Isolation of a phospholipid inhibitor of platelet activating factor-induced activity from perfused rat liver: identification as phosphatidylglycerol.
An endogenous inhibitor of platelet activating factor action was isolated from perfused rat liver. It was purified by thin-layer chromatography and high-performance liquid chromatography and subjected to chemical modifications in order to identify its structure. On the basis of its fast atom bombardment-mass spectrum it was characterized as phosphatidylglycerol composed mainly of 16:0/18:1 and 16:0/20:2 fatty acyl chains ([M+H]+ at m/z 749 and 775, respectively) and very minor levels of 18:0/18:1 and 18:0/20:2. The purified compound exhibited inhibition on rabbit platelet aggregation induced by 5 x 10(-10) M platelet activating factor (PAF) at an EC50 value near 2.5 x 10(-6) M and on the serotonin secretion at an EC50 7 x 10(-6) M. Other phospholipids isolated from the liver preparations, such as phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, sphingomyelin, cardiolipin (diphosphatidylglycerol), and phosphatidic acid, exhibited no inhibitory activity in the concentration range from 1 x 10(-4) to 1 x 10(-7) M nor did they induce any aggregation, or lysis, of the platelets. Of importance, phosphatidylglycerol could inhibit thrombin- and ADP-induced aggregation of rabbit platelets. These results suggested a possible site of inhibition common to the signal transduction pathway of these agonists. Preliminary binding experiments showed a noncompetitive type of inhibition on PAF binding to intact rabbit platelets.
Lekka
M
M
Department of Biochemistry, University of Texas Health Science Center, San Antonio 78284-7760.
Tokumura
A
A
Tsuji
H
H
Hanahan
D J
DJ
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D002855:Chromatography, Thin Layer; D008099:Liver / Q000737:chemistry*; D008297:Male; D010477:Perfusion; D010715:Phosphatidylglycerols / Q000302:isolation & purification* / Q000494:pharmacology*; D010972:Platelet Activating Factor / Q000037:antagonists & inhibitors*; D015539:Platelet Activation / Q000187:drug effects; D010974:Platelet Aggregation / Q000187:drug effects; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D016339:Spectrometry, Mass, Fast Atom Bombardment; D013917:Thrombin / Q000494:pharmacology
D010715:Phosphatidylglycerols; D010972:Platelet Activating Factor; D000244:Adenosine Diphosphate; D013917:Thrombin