Allura red rapidly induces amyloid-like fibril formation in hen egg white lysozyme at physiological pH

Probing the interaction mechanisms between sunset yellow dye and trypsin protein leading to amorphous aggregation under low pH conditions

Protein aggregation poses a significant concern in the field of food sciences, and various factors, such as synthetic food dyes, can contribute to protein aggregation. One such dye, Sunset Yellow (SY), is commonly employed in the food industry. Trypsin was used as a model protein to assess the impact of SY. We employed several biophysical techniques to examine the binding and aggregation mechanisms between SY and trypsin at different pHs. Results from intrinsic fluorescence measurements indicate a stronger interaction between SY and trypsin at pH 2.0 compared to pH 6.0. Turbidity data reveal trypsin aggregation in the presence of 0.05-3.0 mM SY at pH 2.0, while no aggregation was observed at pH 6.0. Kinetic data demonstrate a rapid, lag-phase-free SY-induced aggregation of trypsin. Circular dichroism analysis reveals that trypsin adopts a secondary structure in the presence of SY at pH 6.0, whereas at pH 2.0, the secondary structure was nearly lost with increasing SY concentrations. Furthermore, turbidity and kinetics data suggest that trypsin aggregation depends on trypsin concentrations and pH. Our study highlights potential health risks associated with the consumption of SY, providing insights into its impact on human health and emphasizing the necessity for further research in this field.

Interaction of gallium, indium, and vanadyl curcumin complexes with hen egg-white lysozyme (HEWL): Mechanistic aspects and evaluation of antiamyloidogenic activity

Many proteins and peptides can aggregate into amyloid fibrils with high-ordered and cross-β rich structure characteristics. Amyloid deposition is a common feature of neurodegenerative diseases called amyloidosis. Various natural polyphenolic compounds such as curcumin exhibited antiamyloidogenic activities, but less researches were focused on the metal complexes of these compounds. In this study, the inhibitory effects of gallium curcumin (Ga(cur)3), indium curcumin (In(cur)3), and vanadyl curcumin (VO(cur)2) on the amyloid fibrillation of hen egg white lysozyme (HEWL) have been investigated. Moreover, the details of binding interactions of these metal complexes with HEWL have been explored. The results of fluorescence quenching analyses revealed that In(cur)3 and VO(cur)2 have much higher binding affinities than Ga(cur)3 toward HEWL. The interactions of these metal complexes were accompanied by partial conformational changes in the tertiary structure of HEWL. The kinetic curves of the fibrillation process demonstrated that In(cur)3 and VO(cur)2 have higher inhibitory effects than Ga(cur)3 on the amyloid fibrillation of HEWL. The strength of binding to HEWL is completely in accordance with inhibitory activities of these metal complexes of curcumin.

SDBS induces multiple catalase conformations in a dose-dependent manner

Amyloid fibrils have been linked to several incurable diseases. They are long and thin fibrous proteins that self-assemble into fibrils. Small molecules can stimulate amyloid fibrillation, but the mechanism by which this happens is not well understood. This study examined how a negatively charged benzene ring containing surfactant, sodium dodecylbenzene sulphonate (SDBS), affects the fibrillation of bovine liver catalase (BLC). After SDBS treatment, BLC conformational changes were examined in vitro using turbidity, RLS kinetics, intrinsic fluorescence, ThT fluorescence, far-UV CD, and TEM. BLC in the native state was alpha-helical at pH 7.4, while it was converted to a random coil structure at pH 2.0. Far-UV CD and intrinsic fluorescence data showed that at concentrations <0.1 mM of SDBS, randomly coiled BLC assumed a native-like alpha-helical structure. However, between 0.1 and 1.0 mM SDBS, BLC was aggregated. ThT fluorescence and far-UV CD measurements showed the amyloid-like structures in the aggregated BLC. At higher SDBS concentrations (>1.0 mM) at pH 2.0, BLC again attains a native-like alpha-helical structure. It is essential for therapeutic purposes to clearly understand the process underlying surfactant- or lipid-induced fibrillation.

