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Biomedical subjects

P Couvreur

Publications and source records attributed to P Couvreur.

At least 55 records · Page 3Linked to original sources
PubMed2000

Improvement of in vivo stability of phosphodiester oligonucleotide using anionic liposomes in mice.

Antisense phosphodiester oligonucleotides (ODN) are unstable in biological fluids due to nuclease-mediated degradation and therefore cannot be used in most antisense therapeutic applications. We describe here an in vitro and in vivo stabilization of a 15 mer phosphodiester sequence using anionic liposomes. Two formulations have been studied: DOPC/OA/CHOL and DOPE/OA/CHOL (pH-sensitive liposomes). Our in vitro findings reveal the same stabilization effect in mouse plasma for both anionic liposomes. In vivo investigation showed a great protective effect for both formulations after intravenous administration to mice. By contrast with in vitro results, a higher protection of ODN was observed with DOPC/OA/CHOL liposomes compared to the DOPE/OA/CHOL formulation. The latter was degraded in blood (75% of the injected dose at 5 min) probably due to interactions with blood components, and the remaining (25% at 5 min) was distributed mostly to the liver and spleen. DOPC liposomes were remarkably stable in blood and were distributed more slowly to all studied organs (liver, spleen, kidneys and lungs). Intact ODN was still observed in some organs (liver, spleen, lungs), but not in blood, 24 hours after DOPC liposome administration. These results suggest that this antisense strategy using carrier systems may be applicable to the treatment of diseases involving the reticuloendothelial system.

Animals↗
PubMed2000

Investigation of the role of macrophages on the cytotoxicity of doxorubicin and doxorubicin-loaded nanoparticles on M5076 cells in vitro.

Doxorubicin-loaded PACA nanoparticles have been shown to be more efficient than free drug in mice bearing hepatic metastasis of the M5076 tumour. Due to the high phagocytic activity of Küpffer cells in the liver, it may be that these cells played a role of drug reservoir after nanoparticle phagocytosis. Therefore, the objective of this study was to assess the role of macrophages in mediating the cytotoxicity of doxorubicin-loaded nanoparticles on M5076 cells. The growth inhibition of tumour cells was evaluated in two ways: firstly, the cells were incubated in a coculture system consisting of special wells with two compartments separated by a porous membrane. M5076 cells were seeded into the lower compartment and the macrophages J774.A1 were introduced into the upper part. The macrophages were activated or not by IFN-gamma. The drug preparations were added only in the macrophage insert. Secondly, growth inhibition was also assessed in the conventional way, i.e. in direct contact with the tumour cells to serve as a reference. After direct contact, free doxorubicin (Dox) and doxorubicin-loaded nanoparticles (NP-Dox) had the same efficacy against M5076 cell growth. The coculture experiments led to a 5-fold increase in the IC(50) for both Dox and NP-Dox. The activation of macrophages by IFN-gamma in coculture significantly decreased the IC(50) values. In conclusion, after phagocytosis of doxorubicin-loaded nanoparticles, J774.A1 cells were able to release active drug, allowing it to exert its cytotoxicity against M5076 cells. Drug efficacy was potentiated by the activation of macrophages releasing cytotoxic factors such as NO, which resulted in increased tumour cell death. Thereby, the coculture system permitted us to investigate the macrophage-mediated cytotoxicity of colloidal carriers loaded with an anticancer drug, which is of great interest when further i.v. administration is envisaged.

Animals↗
PubMed2000

Intranasal immunization with protein-linked phosphorylcholine protects mice against a lethal intranasal challenge with streptococcus pneumoniae.

Immunization against phosphorylcholine (PC) linked to a protein protects mice against Streptococcus pneumoniae when used parenterally, and against Salmonella typhimurium when used orally after entrapment in D,L-Lactide-co-Glycolide microspheres. Here, we immunized BALB/c mice intranasally with a serotype 3 S. pneumoniae strain. Immunization was followed by a rise in anti-PC IgA and IgG titers in serum and in pulmonary secretions, but not by any rise in anti ds-DNA antibody nor any glomerular Ig deposition. The survival rates were 91 and 76% in the two groups of mice, respectively. These rates were significantly higher than those in control mice immunized intranasally either with Thyr loaded in microspheres (0%), blank microspheres (22%), free Thyr (17%), and saline (18%). This demonstrates that the mucosal route is effective for vaccination against S. pneumoniae pneumonia with PC linked to a protein carrier. It constitutes another important step forward in the development of the concept that PC can be used as a mucosal immunogen for protection against the different diseases caused by PC-bearing bacteria.

