One- and three-month release injectable microspheres of the LH-RH superagonist leuprorelin acetate

PGE2 signal via EP2 receptors evoked by a selective agonist enhances regeneration of injured articular cartilage

OBJECTIVE

The effect of the prostaglandin E2 (PGE2) signal through prostaglandin E receptor 2 (EP2) receptors on the repair of injured articular cartilage was investigated using a selective agonist for EP2.

METHODS

Chondral and osteochondral defects were prepared on the rabbit femoral concave in both knee joints, and gelatin containing polylactic-co-glycolic acid microspheres conjugated with or without the EP2 agonist was placed nearby. Animals were sacrificed at 4 or 12 weeks post-operation, and regenerated cartilage tissues and subchondral structure remodeling were evaluated by histological scoring. The quality of regenerated tissues was also evaluated by the immunohistochemical staining of EP2, type II collagen, and proliferating cell nuclear antigen (PCNA). As an evaluation of side effects, the inflammatory reaction of the synovial membrane was analyzed based on histology and the mRNA expression of matrix metalloproteinase3 (MMP3), tissue inhibitor of metalloproteinase 3 (TIMP3), and interleukin-1 beta (IL-1 beta). Also, the activity of MMP3 and the amount of tumor necrosis factor-alpha (TNF-alpha) and C-reactive protein in joint fluid were measured.

RESULTS

In both models, the EP2 agonist enhanced the regeneration of the type II collagen-positive tissues containing EP2- and PCNA-positive chondrocytes, and the histological scale of regenerated tissue and subchondral bone was better than that of on the control side, particularly at 12 weeks post-operation. No inflammatory reaction in the synovial membrane was observed, and no induction of pro-inflammatory cytokines was found in joint fluid.

CONCLUSION

Selective stimulation of the PGE2 signal through EP2 receptors by a specific agonist promoted regeneration of cartilage tissues with a physiological osteochondral boundary, suggesting the potential usefulness of this small molecule for the treatment of injured articular cartilages.

A novel biomaterial for osteotropic drug nanocarriers: synthesis and biocompatibility evaluation of a PLGA–ALE conjugate

Background & aims: Osteotropic drug-delivery systems have been proposed as a means to provide drugs with affinity to bone tissues. Drugs or proteins have been linked chemically to bone-seeking agents, such as bisphosphonates (BPs); alternatively, drug-loaded nanoparticles have been used to target specific tissues, such as tumor areas. In our current research, these approaches were merged by synthesizing a novel bone-seeking polymer conjugate, from which targetable nanoparticles can be produced. Materials & methods: An amino-BP, alendronate (ALE) was bound covalently to a biodegradable polymer, poly(lactic-co-glycolide) (PLGA), containing a free end carboxylic group. Blood compatibility and cytotoxicity were assessed in vitro. Results & discussion: By a classical solvent-evaporation method, nanoparticles with a mean size of 200–300 nm were prepared from the conjugate; sterilization was achieved by γ-irradiation, confirming their potential as injectable drug nanocarriers. Owing to the presence of the BP residue, PLGA–ALE nanoparticles were adsorbed onto hydroxyapatite to a higher extent than pure PLGA nanoparticles. The PLGA–ALE conjugate did not induce either hemolysis or alterations of the plasmatic phase of coagulation, or cytotoxic effects on endothelial cells and trabecular osteoblasts. Conclusion: The prepared conjugate represents a novel biomaterial that is able to provide nanoparticles, which can be further loaded with drugs, such as anticancer agents, and addressed to osteolytic or other bone diseases.

Effects of formulation factors on encapsulation efficiency and release behaviourin vitroof huperzine A-PLGA microspheres

To develop a long-acting injectable huperzine A-PLGA microsphere for the chronic therapy of Alzheimer's disease, the microsphere was prepared by using an o/w emulsion solvent extraction evaporation method based on a series of formulation design of the emulsion. The dialysis method was used for release analysis. The encapsulation efficiency and release amount of the microspheres were determined by a UV/VIS spectrophotometer. The morphology of the microspheres was observed by scanning electron microscopy. The distribution of the drug within microspheres was observed by a confocal laser scanning microscope. The results indicated that the PLGA 15,000 microspheres possessed a smooth and round appearance with average particle size of 50 microm or so. The encapsulation percentages of microspheres prepared from PLGA 15,000, 20,000 and 30,000 were 62.75%, 27.52% and 16.63%, respectively. The drug release percentage during the first day decreased from 22.52% of PLGA 30,000 microspheres to 3.97% of PLGA 15,000 microspheres, the complete release could be prolonged to 3 weeks. The initial burst release of microspheres with higher molecular weight PLGA could be explained by the inhomogeneous distribution of drug within microspheres. The encapsulation efficiency of the microspheres improved as the polymer concentration increased in the oil phase and PVA concentration decreased in the aqueous phase. The burst release could be controlled by reducing the polymer concentration. Evaporation temperature had a large effect on the drug release profiles. It had better be controlled under 30 degrees C. Within a certain range of particle size, encapsulation efficiency decreased and drug release rate increased with the reducing of the particle size.

Microspheres from new biodegradable poly(ester amide)s with different ratios ofL- andD-alanine for controlled drug delivery

A series of biodegradable poly (ester amide)s composed of sebacic acid, dodecanediol and different ratios of the stereoisomers of L- and D-alanine were synthesized for applications in drug delivery systems. Microspheres loaded with diclofenac sodium salt, triclosan and clofazimine were prepared with the solvent evaporation technique. No influence of polymer constitution in the drug release rate was found in vitro and no degradation occurred during the period of drug release. It was shown that a sustained delivery of the hydrophilic diclofenac sodium salt in Sörensen media occurred and it was controlled by diffusion. However, exhaustion of microspheres was feasible only from the most porous matrices where channelling had an important contribution.

