Development of a lyophilized plasmid/LPEI polyplex formulation with long-term stability--A step closer from promising technology to application

Cationic polymer/DNA complexes are limited by their instability in aqueous suspensions and usually have to be freshly prepared prior to administration. Thus, the development of isotonic lyophilized polyplex formulations with long-term stability is a desirable goal. Polyplexes based on 22kDa linear polyethylenimine were prepared using a micro-mixer method. Freeze-thawing and lyophilization were performed on a pilot scale freeze-drier. Several excipients (trehalose, sucrose, lactosucrose, dextran, hydroxypropylbetadex or povidone and combinations thereof) at varying concentrations were evaluated for their stabilizing potential against freezing and dehydration induced stresses. For stability testing the lyophilized samples were stored for 6 weeks at 2-8°C, 20°C and 40°C, respectively. Polyplex samples were characterized for particle size, zeta potential, their in vitro transfection efficiency and metabolic activity in Neuro2A cells. In addition, liquid samples were investigated for turbidity and number of sub-visible particles and solid samples were analyzed for residual moisture content, glass transition temperature and sample morphology. L-histidine buffer pH 6.0 was selected as effective buffer. In isotonic formulations with 14% lactosucrose, 10% hydroxypropylbetadex/6.5% sucrose or 10% povidone/6.3% sucrose, particle size was <170nm for all formulations and did not change after storage for 6weeks at 40°C. Polyplexes formulated with lactosucrose or hydroxypropylbetadex/sucrose showed high transfection efficiencies and cellular metabolic activities. Absence of large aggregates was indicated by turbidity and subvisible particle number measurements. The current standard limits for particulate contamination for small volume parenterals were met for all formulations. All samples were amorphous with low residual moisture levels (<1.3%) and high glass transition temperatures (>90°C).

The establishment of an up-scaled micro-mixer method allows the standardized and reproducible preparation of well-defined plasmid/LPEI polyplexes

Polyplexes based on linear polyethylenimine (LPEI) and plasmid DNA are known as efficient non-viral gene delivery systems. However, the requirement for freshly prepared complexes prior to administration due to their instability in aqueous suspension poses the risk of batch-to-batch variations. Therefore, the aim of the study was the establishment of a reproducible and up-scalable method for the preparation of well-defined polyplexes. Polyplexes consisting of pCMVLuc plasmid and 22 kDa linear polyethylenimine (LPEI) were prepared by classical pipetting or with a micro-mixer method using different mixing speeds and plasmid DNA concentrations (20-400 μg/mL). The z-average diameter of the polyplexes was measured by dynamic light scattering. Metabolic activity and transfection efficiency was evaluated on murine neuroblastoma cells after transfection with polyplexes. When varying mixing speeds of the micro-mixer, polyplex size (59-197 nm) and polydispersity index (0.05-0.19) could be directly controlled. The z-average diameter (65-170 nm) and polydispersity index (0.05-0.22) of the polyplexes increased with increasing plasmid DNA concentration (20-400 μg/mL). The established up-scaled micro-mixer method allows the standardized and reproducible preparation of well-defined, transfection-competent plasmid/LPEI polyplexes with high reproducibility.

New insights into the pore structure of poly(d,l-lactide-co-glycolide) microspheres

The objective of this work was to develop a fast and significant method for the determination of the intraparticulate pore size distribution of microspheres. Poly(lactide-co-glycolide) (PLGA) microspheres prepared with a solvent extraction/evaporation process were studied. From the envelope and the skeletal volume of the microspheres the porosity was calculated. The skeletal volume was determined with nitrogen and helium pycnometry and mercury intrusion porosimetry. Based on single particle optical sensing (SPOS) a novel method was developed by which the envelope volume is calculated from the particle size distribution (PSD), provided that all particles have a spherical shape. The penetration capacity of the applied intrusion media is limited by their atomic or molecular diameter or by the surface tension and the pressure in case of mercury. A classification of the pore structure was obtained by comparing these different skeletal values with the values for the envelope volume. Two well separated pore fractions were found, a nanoporous fraction smaller than 0.36nm and a macroporous fraction larger than 3.9μm. The total porosity and the ratio between both fractions is controlled by the preparation process and was shown to depend on the solvent extraction temperature.

Synthesis, characterization and assessment of suitability of trehalose fatty acid esters as alternatives for polysorbates in protein formulation

Nonionic polyethylene glycol-derived surfactants are today's choice as surfactants in protein formulations. Different groups discovered that although surface-induced stresses are reduced by these excipients, the long-term stability of different proteins decreased due to polyethylene glycol-related induction of oxidation processes under static storage conditions. In this paper, the potential of polyoxyethylene-free surfactants for protein formulation was evaluated. Three different sugar-based surfactants, 6-O-monocaprinoyl-α,α-trehalose, 6-O-monolauroyl-α,α-trehalose and 6-O-monopalmitoyl-α,α-trehalose, were synthesized in four reaction steps. These substances lack polyethylene glycol residues and can be produced from renewable resources. The chemical and physical properties of these three surfactants were investigated and compared with polysorbate 20 and 80. 6-O-monopalmitoyl-α,α-trehalose was insoluble in water at room temperature and was hence excluded from some of the further tests. The critical micellar concentration of all surfactants is in a comparable range of approximately 0.001-0.01% (m/V). The sugar-based surfactants showed slightly higher hemolytic activity than the polysorbate references. The surfactants with shorter chain length proved to be comparable to polysorbates in regard to physicochemical properties. Finally for human growth hormone, the protein-stabilizing properties against shaking-induced stress were tested and compared to polysorbate-containing formulations. Whereas in the absence of surfactant, dramatic monomer loss and aggregate formation occurred, it was found that 100% monomer content was maintained when 0.1% (m/V) 6-O-monocaprinoyl-α,α-trehalose or 6-O-monolauroyl-α,α-trehalose was added to the formulation. Polysorbate 80 at a concentration of 0.1% (m/V) also significantly stabilized the protein. Lower amounts of surfactants result in only partial stabilization. Furthermore, adsorption of human growth hormone to the container surface is reduced in the presence of the surfactants. Thus, the new sugar-based surfactants offer a promising alternative and have potential for application in protein formulations.

