Encapsulation and stabilization of nerve growth factor into poly(lactic-co-glycolic) acid microspheres

Current possibilities and future perspectives for improving efficacy of allergen-specific sublingual immunotherapy

Allergen-specific sublingual immunotherapy (SLIT), a safe and efficient route for treating type I hypersensitivity disorders, requires high doses of allergens. SLIT is generally performed without adjuvants and delivery systems. Therefore, allergen formulation with appropriate presentation platforms results in improved allergen availability, targeting the immune cells, inducing regulatory immune responses, and enhancing immunotherapy's efficacy while decreasing the dose of the allergen. In this review, we discuss the adjuvants and delivery systems that have been applied as allergen-presentation platforms for SLIT. These adjuvants include TLRs ligands, 1α, 25-dihydroxy vitamin D3, galectin-9, probiotic and bacterial components that provoke allergen-specific helper type-1 T lymphocytes (TH1), and regulatory T cells (Tregs). Another approach is encapsulation or adsorption of the allergens into a particulate vector system to facilitate allergen capture by tolerogenic dendritic cells. Also, we proposed strategies to increasing the efficacy of SLIT via new immunopotentiators and carrier systems in the future.

Dry Powder for Pulmonary Delivery: A Comprehensive Review

The pulmonary route has long been used for drug administration for both local and systemic treatment. It possesses several advantages, which can be categorized into physiological, i.e., large surface area, thin epithelial membrane, highly vascularized, limited enzymatic activity, and patient convenience, i.e., non-invasive, self-administration over oral and systemic routes of drug administration. However, the formulation of dry powder for pulmonary delivery is often challenging due to restrictions on aerodynamic size and the lung’s lower tolerance capacity in comparison with an oral route of drug administration. Various physicochemical properties of dry powder play a major role in the aerosolization, deposition, and clearance along the respiratory tract. To prepare suitable particles with optimal physicochemical properties for inhalation, various manufacturing methods have been established. The most frequently used industrial methods are milling and spray-drying, while several other alternative methods such as spray-freeze-drying, supercritical fluid, non-wetting templates, inkjet-printing, thin-film freezing, and hot-melt extrusion methods are also utilized. The aim of this review is to provide an overview of the respiratory tract structure, particle deposition patterns, and possible drug-clearance mechanisms from the lungs. This review also includes the physicochemical properties of dry powder, various techniques used for the preparation of dry powders, and factors affecting the clinical efficacy, as well as various challenges that need to be addressed in the future.

Heparin/collagen encapsulating nerve growth factor multilayers coated aligned PLLA nanofibrous scaffolds for nerve tissue engineering

Biomimicing topological structure of natural nerve tissue to direct axon growth and controlling sustained release of moderate neurotrophic factors are extremely propitious to the functional recovery of damaged nervous systems. In this study, the heparin/collagen encapsulating nerve growth factor (NGF) multilayers were coated onto the aligned poly-L-lactide (PLLA) nanofibrous scaffolds via a layer-by-layer (LbL) self-assembly technique to combine biomolecular signals, and physical guidance cues for peripheral nerve regeneration. Scanning electronic microscopy (SEM) revealed that the surface of aligned PLLA nanofibrous scaffolds coated with heparin/collagen multilayers became rougher and appeared some net-like filaments and protuberances in comparison with PLLA nanofibrous scaffolds. The heparin/collagen multilayers did not destroy the alignment of nanofibers. X-ray photoelectron spectroscopy and water contact angles displayed that heparin and collagen were successfully coated onto the aligned PLLA nanofibrous scaffolds and improved its hydrophilicity. Three-dimensional (3 D) confocal microscopy images further demonstrated that collagen, heparin, and NGF were not only coated onto the surface of aligned PLLA nanofibrous scaffolds but also permeated into the inner of scaffolds. Moreover, NGF presented a sustained release for 2 weeks from aligned nanofibrous scaffolds coated with 5.5 bilayers or above and remained good bioactivity. The heparin/collagen encapsulating NGF multilayers coated aligned nanofibrous scaffolds, in particular 5.5 bilayers or above, was more beneficial to Schwann cells (SCs) proliferation and PC12 cells differentiation as well as the SC cytoskeleton and neurite growth along the direction of nanofibrous alignment compared to the aligned PLLA nanofibrous scaffolds. This novel scaffolds combining sustained release of bioactive NGF and aligned nanofibrous topography presented an excellent potential in peripheral nerve regeneration. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1900-1910, 2017.

Pharmaceutical spray freeze drying

Pharmaceutical spray-freeze drying (SFD) includes a heterogeneous set of technologies with primary applications in apparent solubility enhancement, pulmonary drug delivery, intradermal ballistic administration and delivery of vaccines to the nasal mucosa. The methods comprise of three steps: droplet generation, freezing and sublimation drying, which can be matched to the requirements given by the dosage form and route of administration. The objectives, various methods and physicochemical and pharmacological outcomes have been reviewed with a scope including related fields of science and technology.

