Effect of polyols on the conformational stability and biological activity of a model protein lysozyme

Phenylacetylcarbinol biotransformation by disrupted yeast cells using ultrasonic treatment in conjunction with a dipropylene glycol mediated biphasic emulsion system

Biotransformation of a pharmaceutical precursor, phenylacetylcarbinol (PAC), could be achieved by frozen-thawed Candida tropicalis whole cells (FT-WHC). The treatment of FT-WHC, which contained intracellular pyruvate decarboxylase (PDC) enzyme, using high-power ultrasonication with varying amplitudes were compared with glass bead attrition (GBA) as well as control for the release of PDC. Ultrasonication at 20% amplitude (Ult20) proved to be the most effective, resulting in the highest volumetric and specific PDC activities of 0.210 ± 0.004 U/mL and 0.335 ± 0.033 U/mg protein, respectively. Disrupted FT-WHC using Ult20 exhibited a statistically significant (p ≤ 0.05) higher initial PAC production rate (3.26 ± 0.04 mM). The comparison of three organic phases, namely, vegetable oil (Vg-Oil), Vg-Oil + dipropylene glycol (DPG), and octanol in the two-phase emulsion system for PAC biotransformation revealed the highest statistically significant (p ≤ 0.05) overall PAC concentration of 28.9 ± 0.1 mM in Vg-Oil + DPG system. The novel addition of DPG helped facilitating the partitioning of PAC into aqueous phase, stabilizing specific PDC activity, and specific PAC productivity in combination with ultrasonication treatment.

L-tyrosine inhibits the formation of amyloid fibers of human lysozyme at physiological pH and temperature

Amyloid fibers are implicated in numerous diseases, making their study crucial for identifying effective therapeutic compounds. This research highlights the ability of L-tyrosine to inhibit the formation of amyloid fibers in human lysozyme. At a 1:1 molar ratio under physiological conditions (pH 7.4, 37 °C), L-tyrosine significantly reduces amyloid fiber formation, as evidenced by a decrease in thioflavin T fluorescence. Differential scanning calorimetry (DSC) shows a major energy requirement for temperature denaturation when the lysozyme is in the presence of L-tyrosine. Additionally, chemical denaturation experiments reveal a shift in the intrinsic fluorescence spectrum of lysozyme in the presence of L-tyrosine, indicating a direct interaction. Computational docking studies with Molecular Operating Environment (MOE) further confirm that L-tyrosine binds effectively, exhibiting similar binding energies to those of the natural substrate. This study underscores L-tyrosine's potential as a strong inhibitor of amyloid fiber formation, demonstrating its stabilizing effect on lysozyme and its promise in therapeutic applications.

Comparative Analysis of the Osmoprotective Effects of Daily Disposable Contact Lens Packaging Solutions on Human Corneal Epithelial Cells

Purpose

Contact lens (CL) wear challenges the balance of the ocular surface environment by increasing water evaporation and tear osmolarity. Maintaining ocular surface homeostasis during CL wear remains a goal of lens manufacturers and an important consideration for eye care professionals. The purpose of this study was to measure the metabolic activity and inflammatory responses of a transformed human corneal epithelial cell (THCEpiC) line under hyperosmotic conditions in the presence of CL packaging solutions.

Methods

CL packaging solutions sampled from seven daily disposable silicone hydrogel CL blister packages were prepared at 25% and made hyperosmolar (400 mOsm/kg) with NaCl. THCEpiCs were incubated with each solution for 24 hr, after which cell culture supernatants were collected. THCEpiC metabolic activity was determined by an alamarBlue assay. Concentrations in cell culture supernatants of inflammatory cytokine (interleukin [IL]-6) and chemokine (IL-8), as well as monocyte chemoattractant protein-1 (MCP-1), were quantitated by specific enzyme-linked immunosorbent assays.

Results

THCEpiC metabolic activity under hyperosmolar conditions decreased in the presence of somofilcon A and senofilcon A solutions (p=0.04 and 0.004, respectively), but no other solution (all p≥0.09). Concentrations of IL-6 increased in the presence of delefilcon A, somofilcon A, narafilcon A, and senofilcon A solutions (all p≤0.001), but no other solution (all p≥0.08), while those of IL-8 increased in the presence of all solutions (all p≤0.03) but kalifilcon A (p>0.99), and those of MCP-1 increased in the presence of delefilcon A, verofilcon A, somofilcon A, and stenfilcon A solutions (all p<0.0001), but no other solution (all p>0.99).

