Shear-Induced Deformation of Bovine Insulin in Couette Flow

Microfluidic Stress Device to Decouple the Synergistic Effect of Shear and Interfaces on Antibody Aggregation

Protein denaturation and aggregation resulting from the effects of interfacial stress, often enhanced by flow and shear stress, pose significant challenges in the production of therapeutic proteins and monoclonal antibodies. The influence of flow on protein stability is closely intertwined with interfacial effects. In this study, we have developed a microfluidic device capable of exposing low volume (< 320 µL) protein solutions to highly uniform shear. To disentangle the synergistic impact of flow and interfaces on protein aggregation, we fabricated two devices composed of different materials, namely poly(methyl methacrylate) (PMMA) and stainless steel. Upon application of shear, we observed formation of protein particles in the micron-size range. Notably, The number of particles generated in the steel devices was ∼ 3.5 fold lower than in the PMMA device, hinting at an interface-mediated effect. With increasing the protein concentration from 1 to 50 mg/mL we observed a saturation in the amount of aggregates, further confirming the key role of solid-liquid interfaces in inducing particle formation. Introduction of non-ionic surfactants prevented protein aggregation, even at the highest tested protein concentration and low surfactant concentrations of 0.05 mg/mL. Overall, our findings corroborate the synergistic impact of shear and interface effects on protein aggregation. The device developed in this study offers a small-scale platform for assessing the stability of antibody formulations throughout various stages of the development and manufacturing process.

Design of a Reciprocal Injection Device for Stability Studies of Parenteral Biological Drug Products

Formulation screening, essential for assessing the impact of physical, chemical, and mechanical stresses on protein stability, plays a critical role in biologics drug product development. This research introduces a Reciprocal Injection Device (RID) designed to accelerate formulation screening by probing protein stability under intensified stress conditions within prefilled syringes. This versatile device is designed to accommodate a broad spectrum of injection parameters and diverse syringe dimensions. A commercial drug product was employed as a model monoclonal antibody formulation. Our findings effectively highlight the efficacy of the RID in assessing concentration-dependent protein stability. This device exhibits significant potential to amplify the influences of interfacial interactions, such as those with buffer salts, excipients, air, metals, and silicone oils, commonly found in combination drug products, and to evaluate the protein stability under varied stresses.

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.

Effect of Protein Content on Heat Stability of Reconstituted Milk Protein Concentrate under Controlled Shearing

Milk protein concentrates (MPCs) possess significant potential for diverse applications in the food industry. However, their heat stability may be a limitation to achieving optimal functional performance. Shearing, an inherent process in food manufacturing, can also influence the functionality of proteins. The aim of this research was to examine the heat stability of reconstituted MPCs prepared at two protein concentrations (4% and 8% w/w protein) when subjected to varying levels of shearing (100, 1000, or 1500 s-1) during heating at 90 °C for 5 min or 121 °C for 2.6 min. While the impact of shear was relatively minor at 4% protein, it was more pronounced in 8% protein MPC suspensions, leading to a considerable decline in heat stability. An increase in protein concentration to 8% amplified protein interactions, intensified by shearing. This, in turn, resulted in comparatively higher aggregation at elevated temperatures and subsequently reduced the heat stability of the reconstituted MPCs.

Heat-Induced Changes in κ-Carrageenan-Containing Chocolate-Flavoured Milk Protein Concentrate Suspensions under Controlled Shearing

Milk protein dispersions containing added cocoa powder (1.5% (w/w)) and sucrose (7% (w/w)) and varying levels of κ-carrageenan (0.01, 0.03, or 0.05% w/w) were subjected to combined heat treatment (90 °C/5 min or 121 °C/2.6 min) and shear (100 or 1000 s-1) to investigate the heat stability of milk proteins. The application of shear led to a notable reduction in non-sedimentable proteins, resulting in an increase in the average particle size and apparent viscosity of the dispersions, particularly at high concentrations of k-carrageenan and elevated temperatures. This indicates that shear forces induced prominent protein aggregation, especially at higher κ-carrageenan concentrations. This aggregation was primarily attributed to the destabilisation of micelles and presence of loosely bound caseins within the κ-carrageenan network, which exhibited increased susceptibility to aggregation as collision frequencies increased due to shear.