Administration, Intranasal↗
PubMed2000

Oral tolerance elicited in mice by beta-lactoglobulin entrapped in biodegradable microspheres.

Oral administration of antigen is known to be appropriate for some vaccine purposes as well as oral tolerance induction. In the present study, oral administration of beta-lactoglobulin (BLG) loaded poly(D,L-lactide-co-glycolide) (D,L-PLG) microspheres induced tolerance was evaluated. A single feeding of 5 micrograms of encapsulated BLG tolerized BALB/c mice to subsequent BLG parenteral challenge, suppressing the specific humoral, intestinal and cellular responses. The tolerogenic efficient dose was then reduced 10,000 times, compared to oral administration of soluble BLG. This suggests that loading food proteins into D,L-PLG microspheres might be a potential tool for inducing oral tolerance with allergens.

Animals↗
PubMed2000

Role of spleen macrophages in the clearance of scrapie agent early in pathogenesis.

The involvement of spleen macrophages in the early stages of scrapie pathogenesis was studied by applying the 'macrophage-suicide technique' to scrapie-infected mice. This method comprises critically the intravenous administration to mice of dichloromethylene disphosphonate encapsulated into liposomes. Depletion of spleen macrophages before scrapie infection induced an increased amount of scrapie inoculum in the spleen, consequently leading to accelerated scrapie agent replication in the early phase of pathogenesis, as followed by PrPres accumulation, a specific hallmark of scrapie. The same effect was observed when spleen macrophages were depleted just before the beginning of scrapie agent replication. These findings suggest that macrophages may partly control scrapie infection in peripheral tissues by sequestration of the scrapie inoculum and may thus impair early scrapie agent replication in the spleen. In addition to macrophages, most follicular dendritic cells and B lymphocytes, which are thought to support scrapie agent replication, were also transiently depleted by dichloromethylene disphosphonate administration. This suggests that a compensatory mechanism is sufficient to ensure the persistence of infection in these early stages of pathogenesis.

Analgesics, Non-Narcotic↗
PubMed2000

Design of folic acid-conjugated nanoparticles for drug targeting.

The new concept developed in this study is the design of poly(ethylene glycol) (PEG)-coated biodegradable nanoparticles coupled to folic acid to target the folate-binding protein; this molecule is the soluble form of the folate receptor that is overexpressed on the surface of many tumoral cells. For this purpose, a novel copolymer, the poly[aminopoly(ethylene glycol)cyanoacrylate-co-hexadecyl cyanoacrylate] [poly(H(2)NPEGCA-co-HDCA)] was synthesized and characterized. Then nanoparticles were prepared by nanoprecipitation of the obtained copolymer, and their size, zeta potential, and surface hydrophobicity were investigated. Nanoparticles were then conjugated to the activated folic acid via PEG terminal amino groups and purified from unreacted products. Finally, the specific interaction between the conjugate folate-nanoparticles and the folate-binding protein was evaluated by surface plasmon resonance. This analysis confirmed a specific binding of the folate-nanoparticles to the folate-binding protein. This interaction did not occur with nonconjugated nanoparticles used as control. Thus, folate-linked nanoparticles represent a potential new drug carrier for tumor cell-selective targeting.

Capsules↗
PubMed2000

Pharmacological manipulation of early PrPres accumulation in the spleen of scrapie-infected mice.

In most experimental models of scrapie and in some naturally infected species, the lymphoreticular system and the spleen in particular play a major role in the pathogenesis of the disease. Previous studies demonstrated scrapie infectivity in peripheral organs from the day of infection up to the terminal stage. The discovery of the abnormal prion protein, PrPres, as a specific molecular hallmark of scrapie should permit enhanced study of scrapie pathogenesis and has some pharmacological applications. In this study, PrPres accumulation was followed day by day in peripheral organs. Four different phases were identified: the circulation of scrapie inoculum, a clearance phase, the peripheral accumulation of PrPres and a plateau phase. This kinetics was then pharmacologically modified (i) by applying the macrophage "suicide" technique to unveil the cellular types involved in scrapie pathogenesis and (ii) with anti-scrapie drugs such as polyene antibiotics, polyanions and Congo red to investigate their mode and site of action.

