Oral delivery of therapeutic peptides has been a continuous target for the pharmaceutical industry, as most of these drugs are currently administered by parenteral routes. However, a major challenge limiting the success of oral delivery of these drugs is their poor permeability across the intestinal epithelial barrier. Extensive research efforts have investigated different strategies to overcome the epithelial barrier and enhance the oral bioavailability of therapeutic peptides. One of the most widely used strategies is the application of permeability enhancer (PE) agents that are co-administered with peptide drugs to facilitate their permeability across the intestinal epithelial barrier. The safety of most of the available PE agents, however, has always been questioned, because most PE agents act non-specifically in altering intestinal epithelial permeability which in many cases has been associated with epithelial damage.The work presented here investigates a novel strategy to overcome the intestinal epithelial barrier challenge and enhance the oral bioavailability of therapeutic peptides. This is by manipulating an endogenous mechanism that is used by the intestinal epithelial cells to dynamically regulate the permeability across the tight junction (TJ) structures by increasing myosin light chain phosphorylation at serine 19 (MLC-pS19), which is regulated by MLC kinase (MLCK) and MLC phosphatase (MLCP). A small membrane-permeant peptide inhibitor for MLCP, called PIP 640 peptide, was rationally designed to selectively alter MLCP activity in a manner that increases MLC-pS19 to transiently enhance TJ permeability for therapeutic peptides. The PIP 640 peptide was designed to be relatively stable in the intestinal lumen, as it is intended to be co-administered orally with therapeutic peptides. It was initially examined for enhanced TJ permeability of fluorescent dextran and for toxicity induction in vitro. Accordingly, efforts were devoted to explore potential modifications of the peptide sequence that might optimize the PIP 640 peptide function. Moreover, studies were performed to examine the biochemical changes of TJ protein structures associated with the permeability enhancement function of the PIP 640 peptide. Finally, we investigated different aspects of the PIP 640 peptide permeability enhancement function in vivo. An overall outcome of these studies was that the PIP 640 peptide can enhance TJ permeability in vitro and in vivo without causing apparent damage to the epithelial barrier. This outcome suggest that the PIP 640 peptide has the potential to be used as a PE for therapeutic peptides.
|Date of Award||1 Sep 2017|
|Sponsors||University of Ha'il|
|Supervisor||Randy Mrsny (Supervisor) & Ian Eggleston (Supervisor)|