Bovine liver catalase turns into three conformational states after exposure to an anionic surfactant

The mechanism by which anionic surfactants promote amyloid fibril is not well understood. Here, we investigated how sodium dodecyl sulfate (SDS), a negatively charged surfactant, affects the fibrillation of the partially unfolded random-coiled bovine liver catalase (BLC) at a pH of 2.0. We used several methods, including turbidity, RLS kinetics, intrinsic fluorescence, ThT fluorescence, far-UV CD, and TEM imaging, to evaluate the conformational changes of BLC in vitro in response to SDS treatment. BLC is a multimeric protein and well folded at physiological pH but forms a random coil structure at pH 2.0. Intrinsic fluorescence and far-UV CD data showed that below 0.1 mM SDS, random coiled BLC turned into a native-like structure. BLC incubated with an SDS concentration ranging from 0.1 to 2.0 mM led to the formation of aggregates. The ThT fluorescence intensity was enhanced in the aggregated BLC samples (0.1-2.0 mM SDS), and cross beta-sheeted structure was detected by the far UV CD measurements. BLC adopts a complete alpha-helical structure upon interacting with SDS at a more than 2.0 mM concentration at pH 2.0. Understanding the mechanism of surfactant- or lipid-induced fibrillation is important for therapeutic purposes.

Azo dyes in the food industry: Features, classification, toxicity, alternatives, and regulation

Azo dyes, including Tartrazine, Sunset Yellow, and Carmoisine, are added to foods to provide color, but they have no value with regard to nutrition, food preservation, or health benefits. Because of their availability, affordability, stability, and low cost, and because they provide intense coloration to the product without contributing unwanted flavors, the food industry often prefers to use synthetic azo dyes rather than natural colorants. Food dyes have been tested by regulatory agencies responsible for guaranteeing consumer safety. Nevertheless, the safety of these colorants remains controversial; they have been associated with adverse effects, particularly due to the reduction and cleavage of the azo bond. Here, we review the features, classification, regulation, toxicity, and alternatives to the use of azo dyes in food.

Effect of artificial sweetener saccharin on lysozyme aggregation: A combined spectroscopic and in silico approach

The use of saccharin in food products attracts much attention as it involves the risk of lethal allergies and many protein aggregation diseases. However, its role in protein aggregation has not been explored to date. This study embodies the effect of artificial sweeteners on HEWL in the absence and presence of commonly available natural products such as curcumin and EGCG. Various techniques have been used to characterize the protein interaction, such as steady-state emission and time-resolved fluorescence, FTIR, gel electrophoresis, TEM, and molecular docking. Steady-state and time-resolved studies revealed the binding strength and concomitant effect of saccharin on HEWL protein. Kinetic measurements revealed that saccharin causes significant enhancement of HEWL aggregation with a considerable reduction in lag phase time i.e. from 37 hr to 08 hr. Whereas in the presence of natural products, the effect of saccharin on HEWL aggregation was significantly reduced specifically in the case of curcumin. The result obtained in the fluorescence experiment were also supported by the gel electrophoresis technique and morphological images taken by TEM. The rapid change in the secondary structure of the protein in the presence of saccharin was confirmed by the FTIR spectroscopy technique. This study is instrumental in understanding the effect of saccharin on protein aggregation and the role of commonly available natural products in curbing its effect.

SDS induces amorphous, amyloid-fibril, and alpha-helical structures in the myoglobin in a concentration-dependent manner

Amyloid fibrils have been linked to a number of diseases. Surfactants imitate plasma membrane lipids and induce amyloid fibrils. This study examined the effects of the anionic surfactant sodium dodecyl sulfate (SDS) at pH 4.5 on equine skeletal muscle myoglobin (E-Mb). To analyze the effect of SDS on aggregation and amyloid-fibril formation to E-Mb, we used various spectroscopic techniques (turbidity, light scattering, intrinsic fluorescence, ThT fluorescence, and circular dichroism (CD)), electrophoretic, and microscopic techniques. Turbidity, SDS-PAGE, and light scattering all indicated the formation of E-Mb aggregates at SDS concentrations ranging from 0.2 mM to 1.0 mM. In the presence of 0.4 mM SDS, far-UV CD and TEM data indicate that E-MB forms amorphous aggregates. ThT binding, Far-UV CD, and TEM findings indicate that E-Mb forms amyloid-like structures in the presence of 0.6-1.0 mM SDS. However, no aggregation was seen at SDS concentrations above 1 mM. In the presence of high SDS concentrations (> 1 mM), the E-Mb exhibited native-like α-helical structure. As a result, SDS exhibited three distinct behaviors: amorphous aggregates, amyloid-fibrils, and helix-inducer. These findings also shed light on how amyloid fibrils are formed when anionic surfactants are introduced, which is a significant takeaway.

