Vitamin E enhances the acylation of 1-O-alkyl-sn-glycero-3-phosphocholine in human endothelial cells.
1-O-Alkyl-2-acyl-sn-glycero-3-phosphocholine (alkylacyl-GPC) is the precursor of platelet-activating factor. It is formed via the CoA-independent transacylase reaction, which transfers the polyenoyl acyl group from the sn-2 position of a diacyl phospholipid to the sn-2 position of 1-O-alkyl-sn-glycero-3-phosphocholine (alkyl-GPC). We have reported previously that vitamin E alters phospholipid turnover in the endothelial cells by increasing arachidonic acid release and prostacyclin synthesis. In the present study, the role of vitamin E in the formation of alkylacyl-GPC was investigated. Incubation of endothelial cells with vitamin E resulted in an increase in the formation of [3H]alkylacyl-GPC from [3H]alkyl-GPC. The effect of vitamin E was dose-dependent at concentrations below 23 microM. However, vitamin E did not have a direct effect on the transacylase activity. When endothelial cells were incubated with vitamin E, the CoA-independent transacylase activity in the cell homogenate was found to be enhanced. Kinetic analysis of the transacylase activity in the pre-incubated cells showed that the enhancement of enzyme activity was at the enzyme-substrate level. When endothelial cells were incubated with vitamin E analogues (Trolox, tocol and tocopherol acetate), only limited enhancement of the transacylation process was detected. It is clear that vitamin E enhanced the synthesis of alkylacyl-GPC from alkyl-GPC in a very specific manner by an indirect stimulation of the CoA-independent transacylase activity. The regulation by vitamin E of the formation of alkylacyl-GPC may mediate the transfer of arachidonate from the diacyl phospholipid pool into the ether-linked phospholipid pool.
Tran
K
K
Department of Biochemistry, School of Medicine, University of Ottawa, Ontario, Canada.
D'Angelo
A F
AF
Choy
P C
PC
Chan
A C
AC
D000102:Acetyl-CoA C-Acyltransferase / Q000187:drug effects; D000215:Acylation; D000217:Acyltransferases / Q000187:drug effects; D001665:Binding Sites; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000378:metabolism*; D006801:Humans; D010972:Platelet Activating Factor / Q000031:analogs & derivatives* / Q000378:metabolism; D014810:Vitamin E / Q000494:pharmacology*
C036761:1-alkyl-2-acyl-sn-glycero-3-phosphocholine; D010972:Platelet Activating Factor; D014810:Vitamin E; D000217:Acyltransferases; C039766:arachidonyl transacylase; D000102:Acetyl-CoA C-Acyltransferase