Inhibition of IRAK-4 activity for rescuing endotoxin LPS-induced septic mortality in mice by lonicerae flos extract

Abstract

Lonicerae flos extract (HS-23) is a clinical candidate currently undergoing Phase I trial in lipopolysaccharide (LPS)-injected healthy human volunteers, but its molecular basis remains to be defined. Here, we investigated protective effects of HS-23 or its major constituents on Escherichia coli LPS-induced septic mortality in mice. Intravenous treatment with HS-23 rescued LPS-intoxicated C57BL/6J mice under septic conditions, and decreased the levels of cytokines such as tumor necrosis factor α (TNF-α), interleukin (IL)-1β and high-mobility group box-1 (HMGB-1) in the blood. Chlorogenic acid (CGA) and its isomers were assigned as major constituents of HS-23 in the protection against endotoxemia. As a molecular mechanism, HS-23 or CGA isomers inhibited endotoxin LPS-induced autophosphorylation of the IL-1 receptor-associated kinase 4 (IRAK-4) in mouse peritoneal macrophages as well as the kinase activity of IRAK-4 in cell-free reactions. HS-23 consequently suppressed downstream pathways critical for LPS-induced activation of nuclear factor (NF)-κB or activating protein 1 (AP-1) in the peritoneal macrophages. HS-23 also inhibited various toll-like receptor agonists-induced nitric oxide (NO) production, and down-regulated LPS-induced expression of NF-κB/AP-1-target inflammatory genes in the cells. Taken together, HS-23 or CGA isomers exhibited anti-inflammatory therapy against LPS-induced septic mortality in mice, at least in part, mediated through the inhibition of IRAK-4.

Keywords: AP-1; Anti-inflammatory therapy; CGA; Chlorogenic acid isomers; Endotoxin LPS; HS-23; IL-1 receptor-associated kinase 4; IRAK-4; Lonicerae flos extract; MyD88; NF-κB; Septic mortality; TBK-1; TLR; TNF receptor-associated factor (TRAF) family member-associated NF-κB activator (TANK)-binding kinase 1; TRIF; activating protein 1; chlorogenic acid; lonicerae flos extract; myeloid differentiation factor 88; nuclear factor-κB; toll-like receptor; toll/IL-1 receptor (TIR)-containing adaptor inducing IFN-β.