Effect of Surfactants on Surface-Induced Denaturation of Proteins: Evidence of an Orientation-Dependent Mechanism

Protein stability and critical stabilizers in frozen solutions

Freezing is a common unit operation during the processing and storage of therapeutic proteins. Upon freezing, protein molecules and other solutes are excluded from the ice crystals, resulting in the formation of freeze concentrated solution (FCS). Protein destabilization can be prevented due to the low temperature and the formation of a viscous FCS. However, the changes in temperature, pH, salt concentration, and the formation of ice-solution interfaces can induce protein destabilization. The current paper reviews the stresses associated with freezing and thawing and discusses the stabilization strategies. At subambient conditions, protein unfolding is thermodynamically favored when the solution is cooled below the cold denaturation temperature. The formation of a viscous FCS, specifically at a temperature below the glass transition temperature (Tg'), immobilizes and stabilizes the proteins. Protein can adsorb at the ice/solution interface, followed by unfolding and aggregation. Therefore, freezing and thawing rates need to be carefully selected to minimize the ice surface area (due to the formation of small ice crystals) and to avoid ice recrystallization. Besides, stabilizers, including sugars, surfactants, and amino acids, are added as stabilizers (cryoprotectants) to prevent protein destabilization upon freezing and frozen storage. In situ spectroscopic (infrared, Raman, and solid-state NMR) and scattering (X-ray and neutron) techniques provide useful insights into protein stability and phase transitions of excipients in frozen solutions. Finally, we discuss the importance of the freezing process and excipient selection in the successful lyophilization of protein formulations. The review paper comprehensively discusses the challenges during the cryopreservation of therapeutic proteins and provides valuable insights into the critical stabilizers in frozen protein solutions.

Insulin fibrillation under physicochemical parameters of bioprocessing and intervention by peptides and surface-active agents

Even after the centenary celebration of insulin discovery, there prevail challenges concerning insulin aggregation, not only after repeated administration but also during industrial production, storage, transport, and delivery, significantly impacting protein quality, efficacy, and effectiveness. The aggregation reduces insulin bioavailability, increasing the risk of heightened immunogenicity, posing a threat to patient health, and creating a dent in the golden success story of insulin therapy. Insulin experiences various physicochemical and mechanical stresses due to modulations in pH, temperature, ionic strength, agitation, shear, and surface chemistry, during the upstream and downstream bioprocessing, resulting in insulin unfolding and subsequent fibrillation. This has fueled research in the pharmaceutical industry and academia to unveil the mechanistic insights of insulin aggregation in an attempt to devise rational strategies to regulate this unwanted phenomenon. The present review briefly describes the impacts of environmental factors of bioprocessing on the stability of insulin and correlates with various intermolecular interactions, particularly hydrophobic and electrostatic forces. The aggregation-prone regions of insulin are identified and interrelated with biophysical changes during stress conditions. The quest for novel additives, surface-active agents, and bioderived peptides in decelerating insulin aggregation, which results in overall structural stability, is described. We hope this review will help tackle the real-world challenges of insulin aggregation encountered during bioprocessing, ensuring safer, stable, and globally accessible insulin for efficient management of diabetes.

Preparation and characterization of acetylated starch/papain composites

This research aimed to prepare and characterize acetylated starch/papain composites by encapsulating papain within acetylated cassava starch with a low degree of substitution (DS = 0.037) through a stepwise antisolvent precipitation method. The effects of starch concentrations, starch solution volumes, and surfactant types and concentrations were examined. An increase in starch concentration generally enhanced EE, but an excessive concentration led to a decrease in performance due to the aggregation of starch. Furthermore, LC decreased as the starch concentration increased, while the volume of the starch solution primarily influenced LC. Surfactants were employed to disperse the particles and prevent their aggregation during encapsulation, with higher concentrations, particularly of Tween 80, improving both EE and LC but reducing the activity of papain. Optimal results were achieved with a starch concentration of 30 mg mL-1, solution volume of 7 mL, and 3% v/v Tween 80, resulting in an EE of 96.23% and LC of 12.40%. However, the residual papain activity under these conditions dropped to approximately 56%. In contrast, Tween 20 at 1% v/v preserved higher papain activity (87%), although it yielded a lower EE of 69.87% and LC of 9.32%. SEM images revealed that the resulting composite particles had rough, indistinct clusters with surfaces featuring clustered starch nanoparticles. Confirmatory analyses via fluorescence spectra and FTIR confirmed successful entrapment of papain within acetylated starch with a lower degree of substitution.