Effects of formulation factors on encapsulation efficiency and release behaviourin vitroof huperzine A-PLGA microspheres

To develop a long-acting injectable huperzine A-PLGA microsphere for the chronic therapy of Alzheimer's disease, the microsphere was prepared by using o/w emulsion solvent extraction evaporation method based on a series of formulation design of the emulsion. The dialysis method was used for release analysis. The encapsulation efficiency and release amount of the microspheres were determined by UV/VIS spectrophotometry. The morphology of the microspheres was observed by scanning electron microscopy. The distribution of the drug within microspheres was observed by a confocal laser scanning microscope. The results indicated that the PLGA 15 000 microspheres possessed a smooth and round appearance with average particle size of 50 microm or so. The encapsulation percentages of microspheres prepared from PLGA 15 000, 20 000 and 30 000 were 62.75, 27.52 and 16.63%, respectively. The drug release percentage during the first day decreased from 22.52% of PLGA 30 000 microspheres to 3.97% of PLGA 15 000 microspheres, the complete release could be prolonged to 3 weeks. The initial burst release of microspheres with higher molecular weight PLGA could be explained by the inhomogeneous distribution of drug within microspheres. The encapsulation efficiency of the microspheres improved as the polymer concentration increase in oil phase and PVA concentration decreased in aqueous phase. The burst release could be controlled by reducing the polymer concentration. Evaporation temperature had a large effect on the drug release profiles. It had better be controlled under 30 degrees C. Within a certain range of particle size, encapsulation efficiency decreased and drug release rate increased with the reducing of the particle size.

Optimizing double emulsion process to decrease the burst release of protein from biodegradable polymer microspheres

The process parameters such as the compositions of inner and outer aqueous phase and emulsification technique of the primary emulsion were optimized to decrease the burst release of BSA from biodegradable polymer microspheres in double emulsion method. It was found that diminished burst release of -14% was achieved for the microspheres produced by formulations, where no phosphate was present in the inner water phase (non-buffered system). Primary emulsion made by probe sonication rather than homogenization or mechanical stirring led to microspheres with insignificant burst effect. Microspheres obtained using 0.1% aqueous Tween 80 solution as the outer aqueous phase, frequently exhibit reduced burst effect of 2.7%. Low microsphere yield (52.1%), however, was observed. Microsphere yield was, therefore, enhanced by addition of additive such as sodium chloride, glucose or mannitol into the outer aqueous phase. Decrease in BSA entrapment was observed in the presence of sodium chloride, but reduction in entrapment efficiency was observed in the case of glucose. Burst release increased from 2.7% to 9.5% or 3.4% as 2.5% sodium chloride or 7.5% glucose was added into the outer aqueous phase respectively. Marked burst release (>20%) was observed in the presence of additive of higher concentration independent of sodium chloride or glucose. As far as surfactant type was concerned, diminished burst was found when PVP or Tween 80 rather than PVA was utilized as the surfactant during microsphere preparation. In addition to PLGA, the copolymers of L-lactide (LLA) and dimethyl trimethylene carbonate (DTC) or trimethylene carbonate (TMC) were also evaluated. Insignificant burst effect was found for the microspheres composed of DTC or TMC copolymers.

Acidic microclimate pH distribution in PLGA microspheres monitored by confocal laser scanning microscopy

PURPOSE

The acidic microclimate pH (micropH) distribution inside poly(lactic-co-glycolic acid) (PLGA) microspheres was monitored quantitatively as a function of several formulation variables.

METHODS

A ratiometric method by confocal laser scanning microscopy with Lysosensor yellow/blue dextran was adapted from those previously reported, and micropH distribution kinetics inside microspheres was examined during incubation under physiologic conditions for 4 weeks. Effects of PLGA molecular weight (MW) and lactic/glycolic acid ratio, microspheres size and preparation method, and polymer blending with poly(ethylene glycol) (PEG) were evaluated.

RESULTS

micropH kinetics was accurately sensed over a broadly acidic range (2.8 < micropH < 5.8) and was more acidic and variable inside PLGA with lower MW and lactic/glycolic acid ratio. Lower micropH was found in larger microspheres of lower MW polymers, but size effects for lactic-rich polymers were insignificant during 4 weeks. Microspheres prepared by the oil-in-oil emulsion method were less acidic than those prepared by double emulsion, and blending PLGA 50/50 with 20% PEG increased micropH significantly (micropH > 5 throughout incubation).

CONCLUSIONS

Coupling this method with that previously developed (SNARF-1 dextran for micropH 5.8-8.0) should provide microclimate pH mapping over the entire useful pH range (2.8-8.0) for optimization of PLGA delivery of pH-sensitive bioactive substances.

Poly(D,L-lactide-co-glycolide) dispersions containing pluronics: from particle preparation to temperature-triggered aggregation

In this work the preparation mechanism, properties and temperature-triggered aggregation of poly(D, L-lactide- co-glycolide) (PLGA) dispersions are investigated. The dispersions were prepared by interfacial deposition in aqueous solution containing Pluronic L62 (EO(6)PO(30)EO(6)) or F127NF (EO(101)PO(56)EO(101)), where EO and PO are ethylene oxide and propylene oxide, respectively. PLGA dispersions were also prepared in the absence of added Pluronic for comparison. The PLGA particles were characterized using SEM, photon correlation spectroscopy and electrophoretic mobility measurements. It was found that the hydrodynamic diameter (d) increased with PLGA concentration used in the organic solvent phase ( C PLGA(o) ). The value for d was proportional to C(PLGA)(o) (1/3). The value for d increased upon addition of 0.04 M NaNO(3) which demonstrated the importance of electrostatic interactions during particle formation. Electrophoretic mobility measurements were conducted as a function of pH and the data used to estimate the Pluronic layer thicknesses on the PLGA particles. The layer thickness was greatest for the PLGA particles prepared in the presence of Pluronic F127NF. PLGA dispersions containing Pluronic L62 exhibited temperature-triggered aggregation in the presence of 0.15 M NaNO(3). It was found that the critical temperature for dispersion aggregation (T(crit)) was comparable to the cloud point temperature ( T(cp)) for the parent Pluronic L62 solution. Conditions were established for achieving temperature-triggered aggregation at body temperature for PLGA particle/Pluronic L62 dispersions under physiological ionic strength and pH conditions. The PLGA/Pluronic L62 mixtures studied may have potential for use as injectable biodegradable implants for controlled release applications.

