Effect of adenosine and caffeine on Toll-Like Receptor-4 (TLR-4) -

Abstract

Background and aims: The role of Toll-Like Receptor-4 (TLR-4) in innate immunity and inflammation is well established. Lipopolysaccharide (LPS) a constituent of the cell wall of Gram negative bacteria is a ligand for TLR-4. Binding of LPS to TLR-4 activates both myeloid differentiation (MyD88) dependent and independent pathways leading to the production of excessive amount of pro-inflammatory cytokines, including Tumor Necrosis Factor-alpha (TNF-α) and Interleukin-12 (IL-12). The excess production of cytokines can lead to hypotension and shock, in some patients with Gram negative infections. Previous studies have shown that endogenous adenosine, an anti-inflammatory agent, is released at sites of injury and inflammation thereby decreasing the excessive production of cytokines. On the other hand, caffeine, a non-specific adenosine blocker, has been reported in several studies to have opposing immune-modulatory effects. In this study, the effects of caffeine and adenosine on TLR-4 in promoting or decreasing the production of TNF-α and IL-12 by LPS-stimulated monocytes was investigated.Methods: Monocytes were isolated using Pluribead® kit from pooled blood obtained from ten volunteers. The monocytes were then incubated for 24 hours with LPS extracted from Escherichia coli (aTLR-4 ligand activator) , adenosine, caffeine and LPS extracted from Rhodobacter sphaeroides (LPS-RS, a TLR-4 ligand blocker), each alone or in different combinations. Later, the levels of pro-inflammatory cytokines TNFα and IL-12 were assessed using an Enzyme Linked ImmunoAssay (ELISA). Results: Caffeine and adenosine significantly reduced the amount of TNFα and IL-12 produced by LPS-stimulated monocytes. Regarding non-stimulated and LPS-RS blocked monocytes, the presence of adenosine and caffeine significantly decreased TNFα levels produced by these cells but had little or non-significant effect on the levels of IL-12.Conclusion: Both caffeine and adenosine block the production of the pro-inflammatory cytok