Conclusion

CL packaging solutions differ in their capacity to inhibit epithelial inflammation. THCEpiC inflammatory response was less in the presence of a CL packaging solution containing osmoprotectants than in solutions lacking osmoprotectants under moderately hyperosmolar conditions in vitro. Clinical studies are warranted to further substantiate the benefit of osmoprotectants.

The role of glycerol-water mixtures in the stability of FKBP12-rapalog-FRB complexes

The thermodynamic and biophysical implications of the introduction of a co-solvent during protein-ligand binding remain elusive. Using ternary complexes of 12-kDa FK506 binding protein (FKBP12), FKBP-rapamycin binding (FRB) domain of the mammalian/mechanistic target of rapamycin (mTOR) kinase, and rapamycin analogs (rapalogs) in glycerol-water mixtures, the influence of solvent composition on ligand binding dynamics was explored. The pharmaceutical potential of rapalogs and the utility of glycerol as a co-solvent in drug delivery applications were critical in deciding the system to be studied. Consolidation of existing studies on rapamycin modification was first performed to strategically design a new rapalog called T1. The results from 100-ns dual-boost Gaussian accelerated molecular dynamics simulations showed that protein stability was induced in the presence of glycerol. Reweighting of the trajectories revealed that the glycerol-rich solvent system lowers the energy barrier in the conformational space of the protein while also preserving native contacts between the ligand and the residues in the binding site. Calculated binding free energies using MM/GBSA also showed that electrostatic energy and polar contribution of solvation energy are heavily influenced by the changes in solvation. Glycerol molecules are preferentially excluded through electrostatic interactions from the solvation shell which induce complex stability as seen in existing experiments. Hence, using glycerol as a co-solvent in rapamycin delivery has a significant role in maintaining stability. In addition, compound T1 is a potential mTORC1-selective inhibitor with strong affinity for the FKBP12-FRB complex. This study aims to provide insights on the design of new rapalogs, and the applicability of glycerol as co-solvent for FKBP12-rapalog-FRB complexes.

Saliva profiling with differential scanning calorimetry: A feasibility study with ex vivo samples

Differential scanning calorimetry (DSC) has been used widely to study various biomarkers from blood, less is known about the protein profiles from saliva. The aim of the study was to investigate the use DSC in order to detect saliva thermal profiles and determine the most appropriate sampling procedure to collect and process saliva. Saliva was collected from 25 healthy young individuals and processed using different protocols based on centrifugation and filtering. The most effective protocol was centrifugation at 5000g for 10 min at 4°C followed by filtration through Millex 0.45 μm filter. Prepared samples were transferred to 3 mL calorimetric ampoules and then loaded into TAM48 calibrated to 30°C until analysis. DSC scans were recorded from 30°C to 90°C at a scan rate of 1°C/h with a pre-conditioning the samples to starting temperature for 1 h. The results show that the peak distribution of protein melting points was clearly bimodal, and the majority of peaks appeared between 40–50°C. Another set of peaks is visible between 65°C– 75°C. Additionally, the peak amplitude and area under the peak are less affected by the concentration of protein in the sample than by the individual differences between people. In conclusion, the study shows that with right preparation of the samples, there is a possibility to have thermograms of salivary proteins that show peaks in similar temperature regions between different healthy volunteers.

Refolding of Lysozyme in Glycerol as Studied by Fast Scanning Calorimetry

The folding of lysozyme in glycerol was monitored by the fast scanning calorimetry technique. Application of a temperature-time profile with an isothermal segment for refolding allowed assessment of the state of the non-equilibrium protein ensemble and gave information on the kinetics of folding. We found that the non-equilibrium protein ensemble mainly contains a mixture of unfolded and folded protein forms and partially folded intermediates, and enthalpic barriers control the kinetics of the process. Lysozyme folding in glycerol follows the same or similar triangular mechanism described in the literature for folding in water. The unfolding enthalpy of the intermediate must be no lower than 70% of the folded form, while the activation barrier for the unfolding of the intermediate (ca. 140 kJ/mol) is about 100 kJ/mol lower than that of the folded form (ca. 240-260 kJ/mol).

