Optimization of a Raman Microscopy Technique to Efficiently Detect Amorphous–Amorphous Phase Separation in Freeze‐Dried Protein Formulations

Structural Features of the Glassy State and Their Impact on the Solid-State Properties of Organic Molecules in Pharmaceutical Systems

This paper reviews the structure and properties of amorphous active pharmaceutical ingredients (APIs), including small molecules and proteins, in the glassy state (below the glass transition temperature, Tg). Amorphous materials in the neat state and formulated with excipients as miscible amorphous mixtures are included, and the role of absorbed water in affecting glass structure and stability has also been considered. We defined the term "structure" to indicate the way the various molecules in a glass interact with each other and form distinctive molecular arrangements as regions or domains of varying number of molecules, molecular packing, and density. Evidence is presented to suggest that such systems generally exist as heterogeneous structures made up of high-density domains surrounded by a lower density arrangement of molecules, termed the microstructure. It has been shown that the method of preparation and the time frame for handling and storage can give rise to variable glass structures and varying physical properties. Throughout this paper, examples are given of theoretical, computer simulation, and experimental studies which focus on the nature of intermolecular interactions, the size of heterogeneous higher density domains, and the impact of such systems on the relative physical and chemical stability of pharmaceutical systems.

Impact of lyoprotectors on protein-protein separation in the solid state: Neutron- and X-ray-scattering investigation

BACKGROUND

Polyhydroxycompounds (PHC) are used as lyoprotectors to minimize aggregation of pharmaceutical proteins during freeze-drying and storage.

METHODS

Lysozyme/PHC mixtures with 1:1 and 1:3 (w/w) ratios are freeze-dried from either H₂O or D₂O solutions. Disaccharides (sucrose and trehalose), monosaccharide (glucose), and sugar alcohol (sorbitol) are used in the study. Small-angle neutron and X-ray scattering (SANS and SAXS) are applied to study protein-protein interaction in the freeze-dried samples.

RESULTS

Protein interaction peak in the freeze-dried mixtures has been detected by both SANS (D₂O-based samples only) and SAXS (both D₂O- and H₂O-based). In the 1:1 mixtures, protein separation distances are similar (center-of-mass distance of approx. 31 Å) between all lyoprotectors studied. Mixtures with a higher content of the disaccharides (1:3 ratio) have a higher separation distance of approx 40 Å. The higher separation could reduce protein-protein contacts and therefore be associated with less favourable aggregation conditions. In the 1:3 mixtures with glucose and sorbitol, complex SANS and SAXS/WAXS patterns are observed. The pattern for the glucose sample indicate two populations of lysozyme molecules, while the origin of multiple SAXS peaks in the lysozyme/sorbitol 1:3 mixture is uncertain.

CONCLUSIONS

Protein-protein separation distance is determined predominantly by the lyoprotector/protein weight ratio.

GENERAL SIGNIFICANCE

Use of SANS and SAXS improves understanding of mechanisms of protein stabilization by sugars in freeze-dried formulations, and provide a tool to verify hypothesis on relationship between protein/protein separation and aggregation propensity in the dried state.

Enzymatic characterization of D-lactate dehydrogenase and application in alanine aminotransferase activity assay kit

D-lactate dehydrogenase (D-LDH) is widely used for the clinical detection of alanine aminotransferase (ALT) activity. It is a key enzyme in ALT detection kits, and its enzymatic properties directly determine sensitivity and accuracy of such kits. In this study, D-lactate dehydrogenase (WP_011543503, ldLDH) coding sequence derived from Lactobacillus delbrueckii was obtained from the NCBI database by gene mining. LdLDH was expressed and purified in Escherichia coli, and its enzyme activity, kinetic parameters, optimum temperature, and pH were characterized. Furthermore, stabilizers, including sugars, polyols, amino acids, certain salts, proteins, and polymers, were screened to improve stability of ldLDH during freeze-drying and storage. Finally, a kit based on ldLDH was tested to determine whether the enzyme had potential clinical applications. The results showed that ldLDH had a specific activity of 1,864 U/mg, K_m value of 1.34 mM, optimal reaction temperature of 55°C, and an optimal pH between 7.0 and 7.5. When sucrose or asparagine was used as a stabilizer, freeze-dried ldLDH remained stable at 37°C for > 2 months without significant loss of enzymatic activity. These results indicated that ldLDH possesses high activity and stability. Test results using the ALT assay kit prepared with ldLDH were consistent with those of commercial kits, with a relative deviation <5%. These results indicated that ldLDH met the primary requirements for ALT assays, laying a foundation for the development of new ALT kits with potential clinical applications.

