Cell activation by monosaccharide lipid A analogues utilizing Toll‐like receptor 4

Abstract

Lipid A is the bioactive centre of lipopolysaccharide (LPS), and its properties exhibit various endotoxic and biological effects toward host cells. We examined whether Toll-like receptors (TLRs) are mediated by the signals from various synthetic acylated derivatives of d-glucosamine monophosphate. All test synthetic monosaccharide lipid A analogues similar to acylated beta-(1-6)-d-glucosamine disaccharide bisphosphates, such as Escherichia coli-type lipid A (compound 506) and its precursor (compound 406), clearly induced nuclear factor (NF)-kappaB activation in Ba/F3 cells expressing murine TLR4 and its accessory protein MD-2 (Ba/mTLR4/mMD-2), but no induction was found in those expressing murine TLR2 (Ba/mTLR2). Compound 411, the non-reducing sugar moiety of compound 506, exhibited interleukin-8 (IL-8) and tumour necrosis factor-alpha (TNF-alpha)-producing activities in human peripheral blood mononuclear cells (PBMC), whereas compound 401, the reducing moiety of compounds 506 and 406, and Gifu lipid A-46 (GLA-46), the non-reducing moiety of compound 406, induced no production of IL-8 and TNF-alpha, which was similar to the findings for compound 406. Among the synthetic triacylated monosaccharide lipid A analogues, some compounds with three tetradecanoyl (C14) groups or that included a dodecanoyl (C12) group were more active toward murine and human cells than were other analogues with a decanoyl (C10) or hexadecanoyl (C16) group. Furthermore, IL-8 production in PBMC stimulated with the active monosaccharide lipid A analogues as well as compound 506 was clearly inhibited by the monoclonal antibody to human TLR4. These findings suggest that monosaccharide lipid A analogues similar to disaccharide lipid As are capable of activating both murine and human cells through TLR4.

Differential Induction of the Toll-Like Receptor 4-MyD88-Dependent and -Independent Signaling Pathways by Endotoxins

“…Differences in the affinity of endotoxin binding to TLR4 and or MD-2 (40,43) and resulting different conformational changes may create more or less binding sites for specific adaptor proteins on the TIR domain of TLR4, modulating the signaling pathway. Alternatively, the number of TLR4-MD-2 molecules aggregated by endotoxins may be different and lead to differences in adaptor protein binding to the cytoplasmic domain of TLR4.…”

Lipopolysaccharides of Bacteroides fragilis, Chlamydia trachomatis and Pseudomonas aeruginosa signal via Toll-like receptor 2

“…A number of synthetic lipid A molecules with monophosphate and triacyl architecture have also recently been shown to be capable of signalling via TLR4 (Ogawa et al, 2002;Tamai et al, 2003), though it remains possible that these dimerize in the TLR4/ MD-2 complex to constitute the more typical twin phosphate, hexa-acyl format of TLR4-agonist lipid As and hence invoke signalling.…”

TLR4-dependent adjuvant activity of Neisseria meningitidis lipid A

“…Differences in lipid A structure or conformation are known to influence biological activity by changing the supramolecular conformation of lipid A [22][23][24][25]. A bisphosphorylated, C12 and C14, hexa-acylated lipid A structure linked to KDO is the most bioactive when TNFα is the measure of bioactivity [24,26,27].…”