Protein aggregation: pathways, induction factors and analysis

Control and analysis of protein aggregation is an increasing challenge to pharmaceutical research and development. Due to the nature of protein interactions, protein aggregation may occur at various points throughout the lifetime of a protein and may be of different quantity and quality such as size, shape, morphology. It is therefore important to understand the interactions, causes and analyses of such aggregates in order to control protein aggregation to enable successful products. This review gives a short outline of currently discussed pathways and induction methods for protein aggregation and describes currently employed set of analytical techniques and emerging technologies for aggregate detection, characterization and quantification. A major challenge for the analysis of protein aggregates is that no single analytical method exists to cover the entire size range or type of aggregates which may appear. Each analytical method not only shows its specific advantages but also has its limitations. The limits of detection and the possibility of creating artifacts through sample preparation by inducing or destroying aggregates need to be considered with each method used. Therefore, it may also be advisable to carefully compare analytical results of orthogonal methods for similar size ranges to evaluate method performance.

Formulation Development for Hydrophobic Therapeutic Proteins

The major challenges in formulation development for hydrophobic proteins are low solubility often combined with a strong tendency for adsorption. Human serum albumin (HSA) is frequently used as excipient to overcome these problems. Due to several drawbacks with HSA, new ways need to be found to circumvent the use of this excipient in protein formulations. One possible approach is to select an appropriate formulation pH and ionic strength in combination with excipients that provide sufficient stability and solubility for the hydrophobic protein. A reduction in adsorption can be achieved by adding surfactants or using special containers.

Online fluorescent dye detection method for the characterization of immunoglobulin G aggregation by size exclusion chromatography and asymmetrical flow field flow fractionation

The aim of this study was to develop an online fluorescent dye detection method suitable for high-pressure size exclusion chromatography (HP-SEC) and asymmetrical flow field flow fractionation (AF4). The noncovalent extrinsic fluorescent dye 4,4'-dianilino-1,1'-binaphthyl-5,5'-disulfonic acid (Bis-ANS) was added to the mobile phase or the sample, and the fluorescence emission at 488nm was recorded on excitation at 385nm. By combining HP-SEC and AF4 with online dye detection, it was possible to simultaneously detect heat-induced aggregation and structural changes of monomeric and aggregated immunoglobulin G (IgG); an increase in Bis-ANS fluorescence was observed in both the aggregate and monomer fractions. These structural changes of individual fractions, which were not detectable by online UV and multiangle laser light scattering (MALLS) or by stand-alone dynamic light scattering (DLS), intrinsic IgG fluorescence, and far-UV circular dichroism (CD), resulted in progressive aggregation on storage. The developed online fluorescent dye detection for HP-SEC or AF4 with Bis-ANS is a powerful method to detect both aggregation and structural changes of both monomeric and aggregated IgG in heat-stressed formulations.

Stabilization of a hydrophobic recombinant cytokine by human serum albumin

The objective was to evaluate the impact of pH and NaCl content on aggregation, particle formation, and solubility of a hydrophobic recombinant human cytokine in formulations with human serum albumin (HSA) as stabilizing excipient. While cytokine-HSA formulations were stable at physiological pH, a tremendous increase in turbidity at pH 5.0, close to the isoelectric point of HSA was caused by a partially irreversible precipitation. By dynamic light scattering (DLS), disc centrifugation, atomic force microscopy (AFM), and light obscuration it could be shown that the turbidity was mainly caused by particles larger than 120 nm. SDS-PAGE provided evidence that the precipitation at pH 5.0 was mainly caused by the cytokine. The HSA-stabilizers Na-octanoate and Na-N-acetyltryptophante were less effective in preventing the turbidity increase of unstabilized-HSA compared to NaCl. The interactions between HSA and cytokine were weakened by NaCl, as determined by fluorescence spectroscopy. The positive effect of NaCl on the formulation could be attributed to a direct stabilization of HSA and weaker interactions between HSA and the cytokine, which in consequence provided an overall stabilization of the cytokine.

A model describing the effect of enzymatic degradation on drug release from collagen minirods

A drug delivery system, named minirod, containing insoluble non-cross-linked collagen was prepared to investigate the release of model drug compounds. To characterise the complete drug release process properly, a mathematical model was developed. Previously, a mathematical model describing water penetration, matrix swelling and drug release by diffusion from dense collagen matrices has been introduced and tested. However, enzymatic matrix degradation influences the drug release as well. Based on experimental data, a model was developed which describes drug release by collagenolytic matrix degradation based on enzyme diffusion, adsorption and cleavage. Data for swelling, collagen degradation and FITC dextran release from insoluble equine collagen type I minirods were collected. Sorption studies demonstrated a tight sorption of collagenase on collagen surfaces that follows a Freundlich sorption isotherm and results in a degradation constant of 3.8x10(-5) mol/l for the minirods. The diffusion coefficients of FITC dextran 20 and 70 (3x10(-3) and 2.4x10(-3) cm2/h) in water were analyzed by fluorescence correlation spectroscopy (FCS). Using these data, the mathematical model was verified by two-dimensional simulations. The numerical results agreed well with the measurements.

