The molecular chaperone alpha-crystallin as an excipient in an insulin formulation

Chlorogenic Acid Enhances the Chaperone Potential of BSA at Physiological Concentrations on Model Protein Cytochrome c

Neurodegenerative disorders are associated with the accumulation of disease-related proteins intracellularly and extracellularly. Extracellular chaperones play a crucial role in clearing the extracellularly accumulated proteins. In this study, we observed the extracellular chaperone-like potential of BSA at physiological concentrations on model protein cytochrome c (cyt c). Kinetics of heat-induced aggregation of cyt c suggest the nucleation independent first order aggregation kinetics. Aggregation of cyt c was studied in the presence of varying concentrations of BSA to assess its chaperone nature. At lower concentrations of BSA when the sub molar ratio of cyt c:BSA are 1:0.6 and 1:1.2, heat-induced unfolded cyt c promotes the aggregation of BSA. However, as the ratio of cyt c:BSA increases to 1:1.8, the aggregation of cyt c is reduced. When the concentration of BSA reaches physiological levels, yielding a cyt c:BSA ratio of 1:2.4, the rate of aggregation drastically decreases reflecting its chaperone potential. These observations indicate that under physiological conditions, macromolecular crowding stabilizes the native structure of both proteins and enhances their interaction that results in the reduced aggregation of cyt c. Additionally, the presence of the phytochemical chlorogenic acid at a sub-molar ratio of 1:1 stabilizes cyt c and prevents its unfolding and facilitates the binding of cyt c to BSA at physiological concentrations. This interaction further decreases the overall aggregation of cyt c and stabilizes its native fold.

Chaperone/Polymer Complexation of Protein-Based Fluorescent Nanoclusters against Silica Encapsulation-Induced Physicochemical Stresses

Silica encapsulation under ambient conditions is commonly used to shield protein-based nanosystems from chemical stress. However, encapsulation-induced photo- and structural instabilities at elevated temperatures have been overlooked. Using bovine serum albumin-capped fluorescent gold nanoclusters (BSA-AuNCs) as a model, we demonstrated that chaperone/polymer layer-by-layer complexation can stabilize the template to resist encapsulation-induced fragmentation/reorganization and emission increases at 37 °C or higher temperatures. We first wrapped BSA-AuNCs with α-crystallin chaperones (α-Crys) to gain the highest thermal stability at a 1:50 molar ratio and then enfolded BSA-AuNC/α-Crys with thermoresponsive poly-N-isopropylacrylamide (PNIPAM) at 60 °C to shield silica interaction and increase the chaperone-client protein accessibility. The resulting BSA-AuNC/α-Crys/PNIPAM (BαP) was encapsulated by a sol-gel process to yield BαP-Si (∼80 ± 4.5 nm), which exhibited excellent structural integrity and photostability against chemical and thermal stresses. Moreover, targeted BαP-Si demonstrated prolonged fluorescence stability for cancer cell imaging. This template stabilization strategy for silica encapsulation is biocompatible and applicable to other protein-based nanosystems.

Bovine serum albumin prevents human hemoglobin aggregation and retains its chaperone-like activity

This study investigates the ability of bovine serum albumin (BSA) to act as an extracellular chaperone (EC) on human hemoglobin (Hb) at a pH of 7.4. The best temperature for studying this behavior was determined by analyzing Hb's aggregation kinetics at multiple temperatures. 55 °C was chosen as the optimal temperature for forming Hb amyloids. BSA was then tested at various concentrations (20-100 μM) to assess its chaperone-like activity on Hb at 55 °C. At a concentration of 100 μM, BSA exhibits chaperone-like activity with a client protein:BSA ratio of 1:10. The high ratio implies that the chaperone activity of BSA is favored by the effects of macromolecular crowding. The results showed that BSA has the potential to inhibit Hb's dissociation into alpha and beta subunits and protein aggregation by inhibiting secondary nucleation. BSA also causes the depolymerization of fibrils over time. The results were validated using molecular docking and all-atom molecular dynamics simulations. MD analysis such as RMSD, RMSF, Rg, SASA, Hydrogen bond, PCA, Free energy landscape (FEL) revealed that the stability of hemoglobin is greater when it is bound to BSA compared to unbound state. The study suggests that BSA can potentially bind to Hb dimers and reduce excitonic interactions, which reduces Hb aggregation. These results are consistent with the aggregation kinetics experiments.Communicated by Ramaswamy H. Sarma.

