Using TEM to couple transient protein distribution and release for PLGA microparticles for potential use as vaccine delivery vehicles

In the development of tunable PLGA microparticles as vaccine delivery vehicles, it is important to understand the drug distribution within the microparticle over time as well as the long-term release of the drug during polymer degradation. This study addresses the transient 3-D drug distribution in PLGA microparticles during in vitro degradation. Specifically, poly (lactide-co-glycolide) (PLGA 75:25) microparticles containing ovalbumin (OVA) as a model protein were fabricated by double-emulsion (w/o/w) method. The microparticles were incubated at 37 degrees C and 250 rpm in PBS buffer (pH 7.4) over a 100-day period. The in vitro polymer erosion, transient protein distribution profiles and protein release behaviors were investigated. Protein release profiles were determined via spectrophotometry using a BCA assay for the solution. Transmission electron microscopy (TEM) images were obtained for the OVA-loaded microparticles before and during degradation (0 day, 30 days and 60 days), and the corresponding 3-D constructions were developed. From the 3-D constructions, the overall protein distribution of the entire microparticle was vividly reflected. Pixel number analysis of the TEM images was used to quantify transient protein distribution. The transient protein release obtained from the TEM analysis was in good agreement with the BCA analysis. This technique provides an additional tool in helping develop polymer matrices for tunable delivery vehicles in vaccination and other drug delivery scenarios.

Nanoparticulate drug carriers based on hybrid poly(D,L-lactide-co-glycolide)-dendron structures

We describe a general method for incorporating target moieties in a well-defined arrangement into the surface of biocompatible polyester poly(D,L-lactic-co-glycolic acid) (PLGA) materials using dendrons. In this way it is possible to obtain nanoparticles (NPs) with a high degree of surface coverage. This new strategy was successfully applied to the preparation of peptide- and beta-D-glucose-covered NPs. The first application is based on the discovery of NPs made of conjugates between PLGA and short peptidic sequences able to cross the blood-brain barrier (BBB) after systemic administration. In this paper, we used a branched structure (dendron) in order to prepare a derivative of PLGA able to form, by simple nanoprecipitation, NPs with a higher degree of surface coverage than previously reported by us, characteristic that could influence the uptake by the liver and spleen. The NPs thus obtained retain the ability to cross the BBB and possess a core-shell structure, as evidenced from zeta-potential, X-ray photoelectron (ESCA) spectroscopy and elemental analyses. These results are comparable with the NPs obtained by the derivatization of preformed NPs. The same strategy, namely the use of a branched spacer (a dendron or a G1 dendrimer) inserted between one end of the PLGA chain and a derivatizing molecule, was also successfully applied to obtain beta-D-glucose-covered NPs; in this case, the surface analysis of the NPs was performed by using high resolution magic angle spinning (HRMAS) NMR spectroscopy and zeta-potential measurements.

Elevated temperature accelerated release testing of PLGA microspheres

Drug release from four different poly(lactic-co-glycolic) acid (PLGA) microsphere formulations was evaluated under "real-time" (37 degrees C) and accelerated release testing conditions of elevated temperature (45, 53, 60 and 70 degrees C) and increase in flow rate (4-35 ml/min) using United States Pharmacopeia (USP) apparatus 4. Formulation 5 K (composed of low Mw PLGA) exhibited diffusion-controlled kinetics in "real-time". Whereas, formulations 25 K, 28 K and 70 K (composed of medium and high Mw PLGA) followed erosion-controlled kinetics at 37 degrees C. Temperature-induced degradation of the microspheres was studied by monitoring drug release rates, change in molecular weight and morphological changes. Drug release rates at elevated temperature were used to predict "real-time" release applying the Arrhenius equation. The energy of activation for dexamethasone release from PLGA microspheres was calculated as 19.14 kcal/mol. Molecular weight change measured by gel permeation chromatography followed first order kinetics for both "real-time" and accelerated release. All four formulations exhibited morphological changes (such as surface pore closing and geometry change) at elevated temperature with consequent reduction in burst release.