Molecular insight into the modulation of ovalbumin fibrillation by allura red dye at acidic pH

The synthetic food additive dye induces amyloid fibrillation has many implications in the laboratory and industries. The effect of Allura red (AR), on the fibrillation of ovalbumin (Ova) at pH 2.0 was investigated. The influence of salt and pH was also seen on AR-induced Ova aggregation. We have used several spectroscopic and microscopy techniques to characterize the changes. The turbidity data suggest that concentrations above 0.05 mM of AR induce aggregation, and the size of aggregates increased in response to AR concentration. The kinetics data showed that the AR induces Ova aggregation quickly without lag time. The aggregates induced by AR have amyloid-like aggregates confirmed by far-UV CD and TEM. NaCl has very marginal effects in AR-induced aggregation. The turbidity results clearly state that Ova is not forming aggregates with pH above 4.0 due to electrostatic repulsion. However, Ova forms bigger aggregates in the presence of 0.5 mM AR at a pH below 4.0. These spectroscopic data suggest that the amyloid fibrillation that occurs in Ova is due to electrostatic and hydrophobic interaction. The amyloid fibrillation induced by AR dye in protein should be taken seriously for food safety purposes.

Agitation does not induce fibrillation in reduced hen egg-white lysozyme at physiological temperature and pH

Several proteins and peptides tend to form an amyloid fibril, causing a range of unrelated diseases, from neurodegenerative to certain types of cancer. In the native state, these proteins are folded and soluble. However, these proteins acquired β-sheet amyloid fibril due to unfolding and aggregation. The conversion mechanism from well-folded soluble into amorphous or amyloid fibril is not well understood yet. Here, we induced unfolding and aggregation of hen egg-white lysozyme (HEWL) by reducing agent dithiothreitol and applied mechanical sheering force by constant shaking (1000 rpm) on the thermostat for 7 days. Our turbidity results showed that reduced HEWL rapidly formed aggregates, and a plateau was attained in nearly 5 h of incubation in both shaking and non-shaking conditions. The turbidity was lower in the shaking condition than in the non-shaking condition. The thioflavin T binding and transmission electron micrographs showed that reduced HEWL formed amorphous aggregates in both conditions. Far-UV circular dichroism results showed that reduced HEWL lost nearly all alpha-helical structure, and β-sheet secondary structure was not formed in both conditions. All the spectroscopic and microscopic results showed that reduced HEWL formed amorphous aggregates under both conditions.

Role of salts and solvents on the defibrillation of food dye "sunset yellow" induced hen egg white lysozyme amyloid fibrils

Several food dyes are known to induce amyloid fibrillation when interacting with proteins. Here, we studied the role of sunset yellow (SY) in the amyloid fibrillation of hen egg white lysozyme (HEWL) and characterized the changes using spectroscopy techniques. Turbidity results showed that SY dye induces aggregation in HEWL in concentrations dependent manner. The aggregation induced by SY dye is kinetically very fast, no lag phase was detected, and the kinetics process follows an isodesmic kinetics pathway. The SY-dye induce aggregates have cross-β secondary structure confirmed by far-UV CD measurements. The effect of salts and solvents was also seen on SY-induced aggregates. Turbidity, far-UV CD, and kinetics results suggest that certain concentrations of NaCl and (NH₄)₂SO₄ solubilize the SY-induce amyloid fibrils, but (NH₄)₂SO₄ is more effective. Similarly, solvents are also solubilized the SY-induces HEWL amyloid fibrillation but the order of defibrillation is as follows: Isopropanol> ethanol > methanol which signified that isopropanol is more effective than other solvents. The salts and solvents data suggest that the electrostatic, as well as hydrophobic interaction, is responsible for SY-induced amyloid fibrillation. These conformational changes should be examined, more seriously for the purpose of food safety.

Lysozyme amyloid fibril: Regulation, application, hazard analysis, and future perspectives

Self-assembly of misfolded proteins into ordered fibrillar aggregates known as amyloid results in various human diseases. However, more and more proteins, whether in human body or in food, have been found to be able to form amyloid fibrils with in-depth researches. As a model protein for amyloid research, lysozyme has always been the focus of research in various fields. Firstly, the formation mechanisms of amyloid fibrils are discussed concisely. Researches on the regulation of lysozyme amyloid fibrils are helpful to find suitable therapeutic drugs and unfriendly substances. And this review article summarizes a number of exogenous substances including small molecules, nanoparticles, macromolecules, and polymers. Small molecules are mainly connected to lysozyme through hydrophobic interaction, electrostatic interaction, π-π interaction, van der Waals force and hydrogen bond. Nanoparticles inhibit the formation of amyloid fibers by stabilizing lysozyme and fixing β-sheet. Besides, the applications of lysozyme amyloid fibrils in food-related fields are considered furtherly due to outstanding physical and mechanical properties. Nevertheless, the potential health threats are still worthy of our attention. Finally, we also give suggestions and opinions on the future research direction of lysozyme amyloid fibrils.