Heterogeneous and Surface-Catalyzed Amyloid Aggregation Monitored by Spatially Resolved Fluorescence and Single Molecule Microscopy

Amyloid aggregation is associated with many diseases and may also occur in therapeutic protein formulations. Addition of co-solutes is a key strategy to modulate the stability of proteins in pharmaceutical formulations and select inhibitors for drug design in the context of diseases. However, the heterogeneous nature of this multicomponent system in terms of structures and mechanisms poses a number of challenges for the analysis of the chemical reaction. Using insulin as protein system and polysorbate 80 as co-solute, we combine a spatially resolved fluorescence approach with single molecule microscopy and machine learning methods to kinetically disentangle the different contributions from multiple species within a single aggregation experiment. We link the presence of interfaces to the degree of heterogeneity of the aggregation kinetics and retrieve the rate constants and underlying mechanisms for single aggregation events. Importantly, we report that the mechanism of inhibition of the self-assembly process depends on the details of the growth pathways of otherwise macroscopically identical species. This information can only be accessed by the analysis of single aggregate events, suggesting our method as a general tool for a comprehensive physicochemical characterization of self-assembly reactions.

Nano-assemblies enhance chaperone activity, stability, and delivery of alpha B-crystallin-D3 (αB-D3)

Crystallins, small heat shock chaperone proteins that prevent protein aggregation, are of potential value in treating protein aggregation disorders. However, their therapeutic use is limited by their low potency and poor intracellular delivery. One approach to facilitate the development of crystallins is to improve their activity, stability, and delivery. In this study, zinc addition to αB-crystallin-D3 (αB-D3) formed supramolecular nano- and micro- assemblies, induced dose-dependent changes in structure (beta-sheet to alpha-helix) and increased surface hydrophobicity and chemical stability. Further, crystallin assemblies exhibited a size-dependent chaperone activity, with the nano-assemblies being superior to micro-assemblies and 4.3-fold more effective than the native protein in preventing β-mercaptoethanol induced aggregation of insulin. Insulin rescued by crystallin assemblies retained the activity as evidenced by glucose uptake in 3T3-L1 cells. The most active nano-assemblies enhanced protein stability, in the presence of urea, by 1.6-fold, whereas intracellular delivery was enhanced by 3.0-fold. The αB-D3 crystallin nano-assemblies exhibit uniquely enhanced stability, activity, and delivery compared to the native protein.

Science and art of protein formulation development

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

Human αB-crystallin as fusion protein and molecular chaperone increases the expression and folding efficiency of recombinant insulin

Low expression and instability are significant challenges in the recombinant production of therapeutic peptides. The current study introduces a novel expression and purification system for human insulin production using the molecular chaperone αB-crystallin (αB-Cry) as a fusion partner protein. Insulin is composed of A- and B-chain containing three disulfide bonds (one intarchain and two interchains). We have constructed two plasmids harboring the A- or B-chain of insulin joined with human αB-Cry. This system is suitable for cloning of the genes and for directing the synthesis of large amounts of the fusion proteins αB-Cry/A-chain (αB-AC) and αB-Cry/B-chain (αB-BC). The construction of vectors, their efficient expression in Escherichia coli and simple purification of the fusion proteins and two insulin chains are described. A large amount of the recombinant fusion proteins with high purity was obtained by applying a single step anion exchange chromatography or metal chelate affinity. The insulin A- and B-chain were released from the fusion proteins using cyanogen bromide cleavage. The insulin peptides were obtained with an appreciable yield and high purity using one-step gel filtration chromatography. To increase efficiency of chain combination to produce insulin, αB-Cry was used under oxidative conditions. The purification of natively folded insulin was performed by phenyl sepharose hydrophobic interaction chromatography. Finally, using an insulin tolerance test in mice and various biophysical methods, the structure and function of purified human recombinant insulin was compared with authentic insulin, to verify folding of insulin to its native state. Overall, the novel expression system using αB-Cry is highly demanding for producing human insulin and functional protein. The procedure for αB-Cry-mediated insulin folding could be also applicable for the large-scale production of this highly important therapeutic peptide hormone.