Regulation of an important glycolytic enzyme, pyruvate kinase, through phosphorylation in the larvae of a species of freeze-tolerant insect, Eurosta solidaginis

Larvae of the goldenrod gall fly, Eurosta solidaginis, rely on a freeze tolerance strategy to survive the sub-zero temperatures of Canadian winter. Critical to their survival is the accumulation of polyol cryoprotectants and global metabolic rate depression, both of which require the regulation of glycolysis and reorganization of carbohydrate metabolism. This study explored the role that pyruvate kinase (PK) regulation plays in this metabolic reorganization. PK was purified from control (5 °C-acclimated) and frozen (-15 °C-acclimated) larvae and enzyme kinetic properties, structural stability, and post-translational modifications were examined in both enzyme forms. The K_m phosphoenolpyruvate (PEP) of frozen PK was 20% higher than that of control PK, whereas the V_max of frozen PK was up to 50% lower than that of control PK at the lowest assay temperature, suggesting inhibition of the enzyme during the winter. Additionally, the activity and substrate affinity of both forms of PK decreased significantly at low assay temperatures, and both forms were regulated allosterically by a number of metabolites. Pro-Q™ Diamond phosphoprotein staining and immunoblotting experiments demonstrated significantly higher threonine phosphorylation of PK from frozen animals while acetylation and methylation levels remained constant. Together, these results indicate that PK exists in two structurally distinct forms in E. solidaginis. In response to conditions mimicking the transition to winter, PK appears to be regulated to support metabolic rate depression, the accumulation of polyol cryoprotectants, and the need for extended periods of anaerobic carbohydrate metabolism to allow the animal to survive whole-body freezing.

Unraveling the interaction mechanism between collagen and alcohols with different chain lengths and hydroxyl positions

The present study systematically investigated the effects of alcohols, including methanol, ethanol, n-butanol, and propanol with different hydroxyl group numbers and locations on the thermal stability and molecular aggregation behavior of collagen. The results of ultra-sensitive differential scanning calorimetry (US-DSC), dynamic light scattering (DLS) and intrinsic fluorescence showed that with the increase of carbon chain length, alcohols can denature collagen, accompanied by transition in triple helical structure, promoted aggregation behavior, and altered molecular interactions. However, with the number of hydroxyl groups in alcohol molecules increased, the thermal stability of collagen increased and the molecules tended to disperse. Furthermore, radial distribution function (RDF) results showed that alcohols can change the structure of the hydration layer around collagen, thus altering the aggregation morphology of collagen molecules in solution. The results of the interaction between components in different alcohol systems demonstrated that with the decrease of alcohol polarity, bridge bond networks were formed between collagen molecules. Specifically, it was found that because the hydroxyl groups in 1,3-propanediol are located at both ends of the carbon chain, the reticular bridge bond structure formed between the collagen molecules changed into chain-like bridge structure. The bridge bonds between collagen molecules were considered to be weak cross-linking, which was an important reason for the destruction of collagen structure. In this study, the mechanism of interaction between different alcohols and collagen was elucidated, which will be helpful for further development of complex alcohol and collagen products.

The potential of lactoferrin, ovotransferrin and lysozyme as antiviral and immune-modulating agents in COVID-19

Coronavirus disease 2019 (COVID-19), caused by SARS coronavirus 2 (SARS-CoV-2), is spreading rapidly with no established effective treatments. While most cases are mild, others experience uncontrolled inflammatory responses with oxidative stress, dysregulation of iron and coagulation as features. Lactoferrin, ovotransferrin and lysozyme are abundant, safe antimicrobials that have wide antiviral as well as immunomodulatory properties. In particular, lactoferrin restores iron homeostasis and inhibits replication of SARS-CoV, which is closely related to SARS-CoV-2. Ovotransferrin has antiviral peptides and activities that are shared with lactoferrin. Both lactoferrin and lysozyme are ‘immune sensing’ as they may stimulate immune responses or resolve inflammation. Mechanisms by which these antimicrobials may treat or prevent COVID-19, as well as sources and forms of these, are reviewed.

