Biomedical subjects

Wim E Hennink

Publications and source records attributed to Wim E Hennink.

At least 19 recordsLinked to original sources

PubMed2006

Pharmacokinetics of poly(hydroxyethyl-l-asparagine)-coated liposomes is superior over that of PEG-coated liposomes at low lipid dose and upon repeated administration.

'Stealth' liposomes with a poly(ethylene glycol) (PEG) coating are frequently studied for drug delivery and diagnostic purposes because of their prolonged blood circulation kinetics. However, several recent reports have demonstrated that PEG-liposomes are rapidly cleared at single low lipid doses (<1 micromol/kg) and upon repeated administration (time interval between the injections 5 days-4 weeks). Recently, poly(amino acid)-based stealth liposome coatings have been developed as alternative to the PEG-coating. In this study, the pharmacokinetic behavior of liposomes coated with the poly(amino acid) poly(hydroxyethyl-l-asparagine) (PHEA) was evaluated at low lipid doses and upon repeated administration in rats. Blood circulation times and hepatosplenic localization of PHEA-liposomes were assessed after intravenous injection. When administered at a dose of 0.25 micromol/kg or less, PHEA-liposomes showed significantly longer blood circulation times than PEG-liposomes. A second dose of PHEA-liposomes 1 week after the first injection was less rapidly cleared from the circulation than a second dose of PEG-liposomes. Although the mechanisms behind these observations are still not clear yet, the use of PHEA-liposomes appears beneficial when single low lipid doses and/or repeated dosing schedules are being applied.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2006

Rheological studies of thermosensitive triblock copolymer hydrogels.

Hydrogel formation by physical cross-linking is a developing area of research toward materials suitable for pharmaceutical and biomedical applications. Polymers exhibiting lower critical solution temperature (LCST) behavior in aqueous solution are used in this study to prepare hydrogels. Four triblock copolymers (ABA) with thermosensitive poly(N-(2-hydroxypropyl) methacrylamide lactate) A-blocks and a hydrophilic poly(ethylene glycol) B-block have been synthesized. The molecular weight of the hydrophilic PEG block was fixed at 10 kDa, whereas the molecular weight of the pHPMAm-lactate block was varied between 10 and 20 kDa. The rheological characteristics of these polymer hydrogels were studied as a function of temperature, concentration, and the length of the thermosensitive blocks. Gelation occurred rapidly upon increasing the temperature to 37 degrees C, which makes this system suitable as an injectable formulation. The gels became stronger with increasing temperature and concentration, and moreover they behaved as critical gels, which means that G' and G' ' follow power laws over the entire frequency range. Surprisingly, with increasing length of the thermosensitive blocks, weaker hydrogels were formed. This trend can be explained by the cross-link density of the physical network, which increases with decreasing length of the thermosensitive blocks.

Biocompatible Materials↗

PubMed2006

Poly(amino acid)s: promising enzymatically degradable stealth coatings for liposomes.

Poly(amino acid)s (PAAs) were evaluated as coating polymers for long-circulating liposomes. The pharmacokinetics of PAA-coated liposomes were assessed in rats. Prolonged circulation times were obtained, comparable to those reported for poly(ethylene glycol) (PEG)-liposomes. Besides, the enzymatic degradability of PAAs was studied. PAAs - in free as well as liposome-associated form - are degradable by proteases, which is beneficial for reducing the risks of accumulation in vivo. Furthermore, complement activation by PAA-liposomes was evaluated in vitro and in vivo. Like other liposome types, they appear to activate the complement system. However, a role of endotoxin contamination of the PAA-liposome formulations used cannot be excluded in our complement activation studies.

Animals↗

PubMed2006

Effect of cationic carriers on the pharmacokinetics and tumor localization of nucleic acids after intravenous administration.