Rotational Dynamics of a Protein under Shear Flow Studied by the Eckart Frame Formalism

Proteins are natural polymers that play an essential role in both living organisms and biotechnological applications. During certain bioprocessing steps, they can be exposed to significant mechanical stress induced by, for example, shear flow or sonication, resulting in reduced therapeutic efficacy, aggregation, or even a loss of activity. For this reason, there is a need to understand and determine the susceptibility of the protein activity to the experienced mechanical stress. To acquire this knowledge, it is necessary to study the rotational dynamics of the protein. Commonly, the rotational dynamics of soft molecules is interpreted based on a theoretical analysis performed in an inertial laboratory frame. However, the obtained angular velocity mixes pure rotations and vibrations with angular momentum, consequently lacking a clear dynamical interpretation. On the other hand, the use of the noninertial internal Eckart frame allows the determination of pure angular velocity as it minimizes the coupling between the rotational and vibrational degrees of freedom. In the present work, by conducting open-boundary molecular dynamics simulations and exploiting the Eckart frame formalism, we study the rotational dynamics of a small protein under the shear flow of various strengths. Our results show that the angular velocity increases nonlinearly with increasing shear rate. Furthermore, the protein gains vibrational angular momentum at higher shear rates, which is reflected in the higher angular velocity computed by employing the Eckart frame formalism and confirmed by analysis of the contributions to the total kinetic energy of the biomolecule.

Surface-Induced Protein Aggregation and Particle Formation in Biologics: Current Understanding of Mechanisms, Detection and Mitigation Strategies

Protein stability against aggregation is a major quality concern for the production of safe and effective biopharmaceuticals. Amongst the different drivers of protein aggregation, increasing evidence indicates that interactions between proteins and interfaces represent a major risk factor for the formation of protein aggregates in aqueous solutions. Potentially harmful surfaces relevant to biologics manufacturing and storage include air-water and silicone oil-water interfaces as well as materials from different processing units, storage containers, and delivery devices. The impact of some of these surfaces, for instance originating from impurities, can be difficult to predict and control. Moreover, aggregate formation may additionally be complicated by the simultaneous presence of interfacial, hydrodynamic and mechanical stresses, whose contributions may be difficult to deconvolute. As a consequence, it remains difficult to identify the key chemical and physical determinants and define appropriate analytical methods to monitor and predict protein instability at these interfaces. In this review, we first discuss the main mechanisms of surface-induced protein aggregation. We then review the types of contact materials identified as potentially harmful or detected as potential triggers of proteinaceous particle formation in formulations and discuss proposed mitigation strategies. Finally, we present current methods to probe surface-induced instabilities, which represent a starting point towards assays that can be implemented in early-stage screening and formulation development of biologics.

Kinetics of aggregation of amyloid β under different shearing conditions: Experimental and modelling analyses

Amyloid β (Aβ40) is a class of amyloidogenic proteins known to aggregate into a fibrillar network. The rate of aggregation and fibril yield is sensitive to external energy input, such as shear. In this work, simple shear and shaking experiments are performed on Aβ40 solution using a Couette cell and an orbital shaker, respectively. Experiments show that, under uniform shear, both the mass of fibrils and aggregation rate increase with the shear rate. In the case of orbital shaking, the lag time decreases with the rotational speed of the shaker, but the final fibril mass is the same for all agitation speeds. To explain this contrasting behavior of aggregation kinetics, a population balance model is developed to account for the effect of shear on the aggregation of Aβ. The kinetic model includes primary nucleation, secondary nucleation, elongation, fragmentation, and depolymerization steps. The effect of steady uniform shear is encoded in the depolymerization rate constant (k_d), and it is shown that k_d decreases with shear rate initially and saturates at high shear rates. A competition between elongation and depolymerization rates yields different equilibrium masses of fibril at different shear rates. The model results agree quantitatively well with experimental data on the rate of aggregation and mass of fibrils as a function of shear rate. The modeling framework can be used to explain the shear rate-dependent aggregation of other amyloidogenic proteins.

Nanostructured Lipid Carriers (NLCs) for Oral Peptide Drug Delivery: About the Impact of Surface Decoration