Amphotericin B↗
PubMed2000

Reversion of multidrug resistance by co-encapsulation of doxorubicin and cyclosporin A in polyalkylcyanoacrylate nanoparticles.

Individual and combined polyalkylcyanoacrylate nanoparticle formulation of cyclosporin A and doxorubicin were prepared and evaluated in an attempt to show improved growth inhibition efficacy in a resistant cell culture line. The drug loaded nanoparticles were prepared using the well established emulsion polymerization process without using any modification for the hydrophilic doxorubicin drug whereas the incorporation of cyclosporin A needed to wait a moment after the polymerization reaction started. This was necessary to avoid cyclosporin A precipitation and polymer aggregation. Cyclosporin A release from the nanoparticles was rapid probably because the drug was adsorbed onto the nanoparticles surface rather than embedded into the polymeric core. Doxorubicin displayed also a burst effect but with a slower second phase probably related with the nanoparticles bioerosion rate owing to its entrapment in the polymeric network. Finally, it was shown in resistant cell culture experiments that the association of both cyclosporin A and doxorubicin within a single nanoparticle formulation elicited the most effective growth rate inhibition as compared to other combinations of both drugs while using a lower amount of polymer compared to separated nanoparticle formulations. This result was probably due to the synergistic effect achieved by combining the chemo-sensitizing compound cyclosporin A, with an effective cytotoxic drug like doxorubicin.

Animals↗
PubMed2000

Targeted delivery of antibiotics using liposomes and nanoparticles: research and applications.

This review examines current technologies for increasing the bioavailability of antibiotics by means of liposomes or nanoparticles. The main focus is on liposomes. These carriers were preferentially developed because their composition is compatible with biological constituents. Biodegradable polymers in the form of colloidal particles have also been used and show promise for future applications in antimicrobial chemotherapy. The in vivo behaviour of both types of carriers and consequently their therapeutic potential, are determined by their route of administration. Conventional carrier strategies permit the mononuclear phagocyte system to be targeted by intravenous injection of antibiotics. Stealthy strategies avoid major uptake by these cells and extend the systemic presence of these carriers. The purpose of this review is to provide background information in antibiotic targeting gathered from papers published over the last twenty years. It seems clear that such drug carriers (liposomes, nanoparticles) allow increased drug concentration at infected sites but reduce drug toxicity.

Aminoglycosides↗
PubMed2000

Intravitreal administration of antisense oligonucleotides: potential of liposomal delivery.

Antisense oligonucleotides are short synthetic fragments of genes that are able to inhibit gene expression after being internalized by cells. They can therefore be used as antiviral compounds particularly, for the treatment of ocular viral infections (i.e. Herpes simplex virus or Cytomegalovirus, CMV). Antisense oligonucleotides are however poorly stable in biological fluids and their intracellular penetration is limited. Although oligonucleotides are now currently used in therapeutics for the treatment of CMV by intravitreal injection (Vitravene) their main drawbacks impose to repeat the number of administrations which can be very harmful and damaging. A system that is able to permit a protection of oligonucleotides against degradation and their slow delivery into the vitreous would be more favorable for improving patient compliance. The use of liposomes for intravitreal administration can be very promising since these lipid vesicles are able to protect oligonucleotides against degradation by nucleases and they allow to increase the retention time of many drugs in the vitreous. In this review, the potentialities of liposomes for the intravitreal delivery of oligonucleotides will be discussed.

Administration, Topical↗
PubMed2000

Polyisobutylcyanoacrylate nanocapsules containing an aqueous core as a novel colloidal carrier for the delivery of oligonucleotides.