Long-term delivery of protein therapeutics

INTRODUCTION

Proteins are effective biotherapeutics with applications in diverse ailments. Despite being specific and potent, their full clinical potential has not yet been realized. This can be attributed to short half-lives, complex structures, poor in vivo stability, low permeability, frequent parenteral administrations and poor adherence to treatment in chronic diseases. A sustained release system, providing controlled release of proteins, may overcome many of these limitations.

AREAS COVERED

This review focuses on recent development in approaches, especially polymer-based formulations, which can provide therapeutic levels of proteins over extended periods. Advances in particulate, gel-based formulations and novel approaches for extended protein delivery are discussed. Emphasis is placed on dosage form, method of preparation, mechanism of release and stability of biotherapeutics.

EXPERT OPINION

Substantial advancements have been made in the field of extended protein delivery via various polymer-based formulations over last decade despite the unique delivery-related challenges posed by protein biologics. A number of injectable sustained-release formulations have reached market. However, therapeutic application of proteins is still hampered by delivery-related issues. A large number of protein molecules are under clinical trials, and hence, there is an urgent need to develop new methods to deliver these highly potent biologics.

A review of bioactive release from nerve conduits as a neurotherapeutic strategy for neuronal growth in peripheral nerve injury

Peripheral nerve regeneration strategies employ the use of polymeric engineered nerve conduits encompassed with components of a delivery system. This allows for the controlled and sustained release of neurotrophic growth factors for the enhancement of the innate regenerative capacity of the injured nerves. This review article focuses on the delivery of neurotrophic factors (NTFs) and the importance of the parameters that control release kinetics in the delivery of optimal quantities of NTFs for improved therapeutic effect and prevention of dose dumping. Studies utilizing various controlled-release strategies, in attempt to obtain ideal release kinetics, have been reviewed in this paper. Release strategies discussed include affinity-based models, crosslinking techniques, and layer-by-layer technologies. Currently available synthetic hollow nerve conduits, an alternative to the nerve autografts, have proven to be successful in the bridging and regeneration of primarily the short transected nerve gaps in several patient cases. However, current research emphasizes on the development of more advanced nerve conduits able to simulate the effectiveness of the autograft which includes, in particular, the ability to deliver growth factors.

Aligned SF/P(LLA-CL)-blended nanofibers encapsulating nerve growth factor for peripheral nerve regeneration

Artificial nerve guidance conduits (NGCs) containing bioactive neurotrophic factors and topographical structure to biomimic native tissues are essential for efficient regeneration of nerve gaps. In this study, aligned SF/P(LLA-CL) nanofibers encapsulating nerve growth factor (NGF), which was stabilized by SF in core, were fabricated via a coaxial electrospinning technique. The controlled release of NGF from the nanofibers was evaluated using enzyme-linked immune sorbent assay (ELISA) and PC12 cell-based bioassay over a 60-day time period. The results demonstrated that NGF presented a sustained release and remained biological activity over 60 days. Nerve guidance conduits (NGCs) were fabricated by reeling the aligned SF/P(LLA-CL) nanofibrous scaffolds encapsulating NGF and then used as a bridge implanted across a 15-mm defect in the sciatic nerve of rats to promote nerve regeneration. The outcome in terms of regenerated nerve at 12 weeks was evaluated by a combination of electrophysiological assessment, histochemistry, and electron microscopy. All results clarified that the NGF-encapsulated-aligned SF/P(LLA-CL) NGCs promoted peripheral nerve regeneration significantly better than the aligned SF/P(LLA-CL) NGCs, suggesting that the released NGF from nanofibers could effectively promote the regeneration of peripheral nerve.

Freeze-dried and spray-dried zinc-containing silica microparticles entrapping insulin

New approaches for oral administration of insulin are strongly related to novel insulin carriers. The aim of this study was the insulin microencapsulation in a new zinc-silica matrix for drug protection and controlled release. Zinc-silica microparticles loaded with insulin were obtained by sol-gel process via spray drying and freeze drying methods. Inorganic silica matrix isolates and constrains the movement of the biomolecules preventing their aggregation and denaturation, while the zinc oxide improves the system stability. Moreover, formation of insulin hexamers in the presence of zinc ions leads to an increased stability of the insulin three-dimensional structure during preparation, storage and release. The particles were characterized with respect to average size, specific surface area, porosity and morphology. In vitro behavior of insulin-loaded particles together with protein structural conformation was also evaluated. The release profile can be adapted by synthesis route of microparticles.

In vitro evaluation of the effects of various additives and polymers on nerve growth factor microspheres

OBJECTIVE

To evaluate the effects of various additives or polymers on the in vitro characteristics of nerve growth factor (NGF) microspheres.

