Uniform Encapsulation of Stable Protein Nanoparticles Produced by Spray Freezing for the Reduction of Burst Release

Genetically Encoded Self-Assembling Protein Nanoparticles for the Targeted Delivery In Vitro and In Vivo

Targeted nanoparticles of different origins are considered as new-generation diagnostic and therapeutic tools. However, there are no targeted drug formulations within the composition of nanoparticles approved by the FDA for use in the clinic, which is associated with the insufficient effectiveness of the developed candidates, the difficulties of their biotechnological production, and inadequate batch-to-batch reproducibility. Targeted protein self-assembling nanoparticles circumvent this problem since proteins are encoded in DNA and the final protein product is produced in only one possible way. We believe that the combination of the endless biomedical potential of protein carriers as nanoparticles and the standardized protein purification protocols will make significant progress in "magic bullet" creation possible, bringing modern biomedicine to a new level. In this review, we are focused on the currently existing platforms for targeted self-assembling protein nanoparticles based on transferrin, lactoferrin, casein, lumazine synthase, albumin, ferritin, and encapsulin proteins, as well as on proteins from magnetosomes and virus-like particles. The applications of these self-assembling proteins for targeted delivery in vitro and in vivo are thoroughly discussed, including bioimaging applications and different therapeutic approaches, such as chemotherapy, gene delivery, and photodynamic and photothermal therapy. A critical assessment of these protein platforms' efficacy in biomedicine is provided and possible problems associated with their further development are described.

Microspheres as intraocular therapeutic tools in chronic diseases of the optic nerve and retina

Pathologies affecting the optic nerve and the retina are one of the major causes of blindness. These diseases include age-related macular degeneration (AMD), diabetic retinopathy (DR) and glaucoma, among others. Also, there are genetic disorders that affect the retina causing visual impairment. The prevalence of neurodegenerative diseases of the posterior segment is increased as most of them are related with the elderly. Even with the access to different treatments, there are some challenges in managing patients suffering retinal diseases. One of them is the need for frequent interventions. Also, an unpredictable response to therapy has suggested that different pathways may be playing a role in the development of these diseases. The management of these pathologies requires the development of controlled drug delivery systems able to slow the progression of the disease without the need of frequent invasive interventions, typically related with endophthalmitis, retinal detachment, ocular hypertension, cataract, inflammation, and floaters, among other. Biodegradable microspheres are able to encapsulate low molecular weight substances and large molecules such as biotechnological products. Over the last years, a large variety of active substances has been encapsulated in microspheres with the intention of providing neuroprotection of the optic nerve and the retina. The purpose of the present review is to describe the use of microspheres in chronic neurodegenerative diseases affecting the retina and the optic nerve. The advantage of microencapsulation of low molecular weight drugs as well as therapeutic peptides and proteins to be used as neuroprotective strategy is discussed. Also, a new use of the microspheres in the development of animal models of neurodegeneration of the posterior segment is described.

Polymerization-induced self-assembly of large-scale iohexol nanoparticles as contrast agents for X-ray computed tomography imaging

Fundamental research for CT imaging, in which iohexol nanoparticles (INPs) were synthesised using a one-pot strategy via polymerization-induced self-assembly (PISA).

X-ray visible and doxorubicin-loaded beads based on inherently radiopaque poly(lactic acid)-polyurethane for chemoembolization therapy

The aim of current study was to develop drug-loaded polymeric beads with intrinsic X-ray visibility as embolic agents, targeting for noninvasive intraoperative location and postoperative examination during chemoembolization therapy. To endow polymer with inherent radiopacity, 4,4'-isopropylidinedi-(2,6-diiodophenol) (IBPA) was firstly synthesized and employed as a contrast agent, and then a set of radiopaque iodinated poly(lactic acid)-polyurethanes (I-PLAUs) via chain extender method were synthesized and characterized. These I-PLAU copolymers possessed sufficient radiopacity, in vitro non-cytotoxicity with human adipose-derived stem cells, and in vivo biocompatibility and degradability in rabbit model via intramuscular implantation. Doxorubicin (DOX), as a chemotherapeutic agent, was further incorporated into I-PLAU beads via a double emulsification (W/O/W) method. For drug release, two ratios of DOX-loaded I-PLAU beads exhibited calibrated size (200-550μm), porous internal structure, good X-ray visibility, evenly drug loading as well as tunable drug release. A preliminary test on in vitro tumor cell toxicity demonstrated that the DOX-loaded I-PLAU beads performed efficient anti-tumor effect. This study highlights novel X-ray visible drug-loaded I-PLAU beads used as promising embolic agents for non-invasive in situ X-ray tracking and efficient chemotherapy, which could bring opportunities to the next generation of multifunctional embolic agents.

