Transport of angiotensin peptides across the Caco-2 monolayer

The bidirectional transport of the angiotensin peptides—des-Asp-angiotensin I (DAAI), angiotensins III and IV—were studied using human intestinal Caco-2 monolayers. The peptides had low permeability rates but were relatively stable to enzymatic hydrolysis. DAAI was transported by diffusion while angiotensins III and IV were transported by an energy requiring, carrier-mediated process. The physicochemical properties and solution conformations of the peptides were investigated in an attempt to establish structure–transport correlations. Among the three peptides, DAAI was the most hydrophobic, had the highest hydrogen bonding potential and was the only peptide to have a random solution conformation, as determined from circular dichroism, two-dimensional 1 H NMR and molecular modelling. On the other hand, the more hydrophilic angiotensin IV had less hydrogen bonding potential and a solution conformation characterized by a β turn. These factors may influence the transport characteristics of DAAI and angiotensin IV.