In situ study of insulin aggregation induced by water-organic solvent interface

Combined Effect of Shaking Orbit and Vial Orientation on the Agitation-Induced Aggregation of Proteins

Orbital shaking in a glass vial is a commonly used forced degradation test to evaluate protein propensity for agitation-induced aggregation. Vial shaking in horizontal orientation has been widely recommended to maximize the air-liquid interface area while ensuring solution contact with the stopper. We evaluated the impact of shaking orbit diameter and frequency, and glass vial orientation (horizontal versus vertical) on the aggregation of three proteins prepared in surfactant-free formulation buffers. As soon as an orbit-specific frequency threshold was reached, an increase in turbidity was observed for the three proteins in vertical orientation only when using a 3 mm agitation orbit, and in horizontal orientation only when using a 30 mm agitation orbit. Orthogonal analyses confirmed turbidity was linked to protein aggregation. The most turbid samples had a visually more homogeneous appearance in vertical than in horizontal orientation, in line with the predicted dispersion of air and liquid phases obtained from computational fluid dynamics agitation simulations. Both shaking orbits were used to assess the performance of nonionic surfactants. We show that the propensity of a protein to aggregate in a vial agitated in horizontal or vertical orientation depends on the shaking orbit, and confirm that Brij® 58 and FM1000 prevent proteins from agitation-induced aggregation at lower concentrations than polysorbate 80.

The crossroad of nanovesicles and oral delivery of insulin

INTRODUCTION

Diabetes mellitus is one of the challenging health problems worldwide. Multiple daily subcutaneous injection of insulin causes poor compliance in patients. Development of efficient oral formulations to improve the quality of life of such patients has been an important goal in pharmaceutical industry. However, due to serious issues such as low bioavailability and instability, it has not been achieved yet.

AREAS COVERED

Due to functional properties of the vesicles and the fact that hepatic-directed vesicles of insulin could reach the clinical phases, we focused on three main vesicular delivery systems for oral delivery of insulin: liposomes, niosomes, and polymersomes. Recent papers were thoroughly discussed to provide a broad overview of such oral delivery systems.

EXPERT OPINION

Although conventional liposomes are unstable in the presence of bile salts, their further modifications such as surface coating could increase their stability in the GI tract. Bilosomes showed good flexibility and stability in GI fluids. Also, niosomes were stable, but they could not induce significant hypoglycemia in animal studies. Although polymersomes were effective, they are expensive and there are some issues about their safety and industrial scale-up. Also, we believe that other modifications such as addition of a targeting agent or surface coating of the vesicles could significantly increase the bioavailability of insulin-loaded vesicles.

Design and in vitro/in vivo Evaluation of Polyelectrolyte Complex Nanoparticles Filled in Enteric-Coated Capsules for Oral Delivery of Insulin

Insulin is one of the most important drugs in the treatment of diabetes. There is an increasing interest in the oral administration of insulin as it mimics the physiological pathway and potentially reduces the side effects associated with subcutaneous injection. Therefore, insulin-loaded polyelectrolyte complex (PEC) nanoparticles were prepared by the ionic cross-linking method using protamine sulfate as the polycationic and sodium alginate as the anionic polymer. Taguchi experimental design was used for the optimization of nanoparticles by varying the concentration of sodium alginate, the mass ratio of sodium alginate to protamine, and the amount of insulin. The optimized nanoparticle formulation was used for further in vitro characterization. Then, insulin-loaded PEC nanoparticles were placed in hard gelatin capsules and the capsules were enteric-coated by Eudragit L100-55 (PEC-eCAPs). Hypoglycemic effects PEC-eCAPs were determined in vivo by oral administration to diabetic rats. Furthermore, in vivo distribution of PEC nanoparticles was evaluated by fluorescein isothiocyanate (FITC) labelled nanoparticles. The experimental design led to nanoparticles with a size of 194.4 nm and a polydispersity index (PDI) of 0.31. The encapsulation efficiency (EE) was calculated as 95.96%. In vivo studies showed that PEC-eCAPs significantly reduced the blood glucose level of rats at the 8^th hour compared to oral insulin solution. It was concluded that PEC nanoparticles loaded into enteric-coated hard gelatin capsules provide a promising delivery system for the oral administration of insulin.

