Antioxidant activity in HepG2 cells, immunomodulatory effects in RAW 264.7 cells and absorption characteristics in Caco-2 cells of the peptide fraction isolated from Dendrobium aphyllum

DA-P, fraction of peptides with a molecular weight <1kDa isolated from Dendrobium aphyllum, was analysed in three types of cell lines to verify its bioactivity and absorptivity. The cellular antioxidant activity of DA-P in HepG2 cells was used and results revealed an EC50 of 2.88 +/- 0.143mgmL(-1) and a CAA unit of 63.46 +/- 2.11m QE/100g peptides. DA-P treatment enhanced the secretion of cytokines in RAW 264.7 cells. After demonstrating the presence of tight junctions in Caco-2 monolayers, the absorption was 25.57%+/- 0.016% and 19.7%+/- 0.012% from different sides. The relatively high absorption indicated that the antioxidant-relevant immune functions of DA-P had a greater possibility to be absorbed by Caco-2 cells. Free amino acids and LC-MS/MS analysis indicated the degradation and expulsion of components after the absorption of DA-P, and Ser-Ser-Arg was able to come across the monolayers.