Acrylyl-PAF, a synthetic platelet-activating factor analogue.
Acrylyl-PAF, a novel platelet-activating factor analogue with substantial agonist properties, was synthesized from lyso-PAF and acrylyl chloride. Incubation of acrylyl-PAF with partially purified human serum acetylhydrolase inhibited the action of acetylhydrolase on PAF. Kinetic studies using several concentrations of PAF as well as acrylyl-PAF suggested that acrylyl-PAF was a competitive inhibitor of the acetylhydrolase. Reciprocal Lineweaver-Burk plots and Dixon plots showed that acrylyl-PAF has an apparent Ki of 2.6 microM. Radiolabeled 18: 0-acrylyl-PAF was also synthesized. Studies comparing the effectiveness of acrylyl-PAF as a substrate for the acetylhydrolase versus PAF show that approximately 60% more PAF is metabolized by acetylhydrolase than acrylyl-PAF under identical conditions. Acrylyl-PAF was shown to aggregate washed rabbit platelets and to stimulate the release of glucose in the perfused rat liver. Dose-response curves illustrate that acrylyl-PAF was about half an order of magnitude less potent than PAF as an agonist. Tissue extracts of freeze-clamped livers that were perfused with radiolabeled acrylyl-APF indicated that approximately 26% of the label associated with acrylyl-PAF washed through the liver into the perfusate, while 48% of the acrylyl-PAF remained intact in the liver. Only 9% of the acrylyl-PAF was converted to k lyso-PAF with the ramainder metabolized to other lipids. This observations stands in contrast with livers perfused with radiolabeled PAF where less than 1% of the activity associated with PAF washed through the liver while about 70% remained as intact PAF and 30% was converted to lyso-PAF. Repeated bolus infusions of acrylyl-PAF exhibited desensitization of the glycogenolytic response of the perfused rat liver. The present study describes teh synthesis and characterization of acrylyl-PAF, which was shown to be: (a) poorly hydrolyzed by the human serum acetylhydrolase; (b) a competitive inhibitor of the acetylhydrolase; and (c) an agonist with potent activity in both platelet aggregation and hepatic glycogenolytic responses.
Duffy-Krywicki
R H
RH
Department of Biochemistry, University of Texas Health Science Center, San Antonio 78284.
Steinhelper
M E
ME
Olson
M S
MS
D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase; D000179:Acrylates / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D000818:Animals; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D008297:Male; D015394:Molecular Structure; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000097:blood / Q000378:metabolism; D010972:Platelet Activating Factor / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology; D010974:Platelet Aggregation; D051381:Rats; D011919:Rats, Inbred Strains
D000179:Acrylates; D010972:Platelet Activating Factor; C072577:1-O-hexadecyl-2-acrylyl-sn-glycero-3-phosphocholine; D006003:Glycogen; D010741:Phospholipases A; D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase