Biosynthesis of platelet-activating factor (PAF-acether). IV. Impairment of acetyl-transferase activity in thioglycollate-elicited mouse macrophages.

The lower release of PAF-acether exhibited by macrophages (Mϕ) obtained from thioglycotlate-injected mice (TG-Mϕ) as compared with Mϕ from untreated mice (normal Mϕ [N-Mϕ]) has been previously described. We show that this lower release cannot be explained by a simultaneous formation by TG-Mϕ of factors inactivating or impairing the release of PAF-acether for the following reasons: 1) blockade of prostaglandin synthesis did not restore the release; 2) exogeneous synthetic PAF-acether was totally recovered after incubation for 1 hr at 37°C with TG-Mϕ; 3) the ionophore-induced release from N-Mϕ was not altered when performed in the presence of TG-Mϕ supernatants; 4) any transient release of PAF-acether, eventually followed by its disappearance, would not be compatible with our kinetic studies. This impairment may be better explained by a defect in biosynthesis. When stimulated by zymosan phagocytosis, N-Mϕ released 30.8 ± 4.5 ng/ml of the deacylated PAF-acether molecule (2-lyso PAF-acether) vs 35.0 ± 3.0 ng/ml for TG-Mϕ, indicating that the first phospholipase A2-dependent step of PAF-acether production was not implicated in the defect. Addition of acetyl-CoA to zymosan-stimulated cells resulted in the recovery of 3.8 ± 1.9 ng/ml and 1.6 ± 1.0 ng/ml PAF-acether from N-Mϕ and TG-Mϕ, respectively, excluding acetate donor as the limiting step for PAF-acether synthesis in TG-Mϕ. However, TG-Mϕ lysates supplemented with the two synthetic substrates, 2-lyso PAF-acether and acetyl-CoA, synthesized 16.1 ± 4.3 ng/ ml PAF-acether, whereas N-Mϕ lysates yielded 85.0 ± 10.5 ng/ml PAF-acether. It was concluded that a defect in the second acetylation step, as assessed by the low acetyl-transferase activity contained in TG-Mϕ, was responsible for the impairment of the PAF-acether release exhibited by these cells.