PURPOSE: The goal of the present paper was to encapsulate oligonucleotides in a new particulate carrier in order to protect them from enzymatic degradation. METHODS: Nanocapsules with an aqueous core containing oligonucleotides were prepared by interfacial polymerization of isobutylcyanoacrylate in a W/O emulsion. Ultracentrifugation and re-suspension in water yielded a dispersion of these containing an aqueous core nanocapsules. Zeta potential measurements and quenching of fluorescence of fluorescein-bounded oligonucleotides were used to study the localization of the oligonucleotides. Oligonucleotide degradation studies were carried out in fetal calf serum. RESULTS: Polydisperse nanocapsules of size ranging from 20 to 400 nm were obtained. Oligonucleotide loading did not significantly influence the zeta potential, suggesting they were located within the core of the nanocapsules. Fluorescence quenching assays confirmed this localization. When encapsulated in the nanocapsules and incubated in the presence of serum, the oligonucleotides were efficiently protected from degradation by nucleases, whereas oligonucleotides adsorbed onto nanospheres were protected less efficiently. CONCLUSIONS: This paper describes, for the first time, a nanotechnology able to encapsulate oligonucleotides rather than adsorbing them at the surface of a solid support. Such a formulation has great potential for oligonucleotide delivery.

Colloids↗
PubMed2000

Near infrared with principal component analysis as a novel analytical approach for nanoparticle technology.

PURPOSE: To progress in the characterization of a poly(MePEGcyanoacrylate-co-hexadecylcyanoacrylate) (poly(PEGCA-co-HDCA) copolymer and the nanoparticles formed from this copolymer. METHODS: Poly(PEGCA-co-HDCA) at a MePEG/hexadecyl ratio of 1:4 was investigated by 1H-NMR and near infrared spectroscopy. The nanoparticle suspensions, obtained by the methods of nanoprecipitation or emulsion--solvent evaporation, as well as the crude nanoparticles and their dispersion medium--were analyzed by MePEG measurement, 1H-NMR, and near infrared spectroscopy. RESULTS: The 1H-NMR results showed that the (poly(PEGCA-co-HDCA) copolymer obtained bore lateral hydrophilic MePEG chains and lateral hydrophobic hexadecyl chains in a final ratio of 1:4. However, this ratio, although reproducible from batch to batch, represented only a mean value for different molecular species. Indeed, our results demonstrated the formation of more hydrophobic poly(alkyl-cyanoacrylate) oligomers (with a higher content of hexadecyl chains) and other more hydrophilic oligomers (with a higher MePEG content). Only the more hydrophobic oligomers were able to form solid pegylated nanoparticles. As far as these nanoparticles were concerned, determination of their MePEG content allowed the calculation of a distance of 1.2 nm and 1.05 nm between 2 grafted MePEG chains at the nanoparticle surface, when obtained by nanoprecipitation and emulsion-solvent evaporation, respectively. Moreover, when the same copolymer batch was used, different nanoparticles were obtained according to the preparation method, as seen by near infrared spectroscopy. CONCLUSIONS: The nanoparticles obtained by nanoprecipitation or emulsion-solvent evaporation of poly(PEGCA-co-HDCA) 1:4 copolymer displayed a different supramolecular organization, as evidenced by the near infrared spectroscopy results. Moreover, these nanoparticles showed surface characteristics compatible with a long circulating carrier.

Colloids↗
PubMed1999

Study of the mechanism of insulin encapsulation in poly(isobutylcyanoacrylate) nanocapsules obtained by interfacial polymerization.

In previous studies, insulin-loaded poly(alkylcyanoacrylate) nanocapsules were found to reduce the blood glucose level after oral administration to diabetic rats and dogs. The reduction of the glycemia induced by the nanocapsules was the same regardless of the insulin doses administered, but the effect appeared only after a delay of a few days. The purpose of this study was to investigate the mechanism of insulin encapsulation and the type of interactions that may exist between the polymer forming the nanocapsule wall and the insulin. The results of this study showed, based on the interfacial polymerization of isobutylcyanoacrylate, that the insulin molecule is not chemically modified during the nanoencapsulation process. In addition, no interaction between the poly(isobutylcyanoacrylate) and the insulin could be observed. The observed high encapsulation efficiency of intact insulin may be explained by the fact that the ethanol used in the preparation of the nanocapsules is responsible for the initiation of the interfacial polymerization of isobutylcyanoacrylate instead of the insulin. The zeta potential measurements suggest that insulin is located within the core of the nanocapsules. Thus the biological activity of the nanoencapsulated peptide and the high efficiency of insulin encapsulation achieved with this nanoencapsulation process cannot be explained by a specific interaction of the insulin with the polymer forming the nanocapsule's wall. It may be due, however, to the fact that the encapsulated insulin molecule is chemically intact and located within the oily core of the nanocapsules.

