M2000 (β-D-Mannuronic Acid) as a Novel Antagonist for Blocking the TLR2 and TLR4 Downstream Signalling Pathway.

To date, selective blockade of Toll-like receptor (TLR) signalling has been developed as a new approach for treatment for many inflammatory diseases. As β-D-mannuronic acid (M2000) has been known as an anti-inflammatory molecule in several experimental models, we investigated the antagonistic effects of M2000 on TLR2 and TLR4 downstream signalling transduction pathway in human embryonic kidney (HEK) 293 cell lines overexpressing TLR2/CD14 and the TLR4/MD2/CD14 complex, respectively. M2000 effectively inhibited mRNA expression of MyD88 and p65, major subunit of nuclear factor-κB, in HEK293 cells stimulated by lipoteichoic acid (LTA, a TLR2 agonist) and lipopolysaccharide (LPS, a TLR4 agonist) with no evidence of cytotoxicity. In addition, M2000 also suppressed LTA and LPS-induced production of TNF-α and IL-6 inflammatory cytokines in these cells. Furthermore, the results revealed that M2000 had no significant effect on Tollip mRNA expression as a negative regulator of TLR signalling in aforesaid cells. Overall, these data point to M2000 inhibitory effect on Toll-like receptor (TLR) 2, 4 signalling in HEK293 cells. This information might provide new insights into the possible roles of this small drug in order to introduce it as a TLR signalling pathway inhibitor. However, more studies are needed to confirm β-D-mannuronic acid antagonistic effects including the effects of M2000 on peritoneal isolated macrophages and also on blood cells in patients with inflammatory diseases such as ankylosing spondylitis.