The Transepithelial Transport and Transport Pathways of Free and Bound Nε-Carboxymethyllysine Using a Caco-2 Cell Monolayer Model

As a typical marker of dietary advanced glycation end products (AGEs), Nε-carboxymethyllysine (CML) exists in both free and protein-bound forms in foods, exhibiting distinct intestinal transport behaviors. This study aimed to characterize the transepithelial transport, intracellular accumulation and transport pathways of free CML (FC) and protein-bound CML (BC, BSA-CML) using Caco-2 cell monolayers. Since protein-bound CML undergoes digestion in the gastrointestinal tract, BC was subjected to simulated gastrointestinal digestion before transport experiments to better mimic human digestion (BC digests). The results showed that FC exhibited significantly greater transepithelial transport across Caco-2 cell monolayers than BC digests. The transport rate of CML from FC across Caco-2 cell monolayers was 13.04%, significantly higher than that of BC digests (0.99%). Consistently, the intracellular accumulation of total CML was higher for FC (2.62%) than for BC digests (0.14%). Furthermore, FC transport appeared to occur mainly via simple diffusion, whereas the transepithelial transport of CML derived from BC digests likely involved a peptide transporter 1 (PepT1)-associated transport pathway. These findings provide insights into the transepithelial transport pathways and intracellular accumulation of dietary free and bound AGEs.