Self-Assembled Peptides for Drug Delivery, Tissue Regeneration, and Biocatalytic Applications

Abstract

Molecular self-assembly is a process in which individual components interact via non-covalent interactions, like van der Waals, hydrogen bonding, electrostatic, hydrophobic, and π-π stacking in a well-defined manner to form hierarchical, supramolecular materials with desired function. Living organisms generate a wide range of biomolecules, such as polysaccharides, lipids, nucleic acids, and proteins, which spontaneously self-assemble into more complex and highly organized supramolecular nanostructures with clearly defined biological roles. Through rational design and engineering, peptides can adopt certain secondary, tertiary, and quaternary structures and, thus, provide new opportunities to design self-assembled, nanoscale materials with different size and morphology for various applications. The inherent biocompatibility, biodegradability, and flexible mechanical stability with diverse functionality have made peptides a promising entity to design biomaterials. This thesis deals with the design and development of self-assembled peptides for drug delivery, wound healing, tissue regeneration, and biocatalyst-mimic applications, and is organized into six chapters. Chapter 1 of the thesis contains introduction to the self-assembly of peptides and their prospects in a wide range of biomedical applications along with the exhaustive literature survey, definition of problem, and specific objectives and outline of the thesis. In chapter 2, we have developed pH responsive, antioxidant di- and tripeptide gels for the sustained release of an anti-diabetic drug glimepiride. The delivery system has the potential to reduce the side effects of drug, frequency of dosing, and improve the patient compliance and fluctuation in bioavailability, which is related to severe hypoglycemia and gastrointestinal disturbances. The antioxidant nature of peptides will provide protection against the oxidative stress caused by the production of hydrogen peroxide during the oxidation of glucose by glucose oxidase. The peptide gels were non-toxic to cell lines and promoted the glucose uptake at low pH. The gels developed in this work can perform as a multidimensional platform to minimize oxidative stress, hypoglycemia, and repetitive dosing of drugs in diabetes patients. Chronic wound is a major healthcare challenge around the world, which is characterized by the presence of bacterial infection, formation of biofilm, accumulation of reactive oxygen species (ROS), and persistent inflammation. Overexpression of cyclooxygenase 2 (COX-2) prolongs the inflammation phase and deteriorates the wound healing process. Chapter 3 of the thesis deals with the synthesis of ultra-short peptides comprising of D- and L-amino acids with antioxidant and antibacterial properties and their conjugation to naproxen (Npx) and indomethacin (Ind) to provide better selectivity towards COX-2 enzyme, implicated in inflammation. The peptides were self-assembled into supramolecular gels and exhibited high proteolytic stability, potent antibacterial, and radical scavenging activities. These gels decreased the expression of proinflammatory cytokines and elevated the expression of anti-inflammatory cytokines. The gels show a strong potential as a topical agent for treating chronic wounds or as a coating material for medical devices to prevent implant-associated infections. In chapter 4, we have investigated the self-assembled peptide gels to facilitate bone tissue regeneration because the conventional strategies to treat bone defects face challenges, like immunogenicity, lack of cell adhesion, and absence of osteogenic activity. We have developed collagen and non-collagen protein-inspired bioactive peptides with osteoinductive potential, which can play a role in biomineralization and promote bone formation. We have synthesized six amphiphilic tetra-peptides, out of which four were self-assembled into gels. The change in their nanostructured morphology was observed with the change of a single amino acid and have investigated their role in the adsorption of hydroxyapatite and differentiation of mesenchymal stem cells to accelerate bone tissue regeneration. Enzyme is a natural catalyst comprising of proteins, and their remarkable catalytic activity depends on the amino acids present at the active site. Chapter 5 discusses the design and development of self-assembled peptides as enzyme mimetics. We have developed peptide-ceria nanoparticle conjugates and evaluated their potential to act as esterase, phosphatase and haloperoxidase-mimicking enzyme. The biocatalytic activity of the peptide immobilized on ceria nanoparticles can provide benefits in several therapeutic applications like bone tissue regeneration and anti-biofouling material preparation. Chapter 6 provides a conclusion of the work done in this thesis along with the contribution of this work to the existing knowledge and its future prospectives.