Carboxylic acids of different nature induces aggregation of hemoglobin

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.

Effects of polyol excipient stability during storage and use on the quality of biopharmaceutical formulations

Biopharmaceuticals are formulated using a variety of excipients to maintain their storage stability. However, some excipients are prone to degradation during repeated use and/or improper storage, and the impurities generated by their degradation are easily overlooked by end users and are usually not strictly monitored, affecting the stability of biopharmaceuticals. In this study, we evaluated the degradation profile of polyol excipient glycerol during repeated use and improper storage and identified an unprecedented cyclic ketal impurity using gas chromatography with mass spectrometry (GC-MS). The other polyol excipient, mannitol, was much more stable than glycerol. The effects of degraded glycerol and mannitol on the stability of the model biopharmaceutical pentapeptide, thymopentin, were also evaluated. The thymopentin content was only 66.4% in the thymopentin formulations with degraded glycerol, compared to 95.8% in other formulations after the stress test. Most glycerol impurities (i.e., aldehydes and ketones) reacted with thymopentin, affecting the stability of thymopentin formulations. In conclusion, this work suggests that more attention should be paid to the quality changes of excipients during repeated use and storage. Additional testing of excipient stability under real or accelerated conditions by manufacturers would help avoid unexpected and painful results.

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Unprecedented impurities in degraded glycerol were identified with GC-MS.

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Degradation of thymopentin due to glycerol degradation was determined using LC-MS/MS.

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Excipient stability affects biopharmaceutical formulation quality.

Functional block copolymer micelles based on poly (jasmine lactone) for improving the loading efficiency of weakly basic drugs

Functionalization of polymers is an attractive approach to introduce specific molecular forces that can enhance drug–polymer interaction to achieve higher drug loading when used as drug delivery systems. The novel amphiphilic block copolymer of methoxy poly(ethylene glycol) and poly(jasmine lactone) i.e., mPEG-b-PJL, derived from renewable jasmine lactone provides free allyl groups on the backbone thus, allowing flexible and facile post-synthesis functionalization. In this study, mPEG-b-PJL and its carboxyl functionalized polymer mPEG-b-PJL-COOH were utilised to explore the effect of ionic interactions on the drug–polymer behaviour. Various drugs with different pK_a values were employed to prepare drug-loaded polymeric micelles (PMs) of mPEG-b-PJL, mPEG-b-PJL-COOH and Soluplus® (polyvinyl caprolactam–polyvinyl acetate–polyethylene glycol graft copolymer) via a nanoprecipitation method. Electrostatic interactions between the COOH pendant on mPEG-b-PJL-COOH and the basic drugs were shown to influence the entrapment efficiency. Additionally, molecular dynamics (MD) simulations were employed to understand the polymer–drug interactions at the molecular level and how polymer functionalization influenced these interactions. The release kinetics of the anti-cancer drug sunitinib from mPEG-b-PJL and mPEG-b-PJL-COOH was assessed, and it demonstrated a sustainable drug release pattern, which depended on both pH and temperature. Furthermore, the cytotoxicity of sunitinib-loaded micelles on cancer cells was evaluated. The drug-loaded micelles exhibited dose-dependent toxicity. Also, haemolysis capacity of these polymers was investigated. In summary, polymer functionalization seems a promising approach to overcome challenges that hinder the application of polymer-based drug delivery systems such as low drug loading degree.

Block copolymer micelles with a functional core have been synthesized and evaluated for their drug delivery capability. High drug loading was observed due to strong ionic interactions, while cytotoxicity of polymers was found to be low.

