Biomedical subjects

P Couvreur

Publications and source records attributed to P Couvreur.

At least 19 recordsLinked to original sources

PubMed2006

Spontaneous association of hydrophobized dextran and poly-beta-cyclodextrin into nanoassemblies. Formation and interaction with a hydrophobic drug.

New nanoassemblies were instantaneously prepared by mixing two aqueous solutions, one containing a beta-cyclodextrin polymer (pbetaCD), and the other a hydrophobically modified by alkyl chains dextran (MD). The formation mechanism and the inner structure of these nanoassemblies were analysed using surface tension measurements and (1)H NMR spectroscopy. The effect of a hydrophobic guest molecule, such as benzophenone (BZ), on the formation and stability of the nanoassemblies was also evaluated. MD exhibited the typical behaviour of a soluble amphiphilic molecule and adsorbed at the air/water interface. Whereas the injection of native beta-CDs in the solution beneath the adsorbed MD monolayer did not produce any change in the surface tension, that of the pbetaCD resulted in an increase in the surface tension, indicating the desorption of the polymer from the interface. This result accounts for a cooperative effect of beta-CDs linked together in the pbetaCD polymer on dextran desorption. The presence of benzophenone in the system hindered the sequestration of dextran alkyl moieties by beta-CD in the polymer without impeding the formation of associative nanoassemblies of 100-200 nm. (1)H NMR investigations demonstrated that, in the BZ-loaded nanoassemblies, the hydrophobic molecule was mainly located into the cyclodextrin cavities.

Benzophenones↗

PubMed2006

Encapsulation of mono- and oligo-nucleotides into aqueous-core nanocapsules in presence of various water-soluble polymers.

In a previous study, we have shown that cidofovir (CDV) and azidothymidine-triphosphate (AZT-TP) were poorly encapsulated in poly(iso-butylcyanoacrylate) (PIBCA) aqueous-core nanocapsules. This was attributed to the rapid leakage of these small and hydrophilic molecules through the thin polymer wall of the nanocapsules. In the present study, we have selected various water-soluble polymers as increasing Mw adjuvants and investigated their influence on the entrapment of mononucleotides (CDV, AZT-TP) as well as of oligonucleotides (ODN) into these PIBCA aqueous-core nanocapsules. We show here that the presence of cationic polymers (i.e. poly(ethyleneimine) (PEI) or chitosan) in the nanocapsule aqueous compartment allowed successful encapsulation of AZT-TP and ODN.

Cations↗

PubMed2006

Novel self-assembling nanogels: stability and lyophilisation studies.

The stability of new supramolecular nanoassemblies (nanogels), based on the association of a hydrophobically modified dextran (MD) and a beta-cyclodextrin polymer (pbetaCD), has been studied by two complementary methods: (i) size measurements and (ii) turbidity experiments using a Turbiscan optical analyser. Nanogels of about 120-150nm were obtained whatever the concentration of the two polymer solutions. At low concentrations, the suspensions presented little mean diameter variations upon storage. However, the concentrated ones tended to destabilize and their mean diameter increased upon time. Size measurements and Turbiscan investigations have demonstrated that destabilization in the MD-pbetaCD nanogel suspension was only due to particle aggregation and/or fusion, as no sedimentation or creaming occurred. The destabilization of MD-pbetaCD suspensions led to the formation of a highly viscous phase, as a final state. Moreover, the two methods have shown that aggregation and/or fusion phenomena were more pronounced in the concentrated MD-pbetaCD suspensions than in the diluted ones. The stability of MD-pbetaCD suspensions could be improved by their storage at 4 degrees C. Finally, freeze-drying was found to be a convenient method for the long-time storage of MD-pbetaCD nanoassemblies.

Dextrans↗

PubMed2006

Innovative nanotechnologies for the delivery of oligonucleotides and siRNA.

