Drastic acceleration of fibrillation of insulin by transient cavitation bubble

Surface Modification of Ultrasonic Cavitation by Surfactants Improves Detection Sensitivity of α-Synuclein Amyloid Seeds

The rapid amplification and sensitive detection of α-synuclein (αSyn) seeds is an efficient approach for the early diagnosis of Parkinson's disease. Ultrasonication stands out as a promising method for the rapid amplification of αSyn seeds because of its robust fibril fragmentation capability. However, ultrasonication also induces the primary nucleation of αSyn monomers, deteriorating the seed detection sensitivity by generating seed-independent fibrils. In this study, we show that an addition of surfactants to the αSyn monomer solution during αSyn seed detection under ultrasonication remarkably improves the detection sensitivity of the αSyn seeds by a factor of 100-1000. Chemical kinetic analysis reveals that these surfactants reduce the rate of primary nucleation while promoting the fragmentation of the αSyn fibrils under ultrasonication. These effects are attributed to the modification of the ultrasonic cavitation surface by the surfactants. Our study enhances the utility of ultrasonication in clinical assays targeting αSyn seeds as the Parkinson's disease biomarker.

Macromolecular crowding and supersaturation protect hemodialysis patients from the onset of dialysis-related amyloidosis

Dialysis-related amyloidosis (DRA), a serious complication among long-term hemodialysis patients, is caused by amyloid fibrils of β2-microglobulin (β2m). Although high serum β2m levels and a long dialysis vintage are the primary and secondary risk factors for the onset of DRA, respectively, patients with these do not always develop DRA, indicating that there are additional risk factors. To clarify these unknown factors, we investigate the effects of human sera on β2m amyloid fibril formation, revealing that sera markedly inhibit amyloid fibril formation. Results from over 100 sera indicate that, although the inhibitory effects of sera deteriorate in long-term dialysis patients, they are ameliorated by maintenance dialysis treatments in the short term. Serum albumin prevents amyloid fibril formation based on macromolecular crowding effects, and decreased serum albumin concentration in dialysis patients is a tertiary risk factor for the onset of DRA. We construct a theoretical model assuming cumulative effects of the three risk factors, suggesting the importance of monitoring temporary and accumulated risks to prevent the development of amyloidosis, which occurs based on supersaturation-limited amyloid fibril formation in a crowded milieu.

Insulin aggregation starts at dynamic triple interfaces, originating from solution agitation

The consequences of agitation on protein stability are particularly relevant to therapeutic proteins. However, the precise contribution of the different effects induced by agitation in pathways leading to protein denaturation and aggregation at interfaces is not entirely understood. In particular, the contribution of a moving triple line, induced by the sweeping of a solution meniscus on a container wall upon agitation, has only been rarely assessed. In this article, we therefore designed experimental setups to analyze how mixing, shear stress, and dynamic triple interfaces influence insulin aggregation in physiological conditions. This has been achieved by controlling agitation speed, shear stress, and the extension of triple interfaces in order to shed light on the contribution of different agitation-induced effects on insulin aggregation in physiological conditions. We demonstrate that strong agitation is necessary for the onset of insulin aggregation, while the growth of the aggregates is sustained even under weak agitation. Kinetic insulin aggregation studies in conditions of intermittent wetting show that the aggregation rate correlates with the amount of dynamic triple interfaces that the proteins are exposed to. Finally, we demonstrate that the triple line, where the protein solution, the air, and a hydrophobic surface meet constitutes a preferential early aggregation site.

Effect mechanism of ultrasound pretreatment on fibrillation Kinetics, physicochemical properties and structure characteristics of soy protein isolate nanofibrils

