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

Background: Carrageenan (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. Methods: The effects of degraded lambda-carrageenan (lambda-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-alpha) secretion, Toll-like receptor 4 (TLR4) expression, and activation of nuclear factor-kappa b (NF-kappa B) and activation protein-1 (AP-1) pathways. Results: We found that lambda-dCGN was much stronger than native lambda-CGN in the activation of macrophages to secrete TNF-alpha. Treatment of RAW264.7 cells with lambda-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, lambda-dCGN treatment activated NF-kappa B via B-cell lymphoma/leukemia 10 (Bcl10) and nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha (I kappa B alpha) phosphorylation. In addition, lambda-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 lambda-dCGN markedly enhanced LPS-stimulated TNF-alpha secretion. This pretreatment resulted in the enhanced phosphorylation of ERK1/2 and c-Jun N-terminal kinase (JNK) and intensified activation of AP-1. Conclusions: lambda-dCGN induced an inflammatory reaction via both NF-kappa B and AP-1, and enhanced the inflammatory effect of LPS through AP-1 activation. General significance: The study demonstrated the role of lambda-dCGN to induce the inflammatory reaction and to aggravate the effect of LPS on macrophages, suggesting that lambda-dCGN produced during food processing and gastric digestion may be a safety concern. (C) 2014 Elsevier B.V. All rights reserved.