One way to reach intracellular therapeutic targets in cells consists in the use of short nucleic acids which will bind specifically to on targets thanks to either Watson-Crick base pairing or protein nucleic acids recognition rules. Among these short nucleic acids an important class of therapeutic agents is antisense oligonucleotides and siRNAs. However, the major problem of nucleic acids is their poor stability in biological media. One method, among others, to solve the stability problem is the use of colloïdal carriers such as nanoparticles. Nanoparticles have already been applied with success to in vitro drug delivery to particular types of cells and in vivo in several experimental models. Many membrane and intracellular processes deal with nanosized structure (typically 100 nm) which are processed further through the recognition sites of receptors and enzymes. Thus non-viral nanoparticles are interesting candidates to present biochemical molecules such as nucleic acids and proteins to cells as well as to protect them in vivo during delivery. This review focuses on the recent developments in the design of nanotechnologies to improve the delivery of antisense oligonucleotides and siRNAs.

Animals↗

PubMed2006

Encapsulation of antiviral nucleotide analogues azidothymidine-triphosphate and cidofovir in poly(iso-butylcyanoacrylate) nanocapsules.

Nucleoside analogues are widely used in the treatment of various viral infections. However, the poor in vivo conversion of the nucleoside analogues like azidothymidine (AZT) into their active triphosphate nucleotide counterpart limits their pharmacological efficacy. This could be overcome by the direct administration of azidothymidine triphosphate (AZT-TP), but it requires an appropriate drug delivery approach. Besides nucleoside analogues, nucleotide analogues like cidofovir (CDV) are also used in the treatment of viral infections. CDV has raised recent interest because of its promising activity against smallpox, but its use is limited by its poor bioavailability and nephrotoxicity. Here again, a proper drug delivery system should address these issues. In this study, we investigated the encapsulation of the nucleotide analogues AZT-TP and CDV into poly(iso-butylcyanoacrylate) aqueous core nanocapsules, known to efficiently entrap oligonucleotides. We show here that the encapsulation of these mono-nucleotides is less efficient than with oligonucleotides and that a rapid release of AZT-TP from the nanocapsules occurred in vitro. This highlights the importance of the molecular weight of the entrapped molecules which, if they are too small, are diffusing through the thin polymer membrane of the nanocapsules. On the other hand, a good protection of the encapsulated AZT-TP was observed.

Anti-HIV Agents↗

PubMed2006

Novel composite core-shell nanoparticles as busulfan carriers.

This study presents a method for the design of novel composite core-shell nanoparticles able to encapsulate busulfan, a crystalline drug. They were obtained by co-precipitation of mixtures of poly(isobutylcyanoacrylate) (PIBCA) and of a diblock copolymer, poly(epsilon-caprolactone)-poly(ethylene glycol) (PCL-PEG), in different mass ratios. The nanoparticle size, morphology and surface charge were assessed. The chemical composition of the top layers was determined by X-ray photo-electron spectroscopy (XPS). (3)H-labelled busulfan was used in order to determine the drug loading efficiency and the in vitro drug release by liquid scintillation counting. Physico-chemical techniques such as Zeta potential determination and XPS analysis provided evidence about a preferential surface distribution of the PCL-PEG polymer. Therefore, composite nanoparticles have a "core-shell"-type structure, where the "core" is essentially formed by the PIBCA polymer and the "shell" by the PCL-PEG copolymer. The use of PIBCA to form the core of the nanoparticles leads to a 2-4 fold drug loading increase, in comparison to the single PCL-PEG nanoparticles. In addition, the complement activation results showed a significant difference between the composite nanoparticles and the single PIBCA nanoparticles, thus demonstrating that PEG at the surface of the nanoparticles reduced the complement consumption. The PIBCA:PCL-PEG composite nanoparticles prepared using the new co-precipitation method here described represent an original approach for busulfan administration.

Antineoplastic Agents, Alkylating↗

PubMed2006

Freeze-drying of composite core-shell nanoparticles.

The effects of four sugars (glucose, saccharose, maltose, trehalose) and one surfactant (Poloxamer 188), on the freeze-drying of poly(isobutylcyanoacrylate) (PIBCA), poly(epsilon-caprolactone)-poly(ethylene glycol) (PCL-PEG), and novel core (mainly PIBCA)-shell (principally PEG) composite nanoparticles (CNP) obtained by co-precipitation were investigated. The efficiency of the additives against the adverse effect of freeze-drying on the redispersibility of the nanoparticles was evaluated, based on the visual appearance of the nanoparticle suspensions (Tyndall effect and aggregation), and on the determination of the mean diameter ratio of the nanoparticles before and after freeze-drying. The results indicated that the addition of both sugars and surfactant was essential for the good redispersion of freeze-dried nanoparticles displaying hydrophobic (PIBCA) or hydrophilic (PCL-PEG and CNP) surfaces.

