Scope: The basic dipeptide, Trp-His, was found to show an in vivo anti-atherosclerotic effect when orally administered to apo E-deficient mice. In addition, this dipeptide causes vasorelaxation in contracted rat aorta via suppression of intracellular Ca2+ signaling cascades. In this study, we attempted to determine whether Trp-His can be absorbed after single oral administration in Sprague-Dawley (SD) rats. Methods and results: Trp-His and His-Trp (10 or 50 mg/kg) was orally administered to 8-week-old male SD rats. Both peptides in plasma were assayed by LC-MS/MS in combination with 2,4,6-trinitrobenzene sulfonate derivatization technique. In vitro transport experiments using Caco-2 cell monolayers were performed to evaluate the apparent permeability (Papp). A phytic acid-aided MALDI-MS imaging (MSI) was conducted to visualize the distribution of dipeptides in the rat intestinal membrane. Trp-His was absorbed intact into SD rat blood, showing a maximal level at 1 h after administration at 10 mg/kg dose (Cmax, 28.7 ± 8.9 pmol/mL-plasma; area under the curve, 71.3 ± 18.7 pmol·h/mL-plasma). In contrast, His-Trp was surprisingly not detected, although the Papp was compatible to that of Trp-His. MSI analysis provided crucial evidence that Trp-His was visualized in the overall intestinal membrane. The Trp-His peptide was not visualized in the presence of Gly-Sar, which is a model peptide that is transported via the intestinal proton-coupled peptide transporter 1 (PepT1) transporter. The His-Trp molecular ion was not observed at the intestinal membrane. The MSI analysis illustrated that there is no absorption of His-Trp due to its unexpected hydrolysis by brush border proteases. Conclusion: To the best of our knowledge, this is the first study demonstrating that the vasoactive Trp-His is preferably transported across the rat intestinal membrane by PepT1 and is absorbed intact into the circulation. However, no absorption of His-Trp, a reverse sequence of absorbable Trp-His, is observed owing to hydrolysis by intestinal proteases. This suggests that the bioavailability of peptides may be determined in part by their protease resistance in the intestinal membrane.
All Science Journal Classification (ASJC) codes
- Food Science