Activity of the peptic-tryptic caseinate digest with caseinate oligochitosan-glycation in rat intestinal epithelial (IEC-6) cells via the Wnt/β-catenin signaling pathway

Abstract

The caseinate and glycated caseinate generated from the transglutaminase-catalyzed reaction of caseinate and oligochitosan were digested using pepsin and trypsin, and the activity of the resultant digests was measured in rat intestinal epithelial cell line (IEC-6) using several biological responses as indicators. Compared with the caseinate digest, the glycated caseinate digest had similar contents in 17 amino acids but less reactable –NH2 contents, and 6.57 g glucosamine per kg protein; moreover, it showed higher activity in the cells (P < 0.05) to promote cell growth, accumulate the cell-cycle progression at the S-phase, and prevent the camptothecin-induced cell apoptosis. The glycated caseinate digest also showed higher differentiation activity in the cells than the caseinate digest, resulting in enhanced activities of the three brush-border membrane enzymes (P < 0.05) and increased microvilli on the cell surfaces. The real-time reverse transcription-polymerase chain reaction, Western-blot assay, and Dickkopf-1 (a receptor inhibitor of the Wnt/β-catenin signaling pathway) were used to determine both gene and protein expression changes in the cells. A Wnt/β-catenin signaling pathway responsible for these enhanced effects was proposed because the five genes (glycogen synthase kinase 3β, Wnt3a, β-catenin, c-Myc, and cyclin D1) and three proteins (nuclear and cytosolic β-catenin, cyclin D1, and c-Myc) as part of this signaling pathway were regulated in the treated cells. The oligochitosan glycation of caseinate induced by transglutaminase is thus suggested endowing the peptic-tryptic caseinate digest with higher activity in the cells through its effects on the Wnt/β-catenin signaling pathway.