Cyanoacrylates↗

PubMed2005

Colloidal carriers and blood-brain barrier (BBB) translocation: a way to deliver drugs to the brain?

The major problem in drug delivery to the brain is the presence of the blood-brain barrier (BBB) which limits drug penetration even if in certain pathological situations the BBB is partly disrupted. Therefore, various strategies have been proposed to improve the delivery of drugs to this tissue. This review presents the status of the BBB in healthy patients and in pathologies like neurodegenerative, cerebrovascular and inflammatory diseases. The second part of this article aims to review the invasive and non-invasive strategies developed to circumvent the BBB and deliver drugs into the brain. The use of nanotechnologies (liposomes, nanoparticles) is especially discussed in the ultimate part of the review evidencing their potentiality as non-invasive technique in the brain delivery of drugs with the possibility to target specific brain tissue thanks to ligand linked to carrier surface.

Animals↗

PubMed2005

A relevant in vitro rat model for the evaluation of blood-brain barrier translocation of nanoparticles.

Poly(MePEG2000cyanoacrylate-co-hexadecylcyanoacrylate) (PEG-PHDCA) nanoparticles have demonstrated their capacity to reach the rat central nervous system after intravenous injection. For insight into the transport of colloidal systems across the blood-brain barrier (BBB), we developed a relevant in vitro rat BBB model consisting of a coculture of rat brain endothelial cells (RBECs) and rat astrocytes. The RBECs used in our model displayed and retained structural characteristics of brain endothelial cells, such as expression of P-glycoprotein, occludin and ZO-1, and immunofluorescence studies showed the specific localization of occludin and ZO1. The high values of transendothelial electrical resistance and low permeability coefficients of marker molecules demonstrated the functionality of this model. The comparative passage of polyhexadecylcyanoacrylate and PEG-PHDCA nanoparticles through this model was investigated, showing a higher passage of PEGylated nanoparticles, presumably by endocytosis. This result was confirmed by confocal microscopy. Thanks to a good in vitro/in vivo correlation, this rat BBB model will help in understanding the mechanisms of nanoparticle translocation and in designing new types of colloidal carriers as brain delivery systems.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2005

Puromycin-based purification of rat brain capillary endothelial cell cultures. Effect on the expression of blood-brain barrier-specific properties.

One of the main difficulties with primary rat brain endothelial cell (RBEC) cultures is obtaining pure cultures. The variation in purity limits the achievement of in vitro models of the rat blood-brain barrier. As P-glycoprotein expression is known to be much higher in RBECs than in any contaminating cells, we have tested the effect of five P-glycoprotein substrates (vincristine, vinblastine, colchicine, puromycin and doxorubicin) on RBEC cultures, assuming that RBECs would resist the treatment with these toxic compounds whereas contaminating cells would not. Treatment with either 4 microg/mL puromycin for the first 2 days of culture or 3 microg/mL puromycin for the first 3 days showed the best results without causing toxicity to the cells. Transendothelial electrical resistance was significantly increased in cell monolayers treated with puromycin compared with untreated cell monolayers. When cocultured with astrocytes in the presence of cAMP, the puromycin-treated RBEC monolayer showed a highly reduced permeability to sodium fluorescein (down to 0.75 x 10(-6) cm/s) and a high electrical resistance (up to 500 Omega x cm(2)). In conclusion, this method of RBEC purification will allow the production of in vitro models of the rat blood-brain barrier for cellular and molecular biology studies as well as pharmacological investigations.

Animals↗

PubMed2004

A new generation of polymer nanoparticles for drug delivery.