Correlating multidimensional short-term empirical protein properties to long-term protein physical stability data via empirical phase diagrams

Identification of long-term stable biopharmaceutical formulations is essential for biopharmaceutical product development. Reduction of the number of long-term storage experiments and a well-defined formulation search space requires knowledge-based formulation screenings and a detailed protein phase behavior understanding. To achieve this, short-term analytical techniques can serve as predictors for long-term protein phase behavior. Protein phase behavior studies that investigate this concept commonly display shortcomings such as limited and small datasets, sample adjustments, or simplistic data analysis. To overcome these shortcomings, 150 unique lysozyme solutions were analyzed using six different short-term analytical techniques. Lysozyme's structural properties, conformational stability, colloidal stability, surface charge, and surface hydrophobicity were obtained directly after formulation preparation. Employing the empirical phase diagram method, this short-term data was correlated to long-term physical stability data obtained during 40 days of storage. Short-term protein properties showed partial correlation to long-term phase behavior. Structural differences, changing surface properties, colloidal stability, and conformation stability as a function of formulation conditions were observed. This study contributes to long-term protein phase behavior research by presenting a systematic, data-dependent, and multidimensional data evaluation workflow to create a comprehensive overview of short-term protein analytics in relation to long-term protein phase behavior.

Protection effect of polyols on Rhizopus chinensis lipase counteracting the deactivation from high pressure and high temperature treatment

The influence of polyols on Rhizopus chinensis lipase (RCL) was investigated under high pressure. The poor stability of RCL was observed at 500 MPa at 60 °C without polyols which protected RCL against the loss of activity. The lipase is more stable in phosphate buffer than in tris buffer despite the protection of polyols. The activity was maintained 63% by the sorbitol of 2 mol/L in Tris-HCl buffer but 73% in phosphate buffer after the treatment at 500 MPa and 60 °C for 25 min. The same protective effects could be observed at 1 mol/L of sorbitol, erythritol, xylitol, and mannitol. However, further increase of hydroxyl group number could not significantly improve the enzyme stability. The protection of polyols on RCL appears to depend on both of the polyol nature and the hydroxyl group number. Together with fluorescence spectra, circular dichroism spectra indicated that the chaotic conformation of RCL under high pressure became more ordered with 1 mol/L sorbitol. The results showed that sorbitol effectively stabilized the lipase conformation including the hydrophobic core under extreme conditions. It might be attributed to the interaction of polyols with RCL surface to modify intra-/intermolecular hydrogen bonds, maintaining the hydrophobic interactions within RCL.

Nebulization of Single-Chain Tissue-Type and Single-Chain Urokinase Plasminogen Activator for Treatment of Inhalational Smoke-Induced Acute Lung Injury

Single-chain tissue-type plasminogen activator (sctPA) and single-chain urokinase plasminogen activator (scuPA) have attracted interest as enzymes for the treatment of inhalational smoke-induced acute lung injury (ISALI). In this study, the pulmonary delivery of commercial human sctPA and lyophilized scuPA and their reconstituted solution forms were demonstrated using vibrating mesh nebulizers (Aeroneb® Pro (active) and EZ Breathe® (passive)). Both the Aeroneb® Pro and EZ Breathe® vibrating mesh nebulizers produced atomized droplets of protein solution of similar size of less than about 5 μm, which is appropriate for pulmonary delivery. Enzymatic activities of scuPA and of sctPA were determined after nebulization and both remained stable (88.0% and 93.9%). Additionally, the enzymatic activities of sctPA and tcuPA were not significantly affected by excipients, lyophilization or reconstitution conditions. The results of these studies support further development of inhaled formulations of fibrinolysins for delivery to the lungs following smoke-induced acute pulmonary injury.