Biodistribution properties of nanoparticles based on mixtures of PLGA with PLGA–PEG diblock copolymers

The basic characteristics and the biodistribution properties of nanoparticles prepared from mixtures of poly(lactide-co-glycolide) (PLGA) with poly(lactide-co-glycolide)-poly(ethylene glycol) (PLGA-PEG) copolymers were investigated. A PLGA(45)-PEG(5) copolymer of relatively low PEG content and a PLGA(5)-PEG(5) copolymer of relatively high PEG content were included in the study. Increasing the PLGA-PEG content of the PLGA/PLGA-PEG mixture, or when PLGA(45)-PEG(5) was replaced by PLGA(5)-PEG(5), a decrease in the size of the nanoparticles and an increase in the rate of PEG loss from the nanoparticles were observed. The blood residence of the PLGA/PLGA(45)-PEG(5) nanoparticles increased as their PLGA-PEG content was increased, reaching maximum blood longevity at 100% PLGA(45)-PEG(5). On the contrary, the blood residence of PLGA/PLGA(5)-PEG(5) nanoparticles exhibited a plateau maximum in the range of 80-100% PLGA(5)-PEG(5). At PLGA-PEG proportions lower than 80%, the PLGA/PLGA(45)-PEG(5) nanoparticles exhibited lower blood residence than the PLGA/PLGA(5)-PEG(5) nanoparticles, whereas at PLGA-PEG proportions higher than 80%, the PLGA/PLGA(45)-PEG(5) nanoparticles exhibited higher blood residence than the PLGA/PLGA(5)-PEG(5) nanoparticles. These findings indicate that apart from the surface PEG content, the biodistribution properties of the PLGA/PLGA-PEG nanoparticles are also influenced by the size of the nanoparticles and the rate of PEG loss from the nanoparticles.

Controlled release of paclitaxel from microemulsion containing PLGA and evaluation of anti-tumor activity in vitro and in vivo

The main objective of this study was to develop an optimal paclitaxel microemulsion prepared by self-microemulsifying drug delivery system (SMEDDS) which is a mixture of paclitaxel, tetraglycol, Cremophor ELP, and Labrafil 1944 and a paclitaxel microemulsion containing poly(D,L-lactide-co-glycolide) (PLGA) in order to offer controlled release of paclitaxel. To achieve this goal, paclitaxel and PLGA were dissolved by solubilizer like tetraglycol. There was not observed any change in molecular weight of PLGA after being solubilized by tetraglycol. The droplet size for all of the formulation of microemulsion was found in the range of 45-270nm by dynamic light scattering (DLS). It was observed that the droplet size of microemulsion without PLGA was smaller than that of microemulsion containing PLGA by transmission electron microscopy (TEM). The droplet of microemulsion containing PLGA was almost of spherical shape with smooth surface and there was no aggregation or adhesion among droplet of microemulsion by atomic force microscopy (AFM). The release behaviour of paclitaxel from microemulsion containing PLGA having various molecular weights (8K, 33K, and 90K) exhibited a biphasic pattern characterized by a fast initial release during the first 48h, followed by a slower and continuous release for 144h, in contrast that the release of paclitaxel from microemulsion without PLGA was finished during 24h. This result was identical with the result of anti-tumor activity in vitro of paclitaxel from microemulsion containing PLGA against human breast cancer cell line MCF7 and this formulation enhanced anti-tumor activity in vivo compared with microemulsion without PLGA against SKOV-3 human ovarian cancer cells bearing nude mice model.

Influence of the homogenisation procedure on the physicochemical properties of PLGA nanoparticles

Pilocarpine HCl-loaded PLGA nanoparticles were prepared by emulsification solvent evaporation. Three different stabilisers, polyvinylalcohol (PVA), Carbopol and Poloxamer were used, as well as mixtures thereof. The influence of the homogenisation pressure and number of cycles on the properties of nanoparticles were studied. Particle size was shown to depend on the stabiliser used. An increase of the homogenisation pressure or the number of cycles resulted in a decrease in particle size. The zeta potential value was influenced mainly by the nature of the stabiliser. Particles stabilised with poloxamer or PVA showed a slightly negative zeta potential value, while samples stabilised with carbopol possessed a more negative zeta potential, which became less negative after homogenisation. Drug encapsulation depended strongly on the stabiliser used. The higher drug entrapment of the carbopol-stabilised particles could be explained by an electrostatic interaction between the negatively charged carboxyl groups of carbopol and the positively charged, protonated pilocarpine. The drug release patterns of the particles prepared were quite similar. Differences between the release patterns of the homogenised particles could be attributed both to differences in size as well as drug encapsulation. Turbidimetric measurements suggested an interaction between mucin and PLGA nanoparticles exclusively stabilised with Carbopol.