This study was aimed to evaluate the impact of surfactants used for nanostructured lipid carriers (NLCs) to provide enzymatic protection for incorporated peptides. Insulin as a model peptide was ion paired with sodium dodecyl sulfate to improve its lipophilicity. Three NLC formulations containing polyethylene glycol ester (PEG-ester), polyethylene glycol ether (PEG-ether), and polyglycerol ester (PG-ester) surfactants were prepared by solvent diffusion method. NLCs were characterized regarding particle size, polydispersity index, and zeta potential. Biocompatibility of NLCs was assessed on Caco-2 cells via resazurin assay. In vitro lipolysis study was performed using a standard lipid digestion method. Proteolytic studies were performed in simulated gastric fluid containing pepsin and simulated intestinal fluid containing pancreatin. Lipophilicity of insulin in terms of log Poctanol/water was improved from -1.8 to 2.1. NLCs were in the size range of 64-217 nm with a polydispersity index of 0.2-0.5 and exhibited a negative surface charge. PG-ester NLCs were non-cytotoxic up to a concentration of 0.5%, PEG-ester NLCs up to a concentration of 0.25% and PEG-ether NLC up to a concentration of 0.125% (w/v). The lipolysis study showed the release of >90%, 70%, and 10% of free fatty acids from PEG-ester, PG-ester, and PEG-ether NLCs, respectively. Proteolysis results revealed the highest protective effect of PEG-ether NLCs followed by PG-ester and PEG-ester NLCs for incorporated insulin complex. Findings suggest that NLCs bearing substructures less susceptible to degrading enzymes on their surface can provide higher protection for incorporated peptides toward gastrointestinal proteases.

Study of the Enzyme Activity Change due to Inkjet Printing for Biosensor Fabrication

Enzymes, the most commonly used biosensing element, have a great influence on the performance of biosensors. Recently, drop-on-demand (DOD) printing technique has been widely employed for the fabrication of biosensors due to its merits of noncontact, less waste, and rapid deposition. However, enzyme printing studies were rarely conducted on the effect of printing parameters from the aspect of the pressure wave propagation mechanism. This study investigated the effects of pressure wave propagation on enzyme activity from the aspects of wave superposition, wave amplitude, resulting mechanical stress, and protein conformation change using pyruvate oxidase as the model enzyme. We found that the mechanical stress increased the activity of pyruvate oxidase during the inkjet printing process. A shear rate of 3 × 10⁵ s^-1 enhanced the activity by 14.10%. The enhancement mechanism was investigated, and the mechanical activation or mild proteolysis was found to change the conformation of pyruvate oxidase and improve its activity. This study is fundamental to understand the effect of both printing mechanism and induced mechanical stress on the properties of biomolecules and plays an important role in modulating the activity of other enzyme-based inks, which is crucial for the development of biosensors.

Characteristics and influencing factors of amyloid fibers in S. mutans biofilm

There are signs that amyloid fibers exist in Streptococcus mutans biofilm recently. However, the characteristics of amyloid fibers and fibrillation influencing factors are unknown. In this study, we firstly used transmission electron microscopy (TEM) and atomic force microscopy (AFM) to observe the morphology of amyloid fibers in S. mutans. Then the extracted amyloid fibers from biofilm were studied for their characteristics. Further, the influencing factors, PH, temperature and eDNA, were investigated. Results showed there were mainly two morphologies of amyloid fibers in S. mutans, different in width. Amyloid fibers inhibitor-EGCG obviously destroyed biofilm at different stages, which is dose-dependent. The amount of amyloid fibers positively correlated with biofilm biomass in clinical isolates. Acidic pH and high temperature obviously accelerated amyloid fibrillation. During amyloid fibrillation, amyloid growth morphologies were observed by TEM and results showed two growth morphologies. Amyloid fibers formed complex with eDNA, which we call (a)eDNA. The molecular weight of (a)eDNA was similar to genomic DNA, greatly larger than that of eDNA in matrix. Combined use of DNase I and EGCG was more efficiently in inhibiting amyloid fibers and biofilm biomass. In conclusion, amyloid fibers are the crucial structures for S. mutans biofilm formation, showing two types of morphology. Acidic pH and temperature can obviously accelerate amyloid fibrillation. Amyloid fibers form complex with (a)eDNA and combined use of DNase and amyloid fiber inhibitor is more efficiently in inhibiting S. mutans biofilm formation.

Three Weaknesses for Three Perturbations: Comparing Protein Unfolding Under Shear, Force, and Thermal Stresses

The perturbation of a protein conformation by a physiological fluid flow is crucial in various biological processes including blood clotting and bacterial adhesion to human tissues. Investigating such mechanisms by computer simulations is thus of great interest, but it requires development of ad hoc strategies to mimic the complex hydrodynamic interactions acting on the protein from the surrounding flow. In this study, we apply the Lattice Boltzmann Molecular Dynamics (LBMD) technique built on the implicit solvent coarse-grained model for protein Optimized Potential for Efficient peptide structure Prediction (OPEP) and a mesoscopic representation of the fluid solvent, to simulate the unfolding of a small globular cold-shock protein in shear flow and to compare it to the unfolding mechanisms caused either by mechanical or thermal perturbations. We show that each perturbation probes a specific weakness of the protein and causes the disruption of the native fold along different unfolding pathways. Notably, the shear flow and the thermal unfolding exhibit very similar pathways, while because of the directionality of the perturbation, the unfolding under force is quite different. For force and thermal disruption of the native state, the coarse-grained simulations are compared to all-atom simulations in explicit solvent, showing an excellent agreement in the explored unfolding mechanisms. These findings encourage the use of LBMD based on the OPEP model to investigate how a flow can affect the function of larger proteins, for example, in catch-bond systems.