Nucleic acid based therapeutics are currently being studied for their application in cancer therapy. In this study, the effect of different cationic delivery systems on the circulation kinetics, tumor localization, and tissue distribution of short interfering RNA (siRNA) and plasmid DNA (pDNA) was examined, after intravenous administration in mice bearing a s.c. Neuro 2A tumor. Nanosized particles were formed upon complexation of siRNA with the cationic liposome formulation DOTAP/DOPE and the targeted, cationic polymer RGD-PEG-PEI. Both the circulation kinetics and the overall tumor localization of the siRNA complexes were similar to non-complexed siRNA. Importantly, the different carriers changed the intratumoral distribution of siRNA within the tumor. pDNA was effectively condensed with linear polyethylenimine (PEI), PEGylated linear PEI (PEG-PEI) or poly(2-dimethylamino ethylamino)phosphazene. Only PEG-PEI was able to improve the pDNA circulation kinetics. All pDNA complexes yielded similar pDNA tumor localization (1% of the injected dose, 60 min after administration). We conclude that the level of nucleic acid tumor localization is independent on the type of formulation used in this study. Therefore, the value of carrier systems for the intravenous delivery of nucleic acids cannot be solely attributed to benefits relevant during the transport towards the tumor. Rather, the benefits are arising from carrier-induced changes in the intratumoral fate of the nucleic acids.

Animals↗

PubMed2006

Linear poly(amido amine)s with secondary and tertiary amino groups and variable amounts of disulfide linkages: synthesis and in vitro gene transfer properties.

A group of novel poly(amido amine) homo- and copolymers (PAAs) containing secondary and tertiary amine groups in their main chain and different structures in the bisacrylamide segments were synthesized and evaluated as non-viral gene delivery vectors. Among these, also the disulfide-containing cystaminebisacrylamide was employed as a (co)monomer, yielding PAAs with variable amounts of bioreducible disulfide linkages in the main chain. Michael addition the trifunctional 1-(2-aminoethyl) piperazine to equimolar amounts of the appropriate bis(acrylamide) yielded linear polymers as was elucidated by their (13)C NMR spectra. The polymers possess buffering capacities between pH 5.1 and pH 7.4 higher than branched polyethylenimine (pEI) and are able to efficiently condense DNA into nanosized (<150 nm) and positively charged complexes. Transfection experiments with COS-7 cells showed that polyplexes from PAAs with disulfide linkages give significant higher transfections than those from PAAs lacking the disulfide linkage, and XTT assays showed that these polymers are essentially non-toxic. Variation of the disulfide content revealed that polyplexes of PAA copolymers with appropriate disulfide content have largely improved biophysical properties, yielding enhanced levels of gene expression along with low toxicity. The results demonstrate that bioreducible poly(amido amine)s are a very promising class of polymers for safe and efficient gene delivery.

Acrylamides↗

PubMed2006

Synthesis and characterization of hyperbranched polyglycerol hydrogels.

Hyperbranched polyglycerol (HyPG; M(n) 2000g/mol) was derivatized with glycidyl methacrylate (GMA) in dimethyl sulfoxide using 4-(N,N-dimethylamino)pyridine as a catalyst to obtain methacrylated HyPG (HyPG-MA). The degree of substitution (DS, the percentage of derivatized hydroxyl groups), established by NMR and RP-HPLC, was fully controlled in the range of 0.7-70 by varying the molar ratio of GMA to HyPG in the reaction mixture. This indicates that for e.g. a DS of 28, 9 out of the 32 hydroxyl groups of a HyPG molecule were esterified with methacryloyl groups. Under the selected conditions, the reaction reached an equilibrium within 4h. Furthermore, it was demonstrated that under the applied conditions the reaction was reversible. Hydrogels were obtained by crosslinking HyPG-MA in aqueous solutions using potassium peroxodisulfate (KPS) and N,N,N',N'-tetramethylethylenediamine (TEMED) as initiator and catalyst, respectively. Within 10min, 99% of the methacryloyl groups were polymerized. Rheological analysis showed that the storage modulus of these gels could be tailored by varying the concentration of HyPG-MA in the aqueous solution as well as by the DS. Moreover, the obtained hydrogels have a limited swelling capacity indicating that rather dimensionally stable networks were obtained. As an alternative for radical polymerization with KPS and TEMED, the HyPG-MA could also be crosslinked by photopolymerization using Irgacure 2959 as photoinitiator. A methacrylate conversion of 99% was obtained within 3min of illumination. As for the gels prepared with KPS and TEMED, networks formed by photopolymerization also had a high shear storage modulus and showed limited swelling. Hydrogels based on HyPG have great potential as drug delivery matrices and for tissue engineering purposes.