One of the main interests of using polymer nanoparticles as drug carrier systems is to control the delivery of the drugs including their biodistribution. During the last decade, it was clearly demonstrated that surface properties of nanoparticles were the key factor which determined the in vivo fate of such a carrier. Thus, the purpose of this work was to develop a new method which allows the easy fabrication of nanoparticles with versatile surface properties using polysaccharides. This preparation was based on the use of a redox radical polymerization reaction applied for the first time to the emulsion polymerization of alkylcyanoacrylates in aqueous continuous media. The dispersion of nanoparticles was very stable. The nanoparticle surfaces were coated with polysaccharides and their characteristics can be modulated by the type and the molecular weight of the polysaccharides used during the synthesis. Interestingly the biological properties of the polysaccharide immobilized on the nanoparticle surface can be preserved opening very interesting perspectives for such nanoparticles. This method also offers a new strategy for the design of modular biomimetic nanoparticles as drug carrier systems with multiple functions. One of the applications considered in this work was to use these nanoparticles coupled with haemoglobin as an oxygen carrier.

Complement System Proteins↗

PubMed2003

Drug delivery to resistant tumors: the potential of poly(alkyl cyanoacrylate) nanoparticles.

Simultaneous cellular resistance to multiple lipophilic drugs represents a major problem in cancer chemotherapy. This drug resistance may appear clinically either as a lack of tumor size reduction or as the occurrence of clinical relapse after an initial positive response to antitumor treatment. The resistance mechanism can have different origins either directly linked to specific mechanisms developed by the tumor tissue or connected to the more general problem of distribution of a drug towards its targeted tissue. The purpose of this paper is to summarize the results of the use of poly(alkyl cyanoacrylate) nanoparticles to overcome multidrug resistance (MDR) phenomena at both the cellular and the non-cellular level.

Animals↗

PubMed2003

Novel core(polyester)-shell(polysaccharide) nanoparticles: protein loading and surface modification with lectins.

This study describes new lectin-decorated or protein-loaded nanoparticles with a hydrophobic poly(epsilon-caprolactone) (PCL) core and a hydrophilic dextran (Dex) corona. In this view, a family of block Dex-PCLn copolymers was first synthesized, consisting of a Dex backbone to which n preformed PCL blocks were grafted. The ability of these new copolymers to form nanoparticles was evaluated in comparison with a series of PCL homopolymers of various molecular weights (2000, 10,000 and 40,000 g/mole). Two different nanoparticle preparation methods have been developed and tested for their efficacy to incorporate proteins. For this, three proteins were used: a model protein, bovine serum albumin (BSA), a lectin from leaves of Bauhinia monandra (BmoLL) and Lens culinaris (LC) lectin. All these proteins were successfully incorporated in nanoparticles with a mean diameter around 200 nm. Lectins could also be adsorbed onto the surface of Dex-PCLn nanoparticles. Surface-bound BmoLL conserved its hemagglutinating activity, suggesting the possible application of this type of surface-modified nanoparticles for targeted oral administration. Caco-2 cellular viability was higher than 70% when put in contact with Dex-PCLn nanoparticles, even at concentrations as high as 660 microg/ml.

Animals↗

PubMed2003

Cationic emulsions improves the delivery of oligonucleotides to leukemic P388/ADR cells in ascite.

The aim of this study was to investigate the in vivo ability of O/W cationic emulsions to deliver oligonucleotides (ON) in leukemic P388/ADR cells in ascite, after intraperitoneal (IP) administration in mice. Cationic emulsions were prepared by microfluidization as previously described by Teixeira et al. [Pharm. Res 16 (1999) 30]. The formulations consisted mainly of medium chain triglycerides, phosphatidylcholine (PC), poloxamer, and either a monocationic lipid stearylamine (PC/SA-emulsion) or a polycationic lipid RPRC(18) (PC/RPRC(18)-emulsion). A model ON (33P-pdT(16)) was associated with cationic emulsions by single addition at the end of the manufacturing process. Seven days after P388/ADR inoculation IP to mice, ON free or associated with PC/SA or PC/RPRC(18) emulsions was injected IP at a dose of 0.5 mg/kg. At different interval times, ascite including cells, blood and the main organs were collected and the radioactivity counted by liquid scintillation. The overall results showed significantly high amounts of ON in the leukemic cell pellet, 24 h after administration of ON associated to either PC/SA (AUC(0-24 h)=13634, %injected dose/min) or PC/RPRC(18) (AUC(0-24 h)=22592, % injected dose/min), contrary to the free ON solution (AUC(0-24 h)=3095, %injected dose/min), which displayed only reduced capture by cancer cells. In conclusion, complexation of ON with cationic emulsions had a beneficial effect in increasing tumor cells uptake in vivo (up to sevenfold for PC/RPRC(18)-emulsion) after IP administration. This could open interesting prospects for the treatment of ovarian cancers.