Sensitivity of human pluripotent stem cells to insulin precipitation induced by peristaltic pump-based medium circulation: considerations on process development

Controlled large-scale production of human pluripotent stem cells (hPSCs) is indispensable for their envisioned clinical translation. Aiming at advanced process development in suspension culture, the sensitivity of hPSC media to continuous peristaltic pump-based circulation, a well-established technology extensively used in hydraulically-driven bioreactors, was investigated. Unexpectedly, conditioning of low protein media (i.e. E8 and TeSR-E8) in a peristaltic pump circuit induced severe viability loss of hPSCs cultured as aggregates in suspension. Optical, biochemical, and cytological analyses of the media revealed that the applied circulation mode resulted in the reduction of the growth hormone insulin by precipitation of micro-sized particles. Notably, in contrast to insulin depletion, individual withdrawal of other medium protein components (i.e. bFGF, TGFβ1 or transferrin) provoked minor reduction of hPSC viability, if any. Supplementation of the surfactant glycerol or the use of the insulin analogue Aspart did not overcome the issue of insulin precipitation. In contrast, the presence of bovine or human serum albumin (BSA or HSA, respectively) stabilized insulin rescuing its content, possibly by acting as molecular chaperone-like protein, ultimately supporting hPSC maintenance. This study highlights the potential and the requirement of media optimization for automated hPSC processing and has broad implications on media development and bioreactor-based technologies.

Human serum albumin reduces the potency of acetylcholinesterase inhibitor based drugs for Alzheimer's disease

Human serum albumin (HSA) induced modulation of acetylcholinesterase (AChE) inhibition activity of four well-known cholinergic inhibitors like tacrine hydrochloride (TAC), donepezil hydrochloride monohydrate (DON), (-) Huperzine A (HuPA), eserine (ESE) was monitored quantitatively by Ellman's method. Kinetic analysis of enzyme hydrolysis reaction revealed that while the mechanism of inhibition does not change significantly, the inhibition efficiency changes drastically in presence of HSA, particularly for DON and TAC. However, interestingly, no notable difference was observed in the cases of HuPA and/or ESE. For example, the IC50 value of AChE inhibition increases by almost 135% in presence of ∼250 μM HSA (IC50 = 159 ± 8 nM) while comparing with aqueous buffer solution of pH 8.0 (IC50 = 68 ± 4 nM) in DON. On the other hand, the change is almost insignificant (<10%) in case of HuPA under the similar condition. The experimentally observed difference in the extent of modulatory effect was correlated with the sequestration ability of HSA towards different drugs predicted from molecular docking calculations. The result in this study demonstrates the importance to consider the plasma protein binding tendency of a newly synthesized AD drug before claiming its potency over the existing one. Further, development of new and intelligent delivery medium that shields the administered drugs from serum adsorption may reduce the optimal drug dose requirement.

