Synthetic anti-endotoxin peptides inhibit cytoplasmic LPS-mediated responses

Toll-like receptor (TLR) 4-independent recognition of lipopolysaccharide (LPS) in the cytosol by inflammatory caspases leads to non-canonical inflammasome activation and induction of IL-1 secretion and pyroptosis. The discovery of this novel mechanism has potential implications for the development of effective drugs to treat sepsis since LPS-mediated hyperactivation of caspases is critically involved in endotoxic shock. Previously, we demonstrated that Pep19-2.5, a synthetic anti-endotoxin peptide, efficiently neutralises pathogenicity factors of Gram-negative and Gram-positive bacteria and protects against sepsis in vivo. Here, we report that Pep19-2.5 inhibits the effects of cytoplasmic LPS in human myeloid cells and keratinocytes. In THP-1 monocytes and macrophages, the peptide strongly reduced secretion of IL-1β and LDH induced by intracellular LPS. In contrast, the TLR4 signaling inhibitor TAK-242 abrogates LPS-induced TNF and IL-1β secretion, but not pyroptotic cell death. Furthermore, Pep19-2.5 suppressed LPS-induced HMGB-1 production and caspase-1 activation in THP-1 monocytes. Consistent with this observation, we found impaired IL-1β and IL-1α release in LPS-stimulated primary monocytes in the presence of Pep19-2.5 and reduced LDH release and IL-1B and IL-1A expression in LPS-transfected HaCaT keratinocytes. Additionally, Pep19-2.5 completely abolished IL-1β release induced by LPS/ATP in macrophages via canonical inflammasome activation. In conclusion, we provide evidence that anti-endotoxin peptides inhibit the inflammasome/IL-1 axis induced by cytoplasmic LPS sensing in myeloid cells and keratinocytes and activation of the classical inflammasome by LPS/ATP which may contribute to the protection against bacterial sepsis and skin infections with intracellular Gram-negative bacteria.