Reconsidering freeze-induced protein aggregation: Air bubbles as the root cause of ice-water interface stress

Freeze-induced stress causing aggregation of proteins has typically been primarily attributed to the ice-water interface. However, we hypothesize that the underlying observed and perceived detrimental effect of ice is, to some extent, attributed to air bubbles expelled from ice crystal lattices or to nanobubbles existing prior to freezing. The reduction of dissolved air was achieved via a deaeration process by placing samples in a reduced pressure chamber, while the reduction of nanobubbles was achieved by filtering samples via a syringe filter. The results showed that the reduction of both dissolved air molecules and stable colloidal nanobubbles in a bovine IgG solution prior to freezing led to a significant decrease in aggregation after thawing compared to untreated samples (∼6,000 vs. ∼ 40,000 particles/mL at a freezing rate of 100 K/s, respectively). The deaeration-filtration treatment works additively with cryoprotectants such as trehalose, further reducing the freeze-induced aggregation of IgG. The results also demonstrated that air-water interfacial aggregation of IgG in bulk liquid samples is a time-dependent process. The number of IgG subvisible particles increased with time and temperature, suggesting that random collisions of denatured molecules promoted the formation of aggregates with spherical morphology. In contrast, the IgG subvisible count after freeze-thawing had already reached its nominal value, suggesting a time-independent process where denatured protein molecules were compressed between ice crystals into filament-like aggregates. In summary, the findings shift the current paradigm from ice crystals being the main destabilizing factor during freezing to air bubbles, although the two are intertwined. From a translational aspect, this study underscores the value of deaeration-filtration as an essential supplemental process that can be applied in addition to formulation approaches such as the use of cryoprotectants to further reduce freezing stress on proteins and increase their stability.

Engineered polymeric excipients for enhancing the stability of protein biologics: Poly(N-isopropylacrylamide)-poly(ethylene glycol) (PNIPAM-PEG) block copolymers

Protein therapeutics, particularly antibodies, depend on maintaining their native structures for optimal function. Hydrophobic interfaces, such as the air-water interface, can trigger protein aggregation and denaturation. While completely avoiding such interfacial exposures during manufacturing and storage is impractical, minimizing them is crucial for enhancing protein drug stability and extending shelf life. In the biologics industry, surfactants like polysorbates are commonly used as additives (excipients) to mitigate these undesirable interfacial exposures. However, polysorbates, the most prevalent choice, have recognized limitations in terms of polydispersity, purity, and stability, prompting the exploration of alternative excipients. The present study identifies poly(N-isopropylacrylamide)-poly(ethylene glycol) (PNIPAM-PEG) block copolymers as a promising alternative to polysorbates. Due to its stronger affinity for the air-water interface, PNIPAM-PEG significantly outperforms polysorbates in enhancing protein stability. This claim is supported by results from multiple tests. Accelerated dynamic light scattering (DLS) experiments demonstrate PNIPAM-PEG's exceptional efficacy in preserving IgG stability against surface-induced aggregation, surpassing conventional polysorbate excipients (Tween 80 and Tween 20) under high-temperature conditions. Additionally, circular dichroism (CD) spectroscopy results reveal conformational alterations associated with aggregation, with PNIPAM-PEG consistently demonstrates a greater protective effect by mitigating negative shifts at λ ≅ 220 nm, indicative of changes in secondary structure. Overall, this study positions PNIPAM-PEG as a promising excipient for antibody therapeutics, facilitating the development of more stable and effective biopharmaceuticals.

Effect of surfactants on lactate dehydrogenase aqueous solutions: A comparative study of poloxamer 188, polysorbate 20 and 80

The effect of three commonly used surfactants, poloxamer 188 (P188), polysorbate 20 and 80 (PS20 and PS80), on the stability of a model protein, lactate dehydrogenase (LDH), was compared in aqueous solutions. In the absence of a surfactant, protein solution revealed a gradual decrease in surface tension as a function of time. The addition of surfactant resulted in a rapid decrease in the surface tension. This suggested that the surface behavior was dictated by the surfactant. PS20 and PS80 were more effective than P188 in preventing LDH adsorption on the solution surface. The advantage of polysorbates over P188 was also evident from the higher LDH tetramer recovery after shaking (room temperature, 30 h), especially when the surfactants were used at concentrations ≤ 0.01% w/v. However, PS20 and PS80 accelerated protein unfolding during quiescent storage at 40 °C. Based on circular dichroism results, polysorbates perturbed the tertiary structure of LDH but not the secondary structure, while P188 did not impact the protein structure and stability. Polysorbates were more effective in stabilizing LDH against mechanical stress (shaking), but their adverse effects on protein conformational stability need to be carefully evaluated.