Principles of encapsulating hydrophobic drugs in PLA/PLGA microparticles

Injectable biodegradable and biocompatible copolymers of lactic and glycolic acid (PLGA) are an important advanced delivery system for week-to-month controlled release of hydrophobic drugs (e.g., from biopharmaceutical classification system class IV), which often display poor oral bioavailability. The basic principles and considerations to develop such microparticle formulations is reviewed here based on a comprehensive study of papers and patents from the beginnings of hydrophobic drug encapsulation in polylactic acid and PLGA up through the very recent literature. Challenges with the diversity of drug properties, microencapsulation methods, and organic solvents are evaluated in light of the precedence of commercialized formulations and with a focus on decreasing the time to lab-scale encapsulation of water-insoluble drug candidates in the early stage of drug development. The influence of key formulation variables on final microparticle characteristics, and how best to avoid undesired microparticle properties, is analyzed mechanistically. Finally, concepts are developed to manage the common issues of maintaining sink conditions for in vitro drug release assays of hydrophobic compounds. Overall, against the backdrop of an increasing number of new, poorly orally available drug entities entering development, microparticle delivery systems may be a viable strategy to rescue an otherwise undeliverable substance.

Stability of proteins encapsulated in injectable and biodegradable poly(lactide-co-glycolide)-glucose millicylinders

PURPOSE

To characterize protein stability in poly(lactide-co-glycolide) 50/50-glucose star (PLGA-Glu) injectable millicylinders and to compare results with linear PLGA 50/50.

METHODS

Bovine serum albumin (BSA), a model protein, was encapsulated in PLGA-Glu and linear PLGA millicylinders by solvent-extrusion and incubated under physiological conditions. Important system properties were characterized, including: polymer molecular weight distribution, soluble acidic residues, polymer morphology, polymer water uptake, microclimate pH, protein content and release, and protein aggregation. The polymer microclimate late in the release incubation was simulated and protein recovery was analyzed by UV280, size exclusion chromatography, amino acid analysis, and a modified Bradford assay.

RESULTS

PLGA-Glu contained higher levels of low molecular weight oligomers, more rapidly biodegraded, and exhibited a lower microclimate pH than the linear 50/50 PLGA, which is the most acidic type in the PLGA family. BSA, when encapsulated in PLGA-Glu millicylinders, underwent extensive noncovalent insoluble aggregation over 2 weeks in vitro release, which was almost completely inhibited upon co-encapsulation of Mg(OH)2. However, by 5 weeks release for base-containing formulations, although insoluble aggregation was still suppressed, the soluble fraction of protein in the polymer was unrecoverable by the modified Bradford assay. Polymer microclimate simulations with extensive protein analysis strongly suggested that the low recovery was mostly caused by base-catalyzed hydrolysis of the oligomeric fraction of BSA.

CONCLUSIONS

In PLGA-Glu, the acidic microclimate was similarly responsible for insoluble aggregation of encapsulated BSA. BSA aggregation was inhibited in millicylinders by co-incorporation into the polymer an insoluble base, but over a shorter release interval than linear PLGA likely because of a more acidic microclimate in the star polymer.

Applications of supercritical CO2 in the fabrication of polymer systems for drug delivery and tissue engineering

Supercritical CO(2) has the potential to be an excellent environment within which controlled release polymers and dry composites may be formed. The low temperature and dry conditions within the fluid offer obvious advantages in the processing of water, solvent or heat labile molecules. The low viscosity and high diffusivity of scCO(2) offer the possibility of novel processing routes for polymer drug composites, but there are still technical challenges to overcome. Moreover, the low solubility of most drug molecules in scCO(2) presents both challenges and advantages. This review explores the current methods that use high pressure and scCO(2) for the production of drug delivery systems and the more specialized application of the fluid in the formation of highly porous tissue engineering scaffolds.

PLGA microspheres with high drug loading and high encapsulation efficiency prepared by a novel solvent evaporation technique

PLGA microspheres with high drug loading and high encapsulation efficiency were fabricated by a novel solvent evaporation process-in-situ S/O/W process. Insulin was dissolved in DMSO and dispersed into DCM to form fine particles due to an anti-solvent effect. The in-situ formed suspension was then added into an aqueous phase and emulsified. Microspheres were formed following the evaporation of organic solvents. The experimental results showed that the modified S/O/W process could encapsulate more than 90%(w/w) insulin in the microspheres with a drug loading of over 15% and the initial burst was much less than microspheres made by a W1/O/W2 process. Compared with a traditional water-in-oil-in-water (W1/O/W2) process, the in-situ S/O/W process does not require high solubility of the encapsulated drug in water and, because no special pre-treatment is needed to reduce the particle size of the drug, it is superior to an ordinary S/O/W process. The in-situ S/O/W process is particularly applicable to encapsulate peptides and low molecular weight proteins.

Beta7-integrin-independent enhancement of mucosal and systemic anti-HIV antibody responses following combined mucosal and systemic gene delivery

Vaccination strategies that can block or limit heterosexual human immunodeficiency virus (HIV) transmissions to local and systemic tissues are the goal of much research effort. Herein, in a mouse model, we aimed to determine whether the enhancement of antibody responses through mucosal and systemic immunizations, previously observed with protein-based vaccines, applies to immunizations with DNA- or RNA-based vectors. Intranasal (i.n.) followed by intramuscular (i.m.) immunizations (i.n./i.m.) with polylactide-coglycolide (PLG)-DNA microparticles encoding HIV-gag (PLG-DNA-gag) significantly enhanced serum antibody responses, compared with i.m., i.n. or i.m. followed by i.n. (i.m./i.n.) immunizations. Moreover, while i.n./i.m., i.n. or i.m./i.n. immunizations with PLG-DNA-gag resulted in genital tract antibody responses, i.m. immunizations alone failed to do so. Importantly, beta7-deficient mice developed local and systemic antibody responses following i.n./i.m. immunization, or immunization via any other route, similar to those of wild-type mice. To compare the DNA with an RNA delivery system, immunizations were performed with VEE/SIN-gag replicon particles, composed of Venezuelan equine encephalitis virus (VEE) replicon RNA and Sindbis surface structure (SIN). i.n./i.m., compared with any other immunizations, i.n./i.m. immunization with VEE/SIN-gag resulted in enhanced genital tract but not serum antibody responses. These data show for the first time that mucosal followed by systemic immunizations with gene delivery systems enhance B-cell responses independent of the mucosal homing receptors alpha4beta7 and alphaEbeta7.