MATERIALS AND METHODS

NGF microspheres were fabricated using polyethylene glycol (PEG), ovalbumin (OVA), bovine serum albumin (BSA) or glucose as protein protectors, and poly(lactide-co-glycolide) (PLGA) or poly(lactic acid) (PLA)/PLGA blends as encapsulation materials.

RESULTS

Encapsulation efficiencies of the NGF microspheres with various additives or polymers were not more than 30%. A comparative study revealed that OVA was somewhat superior over others, and was thus chosen as the protective additive in subsequent experiments. Polymer analysis showed that NGF release from 1:1 PLA (η = 0.8):PLGA (75/25, η = 0.45) microspheres lasted for 90 d with a burst release rate of 12.7%. About 40% of the original bioactivity was retained on the 28th day, while 10% was left on the 90th day.

DISCUSSION AND CONCLUSION

The combination of OVA as an additive and the PLA/PLGA blend as the coating matrix is suitable for encapsulation of NGF in microspheres for extended release.

From molecular to nanotechnology strategies for delivery of neurotrophins: emphasis on brain-derived neurotrophic factor (BDNF)

Neurodegenerative diseases represent a major public health problem, but beneficial clinical treatment with neurotrophic factors has not been established yet. The therapeutic use of neurotrophins has been restrained by their instability and rapid degradation in biological medium. A variety of strategies has been proposed for the administration of these leading therapeutic candidates, which are essential for the development, survival and function of human neurons. In this review, we describe the existing approaches for delivery of brain-derived neurotrophic factor (BDNF), which is the most abundant neurotrophin in the mammalian central nervous system (CNS). Biomimetic peptides of BDNF have emerged as a promising therapy against neurodegenerative disorders. Polymer-based carriers have provided sustained neurotrophin delivery, whereas lipid-based particles have contributed also to potentiation of the BDNF action. Nanotechnology offers new possibilities for the design of vehicles for neuroprotection and neuroregeneration. Recent developments in nanoscale carriers for encapsulation and transport of BDNF are highlighted.

Localized controlled release of stratifin reduces implantation-induced dermal fibrosis

Localized controlled release of anti-fibrogenic factors can potentially prevent tissue fibrosis surrounding biomedical prostheses, such as vascular stents and breast implants. We have previously demonstrated that therapeutic intervention with topically applied stratifin in a rabbit ear fibrotic model not only prevents dermal fibrosis but also promotes more normal tissue repair by regulating extracellular matrix deposition. In this work, the anti-fibrogenic effect of a controlled release form of stratifin was investigated in the prevention of fibrosis induced by dermal poly(lactic-co-glycolic acid) (PLGA) microsphere/poly(vinyl alcohol) (PVA) hydrogel implants. Pharmacodynamic effects were evaluated by histopathological examination of subcutaneous tissue surrounding implanted composites. Controlled release of stratifin from PLGA microsphere/PVA hydrogel implants significantly moderated dermal fibrosis and inflammation by reducing collagen deposition (30%), total tissue cellularity (48%) and infiltrated CD3(+) immune cells (81%) in the surrounding tissue compared with the stratifin-free implants. The controlled release of stratifin from implants markedly increased the level of matrix metalloproteinase-1 expression in the surrounding tissue, which resulted in less collagen deposition. These stratifin-eluting PLGA/PVA composites show promise as coatings to decrease the typical fibrosis exhibited around implanted biomedical prostheses, such as breast implants and vascular stents.

Formulation strategies for sustained release of proteins

Proteins constitute an increasing proportion of the drugs in development. The barriers to their entry into the blood stream and rapid clearance means that they often have to be injected several times a day, affecting patient compliance. This paper reviews the major technologies enabling the development of injectable sustained-release products and formulation strategies to maintain protein integrity and modify release rates. Whilst many injectable sustained-release products are on the market, these are all delivering small molecular weight drugs and peptides. This is due to the manufacturing processes that denature and degrade the proteins upon encapsulation and release into the body. Formulation strategies are discussed and a number of new technologies reviewed that are able to overcome the issues with conventional manufacturing processes. The reliance of many processes on organic solvents has prevented their application to the development of injectable sustained release protein products. The development of entirely solvent free and aqueous methods of manufacture of these products has meant that numerous sustained-release protein products are close to reaching the market.

