Bioactive compounds with anti-obesity potential from Cassia obtusifolia L. explored by lipase-immobilized magnetic metal-organic frameworks and UPLC-Q-TOF-MS/MS

The seeds of Cassia obtusifolia L. (Cassia seed) have long been utilized as an edible traditional Chinese medicinal herb and tea with various health benefits, including improving obesity and protecting eyesight. In this work, we developed a rapid screening method based on pancreatic lipase (PL)-functionalized magnetic composite nanoparticles coupled with ultra-performance liquid chromatography-quadrupole-time of flight mass spectrometry (UPLC-QTOF-MS/MS) and molecular networking analysis. This method utilized the advantages of polydopamine (PDA) and metal-organic frameworks (MOFs) functionalized magnetic core-shell structures (Fe₃O₄@PDA@MOFs MNPs), significantly enhancing the immobilization efficiency and performance of PL. The enzyme loading capacity was increased by 1.5-fold, and notable improvements in reusability and storage stability were also observed. By using this immobilized enzyme model in combination with UPLC-QTOF-MS/MS, 22 potential PL inhibitors were selectively screened and identified from the seeds of Cassia obtusifolia L. Molecular network analysis was innovatively introduced to improve the efficiency of compound identification by summarizing the similarity of mass spectral fragments. The inhibitory activities of three representative ligands of Cassiaside B, Biochanin A 7-glucoside and Aurantio-obtusin were further investigated. Molecular docking analysis revealed that the amino acid residue ASP249 in lipase contributes a significant role in the binding of active ligands to lipase. Overall, this proposed screening strategy, characterized by its specificity in enzyme binding and the convenience of functionalized magnetic separation, presents promising prospects for rapid and high-throughput screening of active components and drug candidates from natural resources.