Cross-Linking Reagents↗

PubMed2006

Plasmid engineering for controlled and sustained gene expression for nonviral gene therapy.

Gene therapy requires the introduction of genetic material in diseased cells with the aim of treating or ultimately curing a disease. Since the start of gene therapy clinical trials in 1990, gene therapy has proven to be possible, but studies to date have highlighted the difficulty of achieving efficient, specific, and long-term transgene expression. Efforts to improve gene therapy strategies over the past years were mainly aimed at solving the problem of delivery, without paying much attention to the optimization of the expression cassette. With the current understanding of the eukaryotic transcription machinery and advanced molecular biology techniques at our disposition, it has now become possible to create custom-made transgene expression cassettes optimized for gene therapy applications. In this review, we will discuss several strategies that have been explored to improve the level and duration of transgene expression, to increase control over expression, or to restrict transgene expression to specific cell types or tissues. Although still in its infancy, such strategies will eventually lead to improvement of nonviral gene therapy and expansion of the range of possible therapeutic applications.

Active Transport, Cell Nucleus↗

PubMed2006

Degradation behavior of dextran hydrogels composed of positively and negatively charged microspheres.

This paper reports on the degradation behavior of in situ gelling hydrogel matrices composed of positively and negatively charged dextran microspheres. Rheological analysis showed that, once the individual microspheres started to degrade, the hydrogel changed from a mainly elastic to a viscoelastic network. It was shown with gels composed of equal amounts of cationic and anionic microspheres, that both a higher crosslink density of the particles and a decrease in water content of the hydrogels resulted in a slower degradation, ranging from 65 to 140 days. Dispersions containing cationic, neutral or anionic microspheres completely degraded within 30, 55 or 120 days, respectively. The microspheres were loaded with rhodamine-B-dextran and degradation was studied with confocal microscopy and fluorescence spectroscopy. After a lag time of 3 days rhodamine-B-dextran started to release from the positive microspheres with a 50% release after 16 days. In contrast, release of rhodamine-B-dextran from the negative microspheres started after 10 days with a 50% release after 36 days. The faster degradation of the positively charged microspheres as compared to the negatively charged microspheres is attributed to stabilization of the transition state in the hydrolysis process by the protonated tertiary amine groups present in the cationic microspheres. On the other hand, the presence of negatively charged groups causes repulsion of hydroxyl anions resulting in a slower degradation. Combining the oppositely charged microspheres in different ratios makes it possible to tailor the network properties and the degradation behavior of these hydrogels, making them suitable for various applications in drug delivery and tissue engineering.

Anions↗

PubMed2006

The nuclear pore complex: the gateway to successful nonviral gene delivery.

One of the limiting steps in the efficiency of nonviral gene delivery is transport of genetic material across the nuclear membrane. Trafficking of nuclear proteins from the cytoplasm into the nucleus occurs via the nuclear pore complex and is mediated by nuclear localization signals and their nuclear receptors. Several strategies employing this transport mechanism have been designed and explored to improve nonviral gene delivery. In this article, we review the mechanism of nuclear import through the nuclear pore complex and the strategies used to facilitate nuclear import of exogenous DNA and improve gene expression.

Active Transport, Cell Nucleus↗

PubMed2006

Molar-mass characterization of cationic polymers for gene delivery by aqueous size-exclusion chromatography.

PURPOSE: This study was performed to develop a reliable aqueous size-exclusion chromatography (SEC) method to obtain the absolute molar masses and distributions of various cationic polymers used in gene delivery. METHODS: Water-soluble cationic [2-(dimethylamino) ethyl methacrylate] polymers (PDEs) with different molar masses and low polydispersities were synthesized by living polymerization and these were used to optimize the SEC conditions. Online coupled multiangle light scattering (MALS) detection was applied to obtain the absolute molar masses. Narrow fractions of high molar mass were obtained by semipreparative SEC. RESULTS: It was found that 0.3 M NaAc (pH 4.4) is a suitable eluent in combination with Shodex OHpak SB columns for SEC analysis of PDEs and other cationic polymers, such as poly(L-lysine) and poly(ethylene imine). The absolute molar masses of different PDEs were determined directly using SEC-MALS. A calibration curve was established using narrow PDEs. CONCLUSIONS: A reliable routine method for molar-mass characterization of cationic polymers was established. Because standards of known molar masses with narrow distributions are not commercially available for most polymers used in pharmaceutics and biotechnology, the procedure described in this work can also be applied for molar-mass characterization of other water-soluble polymers.