Evaluation of in vitro and in vivo antitumor activity of BCNU-loaded PLGA wafer against 9L gliosarcoma

The purpose of the present study was to develop implantable BCNU-loaded poly(D,L-lactide-co-glycolide) (PLGA) wafer for the controlled release of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and to evaluate its in vitro and in vivo antitumor activity. The release rate of BCNU from PLGA wafer increased with the increase of BCNU amount loaded and the release was continued until 7 days. In vitro and in vivo antitumor activity of BCNU-loaded PLGA wafer was investigated using in vitro cytotoxicity against 9L gliosarcoma cells and a subcutaneous (s.c.) solid tumor model of 9L gliosarcoma, respectively. The wafers containing BCNU showed more effective cytotoxicity than BCNU powder due to its short half-life and inhibited the proliferation of 9L gliosarcoma cells. BCNU-loaded PLGA wafer delayed the growth of the tumors significantly and increasing the dose of BCNU in the wafer resulted in a substantial regression of the tumor. These results of antitumor activity of BCNU-loaded PLGA wafer demonstrate the feasibility of the wafers for clinical application.

Development and characterization of PLGA nanospheres and nanocapsules containing xanthone and 3-methoxyxanthone

The aim of the present work was to develop and characterize two different nanosystems, nanospheres and nanocapsules, containing either xanthone (XAN) or 3-methoxyxanthone (3-MeOXAN), with the final goal of improving the delivery of these poorly water-soluble compounds. The xanthones-loaded nanospheres (nanomatrix systems) and nanocapsules (nanoreservoir systems), made of poly(DL-lactide-co-glycolide) (PLGA), were prepared by the solvent displacement technique. The following characteristics of nanoparticle formulations were determined: particle size and morphology, zeta potential, incorporation efficiency, thermal behaviour, in vitro release profiles and physical stability at 4 degrees C. The nanospheres had a mean diameter <170 nm, a narrow size distribution (polydispersity index <0.1), and a negative surface charge (zeta potential <-36 mV). Their incorporation efficiencies were 33% for XAN and 42% for 3-MeOXAN. The presence of the xanthones did not affect the nanospheres size and zeta potential. DSC studies indicated that XAN and 3-MeOXAN were dispersed at a molecular level within the polymeric nanomatrix. Nanocapsules were also nanometric (mean size <300 nm) and exhibited a negative charge (zeta potential <-36 mV). Their incorporation efficiency values (>77%) were higher than those corresponding to nanospheres for both xanthones. The release of 3-MeOXAN from nanocapsules was similar to that observed for the correspondent nanoemulsion, indicating that drug release is mainly governed by its partition between the oil core and the external aqueous medium. In contrast, the release of XAN from nanocapsules was significantly slower than from the nanoemulsion, a behaviour that suggests an interaction of the drug with the polymer. Nanocapsule formulations exhibited good physical stability at 4 degrees C during a 4-month period for XAN and during a 3-month period for 3-MeOXAN.

Modeling small-molecule release from PLG microspheres: effects of polymer degradation and nonuniform drug distribution

Modeling release of small molecules from degradable microspheres is important to the design of controlled-release drug delivery systems. Release of small molecules from poly(d,l-lactide-co-glycolide) (PLG) particles is often controlled by diffusion of the drug through the polymer and by polymer degradation. In this study, a model is developed to independently determine the contributions of each of these factors by fitting the release of piroxicam from monodisperse 50-microm microspheres made with PLG of different initial molecular weights. The dependence of the drug diffusivity on polymer molecular weight was determined from in vitro release of piroxicam from monodisperse 10-microm PLG microspheres, and the polymer degradation rate was experimentally measured using gel permeation chromatography. The model also incorporates the effect of nonuniform drug distribution within the microspheres, which is obtained from confocal fluorescence microscopy. The model results agree well with experiments despite using only one fit parameter.

PLGA nanoparticles containing praziquantel: effect of formulation variables on size distribution

Praziquantel has been shown to be highly effective against all known species of Schistosoma infecting humans. Spherical nanoparticulate drug carriers made of poly(D,L-lactide-co-glycolide) acid with controlled size were designed. Praziquantel, a hydrophobic molecule, was entrapped into the nanoparticles with theoretical loading varying from 10 to 30% (w/w). This study investigates the effects of some process variables on the size distribution of nanoparticles prepared by emulsion-solvent evaporation method. The results show that sonication time, PLGA and drug amounts, PVA concentration, ratio between aqueous and organic phases, and the method of solvent evaporation have a significant influence on size distribution of the nanoparticles.

PLGA-PEI nanoparticles for gene delivery to pulmonary epithelium

Pulmonary gene delivery is thought to play an important role in treating genetically related diseases and may induce immunity towards pathogens entering the body via the airways. In this study we prepared poly (d,l-lactide-co-glycolide) (PLGA) nanoparticles bearing polyethyleneimine (PEI) on their surface and characterized them for their potential in serving as non-viral gene carriers to the pulmonary epithelium. Particles that were synthesized at different PLGA–PEI ratios and loaded with DNA in several PEI–DNA ratios, exhibited narrow size distribution in all formulations, with mean particle sizes ranging between 207 and 231 nm. Zeta potential was strongly positive (above 30 mV) for all the PEI–DNA ratios examined and the loading efficiency exceeded 99% for all formulations. Internalization of the DNA-loaded PLGA–PEI nanoparticles was studied in the human airway submucosal epithelial cell line, Calu-3, and DNA was detected in the endo-lysosomal compartment 6 h after particles were applied. Cytotoxicity of these nanoparticles was dependent on the PEI–DNA ratio and best cell viability was achieved by PEI–DNA ratios 1:1 and 0.5:1. These findings demonstrate that PLGA–PEI nanoparticles are a potential new delivery system to carry genes to the lung epithelium.

Solid-state solubility influences encapsulation and release of hydrophobic drugs from PLGA/PLA nanoparticles

Biodegradable nanoparticles formulated from poly(D,L-lactide-co-glycolide) (PLGA) and polylactide (PLA) polymers are being extensively investigated for various drug delivery applications. In this study, we hypothesize that the solid-state solubility of hydrophobic drugs in polymers could influence their encapsulation and release from nanoparticles. Dexamethasone and flutamide were used as model hydrophobic drugs. A simple, semiquantitative method based on drug-polymer phase separation was developed to determine the solid-state drug-polymer solubility. Nanoparticles using PLGA/PLA polymers were formulated using an emulsion-solvent evaporation technique, and were characterized for size, drug loading, and in vitro release. X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC) were used to determine the physical state of the encapsulated drug. Results demonstrated that the solid-state drug-polymer solubility depends on the polymer composition, molecular weight, and end-functional groups (ester or carboxyl) in polymer chains. Higher solid-state drug-polymer solubility resulted in higher drug encapsulation in nanoparticles, but followed an inverse correlation with the percent cumulative drug released. The XRD and DSC analyses demonstrated that the drug encapsulated in nanoparticles was present in the form of a molecular dispersion (dissolved state) in the polymer, whereas in microparticles, the drug was present in both molecular dispersion and crystalline forms. In conclusion, the solid-state drug-polymer solubility affects the nanoparticle characteristics, and thus could be used as an important preformulation parameter.