Self-assembly of soy proteins into nanofibrils is gradually considered as an effective method to improve their technical and functional properties. Ultrasound is a non-thermal, non-toxic and environmentally friendly technology that can modulate the formation of protein nanofibrils through controlled structural modification. In this research, the effect of ultrasound pretreatment on soy protein isolate nanofibrils (SPIN) was evaluated by fibrillation kinetics, physicochemical properties and structure characteristics. The results showed that the optimum ultrasound condition (20% amplitude, 15 min, 5 s on-time and 5 s off-time) could increase the formation rate of SPIN by 38.66%. Ultrasound reduced the average particle size of SPIN from 191.90 ± 5.40 nm to 151.83 ± 3.27 nm. Ultrasound could increase the surface hydrophobicity to 1547.67 in the initial stage of nanofibrils formation, and extend the duration of surface hydrophobicity increased, indicating ultrasound could expose more binding sites, creating more beneficial conditions for nanofibrils formation. Ultrasound could change the secondary and tertiary structure of SPIN. The reduction of α-helix content of ultrasound-pretreated soy protein isolate nanofibrils (USPIN) was 12.1% (versus 5.3% for SPIN) and the increase of β-sheet content was 5.9% (versus 3.5% for SPIN) during fibrillation. Ultrasound could accelerate the formation of SPIN by promoting the unfolding of SPI, exposure of hydrophobic groups and formation of β-sheets. Microscopic images revealed that USPIN generated a curlier and looser shape. And ultrasound reduced the zeta potential, free sulfhydryl groups content and viscosity of SPIN. SDS-PAGE results showed that ultrasound could promote the conversion of SPI into low molecular weight peptides, providing building blocks for the nanofibrils formation. The results indicated that ultrasound pretreatment could be a promising technology to accelerate SPIN formation and promote its application in food industry, but further research is needed for the improvement of the functional properties of SPIN.

Half-Time Heat Map Reveals Ultrasonic Effects on Morphology and Kinetics of Amyloidogenic Aggregation Reaction

Ultrasonication has been recently adopted in amyloid-fibril assays because of its ability to accelerate fibril formation, being promising in the early stage diagnosis of amyloidoses in clinical applications. Although applications of this technique are expanding in the field of protein science, its effects on the aggregation reactions of amyloidogenic proteins are poorly understood. In this study, we comprehensively investigated the morphology and structure of resultant aggregates, kinetics of fibril formation, and seed-detection sensitivity under ultrasonication using β₂-microglobulin and compared these characteristics under shaking, which has been traditionally adopted in amyloid-fibril assays. To discuss the ultrasonic effects on the amyloid-fibril formation, we propose the half-time heat map, which describes the phase diagram of the aggregation reaction of amyloidogenic proteins. The experimental results show that ultrasonication greatly promotes fibril formation, especially in dilute monomer solutions, induces short-dispersed fibrils, and is capable of detecting ultra-trace-concentration seeds with a detection limit of 10 fM. Furthermore, we indicate that ultrasonication highly alters the energy landscape of an aggregation reaction due to the effect of ultrasonic cavitation. These insights contribute not only to our understanding of the effects of agitation on amyloidogenic aggregation reactions but also to their effective application in the clinical diagnosis of amyloidoses.

Insulin Fibril Formation Caused by Mechanical Shock and Cavitation

Cavitation can occur when liquids are exposed to pressure waves of sufficient amplitude, producing rapidly expanding and collapsing gas bubbles that generate localized regions of high energy dissipation. When vials containing insulin were subjected to mechanical shock or when ultrasound was applied to the vials, the resulting cavitation events induced formation of insulin amyloid fibril nuclei that were detected by transmission electron microscopy and quantified by fluorescence spectroscopy following staining with the amyloid-sensitive dye thioflavin-T. Dropping insulin solutions in glass vials produced only minute amounts of insulin fibril nuclei, which could be detected by allowing the nuclei to grow. Cavitation-induced formation of amyloid aggregates may be relevant for iatrogenic insulin deposition disease, where insulin fibrils formed in vitro prior to administration to patients could serve as nuclei for growing fibril deposits in vivo.

Optimized sonoreactor for accelerative amyloid-fibril assays through enhancement of primary nucleation and fragmentation

Ultrasonication to supersaturated protein solutions forcibly forms amyloid fibrils, thereby allowing the early-stage diagnosis for amyloidoses. Previously, we constructed a high-throughput sonoreactor to investigate features of the amyloid-fibril nucleation. Although the instrument substantiated the ultrasonication efficacy, several challenges remain; the key is the precise control of the acoustic field in the reactor, which directly affects the fibril-formation reaction. In the present study, we develop the optimized sonoreactor for the amyloid-fibril assay, which improves the reproducibility and controllability of the fibril formation. Using β₂-microglobulin, we experimentally demonstrate that achieving identical acoustic conditions by controlling oscillation amplitude and frequency of each transducer results in identical fibril-formation behavior across 36 solutions. Moreover, we succeed in detecting the 100-fM seeds using the developed sonoreactor at an accelerated rate. Finally, we reveal that the acceleration of the fibril-formation reaction with the seeds is achieved by enhancing the primary nucleation and the fibril fragmentation through the analysis of the fibril-formation kinetics. These results demonstrate the efficacy of the developed sonoreactor for the diagnosis of amyloidoses owing to the accelerative seed detection and the possibility for further early-stage diagnosis even without seeds through the accelerated primary nucleation.