Cations↗

PubMed2006

Modeling the release of proteins from degrading crosslinked dextran microspheres using kinetic Monte Carlo simulations.

To optimize and predict the release of proteins from biodegradable microspheres based on crosslinked dextran, a fundamental understanding of the mechanisms controlling their release is necessary. For that purpose, a mathematical model has been developed to describe the release of proteins from these hydrogel-based microspheres. A kinetic Monte Carlo scheme for the degradation of a small domain inside the microsphere was developed. The results from this were used in a second kinetic Monte Carlo scheme to model the diffusion and the subsequent release of proteins. The only processes included in this model are diffusion and degradation. The general effects of diffusion, crosslink density, protein loading, and clustering of proteins on the release were investigated. The model crosslink density (Xmodel) and the model diffusivity (Dmodel) were fitted to experimental release data of BSA monomer from hydroxyethyl methacrylated dextran (dex-HEMA) microspheres. By using the experimental release curves of liposomes and BSA monomer, it was found that (1) the model crosslink density (Xmodel) scales with the hydrodynamic diameter (dh) as dh(1.64) and (2) the diffusivity of the protein (Dmodel) scales approximately with 1/dh (Stokes-Einstein). Using these scaling relations, quantitative predictions of the release curves of BSA dimer, immunoglobulin G and human growth hormone were possible. In conclusion, this model may play an important role in the optimization, understanding and prediction of the release of various proteins from degradable hydrogels.

Algorithms↗

PubMed2006

Photochemically enhanced transduction of polymer-complexed adenovirus targeted to the epidermal growth factor receptor.

BACKGROUND: The development of methods for specific delivery of genes into target tissues is an important issue for the further progress of gene therapy. Biological and physical targeting techniques may be combined to redirect gene therapy vectors to specific cells and enhance gene transfer. METHODS: The polymer poly(2-(dimethylamino)ethyl methacrylate) (pDMAEMA) was conjugated with avidin or poly(ethylene glycol) (PEG) and complexed with adenovirus serotype 5 (Ad5). Targeting of polymer-coated Ad5 to the epidermal growth factor receptor (EGFR) was accomplished by the binding of biotin-EGF to pDMAEMA-avidin. A photochemical treatment procedure using photosensitizer and light was applied to increase transduction with EGFR-targeted viral complexes. RESULTS: pDMAEMA-avidin efficiently enhanced transduction through unspecific viral uptake into cells, while pDMAEMA-PEG provided charge shielding of the complexes and increased the specificity to EGFR when biotin-EGF ligands were used. Transduction of PEG-containing, EGFR-targeted viral complexes was inhibited by 66% in coxsackie and adenovirus receptor (CAR)-deficient RD cells and by 47% in CAR-expressing DU 145 cells in receptor antibody experiments. The photochemical treatment had a substantial effect on transduction, enhancing the percentage of reporter gene positive cells from 20% to 75% of the total viable RD cell population and from 10% to 70% in DU 145 cells. CONCLUSION: Photochemical treatment of cells infected with targeted viral vectors exhibiting a neutral surface charge is a potent method for enhancing transgene expression.

Adenoviridae↗

PubMed2006

Holmium-loaded poly(L-lactic acid) microspheres: in vitro degradation study.

