Sodium caprate enables the blood pressure-lowering effect of Ile-Pro-Pro and Leu-Lys-Pro in spontaneously hypertensive rats by indirectly overcoming PepT1 inhibition

Abstract The tripeptides, Ile-Pro-Pro (IPP) and Leu-Lys-Pro (LKP), inhibit angiotensin-converting enzyme (ACE) resulting in lowered blood pressure. Our hypothesis was that the medium chain fatty acid permeation enhancer, sodium caprate (C 10 ), may prevent the decrease in permeability of the tripeptides when PepT1 is inhibited by glycyl-sarcosine (Gly-Sar), a situation that may occur in the presence of food hydrolysates. Using Caco-2 monolayers and isolated rat jejunal tissue, the apparent permeability coefficients (P app ) of [ 3 H]-IPP and [ 3 H]-LKP were assessed in the presence of Gly-Sar with and without C 10 . Gly-Sar decreased the P app of both tripeptides across monolayers and isolated jejunal tissue, but C 10 restored it. C 10 likely increased the paracellular permeability of the tripeptides, as indicated by immunofluorescence changes in tight junction proteins in Caco-2 monolayers accompanied by a concentration-dependent decrease in transepithelial electrical resistance (TEER). [ 3 H]-IPP and [ 3 H]-LKP were orally-gavaged to normal rats with Gly-Sar, C 10 , or with a mixture. Plasma levels of both peptides were reduced by Gly-Sar to less than half that of the levels detected in its absence, but were restored when C 10 was co-administered. In spontaneously hypertensive rats (SHRs), unlabelled IPP and LKP lowered blood pressure when delivered either by i.v. or oral routes. Oral gavage of Gly-Sar reduced the hypotensive action of peptides in SHRs, but the effect was restored in the presence of C 10 . In conclusion, there was a reduction in the hypotensive effects of IPP and LKP in SHRs when intestinal PepT1 was inhibited by Gly-Sar, but C 10 may circumvent this by enhancing paracellular permeability.