In vitro binding of matrix metalloproteinase-2 (MMP-2), MMP-9, and bacterial collagenase on collagenous wound dressings

Chronic wounds are characterized by failure in wound-healing response and a delay in healing or nonclosure of the wounds. This results in a high effort in clinical treatment and/or home care. A major difference between acute wounds and chronic wounds is the imbalance of proteinase inhibitors and proteinase activity that regulates the degradation and regeneration of the extracellular matrix proteins. Collagen and collagen/oxidized regenerated cellulose dressings act as a competitive substrate for matrix metalloproteinase-2, matrix metalloproteinase-9, and bacterial collagenase and influence this imbalance positively. Both wound dressings, approved for chronic wound treatment, the bovine collagen type I sponge and the oxidized regenerated cellulose collagen sponge, did not differ significantly in their sorption profiles for all enzymes. In general, binding was enhanced with a longer incubation time. The density of the device and the accessible surface, which can be controlled by the manufacturing process, are the crucial factors for the efficiency of the wound dressing.

Development of HSA-free formulations for a hydrophobic cytokine with improved stability

The goal was to characterize a hydrophobic cytokine with respect to oxidation and aggregation, as well as its adsorption to the container at different pH and ionic strength conditions. The tendency of the cytokine to adsorb on surfaces and its low solubility at physiological pH were the main challenges during the development of HSA-free formulations for the cytokine. When the formulation pH exceeded 5.5 precipitation led to significantly higher turbidity. This turbidity increase and elevated aggregation as determined by HP-SEC and DLS was more pronounced at higher glycine and NaCl concentrations. With rising pH protein adsorption was more distinct compared to pH 3.0. However, protein adsorption could be minimized by polysorbate 20 or the use of glass type I(+). FTIR revealed a reduced thermal stability at higher pH values indicated by a declining denaturation temperature. Five liquid formulations in the pH range 3.5-4.5 and five lyophilized formulations at pH 4.0-5.0 were stored for 6 months and the stability was evaluated with respect to aggregation and chemical modification. Liquid formulations at pH 3.5-4.0 and lyophilized formulations at pH 4.0-5.0 were most stable during 6 months at 2-8 degrees C.

Physicochemical characterization of the freezing behavior of mannitol-human serum albumin formulations

The goal of the study was to analyze the impact of human serum albumin (HSA) quality (stabilized or nonstabilized HSA), the addition of NaCl, and the HSA stabilizers Na-octanoate and Na-N-acetyltryptophanate on the freezing behavior of mannitol-HSA formulations. The focus was on crystallization, Tg' (glass transition temperature of the maximally freeze-concentrated phase), and Tc (collapse temperature). Differential scanning calorimetry (DSC), cryomicroscopy, and low-temperature x-ray powder diffraction (LTXRD) were used to study the frozen state. In mannitol-HSA formulations, mannitol crystallization was inhibited and Tg' lowered to a greater extent by stabilized HSA (containing Na-octanoate, Na-N-acetyltryptophanate, and NaCl) than by unstabilized HSA. Detailed DSC and LTXRD studies showed that in the concentrations used for stabilizing HSA, NaCl led to changes in the freezing behavior, an effect that was less pronounced for the other stabilizers. NaCl further lowered the Tc, which was determined by cryomicroscopy. As the freezing behavior governs the lyophilization process, the changes have to be taken into consideration for the development of a lyophilization cycle, to avoid collapse and instabilities.

Impact of freezing procedure and annealing on the physico-chemical properties and the formation of mannitol hydrate in mannitol–sucrose–NaCl formulations

The goal was to investigate the impact of NaCl on the physico-chemical properties of mannitol-sucrose formulations during freezing and drying, with special focus on mannitol hydrate formation. Differential scanning calorimetry (DSC) and low-temperature X-ray powder diffraction (LTXRD) were used to study the frozen solutions. After lyophilization the products were analyzed with DSC, temperature-modulated DSC (TMDSC), X-ray powder diffraction (XRD) and Karl-Fischer titration. DSC showed an inhibition of mannitol crystallization by sucrose and NaCl during freezing. The glass transitions of the maximally freeze-concentrated solutions (Tg') were lowered by both mannitol and NaCl. By the application of an annealing step during lyophilization mannitol crystallinity could be increased. However, lyophilization with an annealing step promoted the formation of mannitol hydrate, which is known to undergo conversion into the anhydrous polymorphs of mannitol upon storage. LTXRD revealed that mannitol hydrate was formed at temperatures below -30 degrees C, but not at -27 degrees C. The tendency that mannitol hydrate is predominantly formed at lower temperature was confirmed by XRD of lyophilized products, produced at different annealing temperatures. For the development of lyophilization cycles the lowered Tg', as well as the tendency to mannitol hydrate formation predominantly at lower temperature needs to be considered.

