The Use of Disaccharides in Inhibiting Enzymatic Activity Loss and Secondary Structure Changes in Freeze-Dried β-Galactosidase during Storage

Development of novel 3D printable inks for protein delivery

The application of 3D printing technology in the delivery of macromolecules, such as proteins and enzymes, is limited by the lack of suitable inks. In this study, we report the development of novel inks for 3D printing of constructs containing proteins while maintaining the activity of the proteins during and after printing. Different ink formulations containing Pluronic F-127 (20-35 %, w/v), trehalose (2-10 %, w/v) or mannitol, poly (ethylene glycol) diacrylate (PEGDA) (0 or 10 %, w/w), and diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TPO, 0 or 0.2 mg/mL) were prepared for 3D-microextrusion printing. The F2 formulation that contained β-galactosidase (β-gal) as a model enzyme, Pluronic F-127 (30 %), and trehalose (10 %) demonstrated the desired viscosity, printability, and dose flexibility. The shear-thinning property of the F2 formulation enabled the printing of β-gal containing constructs with a good peak force during extrusion. After 3D printing, the enzymatic activity of the β-gal in the constructs was maintained for an extended period, depending on the construct design and storage conditions. For instance, there was a 50 % reduction in β-gal activity in the two-layer constructs, but only a 20 % reduction in the four-layer construct (i.e., 54.5 ± 1.2 % and 82.7 ± 9.9 %, respectively), after 4 days of storage. The β-gal activity in constructs printed from the F2 formulation was maintained for up to 20 days when stored in sealed bags at room temperatures (21 ± 2 °C), but not when stored unsealed in the same conditions (e.g., ∼60 % activity loss within 7 days). The β-gal from constructs printed from F2 started to release within 5 min and reached 100 % after 20 min. With the design flexibility offered by the 3D printing, the β-gal release from the constructs was delayed to 3 h by printing a backing layer of β-gal-free F5 ink on the constructs printed from the F2 ink. Finally, ovalbumin as an alternative protein was also incorporated in similar ink compositions. Ovalbumin exhibited a release profile like that of the β-gal, and the release can also be modified with different shape design and/or ink composition. In conclusion, ink formulations that possess desirable properties for 3D printing of protein-containing constructs while maintaining the protein activity during and after printing were developed.

Chitosan-based oral hydrogel formulations of β-galactosidase to improve enzyme supplementation therapy for lactose intolerance

β-Galactosidase supplementation plays an important role in the life of people with lactose intolerance. However, these formulations are rendered ineffective by the low pH and pepsin in the stomach and pancreatic proteases in the intestine. Therefore, it is necessary to develop oral transport systems for carrying this enzyme in the active form up to the intestine, where the lactose digestion occurs. In this research, a new hydrogel was developed that could potentially be used for enzyme supplement therapy. In this regard, the chitosan-based β-Gal formulations described in the manuscript are an alternative long-acting preparation to the so far available preparations that allow for enzyme protection and mucosal targeting. These hydrogels were prepared from chitosan and polyethylene glycol and contained a covalently immobilized β-galactosidase from Aspergillus oryzae. The β-galactosidase in the hydrogel was protected from degradation in a gastric medium at a pH of 2.5 and retained 75 % of its original activity under subsequent intestinal conditions. In the case of a simulated gastric fluid with a pH of 1.5, a copolymer containing methacrylic acid functional groups was sufficient to protect the hybrid hydrogel from the extremely acidic pH. In addition, the surface of the hydrogel was chemically modified with thiol and amidine groups, which increased the binding to intestinal mucin by 20 % compared with the unmodified hydrogel. These results represent a promising approach for oral transport as a reservoir for β-galactosidase in the small intestine to reduce the symptoms of hypolactasia.

Immobilization of Kluyveromyces lactis β-Galactosidase on Meso-macroporous Silica: Use of Infrared Spectroscopy to Rationalize the Catalytic Efficiency

Enzyme immobilization on adequate carriers is a challenging strategy. Understanding the enzyme-carrier interactions and their effects on enzyme conformation and bioactivity is critical. In this study, a meso-macropores silica (MMS) was used to immobilize β-galactosidase from the yeast Kluyveromyces lactis (β-gal-KL) by physical adsorption. The bioactivity of the immobilized β-gal-KL was altered, evidenced by the increased K_m , decreased V_max and k_cat , and increased activity at alkaline values. By performing infrared spectroscopy analysis and subsequent secondary structure assessment from the amide I band, the immobilized β-gal-KL suffered a β-sheet (∼31-35 %) to α-helix (∼15-19 %) transition with increased turns (∼21-22 %) with respect to the free β-gal-KL having ∼12 % α-helix, ∼42 % β-sheet, and ∼17 % turns. These findings led us to correlate the observed bioactivity performance to structural alterations to a non-native conformation. The presented line of thought can lead to a better understanding of the reasons causing bioactivity alterations upon enzyme immobilization.