The relevance of shear, sedimentation and diffusion during spin freezing, as potential first step of a continuous freeze-drying process for unit doses

Recently, a continuous freeze-drying process for the production of unit doses was presented and evaluated. In this concept, the freezing step is modified compared to traditional batch freeze-drying, as glass vials filled with a liquid formulation, are rotated around their longitudinal axis while cooled and frozen with a cold, sterile and inert gas (i.e. spin freezing). Finally, a thin frozen product layer spread over the entire vial wall is achieved. The aim of this paper is twofold: firstly, the relation between the rotation velocity and the relative difference between top and bottom of the frozen product layer thickness was determined for different vial types. Secondly, the impact of shear and centrifugal forces generated during spinning was examined, to find out whether they might cause pharmaceutical instability and sedimentation, respectively. Mechanistic and experimental evaluation showed that shear has no effect on proteins. Calculations showed that the sedimentation and diffusion velocity is too low to cause inhomogeneity in the product layer. In addition, Global Sensitivity Analysis (GSA) and Uncertainty Analysis (UA) were performed in order to account for the uncertainty of the used mechanistic model.

Molecular Mechanism of Protein Unfolding under Shear: A Lattice Boltzmann Molecular Dynamics Study

Proteins are marginally stable soft-matter entities that can be disrupted using a variety of perturbative stresses, including thermal, chemical, or mechanical ones. Fluid under extreme flow conditions is a possible route to probe the weakness of biomolecules and collect information on the molecular cohesive interactions that secure their stability. Moreover, in many cases, physiological flow triggers the functional response of specialized proteins as occurring in blood coagulation or cell adhesion. We deploy the Lattice Boltzmann molecular dynamics technique based on the coarse-grained model for protein OPEP to study the mechanism of protein unfolding under Couette flow. Our simulations provide a clear view of how structural elements of the proteins are affected by shear, and for the simple study case, the β-hairpin, we exploited the analogy to pulling experiments to quantify the mechanical forces acting on the protein under shear.

Nanoscale Control of Amyloid Self-Assembly Using Protein Phase Transfer by Host-Guest Chemistry

Amyloid fibrils have recently been highlighted for their diverse applications as functional nanomaterials in modern chemistry. However, tight control to obtain a targeted fibril length with low heterogeneity has not been achieved because of the complicated nature of amyloid fibrillation. Herein, we demonstrate that fibril assemblies can be homogeneously manipulated with desired lengths from ~40 nm to ~10 μm by a phase transfer of amyloid proteins based on host-guest chemistry. We suggest that host-guest interactions with cucurbit[6]uril induce a phase transfer of amyloid proteins (human insulin, human islet amyloid polypeptide, hen egg lysozyme, and amyloid-β 1–40 & 1–42) from the soluble state to insoluble state when the amount of cucurbit[6]uril exceeds its solubility limit in solution. The phase transfer of the proteins kinetically delays the nucleation of amyloid proteins, while the nuclei formed in the early stage are homogeneously assembled to fibrils. Consequently, supramolecular assemblies of amyloid proteins with heterogeneous kinetics can be controlled by protein phase transfer based on host-guest interactions.

High-Sensitivity Rheo-NMR Spectroscopy for Protein Studies

Shear stress can induce structural deformation of proteins, which might result in aggregate formation. Rheo-NMR spectroscopy has the potential to monitor structural changes in proteins under shear stress at the atomic level; however, existing Rheo-NMR methodologies have insufficient sensitivity to probe protein structure and dynamics. Here we present a simple and versatile approach to Rheo-NMR, which maximizes sensitivity by using a spectrometer equipped with a cryogenic probe. As a result, the sensitivity of the instrument ranks highest among the Rheo-NMR spectrometers reported so far. We demonstrate that the newly developed Rheo-NMR instrument can acquire high-quality relaxation data for a protein under shear stress and can trace structural changes in a protein during fibril formation in real time. The described approach will facilitate rheological studies on protein structural deformation, thereby aiding a physical understanding of shear-induced amyloid fibril formation.

