Global kinetic analysis of seeded BSA aggregation

Glycyl-l-histidyl-l-lysine prevents copper- and zinc-induced protein aggregation and central nervous system cell death in vitro

Common features of neurodegenerative diseases are oxidative and inflammatory imbalances as well as the misfolding of proteins. An excess of free metal ions can be pathological and contribute to cell death, but only copper and zinc strongly promote protein aggregation. Herein we demonstrate that the endogenous copper-binding tripeptide glycyl-l-histidyl-l-lysine (GHK) has the ability to bind to and reduce copper redox activity and to prevent copper- and zinc-induced cell death in vitro. In addition, GHK prevents copper- and zinc-induced bovine serum albumin aggregation and reverses aggregation through resolubilizing the protein. We further demonstrate the enhanced toxicity of copper during inflammation and the ability of GHK to attenuate this toxicity. Finally, we investigated the effects of copper on enhancing paraquat toxicity and report a protective effect of GHK. We therefore conclude that GHK has potential as a cytoprotective compound with regard to copper and zinc toxicity, with positive effects on protein solubility and aggregation that warrant further investigation in the treatment of neurodegenerative diseases.

Evaluation and Screening of Biopharmaceuticals using Multi-Angle Dynamic Light Scattering

Biopharmaceuticals are large, complex and labile therapeutic molecules prone to instability due to various factors during manufacturing. To ensure their safety, quality and efficacy, a wide range of critical quality attributes (CQAs) such as product concentration, aggregation, particle size, purity and turbidity have to be met. Size exclusion chromatography (SEC) is the gold standard to measure protein aggregation and degradation. However, other techniques such as dynamic light scattering (DLS) are employed in tandem to measure the particle size distribution (PSD) and polydispersity of biopharmaceutical formulations. In this study, the application of multi-angle dynamic light scattering (MADLS) was evaluated for the determination of particle size, particle concentration and aggregation in 3 different protein modalities, namely bovine serum albumin (BSA) and two biopharmaceuticals including a monoclonal antibody (mAb) and an enzyme. The obtained calibration curve (R² > 0.95) for the particle number concentration of the 3 proteins and the observed correlation between MADLS and SEC (R² = 0.9938) for the analysis of aggregation in the enzyme can be employed as a 3-in-1 approach to assessing particle size, concentration and aggregation for the screening and development of products while also reducing the number of samples and experiments required for analysis prior to other orthogonal tests.

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.

Size-based Degradation of Therapeutic Proteins - Mechanisms, Modelling and Control

Protein therapeutics are in great demand due to their effectiveness towards hard-to-treat diseases. Despite their high demand, these bio-therapeutics are very susceptible to degradation via aggregation, fragmentation, oxidation, and reduction, all of which are very likely to affect the quality and efficacy of the product. Mechanisms and modelling of these degradation (aggregation and fragmentation) pathways is critical for gaining a deeper understanding of stability of these products. This review aims to provide a summary of major developments that have occurred towards unravelling the mechanisms of size-based protein degradation (particularly aggregation and fragmentation), modelling of these size-based degradation pathways, and their control. Major caveats that remain in our understanding and control of size-based protein degradation have also been presented and discussed.

Strategies for the functionalisation of gold nanorods to reduce toxicity and aid clinical translation

Gold nanorods (GNRs) show great promise as photothermal therapy agents due to their remarkable ability to convert light into heat. In most cases, gold nanorods are synthesised via a seed-mediated method assisted by surfactants. However, the toxicity of these surfactants, principally cetrimonium ions, has prevented GNRs from being used more widely in vivo. To address this issue, various detoxification and functionalisation approaches have been proposed in recent years to replace or cover surfactant coatings on the gold surface. In this short review, the advantages and limitations of each approach are examined in the context of the recent progress made towards the design of GNRs suitable for use in the body.

Nano-Bio Interaction between Blood Plasma Proteins and Water-Soluble Silicon Quantum Dots with Enabled Cellular Uptake and Minimal Cytotoxicity