Optimization of high-concentration endostatin formulation: Harmonization of excipients' contributions on colloidal and conformational stabilities

Recently, increasing research efforts have been devoted into developing high-concentration protein drugs for subcutaneous injection, especially for those with short half-lives and high-dose requirement. Proteins at high concentrations normally present increased colloidal and structural instability, such as aggregation, fibrillation and gelation, which significantly challenges the high-concentration formulation development of protein drugs. Here we used endostatin, a 20kD recombinant protein, as a model drug for high-concentration formulation optimization. The colloidal and conformational stability of endostatin at high concentration of 30mg/mL were investigated in formulations containing various excipients, including saccharides (mannitol, sorbitol and sucrose), salts (ArgHCl and NaCl), and surfactants (tween 20 and 80). Protein fibrillation was characterized and semi-quantified by optical polarized light microscopy and transmission electron microscopy, and the amount of fiber formation at elevated temperature of 40°C was determined. The soluble protein aggregates were characterized by dynamic and static light scattering before and after dilution. The conformational stability were characterized by polyacrylamide gel electrophoresis, fluorescence, circular dichroism, and differential scanning calorimetry. We observed that the soluble aggregation, fibrillation and gelation, induced by conformational and colloidal instabilities of the protein solution, could be substantially optimized by using suitable stabilizers such as combinations of saccharides and surfactants; while formation of gel and soluble aggregates at high protein concentration (e.g., 30mg/mL) and elevated temperature (40°C) could be prevented by avoiding the usage of salts. It's worth emphasizing that some stabilizers, such as salts and surfactants, could show opposite contributions in conformational and colloidal stabilities of endostatin. Therefore, cautions are needed when one attempts to correlate the colloidal stability of high-concentration proteins with their conformational stability, and the colloidal and conformational protein stabilities must be harmonized by a balanced selection of various types of excipients.

Survival of Microencapsulated Probiotic Bacteria after Processing and during Storage: A Review

The use of live probiotic bacteria as food supplement has become popular. Capability of probiotic bacteria to be kept at room temperature becomes necessary for customer's convenience and manufacturer's cost reduction. Hence, production of dried form of probiotic bacteria is important. Two common drying methods commonly used for microencapsulation are freeze drying and spray drying. In spite of their benefits, both methods have adverse effects on cell membrane integrity and protein structures resulting in decrease in bacterial viability. Microencapsulation of probiotic bacteria has been a promising technology to ensure bacterial stability during the drying process and to preserve their viability during storage without significantly losing their functional properties such acid tolerance, bile tolerance, surface hydrophobicity, and enzyme activities. Storage at room temperatures instead of freezing or low temperature storage is preferable for minimizing costs of handling, transportation, and storage. Concepts of water activity and glass transition become important in terms of determination of bacterial survival during the storage. The effectiveness of microencapsulation is also affected by microcapsule materials. Carbohydrate- and protein-based microencapsulants and their combination are discussed in terms of their protecting effect on probiotic bacteria during dehydration, during exposure to harsh gastrointestinal transit and small intestine transit and during storage.

Evaluation of antioxidants in protein formulation against oxidative stress using various biophysical methods

To evaluate the biophysical stability of protein against oxidative stress, hydrogen peroxide (H2O2) was used to induce non-site-specific protein oxidation. Various biophysical methods were utilized including RP-HPLC, DSC, DLS, and CD. Lysozyme was chosen as a model protein and three different antioxidants (ascorbic acid, N-acetyl-l-cysteine, and l-methionine) were selected to observe their effect. Significant increase in hydrodynamic size, decrease in α-helix propensity, and increase in β-sheet content evident with increasing H2O2 concentration and temperature suggested methionine residues as the most probable site of oxidation. Among the three anti-oxidants, methionine proved superior in suppressing protein oxidation with its increasing concentration. Methionine reacted with H2O2 to form methionine sulfoxide, which aided in decreasing the oxidant concentration to react with the protein. The hydrodynamic size of methionine containing protein was retained when incubated at 40°C after 14 days with unchanged transition temperature (Tm). In contrast, RP-HPLC revealed oxidation alterations when the same samples were stored at 40°C, highlighting the significant impact of temperature on kinetics. N-acetyl-l-cysteine and ascorbic acid were relatively less protective. Their hydrodynamic size was increased with decreasing Tm compared to the reference. In summary, methionine was a superior antioxidant, implicating a promising component in the protein formulation for suppressing oxidation.