Formulation of sustained-release microspheres of granulocyte macrophage colony stimulating factor by freezing-induced phase separation with dextran and encapsulation with blended polymers

This study aimed to assess the potential merits of formulating sustained-release microspheres of recombinant human granulocyte macrophage colony stimulating factor (rhGM-CSF) via freezing-induced phase separation (FIPS) of the protein with dextran followed by encapsulation with binary mixture of poly(lactic-co-glycolic acid) (PLGA) 2A (MW∼12K) and 3A (MW∼47K) or of PLGA2A and polylactic acid (PLA; MW∼83K). The formulated dextran particles and microspheres were characterized in vitro for loading, aggregation, bioactivity and release behavior of the protein where appropriate. rhGM-CSF retained about 60% of bioactivity with no significant aggregation after each formulation step. Encapsulation of protein-loaded dextran particles attained only 80% with the PLGA2A and PLGA3A blend, but 100% with the PLGA2A and PLA mixture. The former formulation exhibited a triphasic in-vitro release profile typical of PLGA microspheres while the latter revealed a much lower initial burst followed by a steady and complete release of rhGM-CSF with preserved bioactivity over a 15-day period.

Systemic and mucosal delivery of drugs within polymeric microparticles produced by spray drying

Encapsulation of therapeutic and diagnostic materials into polymeric particles is a means to protect and control or target the release of active substances such as drugs, vaccines, and genetic material. In terms of mucosal delivery, polymeric encapsulation can be used to promote absorption of the active substance, while particles can improve the half-life of drugs administered systemically. Spray drying is an attractive technology used to produce such microparticles, because it combines both the encapsulation and drying steps in a rapid, single-step operation. Even so, spray drying is not classically associated with processes used for drug and therapeutic material encapsulation, since elevated temperatures could potentially denature the active substance. However, a comprehensive review of the literature revealed a number of studies demonstrating that spray drying can be used to produce microparticulate formulations with labile therapeutics. Polymers commonly employed include synthetics such as methacrylic copolymers and polyesters, and natural materials including chitosan and alginate. Drugs and active substances are diverse and included antibiotics, anti-inflammatory agents, and chemotherapeutics. Regarding the delivery of spray-dried particles, the pulmonary, oral, colonic, and nasal mucosal routes are often investigated because they offer a convenient means of administration, which promotes physician and patient compliance. In addition, spray drying has been widely used to produce polymeric microparticles for systemic delivery in order to control the delivery of drugs, vaccines, or genetic material that may exhibit poor pharmacokinetic profiles or pose toxicity concerns. This review presents a brief introduction to the technology of spray drying and outlines the delivery routes and the applications of spray-dried polymeric microparticles.

Peptide amphiphiles and porous biodegradable scaffolds for tissue regeneration in the brain and spinal cord

Many promising strategies have been developed for controlling the release of drugs from scaffolds, yet there are still challenges that need to be addressed in order for these scaffolds to serve as successful treatments. The RADA4 self-assembling peptide spontaneously forms nanofibers, creating a scaffold-like tissue-bridging structure that provides a three-dimensional environment for the migration of living cells. We have found that RADA4: (1) facilitates the regeneration of axons in the brain of young and adult hamsters, leading to functional return of behavior and (2) demonstrates robust migration of host cells and growth of blood vessels and axons, leading to the repair of injured spinal cords in rats.

In vitro and in vivo release of nerve growth factor from biodegradable poly-lactic-co-glycolic-acid microspheres

Regeneration of peripheral nerves after injury is suboptimal. We now report the long term delivery of nerve growth factor (NGF) by biodegradable poly-lactic-co-glycolic acid (PLGA) microspheres in vitro and in vivo. Lactic to glycolic acid ratios of 50:50 and 85:15 were fabricated using the double emulsion solvent, evaporation technique. Three different inherent viscosities (0.1 dL g(-1) : 1A, 0.4 dL g(-1) : 4A, 0.7 dL g(-1) : 7A) were analyzed. In vitro, release of NGF for 23 days was measured. Electron microscopy demonstrated intact spheres for at least 7 days (50:50 1A), 14 days (50:50 4A), or 35 days (50:50 7A and 85:15 7A). In vitro release kinetics was characterized by burst release, followed by release of NGF at a rate of 0.6-1.6% a day. Release curves for 50:50 1A and 85:15 7A differed significantly from other compositions (p < 0.01). In vivo, release was characterized by a novel radionuclide tracking assay. Release rates varied from 0.9 to 2.2% per day with linear kinetics. All but the 85:15 type of spheres showed different release profiles in vivo compared to in vitro conditions. On the basis of the surface morphology and release profiles, we found microspheres fabricated from 50:50 4A PLGA to be best suited for the use in a rat sciatic nerve injury model.

Forever Young: How to Control the Elongation, Differentiation, and Proliferation of Cells Using Nanotechnology

Within the emerging field of stem cells there is a need for an environment that can regulate cell activity, to slow down differentiation or proliferation, in vitro or in vivo while remaining invisible to the immune system. By creating a nanoenvironment surrounding PC12 cells, Schwann cells, and neural precursor cells (NPCs), we were able to control the proliferation, elongation, differentiation, and maturation in vitro. We extended the method, using self-assembling nanofiber scaffold (SAPNS), to living animals with implants in the brain and spinal cord. Here we show that when cells are placed in a defined system we can delay their proliferation, differentiation, and maturation depending on the density of the cell population, density of the matrix, and the local environment. A combination of SAPNS and young cells can be implanted into the central nervous system (CNS), eliminating the need for immunosuppressants.

