PH Effect On The Photo-Induced Aggregation Of Lysozyme

Drug Delivery Systems (DDS) based on protein nanoparticles, possessing both the properties of nanoparticles and the natural materials of proteins, have attracted widespread interest in last decades. That means protein-based DDS can not only prolong the circulation time of drug and have passive targeting capacity based on the nanoparticle accumulation in tumors by the enhanced permeability retention effect (EPR effect), but also largely improve the biodegradablilty due to its natural component of proteins. In addition, the potential application of protein-based DDS also stimulates people to further improve their synthesis methods. Currently, the synthesis strategies, such as emulsification method and desolvation method, usually require the introduction of chemical cross-linking agents after partial or complete unfolding of proteins under extremely harsh conditions. In fact, these synthesis methods usually not only lack effective control of the self-assembling process of proteins, but may also introduce additional toxicity to the systems.Recently, Xie, et al. provided a novel method to synthesize the protein-based DDS (BLA-DOX nanoparticles) in one step under the illumination of UV light. Both the results from in vitro and in vivo experiments indicated that their BLA-DOX nanoparticles show not only greatly improved homing efficiency on cancer cells, but also enhanced capability on tumor suppression. However, there are still some aspects that must be further improved. For example, the long-time illumination of both protein and drug might destroy the structure of drug and further decrease its anticancer efficiency. Conversely, under the short-time illumination, only a small number of monomers of proteins attend in the assembling process, while others still keep their independent molecular states. In particular, the burst release of drug from nanoparticles is quit sensitive to the acid pH condition, which is similar to the local environment of cancer tissue, through the mechanism behind is still unclear. To investigate the potential mechanism and improve the synthesis method of protein-based DDS, we focus on the effect of pH condition on the protein assembling process under UV illumination and incubation.Our work is divided into three chapters.In the first chapter, we simply introduce the development of protein nanoparticles and their synthesis methods.In the second chapter, we present the history and the latest developments on the study of photo-induced protein aggregation.In the third chapter, we mainly focus on the pH effect on the protein aggregation under UV illumination. We found that lysozyme has a quite different assembling behavior under different pH condition. That is lysozyme molecules at neutral or higher pH are prone to aggregate upon illumination, while under acidic conditions there are no aggregates can be observed. From a general consideration, the different pH condition will influence both the formation of intermolecular disulfide bonds and the intermolecular electrostatic interaction, which may be both important for photo-induced protein aggregation. Combined with many experimental evidences, we speculate that the alteration of the intermolecular electrostatic interaction induced by the change of pH condition should take the main responsibility for the quite different assembling behaviors correlated with pH value.