Glycine attenuates endotoxin-induced liver injury by downregulating TLR4 signaling in Kupffer cells

Am J Surg. 2008 Jul;196(1):139-48. doi: 10.1016/j.amjsurg.2007.09.045.

Abstract

Background: Several experimental studies have observed better outcomes after glycine treatment in patients with endotoxin-induced liver injuries, but its molecular mechanism is not yet fully understood. The purpose of this study was to evaluate the hypothesis that glycine attenuates endotoxin-induced liver injury by affecting endotoxin signal transduction in liver macrophages.

Methods: An animal model of endotoxin-induced liver injury was established by intraperitoneally injecting mice with 10 mg/kg body weight endotoxin fed a pretreatment diet with or without 5% (w/w) glycine. Blood and liver samples were obtained for analysis of liver morphology and to determine concentrations of alanine aminotransferase, endotoxin receptor Toll-like receptor 4 (TLR4), tumor necrosis factor-alpha (TNF-alpha), and interleukin (IL)-10 at various time points after injection. To investigate the effect of glycine on liver macrophages, Kupffer cells (KCs) were isolated and challenged by LPS (100 ng/mL), with or without glycine (4 mmol/l) pretreatment, and the expressions of TLR4, IL-10, and TNF-alpha were assayed at mRNA and protein levels. DNA-binding activity of nuclear factor-kappa B (NF-kappaB) was also analyzed using enzyme-linked immunosorbent assay.

Results: Dietary glycine significantly improved the survival rate of endotoxemic mice (P < .05), whereas serum alanine aminotransferase and TNF-alpha levels were significantly decreased at different time points (P < .05); IL-10 levels were increased (P < .05). Concurrently, LPS-induced hepatic tissue injury was attenuated as indicated by morphologic analysis; secretion of IL-10 in liver tissue (P < .05) was enhanced; and expression of TLR4 and TNF-alpha in liver tissue was downregulated (P < .05). Consistent with these in vivo experiments, enhanced secretion of IL-10 and inhibited expression of TLR4 and TNF-alpha caused by glycine pretreatment were also observed in LPS-stimulated KCs. NF-kappaB DNA-binding activity was also significantly inhibited by glycine (P < .05, respectively).

Conclusions: Dietary glycine improved survival rates and liver function in endotoxemic mice by regulating the production of proinflammatory or anti-inflammatory cytokines in liver. It attenuated liver injury by deactivating KCs through inhibiting TNF-alpha secretion and increasing IL-10 production. The downregulative effect of glycine on the endotoxin signaling pathway and TLR4/NF-kappaB/TNF-alpha may be a novel potential mechanism by which glycine inhibits KC activity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Administration, Oral
  • Animals
  • Anti-Inflammatory Agents / administration & dosage*
  • Disease Models, Animal
  • Down-Regulation
  • Female
  • Glycine / administration & dosage*
  • Kupffer Cells / metabolism*
  • Lipopolysaccharides / adverse effects
  • Liver Diseases / etiology
  • Liver Diseases / microbiology
  • Liver Diseases / prevention & control*
  • Male
  • Mice
  • Mice, Inbred BALB C
  • Signal Transduction
  • Toll-Like Receptor 4 / metabolism*

Substances

  • Anti-Inflammatory Agents
  • Lipopolysaccharides
  • Tlr4 protein, mouse
  • Toll-Like Receptor 4
  • Glycine