A better understanding of the compatibility of water-soluble semiconductor quantum dots (QDs) upon contact with the bloodstream is important for biological applications, including biomarkers working in the first therapeutic spectral window for deep tissue imaging. Herein, we investigated the conformational changes of blood plasma proteins during the interaction with near-infrared light-emitting nanoparticles, consisting of Pluronic F127 shells and cores comprised of assembled silicon QDs terminated with decane monolayers. Albumin and transferrin have high quenching constants and form a hard protein corona on the nanoparticle. In contrast, fibrinogen has low quenching constants and forms a soft protein corona. A circular dichroism (CD) spectrometric study investigates changes in the protein’s secondary and tertiary structures with incremental changes in the nanoparticle concentrations. As expected, the addition of nanoparticles causes the denaturation of the plasma proteins. However, it is noteworthy that the conformational recovery phenomena are observed for fibrinogen and transferrin, suggesting that the nanoparticle does not influence the ordered structure of proteins in the bloodstream. In addition, we observed enabled cellular uptake (NIH3T3 Fibroblasts) and minimal cytotoxicity using different cell lines (HeLa, A549, and NIH3T3). This study offers a basis to design QDs without altering the biomacromolecule’s original conformation with enabled cellular uptake with minimal cytotoxicity.

Molecular Interaction of Protein-Pigment C-Phycocyanin with Bovine Serum Albumin in a Gomphosis Structure Inhibiting Amyloid Formation

Accumulation of amyloid fibrils in organisms accompanies many diseases. Natural extracts offer an alternative strategy to control the process with potentially fewer side effects. In this study, the inhibition of C-phycocyanin from Spirulina sp. on amyloid formation of bovine serum albumin (BSA) during a 21-day incubation was investigated using fluorescence and circular dichroism (CD), and mechanisms were explored via kinetic fitting and molecular docking. C-phycocyanin (0-50 µg/mL) hindered the amyloid formation process of BSA with increased half-lives (12.43-17.73 days) based on fluorescence intensity. A kinetic model was built and showed that the k₁ decreased from 1.820 × 10^-2 d^-1 to 2.62 × 10^-3 d^-1 with the increase of C-phycocyanin, while k₂ showed no changes, indicating that the inhibition of BSA fibrillation by C-phycocyanin occurred in a spontaneous process instead of self-catalyzed one. CD results show that C-phycocyanin inhibited conformational conversion (α-helices and β-sheets) of BSA from day 6 to day 18. Molecular docking suggested that C-phycocyanin may hinder BSA fibrillation by hydrogen-bonding > 6 of 27 α-helices of BSA in a gomphosis-like structure, but the unblocked BSA α-helices might follow the self-catalytic process subsequently.

Room Temperature Intrinsic Emission Ratio of BSA Correlates With Percent Aggregates During Long-Term Storage

Successful formulation development hinges on the ability to screen and identify excipients that stabilize drug products during long-term storage. Biophysical and accelerated stability studies are used to screen for excipients that stabilize protein drug products. However, these studies are not always predictive of aggregation during long-term storage. In this study, we used multivariate experimentation to compare the effectiveness of intrinsic fluorescence and size exclusion chromatography accelerated stability parameters to predict excipients that stabilized bovine serum albumin (BSA) against aggregation on long-term storage at 4 °C. Emission intensity ratio (IR_330/350) data was more sensitive than emission maxima (λ_max) or intensity measurements in identifying significant factors and interactions. We observed the expected inverse correlation between the mid-points of fluorescence thermal transitions (T_ms) and insoluble aggregates at 4 and 40 °C. However, there were positive correlations between T_ms and % aggregates at 4 °C, indicating that if T_m was used as a predictive tool, it would select formulations that promoted soluble aggregates on long-term storage. Ambient temperature IR_330/350 measurements identified excipients that reduced BSA soluble aggregates on long-term storage. The results show ambient temperature emission ratio measurements can be useful for protein formulation development.

Protein corona formation and its constitutional changes on magnetic nanoparticles in serum featuring a polydehydroalanine coating: effects of charge and incubation conditions

The inevitable formation of a protein corona upon contact of nanoparticles with different biological fluids is of great interest in the context of biomedical applications. It is well established that the surface chemistry of the respective nanomaterial has tremendous impact on protein adsorption, both in terms of the actual amount as well as the type of proteins adsorbed. In that regard, especially polyzwitterions are discussed as coating materials as they are known to partially inhibit protein adsorption. We herein present comparative incubation studies on iron oxide nanoparticles (either single core (SPION) or multicore nanoparticles (MCNP)) after coating with either polyanionic or polyzwitterionic polymeric shells based on polydehydroalanine (PDha). Apart from varying surface charge and chemistry, also the influence of incubation time and temperature on the formation and composition of a protein corona upon exposure to fetal calf serum was investigated. The amounts of adsorbed biomolecules were determined using thermogravimetric analysis. SDS-PAGE experiments revealed information on protein composition as major components of the biomolecule corona. Our results show that distinctly lower amounts of proteins are adsorbed onto polyzwitterionic hybrid nanoparticles in general, but also the corona composition varies as indicated by elevated relative ratios of medium molecular weight proteins (i.e. proteins 25-100 kDa) estimated by non-specific silver protein staining. In addition, increasing relative amounts of albumin (67 kDa) via specific Western blot assays on PDha-coated MCNP are detected.