Shear stress as a driver of degradation for protein-based therapeutics: More accomplice than culprit

Protein degradation is a major concern for protein-based therapeutics. It may alter the biological activity of the product and raise the potential for undesirable effects on the patients. Among the numerous drivers of protein degradation, shear stress has been the focus around which much work has revolved since the 1970s. In the pharmaceutical realm, the product is often processed through several unit operations, which include mixing, pumping, filtration, filling, and atomization. Nonetheless, the drug might be exposed to significant shear stresses, which might cooperatively contribute to product degradation, together with interfacial stress. This review presents fundamentals of shear stress about protein structure, followed by an overview of the drivers of product degradation. The impact of shear stress on protein stability in different unit operations is then presented, and recommendations for limiting the adverse effects on the biopharmaceutical formulations are outlined. Finally, several devices used to explore the effects of shear stress are discussed.

Interaction of βL- and γ-Crystallin with Phospholipid Membrane Using Atomic Force Microscopy

Highly concentrated lens proteins, mostly β- and γ-crystallin, are responsible for maintaining the structure and refractivity of the eye lens. However, with aging and cataract formation, β- and γ-crystallin are associated with the lens membrane or other lens proteins forming high-molecular-weight proteins, which further associate with the lens membrane, leading to light scattering and cataract development. The mechanism by which β- and γ-crystallin are associated with the lens membrane is unknown. This work aims to study the interaction of β- and γ-crystallin with the phospholipid membrane with and without cholesterol (Chol) with the overall goal of understanding the role of phospholipid and Chol in β- and γ-crystallin association with the membrane. Small unilamellar vesicles made of Chol/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (Chol/POPC) membranes with varying Chol content were prepared using the rapid solvent exchange method followed by probe tip sonication and then dispensed on freshly cleaved mica disk to prepare a supported lipid membrane. The βL- and γ-crystallin from the cortex of the bovine lens was used to investigate the time-dependent association of βL- and γ-crystallin with the membrane by obtaining the topographical images using atomic force microscopy. Our study showed that βL-crystallin formed semi-transmembrane defects, whereas γ-crystallin formed transmembrane defects on the phospholipid membrane. The size of semi-transmembrane defects increases significantly with incubation time when βL-crystallin interacts with the membrane. In contrast, no significant increase in transmembrane defect size was observed in the case of γ-crystallin. Our result shows that Chol inhibits the formation of membrane defects when βL- and γ-crystallin interact with the Chol/POPC membrane, where the degree of inhibition depends upon the amount of Chol content in the membrane. At a Chol/POPC mixing ratio of 0.3, membrane defects were observed when both βL- and γ-crystallin interacted with the membrane. However, at a Chol/POPC mixing ratio of 1, no association of γ-crystallin with the membrane was observed, which resulted in a defect-free membrane, and the severity of the membrane defect was decreased when βL-crystallin interacted with the membrane. The semi-transmembrane or transmembrane defects formed by the interaction of βL- and γ-crystallin on phospholipid membrane might be responsible for light scattering and cataract formation. However, Chol suppressed the formation of such defects in the membrane, likely maintaining lens membrane homeostasis and protecting against cataract formation.

Combining Molecular Dynamics Simulations and Biophysical Characterization to Investigate Protein-Specific Excipient Effects on Reteplase during Freeze Drying

We performed molecular dynamics simulations of Reteplase in the presence of different excipients to study the stabilizing mechanisms and to identify the role of excipients during freeze drying. To simulate the freeze-drying process, we divided the process into five distinct steps: (i) protein-excipient formulations at room temperature, (ii) the ice-growth process, (iii)-(iv) the partially solvated and fully dried formulations, and (v) the reconstitution. Furthermore, coarse-grained (CG) simulations were employed to explore the protein-aggregation process in the presence of arginine. By using a coarse-grained representation, we could observe the collective behavior and interactions between protein molecules during the aggregation process. The CG simulations revealed that the presence of arginine prevented intermolecular interactions of the catalytic domain of Reteplase, thus reducing the aggregation propensity. This suggests that arginine played a stabilizing role by interacting with protein-specific regions. From the freeze-drying simulations, we could identify several protein-specific events: (i) collapse of the domain structure, (ii) recovery of the drying-induced damages during reconstitution, and (iii) stabilization of the local aggregation-prone region via direct interactions with excipients. Complementary to the simulations, we employed nanoDSF, size-exclusion chromatography, and CD spectroscopy to investigate the effect of the freeze-drying process on the protein structure and stability.