Conformational analysis of protein secondary structure during spray-drying of antibody/mannitol formulations

Inhalation of spray-dried particles is a promising delivery route for proteins as an alternative to injection. Changes in the protein structure and aggregation have to be avoided. The effect of mannitol, a stabilizing agent typically used in both liquid and lyophilized protein formulations, on an antibody (IgG1) in a spray-dried powder was studied using different biophysical and chromatographic techniques. At first, different solutions composed of antibody (IgG1) and mannitol at a ratio between 20/80 and 100/0 IgG1/mannitol (100 mg/ml total solid) were investigated for their stability. Protein solutions containing the IgG1 showed mannitol-dependent aggregation. High amounts of mannitol (50-80%) exerted a destabilizing effect on the antibody and the aggregate 9 level increased to 2.6-4.2%. In contrast, solutions with only 20-40% mannitol showed the same amount of aggregates as the pure antibody solution. The antibody mannitol solutions were investigated by circular dichroism (CD) and Fourier transform infrared spectroscopy (FTIR) to evaluate whether changes in the protein secondary structure can be correlated with aggregation. Considering the sensitivity of the used methods and data evaluation, FTIR spectra did not reveal structural changes in the IgG1/mannitol solutions compared to the pure antibody, despite varying aggregate levels. Thermal stress was reflected in perturbations of the secondary structure, but mannitol-dependent aggregation could not be correlated to detectable alterations in the FTIR spectra. Analyzing the CD spectra revealed no distinctive change in the shape of the CD curve, indicating that the protein secondary structure is mainly retained. This is in agreement with the infrared data. Subsequently, the IgG1/mannitol solutions were spray-dried at Tin/Tout of 90/50 degrees C. Using ATR-FTIR for the investigation of the protein amide I band in the spray-dried powder revealed changes in the sub-components of the amide I band. This indicates that the peptide groups (CO and NH) of the protein are found in a different environment in the solid state, compared to the liquid protein formulation. After redissolution of the powders, the native structure of the pure antibody solution was found identical to the protein secondary structure before spray-drying, indicating that the protein secondary structure is not strongly altered in the dry state, and not affected by the spray-drying process. Thus, from the presented study it can be concluded that the formation of antibody aggregates in mannitol formulations cannot be correlated with significant perturbations of the protein secondary structure elements.

A Critical Evaluation of Tm(FTIR) Measurements of High-Concentration IgG1 Antibody Formulations as a Formulation Development Tool

PURPOSE

Fourier-transform infrared (FTIR) spectroscopy was applied for the determination of protein melting temperature (Tm(FTIR)) and to assess the stability predictability of a 100-mg/mL liquid IgG1 antibody formulation.

METHODS

Tm(FTIR) values of various formulations (different pH, buffers, excipients) were compared to the results of a stability study under accelerated conditions (40 degrees C/75% relative humidity), using size-exclusion high-performance liquid chromatography (SE-HPLC) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for the detection of soluble aggregates and covalent modifications.

RESULTS

The highest Tm(FTIR) was achieved at pH 5.5, and, similarly, SE-HPLC and SDS-PAGE results suggested a pH optimum between 5.5 and 6.0. Transition temperatures were comparable for all tested buffers. However, the decrease in the monomer fraction upon thermal storage was the lowest for citrate buffers. Whereas sugars and polyols resulted in an increase in Tm(FTIR) and enhanced monomer fraction after storage, amino acids showed a destabilization according to SE-HPLC analysis, albeit no change or even an increase in the melting temperature was observed.

CONCLUSIONS

All examples gave evidence that Tm(FTIR) values did not necessarily correspond to the storage stability at 40 degrees C analyzed by means of SE-HPLC and SDS-PAGE. Tm values, e.g., determined by FTIR, should only be employed as supportive information to the results from both real-time and accelerated stability studies.

Physico-chemical lyophilization behavior of mannitol, human serum albumin formulations

The lyophilization behavior is influenced by the presence of salts. The impact of NaCl on drying-time and the morphology after lyophilization was studied for formulations with mannitol and HSA, using different freezing-protocols. The drying-process was monitored by thermocouples and microbalance technique. Karl-Fischer titration, DSC, XRD, SEM and turbiditimetry and HP-SEC were used to study the products after lyophilization and 6 months storage at 2-8 degrees C, 25 degrees C/60% RH and 40 degrees C/75% RH. NaCl decreases the drying-time of mannitol-HSA formulations, indicating morphological changes, which was confirmed by XRD and SEM. Without NaCl exclusively delta-mannitol is formed, which remains physico-chemically stable upon storage for 6 months. With increasing NaCl concentrations more beta-mannitol and finally amorphous products are formed, whereby the freezing-protocol determines how much NaCl is needed to achieve an amorphous product. Upon storage, the amorphous state cannot be preserved and mannitol and NaCl crystallize, which can damage proteins in the formulations. However, regarding the stability of HSA in the lyophilized products, monitored by turbidimetry and HP-SEC, the addition of NaCl can prevent increases in turbidity upon storage. Here the benefit of NaCl on HSA stability outbalances the potential drawbacks that morphological changes, like crystallization impose on protein stability in the lyophilized products.