Bioactive Insulin-Loaded Electrospun Wound Dressings for Localized Drug Delivery and Stimulation of Protein Expression Associated with Wound Healing

Effective therapy of wounds is difficult, especially for chronic, non-healing wounds, and novel therapeutics are urgently needed. This challenge can be addressed with bioactive wound dressings providing a microenvironment and facilitating cell proliferation and migration, ideally incorporating actives, which initiate and/or progress effective healing upon release. In this context, electrospun scaffolds loaded with growth factors emerged as promising wound dressings due to their biocompatibility, similarity to the extracellular matrix, and potential for controlled drug release. In this study, electrospun core-shell fibers were designed composed of a combination of polycaprolactone and polyethylene oxide. Insulin, a proteohormone with growth factor characteristics, was successfully incorporated into the core and was released in a controlled manner. The fibers exhibited favorable mechanical properties and a surface guiding cell migration for wound closure in combination with a high uptake capacity for wound exudate. Biocompatibility and significant wound healing effects were shown in interaction studies with human skin cells. As a new approach, analysis of the wound proteome in treated ex vivo human skin wounds clearly demonstrated a remarkable increase in wound healing biomarkers. Based on these findings, insulin-loaded electrospun wound dressings bear a high potential as effective wound healing therapeutics overcoming current challenges in the clinics.

Fatty Acid-Based Polymeric Micelles to Ameliorate Amyloidogenic Disorders

To develop anti-amyloidogenic inhibitors for ameliorating the treatment of diabetes, herein, we have synthesized amphiphilic block copolymers with side-chain fatty acid (FA) moieties via reversible addition fragmentation chain-transfer (RAFT) polymerization....

Modulating Insulin Aggregation with Charge Variable Cholic Acid-Derived Polymers

To understand the effect of cholic acid (CA)-based charge variable polymeric architectures on modulating the insulin aggregation process, herein, we have designed side-chain cholate-containing charge variable polymers. Three different types of copolymers from 2-(methacryloyloxy)ethyl cholate with anionic or cationic or neutral units have been synthesized by reversible addition-fragmentation chain transfer polymerization. The effects of these copolymers on the insulin fibrillation process was studied by multiple biophysical approaches including different types of spectroscopic and microscopic analyses. Interestingly, the CA-based cationic polymer (CP-10) was observed to inhibit the insulin fibrillation process in a dose-dependent manner and to act as an effective anti-amyloidogenic agent. Corresponding anionic (AP-10) and neutral (NP-10) copolymers with cholate pendants remained insignificant in controlling the aggregation process. Tyrosine fluorescence assays and Nile red fluorescence measurements demonstrate the role of hydrophobic interaction to explain the inhibitory potencies of CP-10. Furthermore, circular dichroism spectroscopic measurements were carried out to explore the secondary structural changes of insulin fibrils in the presence of cationic polymers with and without cholate moieties. Isothermal titration calorimetry measurements revealed the involvement of electrostatic polar interaction between the CA-based cationic polymer and insulin at different stages of fibrillation. Overall, this work demonstrates the efficacy of the CA-based cationic polymer in controlling the insulin aggregation process and provides a novel dimension to the studies on protein aggregation.

Interfacial tension effects on the properties of PLGA microparticles

Many types of long-acting injectables, including in situ forming implants, preformed implants, and polymeric microparticles, have been developed and ultimately benefited numerous patients. The advantages of using long-acting injectables include greater patient compliance and more steady state drug plasma levels for weeks and months. However, the development of long-acting polymeric microparticles has been hampered by the lack of understanding of the microparticle formation process, and thus, control of the process. Of the many parameters critical to the reproducible preparation of microparticles, the interfacial tension (IFT) effect is an important factor throughout the process. It may influence the droplet formation, solvent extraction, and drug distribution in the polymer matrix, and ultimately drug release kinetics from the microparticles. This mini-review is focused on the IFT effects on drug-loaded poly(lactic-co-glycolic acid) (PLGA) microparticles.

