Absorption and Metabolism of Peptide WDHHAPQLR Derived from Rapeseed Protein and Inhibition of HUVEC Apoptosis under Oxidative Stress

WDHHAPQLR (RAP) is an antioxidative peptide derived from rapeseed protein. Although the health benefits from RAP, due to its antioxidant activities, have been determined by chemical methods, a systematic assessment regarding the absorption, metabolism, and antioxidation processes of RAP is still lacking attention. Hence, Caco-2 cell monolayer models and animal experiments were used to evaluate the absorption and bioavailability of RAP. As expected, RAP could be absorbed by intestinal epithelial cells, and the Papp was 0.82 +/- 0.19 X 10(-6) cm/s. Three main fragments, RAP, DHHAPQLR, and WDHHAP were transported by the paracellular pathway, and QLR was transported by PepT1. An important modified product of RAP (EGDHHAPQLR) was found to contribute to the elimination of intracellular reactive oxygen species. The absolute bioavailability of RAP was 3.56%, and three degradation products of RAP were also detected in rat serum. More importantly, RAP exerts its antioxidant activity by inhibiting the apoptosis of oxidative stress cells. RAP could downregulate the expression of Bax and caspase-3 and upregulate the expression of Bcl-2 in H2O2-induced HUVECs (human umbilical vein endothelial cells). In general, using in vitro and in vivo experimental models, the in vivo absorption and transformation processes of RAP and its antioxidative molecular mechanisms by inhibiting apoptosis of cells were revealed.