Related Experiment Videos
The induction of a unique procoagulant activity in rabbit hepatic macrophages by bacterial lipopolysaccharides
Abstract:
Disseminated intravascular coagulation (DIC) is a common occurrence during clinical sepsis and can be induced in the experimental host by LPS. Fibrin deposition in the hepatic microcirculation has been observed within 30 min of i.v. injection of LPS. Because mononuclear phagocytes have been shown to produce a PCA after exposure to LPS, we have examined the ability of a homogeneous population of explanted hepatic macrophages to express PCA. Addition of as little as 10 ng/ml of LPS stimulated a 15- to 20-fold increase in PCA over control culture levels within 7 1/2 hr post-treatment. The PCA was found to be membrane-associated, with approximately 90 to 95% of the total PCA present in the cellular lysates, and more than 85% was inhibited by pretreatment of the cells with the diazonium salt of sulfanilic acid, an inhibitor of ecto-enzymes. In contrast to tissue thromboplastin produced by other M phi populations, the H-M phi PCA was found to be markedly sensitive both to heat inactivation at 56 degrees C and to inhibition by 1 mM DFP. Additionally, assays involving both a 1-stage coagulation test as well as an enzyme assay with a Factor Xa-specific substrate (using normal and deficient human plasmas) demonstrated that the H-M phi PCA appears to activate Factor X directly. Unlike tissue thromboplastin, the H-M phi PCA is non-dependent of Factor VII activation. These studies: 1) demonstrate the LPS induces a unique PCA in the H-M phi, and 2) support a role for the H-M phi in the initiation of DIC in endotoxemic shock.
Insights
Lipopolysaccharide (LPS) induces a unique procoagulant activity (PCA) in hepatic macrophages, contributing to disseminated intravascular coagulation (DIC) during endotoxemic shock.
Area of Science:
- Biochemistry
- Immunology
- Hematology
Background:
- Disseminated intravascular coagulation (DIC) is a frequent complication of clinical sepsis.
- Lipopolysaccharide (LPS) administration can experimentally induce DIC and rapid fibrin deposition in the liver.
- Mononuclear phagocytes are known to produce procoagulant activity (PCA) upon LPS exposure.
Purpose of the Study:
- To investigate the capacity of explanted hepatic macrophages (H-M phi) to express PCA after LPS stimulation.
- To characterize the nature and enzymatic activity of the PCA produced by H-M phi.
Main Methods:
- Primary hepatic macrophages were cultured and stimulated with varying concentrations of LPS.
- PCA expression was quantified using coagulation assays and enzyme activity measurements.
- Characterization involved assessing PCA localization, sensitivity to inhibitors (sulfanilic acid diazonium salt, DFP), heat inactivation, and dependence on coagulation factors.
Main Results:
- LPS (as little as 10 ng/ml) significantly increased PCA in H-M phi by 15-20 fold within 7.5 hours.
- The PCA was primarily membrane-associated and sensitive to ecto-enzyme inhibition.
- H-M phi PCA exhibited unique properties, including heat sensitivity and DFP inhibition, distinguishing it from other tissue thromboplastins.
- The H-M phi PCA directly activated Factor X, independent of Factor VII activation.
Conclusions:
- LPS induces a distinct form of PCA in hepatic macrophages.
- Hepatic macrophages play a significant role in initiating DIC during endotoxemic shock through their unique PCA production.