Hydrophobic ion pairing (HIP) of (poly)peptide drugs: Benefits and drawbacks of different preparation methods

In order to incorporate hydrophilic macromolecular drugs into lipid-based formulations (LBF), HIP has shown great potential. In this study, different HIP methods were compared with each other. Hydrophobic complexes were formed between bovine serum albumin (BSA) and either dodecyl sulfate, cetyl trimethylammonium or 1,2-dipalmitoyl-sn-glycero-3-phosphate applying the organic solvent-free method, Bligh-Dyer method and biphasic metathesis reaction either with ethyl acetate or chloroform as organic phase. Complex formation efficiency was determined. Hydrophobicity of the obtained complexes was characterized by their apparent partition coefficient between 1-butanol and water. The highest complex formation efficiency was achieved with the Bligh-Dyer method, followed by the organic solvent-free method and the biphasic metathesis reaction. When applying the organic solvent-free method, complex formation efficiency was hampered at higher surfactant concentrations due to the formation of micelles. Furthermore, this method could only be applied for water-soluble compounds. On the contrary, the Bligh-Dyer method was robust towards high surfactant concentrations. Moreover, it enables the use of water-insoluble compounds. The rank order Bligh-Dyer method > organic solvent-free method > biphasic metathesis reaction was confirmed by the log D. According to these results, the Bligh-Dyer method appears advantageous for HIP. However, the organic-solvent free method is an adequate alternative for water-soluble compounds.

Toward Dosing Precision and Insulin Stability in an Artificial Pancreas System

A fully implantable artificial pancreas (AP) still represents the holy grail for diabetes treatment. The quest for efficient miniaturized implantable insulin pumps, able to accurately regulate the blood glucose profile and to keep insulin stability, is still persistent. This work describes the design and testing of a microinjection system connected to a variable volume insulin reservoir devised to favor insulin stability during storage. The design, the constitutive materials, and the related fabrication techniques were selected to favor insulin stability by avoiding—or at least limiting—hormone aggregation. We compared substrates made of nylon 6 and Teflon, provided with different surface roughness values due to the employed fabrication procedures (i.e., standard machining and spray deposition). Insulin stability was tested in a worst case condition for 14 days, and pumping system reliability and repeatability in dosing were tested over an entire reservoir emptying cycle. We found that nylon 6 guarantees a higher insulin stability than Teflon and that independent of the material used, larger roughness determines a higher amount of insulin aggregates. A dedicated rotary pump featured by a 1-μL delivery resolution was developed and connected through a proper gear mechanism to a variable volume air-tight insulin reservoir. The microinjection system was also able to operate in a reverse mode to enable the refilling of the implanted reservoir. The developed system represents a fundamental building block toward the development of a fully implantable AP and could be advantageously integrated even in different implantable drug delivery apparatus (e.g., for pain management).

Metal-Organic Framework Encapsulation Preserves the Bioactivity of Protein Therapeutics

Protein therapeutics are prone to lose their structure and bioactivity under various environmental stressors. This study reports a facile approach using a nanoporous material, zeolitic imidazolate framework-8 (ZIF-8), as an encapsulant for preserving the prototypic protein therapeutic, insulin, against different harsh conditions that may be encountered during storage, formulation, and transport, including elevated temperatures, mechanical agitation, and organic solvent. Both immunoassay and spectroscopy analyses demonstrate the preserved chemical stability and structural integrity of insulin offered by the ZIF-8 encapsulation. Biological activity of ZIF-8-preserved insulin after storage under accelerated degradation conditions (i.e., 40 °C) is evaluated in vivo using a diabetic mouse model, and shows comparable bioactivity to refrigeration-stored insulin (-20 °C). It is also demonstrated that ZIF-8-preserved insulin has low cytotoxicity in vitro and does not cause side effects in vivo. Furthermore, ZIF-8 residue can be completely removed by a simple purification step before insulin administration. This biopreservation approach is potentially applicable to diverse protein therapeutics, thus extending the benefits of advanced biologics to resource-limited settings and underserved populations/regions.

