Synthesis of 1-acyl-2-acetyl-sn-glycero-3-phosphocholine by an enriched preparation of the human lung mast cell.
Our study has examined the synthesis of platelet activating factor (PAF; 1-0-alkyl-2-acetyl-sn-glycero-3-phosphocholine) and of structurally related molecules by an enriched preparation (greater than 70%) of the human lung mast cell (HLMC) in response to immunologic stimulation. Upon activation with anti-IgE, HLMC incorporated exogenously provided acetate into a phospholipid that migrated with authentic PAF on TLC. The formation of this product in HLMC occurred concomitantly with histamine and leukotriene C4 release. Further analysis of this phospholipid revealed that 1-acyl-2-acetyl-sn-glycero-3-phosphocholine (GPC) and not 1-alkyl-2-acetyl-GPC was the major 1-radyl-2-acetyl-GPC subclass formed during cell activation. The presence of 1-alkyl-2-acetyl-GPC was confirmed by negative ion chemical ionization mass spectrometry. In addition to this product, anti-IgE-stimulated HLMC synthesized relatively small quantities of another 2-acetylated phospholipid migrating on TLC between phosphatidylcholine and phosphatidylinositol. The chromatographic characteristics of this product suggested that it is a subclass of 1-radyl-2-acetyl-sn-glycero-3-phosphoethanolamine. The catabolism of both 1-acyl-2-acetyl-GPC and 1-alkyl-2-acetyl-GPC was next examined to determine if the predominant formation of 1-acyl-2-acetyl-GPC over 1-alkyl-2-acetyl-GPC were metabolized by the HLMC at similar rates. There was, however, a qualitative difference in the metabolic products derived from the two phospholipids. 1-Alkyl-2-acetyl-GPC was rapidly inactivated by removal of the acetate moiety at the sn-2 position followed by rapid reacylation with arachidonate. By contrast, 1-acyl-2-acetyl-GPC was catabolized mainly by removal of the fatty acyl moiety at the sn-1 position. These data demonstrate the natural occurrence of PAF and at least two structurally similar molecules in anti-IgE stimulated HLMC. Furthermore, an analog containing an ester linkage at the sn-1 position, 1-acyl-2-acetyl-GPC, appears to be the major acetylated product synthesized under these conditions.
Triggiani
M
M
Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21224.
Hubbard
W C
WC
Chilton
F H
FH
D000944:Antigens, Differentiation, B-Lymphocyte / Q000502:physiology; D002478:Cells, Cultured; D002855:Chromatography, Thin Layer; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D007073:Immunoglobulin E / Q000494:pharmacology; D066298:In Vitro Techniques; D008264:Macrophages / Q000378:metabolism; D008407:Mast Cells / Q000378:metabolism*; D010743:Phospholipids / Q000096:biosynthesis* / Q000378:metabolism; D010972:Platelet Activating Factor / Q000096:biosynthesis* / Q000378:metabolism; D011961:Receptors, Fc / Q000502:physiology; D017455:Receptors, IgE
D000944:Antigens, Differentiation, B-Lymphocyte; D010743:Phospholipids; D010972:Platelet Activating Factor; D011961:Receptors, Fc; D017455:Receptors, IgE; D007073:Immunoglobulin E