Pathogen-Associated Molecules from Gut Translocation Enhance Severity of Cecal Ligation and Puncture Sepsis in Iron-Overload β-Thalassemia Mice
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Published on: February 19, 2013
Kritsanawan Sae-Khow1, Awirut Charoensappakit2, Peerapat Visitchanakun1
1Medical Microbiology, Interdisciplinary and International Program, Graduate School, Chulalongkorn University, Bangkok, Thailand.
Introduction:
Systemic inflammation induced by gut translocation of lipopolysaccharide (LPS), a major component of Gram-negative bacteria, in thalassemia with iron-overload worsens sepsis. However, the impact of (1→3)-β-D-glucan (BG), a major fungal molecule, in iron-overload thalassemia is still unclear. Hence, the influence of BG was explored in 1) iron-overload mice with sepsis induced by cecal ligation and puncture (CLP) surgery; and 2) in bone marrow-derived macrophages (BMMs).
Methods:
The heterozygous β-globin-deficient mice, Hbbth3/+ mice, were used as representative thalassemia (TH) mice. Iron overload was generated by 6 months of oral iron administration before CLP surgery- induced sepsis in TH mice and wild-type (WT) mice. Additionally, BMMs from both mouse strains were used to explore the impact of BG.
Results:
Without sepsis, iron-overload TH mice demonstrated more severe intestinal mucosal injury (gut leakage) with higher LPS and BG in serum, from gut translocation, when compared with WT mice. With CLP in iron-overload mice, sepsis severity in TH mice was more severe than WT as determined by survival analysis, organ injury (kidney and liver), bacteremia, endotoxemia, gut leakage (FITC-dextran) and serum BG. Activation by LPS plus BG (LPS+BG) in BMMs and in peripheral blood-derived neutrophils (both WT and TH cells) demonstrated more prominent cytokine production when compared with LPS activation alone. In parallel, LPS+BG also prominently induced genes expression of M1 macrophage polarization (iNOS, TNF-α and IL-1β) in both WT and TH cells in comparison with LPS activation alone. In addition, LPS+BG activated macrophage cytokine production was enhanced by a high dose of ferric ion (800 mM), more predominantly in TH macrophages compared with WT cells. Moreover, LPS+BG induced higher glycolysis activity with similar respiratory capacity in RAW264.7 (a macrophage cell line) compared with LPS activation alone. These data support an additive pro-inflammatory effect of BG upon LPS.
Conclusion:
The enhanced-severity of sepsis in iron-overload TH mice was due to 1) increased LPS and BG in serum from iron-induced gut-mucosal injury; and 2) the pro-inflammatory amplification by ferric ion on LPS+BG activation.
Insights
Iron overload in thalassemia worsens sepsis by increasing gut leakage of bacterial lipopolysaccharide (LPS) and fungal (1→3)-β-D-glucan (BG). Ferric ions amplify inflammation from LPS and BG activation, increasing sepsis severity.
Area of Science:
- Immunology
- Hematology
- Microbiology
Background:
- Systemic inflammation from gut translocation of lipopolysaccharide (LPS) exacerbates sepsis in iron-overload thalassemia.
- The role of fungal (1→3)-β-D-glucan (BG) in this context remains unclear.
Purpose of the Study:
- To investigate the influence of BG on sepsis severity in iron-overload thalassemia models.
- To explore the combined effects of LPS, BG, and iron on immune cells.
Main Methods:
- Utilized heterozygous β-globin-deficient mice (Hbbth3/+) with induced iron overload and cecal ligation and puncture (CLP) surgery to model sepsis.
- Examined bone marrow-derived macrophages (BMMs) and neutrophils for responses to LPS, BG, and ferric ions.
Main Results:
- Iron-overload thalassemia mice showed increased gut leakage, serum LPS, and serum BG compared to wild-type mice, even without sepsis.
- CLP-induced sepsis was more severe in iron-overload thalassemia mice, with higher mortality, organ injury, bacteremia, and endotoxemia.
- Combined LPS and BG activation of immune cells led to enhanced cytokine production and M1 macrophage polarization, further amplified by ferric ions, particularly in thalassemia cells.
- LPS+BG stimulation increased glycolysis in macrophages.
Conclusions:
- Increased sepsis severity in iron-overload thalassemia is attributed to iron-induced gut injury leading to higher serum LPS and BG.
- Ferric ions potentiate the pro-inflammatory effects of LPS and BG, amplifying sepsis severity.