Studies on the poly(lactic-co-glycolic) acid microspheres of cisplatin for lung-targeting

Lung-targeting cisplatin-loaded poly(lactic-co-glycolic) acid microspheres (CDDP-PLGA-MS) were prepared by a solvent evaporation method. The uniform design was used to optimize the technology of preparation, the appearance and size distribution were examined by scanning electron microscope, and the aspects such as in vitro release characteristics, stability, drug loading, loading efficiency, pharmacokinetics and tissue distribution in rabbit were studied. The experimental results showed that the microspheres were globular in appearance and dispersed well. The average particle size was 12.8 microm with 98% of the microspheres being in the range of 5-30 microm. The drug loading and loading efficiency were 17.68 and 53.2%, respectively. The in vitro release behavior could be expressed by the following equation: 1-Q=0.424e(-0.360t)+0.474e(-0.001t). After i.v. administration (15 min), the drug concentration of microspheres group in lung in rabbits was 212 microg/g, while that of controlled group was 1.37 microg/g. CDDP-PLGA-MS showed a combination of lung-targeting and sustained drug release in experiments on rabbits.

Oral delivery of spray dried PLGA/amifostine nanoparticles

Amifostine (Ethyol, WR-2721) is a cytoprotective drug approved by the US Food & Drug Administration for intravenous administration in cancer patients receiving radiation therapy and certain forms of chemotherapy. The primary objective of this project was to develop orally active amifostine nanoparticles using spray drying technique. Two different nanoparticle formulations (Amifostine-PLGA (0.4:1.0 and 1.0:1.0)) were prepared using a Buchi B191 Mini Spray Dryer. A water-in-oil emulsion of amifostine and PLGA (RG 502) was spray dried using an airflow of 600 L h(-1) and input temperature of 55 degrees C. A tissue distribution study in mice was conducted following oral administration of the formulation containing drug-polymer (0.4:1.0). The efficiency of encapsulation was 90% and 100%, respectively, for the two formulations while the median particle sizes were 257 and 240 nm, with 90% confidence between 182 and 417 nm. Since amifostine is metabolized to its active form, WR-1065, by intracellular alkaline phosphatase, the tissue levels of WR-1065 were measured, instead of WR-2721. WR-1065 was detected in significant amounts in all tissues, including bone marrow, jejunum and the kidneys, and there was some degree of selectivity in its distribution in various tissues. This work demonstrates the feasibility of developing an orally effective formulation of amifostine that can be used clinically.

PLGA microspheres for the ocular delivery of a peptide drug, vancomycin using emulsification/spray-drying as the preparation method: in vitro/in vivo studies

The aim of this study was an in vitro/in vivo investigation on poly(lactide-co-glycolide) (PLGA) microspheres as carriers for the topical ocular delivery of a peptide drug vancomycin (VA). The microspheres were prepared by an emulsification/spray-drying technique that can be proposed as an alternative to the double emulsion method for preparation of peptide-loaded microparticles. The drug encapsulation efficiencies were close to the theoretical values (84.2-99.5%); the average particle size, expressed as dvs, was about 11 microm. The microspheres were able to modulate the in vitro drug release of VA with a behavior dependent on their composition: the highest drug content corresponded to the highest release rate. In vivo studies were carried out by assessing the pharmacokinetic profile of VA in the aqueous humor of rabbits after topical administration of aqueous suspensions of microspheres. High and prolonged VA concentrations and increased AUC values (2-fold) with respect to an aqueous solution of the drug were observed. Increasing the viscosity of the microsphere suspension by addition of a suspending-viscosizing agent (hydroxypropylcellulose) did not produce an increase of the ocular bioavailability. PLGA microspheres can be proposed as a system for ocular delivery of peptide drugs.

Control of encapsulation efficiency and initial burst in polymeric microparticle systems

Initial burst is one of the major challenges in protein-encapsulated microparticle systems. Since protein release during the initial stage depends mostly on the diffusional escape of the protein, major approaches to prevent the initial burst have focused on efficient encapsulation of the protein within the microparticles. For this reason, control of encapsulation efficiency and the extent of initial burst are based on common formulation parameters. The present article provides a literature review of the formulation parameters that are known to influence the two properties in the emulsion-solvent evaporation/extraction method. Physical and chemical properties of encapsulating polymers, solvent systems, polymer-drug interactions, and properties of the continuous phase are some of the influential variables. Most parameters affect encapsulation efficiency and initial burst by modifying solidification rate of the dispersed phase. In order to prevent many unfavorable events such as pore formation, drug loss, and drug migration that occur while the dispersed phase is in the semi-solid state, it is important to understand and optimize these variables.