Preparation-free method can enable rapid surfactant screening during industrial processing of influenza vaccines

Triton X-100 (TX-100) is the most common surfactant used to split viruses during the production of influenza split-virus vaccines. It is a mild surfactant not known to denature the viral proteins; this property makes TX-100 useful for maintaining antigen conformational structure, and, as an added benefit, for partially stabilizing vaccine formulations against protein aggregation. Despite its benefits, TX-100 needs to be filtered out after virus splitting has been achieved, due to its toxicity in large quantities. Accordingly, residual TX-100 presence in vaccine formulations has implications for both formulation stability and safety, necessitating both accurate screening during processing to guide decision-making about filtration repeats and accurate quantitation in the final product. Accurate HPLC-based methods are used successfully for the latter but their use for routine screening during processing is far from ideal because they often require extensive sample preparation and are fairly slow, complicated and costly. Here, "deconstruction" of UV-Vis absorption spectra into components corresponding to different absorbing "species" is demonstrated as a novel and viable method for routine TX-100 screening in vaccine samples from different industrial processing steps. This method is fairly accurate and, more importantly, preparation-free, rapid, simple/user-friendly and comparatively inexpensive. It is evaluated in depth in terms of applicability conditions, limitations and potential for high-throughput adaptation as well as generalization to other complex biopharmaceutical formulations.

Nile Red fluorescence spectrum decomposition enables rapid screening of large protein aggregates in complex biopharmaceutical formulations like influenza vaccines

The extensive presence of large (high molecular weight) protein aggregates in biopharmaceutical formulations is a concern for formulation stability and possibly safety. Tests to screen large aggregate content in such bioformulations are therefore needed for rapid and reliable quality control in industrial settings. Herein, non-commercial seasonal influenza split-virus vaccine samples, produced using various strains and extracted from selected industrial processing steps, were used as model complex bioformulations. Orthogonal characterization through transmission electron microscopy, UV-Vis absorption spectroscopy, fluorescence emission spectroscopy, high-performance liquid chromatography and single-radial immunodiffusion revealed that large, amorphous protein aggregates are formed after virus splitting and their presence is linked mainly, albeit not only, to surfactant (Triton X-100) content in a sample. Importantly, the presence of large virus aggregates in purified whole virus samples and large protein aggregates in vaccine samples was found to correlate with broadening/shouldering in Nile Red fluorescence spectra. Accordingly, decomposition of Nile Red spectra into components allowed the development of a novel, rapid, reliable and user-friendly test with high-throughput potential for screening large aggregate content in influenza split-virus vaccines. The test can be adapted for screening other complex biopharmaceutical formulations, provided relevant controls are done for informed decomposition of fluorescence spectra into their components.

Kinetics of Thermal Denaturation and Aggregation of Bovine Serum Albumin

Thermal aggregation of bovine serum albumin (BSA) has been studied using dynamic light scattering, asymmetric flow field-flow fractionation and analytical ultracentrifugation. The studies were carried out at fixed temperatures (60°C, 65°C, 70°C and 80°C) in 0.1 M phosphate buffer, pH 7.0, at BSA concentration of 1 mg/ml. Thermal denaturation of the protein was studied by differential scanning calorimetry. Analysis of the experimental data shows that at 65°C the stage of protein unfolding and individual stages of protein aggregation are markedly separated in time. This circumstance allowed us to propose the following mechanism of thermal aggregation of BSA. Protein unfolding results in the formation of two forms of the non-native protein with different propensity to aggregation. One of the forms (highly reactive unfolded form, U_hr) is characterized by a high rate of aggregation. Aggregation of U_hr leads to the formation of primary aggregates with the hydrodynamic radius (R_h,1) of 10.3 nm. The second form (low reactive unfolded form, U_lr) participates in the aggregation process by its attachment to the primary aggregates produced by the U_hr form and possesses ability for self-aggregation with formation of stable small-sized aggregates (A_st). At complete exhaustion of U_lr, secondary aggregates with the hydrodynamic radius (R_h,2) of 12.8 nm are formed. At 60°C the rates of unfolding and aggregation are commensurate, at 70°C the rates of formation of the primary and secondary aggregates are commensurate, at 80°C the registration of the initial stages of aggregation is complicated by formation of large-sized aggregates.