Effect of Collapse on the Stability of Freeze-Dried Recombinant Factor VIII and α-amylase

Optical coherence tomography-based freeze-drying microscopy

A new type of freeze-drying microscope based upon time-domain optical coherence tomography is presented here (OCT-FDM). The microscope allows for real-time, in situ 3D imaging of pharmaceutical formulations in vials relevant for manufacturing processes with a lateral resolution of <7 μm and an axial resolution of <5 μm. Correlation of volumetric structural imaging with product temperature measured during the freeze-drying cycle allowed investigation of structural changes in the product and determination of the temperature at which the freeze-dried cake collapses. This critical temperature is the most important parameter in designing freeze-drying processes of pharmaceutical products.

Comparative evaluation of the antioxidant potential of infant cereals produced from purple wheat and red rice grains and LC-MS analysis of their anthocyanins

Cellular oxidative damage by endogenous and exogenous sources of free radicals and reactive oxygen species is a particular threat in infants. Antioxidant protection is normally achieved through a balance between pro-oxidants and endogenous and/or dietary antioxidants. Comprehensive research is required on optimization to achieve good antioxidant protection through infant foods, in particular, the commercially available infant cereals. This study therefore investigated the properties of whole purple wheat, unpolished red rice, and partially polished red rice before and after processing to produce infant cereals. Total phenolic content (TPC), total anthocyanin content (TAC), oxygen radical absorbance capacity (ORAC), individual anthocyanin components, and cellular antioxidant activity were measured. Home-made and laboratory-made pigmented infant cereals differed in that the latter required longer exposure to higher temperature and enzymatic hydrolysis. Home-made and laboratory-made unpolished red rice infant cereals showed higher total phenolic contents and peroxyl radical scavenging activity than home-made and laboratory-made purple wheat infant cereals; however, the latter had higher TAC. Pigmented infant cereals generally had higher TPC, TAC, and ORAC than the commercial ones (p < 0.05). Anthocyanins were identified in whole purple wheat, but they were not detected in unpolished red rice. C-Glycosyl apigenin was found in both whole purple wheat and unpolished red rice. Processing significantly decreased anthocyanin and C-glycosyl apigenin contents (p < 0.05). Purple wheat infant cereals had higher cellular antioxidant activity than unpolished red rice ones (p < 0.05). Whole purple wheat infant cereals showed higher antioxidant activity than the commercial infant cereal, suggesting a possibility of improving infant antioxidant status by incorporating this grain in their diet.

Characterizing the freeze-drying behavior of model protein formulations

The freeze-drying behavior of three model proteins, namely, lysozyme, BSA, and IgG, has been studied using a variety of techniques under two different primary drying conditions (shelf temperatures of -25°C and +25°C, respectively) in an amorphous formulation. Manometric temperature measurements were used to characterize product temperature (T (pr)), sublimation rates, and product resistance (R (p)) during primary drying. Biophysical techniques such as circular dichroism, fluorescence, and Fourier transform infrared spectroscopy were used to study protein conformation. Size exclusion chromatography was used to monitor the formation of high-molecular-weight species (HMWS) over time on storage, and cake morphology was studied using scanning electron microscopy. The differences in the freeze-drying behavior of the three proteins were more evident at higher protein concentrations, where the protein significantly influences the behavior of the formulation matrix. However, these differences were minimized in the aggressive mode and were insignificant at lower protein concentrations where excipients dominated the freeze-drying behavior. Differences in cake morphology were observed between the two drying conditions employed as well as between the three proteins studied. The stability and the protein structure, however, were equivalent for the protein cakes generated using the two different primary drying conditions.

Physical Characterization of Pharmaceutical Formulations in Frozen and Freeze-Dried Solid States: Techniques and Applications in Freeze-Drying Development

Physical characterization of formulations in frozen and freeze-dried solid states provides indispensable information for rational development of freeze-dried pharmaceutical products. This article provides an overview of the physical characteristics of formulations in frozen and freeze-dried solid states, which are essential to both formulation and process development. Along with a brief description of techniques often used in physical characterization for freeze-drying development, applications of and recent improvements to these techniques are discussed. While most of these techniques are used conventionally in physical characterization of pharmaceuticals, some techniques were designed or modified specifically for studies in freeze-drying. These include freeze-drying microscopy, freeze-drying X-ray powder diffractometry and cryoenvironmental scanning microscopy, which can be used to characterize the physical properties of the formulation under conditions similar to the real vial lyophilization process. Novel applications of some conventional techniques, such as microcalorimetry and near infrared (NIR) spectroscopy, which facilitated freeze-drying development, receive special attention. Research and developmental needs in the area of physical characterization for freeze-drying are also addressed, particularly the need for a better understanding of the quantitative correlation between the molecular mobility and the storage stability (shelf life).