The clinical application of holmium-loaded poly(L-lactic acid) (PLLA) microspheres for the radionuclide treatment of liver malignancies requires in depth understanding of the degradation characteristics of the microspheres. To this end, an in-vitro degradation study was conducted. PLLA-microspheres with and without HoAcAc loading, and before and after neutron or gamma irradiation, were incubated in a phosphate buffer at 37 degrees C for 12 months. In contrast with the other microsphere formulations, only the neutron-irradiated Ho-PLLA-MS disintegrated. At the end of the experiment (52 weeks) highly crystalline fragments, as evidenced from Differential Scanning Calorimetry, were present. Infrared spectroscopy showed that these fragments consisted of holmium lactate. In conclusion, this study demonstrates that the degradation of neutron-irradiated Ho-PLLA-MS was substantially accelerated by the HoAcAc incorporation and subsequent neutron irradiation. The degradation of these microspheres in aqueous solution resulted in the formation of insoluble holmium lactate microcrystals without release of Ho3+.

Calorimetry, Differential Scanning↗

PubMed2006

In vitro degradation behavior of microspheres based on cross-linked dextran.

The aim of this study was to investigate the in vitro degradation of hydroxyl ethyl methacrylated dextran (dex-HEMA) microspheres. Dextran microspheres were incubated in phosphate buffer pH 7.4 at 37 degrees C, and the dry mass, mechanical strength, and chemical composition of the microspheres were monitored in time. The amount and nature of the formed degradation products were established for microspheres with different cross-link densities by FT-IR (Fourier transformed infrared spectroscopy), NMR, mass spectrometry, SEC analysis, and XPS (X-ray photoelectron microscopy). The dex-HEMA microspheres DS 12 (degree of HEMA substitution; the number of HEMA groups per 100 glucose units) incubated at pH 7.4 and 37 degrees C showed a continuous mass loss, leaving after 6 months a residue of about 10% (w/w) of water-insoluble products. NMR, mass spectrometry, and SEC showed that the water-soluble degradation products consisted of dextran, low molecular weight pHEMA (M(n) approximately 15 kg/mol), and small amounts of unreacted HEMA and HEMA-DMAP (intermediate reaction product of the Baylis-Hillman reaction of HEMA with DMAP (4-dimethyl aminopyridine)). Microscopy revealed that the water-insoluble residue consisted of particles with shape and size similar to that of nondegraded microspheres. However, these particles had lost their mechanical strength as evidenced from micromanipulation experiments. FT-IR and XPS (X-ray photoelectron microscopy) revealed that these particles consisted of pHEMA, of which a small fraction was soluble in methanol (M(n) ranging between 27 and 82 kg/mol). The insoluble material likely consisted of lightly cross-linked pHEMA. In conclusion, in vitro degradation of dex-HEMA microspheres results in the formation of water-soluble degradation products (mainly dextran), leaving a small water-insoluble residue mainly consisting of pHEMA.

Chromatography, Gel↗

PubMed2006

Artificial viruses: a nanotechnological approach to gene delivery.

Nanotechnology is a rapidly expanding multidisciplinary field in which highly sophisticated nanoscale devices are constructed from atoms, molecules or (macro)molecular assemblies. In the field of gene medicine, systems for delivering nucleic acids are being developed that incorporate virus-like functions in a single nanoparticle. Although their development is still in its infancy, it is expected that such artificial viruses will have a great impact on the advancements of gene therapeutics.

Animals↗

PubMed2005

Preparation and characterization of protein-loaded N-trimethyl chitosan nanoparticles as nasal delivery system.

In this study, the potential of N-trimethyl chitosan (TMC) nanoparticles as a carrier system for the nasal delivery of proteins was investigated. TMC nanoparticles were prepared by ionic crosslinking of TMC solution (with or without ovalbumin) with tripolyphosphate, at ambient temperature while stirring. The size, zeta-potential and morphology of the nanoparticles were investigated as a function of the preparation conditions. Protein loading, protein integrity and protein release were studied. The toxicity of the TMC nanoparticles was tested by ciliary beat frequency measurements of chicken embryo trachea and in vitro cytotoxicity assays. The in vivo uptake of FITC-albumin-loaded TMC nanoparticles by nasal epithelia tissue in rats was studied by confocal laser scanning microscopy. The nanoparticles had an average size of about 350 nm and a positive zeta-potential. They showed a loading efficiency up to 95% and a loading capacity up to 50% (w/w). The integrity of the entrapped ovalbumin was preserved. Release studies showed that more than 70% of the protein remained associated with the TMC nanoparticles for at least 3 h on incubation in PBS (pH 7.4) at 37 degrees C. Cytotoxicity tests with Calu-3 cells showed no toxic effects of the nanoparticles, whereas a partially reversible cilio-inhibiting effect on the ciliary beat frequency of chicken trachea was observed. In vivo uptake studies indicated the transport of FITC-albumin-associated TMC nanoparticles across the nasal mucosa. In conclusion, TMC nanoparticles are a potential new delivery system for transport of proteins through the nasal mucosa.

