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

Impact of the Plastein Reaction of Casein Hydrolysates in the Presence of Exogenous Amino Acids on Their Anti-Inflammatory Effect in the Lipopolysaccharide-Stimulated Macrophages

In this study, papain-generated casein hydrolysates (CH) with a degree of hydrolysis of 13.7% were subjected to a papain-mediated plastein reaction in the absence or presence of one of the exogenous amino acids-Gly, Pro, and Hyp-to prepare four plastein modifiers, or mixed with one of three amino acids to prepare three mixtures. The assay results confirmed that the reaction reduced free NH2 for the modifiers and caused amino acid incorporation and peptide condensation. When RAW264.7 macrophages were exposed to the CH, modifiers, and mixtures, these samples promoted macrophage growth and phagocytosis in a dose-dependent manner. In addition, the CH shared similar activity in the cells as the mixtures, while the modifiers (especially the PCH-Hyp prepared with Hyp addition) exerted higher potential than CH, the mixtures, and PCH (the modifier prepared without amino acid addition). The plastein reaction thus enhanced CH bioactivity in the cells. When RAW264.7 macrophages were stimulated with lipopolysaccharide (LPS), the inflammatory cells produced more lactate dehydrogenase (LDH) release and reactive oxygen species (ROS) formation, and caused more four inflammatory mediators (NO, PGE2, TNF-α, and IL-6) and two anti-inflammatory mediators (TGF-β1 and IL-10). However, the PCH-Hyp, PCH, and CH at dose levels of 100 μg/mL could combat against the LPS-induced inflammation. Overall, the PCH-Hyp was more active than the CH and PCH in reducing LDH release, ROS formation, and the secretion of these inflammatory mediators, or in increasing the secretion of the anti-inflammatory mediators. The qPCR and Western blot analysis results further confirmed that these samples had anti-inflammatory effects on the stimulated cells by suppressing the LPS-induced activation of the NF-κB signaling pathway, via regulating the mRNA/miRNA expression of iNOS, IL-6, TNF-α, IL-1β, COX-2, TLR4, IL-10, TGF-β1, miR-181a, miR-30d, miR-155, and miR-148, as well as the protein expression of MyD88, p-IKKα, p-IκBα, p-NF-κB p65, and iNOS, involved in this signaling pathway. In addition, the immunofluorescence assay results revealed that these samples could block the LPS-mediated nuclear translocation of the p65 protein and displayed the same function as the NF-κB inhibitor BAY 11-7082. It was concluded that CH could be endowed with higher anti-inflammatory activity to the macrophages by performing a plastein reaction, particularly that in the presence of exogenous Hyp.

Effect of the Plastein Reaction in Presence of Extrinsic Amino Acids on the Protective Activity of Casein Hydrolysate against Ethanol-Induced Damage in HHL-5 Cells

Casein hydrolysates (CH) were prepared using papain and modified by the plastein reaction (CH-P) in the presence of extrinsic phenylalanine (CH-P-Phe) or tryptophan (CH-P-Trp). The in vitro protective activity of CH and its modified products against ethanol-induced damage in HHL-5 cells was investigated. The results showed that the modification by the plastein reaction reduced the amino group content of CH. However, the modification by the plastein reaction in the presence of extrinsic amino acids could enhance the antioxidant, proliferative, cell cycle arresting, and anti-apoptosis activity of CH. Biological activities of CH and its modified products in the HHL-5 cells varied depending on the hydrolysate concentration (1, 2, and 3 mg/mL) and treatment time (24, 48, and 72 h). Generally, higher biological activities were found after cell treatment with CH or its modified products at concentration of 2 mg/mL for 48 h compared to other treatments. In addition, CH modified in the presence of tryptophan (CH-P-Trp) showed higher biological activity than that modified in the presence of phenylalanine (CH-P-Phe). Based on the obtained results, it can be concluded that casein hydrolysates with enhanced biological activity and potential health benefits can be produced by papain and the plastein reaction with the incorporation of extrinsic amino acids.