Degraded λ-carrageenan activates NF-κB and AP-1 pathways in macrophages and enhances LPS-induced TNF-α secretion through AP-1

• λ-dCGN induced a stronger secretion of TNF-α in macrophages than λ-CGN.
• λ-dCGN induced TNF-α secretion by TLR4–Bcl10–NF-κB and ERK1/2–AP-1 pathways.
• λ-dCGN markedly enhanced LPS-stimulated TNF-α secretion.
• λ-dCGN promoted the inflammation of LPS by ERK1/2–JNK–AP-1 pathway.

BackgroundCarrageenan (CGN), a high molecular weight sulfated polysaccharide, is a traditional ingredient used in food industry. Its degraded forms have been identified as potential carcinogens, although the mechanism remains unclear.MethodsThe effects of degraded λ-carrageenan (λ-dCGN) on murine RAW264.7 cells and human THP-1-derived macrophage cells were investigated by studying its actions on tumor necrosis factor alpha (TNF-α) secretion, Toll-like receptor 4 (TLR4) expression, and activation of nuclear factor-κb (NF-κB) and activation protein-1 (AP-1) pathways.ResultsWe found that λ-dCGN was much stronger than native λ-CGN in the activation of macrophages to secrete TNF-α. Treatment of RAW264.7 cells with λ-dCGN resulted in the upregulation of TLR4, CD14 and MD-2 expressions, but it did not increase the binding of lipopolysacchride (LPS) with macrophages. Meanwhile, λ-dCGN treatment activated NF-κB via B-cell lymphoma/leukemia 10 (Bcl10) and nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha (IκBα) phosphorylation. In addition, λ-dCGN induced extracellular signal-regulated kinases/1/2/mitogen-activated protein kinases (ERK1/2/MAPK) and AP-1 activation. Interestingly, pretreatment of RAW264.7 cells with λ-dCGN markedly enhanced LPS-stimulated TNF-α secretion. This pretreatment resulted in the enhanced phosphorylation of ERK1/2 and c-Jun N-terminal kinase (JNK) and intensified activation of AP-1.Conclusionsλ-dCGN induced an inflammatory reaction via both NF-κB and AP-1, and enhanced the inflammatory effect of LPS through AP-1 activation.General significanceThe study demonstrated the role of λ-dCGN to induce the inflammatory reaction and to aggravate the effect of LPS on macrophages, suggesting that λ-dCGN produced during food processing and gastric digestion may be a safety concern.