Evaluation of thermo-stability of bluetongue virus recombinant VP7 antigen in indirect ELISA

This study shows the thermo-stability of lyophilized and purified recombinant VP7 bluetongue virus (BTV) protein in the presence of two sugar stabilizers (trehalose and mannitol) at different temperature. Truncated VP7 protein purified by nickel affinity column was lyophilized in the presence of trehalose and mannitol at 60 mM final concentration and then exposed to different temperature like 4, 25, 37 and 45 °C for various periods like 5 months, 7 weeks, 7 days and 48 h, respectively. After thermal treatment, the reactivity of the protein was evaluated in indirect ELISA. At 4 and 25 °C, the protein was stable up to 5 months and 7 weeks, respectively, irrespective of stabilizers used. At 37 °C, it was stable up to 3 days with both the stabilizers, after which it lost its stability and reactivity. At 45 °C, the protein was stable up to 30 and 24 h with trehalose and mannitol stabilizers, respectively. Both stabilizers found suitable for stability of the protein. However, trehalose appeared to have better stabilizing effect, particularly at higher temperatures than the mannitol. Trehalose could be used as stabilizer for freeze-drying the recombinant VP7 protein if an indirect ELISA kit based on the purified rVP7 protein is supplied to different laboratories of the country for detection of BTV antibody in sheep.

The importance of formulation in the successful lyophilization of influenza reference materials

Lyophilized Influenza antigen reference reagents are a critical resource in the quality control of influenza vaccines. A standard formulation has been used successfully at NIBSC for many years however, following the unexpected occurrence of a collapsed appearance in a particular batch a study was carried out to establish the impact of the sugar concentration in the formulation using modulated differential scanning calorimetry (mDSC) and nuclear magnetic resonance spectroscopy (NMR). There was a correlation between the presence and size of the mDSC eutectic temperature events and the freeze dried appearance of the cakes, which became progressively worse with increasing amounts of sugar. NMR spectroscopy could be used to positively identify and quantify the sugars in the formulations. MDSC can rapidly predict if the freeze dried appearance will be acceptable so as to assure the successful lyophilization of influenza reference preparations.

Protein stabilization by an amphiphilic short monodisperse oligo(ethylene glycol)

Phenyl-appended octa(ethylene glycol) suppresses aggregation of thermally and chemically denatured lysozyme, demonstrating that octa(ethylene glycol) is almost the shortest oligoethylene glycol for providing the capability of stabilizing proteins to molecules.

Artificial environments for the co-translational stabilization of cell-free expressed proteins

An approach for designing individual expression environments that reduce or prevent protein aggregation and precipitation is described. Inefficient folding of difficult proteins in unfavorable translation environments can cause significant losses of overexpressed proteins as precipitates or inclusion bodies. A number of chemical chaperones including alcohols, polyols, polyions or polymers are known to have positive effects on protein stability. However, conventional expression approaches can use such stabilizing agents only post-translationally during protein extraction and purification. Proteins that already precipitate inside of the producer cells cannot be addressed. The open nature of cell-free protein expression systems offers the option to include single chemicals or cocktails of stabilizing compounds already into the expression environment. We report an approach for systematic screening of stabilizers in order to improve the solubility and quality of overexpressed proteins co-translationally. A comprehensive list of representative protein stabilizers from the major groups of naturally occurring chemical chaperones has been analyzed and their concentration ranges tolerated by cell-free expression systems have been determined. As a proof of concept, we have applied the method to improve the yield of proteins showing instability and partial precipitation during cell-free synthesis. Stabilizers that co-translationally improve the solubility and functional folding of human glucosamine 6-phosphate N-acetyltransferase have been identified and cumulative effects of stabilizers have been studied.

Investigation of effects of terpene skin penetration enhancers on stability and biological activity of lysozyme

