Biotransformed citrus extract counteracts oxidative stress in THP-1 macrophages and Caenorhabditis elegans via Nrf2/SKN-1 dependent mechanisms

Evidence suggests that citrus flavonoids activate nuclear factor erythroid 2-related factor 2 (Nrf2) that regulates cellular defense against oxidative damage. The effects of citrus flavonoids on the homologous transcription factor skinhead-1 (SKN-1) in the nematode Caenorhabditis elegans are insufficiently studied. Here, we investigated the molecular mechanisms behind the biological activity of a biotransformed citrus extract (FermCAE) and related flavonoids in THP-1 macrophages and in C. elegans . FermCAE upregulated the expression of the Nrf2 target genes heme oxygenase 1 ( HMOX1 ) and NAD(P)H-quinone oxidoreductase 1 ( NQO1 ) in THP-1 macrophages. The formation of excessive reactive oxygen species (ROS) was reduced in stressed cells and nematodes. Transcriptome analysis further indicated that FermCAE modulates stress-response pathways in C. elegans , particularly mitochondrial energy metabolism, nucleotide biosynthesis and ribosome biosynthesis, correlating with improved worm motility and reduced ROS levels. Notably, FermCAE could counteract the paraquat-induced reduction in worm motility in wild-type worms but not in SKN-1 loss-of-function mutants. An elevated GCS-1P::GFP signal in transgenic nematodes further confirmed SKN-1 involvement. These findings suggest that FermCAE protects against oxidative stress by inducing Nrf2/SKN-1 and modulating energy and metabolic pathways to enhance stress resilience. • Citrus extracts and flavonoids upregulate HMOX1 and NQO1 via Nrf2 in THP-1 cells. • Excessive ROS levels are significantly reduced by FermCAE in cells and C. elegans . • FermCAE restores paraquat-impaired motility in wild-type but not SKN-1 loss-of-function worms. • FermCAE elevates the GCS-1P::GFP signal in transgenic worms under PQ stress. • FermCAE protects against oxidative stress via Nrf2/SKN-1 and energy regulation