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.

A method of lyophilizing vaccines containing aluminum salts into a dry powder without causing particle aggregation or decreasing the immunogenicity following reconstitution

Many currently licensed and commercially available human vaccines contain aluminum salts as vaccine adjuvants. A major limitation with these vaccines is that they must not be exposed to freezing temperatures during transport or storage such that the liquid vaccine freezes, because freezing causes irreversible coagulation that damages the vaccines (e.g., loss of efficacy). Therefore, vaccines that contain aluminum salts as adjuvants are formulated as liquid suspensions and are required to be kept in cold chain (2-8°C) during transport and storage. Formulating vaccines adjuvanted with aluminum salts into dry powder that can be readily reconstituted before injection may address this limitation. Spray freeze-drying of vaccines with low concentrations of aluminum salts and high concentrations of trehalose alone, or a mixture of sugars and amino acids, as excipients can convert vaccines containing aluminum salts into dry powder, but fails to preserve the particle size and/or immunogenicity of the vaccines. In the present study, using ovalbumin as a model antigen adsorbed onto aluminum hydroxide or aluminum phosphate, a commercially available tetanus toxoid vaccine adjuvanted with potassium alum, a human hepatitis B vaccine adjuvanted with aluminum hydroxide, and a human papillomavirus vaccine adjuvanted with aluminum hydroxyphosphate sulfate, it was shown that vaccines containing a relatively high concentration of aluminum salts (i.e., up to ~1%, w/v, of aluminum hydroxide) can be converted into a dry powder by thin-film freezing followed by removal of the frozen solvent by lyophilization while using low levels of trehalose (i.e., as low as 2% w/v) as an excipient. Importantly, the thin-film freeze-drying process did not cause particle aggregation, nor decreased the immunogenicity of the vaccines. Moreover, repeated freezing-and-thawing of the dry vaccine powder did not cause aggregation. Thin-film freeze-drying is a viable platform technology to produce dry powders of vaccines that contain aluminum salts.

Effect of MgO nanofillers on burst release reduction from hydrogel nanocomposites

In this study, MgO nanoparticles are applied to control the initial burst release by modification of matrix structure, thereby affecting the release mechanism. The effects of MgO nanofiller loading on the in vitro release of a model drug are investigated. Surface topography and release kinetics of hydrogel nanocomposites are also studied in order to have better insight into the release mechanism. It was found that the incorporation of MgO nanofillers can significantly decrease the initial burst release. The effect of genipin (GN) on burst release was also compared with MgO nanoparticles, and it was found that the impact of MgO on burst release reduction is more obvious than GN; however, GN cross-linking caused greater final release compared to blanks and nanocomposites. To confirm the capability of nanocomposite hydrogels to reduce burst release, the release of β-carotene in Simulated Gastric Fluid and Simulated Intestinal Fluid was also carried out. Thus, the application of MgO nanoparticles seems to be a promising strategy to control burst release.

Microencapsulation of dye- and drug-loaded particles for imaging and controlled release of multiple drugs

A polymeric microcapsule that can house different drug-loaded particles using a simple emulsion packaging technique is presented. Compared to the neat microparticles, microcapsules simultaneously release multiple drugs in a sustained manner. These microcapsules could provide a means of controlling release of multiple drugs.

Glycosylation improves α-chymotrypsin stability upon encapsulation in poly(lactic-co-glycolic)acid microspheres

Enhancing protein stability upon encapsulation and release from polymers is a key issue in sustained release applications. In addition, optimum drug dispersion in the polymer particles is critical for achieving release profiles with low unwanted initial “burst” release. Herein, we address both issues by formulating the model enzyme α-chymotrypsin (α-CT) as nanoparticles to improve drug dispersion and by covalently modifying it with glycans to afford improved stability during encapsulation in poly(lactic-co-glycolic) acid (PLGA) microspheres. α-CT was chemically modified with activated lactose (500 Da) to achieve molar ratios of 4.5 and 7.1 lactose-to-protein. The bioconjugates were co-lyophilized with methyl-β-cyclodextrin followed by suspension in ethyl acetate to afford nanoparticles. Nanoparticle formation did not significantly impact protein stability; less than 5% of the protein was aggregated and the residual activity remained above 90% for all formulations. Using a solid-in-oil-in-water (s/o/w) methodology developed in our laboratory for nanoparticles, we obtained a maximum encapsulation efficiency of 61%. Glycosylation completely prevented otherwise substantial protein aggregation and activity loss during encapsulation of the non-modified enzyme. Moreover, in vitro protein release was improved for glycosylated formulations. These results highlight the potential of chemical glycosylation to improve the stability of pharmaceutical proteins in sustained release applications.

