In vivo Lipopolysaccharide Tolerance Recruits CD11b+ Macrophages to the Liver with Enhanced Bactericidal Activity and Low Tumor Necrosis Factor-Releasing Capability, Resulting in Drastic Resistance to Lethal Septicemia

OBJECTIVES

In vivo lipopolysaccharide (LPS) tolerance on bacterial infection was investigated, focusing on liver macrophages.

METHODS

LPS tolerance was induced by intraperitoneal injections with 5 μg/kg of LPS for 3 consecutive days, and then mice were intravenously infected with Escherichia coli.

RESULTS

All LPS-primed mice survived lethal bacterial infection. Drastic enhancement of bactericidal activity of liver macrophages strongly contributed to bacterial clearance. Although LPS-primed mice produced substantial amounts of tumor necrosis factor (TNF) inside the liver, TNF efflux into the systemic circulation was markedly suppressed. These mice showed a dramatic increase in CD11b+ monocyte- derived macrophages in the liver. The CD11b+ macrophages that increased in LPS-primed mice were those with strong phagocytic/bactericidal activity and an upregulated expression of Fcγ receptor I, but the subfraction with a potent TNF-producing capacity and poor phagocytic activity diminished. The adoptive transfer of CD11b+ macrophages from LPS-primed mice to control mice increased survival after bacterial infection and reduced the elevation of plasma TNF. LPS priming did not affect the CD68+ resident Kupffer cells, and CD68+ Kupffer cell-depleted mice still exhibited LPS tolerance with strong resistance to bacteremia.

CONCLUSIONS

LPS tolerance recruits CD11b+ macrophages to the liver with enhanced bactericidal activity, which plays a central role in resistance to lethal bacteremia.

Starring role of toll-like receptor-4 activation in the gut-liver axis

Since the introduction of the term “gut-liver axis”, many studies have focused on the functional links of intestinal microbiota, barrier function and immune responses to liver physiology. Intestinal and extra-intestinal diseases alter microbiota composition and lead to dysbiosis, which aggravates impaired intestinal barrier function via increased lipopolysaccharide translocation. The subsequent increased passage of gut-derived product from the intestinal lumen to the organ wall and bloodstream affects gut motility and liver biology. The activation of the toll-like receptor 4 (TLR-4) likely plays a key role in both cases. This review analyzed the most recent literature on the gut-liver axis, with a particular focus on the role of TLR-4 activation. Findings that linked liver disease with dysbiosis are evaluated, and links between dysbiosis and alterations of intestinal permeability and motility are discussed. We also examine the mechanisms of translocated gut bacteria and/or the bacterial product activation of liver inflammation and fibrogenesis via activity on different hepatic cell types.

Glycogen synthase kinase 3 inhibitor attenuates endotoxin-induced liver injury

BACKGROUND/AIMS

Endotoxin (lipopolysaccharide, LPS)-induced acute liver injury was attenuated by endotoxin tolerance (ET), which is characterized by phosphatidylinositol 3-kinase pathway/Akt signaling. Glycogen synthase kinase 3 (GSK-3) acts downstream of phosphatidylinositol 3-kinase pathway/Akt and GSK-3 inhibitor protects against organic injury. This study evaluates the hypothesis that ET attenuated LPS-induced liver injury through inhibiting GSK-3 functional activity and downstream signaling.

METHODS

Sprague-Dawley rats with or without low-dose LPS pretreatment were challenged with or without large dose of LPS and subsequently received studies. Serum tumor necrosis factor-alpha, interleukin-10, alanine aminotransferase, lactate dehydrogenase, and total bilirubin levels were analyzed, morphology of liver tissue was performed, glycogen content, myeloperoxidase content, phagocytosis activity of Kupffer cells, and the expression and inhibitory phosphorylation as well as kinase activity of GSK-3 were examined. Survival after LPS administration was also determined.

RESULTS

LPS induced significant increases of serum TNF-α, alanine aminotransferase, lactate dehydrogenase, and total bilirubin (P < 0.05), which were companied by obvious alterations in liver: the injury of liver tissue, the decrease of glycogen, the infiltration of neutrophils, and the enhancement of phagocytosis of Kupffer cells (P < 0.05). LPS pretreatment significantly attenuated these alterations, promoted the inhibitory phosphorylation of GSK-3 and inhibited its kinase activity, and improved the survival rate (P < 0.05).

CONCLUSIONS

ET attenuated LPS-induced acute liver injury through inhibiting GSK-3 functional activity and its downstream signaling.