The transport of proteins through skin can be facilitated potentially by using terpenes as chemical enhancers. However, we do not know about the effects of these enhancers on the stability and biological activity of proteins which is crucial for the development of safe and efficient formulations. Therefore, this project investigated the effects of terpene-based skin penetration enhancers which are reported as nontoxic to the skin (e.g., limonene, p-cymene, geraniol, farnesol, eugenol, menthol, terpineol, carveol, carvone, fenchone, and verbenone), on the conformational stability and biological activity of a model protein lysozyme. Terpene (5% v/v) was added to lysozyme solution and kept for 24 h (the time normally a transdermal patch remains) for investigating conformational stability profiles and biological activity. Fourier transform infrared spectrophotometer was used to analyze different secondary structures, e.g., α-helix, β-sheet, β-turn, and random coil. Conformational changes were also monitored by differential scanning calorimeter by determining midpoint transition temperature (Tm) and calorimetric enthalpy (ΔH). Biological activity of lysozyme was determined by measuring decrease in A (450) when it was added to a suspension of Micrococcus lysodeikticus. The results of this study indicate that terpenes 9, 10, and 11 (carvone, L-fenchone, and L-verbenone) decreased conformational stability and biological activity of lysozyme significantly (p < 0.05) less than other terpenes used in this study. It is concluded that smaller terpenes containing ketones with low lipophilicity (log K (ow) ∼2.00) would be optimal for preserving conformational stability and biological activity of lysozyme in a transdermal formulation containing terpene as permeation enhancer.

Forced degradation of therapeutic proteins

The scope of this paper is to review approaches used for forced degradation (synonym, stress testing) of therapeutic proteins. Forced degradation studies play a central role in the development of therapeutic proteins, for example, for candidate selection, molecule characterization, formulation development, assay development, and comparability studies. Typical stress methods are addressed within this review, such as exposure to elevated temperatures, freeze-thawing, mechanical stress, oxidation, light, as well as various materials and devices used in the clinics during final administration. Stability testing is briefly described as far as relevant to the discussion of forced degradation studies. Whereas stability-testing requirements are defined in regulatory guidelines, standard procedures for forced degradation of therapeutic proteins are largely unavailable, except for photostability. Possible selection criteria to identify appropriate stress conditions and recommendations for setting up forced degradation studies for the different phases of development of therapeutic proteins are presented.

Insights into protein-polysorbate interactions analysed by means of isothermal titration and differential scanning calorimetry

Therapeutic proteins formulated as liquid solutions at high protein concentration are very sensitive to chemical and physical degradation. Especially avoiding the formation of protein aggregates is very crucial for product quality. In order to stabilize the colloidal properties of protein therapeutics various excipient are used. Especially the detergents polysorbate 20 and 80 are common. However, the mechanism upon which the detergents protect the protein from aggregation is not really known. The present study investigates the interaction of polysorbate 20 and 80 with different proteins: lysozyme, bovine serum albumin (BSA) and an immunoglobulin. The interaction and binding of the detergents to the proteins is investigated by isothermal titration calorimetry (ITC). From ITC the thermodynamic parameters (DeltaH: change in enthalpy, DeltaS: entropy and DeltaG: free energy) upon binding are derived as well as the binding constant K (a). The thermal stability of the proteins in the presence of the detergent is assessed by differential scanning calorimetry (DSC). The results show that both detergents bind to BSA with K (a) between 8 and 12 x 10(3) M(-1) with DeltaH -50 to -60 kJ/mol (25 degrees C). One to two detergent molecules bind to BSA. The presence of both detergents induces a weak stabilisation of the thermal denaturation properties of BSA. However, the interaction of polysorbate 20 and 80 with lysozyme and the immunoglobulin is quite negligible. The presence of the detergents up to a concentration of 2 mM has no impact on the heat capacity curve neither a destabilisation nor a stabilisation of the native conformation is observed.

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.

Thermodynamic stability and formation of aggregates of human immunoglobulin G characterised by differential scanning calorimetry and dynamic light scattering

The final process step of polyclonal human immunoglobulin G is formulation with agents such as sugars, polyols, amino acid and salts. Often the most stable formulations were empirically identified. Physicochemical methods, such as differential scanning calorimetry and dynamic light scattering, provide a deeper insight on the biophysical properties of such a protein solution. The combination of these methods proved to be sensitive enough to detect fine differences in the properties relevant for the development of stable protein solutions. The influence of additives, such as maltose and glycine in combination with water or low concentrations of salts, on human immunoglobulin preparations was analysed. Differential scanning calorimetry illustrated that 0.2 M glycine had better stabilising effects compared to 10% maltose. Dynamic light scattering and differential scanning calorimetry revealed that solutions preventing aggregation were not optimal in terms of thermodynamic stability. Aggregation was minimised with increasing ionic strength, shown by dynamic light scattering, whereas thermodynamic stability for heat sensitive parts of human immunoglobulin G, analysed with differential scanning calorimetry, was decreased.