Formation of spherical protein nanoparticles without impacting protein integrity

Protein formulation at the nanoscale is challenging because of protein susceptibility to chemical and physical degradation during processing. Herein, we present a straightforward method to prepare spherical protein nanoparticles by co-lyophilizing five structurally different enzymes (horseradish peroxidase, carbonic anhydrase, lysozyme, subtilisin Carlsberg and α-chymotrypsin) with methyl-β-cyclodextrin followed by suspension of the powders in ethyl acetate. The size distribution was narrow and varied from 88 ± 14 to 148 ± 16 nm as determined by dynamic light scattering. Scanning and transmission electron micrographs confirmed the size and spherical morphology of the protein nanoparticles. Residual activities for all enzymes tested were 100% upon dissolving the nanoparticles in buffer and no insoluble aggregates were formed.

Bioinspired nanoencapsulation of purple membranes

Embedding biological compounds, e.g. enzymes or whole cells, in solid host material seems to be a promising approach to widen their field of application far beyond the limits of natural conditions. In fields such as medicine and biotechnology, there is great interest in new methods to produce these types of composite materials in the form of micro- or nanosized particles. Such methods should be applicable to large amounts of substance. Inspired by one of nature's remarkable features-its ability to combine (bio)organic and inorganic components at the nanoscale-we developed a generic silica encapsulation method for biomolecules based on the concepts of polyelectrolyte layer adsorption followed by templated silica mineralization similar to biomineralization in diatoms. Application of this method to the model substance purple membrane (PM) resulted in a defined hybrid material with a nanoscale protective encapsulating silica shell providing a high barrier for the diffusion of low molecular weight molecules.

Polymer-surfactant nanoparticles for sustained release of water-soluble drugs

Poor drug encapsulation efficiency and rapid release of the encapsulated drug limit the use of nanoparticles in biomedical applications involving water-soluble drugs. We have developed a novel polymer-surfactant nanoparticle formulation, using the anionic surfactant Aerosol OT (AOT) and polysaccharide polymer alginate, for sustained release of water-soluble drugs. Particle size of nanoparticles, as determined by atomic force microscopy and transmission electron microscopy, was in the range of 40-70 nm. Weakly basic molecules like methylene blue, doxorubicin, rhodamine, verapamil, and clonidine could be encapsulated efficiently in AOT-alginate nanoparticles. In vitro release studies with basic drug molecules indicate that nanoparticles released 60-70% of the encapsulated drug over 4 weeks, with near zero-order release during the first 15 days. Studies with anionic drug molecules demonstrate poorer drug encapsulation efficiency and more rapid drug release than those observed with basic drugs. Further studies investigating the effect of sodium concentration in the release medium and the charge of the drug suggest that calcium-sodium exchange between nanoparticle matrix and release medium and electrostatic interaction between drug and nanoparticle matrix are important determinants of drug release. In conclusion, we have formulated a novel surfactant-polymer drug delivery carrier demonstrating sustained release of water-soluble drugs.

Effect of the microencapsulation of nanoparticles on the reduction of burst release

The initial burst release is one of the major problems in the development of controlled release formulations including drug-loaded micro- and nanoparticles, especially with low molecular weight drugs. The objective of the present work was to encapsulate, by the W/O/W emulsion, polymeric nanoparticles into polymeric microparticles by using non-water soluble polymers and appropriate organic solvents for the preparation of these composite microparticles. They were characterized in vitro (encapsulation efficiency, mean diameter and release kinetics) and compared with nanoparticles and classical microparticles prepared by the same method. Poly-epsilon-caprolactone (PCL) dissolved in methylene chloride was used to make nanoparticles, whereas ethylcellulose and Eudragit RS dissolved in ethyl acetate, a non-solvent of poly-epsilon-caprolactone, were used for the preparation of microparticles. Ibuprofen and triptorelin acetate were chosen as lipophilic and hydrophilic model drugs, respectively. High entrapment efficiencies were obtained with ibuprofen whereas lower amounts of triptorelin acetate were encapsulated, mainly with formulations prepared with poly-epsilon-caprolactone and Eudragit RS used alone or blended with ethylcellulose. The burst was significantly lower with composite microparticles and may be explained by the slower diffusion of the drugs through the double polymeric wall formed by the nanoparticle matrix followed by another diffusion step through the microparticle polymeric wall.

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.

