Phenolic Acid–Amino Acid Adducts Exert Distinct Immunomodulatory Effects in Macrophages Compared to Parent Phenolic Acids

Abstract

Caffeic acid (CA) and chlorogenic acid (CGA) are commonly found phenolic acids in plant-derived foods and beverages. Their corresponding adducts with cysteine (Cys) have been detected in coffee-containing beverages. However, despite the well-documented antioxidant and anti-inflammatory activity of CA and CGA, the immunomodulatory activities of the Cys adducts (CA–Cys and CGA–Cys) are unknown. The adducts were therefore synthesized, and their immunomodulatory effects were studied in lipopolysaccharide (LPS)-treated RAW 264.7 cells and compared to the activity of the parent phenolic acids. CA and CGA generally down-regulated the inflammatory responses. However, RNA-sequencing showed that the LPS-induced pathways related to Toll-like receptor signaling, chemokine signaling, and NOD-like receptor signaling, and JAK-STAT/MAPK signaling pathways were upregulated in adduct-treated cells relative to parent phenolic acids, while neurodegenerative disorder-related pathways and metabolic pathways were downregulated. Production of prostaglandin E 2 (PGE 2 ), interleukin-6, tumor necrosis factor-α (TNF-α), and reactive oxygen species (ROS) was all inhibited by CA and CGA ( P < 0.05). PGE 2 and TNF-α were further suppressed in adduct-stimulated cells ( P < 0.05), but ROS production was increased. For example, TNF-α produced by 100 μM CGA-stimulated cells and 100 μM CGA–Cys adduct-stimulated cells were 4.46 ± 0.23 and 1.61 ± 0.18 ng/mL, respectively. Thus, the addition of the Cys moiety drastically alters the anti-inflammatory activity of phenolic compounds.