Macromolecule Release from Monodisperse PLG Microspheres: Control of Release Rates and Investigation of Release Mechanism

Novel macromolecular therapeutics such as peptides, proteins, and DNA are advancing rapidly toward the clinic. Because of typically low oral bioavailability, macromolecule delivery requires invasive methods such as frequently repeated injections. Parenteral depots including biodegradable polymer microspheres offer the possibility of reduced dosing frequency but are limited by the inability to adequately control delivery rates. To control release and investigate release mechanisms, we have encapsulated model macromolecules in monodisperse poly(D,L-lactide-co-glycolide) (PLG) microspheres using a double-emulsion method in combination with the precision particle fabrication technique. We encapsulated fluorescein-dextran (F-Dex) and sulforhodamine B-labeled bovine serum albumin (R-BSA) into PLG microspheres of three different sizes: 31, 44, and 80 microm and 34, 47, and 85 microm diameter for F-Dex and R-BSA, respectively. The in vitro release profiles of both compounds showed negligible initial burst. During degradation and release, the microspheres hollowed and swelled at critical time points dependant upon microsphere size. The rate of these events increased with microsphere size resulting in the largest microspheres exhibiting the fastest overall release rate. Monodisperse microspheres may represent a new delivery system for therapeutic proteins and DNA and provide enhanced control of delivery rates using simple injectable depot formulations.

Estradiol loaded PLGA nanoparticles for oral administration: Effect of polymer molecular weight and copolymer composition on release behavior in vitro and in vivo

The present investigation was aimed at optimization of estradiol loaded PLGA nanoparticulate formulations resulting in improved oral bioavailability and sustained release of estradiol by varying the molecular weight and copolymer composition of PLGA. Nanoparticles were prepared following emulsion-diffusion-evaporation method employing didodecyldimethyl ammonium bromide (DMAB) as stabilizer. The effect of polymer molecular weight and copolymer composition on particle properties and release behavior (in vitro and in vivo) has been reported. Drug release in vitro decreased with increase in molecular weight and lactide content of PLGA. Zero order release was obtained with low molecular weight (14,500 and 45,000 Da) PLGA, while high molecular weight (85,000 and 213,000 Da) and different copolymer compositions followed square root of time (Higuchi's pattern) dependent release. The bioavailability of estradiol from nanoparticles was assessed in male Sprague Dawley (SD) rats at a dose of 1 mg estradiol/rat. The in vivo performance of the nanoparticles was found to be dependent on the particle size, polymer molecular weight and copolymer composition. The C(max) of drug in the plasma was dependent on the polymer molecular weight and composition while particle size was found to influence the duration of release, suggesting smaller is better. The histopathological examination revealed absence of any inflammatory response with the formulations prepared of low/high molecular weight or high lactide content polymers for the studied period. Together, these results indicate that nanoparticulate formulations are ideal carriers for oral administration of estradiol having great potential to address the dose related issues of estradiol.

Microencapsulation of insulin into biodegradable microcapsules by the high voltage field method

To produce and evaluate sustained microcapsules of insulin made by a novel encapsulation process. The insulin was encapsulated into microcapsules of poly(D, L-lactide co-glycolide) (PLGA) by the high voltage field method. The preparation process was cryogenic, non-aqueous, and did not utilize emulsification. When the ratio of insulin/PLGA was 1:9, the median particle size of insulin microcapsules was less than 200&#956;m, the drug loaded was 8.82%, and the efficiency of encapsulation was 83.2%. Drug release continued over 300h. In conclusion, the process was a novel way to produce insulin microcapsules, and the basic characteristics were satisfactory.

Stabilization of recombinant human growth hormone against emulsification-induced aggregation by Pluronic surfactants during microencapsulation

Protein aggregation upon exposing to the water/organic solvent interface is one of the most significant obstacles in developing poly(lactic-co-glycolic acid) (PLGA) microspheres with double emulsion process. The aim of present study is to devise a formulation strategy to prevent recombinant human growth hormone (rhGH) from aggregation during microencapsulation. The excipients used for stabilizing rhGH were selected from sugars, nonionic surfactants, polyol, and protein. Among the candidates, surfactants exhibited potentialities in protecting rhGH against emulsification-induced aggregation. It was also found that Pluronic F127 showed an outstanding as well as concentration-dependent stabilizing effect on rhGH, which was different to Pluronic F68 and Tween 20. After the rhGH solution comprising F127 and sucrose was emulsified with methylene chloride, the recovery of monomeric protein achieved 99.0%, principally attributed to the presence of F127. This solution was subsequently encapsulated as inner aqueous phase in the PLGA microspheres by a conventional double emulsion process, with the encapsulation efficiency higher than 98%. Improvement in the release of rhGH was observed for the microspheres co-encapsulating Pluronic F127 regardless in the presence or absence of sucrose, compared to the microspheres containing rhGH alone. The result further implied that co-encapsulation of Pluronic F127 in the microspheres played an important role in the stabilization of rhGH.