Stabilizers and their interaction with formulation components in frozen and freeze-dried protein formulations

This review aims to provide an overview of the current knowledge on protein stabilization during freezing and freeze-drying in relation to stress conditions commonly encountered during these processes. The traditional as well as refined mechanisms by which excipients may stabilize proteins are presented. These stabilizers encompass a wide variety of compounds including sugars, sugar alcohols, amino acids, surfactants, buffers and polymers. The rational selection of excipients for use in frozen and freeze-dried protein formulations is presented. Lyophilized protein formulations are generally multicomponent systems, providing numerous possibilities of excipient-excipient and protein-excipient interactions. The interplay of different formulation components on the protein stability and excipient functionality in the frozen and freeze-dried systems are reviewed, with discussion of representative examples of such interactions.

Instability of therapeutic proteins - An overview of stresses, stabilization mechanisms and analytical techniques involved in lyophilized proteins

Solid-state is the preferred choice for storage of protein therapeutics to improve stability and preserve the biological activity by decreasing the physical and chemical degradation associated with liquid protein formulations. Lyophilization or freeze-drying is an effective drying method to overcome the instability problems of proteins. However, the processing steps (freezing, primary drying and secondary drying) involved in the lyophilization process can expose the proteins to various stress and harsh conditions, leading to denaturation, aggregation often a loss in activity of protein therapeutics. Stabilizers such as sugars and surfactants are often added to protect the proteins against physical stress associated with lyophilization process and storage conditions. Another way to curtail the degradation of proteins due to process related stress is by modification of the lyophilization process. Slow freezing, high nucleation temperature, decreasing the extent of supercooling, and annealing can minimize the formation of the interface (ice-water) by producing large ice crystals with less surface area, thereby preserving the native structure and stability of the proteins. Hence, a thorough understanding of formulation composition, lyophilization process parameters and the choice of analytical methods to characterize and monitor the protein instability is crucial for development of stable therapeutic protein products. This review provides an overview of various stress conditions that proteins might encounter during lyophilization process, mechanisms to improve the stability and analytical techniques to tackle the proteins instability during both freeze-drying and storage.

Inhomogeneous Distribution of Components in Solid Protein Pharmaceuticals: Origins, Consequences, Analysis, and Resolutions

Successful development of stable solid protein formulations usually requires the addition of one or several excipients to achieve optimal stability. In these products, there is a potential risk of an inhomogeneous distribution of the various ingredients, specifically the ratio of protein and stabilizer may vary. Such inhomogeneity can be detrimental for stability but is mostly neglected in literature. In the past, it was challenging to analyze inhomogeneous component distribution, but recent advances in analytical techniques have revealed new options to investigate this phenomenon. This paper aims to review fundamental aspects of the inhomogeneous distribution of components of freeze-dried and spray-dried protein formulations. Four key topics will be presented and discussed, including the sources of component inhomogeneity, its consequences on protein stability, the analytical methods to reveal component inhomogeneity, and possible solutions to prevent or mitigate inhomogeneity.

Science and art of protein formulation development

Protein pharmaceuticals have become a significant class of marketed drug products and are expected to grow steadily over the next decade. Development of a commercial protein product is, however, a rather complex process. A critical step in this process is formulation development, enabling the final product configuration. A number of challenges still exist in the formulation development process. This review is intended to discuss these challenges, to illustrate the basic formulation development processes, and to compare the options and strategies in practical formulation development.