Exploring Species-Specificity in TLR4/MD-2 Inhibition with Amphiphilic Lipid A Mimicking Glycolipids

• Published in: Molecules (Basel, Switzerland) Switzerland), 2023-08, Vol.28 (16), p.5948
• Main Authors: Borio, Alessio, Holgado, Aurora, Passegger, Christina, Strobl, Herbert, Beyaert, Rudi, Heine, Holger, Zamyatina, Alla
• Format: Article
• Language: English
• Subjects: Animals; Asthma; Austria; carbohydrate-based inhibitors; carbohydrates; Cell Differentiation; Cytokines; Diseases; E coli; Germany; Glycolipids - pharmacology; Health aspects; Humans; Inflammation; Ligands; Lipid A; Lipids; lipopolysaccharide; Membrane lipids; Mice; Mutation; Phosphates; Proteins; Sepsis; Toll-like receptor; Toll-Like Receptor 4; Viral infections
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules28165948

The Toll-like receptor 4 (TLR4)/myeloid differentiation factor 2 (MD-2) complex is a key receptor of the innate immune system and a major driver of inflammation that is responsible for the multifaceted defense response to Gram-negative infections. However, dysfunction in the tightly regulated mechanisms of TLR4-mediated signaling leads to the uncontrolled upregulation of local and systemic inflammation, often resulting in acute or chronic disease. Therefore, the TLR4/MD-2 receptor complex is an attractive target for the design and development of anti-inflammatory therapies which aim to control the unrestrained activation of TLR4-mediated signaling. Complex structure-activity relationships and species-specificity behind ligand recognition by the TLR4/MD-2 complex complicate the development of MD-2-specific TLR4 antagonists. The restriction of the conformational flexibility of the disaccharide polar head group is one of the key structural features of the newly developed lipid A-mimicking glycophospholipids, which are potential inhibitors of TLR4-mediated inflammation. Since phosphorylation has a crucial influence on MD-2-ligand interaction, glycolipids with variable numbers and positioning of phosphate groups were synthesized and evaluated for their ability to inhibit TLR4-mediated pro-inflammatory signaling in human and murine immune cells. A bis-phosphorylated glycolipid was found to have nanomolar antagonist activity on human TLR4 while acting as a partial agonist on murine TLR4. The glycolipid inhibited mTLR4/MD-2-mediated cytokine release, acting as an antagonist in the presence of lipopolysaccharide (LPS), but at the same time induced low-level cytokine production.