Biomaterials for manipulating mast cell activity
Creators: Raj, Shammy
Publisher: name: University of Alberta Library
Year: 2022

<p>Inflammation is a symphony of immune responses orchestrated by the different cells of immune system. The effect is soothing when the triggered immune response is healing against pathological invasions, tissue injuries, or an ailment. However, it becomes unpleasant when the immune response aggravates to allergies, autoimmune diseases, or when it complicates transplantations. The complexity of immune response is so vast that even after the given scientific advancements, only a few of the many discrete events pertaining to inflammations has been deciphered. Our understating of immune response is very specific, both with respect to the cells of immune system, and with respect to an inflammatory event; and that the interplay between these is yet to be comprehended. Having said that, it is incumbent upon engineers, to use these scientific understandings, however limited it may be, to better the lives of humankind.</p>

<p>Of various cells involved in an immune response, mast cells are the first responders. These cells are strategically located at the interface of a tissue and its external environment and get activated in response to a pathogenic agent. Activated mast cells release a plenty of biomolecules in their extracellular space, which act as chemoattractant for the downstream immune signaling. Immune mediators, as the released biomolecules are called, consists of cytokines, enzymes, biogenic amines, growth factors and reactive oxygen species (ROS). The premise of the thesis lies in designing materials, which would be useful in inflammation-targeted therapeutics.  Since mast cells are de facto present as the first responders, emphasis has been put on designing materials which are responsive to mast cell functionality and characteristics. </p>

<p>Out of several mediators, ROS have been chosen as the primary mast cell specific mediator due to their immediate and localized release profiles. Furthermore, the selection of the stimulus mediator was also governed by the easy synthesis of a ROS responsive molecules and its facile utilization in material design. A ROS responsive, bioactive thioketal (TK) molecule was synthesized and characterized. TK is cleaved into its parent molecules in ROS extensive environment. Synthesized TK was stable at physiological conditions (pH = 7.4). ROS activity of TK was ascertained by subjecting TK to Fenton’s reagent. The in vitro biocompatibility and cell toxicity of TK was confirmed against islet cells. TK was deemed nontoxic to cells. TK was also used in in vivo transplantation of mouse islets where its biocompatibility was reaffirmed.</p>

<p>TK was then used to develop ROS responsive drug delivery platforms for the targeted delivery of anti-inflammatory dexamethasone (Dex) to the site of inflammation. Dex was successfully conjugated to the polyethylene glycol – polylactic acid (PEG-PLA) copolymer, and polyethylene glycol (PEG) through TK as a linker. ROS stimulated Dex release was confirmed in stimulated Fenton’s reagent ROS solution. Both PEG-PLA and PEG systems responded to ROS by releasing cleaved Dex from the polymeric constructs. Nanoparticles were formed from the PEG-PLA construct through the film hydration method which showed a size of 14 nm and a –ve zeta potential. The nanoparticles were further subjected to Fenton’s reagent to confirm Dex release.</p>

<p>Finally, a design rule to synthesize peptides specific to mast cell mas related G-protein receptor X2 (MRGPRX2) was devised, and a corresponding library of various peptides with differential mast cell activating potential was generated. Peptide activators of MRGPRX2 follows a generic rule of Xa-(Y)(n ≥ 3)-Xb where: Xa is an aromatic residue; Xb is a hydrophobic residue; and Y is a minimum 3 residue long sequence, containing a minimum of one positively charged residue with the remainder being uncharged residues. The design rule is an excellent tool to design inflammation targeted peptides with a desired mast cell activity. These could be very efficiently tethered on therapeutic systems to localize the therapy to the inflamed tissue.</p>