血漿platelet-activating factor (PAF) acetylhydrolaseとリポ蛋白

Abstract

Platelet-activating factor (PAF) has been identified as 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine, and is inactivated through the hydrolytic removal of sn-2 acetate by the action of a specific enzyme, PAF acetylhydrolase. This enzyme has been found in plasma in the form of complexes with low density and high density lipoproteins. Although PAF has been implicated in various pathological conditions such as inflammatory reactions, atherogenesis, thrombogenesis, etc., its precise role in these disease processes is not known due mainly to difficulty in quantifying the content of PAF or its metabolite in biological materials; and estimation of plasma PAF acetylhydrolase activity may provide an effective measure to investigate the role of PAF in various diseases. Therefore, in this study, the relationship between PAF acetylhydrolase and plasma lipoproteins in healthy adults was observed.Thirty-nine male and fifty-five female healthy adults ranging in age from 33 to 89 years old were studied. Fasting blood samples were obtained using 1/10 volume of 3.8% trisodium citrate as an anticoagulant. Plasma PAF acetylhydrolase activity was estimated according to the method of Stafforini et al., in which [3H]acetate liberated from [2-acetyl-3H]PAF, by incubation with plasma, was quantified by scintillation spectrometry. In 29 cases, plasma lipoproteins were separated by ultracentrifugation and PAF acetylhydrolase activity in each fraction was assayed in a similar manner.The average values of PAF acetylhydrolase activity in male healthy adults were 83±35.9nmol/ml/min, and it was significantly higher than that in female: 67±33.1nmol/ml/min (p<0.05). There was a tendency for the activity to increase with advancing age until the fifth decade in men and the sixth decade in women; and the activity plateaued thereafter. In 29 subjects, LDL and HDL were found to carry the activity of 62±34.2 and 18±8.9nmol/ml/min, respectively; these were 77±9.5% and 23±9.3% of the total plasma activity. Plasma PAF acetylhydrolase activity correlated positively with the levels of total cholesterol, LDL-cholesterol and apo B.These results may serve as a basis for the further studies of PAF acetylhydrolase and lipoprotein metabolism.