Transport of Free and Peptide-Bound Pyrraline at Intestinal and Renal Epithelial Cells

Abstract

Pyrraline is a quantitatively dominating glycation compound of the advanced Maillard reaction in foods and can be found in urine after consumption of pyrraline-containing food items. The purpose of this study was to investigate the transport of pyrraline and its dipeptide derivatives alanylpyrraline (Ala-Pyrr) and pyrralylalanine (Pyrr-Ala) at intestinal and renal cell lines. Pyrraline inhibited the l-[(3)H]lysine uptake with IC(50) values of 0.3 mM (Caco-2 cells) and 3.5 mM (OK cells), respectively, but not the uptake of [(14)C]Gly-Sar (Caco-2 and SKPT cells). In contrast, Ala-Pyrr strongly inhibited the uptake of [(14)C]Gly-Sar in Caco-2 and SKPT cells with IC(50) values of 0.19 and 0.017 mM, respectively. Pyrr-Ala inhibited the carrier-mediated uptake of [(14)C]Gly-Sar in Caco-2 and SKPT cells by 50% at concentrations of 0.03 and 0.008 mM, respectively. The transepithelial flux of peptide-bound pyrraline across Caco-2 cell monolayers was up to 15-fold higher compared to the flux of free pyrraline. We conclude that free pyrraline is not a substrate for the intestinal lysine transporter and that the absorption of dietary pyrraline occurs most likely in the form of dipeptides rather than as the free amino acid.

Quantification of the Maillard reaction product 6-(2-formyl-1-pyrrolyl)-l-norleucine (formyline) in food

“…The water used for the preparation of buffers and solutions was obtained using a Purelab plus purification system (USFilter, Ransbach-Baumbach, Germany). Formyline [8] and pyrraline [20] were prepared according to the literature stated.…”

“…A linear gradient from 3 to 13 % B in 30 min was applied at a flow rate of 1 mL/min. External calibration was performed with the standards synthesized as described in the literature [8,20]. The limits of detection (LOD) and quantification (LOQ), respectively, represent the concentrations of the analytes that are necessary to show a peak with signal-to-noise ratios of 3 and 10, respectively.…”

“…Based on the model diet of Henle [27], the daily intake of protein-bound formyline can be estimated to approximately 2-3 mg, and that of pyrraline to 20-40 mg with bakery products as the predominant source. Due to its structural similarity to pyrraline, formyline should be hydrolyzed from proteins during digestion and taken up into the body in the form of peptides [18,20]. Since the in vivo transport of formyline peptides exceeds that of pyrraline peptides [20,22], it might be interesting to comparatively study the metabolic transit of the pyrrole compounds from foods containing both derivatives in balance studies in vivo.…”

“…The absorption of this amino acid can be explained by the transport capabilities of the human intestinal peptide transporter PEPT1. This membrane-bound multi-substrate carrier protein is able to translocate dipeptide-bound pyrraline into the cell, from where free pyrraline can pass into the circulation after peptidolysis [20,21]. Recent data on the transport properties of a variety of other dipeptidebound AGEs indicate that products such as formyline will also show high bioavailability [22].…”

Preparation, Identification and Antioxidant Properties of Black-Bone Silky Fowl (Gallus gallus domesticus Brisson) Oligopeptide-Chelated Ferrous Iron

“…Compared with amino acids, peptides are diffi cult to saturate with metals, although their absorption effi ciency is higher (8). The peptide transporter 1 (PepT1), found in the small intestine, promotes the absorption of peptides (9).…”