Pepsin-catalyzed plastein reaction with tryptophan increases the in vitro activity of lactoferrin hydrolysates with BGC-823 cells

Abstract

Lactoferrin hydrolysates (LF-H) were digested using pepsin and modified using a pepsin-catalyzed plastein reaction with tryptophan (Trp) to obtain a target product. LF-H, the target product, plastein reaction-modified LF-H alone, and a mixture of LF-H and Trp were evaluated for their activities with human gastric cancer BGC-823 cells at 24 and 48 h. Assay results indicated that the target product had decreased free amino groups and had incorporated Trp. LF-H and the plastein reaction-modified LF-H alone did not show detectable growth inhibition on BGC-823 cells at 1–3 mg/mL; however, the target product at the same dose levels inhibited cell growth, and showed higher activity than the mixture (P < 0.05). The target product at 2 and 3 mg/mL stopped cell cycle progression at the G0/G1-phase, induced DNA fragmentation, and showed apoptosis induction, which increased the number of apoptotic cells. Moreover, time- and dose-dependent responses were observed in these experiments. RT-PCR assay results indicated that exposure of the cells to the target product resulted in up- and down-regulated mRNA expression for 7 apoptosis-related genes, namely Bcl-2, Bcl-xl, Bad, Bax, caspase-3, caspase-6, and caspase-9. Thus, the plastein reaction increased in vitro anticancer activities of LF-H with BGC-823 cells, and more importantly, both the plastein reaction and Trp incorporation contributed to enhanced activities.