Practical Formulation and Process Development of Freeze-Dried Products

Freeze-drying science and technology continues to evolve and increase in importance because of the emergence of biotechnology drugs that are too unstable to be commercially available as ready-to-use solutions. As more new drug compounds need to be developed as freeze-dried products, this mini-review article provides practical guidance and commentary on the latest literature articles on formulation and process development of freeze-dried products. This article contains a table that provides the quantitative formulations of all commercial freeze-dried protein pharmaceutical products through 2004.

Lyophilization of proteins

This chapter describes the methods that can be applied to successfully freeze-dry proteins. Laboratory applications are given at small scale, typified by the purification of a protein intermediate as part of the analytical characterization of a protein, and at intermediate scale, as illustrated by the pilot development of a lyophilized protein reference material such as for use in bioassay or immunoassay. Advice on common problems with freeze-drying of proteins is also given.

Investigation of Drying Stresses on Proteins during Lyophilization: Differentiation between Primary and Secondary-Drying Stresses on Lactate Dehydrogenase Using a Humidity Controlled Mini Freeze-Dryer

This article describes the design, performance testing, and application of a controlled humidity mini-freeze-dryer in studying the physical stability of lactate dehydrogenase during lyophilization. Performance evaluation of the mini-freeze-dryer was conducted with tests, namely water sublimation, radiation heat exchange, lowest achievable temperature, and leak testing. Protein stability studies were conducted by comparing protein activity at various stages of lyophilization with the initial activity. The shelf and condenser temperature were stable at <-40 degrees C, wall temperature was within 2 degrees C of the shelf temperature, and the leak rate was small. The chamber pressure was controlled by the ice on the condenser and the product temperature during sublimation was equal to the shelf temperature. Addition of Tween 80 prevented activity loss in solution and after freeze-thaw. No activity loss was observed after primary-drying even in absence of lyoprotectants and with collapse of cake structure. Five percent (w/w) sucrose concentration was required to achieve full stabilization. In conclusion, performance testing established that the mini-freeze-dryer was suitable for mechanistic freeze-drying studies. Secondary-drying was the critical step for protein stability. The concentration of sucrose required to stabilize the protein completely was several orders of magnitude higher than that required to satisfy the direct interaction requirement of the protein.

Influence of Processing Conditions on the Physical State of Mannitol—Implications in Freeze-Drying

PURPOSE

To study the effect of processing conditions on the physical state of mannitol during various stages of the lyophilization cycle of a protein formulation.

MATERIALS AND METHODS

Mannitol and trehalose were used as the bulking agent and lyoprotectant, respectively. The physical state of mannitol during various stages of freeze-drying cycle, in the absence and presence of a model protein, was characterized using low temperature X-ray powder diffractometry (XRD) and differential scanning calorimetry (DSC).

RESULTS

Mannitol did not crystallize even when the solution for lyophilization was cooled to -45 degrees C at a slow cooling rate of 1 degree C/min. Annealing facilitated mannitol crystallization, and in the absence of the protein, a mixture of delta-mannitol and mannitol hemihydrate was obtained at both low (-18 degrees C) and high (-8 degrees C) annealing temperatures. However, in the presence of protein, the high annealing temperature promoted delta-mannitol crystallization and inhibited formation of mannitol hemihydrate, while the low annealing temperature facilitated the formation of mannitol hemihydrate. Interestingly, the hemihydrate in the frozen solution was retained in the final lyophile, even when the primary and secondary drying temperatures were as high as -5 and 65 degrees C, respectively.

CONCLUSIONS

The presence of protein as well as the processing conditions (annealing temperature and time, primary and secondary drying temperatures) influenced the physical form of mannitol in the final lyophile. The protein promoted formation of delta-mannitol while inhibiting the formation of mannitol hemihydrate. Since the physical form of mannitol was greatly influenced by the presence of protein, it will be prudent to conduct the preliminary lyophilization cycle development studies in the presence of the protein. If mannitol hemihydrate is formed during annealing, its dehydration may require high secondary drying temperature.

Impact of residual moisture and formulation on Factor VIII and Factor V recovery in lyophilized plasma reference materials

Residual moisture content and formulation are important parameters when preparing lyophilized reference materials containing labile proteins. The protection of Factor VIII and Factor V activities were monitored in a lyophilized plasma preparation following formulation with either no additional excipient, 40 mM Hepes (4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid), 10 mg/mL glycine or a combination of 40 mM Hepes and 10 mg/mL glycine. The preservation of Factor VIII activity during freeze-drying was improved by the addition of either stabiliser and improved most, amongst the options studied, by the addition of both glycine and Hepes. The predicted stability at -20 degrees C and 20 degrees C was estimated using accelerated degradation studies. Although for plasma lyophilized alone there was some benefit from further desiccation over phosphorus pentoxide, resulting in very low moistures, for suitably formulated samples the predicted stability was as good for freeze-dried only samples as for those with further desiccation. This study emphasises the importance of optimum formulation on the stability of lyophilized proteins.