Shield, Anchor, and Adhesive Roles of Methylene Blue in Tyrosinase Adsorbed on Carbon Felt for a Flow Injection Amperometric Enzyme Biosensor for Phenolic Substrates and Inhibitors

Methylene blue (MB) acted as a stabilizer for preventing surface-induced denaturation of tyrosinase (TYR) adsorbed on a carbon felt (CF) surface, which is based on shield and anchor roles preventing the unfavorable conformational change of TYR on the hydrophobic CF surface. Furthermore, MB acted as an effective adhesive for TYR immobilization on CF. The resulting TYR and MB coadsorbed CF (TYR/MB-CF) worked as an excellent working electrode unit in an electrochemical detector in a flow injection amperometric biosensor, which allowed highly sensitive consecutive determination of not only TYR substrates but also competitive inhibitors. Simultaneous adsorption of TYR and MB from their mixed solution was much useful as compared with step-wise separated adsorption of TYR on the MB-adsorbed CF, which suggests that the binding interaction of MB with TYR in the solution phase is important for this phenomenon. Fluorescence and UV-vis spectroscopy revealed that not only electrostatic forces between the cationic MB and anionic amino acid residues of TYR but also hydrophobic interactions via the phenothiazine ring of MB play a principal binding driving force of MB with TYR at the surface of the TYR molecules. Synchronous fluorescence, three-dimensional fluorescence, and circular dichroism (CD) spectroscopy clarified that the conformation and the secondary structure of TYR slightly changed upon the MB binding, implying that MB binding leads to the modification of the original intramolecular bonding in part.

Analysis of the Shear Stresses in a Filling Line of Parenteral Products: The Role of Tubing

Parenteral products appear to be sensitive to process conditions in bioprocessing steps, such as interfacial stress and shear stress. The combination of these elements is widely believed and proven to influence product stability, but the defined roles of these players in the product damage process have not yet been identified. The present work addresses a current industrial problem, by focusing on the analysis of shear stress on protein-based therapeutics flowing in tubing by means of Computational Fluid Dynamics simulations. The purpose of this article is not to pinpoint the mechanism triggering the damage of the product, but it represents the first step towards wider experimental investigations and introduces a new strategy to quantify the average shear stress. The field of scale-down approaches, used to scale the commercial process down to the laboratory level, is also explored. Since quality control is critical in the pharmaceutical realm, it is essential that the scale-down approach preserves the same stress exposure as the commercial scale, which in the present work is considered to be that resulting from shear effects. Therefore, a new approach for scaling down the commercial process is proposed, which has been compared with traditional approaches and shown to provide greater representativeness between the two scales.

Afraid of the wall of death? Considerations on monoclonal antibody characteristics that trigger aggregation during peristaltic pumping

Protein aggregation is of major concern in manufacturing of biopharmaceutics. Protein aggregation upon peristaltic pumping for filtration, transfer or filling is triggered by protein adsorption to the tubing surface and subsequent film rupture during roller movement. While the impact of tubing type and formulation has been studied in more detail, the contribution of the protein characteristics is not fully resolved. We studied the aggregation propensity of six monoclonal antibodies during peristaltic pumping and characterized their colloidal and conformational stability, hydrophobicity, and surface activity. A high affinity to the surface resulting in faster adsorption and film renewal was key for the formation of protein particles ≥ 1 µm. Film formation and renewal were influenced by the antibody hydrophobicity, potential for electrostatic self-interaction and conformational stability. The initial interfacial pressure increase within the first minute can serve as a good predictor for antibody adsorption and particle formation propensity. Our results highlight the complexity of protein adsorption and emphasize the importance of formulation development to reduce protein particle formation by avoidance of adsorption to interfaces.

Large-Scale Freeze-Thaw of Protein Solutions: Study of the Relative Contributions of Freeze-Concentration and Ice Surface Area on Stability of Lactate Dehydrogenase

