Linkage-dependent effects of procyanidin dimers on TNFα-mediated intestinal epithelial barrier dysfunction, redox homeostasis and inflammation

Abstract

The gastrointestinal (GI) tract is generally exposed to high concentrations of dietary components, positioning diet as a key determinant of intestinal inflammation and barrier function, implicated in the onset of chronic systemic diseases. Procyanidins (PCAs), oligomeric flavan-3-ols abundant in plant-derived foods exert GI health benefits despite poor systemic bioavailability. We previously found that galloylated PCA dimers protected intestinal epithelial integrity more effectively than non-galloylated dimers. However, the role of linkage type remains unclear. This study investigated the comparative effects of PCA dimers with distinct linkages (A1, A2, B1, B2) on tumor necrosis factor-α (TNFα)-induced altered barrier function, inflammation and oxidative stress in Caco-2 cell monolayers. At physiologically relevant concentrations (0.1–10 µM), all dimers attenuated TNFα-induced increases in monolayer permeability, preserved tight junction proteins, inhibited NOX1-associated oxidant production, and mitigated NF-κB and ERK1/2 activation. The B2 dimer was the most effective at inhibiting IL-1β, TNFα expression. In addition, B2 increased the mRNA abundance of NRF2-regulated antioxidant genes, including NQO1, GCLC, and GCLM, suggesting that B2 may upregulate antioxidant defenses, limit inflammatory oxidant responses. Collectively, these findings identify structural specificity in PCA bioactivity and identify B2 as the most effective dimer at inhibiting intestinal inflammation and oxidative stress, protecting barrier integrity under proinflammatory conditions.