Anti-Inflammatory Activity of In Vitro Digested Manna in a Caco-2 and RAW264.7 Cells Co-Culture Model of Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) involves intestinal barrier dysfunction and chronic inflammation. Manna, derived from the solidified phloem sap of Fraxinus species, is rich in mannitol and polyphenols and valued for its laxative, antioxidant, and anti-inflammatory properties. In this study, manna was digested in vitro to obtain its bioaccessible fraction (BFM), whose anti-inflammatory activity was tested in a Caco-2/RAW264.7 co-culture model. Caco-2 cells were pretreated with BFM (1/20 v/v, 6 mg/mL) 90 min before LPS stimulation (1 µg/mL, 24 h) of macrophages, using budesonide (1 μM) as reference. BFM pretreatment significantly reduced IL-8 secretion (70.8%) in Caco-2 cells, and IL-6 (43.1%) and TNF-α (83.1%) in RAW264.7 macrophages. It also improved redox balance in Caco-2 cells by decreasing iNOS (48.2%), NOx (33.2%), and ROS (26.4%), while stabilizing tight junctions through occludin upregulation (18.3%). Mechanistically, BFM downregulated NF-κB-COX-2-PGE2 signaling in macrophages, reducing NF-κB p65 nuclear translocation (65.6%), COX-2 levels (79.3%), and PGE2 production (50.8%). Co-treatment with budesonide showed antagonism for most markers (Combination Index (CI), 0.41–0.76), but additive/synergistic effects on ROS (CI, 1.06 ± 0.06) and NOx (CI, 1.10 ± 0.04). These findings highlight manna’s strong anti-inflammatory activity at a low, non-laxative dose (3.8 g/day), supporting its nutraceutical potential in IBD management.