The Inhibitory Effect of Natural Products on Protein Fibrillation May Be Caused by Degradation Products--A Study Using Aloin and Insulin

Protein fibrillation is the pathological hallmark of several neurodegenerative diseases and also complicates the manufacturing and use of protein drugs. As a case study, the inhibitory activity of the natural compound aloin against insulin fibrillation was investigated. Based on Thioflavin T assays, high-performance liquid chromatography and transmission electron microscopy it was found that a degradation product of aloin, formed over weeks of storage, was able to significantly inhibit insulin fibrillation. The activity of the stored aloin was significantly reduced in the presence of small amounts of sodium azide or ascorbic acid, suggesting the active compound to be an oxidation product. A high-performance liquid chromatography method and a liquid chromatography-mass spectrometry method were developed to investigate the degradation products in the aged aloin solution. We found that the major compounds in the solution were aloin A and aloin B. In addition, 10-hydroxy aloin and elgonica dimers were detected in smaller amounts. The identified compounds were isolated and tested for activity by means of Thioflavin T assays, but no activity was observed. Thus, the actual fibrillation inhibitor is an as yet unidentified and potentially metastable degradation product of aloin. These results suggest that degradation products, and in particular oxidation products, are to be considered thoroughly when natural products are investigated for activity against protein fibrillation.

Introducing DInaMo: A Package for Calculating Protein Circular Dichroism Using Classical Electromagnetic Theory

The dipole interaction model is a classical electromagnetic theory for calculating circular dichroism (CD) resulting from the π-π* transitions of amides. The theoretical model, pioneered by J. Applequist, is assembled into a package, DInaMo, written in Fortran allowing for treatment of proteins. DInaMo reads Protein Data Bank formatted files of structures generated by molecular mechanics or reconstructed secondary structures. Crystal structures cannot be used directly with DInaMo; they either need to be rebuilt with idealized bond angles and lengths, or they need to be energy minimized to adjust bond lengths and bond angles because it is common for crystal structure geometries to have slightly short bond lengths, and DInaMo is sensitive to this. DInaMo reduces all the amide chromophores to points with anisotropic polarizability and all nonchromophoric aliphatic atoms including hydrogens to points with isotropic polarizability; all other atoms are ignored. By determining the interactions among the chromophoric and nonchromophoric parts of the molecule using empirically derived polarizabilities, the rotational and dipole strengths are determined leading to the calculation of CD. Furthermore, ignoring hydrogens bound to methyl groups is initially explored and proves to be a good approximation. Theoretical calculations on 24 proteins agree with experiment showing bands with similar morphology and maxima.

Advanced protein formulations

It is well recognized that protein product development is far more challenging than that for small-molecule drugs. The major challenges include inherent sensitivity to different types of stresses during the drug product manufacturing process, high rate of physical and chemical degradation during long-term storage, and enhanced aggregation and/or viscosity at high protein concentrations. In the past decade, many novel formulation concepts and technologies have been or are being developed to address these product development challenges for proteins. These concepts and technologies include use of uncommon/combination of formulation stabilizers, conjugation or fusion with potential stabilizers, site-specific mutagenesis, and preparation of nontraditional types of dosage forms-semiaqueous solutions, nonfreeze-dried solid formulations, suspensions, and other emerging concepts. No one technology appears to be mature, ideal, and/or adequate to address all the challenges. These gaps will likely remain in the foreseeable future and need significant efforts for ultimate resolution.

Amide I vibrational mode suppression in surface (SERS) and tip (TERS) enhanced Raman spectra of protein specimens

Surface- and tip-enhanced Raman spectroscopy (SERS and TERS) are modern spectroscopic techniques, which are becoming widely used and show a great potential for the structural characterisation of biological systems. Strong enhancement of the Raman signal through localised surface plasmon resonance enables chemical detection at the single-molecule scale. Enhanced Raman spectra collected from biological specimens, such as peptides, proteins or microorganisms, were often observed to lack the amide I band, which is commonly used as a marker for the interpretation of the secondary protein structure. The cause of this phenomenon was unclear for many decades. In this work, we investigated this phenomenon for native insulin and insulin fibrils using both TERS and SERS and compared these spectra to the spectra of well-defined homo peptides. The results indicate that the appearance of the amide I Raman band does not correlate with the protein aggregation state, but is instead determined by the size of the amino acid side chain. For short model peptides, the absence of the amide I band in TERS and SERS spectra correlates with the presence of a bulky side chain. Homo-glycine and -alanine, which are peptides with small side chain groups (H and CH(3), respectively), exhibited an intense amide I band in almost 100% of the acquired spectra. Peptides with bulky side chains, such as tyrosine and tryptophan, exhibited the amide I band in 70% and 31% of the acquired spectra, respectively.