Although bulk biotherapeutics are often frozen during fill finish and shipping to improve their stability, they can undergo degradation leading to losses in biological activity during sub-optimal freeze-thaw (F/T) process. Except for a few small-scale studies, the relative contribution of various F/T stresses to the instability of proteins has not been addressed. Thus, the objective of this study was to determine the individual contributions of freeze-concentration, ice surface area, and processing time to protein destabilization at a practical manufacturing-scale. Lactate dehydrogenase (LDH) in histidine buffer solutions were frozen in 1L containers. The frozen solutions were sliced into representative samples and assessed for the ice specific surface area (SSA) and extent of solutes freeze-concentration. For the first time to our knowledge, ice SSA was measured in dried samples from large-volume protein solutions using volumetric nitrogen adsorption isotherms. SSA measurements of the freeze-dried cakes showed that the ice surface area increased with an increase in the freezing rate. The ice SSA was also impacted by the position of the sample within the container: samples closer to the active cooled surface of the container exhibited smaller ice surface area compared to ice-cored samples from the center of the bottle. The freeze-concentrate composition was determined by measuring LDH concentration in the ice-cored samples. The protein distributed more evenly throughout the frozen solution after fast freezing which also correlated with enhanced protein stability compared to slow freezing conditions. Overall, better protein stability parameters correlated with higher ice SSA and lower freeze-concentration extent which was achieved at a faster freezing rate. Thus, extended residence time of the protein at the freeze-concentrated microenvironment is the critical destabilizing factor during freezing of LDH in bulk histidine buffer system. This study expands the understanding of the relative contributions of freezing stresses which, coupled with the knowledge of cryoprotection mechanisms, is imperative to the development of optimized processes and formulations aiming stable frozen protein solutions.

A Novel MATLAB®-Algorithm-Based Video Analysis to Quantitatively Determine Solution Creeping in Intact Pharmaceutical Glass Vials

During the filling process of a biopharmaceutical drug product (DP), a liquid DP film might creep up the inner vial wall which is barely discernible, appears as milky-white haze after lyophilisation and is known as fogging. Creeping and fogging are mainly dependent on the primary packaging material surface and its hydration, vial preparation process as well as DP composition. The occurrence of both can impede visual inspection and might lead to DP rejection. Hence, our studies focused on the early detection of liquid solution and glass vial surface interaction directly after filling. For a fast and highly sensitive evaluation a novel video-based analysis was used. To our knowledge, this is the first time a MATLAB®-algorithm-based video analysis was applied to quantitatively determine creeping time-resolved. Furthermore, creeping in dependence of vial processing sites, surfactant type and concentration, filling temperature, and vial format were investigated. The results were verified using orthogonal conventional methods such as surface tension, wetting behaviour, and contact angle measurements, as well as ToF-SIMS, ICP-MS, and SEM. Additionally, the methods applied were assessed regarding their cross-validation capability. The observations indicate that the vial preparation process can have a pronounced impact on alteration of the glass vial surface and related creeping behaviour of the filled solution.

Staphylococcus aureus-targeting peptide/surfactant assemblies for antibacterial therapy

To address the challenge from microbial resistance, this work developed a surfactant with 18-carbon single hydrocarbon chain and multi-amine head groups (C18N3). After assembling with Staphylococcus aureus-targeting peptide (CARG), the obtained C18N3/CARG assemblies exhibited excellent antimicrobial activities against Staphylococcus aureus and methicillin-resistant Staphylococcus aureus in vitro and in vivo, in which the targeting peptide CARG bonded specifically to Staphylococcus aureus and C18N3 killed bacteria with a mechanism of membrane disruption. Importantly, C18N3 could also work as a β-lactamase inhibitor to overcome the bacterial resistance to β-lactam antibiotics through noncompetitive inhibition. The combination of β-lactam antibiotic and C18N3/CARG assemblies more effectively suppressed methicillin-resistant Staphylococcus aureus in vitro and in vivo relative to equivalent dose of free antibiotic or C18N3. Thus, the antibacterial platform of antibiotic-carrying surfactant assemblies bearing bacteria-targeted peptides, in which C18N3 performed dual function, antibacterial agent and β-lactamase inhibitor, may help fight against the difficult-to-treat infections.

Stereoisomeric Pam2CS Based TLR2 Agonists: Synthesis, Structural Modelling and Activity as Vaccine Adjuvants

Lipopeptides including diacylated Pam2CSK4 as well as triacylated Pam3CSK4 act as ligands of Toll-like receptor (TLR)-2, a promising target for the development of vaccine adjuvants. The highly investigated Pam2CSK4 and...