Adjuvant activity of polymer microparticles and Montanide ISA 720 on immune responses to Plasmodium falciparum MSP2 long synthetic peptides in mice

The purpose of this work was to test the immunogenicity in C57BL mice of two synthetic peptides derived from the constant region of 3D7 and FC27 Plasmodium falciparum MSP2 dimorphic proteins, either microencapsulated into poly-lactide-co-glycolide acid microparticles (PLGA MP) or delivered with the human compatible adjuvant Montanide ISA 720 for comparison. Potent and prolonged antibody responses were obtained for both peptides by using PLGA MP formulations after subcutaneous or intradermal injections. As compared to the subcutaneous route of immunization, the intradermal route induced greater immune responses. Montanide adjuvant was effective in eliciting antibodies against the 3D7 peptide but not against the FC27 peptide. Peptide-specific cytophilic antibodies (IgG2a) were detected after boosting with homologous peptide for all vaccine formulations. MP formulations elicited a lower IgE secretion as compared to that observed for both Montanide formulated vaccines. Our results demonstrate the ability of the polymer microparticles to overcome the lack of immunogenicity of FC27 MSP2 peptide in C57BL mice and their potential to induce desirable immune responses against malaria.

Concurrent delivery of dexamethasone and VEGF for localized inflammation control and angiogenesis

Localized elution of corticosteroids has been used in suppressing inflammation and fibrosis associated with implantation and continuous in vivo residence of bio-medical devices. However, these agents also inhibit endogenous growth factors preventing angiogenesis at the local tissue, interface thereby delaying the healing process and negatively impacting device performance. In this work, a combination of dexamethasone and vascular endothelial growth factor (VEGF) was investigated for concurrent localized delivery using PLGA microsphere/PVA hydrogel composites. Pharmacodynamic effects were evaluated by histopathological examination of subcutaneous tissue surrounding implanted composites using a rat model. The hydrogel composites were capable of simultaneously releasing VEGF and dexamethasone with approximately zero order kinetics. Composites were successful in controlling the implant/tissue interface by suppressing inflammation and fibrosis as well as facilitating neo-angiogenesis at a fraction of their typical oral or i.v. bolus doses. Implants containing VEGF showed a significantly higher number of mature blood vessels at the end of the 4 week study irrespective of the presence of dexamethasone. Thus, localized concurrent elution of VEGF and dexamethasone can overcome the anti-angiogenic effects of the corticosteroid and can be used to engineer inflammation-free and well-vascularized tissue in the vicinity of the implant. These PLGA microsphere/PVA hydrogel composites show promise as coatings for implantable bio-medical devices to improve biocompatibility and ensure in vivo performance.

Preparation of Polymeric Submicron Particle-Containing Microparticles Using a 4-Fluid Nozzle Spray Drier

PURPOSE

We studied a novel method for preparing polymeric submicron particle-containing microparticles using a 4-fluid nozzle spray drier.

METHOD

Ethylcellulose (EC) and poly(lactic-co-glycolic acid) (PLGA), either alone or in combination with polyethylenimine (PEI), were used as polymers to produce submicron particles, and mannitol (MAN) was used as a water-soluble carrier for the microparticles. The polymer and MAN solutions were supplied through different liquid passages of a 4-fluid nozzle and then dried to obtain MAN microparticles containing EC or PLGA submicron particles. The polymer/MAN ratio was controlled by changing the concentration of the polymer and MAN solutions. EC or PLGA microparticles were observed via scanning electron microscopy, and the size of microparticles was determined by image analysis. The particle size distribution of EC or PLGA submicron particles was measured with a super dynamic light scattering spectrophotometer.

RESULTS

The method generated submicron-sized (<1 microm) particles of EC and PLGA. The mean diameters of EC and PLGA particles at a polymer/MAN ratio of 1:10 were 631 and 490 nm, respectively. The mean diameter of PLGA particles decreased as the PLGA/MAN ratio was reduced, reaching approximately 200 nm at a PLGA/MAN ratio of 1:100. The mean diameter of PLGA/PEI particles at PLGA/PEI/MAN ratios of 1:0.5:10 and 1:0.5:100 were 525 and 223 nm, respectively, and their zeta potentials were +50.8 and +58.2 mV, respectively. The size of EC submicron particles could be controlled by varying the spray conditions.

CONCLUSIONS

This study demonstrated that it is possible to prepare polymeric submicron particles dispersed in MAN microparticles in a single process using the 4-fluid nozzle spray drying method. Cationic PLGA particles with a diameter of approximately 200 nm could be prepared by adding PEI, suggesting the possibility of its use as a carrier for delivering DNA into cells. The precipitation of EC may occur by the mutual dispersion and mixing of solvents after collision of EC and MAN mists by antisolvent effect, thereby producing MAN microparticles containing EC submicron particles.

The use of soluble polymers and polymer microparticles to provide improved vaccine responses after parenteral and mucosal delivery

It is important when developing new vaccine systems to give proper attention to the question of delivery. In some cases the judicious choice of a delivery system can provide a greatly enhanced immune response and avoid the need to use a vaccine adjuvant. Delivery systems that have been developed originally for the administration of challenging drug can be used with success for vaccines. Polymer microspheres and lamellar particle based on the biodegradable materials polylactide and polylactide co-glycolide can be employed for the improved parenteral and mucosal administration of antigens. Likewise soluble biopolymers such as chitosan can be used for the improved nasal delivery of various antigens as well as DNA. Results from animal studies and recent clinical trials are provided.

Granuloma caused by subcutaneous injection of leuprorelin acetate product: Case report and histopathological findings

Leuprorelin acetate is a luteinizing hormone-releasing hormone (LH-RH) analog, which is used for chemical castration. Chemical castration treatment has an especially important role for prostate cancer. To ensure ongoing chemical castration, a novel sustained-action injection system using spherical microcapsules has been developed. We report a patient who had granuloma caused by administration of the 11.25 mg leuprorelin acetate product. Histological examination revealed many giant cells with vacuoles. On the basis of reported cases, these vacuoles are characteristic for the granuloma caused by leuprorelin acetate product. The vacuoles in the granuloma are the same size as the microcapsules, and their shape is almost spherical. We assume that the vacuoles in the granuloma are actually the microcapsules. We expect that there will be investigations regarding the procatarctic cause of granuloma formation.