The stability of insulin solutions in syringes is improved by ensuring lower molecular weight silicone lubricants are absent

Protein drugs such as insulin are almost universally delivered via glass syringes lubricated with silicone oil. It is not uncommon for prefilled syringes (PFS) to become cloudy, which may affect bioavailability or total drug dose. To examine the role, if any, of the silicone oil lubricant in this process, a systematic evaluation of the degree of insulin denaturation and aggregation as a function of silicone oils of different molecular weights was undertaken. The former was measured using fluorescence changes of aqueous insulin/silicone dispersions, while the latter examined changes in turbidity as a function of mixing and silicone oil type; the results were confirmed at two different insulin concentrations and agitation speeds. Lower molecular weight silicones led to the most rapid denaturation and aggregation, and when examined in blends of silicones at a fixed viscosity of 1000 cSt, commonly used for syringe lubrication, more rapid denaturation/aggregation was noted in blends of silicones containing the largest fractions of low molecular weight materials. As a consequence, the molecular weight profile of silicone lubricants should be established prior to the preparation of prefilled syringes.

SDS induced dissociation of STY3178 oligomer: experimental and molecular dynamics studies

STY3178 the yfdX Salmonella Typhi protein dissociates reversibly in presence of sodium dodecyl sulphate from trimer to monomer.

Particle designs for the stabilization and controlled-delivery of protein drugs by biopolymers: a case study on insulin

Natural biopolymers have attracted considerable interest for the development of delivery systems for protein drugs owing to their biocompatibility, non-toxicity, renewability and mild processing conditions. This paper offers an overview of the current status and future perspectives of particle designs using biopolymers for the stabilization and controlled-delivery of a model protein drug--insulin. We first describe the design criteria for polymeric encapsulation and subsequently classify the basic principles of particle fabrication as well as the existing particle designs for oral insulin encapsulation. The performances of these existing particle designs in terms of insulin stability and in vitro release behavior in acidic and alkaline media, as well as their in vivo performance are compared and reviewed. This review forms the basis for future works on the optimization of particle design and material formulation for the development of an improved oral delivery system for protein drugs.

Light scattering coupled with reversed phase chromatography to study protein self-association under separating conditions

An on-line method, coupling reversed phase chromatography with static light scattering, was developed to determine the association state of freshly eluted proteins. Under downstream process conditions, human insulin desB30 and human insulin AspB28 were tested at concentrations up to 8.5mg/mL. The refractive index increment (dn/dc) for insulin was found to depend strongly on the solvent used. A refractive index increment of 0.184±0.003mL/g was found in an aqueous buffer, pH 7.4, whereas the value was 0.155±0.003mL/g in 30%, w/w ethanol. The methodology combines on-line SLS and UV measurements with the pre-determined refractive index increment values. The developed on-line method was verified by standard off-line measurements establishing the association state at concentrations between 0.2 and 6.0mg/mL. The equipment was calibrated utilizing insulin under conditions reported to ensure either monomer or hexamer forms. The self-association of human insulin desB30 was found to be strongly suppressed in 30%, w/w ethanol at pH 7.4 in which the monomer predominates. When stabilized by zinc ions in 30%, w/w ethanol at pH 7.4, an average association number of 3.7 was found. These data demonstrate the effect of ethanol to lower strongly the energy advantage by protein self-association. Potassium chloride and/or calcium chloride in the eluents were found to be of no consequence to the association state.