The stability of insulin solutions in syringes is improved by ensuring lower molecular weight silicone lubricants are absent

Protein drugs such as insulin are almost universally delivered via glass syringes lubricated with silicone oil. It is not uncommon for prefilled syringes (PFS) to become cloudy, which may affect bioavailability or total drug dose. To examine the role, if any, of the silicone oil lubricant in this process, a systematic evaluation of the degree of insulin denaturation and aggregation as a function of silicone oils of different molecular weights was undertaken. The former was measured using fluorescence changes of aqueous insulin/silicone dispersions, while the latter examined changes in turbidity as a function of mixing and silicone oil type; the results were confirmed at two different insulin concentrations and agitation speeds. Lower molecular weight silicones led to the most rapid denaturation and aggregation, and when examined in blends of silicones at a fixed viscosity of 1000 cSt, commonly used for syringe lubrication, more rapid denaturation/aggregation was noted in blends of silicones containing the largest fractions of low molecular weight materials. As a consequence, the molecular weight profile of silicone lubricants should be established prior to the preparation of prefilled syringes.

Protein structural changes during processing of vegetable feed ingredients used in swine diets: implications for nutritional value

Protein structure influences the accessibility of enzymes for digestion. The proportion of intramolecular β-sheets in the secondary structure of native proteins has been related to a decrease in protein digestibility. Changes to proteins that can be considered positive (for example, denaturation and random coil formation) or negative (for example, aggregation and Maillard reactions) for protein digestibility can occur simultaneously during processing. The final result of these changes on digestibility seems to be a counterbalance of the occurrence of each phenomenon. Occurrence of each phenomenon depends on the conditions applied, but also on the source and type of the protein that is processed. The correlation between denaturation enthalpy after processing and protein digestibility seems to be dependent on the protein source. Heat seems to be the processing parameter with the largest influence on changes in the structure of proteins. The effect of moisture is usually limited to the simultaneous application of heat, but increasing level of moisture during processing usually increases structural changes in proteins. The effect of shear on protein structure is commonly studied using extrusion, although the multifactorial essence of this technology does not allow disentanglement of the separate effects of each processing parameter (for example, heat, shear, moisture). Although most of the available literature on the processing of feed ingredients reports effects on protein digestibility, the mechanisms that explain these effects are usually lacking. Clarifying these mechanisms could aid in the prediction of the nutritional consequences of processing conditions.

Catalase-only nanoparticles prepared by shear alone: Characteristics, activity and stability evaluation

Catalase is a promising therapeutic enzyme; however, it carries risks of inactivation and rapid degradation when it is used in practical bioprocess, such as delivery in vivo. To overcome the issue, we made catalase-only nanoparticles using shear stress alone at a moderate shear rate of 217s(-1) in a coaxial cylinder flow cell. Properties of nanoparticles, including particle size, polydispersity index and zeta potential, were characterized. The conformational changes of pre- and post-sheared catalase were determined using spectroscopy techniques. The results indicated that the conformational changes of catalase and reduction in α-helical content caused by shear alone were less significant than that by desolvation method. Catalase-only nanoparticles prepared by single shear retained over 90% of its initial activity when compared with the native catalase. Catalase nanoparticles lost only 20% of the activity when stored in phosphate buffer solution for 72h at 4°C, whereas native catalase lost 53% under the same condition. Especially, the activity of nanogranulated catalase was decreased only slightly in the simulated intestinal fluid containing α-chymotrypsin during 4h incubation at 37°C, implying that the catalase nanoparticle was more resistant to the degradation of proteases than native catalase molecules. Overall, catalase-only nanoparticles offered a great potential to stabilize enzymes for various pharmaceutical applications.

Kinetics and cluster morphology evolution of shear-driven aggregation of well-stabilized colloids

We investigate the shear-driven aggregation of polystyrene colloids that are stabilized by both fixed and surfactant charges, using a microchannel device, in various particle volume fractions. The objective is to understand how the primary particles evolve to clusters with shearing time, how the cluster morphology develops along the aggregation with the effect of breakage and restructuring, and whether non-Derjaguin-Landau-Verwey-Overbeek (DLVO) interactions are present, affecting the kinetics. The time evolution of the primary particle conversion to big clusters is characterized by an induction time, followed by an explosive increase when the cluster size reaches a certain critical value, which confirms the self-acceleration kinetics developed in the literature. The size of the critical clusters has been quantified for the first time, and its scaling with the shear rate follows the literature prediction well. Moreover, analysis of the shear-driven kinetics confirms the presence of substantial non-DLVO interactions in the given system.

