Anti-Inflammatory and Transepithelial Transport Activities of Rapeseed (Brassica napus) Napin-Derived Dipeptide Thr-Leu in Caco-2 and RAW264.7 Cocultures

This study aimed to investigate the anti-inflammatory molecular activity of rapeseed napin-derived dipeptide Thr-Leu (TL) using Caco-2/RAW264.7 cell cocultures. This in vitro coculture intestinal inflammation model was used to assess the absorption, evolution, and anti-inflammatory effects of peptides. TL was absorbed by the intestinal epithelial cells with an apparent permeability of (2.48 ± 0.18) × 10^-6 cm/s, primarily through the PepT1 pathway. TL treatment exerted anti-inflammatory and restorative effects on the impaired intestinal barrier function by enhancing the expression levels of occludin and ZO-1 in lipopolysaccharide (LPS)-induced Caco-2 cells. No significant change (P < 0.05) was detected in claudin-1 expression levels; however, the occludin expression levels were upregulated through the protein kinase C (PKC) signaling pathway. Compared with the LPS-induced group, TL (2.0 mM) reduced the levels of intracellular inflammation-related enzymes (iNOS: by 50.84%; COX-2: by 49.64%) on the coculture cell model. In addition, the interleukin (IL)-1β, IL-6, and TNF-α levels in RAW264.7 cells were significantly (P < 0.05) downregulated following TL treatment (2.0 mM) due to the suppression of the phosphorylation of the JNK-independent pathway on the basolateral side of the coculture cell model. These findings highlight the potential use of TL in functional foods or nutraceuticals to prevent intestinal inflammation.