Valorization of Pinus koraiensis Nut Skin Byproducts: Polyphenols Alleviate Doxorubicin-Induced Cardiotoxicity via the Nrf2/Keap1-Mediated Oxidative Stress Response

Doxorubicin (Dox)-induced cardiotoxicity is a major dose-limiting adverse effect of chemotherapy and is closely linked to oxidative stress and impaired endogenous antioxidant defenses. Food-derived polyphenols that reinforce cellular redox resilience may therefore offer a safe adjuvant strategy. Pinus koraiensis nut skin (PNS), an underutilized nut-processing residue, is rich in polyphenols, yet its bioactive profile and cardioprotective mechanism remain insufficiently defined. Here, we optimized the extraction of PNS polyphenols (PNSP), profiled its phytochemical composition, and investigated its protective effects against Dox-induced cardiomyopathy (DIC). Under optimized conditions, PNSP exhibited strong in vitro antioxidant capacity. UPLC-Q-TOF-MS tentatively identified 26 phytochemicals dominated by procyanidins and flavonoids. In a zebrafish DIC model, post-treatment with PNSP (10 – 40 μg/mL) dose-dependently rescued cardiac dysfunction. Notably, 40 μg/mL PNSP restored heart rate from 112.00 ± 24.28 to 157.00 ± 13.98 beats/min and reduced ROS accumulation. Mechanistically, PNSP reactivated endogenous antioxidant enzymes (SOD, GSH-Px) by activating the Nrf2/Keap1 signaling pathway. Procyanidin C1 and the Pinus -specific flavonoid pinobanksin 3-acetate were identified as key ligands that competitively occupy the Keap1 Kelch pocket, thereby facilitating Nrf2 nuclear translocation. This non-covalent, competitive activation mechanism was robustly validated by molecular docking, stable Keap1 protein expression, and enhanced ARE-luciferase reporter activity. Collectively, these findings identify PNSP as a food-relevant Nrf2 activator with potential to mitigate chemotherapy-associated cardiotoxicity, highlighting its potential as a high-value functional food ingredient.