Commercial challenges of protein drug delivery

The discovery of insulin in 1922 marked the beginning of research and development to improve the means of delivering protein therapeutics to patients. From that period forward, investigators have contemplated every possible route of delivery. Their research efforts have followed two basic pathways: one path has focused on non-invasive means of delivering proteins to the body; and the second path has been primarily aimed at increasing the biological half-life of the therapeutic molecules. Thus far, the commercial successes of protein delivery by the nasal, oral and pulmonary routes have been more opportunistic rather than the application of platform technologies applicable to every protein or peptide. In several limited cases, sustained delivery of peptides and proteins has employed the use of polymeric carriers. More successes have been achieved by chemical modification using amino acid substitutions, protein pegylation or glycosylation to improve the pharmacodynamic properties of certain macromolecules. Today, commercial successes for protein and peptide delivery systems remain limited. The needle and syringe remain the primary means of protein delivery. Major hurdles remain in order to overcome the combined natural barriers of drug permeability, drug stability, pharmacokinetics and pharmacodynamics of protein therapeutics.

Controlled release of huperzine A from biodegradable microspheres: In vitro and in vivo studies

The objective of the present work was to further study the in vitro characteristics, in vivo pharmacokinetics and pharmacodynamics of huperzine A (HupA) loaded biodegradable microspheres designed for sustained release of HupA over several weeks. A conventional o/w emulsion-solvent evaporation method was used to incorporate HupA, which is of interest in the palliative treatment of Alzheimer's disease (AD), into end-group uncapped poly(D,L-lactide-co-glycolide) (PLG-H). A prolonged in vitro drug release profile was observed, with a complete release of the incorporated drug within 5-6 weeks. The in vivo pharmacokinetics study of HupA loaded microspheres showed sustained plasma HupA concentration-time profile after subcutaneous injection into rats. The pharmacodynamics evaluated by determination of the activity of acetylcholinesterase in the rat cortex also showed a prolonged pharmacological response. Both the in vitro release and in vivo pharmacological responses correlated well with the in vivo pharmacokinetics profile. The results suggest the potential use of HupA-loaded biodegradable microspheres for treatment of AD over long periods.

PLA-microparticles formulated by means a thermoreversible gel able to modify protein encapsulation and release without being co-encapsulated

The aim of this work was to develop a novel strategy for the formulation of biodegradable PLA microspheres as delivery systems for proteins or peptides. The strategy is based on the exploitation of the gel-sol transition of the thermoreversible Pluronic F127 gel. The gel allows the formation of the particles without be co-entrapped in the matrix. The microspheres prepared using the novel technique (TG-Ms, or thermoreversible gel-method microspheres) were characterized in vitro (as concerns the size, the morphology, the protein encapsulation, the release and the protein distribution in the polymer matrix), in comparison with microspheres prepared using the classical double emulsion/solvent evaporation method (w/o/w-Ms). Two types of bovine serum albumin (BSA), with different water solubility, were used as model proteins. TG-Ms exhibited small size (7-50 m) and high protein content (8.6%, w/w) regardless of the BSA water solubility, in contrast with w/o/w-Ms, which revealed a size range of 100-130 microm and a protein content related to the BSA water solubility. TG-Ms, in spite of their smaller size respect of the w/o/w-Ms, displayed a reduced initial burst effect and a higher rate in the second release phase that resulted in a quasi-constant profile. The release behavior of the TG-Ms may be attributable to both the localization of the protein in the particle core, as shown by the confocal laser scanning microscopy analysis on labeled-BSA loaded microspheres, and the few pores in the matrix, as shown by the scanning electron microscopy. A working hypothesis about the mechanism of the particle formation was also discussed.

Modification of the tri-phasic drug release pattern of leuprolide acetate-loaded poly(lactide-co-glycolide) microparticles

Leuprolide acetate-loaded poly(lactide-co-glycolide) (PLGA RG503H) microparticles prepared by the solvent evaporation method had a tri-phasic drug release pattern over a duration of up to 2 months. An initial release was followed by a slow drug release phase and a final rapid drug release. The objective of this study was to identify parameters, which shift the release profile from the tri-phasic to a more continuous release profile. Varying formulation and processing parameters (e.g., drug loading, volume of the external aqueous phase, using low molecular weight PLGA, different microparticle drying methods) affected the initial release (burst) but did not influence the drug release thereafter. The addition of the hydrophilic polymer polyvinylpyrrolidone (PVP) led to the formation of more porous microparticles. This influenced the initial release but did not change the tri-phasic drug release pattern. The inclusion of medium chain triglycerides (MCT) successfully shifted the tri-phasic pattern to a continuous release profile. MCT accelerated the leuprolide release in the second, slow release phase and reduced it in the final rapid release phase. MCT led to the formation of microparticles with an irregular surface and a highly porous inner structure. Differential scanning calorimetry (DSC) revealed a high encapsulation efficiency of MCT (88-105%) in the microparticles and an unchanged glass transition temperature (Tg) of PLGA.

Properties of poly(lactic-co-glycolic acid) nanospheres containing protease inhibitors: Camostat mesilate and nafamostat mesilate

Poly(lactic-co-glycolic acid) (PLGA) nanospheres containing protease inhibitors, camostat mesilate (CM) and nafamostat mesilate (NM), were prepared by the emulsion solvent diffusion methods in water or in oil, and the w/o/w emulsion solvent evaporation method. The average diameter of PLGA nanospheres prepared in the water system were about 150-300 nm, whereas those prepared in the oil system were 500-600 nm. Among the three methods, these drugs were the most efficiently encapsulated up to 60-70% in PLGA nanospheres in the oil system. Other factors that may influence drug encapsulation efficiency and in vitro release such as drug load, molecular weight of polymer were also investigated. Both the CM- and NM-loaded nanospheres prepared in the water system immediately released about 85% of the drug upon dispersed in the release medium while the drug initial burst of nanospheres prepared by the emulsion solvent diffusion in oil method reduced to 30% and 60% for CM and NM, respectively. Poly(aspartic acid) (PAA), a complexing agent for cationic water soluble drugs, showed little effect on the encapsulation efficiency and release behavior for CM and NM. The DSC study and AFM pictures of nanospheres demonstrated that temperature-dependent drug release behavior was ascribable to the glass transition temperature of the polymer, which also affected the morphology of nanospheres upon dispersed in the release medium and influenced the drug release consequently.