Sterilization of gentamicin containing collagen/PLGA microparticle composites

In order to achieve implants which provide sustained release of gentamicin, microparticles based on a 50/50 Resomer 503/Resomer 502H blend were combined with collagen in order to achieve their fixation and to utilize the favorable effect of collagen on wound healing. Ethylene oxide treatment as well as beta- and gamma-irradiation were tested for sterilization of the collagen/PLGA-microparticle composite. All methods resulted in a decrease of molecular weight and glass transition temperature of polymer raw material and microparticles. In addition, ethylene oxide treatment yielded aggregation of microparticles leading to a substantial increase in the initially liberated gentamicin dose. Furthermore, chemical changes of gentamicin after ethylene oxide sterilization could be identified using NMR spectroscopy. Despite a decrease in the molecular weight and glass transition temperature after irradiation, neither morphological changes of the composites nor changes regarding the gentamicin release profile from beta- and gamma-sterilized material were observed. Free radicals, which could only be detected in gentamicin drug substance and at marginal level in gentamicin-loaded MPs, disappeared within 4 weeks. Additional microbiological testing verified the microbiological activity of gentamicin liberated from beta-sterilized composites. Storage of beta-sterilized composite at 4 degrees C/35% r.h. for 3 months did not influence morphology, molecular weight, glass transition temperature, and release profiles of microparticles and composites. However, at 25 degrees C/60% r.h. and 40 degrees C/75% r.h. a marked decrease in molecular weight and glass transition temperature resulted. This effect was due to a higher humidity, water uptake into polymers, and subsequent hydrolysis of polymers and microparticles, which was more pronounced for RG 502H because of its hydrophilicity. Upon storage at 25 degrees C/60% r.h. and 40 degrees C/75% r.h. particles collapsed resulting in an increased gentamicin liberation. Thus, all sterilization techniques have their pros and cons, but based on drug release profile and chemical changes of gentamicin irradiation treatment appears to be more suitable for collagen/gentamicin-loaded PLGA microparticle composites.

FTIR and nDSC as analytical tools for high-concentration protein formulations

PURPOSE

The aim of the study is to evaluate Fourier-transform infrared spectroscopy (FTIR) as an analytical tool for high-concentrated protein formulations.

METHODS

FTIR is used to determine the melting temperature (T(m (FTIR))) of various proteins, such as bovine serum albumin (BSA), immunoglobulin (IgG1), beta-lactoglobulin (beta-LG), and lysozyme (HEWL), at different protein concentrations (5-100 mg/mL), where four data interpretation methods are discussed. The obtained T(m (FTIR)) values are further compared to the T(m) measured by the nanodifferential scanning calorimetry (nDSC) technique.

RESULTS

The T(m (FTIR)) values of IgG1 and beta-LG showed strong consistency and corresponded to the nDSC results irrespective of the method of data interpretation and the protein concentration applied. In contrast, the T(m (FTIR)) of BSA and HEWL is characterized by significant deviations. Only the midpoint of the second-derivative intensity-temperature curve of the intermolecular beta-sheet mode measured at a concentration of 100 mg/mL is consistent with the nDSC results.

CONCLUSIONS

Determination of a T(m (FTIR)) is feasible by the midpoint of the intensity-temperature plot of the arising intermolecular beta-sheet band. More significant results are obtained for proteins, which are predominantly composed of intramolecular beta-sheet elements as well as at higher protein concentrations. A further study was started to assess the predictability of long-term protein stability by T(m (FTIR)).

Integrity and stability studies of precipitated rhBMP-2 microparticles with a focus on ATR-FTIR measurements

A major obstacle in the development of protein drug formulations is the need to maintain the native, active protein structure both during the formulation process and upon long time storage. Controlled precipitation was evaluated for its potential to supply stable microparticulate formulations of bone-regenerating recombinant human Bone Morphogenetic Protein-2 (rhBMP-2). Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) did provide insight into the protein formulation and stability. Temperature dependent ATR-FTIR measurements and DSC measurements allow for the study of changes in the protein structure during melting. To address the question of isomerization, peptide mapping was performed, and protein aggregation was monitored by size exclusion chromatography (SEC). It could be demonstrated by ATR-FTIR that controlled precipitation did not harm the protein and the process is fully reversible. DSC measurements further confirmed these findings. No changes in the transition temperature and process were observed after precipitation and redissolution. Upon storage, isomerization and aggregation could be detected, but to a lower extent in the precipitated formulation as compared to a solution reference. Thus, controlled precipitation of rhBMP-2 is fully reversible and has the potential as alternative formulation tool for the generation of a microparticulate drug delivery system.

Induction and analysis of aggregates in a liquid IgG1-antibody formulation

The objective of this study was to compare different agitation stress methods (stirring in Reacti Vials versus horizontal shaking) in their effect on protein destabilization, to assess several analytical techniques (light obscuration, turbidimetric and light scattering analysis) for detection of aggregates of various sizes and to evaluate the protecting effect of polysorbate 80 on protein aggregation. A monoclonal IgG1 antibody was used as model protein. Both mechanical stress methods can provoke aggregate formation. The method of stirring induces particles in the range of 10-25 microm comparable to shaking stress. However, stirred samples show a much higher absorbance and reveal a second particle species in DLS analysis, suggesting that stirring stress induces a higher amount of smaller protein aggregates. Addition of polysorbate 80 protects the antibody against aggregation. Only in stirred samples a slight increase in sub-visible particles and turbidity was noted. However, a greater extent of aggregation products was detected by DLS as compared to surfactant-free formulations. Thus, polysorbate 80 appears to stabilise small aggregates and prevents further proceeding of the aggregation process. The induction of aggregates by stirring stress in Reacti Vials analysed by absorbance measurement seems to be a good combination for high-throughput formulation studies.