Preparation and characterization of insulin-surfactant complexes for loading into lipid-based drug delivery systems

Insulin suffers from poor oral bioavailability, but lipid-based drug delivery systems (DDS) may constitute promising tools for improving this. Loading of protein drugs into lipid matrices may, however, be challenging, and different formulation approaches must be taken to achieve sufficient loading and preservation of native structure. The aim of the present study was to characterize insulin after complexation with biocompatible surfactants to improve loading into lipid-based DDS. Insulin-surfactant complexes were prepared by freeze-drying with distearyldimethylammonium bromide or soybean phospholipid as complexing surfactant and dimethyl sulfoxide (DMSO) as solvent. Significant change in secondary structure of insulin freeze dried from DMSO was observed using Fourier transform infrared spectroscopy. Changes were quantitatively smaller in the presence of surfactants, demonstrating both a stabilizing effect of surfactants, but also a nonnative secondary structure in the solid state. Finally, circular dichroism analysis of rehydrated complexes showed that the processing did not irreversibly alter the secondary structure of insulin. In short, the present study demonstrates changes in the secondary structure of insulin after freeze-drying from DMSO, constituting a potential generic issue with this technique for protein processing. In the specific case of insulin, the changes were found to be reversible, explaining the success of this strategy in previous studies.

Multimerization and aggregation of native-state insulin: effect of zinc

The aggregation of insulin is complicated by the coexistence of various multimers, especially in the presence of Zn(2+). Most investigations of insulin multimerization tend to overlook aggregation kinetics, while studies of insulin aggregation generally pay little attention to multimerization. A clear understanding of the starting multimer state of insulin is necessary for the elucidation of its aggregation mechanism. In this work, the native-state aggregation of insulin as either the Zn-insulin hexamer or the Zn-free dimer was studied by turbidimetry and dynamic light scattering, at low ionic strength and pH near pI. The two states were achieved by varying the Zn(2+) content of insulin at low concentrations, in accordance with size-exclusion chromatography results and literature findings (Tantipolphan, R.; Romeijn, S.; Engelsman, J. d.; Torosantucci, R.; Rasmussen, T.; Jiskoot, W. J. Pharm. Biomed. 2010, 52, 195). The much greater aggregation rate and limiting turbidity (τ(∞)) for the Zn-insulin hexamer relative to the Zn-free dimer was explained by their different aggregation mechanisms. Sequential first-order kinetic regimes and the concentration dependence of τ(∞) for the Zn-insulin hexamer indicate a nucleation and growth mechanism, as proposed by Wang and Kurganov (Wang, K.; Kurganov, B. I. Biophys. Chem. 2003, 106, 97). The pure second-order process for the Zn-free dimer suggests isodesmic aggregation, consistent with the literature. The aggregation behavior at an intermediate Zn(2+) concentration appears to be the sum of the two processes.

Effect of PLGA hydrophilia on the drug release and the hypoglucemic activity of different insulin-loaded PLGA microspheres

The effects of viscosity and hydrophilic characteristics of different PLGA polymers on the microencapsulation of insulin have been studied in vitro and in vivo after subcutaneous administration to hyperglycemic rats. Hydrophilic PLGA polymers produced a higher burst effect than the hydrophobic ones. Moreover, an incomplete insulin release was observed with the hydrophilic PLGA polymers in comparison with the hydrophobic ones. An explanation for that incomplete release can be the development of polymer-insulin interactions associated to the polymer hydrophilic/hydrophobic character, as detected by DSC analysis. Differences in the release rate of microsphere formulations lead to differences in the hypoglycemic action and the weight of animals. Hydrophobic PLGA was able to prolong the hypoglycemic action up to 4 weeks which is at least double than that obtained with hydrophilic PLGA of a similar viscosity. Comparing insulin microspheres with an immediate release formulation, microspheres can increase insulin relative bioavailability up to four times.