The influence of the use of viscosifying agents as dispersion media on the drug release properties from PLGA nanoparticles

Poly(lactide-co-glycolide) nanoparticles incorporating ciprofloxacin HCl were prepared by means of a W/O/W emulsification solvent evaporation method. The physicochemical properties of these particles were evaluated by measuring particle size, zeta potential and drug loading efficiency. Gamma-sterilised nanoparticles were dispersed in different isoviscous polymer solutions, commonly used as vehicles in eye drops. The influence of gamma-irradiation of the viscosifying agents on the drug release properties of the dispersed nanoparticles was evaluated with respect to release in mannitol solution. The viscosity of the polymer solutions prepared was measured by flow rheometry and thereby the influence of temperature and sterilisation by autoclaving on viscosity was examined. Before and after freeze-drying and subsequent sterilisation by gamma-irradiation, the polymer solutions were also characterised by dynamic stress sweep and dynamic frequency sweep oscillation measurements to deduce possible structural changes. A possible relationship between the differences in ciprofloxacin release from the nanoparticles suspended in the various media and the network structure or rheological behaviour of the polymers was investigated.

Poly(lactide-co-glycolide) microparticles as systems for controlled release of proteins -- preparation and characterization

Poly(DL-lactide-co-glycolide) (PDLLGA) and poly(L-lactide-co-glycolide) (PLLGA) copolymers were prepared by bulk ring opening polymerization of lactide and glycolide and characterized by GPC, FTIR, 1H NMR and DSC. Copolymers with different molar masses at a constant lactide/glycolide ratio were used for preparation of bovine serum albumin (BSA)-loaded microparticles by the double emulsion w/o/w method. The influence of the copolymer molar mass and composition on the microparticle morphology, size, yield, degradation rate, BSA-loading efficiency and BSA release profile were studied. For microparticles prepared from PDLLGA copolymers, a biphasic profile for BSA release was found and for those made from PLLGA copolymers the release profile was typically triphasic; both of them were characterized by high initial burst release. Possible reasons for such behavior are discussed.

Comparative study on sustained release of human growth hormone from semi-crystalline poly(L-lactic acid) and amorphous poly(D,L-lactic-co-glycolic acid) microspheres: morphological effect on protein release

Recombinant human growth hormone (rhGH) was encapsulated by a double emulsion solvent evaporation method within two biodegradable microspheres having different polymer compositions. Semi-crystalline poly(L-lactic acid) (PLA) and amorphous poly(D,L-lactic-co-glycolic acid) (PLGA) were used for the encapsulation of hGH. Protein release profiles from the two microspheres were comparatively evaluated with respect to their morphological difference. Both of the microspheres similarly exhibited rugged surface and porous internal structures, but their inner pore wall morphologies were quite different. The slowly degrading PLA microspheres had many nano-scale reticulated pores on the wall, while the relatively fast degrading PLGA microspheres had a non-porous and smooth wall structure. From the PLA microspheres, hGH was released out in a sustained manner with an initial approximately 20% burst, followed by constant release, and almost 100% complete release after a 1-month period. In contrast, the PLGA microspheres showed a similar burst level of approximately 20%, followed by much slower release, but incomplete release of approximately 50% after the same period. The different hGH release profiles between PLA and PLGA microspheres were attributed to different morphological characters of the pore wall structure. The inter-connected nano-porous structure of PLA microspheres was likely to be formed due to the preferable crystallization of PLA during the solvent evaporation process.

Design of Amine-Modified Graft Polyesters for Effective Gene Delivery Using DNA-Loaded Nanoparticles

PURPOSE

The purpose of this study was the design of a polymeric platform for effective gene delivery using DNA-loaded nanoparticles.