Strategies to improve plasma half life time of peptide and protein drugs

Due to the obvious advantages of long-acting peptide and protein drugs, strategies to prolong plasma half life time of such compounds are highly on demand. Short plasma half life times are commonly due to fast renal clearance as well as to enzymatic degradation occurring during systemic circulation. Modifications of the peptide/protein can lead to prolonged plasma half life times. By shortening the overall amino acid amount of somatostatin and replacing L: -analogue amino acids with D: -amino acids, plasma half life time of the derivate octreotide was 1.5 hours in comparison to only few minutes of somatostatin. A PEG(2,40 K) conjugate of INF-alpha-2b exhibited a 330-fold prolonged plasma half life time compared to the native protein. It was the aim of this review to provide an overview of possible strategies to prolong plasma half life time such as modification of N- and C-terminus or PEGylation as well as methods to evaluate the effectiveness of drug modifications. Furthermore, fundamental data about most important proteolytic enzymes of human blood, liver and kidney as well as their cleavage specificity and inhibitors for them are provided in order to predict enzymatic cleavage of peptide and protein drugs during systemic circulation.

Treatment of experimental autoimmune uveoretinitis with poly(lactic acid) nanoparticles encapsulating betamethasone phosphate

We have developed nanoparticles (NPs), which are capable of targeting a specific lesion and gradually releasing the agent at the site over a prolonged time period after a single intravenous administration. In this study, we evaluated the effects of intravenously administered poly(lactic acid) nanoparticles encapsulating betamethasone phosphate (BP-PLA NPs) on experimental autoimmune uveoretinitis (EAU) in Lewis rats. To determine the localization of NPs within the retina and choroid of rats with EAU, rhodamine (Rh)-encapsulated PLA NPs were injected intravenously and visualized by confocal microscopy. After the disease onset of EAU induced by S-antigen peptide in Lewis rats, either BP-PLA NPs, BP, or saline was injected intravenously, and the eyes were obtained 7 days following treatment and the histological score was determined. The clinical course of EAU was examined using pathological findings and the expression of the glial fibrillary acidic protein, rod opsin, and the surface markers of inflammatory cells (ED1 and pan T-cell) were immunohistochemically determined. Furthermore, T-cell proliferation and delayed-type hypersensitivity (DTH) to S-antigen were assessed. Intravenously injected Rh-PLA NPs accumulated in the retina and choroid of rats with EAU within 3 hr and remained over the succeeding 7-day-period. Furthermore, systemically administered BP-PLA NPs reduced the clinical scores of rats with EAU in 1 day, which were maintained for 2 weeks and decreased the histological scores. In addition, the ocular infiltration of activated T-cells and macrophages in addition to the hypertrophy of Müller cells were markedly reduced with this treatment. Meanwhile, T-cell proliferation and DTH of BP-PLA NPs-treated rats against S-antigen peptide were not significantly different from those of saline-treated rats. Systemically administered BP-PLA NPs inhibit the development of EAU due to the targeting and the sustained release of steroids in situ. The results of these studies suggest that the systemic administration of BP-PLA NPs may lead to a new therapeutic strategy in controlling intraocular inflammation.

In vitro and in vivo characterization of huperzine a loaded microspheres made from end-group uncapped poly(d,l-lactide acid) and poly(d,l-lactide-co-glycolide acid)

The purpose of this work was to develop biodegradable microspheres for long term delivery of a potent acetyl cholinesterase inhibitor, huperzine A (Hup-A), which is of interest in the palliative treatment of Alzheimer's disease. Microspheres were successfully prepared with specifically end-group uncapped poly(d,l-lactide acid) and poly(d,l-lactide-co-glycolide acid) using a simple o/w solvent evaporation method. The morphology, particle size and size distribution, drug loading capacity, drug entrapment efficiency (EE) and in vitro drug release were studied in detail. It was found that the terminal group and the inherent viscosity (IV) of the polymers played key role in the drug encapsulation: higher EE was achieved with end-group uncapped and low IV polymers. In vitro drug release from microspheres made from the selected three kinds of polymers revealed sustained release of Hup-A without significant burst release. Preliminary pharmacokinetic study following subcutaneous injection of Hup-A loaded microspheres illustrated the sustained release of the drug over 6-8 weeks at clinically relevant doses in vivo. The studies demonstrated the feasibility of long term delivery of Hup-A using biodegradable microspheres.

Granulomas induced by subcutaneous injection of leuprorelin acetate

Leuprorelin acetate, a chemotherapeutic agent used to treat prostate cancer, is a synthetic luteinizing hormone-releasing hormone (LHRH) agonist. We report a 75-year-old man who presented with several large subcutaneous nodules at the site of leuprorelin acetate injections for his prostatic cancer. A biopsy of the nodules disclosed epithelioid granulomatous inflammation and resulted in a diagnosis of drug-induced granulomatous reaction to leuprorelin acetate.

