Galacturonic Acid Alleviates Lipopolysaccharide-Induced Macrophage Inflammation Potentially Through Competitively Inhibiting the TLR4/NF-κB Pathway

d-Galacturonic acid (GA) is a primary component of pectins that spread widely in multifarious plant-derived foods. However, studies on the bioactivity of GA are relatively limited. This study aimed at investigating the anti-inflammatory properties of GA on inflammatory damages induced by lipopolysaccharide (LPS) in RAW264.7 macrophages. The results demonstrated that GA not only alleviated the LPS-induced sharp increase in the mRNA expression of various inflammatory factors but also suppressed LPS-induced activation of the Toll-like Receptor (TLR)4/NF-κB pathway by decreasing the protein expression levels of TLR4, Phospho (P)-p65, and P-IκB-α in macrophages. Furthermore, we found that the above effects of GA depended on the TLR4/NF-κB pathway by pre-treating macrophages with specific inhibitors targeting TLR4 and p65. Molecular docking analysis identified a potential binding interaction between GA and CD14 (an accessory protein contributing to the recognition of LPS by TLR4). Finally, we found that treating macrophages with GA alone increased the expression of CD14 and TLR4 along with several inflammatory cytokines in macrophages, but the increased amplitude was relatively low. In conclusion, GA can mildly activate the immune responses in macrophages potentially by binding to CD14, but it is capable of competitively inhibiting the binding of LPS to CD14, thereby mitigating LPS-induced inflammation via TLR4/NF-κB pathway in macrophages. PRACTICAL APPLICATIONS: This study suggests that galacturonic acid (GA, a monosaccharide present in pectin) exhibits notable anti-inflammatory and anti-apoptotic properties. It is expected that the intake of GA or Other GA-rich substances will enhance the body's immunity.