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Plasmin is a specific stimulus of the 5-lipoxygenase pathway of human peripheral monocytes
I Weide1, B Tippler, T Syrovets
1Department of Pharmacology and Toxicology, Ruhr University, Bochum, Germany.
Abstract:
The objective of this study was to characterize the plasmin-induced stimulation of leukotriene (LT) B4 biosynthesis in human peripheral monocytes (PM). Plasmin up to 175 x 10(-3) CTA U/ml triggers a concentration-dependent release of 5-lipoxygenase-derived LTB4 while release of the cyclooxygenase products thromboxane (TX) B2 and prostaglandin (PG) E2 remained unaffected. The stimulatory effect appeared to be specific in as much as 1) it was found in PM, but not in polymorphonuclear neutrophils (PMN), 2) it requires the lysine binding sites of plasmin molecule since it was inhibited by the lysine analogues 6-aminohexanoic acid (6-AHA) and trans-4(aminomethyl)cyclohexane-1-carboxylic acid (t-AMCA), 3) the intact catalytic center of plasmin is required since neither plasminogen nor catalytic center-blocked plasmin share the stimulatory effect of active plasmin, 4) other serine proteases such as alpha-chymotrypsin, human neutrophil elastase and cathepsin G did not stimulate release of detectable amounts of LTB4 from PM. In addition, catalytic center-blocked plasmin antagonized the stimulatory effect of active plasmin. Plasmin-mediated monocyte activation apparently proceeds via a pertussis toxin-sensitive G protein. Plasmin did not increase inositol (1,4,5) trisphosphate levels, but a time- and concentration-dependent stimulation of cyclic GMP formation was observed. The data show that plasmin is a specific stimulus for human peripheral monocytes. Plasmin may be an important link between the coagulation cascade and inflammatory reactions.
Insights
Plasmin specifically stimulates leukotriene B4 (LTB4) release from human monocytes, not neutrophils. This effect requires plasmin
Area of Science:
- Biochemistry
- Immunology
- Cell Biology
Background:
- Leukotriene B4 (LTB4) is a potent inflammatory mediator.
- Monocytes play a crucial role in inflammatory responses.
- The coagulation cascade and inflammatory pathways are interconnected.
Purpose of the Study:
- To investigate the effect of plasmin on leukotriene B4 (LTB4) biosynthesis in human peripheral monocytes (PM).
- To determine the specificity and mechanism of plasmin-induced LTB4 release.
Main Methods:
- Monocytes and neutrophils were isolated from human peripheral blood.
- Cells were stimulated with varying concentrations of plasmin.
- LTB4, thromboxane B2 (TXB2), and prostaglandin E2 (PGE2) levels were measured.
- Inhibition studies were performed using lysine analogues and catalytic center-blocked plasmin.
- Intracellular signaling pathways, including G protein activation and cyclic nucleotide formation, were assessed.
Main Results:
- Plasmin induced a concentration-dependent release of LTB4 from monocytes, but not neutrophils.
- The stimulatory effect was specific to active plasmin and required its lysine binding sites and intact catalytic center.
- Plasmin-mediated monocyte activation involved a pertussis toxin-sensitive G protein and stimulated cyclic GMP formation.
- Other serine proteases did not induce LTB4 release.
Conclusions:
- Plasmin is a specific stimulus for human peripheral monocytes, promoting LTB4 biosynthesis.
- Plasmin may act as a molecular link between the coagulation cascade and inflammatory processes.
- Targeting plasmin could offer novel therapeutic strategies for inflammatory diseases.