Soybean contains several biologically active components and one of this belongs to the bioactive peptide group. The objectives of this study were to produce different lunasin-enriched preparations (LEP) and determine the effect of Bowman-Birk inhibitor (BBI) and Kunitz trypsin inhibitor (KTI) concentrations on the stability of lunasin against pepsin-pancreatin hydrolysis (PPH). In addition, the effect of KTI mutation on lunasin stability against PPH was determined. LEP were produced by calcium and pH precipitation methods of 30% aqueous ethanol extract from defatted soybean flour. LEP, lunasin-enriched commercially available products and KTI control and mutant flours underwent PPH and samples were taken after pepsin and pepsin-pancreatin hydrolysis. The concentrations of BBI, KTI, and lunasin all decreased after hydrolysis, but they had varying results. BBI concentration ranged from 167.5 to 655.8μg/g pre-hydrolysis and 171.5 to 250.1μg/g after hydrolysis. KTI concentrations ranged from 0.3 to 122.3μg/g pre-hydrolysis and 9.0 to 18.7μg/g after hydrolysis. Lunasin concentrations ranged from 8.5 to 71.0μg/g pre-hydrolysis and 4.0 to 13.2μg/g after hydrolysis. In all products tested, lunasin concentration after PPH significantly correlated with BBI and KTI concentrations. Mutation in two KTI isoforms led to a lower concentration of lunasin after PPH. This is the first report on the potential role of KTI in lunasin stability against PPH and must be considered in designing lunasin-enriched products that could potentially survive digestion after oral ingestion.
Inflammation caused by the NLRP3 inflammasome has been linked to many diseases. Lunasin is a bioactive peptide from soybeans with reported anti-inflammatory properties. The objective of this work was to determine the effect of pepsin-pancreatin hydrolysis (PPH) on the ability of lunasin-enriched preparation (LEP) to inhibit inflammasome activation in differentiated THP-1 human macrophages. THP-1 macrophages were treated with different concentrations of LEP (0.0625 to 0.25 mg mL), primed with 1 μg mL lipopolysaccharide for 6 h and activated by 5 mM adenosine triphosphate for 1 h. LEP reduced secretion of IL-1β and IL-18. In addition, LEP treatment inhibited the production of intracellular reactive oxygen species (ROS) in THP-1 human macrophages without affecting the expressions of NLRP3 and ASC proteins involved in inflammasomes. PPH reduced the ability of LEP to inhibit production of intracellular ROS. Our results showed that LEP inhibited activation of inflammasomes by reducing intracellular ROS in vitro which was reduced by PPH.
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