Effects of polymer, organic solvent and mixing strength on integrity of proteins and liposomes encapsulated in polymeric microspheres fabricated by the double emulsion process

The double emulsion process has commonly been applied to encapsulate water-soluble bioactive agents into polymeric microspheres. However, the integrity of many of these agents may be destroyed by the highly energetic procedures such as sonication that are routinely used to produce stable water-in-oil (w/o) emulsion. The aim of this research was to pursue the possibility of replacing the sonication by a mild emulsification procedure such as vortex mixing, with the use of certain materials to help to obtain stable w/o emulsion. The following materials were examined: poly(lactide-co-ethylene glycol) (PELA) as the polymer, ethyl acetate and acetone as the solvents, poly(vinyl alcohol) (PVA) and d-alpha tocopheryl polyethylene glycol 1000 succinate (Vitamin E TPGS) as the emulsifiers in w/o emulsion. The experimental results, with human serum albumin (HSA) as the encapsulated agent, showed that, when vortex mixing was used, these materials could significantly improve w/o emulsion stability and help to obtain satisfactory encapsulation effects, i.e. high encapsulation efficiency (EE) and low initial release burst. A delicate structure, i.e. liposomes, which is very sensitive to sonication, was then incorporated into microspheres by the 'modified double emulsion process'. It was found that the liposomes were intact and the encapsulation effects were good. Therefore, it can be concluded that the modified double emulsion process could be advantageous for the encapsulation of delicate substances.

Self-dissolving micropiles for the percutaneous absorption of recombinant human growth hormone in rats

The feasibility of self-dissolving micropiles (SDMP) as a percutaneous delivery system of recombinant human growth hormone (rhGH) has been studied in rats using SDMP where dextran was used as a base. After mixing dextran solution with rhGH, SDMPs were prepared by pulling with polypropyrene tips. The mean weight, length and diameter were 0.68+/-0.05 mg, 3.2+/-0.5 mm and 0.6+/-0.2 microm, respectively. To evaluate the bioavailability (BA) of rhGH percutaneously administered by SDMP, an absorption experiment was performed in rats. RhGH SDMPs were inserted into the rats skin, 200 microg kg(-1), and plasma rhGH levels were measured by an ELISA method. Peak plasma rhGH level, 132.8+/-11.8 ng ml(-1), appeared at 0.8+/-0.2 h. By comparing the plasma rhGH levels vs. time profiles after the administration of SDMP and intravenous injection of rhGH solution, 5 microg kg(-1), BA of rhGH from SDMP was calculated to be 87.5%. Theses results may suggest that SDMP can be used as a novel percutaneous drug delivery system.

Controlled drug delivery in tissue engineering

The concept of tissue and cell guidance is rapidly evolving as more information regarding the effect of the microenvironment on cellular function and tissue morphogenesis become available. These disclosures have lead to a tremendous advancement in the design of a new generation of multifunctional biomaterials able to mimic the molecular regulatory characteristics and the three-dimensional architecture of the native extracellular matrix. Micro- and nano-structured scaffolds able to sequester and deliver in a highly specific manner biomolecular moieties have already been proved to be effective in bone repairing, in guiding functional angiogenesis and in controlling stem cell differentiation. Although these platforms represent a first attempt to mimic the complex temporal and spatial microenvironment presented in vivo, an increased symbiosis of material engineering, drug delivery technology and cell and molecular biology may ultimately lead to biomaterials that encode the necessary signals to guide and control developmental process in tissue- and organ-specific differentiation and morphogenesis.

Physicochemical characterization and release mechanism of a novel prednisone biodegradable microsphere formulation

The aim of this work was the characterization of a new formulation of prednisone long-term controlled release biodegradable microspheres. Poly(DL-lactide-co-glycolide) (PLGA) polymers were used for MS preparation. A S/O/W solvent evaporation method was employed for prednisone entrapment. The system was characterized by using UV spectrophotometry, particle sizing, scanning electron microscopy, differential scanning calorimetry, X rays diffractometry, and microRaman spectroscopy. The release mechanism was studied by fitting Weibull, Peppas, Higuchi, and zero order kinetic models. The microspheres (MS) showed a good encapsulation efficiency and morphology, a suitable size and long-term release profile. Burst release was seen to depend on crystalline prednisone distributing close to the MS surface, and no particular prednisone-polymer interaction occurred. Weibull and Peppas were the best fitting models. Prednisone was released from PLGA MS following a Fickian diffusion and case II transport for higher molecular weight (MW) polymers, and a more complex mechanism involving solubilization, diffusion, and erosion, for low MW PLGA. Fully characterized PLGA MS may represent a good tool for a long-term delivery of prednisone in low-dose regimen treatments.

