Structure–activity relationship and antioxidant mechanisms of rabbit-derived peptides with Keap1-binding potential: In vitro, in silico, and in vivo evaluation

Oxidative stress, arising from a dysregulation between the generation of reactive oxygen species (ROS) and antioxidant defense mechanisms, is closely linked to the pathogenesis of numerous chronic diseases. To identify natural peptide-based antioxidants, rabbit meat proteins were enzymatically hydrolyzed using seven proteases. Among them, Hydrolysates produced by papain demonstrated the greatest radical scavenging activity, with DPPH and ABTS inhibition rates of 51.50 % and 61.50 %, respectively. Ultrafiltration and Sephadex G-15 fractionation revealed that the <3 kDa fraction (PH3) and its subfraction F5 possessed the strongest antioxidant activity. LC-MS/MS analysis of F5 identified 163 peptides, of which 56 were predicted to exhibit antioxidant potential using PeptideRanker and AnOxPePred algorithms. Notably, seven novel peptides showed strong binding affinities to Keap1 (binding energy < −8.0 kcal/mol) in molecular docking, suggesting possible modulation of the Keap1–Nrf2 antioxidant pathway. Quantum chemical analysis (HOMO–LUMO orbitals and electrostatic potential mapping) combined with radical scavenging assays demonstrated that electron-donating aromatic residues (Trp, Tyr) played key roles in antioxidant activity via hydrogen atom and electron transfer mechanisms, establishing a molecular-level structure–activity relationship. In vivo validation using an AAPH-induced zebrafish model confirmed the peptides' safety and efficacy, including reduced ROS levels and restored endogenous antioxidant enzyme activities (SOD and CAT). Collectively, these findings provide mechanistic insight into the antioxidant action of rabbit-derived peptides and support their potential application as natural antioxidants for functional food development and oxidative stress-related disease prevention.