On the Effect of pH, Temperature, and Surfactant Structure on Bovine Serum Albumin-Cationic/Anionic/Nonionic Surfactants Interactions in Cacodylate Buffer-Fluorescence Quenching Studies Supported by UV Spectrophotometry and CD Spectroscopy

Due to the fact that surfactant molecules are known to alter the structure (and consequently the function) of a protein, protein–surfactant interactions are very important in the biological, pharmaceutical, and cosmetic industries. Although there are numerous studies on the interactions of albumins with surfactants, the investigations are often performed at fixed environmental conditions and limited to separate surface-active agents and consequently do not present an appropriate comparison between their different types and structures. In the present paper, the interactions between selected cationic, anionic, and nonionic surfactants, namely hexadecylpyridinium chloride (CPC), hexadecyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), polyethylene glycol sorbitan monolaurate, monopalmitate, and monooleate (TWEEN 20, TWEEN 40, and TWEEN 80, respectively) with bovine serum albumin (BSA) were studied qualitatively and quantitatively in an aqueous solution (10 mM cacodylate buffer; pH 5.0 and 7.0) by steady-state fluorescence spectroscopy supported by UV spectrophotometry and CD spectroscopy. Since in the case of all studied systems, the fluorescence intensity of BSA decreased regularly and significantly under the action of the surfactants added, the fluorescence quenching mechanism was analyzed thoroughly with the use of the Stern–Volmer equation (and its modification) and attributed to the formation of BSA–surfactant complexes. The binding efficiency and mode of interactions were evaluated among others by the determination, comparison, and discussion of the values of binding (association) constants of the newly formed complexes and the corresponding thermodynamic parameters (ΔG, ΔH, ΔS). Furthermore, the influence of the structure of the chosen surfactants (charge of hydrophilic head and length of hydrophobic chain) as well as different environmental conditions (pH, temperature) on the binding mode and the strength of the interaction has been investigated and elucidated.

Tween® Preserves Enzyme Activity and Stability in PLGA Nanoparticles

Enzymes, as natural and potentially long-term treatment options, have become one of the most sought-after pharmaceutical molecules to be delivered with nanoparticles (NPs); however, their instability during formulation often leads to underwhelming results. Various molecules, including the Tween^® polysorbate series, have demonstrated enzyme activity protection but are often used uncontrolled without optimization. Here, poly(lactic-co-glycolic) acid (PLGA) NPs loaded with β-glucosidase (β-Glu) solutions containing Tween^® 20, 60, or 80 were compared. Mixing the enzyme with Tween^® pre-formulation had no effect on particle size or physical characteristics, but increased the amount of enzyme loaded. More importantly, NPs made with Tween^® 20:enzyme solutions maintained significantly higher enzyme activity. Therefore, Tween^® 20:enzyme solutions ranging from 60:1 to 2419:1 mol:mol were further analyzed. Isothermal titration calorimetry analysis demonstrated low affinity and unquantifiable binding between Tween^® 20 and β-Glu. Incorporating these solutions in NPs showed no effect on size, zeta potential, or morphology. The amount of enzyme and Tween^® 20 in the NPs was constant for all samples, but a trend towards higher activity with higher molar rapports of Tween^® 20:β-Glu was observed. Finally, a burst release from NPs in the first hour with Tween^®:β-Glu solutions was the same as free enzyme, but the enzyme remained active longer in solution. These results highlight the importance of stabilizers during NP formulation and how optimizing their use to stabilize an enzyme can help researchers design more efficient and effective enzyme loaded NPs.

Rapid Capture of Cancer Extracellular Vesicles by Lipid Patch Microarrays

Extracellular vesicles (EVs) contain various bioactive molecules such as DNA, RNA, and proteins, and play a key role in the regulation of cancer progression. Furthermore, cancer-associated EVs carry specific biomarkers and can be used in liquid biopsy for cancer detection. However, it is still technically challenging and time consuming to detect or isolate cancer-associated EVs from complex biofluids (e.g., blood). Here, a novel EV-capture strategy based on dip-pen nanolithography generated microarrays of supported lipid membranes is presented. These arrays carry specific antibodies recognizing EV- and cancer-specific surface biomarkers, enabling highly selective and efficient capture. Importantly, it is shown that the nucleic acid cargo of captured EVs is retained on the lipid array, providing the potential for downstream analysis. Finally, the feasibility of EV capture from patient sera is demonstrated. The demonstrated platform offers rapid capture, high specificity, and sensitivity, with only a small need in analyte volume and without additional purification steps. The platform is applied in context of cancer-associated EVs, but it can easily be adapted to other diagnostic EV targets by use of corresponding antibodies.