Approaches to neural tissue engineering using scaffolds for drug delivery

This review seeks to give an overview of the current approaches to drug delivery from scaffolds for neural tissue engineering applications. The challenges presented by attempting to replicate the three types of nervous tissue (brain, spinal cord, and peripheral nerve) are summarized. Potential scaffold materials (both synthetic and natural) and target drugs are discussed with the benefits and drawbacks given. Finally, common methods of drug delivery, including degradable/diffusion-based delivery systems, affinity-based delivery systems, immobilized drug delivery systems, and electrically controlled drug delivery systems, are examined and critiqued. Based on the current body of work, suggestions for future directions of research in the field of neural tissue engineering are presented.

Role of a novel excipient poly(ethylene glycol)-b-poly(L-histidine) in retention of physical stability of insulin at aqueous/organic interface

The aim of this study was to investigate whether a cationic polyelectrolyte, poly(ethylene glycol)-b-poly(L-histidine) diblock copolymer (PEG-polyHis), can stabilize insulin, at the aqueous/methylene chloride interface formed during the microencapsulation process. Insulin aggregation at this interface was monitored spectrophotometrically at 276 nm. The effects of protein concentration, pH of the aqueous medium, and the presence of poly(lactic-co-glycolic acid) (PLGA) in methylene chloride (MC) on insulin aggregation were observed. For the 2.0 mg/mL insulin solutions in phosphate buffer (PB), the effect of addition of Pluronic F-127 as a positive control and addition of PEG-polyHis as a novel excipient in PB was also evaluated at various insulin/polymeric excipient weight ratios. The conformation of insulin protected by PEG-polyHis and recovered after interfacial exposure was evaluated via circular dichroism (CD) spectroscopy. Greater loss in soluble insulin was observed with increasing insulin concentrations. pH 6.0 was selected for optimal ionic interactions between insulin and PEG-polyHis based on zeta potential and particle size studies. pH 4.5 and 7.4 (no ionic complexation between insulin and PEG-polyHis) were selected as controls to compare the stabilization effect of PEG-polyHis with that at pH 6.0. Incubation of PEG-polyHis with insulin at pH 6.0 drastically reduced protein aggregation, even in the presence of PLGA. PEG-polyHis and F-127 reduced insulin aggregation in noncomplexing pH conditions pointing to the role played by PEG in modulation of insulin adsorption at the interface. Far-UV (205-250 nm) CD study revealed negligible qualitative effects on soluble insulin's secondary structure after interfacial exposure. RP-HPLC and size-exclusion HPLC showed no deamidation of insulin or formation of soluble high molecular weight transformation products respectively. MALDI-TOF mass spectrometry confirmed the results from chromatographic procedures. Radioimmunoassay carried out on select samples showed that recovered soluble insulin had retained its immunoreactivity. An experimental method to simulate interfacial denaturation of proteins was designed for assessment of protein stability at the interface and screening for novel protein stabilizers. Understanding and manipulation of such polyelectrolyte-insulin complexation will likely play a role in insulin controlled delivery via microsphere formulation(s).

Stable high surface area lactate dehydrogenase particles produced by spray freezing into liquid nitrogen

Enzyme activities were determined for lactate dehydrogenase (LDH) powder produced by lyophilization, and two fast freezing processes, spray freeze-drying (SFD) and spray freezing into liquid (SFL) nitrogen. The 0.25 mg/mL LDH aqueous feed solutions included either 30 or 100 mg/mL trehalose. The SFL process produced powders with very high enzyme activities upon reconstitution, similar to lyophilization. However, the specific surface area of 13 m(2)/g for SFL was an order of magnitude larger than for lyophilization. In SFD activities were reduced in the spraying step by the long exposure to the gas-liquid interface for 0.1-1s, versus only 2 ms in SFL. The ability to produce stable high surface area submicron particles of fragile proteins such as LDH by SFL is of practical interest in protein storage and in various applications in controlled release including encapsulation into bioerodible polymers. The SFL process has been scaled down for solution volumes <1 mL to facilitate studies of therapeutic proteins.

Particle Engineering for Pulmonary Drug Delivery

With the rapidly growing popularity and sophistication of inhalation therapy, there is an increasing demand for tailor-made inhalable drug particles capable of affording the most efficient delivery to the lungs and the most optimal therapeutic outcomes. To cope with this formulation demand, a wide variety of novel particle technologies have emerged over the past decade. The present review is intended to provide a critical account of the current goals and technologies of particle engineering for the development of pulmonary drug delivery systems. These technologies cover traditional micronization and powder blending, controlled solvent crystallization, spray drying, spray freeze drying, particle formation from liquid dispersion systems, supercritical fluid processing and particle coating. The merits and limitations of these technologies are discussed with reference to their applications to specific drug and/or excipient materials. The regulatory requirements applicable to particulate inhalation products are also reviewed briefly.