Development of interferon alpha-2b microspheres with constant release

Interferon alpha-2b (IFNα-2b) is an important immune regulator used widely in clinic. However, frequent subcutaneous injection and substantial toxicity decrease patients' compliance. So, drug delivery with more precisely controlled drug release is urgent for IFNα-2b. Microsphere is a promising sustained drug delivery system, which has been studied widely for delivery of proteins. However, it was found difficult to keep proteins' activity and guarantee complete release. In this study, we solidified IFNα-2b as microparticles firstly by co-lyophilizing it with gelatin and ZnSO(4). Microspheres were then prepared. The preparing procedure and formulation were optimized with encapsulation efficiency and in vitro release as main parameters. Finally, the microspheres were prepared by S/O/W method with microparticle size about 5 μm and PEGT/PBT-PLGA (9:1, w/w) as matrix material. The diameter of microspheres was 28.94 μm, the encapsulation efficiency was 86.01%, the burst release was 16.69%, the cumulative release was 83.06% at 23th day, and IFNα-2b was released from microspheres with a zero-order profile. These microspheres also demonstrated sustained and steady release for about 13 days in rats. In conclusion, the procedure and formulation used in this study were supposed to be successful to keep IFNα-2b active and released constantly and completely.

Preparation of solid lipid nanoparticles from W/O/W emulsions: preliminary studies on insulin encapsulation

A method to produce solid lipid nanoparticles (SLN) from W/O/W multiple emulsions was developed applying the solvent-in-water emulsion-diffusion technique. Insulin was chosen as hydrophilic peptide drug to be dissolved in the acidic inner aqueous phase of multiple emulsions and to be consequently carried in SLN. Several partially water-miscible solvents with low toxicity were screened in order to optimize emulsions and SLN composition, after assessing that insulin did not undergo any chemical modification in the presence of the different solvents and under the production process conditions. SLN of spherical shape and with mean diameters in the 600-1200 nm range were obtained by simple water dilution of the W/O/W emulsion. Best results, in terms of SLN mean diameter and encapsulation efficiencies, were obtained using glyceryl monostearate as lipid matrix, butyl lactate as a solvent, and soy lecithin and Pluronic F68 as surfactants. Encapsulation efficiencies up to 40% of the loaded amount were obtained, owing to the actual multiplicity of the system; the use of multiple emulsion-derived SLN can be considered a useful strategy to encapsulate a hydrophilic drug in a lipid matrix.

Peptide-Loaded Solid Lipid Nanoparticles Prepared through Coacervation Technique

Stearic acid solid lipid nanoparticles were prepared according to a new technique, called coacervation. The main goal of this experimental work was the entrapment of peptide drugs into SLN, which is a difficult task, since their chemical characteristics (molecular weight, hydrophilicity, and stability) hamper peptide-containing formulations. Insulin and leuprolide, chosen as model peptide drugs, were encapsulated within nanoparticles after hydrophobic ion pairing with anionic surfactants. Peptide integrity was maintained after encapsulation, and nanoparticles can actin vitroas a sustained release system for peptide.

On the stability of Insulin delivered through a new glucose-responsive polymeric composite membrane

A new glucose-responsive polymeric composite membrane that provided pulsatile insulin release was developed in our laboratory previously. To develop a clinically useful insulin delivery system, this study was designed to investigate factors influencing insulin stability during delivery by this membrane. The effects of stirring, release duration, insulin concentration and surfactant on insulin stability were studied under both incubation and delivery conditions in a buffer solution at 37°C. The structural change of insulin was characterized by reverse-phase HPLC and circular dichroism. Hydrophobicity of various contact surfaces was determined by contact angle measurement. The results indicated that insulin concentration played an important role in the insulin stability, followed by stirring. Treating the membrane with a non-ionic surfactant prevented insulin denaturation during delivery through the membrane.

Dual behavior of sodium dodecyl sulfate as enhancer or suppressor of insulin aggregation and chaperone-like activity of camel alphaS(1)-casein

Sodium dodecyl sulfate (SDS) at low concentrations considerably enhanced insulin aggregation and reduced the chaperone-like activity of purified camel alphaS(1)-casein (alphaS(1)-CN). These observed changes were the result of repulsive electrostatic interactions between both negative charged head groups of SDS and alphaS(1)-CN, and the net negative charge of insulin molecules, resulting in the greater exposure of hydrophobic patches of insulin and its enhanced aggregation. In contrast, enhanced hydrophobic interactions were primarily responsible for the conformational changes observed in insulin and alphaS(1)-CN at high SDS concentrations, resulting in increased binding of SDS and alphaS(1)-CN to insulin and its reduced aggregation.