Animals↗

PubMed2003

N-methylation of anthracyclines modulates their cytotoxicity and pharmacokinetic in wild type and multidrug resistant cells.

Anthracyclines are the most commonly used classes of anticancer agents in chemotherapy. Development of resistance to these molecules is one of the major reasons for treatment failure. The overexpression of the membrane transporter P-glycoprotein (P-gp) is among the principal mechanisms involved in this phenomenon. This pump, which is responsible for the multidrug resistance (MDR) phenotype, decreases the toxicity of a wide range of unrelated anticancer drugs by increasing their cellular efflux. Structure-activity relationship experiments have shown that the positively charged amino group of the anthracyclines could be responsible for their transport by P-gp. Here, we used three new anthracyclines that shared the same chromophore but differed by the degree of N-methylation of their sugar moiety. Oxaunomycin (OXN) possessed a non-methylated amino group, while LB-1 was monomethylated and beta-clamycin T (BCT) was dimethylated. In sensitive cells (FLC), reduced cytotoxicity was related to the level of N-methylation; whereas in resistant cells (DOX-RFLC(1) and DOX-RFLC(2)) overexpressing different levels of P-gp, increased N-methylation enhanced anthracycline cytotoxicity. Decreased resistance in DOX-RFLCs was associated with an increased drug accumulation due to a reduced cellular efflux. As expected, the MDR modulator verapamil decreased resistance to these anthracyclines by increasing the cellular accumulation. These results suggest that N-methylation of anthracyclines circumvents resistance by diminishing drug transport by P-gp in MDR-positive cells. These observations could be the consequence of the steric hindrance created by the methyl group(s) which may impair the interaction between the positively charged amino group and the active site of P-gp.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2003

Therapeutic potentialities of EWS-Fli-1 mRNA-targeted vectorized antisense oligonucleotides.

We have used structured antisense oligonucleotides (AON), which are protected against extra and intracellular degradation by their internal structure. We have shown that if correctly designed this structure does not prevent them from hybridizing to the mRNA target. This concept allows reducing the number of thioate groups in the oligonucleotide and therefore the potential toxicity. Junction oncogenes are found in cancers such as certain leukemias, Ewing sarcoma, and thyroid papillary carcinomas. Ewing sarcoma is a cancer of children and young adults with bone metastasis. It is caused by a chromosomic translocation t(11;22) (q24;q12) creating a fusion gene between the genes EWS and Fli-1 giving rise to a chimeric protein which is an unnatural transcription factor. Immortalized NIH/3T3 cells transfected by the EWS-Fli-1 cDNA under the control of the LTR retroviral promoter--which do not undergo apoptosis and which became tumoral--were used for this study. As a model of Ewing sarcoma in nude mice, we have used permanently expressing human EWS-Fli-1 cells grafted to nude mice. The nanospheres or nanocapsules have been used to deliver two different AON: a phosphorothioate, and a structured chimeric AON, both targeted toward the junction area of EWS-Fli-1. Both types of AON-loaded nanoparticles inhibited the growth of the xenografted tumor after intratumoral injections into nude mice, whereas similar nanoparticles with control oligonucleotides had no effect. With AON in nanospheres, we have shown after 24 hours that the mRNA of EWS-Fli-1 was specifically down-regulated, confirming the antisense activity of the targeted AON.

Animals↗

PubMed2002

Polyunsaturated fatty acids (PUFA) and eicosanoids in human health and pathologies.

