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In vivo characterization of zymosan-induced mouse peritoneal inflammation
T S Rao1, J L Currie, A F Shaffer
1Searle Research & Development, St. Louis, Missouri.
Abstract:
Intraperitoneal administration of zymosan to mice resulted in marked biosynthesis of eicosanoids and influx of neutrophils with distinct time course profiles. 6-Keto-prostaglandin-F1 alpha (6-KPA) increased between 30 and 60 min and rapidly decreased thereafter. Leukotriene (LT)C4 levels showed similar patterns, but were sustained for several hours. LTB4 increased in a biphasic manner with peak increases between 2 to 3 hr. Repeated injections with zymosan suggested that incoming neutrophils generate most of the LTB4. Myeloperoxidase (MPO), an enzyme marker for neutrophils, continued to increase throughout the time course. Mast cells regulate LTB4 biosynthesis and neutrophil trafficking, whereas resident macrophages contribute to 6-KPA and LTC4 biosynthesis. The complement fragment C5a has a minimal role in zymosan-induced inflammation. Selective 5-lipoxygenase (5-LO) inhibitors, zileuton [N-(1-benzo[b]thienyl-2yl-ethyl)-N-hydroxyurea], TZI-41127 [2-(4-hydroxy-3,5-dimethylphenyl)-5-methoxy-3-methylindole] and cyclooxygenase (CO) inhibitors selectively modulated eicosanoid biosynthesis. Both 5-LO and CO inhibitors attenuated influx of neutrophils to varying degrees. A LTB4 receptor antagonist, SC-41930 [7-(3-(4-acetyl-3-methoxy-2-propylphenoxy)-propoxy]-3,4-dihydro-8- propyl-2H-1-benzopyran-2-carboxylic acid) and an LTD4 receptor antagonist, LY-171883 [1-(2-hydroxy-3-propyl-4-(4-1H-tetrazol-5-yl)butoxy-phenyl) ethanone)] (i.v.) attenuated influx of neutrophils and associated LTB4 biosynthesis. These results suggest that both 5-LO and CO metabolites regulate neutrophil influx in this model. Marked eicosanoid biosynthesis and cellular influx in response to zymosan provides an attractive experimental paradigm to evaluate anti-inflammatory effects of inhibitors of arachidonate CO or 5-LO pathways.
Insights
Zymosan-induced inflammation in mice involves significant eicosanoid production and neutrophil influx. Inhibitors of 5-lipoxygenase (5-LO) and cyclooxygenase (CO) pathways, along with receptor antagonists, effectively reduced neutrophil migration, highlighting their therapeutic potential.
Area of Science:
- Immunology
- Pharmacology
- Biochemistry
Background:
- Zymosan administration triggers inflammatory responses in mice, characterized by eicosanoid biosynthesis and neutrophil infiltration.
- Distinct temporal profiles exist for the production of 6-keto-prostaglandin-F1 alpha (6-KPA), leukotriene (LT)C4, and LTB4.
- Neutrophils are identified as key producers of LTB4, while mast cells and macrophages play specific roles in regulating inflammatory mediators.
Purpose of the Study:
- To investigate the temporal dynamics of eicosanoid biosynthesis and neutrophil influx following zymosan challenge.
- To elucidate the cellular sources and regulatory mechanisms of key inflammatory mediators.
- To evaluate the efficacy of 5-lipoxygenase (5-LO) and cyclooxygenase (CO) inhibitors, as well as receptor antagonists, in modulating zymosan-induced inflammation.
Main Methods:
- Intraperitoneal administration of zymosan to mice.
- Measurement of eicosanoids (6-KPA, LTC4, LTB4) and myeloperoxidase (MPO) activity over time.
- Assessment of cellular infiltration, including neutrophils.
- Pharmacological intervention using selective 5-LO inhibitors (zileuton, TZI-41127), CO inhibitors, LTB4 receptor antagonist (SC-41930), and LTD4 receptor antagonist (LY-171883).
Main Results:
- Zymosan induced time-dependent increases in 6-KPA, LTC4, and LTB4, with LTB4 showing a biphasic pattern.
- Neutrophil influx, indicated by MPO activity, increased throughout the observation period.
- Both 5-LO and CO inhibitors, as well as LTB4 and LTD4 receptor antagonists, significantly attenuated neutrophil influx and associated LTB4 biosynthesis.
- The complement fragment C5a demonstrated a minimal role in this inflammatory model.
Conclusions:
- Both 5-LO and CO metabolites are critical regulators of neutrophil influx in zymosan-induced inflammation.
- The zymosan model provides a valuable platform for assessing the anti-inflammatory potential of inhibitors targeting arachidonate pathways.
- Targeting 5-LO and CO pathways offers a promising therapeutic strategy for inflammatory conditions characterized by neutrophil recruitment.