Is platelet-activating factor (PAF-acether) synthesis by murine peritoneal cells (PC) a two-step process?

Area of Science:

• Biochemistry
• Cell Biology
• Immunology

Background:

• Platelet-activating factor (PAF-acether) is a potent lipid mediator.
• PAF-acether is released alongside an inactive precursor, lyso-PAF-acether.
• Lyso-PAF-acether formation is hypothesized to involve phospholipase A2 (PLA2) activation.

Purpose of the Study:

• To investigate the enzymatic mechanisms underlying PAF-acether release.
• To determine the roles of PLA2 and acetylation in PAF-acether biosynthesis.

Main Methods:

• Utilized PLA2 inhibitors (bromophenacyl bromide, mepacrine, EDTA) to block PAF-acether release.
• Administered acetyl coenzyme A (acetyl-CoA) to stimulated cells to assess its effect on PAF-acether production.
• Employed radiolabeled acetyl-CoA (3H acetyl-CoA) to trace acetate incorporation into PAF-acether.
• Characterized enzymatic activity using PLA2 and lipase from Rhizopus arrhizus.

Main Results:

• PLA2 inhibitors significantly blocked zymosan-induced PAF-acether release.
• EDTA and bromophenacyl bromide reduced lyso-PAF-acether release.
• Acetyl-CoA addition dose-dependently enhanced PAF-acether release, up to 200% at 100 microM.
• Evidence of acetate incorporation into PAF-acether was confirmed via radiolabeling and enzymatic treatment.
• PAF-acether was synthesized from lyso-PAF-acether and acetyl-CoA in vitro.

Conclusions:

• PAF-acether release is a two-step process: PLA2-mediated hydrolysis of a precursor, followed by enzymatic acetylation of the resulting lyso-PAF-acether.
• This pathway clarifies the biosynthesis of this critical inflammatory mediator.