Release of acetylhydrolase from platelets on aggregation with platelet-activating factor

Area of Science:

• Biochemistry
• Hematology
• Enzymology

Background:

• Platelet-activating factor (PAF) is a potent lipid mediator involved in inflammation and thrombosis.
• Acetylhydrolase is the primary enzyme responsible for inactivating PAF.
• Understanding the release and function of platelet acetylhydrolase is crucial for platelet biology.

Purpose of the Study:

• To investigate the selective release of acetylhydrolase from bovine platelets.
• To characterize the enzymatic properties of released acetylhydrolase.
• To explore the physiological relevance of platelet-derived acetylhydrolase.

Main Methods:

• Bovine platelets were aggregated using physiological concentrations of PAF, ADP, or thrombin.
• Acetylhydrolase activity in the supernatant was measured.
• Enzyme kinetics (Km) and inhibition by PAF antagonists (CV-3988, ONO-6040) were determined.
• Effect of Ca2+ and EDTA on enzyme activity was assessed.

Main Results:

• PAF (0.1-10 nM) induced selective release of active acetylhydrolase without cell lysis.
• Serotonin release paralleled acetylhydrolase release.
• The enzyme exhibited broad pH activity (5.4-8.6) and was unaffected by Ca2+ or EDTA.
• Km was 4.6 microM; Ki values for antagonists were 1.17 microM (CV-3988) and 0.84 microM (ONO-6040).
• Enzyme release was also observed upon ADP or thrombin aggregation.

Conclusions:

• Bovine platelets release functional acetylhydrolase upon aggregation.
• This released enzyme may play a physiological role in modulating PAF activity in blood plasma.
• The findings provide insights into platelet-mediated inflammatory and hemostatic processes.