Pressure Unfolding of Proteins: New Insights into the Role of Bound Water

High pressures can be detrimental for protein stability, resulting in unfolding and loss of function. This phenomenon occurs because the unfolding transition is accompanied by a decrease in volume, which is typically attributed to the elimination of cavities that are present within the native state as a result of packing defects. We present a novel computational approach that enables the study of pressure unfolding in atomistically detailed protein models in implicit solvent. We include the effect of pressure using a transfer free energy term that allows us to decouple the effect of protein residues and bound water molecules on the volume change upon unfolding. We discuss molecular dynamics simulations results using this protocol for two model proteins, Trp-cage and staphylococcal nuclease (SNase). We find that the volume reduction of bound water is the key energetic term that drives protein denaturation under the effect of pressure, for both Trp-cage and SNase. However, we note differences in unfolding mechanisms between the smaller Trp-cage and the larger SNase protein. Indeed, the unfolding of SNase, but not Trp-cage, is seen to be further accompanied by a reduction in the volume of internal cavities. Our results indicate that, for small peptides, like Trp-cage, pressure denaturation is driven by the increase in solvent accessibility upon unfolding, and the subsequent increase in the number of bound water molecules. For larger proteins, like SNase, the cavities within the native fold act as weak spots, determining the overall resistance to pressure denaturation. Our simulations display a striking agreement with the pressure-unfolding profile experimentally obtained for SNase and represent a promising approach for a computationally efficient and accurate exploration of pressure-induced denaturation of proteins.

A Critical Review of the Use of Surfactant-Coated Nanoparticles in Nanomedicine and Food Nanotechnology

Surfactants, whose existence has been recognized as early as 2800 BC, have had a long history with the development of human civilization. With the rapid development of nanotechnology in the latter half of the 20th century, breakthroughs in nanomedicine and food nanotechnology using nanoparticles have been remarkable, and new applications have been developed. The technology of surfactant-coated nanoparticles, which provides new functions to nanoparticles for use in the fields of nanomedicine and food nanotechnology, is attracting a lot of attention in the fields of basic research and industry. This review systematically describes these "surfactant-coated nanoparticles" through various sections in order: 1) surfactants, 2) surfactant-coated nanoparticles, application of surfactant-coated nanoparticles to 3) nanomedicine, and 4) food nanotechnology. Furthermore, current progress and problems of the technology using surfactant-coated nanoparticles through recent research reports have been discussed.

Novel Algorithm to Generate Hydrogen-Disordered Ice Structures

We propose an efficient algorithm for generating hydrogen-disordered ice networks utilizing graph theory and the topological characteristic of the network. The computational efficiency with the new algorithm is much higher than the conventional ones developed by Rahman and Stillinger and Buch et al. The difference in the computational time between our algorithm and either of the two conventional ones increases with increasing the system size.

The Role of Cyclodextrins against Interface-Induced Denaturation in Pharmaceutical Formulations: A Molecular Dynamics Approach

Protein-based pharmaceutical products are subject to a variety of environmental stressors, during both production and shelf-life. In order to preserve their structure, and, therefore, functionality, it is necessary to use excipients as stabilizing agents. Among the eligible stabilizers, cyclodextrins (CDs) have recently gained interest in the scientific community thanks to their properties. Here, a computational approach is proposed to clarify the role of β-cyclodextrin (βCD) and 2-hydroxypropyl-β-cyclodextrin (HPβCD) against granulocyte colony-stimulating (GCSF) factor denaturation at the air–water and ice–water interfaces, and also in bulk water at 300 or 260 K. Both traditional molecular dynamics (MD) simulations and enhanced sampling techniques (metadynamics, MetaD) are used to shed light on the underlying molecular mechanisms. Bulk simulations revealed that CDs were preferentially included within the surface hydration layer of GCSF, and even included some peptide residues in their hydrophobic cavity. HPβCD was able to stabilize the protein against surface-induced denaturation in proximity of the air–water interface, while βCD had a destabilizing effect. No remarkable conformational changes of GCSF, or noticeable effect of the CDs, were instead observed at the ice surface. GCSF seemed less stable at low temperature (260 K), which may be attributed to cold-denaturation effects. In this case, CDs did not significantly improve conformational stability. In general, the conformationally altered regions of GCSF seemed not to depend on the presence of excipients that only modulated the extent of destabilization with either a positive or a negative effect.

