be overcome in vitro. However, increased cytotoxicity is not always correlated with an increased level of intracellular drug. Although we have previously shown that PACA nanoparticles are not endocytosed by tumour cells, we report here that a direct interaction between nanoparticles and cells is a necessary requirement for overcoming resistance. In addition, the results showed that the degradation products of PACA (mainly polycyanoacrylic acid) in the presence of doxorubicin are able to increase both accumulation and cytotoxicity, thus suggesting the formation of a doxorubicin-polycyanoacrylic acid ion pair. It is therefore concluded that resistance is overcome as a result of both the adsorption of nanoparticles to the cell surface and increased doxorubicin diffusion by the accumulation of an ion pair at the plasma membrane.

Animals↗
PubMed1997

Protective immunity against Salmonella typhimurium elicited in mice by oral vaccination with phosphorylcholine encapsulated in poly(DL-lactide-co-glycolide) microspheres.

Encapsulation of vaccines in biodegradable microspheres provides excellent mucosal immunogens with a high potential for immunization against bacterial infections. We tested the protective immunity elicited by intragastric vaccination with phosphorylcholine (PC) encapsulated in poly(DL-lactide-co-glycolide) (DL-PLG) microspheres against Salmonella typhimurium in a mouse model of invasive intestinal infection. We chose PC as the antigen because it was found to elicit an immune response after intestinal exposure of mice to PC-bearing S. typhimurium and because anti-PC immunity protects mice against Streptococcus pneumoniae, another PC-bearing microorganism. Mice were primed intragastrically on days 1, 2, and 3 and boosted on days 28, 29, and 30 with PC (280 microg) coupled to porcine thyroglobulin (PC-thyr) encapsulated in DL-PLG microspheres, free PC-thyr, or blank microspheres. A significant rise in anti-PC immunoglobulin A (IgA) titers, as measured by an enzyme-linked immunosorbent assay, was observed in the intestinal secretions after immunization with PC-loaded microspheres, compared to the titers of mice immunized with free PC-thyr or blank microspheres. This antibody response peaked 14 days after the last boost and correlated with a highly significant resistance to oral challenge by S. typhimurium C5 (P < 10(-3)). Control mice were primed intraperitoneally on day 1 with 15 microg of PC in complete Freund's adjuvant and boosted on days 10, 14, and 20 with the same dose without adjuvant but via the same route. In these mice, the levels of anti-PC IgA in intestinal secretions were equivalent to those of the mice intragastrically immunized with PC-loaded microspheres, but protection was significantly weaker, suggesting that either the IgAs were not functional or that other immune mechanisms are important in protection. Taken together, our results highlight the potential of antigen encapsulation in DL-PLG microspheres for eliciting protective immunity against invasive intestinal bacterial diseases and suggest that a similar strategy could be used against diseases caused by other PC-bearing microorganisms.

Administration, Oral↗
PubMed1996

Development of a quantitative polyacrylamide gel electrophoresis analysis using a multichannel radioactivity counter for the evaluation of oligonucleotide-bound drug carrier.

A quantitative polyacrylamide gel electrophoresis (PAGE) analysis using a multichannel radioactivity counter was designed for the evaluation of 33P-labeled antisense oligonucleotide associated with polymeric drug carrier (nanoparticles). The proposed analytical method was first validated. The criteria of specificity, linearity, reliability, detection and quantification limits, and resolution power were determined. Results were compared to those obtained using liquid scintillation counting of crude samples or after solubilization of gel slices. The proposed method gave a better linearity and reliability than liquid scintillation counting of solubilized gel slices. In comparison with the liquid scintillation counting of crude samples, the method presented the advantage of being able to directly separate oligonucleotides differing by only one nucleotide in length. This method was applied for the separation of free oligonucleotides and oligonucleotides bound onto nanoparticles, allowing quantification of the amount of free and bound oligonucleotides without any further separation steps. Thus, because it is easy and rapid, the quantitative PAGE analysis using a multichannel radioactivity counter offers interesting possibilities for the characterization of oligonucleotide nanoparticles.

Cyanoacrylates↗
PubMed1996

Retrovirus budding may constitute a port of entry for drug carriers.

This paper investigates the relation between viral infection and cell uptake of liposomes and nanoparticles. A defective virus was used to infect two types of cells: cells allowing virus budding (psi2neo cells) and cells bereft of a virus exit process (NIH 3T3 cells). This study has revealed that cell uptake of pH-sensitive-liposomes is highly dependent on the virus exit process, since it ensued only when virus budding occurred. This preferential uptake of pH-sensitive liposomes by infected cells was not carrier-specific because similar uptake was observed with non-biodegradable fluorescent nanoparticles using confocal microscopy. Also, inhibition of neo gene expression by oligonucleotide pH-sensitive-liposomes was only observed in the cell system (psi2neo) endowed with a virus exit process. Finally, increased membrane fluidity was noted in the infected cells, possibly reflecting membrane perturbation due to virus budding. We suggest that this membrane perturbation may be the key to the uptake of the different colloidal carriers. Infected cells could, thus, constitute a natural target for particulate drug carriers.

3T3 Cells↗
PubMed1996

Effect of polymeric nanoparticle administration on the clearance activity of the mononuclear phagocyte system in mice.

We investigated the consequences of acute and subacute administration of mice with polyisobutylcyanoacrylate (PIBCA), polyisohexylcyanoacrylate (PIHCA), poly(D,L-lactic) acid (PLA), and polystyrene (PS) nanoparticles on the mononuclear phagocyte system phagocytic function. This was done by measuring the clearance rate of colloidal carbon. Single administration of PIBCA and PIHCA (but not PLA and PS) nanoparticles reduced carbon clearance in both a time- and dose-dependent fashion. Since clearance of preopsonized carbon was normal, it was assumed that PIBCA and PIHCA nanoparticles deplete opsonins specific for carbon recognition. A decrease in plasma fibronectin levels resulting from nanoparticle administration suggested its implication in their removal from blood. However, fibronectin does not seem to be responsible for PIBCA and PIHCA blockade. Phagocytic function was preserved after repeated treatment with nanoparticles, probably as a result of increased Kupffer cell phagocytic activity and the contribution of spleen macrophages. Neither toxicity nor effects due to nanoparticle hepatic accumulation were observed.