Zinc gluconate in the treatment of dysgeusia--a randomized clinical trial

In the treatment of dysgeusia, the use of zinc has been frequently tried, with equivocal results. The aim of the present randomized clinical trial, which involved a sufficiently large sample, was therefore to determine the efficacy of zinc treatment. Fifty patients with idiopathic dysgeusia were carefully selected. Zinc gluconate (140 mg/day; n=26) or placebo (lactose; n=24) was randomly assigned to the patients. The patients on zinc improved in terms of gustatory function (p <0.001) and rated the dysgeusia as being less severe (p <0.05). Similarly, signs of depression in the zinc group were less severe (Beck Depression Inventory, p <0.05; mood scale, p <0.05). With the exception of the salivary calcium level, which was higher in the zinc patients (p <0.05), no other significant group differences were found. In conclusion, zinc appears to improve general gustatory function and, consequently, general mood scores in dysgeusia patients.

Collagen sponges for bone regeneration with rhBMP-2

In the US alone, approximately 500,000 patients annually undergo surgical procedures to treat bone fractures, alleviate severe back pain through spinal fusion procedures, or promote healing of non-unions. Many of these procedures involve the use of bone graft substitutes. An alternative to bone grafts are the bone morphogenetic proteins (BMPs), which have been shown to induce bone formation. For optimal effect, BMPs must be combined with an adequate matrix, which serves to prolong the residence time of the protein and, in some instances, as support for the invading osteoprogenitor cells. Several factors involved in the preparation of adequate matrices, specifically collagen sponges, were investigated in order to test the performance in a new role as an implant providing local delivery of an osteoinductive differentiation factor. Another focus of this review is the current system consisting of a combination of recombinant human BMP-2 (rhBMP-2) and an absorbable collagen sponge (ACS). The efficacy and safety of the combination has been clearly proven in both animal and human trials.

Collagen as a carrier for on-site delivery of antibacterial drugs

Due to its biocompatibility and well-established safety profile, collagen represents a favourable matrix for on-site drug delivery. In this review, we summarize some of the recent developments and applications of collagen as a biomaterial in drug delivery systems for antibiotics, especially gentamicin. The main clinical and experimental applications covered include: treatment and prophylaxis of bone and soft tissue infections, wound healing, as well as ophthalmic and periodontal treatment. Advantages of local drug application and the rationale of use local drug delivery systems for adjuvant (ancillary) therapy are discussed. Recent efforts in the use of collagen and collagen-synthetic polymer composites for controlled drug delivery as well as collagen-based diffusion membranes for prolonged drug release have also been included in this review.

Collagen/PLGA Microparticle Composites for Local Controlled Delivery of Gentamicin

To preserve the positive effect of collagen on tissue regeneration and to locally deliver low molecular weight compounds for an extended time period, a composite for parenteral application was devised based on a collagen sponge with gentamicin-loaded PLGA microparticles incorporated. Antibiotic liberation from the particles was sustained over 1 week by blending two PLGA polymers. Homogenous incorporation of the microspheres in the porous carrier could be realized by lyophilization of a particle suspension in the aqueous collagen preparation. Particle loss upon incubation was reduced with higher collagen concentration enabling local particle retention after application. Lower freezing rate and longer exposure of the PLGA microparticles to the acidic collagen dispersion at temperatures below the glass transition temperature resulted in an increase of the gentamicin burst. The final implant containing both nonencapsulated gentamicin and an equivalent amount incorporated in the microparticles reflected the microbiological demands and exhibited liberation of a high gentamicin dose initially and subsequently extended antibiotic liberation for about one week.

Mechanical properties and in vitro cell compatibility of hydroxyapatite ceramics with graded pore structure

In order to improve the mechanical strength of hydroxyapatite (HA) ceramics used as osteoimplants and to enhance cellular penetration functionally graded ceramics with a transition in porosity from the surface towards the centre were designed. The multilayer structures were prepared by multiple tape casting based on an aqueous HA slurry containing polybutylmethacrylate (PBMA) spheres with diameters ranging from 100 to 300 microns. After burning out the PBMA, pores of 70-200 microns were generated. The pore-graded laminates were sintered at temperatures between 1250 degrees C and 1450 degrees C. Bending strength of the pore-graded ceramics was approximately 50% higher as compared to HA of the same pore volume fraction but without gradient structure. The materials were tested in vitro for attachment and activity of osteoblast-like MC3T3-E1 cells over a period of 3 weeks. Cells formed confluent layers on the ceramic surface, penetrated into the graded porosity ranging from 100-150 microns to 250-300 microns in size and showed increasing alkaline phosphatase activity over 3 weeks. The results demonstrated initial in vitro cell compatibility of the functionally graded HA materials and their potential as osteoimplants.

Modifying the release of gentamicin from microparticles using a PLGA blend

Carrier systems for local gentamicin (GS) treatment based on collagen sponges and polymethylmethacrylate beads show pharmacokinetic disadvantages in their GS-release profiles. Therefore, poly(lactic-co-glycolic acid) (PLGA) microparticles were devised. None of the five poly(alpha-hydroxy acid)s tested resulted in the desired antibiotic release over approximately one week. However, preparing microparticles from a 50/50 blend of Resomer RG 502H, an uncapped variety, and Resomer RG 503, an endcapped polymer, yielded the targeted liberation profile. The mechanism of GS release was investigated by analyzing water uptake and polymer molecular weight. Release of GS from RG 502H particles occurred instantaneously and coincided with substantial water penetration. Particles prepared from RG 503 started out at a higher molecular weight and since the endcapped polymer takes up less water, the decrease in molecular weight was delayed. The threshold of collapse was reached after two weeks, which coincided with water penetration and GS release. For the 50/50 RG 502H/RG 503 blend, this process was delayed for two to three days. Hydrolysis occurred at the same rate as for RG 502H due to the high water content as a consequence of the uncapped polymer fraction and renders GS release over one week with release limited to 30% in the first two days due to the endcapped polymer fraction of higher molecular weight. Thus, the mixture of endcapped and uncapped Resome exhibits a new quality for adjusting drug release from poly(alpha-hydroxy acid)s.