Formation of platinum-coated templates of insulin nanowires used in reducing 4-nitrophenol

Modern technology demands ever smaller and more efficient nanoparticles, wires and networks. The natural tendency for amyloid proteins to form fibrillar structures is leveraged in creating high aspect ratio, nano-sized protein fibers as scaffolds for metallized nanowires. The morphology of fibrils is influenced by induced strain during denaturing and early aggregation and subsequent fibril deposition with platinum leads to controlled catalyst surfaces based on the initial protein precipitate. Here we have created insulin fibrils with varying morphologies produced in the presence of heat and strain and investigated their metallization with platinum by TEM. The catalytic activity of the metal-coated protein fibrils was resolved by tracking the reaction kinetics of the conversion of 4-nitrophenol to 4-aminophenol in the presence of the produced nanowires using UV-Vis spectroscopy. The effects of fibril morphology and temperature on the pseudo-first-order kinetics of conversion are investigated. Conversion to 4-aminophenol occurs on the order of minutes and is independent of temperature in the range tested (7 to 20°C). Two regimes of conversion are identified, an early higher rate, followed by a slower later rate.

Agitation of amyloid proteins to speed aggregation measured by ThT fluorescence: a call for standardization

This retrospective study of protein aggregation measured by Thioflavin T (ThT) fluorescence assay in published literature has assessed protein sensitivity to denaturing conditions that include elevated temperatures, fluctuations in pH, and concentration and, in particular, agitation to induce amyloid structure formation. The dynamic tracking of fluorescence shows a sigmoidal evolution as aggregates form; the resulting kinetics of association have been analyzed to explore the range of aggregation behavior which occurs based on environmental parameters. Comparisons between the experimental results of different groups have been historically difficult due to subtleties of experimental procedures including denaturing temperature, protein type and concentration, formulation differences, and how agitation is achieved. While it is clear that agitation has a strong influence on the driving force for aggregation, the use of magnetic stirring bar or shaker table rotational speed is insufficient to characterize the degree of turbulence produced during shear. The pathway forward in resolving dependence of aggregate formation on shear may require alternative methodologies or better standardization of the experimental protocols.

A brief overview of amyloids and Alzheimer's disease

Amyloid fibrils are self-assembled fibrous protein aggregates that are associated with a number of presently incurable diseases such as Alzheimer's and Parkinson's disease. Millions of people worldwide suffer from amyloid diseases. This review summarizes the unique cross-β structure of amyloid fibrils, morphological variations, the kinetics of amyloid fibril formation, and the cytotoxic effects of these fibrils and oligomers. Alzheimer's disease is also explored as an example of an amyloid disease to show the various approaches to treat these amyloid diseases. Finally, this review investigates the nanotechnological and biological applications of amyloid fibrils; as well as a summary of the typical biological pathways involved in the disposal of amyloid fibrils and their precursors.

Electric field induced changes in protein conformation

The effect of a low strength oscillating electric field on the conformation of Bovine Serum Albumin (BSA) and Lysozyme in solution has been measured. A purpose built cell has been used to measure the real time autofluorescence and Circular Dichroism of the protein solutions exposed to electric fields of differing strength and frequency. Exposure to the electric fields results in protein unfolding for both Lysozyme and BSA. The applied field strengths are extremely small compared to the protein inter-chain intra-molecular forces. We propose a model whereby the electrophoretic motion of the proteins leads to a frictional force that results in protein unfolding. For BSA and Lysozyme in the electric fields used in this study, the shear rates at the protein surface under electrophoretic motion are of order 10(3) and 10(4) s(-1) respectively. Prolonged electric field exposure results in significant frictional energy dissipation in the proteins. The energy dissipated in the proteins results in protein unfolding, which is a critical initial step for protein aggregation and potentially amyloid fibril formation.