Linoleic and alpha-linolenic acids, obtained from plant material in the diet are the precursors in tissues of two families with opposing effects which are referred to as "essential fatty acids" (EFA): arachidonic acid (AA) and pentaene (eicosapentaenoic acid: EPA) and hexaene (docosahexaenoic acid: DHA) acids. The role of EFA is crucial, without a source of AA or compounds which can be converted into AA, synthesis of prostaglandins (PGs) by a cyclooxygenase (COX) enzyme would be compromised, and this would seriously affect many normal metabolic processes. COX, also known as prostaglandin endoperoxide synthase (Pghs) or as prostaglandin G/H synthase, is a key membrane bound enzyme responsible for the oxidation of AA to PGs. Two COX isoforms have been identified, COX-1 and COX-2 that form PGH2, a common precursor for the biosynthesis of thromboxane A2 (TxA2), prostacyclin (PGI2) and PGs (PGD2, PGE2, PGF2alpha. COX-1 enzyme is expressed constitutively in most cells and tissues. Its expression remains constant under either physiological or pathological conditions controlling synthesis of those PGs primarily involved in the regulation of homeostatic functions. In contrast, COX-2 is an intermediate response gene that encodes a 71-kDa protein. COX-2 is normally absent from most cells but highly inducible in certain cells in response to inflammatory stimuli resulting in enhanced PG release. PGs formed by COX-2 primarily mediate pain and inflammation but have multiple effects that can favour tumorigenesis. They are more abundant in cancers than in normal tissues from which the cancers arise. COX-2 is a participant in the pathway of colon carcinogenesis, especially when mutation of the APC (Adenomatous Polyposis Coli) tumour suppressor gene is the initiating event. In addition, COX-2 up-regulation and elevated PGE2 levels are involved in breast carcinogenesis. It seems that there is a correlation between COX-2 level of expression and the size of the tumours and their propensity to invade underlying tissue. Inhibition by non-steroidal anti-inflammatory drugs (NSAIDs) of COX enzymes which significantly suppress PGE2 levels, reduced breast cancer incidence and protected against colorectal cancer. Therefore it is suggested that consumption of a diet enriched in n-3 PUFA (specifically EPA and DHA) and inhibition of COX-2 by NSAIDs may confer cardioprotective effects and provide a significant mechanism for the prevention and treatment of human cancers.

Cardiovascular Diseases↗

PubMed2002

I. Arginine.

L-Arginine (Arg) is classified as an essential amino acid for birds, carnivores and young mammals and a conditionally essential amino acid for adults. It is converted by arginase to L-ornithine, a precursor of polyamines and urea, which is important in the urea cycle. Arg serves as a precursor for creatine, which plays an essential role in the energy metabolism of muscle, nerve and testis and accounts for Arg catabolism and for the synthesis of agmatine and proteins. Via its ability to increase growth hormone secretion it influences immune function. Depending on nutritional status and developmental stage, normal plasma Arg concentrations in humans and animals range from 95 to 250 micromol/l. Systemic or oral Arg administration has been shown to improve cardiovascular function and reduce myocardial ischemia in coronary artery disease patients. It reduces blood pressure and renal vascular resistance in essential hypertensive patients with normal or insufficient renal function. Although Arg plasma concentrations are not altered in hypercholesterolemic individuals, oral or intravenous Arg administration can reverse endothelial dysfunction in hypercholesterolemic patients and in cigarette smokers. The main importance of Arg is attributed to its role as a precursor for the synthesis of nitric oxide (NO), a free radical molecule that is synthesized in all mammalian cells from L-Arg by NO synthase (NOS). NO appears to be a major form of the endothelium-derived relaxing factor (EDRF). NO and EDRF share similar chemical and pharmacological properties and are derived from the oxidation of a terminal guanidine group of L-Arg. Various mechanisms have been implicated in the defect in vascular relaxation. These include, increased diffusional barrier for NO, L-Arg depletion, altered levels of reactive oxygen, inactivation of NO by superoxide anions (O2-). The independent reactions of O2-, NO and their reaction yielding peroxynitrite are critical in the initiation and maintenance of the atherosclerotic state and contribute to the defect in vasorelaxation. NO also plays a role as a neurotransmitter, mediator of immune response and as signaling molecule. The NO synthesized by iNOS in macrophages contributes to their cytotoxic activity against tumor cells, bacteria and protozoa. Our aim here is to review on some amino acids with high functional priority such as Arg and to define their effective activity in human health and pathologies.

Animals↗