Polyelectrolyte complex of chondroitin sulfate and peptide with lower pI value in poly(lactide-co-glycolide) microsphere for stability and controlled release

A polyelectrolyte complex between a therapeutic peptide and chargeable polymer was applied to prevent peptide denaturation in poly(lactide-co-glycolide) (PLGA) microspheres. Chondroitin sulfate A (CsA) was employed as a polymeric additive for the formation of an ionic complex with insulin (InS). The complex prepared at pH 3.0 evidenced a nano-size in the range of 100-400 nm with a mono distribution. The stability of InS in the complex in an organic/water (O/W) interface was verified via RP-HPLC. The insulin in the complex evidenced a retention time almost identical to native InS, whereas free insulin did not evidence such a retention time. On the basis of these studies, PLGA microspheres including a complex with various CsA/InS ratios were prepared via a double-emulsion method (PLGA/CsA MS). InS loading efficiency in the system is higher than that of the microspheres without CsA. The system evidenced a lower initial burst and, following the initial burst, continuous release kinetics for 30 days. Circular dichroism (CD) spectra demonstrated that the insulin in PLGA/CsA MS is more stable than the PLGA-only microspheres (PLGA/only MS) for 20 days. These results indicate that the complex system with CsA is useful for the long-term delivery of peptides with lower pI values.

Development of protein delivery microsphere system by a novel S/O/O/W multi-emulsion

A novel method has been developed to protect protein drugs in poly (lactic-co-glycolic acid) (PLGA) microspheres using S/O/O/W multi-emulsion method. This method develops a novel protein drug sustained-release system, which is based on the combination of protein-loaded dextran glassy microparticles (protein-loaded AqueSpheres) and PLGA microspheres. The protein molecules are encapsulated in the dextran glassy particles and the drug-containing dextran glassy particles are further dispersed in the PLGA microspheres. The protein-loaded AqueSpheres based PLGA composite microspheres have spherical shape and a smooth surface. They possess a normal size distribution and a mean diameter of 67.08 microm. The method may decrease protein aggregations and incomplete release due to avoiding protein contacting with oil/water interfaces and hydrophobic PLGA. The dextran glassy particles can stabilize proteins in the PLGA matrix, which is the major advantage of this novel protein sustained-release system over preparation for the PLGA microspheres using W/O/W double-emulsion method.

Antihyperglycemic effect of insulin from self-dissolving micropiles in dogs

As a percutaneous delivery device, self-dissolving micropiles (SDMPs) composed of chondroitin sulfate and insulin were prepared under room temperature from highly concentrated solution, glue. The mean weight of SDMP was 1.03+/-0.04 mg. One insulin SDMP was percutaneously administered to the shaved abdominal skin of four beagle dogs at insulin dose level of 1.0 and 2.0 IU/dog. After administration, blood samples were collected for 6 h and plasma glucose levels were measured. The time when minimum plasma glucose level appeared, T(min), was 1.38+/-0.2 h for 1.0 IU study and 1.38+/-0.1 h for 2.0 IU study and clear dose-dependent hypoglycemic effect of insulin was observed in the dose range. By comparing the area above the plasma glucose level vs. time curve (AAC) between insulin SDMP and subcutaneous (s.c.) injection solution, the relative pharmacological availabilities were 99% (1.0 IU) and 90% (2.0 IU), respectively. To ascertain the usefulness of insulin SDMP, oral glucose tolerance test (OGTT) was performed. When dogs were treated with insulin SDMPs, 2.0 IU, followed by an OGTT 30 min, glycemia did not appear for 5 h. On the other hand, when OGTT was performed at 1 h after insulin SDMP administration, hypoglycemia appeared as in the case of s.c. injection of insulin solution, 2.0 IU. Insulin SDMP improved the oral glucose challenge for 3 h, with a maximum effect at 30 min before the administration of glucose. Those results suggest the usefulness of a SDMP for the percutaneous delivery of peptide/protein drugs like insulin.

