Maillard products arise from condensation reactions between amino acids or proteins with reducing sugars during food processing. As ubiquitous components of human food, these early or advanced glycation products may be subject to intestinal absorption. The present study was performed to investigate the intestinal uptake of Maillard products and to determine whether they are substrates for peptide and amino acid transporters expressed at the apical membrane of Caco-2 cells. At a concentration of 10 mM, H]leucine by more than 15 %. We also studied the transepithelial flux of Maillard products across Caco-2 cell monolayers cultured on permeable filters. The flux rates of Maillard products ranged from 0·01 to 0·3 %/cm 2 per h and were shown to be much lower than those of carrier substrates such as glycylsarcosine, L-proline and the space marker [ 14 C]mannitol. We conclude that the Maillard products investigated in the present study are neither transported by PEPT1 nor by carriers for neutral amino acids. The low transepithelial flux measured for these compounds most probably occurs by simple diffusion.

The interaction of the antibacterial phosphonodipeptide alafosfalin with mammalian H + /peptide cotransporters was studied in Caco-2 cells, expressing the low-affinity intestinal type peptide transporter 1 (PEPT1), and SKPT cells, expressing the high-affinity renal type peptide transporter 2 (PEPT2). Alafosfalin strongly inhibited the uptake of [ 14 C]glycylsarcosine with K i values of 0.19 ± 0.01 mM and 0.07 ± 0.01 mM for PEPT1 and PEPT2, respectively. Saturation kinetic studies revealed that in both cell types alafosfalin affected only the affinity constant (K t ) but not the maximal velocity (V max ) of glycylsarcosine (Gly-Sar) uptake. The inhibition constants and the competitive nature of inhibition were confirmed in Dixon-type experiments. Caco-2 cells and SKPT cells were also cultured on permeable filters: apical uptake and transepithelial apical to basolateral flux of [ 14 C]Gly-Sar across Caco-2 cell monolayers were reduced by alafosfalin (3 mM) by 73%. In SKPT cells, uptake of [ 14 C]Gly-Sar but not flux was inhibited by 61%. We found no evidence for an inhibition of the basolateral to apical uptake or flux of [ 14 C]Gly-Sar by alafosfalin. Alafosfalin (3 mM) did not affect the apical to basolateral [ 14 C]mannitol flux. Determined in an Ussing-type experiment with Caco-2 cells cultured in Snapwells TM , alafosfalin increased the shortcircuit current through Caco-2 cell monolayers. We conclude that alafosfalin interacts with both H + /peptide symporters and that alafosfalin is actively transported across the intestinal epithelium in a H + -symport, explaining its oral availability. The results also demonstrate that dipeptides where the C-terminal carboxyl group is substituted by a phosphonic function represent high-affinity substrates for mammalian H + /peptide cotransporters.Keywords: alafosfalin; alaphosphin; Caco-2 cells; SKPT cells; Ussing technique.Alafosfalin (alaphosphin, L-alanyl-L-1-aminoethylphosphonic acid) is an antibacterial dipeptide analogue where the carboxyl group at the C-terminal alanine is replaced with a phosphonic [P(O)(OH) 2 ] function. The compound was one of the most promising aminophosphonic acids obtained in an extensive study synthesizing more than 300 di-to penta-peptide alanine mimetics with varying stereometry and different substituents for the C-terminal carboxyl function [1]. It displays good oral availability, substantial antibacterial activity mainly against Gramnegative bacteria and synergism with b-lactam antibiotics [1][2][3][4][5]. In clinical studies alafosfalin was tested for the treatment of gastrointestinal [3] and urinary tract infections [2,4]. Studies demonstrated the competitive effect of food on its enzymatic breakdown in the intestinal lumen [6]. In a recent publication Kafarski & Lejczak [7] reviewed the potential medical importance of aminophosphonic acids and conclude that, due to their negligible mammalian toxicity and the fact that they very efficiently mimic aminocarboxylic acids making them extremely important antimetabolites, aminophosphonic aci...

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In order to assess the health risk that associated with the consumption of unknown feed or food ingredients, there is a strong need of developing an in vitro screening system. The test system should be fast, reliable, inexpensive and without the necessity of performing animal tests. Furthermore, it should also provide important clues to the potential danger of unknown substances. The present study examines the extent to which cell and tissue cultures can be used for such studies. It should be ascertained whether the cell cultures can replace the native intestinal epithelium in terms of their sensitivity and provide accurate results as a quick "screening system". As a model for intestinal operations ex vivo tissue cultures from the native intestinal epithelium of the pig and the permanent cell line IPEC-J2 were used. The cell culture was characterized in terms of their morphological and functional properties (TEER, tight-junction proteins).Various studies (short-circuit measurements, translocation of [ 3 H]-mannitol) were performed to IPEC-J2 cells and the native intestinal epithelium in order to compare the functional properties of both systems. Finally, the response of the addition of "unknown" test substances (papain and wheat extract) were investigated to determine whether the functional parameters of both systems are affected by these test substances or not. The IPEC-J2 cells show a more significant influence in their functionality by "unknown" substances than the control variant. Results of study revealed that the in vitro system reacts rapidly in response of unknown test substances and it is more sensitive. Therefore, it is possible to operate a "risk assessment" for "unknown" substances with the help of this developed screening system.