Misfolding of amyloidogenic proteins and their interactions with membranes

In this paper, we discuss amyloidogenic proteins, their misfolding, resulting structures, and interactions with membranes, which lead to membrane damage and subsequent cell death. Many of these proteins are implicated in serious illnesses such as Alzheimer’s disease and Parkinson’s disease. Misfolding of amyloidogenic proteins leads to the formation of polymorphic oligomers and fibrils. Oligomeric aggregates are widely thought to be the toxic species, however, fibrils also play a role in membrane damage. We focus on the structure of these aggregates and their interactions with model membranes. Study of interactions of amlyoidogenic proteins with model and natural membranes has shown the importance of the lipid bilayer in protein misfolding and aggregation and has led to the development of several models for membrane permeabilization by the resulting amyloid aggregates. We discuss several of these models: formation of structured pores by misfolded amyloidogenic proteins, extraction of lipids, interactions with receptors in biological membranes, and membrane destabilization by amyloid aggregates perhaps analogous to that caused by antimicrobial peptides.

Understanding the relationship between biotherapeutic protein stability and solid-liquid interfacial shear in constant region mutants of IgG1 and IgG4

Relative stability of therapeutic antibody candidates is currently evaluated primarily through their response to thermal degradation, yet this technique is not always predictive of stability in manufacture, shipping, and storage. A rotating disk shear device is proposed that produces defined shear conditions at a known solid–liquid interface to measure stability in this environment. Five variants of IgG1 and IgG4 antibodies were created using combinations of two discrete triple amino acid sequence mutations denoted TM and YTE. Antibodies were ranked for stability based on shear device output (protein decay coefficient, PDC), and compared with accelerated thermal stability data and the melting temperature of the CH2 domain (T_m1) from differential scanning calorimetry to investigate technique complimentarity. Results suggest that the techniques are orthogonal, with thermal methods based on intramolecular interaction and shear device stability based on localized unfolding revealing less stable regions that drive aggregation. Molecular modeling shows the modifications’ effects on the antibody structures and indicates a possible role for Fc conformation and Fab-Fc docking in determining suspended protein stability. The data introduce the PDC value as an orthogonal stability indicator, complementary to traditional thermal methods, allowing lead antibody selection based on a more full understanding of process stability. © 2013 The Authors. Journal of Pharmaceutical Sciences published by Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 103:437–444, 2014

Manufacturing and device options for the delivery of biotherapeutics

Biotherapeutic aerosol formulations are an intense area of interest for systemic and local drug delivery. This article provides a short overview of typical factors required specifically for biotherapeutic aerosol formulation design, the processing options open for consideration, and the issue of inhalation device selection. Focusing on spray drying, four case studies are used to highlight the relevant issues, describing investigations into: (1) the mechanical stresses occurring in bacteriophage formulations during spray-dryer atomization; (2) modeling of the spray-dryer process and droplet drying kinetics, to assist process design and predictions of formulation stability; (3) a predictive approach to the design and processing of a five-component dry powder aerosol formulation; and (4) the survival of bacteriophages after pressurized metered dose inhaler atomization.

The effect of concentration, temperature and stirring on hen egg white lysozyme amyloid formation

Lysozyme is associated with hereditary systemic amyloidosis in humans. Hen egg white lysozyme (HEWL) has been extensively studied as an amyloid forming protein. In this study, we investigated HEWL amyloid formation over a range of temperatures at two stirring speeds and at low concentrations to avoid gel formation. The amyloid fibril formation was found to follow first order kinetics with the rate determining step being the unfolding of the lysozyme. Both the rate of formation and final amount of amyloid formed show maxima with temperature at approximately at 65 °C. CD measurements show that the lysozyme is unfolded by 55 °C. The decrease in amyloid formation at temperatures above 65 °C is attributed to competing amorphous aggregation. The majority of the non-fibrillar aggregates are small and uniform in size with a few larger amorphous aggregates observed in the AFM images.

Vortex-induced amyloid superstructures of insulin and its component A and B chains

Insulin is an amyloid-forming polypeptide built of two disulfide-linked chains (A and B), both themselves amyloidogenic. An interesting property of insulin is that agitation strongly influences the course of its aggregation, resulting in characteristic chiral superstructures of amyloid fibrils. Here, we investigate the self-assembly of these superstructures by comparing the quiescent and vortex-assisted aggregation of insulin and its individual A and B chains in the presence or absence of reducing agent tris(2-carboxyethyl)phosphine (TCEP). Our study shows that only the B chain in the presence of TCEP is converted into aggregates with morphology (according to atomic force microscopy) and optical activity (manifested as an extrinsic Cotton effect induced in bound thioflavin T) characteristic of amyloid superstructures that are normally formed by insulin in the absence of TCEP. In contrast to more rigid B-peptide fibrils, elongated aggregates of the A peptide become amorphous upon agitation. Moreover, the aggregation of equimolar mixture of both peptides does not produce highly ordered entities. Our results suggest that the dynamics of the B chain are the driving force for the assembly of superstructures, with the A chain being complicit as long as its own dynamics are controlled by the firm attachment to the B chain provided by the intact covalent structure of insulin.

