Therapeutic approach to regulate innate immune response by Toll‐like receptor 4 antagonist E5564 in rats with D‐galactosamine‐induced acute severe liver injury

Background and Aims:  Toll‐like receptor 4 (TLR4) is a transmembrane protein, existing mainly in macrophages, such as Kupffer cells of the liver. It plays an important role in recognizing and mediating macrophage activation and pro‐inflammatory cytokine release. Activation of pro‐inflammatory cytokines, including tumor necrosis factor (TNF)‐α is pivotal in the progression of liver injury. Gut‐derived endotoxin has been considered to play an important role in the development and progression of a D‐galactosamine (GalN)‐induced acute severe liver injury (ALI) model. E5564, a synthetic analog of the lipid A component of endotoxin, inhibits endotoxin‐stimulated inflammation and is under study for patients with sepsis. In this study, we seek to explore the effect of TLR4 antagonist E5564 on GalN‐induced ALI in rats. Methods:  ALI was induced in male Wistar rats by the i.p. injection of 1 g/kg bodyweight of GalN and immediately after GalN injection they were treated with an i.v. injection of 3 mg/kg bodyweight of E5564. At 24 h after GalN injection with or without E5564, serum levels of total bilirubin (T.Bil), alanine aminotransferase (ALT) and TNF‐α were analyzed. Expression levels of TNF‐α, TLR4 and CD14 mRNA in the whole liver of rats was detected by reverse transcription polymerase chain reaction analysis. Results:  The i.v. injection of E5564 reduced the elevation of serum T.Bil, ALT and TNF‐α levels in rats treated with GalN. The expression level of TNF‐α mRNA in the whole liver, which was increased at 24 h after GalN injection, was also reduced by i.v. injection of E5564. Conclusion:  TLR4 antagonist E5564 reduced GalN‐induced ALI in rats. It may contribute to the treatment of acute liver failure through blocking endotoxin‐induced TNF‐α overproduction of macrophages.