Animals↗

PubMed2005

Poly(ethylene glycol)--oligolactates with monodisperse hydrophobic blocks: preparation, characterization, and behavior in water.

Methoxypoly(ethylene glycol)-b-oligo-L-lactate (mPEG-b-OLA) diblock oligomers with monodisperse OLA blocks were obtained by fractionation of polydisperse block oligomers using preparative HPLC. The fractionated oligomers were composed of an mPEG block with a molecular weight of 350, 550, or 750 and an OLA block with a degree of polymerization of 4, 6, 8, or 10. The diblock oligomers with a low PEG content were fully amorphous, with glass transition temperatures ranging from -60 to -20 degrees C, indicating that the blocks were miscible. Upon heating aqueous dispersions of the block oligomers, cloud points, depending on the PEG/OLA ratio of the block oligomer, were observed at temperatures above 40 degrees C. The monodispersity of the hydrophobic block enabled the amphiphilic molecules to form nanoparticles in water with a hydrodynamic radius of 130-300 nm, at concentrations above the critical aggregation concentration (0.4-1 mg/mL), whereas polydisperse mPEG-b-OLAs gave formation of large aggregates. Static light scattering measurements showed that the nanoparticles have a low density (0.6-25 mg/mL), indicating that the particles are highly hydrated. In agreement herewith, the (1)H NMR spectra of nanoparticles in D2O closely resembled spectra in a good solvent for both blocks (CDCl3). It is therefore suggested that the nanoparticles contain a hydrated core of mPEG-b-OLA block oligomers, stabilized by a thin outer PEG layer. The particles were stable for two weeks, except for the mPEG350 series and mPEG750-b-OLA4, indicating that both the PEG block size and the PEG weight fraction of the oligomers determine their stability. The evident self-emulsifying properties of mPEG-b-oligo-l-lactates with monodisperse hydrophobic blocks as demonstrated in this study, together with their expected biocompatibility and biodegradability, make these systems well suitable for pharmaceutical applications.

Journal Article↗

PubMed2005

Mobility of model proteins in hydrogels composed of oppositely charged dextran microspheres studied by protein release and fluorescence recovery after photobleaching.

In this paper, the release of proteins from a novel self-gelling hydrogel based on biodegradable dextran microspheres is investigated. The protein-loaded macroscopic gels are obtained by hydration of mixtures of oppositely charged hydroxyethyl methacrylate-derivatized dextran microspheres with a protein solution. In media of low ionic strength (100 mM Hepes pH 7.0) it was found that the release of the entrapped model proteins (lysozyme, BSA and IgG) was slower than in saline (150 mM NaCl, 100 mM Hepes pH 7.0). The reason behind this observation is that substantial adsorption of the proteins onto the microspheres' surface and/or absorption in the microspheres takes place. Confocal images showed that independent of their crosslink density the microspheres are impermeable for BSA and IgG. BSA, bearing a negative charge at neutral pH, was adsorbed onto the surface of positively charged microspheres. Lysozyme, which is positively charged at neutral pH, was able to penetrate into the negatively charged microspheres. In saline, the gels showed continuous release of the different proteins for 25 to 60 days. Importantly, lysozyme was quantitatively and with full preservation of its enzymatic activity released in about 25 days. This emphasizes the protein friendly technology to prepare the protein-loaded gels. Mathematical modeling revealed that protein release followed Fick's second law, indicating that the systems are primarily diffusion controlled. These results show that these hydrogels are very suitable as injectable matrix for diffusion-controlled delivery of pharmaceutically active proteins.

Adsorption↗