Animals↗
PubMed1996

On the mechanism of action of doxorubicin encapsulation in nanospheres for the reversal of multidrug resistance.

We had previously shown that doxorubicin encapsulation in polyisohexylcyanocrylate nanospheres could circumvent the P-glycoprotein-mediated multidrug resistance (MDR) exhibited by C6 rat glioblastoma in culture. We then investigated what could be the mechanism of such a circumvention. The cytotoxicity of free and encapsulated doxorubicin was evaluated in two MDR variants of the C6 cell line in a device allowing the separation of cells from drugs by a polycarbonate membrane of 0.2 micron pore size. We observed that the progressive disruption of the nanospheres allowed their doxorubicin content to reach the cell monolayer and exert its cytotoxicity in a fashion similar to that exhibited by free doxorubicin. However, no circumvention of MDR is obtained by doxorubicin encapsulation when drug-containing nanospheres are separated from the cells by the polycarbonate membrane. In addition, no effect on azidopine binding to P-glycoprotein-enriched membranes is exerted by unloaded nanospheres, even after their spontaneous degradation in cell-culture medium. Taken together, these results suggest that a physical contact between doxorubicin-containing nanospheres and the cells is required for the circumvention of MDR. The role of degradation products from the nanospheres as modulators of P-glycoprotein activity can be ruled out.

Animals↗
PubMed1996

Cells involved in the capture of nanoparticles in hematopoietic organs.

The affinity of nanoparticles for hematopoietic organs could be valuable for the targeting of certain stimulating factors to those tissues, but this affinity should also be taken into account in the toxicological evaluation of those carriers, especially when they are loaded with antimitotic compounds such as doxorubicin. However, the cells responsible for the capture of the nanoparticles and their localization in these organs is an important point to know before trying to modulate the nanoparticle's tissue distribution. Thus, we have studied, in this paper, the capture, the localization, and the retention in the bone marrow and in the spleen of biodegradable poly(isohexyl cyanoacrylate) nanoparticles as well as of nonbiodegradable polystyrene nanoparticles. The histological localization of these nanoparticles has been completed by cytological localization with a method used in cytochemistry for the evaluation of intracellular accumulation of various substances, such as iron deposits in bone marrow sideroblasts. These data indicate that, in the bone marrow, after a quick passage through the endothelium, nanoparticles were dispersed throughout in the tissue and captured by all types of phagocytizing cells. In the spleen, nanoparticles were mainly localized in large angular capturing cells in the marginal zone of the lymphoid follicles.

Animals↗
PubMed1996

Pharmacokinetics and biodistribution of oligonucleotide adsorbed onto poly(isobutylcyanoacrylate) nanoparticles after intravenous administration in mice.

PURPOSE: The goal of this study was to evaluate the ability of nanoparticles to be used as a targeted delivery system for oligonucleotides. METHODS: Pharmacokinetic and tissue distribution were carried out in mice by measuring radioactivity associated to the model oligothymidylate 33P-pdT16 loaded to poly(isobutylcyanoacryate) (PIBCA) nanoparticles. In addition, we have used a TLC linear analyzer to measure quantitatively on a polyacrylamide gel electrophoresis, the amount of non degraded pdT16. RESULTS: Organ distribution study has shown that nanoparticles deliver 33P-pdT16 specifically to the liver reducing its distribution in the kidney and in the bone marrow. Nanoparticles could partially protect pdT16 against degradation in the plasma and in the liver 5 min after administration, whereas free oligonucleotide was totally degraded at the same time. CONCLUSIONS: Nanoparticles protect oligonucleotides in vivo against degradation and deliver them to the liver.

Adsorption↗
PubMed1996

Slow delivery of the selective cholecystokinin agonist pBC 264 into the rat nucleus accumbens using microspheres.

Neuropeptides have been shown to play a critical role in adaptational processes, probably by long-term modulation of neuronal pathways. It could therefore be interesting to study behavioral changes induced by chronic local stimulation of neuropeptide receptors. With this aim poly(lactide-co-glycolide) microspheres loaded with a highly potent, peptidase-resistant, cholecystokinin (CCK)-B-selective CCK peptidomimetic agonist (pBC 264) were prepared by a water in oil in water emulsion solvent evaporation method and stereotaxically implanted into the anterior part of the rat nucleus accumbens. Two different kinds of loaded polymeric microspheres differing only by the stabilizing agent [ovalbumin (OVA) or Pluronic F 68] added to the inner emulsion were used. The histological and behavioral studies done 24 h and 8 days after implantation of nonloaded microspheres in the nucleus accumbens indicated that the microspheres were well tolerated. The in vivo release of the selective CCK-B agonist pBC 264 (associated with a tracer dose of [3H]pBC 264) from microspheres prepared with OVA was very fast (92% after 6 h), whereas only 26% (88 pmol) of pBC 264 was released from the formulation with Pluronic F 68 after 24 h. Eight days after implantation 36% of pBC 264 had diffused from the microspheres, and 8% (approximately 30 pmol) was still present in the brain concentrated around the site of administration. In all cases the released material was found to correspond to intact pBC 264, thus demonstrating the possibility of obtaining a slow controlled release of peptide in vivo. This method opens up interesting perspectives to study the long-term effects of neuropeptides.

Animals↗