A comparative study of the effects of 1-acyl-2-acetyl-sn-glycero-3-phosphocholine and platelet activating factor on histamine and leukotriene C₄ release from human leukocytes

Background: IgE-mediated stimulation of human basophils and lung mast cells causes the synthesis of larger amounts of 1-acyl-2-acetyl-sn-glycero-3-phosphocholine (1-acyl-2-acetyl-GPC) than 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine (platelet activating factor [PAF]). Methods: To study the biologic activity of 1-acyl-2-acetyl-GPC, we compared its effects and those of PAF on histamine and leukotriene C₄ (LTC₄) release from human mixed leukocytes that contained basophils. Results: 1-Acyl-2-acetyl-GPC (0.1 to 10 μmol/L) failed to release significant amounts of histamine (≥ 10%) in most donors tested (20 of 24), whereas PAF (0.01 to 1 μmol/L) was active in 58%. 1-Acyl-2-acetyl-GPC (0.1 to 10 μmol/L) was a stimulus for LTC₄ release (132 ± 30 ng/μg of histamine) with a potency of about 1000 times less than PAF. The kinetics of 1-acyl-2-acetyl-GPC-activated LTC₄ release were similar to those of PAF (half-life ≅ 2 minutes). The specific PAF receptor antagonist, WEB 2086 (10 nmol/L to 10 μmol/L), inhibited both 1-acyl-2-acetyl-GPC- and PAF-mediated LTC₄ release with the same potency (inhibitory concentration of 50% ≅ 1.5 μmol/L). Brief (2-minute) cell preincubation with 1-acyl-2-acetyl-GPC in the absence of extracellular Ca²⁺ induced a decrease in the subsequent Ca²⁺ dependent activation of PAF. Similarly, 1-acyl-2-acetyl-GPC (0.1 to 10 μmol/L) caused a concentration-dependent inhibition of PAF-activated histamine secretion (inhibitory concentration of 50% ≅ 0.2 μmol/L). Conclusions: Our data suggest that 1-acyl-2-acetyl-GPC may represent, under certain circumstances, a modulator of human basophil mediator release via mechanisms shared with PAF.