Deconstruction of stable cross-Beta fibrillar structures into toxic and nontoxic products using a mutated archaeal chaperonin

Our group recently determined that a mutant archaeal chaperonin (Hsp 60) exhibited substantially enhanced protein folding activity at low temperatures and was able to deconstruct refractory protein aggregates. ATP dependent conversion of fibril structures into amorphous aggregates was observed in insulin amyloid preparations (Kurouski et al. Biochem. Biophys. Res. Commun. 2012). In the current study, mechanistic insights into insulin fibril deconstruction were obtained by examination of early stage complexes between Hsp60 and fibrils in the absence of ATP. Activity of the Hsp60 was significantly curtailed without ATP; however, some fibril deconstruction occurred, which is consistent with some models of the folding cycle that predict initial removal of unproductive protein folds. Chaperonin molecules adsorbed on the fibril surface and formed chaperonin clusters with no ATP present. We propose that there are specific locations on the fibril surface where chaperonin can unravel the fibril to release short fragments. Spontaneous coagulation of these fibril fragments resulted in the formation of amorphous aggregates without the release of insulin into solution. The addition of ATP significantly increased the toxicity of the insulin fibril-chaperonin reaction products toward mammalian cells.

Serum albumin prevents protein aggregation and amyloid formation and retains chaperone-like activity in the presence of physiological ligands

Although serum albumin has an established function as a transport protein, evidence is emerging that serum albumin may also have a role as a molecular chaperone. Using established techniques to characterize chaperone interactions, this study demonstrates that bovine serum albumin: 1) preferentially binds stressed over unstressed client proteins; 2) forms stable, soluble, high molecular weight complexes with stressed client proteins; 3) reduces the aggregation of client proteins when it is present at physiological levels; and 4) inhibits amyloid formation by both WT and L55P transthyretin. Although the antiaggregatory effect of serum albumin is maintained in the presence of physiological levels of Ca(2+) and Cu(2+), the presence of free fatty acids significantly alters this activity: stabilizing serum albumin at normal levels but diminishing chaperone-like activity at high concentrations. Moreover, here it is shown that depletion of albumin from human plasma leads to a significant increase in aggregation under physiologically relevant heat and shear stresses. This study demonstrates that serum albumin possesses chaperone-like properties and that this activity is maintained under a number of physiologically relevant conditions.

Materials for diabetes therapeutics

This review is focused on the materials and methods used to fabricate closed-loop systems for type 1 diabetes therapy. Herein, we give a brief overview of current methods used for patient care and discuss two types of possible treatments and the materials used for these therapies-(i) artificial pancreases, comprised of insulin producing cells embedded in a polymeric biomaterial, and (ii) totally synthetic pancreases formulated by integrating continuous glucose monitors with controlled insulin release through degradable polymers and glucose-responsive polymer systems. Both the artificial and the completely synthetic pancreas have two major design requirements: the device must be both biocompatible and be permeable to small molecules and proteins, such as insulin. Several polymers and fabrication methods of artificial pancreases are discussed: microencapsulation, conformal coatings, and planar sheets. We also review the two components of a completely synthetic pancreas. Several types of glucose sensing systems (including materials used for electrochemical, optical, and chemical sensing platforms) are discussed, in addition to various polymer-based release systems (including ethylene-vinyl acetate, polyanhydrides, and phenylboronic acid containing hydrogels).