Sunset Yellow Dye Induces Amorphous Aggregation in β-Lactoglobulin at Acidic pH: A Multi-Techniques Approach

Protein aggregation is of two types: (i) amorphous and (ii) amyloid fibril. Several extrinsic factors (temperature, pH, and small ligands) stimulate protein aggregation in vitro. In this study, we have examined the role of sunset yellow (SY) on the β-lactoglobulin (BLG) aggregation at pH 2.0. We have used spectroscopic (turbidity, Rayleigh light scattering (RLS), far-UV CD) and microscopic (transmission electron microscopy [TEM]) techniques to describe the effects of SY on BLG aggregation. Our results showed that BLG aggregation is dependent on SY concentrations. Very low concentrations (0.0–0.07 mM) of SY were unable to induce aggregation, while SY in the concentrations range of 0.1–5.0 mM induces aggregation in BLG. The kinetics of SY-stimulated aggregation is very fast and monomeric form of BLG directly converted into polymeric aggregates. The kinetics results also showed SY-induced BLG aggregation disappeared in the presence of NaCl. The far-UV CD and TEM results indicated the amorphous nature of SY-induced BLG aggregates. We believe that our results clearly suggest that SY dye effectively stimulates BLG aggregation.

Elevated temperatures accelerate the formation of toxic amyloid fibrils of hen egg-white lysozyme

The formation of amyloid fibrils is critical for neurodegenerative diseases. Some physiochemical conditions can promote the conversion of proteins from soluble globular shapes into insoluble well‐organized amyloid fibrils. The aim of this study was to investigate the effect of temperatures on amyloid fibrils formation in vitro using the protein model of hen egg‐white lysozyme (HEWL). The HEWL fibrils were prepared at temperatures of 37, 45, 50 and 57°C in glycine solution of pH 2.2. Under transmission electron microscopy, we found the well‐organized HEWL amyloid fibrils at temperatures of 45, 50 and 57°C after 10 days of incubation. Thioflavin T and Congo red florescence assays confirmed that the formation and growth of HEWL fibrils displayed a temperature‐dependent increase, and 57°C produced the most amounts. Meanwhile, the surface hydrophobicity of aggregates was greatly increased by ANS binding assay, and β‐sheet contents by circular dichroism analysis were increased by 17.8%, 22.0% and 34.9%, respectively. Furthermore, the HEWL fibrils formed at 57°C caused significant cytotoxicity in SH‐SY5Y cells after 48 hr exposure, and the cell viability determined by MTT assay was decreased, with 81.35 ± 0.29% for 1 μM, 61.45 ± 2.62% for 2 μM, and 11.58 ± 0.39% (p < .01) for 3 μM. Nuclear staining results also confirmed the apoptosis features. These results suggest that the elevated temperatures could accelerate protein unfolding of the native structure and formation of toxic amyloid fibrils, which can improve understanding the mechanisms of the unfolding and misfolding process of prion protein.

Development and characterization of regenerable chitosan-coated nickel selenide nano-photocatalytic system for decontamination of toxic azo dyes

In this investigation, chitosan-coated nickel selenide nano-photocatalyst (CS-NiSe) was successfully prepared through the chemical reduction method. FTIR spectroscopy confirmed the synthesis of CS-NiSe nano-photocatalyst. Further, XRD analysis exhibited a monoclinic crystalline phase of photocatalyst with a crystallite size of 32 nm based on Scherer's equation. The SEM micrographs showed that the photocatalyst has an average particle size of 60 nm. The bandgap of CS-NiSe was (2.85 eV) in the visible region of the spectrum. Due to this reason, the CS-NiSe was applied under solar light illumination for the photocatalytic activity of Erythrosine and Allura red dyes. The CS-NiSe presented the highest degradation efficiency of 99.53% for Erythrosine dye in optimized experimental conditions of 100 min at 30 °C, 30 ppm concentration, pH 5.0, and 0.14 g catalyst dose. For Allura red dye, a high degradation of 96.12% was attained in 120 min at pH 4.0, 100 ppm initial dye concentration, 35 °C temperature, and 0.1 g catalyst dose. The CS-NiSe showed excellent degradation efficiency and reduced to (95% for Erythrosine and 91% for Allura red dye) after five consecutive batches. Moreover, the statistical and neural network modelling analysis showed the significant influence of all studied variables on dyes degradation performance. The results demonstrated that CS-NiSe exhibited excellent photocatalytic performances for Erythrosine and Allura red dyes and could be a better photocatalyst for removing these dyes from industrial effluents.