Structure and enzyme properties of Zabrotes subfasciatus alpha-amylase

Digestive alpha-amylases play an essential role in insect carbohydrate metabolism. These enzymes belong to an endo-type group. They catalyse starch hydrolysis, and are involved in energy production. Larvae of Zabrotes subfasciatus, the Mexican bean weevil, are able to infest stored common beans Phaseolus vulgaris, causing severe crop losses in Latin America and Africa. Their alpha-amylase (ZSA) is a well-studied but not completely understood enzyme, having specific characteristics when compared to other insect alpha-amylases. This report provides more knowledge about its chemical nature, including a description of its optimum pH (6.0 to 7.0) and temperature (20-30 degrees C). Furthermore, ion effects on ZSA activity were also determined, showing that three divalent ions (Mn2+, Ca2+, and Ba2+) were able to enhance starch hydrolysis. Fe2+ appeared to decrease alpha-amylase activity by half. ZSA kinetic parameters were also determined and compared to other insect alpha-amylases. A three-dimensional model is proposed in order to indicate probable residues involved in catalysis (Asp204, Glu240, and Asp305) as well other important residues related to starch binding (His118, Ala206, Lys207, and His304).

Measurement of the kinetics of protein unfolding in viscous systems and implications for protein stability in freeze-drying

PURPOSE

The aim of the study is to determine the degree of coupling between protein unfolding rate and system viscosity at low temperatures in systems relevant to freeze-drying.

METHODS

The cold denaturation of both phosphoglycerate kinase (PGK) and beta-lactoglobulin were chosen as models for the protein unfolding kinetics study. The system viscosity was enhanced by adding stabilizers (such as sucrose), and denaturant (guanidine hydrochloride or urea) was added to balance the stabilizing effect of sucrose to maintain the cold denaturation temperature roughly constant. The protein unfolding kinetics were studied by both temperature-controlled tryptophan emission fluorescence spectroscopy and isothermal high-sensitivity modulated differential scanning calorimetry (MDSC) (Tzero). Viscometers were used to determine the system viscosity. To verify the predictions of structure based on protein unfolding dynamics, protein formulations were freeze-dried above the glass transition temperatures, and the protein structures in dry products were determined by fluorescence spectroscopy of reconstituted solids by extrapolation of the solution data to the time of reconstitution.

RESULTS

Empirical equations describing the effect of sucrose and denaturant (urea and guanidine hydrochloride) on protein cold denaturation were developed based on DSC observations [X. C. Tang and M. J. Pikal. The Effects of Stabilizers and Denaturants on the Cold Denaturation Temperature of Proteins and Implications for Freeze-Drying. Pharm. Res. Submitted (2004)]. It was found that protein cold denaturation temperature can be maintained constant in system of increasing sucrose concentration by simultaneous addition of denaturants (urea and guanidine hydrochloride) using the empirical equations as a guide. System viscosities were found to increase dramatically with increasing sucrose concentration and decreasing temperature. The rate constants of protein unfolding (or the half-life of unfolding) below the cold denaturation temperature were determined by fitting the time dependence of either fluorescence spectroscopy peak position shift or DSC heat capacity increase to a first-order reversible kinetic model. The half-life of unfolding did slow considerably as system viscosity increased. The half-life of PGK unfolding, which was only 3.5 min in dilute buffer solution at -10 degrees C, was found to be about 200 min in 37% sucrose at the same temperature. Kinetics of protein unfolding are identical as measured by tryptophan fluorescence emission spectroscopy and by high-sensitivity modulated DSC. The coupling between protein unfolding kinetics and system viscosity for both proteins was significant with a stronger coupling with PGK than with beta-lactoglobulin. The half-lives of PGK and beta-lactoglobulin unfolding are estimated to be 5.5 x 10(11) and 2.2 years, respectively, even when they are freeze-dried in sucrose formulations 20 degrees C above Tg'. Thus, freeze-drying below Tg' should not be necessary to preserve the native conformation. In support of this conclusion, native PGK was obtained after the freeze-drying of PGK at a temperature more than 60 degrees C above the system Tg' in a thermodynamically unstable system during freeze-drying.

CONCLUSIONS

Protein unfolding kinetics is highly coupled with system viscosity in high viscosity systems, and the coupling coefficients are protein dependent. Protein unfolding is very slow on the time scale of freeze-drying, even when the system is freeze-dried well above Tg'. Thus, it is not always necessary to freeze-dry protein formulations at temperature below Tg' to avoid protein unfolding. That is, protein formulations could be freeze-dried at product temperature far above the Tg', thereby allowing much shorter freeze-drying cycle times, with dry cake structure being maintained by the simultaneous use of a bulking agent and a disaccharide stabilizer.