DnaK prevents human insulin amyloid fiber formation on hydrophobic surfaces

We have developed a multiwell-based protein aggregation assay to study the kinetics of insulin adsorption and aggregation on hydrophobic surfaces and to investigate the molecular mechanisms involved. Protein-surface interaction progresses in two phases: (1) a lag phase during which proteins adsorb and prefibrillar aggregates form on the material surface and (2) a growth phase during which amyloid fibers form and then are progressively released into solution. We studied the effect of three bacterial chaperones, DnaK, DnaJ, and ClpB, on insulin aggregation kinetics. In the presence of ATP, the simultaneous presence of DnaK, DnaJ, and ClpB allows good protection of insulin against aggregation. In the absence of ATP, DnaK alone is able to prevent insulin aggregation. Furthermore, DnaK binds to insulin adsorbed on hydrophobic surfaces. This process is slowed in the presence of ATP and can be enhanced by the cochaperone DnaJ. The peptide LVEALYL, derived from the insulin B chain, is known to promote fast aggregation in a concentration- and pH-dependent manner in solution. We show that it also shortens the lag phase for insulin aggregation on hydrophobic surfaces. As this peptide is also a known DnaK substrate, our data indicate that the peptide and the chaperone might compete for a common site during the process of insulin aggregation on hydrophobic surfaces.

Plain and mono-pegylated recombinant human insulin exhibit similar stress-induced aggregation profiles

PEGylation has been suggested to improve the stability of insulin, but evidence for that is scarce. Here, we compared the forced aggregation behavior of insulin and mono-PEGylated insulin. Therefore, recombinant human insulin was conjugated on lysine B29 with 5-kDa PEG. PEG-insulin was purified by size-exclusion chromatography (SEC) and characterized by mass spectrometry (MS). Next, insulin and PEG-insulin were subjected to heating at 75 °C, metal-catalyzed oxidation, and glutaraldehyde cross-linking. The products were characterized physicochemically by complementary analytical methods. Mono-PEGylation of insulin was confirmed by SEC and MS. Under each of the applied stress conditions, insulin and PEG-insulin showed comparable degradation profiles. All the stressed samples showed submicron aggregates in the size range between 50 and 500 nm. Covalent aggregates and conformational changes were found for both oxidized products. Insulin and its PEGylated counterpart also exhibited similar characteristics when exposed to heat stress, that is, slightly changed secondary and tertiary structures, covalent aggregates with partially intact epitopes, and separation of chain A from chain B. Both glutaraldehyde-treated insulin and PEG-insulin contained covalent and noncovalent aggregates with intact epitopes, showed partially perturbed secondary structure, and substantial loss of tertiary structure. From these results, we conclude that PEGylation does not protect insulin against forced aggregation.

Paradoxical acceleration of dithiothreitol-induced aggregation of insulin in the presence of a chaperone

The kinetics of dithiothreitol (DTT)-induced aggregation of human recombinant insulin and the effect of α-crystallin, a representative of the family of small heat shock proteins, on the aggregation process have been studied using dynamic light scattering technique. Analysis of the distribution of the particles by size measured in the course of aggregation showed that the initial stage of the aggregation process was the stage of formation of the start aggregates with a hydrodynamic radius (R(h)) of about 90 nm. When studying the effect of α-crystallin on the rate of DTT-induced aggregation of insulin, it was demonstrated that low concentrations of α-crystallin dramatically accelerated the aggregation process, whereas high concentrations of α-crystallin suppressed insulin aggregation. In the present study, at the molar stoichiometric ratio (insulin:α-crystallin) less than 1:0.5, a pronounced accelerating effect of α-crystallin was observed; whereas a ratio exceeding the value of 1:0.6 caused suppression of insulin aggregation. The mechanisms underlying the dual effect of α-crystallin have been proposed. It is assumed that heterogeneous nucleation occurring on the surface of the α-crystallin particle plays the key role in the paradoxical acceleration of insulin aggregation by α-crystallin that may provide an alternative biologically significant pathway of the aggregation process.