Cryogenic liquids, nanoparticles, and microencapsulation

The biopharmaceutical classification system (BCS) is used to group pharmaceutical actives depending upon the solubility and permeability characteristics of the drug. BCS class II compounds are poorly soluble but highly permeable, exhibiting bioavailability that is limited by dissolution. The dissolution rate of BCS class II drug substances may be accelerated by enhancing the wetting of the bulk powder and by reducing the primary particle size of the drug to increase the surface area. These goals may be achieved by nucleating drug particles from solution in the presence of stabilizing excipients. In the spray freezing into liquid (SFL) process, a drug containing solution is atomized and frozen rapidly to engineer porous amorphous drug/excipient particles with high surface areas and dissolution rates. Aqueous suspensions of nanostructured particles may be produced from organic solutions by evaporative precipitation into aqueous solution (EPAS). The suspensions may be dried by lyophilization. The particle size and morphology may be controlled by the type and level of stabilizers. In vivo studies have shown increased bioavailability of a wide variety of drugs particles formed by SFL or EPAS. For both processes, increased serum levels of danazol (DAN) were observed in mice relative to bulk DAN and the commercial product, Danocrine. Orally dosed itraconazole (ITZ) compositions, formed by SFL, produce higher serum levels of the drug compared to the commercial product, Sporanox oral solution. Additionally, nebulized SFL processed ITZ particles suspended in normal saline have been dosed via the pulmonary route and led to extended survival times for mice inoculated with Aspergillis flavus. SFL and EPAS processes produce amorphous drug particles with increased wetting and dissolution rates, which will subsequently supersaturate biological fluids in vivo, resulting in increased drug bioavailability and efficacy.

Morphology of protein particles produced by spray freezing of concentrated solutions

The mechanisms for the formation of high surface area lysozyme particles in spray freezing processes are described as a function of spray geometry and atomization, solute concentration and the calculated cooling rate. In the spray freeze-drying (SFD) process, droplets are atomized into a gas and then freeze upon contact with a liquid cryogen. In the spray freezing into liquid (SFL) process, a solution is sprayed directly into the liquid cryogen below the gas-liquid meniscus. A wide range of feed concentrations is examined for two cryogens, liquid nitrogen (LN2) and isopentane (i-C5). The particle morphologies are characterized by SEM micrographs and BET measurements of specific surface area. As a result of boiling of the cryogen (Leidenfrost effect), the cooling rate for SFL into LN2 is several orders of magnitude slower than for SFL into i-C5 and for SFD in the case of either LN2 or i-C5. For 50 mg/mL concentrated feed solutions, the slower cooling of SFL into LN2 leads to a surface area of 34 m(2)/g. For the other three cases with more rapid cooling rates, surface areas were greater than 100 m(2)/g. The ability to adjust the cooling rate to vary the final particle surface area is beneficial for designing particles for controlled release applications.

Spray freezing into liquid versus spray-freeze drying: Influence of atomization on protein aggregation and biological activity

Protein aggregation and enzyme activity were compared for reconstituted lysozyme particles produced by two cryogenic technologies, spray freezing into liquid (SFL) and spray-freeze drying (SFD). The particles were characterized by enzyme activity measurements, scanning electron microscopy (SEM), light scattering, X-ray photoelectron spectroscopy (XPS) and BET specific surface area analysis. Highly porous microparticle aggregates of protein nanoparticles, observed by SEM, were produced by both processes. The smaller degree of protein aggregation and smaller losses in enzyme activity for the SFL process relative to the SFD process were due primarily to the spraying step. The higher stability of the SFL versus SFD powders was consistent with the smaller surface excess of lysozyme measured by XPS in SFL, resulting from the reduced time of exposure to the air-water interface during atomization. For pure lysozyme, the degree of aggregation and enzyme activity were comparable for lyophilization and SFL, despite the much larger particle surface area for SFL.

Encapsulation of protein nanoparticles into uniform-sized microspheres formed in a spinning oil film

A new spinning oil film (SOF) solid-in-oil-in-oil emulsion process was developed to produce uniform-sized protein-loaded biodegradable microspheres. A thin SOF on a cylindrical rotor was used to shear droplets from a nozzle tip to control droplet size. The resulting microspheres with low polydispersity (6%) produced a low burst (6%-11%) release even at high loadings (13%-18% encapsulated solids, 8%-12% protein). The SOF process had a high yield and did not require the presence of water, which can cause protein denaturation, or surfactants, which may be unwanted in the final product. Amorphous protein and crystalline excipient solids were encapsulated into 3 different polymers, giving a homogenous drug distribution throughout the microspheres, and an essentially complete protein encapsulation efficiency (average = 99%). In contrast, large burst release was observed for polydisperse microspheres produced by a conventional emulsification technique, particularly for microspheres smaller than 25 mum in diameter, which gave 93% burst at 15% loading. The uniform encapsulation of high loadings of proteins into microspheres with low polydispersity in an anhydrous process is of practical interest in the development of controlled-release protein therapeutics.