Nanoparticle Mediated Suppression of Protein Aggregation

Abstract

The increasing demands for biopharmaceuticals to treat different diseases have raised concerns about controlling the quality and efficacy of such pharmaceuticals. The design and formulation of a stable protein or peptide based biopharmaceutical runs into the limitation that at high concentrations (> 100 mg/ml) or during long storage process the drug undergoes aggregation. During synthesis, purification, storage or packaging of these drugs different kinds of stresses like chemical, oxidative, thermal, shear, etc. are encountered. These stresses promote the non-native aggregation of protein and peptide based drugs. Injection or administration of such drugs if contaminated with aggregates causes patient discomfort or development of an antibody which can adversely affect patient’s conditions. This brings out the necessity of finding a way so that such aggregation is avoided. Nanoparticles have been used as vehicles for drug delivery and diagnostic agents in biology for a while. The surface of the nanoparticles is known to adsorb small as well as large molecules with different kinetics and energetics of interaction. I have used nanoparticles to adsorb proteins to protect them against aggregation when they are subjected to denaturing conditions. The effectiveness of the nanoparticles in stopping protein aggregation, recovery of the proteins and reversibility of the adsorption process, the catalytic activity of the proteins before and after adsorption on the surface have all been studied in details. The work described here has been divided in 8 chapters and the contents of each chapter are described below. In Chapter 1 I have provided a brief introduction to the protein aggregation problem. The motivation and scope of the current work has been presented in this chapter. Materials and methods have been described in Chapter 2. Synthesis of gold and silica nanoparticles, their characterization and stability under experimental conditions have been illustrated in this chapter. The spectroscopic assays and techniques which I have used to study the effect of gold and silica nanoparticles on protein aggregation have been discussed at lengths in this chapter. In Chapter 3 I have demonstrated the effect of gold nanoparticles on thermal aggregation of alcohol dehydrogenase (ADH). The size of the nanoparticle was varied in the range of 15-60 nm and the effect was measured by various spectroscopic assays and techniques. I have observed that gold nanoparticles prevent thermal aggregation of ADH and the efficiency is high. Gold nanoparticles in nanomolar or even picomolar concentrations are capable of preventing the aggregation of ADH at micromolar concentrations. In Chapter 4 the role of gold nanoparticles as suppressor of protein aggregation was extended to another protein, insulin. Chemically induced aggregation of insulin using dithiothreitol (DTT) in the presence of gold nanoparticles was studied in the same manner as was done for ADH. Similar prevention property of gold nanoparticles was established by making the observation independent of the method of denaturation or the type of protein used in the prevention experiments. In Chapter 5 huge second harmonic light scattering (SHS) signal from pure gold nanoparticles has been used to measure the free energy of interaction of ADH and insulin with nanoparticles in solution, for the first time. The change in the second harmonic scattered signal was monitored which decreased steadily as a function of added protein concentration to the aqueous solution of gold nanoparticles. The fitting of the second harmonic signal decay was done with a modified Langmuir adsorption isotherm to extract the free energy change in the interaction and the number of protein molecules adsorbed on the surface. In Chapter 6 I have demonstrated a way to recover the adsorbed ADH and insulin from the gold nanoparticle surface and tested the activity of ADH by an assay. The structure of the proteins in the adsorbed state has been probed by CD spectroscopy and described in this chapter. It is found that ADH retains its activity in the adsorbed state. Both the proteins retain the native secondary structures in their adsorbed state. However, the structures change drastically under denaturing conditions. In Chapter 7 the effect silica nanoparticles which are known to have hydrophilic surface has been examined on the aggregation of ADH and insulin in pretty much the same way as was done with gold nanoparticles. The efficiency of silica nanoparticle was found to be lower compared to gold nanoparticles. In addition, the size dependency of prevention efficiency of silica and gold nanoparticles was found to be completely opposite to each other. In Chapter 8 I have presented the overall summary and possible future directions of this work