Lysozyme adsorption on carbonaceous nanoparticles probed by second harmonic light scattering

The first hyperpolarizability (β) of two different sizes (15 and 35 nm) of carbonaceous nanoparticle (CNP) is reported for the first time using second harmonic light scattering (SHLS). The β values of the CNPs were found to be larger than those of organic molecules like pNA but lower than those of plasmonic nanoparticles like gold and silver. SHLS was further used to investigate the adsorption of a model protein Lysozyme (Lyz) on these CNPs, which is crucial for the design of safe and effective CNP-based therapeutics. The change in SH intensity from the CNPs on the addition of Lyz was recorded and fitted to the modified Langmuir adsorption model (MLM). The binding constant, free energy changes and surface coverage values show that Lyz is physisorbed on the CNPs forming less than a monolayer. The temperature dependent SH intensity measurements enabled direct determination of enthalpy and entropy changes for Lyz adsorption. The enthalpy and entropy changes reveal that Lyz adsorption is endothermic and entropically driven.

Progress and prospects of polysaccharide-based nanocarriers for oral delivery of proteins/peptides

The oral route has long been recognized as the most preferred route for drug delivery as it offers high patient compliance and requires minimal expertise. Unlike small molecule drugs, the harsh environment of the gastrointestinal tract and low permeability across the intestinal epithelium make oral delivery extremely ineffective for macromolecules. Accordingly, delivery systems that are rationally constructed with suitable materials to overcome barriers to oral delivery are exceptionally promising. Among the most ideal materials are polysaccharides. Depending on the interaction between polysaccharides and proteins, the thermodynamic loading and release of proteins in the aqueous phase can be realized. Specific polysaccharides (dextran, chitosan, alginate, cellulose, etc.) endow systems with functional properties, including muco-adhesiveness, pH-responsiveness, and prevention of enzymatic degradation. Furthermore, multiple groups in polysaccharides can be modified, which gives them a variety of properties and enables them to suit specific needs. This review provides an overview of different types of polysaccharide-based nanocarriers based on different kinds of interaction forces and the influencing factors in the construction of polysaccharide-based nanocarriers. Strategies of polysaccharide-based nanocarriers to improve the bioavailability of orally administered proteins/peptides were described. Additionally, current restrictions and future trends of polysaccharide-based nanocarriers for oral delivery of proteins/peptides were also covered.

The curious cases of nanoparticle induced amyloidosis during protein corona formation and anti-amyloidogenic nanomaterials: Paradox or prejudice?

Protein corona (PC) formation remains a major hurdle in the successful delivery of nanomedicines to the target sites. Interacting proteins have been reported to undergo structural changes on the nanoparticle (NP) surface which invariably impacts their biological activities. Such structural changes are the result of opening of more binding sites of proteins to adsorb on the NP surface. The process of conversion of α-helix proteins to their β-sheet enriched counterpart is termed as amyloidosis and in case of PC formation, NPs apparently play the crucial role of being the nucleation centres where this process takes place. Conversely, increasing numbers of artificial nano-chaperones are being used to treat the protein misfolding disorders. Anti-amyloidogenic nanomaterials (NM) have been gaining utmost importance in inhibiting Aβ42 (hallmark peptide for Alzheimer's disease) and Hen egg white lysozyme (HEWL, model protein for systemic amyloidosis) aggregation. Interestingly, in this process, NPs inhibit protein β-sheet enrichment. These two seemingly opposite roles of NPs, propelling confirmatory change onto the smorgasbord of adsorbed native proteins and the ability of NPs in inhibiting amyloidosis creates a paradox, which has not been discussed earlier. Here, we highlight the key points from both the facets of the NP behaviour with respect to their physicochemical properties and the nature of proteins they adsorb onto them to unravel the mystery. BRIEF: Protein corona formation remains a major hurdle in achieving the desired efficacy of nanomedicine. Proteins when interact with nanoparticle (NP) surface, undergo both structural and biological changes. Again, NPs are known to exhibit anti-amyloidogenic behaviour where these play the crucial role of preventing any change in their native structure. Such seemingly different roles of NPs need sincere inquisition.

Thermodynamics of adsorption of lysozyme on gold nanoparticles from second harmonic light scattering