METHODS

The polymers were synthesized by carbonyldiimidazole (CDI)-mediated coupling of diamines diethylaminopropylamine (DEAPA), dimethylaminopropylamine (DMAPA) or diethylaminoethylamine (DEAEA) to poly(vinyl alcohol) (PVA) with subsequent grafting of D,L-lactide and glycolide (1:1) in the stoichiometric ratios of 1:10 and 1:20 (free hydroxyl groups/monomer units). The polymers were characterized by 1H-NMR, gel permeation chromatography-multiple-angle laser-light-scattering, and differential scanning calorimetry. DNA-loaded nanoparticles prepared by a modified solvent displacement method were characterized with regard to their zeta (zeta)-potential and size. The transfection efficiency was assessed with the plasmid DNA pCMV-luc in L929 mouse fibroblasts.

RESULTS

The polymers were composed of highly branched, biodegradable cationic polyesters exhibiting amphiphilic properties. The amine modification enhanced the rapid polymer degradation and resulted in the interaction with DNA during particle preparation. The nanoparticles exhibited positive zeta-potentials up to +42 mV and high transfection efficiencies, comparable to polyethylenimine (PEI) 25 kDa/DNA complexes at a nitrogen to phosphate ratio of 5.

CONCLUSIONS

The polymers combined amine-functions and short poly(D,L-lactic-co-glycolic acid) (PLGA) chains resulting in water-insoluble polymers capable of forming biodegradable DNA nanoparticles through coulombic interactions and polyester precipitation in aqueous medium. The high transfection efficiency was based on fast polymer degradation and the conservation of DNA bioactivity.

The Characteristics and Mechanisms of Uptake of PLGA Nanoparticles in Rabbit Conjunctival Epithelial Cell Layers

PURPOSE

To delineate the characteristics and mechanisms of uptake of biodegradable poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles in primary cultured rabbit conjunctival epithelial cells (RCECs).

METHODS

Poly(D,L-lactide-co-glycolide) nanoparticles (PLGA 50:50. 101 nm in diameter) containing 6-coumarin (as a fluorescent marker) were used. The effect of size was studied using various particle sizes (100 nm, 800 nm, and 10 microm). The effect of cytochalasin D, nocodazole, and metabolic inhibitors on nanoparticle uptake was investigated. The capability of nanoparticles to enhance the uptake of an encapsulated protein. BSA bound to Texas red (TR-BSA), was evaluated.

RESULTS

Maximal uptake of nanoparticles at 37 degrees C occurred at 2 h, and 100-nm particles had the highest uptake in RCECs in comparison with 800-nm and 10-microm particles. Nanoparticle uptake was saturable over the 0.1-4 mg/ml concentration range. Nanoparticle uptake was confirmed by confocal microscopy and was inhibited significantly by coumarin-free nanoparticles (of similar size), by lower incubation temperature, and by the presence of metabolic inhibitors and cytochalasin D. The uptake of encapsulated TR-BSA in RCECs at 4 h was 28% higher than free BSA application.

CONCLUSION

Our findings suggest that PLGA nanoparticle uptake in primary cultured rabbit conjunctival epithelial cells occurs most likely by adsorptive-type endocytosis.

Preparation and characteristics of DNA-nanoparticles targeting to hepatocarcinoma cells

AIM: To prepare thymidine kinase gene (TK gene) nanoparticles and to investigate the expression of TK gene.

METHODS: Poly(D,L-lactic-co-glycolic acid) (PLGA), a biodegradable and biocompatible polymer, was used to prepare recombinant plasmid P^EGFP-AFP nanoparticles by a double-emulsion evaporation technique. Characteristics of the nanoparticles were investigated in this study, including morphology, entrapment efficiency, and tissue distribution. The expression of TK gene was also investigated by MTT assay, by which the viable cells were determined after the addition of ganciclovir (GCV). The enhanced green fluorescent protein (EGFP) expression in human hepatocellular carcinoma SMMC-7721 cells and normal parenchymal Chang liver cells were assessed by flow cytometry.

RESULTS: The prepared plasmid-nanoparticles had regular spherical surface and narrow particle size span with a mean diameter of 72 ± 12 nm. The mean entrapment efficiency was 91.25%. A total of 80.14% DNA was found to be localized in the livers after 1-h injection with ³²P-DNA-PLGA nanoparticles in mouse caudal vein. The expression of DNA encapsulated in nanoparticles was much higher than that in naked DNA, and human hepatocellular carcinoma SMMC-7721 cells were more sensitive to GCV than human normal parenchymal Chang liver cells.