Time-Resolved Observation of Evolution of Amyloid-β Oligomer with Temporary Salt Crystals

The aggregation behavior of amyloid-β (Aβ) peptides remains unclarified despite the fact that it is closely related to the pathogenic mechanism of Alzheimer's disease. Aβ peptides form diverse oligomers with various diameters before nucleation, making clarification of the mechanism involved a complex problem with conventional macroscopic analysis methods. Time-resolved single-molecule level analysis in bulk solution is thus required to fully understand their early stage aggregation behavior. Here, we perform time-resolved observation of the aggregation dynamics of Aβ oligomers in bulk solution using liquid-state transmission electron microscopy. Our observations reveal previously unknown behaviors. The most important discovery is that a salt crystal can precipitate even with a concentration much lower than its solubility, and it then dissolves in a short time, during which the aggregation reaction of Aβ peptides is significantly accelerated. These findings will provide new insights in the evolution of the Aβ oligomer.

Acceleration of nucleation of prion protein during continuous ultrasonication

Although pulsatile irradiation of ultrasonication is frequently used for generating amyloid fibrils in vitro, the potential for inducing amyloid fibrillation of proteins during continuous ultrasonication is unknown. In this study, we implemented a continuous irradiation system and measured far-ultraviolet circular dichroism in a real-time manner. During the continuous ultrasonication, the conformation of full-length mouse prion protein (mPrP) was rapidly altered without a lag time and electron microscopy revealed that distorted fibrils, β-oligomers and amorphous aggregates were formed at pH 2.2, 4.0 and 9.1, respectively. Similarly, hen egg white lysozyme formed distorted fibrils and small and large amorphous aggregates at pH 2.2 and 7.1 and 11.9, respectively, without a lag time. The concentration dependencies of the initial rates were different between the two systems. The aggregate formation of mPrP followed a first-order reaction, whereas that of lysozyme followed the zeroth-order reaction. Importantly, the reactions were immediately stopped by switching off ultrasonication, and restarted instantaneously when ultrasonication was restarted. Thus, the continuous ultrasonication significantly accelerates the nucleations of mPrP and lysozyme aggregates by the interaction between monomer and cavitation bubble. These cavitation bubbles may act as catalysts that decrease the activation free energy for nucleation, which is low in mPrP and high in lysozyme.

Degradation of organic wastewater by hydrodynamic cavitation combined with acoustic cavitation

In this paper, the decomposition of Rhodamine B (RhB) by hydrodynamic cavitation (HC), acoustic cavitation (AC) and the combination of these individual methods (HAC) have been investigated. The degradation of 20 L RhB aqueous solution was carried out in a self-designed HAC reactor, where hydrodynamic cavitation and acoustic cavitation could take place in the same space simultaneously. The effects of initial concentration, inlet pressure, solution temperature and ultrasonic power were studied and discussed. Obvious synergies were found in the HAC process. The combined method achieved the best conversion, and the synergistic effect in HAC was even up to 119% with the ultrasonic power of 220 W in a treatment time of 30 min. The time-independent synergistic factor based on rate constant was introduced and the maximum value reached 40% in the HAC system. Besides, the hybrid HAC method showed great superiority in energy efficiency at lower ultrasonic power (88-176 W). Therefore, HAC technology can be visualized as a promising method for wastewater treatment with good scale-up possibilities.

Formation and properties of amyloid fibrils of prion protein

Amyloid fibrils formed from prion protein (PrP) are associated with prion diseases. In this review we discuss a number of extrinsic and intrinsic experimental factors related to the formation of PrP amyloid fibrils in vitro. We first examined the effects of ultrasonic power on the induction of amyloid fibrillation from PrP. The most important conclusion drawn from the results is that an applied ultrasonic power of approximately 2 W enhanced the nucleation of amyloid fibrils efficiently but that more powerful ultrasonication led to retardation of growth. We also reviewed evidence on the amyloidogenic regions of PrP based on peptide screening throughout the polypeptide sequence. These results showed that helix 2 (H2) peptides of PrP were capable of both the fibrillation and propagation of straight, long fibrils. Moreover, the conformation of preformed H2 fibrils changed reversibly depending on the pH of the solution, implying that interactions between side-chains modulated the conformation of amyloid fibrils. The evidence discussed in this review relates specifically to PrP but may be relevant to other amyloidogenic proteins.

Active site-targeted carbon dots for the inhibition of human insulin fibrillation

This work aimed to study the inhibitory mechanism of carbon dots for HI fibrillation using isothermal titration calorimetry.