Shear flow induced changes in apolipoprotein C-II conformation and amyloid fibril formation

The misfolding and self-assembly of proteins into amyloid fibrils that occur in several debilitating diseases are affected by a variety of environmental factors, including mechanical factors associated with shear flow. We examined the effects of shear flow on amyloid fibril formation by human apolipoprotein C-II (apoC-II). Shear fields (150, 300, and 500 s(-1)) accelerated the rate of apoC-II fibril formation (1 mg/mL) approximately 5-10-fold. Fibrils produced at shear rates of 150 and 300 s(-1) were similar to the twisted ribbon fibrils formed in the absence of shear, while at 500 s(-1), tangled ropelike structures were observed. The mechanism of the shear-induced acceleration of amyloid fibril formation was investigated at low apoC-II concentrations (50 μg/mL) where fibril formation does not occur. Circular dichroism and tryptophan fluorescence indicated that shear induced an irreversible change in apoC-II secondary structure. Fluorescence resonance energy transfer experiments using the single tryptophan residue in apoC-II as the donor and covalently attached acceptors showed that shear flow increased the distance between the donor and acceptor molecules. Shear-induced higher-order oligomeric species were identified by sedimentation velocity experiments using fluorescence detection, while fibril seeding experiments showed that species formed during shear flow are on the fibril formation pathway. These studies suggest that physiological shear flow conditions and conditions experienced during protein manufacturing can exert significant effects on protein conformation, leading to protein misfolding, aggregation, and amyloid fibril formation.

Detecting the early onset of shear-induced fibril formation of insulin in situ

A new approach is presented for detecting the early onset of amyloid fibril formation of insulin in a fluidic environment. The fibrillogenesis of insulin in a well-characterized Taylor-Couette flow cell was analyzed in situ using Raman spectroscopy in combination with principal components analysis (PCA). Raman spectra recorded using a 532.5 nm excitation laser revealed a more rapid fibrillogenesis process during the first 90 min of shearing than previously reported for samples exposed to flow. Bands corresponding to intermolecular H-bonded β-sheet structure of insulin at 1678, 1630, and 1625 cm(-1) observed in the Raman difference spectra between unsheared insulin and sheared insulin show an increase in intensity as a function of shear exposure time, which is characteristic of fibril formation, with the first changes detected after 10 min. Additional analysis of samples removed from the flow cell after specific time periods provided conformation of the flow-enhanced fibrillogenesis process, including the detection of early fibril formation after only 1 min of shearing. FT-IR spectra of the insulin solutions showed evolution of bands at 1673 and 1633 cm(-1) from an increase in H-bonded β-turn and β-sheet structures, respectively, while fluorescence emission spectra detected the presence of a new emission band at 482 nm. TEM images confirmed the early onset of fibril formation at 1 min shear exposure, before a maturation and concentration increase of fibrils with further shearing. This study highlights the ability of fluid flows to accelerate insulin fibril formation, which has important implications for biotechnology applications such as the purification process of insulin therapeutic drugs in the pharmaceutical industry, as well as the use of optical-based methods for detecting fibrillogenesis.

Rheo-NMR studies of an enzymatic reaction: evidence of a shear-stable macromolecular system

Understanding the effects of shear forces on biopolymers is key to understanding how biological systems function. Although currently there is good agreement between theoretical predictions and experimental measurements of the behavior of DNA and large multimeric proteins under shear flow, applying the same arguments to globular proteins leads to the prediction that they should only exhibit shear-induced conformational changes at extremely large shear rates. Nevertheless, contradictory experimental evidence continues to appear, and the effect of shear on these biopolymers remains contentious. Here, a custom-built rheo-NMR cell was used to investigate whether shear flow modifies enzyme action compared with that observed quiescently. Specifically, (1)H NMR was used to follow the kinetics of the liberation of methanol from the methylesterified polysaccharide pectin by pectinmethylesterase enzymes. Two different demethylesterifying enzymes, known to have different action patterns, were used. In all experiments performed, Couette flows with shear rates of up to 1570 s(-1) did not generate detectable differences in the rate of methanol liberation compared to unsheared samples. This study provides evidence for a shear-stable macromolecular system consisting of a largely beta-sheet protein and a polysaccharide, in line with current theoretical predictions, but in contrast to some other experimental work on other proteins.