Release mechanisms from gentamicin loaded poly(lactic-co-glycolic acid) (PLGA) microparticles

To provide local gentamicin delivery for 1 week based on a biodegradable system, poly(lactic-co-glycolic acid) (PLGA) microparticles were developed utilizing a 50/50 blend of Resomer RG 502H, an uncapped variety of 13.5 kD, and Resomer RG 503, an endcapped polymer of 36.2 kD. The liberation mechanism was investigated by analysis of morphological changes and thermal analysis focusing on the polymer glass transition temperature (T(g)) and the mechanical properties. The release of gentamicin was related to a structural breakdown of the particles reaching a critical molecular weight. A T(g) of < 37 degrees C in the hydrated state was not indicative of collapse and agglomeration of the particles because the mechanical strength of the polymer structures in the rubbery state may still render sufficient support. As the gap between incubation temperature and T(g) widened, the mechanical stability of the PLGA microparticles decreased and became decisive. Particles prepared with RG 502H show a lower ability to bear mechanical stress than RG 503 and 50/50 RG 502H/RG 503 microparticles.

Delivery systems for BMPs: factors contributing to protein retention at an application site

BACKGROUND

Recombinant human bone morphogenetic proteins (rhBMPs) are being tested in clinical studies for their capacity to elicit bone formation. Biomaterials used in delivery systems also play a critical role in supporting the osteoinductive activity of BMPs, attributable to the controlled presentation of the BMPs to target cells. Despite extensive preclinical studies, the factors contributing to local rhBMP pharmacokinetics remain to be elucidated.

METHODS

The rhBMP pharmacokinetics were studied in a rat subcutaneous implant and in an intramuscular injection model. In situ levels of rhBMPs were quantitated with use of 125I-labeled tracers. The effects of protein structural features and the nature of the biomaterial implant were explored. Osteoinduction by biomaterial+rhBMP combinations was assessed by a semiquantitative, histology-based bone score.

RESULTS

With the use of rhBMP-2, rhBMP-4, and an N-truncated rhBMP-2, the protein isoelectric point was found critical for the initial retention of rhBMPs in an implant. Osteoinduction studies carried out in parallel indicated that rhBMPs with a higher implant retention elicited more bone formation. In the clinically used collagen+rhBMP-2 device, collagen crosslinking and sterilization were most influential in rhBMP-2 retention. To increase retention at an application site, thermoreversible polymers were engineered and shown to enhance local rhBMP-2 retention, especially by injectable delivery.

CONCLUSIONS

Two critical components of an osteoinductive device--namely, the biomaterial and the rhBMP--were shown to influence local protein pharmacokinetics and osteoinductive activity of the device. Designer biomaterials can provide an additional mechanism to modulate local protein pharmacokinetics.

CLINICAL RELEVANCE

These studies form the foundation of next-generation osteoinductive devices with improved potency at sites of desired bone regeneration and reduced side effects at other sites.

Effects of processing conditions on the rheological behavior of collagen dispersions

Biomedical collagen preparations are mainly based on liquid aqueous preparations either used directly as injectables or transferred for example into solid implants or porous devices. In all cases the viscosity of the dispersion or solution has to be controlled or adjusted by pH, temperature, collagen concentration or crosslinking. We tested these effects on the rheological and structural properties of collagen fiber dispersions focusing on oscillatory rheometry. With increasing difference between pH and pI viscosity increased and went through a maximum with less rigidity of the fibers. The dispersions acted like a predominantly permanently linked network. This character changed to only partially linked at low collagen concentration due to isolation of the individual fibers. Up to 40 degrees C, temperature is a tool suitable for adjusting viscosity without changes in the network structure. At 50 degrees C, fourier transform - infrared spectroscopy (FT-IR) spectroscopy indicated the transition of the helical into random coil structure. Renaturation of the helices was found upon cooling but atomic force microscopy (AFM) indicated severe temperature induced damages of the fibers. Crosslinking with glutaraldehyde (GTA) leads to an increase in viscosity and the effect on the network structure depends on the processing conditions.

Characterization of absorbable collagen sponges as rhBMP-2 carriers

For clinical use recombinant human bone morphogenetic protein (rhBMP-2) is soaked onto an absorbable collagen sponge (ACS) for bone regeneration. Therefore, loss of rhBMP-2 upon mechanical handling during implantation and a potential effect of the carrier on in vivo retention is of interest. The interactions between drug and carrier were looked at from the application mode and the amount of protein which can be mechanically expressed from the combination was investigated. The results indicated that rhBMP-2 binds to the collagen system. The most hydrophilic double extended homodimer showed the least binding affinity to ACS. By extending the waiting time between soaking and implantation, protein incorporation could be increased. In addition, the amount of rhBMP-2 which could be expressed was reduced by heavier ACS material and allowed for a shorter waiting period, especially at lower rhBMP-2 concentration. Crosslinking of ACS with formaldehyde led to reduced binding of rhBMP-2 to collagen either by direct hindrance of binding or reduction in swelling and number of binding sites available. Higher product pH or anion concentration enabled to increase rhBMP-2 incorporation but was limited by the potential precipitation of rhBMP-2. Despite a variety of chemical changes of ACS by ethylene oxide sterilization incorporation was not changed significantly. The in vivo release kinetics of 125I-rhBMP-2 from the collagen sponge were studied using a rat ectopic implant model. The ACS/rhBMP-2 systems tested demonstrated small, but significant differences in the in vivo retention of rhBMP-2. Consequently, it is important to have as little variability in pH, anion concentration, crosslinking and ACS mass as possible to achieve consistent or maximum binding and to avoid rhBMP-2 precipitation. Furthermore, these characteristics can be important for other in vivo applications.