Preparation, Characterization, and Mechanism of Antifreeze Peptides from Defatted Antarctic Krill (Euphausia superba) on Lactobacillus rhamnosus

Defatted Antarctic krill powder is the main by-product in the manufacturing of krill oil. Exploring a high value-added approach for utilizing this protein-rich material has received much attention in research and industry. Given this, the preparation and primary characterization of antifreeze peptides from defatted Antarctic krill (AKAPs) were carried out in this study. The cryoprotective effect of AKAPs on Lactobacillus rhamnosus ATCC7469 was also investigated. The results showed that Protamex was the optimum protease for AKAP preparation from defatted Antarctic krill. AKAPs were found to be rich in short peptides, with the MW ranging from 600 to 2000 Da (69.2%). An amino acid composition analysis showed that AKAPs were rich in glutamic acid (18.71%), aspartic acid (12.19%), leucine (7.87%), and lysine (7.61%). After freezing, the relative survival rate of Lactobacillus rhamnosus in the 1.0 mg/mL AKAP-treated group (96.83%) was significantly higher than in the saline group (24.12%) (p < 0.05). AKAPs also retarded the loss of acidifying activity of L. rhamnosus after freezing. AKAPs showed even better cryoprotective activity than three commercial cryoprotectants (sucrose, skim milk, and glycerol). In addition, AKAPs significantly alleviated the decrease in β-galactosidase and lactic dehydrogenase activities of L. rhamnosus (p < 0.05). Furthermore, AKAPs effectively protected the integrity of L. rhamnosus cell membranes from freezing damage and alleviated the leakage of intracellular substances. These findings demonstrate that AKAPs can be a potential cryoprotectant for preserving L. rhamnosus, providing a new way to use defatted Antarctic krill.

Antifreeze Peptides Preparation from Tilapia Skin and Evaluation of Its Cryoprotective Effect on Lacticaseibacillus rhamnosus

Antifreeze peptides can protect cell membranes and maintain the cell viability of probiotics under cold stress. Given this, antifreeze peptides were prepared from tilapia processing byproducts of tilapia skin by enzymolysis using the response surface methodology (RSM) method. The cryoprotective effects on Lacticaseibacillus rhamnosus ATCC7469 were investigated. Trypsin was selected as the protease for tilapia skin hydrolysis. The optimal hydrolysis conditions consisted of the amount of enzyme (2200 U/g), solid–liquid ratio (1:10, w/v), reaction temperature (49 °C), and reaction time (6.8 h), and the relative survival rate of L. rhamnosus reached 98.32%. Molecular weight (M_w) distribution and peptide sequences of the antifreeze peptides prepared from tilapia skin (APT) under the optimal conditions were analyzed. APT significantly reduced the leakage of extracellular proteins and protected β-galactosidase and lactate dehydrogenase activities of L. rhamnosus. Compared with the saline group, scanning electron microscopy (SEM) observation showed that cells had a more normal, smooth, and entire surface under the protection of APT. These findings indicate that APT can be a new cryoprotectant in preserving probiotics.

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.

Screening of novel excipients for freeze-dried protein formulations

The typical excipients used as bulking agents and lyoprotectants for freeze-drying are usually limited to only a few selected substances, such as sucrose and mannitol. Considering the sheer diversity amongst proteins, it is doubtful that this limited choice should, in every case, provide the best possible option in order to achieve the most stable product. In this work, a screening of 12 proteins with 64 excipients was conducted in order to increase the knowledge space of potential excipients. Three critical quality attributes (CQAs) of the freeze-dried products, namely the solid state, the cake appearance and the protein integrity based on changes in tryptophan fluorescence were investigated by high throughput X-ray powder diffraction, image analysis and intrinsic fluorescence spectroscopy, respectively. It was found, that in some cases the excipient had a dominating influence on the CQAs, whilst in other cases the CQAs were primarily protein dependent, or that the CQAs were dependent on the combination of both. In the course of this investigation, a general view of potentially relevant excipients, and their interplay with various proteins, was obtained, thereby furthermore paving the way for the use of novel freeze-drying excipients.

Spray-dried amorphous isomalt and melibiose, two potential protein-stabilizing excipients

The possibility of producing amorphous isomalt and melibiose by spray drying was studied. The impact of process parameters on yield and solid-state stability was compared to sucrose and trehalose. All powders remained amorphous during 2-3 weeks. Processing was challenging due to powder stickiness. Low-temperature and low-humidity drying processes generally performed best. Most isomalt and sucrose powder was retrieved when using 60°C inlet temperature, 800L/h atomizing rate, 1.4ml/min feed rate, 15% concentration and 100% aspirator rate, giving 42-43°C outlet temperature. Isomalt was the most problematic, because it had the lowest Tg and became sticky very easily, therefore process parameters needed to be precisely balanced. There was more freedom in designing processes for melibiose but best yields were obtained with low-temperature (50°C inlet temperature, 800L/h atomizing rate, 4.9ml/min feed rate, 10% concentration and 100% aspirator, 39°C outlet temperature). Trehalose was different in that higher temperatures resulted in better yields. Yet, trehalose generally contained the highest moisture contents. The possibility to produce amorphous isomalt and melibiose at low-temperature process conditions makes them promising considering spray drying applications for heat-sensitive proteins. Melibiose is a better candidate than isomalt because of easier processability and superior solid-state stability.