Treatment of focal cerebral ischemia with liposomal nerve growth factor

Liposomal nerve growth factor (NGF) was used for the treatment of focal cerebral ischemia in a rat model. Positive charge inducing agents of sphingosine (SP) and stearylamine (S) were formulated in the liposomal NGF. Dose-response of intraventricular injection of liposomal NGF showed significant reduction in infarct volume at the dose of 5 and 10 microg/rat of NGF. The liposomal NGF formulated with SP or S demonstrated similar results in the reduction of total infarct volume in rats. When we increased the molar ratio of SP and S from 0.15 to 0.3, the infarct volume from rats showed a similar value as that of the control treated with NGF solution. Liposomal NGF was given prior to the development of ischemia. We found that NGF was effective in prevention of neuronal death. The NGF concentrations in brain for liposomal NGF were maintained in a level significantly higher than those for NGF solution. This was attributed to the positively charged liposomal NGF bound effectively in brain ventricle and caused longer retention time than free NGF for localization in brain. Therefore, the effect of liposomal NGF on reduction of infarct volume was significant. We assumed that the transportation of NGF might go through the cerebrospinal fluid pathway throughout the ventricular system and subarachnoid system to cerebral cortex to produce a therapeutic effect on ischemia.

Microspheres for Drug Delivery

With advances in biotechnology, genomics, and combinatorial chemistry, a wide variety of new, more potent and specific therapeutics are being created. Because of common problems such as low solubility, high potency, and/or poor stability of many of these new drugs, the means of drug delivery can impact efficacy and potential for commercialization as much as the nature of the drug itself. Thus, there is a corresponding need for safer and more effective methods and devices for drug delivery. Indeed, drug delivery systems—designed to provide a therapeutic agent in the needed amount, at the right time, to the proper location in the body, in a manner that optimizes efficacy, increases compliance and minimizes side effects—were responsible for $47 billion in sales in 2002, and the drug delivery market is expected to grow to $67 billion by 2006.

Influence of the active pharmaceutical ingredient concentration on the physical state of mannitol--implications in freeze-drying

PURPOSE

The aim of this study was to investigate the effect of the concentration of the active pharmaceutical ingredient on the physical state of mannitol in frozen aqueous systems.

METHODS

A human monoclonal antibody was used as the model protein. Mannitol and sucrose were used as the bulking agent and the lyoprotectant, respectively. The thermal behavior of frozen mannitol-sucrose solutions during and after annealing, in the absence and presence of the protein, were characterized by low-temperature powder X-ray diffractometry and differential scanning calorimetry. The influence of the protein on the crystallization behavior of mannitol was also evaluated.

RESULTS

The excipient concentration had a pronounced effect on the glass transition temperature of maximally freeze-concentrated amorphous phase (T(g)'). At fixed excipient compositions, the protein had no effect on the T(g)' if the protein concentration was < or =20 mg/ml. However, at higher protein concentrations, there was a marked increase in T(g)' as a function of protein concentration. The inhibitory effect of the protein on mannitol crystallization was concentration dependent and was directly evident from X-ray diffractometry experiments. Annealing facilitated both mannitol nucleation and crystal growth even in the presence of the protein.

CONCLUSIONS

The ratio of mannitol to sucrose and the protein concentration have an impact on the T(g)' and may therefore influence the primary drying temperature. The protein inhibits both the nucleation and growth of mannitol crystals and this effect seems to be concentration dependent. The presence of the protein and the protein concentration dictate the processing conditions, i.e., annealing time, annealing temperature, and primary drying temperature.

Role of zinc in formulation of PLGA/PLA nanoparticles encapsulating betamethasone phosphate and its release profile

The purpose of this study was to develop poly(D,L-lactic/glycolic acid) (PLGA) or poly(D,L-lactic acid) (PLA) nanoparticles of less than 200 nm in diameter that encapsulated water-soluble corticosteroid derivatives for sustained release and targeting to inflammatory sites. Nanoparticles were prepared with PLGA (or PLA), zinc, betamethasone phosphate and surfactant by an oil-in-water solvent diffusion method. With this method, the efficiency of encapsulating betamethasone phosphate in the nanoparticles and the particle size were significantly affected by various factors, such as the concentration of PLGA (or PLA) and the amount of zinc added. Nanoparticles ranging from 80 to 250 nm in diameter could be prepared, with a maximum betamethasone phosphate content of 8% (w/w). Betamethasone phosphate was gradually released from the nanoparticles in diluted serum, and the release rate depended on the glycolic/lactic acid ratio and on the molecular weight of PLGA or PLA. Betamethasone was gradually released over at least 8 days from murine macrophages that had internalized betamethasone phosphate-encapsulated nanoparticles in vitro, and the rate of release was slower than from nanoparticles prepared without zinc. These results suggest that zinc increases the efficiency of encapsulating betamethasone phosphate in nanoparticles and also promotes sustained release of betamethasone phosphate from the nanoparticles.