Characterization of absorbable collagen sponges as recombinant human bone morphogenetic protein-2 carriers

For clinical use recombinant human bone morphogenetic protein-2 (rhBMP-2) is soaked onto an absorbable collagen sponge (ACS) for bone regeneration. Therefore, loss of rhBMP-2 upon mechanical handling during implantation and a potential effect of the carrier on in vivo retention is of interest. The interactions between drug and carrier were looked at from the application mode and the amount of protein which can be mechanically expressed from the combination was investigated. The results indicated that rhBMP-2 binds to the collagen system. The most hydrophilic double extended homodimer showed the least binding affinity to ACS. By extending the waiting time between soaking and implantation, protein incorporation could be increased. In addition, the amount of rhBMP-2 which could be expressed was reduced by heavier ACS material and allowed for a shorter waiting period, especially at lower rhBMP-2 concentration. Crosslinking of ACS with formaldehyde led to reduced binding of rhBMP-2 to collagen either by direct hindrance of binding or reduction in swelling and number of binding sites available. Higher product pH or anion concentration enabled to increase rhBMP-2 incorporation but was limited by the potential precipitation of rhBMP-2. Despite a variety of chemical changes of ACS by ethylene oxide sterilization incorporation was not changed significantly. The in vivo release kinetics of (125)I-rhBMP-2 from the collagen sponge were studied using a rat ectopic implant model. The ACS/rhBMP-2 systems tested demonstrated small but significant differences in the in vivo retention of rhBMP-2. Consequently, it is important to have as little variability in pH, anion concentration, crosslinking, and ACS mass as possible to achieve consistent or maximum binding and to avoid rhBMP-2 precipitation. Furthermore, these characteristics can be important for other in vivo applications.

Bone regeneration with recombinant human bone morphogenetic protein-2 (rhBMP-2) using absorbable collagen sponges (ACS): influence of processing on ACS characteristics and formulation

The effects of variability in three parameters (mass, cross-linking with CH2O, and EtO sterilization) of three surgically implantable absorbable collagen sponges (ACS) were studied. Sponges soaked with recombinant human bone morphogenetic protein-2 (rhBMP-2) solution were analyzed for pH, conductivity, and rhBMP-2 precipitation. A method using trinitrobenzenesulfonic acid was developed to quantify the free amino groups of the collagen sponge. With up to 240 min exposure to CH2O, the amount of free amino groups was reduced to 80%. In comparison, the denaturation temperature as determined by differential scanning calorimetry (DSC) after the sponges were soaked with phosphate-buffered saline, increased from 48 to 55 degrees C, indicating stronger interactions due to cross-linking. Subsequent sterilization with EtO caused a marked decrease in the amount of free amino groups (approximately 33% of nonsterilized controls) independent of previous CH2O treatment. However, the denaturation temperature was on average 5 degrees C lower in sterilized sponges than in nonsterilized material. In contrast to CH2O exposure, the strong reaction with EtO appeared to weaken the collagen structure. Resistance of the sponge to collagenase correlated with the degree of collagen cross-linking but was slightly reduced by sterilization. In addition, the pH of ACS soaked with water was substantially increased by sterilization. Protein precipitation was a function of pH and salt concentration but there was no effect due to collagen alone. Results indicated that ACS weight has to be limited to avoid rhBMP-2 precipitation.

rhBMP-collagen sponges as osteoinductive devices: effects of in vitro sponge characteristics and protein pI on in vivo rhBMP pharmacokinetics

Osteoinductive devices, comprised of biodegradable collagen scaffolds and recombinant human Bone Morphogenetic Proteins (rhBMPs), are being currently pursued for local bone induction. To better understand the biological performance of such devices, we have carried out a series of studies to investigate the effects of sponge properties and protein structural features on the pharmacokinetics of implanted rhBMPs. The results indicated little dependence of the rhBMP-2 pharmacokinetics on the in vitro determined sponge properties. The protein isoelectric point (pI), on the other hand, was found to significantly affect the initial implant retention of rhBMPs, but not the subsequent pharmacokinetics. A 100-fold difference in the implant-retained dose could be observed depending on the type of rhBMP implanted. We conclude that protein structural features are important variables controlling in vivo pharmacokinetics of rhBMPs, and possibly the osteoinductive potency of the devices.

Collagen--biomaterial for drug delivery

The use of collagen as a biomaterial is currently undergoing a renaissance in the tissue engineering field. The biotechnological applications focus on the aspects of cellular growth or delivery of proteins capable of stimulating cellular response. However, basic knowledge about collagen biochemistry and the processing technology in combination with understanding of the physico-chemical properties is necessary for an adequate application of collagen for carrier systems. The purpose of this review article is to summarize information available on collagen dosage forms for drug delivery as well as to impart an overview of the chemical structures and the galenical properties including detailed description of the processing steps - extraction, purification, chemical crosslinking and sterilization. The most successful and stimulating applications are shields in ophthalmology, injectable dispersions for local tumor treatment, sponges carrying antibiotics and minipellets loaded with protein drugs. However, the scientific information about manipulating release properties or mechanistic studies is not as abundant as for some synthetic polymers.