Investigating the Interaction between a Lipophilic Bioactive Compound and Digestive Enzymes via Interference Effects in Colloidal Crystal Films

Abstract Curcumin, as an example of a lipophilic bioactive compound, is typically ingested orally for absorption into the human body. However, dynamically tracking the interaction between lipophilic bioactive compounds and digestive enzymes remains a significant challenge in the study of lipophilic bioactive compounds’ absorption, translocation, and metabolism within the gastrointestinal tract. The interaction between curcumin and lipase or trypsin was monitored in real time using an ordered porous layer interference (OPLI) system based on silica colloidal crystal (SCC) films. The trypsin or lipase layers were obtained by adsorbing trypsin or lipase onto the SCC films. The optical thickness (OT) received by the OPLI system was used to monitor the interaction between curcumin and digestive enzymes in real time. By comparing the interaction processes of curcumin on trypsin layers at different pH values, it was determined that the structure of curcumin under varying pH conditions influenced its interaction with trypsin. The results for changes in optical thickness (ΔOT) showed that the ΔOT of curcumin was greater in the trypsin (24.79 ± 4.94 nm) than in the lipase (2.49 ± 0.84 nm). The combination or dissociation rate constant (Kon or Koff) of curcumin in the presence of the trypsin and lipase layers was compared and analyzed through ΔOT. The calculated results revealed that the affinity constant (KA) of curcumin on the trypsin layer and the lipase layer were 1.15 × 103 M–1 and 5.33 × 103 M–1, respectively. Analyzing the association and dissociation of curcumin with digestive enzymes offers real-time information and dynamic parameters for a more profound comprehension of the behavior of lipid-soluble drugs in the gastrointestinal tract.