Untargeted Metabolomics Reveals Organ-Specific Metabolites Associated with Antioxidant and Anti-Inflammatory...

Finger citron (Citrus medica L. var. sarcodactylis Swingle, CM) is an important edible and medicinal plant. Owing to its diverse pharmacological properties, its fruit has long served as a traditional Chinese medicine and has increasingly been developed for functional food applications. However, its non-fruit parts, including leaves, branches, and roots, remain underutilized.

In this study, CM fruit (CMF), leaves (CML), roots (CMR), and branches (CMB) were selected to systematically compare their small-molecule metabolic profiles and antioxidant and anti-inflammatory activities. Untargeted metabolomics was conducted based on ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Meanwhile, antioxidant capacity was evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging assays, and anti-inflammatory activity was assessed using a lipopolysaccharide (LPS)-induced RAW 264.7 macrophage inflammation model.

Metabolomic analysis revealed 826 differential metabolites across the four CM parts (CMs), reflecting pronounced organ-specific metabolic features. According to Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, the variations in metabolite profiles across the four CMs were primarily linked to amino acid metabolism, phenylalanine metabolism, and unsaturated fatty acid metabolism. In the antioxidant assays, the DPPH radical scavenging activity at 2 mg/mL followed the order CML (78.37 ± 7.29%), CMR (73.30 ± 2.68%), CMB (40.71 ± 0.16%), and CMF (36.67 ± 1.67%), whereas ABTS radical scavenging activity followed the order CMR (51.36 ± 2.17%), CML (48.30 ± 1.64%), CMB (45.23 ± 1.72%), and CMF (18.48 ± 0.22%). In the LPS-stimulated RAW 264.7 macrophage model, at 0.4 mg/mL, inhibition of nitric oxide (NO) production followed the order CML (88.18 ± 4.02%), CMB (87.21 ± 3.02%), CMF (68.05 ± 2.54%), and CMR (67.21 ± 9.12%). Correlation analysis further suggested that features putatively annotated as minecoside, maltotetraose, and (+)-catechin may be associated with antioxidant or anti-inflammatory activities.

The study revealed differences in metabolite composition and bioactivities among different CMs, providing an experimental basis for the development and utilization of non-fruit parts, especially leaves, and for further investigation of their bioactive constituents.