The modulation of structural stability of horseradish peroxidase as a consequence of macromolecular crowding

Macromolecular crowding plays an inevitable role in all biological processes influencing association, conformation, and other characteristics of proteins. Present study is based on the effect of macromolecular crowding on structure of horseradish peroxidase (HRP) enzyme. Concentration-dependent conformational changes induced by crowding agents, dextran 70 and polyethylene glycol (PEG)-4000, were monitored employing a range of biophysical techniques. The intrinsic fluorescence spectra showed transition of protein from native to unfolded state. Marked increase in 8-Anilino-1-naphthalene-sulphonoic acid and Thioflavin T fluorescence indicated presence of non-native moieties with 80 mg/mL dextran. Enhanced absorbance in turbidity, Soret, and Congo red in corroboration with scattering intensity at 350nm results revealed incidence of HRP aggregates. A new peak around 218 nm in CD spectra pointed towards change in secondary structure towards β-sheets. Significant loss of enzyme activity upon structural disruption was seen. Comet assay demonstrated DNA damage and genotoxic nature of HRP aggregates, supporting spectroscopic, and fluorescence results. The normalized results were obtained with 120 mg/mL PEG-4000 close to that of native HRP implying no disruptive effect on structure. It can be hypothesized that macromolecular crowding is a vital element, which can have diverse effects. In this study, dextran 70 was observed to have pro-aggregatory effect while enhanced stability of native enzyme was witnessed with PEG. Hence, it can be stated that PEG has potentially better crowder as it helps retain the native enzyme structure. Routine addition of crowding agents is recommended if biological molecules are to be studied under more physiologically appropriate environments.

Consequence of macromolecular crowding on aggregation propensity and structural stability of haemoglobin under glycating conditions

Cell interiors are extremely congested with biological macromolecules exerting crowding effect, influencing various physiognomies of protein life. Present work deals with effect of crowding on folding behaviour of haemoglobin (Hb) under glycating conditions. Macromolecular crowding was mimicked by concentrated solutions of dextran 70. Hb with 0.2 M fructose and ribose was incubated separately for 96 h in dilute and crowded solution to analyse conformational changes. Reduced intrinsic and ANS fluorescence, decreased Soret absorbance, enhanced turbidity, browning of protein, red shift in ThT and Congo red spectra significantly unveiled protein aggregation. FTIR and CD results revealed transition from α-helix to β-sheets confirming aggregation. Transmission electron microscopy exhibited incidence of aggregates. Macromolecular crowding was witnessed to defend conformational stability of native Hb under stress condition at 100 mg/ml dextran, noticeably indicating deceleration of aggregation. Stabilising effect of crowding was marginally better in fructosylated Hb than with ribose due to difference in their glycation potential. Contrarily, in over-crowded solution where dextran concentration was 500 mg/ml, heightened aggregation was perceived implying concentration dependant, dual nature of macromolecular crowding. The novelty of this study lies in idea of considering macromolecular crowding as a key player in regulation of protein stability which was safely ignored previously.

Macromolecular crowding stabilises native structure of α-chymotrypsinogen-A against hexafluoropropanol-induced aggregates

Cell interior is extremely congested with tightly packed biological macromolecules that exerts macromolecular crowding effect, influencing biophysical properties of proteins. To have a deeper insight into it we studied consequences of crowding on aggregation susceptibility and structural stability of α-chymotrypsinogen-A, pro-enzyme of serine protease family, upon addition of co-solvent reported to exert stress on polypeptides crafting favourable conditions for aggregation. Hexafluoropropan-2-ol (HFIP), a fluorinated alcohol caused structural disruption at 5% v/v unveiled by reduced intrinsic intensity and blue shifted ANS spectra. Significantly enhanced, red-shifted ThT and Congo red spectra sustained conformational changes concomitant with aggregation. FTIR and CD results confirmed transition of native structure to non-native extended, cross-linked beta-sheets. Transmission electron micrographs visibly exhibited incidence of amorphous aggregates. Macromolecular crowding, typically mimicked by concentrated solutions of dextran 70, was noticeably witnessed to defend conformational stability under denaturing condition. The native structure was retained maximally in presence of 100 mg/ml followed by 200 and 300 mg/ml dextran indicating concentration dependent deceleration of aggregate formation. It can be established that explicit consideration of crowding effects using relevant range of inert crowding agents must be a requisite for presumptions on intracellular conformational behaviour of proteins deduced from in vitro experiments.

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.