Controlled release from fibers of polyelectrolyte complexes

Controlled release systems for delicate compounds, such as proteins, often suffer the drawbacks of decreased bioactivity and low encapsulation efficiency. This study introduces the concept of producing drug-loaded fibers from interfacial polyelectrolyte complexation. Chitosan-alginate fibers were produced by pulling from the interface between two polyelectrolyte solutions at room temperature. Depending on the component properties, the release time of encapsulated components from these fibers can range from hours to weeks. Dexamethasone was completely released within 2 h, whereas charged compounds such as BSA, PDGF-bb, and avidin showed sustained release for 3 weeks. The fibers were able to release PDGF-bb in a steady fashion for over 3 weeks without an initial burst. Furthermore, the bioactivity of PDGF-bb was retained over this period. Release kinetics could be controlled by the inclusion of heparin, which contains specific binding sites for various growth factors. By varying the alginate/heparin ratios in the anionic polyelectrolyte solution, the release of PDGF-bb could be significantly altered. In this study, interfacial polyelectrolyte complexation has been demonstrated to be a promising technique for producing drug-loaded fibers with high encapsulation efficiency, sustained release kinetics, and capacity to retain the bioactivity of the encapsulants.

In vivo induction and delivery of nerve growth factor, using HEK-293 cells

Tissue-engineering strategies offer hope to patients facing functional impairment after nerve injury. We have previously demonstrated that HEK-293 cells can release nerve growth factor (NGF) in vitro, using an inducible system of expression. In this study, our objective was to assess the efficacy of the NGF delivery system in vivo, using nude rats. HEK-293 cells were transfected with human NGF cDNA. Ponasterone A (PonA) was used as the inducing agent. NGF collection chambers were implanted subcutaneously in nude rats. Sealed chambers were filled with one of the following: (1) DMEM, (2) untransfected 293 cells (EcR-293) plus PonA, (3) untransfected EcR-293 without PonA, (4) transfected 293 cells (hNGF-EcR-293) plus PonA, or (5) transfected hNGF-EcR-293 without PonA. Chambers were aspirated 24, 48, and 120 h postimplantation. NGF secretion was analyzed in the following ways: (1) NGF protein expression bioactivity was assessed in a PC-12 cell bioassay, and (2) the concentration of secreted NGF was quantified by NGF ELISA. NGF quantification by ELISA reached a maximal release of 12.9 +/- 3.57 ng/mL at 120 h. PC-12 cells exposed to media from induced transfected HEK-293 cell chambers demonstrated higher levels of differentiation compared with controls. We conclude that hNGF-EcR-293 cells can inducibly secrete bioactive NGF when exposed to the induction agent PonA. This regulated delivery system can secrete bioactive NGF for up to 5 days in vivo. We believe this regulated delivery system will be useful for tissue-engineered nerve constructs.

Strategic approaches for overcoming peptide and protein instability within biodegradable nano- and microparticles

This paper reviews the major factors that are closely involved in peptide and protein degradation during the preparation of biodegradable nano- and microparticles. The various means usually employed for overcoming these obstacles are described, in order to bring to the fore the strategies for protein stabilization. Both processing and formulation parameters can be modified and are distinctly considered from a strategic point of view. We describe how partial or full protein stability retention within the carriers and during drug release might be achieved by individual or combined optimized strategies. Additionally, problems commonly encountered during protein quantification, stability determination and release are briefly reviewed. Artefacts that might occur during sampling and analytical procedures and which might hinder critical interpretation of results are discussed.

Microspheres for controlled release drug delivery

Controlled release drug delivery employs drug-encapsulating devices from which therapeutic agents may be released at controlled rates for long periods of time, ranging from days to months. Such systems offer numerous advantages over traditional methods of drug delivery, including tailoring of drug release rates, protection of fragile drugs and increased patient comfort and compliance. Polymeric microspheres are ideal vehicles for many controlled delivery applications due to their ability to encapsulate a variety of drugs, biocompatibility, high bioavailability and sustained drug release characteristics. Research discussed in this review is focused on improving large-scale manufacturing, maintaining drug stability and enhancing control of drug release rates. This paper describes methods of microparticle fabrication and the major factors controlling the release rates of encapsulated drugs. Furthermore, recent advances in the use of polymer microsphere-based systems for delivery of single-shot vaccines, plasmid DNA and therapeutic proteins are discussed, as well as some future directions of microsphere research.