Does Surface Chirality of Gold Nanoparticles Affect Fibrillation of HSA?

In order to demonstrate the influence of the surface chirality of the nanoparticles on amyloid fibrillation, the inhibiting effectiveness of the chiral gold nanoparticles, synthesized using the two enantiomeric forms (i.e., d- and l-) of glutamic acid, toward the fibrillation of human serum albumin (HSA) has been investigated. Here the enantiomers of glutamic acid are used as both reducing and stabilizing/capping agents. It is found that the surface chirality is the only major difference between the d-glutamic acid mediated gold (DGAu) and l-glutamic acid mediated gold (LGAu) nanoparticles. The fibrillation process has been monitored using various biophysical techniques, e.g., turbidity assay, Thioflavin T fluorescence kinetics, Congo red binding study, circular dichroism spectroscopy, fluorescence microscopy, and transmission electron microscopy. The experimental results illustrate that DGAu is more effective in inhibiting the formation of HSA fibrils than LGAu. Furthermore, the differential inhibiting effect of DGAu and LGAu toward HSA fibrillation has been described on the basis of the dissimilar interaction behavior of the nanoparticles with the HSA molecules, as revealed by the Trp fluorescence quenching, and the isothermal titration calorimetry. It is suggested that the surface chirality of the gold nanoparticles strongly influences the protein adsorption dynamics including the modes of orientation of adsorbed HSA molecules, causing the inhibition of fibrillation to different extents

Inhibition of Human Serum Albumin Fibrillation by Two-Dimensional Nanoparticles

The formation and deposition of amyloid fibrils have been linked to the pathogenesis of numerous debilitating neurodegenerative disorders. Serum albumins serve as good model proteins for understanding the molecular mechanisms of protein aggregation and fibril formation. Graphene-based nanotherapeutics appear to be promising candidates for designing inhibitors of protein fibrillation. The inhibitory effect of graphene oxide (GO) nanoparticles on the fibrillation of human serum albumin (HSA) in an in vitro mixed solvent system has been investigated. The methods used include ThT fluorescence, ANS binding, Trp fluorescence, circular dichroism, fluorescence microscopy, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy. It was observed that GO inhibits HSA fibrillation and forms agglomerates with β-sheet rich prefibrillar species. Binding of GO prevents the formation of mature fibrils with characteristic cross-β sheet but does not promote refolding to the native state

Complexation With Human Serum Albumin Facilitates Sustained Release of Morin From Polylactic-Co-Glycolic Acid Nanoparticles

Understanding the interaction of proteins with nanoparticles has become an important area of research in biomedical and pharmaceutical fields. Morin is a flavonol which shows several properties including antioxidant, anticancer, and anti-inflammatory activities. However, the major limitation is its poor aqueous solubility. Therefore, morin-loaded polylactic-<i>co</i>-glycolic acid (PLGA) nanoparticles (MPNPs) were prepared to improve the solubility of morin. The resulting MPNPs were characterized by spectroscopic and microscopic techniques. The nanoparticles were spherical with an average size of 237 ± 17 nm. UV–visible, fluorescence, and circular dichroism (CD) spectroscopy were employed to study the interaction of the MPNPs with human serum albumin (HSA). Our study revealed that a static fluorescence quenching mechanism was involved in the interaction between HSA and MPNPs. Hydrophobic interactions also play an important role in stabilizing the HSA-MPNP complex. CD results suggest that there is an alteration of the secondary structure of HSA in the presence of MPNPs. MPNPs exhibit antioxidant properties which are supported by the DPPH assay. We have further checked the effect of HSA on the antioxidant property of morin and MPNPs. HSA binding with MPNPs was also found to influence the <i>in vitro</i> release property of morin from MPNPs wherein a delayed release response is observed

An investigation into the altered binding mode of green tea polyphenols with human serum albumin on complexation with copper

<div><p>Green tea is rich in several polyphenols, such as (−)-epicatechin-3-gallate (ECG), (−)-epigallocatechin (EGC), and (−)-epigallocatechin-3-gallate (EGCG). The biological importance of these polyphenols led us to study the major polyphenol EGCG with human serum albumin (HSA) in an earlier study. In this report, we have compared the binding of ECG, EGC, and EGCG and the Cu(II) complexes of EGCG and ECG with HSA. We observe that the gallate moiety of the polyphenols plays a crucial role in determining the mode of interaction with HSA. The binding constants obtained for the different systems are 5.86 ± 0.72 × 10⁴ M⁻¹ (<i>K</i>_ECG-HSA), 4.22 ± 0.15 × 10⁴ M⁻¹ (<i>K</i>_{ECG-Cu(II)-HSA}), and 9.51 ± 0.31 × 10⁴ M⁻¹ (<i>K</i>_{EGCG-Cu(II)-HSA}) at 293 K. Thermodynamic parameters thus obtained suggest that apart from an initial hydrophobic association, van der Waals interactions and hydrogen bonding are the major interactions which held together the polyphenols and HSA. However, thermodynamic parameters obtained from the interactions of the copper complexes with HSA are indicative of the involvement of the hydrophobic forces. Circular dichroism and the Fourier transform infrared spectroscopic measurements reveal changes in α-helical content of HSA after binding with the ligands. Data obtained by fluorescence spectroscopy, displacement experiments along with the docking studies suggested that the ligands bind to the residues located in site 1 (subdomains IIA), whereas EGC, that lacks the gallate moiety, binds to the other hydrophobic site 2 (subdomain IIIA) of the protein.</p> </div