Enhancing the preservation of liposomes: The role of cryoprotectants, lipid formulations and freezing approaches

In the last decades, liposomes acquired a striking success in the biomedical field thanks to their biocompatibility and drug delivery ability. Many liposomal drug formulations have been already approved by the Food and Drug Administration (FDA) and used for the treatment of a wide range of pathologies with or without further engineering. Their clinical application requires strict compliance with high standard quality rules, and it is crucial to employ storage methods that do not affect the integrity of the vesicles and preventing the leakage of their cargo. In this work, the design of a suitable formulation for freeze-drying had been investigated for two different liposomes, DOPC-DOTAP and the PEGylated counterpart, DOPC-DOTAP-DSPE-PEG. The role of various cryoprotectants was evaluated paying attention to their ability to preserve the structural integrity of liposomes. At first, the study was focused on freezing and two methodologies were investigated, quenching in liquid nitrogen and shelf-ramped freezing. This analysis showed that the disaccharides (cellobiose, glucose, lactose, sucrose, and trehalose) and the polyol (mannitol) protected successfully the integrity of liposomes, while during the process, in the presence of a surfactant, liposomes were strongly damaged and fragmented by the ice crystals. Furthermore, the choice of the rate of freezing depended on the different compositions of the lipid bilayer. Finally, the effects of lyophilization on liposomes with and without additives were studied; cellobiose, lactose and trehalose showed encouraging results for the maintenance of the morpho-functional parameters of liposomes during the entire freeze-drying process.

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.

A model-based approach for the rational design of the freeze-thawing of a protein-based formulation

Proteins are unstable molecules that may be severely injured by stresses encountered during freeze-thawing. Despite this, the selection of freeze-thaw conditions is currently empirical, and this results in reduced process control. Here we propose a mathematical model that takes into account the leading causes of protein instability during freeze-thawing, i.e. cold denaturation and surface-induced unfolding, and may guide the selection of optimal operating conditions. It is observed that a high cooling rate is beneficial for molecules that are extremely sensitive to cold denaturation, while the opposite is true when ice-induced unfolding is dominant. In all cases, a fast thawing rate is observed to be beneficial. The simulation outputs are confirmed by experimental data for myoglobin and lactate dehydrogenase, suggesting that the proposed modeling approach can reproduce the main features of protein behavior during freeze-thawing. This approach can therefore guide the selection of optimal conditions for protein-based formulations that are stored in a frozen or freeze-dried state.

Denaturant-Mediated Modulation of the Formation and Drug Encapsulation Responses of Gold Nanoparticles

The extensive and diversified applications of the well-known plasmonic nanoparticle systems along with their easy and environment-friendly synthesis strategies drive us to investigate in-depth this important research field. In the current scenario, our present study deals with an important plasmonic nanomaterial, i.e., globular protein, and human serum albumin (HSA)-conjugated gold nanoparticle (HSA-Au NP) system. The well-known chemical denaturants, urea and guanidine hydrochloride (GdnHCl or GnHCl), are investigated to show detrimental effects toward the formation of gold nanoparticles; however, the effect of GdnHCl is observed to be much prominent compared to that of urea. The synthesized nanoparticle system is found to be highly biocompatible from the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)-based cytotoxicity assay, and therefore, the applications of encapsulation of the well-known anticancer drug molecule, doxorubicin hydrochloride (Dox), in the nanoparticle system are further studied. In this drug encapsulation study, drug-metal complexation between Dox and HAuCl₄·3H₂O has been discussed elaborately. Similar to the nanoparticle formation, the effects of denaturants on drug encapsulation have also been discovered, and interestingly, it has been observed that urea plays a positive role, whereas GdnHCl plays a negative or detrimental role toward drug encapsulation in the synthesized gold nanoparticle system. The detailed photophysical mechanisms behind the drug encapsulation in the synthesized plasmonic nanosystem at every stage have also been explored. Overall, this study will conclusively explain the influences of the extensively used chemical denaturants on the synthesis and drug encapsulation behaviors of a well-known protein-conjugated gold nanoparticle, and as a consequence, it can be highly useful and acceptable to the biomedical and pharmaceutical research communities.

Considerations on Protein Stability During Freezing and Its Impact on the Freeze-Drying Cycle: A Design Space Approach

Freezing is widely used during the manufacturing process of protein-based therapeutics, but it may result in undesired loss of biological activity. Many variables come into play during freezing that could adversely affect protein stability, creating a complex landscape of interrelated effects. The current approach to the selection of freezing conditions is however nonsystematic, resulting in poor process control. Here we show how mathematical models, and a design space approach, can guide the selection of the optimal freezing protocol, focusing on protein stability. Two opposite scenarios are identified, suggesting that the ice-water interface is the dominant cause of denaturation for proteins with high bulk stability, while the duration of the freezing process itself is the key parameter to be controlled for proteins that are susceptible to cold denaturation. Experimental data for lactate dehydrogenase and myoglobin as model proteins support the model results, with a slow freezing rate being optimal for lactate dehydrogenase and the opposite being true for myoglobin. A possible application of the calculated design space to the freezing and freeze-drying of biopharmaceuticals is finally described, and some considerations on process efficiency are discussed as well.