טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentBourdetsky Dmitry
SubjectAnti-Endotoxin and Immunomodulatory Properties of Host
Defense Peptides Mimics
DepartmentDepartment of Biotechnology
Supervisor Professor Amram Mor
Full Thesis textFull thesis text - English Version


Abstract

Host defense peptides (HDPs) are important components of the natural defenses of most living organisms against microbial infection. HDP's are characterized by a remarkable set of advantageous properties ranging from molecular simplicity to low-resistance rapid-kill of a broad range of microbial cells.  The antimicrobial effect exerted by these peptides is mediated by both direct (mostly receptor-independent) and indirect (immunomodulatory) mechanisms. Thus, the resulting broad-spectrum antimicrobial activity exerted via non-specific multi-target mechanisms place the HDPs as a promising group of new therapeutic agents. However, as drug candidates, peptides represent a less than ideal formula, namely because of poor bioavailability issues, potential immunogenicity, optional toxicity and high production costs. To address these issues, the lab has recently designed novel backbone-flexible peptide-mimetics termed oligo-acyl-lysyl (OAK).

   My research therefore focused on understanding if OAKs which are capable of exerting direct antimicrobial effect in a HDP-like fashion, are able to mimic the immunomodulatory properties of the natural peptides as well. Initially, the ability of OAKs to neutralize toxic effects of endotoxin was evaluated both in-vitro and in-vivo. In vitro, representative OAKs are shown to bind endotoxin in hydrophobicity-dependent manner, while high positive charge contributed to the binding affinity as well. Endotoxin pre-incubated with OAKs induced lower extent of inflammation on cell cultures, compared to endotoxin alone. It is worth to note that ability of OAKs to protect animals in septic shock model, was in full accordance with affinity to bind endotoxin in vitro and the ability to decrease inflammation in cell culture

  Next I tested several aspects reflecting immunomodulatory activity. Tested OAKs have attracted the human monocytes similarly to the natural host defense peptide LL-37. In addition, the chemotactic OAKs were capable of moderately enhancing production of pro-inflammatory and immunomodulating cytokine from primary murine macrophages as indicated by both Real-Time PCR and ELISA methods.

   Finally, the bioavailability of selected OAKs was assessed. A representative OAK preserved its antimicrobial activity in complex media like human and murine whole blood. In pharmacokinetics experiments OAKs were characterized with rapid entrance to the blood circulation and maintaining quite high blood concentrations compared to natural HDPs.

   Collectively, the data support the view that OAKs might mimic both the direct and immunomodulatory  anti-infective activities of host defense peptides, while possessing advantageous properties like improved bioavailability.