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Modulation of macrophage procoagulant activity by arachidonic acid metabolites
D S Kucey1, P Y Cheung, J C Marshall
1Department of Surgery, University of Toronto, Ontario, Canada.
Abstract:
Macrophage (M phi)-mediated fibrin deposition via induction of procoagulant activity (PCA) is an important component of the host response during various infections. While endotoxin (LPS) is a well-known stimulus of PCA, the factors modulating its activity within the inflammatory microenvironment are unknown. The purpose of these studies was to determine the relative roles of two pathways of arachidonic acid metabolism, i.e., the cyclooxygenase (CO) and 5-lipoxygenase (5-LO) pathways, in modulating M phi PCA induction by LPS. Thioglycolate-elicited murine peritoneal M phi were treated with the CO inhibitor indomethacin (INDO), the 5-LO inhibitor nordihydroguaiaretic acid (NDGA), or control vehicle for 15 min prior to a 4-hr exposure to LPS (10 micrograms/ml). The ability of M phi to shorten the clotting time of plasma (i.e., PCA) was measured and clotting times were converted to PCA units via a thromboplastin standard. While CO blockade had no effect on PCA induction by LPS (without INDO 30 microM 446 +/- 131, with INDO 30 microM 546 +/- 193, mU/2 x 10(6) cells, n = 4), NDGA caused a dose-dependent inhibition (IC50 = 3 microM) without affecting cell viability (without NDGA 3 microM 446 +/- 131, with NDGA 3 microM 191 +/- 67, mU/2 x 10(6) cells, n = 6, P less than 0.05). Induction of PCA by Escherichia coli was similarly inhibited (E. coli 10(6) alone = 518 +/- 130; with NDGA 3 microM = 234 +/- 100, n = 2). Combined NDGA/INDO reduced PCA comparable to NDGA alone, ruling out the possibility that NDGA acted through generation of inhibitory prostanoids like PGE2.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
The 5-lipoxygenase (5-LO) pathway, but not the cyclooxygenase (CO) pathway, is crucial for macrophage procoagulant activity (PCA) induction by lipopolysaccharide (LPS). Inhibiting 5-LO significantly reduces PCA, highlighting its role in host defense during infection.
Area of Science:
- Immunology
- Inflammation Biology
- Hemostasis
Background:
- Macrophage (M phi)-mediated fibrin deposition via procoagulant activity (PCA) is vital for host defense during infections.
- Lipopolysaccharide (LPS) is a known inducer of M phi PCA, but factors influencing this activity in the inflammatory microenvironment remain unclear.
Purpose of the Study:
- To investigate the roles of the cyclooxygenase (CO) and 5-lipoxygenase (5-LO) pathways in modulating M phi PCA induction by LPS.
Main Methods:
- Murine peritoneal M phi were treated with CO inhibitor (indomethacin) or 5-LO inhibitor (nordihydroguaiaretic acid) before LPS exposure.
- PCA was quantified by measuring the plasma clotting time reduction.
- Dose-dependent inhibition and cell viability were assessed.
Main Results:
- CO inhibition (indomethacin) did not affect LPS-induced PCA.
- 5-LO inhibition (nordihydroguaiaretic acid) dose-dependently inhibited LPS-induced PCA (IC50 = 3 microM) without affecting cell viability.
- NDGA also inhibited PCA induced by Escherichia coli, suggesting a general role for 5-LO.
Conclusions:
- The 5-LO pathway plays a significant role in M phi PCA induction by LPS.
- Targeting the 5-LO pathway may offer therapeutic strategies for modulating host response in infections.