Physical Stability of Freeze-Dried Isomalt Diastereomer Mixtures

PURPOSE

Isomalt is a sugar alcohol used as an excipient in commercially available solid oral dosage forms. The potential of isomalt as a novel freeze-drying excipient was studied in order to increase knowledge of the behavior of isomalt when it is freeze-dried.

METHODS

Isomalt was freeze-dried in four different diastereomer compositions and its physical stability was investigated with differential scanning calorimetry, Fourier-transform infrared and Raman spectroscopy, X-ray powder diffraction, Karl-Fischer titration and thermogravimetric analysis in order to verify the solid state form of isomalt after freeze-drying and observe any changes occurring during storage in three different relative humidity conditions.

RESULTS

Isomalt was successfully transformed into the amorphous form with freeze-drying and three diastereomer combinations remained stable as amorphous during storage; one of the diastereomer compositions showed signs of physical instability when stored in the highest relative humidity condition. The four different crystalline diastereomer mixtures showed specific identifiable solid state properties.

CONCLUSIONS

Isomalt was shown to be a suitable excipient for freeze-drying. Preferably a mixture of the diastereomers should be used, as the mixture containing only one of the isomers showed physical instability. A mixture containing a 1:1 ratio of the two diastereomers showed the best physical stability in the amorphous form.

Optimization of storage and stability of camel liver glutathione S-transferase

Glutathione S-transferases (GSTs) are multifunctional enzymes and play an important role in cellular detoxification. Besides this, GSTs act as cytosolic carrier proteins that bind hydrophobic compounds such as heme, bilirubin, steroids, and polycyclic hydrocarbons. GST has great importance in biotechnology, as it is a target for vaccine and drug development and biosensors development for xenobiotics. Moreover, the GST tag has been extensively used for protein expression and purification. Until now, biophysical properties of camel liver GST have not been characterized. In the present study we have purified camel (Camelus dromedarius) liver GST to homogeneity in a single step by affinity chromatography with 23.4-fold purification and 60.6% yield. Our results showed that maximal activity of GST was at pH 6.5 and it was stable in the pH range of 5 to 10. The optimum temperature was 55°C and the Tm was 57°C. The chemical chaperone glycerol (3.3 M) was able to protect GST activity and aggregation against thermal denaturation by stabilizing the protein structure at 50 and 57°C, respectively. However, L-arginine (125 mM) did not protect GST against thermal stress. Far-ultraviolet circular dichroism (CD) spectra showed that glycerol protected the secondary structure of GST while L-arginine induced conformational changes under thermal stress. In conclusion, our studies on the GST stability suggest that glycerol works as a stabilizer and L-arginine acts as a destabilizer.

The effect of relative humidity on the physical properties of two melibiose monohydrate batches with differing particle size distributions and surface properties

Melibiose monohydrate has shown promise when employed as a pharmaceutical excipient, but its physical properties have not been adequately characterized. Therefore, two different melibiose monohydrate batches were analyzed as received or after storage under different relative humidity (RH) atmospheres. The particle size distributions and specific surface areas of the two batches were shown to differ considerably, which also had an effect on their water sorption tendencies and on the intermolecular structure of melibiose after storage. The relatively large primary particles that were more abundant in one of the batches were shown to possess a porous surface structure, and water evaporation from them occurred in two phases when heated. Furthermore, storing the batch with smaller mean particle size under dry conditions affected the crystal structure and molecular vibrations of the sample more than in the case of the batch with larger mean particle size. It was concluded that the physical properties of melibiose monohydrate after storage at different RH atmospheres is largely governed by the primary particle size and porosity.

Freeze-dried heart valve scaffolds

In this study, structure and biomechanical properties of freeze-dried decellularized porcine pulmonary heart valves were investigated. Heart valves were dissected from porcine hearts. The tissues were decellularized and separated in three groups: (1) without lyoprotectant, (2) with 5% sucrose, and (3) with a mixture of 2.5% sucrose and 2.5% hydroxyl ethylene starch (HES), and then underwent freeze-drying. Freeze-drying in the absence of lyoprotectants caused an overall more disintegrated appearance of the histological architecture of the porcine valves, especially between the fibrosa and the ventricularis layers. Freeze-dried tissues with lyoprotectants have a looser network of collagen and elastic fibers with bigger pore sizes. Tissue freeze-dried in the absence of lyoprotecants had the largest pore sizes, whereas the tissue freeze-dried in the presence of protectants showed pores of intermediate sizes between the decellularized tissue and the unprotected freeze-dried samples. Tissue freeze-dried with sucrose alone displayed less porosity than tissue freeze-dried with the sucrose/HES mixture, whereas no significant differences in biomechanical properties were observed. Decellularization decreased the elastic modulus of artery tissue. The elastic modulus of freeze-dried tissue without protectants resembled that of decellularized tissue. The elastic modulus values of freeze-dried tissue stabilized by lyoprotectants were greater than those of decellularized tissue, but similar to those of native tissue.