Assessment of a Tat-Derived Peptide as a Vector for Hormonal Transport

摘要

Glucagon-like Peptide 1 (GLP-1) is a 30 amino acid gastrointestinal peptide hormone that is secreted in response to an oral glucose load to contribute to the normalization of plasma glucose levels by stimulating postprandial insulin secretion from pancreatic β cells while inhibiting glucagon secretion from pancreatic a cells. Furthermore, GLP-1 regulates glucose homeostasis through extra-pancreatic affects, including promoting feelings of satiety and delaying gastric emptying [1]. The reptilian-derived analog of GLP-1, exendin-4 (Byetta), is an FDA-approved medicine for treatment of type 2 diabetes. Because exendin-4 and GLP-1 are peptides, they are inherently impermeable to cellular membranes and are not passively taken up by cells, meaning they are not transported across a cell monolayer and are not absorbed through the small intestine. Therefore, GLP-1 and exendin-4 must be administered through a subcutaneous injection. Conversion of exendin-4 or GLP-1 to a more orally bio-available form could improve the therapeutic quality, patient compliance, and appeal of the drug. Extracellular HIV-1 Tat is a 101 amino acid protein that is taken up by cells to activate the transcription of the HIV-1 genome, and it has been shown that the cationic cluster that is derived from amino acids 47-57 of the HIV-1 Tat protein can be covalently fused to a wide degree of cargo molecules to stimulate delivery into cells [2]. Not only is this cationic cluster responsible for stimulating cellular uptake, but this same sequence is responsible for the secretion of expressed proteins from cells [3]. We hypothesize that this Tat-derived cationic peptide could function as a vector to improve the transduction efficiency of GLP-1 across the human epithelial cell layer of the small intestine.