Quinoline yellow dye stimulates whey protein fibrillation via electrostatic and hydrophobic interaction: A biophysical study

Amyloid fibril formation of proteins is associated with a number of neurodegenerative diseases. Several small molecules can accelerate the amyloid fibril formation in vitro and in vivo. However, the molecular mechanism of amyloid fibrillation is still unclear. In this study, we investigated how the food dye quinoline yellow (QY) induces amyloid fibrillation in α-lactalbumin (α-LA), a major whey protein, at pH 2.0. We used several spectroscopy techniques and a microscopy technique to explore how QY provokes amyloid fibrillation in α-LA. From turbidity and Rayleigh light scattering experiments, we found that QY promotes α-LA aggregation in a concentration-dependent manner; the optimal concentration for α-LA aggregation was 0.15 to 10.00 mM. Below 0.1 mM, no aggregation occurred. Quinoline yellow-induced aggregation was a rapid process that escaped the lag phase, but it depended on the concentrations of both α-LA and QY. We also demonstrated that aggregation switched the secondary structure of α-LA from α-helices to cross-β-sheets. We then confirmed the amyloid-like structure of aggregated α-LA by transmission electron microscopy measurements. Molecular docking and simulation confirmed the stability of the α-LA-QY complex due to the formation of 1 hydrogen bond with Lys99 and 2 electrostatic interactions with Arg70 and Lys99, along with hydrophobic interactions with Leu59 and Tyr103. This study will aid in our understanding of how small molecules induce aggregation of proteins inside the stomach (low pH) and affect the digestive process.

Performance evaluation of photolytic and electrochemical oxidation processes for enhanced degradation of food dyes laden wastewater

Wastewater containing dyes is considered as the top-priority pollutant when discharged into the environment. Herein, we report for the applicability of 254 nm ultraviolet light and electrochemical process using a titanium ruthenium oxide anode for the degradation of Allura red and erythrosine dyes. During the photolytic process, 95% of Allura red dye (50 ppm) was removed after 1 h at pH 12 and 35 °C, whereas 90% color removal of erythrosine dye (50 ppm) was achieved after 6 h of treatment at pH 6.0 and 30 °C. On the other hand, 99.60% of Allura red dye (200 ppm) was removed within 5 min by the electrochemical process applying a current density (5 mA cm^-2) at pH 5.0 and 0.1 mol L^-1 sodium chloride (NaCl) electrolytic medium. Similarly, 99.61% of erythrosine dye (50 ppm) degradation was achieved after 10 min at a current density of 8 mA cm^-2, pH 6.0, and 0.1 mol L^-1 of NaCl electrolyte. The minimum energy consumption value for Allura red and erythrosine dyes (0.196 and 0.941 kWh m^-3, respectively) was calculated at optimum current densities of 5 and 8 mA cm^-2. The results demonstrated that the electrochemical process is more efficient at removing dyes in a shorter time than the photolytic process since it generates powerful oxidants like the chlorine molecule, hypochlorous acid, and hypochlorite on the surface of the anode and initiates a chain reaction to oxidize the dyes molecules.

Comprehensive biophysical and functional study of ziv-aflibercept: characterization and forced degradation

Aflibercept (AFL) is an Fc fusion protein used in the treatment of colorectal cancers and different ophthalmological diseases. There are two medicines in which AFL is the active substance: Zaltrap and Eylea, referred as ziv-AFL and AFL respectively. No proper accelerated degradation studies were published on either AFL or ziv-AFL. These studies are essential during research, development and manufacturing stages. Here, we characterized ziv-AFL and submitted it to different stress conditions: light, 60 °C, freeze-thaw cycles, changes in pH, high hypertonic solution and strong denaturing conditions. We used an array of techniques to detect aggregation (SE-HPLC/DAD and DLS), changes in secondary structure (Far-UV circular dichroism), changes in conformation or tertiary structure (Intrinsic tryptophan fluorescence) and alterations in functionality (ELISA). Results indicate that aggregation is common degradation pathway. Two different types of aggregates were detected: dimers and high molecular weight aggregates attributed to β-amyloid-like structures. Secondary structure was maintained in most of the stress tests, while conformation was altered by almost all the tests except for the freeze-thaw cycles. Functionality, evaluated by its immunochemical reaction with VEGF, was found to be stable but with decrease when exposed to light and with likely partial inactivation of the drug when pH was altered.