CONCLUSION: The enhanced transfection efficiency and stronger ability to protect plasmid DNA from being degraded by nucleases are due to nanoparticles encapsulation.

Controlled release of the fibronectin central cell binding domain from polymeric microspheres

Non-ionic surfactants have been employed as alternatives to PVA for the emulsification-encapsulation of a conformationally labile protein (FIII9'-10) into PLGA microspheres. FIII9'-10 was encapsulated using a w/o/w double emulsification-evaporation technique and the microspheres fabricated were characterized by SEM and CLSM. The peptide backbone integrity of FIII9'-10 was assayed by SDS-PAGE and the degree of unfolding of FIII9'-10 following emulsification-encapsulation was assessed using a fibroblast cell-attachment assay. The encapsulation efficiency for FIII9'-10 was 25% when using PVA, compared to 50-60% when using Igepal CA-630 or Triton-X100, with values below for the other surfactants. FIII9'-10 released from microspheres promoted cell attachment in a concentration-dependent manner, only Igepal CA-630 and Triton X-100 maintaining near-maximal cell attachment, indicating that the conformation of the relatively unstable FIII9' domain was preserved. All non-ionic surfactants reduced microsphere surface porosity, compared to PVA, and an increasing surface rugosity (leading to minor 'ridges') could be correlated with decreasing surfactant HLB. Low surface porosities did not effect the diffusion of FIII9'-10 from the microspheres' internal pores in a 'burst release', as may have been imagined. In summary, non-ionic surfactants should be considered over PVA for the maintenance of biological activity of conformationally labile proteins during encapsulation.

Methadone implants for methadone maintenance treatment. In vitro and in vivo animal studies

Methadone implant formulations elaborated with polylactide-co-glycolide (PLGA) and polylactic acid (PLA) for 1 week and 1 month release duration, respectively, were evaluated in vitro and in vivo. One-week implants prepared with methadone clorhydrate, methadone clorhydrate/methadone base blend or methadone base were tested in vitro. Results showed that the methadone release rate decreased as the methadone base increased. The best release profile was achieve when the methadone base implants, made by compression of a 50:50 PLGA (12 kDa) and methadone base mix, were coated with PLA (30 kDa). For 1-month implants, the methadone base load was increased to 65% and PLA of 30 kDa was used as a matrix component. In this case the implants were coated with the same polymer. Deconvolution methods could not be used for in vivo release estimation because an increase in methadone clearance was observed with methadone clorhydrate solution multiple-dose treatment. Therefore the amount of drug remaining within the implants was evaluated and the deconvolution was only used to establish the release profile range. The upper limit was estimated applying the absorption-disposition function obtained after multiple-dose administrations while the lower curve was estimated using the single-dose function. Methadone serum levels were maintained around 200 ng/ml during 1 week and approximately 5 weeks with the optimised implants. In vivo-in vitro correlations were always very good with slopes near 1.

In vivo sustained release of adenoviral vectors from poly(d,l-lactic-co-glycolic) acid microparticles prepared by TROMS

We have prepared and characterised injectable adenovirus-loaded polymeric microparticles to be used for in vitro and in vivo gene transfer studies. Microparticles were prepared by the water-in-oil-in-water solvent evaporation method using a novel system where the emulsification process is carried out by the turbulent injection of the phases in the total recirculation one-machine system (TROMS) apparatus. In vitro studies were performed to assess the amount of infectious adenovirus released from the microparticles, showing that these microparticles release higher amounts of infectious adenovirus than microparticles prepared by standard emulsification techniques. We also tested whether sustained release in vivo could overcome the short-lived gene expression profile which is typical of adenovirus delivery into muscle. Intramuscular injection of adenovirus-loaded microparticles in immunocompetent mice showed transgene (beta-galactosidase) expression for at least 7 weeks in two out of four muscles injected with adenovirus-loaded microparticles prepared by TROMS, but not in control muscles injected with purified adenovirus stocks.