Structure of human insulin monomer in water/acetonitrile solution

Here we present evidence that in water/acetonitrile solvent detailed structural and dynamic information can be obtained for important proteins that are naturally present as oligomers under native conditions. An NMR-derived human insulin monomer structure in H2O/CD3CN, 65/35 vol%, pH 3.6 is presented and compared with the available X-ray structure of a monomer that forms part of a hexamer (Acta Crystallogr. 2003 Sec. D59, 474) and with NMR structures in water and organic cosolvent. Detailed analysis using PFGSE NMR, temperature-dependent NMR, dilution experiments and CSI proves that the structure is monomeric in the concentration and temperature ranges 0.1-3 mM and 10-30 degrees C, respectively. The presence of long-range interstrand NOEs, as found in the crystal structure of the monomer, provides the evidence for conservation of the tertiary structure. Starting from structures calculated by the program CYANA, two different molecular dynamics simulated annealing refinement protocols were applied, either using the program AMBER in vacuum (AMBER_VC), or including a generalized Born solvent model (AMBER_GB).

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).

Adsorption of human insulin and AspB28 insulin on a PTFE-like surface

The interactions of human insulin, Zn-free human insulin, and AspB28 insulin with a hydrophobic surface were studied by ellipsometry. All three insulin types investigated adsorbed with high affinity onto the hydrophobic surface, as the plateau of the adsorption isotherm, represented by the irreversible bound fraction, was reached at concentrations >10(-3) mg/ml. The plateau values for human insulin and Zn-free human insulin could not be distinguished with statistical significance, whereas the plateau value for AspB28 insulin was lower than those for the two others, with an adsorbed amount corresponding to a monolayer of insulin monomers. The results observed may be explained by differences in self-association patterns of the insulin types or by enhanced charge repulsion between the AspB28 analog and the negatively charged surface.

Interfacial adsorption of insulin

The adsorption of human insulin to Teflon particles was studied with respect to conformational changes and the reversibility of adsorption was examined by total internal reflection fluorescence (TIRF). Adsorption isotherms for the adsorption of human insulin indicated high affinity adsorption, even at electrostatic repulsive conditions. The plateau value for adsorption was in accordance with a protein layer consisting primarily of insulin monomers. Conformational changes of the insulin upon adsorption, was investigated by circular dicroism (CD) and fluorescence spectroscopy. The results suggested unfolding of adsorbed insulin, as observed by a decrease in alpha-helix and increase in random coil conformation. The changes in protein structure was not only related to the adsorbed species being monomeric, since CD and fluorescence results were different for adsorbed insulin compared to a monomeric analog of human insulin. Furthermore, the thermal stability in the adsorbed state was changed compared to insulin in solution. On the basis of the TIRF studies with FITC-labelled insulin it was not possible to firmly conclude whether exchange between human insulin in the adsorbed state and in solution takes place, due to the limited time range investigated. However, the desorption mechanism appeared to be different with unlabelled insulin in the bulk solution compared to phosphate buffer.

Release of albumin from oligoester plastic matrices: effect of magnesium oxide and bivalent stearates

Biodegradable implantable matrices containing bovine serum albumin were prepared from oligoesters by melting, and subsequently tested on in vitro albumin release. The linear poly (DL-lactic acid) and the branched terpolymer of DL-lactic acid, glycolic acid, and mannitol were synthesized. Products were of similar molecular weight and possessed different thermal and swelling characteristics. Oligoesters were loaded with 4% albumin and plasticized by 30% triacetin. Other additives added into the matrices as albumin stabilizers were divalent stearates and magnesium oxide. The influences of oligomer molecules constitution, divalent ion stearates or magnesium oxide addition, and triacetin concentration on the albumin release were quantified. SDS-PAGE revealed protein hydrolysis during the dissolution tests.

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.