Important role of P-selectin for leukocyte recruitment, hepatocellular injury, and apoptosis in endotoxemic mice

Staphylococcal enterotoxin A-induced hepatotoxicity is predominantly mediated by Fas ligand (CD95L)

OBJECTIVE

To determine the role of tumor necrosis factor alpha (TNF-alpha) and Fas ligand (FasL, CD95L) in superantigen-induced and endotoxin-induced liver injury.

SUMMARY BACKGROUND DATA

Gram-positive bacteria are increasingly common causes of sepsis and multiorgan failure, but the pathophysiologic mechanisms of superantigen-provoked hepatotoxicity remain elusive.

METHODS

Intravital fluorescence microscopy was used to study the liver microcirculation in mice challenged with superantigen (staphylococcal enterotoxin A, SEA) or endotoxin (lipopolysaccharide, LPS) combined with D-galactosamine.

RESULTS

Administration of 10 microg LPS and 50 microg SEA caused similar hepatocellular damage as determined by liver enzymes and apoptosis. Notably, TNF-alpha-deficient mice were completely protected against hepatic injury provoked by LPS, whereas no protection was observed in response to SEA. On the other hand, FasL-deficient mice were protected against liver injury induced by SEA, but no protection was found when challenged with LPS. LPS increased clear-cut leukocyte recruitment, whereas SEA had no significant effect on leukocyte responses in the liver microcirculation. Leukocyte responses to LPS were decreased by >56% in TNF-alpha gene-targeted animals. Moreover, antiadhesive therapy, ie, immunoneutralization of P-selectin, which is an effective inhibitor of leukocyte recruitment, protected against LPS-induced but not against SEA-induced hepatic damage.

CONCLUSIONS

These novel findings demonstrate that the mechanisms of hepatic injury in endotoxin-induced and superantigen-induced sepsis are principally different. On one hand, SEA-provoked hepatotoxicity is mediated by FasL and is not associated with leukocyte recruitment. On the other hand, liver damage provoked by LPS is mediated by TNF-alpha and characterized by prominent leukocyte responses. These data may facilitate development of more specific therapies against sepsis of different origins.

Interleukin-10 mediates the protective effect of Linomide by reducing CXC chemokine production in endotoxin-induced liver injury

The immunomodulator Linomide has been shown to protect against septic liver injury by reducing hepatic accumulation of leukocytes although the detailed anti-inflammatory mechanisms remain elusive. This study examined the effect of Linomide on the production of CXC chemokines, including macrophage inflammatory protein-2 (MIP-2) and cytokine-induced neutrophil chemoattractant (KC) and interleukin-10 (IL-10) in lipopolysaccharide (LPS)/d-galactosamine (Gal)-induced liver injury in mice. It was found that pretreatment with 300 mg kg(-1) of Linomide markedly suppressed leukocyte recruitment, perfusion failure, and hepatocellular damage and apoptosis in the liver of endotoxemic mice. Administration of Linomide inhibited endotoxin-induced gene expression of MIP-2 and KC and significantly reduced the hepatic production of MIP-2 and KC by 63 and 80%, respectively. Moreover, it was found that Linomide increased the liver content of IL-10 by more than three-fold in endotoxemic mice. The protective effect of Linomide against endotoxin-induced inflammation and liver injury was abolished in IL-10-deficient mice, suggesting that the beneficial effect of Linomide is dependent on the function of IL-10. Taken together, these novel findings suggest that the protective effect of Linomide is mediated via local upregulation of IL-10, which in turn decreases the generation of CXC chemokines and pathological recruitment of leukocytes in the liver of endotoxemic mice.

Lymphocyte function antigen-1 mediates leukocyte adhesion and subsequent liver damage in endotoxemic mice

1. Sepsis is associated with leukocyte activation and recruitment in the liver. We investigated the role of lymphocyte function antigen-1 (LFA-1) in endotoxin-induced leukocyte-endothelium interactions, microvascular perfusion failure, hepatocellular injury and apoptosis in the liver by use of gene-targeted mice, blocking antibodies and a synthetic inhibitor of LFA-1 (LFA703). For this purpose, mice were challenged with lipopolysaccharide (LPS)+D-galactosamine (Gal), and intravital microscopy of the liver microcirculation was conducted 6 h later. 2. The number of firmly adherent leukocytes in response to LPS/Gal was reduced by 48% in LFA-1-deficient mice. Moreover, endotoxin-induced increases of apoptosis and enzyme markers of hepatocellular injury were decreased by 64 and 69-90%, respectively, in LFA-1-deficient mice. Furthermore, sinusoidal perfusion was improved in endotoxemic mice lacking LFA-1. 3. A similar protective pattern was observed in endotoxemic mice pretreated with an antibody against LFA-1. Thus, immunoneutralization of LFA-1 reduced endotoxin-induced leukocyte adhesion by 55%, liver enzymes by 64-66% and apoptosis by 42%, in addition to the preservation of microvascular perfusion. 4. Administration of a novel statin-derived inhibitor of LFA-1, LFA703, significantly decreased leukocyte adhesion (more than 56%) and the subsequent liver injury in endotoxemic mice. 5. Thus, this study demonstrates a pivotal role of LFA-1 in supporting leukocyte adhesion in the liver. Moreover, interference with LFA-1-mediated leukocyte adhesion protects against endotoxemic liver damage, and may constitute a potential therapeutic strategy in sepsis.