Gold nanoparticle (GNP) interaction with hen egg white lysozyme (Lyz) has been investigated by many groups in order to understand protein mediated aggregation of GNPs and the underlying mechanism of aggregation. In this article, we have studied the interaction of citrate-capped GNPs of 16, 28, 41, and 69 nm sizes with Lyz by the non-destructive label-free second harmonic light scattering (SHLS) technique at physiological pH in phosphate buffer. The surface sensitivity of the nonlinear optical SHLS technique is very high and we have looked at the GNP-Lyz interaction at nanomolar concentrations. We have followed the increase in the SHLS intensity of GNPs as a function of the added concentration of Lyz in small aliquots. The SH intensity profile exhibits saturation behaviour and was fitted with a modified Langmuir adsorption model which yielded the binding constant (Kb), the binding stoichiometry (nsat) at saturation and the free energy change (ΔG) in the adsorption process. The free energy change was further decomposed into changes in the enthalpy (ΔH) and entropy (ΔS) of adsorption by carrying out temperature dependent SHLS measurements in a specially designed cell. The thermodynamic quantities extracted from the measurements show that the binding is exothermic (ΔH < 0) as well as spontaneous (ΔS > 0). We find that the first step in the adsorption of Lyz on the GNP surface is nanoparticle protein corona (NP-PC) formation driven predominantly by electrostatic attraction. In the second step of adsorption, the adsorbed lysozymes on the surface form a bridge between two or more GNPs leading to the latter's aggregation, which is the main reason for the enhancement of the SH scattering signal. Although the interaction between the GNPs and Lyz is driven by strong electrostatic attraction, the thermodynamic quantities reported here indicate that the protein is physisorbed on the nanoparticle surface. We have also demonstrated that SHLS provides a new tool for full thermodynamic characterization of protein adsorption on metal nanoparticles at ultralow concentrations.

Improved protein determination assays obtained after substitution of copper sulfate by copper oxide nanoparticles

Copper oxide nanoparticles (nano CuO) provide Cu²⁺ ions which can be easily harnessed for protein determination as an alternative to the use of copper sulfate (CuSO₄). In the present work, nano CuO of size <25 nm were substituted for CuSO₄ in two of the well-known protein assays viz. Lowry method and bicinchoninic acid (BCA) method. Use of nano CuO in the Lowry's assay had no effect on the assay time (30 min) but significantly lowered the limit of detection (LOD) from 0.01 to 0.001 μg/ml, while the BCA method when performed using nano CuO resulted in notable reduction of not only the assay time from 30 to 20 min but also the LOD from 0.1 to 0.001 μg/ml. Nano CuO based protein determination in the human serum and urd bean seeds extract produced reliable, reproducible and consistent results. Nano CuO also alleviated the inhibition of both the methods by common interfering substances such as ammonium sulfate, glucose, EDTA, SDS, Triton X-100, dithiothreitol and 2-mercaptoethanol. Hence, successful modification and improvement of Lowry and BCA methods by substitution of CuSO₄ with nano CuO for protein determination has been demonstrated.

Enzyme Adsorption on Nanoparticle Surface Probed by Highly Sensitive Second Harmonic Light Scattering

Recent developments in second harmonic light scattering technique and the associated theoretical models have provided a deeper insight of molecular interactions on micro- and nanoparticle surfaces. This technique is extended to probe the thermodynamics of protein adsorption on nanoparticle surface which is crucial for understanding the fate of nanoparticle-based formulations in biomedical applications. A modified Langmuir adsorption model has been applied to extract the thermodynamic parameters from the experimental data. The general applicability of the technique is established by extracting free energy change, association constant, and binding stoichiometry of adsorption of a moderate size protein, alcohol dehydrogenase, and a small size protein, insulin, on gold nanoparticles. The free energy change for the adsorption is found to be of the order of -55kJ/mol, which indicates that the interaction of proteins with the nanoparticle surface involves weak forces. On the other hand, the low value of the free energy change makes the detachment of the protein from the particle surface easier and guarantees reversibility of the binding process. In addition, one gets the binding stoichiometry of the proteins with the nanoparticle surface which opens up the possibility of controlling the payload of the protein- or peptide-based therapeutics in future biomedical applications.

Gold nanoparticles increases UV and thermal stability of human serum albumin

Ultraviolet (UV) radiation, temperature, and time can degrade proteins. Here, the authors show that gold nanoparticles significantly protect human serum albumin from denaturation when exposed to "stressing" conditions such as UV irradiation and sustained exposure in suboptimal conditions. In particular, the authors show that gold nanoparticles significantly reduce the decrease in secondary structure induced by UV irradiation or extended exposure to ambient temperature.

Probing protein adsorption on a nanoparticle surface using second harmonic light scattering

A new application of second harmonic light scattering to probe protein physisorption on a gold nanoparticle surface in aqueous buffer is reported. The free energies of adsorption, the number of protein molecules adsorbed on the surface and the binding affinity of a moderate size protein, alcohol dehydrogenase (ADH), and a small protein, insulin, have been determined using the change in the second harmonic scattered light signal as a function of binding. Four different size gold nanoparticles from 15 to 60 nm were used to determine the effect of size on the free energy change, the affinity constant and the number of protein molecules adsorbed on the surface. All were shown to increase with an increase in size. The binding can be reversed by centrifugation, and the protein molecules can be desorbed quantitatively. The application of this method for studying thermodynamic parameters of weakly interacting biomolecules with nanoparticles for nanoparticle based diagnostic and therapeutic formulations is important.

Inhibition of fibrillation of human serum albumin through interaction with chitosan-based biocompatible silver nanoparticles

Electrostatic interaction of chitosan-based silver nanoparticles with human serum albumin leads to inhibition of fibrillogenesis.