Methods to assess in vitro drug release from injectable polymeric particulate systems

This review provides a compilation of the methods used to study real-time (37 degrees C) drug release from parenteral microparticulate drug delivery systems administered via the subcutaneous or intramuscular route. Current methods fall into three broad categories, viz., sample and separate, flow-through cell, and dialysis techniques. The principle of the specific method employed along with the advantages and disadvantages are described. With the "sample and separate" technique, drug-loaded microparticles are introduced into a vessel, and release is monitored over time by analysis of supernatant or drug remaining in the microspheres. In the "flow-through cell" technique, media is continuously circulated through a column containing drug-loaded microparticles followed by analysis of the eluent. The "dialysis" method achieves a physical separation of the drug-loaded microparticles from the release media by use of a membrane, which allows for sampling without interference of the microspheres. With all these methods, the setup and sampling techniques seem to influence in vitro release; the results are discussed in detail, and criteria to aid in selection of a method are stated. Attempts to establish in vitro-in vivo correlation for these injectable dosage forms are also discussed. It would be prudent to have an in vitro test method for microparticles that satisfies compendial and regulatory requirements, is user friendly, robust, and reproducible, and can be used for quality-control purposes at real-time and elevated temperatures.

Influence of the poly(lactide-co-glycolide) type on the leuprolide release from in situ forming microparticle systems

The objective was to investigate the influence of poly(lactide-co-glycolide) (PLGA) type (molecular weight and end-group functionality) on the leuprolide release from in situ forming microparticle (ISM) systems. ISM systems are based on an emulsion of the PLGA solution dispersed in an oil phase. The polymer droplets solidify after contact with aqueous fluids and form microparticles in situ. In contrast to microparticles prepared by the classical solvent evaporation method, the use of the lower molecular weight PLGA resulted in ISM with a lower initial release than ISM prepared with the higher molecular weight PLGA. ISM prepared with PLGA combinations showed a decreasing initial release with increasing low-molecular-weight PLGA content. A slower solvent diffusion from the low-molecular-weight PLGA solution droplets into the release medium led to a less porous structure of the resulting microparticles, thus explaining the lower initial release. PLGA with free carboxylic acid end groups led to a lower drug release compared to PLGA with esterified end groups. 6-month controlled release leuprolide ISM could be obtained by blending poly(lactides) (PLA) with different molecular weights.

Biodegradable PLGA Microspheres as a Sustained Release System for a New Luteinizing Hormone-Releasing Hormone (LHRH) Antagonist

A sustained release poly(DL-lactide-co-glycolide) (PLGA) microsphere delivery system to treat prostate cancer for a luteinizing hormone-releasing hormone (LHRH) antagonists, LXT-101 was prepared and evaluated in the paper. LXT-101 microspheres were prepared from PLGA by three methods: (1) double-emulsion solvent extraction/evaporation technique, (2) single-emulsion solvent extraction/evaporation technique, and (3) S/O/O (solid-in-oil-in-oil) method. The microspheres were investigated on drug loading, particle size, surface morphology and in vitro release profiles. An accelerated release approach was also established in order to expedite the evaluation periods. The in vivo evaluation of the microspheres was made by monitoring testosterone levels after subcutaneous administration to rats. The LXT-101 PLGA microspheres showed smooth and round surfaces according to a scanning electron microscopic investigation, and average particle size of ca. 30 mum according to laser diffractometry. The drug encapsulation efficiency of microspheres was influenced by LA/GA ratio of PLGA, salt concentrations, solvent mixture and preparation methods. Moreover, LA/GA ratio of PLGA, different preparation methods and different peptide stabilizers affected in vitro release of drugs. In vivo study, the testosterone levels were suppressed to castration up to 42 d as for the 7.5 mg/kg dose. And in vivo performance of LXT-101 microspheres was dose-dependent. The weights of rat sexual organs decreased and histopathological appearance of testes had little changes after 4-month microspheres therapy. This also testified that LXT-101 sustained release microspheres could exert the efficacy to suppress the testosterone level to castration with little toxicity. In conclusion, the PLGA microspheres could be a well sustained release system for LXT-101.

In situ forming microparticle system for controlled delivery of leuprolide acetate: influence of the formulation and processing parameters

The objective of present study was to control the delivery of leuprolide acetate using in situ forming microparticle (ISM) systems. A solution of leuprolide acetate and poly(lactide-co-glycolide) (PLGA RG 503H) or poly(lactide) (PLA R 202H) in N-methyl-2-pyrrolideone (NMP) was emulsified into an external oil phase using a two-syringe/connector system. After injection into an aqueous environment, NMP diffusion led to polymer precipitation and microparticle formation in situ. ISM-systems were characterized with respect to particle morphology and the influence of formulation and processing parameters on the in vitro release. ISM from RG 503H showed a high initial release (approximately 40%), which could be attributed to the high porosity of microparticles. The initial release could be reduced by increasing the polymer concentration, increasing the amount and viscosity of the oil phase, and decreasing the drug loading. ISM-systems from R 202H had a much lower initial release (approximately 9%) compared to that from RG 503H, which was followed by a slow and continuous drug release. In comparison to conventional microparticles prepared by a solvent evaporation method, ISM from R 202H showed a lower initial release and a more linear continuous release.

Preparation and in vitro and in vivo release studies of Huperzine A loaded microspheres for the treatment of Alzheimer's disease

The purpose of this study was to prepare microspheres containing Huperzine A, which is used for patients suffering from Alzheimer's disease because of its potent anticholineestase activity, and to clarify in vitro and in vivo release characteristics of them. The preparation and in vitro and in vivo release studies of Huperzine A loaded microspheres were described. By spray drying method, Huperzine A was encapsulated successfully in the microspheres which were spherical with a non-porous and smooth surface. In vitro studies showed that the release of Huperzine A from microspheres was depended on the properties of polymers and the release medium. Counter-ionic interaction between the primary amine group of Huperzine A and the carboxylic terminal group of PLG polymers improves the encapsulation of Huperzine A, reducing the initial burst and extending the sustained release. High molecular weight of PLG polymer leads to a negative influence on sustained release of Huperzine A due to less carboxylic terminal groups. Acidic medium also reduces the initial burst and sustained the release due to decreased swelling of the polymeric matrix. In vivo experiment showed, after intramuscular injection, that the plasma concentration of Huperzine A reached the max. at 2 h, then fell rapidly to a stable and near constant level of 0.5 to 2.5 ng/ml within 2 weeks, until the drug was exhausted from the microspheres. It indicates the potential of a 2-week sustained release system of Huperzine A.