Animals↗
PubMed1999

Stealth PEGylated polycyanoacrylate nanoparticles for intravenous administration and splenic targeting.

The aim of the present work was to investigate the biodistribution characteristics of PEG-coated polycyanoacrylate nanoparticles prepared by the nanoprecipitation/solvent diffusion method using the previously synthesized poly(MePEGcyanoacrylate-hexadecylcyanoacrylate) copolymer. It was observed that [14C]-radiolabeled PEGylated nanoparticles remained for a longer time in the blood circulation after intravenous administration to mice, compared to the non-PEGylated poly(hexadecylcyanoacrylate) (PHDCA) nanoparticles. Furthermore, hepatic accumulation was dramatically reduced, whereas a highly increased spleen uptake was shown. The PEGylation degree of the polymer seemed not to affect the in vivo behavior of the nanoparticles, whereas previously obtained in vitro data have shown a modification of plasma protein adsorption depending on the density of PEG at the surface of the particles. Moreover, the study of the in vitro cytotoxicity of the nanoparticles revealed that the PEGylation of the cyanoacrylate polymer reduced its toxicity. These results open up interesting perspectives for the targeting of drugs to other tissues than the liver.

Animals↗
PubMed1999

Physico-chemical characterization of insulin-loaded poly(isobutylcyanoacrylate) nanocapsules obtained by interfacial polymerization.

Insulin could be encapsulated very efficiently in oily containing poly(isobutylcyanoacrylate) nanocapsules obtained by interfacial polymerization. In addition, these nanocapsules showed unexpected biological activity after intragastric administration. The hypoglycemic effect was characterized by a lag time period of 2 days and a prolonged effect over a period of 20 days. To explain, the high encapsulation rate of insulin achieved in these nanocapsules and the biological effect, this work was focused on the characterization of the nanocapsules and on the study of the mechanism of nanocapsule formation. Results showed that insulin was found unmodified during the nanoencapsulation process. This was due to the large amount of ethanol used in the preparation of the nanocapsules that initiated the polymerization of isobutylcyanoacrylate preserving the peptide from a reaction with the monomer. Results also showed that insulin was located inside the core of the nanocapsules and not simply adsorbed onto their surface.

Bucrylate↗
PubMed1999

Optimization of the encapsulation and release of beta-lactoglobulin entrapped poly(DL-lactide-co-glycolide) microspheres.

The goal of the present paper was to optimize the encapsulation of beta-lactoglobulin (BLG) within poly(lactide-co-glycolide) (PLGA) microparticles prepared by the multiple emulsion solvent evaporation method. The role of the pH of the external phase and the introduction of the surfactant Tween 20, in the modulation of the entrapment and release of BLG from microparticles, was studied. Reducing the solubility of BLG by decreasing the pH of the external phase to a value close to the pI of BLG resulted in a better encapsulation with, however, a larger burst release effect. By contrast, Tween 20 was shown to increase the encapsulation efficiency of BLG and reduce considerably the burst release effect. In fact, Tween 20 was shown to be responsible for removing the BLG molecules that were adsorbed on the particle surface. In addition, Tween 20 reduced the number of aqueous channels between the internal aqueous droplets as well as those communicating with the external medium. Thus, the more dense structure of BLG microspheres could explain the decrease in the burst release. These results constitute a step ahead in the improvement of an existing technology in controlling protein encapsulation and delivery from microspheres prepared by the multiple emulsion solvent evaporation method.

Hydrogen-Ion Concentration↗
PubMed1999

In vivo fate and immune pulmonary response after nasal administration of microspheres loaded with phosphorylcholine-thyroglobulin.

Phosphorylcholine is a widely occurring hapten which is present in the cell wall of many prokaryotes. It is, therefore, an attractive candidate for the development of a vaccine against many bacterial diseases. Poly(D,L-lactide-co-glycolide) microspheres loaded with phosphorylcholine linked to thyroglobulin (PC-Thyr) as protein carrier were prepared. The effect of the protein concentration on antigen encapsulation and release as well as on microsphere morphology has been investigated. When administered intranasally, PC-Thyr-loaded microspheres were taken up by epithelial cells of the nasopharyngeal associated lymphoid tissue and induced a specific IgA and IgG response in pulmonary secretions as well as a strong systemic immune response in BALB/c mice.

Administration, Intranasal↗