Effect of Functionalized Magnetic MnFe₂O₄ Nanoparticles on Fibrillation of Human Serum Albumin

Pathogenesis of amyloid-related diseases is related to nonnative folding of proteins with the formation of insoluble deposits in the extracellular space of various tissues. Having the unique properties of small size, large surface area, biodegradability, and relative nontoxicity, magnetic nanoparticles have drawn a lot of attention in biomedical applications. Herein, we demonstrate the effect of bare and differently functionalized magnetic MnFe₂O₄ nanoparticles on fibrillation of human serum albumin <i>in vitro</i>. The process has been monitored using Thioflavin T fluorescence, Congo red binding assay, circular dichroism, fluorescence microscopy, and transmission electron microscopy. From our experimental results, amine functionalized MnFe₂O₄ nanoparticles are found to inhibit formation of fibrils more effectively than bare ones, while carboxylated nanoparticles do not have a significant effect on fibrillation. This study has explored the prospects of using specific magnetic nanoparticles with appropriate modification to control self-assembly of proteins and may act as a precursor in therapeutic applications

Fibrillation of human serum albumin shows nonspecific coordination on stoichiometric increment of Copper(II)

<div><p>Protein aggregation is related to a series of pathological disorders the main cause of which are the fibrillar species generated during the process. Human serum albumin (HSA) undergoes rapid fibrillation in the presence of Cu(II) at pH 7.4 in 60% ethanol after 6-h incubation (∼65 °C) followed by room temperature incubation. Here, we have investigated the effect of a stoichiometric variation of Cu(II) on the self-assembly of HSA using Congo red and thioflavin T dye-binding studies, circular dichroism spectroscopy, Fourier transform infrared spectroscopy, electron paramagnetic resonance spectroscopy, fluorescence microscopy and transmission electron microscopy. The simulation of EPR spectra suggests that with the increment in Cu(II) ion concentration, there is a change in ligand field coordination. Kinetic parameters indicate reduced cooperativity that may be related to the nonspecific coordination on increment of Cu(II) concentration. Cu(II) is also able to direct the accumulation of a large number of fibers along with a formation of dense fibrillar network which is evident from microscopic images.</p></div

Prolonged Glycation of Hen Egg White Lysozyme Generates Non Amyloidal Structures

<div><p>Glycation causes severe damage to protein structure that could lead to amyloid formation in special cases. Here in this report, we have shown for the first time that hen egg white lysozyme (HEWL) does not undergo amyloid formation even after prolonged glycation in the presence of D-glucose, D-fructose and D-ribose. Cross-linked oligomers were formed in all the cases and ribose was found to be the most potent among the three sugars. Ribose mediated oligomers, however, exhibit Thioflavin T binding properties although microscopic images clearly show amorphous and globular morphology of the aggregates. Our study demonstrates that the structural damage of hen egg white lysozyme due to glycation generates unstructured aggregates.</p> </div

Characterization of different AGE products formed during glycation of HEWL in the presence of different sugars using fluorescence spectroscopy.

<p>Histograms represent fluorescence intensity of different HEWL solutions incubated in the presence of glucose, fructose and ribose respectively over a period of 120 days. Formation of different AGE products such as (a) other AGE products (λ_ex=350 nm), (b) pentosidine (λ_ex=335 nm) and (c) malondialdehyde (MDA) (λ_ex=370 nm). [HEWL]=5 µM in each case. Control represents native HEWL incubated in the absence of sugars at pH 7.4 at 37 °C keeping other conditions similar as that of sets in each case.</p

Densitometric analysis of SDS-PAGE.

<p>Histograms represent relative mean band intensity of different oligomeric species (dimer, trimer and tetramer) with respect to their corresponding monomer at definite time intervals (a) 1 day, (b) 20 days and (c) 31 days respectively.</p

Identification of the nature of the aggregates formed during glycation of HEWL.

<p>FESEM (a-d) and TEM images (e-h) of different HEWL solutions obtained after an incubation at pH 7.4 at 37 °C at different time intervals in the presence of different sugars. For FESEM images scale bars represent 2 µm for HEWL-glucose and HEWL-fructose; 20 µm for Control and HEWL-ribose respectively. For TEM images scale bars represent 200 nm.</p