Stability, toxicity and intestinal permeation enhancement of two food-derived antihypertensive tripeptides, Ile-Pro-Pro and Leu-Lys-Pro

Two food-derived ACE inhibitory peptides, Ile-Pro-Pro (IPP) and Leu-Lys-Pro (LKP), may have potential as alternative treatments for treatment of mild- or pre-hypertension. Lack of stability to secretory and intracellular peptidases and poor permeability across intestinal epithelia are typical limiting factors of oral delivery of peptides. The stability of IPP and LKP was confirmed in vitro in rat intestinal washes, and intestinal and liver homogenates over 60min. A positive protein control for peptidases, insulin, was significantly digested in each format over the same period. Neither tripeptide showed cytotoxic activity on Caco-2 and Hep G2 cells using the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay, even after chronic exposure. The basal Papp of fluorescein isothiocyanate (FITC)-labeled IPP and FITC-LKP across isolated rat jejunal and colonic mucosae were low, but were significantly increased in each tissue type by the medium chain fatty acids (MCFA) permeation enhancers, sodium caprate (C10) and the sodium salt of 10-undecylenic acid (uC11). IPP and LKP were therefore stable against intestinal and liver peptidases and were non-cytotoxic; their Papp values across rat intestinal mucosae were low, but could be increased by MCFA. There is potential to make on oral dosage form once in vivo pharmacology is confirmed.